Susceptibility to methylmercury toxicity: A role for cytochrome p450 enzymes

对甲基汞毒性的敏感性：细胞色素 p450 酶的作用

• 批准号: 8516513
• 负责人: MATTHEW D RAND
• 金额: $ 17.46万
• 依托单位: UNIVERSITY OF ROCHESTER
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-11-06 至 2016-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8516513
• 关键词: Addendum; Adult; African; Alleles; Benefits and Risks; Biological Assay; CYP3A4 gene; CYP3A5 gene; Caucasians; Caucasoid Race; Child; Clinical; Consumption; Country; Cytochrome P450; Development; Diet; Dietary intake; Drosophila genus; Drug Metabolic Detoxication; Enzymes; Exposure to; Family member; Fetus; Fishes; Frequencies; Genes; Genetic; Genetic Markers; Genetic Polymorphism; Genetic Predisposition to Disease; Genotype; Goals; Haplotypes; Health; Health Personnel; Homologous Gene; Human; Individual; Island; Isoenzymes; Knowledge; Lead; Light; Liver; Measures; Metabolism; Methylmercury Compounds; Modeling; Molecular Genetics; Multivariate Analysis; Nervous system structure; Neurological outcome; Outcome; Pathway interactions; Phase; Population Study; Predisposition; Reaction; Relative (related person); Resistance; Risk; Risk Assessment; Role; Single Nucleotide Polymorphism; Testing; Time; Toxic Environmental Substances; Toxic effect; Toxin; Transgenes; Transgenic Organisms; Translating; Uncertainty; Variant; Xenobiotics; base; cohort; design; experience; fetal; fly; genetic association; genetic profiling; improved; member; nervous system development; novel; postnatal; prenatal; research study; sound; stem

DESCRIPTION (provided by applicant): Methylmercury (MeHg) is a persistent environmental toxin that preferentially targets the developing nervous system. MeHg exposure is of great concern for human health due to its presence in dietary fish. However, the risks of MeHg exposure commonly encountered today remain uncertain, largely due to the variable outcomes observed among individuals experiencing similar levels of MeHg exposure. Our long-term objective is to resolve the molecular and genetic mechanisms that control MeHg toxicity and thereby contribute to more scientifically sound risk assessment. Our overall aim is to investigate a genetic component for susceptibility and tolerance to MeHg. In a screen for genes that confer tolerance to MeHg during development in Drosophila, we have identified cytochrome p450 (CYP) family members as candidates. CYPs are Phase I metabolism enzymes that modify xenobiotics in detoxification pathways and perform essential activating reactions for endogenous and exogenous biomolecules. We found CYP6g1 is the most highly expressed and regulated CYP in MeHg-tolerant flies and that over-expression of CYP6g1 by transgene or via a naturally occurring high-expressing allele confers MeHg tolerance. We therefore propose a novel hypothesis that predisposition to MeHg toxicity is influenced by innate levels of CYP activity. With this proposal we intend to improve scientific knowledge by translating our findings in flies to humans. Our two Specific Aims are designed to investigate the functional and genetic association of the human homologs of CYP6g1 (CYP3A4, CYP3A5 and CYP3A7) with tolerance to MeHg toxicity in people. CYP3A members are the most highly expressed CYPs in the human liver. CYP3A7 and CYP3A4 are distinguished by being the predominant fetal and adult CYPs, respectively. In addition, CYP3A4, CYP3A5 and CYP3A7 polymorphisms and haplotypes exist that are predicted to be more and less active, and which show high frequency Africans versus Caucasians, respectively. In Aim1 we will determine the relative activity of each of the CYP3A isozymes in conferring MeHg tolerance during development. This will be accomplished using our established MeHg-tolerance assay in transgenic Drosophila. In Aim2 we will probe for the association of CYP3A genotypes and MeHg toxicity outcomes in two established cohorts of MeHg-exposed children that are predominantly African or Caucasian. Our CYP single nucleotide polymorphism (SNP) probe analyses will be done as an addendum to an ongoing large-scale genotyping project with these two cohorts. Association of MeHg outcomes with CYP genotype will be resolved through multivariate analyses of CYP alleles with consideration of potential confounders. Results from this study will have a potentially lasting impact by identifying a genetic component of variability in susceptibility to MeHg in developing children. Identification of CYPs as genetic markers of susceptibility to MeHg would greatly advance risk assessment by bringing new technical abilities to health care providers for identifying and advising at-risk individuals in a clinical setting.

描述（由申请人提供）：甲基汞（MeHg）是一种持久性环境毒素，优先针对发育中的神经系统。甲基汞存在于食用鱼类中，对人类健康造成严重影响。然而，目前常见的甲基汞暴露风险仍然不确定，这主要是由于在经历相似水平甲基汞暴露的个体中观察到的不同结果。我们的长期目标是解决控制甲基汞毒性的分子和遗传机制，从而有助于更科学合理的风险评估。我们的总体目标是研究甲基汞易感性和耐受性的遗传成分。在筛选果蝇发育过程中赋予甲基汞耐受性的基因时，我们已经确定了细胞色素p450 （CYP）家族成员作为候选基因。CYPs是I期代谢酶，在解毒途径中修饰外源生物，并对内源和外源生物分子进行必要的激活反应。我们发现CYP6g1是MeHg耐受性果蝇中表达和调控最高的CYP，通过转基因或通过自然存在的高表达等位基因过度表达CYP6g1会产生MeHg耐受性。因此，我们提出了一个新的假设，即甲基汞毒性易感性受到先天CYP活性水平的影响。有了这个建议，我们打算通过将我们在苍蝇身上的发现转化为人类来提高科学知识。我们的两个特定目标旨在研究CYP6g1的人类同源物（CYP3A4， CYP3A5和CYP3A7）与人对甲基汞毒性耐受的功能和遗传关联。CYP3A成员是人肝脏中表达量最高的cypp。CYP3A7和CYP3A4分别是胎儿和成人的显性cypp。此外，CYP3A4、CYP3A5和CYP3A7的多态性和单倍型存在，预测它们的活跃度更高和更低，分别在非洲人与高加索人中显示出较高的频率。在Aim1中，我们将确定在发育过程中赋予甲基汞耐受性的每个CYP3A同工酶的相对活性。这将通过我们在转基因果蝇中建立的mehg耐受性试验来完成。在目的2中，我们将在两个主要为非洲或白种人的MeHg暴露儿童队列中探讨CYP3A基因型与MeHg毒性结果的关系。我们的CYP单核苷酸多态性（SNP）探针分析将作为这两个队列正在进行的大规模基因分型项目的补充。MeHg结果与CYP基因型的关联将通过考虑潜在混杂因素的CYP等位基因的多变量分析来解决。这项研究的结果将通过确定发育中儿童对甲基汞易感性变异的遗传成分，产生潜在的持久影响。将CYPs识别为甲汞易感性的遗传标记，将极大地推进风险评估，为卫生保健提供者在临床环境中识别和建议高危个体带来新的技术能力。