Shimada T, Yamazaki H, Foroozesh M, Hopkins N E, Alworth W L, Guengerich F P
Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
Chem Res Toxicol. 1998 Sep;11(9):1048-56. doi: 10.1021/tx980090+.
Human cytochrome P450s 1A1, 1A2, and 1B1 are known to have overlapping substrate specificities. All are regulated in part by the Ah locus; P450 1A2 is expressed essentially only in liver, but P450s 1A1 and 1B1 are both expressed in many extrahepatic tissues. Twenty-five polycyclic hydrocarbons, many containing acetylenic side chains, were examined as inhibitors of the three enzymes using 7-ethoxyresorufin O-deethylation as the enzyme assay in all cases. Several compounds were inhibitory at low nanomolar concentrations. 1-(1-Propynyl)pyrene and 2-(1-propynyl)phenanthrene nearly completely inhibited P450 1A1 at concentrations at which no P450 1B1 inhibition was observed. 2-Ethynylpyrene and alpha-naphthoflavone (7, 8-benzoflavone) nearly completely inhibited P450 1B1 at concentrations at which no P450 1A1 inhibition was noted. All four of the above compounds also inhibited P450 1A2. Several polycyclic hydrocarbons devoid of acetylenic groups were also inhibitory with respect to all three P450s. Some of the acetylenic compounds examined showed enhanced inhibition following preincubation with the P450s in the presence of cofactors NADPH and O2. However, of seven compounds (five acetylenes) tested with P450 1B1, only two [2-ethynylpyrene and 4-(1-propynyl)biphenyl] showed such evidence for mechanism-based inactivation. We conclude that (i) several polycyclic hydrocarbons and their oxidation products are very inhibitory with respect to human P450s 1A1, 1A2, and 1B1; (ii) of these inhibitors only some are mechanism-based inactivators; and (iii) some of the inhibitors are potentially useful for distinguishing between human P450s 1A1 and 1B1.
已知人类细胞色素P450 1A1、1A2和1B1具有重叠的底物特异性。它们都部分受芳香烃受体（Ah）位点调控；P450 1A2基本上只在肝脏中表达，但P450 1A1和1B1在许多肝外组织中均有表达。以7-乙氧基异吩恶唑酮O-脱乙基化作为所有情况下的酶分析方法，检测了25种多环烃（其中许多含有炔侧链）作为这三种酶的抑制剂。有几种化合物在低纳摩尔浓度下具有抑制作用。1-（1-丙炔基）芘和2-（1-丙炔基）菲在未观察到对P450 1B1抑制作用的浓度下几乎完全抑制了P450 1A1。2-乙炔基芘和α-萘黄酮（7,8-苯并黄酮）在未观察到对P450 1A1抑制作用的浓度下几乎完全抑制了P450 1B1。上述所有四种化合物也抑制了P450 1A2。几种不含炔基的多环烃对所有三种P450也有抑制作用。在辅因子NADPH和O2存在的情况下，一些检测的炔化合物在与P450预孵育后显示出增强的抑制作用。然而，在用P450 1B1检测的7种化合物（5种炔烃）中，只有两种[2-乙炔基芘和4-（1-丙炔基）联苯]显示出基于机制的失活证据。我们得出以下结论：（i）几种多环烃及其氧化产物对人类P450 1A1、1A2和1B1具有很强的抑制作用；（ii）在这些抑制剂中，只有一些是基于机制的失活剂；（iii）一些抑制剂可能有助于区分人类P450 1A1和1B1。
