Cholesterol absorption and synthesis during pravastatin, gemfibrozil and their combination

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 We also contacted authors of relevant papers regarding further published and unpublished work.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.

Plasma Non-cholesterol Sterols as Markers of Cholesterol Synthesis and Intestinal Absorption: A Critical Review

Plasma concentrations of phytosterols and non-cholesterol sterol precursors of cholesterol synthesis have been used as markers of intestinal cholesterol absorption and synthesis in inherited and secondary dyslipidemias and in population-based investigations to evaluate the risk for cardiovascular disease, respectively. The method aims at replacing initial research procedures such as the use of stable isotopes associated with fecal steroid balance, which are limited by the high cost and tedious procedures. However, we show in this review that numerous results obtained with serum sterol measurements are contradictory. In this regard, the following points are discussed: 1) how phytosterols relate to atherosclerosis considering that defects in biliary output or in the transport of phytosterols from the intestinal mucosa back into the intestinal lumen provide increased content of phytosterols and other sterols in plasma and tissues, thus not allowing to conclude that their presence in arteries and atheromas represents the etiology of atherosclerosis; 2) serum non-cholesterol sterols as markers of cholesterol synthesis and absorption, such as cholestanol, present discrepant results, rendering them often inadequate to identify cases of coronary artery disease as well as alterations in the whole body cholesterol metabolism; 3) such methods of measurement of cholesterol metabolism are confounded by factors like diabetes mellitus, body weight and other pathologies including considerable hereditary hyperlipidemias biological variabilities that influence the efficiency of synthesis and intestinal absorption of cholesterol.

Effects of K-877, a novel selective PPARα modulator, on small intestine contribute to the amelioration of hyperlipidemia in low-density lipoprotein receptor knockout mice

Peroxisome proliferator-activated receptor α (PPARα) is a well-known therapeutic target for treating hyperlipidemia. K-877 is a novel selective PPARα modulator (SPPARMα) that enhances PPARα transcriptional activity with high selectivity and potency, resulting in reduced plasma lipid levels. This study aimed to evaluate the effects of K-877 on hyperlipidemia in low-density lipoprotein receptor knockout (Ldlr^-/-) mice, a mouse model of atherosclerosis. We revealed that K-877 administration significantly decreased plasma triglyceride (TG) and total cholesterol (TC) levels and increased plasma high-density lipoprotein cholesterol (HDL-C) levels in Ldlr^-/- mice. K-877 administration to Ldlr^-/- mice efficiently increased the gene expression of PPARα and its target genes related to fatty acid oxidation in the liver and small intestine. The same treatment significantly increased ATP-binding cassette a1 gene expression in the liver and small intestine and reduced Niemann Pick C1-like 1 gene expression in the small intestine, suggesting that K-877 administration induced HDL-C production in the liver and small intestine and reduced cholesterol absorption in the small intestine. In conclusion, K-877 administration had pronounced effects on the liver and small intestine in Ldlr^-/- mice. K-877 is an attractive PPARα-modulating drug for treating hyperlipidemia that works equally well in both the liver and small intestine.

Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

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.

Niemann-pick C1-like 1 (NPC1L1) protein in intestinal and hepatic cholesterol transport

Increased blood cholesterol is an independent risk factor for atherosclerotic cardiovascular disease. Cholesterol homeostasis in the body is controlled mainly by endogenous synthesis, intestinal absorption, and hepatic excretion. Niemann-Pick C1-Like 1 (NPC1L1) is a polytopic transmembrane protein localized at the apical membrane of enterocytes and the canalicular membrane of hepatocytes. It functions as a sterol transporter to mediate intestinal cholesterol absorption and counter-balances hepatobiliary cholesterol excretion. NPC1L1 is the molecular target of ezetimibe, a potent cholesterol absorption inhibitor that is widely used in treating hypercholesterolemia. Recent findings suggest that NPC1L1 deficiency or ezetimibe treatment also prevents diet-induced hepatic steatosis and obesity in addition to reducing blood cholesterol. Future studies should focus on molecular mechanisms underlying NPC1L1-dependent cholesterol transport and elucidation of how a cholesterol transporter modulates the pathogenesis of metabolic diseases.

Where does the interplay between cholesterol absorption and synthesis in the context of statin and/or ezetimibe treatment stand today?

The evidence of the different concepts underlying the interplay between cholesterol absorption and synthesis in the context of statin and ezetimibe treatment were reviewed in the light of the eight major trials where cholesterol absorption and synthesis were analyzed on a large scale using the plasma levels of precursors of cholesterol and plant sterols. The only concept supported in all studies is a significant and consistent increase of cholesterol absorption with statin (correlated with the inhibition of synthesis) and of cholesterol synthesis with ezetimibe, whereas in combination, statin and ezetimibe reduce both cholesterol synthesis and absorption. In contrast, most of the other concepts failed to be clearly proven. At baseline, the inverse relationship between cholesterol absorption and synthesis (only examined in two studies) was found to be weak. On statin treatment, four studies showed that the changes in cholesterol synthesis and absorption, contributed less than 9% to the variability in cholesterol response to statin therapy. It has not been consistently demonstrated that good absorbers/bad synthesizers are bad responders to statin (6 studies) and good responders for ezetimibe (3 studies). There is also no clear inverse correlation between LDL reduction on statin treatment and that on ezetimibe treatment. Finally, the original idea from the first pioneer study of Miettinen et al. that, the higher the baseline intestinal ability to absorb cholesterol, the lower the benefit on the clinical cardiovascular outcomes was not reproduced in the PROSPER study. In conclusion, with the exception of a reverse effect of statin and ezetimibe on absorption and synthesis, most ideas supporting the interplay between cholesterol absorption and synthesis lacked consistency between studies. At present, the use of the plasma levels of plant sterols and cholesterol precursors as markers of cholesterol absorption and synthesis is far too limited to definitively solve these questions.

Protein mediators of sterol transport across intestinal brush border membrane

Dysregulation of cholesterol balance contributes significantly to atherosclerotic cardiovascular disease (ASCVD), the leading cause of death in the United States. The intestine has the unique capability to act as a gatekeeper for entry of cholesterol into the body, and inhibition of intestinal cholesterol absorption is now widely regarded as an attractive non-statin therapeutic strategy for ASCVD prevention. In this chapter we discuss the current state of knowledge regarding sterol transport across the intestinal brush border membrane. The purpose of this work is to summarize substantial progress made in the last decade in regards to protein-mediated sterol trafficking, and to discuss this in the context of human disease.

Therapeutic effects of fibrates in postprandial lipemia

Hypertriglyceridemia is observed in many metabolic diseases such as the metabolic syndrome, diabetes mellitus, or mixed dyslipidemia frequently leading to premature coronary heart disease (CHD). Additionally, several studies have shown that postprandial hypertriglyceridemia is pronounced in patients with CHD, metabolic syndrome, hypertension, and other pathologic conditions. The triglyceride-rich lipoprotein remnants accumulating in the postprandial state seem to be involved in atherogenesis and in events leading to thrombosis. Since abnormal postprandial lipemia is associated with pathologic conditions, its treatment is of clinical importance.Fibrates are of significant help in managing hypertriglyceridemia. This review summarizes the effect of fibric acid derivatives on postprandial lipemia. Fibrates decrease the production of and enhance the catabolism of triglyceride-rich lipoproteins through the activation of peroxisome proliferator-activated receptor-alpha. Results of clinical studies with fibrates have confirmed their action in decreasing postprandial triglyceride levels by increasing lipoprotein lipase activity, decreasing apolipoprotein CIII production, and by increasing fatty acid oxidation in the liver.It is concluded that fibrates are effective agents in lowering the postprandial increase in remnant lipoprotein particles and retinyl palmitate. Furthermore, fibrates can also affect the postprandial lipid profile by increasing hepatic lipase levels and in some cases, by reducing cholesterol ester transfer protein activity. The main target of fibrate therapy is to improve fasting hypertriglyceridemia, which is an essential component associated with improving postprandial lipemia. Fibrates are well tolerated by patients and adverse effects have been reported rarely after their administration.

Comparison of the effects of maximal dose atorvastatin and rosuvastatin therapy on cholesterol synthesis and absorption markers

We measured plasma markers of cholesterol synthesis (lathosterol) and absorption (campesterol, sitosterol, and cholestanol) in order to compare the effects of maximal doses of rosuvastatin with atorvastatin and investigate the basis for the significant individual variation in lipid lowering response to statin therapy. Measurements were performed in participants (n = 135) at baseline and after 6 weeks on either rosuvastatin (40 mg/day) or atorvastatin (80 mg/day) therapy. Plasma sterols were measured using gas-liquid chromatography. Rosuvastatin and atorvastatin significantly (P < 0.001) altered plasma total cholesterol (C) levels by -40%, and the ratios of lathosterol/C by -64% and -68%, and campesterol/C by +52% and +72%, respectively, with significant differences (P < 0.001) between the treatment groups for the latter parameter. When using absolute values of these markers, subjects with the greatest reductions in both synthesis (lathosterol) and absorption (campesterol) had significantly greater reductions in total C than subjects in whom the converse was true (-46% versus -34%, P = 0.001), with similar effects for LDL-C. Rosuvastatin and atorvastatin decreased markers of cholesterol synthesis and increased markers of fractional cholesterol absorption, with rosuvastatin having significantly less effect on the latter parameter than atorvastatin. In addition, alterations in absolute values of plasma sterols correlated with the cholesterol lowering response.

Effects of ezetimibe, simvastatin, atorvastatin, and ezetimibe-statin therapies on non-cholesterol sterols in patients with primary hypercholesterolemia

BACKGROUND

Levels of cholesterol are regulated by its synthesis, absorption, and elimination. Plasma levels of phytosterols (e.g., sitosterol, campesterol) and ratios of these sterols to total cholesterol (TC) are reported to correlate with efficiency of intestinal cholesterol absorption, whereas levels of certain cholesterol precursor sterols (e.g., desmosterol, lathosterol) and their ratios to TC correlate with cholesterol biosynthesis. However, there is a paucity of published data concerning the effects of combined treatment using HMG-CoA reductase inhibitors (statins) and a cholesterol absorption inhibitor (ezetimibe) on these parameters.

OBJECTIVES

To characterize the effects of ezetimibe co-administered with statins, compared with each treatment alone, on cholesterol precursor sterols and plasma phytosterol levels.

METHODS

A post-hoc analysis was performed to determine the effects of treatment with ezetimibe 10 mg, simvastatin (10-80 mg), and atorvastatin (10-80 mg), alone or in combination, on these non-cholesterol sterols using plasma samples from two randomized controlled trials involving patients with primary hypercholesterolemia (low-density lipo protein [LDL-C] = 145-250 mg/dL; triglycerides < or = 350 mg/dL; N = 975) but without a recent (< or = 6-month) history of coronary heart disease (CHD) or either uncontrolled or newly diagnosed diabetes mellitus.

RESULTS

Ezetimibe monotherapy significantly reduced plasma sitosterol and campesterol concentrations from baseline compared with placebo (both p < 0.001), whereas statins significantly lowered desmo sterol and lathosterol levels (p < 0.001 vs. placebo). Co-administration of ezetimibe and statins significantly decreased plasma levels of all of these sterols (p < 0.001).

CONCLUSIONS

The observed effects of co-administration of ezetimibe and statins on non-cholesterol sterols are consistent with net inhibition of sterol absorption (driven by ezetimibe) in conjunction with net inhibition of cholesterol synthesis (driven by statins). The potential influence of treatment-induced changes in phytosterols on cardiovascular risk warrants further investigation in long-term, prospective, randomized controlled trials. This post-hoc study was by nature exploratory, and, because data from such analyses are not customarily adjusted for multiple comparisons, some associations may have emerged as statistically significant by chance. Future prospective randomized controlled studies may help to confirm our findings and address other research issues, such as the generalizability of our findings to patients with CHD or diabetes mellitus and possible dose:response relationships between escalating statin (or ezetimibe-statin) doses and circulating non-cholesterol levels.

Fenofibrate reduces intestinal cholesterol absorption via PPARalpha-dependent modulation of NPC1L1 expression in mouse

Fibrates, including fenofibrate, exert their biological effects by binding peroxisome proliferator-activated receptor alpha (PPARalpha), a member of the nuclear receptor superfamily of ligand-activated transcription factors. Treatment with PPARalpha agonists enhances fatty acid oxidation, decreases plasma triglycerides, and may promote reverse cholesterol transport. In addition, fibrate administration can reduce intestinal cholesterol absorption in patients, although the molecular mechanism for this effect is unknown. Because Niemann-Pick C1-Like 1 (NPC1L1) is already known to be a critical protein for cholesterol absorption, we hypothesized that fenofibrate might modulate NPC1L1 expression to alter intestinal cholesterol transport. Here, we find that fenofibrate-treated wild-type mice have decreased fractional cholesterol absorption (35-47% decrease) and increased fecal neutral sterol excretion (51-83% increase), which correspond to decreased expression of NPC1L1 mRNA and protein (38-66% decrease) in the proximal small intestine. These effects of fenofibrate are dependent on PPARalpha, as Ppar alpha-knockout mice fail to respond like wild-type littermates. Fenofibrate affects the ezetimibe-sensitive pathway and retains the ability to decrease cholesterol absorption and NPC1L1 mRNA expression in chow-fed liver X receptor alpha/beta-double-knockout mice and high-cholesterol- or cholic acid-fed wild-type mice. These data demonstrate that fenofibrate specifically acts via PPARalpha to decrease cholesterol absorption at the level of intestinal NPC1L1 expression.

Body weight, plasma insulin, and coronary events with gemfibrozil in the Veterans Affairs High-Density Lipoprotein Intervention Trial (VA-HIT)

BACKGROUND

The Veterans Affairs High-Density Lipoprotein Intervention Trial (VA-HIT) showed that gemfibrozil significantly reduced major coronary events in men with known coronary heart disease (CHD). To better understand why therapy was especially effective with obesity, diabetes, and hyperinsulinemia, changes in body weight and plasma insulin were determined after 1 year of gemfibrozil or placebo therapy and related to changes in lipids and CHD events.

RESULTS

With gemfibrozil significantly more subjects lost weight (51.7% versus 38.6%, P<0.0001) and significantly fewer subjects gained weight (42.5% versus 54.0%, P<0.0001) than with placebo. Both a greater loss and smaller gain in weight with gemfibrozil were age-related and significant in subjects > or =66 years (median age), but not in younger subjects. Weight change was paralleled by changes in insulin. With gemfibrozil, CHD events were significantly reduced with weight loss (hazard ratio [HR], 0.61; 95% CI, 0.44-0.84; P=0.002) and, particularly, with diabetes or hyperinsulinemia (HR, 0.53; 95% CI, 0.34-0.83; P=0.006). In contrast, CHD events were not significantly reduced without weight loss (HR, 0.83; 95% CI, 0.62-1.12; P=0.22).

CONCLUSIONS

In VA-HIT, gemfibrozil resulted in weight loss associated with reductions in insulin. With weight loss gemfibrozil produced a significant reduction in CHD events that did not occur in the absence of weight loss.

Type of Preexisting Lipid Therapy Predicts LDL-C Response to Ezetimibe

Background:

Ezetimibe as monotherapy or in combination with statins effectively lowers low-density lipoprotein cholesterol (LDL-C). However, there are few reports of ezetimibe's effect when added to ongoing non-statin lipid-lowering drugs or combination lipid-lowering therapy.

Objective:

To evaluate the impact of preexisting lipid therapy on LDL-C response to ezetimibe.

Methods:

We performed a retrospective review of all patients started on ezetimibe therapy at the Veterans Affairs Long Beach Healthcare System between March 1, 2003, and March 1, 2005. We calculated the ezetimibe-induced percent change in LDL-C in patients without concomitant changes in other lipid-lowering medications. We then stratified the population according to the type and number of preexisting lipid therapies and compared the LDL-C–lowering efficacy of ezetimibe among these groups.

Results:

Overall, ezetimibe was associated with a 23.0% reduction in LDL-C. Patients with preexisting statin monotherapy had significantly greater LDL-C reduction with ezetimibe than did those with preexisting non-statin drugs (–26.1% vs –9.3%; p = 0.0138). In patients with no preexisting lipid therapy (n = 58), monotherapy (n = 115), double therapy (n = 36), or triple therapy (n = 9), ezetimibe decreased LDL-C by 17.3%, 21.4%, 33.5%, and 38.1%, respectively. This stepwise trend in increased ezetimibe efficacy was statistically significant, even with adjustments for baseline LDL-C.

Conclusions:

Ezetimibe's LDL-C–lowering effects are most pronounced when added to preexisting combination lipid therapy. It appears to be more effective when added to statin therapy compared with other lipid-lowering therapies.

Cholesterol absorption: influence of body weight and the role of plant sterols

Cholesterol absorption and synthesis are inter-regulated, so if one changes then the other changes in the opposite direction. The regulation and detailed mechanism of cholesterol absorption have been intensely investigated. Inhibition of cholesterol absorption has become an additional factor for cholesterol lowering. Agents inhibiting cholesterol absorption, mainly plant stanols and sterols or ezetimibe, usually lower low-density lipoprotein cholesterol in monotherapy by less than 20%, indicating that these inhibitors can normalize cholesterol levels only in patients with a modest baseline hypercholesterolemia. Body weight, especially obesity with and without diabetes, and dietary plant sterols alter cholesterol absorption differently. This article briefly reviews some special questions of cholesterol absorption under these conditions.

Cholesterol Absorption and Synthesis in Pediatric Kidney, Liver, and Heart Transplant Recipients

BACKGROUND

Hypercholesterolemia after organ transplantation is common. Previously, we observed higher serum total cholesterol (TC) concentrations in our pediatric kidney than liver or heart transplant recipients. To find an explanation to the observed difference, our kidney recipients' cholesterol synthesis and absorption efficiency was compared to those of liver and heart recipients.

METHODS

Serum noncholesterol sterol ratios (10 x mmol to the mol of TC, surrogate estimates of hepatic cholesterol synthesis and intestinal absorption) were studied in 50 pediatric kidney, 25 liver and 12 heart transplant recipients without diabetes or cholestasis, and in 29 controls.

RESULTS

The kidney recipients had lower Delta-cholesterol (P=0.031), similar lathosterol and higher desmosterol ratios (markers of cholesterol synthesis) (P=0.020), and similar campesterol and sitosterol ratios (markers of cholesterol absorption) when compared to the controls. The liver recipients had lower campesterol ratios than the kidney recipients and controls (P=0.002). Glomerular filtration rates were not associated with the ratios of noncholesterol sterols. Multivariate analysis showed markers of cholesterol synthesis to be lower and absorption to be higher in the kidney than the liver or the heart transplant recipients. Weight-adjusted dosages of immunosuppressive agents were associated with some ratios of noncholesterol sterols and cholestanol though these varied between the transplant recipient groups.

CONCLUSIONS

Serum TC concentration in kidney recipients was not significantly associated with absorption efficiency or synthesis of cholesterol, though kidney transplantation was associated with low synthesis and high absorption efficiency of cholesterol. Immunosuppressive therapy with cyclosporine and methylprednisolone may modulate absorption efficiency and synthesis of cholesterol.

The gene encoding the human ileal bile acid-binding protein (I-BABP) is regulated by peroxisome proliferator-activated receptors

Peroxisome proliferator-activator receptors (PPAR) are involved in cholesterol homeostasis through the regulation of bile acids synthesis, composition, and reclamation. As ileal bile acid-binding protein (I-BABP) is thought to play a crucial role in the enterohepatic circulation of bile acids, we investigated whether I-BABP gene expression could also be affected by PPAR. Indeed, treatment with the PPARalpha-PPARbeta/delta agonist bezafibrate led to the up-regulation of I-BABP mRNA levels in the human intestine-derived Caco-2 cells. Cotransfections of the reporter-linked human I-BABP promoter (hI-BABP-2769/+44) together with PPAR and RXR expression vectors demonstrated that the fibrate-mediated induction of the I-BABP gene is dependent on PPARalpha or PPARbeta/delta. Using progressive 5' deletions of the hI-BABP promoter and sequence analysis, we identified a putative PPAR-binding site located at the position -198 and -186 upstream of the transcription initiation site. Electrophoretic mobility shift assays showed that the PPAR/RXR heterodimer can specifically bind to this PPRE-like motif. The deletion of the PPRE within the hI-BABP promoter abolished the PPAR-mediated transactivation in transient transfection assays. The regulation of the I-BABP promoter by PPAR appears species-specific, as the mouse I-BABP promoter, which lacks a conserved PPRE, was not responsive to exogenous PPAR expression in the presence of bezafibrate. Our findings show that the I-BABP gene may be a novel target for PPAR in humans and further emphasize the role for PPAR in the control of bile acid homeostasis.

Comparison of efficacy of plant stanol ester and sterol ester: short-term and longer-term studies

Published data suggest that the cholesterol-lowering effect of dietary plant sterol esters is less marked in longer-term than in short-term studies, whereas plant stanol esters maintain their efficacy. To investigate this further, healthy subjects and patients with familial hypercholesterolemia (FH) receiving statins were randomized to receive plant sterol ester 1.6 g/day or plant stanol ester 1.6 g/day or 2.6 g/day for 2 months. There was no difference among the 3 groups in the pooled low-density lipoprotein (LDL)-lowering response of FH patients and healthy subjects, but the effect of plant sterol diminished at 2 months and was not significantly different from baseline. This was accompanied by increases in serum plant sterols and a significant decrease in 7alpha-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis, especially in FH patients not taking bile acid sequestrants. In contrast, plant stanol esters lowered significantly both LDL cholesterol and plant sterols at 2 months and had no effect on bile acid synthesis. Slight decreases in serum lipid-soluble antioxidants occurred with both plant sterol and stanol esters. Our findings suggest that absorption of dietary plant sterols downregulates bile acid synthesis, which attenuates their cholesterol-lowering efficacy. We conclude that plant stanol esters are preferable for the long-term management of hypercholesterolemia.

Efficacy and safety of high-density lipoprotein cholesterol-increasing compounds: a meta-analysis of randomized controlled trials

OBJECTIVES

The aim of this research was to estimate the efficacy and safety of current high-density lipoprotein cholesterol (HDL-C)-increasing drugs.

BACKGROUND

Epidemiologic evidence has shown that HDL-C is inversely related to coronary heart disease (CHD) risk. However, the evidence for reducing CHD risk by raising HDL-C is thin, predominantly due to the paucity of effective and safe HDL-increasing drugs.

METHODS

Randomized controlled trials with fibrates and niacin, published between 1966 through February 2004 (MEDLINE), were retrieved. Information on treatment, baseline characteristics, serum lipids, end points, and side-effects were independently abstracted by two authors using a standardized protocol.

RESULTS

Data from 53 trials (16,802 subjects) using fibrates and 30 trials (4,749 subjects) using niacin were included. Random-effects model showed 11% versus 10% reduction in total cholesterol, 36% versus 20% reduction in triglycerides, 8% versus 14% reduction in low-density lipoprotein cholesterol, and 10% versus 16% increase in HDL-C for fibrates and niacin, respectively. Apart from flushes in the niacin group, both fibrates and niacin were shown to be well-tolerated and safe. Fibrates reduced the risk for major coronary events by 25% (95% confidence interval 10% to 38%), whereas current available data for niacin indicate a 27% reduction.

CONCLUSIONS

Fibrates reduce major coronary events and increase HDL-C levels without significant toxicity. Niacin has a more potent effect on HDL-C levels, whereas data on cardiovascular event rate reduction are limited. Future studies need to evaluate whether additional HDL increase by fibrates or particularly newer niacin formulations on top of statin therapy translates into further event reduction in high-risk subjects, without significant toxicity.

Bile acid signaling to the nucleus: finding new connections in the transcriptional regulation of metabolic pathways

Recent findings indicate that the function of metabolically relevant genes is finely regulated at the level of gene transcription. Disturbances of these regulatory pathways often lead to metabolic unbalance and to the onset of socially relevant diseases, i.e. diabetes, metabolic syndrome, atherosclerosis and cardiovascular diseases. The ability of lipid metabolites, such as fatty acids and oxysterols, to signal to cells and tissues and to affect gene transcription by activating specific nuclear receptors has been known since several years. Bile acids have been known in the past as cholesterol end products, purely acting as detergents. Only recently new biological properties of bile acids as signaling molecules have been disclosed and appreciated. In this review, we will describe how bile acids can regulate their own synthesis and other metabolic pathways (i.e. glucose metabolism) by modulating gene transcription through multiple mechanisms. These findings also open new perspectives towards the exploitation of bile acid metabolism as a pharmacological target.

Effects of peroxisome proliferator-activated receptor α activation on pathways contributing to cholesterol homeostasis in rat hepatocytes

Peroxisome proliferator-activated receptor alpha (PPARalpha) activation by fibrates controls expression of several genes involved in hepatic cholesterol metabolism. Other genes could be indirectly controlled in response to changes in cellular cholesterol availability. To further understand how fibrates may affect cholesterol synthesis, we investigated in parallel the changes in the metabolic pathways contributing to cholesterol homeostasis in liver. Ciprofibrate increased HMG-CoA reductase and FPP synthase mRNA levels in rat hepatocytes, together with cholesterogenesis from [(14)C] acetate and [(3)H] mevalonate. The up-regulation observed in fenofibrate- and WY-14,643-treated mice was abolished in PPARalpha-null mice, showing an essential role of PPARalpha. Among the three sterol regulatory element-binding protein (SREBP) mRNA species, only SREBP-1c level was significantly increased. In ciprofibrate-treated hepatocytes, cholesterol efflux was decreased, in parallel with cholesteryl ester storage and bile acids synthesis. As expected, AOX expression was strongly induced, supporting evidence of the peroxisome proliferation. Taken together, these results show that fibrates can cause cholesterol depletion in hepatocytes, possibly in part as a consequence of an important requirement of cholesterol for peroxisome proliferation, and increase cholesterogenesis by a compensatory phenomenon afterwards. Such cholesterogenesis regulation could occur in vivo, in species responsive to the peroxisome proliferative effect of PPARalpha ligands.

Effects of plant stanol and sterol esters on serum phytosterols in a family with familial hypercholesterolemia including a homozygous subject

We studied the concentrations and ratios to cholesterol of noncholesterol sterols reflecting absorption (eg, campesterol) or synthesis (eg, lathosterol) of cholesterol off and on plant sterol and stanol ester spreads in serum and in different lipoproteins of a family with familial hypercholesterolemia, including heterozygous parents receiving no treatment and their homozygous offspring undergoing long-term treatment with statins and apheresis. Serum cholesterol levels were similar in the homozygous and heterozygous individuals, but the concentrations of sterols reflecting cholesterol absorption were as much as 10 times greater in the homozygous child than in the heterozygous parents, whereas the respective markers of cholesterol synthesis only tended to be higher. About 70% of squalene in the homozygous individual (60% in the heterozygous family members) and 85% to 90% of noncholesterol sterols (60%-80% in the heterozygous subjects) were transported by low-density lipoprotein. The ratios of absorption sterols to cholesterol were higher in high-density lipoprotein (HDL) than in very low-density lipoprotein (VLDL), whereas those of synthesis markers and plant stanols were highest in VLDL. The ratios of absorption sterols in serum were mostly lower than those in HDL but higher than in VLDL, whereas the ratios of synthesis sterols in serum were lower than they were in VLDL. Both spreads reduced serum total cholesterol by about 14% in the heterozygous family members and 9% in the homozygous individual. The sterol ester spread increased serum plant sterol concentrations (eg, campesterol in the homozygous family member increased from 5 to 9 mg/dL) and the ratios to cholesterol, but the stanol ester spread decreased them. Plant sterol esters seemed to similarly decrease serum cholesterol in this family with familial hypercholesterolemia, but the clinical role of increased plant sterol concentrations, almost doubled in the LDL of homozygous individuals, is not known.

Synthesis and absorption markers of cholesterol in serum and lipoproteins during a large dose of statin treatment

BACKGROUND

Serum contains noncholesterol sterols, which are reliable markers of cholesterol metabolism, but their presence and importance in different lipoproteins have been insufficiently studied.

MATERIALS AND METHODS

Serum and lipoprotein cholesterol precursors squalene, cholestanol, desmosterol and lathosterol (markers of cholesterol synthesis) and cholestanol and plant sterols (markers of cholesterol absorption), and absorption efficacy and absolute synthesis of cholesterol were studied at baseline and during 6-month atorvastatin (80 mg day(-1)) treatment by the sterol balance technique in men with type 2 diabetes.

RESULTS

At baseline, approximately 14% of serum squalene was transported by VLDL, 12% by IDL, 40% by LDL and 30% by HDL. The respective values for the noncholesterol sterols were approximately 8, 4, 61 and 26%. The squalene to cholesterol ratios were highest in VLDL and IDL, those of cholestanol, desmosterol and absorption marker sterols were gradually higher, and that of lathosterol lower from VLDL to HDL. Atorvastatin reduced LDL cholesterol by approximately 50%, decreased the absolute cholesterol synthesis and turnover by approximately 40%, but increased significantly the fractional and mass absorption of cholesterol. In accordance with the fecal data, the ratios of the precursor sterols to cholesterol were reduced (-50%), but those of squalene (+48%) and the absorption sterols increased (e.g. 2.6-fold for sitosterol) similarly in each lipoprotein, but progressively from VLDL to HDL.

CONCLUSIONS

Effective lowering of LDL cholesterol by large dose of statin is associated with decreased synthesis and turnover of cholesterol and increased fractional and mass absorption of cholesterol. These changes are detectable by noncholesterol sterols in serum and in different lipoprotein fractions.

Serum noncholesterol sterols during inhibition of cholesterol synthesis by statins

We studied changes in serum cholestanol and plant sterols (indexes of cholesterol absorption) and cholesterol precursors (indexes of cholesterol synthesis) in response to cholesterol reduction by way of 1 year's treatment with atorvastatin (n = 102) and simvastatin (n = 105) treatments in patients with coronary heart disease. Serum cholesterol levels and ratios of the precursor sterols to cholesterol after 1 year of treatment were reduced in proportion to the pretreatment values (33% +/- 1% by simvastatin and 36% +/- 1% by atorvastatin; P <.01 for difference between groups) for cholesterol; the respective reductions in the precursor sterol:cholesterol ratios were also higher with atorvastatin (50% +/- 2% for lathosterol) than with simvastatin (42% +/- 1%; P <.01 between groups), but the ratio of squalene to cholesterol was increased (17% +/- 5%, P <.001) by atorvastatin. Plant sterol concentrations were gradually increased by atorvastatin but decreased initially by simvastatin. However, their ratios with respect to cholesterol were increased by as much as 82% with atorvastatin and by as much as 39% with simvastatin. In conclusion, effective inhibition of cholesterol synthesis and subsequent reduction in serum cholesterol levels by statins lead to increases in serum plant-sterol levels, probably as a result of reduced biliary secretion and enhanced absorption of these sterols. Because serum plant sterols have been claimed to be involved in the early development of atherosclerosis, the question arises whether continuously increasing serum plant sterols during long-term statin treatment should be prevented by cholesterol malabsorption (eg, by plant stanol ester consumption), especially in subjects with high baseline plant sterol values and effective sterol absorption.

Acute effects of weight reduction on cholesterol metabolism in obese type 2 diabetes

BACKGROUND

Weight reduction in obese type 2 diabetes increases the absorption efficiency of cholesterol and serum plant sterol levels from baseline. However, there is no information on the effects of acute restriction of calories and lack of dietary cholesterol and plant sterols on serum cholesterol precursor and plant sterols and on cholesterol metabolism. Thus, 10 obese (BMI>30 kg/m(2)) type 2 diabetes subjects consumed very low energy diet virtually free of cholesterol, cholestanol and plant sterols for 3 months.

METHODS

Serum sterols were measured with gas-liquid chromatography.

RESULTS

Body weight was reduced by 15.5+/-1.7 kg (p<0.001), serum cholesterol by 21+/-3%, triglycerides 45+/-5%, glucose 23+/-3%, insulin 59+/-5% and HbAIc by 8+/-2%, whereas serum sex hormone binding globulin increased by 108+/-25% (p<0.05-0.001 for all). Serum desmosterol and lathosterol to cholesterol ratios (indicators of cholesterol synthesis) were significantly decreased by 20% suggesting that cholesterol synthesis was suppressed. Serum squalene ratio was unchanged. Despite lack of dietary plant sterols and cholestanol, serum campesterol and sitosterol ratios (indicators of cholesterol absorption efficiency) only tended to decrease, whereas serum cholestanol ratio, also an absorption indicator, was increased by 33+/-3% (p<0.001), and its ratios to campesterol and sitosterol were increased by 60% and 31%, suggesting that sterol absorption efficiency might have been increased and their turnover reduced.

CONCLUSIONS

In obese type 2 diabetes, restriction of calories and dietary sterols improved markedly control of diabetes, decreased serum cholesterol precursor sterols suggesting that cholesterol synthesis was decreased, but only tended to decrease serum values of plant sterols probably due to their release from the adipose tissues associated with their impaired turnover.

Fibrates suppress bile acid synthesis via peroxisome proliferator-activated receptor-alpha-mediated downregulation of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase expression

Fibrates are hypolipidemic drugs that affect the expression of genes involved in lipid metabolism by activating peroxisome proliferator-activated receptors (PPARs). Fibrate treatment causes adverse changes in biliary lipid composition and decreases bile acid excretion, leading to an increased incidence of cholesterol gallstones. In this study, we investigated the effect of fibrates on bile acid synthesis. Ciprofibrate and the PPARalpha agonist Wy14,643 decreased bile acid synthesis in cultured rat hepatocytes and suppressed cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities, paralleled by a similar reduction of the respective mRNAs. Treatment of rats with 0.05% (wt/wt) ciprofibrate decreased cholesterol 7alpha-hydroxylase enzyme activity and mRNA. The functional involvement of PPARalpha in the suppression of both enzymes was proven with the use of PPARalpha-null mice. In wild-type mice, ciprofibrate reduced cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase enzyme activities and mRNA. The decrease in mRNA of both enzymes is regulated transcriptionally and posttranscriptionally, respectively, resulting in a decline in the output of fecal bile acids (-45%) and a 3-fold increase in fecal cholesterol secretion. These effects were completely abolished in PPARalpha-null mice. A decreased bile acid production by PPARalpha-mediated downregulation of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase may contribute to the increased risk of gallstone formation after fibrate treatment.

Statin-fibrate combination therapy

BACKGROUND

Precautionary warnings for severe myopathy and rhabdomyolysis from the coadministration of statins and fibrates have been well publicized. However, a recent cerivastatin labeling change made the combined use with fibric acid derivatives a contraindication. Practical recommendations for clinicians who care for patients with refractory mixed hyperlipidemia are needed.

OBJECTIVE

To provide recommendations for clinicians in the treatment of refractory mixed hyperlipidemia.

DATA SOURCES

A comprehensive MEDLINE (1966-July 2000) and bibliographic search was performed.

DATA SYNTHESIS

Thirty-six published clinical trials and 29 case reports involving combination therapy with hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors and fibric acid derivatives regarding the occurrence of rhabdomyolysis or myopathy were reviewed. The literature review demonstrated that combination therapy with a statin and fibrate increases the risk of muscle damage, with an incidence of 0.12%. Risk factors that predispose patients to myopathy caused by combination statin-fibrate therapy include increased age, female gender, renal or liver disease, diabetes, hypothyroidism, debilitated status, surgery, trauma, excessive alcohol intake, and heavy exercise.

CONCLUSIONS

Combination therapy with a statin and fibrate offers significant therapeutic advantage for the treatment of severe or refractory mixed hyperlipidemia. Although such a combination does increase the risk of myopathy, with an incidence of approximately 0.12%, this small risk of myopathy rarely outweighs the established morbidity and mortality benefits of achieving lipid goals. Nevertheless, a higher incidence of myopathy has been reported with statin monotherapy. When monotherapy with a statin fails to control mixed hyperlipidemia, combination therapy may be considered. Niacin may be added before a fibrate is considered, as it appears to have less risk of myopathy. Statin-fibrate combination therapy must be undertaken cautiously and only after careful risk-benefit analysis. Patient counseling on the risks and warning signs of myopathy is extremely important.

Noncholesterol sterols and cholesterol lowering by long-term simvastatin treatment in coronary patients: relation to basal serum cholestanol

Coronary patients with low baseline ratios of serum cholestanol and plant sterols to cholesterol (indicating low cholesterol absorption) but not those with high ratios (high absorption) experienced reduced recurrences of coronary events during simvastatin treatment in the Scandinavian Simvastatin Survival Study. Thus, in the present study, serum cholesterol, its precursor sterols (reflecting cholesterol synthesis), plant sterols (campesterol and sitosterol), and cholestanol were measured before and during a 5-year period of placebo treatment (n=433) and simvastatin treatment (n=434) in patients from a subgroup of the Scandinavian Simvastatin Survival Study to determine whether changes in cholesterol synthesis and serum levels were related to cholesterol absorption. Serum cholesterol level was unchanged, the ratios of cholesterol precursor sterols to cholesterol were decreased, and the ratios of plant sterols to cholesterol were increased in relation to increasing baseline ratios of cholestanol quartiles. The latter predicted 5-year ratios and simvastatin-induced reductions of the precursor sterols, with the lowering of the ratios (cholesterol synthesis reduction) being almost twice higher in the lowest versus the highest quartile. The ratios of plant sterols, especially campesterol, to cholesterol were markedly increased during simvastatin treatment, mostly in subjects with the highest baseline cholestanol quartiles. Simvastatin reduced serum cholesterol more (P=0.003) in the lowest versus the highest cholestanol quartile during the 5-year treatment period. The results show for the first time that baseline cholesterol metabolism, measured by serum noncholesterol sterols, predicts the effectiveness of simvastatin in reducing cholesterol synthesis and serum levels of cholesterol. The drug suppresses the synthesis of cholesterol markedly more effectively in subjects with high than with low baseline synthesis but reduces respective serum cholesterol levels less markedly than synthesis. Subjects with high cholesterol absorption and low synthesis may need a combination therapy to lower more effectively their serum cholesterol levels and prevent an increase in the levels of plant sterols.

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.

Long-term safety and efficacy of combination gemfibrozil and HMG-CoA reductase inhibitors for the treatment of mixed lipid disorders

BACKGROUND

Combinations of gemfibrozil and a 3-hydroxy-3-methylglutaryl (HMG) coenzyme A reductase inhibitor show promise in treating mixed lipid abnormalities. However, concern regarding the risk of myopathy and hepatic toxicity has limited the use of this combination. To determine the long-term safety and efficacy of this combination, we prospectively identified all patients placed on a combination of gemfibrozil and any HMG reductase inhibitor.

METHODS

Pravastatin, simvastatin, fluvastatin, lovastatin, or atorvastatin at incremental doses was combined with gemfibrozil (600 mg twice daily). Lipid profiles, creatine kinase levels, and aminotransferase levels were monitored. Two hundred fifty-two patients with established atherosclerosis receiving combination therapy for a mean of 2.36 +/- 1.52 years spanning a total of 593.6 patient-years were monitored.

RESULTS

In 148 patients, gemfibrozil was started before an HMG was added. The pretreatment total cholesterol level fell from 222 +/- 34 mg/dL to 181 +/- 26 mg/dL (P <.001) on combination therapy. HDL cholesterol level rose from 30 +/- 5 mg/dL to 36 +/- 7 mg/dL (P <.01), triglyceride level fell from 361 +/- 141 mg/dL to 212 +/- 101 mg/dL (P <.03). The ratio of total cholesterol to HDL fell from 7.6 +/- 1. 7 to 5.3 +/- 1.6 (P <.001). In 104 patients an HMG was begun before gemfibrozil was added. Pretreatment total cholesterol level fell from 246 +/- 54 mg/dL to 192 +/- 40 mg/dL on combination therapy (P <.01). HDL level rose from 33 +/- 9 mg/dL to 38 +/- 9 mg/dL (P <.03) and triglyceride level fell from 314 +/- 183 mg/dL to 183 +/- 93 mg/dL (P <.001). The ratio of total cholesterol to HDL fell from 7.9 +/- 3.6 to 5.2 +/- 1.4 (P <.001). In both groups the lipid profile on combination therapy was significantly better than that obtained on single-agent therapy. One episode of myopathy (0.4%) and one episode of aminotransferase level elevation (0.4%) of greater than 3 times upper limit of normal occurred. Both resolved with cessation of therapy without consequence.

CONCLUSIONS

Combinations of gemfibrozil and an HMG, compared with either agent alone, results in improved long-term control of lipid abnormalities in mixed lipid disorders. The low incidence of toxicity permits the use of combination therapy in patients at high risk of atherosclerotic complications.

The sedimentable sterols in gallstone patients before and during ursodeoxycholic acid and simvastatin treatments

BACKGROUND

The insoluble material in supersaturated bile is prerequisite for the formation of gallstones. We therefore studied the biliary precipitable and soluble cholesterol and noncholesterol sterols, including the cholesterol precursor sterols (including lanosterol and lathosterols), and the plant sterols campesterol and sitosterol, and cholestanol, which usually reflect cholesterol synthesis and absorption, respectively, before and after a 6-month treatment with ursodeoxycholic acid (UCDA), 15.4 +/- 4 mg/kg/day (standard error of the mean) or simvastatin (40 mg/day) in 21 patients with cholesterol gallstones, to obtain further information about the factors contributing to the formation of gallstones.

METHODS

The sediment and supernatant fractions of duodenal bile samples were separated by ultracentrifugation and analyzed with gas-liquid chromatography.

RESULTS

At the base line (n = 21) 50% +/- 3% of biliary cholesterol and a variable amount of the noncholesterol sterols (from 14% of lanosterol to 62% of cholestanol) were in the sediment fraction. The pattern of the noncholesterol sterols in the sediment resembled that of gallstones described previously. At base line body mass index was positively related to the percentage of precipitable cholesterol in bile (r = 0.46, P < 0.05), and the serum sitosterol proportion negatively related to the molar percentage of biliary cholesterol and positively to that of bile acids (r = -0.46 and r = 0.50, P < 0.05 for both). UDCA decreased the precipitable percentage of cholesterol from 46% to 31% (P < 0.03) and simvastatin from 57% to 42% (P = 0.05). Both drugs also decreased the precipitable percentages of lathosterols and cholestanol while increasing that of lanosterol. In relation to cholesterol, the sediment to supernatant ratios of all methylsterols were increased, whereas those of polar lathosterols tended to decrease during UDCA treatment.

CONCLUSIONS

Patients with high body mass index have more precipitable cholesterol in their bile. Although both UDCA and simvastatin decreased the precipitable cholesterol, the bile still contained one-third of its cholesterol in the sedimentable form.

Gemfibrozil reduces non-high-density lipoprotein cholesterol in exogenously hypercholesterolemic (ExHC) rats fed a high-cholesterol diet

Gemfibrozil is a widely used drug prescribed to elevate serum high-density lipoprotein (HDL) cholesterol levels and lower triacylglycerols. The present study was done to determine if the drug would alleviate hypercholesterolemia in exogenously hypercholesterolemic (ExHC) rats. In the drug-treated ExHC rats, the serum non-HDL cholesterol levels were lowered and the ratio of the non HDL cholesterol to serum triacylglycerols was decreased to the extent seen in the drug-treated SD rats. Liver cholesterol and triacylglycerols were lowered in the drug-treated rats. There was also an increase in fecal excretion of neutral sterols and bile acids, particularly chenodeoxycholic and beta-muricholic acids. The drug elevated cholesterol 7 alpha-hydroxylase activity and mRNA abundance and acyl-CoA cholesterol acyltransferase activity in the liver, but did not influence low-density lipoprotein receptor mRNA level in the liver. Thus, gemfibrozil is effective in alleviating hypercholesterolemia in exogenously hypercholesterolemic rats, by partitioning hepatic cholesterol into biliary excretion.

Effects of pravastatin on cholesterol metabolism of cholesterol-fed heterozygous WHHL rabbits

1. We administered the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor pravastatin at a daily dose of 1 mg kg(-1) body weight to cholesterol-fed (0.03%) heterozygous Watanabe heritable hyperlipidaemic rabbits, an animal model for heterozygous familial hypercholesterolaemia. 2. After 12 months of cholesterol treatment, immunohistochemistry with the monoclonal antibody 9D9 was used to detect hepatic low density lipoprotein (LDL) receptors, which were quantified by densitometry. In addition we determined LDL receptor mRNA by competitive reverse transcriptase polymerase chain reaction. The cholesterol precursor lathosterol and the plant sterol campesterol were analysed by gas-liquid chromatography. 3. The drug reduced total plasma cholesterol levels by 51% (P=0.04), when compared to the control group. Unexpectedly, hepatic LDL receptor density and mRNA showed no significant differences between the groups. Total plasma levels of lathosterol and campesterol also revealed no significant differences between the groups, if expressed relative to plasma cholesterol. 4. The findings suggest that mechanisms other than induced hepatic LDL receptors are responsible for the cholesterol-lowering effect of pravastatin in this animal model. We propose a reduced cholesterol absorption efficiency compatible with similar campesterol levels between both groups observed in our study.

Cholesterol metabolism and serum and biliary noncholesterol sterols in gallstone patients during simvastatin and ursodeoxycholic acid treatments

Effects of long-term high-dose ursodeoxycholic acid (UDCA) and simvastatin treatments on cholesterol metabolism and biliary lipid compositions were compared in patients with cholesterol gallstones. Absorption and synthesis of cholesterol, serum and biliary noncholesterol sterols and lipids were determined in 14 patients randomized to UDCA (23-25 mg/kg/d) or simvastatin (40 mg/d) for 1 year. Simvastatin reduced serum low-density lipoprotein cholesterol by 55%, and UDCA, by 9%. Cholesterol absorption was decreased (35%) by UDCA, but nonsignificantly increased by simvastatin (P < .05 for difference of changes caused by the two drugs). Whole-body synthesis and biliary output of cholesterol were both significantly decreased only by UDCA. In addition, UDCA inconsistently increased the proportions of serum and biliary precursor sterols of cholesterol, known to reflect cholesterol synthesis, but did not affect their biliary secretions. Simvastatin, however, dramatically reduced serum and also biliary cholesterol precursor sterol proportions and their biliary secretions and increased proportions of serum and biliary plant sterols and cholestanol, known to reflect cholesterol absorption, but had no effect on their biliary secretion. Only UDCA significantly decreased the molar percentage of cholesterol, the lithogenic index, and the cholesterol/phospholipid (CH/ PL) ratio in bile, whereas both treatments inconsistently decreased the vesicular CH/PL ratio (P < .07 in both groups). It is concluded that both drugs decreased serum cholesterol and inhibited cholesterol synthesis, but had a differing influence on precursor sterols and the absorption of cholesterol. UDCA had more beneficial effects than simvastatin on the antilithogenic properties of bile.