Filarial glutathione S-transferase: its induction by xenobiotics and potential as drug target

Glutathione-S-transferase (GST) a Phase-II drug detoxification enzyme, was detected in Setaria cervi, a bovine filarial parasite. In vitro effect of diethylcarbamazine, butylated hydroxyanisole and phenobarbitone on the GST of adult female S. cervi was assayed by the addition of these compounds in the maintenance medium. The specific activity of GST towards 1-chloro-2,4-dinitrobenzene was increased progressively 1.2-1.97, 1.3-2.4 and 1.2-2.7 times at 10-100 µM of diethylcarbamazine, butylated hydroxyanisole and phenobarbitone, respectively, after 5 h at 37°C. Substrate specificity studies showed a higher increase in specific activity with ethacrynic acid and no change with cumene hydroperoxide. Although the intensity of GST activity band was more in extract from diethylcarbamazine or butylated hydroxyanisole treated worms extract, an extra band of activity appeared in those worm extracts compared to control worm extract. SDS/PAGE showed increased thickness of the band corresponding to purified GST in extracts from diethylcarbamazine/butylated hydroxyanisole/phenobarbitone treated worms. Purification and quantification of GST from diethylcarbamazine and butylated hydroxyanisole treated worms indicated an increase in enzyme specific activity. The increase in GST protein by these agents was blocked by prior treatment with actinomycin D, indicative of a transcription dependent response. The role of this enzyme in motility and viability of microfilariae and adult female was tested in vitro using a range of known GST inhibitors. Of those tested, ethacrynic acid, ellagic acid, 1-chloro-2,4-dinitrobenzene, cibacron blue and butylated hydroxyanisole reduced the viability and motility of microfilariae and adult female worms at micromolar concentrations. These results suggest that S. cervi GST is inducible in response to the antifilarial drug diethylcarbamazine and may play an important role in parasite's survival, thus could be a potential drug target.