[14C]Acetate incorporation by cultured normal,familial hypercholesterolemia and Down's syndrome fibroblasts

Fibroblasts from patients with homozygous familial hypercholesterolemia (FH), a disease characterized by accelerated atherogenesis, are known to lack functional low-density-lipoprotein receptors, which ultimately results in increased cholesterol biosynthesis in the cultured cells. ¹⁴C]Acetate incorporation in these cells was compared to that of normal fibroblasts and to fibroblasts from patients with Down's syndrome, a disease in which atherosclerosis is rare. Total ¹⁴C]acetate incorporation did not differ significantly between normal and Down's fibroblasts, nor did its partitioning into the hexane-extractable and aqueous fractions of the cell hydrolysates. ¹⁴C]Acetate incorporation was much greater in FH cells in both the aqueous and hexane-extractable fractions. Preincubation in fetal bovine serum increased acetate incorporation only by FH cells, while 50 μg low-density lipoprotein/ml medium depressed acetate incorporation in all three groups. A C₂₇ sterol, identified by gas chromatography-mass spectrometry as a probable isomer of cholesterol, was present in small amounts in FH fibroblasts, but was not detectable in the normal or Down's cells. The absolute amounts of ¹⁴C]acetate incorporated into the non-sterol lipids were greater in the FH fibroblasts, indicating that these cells may have to synthesize, in addition to cholesterol, other required cellular lipids which are delivered to the normal cells by low-density lipoproteins.