In vitro antifilarial activity of glutathione S-transferase inhibitors

Abstract

Female adult bovine filarial worms Setaria digitata were extracted with phosphate-buffered saline (pH 7.4) and glutathione S-transferase (GST) activity and protein content were determined. The protein content, GST enzyme activity, and specific activity were 10.61 +/- 3.41 mg ml(-1), 0.09 +/- 0.019 micromol min(-1) ml(-1), and 0.009 +/- 0.002 micromol min(-1) mg(-1) protein, respectively. The GST inhibition studies were performed with and without the inhibitors resulted from earlier molecular docking studies viz., ethacrynic acid, plumbagin, and curcumin for which the IC(50) values were 19.42, 51.41, and 114.86 microM, respectively. The in vitro macrofilaricidal activity of these molecules was studied by worm motility and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction assay at 24- and 48-h incubation. Plumbagin and ethacrynic acid showed 100% inhibition in worm motility at lower concentrations of 3.19 and 6.6 microM, respectively, at 48-h incubation while curcumin was effective at 54.29 microM. In MTT reduction assay, the ED(50) values (50% inhibition in formazan formation) for plumbagin, ethacrynic acid, and curcumin at 48-h incubation were 1.20, 2.48, and 19.86 microM, respectively. MTT reduction assay showed that plumbagin was the most effective in killing the adult S. digitata worms followed by ethacrynic acid and curcumin. In conclusion, all the three molecules selected by molecular modeling and docking studies inhibited the GST enzyme isolated from S. digitata and exhibited macrofilaricidal activity in vitro.