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Biomedical subjects

T Olivecrona

Publications and source records attributed to T Olivecrona.

At least 127 records · Page 7Linked to original sources
PubMed1983

Transfer of cholesteryl linoleyl ether from phosphatidylcholine and phosphatidylethanolamine liposomes to cultured cells catalyzed by lipoprotein lipase.

Unilamellar liposomes prepared from purified phospholipids (phosphatidylcholine, phosphatidylethanolamine or sphingomyelin) and labeled cholesteryl linoleyl ether were used to study lipoprotein lipase-catalyzed transfer of cholesteryl ester into cells in culture. In mesenchymal rat heart cell cultures, the transfer of cholesteryl linoleyl ether and cholesteryl linoleate was similar and related to the activity of endogenously produced lipoprotein lipase. In human skin fibroblasts transfer of labeled cholesteryl linoleyl ether was proportional to the concentration of milk lipoprotein lipase added to the incubation medium. Liposomes prepared from phosphatidylcholine or phosphatidylethanolamine were much better donors of cholesteryl ether to normal and apolipoprotein E-B receptor-negative fibroblasts and to endothelial cells than those prepared from sphingomyelin. Lysophosphatidylcholine was formed during incubation with milk lipoprotein lipase but was not considered to be directly responsible for the lipoprotein lipase-catalyzed transfer of cholesteryl ether. This conclusion was drawn because in the absence of lipoprotein lipase addition of lysophosphatidylcholine to liposomes, or almost complete phospholipolysis by phospholipase A2, did not result in the transfer of cholesteryl linoleyl ether from liposomes to cells. Attachment of lipoprotein lipase to the cell surface was mandatory for the transfer of cholesteryl ether and could be prevented by heparin. High density apolipoprotein reduced also the transfer of cholesteryl linoleyl ether, even though it did not interfere with the binding of labeled milk lipoprotein lipase to cultured fibroblasts. The present results provide evidence that lipoprotein lipase, and not the products of phospholipid hydrolysis, is the ligand for the non-apolipoprotein E-B receptor-mediated transfer of cholesteryl ester to cells.

Animals↗
PubMed1983

Free cholesterol distribution during in vitro lipolysis of rat plasma very low density lipoprotein: lack of a role for blood and heart cells.

In the present study, an attempt was made to quantify free cholesterol transfer from lipolyzed VLDL to HDL, blood cells and heart cells. The experiments were carried out in vitro or in the isolated perfused rat heart with rat plasma VLDL labelled biosynthetically with [14C]-palmitic acid and [3H]cholesterol, and with bovine milk lipoprotein lipase, human blood cells (erythrocytes, leucocytes and platelets) or rat plasma HDL. Exchange and transfer of free cholesterol was followed by radioactivity and specific activity determinations. The study demonstrated an exchange of free cholesterol between VLDL and blood cells (6-10 h) and VLDL and HDL (120 min). However, none of the blood cells tested served as acceptor for lipolysis-generated free cholesterol, whereas HDL did. In the isolated perfused rat heart, a maximum of 25% of the free cholesterol radioactivity lost from VLDL was found in the tissue. Since exchange must have contributed to this process, the transfer of free cholesterol molecules to the heart is necessarily lower. The study thus demonstrated minimal or possibly no net transport of free cholesterol from VLDL to cells and cell membranes.

Animals↗
PubMed1983

Metabolic heterogeneity of post-lipolysis rat mesenteric lymph small chylomicrons produced in vitro.

The study was undertaken to investigate the metabolic rat of post-lipolysis mesenteric lymph small chylomicrons produced in vitro. Small chylomicrons doubly labeled with [3H]cholesterol (more than 70% in cholesteryl esters) and [14C]palmitate-labeled triglycerides were collected from rat mesenteric lymph during periods of fasting. Lipolysis was performed in vitro with lipoprotein lipase purified from bovine milk. More than 98% of the chylomicron-triglycerides could be hydrolyzed to fatty acids. Post-lipolysis chylomicrons were separated by zonal ultracentrifugation, characterized, and tested for biological behavior in intact rats. Following lipolysis the lipoproteins lost nearly all their triglycerides, apoA-I, and apoC, and were relatively enriched with cholesteryl esters, unesterified cholesterol, phospholipids, and apoB. Three preparations were tested for biological behavior: pooled (total) post-lipolysis chylomicrons (diameter approximately 250 A); particles at the ascending part of the zonal effluent (diameter approximately 300 A), and at the descending part (diameter approximately 200 A). After intravenous injection to intact rats, [3H]cholesteryl ester decay was very rapid with pooled lipoproteins and the 300-A preparation (t1/2 = 5-10 min). The 200-A preparation in contrast stayed in circulation much longer (t1/2 = 60-90 min). The study thus demonstrated metabolic heterogeneity of post-lipolysis small chylomicrons and indicated that some may form an LDL-like subpopulation with a plasma lifetime slower than "remnants" but faster than LDL.

Animals↗
PubMed1982

On the pH dependency of lipoprotein lipase activity.

The relation between pH and activity for lipoprotein lipase against emulsions of long-chain triacylglycerols has previously been studied in several laboratories and found to be a bell-shaped curve with optimum activity between pH 8 and 9. In contrast, using short-chain triacylglycerols or monoacylglycerols as substrates we had found that the activity rises continuously with pH to at least pH 10.5. This suggested that some factor other than the active site mechanism limited the activity at high pH in traditional assay systems. We, therefore, reinvestigated the activity against long-chain triacylglycerols under conditions where binding of the enzyme to the emulsion droplets and enzyme stability was not limiting. Under these conditions the activity continued to rise from pH 8 to pH 10, and the degree of stimulation by apolipoprotein C-II was found to be the same over the whole range studied (pH 6.5-10.5).

Animals↗
PubMed1982

Binding of lipoprotein lipase to the cell surface is essential for the transmembrane transport of chylomicron cholesteryl ester.

Four cell types, F1 rat heart cells, rat preadipocytes, human skin fibroblasts and bovine endothelial cells, were used to investigate whether surface binding of lipoprotein lipase was essential in the transmembrane transport of chylomicron cholesteryl ester. Exposure of F1 heart cells to colchicine resulted in decrease in endogenous surface-bound lipoprotein lipase and a concomitant fall in the uptake of chylomicron cholesteryl linoleyl ether, a nondegradable analog of cholesteryl ester. Uptake of chylomicron cholesteryl linoleyl ether was enhanced by addition of milk lipoprotein lipase and this enhancement also persisted in the presence of colchicine. The drug did not reduce surface binding to the enzyme. Milk lipoprotein lipase was bound to the cell surface of the different cell types and its fate during chase in enzyme-free medium was determined. The t 1/2 of surface-bound enzyme in endothelial cells and in F1 heart cells was about 2 h; it was 4 h in skin fibroblasts. The decrease in surface-bound lipoprotein lipase was accompanied by a parallel fall in the binding and uptake of chylomicron cholesteryl linoleyl ether by the various cell types examined. This decrease in the uptake of cholesteryl linoleyl ether occurred even though lipoprotein lipase activity in the medium was present, as evidenced by the hydrolysis of [14C]triacylglycerol. Release of surface-bound endogenous or exogenous lipoprotein lipase by heparin was accompanied by almost complete elimination of uptake of cholesteryl linoleyl ether in presence of complete hydrolysis of [14C]triacylglycerol. The present results indicate that the transmembrane transport of cholesteryl ester is catalyzed by lipoprotein lipase only when the enzyme is bound to the cell membrane.

Adipose Tissue↗
PubMed1982

Purification and properties of lipoprotein lipase in guinea pig milk.

Lipoprotein lipase was purified from guinea pig milk by chromatography on heparin-Sepharose followed by chromatography on an immobilized preparation of heparin that had been N-desulphated and then acetylated. This second step was necessary to separate a plasma protein, presumably antithrombin, from the lipase. The guinea pig enzyme turned out to be quite similar to lipoprotein lipase from bovine milk with respect to composition and molecular size. Furthermore, the specific activities and the dose-response relations for activation by apolipoprotein C-II were quite similar for the two enzymes. Antibodies raised against the guinea pig milk enzyme inhibited not only this enzyme but also the lipoprotein lipase activity in post-heparin plasma and in homogenates from adipose tissue and heart.

Amino Acids↗
PubMed1982

Fate of milk 125I-labelled lipoprotein lipase in cells in culture. Comparison of lipoprotein lipase- and non-lipoprotein lipase-synthesizing cells.

Radioiodinated lipoprotein lipase, isolated from bovine milk (125I-labeled milk lipoprotein lipase) was shown to retain full hydrolytic activity towards its native substrate, i.e., chylomicron triacylglycerol. The 125I-labeled enzyme interacted with various cells in culture by being bound to the cellular surface, internalized and degraded. Cellular binding of the labeled enzyme occurred in the presence or absence of substrate and was related to enzyme concentration. Heparin reduced cellular binding by 50% but inhibited uptake and degradation more extensively. Cellular uptake was not affected by chloroquine or NH4Cl, but degradation of the labeled enzyme was blocked. Uptake and degradation were not inhibited by mannose 6-phosphate. The interaction between the exogenous enzyme and cells which do not synthesize lipoprotein lipase, i.e., fibroblasts and endothelial cells, resulted in a high ratio of surface binding to degradation. In heart cell cultures and preadipocyte cultures, which produce lipoprotein lipase, the ratio of enzyme catabolized to that bound was high at all time points examined. Since in the intact organism lipoprotein lipase acts at the luminal surface of vascular endothelium, it seems expedient that these cells are able to bind the enzyme, but will catabolize it only slowly. The rapid and extensive degradation of the 125I-labeled lipoprotein lipase in heart cells and preadipocytes may be related to the metabolism of the endogenously produced lipoprotein lipase.

Adipose Tissue↗
PubMed1982

Molecular properties of lipoprotein lipase. Effects of limited trypsin digestion on molecular weight and secondary structure.

The monomer molecular size of bovine lipoprotein lipase was evaluated by sedimentation equilibrium measurements and by gel permeation chromatography in 6 M guanidinium chloride. To establish molecular weight unequivocally we determined the partial specific volume (v) experimentally. This was done by analyzing equilibrium concentration profiles from analytical ultracentrifugation in 6 M guanidinium chloride using buffers made up in H2O and 2H2O. The combined results gave a v of 0.71 +/- 0.007 ml/g and a molecular weight of 41,700 +/- 1000 for monomeric bovine lipoprotein lipase. This value did not change upon mild tryptic digestion; the elution volume upon gel permeation chromatography in 6 M guanidinium chloride was also unaffected by treatment with trypsin. Sedimentation equilibrium measurements of the trypsin-treated material in the presence of reducing agents gave limiting molecular weights of 19,000 and 23,000, demonstrating that mild trypsin digestion cleaved lipoprotein lipase into two polypeptide chains of similar size held together by disulfide bonds. Mild trypsin digestion also resulted in a loss of secondary structure as determined by circular dichroic measurements. Discussion centers around the correlation between these effects of trypsin on the molecular properties of lipoprotein lipase and the previously reported effects on the kinetic properties of the enzyme.

Animals↗
PubMed1982

Transfer of human lymph chylomicron constituents to other lipoprotein density fractions during in vitro lipolysis.

To ascertain whether chylomicron constituents would be transferred to low density lipoprotein (LDL, d 1.019-1.063 g/ml) and high density lipoprotein (HDL, d 1.063-1.21 g/ml) density fractions during lipolysis in the absence of other lipoproteins, the in vitro effect of bovine milk lipoprotein lipase on human thoracic duct lymph chylomicrons in the presence of albumin was examined. In incubations without lipase, over 90% of chylomicron constituents remained in the 1.006 g/ml supernate, and large particles ranging in diameter mainly from 750-6000 A were observed by electron microscopy. After the addition of lipase, lipolysis ranged from 69.0-94.6% and numerous collapsed particles with redundant surface were seen, as well as smaller particles within the LDL and HDL density region. With lipolysis, the majority of chylomicron cholesterol and phospholipid mass was transferred to LDL and HDL, while chylomicron apolipoprotein (apo) A-I, A-II, and C-II mass was transferred mainly to HDL. Utilizing either radioiodinated apoA-I and apoA-II reassociated with chylomicrons or radiolabeled chylomicrons, a similar redistribution of apoA-I and apoA-II radioactivity was noted with lipolysis. In contrast, chylomicron apoB (mainly B-48) radioactivity was transferred predominantly to LDL with lipolysis. These data are consistent with the concept that during lymph chylomicron triglyceride hydrolysis, chylomicron apolipoproteins, cholesterol, and phospholipid can be transferred to the LDL and HDL density regions in the absence of acceptor particles.

Animals↗
PubMed1981

Effects of two albumins and two detergents on the activity of bovine milk lipoprotein lipase against very low density and high density lipoprotein lipids.

In this study we have determined the effects of two commercial albumin preparations (Sigma and Pentex albumins) and two detergents (sodium deoxycholate and Triton X-100) on the activity of lipoprotein lipase purified from bovine milk against biosynthetically labeled triacylglycerol in very low density lipoprotein and biosynthetically labeled phosphatidylcholine in very low density and high density lipoproteins. Pentex albumin decreased the activity of lipoprotein lipase in all assays to about one-fourth to one-third of that observed with Sigma albumin. Quantitative differences were observed in the distribution of labeled surface constituents (32P-labeled phospholipids, [3H]cholesterol and 125I-labeled apolipoprotein C) among density fractions during lipolysis of very low density lipoprotein carried out in the presence of Pentex or Sigma albumins. With Pentex albumin, more phospholipids and apolipoprotein C distributed to the density fraction of d 1.04-1.21 g/ml than with Sigma albumin. Sodium deoxycholate at a concentration of up to 2 mM had little effect in all assays. Triton X-100 decreased the activity of lipoprotein lipase against very low density lipoprotein lipids but increased the activity of the enzyme against high density lipoprotein lipids. The study has thus demonstrated marked quantitative differences of lipoprotein lipase activities when determined under slightly differing incubation conditions.

Animals↗
PubMed1981

Demonstration of hepatic heparin-releasable lipase in the guinea-pig.

It was recently reported by Yamada et al. (Yamada, N., Murase, T., Akanuma, Y., Ikakura, H. and Kosaka, K. (1979) Biochim. Biophys. Acta 575, 128-134) that the guinea-pig has no hepatic heparin-releasable lipase. We have, however, found a low but definite lipase activity in guinea-pig post-heparin plasma with the characteristics of the hepatic lipase. This activity, as measured in our assay, is only about one-tenth of that in rat post-heparin in plasma. Although the activity is thus much lower than in some other animals, its presence demonstrates that the guinea-pig is not qualitatively but only quantitatively different in this respect.

Animals↗