Betaine and choline status modify the effects of folic acid and creatine supplementation on arsenic methylation in a randomized controlled trial of Bangladeshi adults.

PURPOSE: Methylation of ingested inorganic arsenic (InAs) to monomethyl- (MMAs) and dimethyl-arsenical species (DMAs) facilitates urinary arsenic elimination. Folate and creatine supplementation influenced arsenic methylation in a randomized controlled trial. Here, we examine if baseline status of one-carbon metabolism nutrients (folate, choline, betaine, and vitamin B12) modified the effects of FA and creatine supplementation on changes in homocysteine, guanidinoacetate (GAA), total blood arsenic, and urinary arsenic metabolite proportions and indices. METHODS: Study participants (N = 622) received 400 or 800 µg FA, 3 g creatine, 400 µg FA + 3 g creatine, or placebo daily for 12 weeks. RESULTS: Relative to placebo, FA supplementation was associated with greater mean increases in %DMAs among participants with betaine concentrations below the median than those with levels above the median (FDR < 0.05). 400 µg FA/day was associated with a greater decrease in homocysteine among participants with plasma folate concentrations below, compared with those above, the median (FDR < 0.03). Creatine treatment was associated with a significant decrease in %MMAs among participants with choline concentrations below the median (P = 0.04), but not among participants above the median (P = 0.94); this effect did not significantly differ between strata (P = 0.10). CONCLUSIONS: Effects of FA and creatine supplementation on arsenic methylation capacity were greater among individuals with low betaine and choline status, respectively. The efficacy of FA and creatine interventions to facilitate arsenic methylation may be modified by choline and betaine nutritional status. CLINICAL TRIAL REGISTRATION: Clinical Trial Registry Identifier: NCT01050556, U.S. National Library of Medicine, https://clinicaltrials.gov ; registered January 15, 2010.

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.

BACKGROUND: Folic acid (FA) supplementation facilitates urinary excretion of arsenic, a human carcinogen. A better understanding of interactions between one-carbon metabolism intermediates may improve the ability to design nutrition interventions that further facilitate arsenic excretion. OBJECTIVE: The objective was to determine if FA and/or creatine supplementation increase choline and betaine and decrease dimethylglycine (DMG). METHODS: We conducted a secondary analysis of the Folic Acid and Creatine Trial, a randomized trial in arsenic-exposed Bangladeshi adults (n = 605, aged 24-55 y, 50.3% male) who received arsenic-removal water filters. We examined treatment effects of FA and/or creatine supplementation on plasma choline, betaine, and DMG concentrations, measured by LC-tandem mass spectrometry at baseline and at week 12. Group comparisons were between 1) 400 and 800 µg FA/d (FA400 and FA800, respectively) compared with placebo, 2) creatine (3 g/d) compared with placebo, and 3) creatine plus FA400 compared with FA400. RESULTS: Choline decreased in the placebo group (-6.6%; 95% CI: -10.2%, -2.9%) but did not change in the FA groups (FA400: 2.5%; 95% CI: -0.9%, 6.1%; FA800: 1.4%; 95% CI: -2.5%, 5.5%; P < 0.05). Betaine did not change in the placebo group (-3.5%; 95% CI: -9.3%, 2.6%) but increased in the FA groups (FA400: 14.1%; 95% CI: 9.4%, 19.0%; FA800: 13.0%; 95% CI: 7.2%, 19.1%; P < 0.01). The decrease in DMG was greater in the FA groups (FA400: -26.7%; 95% CI: -30.9%, -22.2%; FA800: -27.8%; 95% CI: -31.8%, -23.4%) than in the placebo group (-12.3%; 95% CI: -18.1%, -6.2%; P < 0.01). The percentage change in choline, betaine, and DMG did not differ between creatine treatment arms and their respective reference groups. CONCLUSION: Supplementation for 12 wk with FA, but not creatine, increases plasma betaine, decreases plasma DMG, and prevents a decrease in plasma choline in arsenic-exposed Bangladeshi adults. This trial was registered at clinicaltrials.gov as NCT01050556.

Low-Dose Creatine Supplementation Lowers Plasma Guanidinoacetate, but Not Plasma Homocysteine, in a Double-Blind, Randomized, Placebo-Controlled Trial.

BACKGROUND: Creatine synthesis from guanidinoacetate consumes ~50% of s-adenosylmethionine (SAM)-derived methyl groups, accounting for an equivalent proportion of s-adenosylhomocysteine (SAH) and total homocysteine (tHcys) synthesis. Dietary creatine inhibits the synthesis of guanidinoacetate, thereby lowering plasma tHcys in rats. OBJECTIVE: We tested the hypotheses that creatine supplementation lowers plasma guanidinoacetate, increases blood SAM, lowers blood SAH, and lowers plasma tHcys. METHODS: Bangladeshi adults were randomly assigned to receive 1 of 4 treatments for 12 wk: placebo (n = 101), 3 g/d creatine (Cr; n = 101), 400 µg/d folic acid (FA; n = 153), or 3 g/d creatine plus 400 µg/d folic acid (Cr+FA; n = 103). The outcomes of plasma guanidinoacetate and tHcys, as well as whole blood SAM and SAH, were analyzed at baseline and week 12 by HPLC. Treatment effects of creatine supplementation were examined with the use of the group comparisons of Cr vs. placebo and Cr+FA vs. FA. RESULTS: Plasma guanidinoacetate declined by 10.6% (95% CI: 4.9, 15.9) in the Cr group while increasing nonsignificantly in the placebo group (3.7%; 95% CI: -0.8, 8.5) (Pgroup difference = 0.0002). Similarly, plasma guanidinoacetate declined by 9.0% (95% CI: 3.4, 14.2) in the Cr+FA group while increasing in the FA group (7.0%; 95% CI: 2.0, 12.2) (Pgroup difference < 0.0001). Plasma tHcys declined by 23.4% (95% CI: 19.5, 27.1) and 21.0% (95% CI: 16.4, 25.2) in the FA and Cr+FA groups, respectively (Pgroup difference = 0.41), with no significant changes in the placebo or Cr groups (Pgroup difference = 0.35). A decrease in guanidinoacetate over time was associated with a decrease in tHcys over time in the Cr+FA group (ß = 0.30; 95% CI: 0.17, 0.43; P < 0.0001). CONCLUSIONS: Our findings indicate that whereas creatine supplementation downregulates endogenous creatine synthesis, this may not on average lower plasma tHcys in humans. However, tHcys did decrease in those participants who experienced a decline in plasma guanidinoacetate while receiving creatine plus folic acid supplementation. This trial was registered at clinicaltrials.gov as NCT01050556.

Renal function is associated with indicators of arsenic methylation capacity in Bangladeshi adults.

BACKGROUND: Arsenic (As) methylation capacity in epidemiologic studies is typically indicated by the proportions of inorganic As (%InAs), monomethylarsonic acid (%MMA), and dimethylarsinic acid (%DMA) in urine as a fraction of total urinary As. The relationship between renal function and indicators of As methylation capacity has not been thoroughly investigated. OBJECTIVES: Our two aims were to examine (1) associations between estimated glomerular filtration rate (eGFR) and %As metabolites in blood and urine, and (2) whether renal function modifies the relationship of blood %As metabolites with respective urinary %As metabolites. METHODS: In a cross-sectional study of 375 As-exposed Bangladeshi adults, we measured blood and urinary As metabolites, and calculated eGFR from plasma cystatin C. RESULTS: In covariate-adjusted linear models, a 1 ml/min/1.73 m(2) increase in eGFR was associated with a 0.39% increase in urinary %InAs (p<0.0001) and a mean decrease in urinary %DMA of 0.07 (p=0.0005). In the 292 participants with measurable blood As metabolites, the associations of eGFR with increased blood %InAs and decreased blood %DMA did not reach statistical significance. eGFR was not associated with urinary or blood %MMA in covariate-adjusted models. For a given increase in blood %InAs, the increase in urinary %InAs was smaller in those with reduced eGFR, compared to those with normal eGFR (p=0.06); this effect modification was not observed for %MMA or %DMA. CONCLUSIONS: Urinary excretion of InAs may be impaired in individuals with reduced renal function. Alternatively, increased As methylation capacity (as indicated by decreased urinary %InAs) may be detrimental to renal function.

Folate and cobalamin modify associations between S-adenosylmethionine and methylated arsenic metabolites in arsenic-exposed Bangladeshi adults.

Chronic exposure to inorganic arsenic (InAs) through drinking water is a major problem worldwide. InAs undergoes hepatic methylation to form mono- and dimethyl arsenical species (MMA and DMA, respectively), facilitating arsenic elimination. Both reactions are catalyzed by arsenic (+3 oxidation state) methyltransferase (AS3MT) using S-adenosylmethionine (SAM) as the methyl donor, yielding the methylated product and S-adenosylhomocysteine (SAH), a potent product-inhibitor of AS3MT. SAM biosynthesis depends on folate- and cobalamin-dependent one-carbon metabolism. With the use of samples from 353 participants in the Folate and Oxidative Stress Study, our objective was to test the hypotheses that blood SAM and SAH concentrations are associated with arsenic methylation and that these associations differ by folate and cobalamin nutritional status. Blood SAM and SAH were measured by HPLC. Arsenic metabolites in blood and urine were measured by HPLC coupled to dynamic reaction cell inductively coupled plasma MS. In linear regression analyses, SAH was not associated with any of the arsenic metabolites. However, log(SAM) was negatively associated with log(% urinary InAs) (ß: -0.11; 95% CI: -0.19, -0.02; P = 0.01), and folate and cobalamin nutritional status significantly modified associations between SAM and percentage of blood MMA (%bMMA) and percentage of blood DMA (%bDMA) (P = 0.02 and P = 0.01, respectively). In folate- and cobalamin-deficient individuals, log(SAM) was positively associated with %bMMA (ß: 6.96; 95% CI: 1.86, 12.05; P < 0.01) and negatively associated with %bDMA (ß: -6.19; 95% CI: -12.71, 0.32; P = 0.06). These findings suggest that when exposure to InAs is high, and methyl groups are limiting, SAM is used primarily for MMA synthesis rather than for DMA synthesis, contributing additional evidence that nutritional status may explain some of the interindividual differences in arsenic metabolism and, consequently, susceptibility to arsenic toxicity.

Mathematical modeling of the effects of glutathione on arsenic methylation.

BACKGROUND: Arsenic is a major environmental toxin that is detoxified in the liver by biochemical mechanisms that are still under study. In the traditional metabolic pathway, arsenic undergoes two methylation reactions, each followed by a reduction, after which it is exported and released in the urine. Recent experiments show that glutathione plays an important role in arsenic detoxification and an alternative biochemical pathway has been proposed in which arsenic is first conjugated by glutathione after which the conjugates are methylated. In addition, in rats arsenic-glutathione conjugates can be exported into the plasma and removed by the liver in the bile. METHODS: We have developed a mathematical model for arsenic biochemistry that includes three mechanisms by which glutathione affects arsenic methylation: glutathione increases the speed of the reduction steps; glutathione affects the activity of arsenic methyltranferase; glutathione sequesters inorganic arsenic and its methylated downstream products. The model is based as much as possible on the known biochemistry of arsenic methylation derived from cellular and experimental studies. RESULTS: We show that the model predicts and helps explain recent experimental data on the effects of glutathione on arsenic methylation. We explain why the experimental data imply that monomethyl arsonic acid inhibits the second methylation step. The model predicts time course data from recent experimental studies. We explain why increasing glutathione when it is low increases arsenic methylation and that at very high concentrations increasing glutathione decreases methylation. We explain why the possible temporal variation of the glutathione concentration affects the interpretation of experimental studies that last hours. CONCLUSIONS: The mathematical model aids in the interpretation of data from recent experimental studies and shows that the Challenger pathway of arsenic methylation, supplemented by the glutathione effects described above, is sufficient to understand and predict recent experimental data. More experimental studies are needed to explicate the detailed mechanisms of action of glutathione on arsenic methylation. Recent experimental work on the effects of glutathione on arsenic methylation and our modeling study suggest that supplements that increase hepatic glutathione production should be considered as strategies to reduce adverse health effects in affected populations.

The Folic Acid and Creatine Trial: Treatment Effects of Supplementation on Arsenic Methylation Indices and Metabolite Concentrations in Blood in a Bangladeshi Population.

BACKGROUND: Chronic arsenic (As) exposure is a global environmental health issue. Inorganic As (InAs) undergoes methylation to monomethyl (MMAs) and dimethyl-arsenical species (DMAs); full methylation to DMAs facilitates urinary excretion and is associated with reduced risk for As-related health outcomes. Nutritional factors, including folate and creatine, influence one-carbon metabolism, the biochemical pathway that provides methyl groups for As methylation. OBJECTIVE: Our aim was to investigate the effects of supplementation with folic acid (FA), creatine, or the two combined on the concentrations of As metabolites and the primary methylation index (PMI: MMAs/InAs) and secondary methylation index (SMI: DMAs/MMAs) in blood in Bangladeshi adults having a wide range of folate status. METHODS: In a randomized, double-blinded, placebo (PBO)-controlled trial, 622 participants were recruited independent of folate status and assigned to one of five treatment arms: a) PBO (n=102), b) 400µg FA/d (400FA; n=153), c) 800µg FA/d (800FA; n=151), d) 3g creatine/d (creatine; n=101), or e) 3g creatine+400µg of FA/d (creatine+400FA; n=103) for 12 wk. For the following 12 wk, half of the FA participants were randomly switched to the PBO while the other half continued FA supplementation. All participants received As-removal water filters at baseline. Blood As (bAs) metabolites were measured at weeks 0, 1, 12, and 24. RESULTS: At baseline, 80.3% (n=489) of participants were folate sufficient (≥9 nmol/L in plasma). In all groups, bAs metabolite concentrations decreased, likely due to filter use; for example, in the PBO group, blood concentrations of MMAs (bMMAs) (geometric mean±geometric standard deviation) decreased from 3.55±1.89µg/L at baseline to 2.73±1.74 at week 1. After 1 wk, the mean within-person increase in SMI for the creatine+400FA group was greater than that of the PBO group (p=0.05). The mean percentage decrease in bMMAs between baseline and week 12 was greater for all treatment groups compared with the PBO group [400FA: -10.4 (95% CI: -11.9, -8.75), 800FA: -9.54 (95% CI: -11.1, -7.97), creatine: -5.85 (95% CI: -8.59, -3.03), creatine+400FA: -8.44 (95% CI: -9.95, -6.90), PBO: -2.02 (95% CI: -4.03, 0.04)], and the percentage increase in blood DMAs (bDMAs) concentrations for the FA-treated groups significantly exceeded that of PBO [400FA: 12.8 (95% CI: 10.5, 15.2), 800FA: 11.3 (95% CI: 8.95, 13.8), creatine+400FA: 7.45 (95% CI: 5.23, 9.71), PBO: -0.15 (95% CI: -2.85, 2.63)]. The mean decrease in PMI and increase in SMI in all FA groups significantly exceeded PBO (p<0.05). Data from week 24 showed evidence of a reversal of treatment effects on As metabolites from week 12 in those who switched from 800FA to PBO, with significant decreases in SMI [-9.0% (95% CI: -3.5, -14.8)] and bDMAs [-5.9% (95% CI: -1.8, -10.2)], whereas PMI and bMMAs concentrations continued to decline [-7.16% (95% CI: -0.48, -14.3) and -3.1% (95% CI: -0.1, -6.2), respectively] for those who remained on 800FA supplementation. CONCLUSIONS: FA supplementation lowered bMMAs and increased bDMAs in a sample of primarily folate-replete adults, whereas creatine supplementation lowered bMMAs. Evidence of the reversal of treatment effects on As metabolites following FA cessation suggests short-term benefits of supplementation and underscores the importance of long-term interventions, such as FA fortification. https://doi.org/10.1289/EHP11270.

Mathematical model insights into arsenic detoxification.

BACKGROUND: Arsenic in drinking water, a major health hazard to millions of people in South and East Asia and in other parts of the world, is ingested primarily as trivalent inorganic arsenic (iAs), which then undergoes hepatic methylation to methylarsonic acid (MMAs) and a second methylation to dimethylarsinic acid (DMAs). Although MMAs and DMAs are also known to be toxic, DMAs is more easily excreted in the urine and therefore methylation has generally been considered a detoxification pathway. A collaborative modeling project between epidemiologists, biologists, and mathematicians has the purpose of explaining existing data on methylation in human studies in Bangladesh and also testing, by mathematical modeling, effects of nutritional supplements that could increase As methylation. METHODS: We develop a whole body mathematical model of arsenic metabolism including arsenic absorption, storage, methylation, and excretion. The parameters for arsenic methylation in the liver were taken from the biochemical literature. The transport parameters between compartments are largely unknown, so we adjust them so that the model accurately predicts the urine excretion rates of time for the iAs, MMAs, and DMAs in single dose experiments on human subjects. RESULTS: We test the model by showing that, with no changes in parameters, it predicts accurately the time courses of urinary excretion in mutiple dose experiments conducted on human subjects. Our main purpose is to use the model to study and interpret the data on the effects of folate supplementation on arsenic methylation and excretion in clinical trials in Bangladesh. Folate supplementation of folate-deficient individuals resulted in a 14% decrease in arsenicals in the blood. This is confirmed by the model and the model predicts that arsenicals in the liver will decrease by 19% and arsenicals in other body stores by 26% in these same individuals. In addition, the model predicts that arsenic methyltransferase has been upregulated by a factor of two in this population. Finally, we also show that a modification of the model gives excellent fits to the data on arsenic metabolism in human cultured hepatocytes. CONCLUSIONS: The analysis of the Bangladesh data using the model suggests that folate supplementation may be more effective at reducing whole body arsenic than previously expected. There is almost no data on the upregulation of arsenic methyltransferase in populations chronically exposed to arsenic. Our model predicts upregulation by a factor of two in the Bangladesh population studied. This prediction should be verified since it could have important public health consequences both for treatment strategies and for setting appropriate limits on arsenic in drinking water. Our model has compartments for the binding of arsenicals to proteins inside of cells and we show that these comparments are necessary to obtain good fits to data. Protein-binding of arsenicals should be explored in future biochemical studies.

Folic acid supplementation enhances arsenic methylation: results from a folic acid and creatine supplementation randomized controlled trial in Bangladesh.

Background: Arsenic exposure through drinking water persists in many regions. Inorganic As (InAs) is methylated to monomethyl-arsenical species (MMAs) and dimethyl-arsenical species (DMAs), facilitating urinary excretion. Arsenic methylation is dependent on one-carbon metabolism, which is influenced by nutritional factors such as folate and creatine. Objective: This study investigated the effects of folic acid (FA) and/or creatine supplementation on the proportion of As metabolites in urine. Design: In a 24-wk randomized, double-blinded, placebo-controlled trial, 622 participants were assigned to receive FA (400 or 800 µg per day), 3 g creatine per day, 400 µg FA + 3 g creatine per day, or placebo. The majority of participants were folate sufficient; all received As-removal water filters. From wk 12-24, half of the participants receiving FA received placebo. Results: Among groups receiving FA, the mean decrease in ln(%InAs) and %MMAs and increase in %DMAs exceeded those of the placebo group at wk 6 and 12 (P < 0.05). In the creatine group, the mean decrease in %MMAs exceeded that of the placebo group at wk 6 and 12 (P < 0.05); creatine supplementation did not affect change in %InAs or %DMAs. The decrease in %MMAs at wk 6 and 12 was larger in the 800 µg FA than in the 400 µg FA group (P = 0.034). There were no differences in treatment effects between the 400 µg FA and creatine + FA groups. Data suggest a rebound in As metabolite proportions after FA cessation; at wk 24, log(%InAs) and %DMAs were not significantly different than baseline levels among participants who discontinued FA supplementation. Conclusions: The results of this study confirm that FA supplementation rapidly and significantly increases methylation of InAs to DMAs. Further research is needed to understand the strong cross-sectional associations between urinary creatinine and As methylation in previous studies. This trial was registered at https://clinicaltrials.gov as NCT01050556.

A 22-year prospective study of fish, n-3 fatty acid intake, and colorectal cancer risk in men.

BACKGROUND: Fish is the main dietary source of long-chain n-3 fatty acids, which have been suggested to play a protective role in colorectal cancer development in laboratory and animal studies. Human studies have not shown consistent results. We examined the association between intakes of fish and n-3 fatty acids from fish and colorectal cancer risk in men enrolled in the Physicians' Health Study. METHODS: The Physicians' Health Study began as a randomized trial to examine the effect of aspirin and beta-carotene supplementation on cancer and cardiovascular disease. Fish intake was assessed at the 12-month follow-up with an abbreviated food-frequency questionnaire. Cox proportional hazards models were used to estimate multivariate relative risks for colorectal cancer for the categories of fish intake and quartiles of n-3 fatty acid intake. RESULTS: During 22 years of follow-up, 500 men had a confirmed diagnosis of colorectal cancer. Fish intake was inversely associated with colorectal cancer risk [multivariate relative risk (95% confidence interval) for highest versus lowest category, 0.63 (0.42-0.95); P trend = 0.02] [corrected] The inverse association was observed for both colon and rectal cancers. Our findings for n-3 fatty acids were similar to those for fish; the multivariate relative risk (95% confidence interval) of total colorectal cancer for the highest versus lowest quartile of n-3 fatty acids was 0.74 (0.57-0.95; P trend = 0.01). CONCLUSIONS: Our results from this long-term prospective study suggest that intakes of fish and long-chain n-3 fatty acids from fish may decrease the risk for colorectal cancer.

The South African Rea Phela Health Study: A randomized controlled trial of communication retention strategies.

Epidemiological transitions are occurring throughout Africa. To inform public health programs and policies, longitudinal cohorts investigating non-communicable diseases are needed. However, loss-to-follow up is a major problem. In preparation for a longitudinal study, we conducted a randomized controlled trial to test communication-based retention strategies (message content and delivery methods) among a pilot cohort of South African healthcare workers (n = 1536; median age = 36; women = 1270). Two messaging formats across three delivery modes were tested. Response rates were analyzed by intervention, survey return date and method using chi-square tests and univariate logistic regression. Sixty-seven of 238 (17.4%) control group participants and 238 of 1152 (24.6%) intervention group participants were retained (OR 1.54: CI 1.15-2.07; P = 0.004). Odds of being retained were 1.68 times greater for participants who received regular contact and themed messages compared to control (CI 1.22-2.32; P = 0.001). Neither health status nor clinical condition affected response rates (P>0.05). Time-to-first contact did not impact response rates (P>0.05). Message content and delivery method influenced response rates compared to the control, however no difference was found between intervention groups. Although greater retention is required for valid cohort studies, these findings are the first to quantitatively assess retention factors in Africa.

Serum homocysteine, arsenic methylation, and arsenic-induced skin lesion incidence in Bangladesh: A one-carbon metabolism candidate gene study.

BACKGROUND: Inorganic arsenic (As) is methylated via one carbon metabolism (OCM) to mono- and dimethylated arsenicals (MMA and DMA), facilitating urinary excretion. Hyperhomocysteinemia (HHcys), a marker of impaired OCM, is a risk factor for As-induced skin lesions, but the influences of single nucleotide polymorphisms (SNPs) in OCM genes on Hcys, As metabolism and skin lesion risk is unclear. OBJECTIVES: To (i) explore genetic sources of Hcys and the causal role of HHcys in As-induced skin lesion development using OCM genetic proxies for HHcys and (ii) identify OCM SNPs associated with urinary As metabolite proportions and/or skin lesion incidence. METHODS: We conducted a case-control study nested in the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh which 876 incident skin lesion cases were matched to controls on sex, age, and follow-up time. We measured serum Hcys, urinary As metabolites, and 26 SNPs in 13 OCM genes. RESULTS: Serum Hcys and urinary %DMA were independently associated with increased and decreased odds of skin lesions, respectively. The T allele of MTHFR 677 C ➔ T (rs1801133) was associated with HHcys, higher %MMA, and lower %DMA, but not with skin lesions. Interactions between SNPs and water As on skin lesion risk were suggestive for three variants: the G allele of MTRR rs1801394 and T allele of FOLR1 rs1540087 were associated with lower odds of skin lesions with lower As (≤50 µg/L), and the T allele of TYMS rs1001761 was associated with higher odds of skin lesions with higher As. CONCLUSIONS: While HHcys and decreased %DMA were associated with increased risk for skin lesions, and MTHFR 677 C ➔ T was a strong predictor of HHcys, MTHFR 677 C ➔ T was not associated with skin lesion risk. Future studies should explore (i) non-OCM and non-genetic determinants of Hcys and (ii) if genetic findings are replicated in other As-exposed populations, mechanisms by which OCM SNPs may influence the dose-dependent effects of As on skin lesion risk.

Blood levels of long-chain polyunsaturated fatty acids, aspirin, and the risk of colorectal cancer.

BACKGROUND: N-3 fatty acids may decrease risk of colorectal cancer by inhibiting the cyclooxygenase-2 enzyme and production of proinflammatory eicosanoids derived from arachidonic acid (20:4n-6). Aspirin also inhibits the cyclooxygenase-2 enzyme and may share with n-3 fatty acids a potential mechanism to decrease the risk of colorectal cancer. METHODS: We conducted a nested case-control analysis using blood samples collected from the Physicians' Health Study participants in 1982 to 1984. N-3 and n-6 fatty acid levels were measured using gas-liquid chromatography for 178 men who developed colorectal cancer through December 31, 1995 and 282 age- and smoking-matched controls. We used conditional logistic regression to examine associations. All statistical tests were two-sided. RESULTS: Total long-chain n-3 fatty acids were nonsignificantly inversely associated with colorectal cancer risk [relative risk (RR) for highest versus lowest quartile, 0.60; 95% confidence interval (95% CI), 0.32 to 1.11; P(trend) = 0.10], after adjustment for possible confounders. We observed potential interaction between randomized aspirin assignment and long-chain n-3 fatty acid levels (P(interaction) = 0.04). Among men not on aspirin, RRs (95% CI) for increasing quartiles of long-chain n-3 fatty acids were 1.00 (reference), 0.60 (0.28-1.28), 0.51 (0.22-1.17), and 0.34 (0.15-0.82), P(trend) = 0.006. For participants taking aspirin, there was no additional benefit of increasing n-3 fatty acid levels. The RR (95% CI) for the highest versus lowest quartile of n-6 fatty acids was 0.64 (0.35-1.17). CONCLUSIONS: Blood levels of long-chain n-3 fatty acids were associated with decreased risk of colorectal cancer among men not using aspirin. N-6 fatty acids were nonsignificantly inversely associated with colorectal cancer risk.

Sex-Specific Associations between One-Carbon Metabolism Indices and Posttranslational Histone Modifications in Arsenic-Exposed Bangladeshi Adults.

BACKGROUND: Posttranslational histone modifications (PTHMs) are altered by arsenic, an environmental carcinogen. PTHMs are also influenced by nutritional methyl donors involved in one-carbon metabolism (OCM), which may protect against epigenetic dysregulation. METHODS: We measured global levels of three PTHMs, which are dysregulated in cancers (H3K36me2, H3K36me3, H3K79me2), in peripheral blood mononuclear cells (PBMC) from 324 participants enrolled in the Folic Acid and Creatine Trial, a randomized trial in arsenic-exposed Bangladeshi adults. Sex-specific associations between several blood OCM indices (folate, vitamin B12, choline, betaine, homocysteine) and PTHMs were examined at baseline using regression models, adjusted for multiple tests by controlling for the false discovery rate (PFDR). We also evaluated the effects of folic acid supplementation (400 µg/d for 12 weeks), compared with placebo, on PTHMs. RESULTS: Associations between choline and H3K36me2 and between vitamin B12 and H3K79me2 differed significantly by sex (Pdiff < 0.01 and <0.05, respectively). Among men, plasma choline was positively associated with H3K36me2 (PFDR < 0.05), and among women, plasma vitamin B12 was positively associated with H3K79me2 (PFDR < 0.01). Folic acid supplementation did not alter any of the PTHMs examined (PFDR = 0.80). CONCLUSIONS: OCM indices may influence PTHMs in a sex-dependent manner, and folic acid supplementation, at this dose and duration, does not alter PTHMs in PBMCs. IMPACT: This is the first study to examine the influences of OCM indices on PTHMs in a population that may have increased susceptibility to cancer development due to widespread exposure to arsenic-contaminated drinking water and a high prevalence of hyperhomocysteinemia. Cancer Epidemiol Biomarkers Prev; 26(2); 261-9. ©2016 AACR.

Associations between Blood and Urine Arsenic Concentrations and Global Levels of Post-Translational Histone Modifications in Bangladeshi Men and Women.

BACKGROUND: Exposure to inorganic arsenic is associated with numerous adverse health outcomes, with susceptibility differing by sex. Although evidence from in vitro studies suggests that arsenic alters post-translational histone modifications (PTHMs), evidence in humans is limited. OBJECTIVES: The objectives were to determine: a) if arsenic exposure is associated with global (percent) levels of PTHMs H3K36me2, H3K36me3, and H3K79me2 in a sex-dependent manner, and b) if %PTHMs are stable when arsenic exposure is reduced. METHODS: We examined associations between arsenic, measured in blood and urine, and %PTHMs in peripheral blood mononuclear cells from 317 participants enrolled in the Bangladesh Folic Acid and Creatine Trial (FACT). We also examined the stability of %PTHMs after the use of arsenic-removal water filters (n = 60). RESULTS: Associations between natural log-transformed (ln) urinary arsenic, adjusted for creatinine (uAsCr), and %H3K36me2 differed significantly between men and women (p = 0.01). ln(uAsCr) was positively associated with %H3K36me2 in men [ß = 0.12; 95% confidence interval (CI): 0.01, 0.23, p = 0.03] but was negatively associated with %H3K36me2 in women (ß = -0.05; 95% CI: -0.12, 0.02, p = 0.19). The patterns of associations with blood arsenic were similar. On average, water filter use was also associated with reductions in %H3K36me2 (p < 0.01), but this did not differ significantly by sex. Arsenic was not significantly associated with %H3K36me3 or %H3K79me2 in men or women. CONCLUSIONS: Arsenic exposure was associated with %H3K36me2 in a sex-specific manner but was not associated with %H3K36me3 or %H3K79me2. Additional studies are needed to assess changes in %H3K36me2 after arsenic removal. CITATION: Howe CG, Liu X, Hall MN, Slavkovich V, Ilievski V, Parvez F, Siddique AB, Shahriar H, Uddin MN, Islam T, Graziano JH, Costa M, Gamble MV. 2016. Associations between blood and urine arsenic concentrations and global levels of post-translational histone modifications in Bangladeshi men and women. Environ Health Perspect 124:1234-1240; http://dx.doi.org/10.1289/ehp.1510412.

Mathematical analysis of the regulation of competing methyltransferases.

BACKGROUND: Methyltransferase (MT) reactions, in which methyl groups are attached to substrates, are fundamental to many aspects of cell biology and human physiology. The universal methyl donor for these reactions is S-adenosylmethionine (SAM) and this presents the cell with an important regulatory problem. If the flux along one pathway is changed then the SAM concentration will change affecting all the other MT pathways, so it is difficult for the cell to regulate the pathways independently. METHODS: We created a mathematical model, based on the known biochemistry of the folate and methionine cycles, to study the regulatory mechanisms that enable the cell to overcome this difficulty. Some of the primary mechanisms are long-range allosteric interactions by which substrates in one part of the biochemical network affect the activity of enzymes at distant locations in the network (not distant in the cell). Because of these long-range allosteric interactions, the dynamic behavior of the network is very complicated, and so mathematical modeling is a useful tool for investigating the effects of the regulatory mechanisms and understanding the complicated underlying biochemistry and cell biology. RESULTS: We study the allosteric binding of 5-methyltetrahydrofolate (5 mTHF) to glycine-N-methyltransferase (GNMT) and explain why data in the literature implies that when one molecule binds, GNMT retains half its activity. Using the model, we quantify the effects of different regulatory mechanisms and show how cell processes would be different if the regulatory mechanisms were eliminated. In addition, we use the model to interpret and understand data from studies in the literature. Finally, we explain why a full understanding of how competing MTs are regulated is important for designing intervention strategies to improve human health. CONCLUSIONS: We give strong computational evidence that once bound GNMT retains half its activity. The long-range allosteric interactions enable the cell to regulate the MT reactions somewhat independently. The low K m values of many MTs also play a role because the reactions then run near saturation and changes in SAM have little effect. Finally, the inhibition of the MTs by the product S-adenosylhomocysteine also stabilizes reaction rates against changes in SAM.

Arsenic exposure, inflammation, and renal function in Bangladeshi adults: effect modification by plasma glutathione redox potential.

Exposure to arsenic (As) in drinking water is a widespread public health problem leading to increased risk for multiple outcomes such as cancer, cardiovascular disease, and possibly renal disease; potential mechanisms include inflammation and oxidative stress. We tested the hypothesis that As exposure is associated with increased inflammation and decreased estimated glomerular filtration rate (eGFR) and examined whether the effects of As were modified by plasma glutathione (GSH), glutathione disulfide (GSSG), or the reduction potential of the GSSG/2GSH pair (EhGSH). In a cross-sectional study of N = 374 Bangladeshi adults having a wide range of As exposure, we measured markers of inflammation (plasma C-reactive protein (CRP), α-1 acid glycoprotein (AGP)), renal function (eGFR), GSH, and GSSG. In covariate-adjusted models, a 10% increase in water As, urinary As adjusted for specific gravity (uAs), or blood As (bAs) was associated with a 0.74% (p = 0.01), 0.90% (p = 0.16), and 1.39% (p = 0.07) increase in CRP, respectively; there was no association with AGP. A 10% increase in uAs or bAs was associated with an average reduction in eGFR of 0.16 (p = 0.12) and 0.21 ml/min/1.73 m(2) (p = 0.08), respectively. In stratified analyses, the effect of As exposure on CRP was observed only in participants having EhGSH > median (uAs p(Wald) = 0.03; bAs p(Wald) = 0.05). This was primarily driven by stronger effects of As exposure on CRP in participants with lower plasma GSH. The effects of As exposure on eGFR were not modified significantly by EhGSH, GSH, or GSSG. These data suggest that participants having lower plasma GSH and a more oxidized plasma EhGSH are at increased risk for As-induced inflammation. Future studies should evaluate whether antioxidant treatment lowers plasma EhGSH and reduces risk for As-induced diseases.

Sex-specific associations of arsenic exposure with global DNA methylation and hydroxymethylation in leukocytes: results from two studies in Bangladesh.

BACKGROUND: Depletion of global 5-hydroxymethylcytosine (5-hmC) is observed in human cancers and is strongly implicated in skin cancer development. Although arsenic (As)-a class I human carcinogen linked to skin lesion and cancer risk-is known to be associated with changes in global %5-methylcytosine (%5-mC), its influence on 5-hmC has not been widely studied. METHODS: We evaluated associations of As in drinking water, urine, and blood with global %5-mC and %5-hmC in two studies of Bangladeshi adults: (i) leukocyte DNA in the Nutritional Influences on Arsenic Toxicity study (n = 196; 49% male, 19-66 years); and (ii) peripheral blood mononuclear cell DNA in the Folate and Oxidative Stress study (n = 375; 49% male, 30-63 years). RESULTS: Overall, As was not associated with global %5-mC or %5-hmC. Sex-specific analyses showed that associations of As exposure with global %5-hmC were positive in males and negative in females (P for interaction < 0.01). Analyses examining interactions by elevated plasma total homocysteine (tHcys), an indicator of B-vitamin deficiency, found that tHcys also modified the association between As and global %5-hmC (P for interaction < 0.10). CONCLUSION: In two samples, we observed associations between As exposure and global %5-hmC in blood DNA that were modified by sex and tHcys. IMPACT: Our findings suggest that As induces sex-specific changes in 5-hmC, an epigenetic mark that has been associated with cancer. Future research should explore whether altered %5-hmC is a mechanism underlying the sex-specific influences of As on skin lesion and cancer outcomes.

Folic Acid and Creatine as Therapeutic Approaches to Lower Blood Arsenic: A Randomized Controlled Trial.

BACKGROUND: The World Health Organization estimates that > 140 million people worldwide are exposed to arsenic (As)-contaminated drinking water. As undergoes biologic methylation, which facilitates renal As elimination. In folate-deficient individuals, this process is augmented by folic acid (FA) supplementation, thereby lowering blood As (bAs). Creatinine concentrations in urine are a robust predictor of As methylation patterns. Although the reasons for this are unclear, creatine synthesis is a major consumer of methyl donors, and this synthesis is down-regulated by dietary/supplemental creatine. OBJECTIVES: Our aim was to determine whether 400 or 800 µg FA and/or creatine supplementation lowers bAs in an As-exposed Bangladeshi population. METHODS: We conducted a clinical trial in which 622 participants were randomized to receive 400 µg FA, 800 µg FA, 3 g creatine, 3 g creatine+400 µg FA, or placebo daily. All participants received an As-removal filter on enrollment, and were followed for 24 weeks. After the 12th week, half of the two FA groups were switched to placebo to evaluate post-treatment bAs patterns. RESULTS: Linear models with repeated measures indicated that the decline in ln(bAs) from baseline in the 800-µg FA group exceeded that of the placebo group (weeks 1-12: ß= -0.09, 95% CI: -0.18, -0.01; weeks 13-24: FA continued: ß= -0.12, 95% CI: -0.24, -0.00; FA switched to placebo: ß= -0.14, 95% CI: -0.26, -0.02). There was no rebound in bAs related to cessation of FA supplementation. Declines in bAs observed in the remaining treatment arms were not significantly different from those of the placebo group. CONCLUSIONS: In this mixed folate-deficient/replete study population, 12- and 24-week treatment with 800 µg (but not 400 µg) FA lowered bAs to a greater extent than placebo; this was sustained 12 weeks after FA cessation. In future studies, we will evaluate whether FA and/or creatine altered As methylation profiles.

Creatinine, arsenic metabolism, and renal function in an arsenic-exposed population in Bangladesh.

Kidney disease is emerging as an arsenic (As)-linked disease outcome, however further evidence of this association is warranted. Our first objective for this paper was to examine the potential renal toxicity of As exposure in Bangladesh. Our second objective relates to examining whether the previously reported positive association between urinary creatinine (uCrn) and As methylation may be explained by renal function. We had hypothesized that these associations relate to supply and demand for s-adenosylmethionine, the methyl donor for both creatine synthesis and As methylation. Alternatively, renal function could influence both As and creatinine excretion, or the As metabolites may influence renal function, which in turn influences uCrn. We conducted a cross-sectional study (N = 478) of adults, composed of a sample recruited in 2001 and a sample recruited in 2003. We assessed renal function using plasma cystatin C, and calculated the estimated glomerular filtration rate (eGFR). Consistent with renal toxicity of As, log-uAs had a marginal inverse association with eGFR in the 2003 sample (b = -5.6, p = 0.07), however this association was not significant in the 2001 sample (b = -1.9, p = 0.24). Adjustment for eGFR did not alter the associations between uCrn and the %uAs metabolites, indicating that GFR does not explain these associations. Increased eGFR was associated with increased odds of having %uInAs >12.2% (2001: OR = 1.01, 95%CI (1.00,1.03); 2003: OR = 1.04, 95%CI (1.01,1.07)). In the 2003 sample only, there was a negative association between eGFR and %uDMA (b = -0.08, p = 0.02). These results may indicate differential effects of renal function on excretion of InAs and DMA. Alternatively, a certain methylation pattern, involving decreased %InAs and increased %DMA, may reduce renal function. Given that these studies were cross-sectional, we cannot distinguish between these two possibilities. Discrepancies between the samples may be due to the higher As exposure, poorer nutrition, and lower As methylation capacity in the 2003 sample.