Cholesterol absorption inhibitors: defining new options in lipid management

Monocyclic beta-lactams for therapeutic uses: a patent overview (2010-2020)

INTRODUCTION

Monocyclic beta-lactams are four-membered cyclic amides with various structural modifications of the nucleus that determine their chemical reactivity and target specificity. Their historical use is based on their antibacterial activity, but they have recently appeared in other areas as well.

AREAS COVERED

This review summarizes the relevant patent development on monocyclic beta-lactams in various therapeutic areas over the last 10 years. The majority of patents describe compounds with antibacterial activity, while there are some recent patents describing the neuroprotective, anti-inflammatory, anti-cancer, anticoagulant and antihyperlipidemic effects of 2-azetidinones.

EXPERT OPINION

Monocyclic beta-lactams can be considered safe and nontoxic drugs, as they have been used in the clinic for almost half of the century. Recently, monocyclic beta-lactams have been increasingly recognized for their non-antibiotic activity, which has led to some promising new clinical candidates in the field of neurodegenerative diseases and coagulation therapy. With regard to their antibacterial activity, there is still room for improvement of their activity and broadening of their spectrum of action, especially in Gram-positive bacteria and on drug-insensitive penicillin-binding proteins, and in increasing their beta-lactamase stability.

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.

LXRβ activation increases intestinal cholesterol absorption, leading to an atherogenic lipoprotein profile

OBJECTIVES

Liver X receptors (LXRs) are essential for the regulation of intestinal cholesterol absorption. Because two isoforms exist, LXRα and LXRβ, with overlapping but not identical functions, we investigated whether LXRα and LXRβ exert different effects on intestinal cholesterol absorption.

DESIGN

Wild-type (WT), LXRα(-/-) and LXRβ(-/-) mice were fed control diet, 0.2% cholesterol-enriched diet or 0.2% cholesterol-enriched diet plus the LXR agonist GW3965.

RESULTS

When fed a control diet, all three genotypes showed similar levels of cholesterol absorption. Of interest, a significant increase in cholesterol absorption was found in the LXRα(-/-) mice, but not in the WT or LXRβ(-/-) animals, when fed a diet enriched with 0.2% cholesterol or 0.2% cholesterol + GW3965. Reduced faecal neutral sterol excretion and a hydrophobic bile acid profile were also observed in LXRα(-/-) mice. Greater increases in the apolipoprotein (apo)B-containing lipoproteins in serum were seen in the LXRα(-/-) mice. A 0.2% cholesterol +GW3965 diet suppressed intestinal Npc1l1 protein expression to the same extent for all genotypes, while Abca1 and Abcg5 were elevated to the same degree.

CONCLUSIONS

In the intestine, LXRα and LXRβ seem to exert similar effects on expression of cholesterol-transporting proteins such as Npc1l1. Selective activation of LXRβ may generate effects such as increased cholesterol absorption and elevated serum levels of apoB-containing lipoproteins, which seem to be counteracted by LXRα. Therefore, an intestinal LXRβ-specific pathway might exist in terms of cholesterol transportation in addition to the main pathway.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Moderately decreased cholesterol absorption rates are associated with a large atheroprotective effect

OBJECTIVE

Human treatment with ezetimibe results in a moderate 50% to 54% decrease in cholesterol absorption and a 15% to 20% decrease in plasma LDL-cholesterol levels; nevertheless, the efficacy of ezetimibe therapy has been recently challenged by the ENHANCE trial. We examined the efficacy of a moderate decrease in cholesterol absorption in preventing atherosclerosis formation in the mouse.

METHODS AND RESULTS

Congenic 14DKK animals, consisting of a castaneus (CASA/Rk) chromosome 14 interval introgressed onto the C57BL/6J background, displayed a moderate decrease in cholesterol absorption rates. The effect of moderately decreased absorption on atherosclerosis formation was determined in 14DKK apolipoprotein E knockouts (14DKK-apoEKO). When compared to chow diet-fed control apoEKO mice, congenic 14DKK-apoEKO displayed a moderate 41% decrease in cholesterol absorption rates, 30% to 37% decrease in plasma cholesterol levels, and a 70% decrease in atherosclerosis formation. Studies on cholesterol efflux and reverse cholesterol transport (RCT) from 14DKK bone marrow-derived macrophages rejected a 14DKK interval-dependent atheroprotective effects that operate in macrophages. In contrast, 14DKK-apoEKO congenics were characterized by a 60% increase in RCT from peripheral tissue macrophages.

CONCLUSIONS

These studies strongly suggest that moderately decreased cholesterol absorption rates result in a large atheroprotective effect attributable to a decrease in plasma cholesterol levels and an increase in RCT from peripheral tissue macrophages.

Effect of melatonin on cholesterol absorption in rats

This study evaluated the influence of melatonin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic and plasma total cholesterol, plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol, a decrease in high density lipoprotein (HDL) cholesterol and an elevation in triacylglyceride (TG) levels in plasma and in the liver. Melatonin suspension (10 mg/kg), specially prepared for this purpose, cholestyramine (230 mg/kg) and ezetimibe (145 microg/kg) were administered orally to the rats fed HCD for 30 days. Melatonin significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in total cholesterol, TG, VLDL- and LDL-cholesterol in the plasma and contents of cholesterol and TG in the liver. The level of HDL cholesterol was significantly increased after melatonin. These results suggested that inhibition of cholesterol absorption caused by melatonin could be a mechanism contributing to the positive changes in plasma cholesterol, lipoprotein profile and the lipid contents in the liver.

Plasma cholesterol and related lipid levels of seemingly healthy public service employees in Kampala, Uganda

BACKGROUND

As Uganda's economy improves, many people tend to adopt western diets and sedentary life styles that predispose to cardiovascular diseases including hypertension. These may be in silent danger without any typical symptoms to send early warning signals. In Uganda, cardiovascular diseases (CVD) and diabetes mellitus are rapidly emerging as major causes of morbidity and mortality.

OBJECTIVE

This study was conducted to determine spot levels of plasma lipid indicators of CVD in seemingly healthy public service employees in Kampala, Uganda. The purpose of this study was achieved through analysis of fasting plasma samples for the following: Total cholesterol (TC), Triacylglycerols (TG), High density lipoprotein cholesterol (HDL), Low density lipoprotein cholesterol (LDL), and molar ratios of LDL/HDL, TC/ HDL, and TC/TG.

METHODS

One hundred and seventy four fasting executives 85 males and 89 females employed in public service in Kampala, Uganda, were investigated to determine enzymatically spot levels of TC, TG, HDL, and LDL from which their mutual ratios were calculated.

RESULTS

In each of the 7 parameters studied, the samples showed risk factors for CVD at the following rates: HDL 10%, LDL/HDL 12%, TG 47%, LDL 48%, TC/HDL 53% TC 66%, TG/HDL 68%,.

CONCLUSIONS

In all the cut off points used, each analyte had a significant percentage of public service employees at risk of CVD. It is therefore concluded that hypercholesterolaemia and other dyslipidemias exist among seemingly healthy public service employees in Kampala, Uganda, and this needs urgent intervention at both individual and national levels.

The Metabolic Syndrome: Recognition and Management

The National Cholesterol Education Program defines the metabolic syndrome as three or more of five abnormalities: waist circumference of >40 in (102 cm) for men or >35 in (88 cm) for women, triglyceride level of > or =150 mg/dL, high-density lipoprotein cholesterol of <40 mg/dL in men or <50 mg/dL in women, blood pressure of > or =130 or > or =85 mm Hg, and fasting glucose of > or =110 mg/dL. It is related to insulin resistance, but the two terms are not synonymous. Both are associated strongly with obesity. The metabolic syndrome is important as an indicator of increased risk of cardiovascular disease (CVD) in patients with and without clinical CVD. The CVD risk of the metabolic syndrome is greater than that conferred by any single CVD risk factor. Since risk factors tend to cluster, if one component of the metabolic syndrome is present, one should assess for other risk factors. The metabolic syndrome is also predictive of new-onset type 2 diabetes. Early diagnosis provides justification for measures that can improve components of the syndrome and reduce CVD risk. The management strategy for metabolic syndrome focuses on overall CVD risk rather than single risk factors; effective therapy includes priority for weight reduction and increased physical activity. Pharmacotherapy is typically needed for control of high blood pressure, hypercoagulability, and increased levels of blood glucose and triglycerides.

Effect of silymarin and its polyphenolic fraction on cholesterol absorption in rats

This study evaluated the influence of silymarin (SM) and polyphenolic fraction (PF) of silymarin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic, plasma, VLDL and LDL cholesterol, a decrease in HDL cholesterol and an elevation in triacylglycerol (TAG) levels in plasma, VLDL and in the liver. SM and PF were administered as dietary supplements (1.0%) in HCD for 18 days. Intestinal cholesterol absorption was measured by dual-isotope plasma ratio method, which calculates percent of cholesterol absorption from the ratio of two labelled cholesterol doses, one given intragastrically (14C) and one intravenously (3H). Silymarin and PF significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in plasma and VLDL cholesterol and content of cholesterol and TAG in the liver. The level of HDL cholesterol was significantly increased after silymarin, but not after administration of PF. The levels of TAG in plasma and VLDL were not affected by either silymarin or PF. These results suggest that the inhibition of cholesterol absorption caused by silymarin and its polyphenolic fraction could be a mechanism contributing to the positive changes in plasma cholesterol lipoprotein profile and in lipid content in liver.

An ezetimibe-policosanol combination has the potential to be an OTC agent that could dramatically lower LDL cholesterol without side effects

Although many risk factors influence atherogenesis, LDL appears to play a primary role in this process. In prospective epidemiology, coronary risk increases as LDL cholesterol increases, throughout the entire range of concentrations encountered in healthy humans. Coronary risk is minimal in individuals and populations whose serum cholesterol remains quite low throughout life. Thus, practical strategies for achieving large reductions of LDL cholesterol in the general population could have a dramatic impact on coronary mortality rates. Dietary measures have limited potential in this regard; modest restriction of saturated fat has a rather trivial effect on LDL cholesterol, and the very-low-fat quasi-vegan diets that do have a notable effect in this regard currently have little appeal to the majority of the population. With respect to pharmacotherapy, most available hypolipidemic agents with reasonably potent activity entail side effects or compliance difficulties that would render their use too expensive or impractical for population-wide application. However, two agents may have great potential in this regard: policosanol and ezetimibe. The former, a mixture of long-chain alcohols derived from sugar cane wax, has effects on serum lipids comparable to those of statins, and may work by down-regulating expression of HMG-CoA reductase. However, unlike statins, policosanol appears to be devoid of side effects or risks. Ezetimibe is a newly approved drug that is a potent and highly specific inhibitor of an intestinal sterol permease; in daily doses as low as 10 mg, it suppresses intestinal absorption of cholesterol and decreases serum LDL cholesterol by approximately 18%. No side effects have been seen in clinical doses, and the fact that its hypolipidemic activity is additive to that of statins has generated considerable interest. Both policosanol and ezetimibe can be administered once daily. Future studies should determine whether policosanol, like statins, interacts additively with ezetimibe. If so, it may be feasible someday to produce a tablet combining policosanol and ezetimibe that could reduce LDL cholesterol by about 40%, without side effects, and that could be recommended to virtually anyone whose LDL cholesterol levels were not already ideal.

Inhibición selectiva de la absorción de colesterol: una nueva perspectiva en el tratamiento de la hipercolesterolemia

Ezetimibe is the first of a new class of lipid-lowering drugs, the 2-azetidinones, which selectively inhibits the absorption of intestinal cholesterol. Ezetimibe's mechanism of action complements that of cholesterol synthesis inhibitors. Ezetimibe as monotherapy or in combination with statins significantly decreases plasma cLDL levels. As monotherapy, ezetimibe is well tolerated with a side-effect profile similar to placebo, whereas in combination with statins no differences in the incidence of myopathy, rhabdomyolysis or elevated liver enzymes are reported.

Ezetimibe/Simvastatin: a review of its use in the management of hypercholesterolemia

Ezetimibe/simvastatin (Inegy, Vytorin) therapy combines two lipid-lowering compounds with complementary mechanisms of action, thereby blocking the two sources of plasma cholesterol and improving lipid profiles. Thus, intestinal absorption of dietary cholesterol and related phytosterols is blocked by ezetimibe, with the biosynthesis of cholesterol in the liver inhibited by simvastatin. Developing management trends for primary hypercholesterolemia include the aggressive reduction of low-density lipoprotein cholesterol (LDL-C) to goals lower than previously considered appropriate, the targeting of lipid subfractions and atherogenic indices other than LDL-C alone, and the broader use of combination lipid-lowering therapy. In line with these trends, ezetimibe/simvastatin is an effective and generally well tolerated adjunct to dietary therapy for markedly reducing LDL-C levels, providing a 52% reduction with the recommended starting dosage. Furthermore, ezetimibe/simvastatin is formulated with variable doses of simvastatin (i.e. 10/10 mg, 10/20 mg, 10/40 mg, and 10/80 mg) and hence, the dosage may be adjusted to suit the individual patient's needs. As longer-term efficacy, tolerability, economic and outcome data accrue, ezetimibe/simvastatin will be positioned more definitively relative to existing and emerging lipid-lowering treatments. Currently, ezetimibe/simvastatin therapy represents a valuable novel option for the management of primary hypercholesterolemia across diverse patient populations and as an adjunct to other lipid-lowering treatments in those with homozygous familial hypercholesterolemia.

Management of Dyslipidaemia in HIV-Infected Patients Receiving Antiretroviral Therapy

Dyslipidaemia associated with the treatment of HIV infection, particularly with the use of protease inhibitors (PIs), can raise cholesterol and triglyceride (TG) levels to the thresholds indicated for intervention. Recent evidence from epidemiological studies has shown that there are correlations between antiretroviral drug use and increased risks for, and incidences of, cardiovascular disease, including myocardial infarction and coronary heart disease. The primary goals of dyslipidaemia therapy for HIV patients are reductions of both low-density lipoprotein cholesterol (LDL-C) and markedly elevated TG levels. Dietary strategies and exercise programs may be tried, although these have shown inconsistent results. The two options for drug therapy are switching anti-retroviral agents and using lipid-lowering drugs. Each approach is associated with advantages and limitations, and the need to maintain viral suppression must be balanced with the need to treat abnormal lipid levels. Most drug switches replace the PI component with drugs from another antiretroviral class. Selection of drug therapy for lipid lowering depends on the type of dyslipidaemia predominating and the potential for drug interactions. The use of the statins pravastatin and atorvastatin is recommended for the treatment of patients with elevated LDL-C levels and gemfibrozil or fenofibrate for patients with elevated TG concentrations. Development of new PIs with more favourable effects on the lipid profile should be of benefit.