Cholesterol absorption inhibitor Ezetimibe blocks uptake of oxidized LDL in human macrophages

Myeloid-specific deficiency of pregnane X receptor decreases atherosclerosis in LDL receptor-deficient mice

The pregnane X receptor (PXR) is a nuclear receptor that can be activated by numerous drugs and xenobiotic chemicals. PXR thereby functions as a xenobiotic sensor to coordinately regulate host responses to xenobiotics by transcriptionally regulating many genes involved in xenobiotic metabolism. We have previously reported that PXR has pro-atherogenic effects in animal models, but how PXR contributes to atherosclerosis development in different tissues or cell types remains elusive. In this study, we generated an LDL receptor-deficient mouse model with myeloid-specific PXR deficiency (PXR^ΔMyeLDLR^-/-) to elucidate the role of macrophage PXR signaling in atherogenesis. The myeloid PXR deficiency did not affect metabolic phenotypes and plasma lipid profiles, but PXR^ΔMyeLDLR^-/- mice had significantly decreased atherosclerosis at both aortic root and brachiocephalic arteries compared with control littermates. Interestingly, the PXR deletion did not affect macrophage adhesion and migration properties, but reduced lipid accumulation and foam cell formation in the macrophages. PXR deficiency also led to decreased expression of the scavenger receptor CD36 and impaired lipid uptake in macrophages of the PXR^ΔMyeLDLR^-/- mice. Further, RNA-Seq analysis indicated that treatment with a prototypical PXR ligand affects the expression of many atherosclerosis-related genes in macrophages in vitro. These findings reveal a pivotal role of myeloid PXR signaling in atherosclerosis development and suggest that PXR may be a potential therapeutic target in atherosclerosis management.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

Ezetimibe suppresses development of liver tumors by inhibiting angiogenesis in mice fed a high-fat diet

Nonalcoholic steatohepatitis (NASH) is a common cause of liver cirrhosis and hepatocellular carcinoma (HCC). However, effective therapeutic strategies for preventing and treating NASH‐mediated liver cirrhosis and HCC are lacking. Cholesterol is closely associated with vascular endothelial growth factor (VEGF), a key factor that promotes HCC. Recent reports have demonstrated that statins could prevent HCC development. In contrast, we have little information on ezetimibe, an inhibitor of cholesterol absorption, in regards to the prevention of NASH‐related liver cirrhosis and HCC. In the present study, a steatohepatitis‐related HCC model, hepatocyte‐specific phosphatase and tensin homolog (Pten)‐deficient (Pten^Δhep) mice were fed a high‐fat (HF) diet with/without ezetimibe. In the standard‐diet group, ezetimibe did not reduce the development of liver tumors in Pten^Δhep mice, in which the increase of serum cholesterol levels was mild. Feeding of a HF diet increased serum cholesterol levels markedly and subsequently increased serum levels of VEGF, a crucial component of angiogenesis. The HF diet increased the number of VEGF‐positive cells and vascular endothelial cells in the tumors of Pten^Δhep mice. Kupffer cells, macrophages in the liver, increased VEGF expression in response to fat overload. Ezetimibe treatment lowered cholesterol levels and these angiogenetic processes. As a result, ezetimibe also suppressed inflammation, liver fibrosis and tumor growth in Pten^Δhep mice on the HF diet. Tumor cells were highly proliferative with HF‐diet feeding, which was inhibited by ezetimibe. In conclusion, ezetimibe suppressed development of liver tumors by inhibiting angiogenesis in Pten^Δhep mice with hypercholesterolemia.

Potential of Vitamin E Deficiency, Induced by Inhibition of α-Tocopherol Efflux, in Murine Malaria Infection

Although epidemiological and experimental studies have suggested beneficial effects of vitamin E deficiency on malaria infection, it has not been clinically applicable for the treatment of malaria owing to the significant content of vitamin E in our daily food. However, since α-tocopherol transfer protein (α-TTP) has been shown to be a determinant of vitamin E level in circulation, manipulation of α-tocopherol levels by α-TTP inhibition was considered as a potential therapeutic strategy for malaria. Knockout studies in mice indicated that inhibition of α-TTP confers resistance against malaria infections in murines, accompanied by oxidative stress-induced DNA damage in the parasite, arising from vitamin E deficiency. Combination therapy with chloroquine and α-TTP inhibition significantly improved the survival rates in murines with malaria. Thus, clinical application of α-tocopherol deficiency could be possible, provided that α-tocopherol concentration in circulation is reduced. Probucol, a recently found drug, induced α-tocopherol deficiency in circulation and was effective against murine malaria. Currently, treatment of malaria relies on the artemisinin-based combination therapy (ACT); however, when mice infected with malarial parasites were treated with probucol and dihydroartemisinin, the beneficial effect of ACT was pronounced. Protective effects of vitamin E deficiency might be extended to manage other parasites in future.

Aberrant de novo cholesterogenesis: Clinical significance and implications

Human cells can acquire cholesterol from the circulation but also have the ability to synthesize it via de novo cholesterogenesis (DC). Cholesterol absorption and de novo cholesterogenesis are the key processes that modulate cholesterol homeostasis in the human body. The endogenous biosynthesis of cholesterol substantially contributes to the whole-body cholesterol pool. Additionally, dysregulation of this pathway is associated with diverse medical conditions. The present review focuses on our current understanding of the cholesterogenic pathway and the various different factors regulating this pathway. It also highlights dysregulation of this pathway in various physiological and pathological conditions including cardiovascular diseases, type II diabetes, obesity and viral infections.

Effect of anti-hyperlipidemia drugs on the alpha-tocopherol concentration and their potential for murine malaria infection

The current preventions of malaria are protection against mosquito bites and taking chemoprophylactic anti-malarial drugs. However, drug therapies are usually associated with adverse events and emergency of drug-resistant malaria parasites. Previous study showed that host plasma alpha-tocopherol deficiency enhanced resistance against malaria infection in mice. Here, we report a new prevention strategy against malaria by using anti-hyperlipidemia drugs, ezetimibe, berberine, cholestyramine, and probucol to modify the host plasma alpha-tocopherol concentration. The drugs were mixed with diet and fed to C57BL/6J mice for 2 weeks. Although all drugs reduced plasma alpha-tocopherol concentration after 2 weeks of feeding, probucol-treated mice showed 90 % reduction and it was the lowest alpha-tocopherol concentration among the four drugs. Ezetimibe, berberine, and combination of ezetimibe and berberine pretreatment for 2 weeks were not effective against infection of Plasmodium yoelii XL17, a lethal strain, for survival and parasitemia in mice. Two-week pretreatment and 1-week treatment after infection of cholestyramine had also no effect on malaria infection. Survival rates of cholestyramine, ezetimibe, and/or berberine treated mice were 0-22 %. However, probucol caused significant decrease in parasitemia and increased in mice survival following 2-week pretreatment and 1-week treatment after infection. All control mice died while all probucol treated mice survived during the course of infection. Thus, probucol which reduced plasma alpha-tocopherol concentration was effective in enhancing the host to resist malaria infection in mice. Our finding indicates that plasma alpha-tocopherol reducing drugs like probucol might be a candidate for beneficial prevention strategy for travelers from malaria-free area.

NMR crystallography of ezetimibe co-crystals

An efficient, simplified protocol for solvent-drop assisted co-crystal preparation of ezetimibe (a drug for the treatment of primary hypercholesterolemia) with both imidazole and l-proline has been derived. The structures of the white powders were successfully solved via "NMR crystallography" combining solid-state NMR, powder X-ray diffraction and DFT chemical shift computations. Detailed insights into the likely crystallization mechanism were obtained from competition experiments, where efficient co-crystallization was feasible using ezetimibe monohydrate as precursor indicating that the crystal water acts as "molecular catalyst". It was also found that co-crystallization of imidazole is favored over l-proline, thus suggesting a clear preference of neutral hydrogen bonds compared to charge-assisted motifs.

Ezetimibe-mediated protection of vascular smooth muscle cells from cholesterol accumulation through the regulation of lipid metabolism-related gene expression

BACKGROUND

Ezetimibe is a potent inhibitor of Niemann-Pick type C1-Like 1 and has been approved for the treatment of hypercholesterolemia. Our preliminary study showed that ezetimibe promotes cholesterol efflux from vascular smooth muscle cells (VSMCs). Our aim was to investigate the cellular mechanisms underlying the ezetimibe actions.

METHODS AND RESULTS

Rat VSMCs were converted to foam cells by incubation with cholesterol:methyl-β-cyclodextrin. The intracellular free cholesterol, total cholesterol, and the ratio of cholesteryl ester to total cholesterol were decreased after the incubation of VSMCs with different concentrations of ezetimibe (3, 10, 30, and 30 μmol/l) or treated with 30 μmol/l of ezetimibe for different time periods (6, 12, 24, and 48 h). Our results also showed that the expression of caveolin-1, liver X receptor α, and ATP-binding cassette transporter ABCA1 was enhanced, but the expression of nSREBP-1c was decreased in a concentration- and time-dependent manner. RNA interference was used to determine the roles of caveolin-1 and SREBP-1 in the lipid-lowering effect of ezetimibe. The results showed that caveolin-1 was involved in the regulation of intracellular cholesterol content, and the expression of caveolin-1 was repressed by SREBP-1.

CONCLUSION

The present study indicates that ezetimibe protects VSMCs from cholesterol accumulation by regulating the expression of lipid metabolism-related genes.

Lipid-lowering treatment and inflammatory mediators in diabetes and chronic kidney disease

BACKGROUND

Inflammation may contribute to the high cardiovascular risk in diabetes mellitus (DM) and chronic kidney disease (CKD). Monocyte chemoattractant protein-1 (MCP-1) facilitates the recruitment of monocytes into atherosclerotic lesions and is involved in diabetic nephropathy. Interferon gamma (IFNγ) is important in atherosclerosis and increases the synthesis of chemokines including MCP-1. Lipid-lowering treatment (LLT) with statins may have anti-inflammatory effects, and ezetimibe cotreatment provides additional cholesterol lowering.

METHODS

After a placebo run-in period, the effects of simvastatin alone (S) or simvastatin + ezetimibe (S+E) were compared in a randomized, double-blind, cross-over study on inflammatory parameters. Eighteen DM patients with estimated glomerular filtration rate (eGFR) 15-59 mL/min × 1·73 m(2) (CKD stages 3-4) (DM-CKD) and 21 DM patients with eGFR > 75 mL/min (DM only) were included.

RESULTS

At baseline, monocyte chemoattractant protein 1 (MCP-1) (P = 0·03), IFNγ (P = 0·02), tumour necrosis factor-α (TNFα) (P < 0·01) and soluble vascular adhesion molecule (sVCAM) (P = 0·001) levels were elevated in DM-CKD compared with DM-only patients. LLT with S and S+E reduced MCP-1 levels (P < 0·01 by anova) and IFNγ levels (P < 0·01) in DM-CKD patients but not in DM-only patients. Reductions were most pronounced with the combination treatment.

CONCLUSIONS

DM patients with CKD stages 3-4 had increased inflammatory activity compared with DM patients with normal GFR. Lipid-lowering treatment decreased the levels of MCP-1 and IFNγ in DM patients with concomitant CKD, which may be beneficial with regard to the progression of both atherosclerosis and diabetic nephropathy.

The effect of ezetimibe, administered alone or in combination with simvastatin, on lymphocyte cytokine release in patients with elevated cholesterol levels

OBJECTIVE

Studies assessing the extra-lipid effects of ezetimibe have provided contrasting results. In the present study, we compared the effects of ezetimibe and simvastatin, administered alone or in combination, on the secretory function of human lymphocytes, systemic inflammation and endothelial function in subjects with elevated cholesterol levels.

METHODS

A prospective study involving a group of 178 ambulatory patients with isolated hypercholesterolaemia who were randomly assigned in a double-blind fashion to 90days of treatment with ezetimibe (10mg), simvastatin (40mg), ezetimibe (10mg) plus simvastatin (4mg) or placebo. A total of 170 patients completed the study.

MAIN OUTCOME MEASURES

Lymphocyte cytokine release and plasma levels of high-sensitivity C-reactive protein (hsCRP) and intercellular adhesion molecule 1 (ICAM-1).

RESULTS

Although both drugs reduced lymphocyte release of tumour necrosis factor-α, interferon-γ and interleukin-2 in a lipid-independent manner, only the effect of simvastatin was statistically significant (P<0.001). This lymphocyte-suppressing effect, which was accompanied by a decrease in plasma levels of hsCRP and ICAM-1 (P<0.001), was strongest in patients receiving both simvastatin and ezetimibe. There were no differences in lymphocyte-suppressing, systemic anti-inflammatory and endothelial protective effects of simvastatin between insulin-resistant and insulin-sensitive subjects, whereas the effects of ezetimibe and the combined treatment were greater in the former group of patients (P<0.01 and P<0.001, respectively).

CONCLUSIONS

The results of this study indicate that simvastatin is superior to ezetimibe in producing lymphocyte-suppressing, systemic anti-inflammatory and endothelial protective effects in patients with elevated cholesterol levels. Hypercholesterolaemic patients with high cardiovascular risk may receive the greatest benefits from concomitant treatment with a statin and ezetimibe.

Impact of hypertriglyceridemia on endothelial dysfunction during statin ± ezetimibe therapy in patients with coronary heart disease

Despite the use of statin therapy and achieving the target for low-density lipoprotein cholesterol, a substantial number of coronary events are not prevented, and residual risk factors remain unsettled. Recently, ezetimibe has been shown to reduce not only low-density lipoprotein cholesterol but also triglyceride (TG) levels. The aim of this study was to investigate the associations of residual risk factors, mainly hypertriglyceridemia, with endothelial function during statin therapy in patients with coronary heart disease and examine the effect of ezetimibe add-on therapy. A total of 109 consecutive patients with coronary heart disease during statin therapy were enrolled. Lipid profile was measured and endothelial function was assessed by flow-mediated dilation (FMD) of the brachial artery in a fasting state. Next, 32 patients with high TG levels (≥150 mg/dl) were prospectively assigned to the ezetimibe add-on group or the no-ezetimibe group, and endothelial function was assessed after 3 months. Multivariate linear regression analysis demonstrated that serum TG and high-density lipoprotein cholesterol levels were independent determinants of percentage FMD (β = -0.210 and 0.208, respectively, p <0.05). In patients with high TG levels, ezetimibe add-on therapy significantly improved percentage FMD (from 3.3 ± 1.1% to 4.0 ± 1.1%, p <0.005), whereas no significant change was observed in the no-ezetimibe group. Moreover, the improvement in percentage FMD was significantly associated with reduction in serum TG levels (β = -0.387, p <0.05) independent of the change in serum low-density lipoprotein cholesterol levels. In conclusion, hypertriglyceridemia is independently associated with endothelial dysfunction in patients with coronary heart disease during statin therapy. Ezetimibe add-on therapy improves endothelial function in these high-risk populations.

Effects of lipid-lowering drugs on reverse cholesterol transport gene expressions in peripheral blood mononuclear and HepG2 cells

AIMS

The ATP-binding cassette transporters, ABCA1 and ABCG1, are LXR-target genes that play an important role in reverse cholesterol transport. We examined the effects of inhibitors of the cholesterol absorption (ezetimibe) and synthesis (statins) on expression of these transporters in HepG2 cells and peripheral blood mononuclear cells (PBMCs) of individuals with primary (and nonfamilial) hypercholesterolemia (HC).

MATERIALS & METHODS

A total of 48 HC individuals were treated with atorvastatin (10 mg/day/4 weeks) and 23 were treated with ezetimibe (10 mg/day/4 weeks), followed by simvastatin (10 mg/day/8 weeks) and simvastatin plus ezetimibe (10 mg of each/day/4 weeks). Gene expression was examined in statin- or ezetimibe-treated and control HepG2 cells as well as PBMCs using real-time PCR.

RESULTS

In PBMCs, statins and ezetimibe downregulated ABCA1 and ABCG1 mRNA expression but did not modulate NR1H2 (LXR-β) and NR1H3 (LXR-α) levels. Positive correlations of ABCA1 with ABCG1 and of NR1H2 with NR1H3 expressions were found in all phases of the treatments. In HepG2 cells, ABCA1 mRNA levels remained unaltered while ABCG1 expression was increased by statin (1.0-10.0 µM) or ezetimibe (5.0 µM) treatments. Atorvastatin upregulated NR1H2 and NR1H3 only at 10.0 µM, meanwhile ezetimibe (1.0-5.0 µM) downregulated NR1H2 but did not change NR1H3 expression.

CONCLUSION

Our findings reveal that lipid-lowering drugs downregulate ABCA1 and ABCG1 mRNA expression in PBMCs of HC individuals and exhibit differential effects on HepG2 cells. Moreover, they indicate that the ABCA1 and ABCG1 transcript levels were not correlated directly to LXR mRNA expression in both cell models treated with lipid-lowering drugs.

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.

Pleiotropic effects of ezetimibe: do they really exist?

Ezetimibe represents a new lipid lowering agent which inhibits cholesterol absorption. It effectively reduces low-density lipoprotein cholesterol when administered either alone or in combination with statins. However, its effect on cardiovascular mortality remains under question since it failed to demonstrate any significant changes in the primary endpoints of the recently published ENHANCE and SEAS studies. A possible explanation for this unsuccessful outcome is that ezetimibe lacks pleiotropic effects. This article aims to review the potential pleiotropic effects of the drug mainly on inflammation markers, lipoprotein subfractions and endothelial function.

Update on patented cholesterol absorption inhibitors

BACKGROUND

Atherosclerosis is one of the most life-threatening diseases primarily associated with hypercholesterolemia and is characterized by increased serum cholesterol level. Cholesterol originates from both its de novo synthesis within the hepatic cells and its absorption into the intestine in the form of dietary or bile cholesterol. Interventions influencing both of these processes are promising therapeutic options to lower the cholesterol level. Hydroxymethyl glutaryl-CoA reductase inhibitors, commonly known as statins, effectively block the rate determining step in the biosynthesis of cholesterol. Ezetimibe is the first new class of drugs used to treat hypercholesterolemia by inhibition of cholesterol absorption through Niemann Pick C1 Like 1 membrane of enterocytes. Therefore, combination therapy of ezetimibe and statins offers an efficacious new approach for the prevention and treatment of hypercholesterolemia.

OBJECTIVES

The present review focuses on updates on ezetimibe and patented profile of novel cholesterol absorption inhibitors followed by critical analysis of different targets such as cholesterol esterase inhibitors, bile acid transport inhibitors or phospholipase-A(2) inhibitors, etc.which play an important role in the lipid absorption.

CONCLUSION

The discovery of ezetimibe has opened a new door for the management of hyper-cholesterolemia in combination with statins. There are newer analogues that are under clinical trials, among which darapladib, FM-VP4 and A-002 are promising compounds.

Ezetimibe: cholesterol lowering and beyond

Ezetimibe is a cholesterol absorption inhibitor that blocks the intestinal absorption of both biliary and dietary cholesterol. It appears to exert its effect by blocking intestinal sterol transporters, specifically Niemann-Pick C1-like 1 proteins, thereby inhibiting the intestinal absorption of cholesterol, phytosterols and certain oxysterols. Ezetimibe monotherapy and in combination with statin therapy is primarily indicated for lowering LDL-cholesterol levels. In addition, it may favorably affect other parameters that could potentially further reduce atherosclerotic coronary heart disease risk, such as raising HDL-cholesterol and lowering levels of triglycerides, non-HDL-cholesterol, apolipoprotein B and remnant-like particle cholesterol. Further effects of ezetimibe include a reduction in circulating phytosterols and oxysterols and, when used in combination with statins, a reduction in high-sensitivity C-reactive protein. The clinical significance of the LDL-cholesterol lowering and other effects of ezetimibe is being evaluated in clinical outcome studies.

The pharmacologic elegance of inhibiting cholesterol absorption and synthesis while providing a homeostatic balance

The recent discoveries on the concerted role of several mechanisms involved in regulating the balance of body cholesterol highlight the role of intestinal absorption. Selective modulators of intestinal cholesterol absorption are available that offer a new pharmacologic approach to the modulation of total body cholesterol homeostasis and to a more effective reduction of low-density-lipoprotein cholesterol.

Combination therapy in cholesterol reduction: focus on ezetimibe and statins

Although widely used in lipid lowering therapy, HMG CoA reductase inhibitors (even when administered at high doses) are frequently insufficient to achieve guideline-recommended LDL-C goals for many patients with hypercholesterolemia in everyday clinical practice. Many patients do not achieve LDL-C goal on the initial dose of statin and the majority of these patients does not reach their goal after 6 months. As a consequence, a wide therapeutic gap exists between target LDL-C levels and those typically achieved in clinical practice. A recent and more effective therapeutic hypocholesterolemic strategy is to treat the two main sources of cholesterol simultaneously (production of cholesterol, mainly in the liver, and absorption of cholesterol in the intestine) with a complementary mechanism of action, by co-administering ezetimibe, a novel agent inhibiting cholesterol absorption, with a statin, which inhibits cholesterol production in the liver. Ezetimibe can be effectively and safely co-administered with any dose of any statin and, compared with the single inhibition of cholesterol production, afforded by statins alone, provides consistently greater reductions in LDL-C through dual inhibition of both cholesterol production and absorption. We summarize the pivotal role of both the liver and intestine in the overall balance of cholesterol in the body and describe the clinical impact and relevance of using ezetimibe either alone or co-administered with statins in controlling elevated levels of plasma LDL cholesterol.

Ezetimibe, a selective inhibitor of the transport of cholesterol

Niemann-Pick C1-like 1 (NPC1L1) has recently been identified and has been shown to have features of a plasma membrane transporter, including a secretion signal, 13 predicted transmembrane domains, extensive N-linked glycosylation sites and a sterol-sensing domain. It is highly expressed on the surface of absorptive jejunal enterocytes. NPC1L1 has been shown to be a direct target of ezetimibe, and an ezetimibe-sensitive pathway plays a role in intestinal cholesterol absorption. Ezetimibe-based therapy represents an exciting new area in the treatment of dyslipidemia.

Effects of ezetimibe and/or simvastatin on LDL receptor protein expression and on LDL receptor and HMG-CoA reductase gene expression: a randomized trial in healthy men

OBJECTIVE

The combination of simvastatin, an HMG-CoA reductase inhibitor, and ezetimibe, an inhibitor of Niemann-Pick C1-like 1 protein, decreases cholesterol synthesis and absorption and reduces circulating LDL-cholesterol concentrations. The molecular mechanisms underlying the pronounced lipid-lowering effects of this combination have not been fully elucidated in humans.

METHODS AND RESULTS

One center, prospective, randomized, parallel three-group study in 72 healthy men (mean age 32+/-9 years, mean body mass index 25.7+/-3.2 kg/m(2)). Each group of twenty-four subjects received a 14-day treatment with either ezetimibe (10mg/day), simvastatin (40 mg/day) or their combination. Lipid levels, the ratio of non-cholesterol sterols to cholesterol concentrations (used as markers of cholesterol synthesis and absorption), cell surface LDL receptor (LDLR) protein as well as LDLR and HMG-CoA reductase gene expression in mononuclear blood cells were measured at baseline and at the end of the study. LDL-C decreased in all groups. Simvastatin decreased, ezetimibe increased and their combination had no effect on HMG-CoA reductase activity. Simvastatin and the combination of ezetimibe and simvastatin increased the HMG-CoA reductase and LDLR gene expression while ezetimibe had no effect. The cell surface LDLR protein expression remained unchanged in all groups. The combination of ezetimibe and simvastatin increased the expression of the serine protease proprotein convertase subtilisin/kexin 9 (PCSK9), an enzyme shown to down-regulate LDLR protein levels.

CONCLUSIONS

The co-administration of ezetimibe and simvastatin abrogates the ezetimibe-induced increase in cholesterol synthesis and up-regulates the LDLR gene but not protein expression, an effect possibly mediated through a parallel upregulation of PCSK9 expression.

Role of 57-72 loop in the allosteric action of bile salts on pancreatic IB phospholipase A(2): regulation of fat and cholesterol homeostasis

Mono- and biphasic kinetic effects of bile salts on the pancreatic IB phospholipase A2 (PLA2) catalyzed interfacial hydrolysis are characterized. This novel phenomenon is modeled as allosteric action of bile salts with PLA2 at the interface. The results and controls also show that these kinetic effects are not due to surface dilution or solubilization or disruption of the bilayer interface where in the mixed-micelles substrate replenishment becomes the rate-limiting step. The PLA2-catalyzed rate of hydrolysis of zwitterionic dimyristoylphosphatidylcholine (DMPC) vesicles depends on the concentration and structure of the bile salt. The sigmoidal rate increase with cholate saturates at 0.06 mole fraction and changes little at the higher mole fractions. Also, with the rate-lowering bile salts (B), such as taurochenodeoxycholate (TCDOC), the initial sigmoidal rate increase at lower mole fraction is followed by nearly complete reversal to the rate at the pre-activation level at higher mole fractions. The rate-lowering effect of TCDOC is not observed with the (62-66)-loop deleted DeltaPLA2, or with the Naja venom PLA2 that is evolutionarily devoid of the loop. The rate increase is modeled with the assumption that the binding of PLA2 to DMPC interface is cooperatively promoted by bile salt followed by allosteric k(cat)(*)-activation of the bound enzyme by the anionic interface. The rate-lowering effect of bile salts is attributed to the formation of a specific catalytically inert E(*)B complex in the interface, which is noticeably different than the 1:1 EB complex in the aqueous phase. The cholate-activated rate of hydrolysis is lowered by hypolidemic ezetimibe and guggul extract which are not interfacial competitive inhibitors of PLA2. We propose that the biphasic modulation of the pancreatic PLA2 activity by bile salts regulates gastrointestinal fat metabolism and cholesterol homeostasis.

The role of the Niemann-Pick C1-like 1 protein in the subcellular transport of multiple lipids and their homeostasis

PURPOSE OF REVIEW

In the past 2 years the Niemann-Pick C1-like 1 protein has rapidly emerged as a key regulator of intestinal cholesterol absorption. This review covers the limited number of published reports to develop a hypothesis of the potential function of Niemann-Pick C1-like 1 protein and outlines questions that should be addressed in future studies.

RECENT FINDINGS

Considerable disagreement regarding the potential function and subcellular location of Niemann-Pick C1-like 1 protein has complicated interpretation of published results and evaluation of their biologic significance. Recent reports suggest, however, that Niemann-Pick C1-like 1 protein plays a key role in modulating the subcellular fate of multiple lipids including cholesterol and sphingolipids. In addition, this function may require Niemann-Pick C1-like 1 protein to move between different cellular locations.

SUMMARY

This paper proposes a model of Niemann-Pick C1-like 1 protein function based on available data and on knowledge of its close relative and homologue the Niemann-Pick C1 protein, whose precise function, albeit still elusive, is more extensively characterized. It also raises new questions with respect to Niemann-Pick C1-like 1 protein function and discusses potential future directions.