鱼类肝脏微粒体对于硫代磷酸酯类杀虫剂活化代谢率的种间差异(Species-Related Difference of Liver Microsomes of Fish in Activation of Organothiophosphorus Insecticides)

为了弄清鱼类肝脏微粒体细胞色素P450s(CYPs)对于硫代磷酸酯类杀虫剂活化代谢率的种间差别,选用斑马鱼Brachydanio rerio、麦穗鱼Pseudorasbora parva、剑尾鱼Xiphophorus helleri、篮鳃太阳鱼Leponus macrohirus四种鱼作为受试生物,选用对硫磷、马拉硫磷、毒死蜱三种硫代磷酸酯类杀虫剂作为受试药剂,以外源乙酰胆碱酯酶(AchE)的抑制率为指标,在离体状态下间接测量了杀虫剂活化代谢物的相对生成量.离体试验表明,对于对硫磷,活化代谢物生成量的高低顺序为:斑马鱼、剑尾鱼、麦穗鱼>太阳鱼(p<0.05),最高的麦穗鱼和最低的太阳鱼之间相差10.0倍;对于马拉硫磷和毒死蜱,活化代谢物生成量的高低顺序均为:剑尾鱼>太阳鱼>斑马鱼、麦穗鱼(p<0.05),最高的剑尾鱼和最低的麦穗鱼之间的分别相差66.9和137倍.毒性测定表明,对于对硫磷、马拉硫磷和毒死蜱,四种鱼96hLC50之间的最大差别分别是45、18和77倍.对马拉硫磷而言,96hLC50的种间差异特征与活化代谢物生成量的种间差异特征比较吻合,而对于对硫磷和毒死蜱而言,两者之间的吻合度较低.研究证实了肝脏CYP在活化硫代磷酸酯杀虫剂方面具有明显的种间差异,同时也证实仅以活化代谢物的离体生成量这一指标来衡量鱼类对于硫代磷酸酯杀虫剂的敏感性,其结论可能会较大幅度地偏离生测结果.尽管如此,本研究证实在所测的鱼类当中,斑马鱼属于CYP活性较低的鱼种,而这一特性很可能是造成斑马鱼对于硫代磷酸酯杀虫剂的敏感性偏低的重要原因.

Species-Related Difference of Liver Microsomes of Fish in Activation of Organothiophosphorus Insecticides

To evaluate species-based diversity concerning activation of organothiophosphorus insecticides,which was believed to be dominated by fish liver microsomal cytochrome P450s(CYPs),relative rates of production of active metabolites of the insecticides were scaled in vitro by rates of inhibition of exogenous acetylcholinesterase(AchE) by the metabolites.Four species of fish,namely zebra fish Brachydanio rerio,swordtail fish Xiphophorus helleri,topmouth gudgeon Pseudorasbora parva,and sunfish Leponus macrohirus,and three types of organothionphosphorus insecticides,including parathion,malathion,and chlorpyrifos,were involved in the study.Result of the in vitro study indictes that for parathion,the rate of production of the active metabolite was significantly higher in the zebrafish,the swordtail fish,and the topmouth gudgeon than in the sunfish(p<0.05).The maximal discrepancy was 10.0 times between the topmouth gudgeon and the sunfish.For both malathion and chlorpyrifos,species order concerning rate of production of the active metabolites is swordtail fish>sunfish>zebrafish and topmouth gudgeon(p<0.05) with a maximal discrepancy of 66.9 times and 137 times,respectively,between the swordtail fish and the topmouth gudgeon.Result of bioassays indicated that for parathion,malathion,and chlorpyrifos,maximal discrepancy in terms of 96h LC50s was 45,18,and 77 times,respectively.For malathion,variation pattern of LC50 was basically in accord with that of the rate of production of the active metabolite,whereas the case was not so for both parathion and chlorpyrifos.This study demonstrated an obvious diversity in terms of CYP mediated activation of organothiophosphorus insecticides among different species of fish.It also demonstrated that in predicting susceptibility of fish towards organothiophosphorus insecticides,the result might significantly depart from that of bioassays in condition that the prediction was based merely on the rate of in vitro production of the active metabolites.In spite of that,this study proofed that among the fish to be tested,the zebrafish belonged to population with relatively low activity of CYP,and this character might be one of the principal reasons that the fish is relatively insensitive to organothiophosphorus insecticides.