Cholesterol absorption

In Vitro Hypocholesterolemic Effect of Coffee Compounds

(1) Background: Cholesterol bioaccessibility is an indicator of cholesterol that is available for absorption and therefore can be a measure of hypocholesterolemic potential. In this work, the effect of commercial espresso coffee and coffee extracts on cholesterol solubility are studied in an in vitro model composed by glycodeoxycholic bile salt, as a measure of its bioaccessibility. (2) Methods: Polysaccharide extracts from coffees obtained with different extraction conditions were purified by selective precipitation with ethanol, and their sugars content were characterized by GC-FID. Hexane extraction allowed us to obtain the coffee lipids. Espresso coffee samples and extracts were tested regarding their concentration dependence on the solubility of labeled 13C-4 cholesterol by bile salt micelles, using quantitative 13C NMR. (3) Results and Discussion: Espresso coffee and coffee extracts were rich in polysaccharides, mainly arabinogalactans and galactomannans. These polysaccharides decrease cholesterol solubility and, simultaneously, the bile salts' concentration. Coffee lipid extracts were also found to decrease cholesterol solubility, although not affecting bile salt concentration. (4) Conclusions: Coffee soluble fiber, composed by the arabinogalactans and galactomannans, showed to sequester bile salts from the solution, leading to a decrease in cholesterol bioaccessibility. Coffee lipids also decrease cholesterol bioaccessibility, although the mechanism of action identified is the co-solubilization in the bile salt micelles. The effect of both polysaccharides and lipids showed to be additive, representing the overall effect observed in a typical espresso coffee. The effect of polysaccharides and lipids on cholesterol bioaccessibility should be accounted on the formulation of hypocholesterolemic food ingredients.

Health benefits of vitamins and secondary metabolites of fruits and vegetables and prospects to increase their concentrations by agronomic approaches

Fruits and vegetables (FAVs) are an important part of the human diet and a major source of biologically active substances such as vitamins and secondary metabolites. The consumption of FAVs remains globally insufficient, so it should be encouraged, and it may be useful to propose to consumers FAVs with enhanced concentrations in vitamins and secondary metabolites. There are basically two ways to reach this target: the genetic approach or the environmental approach. This paper provides a comprehensive review of the results that have been obtained so far through purely agronomic approaches and brings them into perspective by comparing them with the achievements of genetic approaches. Although agronomic approaches offer very good perspectives, the existence of variability of responses suggests that the current understanding of the way regulatory and metabolic pathways are controlled needs to be increased. For this purpose, more in-depth study of the interactions existing between factors (light and temperature, for instance, genetic factors × environmental factors), between processes (primary metabolism and ontogeny, for example), and between organs (as there is some evidence that photooxidative stress in leaves affects antioxidant metabolism in fruits) is proposed.

Spiroimidazolidinone NPC1L1 inhibitors. Part 2: structure-activity studies and in vivo efficacy

Ezetimibe (Zetia®), a cholesterol-absorption inhibitor (CAI) approved by the FDA for the treatment of hypercholesterolemia, is believed to target the intestine protein Niemann-Pick C1-Like 1 (NPC1L1) or its pathway. A spiroimidazolidinone NPC1L1 inhibitor identified by virtual screening showed moderate binding activity but was not efficacious in an in vivo rodent model of cholesterol absorption. Synthesis of analogs established the structure-activity relationships for binding activity, and resulted in compounds with in vivo efficacy, including 24, which inhibited plasma cholesterol absorption by 67% in the mouse, thereby providing proof-of-concept that non-β-lactams can be effective CAIs.

Change in the cholesterol metabolism associated with the combined inhibition of synthesis and absorption

A cardiovascularis prevencióban, a lipid célértékek elérésére törekedve megelégszünk a szérum-koleszterinszint mérésével, és keveset törődünk azzal, hogy ez milyen hatások eredményeként alakul ki. A koleszterin vérszintje a diétával elfogyasztott mennyiségen túl nagymértékben függ a bélbe történő felszívódás/kiválasztás és a szintézis egyensúlyától. A felszívódás és a szintézis arányának vizsgálata csak az utóbbi időben került az érdeklődés előterébe. Számos megfigyelés igazolja, hogy a ma legerősebbnek ismert koleszterincsökkentő gyógyszerek hatására, amellett, hogy a májban csökken a szintézis, akár 50%-ot meghaladó mértékben is nőhet a koleszterin felszívódása. Amikor egy statinkezelés hatékonyságát vizsgáljuk, a mindennapi gyakorlatban csak a végeredményt, a szérum-koleszterinszint csökkenését mérjük, és nem vizsgáljuk a szintézis és a felszívódás mértékének változását sem. Az, hogy a szervezetben mennyi koleszterinszintetizálódik,illetve szívódik fel – indirekt módon – a nem-koleszterin szterinek (fitoszterinek) mennyiségének mérésével állapítható meg. Azabszorpciómarkerei a kampeszterin, a szitoszterin, az avenaszterin, valamint a kolesztanol. A koleszterinbioszintézisea latoszterin, a kolesztenol, a dezmoszterin szintjével korrelál. A gyakorlatban a latoszterin vagy latoszterin/koleszterin-koncentráció a szintézis, a kampeszterin vagy kampeszterin/koleszterin-arány a felszívódás markereként értékelhető. Az újabb vizsgálati eredmények tehát azt igazolják, hogy a koleszterin szintézisét gátló statin adása mellett fokozódik a koleszterin felszívódása, és a felszívódást gátló ezetimib hatása pedig a szintézis erősödését eredményezi. A statinok okozta felszívódás emelkedését ezetimibbel kombinálva tudjuk csökkenteni, illetve kivédeni. Ezen adatok azt támasztják alá, hogy a statin és ezetimib kombinációja, a szintézis és felszívódás együttes gátlása biztosítja a leghatékonyabb és legkevesebb mellékhatással járó koleszterinszint-csökkenést.

Regulation of cholesterol absorption by phytosterols

Phytosterols are chemical homologs of cholesterol that are found in most plant foods and are particularly abundant in vegetable oils and whole grains. They interfere with the micellar solubilization of cholesterol in the intestine and reduce the efficiency of cholesterol absorption. The net absorption of phytosterols themselves is very small and most clinical studies suggest that consumption is safe. Phytosterols naturally present in foods appear to be bioactive, but many commercial phytosterol supplements are comprised of purified crystals with limited bioavailability. Proper formulation to improve bioavailability is critical for phytosterol supplements. Phytosterols appear to be quantitatively as important to cholesterol lowering as reducing saturated fat consumption, and they provide an additional tool for regulation of circulating cholesterol through lifestyle changes.

Phytosterols, cholesterol absorption and healthy diets

The purpose of this review is to outline the emerging role of dietary phytosterols in human health. Dietary saturated fat, cholesterol and fiber are currently emphasized in the reduction of low-density lipoprotein cholesterol levels. However, other dietary components such as phytosterols may have equivalent or even larger effects on circulating cholesterol and need further study with respect to the potential for coronary heart disease risk reduction. Phytosterol effects were not considered in classic fat-exchange clinical trials and may account for some of the differences attributed to the food fats studied. Phytosterols reduce cholesterol absorption while being poorly absorbed themselves and the effects can be studied in human subjects in single-meal tests using stable isotopic tracers. Because phytosterols are insoluble and biologically inactive when purified, careful attention needs to be given to ensuring that commercial supplement products are rendered bioavailable by dissolution in fat or by emulsification. Recent work shows that phytosterols in natural food matrices are also bioactive. The retention of phytosterols during food manufacturing and the use of foods with high phytosterol content may constitute an alternative to the use of supplements.

Intake occasion affects the serum cholesterol lowering of a plant sterol-enriched single-dose yoghurt drink in mildly hypercholesterolaemic subjects

OBJECTIVE

To determine the impact of intake occasion (with or without a meal), and product fat level on the cholesterol-lowering efficacy of a plant sterol (PS)-enriched (3 g/day) single-dose yoghurt drink.

DESIGN

Double-blind, randomized, placebo-controlled, parallel study with a 4 weeks run-in and 4 weeks intervention period.

SETTING

Subjects recruited from the general community.

SUBJECTS

A total of 184 moderate hypercholesterolaemic subjects (81 men and 103 women) (age 57+/-2 years) completed the study.

INTERVENTIONS

The study product was a 100-g single-dose yoghurt drink with or without added PS in the form of PS esters. The subjects were randomly assigned to one of five 4-week treatments: (i) drink A (0.1% dairy fat, 2.2% total fat) with a meal, (ii) drink A without a meal, (iii) drink B (1.5% dairy fat, 3.3% total fat) with a meal, (iv) drink B without a meal and (v) placebo drink with a meal.

RESULTS

LDL-cholesterol (LDL-C) was significantly lowered when the single-dose drink was taken with a meal independent of its fat content (drink A: -9.5% (P<0.001, 95% CI: -13.8 to -5.2); drink B: -9.3% (P<0.001, 95% CI: -13.7 to -4.9)) as compared to placebo. When consumed without a meal, LDL-C was also significantly decreased (drink A: -5.1% (P<0.05, 95% CI: -9.4 to -0.8); drink B: -6.9% (P<0.01, 95% CI: -11.3 to -2.5) as compared to placebo, however the effect was significantly smaller as compared to the intake with a meal.

CONCLUSION

These results indicate that a PS-ester-enriched single-dose yoghurt drink effectively reduces LDL-C irrespective of the fat content of the product. A substantially larger decrease in serum cholesterol concentration was achieved when the single-dose drink was consumed with a meal emphasizing the importance of the intake occasion for optimal cholesterol-lowering efficacy.

SPONSORSHIP

Unilever Research and Development, Vlaardingen, The Netherlands.

Cholesterol metabolism and its implications for therapeutic interventions in patients with hypercholesterolaemia

Cardiovascular diseases are the principal causes of mortality in middle-aged people and in older people. Coronary heart disease (CHD) is the most common of the cardiovascular diseases; high serum levels of cholesterol are associated with atherosclerosis and an increased risk of CHD. Cholesterol homeostasis is achieved by means of a fine balance between cholesterol intake, absorption/excretion and synthesis. All of these processes are tightly linked and a change in one of them can significantly influence the others. Results from both experimental studies and clinical trials have shown that inhibition of cholesterol synthesis with a statin increases absorption and that conversely, inhibition of cholesterol absorption increases synthesis. The tight linkage of cholesterol absorption and synthesis in maintaining cholesterol homeostasis suggests that treatment with an agent that influences only one of these two processes is likely to have distinct limits with respect to its effects on cholesterol levels. Better understanding of cholesterol homeostasis, particularly the close interrelationship between cholesterol synthesis and absorption, may result in the design of rational integrated treatment regimens that employ multiple agents with complementary actions that attack multiple mechanisms to lower cholesterol.

New drugs for the treatment of hypercholesterolaemia

Endogenous and exogenous pathways determine plasma levels of cholesterol and lipoproteins. Plasma cholesterol levels and coronary heart disease risk can be reduced pharmacologically by decreasing cholesterol synthesis, increasing its elimination and/or reducing its absorption from the intestine. The more profound knowledge about cholesterol homeostasis has allowed the development of several lipid-lowering drugs with different mechanisms of action, with the purpose of reducing both morbidity and mortality associated with coronary heart disease. Two new and more potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), also called superstatins (rosuvastatin and pitavastatin), are being studied for their ability to improve lipid profiles. Rosuvastatin is a potent, hepato-selective and relatively hydrophilic statin with a low propensity for muscle toxicity and drug interactions. Pitavastatin is another statin with a high oral bioavailability and minimal propensity for cytochrome p450-mediated drug interactions. Rosuvastatin seems to be more potent than other available statins while pitavastatin presents with a similar potency to that of atorvastatin. Another promising approach for lowering total and low-density lipoprotein cholesterol levels is inhibition of cholesterol absorption. A wide variety of new agents with the capacity for inhibiting the intestinal cholesterol absorption is currently being investigated. Ezetimibe is a selective cholesterol absorption inhibitor whose clinical efficacy has been recently demonstrated both in monotherapy and in combination with other lipid-lowering drugs. Colesevelam, a new bile acid sequestrant, has shown a clinical efficacy similar to that of other resins, with minimal gastrointestinal side effects, improving tolerability and patient compliance. Other lipid-lowering drugs with the ability to act at the enterocyte level, such as avasimibe and implitapide, are currently being investigated in humans.

Pharmacotherapy for dyslipidaemia--current therapies and future agents

Current lipid-altering agents that lower low density lipoprotein cholesterol (LDL-C) primarily through increased hepatic LDL receptor activity include statins, bile acid sequestrants/resins and cholesterol absorption inhibitors such as ezetimibe, plant stanols/sterols, polyphenols, as well as nutraceuticals such as oat bran, psyllium and soy proteins; those currently in development include newer statins, phytostanol analogues, squalene synthase inhibitors, bile acid transport inhibitors and SREBP cleavage-activating protein (SCAP) activating ligands. Other current agents that affect lipid metabolism include nicotinic acid (niacin), acipimox, high-dose fish oils, antioxidants and policosanol, whilst those in development include microsomal triglyceride transfer protein (MTP) inhibitors, acylcoenzyme A: cholesterol acyltransferase (ACAT) inhibitors, gemcabene, lifibrol, pantothenic acid analogues, nicotinic acid-receptor agonists, anti-inflammatory agents (such as Lp-PLA(2) antagonists and AGI1067) and functional oils. Current agents that affect nuclear receptors include PPAR-alpha and -gamma agonists, while in development are newer PPAR-alpha, -gamma and -delta agonists, as well as dual PPAR-alpha/gamma and 'pan' PPAR-alpha/gamma/delta agonists. Liver X receptor (LXR), farnesoid X receptor (FXR) and sterol-regulatory element binding protein (SREBP) are also nuclear receptor targets of investigational agents. Agents in development also may affect high density lipoprotein cholesterol (HDL-C) blood levels or flux and include cholesteryl ester transfer protein (CETP) inhibitors (such as torcetrapib), CETP vaccines, various HDL 'therapies' and upregulators of ATP-binding cassette transporter (ABC) A1, lecithin cholesterol acyltransferase (LCAT) and scavenger receptor class B Type 1 (SRB1), as well as synthetic apolipoprotein (Apo)E-related peptides. Fixed-dose combination lipid-altering drugs are currently available such as extended-release niacin/lovastatin, whilst atorvastatin/amlodipine, ezetimibe/simvastatin, atorvastatin/CETP inhibitor, statin/PPAR agonist, extended-release niacin/simvastatin and pravastatin/aspirin are under development. Finally, current and future lipid-altering drugs may include anti-obesity agents which could favourably affect lipid levels.

Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ

BACKGROUND

Low-fat vegetable foods contain phytosterols, but it is not known whether they are in biologically active forms or whether their concentrations are high enough to reduce cholesterol absorption and favorably affect lipid metabolism.

OBJECTIVE

The objective was to establish whether the selective removal of phytosterols from wheat germ would increase the cholesterol absorption measured from test meals composed of wheat germ muffins.

DESIGN

Wheat germ, which has a high content of phytosterols relative to total fat, was chosen as a low-fat test food. Cholesterol absorption was measured 3 times in 10 subjects. Each test meal was a muffin containing 30 mg heptadeuterated cholesterol tracer and, in random order, 80 g original wheat germ containing 328 mg phytosterols, wheat germ from which phytosterols had been selectively extracted, or extracted wheat germ reconstituted with purified phytosterols. Changes in cholesterol absorption were monitored by the measurement of tracer enrichment of plasma cholesterol 4 and 5 d after each meal with the use of negative ion mass spectrometry.

RESULTS

Tracer enrichment of plasma cholesterol was 42.8% higher after consumption of phytosterol-free wheat germ than after that of the original wheat germ (0.415 +/- 0.035 compared with 0.291 +/- 0.024 micro mol tracer/mmol cholesterol; P < 0.01). Tracer enrichment of plasma cholesterol was not significantly different between the wheat germ with extracted-and-reconstituted phytosterol (0.305 +/- 0.022 micro mol tracer/mmol cholesterol) and the original wheat germ.

CONCLUSION

The efficiency of cholesterol absorption from test meals was substantially lower after consumption of original wheat germ than after consumption of phytosterol-free wheat germ, which suggests that endogenous phytosterols in wheat germ and possibly in other low-fat vegetable foods may have important effects on cholesterol absorption and metabolism that are independent of major nutrients.

Ezetimibe

Ezetimibe is a cholesterol absorption inhibitor that significantly lowers low- density lipoprotein cholesterol (LDL-C), and favourably affects triglyceride and high-density lipoprotein cholesterol blood levels in monotherapy and in combination with statins. Hepatic and extrahepatic (peripheral) cholesterol synthesis are well-known sources of cholesterol found in LDL-C. However, the emergence of ezetimibe has highlighted intestinal cholesterol absorption as an additional, important source of cholesterol in LDL-C, and has better illuminated how genetic factors, dietary content, pharmaceutical agents, and nuclear receptor activation (such as liver X receptors) all influence the relative contribution of these important cholesterol sources to LDL-C. In fact, investigations into ezetimibe have sometimes challenged existing scientific dogma, has prompted reconsideration of older data, and has helped create 'new' paradigms in cholesterol metabolism. Thus, ezetimibe's efficacy, excellent tolerability, and safety has not only expanded potential treatment options for dyslipidaemic patients, but also has promoted exploration of new frontiers of lipid research towards a better understanding of cholesterol metabolism.

Ezetimibe: the first in a novel class of selective cholesterol-absorption inhibitors

Zetia (ezetimibe) is the first medication in the novel class of selective cholesterol-absorption inhibitors to be released in the United States. Ezetimibe selectively inhibits the uptake of cholesterol from the intestinal lumen at the level of the enterocyte in the intestinal brush border while having no effect on other sterols or lipid-soluble vitamins. Ezetimibe 10 mg daily produces a consistent reduction in low-density lipoprotein cholesterol (LDL-C) by approximately 15 to 20% when used as monotherapy or in combination with 3-hydroxy-3-methylglutaryl coenzyme A inhibitors (statins) or fenofibrate and a 4 to 9% increase in high-density lipoprotein cholesterol. Unlike other lipid-lowering medications that act in the gastrointestinal tract, ezetimibe does not appear to worsen hypertriglyceridemia. Ezetimibe also has an adverse-event profile that is similar to placebo when used as monotherapy or in combination with statins and fenofibrate. Studies of longer duration and with niacin, bile acid sequestrants, and gemfibrozil are warranted to more completely assess the safety of ezetimibe in combination therapy. To date, no clinically significant drug-drug interactions have been noted with the use of ezetimibe; however, further studies are warranted. Ezetimibe will be useful as monotherapy in patients who need modest reductions in LDL-C or are intolerant to other lipid-lowering medication, and in combination with a statin in patients who are unable to tolerate large doses of statins or need further reductions in LDL-C despite maximum doses of a statin. The long-term safety and the effect on cardiovascular morbidity and mortality of ezetimibe are unknown.