NPC1L1: Evolution From Pharmacological Target to Physiological Sterol Transporter

Cholesin and GPR146 in Modulating Cholesterol Biosynthesis

BACKGROUND

Cholesterol homeostasis in the human body is a crucial process that involves a delicate balance between dietary cholesterol absorption in the intestine and de novo cholesterol synthesis in the liver. Both pathways contribute significantly to the overall pool of cholesterol in the body, influencing plasma cholesterol levels and impacting cardiovascular health. Elevated absorption of cholesterol in the intestines has a suppressive impact on the synthesis of cholesterol in the liver, serving to preserve cholesterol balance. Nonetheless, the precise mechanisms driving this phenomenon remain largely unclear.

SUMMARY

This review aimed to discuss the previously unrecognized role of cholesin and GPR146 in the regulation of cholesterol biosynthesis, providing a novel conceptual framework for understanding cholesterol homeostasis.

KEY MESSAGES

The discovery of cholesin, a novel protein implicated in the regulation of cholesterol homeostasis, represents a significant advancement in our understanding of cholesterol biosynthesis and its associated pathways. The cholesin-GPR146 axis could have profound implications across various therapeutic areas concerning abnormal cholesterol metabolism, offering new hope for patients and improving overall healthcare outcomes.

Lipid-lowering drugs and inflammatory bowel disease's risk: a drug-target Mendelian randomization study

BACKGROUND

Inflammatory bowel disease (IBD) has been associated with lipid-lowering drugs in observational studies. Drug-target Mendelian randomization (MR) was utilized in this study to examine the causal relationship between lipid-lowering drugs and incidence of IBD, aiming to identify new preventive uses for the drugs.

METHODS

We identified instrumental variables for three classes of lipid-lowering drugs: HMGCR inhibitors, PCSK9 inhibitors, and NPC1L1 inhibitors, using data from the Global Lipids Genetics Consortium. Summary statistics of IBD were obtained from UK Inflammatory Bowel Disease Genetics. The summary-data-based MR (SMR) and the inverse-variance weighted (IVW) MR were used for analysis. Sensitivity analyses were performed by conventional MR methods.

RESULTS

The SMR analysis showed no significant genetic association between increased gene expression of HMGCR, PCSK9, and NPC1L1 and IBD, Crohn's disease (CD) and ulcerative colitis (UC). According to IVW-MR analysis, increased HMGCR expression is associated with a reduced risk of IBD (OR = 0.73, 95% confidence interval (CI) 0.59-0.90, P = 0.003) and CD (OR = 0.75, 95% CI 0.57-0.97, P = 0.03), but not with UC. Additionally, increased NPC1L1 gene expression was associated with elevated risk of IBD (OR = 1.60, 95% CI 1.07-2.40, P = 0.023), but not with CD and UC. However, no significant causal relationships were found between PCSK9 gene expression and IBD, CD, and UC. The sensitivity analysis demonstrated no evidence of heterogeneity or pleiotropy among the reported results.

CONCLUSIONS

The heightened expression of genetic variations in HMGCR inhibitor targets could potentially reduce the risk of IBD and CD, while genetic variation in the expression of NPC1L1 targets was positively associated with IBD.

Robustness of heteroaggregates involving hydrophobic cholesterol and its mimetics

Exploring the self and cross aggregation affinity of cholesterol (CHL) and some of its lookalikes, e.g., cholesteryl hemisuccinate (CHM), campesterol (CAM) and arjunic acid (ARJ), provides crucial understanding towards the influence of weak forces in inducing mixed micellization through heteroaggregation. Strongly hydrophobic CHL, with a benchmark inclination towards aggregation, often forms detrimental plaques in crucial human organs that are fairly difficult to disintegrate. Traditionally known anti-dyslipidemic agents like CAM and ARJ are known to interact strongly with CHL in the gut when ingested. They further form mixed micelles along with the bile components and interfere with the CHL absorption across the epithelial cell layer of the intestine. Some invariant questions like how robust are the heteroaggregates formed between these mimetics and CHL are very important to appreciate the efficacy of such anti-dyslipidemic agents. In this work using molecular dynamics simulations and varied structural analysis, we characterize the heteroaggregates. Simulations indicate that CHL-CHM mixed assemblies are comparatively bigger and significantly stabilized by strong electrostatic and favourable vdW forces. Small and diffused CHL-ARJ aggregates are observed in our simulations with a not so favourable energetics, indicating a possible attenuation pathway of CHL aggregation in the presence of ARJ.

The Hypocholesterolemic Potential of the Edible Algae Fucus vesiculosus: Proteomic and Quantitative PCR Analysis

A brown seaweed consumed worldwide, Fucus vesiculosus, has been used to prevent atherosclerosis and hypercholesterolemia, among other uses. However, the mechanisms of action that lead to these effects are not yet fully understood. This work aims to study the in vitro effect of an aqueous extract of F. vesiculosus, previously characterized as rich in phlorotannins and peptides, on the expression of different proteins involved in the synthesis and transport of cholesterol. A proteomic analysis, Western blot, and qRT-PCR analysis were performed to identify protein changes in HepG2 cells exposed to 0.25 mg/mL of the F. vesiculosus extract for 24 h. The proteomic results demonstrated that, in liver cells, the extract decreases the expression of four proteins involved in the cholesterol biosynthesis process (CYP51A1, DHCR24, HMGCS1 and HSD17B7). Additionally, a 12.76% and 18.40% decrease in the expression of two important transporters proteins of cholesterol, NPC1L1 and ABCG5, respectively, was also observed, as well as a 30% decrease in NPC1L1 mRNA levels in the cells exposed to the extract compared to control cells. Our study reveals some of the mechanisms underlying the actions of bioactive compounds from F. vesiculosus that may explain its previously reported hypocholesterolemic effect, future prospecting its use as a functional food.

Recent advances in the screening methods of NPC1L1 inhibitors

NPC1L1 is a crucial protein involved in sterol lipid absorption and has been shown to play an important role in intestinal cholesterol absorption. Hypercholesterolemia is a significant risk factor for cardiovascular diseases such as coronary heart disease. Screening of NPC1L1 inhibitors is critical for gaining a full understanding of lipid metabolism, developing new cholesterol-lowering medicines, and treating cardiovascular diseases. This work summarized existing methodologies for screening NPC1L1 inhibitors and evaluated their challenges, and will assist the development of novel cholesterol-lowering medications and therapeutic strategies for hypercholesterolemia and other cholesterol-related metabolic disorders.

Regulation of cholesterol homeostasis in health and diseases: from mechanisms to targeted therapeutics

Disturbed cholesterol homeostasis plays critical roles in the development of multiple diseases, such as cardiovascular diseases (CVD), neurodegenerative diseases and cancers, particularly the CVD in which the accumulation of lipids (mainly the cholesteryl esters) within macrophage/foam cells underneath the endothelial layer drives the formation of atherosclerotic lesions eventually. More and more studies have shown that lowering cholesterol level, especially low-density lipoprotein cholesterol level, protects cardiovascular system and prevents cardiovascular events effectively. Maintaining cholesterol homeostasis is determined by cholesterol biosynthesis, uptake, efflux, transport, storage, utilization, and/or excretion. All the processes should be precisely controlled by the multiple regulatory pathways. Based on the regulation of cholesterol homeostasis, many interventions have been developed to lower cholesterol by inhibiting cholesterol biosynthesis and uptake or enhancing cholesterol utilization and excretion. Herein, we summarize the historical review and research events, the current understandings of the molecular pathways playing key roles in regulating cholesterol homeostasis, and the cholesterol-lowering interventions in clinics or in preclinical studies as well as new cholesterol-lowering targets and their clinical advances. More importantly, we review and discuss the benefits of those interventions for the treatment of multiple diseases including atherosclerotic cardiovascular diseases, obesity, diabetes, nonalcoholic fatty liver disease, cancer, neurodegenerative diseases, osteoporosis and virus infection.

Molecular cloning and characterization of NPC1L1 in the Chinese tree shrew (Tupaia belangeri chinensis)

BACKGROUND

The Niemann-Pick C1-Like 1 protein, a multi-transmembrane domain molecule, is critical for intestinal cholesterol absorption, and is the entry factor for hepatitis C virus (HCV). The Chinese tree shrew (Tupaia belangeri chinensis) is closer to primates in terms of genetic evolution than rodents. Previous studies indicated that the tree shrew was suitable for HCV research; however, little is known about tree shrew NPC1L1.

METHODS AND RESULTS

TsNPC1L1 cDNA was amplified by rapid amplification of cDNA ends (RACE) technology. The cDNA sequence, its encoded protein structure, and expression profile were analyzed. Results indicated that the tsNPC1L1 mRNA is 4948 bp in length and encodes a 1326 amino acid protein. TsNPC1L1 possesses 84.97% identity in homology to human NPC1L1 which is higher than both mouse (80.37%) and rat (81.80%). The protein structure was also similar to human with 13 conserved transmembrane helices, and a sterol-sensing domain (SSD). Like human NPC1L1, the tsNPC1L1 mRNA transcript is highly expressed in small intestine, but it was also well-expressed in the lung and pancreas of the tree shrew.

CONCLUSION

The homology of tree shrew NPC1L1 was closer to human than that of rodent NPC1L1. The expression of tsNPC1L1 was the highest in small intestine, and was detectable in lung and pancreas. These results may be useful in the study of tsNPC1L1 function in cholesterol absorption and HCV infection.

Effect of NPC1L1 polymorphism on warfarin stable dose in Chinese patients under heart valve replacement surgery

Warfarin is the most often anticoagulant choice for preventable thromboembolism. Notably, vitamin K plays a vital role in the process of warfarin's anticoagulant effect. Therefore, we presume NPC1L1, a key transporter of vitamin K (VK) intestinal absorption, may modulate the anticoagulant effect of warfarin. Studies have shown that NPC1L1(-762T>C, rs2073548) and p53 (P72R, rs1042522) variations are implicated in influencing NPC1L1 expression. This study aimed to assess the association between these two variants and warfarin stable dose (WSD). A two-stage extreme phenotype design was used to explore the influence of these two variants (rs2073548, rs1042522) on WSD variance in 655 Chinese patients undergoing heart valve replacement surgery. NPC1L1 rs2073548, p53 rs1042522, VKORC1 rs9923231 and CYP2C9*1/*3 polymorphisms were genotyped by polymerase chain reaction-restriction fragment polymorphism (PCR-RFLP) or Sanger sequencing, respectively. WSD was identified when target monitoring international normalized ratio (INR) value at 2.0-3.0. In the discovery phase, NPC1L1 rs2073548 A allele carriers occupied a significantly higher rate in the low dose group (P = .019). However, in the validation group, warfarin dosage in patients with the rs2073548 AA, AG and GG genotypes were 2.91 ± 0.97 mg/day, 3.02 ± 1.00 mg/day and 3.00 ± 1.06 mg/day, respectively. Multiple linear regression analysis results suggested that CYP2C9*3 and VKORC1 rs9923231, but not NPC1L1 rs2073548, were independent predictors of WSD in Chinese heart valve replacement (HVR) surgical patients.

Resolving the Egg and Cholesterol Intake Controversy: New Clinical Insights Into Cholesterol Regulation by the Liver and Intestine

OBJECTIVE

Cardiovascular disease is the number one cause of death. Achieving American Heart Association low-density lipoprotein (LDL) cholesterol treatment goals is very difficult for many patients. The importance of a low cholesterol diet is controversial and not emphasized by most physicians. Of critical importance is determining whether each individual is a "hyper- or hypo-absorber" of dietary cholesterol. Furthermore, the quantity of each individual's baseline daily dietary cholesterol and saturated fat intake is important in assessing the effect of added egg yolk cholesterol and saturated fat on blood LDL cholesterol.

METHODS

Gut cholesterol is absorbed via a specific enteric receptor (the Niemann- Pick-like receptor). Dietary cholesterol contributes one fourth of the absorbed cholesterol, while the remaining gut cholesterol is derived from secreted bile cholesterol. This dietary quantity of cholesterol is significant when other determinants are constant. For some individuals, dietary cholesterol has no adverse effects and in others, a significant elevation in blood LDL cholesterol may occur.

RESULTS

There are no readily available blood tests to determine the effect of egg yolk cholesterol and saturated fat on an individual's plasma LDL cholesterol. However, a one month trial of a low cholesterol and saturated fat diet will provide the needed information to make clinical decisions.

CONCLUSION

This article delineates the mechanisms that are altered by genetic and environmental factors that determine the net effects of dietary cholesterol and saturated fat on circulating LDL cholesterol. It then makes a practical clinical recommendation based on these mechanisms.

Phytosterols, Cholesterol Control, and Cardiovascular Disease

The use of phytosterols (or plant sterols) for the control of plasma cholesterol concentrations has recently gained traction because their efficacy is acknowledged by scientific authorities and leading guidelines. Phytosterols, marketed as supplements or functional foods, are formally classified as food in the European Union, are freely available for purchase, and are frequently used without any health professional advice; therefore, they are often self-prescribed, either inappropriately or in situations in which no significant advantage can be obtained. For this reason, a panel of experts with diverse medical and scientific backgrounds was convened by NFI—Nutrition Foundation of Italy—to critically evaluate and summarize the literature available on the topic, with the goal of providing medical doctors and all health professionals useful information to actively govern the use of phytosterols in the context of plasma cholesterol control. Some practical indications to help professionals identify subjects who will most likely benefit from the use of these products, optimizing the therapeutic outcomes, are also provided. The panel concluded that the use of phytosterols as supplements or functional foods to control Low Density Lipoprotein (LDL) cholesterol levels should be preceded by the assessment of some relevant individual characteristics: cardiovascular risk, lipid profile, correct understanding of how to use these products, and willingness to pay for the treatment.

Structures of dimeric human NPC1L1 provide insight into mechanisms for cholesterol absorption

Polytopic Niemann-Pick C1-like 1 (NPC1L1) plays a major role in intestinal absorption of biliary cholesterol, vitamin E (VE), and vitamin K (VK). The drug ezetimibe inhibits NPC1L1-mediated absorption of cholesterol, lowering of circulating levels of low-density lipoprotein cholesterol. Here, we report cryo-electron microscopy structures of human NPC1L1 (hNPC1L1) bound to either cholesterol or a lipid resembling VE. These findings, together with functional assays, reveal that the same intramolecular channel in hNPC1L1 mediates transport of VE and cholesterol. hNPC1L1 exists primarily as a homodimer; dimerization is mediated by aromatic residues within a region of transmembrane helix 2 that exhibits a horizonal orientation in the membrane. Mutation of tryptophan-347 lies in this region disrupts dimerization and the resultant monomeric NPC1L1 exhibits reduced efficiency of cholesterol uptake. These findings identify the oligomeric state of hNPC1L1 as a target for therapies that inhibit uptake of dietary cholesterol and reduce the incidence of cardiovascular disease.

An active and selective molecular mechanism mediating the uptake of sex steroids by prostate cancer cells

Steroid hormones play important roles in normal physiological functions and diseases. Sex steroids hormones are important in the biology and treatment of sex hormone-related cancer such as prostate cancer and breast cancer. Cells may take up steroids using multiple mechanisms. The conventionally accepted hypothesis that steroids cross cell membrane through passive diffusion has not been tested rigorously. Experimental data suggested that cells may take up sex steroid using an active uptake mechanism. ³H-testosterone uptake by prostate cancer cells showed typical transporter-mediated uptake kinetic. Cells retained testosterone taken up from the medium. The uptake of testosterone was selective for certain steroid hormones but not others. Data also indicated that the active and selective uptake mechanism resided in cholesterol-rich membrane domains, and may involve ATP and membrane transporters. In summary, the present study provided strong evidence to support the existence of an active and selective molecular mechanism for sex steroid uptake.

Effect of fixed-dose combinations of ezetimibe plus rosuvastatin in patients with primary hypercholesterolemia: MRS-ROZE (Multicenter Randomized Study of ROsuvastatin and eZEtimibe)

AIM

We aimed to compare the effects of fixed-dose combinations of ezetimibe plus rosuvastatin to rosuvastatin alone in patients with primary hypercholesterolemia, including a subgroup analysis of patients with diabetes mellitus (DM) or metabolic syndrome (MetS).

METHOD

This multicenter eight-week randomized double-blind phase III study evaluated the safety and efficacy of fixed-dose combinations of ezetimibe 10 mg plus rosuvastatin, compared with rosuvastatin alone in patients with primary hypercholesterolemia. Four hundred and seven patients with primary hypercholesterolemia who required lipid-lowering treatment according to the ATP III guideline were randomized to one of the following six treatments for 8 weeks: fixed-dose combinations with ezetimibe 10 mg daily plus rosuvastatin (5, 10, or 20 mg daily) or rosuvastatin alone (5, 10, or 20 mg daily).

RESULTS

Fixed-dose combination of ezetimibe plus rosuvastatin significantly reduced LDL cholesterol, total cholesterol, and triglyceride levels compared with rosuvastatin alone. Depending on the rosuvastatin dose, these fixed-dose combinations of ezetimibe plus rosuvastatin provided LDL cholesterol, total cholesterol, and triglyceride reductions of 56%-63%, 37%-43%, and 19%-24%, respectively. Moreover, the effect of combination treatment on cholesterol levels was more pronounced in patients with DM or MetS than in non-DM or non-MetS patients, respectively, whereas the effect of rosuvastatin alone did not differ between DM vs non-DM or MetS vs non-MetS patients.

CONCLUSION

Fixed-dose combinations of ezetimibe and rosuvastatin provided significantly superior efficacy to rosuvastatin alone in lowering LDL cholesterol, total cholesterol, and triglyceride levels. Moreover, the reduction rate was greater in patients with DM or MetS.

Recent advances in the treatment of homozygous familial hypercholesterolaemia

PURPOSE OF REVIEW

To review publications in the English literature over the past 18 months relating to the management of homozygous familial hypercholesterolaemia.

RECENT FINDINGS

Experience with plasmapheresis has been summarized, guidelines are being introduced to enhance patient care and registries are under consideration to improve analysis of management in this rare but serious disorder. Liver transplantation has been reviewed for its biochemical efficacy, but still does not ensure freedom from vascular complications. For patients without access to plasmapheresis, there is now evidence that high-dose statins do improve the prognosis, but combination therapy with additional agents should still be considered for better outcome. Promising new agents that inhibit LDL production by limiting apolipoprotein B100 synthesis by means of antisense oligonucleotides (mipomersen) or by inhibition of microsomal triacylglycerol transfer protein (lomitapide) have made significant additional LDL reduction possible but are associated with hepatic fat accumulation and long-term safety data is still required. Several other lipid modulating agents and gene therapy are still being explored.

SUMMARY

The management of homozygous familial hypercholesterolaemia by pharmacological means is improving with agents that limit lipoprotein production but plasmapheresis, generally in combination with additional pharmacological treatment, remains the proven option. Liver transplantation is now less likely to be undertaken owing to improved pharmacological options and prognosis.

The chylomicron: relationship to atherosclerosis

The B-containing lipoproteins are the transporters of cholesterol, and the evidence suggests that the apo B48-containing postprandial chylomicron particles and the triglyceride-rich very low density lipoprotein (VLDL) particles play an important part in the development of the plaque both directly and indirectly by their impact on LDL composition. The ratio of dietary to synthesised cholesterol is variable but tightly regulated: hence intervention with diet at best reduces serum cholesterol by <20% andusually <10%. Statins are the mainstay of cholesterol reduction therapy, but they increase cholesterol absorption, an example of the relationship between synthesis and absorption. Inhibition of cholesterol absorption with Ezetimibe, an inhibitor of Niemann Pick C1-like 1 (NPC1-L1), the major regulator of cholesterol absorption, increases cholesterol synthesis and hence the value of adding an inhibitor of cholesterol absorption to an inhibitor of cholesterol synthesis. Apo B48, the structural protein of the chylomicron particle, is synthesised in abundance so that the release of these particles is dependent on the amount of cholesterol and triglyceride available in the intestine. This paper will discuss cholesterol absorption and synthesis, chylomicron formation, and the effect of postprandial lipoproteins on factors involved in atherosclerosis.

Lipid modification in the elderly using the combination of a statin and a cholesterol absorption inhibitor

While the optimal lipid-lowering treatment to reduce cardiovascular disease (CVD) risk in elderly patients has not been definitively established, evidence so far indicates that reducing low-density lipoprotein cholesterol (LDL-C) should be a primary goal, as with other patient groups. The VYTELD (VYTorin in the ELDerly) study--a multicenter, 12-week, randomized, double-blind trial--evaluated the efficacy and safety of combination therapy comprised of ezetimibe plus simvastatin (eze/simva) versus atorvastatin in 1289 hypercholesterolemic patients aged ? 65 years. For all prespecified comparisons, patients randomized to eze/simva were found to have significantly greater percentage decreases in LDL-C and were significantly more likely to achieve LDL-C target levels compared with those on atorvastatin monotherapy (p < 0.05 to < 0.001). Also, the proportions of subjects reaching secondary biochemical targets were similarly greater with eze/simva than with atorvastatin monotherapy for all prespecified comparisons (p < 0.01 to < 0.001). Finally, there were no differences in tolerability between the treatments. The authors concluded that in patients aged ≥ 65 years, the eze/simva combination provided significantly greater improvements in key lipid variables, with a larger proportion of subjects reaching target LDL-C compared with atorvastatin monotherapy. Despite these promising short-term results, the longer-term safety and efficacy of combination treatment across diverse populations requires further evaluation.

Efficacy of ezetimibe for the treatment of non-alcoholic steatohepatitis: An open-label, pilot study

AIM

Non-alcoholic steatohepatitis (NASH) is considered a hepatic manifestation of metabolic syndrome. However, effective drug therapy for NASH has not been established yet. In the present study, we evaluated the efficacy of 6 months of ezetimibe treatment for NASH patients with dyslipidemia for the comparison of improvement of the clinical parameters and histological alterations.

METHODS

We prospectively evaluated 10 consecutive NASH patients with dyslipidemia who agreed to participate in this study. The patients were given ezetimibe (10 mg/day) for 6 months, and clinical parameters and histological alterations were comparatively evaluated before and after treatment. All the patients were given standard calorie diet (30 kcal/kg per day, carbohydrate 50-60%, fat 20-30%, protein 15-20%) and exercise counseling from 3 months before the ezetimibe treatment.

RESULTS

The serum aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transpeptidase, low-density lipoprotein cholesterol, high-sensitivity C-reactive protein and type IV collagen 7 s levels were significantly improved by the treatment with ezetimibe for 6 months. In histological observations, follow-up liver biopsies revealed that the NAS score and steatosis grade were also significantly improved. The fibrosis stage did not change significantly, but six of the 10 patients exhibited an improvement in their fibrosis stage.

CONCLUSION

Major clinical parameters and histological observations were significantly improved by the treatment with ezetimibe. Our pilot study demonstrated the efficacy of ezetimibe for drug therapy of NASH and may lead to a large-scale clinical trial in the future.

Current and emerging strategies for treating dyslipidemia and macrovascular disease

Statins, inhibitors of hydroxymethylglutaryl CoA (HMG-CoA) reductase, have been in clinical use for over 20 years. The widespread use of these agents has left doubt of the efficacy of cholesterol-lowering therapy to prevent cardiovascular disease. In spite of the widespread use of these agents and the successful lowering of circulating cholesterol together with reduction of cardiovascular-related deaths, there is consensus that further improvements in therapy are needed. Cardiovascular disease remains a major cause of premature death and continues to exert an extensive drain on the health-care costs. This chapter outlines some of the emerging strategies for discovering and developing novel treatments of dyslipidemia and macrovascular disease. Mechanisms considered include alternate ways to lower total cholesterol through inhibition of synthesis, limitation of absorption, or recycling. Other approaches include the modification of circulating forms of cholesterol and changes in gene expression at the key sites of storage, utilization, and pathology. The next successful strategy will likely be one that works well in concert with existing statins.

Inhibition of intestinal absorption of cholesterol by surface-modified nanostructured aluminosilicate compounds

The aim of this work was to assess the ability of aqueous suspensions of surface-modified nanostructured aluminosilicate (NSAS) compounds to reduce the intestinal absorption of cholesterol in a rat model. The rats were divided into 10 treatment groups which included several NSAS compounds at various doses, ezetimibe at 10 mg/kg, stigmastanol at 50 mg/kg, and normal saline. All compounds and controls were independently administered by oral gavage and then a mixture of [(3)H]cholesterol and cold cholesterol in 10% Intralipid(R) was immediately administered orally to the animals. Systemic blood was sampled and the concentration of cholesterol in plasma was determined by means of radioactivity. Protonation of NSAS using an ion-exchange column resulted in significant inhibition of cholesterol absorption relative to the control group (31.5% and 38.6% reduction in absorption of cholesterol for 50 and 100 mg/kg doses, respectively). Other surface-ion modifications of NSAS compounds did not show significant effect on intestinal cholesterol absorption. The inhibition of cholesterol absorption by ezetimibe was superior and by stigmastanol was equal to the effect of protonated NSAS in the doses investigated in this study. In conclusion, protonated NSAS material seems to inhibit significantly the intestinal absorption of dietary cholesterol in a rat model.

Ezetimibe improves postprandial hyperlipidaemia in patients with type IIb hyperlipidaemia

BACKGROUND

Postprandial hyperlipidaemia is known to be a high-risk factor for atherosclerotic disease because of rapid and lasting accumulations of triglyceride-rich lipoproteins and remnants. The Niemann-Pick C1-Like 1 (NPC1L1) protein acts as an intestinal cholesterol transporter and ezetimibe, which inhibits NPC1L1, has been used in patients with hypercholesterolaemia. We investigated effects of ezetimibe on fasting lipid and lipoprotein profiles and postprandial hyperlipidaemia in patients with type IIb hyperlipidaemia.

MATERIALS AND METHODS

Ezetimibe 10 mg per day was administered in ten patients with type IIb hyperlipidaemia for 2 months, and lipid and lipoprotein profiles were examined during fasting and after an oral fat loading (OFL) test.

RESULTS

In the fasting state, ezetimibe significantly decreased not only total cholesterol, low density lipoprotein (LDL)-cholesterol and apolipoproteinB-100 (apoB-100) levels but triglycerides (TG), apoB-48 and remnant lipoprotein cholesterol (RemL-C) levels. High performance liquid chromatography analysis showed that ezetimibe decreased cholesterol and TG levels in the very low density lipoprotein (VLDL) and LDL size ranges as well as apoB-100 levels, suggesting a decrease in numbers of VLDL and LDL particles. After OFL, ezetimibe decreased the area under the curve for TG, apoB-48 and RemL-C. Ezetimibe decreased postprandial elevations of cholesterol and TG levels in the chylomicrons (CM) size range, suggesting that the postprandial production of CM particles was suppressed by ezetimibe.

CONCLUSIONS

These findings suggest that ezetimibe improves fasting lipoprotein profiles and postprandial hyperlipidaemia by suppressing intestinal CM production in patients with type IIb hyperlipidaemia and such treatment may prove to be effective in reducing atherosclerosis.

Intestinal lipid absorption

Our knowledge of the uptake and transport of dietary fat and fat-soluble vitamins has advanced considerably. Researchers have identified several new mechanisms by which lipids are taken up by enterocytes and packaged as chylomicrons for export into the lymphatic system or clarified the actions of mechanisms previously known to participate in these processes. Fatty acids are taken up by enterocytes involving protein-mediated as well as protein-independent processes. Net cholesterol uptake depends on the competing activities of NPC1L1, ABCG5, and ABCG8 present in the apical membrane. We have considerably more detailed information about the uptake of products of lipid hydrolysis, the active transport systems by which they reach the endoplasmic reticulum, the mechanisms by which they are resynthesized into neutral lipids and utilized within the endoplasmic reticulum to form lipoproteins, and the mechanisms by which lipoproteins are secreted from the basolateral side of the enterocyte. apoB and MTP are known to be central to the efficient assembly and secretion of lipoproteins. In recent studies, investigators found that cholesterol, phospholipids, and vitamin E can also be secreted from enterocytes as components of high-density apoB-free/apoAI-containing lipoproteins. Several of these advances will probably be investigated further for their potential as targets for the development of drugs that can suppress cholesterol absorption, thereby reducing the risk of hypercholesterolemia and cardiovascular disease.

The effects of ezetimibe and orlistat, alone or in combination, on high-density lipoprotein (HDL) subclasses and HDL-associated enzyme activities in overweight and obese patients with hyperlipidaemia

BACKGROUND

High-density lipoprotein (HDL) includes discrete subfractions. HDL exhibits anti-atherogenic properties, which have been partly linked to the activity of HDL-associated enzymes, such as the lipoprotein associated phospholipase A(2) (HDL-LpPLA(2)) and paraoxonase-1 (PON1).

OBJECTIVE

We assessed in an open-label randomised study the effect of orlistat and ezetimibe, alone or in combination, on plasma HDL subclasses and HDL-associated enzyme activities in overweight and obese subjects (body mass index > 28 kg/m(2)) with hypercholesterolemia [total cholesterol > 200 mg/100 ml (5.2 mmol/l)].

METHODS

Eighty-six people were prescribed a low-fat low-calorie diet and were randomly allocated to receive orlistat 120 mg, three times daily (O group), ezetimibe 10 mg/day (E group) or both (OE group) for 6 months. HDL subfractions were determined using a polyacrylamide gel-tube electrophoresis method.

RESULTS

Levels of HDL cholesterol (HDL-C) and apolipoprotein AI did not change significantly in any group. In group O the cholesterol concentration of HDL-2 subclass increased significantly, while the cholesterol of HDL-3 subclass decreased significantly. In groups E and OE HDL-2 subclass did not significantly change, while the cholesterol concentration of HDL-3 subclass decreased significantly. We observed a non-significant decrease in the HDL-LpPLA(2) and PON1 activity in all groups. However, the ratios of both enzyme activities to low-density lipoprotein cholesterol (LDL-C) levels (an index of atherogenicity) significantly increased in all groups.

CONCLUSION

Although HDL-C levels did not change after treatment with orlistat and ezetimibe, alone or in combination, there were alterations of the HDL-2 and HDL-3 subclasses. The activity of HDL-LpPLA(2) and PON1 per mg LDL-C increased significantly in all groups.

Niemann-Pick C1 Like 1 (NPC1L1) an intestinal sterol transporter

Niemann-Pick C1 Like 1 (NPC1L1) has been identified and characterized as an essential protein in the intestinal cholesterol absorption process. NPC1L1 localizes to the brush border membrane of absorptive enterocytes in the small intestine. Intestinal expression of NPC1L1 is down regulated by diets containing high levels of cholesterol. While otherwise phenotypically normal, Npc1l1 null mice exhibit a significant reduction in the intestinal uptake and absorption of cholesterol and phytosterols. Characterization of the NPC1L1 pathway revealed that cholesterol absorption inhibitor ezetimibe specifically binds to an extracellular loop of NPC1L1 and inhibits its sterol transport function. Npc1l1 null mice are resistant to diet-induced hypercholesterolemia, and when crossed with apo E null mice, are completely resistant to the development of atherosclerosis. Intestinal gene expression studies in Npc1l1 null mice indicated that no exogenous cholesterol was entering enterocytes lacking NPC1L1, which resulted in an upregulation of intestinal and hepatic LDL receptor and cholesterol biosynthetic gene expression. Polymorphisms in the human NPC1L1 gene have been found to influence cholesterol absorption and plasma low density lipoprotein levels. Therefore, NPC1L1 is a critical intestinal sterol uptake transporter which influences whole body cholesterol homeostasis.

Molecular processes that handle -- and mishandle -- dietary lipids

Overconsumption of lipid-rich diets, in conjunction with physical inactivity, disables and kills staggering numbers of people worldwide. Recent advances in our molecular understanding of cholesterol and triglyceride transport from the small intestine to the rest of the body provide a detailed picture of the fed/fasted and active/sedentary states. Key surprises include the unexpected nature of many pivotal molecular mediators, as well as their dysregulation - but possible reversibility - in obesity, diabetes, inactivity, and related conditions. These mechanistic insights provide new opportunities to correct dyslipoproteinemia, accelerated atherosclerosis, insulin resistance, and other deadly sequelae of overnutrition and underexertion.

Ezetimibe/simvastatin compared with atorvastatin or rosuvastatin in lowering to specified levels both LDL-C and each of five other emerging risk factors for coronary heart disease: Non-HDL-cholesterol, TC/HDL-C, apolipoprotein B, apo-B/apo-A-I, or C-reactive protein

BACKGROUND

Recent evidence suggests that in addition to low-density lipoprotein cholesterol (LDL-C), apolipoprotein B (Apo-B), non-high-density lipoprotein cholesterol (non-HDL-C), some lipoprotein ratios, and C-reactive protein (CRP) are predictive of coronary heart disease (CHD) risk. This post-hoc analysis of two trials comparing single-tablet ezetimibe/simvastatin (EZE/SIMVA) to atorvastatin (ATORVA) or rosuvastatin (ROSUVA) evaluates the proportion of patients attaining LDL-C <70 mg/dL and specific levels of these emerging risk factors.

METHODS

These were double-blind, 6-week, parallel group trials of hypercholesterolemic patients randomized to milligram equivalent doses of ATORVA versus EZE 10 mg/SIMVA, or to usual starting, next higher, and maximum doses of ROSUVA versus EZE/SIMVA. This analysis examined the percent of patients in prespecified dose comparisons and overall achievement of LDL-C <70 mg/dL and/or Apo-B <90 mg/dL, total cholesterol (TC)/HDL-C <4.0, or Apo-B/Apo-A-I <0.7 among all treated patients, non-HDL-C <100 mg/dL among patients with baseline triglycerides ≥200 mg/dL, or CRP <2.0 mg/L among patients with baseline CRP ≥2.0 mg/L.

RESULTS

Within each trial, baseline characteristics were similar among groups. At all dose comparisons, significantly more patients receiving EZE/SIMVA reached LDL-C <70 mg/dL and achieved both LDL-C <70 mg/dL and either Apo-B <90 mg/dL, TC/HDL-C <4.0, or Apo-B/Apo-A-I <0.7 (EZE/SIMVA versus ATORVA) compared to ATORVA and ROSUVA. For most dose comparisons, significantly more patients receiving EZE/SIMVA attained both LDL-C <70 mg/dL and either non-HDL-C <100 mg/dL or CRP <2 mg/L compared to ATORVA or ROSUVA.

CONCLUSION

The greater efficacy related to changes in blood lipids of EZE/SIMVA compared with both ATORVA and ROSUVA extends to changes in many emerging risk factors. Ultimate clinical implications of these findings still need to be defined.

The effect of orlistat and ezetimibe, alone or in combination, on serum LDL and small dense LDL cholesterol levels in overweight and obese patients with hypercholesterolaemia

BACKGROUND

Increased concentrations of low density lipoprotein cholesterol (LDL-C), as well as of small dense LDL-C (sdLDL-C), are considered as cardiovascular risk factors.

OBJECTIVE

An assessment of the effects of ezetimibe and orlistat administration, alone or in combination, on LDL-C and sdLDL-C levels (primary endpoint), as well as on anthropometric variables and metabolic parameters (secondary endpoints) in overweight and obese patients [body mass index (BMI)>28 kg/m(2)] with hypercholesterolaemia [total cholesterol>200 mg/dL (5.2 mmol/L)].

METHODS

Eighty six subjects were prescribed a low-fat low-calorie diet and were randomly allocated to receive orlistat 120 mg, 3 times daily (O group), ezetimibe 10 mg/day (E group) or both (OE group) for 6 months.

RESULTS

Significant reductions in LDL-C (-19%, -21%, -32% in groups O, E and OE, respectively, all p<0.01 vs. baseline) and sdLDL-C levels (-45%, -48%, -76% in groups O, E, OE, respectively, all p<0.01 vs. baseline) were observed. Group OE experienced a significantly greater reduction in LDL-C and sdLDL-C levels compared with groups O and E (p<0.05). Furthermore, significant reductions of BMI, homeostasis model assessment (HOMA) index, serum uric acid, transaminase activities and plasma lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) activity were observed in the O and OE groups. Gamma-glutamyl transpeptidase activity and Lp-PLA(2) activity improved significantly more with the combination treatment compared with either orlistat or ezetimibe monotherapy.

CONCLUSIONS

Orlistat and ezetimibe combination had a more favourable effect on LDL-C and sdLDL-C levels in overweight and obese hypercholesterolaemic patients than either drug alone. Furthermore, orlistat, alone or in combination with ezetimibe, additionally improved several anthropometric and metabolic variables.

Cholesterol homeostasis by the intestine: lessons from Niemann-Pick C1 Like 1 [NPC1L1)

Ezetimibe is a selective cholesterol absorption inhibitor, which potently inhibits the uptake and absorption of biliary and dietary cholesterol from the small intestine without affecting the absorption of fat-soluble vitamins, triglycerides or bile acids. Identification and characterization of Niemann-Pick C1 Like 1 (NPC1L1) has established NPC1L1 as an essential protein in the intestinal cholesterol absorption process. While otherwise phenotypically normal, Npc1l1 null mice exhibit a significant reduction in the intestinal uptake and absorption of cholesterol and phytosterols. Characterization of the NPC1L1 pathway revealed that ezetimibe specifically binds to NPC1L1 and inhibits its sterol transport function. Npc1l1 null mice were resistant to diet-induced hypercholesterolemia, and when crossed with apoE null mice, were completely resistant to the development of atherosclerosis. In Npc1l1/apoE null mice or apoE null mice treated with ezetimibe plasma cholesterol levels were reduced primarily in the apoB48 containing chylomicron remnant lipoproteins relative to untreated apoE null mice. SR-B1 has been proposed to play a role in intestinal cholesterol uptake, but in Npc1l1/SR-B1 double null mice intestinal cholesterol absorption was not different than Npc1l1 null alone mice. Therefore, NPC1L1 is the critical intestinal sterol transporter which influences whole body cholesterol homeostasis, and is the molecular target of ezetimibe.

Madin-Darby canine kidney II cells: a pharmacologically validated system for NPC1L1-mediated cholesterol uptake

Absorption of dietary cholesterol in the proximal region of the intestine is mediated by Niemann-Pick C1-like protein (NPC1L1) and is sensitive to the cholesterol absorption inhibitor ezetimibe (EZE). Although a correlation exists between EZE binding to NPC1L1 in vitro and efficacy in vivo, the precise nature of interaction(s) between NPC1L1, EZE, and cholesterol remain unclear. Here, we analyze the direct relationship between EZE analog binding to NPC1L1 and its influence on cholesterol influx in a novel in vitro system. Using the EZE analog [(3)H]AS, an assay that quantitatively measures the expression of NPC1L1 on the cell surface has been developed. It is noteworthy that whereas two cell lines (CaCo-2 and HepG2) commonly used for studying NPC1L1-dependent processes express almost undetectable levels of NPC1L1 at the cell surface, polarized Madin-Darby canine kidney (MDCKII) cells endogenously express 4 x 10(5) [(3)H]AS sites/cell under basal conditions. Depleting endogenous cholesterol with the HMG CoA reductase inhibitor lovastatin leads to a 2-fold increase in the surface expression of NPC1L1, supporting the contention that MDCKII cells respond to changes in cholesterol homeostasis by up-regulating a pathway for cholesterol influx. However, a significant increase in surface expression levels of NPC1L1 is necessary to characterize a pharmacologically sensitive, EZE-dependent pathway of cholesterol uptake in these cells. Remarkably, the affinity of EZE analogs for binding to NPC1L1 is almost identical to the IC(50) blocking cholesterol flux through NPC1L1 in MDCKII cells. From a mechanistic standpoint, these observations support the contention that EZE analogs and cholesterol share the same/overlapping binding site(s) or are tightly coupled through allosteric interactions.

Genetic determinants of plasma lipoproteins

The search for common genetic determinants of plasma lipoproteins began in the early 1980s. Despite some exceptions, these efforts have not yet yielded a set of biological markers that can be used in clinical practice. By contrast, successes in defining the molecular basis of rare single-gene disorders, such as familial hypoalphalipoproteinemia, have shown the value of experimental designs that focus on genomic analysis of individuals within the tails of Gaussian distributions of quantitative lipoprotein traits. For example, this strategy showed that a small but relevant proportion of individuals within the <5% tail of plasma HDL-cholesterol distribution have mutations in genes that cause familial hypoalphalipoproteinemia. The value of clinical testing for genomic variants as an adjunct to a biochemical measurement of plasma lipoproteins, however, is at best questionable. A more direct impact of genetic studies is that definitions of 'common' and 'large genetic effects' have become more tempered, reflecting perhaps the biological reality that plasma lipoproteins are probably determined by the aggregate of numerous modest and occasional large genetic effects in addition to environmental factors. Here, we review recent progress on genomic variants and cholesterol metabolism, and discuss the impact these genetic studies will have on clinical cardiology.

Substituted oxazolidinones as novel NPC1L1 ligands for the inhibition of cholesterol absorption

Cholesterol absorption inhibition (CAI) represents an important treatment option for hypercholesterolemia. Herein, we report the design and evaluation of a series of substituted oxazolidinones as ligands for the Niemann Pick C1 Like 1 (NPC1L1) protein, a key mediator of cholesterol transport. Novel analogs were initially evaluated in a brush border membrane NPC1L1 binding assay; subsequently, promising compounds were evaluated in vivo for acute inhibition of cholesterol absorption. These studies identified analogs with low micromolar NPC1L1 binding affinity and acute in vivo efficacy of >50% absorption inhibition at 3mg/kg.

Ezetimibe improves liver steatosis and insulin resistance in obese rat model of metabolic syndrome

Non-alcoholic fatty liver disease (NAFLD) is associated with the metabolic syndrome characterized by dislipidemia and insulin resistance. We hypothesized that ezetimibe, an inhibitor of NPC1L1, improves these metabolic disorders in Zucker obese fatty rats (ZOF). Ezetimibe significantly lowered total cholesterol and triglycerides in ZOF with prominent reduction in the remnant lipoprotein fraction and small dense low density lipoprotein fraction. Moreover, lipid deposition and fibrosis of liver were decreased by ezetimibe. Interestingly, ezetimibe improved insulin and plasma glucose response after intraperitoneal glucose injection. Further, ezetimibe enhanced insulin signaling in cultured hepatocytes. Our results indicate the potential of ezetimibe in treating the metabolic syndrome and NAFLD.

Non-vesicular sterol transport in cells

Sterols such as cholesterol are important components of cellular membranes. They are not uniformly distributed among organelles and maintaining the proper distribution of sterols is critical for many cellular functions. Both vesicular and non-vesicular pathways move sterols between membranes and into and out of cells. There is growing evidence that a number of non-vesicular transport pathways operate in cells and, in the past few years, a number of proteins have been proposed to facilitate this transfer. Some are soluble sterol transfer proteins that may move sterol between membranes. Others are integral membranes proteins that mediate sterol efflux, uptake from cells, and perhaps intracellular sterol transfer as well. In most cases, the mechanisms and regulation of these proteins remains poorly understood. This review summarizes our current knowledge of these proteins and how they could contribute to intracellular sterol trafficking and distribution.

Ezetimibe: an update on the mechanism of action, pharmacokinetics and recent clinical trials

Elevated serum cholesterol is a known risk factor for the development of coronary artery disease. Circulating cholesterol is a product of both cholesterol absorption from the gut and cellular cholesterol production. Ezetimibe is a novel cholesterol-lowering drug that acts at the brush border of the small intestine. Recent studies have further identified the molecular target as the Niemann-Pick C1-like transporter. Ezetimibe blocks the absorption of dietary and biliary cholesterol and plant sterols resulting in intracellular cholesterol depletion. Clinical studies have demonstrated beneficial improvements in the lipid profile with ezetimibe as monotherapy, but dramatic effects are seen when ezetimibe is combined with other lipid-lowering drugs, particularly 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Combination studies of ezetimibe with statins, bile acid sequestrants, fenofibrate and niacin all demonstrate significant total and low density lipoprotein cholesterol lowering. An excellent safety and tolerability profile combined with once-daily dosing make this attractive adjunct therapy for the treatment of hypercholesterolemia.

Zetia: inhibition of Niemann-Pick C1 Like 1 (NPC1L1) to reduce intestinal cholesterol absorption and treat hyperlipidemia

Zetia (ezetimibe) is a selective cholesterol absorption inhibitor, which potently inhibits the absorption of biliary and dietary cholesterol from the small intestine without affecting the absorption of fat-soluble vitamins, triglycerides or bile acids. Ezetimibe reduces the small intestinal enterocyte uptake and absorption of cholesterol by binding to Niemann-Pick C1 Like 1 (NPC1L1), which keeps cholesterol in the intestinal lumen for excretion. Ezetimibe undergoes glucuronidation to a single metabolite and localizes at the intestinal wall, where it binds with higher affinity for NPC1L1 than ezetimibe to prevent cholesterol absorption. Enterohepatic recirculation of ezetimibe and/or its glucuronide ensures repeated delivery to the intestinal site of action and limited peripheral exposure. Ezetimibe has no effect on the activity of major drug metabolizing enzymes (CYP450), which reduces any potential drug-drug interactions with other medications. Ezetimibe (10 mg/day) was found to inhibit cholesterol absorption by an average of 54% in hypercholesterolemic individuals and by 58% in vegetarians. Ezetimibe alone reduced plasma total and LDL-Cholesterol (18%) levels in patients with primary hypercholesterolemia. When ezetimibe was added to on-going statin treatment, an additional 25% reduction in LDL-C was found in patients with primary hypercholesterolemia and an additional 21% reduction in LDL-C in homozygous familial hypercholesterolemia. Ezetimibe in combination with statins produces additional reductions in plasma cholesterol levels and allows for more patients to achieve their LDL-C goals.