Identification and composition of lipid classes in surface and somatic preparations of adult Brugia malayi

Abstract

The cuticle of adult Brugia malayi is the organism's major point of interaction with the mammalian host environment. We therefore undertook an investigation in order to define the lipid composition of this outermost layer of the parasite. The lipid class and fatty acid composition of the cuticle of adult Brugia malayi was examined by surface specific radioiodination, organic extraction, thin layer chromatography and gas chromatography. The data were compared with those derived from similar analyses of somatic preparations of the parasites. The composition of the cuticular lipid fraction was found to be highly unusual and distinct from that of the internal lipids. Cholesterol esters and wax esters were absent from the cuticular lipid fraction, which was however enriched in unesterified fatty acids. The major polar lipids in both cuticular and somatic preparations were phosphatidylcholine and phosphatidylethanolamine, but unusually high levels of lysophosphatidylethanolamine were observed in the cuticular extracts. Analyses of cuticular polar lipids indicated that there is an asymmetric distribution of the fatty acids in phosphatidylethanolamine, assuming that lysophosphatidylethanolamine is derived from deacylation of the former molecule in the cuticle. The major fatty acids in all lipid fractions examined were the 18-carbon, mono- and di-unsaturated type, while significant amounts of palmitic, palmitoleic, stearic and eicosatrienoic acids were also found. A highly unusual feature of the cuticular lipid fraction was that it contained large amounts of a novel polar lipid species which, on exposure to atmospheric oxygen, degraded to a hydrophobic and a hydrophilic moiety. This polar lipid was absent from the somatic preparations. The data are discussed in terms of the possible resistance or susceptibility of the parasite to reactive oxygen species.