AbstractA large number of organophosphorous insecticides (OPs) are chiral compounds, and yet enantioselectivity in their environmental fate and effects is rarely addressed. In the present study, we isolated individual enantiomers of three OPs, profenofos, fonofos, and crotoxyphos, and evaluated enantioselectivity in their inhibition of acetylcholinesterase (AChE). Acetylcholinesterase inhibition by the enantiomers and racemates was determined in vivo in the aquatic invertebrate Daphnia magna and in Japanese medaka (Oryzias latipes) as well as in vitro with electric eel (Electrophorus electricus) and human recombinant AChEs. The overall results showed variable sensitivity between AChE enzymes from different species as well as variable magnitude of enantioselectivity in enzyme inhibition. The (—)‐enantiomer of profenofos was 4.3‐ to 8.5‐fold more inhibitory to AChE in vivo, whereas (—)‐fonofos was 2.3‐ to 29‐fold more potent than the corresponding (+)‐enantiomer. The (+)‐enantiomer of crotoxyphos was 1.1‐ to 11‐fold more inhibitory to AChE than the (—)‐enantiomer. In contrast, the in vitro results showed (+)‐profenofos to be 2.6‐ to 71.8‐fold more inhibitory than the (—)‐enantiomer and (—)‐crotoxyphos to be 1.6‐ to 1.9‐fold more active than the (+)‐enantiomer. The reversed direction of enantioselectivity observed between the in vivo and in vitro assays suggests enantioselectivity within toxicodynamic processes such as uptake, biotransformation, or elimination. Findings from the present study provide evidence of enantioselectivity in the AChE inhibition of chiral OPs in nontarget organisms and indicate the need to consider enantiomers individually when assessing environmental risk of these chiral pesticides.
摘要 许多有机磷杀虫剂(OPs)都是手性化合物,但它们在环境转归和影响方面的对映体选择性却很少得到关注。在本研究中,我们分离了三种有机磷杀虫剂(丙溴磷、福诺磷和克磷)的对映体,并评估了它们抑制乙酰胆碱酯酶(AChE)的对映选择性。对映体和外消旋体对乙酰胆碱酯酶的抑制作用是在水生无脊椎动物大型蚤(Daphnia magna)和日本青鳉(Oryzias latipes)体内以及电鳗(Electrophorus electricus)和人类重组乙酰胆碱酯酶体外进行测定的。总体结果显示,不同物种的 AChE 酶之间的敏感性不同,酶抑制的对映体选择性也不同。丙溴磷的(-)-对映体在体内对乙酰胆碱酯酶的抑制作用比(-)-对映体强4.3-8.5倍,而(-)-福诺磷比相应的(+)-对映体强2.3-29倍。克芜踪的(+)-对映体对乙酰胆碱酯酶的抑制作用是(-)-对映体的1.1-11倍。相反,体外研究结果显示,(+)-丙溴磷的抑制作用是(-)-对映体的2.6-71.8倍,而(-)-克罗托磷的活性是(+)-对映体的1.6-1.9倍。在体内和体外试验中观察到的对映体选择性方向相反,这表明在摄取、生物转化或消除等毒力作用过程中存在对映体选择性。本研究结果提供了手性 OPs 在抑制非目标生物 AChE 过程中的对映体选择性证据,并表明在评估这些手性农药的环境风险时需要单独考虑对映体。