Mechanism of Furan-Induced Toxicity and Carcinogencity

描述(申请人提供)：呋喃是一种重要的工业化合物，也存在于环境中。它对小鼠和大鼠都有肝脏毒性和致癌作用。根据这些结果和人类接触的可能性，呋喃已被列为可能的人类致癌物质。呋喃诱导肿瘤的机制尚不清楚。现有的实验证据表明，非遗传毒性和遗传毒性两种机制都对总体致癌结果有贡献。细胞色素P450催化呋喃氧化生成α，(3-不饱和二醛，c/S-2-丁烯-1，4-二乙二胺)是其毒性和致癌性的起始。然而，c/S-2-丁烯-1，4-Dial的进一步代谢可能会产生其他反应性代谢物，从而导致呋喃的毒性效应。我们的长期目标是确定呋喃在啮齿类动物中的致癌机制，以便我们能够开发有效的工具来确定接触呋喃的人类是否对其毒理学特性敏感。这项应用的目的是确定呋喃在体内是否是一种基因毒性致癌物质，并更好地确定导致其激活或解毒的代谢过程。中心假说是，细胞毒性和遗传毒性途径都参与了呋喃的整体致癌作用，涉及多个代谢途径。我们根据强有力的初步数据提出了这一假设，这些数据表明呋喃氧化成c/S-2-丁烯-1，4-Dial启动了这一过程。虽然这种反应性代谢物在体外可以使DNA和蛋白质烷化，但在体内也可能进一步代谢成其他有毒化合物。我们计划通过追求以下特定目标来验证我们的假设：1)确定呋喃在大型蓝色啮齿动物中的诱变活性；2)表征呋喃在体内的代谢途径；3)比较呋喃在人和啮齿动物肝细胞中的代谢途径，并确定每个途径所涉及的酶。总而言之，这些特定的目标将为测试呋喃毒性和肿瘤发生的机制提供重要的数据。有了这些信息，我们可以开发合适的模型系统来评估遗传毒性和细胞毒性在呋喃致癌特性中的作用。此外，这些研究将有助于开发适当的生物标记物(尿代谢物、蛋白质和/或DNA加合物)，可用于确定这些毒理上重要的反应是否发生在接触呋喃的人类身上。 这是一位久负盛名的研究人员修改后的申请，旨在进一步确定呋喃的毒性和诱变性机制。这项建议的优点是申请者在有机代谢物阐明和DNA损伤机制方面的强大背景，在具体目标中提出的明确和合乎逻辑的方法，以及对以前的批评的回应。这个应用程序的弱点很小。一些担忧是，在特定的目标1中，特别是在目标3中，可能会出现无效结果，这可能会否定使用啮齿动物模型来确定呋喃对人类的毒性和致突变性。

DESCRIPTION (provided by applicant): Furan is an important industrial compound that is also present in the environment. It is both hepatoxic and carcinogenic in mice and rats. Based on these results and the potential for human exposure, furan has been listed as a possible human carcinogen. The mechanism of tumor induction by furan is unknown. The available experimental evidence suggests that both nongenotoxic and genotoxic mechanisms contribute to the overall carcinogenic outcome. It is clear that the toxicity and carcinogenicity is initiated by cytochrome P450 catalyzed oxidation of furan to an a,(3-unsaturated dialdehyde, c/s-2-butene-1,4-dial. However, it is possible that further metabolism of c/s-2-butene-1,4-dial generates other reactive metabolites that contribute to the toxic effects of furan. Our long-range goal is to determine the mechanism of furan-induced carcino- genesis in rodents so that we can develop effective tools to determine if humans exposed to furan are sus- ceptible to its toxicological properties. The objective of this application is to determine if furan is a genotoxic carcinogen in vivo and to better define the metabolic processes that lead to its activation or detoxification. The central hypothesis is that both cytotoxic and genotoxic pathways contribute to the overall carcinogenic effects of furan with the involvement of multiple metabolic pathways. We formulated this hypothesis on the basis of strong preliminary data that suggest that the oxidation of furan to c/s-2-butene-1,4-dial initiates the process. While this reactive metabolite can alkylate both DNA and protein in vitro, it is also likely to be further metabolized to other toxic compounds in vivo. We plan to test our hypothesis by pursuing the following specific aims: 1) Determine the mutagenic activity of furan in Big Blue rodents; 2) Characterize the in vivo metabolic pathways of furan; 3) Compare the pathways of furan metabolism in human and rodent hepatocytes and determine the enzymes involved in each pathway. Collectively, these specific aims will provide important data for testing mechanisms of furan toxicity and tumorigenesis. With this information, we can develop appropriate model systems to assess th6 role of genotoxicity and cytotoxicity in the carcino- genic properties of furan. In addition, these studies will aid in the development of appropriate biomarkers (urinary metabolites, protein and/or DNA adducts) that can be used to determine if these toxicologically important reactions are occurring in humans exposed to furan. This is a revised application from a well established investigator that seeks to further determine the mechanism of furan toxicity and mutagenicity. The strengths of this proposal are the strong background of the applicant in organic metabolite elucidation and DNA damage mechanisms, the clear and logical approach laid out in the specific aims and the responsiveness to the previous critiques. The weaknesses of this application are minimal. Some concerns are the potential for a null result in specific aims 1 and, particularly in aim 3 which may negate the use of a rodent model for determination of furan toxicity and mutagenicity in humans.