Studies of crude proteins in leishmania donovani parasites that are resistant to sodium stibogluconate (pentostamR)

Abstract

Leishmania donovani, the causative agent of visceral Leishmaniasis (Kala-azar) has been knwon to develop resistance to sodium stibogluconate (PentostamR). The present study aimed at developing a Pentostam--resistant L. donovani promastigote strains in vitro. This was done by continually exposing the parent susceptible L. donovani promastigotes (NLB 065) to increasing concentrations of PentostamR for a period of 3 until the promastigotes were multipying in 10mg/ml of PentostamR. The differences in polypeptide composition of the crude proteins (antigens) of the parent susceptible L. donovani promastigotes (NLB 065R) were detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The mean of inhibitory concentration of PentostamR which killed 50% (IC50) of the parent susceptible L. donovani promastigotes was 0.084 mg/ml + 0.01 (SD). The Pentostam-resistant L. donovani promastigotes had a mean of IC50 2.90 mg/ml + 0.83 (SD) and this was significantly different (t0.05 6=2.447, P<0.01) from the mean IC50 for PentostamR against the parent susceptible L. donovani promastigotes. The in vitro induced, Pentostam-resistant L. donovani promastigotes were 35 times more resistant to Pentostam killing than the parent susceptible L. donovani promastigotes and this resistance to PentostamR was maintained after 4 months of continuous culture in the absence of drug pressure. This indicated that the PentostamR resistance in NLB 065R was genetically stable. The Pentostam-resistant L. donovani promastigotes had in their polypeptide composition, a polypeptide band of molecular weight 85,000 + 500 Daltons (D). This polypeptide band was observed in both logarithmic and stationary phase cultures of NLB 065R promastogotes. These results suggest that the polypeptide of molecular weight 85,000 + 500 D is unique only to the Pentostam-resitant L. donovani promastigotes.