|Straus, David - Dave|
Submitted to: Toxicology Mechanisms and Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2005
Publication Date: 5/26/2006
Citation: Straus, D.L., Chambers, J.E. 2006. Effects of piperonyl butoxide on the metabolism of DEF (S,S,S-tributyl phosphorotrithioate) in fingerling channel catfish. Toxicology Mechanisms and Methods. 16(4):235-239. Interpretive Summary: The importance of metabolism in making a herbicide (DEF defoli- ant; used to make the leaves of cotton plants die) a better inhibitor of a nervous system enzyme (acetylcholinesterase) in channel catfish was examined. Cotton is sometimes grown in areas where catfish are farmed. Therefore, a potential for herbicide contamination of catfish ponds exits. In the experiment catfish were placed in an aquarium containing piperonyl butoxide (PBO; a chemical that can speed up or slow down metabolism) for 20 hours and then the DEF defoliant was added for 4 hours. Aquariums were also set up with no chemical, DEF only, and PBO only. Acetylcholinesterase (AChE) levels were measured at 0 and 12 h after the exposure period. The results suggest that PBO slows the metabolism of DEF that inhibit AChE, and that DEF is an effective inhibitor of ALiEs without metabolic activation.
Technical Abstract: The present study was undertaken to investigate the significance of monooxygenases in bioactivation of DEF to a more effective anticholinesterase in fish. Channel catfish were exposed via the water column for 20 h to piperonyl butoxide (PBO) followed by a 4 h exposure to the organophosphate defolient DEF (concurrent with the PBO). Acetylcholinesterase (AChE) and aliesterases (ALiEs) activities were determined at 0 and 12 h after the exposure period. Inhibition of brain, plasma, and liver AChE activity by DEF was antagonized by PBO; muscle AChE was not inhibited by DEF. Piperonyl butoxide did not antagonize the inhibition of liver or plasma ALiEs by DEF. These results suggest that PBO retards the formation of the metabolite(s) of DEF that inhibit AChE, and that DEF is an effective inhibitor of ALiEs without metabolic activation.