The Toxicologist - Society of Toxicology

MMA/IA and urinary As concentration of the hetero type of GSTP1 Ile105Val was
more significant than that of the wild type. Increased DMA/MMA with an increase
in urinary As concentration was observed for the GSTM1 wild type but not for the
null. Although the relationship between As[III]/As[V] and As concentration in the
urine showed a significant positive correlation in the wild type of GSTP1
Ile105Val, it was not significant in the hetero type. For GSTO1 Ala140Asp, the
heterozygote was associated with larger coefficients between As[III]/As[V] and urinary
As level than the homozygote. These results suggest that the metabolism of As
are affected by both As exposure and genetic polymorphisms.
1980 AS3MT/M287T POLYMORPHISM IS A RISK FACTOR
FOR DIABETES ASSOCIATED WITH CHRONIC
EXPOSURE TO INORGANIC ARSENIC.
D. Loomis 1 , L. M. Del Razo 2 , G. G. Garcia-Vargas 3 , Z. Drobná 4 and M.
Styblo 4 . 1 Medical Center, University of Nebraska, Omaha, NE, 2 Department of
Toxicology, CINVESTAV-IPN, Mexico, Mexico, 3 Faculty of Medicine, Juarez
University of Durango State, Gomez-Palacio, Mexico and 4 Nutrition, University of
North Carolina at Chapel Hill, Chapel Hill, NC.
Our recent work in Zimapan and Lagunera regions in Mexico has linked chronic
exposure to inorganic arsenic (iAs) in drinking water to an increased risk of diabetes.
We have also shown that this risk is associated with increased urinary concentrations
of dimethylarsinite (DMAsIII), a toxic methylated metabolite of iAs.
Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the
pathway for iAs methylation. AS3MT expression and polymorphism is, in part, responsible
for inter-individual differences in iAs metabolism. We have, therefore, examined
associations between AS3MT polymorphism, iAs metabolism and risk of
diabetes among Zimapan and Lagunera residents. Our results show that
AS3MT/287T genotype was associated with a higher average fasting blood glucose
(FBG = 114 ±59 mg/dl) as compared to a more common AS3MT/287M genotype
(89.85 ±35 mg/dl; p = 0.006) and with an increase in 2-hour blood glucose
(2HBG) recorded during oral glucose tolerance test (135 ±98 vs. 103 ±46 mg/dl; p
= 0.001). Similarly, the average HbA1c level was significantly higher in the blood of
the 287T carriers as compared to 287M carriers: 7 ±1.87% vs. 6.3 ±1.15% (p =
0.020). The associations of FBG, 2HBG and HbA1c with Met287Thr polymorphism
remained statistically significant after logarithmic transformation. The 287T
carriers were more likely to have FBG ≥126 mg/dl (OR = 2.36) and 2HBG ≥200
mg/dl (OR = 2.86), although neither association was statistically significant.
Notably, the average DMAsIII concentration was higher in urine of the 287T carriers
as compared to 287M carriers before (p = 0.023) and after (p = 0.032) logarithmic
transformation. Taken together, these results suggest that AS3MT/287T carriers
are more likely to develop diabetes when exposed to iAs because they produce
more DMAsIII than do 287M carriers.
1981 METHYLATION OF ARSENIC BY RECOMBINANT
HUMAN AS3MT/287M AND AS3MT/287T
POLYMORPHS.
L. Ding 1 , J. Saunders 1 , Z. Drobná 1 , D. J. Thomas 2 and M. Styblo 1 . 1 Nutrition,
University of North Carolina at Chapel Hill, Chapel Hill, NC and 2 ETD, NHEERL,
U.S. EPA, Research Triangle Park, NC.
Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the
pathway for methylation of inorganic arsenic (iAs). AS3MT polymorphism is, in
part, responsible for inter-individual differences in iAs metabolism.
AS3MT/M287T polymorphism that is found in ~10% of Caucasian and Hispanic
populations has been shown to affect the profiles of iAs metabolites in urine of subjects
chronically exposed to iAs. Previous work using a suboptimal in vitro system
containing glutathione (GSH) showed a significant difference between the rates of
iAs methylation by recombinant human AS3MT/287M and AS3MT/287T. We
compared the catalytic properties of recombinant human AS3MT/287M and
AS3MT/287T variants in an optimized in vitro reaction mixture containing arsenite
(iAsIII), S-adenosylmethionine and an endogenous reducing system consisting
of thioredoxin (Trx), TRx reductase (TR), and NADPH. The AS3MT variants
methylated 0.1-1 μM iAsIII with similar efficiencies to yield primarily dimethylarsinate
(DMAsV) and dimethylarsinite (DMAsIII); methylarsonate (MAsV) and
methylarsonite (MAsIII) were only minor metabolites. However, MAsV and
MAsIII yields increased in reaction mixtures containing 10 μM iAsIII. Addition of
1-10 mM GSH into the reaction mixture resulted in a 2- to 3-fold increase in the
rate of iAs methylation by either variant, favoring production of trivalent methylated
metabolites, MAsIII and DMAsIII. Under these conditions, the
424 SOT 2011 ANNUAL MEETING
AS3MT/287T variant produced significantly more DMAsIII than did
AS3MT/287M variant. Notably, in the absence of the TRx/TR/NADPH system,
addition of GSH was not sufficient to support iAsIII methylation by either
AS3MT/287T or AS3MT/287M. These results suggest that: (1) GSH is not essential
for iAs methylation but is an important modulator of AS3MT activity in
human tissues; (2) the carriers of AS3MT/287T genotype may be more susceptible
to adverse effects of iAs exposure due to an increased production of DMAsIII. (This
abstract does not reflect U.S. EPA policy.)
1982 GST-T1 AND GST-M1 GENOTYPES MODULATE THE
METABOLISM AND DIABETOGENIC EFFECTS OF
INORGANIC ARSENIC.
Z. Drobna 1 , L. Del Razo 2 , G. Garcia-Vargas 3 , D. Loomis 4 and M. Styblo 1 .
1 Nutrition, CB#7461, UNC Chapel Hill, NC, Chapel Hill, NC, 2 Toxicology,
CINVESTAV-IPN, Mexico City, Mexico, 3 Faculty of Medicine, Juarez University of
Durango State, Durango, Mexico and 4 Epidemiology, University of Nebraska Medical
Center, Omaha, NE.
Glutathione S-transferase (GST)-T1 and GST-M1 are among enzymes involved in
the metabolism and detoxification of inorganic arsenic (iAs). GST-T1 and GST-
M1 null genotypes have been shown to affect the levels of methylated metabolites
of iAs, methyl-arsenic (MAs) and dimethyl-arsenic (DMAs), in urine of subjects exposed
to iAs. To streamline examination of GST-T1 and GST-M1 null genotypes
in human DNA, we have developed a multiplex qPCR-High Resolution Melting
procedure using the LightCycler 480 instrument and software. This procedure is
based on analysis of the PCR product melting curve that represents the dynamics of
thermal dissociation of double-stranded DNA. We used the newly developed procedure
to identify GST-T1 and GST-M1 null genotypes in DNA samples collected
from 238 residents of Zimapan and Lagunera (Mexico) who were exposed to iAs in
drinking water. Null genotype for GST-T1 was detected in 17 (7.1%) subjects and
for GST-M1 in 92 (38.7%) subjects; 5 individuals (2.1%) were carriers of both
GST-T1 and -M1 null genotypes. Analysis of genotype-phenotype associations
showed that GST-T1 null genotype is associated with a significantly higher urinary
DMAs/MAs ratio: 7.21±5.46 as compared to 5.43±3.12 for GST-T1 positive subjects
(p=0.022). GST-M1 null genotype did not affect urinary profiles of iAs
metabolites. However, carriers of GST-M1 null genotype had, on average, significantly
lower fasting blood glucose levels (81.22±18.31) than GST-M1 positive subjects
(86.15±14.30, p = 0.0251). In summary, we have developed a high-throughput
technique for identification of GST-T1 and GST-M1 null genotypes and
validated it in a field study in Mexico. Our data suggest that the GST-T1 null carriers
have a higher capacity for conversion of MAs to DMAs while GST-M1 null
genotype may decrease diabetogenic effects of chronic exposures to iAs.
1983 ARSENIC METHYLATION IS ASSOCIATED WITH
BREAST CANCER RISK IN NORTHERN MEXICO.
M. E. Cebrián 1 , A. Gandolfi 2 , R. U. Hernandez 3 , J. M. Ornelas 4 , L. Torres-
Sanchez 3 and L. Lopez-Carrillo 3 . 1 Toxicology, Cinvestav IPN, Mexico City, DF,
Mexico, 2 Pharmacology and Toxicology, University of Arizona, Tucson, AZ, 3 CISP,
INSP, Cuernavaca, Morelos, Mexico and 4 Pathology, IMSS, Ciudad Obregón, Sonora,
Mexico.
Inorganic As exposure has been associated with skin, bladder, liver, lung, and
prostate tumors in humans. However, most studies to date have not yet implicated
As as a cofactor for breast cancer (BC). In northern Mexico, As exposure via drinking
water is endemic and BC mortality is 3-fold higher than in the rest of the country.
Our aim was to explore the potential association between As exposure, the profile
of As metabolites and BC. From an ongoing population-based case–control
study, the first 603 confirmed BC incident cases, as well as 477 population controls
were available for this report. Women were directly interviewed about their reproductive
and dietary history. The profile of As metabolites in urine was determined
by HPLC/ICP-MS. Methylation capacity was assessed by calculating the percentage
of arsenic species and the primary [MMA(V)/(As(III)+As(V)] and secondary
[DMA(V)/MMA(V)] methylation indexes. The range of total urinary As values
(TAs) was 0.4 to 254.9 ug/L. Urinary concentrations of Asi, DMA and TAs were
slightly lower in BC cases. However, the percentage of MMA was significantly
higher in BC cases, while the percentage of DMA was significantly lower. Age-adjusted
odd ratios showed a significantly positive association between MMA/Asi values
and BC risk (OR T3 vs T1 = 1.59; CI95=1.18-2.13; p for trend = 0.002). In
contrast, the DMA/MMA ratio was negatively associated (OR T3 vs T1 = 0.48;
CI95=0.35-0.65; p for trend = 0.000). This is the first report suggesting that As exposure
may pose a risk for BC and that women with higher capacity to methylate in-