BRUGIA-MALAYI - DIFFERENTIAL SUSCEPTIBILITY TO AND METABOLISM OF HYDROGEN-PEROXIDE IN ADULTS AND MICROFILARIAE

The sensitivity of microfilariae and adult Brugia malayi to hydrogen p eroxide (H2O2) was determined in vitro, and parasite viability assesse d by incorporation of 2-deoxy-D-[1-H-3]glucose. Both stages were surpr isingly resistant to peroxide stress. Microfilariae tolerated the dire ct addition of H2O2 to medium in which they were incubated at concentr ations up to 50 mu M, whereas adult worms survived the addition of 100 mu M H2O2 and showed slightly impaired viability at 150 mu M H2O2. Hi gher concentrations were lethal in both cases. This observation of dif ferential susceptibility was reproducible when parasites were subjecte d to continuous generation of H2O2 via glucose/glucose oxidase. Microf ilariae remained viable over a 4-hr period when challenged with concen trations which generated 20 mu M H2O2 in the absence of parasites. Adu lts survived higher concentrations of glucose oxidase, which generated 200 mu M H2O2 over the same time period. Under these conditions the p arasites effectively countered the rate of peroxide generation by meta bolising the product. Protein carbonyl formation was detectable at sub lethal concentrations of glucose/glucose oxidase, but malonaldehyde fo rmation was only detectable coincident with parasite death. The rate o f H2O2 consumption by parasites was determined and showed that adult w orms metabolised it at a rate 23 x faster than microfilariae, expresse d as activity per wet weight. Assessment of enzyme activities in paras ite extracts demonstrated that H2O2 metabolism was effected principall y by catalase activity, which was elevated in adult worms relative to microfilariae. Cytochrome c peroxidase activity was also detected and was roughly equivalent in both stages. Glutathione peroxidase and NADH /NADPH-dependent consumption of H2O2 were absent, and the rate of none nzymic reduction of H2O2 coupled to glutathione oxidation did not cont ribute significantly to metabolism. Glutathione reductase activity and total glutathione content were equivalent in adults and microfilariae . This study illustrates that Brugia,malayi are much more resistant to H2O2 than other filarial species examined to date and can effectively metabolise levels in excess of those potentially generated by activat ed leucocytes. (C) 1995 Academic Press, Inc.