Chronic arsenic (As) exposure currently affects roughly 140 million people worldwide. Methylation of ingested inorganic arsenic (InAs) to methylarsonic- (MMA) and dimethylarsinic acids (DMA) relies on folate- dependent one carbon metabolism and facilitates urinary arsenic (As) elimination. We recently completed a randomized placebo-controlled trial of folic acid (FA) supplementation in 200 folate-deficient As-exposed residents of Araihazar, Bangladesh. The results indicate 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, FA supplementation facilitates As elimination and significantly lowers blood As concentrations in individuals who are folate deficient. We have also determined that blood As is a good biomarker of As exposure and is directly associated with the risk for As-induced skin lesions. While these findings are extremely compelling, several fundamental questions must be addressed prior to a large scale intervention aimed at assessing the possible impact of FA supplementation on As-induced disease-related outcomes. The proposed studies will address the following questions:
Aim 1 : a) Does FA supplementation lower blood arsenic concentrations in the general population? b) Does a higher dose of FA lead to an incremental lowering of bAs?, Aim 2: a) What is the time-course of the decline in blood As, and at what point is a nadir in blood As achieved? b) Is there a rebound in blood As after the cessation of FA supplementation due to release of As from tissue stores? Aim 3: a) 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. We have previously found that urinary creatinine (a catabolite of creatine) is by far the strongest predictor of As methylation, and that participants with lower urinary creatinine are at increased risk for As- induced skin lesions. Urinary creatinine is influenced by dietary intake of creatine (derived from meat), which downregulates endogenous creatine biosynthesis. Since creatine biosynthesis is the major consumer of methyl groups, we will test the hypothesis that creatine supplementation will spare methyl groups, lower homocysteine and facilitate the methylation of As, and thereby lower blood As. To answer all of these questions, we propose to conduct 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 would have enormous therapeutic potential for ameliorating the long-term health consequences of As exposure for the many populations at risk.
Chronic arsenic (As) exposure currently affects more than 140 million people worldwide. Methylation of ingested arsenic relies on folate-dependent one carbon metabolism and facilitates urinary arsenic elimination. We recently completed a trial of folic acid supplementation in folate-deficient As-exposed residents of Araihazar, Bangladesh. The results indicate that folate deficiency and hyperhomocysteinemia are associated with a reduced capacity to methylate As and are risk factors for As-induced skin lesions. Furthermore, folic acid supplementation facilitates As elimination and significantly lowers blood As concentrations by 14% in individuals who are folate deficient. Using data from our previously published work, we estimate that by reducing blood As with FA supplementation, the percent reduction in population attributable risk for skin lesions (the precursors for skin cancer) to be 13%. The proposed studies will address fundamental questions regarding the dose and duration of therapy and will test a novel new therapeutic approach to further lower blood As. Considering the magnitude of the exposed population worldwide, and the severity of the numerous associated health outcomes, we feel this work is highly significant as it implies that a simple, low-cost, low-risk intervention could potentially reduce disease risk for hundreds of thousands of people.
|Niedzwiecki, Megan M; Liu, Xinhua; Zhu, Huiping et al. (2018) Serum homocysteine, arsenic methylation, and arsenic-induced skin lesion incidence in Bangladesh: A one-carbon metabolism candidate gene study. Environ Int 113:133-142|
|Howe, Caitlin G; Liu, Xinhua; Hall, Megan N et al. (2017) Sex-Specific Associations between One-Carbon Metabolism Indices and Posttranslational Histone Modifications in Arsenic-Exposed Bangladeshi Adults. Cancer Epidemiol Biomarkers Prev 26:261-269|
|Hall, Megan N; Howe, Caitlin G; Liu, Xinhua et al. (2016) Supplementation with Folic Acid, but Not Creatine, Increases Plasma Betaine, Decreases Plasma Dimethylglycine, and Prevents a Decrease in Plasma Choline in Arsenic-Exposed Bangladeshi Adults. J Nutr 146:1062-7|
|Howe, Caitlin G; Liu, Xinhua; Hall, Megan N et al. (2016) Associations between Blood and Urine Arsenic Concentrations and Global Levels of Post-Translational Histone Modifications in Bangladeshi Men and Women. Environ Health Perspect 124:1234-40|
|Sanchez, Tiffany R; Levy, Diane; Shahriar, Mohammad Hasan et al. (2016) Provision of well-water treatment units to 600 households in Bangladesh: A longitudinal analysis of urinary arsenic indicates fading utility. Sci Total Environ 563-564:131-7|
|Howe, Caitlin G; Gamble, Mary V (2016) Influence of Arsenic on Global Levels of Histone Posttranslational Modifications: a Review of the Literature and Challenges in the Field. Curr Environ Health Rep 3:225-37|
|Muñoz, Alexandra; Chervona, Yana; Hall, Megan et al. (2015) Sex-specific patterns and deregulation of endocrine pathways in the gene expression profiles of Bangladeshi adults exposed to arsenic contaminated drinking water. Toxicol Appl Pharmacol 284:330-8|
|Reed, Michael C; Gamble, Mary V; Hall, Megan N et al. (2015) Mathematical analysis of the regulation of competing methyltransferases. BMC Syst Biol 9:69|
|Howe, Caitlin G; Gamble, Mary V (2015) Enzymatic cleavage of histone H3: a new consideration when measuring histone modifications in human samples. Clin Epigenetics 7:7|
|Niedzwiecki, Megan M; Liu, Xinhua; Hall, Megan N et al. (2015) Sex-specific associations of arsenic exposure with global DNA methylation and hydroxymethylation in leukocytes: results from two studies in Bangladesh. Cancer Epidemiol Biomarkers Prev 24:1748-57|
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