Cholesterol and 7-dehydrocholesterol inhibit the in situ degradation of sphingomyelin by cultured human fibroblasts.

Feeding cultured human fibroblasts with cholesterol and 7-dehydrocholesterol resulted in a strong decrease of the in situ degradation of sphingomyelin (about 20 and 40 fold reduction for cholesterol and 7-dehydrocholesterol respectively, at 50 micrograms/ml of medium, and for 24 h incubation). Measurement performed on cell homogenates showed a slight decrease of the sphingomyelinase activity (about 75% of controls), whereas the activities of other lysosomal enzymes (beta glucosaminidase, beta galactosidase) were not significantly affected.