Interconversion of sphingomyelin and ceramide in adult Schistosoma mansoni

Fluorescent lipid analogues of the lipids ceramide and sphingomyelin, namely BODIPY FL C5-ceramide ((N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-sindacene-3-pentanoyl) sphingosine) and BODIPY C5-sphingomyelin ((N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl) sphingosyl phosphocholine), respectively, were used to investigate the presence of a sphingomyelin cycle in Schistosoma mansoni adult males. The parasites were able to convert BODIPY FL C5-ceramide into a fluorescent sphingomyelin analogue, and traffic it to the outer monolayer where it was lost to the medium. The vesicular trafficking inhibitors Brefeldin A and monensin were found, however, to have no effect on either the rate of sphingomyelin synthesis or its trafficking to the surface. Parasites were also shown to break BODIPY FL sphingomyelin down, forming a fluorescent ceramide analogue. Inhibitors of lysosomal function, NH4Cl, desipramine and perhexiline, did not inhibit this breakdown, suggesting that endocytosis and trafficking to lysosomes was not involved. In addition, assays carried out on parasite homogenates for sphingomyelinase activity were unable to detect sphingomyelin breakdown at acidic pH, but did detect activity at pH 7.4. This activity was stimulated by arachidonic acid and MgCl2. The results are discussed with respect to tegument synthesis and turnover, and cellular signalling.