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: 8588603
• 负责人: MATTHEW D RAND
• 金额: $ 22.33万
• 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 2014-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8588603
• 关键词: Susceptibility; methylmercury; toxicity; role; cytochrome

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, CYP 3A5 and CYP 3A7 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。由于食用鱼类中含有甲基汞，因此甲基汞暴露对人类健康极为重要。然而，今天常见的甲基汞接触风险仍然不确定，这主要是由于在接触类似甲基汞水平的个人中观察到的结果不同。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。我们的总体目标是调查遗传因素对甲基汞的敏感性和耐受性。在筛选基因，赋予耐受甲基汞在果蝇的发展过程中，我们已经确定了细胞色素p450（p450）家族成员的候选人。CYP是I相代谢酶，其在解毒途径中修饰外源性物质并对内源性和外源性生物分子进行必要的活化反应。我们发现CYP6g1是最高表达和调节的甲基汞耐受性果蝇和CYP6g1的过表达转基因或通过一个天然存在的高表达等位基因赋予甲基汞耐受性。因此，我们提出了一个新的假说，即易感性甲基汞毒性的影响，先天水平的活性。有了这个提议，我们打算通过将我们在苍蝇中的发现转化为人类来提高科学知识。我们的两个特定目的旨在研究CYP6g1（CYP3A4，CYP3A5和CYP3A7）的人类同源物与人体对甲基汞毒性耐受性的功能和遗传关联。CYP3A成员是人类肝脏中表达最高的CYP。CYP3A7和CYP3A4分别是主要的胎儿和成人CYP。此外，CYP3A4、CYP3A5和CYP3A7多态性和单倍型的存在被预测为更活跃和更不活跃，并且分别显示出非洲人与高加索人的高频率。在Aim 1中，我们将确定每个CYP3A同工酶在发育过程中赋予甲基汞耐受性的相对活性。这将使用我们在转基因果蝇中建立的甲基汞耐受性测定来完成。在目标2中，我们将在两个已建立的主要是非洲人或高加索人的甲基汞暴露儿童队列中探索CYP3A基因型与甲基汞毒性结果的关联。我们的单核苷酸多态性（SNP）探针分析将作为一个正在进行的大规模基因分型项目与这两个队列的附录。将通过考虑潜在混杂因素的多变量分析α等位基因来解决甲基汞结果与α基因型的关联。这项研究的结果将通过确定发育中儿童对甲基汞敏感性变异的遗传组成部分，产生潜在的持久影响。确定CYP作为甲基汞易感性的遗传标记，将大大推进风险评估，因为这将为医疗保健提供者提供新的技术能力，以便在临床环境中识别和指导有风险的个人。