Klein P J, Buckner R, Kelly J, Coulombe R A
Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, Utah, 84322-4620, USA.
Toxicol Appl Pharmacol. 2000 May 15;165(1):45-52. doi: 10.1006/taap.2000.8926.
Poultry are the most susceptible food animal species to the toxic effects of the mycotoxin aflatoxin B(1) (AFB(1)). Feed contaminated with even small amounts of AFB(1) results in significant adverse health effects in poultry. The purpose of this study was to explain the biochemical mechanism(s) for this extreme sensitivity. We measured microsomal activation of AFB(1) to the AFB(1)-8,9-epoxide (AFBO), the putative toxic intermediate, as well as cytosolic glutathione S-transferase (GST)-mediated detoxification of AFBO, in addition to other hepatic phase I and phase II enzyme activities, in 3-week-old male Oorlop strain turkeys. Liver microsomes prepared from these turkeys activated AFB(1) in vitro with an apparent K(m) of 109 microM and a V(max) of 1.25 nmol/mg/min. Preliminary evidence for the involvement of cytochromes P450 (CYP) 1A2 and, to a lesser extent, 3A4 for AFB(1) activation was assessed by the use of specific mammalian CYP inhibitors. The possible presence of avian orthologues of these CYPs was supported by activity toward ethoxyresorufin and nifedipine, as well as by Western immunoblotting using antibodies to human CYPs. Cytosol prepared from turkey livers exhibited GST-mediated conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB), but at a much lower rate than that observed in other species. Western immunoblotting indicated the presence of alpha and sigma class GSTs and another AFB(1)-detoxifying enzyme, AFB(1)-aldehyde reductase (AFAR). Turkey liver cytosol also had quinone oxidoreductase (QOR) activity. Importantly, cytosol exhibited no measurable GST-mediated detoxification of microsomally activated AFB(1), indicating that turkeys are deficient in the most crucial AFB(1)-detoxification pathway. In total, our data indicate that the extreme sensitivity of turkeys to AFB(1) may be attributed to a combination of efficient AFB(1) activation and deficient detoxification by phase II enzymes, such as GSTs.
家禽是对霉菌毒素黄曲霉毒素B1（AFB1）的毒性作用最敏感的食用动物物种。即使是被少量AFB1污染的饲料也会对家禽产生显著的不良健康影响。本研究的目的是解释这种极端敏感性的生化机制。我们测量了3周龄雄性奥洛普品系火鸡微粒体将AFB1活化为假定的有毒中间体AFB1-8,9-环氧化物（AFBO）的情况，以及胞质谷胱甘肽S-转移酶（GST）介导的AFBO解毒作用，此外还测量了其他肝脏I相和II相酶活性。从这些火鸡制备的肝微粒体在体外激活AFB1，其表观K（m）为109微摩尔，V（max）为1.25纳摩尔/毫克/分钟。通过使用特异性哺乳动物细胞色素P450（CYP）抑制剂评估了CYP 1A2以及在较小程度上CYP 3A4参与AFB1激活的初步证据。这些CYP的禽类直系同源物的可能存在得到了对乙氧基试卤灵和硝苯地平的活性以及使用针对人CYP的抗体进行的Western免疫印迹的支持。从火鸡肝脏制备的胞质溶胶表现出GST介导的1-氯-2,4-二硝基苯（CDNB）和3,4-二氯硝基苯（DCNB）的结合，但速率远低于在其他物种中观察到的速率。Western免疫印迹表明存在α和σ类GST以及另一种AFB1解毒酶AFB1-醛还原酶（AFAR）。火鸡肝脏胞质溶胶也具有醌氧化还原酶（QOR）活性。重要的是，胞质溶胶未表现出对微粒体激活的AFB1的可测量的GST介导的解毒作用，这表明火鸡在最关键的AFB1解毒途径中存在缺陷。总体而言，我们的数据表明火鸡对AFB1的极端敏感性可能归因于高效的AFB1激活和II相酶（如GST）解毒不足的综合作用。
