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: U R-6, avirulent strain) to hydrogen peroxide has been studied in vitro conditions. There was a dose-dependent toxic effect of H2O2 on both st rains. The promastigotes of Dd-8 strain, however, were more resistant compared to UR-6 strain. The cell response was not affected by the for ms of H2O2 stress, for instance, single-dose exposure with reagent H2O 2 or equivalent amount generated over a period of 1 h. Dd-8 promastigo tes 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) ce lls/ml). Hydrogen peroxide metabolism by Dd-8 cells was significantly inhibited by aminotriazole, azide, and thiol reagents, while that of U R-6 cells was sensitive only to thiol reagents. The results are consis tant with the negligible activity of glutathione peroxidase and nondet ectable catalase in UR-6 promastigotes; both enzyme activities were pr esent in Dd-8 promastigotes. These findings suggest that the ability o f the parasite to resist H2O2 toxicity may have a potential role in it s virulence.