Benedict Rae T, Stapleton Heather M, Letcher Robert J, Mitchelmore Carys L
University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, P.O. Box 38, Solomons, MD 20688, USA.
Chemosphere. 2007 Oct;69(6):987-93. doi: 10.1016/j.chemosphere.2007.05.010. Epub 2007 Jul 20.
Based on previous findings in dietary studies with carp (Cyprinus carpio), we investigated the mechanism of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) debromination to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) using liver and intestinal components. In vitro aerobic and anaerobic experiments tested the ability of carp intestinal microflora to debrominate BDE-99. No debromination of BDE-99 to BDE-47 was observed in microfloral samples; therefore, carp enzymatic pathways were assessed for debromination ability. After sixty-min incubation, intestine and liver microsomes exhibited 83+/-34% and 106+/-18% conversions, respectively, of BDE-99 to BDE-47; with no significant (p>0.05) difference between organ debromination capabilities. Microsomal incubations with BDE-99, enzyme cofactors and competing substrates assessed the potential mechanisms of debromination. The presence of NADPH in the microsomal assay did not significantly (p>0.05) affect BDE-99 debromination, which suggest that cytochrome P450 enzymes are not the main debrominating pathway for BDE-99. Co-incubation of BDE-99 spiked microsomes with reverse thyronine (rT3) significantly (p<0.05) decreased the debromination capacity of intestinal microsomes indicating the potential of catalytic mediation via thyroid hormone deiodinases. The significant findings of this study are that intestinal microflora are not responsible for BDE-99 debromination, however, it is an endogenous process which occurs with approximately equal activity in intestine and liver microsomes and it can be inhibited by rT3.
基于之前对鲤鱼（Cyprinus carpio）的饮食研究结果，我们利用肝脏和肠道成分研究了2,2',4,4',5-五溴二苯醚（BDE-99）脱溴生成2,2',4,4'-四溴二苯醚（BDE-47）的机制。体外需氧和厌氧实验测试了鲤鱼肠道微生物群落对BDE-99脱溴的能力。在微生物样本中未观察到BDE-99脱溴生成BDE-47的情况；因此，对鲤鱼的酶促途径进行了脱溴能力评估。孵育60分钟后，肠道和肝脏微粒体分别将83±34%和106±18%的BDE-99转化为BDE-47；各器官的脱溴能力之间无显著差异（p>0.05）。用BDE-99、酶辅因子和竞争性底物进行微粒体孵育，评估了脱溴的潜在机制。微粒体测定中NADPH的存在对BDE-99脱溴没有显著影响（p>0.05），这表明细胞色素P450酶不是BDE-99的主要脱溴途径。将添加了BDE-99的微粒体与反式甲状腺素（rT3）共同孵育，显著降低了肠道微粒体的脱溴能力（p<0.05），这表明甲状腺激素脱碘酶具有催化介导的潜力。本研究的重要发现是，肠道微生物群落不负责BDE-99的脱溴，然而，这是一个内源性过程，在肠道和肝脏微粒体中以大致相同的活性发生，并且可以被rT3抑制。
