Faculty Bibliography

Environmental arsenic compounds and their methylated metabolites do not form adducts with DNA, but do cause oxidative DNA damage. Chromosome aberrations are seen at toxic concentrations. Genetic effects that occur at non-toxic concentrations include aneuploidy, comutagenesis (resulting from indirect effects on DNA repair), and delayed mutagenesis (probably secondary to aneuploidy and/or epigenetic effects). Effects of trivalent arsenicals on poly(ADP ribose) polymerase and P53 activation may mediate effects on DNA repair and aneuploidy. A growing literature points to the epigenetic effects of arsenic compounds in cells and in vivo. A review of the current literature on DNA methylation, histone modifications and microRNA effects is presented

Arsenite is an environmental pollutant. Exposure to inorganic arsenic in drinking water is associated with elevated cancer risk, especially in skin. Arsenite alone does not cause skin cancer in animals, but arsenite can enhance the carcinogenicity of solar UV. Arsenite is not a significant mutagen at non-toxic concentrations, but it enhances the mutagenicity of other carcinogens. The tumor suppressor protein P53 and nuclear enzyme PARP-1 are both key players in DNA damage response. This laboratory demonstrated earlier that in cells treated with arsenite, the P53-dependent increase in p21(WAF1/CIP1) expression, normally a block to cell cycle progression after DNA damage, is deficient. Here we show that although long-term exposure of human keratinocytes (HaCaT) to a nontoxic concentration (0.1 microM) of arsenite decreases the level of global protein poly(ADP-ribosyl)ation, it increases poly(ADP-ribosyl)ation of P53 protein and PARP-1 protein abundance. We also demonstrate that exposure to 0.1 microM arsenite depresses the constitutive expression of p21 mRNA and P21 protein in HaCaT cells. Poly(ADP-ribosyl)ation of P53 is reported to block its activation, DNA binding and its functioning as a transcription factor. Our results suggest that arsenite's interference with activation of P53 via poly(ADP-ribosyl)ation may play a role in the comutagenic and cocarcinogenic effects of arsenite

Hexavalent chromium (Cr (VI)) is a well known-human carcinogen with exposures occurring in both occupational and environmental settings. Although lung carcinogenicity has been well documented for occupational exposure via inhalation, the carcinogenic hazard of drinking water exposure to Cr (VI) has yet to be established. We used a hairless mouse model to study the effects of K(2)CrO(4) in the drinking water on ultraviolet radiation (UVR)-induced skin tumors. Hairless mice were unexposed or exposed to UVR alone (1.2 kJ/m(2)), K(2)CrO(4) alone at 2.5 and 5.0 ppm, or the combination of UVR and K(2)CrO(4) at 0.5, 2.5, and 5.0 ppm. Mice were observed on a weekly basis for the appearance of skin tumors larger than 2 mm. All the mice were euthanized on day 182. The skin tumors were excised and subsequently analyzed microscopically for malignancy by histopathology. There was a total absence of observable skin tumors in untreated mice and in mice exposed to chromate alone. However, there was a dose-dependent increase in the number of skin tumors greater than 2 mm in mice exposed to K(2)CrO(4) and UV compared with mice exposed to UV alone. The increase in tumors larger than 2 mm was statistically significant (P < 0.05) for UV and K(2)CrO(4) at the two highest K(2)CrO(4) doses (2.5 and 5.0 ppm), and there was a statistically significant increase in the numbers of malignant tumors per mouse in the UVR plus K(2)CrO(4) (5 ppm) group compared with UV alone. The data presented here indicate that K(2)CrO(4) increases the number of UV-induced skin tumors in a dose-dependent manner, and these results support the concern that regulatory agencies have relative to the carcinogenic health hazards of widespread human exposure to Cr (VI) in drinking water

BACKGROUND: Hairless mice that ingested arsenite in drinking water exhibited more than a 5-fold enhancement of ultraviolet radiation (UVR) carcinogenesis, whereas arsenite alone was carcinogenically inactive. Dietary organoselenium blocked the cancer enhancement effect of arsenic but not cancer induction by UVR. OBJECTIVE: In this study we sought to explain selenium blockage of As enhancement by establishing the extent that As and Se tissue distributions are coincident or divergent. METHODS: We used the X-ray fluorescence microprobe at the Advanced Photon Source (Argonne National Laboratory) to probe sections of skin and liver from hairless mice exposed to a) UVR, b) UVR + As, c) UVR + organoselenium, or d) UVR + As + organoselenium. RESULTS: We found elevated levels of As in the skin epithelium (hair follicles and epidermis) and diffusely in the liver of mice exposed to UVR + As. Arsenic was entirely absent in skin in mice exposed to UVR + As + organoselenium, but a diffuse low level was seen in the liver. As and Se locations were consistently divergent in skin; As was more diffusely distributed, whereas Se was strongly associated with membranes. X-ray absorption near-edge spectra are consistent with the presence of the seleno-bis(S-glutathionyl) arsinium ion in the liver. CONCLUSIONS: Supplemental Se was uncommonly effective at preventing even a trace of As in skin at 14 or 196 days of continuous exposure to As in drinking water. Traces of the seleno-bis(S-glutathionyl) arsinium ion in the liver suggested that formation of this compound was more likely to be responsible for the As-blocking effect of Se than was a mechanism based on antioxidation

The skin cancer enhancing effect of chromium (in male mice) and nickel in UVR-irradiated female Skh1 mice was investigated. The dietary vitamin E and selenomethionine were tested for prevention of chromium-enhanced skin carcinogenesis. The mice were exposed to UVR (1.0 kJ/m(2) 3x weekly) for 26 weeks either alone, or combined with 2.5 or 5.0 ppm potassium chromate, or with 20, 100 or 500 ppm nickel chloride in drinking water. Vitamin E or selenomethionine was added to the lab chow for 29 weeks beginning 3 weeks before the start of UVR exposure. Both chromium and nickel significantly increased the UVR-induced skin cancer yield in mice. In male Skh1 mice, UVR alone induced 1.9+/-0.4 cancers/mouse, and 2.5 or 5.0 ppm potassium chromate added to drinking water increased the yields to 5.9+/-0.8 and 8.6+/-0.9 cancers/mouse, respectively. In female Skh1 mice, UVR alone induced 1.7+/-0.4 cancers/mouse, and the addition of 20, 100 or 500 ppm nickel chloride increased the yields to 2.8+/-0.9, 5.6+/-0.7 and 4.2+/-1.0 cancers/mouse, respectively. Neither vitamin E nor selenomethionine reduced the cancer yield enhancement by chromium. These results confirm that chromium and nickel, while not good skin carcinogens per se, are enhancers of UVR-induced skin cancers in Skh1 mice. Data also suggest that the enhancement of UVR-induced skin cancers by chromate may not be oxidatively mediated since the antioxidant vitamin E as well as selenomethionine, found to prevent arsenite-enhanced skin carcinogenesis, failed to suppress enhancement by chromate

Inorganic arsenic (arsenite and arsenate) in drinking water has been associated with skin cancers and increased incidence of cardiovascular diseases. Additionally, studies have demonstrated the pro-angiogenic effect of arsenite and its potential promotion of tumor angiogenesis and tumor progression. Furthermore, recent reports demonstrated reversal of skin co-carcinogenesis by an organoselenium compound. The present study was undertaken to determine the effect and mechanism on angiogenesis of arsenite at low level and its potential reversal by various selenium-derived compounds. The pro-angiogenesis effects and mechanisms of sodium arsenite were determined using the chick chorioallantoic membrane (CAM) model over 3 days and compared with standard pro-angiogenesis factors, such as basic fibroblast growth factor (b-FGF). Additionally, the potential effect of various selenium-derived compounds-such as dimethyl selenone, diphenyl selenone, sodium selenite or Se-methyl selenocysteine-in reversing the pro-angiogenesis effect of arsenite or b-FGF was also determined in the CAM model. The pro-angiogenesis effect of arsenite or b-FGF was significantly (P < 0.01) blocked by dimethyl selenone, diphenyl selenone, sodium selenite or Se-methyl selenocysteine. The pro-angiogenesis effect of either sodium arsenite at 33 nM or b-FGF was blocked (P < 0.01) by the extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation inhibitor, PD 98059. Additionally, the pro-angiogenic effect of arsenic or b-FGF was blocked as well (P < 0.01) by the alphavbeta3 antagonist, XT199. These data suggest that the pro-angiogenesis effect of arsenic is initiated at the plasma membrane integrin alphavbeta3, involves activation of the ERK1/2 pathway and is effectively reversed by various selenium-derived compounds

Arsenic-induced carcinogenesis is a worldwide problem for which there is currently limited means for control. Recently, we showed that arsenite in drinking water greatly potentiates solar ultraviolet radiation (UVR) induced skin cancer in mice, at concentrations as low as 1.25 mg/l. In this study, we examined the protective efficacy of vitamin E and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) against tumors induced by UVR and UVR + arsenite. Hairless mice were exposed to UVR alone (1.0 kJ/m(2) x 3 times weekly) or UVR + sodium arsenite (5 mg/l in drinking water) and fed lab chow supplemented or not with vitamin E (RRR-alpha-tocopheryl acetate, 62.5 IU/kg diet) or p-XSC (10 mg/kg) for 26 weeks. The tumor yield for mice receiving UVR alone was 3.6 tumors/mouse and the addition of arsenite to the drinking water increased the yield to 7.0 tumors/mouse (P < 0.005). Vitamin E and p-XSC reduced the tumor yield in mice given UVR + arsenite by 2.1-fold (P < 0.001) and 2-fold (P < 0.002), respectively. Vitamin E, but not p-XSC, reduced the tumor yield induced by UVR alone by 30% (P < 0.05). No significant difference in tumor types or grade of malignancy was observed in mice treated with or without chemopreventives. Immunostaining of mouse skin for 8-oxo-2'-deoxyguanosine (8-oxo-dG) revealed a significant reduction of 8-oxo-dG formation in mice treated with vitamin E or p-XSC compared with those treated with UVR + arsenite. These results show that vitamin E and p-XSC protect strongly against arsenite-induced enhancement of UVR carcinogenesis

Recent evidence suggests that inflammatory cytokines and growth factors contribute to arsenite (As)-induced human carcinogenesis. We investigated the expression of inflammatory cytokine mRNAs during the transformation process induced by chronic As exposure in non-tumorigenic human osteogenic sarcoma (N-HOS) cells using gene arrays, and results were confirmed by RT-PCR and protein arrays. Caffeic acid phenethyl ester (CAPE), a naturally occurring immunomodulating agent, was used to evaluate the role of inflammatory factors in the process of As-mediated N-HOS cell transformation and in As-transformed HOS (AsT-HOS) cells. We found that an 8-week continuous exposure of N-HOS to 0.3 microM arsenite resulted in HOS cell transformation. That exposure also caused substantial decreases in inflammatory cytokine mRNAs, such as interleukin (IL) IL-1alpha, IL-2, IL-8, IL-18, MCP-1, TGF-beta2, and TNF-alpha, while it increased c-jun mRNA in a time-dependent manner. Co-incubation of N-HOS with As and CAPE (0.5-2.5 microM) prevented As-mediated declines in cytokine mRNAs in the co-treated cells, as well as their transformation to anchorage independence, while it caused decreases in c-jun mRNA. CAPE (up to 10 microM) had no effect on growth of N-HOS cells. However, CAPE (1-10 microM) treatment of AsT-HOS cells inhibited cell growth, induced cell cycle G2/M arrest, and triggered apoptosis, accompanied by changes in cytokine gene expression, as well as decreases in cyclin B1 and cdc2 abundance. Resveratrol (RV) and (-)(.) epigallocatechin gallate (EGCG), preventive agents present in grapes and green tea, respectively, induced similar changes in AsT-HOS cell growth but required much higher doses than CAPE to cause 50% growth arrest (<2.5 microM CAPE versus 25 microM RV or 50 microM EGCG). Overall, our findings suggest that inflammatory cytokines play an important role in the suppressive effects of CAPE on As-induced cell transformation and in the selective cytotoxicity of CAPE to As-transformed HOS cells

The human enzyme As(III) S-adenosylmethionine methyltransferase (AS3MT) catalyzes arsenic biotransformations and is considered to contribute to arsenic-related diseases. AS3MT is expressed in various tissues and cell types including liver, brain, adrenal gland, and peripheral blood mononuclear cells but not in human keratinocytes, urothelial, or brain microvascular endothelial cells. This indicates that AS3MT expression is regulated in a tissue/cell type-specific manner, but the mechanism of transcriptional regulation of expression of the AS3MT gene is not known. In this study, we define the DNA sequence of the core promoter region of the human AS3MT gene. We identify a GC box in the promoter to which the stress-related transcription factor Sp1 binds, indicating involvement of regulatory elements in AS3MT gene expression.

Antimony (Sb) and its compounds are negative in gene mutation assays in bacteria and cultured mammalian cells but positive in some assays for clastogenicity and/or DNA damage. In order to better understand the modes of action for antimony genotoxicity, we assessed reporter gene activation by antimony and antimony compounds in the new expanded ToxTracker assay. ToxTracker evaluates the activation of biomarkers for different cellular defense mechanisms using a series of green fluorescent protein reporters inserted into mouse embryonic stem cell lines. The assay responds to: 1) DNA damage and inhibition of DNA replication; 2) oxidative stress; 3) unfolded protein response (protein damage); and 4) p53-dependent cellular stress. Sb metal powder, six trivalent (Sb(III)) compounds, and five pentavalent antimony (Sb(V)) compounds were assessed. Sb powder and all six Sb(III) compounds activated oxidative stress ToxTracker reporters at non-toxic doses. Of the five Sb(V) compounds, antimony pentachloride and potassium hexahydroantimonate induced a robust oxidative stress response while sodium antimonate induced only a weak oxidative stress response. At higher concentrations (up to either 75 % toxicity or the highest dissolved concentration tested), Sb powder and all Sb(III) compounds except for antimony trichloride induced the unfolded protein response. Of the five Sb(V) compounds tested, only potassium hexahydroantimonate induced weak activation of the unfolded protein response and was also the only pentavalent compound to yield modest (30 %) cytotoxicity. None of the compounds tested activated the DNA damage/inhibition of DNA replication reporters, nor did they activate the p53-dependent response. All Sb(III) compounds, Sb powder, and three of the five Sb(V) compounds activated the oxidative stress reporters, but there was no activation of reporters associated with DNA damage and repair or p53-dependent cellular stress. The consistent activation of reporters for oxidative stress suggests this mode of action may underlie genotoxicity responses for antimony and its compounds.