Department of Analytical, Environmental and Forensic Sciences, MRC-PHE Centre for Environment and Health , King's College London , SE1 9NH , United Kingdom.
NIHR Health Protection Research Unit in Health Impact of Environmental Hazards , King's College London in partnership with Public Health England and Imperial College London , London SE1 9NH , United Kingdom.
Chem Res Toxicol. 2018 Nov 19;31(11):1277-1288. doi: 10.1021/acs.chemrestox.8b00250. Epub 2018 Nov 8.
3-Nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen detected in diesel exhaust particulate and ambient air pollution. It requires metabolic activation via nitroreduction to promote DNA adduct formation and tumorigenesis. NAD(P)H:quinone oxidoreductase 1 (NQO1) has been previously implicated as the major nitroreductase responsible for 3-NBA activation, but it has recently been reported that human aldo-keto reductase 1C3 (AKR1C3) displays nitroreductase activity toward the chemotherapeutic agent PR-104A. We sought to determine whether AKR1C isoforms could display nitroreductase activity toward other nitrated compounds and bioactivate 3-NBA. Using discontinuous enzymatic assays monitored by UV-HPLC, we determined that AKR1C1-1C3 catalyze three successive two-electron nitroreductions toward 3-NBA to form the reduced product 3-aminobenzanthrone (3-ABA). Evidence of the nitroso- and hydroxylamino- intermediates were obtained by UPLC-HRMS. K, k, and k/ K values were determined for recombinant AKR1C and NQO1 and compared. We found that AKR1C1, AKR1C3, and NQO1 have very similar apparent catalytic efficiencies (8 vs 7 min mM) despite the higher k of NQO1 (0.058 vs 0.012 min). AKR1C1-1C3 possess a K much lower than that of NQO1, which suggests that they may be more important than NQO1 at the low concentrations of 3-NBA to which humans are exposed. Given that inhalation represents the primary source of 3-NBA exposure, we chose to evaluate the relative importance of AKR1C1-1C3 and NQO1 in human lung epithelial cell lines. Our data suggest that the combined activities of AKR1C1-1C3 and NQO1 contribute equally to the reduction of 3-NBA in A549 and HBEC3-KT cell lines and together represent approximately 50% of the intracellular nitroreductase activity toward 3-NBA. These findings have significant implications for the metabolism of nitrated polycyclic aromatic hydrocarbons and suggest that the hitherto unrecognized nitroreductase activity of AKR1C enzymes should be further investigated.
3-硝基苯并蒽（3-NBA）是一种强诱变剂和可疑的人类致癌物，存在于柴油废气颗粒和环境空气污染中。它需要通过硝基还原作用进行代谢激活，以促进 DNA 加合物的形成和肿瘤发生。NAD(P)H：醌氧化还原酶 1（NQO1）先前被认为是负责 3-NBA 激活的主要硝基还原酶，但最近有报道称，人类醛酮还原酶 1C3（AKR1C3）对化疗药物 PR-104A 显示出硝基还原酶活性。我们试图确定 AKR1C 同工酶是否可以对其他硝化化合物显示硝基还原酶活性并生物激活 3-NBA。使用连续酶促测定法（通过 UV-HPLC 监测），我们确定 AKR1C1-1C3 催化 3-NBA 的三个连续的两电子硝基还原，形成还原产物 3-氨基苯并蒽（3-ABA）。通过 UPLC-HRMS 获得了硝基亚硝和羟氨基中间体的证据。测定了重组 AKR1C 和 NQO1 的 K、k 和 k/K 值，并进行了比较。我们发现，尽管 NQO1 的 k 更高（0.058 比 0.012 min），但 AKR1C1、AKR1C3 和 NQO1 的表观催化效率非常相似（8 与 7 min mM）。AKR1C1-1C3 的 K 远低于 NQO1，这表明在人类暴露的低浓度 3-NBA 下，它们可能比 NQO1 更为重要。鉴于吸入是 3-NBA 暴露的主要来源，我们选择评估 AKR1C1-1C3 和 NQO1 在人肺上皮细胞系中的相对重要性。我们的数据表明，AKR1C1-1C3 和 NQO1 的联合活性同样有助于 A549 和 HBEC3-KT 细胞系中 3-NBA 的还原，共同代表了细胞内 3-NBA 硝基还原酶活性的约 50%。这些发现对硝化多环芳烃的代谢具有重要意义，并表明 AKR1C 酶迄今为止尚未被认识到的硝基还原酶活性应进一步研究。
