I first met Peter a couple of years ago at an Autism Research Institute Think Tank. At the Think Tank Peter impressed everybody with his knowledge, specially about biochemical pathways. He was my lunch buddy for that couple of days and ever since we have kept in touch. I invited him to write a contribution to my blog and he obliged. You can read about his ideas regarding fever and the clinical manifestations of ASD in a previous blog: http://bit.ly/10NyJFk. For more information about Peter’s work you can visit his web site at bit.ly/1KsOORy
The “vaccine wars” focused great attention on mercury (thimerosal) and aluminum as toxins in childhood vaccines that might cause autism. Lead in air and water has also been implicated, and the body’s own oxidizing molecules like hydrogen peroxide. One obvious common denominator of these agents is they all deplete the body’s primary antitoxin/antioxidant glutathione, found in virtually all cells, and especially in the liver .
Jill James, Richard Frye, and colleagues at Arkansas Children’s Hospital Research Institute have studied the status of glutathione and related cysteine metabolites in autistic disorders (ASD) for more than a decade [2–4]. Many studies found reduced glutathione (GSH – the good kind) low in ASD children and adults compared to oxidized glutathione. Geier and Geier too implicated glutathione depletion in ASD, proposing it limits sulfation of the fetal adrenal androgen DHEA to its “normally favored storage molecule” DHEAS  – primary precursor of placental estrogens . Does lack of DHEAS explain the “extreme male brain” of autism ?
Equally intriguing in this context is fresh evidence that glutathione is necessary to mature myelin – the fatty insulation wrapped around nerves that gives “white matter” its name – and glutathione sustains release of nitric oxide, primary dilator of blood vessels in the brain. Does glutathione depletion thus explain two major enigmas of autism – (1) impaired connectivity between and within brain hemispheres, and (2) consistently low brain blood flow despite frequent hyperexcitability?
Martha Herbert and colleagues found the brains of autistic children were unusually large a few months after birth because white-matter tracts within hemispheres were larger than normal, and white-matter tracts between hemispheres (notably the corpus callosum) smaller than normal . Impaired brain ‘wiring’ in ASD has been implicated by many groups, notably Just and colleagues, who reported that adults with high-functioning autism paid more attention to the meaning of individual words than the meaning of sentences. They concluded: “We propose that autism is a cognitive and neurobiological disorder marked and caused by under-functioning integrative circuitry that results in a deficit of integration of information at the neural and cognitive levels. . . . The dissociation between intact or enhanced simple abilities and impaired higher order abilities is a recurring profile across cognitive and neurological domains in autism . . . .”
Nordahl and colleagues, scanning the corpus callosum by magnetic resonance imaging (MRI), noted: “In older children, adolescents and adults with ASD, the corpus callosum is consistently reported to be smaller, with decreased fractional anisotropy and reduced interhemispheric functional connectivity.” This is a critical clue, because anisotropy – parallel myelin layers restraining perpendicular water diffusion – increases as myelin matures! Beaulieu: “[S]tudies of cerebral white matter development in human neonates and infants in vivo have shown, in general, a decrease in the mean diffusivity and an increase in the degree of anisotropy with maturation.”
Monin and colleagues reported glutathione is necessary to mature myelin in children: “Taken all together, these data suggest the presence of a critical developmental period during which a proper redox regulation and GSH levels are required for myelination processes. Adverse events during early life are risk factors for the psychopathology and myelin development. This also suggests that there are several critical periods during which environmental risk factors could impact the normal development of myelin. Indeed, transient changes in GSH levels induced by environmental insults during pre-, peri- and post-natal periods may have an impact on oligodendrocyte maturation, consequently affecting later structural connectivity.”  Are white-matter tracts abnormal in ASD, and brain hemispheres dysconnected, because glutathione depletion prevents maturation of oligodendrocytes – and the myelin they make?
McKinley-Barnard and colleagues studied effects of oral citrulline and glutathione supplements in healthy athletes. Citrulline is the free (nonprotein) amino acid precursor of the protein amino acid arginine – only substrate for the primary vasodilator nitric oxide (NO). They concluded: “Due to its effects on nitric oxide synthase (NOS), reduced glutathione (GSH) may protect against the oxidative reduction of NO. . . . In some cell types, GSH appears to be necessary for NO synthesis and NO has been shown to be correlated with intracellular GSH. GSH stimulates total L-arginine turnover and, in the presence of GSH, NOS activity is increased. . . . Therefore, combining L-citrulline with GSH may augment the production of NO.”
The best evidence that brain nitric oxide is low in ASD children is probably their consistently low brain blood flow despite frequent hyperexcitability – as if neurovascular coupling has failed. When neurons fire they release molecules that dilate nearby blood vessels, notably neuronal nitric oxide. Reynell and Harris discussed explanations for failure of neurovascular coupling in autism, including depletion of neuronal nitric oxide . The problem is that nitric oxide appears high in these children, to judge from high levels of metabolites nitrite and nitrate in their blood . The source of this nitric oxide appears to be inducible nitric oxide synthase (iNOS)  induced in brain microglia, astrocytes, macrophages and other cells as part of the inflammatory/immune response. Two constitutive forms of nitric oxide synthase continuously present in blood vessel endothelial cells (eNOS) and neurons (nNOS) synthesize and release lesser amounts of nitric oxide.
Frye and colleagues recently tested nitric oxide metabolism in ASD children using sapropterin, a synthetic form of tetrahydrobiopterin (BH4), a cofactor for NOS . Confirming the successes of Naruse and colleagues with sapropterin, Frye et al. found sapropterin improved communicative language in these children, which they attributed to stabilization of nitric oxide metabolism. But sapropterin also stimulates release of neuronal and endothelial nitric oxide . Furthermore, induced nitric oxide commonly compensates depletion of constitutive nitric oxide , and nitrite serves as a reservoir “pool” to regenerate nitric oxide by reduction .
Why would nitric oxide be low in ASD brains? The simplest explanation is depletion of its only substrate arginine. Most arginine ingested as protein by ASD children may be needed by the liver to detoxify ammonia, a common problem from intestinal bacteria and yeast . Arginine vasopressin is high in ASD boys, further depleting arginine. Creatine (arginine + glycine) is low. Furthermore, arginine’s precursor citrulline arises from the amino acid glutamine – consistently low in plasma of ASD children, and often low in their brain . Children with high brain glutamine from urea cycle disorders rarely show autistic behavior .
Glutathione depletion also depletes glutamine, because glutamine enters cells more readily than glutamate, thus often provides glutamate to synthesize glutathione . Substantial evidence now implicates acetaminophen (Tylenol) depleting glutathione as a primary cause of the autism epidemic in this country [23–26]. The first-person account by Kerry Scott Lane (MD) of his inadvertent role in our national switch from aspirin to acetaminophen for children in 1980, and his 2009 efforts to convince the Food and Drug Administration (FDA) of acetaminophen’s toxicity, deserves wide audience: “Having studied the toxicology of acetaminophen and how it depletes glutathione, the body’s master antioxidant, it is clear as day to me, the trigger for regressive autism is Tylenol/acetaminophen/paracetamol.”
What can be done? Clearly the first goal must be restoring brain blood flow to these children. Citrulline supplements  appear most promising, because citrulline is not taken up by the liver like arginine, but bypasses the liver and forms arginine in the kidneys, increasing systemic arginine . Citrulline is also safer in large doses than arginine . Watermelon and its juice are rich in citrulline and arginine . The free amino acid taurine also increases brain blood flow, by stimulating endothelial nitric oxide synthase . The Autism Research Institute (ARI) recommended 250–500mg/day of taurine for ASD children, up to 2g/day for adults and adult-sized children .
Supplementing glutathione is not as simple, because glutathione can’t enter cells but must be synthesized within cells . A pharmacologist suggested N-acetylcysteine (NAC) or whey protein for glutathione precursors . My 2006 PDR warned against denatured whey protein: “When subject to heat or shearing forces (inherent in most extraction processes), the fragile disulfide bonds within the peptides are broken and the bio-availability of cysteine [rate-limiting amino acid in glutathione] is greatly diminished.”
ARI pediatrician John Green (MD) has used NAC extensively for ASD for 15 years – orally, iv, and topically: “It is a potent GSH support, being the rate limiting step in GSH synthesis, and is consumed molecule for molecule in detoxification. Hardan at Stanford did a study of pharmaNAC in ASD children, dosing from 900 to 2700 mg/day in stepwise fashion, and demonstrated significant neurologic improvements. It is also a competitive amino acid in glutamate transport, and could thus be calming. . . . Clinically, responses are very split, with an almost equal number of patients showing agitation vs. enhanced cognitive function in others. I start with 900 mg and move up as able. We tested five different preparations with a biochemist, and found the commercial preparations have very little actual NAC, being composed instead of congeners, cysteine, and degradation products. It is very fragile, oxidizes upon opening the bottle, so is of limited antioxidant value, though may still contribute to GSH synthesis. The pharmaNAC preparation is blister packed, so that the stability is much more secure.”
For more information about Peter and his research interest please visit his website at: http://autismstudies.net/Home.html
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