Arsenic and UVR co-exposure results in unique gene expression profile identifying key co-carcinogenic mechanisms.

Changes in gene expression underlie many pathogenic endpoints including carcinogenesis. Metals, like arsenic, alter gene expression; however, the consequences of co-exposures of metals with other stressors are less understood. Although arsenic acts as a co-carcinogen by enhancing the development of UVR skin cancers, changes in gene expression in arsenic UVR co-carcinogenesis have not been investigated. We performed RNA-sequencing analysis to profile changes in gene expression distinct from arsenic or UVR exposures alone. A large number of differentially expressed genes (DEGs) were identified after arsenic exposure alone, while after UVR exposure alone fewer genes were changed. A distinct increase in the number of DEGs was identified after exposure to combined arsenic and UVR exposure that was synergistic rather than additive. In addition, a majority of these DEGs were unique from arsenic or UVR alone suggesting a distinct response to combined arsenic-UVR exposure. Globally, arsenic alone and arsenic plus UVR exposure caused a global downregulation of genes while fewer genes were upregulated. Gene Ontology analysis using the DEGs revealed cellular processes related to chromosome instability, cell cycle, cellular transformation, and signaling were targeted by combined arsenic and UVR exposure, distinct from UVR alone and arsenic alone, while others were related to epigenetic mechanisms such as the modification of histones. This result suggests the cellular functions we identified in this study may be key in understanding how arsenic enhances UVR carcinogenesis and that arsenic-enhanced gene expression changes may drive co-carcinogenesis of UVR exposure.

Zinc supplementation alters tissue distribution of arsenic in Mus musculus.

Arsenic occurs naturally in the environment and humans can be exposed through food, drinking water and inhalation of air-borne particles. Arsenic exposure is associated with cardiovascular, pulmonary, renal, immunologic, and developmental toxicities as well as carcinogenesis. Arsenic displays dose-depen toxicities in target organs or tissues with elevated levels of arsenic. Zinc is an essential micronutrient with proposed protective benefits due to its antioxidant properties, integration into zinc-containing proteins and zinc-related immune signaling. In this study, we tested levels of arsenic and zinc in plasma, kidney, liver, and spleen as model tissues after chronic (42-day) treatment with either arsenite, zinc, or in combination. Arsenite exposure had minimal impact on tissue zinc levels with the exception of the kidney. Conversely, zinc supplementation of arsenite-exposed mice reduced the amount of arsenic detected in all tissues tested. Expression of transporters associated with zinc or arsenic influx and efflux were evaluated under each treatment condition. Significant effects of arsenite exposure on zinc transporter expression displayed tissue selectivity for liver and kidney, and was restricted to Zip10 and Zip14, respectively. Arsenite also interacted with zinc co-exposure for Zip10 expression in liver tissue. Pairwise comparisons show neither arsenite nor zinc supplementation alone significantly altered expression of transporters utilized by arsenic. However, significant interactions between arsenite and zinc were evident for Aqp7 and Mrp1 in a tissue selective manner. These findings illustrate interactions between arsenite and zinc leading to changes in tissue metal level and suggest a potential mechanism by which zinc may offer protection from arsenic toxicities.

Arsenic co-carcinogenesis: Inhibition of DNA repair and interaction with zinc finger proteins.

Arsenic is widely present in the environment and is associated with various population health risks including cancers. Arsenic exposure at environmentally relevant levels enhances the mutagenic effect of other carcinogens such as ultraviolet radiation. Investigation on the molecular mechanisms could inform the prevention and intervention strategies of arsenic carcinogenesis and co-carcinogenesis. Arsenic inhibition of DNA repair has been demonstrated to be an important mechanism, and certain DNA repair proteins have been identified to be extremely sensitive to arsenic exposure. This review will summarize the recent advances in understanding the mechanisms of arsenic carcinogenesis and co-carcinogenesis, including DNA damage induction and ROS generation, particularly how arsenic inhibits DNA repair through an integrated molecular mechanism which includes its interactions with sensitive zinc finger DNA repair proteins.

Contribution of NADPH oxidase to the retention of UVR-induced DNA damage by arsenic.

Arsenic is a naturally occurring element present in food, soil and water and human exposure is associated with increased cancer risk. Arsenic inhibits DNA repair at low, non-cytotoxic concentrations and amplifies the mutagenic and carcinogenic impact of other DNA-damaging agents, such as ultraviolet radiation (UVR). Arsenic exposure leads to oxidation of zinc coordinating cysteine residues, zinc loss and decreased activity of the DNA repair protein poly(ADP)ribose polymerase (PARP)-1. Because arsenic stimulates NADPH oxidase (NOX) activity leading to generation of reactive oxygen species (ROS), the goal of this study was to investigate the role of NOX in arsenic-induced inhibition of PARP activity and retention of DNA damage. NOX involvement in the arsenic response was assessed in vitro and in vivo. Keratinocytes were treated with or without arsenite, solar-simulated UVR, NOX inhibitors and/or isoform specific NOX siRNA. Knockdown or inhibition of NOX decreased arsenite-induced ROS, PARP-1 oxidation and DNA damage retention, while restoring arsenite inhibition of PARP-1 activity. The NOX2 isoform was determined to be the major contributor to arsenite-induced ROS generation and DNA damage retention. In vivo DNA damage was measured by immunohistochemical staining and analysis of dorsal epidermis sections from C57BI/6 and p91phox knockout (NOX2-/-) mice. There was no significant difference in solar-simulated UVR DNA damage as detected by percent PH2AX positive cells within NOX2-/- mice versus control. In contrast, arsenite-dependent retention of UVR-induced DNA damage was markedly reduced. Altogether, the in vitro and in vivo findings indicate that NOX is involved in arsenic enhancement of UVR-induced DNA damage.

The immunotoxicity of natural and depleted uranium: From cells to people.

Uranium is a naturally occurring element found in the environment as a mixture of isotopes with differing radioactive properties. Enrichment of mined material results in depleted uranium waste with substantially reduced radioactivity but retains the capacity for chemical toxicity. Uranium mine and milling waste are dispersed by wind and rain leading to environmental exposures through soil, air, and water contamination. Uranium exposure is associated with numerous adverse health outcomes in humans, yet there is limited understanding of the effects of depleted uranium on the immune system. The purpose of this review is to summarize findings on uranium immunotoxicity obtained from cell, rodent and human population studies. We also highlight how each model contributes to an understanding of mechanisms that lead to immunotoxicity and limitations inherent within each system. Information from population, animal, and laboratory studies will be needed to significantly expand our knowledge of the contributions of depleted uranium to immune dysregulation, which may then inform prevention or intervention measures for exposed communities.

The R-enantiomer of ketorolac reduces ovarian cancer tumor burden in vivo.

BACKGROUND: Rho-family GTPases, including Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42), are important modulators of cancer-relevant cell functions and are viewed as promising therapeutic targets. Based on high-throughput screening and cheminformatics we identified the R-enantiomer of an FDA-approved drug (ketorolac) as an inhibitor of Rac1 and Cdc42. The corresponding S-enantiomer is a non-steroidal anti-inflammatory drug (NSAID) with selective activity against cyclooxygenases. We reported previously that R-ketorolac, but not the S-enantiomer, inhibited Rac1 and Cdc42-dependent downstream signaling, growth factor stimulated actin cytoskeleton rearrangements, cell adhesion, migration and invasion in ovarian cancer cell lines and patient-derived tumor cells. METHODS: In this study we treated mice with R-ketorolac and measured engraftment of tumor cells to the omentum, tumor burden, and target GTPase activity. In order to gain insights into the actions of R-ketorolac, we also performed global RNA-sequencing (RNA-seq) analysis on tumor samples. RESULTS: Treatment of mice with R-ketorolac decreased omental engraftment of ovarian tumor cells at 18 h post tumor cell injection and tumor burden after 2 weeks of tumor growth. R-ketorolac treatment inhibited tumor Rac1 and Cdc42 activity with little impact on mRNA or protein expression of these GTPase targets. RNA-seq analysis revealed that R-ketorolac decreased expression of genes in the HIF-1 signaling pathway. R-ketorolac treatment also reduced expression of additional genes associated with poor prognosis in ovarian cancer. CONCLUSION: These findings suggest that R-ketorolac may represent a novel therapeutic approach for ovarian cancer based on its pharmacologic activity as a Rac1 and Cdc42 inhibitor. R-ketorolac modulates relevant pathways and genes associated with disease progression and worse outcome.

The R-Enantiomer of Ketorolac Delays Mammary Tumor Development in Mouse Mammary Tumor Virus-Polyoma Middle T Antigen (MMTV-PyMT) Mice.

Epidemiologic studies report improved breast cancer survival in women who receive ketorolac (Toradol) for postoperative pain relief compared with other analgesic agents. Ketorolac is a racemic drug. The S-enantiomer inhibits cyclooxygenases; R-ketorolac is a selective inhibitor of the small GTPases Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42), which are signaling molecules up-regulated during breast cancer progression and metastasis. The goal of this study was to determine whether R-ketorolac altered breast cancer development in the mouse mammary tumor virus-polyoma middle T-antigen model. Mice were administered ketorolac orally at 1 mg/kg twice daily to approximate the typical human dose. Mammary glands were analyzed for tumor number and immunohistochemical markers of proliferation and differentiation. R-ketorolac treatment significantly reduced mammary epithelial proliferation, based on Ki67 staining, and suppressed tumor development. Proliferative mammary epithelium from R-ketorolac-treated mice displayed greater differentiation, based on significantly higher total E-cadherin and decreased keratin 5 staining than epithelium of placebo-treated mice. No differences were detected in estrogen receptor, progesterone receptor, ß-catenin, or vimentin expression between placebo and R-ketorolac treatment groups. These findings indicate that R-ketorolac treatment slows tumor progression in an aggressive model of breast cancer. R-ketorolac may thus represent a novel therapeutic approach for breast cancer prevention or treatment based on its pharmacologic activity as a Rac1 and Cdc42 inhibitor.

Peroxynitrite contributes to arsenic-induced PARP-1 inhibition through ROS/RNS generation.

Arsenic, in the trivalent form (AsIII), is a human co-carcinogen reported to enhance mutagenesis effects of other carcinogens such as UV radiation by inhibiting DNA repair. The zinc finger DNA repair protein Poly (ADP-ribose) polymerase 1 (PARP-1) is a sensitive target of AsIII and both reactive oxygen and nitrogen species (ROS/RNS) generated by AsIII contribute to PARP-1 inhibition. However, the mechanisms of ROS/RNS-mediated PARP inhibition and how AsIII-generated ROS/RNS may be interconnected are still unclear. In this study, we found AsIII exposure of normal human keratinocyte (HEKn) cells generated peroxynitrite through superoxide and nitric oxide production in an AsIII concentration dependent manner. Peroxynitrite inhibited PARP-1 activity and caused zinc loss from PARP-1 protein while scavenging peroxynitrite was protective of the impacts on PARP-1. We identified peroxynitrite was responsible for S-nitrosation on cysteine residues resulting in PARP-1 zinc finger conformational changes. Taken together, the evidence indicates AsIII generates peroxynitrite through superoxide and nitric oxide production, induces S-nitrosation on PARP-1, leading to zinc loss and activity inhibition of PARP-1, thus enhancing DNA damage caused by UV radiation. These findings highlight a role for peroxynitrite as a key molecule of ROS/RNS mediated DNA repair inhibition by AsIII which should inform the development of prevention and intervention strategies against AsIII co-carcinogenesis.

Zinc deficiency alters the susceptibility of pancreatic beta cells (INS-1) to arsenic exposure.

Pancreatic beta cells produce and release insulin, a hormone that regulates blood glucose levels, and their dysfunction contributes to the development of diabetes mellitus. Zinc deficiency and inorganic arsenic exposure both independently associate with the development of diabetes, although the effects of their combination on pancreatic beta cell health and function remain unknown. We hypothesized zinc deficiency increases the toxicity associated with arsenic exposure, causing an increased susceptibility to DNA damage and disruption of insulin production. Zinc deficiency decreased cell proliferation by 30% in pancreatic INS-1 rat insulinoma cells. Arsenic exposure (0, 50 or 500 ppb exposures) significantly decreased cell proliferation, and increased mRNA levels of genes involved in stress response (Mt1, Mt2, Hmox1) and DNA damage (p53, Ogg1). When co-exposed to both zinc deficiency and arsenic, zinc deficiency attenuated this response to arsenic, decreasing the expression of Mt1, Hmox1, and Ogg1, and significantly increasing DNA double-strand breaks 2.9-fold. Arsenic exposure decreased insulin expression, but co-exposure did not decrease insulin levels beyond the arsenic alone condition, but did result in a further 33% decline in cell proliferation at the 500 ppb arsenic dose, and a significant increase in beta cell apoptosis. These results suggest zinc deficiency and arsenic, both independently and in combination, adversely affect pancreatic beta cell health and both factors should be considered in the evaluation of health outcomes for susceptible populations.

Two-step approach for assessing the health effects of environmental chemical mixtures: application to simulated datasets and real data from the Navajo Birth Cohort Study.

BACKGROUND: There is increasing interest in examining the consequences of simultaneous exposures to chemical mixtures. However, a consensus or recommendations on how to appropriately select the statistical approach analyzing the health effects of mixture exposures which best aligns with study goals has not been well established. We recognize the limitations that existing methods have in effectively reducing data dimension and detecting interaction effects when analyzing chemical mixture exposures collected in high dimensional datasets with varying degrees of variable intercorrelations. In this research, we aim to examine the performance of a two-step statistical approach in addressing the analytical challenges of chemical mixture exposures using two simulated data sets, and an existing data set from the Navajo Birth Cohort Study as a representative case study. METHODS: We propose to use a two-step approach: a robust variable selection step using the random forest approach followed by adaptive lasso methods that incorporate both dimensionality reduction and quantification of the degree of association between the chemical exposures and the outcome of interest, including interaction terms. We compared the proposed method with other approaches including (1) single step adaptive lasso; and (2) two-step Classification and regression trees (CART) followed by adaptive lasso method. RESULTS: Utilizing simulated data sets and applying the method to a real-life dataset from the Navajo Birth Cohort Study, we have demonstrated good performance of the proposed two-step approach. Results from the simulation datasets indicated the effectiveness of variable dimension reduction and reliable identification of a parsimonious model compared to other methods: single-step adaptive lasso or two-step CART followed by adaptive lasso method. CONCLUSIONS: Our proposed two-step approach provides a robust way of analyzing the effects of high-throughput chemical mixture exposures on health outcomes by combining the strengths of variable selection and adaptive shrinkage strategies.

Differential sensitivities of cellular XPA and PARP-1 to arsenite inhibition and zinc rescue.

Arsenite directly binds to the zinc finger domains of the DNA repair protein poly (ADP ribose) polymerase (PARP)-1, and inhibits PARP-1 activity in the base excision repair (BER) pathway. PARP inhibition by arsenite enhances ultraviolet radiation (UVR)-induced DNA damage in keratinocytes, and the increase in DNA damage is reduced by zinc supplementation. However, little is known about the effects of arsenite and zinc on the zinc finger nucleotide excision repair (NER) protein xeroderma pigmentosum group A (XPA). In this study, we investigated the difference in response to arsenite exposure between XPA and PARP-1, and the differential effectiveness of zinc supplementation in restoring protein DNA binding and DNA damage repair. Arsenite targeted both XPA and PARP-1 in human keratinocytes, resulting in zinc loss from each protein and a pronounced decrease in XPA and PARP-1 binding to chromatin as demonstrated by Chip-on-Western assays. Zinc effectively restored DNA binding of PARP-1 and XPA to chromatin when zinc concentrations were equal to those of arsenite. In contrast, zinc was more effective in rescuing arsenite-augmented direct UVR-induced DNA damage than oxidative DNA damage. Taken together, our findings indicate that arsenite interferes with PARP-1 and XPA binding to chromatin, and that zinc supplementation fully restores DNA binding activity to both proteins in the cellular context. Interestingly, rescue of arsenite-inhibited DNA damage repair by supplemental zinc was more sensitive for DNA damage repaired by the XPA-associated NER pathway than for the PARP-1-dependent BER pathway. This study expands our understanding of arsenite's role in DNA repair inhibition and co-carcinogenesis.

Selective Sensitization of Zinc Finger Protein Oxidation by Reactive Oxygen Species through Arsenic Binding.

Cysteine oxidation induced by reactive oxygen species (ROS) on redox-sensitive targets such as zinc finger proteins plays a critical role in redox signaling and subsequent biological outcomes. We found that arsenic exposure led to oxidation of certain zinc finger proteins based on arsenic interaction with zinc finger motifs. Analysis of zinc finger proteins isolated from arsenic-exposed cells and zinc finger peptides by mass spectrometry demonstrated preferential oxidation of C3H1 and C4 zinc finger configurations. C2H2 zinc finger proteins that do not bind arsenic were not oxidized by arsenic-generated ROS in the cellular environment. The findings suggest that selectivity in arsenic binding to zinc fingers with three or more cysteines defines the target proteins for oxidation by ROS. This represents a novel mechanism of selective protein oxidation and demonstrates how an environmental factor may sensitize certain target proteins for oxidation, thus altering the oxidation profile and redox regulation.

Inhibition of poly(ADP-ribose)polymerase-1 and DNA repair by uranium.

Uranium has radiological and non-radiological effects within biological systems and there is increasing evidence for genotoxic and carcinogenic properties attributable to uranium through its heavy metal properties. In this study, we report that low concentrations of uranium (as uranyl acetate; <10 µM) is not cytotoxic to human embryonic kidney cells or normal human keratinocytes; however, uranium exacerbates DNA damage and cytotoxicity induced by hydrogen peroxide, suggesting that uranium may inhibit DNA repair processes. Concentrations of uranyl acetate in the low micromolar range inhibited the zinc finger DNA repair protein poly(ADP-ribose) polymerase (PARP)-1 and caused zinc loss from PARP-1 protein. Uranyl acetate exposure also led to zinc loss from the zinc finger DNA repair proteins Xeroderma Pigmentosum, Complementation Group A (XPA) and aprataxin (APTX). In keeping with the observed inhibition of zinc finger function of DNA repair proteins, exposure to uranyl acetate enhanced retention of induced DNA damage. Co-incubation of uranyl acetate with zinc largely overcame the impact of uranium on PARP-1 activity and DNA damage. These findings present evidence that low concentrations of uranium can inhibit DNA repair through disruption of zinc finger domains of specific target DNA repair proteins. This may provide a mechanistic basis to account for the published observations that uranium exposure is associated with DNA repair deficiency in exposed human populations.

Characterization of a Cdc42 protein inhibitor and its use as a molecular probe.

Cdc42 plays important roles in cytoskeleton organization, cell cycle progression, signal transduction, and vesicle trafficking. Overactive Cdc42 has been implicated in the pathology of cancers, immune diseases, and neuronal disorders. Therefore, Cdc42 inhibitors would be useful in probing molecular pathways and could have therapeutic potential. Previous inhibitors have lacked selectivity and trended toward toxicity. We report here the characterization of a Cdc42-selective guanine nucleotide binding lead inhibitor that was identified by high throughput screening. A second active analog was identified via structure-activity relationship studies. The compounds demonstrated excellent selectivity with no inhibition toward Rho and Rac in the same GTPase family. Biochemical characterization showed that the compounds act as noncompetitive allosteric inhibitors. When tested in cellular assays, the lead compound inhibited Cdc42-related filopodia formation and cell migration. The lead compound was also used to clarify the involvement of Cdc42 in the Sin Nombre virus internalization and the signaling pathway of integrin VLA-4. Together, these data present the characterization of a novel Cdc42-selective allosteric inhibitor and a related analog, the use of which will facilitate drug development targeting Cdc42-related diseases and molecular pathway studies that involve GTPases.

Arsenite binding-induced zinc loss from PARP-1 is equivalent to zinc deficiency in reducing PARP-1 activity, leading to inhibition of DNA repair.

Inhibition of DNA repair is a recognized mechanism for arsenic enhancement of ultraviolet radiation-induced DNA damage and carcinogenesis. Poly(ADP-ribose) polymerase-1 (PARP-1), a zinc finger DNA repair protein, has been identified as a sensitive molecular target for arsenic. The zinc finger domains of PARP-1 protein function as a critical structure in DNA recognition and binding. Since cellular poly(ADP-ribosyl)ation capacity has been positively correlated with zinc status in cells, we hypothesize that arsenite binding-induced zinc loss from PARP-1 is equivalent to zinc deficiency in reducing PARP-1 activity, leading to inhibition of DNA repair. To test this hypothesis, we compared the effects of arsenite exposure with zinc deficiency, created by using the membrane-permeable zinc chelator TPEN, on 8-OHdG formation, PARP-1 activity and zinc binding to PARP-1 in HaCat cells. Our results show that arsenite exposure and zinc deficiency had similar effects on PARP-1 protein, whereas supplemental zinc reversed these effects. To investigate the molecular mechanism of zinc loss induced by arsenite, ICP-AES, near UV spectroscopy, fluorescence, and circular dichroism spectroscopy were utilized to examine arsenite binding and occupation of a peptide representing the first zinc finger of PARP-1. We found that arsenite binding as well as zinc loss altered the conformation of zinc finger structure which functionally leads to PARP-1 inhibition. These findings suggest that arsenite binding to PARP-1 protein created similar adverse biological effects as zinc deficiency, which establishes the molecular mechanism for zinc supplementation as a potentially effective treatment to reverse the detrimental outcomes of arsenic exposure.

Differential binding of monomethylarsonous acid compared to arsenite and arsenic trioxide with zinc finger peptides and proteins.

Arsenic is an environmental toxin that enhances the carcinogenic effect of DNA-damaging agents, such as ultraviolet radiation and benzo[a]pyrene. Interaction with zinc finger proteins has been shown to be an important molecular mechanism for arsenic toxicity and cocarcinogenesis. Arsenicals such as arsenite, arsenic trioxide (ATO), and monomethylarsonous acid (MMA(III)) have been reported to interact with cysteine residues of zinc finger domains, but little is known about potential differences in their selectivity of interaction. Herein we analyzed the interaction of arsenite, MMA(III), and ATO with C2H2, C3H1, and C4 configurations of zinc fingers using UV-vis, cobalt, fluorescence, and mass spectrometry. We observed that arsenite and ATO both selectively bound to C3H1 and C4 zinc fingers, while MMA(III) interacted with all three configurations of zinc finger peptides. Structurally and functionally, arsenite and ATO caused conformational changes and zinc loss on C3H1 and C4 zinc finger peptide and protein, respectively, whereas MMA(III) changed conformation and displaced zinc on all three types of zinc fingers. The differential selectivity was also demonstrated in zinc finger proteins isolated from cells treated with these arsenicals. Our results show that trivalent inorganic arsenic compounds, arsenite and ATO, have the same selectivity and behavior when interacting with zinc finger proteins, while methylation removes the selectivity. These findings provide insights on the molecular mechanisms underlying the differential effects of inorganic versus methylated arsenicals, as well as the role of in vivo arsenic methylation in arsenic toxicity and carcinogenesis.

Poly(ADP-ribose) contributes to an association between poly(ADP-ribose) polymerase-1 and xeroderma pigmentosum complementation group A in nucleotide excision repair.

Exposure to ultraviolet radiation (UVR) promotes the formation of UVR-induced, DNA helix distorting photolesions such as (6-4) pyrimidine-pyrimidone photoproducts and cyclobutane pyrimidine dimers. Effective repair of such lesions by the nucleotide excision repair (NER) pathway is required to prevent DNA mutations and chromosome aberrations. Poly(ADP-ribose) polymerase-1 (PARP-1) is a zinc finger protein with well documented involvement in base excision repair. PARP-1 is activated in response to DNA damage and catalyzes the formation of poly(ADP-ribose) subunits that assist in the assembly of DNA repair proteins at sites of damage. In this study, we present evidence for PARP-1 contributions to NER, extending the knowledge of PARP-1 function in DNA repair beyond the established role in base excision repair. Silencing the PARP-1 protein or inhibiting PARP activity leads to retention of UVR-induced photolesions. PARP activation following UVR exposure promotes association between PARP-1 and XPA, a central protein in NER. Administration of PARP inhibitors confirms that poly(ADP-ribose) facilitates PARP-1 association with XPA in whole cell extracts, in isolated chromatin complexes, and in vitro. Furthermore, inhibition of PARP activity decreases UVR-stimulated XPA chromatin association, illustrating that these relationships occur in a meaningful context for NER. These results provide a mechanistic link for PARP activity in the repair of UVR-induced photoproducts.

Reduction of arsenite-enhanced ultraviolet radiation-induced DNA damage by supplemental zinc.

Arsenic is a recognized human carcinogen and there is evidence that arsenic augments the carcinogenicity of DNA damaging agents such as ultraviolet radiation (UVR) thereby acting as a co-carcinogen. Inhibition of DNA repair is one proposed mechanism to account for the co-carcinogenic actions of arsenic. We and others find that arsenite interferes with the function of certain zinc finger DNA repair proteins. Furthermore, we reported that zinc reverses the effects of arsenite in cultured cells and a DNA repair target protein, poly (ADP-ribose) polymerase-1. In order to determine whether zinc ameliorates the effects of arsenite on UVR-induced DNA damage in human keratinocytes and in an in vivo model, normal human epidermal keratinocytes and SKH-1 hairless mice were exposed to arsenite, zinc or both before solar-simulated (ss) UVR exposure. Poly (ADP-ribose) polymerase activity, DNA damage and mutation frequencies at the Hprt locus were measured in each treatment group in normal human keratinocytes. DNA damage was assessed in vivo by immunohistochemical staining of skin sections isolated from SKH-1 hairless mice. Cell-based findings demonstrate that ssUVR-induced DNA damage and mutagenesis are enhanced by arsenite, and supplemental zinc partially reverses the arsenite effect. In vivo studies confirm that zinc supplementation decreases arsenite-enhanced DNA damage in response to ssUVR exposure. From these data we can conclude that zinc offsets the impact of arsenic on ssUVR-stimulated DNA damage in cells and in vivo suggesting that zinc supplementation may provide a strategy to improve DNA repair capacity in arsenic exposed human populations.

An adjusted partial least squares regression framework to utilize additional exposure information in environmental mixture data analysis.

In a large-scale environmental health population study that is composed of subprojects, often different fractions of participants out of the total enrolled have measures of specific outcomes. It's conceptually reasonable to assume the association study would benefit from utilizing additional exposure information from those with a specific outcome not measured. Partial least squares regression is a practical approach to determine the exposure-outcome associations for mixture data. Like a typical regression approach, however, the partial least squares regression requires that each data observation must have both complete covariate and outcome for model fitting. In this paper, we propose novel adjustments to the general partial least squares regression to estimate and examine the association effects of individual environmental exposure to an outcome within a more complete context of the study population's environmental mixture exposures. The proposed framework takes advantage of the bilinear model structure. It allows information from all participants, with or without the outcome values, to contribute to the model fitting and the assessment of association effects. Using this proposed framework, incorporation of additional information will lead to smaller root mean square errors in the estimation of association effects, and improve the ability to assess the significance of the effects.