The effects of simvastatin on plasma lipoproteins and cholesterol homeostasis in patients with heterozygous familial hypercholesterolaemia.

We have examined the influence of simvastatin, a competitive inhibitor of 3-hydroxy-3-methyl glutaryl coenzyme A reductase on plasma concentrations of lipids and lipoproteins, the rates of cholesterol biosynthesis and degradation of 125I-labelled LDL by freshly isolated mononuclear leucocytes and the 24 h urinary excretion of mevalonic acid in patients with heterozygous familial hypercholesterolaemia. Patients were treated with progressively increasing doses of simvastatin (20, 40, and 80 mg day-1) taken in a twice-daily dosage for a period of 6 weeks on each dose. Plasma concentrations of LDL cholesterol decreased by 36.6%, 45.6% and 47.1% respectively on the three doses. High-affinity degradation of 125I-LDL by freshly isolated mononuclear leucocytes increased significantly on the 20 mg day-1 dosage but no further increase was observed on doses of 40 and 80 mg of simvastatin per day. Rates of 2-14C acetate incorporation into cholesterol by freshly isolated mononuclear leucocytes (obtained 12-15 h after the last dose of simvastatin) increased by 62%, 71% and 29% in cells isolated from patients on 20, 40, and 80 mg day-1 of simvastatin compared with values at baseline. In contrast, the 24 h excretion of mevalonic acid in the urine fell by 16.9%, 31.4% and 31.9% respectively on these three doses. Our results indicate that the potent hypocholesterolaemic effects of simvastatin are accompanied by increases in high-affinity LDL receptor-mediated degradation of LDL and a compensatory increase in cholesterol biosynthesis in freshly isolated mononuclear leucocytes but that rates of mevalonic acid excretion in the urine decrease.

Cholesterol homeostasis in mononuclear leukocytes from patients with familial hypercholesterolemia treated with lovastatin.

We evaluated the effects of different doses of lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and the rate-limiting enzyme in cholesterol biosynthesis, on parameters of cholesterol homeostasis in freshly isolated mononuclear leukocytes from 19 patients with heterozygous familial hypercholesterolemia. Patients were treated with sequentially increasing doses of lovastatin (10 to 80 mg/day in a twice-daily regimen). The in vitro activity of HMG CoA reductase and cholesterol synthesis from 2-14C-acetate was determined in mononuclear cells obtained under steady-state conditions after patients had spent 6 weeks on doses of 20, 40, or 80 mg/day. The total and high affinity degradation of 125I-low density lipoprotein (LDL) was determined at baseline and on lovastatin at a dose of 80 mg/day. LDL cholesterol levels fell progressively on lovastatin (38% reduction on 80 mg daily, p less than 0.005). These changes were paralleled by a 121% increase in the activity of HMG CoA reductase (p less than 0.05) and a 39% increase in cholesterol synthesis from 2-14C-acetate (p less than 0.005). Total and high affinity degradation of 125I-LDL increased from 27 +/- 3.3 and 12.1 +/- 1.6 ng/4 x 10(6) cells/4 hours on the diet only to 69.7 +/- 7.2 and 32.9 +/- 3.6 ng/4 x 10(6) cells/4 hours, respectively, (mean +/- SEM) in mononuclear cells isolated from patients on 80 mg of lovastatin daily (p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of low-density lipoprotein receptors in the human hepatoma cell line Hep G2.

The human hepatoma cell line Hep G2 can be maintained in continuous culture and secretes numerous plasma proteins and lipoproteins into the medium. To better characterize cholesterol homeostasis in these cells we have examined the binding, internalization and degradation of [125I]LDL by cultured Hep G2 cells. Hep G2 cells express high-affinity low-density lipoprotein (LDL) receptors which facilitate the binding, internalization and degradation of [125I]LDL; these receptors can be induced by growth in LDL-depleted medium and repressed by further incubation in medium supplemented with LDL. The degradation of [125I]LDL by derepressed Hep G2 cells was inhibited by greater than 90% by monensin. Incubation of Hep G2 cells in the presence of increasing concentrations of LDL also inhibited cholesterol biosynthesis. Our results indicate that Hep G2 cells possess high affinity LDL receptors which are subject to metabolic regulation and suggest that this cell line affords a valuable model to further examine cholesterol and lipoprotein metabolism in human liver cells.

Cholesteryl ester hydrolase activity in mononuclear cells from patients with type II hypercholesterolemia.

Cholesteryl ester hydrolase (CEH) activity was measured in freshly isolated mononuclear cells from patients with primary Type II hypercholesterolemia, heterozygous familial hypercholesterolemia (FH) and familial combined hyperlipidemia (CFH). CEH activity was significantly lower in mononuclear cells from Type II patients than in cells from matched normolipidemic individuals. Moreover, the reduced CEH activity in cells from the hypercholesterolemic patients was accompanied by significant accumulation of cholesteryl ester. This pattern of reduced CEH activity and cholesteryl ester accumulation was identical for cells from both the FH and CFH patients. Since low density lipoprotein (LDL) cholesterol concentrations were higher in the Type II patients, we incubated mononuclear cells from normolipidemic individuals with high concentrations of LDL-cholesterol (greater than 150 mg/dl). Under these conditions CEH activity was significantly decreased, cholesteryl ester content increased, and cholesterol linoleate, in particular, accumulated. These data suggest that the intracellular accumulation of cholesteryl esters is determined in part by the extracellular concentrations of LDL-cholesterol and by the activity of CEH within the cells.

The effect of oral contraceptives on mononuclear cell cholesteryl ester hydrolase activity.

The influence of sex steroids on mononuclear cell cholesteryl ester hydrolase (CEH) activity in premenopausal women and women on combined estrogen-progestin oral contraceptives has been studied. In addition, plasma and mononuclear cell cholesterol and esters were measured along with plasma estrogen and progesterone levels. Mononuclear cell CEH activity in control women is highest on Day 20 of their menstrual cycle. The control women had significantly higher CEH activities than women on oral contraceptives. Plasma esters were higher in the oral contraceptive group. However, in mononuclear cells, free cholesterol but not cholesteryl esters were higher in women on oral contraceptives.

PIP: Premenopausal women, 1 control group (n=9) taking no medication or using no oral contraceptives (OCs) and 1 treated group (n=10) receiving OCs for contraception, were studied to determine any effects OCs have on mononuclear cell cholesteryl ester hydrolase (CEH) activity. 9 of the 10 medicated women were taking Ortho Novum 1/50 and the other person was receiving Norlestrin 1/50. Normally menstruating women (controls) showed a significant rise in CEH levels on Day 20 of the menstrual cycle (P .05). The enzyme activity in women on OCs was significantly lower than control women in 3 of 4 testing periods. In addition, plasma and mononuclear cell cholesterol and esters were measured along with plasma estrogen and progesterone levels. Although free cholesterol levels in normal cycling (control) women and in the OC group did not vary significantly during the menstrual cycle between the 2 groups, the women on OCs had significantly higher ester levels than the control women in 3 of the 4 test periods P .05-.005). When paired ratios of plasma cholesterol to esterified cholesterol were compared between control and OC groups, the ratio of free/esterified was significantly higher in the control group in 3 of 4 tests. In the mononuclear cells, on the other hand, the cholesterol/cholesteryl ester ratio was significantly lower in the control group during the 4 test periods. No association between levels of endogenous sex hormones (estradiol, progesterone) and CEH activity were found. CEH levels may be related to incidence of atherosclerosis, and women taking OCs may have increased chances of developing this disease.

The effect of oral contraceptives on mononuclear cell cholesterol ester hydrolase activity in premenopausal women taking oral contraceptives: relevance to atherosclerosis.

PIP: Among the many, multifactorial etiologies of atherosclerosis is excessive filtration and deposition of lipids, particularly cholesterol esters, in arterial walls; furthermore, the monoclonal theory purports that the artheroma is an uncontrolled proliferation of cells similar to a benign tumor. These 2 aspects of atherosclerosis pathogenesis were studied in 5 healthy women on birth control pills by investigating the level of mononuclear cell cholesterol ester hydrolase (CEH). Control subjects underwent identical investigation. Mononuclear CEH activity was signficantly lower in women on oral contraceptives than in controls in 4 of the 5 test intervals and showed no signficant fluctuation in activity. Average value of CEH in 5 women on birth control pills was 927+ or -81 pmol/mg of protein/hour. In 5 men followed at 5-day intervals, no significant fluctuation of CEH activity was found. Mean average was 2373+ or -92. Total cholesterol and its ester in both plasma and mononuclear cells showed no signficant differences at the 5-day intervals between men and women. However, plasma cholesterol/cholesterol ester ratios were significantly higher in women than men at each of the 5-day intervals from Days 5-25. An additional link between female hormones and atherosclerosis is suggested by the finding that women on oral contracepitves, known to be predisposed to premature atherosclerosis, show reduced and nonfluctuating levels of mononuclear cell CEH.^ieng

The effect of fetal hypophysectomy on placental biosynthesis of progesterone in rhesus.

Placental slices from intact rhesus fetuses were incubated without added substrate. The incubated tissue levels of progesterone (P4) differed according to the sex of the fetus. Slices from female placentas contained significantly more P4 than did those of males. The addition of pregnenolone (P5) to the incubation media caused tissue levels of P4 to increase 1.5 to 3 times control tissue levels for both female and male placentas. Moreover, the sex difference in P4 biosynthesis was eliminated by adding P5 to the incubations. Since control incubations of male placental tissue produced less P4 than those of females, the net increase in P4 synthesis with added P5 was greater for male than female placental tissue. These observations indicated that the step(s) in P4 biosynthesis which were affected by the fetal genotype lay between cholestrol and P5. Incubation of placental slices derived from decapitated fetuses secreted significantly less P4 into the incubation medium than those of intact fetuses. Moreover, the sex difference in the media content of P4 was eliminated. However, decapitation did not eliminate the sex difference in the tissue content of P4 during control incubations. When P5 was added to the incubations, media and tissue levels of P4 increased significantly over control levels for placentas from both sexes. However, the addition of P5 to the incubations from decapitated males did not restore P4 production in the tissue or the medium to levels observed for intact males. However, this did occur when P5 was added to incubations from decapitated females. It appears that fetal decapitation decreased cholesterol side chain cleaving activity and delta5-3beta-hydroxy-steroid dehydrogenase content of the placenta. These data indicate that hormones of fetal origin may control P4 production by the placenta.