Chen H, Fantel A G, Juchau M R
Department of Pharmacology, School of Medicine, University of Washington, Seattle 98195, USA.
Drug Metab Dispos. 2000 Sep;28(9):1051-7.
Cytochrome P4503A7 (CYP3A7) is the primary CYP isoform expressed in human fetal hepatic microsomes, and its potential role in human embryotoxicity has attracted considerable investigative attention. In this study, we investigated the 4-hydroxylation of highly embryotoxic and teratogenic retinoic acids (RA) as catalyzed by human fetal liver microsomes (HFLM) and demonstrated that CYP3A7 is an efficient RA hydroxylase. When all-trans-retinoic acid (tRA), 9-cis-retinoic acid (9cRA), or 13-cis-retinoic acid (13cRA) were incubated with HFLM (54-109 gestational days) plus NADPH, each of these three retinoic acids was rapidly converted to its corresponding 4-hydroxy and 4-oxo metabolites. The reactions were strongly inhibited by CO (CO:O(2), 80:20) and were NADPH-dependent, indicating that the reactions were catalyzed by P450 isoenzymes. At 54 to 89 gestational days, 4-hydroxylase activities were relatively low. However, at gestational days 96 to 109, activities were much higher. Selective inhibitors were employed for elucidation of the roles of individual CYP isoenzymes in HFLM. alpha-Naphthoflavone, paclitaxel, and diethyldithiocarbamate showed little or no effects on HFLM-catalyzed reactions, indicating that CYP1A1, CYP1A2, CYP1B1, CYP2C8, and CYP2E1 did not play significant roles in the catalysis. By contrast, troleandomycin strongly inhibited the reaction (70-75% inhibition), suggesting that CYP3A7 was primarily responsible for the observed catalysis. It was also discovered that CYP3A7 SUPERSOMES efficiently catalyzed the 4-hydroxylations of tRA, 9cRA, and 13cRA. Because 4-hydroxylated metabolites of RA are much less potent embryotoxins and teratogens, the results indicated that the 4-hydroxylation of RA, catalyzed prenatally by CYP3A7, might play an important role in protecting the human fetus against RA-induced embryotoxicity.
细胞色素P4503A7（CYP3A7）是在人胎儿肝微粒体中表达的主要细胞色素P450同工酶，其在人类胚胎毒性中的潜在作用已引起了大量的研究关注。在本研究中，我们研究了人胎儿肝微粒体（HFLM）催化的高胚胎毒性和致畸性视黄酸（RA）的4-羟基化反应，并证明CYP3A7是一种有效的RA羟化酶。当全反式视黄酸（tRA）、9-顺式视黄酸（9cRA）或13-顺式视黄酸（13cRA）与HFLM（妊娠54 - 109天）及NADPH一起孵育时，这三种视黄酸中的每一种都迅速转化为其相应的4-羟基和4-氧代代谢产物。这些反应被CO（CO:O₂，80:20）强烈抑制且依赖于NADPH，表明这些反应是由P450同工酶催化的。在妊娠54至89天时，4-羟化酶活性相对较低。然而，在妊娠96至109天时，活性要高得多。使用选择性抑制剂来阐明各个细胞色素P450同工酶在HFLM中的作用。α-萘黄酮、紫杉醇和二乙基二硫代氨基甲酸盐对HFLM催化的反应几乎没有影响，表明CYP1A1、CYP1A2、CYP1B1、CYP2C8和CYP2E1在催化过程中不起重要作用。相比之下，三乙酰竹桃霉素强烈抑制该反应（70 - 75%抑制），表明CYP3A7是观察到的催化反应的主要原因。还发现CYP3A7微粒体高效催化tRA、9cRA和13cRA的4-羟基化反应。由于RA的4-羟基化代谢产物的胚胎毒性和致畸性要弱得多，结果表明产前由CYP3A7催化的RA的4-羟基化反应可能在保护人类胎儿免受RA诱导的胚胎毒性方面发挥重要作用。
