Metabolism of glucosyl [13H]ceramide by human skin fibroblasts from normal and glucosylceramidotic subjects.

Metabolic utilization of glucosyl [3H]ceramide (glucocerebroside) by human skin fibroblasts from normal and glucosylceramidotic subjects was examined in cell culture. Exogenous glucosyl [3H]ceramide in the culture medium did not influence activity of "acid" beta glucosidase in either cell type. Expectedly in the lipidotic cells, the enzymatic activity was markedly (similar to 20-fold) lower. Normal cells were found preferentially to utilize exogenous tritium-labeled glucosylceramide for a source of precursors for phopholipid biosynthesis. The fatty acid and the sphingosine components of sphingomyelin, and the fatty acid components of phosphatidylcholine and phosphatidylethanolamine, but not phosphatidylserine and phosphatidylinositol, were tritium-labeled. In contrast, glucosylceramidotic cells utilized labeled glucosylceramide far more for synthesis of lactosylceramide (lactocerebroside) and also higher neutral glycosphingolipid homologues. These experimental findings suggest that glucosyl [3H]ceramide is hydrolyzed in normal skin fibroblasts to [3H]ceramide and further to [3H]dihydrosphingosine and 3H-labeled fatty acids. These compounds are subsequently incorporated into cellular phospholipids. Flux of glucosyl [3H]ceramide through this catabolic sequence and reincorporation of its breakdown products into phospholipids predominates in normal skin fibroblasts. In contrast, it is greatly reduced in glucosylceramidotic skin fibroblasts. Consequently, a greater amount of glucosyl [3H]ceramide remains intact for the synthesis of more highly glycosylated glycosphingolipids in the latter cells.