The molecular mechanisms underlying the reduction of LDL apoB-100 by ezetimibe plus simvastatin

The combination of ezetimibe, an inhibitor of Niemann-Pick C1-like 1 protein (NPC1L1), and an HMG-CoA reductase inhibitor decreases cholesterol absorption and synthesis. In clinical trials, ezetimibe plus simvastatin produces greater LDL-cholesterol reductions than does monotherapy. The molecular mechanism for this enhanced efficacy has not been defined. Apolipoprotein B-100 (apoB-100) kinetics were determined in miniature pigs treated with ezetimibe (0.1 mg/kg/day), ezetimibe plus simvastatin (10 mg/kg/day), or placebo (n = 7/group). Ezetimibe decreased cholesterol absorption (-79%) and plasma phytosterols (-91%), which were not affected further by simvastatin. Ezetimibe increased plasma lathosterol (+65%), which was prevented by addition of simvastatin. The combination decreased total cholesterol (-35%) and LDL-cholesterol (-47%). VLDL apoB pool size decreased 26%, due to a 35% decrease in VLDL apoB production. LDL apoB pool size decreased 34% due to an 81% increase in the fractional catabolic rate, both of which were significantly greater than monotherapy. Combination treatment decreased hepatic microsomal cholesterol (-29%) and cholesteryl ester (-65%) and increased LDL receptor (LDLR) expression by 240%. The combination increased NPC1L1 expression in liver and intestine, consistent with increased SREBP2 expression. Ezetimibe plus simvastatin decreases VLDL and LDL apoB-100 concentrations through reduced VLDL production and upregulation of LDLR-mediated LDL clearance.     

Changes in cholesterol absorption and cholesterol synthesis caused by ezetimibe and/or simvastatin in men

This study evaluates changes in cholesterol balance in hypercholesterolemic subjects following treatment with an inhibitor of cholesterol absorption or cholesterol synthesis or coadministration of both agents. This was a randomized, double blind, placebo-controlled, four-period crossover study to evaluate the effects of coadministering 10 mg ezetimibe with 20 mg simvastatin (ezetimibe/simvastatin) on cholesterol absorption and synthesis relative to either drug alone or placebo in 41 subjects. Each treatment period lasted 7 weeks. Ezetimibe and ezetimibe/simvastatin decreased fractional cholesterol absorption by 65% and 59%, respectively (P < 0.001 for both relative to placebo). Simvastatin did not significantly affect cholesterol absorption. Ezetimibe and ezetimibe/simvastatin increased fecal sterol excretion (corrected for dietary cholesterol), which also represents net steady state cholesterol synthesis, by 109% and 79%, respectively (P < 0.001). Ezetimibe, simvastatin, and ezetimibe/simvastatin decreased plasma LDL-cholesterol by 20, 38, and 55%, respectively. The coadministered therapy was well tolerated. The decreases in net cholesterol synthesis and increased fecal sterol excretion yielded nearly additive reductions in LDL-cholesterol for the coadministration of ezetimibe and simvastatin.     

Delineation of molecular changes in intrahepatic cholesterol metabolism resulting from diminished cholesterol absorption

The absorption of cholesterol by the small intestine is a major route for the net entry of cholesterol into the body and can therefore affect the plasma low density lipoprotein-cholesterol (LDL-C) concentration. These studies used ezetimibe, a potent inhibitor of cholesterol absorption, to delineate the biochemical and molecular changes in intrahepatic metabolism and biliary lipid secretion when there is a major reduction in chylomicron cholesterol delivery to the liver. In female LDL receptor (LDLR)-deficient (LDLR-/-) mice fed a basal diet containing ezetimibe (0-10 mg/day/kg body weight), cholesterol absorption was reduced up to 91%, fecal neutral sterol excretion was increased up to 4.7-fold, and plasma total cholesterol concentrations decreased by up to 18%. Blocking cholesterol absorption prevented the accumulation of very low density lipoproteins and LDL in the circulation of LDLR-/- mice fed a lipid-rich diet. In female LDLR+/+ mice fed the lipid-rich diet with ezetimibe, the relative mRNA level for the LDLR in the liver was 2-fold greater than in matching mice given the lipid-rich diet alone. We conclude that in the mouse the reduction in plasma LDL-C levels induced by blocking cholesterol absorption reflects both a diminished rate of LDL-C production and a modest increase in hepatic LDLR expression.     

VAP II analysis of lipoprotein subclasses in mixed hyperlipidemic patients on treatment with ezetimibe/simvastatin and fenofibrate

This analysis evaluates the effects on lipoprotein subfractions and LDL particle size of ezetimibe/simvastatin with or without coadministration of fenofibrate in patients with mixed hyperlipidemia. This multicenter, double-blind, placebo-controlled, parallel-group study included 611 patients aged 18-79 years randomized in 1:3:3:3 ratios to one of four 12 week treatment groups: placebo; ezetimibe/simvastatin 10/20 mg/day; fenofibrate 160 mg/day; or ezetimibe/simvastatin 10/20 mg/day + fenofibrate 160 mg/day. At baseline and study endpoint, cholesterol associated with VLDL, intermediate density lipoprotein (IDL), LDL, and HDL subfractions was quantified using the Vertical Auto Profile II method. LDL particle size was determined using segmented gradient gel electrophoresis. Whereas fenofibrate reduced cholesterol mass within VLDL and IDL, and shifted cholesterol from dense LDL subfractions into the more buoyant subfractions and HDL, ezetimibe/simvastatin reduced cholesterol mass within all apolipoprotein B-containing particles without significantly shifting the LDL particle distribution profile. When administered in combination, the effects of the drugs were complementary, with more-pronounced reductions in VLDL, IDL, and LDL, preferential loss of more-dense LDL subfractions, and increased HDL, although the effects on most lipoprotein subfractions were not additive. Thus, ezetimibe/simvastatin + fenofibrate produced favorable effects on atherogenic lipoprotein subclasses in patients with mixed hyperlipidemia.     

Ezetimibe inhibits the incorporation of dietary oxidized cholesterol into lipoproteins

Oxidized cholesterol is present in significant quantities in the typical Western diet. When ingested, oxidized cholesterol is absorbed by the small intestine and incorporated into both chylomicrons and LDL, resulting in LDL that is more susceptible to further oxidation. Feeding studies in animal models and epidemiological studies in humans have suggested that oxidized cholesterol in the diet increases the development of atherosclerosis. In this study, we determined the effect of ezetimibe, a drug that inhibits small intestinal absorption of cholesterol, on the levels of oxidized cholesterol in the serum after a test meal containing oxidized cholesterol. We demonstrate that ezetimibe, 10 mg per day for 1 month, markedly reduced the levels (50% decrease) of oxidized cholesterol in the serum after feeding a test meal containing either alpha-epoxy cholesterol or 7-keto cholesterol, two of the predominant oxidized cholesterols found in the diet. Moreover, the decrease in oxidized cholesterol in the serum was attributable to a decrease in the incorporation of dietary oxidized cholesterol into both chylomicrons and LDL. Because there was no decrease in postprandial triglyceride levels, we conclude that this decrease in oxidized cholesterol levels in the serum is attributable to decreased absorption and not to enhanced clearance. Whether this decrease in oxidized cholesterol absorption prevents or delays the development of atherosclerosis remains to be determined.     

Reduction of cholesterol absorption by dietary oleinate and fish oil in African green monkeys.

To determine whether diets enriched in monounsaturated or n-3 fatty acids cause a reduction in cholesterol absorption relative to those more enriched in saturated fatty acids, we measured cholesterol absorption in 18 African green monkeys fed diets enriched in lard, oleinate (oleic acid-rich safflower oil), or fish oil at two levels of dietary cholesterol (0.05 vs. 0.77 mg/kcal). All animals were initially challenged with the lard, high cholesterol diet to ascertain their responsiveness to dietary cholesterol. Based on the results of this challenge, low versus high responders were equally distributed in assignation to the low (n = 6) and high (n = 12) cholesterol regimens. Within each level of dietary cholesterol animals consumed all three dietary fats in random sequences during three experimental phases each lasting 9-12 months with a monkey chow washout period between each phase, so that each animal served as its own control. During each dietary phase measurements of plasma lipids and cholesterol absorption were performed. The animals fed the higher versus lower level of dietary cholesterol had significantly higher plasma total cholesterol and low density lipoprotein (LDL) cholesterol concentrations and lower percentage cholesterol absorption; high density lipoprotein (HDL) cholesterol levels were not affected by the level of dietary cholesterol. Dietary fish oil resulted in a 20-30% reduction (P less than 0.01) in total plasma and LDL cholesterol and a 30-40% reduction (P less than 0.01) in HDL cholesterol concentrations compared to lard and oleinate regardless of the level of dietary cholesterol. At the high level of cholesterol intake, the oleinate and fish oil diets resulted in significantly lower percentage cholesterol absorption compared to the lard fat diet (35 +/- 2%, 34 +/- 3%, 41 +/- 4%, respectively). At the lower level of dietary cholesterol, percentage cholesterol absorption values were higher than those at the high cholesterol intake (45-52% vs. 34-41%) but were not affected by the type of dietary fat. There was a significant positive correlation between plasma LDL cholesterol concentrations and percentage cholesterol absorption for the oleinate and lard diets at the high level of dietary cholesterol and a significant inverse association between plasma HDL cholesterol and percentage cholesterol absorption. We conclude that the type of dietary fat can influence cholesterol absorption in African green monkeys and that oleinate and fish oil reduce cholesterol absorption relative to lard when a high amount of cholesterol (0.77 mg/kcal) is present in the diet.     

Blockade of cholesterol absorption by ezetimibe reveals a complex homeostatic network in enterocytes

Enterocyte cholesterol homeostasis reflects aggregated rates of sterol synthesis, efflux, and uptake from plasma and gut lumen. Cholesterol synthesis and LDL uptake are coordinately regulated by sterol regulatory element-binding proteins (SREBP), whereas sterol efflux is regulated by liver X receptors (LXR). How these processes are coordinately regulated in enterocytes, the site of cholesterol absorption, is not well understood. Here, we treat mice with ezetimibe to investigate the effect of blocking cholesterol absorption on intestinal SREBPs, LXRs, and their effectors. Ezetimibe increased nuclear SREBP-2 8-fold. HMG-CoA reductase (HMGR) and LDL receptor (LDLR) mRNA levels increased less than 3-fold, whereas their protein levels increased 30- and 10-fold, respectively. Expression of inducible degrader of LDLR (IDOL), an LXR-regulated gene that degrades LDLRs, was reduced 50% by ezetimibe. Coadministration of ezetimibe with the LXR agonist T0901317 abolished the reduction in IDOL and prevented the increase in LDLR protein. Ezetimibe-stimulated LDLR expression was independent of proprotein convertase subtilisin/kexin type 9 (PSCK9), a protein that degrades LDLRs. To maintain cholesterol homeostasis in the face of ezetimibe, enterocytes boost LDL uptake by increasing LDLR number, and they boost sterol synthesis by increasing HMGR and other cholesterologenic genes. These studies reveal a hitherto undescribed homeostatic network in enterocytes triggered by blockade of cholesterol absorption.     

Inhibition of cholesterol absorption by the combination of dietary plant sterols and ezetimibe: effects on plasma lipid levels

Consumption of plant sterols and treatment with ezetimibe both reduce cholesterol absorption in the intestine. However, the mechanism of action differs between the two treatments, and the consequences of combination treatment are unknown. Therefore, we performed a double-blind, placebo-controlled, crossover study for the plant sterol component with open-label ezetimibe treatment. Forty mildly hypercholesterolemic subjects were randomized to the following treatments for 4 weeks each: 10 mg/day ezetimibe combined with 25 g/day control spread; 10 mg/day ezetimibe combined with 25 g/day spread containing 2.0 g of plant sterols; 25 g/day spread containing 2.0 g of plant sterols; and placebo treatment consisting of 25 g/day control spread. Combination treatment of plant sterols and ezetimibe reduced low density lipoprotein cholesterol (LDL-C) by 1.06 mmol/l (25.2%; P < 0.001) compared with 0.23 mmol/l (4.7%; P = 0.006) with plant sterols and 0.94 mmol/l (22.2%; P < 0.001) with ezetimibe monotherapy. LDL-C reduction conferred by the combination treatment did not differ significantly from ezetimibe monotherapy (-0.12 mmol/l or -3.5%; P = 0.13). Additionally, the plasma lathosterol-to-cholesterol ratio increased with all treatments. Sitosterol and campesterol ratios increased after plant sterol treatment and decreased upon ezetimibe and combination therapy. Our results indicate that the combination of plant sterols and ezetimibe has no therapeutic benefit over ezetimibe monotherapy in subjects with mild hypercholesterolemia.     

Does dietary magnesium modulate blood lipids?

In a randomized, single-blind, controlled study (400 patients aged 25-63 yr; 374 males, 26 females), 206 subjects were administered a magnesium-rich diet, and 194 subjects their usual diet, for 6 wk. Age, sex, body weight, hypertension, hyperlipidemia, smoking, obesity, diuretic therapy, and diabetes were comparable between the two groups, as were laboratory data at entry to the study. Intervention-group A received a significantly higher amount of dietary magnesium and potassium compared to group B, which received its usual diet. After 6 wk, there was a significant fall in total serum cholesterol (228.5 +/- 46.2 mg/dL), LDL cholesterol 146.5 +/- 75.5 mg/dL), and triglyceride (143.8 +/- 40.5 mg/dL) in group A compared to serum cholesterol (242.5 +/- 58.2 mg/dL), LDL cholesterol (157.0 +/- 78.4 mg/dL), and triglyceride (156.5 +/- 60.0 mg/dL) at entry to study, but no such changes in group-B subjects. HDL cholesterol showed a marginal mean decrease of 0.8 mg/dL in group B and a 2.5 mg/dL increase in group A. The changes in blood lipids were consistent with an increased intake of magnesium and with a rise in serum levels. Although a general blood-lipid-reducing effect of such a diet cannot be excluded, it is possible that dietary magnesium may have contributed to the reduction of total serum cholesterol, LDL cholesterol, and triglyceride, and the marginal rise in HDL cholesterol. More studies with longer follow-up periods are needed to confirm this observation.     

Effects of psyllium hydrophilic mucilloid on LDL-cholesterol and bile acid synthesis in hypercholesterolemic men.

The goal of the current study was to determine the mechanism of the hypocholesterolemic effect of psyllium using a randomized, double-blind, crossover design. Twenty males (age 44 +/- 4 yr, weight 79 +/- 10 kg) with moderate hypercholesterolemia (total 265 +/- 17 mg/dl, low density lipoprotein (LDL) 184 +/- 15 mg/dl) were studied at baseline (B) and after randomization to receive a 40-day course of 15 g/day of either psyllium (Ps) or placebo (Pl) (cellulose). After a washout period (11 +/- 2 days), subjects were crossed over to the other fiber treatment for an additional 40 days and restudied. Intestinal cholesterol absorption, cholesterol synthesis in isolated peripheral blood mononuclear cells, bile acid kinetics, gallbladder motility, and intestinal transit were measured at each study period. Psyllium lowered LDL cholesterol (x:184 (B), 169 (Ps), and 179 (Pl) mg/dl; Ps vs. B,Pl: P less than 0.004, P less than 0.02), decreased relative cholesterol absorption (x:51 (B), 45 (Ps), and 49 (Pl) %; Ps vs. B,Pl: P less than 0.03, P less than 0.03), did not alter absolute cholesterol absorption, and increased the fractional turnover of both chenodeoxycholic acid (x:0.176 (B), 0.203 (Ps), and 0.170 (Pl) day-1; Ps vs. B,Pl: P less than 0.0001, P less than 0.01) and cholic acid (x:0.303 (B), 0.411 (Ps), and 0.301 (Pl) d-1; Ps vs. B, Pl: P less than 0.006, P less than 0.002). Bile acid synthesis increased in subjects whose LDL cholesterol was lowered by more than 10% (Ps vs. B: 1304 +/- 489 vs 992 +/- 307 mumol/day, P less than 0.006; Ps vs. PI: 1304 +/- 489 vs. 914 +/- 321 mumol/day, P less than 0.0002). We conclude that psyllium lowers LDL cholesterol primarily via stimulation of bile acid synthesis.     

Intestinal cholesterol absorption in the chyluria model

Isotopic methods for the measurement of dietary cholesterol absorption were compared with the lymph cholesterol balance procedure in filarial chyluria patients. After a single intravenous injection of radioactive cholesterol, absorption was found to be 746 +/- 136 mg/day by method I, which is based upon the fecal endogenous neutral steroid mass measurement, and 471 +/- 135 mg/day by the simultaneously measured lymph/plasma ratio of cholesterol specific activity (dpm/mg). The corresponding value, determined as the difference between lymph cholesterol transport on a cholesterol-containing diet (1500 mg) and on a cholesterol-free diet, was 622 mg/day. When radioactive cholesterol (1487 mg/day) was fed daily to a second patient, absorption determined by isotopic fecal recovery (353 mg/day) matched that obtained by the lymph balance procedure (326 mg/day). Transudation of plasma cholesterol into the intestinal lymph, estimated by the single intravenous injection of radioactive beta-sitosterol, was independent of both the luminal content of plant sterols and the absorption of dietary cholesterol. The absorption of endogenous cholesterol was calculated by: 1) subtracting the cholesterol originating from plasma (transudation) together with the absorbed dietary cholesterol found in lymph from the total mass of cholesterol transported in lymph, and 2) the lymph balance method, i.e., after interrupting the endogenous cholesterol mucosal uptake by beta-sitosterol feeding (9 g/day) while on a cholesterol-free diet. Endogenous cholesterol was preferentially absorbed compared to dietary cholesterol, but there was no competition for absorption. The major portion of dietary cholesterol found in lymph was esterified, but esterification was not a prerequisite for absorption.     

Effect of ursodeoxycholic acid on cholesterol absorption and metabolism in humans

Qualitative and quantitative changes in intraluminal bile acid composition may alter cholesterol absorption and synthesis and LDL receptor expression. In a randomized crossover design outpatient study, 12 adults aged 24-36 years took 15 mg/kg/day ursodeoxycholic acid (UDCA) or no bile acid supplement (control) for 20 days while being fed a controlled diet (AHA Step II). A liquid meal of defined composition was then given and luminal samples collected. Cholesterol absorption and cholesterol fractional synthetic rate (FSR) were assessed by stable isotopic methods. With UDCA treatment, bile was enriched significantly (P < 0.0001) to 40.6 +/- 2.6% (mean +/- SEM) compared with 2.2 +/- 2.6% for controls. Regardless, plasma total, HDL, and LDL cholesterol were unchanged with UDCA treatment. Intraluminal cholesterol solubilized in the aqueous phase during the entire collection was decreased (P = 0.012) in UDCA-treated subjects (101.0 +/- 7.2 mg/ml/120 min) compared with controls (132.5 +/- 7.2 mg/ml/120 min.). Percent micellar cholesterol was increased in UDCA-treated versus controls after meal ingestion. No changes were found in cholesterol absorption, FSR, or LDL receptor mRNA with UDCA treatment compared with controls. Thus, despite marked enrichment in luminal bile with UDCA and decreased cholesterol solubilization, no differences in cholesterol absorption or metabolism are found when diet and genetic differences in absorption are carefully controlled.     

Intestinal absorption of calcium from yogurt in lactase-deficient subjects.

Fractional intestinal absorption of calcium (FACa) was measured using radioactive calcium and 200 mg of calcium carrier provided either by yogurt or by CaCl2 in 7 lactase-deficient (L(-] and 7 normal (L(+] subjects. During the control period prior to yogurt consumption, mean calcium intake was 819 mg per day in L(-) and 931 mg per day in L(+) subjects (NS). In both groups of subjects yogurt increased FACa from 20.8 +/- 3.9% to 26.9 +/- 7.2% (P = 0.065) in L(+) subjects and from 20.2 +/- 5.6% to 23.5 +/- 6.4% (P = 0.050) in L(-) subjects. The significant increase in FACa observed in L(-) subjects indicates that yogurt, which is an autodigesting source of lactose, does not impair calcium absorption. FACa increase could reflect the lower dietary calcium intake in L(-) subjects when compared with L(+) subjects, due to avoidance of milk and non-fermented dairy products which could cause intestinal discomfort. It is concluded that yogurt is a well-tolerated and efficient source of calcium in subjects with lactase deficiency.     

Lysosomal unesterified cholesterol content correlates with liver cell death in murine Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a multisystem disorder resulting from mutations in the NPC1 gene that encodes a protein involved in intracellular cholesterol trafficking. Significant liver dysfunction is frequently seen in patients with this disease. The current studies used npc1 mutant mice to investigate the association between liver dysfunction and unesterified cholesterol accumulation, a hallmark of NPC disease. Data from 92 npc1(-/-) mice (age range, 9-56 days) revealed a significant positive correlation between the plasma activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and whole liver cholesterol content. In 56 day old npc1(-/-) mice that had been fed from 35 days of age a rodent diet or the same diet containing either cholesterol (1.0%, w/w) or ezetimibe (a sterol absorption inhibitor; 0.0125%, w/w), whole liver cholesterol content averaged 33.5 +/- 1.1, 87.9 +/- 1.7, and 20.8 +/- 0.9 mg, respectively. Again, plasma ALT and AST activities were positively correlated with hepatic cholesterol content. In contrast, plasma transaminase levels remained in the normal range in npc1(+/+) mice, in which hepatic esterified cholesterol content had been increased by 72-fold by feeding a high-cholesterol, high-fat diet. These studies suggest that the late endosomal/lysosomal content of unesterified cholesterol correlates with cell damage in NPC disease.     

Identification and origins of neutral fecal sterols in adult Large White sows: occurrence of externally-secreted intestinal cholesterol

Cholesterol, the main neutral fecal sterol (54-84 p. 100) in adult Large White sows fed a controlled semi-purified diet containing 0.08 p. 100 cholesterol (500 g twice a day; 3 510 kcal/day), was partially converted into coprostanol (10-44 p. 100). Exceptionally, epicoprostanol was present, indicating a second pathway of bacterial cholesterol degradation. In this paper, the term "fecal cholesterol" is restricted to the sum of cholesterol + coprostanol. The contribution of fecal cholesterol to the bulk of neutral fecal sterols eliminated daily, averaged 97 +/- 1 p. 100. For a given dietary cholesterol intake of 80 mg per day, eliminated fecal cholesterol was estimated to be 392 +/- 47 mg/day and mean fecal cholesterol concentration 1.88 +/- 0.12 mg/g of stools. The various sources of fecal cholesterol were unabsorbed ingested cholesterol, cholesterol excreted from the plasma, and externally-secreted intestinal cholesterol, synthesized by the digestive tract, discharged into the lumen and not absorbed. The respective contributions of these different sources were as follows: unabsorbed dietary cholesterol 34 +/- 2 mg/day, excreted cholesterol 234 +/- 28 mg/day and externally-secreted cholesterol 125 +/- 23 mg/day.     

Aggravation of cholesterol induced hyperlipidemia by chronic vitamin C deficiency: experimental study in guinea pigs

Chronic vitamin C deficiency was induced in guinea pigs by restricting their vitamin C intake to 0.5 mg daily. This was just sufficient to prevent rapidly fatal scurvy and 55 per cent of the animals survived. In 16 weeks their serum ascorbic acid (SAA) fell to 0.16 +/- 0.06 mg/dl as compared to 0.73 +/- 0.11 in control animals receiving 5 mg vitamin C daily. There was a marked increase in serum cholesterol, LDL-cholesterol, VLDL-cholesterol, triglycerides and total lipids. HDL-cholesterol was, however, decreased resulting in a shift of the LDL/HDL ratio from 1.13 +/- 0.16 in the control to 5.91 +/- 1.70 in the low vitamin C group. Cholesterol feeding (100 mg/day) by itself lowered the SAA significantly, besides producing hyperlipidemia. When the vitamin C intake was reduced to only 0.5 mg/day, the effects of cholesterol feeding were exaggerated; the magnitude of hyperlipidemia was now significantly greater than with simple cholesterol feeding. The LDL/HDL ratio rose to 19.02 +/- 3.32 from 1.13 +/- 0.16 in the normal guinea pigs. Chronic vitamin C deficiency seems to affect the blood lipid profile unfavourably which could promote atherogenesis.     

Hepatic ABCG5/G8 overexpression reduces apoB-lipoproteins and atherosclerosis when cholesterol absorption is inhibited

We previously reported that liver-specific overexpression of ABCG5/G8 in mice is not atheroprotective, suggesting that increased biliary cholesterol secretion must be coupled with decreased intestinal cholesterol absorption to increase net sterol loss from the body and reduce atherosclerosis. To evaluate this hypothesis, we fed low density lipoprotein receptor-knockout (LDLr-KO) control and ABCG5/G8-transgenic (ABCG5/G8-Tg)xLDLr-KO mice, which overexpress ABCG5/G8 only in liver, a Western diet containing ezetimibe to reduce intestinal cholesterol absorption. On this dietary regimen, liver-specific ABCG5/G8 overexpression increased hepatobiliary cholesterol concentration and secretion rates (1.5-fold and 1.9-fold, respectively), resulting in 1.6-fold increased fecal cholesterol excretion, decreased hepatic cholesterol, and increased (4.4-fold) de novo hepatic cholesterol synthesis versus LDLr-KO mice. Plasma lipids decreased (total cholesterol, 32%; cholesteryl ester, 32%; free cholesterol, 30%), mostly as a result of reduced non-high density lipoprotein-cholesterol and apolipoprotein B (apoB; 36% and 25%, respectively). ApoB-containing lipoproteins were smaller and lipid-depleted in ABCG5/G8-TgxLDLr-KO mice. Kinetic studies revealed similar 125I-apoB intermediate density lipoprotein/LDL fractional catabolic rates, but apoB production rates were decreased 37% in ABCG5/G8-TgxLDLr-KO mice. Proximal aortic atherosclerosis decreased by 52% (male) and 59% (female) in ABCG5/G8-TgxLDLr-KO versus LDLr-KO mice fed the Western/ezetimibe diet. Thus, increased biliary secretion, resulting from hepatic ABCG5/G8 overexpression, reduces atherogenic risk in LDLr-KO mice fed a Western diet containing ezetimibe. These findings identify distinct roles for liver and intestinal ABCG5/G8 in modulating sterol metabolism and atherosclerosis.     

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.     

Quantifying effect of statins on low density lipoprotein cholesterol, ischaemic heart disease,and stroke: systematic review and meta-analysis

Objectives To determine by how much statins reduce serum concentrations of low density lipoprotein (LDL) cholesterol and incidence of ischaemic heart disease (IHD) events and stroke, according to drug, dose, and duration of treatment.Design Three meta-analyses: 164 short term randomised placebo controlled trials of six statins and LDL cholesterol reduction; 58 randomised trials of cholesterol lowering by any means and IHD events; and nine cohort studies and the same 58 trials on stoke.Main outcome measures Reductions in LDL cholesterol according to statin and dose; reduction in IHD events and stroke for a specified reduction in LDL cholesterol.Results Reductions in LDL cholesterol (in the 164 trials) were 2.8 mmol/l (60%) with rosuvastatin 80 mg/day, 2.6 mmol/l (55%) with atorvastatin 80 mg/day, 1.8 mmol/l (40%) with atorvastatin 10 mg/day, lovastatin 40 mg/day, simvastatin 40 mg/day, or rosuvastatin 5 mg/day, all from pretreatment concentrations of 4.8 mmol/l. Pravastatin and fluvastatin achieved smaller reductions. In the 58 trials, for an LDL cholesterol reduction of 1.0 mmol/l the risk of IHD events was reduced by 11% in the first year of treatment, 24% in the second year, 33% in years three to five, and by 36% thereafter (P < 0.001 for trend). IHD events were reduced by 20%, 31%, and 51% in trials grouped by LDL cholesterol reduction (means 0.5 mmol/l, 1.0 mmol/l, and 1.6 mmol/l) after results from first two years of treatment were excluded (P < 0.001 for trend). After several years a reduction of 1.8 mmol/l would reduce IHD events by an estimated 61%. Results from the same 58 trials, corroborated by results from the nine cohort studies, show that lowering LDL cholesterol decreases all stroke by 10% for a 1 mmol/l reduction and 17% for a 1.8 mmol/l reduction. Estimates allow for the fact that trials tended to recruit people with vascular disease, among whom the effect of LDL cholesterol reduction on stroke is greater because of their higher risk of thromboembolic stroke (rather than haemorrhagic stroke) compared with people in the general population.Conclusions Statins can lower LDL cholesterol concentration by an average of 1.8 mmol/l which reduces the risk of IHD events by about 60% and stroke by 17%.