Effects of carbaryl and azinphos methyl on juvenile rainbow trout (Oncorhynchus mykiss) detoxifying enzymes

In this study, the effects of sublethal exposures to the anticholinesterase insecticides azinphos methyl (AzMe) and carbaryl on the detoxifying responses of juvenile rainbow trout Oncorhynchus mykiss were investigated. Juvenile specimen were exposed to sublethal concentrations of AzMe (2.5 and 5 μg/L) and carbaryl (1 and 3 mg/L) for 24, 48 and 96 h. Carboxylesterase (CbE), catalase (CAT) and glutathione S-transferase (GST) activities as well as reduced glutathione (GSH) and cytochrome P450-1A (CYP1A) levels were monitored in liver and/or kidney. In all exposed groups liver CbE was significantly inhibited. Liver and kidney GSH level was reduced after sublethal exposure to both compounds. Carbaryl induced CAT activity during the first 48 h of exposure, followed by a significant decrease, whereas AzMe continuously decreased CAT activity. GST activity and CYP1A were transiently induced at 24 h by carbaryl exposure (3 mg/L) but sublethal exposure to AzMe did not affect GST activity or CYP1A. Our results show that the O. mykiss detoxifying system are a target for carbaryl and AzMe action, probably affecting redox balance. Although the responses showed similar trends in both organs, they were more important in liver than in kidney. The early inhibitory effect in CAT activity and GSH content produced by AzMe may be associated with a high degree of oxidative stress. Early induction of CYP1A, GST and CAT by carbaryl followed by enzyme inhibition suggests a milder or delayed oxidative stress, revealing differences between both pesticides metabolization. CbE inhibition is a good biomarker for AzMe and carbaryl exposure.