Raza H, King R S, Squires R B, Guengerich F P, Miller D W, Freeman J P, Lang N P, Kadlubar F F
Division of Molecular Epidemiology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
Drug Metab Dispos. 1996 Apr;24(4):395-400.
2-Amino-alpha-carboline (A alpha C) is a mutagenic and carcinogenic heterocyclic amine that is formed as a pyrolysis product during the high temperature cooking of food and the burning of tobacco. Human, rat, and mouse hepatic microsomes each catalyzed the NADPH-dependent oxidation of A alpha C to form six products separable by HPLC. The two major metabolites, which together accounted for approximately 85% of the total metabolism, were characterized by UV, fluorescence, proton magnetic resonance, and mass spectral analyses as 3-hydroxy-A alpha C and 6-hydroxy-A alpha C. The remaining 15% were judged to be N-hydroxy-A alpha C and its oxidation products, based on chromatographic and spectral comparisons with a standard, whose synthesis and characterization are also described. Although the proportions of each metabolite were similar across species and individuals, the overall rate of metabolism of A alpha C by human hepatic microsomes showed a wide interindividual variation (37-fold), with a mean activity that was comparable with that observed with rat or mouse liver microsomes. alpha-Naphthoflavone, a selective inhibitor for cytochromes P4501A1 and P4501A2, strongly inhibited formation of both ring-hydroxylation and N-oxidation products by human, rat, or mouse liver hepatic microsomes. In addition, A alpha C oxidation was strongly correlated (r = 0.98; p < 0.001) with the oxidation of 4-aminobiphenyl, a known selective substrate for human and rodent cytochromes P4501A2. Immunoblot analyses confirmed the presence of cytochromes P4501A2, and not P4501A1, in human liver microsomes. Additional studies using recombinant human cytochromes P450 show that high catalytic activity for A alpha C metabolism was associated with human cytochrome P4501A2. Lower, but significant activity was also noted for P4501A1 and P4502C10, which could have important implications for the metabolic activation of A alpha C extrahepatic tissues. Neither A alpha C metabolism nor immunoreactive cytochrome P4501A2 (or P4501A1) was detected in human pancreatic microsomes. Although further carcinogenicity and biomarker studies for A alpha C are needed, the high rate of A alpha C metabolism by human liver cytochrome P4501A2 suggests that humans with the rapid P4501A2 phenotype with may be more susceptible than rodents to this heterocyclic amine carcinogen.
2-氨基-α-咔啉（AαC）是一种具有致突变性和致癌性的杂环胺，它是在食物高温烹饪和烟草燃烧过程中作为热解产物形成的。人、大鼠和小鼠的肝微粒体均催化了AαC依赖NADPH的氧化反应，生成六种可通过高效液相色谱分离的产物。通过紫外、荧光、质子磁共振和质谱分析鉴定出两种主要代谢产物，它们总共约占总代谢量的85%，分别为3-羟基-AαC和6-羟基-AαC。根据与一种标准品的色谱和光谱比较，判断其余15%为N-羟基-AαC及其氧化产物，文中还描述了该标准品的合成与表征。尽管各代谢产物的比例在不同物种和个体间相似，但人肝微粒体对AαC的总体代谢速率显示出较大的个体间差异（37倍），其平均活性与大鼠或小鼠肝微粒体的相当。α-萘黄酮是细胞色素P4501A1和P4501A2的选择性抑制剂，它强烈抑制人、大鼠或小鼠肝微粒体中环羟基化和N-氧化产物的形成。此外，AαC氧化与4-氨基联苯的氧化密切相关（r = 0.98；p < 0.001），4-氨基联苯是人和啮齿动物细胞色素P4501A2已知的选择性底物。免疫印迹分析证实人肝微粒体中存在细胞色素P4501A2，而非P4501A1。使用重组人细胞色素P450的进一步研究表明，AαC代谢的高催化活性与人细胞色素P4501A2相关。P4501A1和P4502C10也具有较低但显著的活性，这可能对AαC在肝外组织的代谢活化具有重要意义。在人胰腺微粒体中未检测到AαC代谢或免疫反应性细胞色素P4501A2（或P4501A1）。尽管还需要对AαC进行进一步的致癌性和生物标志物研究，但人肝细胞色素P4501A2对AαC的高代谢率表明，具有快速P4501A2表型的人可能比啮齿动物对这种杂环胺致癌物更敏感。
