Use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in various forms of dyslipidemia

The inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase are highly effective in treating severe elevations of serum cholesterol, and are being widely used for this purpose. In our laboratory, these drugs have been used for the treatment of other forms of dyslipidemia including primary moderate hypercholesterolemia, primary mixed hyperlipidemia, diabetic dyslipidemia, hyperlipidemia of the nephrotic syndrome, and primary hypoalphalipoproteinemia. In these conditions, the HMG CoA reductase inhibitors proved effective in substantially decreasing levels of both low-density lipoproteins and very low density lipoproteins, as well as apolipoprotein B. In some patients, they may even increase levels of high-density lipoproteins. The primary mode of action of HMG CoA reductase inhibitors appears to be to increase the synthesis of hepatic receptors for lipoproteins containing apolipoprotein B, although a reduction in synthesis of these lipoproteins has not been ruled out with certainty. Regardless of mechanisms, drugs of this type appear to have the potential for effective therapy of various forms of dyslipidemia beyond primary severe hypercholesterolemia.     

Effecacy of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors for prevention of stroke

OBJECTIVE: To determine if 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are effective in preventing fatal and nonfatal strokes in patients at increased risk of coronary artery disease. DESIGN: Meta-analysis of randomized controlled trials. Clinical trials were identified by a computerized search of MEDLINE (1983 to June 1996), by an assessment of the bibliographies of published studies, meta-analyses and reviews, and by contacting pharmaceutical companies that manufacture statins. Trials were included in the analysis if their patients were randomly allocated to a statin or placebo group, and reported data on stroke events. Thirteen of 28 clinical trials were selected for review. Data were extracted for details of study design, patient characteristics, interventions, duration of therapy, cholesterol measurements, and the number of fatal and nonfatal stroke events in each arm of therapy. Missing data on stroke events were obtained by contacting the investigators of the clinical trials. MAIN RESULTS: Among 19,921 randomized patients, the rate of total stroke in the placebo group was 2.38% (90% nonfatal and 10% fatal). In contrast, patients who received statins had a 1.67% stroke rate. Using an exact stratified analysis, the pooled odds ratio (OR) for total stroke was 0.70 (95% confidence interval [CI] 0.57, 0.86; p =.0005). The pooled OR for nonfatal stroke was 0.64 (95% CI 0.51, 0.79; p =.00001), and the pooled OR for fatal stroke was 1.25 (95% CI 0.71, 2.24; p =.4973). In separate analyses, reductions in total and nonfatal stroke risk were found to be significant only for trials of secondary coronary disease prevention. Regression analysis showed no statistical association between the magnitude of cholesterol reduction and the relative risk for any stroke outcome. CONCLUSIONS: The available evidence clearly shows that HMG-CoA reductase inhibitors reduce the morbidity associated with strokes in patients at increased risk of cardiac events. Data from 13 placebo-controlled trials suggest that on average one stroke is prevented for every 143 patients treated with statins over a 4-year period.     

Regulation of hamster adrenal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity

In the adrenal gland of the hamster, the activity of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase [mevalonate:NADP+ oxidoreductase (acylating CoA); EC 1.1.1.34] is mainly located in the postmitochondria fraction. This enzyme exhibits a diurnal rhythm, with a maximum at 1900 h. Peak activity levels are about 1667 pmol/mg protein . min, roughly 8 times the minimum levels. Plasma corticosteroid concentrations closely parallel reductase activity levels. The administration of ACTH or metyrapone (a drug which increases in vivo ACTH secretion) to hamsters enhanced the adrenal reductase activity, whereas aminoglutethimide, an inhibitor of the side chain cleavage of cholesterol, diminished it. The feeding of a 5% cholesterol diet and treatment with 4-aminopyrazolopyrimidine resulted in an increase and a decrease in plasma cholesterol, respectively. Neither treatment significantly altered adrenal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity or the cholesterol content of the gland. Hamster adrenals contain very little free cholesterol (7-11 microgram/mg protein) and even less esterified cholesterol (0.5-2.0 microgram/mg protein). These findings suggest that in the hamster the adrenal gland may be largely autonomous in cholesterol production.     

Characterization of 3-hydroxy-3-methylglutaryl coenzyme A reductase in human adrenal cortex

Our study compares the properties of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase from a human metastatic virilizing carcinoma and that from normal adrenal glands obtained from kidney donors. Optimal conditions for enzyme assay were obtained when a 50-mM imidazole buffer (pH 7.2) containing 5 mM EDTA, 250 mM NaCl, 1 mM phenyl-methylsulfonylfluoride, 0.1 mM leupeptin, and 5.5 mM dithiothreitol (DTT) was used. A 30-min preincubation period preceding addition of substrates enhanced reductase activity by 1.75-fold. In crude microsomal preparations, Km values were similar for both tumor and normal tissues and varied between 4 and 5 microM (S)HMG-CoA. The presence of NaF in homogenization and incubation media decreased the maximum velocity, but not the Km. A partially purified rat liver phosphorylase phosphatase preparation or a similar preparation from the carcinoma restored to maximal levels the reductase activity of microsomes prepared in the presence of NaF. A Km of 96 microM NADP was found for the carcinoma microsomal preparation. Preincubation of microsomes in the presence of monothioglycerol or DTT resulted in an increased reductase activity, suggesting a possible inactive enzyme precursor(s) consisting of disulfide-linked units. Reactions of the DTT-activated enzyme incubated in the presence of increasing amounts of NADPH showed sigmoidal kinetics. Under reducing conditions, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting revealed the presence of a 92.5K mol wt protein band that reacted with a rat antireductase antibody. Reductase activity in different regions of the carcinoma varied from 679-1763 pmol/mg protein, with an average of 1146 pmol. In three normal adrenal glands we found values of 23.4, 48.1, and 36 pmol. We concluded that the expression of HMG-CoA reductase activity was elevated in human adrenal carcinoma.     

Withdrawal of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors elicits oxidative stress and induces endothelial dysfunction in mice

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) improve endothelial function. We determined whether withdrawal of statin therapy affects endothelium-dependent relaxation in mice and studied the underlying mechanism. Mice were treated with daily injections of cerivastatin (2 mg/kg per day SC), atorvastatin (1 and 10 mg/kg per day SC), or placebo. Vascular reactivity was studied in aortic rings from these mice after 10 days of treatment and after cessation of therapy for several days. Both statins improved endothelium-dependent relaxation to acetylcholine. Compared with control, withdrawal of statin treatment transiently (from day 4 to 7) attenuated endothelium-dependent relaxation. In vessels from animals subjected to atorvastatin withdrawal, the antioxidant tiron restored relaxations. Vascular superoxide anion generation was unaffected by statin therapy but was increased during withdrawal. In mice lacking the gp91phox subunit of the NADPH oxidase, no attenuation of acetylcholine-induced relaxation and no increase in superoxide generation were observed after withdrawal of atorvastatin. In human umbilical vein endothelial cells, statins, which decrease the membrane association of NADPH oxidase-activating Rac-1, increased the activity of this GTPase in whole-cell lysates. Withdrawal of statins induced a translocation of Rac-1 from the cytosol to the membrane and transiently increased NADPH-induced lucigenin chemiluminescence in membrane preparations. Rac-1 inactivation by Clostridium difficile toxin B inhibited the cerivastatin-induced oxygen radical production in human umbilical vein endothelial cells. These observations indicate that the withdrawal of statins induces endothelial dysfunction. The underlying mechanism involves activation of a gp91phox-containing NADPH oxidase by Rac-1 and the subsequent scavenging of endothelium-derived NO by superoxide anions generated from this enzyme.     

Hypercholesterolemia and 3-hydroxy-3-methylglutaryl coenzyme A reductase regulation in aged female rats

Coronary heart disease is less prevalent in pre-menopausal women than in men, but increases at the onset of menopause. This delay is due to estrogen protective effects. The rise of cholesterolemia is one of the main risk factors for coronary disease. Since 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is the rate-limiting enzyme of the cholesterol biosynthetic pathway, it plays a pivotal role in cholesterol homeostasis maintenance. Aim of this study is to investigate whether HMGR is involved in the cholesterolemia increase that occurs during aging, and to consider its potential role as a target for estrogen protective effects. “In vivo” studies have been performed using the livers of 12-month-old female rats (whose estrogen level decrease is comparable to the one detected at the occurrence of human menopause), 12-month-old female rats treated with 17-β-estradiol, and 3-month-old untreated male and female rats. The results indicated hypercholesterolemic status and a significant increase of HMGR activity according to a reduced activation of AMPK detected in treated rats compared to controls. Furthermore, 17-β estradiol treatment reduced HMGR activity restoring AMPK activation. These findings highlight the correlation between estrogen and HMGR short-term regulation, and suggest the presence of another mechanism underlying the protective role of estrogen in age-related diseases.     

Mevalonate-mediated suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase function in alpha-toxin-perforated cells.

The regulation of mevalonic acid synthesis requires both nonsterol isopentenoid and sterol regulatory signal molecules. A primary target of this multivalent control process is the enzyme which catalyzes mevalonate synthesis: 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34). In this report Staphylococcus aureus alpha-toxin perforated Chinese hamster ovary cells were used to facilitate the identification of isopentenoidogenic reactions and metabolites required for mevalonate-mediated loss of HMG-CoA reductase activity. alpha-Toxin-perforated cells retained the capacity to decrease, upon demand, HMG-CoA reductase activity and protein in response to mevalonate or isopentenoid pyrophosphate esters. Also, it was deduced with highly specific metabolic inhibitors, that conversion of farnesyl 1-diphosphate to squalene was required for mevalonate-mediated suppression of reductase activity. Since squalene (2 microM) did not downregulate reductase activity, pre-squalene pyrophosphate or a derivative, or polyprenyl-1-pyrophosphate-generated inorganic pyrophosphate, or a combination of these metabolites are proposed as candidate regulatory nonsterol isopentenoid signal molecules.     

Differential activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in zones of the adrenal cortex

Cholesterol metabolism and steroidogenesis in the outer (zona fasciculata/glomerulosa) and inner (zona reticularis) zones of the adrenal cortex were examined in the guinea pig. It is known from previous studies that the content of cholesterol in the inner zone is considerably lower than that in the outer zone, although basal low density lipoprotein (LDL) receptor activity is similar in the two zones. To further explore cholesterol metabolism in the guinea pig adrenal cortex, the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting step in cholesterol synthesis, has been examined for which this paper forms the initial report. It was found that the basal specific activity of HMG-CoA reductase was similar in the outer and inner adrenocortical zones (approximately 230 pmol mevalonate formed/min X mg microsomal protein). The administration of ACTH caused 4- and 5-fold increases in HMG-CoA reductase activity in the outer and inner zones, respectively. In fact, the increase in HMG-CoA reductase activity with ACTH treatment was always greater for the inner zone than for the outer zone. This is in contrast to LDL receptor activity, which does not increase in the inner zone as it does in the outer zone with ACTH treatment. When dexamethasone was administered, HMG-CoA reductase activity decreased in the outer zone by about 50%, while there was no change in reductase activity in the inner zone. The latter finding is similar to what happens with LDL receptor activity during dexamethasone administration. Why suppression of endogenous ACTH had no effect on HMG-CoA reductase activity in the inner zone while exogenous ACTH administration caused a marked increase in enzyme activity is not clear, but may be related to phosphorylation/dephosphorylation mechanisms. Based on the use of sodium fluoride in solutions to block HMG-CoA reductase phosphatase, evidence is presented which indicates that a pharmacological dose of ACTH alters the phosphorylation/dephosphorylation status of HMG-CoA reductase in the inner adrenocortical zone, but not in the outer cortical zone.     

Cost-effectiveness of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor therapy in older patients with myocardial infarction

BACKGROUND: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) therapy has proven efficacy in reducing the rate of coronary and cerebrovascular events in patients 75 years of age or younger with a history of myocardial infarction. However, in patients older than 75 years of age, the efficacy and potential cost-effectiveness of statins are unknown. OBJECTIVE: To estimate the incremental cost-effectiveness of statin therapy compared with usual care in patients 75 to 84 years of age with previous myocardial infarction. DESIGN: Cost-effectiveness analysis. DATA SOURCES: Published data from cohort studies. TARGET POPULATION: Patients 75 to 84 years of age with a history of myocardial infarction. TIME HORIZON: Lifetime. PERSPECTIVE: Societal. INTERVENTION: Statin therapy. OUTCOME MEASURES: Life expectancy, quality-adjusted life expectancy, and incremental cost-effectiveness. RESULTS OF BASE-CASE ANALYSIS: The incremental cost-effectiveness of statin therapy compared with usual care in patients 75 to 84 years of age with previous myocardial infarction was $18800 per quality-adjusted life-year (QALY). RESULTS OF SENSITIVITY ANALYSIS: On the basis of a probabilistic sensitivity analysis, there is a 75% chance that statin therapy costs less than $39800 per QALY compared with usual care. If the cost of statin therapy and efficacy of statin therapy at reducing myocardial infarction were set to their most favorable values, statin therapy cost $5400 per QALY; if cost and efficacy were set to their least favorable values, statin therapy cost $97800 per QALY. CONCLUSIONS: The cost-effectiveness ratios of statin therapy in older patients with previous myocardial infarction are reasonable under a wide variety of assumptions about drug efficacy, drug cost, and rates of cardiac and cerebrovascular events. Pending results of randomized, controlled trials of secondary prevention in patients in this age group, statin therapy seems to be as cost-effective as many routinely accepted medical interventions in this setting.     

A comparative study of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in vertebrate adrenocortical tissues

Our study compares the activities in vitro of HMG-CoA reductase in hamster, rabbit, rat, chicken, and frog adrenocortical tissues. Microsomal and mitochondrial preparations obtained by differential centrifugation were incubated with [3-¹⁴C]HMG-CoA and a NADPH generating system, and the [¹⁴C]mevalonic acid formed was isolated on a silica gel column and by thin-layer chromatography. The identity of the product was confirmed by formation of the benzhydrylamide derivative followed by crystallization to constant isotope ratio. The following adrenocortical HMG-CoA reductase activities were found (nanomoles of mevalonic acid formed per milligram of protein per 30 min): hamster microsomal fraction, 19.3; hamster mitochondrial fraction, 15.1; rabbit microsomal fraction, 2.8; rat microsomal fraction, 0.35; chicken microsomal fraction, 7.4; chicken mitochondrial fraction, 3.4; and frog microsomal fraction, 0.14. Our results suggest that the ability of various adrenocortical tissues to synthetize cholesterol is related to the level of HMG-CoA reductase activity present.     

Ezetimibe-associated myopathy in monotherapy and in combination with a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Two cases of myopathy associated with ezetimibe are reported. In the first case, a woman on ezetimibe monotherapy presented with muscle pain and an elevated concentration of creatine kinase (CK) on two occasions, with ezetimibe 10 mg and with ezetimibe 5 mg after a washout period. The recurrence of muscle pain after washout and the CK increase both supported the hypothesis that ezetimibe alone can be linked to myalgia. In the second case, a man had been treated with atorvastatin, and ezetimibe 10 mg was added to improve his lipid profile. Two months later, the patient complained of muscle pain and a CK increase was noted. The appearance of symptoms when adding ezetimibe to atorvastatin supports a potential pharmacokinetic and/or a pharmacodynamic interaction between these two drugs. These cases suggest that ezetimibe monotherapy as well as ezetimibe associated with the use of a statin may induce myalgia. The mechanism by which ezetimibe could cause muscle pain is not known.     

Multitasking of the 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitor: Beyond cardiovascular diseases

Statins can profoundly affect cellular metabolism by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A reductase, which is the rate-limiting enzyme responsible for cholesterol synthesis. Many physicians prescribe statins to lower plasma cholesterol levels, which has beneficial effects in both the primary and secondary prevention of coronary artery disease. However, in vitro, in vivo, animal, and clinical studies have all shown that statins may also have important pleiotropic properties. In fact, a number of clinical studies have suggested that statins are involved in modulating diseases such as cancer, osteoporosis, and dementia (including Alzheimer’s disease). However, because these studies have been only preliminary and observational in nature, large randomized, placebo-controlled studies are needed to confirm the modulatory role of statins in these important diseases.