Growth Factors and Inflammatory Mediators in Arsenic-Induced Toxicity

砷已被归类为皮肤、肺和膀胱的已知人类致癌物，然而，砷致癌作用的机制尚不清楚，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。我们目前正在调查个体间的变化，在砷的反应，以解决为什么有些人或人群似乎是砷引起的毒性不太敏感的问题。我们已经研究了由几种不同的角质形成细胞捐助者在砷治疗的反应中产生的细胞因子的配置文件，并已表明，虽然细胞因子的反应是定性相似的，在类似的细胞因子的产生，剂量和定量细胞因子分泌的敏感性不同的捐助者。在与Miroslav Styblo博士的合作中，我们正在研究不同供体的不同敏感性是否反映了它们甲基化砷的能力。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，角质形成细胞具有非常小的甲基化砷的能力。然而，在无机砷的吸收和单甲基砷的产量和分布的差异表明，个体间的差异可能发生在人体皮肤在体内。我们已经评估了砷暴露对p53小鼠细胞因子谱改变的影响，这些小鼠喂食胆碱缺乏和胆碱充足的饮食以改变其甲基化（和解毒）砷的能力。与相应的对照组相比，喂食胆碱缺乏饮食的p53小鼠在其皮肤中表现出更高水平的TNF α、TGF α和GM-CSF mRNA。这些研究表明，甲基化的缺陷可能会影响个体组织中产生的细胞因子对砷的反应。我们还研究了砷III和砷V及其单甲基和二甲基代谢产物在角质形成细胞培养物中的毒性。正如预期的那样，无机三价砷对所有供体的毒性最大。令人惊讶的是，单甲基砷化物对角质形成细胞也具有高度毒性。我们的特点是毒性的剂量反应曲线，并检查细胞因子分泌模式和增殖活性暴露后的三价和五价代谢产物。由于超敏反应高度依赖于细胞因子的分泌和调节，并且我们先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。在砷暴露动物的引流淋巴结中，由中等和强致敏剂诱导的抗原特异性增殖反应显着减少，特别是在低剂量下。与此相反，有丝分裂原刺激的增殖反应在引流淋巴结不受砷暴露。砷还降低了先前致敏小鼠的激发诱导反应。为了研究这些变化的潜在机制，我们研究了砷对朗格汉斯细胞迁移和抗原呈递的影响。通过饮水暴露于砷的小鼠，郎格罕氏细胞从耳中迁移出来的能力增强。据报道，TNF α是朗格汉斯细胞迁移的主要刺激物，这与我们以前的发现一致，即TNF α水平在砷处理的小鼠皮肤中升高。目前正在研究这些动物皮肤中调节细胞因子表达的定量。- 砷，皮肤，角质形成细胞，癌，细胞增殖，细胞因子，生长因子，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