Relative resistance of promastigotes of a virulent and an avirulent strain of Leishmania donovani to hydrogen peroxide

Sensitivity of promastigotes of Leishmania donovani (Dd-8, virulent: UR-6, avirulent strain) to hydrogen peroxide has been studied in vitro conditions. There was a dose-dependent toxic effect of H2O2 on both strains. The promastigotes of Dd-8 strain, however, were more resistant compared to UR-6 strain. The cell response was not affected by the forms of H2O2 stress, for instance, single-dose exposure with reagent H2O2 or equivalent amount generated over a period of 1 h. Dd-8 promastigotes removed H,Oz from medium at a higher rate (6.43 nmol/min/ 3 x 10(7) cells/ml) compared to UR-6 promastigotes (3.17 nmol/min/3 x 10(7) cells/ml). Hydrogen peroxide metabolism by Dd-8 cells was significantly inhibited by aminotriazole, azide, and thiol reagents, while that of UR-6 cells was sensitive only to thiol reagents. The results are consistant with the negligible activity of glutathione peroxidase and nondetectable catalase in UR-6 promastigotes; both enzyme activities were present in Dd-8 promastigotes. These findings suggest that the ability of the parasite to resist H2O2 toxicity may have a potential role in its virulence.