Hypercholesterolaemia: simvastatin and pravastatin alter cholesterol metabolism by different mechanisms

Pravastatin for lowering lipids

BACKGROUND

A detailed summary and meta-analysis of the dose-related effect of pravastatin on lipids is not available.

OBJECTIVES

Primary objective To assess the pharmacology of pravastatin by characterizing the dose-related effect and variability of the effect of pravastatin on the surrogate marker: low-density lipoprotein (LDL cholesterol). The effect of pravastatin on morbidity and mortality is not the objective of this systematic review. Secondary objectives • To assess the dose-related effect and variability of effect of pravastatin on the following surrogate markers: total cholesterol; high-density lipoprotein (HDL cholesterol); and triglycerides. • To assess the effect of pravastatin on withdrawals due to adverse effects.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials (RCTs) up to September 2021: CENTRAL (2021, Issue 8), Ovid MEDLINE, Ovid Embase, Bireme LILACS, the WHO International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions.

SELECTION CRITERIA

Randomized placebo-controlled trials evaluating the dose response of different fixed doses of pravastatin on blood lipids over a duration of three to 12 weeks in participants of any age with and without evidence of cardiovascular disease.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility criteria for studies to be included, and extracted data. We entered lipid data from placebo-controlled trials into Review Manager 5 as continuous data and withdrawal due to adverse effects (WDAEs) data as dichotomous data. We searched for WDAEs information from all trials. We assessed all trials using Cochrane's risk of bias tool under the categories of sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting, and other potential biases.

MAIN RESULTS

Sixty-four RCTs evaluated the dose-related efficacy of pravastatin in 9771 participants. The participants were of any age, with and without evidence of cardiovascular disease, and pravastatin effects were studied within a treatment period of three to 12 weeks. Log dose-response data over the doses of 5 mg to 160 mg revealed strong linear dose-related effects on blood total cholesterol and LDL cholesterol, and a weak linear dose-related effect on blood triglycerides. There was no dose-related effect of pravastatin on blood HDL cholesterol. Pravastatin 10 mg/day to 80 mg/day reduced LDL cholesterol by 21.7% to 31.9%, total cholesterol by 16.1% to 23.3%,and triglycerides by 5.8% to 20.0%. The certainty of evidence for these effects was judged to be moderate to high. For every two-fold dose increase there was a 3.4% (95% confidence interval (CI) 2.2 to 4.6) decrease in blood LDL cholesterol. This represented a dose-response slope that was less than the other studied statins: atorvastatin, rosuvastatin, fluvastatin, pitavastatin and cerivastatin. From other systematic reviews we conducted on statins for its effect to reduce LDL cholesterol, pravastatin is similar to fluvastatin, but has a decreased effect compared to atorvastatin, rosuvastatin, pitavastatin and cerivastatin. The effect of pravastatin compared to placebo on WADES has a risk ratio (RR) of 0.81 (95% CI 0.63 to 1.03). The certainty of evidence was judged to be very low.

AUTHORS' CONCLUSIONS

Pravastatin lowers blood total cholesterol, LDL cholesterol and triglyceride in a dose-dependent linear fashion. This review did not provide a good estimate of the incidence of harms associated with pravastatin because of the lack of reporting of adverse effects in 48.4% of the randomized placebo-controlled trials.

Hypocholesterolemic effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in the guinea pig: atorvastatin versus simvastatin

Male Hartley guinea pigs were fed a hypercholesterolemic diet rich in lauric and myristic acids with 0, 10, or 20 mg/kg of simvastatin or atorvastatin for 21 days. Atorvastatin and simvastatin resulted in a lowering of plasma low-density lipoprotein (LDL) cholesterol in a dose-dependent manner by an average of 48 and 61% with 10 and 20 mg/kg, respectively. Both statins were equally effective in lowering plasma LDL cholesterol and apolipoprotein B (apo-B) levels. Atorvastatin and simvastatin treatments yielded LDL particles that differed in composition from the control. Due to the relevance of LDL oxidation and cholesteryl ester transfer in plasma to the progression of atherosclerosis, these parameters were analyzed after statin treatment. Atorvastatin and simvastatin treatment decreased the susceptibility of LDL particles to oxidation by 95% as determined by the formation of thiobarbituric acid reactive substances. An 80% decrease in the transfer of cholesteryl ester between high-density lipoprotein (HDL) and the apo-B-containing lipoproteins was observed after simvastatin and atorvastatin treatment. In addition, statin effects on plasma LDL transport were studied. Simvastatin- and atorvastatin-treated guinea pigs exhibited 125 and 175% faster LDL fractional catabolic rates, respectively, compared with control animals. No change in LDL apo-B flux was induced by either treatment; however, LDL apo-B pool size was reduced after statin treatment. Hepatic microsomal free cholesterol was lower in the atorvastatin and simvastatin groups. However, only atorvastatin treatment resulted in an 80% decrease of acyl-CoA:cholesterol acyltransferase activity (P < 0.001). In summary, atorvastatin and simvastatin had similar LDL cholesterol lowering properties, but these drugs modified LDL transport and hepatic cholesterol metabolism differently.

The pravastatin-induced decrease of biliary cholesterol secretion is not directly related to an inhibition of cholesterol synthesis in humans

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been reported to suppress biliary cholesterol secretion and saturation. It remains unproven whether this is mediated by inhibition of cholesterol synthesis. Therefore, the effect of a long-term administration of pravastatin on cholesterogenesis and on biliary lipid secretion was investigated in seven healthy volunteers. Placebo or 40 mg of pravastatin were taken daily at bedtime for 5 weeks using a double-blind crossover design. During the last week, 12 hours after the last drug intake 0.04 mmol [1-13C]acetate/kg. h and 0.5 g polyethylene glycol 4,000/h were infused intraduodenally for 15 hours. Plasma and duodenal bile samples were collected hourly. Thereafter, the decay of [13C]labeled plasma cholesterol was measured during the following 3 days. The fractional and absolute syntheses of plasma and biliary cholesterol were determined by gas chromatography mass spectrometry using mass isotopomer distribution analysis. At the end of the pravastatin period plasma total and low-density lipoprotein (LDL) cholesterol had decreased by 20% and 24%, respectively. Similarly, pravastatin suppressed biliary secretion rates of cholesterol, total bile acids and phospholipids (P <.05) by 46%, 36%, and 51%. As a consequence, cholesterol saturation index remained unchanged. However, fractional syntheses of cholesterol were comparable (P >.05) on placebo compared with pravastatin with 3.1% versus 4.0% in plasma and 4.3% versus 5.2% in bile after 15 hours, respectively. The mean absolute synthesis rates amounted to 0.3 mg/kg/h on placebo versus 0.4 on pravastatin (P >. 05). In conclusion, the pravastatin-induced reduction of biliary cholesterol secretion is not directly related to an inhibition of cholesterol synthesis.

Different effect of simvastatin and atorvastatin on key enzymes involved in VLDL synthesis and catabolism in high fat/cholesterol fed rabbits

The effects of atorvastatin (3 mg kg(-1)) and simvastatin (3 mg kg(-1)) on hepatic enzyme activities involved in very low density lipoprotein metabolism were studied in coconut oil/cholesterol fed rabbits. Plasma cholesterol and triglyceride levels increased 19 and 4 fold, respectively, after 7 weeks of feeding. Treatment with statins during the last 4 weeks of feeding abolished the progression of hypercholesterolaemia and reduced plasma triglyceride levels. 3-Hydroxy-3-methyl-glutaryl Coenzyme A reductase, acylcoenzyme A:cholesterol acyltransferase, phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities were not affected by drug treatment. Accordingly, hepatic free cholesterol, cholesteryl ester and triglyceride content were not modified. Simvastatin treatment caused an increase (72%) in lipoprotein lipase activity without affecting hepatic lipase activity. Atorvastatin caused a reduction in hepatic phospholipid content and a compensatory increase in CTP:phosphocholine cytidylyl transferase activity. The results presented in this study suggest that, besides the inhibitory effect on 3-hydroxy-3-methyl-glutaryl Coenzyme A reductase, simvastatin and atorvastatin may have additional effects that contribute to their triglyceride-lowering ability.

Effect of hypolipidemic drugs on key enzyme activities related to lipid metabolism in normolipidemic rabbits

The effect of atorvastatin (3 mg kg(-1) day(-1)), simvastatin (3 mg kg(-1) day(-1)) and bezafibrate (100 mg kg(-1) day(-1)) administered for 4 weeks to male New Zealand white rabbits on enzyme activities related to lipid metabolism has been studied. Only the statins reduced plasma cholesterol values, while none of the drugs modified plasma triglyceride or high density lipoprotein (HDL)-cholesterol concentrations, nor the activity of enzymes such as hepatic diacylglycerol acyltransferase, lipoprotein lipase or hepatic lipase, directly involved in triglyceride metabolism. Both statins elicited similar increases in the hepatic microsomal 3-hydroxy-3-methyl-glutaryl Coenzyme A (CoA) reductase activity (147 and 109% induction for simvastatin and atorvastatin, respectively), and none of the drugs assayed modified hepatic acyl-coenzyme A:cholesterol acyltransferase activity significantly. Only bezafibrate induced a significant 57% reduction in the activity of hepatic microsomal cholesterol 7alpha-hydroxylase. Regarding the rate limiting enzyme of phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyl transferase, atorvastatin and bezafibrate behaved similarly, decreasing the enzyme activity in the liver by 45% and 54%, respectively; simvastatin induced no modification of this activity. The reduction of CTP:phosphocholine cytidylyl transferase activity is not caused by a direct inhibition of the enzyme by bezafibrate and atorvastatin. Further, the inhibitory effect of atorvastatin appears to be unrelated to the inhibition of 3-hydroxy-3-methyl-glutaryl CoA reductase elicited in vivo.

Reduced cholesterol esterification in CaCo-2 cells by indirect action of pravastatin

In microsomal preparations of CaCo-2 cells pravastatin decreased cholesterol esterifying activity at 25 micrograms/ml to 82.5% and at 800 micrograms/ml to 56.2% of controls. Pravastatin reduced cholesteryl ester formation dose-dependently also in viable CaCo-2 cells. However, the maximal inhibition was by 90.4% at pravastatin concentration of 25 micrograms/ml, half maximal inhibition occurred between concentrations of 5 and 10 micrograms/ml. Addition of mevalonolactone, which serves as endogenous source of cholesterol, antagonized this effect. At 10 mM mevalonolactone (MVL) even doses up to 200 micrograms/ml of pravastatin were ineffective. On the other hand, pravastatin suppressed cholesteryl ester formation when acyl-CoA cholesterol acyltransferase (ACAT) (E.C. 2.3.1.26) activity was stimulated by addition of exogenous liposomal or Low Density Lipoprotein (LDL)-derived cholesterol. This inhibition was refractory to increasing amounts of exogenous cholesterol up to 400 micrograms/ml. Therefore we conclude that only excessive doses of pravastatin suppress ACAT activity directly. In viable cells the observed inhibition of cholesteryl ester formation is due to the block in de novo synthesis of cholesterol, causing a lack of substrate for ACAT and of non-sterol products of mevalonic acid. Furthermore pravastatin interferes with the esterification and/or intracellular transport only of exogenous cholesterol, confirming former results of a compartmentalized cholesterol metabolism in the enterocyte.

Therapy with HMG CoA reductase inhibitors: characteristics of the long-term permanence of hypocholesterolemic activity

Treatment with hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors has gained considerable success in the management of hypercholesterolemia. A large number of studies have shown the efficacy of these drugs in lowering plasma total and low density lipoprotein (LDL) cholesterol levels, but there have been less studies evaluating their effectiveness in standard clinical practice, particularly relating to the maintenance of hypocholesterolemic activity. In the present study, the long-term effectiveness of HMG CoA reductase inhibitors has been tested in 177 patients with familial hypercholesterolemia (FH) who had been on statin therapy (simvastatin or pravastatin) for at least 12 months and up to 5 years or longer. The mean 'dose normalized' LDL cholesterol reduction in the whole group was around 20%. However, in spite of a generally good efficacy of both statins in lowering total and LDL cholesterol, a wide variety of responses, either after short- or long-term treatment, was noted. Individual responses were calculated and patients classified into three different groups: (a) responders, (b) non-responders, and (c) response losers. Of the 177 patients, 4% did not respond to treatment and a further 10% showed an initial unsatisfactory response (LDL cholesterol reduction < or = 10%). Another 10% experienced a progressive loss of response over time. There appeared to be little difference between the two treatments in the long-term efficacy and no predictive index could be established. Treatment with HMG CoA reductase inhibitors is generally effective and well tolerated, but a non-negligible number of patients may show a primary non-response or a progressive loss of response.

The effects of simvastatin and cholestyramine, alone and in combination, on hepatic cholesterol metabolism in the male rat. off

The influence of dietary simvastatin, cholestyramine, and the combination of simvastatin plus cholestyramine on hepatic cholesterol metabolism has been investigated in male rats. Recovery from the effects of the drugs was also investigated by refeeding normal chow for 24 h. Both drugs, alone and in combination, increased 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity in vitro, but activity returned toward control values, after drug withdrawal. Acyl-CoA:cholesterol acyltransferase (ACAT) was significantly reduced (P < 0.001) by simvastain (-75%), cholestyramine (-71%), and by the drug combination (-81%), due both to a decrease in microsomal cholesterol and to nonsubstrate-dependent modulation of enzyme activity. Refeeding control diet increased ACAT activity but not to control levels. The enhanced activity arose partly from higher microsomal cholesterol and partly from increases in total enzyme activity. Cytosolic neutral cholesteryl ester hydrolase (CEH) activity was substantially elevated by simvastatin (3-fold) and by the drug combination (6-fold), whereas the effect of cholestyramine was smaller (1.5-fold). Normal chow for 24 h only partially returned cytosolic CEH activity to control values. Microsomal CEH activity was increased by simvastatin, alone and in combination with cholestyramine (1.4 to 1.7-fold), and was also enhanced, in the cholestyramine-treated animals, following drug withdrawal. Removal of simvastatin did not allow recovery of this enzyme activity, while withdrawal of the drug combination led to values 29% below controls. The results indicate that in the rat, simvastatin and cholestyramine alter both ACAT and CEH activity, as well as inhibiting HMG-CoA reductase activity.

Pravastatin inhibits cellular cholesterol synthesis and increases low density lipoprotein receptor activity in macrophages: in vitro and in vivo studies

1. Pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) inhibitor, is a highly selective inhibitor of hepatic cholesterol synthesis. We studied the in vivo and in vitro effects of pravastatin on macrophage cholesterol metabolism. 2. The effects of incubating pravastatin with human monocyte derived macrophages (HMDM), mouse peritoneal macrophages (MPM) and a J-774 A.1 macrophage-like cell line, on macrophage cholesterol synthesis, cellular degradation of native low density lipoprotein (LDL) and modified LDL, cholesterol efflux from these cells and the cholesterol esterification rate were determined. 3. Pravastatin was administered either as one 40 mg dose or 40 mg daily for 8 weeks to normocholesterolaemic and hypercholesterolaemic individuals. The effects on cholesterol synthesis and degradation in monocytes derived from these subjects were studied. 4. In vitro, pravastatin resulted in a dose-dependent inhibition of macrophage cholesterol synthesis. Cellular degradation of native LDL increased by 119% in the presence of 0.1 mg ml-1 pravastatin. Degradation of both acetyl LDL and oxidized LDL was unaffected. Small concentrations of pravastatin (up to 0.19 micrograms ml-1) increased the cellular cholesterol esterification rate after incubation with LDL, but higher concentrations resulted in an inhibition of the esterification. 5. Single dose pravastatin administration caused a reduction in cholesterol synthesis by the subjects own HMDM by 62% and 47% in normocholesterolaemic and hypercholesterolaemic individuals, respectively. Chronic administration resulted in a 55% inhibition of cholesterol synthesis and a 57% increase in LDL degradation. 6. The results indicate that the selective uptake of pravastatin shown for hepatocytes can be extended to macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Short- and long-term effects of lovastatin and pravastatin alone and in combination with cholestyramine on serum lipids, lipoproteins and apolipoproteins in primary hypercholesterolaemia

The effects of the HMG CoA reductase inhibitors lovastatin and pravastatin on serum lipids, lipoproteins and apolipoproteins have been studied in 35 patients with primary hypercholesterolaemia. LDL cholesterol was lowered to the same extent by both agents compared on a mg basis of each drug per day. HDL cholesterol was increased by lovastatin but not by pravastatin. The reduction in serum triglycerides, VLDL triglycerides and VLDL cholesterol was more pronounced after lovastatin than pravastatin. After 1 year the effect of combined treatment with 40 mg pravastatin and 8 g cholestyramine on the reduction in LDL cholesterol (-39%) in 13 patients was comparable to that of 80 mg lovastatin plus 8 g cholestyramine (-40%) in 12 patients with identical baseline values. Differences were also found in the effects of the combination therapy with the two drugs on HDL cholesterol, serum triglycerides, VLDL triglycerides, VLDL cholesterol, and apolipoproteins.

Alterations in cellular cholesterol metabolism following administration of 6-hydroxydopamine to rabbits

1. The role of adrenergic mechanisms in the regulation of cholesterol metabolism was investigated by studying the effects of 6-hydroxydopamine (6-OHDA) on serum cholesterol levels and on the activities of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, acyl coenzyme A: cholesterol-O-acyl-transferase (ACAT) in the livers and intestines, and cholesterol 7 alpha-hydroxylase in the livers of male New Zealand White rabbits. 2. Total serum cholesterol levels were significantly reduced (P less than 0.01) in 6-OHDA-treated animals. This was reflected in the very low density lipoprotein, low density lipoprotein and high density lipoprotein fractions. The reduction in lipoprotein cholesterol levels reflected reduced cholesterol proportions in the lipoprotein fractions. 3. The 6-OHDA-treated animals also had significantly lower activities of intestinal (P less than 0.001) and hepatic (P less than 0.01) HMGCoA reductase. The specific activities of intestinal ACAT, hepatic ACAT and cholesterol 7 alpha-hydroxylase were comparable in both groups. 4. In contrast to the results observed in vivo, 6-OHDA did not have any in vitro effect on cholesterol biosynthesis in cultured human leucocytes. 5. This latter finding suggests that the effects of 6-OHDA on cellular cholesterol biosynthesis in vivo are indirect, possibly resulting from the known toxic effect of this drug in sympathetic nerve terminals, and imply a potential role for the sympathetic nervous system in the regulation of cellular cholesterol biosynthesis in vivo.