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Y Stein

Publications and source records attributed to Y Stein.

At least 73 records · Page 4Linked to original sources
PubMed1989

Phosphatidylinositol-specific phospholipase C releases lipoprotein lipase from the heparin releasable pool in rat heart cell cultures.

The effect of phosphatidylinositol-specific phospholipase C (PI-PLC) on the release of lipoprotein lipase was studied in F1 heart cell cultures. Exposure of the cultures for 10 min to PI-PLC resulted in a 2-fold increase in the release of lipoprotein lipase (LPL) into the culture medium. PI-PLC released LPL from the heparin-releasable pool and PI-PLC was not effective in cultures pretreated with heparin. Insulin had no influence on the release of LPL from the heart cell cultures, even though it enhanced the uptake of 2-deoxy[3H]glucose by these cells. In cultures labeled with 35S, treatment with PI-PLC resulted in an increase in the release of 35S-labeled proteoglycan. PI-PLC was also effective in enhancing the release of bovine LPL exogenously bound to cultured aortic smooth muscle cells. The findings that PI-PLC was not effective after heparin, that it did release exogenously added LPL to cell cultures and that it released 35S-labeled proteoglycan, were interpreted to indicate that PI-PLC apparently acts on the release of LPL in an indirect manner, releasing heparan sulphate to which LPL is bound. As there is a previously described correlation between circulating LPL and the heparin-releasable LPL, we hypothesize that the activity of PI-PLC in the endothelial cell membrane or plasma phosphatidyl-specific phospholipase D regulates the plasma LPL levels.

Animals↗
PubMed1989

Cholesterol removal by peritoneal lavage with phospholipid-HDL apoprotein mixtures in hypercholesterolemic hamsters.

Syrian hamsters were rendered hypercholesterolemic by supplementation of their diet with 1% cholesterol and 15% butter. The hamsters were injected intraperitoneally (i.p.) with about 20 mg of phospholipid liposomes containing trace amounts of [3H]cholesteryl linoleyl ether ([ 3H]CLE) alone or combined with 10 mg delipidated high-density lipoprotein (apoHDL). After 2 h the peritoneal cavity was washed repeatedly with up to 15 ml phosphate-buffered saline. 60%-70% of [3H]CLE were retained after i.p. injection without apoHDL, 30-50% in the presence of apoHDL. The amount of free cholesterol recovered in the peritoneal lavage was significantly higher when apoHDL was combined with 18:2 sphingomyelin or dilinoleyl phosphatidylcholine liposomes, when compared to either liposomes or apoHDL alone. It is suggested that supplementation of dialysate with HDL apolipoproteins and phospholipids in patients undergoing continuous peritoneal dialysis could be of use in a cholesterol depletion regimen.

Animals↗
PubMed1989

Modification of cellular fatty acid composition of Hep-G2 cells: effect of antioxidants on cholesterol esterification and secretion.

Modification of fatty acid composition of Hep-G2 cells was achieved by 7-9 days of supplementation of culture medium with palmitic, oleic or linoleic acid. Cholesterol release into serum-free culture medium during 24 h of incubation was significantly lower in cells supplemented with linoleic acid, when compared to those supplemented with palmitic, oleic or no additional fatty acid. In cells cultured in the presence of linoleic acid, less [3H]cholesterol was esterified to cholesteryl ester and the mass of cholesteryl ester was significantly lower than in cells cultured with palmitic acid or with no additional fatty acid. The reduction in [3H]cholesterol secretion and the impairment in cholesterol esterification in linoleic acid-treated cells was prevented by addition of butylated hydroxytoluene or probucol concurrently with the fatty acid. The antioxidants also increased esterification and [3H]cholesterol release in cells supplemented with the other fatty acids. It is suggested that cholesterol secretion and esterification are sensitive to peroxidation.

Antioxidants↗
PubMed1989

Divergent fate of unsaturated and saturated ceramides and sphingomyelins in rat liver and cells in culture.

The metabolism of sphingomyelins and ceramides with defined labeled fatty acids was compared after injection in vivo or incubation with cultured cells. The liver was the major site of uptake of sphingomyelins and ceramides with 18:2 or 16:0 fatty acids, but with both sphingolipids a higher recovery of radioactivity was found with 16:0 species. The distribution of radioactivity among liver lipids showed that 1.5 h after injection of 18:2 sphingomyelin, only 21% of the label was found as sphingomyelin, and this value was 37% in the case of 16:0 sphingomyelin. There was a very marked difference in the metabolism of 18:2 and 16:0 ceramides. After injection of 18:2 ceramide only 14% of the radioactivity was recovered as sphingomyelin, and this value was more than 50% with 16:0 ceramide. [14C]18:2 ceramide was converted also to glucoceramide and hydrolyzed more extensively than 16:0 ceramide. These observations were extended to sphingomyelins and ceramides with other fatty acids, using Hep-G2 cells in culture. Significantly more radioactivity was recovered as labeled sphingomyelin after incubation with 16:0, 18:0, 20:0 and 24:0 sphingomyelins than with 18:1 and 18:2 sphingomyelins, while more labeled phosphatidylcholine and phosphatidylethanolamine were found with the unsaturated sphingomyelins. In analogy to the findings in vivo, in the Hep-G2 cells more 16:0, 18:0 and 24:0 ceramides were converted to sphingomyelin than 18:1 or 18:2 ceramides. These differences were also seen with cultured macrophages, in which a more marked reutilization for sphingomyelin formation was found with the saturated ceramide series. The sphingomyelin liposomes were tested also for their capacity to mobilize cholesterol, and a rise in plasma unesterified cholesterol occurred after injection of 18:2 sphingomyelin. Marked enhancement of cholesterol efflux from cholesterol ester-loaded macrophages was also seen with 18:1 and 18:2, 20:0 sphingomyelin in the presence of delipidated high-density lipoprotein. The present results demonstrate that the metabolic fate of sphingolipids is related to their fatty acid composition. While ceramides with saturated fatty acids are predominantly reutilized for sphingomyelin formation, those with unsaturated fatty acids undergo probably more rapid hydrolysis with liberation of fatty acids and channeling into glycerolipids.

Animals↗
PubMed1989

Mechanism of the hypertriglyceridemia induced by tumor necrosis factor administration to rats.

4 h after intravenous injection of recombinant HuTNF-alpha to fed rats, an increase in heart, diaphragm, and plasma lipoprotein lipase activity was observed. At the same time, a 40-60% decrease in enzymic activity in epididymal fat pad and kidney and 40% decrease in hepatic lipase activity in liver had occurred. Similar results were obtained 20 h after injection of recombinant HuTNF-alpha into fasted rats. Pretreatment with Indomethacin did not affect the changes in tissue lipoprotein lipase activity observed following recombinant HuTNF-alpha administration. Serum triacylglycerol concentration increased by 2- and 6-fold; 4 and 20 h after recombinant HuTNF-alpha administration. Disappearance of 14C-labeled triacylglycerol from the circulation after injection of small chylomicrons, biosynthetically labeled in their triacylglycerol and cholesterol moieties, was lower in TNF-treated than in control rats. However, the clearance rate of triacylglycerol was the same or even higher in recombinant HuTNF-alpha treated rats (assuming that 14C-labeled chylomicron triacylglycerol represents the serum triacylglycerol pool). The livers of recombinant HuTNF-alpha-treated rats and controls contained similar amounts of 14C-labeled lipids, but less [3H]cholesterol, suggesting that in recombinant HuTNF-alpha-treated rats, the liver took up chylomicron remnant particles enriched with triacylglycerol. Separation of the d less than 1.04 g/ml fraction of serum obtained from control and recombinant HuTNF-alpha treated rats by zonal ultracentrifugation revealed that in recombinant HuTNF-alpha-treated rats the lipoprotein particles were less lipolyzed than in controls. The secretion rate of [3H]triacylglycerol into the serum was determined 90 min after injection of [3H]palmitate albumin complex and Triton WR 1339. In recombinant HuTNF-alpha-treated rats, the secretion of [3H]triacylglycerol into plasma was 48% higher than in controls. It is suggested that the increase in lipoprotein lipase activity of heart and diaphragm resulted from an indirect effect of TNF. It is concluded that the increase in serum triacylglycerol in the recombinant HuTNF-alpha-treated rats is due mainly to an increased secretion of triacylglycerol by the liver. Impaired lipolysis, probably due to a fall in hepatic lipase could also contribute to the rise in plasma triacylglycerol.

Animals↗
PubMed1989

Cigarette smoking renders LDL susceptible to peroxidative modification and enhanced metabolism by macrophages.

The effect of cigarette smoking on peroxidation of plasma low density lipoprotein (LDL) was studied in 16 smokers aged 23-56 years; 12 nonsmokers of similar age served as controls. The smokers were asked to refrain from smoking 24-40 h prior to testing. Peroxidation was assessed by determination of thiobarbituric acid reactive substances (TBARS) in fresh plasma and LDL and by an increase in 125I-LDL metabolism by peritoneal macrophages. There was no difference in TBARS in freshly prepared plasma or LDL of smokers and nonsmokers. However, LDL of smokers, conditioned by incubation with bovine aortic smooth muscle cells (SMC), had 2-fold or higher TBARS values when compared to SMC conditioned LDL of nonsmokers. 2-4-fold higher TBARS values were seen also in SMC conditioned LDL when the comparison was made between LDL isolated from plasma before smoking of 6-7 cigarettes (time 0), and LDL of the same individual isolated from plasma 90 min thereafter. The metabolism of SMC conditioned 125I-LDL by peritoneal macrophages was examined; LDL isolated from plasma of smokers at time 0 was metabolized twice as avidly as LDL of nonsmokers and a further increase was seen with LDL isolated 90 min after acute smoking. The present results indicate that cigarette smoking renders plasma LDL more susceptible to subsequent peroxidative modification by cellular elements.

Adult↗
PubMed1989

Lack of effect of probucol on atheroma formation in cholesterol-fed rabbits kept at comparable plasma cholesterol levels.

Rabbits were fed cholesterol for 14 weeks to study the effect of probucol on atheroma formation. Three groups of animals were investigated: group CHOL was fed 1% cholesterol and served as control for group P + CHOL. fed 1% cholesterol and 1% probucol from the onset till the end of the experiment: group CHOL + P received 1% cholesterol throughout the experiment and 1% probucol during the last 4 weeks only. Plasma cholesterol concentrations were monitored at frequent intervals and were modulated by dietary perturbations so that the areas under the curve expressing plasma cholesterol changes with time, were similar in probucol and non-treated rabbits. The efficacy of long-term probucol treatment was evidenced by a significant reduction in plasma apolipoprotein A-I throughout the experiment and lower plasma TBARs during the first 6 weeks, when the hypocholesterolemic effect of probucol was also seen. Two weeks prior to the termination of the experiment, the rabbits were injected with rabbit plasma labeled with [3H]cholesteryl linoleyl ether [( 3H]CLE). Aortic atheromatosis was quantified by determination of total and cholesteryl ester (CE). The aortic cholesterol content was related to the arch, thoracic and abdominal segments, to the surface area of each segment or its dry defatted weight. Total and esterified cholesterol were highest in the aortic arch in all 3 groups when related to any of the above mentioned parameters. No statistically significant difference in aortic total cholesterol and CE content was seen among the three groups studied. The [3H]CLE recovered in the aortic segment correlated with the CE content and the [3H]CLE (dpm)/mg CE in all segments was similar. No statistically significant difference in the [3H]CLE recovered in the aortic segments among the 3 groups was seen. We conclude that in cholesterol-fed rabbits, in which the plasma cholesterol levels were maintained at comparable levels, probucol treatment did not affect plasma CE influx into the aorta and did not attenuate development of aortic atherosclerosis.

Animals↗
PubMed1988

Tissue distribution of [3H]cholesteryl linoleyl ether-labeled human Lp(a) in different rat organs.

The sites of tissue uptake of human lipoprotein(a) (Lp(a] were studied in rats using [3H]cholesteryl linoleyl ether [( 3H]CLE) as a marker. Since rat plasma has no cholesteryl ester transfer activity, the amount of label in various tissues should reflect the quantitative uptake of Lp(a). Isolated Lp(a) was labeled with [3H]CLE by incubation overnight of Lp(a), a source of cholesteryl ester transfer activity (1.23 g/ml infranate of human plasma), and [3H]CLE-labeled Intralipid. Following labeling, the homogeneity and integrity of Lp(a) was shown by agarose electrophoresis and immunoblotting. Intact Lp(a) was injected via the tail vein of rats (120-170 g, n = 4 at each time point), and tissues were collected at various times thereafter (4-48 h). The disappearance curve of [3H]CLE-labeled Lp(a) from rat plasma was bimodal and had an initial rapid t1/2 of 1.8 h followed by a slower component, t1/2 = 13.3 h. Tissue uptake at all sampling times was greatest in liver (28.5% at 48 h of total dpm injected), followed by the intestine (9-12%), with less than 3% uptake by spleen. The small intestine was divided into four segments, and while the 3H radioactivity was similar in the proximal segments, a time-related increase in [3H]CLE was seen in its most distal portion. These studies indicate that the tissue sites of degradation in the rat of human Lp(a) are similar to human low-density lipoproteins (LDL); the increase in label in the distal portion of the small intestine with time may represent [3H]CLE excreted through the bile and absorbed by the mucosal cells.

Animals↗
PubMed1988

Modulation of lipoprotein lipase activity in mouse peritoneal macrophages by recombinant human tumor necrosis factor.

Thioglycollate-elicited mouse peritoneal macrophages spontaneously secrete lipoprotein lipase during culture. Exposure of the cultures to 50 ng/ml of recombinant human tumor necrosis factor (rTNF) for 48 h resulted in a 69% reduction in lipoprotein lipase activity in the culture medium with a concomitant decrease in cellular enzyme activity. The decrease in enzyme activity was not the result of rTNF-dependent reduction in the total protein synthesis, since the presence of rTNF did not affect [3H]leucine incorporation into cellular proteins. The effect of rTNF on lipoprotein lipase was reversible; upon TNF withdrawal, enzyme activity returned to basal levels after 60 h. The reduction of lipoprotein lipase in rTNF-treated cultures could be completely prevented by preincubation with a specific antiserum against recombinant human TNF. The late onset of decrease of lipoprotein lipase (LPL) activity suggests that rTNF might induce a mediator, which in turn suppresses LPL production. While rTNF was very effective in reducing lipoprotein lipase activity in mouse peritoneal macrophages, it did not affect lipoprotein lipase activity when added to the murine J774 cell line and to CT2 macrophage-like cells, a variant of the J774 cell line.

Animals↗
PubMed1988

Sphingomyelin liposomes with defined fatty acids: metabolism and effects on reverse cholesterol transport.

Small unilamellar liposomes prepared from sphingomyelins with defined 14C-labeled fatty acids were studied after injection into rats. The liposomes contained trace amounts of [3H]cholesteryl linoleyl ether (CLE), which served as a nonexchangeable and nonhydrolyzable marker. The liposomes were cleared from the circulation with an initial t1/2 of about 90 min. [14C]18:0- and [14C]18:1-containing sphingomyelins were cleared at a similar rate, but [14C]18:2-sphingomyelin disappeared much faster. The liver accounted for up to 70% of [3H]cholesteryl ether injected with 18:0-sphingomyelin liposomes, and for up to 50% with liposomes prepared from 18:1 or 18:2-sphingomyelin. The initial uptake of the liver appeared to be of the entire particle, and the loss of 14C label with time indicated metabolism of the sphingomyelins. With [14C]18:0-sphingomyelin liposomes, up to 8% of liver radioactivity was recovered in neutral lipids 6 h after injection, and this value was 17 and 22% with [14C]18:2- and [14C]18:1-sphingomyelins, respectively. The recovery in 'carcass' of [3H]cholesteryl ether 3 h after injection of [14C]18:2-sphingomyelin liposomes was 33% and of 14C label, 21%. Injection of 18:1- or 18:2-sphingomyelin liposomes (5.4 mumol/100 g body weight) resulted in a 2-fold increase of plasma unesterified cholesterol; a 30% increase was seen with 18:0 liposomes (2.63 mumol/100 g body weight). In experiments with cultured cells, the unsaturated sphingomyelin liposomes alone enhanced cholesterol efflux more extensively than the saturated ones, but their efficacies became similar when mixed with apoprotein (apo) A-I. At equimolar concentration, apo C-III1 or C-III2 had a smaller effect than apo A-I. It is concluded that 18:1- or 18:2-sphingomyelin tends to form small unilamellar liposomes which may reach also extrahepatic tissues. The liposomes able to enhance cholesterol release in vitro and in vivo. Since they are not a substrate for lecithin-cholesterol acyltransferase, they should be able to deliver the free cholesterol to the liver, where they are also rapidly metabolized.

Adrenal Glands↗
PubMed1988

Tunicamycin-treated rat heart cell cultures synthesize an inactive nonreleasable lipoprotein lipase.

Cells isolated from newborn rat hearts were cultured in the presence of 100 mM Hepes (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid). Lipoprotein lipase activity was present in an intracellular and heparin-releasable pool and was also secreted into the culture medium. Treatment of the cultures with 5 micrograms/ml tunicamycin caused almost complete loss of lipoprotein lipase activity in all three compartments. In control cultures, immunoblotting of lipoprotein lipase derived from all three pools revealed a single band of lipoprotein lipase with an apparent Mr of 56,000. In the tunicamycin-treated cultures, the enzyme appeared only intracellularly and had an apparent Mr of 49,000. No immunoreactive enzyme was found in the medium. Thus, glycosylation of lipoprotein lipase in heart cell cultures is mandatory for enzyme activity and translocation from an intracellular to the heparin-releasable pool and for secretion into the medium.

Animals↗
PubMed1988

Lipoprotein lipase in heart cell cultures is suppressed by bacterial lipopolysaccharide: an effect mediated by production of tumor necrosis factor.

Exposure of rat heart cell cultures, consisting mainly of nonbeating mesenchymal cells, to 50 ng/ml of bacterial lipopolysaccharide (LPS) for 24 h resulted in a more than 80% reduction in lipoprotein lipase activity. The loss of enzymic activity was accompanied by a concomitant reduction in enzyme protein, as shown by immunoblotting. Addition of LPS to the culture medium resulted also in the production of tumor necrosis factor (TNF), and the fall in lipoprotein lipase in LPS-treated cultures could be prevented by an antibody to TNF. Addition of recombinant human TNF to the heart cell cultures also depressed lipoprotein lipase activity. LPS treatment of preadipocytes in culture resulted in a fall in lipoprotein lipase activity and TNF production. Since TNF is known as a macrophage product, the cultures were tested for phagocytic capacity, and only 0.2-1.3% of the cells were shown to engulf Staphylococcus albus. Immunofluorescent staining with monoclonal antibodies OX-1, which identify leukocyte common antigen, was negative, and only 0.1 +/- 0.07% of the cells were positive after staining with OX-42 antibody to iC3b receptor. Both antibodies stained more than 98% of rat peritoneal macrophages used as controls. Since LPS treatment of macrophages at numbers comparable to or exceeding the number of phagocytic cells present in the heart cell cultures did not induce measurable amounts of TNF, it is suggested that in the heart cell cultures, TNF may be produced by cells other than macrophages.

Animals↗
PubMed1988

Preferential metabolism by macrophages of conditioned rabbit hypercholesterolemic remnant lipoproteins.

Rabbits were fed a diet containing 1% cholesterol, and lipoproteins were isolated from their plasma by sequential ultracentrifugation. Lipoprotein remnants (d = 1.019-1.063) were conditioned by incubation with bovine aortic smooth muscle cells for 24 h and then incubated for 4 h with J774 cells or mouse peritoneal macrophages. Conditioning of remnants and low-density lipoproteins resulted in enhancement of their uptake and metabolism by the macrophages in culture. The macrophages metabolized conditioned remnant lipoproteins more extensively than controls at all concentrations tested. Addition of 10% safflower oil or 10% butter to the 1% cholesterol diet resulted in a molar ratio of linoleic/oleic acid of 1.62 and 0.62 in plasma neutral lipids and of 5.7 and 2.5 in plasma phospholipids. Conditioned remnants, derived after safflower oil feeding, were metabolized more extensively by macrophages than those obtained after butter feeding. This was also true for control remnants (preincubated without cells). Thiobarbituric acid-reactive substances were higher in remnants from safflower oil-fed than butter-fed rabbit plasma prior to and after conditioning. Mouse peritoneal macrophages metabolized remnant lipoproteins more extensively than low-density lipoproteins. The present results indicate that modification of remnant lipoproteins, the major atherogenic fraction of cholesterol-fed rabbit plasma, results in their enhanced metabolism by macrophages, and that an increase in the linoleic/oleic acid ratio in these lipoproteins might enhance their susceptibility to peroxidative modification.

Animals↗
PubMed1988

Biological and cultural sources of familial resemblance in plasma lipids: a comparison between North America and Israel--the Lipid Research Clinics Program.

Heterogeneity in determinants of familial resemblance of lipid and lipoprotein levels between populations in North America and Israel was investigated using path analysis. A common protocol, identical measurement techniques, and the same statistical procedures were used in the two samples. Both genetic (h2) and cultural (c2) determinants of inheritance were significant for all lipid variables in the two studies. Genetic and cultural heritability of total cholesterol (h2 = 0.61, c2 = 0.02), low-density lipoprotein cholesterol (h2 = 0.59, c2 = 0.02), and high-density lipoprotein cholesterol (h2 = 0.55, c2 = 0.06) did not differ significantly between North America and Israel, while there was a significant difference for triglyceride (h2 = 0.41, c2 = 0.07 in North America; h2 = 0.61, c2 = 0.05 in Israel). Secondary parameters of the path model describing intrafamilial environmental relationships differed between the two countries. In particular, there was a higher correlation between marital environments in Israel for all traits except triglyceride, and a larger effect of father's environment on offspring's environment in Israel for all traits. Within both populations, variation of plasma lipids and lipoproteins was mostly explained by genetic factors and random unmeasured environmental factors. The contribution of common family environment was found to be small, though statistically significant. This is probably due to homogeneity of the distribution of familial environmental determinants within both countries.

Cholesterol↗
PubMed1988

Family resemblance for serum uric acid in a Jerusalem sample of families.

Familial aggregation of serum uric acid was studied in a sample of families examined in the Jerusalem Lipid Research Clinic. We first examined homogeneity of familial correlations across the major origin groups in the Israeli population sample. In general correlations were homogeneous across origin groups, except for spouse pairs. Pooled correlations among biological relatives across the origin groups were all statistically significant. Spouse correlation upon adjustment for concomitant variables was moderately positive (r = 0.115), yet significantly different from zero. Genetic and cultural determinants of uric acid were estimated utilizing a path model with 10 parameters to be estimated from a total of 16 correlations. Under a reduced model, genetic heritability (h2) was estimated to be 0.47 +/- 0.05 and cultural heritability (c2) was 0.11 +/- 0.03. However, our data gave suggestive evidence that cultural heritability was higher in parents (c2 = 0.28) than in children (c2 = 0.10). Commingling analysis and segregation analysis were also performed, and our findings imply that in the Israeli population there is no evidence for a major gene for high uric acid levels segregating in families.

Adult↗