DOI: 10.31038/JNNC.2018114

Introduction

The pathophysiology of schizophrenia is not completely understood, but most hypotheses center around the core philosophy that schizophrenia is subject to the influence of neurotransmitters, specifically dopamine [1, 2]. While traditional psychotropic agents used to treat psychiatric illness correct neurotransmitter dysfunction to alleviate symptoms, there is growing evidence to suggest that inflammation, oxidative stress, and glutamate pathological changes have an effect in psychiatric conditions.

In the glutamate hypothesis of schizophrenia, abnormal glutamate uptake by glial cells can result in decreased N-methyl-D-aspartate (NMDA) receptor function [1, 3–7]. Dysfunction of NMDA receptors results in the disruption of downstream dopamine signaling. Specifically, hypofunction of the NMDA receptors in the mesolimbic dopamine pathway can result in hyperactivation of neurons, which can present as hallucinatory symptoms. Whereas, in the mesocortical pathway, NMDA receptor hypofunction can lead to negative symptoms, including anhedonia and impaired cognition. The affinity of glutamate for the NMDA receptor can be influenced by NMDA cofactors glycine and glutathione.

Modulation of the NMDA receptor via allosteric binding of glycine can enhance glutamate binding [1, 3–4]. Sarcosine (N-methyl glycine) is a type 1 glycine transporter inhibitor (GlyT1), that increases the synaptic concentration of glycine by preventing its reuptake by glial cells. Increased glycine in the synapse is proposed to augment glutamate binding at the NMDA receptor, in theory, alleviating the many symptoms of schizophrenia.

It is also thought that the abnormal metabolism of neurotransmitters in patients with schizophrenia can consequently result in oxidative stress and damaged neurons [5]. N- acetylcysteine (NAC) is thought to relieve oxidative stress by replenishing glutathione levels to prevent neurodegenerative effects and further cognitive dysfunction [5, 8–9]. NAC increases glutathione levels by delivering cysteine to the brain, which is necessary for glutathione synthesis. Similar to the cofactor glycine, increased glutathione levels will also augment glutamate binding at the NMDA receptor.

While current approved treatment options for
neuropsychiatric disorders, including schizophrenia, have
substantial documented efficacy, there are instances in which
response to these treatment options is suboptimal [10]. In these situations, patients can be further diagnosed with treatment-resistant schizophrenia. Complementary and alternative medicine (CAM) is a treatment intervention not approved by the Food and Drug Administration (FDA), however offers additional options When other treatments Fail. Both sarcosine and NAC are recognized as CAM therapy options. This report will discuss the efficacy and safety of adjunctive sarcosine and NAC in the treatment of treatment-resistant schizophrenia.

Current Literature Evaluating Sarcosine

Recent literature has evaluated the efficacy of sarcosine in the treatment of schizophrenia. In an open-label, preliminary trial by Amiaz et al., sarcosine was initiated in 22 patients with schizophrenia. To be included, subjects had to be stabilized on an antipsychotic regimen for at least four weeks prior to the addition of sarcosine. The antipsychotic agents patients were receiving included risperidone
(n = 7), quetiapine (n = 4), zuclopenthixol intramuscular (IM) injection (n = 4), olanzapine (n = 3), fluphenazine IM injection (n = 2) and paliperidone (n = 2). Five of the 22 patients received sarcosine 2g/day, while 17 patients received 4g/day. Significant improvement from baseline was noted  on the positive symptoms subscale of Positive and Negative Syndrome Scale (PANSS) following eight days of treatment (p = 0.007). Significant improvement was also seen on general psychopathology subscale of PANSS (p = 0.003). However, no significant improvement was detected in Clinical Global Impression Severity of Illness scale (CGI-S) (p = 0.08) and total PANSS score (p = 0.06) following treatment. The recruitment of this primary study was terminated following a documented safety issue reporting sarcosine may be linked to prostate cancer progression. This study was limited by the small sample size and short observation period.

A previous double-blind trial by Tsai et al. evaluated 38 patients with schizophrenia who received either adjunctive sarcosine or placebo in addition to their current antipsychotic therapy regimen for 6 weeks [12]. Patients were required to have been stabilized on their antipsychotic regimen for at least three months prior to enrollment in the study. The antipsychotic therapy regimens received included risperidone (n = 20), sulpiride (n = 6), haloperidol (n = 5), chlorpromazine (n = 1), fluphenazine decanoate (n = 1), trifluoperazine (n = 1), etumine (n = 1), sulpiride combined with chlorpromazine (n = 1), pipotiazine combined with chlorpromazine (n = 1) and medication free (n = 1). Significant improvements in positive (p < 0.0001), cognitive (p < 0.0001), and general psychiatric (p = 0.0002) symptom subscales of PANSS were observed in patients adjunctively treated with sarcosine when compared to placebo. Significant improvement was also found in Scales for the Assessment of Negative Symptoms (SANS) (p < 0.0001) and Brief Psychiatric Rating Scale (BPRS) (p = 0.0001) in patients receiving sarcosine therapy. When risperidone with adjunctive sarcosine was analyzed separately, similar results were found, as significant improvement was noted in PANSS, SANS and BPRS scales.

Lane et al. (2005) evaluated sarcosine use in patients experiencing acute exacerbations of schizophrenia [13]. It was difficult to derive clinically significant conclusions due to the numerous limitations of this study. However, improvement in general psychiatric symptoms, depression, and possibly negative symptoms was observed. Lane et al. (2008) assessed sarcosine use in 20 patients with schizophrenia as monotherapy as opposed to adjunctive therapy[14]. Compared to patients who received sarcosine 1g/day, patients who received sarcosine 2g/day experienced a 20% or greater reduction in total PANSS score. A follow-up double-blind trial, also conducted by Lane et al. (2010), randomized 60 patients with schizophrenia to receive sarcosine 2g/day or placebo[15]. Compared to placebo, sarcosine showed improvement in positive, negative and cognitive symptom subscales of PANSS. Improvement was also found among total PANSS (p=0.005), SANS (p=0.021), Quality of Life (QOL) scale (p = 0.025) and Global Assessment of Functioning (GAF) scale (p = 0.042). Similar to previous studies, the sarcosine treatment group had greater than a 20% reduction in total PANSS score. It is evident that adjunctive sarcosine therapy may provide significant benefit in patients with treatment-resistant schizophrenia who have exhausted traditional antipsychotic therapy options.

Current Literature Evaluating N-acetylcysteine (NAC)

A double-blind, placebo-controlled trial assessing the impact of adjunctive NAC in patients diagnosed with schizophrenia evaluated a primary outcome of improvement on PANSS score [5]. The treatment group received NAC 2g daily compared to placebo for 4 months. NAC was administered in addition to each patient’s current antipsychotic regimen. Four weeks following NAC discontinuation, the treatment group demonstrated a statistically significant improvement in PANSS total (p = 0.009), negative (p = 0.018) and general (p = 0.035) subscales. No significant improvement in PANSS positive subscale was found. A second randomized, double-blind, placebo-controlled trial assessed efficacy of NAC (up to 2g/day), in addition to risperidone (up to 6mg/ day), for 8 weeks in 42 patients with a baseline PANSS score greater than 20 [16]. A significant improvement in PANSS negative (p < 0.001) and total (p = 0.006) scales was found, but positive and general subscales lacked statistically significant improvements.

A systematic review and meta-analysis examined the efficacy and safety of adjunctive NAC in patients with schizophrenia among three randomized controlled trials [17]. Adjunctive NAC (2 to 6g/day) significantly improved total psychopathology (p = 0.03), but not general, positive or negative PANSS subscales. There were no significant differences observed in discontinuation rates or adverse effects (drowsiness, headache, nauseas and constipation) between placebo and treatment groups, which indicates favorable tolerability. These studies conclude that there is a modest benefit observed in augmenting maintenance antipsychotic therapy with NAC.

Case Report

A 43-year-old, single, white, female patient, with borderline intellectual functioning, has been continuously hospitalized at an inpatient New York State psychiatric institute since February 2003. She had been admitted to this same facility five times prior, with her first inpatient hospitalization dating back to June 1997, when she was diagnosed with schizophrenia, paranoid type. Her symptoms include paranoia, delusional ideation, hallucinations, disorganized thoughts, poor insight, impaired judgement, irritability, agitation and aggression. The patient has a history of physical and sexual abuse, as well as polysubstance abuse with marijuana, Lysergic Acid Diethylamide (LSD) and alcohol. The patient’s father reportedly suffered from schizophrenia, and died at age 48 from myocardial infarction.

Despite multiple treatment regimens over her lengthy hospital stay, the patient continued to have episodes of severe symptoms that interfered with daily functioning, including aggression. A trial of clozapine (Clozaril) was initiated, but was discontinued due to the development of myocarditis, leaving the patient ineligible for treatment rechallenge. After subsequent failed attempts to stabilize the patient with the use of alternative antipsychotic agents, either as monotherapy or in combination, including risperidone (Risperdal), olanzapine (Zyprexa), fluphenazine (Prolixin) and quetiapine (Seroquel), the patient’s treating psychiatrist requested a trial of CAM to augment her current psychiatric medication regimen of fluphenazine (Prolixin) decanoate 75mg intramuscular injection (IM) every other week along with oral doses of olanzapine (Zyprexa) 20mg twice daily, topiramate (Topamax) 200mg twice daily and lorazepam (Ativan) 2mg four times daily (Table 1). On 12/27/12, the patient was initiated on oral doses of NAC 600mg twice daily, followed by sarcosine 1g twice daily  on 1/17/13, for treatment resistant schizophrenia. The patient was additionally treated with chloral hydrate as needed (PRN) until it was removed from the market by the Food and Drug Administration (FDA) in October 2012. The patient received   hydroxyzine pamoate (Vistaril) 50mg every 4 hours PRN as a replacement for the chloral hydrate (Figures 1A-C).

Figure 1A. Monthly PRN use before initiation of sarcosine.

Figure 1B. Monthly PRN use after discontinuation of sarcosine.

Figure 1C. Monthly PRN use during sarcosine therapy.

Table 1. Medication regimen changes over course of hospitalization.

BID=twice daily
QHS=at bedtime
QAM=in the morning
4x daily=four times daily
All doses were administered by mouth unless otherwise noted

BPRS was utilized to document the progression of her treatment and the impact medication interventions had on her delusional thoughts and behaviors, including paranoia, anxiety and hostility. Prior to the initiation of NAC and sarcosine, the patient’s BPRS score was 72 in October 2012. Following the initiation of NAC and sarcosine, the patient’s BPRS score decreased, over the following 6 months of therapy, to a score of 50 in June 2013. Improvements were specifically seen in the areas of emotional withdrawal, conceptual disorganization, tension, mannerisms, hallucinatory behavior, uncooperativeness and blunted affect (Table 2).

Table 2. Improvement in BPRS score by date and domain. (highlighted boxes represent the score domains with the greatest improvements noted)

Emergent psychiatric interventions, including Code Greens (CG) and Restraint and Seclusions (R/S), along with PRN medication use, were also included in the analysis to evaluate the efficacy of the patient’s psychiatric medication regimen, as these are indicators of symptoms pertaining to agitation and aggression (Table 3). In the one year prior to the initiation of NAC and sarcosine, the patient required 2 CG (3/12/12, 4/9/12) and had 4 assaults reported (1/2/12, 3/19/12, 5/6/12, 6/11/12). She did not have a R/S. In the year following the initiation of NAC and sarcosine, the patient required 2 CG (1/4/13, 9/23/13) and had 4 assaults reported (2/25/13, 3/24/13, 4/2/13, 7/5/13), with no R/S (Figure 1C). Hydroxyzine pamoate (Vistaril) use fluctuated from month to month. Of note, doxepin (Sinequan) 50mg four times daily was initiated on 2/1/13. Her aggressive behavior, documented by reported assaults and CG, significantly decreased following her assault on 4/2/13, which is when her BPRS score was decreasing towards 50 (Tables 2 and 3). From her assault on 7/5/13 and CG on 9/23/13 until June 2017 (4 years following the initiation of NAC and sarcosine), the patient only required 2 CG (10/12/14, 6/14/16). Of note, thiothixene (Navane) 10mg four times daily was added to the patient’s medication regimen on 1/19/16.

Table 3. Emergent Psychiatric Interventions.

The patient was maintained on fluphenazine (Prolixin Decanoate)  olanzapine (Zyprexa), thiothixene (Navane), topiramate (Topamax), lorazepam (Ativan), hydroxyzine pamoate (Vistaril), NAC and sarcosine, until sarcosine became unavailable in April 2017. The patient was subsequently given 500mg once daily starting on 4/20/17 to conserve the remaining sarcosine supply while the facility searched for alternative sources, but was given her last dose on 6/19/17. The BPRS score closest to the time of sarcosine discontinuation was 47 on 2/29/17. On 8/1/17, nearly 2 months after sarcosine discontinuation, the BPRS score was the same (47).

Of note, in January 2017, the patient required evaluation at an adjoining neurology clinic following ophthalmoplegia, loss of visual acuity in her right eye, and frequent headaches. The patient did present with recurrent headaches upon admission to the state psychiatric hospital. However, the frequency and severity of these headaches increased prior to her neurology consultation. An magnetic resonance imaging (MRI) scan revealed a mass extending through the orbital fissure along the cavernous sinus. The patient was subsequently diagnosed with Tolosa-Hunt Syndrome: a rare disorder characterized by non-specific inflammation in the superior orbital fissure and cavernous sinus [18]. The clinical presentation includes ophthalmoplegia and severe unilateral headaches with orbital pain. The patient received treatment with prednisone 60mg daily tapered to 15mg daily, in addition to acetaminophen (Tylenol) 650mg four times daily as needed, to alleviate her symptoms. Repeat MRI revealed minimal improvement in the mass. The patient continues to be followed by the neurology clinic with an uncertain prognosis.

Discussion

It is unknown whether symptomatic improvement can be attributed to one specific medication or a concomitant synergistic outcome. The patient’s BPRS score was report ed as 70 in November 2012. Following the initiation of NAC, the patient’s BPRS score decreased from 70 to 61 in December 2012. Following the initiation of sarcosine, the patient’s BPRS score was unchanged with a reported score of 61 in January 2012. If sarcosine were to elicit a psychotropic response, a decreased BPRS score would be expected shown as a steeper negative slope of the BPRS data line (shown in Figure 1A). The patient’s BPRS score decreased from 61 to 56 in February 2013, which could indicate a delayed response from sarcosine or be a result of doxepin (Sinequan) initiation. Following the initiation of doxepin (Sinequan) in February 2012, the patient’s BPRS score decreased from 56 to 54 in March 2013, and then continued trending downward.

There were no major fluctuations in PRN use following the initiation of NAC and sarcosine. Figure 1A shows a steep increase in hydroxyzine pamoate (Vistaril) use from December 2012 to January 2013. This was likely a result of the manufacturing discontinuation of chloral hydrate, because the patient was transitioned to hydroxyzine pamoate by the prescriber as the selected alternative to chloral hydrate. There were peaks of hydroxyzine pamoate (Vistaril) and diphenhydramine (Benadryl) use over the course of NAC and sarcosine treatment. These peaks of use tended to occur in May, and again between October and January. It is unclear what may have caused these changes in PRN use, but it may possibly be related to seasonal changes. Increased pain and discomfort, along with long-term steroid treatment may also have resulted in mood and behavioral changes leading to increased PRN use.

Sarcosine became unavailable in April 2017 due to the reclassification of sarcosine to a Category 1 substance by the FDA. Category 1 FDA designation excludes use of the agent for compounding until further efficacy and safety data is available for review [19]. The patient received her last dose of sarcosine on 6/19/17. Following the discontinuation of sarcosine, the patient’s hydroxyzine pamoate (Vistaril) use increased from 14 PRN doses in June 2017 to 26 PRN doses in July 2017.  The increased PRN use following sarcosine discontinuation occurred despite the sustained lower BPRS score and reduced reports of aggressive behavior (Table 3). This could be a result of a “placebo” effect with sarcosine use or may indicate that there could have been an improvement “plateau” with sarcosine use. It could also indicate that NAC is the agent responsible for this initial and continued improvement in BPRS score. Increased risk for loss of behavioral control could have possibly been mitigated by the administration of psychiatric medications as well as the use of behavioral interventions initiated by staff. Thus decreasing the need for a CG or R/S following sarcosine discontinuation.

It is of interest that this patient was diagnosed with Tolosa-Hunt Syndrome. There are previous reports linking sarcosine to the progression of prostate and breast cancer [11, 20, 21]. Two patients diagnosed with breast cancer later presented with diffuse orbital involvement of the extraocular muscles, simulating Tolosa-Hunt syndrome [21]. Breast cancer is known to metastasize and can involve ocular structures. The patient in this case does not have a known personal or  immediate family history of cancer to date. The association between sarcosine, cancer and Tolosa-Hunt syndrome is not clear, but should receive attention as the use of CAM becomes even more common.

Conclusion

There is evidence to suggest that CAM therapies, including sarcosine and NAC, can provide some therapeutic benefit to patients suffering from treatment-resistant schizophrenia who have exhausted other therapy options. The patient discussed in this case report experienced a decrease in her BPRS score following the initiation of NAC, however the magnitude of the decrease was more robust with NAC than that seen with the initiation of sarcosine.  When sarcosine was discontinued there was not an increase of BPRS scores as would be expected if sarcosine were the agent responsible for her improvement.

NAC may have been the agent responsible for the patient’s symptom improvement versus a concomitant synergistic outcome with NAC and sarcosine. However, the patient is still hospitalized to date, which does question the efficacy of these alternative medication therapy options. Little is known about the long-term effects of NAC or sarcosine, when used for any patient, whether diagnosed  with psychiatric illness or not. While there is no clear association, more studies pertaining to the long-term safety outcomes of NAC and sarcosine exposure should be explored before recommendations are made to promote this psychiatric therapy intervention.

References

1. Yang AC, Tsai SJ (2017) New Targets for Schizophrenia Treatment beyond the Dopamine Hypothesis. Int J Mol Sci 18. crossref]
2. Stahl SM, Grady MM Stahl’s (2011) Stahl’s Essential Psychopharmacology: Neuroscientific Basis and Practical Applications. (4^th edn), Cambridge University Press, Cambridge, UK.
3. Javitt DC, Zukin SR, Heresco-Levy U, Umbricht D (2012) Has an angel shown the way? Etiological and therapeutic implications of the PCP/NMDA model of schizophrenia. Schizophr Bull 38: 958–966. [crossref]
4. Lee MY, Lin YR, Tu YS, Tseng YJ, Chan M, et al. (2017) Effects of sarcosine and N, N-dimethylglycine on NMDA receptor-mediated excitatory field potentials. J Biomed Sci 24: 18. [crossref]
5. Berk M, Copolov D, Dean O, Lu K, Jeavons S, et al. (2008) N-acetylcysteine as a glutathione precursor for schizophrenia, double-blind, randomized, placebo-controlled trial. Biol Psychiatry 64: 361–368. [crossref]
6. Dean O, Giorlando F, Berk M (2011) N-acetylcysteine in psychiatry: current therapeutic evidence and potential mechanisms of action. J Psychiatry Neurosci 36: 78–86. [crossref]
7. Gysin R, Kraftsik R, Sandell J, Bovet P, Chappuis C, et al. (2007) Impaired glutathione synthesis in schizophrenia: convergent genetic and functional evidence. Proc Natl Acad Sci USA 104: 16621–16626. [crossref]
8. Dringen R, Gutterer JM, Hirrlinger J (2000) Glutathione metabolism in brain metabolic interaction between astrocytes and neurons in the defense against reactive oxygen species. Eur J Biochem 267: 4912–4916. [crossref]
9. Chen G, Shi J, Hu Z, Hang C (2008) Inhibitory effect on cerebral inflammatory response following traumatic brain injury in rats: a potential neuroprotective mechanism of N-acetylcysteine. Mediators Inflamm 2008: 716458. [crossref]
10. Lehman AF, Lieberman JA, Dixon LB, McGlashan TH, Miller AL, et al. (2004) Practice guideline for the treatment of patients with schizophrenia, second edition. Am J Psychiatry 161: 1–56. [crossref]
11. Amiaz R, Kent I, Rubinstein K, Sela BA, Javitt D, et al. (2015) Safety, tolerability and pharmacokinetics of open label sarcosine added on to anti-psychotic treatment in schizophrenia – preliminary study. Isr J Psychiatry Relat Sci 52: 12–15. [crossref]
12. Tsai G, Lane HY, Yang P, Chong MY, Lange N (2004) Glycine transporter I inhibitor, N-methylglycine (sarcosine), added to antipsychotics for the treatment of schizophrenia. Biol Psychiatry 55: 452–456. [crossref]
13. Lane HY, Chang YC, Liu YC, Chiu CC, Tsai GE (2005) Sarcosine or D-Serine add-on treatment for acute exacerbation of schizophrenia: a randomized, double-blind, placebo-controlled study. Arch Gen Psychiatry 62: 1196–1204. [crossref]
14. Lane HY, Liu YC, Huang CL, Chang YC, Liau CH, et al. (2008) Sarcosine (N-methylglycine) treatment for acute schizophrenia: a randomized, double-blind study. Biol Psychiatry 63: 9–12. [crossref]
15. Lane HY, Lin CH, Huang YJ, Liao CH, Chang YC, et al. (2010) A randomized, double-blind, placebo-controlled comparison study of sarcosine (N-methylglycine) and D-serine add-on treatment for schizophrenia. Int J Neuropsychopharmacol 13: 451–460. [crossref]
16. Farokhnia M, Azarkolah A, Adinehfar F, Khodaie-Ardakani MR, Hosseini SM, et al. (2013) N-acetylcysteine as an adjunct to risperidone for treatment of negative symptoms in patients with chronic schizophrenia: a randomized, double-blind, placebo-controlled study. Clin Neuropharmacol 36: 185–192. [crossref]
17. Zheng W, Zhang QE, Cai DB, Yang XH, Qiu Y, et al. (2018) N-acetylcysteine for major mental disorders: a systematic review and meta-analysis of randomized controlled trials. Acta Psychiatr Scand 137: 391–400. [crossref]
18. Cohn DF, Carasso R, Streifler M (1979) Painful ophthalmoplegia: the Tolosa-Hunt syndrome. Eur Neurol 18: 373–381. [crossref]
19. U.S. Food and Drug Administration (2017) Update: FDA revises final guidance on interim policy for certain bulk drug substances used in compounding. Washington, D.C, USA.
20. Sreekumar A, Poisson LM, Rajendiran TM, Khan AP, Cao Q, et al. (2009) Metabolomic profiles delineate potential role for sarcosine in prostate cancer progression. Nature 457: 910–914. [crossref]
21. Harnett AN, Kemp EG, Fraser G (1999) Metastatic breast cancer presenting as Tolosa-Hunt syndrome. Clin Oncol (R Coll Radiol) 11: 407–409. [crossref]

DOI: 10.31038/JNNC.2018113

Abstract

Spinal meningiomas in childhood are very rare. To the best of our knowledge, recurrent falls has not been previously described in this kind of pediatric tumor as an initial clinical presentation. We present an unusual case of a 13-year-old female with a history of recurrent falls for several months, who was diagnosed with spinal meningioma. After five months of the initial symptom, the patient presented with sudden onset paraparesis, urinary incontinence, and left lower limb hypoesthesia. An urgent MRI was performed revealing cervicothoracic junction meningioma. She underwent C6-T2 superiorly based laminotomy and complete resection of the tumor. Pathologic study revealed a benign transitional meningioma. Post-operative evolution was satisfactory, with full recover of muscular strength in the lower limbs and no new episodes of recurrent falls or of urinary incontinence. A follow-up MRI study, performed 3-months after surgery, demonstrated complete tumor resection with no signs of recurrence. We hypothesize that the patient initially developed recurrent falls due to dorsal cord compression, which resulted in a posterior column dysfunction and proprioception deficit. Recurrent falls may be an unusual presentation of posteriorly based spinal cord tumor.

Key words

meningioma – paraparesis – pediatric neurosurgery – recurrent falls – spinal meningioma

Introduction

Despite accounting for approximately 20% of all primary tumors in the central nervous system [1], meningiomas are very rare in pediatric patients, with an annual incidence of 8 cases per 1, 000, 000 people [2]. Meningiomas are generally benign and their recurrence is mostly related to the histologic type. Until now, approximately 60 cases of spinal meningiomas in childhood (SMCs) have been reported in the English literature. To the best of our knowledge, recurrent falls has not been previously described in this kind of pediatric tumor as an initial clinical presentation. The current standard of treatment for meningiomas in children is surgical resection [3]. We report a case of a 13-year-old female with a history of recurrent falls during several months as an initial presentation of a spinal meningioma.

Case Material

Anamnesis, Physical Exam & Imaging

A 13-year-old female presented without any remarkable medical conditions except for a 5 month history of recurrent falls. She underwent a neurological exam by the pediatrician at the clinic, as well as head MRI and lower limbs CT that revealed no pathology. She presented to the emergency room with acute onset of paraparesis, urinary incontinence, and left lower limb hypoesthesia. Physical examination revealed bilateral reduction in muscle strength of the legs and thighs (both strength grade II/V), bilateral clonus, and bilateral positive pyramidal signs (Babinski, Chaddock, Oppenheim, and Gordon). Examination of the left lower limb demonstrated reduction of temperature and pain senses leveling at T3, with severe proprioception deficit of the left leg. Right side proprioception, temperature, pain and tactile examination were intact. Urgent spinal cord MRI with gadolinium-enhanced T1-weighted imaging, revealed a homogeneously enhancing intradural-extramedullary mass located posteriorly at the cervicothoracic junction area (C7-T1-T2) with a dural tail extending from the C6 to T2 levels (Fig.1 A, B). This mass exerted a local expansive-effect, creating medullar dorsal compression without significant peritumoral cord edema.

Surgical procedure and follow-up

In a prone position, with neurophysiological monitoring, a C6-T2 laminotomy was performed. The outer layer of dura matter was opened and the inner layer was attached to the tumor, a careful dissection was performed between the dural layers. The dura was opened at the lower and the upper ends of the tumor where it was free of disease. A good plain between tumor and the spinal cord was dissected. The tumor was lobulated, well-vascularized, with a hard rock consistency and multiple sites of calcification. Despite not finding a clear cleavage plane with the dura matter and an impressive compression of the spinal cord, an arachnoid plane was used and gross total tumor resection was achieved. The operative and post-operative courses were uneventful. The patient improved immediately after surgery, and returned to normal neurological status within 3 weeks. Paraffin embedded sections stained with H&amp;E displayed a meningothelial neoplasm, with a partial fibrous pattern, and many tight whorls and psammoma bodies. No atypical features were detected. There was no necrosis and mitotic figures were not identified. On immunohistochemical stain the MIB-1 proliferation marker labeling index was about 2–3%. The features are consistent with a pathological diagnosis of transitional meningioma, WHO grade I. (Figure 2). No risk factors for SCM as neurofibromatosis type 2 or exposure to radiation were found. A follow-up MRI study, 3-months after surgery, demonstrated complete tumor resection with no signs of recurrence (Figure 3 A, B). She continue follow-up in our institution and 24 months after surgery the patient remains without neurologic deficit and no signs of tumor recurrence.

(1A) Sagittal

(1B) Axial

Figure 1. Sagittal (A) and axial (B) T1-weighted gadolinium-enhanced MRI showing a homogeneously enhancing intradural-extramedullary mass located posteriorly at the cervico-thoracic junction area (C7-T1-T2) with dural tail extending from the C6 to T2 levels, in a 13-year-old female with a history of recurrent falls.

Figure 2. Paraffin embedded section stained with H&E display a transitional meningioma, with many tight whorls (black arrow) and psammoma bodies (white arrow). No atypical features were detected. There is no necrosis and mitotic figures were not seen.

(3A) Sagittal

(3B) Axial

Figure 3. Sagittal (A) and axial (B) T1-weighted gadolinium-enhanced MRI at 3 month follow-up revealed complete tumor resection with no signs of recurrence.

Discussion

We report a case of a 13-year-old female with a history of recurrent falls for several months as an initial presentation of a spinal meningioma at the level of the cervicothoracic junction. Recurrent falls as the only symptom, with a normal neurological exam, has not been previously reported in the English literature. We hypothesize that the initial neurological deficit was due to dorsal cord compression, resulting in a posterior column dysfunction and proprioception deficit, eventually leading to recurrent falls. Misdiagnosis resulted in a late diagnosis of a spinal meningioma in a child.

In the pediatric population, meningiomas account for less than 5% of brain tumors. Pediatric spinal tumors represent only 5% of tumors of the central nervous system, 25% of which occur in the intradural-extramedullary compartment [3] with an annual incidence of almost 1 per 1, 000, 000 children [4]. Reports from the adult population demonstrate that the majority of cases tend to occur in women (ratio around 2: 1). Nevertheless, this association is not replicated in children, where there are reports of an approximately 1.2: 1 predominance of cases in males [2]. In their retrospective analysis of 20 children, Greene at el. showed a median age of about 13 years at the time of the tumor presentation [2].

Clinical presentation of Spinal Meningiomas in Childhood (SMC) is variable, but consistent with the anatomical localization. The most common presenting symptoms are pain and limb weakness. Wang et al. [5] presented the largest series of SMC, with 10 patients treated from January 2002 to December 2010. They observed back pain in 60%, followed by signs of limb weakness in 40%, gait disturbance in 20%, paresthesia in one patient, and urinary incontinence in another. Conesa D. et al. described a case of recurrent falls caused by spinal meningioma in an elderly woman [6]. Due to the slow growing pattern of meningioma, the symptoms develop gradually during 1–18 months [5].

The etiology of SMC is still not clear but some risk factors have been described, such as association with NF-2 and a history of radiation [7, 8]. The link to NF-2 is becoming clearer, with the most common finding the loss of a tumor suppressor gene in the chromosome 22 (NF-2). Other gene mutations may contribute to the progression of the meningiomas, leading to the more aggressive, anaplastic type. Ionizing radiation is the environmental risk factor most predisposing to meningiomas [8]. The slight predominance of this tumor in women over men in adults raises the hypothesis of the influence of female hormones. Receptors for estrogen and progesterone have been suggested to cause faster tumor growth on the third trimester of pregnancy; however, the exact link between hormones and the development of meningiomas is still not clear [8].

Spinal cord meningioma is rare, with only 60 cases reported in the English literature. Reported ratios of intracranial to spinal meningiomas in children are 20: 1 [12], 14: 1 [1], and 10: 1 [9]. From their review of 15 cases of SMCs, Colen et al. [13] reported that in 14 children the tumor was located in the thoracic and lumbar spinal canal. However, in Wang’s et al. series [5] none of the tumors was in the lumbar area, with 50% in the cervical area, 30% thoracic, and 20% in the cervicothoracic junction.

The standard exam for diagnosing SMC is MRI study. The most common appearance in T1 and T2-weighted imaging is an extra-axial isointense mass. In the post-gadolinium injection, T1-weighted image, SMC appears as a homogeneously enhancing mass. Different degrees of peritumoral edema may be observed.

In 1993 the World Health Organization (WHO) ratified a new comprehensive classification of neoplasms affecting the central nervous system; its last edition (fifth) was published in 2016. According to the WHO classification,  meningiomas are divided in to 3 grades – benign (grade I), atypical (grade II) and anaplastic or malignant (grade III). In the literature, psammomatous and fibroblastic meningiomas are the most common pathological subtypes reported in the largest series of pediatric [13] and adult [14] spinal meningiomas.

Gross total resection is the treatment of choice for SMC, with special care required to preserve the neurological function and stability of the growing spinal canal [14]. However, many factors should be considered in order to achieve a gross total resection, such as location, size, blood loss, adhesion, and the pathological subtypes (causing severe adhesion) [9]. Complete resection has been achieved with good post-operative outcome in most reported cases [5]. The extent of resection may also be predictive for recurrence.

In summary, spinal meningioma is a rare disease in the pediatric population. Not only pediatric neurosurgeons, but also pediatricians need be aware of this highly unusual presentation of SMC when facing recurrent falls in children. The diagnosis and treatment are relatively straightforward using an imaging study (MRI) and surgical tumor excision, respectively.

Conflicts of Interest/Disclosure

The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.

References

1. Rushing EJ, Olsen C, Mena H, Rueda ME, Lee YS, et al. (2005) Central nervous system meningiomas in the first two decades of life: a clinicopathological analysis of 87 patients. J Neurosurg 103: 489–495.
2. Greene S, Nair N, Ojemann JG, Ellenbogen RG, Avellino AM (2008) Meningiomas in children. Pediatr Neurosurg 44: 9–13. [crossref]
3. Binning M, Klimo P, Gluf W, Goumnerova L (2007) Spinal tumors in children. Neurosurg Clin N Am 18: 631–658. [crossref]
4. Kumar R, Giri PJ (2008) Pediatric extradural spinal tumors. Pediatr Neurosurg 44: 181–189. [crossref]
5. Wang XQ, Zeng XW, Zhang BY, Dou YF, Wu JS, et al. (2012) Spinal meningioma in childhood: clinical features and treatment. Childs Nerv Syst 28: 129–136. [crossref]
6. Conesa D, Ferrer A, Torres A, Formiga F, Pujol R, et al. (2013) An unusual and reversible cause of falls: spinal meningioma in an elderly woman. J Am Geriatr Soc 61: 166–168. [crossref]
7. Mekitarian Filho E, Horigoshi NK, Carvalho WB, Hirscheimer MR, Bresolin AU, et al. (2010) Primary spinal meningioma in a 10-year-old boy. Arq Neuropsiquiatr 68: 804–806. [crossref]
8. Riemenschneider MJ, Perry A, Reifenberger G (2006) Histological classification and molecular genetics of meningiomas. Lancet Neurol 5: 1045–1054
9. Campbell BA, Jhamb A, Maguire JA, Toyota B, Ma R (2009) Meningiomas in 2009: controversies and future challenges. Am J Clin Oncol 32: 73–85. [crossref]
10. Hanel RA, Tatsui CE, Araujo JC, Grande CV, Antoniuk A, et al. (2001) [Meningiomas in pediatric patients: report of 2 cases]. Arq Neuropsiquiatr 59: 623–627. [crossref]
11. Watanabe M, Chiba K, Matsumoto M, Maruiwa H, Fujimura Y, et al. (2001) Infantile spinal cord meningioma. Case illustration. J Neurosurg 94: 334. [crossref]
12. Colen CB, Rayes M, McClendon J Jr, Rabah R, Ham SD (2009) Pediatric spinal clear cell meningioma. Case report. J Neurosurg Pediatr 3: 57–60. [crossref]
13.  Loh JK, Lin CK, Hwang YF, Hwang SL, Kwan AL, et al. (2005) Primary spinal tumors in children. J Clin Neurosci 12: 246–248. [crossref]
14. Engelhard HH, Villano JL, Porter KR, Stewart AK, Barua M, et al. (2010) Clinical presentation, histology, and treatment in 430 patients with primary tumors of the spinal cord, spinal meninges, or cauda equina. J Neurosurg Spine 13: 67–77. [crossref]

DOI: 10.31038/JNNC.2018112

Abstract

Objective

Malignant peripheral nerve sheath tumors are uncommon malignant spindle cell tumors that account for 5% to 10% of all soft tissue sarcomas. Localization of such tumors in the scalp is extremely rare. Diagnosing and treating these tumors is very challenging.

Methods

Case presentation and Literature review.

Results

We found 18 cases of malignant peripheral nerve sheath tumors including our case. The occipital region was the most common site of the tumor. Five patients had h intracranial invasion and two patients had distant metastasis. All the patients were treated surgically. Four patients had recurrence of their tumors and two of them died from the disease

Conclusion

MPNSTs should be considered in the differential diagnosis of rapidly enlarging scalp tumors. Radical excision with wide margins and adjuvant radiation therapy should be considered as the standard treatment for these highly malignant tumors

Keywords

Malignant Peripheral Nerve Sheath Tumor, Scalp Tumor, Neurosarcoma, Shwannsarcoma, Malignant Schwannoma

Introduction

Malignant peripheral nerve sheath tumors (MPNST) are soft tissue sarcomas of ectomesenchymal origin. They derived from components of nerve sheath such as Schwann cells or perineural fibroblasts. The incidence of MPNST is around 0.001% in the general population and 3–4.6% in patients with NF 1. They account for 5–10% of all soft tissue sarcomas. The head and neck region is an unusual site for their development; they are located mostly in the extremities and the trunk (1, 2). We hereby describe a case of giant MPNST of the scalp and discuss the management of such a rare case with a review of the literature.

Case report

A forty-year-old female patient presented to her family physician for a painless mass on her vertex of 5-year duration. The tumor was first a small subcutaneous nodule that gradually increased in size for three years and then experienced rapid growth over the next year with recent onset of ulceration and bleeding from the tumor. No history of previous trauma.

Physical examination revealed an 8x8x6 cm occipital-parietal mass with superficial ulcerations and crusting. It was hard, non-tender, non-pulsating and adherent to the underlying skull. No cervical or occipital lymph nodes were palpated. The patient had no skin lesions elsewhere and no clinical manifestations of neurofibromatosis. Computerized tomography showed a large irregular exophytic, heterogeneously enhancing scalp mass obliterating the subcutaneous tissue reaching the periosteum, the underlying bone was intact (Figure 1). A whole body CT scan revealed no metastatic lesions. Biopsy of the tumor was done under local anesthesia. The histopathologic examination revealed a dermal proliferation of haphazardly arranged pleomorphic spindle cells. The background displayed lymphoid cells and histiocytes. Mitotic figures were evident and abundant. Immunohistochemistry for melanoma associated antigen (HMB-45), Melan A, AlK, MSA, CD34 and CD68 did not reveal any positivity. The tumor cells were positive for vimentin and Ki-67 proliferation marker was up to 10 %. Immunostaining for neural antigen S-100 protein led the pathologists to the diagnosis of high grade malignant peripheral nerve sheet tumor of the scalp (Figure 2).

Figure 1A. Scalp tumor in a 45-year-old female manifesting as a dome-shaped tumor measuring 8 × 8 × 6 cm with superficial superficial ulcers and crusting

Figure 1B. Sagittal CT scans showing the enhancing scalp tumor with an intact underlying bone.

Figure 1C. oronal CT scans showing the enhancing scalp tumor with an intact underlying bone

The patient was referred to the ENT department for surgical management. Under general anesthesia the tumor was excised with a 2-cm margin of healthy tissue. The tumor was highly vascularized; the periosteum was involved by the tumor but no bony erosions were noted. The tabula externa of the skull was removed using the drill and the resulting defect was covered by three local rotation flaps (Figure 3). The postoperative period was uneventful. The surgical field was treated by radiation therapy with a total dose of 50 Gy 1 month postoperatively. There was no recurrence at 18 months of follow-up (Table 1).

Figure 2A. Low power view (4X) of a Hematoxylin and eosins section showing a variably cellular spindle cell proliferation with focal palisading and necrosis.

Figure 2B. High power view (40X) on a Hematoxylin and eosin section showing moderate nuclear Pleomorphism and brisk mitotic activity.

Figure 2C. High power view showing S100 Positivity in Tumor cells.

Figure 3A. Intraoperative Picture Showing the Scalp Defect with Preparation of Local Myocutaneous Rotation Flaps.

Figure 3B. Postoperative Image of the Patient.

Figure 3C. Image of the Patient at 18 month of Follow-Up.

Table 1. Literature review of studies of malignant peripheral nerve sheath tumor of the scalp

Abbreviations:

F-female, M-male, m-Month; AWD-Alive With Disease; Chemo-Chemotherapy; DOD-Dead of Disease; Dx-Diagnosis; FTSG-Full Thickness Skin Graft; LD-Latissimus Dorsi; NED-No Evidence of Disease; NA-Non Available; NF1-Neurofibromatosis type 1; RT-radiation therapy; SS-symptoms; TM-Trapezius Muscle; Yrs-years

Discussion

Malignant Peripheral Nerve Sheath Tumor (MPNST) is a rare neoplasm of the nervous system. It is a malignant spindle-cell tumor derived from components of nerve sheath. Although the universal terminology defined by the World Health Organization is MPNST, a variety of terminologies are recognized including malignant schwannoma, neurofibrosarcoma, malignant neurofibroma, malignant neurilemomma, and shwannsarcoma (2, 3).

The etiology is still uncertain but MPNSTs are commonly associated with Von Recklinghausen disease in whom gene mutations are found, such as loss of the neurofibromatosis 1 gene and rearrangement of the p16 (INK4A) gene (4, 5). It has been reported that 60% of all MPNSTs represent a malignant transformation of a preexisting benign neurofibroma, whereas 30% arise de novo, and approximately 10% occur in patients with history of previous radiation at the tumor site. MPNST usually affects the patients in their third to sixth decades of life. Medium and larger nerves like brachial plexus and sciatic nerve are commonly affected, consequently MPNSTs have a propensity to occur in the proximal limbs and the trunk (6, 7). MPNST of the scalp is extremely rare. We performed a detailed search in Pubmed and Medline database with a complete review of all the English literature published. We found 18 cases of MPNST of the scalp, including our case (Table 1).

Patients were aged from 36 to 89 (mean age 50) with male predominance (61.1%). Tumors measured from 2 to 22 cm in their largest diameter (mean 9.1 cm). The occipital region was the most common site. Of these 18 patients, four had neurofibromatosis. The interval time between tumor diagnosis and symptoms ranged from 4 months to 30 years, only 2 patients had rapid onset of their tumors suggesting the theory of de-novo tumor. In 16 cases, the tumor had a slow growth pattern at the beginning and then became rapid in the last several months, suggesting malignant transformation of a previously benign tumor. Five patients had calvarial destruction with intracranial invasion and only 2 patient had distant metastasis. All the patients were treated surgically. Ten patients received postoperative radiation therapy and only one patient received chemotherapy. Follow-up periods ranged from 4 months to 11 years. Four patients had recurrence of their tumors and two of them died from the disease.

MPNSTs are poorly defined sarcomas. They can easily be identified when the surgeon or the pathologist demonstrates a neurofibroma or a nerve trunk; but in the absence of these findings as in skin tumors, differentiating MPNSTs from other benign or malignant spindle cell tumors and melanoma is very challenging. Microscopically, MPNST is a densely cellular tumor that shows fascicular areas. The cells may be spindle or polygonal in shape with irregular contours. Malignancy is suggested when there is invasion of surrounding tissues, necrosis, focal hemorrhage, mitotic activity, nuclear pleomorphism and atypia (7–10). Immunohistochemical studies with a combination of should be used to exclude other spindle cell tumors and to give an accurate diagnosis. Up to 90% of MPNSTs stain positive for S-100 protein. Ki-67 is a proliferation marker that reflects the increased mitotic index and support malignancy. The differential diagnosis of MPNST in the scalp includes leiomyosarcoma, dermatofibrosarcoma protuberans (excluded by a negative MSA and CD34 respectively) and melanoma which is excluded by a negative Melan A and HMB-45 (1, 3, 11, 12).

The International Consensus Group has recommended that the current management of MPNST should be identical to that of any other soft tissue tumors. Accordingly, the mainstay of treatment is complete surgical excision of the tumor with wide margins (≥2cm). The bone and dura involved should be resected together (6). The scalp defect is reconstructed using skin graft, local cutaneous flap, myocutaneous flap or free flaps depending on the size of the defect. A cranioplasty should be done in case of significant calvarial destruction (13). Adjuvant radiation therapy should be considered for all intermediate- and high-grade lesions as well as low-grade tumors with positive margins. The role of chemotherapy is usually limited to the treatment of metastatic disease (13, 14). It is well known that the majority of MPNSTs have a poor prognosis because they are usually high-grade deep-seated tumors (7, 10). This is not applicable for MPNST of the scalp (table1). Although the present data is based on a small patient number with short follow-up periods; but the fact that scalp tumors have early clinical manifestations with the possibility of radical excision make them having a more-favorable prognosis (3, 14).

Conclusion

In conclusion, MPNSTs should be considered in the differential diagnosis of any rapidly enlarging scalp tumor especially in the context of neurofibromatosis. Accurate histopathologic and immunohistochemical findings are indispensable for the confirmation of the diagnosis. Considering the high malignancy and the invasive growth of MPNST of the scalp, radical excision with wide margins (≥2 cm), and adjuvant radiation should be considered as the standard treatment for these highly malignant tumors

References

1. Fukushima S, Kageshita T, Wakasugi S, Matsushita S, Kaguchi A, et al. (2006) Giant malignant peripheral nerve sheath tumor of the scalp. J Dermatol 33: 865–868. [crossref]
2. Demir Y, Tokyol C (2003) Superficial malignant schwannoma of the scalp. Dermatol Surg 29: 879–881. [crossref]
3. Wang J, Ou S, Guo Z, Wang Y, Xing D (2013) Microsurgical management of giant malignant peripheral nerve sheath tumor of the scalp: two case reports and a literature review. World J Surg Oncol 11: 269.
4. Williams SB, Szlyk GR, Manyak MJ (2006) Malignant peripheral nerve sheath tumor of the kidney. Int J Urol 13: 74–75. [crossref]
5. Ge P, Fu S, Lu L, Zhong Y, Qi B, et al. (2010) Diffuse scalp malignant peripheral nerve sheath tumor with intracranial extension in a patient with neurofibromatosis type 1. J Clin Neurosci 17: 1443–1444. [crossref]
6. Kumar P, Jaiswal S, Agrawal T, Verma A, Datta NR (2007) Malignant peripheral nerve sheath tumor of the occipital region: case report. Neurosurgery 61: 1334–1335. [crossref]
7. Garg A, Gupta V, Gaikwad SB, Mishra NK, Ojha BK, et al. (2004) Scalp malignant peripheral nerve sheath tumor (MPNST) with bony involvement and new bone formation: case report. Clin Neurol Neurosurg 106: 340–344. [crossref]
8. Shintaku M, Wada K, Wakasa T, Ueda M (2011) Malignant peripheral nerve sheath tumor with fibroblastic differentiation in a patient with neurofibromatosis type 1: imprint cytological findings. Acta Cytol 55: 467–472.
9. Jhawar SS, Mahore A, Goel N, Goel A (2012) Malignant peripheral nerve sheath tumour of scalp with extradural extension: case report. Turk Neurosurg 22: 254–256. [crossref]
10. Schaefer IM, Fletcher CD (2015) Malignant peripheral nerve sheath tumor (MPNST) arising in diffuse-type neurofibroma: clinicopathologic characterization in a series of 9 cases. Am J Surg Pathol. 39: 1234–1241. [crossref]
11. Kikuchi A, Akiyama M, Han-Yaku H, Shimizu H, Naka W, et al. (1993) Solitary cutaneous malignant schwannoma. Immunohistochemical and ultrastructural studies. Am J Dermatopathol 15: 15–19. [crossref]
12. George E, Swanson PE, Wick MR (1989) Malignant peripheral nerve sheath tumors of the skin. Am J Dermatopathol 11: 213–221. [crossref]
13. Hasturk AE, Basmaci M, Bayram C, Bozdogan N (2011) Surgical management of recurrent malignant schwannoma of the scalp. J Craniofac Surg 22: 1120–1122. [crossref]
14. Voth H, Nakai N, Wardelmann E, Wenzel J, Bieber T, et al. (2011) Malignant peripheral nerve sheath tumor of the scalp: case report and review of the literature. Dermatol Surg 37: 1684–1688. [crossref]

DOI: 10.31038/JNNC.2018111

Abstract

Recent studies have revealed that autistic spectrum disorders (ASD) is associated with enhanced glycolysis (i.e. establishment of the Warburg effect) accompanied by increased formation of glycated proteins in sera and urine. Both carnosine and agmatine levels in sera of autistic individuals are reported to be lower than in control subjects. Carnosine and agmatine can influence cellular energy metabolism, in part via effects on mTOR, thereby decreasing glycolysis and enhancing mitochondrial activity and thus countering onset of Warburg-like metabolism: other mechanisms including suppressing methylglyoxal toxicity are also discussed. Dietary supplementation studies with carnosine and arginine (agmatine precursor) indicate ameliorative activity towards behaviour in ASD subjects. It is suggested that co-administration of carnosine and agmatine should be explored as a potential route for ASD amelioration.

Key words

Carnosine, Agmatine, Autism, Glycolysis, Glycation, Mitochondria, Methylglyoxal, Propionic Acid, Rapamycin, Mtor

Introduction

A recent publication has suggested that Autism Spectrum Disorders (ASD) is accompanied, associated and/or related to changes in energy metabolism, more specifically the imposition of enhanced aerobic glycolysis, coupled with a suppression of mitochondrial ATP synthesis, also known as the Warburg effect [1]. Another recent paper has revealed the presence of elevated amounts of oxidized, nitrated and glycated proteins in the plasma of some ASD subjects, as well as a disturbance in arginine metabolism and/or clearance [2]. The objective of the present piece is to attempt to integrate these findings by highlighting the possible ameliorative roles of carnosine and agmatine (decarboxylated arginine), both of which are diminished in sera of some ASD subjects [3–5].

Energy metabolism and ASD

The Vallée and Vallée hypothesis [1] proposes that ASD is strongly associated with “a shift in energy production from mitochondrial oxidative phosphorylation to aerobic glycolysis – despite the availability of oxygen” i.e. the imposition of the Warburg effect. Plausible mechanistic routes proposed include the WNT/beta-catenin pathway, and activation of the regulatory complex PI3Akt/mTOR [1]. It is uncertain whether the induction of the predominantly glycolytic metabolism is caused primarily by dysfunction of the PI3AktmTOR regulatory complex, provoked perhaps by glycated protein (also called advanced glycation end-products i.e. AGEs) [6] or whether the imposition of the Warburg-type metabolism is a response to some other causative event or events, such as mitochondrial dysfunction. Indeed, it has been claimed that ASD is associated with mitochondrial dysfunction [7–10], and a three-fold decline in oxidative phosphorylation has been detected in ASD subjects’ granulocytes [10]. It would obviously be informative to determine if this deficit is systemic and also occurring in the CNS, or exhibited solely in granulocytes.

There is evidence suggesting that formation and/or accumulation of propionic acid is associated with some cases of ASD [11–13], possibly originating in the gut tissue or more likely in the microbiome (mostly Clostridia bacterial species) [14]. It is thought that, in the brain, propionic acid inhibits GABA breakdown causing its accumulation thereby affecting brain function. Interestingly, raised levels of β-alanine have been detected in the urine of some autistic subjects [4], whilst in other autistic individuals a decrease was detected [3] These observations, although seemingly contradictory, may reflect differences in β-alanine generation and utilisation by the micro-organisms in the gut. β-Alanine is a precursor pantothenic acid which, in turn, is a precursor of Co-enzyme-A (CoA) (synthesized by the gut micro-organisms). The microbiome is the predominant source of pantothenic acid in the human body. One speculative suggestion is that propionic acid accumulates as a result of a failure in its carboxylation, which requires functional CoA, hence propionic acid accumulates if synthesis of Co-A is compromised. General deficiency in CoA availability would also decrease fatty acid oxidation, as found in ASD [7,8,10,16,17]. The resultant mitochondrial dysfunction would have two important consequences which directly impact ASD. First, the decreased supply of electrons (i.e. acetyl units attached to CoA) will provoke an increase in the generation of incompletely reduced oxygen molecules, i.e. oxygen free-radicals [18], the presence of which will provoke formation of deleterious Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS). Such a mechanism may account for the raised levels of protein oxidation and nitration recently detected in autistic patients’ urine and plasma [2]. A second consequence of insufficient mitochondrial ATP synthesis may be a compensating upregulation of glycolysis in an attempt to maintain ATP levels [1]. Indeed enhanced glycolysis accompanied by mitochondrial abnormalities have been detected in ASD subjects (compared to siblings and controls) [19]. Importantly, upregulated glycolysis would enhance generation of the highly toxic bicarbonyl compound, Methylglyoxal (MG), produced following spontaneous decomposition of the glycolytic intermediates, dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate. MG is a strong glycating agent and well-recognised as a major source of the post-synthetic protein modifications which characterise both type-2 diabetes and ageing [20,21]. The notion that ASD is associated with enhanced MG generation is supported by the detection in some autistic subjects of gene polymorphisms in the MG detoxification enzyme, glyoxalase-1 [22–25], which could result in decreased MG elimination and increased macromolecular glycation. The increased glycolytic activity could therefore account for the raised levels of glycated proteins detected in autistic patients’ plasma and urine [2], especially if glyoxalase-1 activity was insufficient to meet the increased generation of MG. However it must be pointed out that the suggestion that ASD is associated with glyoxalase dysfunction has been disputed [26,27]. Never-the-less, it is interesting that (i) changes in glyoxalase-1 expression in white blood cells seems to influence mood in human subjects [28], and (ii) it has recently been reported that erythrocytes of autistic boys possess lower levels of the detoxification enzyme retinal dehydrogenase (RALDH1), than was present in controls [29], observations which suggest that detoxification deficiency may influence behaviour in ASD individuals. The possibility that autism is associated with aldehyde toxicity generally and acetaldehyde in particular, has been proposed [30]. Furthermore, it has recently been shown that MG readily reacts with β-alanine [31], a reaction which would decrease pantothenate synthesis and further compromise formation of the CoA in the microbiome, as outlined above. Additionally the microbiome can also generate a well-studied neurotoxin, 3-Nitropropionic Acid (3NPA), presumably from propionic acid, which can induce a range of neuropathologies in model animals [32], although no specific claims for ASD have been made. Biochemically, 3NPA inhibits the TCA cycle enzyme succinate dehydrogenase, thereby compromising mitochondrial ATP synthesis and so could induce a Warburg-like metabolic state. It is likely that any gut organism in which propionic acid accumulates (as discussed above) may also increase the potential for 3NPA generation following attack by Reactive Nitrogen Species (RNS); it is noteworthy ASD sera is enriched with nitrated proteins [2]. Consequently, it is possible to integrate a number of observations associated with ASD, including mitochondrial dysfunction, propionic acid accumulation, increased urinary β-alanine levels, decreased pantothenate levels, decreased glyoxalase-1 activity, and raised levels of sera oxidized, nitrated and glycated proteins.

There is additional evidence that ASD may be associated directly with changes in energy metabolism. A number of studies showing that the anti-aging agent rapamycin, which suppresses mTOR signalling activity to decrease glycolysis and upregulate oxidative phosphorylation, also suppresses autism-like behaviour in animal models [33,34]. Glycated proteins (AGEs) have been shown to activate mTOR [6] and elevated mTOR activity was detected in cells obtained from ASD children [35,36], suggesting a possible causative relationship between these phenomena. Animals exposed to valproic acid have been used as an animal model of ASD see Nicolini & Fahnestock, 2018 for recent review [37]: amongst the resultant effects of valproic acid is a dose dependent stimulation of glycolysis [38] and, perhaps even more importantly, it has previously been observed that resveratrol, an anti-diabetic agent which inhibits non-enzymic glycosylation (glycation) of proteins, prevents valproic acid-induced social impairment in these animals [40]. Furthermore, ketogenic diets (presumably provoking very little glycolysis) have been shown to be somewhat effective in controlling ASD behavioural symptoms in human subjects [41]. Although it is uncertain whether these effects are mediated via the microbiome or specifically in the cells of CNS, these findings are nevertheless consistent with the suggestion that ASD is associated with increased protein glycation resulting from enhanced glycolysis and MG generation.

Deficiency in vitamin-D has also been proposed to play a role in ASD [42–44] and it has been claimed that vitamin D supplementation in children may improve symptoms of ASD [45]. It is interesting to note that vitamin D appears to play a role in controlling the reaction between advanced glycation end-products (AGEs) with their cellular receptors (RAGEs) [46–48], again observations consistent with the findings of elevated levels of protein glycation in ASD subjects.

Carnosine and ASD

The dipeptide carnosine (β-alanyl-L-histidine), when given as a dietary supplement to autistic children, has been shown to exert beneficial effects on behaviour [49,50]. Furthermore the levels of carnosine in urine [51] and sera [17,52 ] of autistic subjects are reported to be substantially lower (by up to 75%) than in controls. Although first described more than 100 years ago [53], carnosine was regarded as “enigmatic” [54]; its precise physiological function still remains uncertain. Amongst the variety of suggestions, all supported with evidence using model and/or cell and animal studies, carnosine can behave as a hydrogen ion buffer, anti-oxidant, anti-glycator, wound-healing agent, metal ion chelator, whilst beneficial effects towards diabetes, atherosclerosis, heart failure, tumour cell growth and cellular ageing have also been reported [55–57]. Interestingly, dietary supplementation studies in human subjects have revealed improvement in cognition and/or behaviour in schizophrenics [58], elderly subjects [59], Gulf War veterans [60] and as well as autistic children [3, 52].

There are a number of possible mechanisms by which carnosine might ameliorate aspects of ASD. First, the additional presence of dietary dipeptide carnosine could, following its hydrolysis, provide a supply of β-alanine and thus allow pantothenate and CoA synthesis in the microbiome, and thereby permit effective oxidative phosphorylation and perhaps additionally ensuring removal of the propionic acid via its carboxylation using acetyl-CoA kinase. Secondly, as outlined above, in order to maintain ATP levels, a compensating response to mitochondrial dysfunction would be enhanced glycolysis, despite the presence of oxygen (i.e. Warburg effect). There is evidence that carnosine can partially suppress glycolysis and decrease glycolytic ATP synthesis in yeast [61] and in transformed cells [62–64 ], which may decrease synthesis of triose phosphates and MG formation. Carnosine can also directly react with methylglyoxal [65] and other reactive carbonyl compounds [66], as well as inhibit formation of glycated proteins as shown in whole animal studies [67,68] and in humans [69]. Carnosine has also been shown to exert regulatory effects on mitochondrial function [70,71] as well as activate the Nrf2 transcription factor (regulator of the antioxidant response) and thereby enhance oxidative defence [72,73]. It is relevant to note that autism in young boys is associated with alteration in Nfr2 expression and/or function [10,74]. Furthermore it should be noted that carnosine may mimic rapamycin to some degree in its ability to inhibit mTOR activity [75]; as noted above, rapamycin is a well-recognised mTOR inhibitor that exerts beneficial effects towards ASD subjects and in animal models [33–35].

These properties (inhibitory effects on mTOR and glycolysis, suppression of MG-induced macromolecular modifications and enhancement of anti-oxidant defence) exhibited by carnosine would appear to counter the onset of the Warburg effect and might account for the beneficial effects of carnosine towards at least some aspects of ASD. Furthermore carnosine has been shown to suppress acetaldehyde-mediated toxicity towards cultured cells [76] and DNA-protein cross-linking in a model system [77], observations consistent with the proposal that ASD is somehow associated with acetaldehyde-mediated dysfunction [30]. It is interesting to note that carnosine seems to possess many of the properties which are likely to suppress generation of the changes exhibited by sera and urinary proteome detected in ASD subjects [2].

There is also a study showing that carnosine can ameliorate the deleterious effect of propionic acid in an animal model of ASD, although the mechanisms responsible have not been explored [78]. Recent studies have suggested that the DJ-1 protein complex can facilitate protein deglycation [31], including glycated β-alanine (induced by MG). Many years ago it was suggested that carnosine might participate the repair of glycated proteins (via deglycation and/or transglycation), perhaps acting as a recipient of the detached glycating agent [79]. However, the possibility that carnosine might participate in protein deglycation has not been explored experimentally.

Carnosine can also inhibit protein nitration by forming adducts such as NO-carnosine and carnosine nitrite [80]. Given that raised levels of protein nitration have been detected in ASD plasma and urine [2], as well as in hair and nails [81], this may partly explain carnosine’s ability to moderate aspects ASD behaviour [49]. More recently it has been shown that romidepsin can ameliorate autism-like behavioural symptoms in a mouse model of ASD [82] by binding to zinc ions in the zinc pocket of histone deacetylase and thus altering gene expression. As carnosine is a well-known zinc chelator, one wonders if the dipeptide might also bind the zinc in histone deacetylase in a manner similar to romidepsin.

Agmatine and ASD

There is evidence from an animal study that agmatine (decarboxylated arginine) can be beneficial towards valproic acid-induced autism-like symptoms of ASD in an animal model [83,84] and that some ASD subjects possess decreased levels of agmatine in their sera [5]. While there is evidence that agmatine possesses anti-inflammatory properties [84,85], there is little direct evidence of any anti-glycation activity of agmatine, although the structure of the molecule (an amino group plus the guanidino group) resembles the strong but toxic anti-glycator, aminoguanidine. Consequently, it is suggested that agmatine should be very readily glycated by a variety of reactive aldehydes, including MG and acetaldehyde, although this property does not appear to have been investigated. Never-the-less it is very relevant to note that agmatine can bind ADP-ribose [86] which may indicate agmatine’s possible inhibitory action towards protein modification by ADP-ribose, or its participation in reversible protein modification (e.g. NAD-dependent histone deacetylation or polyADP ribosylation). The fact that agmatine activity has been likened to that of the anti-aging agent rapamycin [87], including mTOR inhibition, suppression of glycolysis and activation of mitochondrial activity [88], supports this idea. The findings that ASD is associated with changes in arginine metabolism [34] and its intracellular distribution [2] reinforces the proposal that arginine’s decarboxylation product, agmatine, might be ameliorative [89].

It is perhaps also interesting to note that agmatine can promote an increase in cyclic-AMP levels in tissues [88], but cyclic-AMP has been reported to suppress carnosine synthesis [90]. Such observations might suggest that while agmatine can suppress carnosine synthesis, but upon its glycation agmatine may not suppress carnosine synthesis, which could indicate a possible regulatory mechanism of carnosine production in response to endogenous and exogenous glycating agents. Agmatine has been shown to inhibit polyamine synthesis, but whether this property is suppressed following agmatine glycation has not been investigated. However it has been proposed that polyamines generally can, by being readily glycated themselves [91], behave protectively and thereby prevent glycation of polypeptides and nucleic acids.

Conclusions

ASD causation is undoubtedly complex [92]; amongst the factors so far recognised are changes in the microbiome, enhanced glycolytic activity, mitochondrial dysfunction and alteration in redox activity, all of which, presumably together with unrecognised metabolic and exogenous agents, contribute to varying degrees to the changes in behaviour and social interaction which characterise autism. Amongst these factors are agents such as AGEs which affect energy metabolism directly or indirectly, especially glycolysis, oxidative phosphorylation and their potentially dysfunctional, glycated, by-products.

The proposal that ASD is associated with mTOR activation leading to enhanced glycolytic activity as exemplified by the establishment of the Warburg effect (as proposed by Vallée & Vallée, [1] is supported by the findings that not only is a ketogenic diet beneficial towards ASD [93], but that glycated proteins (i.e. AGEs) can indeed activate mTOR to provoke onset of the Warburg effect [6]. Thus carnosine and possibly agmatine, both being pluripotent and essentially non-toxic endogenous molecules which can decrease glycolysis, possibly via effects on mTOR [75,87], plus their reactivity towards reactive carbonyls such as MG, may inhibit protein glycation and thereby ameliorate some of the consequences of increased glycolytic activity and exert beneficial effects on aspects of behaviour in ASD children. Although the specific mechanisms by which some of these effects are mediated may differ; for example control of protein nitration may occur via carnosine’s direct reaction with the nitrating agent whereas agmatine may inhibit nitric oxide synthesis, such complementary mechanisms could conceivably be therapeutically efficacious. That changes in both carnosine and agmatine may be connected to ASD is also supported by the findings that their serum levels are substantially lower in ASD subjects and that they both can also ameliorate the effects of propionic acid, which is known to sometimes accumulate in ASD. It is also suggested that the ability of carnosine and agmatine to ameliorate the effects of MG, either directly or following upregulation of antioxidant defences may also contribute to their efficacy towards ASD. It is interesting to note that two of propionic acid’s likely metabolites, 3-nitropropionate [94] and propionaldehyde [95], have also been associated with ASD; both carnosine and agmatine, could theoretically antagonise either their formation and/or toxicity via inhibiting propionate nitration or promoting aldehyde scavenging.

Whether combined treatment with both carnosine and agmatine is therapeutic towards ASD has not been explored. However, it has been noted that co-administration of carnosine and arginine (agmatine precursor) was more effective in combating hypoxic stress in rats than when either agent was supplied singly [96], an observation at least consistent with the above suggestion. More generally, as both carnosine and agmatine [97] when administered separately seem to exert beneficial effects towards aspects of both Parkinson’s disease [70, 98, 99] and Alzheimer’s disease [100–102] in cellular and animal models, then perhaps their co-administration should be also explored towards these age-related neurodegenerative conditions.

References

1. Vallée A, Vallée JN (2018) Warburg effect hypothesis in autism Spectrum disorders. Mol Brain 11: 1. [crossref]
2. Anwar A, Abruzzo PM, Pasha S, Rajpoot K, Bolotta A, et al (2018) Advanced glycation endproducts, dityrosine and arginine transporter dysfunction in autism – a source of biomarkers for clinical diagnosis. Mol. Autism 9: 3.
3. Zaki MM, Abdel-Al H, Al-Sawi M (2017). Assessment of plasma amino acid profile in autism using cation-exchange chromatography with postcolumn derivatization by ninhydrin. Turk J Med Sci 47: 260–267.
4. Mavel S, Nadal-Desbarats L, Blasco H, Bonnet-Brilhault F, Barthélémy C (2013) 1H-13C NMR-based urine metabolic profiling in autism spectrum disorders. Talanta 114: 95–102.
5. Esnafoglu E, Irende I (2018) Decreased plasma agmatine levels in autistic subjects. J Neural Transm .
6. Zhao X, Chen Y, Tan X, Zhang L, Zhang H, et al (2018) Advanced glycation end-products suppress autophagic flux in podocytes by activating mammalian target of rapamycin and inhibiting nuclear translocation of transcription factor EB. J Pathol. Mar 23.
7. Varga NÁ, Pentelényi K, Balicza P, Gézsi A, Reményi V, et al (2018) Mitochondrial dysfunction and autism: comprehensive genetic analyses of children with autism and mtDNA deletion. Behav Brain Funct 14: 4.
8. Hollis F, Kanellopoulos AK, Bagni C (2017) Mitochondrial dysfunction in Autism Spectrum Disorder: clinical features and perspectives. Curr Opin Neurobiol 45: 178–187.
9. Pei L, Wallace DC (2017) Mitochondrial Etiology of Neuropsychiatric Disorders. Biol Psychiatry : S0006–3223(17)32209–32216.
10. Napoli E, Wong S, Hertz-Picciotto I, Giulivi C (2014) Deficits in bioenergetics and impaired immune response in granulocytes from children with autism. Pediatrics 133: 1405–1410. [crossref]
11. de la Bâtie CD, Barbier V, Roda C, Brassier A, Arnoux JB, et al. (2017) Autism spectrum disorders in propionic acidemia patients. J Inherit Metab Dis . [crossref]
12. Frye RE, Nankova B, Bhattacharyya S, Rose S, Bennuri SC, et al (2017). Modulation of Immunological Pathways in Autistic and Neurotypical Lymphoblastoid Cell Lines by the Enteric Microbiome Metabolite Propionic Acid. Front Immunol 8: 1670
13. Choi J, Lee S (2018) Pathophysiological and neurobehavioral characteristics of a propionic acid-mediated autism-like rat model. PLoS One 13: 192925. [crossref]
14. Macfabe D (2013) Autism: metabolism, mitochondria, and the microbiome. Glob. Adv. Health Med 2; 52–66.
15. Morland C, Frřland AS, Pettersen MN, Storm-Mathisen J, Gundersen V, et al (2018) Propionate enters GABAergic neurons, inhibits GABA transaminase, causes GABA accumulation and lethargy in a model of propionic acidemia. Biochem J 475: 749–758.
16. Patowary A, Nesbitt R, Archer M, Bernier R, Brkanac Z (2017) Next Generation Sequencing Mitochondrial DNA Analysis in Autism Spectrum Disorder. Autism Res 10: 1338–1343.
17. Xie Z, Jones A, Deeney JT, Hur SK, Bankaitis VA (2016) Inborn Errors of Long-Chain Fatty Acid β-Oxidation Link Neural Stem Cell Self-Renewal to Autism. Cell Rep 14: 991–999. [crossref]
18. Powers SK (2014) Can antioxidants protect against disuse muscle atrophy? Sports Med 44: 155–165. [crossref]
19. Rose S, Bennuri SC, Wynne R, Melnyk S, James SJ, Frye RE. (2017) Mitochondrial and redox abnormalities in autism lymphoblastoid cells: a sibling control study. FASEB J 31: 904–909.
20. Rabbani N, Xue M, Thornalley PJ (2016) Methylglyoxal-induced dicarbonyl stress in aging and disease: first steps towards glyoxalase 1-based treatments. Clin Sci (Lond) 130: 1677–1696.
21. Allaman I, Bélanger M, Magistretti PJ2 (2015) Methylglyoxal, the dark side of glycolysis. Front Neurosci 9: 23. [crossref]
22. Gabriele S, Lombardi F, Sacco R, Napolioni V, Altieri L, Tirindelli MC, Gregorj C, Bravaccio C, Rousseau F, Persico AM (2014) The GLO1 C332 (Ala111) allele confers autism vulnerability: family-based genetic association and functional correlates. J Psychiatr Res 59: 108–116.
23. Junaid MA, Kowal D, Barua M, Pullarkat PS, Sklower Brooks S, et al. (2004) Proteomic studies identified a single nucleotide polymorphism in glyoxalase I as autism susceptibility factor. Am J Med Genet A 131: 11–17. [crossref]
24. Barua M, Jenkins EC, Chen W, Kuizon S, Pullarkat RK, Junaid MA (2011) Glyoxalase I polymorphism rs2736654 causing the Ala111Glu substitution modulates enzyme activity–implications for autism. Autism Res 4: 262–270.
25. Maher P (2012). Methylglyoxal, advanced glycation end products and autism: is there a connection? Med Hypotheses 78: 548–552.
26. KovaÄŤ J, Podkrajšek KT, LukšiÄŤ MM, Battelino T (2015) Weak association of glyoxalase 1 (GLO1) variants with autism spectrum disorder. Eur Child Adolesc Psychiatry 24: 75–82. [crossref]
27. Wu YY1, Chien WH, Huang YS, Gau SS, Chen CH (2008) Lack of evidence to support the glyoxalase 1 gene (GLO1) as a risk gene of autism in Han Chinese patients from Taiwan. Prog Neuropsychopharmacol Biol Psychiatry 32: 1740–1744. [crossref]
28. Fujimoto M, Uchida S, Watanuki T, Wakabayashi Y, Otsuki K, et al. (2008) Reduced expression of glyoxalase-1 mRNA in mood disorder patients. Neurosci Lett 438: 196–199. [crossref]
29. Paval D, Rad F, Rusu R, Niculae AS, Colosi HA, et al (2017) Low Retinal Dehydrogenase 1 (RALDH1) Level in Prepubertal Boys with Autism Spectrum Disorder: A Possible Link to Dopamine Dysfunction? Clin Psychopharmacol Neurosci 15: 229–236.
30. Jurnak F (2016) The Pivotal Role of Aldehyde Toxicity in Autism Spectrum Disorder: The Therapeutic Potential of Micronutrient Supplementation. Nutr Metab Insights 14: 57–77.
31. Matsuda N, Kimura M, Queliconi BB, Kojima W, Mishima M, et al (2017) Parkinson’s disease-related DJ-1 functions in thiol quality control against aldehyde attack in vitro. Sci Rep 7: 12816.
32. Liachenko S, Ramu J, Paule MG, Hanig J (2018) Comparison of quantitative T2 and ADC mapping in the assessment of 3-nitropropionic acid-induced neurotoxicity in rats. Neurotoxicology 65: 52–59. [crossref]
33. Winden KD, Ebrahimi-Fakhari D, Sahin M (2018) Abnormal mTOR Activation in Autism. Annu Rev Neurosci . [crossref]
34. Zhang J, Liu LM, Ni JF (2017) Rapamycin modulated brain-derived neurotrophic factor and B-cell lymphoma 2 to mitigate autism spectrum disorder in rats. Neuropsychiatr Dis Treat 13: 835–842
35. Onore C, Yang H, Van de Water J, Ashwood P (2017) Dynamic Akt/mTOR Signaling in Children with Autism Spectrum Disorder. Front Pediatr 5: 43. [crossref]
36. Nicolini C, Ahn Y, Michalski B, Rho JM, Fahnestock M (2015). Decreased mTOR signaling pathway in human idiopathic autism and in rats exposed to valproic acid. Acta Neuropathol Commun 3: 3.
37. Nicolini C, Fahnestock M (2018) The valproic acid-induced rodent model of autism. Exp Neurol 299: 217–227. [crossref]
38.  Aucamp J, Van Dyk HC, Bronkhorst AJ, Pretorius PJ (2017) Valproic acid alters the content and function of the cell-free DNA released by hepatocellular carcinoma (HepG2) cells in vitro. Biochimie 140: 93–105. [crossref]
39. Shen Y, Xu Z, Sheng Z. (2017). Ability of resveratrol to inhibit advanced glycation end product formation and carbohydrate-hydrolyzing enzyme activity, and to conjugate methylglyoxal. Food Chem 216: 153–160.
40. Bambini-Junior V, Zanatta G, Della Flora Nunes G, Mueller de Melo G, Michels M, et al (2014) Resveratrol prevents social deficits in animal model of autism induced by valproic acid. Neurosci Lett 583: 176–81.
41. El-Rashidy O, El-Baz F, El-Gendy Y, Khalaf R, Reda D, et al (2017) Ketogenic diet versus gluten free casein free diet in autistic children: a case-control study. Metab Brain Dis 32: 1935–1941. [crossref]
42. Berridge MJ (2018) Vitamin D deficiency: infertility and neurodevelopmental diseases (attention deficit hyperactivity disorder, autism, and schizophrenia). Am J Physiol Cell Physiol 314: 135–151.
43. El-Ansary A, Cannell JJ, Bjřrklund G, Bhat RS, Al Dbass AM (2018) In the search for reliable biomarkers for the early diagnosis of autism spectrum disorder: the role of vitamin D. Metab Brain Dis
44. Guo M1, Zhu J1, Yang T1, Lai X1, Lei Y1, et al. (2018) Vitamin A and vitamin D deficiencies exacerbate symptoms in children with autism spectrum disorders. Nutr Neurosci  [crossref]
45. Saad K. Abdel-Rahman AA, Elserogy YM, Al-Atram AA, El-Houfey AA, Othman HA, et al (2018) Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder. J Child Psychol Psychiatry 59: 20–29.
46. Rüster C, Franke S, Reuter S, Mrowka R, Bondeva T, Wolf G (2016) Vitamin D3 Partly Antagonizes Advanced-Glycation Endproducts-Induced NF?B Activation in Mouse Podocytes. Nephron 134: 105–116.
47. Merhi Z, Buyuk E, Cipolla MJ (2018) Advanced glycation end products alter steroidogenic gene expression by granulosa cells: an effect partially reversible by vitamin D. Mol Hum Reprod Mar 12.
48. Molinuevo MS, Fernández JM, Cortizo AM, McCarthy AD, Schurman L, et al (2017) Advanced glycation end products and strontium ranelate promote osteogenic differentiation of vascular smooth muscle cells in vitro: Preventive role of vitamin D. Mol Cell Endocrinol. 450: 94–104.
49. Chez MG, Buchanan CP, Aimonovitch MC, Becker M, Schaefer K, et al (2002) Double-blind, placebo-controlled study of L-carnosine supplementation in children with autistic spectrum disorders. J Child Neurol 17: 833–837.
50. Hajizadeh-Zaker R, Ghajar A, Mesgarpour B, Afarideh M, Mohammadi MR, (2018) L-Carnosine as an Adjunctive Therapy to Risperidone in Children with Autistic Disorder: A Randomized, Double-Blind, Placebo-Controlled Trial. J Child Adolesc Psychopharmacol 28: 74–81.
51. Ming X, Stein TP, Barnes V, Rhodes N, Guo L (2012) Metabolic perturbance in autism spectrum disorders: a metabolomics study. J Proteome Res 11: 5856–5862.
52. Bala KA, Doğan M, Mutluer T, Kaba S, Aslan O, et al (2016) Plasma amino acid profile in autism spectrum disorder (ASD). Eur Rev Med Pharmacol Sci 20: 923–929.
53. Boldyrev AA (2000) Problems and perspectives in studying the biological role of carnosine. Biochemistry (Mosc) 65: 751–756.
54. Bauer K (2005) Carnosine and homocarnosine, the forgotten, enigmatic peptides of the brain. Neurochem Res 30: 1339–1345. [Crossref]
55. Boldyrev AA, Aldini G, Derave W (2013) Physiology and pathophysiology of carnosine. Physiol Rev 93: 1803–1845.
56. Hipkiss AR, Baye E, de Courten B (2016) Carnosine and the processes of ageing. Maturitas 93: 28–33.
57. Cararo JH, Streck EL, Schuck PF, Ferreira Gda C (2015) Carnosine and Related Peptides: Therapeutic Potential in Age-Related Disorders. Aging Dis 6: 369–379
58. Chengappa KN, Turkin SR, DeSanti S, Bowie CR, Brar JS (2012). A preliminary, randomized, double-blind, placebo-controlled trial of L-carnosine to improve cognition in schizophrenia. Schizophr Res 142: 145–52.
59. Szcześniak D, Budzeń S, Kopeć W, Rymaszewska J (2014) Anserine and carnosine supplementation in the elderly: Effects on cognitive functioning and physical capacity. Arch Gerontol Geriatr 59: 485–90.
60. Baraniuk JN, El-Amin S, Corey R, Rayhan R, Timbol C (2013) Carnosine treatment for gulf war illness: a randomized controlled trial. Glob J Health Sci 5: 69–81.
61. Cartwright SP, Bill RM, Hipkiss AR (2012) L-carnosine affects the growth of Saccharomyces cerevisiae in a metabolism-dependent manner. PLoS One 7: 45006.
62. Holliday R, McFarland GA (1996) Inhibition of the growth of transformed and neoplastic cells by the dipeptide carnosine. Br. J. Cancer. 73: 966–971
63. Renner C, Asperger A, Seyffarth A, Meixensberger J, Gebhardt R, Gaunitz F (2010) Carnosine inhibits ATP production in cells from malignant glioma. Neurol Res. 32: 101–105.
64. Renner C, Zemitzsch N, Fuchs B, Geiger KD, Hermes M (2010) Carnosine retards tumor growth in vivo in an NIH3T3-HER2/neu mouse model. Mol Cancer 9: 2.
65. Hipkiss AR, Chana H (1998) Carnosine protects proteins against methylglyoxal-mediated modifications. Biochem Biophys Res Commun 248: 28–32.
66. Vistoli G, Colzani M, Mazzolari A, Gilardoni E, Rivaletto C, et al (2017) Quenching activity of carnosine derivatives towards reactive carbonyl species: Focus on α-(methylglyoxal) and β-(malondialdehyde) dicarbonyls. Biochem Biophys Res Commun 492: 487–492.
67. Aydın AF, Küçükgergin C, Çoban J, Doğan-Ekici I, Doğru-Abbasoğlu S, Uysal M, Koçak-Toker N. (2018). Carnosine prevents testicular oxidative stress and advanced glycation end product formation in D-galactose-induced aged rats. Andrologia. 50(3).
68. Bingül İ, Yılmaz Z, Aydın AF, Çoban J, Doğru-Abbasoğlu S, et al (2017) Antiglycation and anti-oxidant efficiency of carnosine in the plasma and liver of aged rats. Geriatr Gerontol Int 17: 2610–2614.
69. Houjeghani S, Kheirouri S, Faraji E, Jafarabadi MA (2018) L-Carnosine supplementation attenuated fasting glucose, triglycerides, advanced glycation end products, and tumor necrosis factor-α levels in patients with type 2 diabetes: a double-blind placebo-controlled randomized clinical trial. Nutr Res 49: 96–106.
70. Zhao J, Shi L, Zhang LR (2017) Neuroprotective effect of carnosine against salsolinol-induced Parkinson’s disease. Exp Ther Med 14: 664–670.
71. Baek SH, Noh AR, Kim KA, Akram M, Shin YJ, (2014) Modulation of mitochondrial function and autophagy mediates carnosine neuroprotection against ischemic brain damage. Stroke 45: 2438–2443.
72. Ooi TC, Chan KM, Sharif R (2017) Zinc L-carnosine suppresses inflammatory responses in lipopolysaccharide-induced RAW 264.7 murine macrophages cell line via activation of Nrf2/HO-1 signalling pathway. Immunopharmacol Immunotoxicol 39: 259–267.
73. Ahshin-Majid S, Zamani S, Kiamari T, Kiasalari Z, Baluchnejadmojarad T, Roghani M (2016) Carnosine ameliorates cognitive deficits in streptozotocin-induced diabetic rats: Possible involved mechanisms. Peptides 86: 102–111.
74. Stamova BS, Tian Y, Nordahl CW, Shen MD, Rogers S, et al (2013) Evidence for differential alternative splicing in blood of young boys with autism spectrum disorders. Mol Autism. 4: 30.
75. Zhang Z, Miao L, Wu X, Liu G, Peng Y (2014) Carnosine Inhibits the Proliferation of Human Gastric Carcinoma Cells by Retarding Akt/mTOR/p70S6K Signaling. J Cancer 5: 382–389.
76. Hipkiss AR, Michaelis J, Syrris P, Dreimanis M (1995) Strategies for the extension of human lifespan. Perspect. in Human Biol 1: 59–70.
77. Hipkiss AR, Preston JE, Himsworth DT, Worthington VC, Keown M, Michaelis J, et al (1998) Pluripotent protective effects of carnosine, a naturally occurring dipeptide. Ann N Y Acad Sci 854: 37–53
78. El-Ansary A, Shaker GH, El-Gezeery AR, Al-Ayadhi L (2013) The neurotoxic effect of clindamycin – induced gut bacterial imbalance and orally administered propionic acid on DNA damage assessed by the comet assay: protective potency of carnosine and carnitine. Gut Pathog 5: 9.
79. Szwergold BS (2005) Intrinsic toxicity of glucose, due to non-enzymatic glycation, is controlled in-vivo by deglycation systems including: FN3K-mediated deglycation of fructosamines and transglycation of aldosamines. Med Hypotheses 65: 337–348.
80. Fontana M, Pinnen F, Lucente G, Pecci L (2002) Prevention of peroxynitrite-dependent damage by carnosine and related sulphonamido pseudodipeptides. Cell Mol Life Sci 59: 546–551.
81. Lakshmi Priya MD, Geetha A (2011) A biochemical study on the level of proteins and their percentage of nitration in the hair and nail of autistic children. Clin Chim Acta 412: 1036–1042.
82. Qin L, Ma K, Wang ZJ, Hu Z, Matas E (2018) Social deficits in Shank3-deficient mouse models of autism are rescued by histone deacetylase (HDAC) inhibition. Nat Neurosci. Mar 12.
83. Kim JW, Seung H, Kim KC, Gonzales ELT, Oh HA, et al (2017) Agmatine rescues autistic behaviors in the valproic acid-induced animal model of autism. Neuropharmacology. 113: 71–81.
84. Kim JM, Lee JE, Cheon SY, Lee JH, Kim SY (2017) The Anti-inflammatory Effects of Agmatine on Transient Focal Cerebral Ischemia in Diabetic Rats. J Neurosurg Anesthesiol 28
85. Turan I, Ozacmak HS, Ozacmak VH, Barut F, Araslı M (2017) Agmatine attenuates intestinal ischemia and reperfusion injury by reducing oxidative stress and inflammatory reaction in rats. Life Sci. 189: 23–28.
86. Laing S, Unger M, Koch-Nolte F, Haag F (2011) ADP-ribosylation of arginine. Amino Acids 41: 257–269.
87. Neis VB, Moretti M, Bettio LE, Ribeiro CM, Rosa PB (2016) Agmatine produces antidepressant-like effects by activating AMPA receptors and mTOR signaling. Eur Neuropsychopharmacol 26: 959–971.
88. Nissim I, Horyn O, Daikhin Y, Chen P, Li C (2014) The molecular and metabolic influence of long term agmatine consumption. J Biol Chem 289: 9710–9729.
89. Gilad GM, Gilad VH (2013) Evidence for oral agmatine sulfate safety–a 95-day high dosage pilot study with rats. Food Chem Toxicol 62: 758–762.
90. Schulz M, Hamprecht B, Kleinkauf H, Bauer K (1989) Regulation by dibutyryl cyclic AMP of carnosine synthesis in astroglia-rich primary cultures kept in serum-free medium. J. Neurochem. 52: 229–234.
91. Gugliucci A, Menini T (2003) The polyamines spermine and spermidine protect proteins from structural and functional damage by AGE precursors: a new role for old molecules? Life Sci 72: 2603–2616.
92. Ji X, Kember RL, Brown CD, Bucan M. (2016). Increased burden of deleterious variants in essential genes in autism spectrum disorder. PNAS 113: 15054–15059.
93. Newell C, Bomhof MR, Reimer RA, Hittel DS, Rho JM, Shearer J (2016) Ketogenic diet modifies the gut microbiota in a murine model of autism spectrum disorder. Mol Autism. 7: 37.
94. Alarcón-Herrera N, Flores-Maya S, Bellido B, García-Bores AM, Mendoza E, et al (2017) Protective effects of chlorogenic acid in 3-nitropropionic acid induced toxicity and genotoxicity. Food Chem Toxicol 109: 1018–1025
95. Kalkbrenner AE, Windham GC, Zheng C, McConnell R, Lee NL, Schauer JJ, Thayer B, Pandey J, Volk HE (2018) Air Toxics in Relation to Autism Diagnosis, Phenotype, and Severity in a U.S. Family-Based Study. Environ Health Perspect 126: 037004.
96. Fadda LM, Attia HA, Al-Rasheed NM, Ali HM, Aldossari M. (2017). Attenuation of DNA damage and mRNA gene expression in hypoxic rats using natural antioxidants. J Biochem Mol Toxicol 31
97. Laube G, Bernstein HG (2017) Agmatine: multifunctional arginine metabolite and magic bullet in clinical neuroscience? Biochem J 474: 2619–2640.
98. Hipkiss AR (2018) Glycotoxins: Dietary and Metabolic Origins; Possible Amelioration of Neurotoxicity by Carnosine, with Special Reference to Parkinson’s Disease. Neurotox Res Feb 7.
99. Tsai SJ, Kuo WW, Liu WH, Yin MC (2010) Antioxidative and anti-inflammatory protection from carnosine in the striatum of MPTP-treated mice. J Agric Food Chem 58: 11510–11516.
100. Kawahara M, Tanaka KI, Kato-Negishi M (2018) Zinc, Carnosine, and Neurodegenerative Diseases. Nutrients 10: 147.
101. Herculano B, Tamura M, Ohba A, Shimatani M, Kutsuna N, Hisatsune T (2013) β-alanyl-L-histidine rescues cognitive deficits caused by feeding a high fat diet in a transgenic mouse model of Alzheimer’s disease. J Alzheimers Dis 33: 983–997.
102. Hipkiss AR (2007) Could carnosine or related structures suppress Alzheimer’s disease? J Alzheimers Dis 11: 229–40.