Mary V. Gamble, PhD

Nutritional Influences on Arsenic Toxicity, Bangladesh: The largest known mass exposure to arsenic is presently occurring due to ground water contamination of well water throughout the Ganges-Brahmaputra Delta. There is a significant inter-individual variability in susceptibility to progression from arsenic exposure to clinical manifestations of arsenic toxicity (e.g. skin, lung, liver and bladder cancers). Several observational as well as biochemical studies have led to a prevalent hypothesis that nutritional status may account for a substantial portion of this variability, though no controlled clinical studies have addressed this important hypothesis. Methylation of inorganic arsenic (InAs) has generally been considered to be a detoxification pathway. InAs and DNA are both methylated via one-carbon metabolism, a biochemical pathway which is dependent on folate for de novo generation of one-carbon groups, and also uses vitamins B12 and B6 as cofactors. The primary hypothesis of this proposal is that nutritional regulation of one-carbon metabolism, specifically folate availability, contributes substantially to the large inter-individual variability observed in InAs and DNA methylation, and thus progression from arsenic exposure to toxicity. These hypotheses have been tested in a randomized, controlled folic acid supplementation trial of adults chronically exposed to arsenic-contaminated drinking water in Bangladesh. These studies have also revealed complex interations between arsenic exposure, folate deficiency and DNA methylation that influence risk for development of arsenic-induced premalignant skin lesions.

Folic acid and creatine as therapeutic approaches for lowering blood arsenic, Bangladesh: Arsenic (As) exposure affects more than 140 million people worldwide. Methylation of inorganic-arsenic (InAs) to methylarsonic- (MMA) and dimethylarsinic acids (DMA) relies on folate-dependent one-carbon metabolism and facilitates urinary arsenic (As) elimination. Our studies indicated that folate deficiency and hyperhomocysteinemia (HHcys) are associated with a reduced capacity to methylate As and are risk factors for As-induced skin lesions. Furthermore, folic acid (FA) supplementation significantly lowers blood As concentrations in individuals who are folate deficient. However, several fundamental questions still needed to be addressed: a) Does FA supplementation lower blood As concentrations in the general population? b) What is the optimal dose?, c) What is the time-course of the decline in blood As? d) Is there a rebound in blood As after the cessation of FA supplementation due to release of As from tissue stores? e) Can the ability of FA to lower blood As and homocysteine be enhanced by the addition of a novel new alternative approach: reduce methylation demand. The methylation of guanadinoacetate represents the final step in creatine biosynthesis. This reaction is the major consumer of methyl groups and every molecule of creatine synthesized ultimately generates a molecule of homocysteine. Furthermore, creatinine concentrations are a robust predictor of arsenic methylation. We tested the hypothesis that creatine supplementation, which downregulates endogenous creatine biosynthesis, will spare methyl groups, facilitate the methylation of other substrates - including As - and thereby lower blood As. To answer all of these questions, we conducted a randomized, double-blind, placebo controlled trial of FA (a comparison of two doses and durations), creatine, and creatine plus FA. Positive results of these interventions could have important therapeutic potential for ameliorating the long-term health consequences of As exposure for the many populations at risk.