MOLECULAR MECHANISMS OF COMPLEX MIXTURE TOXICITY

这项研究的长期目标是发展对 导致不良健康影响和毒性的潜在机制 暴露于多环芳烃(PAH)和 致癌金属砷和铬，通常作为共同污染物存在于 环境。本研究项目的目的是：(1)阐明 砷和铬影响诱导基因表达的机制，以及 (2)评价典型化合物苯并[α]芘(B[α]P)的混合效应。 PAK与铬、砷对细胞I、II期表达的影响 排毒精灵。环境政策的发展依赖于风险 有关个人接触的化学物质的信息。虽然 已经有机制来测试个别化学品对健康的影响，有 关于复杂环境混合物毒性的数据很少。在没有的情况下 具体数据，进行风险评估时必须使用默认假设 对于混合物。例如，在缺乏证据的情况下。相反，两个 具有类似毒性作用的化学品被认为是以相加的方式起作用的。 这种方法对于许多复杂的混合物来说并不令人满意，在这些混合物中 从抑制效应到协同作用，相互作用的光谱是存在的。因为大多数人 人类暴露在复杂的环境污染物混合物中，方法 为了评估这些暴露的风险，需要制定。 接触多环芳烃的大部分(如果不是全部)毒性效应是由芳香族化合物介导的 烃(Ah)受体，一种配体激活的转录因子，在 与ah受体核转运体(ARNT)的结合导致 I期解毒基因的转录激活，如编码 细胞色素P450单加氧酶CyP1A1、CyP1B1和CyPIA2，以及 II期解毒基因，如编码苯醌氧化还原酶的基因 (NQO_1)、谷胱甘肽-S转移酶和UDP-葡萄糖醛酸基转移酶 (UGTIA6)。第二阶段基因也可以被抗氧化剂和亲电体诱导。 通过不依赖于受体的机制。来自我们的初步工作 实验室已经表明，培养的哺乳动物细胞暴露在铬酸盐或 亚砷酸盐破坏了二恶英对I期和II期基因的协同诱导， 该原型为卤代芳烃的芳香烃受体配体。铬酸盐 抑制II期基因诱导的程度比抑制I期基因诱导的程度更大 基因，而亚砷酸盐抑制I期基因诱导并引起剂量依赖关系 氧化应激反应，超诱导电泳性反应元件(EpRE)- 介导的II期基因转录。这些观察将我们引向我 假设接触B[α]P和铬酸盐或亚砷酸盐的混合物，(1) 将扰乱控制B[α]P-转录的调控机制 可诱导的基因启动子，以及(2)会导致I期和II期的解偶联 B[α]P代谢中的基因表达和伴随的失衡。结果来自 这项工作将有助于开发一种方法来预测由以下因素引起的健康风险 暴露在化学混合物中。

The long-range goal of this research is to develop an understanding of the mechanisms underlying the adverse health effects and toxicity resulting from exposure to complex mixtures of polycyclic aromatic hydrocarbons (PAH) and the carcinogenic metals arsenic and chromium, often found as co-contaminants in the environment. The objectives of this research project are, (1) to elucidate the mechanisms by which arsenic and chromium affect inducible gene expression, and (2), to evaluate the effect of mixtures of benzo[alpha]pyrene (B[alpha]P), a prototypical PAK and chromium and arsenic on the expression of phase I and phase II detoxification genies. Development of environmental policy relies on risk information about the chemicals to which individuals are exposed. Although mechanisms are in place to test the health effects of individual chemicals, there is little data on the toxicity of complex environmental mixtures. In the absence of specific data, default assumptions must be used when conducting risk assessment for mixtures. For example, in the absence of evidence. to the contrary, two chemicals having similar toxic effects are assumed to act in an additive manner. This approach is not satisfactory for many complex mixtures in which a wide spectrum of interactions, from repression of effects to synergy, exist. Since most humane are exposed to complex mixtures of environmental contaminants, methods for assessing the risk of these exposures need to be developed. Most if not all the toxic effects of PAH exposure are mediated by the aromatic hydrocarbon (Ah) receptor, a ligand-activated transcription factor that, in combination with the Ah receptor nuclear translocator (ARNT) causes the transcriptional activation of phase I detoxification genes, such as those coding for the cytochromes P450 monooxygenases CYP1Al, CYP1B1 and CYPIA2, and of phase II detoxification genes, such as those coding for quinone oxidoreductase (NQO1), glutathione-S-transferase (GSTP) and UDP-glucuronosyl transferase (UGTIA6). Phase II genes can also be induced by antioxidants and electrophiles through Ah receptor-independent mechanisms. Preliminary work from our laboratory has shown that exposure of cultured mammalian cells to chromate or arsenite disrupts the coordinate induction of phase I and phase II genes by dioxin, the protype halogenated aromatic hydrocarbon Ah receptor ligand. Chromate inhibits induction of phase II genes to a greater extent than induction of phase I genes, whereas arsenite inhibits phase I gene induction and elicits a dose-dependent oxidative stress response that superinduces electrophile response element (EpRE)- mediated transcription of phase II genes. These observations lead us to me hypothesis that combined exposure to a mixture B[alpha]P and chromate or arsenite, (1) Will disrupt the regulatory mechanisms that control transcription from B[alpha]P- inducible gene promoters, and (2) will cause an uncoupling of phase I and phase II gene expression and concomitant imbalance in B[alpha]P metabolism. Results from this work will help develop a means to predict the health risks arising from exposure to chemical mixtures.