The Activation of Parathion by Brain and Liver of a Brazilian Suckermouth Benthic Fish Shows Comparable in Vitro Kinetics

• Published in: Pesticide biochemistry and physiology 1999-07, Vol.64 (3), p.149-156
• Main Authors: Cunha Bastos, V.L.F., Silva Filho, M.V., Rossini, A., Cunha Bastos, J.
• Format: Article
• Language: English
• Subjects: acetylcholinesterase; Agnatha. Pisces; animal tissues; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; brain; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; enzyme activity; fish; Fundamental and applied biological sciences. Psychology; hypostomus punctatus; in vitro; inhibition; kinetics; liver; Medical sciences; metabolic detoxification; metabolites; parathion; Pesticides, fertilizers and other agrochemicals toxicology; poisoning; sublethal effects; Toxicology
• ISSN: 0048-3575; 1095-9939
• DOI: 10.1006/pest.1999.2418

A constant influx of parathion into livers of benthic fishes could overflow their ability to both activate (into paraoxon) and detoxify (through hydrolysis) molecules and metabolites of this phosphorothioate. This could allow parathion to be activated in brain cells with consequent nervous intoxication. Assay of acetylcholinesterase (AChE) enzyme activities allowed the nanomolar quantification of paraoxon produced from parathion in vitro by liver and brain homogenates of cascudo, a Brazilian suckermouth benthic fish. Using comparable kinetic conditions, we have determined that the initial velocities at which parathion desulfuration occurred in homogenates of liver and brain of cascudo responded to increasing micromolar parathion concentrations as a sigmoidal function. Our data also suggest that cascudo brain tissues may produce paraoxon from parathion at a rate approximately two-thirds that of the liver tissues, when parathion concentrations are lower than 30 μM. Moreover, cascudo brain would be faster than liver to promote oxidative desulfuration of parathion between 35 and 55 μM. As no parathion cleavage was measured using brain or liver homogenates of cascudo it became clear that direct hydrolysis of parathion would not work as a detoxification process in these tissues. These results may reveal typical processes of organophosphate metabolism present in benthic fish which could produce sublethal nervous intoxication.