Pesticide Exposure and DNA Methylation in Pesticide Applicators

描述（由申请人提供）：尽管进行了50多年的流行病学和毒理学研究，但目前市场上几乎所有农药的人类致癌性都没有得到充分的评估和充分的了解。大多数目前使用的农药在体外和动物研究中都没有明显的基因毒性或诱变性，但人类研究发现，接触特定农药会增加患各种癌症的风险。我们研究的目的是调查农药是否通过表观遗传机制起作用，特别是通过影响异常DNA甲基化，从而增加人类癌症风险。我们假设，在一组健康的农药施用者中，高寿命农药暴露将与DNA甲基化模式的改变有关，包括全球基因组低甲基化和基因特异性高甲基化。我们提出了一项研究，在一个大型的，前瞻性队列的许可农药施药者，农业健康研究，这提供了独特的机会，提供了少数其他研究，以评估生物反应，明确农药暴露在人类。在此之前，还没有关于不同程度的农药暴露对人体DNA甲基化的影响的研究。我们将利用大约700名患者的血液样本，提取基因组DNA，并对该队列关注的癌症中最常见的四个沉默基因p16INK4、MGMT、CDH-1和GSTp1的全球DNA甲基化和启动子区域甲基化进行量化。我们的主要目的是研究暴露于特定农药和化学类别农药是否会预测(1)特定基因（p16INK4， MGMT， CDH-1和GSTp1）的高甲基化和(2)血细胞中CpG重复序列的Alu家族和DNA的LINE-1（长点缀核苷酸元件-1）序列的全球基因组甲基化（低甲基化）的减少。我们的第二个目标是探索其他与农场相关的暴露，如溶剂、谷物粉尘、焊接烟雾和高农药暴露事件是否会改变农药暴露与基因特异性或全局甲基化之间的关系，并根据基线特征（如年龄、最近和过去吸烟、饮酒和饮食）探索和阐明基因特异性和全局甲基化模式。我们提出的研究有可能确定一种以前未被探索的潜在致癌性机制，通过这种机制，农药可能在人体中起作用。公共卫生相关性：全球农药使用的程度，并强调这些暴露可能对公共卫生产生巨大影响。目前市场上和美国公众广泛使用的许多农药通过了基于遗传毒性和诱变性分析的安全测试，然而流行病学研究表明它们对人类具有致癌性。我们提出的研究将解决我们对农药致癌性知识的重大空白，特别是农药是否通过表观遗传机制起作用，如DNA甲基化，从而增加人类的癌症风险。

DESCRIPTION (provided by applicant): The human carcinogenicity of almost all pesticides currently on the market is poorly evaluated and inadequately understood in spite of over 50 years of epidemiologic and toxicologic research. Most currently used pesticides are not overtly genotoxic or mutagenic in vitro and animal studies, however human studies have found suggestive evidence of increased risk for various cancers from exposure to specific pesticides. The objective of our study is to investigate whether pesticides act via an epigenetic mechanism, specifically by effecting aberrant DNA methylation, to confer increased cancer risk in humans. We hypothesize that high lifetime pesticide exposures will be associated with altered DNA methylation patterns, including global genomic hypomethylation and gene-specific hypermethylation, in a group of healthy pesticide applicators. We propose a study nested in a large, prospective cohort of licensed pesticide applicators, The Agricultural Health Study, which provides the unique opportunity afforded in few other studies to evaluate biologic responses to well characterized pesticide exposures in humans. There are no previous studies of DNA methylation measured in humans with respect to varying degrees of pesticide exposure. We will utilize blood samples from approximately 700 applicators, will extract genomic DNA, and will quantify both global DNA methylation and promoter region methylation for four of the most commonly silenced genes in cancers of concern to this cohort, p16INK4, MGMT, CDH-1, and GSTp1. Our primary aim is to investigate whether exposure to specific pesticides and chemical classes of pesticides predicts (1) hypermethylation of specific genes (p16INK4, MGMT, CDH-1, and GSTp1) and (2) decreased global genomic methylation (hypomethylation) estimated in Alu family of CpG repeats and LINE-1 (long interspersed nucleotide element-1) sequences of DNA in blood cells. Our secondary aims are to explore whether other farm related exposures, such as solvents, grain dust, welding fumes, and high pesticide exposure events modify the associations between pesticide exposures and gene specific or global methylation and to explore and elucidate patterns of gene specific and global methylation according to baseline characteristics, such as age, recent and past tobacco smoking, alcohol consumption and diet among a low pesticide exposure group. Our proposed study has the potential to identify a previously unexplored, potential mechanism of carcinogenicity through which pesticides may operate in humans. PUBLIC HEALTH RELEVANCE: The extent of worldwide pesticide usage and underscores the potential for these exposures to have enormous public health implications. Many pesticides currently on the market and in widespread use by the American public pass safety testing based on genotoxicity and mutagenicity assays, however epidemiologic studies suggest carcinogenicity in humans. Our proposed study will address a significant gap in our knowledge of pesticide carcinogenicity, specifically whether pesticides operate via an epigenetic mechanism, such as DNA methylation to confer increased cancer risk in humans.