Inhibition of cholinesterase activity by azinphos-methyl in two freshwater invertebrates: Biomphalaria glabrata and Lumbriculus variegatus.

KRISTOFF, G.; VERRENGIA GUERRERO, N; PECHÉN D ANGELO, AM; COCHÓN, A.

TOXICOLOGY

ELSEVIER IRELAND LTD

Lugar: Amsterdam; Año: 2006 vol. 222 p. 185 - 194

0300-483X

In this study, some biochemical features and the extent of inhibition induced by the organophosphorous pesticide azinphos-methylon the cholinesterase (ChE) activity present in whole soft tissue of two freshwater invertebrate species, the gastropod Biomphalaria and the oligochaete Lumbriculus variegatus were investigated. Both invertebrate organisms presented marked differences in ChE activity, type of enzymes and subcellular location. Acetylthiocholinewas the substrate preferred by B. glabrata ChE. The enzyme activity was located preferentially in the supernatant of 11,000 centrifugation and was inhibited by increasing concentrations of substrate but not by ISO OMPA. Results showed that there were progressive inhibitions of the enzyme activity, with values 21%, 59%, 72%, 76%, and 82% lower than the control at levels of 1, 10, 50, 100 and 1000 "1">M of eserine, respectively. In contrast, L. variegatus ChE activity was distributed both in the supernatant and pellet fractions, with values approximately 6 and 20 times higher B. glabrata respectively. Studies with butyrylthiocholine and ISO OMPA suggested that about 72% of the activity corresponded to butyrylcholinesterase. A strong enzyme inhibition (88–94%) was found at low eserine concentrations (1–10 M). ChE activity B. glabrata was inhibited by in vivo exposure to azinphos-methyl suggesting that both species can form the oxon derivative of this pesticide. However, both invertebrate species showed a very different susceptibility to the insecticide.NOEC and EIC values were 500 and 1000 times lower for L. variegatus B. glabrata reflecting that the oligochaetes were >much more sensitive organisms. A different pattern was also observed for the recovery of the enzymatic activity when the organisms were transferred to clean water. The recuperation process was faster for the oligochaetes than for the gastropods. Mortality was not observed in either of the experimental conditions assayed, not even at concentrations that induced 90% of ChE inhibition. The differences in substrate specificity, sensitivity to inhibitors, and subcellular location between the ChEs of B. glabrata Aand L. variegatus could be the main factors contributing to the differential susceptibility to azinphos-methyl ChE inhibition found in the present study.