Altered arsenic disposition in experimental nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is represented by a spectrum of liver pathologies ranging from simple steatosis to nonalcoholic steatohepatitis (NASH). Liver damage sustained in the progressive stages of NAFLD may alter the ability of the liver to properly metabolize and eliminate xenobiotics. The purpose of the current study was to determine whether NAFLD alters the disposition of the environmental toxicant arsenic. C57BL/6 mice were fed either a high-fat or a methionine-choline-deficient diet to model simple steatosis and NASH, respectively. At the conclusion of the dietary regimen, all mice were given a single oral dose of either sodium arsenate or arsenic trioxide. Mice with NASH excreted significantly higher levels of total arsenic in urine (24 h) compared with controls. Total arsenic in the liver and kidneys of NASH mice was not altered; however, NASH liver retained significantly higher levels of the monomethyl arsenic metabolite, whereas dimethyl arsenic was retained significantly less in the kidneys of NASH mice. NASH mice had significantly higher levels of the more toxic trivalent form in their urine, whereas the pentavalent form was preferentially retained in the liver of NASH mice. Moreover, hepatic protein expression of the arsenic biotransformation enzyme arsenic (3+ oxidation state) methyltransferase was not altered in NASH animals, whereas protein expression of the membrane transporter multidrug resistance-associated protein 1 was increased, implicating cellular transport rather than biotransformation as a possible mechanism. These results suggest that NASH alters the disposition of arsenical species, which may have significant implications on the overall toxicity associated with arsenic in NASH.

Environmental Arsenic Exposure and Urinary 8-OHdG in Arizona and Sonora.

Although at high levels arsenic exposure is associated with increased cancer incidence, information on the health effects of lower exposure levels is limited. The objective of this study was to determine whether arsenic at concentrations below 40 microg/L in drinking water is associated with increased urinary 8-hydroxydeoxyguanosine (8-OHdG), a biomarker of DNA oxidative damage and repair. Urine samples were collected from 73 nonsmoking adults residing in two communities in Arizona (mean tap water arsenic (microg/L) 4.0 +/- 2.3 and 20.3 +/- 3.7), and 51 subjects in four communities in Sonora, Mexico (mean tap water arsenic (microg/L) ranging from 4.8 +/- 0.1 to 33.3 +/- 0.6). Although urinary arsenic concentration increased with higher exposure in tap water, urinary 8-OHdG concentration did not differ by community within Arizona or Sonora, and was not associated with urinary arsenic concentration. At the exposure levels evaluated in this study, drinking water arsenic was not associated with increased DNA oxidation as measured by urinary 8-OHdG.

Environmental arsenic exposure, selenium and sputum alpha-1 antitrypsin.

Exposure to arsenic in drinking water is associated with increased respiratory disease. Alpha-1 antitrypsin (AAT) protects the lung against tissue destruction. The objective of this study was to determine whether arsenic exposure is associated with changes in airway AAT concentration and whether this relationship is modified by selenium. A total of 55 subjects were evaluated in Ajo and Tucson, Arizona. Tap water and first morning void urine were analyzed for arsenic species, induced sputum for AAT and toenails for selenium and arsenic. Household tap-water arsenic, toenail arsenic and urinary inorganic arsenic and metabolites were significantly higher in Ajo (20.6±3.5 µg/l, 0.54±0.77 µg/g and 27.7±21.2 µg/l, respectively) than in Tucson (3.9±2.5 µg/l, 0.16±0.20 µg/g and 13.0±13.8 µg/l, respectively). In multivariable models, urinary monomethylarsonic acid (MMA) was negatively, and toenail selenium positively associated with sputum AAT (P=0.004 and P=0.002, respectively). In analyses stratified by town, these relationships remained significant only in Ajo, with the higher arsenic exposure. Reduction in AAT may be a means by which arsenic induces respiratory disease, and selenium may protect against this adverse effect.

Glutathione-S-transferase-omega [MMA(V) reductase] knockout mice: enzyme and arsenic species concentrations in tissues after arsenate administration.

Inorganic arsenic is a human carcinogen to which millions of people are exposed via their naturally contaminated drinking water. Its molecular mechanisms of carcinogenicity have remained an enigma, perhaps because arsenate is biochemically transformed to at least five other arsenic-containing metabolites. In the biotransformation of inorganic arsenic, GSTO1 catalyzes the reduction of arsenate, MMA(V), and DMA(V) to the more toxic +3 arsenic species. MMA(V) reductase and human (hGSTO1-1) are identical proteins. The hypothesis that GST-Omega knockout mice biotransformed inorganic arsenic differently than wild-type mice has been tested. The livers of male knockout (KO) mice, in which 222 bp of Exon 3 of the GSTO1 gene were eliminated, were analyzed by PCR for mRNA. The level of transcripts of the GSTO1 gene in KO mice was 3.3-fold less than in DBA/1lacJ wild-type (WT) mice. The GSTO2 transcripts were about two-fold less in the KO mouse. When KO and WT mice were injected intramuscularly with Na arsenate (4.16 mg As/kg body weight); tissues removed at 0.5, 1, 2, 4, 8, and 12 h after arsenate injection; and the arsenic species measured by HPLC-ICP-MS, the results indicated that the highest concentration of the recently discovered and very toxic MMA(III), a key biotransformant, was in the kidneys of both KO and WT mice. The highest concentration of DMA(III) was in the urinary bladder tissue for both the KO and WT mice. The MMA(V) reducing activity of the liver cytosol of KO mice was only 20% of that found in wild-type mice. There appears to be another enzyme(s) other than GST-O able to reduce arsenic(V) species but to a lesser extent. This and other studies suggest that each step of the biotransformation of inorganic arsenic has an alternative enzyme to biotransform the arsenic substrate.

Environmental arsenic exposure and sputum metalloproteinase concentrations.

Exposure to arsenic in drinking water is associated with an increased rate of lung cancer. The objective of this study was to determine whether arsenic exposure at relatively low concentrations (approximately 20 microg/L) is associated with changes in biomarkers of lung inflammation, as measured by the ratio of sputum metalloproteinase and antiproteinase activity. A total of 73 subjects residing in Ajo and Tucson, Arizona were recruited for this cross-sectional study. Tap water and first morning void urine were analyzed for arsenic. Matrix metalloproteinase 2 (MMP-2), 9 (MMP-9) and tissue inhibitor of metalloproteinase 1 (TIMP-1) were measured in induced sputum. Household tap water arsenic levels in Ajo (20.3+/-3.7 microg/L) were higher than in those Tucson (4.0+/-2.3 microg/L), as were mean urinary total inorganic arsenic levels (29.1+/-20.4 and 11.0+/-12.0 microg/L, respectively). Log-normalized MMP-2, MMP-9, and TIMP-1 concentrations in sputum were not significantly different between towns. However, after adjusting for town, asthma, diabetes, urinary monomethylarsonic acid/inorganic arsenic, and smoking history, total urinary arsenic was negatively associated with MMP-2 and TIMP-1 levels in sputum and positively associated with the ratio of MMP-2/TIMP-1 and MMP-9/TIMP-1 in sputum. Increased sputum proteinase/antiproteinase activity suggests a potential toxic mechanism for low-level arsenic exposure.

Arsenic drinking water exposure and urinary excretion among adults in the Yaqui Valley, Sonora, Mexico.

The objective of this study was to determine arsenic exposure via drinking water and to characterize urinary arsenic excretion among adults in the Yaqui Valley, Sonora, Mexico. A cross-sectional study was conducted from July 2001 to May 2002. Study subjects were from the Yaqui Valley, Sonora, Mexico, residents of four towns with different arsenic concentrations in their drinking water. Arsenic exposure was estimated through water intake over 24 h. Arsenic excretion was assessed in the first morning void urine. Total arsenic concentrations and their species arsenate (As V), arsenite (As III), monomethyl arsenic (MMA), and dimethyl arsenic (DMA) were determined by HPLC/ICP-MS. The town of Esperanza with the highest arsenic concentration in water had the highest daily mean intake of arsenic through drinking water, the mean value was 65.5 microg/day. Positive correlation between total arsenic intake by drinking water/day and the total arsenic concentration in urine (r = 0.50, P < 0.001) was found. Arsenic excreted in urine ranged from 18.9 to 93.8 microg/L. The people from Esperanza had the highest geometric mean value of arsenic in urine, 65.1 microg/L, and it was statistically significantly different from those of the other towns (P < 0.005). DMA was the major arsenic species in urine (47.7-67.1%), followed by inorganic arsenic (16.4-25.4%), and MMA (7.5-15%). In comparison with other reports the DMA and MMA distribution was low, 47.7-55.6% and 7.5-9.7%, respectively, in the urine from the Yaqui Valley population (except the town of Cocorit). The difference in the proportion of urinary arsenic metabolites in those towns may be due to genetic polymorphisms in the As methylating enzymes of these populations.

Selenium and selenomethionine levels in prostate cancer patients.

OBJECTIVE: Selenium (Se) and selenomethionine (Se-Met) have been identified as potential chemopreventive agents of prostate cancer. Using an assay for the speciation (separation and identification) and quantification of selenoamino acids, Se-Met was profiled in serum and prostate tissue from prostate cancer patients. Total Se was measured also. METHODS: Serum and prostate tissue samples were analyzed using high performance liquid chromatography ion channel plasma-mass spectrometry (HPLC ICP-MS). Samples were provided by 25 subjects undergoing radical prostatectomy for the treatment of prostate cancer. RESULTS: The mean serum Se-Met concentration was 59.4 +/- 19.5 ng/ml. Mean total serum Se levels were 133.8 +/- 29.2 ng/ml. Total Se levels in paired samples from the transitional and peripheral zones of the prostate were also compared. Total mean Se levels in peripheral zone tissue was higher than in transitional zone tissue (0.432 +/- 0.212 microg/g versus 0.293 +/- 0.172 microg/g, P = 0.01). Se-Met was detected in the majority of prostate tissues. CONCLUSION: This group of prostate cancer patients had total Se levels in serum and in prostate tissue in a range expected for normal Se intake. There was a significantly higher total Se level found in peripheral versus transitional zone tissues. This is the first time that Se-Met has been detected in prostate tissue.

Oxidation and detoxification of trivalent arsenic species.

Arsenic compounds with a +3 oxidation state are more toxic than analogous compounds with a +5 oxidation state, for example, arsenite versus arsenate, monomethylarsonous acid (MMA(III)) versus monomethylarsonic acid (MMA(V)), and dimethylarsinous acid (DMA(III)) versus dimethylarsinic acid (DMA(V)). It is no longer believed that the methylation of arsenite is the beginning of a methylation-mediated detoxication pathway. The oxidation of these +3 compounds to their less toxic +5 analogs by hydrogen peroxide needs investigation and consideration as a potential mechanism for detoxification. Xanthine oxidase uses oxygen to oxidize hypoxanthine to xanthine to uric acid. Hydrogen peroxide and reactive oxygen are also products. The oxidation of +3 arsenicals by the hydrogen peroxide produced in the xanthine oxidase reaction was blocked by catalase or allopurinol but not by scavengers of the hydroxy radical, e.g., mannitol or potassium iodide. Melatonin, the singlet oxygen radical scavenger, did not inhibit the oxidation. The production of H2O2 by xanthine oxidase may be an important route for decreasing the toxicity of trivalent arsenic species by oxidizing them to their less toxic pentavalent analogs. In addition, there are many other reactions that produce hydrogen peroxide in the cell. Although chemists have used hydrogen peroxide for the oxidation of arsenite to arsenate to purify water, we are not aware of any published account of its potential importance in the detoxification of trivalent arsenicals in biological systems. At present, this oxidation of the +3 oxidation state arsenicals is based on evidence from in vitro experiments. In vivo experiments are needed to substantiate the role and importance of H2O2 in arsenic detoxication in mammals.

Polymorphisms in the human monomethylarsonic acid (MMA V) reductase/hGSTO1 gene and changes in urinary arsenic profiles.

Large interindividual variability in urinary arsenic profiles, following chronic inorganic arsenic exposure, is well-known in humans. To understand this variability, we studied the relationship between polymorphisms in the gene for human monomethylarsonic acid (MMA(V)) reductase/hGSTO1 and the urinary arsenic profiles of individuals chronically exposed to arsenic in their drinking water. To ensure that we did not overlook rare polymorphisms, not included in the public databases, we amplified and sequenced all six exons of the gene and their flanking regions, using DNA isolated from peripheral blood samples of 75 subjects, living in the vicinity of Torreon, Mexico. Four groups, based on the levels of arsenic (9-100 microg/L) in their drinking water, were studied. We identified six novel polymorphisms and two reported previously. The novel polymorphisms were a three base pair deletion (delGGC) in the first intron; a G > C transversion, leading to a serine-to-cysteine substitution at amino acid 86; a G > T transversion and a A > T transversion in intron 5; a G > A transition resulting in glutamate-to-lysine substitution in amino acid 208; and a C > T transition producing an alanine-to-valine substitution in amino acid 236. Two subjects displayed significant differences in patterns of urinary arsenic; they had increased levels of urinary inorganic arsenic and reduced levels of methylated urinary arsenic species as compared to the rest of the study population. These two subjects had the same unique polymorphisms in hGSTO1 in that they were heterozygous for E155del and Glu208Lys. The identified SNPs may be one of the reasons for the large interindividual variability in the response of humans to chronic inorganic arsenic exposure. The findings suggest the need for further studies to identify unambiguously specific polymorphisms that may account for interindividual variability in the human response to chronic inorganic arsenic exposure.