Effect of simvastatin on receptor-dependent low density lipoprotein catabolism in normocholesterolemic human volunteers

Simvastatin treatment upregulates intestinal lipid secretion pathways in a rodent model of the metabolic syndrome

OBJECTIVE

Statins are widely used for the treatment of hyperlipidemia to reduce cardiovascular disease (CVD) risk. Intriguingly, recent reports suggest that whilst statins are effective in reducing hepatic cholesterol synthesis, they in turn may up-regulate intestinal cholesterol absorption. The direct effects and/or mechanisms of this phenomenon remain largely unknown. The aim of this study was to investigate the potential for statins to increase intestinal lipid absorption and/or secretion in a rodent model of the metabolic syndrome (MetS).

METHODS AND RESULTS

Mets JCR:LA-cp rats received a 1% cholesterol diet containing Simvastatin (0.01% w/w), for 8 weeks. Fasting and postprandial plasma biochemical profile was assessed using enzymatic assays and a modified apoB48 (chylomicron; CM) western blotting protocol. Statin treatment reduced fasting plasma TG (-49%), cholesterol (-24%) and postprandial plasma apoB48 (-58%). The intestinal secretion of lipids into mesenteric lymph was assessed using lymph fistulae procedures. Interestingly, MetS rats treated with statin secreted greater cholesterol (1.9-fold) and TG (1.5-fold) per apoB48 particle, into mesenteric lymph. This was shown to be as a result of simvastatin-induced increase in intestinal cholesterol absorption (31.5%). Experiments using in vivo inhibition of lipoprotein lipase (LPL; poloxamer-407) demonstrated statin treatment reduced hepatic cholesterol secretion (-49%), but significantly increased hepatic (73%) TG secretion in MetS rats. Statin treatment also increased the expression of genes involved in lipid synthesis (Hmgcr, Srebp1, Fas, Acc; 33-67%) and reduced those involved in efflux (Abca1, Abcg8; -36 to 73%) in enterocytes and liver of MetS rats versus untreated control.

CONCLUSIONS

In a rodent model of MetS, statin treatment adversely up-regulates intestinal lipid secretion as a result of increased intestinal cholesterol absorption, and increases the intestinal expression of genes involved in lipid synthesis; effects which may confound clinical benefits to remnant dyslipidemia.

Influence of simvastatin on apoB-100 secretion in non-obese subjects with mild hypercholesterolemia

Statins decrease apoB-100-containing lipoproteins by increasing their fractional catabolic rates through LDL receptor-mediated uptake. Their influence on hepatic secretion of these lipoproteins is controversial. The objective of the study was to examine the influence of simvastatin on the secretion of apoB-100-containing lipoproteins in fasting non-obese subjects. Turnover of apoB-100-containing lipoproteins was investigated using stable isotope-labeled tracers. Multicompartmental modeling was used to derive kinetic parameters. Eight male subjects (BMI 25 +/- 3 kg/m(2)) with mild hypercholesterolemia (LDL cholesterol 135 +/- 30 mg/dL) and normal triglycerides (111 +/- 44 mg/dL) were examined under no treatment (A), under chronic treatment with simvastatin 40 mg/day (B) and after an acute-on-chronic dosage of 80 mg simvastatin under chronic simvastatin treatment (C). Lipoprotein concentrations changed as expected under 40 mg/day simvastatin. Fractional catabolic rates increased in IDL and LDL but not in VLDL fractions versus control [VLDL +35% in B (n.s.) and +21% in C (n.s.); IDL +169% in B (P = 0.08) and +187% in C (P = 0.032); LDL +87% in B (P = 0.025) and +133% in C (P = 0.025)]. Chronic (B) and acute-on-chronic simvastatin treatment (C) did not affect lipoprotein production rates [VLDL -8 and -13%, IDL +47 and +38%, and LDL +19 and +30% in B and C, respectively (all comparisons n.s.)]. The data indicate that simvastatin does not influence the secretion of apoB-100-containing lipoproteins in non-obese subjects with near-normal LDL cholesterol concentrations.

Atorvastatin increases expression of low-density lipoprotein receptor mRNA in human circulating mononuclear cells

1. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) inhibitors, or statins, are commonly used to lower plasma cholesterol levels. HMGCR and the low-density lipoprotein (LDL) receptor (LDLR) are of central importance to cholesterol homeostasis and yet there is a paucity of data on the effect of statins on the regulation of the LDLR and HMGCR in humans. 2. In the present study, we examined the effect of atorvastatin on the expression of HMGCR, LDLR and LDLR-related protein (LRP) mRNA in circulating mononuclear cells. Twelve human volunteers were treated with atorvastatin, 20 mg/day for 4 weeks. 3. Atorvastatin decreased plasma total and LDL-cholesterol by 29% (P < 0.0001) and 41% (P < 0.001), respectively, and increased LDLR mRNA abundance, in absolute terms, by 35% (P < 0.001) and 31% (P < 0.0001) and 37% (P = 0.01) relative to reference GAPDH and beta-actin mRNA, respectively. In contrast, atorvastatin had no significant effect on LRP or HMGCR mRNA levels. 4. The increase in LDLR mRNA in circulating mononuclear cells agrees with the few human studies conducted, as well as with in vitro and animal studies, whereas the unchanged HMGCR mRNA is consistent with the hepatic specificity of atorvastatin. The present study firmly documents an increase in LDLR mRNA levels in response to statin administration in normal humans.

Effects of ezetimibe and simvastatin on apolipoprotein B metabolism in males with mixed hyperlipidemia

Sixteen hyperlipidemic men were enrolled in a randomized, placebo-controlled, double-blind, cross-over study to evaluate the effect of ezetimibe 10 mg and simvastatin 40 mg, coadministered and alone, on the in vivo kinetics of apolipoprotein (apo) B-48 and B-100 in humans. Subjects underwent a primed-constant infusion of a stable isotope in the fed state. The coadministration of simvastatin and ezetimibe significantly reduced plasma concentrations of cholesterol (-43.0%), LDL-C (-53.6%), and triglycerides (-44.0%). Triglyceride-rich lipoproteins (TRL) apoB-48 pool size (PS) was significantly decreased (-48.9%) following combination therapy mainly through a significant reduction in TRL apoB-48 production rate (PR) (-38.0%). The fractional catabolic rate (FCR) of VLDL and LDL apoB-100 were significantly increased with all treatment modalities compared with placebo, leading to a significant reduction in the PS of these fractions. We also observed a positive correlation between changes in TRL apoB-48 PS and changes in TRL apoB-48 PR (r = 0.85; P < 0.0001) with combination therapy. Our results indicate that treatment with simvastatin plus ezetimibe is effective in reducing plasma TRL apoB-48 levels and that this effect is most likely mediated by a reduction in the intestinal secretion of TRL apoB-48. Our study also indicated that the reduction in LDL-C concentration following combination therapy is mainly driven by an increase in FCR of apoB-100 containing lipoproteins.

Effects of different doses of atorvastatin on human apolipoprotein B-100, B-48, and A-I metabolism

Nine hypercholesterolemic and hypertriglyceridemic subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study to test the effect of atorvastatin 20 mg/day and 80 mg/day on the kinetics of apolipoprotein B-100 (apoB-100) in triglyceride-rich lipoprotein (TRL), intermediate density lipoprotein (IDL), and LDL, of apoB-48 in TRL, and of apoA-I in HDL. Compared with placebo, atorvastatin 20 mg/day was associated with significant reductions in TRL, IDL, and LDL apoB-100 pool size as a result of significant increases in fractional catabolic rate (FCR) without changes in production rate (PR). Compared with the 20 mg/day dose, atorvastatin 80 mg/day caused a further significant reduction in the LDL apoB-100 pool size as a result of a further increase in FCR. ApoB-48 pool size was reduced significantly by both atorvastatin doses, and this reduction was associated with nonsignificant increases in FCR. The lathosterol-campesterol ratio was decreased by atorvastatin treatment, and changes in this ratio were inversely correlated with changes in TRL apoB-100 and apoB-48 PR. No significant effect on apoA-I kinetics was observed at either dose of atorvastatin. Our data indicate that atorvastatin reduces apoB-100- and apoB-48-containing lipoproteins by increasing their catabolism and has a dose-dependent effect on LDL apoB-100 kinetics. Atorvastatin-mediated changes in cholesterol homeostasis may contribute to apoB PR regulation.

Thematic review series: patient-oriented research. What we have learned about VLDL and LDL metabolism from human kinetics studies

Lipoprotein metabolism is the result of a complex network of many individual components. Abnormal lipoprotein concentrations can result from changes in the production, conversion, or catabolism of lipoprotein particles. Studies in hypolipoproteinemia and hyperlipoproteinemia have elucidated the processes that control VLDL secretion as well as VLDL and LDL catabolism. Here, we review the current knowledge regarding apolipoprotein B (apoB) metabolism, focusing on selected clinically relevant conditions. In hypobetalipoproteinemia attributable to truncations in apoB, the rate of secretion is closely linked to the length of apoB. On the other hand, in patients with the metabolic syndrome, it appears that substrate, in the form of free fatty acids, coupled to the state of insulin resistance can induce hypersecretion of VLDL-apoB. Studies in patients with familial hypercholesterolemia, familial defective apoB, and mutant forms of proprotein convertase subtilisin/kexin type 9 show that mutations in the LDL receptor, the ligand for the receptor, or an intracellular chaperone for the receptor are the most important determinants in regulating LDL catabolism. This review also demonstrates the variance of results within similar, or even the same, phenotypic conditions. This underscores the sensitivity of metabolic studies to methodological aspects and thus the importance of the inclusion of adequate controls in studies.

REVIEW: Efficacy and mechanisms of action of statins in the treatment of diabetic dyslipidemia

CONTEXT

The Adult Treatment Panel III recommends 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, as first-line lipid-altering therapy for all adult patients with diabetes mellitus. This is based on the well-characterized efficacy and safety profiles of this class of agents as well as several clinical trials demonstrating that statin treatment reduces the risk of cardiovascular events.

EVIDENCE ACQUISITION

This review provides an overview of the effectiveness and mechanisms of action of statins in patients with diabetes mellitus using small efficacy trials and large clinical outcomes trials as well as studies of the effects of statins on apolipoprotein B (apoB) metabolism.

EVIDENCE SYNTHESIS

The major findings presented are a review of mechanistic studies of selected subjects with diabetes mellitus and dyslipidemia and a compilation of results from large-scale clinical trials of patients with diabetes.

CONCLUSIONS

Statins are highly efficacious as low-density lipoprotein cholesterol-lowering agents and have more modest effects on very low-density lipoprotein triglyceride and high-density lipoprotein cholesterol levels. The effects of statins on plasma lipids and lipoproteins result from their ability to both increase the efficiency with which very low-density lipoprotein and low-density lipoprotein are cleared from the circulation and reduce the production of apoB-containing lipoproteins by the liver. Additional investigations are needed to clarify the mechanisms by which statins reduce apoB secretion from the liver.

Treatment with high-dose simvastatin reduces secretion of apolipoprotein B-lipoproteins in patients with diabetic dyslipidemia

HMG-CoA reductase inhibitors (statins) are effective lipid-altering drugs for the treatment of dyslipidemia in patients with type 2 diabetes mellitus. We conducted a randomized, double-blind, placebo-controlled, crossover design trial to determine the effects of simvastatin, 80 mg/day, on plasma lipid and lipoprotein levels and on the metabolism of apolipoprotein B (apoB) in VLDL, intermediate density lipoprotein (IDL), and LDL and of triglycerides (TGs) in VLDL. Simvastatin therapy decreased TG, cholesterol, and apoB significantly in VLDL, IDL, and LDL. These effects were associated with reduced production of LDL-apoB, mainly as a result of reduced secretion of apoB-lipoproteins directly into the LDL density range. Statin therapy also reduced hepatic production of VLDL-TG. There were no effects of simvastatin on the fractional catabolic rates of VLDL-apoB or -TG or LDL-apoB. The basis for decreased VLDL-TG secretion during simvastatin treatment is not clear, but recent studies suggest that statins may activate peroxisomal proliferator-activated receptor alpha (PPARalpha). Activation of PPARalpha could lead to increased hepatic oxidation of fatty acids and less synthesis of TG for VLDL assembly.

Lipoprotein(a)- and low-density lipoprotein-derived cholesterol in nephrotic syndrome: Impact on lipid-lowering therapy?

BACKGROUND

Patients with nephrotic syndrome have the highest lipoprotein(a) [Lp(a)] concentrations known. Lp(a) is an low-density lipoprotein (LDL)-like particle consisting of 45% cholesterol. The usual methods to determine LDL cholesterol do not distinguish between cholesterol derived from LDL and Lp(a) and are thus the net result of cholesterol levels from both lipoproteins. High Lp(a) concentrations therefore significantly contribute to the measured or calculated LDL cholesterol levels. Since statins have no influence on Lp(a) levels, it can be expected that the LDL cholesterol-lowering effect of statins may be diminished in patients who have a pronounced elevation of Lp(a) levels accompanied by only moderate elevations of LDL cholesterol.

METHODS

We investigated 207 patients with nondiabetic nephrotic syndrome in whom Lp(a) concentrations were strikingly elevated when compared to 274 controls (60.4 +/- 85.4 mg/dL vs. 20.0 +/- 32.8 mg/dL, P < 0.0001).

RESULTS

According to National Kidney Foundation Dialysis Outcomes Quality Initiative (K/DOQI) Clinical Practice Guidelines for Managing Dyslipidemias, almost 95% of these patients are candidates for a therapeutic intervention to lower LDL cholesterol. LDL cholesterol levels corrected for Lp(a)-derived cholesterol, however, were 27 mg/dL lower than uncorrected concentrations (compared to only 9 mg/dL in controls). If Lp(a)-corrected levels instead of total LDL cholesterol levels were used, 25.7% of patients with low-molecular-weight (LMW) apolipoprotein(a) [apo(a)] isoforms were classified no longer to be in need of LDL cholesterol-lowering therapeutic intervention compared to only 2.3% of patients with high-molecular-weight (HMW) apo(a) phenotypes (P < 0.00001). This ("pseudo") pharmacogenetic effect results in incorrect determination of LDL cholesterol.

CONCLUSION

Our observation has an impact on the indication for, and assessment of efficacy of intervention. This potential artifact should be investigated in ongoing large trials in renal patients as well as in nonrenal African American subjects who have on average markedly higher Lp(a) levels. In nonrenal Caucasian subjects with much lower Lp(a) concentrations, this issue will be less relevant.

Effect of atorvastatin on apolipoprotein B100 containing lipoprotein metabolism in type-2 diabetes

Seven hypertriglyceridemic patients with type-2 diabetes were treated with atorvastatin (40 mg/day) for 2 months. Kinetics of apolipoprotein B100 (apoB100)-containing lipoproteins were determined before and after atorvastatin treatment and compared with data obtained in five normolipidemic volunteers. ApoB100 metabolism was studied using stable isotopes and multicompartmental modeling. Compared with normolipidemic obese subjects, type-2 diabetic patients had a higher apoB100 concentration in very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), and low-density lipoproteins (LDL) (P < 0.005). Kinetic analysis showed an increase in the total apoB100 production rate (P < 0.005) related to VLDL apoB100 overproduction (P < 0.005). Patients were also characterized by a lower fractional catabolic rate (FCR) in VLDL (not significant) or IDL (P < 0.005) mainly related to a decrease in VLDL and IDL delipidation rate (P < 0.005). Catabolism of LDL was also lower in diabetic patients (P < 0.05). Atorvastatin treatment significantly decreased plasma triglycerides (P < 0.05), total and LDL cholesterol (P < 0.05), apoB100 in LDL, IDL, and VLDL (P < 0.05). Treatment significantly decreased total apoB100 production rate (P < 0.05), but only for VLDL (P < 0.05). Treatment normalized FCR in IDL and LDL (P < 0.05). We concluded that atorvastatin improved lipid abnormalities in type-2 diabetic patients not only by increasing the clearance of apoB100-containing lipoproteins but also by decreasing VLDL production.

Simvastatin in primary biliary cirrhosis: effects on serum lipids and distinct disease markers

BACKGROUND/AIMS

Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver with inflammation of small and middle-sized bile ducts. Serum lipids are frequently elevated, but the use of a lipid lowering drug therapy in PBC is still a matter of debate. Application of an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in hypercholesterolemic PBC patients was therefore the subject of the present study.

METHODS

Six female patients (aged 46.5 (32-61) years; median (range)) were treated with the HMG-CoA reductase inhibitor simvastatin (5 or 20 mg/day). Levels of serum total cholesterol, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol were determined prior to and after 2 months of treatment. Concentrations of serum markers of cholestasis, antimitochondrial antibodies (AMA), and immunoglobulins A, G and M were also assessed.

RESULTS

Simvastatin significantly (P<0.05) reduced serum levels of total cholesterol, LDL cholesterol, alkaline phosphatase, -glutamyltransferase, and immunoglobulin M (by 19, 26, 12, 37 and 14%, respectively).

CONCLUSIONS

The lipid lowering potency of the HMG-CoA reductase inhibitor simvastatin was confirmed in hypercholesterolemic patients with PBC. The drug might also prove useful as modulator of cholestasis and of immune response in this disease.

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.

Metabolic modes of action of the statins in the hyperlipoproteinemias

Conflicting results have been published during the past few years regarding the physiologic modes of action of the hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors, generally referred to as statins, using standard doses. Three mechanisms have been described: increased LDL catabolic rate, increased removal of LDL precursors resulting in decreased LDL production and decreased VLDL production. The physiologic effects of statins seem to depend on the underlying pathology of the disorders under therapy. More recent data using either the more potent atorvastatin or larger doses of previously available statins (e.g. simvastatin 80-160 mg/day), suggest that both the potency of the statins and the underlying pathopHysiology are important in determining the predominant physiologic responses of patients. To understand physiologic responses more completely, drug-dose-physiologic response curves of apo B kinetics in various groups of patients are needed. Simultaneous studies of apo B, triglycerides and cholesterol metabolism are also needed and are currently feasible.

Role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors ("statins") in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is a heterogeneous genetic disorder characterized by multiple lipoprotein phenotypes. The genetic defect is unknown, although linkage to the region of the apolipoprotein (apo) A-I-apoC-III-apo A-IV gene cluster on chromosome 11 has been suggested. The metabolic abnormality in many affected individuals is overproduction of apoB-containing lipoproteins causing elevated levels of plasma cholesterol, triglycerides, or both. Low levels of high-density lipoprotein (HDL) cholesterol and an abundance of dense low-density lipoprotein (LDL) particles are other features contributing to the high association of this disorder with premature coronary artery disease. Many affected individuals need drug therapy to lower their lipid levels. The hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or "statins," offer a potent therapeutic option in patients with FCHL. These drugs significantly decrease levels of total cholesterol, LDL cholesterol, and apoB, although their effects on HDL cholesterol and triglycerides are limited. The mechanisms by which statins exert their beneficial effects in patients with FCHL remain controversial. We studied 7 patients with FCHL and 5 genetically uncharacterized patients with mixed lipemia during treatment with pravastatin 20 mg/day. Metabolic parameters of very-low-density lipoprotein (VLDL)-apoB and LDL-apoB were studied using endogenous labeling with stable isotopes. In all patients pravastatin caused an increase in fractional catabolic rates of LDL-apoB without a significant effect on the production rates of apoB-containing lipoproteins. We cannot exclude the possibility that higher doses of statins may decrease VLDL and LDL production.

Lovastatin decreases de novo cholesterol synthesis and LDL Apo B-100 production rates in combined-hyperlipidemic males

The effect of lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, on the kinetics of de novo cholesterol synthesis and apolipoprotein (apo) B in very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) was investigated in five male patients with combined hyperlipidemia. Subjects were counseled to follow a Step 2 diet and were treated with lovastatin and placebo in randomly assigned order for 6-week periods. At the end of each experimental period, subjects were given deuterium oxide orally and de novo cholesterol synthesis was assessed from deuterium incorporation into cholesterol and expressed as fractional synthesis rate (C-FSR) and production rate (C-PR). Simultaneously, the kinetics of VLDL, IDL, and LDL apo B-100 were studied in the fed state using a primed-constant infusion of deuterated leucine to measure fractional catabolic rates (FCR) and production rates (PR). Drug treatment resulted in significant decreases in total cholesterol (-29%), VLDL cholesterol (-40%), LDL cholesterol (-27%), and apo B (-16%) levels and increases in HDL cholesterol (+13%) and apolipoprotein (apo) A-I (+11%) levels. Associated with these plasma lipoprotein responses was a significant reduction in both de novo C-FSR (-40%; P = .04) and C-PR (-42%; P = .03). Treatment with lovastain in these patients had no significant effect on the FCR of apoB-100 in VLDL, IDL, or LDL, but resulted in a significant decrease in the PR of apoB-100 in IDL and LDL. Comparing the kinetic data of these patients with those of 10 normolipidemic control subjects indicates that lovastatin treatment normalized apoB-100 IDL and LDL PR. The results of these studies suggest that the declines in plasma lipid levels observed after treatment of combined hyperlipidemic patients with lovastatin are attributable to reductions in the C-FSR and C-PR of de novo cholesterol synthesis and the PR of apoB-100 containing lipoproteins. The decline in de novo cholesterol synthesis, rather than an increase in direct uptake of VLDL and IDL, may have contributed to the decline in the PR observed.

Statin therapy in a kindred with both apolipoprotein B and low density lipoprotein receptor gene defects

We studied an extended family of similar genetic and environmental background to determine whether there is a difference in response to statin therapy in those subjects with heterozygous familial hypercholesterolaemia (FH Afrikaner-1 (FH1) or FH Afrikaner-2 (FH2)) compared to those with familial defective apo B-100 (FDB), or both FH plus FDB. Fasting lipid profiles and Lp(a) levels were done on 18 members of the family and then repeated following 6 weeks of therapy with simvastatin 20 mg daily. Statin therapy reduced LDL-cholesterol (LDL-C) by 31% in those with FH (n = 7); 29.8% in FDB (n = 5) and 25.4% in those with both FDB and FH (n = 5). There was no response to statin therapy in the single subject with both FH1, FH2, as well as FDB. Lp(a) levels did not change significantly either within or between any of the groups following statin therapy (FH from 6.5 (1.2-72.3) to 5.3 (1.2-52.3), FDB from 6.1 (4.70-71) to 8.2 (5.7 79) and FDB plus FH from 4.5 (2.6-17.4) to 3.1 (1.9-24) mg/dl). Statins are equally effective in lowering LDL-C in related subjects with heterozygous FH, FDB or both FDB plus FH. The ability of statins to lower LDL-C in FDB is probably due to increased hepatic uptake of lipoprotein precursors of LDL that can bind via apo E receptors. Lp(a) concentration is not reduced by drugs that stimulate LDL receptor activity implying that LDL receptors do not contribute greatly to normal clearance of Lp(a) in hypercholesterolaemic subjects with defects in receptor-mediated endocytosis of LDL.

Clinical pharmacokinetics of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is the key enzyme of cholesterol synthesis. HMG-CoA reductase inhibitors are potent reversible inhibitors of this enzyme, which act by competing for the substrate HMG-CoA. This review is mainly devoted to the 4 main HMG-CoA reductase inhibitors used today: lovastatin, simvastatin, pravastatin and fluvastatin. Depending upon the dosage, these drugs are able to reduce plasma cholesterol levels by more than 40%. After absorption, each undergoes extensive hepatic first-pass metabolism. Up to 5 primary metabolites are formed, some of which are active inhibitors. The elimination half-lives vary from 0.5 to 3.5 hours and excretion is mainly via the faeces. A limited number of drug interactions has been reported. Increases in liver enzymes and muscle creatine kinase activity are among the most severe adverse effects. These powerful drugs should be reserved for patients with high plasma cholesterol levels and/or those with cardiovascular disease. New therapeutic approaches to atherosclerosis are currently under investigation. HMG-CoA reductase inhibitors are the cornerstone of this research.

Familial defective apolipoprotein B-100 (FDB): effect of simvastatin therapy on LDL-receptor binding

Heterozygotes for familial defective apolipoprotein B-100 (FDB) have two populations of low density lipoprotein (LDL), one bearing normal apolipoprotein B-100 (apo B) and the other bearing defective apo B which exhibits a much lower affinity for the LDL-receptor. If HMGCoA reductase inhibitors such as simvastatin lowered LDL mainly by up-regulating LDL-receptor mediated clearance, they should decrease the overall binding affinity of LDL from an FDB heterozygote by selectively decreasing LDL bearing normal apo B. We compared how LDL from FDB heterozygotes competed with normal 125I-labelled LDL for binding to LDL-receptors while on and off therapy with simvastatin. The LDL of FDB heterozygotes had 40% (n = 10) the affinity of normal LDL (n = 12) for the LDL receptor on cultured fibroblasts, and 55% (n = 6) of normal LDL (n = 6) for that on HepG2 cells. Treatment of FDB subjects with simvastatin (n = 10) decreased serum LDL by 22% but had no effect on its binding affinity for LDL receptors, indicative of lowering of LDL containing both normal and defective apo B. This is consistent with the major LDL lowering effect being associated with decreased synthesis of LDL, rather than enhanced LDL-receptor clearance.

Reduction of lipoprotein(a) following treatment with lovastatin in patients with unremitting nephrotic syndrome

Pharmocologic treatment of the hyperlipidemia associated with the nephrotic syndrome with lovastatin has been previously shown to be safe and effective. However, there is no information on the effect of lovastatin treatment on plasma lipoprotein(a) [Lp(a)] levels in patients with the nephrotic syndrome. We administered lovastatin (40 to 80 mg/day) to 20 adult patients with unremitting nephrotic syndrome for 8 weeks to assess its effect on plasma Lp(a) and other plasma lipid concentrations. Apoprotein(a) (apo(a)) phenotype was determined in all patients. Patients were grouped according to their plasma Lp(a) levels. Those with elevated plasma Lp(a) (> or = 30 mg/dL) were placed in group I and those with normal Lp(a) levels (< 30 mg/dL) were placed in group II. Mean total cholesterol and LDL cholesterol were similarly and significantly reduced in groups I and II (-35.9% and -43.3%, P < 0.0005, P < 0.0005 group I, and -31.0% and -42.0%, P < 0.02, P < 0.03 group II, respectively). The median reduction in plasma Lp(a) was -32% (P < 0.003) in nephrotic patients in group I, whereas the median decline in plasma Lp(a) levels in nephrotic patients in group II was only -8.0% (P = 0.052). The overall frequency of the high molecular weight (M(r)) apo(a) phenotype S4 was 70% in nephrotic patients. There was no correlation between plasma Lp(a) and apo(a) phenotype. Treatment with lovastatin results in a favorable response in terms of total and low-density lipoprotein cholesterol lowering in patients with the nephrotic syndrome; however, plasma Lp(a) levels are uniformly and significantly reduced only in nephrotic patients with elevated baseline plasma Lp(a) concentrations. There was no correlation between plasma Lp(a) concentration and other lipid and biochemical parameters.

Effects of simvastatin on plasma lipoprotein subfractions, cholesterol esterification rate, and cholesteryl ester transfer protein in type II hyperlipoproteinemia

We investigated the effects of simvastatin on plasma levels of lipoprotein subfractions, cholesterol esterification rates and activities of cholesteryl ester transfer protein in 28 patients with type II hyperlipoproteinemia (i.e., nonfamilial hyperlipoproteinemia type IIa and type IIb, and heterozygous familial hypercholesterolemia (FH)). Plasma levels of VLDL-cholesterol (C) and VLDL-triglyceride (TG) were significantly reduced overall by 12.9 +/- 58.0% (mean +/- S.D.; P < 0.05) and 4.2 +/- 54.2% (P < 0.05) respectively, but not in FH. Plasma levels of IDL-C and IDLT-G were decreased overall by 23.2 +/- 47.5% (P < 0.001) and 12.3 +/- 49.7% (P < 0.05), respectively, again mainly due to decreases seen in nonfamilial type II hyperlipoproteinemia. Plasma levels of LDL1 (1.019 < d < 1.045)-C and LDL1-TG were significantly reduced by 33.1 +/- 12.9% (P < 0.001) and 23.3 +/- 24.7% (P < 0.001), respectively. Plasma levels of LDL2 (1.045 < d < 1.063)-C were significantly reduced by 22.9 +/- 18.1% (P < 0.001) overall but not in FH. Gradient PAGE showed no consistent changes in the distribution of LDL particles. Thus, plasma levels of all apo B-containing lipoprotein subfractions were reduced by simvastatin, but its effects varied among the three subgroups. Cholesterol esterification rates were suppressed by 9.3 +/- 19.7% (P < 0.01) and activities of cholesteryl ester transfer protein were reduced by 30.6 +/- 21.5% (P < 0.001). Changes in CETP activity and in plasma levels of cholesterol in lipoprotein subfractions were not correlated. Thus, the changes in distribution of lipoprotein subfractions were not due mainly to CETP suppression.

In vivo regulation of hepatic lipase activity and mRNA levels by diets which modify cholesterol influx to the liver

The aim of this study was to assess whether diets enriched in cholesterol, sodium cholate and drugs known to modify liver cholesterol biosynthesis can modulate hepatic lipase (H-TGL) expression and activity in vivo. Female lean Zucker rats, known to be good responders to cholesterol, were fed for 7 days with a control C diet or the C diet supplemented (w/w) with either 2% cholesterol, 0.5% sodium cholate, 2% cholestyramine or simvastatin (0.1%) added to the cholestyramine diet or given by gavage (10 mg/rat) for 3 days. H-TGL activity decreased by 34% with cholesterol, and by 27% when both cholesterol and cholate were administered to the rats. Under these conditions, H-TGL mRNA decreased by 34% and 87%, respectively. The sharp decrease in H-TGL expression was associated with a strong increase in cholesteryl ester in total liver and in the liver microsome fraction. H-TGL activity decreased by 33% with cholestyramine and the mRNA level decreased by 47%. Simvastatin lowered H-TGL activity by 55% when added to the cholestyramine diet, probably because of a reduction in food intake. When administrated by gavage, simvastatin increased both the H-TGL activity (by 28%) and mRNA (by 23%). These variations may be linked to the availability of mevalonate-derived sterol and non-sterol products.

Effect of simvastatin treatment on plasma apolipoproteins and hepatic apolipoprotein mRNA levels in the genetically hypercholesterolemic rat (RICO)

The effects of long-term treatment with simvastatin on plasma lipoproteins, plasma apolipoproteins, and on hepatic apolipoprotein gene expression were evaluated in genetically hypercholesterolemic (RICO) rats. Simvastatin administration caused a decrease in plasma triglyceride and phospholipid concentrations. Plasma cholesterol concentration was not changed by simvastatin, but cholesterol distribution among plasma lipoproteins was altered. Plasma apo B, apo A-I, and apo A-IV concentrations were lowered by simvastatin treatment whereas plasma apo E concentration was not affected by this drug. In the liver, simvastatin treatment induced a significant decrease of apo E mRNA level but had no effect on apo B, apo A-I, and apo A-IV mRNA abundances. It appears that simvastatin may modify plasma apolipoprotein concentrations by influencing their hepatic synthesis at both pre- and posttranscriptional levels.

The effects of hypercholesterolaemia, simvastatin and dietary fat on the low density lipoprotein receptor of unstimulated mononuclear cells

The in vivo expression and regulation of the LDL receptor of circulating mononuclear cells was studied using a sensitive spectrophotometric assay with low density lipoproteins conjugated to colloidal gold (LDL-gold). The high plasma cholesterol of familial hypercholesterolemic subjects was shown to be related to a low in vivo LDL receptor activity; cells from a homozygote had virtually no activity and those from 24 heterozygotes expressed 45% of the activity of cells from 35 normals. The average receptor activity of cells from 18 polygenic hypercholesterolemic (PH) subjects was not significantly different from normal but a low expression may have been a factor in six of these subjects. Simvastatin increased the LDL receptor activity of cells from the PH subjects by 70% while lowering their plasma cholesterol by 26%, but reducing the fat intake from 38% to 20% of energy and cholesterol from 239 to 96 mg/day had no effect on the receptor despite a 10% reduction in plasma cholesterol. Upregulation of the LDL receptor may therefore have been involved in the lowering of plasma cholesterol by simvastatin but not by the reduction in dietary fat and cholesterol.

One year experience in the treatment of familial hypercholesterolaemia with simvastatin

Patients with heterozygous familial hypercholesterolaemia (FH) have a substantially increased risk of atherosclerosis due to very high plasma levels of cholesterol. Recent evidence has shown that coronary heart disease in these patients may regress with lipid-lowering therapy. In this study the efficacy and safety of simvastatin, an inhibitor of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A, was investigated in 30 patients with FH over a period of one year. Substantial reductions in the plasma concentrations of total cholesterol (-28%), low-density lipoprotein (LDL) cholesterol (-32%), intermediate-density lipoprotein (IDL) cholesterol and apolipoprotein (apo) B (-33%) were achieved with 20 mg/day of simvastatin; there were no significant changes in triglycerides high-density lipoprotein cholesterol or apo A. In contrast to previous studies, 40 mg/day of simvastatin did not result in a further statistically significant fall in LDL cholesterol, IDL cholesterol or apo B in the group as a whole. The drug was well tolerated and no adverse clinical or laboratory events were recorded. In particular, no ophthalmological, hepatic or renal disorders were observed and there were no sleep disturbances. We conclude that simvastatin is an efficacious and safe drug to treat patients with heterozygous FH and that rarely will the dose need to be increased above 20 mg/day.

Effect of simvastatin, ursodeoxycholic acid and simvastatin plus ursodeoxycholic acid on biliary lipid secretion and cholic acid kinetics in nonfamilial hypercholesterolemia

It has been recently shown that the newest hypocholesterolemic agent, simvastatin, lowers the biliary cholesterol saturation index and that its association with ursodeoxycholic acid renders it more effective. To determine the mechanism by which simvastatin decreases the biliary cholesterol saturation index, we evaluated hepatic secretion rates of cholesterol, bile acids and phospholipids, and cholic acid pool size, turnover and synthesis in eight hyperlipidemic patients (five women and three men, age range = 38 to 65 yr). These assessments were conducted before treatment, after 4 wk of simvastatin (40 mg/day), after 4 wk of ursodeoxycholic acid (600 mg/day) and after a further 4 wk of a combination therapy of simvastatin (40 mg/day) plus ursodeoxycholic acid (600 mg/day). The cholesterol saturation index was significantly reduced with simvastatin (from 1.51 +/- 0.10 to 0.94 +/- 0.05, mean +/- S.E.; p less than 0.02), with ursodeoxycholic acid (from 1.51 +/- 0.10 to 0.86 +/- 0.03, mean +/- S.E.; p less than 0.02) and with the combination of simvastatin plus ursodeoxycholic acid (from 1.51 +/- 0.01 to 0.70 +/- 0.05, p less than 0.02). The cholesterol saturation index during combination therapy was significantly lower (p less than 0.02) than that reached during the use of simvastatin and ursodeoxycholic acid. Both simvastatin and ursodeoxycholic acid significantly reduced the hepatic secretion rate of cholesterol (from 130 +/- 14 mumols/hr to 81 +/- 12 mumols/hr, p less than 0.01, and 70 +/- 9 mumols/hr, p less than 0.01) without affecting bile acid and phospholipid outputs.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-dependent and -independent catabolism of low-density lipoprotein in a kindred with familial hypobetalipoproteinemia

Three affected members of a kindred with asymptomatic hypobetalipoproteinemia (HBL) were injected intravenously with 125I-labeled native low-density lipoproteins (LDL) and 131I-labeled cyclohexanedione (CHD)-treated LDL. Plasma and urine radioactivity data were collected for 15 days at regular intervals. A compartmental model using the SAAM program was built to fit simultaneously 125I and 131I plasma radioactivity decay and urine excretion data. This model allows precise calculation of the kinetic parameters of both receptor-independent (NR) and receptor-dependent (R) pathways. Compared with normal subjects, HBL patients show a 90% increased fractional catabolic rate (FCR) of LDL by both routes, more marked for the R pathway (215% increase), and an approximately 50% reduced production rate (PR). Structural analysis did not show significant abnormalities of apolipoprotein (apo) B in HBL patients compared with normal. These data suggest that the very reduced, LDL-apo B plasma levels result from a combination of two processes: (1) an increased activity of all catabolic routes, and (2) a reduced "synthesis" rate. The latter may result from a decreased conversion of very-low-density lipoprotein (VLDL) to LDL secondary to an increased direct removal of large VLDL, suggested by apo C-II and C-III turnover studies previously reported.

Influence of lovastatin therapy on metabolism of low density lipoproteins in mixed hyperlipidaemia

To determine the mechanisms whereby HMG-CoA reductase inhibitors lower the levels of low density lipoproteins (LDL) in patients with mixed hyperlipidaemia, LDL turnover studies were conducted in 12 such patients during placebo and then during treatment with lovastatin. Drug therapy reduced total cholesterol and triglyceride concentrations by 33% and 32%, respectively. During lovastatin therapy, LDL-cholesterol levels fell by 37%, and LDL-apo B concentrations decreased by an average of 29%. The decrease in LDL-apo B concentrations on lovastatin therapy was largely due to an increase in fractional catabolic rates (FCRs) for LDL apo B. The average increase in FCRs was 34%, whereas transport rates (production rates) for LDL apo B remained unchanged. These results strongly suggest that an increase in LDL-receptor activity is the major mechanism whereby LDL levels are lowered during lovastatin therapy. The data do not indicate that this drug inhibited the input of apo B-containing lipoproteins, which would have been expected to result in a decrease in the rate of production of LDL.

Effect of simvastatin on receptor mediated metabolism of low density lipoprotein in guinea pigs

This study examined the effects of simvastatin, an inhibitor of HMG-CoA reductase, on the metabolism of labelled human low density lipoprotein (LDL) in animal models. Administration of 10 mg/kg per day simvastatin for 2 weeks reduced the levels of total cholesterol, LDL-cholesterol and triglycerides by 5.7 mg/dl (16%), 8.8 mg/dl (36%) and 4.9 mg/dl (13%), respectively in guinea pigs. High density lipoprotein-cholesterol levels rose 0.8 mg/dl (29%) by simvastatin treatment. Measurements of turnover of LDL were determined between simvastatin-treated guinea pigs and untreated guinea pigs using intravenous injection of 131I-labelled LDL and 125I-labelled galactose-treated LDL to quantify the LDL receptor pathway. Simvastatin significantly increased the fractional catabolic rate (FCR) of the LDL receptor-dependent pathway. In contrast, the FCR of the LDL receptor-independent pathway was not altered by simvastatin therapy. The FCR for LDL isolated from simvastatin-treated subjects compared to that from control subjects was very similar in both control and simvastatin-fed guinea pigs. These findings suggest that simvastatin mainly reduced serum cholesterol levels by accelerated FCR of LDL receptor mediated pathway.

Hypercholesterolaemia: simvastatin and pravastatin alter cholesterol metabolism by different mechanisms

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin, reduced low-density-lipoprotein (LDL) cholesterol in hypercholesterolaemic patients by 40% (P less than 0.001). The reduction in LDL cholesterol was accompanied by a significant decrease in the esterified/free cholesterol ratio of the patients' LDL from 2.51 +/- 0.13 to 2.06 +/- 0.14 (P less than 0.01). This change led to a significant increase (P less than 0.05) in the capacity of the LDL to suppress [14C]acetate incorporation into cholesterol in mononuclear leucocytes. Furthermore, [14C]acetate incorporation into the patients mononuclear leucocytes was significantly lower (P less than 0.02) following drug treatment (117 +/- 22 vs. 162 +/- 29 nmol/mg cell protein). Comparison of simvastatin with another HMG-CoA reductase inhibitor pravastatin, showed similar reduction in LDL cholesterol. Pravastatin treatment however, did not result in a reduction in the LDL esterified/free cholesterol ratio or in the changes in cellular cholesterol synthesis and its regulation by LDL which accompanied simvastatin treatment. The activity of the enzyme acyl-coenzyme A: cholesterol acyltransferase (ACAT) in patients' mononuclear cells remained unchanged after treatment with either drug. Results of the study show that while the drugs are equally effective in lowering LDL cholesterol, simvastatin has additional compositional effects on LDL which increase its capacity to regulate mononuclear leucocyte cholesterologenesis.

In vivo effect of simvastatin on lipoprotein cholesteryl ester metabolism in normocholesterolemic volunteers

A kinetic study on lipoprotein cholesteryl ester metabolism was carried out in 4 normolipidemic volunteers before and after treatment with simvastatin. They received LDL labelled with 3H-cholesteryl linoleate. A lipoprotein cholesteryl ester model was developed that fit the radioactivity in LDL, HDL and VLDL cholesteryl ester during 24 hours following injection. Before treatment, the model is consistent with previously reported data. Moreover our results suggest that, in normal fasting subjects, the efflux of plasma cholesteryl ester is almost exclusively derived from LDL. Administration of drug decreased LDL cholesteryl ester concentration by 35%. After treatment, the rate constant concerning LDL catabolism was increased by 25% and the model required the existence of a direct removal of VLDL cholesteryl ester (40% of total VLDL turnover). Our results suggest that the reduction in the LDL cholesteryl ester concentration induced by treatment with simvastatin is due to an increase in the uptake of LDL and LDL precursors (VLDL, VLDL remnants) by LDL receptors.

Lack of effect of lovastatin therapy on the parameters of whole-body cholesterol metabolism

The effects of lovastatin therapy on the parameters of body cholesterol metabolism were explored in nine hypercholesterolemic patients. Long-term cholesterol turnover studies were performed before therapy, and were repeated after 15 mo of lovastatin therapy (40 mg/d) while continuing on therapy. The major question addressed was whether a reduction in plasma cholesterol level with lovastatin would be associated with a reduction in the whole-body production rate of cholesterol or with the sizes of exchangeable body cholesterol pools as determined by the three-pool model of cholesterol turnover. The mean plasma cholesterol level decreased 19.4% (from 294 to 237 mg/dl), and low-density lipoprotein cholesterol decreased 23.8% (from 210 to 159 mg/dl) with lovastatin therapy. Changes in high-density lipoprotein cholesterol level were not significant. The cholesterol production rate did not change significantly with therapy (1.09 +/- 0.10 [mean +/- S.D.] vs. 1.17 +/- 0.09 g/d). By comparison, colestipol and niacin treatment in three other subjects more than doubled the cholesterol production rate (1.14 +/- 0.28 vs. 2.42 +/- 0.34 g/d). Thus, hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibition by lovastatin at the therapeutic dose used here did not change the steady-state rate of whole-body cholesterol synthesis. Despite the changes in plasma cholesterol levels, no significant changes were seen in the values of M1, of M3 or of Mtot, the sizes of the pools of rapidly, of slowly, and of total body exchangeable cholesterol.

CONCLUSION

lovastatin therapy to lower plasma cholesterol does not lead to corresponding reductions in body cholesterol pools or to a reduction in the rate of whole-body cholesterol synthesis. In the new steady state that exists during long-term lovastatin therapy, along with increased expression of the genes for HMG-CoA reductase and the LDL receptor, the body compensates for the effects of the drug so that cholesterol production rate and tissue pool sizes are not changed from pretreatment values.

Influence of pravastatin, a specific inhibitor of HMG-CoA reductase, on hepatic metabolism of cholesterol

BACKGROUND

Inhibitors of the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase, are now used frequently to treat hypercholesterolemia. We studied the effects of specific inhibition of cholesterol synthesis by one of these agents (pravastatin) on the hepatic metabolism of cholesterol in patients with gallstone disease who were scheduled to undergo cholecystectomy.

METHODS

Ten patients were treated with pravastatin (20 mg twice a day) for three weeks before cholecystectomy; 20 patients not treated served as controls. A liver specimen was obtained from each patient at operation, and the activities of rate-determining enzymes in cholesterol metabolism as well as low-density-lipoprotein (LDL)-receptor binding activity were determined.

RESULTS

Pravastatin therapy reduced plasma total cholesterol by 26 percent and LDL cholesterol by 39 percent (P less than 0.005). Serum levels of free lathosterol, a precursor of cholesterol whose concentration reflects the rate of cholesterol synthesis in vivo, decreased by 63 percent (P less than 0.005), indicating reduced de novo biosynthesis of cholesterol. Microsomal HMG-CoA reductase activity, when analyzed in vitro in the absence of the inhibitor, was increased 11.8-fold (1344 +/- 311 vs. 105 +/- 14 pmol per minute per milligram of protein in the controls; P less than 0.001). The expression of LDL receptors was increased by 180 percent (P less than 0.005), whereas the activities of cholesterol 7 alpha-hydroxylase (which governs bile acid synthesis) and of acyl-coenzyme A:cholesterol O-acyltransferase (which regulates cholesterol esterification) were unaffected by treatment.

CONCLUSIONS

Inhibition of hepatic HMG-CoA reductase by pravastatin results in an increased expression of hepatic LDL receptors, which explains the lowered plasma levels of LDL cholesterol.