Mechanism of Furan-Induced Toxicity and Carcinogencity

描述（由申请人提供）：呋喃是一种重要的工业化合物，也存在于环境中。它对小鼠和大鼠具有肝毒性和致癌性。基于这些结果和人类接触呋喃的可能性，呋喃已被列为一种可能的人类致癌物。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机制都有助于总体致癌结果。很明显，毒性和致癌性是由细胞色素P450催化呋喃氧化成a，(3-不饱和双醛，c/s-2-丁烯-1,4-dial引起的。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作用。我们的长期目标是确定呋喃在啮齿类动物中致癌的机制，这样我们就可以开发出有效的工具来确定暴露于呋喃的人类是否易受其毒理学特性的影响。本应用程序的目的是确定呋喃在体内是否是一种遗传毒性致癌物，并更好地确定导致其激活或解毒的代谢过程。核心假设是，细胞毒性和基因毒性途径都参与了呋喃的总体致癌作用，并涉及多种代谢途径。我们在强有力的初步数据的基础上提出了这一假设，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。虽然这种活性代谢物在体外可以烷基化DNA和蛋白质，但在体内也可能进一步代谢成其他有毒化合物。我们计划通过以下具体目标来验证我们的假设：1)确定呋喃在大蓝鼠中的诱变活性；2)表征呋喃的体内代谢途径；3)比较人和啮齿动物肝细胞中呋喃代谢的途径，确定各途径所涉及的酶。总的来说，这些特定的目标将为呋喃毒性和肿瘤发生机制的测试提供重要的数据。有了这些信息，我们可以开发适当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志物（尿代谢物、蛋白质和/或DNA加合物），这些生物标志物可用于确定这些重要的毒理学反应是否发生在暴露于呋喃的人类身上。

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.