Increased amounts of cholesterol precursors in lipoproteins after ileal exclusion.

Serum cholesterol precursor sterols reflect the activity of cholesterol synthesis. In this study, squalene, methyl sterol and lathosterol contents were studied in very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) of heterozygous familial hypercholesterolemia patients without and with ileal bypass. The contents of lathosterol and all methyl sterols (lanosterol, delta 8,24-dimethylsterol, delta 8-dimethylsterol, delta 8-methostenol and methostenol), but not of squalene were increased in all lipoproteins by ileal bypass. The increase in the free methyl sterols was more marked than that in the esterified ones. The percentage esterification of the methyl sterols was highest in HDL and lowest in VLDL. Lipoprotein methyl sterol contents were positively correlated with each other and with cholesterol synthesis. The methyl sterols were slightly concentrated in LDL, and squalene strongly concentrated in VLDL. It is concluded that long-term stimulation of cholesterol synthesis increases the methyl sterols in all lipoproteins.