Inhibitors of sterol synthesis. Differential effects of 14 alpha-hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol and 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol on sterol synthesis in cell-free homogenates of rat liver

Effects of 26-aminocholesterol, 27-hydroxycholesterol, and 25-hydroxycholesterol on proliferation and cholesterol homeostasis in arterial myocytes

The major relation existing between cell growth and cholesterol homeostasis prompted us to investigate the effect of 26-aminocholesterol (26-NH2), 27-hydroxycholesterol (27-OH), and 25-hydroxycholesterol (25-OH) on these cellular events. To test this relation, we incubated human and rat arterial myocytes with the sterols for 72 hours. All the tested compounds (0.5 to 7.5 mumol/L) inhibited rat and human myocyte proliferation and cholesterol biosynthesis in a dose-dependent manner. 26-NH2 was more potent than oxysterols in inhibiting human myocyte proliferation but equieffective in rat cells; 27-OH and 25-OH displayed similar activity in both cell lines. Inhibition of nuclear incorporation of thymidine in rat myocytes is consistent with decreased cell count. The antiproliferative effect of the tested sterols was reversible. The high inhibition (80%) of cholesterol biosynthesis necessary to induce a decrease in myocyte proliferation suggests a causal relation between the cholesterol synthetic pathway and these cellular processes. In addition, all the tested sterols were able to inhibit hydroxymethyl glutaryl-coenzyme A reductase activity in intact myocytes but not in cell-free extracts. The finding that 26-NH2 but not 27-OH or 25-OH does not suppress LDL receptor activity in either human or rat myocytes supports the achievement of selectivity over the coordinately regulated LDL receptor gene. The ability of 26-NH2 to interfere with myocyte proliferation and cholesterol synthesis without affecting the LDL receptor pathway confers at least in vitro a pharmacological interest on the compound in the process of atherogenesis.

Synthesis of new C-19-functionalized cholesterols

A series of new derivatives of cholesterol bearing polar functional groups on carbon-19 were synthesized, including 19-oximino-, 19-amino-, 19-(methylamino)-, 19-mercapto-, and 19-(methylthio) cholesterol, and 3 beta-hydroxycholest-5-en-19-oic acid, as well as an unusual cyclosterol, 5,19-cyclocholest-6-en-3 beta-ol.

Inhibitors of sterol synthesis. Metabolism of [2,4-3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one after oral administration to a nonhuman primate

5 alpha-Cholest-8(14)-en-3 beta-ol-15-one is a potent inhibitor of cholesterol biosynthesis which has significant hypocholesterolemic activity upon oral administration to rodents and nonhuman primates. In the present study the metabolism of the 15-ketosterol has been investigated after the oral administration of a mixture of [2,4-3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one and [4-14C]cholesterol to 8 baboons. Blood samples were obtained at 4, 8, 12, 16, and 24 h after administration of the labeled sterols. Clear differences in the time courses of the levels of 3H and 14C in plasma were observed. 3H in plasma showed maximum values at 4 to 8 h, whereas maximum values for the levels of 14C were observed much later. 3H in plasma was shown to be primarily in the form of its metabolites, i.e. esters of the 15-ketosterol, cholesterol, and cholesteryl esters. The levels of the 15-ketosterol and of each of these metabolites showed different changes with time. The labeled cholesterol (and the cholesterol moiety of the cholesteryl esters), formed from the [2,4-3H]-15-ketosterol, was characterized by chromatography and by purification by way of its dibromide derivative. At 24 h after the administration of the labeled sterols, the distribution of 3H in plasma lipoprotein fractions paralleled that of 14C, with most of the 3H and 14C in high density lipoprotiens (HDL) and low density lipoproteins (LDL). Almost all of the 3H in HDL and in LDL was found as cholesterol, cholesteryl esters and esters of the 15-ketosterol. The distribution of 3H in HDL and in LDL of the free 15-ketosterol, esters of the 15-ketosterol, cholesterol, and cholesteryl esters was similar to that of plasma, thereby indicating no unusual concentration of any of the 3H labeled components in HDL or LDL.

Inhibitors of cholesterol biosynthesis. Further studies of the metabolism of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one in rat liver preparations

5 alpha-Cholest-8(14)-en-3 beta-ol-15-one is a potent inhibitor of sterol biosynthesis in mammalian cells in culture and has significant hypocholesterolemic activity upon oral administration to rodents and non-human primates. The conversion of the 15-ketosterol to cholesterol upon incubation with the 10,000 x g supernatant fraction of rat liver homogenate preparations under aerobic conditions has been reported (D.J. Monger, E.J. Parish and G.J. Schroepfer, Jr. (1980) J. Biol. Chem. 255, 11122-11129). Presented herein are results of studies of the metabolism of [2,4-3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one obtained upon incubation with the microsomal, cytosolic and the 10,000 x g supernatant fractions of liver homogenates of female rats under a variety of conditions. The results of these studies indicated metabolism of the 15-ketosterol to materials with the chromatographic properties of fatty acid esters of the 15-ketosterol, fatty acid esters of C27-monohydroxysterols, a component similar to the 15-ketosterol (possibly an isomer of the delta 8(14)-15-ketosterol), and a polar component. Detailed studies of the C27-monohydroxysterols obtained from incubation of the 15-ketosterol under anaerobic conditions indicated the formation of labeled 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol which were characterized by their behavior on silicic acid column chromatography, by the behavior of their acetate derivatives on medium pressure liquid chromatography on alumina-AgNO3 columns, and by co-crystallization of the labeled sterols with authentic unlabeled standards. The identification of 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol as metabolites of the 15-ketesterol, coupled with previous studies of the metabolism of 5 alpha-cholesta-8,14-dien-3 beta-ol and of 5 alpha-cholest-8(14)-ene-3 beta, 15 alpha-diol and 5 alpha-cholest-8(14)-ene-3 beta, 15 beta-diol has permitted the formulation of a scheme for the overall metabolism of the 15-ketosterol to cholesterol.

Oxygenated cholesterols synergistically immobilize acyl chains and enhance protein helical structure in human erythrocyte membranes

Fourier transform infrared spectroscopy revealed that insertion of 20 alpha-hydroxycholesterol into human erythrocyte membranes (10% of total membrane sterol) immobilized the lipid acyl chains to a degree equivalent to enriching total membrane cholesterol by 50% (Rooney, M.W., Lange, Y. and Kauffman, J.W. (1984) J. Biol. Chem. 259, 8281-8285). Raman spectroscopy showed that the amount of acyl chain rotamers was not significantly altered by the presence of 20 alpha-hydroxycholesterol, indicating that acyl chain immobilization was limited to an inhibition of lateral motion. The presence of 20 alpha-hydroxycholesterol may synergistically enhance the acyl-chain-immobilizing behavior of membrane cholesterol. In addition, protein helical structure was not altered by 20 alpha-hydroxycholesterol. The insertion of 7 alpha-hydroxycholesterol into erythrocyte membranes resulted in an increase in protein helical structure which was comparable to that observed for erythrocyte membranes enriched with pure cholesterol by 50%. However, both acyl chain mobility and conformation were unchanged. These results suggest a synergistic behavior between oxysterols and cholesterol in modifying erythrocyte membrane packing.

cAMP-independent stimulation of glycogen phosphorylase in newborn rat hepatocytes

Postnatal development of glycogen phosphorylase activation by the cAMP-independent pathway was examined in isolated rat hepatocytes from control and propylthiouracil-treated congenital hypothyroid rat pups. At 5 days postnatum there was complete phosphorylase activation by beta-adrenergic stimulation, glucagon, and the calcium ionophore A23187, but no activation by alpha-adrenergic stimulation. Activation of phosphorylase by angiotensin or vasopressin was less than in hepatocytes from adult rats (P less than 0.01). At 28 days postnatum activation by all of these hormones was complete. In the propylthiouracil-treated group hormone responsiveness was similar to the control at 5 days postnatum. However, alpha-adrenergic (P less than 0.025), angiotensin, and vasopressin (P less than 0.05) activation was decreased at 28 days postnatum, and beta-adrenergic, glucagon, and A23187 activation was complete. The attenuated responses were restored by thyroxine replacement from 15 days postnatum. [32P]Pi incorporation into phosphatidylinositol by epinephrine and vasopressin in 28-day propylthiouracil-treated rats was lower than the control (P less than 0.01). We speculate that the diminished phosphorylase response of hepatocytes to alpha-adrenergic, vasopressin, or angiotensin stimuli in the early neonatal period could be related to low receptor numbers and the weaker phosphoinositide response during this period. Also, the depressed phosphorylase response to alpha-adrenergic, vasopressin, and angiotensin stimulation in congenital hypothyroidism at 28 days postnatum could be related to a decrease in number of plasma membrane receptors for these agonists.