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Biomedical subjects

P Brecher

Publications and source records attributed to P Brecher.

At least 73 records · Page 4Linked to original sources
PubMed1987

Effects of deoxycorticosterone/salt hypertension on cell ploidy in rat aortic smooth muscle cells.

The effect of hypertension on DNA content of isolated aortic smooth muscle cells and their nuclei has been studied in Wistar rats treated with deoxycorticosterone and salt (DOC/salt). Eight weeks of DOC/salt administration induced a significant increase in aortic smooth muscle cells with tetraploid nuclei from 9.7 +/- 0.8% (mean +/- SE) in control animals to 26.6 +/- 2.4% with DOC/salt. The tetraploid cells appeared approximately 60% larger in size than diploid cells as estimated by forward light scatter. Prolonged reversal of hypertension by withdrawal of DOC/salt for 3 months did not reduce nuclear tetraploidy significantly but appeared to prevent further increases. The results suggest that hypertension influences the growth cycle of aortic smooth muscle cells and increases nuclear polyploidy and cellular hypertrophy. Preliminary studies have also been performed to measure transmembrane potential in isolated viable aortic smooth muscle cells with a lipophilic cationic fluoroprobe, 3,3 dipentyloxacarbocyanine, which distributes into cells in a potential-dependent manner. Norepinephrine (10(-6)M to 10(-3)M) appeared to produce a concentration-dependent reduction in membrane potential that was blocked by equimolar concentrations of prazosin but not of yohimbine. The studies suggest that norepinephrine can cause depolarization of smooth muscle cells through an alpha 1-mediated mechanism.

Animals↗
PubMed1986

Binding of lysophosphatidylcholine to the rat liver fatty acid binding protein.

In this study, lysophosphatidylcholine (lysoPC) was shown to bind to a fatty acid binding protein isolated from rat liver. To demonstrate the binding, lysoPC was incorporated into multilamellar liposomes and incubated with protein. For comparison, binding of both lysoPC and fatty acid to liver fatty acid binding protein, albumin, and heart fatty acid binding protein were measured. At conditions where palmitic acid bound to liver fatty acid binding protein and albumin at ligand to protein molar ratios of 2:1 and 5:1, respectively, lysoPC binding occurred at molar ratios of 0.4:1 and 1:1. LysoPC did not bind to heart fatty acid binding protein under conditions where fatty acid bound at a molar ratio of 2:1. Competition experiments between lysoPC and fatty acid to liver fatty acid binding protein indicated separate binding sites for each ligand. An equilibrium dialysis cell was used to demonstrate that liver fatty acid binding protein was capable of transporting lysoPC from liposomes to rat liver microsomes, thereby facilitating its metabolism. These studies suggest that liver fatty acid binding protein may be involved in the intracellular metabolism of lysoPC as well as fatty acids, and that functional differences may exist between rat liver and heart fatty acid binding protein.

Animals↗
PubMed1986

Characterization of a fatty acid-binding protein from rat heart.

A fatty acid-binding protein has been isolated from rat heart and purified by gel filtration chromatography on Sephadex G-75 and anion-exchange chromatography on DE52. The circular dichroic spectrum of this protein was not affected by protein concentration, suggesting that it does not aggregate into multimers. Computer analyses of the circular dichroic spectrum predicted that rat heart fatty acid-binding protein contains approximately 22% alpha-helix, 45% beta-form and 33% unordered structure. Immunological studies showed that the fatty acid-binding proteins from rat heart and rat liver are immunochemically unrelated. The amino acid composition and partial amino acid sequence of the heart protein indicated that it is structurally related to, but distinct from, other fatty acid-binding proteins from liver, intestine, and 3T3 adipocytes. Using a binding assay which measures the transfer of fatty acids between donor liposomes and protein (Brecher, P., Saouaf, R., Sugarman, J. M., Eisenberg, D., and LaRosa, K. (1984) J. Biol. Chem. 259, 13395-13401), it was shown that both rat heart and liver fatty acid-binding proteins bind 2 mol of oleic acid or palmitic acid/mol of protein. The structural and functional relationship of rat heart fatty acid-binding protein to fatty acid-binding proteins from other tissues is discussed.

Amino Acids↗
PubMed1986

Phospholipid methylation in rabbit aorta.

The formation of phosphatidylcholine by successive methylations of phosphatidylethanolamine using S-adenosylmethionine as the methyl donor was studied in homogenates of rabbit aorta. Addition of phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine, but not phosphatidylethanolamine, stimulated methyltransferase activity and this activity was further stimulated when the phospholipids were dispersed in taurocholate prior to addition to the assay system. No incorporation of radiolabel into sphingomyelin or lysolecithin was detected indicating minimal metabolism of newly formed phosphatidylcholine. The majority of methyltransferase activity was detected in the high-speed pellet of the aortic homogenate; however, since activity was also detected in the high-speed supernatant, the low-speed supernatant preparation was used as the source of enzyme. Methyltransferase activity was characterized in cultured arterial smooth muscle cells using methionine as the radiolabeled precursor. The major product formed was phosphatidylcholine. No difference in enzyme activity was seen as a function of the length of time that cells were in culture or anatomic location of the aortic explant used as a source of cells. Treatment of the cells with cycloheximide did not affect methyltransferase activity. The ability of catecholamine agonists and vasoactive peptides to influence methyltransferase activity was investigated both in the cell-free preparation and in cultured cells. These compounds did not appear to alter methyltransferase activity in rabbit aortic smooth muscle cells.

Animals↗
PubMed1986

Effects of deoxycorticosterone-salt hypertension on cell ploidy in the rat aorta.

We investigated the effect of deoxycorticosterone-salt hypertension and its reversal on nuclear ploidy in rat aortic smooth muscle cells, using flow cytometry. Systolic blood pressure and the percentage of cells with tetraploid nuclei increased over a 4-week period and then remained constant. In control rats 6.0 +/- 0.6% of aortic cells had tetraploid nuclei, and this increased to 27.0 +/- 1.1 and 26.6 +/- 2.4% after 4 and 8 weeks of deoxycorticosterone-salt treatment, respectively. Computer analysis of the forward light scatter data obtained from the cell sorter indicated that the average tetraploid cell was approximately 1.6-fold larger than the average diploid cell in both normotensive and hypertensive animals. Analysis of the DNA content of intact cells and isolated nuclei indicated that the increased DNA content per cell was predominantly attributable to tetraploid nuclei rather than binucleated cells. Reversal of hypertension with either a low sodium diet for 8 to 13 weeks or chlorothiazide administration failed to reverse the abnormalities seen in arterial smooth muscle cell ploidy, despite normalization of the blood pressure and the ratio of heart to body weight.

Animals↗
PubMed1985

Effects of propranolol on atherogenesis in the cholesterol-fed rabbit.

These studies have examined the effects of dl-propranolol, d-propranolol, and metoprolol on aortic atherogenesis in the cholesterol-fed rabbit and have correlated the vascular effects of the drugs with their influence on blood pressure, plasma lipids and lipoproteins, arterial metabolism, and arterial permeability. dl-Propranolol, and, to a lesser extent, d-propranolol, used in clinically relevant doses of 5 mg/kg body weight per day, inhibited the development of aortic atherosclerosis in association with significant reductions in aortic free and esterified cholesterol content. No significant effects of the drugs on blood pressure or on the total amounts or types of circulating lipoproteins were apparent. Accumulation of cholesterol in the liver and adrenal gland was not influenced by propranolol. Aortic acyl CoA:cholesterol acyltransferase and lysosomal enzyme activities were reduced by propranolol administration, but the inhibition may have been secondary to the lesser degrees of atherosclerosis and cholesterol accumulation present. In vitro inhibition of acyl CoA:cholesterol acyltransferase activity by either dl- or d-propranolol was also observed, but occurred only at propranolol concentrations of 10(-3) M or greater. Treatment with dl-propranolol had no significant effect on the rate of transport of labeled albumin across the isolated carotid artery of cholesterol-fed rabbits. Metoprolol administration (6.25 mg/kg body weight per day) had no significant influence on atherogenesis or arterial metabolism in this model. The results suggest that propranolol inhibits in part the development of atherosclerosis in the cholesterol-fed rabbit, and that the effect may be related to a direct action on the arterial wall.

Animals↗
PubMed1985

Effect of fasting on the composition of plasma lipoproteins in cholesterol-fed diabetic rabbits.

Cholesterol-fat feeding is associated with unusual alterations in the composition of plasma lipoproteins in alloxan-diabetic rabbits. In the present study plasma lipoprotein lipid and apoprotein composition was studied before and after 48 hr of fasting in cholesterol-fed diabetic and control rabbits in order to further characterize these alterations. Compared with control rabbits, the diabetic rabbits had similar plasma cholesterol levels, but 100-fold higher triglyceride levels prior to fasting. These plasma lipids were distributed mainly to large, Sf greater than 400 plasma lipoproteins in the diabetic rabbits, and to beta-VLDL in control rabbits. Sf greater than 400 lipoproteins, VLDL, IDL, LDL, and HDL from diabetic rabbits had triglyceride as the predominant lipoprotein core lipid. Sf greater than 400 lipoproteins and VLDL from diabetic rabbits had lesser amount of apoprotein E, and greater amounts of apoproteins A-I, A-IV, and B-48 as percent of total apoprotein mass in comparison with control rabbits. Fasting reduced plasma triglyceride levels by 55% in diabetic rabbits. Sf greater than 400 lipoprotein and VLDL triglyceride content decreased but remained a major core lipid. Fasting eliminated apoproteins A-I and A-IV from Sf greater than 400 lipoproteins and VLDL, but had no significant effect on apoB-48 content. Insulin treatment of the diabetic rabbits reduced plasma triglyceride by approximately 90% resulting in cholesteryl ester-rich particles reassembling beta-VLDL both in the Sf greater than 400 lipoprotein and VLDL fractions. These results indicate that the alterations in plasma lipoproteins in cholesterol-fed diabetic rabbits result from the presence in the d less than 1.006 g/ml plasma lipoprotein class of partially metabolized, intestinally derived particles.

Animals↗
PubMed1984

Fatty acid transfer between multilamellar liposomes and fatty acid-binding proteins.

A simple experimental system was developed for studying the movement of long-chain fatty acids between multilamellar liposomes and soluble proteins capable of binding fatty acids. Oleic acid was incorporated into multilamellar liposomes containing cholesterol and egg yolk lecithin and incubated with albumin or hepatic fatty acid-binding protein. It was found that the fatty acid transferred from the liposomes to either protein rapidly and selectively under conditions where phospholipid and cholesterol transfer did not occur. More than 50% of the fatty acid contained within liposomes could become protein bound, suggesting that the fatty acid moved readily between and across phospholipid bilayers. Transfer was reduced at low pH, and this reduction appeared to result from decreased dissociation of the protonated fatty acid from the bilayer. Liposomes made with dimyristoyl or dipalmitoyl lecithin and containing 1 mol per cent palmitic acid were used to show the effect of temperature on fatty acid transfer. Transfer to either protein did not occur at temperatures where the liposomes were in a gel state but occurred rapidly at temperatures at or above the transition temperatures of the phospholipid used.

Carbon Radioisotopes↗
PubMed1984

Effect of surface composition on triolein hydrolysis in phospholipid vesicles and microemulsions by a purified acid lipase.

Sonicated dispersions of egg yolk phosphatidylcholine and triolein as vesicles and microemulsions have been used as substrates for the assay of a purified acid lipase. Previous studies have also shown that triolein localized in the surface phase of emulsions is the preferred substrate. In this study, we examined enzyme activity following several surface modifications using both vesicles and microemulsions. When the acidic phospholipids phosphatidylserine and phosphatidic acid were incorporated into both vesicles and microemulsions at up to 10 mol % of the total phospholipid, a dose-dependent reduction in the apparent Km was observed. Using the vesicles as substrate, a dose-dependent decrease in Vmax was also observed. Agarose gel electrophoresis was used to verify suspected changes in net particle charge. Analogous inclusion of phosphatidylethanolamine, sphingomyelin, or cholesterol did not affect kinetic parameters. Addition of oleic acid to sonication mixtures produced vesicles with a decreased apparent Km and Vmax, but triolein hydrolysis in microemulsions was not significantly altered. Triolein-containing vesicles prepared by using dimyristoyl- or dipalmitoylphosphatidylcholine were hydrolyzed maximally at the gel liquid-crystalline transition temperatures of the appropriate phospholipid. Differential scanning calorimetry was used to verify the temperatures of transition in these vesicles. The results indicate that acid lipase activity is influenced by the charge or physical state of the surface phase of model substrates and suggest that degradation of core components of naturally occurring substrates such as lipoprotein may be influenced by chemical changes on the surface of these particles.

Animals↗
PubMed1983

Hydrolysis of triolein in phospholipid vesicles and microemulsions by a purified rat liver acid lipase.

An acid lipase was purified from rat liver lysosomes. Lipase purification involved affinity chromatography, gel filtration, and stabilization of the purified preparation using ethylene glycol and Triton X-100. A molecular weight of 67,000-69,000 was determined independently using density gradient centrifugation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and gel filtration. To study enzyme action, model substrates were prepared by incorporating radiolabeled triolein into either unilamellar vesicles or microemulsions. Substrates were prepared by cosonicating aqueous dispersions of lecithin and triolein. Formation of vesicles or emulsions depended on the relative amount of each lipid and on sonication conditions. Vesicles were prepared at molar ratios between 70:1 and 26:1 (lecithin:triolein) and the microemulsion preparation at a molar ratio of 1:1. The substrate particles were of similar size (220-250 A) as determined by Bio-Gel A-15m chromatography. Hydrolysis of triolein contained in vesicles or emulsions was similar with respect to pH, temperature, and reaction products. Kinetic studies on vesicles with increasing triolein content showed progressively greater Vmax values (0-0.6 mumol/min/mg), and Vmax for the emulsion was 3.1 mumol/min/mg. Addition of human very low or low density lipoprotein produced a dose-dependent inhibition with both substrates. The results show that synthetically prepared microemulsions are stable and effective substrates for the acid lipase and indicate that surface-oriented triolein is hydrolyzed in both preparations.

Animals↗
PubMed1983

Esterification of cholesterol and 25-hydroxycholesterol by rat liver microsomes.

The properties of an enzyme in rat liver microsomes was described that catalyzed the formation of 25-hydroxycholesteryl ester in the presence of labeled sterol and oleoyl-CoA. The reaction was similar in several respects to that of cholesteryl ester formation by acyl-CoA: cholesterol acyltransferase. Trypsin pretreatment of microsomes inhibited the esterification of both sterols and a similar dose-dependent inhibition was produced by addition of progesterone and several androgens. Microsomes with an enhanced cholesterol content resulting from in vivo treatment with ethinyl estradiol showed increased esterifying activity towards both cholesterol and 25-hydroxycholesterol. Esterification of endogenous microsomal cholesterol was increased by the addition of 25-hydroxycholesterol, concomitant with 25-hydroxycholesteryl ester formation. To assess the relationship between the association of sterols with membranes and sterol ester formation, microsomes were preincubated with either sterol, reisolated by ultracentrifugation in a density gradient and then analyzed chemically or enzymatically. Cholesterol and 25-hydroxycholesterol both associated with microsomes and the added sterol was subsequently esterified. Maximal esterification was only partially dependent on the amount bound. Progesterone, which inhibited sterol esterification, did not bind to microsomes and no inhibition was observed in reisolated microsomes, indicating that the inhibition produced by progesterone was reversible.

Animals↗
PubMed1983

The interaction of long-chain acyl CoA with membranes.

Published data regarding the interaction of long-chain acyl CoA derivatives with the protein and phospholipid constituents of biological membranes is reviewed and discussed in relationship to the premise that such interactions may lead to membrane damage during pathological situations. The topics considered include: the detergent properties of long-chain CoA, the interaction with membrane-associated enzymes, biological membranes, or model membrane systems, and the binding to a soluble protein that may facilitate intracellular transport. The effects of long-chain acyl CoA on heart mitochondria and the relevance of such studies to myocardial ischemia also is emphasized.

Acyl Coenzyme A↗
PubMed1983

Relationship of an abnormal plasma lipoprotein to protection from atherosclerosis in the cholesterol-fed diabetic rabbit.

Alloxan-diabetic rabbits develop a pronounced hypercholesterolemia and hypertriglyceridemia in response to cholesterol feeding. Despite higher levels of plasma cholesterol, these animals have much less atherosclerosis than cholesterol-fed nondiabetics. To determine whether this effect is due to properties of the lipoproteins, we compared chemical, physical, and metabolic characteristics of a very low density lipoprotein (VLDL) fraction (d less than 1.019 g/ml) from the diabetic and nondiabetic cholesterol-fed rabbits. The molar ratio of triglyceride to cholesteryl ester in the particles from diabetic animals ranged from 2:1 to 6:1, and this ratio remained constant in subfractions from individual rabbits. Triglyceride from nondiabetic control animals was a minor component. Differential scanning calorimetry showed a distinct order-disorder phase transition for cholesteryl ester at approximately 42 degrees C in the fractions from control animals, whereas in fractions from most of the diabetics no such transition was observed, indicating that both triglyceride and cholesteryl ester are present in the core of the same particle. The relative amount of apoprotein E in particles from diabetic animals was much less than that of cholesterol-fed controls. The ability of the lipoproteins from both groups to stimulate cholesteryl ester formation in mouse peritoneal macrophages also was tested. Lipoproteins from cholesterol-fed controls stimulated cholesteryl ester formation in a dose-dependent manner, but particles from the diabetic group had little or no effect. The results suggest that the presence of unusual VLDL particles in diabetic cholesterol-fed rabbits is responsible, at least in part, for the reduced incidence of atherosclerosis in this animal model.

Animals↗
PubMed1981

Cholesteryl ester transfer from phospholipid vesicles to human density lipoproteins.

The exchange of cholesteryl esters between different lipoproteins was reported to bae mediated by a protein present in human plasma. In this study wer have examined the movement of cholesteryl ester from unilamellar phospholipid vesicles to high density lipoprotein (HDL). Experimental conditions were establisehd so that vesicles containing egg yolk lecithin and cholesteryl oleatea (molar ratio of 86:1) could be incubated with human HDL so that neaither disruption of particles nor transfer of lipid occurred. Addition of human lipoprotein-deficient plasma to the system promoted the transfer of cholesteryl oleate, but not phospholipid, from vesicles to HDL. Cholesteryl oleate transfer was dependent upon amount of HDL or lipoproteain-deficient plasma added and occurred when either HDL2 or HDL3 were present. Addition of unesterified cholesterol to the vesicles did not influence lcholesteryl ester transfer to HDL. When phospholipid vesicles containing both cholesteryl oleate and triolein (molar ratio 86:1:1) were incubated with HDL and lipoprotein-deficient plasma, only cholesteryl oleate was transferred from the vesicles to HDL. Lipoprotein-deficient plasma derived from rabbits promoted the selective transfer of cholesteryl oleate from these visicles, but rat plasma did not cause any movement of cholesteryl oleate or triolein from vesicles to HDL. HDL containing labeled cholesteryl esters was prepared and incubated with vesicles containing unlabeled cholesteryl esters or phospholipid alone. Addition of lipoprotein-deficient plasma did not promote transfer of cholesteryl esters from HDL to vesicles, whereas transfer from HDL to low density lipoprotein was readily observed. The results indicated that a protein present in rabbit and human plasma is effective in the selective, unidirectional transport of cholesteryl esters from a phospholipid bilayer to a plasma lipoprotein.

Animals↗