Duke University, Nicholas School of the Environment, Integrated Toxicology and Environmental Health Program, Durham, NC, USA.
Aquat Toxicol. 2010 Apr 15;97(2):142-50. doi: 10.1016/j.aquatox.2009.12.013. Epub 2009 Dec 21.
Polybrominated diphenyl ethers (PBDEs) are a class of flame retardant chemicals known to biomagnify in aquatic foodwebs. However, significant biotransformation of some congeners via reductive dehalogenation has been observed during in vivo and in vitro laboratory exposures, particularly in fish models. Little information is available on the enzyme systems responsible for catalyzing this metabolic pathway in fish. This study was undertaken to characterize the biotransformation of one primary BDE congener, 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), using in vitro techniques. Hepatic sub-cellular fractions were first prepared from individual adult common carp (Cyprinus carpio) to examine metabolism in both microsomal and cytosolic sub-cellular fractions. Debromination rates (i.e. BDE-99 biotransformation to BDE-47) were generally higher in the microsomal fraction than in the cytosolic fraction, and some intra-species variability was observed. Further experiments were conducted to determine the biotransformation kinetics and the influence of specific co-factors, inhibitors and competitive substrates on metabolism using pooled carp liver microsomes. The apparent K(m) and V(max) values were 19.4microM and 1120pmolesh(-1)mgprotein(-1), respectively. Iodoacetate (IaC) and the two thyroid hormones, reverse triodothyronine (rT3) and thyroxine (T4), significantly inhibited the debromination of BDE-99 in microsomal sub-cellular fractions with IC(50) values of 2.2microM, 0.83microM, and >1.0microM, respectively. These results support our hypothesis that deiodinase enzymes may be catalyzing the metabolism of PBDEs in fish liver tissues. Further studies are needed to evaluate metabolic activity in other species and tissues that contain these enzymes.
多溴联苯醚（PBDEs）是一类阻燃化学物质，已知在水生食物网中具有生物放大作用。然而，在体内和体外实验室暴露实验中，特别是在鱼类模型中，观察到一些同系物通过还原脱卤作用发生了显著的生物转化。关于鱼类中催化这种代谢途径的酶系统的信息很少。本研究旨在使用体外技术来表征一种主要的 BDE 同系物 2,2',4,4',5-五溴二苯醚（BDE-99）的生物转化。首先从单个成年鲤鱼（Cyprinus carpio）中制备肝亚细胞级分，以检查微粒体和胞质亚细胞级分中的代谢。脱溴率（即 BDE-99 生物转化为 BDE-47）在微粒体级分中通常高于胞质级分，并且观察到一些种内变异性。进一步的实验旨在使用鲤鱼肝微粒体确定生物转化动力学以及特定共因子、抑制剂和竞争性底物对代谢的影响。表观 K(m)和 V(max)值分别为 19.4μM 和 1120pmolesh(-1)mgprotein(-1)。碘乙酸（IaC）和两种甲状腺激素，反三碘甲状腺原氨酸（rT3）和甲状腺素（T4），以分别为 2.2μM、0.83μM 和 >1.0μM 的 IC(50)值显著抑制微粒体亚细胞级分中 BDE-99 的脱溴作用。这些结果支持我们的假设，即脱碘酶可能催化鱼类肝组织中 PBDEs 的代谢。需要进一步研究来评估含有这些酶的其他物种和组织的代谢活性。
