The effects of clofazimine, niclosamide & amphotericin B, on electron transport of Leishmania donovani promastigotes

Background & objectives. The study was undertaken to explore the locus of i nteraction of clofazimine and niclosamide which showed substantial growth i nhibition property in Leishmania donovani promastigotes. Methods: The uptake of final electron acceptor oxygen and 2, 6-dichlorophen olindophenol (DCPIP) reduction in the electron transport chain were measure d by constant volume Warburg respirometer and monitoring absorbance at 600 nm, respectively. Irreversibility of O-2 uptake inhibition by clofazimine a nd niclosamide was determined by dilution of cell suspension followed by ce ntrifugation. Results: Clofazimine and niclosamide showed their minimum inhibitory concen tration (MIC) at 33 and 150 mu g/ml, respectively. Oxygen uptake inhibition by clofazimine and niclosamide was not reversed by removal of the drug by centrifugation. Rotenone, a potent inhibitor of mammalian electron transpor t chain showed no inhibition on the electron transport chain of L. donovani promastigotes. Cyanide at 1 mM concentration showed partial inhibition in L. donovani promastigotes. Oxygen uptake and DCPIP reduction by L. donovani promastigotes were highly sensitive to sulphhydryl group inhibitors. Stron g inhibition of oxygen uptake (80-100%) by L. donovani promastigotes was ac hieved by clofazimine, niclosamide and amphotericin B. Amphotericin B faile d to inhibit DCPIP reduction by L. donovani promastigotes, whereas DCPIP re duction was inhibited by clofazimine and niclosamide, respectively. Interpretation & conclusion: DCPIP reduction was mediated by transplasma me mbrane electron transport as evidenced by its inhibition with membrane impe rmeable quinone I, 2-naphthoquinone-4-sulphonic acid (NQSA). Transplasma me mbrane electron transport requires b-cytochromes and sulphhydryl groups for its function and was inhibited by clofazimine and niclosamide.