Yechezkiel Stein

Atheroprotective mechanisms of HDL

The aim of this review was to bring together results obtained from studies on different aspects of HDL as related to CHD and atherosclerosis. As atherosclerosis is a multistep process, the various components of HDL can intervene at different stages, such as induction of monocyte adhesion molecules, prevention of LDL modification and removal of excess cholesterol by reverse cholesterol transport. Transgenic technology has provided a model for atherosclerosis, and permitted evaluation of the contributions of different HDL components towards the global effect. The availability of apo AIV transgenic mice amplified the results obtained from apo AI overexpressors with respect to prevention of atherosclerosis. Prevention of atherosclerosis in apo E deficient mice by relatively small amounts of macrophage derived apo E may open new possibilities for therapeutic intervention. Contrary to early notions, increased plasma levels of CETP, even in the presence of low but functionally normal HDL, were atheroprotective. The extent to which paraoxonase and apo J participate in prevention of human atherosclerosis needs further evaluation. The findings that LCAT overexpression in rabbits was atheroprotective in contrast to increase in atherosclerosis in h LCAT tg mice, which was only partially corrected by CETP expression, call for some caution in the extrapolation of results from transgenic animals to humans. The important discovery of SR-BI as the receptor for selective uptake of CE from HDL revived interest in the clearance of CE from plasma. This pathway supplies also the vital precursor for steroidogenesis in adrenals and gonads and was shown to be dependent on apo AI.

The incorporation and disappearance of fatty acids in the rat epididymal fat pad studied by the in vivo incubation technique

Abstract Using the in vivo incubation technique it has been shown that the rat epididymal fat pad incubated in a mixture of two fatty acids incorporates palmitic acid slightly faster than oleic or linoleic acid and considerably more rapidly than stearic acid. Fasting induces mobilization of palmitic, oleic and linoleic acids at the same rate, with conservation of the adipose-tissue fatty acid composition. During 60 days no measurable saturation of linoleic to oleic or stearic acids occurred. The half life of palmitic and linoleic acids in the epididymal fat pad has been estimated as 163 and 187 days, respectively. Comparable values have been obtained when the disappearance rate of [ 14 C]palmitic acid from the epididymal fat pad has been measured following a single oral dose.

Comparative Uptake of Rat and Human Serum Low-Density and High-Density Lipoproteins by Rat Aortic Smooth Muscle Cells in Culture

Rat aortic smooth muscle cells in culture were exposed to rat and human serum low-(LDL) and high-density (HDL) lipoproteins labeled with 125I. 125I-lipid was taken up preferentially from all of the lipoproteins used. 125I-protein uptake of both rat LDL and HDL was significantly higher than that of the corresponding human lipoproteins, and human LDL was preferred to human HDL. The uptake of delipidated high-density apolipoproteins of either rat or human origin was very low. About 3–4% of the interiorized rat LDL and HDL was catabolized during 48 hours of incubation. On electron microscopic autoradiography of cells incubated with rat 125I-LDL, the concentration of label, representing mainly 125I-protein, was associated with secondary lysosomes. These results suggest that, if the protein uptake represents particle uptake, the preferential uptake of human LDL compared with human HDL could account in part for the finding that LDL acts as a more potent feedback suppressor of 3-hydroxy-3-methylglutaryl CoA reductase than does HDL.

Metabolic activity of rat epididymal fat pad labeled selectively by an in vivo incubation technique

Abstract A method of in vivo incubation of rat epididymal fat pads for selective labeling of this tissue is described. The effects of buffer, fatty acid concentration, time, glucose and hormones on the incorporation of [I−14C]palmitic acid were inveestigated. These studies revealed the presence of two glyceride compartments in adipose tissue: a small one, located in the cytoplasmic particulate fraction, with a half-life of 20–25 min, and a large slowly turning over compartment containing most of the glycerides in the fat cell. After 20 min of in vivo incubation of the epididymal fat pad a diglyceride of high specific activity can be separated from the labeled triglyceride. It was also shown that newly deposited fat mixes rapidly with the pre-existing fat of the adipose cell.

Efficacy and safety of a combination fluvastatin-bezafibrate treatment for familial hypercholesterolemia: Comparative analysis with a fluvastatin-cholestyramine combination☆

PURPOSEnFamilial hypercholesterolemia (FH) carries a markedly increased risk for coronary artery disease (CAD). Reduction of plasma low-density lipoprotein cholesterol (LDL-C) levels to the normal range may prevent premature atherosclerosis and usually requires a combination of cholesterol-lowering drugs. The major objective of this study is to compare two different drug combinations for the treatment of heterozygous FH.nnnPATIENTS AND METHODSnThe current investigation is a short-term, double-blind study comparing the efficacy and safety of fluvastatin when combined with cholestyramine (group 1) or with bezafibrate (group 2) in 38 patients with heterozygous FH.nnnRESULTSnAfter 6 weeks of combination treatment, in comparison to a drug-free baseline (patients receiving single-blind placebo during the lead-in period of an earlier study, ie, before ever receiving fluvastatin), the combination of 40 mg/d of fluvastatin with 400 mg/d of bezafibrate in group 2 reduced plasma LDL-C levels by 35% as compared with 32% in group 1, and reduced the LDL-C/high-density cholesterol (HDL-C) ratio by 46%, compared to 37% in group 1 (a non-significant difference for both comparisons). When compared to an intermittent 6-week open-label administration of 40 mg fluvastatin monotherapy, the addition of cholestyramine or bezafibrate each reduced LDL-C by an additional 13% (P < 0.01 for both regimens).nnnCONCLUSIONSnFluvastatin-bezafibrate is superior to a fluvastatin-cholestyramine combination for lowering serum triglycerides and elevating HDL-C serum levels in patients in conjunction with a significant lowering of LDL-C/HDL-C ratios, and may be an effective synergistic therapy for heterozygous FH. No episodes of myositis were seen in this short-term study, a finding that is in agreement with most of the reported studies on statin-fibrate combinations reviewed here.

Is there a genetic basis for resistance to atherosclerosis

Atherosclerosis and its major clinical manifestation, coronary heart disease, is and will remain the main cause of mortality. Reviews on this subject dealt with factors that enhance development of atherosclerosis. This review deals with a new facet, that some individuals are less prone to develop atherosclerosis: (1) despite high cholesterol intake or (2) despite hypercholesterolemia with elevated low-density lipoprotein cholesterol (LDL-C) levels. The variability of response of plasma cholesterol to dietary intake was shown to be regulated by liver x receptor (LXR) that determines the rate of intestinal cholesterol absorption through the ATP-binding cassette (ABC) gene family. Other gene products, such as apolipoprotein-E (apo-E), scavenger receptor-B1 (SR-B1) and acyl coenzyme: cholesterol acyltransferase-2 (ACAT-2) affect cholesterol absorption also. The role of a genetic background for relative resistance to atherosclerosis is highlighted by subjects with familial hypercholesterolemia in whom high plasma cholesterol levels has not curtailed their expected life span. Studies in animals have shown that resistance to atherosclerosis in spite of hypercholesterolemia is affected by factors such as high-density lipoprotein (HDL) phospholipids that enhance reverse cholesterol transport, non-responsiveness to induction or lack of monocyte chemotactic protein-1 (MCP-1), C-C chemokine receptor 2 (CCR2), macrophage colony stimulating factor (MCSF), or vascular cell adhesion molecule-1 (VCAM-1). Since macrophages have been regarded as pro- or anti-atherogenic, evidence was collated that the high activity of scavenger receptors may contribute towards resistance to atherosclerosis if accompanied by adequate amounts of apo-E for cholesterol removal.

Study of causes underlying the low atherosclerotic response to dietary hypercholesterolemia in a selected strain of rabbits

We have recently characterized a strain of rabbits that shows a low atherosclerotic response (LAR) to dietary hypercholesterolemia in contrast to the usual high atherosclerotic response (HAR) of rabbits [1]. Presently, we have focused on three well established and important stages of atherogenesis, i.e., monocyte adhesion to endothelium, cell mediated peroxidative modification of lipoproteins and induction of a receptor that recognizes modified low density lipoprotein (LDL). The results obtained show that (1) beta-very low density lipoprotein (beta-VLDL) from LAR and HAR rabbits enhanced monocyte adhesion to endothelial cells to the same extent; (2) Cell mediated peroxidation of LDL and beta-VLDL, tested by loss of alpha-tocopherol and formation of thiobarbituric acid reacting substances (TBARS), was compared using macrophages, fibroblasts and smooth muscle cells (SMC) of LAR and HAR rabbits and no significant differences were found; (3) Induction of scavenger receptor by phorbol ester (phorbol 12-myristate 13-acetate (PMA)) and platelet-derived growth factor-BB (PDGF-BB) was determined in SMC or fibroblasts from LAR and HAR rabbits using 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate-acetylated LDL (DiL-acLDL). We found a significantly higher uptake of DiI-acLDL in SMC and fibroblasts derived from HAR rabbits as compared with cells from LAR rabbits. Similar results were also obtained with [125I]-acLDL in fibroblasts from LAR and HAR rabbits with respect to cellular lipoprotein degradation after PMA pretreatment. Even though the attenuated atherosclerotic response to hypercholesterolemia of LAR rabbits may have multiple underlying causes, the most prominent so far is an apparent difference in inducibility of scavenger receptor in SMC and fibroblasts.

Religious observance and plasma lipids and lipoproteins among 17-year-old Jewish residents of Jerusalem

The association of religious observance and plasma lipids and lipoproteins was studied in a sample of 673 Jewish residents of Jerusalem ages 17-18 years. Religious observance was classified according to the parents ranking of their perceived degree of religiosity. The study group included children whose parents were orthodox Jews who pedantically observed religious commandments, children of traditional parents who observed some of the rules, and children of nonobservant secular parents. Plasma levels of cholesterol, triglyceride, and low-density lipoprotein were higher in secular children than in the orthodox group. These associations were independent of sex, origin, social class, body mass, and season. High-density lipoprotein cholesterol was somewhat higher in the orthodox group than in the secular children although this difference was not statistically significant. Regression analysis showed that offsprings environment and parental phenotype were the most important predictors of lipid concentrations in adolescents. The association of religious observance with plasma lipids and lipoproteins, however, was independent of parental phenotype lipid values and the contribution of offspring and parents environment. These findings are consistent with similar differences in plasma lipids described previously among the parents, as well as the lower incidence of myocardial infarction in the orthodox religious group, which has been shown in the Israeli adult population.

Use of 3H-cholesteryl linoleyl ether for the quantitation of plasma cholesteryl ester influx into the aortic wall in hypercholesterolemic rabbits.

In this study use was made of 3 H-cholesteryl linoleyl ether (CLE), a nondegradable analogue of cholesteryi ester (CE) to measure plasma lipoprotein CE influx into rabbit aorta. Autologous serum labeled with 3 H-CLE was injected into seven hypercholesterolemic rabbits, and more than 90% of the label was recovered in the plasma compartment 10 minutes after injection. Between 4 hours and 3 days the label was cleared from the circulation with a tV2 of about 24 hours. Between 4 and 24 hours the lipoproteins isolated at d < 1.006, d < 1.019, and d < 1.063 approached similar specific activity, assuming that 3 H-CLE had mixed with the lipoprotein CE pool. The rabbits were killed 7 to 14 days after injection when plasma radioactivity decreased to < 0.03% of injected dose/ml. Total recovery of the CLE ranged from 70% to 95% and 48% to 72% were found in the liver. The minimum influx of plasma CE into the aortic Intima was determined by dividing the label found in the artery by the mean specific activity of the labeled compound in the plasma. The minimum influx into regions with atheromatous involvement ranged from 0.8 to 3.4 jug CE/cm2/hr. The rate of influx was highly correlated with the amount of CE mass in the jntima and media indicating that the bulk of aortic CE is derived from plasma lipoprotein CE. The method described might be useful in distinguishing between possible effects of antiatherogenic drugs on plasma CE influx into the aortic wall from an effect on intracellular CE hydrolysis and subsequent efflux of free cholesterol from the artery.

Synthesis of ether analogs of lipoprotein lipids and their biological applications.

Publisher Summary This chapter reviews the synthesis of cholesteryl ethers, retinyl ethers, tri- and dialkyl glycerols, and dialkyl phospholipids, which are nonhydrolyzable analogs of the lipid moieties of lipoproteins. In recent years, there has been considerable interest in the use of liposomes as carriers of drugs to be delivered to specific target sites. If liposomes are to be used to deliver therapeutic compounds to cells it may be important to use phospholipids which are not readily degraded by cellular or circulating enzymes. The lipids transferred by lipoprotein lipase (LPL) to cells were localized in three compartments: trypsin releasable, resistant, and metabolic; the latter was a chloroquine-sensitive pool as evidenced by inhibition of cholesteryl ester hydrolysis. Labeled phosphatidylcholine (PC) and, to a lesser extent, dioleyl ether phosphatidylcholine (DOEPC), in the trypsin releasable pool returns to the medium, while cholesteryl linoleyl ether (CLE) and cholesteryl ester (CE) required cholesteryl ester transfer protein for release. The transfer of CLE and CE into a trypsin-resistant compartment does not require metabolic energy and occurs also in formaldehyde-fixed cells; metabolic energy is needed for the translocation of CLE and CE into the lysosomal compartment, presumably by a process of endocytosis.