Chou Ming W, Wang Yu-Ping, Yan Jian, Yang Ya-Chen, Beger Richard D, Williams Lee D, Doerge Daniel R, Fu Peter P
Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
Toxicol Lett. 2003 Dec 10;145(3):239-47. doi: 10.1016/s0378-4274(03)00293-5.
Pyrrolizidine alkaloids (PAs) and their N-oxide derivatives are naturally-formed genotoxic phytochemicals that are widely distributed throughout the world. Although, the quantities of PAs and PA N-oxides in plants are nearly equal, the biological and genotoxic activities of PA N-oxides have not been studied extensively. PA N-oxides are major metabolites of PAs and are generally regarded as detoxification products. However, in this study, we report that rat liver microsomes converted riddelliine N-oxide to the genotoxic 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) metabolite. Metabolism of riddelliine N-oxide by rat liver microsomes under hypoxic conditions (argon) generated predominantly the parent PA, riddelliine. The reduction of riddelliine N-oxide to riddelliine was diminished, when the metabolism of riddelliine N-oxide with rat liver microsomes was conducted aerobically. Rat liver microsomal incubations of riddelliine N-oxide in the presence of calf thymus DNA produced a set of DHP-derived DNA adducts as detected and quantified by 32P-postlabeling/HPLC. The same DHP-derived DNA adducts were also found in liver DNA of F344 rats fed riddelliine N-oxide or riddelliine. When rats received doses of 1.0 mg/kg riddelliine N-oxide for three consecutive days, the level of DNA adducts was 39.9 +/- 0.6 adducts/10(7) nucleotides, which was 2.6-fold less than that measured in rats treated with riddelliine at the same dose. We have previously shown that these DHP-derived DNA adducts are produced by chronic feeding of riddelliine and that the adduct levels correlated with liver tumor formation. Results presented in this paper indicate that riddelliine N-oxide, through its conversion to riddelliine, is also a potential genotoxic hepatocarcinogen.
吡咯里西啶生物碱（PAs）及其N-氧化物衍生物是天然形成的具有基因毒性的植物化学物质，广泛分布于世界各地。虽然植物中PAs和PA N-氧化物的含量几乎相等，但对PA N-氧化物的生物学和基因毒性活性尚未进行广泛研究。PA N-氧化物是PAs的主要代谢产物，通常被视为解毒产物。然而，在本研究中，我们报告大鼠肝微粒体将瑞德利碱N-氧化物转化为具有基因毒性的6,7-二氢-7-羟基-1-羟甲基-5H-吡咯里西啶（DHP）代谢物。在缺氧条件下（氩气），大鼠肝微粒体对瑞德利碱N-氧化物的代谢主要生成母体PA，即瑞德利碱。当在有氧条件下进行大鼠肝微粒体对瑞德利碱N-氧化物的代谢时，瑞德利碱N-氧化物还原为瑞德利碱的过程减弱。在小牛胸腺DNA存在的情况下，大鼠肝微粒体对瑞德利碱N-氧化物的孵育产生了一组DHP衍生的DNA加合物，通过32P后标记/HPLC进行检测和定量。在喂食瑞德利碱N-氧化物或瑞德利碱的F344大鼠的肝脏DNA中也发现了相同的DHP衍生的DNA加合物。当大鼠连续三天接受1.0mg/kg瑞德利碱N-氧化物的剂量时，DNA加合物水平为39.9±0.6个加合物/10（7）个核苷酸，这比以相同剂量用瑞德利碱处理的大鼠中测得的水平低2.6倍。我们之前已经表明，这些DHP衍生的DNA加合物是通过长期喂食瑞德利碱产生的，并且加合物水平与肝肿瘤形成相关。本文给出的结果表明，瑞德利碱N-氧化物通过转化为瑞德利碱，也是一种潜在的具有基因毒性的肝癌致癌物。
