Pravastatin and lovastatin similarly reduce serum cholesterol and its precursor levels in familial hypercholesterolaemia

Interindividual variability in the cholesterol-lowering effect of supplementation with plant sterols or stanols

Low-density lipoprotein cholesterol (LDL-C) plays a causal role in atherosclerosis. One way to reduce LDL-C levels is to inhibit cholesterol absorption. Plant sterols and stanols compete with cholesterol for absorption in the intestine and induce an average decrease in LDL-C by 5% to 15% in a dose-dependent manner, but not in all individuals. This review focuses on the interindividual variability in response to dietary supplementation with plant sterols and stanols. Dietary plant sterols and stanols have no significant effects on LDL-C in substantial numbers of individuals. Higher responses, in absolute value and percentage of LDL-C, are observed in individuals with higher cholesterol absorption and a lower rate of cholesterol synthesis. Some data provide evidence of the influence of genetics on the response to plant sterols and stanols. Further studies in large populations are required to extend these conclusions about genetic influences.

Influence of previous statin therapy on cholesterol-lowering effect of ezetimibe

BACKGROUND AND OBJECTIVES

The inhibition of cholesterol absorption by ezetimibe increases cholesterol synthesis. The effect of inhibition of cholesterol synthesis on cholesterol absorption is controversial. The influence of these interactions on cholesterol levels is unknown. We investigated on the extent to which cholesterol levels were affected by the reaction of one pathway to the inhibition of the other pathway.

SUBJECTS AND METHODS

This case-controlled study enrolled 198 patients who needed cholesterol-lowering drugs. Ezetimibe (10 mg) was administered to the patients with (n=58) and without on-going statin therapy (n=58). Simvastatin (20 mg) was administered to the patients treated with (n=41) and without ezetimibe (n=41).

RESULTS

Ezetimibe without statin lowered the total cholesterol by 13.3±8.8% (p<0.001) and the low density lipoprotein-cholesterol (LDL-C) by 18.7±15.3% (p<0.001). Ezetimibe added to statin decreased the total cholesterol by 21.1±7.7% (p<0.001) and the LDL-C by 29.9±12.6% (p<0.001). The total cholesterol and LDL-C were reduced more by ezetimibe in patients with statin therapy than in those without statin therapy (p<0.001 and p<0.001, respectively). The differences in the effect of simvastatin on total cholesterol and LDL-C between the patients with and without ezetimibe showed borderline significance (p=0.10 and p=0.055, respectively).

CONCLUSION

A prior inhibition of cholesterol synthesis by statin enhanced the effect of ezetimibe on total cholesterol and LDL-C by 7.8% and 11.2%, respectively. This finding suggests that ezetimibe increased cholesterol synthesis, resulting in a significant elevation of cholesterol levels.

Model selection criterion for causal parameters in structural mean models based on a quasi-likelihood

Structural mean models (SMMs) have been proposed for estimating causal parameters in the presence of non-ignorable non-compliance in clinical trials. To obtain a valid causal estimate, we must impose several assumptions. One of these is the correct specification of the structural model. Building on Pan's work (2001, Biometrics 57, 120-125) on developing a model selection criterion for generalized estimating equations, we propose a new approach for model selection of SMMs based on a quasi-likelihood. We provide a formal model selection criterion that is an extension of Akaike's information criterion. Using subset selection of baseline covariates, our method allows us to understand whether the treatment effect varies across the available baseline covariate levels, and/or to quantify the treatment effect on a specific covariates level to target specific individuals to maximize treatment benefit. We present simulation results in which our method performs reasonably well compared to other testing methods in terms of both the probability of selecting the correct model and the predictive performances of the individual treatment effects. We use a large randomized clinical trial of pravastatin as a motivation.

Effects of ezetimibe added to statin therapy on markers of cholesterol absorption and synthesis and LDL-C lowering in hyperlipidemic patients

OBJECTIVE

Statins inhibit cholesterol synthesis but can upregulate cholesterol absorption, with higher doses producing larger effects. Ezetimibe inhibits cholesterol absorption but also upregulates synthesis. We tested whether ezetimibe added to on-going statin therapy would be most effective in lowering LDL-cholesterol (LDL-C) in subjects on high-potency statins and whether these effects would be related to alterations in cholesterol absorption (β-sitosterol) and synthesis (lathosterol) markers.

METHODS

Hypercholesterolemic subjects (n = 874) on statins received ezetimibe 10 mg/day. Plasma lipids, lathosterol, and β-sitosterol were measured at baseline and on treatment. Subjects were divided into low- (n = 133), medium- (n = 582), and high- (n = 159) statin potency groups defined by predicted LDL-C-lowering effects of each ongoing statin type and dose (reductions of ~20-30%, ~31-45%, or ~46-55%, respectively).

RESULTS

The high-potency group had significantly lower baseline lathosterol (1.93 vs. 2.58 vs. 3.17 μmol/l; p < 0.001) and higher baseline β-sitosterol values (6.21 vs. 4.58 vs. 4.51 μmol/l, p < 0.001) than medium-/low-potency groups. Ezetimibe treatment in the high-potency group produced significantly greater reductions from baseline in LDL-C than medium-/low-potency groups (-29.1% vs. -25.0% vs. -22.7%; p < 0.001) when evaluating unadjusted data. These effects and group differences were significantly (p < 0.05) related to greater β-sitosterol reductions and smaller lathosterol increases. However, LDL-C reduction differences between groups were no longer significant after controlling for placebo effects, due mainly to modest LDL-C lowering by placebo in the high-potency group.

CONCLUSION

Patients on high-potency statins have the lowest levels of cholesterol synthesis markers and the highest levels of cholesterol absorption markers at baseline, and the greatest reduction in absorption markers and the smallest increases in synthesis markers with ezetimibe addition. Therefore, such patients may be good candidates for ezetimibe therapy if additional LDL-C lowering is needed.

Phytosterols and phytosterolemia: gene-diet interactions

Phytosterol intake is recommended as an adjunctive therapy for hypercholesterolemia, and plant sterols/stanols can reduce cholesterol absorption at the intestinal lumen through the Niemann-Pick C1 Like 1 (NPC1L1) transporter pathway by competitive solubilization in mixed micelles. Phytosterol absorption is of less magnitude than cholesterol and is preferably secreted in the intestinal lumen by ABCG5/G8 transporters. Therefore, plasma levels of plant sterols/stanols are negligible compared with cholesterol, under an ordinary diet. The mechanisms of cholesterol and plant sterols absorption and the whole-body pool of sterols are discussed in this chapter. There is controversy about treatment with statins inducing further increase in plasma non-cholesterol sterols raising concerns about the safety of supplementation of plant sterols to such drugs. In addition, increase in plant sterols has also been reported upon consumption of plant sterol-enriched foods, regardless of other treatments. Rare mutations on ABCG5/G8 transporters affecting cholesterol/non-cholesterol extrusion, causing sitosterolemia with xanthomas and premature atheroslerotic disease are now known, and cholesterol/plant sterols absorption inhibitor, ezetimibe, emerges as the drug that reduces phytosterolemia and promotes xanthoma regression. On the other hand, common polymorphisms affecting the NPC1L1 transporter can interfere with the action of ezetimibe. Gene-diet interactions participate in this intricate network modulating the expression of genetic variants on specific phenotypes and can also affect the individual response to the hypolipidemic treatment. These very interesting aspects promoted a great deal of research in the field.

Effect of statins on noncholesterol sterol levels: implications for use of plant stanols and sterols

Normal serum contains small amounts of noncholesterol sterols, including those reflecting cholesterol absorption and those that are markers of cholesterol synthesis. Absorption marker sterols include serum plant sterols, whereas cholesterol precursor sterols correlate with whole-body synthesis of cholesterol. Thus, serum noncholesterol sterols, and especially their ratios to cholesterol, can be used to evaluate the major features of cholesterol metabolism (ie, synthesis and absorption). Statin treatment reduces serum cholesterol precursors but increases serum plant sterols severalfold, especially in subjects with high-absorption marker sterol levels indicative of efficient cholesterol and sterol absorption in general. Statin therapy is most effective in subjects with high serum cholesterol precursor levels. In subjects with high-absorption sterol markers, dietary cholesterol absorption inhibition (eg, with plant stanol and sterol ester margarine) needs to be combined with a statin to achieve effective serum cholesterol reduction. However, whereas dietary plant stanol esters reduce statin-induced elevations of serum plant sterol levels, serum plant sterol levels remain elevated during dietary plant sterol ester consumption. The clinical implication of high serum plant sterol levels is under active investigation.

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.

Xuezhikang decreases serum lipoprotein(a) and C-reactive protein concentrations in patients with coronary heart disease

BACKGROUND

Increased serum lipoprotein(a) [Lp(a)] and high-sensitivity C-reactive protein (hsCRP) concentrations are independent risk factors for coronary heart disease (CHD). Xuezhikang, an extract of cholestin, effectively lowers fasting cholesterol and triglyceride concentrations. We studied whether xuezhikang lowered Lp(a) and hsCRP concentrations.

METHODS

We randomly divided 60 CHD patients into two groups to receive xuezhikang (1200 mg daily) or placebo for 6 weeks. The fasting hsCRP concentration and the postprandial changes of serum lipid concentrations at 2, 4, and 6 h after a high-fat meal (800 calories; 50 g of fat) were measured before and after the 6-week protocol.

RESULTS

The two groups had similar baseline fasting lipid and hsCRP concentrations. The postprandial triglyceride and Lp(a) concentrations were significantly increased (P <0.05). After 6 weeks, the fasting and postprandial lipid concentrations decreased significantly in the xuezhikang group, accompanied by a significant reduction in fasting hsCRP concentration (P <0.001). The placebo group had no significant change in lipid concentrations, whereas the fasting serum hsCRP concentration was reduced significantly (P <0.05). The reduction in hsCRP was closely related to the changes in fasting Lp(a) concentration (r = 0.402; P <0.05) and triglyceride area under the curve (r = 0.441; P <0.001).

CONCLUSIONS

Xuezhikang effectively decreased fasting Lp(a) and postprandial triglyceride concentrations, which were associated with reductions of fasting hsCRP concentrations in CHD patients.

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.

Erythrocyte membrane cholesterol/phospholipid changes and hemorheological modifications in familial hypercholesterolemia treated with lovastatin

Fourteen patients with familial hypercholesterolemia treated with lovastatin (40 mg/day) for three months were studied to find out whether the expected changes in plasma lipids are accompanied by modifications in the lipid composition of the erythrocyte membrane and whether these in turn induce changes in the rheological behavior of the red blood cell. Our results demonstrate the efficacy of lovastatin in reducing the plasma concentration of cholesterol and LDL cholesterol. The changes observed in the plasma lipids correlate with a significant decrease in the cholesterol/phospholipid ratio of the red blood cell membrane, from 1.19 +/- 0.19 in a basal situation to 0.92 +/- 0.23 (p < 0.01) at the end of treatment. These changes in the lipid composition of the cell are statistically related to a decrease in erythrocyte aggregability and an improvement in blood filterability, which means beneficial change in the patients' hemorheological situation.

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

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

Effective lovastatin therapy in elderly hypercholesterolemic patients — an antioxidative impact?

The effect of 3 months lovastatin therapy on serum lipids, apolipoproteins, alpha-tocopherol and red cell membrane fatty acid pattern was assessed in twelve elderly ambulatory patients (mean age 70.9+/-8.0 years) with hypercholesterolemia type IIa according to Fredrickson. After a run-in period of 4 weeks without drug therapy, the patients were given a daily dose of 20 mg lovastatin. The treatment resulted in statistically significant decreases in mean serum low density lipoprotein cholesterol (LDL-CH, -34%), in the atherogenic index LDL-CH/HDL-CH (-35%) and in the concentration of apolipoprotein B (-26%). No change in the vitamin E status, as related to plasma total lipids, was observed during the 3 months of therapy. The fatty acid pattern of phospholipids from red cell membranes showed an increase in linoleic acid metabolites and a decrease in the precursor linoleic acid, indicating an induction of fatty acid desaturases by lovastatin. In addition, an increase in the plasmalogen portion of erythrocyte membrane phospholipids was exhibited by increases in the proportion of fatty aldehyde dimethyl acetals (DMA) in the fatty acid pattern. The plasmalogens increase may counteract the slow but consistent decrease in their concentration in red cell membranes and human aortas with increasing donor age and in arteriosclerosis. Since plasmalogens may function as physiological antioxidants, the observed increase in DMA concentration might reflect a previously unrecognized antioxidative principle of a lovastatin therapy.

Cholesterol absorption and synthesis during pravastatin, gemfibrozil and their combination

The study evaluates cholesterol metabolism off and on treatment with pravastatin (P), gemfibrozil (G) and their combination (PG) in 38 middle-age hyperlipidemic primary care patients with serum cholesterol > 6 mmol/l and serum triglycerides < 4 mmol/l after a low-fat low-cholesterol diet. The subjects were randomized to P (40 mg/g), G (1200 mg/day), PG (40 + 1200 mg/day) or placebo for 12 weeks. We analyzed serum lipids, apolipoproteins A-I, B and E, serum cholesterol precursors (markers of cholesterol synthesis), serum plant sterols and cholestanol (markers of cholesterol absorption) and cholesterol metabolism by the sterol balance technique and cholesterol absorption efficiency. P alone or in combination with G lowered apoprotein E concentration, and serum cholesterol levels by inhibiting cholesterol synthesis measured by the precursor/cholesterol proportions with inconsistent change in fecal output of cholesterol. G alone decreased bile acid synthesis and increased biliary cholesterol secretion which were associated with reduced cholesterol absorption efficiency and the serum plant sterol and cholestanol proportions, and increased synthesis of cholesterol as measured both by the sterol balance technique and the precursor sterol proportions. A combination of PG also lowered LDL cholesterol similarly but triglyceride-rich lipoproteins significantly more than P alone, and otherwise inhibited the changes caused by G in cholesterol metabolism except that the precursor sterol proportions still indicated reduced cholesterol synthesis. Overall, the changes of the cholesterol precursor proportions were negatively related to that of cholesterol absorption efficiency and positively to that of cholesterol synthesis. The respective plant sterol and cholestanol values correlated oppositely to cholesterol absorption efficiency and synthesis. Serum precursor sterols reflected changes in cholesterol synthesis more sensitively than the sterol balance technique, even though only the latter method can quantitate cholesterol synthesis.