Evidence for rate-limiting steps in sterol synthesis beyond 3-hydroxy-3-methylglutaryl-coenzyme A reductase in human leukocytes.

When human blood leukocytes are incubated with [2-14C]acetate only about 32% of the nonsaponifiable lipid radioactivity is recovered in digitonin-precipitable material. Using thin-layer chromatography and gas-liquid radiochromatography, we have determined that most of the label from [2-14C]acetate in the nonsaponifiable fractions is in lanosterol, squalene and an unidentified sterol. Only 11% of the acetate radioactivity is contained in cholesterol. This distribution does not change when cholesterol synthesis is depressed by the addition of lipoproteins to the medium. These findings are in marked contrast to studies with liver, where most of the nonsaponifiable radioactivity derived from acetate is recovered in digitonin-precipitable sterols. Furthermore, they suggest that rate-limiting steps beyond the 3-hydroxy-3-methylglutaryl coenzyme A reductase reaction exist in the sterol synthesis pathway of human leukocytes.