Glucosylceramide and Glucosylsphingosine Metabolism in Cultured Fibroblasts Deficient in Acid β-Glucosidase Activity1

Abstract

The metabolism of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph) was studied using cultured fibroblasts deficient in acid beta-glucosidase activity. In fibroblasts from patients with Gaucher's disease, in vitro beta-glucosidase activities were 2.7-11.7% and 4.8-13.6% of control values when 4-methylumbelliferyl beta-D-glucoside and GlcSph were used as substrates, respectively. In spite of the enzyme deficiency, GlcCer and GlcSph, the natural substrates of the deficient enzyme, did not accumulate in the cells. When normal fibroblasts were incubated with conduritol B epoxide (CBE), a specific inhibitor of acid beta-glucosidase, the in vitro enzyme activities decreased dose-dependently (2.2-2.4% of control values at 50 microM CBE), and GlcCer and GlcSph accumulated in the cells at concentrations of CBE higher than 50 microM. To investigate the intracellular metabolism of GlcCer and GlcSph, either radioactive GlcCer or GlcSph was loaded onto cultured fibroblasts. In fibroblasts treated with a high dose of CBE (1 mM), the degradation of GlcCer and GlcSph was retarded (5-21% on day 7; normal range, 81-99%), while in fibroblasts from patients with Gaucher's disease, both the pattern and rate of the degradation of the lipids (83-97% on day 7) were almost the same as those seen in the control cells. These results indicate that in Gaucher's disease fibroblasts the intracellular metabolism of GlcCer and GlcSph is normal in spite of the deficiency in beta-glucosidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)