Dori R. Germolec

Comparative toxicity of trivalent and pentavalent inorganic and methylated arsenicals in rat and human cells

Abstract. Biomethylation is considered a major detoxification pathway for inorganic arsenicals (iAs). According to the postulated metabolic scheme, the methylation of iAs yields methylated metabolites in which arsenic is present in both pentavalent and trivalent forms. Pentavalent mono- and dimethylated arsenicals are less acutely toxic than iAs. However, little is known about the toxicity of trivalent methylated species. In the work reported here the toxicities of iAs and trivalent and pentavalent methylated arsenicals were examined in cultured human cells derived from tissues that are considered a major site for iAs methylation (liver) or targets for carcinogenic effects associated with exposure to iAs (skin, urinary bladder, and lung). To characterize the role of methylation in the protection against toxicity of arsenicals, the capacities of cells to produce methylated metabolites were also examined. In addition to human cells, primary rat hepatocytes were used as methylating controls. Among the arsenicals examined, trivalent monomethylated species were the most cytotoxic in all cell types. Trivalent dimethylated arsenicals were at least as cytotoxic as trivalent iAs (arsenite) for most cell types. Pentavalent arsenicals were significantly less cytotoxic than their trivalent analogs. Among the cell types examined, primary rat hepatocytes exhibited the greatest methylation capacity for iAs followed by primary human hepatocytes, epidermal keratinocytes, and bronchial epithelial cells. Cells derived from human bladder did not methylate iAs. There was no apparent correlation between susceptibility of cells to arsenic toxicity and their capacity to methylate iAs. These results suggest that (1) trivalent methylated arsenicals, intermediary products of arsenic methylation, may significantly contribute to the adverse effects associated with exposure to iAs, and (2) high methylation capacity does not protect cells from the acute toxicity of trivalent arsenicals.

Evaluation of nanoparticle immunotoxicity

The pharmaceutical industry is developing increasing numbers of drugs and diagnostics based on nanoparticles, and evaluating the immune response to these diverse formulations has become a challenge for scientists and regulatory agencies alike. An international panel of scientists and representatives from various agencies and companies reviewed the imitations of current tests at a workshop held at the National Cancer Institute in Frederick, Maryland. This article outlines practical strategies for identifying and controlling interferences in common evaluation methods and the implications for regulation.

Arsenic Enhancement of Skin Neoplasia by Chronic Stimulation of Growth Factors

Although numerous epidemiological studies have shown that inorganic arsenicals cause skin cancers and hyperkeratoses in humans, there are currently no established mechanisms for their action or animal models. Previous studies in our laboratory using primary human keratinocyte cultures demonstrated that micromolar concentrations of inorganic arsenite increased cell proliferation via the production of keratinocyte-derived growth factors. As recent reports demonstrate that overexpression of keratinocyte-derived growth factors, such as transforming growth factor (TGF)-alpha, promote the formation of skin tumors, we hypothesized that similar events may be responsible for those associated with arsenic skin diseases. Thus, the influence of arsenic in humans with arsenic skin disease and on mouse skin tumor development in transgenic mice was studied. After low-dose application of tetradecanoyl phorbol acetate (TPA), a marked increase in the number of skin papillomas occurred in Tg.AC mice, which carry the v-Ha-ras oncogene, that received arsenic in the drinking water as compared with control drinking water, whereas no papillomas developed in arsenic-treated transgenic mice that did not receive TPA or arsenic/TPA-treated wild-type FVB/N mice. Consistent with earlier in vitro findings, increases in granulocyte/macrophage colony-stimulating factor (GM-CSF) and TGF-alpha mRNA transcripts were found in the epidermis at clinically normal sites within 10 weeks after arsenic treatment. Immunohistochemical staining localized TGF-alpha overexpression to the hair follicles. Injection of neutralizing antibodies to GM-CSF after TPA application reduced the number of papillomas in Tg.AC mice. Analysis of gene expression in samples of skin lesions obtained from humans chronically exposed to arsenic via their drinking water also showed similar alterations in growth factor expression. Although confirmation will be required in nontransgenic mice, these results suggest that arsenic enhances development of skin neoplasias via the chronic stimulation of keratinocyte-derived growth factors and may be a rare example of a chemical carcinogen that acts as a co-promoter.

Oxidative Stress and Its Role in Skin Disease

Skin is a major target of oxidative stress due to reactive oxygen species (ROS) that originate in the environment and in the skin itself. ROS are generated during normal metabolism, are an integral part of normal cellular function, and are usually of little harm because of intracellular mechanisms that reduce their damaging effects. Antioxidants attenuate the damaging effects of ROS and can impair and/or reverse many of the events that contribute to epidermal toxicity and disease. However, increased or prolonged free radical action can overwhelm ROS defense mechanisms, contributing to the development of cutaneous diseases and disorders. Although ROS play a role in diseases such as skin cancer, their biological targets and pathogenic mode of action are still not fully understood. In addition, strategies useful in the therapeutic management of ROS action in human skin are still lacking. This review is intended to give investigators an introduction to ROS, antioxidants, two skin disorders influenced by ROS action (skin cancer and psoriasis), and relevant model systems used to study ROS action.

It's all about sex : gender, lung development and lung disease

Accumulating evidence suggests that gender affects the incidence, susceptibility and severity of several lung diseases. Gender also influences lung development and physiology. Data from both human and animal studies indicate that sex hormones might contribute to disease pathogenesis or serve as protective factors, depending on the disease involved. In this review, the influence of gender and sex hormones on lung development and pathology will be discussed, with specific emphasis on pulmonary fibrosis, asthma and cancer.

Immunotoxicity of Perfluorinated Compounds: Recent Developments

Perfluorinated compounds (PFCs) are environmentally widespread, persistent, and bioaccumulative chemicals with multiple toxicities reported in experimental models and wildlife, including immunomodulation. The two most commonly detected compounds, which also generally occur in the highest concentrations in environmentally exposed organisms, are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). PFOA and PFOS have been reported to alter inflammatory responses, production of cytokines, and adaptive and innate immune responses in rodent models, avian models, reptilian models, and mammalian and nonmammalian wildlife. Mounting evidence suggests that immune effects in laboratory animal models occur at serum concentrations below, within the reported range, or just above those reported for highly exposed humans and wildlife. Thus, the risk of immune effects for humans and wildlife exposed to PFCs cannot be discounted, especially when bioaccumulation and exposure to multiple PFCs are considered. This review contains brief descriptions of current and recently published work exploring immunomodulation by PFOA, PFOS, and other PFCs in rodent models, alternative laboratory models, and wildlife.

Prevalence and sociodemographic correlates of antinuclear antibodies in the United States

OBJECTIVE To estimate the prevalence, types, and sociodemographic and biobehavioral correlates of antinuclear antibodies (ANAs) in the US. METHODS We conducted a cross-sectional analysis of 4,754 individuals from the National Health and Nutrition Examination Survey 1999-2004. ANAs were assessed by indirect immunofluorescence. In ANA-positive individuals, cellular staining patterns were determined, and specific autoantibody reactivities were assessed by immunoprecipitation. RESULTS The ANA prevalence in the US population of individuals ages 12 years and older was 13.8% (95% confidence interval [95% CI] 12.2-15.5%). ANA prevalence increased with age (P=0.01), and ANAs were more prevalent among females than males (17.8% versus 9.6%; P<0.001), with the female-to-male ratio peaking at 40-49 years of age. ANA prevalence was modestly higher in African Americans compared with whites (age-adjusted prevalence odds ratio [POR] 1.30, 95% CI 1.00-1.70). Remarkably, ANAs were less common in overweight and obese individuals (age-adjusted POR 0.74) than in persons of normal weight. No significant associations of ANA with education, family income, alcohol use, smoking history, serum levels of cotinine, or C-reactive protein were observed. In ANA-positive individuals, nuclear patterns were seen in 84.6%, cytoplasmic patterns were seen in 21.8%, and nucleolar patterns were seen in 6.1%; the most common specific autoantibodies were anti-Ro (3.9%) and anti-Su (2.4%). CONCLUSION These findings suggest that more than 32 million persons in the US have ANAs, and that the prevalence is higher among females, older individuals, African Americans, and those with a normal body weight. These data will serve as a useful baseline for future investigations of predictors and changes in ANA prevalence over time.

Arsenic can mediate skin neoplasia by chronic stimulation of keratinocyte-derived growth factors

Although numerous epidemiological studies have shown that inorganic arsenicals are human skin carcinogens, there is currently no accepted mechanism for its action or an established animal model for its study. We observed increased mRNA transcripts and secretion of keratinocyte growth factors, including granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-alpha (TGF-alpha) and the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) in primary human epidermal keratinocytes cultured in the presence of low micromolar concentrations of sodium arsenite. Total cell numbers, as well as c-myc expression and incorporation of [3H]thymidine, both indicators of cell proliferation, were also elevated in keratinocyte cultures treated with sodium arsenite. As an in vivo model, the influence of arsenic on mouse skin tumor development was studied in transgenic TG.AC mice which carry the v-Ha-ras oncogene, and can serve as a genetically initiated model for skin carcinogenesis. Following low-dose application of 12-O-tetradecanoyl phorbol-13-acetate (TPA), a marked increase in the number of skin papillomas occurred in transgenic mice receiving arsenic in the drinking water as compared to control drinking water. Papillomas did not develop in arsenic-treated transgenic mice that had not received TPA or arsenic-treated wild-type FVB/N mice, suggesting that arsenic is neither a tumor initiator or promoter but rather an enhancer. Injection of anti-GM-CSF antibodies following application of TPA in transgenic mice reduced the number of papillomas. Consistent with that observed in human keratinocyte cultures, increases in GM-CSF and TGF-alpha mRNA transcripts were found within the epidermis of arsenic-treated mice when compared to controls within 6 weeks of treatment. These results suggest that arsenic enhances papilloma development via the chronic stimulation of keratinocyte-derived growth factors and represents the first example of a chemical carcinogen that acts in this manner. These studies suggest that in vitro studies with human keratinocyte cultures examined in conjunction with TG.AC transgenic mice can provide a useful model for examining the tumor enhancing properties of environmental chemicals.

Arsenic induces overexpression of growth factors in human keratinocytes.

Although epidemiological studies have shown that inorganic arsenicals are human skin carcinogens and induce hyperproliferation and hyperkeratosis, there is currently no known mechanism for their action or an established animal model for its study. We observed increased mRNA transcripts and secretion of keratinocyte growth factors, including granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-alpha (TGF alpha) and the proinflammatory cytokine tumor necrosis factor-alpha in primary human epidermal keratinocytes cultured in the presence of low micromolar concentrations of sodium arsenite. Treatment with sodium arsenite resulted in a significant increase in cell proliferation, as indicated by increases in cell numbers, c-myc gene expression, and incorporation of [3H]thymidine into cellular DNA. Studies of transcriptional regulation indicate that the rate of GM-CSF mRNA transcription is increased, while the elevated TGF alpha is likely the results of message stabilization. While a number of cytokine regulatory networks exist in the skin, studies utilizing neutralizing antibodies against the growth factors of interest indicate that inhibition of the arsenic-induced increase in TGF alpha results in a corresponding decrease in the gene expression and secretion of GM-CSF. The present studies demonstrate that growth-promoting cytokines and growth factors are induced in keratinocytes following treatment with arsenic and could play a significant role in arsenic-induced skin cancer.

Occupational exposures and autoimmune diseases

Autoimmune diseases are pathologic conditions defined by abnormal autoimmune responses and characterized by immune system reactivity in the form of autoantibodies and T cell responses to self-structures. Here we review the limited but growing epidemiologic and experimental literature pertaining to the association between autoimmune diseases and occupational exposure to silica, solvents, pesticides, and ultraviolet radiation. The strongest associations (i.e., relative risks of 3.0 and higher) have been documented in investigations of silica dust and rheumatoid arthritis, lupus, scleroderma and glomerulonephritis. Weaker associations are seen, however, for solvent exposures (in scleroderma, undifferentiated connective tissue disease, and multiple sclerosis) and for farming or pesticide exposures (in rheumatoid arthritis). Experimental studies suggest two different effects of these exposures: an enhanced proinflammatory (TH1) response (e.g., TNF-alpha and IL-1 cytokine production with T cell activation), and increased apoptosis of lymphocytes leading to exposure to or modification of endogenous proteins and subsequent autoantibody formation. The former is a general mechanism that may be relevant across a spectrum of autoimmune diseases, whereas the latter may be a mechanism more specific to particular diseases (e.g., ultraviolet radiation, Ro autoantibodies, and lupus). Occupational exposures are important risk factors for some autoimmune diseases, but improved exposure assessment methods and better coordination between experimental/animal models and epidemiologic studies are needed to define these risks more precisely.