SCAVENGING OF REACTIVE OXYGEN SPECIES BY A GLYCOLIPID FRACTION OF MYCOBACTERIUM-AVIUM SEROVAR-2

Previous experiments indicated that MIF-A3, a peptidoglycolipid extrac ted from Mycobacterium avium serovar 2 (Mycobacterium paratuberculosis 18), inhibits the killing of Candida albicans by activated bovine per ipheral blood-derived macrophages and murine thioglycollate-elicited p eritoneal macrophages in vitro. Subsequent in vitro data from our labo ratory indicated that this reduction in killing may be related to the ability of MIF-A3 to scavenge reactive oxygen species (ROS). In this s tudy we examined this hypothesis directly by determining if MIF-A3 red uced exogenous H2O2-induced candidacidal activity. When Candida albica ns was incubated with H2O2 (4 mM) alone, colony-forming units/ml x 10( 4)(CFU/ml) were 0.4 +/- 0.1 (mean +/- SE, n = 4) as compared to 11.3 /- 2.0 CFU/ml in control (untreated) cultures (p < .05). The addition of catalase at concentrations greater than or equal to 6.8 U/ml, compl etely blocked the fungicidal effect of H2O2 However, reducing the amou nt of catalase from 6.8 U/ml to 3.4 U/ml resulted in a loss of scaveng ing activity, which was associated with a 50% increase in H2O2-mediate d killing. Substituting MTF-AS (400 mu g/ml) for catalase, also reduce d H2O2-induced fungicidal activity. In the absence of MIF-A3, H2O2 red uced Candida albicans to less than 10(3) CFU/ml. However, in the prese nce of MIF-A3 the CFU/ml of Candida albicans increased 7.5-fold. Based on concentration-response curves of H2O2 inhibition vs. increasing am ounts of catalase we determined that the relative inhibitory capacity of the MIF-A3 (400 mu g/ml) was similar to 1.0 U/ml ''catalase equival ents.'' These findings provide direct evidence that MIF-A3 can scaveng e H2O2, and reduce H2O2-induced killing of Candida albicans. Copyright (C) 1996 Elsevier Science Inc.