Role of biotransformation in determining aldicarb toxicity in fish

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in fish, and is readily biotransformed by most organisms studied. In fish, both the cytochrome P450 (CYP) and the flavin monooxygenase systems (FMO) are involved in bioactivating aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of acetylcholinesterase (AChE). Channel catfish (Ictalurus punctatus), along with many other fresh water species, do not express FMO and are relatively resistant to the effects of aldicarb. This project examined the toxicity, AChE inhibition, metabolism, and toxicokinetic of aldicarb in channel catfish, and compared these values with an aldicarb-sensitive species, rainbow trout, which expresses FMO. Studies of in vitro and in vivo aldicarb biotransformation in catfish suggest that a low rate of bioactivation (10 times slower Vmax), resulting in less initial conversion to the activated metabolite, aldicarb sulfoxide, may be a contributing factor to resistance of channel catfish to aldicarb toxicity. These data are supported by toxicokinetic and enzyme inhibition studies. This work demonstrates that differences in FMO expression among fish species may have significant influence on toxicity resulting from exposure to some xenobiotics.