A group of oxygenated sterols has been identified as potent and specific inhibitors of sterol biosynthesis. The ability of these compounds to inhibit sterol synthesis in cultured cells and the ineffectiveness of cholesterol under the same conditions suggest that feedback regulation of sterol biosynthesis may be brought about by an oxygenated sterol rather than by cholesterol. The nature of the regulatory sterol may vary in different cells with their specific requirements for cholesterol as a structural component or as a precursor of other steroid products. The use of oxygenated sterols to block sterol synthesis in cultured cells provides new information regarding the role of sterol in cell membrane structure and function. For example, de novo sterol synthesis is required for DNA synthesis and cell division by some cultured cells. Studies with cultured cells, and with rats and mice in vivo, suggest that oxygenated sterols could be of value in the treatment of several important human diseases.

The prevalence of cholesterol gallstones differs among inbred strains of mice fed a diet containing 15% (wt/wt) dairy fat, 1% (wt/wt) cholesterol, and 0.5% (wt/wt) cholic acid. Strains C57L, SWR, and A were notable for a high prevalence of cholelithiasis; strains C57BL/6, C3H, and SJL had an intermediate prevalence; and strains SM, AKR, and DBA/2 exhibited no cholelithiasis after consuming the diet for 18 weeks. Genetic analysis of the difference in gallstone prevalence rates between strains AKR and C57L was carried out by using the AKXL recombinant inbred strain set and (AKR x C57L)F1 x AKR backcross mice. Susceptibility to gallstone formation was found to be a dominant trait determined by at least two genes. A major gene, named Lithl, mapped to mouse chromosome 2. When examined after 6 weeks on the lithogenic diet, the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (EC 1.1.1.88) was downregulated as expected in the gallstone-resistant strains, AKR and SJL, but this enzyme failed to downregulate in C57L and SWR, the gallstone-susceptible strains. This suggests that regulation of the rate-limiting enzyme in cholesterol biosynthesis may be pivotal in determining the occurrence and severity of cholesterol hypersecretion and hence lithogenicity of gallbladder bile. These studies indicate that genetic factors are critical in determining gallstone formation and that the genetic resources of the mouse model may permit these factors to be identified.Both atherosclerosis and cholelithiasis result from excess cholesterol; in the one case cholesterol is deposited in arterial walls, and in the other case cholesterol precipitates in the gallbladder. Both diseases are prevalent in cultures consuming a Western diet, and both can be induced in animal models by a diet high in cholesterol (1,2). In Western cultures, heart disease is the major cause of death, and gallstone disease is present in 10-40% of individuals over the age of 60 (3).Genetic factors apparently play an important role in the development of cholesterol gallstone disease. Among studies of gallstone formation in animals, Alexander and Portman (4) demonstrated that C57BL/6 mice are susceptible to cholelithiasis, but CBA mice are resistant. In both strains bile was supersaturated with cholesterol but not to the same degree (4). Fujihara et al. (5) reported that the prevalence of gallstones varied from 0% to 100% among six strains of laboratory mice.Evidence for the importance of genetic factors in human cholelithiasis is limited. Gallstone disease can be familial (6-11), and the bile from healthy sisters of female gallstone patients is more lithogenic than controls (11,12). In certain native populations of North and South America, a high percentage of adults develop cholesterol gallstones, suggesting common genetic factors (13,14).In previous studies, high fat plus high cholesterol diets produced atherosclerosis and gallstones in some strains of mice (15). In this report, we survey common inbred strains of mice for susceptibility to cholelith...

Incubation of peripheral blood or isolated lymphocytes of C57L/J mice with phytohemagglutinin stimulated the incorporation of thymidine into DNA of lymphocytes as they transformed into large lymphoblasts. DNA synthesis began after about 24 hr of incubation and reached a peak at 48 hours. The de-novo synthesis of sterols from acetate was stimulated much earlier, at 4 hr of incubation, and the rate reached a maximum at 24 hr, approximately at the time DNA synthesis began. (6)(7)(8)11) prevented both the increase in sterol synthesis and the increase in DNA synthesis that are associated with blastogenesis. DNA synthesis was not affected when the inhibitor was added after the cycle in sterol synthesis had reached its maximum. These observations of an apparent relationship between sterol synthesis and DNA synthesis are described in this report. MATERIALS AND METHODSAnalysis of Lipid, CO2 Production and 3-Hydroxy-3-methylglutaryl Coenzyme A (HAIG-CoA) Reductase Activity in Whole Blood and Isolated Lymphocytes. Female C57L/J strain mice, aged 3-4 months old, were supplied by the Production Department of the Jackson Laboratory. They were decapitated following asphyxiation in CO2 and blood was pooled from several animals in sterile test tubes that contained sodium heparin (30 USP units of heparin per ml of blood; Sigma). Aliquots (0.5 ml) of the heparinized blood were pipetted into sterile 24 ml Erlenmeyer flasks containing 5 ml of RPMI 1640 medium (Grand Island Biological Co.) with or without PHA (Difco, PHA-MI 0.5 mg/ml of final concentration). The flasks were sealed with stoppers and incubated in a shaking water bath at 370 for various lengths of time. Two hours before the end of incubation 50 jl of RPMI medium containing 25 4Ci of [1-_4C]acetate (58.5 Ci/mol, New England Nuclear) was added to the incubation mixture and the flasks were sealed with stoppers fitted with plastic cups (Kontes). The procedures for analysis of radioactive C02, fatty acids, and sterol fractions of the samples were described l)reviously (4,5).In some experiments isolated lymphocytes were used in place of whole blood. The procedure used for isolation of lymphocytes has been described (4, 9). Approximately 7 ml of heparinized blood pooled from eight animals was passed through a column containing an equal volume of 0.3 mm glass beads to remove the "sticky" population of platelets. The blood was then mixed with 7 ml of RPMLI medium containing Hepes (N-2-hydroxyetlhylp)iperazinie-N'-2-ethanesulfonic acid) 1950

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