Autism advances - Pollutants

Advances in Autism Research
compiled by Teresa Binstock for
Autism Research Institute
April 2008

Metabolic pathways -- Clinical Significance

Methionine synthase - Glutathione - Homocysteine - etc

In recent years, several studies have presented data and an overview of a primary metabolic pathway relevant to many and perhaps most cases of autism (1-4). Jill James and her colleagues have published widely in peer-reviewed journals, as has Richard Deth and members of his team. Their findings in autism are among the most important to be published in recent years. The intra-cellular pathways to which these researchers are calling attention have treatment ramifications already being utilized by clinicians (eg, 5-7).

The "methionine cycle" merits our attention (reviewed in 44, free online). Most human genes are controlled by methylation, and errors of methylation can affect how genes function or malfunction. Atypical methylation has been found in autism (1). Many reviews of methylation are available (eg, 8-17). Some focus upon nutrients(eg, 12). Others specifically mention transsulferation and homocysteine (eg, 11) and ramifications for toxicology (eg, 13). All studies in these domains - and not just those presented herein - are relevant to autism in ways delineated by James et al, Deth et al (eg, 1-4) and others.

Individuals wanting to delve into this aspect of autism research are invited to view diagrams of biochemical pathways related to "methionine synthase". Useful but not first-glance-easy graphics and explanations are presented (1-4). Other summaries of methione synthase pathways can be found online, eg, via a google-image search for "methionine synthase".

As studies by the Jill James group and by the Richard Deth group are perused, some markers begin to have enhanced significance. The purpose here isn't to present an in-depth autism-biochemistry textbook, though the citations herein would be a good starting point. Instead, the purpose is to present citations that reflect biochemical advances in autism research.

A section on porphyrins and their clinical use is presented (34-43).

1: Metabolic biomarkers of increased oxidative stress and impaired methylation capacity in children with autism

James SJ et al.
Am J Clin Nutr. 2004 Dec;80(6):1611-7.
http://www.ajcn.org/cgi/reprint/80/6/1611

BACKGROUND: Autism is a complex neurodevelopmental disorder that usually presents in early childhood and that is thought to be influenced by genetic and environmental factors. Although abnormal metabolism of methionine and homocysteine has been associated with other neurologic diseases, these pathways have not been evaluated in persons with autism. OBJECTIVE: The purpose of this study was to evaluate plasma concentrations of metabolites in the methionine transmethylation and transsulfuration pathways in children diagnosed with autism. DESIGN: Plasma concentrations of methionine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), adenosine, homocysteine, cystathionine, cysteine, and oxidized and reduced glutathione were measured in 20 children with autism and in 33 control children. On the basis of the abnormal metabolic profile, a targeted nutritional intervention trial with folinic acid, betaine, and methylcobalamin was initiated in a subset of the autistic children. RESULTS: Relative to the control children, the children with autism had significantly lower baseline plasma concentrations of methionine, SAM, homocysteine, cystathionine, cysteine, and total glutathione and significantly higher concentrations of SAH, adenosine, and oxidized glutathione. This metabolic profile is consistent with impaired capacity for methylation (significantly lower ratio of SAM to SAH) and increased oxidative stress (significantly lower redox ratio of reduced glutathione to oxidized glutathione) in children with autism. The intervention trial was effective in normalizing the metabolic imbalance in the autistic children. CONCLUSIONS: An increased vulnerability to oxidative stress and a decreased capacity for methylation may contribute to the development and clinical manifestation of autism.
PMID: 15585776

2. How environmental and genetic factors combine to cause autism: A redox/methylation hypothesis

Deth R et al.
Neurotoxicology. 2008 Jan;29(1):190-201.
http://tinyurl.com/65f8jb

Recently higher rates of autism diagnosis suggest involvement of environmental factors in causing this developmental disorder, in concert with genetic risk factors. Autistic children exhibit evidence of oxidative stress and impaired methylation, which may reflect effects of toxic exposure on sulfur metabolism. We review the metabolic relationship between oxidative stress and methylation, with particular emphasis on adaptive responses that limit activity of cobalamin and folate-dependent methionine synthase. Methionine synthase activity is required for dopamine-stimulated phospholipid methylation, a unique membrane-delimited signaling process mediated by the D4 dopamine receptor that promotes neuronal synchronization and attention, and synchrony is impaired in autism. Genetic polymorphisms adversely affecting sulfur metabolism, methylation, detoxification, dopamine signaling and the formation of neuronal networks occur more frequently in autistic subjects. On the basis of these observations, a "redox/methylation hypothesis of autism" is described, in which oxidative stress, initiated by environment factors in genetically vulnerable individuals, leads to impaired methylation and neurological deficits secondary to reductions in the capacity for synchronizing neural networks.
PMID: 18031821

3: Metabolic endophenotype and related genotypes are associated with oxidative stress in children with autism

James SJ et al.
Am J Med Genet B Neuropsychiatr Genet. 2006 Dec 5;141(8):947-56.

Autism is a behaviorally defined neurodevelopmental disorder usually diagnosed in early childhood that is characterized by impairment in reciprocal communication and speech, repetitive behaviors, and social withdrawal. Although both genetic and environmental factors are thought to be involved, none have been reproducibly identified. The metabolic phenotype of an individual reflects the influence of endogenous and exogenous factors on genotype. As such, it provides a window through which the interactive impact of genes and environment may be viewed and relevant susceptibility factors identified. Although abnormal methionine metabolism has been associated with other neurologic disorders, these pathways and related polymorphisms have not been evaluated in autistic children. Plasma levels of metabolites in methionine transmethylation and transsulfuration pathways were measured in 80 autistic and 73 control children. In addition, common polymorphic variants known to modulate these metabolic pathways were evaluated in 360 autistic children and 205 controls. The metabolic results indicated that plasma methionine and the ratio of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), an indicator of methylation capacity, were significantly decreased in the autistic children relative to age-matched controls. In addition, plasma levels of cysteine, glutathione, and the ratio of reduced to oxidized glutathione, an indication of antioxidant capacity and redox homeostasis, were significantly decreased. Differences in allele frequency and/or significant gene-gene interactions were found for relevant genes encoding the reduced folate carrier (RFC 80G > A), transcobalamin II (TCN2 776G > C), catechol-O-methyltransferase (COMT 472G > A), methylenetetrahydrofolate reductase (MTHFR 677C > T and 1298A > C), and glutathione-S-transferase (GST M1). We propose that an increased vulnerability to oxidative stress (endogenous or environmental) may contribute to the development and clinical manifestations of autism. (c) 2006 Wiley-Liss, Inc.
PMID: 16917939

4. Activation of methionine synthase by insulin-like growth factor-1 and dopamine: a target for neurodevelopmental toxins and thimerosal

Waly M et al.
Mol Psychiatry. 2004 Apr;9(4):358-70.

Methylation events play a critical role in the ability of growth factors to promote normal development. Neurodevelopmental toxins, such as ethanol and heavy metals, interrupt growth factor signaling, raising the possibility that they might exert adverse effects on methylation. We found that insulin-like growth factor-1 (IGF-1)- and dopamine-stimulated methionine synthase (MS) activity and folate-dependent methylation of phospholipids in SH-SY5Y human neuroblastoma cells, via a PI3-kinase- and MAP-kinase-dependent mechanism. The stimulation of this pathway increased DNA methylation, while its inhibition increased methylation-sensitive gene expression. Ethanol potently interfered with IGF-1 activation of MS and blocked its effect on DNA methylation, whereas it did not inhibit the effects of dopamine. Metal ions potently affected IGF-1 and dopamine-stimulated MS activity, as well as folate-dependent phospholipid methylation: Cu(2+) promoted enzyme activity and methylation, while Cu(+), Pb(2+), Hg(2+) and Al(3+) were inhibitory. The ethylmercury-containing preservative thimerosal inhibited both IGF-1- and dopamine-stimulated methylation with an IC(50) of 1 nM and eliminated MS activity. Our findings outline a novel growth factor signaling pathway that regulates MS activity and thereby modulates methylation reactions, including DNA methylation. The potent inhibition of this pathway by ethanol, lead, mercury, aluminum and thimerosal suggests that it may be an important target of neurodevelopmental toxins.
PMID: 14745455

5. Methyl-B12: A Treatment for ASD with Methylation Issues
James Neubrander, M.D., and others
http://talkaboutcuringautism.org/medical/methyl-b12-treatments.htm

6. James Neubrander, M.D. and MethylCobalamin (mB12) links
http://www.drneubrander.com/page2old.html

7. Molecular Aspects of Thimerosal-induced Autism
Richard C. Deth, Ph.D.
http://www.drneubrander.com/Files/Deth%20Testimony.pdf

8. On the biological significance of DNA methylation
Doerfler W.
Biochemistry (Mosc). 2005 May;70(5):505-24.
http://protein.bio.msu.ru/biokhimiya/contents/v70/pdf/bcm_0505.pdf
PMID: 15948705

9. The prima donna of epigenetics: the regulation of gene expression by DNA methylation
Santos KF, Mazzola TN, Carvalho HF.
Braz J Med Biol Res. 2005 Oct;38(10):1531-41. Epub 2005 Sep 6.
http://tinyurl.com/5vkn2f
PMID: 16172746

10. DNA methylation and epigenotypes

Holliday R.
Biochemistry (Mosc). 2005 May;70(5):500-4.
http://protein.bio.msu.ru/biokhimiya/contents/v70/pdf/bcm_0500.pdf
PMID: 15948704

11. Methylation demand: a key determinant of homocysteine metabolism

Brosnan JT et al.
Acta Biochim Pol. 2004;51(2):405-13.
http://www.actabp.pl/pdf/2_2004/405.pdf

Elevated plasma homocysteine is a risk factor for cardiovascular disease and Alzheimer's disease. To understand the factors that determine the plasma homocysteine level it is necessary to appreciate the processes that produce homocysteine and those that remove it. Homocysteine is produced as a result of methylation reactions. Of the many methyltransferases, two are, normally, of the greatest quantitative importance. These are guanidinoacetate methyltransferase (that produces creatine) and phosphatidylethanolamine N-methyltransferase (that produces phosphatidylcholine). In addition, methylation of DOPA in patients with Parkinson's disease leads to increased homocysteine production. Homocysteine is removed either by its irreversible conversion to cysteine (transsulfuration) or by remethylation to methionine. There are two separate remethylation reactions, catalyzed by betaine:homocysteine methyltransferase and methionine synthase, respectively. The reactions that remove homocysteine are very sensitive to B vitamin status as both the transsulfuration enzymes contain pyridoxal phosphate, while methionine synthase contains cobalamin and receives its methyl group from the folic acid one-carbon pool. There are also important genetic influences on homocysteine metabolism.
PMID: 15218538

12. Gene-nutrient interactions and DNA methylation

Friso S, Choi SW.
J Nutr. 2002 Aug;132(8 Suppl):2382S-2387S.
http://jn.nutrition.org/cgi/content/full/132/8/2382S

Many micronutrients and vitamins are critical for DNA synthesis/repair and maintenance of DNA methylation patterns. Folate has been most extensively investigated in this regard because of its unique function as methyl donor for nucleotide synthesis and biological methylation. Cell culture and animal and human studies showed that deficiency of folate induces disruption of DNA as well as alterations in DNA methylation status. Animal models of methyl deficiency demonstrated an even stronger cause-and-effect relationship than did studies using a folate-deficient diet alone. Such observations imply that the adverse effects of inadequate folate status on DNA metabolism are mostly due to the impairment of methyl supply. Recently, an interaction was observed between folate status and a common mutation in the gene encoding for methylenetetrahydrofolate reductase, an essential enzyme in one-carbon metabolism, in determining genomic DNA methylation. This finding suggests that the interaction between a nutritional status with a genetic polymorphism can modulate gene expression through DNA methylation, especially when such polymorphism limits the methyl supply. DNA methylation, both genome-wide and gene-specific, is of particular interest for the study of cancer, aging and other conditions related to cell-cycle regulation and tissue-specific differentiation, because it affects gene expression without permanent alterations in DNA sequence such as mutations or allele deletions. Understanding the patterns of DNA methylation through the interaction with nutrients is fundamental, not only to provide pathophysiological explanations for the development of certain diseases, but also to improve the knowledge of possible prevention strategies by modifying a nutritional status in at-risk populations.
PMID: 12163697

13. Epigenetics and DNA methylation come of age in toxicology

Watson RE, Goodman JI.
Toxicol Sci. 2002 May;67(1):11-6.
http://toxsci.oxfordjournals.org/cgi/content/full/67/1/11

A wide variety of chemical and physical agents have the potential to produce adverse effects by causing heritable changes to the genome, resulting in heritable alterations in phenotype. These are often assumed to be a consequence of mutation. However, mutagenesis is not the only mechanism underlying heritable alterations to the genome. It is important to understand that there may also be an epigenetic basis for this. DNA methylation is the epigenetic mechanism that this review focuses upon. We indicate how altered methylation may play a key role in a variety of chemical-induced toxicities, including, but not limited to, carcinogenesis, and we point out how an assessment of methylation status can provide important information as a component of an overall safety assessment.
PMID: 11961211

14. Methylation matters

Costello JF, Plass C.
J Med Genet. 2001 May;38(5):285-303.
http://jmg.bmj.com/cgi/content/full/38/5/285

DNA methylation is not just for basic scientists any more. There is a growing awareness in the medical field that having the correct pattern of genomic methylation is essential for healthy cells and organs. If methylation patterns are not properly established or maintained, disorders as diverse as mental retardation, immune deficiency, and sporadic or inherited cancers may follow...
PMID: 11333864

15. Role of DNA methylation in the regulation of cell function: autoimmunity, aging and cancer

Richardson BC.
J Nutr. 2002 Aug;132(8 Suppl):2401S-2405S.
http://jn.nutrition.org/cgi/content/full/132/8/2401S
PMID: 12163700

16. Role of protein methylation in regulation of transcription

Lee DY et al.
Endocr Rev. 2005 Apr;26(2):147-70.
http://edrv.endojournals.org/cgi/content/full/26/2/147

In the last few years, the discovery of lysine and arginine methylation in histones and other proteins and the enzymes that carry out these posttranslational modifications has added a new dimension to the signal transduction field. In particular, there has been a huge surge in our understanding of how methylation of nucleosomal histones at specific lysine or arginine residues affects chromatin conformations and either facilitates or inhibits transcription from neighboring genes. It appears that the responsible methyltransferases can be targeted in some cases to specific genes and in other cases to broader regions of euchromatin or heterochromatin. Methylation of histones is mechanistically linked to other types of histone modifications, such as acetylation, phosphorylation, and monoubiquitylation; combinations of these modifications cooperate to regulate chromatin structure and transcription by stimulating or inhibiting binding of specific proteins. Although lysine methylation has thus far been observed almost exclusively on histones, arginine methylation has been observed on a variety of other proteins associated with gene regulation, including DNA-binding transcriptional activators, transcriptional coactivators, and many RNA binding proteins involved in RNA processing, transport, and stability. Thus, lysine and arginine methylation of proteins, like many other types of posttranslational modifications, are regulated steps of many specific signaling pathways.
PMID: 15479858

17. Epigenetic regulation by histone methylation and histone variants

Cheung P, Lau P.
Mol Endocrinol. 2005 Mar;19(3):563-73. Epub 2005 Jan 27.
http://mend.endojournals.org/cgi/content/full/19/3/563

Epigenetics is the study of heritable changes in gene expression that are not mediated at the DNA sequence level. Molecular mechanisms that mediate epigenetic regulation include DNA methylation and chromatin/histone modifications. With the identification of key histone-modifying enzymes, the biological functions of many histone posttranslational modifications are now beginning to be elucidated. Histone methylation, in particular, plays critical roles in many epigenetic phenomena. In this review, we provide an overview of recent findings that shape the current paradigms regarding the roles of histone methylation and histone variants in heterochromatin assembly and the maintenance of the boundaries between heterochromatin and euchromatin. We also highlight some of the enzymes that mediate histone methylation and discuss the stability and inheritance of this modification.
PMID: 15677708

18: A clinical and laboratory evaluation of methionine cycle-transsulfuration and androgen pathway markers in children with autistic disorders

Geier DA, Geier MR.
Horm Res. 2006;66(4):182-8.

BACKGROUND/AIMS: The prevalence of autism spectrum disorders (ASDs) is 1 in 300 children in the US. ASDs are characterized by impairments in social relatedness and communication, repetitive behaviors, abnormal movement patterns, and sensory dysfunction. Pre-pubertal age children with ASDs were assessed for metabolites in the methionine cycle-transsulfuration and androgen pathways, and for present physical development/behaviors indicative of hyperandrogenicity. METHODS: The Institutional Review Board of the Institute for Chronic Illnesses (Office for Human Research Protections, US Department of Health and Human Services IRB number: IRB00005375) approved the present study. Sixteen consecutive pre-pubertal age children (</=11 years old; mean +/- SD: 5.9 +/- 2.1 years old) with previously diagnosed ASDs that presented to the Genetic Centers of America for outpatient care were evaluated. RESULTS: Significantly (p < 0.01) increased levels of serum/plasma dehydroepiandrosterone and serum total testosterone relative to the age- and sex-specific normal laboratory reference ranges were observed. Conversely, serum follicle-stimulating hormone levels were significantly (p < 0.01) decreased. Plasma-reduced glutathione (p < 0.01), plasma cysteine (p < 0.01), plasma methionine (p < 0.01), serum cystathionine (p < 0.05), and serum homocysteine (p < 0.01) were all significantly decreased. CONCLUSION: The results suggest a possible cyclical interaction between the methionine cycle-transsulfuration and androgen pathways in some children with ASDs. Copyright (c) 2006 S. Karger AG, Basel.
PMID: 16825783

19. Sulfhydryl-reactive metals in autism

Kern JK et al.
J Toxicol Environ Health A. 2007 Apr 15;70(8):715-21.

This study examined the difference between sulfhydryl-reactive metals (mercury, lead, arsenic, and cadmium) in the hair of 45 children with autism (1-6 yr of age) as compared to 45 gender-, age-, and race-matched typical children. Hair samples were measured with inductively coupled mass spectrometry. Some studies, such as Holmes et al. (2003), suggested that children with autism may be poor detoxifiers relative to normally developing children. Metals that are not eliminated sequester in the brain. Our study found that arsenic, cadmium, and lead were significantly lower in the hair of children with autism than in matched controls. Mercury was in the same direction (lower in autism) following the same pattern, but did not achieve statistical significance. The evidence from our study supports the notion that children with autism may have trouble excreting these metals, resulting in a higher body burden that may contribute to symptoms of autism.
PMID: 17365626

20. Altered Sulfur Amino Acid Metabolism In Immune Cells of Children Diagnosed With Autism

Jung H. Suh et al.
Am J Biochem Biotech 4(2): 105-113, 2008.
http://www.scipub.org/fulltext/ajbb/ajbb42105-113.pdf

Autism Spectrum Disorder (ASD) is a behaviorally defined neurodevelopmental disorder whose etiology is poorly understood. Recent studies have shown that autistic children may be experiencing increased inflammation and oxidative stress. Altered immune regulation may be one contributing factor to inflammation and oxidative stress in autistic children. Sulfur amino acid (SAA) metabolism plays a critical role in regulating blood leukocyte functions and oxidative stress. However, it is not known whether autism impacts SAA metabolism in peripheral immune cells. To address this question, a novel liquid chromatography linked tandem mass spectrometric (LC/MS/MS) method was used to determine the levels of SAA metabolites in peripheral blood mononuclear cells obtained from 11 healthy controls and 31 autistic children. Improved detection sensitivity and selectivity of the LC/MS/MS method allowed accurate quantification using small samples. Results show that leukocytes from autistic children contained significantly lower concentrations of S-adenosylmethionine (-35%; p = 0.01), and elevated levels of intracellular homocysteine content (+80%; p=0.003). Additionally, the levels of intracellular total cysteine and glutathione (GSH) were reduced by 39% (p=0.004) and 25% (p=0.01), respectively. These autism-associated changes were leukocyte specific in that no significant alterations in SAA metabolite concentrations were detected in the plasma samples. Our results provide novel evidence for altered metabolism in immune cells; furthermore, this data suggest the involvement of inflammation in autism. Dietary differences between controls and patients, however, remain a potential confounder.

21. Risk of autistic disorder in affected offspring of mothers with a glutathione S-transferase P1 haplotype

Williams TA et al.
Arch Pediatr Adolesc Med. 2007 Apr;161(4):356-61.
http://archpedi.ama-assn.org/cgi/content/full/161/4/356

OBJECTIVE: To test whether polymorphisms of the glutathione S-transferase P1 gene (GSTP1) act in the mother during pregnancy to contribute to the phenotype of autistic disorder (AD) in her fetus. DESIGN: Transmission disequilibrium testing (TDT) in case mothers and maternal grandparents. SETTING: Autistic disorder may result from multiple genes and environmental factors acting during pregnancy and afterward. Teratogenic alleles act in mothers during pregnancy to contribute to neurodevelopmental disorders in their offspring; however, only a handful have been identified. GSTP1 is a candidate susceptibility gene for AD because of its tissue distribution and its role in oxidative stress, xenobiotic metabolism, and JNK regulation. PARTICIPANTS: We genotyped GSTP1*G313A and GSTP1*C341T polymorphisms in 137 members of 49 families with AD. All probands received a clinical diagnosis of AD by Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule-Generic testing. MAIN OUTCOME MEASURES: Association of haplotypes with AD was tested by the TDT-Phase program, using the expectation-maximization (EM) algorithm for uncertain haplotypes and for incomplete parental genotypes, with standard measures of statistical significance. RESULTS: The GSTP1*A haplotype was overtransmitted to case mothers (P = .01 [P = .03 using permutation testing]; odds ratio, 2.67 [95% confidence interval, 1.39-5.13]). Results of the combined haplotype and genotype analyses suggest that the GSTP1-313 genotype alone determined the observed haplotype effect. CONCLUSIONS: Overtransmission of the GSTP1*A haplotype to case mothers suggests that action in the mother during pregnancy likely increases the likelihood of AD in her fetus. If this is confirmed and is a result of a gene-environment interaction occurring during pregnancy, these findings could lead to the design of strategies for prevention or treatment.
PMID: 17404132

22. Homozygous gene deletions of the glutathione S-transferases M1 and T1 are associated with thimerosal sensitization

Westphal GA et al.
Int Arch Occup Environ Health. 2000 Aug;73(6):384-8.

OBJECTIVE: Thimerosal is an important preservative in vaccines and ophthalmologic preparations. The substance is known to be a type IV sensitizing agent. High sensitization rates were observed in contact-allergic patients and in health care workers who had been exposed to thimerosal-preserved vaccines. There is evidence for the involvement of the glutathione system in the metabolism of thimerosal or its decomposition products (organomercury alkyl compounds). Thus detoxification by polymorphically expressed glutathione S-transferases such as GSTT1 and GSTM1 might have a protective effect against sensitization by these substances. METHODS: To address this question, a case control study was conducted, including 91 Central European individuals with a positive patch-test reaction to thimerosal. This population was compared with 169 healthy controls and additionally with 114 individuals affected by an allergy against para-substituted aryl compounds. The latter population was included in order to test whether possible associations were due to substance-specific effects, or were a general feature connected with type IV immunological diseases. Homozygous deletions of GSTT1 and GSTM1 were determined by polymerase chain reaction. RESULTS: Glutathione S-transferase M1 deficiency was significantly more frequent among patients sensitized to thimerosal (65.9%, P = 0.013) compared with the healthy control group (49.1%) and the "para-compound" group (48%, P = 0.034). Glutathione S-transferase T1 deficiency in the thimerosal/mercury group (19.8%) was barely elevated versus healthy controls (16.0%) and the "para-compound" group (14.0%). The combined deletion (GSTT1-/GSTM1-) was markedly more frequent among thimerosal-sensitized patients than in healthy controls (17.6% vs. 6.5%, P = 0.0093) and in the "para-compound" group (17.6% vs. 6.1%, P =0.014), revealing a synergistic effect of these enzyme deficiencies (healthy controls vs. thimerosal GSTM1 negative individuals, OR = 2.0 [CI = 1.2-3.4], GSTT1-, OR = 1.2 [CI = 0.70-2.1], GSTM1/T1-, OR = 3.1 [CI = 1.4-6.5]). CONCLUSIONS: Since the glutathione-dependent system was repeatedly shown to be involved in the metabolism of thimerosal decomposition products, the observed association may be of functional relevance.
PMID: 11007341

23. Inhibition of the human erythrocytic glutathione-S-transferase T1 (GST T1) by thimerosal

Müller M et al.
Int J Hyg Environ Health. 2001 Jul;203(5-6):479-81.

We have investigated the interaction of thimerosal, a widely used antiseptic and preservative, with the human erythrocytic GST T1 (glutathione-S-transferase T1). This detoxifying enzyme is expressed in the erythrocytes of solely the human species and it displays a genetic polymorphism. Due to this polymorphism about 25% of the individuals of the caucasian population lack this activity ("non-conjugators"), while 75% show it ("conjugators") (Hallier, E., et al., 1993). Using our newly developed HPLC-fluorescence detection assay (Müller, M., et al., 2001) we have profiled the kinetics of enzyme inhibition in erythrocyte lysates of two individuals previously identified as "normal conjugator" (medium enzyme activity) and "super-conjugator" (very high activity). For the normal conjugator we have determined a 2.77 mM thimerosal concentration to inhibit 50% of the GST T1 activity. In the case of the super-conjugator a 2.3 mM thimerosal concentration causes a 50% inhibition of the enzyme activity. For both phenotypes a 14.8 mM thimerosal concentration results in residual enzyme activities equal to those typically detected in non-conjugator lysates. Thus, sufficiently high doses of thimerosal may be able to change the phenotypic status of an individual--at least in vitro--by inhibition of the GST T1 enzyme.
PMID: 11556154

24. The Frequency of Polymorphisms affecting Lead and Mercury Toxicity among Children with Autism

Shannon Rose et al.
Am J Biochem Biotech 4(2): 85-94 , 2008.
http://www.scipub.org/fulltext/ajbb/ajbb4285-94.pdf

Individual risk of developmental neurotoxicity with exposure to environmentally relevant levels of lead and mercury is likely to be determined by genetic susceptibility factors as well as additive interactions with other environmental pollutants, cumulative dose, and the developmental stage of exposure. The apparent increase in autism diagnosis over the last 15 years has enhanced interest in the possibility that an environmental trigger may be required to uncover the genetic liability in some cases of autism. The exquisite sensitivity of the developing brain and immune system to very low levels of lead and mercury give this hypothesis biologic plausibility. Delta aminolevulinic acid dehydratase (ALAD) and coproporphyin oxidase (CPOX) are two enzymes inhibited by low levels of lead and mercury, respectively. Common polymorphisms in these genes have been associated with elevated blood levels of lead and mercury and could potentially increase vulnerability to prenatal and/or postnatal developmental neurotoxicity. To explore this possibility, the frequency of the ALAD2 variant and variants in CPOX-4 and CPOX-5 were evaluated in 450 autistic children and 251 unaffected controls. A significant increase in the frequency of the ALAD2 allele was observed; however, contrary to our hypothesis, the frequency of both CPOX variants was significantly lower among the autistic children. Both lead and mercury induce oxidative stress by depleting the major intracellular antioxidant, glutathione. Among 242 autistic children with the variant ALAD2 allele, significant decreases in plasma glutathione and in the glutathione redox ratio were observed. These results suggest that children with autism who inherit the ALAD2 allele with lower glutathione levels may be at increased risk for lead toxicity during prenatal and postnatal neurodevelopment.

25. High levels of homocysteine and low serum paraoxonase 1 arylesterase activity in children with autism

Paşca SP et al.
Life Sci. 2006 Apr 4;78(19):2244-8.

Autism is a behaviorally defined disorder of unknown etiology that is thought to be influenced by genetic and environmental factors. High levels of homocysteine and oxidative stress are generally associated with neuropsychiatric disorders. The purpose of this study was to compare the level of homocysteine and other biomarkers in children with autism to corresponding values in age-matched healthy children. We measured total homocysteine (tHcy), vitamin B(12), paraoxonase and arylesterase activities of human paraoxonase 1 (PON1) in plasma and glutathione peroxidase (GPx) activity in erythrocytes from 21 children: 12 with autism (age: 8.29 +/- 2.76 years) and 9 controls (age: 8.33 +/- 1.82 years). We found statistically significant differences in tHcy levels and in arylesterase activity of PON1 in children with autism compared to the control group: 9.83 +/- 2.75 vs. 7.51 +/- 0.93 micromol/L (P < or =0.01) and 72.57 +/- 11.73 vs. 81.83 +/- 7.39 kU/L (P < or =0.005). In the autistic group there was a strong negative correlation between tHcy and GPx activity and the vitamin B(12) level was low or suboptimal. In conclusion, our study shows that in children with autism there are higher levels of tHcy, which is negatively correlated with GPx activity, low PON1 arylesterase activity and suboptimal levels of vitamin B(12).
PMID: 16297937

26: Polymorphisms in xenobiotic metabolism genes and autism

Serajee FJ et al.
J Child Neurol. 2004 Jun;19(6):413-7.

Autism is a neurodevelopmental syndrome defined by deficits in social reciprocity and communication and by unusual repetitive behaviors. Although there is an underlying genetic predisposition, the etiology of autism is currently unknown. A recent increase in prevalence suggests that genetically determined vulnerability to environmental exposure might contribute to the causation of autism. We performed family-based association studies of polymorphisms in metal-regulatory transcription factor 1(MTF1), a multispecific organic anion transporter (ABCC1), proton-coupled divalent metal ion transporters (SLC11A3 and SLC11A2), paraoxonase 1 (PON1), and glutathione S-transferase (GSTP1) genes in 196 autistic disorder families. There was deviation from the expected pattern of transmission for polymorphisms in MTF1 (Single nucleotide polymorphism database reference identification number, dbSNP rs3790625, P = .02) and divalent metal ion transporter SLC11A3 (dbSNP rs2304704, P = .07) genes. Although these results might represent chance finding, further investigations of genetic variations of metal metabolism in autism are warranted.
PMID: 15446388

27: Phenotypic variation in xenobiotic metabolism and adverse environmental response: focus on sulfur-dependent detoxification pathways

McFadden SA.
Toxicology. 1996 Jul 17;111(1-3):43-65.

Proper bodily response to environmental toxicants presumably requires proper function of the xenobiotic (foreign chemical) detoxification pathways. Links between phenotypic variations in xenobiotic metabolism and adverse environmental response have long been sought. Metabolism of the drug S-carboxymethyl-L-cysteine (SCMC) is polymorphous in the population, having a bimodal distribution of metabolites, 2.5% of the general population are thought to be nonmetabolizers. The researchers developing this data feel this implies a polymorphism in sulfoxidation of the amino acid cysteine to sulfate. While this interpretation is somewhat controversial, these metabolic differences reflected may have significant effects. Additionally, a significant number of individuals with environmental intolerance or chronic disease have impaired sulfation of phenolic xenobiotics. This impairment is demonstrated with the probe drug acetaminophen and is presumably due to starvation of the sulfotransferases for sulfate substrate. Reduced metabolism of SCMC has been found with increased frequency in individuals with several degenerative neurological and immunological conditions and drug intolerances, including Alzheimer's disease, Parkinson's disease, motor neuron disease, rheumatoid arthritis, and delayed food sensitivity. Impaired sulfation has been found in many of these conditions, and preliminary data suggests that it may be important in multiple chemical sensitivities and diet responsive autism. In addition, impaired sulfation may be relevant to intolerance of phenol, tyramine, and phenylic food constituents, and it may be a factor in the success of the Feingold diet. These studies indicate the need for the development of genetic and functional tests of xenobiotic metabolism as tools for further research in epidemiology and risk assessment.
PMID: 8711748

28. Evidence of toxicity, oxidative stress, and neuronal insult in autism

Kern JK, Jones AM.
J Toxicol Environ Health B Crit Rev. 2006 Nov-Dec;9(6):485-99.

According to the Autism Society of America, autism is now considered to be an epidemic. The increase in the rate of autism revealed by epidemiological studies and government reports implicates the importance of external or environmental factors that may be changing. This article discusses the evidence for the case that some children with autism may become autistic from neuronal cell death or brain damage sometime after birth as result of insult; and addresses the hypotheses that toxicity and oxidative stress may be a cause of neuronal insult in autism. The article first describes the Purkinje cell loss found in autism, Purkinje cell physiology and vulnerability, and the evidence for postnatal cell loss. Second, the article describes the increased brain volume in autism and how it may be related to the Purkinje cell loss. Third, the evidence for toxicity and oxidative stress is covered and the possible involvement of glutathione is discussed. Finally, the article discusses what may be happening over the course of development and the multiple factors that may interplay and make these children more vulnerable to toxicity, oxidative stress, and neuronal insult.
PMID: 17090484

29. A case series of children with apparent mercury toxic encephalopathies manifesting with clinical symptoms of regressive autistic disorders

Geier DA, Geier MR.
J Toxicol Environ Health A. 2007 May 15;70(10):837-51.

Impairments in social relatedness and communication, repetitive behaviors, and stereotypic abnormal movement patterns characterize autism spectrum disorders (ASDs). It is clear that while genetic factors are important to the pathogenesis of ASDs, mercury exposure can induce immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with ASDs. The Institutional Review Board of the Institute for Chronic Illnesses (Office for Human Research Protections, U.S. Department of Health and Human Services, IRB number IRB00005375) approved the present study. A case series of nine patients who presented to the Genetic Centers of America for a genetic/developmental evaluation are discussed. Eight of nine patients (one patient was found to have an ASD due to Rett's syndrome) (a) had regressive ASDs; (b) had elevated levels of androgens; (c) excreted significant amounts of mercury post chelation challenge; (d) had biochemical evidence of decreased function in their glutathione pathways; (e) had no known significant mercury exposure except from Thimerosal-containing vaccines/Rho(D)-immune globulin preparations; and (f) had alternate causes for their regressive ASDs ruled out. There was a significant dose-response relationship between the severity of the regressive ASDs observed and the total mercury dose children received from Thimerosal-containing vaccines/Rho (D)-immune globulin preparations. Based upon differential diagnoses, 8 of 9 patients examined were exposed to significant mercury from Thimerosal-containing biologic/vaccine preparations during their fetal/infant developmental periods, and subsequently, between 12 and 24 mo of age, these previously normally developing children suffered mercury toxic encephalopathies that manifested with clinical symptoms consistent with regressive ASDs. Evidence for mercury intoxication should be considered in the differential diagnosis as contributing to some regressive ASDs.
PMID: 17454560

30. Spot urinary creatinine excretion in pervasive developmental disorders

Whiteley P et al.
Pediatr Int. 2006 Jun;48(3):292-7.

BACKGROUND: Excretion of creatinine in urine represents the end-point of endogenous energy transfer from stored adenosine triphosphate in skeletal and cardiac muscle. Measurement of urinary creatinine is commonly used to correct for total urine concentration. Various quantitative measures of compounds suspected to be either pathological to, or indicative of, possible therapeutic interventions for Pervasive Developmental Disorders (PDD) have relied extensively on spot creatinine as a ratio quantity, although this important metabolite has not been exclusively studied within this population. METHODS: Levels of urinary creatinine in spot urine samples were analyzed for a group of children diagnosed with PDD (n=24; median age, 75 months; range, 39-137 months) and a control group (n=50; median age, 109 months; range, 59-140 months). Diagnosis of PDD was confirmed using the Autism Diagnostic Interview-Revised. Samples were collected and analyzed blind for creatinine content using an improved Jaffe's reaction method. RESULTS: Controlling for sample pH and body mass index, a significant decrease in urinary creatinine concentration was found in the PDD group compared to controls using a Mann-Whitney two-tailed ranks test (P=0.001). CONCLUSION: Further studies of protein catabolism and renal function in autism are required to ascertain the relevance of decreased spot urinary creatinine excretion identified in this preliminary study. Issues regarding the use of single urine creatinine measurements and associated confounding variables are discussed in light of the findings, together with recommendations to use other internal or external standards for the quantification of urinary compounds in PDD research.
PMID: 16732798

31. Sulphation deficit in "low-functioning" autistic children: a pilot study

Alberti A et al.
Biol Psychiatry. 1999 Aug 1;46(3):420-4.

BACKGROUND: Parents of autistic children and autism support groups often report that autistic episodes are exacerbated when the children eat certain foodstuffs such as dairy products, chocolates, wheat, corn sugar, apples, and bananas. The hypothesis that autistic behavior might be related to metabolic dysfunctions has led us to investigate in a group of "low functioning" autistic children and in an age-matched control group each made up of 20 subjects, the sulphation capacity available. METHODS: Utilizing the biochemical characteristics of paracetamol we evaluated by high performance liquid chromatography, the urine paracetamol-sulfate/paracetamol-glucuronide (PS/PG) ratio in all subjects following administration of this drug. RESULTS: The PS/PG ratio in the group of autistic subjects gave a significantly lower results than the control group with p < .00002. CONCLUSIONS: The inability to effectively metabolize certain compounds particularly phenolic amines, toxic for the CNS, could exacerbate the wide spectrum of autistic behavior.
PMID: 10435209

32. Plasma amino acid levels in children with autism and their families

Aldred S et al.
J Autism Dev Disord. 2003 Feb;33(1):93-7.

Plasma amino acid levels were measured in autistic and Asperger syndrome patients, their siblings, and parents. The results were compared with values from age-matched controls. Patients with autism or Asperger syndrome and their siblings and parents all had raised glutamic acid, phenylalanine, asparagine, tyrosine, alanine, and lysine (p < .05) than controls, with reduced plasma glutamine. Other amino acids were at normal levels. These results show that children with autistic spectrum disorders come from a family background of dysregulated amino acid metabolism and provide further evidence for an underlying biochemical basis for the condition.
PMID: 12708584

33. Red-Cell Trace Minerals in Children with Autism

Joan Jory and Woody R. McGinnis
Am J Biochem Biotech 4(2): 101-104, 2008.
http://www.scipub.org/fulltext/ajbb/ajbb42101-104.pdf

Abnormalities in mineral-dependent antioxidant enzymes in children with autism raise interest in the determination of trace mineral status in this population. A cross sectional investigation of red cell mineral levels was carried out among 20 children with autism and 15 controls. Children with autism demonstrated significantly lower red cell selenium (p<0.0006) and higher molybdenum (p<0.01) than the controls. There was a trend toward lower red cell zinc and higher cobalt and vanadium, among the children with autism. There were no differences in red cell levels of chromium, copper, manganese, or magnesium. These findings confirm an earlier report of low red cell selenium in autism and support a role for decreased trace mineral status in oxidative stress in autism through alteration of selenium-dependent antioxidant enzymes and increased lipid peroxidation.

34. Porphyrinuria in childhood autistic disorder: implications for environmental toxicity

Nataf R et al.
Toxicol Appl Pharmacol. 2006 Jul 15;214(2):99-108.

To address a possible environmental contribution to autism, we carried out a retrospective study on urinary porphyrin levels, a biomarker of environmental toxicity, in 269 children with neurodevelopmental and related disorders referred to a Paris clinic (2002-2004), including 106 with autistic disorder. Urinary porphyrin levels determined by high-performance liquid chromatography were compared between diagnostic groups including internal and external control groups. Coproporphyrin levels were elevated in children with autistic disorder relative to control groups. Elevation was maintained on normalization for age or to a control heme pathway metabolite (uroporphyrin) in the same samples. The elevation was significant (P < 0.001). Porphyrin levels were unchanged in Asperger's disorder, distinguishing it from autistic disorder. The atypical molecule precoproporphyrin, a specific indicator of heavy metal toxicity, was also elevated in autistic disorder (P < 0.001) but not significantly in Asperger's. A subgroup with autistic disorder was treated with oral dimercaptosuccinic acid (DMSA) with a view to heavy metal removal. Following DMSA there was a significant (P = 0.002) drop in urinary porphyrin excretion. These data implicate environmental toxicity in childhood autistic disorder.
PMID: 16782144

35. A prospective assessment of porphyrins in autistic disorders: a potential marker for heavy metal exposure

Geier DA, Geier MR.
Neurotox Res. 2006 Aug;10(1):57-64.

Autism was recently associated with a urinary porphyrin pattern indicative of mercury toxicity in a large cohort of French children. The IRB of the Institute for Chronic Illnesses approved the present study. A total of 37 consecutive American patients (> or = 7 years-old) with autism spectrum disorders (ASDs) (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-DSM IV), born from 1983-1998, that presented to the Genetic Centers of America for outpatient genetic evaluations were prospectively examined for urinary prophryin levels (LabCorp, Inc.) from June 2005-June 2006. Imaging and laboratory testing were conducted on each patient to rule-out other causal factors for their ASDs. As controls, age-, sex-, and race-matched neurotypical ASD siblings were examined. An apparent dose-response effect was observed between autism severity and increased urinary coproporphyrins. Patients with non-chelated autism (2.25-fold, 83% had levels > 2 SD above the control mean) and non-chelated ASDs (2-fold, 58% had levels > 2 SD above the control mean), but not patients with non-chelated pervasive developmental delay-not otherwise specified (PDD-NOS) or Asperger's disorder (1.4-fold, 46% had levels > 2 SD above the control mean), had significantly increased median coproporphyrin levels versus controls. A significant increase (1.7-fold) in median coproporphyrin levels was observed among non-chelated ASD patients versus chelated ASD patients. Porphyrins should be routinely clinically measured in ASDs, and potential ASD treatments should consider monitoring porphyrin levels. Additional research should be conducted to evaluate the potential role for mercury exposure in some ASDs.
PMID: 17000470

36. A prospective study of mercury toxicity biomarkers in autistic spectrum disorders

Geier DA, Geier MR.
J Toxicol Environ Health A. 2007 Oct;70(20):1723-30.

Porphyrins are derivatives formed in the heme synthesis pathway and porphyrins afford a measure of xenobiotic exposure. The steps in the heme pathway most vulnerable to heavy metal inhibition are uroporphyrin decarboxylase (UROD) and coproporphyrinogen oxidase (CPOX) reactions. Mercury toxicity was associated with elevations in urinary coproporphyrin (cP), pentacarboxyporphyrin (5cxP), and precoproporphyrin (prcP) (also known as keto-isocoproporphyrin) levels. Two cohorts of autistic patients in the United States and France had urine porphyrin levels associated with mercury toxicity. A prospective study of urinary porphyrin testing at LabCorp (United States) and the Laboratoire Philippe Auguste (France) involving 71 autism spectrum disorder (ASD) patients, neurotypical sibling controls, and general population controls was undertaken. ASD patients had significant elevations in urinary levels of cP, 5cxP, and prcP relative to controls, and > 50% of ASD patients had urinary cP levels more than 2 standard deviations above the mean values for neurotypical sibling controls. Significant reductions in urinary 5cxP and cP levels were observed in ASD patients following chelation. A significant correlation was found between urinary porphyrins measured at LabCorp and those measured at the Laboratoire Philippe Auguste on individual ASD patients. The established developmental neurotoxicity attributed to mercury and biochemical/genomic evidence for mercury susceptibility/toxicity in ASDs indicates a causal role for mercury. Urinary porphyrin testing is clinically available, relatively inexpensive, and noninvasive. Porphyrins need to be routinely measured in ASDs to establish if mercury toxicity is a causative factor and to evaluate the effectiveness of chelation therapy.
PMID: 17885929

37. Acute intermittent porphyria: psychosis as the only clinical manifestation

Ellencweig N, Schoenfeld N, Zemishlany Z.
Isr J Psychiatry Relat Sci. 2006;43(1):52-6.
http://www.psychiatry.org.il/ or http://tinyurl.com/4mqtd2

Acute intermittent porphyria (AIP) is the most common of the four forms of neuroporphyria. AIP mimics a variety of disorders and thus poses a diagnostic quagmire. Abdominal pain occurs in 90-95% of the attacks. Some patients develop psychiatric symptoms such as psychosis similar to schizophrenia. The diagnostic difficulty may lead to under-diagnosis of patients who present with strictly psychiatric symptoms. This assumption is supported by a high prevalence of AIP in psychiatric hospitals. Therefore, we encourage a high index of suspicion for AIP in psychiatric patients in order to prevent false psychiatric diagnosis. In addition we discuss psychotropic drugs that may exacerbate acute attacks in undiagnosed patients. We report a case in which the diagnosis of AIP was clouded by the presence of only psychiatric symptoms. The clue for diagnosis was an anamnestic detail of the use of a porphyrogenic drug prior to the admission. The diagnosis of AIP was supported by excess of alpha aminolevulinic acid (ALA) and porphobilinogen (PBG) in urine concomitantly with a decrease in porphobilinogen deaminase (PBGD) activity in erythrocytes. The diagnosis was further strengthened by the fact that the patient's father was identified as an AIP carrier. However, in the absence of typical organic symptoms of porphyria, one cannot definitely rule out the presence of schizophrenia in this patient in addition to AIR
PMID: 16910386

38. Lead, chemical porphyria, and heme as a biological mediator

Fujita H, Nishitani C, Ogawa K.
Tohoku J Exp Med. 2002 Feb;196(2):53-64.
http://www.jstage.jst.go.jp/article/tjem/196/2/53/_pdf

One of the most well-characterized symptoms of lead poisoning is porphyria. The biochemical signs of lead intoxication related to porphyria are delta-aminolevulinic aciduria, coproporphyrinuria, and accumulation of free and zinc protoporphyrin in erythrocytes. From the 1970s to the early 80s, almost all of the enzymes in the heme pathway had been purified and characterized, and it was demonstrated that delta-aminolevulinic aciduria is due to inhibition of delta-aminolevulinate dehydratase by lead. Lead also inhibits purified ferrochelatase; however, the magnitude of inhibition was essentially nil even under pathological conditions. Further study proved the disturbance of iron-reducing activity by moderate lead exposure. Far different from these two enzymes, lead failed to inhibit purified coproporphyrinogen oxidase, i.e., the mechanism of coproporphyrinuria has not yet been understood. During the 80s to the 90s, the effects of environmental hazards including lead were elucidated through stress proteins, indicating the induction of some heme pathway enzymes as stress proteins. At that time, gene environment interaction was another focus of toxicology, since gene carriers of porphyrias are considered to be a high-risk group to chemical pollutants. Toxicological studies from the 70s to the 90s focused on the direct effect of hazards on biological molecules, such as the heme pathway enzymes, and many environmental pollutants were proved to affect cytosolic heme. Recently, we demonstrated the mechanism of the heme-controlled transcription system, which suggests that the indirect effects of environmental hazards are also important for elucidating toxicity, i.e., the hazards can affect cell functions through such biological mediators as regulatory heme. It is, therefore, probable that toxicology in the future will focus on biological systems such as gene regulation and signal transduction systems.
PMID: 12498316

39. Porphyrinurias induced by mercury and other metals

Fowler BA.
Toxicol Sci. 2001 Jun;61(2):197-8.
http://toxsci.oxfordjournals.org/cgi/content/full/61/2/197
PMID: 11353126

40. Quantitative evaluation of urinary porphyrins as a measure of kidney mercury content and mercury body burden during prolonged methylmercury exposure in rats

Pingree SD et al.
Toxicol Sci. 2001 Jun;61(2):234-40.
http://toxsci.oxfordjournals.org/cgi/content/full/61/2/234

Changes in urinary porphyrin excretion patterns (porphyrin profiles) during prolonged mercury exposure are attributable to mercury accumulation in the kidney and to consequent effects of Hg2+ on renal porphyrin metabolism. In the present study, we evaluated the quantitative relationship of urinary porphyrin concentrations to mobilizable renal mercury content, using the metal chelator 2,3-dimercapto-1-propanesulfonic acid (DMPS) to modulate kidney mercury levels. Rats exposed to methylmercury hydroxide (MMH) at 10 ppm in drinking water for 6 weeks were treated with up to 3 consecutive doses of DMPS (100mg/kg, ip) at 72-h intervals. Consistent with previous findings, the concentrations of pentacarboxyl- (5-) and copro- (4-) porphyrins and of an atypical porphyrin specific to mercury exposure, precoproporphyrin, were significantly elevated in urine of MMH-exposed rats, compared with that of rats exposed to distilled water (dH2O) for the same period. Consecutive DMPS treatments of MMH-exposed rats significantly decreased kidney concentrations of total, as well as Hg2+ and CH3Hg+ species, and promoted increased urinary mercury excretion. Concomitantly, DMPS treatment decreased both kidney and urinary porphyrin concentrations, consistent with depletion of renal mercury levels. Regression analyses demonstrated a high correlation (r approximately 0.9) between prechelation urinary porphyrins and postchelation urinary mercury levels and also between prechelation urinary porphyrins and prechelation kidney mercury concentrations. These findings demonstrate that urinary porphyrin concentrations relate quantitatively to DMPS-mobilizable mercury in the kidney and, therefore, serve as a biochemical measure of renal mercury content.
PMID: 11353132

41. The porphyrias: recent advances

Hindmarsh JT.
Clin Chem. 1986 Jul;32(7):1255-63.
http://www.clinchem.org/cgi/reprint/32/7/1255.pdf

Recent research has elucidated several of the hitherto poorly understood steps in heme synthesis. This review describes this metabolic pathway and pinpoints the enzymatic blockages in the various porphyrias. Recent advances in the understanding of the etiology of porphyria cutanea tarda are discussed, as are the abnormalities of porphyrin metabolism seen in chronic renal failure and in lead poisoning. An outline is given of the clinical and biochemical abnormalities seen in the porphyrias. Included is an algorithm to aid in the differential diagnosis of these diseases, and a brief review of the new analytical techniques available for the identification and quantification of porphyrins and their precursors in body fluids.
PMID: 3521939

42. Effects of polyhalogenated aromatic compounds on porphyrin metabolism

Hill RH Jr.
Environ Health Perspect. 1985 May;60:139-43.
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1568569&blobtype=pdf

Heme production is a vital metabolic process that occurs in the bone marrow and liver. Porphyrins are unused by-products of this biosynthetic process and normally occur in urine and other body fluids in low concentrations. Various disorders can disrupt the heme biosynthetic process, causing greater quantities of porphyrins in urine. The porphyrias are a group of diseases characterized by excessive porphyrins and other precursors in urine. Porphyrias may be either hereditary or acquired through exposure to certain drugs or chemicals. Porphyria cutanea tarda (PCT) is the disease associated with exposure to polyhalogenated aromatic compounds. The urinary porphyrin pattern is of great value in diagnosing PCT and defining the etiology of the disease. As this liver disease from chemical damage develops, the urinary pattern progressively changes. With the development of a rapid and sensitive high-performance liquid chromatography analysis, urinary porphyrin patterns can be easily monitored. All free porphyrin acids can be quantitatively analyzed in less than 15 min. In our studies of groups exposed to porphyrinogenic chemicals, we have not observed clear differences in the urinary porphyrin patterns of cases when compared with carefully selected controls. In animal studies, however, PCT was clearly associated with polybrominated biphenyl exposure. Future evaluation of the utility of urinary porphyrin patterns as a diagnostic tool will require a cohort that has received a recent, well-documented exposure and a comparable control population. Assay of erythrocyte uroporphyrinogen decarboxylase activity will also be needed to define the form of the PCT.
PMID: 4029097

43. Porphyrin patterns in different types of porphyria

Chu TC, Chu EJ.
Clin Chem. 1967 May;13(5):371-87.
http://www.clinchem.org/cgi/reprint/13/5/371.pdf
PMID: 6024049

44. The methionine-homocysteine cycle and its effects on cognitive diseases

Miller AL.
Altern Med Rev. 2003 Feb;8(1):7-19.
http://tinyurl.com/6mr7cm

Related articles, via PubMed
http://tinyurl.com/6q2rx3

Homocysteine, a sulfur-containing amino acid, is a metabolite of the essential amino acid methionine, and exists at a critical biochemical intersection in the methionine cycle - between S-adenosylmethionine, the indispensable ubiquitous methyl donor, and vitamins B12 and folic acid. High blood levels of homocysteine signal a breakdown in this vital process, resulting in far-reaching biochemical and life consequences. The link between homocysteine and cardiovascular disease is well established, and decreasing plasma total homocysteine by providing nutritional cofactors for its metabolism has been shown to reduce the risk of cardiovascular events. Information has been emerging regarding a connection between homocysteine metabolism and cognitive function, from mild cognitive decline (age-related memory loss) to vascular dementia and Alzheimer's disease. Significant deficiencies in the homocysteine re-methylation cofactors cobalamin (B12) and folate, as well as the trans-sulfuration cofactor vitamin B6, are commonly seen in the elderly population, with a resultant increase in homocysteine with advancing age. Hyperhomocysteinemia has been shown to be an independent risk factor for cognitive dysfunction. Indirect and direct vascular damage can be caused by homocysteine, which has been implicated in vascular dementia, with an increased risk of multiple brain infarcts and dementia as homocysteine levels rise. A significant correlation has been found between risk of Alzheimer's disease and high plasma levels of homocysteine, as well as low levels of folic acid, and vitamins B6 and B12. All of these disease associations are thought to be interrelated via increased homocysteine and S-adenosylhomocysteine and subsequent hypomethylation of numerous substances, including DNA and proteins, that render vascular structures and neurons more susceptible to damage and apoptosis. Providing the nutritional cofactors for proper functioning of the methionine cycle may improve methylation and protect the brain from damage. Further studies need to be performed to assess whether this will also reduce the risk of cognitive diseases and/or improve cognitive functioning.
PMID: 12611557