Cholesterol absorption inhibitors as a therapeutic option for hypercholesterolaemia

Drug discovery effectiveness from the standpoint of therapeutic mechanisms and indications

The productivity of the pharmaceutical industry has been widely discussed in recent years, particularly with regard to concerns that substantial expenditures on research and development have failed to translate into approved drugs. Various analyses of this productivity challenge have focused on aspects such as attrition rates at particular clinical phases or the physicochemical properties of drug candidates, but relatively little attention has been paid to how the industry has performed from the standpoint of the choice of therapeutic mechanisms and their intended indications. This article examines what the pharmaceutical industry has achieved in this respect by analysing comprehensive industry-wide data on the mechanism-indication pairs that have been investigated during the past 20 years. Our findings indicate several points and trends that we hope will be useful in understanding and improving the productivity of the industry, including areas in which the industry has had substantial success or failure and the relative extent of novelty in completed and ongoing projects.

Black rice and anthocyanins induce inhibition of cholesterol absorption in vitro

Black rice (Oryza sativa L.) is often associated with blood lipid control. This study systematically assessed the inhibition of cholesterol absorption in vitro by black rice and explored cholesterol-lowering compounds present in this rice. Our results indicated that black rice extracts (BRE), which were aqueous, ethanol extracts and a fraction of macroporous resin caused the reduction of cholesterol absorption by inhibiting pancreatic lipase, decreasing the micellar cholesterol solubility and suppressing cholesterol uptake in Caco-2 cells. The inhibitory activity was positively associated with anthocyanin (cyanidin-3-glucoside (Cy-3-G) and peonidin-3-glucoside (Pn-3-G)) contents of the extracts. Therefore, the cholesterol absorption inhibiting properties of anthocyanins were further explored. The IC50 values of Cy-3-G and Pn-3-G against pancreatic lipase were 42.53 ± 4.45 and 18.13 ± 4.22 μg mL(-1), respectively. Kinetic analysis suggested that the enzymatic inhibitory mode of Cy-3-G and Pn-3-G belonged to the competitive type. In mixed micelles, Cy-3-G and Pn-3-G dose dependently reduced the solubility of cholesterol. Meanwhile, a potential mechanism of cholesterol reduction by anthocyanins was investigated. Results showed that anthocyanins led to precipitation of cholesterol from micellar solution, which may induce the reduction of cholesterol. In Caco-2 cells, Cy-3-G and Pn-3-G (40 μg mL(-1)) exhibited a significant reduction in cholesterol uptake, and the degree of this reduction was almost the same as that observed in the group treated with Ezetimibe at the same concentration. These findings provide important evidence that anthocyanins may partly contribute to the inhibitory effects of black rice on cholesterol absorption, and thus may be applied for the prevention and treatment of hypercholesterolaemia.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of hyzetimibe (HS-25) in healthy Chinese subjects

Hyzetimibe (HS-25) is a new cholesterol absorption inhibitor. We performed the first-in-human study to assess the safety, tolerability, and pharmacokinetics (including the effect of food) and pharmacodynamics (effect on blood lipid level) following single (1, 3, 5, 10, 20, and 30 mg) and multiple (5, 10, and 20 mg) ascending-dose of hyzetimibe in healthy subjects. An increase of exposure (area under the plasma concentration-time curve and maximum plasma concentration) to hyzetimibe and hyzetimibe-glucuronide (HS-25M1) was observed in an approximately dose-proportional manner. A terminal half-life of approximately 21 hours was observed with doses ranging between 5 and 30 mg. Steady state was achieved by day 8 of once-daily dosing with 1.6- and 1.2-fold accumulation for hyzetimibe and hyzetimibe-glucuronide, respectively. Food did not have any effect on hyzetimibe and hyzetimibe-glucuronide exposure. Administration of hyzetimibe once daily for 10 days reduced the levels of low-density lipoprotein cholesterol levels in healthy subjects and these recovered after discontinuation of this drug. All of the adverse events were mild or moderate in severity, and the majority of them were unrelated to hyzetimibe, with no dose-dependent trends. These findings suggest that hyzetimibe could be a potential treatment for hypercholesterolemia.

Knee pain: an unanticipated finding related to a rare genetic disorder--abetalipoproteinemia

PURPOSE

The purpose of this case study is to raise awareness about an uncommon cause of knee pain.

DATA SOURCES

Review of literature was done using PubMed, CINAHL, and Medline. There was no limitation placed on the publication year. Only articles written in English were included.

CONCLUSION

Knee pain is a common diagnosis that many healthcare providers see on a daily basis in their practice. Musculoskeletal injury or trauma is most commonly identified as the cause of this symptom. However, there are rare instances in which an unexpected finding in a client's history and physical exam lead us to an unexpected cause, such as abetalipoproteinemia. Abetalipoproteinemia is a rare autosomal recessive disorder in which an affected individual does not absorb lipids or the lipid-soluble vitamins A, D, E, and K. Multiple body systems are impacted by this fat malabsorption and resultant vitamin deficiencies. Without corrective supplementation, clinical manifestations which are directly related to the vitamin deficiencies will appear as presented in this case study-knee pain.

IMPLICATIONS FOR PRACTICE

This case study emphasizes the need for nurse practitioners to seek out opportunities to further our knowledge which will enhance our clinical expertise as well as the quality of the health care we provide to our clients.

Comparison of the pharmacological profiles of murine antisense oligonucleotides targeting apolipoprotein B and microsomal triglyceride transfer protein

Therapeutic agents that suppress apolipoprotein B (apoB) and microsomal triglyceride transfer protein (MTP) levels/activity are being developed in the clinic to benefit patients who are unable to reach target LDL-C levels with maximally tolerated lipid-lowering drugs. To compare and contrast the metabolic consequences of reducing these targets, murine-specific apoB or MTP antisense oligonucleotides (ASOs) were administered to chow-fed and high fat-fed C57BL/6 or to chow-fed and Western diet-fed LDLr⁻/⁻ mice for periods ranging from 2 to 12 weeks, and detailed analyses of various factors affecting fatty acid metabolism were performed. Administration of these drugs significantly reduced target hepatic mRNA and protein, leading to similar reductions in hepatic VLDL/triglyceride secretion. MTP ASO treatment consistently led to increases in hepatic triglyceride accumulation and biomarkers of hepatotoxicity relative to apoB ASO due in part to enhanced expression of peroxisome proliferator activated receptor γ target genes and the inability to reduce hepatic fatty acid synthesis. Thus, although both drugs effectively lowered LDL-C levels in mice, the apoB ASO produced a more positive liver safety profile.

Ezetimibe therapy: mechanism of action and clinical update

The lowering of low-density lipoprotein cholesterol (LDL-C) is the primary target of therapy in the primary and secondary prevention of cardiovascular events. Although statin therapy is the mainstay for LDL-C lowering, a significant percentage of patients prescribed these agents either do not achieve targets with statin therapy alone or have partial or complete intolerance to them. For such patients, the use of adjuvant therapy capable of providing incremental LDL-C reduction is advised. One such agent is ezetimibe, a cholesterol absorption inhibitor that targets uptake at the jejunal enterocyte brush border. Its primary target of action is the cholesterol transport protein Nieman Pick C1 like 1 protein. Ezetimibe is an effective LDL-C lowering agent and is safe and well tolerated. In response to significant controversy surrounding the use and therapeutic effectiveness of this drug, we provide an update on the biochemical mechanism of action for ezetimibe, its safety and efficacy, as well as the results of recent randomized studies that support its use in a variety of clinical scenarios.

Effects of fenofibrate on cardiovascular events in patients with diabetes, with and without prior cardiovascular disease: The Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study

BACKGROUND

In the FIELD study, comparison of the effect of fenofibrate on cardiovascular disease (CVD) between those with prior CVD and without was a prespecified subgroup analysis.

METHODS

The effects of fenofibrate on total CVD events and its components in patients who did (n = 2,131) and did not (n = 7,664) have a history of CVD were computed by Cox proportional hazards modeling and compared by testing for treatment-by-subgroup interaction. The analyses were adjusted for commencement of statins, use of other CVD medications, and baseline covariates. Effects on other CVD end points were explored.

RESULTS

Patients with prior CVD were more likely than those without to be male, to be older (by 3.3 years), to have had a history of diabetes for 2 years longer at baseline, and to have diabetic complications, hypertension, and higher rates of use of insulin and CVD medications. Discontinuation of fenofibrate was similar between the subgroups, but more patients with prior CVD than without, and also more placebo than fenofibrate-assigned patients, commenced statin therapy. The borderline difference in the effects of fenofibrate between those who did (hazard ratio [HR] 1.02, 95% CI 0.86-1.20) and did not have prior CVD (HR 0.81, 95% CI 0.70-0.94; heterogeneity P = .045) became nonsignificant after adjustment for baseline covariates and other CVD medications (HR 0.96, 95% CI 0.81-1.14 vs HR 0.78, 95% CI 0.67-0.90) (heterogeneity P = .06).

CONCLUSIONS

Our findings do not support treating patients with fenofibrate differently based on any history of CVD, in line with evidence from other trials.

Molecular mechanisms of membrane transport of vitamin E

Vitamin E is an essential fat-soluble micronutrient for higher mammals and functions as an antioxidant for lipids and also as a regulator of gene expression and a modulator of cell signaling and proliferation. To exert its physiological functions, vitamin E must achieve an appropriate disposition throughout the body via several processes, such as intestinal absorption, uptake and efflux in peripheral tissues and biliary secretion. In this review, we mainly discuss membrane proteins involved in these transport processes (ATP-binding cassette transporter A1, scavenger receptor class B type I, Niemann-Pick C1-like 1 and multidrug resistance 3) and vitamin E-mediated regulation of their expression.

Disodium ascorbyl phytostanol phosphate (FM-VP4), a modified phytostanol, is a highly active hypocholesterolaemic agent that affects the enterohepatic circulation of both cholesterol and bile acids in mice

Disodium ascorbyl phytostanol phosphate (FM-VP4) is a synthetic compound derived from sitostanol and campestanol that has proved to be efficient as a cholesterol-lowering therapy in mice and human subjects. However, the mechanism of action of FM-VP4 remains unknown. The present study tests the ability of FM-VP4 to alter intestinal and liver cholesterol homeostasis in mice. Female C57BL/6J mice were fed either a control chow or a 2 % FM-VP4-enriched diet for 4 weeks. FM-VP4 reduced the in vivo net intestinal cholesterol absorption and plasma and liver cholesterol concentrations by 2.2-, 1.5- and 1.6-fold, respectively, compared with control mice. Furthermore, FM-VP4 also showed an impact on bile acid homeostasis. In FM-VP4 mice, liver and intestinal bile acid content was increased by 1.3- and 2.3-fold, respectively, whereas faecal bile acid output was 3.3-fold lower. FM-VP4 also increased the intestinal absorption of orally administered [3H]taurocholic acid to small intestine in vivo. Inhibition of intestinal cholesterol absorption by FM-VP4 was not mediated via transcriptional increases in intestine liver X receptor (LXR)-alpha, adenosine triphosphate-binding cassette transporter (ABC)-A1, ABCG5/G8 nor to decreases in intestinal Niemann-Pick C1-like 1 (NPC1L1) expression. In contrast, FM-VP4 up-regulated liver LXRalpha, ABCA1, ABCG5, scavenger receptor class BI (SR-BI) and hydroxymethylglutaryl coenzyme A reductase (HMGCoA-R) gene expression, whereas it down-regulated several farnesoid X receptor (FXR)-target genes such as cytochrome P450 family 7 subfamily A polypeptide 1 (CYP7A1) and Na+/taurocholate co-transporter polypeptide (NTCP). In conclusion, FM-VP4 reduced intestinal cholesterol absorption, plasma and liver cholesterol and affected bile acid homeostasis by inducing bile acid intestinal reabsorption and changed the liver expression of genes that play an essential role in cholesterol homeostasis. This is the first phytosterol or stanol that affects bile acid metabolism and lowers plasma cholesterol levels in normocholesterolaemic mice.

Current and future pharmacologic options for the management of patients unable to achieve low-density lipoprotein-cholesterol goals with statins

Low-density lipoprotein-cholesterol (LDL-C) lowering is the mainstay of the current treatment guidelines in the management of cardiovascular risk. HMG-CoA reductase inhibitors (statins) are currently the most effective LDL-C-lowering drugs. However, a substantial number of patients do not reach treatment targets with statins. Therefore, an unmet medical need exists for lipid-lowering drugs with novel mechanisms of action to reach the recommended cholesterol target levels, either by monotherapy or combination therapy. Upregulation of the LDL receptor with squalene synthase inhibitors has shown promising results in animal studies but the clinical development of the lead compound lapaquistat (TAK-475) has recently been discontinued. Ezetimibe combined with statins allowed significantly more patients to reach their LDL-C targets. Other inhibitors of intestinal cholesterol absorption such as disodium ascorbyl phytostanol phosphate (FM-VP4) and bile acid transport inhibitors have shown positive results in early development trials, whereas the prospect of acyl coenzyme A: cholesterol acyltransferase inhibition in cardiovascular prevention is dire. Selective inhibition of messenger RNA (mRNA) by antisense oligonucleotides is a new approach to modify cholesterol levels. The inhibition of apolipoprotein B mRNA is in advanced development and mipomersen sodium (ISIS 301012) has shown striking results in phase II studies both as monotherapy as well as in combination with statins.

Porcine circovirus 2 infection of epithelial cells is clathrin-, caveolae- and dynamin-independent, actin and Rho-GTPase-mediated, and enhanced by cholesterol depletion

Epithelial cells are the major in vivo target cells for porcine circovirus type 2 (PCV2). Although these cells are used for most studies of PCV2 gene expression and, little is known on PCV2 entry, attachment and internalization, in epithelial cells. PCV2 attachment to epithelial cells occurred rapidly and in a time-dependent manner. In contrast to attachment, internalization was slow. Immunofluorescent stainings revealed that during internalization, PCV2 co-localized with clathrin, but not caveolin. Blocking clathrin-mediated endocytosis increased instead of decreased the number of PCV2-infected cells by threefold, suggesting that it does not represent the main internalization pathway leading to a full replication. Further analysis with different inhibitors revealed that also macropinocytosis, dynamin-dependent internalization and membrane cholesterol play no role in PCV2 entry that leads to infection. Inhibition of small GTPases with Clostridium difficile toxin B reduced the number of PCV2-infected PK-15, SK and STs to 63+/-25%, 47+/-21% and 14+/-6%, respectively. Finally, inhibiting actin polymerization also blocked PCV2 infection, showing the need for actin during PCV2 infection. Together, these data indicate that a dynamin- and cholesterol-independent, but actin- and small GTPase-dependent pathway, allows PCV2 internalization in epithelial cells that leads to infection and that clathrin-mediated PCV2 internalization in epithelial cells is not followed by a full replication.

Emerging antidyslipidemic drugs

BACKGROUND

Many patients at high risk for coronary heart disease (CHD) fail to reach target lipid levels with currently available medications, and a small but clinically relevant proportion of patients experience adverse effects. Thus, additional pharmaceutical strategies are required to fill these gaps in efficacy and tolerability.

OBJECTIVE

To provide an overview of both current and emerging antidyslipidemic drugs.

METHODS

For the current antidyslipidemic drugs, we focus primarily on statins, bile acid sequestrants, fibrates, ezetimibe, and niacin. Emerging antidyslipidemic drugs herein discussed were identified by searching the Pharmaprojects database for 'hypercholesterolemia drugs' (Phase II or Phase III), 'HDL-based therapies', and 'PCSK9 inhibition'.

RESULTS/CONCLUSIONS

Combinations of currently existing medications are most easily applicable. Meanwhile, strategies to raise HDL-C rely on a deep understanding of the complexity of HDL metabolism. Furthermore, novel approaches to further reduce LDL-C warrant careful evaluation of benefit-risk ratio. Finally, the medical community will have to rely on late-phase CHD outcome studies as the final arbiter of clinical application for any new antidyslipidemia treatment.

Cardiovascular effects of prorenin blockade in genetically spontaneously hypertensive rats on normal and high-salt diet

Recent reports have demonstrated a potential role of tissue prorenin in the pathogenesis of cardiovascular and renal damage. This study was designed to examine the role of prorenin in the pathogenesis of target organ damage in spontaneously hypertensive rats (SHRs), the best naturally occurring experimental model of essential hypertension. To this end, we studied 20-wk-old male SHRs receiving a normal diet and 8-wk-old male SHRs given food with 8% NaCl. One-half the rats in each group were given prorenin inhibitor (PRAM-1, 0.1 mg.kg(-1).day(-1)) via osmotic minipumps; the other half served as controls. Arterial pressure, left ventricular function, cardiovascular mass indexes, cardiac fibrosis, and renal function were examined at the end of the experiment. Arterial pressure was unaffected by PRAM-1 in rats on either regular or salt-excess diets. In those rats receiving a normal diet, the blockade of prorenin activation consistently reduced left ventricular mass but affected no other variable. Salt-loaded rats given PRAM-1 for 8 wk demonstrated (1) reduced serum creatinine level, (2) decreased left ventricular mass, (3) improved left ventricular function, and (4) reduced left ventricular fibrosis. These data demonstrated that the blockade of nonproteolytic activation of prorenin exerted significant cardiovascular and renal benefit in SHRs with cardiovascular damage produced by salt excess and suggested that the activation of cardiovascular or renal prorenin may be a major mechanism that mediates cardiac and renal damage in this form of accelerated hypertension.

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.

Inhibition of intestinal absorption of cholesterol by ezetimibe or bile acids by SC-435 alters lipoprotein metabolism and extends the lifespan of SR-BI/apoE double knockout mice

SR-BI/apoE double knockout (dKO) mice exhibit many features of human coronary heart disease (CHD), including hypercholesterolemia, occlusive coronary atherosclerosis, cardiac hypertrophy, myocardial infarctions, cardiac dysfunction and premature death. Ezetimibe is a FDA-approved, intestinal cholesterol absorption inhibitor that lowers plasma LDL cholesterol in humans and animals and inhibits aortic root atherosclerosis in apoE KO mice, but has not been proven to reduce CHD. Three-week-ezetimibe treatment of dKO mice (0.005% (w/w) in standard chow administered from weaning) resulted in a 35% decrease in cholesterol in IDL/LDL-size lipoproteins, but not in VLDL- and HDL-size lipoproteins. Ezetimibe treatment significantly reduced aortic root (57%) and coronary arterial (68%) atherosclerosis, cardiomegaly (24%) and cardiac fibrosis (57%), and prolonged the lives of the mice (27%). This represents the first demonstration of beneficial effects of ezetimibe treatment on CHD. The dKO mice were similarly treated with SC-435 (0.01% (w/w)), an apical sodium codependent bile acid transporter (ASBT) inhibitor, that blocks intestinal absorption of bile acids, lowers plasma cholesterol in animals, and reduces aortic root atherosclerosis in apoE KO mice. The effects of SC-435 treatment were similar to those of ezetimibe: 37% decrease in ILD/LDL-size lipoprotein cholesterol and 57% prolongation in median lifespan. Thus, inhibition of intestinal absorption of either cholesterol (ezetimibe) or bile acids (SC-435) significantly reduced plasma IDL/LDL-size lipoprotein cholesterol levels and improved survival of SR-BI/apoE dKO mice. The SR-BI/apoE dKO murine model of atherosclerotic occlusive, arterial CHD appears to provide a useful system to evaluate compounds that modulate cholesterol homeostasis and atherosclerosis.

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.

MTP inhibition as a treatment for dyslipidaemias: time to deliver or empty promises?

The development of cholesterol-lowering drugs, including a statins, bile acid sequestrants and cholesterol absorption inhibitors has expanded the options for cardiovascular prevention. Recent treatment guidelines emphasise that individuals at substantial risk for atherosclerotic coronary heart disease should meet defined lipid targets. Combination therapy with drugs that have different and complementary mechanisms of action is often needed to achieve these goals. Existing approaches to the treatment of hypercholesterolaemia are still ineffective in halting the progression of coronary artery disease in some patients despite combination therapies. Other patients are resistant to, or intolerant of, conventional pharmacotherapy and remain at high-risk of atherosclerotic cardiovascular disease, so that alternative approaches are needed. New agents, including inhibitors of microsomal triglyceride transfer protein (MTP), may play a future role, either alone or in combination, in the treatment of hyperlipidaemias. This review focuses on novel approaches to treat dyslipidaemias via the inhibition of MTP. Patients most suitable for use of MTP inhibitors include those with hepatic hypersecretion of apoB, including the metabolic syndrome, Type 2 diabetes mellitus and familial combined hyperlipidaemia, as well as homozygous and heterozygous familial hypercholesterolaemia. However, certain safety issues with these agents need resolving, particularly fatty liver disease.