Shimada T, Yamazaki H, Mimura M, Wakamiya N, Ueng Y F, Guengerich F P, Inui Y
Osaka Prefectural Institute of Public Health, Japan.
Drug Metab Dispos. 1996 May;24(5):515-22.
Levels and catalytic activities of cytochrome P450 (P450) enzymes involved in the oxidation of drugs and carcinogens were determined in human adult lungs and fetal livers and compared with those in microsomes from adult livers. P450s immunoreactive with anti-human P4501A1 and anti-human P4503A antibodies were detected in fetal liver microsomes by immunoblotting analysis, and P450s related P4501A1, 2A6, 2C9, 2E1, and 3A4 were determined in adult lung microsomes; all of these P450 enzymes were detected in much higher amounts in adult liver microsomes except that P4501A2 was only the 1A subfamily of P450 found in adult livers. Drug oxidation activities with the substrates ethoxyresorufin, coumarin, 7-ethoxycoumarin, bufuralol, and testosterone were determined in these microsomes, and we found that none of the activities were higher in microsomes of adult lungs and fetal livers than in adult livers. Activation of procarcinogens to reactive metabolites that induce umu gene expression in Salmonella typhimurium TA1535/pSK1002 or NM2009 was also examined and it was found that activities with (+)- and (-)-enantiomers of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene were higher in fetal liver microsomes than adult lung or liver microsomes. The adult liver and lung activities for these two procarcinogens were similar on the basis of microsomal protein contents despite the fact that p450 contents are higher in liver than lung microsomes. alpha-Naphthoflavone, a known inhibitor of P4501A-related activities, did not affect these procarcinogen activation in fetal liver microsomes. Fetal liver microsomes catalyzed activation of aflatoxin B1 and sterigmatocystin, two procarcinogens known to be activated by P4503A4/7 in humans, although activation of carcinogenic arylamines that are good substrates for P4501A2 was much lower in microsomes of fetal livers and adult lungs than in adult livers. These results suggest that in human fetal livers at least two P450 enzymes, a form of P450 that is immunoreactive P4501A1 and P4503A7, are actually expressed and these enzymes are suggested as being involved in the activation of the (+)- and (-)-enantiomers of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene and the carcinogenic mycotoxins, respectively. The exact nature of the former enzyme in fetal livers is unknown. In adult human lungs, several P450 enzymes are expressed, although the precise roles of these enzymes in the oxidation of xenobiotics were not determined due to the low level of expression of these P450s.
测定了参与药物和致癌物氧化的细胞色素P450（P450）酶在成人肺组织和胎儿肝脏中的水平及催化活性，并与成人肝脏微粒体中的水平及活性进行了比较。通过免疫印迹分析在胎儿肝脏微粒体中检测到了与抗人P4501A1和抗人P4503A抗体发生免疫反应的P450；在成人肺微粒体中测定了与P4501A1、2A6、2C9、2E1和3A4相关的P450；除了P4501A2是在成人肝脏中发现的P450的1A亚家族外，所有这些P450酶在成人肝脏微粒体中的含量都要高得多。在这些微粒体中测定了对底物乙氧基试卤灵、香豆素、7-乙氧基香豆素、布非洛尔和睾酮的药物氧化活性，我们发现成人肺和胎儿肝脏微粒体中的活性均不高于成人肝脏微粒体中的活性。还检测了前致癌物活化为能在鼠伤寒沙门氏菌TA1535/pSK1002或NM2009中诱导umu基因表达的反应性代谢物的情况，发现胎儿肝脏微粒体中7,8-二羟基-7,8-二氢苯并[a]芘的（+）-和（-）-对映体的活性高于成人肺或肝脏微粒体。尽管肝脏微粒体中的p450含量高于肺微粒体，但基于微粒体蛋白含量，这两种前致癌物在成人肝脏和肺中的活性相似。α-萘黄酮是一种已知的P4501A相关活性抑制剂，它对胎儿肝脏微粒体中的这些前致癌物活化没有影响。胎儿肝脏微粒体催化了黄曲霉毒素B1和杂色曲霉素的活化，这两种前致癌物在人体内已知可被P4503A4/7活化，尽管作为P4501A2良好底物的致癌芳胺在胎儿肝脏和成人肺微粒体中的活化程度远低于成人肝脏。这些结果表明，在人类胎儿肝脏中至少有两种P450酶，一种与P4501A1发生免疫反应的P450形式和P4503A7实际上是表达的，并且这些酶分别被认为参与了7,8-二羟基-7,8-二氢苯并[a]芘的（+）-和（-）-对映体以及致癌霉菌毒素的活化。胎儿肝脏中前一种酶的确切性质尚不清楚。在成人人类肺中，几种P450酶是表达的，尽管由于这些P450的表达水平较低，它们在异源生物氧化中的具体作用尚未确定。
