Pesticide Exposure and DNA Methylation in Pesticide Applicators

描述(申请人提供)：尽管经过50多年的流行病学和毒理学研究，目前市场上几乎所有杀虫剂的人类致癌性都没有得到很好的评估和充分的了解。目前使用的大多数杀虫剂在体外和动物研究中都没有明显的遗传毒性或诱变性，然而，人类研究发现了暴露于特定杀虫剂会增加各种癌症风险的证据。我们研究的目的是调查杀虫剂是否通过表观遗传机制发挥作用，特别是通过影响异常的DNA甲基化，从而增加人类的癌症风险。我们假设，在一组健康的农药施用者中，长期接触农药将与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。我们提出了一项嵌套在获得许可的农药施用者的大型预期队列中的研究，即农业健康研究，它提供了少数其他研究提供的独特机会，以评估对人类暴露于具有良好特征的农药的生物反应。以前还没有关于人类接触不同程度的杀虫剂的DNA甲基化的研究。我们将利用大约700名受试者的血液样本，提取基因组DNA，并对该队列中最常见的四种沉默基因p16INK4、MGMT、CDH-1和GSTP1的全局DNA甲基化和启动子区域甲基化进行量化。我们的主要目的是调查暴露于特定杀虫剂和化学类别的杀虫剂是否可以预测(1)特定基因(p16INK4、MGMT、CDH-1和GSTP1)的高甲基化和(2)在CpG重复序列和LINE-1(长散布核苷酸元素-1)序列中估计的Alu家族血细胞DNA的整体基因组甲基化(低甲基化)减少。我们的次要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联，并根据基线特征，如年龄、最近和过去吸烟、饮酒和低农药暴露组的饮食，探索和阐明基因特异性和全局甲基化的模式。我们提议的研究有可能确定一种以前未被探索的潜在致癌机制，通过这种机制，杀虫剂可能在人类体内发挥作用。公共卫生相关性：世界范围内农药使用的程度，并强调这些暴露可能对公共健康产生巨大影响。目前市场上和美国公众广泛使用的许多杀虫剂都通过了基于遗传毒性和诱变性测试的安全测试，但流行病学研究表明，它对人类具有致癌性。我们拟议的研究将解决我们对农药致癌性知识的一个重大空白，特别是农药是否通过表观遗传机制发挥作用，例如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.