Growth Factors and Inflammatory Mediators in Arsenic-Induced Toxicity

砷已被列为已知的人类皮肤、肺和膀胱致癌物，然而，砷致癌的机制尚不清楚，部分原因是缺乏适当的动物模型。我们实验室正在进行的研究表明，砷通过刺激细胞因子和生长因子（包括粒细胞巨噬细胞集落刺激因子、转化生长因子α和肿瘤坏死因子α）的慢性产生，在皮肤中起到肿瘤增强剂或进展剂的作用。我们目前正在调查对砷反应的个体间差异，以解决为什么一些个体或群体似乎对砷引起的毒性不太敏感的问题。我们研究了几种不同角质细胞供体对砷处理产生的细胞因子谱，结果表明，虽然细胞因子的反应在质量上是相似的，因为产生了相似的细胞因子，但对剂量的敏感性和细胞因子分泌的数量因供体而异。我们与北卡罗来纳大学的Miroslav stybloo博士合作，正在研究不同供体的不同敏感性是否反映了他们甲基化砷的能力。迄今为止，这些研究表明，与来自其他组织（如膀胱和肝脏）的细胞相比，角化细胞对砷的甲基化能力非常弱。然而，无机砷的吸收和一甲基砷的产量和分布的差异表明，人体内皮肤可能存在个体间差异。我们已经评估了砷暴露对喂养胆碱缺乏和胆碱充足饮食的p53小鼠细胞因子谱变化的影响，以改变它们甲基化（和解毒）武器库的能力。被喂食胆碱缺乏饮食的p53小鼠，其皮肤中TNFalpha、TGFalpha和GM-CSF mrna的水平高于相应的对照组。这些研究表明，甲基化缺陷可能影响个体组织对砷的反应产生的细胞因子。我们还研究了砷ii和砷v及其单甲基和二甲基代谢物在角化细胞培养中的毒性。不出所料，无机三价砷对所有捐赠者毒性最大。令人惊讶的是，单甲基砷对角质形成细胞也有很高的毒性。我们描述了毒性的剂量反应曲线，并检查了暴露于三价和五价代谢物后的细胞因子分泌模式和增殖活性。由于超敏反应高度依赖于细胞因子的分泌和调节，并且我们之前已经证明砷暴露可调节生长和炎症细胞因子，因此我们研究了低水平砷暴露如何调节超敏反应。中等和强致敏剂诱导的抗原特异性增殖反应在砷暴露动物的引流淋巴结中显著减少，特别是在低剂量时。相比之下，有丝分裂原刺激下的引流淋巴结的增殖反应不受砷暴露的影响。砷还减少了先前致敏的小鼠的攻击诱导反应。为了研究这些改变的潜在机制，我们研究了砷对朗格汉斯细胞迁移和抗原呈递的影响。通过饮用水接触砷的小鼠朗格汉斯细胞的耳外迁移增强。据报道，TNFalpha是朗格汉斯细胞迁移的主要刺激物，这与我们之前的研究结果一致，即砷处理小鼠皮肤中TNFalpha水平升高。目前正在对这些动物皮肤中调节细胞因子的表达进行定量研究。-砷，皮肤，角质形成细胞，癌症，细胞增殖，细胞因子，生长因子，Tg。AC转基因小鼠，PCR

Arsenic has been classified as a known human carcinogen of the skin, lung and urinary bladder, however, the mechanisms involved in carcinogenesis by arsenic are not known, due in part to a lack of appropriate animal models. Ongoing studies in our laboratory have suggested that arsenic serves as a tumor enhancer or progressor in the skin via stimulation of the chronic production of cytokines and growth factors, including granulocyte macrophage colony stimulating factor, transforming growth factor alpha and tumor necrosis factor alpha. We are currently investigating inter-individual variation in responses to arsenic, to address the question of why some individuals or populations appear to be less sensitive to arsenic-induced toxicities. We have examined the cytokine profiles produced by several different keratinocyte donors in response to arsenic treatment and have shown that while cytokine responses are qualitatively similar, in that similar cytokines are produced, sensitivity to dose and quantitative cytokine secretion vary from donor to donor. In collaboration with Dr. Miroslav Styblo at UNC we are examining whether the differential sensitivity seen with various donors may be a reflection of their ability to methylate arsenic. To date these studies have indicated that keratinocytes have very little ability to methylate arsenicals, as compared with cells from other tissues such as the bladder and liver. However, differences in the uptake of inorganic arsenic and in the yield and distribution of monomethylarsenic suggest that interindividual differences could occur in human skin in vivo. We have evaluated the effects of arsenic exposure on alterations in cytokine profiles in p53 mice fed choline deficient and choline sufficient diets to alter their ability to methylate (and detoxify) arsenals. p53 mice fed a choline deficient diet exhibit higher levels of TNFalpha, TGFalpha and GM-CSF mRNAs in their skin than corresponding controls. These studies suggest that deficiencies in methylation may influence the cytokines produced in individual tissues in response to arsenic. We have also examined the toxicity of both ArsenicIII and ArsenicV and their monomethyl and dimethyl metabolites in keratinocyte cultures. As expected, inorganic trivalent arsenic is the most toxic to all donors. Surprisingly, monomethyl arsenicals are also highly toxic to keratinocytes. We have characterized the dose response curves for toxicity and examined cytokine secretion patterns and proliferative activity after exposure to the trivalent and pentavalent metabolites. As hypersensitivity responses are highly dependent on cytokine secretion and regulation, and as we have previously demonstrated that growth and inflammatory cytokines are modulated by arsenic exposure, we have investigated how low level arsenic exposure modulates hypersensitivity responses. Antigen-specific proliferative responses induced by moderate and strong sensitizing agents are significantly reduced in the draining lymph nodes of arsenic-exposed animals, particularly at low doses. In contrast, mitogen-stimulated proliferative responses in the draining lymph nodes were not affected by arsenic exposure. Arsenic also reduced challenged-induced responses in previously sensitized mice. To investigate the potential mechanisms of these alterations we examined the effects of arsenic on Langerhans cell migration and antigen presentation. Langerhans cell migration out of the ear was enhanced in mice exposed to arsenic via the drinking water. As TNFalpha is reported to be a primary stimulator of Langerhans cell migration, this is consistent with our previous findings that TNFalpha levels are elevated in the skin of arsenic treated mice. Quantitation of the expression of regulatory cytokines in the skin of these animals is currently under investigation. - arsenic, skin, keratinocytes, cancer, cell proliferation, cytokines, growth factors, Tg.AC transgenic mice, PCR