Bovine chromaffin cells in culture show carboxylesterase activities sensitive to organophosphorus compounds

Abstract

Carboxylesterase activities are widely distributed in a great variety of tissues; however, the biological function of these enzymes remains unclear. Some organophosphorus compounds induce a neurodegenarative syndrome related to the covalent modification of a carboxylesterase known as neuropathy target esterase. We investigated the expression of neuropathy target esterase and related carboxylesterase in bovine chromaffin cells with the aim of developing a potential in vitro model for studying the cellular function of carboxylesterase enzymes and toxic effects of organophosphorus compounds. Total phenyl valerate esterase exhibited an activity of 1.27 ± 0.19 mU/10 5 cells (SD, n = 15). From the phenyl valerate esterase paraoxon and mipafox inhibition curves the following activities have been determined: B-activity (resistant to 40 μM paraoxon), 1.05 ± 0.08 mU/10 5 cells ( n = 8); C-activity (resistant to 40 μM paraoxon plus 250 μM mipafox), 0.12 ± 0.05 mU/10 5 cells ( n = 8); and neuropathy target esterase, calculated by the difference between B- and C-activities, 0.93 ± 0.08 mU/10 5 cells ( n = 8). All of these activities increased linearly with the number of cells and time of incubation with the substrate. Most of the phenol product of the reaction was released and detected in the extracellular medium. None of the components of the reaction were shown to affect cell viability when assessed by trypan blue exclusion. The study shows that bovine chromaffin cells possess carboxylesterase activities and respond to inhibition by paraoxon and mipafox, thus facilitating the discrimination of neuropathy target esterase. In conclusion, bovine chromaffin cells are appropriate as an in vitro cell model for studying toxic effects of organophosphorus compounds.