The Toxicologist - Society of Toxicology

organic As to MMA(V) and a lower capacity to further methylate this metabolite to
DMA(V), have a higher risk of BC. Further research is needed to investigate the role
of genetic polymorphisms involved in As metabolism and their relevance for BC.
Supported by: FOSSIS: 2005-C02-14373 and 2009-01-11384, U.S.-Mexico
Binational Center for Environmental Science and Toxicology.
1984 INFLUENCE OF INDIGENOUS AMERICAN ANCESTRY
AND BODY MASS INDEX ON ARSENIC
METHYLATION EFFICIENCY IN NORTHWEST
MEXICO.
P. Gomez-Rubio 1 , M. M. Meza-Montenegro 2 , E. Cantu-Soto 2 , Y. C.
Klimentidis 3 and W. T. Klimecki 1 . 1 Pharmacology and Toxicology, University of
Arizona, Tucson, AZ, 2 Environmental Sciences, Instituto Tecnologico de Sonora,
Obregon, Sonora, Mexico and 3 Biostatistics, University of Alabama at Birmingham,
Birmingham, AL.
Environmental exposure to arsenic has been widely associated with the development
of a vast array of cancerous and non-cancerous diseases. Human arsenic
methylation efficiency, measured as the percentage of urinary monomethylarsonic
acid excretion (%uMMA), has been reliably associated with the risk of arsenic-induced
diseases. Previous epidemiological studies have suggested that Indigenous
Americans may have better methylation efficiency than other ethnic groups. With
the aim of characterizing the association between genetic Indigenous American ancestry
(IA) and arsenic methylation efficiency, we studied a population of 635 arsenic-exposed
individuals from Northwest Mexico. Arsenic species were determined
in urine samples, anthropometric measurements were recorded, and a panel
of 58 ancestry informative markers was used to determine the European and IA
proportion in each individual. The mean urinary levels of inorganic arsenic, MMA
and DMA were 26, 21.1 and 132.5 μg/L. Mean IA and body mass index (BMI)
were 77% and 24.6 respectively. Adjusted multiple linear regression analysis (sex,
age, AS3MT genetic variation, BMI, and total urinary arsenic) showed that IA proportion
is significantly associated with arsenic methylation efficiency. Additionally
we also observed a very strong association between BMI and arsenic methylation efficiency.
Individuals with higher proportion of IA and higher BMI showed less
%uMMA, and higher uDMA/uMMA than their counterparts. These associations
highlight the importance of BMI and ancestry as potential arsenic-associated risk
factors, and should be carefully considered in future arsenic association studies, especially
those carried out in admixed populations. Additional studies will be needed
in order to understand the mechanistic nature of these associations. (Funded by
ES006694 and ES04940).
1985 THE INFLUENCE OF GENETICS, NUTRITION, AND
PREGNANCY ON ARSENIC METABOLISM: A
LONGITUDINAL COHORT STUDY.
R. M. Gardner 1 , K. Engström 2 , K. Broberg 2 and M. Vahter 1 . 1 Institute of
Environmental Medicine, Karolinska Institutet, Stockholm, Sweden and 2 Department
of Laboratory Medicine, Lund University, Lund, Sweden.
Exposure to inorganic arsenic during pregnancy may negatively influence the offspring,
although efficient metabolism of arsenic to dimethylarsinic acid (DMA)
likely reduces the health risks. This study aimed to evaluate methylation of arsenic
over the entire pregnancy and the influence of nutritional status and genetic background.
We studied longitudinally the arsenic metabolite pattern in the urine of
294 pregnant women exposed to arsenic via drinking water and food in rural
Bangladesh. Urine was collected from women at three time points throughout
pregnancy (at approximately weeks 8, 19, and 30). Urinary arsenic metabolites
were measured by HPLC-ICPMS. Women were genotyped for 22 polymorphisms
in five methyltransferases: arsenic(+III)methyltransferase (AS3MT), DNA-methyltransferase
1a and 3b (DNMT1a and 3b), phosphatidylethanolamine transferase
(PEMT) and betaine-homocysteine methyltransferase (BHMT). Because the data
on arsenic metabolites in urine were collected longitudinally, changes in these biomarkers
over time were modeled using linear mixed effects models fit with maximum
likelihood estimation. Metabolism of arsenic to DMA increased markedly
over the course of pregnancy, with the greatest improvement occurring in the first
trimester, along with a marked decrease in the most risk-associated monomethylated
metabolite. This improvement in methylation was not associated with nutritional
status, including vitamin B12 and folate. Six AS3MT polymorphisms and
four polymorphisms in the DNMTs significantly influenced metabolite pattern in
the pregnant women, with consistent effects of genotype over the entire course of
pregnancy. Efficient methylation to DMA was associated with improved urinary
excretion of arsenic, relative to blood arsenic concentrations, indicating that micronutrient-independent
up-regulation of arsenic metabolism occurring in early
pregnancy may provide protection for the fetus.
1986 DETECTION AND STABILITY OF METHYLATED
TRIVALENT ARSENIC METABOLITES IN MOUSE
LIVER HOMOGENATES.
J. Currier 1 , J. Saunders 2 , Z. Drobná 2 and M. Styblo 2 . 1 Curriculum in Toxicology,
University of North Carolina, Chapel Hill, NC and 2 Nutrition, University of North
Carolina, Chapel Hill, NC.
Chronic exposure to inorganic arsenic (iAs) is associated with a variety of diseases,
including cancer, hypertension and diabetes. Current evidence suggests that the
toxic methylated trivalent metabolites of iAs, methylarsonite (MAsIII) and dimethylarsinite
(DMAsIII), play a key role in the etiology of these diseases. Both
MAsIII and DMAsIII have been detected in urine of subjects exposed to iAs.
However, the rapid oxidation of DMAsIII and, to a lesser extent, MAsIII leads to
difficulties in the analysis of these metabolites in samples of urine collected in field
studies. Results of our previous work indicate that MAsIII and DMAsIII are relatively
stable in a reducing cellular environment, suggesting that analysis of cells or
tissues rather than urine, could be used to characterize internal exposures to these
toxic metabolites. In the present study, we used the oxidation state-specific hydride
generation-cryotrapping-atomic absorption spectroscopy (HG-CT-AAS) to examine
presence and stability of MAsIII and DMAsIII in livers of mice exposed to iAs
in drinking water. Liver homogenates were prepared in deionized water and stored
at either 0°C or -80°C for up to 22 days. Tri- and pentavalent metabolites of iAs
were analyzed in homogenates directly (without chemical digestion); analysis of homogenates
digested in phosphoric acid was used to determine the recovery of As
species during the direct analyses. In fresh homogenates, MAsIII and DMAsIII represented
12% and 45% of total As, respectively. Both MAsIII and DMAsIII were
stable in homogenates stored at -80°C. In contrast, DMAsIII in homogenates
stored at 0°C began to oxidize to its pentavalent counterpart after 1 day, whereas
MAsIII remained stable for at least 3 weeks under these conditions. At least 95% of
all As species were recovered by the direct analyses, suggesting that this method is
suitable for quantitative analysis of iAs metabolites, including MAsIII and
DMAsIII in tissues or cells collected in laboratory and population-based studies.
1987 THE EFFECT OF PRENATAL FOLATE
SUPPLEMENTATION ON DNA METHYLATION AND
GENE EXPRESSION IN MALE CD1 MOUSE FETUSES
EXPOSED IN UTERO TO ARSENIC.
V. Tsang 1 , R. Fry 2 , M. Niculescu 3 , J. Saunders 1 , M. Waalkes 4 , M. Styblo 1 and
Z. Drobna 1 . 1 Nutrition, CB#7461, UNC Chapel Hill, NC, Chapel Hill, NC,
2 Environmental Sciences and Engineering, UNC Cahpel Hill, Chapel Hill, NC,
3 Nutrition Research Institute, Kannapolis, NC and 4 NTP at NIEHS, Research
Triangle Park, NC.
In humans and mice, inorganic arsenic (iAs), an environmental carcinogen, is
methylated prior to excretion. Recent studies suggest that utilization of S-adenosylmethionine
(SAM) for iAs methylation during prenatal exposure can cause cancer
by changing fetal DNA methylation, followed by aberrant gene expression in adulthood.
We examined whether prenatal folate supplementation would prevent iAsinduced
changes in DNA methylation. Pregnant CD1 mice were exposed to 0 or
85 μg As/L of arsenite in drinking water and received a folate-supplemented or
control diet from gestation day (GD) 8 to 18. At GD 18, fetal livers were harvested
to determine concentrations of SAM and iAs metabolites. The methylation patterns
for genomic DNA in the livers were examined using a two color Mouse CpG-
Island Microarray containing 16,030 CpG islands. Molecular network analyses
identified affected genes and associated networks. Expression of genes with modified
methyl-CpG island profiles was examined by quantitative PCR. Treatments
with iAs and/or folate increased SAM and S-adenosylhomocysteine concentrations
in fetal livers as compared to untreated controls. Prenatal iAs exposure alone did not
alter the DNA methylation status in mouse fetuses. In contrast, folate supplementation
alone and, especially combined with iAs, altered the methylation of hundreds
of CpG islands. The most affected genes were associated with the cell cycle,
cancer, and neurological diseases. The exposure to iAs combined with folate supplementation
altered the expression of cyclin dependent kinase inhibitors 1b and 2a,
and of the imprinted tumor suppressor gene Dlk1. Our data suggest that when
combined with exposure to iAs, prenatal folate supplementation results in extensive
changes in fetal DNA methylation with possible consequences for fetal or offspring
health.
SOT 2011 ANNUAL MEETING 425