Double-Blind, Placebo-Controlled Study of l-Carnosine Supplementation in Children With Autistic Spectrum Disorders

Michael G. Chez, MD; Cathleen P. Buchanan, PhD; Mary C. Aimonovitch;
Marina Becker, RN; Karla Schaefer, RN; Carter Black, RPh; Jamie Komen, MA

ABSTRACT

l-Carnosine, a dipeptide, can enhance frontal lobe function or be neuroprotective.  It can also correlate with g-aminobutyric acid (GABA)-homocarnosine interaction, with possible anticonvulsive effects.  We investigated 31 children with autistic spectrum disorders in an 8-week, double-blinded study to determine if 800 mg l-carnosine daily would result in observable changes versus placebo.  Outcome measures were the Childhood Autism Rating Scale, the Gilliam Autism Rating Scale, the Expressive and Receptive One-Word Picture Vocabulary tests, and Clinical Global Impressions of Change.  Children on placebo did not show statistically significant changes.  After 8 weeks on l-carnosine, children showed statistically significant improvements on the Gilliam Autism Rating Scale (total score and the Behavior, Socialization, and Communication subscales) and the Receptive One-Word Picture Vocabulary test (all P<.05).  Improved trends were noted on other outcome measures.  Although the mechanism of action of l-carnosine is not well understood, it may enhance neurologic function, perhaps in the enterorhinal or temporal cortex. (J Child Neurol 2002;17:833-837).  

Autistic spectrum disorders (autistic disorder, pervasive developmental delay not otherwise specified, and Asperger’s syndrome) are long-term, developmental disorders with no known or agreed on nervous system pathology or definitive genetic site.^1,2  Unfortunately, very few double-blind studies have been performed involving autistic spectrum-disorders, owing to the different degrees of presentation and the multiple phenotypes of the disease.  The varying symptoms observed with the autistic spectrum disorder syndrome indicate more than a single region of injury that results in   an assortment of behaviors.¹  With no available cure, treatment is contained to modifying the course of the disease. 

Research in the past several years has shown an association between sleep electroencephalograms (EEGs) and autism.^3-7  One third of autistic children suffer one or more seizures by adolescence, perhaps linking epileptiform activity with some instances of autistic spectrum disorders.⁵  Magnetoencephalographic data have suggested that the percentage may even be higher; in a recent autistic study, 14% more children were identified as having epileptiform activity by magnetoencephalography (82%) who were not identified by concurrent EEG (68%).⁵

Valproic acid, an anticonvulsant effective in treating seizure disorders, is hypothesized to increase g-aminobutyric acid (GABA) concentrations within the central nervous system.^{8, 9}  GABA is the major inhibitory neurotransmitter in the cerebral cortex.^10,11  Positive results have been observed in administration of valproic acid to autistic patients, especially in patients with EEG abnormalities.^12-16  Anticonvulsants have also been successful in psychiatric disease use, particularly bipolar disorder. 

Recent work by Petroff and his colleagues at Yale University has demonstrated that GABA activity can be measured using magnetic resonance imaging spectroscopy with a higher field strength.¹⁷  Although Petroff and colleagues studied cases of generalized myoclonic epilepsies, his finding is significant because of the correlation established between levels of GABA and homocarnosine levels.  Even in cases of low GABA function, homocarnosine levels can correlate with better seizure control.  Other investigators have reported elevated homocarnosine  levels in infants with epilepsy or brain injury.¹⁸  Cases of temporal lobe or generalized seizures have also shown seizure control to correlate with homocarnosine levels.¹⁷

Homocarnosine is formed when GABA and carnosine bind.  Carnosine appears to modulate copper and zinc influx into cells and near GABA receptors, thereby affecting potential epileptic inhibition.  Further, modulation of zinc and copper can have complementary antiepileptiform effects in the hippocampus and frontal lobe,¹⁹ as well as being neuroprotective against ischemia.^{20, 21}  Carnosine can offer anticonvulsant protection in vitro and in rats in prior studies, perhaps by altering homocarnosine levels or by a direct chelating effect on zinc at GABA receptor sites.²²  Because carnosine has been described as accumulating in the enterorhinal subfrontal cortex, we hypothesize that it might act in a protective or activating role for the frontal lobe.  Dysfunction of the frontal lobe is hypothesized to be linked to expression and behavior; both areas characteristically impaired in autistic spectrum disorders.^23-25

We therefore designed a study to target some of the purported brain regions of dysfunction in autistic spectrum disorders via supplementation with a naturally occurring amino acid that is believed to act on frontal lobe systems or GABA receptors.  We sought to eliminate the “expectancy effect” of medication augmentation by enrolling children in study so that both the clinicians and the parents were blind to group assignment. 

METHODS

Children were included for study if they met the following criteria: age 3-12 years and prior diagnoses of autistic spectrum disorder (including either pervasive developmental disorder or autistic disorder; by the Diagnostic and Statistical Manual of Mental Disorders –IV-Revised).²⁶  Thirteen subjects had a current abnormal EEG, and 13 were being maintained on valproic acid.  Children were excluded if they had a family history of seizure disorder, fragile X syndrome, or other genetic disorder or etiology of their spectrum disorder.  Children were enrolled in the study irrespective of cognitive ability level.  All children were tested at baseline in the following domains: expressive language (Expressive One-Word Picture Vocabulary test), receptive language (Receptive One-Word Picture Vocabulary test), autism severity ratings (Childhood Autism Rating Scale and Gilliam Autism Rating Scale), and Clinical Global Impressions of Change, which were completed by the parents. At baseline and 8-week testing, all children underwent the Childhood Autism Rating Scale, the Gilliam Autism Rating Scale, the Expressive One-Word Picture Vocabulary test, the Receptive One-Word Picture Vocabulary test, and the Clinical Global Impression of Change.  Children were tested with their parents in a pediatric neurology clinic in a room dedicated to assessment.  The parents signed informed written consent (approved by the Lake Forest Hospital Institutional Review Board) before being randomly assigned to either active-agent or placebo, and reporting of adverse events was explained per office emergency policy.  Parents, clinicians, and neurologists were all blinded to placebo versus active carnosine.  At the completion of the study, the blind code was broken by identifying the patient’s bottle number with the placebo or carnosine administration.

Because of our prior experience with the substance in an open label format, we were able to caution regarding the following potential adverse events: hyperactivity and excitability.  Both placebo and active substances were identical  in powdered appearance, without taste or smell.  All pills were contained by a gelatin capsule; parents were instructed to mix the powder with either food or drink.  Dosage of carnosine was 400 mg by mouth twice daily. 

Every 2 weeks, parents faxed a Clinical Global Impression of Change regarding their child.  The Clinical Global Impression was a 5-point rating scale covering the following domains: (1)socialization, interaction with others during play; (2)spontaneous, expressive language or vocal- izations; (3)attention span, “focus”/eye contact, alertness level; (4)agitation and hyperactivity or lethargy, energy level; (5)coordination, body use, gross motor movements; and (6)anxiety, rigidity, perseveration, adaptation to change.  A score of 0 indicated “no change,” and a score of 5 indicated a “great improvement”  Parents were not allowed to refer back to faxes from the prior 2-week period, so that each rating was essentially “blinded” to the week before.  An overall baseline Clinical Global Impression was then compared with an ending Clinical Global Impression.    

Statistical analyses included descriptive statistics and comparisons of baseline and ending means.  Pairwise t-tests were conducted with Turkey ’s correction for multiple comparisons.

RESULTS

Thirty-one children (21 males, 10 females, mean age=7.45; range 3.2-12.5) meeting inclusion criteria were enrolled in an 8-week, double-blind, placebo-controlled study.  Children were entered randomly into one of two groups: group 1(n=17) received a placebo for the first 8 weeks, whereas group 2(n=14) received the active substance.  Children were assessed at baseline in the domains show in Table 1.

There were no statistically significant differences in any of the baseline measures with the exception of the Communication subscale of the Gilliam Autism Rating Scale.  Although the group on the active substance started out with a higher level on the Communication scale, there were no statistically significant differences when tested on the objective language measures, the Receptive One-Word Picture Vocabulary test and the Expressive One-Word Picture Vocabulary test.  Being medicated with valproic acid or having a current abnormal EEG did not make a difference in terms of group differences.  

Table 1.     Baseline Measures for Children in Blinded Carnosine Study

                                                                                                            Baseline                         8 Weeks            
       Measure                                                                                         Mean (SD)                    Mean (SD)          Significance

  NS = not significant

After 8 weeks, children returned for repeat testing.  The scores for the follow-up test appear in Table 2.  As may be seen form Table 2, any changes that occurred within the placebo group did not result in any statistically significant changes after 8 wee ks.

 Table 2.  Changes in Children after 8 Weeks on Placebo

                                                                                                            Baseline                         8 Weeks            
       Measure                                                                                         Mean (SD)                    Mean (SD)          Significance

It is important from examination of Table 3 that there were significant changes across several measures in multiple domains for those children who were given the carnosine for 8 weeks.  Significant improvements with carnosine compared with the placebo were seen in the 2-week versus 6-week faxed Clinical Global Impression ratings (P =.04), Receptive One-Word Picture Vocabulary test scores (P =.01), and Gilliam Autism Rating Scale scores (P =.01), including the Behavior (P =.04), Socialization (P =.01). and Communication (P =.03) subscales.  The baseline to 8-week Clinical Global Impression and Childhood Autism Rating scale testing measures also showed improving trends, although not statistically significant (P =.06, P =.07, respectively).  Pairwise t-tests performed on the placebo group showed that there were no significant changes on any of the measures after 8 weeks on the inert pills with a confidence level of P<.05.

Table 3.  Changes in Children after 8 Weeks on Active Carnosine

                                                                                                                Baseline                       8 Weeks            
       Measure                                                                                            Mean (SD)                 Mean (SD)          Significance

NS = not significant.

 DISCUSSION

 The results of this study suggest that supplementation with carnosine can significantly improve receptive speech, socialization, and behavior with autistic spectrum disorders.   These gains are observable both by parents and clinicians blinded to study group, as evidenced by the scores on the Clinical Global Impression.  Although not statistically significant, improved trends in extreme speech, baseline versus 8-week Clinical Global Impression ratings, and the Childhood Autism Rating Scale scores were noted, correlating with subjective reports of improvement by parents to the neurologists.   The extra data points of the Clinical Global Impression between weeks 2 and 6 do reach significance, further supporting overt clinical observation.  Moreover, improvements on objective standardized rating scores such as the Receptive One-Word Picture Vocabulary test, tests for which practice effects are not of concern to reliability, also validate these observations.  Several patients had individually noticeable expressive speech improvement on the Expressive One-Word Picture Vocabulary test, but, as a group, only a trend was obtained.  This was because of some individuals who, owing to the heterogeneous  nature of autistic spectrum disorders, had very low scores at baseline.

          Not a single child had to discontinue the study because of side effects.  Parents reported only sporadic hyperactivity, which was alleviated by decreasing the dose.  Previous studies involving carnosine have indicated a very low toxicity level; among 691 cases of adult clinical trials, no symptomatic side effects were reported.²⁷ 

The mechanism of action of carnosine is not well understood.  Carnosine is recognized for its antioxidant^{20, 28-30} and proton buffer^{20, 28, 31} properties, protection against oxidative stress, and resistance toward senescence.^{30, 32-35}  More significantly, it will complex with endogenous transitional metals of biological significance.^{19, 27, 36-38}  Zinc and copper have been found in pools in brain regions (hippocampus, locus ceruleus, hypothalamus, olfactory bulb, and cortex) at concentrations that allow them to exert neuromodulator effects.¹⁹  Although these transition metals are required for normal functioning in the nervous system, they have also been found to be neurotoxic.^{19, 37}  Shifts in zinc and copper may be involved in the neuropathology of Alzheimer’s disease, ischemic stroke, and seizures.³⁷  Further, zinc and copper have been shown to suppress GABA-mediated inhibitory synaptic transmission.  Petroff and colleagues’ work has shown a critical relationship between homocarnosine and GABA acid levels in epilepsy control.¹⁷  Carnosine can also prevent the influx of copper and zinc and enhance GABA function.³⁷

          A majority of our subset of children with autistic spectrum disorders were those who had a positive history of abnormal EEG or partial response to valproic acid therapy.  If, indeed, carnosine acts to affect GABA bioavailability, it may likely alter the subclinical seizure threshold or GABA function.  Carnosine is the first dietary supplement that may alter the neuronal function in children with autistic-spectrum disorders that can be attributed in a double-blind controlled fashion.  Further study is needed to investigate the mechanism of carnosine supplementation on brain biochemistry.  Our observations regarding the autistic spectrum population suggest improved receptive speech and improved social attention, less apraxia, and overall global improvements.   

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