Bioactivation of PBDEs by Human Cytochrome P-450

描述（由申请人提供）：在过去十年中，动物和人类研究都支持多溴二苯醚（PBDE）阻燃剂与神经行为/神经发育障碍之间的关联，特别是在子宫内和出生后暴露之后。最近，人们发现多溴二苯醚的羟基化代谢物（OH-PBDEs）在人体血清中的积累水平与多溴二苯醚母体的水平相似，在某些情况下甚至更高。机理研究表明，羟基多溴二苯醚往往比母体化合物更有效，并通过涉及钙离子信号失调的直接神经毒性和/或通过改变甲状腺功能间接导致神经发育障碍，从而进一步突出了这一发现的重要性。总之，这些研究和其他研究表明，氧化代谢的生物活化作用大大增加了多溴二苯醚的神经毒性潜力。因此，迫切需要进一步了解人体内多溴二苯醚的代谢情况。这项申请的总体目标是确定人体内多溴二苯醚的酶和同系物代谢特性，并调查与关键生物转化酶的遗传变异性有关的代谢的定性和定量差异。我们最近发现，2，2 '，4，4'-四溴二苯醚-47可通过人类细胞色素P-450 2B 6（CYP 2B 6）进行特异性代谢，由于调节现象和常见的遗传多态性，已知CYP 2B 6在肝脏蛋白表达方面表现出高达100倍的变异性。因此，据推测，除了不同的暴露量外，多溴二苯醚的CYP特异性代谢的遗传变异性也导致了多溴二苯醚体内负荷和有毒代谢物形成的个体间差异。以下目标将解决这一假设，并生成关于多溴二苯醚特定同源物代谢的重要人类数据。目标1将对2，2 '，4，4'-四-（BDE-47）、2，2 '，4，5'-四-（BDE-49）、2，2 '，4，4'，5-五-（BDE-99）和2，2 '，4，4'，6-五-（BDE-100）的人体CYP特异性体外代谢进行定性和定量表征，这些物质是人体内含量最高的同系物，并且对形成潜在毒理学活性代谢物的代谢敏感。将利用人类肝微粒体（CYP 2B 6活性水平范围高达100倍）和人类CYP 2B 6的重组多态变体来评估多溴二苯醚体外代谢的个体间差异。目标2将确定和量化母乳和血清中的羟基多溴二苯醚，并评估CYP 2B 6基因型对多溴二苯醚体内负荷的潜在影响，此前发现这些受试者体内多溴二苯醚的变化超过100倍。拟议的研究最终将更好地为今后调查多溴二苯醚及其代谢物造成神经发育障碍的可能性的机制和流行病学研究提供信息。此外，这些研究将有助于确定潜在的遗传生物标志物，这些生物标志物有助于多溴联苯醚生物活化过程中的个体间差异，并最终导致多溴联苯醚的相对毒性。 个体对这些药剂的潜在不利影响的易感性。 公共卫生相关性：在过去十年中，动物和人类研究都支持多溴二苯醚阻燃剂与神经行为/神经发育障碍之间的联系，最近的机理研究表明，氧化代谢的生物活化大大增加了多溴二苯醚的神经毒性潜力。关于多溴二苯醚的人体细胞色素P-450特异性代谢的拟议研究最终将更好地为今后调查多溴二苯醚及其代谢物造成神经发育障碍的可能性的机制和流行病学研究提供信息。此外，这些研究还将有助于确定潜在的遗传生物标志物，这些生物标志物有助于多溴二苯醚生物活化过程中的个体间差异，并最终有助于确定个体对这些物质的潜在不利影响的相对敏感性。

DESCRIPTION (provided by applicant): During the past decade both animal and human studies have supported an association between polybrominated diphenyl ether (PBDE) flame retardants and neurobehavioral / neurodevelopmental disorders, particularly following in utero and postnatal exposure. Recently, hydroxylated metabolites of PBDEs (OH- PBDEs) have been found to accumulate in human serum at levels similar to and in some cases greater than that of the parent PBDEs. The significance of this finding is heightened by mechanistic studies showing that OH-PBDEs are often more potent than parent compounds and contribute substantially to neurodevelopmental disorders via direct neurotoxicity involving dysregulation of Ca2+ signaling and/or indirectly through altered thyroid disruption. Together, these and other studies suggest that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. Thus, there is a critical need to further our understanding of PBDE metabolism in humans. The overall objectives of this application are to characterize the enzyme- and congener-specific metabolism of PBDEs in humans and investigate qualitative and quantitative differences in metabolism which are related to genetic variability in key biotransforming enzymes. We have recently found that 2,2',4,4'-tetra-(BDE-47) is metabolized specifically by human cytochrome P-450 2B6 (CYP2B6), which is known to exhibit up to 100-fold variability in hepatic protein expression, due to regulatory phenomena and common genetic polymorphisms. Thus, it is hypothesized that in addition to variable exposures, genetic variability in the CYP-specific metabolism of PBDEs contributes to interindividual variability in the body burden of PBDEs and the formation of toxic metabolites. The following aims will address this hypothesis and generate critical human data on the congener-specific metabolism of PBDEs. Aim 1 will conduct a qualitative and quantitative characterization of the human CYP-specific in vitro metabolism of 2,2',4,4'-tetra-(BDE-47), 2,2',4,5'-tetra-(BDE-49), 2,2',4,4',5-penta-(BDE-99), and 2,2',4,4',6- penta-(BDE-100), which are the most abundant congeners in humans, and are susceptible to metabolism that forms potentially toxicologically active metabolites. Interindividua variability in the in vitro metabolism of PBDEs will be assessed utilizing both human liver microsomes, with up to a 100-fold range in the level of CYP2B6 activity, and recombinant polymorphic variants of human CYP2B6. Aim 2 will identify and quantify OH-PBDEs in human milk and serum, and assess the potential impact of CYP2B6 genotype on the body burden of PBDEs which was previously found to vary by over a 100-fold in these subjects. The proposed studies will ultimately better inform future mechanistic and epidemiological studies investigating the potential of PBDEs and their metabolites to produce neurodevelopmental disorders. In addition, these studies will lead to the identification of potential genetic biomarkers that contribute to interindividual variability in the bioactivation of PBDEs and ultimately the relative susceptibility of individuals to potential adverse effects of these agents. PUBLIC HEALTH RELEVANCE: During the past decade both animal and human studies have supported an association between polybrominated diphenyl ether (PBDE) flame retardants and neurobehavioral / neurodevelopmental disorders, and recent mechanistic studies suggest that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. The proposed studies on the human cytochrome P-450-specific metabolism of PBDEs will ultimately better inform future mechanistic and epidemiological studies investigating the potential of PBDEs and their metabolites to produce neurodevelopmental disorders. In addition, these studies will lead to the identification of potential genetic biomarkers that contribute to interindividual variability in the bioactivation of PBDEs and ultimately the relative susceptibilit of individuals to potential adverse effects of these agents.