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Proteinuria has been recognized as a marker for an increased risk of chronic renal disease. It is unclear whether arsenic (As) exposure from drinking water is associated with proteinuria.We evaluated the association between As exposure from drinking water and proteinuria in 11,122 participants in the Health Effects of Arsenic Longitudinal Study (HEALS). Proteinuria was detected by urinary dipstick tests at baseline and at 2-year intervals. As exposure variables included baseline well As and changes in urinary As during follow-up modelled as time-dependent variables in the analyses.At baseline, well As was positively related to prevalence of proteinuria; prevalence odds ratios (PORs) for proteinuria in increasing quintiles of well As (≤ 7, 8-39, 40-91, 92-179 and 180-864 µg/l) were 1.00 (ref), POR 0.99 [95% confidence interval (CI) 0.77-1.27], POR 1.23 (95% CI 0.97-1.57), POR 1.50 (95% CI 1.18-1.89) and POR 1.59 (95% CI 1.26-2.00) (P for trend0.01). Hazard ratios for incidence of proteinuria were POR 0.83 (95% CI 0.67-1.03) and POR 0.91 (95% CI 0.74-1.12) for participants with a decreasing level of70 and 17-70 µg/l in urinary As over time, respectively, and were POR 1.17 (95% CI 0.97-1.42) and POR 1.42 (95% CI 1.16-1.73) for participants with an increasing level of 16-68 and68 µg/l in urinary As over time, respectively, compared with the group with relatively little changes in urinary As as the reference group (urinary As -16 to 15 µg/l).The findings suggest that there are adverse effects of As exposure on the risk of proteinuria and the effects are modifiable by recent changes in As exposure.

The contamination of groundwater by arsenic in Bangladesh is a major public health concern affecting 35-75 million people. Although it is evident that high levels (>300 microg/L) of arsenic exposure from drinking water are related to adverse health outcomes, health effects of arsenic exposure at low-to-moderate levels (10-300 microg/L) are not well understood. We established the Health Effects of Arsenic Longitudinal Study (HEALS) with more than 20,000 men and women in Araihazar, Bangladesh, to prospectively investigate the health effects of arsenic predominantly at low-to-moderate levels (0.1 to 864 microg/L, mean 99 microg/L) of arsenic exposure. Findings to date suggest adverse effects of low-to-moderate levels of arsenic exposure on the risk of pre-malignant skin lesions, high blood pressure, neurological dysfunctions, and all-cause and chronic disease mortality. In addition, the data also indicate that the risk of skin lesion due to arsenic exposure is modifiable by nutritional factors, such as folate and selenium status, lifestyle factors, including cigarette smoking and body mass index, and genetic polymorphisms in genes related to arsenic metabolism. The analyses of biomarkers for respiratory and cardiovascular functions support that there may be adverse effects of arsenic on these outcomes and call for confirmation in large studies. A unique strength of the HEALS is the availability of outcome data collected prospectively and data on detailed individual-level arsenic exposure estimated using water, blood and repeated urine samples. Future prospective analyses of clinical endpoints and related host susceptibility will enhance our knowledge on the health effects of low-to-moderate levels of arsenic exposure, elucidate disease mechanisms, and give directions for prevention.

One plausible mechanism for the environment to alter cancer susceptibility is through DNA methylation. Alterations in DNA methylation can lead to genomic instability and altered gene transcription. Genomic DNA methylation levels have been inversely associated with age, suggesting that factors throughout life may be associated with declines in DNA methylation. Using information from a multiethnic New York City birth cohort (born between 1959 and 1963), we examined whether genomic DNA methylation, measured in peripheral blood mononuclear cells, was associated with smoking exposure and other epidemiologic risk factors across the life course. Information on prenatal and childhood exposures was collected prospectively through 1971, and information on adult exposures and blood specimens were collected in adulthood from 2001 to 2007. Methylation levels of leukocyte DNA were determined using a [3H]-methyl acceptance assay where higher values of disintegrations per minute per microgram DNA indicate less DNA methylation. Genomic methylation of leukocyte DNA differed by ethnicity (66% of Blacks, 48% of Whites, and 29% of Hispanics were above the median level of disintegrations per minute per microgram DNA; P = 0.03). In multivariable modeling, DNA methylation was statistically significantly associated with maternal smoking during pregnancy, longer birth length, later age at menarche, nulliparity, and later age at first birth. These data, if replicated in larger samples, suggest that risk factors across the life course may be associated with DNA methylation in adulthood. Larger studies and studies that measure within-individual changes in DNA methylation over time are a necessary next step. (Cancer Epidemiol Biomarkers Prev 2008;17(9):2306–10)

Background Arsenic methylation relies on folate-dependent one-carbon metabolism and facilitates urinary As elimination. Clinical manifestations of As toxicity vary considerably among individuals and populations, and poor methylation capacity is thought to confer greater susceptibility. Objective After determining that folate deficiency, hyperhomocysteinemia, and low urinary creatinine are associated with reduced As methylation, and that As exposure is associated with increased genomic methylation of leukocyte DNA, we asked whether these factors are associated with As-induced skin lesion risk among Bangladeshi adults. Methods We conducted a nested case–control study of 274 cases who developed lesions 2 years after recruitment, and 274 controls matched to cases for sex, age, and water As. Results The odds ratios and 95% confidence intervals (CIs) for development of skin lesions for participants who had low folate (< 9 nmol/L), hyperhomocysteinemia (men, > 11.4 μmol/L; women, > 10.4 μmol/L), or hypomethylated leukocyte DNA at recruitment (< median) were 1.8 (95% CI, 1.1–2.9), 1.7 (95% CI, 1.1–2.6), and 1.8 (95% CI, 1.2–2.8), respectively. Compared with the subjects in the first quartile, those in the third and fourth quartiles for urinary creatinine had a 0.4-fold decrease in the odds of skin lesions (p < 0.01). Conclusions These results suggest that folate deficiency, hyperhomocysteinemia, and low urinary creatinine, each associated with decreased As methylation, are risk factors for As-induced skin lesions. The increased DNA methylation associated with As exposure previously observed, and confirmed among controls in this study, may be an adaptive change because hypomethylation of leukocyte DNA is associated with increased risk for skin lesions.

Background: Studies in cell culture and animal models indicate that arsenic exposure induces modifications in DNA methylation, including genome-wide DNA hypomethylation. It is not known whether arsenic exposure influences genomic DNA methylation in human populations chronically exposed to arsenic-contaminated drinking water. Objective: The objective of this study was to determine whether arsenic is associated with genomic hypomethylation of peripheral blood leukocyte (PBL) DNA in Bangladeshi adults who are chronically exposed to arsenic. We also investigated whether arsenic-induced alterations in DNA methylation may be influenced by folate nutritional status. Design: PBL DNA methylation and concentrations of plasma folate, plasma arsenic, and urinary arsenic were assessed in 294 adults in Araihazar, Bangladesh. Genomic PBL DNA methylation was measured by using a [ 3 H]-methyl incorporation assay. Results: Urinary arsenic, plasma arsenic, and plasma folate were positively associated with the methylation of PBL DNA (P = 0.009, 0.03, and 0.03, respectively). Stratification of participants by folate nutritional status [

Background In Bangladesh, tens of millions of people have been consuming waterborne arsenic for decades. The extent to which As is transported to the fetus during pregnancy has not been well characterized. Objectives We therefore conducted a study of 101 pregnant women who gave birth in Matlab, Bangladesh. Methods Maternal and cord blood pairs were collected and concentrations of total As were analyzed for 101 pairs, and As metabolites for 30 pairs. Maternal urinary As metabolites and plasma folate, cobalamin, and homocysteine levels in maternal cord pairs were also measured. Household tube well–water As concentrations exceeded the World Health Organization guideline of 10 μg/L in 38% of the cases. Results We observed strong associations between maternal and cord blood concentrations of total As (r = 0.93, p < 0.0001). Maternal and cord blood arsenic metabolites (n = 30) were also strongly correlated: in dimethylarsinate (DMA) (r = 0.94, p < 0.0001), monomethylarsonate (r = 0.80, p < 0.0001), arsenite (As+3) (r = 0.80, p < 0.0001), and arsenate (As+5) (r = 0.89, p < 0.0001). Maternal homocysteine was a strong predictor of %DMA in maternal urine, maternal blood, and cord blood (β = −6.2, p < 0.02; β = −10.9, p < 0.04; and β = −13.7, p < 0.04, respectively). Maternal folate was inversely associated with maternal blood As5+ (β = 0.56, p < 0.05), and maternal cobalamin was inversely associated with cord blood As5+ (β = −1.2, p < 0.01). Conclusions We conclude that exposure to all metabolites of inorganic As occurs in the prenatal period.

Populations in South and East Asia and many other regions of the world are chronically exposed to arsenic-contaminated drinking water. To various degrees ingested inorganic arsenic (InAs) is methylated to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) via folate-dependent one-carbon metabolism; impaired methylation is associated with adverse health outcomes. Consequently folate nutritional status may influence arsenic methylation and toxicity. The objective of this study was to test the hypothesis that folic acid supplementation of arsenic-exposed adults would increase arsenic methylation. Two hundred adults in a rural region of Bangladesh previously found to have low plasma concentrations of folate (= 9 nmol/L) were enrolled in a randomized double-blind placebo-controlled folic acid-supplementation trial. Plasma concentrations of folate and homocysteine and urinary concentrations of arsenic metabolites were analyzed at baseline and after 12 wk of supplementation with folic acid at a dose of 400 µg/d or placebo. The increase in the proportion of total urinary arsenic excreted as DMA in the folic acid group (72% before and 79% after supplementation) was significantly (P < 0.0001) greater than that in the placebo group as was the reduction in the proportions of total urinary arsenic excreted as MMA (13% and 10% respectively; P < 0.0001) and as InAs (15% and 11% respectively; P < 0.001). These data indicate that folic acid supplementation to participants with low plasma folate enhances arsenic methylation. Because persons whose urine contains low proportions of DMA and high proportions of MMA and InAs have been reported to be at greater risk of skin and bladder cancers and peripheral vascular disease these results suggest that folic acid supplementation may reduce the risk of arsenic-related health outcomes. (authors)

BACKGROUND Indian Asian men residing in the United Kingdom have a higher prevalence of hyperhomocysteinemia than do their European counterparts. This has been largely attributed to dietary deficiencies in cobalamin associated with vegetarianism among these Indian Asians. OBJECTIVE We aimed to ascertain the prevalence of folate and cobalamin deficiencies and hyperhomocysteinemia in Bangladesh. DESIGN Plasma concentrations of homocysteine, folate, and cobalamin and urinary concentrations of creatinine were assessed in 1650 adults in Bangladesh. RESULTS The prevalence of hyperhomocysteinemia (men: >11.4 micromol/L; women: >10.4 micromol/L) was markedly (P < 0.0001) greater among men (63%; x +/- SD: 15.3 +/- 9.5 micromol/L) than among women (26%; 9.5 +/- 4.7 micromol/L). Folate was lower (9.8 +/- 6.5 and 12.3 +/- 7.6 nmol/L, respectively), whereas cobalamin was higher (281 +/- 115 and 256 +/- 118 pmol/L, respectively) (P < 0.0001 for both) among men than among women. Folate explained 15% and cobalamin explained 5% of the variation in homocysteine concentrations. For men, folate (P = 0.005) and cobalamin (P = 0.03) were positively correlated with urinary creatinine. Smoking (P < 0.0003) and betelnut use (P < 0.0002) were independent negative predictors of folate. CONCLUSIONS Bangladeshi men have a high prevalence of hyperhomocysteinemia, which is more closely associated with folate than with cobalamin, although other factors, eg, smoking and betelnut use, may also contribute to its cause. The positive correlations between urinary creatinine and plasma folate and cobalamin were unanticipated and could suggest that, in marginal nutrition, these vitamins may be limiting for creatine biosynthesis.

Although carotenoids are known to be important dietary sources of vitamin A, there have been few epidemiological studies that have characterized the serum concentrations of major dietary carotenoids among preschool children with vitamin A deficiency. We conducted a population-based, cross-sectional study of serum pro-vitamin A carotenoids (alpha -carotene, beta-carotene, beta-cryptoxanthin), non-provitamin A carotenoids (lutein/zeaxanthin, and lycopene), and retinol among 278 children, aged 1-5 y, in the Republic of the Marshall Islands. Vitamin A deficiency was defined as serum retinol0.70 micromol/L. Geometric mean serum concentrations of carotenoids among children with and without vitamin A deficiency were 0.003 vs 0.006 micromol/L for alpha-carotene (P = 0.0017), 0.011 vs 0.023 micromol/L for beta-carotene (P0.0001), 0.023 vs 0.034 micromol/L for beta-cryptoxanthin (P = 0.0075), 0.007 vs 0.012 micromol/L for lycopene (P = 0.037), 0.044 vs 0.052 micromol/L for lutein/zeaxanthin (P = 0.2), and 0.045 vs 0.074 micromol/L for total provitamin A carotenoids (P0.0001) respectively. In a multivariate analysis adjusting for sex, age (Odds Ratio [O.R.] 1.44, 95% confidence interval [C.I.] 1.16-1.78), and serum provitamin A carotenoids (O.R. 0.49, 95% C.I. 0.34-0.71) were associated with vitamin A deficiency, but serum non-provitamin A carotenoids were not associated with vitamin A deficiency (O.R. 0.93, 95% C.I. 0.67-1.28). Preschool children with vitamin A deficiency in the Republic of the Marshall Islands have extremely low serum concentrations of provitamin A carotenoids and interventions are needed to improve the dietary intake of provitamin A carotenoids among Marshallese children.

Background The exclusion of individuals with elevated acute phase proteins has been advocated in order to improve prevalence estimates of vitamin A deficiency in surveys, but it is unclear whether this will lead to sampling bias. The purpose of the study was to determine whether the exclusion of individuals with elevated acute phase proteins is associated with sampling bias and to characterize inflammation in children with night blindness. Methods In a survey in the Republic of the Marshall Islands involving 281 children, aged 1–5 years, serum retinol, C-reactive protein (CRP), and α1-acid glycoprotein (AGP) were measured. Results Of 281 children, 24 (8.5%) had night blindness and 165 (58.7%) had serum retinol 5 mg/L and/or AGP >1000 mg/L). Among children with and without night blindness, the proportion with serum retinol P = 0.03) and with anemia was 58.3% and 35.7% (P = 0.029), respectively. The proportion of children with serum retinol P = 0.016), the proportion of boys was 43.1% vs. 54.3% (P = 0.075), with no hospitalizations in the last year was 11.0% vs 23.6% (P = 0.024), and with anemia was 43.8% vs 31.7% (P = 0.05), respectively. Conclusions Exclusion of children with inflammation in this survey of vitamin A deficiency does not improve prevalence estimates for vitamin A deficiency and instead leads to sampling bias for variables such as age, gender, anemia, and hospitalization history.

Although vitamin A deficiency, iron deficiency, and inflammation may contribute to anemia, their relative contribution to anemia has not been well characterized in preschool children in developing countries.To characterize the contributions of vitamin A and iron deficiencies and inflammation to anemia among preschool children in the Republic of the Marshall Islands.A community-based survey, the Republic of the Marshall Islands Vitamin A Deficiency Study, was conducted among 919 preschool children. The relationship of vitamin A and iron status and markers of inflammation, tumor necrosis factor-alpha, alpha1-acid glycoprotein, and interleukin-10, to anemia were studied in a subsample of 367 children.Among the 367 children, the prevalence of anemia was 42.5%. The prevalence of severe vitamin A deficiency (serum vitamin A0.35 micromol/l) and iron deficiency (serum ferritin12 microg/dl) were 10.9 and 51.7%, respectively. The respective prevalence of iron deficiency anemia (hemoglobin110 g/l and iron deficiency), anemia with inflammation (anemia with TNF-alpha2 pg/ml and/or AGP1000 mg/l), and severe vitamin A deficiency combined with anemia was 26.7, 35.6, and 7.6%. In multivariate linear regression models that adjusted for age, sex, and inflammation, both iron deficiency (odds ratio (OR) 1.74, 95% confidence interval (CI) 1.08-2.83, P = 0.023) and severe vitamin A deficiency (OR 4.85, 95% CI 2.14-10.9, P0.0001) were significantly associated with anemia.Both iron and vitamin A deficiencies were independent risk factors for anemia, but inflammation was not a significant risk factor for anemia among these preschool children.

The site where bulk lipid is added to apoB100 low density lipoproteins (LDL)/high density lipoproteins (HDL) particles to form triglyceride-enriched very low density lipoproteins (VLDL) has not been identified definitively. We employed several strategies to address this question. First, McA RH7777 cells were pulse-labeled for 20 min with [35S]methionine/cysteine and chased for 1 h (Chase I) to allow study of newly synthesized apoB100 LDL/HDL remaining in the endoplasmic reticulum (ER). After Chase I, cells were incubated for another hour (C2) with/without brefeldin A (BFA) and nocodazole (Noc) (to block ER to Golgi trafficking) and with/without oleic acid (OA). OA treatment alone during C2 increased VLDL secretion. This was prevented by the addition of BFA/Noc in C2. When C2 media were replaced by control media for another 1-h chase (C3), VLDL formed during OA treatment in C2 were secreted into C3 medium. Thus, OA-induced conversion of apoB100 LDL/HDL to VLDL during C2 occurred in the ER. Next, newly synthesized apoB100 lipoproteins were trapped in the Golgi by treatment with Noc and monensin during Chase I (C1), and C2 was carried out in the presence of BFA/Noc with/without OA and without monensin. Under these conditions, OA treatment during C2 did not stimulate VLDL secretion. The same pulse/chase protocols were followed by iodixanol subcellular fractionation, extraction of lipoproteins from ER and Golgi, and sucrose gradient separation of extracted lipoproteins. Cells treated with BFA/Noc and OA in C2 had VLDL in the ER. In the absence of OA, only LDL/HDL were present in the ER. The density of Golgi lipoproteins in these cells was not affected by OA. Similar results were obtained when ER were immuno-isolated with anti-calnexin antibodies. In conclusion, apoB100 bulk lipidation, resulting in conversion of LDL/HDL to VLDL, can occur in the ER, but not in the Golgi, in McA RH7777 cells.

We investigated the co-occurrence of vitamin A deficiency, iron deficiency, and anemia among young children in the Republic of the Marshall Islands.Hemoglobin, serum retinol, and serum ferritin were assessed in the Republic of the Marshall Islands Vitamin A Deficiency Study, a community-based survey that involved 919 children ages 1 to 5 y.The proportion of children with vitamin A deficiency (serum retinol concentrations0.70 microM/L) was 59.9%. The prevalences of anemia (hemoglobin110 g/L), iron deficiency (serum ferritin12 microg/L), and iron deficiency anemia (iron deficiency and anemia) were 36.4%, 53.5%, and 23.8%, respectively. The proportion of children who had co-occurrence of vitamin A and iron deficiencies was 33.2%. The mean ages of children with and without vitamin A deficiency were 3.2 +/- 1.4 and 2.9 +/- 1.5 y, respectively (P = 0.01), and the mean ages of those with and without iron deficiency were 2.7 +/- 1.3 and 3.5 +/- 1.4 y, respectively (P0.0001).Children in the Republic of the Marshall Islands, ages 1 to 5 y, are at high risk of anemia, vitamin A deficiency, and iron deficiency, and one-third of these children had the co-occurrence of vitamin A and iron deficiencies. Further investigation is needed to identify risk factors and evaluate interventions to address vitamin A and iron deficiencies among children.

Although plasma retinol-binding protein (RBP) has been proposed as an indicator of vitamin A status of populations in less technologically developed settings, potential factors which could influence this indicator include inflammation and protein energy status. Plasma RBP, retinol, alpha1-acid glycoprotein (AGP), C-reactive protein (CRP), and albumin were measured in a study of 236 preschool children in Bandung, Indonesia. Spearman correlation coefficient between plasma RBP and retinol concentrations was 0.55 (p < 0.0001). By linear regression, 0.70 pmol/l retinol was equivalent to 0.69 micromol/l RBP. With these cut-off points for defining vitamin A deficiency and plasma retinol as the standard for comparison, RBP had a sensitivity and specificity of 75.0 per cent and 63.2 per cent, respectively. The correlation between RBP and retinol was not affected by plasma AGP, CRP, or albumin concentration. Measurement of plasma RBP by radial immunodiffusion is simple and inexpensive, and this test can be used as a simple surrogate measure for vitamin A concentrations in large field studies.

Background: Serum retinol is transported by retinol binding protein (RBP), which has one high-affinity binding site for retinol; consequently, the molar ratio of retinol to RBP in the circulation is 1 to 1. In vitamin A deficiency (VAD), both serum retinol and RBP decline. However, the retinol-RBP relation has not been well studied in populations with a high incidence of severe VAD. Objective: The purpose of this study was to determine whether RBP is a good surrogate for serum retinol at the very low retinol concentrations encountered in VAD. Design: The stoichiometric relation between retinol and RBP was studied in 239 Marshallese children: 65 with severe VAD (≤0.35 μmol retinol/L), 94 with moderate VAD (0.36-0.70 μmol retinol/L), and 80 with vitamin A sufficiency (>0.70 μmol retinol/L). Results: Excellent correlation between retinol and RBP (r = 0.94) was observed across all retinol concentrations. Severe VAD was predicted with 96% sensitivity and 91% specificity on the basis of an RBP cutoff of ≤0.48 μmol/L, whereas moderate VAD was predicted with 87% sensitivity and 98% specificity on the basis of an RBP cutoff of ≤0.70 μmol/L. Conclusions: The use of RBP results in the classification of essentially the same children with VAD as does retinol, and RBP is an excellent surrogate for serum retinol. Considering the relative ease of measuring RBP with immunodiagnostic kits compared with that of serum retinol by HPLC, the use of RBP concentrations to assess VAD may be particularly advantageous in field settings. Consequently, measuring RBP concentrations may be a practical alternative to measuring serum retinol in population surveys assessing the prevalence of VAD.

Background We utilized data from the Health Effects of Arsenic Longitudinal Study (HEALS) in Araihazar, Bangladesh, to evaluate the association of steamed rice consumption with urinary total arsenic concentration and arsenical skin lesions in the overall study cohort (N=18,470) and in a subset with available urinary arsenic metabolite data (N=4,517). Methods General linear models with standardized beta coefficients were used to estimate associations between steamed rice consumption and urinary total arsenic concentration and urinary arsenic metabolites. Logistic regression models were used to estimate prevalence odds ratios (ORs) and their 95% confidence intervals (CIs) for the associations between rice intake and prevalent skin lesions at baseline. Discrete time hazard models were used to estimate discrete time (HRs) ratios and their 95% CIs for the associations between rice intake and incident skin lesions. Results Steamed rice consumption was positively associated with creatinine-adjusted urinary total arsenic (β=0.041, 95% CI: 0.032-0.051) and urinary total arsenic with statistical adjustment for creatinine in the model (β=0.043, 95% CI: 0.032-0.053). Additionally, we observed a significant trend in skin lesion prevalence (P-trend=0.007) and a moderate trend in skin lesion incidence (P-trend=0.07) associated with increased intake of steamed rice. Conclusions This study suggests that rice intake may be a source of arsenic exposure beyond drinking water.

Transthyretin (TTR) acts physiologically in the transport of retinol in the circulation. We previously reported the generation and partial characterization of TTR-deficient (TTR(-)) mice. TTR(-) mice have very low circulating levels of retinol and its specific transport protein, retinol-binding protein (RBP). We have examined the biochemical basis for the low plasma retinol-RBP levels. Cultured primary hepatocytes isolated from wild type (WT) and TTR(-) mice accumulated RBP in their media to an identical degree, suggesting that RBP was being secreted from the hepatocytes at the same rate. In vivo experiments support this conclusion. For the first 11 h after complete nephrectomy, the levels retinol and RBP rose in the circulations of WT and TTR(-) mice at nearly identical rates. However, human retinol-RBP injected intravenously was more rapidly cleared from the circulation (t(12) = 0.5 h for TTR(-) versus t(12)6 h for WT) and accumulated faster in the kidneys of TTR(-) compared with WT mice. The rate of infiltration of the retinol-RBP complex from the circulation to tissue interstitial fluids was identical in both strains. Taken together, these data indicate that low circulating retinol-RBP levels in TTR(-) mice arise from increased renal filtration of the retinol-RBP complex.

Recent studies of the human, mouse and bovine genes for 11-cis-retinol dehydrogenase (11cRDH) and human and mouse 9-cis-retinol dehydrogenase (9cRDH) suggest that they are homologs of the same enzyme. This conclusion is inconsistent with earlier literature indicating that 11cRDH is expressed solely in the eye and does not utilize 9-cis-retinol as a substrate. We have compared directly the kinetic properties of recombinant human and mouse 9cRDH with those of bovine 11cRDH for 9-cis- and 11-cis-retinol and investigated the inhibitory properties of 13-cis-retinoic acid on each of these enzymes. Human and mouse 9cRDH and bovine 11cRDH have very similar kinetic properties towards 9-cis- and 11-cis-retinol oxidation and they respond identically to 13-cis-retinoic acid inhibition. Our biochemical data are consistent with the conclusion that 9cRDH and 11cRDH are the same enzyme.

All-trans-retinoic acid (RA) activates ligand-dependent transcription factors that regulate retinoid-responsive gene expression. It is assumed that all-trans-RA is formed within cells through in situ oxidation of retinol derived from the circulation. However, the circulation contains low levels of all-trans-RA (approximately 0.2-0.7% of that of plasma retinol). Our studies investigated the extent to which plasma all-trans-RA contributes to tissue pools of this retinoid and explored factors responsible for regulating its uptake by tissues and cells. Rats were continuously infused, to steady state, with all-trans-[3H]RA. From measures of specific activities of all-trans-[3H]RA at steady state, we determined that the preponderance of all-trans-RA in brain and liver was derived from the circulation. For six other tissues, approximately 10-30% of the retinoid was derived from the circulation, but pancreas and testis derived very little from the circulating pool. In other studies, we showed that retinoid nutritional status influences clearance of a bolus dose of all-trans-RA and that neither the rate of cellular all-trans-RA uptake nor its intracellular half-life is influenced by cellular lipid levels. Taken together, our data indicate that plasma all-trans-RA contributes to tissue pools of this retinoid and that specific and physiologically responsive cellular processes mediate its uptake.

Arsenic contamination of drinking water is a major public health issue in many countries, increasing risk for a wide array of diseases, including cancer. There is inter-individual variation in arsenic metabolism efficiency and susceptibility to arsenic toxicity; however, the basis of this variation is not well understood. Here, we have performed the first genome-wide association study (GWAS) of arsenic-related metabolism and toxicity phenotypes to improve our understanding of the mechanisms by which arsenic affects health. Using data on urinary arsenic metabolite concentrations and approximately 300,000 genome-wide single nucleotide polymorphisms (SNPs) for 1,313 arsenic-exposed Bangladeshi individuals, we identified genome-wide significant association signals (P, Author Summary Exposure to arsenic through drinking water is a serious public health issue in many countries, including Bangladesh and the United States. Although there is substantial inter-individual variation in arsenic metabolism and toxicity, the biological basis of this variation is not well understood. Here, we have conducted the first genome-wide association study of arsenic-related traits within a unique population cohort of arsenic-exposed Bangladeshi individuals. Using data on 1,313 well-characterized individuals, we identify multiple association signals for urinary arsenic metabolite concentrations in the 10q24.32 regions, near the AS3MT (arsenite methyltransferase) gene. In a subsequent analysis of >2,000 individuals, we show for the first time that variants that influence arsenic metabolism can also influence risk for arsenical skin lesions (the classical sign of arsenic toxicity) through interaction with arsenic exposure. Using array-based genome-wide gene expression data, we show that several of our lead genetic variants are associated with expression of AS3MT and neighboring gene C10orf32, providing a potential mechanism by which 10q24.32 variants influence arsenic metabolism and toxicity. Knowledge of variation in this region and associated biological processes could be used to develop intervention and pharmacological strategies aimed at preventing large numbers of arsenic-related deaths in arsenic-exposed populations.

Arsenic and arsenic compounds have been classified as group 1 human carcinogens by IARC. Naturally occurring inorganic arsenic, in particular, has been implicated in the development of human skin, lung, and bladder cancers and has also been associated with the development of liver and prostate cancers. However, despite being a formidable carcinogen, arsenic is a poor mutagen and it has been suggested that arsenic-induced carcinogenesis maybe governed by epigenetic mechanisms. We have detected differences in the levels of several histone epigenetic marks, such as H3K9acetylation, H3K9dimethylation and H3K27trimethylation in human peripheral mononuclear cell collected from individuals exposed to varying levels of inorganic arsenic in their drinking water. The changes in the global levels of these epigenetic marks were primarily measured using a novel ELISA method, while changes of arsenic-induced histone modifications in peripheral blood lymphocytes treated in vitro have also been examined via Mass Spectrometry and Western Blotting. Furthermore, we have also found a profound increase in the expression of histone genes after in vitro treatment of peripheral blood lymphocytes with sodium arsenite and will be examining this finding further. To the best of our knowledge, this study is the first in its class to measure arsenic-induced epigenetic modifications in humans and how they relate to changes in gene expression in a human population. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1996. doi:10.1158/1538-7445.AM2011-1996

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world and is increasing in the United States. Epigenetic changes, including genomic DNA hypomethylation, have been implicated in cancer development by inducing chromosomal instability. In the present study, methylation of long interspersed nucleotide element-1(LINE1), a surrogate marker of global hypomethylation, in peripheral white blood cells and plasma DNA in 47 US HCC patients was detected by pyrosequencing. Correlations between LINE1 methylation, and clinical data and other biomarkers were also analyzed. Methylation of LINE1 in WBC DNA is statistically significantly correlated with that in plasma DNA (R=0.32, p=0.04). WBC DNA global hypomethylation was significantly decreased in subjects with hepatitis C (HCV) infection (p=0.05). Plasma folate levels were not correlated with plasma DNA LINE1 methylation (R=0.13, p=0.41) or with WBC LINE1 methylation (R=−0.19, p=0.24). However, WBC folate levels were statistically significantly associated with patients’ survival. HCC patients who survived at least 3 months after diagnosis had lower WBC folate compared to patients who died within 3 months (p=0.004). We are currently expanding the HCC cohort and also analyzing biomarkers of chemical exposure (polycyclic aromatic hydrocarbons and aflatoxin B1) to investigate associations with methylation changes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 295. doi:10.1158/1538-7445.AM2011-295

4101 Background: Folate plays a central role in DNA methylation reactions, but the relationship between folate and methylation status has not been studied in HCC patients. We hypothesized that low folate levels would correlate with global hypomethylation, and worsened survival in HCC patients. Methods: 72 newly-diagnosed HCC patients were enrolled in a prospective study, beginning 10/08, and followed until 9/11. We excluded those with previous malignancy, and uncompensated Child Pugh (CP) B or C disease. We used pyrosequencing to evaluate quartiles of LINE-1 methylation in plasma as a surrogate for global tumor hypomethylation. We evaluated the relationship between folate deficiency (serum folate levels < 6ng/mL), DNA hypomethylation (LINE-1 methylation < 25th percentile i.e., < 69.4%), and overall survival in our cohort. Results: Median age was 60; 82% were men and 67% had hepatitis C. Mean serum folate levels were 12.1 ng/mL (SD = 5.3 ng/mL), while mean % LINE-1 methylation was 69.9 (SD = 4.6). In a univariate analysis, folate deficiency and LINE-1 hypomethylation were significant predictors of poor overall survival (HR = 3.77; 95% CI: 1.37, 10.41, and HR=3.50; 95% CI: 1.51, 8.13, respectively). These markers remained independent predictors of survival in a multivariate model including age, CP class, AJCC stage and AFP. HR for folate deficiency in this model was 3.52 (95% CI: 1.16, 10.70), and HR for LINE-1 hypomethylation was 2.74 (95% CI: 1.10, 6.85). We also found a significant association between folate deficiency and LINE-1 hypomethylation (p = 0.04). Conclusions: We provide novel data that folate deficiency is an independent predictor of worsened overall survival in patients with HCC in a multivariate model. Further, we show that global changes in DNA methylation assesed in plasma correlate with folate levels, supporting a possible mechanistic link between the two. Folate supplementation, and the use of other agents which modulate methylation, deserve further study in HCC.

Background Arsenic can naturally occur in the groundwater without an anthropogenic source of contamination. In Bangladesh over 50 million people are exposed to naturally occurring arsenic concentrations exceeding the World Health Organization’s guideline of 10 μg/L. Selenium and arsenic have been shown to facilitate the excretion of each other in bile. Recent evidence suggests that selenium may play a role in arsenic elimination by forming a selenium-arsenic conjugate in the liver before excretion into the bile. Methods A cross-sectional study of 1601 adults and 287 children was conducted to assess the relationship between blood selenium and urinary and blood arsenic in a study population residing in a moderately arsenic-contaminated rural area in Bangladesh. Results The results of this study indicate a statistically significant inverse relationship between blood selenium and urinary arsenic concentrations in both adult and pediatric populations in rural Bangladesh after adjustment for age, sex, Body Mass Index, plasma folate and B12 (in children), and ever smoking and current betel nut use (in adults). In addition, there appears to be a statistically significant inverse relationship between blood selenium and blood arsenic in children. Conclusions Our results suggest that selenium is inversely associated with biomarkers of arsenic burden in both adults and children. These findings support the hypothesis that Se facilitates the biliary elimination of As, possibly via the putative formation of a Se-As conjugate using a glutathione complex. However, laboratory based studies are needed to provide further evidence to elucidate the presence of Se-As conjugate and its role in arsenic elimination in humans.

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 (5mTHF) 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 Km 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. Electronic supplementary material The online version of this article (doi:10.1186/s12918-015-0215-6) contains supplementary material, which is available to authorized users.

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.