MECHANISM-BASED INACTIVATION OF HUMAN LIVER MICROSOMAL CYTOCHROME-P-450-IIIA4 BY GESTODENE
MECHANISM-BASED INACTIVATION OF HUMAN LIVER MICROSOMAL CYTOCHROME-P-450-IIIA4 BY GESTODENE
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DOI：
10.1021/tx00016a015
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发表时间：
1990-07-01
影响因子：
4.1
通讯作者：
GUENGERICH, FP
中科院分区：
文献类型：
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作者：
GUENGERICH, FP
研究了一系列17α-乙酰化类固醇对人肝微粒体细胞色素P-450(P-450)IIIA4的失活能力，该酶与许多药物、致癌物和类固醇(包括雌激素和孕激素)的氧化有关。在测试的八种化合物中，孕二烯被发现作为P-450 IIIA4的机理失活剂特别有活性。对微粒体硝苯地平氧化和17α-乙炔基雌二醇(EE)2-羟化的抑制作用依赖于NADPH和地孕烯的浓度。失活速率为假一级反应，计算出激活值为0.4min-1，KI=46µm，分配比为9。激活是.apprx。比估计的EE高50倍，是已报道的基于P-450机制的灭活剂中最高的之一。光谱可检测到的P-450在微粒体中也被破坏，但一些实验表明，P-450 IIIA4的氨基酸残基几乎没有共价结合。其他P-450 IIIA4底物的存在可以阻止P-450的微粒体失活，而在P-450 IIIA4的90%失活的条件下，其他P-450催化的几种活性不受抑制。对所研究的17个α-乙酰化类固醇之间的结构/活性关系的考虑表明，β15双键是关键的，但本身不足以进行失活过程，据推测，失活过程是由于P-450对取代的乙酰碳的攻击并导致卟啉N-烷基化。这种基于机制的灭活剂的有效性可能解释了一些在口服避孕药中使用孕二烯的妇女雌激素和类固醇水平升高的报道。
A series of 17.alpha.-acetylenic steroids was examined with regard to ability to inactivate human liver microsomal cytochrome P-450 (P-450) IIIA4, an enzyme involved in the oxidation of a number of drugs, carcinogens, and steroids, including estrogens and progestogens. Of the eight compounds tested, gestodene was found to be particularly active as a mechanism-based inactivator of P-450 IIIA4. Inhibition of both microsomal nifedipine oxidation and 17.alpha.-ethynylestradiol (EE) 2-hydroxylation was dependent upon NADPH and gestodene concentration. Rates of inactivation were pseudo first order.sbd.values of kinactivation = 0.4 min-1 and Ki = 46 .mu.M and a partition ratio of 9 were calculated. The kinactivation is .apprx. 50-fold greater than estimated for EE and is one of the highest reported for P-450 mechanism-based inactivators. Spectrally detectable P-450 was also destroyed in microsomes, but several experiments indicate that little covalent binding to amino acid residues of P-450 IIIA4 occurs. Microsomal inactivation of P-450 could be blocked by the presence of other P-450 IIIA4 substrates, and several activities catalyzed by other P-450s were not inhibited under conditions in which > 90% of P-450 IIIA4 was inactivated. Consideration of structure/activity relationships among the 17.alpha.-acetylenic steroids examined indicates that the .DELTA.15 double bond is critical but is not in itself sufficient for the inactivation process, which is postulated to result from attack of P-450 on the substituted acetylenic carbon and lead to porphyrin N-alkylation. The effectiveness of this mechanism-based inactivator may account for reports of increased estrogen and steroid levels in some women using gestodene in oral contraceptives.