Increased nonsterol isoprenoids, dolichol and ubiquinone, in the Smith-Lemli-Opitz syndrome: effects of dietary cholesterol.

Smith-Lemli-Opitz syndrome (SLOS) is an inherited autosomal recessive cholesterol deficiency disorder. Our studies have shown that in SLOS children, urinary mevalonate excretion is normal and reflects hepatic HMG-CoA reductase activity but not ultimate sterol synthesis. Hence, we hypothesized that in SLOS there may be increased diversion of mevalonate to nonsterol isoprenoid synthesis. To test our hypothesis, we measured urinary dolichol and ubiquinone, two nonsterol isoprenoids, in 16 children with SLOS and 15 controls, all fed a low-cholesterol diet. The urinary excretion of both dolichol (P < 0.002) and ubiquinone (P < 0.02) in SLOS children was 7-fold higher than in control children, whereas mevalonate excretion was comparable. In a subset of 12 SLOS children, a high-cholesterol diet decreased urinary mevalonate excretion by 61% (P < 0.001), dolichol by 70% (P < 0.001), and ubiquinone by 67% (P < 0.03). Our hypothesis that in SLOS children, normal urinary mevalonate excretion results from increased diversion of mevalonate into the production of nonsterol isoprenoids is supported. Dietary cholesterol supplementation reduced urinary mevalonate and nonsterol isoprenoid excretion but did not change the relative ratios of their excretion. Therefore, in SLOS, a secondary peripheral regulation of isoprenoid synthesis may be stimulated.

Medroxyprogesterone acetate and dihydrotestosterone induce coronary hyperreactivity in intact male rhesus monkeys.

Coronary hyperreactivity (CH), characterized by persistent severe vasoconstrictions in response to vasoconstrictor challenge, is oppositely influenced by progesterone (P) and medroxyprogesterone acetate (MPA) treatment in surgically menopausal primates. In this study we tested whether multiweek MPA or dihydrotestosterone (DHT) exposure induced CH in intact male rhesus monkeys. Coronary angiographic experiments with intracoronary serotonin and the thromboxane A(2) analog U46619 stimulated brief vasoconstriction (for 1-3 min) in large epicardial coronaries in untreated male monkeys. In contrast, MPA- and DHT-treated monkeys displayed long-duration constrictions (>5 min), with significantly greater reductions in the minimal diameters of epicardial coronaries. Immunocytochemistry demonstrated androgen receptors (AR) and P receptors in aorta and coronary arteries, and immunocytochemistry and Western blotting showed AR and P receptors in rhesus coronary vascular muscle cells. In vivo, MPA or DHT increased thromboxane prostanoid (TP) receptor expression in the aorta. In vitro, MPA or DHT increased, whereas P did not change, TP receptor expression in primary coronary vascular muscle cell. This MPA- or DHT-mediated increase in TP receptor expression was attenuated by the AR antagonist flutamide. MPA or DHT induction of CH in intact adult male primates, hypothesized to occur via androgenic up-regulation of vascular muscle TP receptor expression, could predispose to CH-mediated myocardial ischemia.

Prevention of coronary hyperreactivity in preatherogenic menopausal rhesus monkeys by transdermal progesterone.

OBJECTIVE: To test if transdermal progesterone (P) confers coronary vascular protection in surgically menopausal preatherosclerotic rhesus monkeys. METHODS AND RESULTS: Ovariectomized rhesus monkeys fed an atherogenic diet (AD) for 19 months were treated with an investigational transdermal P cream (n=7) or identical placebo cream (n=5) for 4 weeks. Aorta and carotids showed fatty streaks and Oil Red O staining demonstrated lipid deposition. Serum P levels in P-treated rhesus monkeys (0.6 ng/mL) were significantly greater than placebo (0.2 ng/mL). Significant elevation of cholesterol, LDL cholesterol, and HDL cholesterol, was noted in all animals. Lp(a) was significantly attenuated in the AD-fed P-treated monkeys. Coronary angiographic experiments stimulating vasoconstriction by intracoronary injections of serotonin plus U46619 showed exaggerated prolonged actions amplified by AD, but significant protection against severe prolonged vasoconstriction in P-treated monkeys. Immunocytochemistry confirmed co-expression of P and thromboxane prostanoid (TP) receptors in coronaries and aorta. Western blotting demonstrated TP receptor attenuation in vascular muscle after P treatment. CONCLUSIONS: Coronary hyperreactivity, a putative component of coronary artery disease mediated via increased vascular muscle thromboxane prostanoid receptors, can be prevented by subphysiological levels of P, not only in nonatherosclerotic (previously shown) but also in preatherosclerotic primates.

Achievement of low-density lipoprotein cholesterol goals: new strategies to address new guidelines.

Evidence that CHD morbidity and mortality can be reduced with reduction of LDL-C to less than 100 mg/dL (2.6 mmol/L) is rapidly accumulating. NCEP-ATP III guidelines should be considered minimal goals of therapy. Regarding the prevention and treatment of CHD, health care providers need to recognize the wide therapeutic gap between evidence-based medicine and customary clinical practice. Aggressive pharmacologic therapy is probably required to achieve optimal LDL-C levels in many hyperlipidemic patients. Novel agents, including selective cholesterol absorption inhibitors, will provide clinicians with a tool to safely and effectively target the exogenous pathway of cholesterol metabolism. Combination therapy with cholesterol-lowering agents that have complementary mechanisms of action and can be safely co-administered may be a new option to achieve broader lipid control.

Residual effects of lovastatin and simvastatin on urinary mevalonate excretions in patients with familial hypercholesterolemia.

3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG CoA) reductase inhibitors are widely used to decrease plasma cholesterol levels in patients with heterozygous familial hypercholesterolemia (FH) who are at increased risk of premature coronary artery disease. Tissue-culture and animal studies have indicated that administration of HMG CoA reductase inhibitors (eg, lovastatin, simvastatin, etc) induces a compensatory increase in the activity of HMG CoA reductase, both by increasing its synthesis and decreasing catabolism. To determine in human subjects whether cessation of therapy with this class of drugs leads to induction of HMG CoA reductase activity and above-normal rates of cholesterol biosynthesis, we measured urinary concentrations of mevalonic acid (an indicator of cholesterol biosynthesis) after the cessation of therapy with lovastatin and simvastatin (80 mg/day) in patients with heterozygous FH. Plasma concentrations of LDL increased promptly on discontinuation of reductase inhibitor therapy but did not increase above pretreatment levels at any point after drug discontinuation. Similarly, the 24-hour urinary excretion of mevalonic acid was reduced during treatment with lovastatin or simvastatin and increased promptly on discontinuation of drug but did not increase to levels exceeding those found at baseline when the patients were receiving dietary therapy only. We conclude that cessation of treatment with HMG CoA reductase inhibitors in patients with FH does not result in a rebound increase in cholesterol biosynthesis and that no rebound overshoot occurs in plasma concentrations of low-density-lipoprotein cholesterol.

Feedback inhibition of the cholesterol biosynthetic pathway in patients with Smith-Lemli-Opitz syndrome as demonstrated by urinary mevalonate excretion.

Smith-Lemli-Opitz syndrome (SLOS) is a genetic disorder characterized by low plasma cholesterol and high 7-dehydrocholesterol (7-DHC). Synthesis of cholesterol and 7-DHC and its metabolites is regulated by HMG-CoA reductase, whose activity can be measured by 24-h excretion of its product mevalonate. We devised a simple, non-invasive method for collecting 24-h urine in our subjects. With a background of a very low cholesterol diet, mean mevalonate excretion did not differ between controls and SLOS children, indicating that SLOS subjects have normal HMG-CoA reductase activity. In a short term feeding study, the effects of a high cholesterol diet in SLOS subjects include a significant 55% increase in plasma cholesterol levels and 39% decrease in mevalonate excretion and no change in plasma 7-DHC levels. However, in four SLOS subjects, fed a high cholesterol diet for 2-3 years, plasma cholesterol levels continued to increase, urinary mevalonate excretion remained low and total 7-DHC decreased significantly, likely from decreased total sterol synthesis. Thus, in SLOS subjects, HMG-CoA reductase activity was normal and was subject to normal cholesterol induced feedback inhibition. However, total sterol synthesis in SLOS may still be decreased because of increased diversion of mevalonate into the shunt pathway away from sterol synthesis.

The effects of lovastatin and simvastatin on the diurnal periodicity of plasma mevalonate concentrations in patients with heterozygous familial hypercholesterolemia.

Animal and human studies have shown that the biosynthesis of cholesterol exhibits diurnal periodicity with nocturnal increases in the level of cholesterol precursors. Dietary cholesterol, which increases the intracellular pool of cholesterol and plasma cholesterol levels, has been shown to blunt the nocturnal increases in cholesterol biosynthesis. Patients with heterozygous familial hypercholesterolemia (FH) have very high levels of plasma low-density lipoprotein cholesterol (LDL) due to their reduced ability to metabolize LDL particles. The present studies were carried out to determine whether diurnal variations in cholesterol synthesis occur in FH patients and to test the effects of 3-hydroxy-3-methyl glutaryl CoA (HMG CoA) reductase inhibitors on the diurnal cycle of cholesterol biosynthesis in these patients. Diurnal rates of cholesterol synthesis were assessed by measuring the plasma concentrations of mevalonate, an intermediate in the pathway of cholesterol biosynthesis. Female FH patients exhibited a diurnal pattern in plasma mevalonate levels similar to that previously reported in controls with peak values occurring at night. Treatment with lovastatin and simvastatin (40 mg b.i.d.) significantly reduced 24-h mean plasma mevalonate levels from baseline values. Administration of lovastatin in the evening reduced the nocturnal increases in mevalonate levels, and the administration of simvastatin completely abolished the nighttime rise. These results demonstrate that inhibition of cholesterol biosynthesis by lovastatin and simvastatin modifies the normal diurnal rhythm of cholesterol biosynthesis in female FH patients.

Effect of Pravastatin in the Treatment of Patients with Type III Hyperlipoproteinemia.

OBJECTIVE: To determine the efficacy and safety of pravastatin in the treatment of subjects with Type III hyperlipoproteinemia. DESIGN: Randomized, double-blind, placebo-controlled, crossover study. SETTING: Four lipid research clinics in the United States. PATIENTS: Twenty subjects between 18 and 70 years old with three diagnostic features of Type III hyperlipoproteinemia: very-low-density lipoprotein cholesterol (VLDL-C)/total plasma triglyceride ratio in excess of 0.30; beta-migrating VLDL pattern on agarose-gel electrophoresis; and the homozygous apolipoprotein E phenotype E(2)/E(2). After 4 weeks of dietary control, the subjects were eligible if their mean plasma total cholesterol level was at least 250 mg/dl and mean plasma trigylceraide level was at least 220 mg/dL. INTERVENTIONS: Subjects were randomly assigned to pravastatin 40 mg hs or placebo hs at the start of the first 6-week double-blind treatment period. After completing this phase, subjects entered a 4-week placebo/drug washout phase before crossing over to the opposite treatment for the second 6-week double-blind treatment period. MEASUREMENTS: Plasma VLDL-C and low density lipoprotein cholesterol (LDL-C) after ultracentrifugation and total triglyceride, cholesterol and high-density lipoprotein cholesterol (HDL-C) after 6 weeks of treatment; adverse clinical events and abnormal laboratory results. RESULTS: After 6 weeks of pravastatin theraphy, plasma levels of VLDL-C and LDL-C decreased 49% and 39%, respectively (p less-than-or-equal 0.01 vs. placebo). Total cholesterol and triglyceride concentrations decreased 36% and 22%, respectively (p less-than-or-equal 0.001 vs. placebo). Levels of HDL-C increased 8% (p less-than-or-equal 0.01 vs. placebo). Pravastatin was tolerated well. One marked laboratory abnormality, an asymptomatic elevation of creatine phosphokinase, resolved upon completing pravastatin treatment. CONCLUSIONS: Pravastatin lowers plasma VLDL-C, LDL-C, total cholesterol, and triglyceride and raises HDL-C in subjects with Type III hyperlipoproteinemia. The safety profile is excellent. Pravastatin reductase inhibitor therapy affords a useful approach to the management of Type III or remnant removal disease.