Eberhart D C, Gemzik B, Halvorson M R, Parkinson A
Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center Kansas City 66103.
Mol Pharmacol. 1991 Nov;40(5):859-67.
In rats, cytochrome P450 (P450) IIIA enzymes are an important determinant of digitoxin toxicity. Induction of these liver microsomal enzymes decreases the toxicity of digitoxin by increasing its oxidative cleavage to digitoxigenin bis- and monodigitoxoside (dt2 and dt1). The present study shows that the susceptibility of different mammalian species to digitoxin toxicity is inversely related to liver microsomal P450 IIIA activity (measured as testosterone 6 beta-hydroxylase activity). Based on this correlation, we correctly predicted that hamsters, which have the highest P450 IIIA activity, are extremely resistant to digitoxin toxicity. To further examine the relationship between digitoxin toxicity and P450 IIIA activity, the pathways of digitoxin metabolism catalyzed by liver microsomes from nine mammalian species were examined by high performance liquid chromatography. The overall rate of digitoxin metabolism varied approximately 90-fold and followed the rank order: hamster greater than rat greater than guinea pig greater than dog greater than mouse approximately monkey greater than rabbit approximately cat greater than human. The qualitative differences in digitoxin metabolism were as striking as the quantitative differences. Formation of 16- and/or 17-hydroxydigitoxin was the major pathway of digitoxin oxidation catalyzed by liver microsomes from hamster, guinea pig, rabbit, cat, dog, and cynomolgus monkey. Guinea pig and, to a lesser extent, hamster liver microsomes also converted digitoxin to an unknown metabolite, the formation of which was catalyzed by P450. None of the species examined catalyzed the 12-hydroxylation of digitoxin to digoxin at a high rate. Similarly, none of the species examined catalyzed a high rate of conversion of digitoxin to dt2, with the notable exception of the rat. However, dt2 formation was the major pathway of digitoxin metabolism catalyzed by human liver microsomes, although humans were much less active (approximately 2%) than rats in this regard. The rate of dt2 formation varied approximately 41-fold among 22 samples of human liver microsomes, which was highly correlated (r = 0.841) with the rate of testosterone 6 beta-hydroxylation. Antibody against rat P450 IIIA1 inhibited the high rate of dt2 formation by rat liver microsomes and the low rate catalyzed by mouse, guinea pig, dog, monkey, and human liver microsomes. In contrast, anti-P450 IIIA1 did not inhibit the 12-, 16-, or 17-hydroxylation of digitoxin (or the formation of the unknown metabolite), despite the fact that anti-P450 IIIA1 strongly inhibited (greater than 70%) the 6 beta-hydroxylation of testosterone by liver microsomes from each of the species examined (except rabbit liver microsomes, which were inhibited only approximately 30%).(ABSTRACT TRUNCATED AT 400 WORDS)
在大鼠中，细胞色素P450（P450）IIIA酶是洋地黄毒苷毒性的一个重要决定因素。这些肝微粒体酶的诱导通过增加洋地黄毒苷氧化裂解为洋地黄毒苷元双糖苷和单洋地黄毒糖苷（dt2和dt1）而降低其毒性。本研究表明，不同哺乳动物物种对洋地黄毒苷毒性的易感性与肝微粒体P450 IIIA活性（以睾酮6β-羟化酶活性衡量）呈负相关。基于这种相关性，我们正确预测出具有最高P450 IIIA活性的仓鼠对洋地黄毒苷毒性具有极强的抗性。为了进一步研究洋地黄毒苷毒性与P450 IIIA活性之间的关系，采用高效液相色谱法检测了9种哺乳动物物种肝微粒体催化的洋地黄毒苷代谢途径。洋地黄毒苷的总体代谢速率相差约90倍，顺序如下：仓鼠＞大鼠＞豚鼠＞狗＞小鼠≈猴＞兔≈猫＞人。洋地黄毒苷代谢的定性差异与定量差异一样显著。16-和/或17-羟基洋地黄毒苷的形成是仓鼠、豚鼠、兔、猫、狗和食蟹猴肝微粒体催化的洋地黄毒苷氧化的主要途径。豚鼠以及程度稍轻的仓鼠肝微粒体还将洋地黄毒苷转化为一种未知代谢物，其形成由P450催化。所检测的物种均未高效催化洋地黄毒苷12-羟基化生成地高辛。同样，所检测的物种均未高效催化洋地黄毒苷转化为dt2，大鼠是显著的例外。然而，dt2的形成是人类肝微粒体催化的洋地黄毒苷代谢的主要途径，尽管在这方面人类的活性比大鼠低得多（约2%）。在22份人肝微粒体样本中，dt2的形成速率相差约41倍，这与睾酮6β-羟化速率高度相关（r = 0.841）。抗大鼠P450 IIIA1抗体抑制了大鼠肝微粒体dt2的高生成速率以及小鼠、豚鼠、狗、猴和人肝微粒体催化的低生成速率。相比之下，抗P450 IIIA1抗体并未抑制洋地黄毒苷的12-、16-或17-羟基化（或未知代谢物的形成），尽管抗P450 IIIA1强烈抑制了（＞70%）所检测的每个物种肝微粒体对睾酮的6β-羟化（兔肝微粒体除外，其仅被抑制约30%）（摘要截于400词）
