Deletion of a single mevalonate kinase (Mvk) allele yields a murine model of hyper-IgD syndrome.

In the current study our objective was to develop a murine model of human hyper-IgD syndrome (HIDS) and severe mevalonic aciduria (MA), autoinflammatory disorders associated with mevalonate kinase deficiency (MKD). Deletion of one Mvk allele (Mvk (+/-)) yielded viable mice with significantly reduced liver Mvk enzyme activity; multiple matings failed to produce Mvk (-/-) mice. Cholesterol levels in tissues and blood, and isoprene end-products (ubiquinone, dolichol) in tissues were normal in Mvk (+/-) mice; conversely, mevalonate concentrations were increased in spleen, heart, and kidney yet normal in brain and liver. While the trend was for higher IgA levels in Mvk (+/-) sera, IgD levels were significantly increased (9-12-fold) in comparison to Mvk (+/+) littermates, in both young (<15 weeks) and older (>15 weeks) mice. Mvk (+/-) animals manifested increased serum TNF-alpha as compared to wild-type littermates, but due to wide variation in levels between individual Mvk (+/-) mice the difference in means was not statistically significant. Mvk (+/-) mice represent the first animal model of HIDS, and should prove useful for examining pathophysiology associated with this disorder.

Effects of colesevelam HC1 on sterol and bile acid excretion in patients with type IIa hypercholesterolemia.

Colesevelam HC1 is a potent bile acid-binding polymer. This study's aim was to determine effects of colesevelam HCl on sterol and bile acid excretion in patients with type IIa hypercholesterolemia. Twenty-four patients (low-density lipoprotein cholesterol, 130 to 220 mg/dL) enrolled in an open-label, parallel-design study, entered an American Heart Association/National Cholesterol Education Program diet for 6 weeks and were randomized to colesevelam HCl, 2.3 or 3.8 g/day for 4 weeks. In an apparent dose-related manner, respective mean serum concentrations HCl of low-density lipoprotein cholesterol decreased by 10% (P < 0.01) and 13% (P = 0.05), mean total cholesterol levels decreased by 4.9% (P = 0.05) and 6.1% (P = 0.09), and total fecal bile acid excretion showed median changes of +324% (P < 0.05) and +316% (P < 0.05). Colesevelam HCl did not affect fecal neutral sterol or fecal fatty acid excretion; however, 24-hr urinary mevalonic acid levels significantly increased in both treatment groups (P < 0.05). The cholesterol-lowering action of colesevelam HCl appears to be mediated through increased bile acid excretion.

Effect of a very-high-fiber vegetable, fruit, and nut diet on serum lipids and colonic function.

We tested the effects of feeding a diet very high in fiber from fruit and vegetables. The levels fed were those, which had originally inspired the dietary fiber hypothesis related to colon cancer and heart disease prevention and also may have been eaten early in human evolution. Ten healthy volunteers each took 3 metabolic diets of 2 weeks duration. The diets were: high-vegetable, fruit, and nut (very-high-fiber, 55 g/1,000 kcal); starch-based containing cereals and legumes (early agricultural diet); or low-fat (contemporary therapeutic diet). All diets were intended to be weight-maintaining (mean intake, 2,577 kcal/d). Compared with the starch-based and low-fat diets, the high-fiber vegetable diet resulted in the largest reduction in low-density lipoprotein (LDL) cholesterol (33% +/- 4%, P <.001) and the greatest fecal bile acid output (1.13 +/- 0.30 g/d, P =.002), fecal bulk (906 +/- 130 g/d, P <.001), and fecal short-chain fatty acid outputs (78 +/- 13 mmol/d, P <.001). Nevertheless, due to the increase in fecal bulk, the actual concentrations of fecal bile acids were lowest on the vegetable diet (1.2 mg/g wet weight, P =.002). Maximum lipid reductions occurred within 1 week. Urinary mevalonic acid excretion increased (P =.036) on the high-vegetable diet reflecting large fecal steroid losses. We conclude that very high-vegetable fiber intakes reduce risk factors for cardiovascular disease and possibly colon cancer. Vegetable and fruit fibers therefore warrant further detailed investigation.

Inhibition of cholesterol synthesis by atorvastatin in homozygous familial hypercholesterolaemia.

Patients with homozygous familial hypercholesterolaemia (HoFH) have markedly elevated low density lipoprotein (LDL) cholesterol levels that are refractory to standard doses of lipid-lowering drug therapy. In the present study we evaluated the effect of atorvastatin on steady state concentrations of plasma lipids and mevalonic acid (MVA), as well as on 24-h urinary excretion of MVA in patients with well characterized HoFH. Thirty-five HoFH patients (18 males; 17 females) received 40 mg and then 80 mg atorvastatin/day. The dose of atorvastatin was increased further to 120 mg/day in 20 subjects and to 160 mg/day in 13 subjects who had not achieved LDL cholesterol goal, or in whom the dose of atorvastatin had not exceeded 2.5 mg/kg body wt per day. LDL cholesterol levels were reduced by 17% at the 40 mg/day and by 28% at the 80 mg/day dosage (P<0.01). Reduction in LDL cholesterol in the five receptor negative patients was similar to that achieved in the 30 patients with residual LDL receptor activity. Plasma MVA and 24-h urinary excretion of MVA, as markers of in vivo cholesterol synthesis, were elevated at baseline and decreased markedly with treatment. Urinary MVA excretion decreased by 57% at the 40 mg/day dose and by 63% at the 80 mg/day dosage (P<0. 01). There was a correlation between reduction in LDL cholesterol and reduction in urinary MVA excretion; those patients with the highest basal levels of MVA excretion and thus the highest rates of cholesterol synthesis having the greatest reduction in LDL cholesterol (r=0.38; P=0.02). Increasing the dose of atorvastatin to 120 and 160 mg/day did not result in any further reduction in LDL cholesterol or urinary MVA excretion suggesting a plateau effect with no further inhibition of cholesterol synthesis at doses of atorvastatin greater than 80 mg/day.

Premenopausal black women are uniquely at risk for coronary heart disease compared to white women.

Premenopausal black women have a two to threefold greater rate of coronary heart disease than premenopausal white women. This study was designed to provide greater insight into the reasons for this difference which is currently unclear. Coronary heart disease risk factors were compared in 100 black and 100 white, healthy premenopausal women, ages 18-45 years, and of relatively advantaged socioeconomic status. Compared to white women, black women had a higher body mass index (32.0±9.2 vs. 29.0±9.4 kg/m2, p=0.021), and higher systolic (124±17 vs. 115±14 mm Hg, p<0.0001) and diastolic (79±14 vs. 75±11 mm Hg, p=0.048) blood pressures. The mean plasma lipoprotein(a) concentration was markedly higher in the black women (40.2±31.3 mg/dL) than in the white women (19.2±23.7 mg/dL, p<0.0001). The plasma total homocysteine level was also higher in the black women (8.80±3.38 vs. 7.81±2.58 mmol/L, p=0.013). The black women, however, had lower plasma triglyceride levels (0.91±0.46 vs. 1.22±0.60 mmol/L, p<0.0001) and a trend toward higher high-density lipoprotein cholesterol levels (1.37±0.34 vs. 1.29±0.31 mmol/L, p=0.064) than the white women. Plasma total and low-density lipoprotein cholesterol levels were similar. Black women consumed more saturated fat and cholesterol. Rates of cigarette smoking and alcohol intake were low and similar between the races. In summary, compared to white women, black women had a higher mean body mass index, higher blood pressures, higher lipoprotein(a) and plasma total homocysteine levels, and greater consumption of saturated fat and cholesterol. The differences in coronary risk factors between these two premenopausal groups may explain the higher incidence of coronary heart disease in black women. (c) 2000 by CHF, Inc.

Treatment of pyruvate carboxylase deficiency with high doses of citrate and aspartate.

A patient with severe pyruvate carboxylase deficiency presented at age 11 weeks with metabolic decompensation after routine immunization. She was comatose, had severe lactic acidemia (22 mM) and ketosis, low aspartate and glutamate, elevated citrulline and proline, and mild hyperammonemia. Head magnetic resonance imaging showed subdural hematomas and mild generalized brain atrophy. Biotin-unresponsive pyruvate carboxylase deficiency was diagnosed. To provide oxaloacetate, she was treated with high-dose citrate (7.5 mol/kg(-1)/day(-1)), aspartate (10 mmol/kg(-1)/day(-1)), and continuous drip feeding. Lactate and ketones diminished dramatically, and plasma amino acids normalized, except for arginine, which required supplementation. In the cerebrospinal fluid (CSF), glutamine remained low and lysine elevated, showing the treatment had not normalized brain chemistry. Metabolic decompensations, triggered by infections or fasting, diminished after the first year. They were characterized by severe lactic and ketoacidosis, hypernatremia, and a tendency to hypoglycemia. At age 3(1/2) years she has profound mental retardation, spasticity, and grand mal and myoclonic seizures only partially controlled by anticonvulsants. The new treatment regimen has helped maintain metabolic control, but the neurological outcome is still poor.

Premenopausal black women have more risk factors for coronary heart disease than white women.

Premenopausal black women have a 2- to 3-fold greater rate of coronary heart disease (CHD) than premenopausal white women. The purpose of this study was to provide greater insight into the reasons for this difference, which are currently unclear. We compared CHD risk factors in 99 black and 100 white, healthy premenopausal women, aged 18 to 45 years, and of relatively advantaged socioeconomic status. Compared with white women, black women had a higher body mass index (32.0 +/- 9.2 vs 29.0 +/- 9.4 kg/m2, p = 0.021), and higher systolic (124 +/- 17 vs 115 +/- 14 mm Hg, p <0.0001) and diastolic (79 +/- 14 vs 75 +/- 11 mm Hg, p = 0.048) blood pressures. The mean plasma lipoprotein(a) concentration was markedly higher in the black women (40.2 +/- 31.3 mg/dl) than in the white women (19.2 +/- 23.7 mg/dl, p <0.0001). The plasma total homocysteine level was also higher in the black women (8.80 +/- 3.38 vs 7.81 +/- 2.58 micromol/L, p = 0.013). The black women, however, had lower plasma triglyceride levels (0.91 +/- 0.46 vs 1.22 +/- 0.60 mmol/L, p <0.0001), and a trend toward higher high-density lipoprotein (HDL) cholesterol levels (1.37 +/- 0.34 vs 1.29 +/- 0.31 mmol/L, p = 0.064) than the white women. Plasma total and low-density lipoprotein (LDL) cholesterol levels were similar, despite a greater consumption of saturated fat and cholesterol by the black women. Rates of cigarette smoking and alcohol intake were low and similar between the races. In summary, premenopausal black women had a higher mean body mass index, blood pressure, lipoprotein(a), and plasma total homocysteine level, and a greater consumption of saturated fat and cholesterol than white women. These differences in coronary risk factors may place the black women in our study at increased risk for CHD compared with the white women.

Expanded-dose simvastatin is effective in homozygous familial hypercholesterolaemia.

Patients with homozygous familial hypercholesterolaemia (HFH) have abnormalities in both low-density lipoprotein (LDL) receptor alleles, resulting in severe hypercholesterolaemia and premature coronary heart disease. Limited treatment options are available and the response to drug therapy has been poor. In the present paper, we have evaluated the efficacy and safety of simvastatin at doses beyond the current maximal dose of 40 mg/day in patients with HFH. After a 4 week placebo diet run-in period, 12 patients with well-characterized HFH were randomized to simvastatin 80 mg/day administered in three divided doses (n = 8; group 1) or 40 mg once daily (n = 4; group 2). After 9 weeks, the dose in group 1 was increased to 160 mg/day while the dose in group 2 was kept at 40 mg/day, but with the drug given in three divided doses and treatment continued for an additional 9 weeks. All 12 patients completed the study and there were no serious or unexpected adverse effects. LDL-cholesterol concentrations fell by 14% at the 40 mg/day dose, but were reduced further at the higher doses (25% at the 80 mg/day and by 31% at the 160 mg/day dosage, P < 0.0001). Excretion of urinary mevalonic acid, as an index of in vivo cholesterol biosynthesis, was reduced but did not correlate with reduction in LDL-cholesterol in the individual patients. The magnitude of response to therapy was not predicted by the LDL-receptor gene defect as patients with the same LDL-receptor mutations responded differently to the same dose of simvastatin therapy. The ability of expanded doses of simvastatin (80 or 160 mg/day) to reduce LDL-cholesterol levels in patients with HFH, even if receptor negative, suggests that at these doses, the drug reduces LDL production. Simvastatin therapy, at doses of 80 or 160 mg/day, should therefore be considered in all patients with HFH, either as an adjunct to apheresis, or as monotherapy for those patients who do not have access to apheresis or other such treatment modalities.

Dietary cholesterol feeding suppresses human cholesterol synthesis measured by deuterium incorporation and urinary mevalonic acid levels.

The objective of this study was to measure the response of cholesterol biosynthesis in subjects to three different amounts of dietary cholesterol: 50 (low), 350 (medium), and 650 (high) mg cholesterol per 2800 kcal. Individuals with low (n = 7), normal (n = 12), and elevated (n = 11) plasma cholesterol concentrations consumed in random order solid-food test diets (15%, 55%, and 30% of energy as protein, carbohydrate, and fat, respectively) at each dietary cholesterol level. The three diets were consumed for 4 weeks each, and each dietary phase was separated by a 4-week washout period. During the final week of each diet, 0.7 g D2O was given per kilogram of body water and deuterium incorporation into the erythrocyte cholesterol pool was measured for 24 hours. Urinary mevalonate levels were also determined in samples obtained during two consecutive 24-hour periods. Both techniques provided measurements of whole-body cholesterol biosynthesis. In all subjects the cholesterol synthesis rate as measured by deuterium incorporation was significantly lower (P < .05) after the transition from low- to medium- and low- to high-cholesterol diets. Urinary mevalonate excretion decreased after the change from the medium- to high- (P < .05) and low- to high- (P < .01) cholesterol diets. Although correspondence between the two methods was poor, they both indicated some suppression of cholesterol synthesis by dietary cholesterol. The response of cholesterogenesis to different amounts of dietary cholesterol was related to the rate of synthesis under depressed conditions of the low-cholesterol diet. These findings indicate modest downregulation of synthesis in response to dietary cholesterol in humans, independent of plasma cholesterol levels.

A genetic model for absent chylomicron formation: mice producing apolipoprotein B in the liver, but not in the intestine.

The formation of chylomicrons by the intestine is important for the absorption of dietary fats and fat-soluble vitamins (e.g., retinol, alpha-tocopherol). Apo B plays an essential structural role in the formation of chylomicrons in the intestine as well as the VLDL in the liver. We have developed genetically modified mice that express apo B in the liver but not in the intestine. By electron microscopy, the enterocytes of these mice lacked nascent chylomicrons in the endoplasmic reticulum and Golgi apparatus. Because these mice could not form chylomicrons, the intestinal villus enterocytes were massively engorged with fat, which was contained in cytosolic lipid droplets. These mice absorbed D-xylose normally, but there was virtually no absorption of retinol palmitate or cholesterol. The levels of alpha-tocopherol in the plasma were extremely low. Of note, the absence of chylomicron synthesis in the intestine did not appear to have a significant effect on the plasma levels of the apo B-containing lipoproteins produced by the liver. The mice lacking intestinal apo B expression represent the first genetic model of defective absorption of fats and fat-soluble vitamins and provide a useful animal model for studying nutrition and lipoprotein metabolism.

Role of dietary cholesterol in the optimal diet for the treatment of hypercholesterolemia.

OBJECTIVE: This paper discusses studies in which the effects of dietary cholesterol on the plasma concentrations of lipids and lipoproteins have been evaluated in adult human subjects including patients with hypo- and hypercholesterolemia. DESIGN: The dietary studies were conducted on an outpatient basis in the Clinical Research Center. Each dietary period was four weeks in duration and an adequate washout period was interposed between each dietary phase. SETTING: A university medical centre. PATIENTS: The participants in these studies were adult men or women with hypocholesterolemia, normal volunteers or patients with primary hypercholesterolemia. INTERVENTIONS: The dietary periods consisted of three separate dietary phases in which dietary cholesterol was a single variable. The diets contained 50 mg/day of cholesterol for the low cholesterol diet, 350 mg/day for the moderate cholesterol diet and 650 mg/day for the high cholesterol diet. RESULTS: Concentrations of total and low density lipoprotein (LDL) cholesterol increased in all three patient groups from the low cholesterol to the moderate cholesterol to the high cholesterol diet but the magnitude of increase in LDL cholesterol concentrations was greater in the patients with pre-existent hypercholesterolemia and least in the patients with hypocholesterolemia. In all three patients groups an increased intake of dietary cholesterol was associated with suppression of endogenous cholesterol biosynthesis as assessed by the urinary excretion of mevalonic acid. CONCLUSIONS: An increased intake of dietary cholesterol results in increases in the plasma concentrations of total and LDL cholesterol in patients with inherently low, normal or high concentrations of LDL cholesterol but the magnitude of increase is greatest in those patients with pre-existent hypercholesterolemia. These results support the view that restriction of dietary cholesterol leads to a reduction in the plasma concentrations of total and LDL cholesterol and is an appropriate recommendation for patients with known hypercholesterolemia or patients in whom medical recommendations call for a reduction in the plasma concentrations of total and LDL cholesterol.

Effect of nibbling versus gorging on cardiovascular risk factors: serum uric acid and blood lipids.

Nibbling has been reported to decrease serum cholesterol under fasting conditions, as well as the incidence of cardiovascular disease. It has been suggested that these effects are partly attributable to reduced concentrations of serum insulin, which are also observed. However, data on the effects of nibbling on serum lipids throughout the day are not available, nor is it known how nibbling affects serum uric acid as a further insulin-related risk factor for cardiovascular disease. We have attempted to address these issues. Seven healthy men consumed identical diets in a randomized crossover design either as three meals daily (control) or as 17 meals daily (nibbling) for 2 weeks. On day 13, serum lipid levels were measured over the course of the day (12 hours) together with the 24-hour urinary excretion of mevalonic acid as an indicator of hepatic cholesterol synthesis. Concentrations of uric acid in serum and 24-hour urinary excretion of uric acid were also determined. Mean (+/- SE) percent treatment differences in day-long total, low-density lipoprotein (LDL), and non-high-density lipoprotein (HDL) cholesterol, and apolipoprotein (apo) B were significant, with lower values on the nibbling diet as compared with the control diet (8.1% +/- 1.6%, P = .002; 12.2% +/- 2.6%, P = .005; 10.1% +/- 1.6%, P < .001; and 9.9% +/- 2.6%, P = .008, respectively). No significant difference was seen in the total to HDL cholesterol ratio or in urinary mevalonic acid excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible role of mevalonate in the hypercholesterolemia seen in experimental chronic renal failure.

Hypercholesterolemia may contribute to the pathogenesis of atherosclerosis associated with chronic renal failure (CRF). The mechanism underlying CRF-induced hypercholesterolemia, however, is still unknown. Mevalonate is the direct product of the rate-limiting step in cholesterol synthesis which is catalyzed by 3-hydroxy-3-methylglutaryl coenzyme A reductase. We studied the changes in mevalonate metabolism in a mouse model of CRF in which serum total cholesterol levels are directly correlated with the degree of severity of the disease as measured by serum urea levels. The results of these experiments indicated that in CRF mice, the urine mevalonate levels were significantly lower, while serum mevalonate and total cholesterol levels were significantly higher than in normal mice. We believe that by restricting the normal urinary excretion of mevalonate CRF results in more of this precursor being available for direct cholesterol synthesis. In addition, an increase in circulating mevalonate may upregulate the shunt pathway of mevalonate metabolism in the liver and peripheral tissues, thus providing increased levels of the substrates acetoacetate and acetyl coenzyme A for cholesterol synthesis.

Diurnal variations in the plasma concentrations of mevalonic acid in patients with abetalipoproteinaemia.

Previous studies have demonstrated that changes in the rates of cholesterol biosynthesis can be evaluated by the determination of plasma concentrations of sterol intermediates, including mevalonic acid and lathosterol and that, in normal human subjects, a diurnal rhythm exists in which the highest concentrations of sterol intermediates are observed at night. The factors responsible for this diurnal rhythm in cholesterol synthesis are, however, unknown. To test the hypothesis that the nocturnal increase in cholesterol biosynthesis is attributable to a reduced rate of hepatic uptake of chylomicron remnants at night as compared to higher rates of uptake during the daytime in response to alimentary lipaemia, we have examined the diurnal rhythm of mevalonic acid in six normal volunteers and three patients with phenotypic abetalipoproteinaemia. The latter patients do not absorb appreciable amounts of dietary cholesterol and are unable to synthesize chylomicron particles. Plasma concentrations of mevalonic acid exhibited a diurnal rhythm in the normal subjects, and the highest plasma concentrations were observed between 24.00 hours/04.00 hours. A similar rhythm was observed in the plasma of patients with abetalipoproteinaemia. These results suggest that the nocturnal increase in cholesterol biosynthesis which occurs in humans is not attributable to reduced hepatic uptake of chylomicron remnants at night; further studies are needed to better define those factors which influence the periodicity of cholesterol biosynthesis in humans.

Mevalonate availability and cardiovascular functions.

Data delineating the relationship between disorders of cholesterol metabolism and elevated blood pressure (BP) do not exist. We postulated that mevalonate, the metabolic precursor of endogenous cholesterol and the direct product of 3-hydroxy-3-methylglutaryl-CoA reductase, was a contributing factor for the maintenance of vascular tone and systemic BP. We conducted in vivo, ex vivo, and in vitro experiments in normotensive and hypertensive rats, where exogenous mevalonate and lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, were used, respectively, to increase or limit mevalonate availability. Mevalonate decreased BP in the whole animal without significant change in plasma cholesterol. Incubation of aortas with mevalonate attenuated their reactivity to norepinephrine and increased their response to endothelium-dependent and -independent relaxing factors. Lovastatin, in contrast, had the opposite effect in vivo and in vitro: it increased BP, enhanced vascular response to norepinephrine, and impaired endothelium-dependent and -independent relaxations. Neither agent modified cholesterol vascular content. Alteration of vascular reactivity was also observed in resistance vessels from animals pretreated with lovastatin. Our findings suggest that mevalonate availability is an unrecognized metabolic contributor to vascular tone and BP. They imply that (i) metabolites of the mevalonate pathway other than cholesterol could potentially control vascular functions and cardiovascular hemodynamics, (ii) elevated arterial pressure could be in part the consequence of primary disorders of this pathway, and (iii) pharmacological inhibition of mevalonate production as a means to lower plasma cholesterol may have an adverse impact on other cardiovascular risk factors, such as BP.

Comparative hypolipidemic effects of lovastatin and simvastatin in patients with heterozygous familial hypercholesterolemia.

We have compared the effects of lovastatin and simvastatin on plasma lipoproteins, fibrinogen and urinary mevalonic acid excretion in twenty-three patients with heterozygous familial hypercholesterolemia. After a baseline period patients were randomly assigned to receive lovastatin or simvastatin at doses of 10, 20 and 40 mg twice daily, for a period of 2 months each, and then, after a 4-week wash-out period, all patients received the alternate drug for a similar period of therapy. Both drugs were well-tolerated and no patients were withdrawn due to side effects. Lipid values returned to baseline after discontinuation of therapy and no carry-over effect was observed. Treatment with lovastatin resulted in decreases in LDL cholesterol concentrations from 274 mg/dl at baseline to 211, 192 and 178 mg/dl, respectively, on doses of 20, 40 and 80 mg/day. Treatment with simvastatin reduced concentrations of LDL cholesterol to 194, 168 and 156 mg/dl, respectively, on doses of 20, 40 and 80 mg/day. Concentrations of HDL cholesterol increased on both drugs, but no dose response relationship was apparent. Both drugs reduced the 24-h urinary excretion of mevalonic acid, an intermediate in cholesterol biosynthesis, but the magnitude of decrease was similar with lovastatin and simvastatin. Small, but statistically non-significant decreases in fibrinogen occurred with both drugs. Patients who showed the greatest hypolipidemic effect during treatment with lovastatin also showed an excellent therapeutic response to simvastatin and vice versa. We conclude that, on a milligram per milligram basis, simvastatin is twice as potent as lovastatin in the treatment of familial hypercholesterolemia and that with both drugs, reductions in LDL cholesterol concentrations are accompanied by decreases in the urinary excretion of mevalonic acid.

Correspondence between plasma mevalonic acid levels and deuterium uptake in measuring human cholesterol synthesis.

To assess the validity of two techniques capable of identifying immediate changes in human cholesterol production, plasma mevalonic acid levels and the rate of uptake of deuterium into plasma free cholesterol were compared in 5 healthy individuals over 48 h. The free-living subjects self-selected three meals per day prior to and during study. At t = 0, deuterium oxide was administered orally. Blood samples were collected before and every 4 h after dosing. Total cholesterol and mevalonic acid levels were determined in plasma at each timepoint. Deuterium enrichment changes in plasma free cholesterol, relative to plasma water content, were used to calculate free cholesterol fractional synthetic rates (FSR) at each timepoint. Total plasma cholesterol levels remained constant, whereas significant circadian rhythmicity was observed in both plasma mevalonic acid and deuterium uptake methods, with nadir and peak formation rates indicated at 14.00 to 16.00 h and about midnight, respectively. It is suggested that plasma mevalonic acid levels and free cholesterol deuterium uptake rate techniques are both suitable techniques for short-term measurement of human cholesterol synthesis.

Role of GH in regulating nocturnal rates of lipolysis and plasma mevalonate levels in normal and diabetic humans.

To define the role that nocturnal increments in growth hormone (GH) play in maintaining lipolysis, glycerol turnover was measured in six patients with GH deficiency and six normal subjects during sleep. Glycerol production initially decreased in both groups but then increased to 1.44 +/- 0.20 mumol.kg-1.min-1 by 0800 h in normal subjects, whereas GH deficiency was associated with a continuous fall to 0.77 +/- 0.10 mumol.kg-1.min-1, P less than 0.02. Nonesterified fatty acid levels paralleled these changes. Six GH-deficient patients received basal GH replacement including a pulse during sleep, which resulted in normal fasting fatty acid levels (P less than 0.05, replaced vs. chronic deficiency). To assess a possible link between the normal nocturnal increase in plasma mevalonate (the product of the rate-limiting step in cholesterol synthesis) and sleep-associated GH release, 11 GH-deficient patients and 11 normal subjects were studied. Peak nocturnal and fasting mevalonate concentrations were not correlated with GH level. We conclude that nocturnal growth hormone secretion is essential for maintaining lipolysis but that it is not related to normal increments in mevalonate and, by inference, to cholesterol synthesis during sleep.

The influence of simvastatin on adrenal corticosteroid production and urinary mevalonate during adrenocorticotropin stimulation in patients with heterozygous familial hypercholesterolemia.

The adrenal gland requires a continuous supply of cholesterol for the biosynthesis of adrenal corticosteroids, which can be supplied by low density lipoprotein receptor-mediated uptake or local synthesis. The present study examined whether hypolipidemic therapy with a potent HMG CoA reductase inhibitor, simvastatin, compromises the adrenal response to ACTH stimulation in adult patients with heterozygous familial hypercholesterolemia. The adrenal response to a 36-h continuous ACTH infusion was determined at baseline and after 2 months of simvastatin treatment (40 mg, twice daily) in eight patients. Simvastatin reduced total and low density lipoprotein cholesterol levels by 36% and 45%, respectively. The time course of the increase in serum cortisol concentrations with continuous ACTH infusion was the same before and during simvastatin therapy, as were the rates of urinary excretion of free cortisol, 17-hydroxycorticosteroids, and 17-ketosteroids. Urinary excretion of mevalonate, which correlates with rates of whole body cholesterol synthesis, decreased from 3.8 +/- 0.42 (+/- SEM) mu,ol/24 h at baseline to 2.75 +/- 0.56 on simvastatin; no significant changes were seen in the urinary mevalonate levels before and after simvastatin therapy during ACTH stimulation. We conclude that the hypolipidemic effects of simvastatin in patients with heterozygous familial hypercholesterolemia are paralleled by a decrease in urinary mevalonate, but that the drug does not adversely affect ACTH-stimulated adrenal corticosteroid production.

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.