Masonic Cancer Center, University of Minnesota, 420 Delaware Street SE, Minneapolis, MN 55455, USA.
Drug Metab Dispos. 2010 Sep;38(9):1397-402. doi: 10.1124/dmd.110.034181. Epub 2010 Jun 14.
Many studies have examined the relationship between polymorphisms in glutathione S-transferase genes and cancer in people exposed to polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (BaP), but the results to date have been modest. Missing from these studies has been an exploration of the formation of the appropriate glutathione conjugates in humans. We incubated human hepatocytes from 10 donors with racemic anti-BaP-7,8-diol-9,10-epoxide (BPDE), believed to be a major ultimate carcinogen of BaP, or with the noncarcinogenic reverse diol epoxide, racemic anti-BaP-9,10-diol-7,8-epoxide (rev-BPDE). Incubations were carried out for 12 or 24 h. We used high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring at m/z 464 --> m/z 317 to analyze the incubation mixtures for the mercapturic acid products that would result from glutathione conjugation. The standard mercapturic acids were synthesized by reaction of BPDE or rev-BPDE with N-acetylcysteine. We obtained convincing evidence in human hepatocytes for mercapturic acid formation from rev-BPDE in all 10 samples, in amounts up to 17 pmol/ml. However, we could detect mercapturic acids from BPDE in only 1 of 10 samples (0.05 pmol/ml). Taken together with our similar previous results of analyses of phenanthrene metabolites in human hepatocytes and human urine, the results of this study indicate that conjugation of BPDE with glutathione is a minor pathway in humans, indicating that glutathione S-transferase genotyping is not an effective method for assessing risk of PAH-induced cancer in humans, at least with respect to the diol epoxide pathway of PAH carcinogenesis.
许多研究都考察了谷胱甘肽 S-转移酶基因多态性与接触多环芳烃（PAH）如苯并[a]芘（BaP）的人群中癌症之间的关系，但迄今为止的结果都较为有限。这些研究都没有探讨人体中适当的谷胱甘肽缀合物的形成。我们用外消旋反式-BaP-7,8-二醇-9,10-环氧化物（BPDE），一种被认为是 BaP 的主要终末致癌剂，或用非致癌的反式二醇环氧化物，外消旋顺式-BaP-9,10-二醇-7,8-环氧化物（rev-BPDE）孵育来自 10 个供体的人肝细胞，孵育时间为 12 或 24 小时。我们使用高效液相色谱-电喷雾电离-串联质谱-选择反应监测，在 m/z 464 --> m/z 317 下分析孵育混合物中谷胱甘肽缀合产生的硫醚尿酸产物。标准硫醚尿酸是通过 BPDE 或 rev-BPDE 与 N-乙酰半胱氨酸反应合成的。我们在所有 10 个样本中都获得了人肝细胞中来自 rev-BPDE 的硫醚尿酸形成的令人信服的证据，其含量高达 17 pmol/ml。然而，我们仅在 10 个样本中的 1 个样本中检测到来自 BPDE 的硫醚尿酸（0.05 pmol/ml）。结合我们之前对人肝细胞和人尿液中菲代谢物的分析的类似结果，本研究结果表明，BPDE 与谷胱甘肽的缀合在人体中是一条次要途径，表明谷胱甘肽 S-转移酶基因分型不是评估人体中 PAH 诱导癌症风险的有效方法，至少对于 PAH 致癌的二醇环氧化物途径而言。
