Blocking Cholesterol Absorption Research Articles

Dominant hydrophobic interactions with β-glucan in nanoarchitectonics with mixed Langmuir monolayers of cholesterol/dipalmitoyl phosphatidyl choline.

The polysaccharide β-glucan, found in the cell wall of cereals such as wheat, oats, and barley, is believed to lower the concentration of bad cholesterol in humans, but the molecular-level mechanisms responsible for such an action are unknown. In this study, we use Langmuir monolayers of cholesterol and dipalmitoyl phosphatidyl choline (DPPC) as cell membrane models that are made to interact with β-glucan. Neat cholesterol and mixed cholesterol/DPPC monolayers were expanded upon incorporating β-glucan from the aqueous subphase. This incorporation was found to induce ordering in mixed monolayers and dehydration of the carbonyl group at higher cholesterol concentrations. These effects are attributed to hydrophobic interactions as identified with polarization-modulated infrared reflection-absorption spectroscopy. They correlate well with the hypothesis that cholesterol levels can be lowered by the formation of soluble fibers with β-glucan through hydrophobic interactions, blocking cholesterol absorption by the organism.

Anaplasma phagocytophilum Hijacks Flotillin and NPC1 Complex To Acquire Intracellular Cholesterol for Proliferation, Which Can Be Inhibited with Ezetimibe.

ABSTRACTThe intracellular cholesterol transport protein Niemann-Pick type C1 (NPC1) and lipid-raft protein flotillin (FLOT) are required for cholesterol uptake by the obligatory intracellular bacterium Anaplasma phagocytophilum and for infection, and each protein localizes to membrane-bound inclusions containing replicating bacteria. Here, we found striking localization of FLOT2 in NPC1-lined vesicles and a physical interaction between FLOT2 and NPC1. This interaction was cholesterol dependent, as a CRAC (cholesterol recognition/interaction amino acid cholesterol-binding) domain mutant of FLOT2 did not interact with NPC1, and the cholesterol-sequestering agent methyl-β-cyclodextrin reduced the interaction. The stomatin-prohibitin-flotillin-HflC/K domain of FLOT2, FLOT21–183, was sufficient for the unique FLOT2 localization and interaction with NPC1. NPC1, FLOT2, and FLOT21–183 trafficked to the lumen of Anaplasma inclusions. A loss-of-function mutant, NPC1P691S (mutation in the sterol-sensing domain), did not colocalize or interact with FLOT2 or with Anaplasma inclusions and inhibited infection. Ezetimibe is a drug that blocks cholesterol absorption in the small intestine by inhibiting plasma membrane Niemann-Pick C1-like 1 interaction with FLOTs. Ezetimibe blocked the interaction between NPC1 and FLOT2 and inhibited Anaplasma infection. Ezetimibe did not directly inhibit Anaplasma proliferation but inhibited host membrane lipid and cholesterol traffic to the bacteria in the inclusion. These data suggest that Anaplasma hijacks NPC1 vesicles containing cholesterol bound to FLOT2 to deliver cholesterol into Anaplasma inclusions to assimilate cholesterol for its proliferation. These results provide insights into mechanisms of intracellular cholesterol transport and a potential approach to inhibit Anaplasma infection by blocking cholesterol delivery into the lumen of bacterial inclusions.

The important role of apolipoprotein A-II in ezetimibe driven reduction of high cholesterol diet-induced atherosclerosis

Background and aimsIt has been well established that ezetimibe blocks cholesterol absorption to prevent the negative effects of a high-fat diet in atherosclerosis. However, the exact mechanism is unknown. Here we use a transgenic zebrafish, which expresses different fluorescent proteins on either endothelial cells or granulocytes and macrophages, to explore the specific mechanism of ezetimibe and its role in reducing atherosclerosis-related hypercholesteremia. MethodsZebrafish larvae were exposed to a control diet, high cholesterol diet (HCD) or a HCD with ezetimibe treatment. Both the control diet and high cholesterol diet were mixed with red or green fluorophore labeled cholesteryl ester to trace lipid distribution. Isobaric tags were used for relative and absolute quantification to examine protein expression profiles of zebrafish larvae in the different treatment groups. To knock down Apo A-II and investigate the role of Apo A-II in the anti-atherosclerotic function of ezetimibe, we used morpholinos to target zebrafish Apoa2 mRNA. To confirm ezetimibe regulatory role on Apo A-II expression, siRNA against HNF4, PPARα, and SREBP1 were transfected into HepG2 cells. ResultsThe results show that ezetimibe increased the expression of Apo A-II but failed to reduce vascular lipid accumulation and macrophage recruitment induced by the HCD diet when Apo A-II was knocked down. Finally, we found that ezetimibe increased the expression of Apo A-II through HNF4 and PPARα transcriptional factors. ConclusionsOur data indicates that ezetimibe may not only prevents atherosclerosis by inhibiting cholesterol absorption in the intestine, but also by increasing the expression of Apo A-II in hepatocytes, thereby enhancing reverse cholesterol transport and removing excess cholesterol from the periphery.

Epidemiologic Analysis Along the Mevalonate Pathway Reveals Improved Cancer Survival in Patients Who Receive Statins Alone and in Combination With Bisphosphonates.

Cohort studies report associations between statin use and improved survival in patients with cancer. We used pharmacoepidemiologic methods to evaluate the survival of patients with cancer who received statins alone or in ostensibly synergistic drug combinations. Patients with cancer who were diagnosed from 2010 to 2013 were identified in a large health care claims database. The rate of all-cause death up to 1 year after diagnosis was compared by Cox proportional hazard regression. Sensitivity analyses included age stratification, statin type and intensity, and comparison with or without bisphosphonates and dipyridamole. Among 312,907 identified patients with cancer, treatment groups included statin users (n = 65,440), nonstatin users who received medications that block cholesterol absorption (n = 9,289), and nonusers (n = 226,007). Statin use before diagnosis was associated with improved overall survival compared with no treatment (hazard ratio [HR], 0.85; 95% CI, 0.80 to 0.91) and specifically in patients with leukemia, lung, or renal cancers. Nonstatin users had increased overall survival compared with no treatment (HR, 0.73; 95% CI, 0.62 to 0.85); when stratified, this difference held true only for pancreatic cancer and leukemia. No differences were observed between statin and nonstatin groups. Bisphosphonate use alone had no effect (n = 4,528), but patients who used both statins and bisphosphonates (n = 4,090) had increased survival compared with no treatment (HR, 0.60; 95% CI, 0.45 to 0.81). The effect of the combination of dipyridamole and statin use (n = 651) was not significant compared with no treatment. This study suggests that the combination of statins with drugs that affect isoprenylation, such as bisphosphonates, improves survival in patients with cancer. Consideration of pathway-specific pharmacology allows for hypotheses testing with the pharmacoepidemiologic approach. Prospective evaluation of these findings warrants clinical investigation and preclinical mechanistic studies.

The PCSK9 revolution and the potential of PCSK9-based therapies to reduce LDL-cholesterol.

[first paragraph of article]A large number of clinical trials over the last 30 years have firmly consolidated the importance of lowering low density lipoprotein cholesterol (LDLc) in the prevention of cardiovascular diseases (CVD) and its associated devastating sequelae. While healthy diets and exercise are highly recommended to lower LDLc levels, in many individuals with high baseline levels of LDLc, this is not sufficient to bring levels down to recommended target values in order to prevent recurrent coronary heart disease and cardiovascular complications. This is especially true for patients at high risk of premature cardiovascular death and disability, including those with familial hypercholesterolaemia (FH). FH is a very common inherited disease – affecting at least 30 million people worldwide, with an overall incidence of 1:200 globally – of whom ≤ 1% have been diagnosed. The advent of HMG-CoA reductase inhibitors, also known as ‘‘statins’’, and their first application to hypercholesterolemic patients over 30 years ago, has revolutionized the treatment of FH patients and resulted in substantial lowering of LDLc. In addition, cholesterol– lowering drugs, such as ‘‘ezetimibe’’ that blocks cholesterol absorption from the gut by inhibiting the Niemann-Pick C1-like 1 (NPC1L1) transporter, have also been successful and a 7-year IMPROVE-IT trial revealed that a ‘‘simvastatin-ezetimibe’’ combination resulted in an incremental lowering of LDLc levels and a modest 2% improved cardiovascular outcomes.3 Therefore, it became clear that additional treatments are needed to substantially decrease LDLc and efficiently protect against CVD.

Efficacy of yogurt drink with added plant stanol esters (Benecol®, Colanta) in reducing total and LDL cholesterol in subjects with moderate hypercholesterolemia: a randomized placebo-controlled crossover trial NCT01461798.

BackgroundCardiovascular diseases have become the leading cause of death from chronic diseases in the world. Main risk factors include hypercholesterolemia, which is caused in most cases by a high saturated fat diet. Plant stanol esters partly block cholesterol absorption in the digestive tract and thereby reduce total cholesterol and low-density lipoprotein (LDL) cholesterol serum levels. Based on epidemiological data, a 10 percent reduction of LDL cholesterol leads to a 20 percent decrease in the coronary heart disease risk throughout life. The aim of this study was to evaluate the efficacy of yogurt drink with added plant stanol esters (Benecol® yogurt drink) in higher doses than the typically used (2g/d stanols), in lowering blood lipids in moderately hypercholesterolemic subjects.MethodsA randomized double-blind crossover, placebo-controlled study in moderately hypercholesterolemic subjects (n = 40) aged between 20 and 50 years old.ResultsYogurt drink with added plant stanols (4 g) as esters (Benecol®, Colanta) consumption compared to regular yogurt drink caused a statistically significant decrease in total cholesterol and low density lipoprotein cholesterol by 7.2% and 10.3%. During the two periods and compared to controls, high-density lipoprotein cholesterol and triglycerides were not significantly different.ConclusionsYogurt drink with an active ingredient in Benecol®, plant stanol esters, reduced total cholesterol and LDL cholesterol in moderately hypercholesterolemic subjects.Trial registrationNCT01461798.

Therapeutic Reflections in Cholesterol Homeostasis and Gallstone Disease: A Review

Cholesterol gallstone disease is one of the most prevalent and the most costly digestive diseases in Western countries. Its pathogenesis is a complex paradigm resulting from the interaction of genetic factors, hepatic hypersecretion of cholesterol, increased intestinal absorption of cholesterol, a constantly "supersaturated" bile, crystallization of biliary cholesterol, and gallbladder stasis. De novo cholesterol biosynthesis, biliary cholesterol output, and intestinal cholesterol absorption are therefore key steps involved in cholesterol homeostasis. Establishing the right pharmacological therapy for cholesterol gallstones is of major importance in Western healthcare systems. Certain drugs might independently influence cholesterol gallstone formation by blocking the 3-hydroxy-3-methylglutaryl-coenzyme A reductase and inhibiting cholesterol biosynthesis in the liver (statins) or blocking cholesterol absorption in the small intestine apical membrane by specifically inhibiting the Niemann-Pick C1-like 1 protein (ezetimibe). This review will focus on the possibility that statins and ezetimibe, by acting at different levels of cholesterol homeostasis, might represent novel therapeutic approaches to prevent cholesterol gallstones in selected subjects at risk.

Physiological role of hepatic NPC1L1 in human cholesterol and lipoprotein metabolism: New perspectives and open questions

The importance of the cholesterol transporter Niemann-Pick C1 like protein 1 (NPC1L1)in the small intestine for efficient absorption of cholesterol is well documented and its physiological importance is clear (1). Similarly, the drug ezetimibe (Zetia™), which blocks function of this transporter, reduces plasma cholesterol, primarily LDL, by dramatically reducing intestinal absorption of dietary and biliary cholesterol (2). There are controversies about the exact mechanism by which NPC1L1 functions: whether the protein is on the apical cell membrane or intracellular vesicles or both (3–5), and whether ezetimibe directly blocks NPC1L1 or interrupts its association with other proteins in the sterol absorption and transport pathway (6–8). Nevertheless, it is now accepted that this protein is the key player in sterol absorption, although other transporters may play ancillary roles (9, 10).

Dose-dependent LDL-cholesterol lowering effect by plant stanol ester consumption: clinical evidence

Elevated serum lipids are linked to cardiovascular diseases calling for effective therapeutic means to reduce particularly LDL-cholesterol (LDL-C) levels. Plant stanols reduce levels of LDL-C by partly blocking cholesterol absorption. Accordingly the consumption of foods with added plant stanols, typically esterified with vegetable oil fatty acids in commercial food products, are recommended for lowering serum cholesterol levels. A daily intake of 1.5 to 2.4 g of plant stanols has been scientifically evaluated to lower LDL-C by 7 to 10% in different populations, ages and with different diseases. Based on earlier studies, a general understanding is that no further reduction may be achieved in intakes in excess of approximately 2.5 g/day. Recent studies however suggest that plant stanols show a continuous dose–response effect in serum LDL-C lowering. This review discusses the evidence for a dose-effect relationship between plant stanol ester consumption and reduction of LDL-C concentrations with daily intakes of plant stanols of 4 g/day or more. We identified five such studies and the overall data demonstrate a linear dose-effect relationship with the most pertinent LDL-Cholesterol lowering outcome, 18%, achieved by a daily intake of 9 to 10 g of plant stanols. Along with reduction in LDL-C, the studies demonstrated a decrease in cholesterol absorption markers, the serum plant sterol to cholesterol ratios, by increasing the dose of plant stanol intake. None of the studies with daily intakes up to 10 g of plant stanols reported adverse clinical or biochemical effects from plant stanols. In a like manner, the magnitude of decrease in serum antioxidant vitamins was not related to the dose of plant stanols consumed and the differences between plant stanol ester consumers and controls were minor and insignificant or nonexisting. Consumption of plant stanols in high doses is feasible as a range of food products are commercially available for consumption including spreads and yoghurt type drinks. In conclusion, a dose-effect relationship of plant stanols in higher doses than currently recommended has been demonstrated by recent clinical studies and a meta-analysis. Further studies are called for to provide confirmatory evidence amenable for new health claim applications and dietary recommendations.

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.

Rafting for gallstones by slowing mass transit

Rafting for gallstones by slowing mass transit

Improved efficacy for ezetimibe and rosuvastatin by attenuating the induction of PCSK9

Reducing circulating LDL-cholesterol (LDL-c) reduces the risk of cardiovascular disease in people with hypercholesterolemia. Current approaches to reduce circulating LDL-c include statins, which inhibit cholesterol synthesis, and ezetimibe, which blocks cholesterol absorption. Both elevate serum PCSK9 protein levels in patients, which could attenuate their efficacy by reducing the amount of cholesterol cleared from circulation. To determine whether PCSK9 inhibition could enhance LDL-c lowering of both statins and ezetimibe, we utilized small interfering RNAs (siRNAs) to knock down Pcsk9, together with ezetimibe, rosuvastatin, and an ezetimibe/rosuvastatin combination in a mouse model with a human-like lipid profile. We found that ezetimibe, rosuvastatin, and ezetimibe/rosuvastatin combined lower serum cholesterol but induce the expression of Pcsk9 as well as the Srebp-2 hepatic cholesterol biosynthesis pathway. Pcsk9 knockdown in combination with either treatment led to greater reductions in serum non-HDL with a near-uniform reduction of all LDL-c subfractions. In addition to reducing serum cholesterol, the combined rosuvastatin/ezetimibe/Pcsk9 siRNA treatment exhibited a significant reduction in serum APOB protein and triglyceride levels. Taken together, these data provide evidence that PCSK9 inhibitors, in combination with current therapies, have the potential to achieve greater reductions in both serum cholesterol and triglycerides.

Cholesterol Intake Modulates Plasma Triglyceride Levels in Glycosylphosphatidylinositol HDL-Binding Protein 1-Deficient Mice

To determine whether plasma triglyceride levels in adult Glycosylphosphatidylinositol HDL-binding protein 1 (GPIHBP1)-deficient (Gpihbp1(-/-)) mice would be sensitive to cholesterol intake. Gpihbp1(-/-) mice were fed a Western diet containing 0.15% cholesterol. After 4 to 8 weeks, their plasma triglyceride levels were 113 to 135 mmol/L. When 0.005% ezetimibe was added to the diet to block cholesterol absorption, Lpl expression in the liver was reduced significantly, and the plasma triglyceride levels were significantly higher (>170 mmol/L). We also assessed plasma triglyceride levels in Gpihbp1(-/-) mice fed Western diets containing either high (1.3%) or low (0.05%) amounts of cholesterol. The high-cholesterol diet significantly increased Lpl expression in the liver and lowered plasma triglyceride levels. Treatment of Gpihbp1(-/-) mice with ezetimibe lowers Lpl expression in the liver and increases plasma triglyceride levels. A high-cholesterol diet had the opposite effects. Thus, cholesterol intake modulates plasma triglyceride levels in Gpihbp1(-/-) mice.

The effect of exogenous cholesterol and lipid-modulating agents on enterocytic amyloid-β abundance

Dietary cholesterol may influence Alzheimer's disease risk, because it regulates the synthesis of amyloid-beta. It was recently demonstrated in enterocytes of wild-type mice that intracellular amyloid-beta expression is enhanced in response to a high-fat diet made up of SFA and cholesterol. Intestinally derived amyloid-beta may be associated with postprandial lipoproteins in response to dietary fats and could be a key regulator in chylomicron metabolism. The present study was designed to investigate the role of cholesterol in modulating amyloid-beta abundance in enterocytes. Wild-type mice were fed a low-fat diet supplemented with 2 % (w/w) cholesterol. The effects of cholesterol absorption inhibition and cholesterol biosynthesis inhibition utilising ezetimibe and atorvastatin, respectively, were also studied. Quantitative immunohistochemistry was utilised to determine enterocytic amyloid-beta homeostasis. We found that enterocytic amyloid-beta concentration was significantly attenuated in mice fed the 2 % (w/w) cholesterol diet. However, blocking cholesterol absorption reversed the cholesterol-feeding effect. Consistent with a suppressive effect of cholesterol on enterocytic amyloid-beta abundance, atorvastatin, an inhibitor of cholesterol biosynthesis, enhanced amyloid-beta. However, providing exogenous cholesterol abolished the atorvastatin-induced effect. In contrast to the suppression of enterocytic amyloid-beta by dietary cholesterol, mice fed a diet enriched in SFA had markedly greater abundance. Collectively, the findings suggest that exogenous and endogenous cholesterol reduce amyloid-beta concentration in enterocytes by suppressing production, or enhancing secretion associated with postprandial lipoproteins. Intestinally derived amyloid-beta will contribute to the pool of plasma protein and may influence cerebral amyloid homeostasis by altering the bi-directional transfer across the blood-brain barrier.

The Cholesterol Absorption Inhibitor Ezetimibe Acts by Blocking the Sterol-Induced Internalization of NPC1L1

Niemann-Pick C1-like 1 (NPC1L1) is a polytopic transmembrane protein that plays a critical role in cholesterol absorption. Ezetimibe, a hypocholesterolemic drug, has been reported to bind NPC1L1 and block cholesterol absorption. However, the molecular mechanism of NPC1L1-mediated cholesterol uptake and how ezetimibe inhibits this process are poorly defined. Here we find that cholesterol specifically promotes the internalization of NPC1L1 and that this process requires microfilaments and the clathrin/AP2 complex. Blocking NPC1L1 endocytosis dramatically decreases cholesterol internalization, indicating that NPC1L1 mediates cholesterol uptake via its vesicular endocytosis. Ezetimibe prevents NPC1L1 from incorporating into clathrin-coated vesicles and thus inhibits cholesterol uptake. Together, our data suggest a model wherein cholesterol is internalized into cells with NPC1L1 through clathrin/AP2-mediated endocytosis and ezetimibe inhibits cholesterol absorption by blocking the internalization of NPC1L1.

Ezetimibe Combined with Low-Dose Statin Effectively Lowers LDL in Protease Inhibitor Treated Patients

Ezetimibe (EZB) lowers cholesterol by blocking cholesterol absorption in the intestine. Data with EZB are limited in HIV-infected patients. We enrolled HIV-infected adults in this prospective, noncontrolled, single-center pilot study if their low-density lipoprotein (LDL) was not at goal despite therapy with a statin. Stable protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) and a low-dose statin were required for inclusion. The primary endpoint was LDL reduction at 18 weeks. In a subgroup of patients on lopinavir/ritonavir (LPV/r), trough concentrations were obtained before and after addition of EZB. Twenty patients were enrolled; 12 (60%) men, 18 (90%) African American. HAART included ritonavir (RTV)-boosted PIs in 17 (85%) patients; 3 (15%) were on nelfinavir. Mean percent changes from baseline in LDL were -10.9%, -12.2%, and -12.4% at weeks 6, 12, and 18, respectively (p < 0.05 for each time period vs. baseline). Mean percent changes from baseline in total cholesterol (TC) were -11.1%, -9.6%, and 9.1% at weeks 6, 12, and 18, respectively (p < 0.05 at each time period vs. baseline). No significant changes in triglycerides, high-density lipoprotein, and LPV/r concentrations were seen. One patient experienced elevated creatine phosphokinase possibly related to study medication; no other adverse effects were seen. Addition of EZB to low-dose statin effectively lowers LDL and TC and appears to be safe and well tolerated.

SREBP-1c Gene Polymorphism is Associated with Increased Inhibition of Cholesterol-Absorption in Response to Ezetimibe Treatment

Sterol regulatory binding proteins 1 and 2 (SREBPs) are transcription factors regulating lipid metabolism. A recent study has associated the CC genotype of the SREBP-1c polymorphism G952G with increased cholesterol synthesis. Further evidence suggests that SREBPs play a role in cholesterol absorption and that SREBP polymorphisms modulate the response to statin therapy. The present study examines whether the G952G polymorphism alters cholesterol synthesis and/or absorption and whether it modulates the response to widely used lipid-lowering drugs such as inhibitors of cholesterol synthesis (simvastatin) or absorption (ezetimibe). Seventy-two healthy male subjects with LDL cholesterol <190 mg/dL participated in the study. Twenty four subjects were treated with ezetimibe (10 mg), simvastatin (40 mg) or their combination, respectively, for two weeks. Blood was drawn before and after the 2-week treatment period. Eleven CC homozygous carriers of the gene were found (15%). There were no differences in cholesterol synthesis or absorption between the CC homozygotes and the G allele-carriers, as measured by the ratios to cholesterol of serum lathosterol, desmosterol and cholestenol (synthesis markers) and cholestanol, sitosterol and campesterol (absorption markers). Ezetimibe had a significantly more potent effect in blocking cholesterol absorption in the CC homozygotes compared to the G-carriers ( P=0.002). The G/C (G952G) polymorphism of the SREBP-1 gene is not associated with cholesterol synthesis or absorption in a German male population. The CC homozygotes have a significantly increased response to the effects of ezetimibe on cholesterol absorption compared to the G allele-carriers, suggesting that SREBP-1 may be implicated in ezetimibe's mechanism of action.

Human cholesterol metabolism and therapeutic molecules

There has been a fascinating interplay between the discovery of some of the key enzymes, receptors and transporters in cholesterol biosynthesis and transfer and the development of drugs for the regulation of cholesterol metabolism. The discovery of the low‐density lipoprotein (LDL) receptor led to the realization that circulating LDL cholesterol could be decreased when hepatic LDL receptor expression was stimulated by decreasing intrahepatic cholesterol levels. The first class of drugs which operate in this way were the bile‐acid sequestrating agents, which, by interrupting the enterohepatic circulation of bile acids, deplete the liver of cholesterol used to replenish the pool of bile salts. Ezetimibe, which was developed to block cholesterol absorption from the intestine, led to the discovery of the Nieman‐Pick C1‐Like 1 sterol transporter channel. The statins, which have proved enormously successful in preventing cardiovascular disease, were discovered amongst fungal metabolites which inhibit hydroxyl methyl CoA reductase, the rate‐limiting enzyme for hepatic cholesterol biosynthesis. Drugs which block enzymes at other stages of the cholesterol biosynthetic pathway, particularly the squalene synthase inhibitors, are entering the clinical phase of their development. Drugs which interfere with hepatic very low‐density lipoprotein assembly in the liver, such as microsomal triglyceride transfer protein inhibitors and apolipoprotein B mRNA antisense oligonucleotides, are currently undergoing evaluation. Cholesteryl ester transfer protein (CETP) inhibitors, which decrease cholesteryl ester heteroexchange within the circulation, have undergone development to the point of clinical evaluation, and this will eventually settle the controversy about whether CETP is pro‐ or antiatherogenic.

Human cholesterol metabolism and therapeutic molecules

There has been a fascinating interplay between the discovery of some of the key enzymes, receptors and transporters in cholesterol biosynthesis and transfer and the development of drugs for the regulation of cholesterol metabolism. The discovery of the low-density lipoprotein (LDL) receptor led to the realization that circulating LDL cholesterol could be decreased when hepatic LDL receptor expression was stimulated by decreasing intrahepatic cholesterol levels. The first class of drugs which operate in this way were the bile-acid sequestrating agents, which, by interrupting the enterohepatic circulation of bile acids, deplete the liver of cholesterol used to replenish the pool of bile salts. Ezetimibe, which was developed to block cholesterol absorption from the intestine, led to the discovery of the Nieman-Pick C1-Like 1 sterol transporter channel. The statins, which have proved enormously successful in preventing cardiovascular disease, were discovered amongst fungal metabolites which inhibit hydroxyl methyl CoA reductase, the rate-limiting enzyme for hepatic cholesterol biosynthesis. Drugs which block enzymes at other stages of the cholesterol biosynthetic pathway, particularly the squalene synthase inhibitors, are entering the clinical phase of their development. Drugs which interfere with hepatic very low-density lipoprotein assembly in the liver, such as microsomal triglyceride transfer protein inhibitors and apolipoprotein B mRNA antisense oligonucleotides, are currently undergoing evaluation. Cholesteryl ester transfer protein (CETP) inhibitors, which decrease cholesteryl ester heteroexchange within the circulation, have undergone development to the point of clinical evaluation, and this will eventually settle the controversy about whether CETP is pro- or antiatherogenic.

Dual Action Of The Ezetimibe Target Niemann-Pick C1-Like 1

Low-density lipoprotein (LDL), the major cholesterol carrier in human blood, is the offending agent of coronary heart disease (CHD), which remains the leading cause of death in developed countries. Levels of blood cholesterol are mainly controlled by de novo biosynthesis, intestinal absorption and biliary/intestinal excretion. Statins, by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme in the pathway of cholesterol biosynthesis, lower plasma LDL-cholesterol (LDL-C) and reduce morbidity and mortality from CHD. In spite of these beneficial effects, considerable inter-individual variation exists in response to statin treatment and many patients receiving statin monotherapy do not achieve the LDL-C goal recommended by the National Cholesterol Education Program [1]. Ezetimibe (commercially known as Zetia®) is the first member of a class of cholesterol-lowering agents that inhibit intestinal cholesterol absorption [2]. Following oral administration, the drug is rapidly glucuronidated in the intestine and undergoes extensive enterohepatic recirculation [3]. Both ezetimibe and its glucuronide are active in blocking cholesterol absorption [3]. Many clinical studies have demonstrated that ezetimibe monotherapy or coadministration of ezetimibe with a statin effectively lowers plasma total and LDL-C in primary hypercholesterolemic subjects [4], and even in homozygous familial hypercholesterolemia [5].