PubMed Health⌕ Search

Biomedical subjects

T Olivecrona

Publications and source records attributed to T Olivecrona.

At least 19 recordsLinked to original sources
PubMed1992

Triacylglycerol and phospholipid hydrolysis in human plasma lipoproteins: role of lipoprotein and hepatic lipase.

To explore the interactions of triacylglycerol and phospholipid hydrolysis in lipoprotein conversions and remodeling, we compared the activities of lipoprotein and hepatic lipases on human VLDL, IDL, LDL, and HDL2. Triacylglycerol and phospholipid hydrolysis by each enzyme were measured concomitantly in each lipoprotein class by measuring hydrolysis of [14C]triolein and [3H]dipalmitoylphosphatidylcholine incorporated into each lipoprotein by lipid transfer processes. Hepatic lipase was 2-3 times more efficient than lipoprotein lipase at hydrolyzing phospholipid both in absolute terms and in relation to triacylglycerol hydrolysis in all lipoproteins. The relationship between phospholipid hydrolysis and triacylglycerol hydrolysis was generally linear until half of particle triacylglycerol was hydrolyzed. For either enzyme acting on a single lipoprotein fraction, the degree of phosphohydrolysis closely correlated with triacylglycerol hydrolysis and was largely independent of the kinetics of hydrolysis, suggesting that triacylglycerol removed from a lipoprotein core is an important determinant of phospholipid removal via hydrolysis by the lipase. Phospholipid hydrolysis relative to triacylglycerol hydrolysis was most efficient in VLDL followed in descending order by IDL, HDL, and LDL. Even with hepatic lipase, phospholipid hydrolysis could not deplete VLDL and IDL of sufficient phospholipid molecules to account for the loss of surface phospholipid that accompanies triacylglycerol hydrolysis and decreasing core volume as LDL is formed (or for conversion of HDL2 to HDL3). Thus, shedding of whole phospholipid molecules, presumably in liposomal-like particles, must be a major mechanism for losing excess surface lipid as large lipoprotein particles are converted to smaller particles. Also, this shedding phenomenon, like phospholipid hydrolysis, is closely related to the hydrolysis of lipoprotein triacylglycerol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Lipoprotein lipase enhances binding of lipoproteins to heparan sulfate on cell surfaces and extracellular matrix.

Lipoprotein lipase enhances binding at 4 degrees C of human plasma lipoproteins (chylomicrons, VLDL, intermediate density lipoprotein, LDL, and HDL3) to cultured fibroblasts and hepG-2 cells and to extracellular matrix. Heparinase treatment of cells and matrix reduces the lipoprotein lipase enhanced binding by 90-95%. Lipoprotein lipase causes only a minimal effect on the binding of lipoproteins to heparan sulfate deficient mutant Chinese hamster ovary cells while it promotes binding to wild type cells that is abolished after heparinase treatment. With 125I-LDL, lipoprotein lipase also enhances uptake and proteolytic degradation at 37 degrees C by normal human skin fibroblasts but has no effect in heparinase-treated normal cells or in LDL receptor-negative fibroblasts. These observations prove that lipoprotein lipase causes, predominantly, binding of lipoproteins to heparan sulfate at cell surfaces and in extracellular matrix rather than to receptors. This interaction brings the lipoproteins into close proximity with cell surfaces and may promote metabolic events that occur at the cell surface, including facilitated transfer to cellular receptors.

Animals↗
PubMed1992

Lipoprotein lipase in plasma after an oral fat load: relation to free fatty acids.

Lipoprotein lipase (LPL) releases fatty acids from triglyceride-rich lipoproteins for use in cellular metabolic reactions. How this hydrolysis, which occurs at the vascular endothelium, is regulated is poorly understood. A fatty acid feedback system has been proposed by which accumulation of fatty acids impedes LPL-catalyzed hydrolysis and dissociates the enzyme from its endothelial binding sites. We examined this hypothesis in humans who were subjected to an oral fat tolerance test of a mixed-meal type. Plasma triglycerides, free fatty acids, and LPL activity were measured before and repeatedly during a 12-h period after intake of the fat load. Since soybean oil with a high content of linoleic fatty acid was the source of triglycerides, a distinction could be made between endogenous free fatty acids (FFA) and FFA derived directly from lipolysis of postprandial triglyceride-rich lipoproteins. Mean LPL activity was almost doubled (P less than 0.01) 6 h after intake of the oral fat load. The rise in LPL activity was accompanied by an increase of plasma triglycerides and linoleic free fatty acids (18:2 FFA), but not of total plasma FFA, which instead displayed a heterogeneous pattern with essentially unchanged mean levels. The postprandial response of LPL activity largely paralleled the postprandial responses of 18:2 FFA and triglycerides. The highest degree of parallelism was seen between postprandial 18:2 FFA and LPL activity levels. Furthermore, the integrated response (area under the curve, AUC) for plasma measurements of LPL correlated with the AUC for 18:2 FFA (r = 0.40, P less than 0.05), but not with the AUC for plasma triglycerides (r = 0.21, ns). The high degree of parallelism and significant correlation between postprandial plasma LPL activity and 18:2 FFA support the hypothesis of fatty acid control of endothelial LPL during physiological conditions in humans.

Dietary Fats↗
PubMed1979

Very low density lipoprotein. Removal of Apolipoproteins C-II and C-III-1 during lipolysis in vitro.

In this study we have investigated the effects of very low density lipoprotein (VLDL) lipolysis on the removal of radiolabeled apolipoprotein C-II and apolipoprotein C-III-1 from in vitro lipolyzed lipoproteins. Lipolysis was carried out in vitro using lipoprotein lipase purified from bovine milk, and mixtures with or without plasma. Lipoproteins were isolated by ultracentrifugation and by gel filtration. Labeled apo-C-II and apo-C-III-1 distributed among plasma lipoproteins, predominantly VLDL and high density lipoprotein (HDL). Lipolysis induced transfer of apo-C-II and apo-C-III-1 from VLDL to HDL. The transfer was proportional to the extent of triglyceride hydrolysis, and similar for the two apoproteins. The apo-C-II/apo-C-III-1 radioactivity ratio did not change in either VLDL or the fraction of d greater than 1.006 g/ml during the progression of the lipolytic process. Similar observations were recorded while using plasma-devoid lipolytic systems. Gel filtration of incubation mixtures, on 6% agarose, revealed that the removal of labeled apo-C molecules from VLDL is not a consequence of either centrifugation or high salt concentration. These results suggest that there is no preferential removal of apo-C-II or apo-C-III-1 from lipolyzed VLDL particles. They further indicate that the ratio of apo-C-II to apo-C-III-1 does not regulate the extent of lipolysis of different VLDL particles, at least in VLDL isolated from normolipidemic humans.

Animals↗
PubMed1979

Guinea pig very low density lipoproteins are a good substrate for lipoprotein lipase.

In contrast to plasma from most other animals, guinea pig plasma causes little or no stimulation of lipoprotein lipase activity. Very low density lipoproteins (VLDL) isolated by ultracentrifugation of guinea pig serum caused a definite stimulation of lipase activity, whereas the infranatant inhibited the activity. Gel filtration in 5 M guanidinium hydrochloride of delipidated VLDL demonstrated that the activation was caused by a low molecular weight protein. The VLDL themselves were hydrolized at similar rates as human VLDL both by guinea pig and by bovine lipoprotein lipases. Thus, guinea pig VLDL contain an activator for lipoprotein lipase analogous to that in other animals and there is enough of the activator to support rapid hydrolysis of the VLDL lipids by the lipase.

Animals↗
PubMed1979

Rapid removal to the liver of intravenously injected lipoprotein lipase.

Lipoprotein lipase was purified from bovine milk and labeled with 125I. After intravenous injection to rats the labeled lipase rapidly disappeared from the blood. The initial half-life was about 1 min and more than 70% of the radioactivity was found in the liver at 10 min. 30 min after the injection about 10% of the injected radioactivity was present in acid-soluble form in blood, indicating that the enzyme had been rapidly degraded. Injection of asialofetuin, ribonuclease B or mannan in amounts known to block the hepatic receptors for glycoproteins with exposed galactose, N-acetylglucosamine or mannose residues did not retard the removal of the lipoprotein lipase. Thus, some other, as yet undefined, receptor is implicated. Lipoprotein lipase is known to bind to heparin and some related polysacchrides. Heparin injected before the enzyme delayed its removal and heparin injected after the enzyme caused an immediate increase in blood radioactivity, signifying return from tissues to blood of labeled enzyme. Lipoprotein lipase is present at the endothelium in several extrahepatic tissues and is rapidly turned over. Its presence in blood in appreciable amounts would cause a derangement of lipid transport. The efficient hepatic removal of the enzyme may thus serve an important physiological purpose in keeping the blood levels of this enzyme low.

Animals↗
PubMed1979

Colipase enhances hydrolysis of dietary triglycerides in the absence of bile salts.

This study explores how dietary lipids are digested when intraduodenal bile salts are low or absent. Long-chain triglycerides emulsified with phosphatidylcholine were found to be hydrolyzed very slowly by pancreatic lipase alone, as if the surface layer of phospholipids enveloping the triglycerides impeded the action of the enzyme. Colipase enhanced triglyceride hydrolysis severalfold, both when added before or after the lipase. Hydrolysis became even more rapid when the emulsion was first incubated with pancreatic phospholipase. Hydrolysis of long-chain triglycerides was also severely impeded when other proteins were added to the system, probably because they adsorbed to the oil-water interface of the emulsion droplets. It was previously known that bile salts can relieve such inhibition, presumably by desorbing the adsorbed proteins. Colipase was found to enhance hydrolysis severalfold in a dose-dependent manner even in the absence of bile salts, i.e., it could partially or completely relieve the inhibition depending upon the amount and the type of inhibitory protein added to the system. Prior exposure of a protein-coated triglyceride emulsion to another lipase also enhanced the rate at which pancreatic lipase could then hydrolyze the lipids. Most dietary triglycerides are probably presented for intestinal digestion in emulsions covered by proteins and/or phospholipids. These emulsions would be hydrolyzed slowly by pancreatic lipase alone. However, through the action of the lipase in stomach contents and of pancreatic phospholipase and through the lipolysis-promoting effects of collipase, these triglycerices can be rather efficiently hydrolyzed, even in the absence of bile salts.

Animals↗
PubMed1979

Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro.

In this study we have determined the fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis of rat plasma very low density lipoprotein (rat VLDL). The experiment was carried out in vitro with lipoprotein lipase purified from bovine milk, VLDL labeled with [(14)C]palmitate, [(3)H]cholesterol, [(32)P]phospholipids, and (125)I-labeled apolipoprotein C and in plasma-devoid systems. Triglyceride hydrolysis ranged between 0 and 98.6%. [(32)P]Phospholipids, unesterified [(3)H]cholesterol, and (125)I-labeled apolipoprotein C were removed from the VLDL (d < 1.019 g/ml) during lipolysis. About one-third of the [(32)P]phosphatidylcholine was hydrolyzed to lysolecithin, and was transferred to the fraction d > 1.21 g/ml. The other two-thirds of the phospholipids were removed unhydrolyzed, mainly to the fraction d 1.04-1.21 g/ml. With the progression of the lipolysis, unesterified [(3)H]cholesterol was removed from VLDL at increasing rates, predominantly to the fraction d 1.04-1.21 g/ml. (125)I-Labeled apolipoprotein C removed from the VLDL partitioned between the fraction of d 1.04-1.21 g/ml and d > 1.21 g/ml. Negative-staining electron microscopy of the fraction d 1.04-1.21 g/ml (containing phospholipids, unesterified cholesterol, and apolipoprotein C) revealed many discoidal lipoproteins. [(3)H]Cholesteryl esters remained associated with the VLDL even when 70-80% of the triglycerides were hydrolyzed. These observations suggest that during in vitro lipolysis of VLDL, surface constituents leave the lipoprotein concomitantly with the hydrolysis of core triglycerides. The process of removal of surface constituents is independent of the presence of an acceptor lipoprotein and may occur in the form of a surface-fragment particle. -Eisenberg, S., and T. Olivecrona. Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro.

Animals↗
PubMed1978

Comparison of the phospholipase activity of bovine milk lipoprotein lipase against rat plasma very low density and high density lipoprotein.

The hydrolytic activity of a lipoprotein lipase from bovine milk against triacylglycerol and phosphatidylcholine of rat plasma very low density lipoprotein was determined and compared to that against phosphatidylcholine of high density lipoprotein. 85--90% of the triacylglycerol in very low density lipoprotein were hydrolyzed to fatty acids and 25--35% of the phosphatidylcholine to lysophosphatidylcholine. High density lipoprotein phosphatidylcholine was only minimally susceptible to the enzyme. Even with high amounts of enzyme and prolonged incubation periods, lysophosphatidylcholine generation did not exceed 2--4% of the original amounts of labeled phosphatidylcholine in the high density lipoprotein. We conclude that phospholipids in high density lipoprotein are not substrates for the phospholipase activity of this lipoprotein lipase. These observations suggest that factors other than the presence of apolipoprotein C-II and of glycerophosphatides are of importance for the activity of lipoprotein lipases.

Animals↗
PubMed1978

The in vitro inhibition of bovine milk lipoprotein lipase by a glycoprotein preparation from human atherosclerotic intima.

Intimal tissue from human atherosclerotic aortae was collected by the Dermatome procedure. The tissue was extraved with 5 mM Tris.HCl buffer containing 0.3 M NaCl and 1 mM EDTA, pH 7.4. The ammonium sulfate precipitate between 0.4--0.8 saturation obtained from the extract was fractionated on a DEAE-cellulose column and the effluent was monitored for lipoprotein lipase inhibition employing purified bovine milk enzyme. The substrate used was an emulsion of purified olive oil and tritiated triolein. Human serum was the source of activator of the substrate. A peak of inhibitory activity was eluted between 0.15--0.17 M NaCl. The major component in the purified material had properties similar to a glycoprotein (lipolipin) which has previously been purified from porcine aorta and shown to inhibit lipoprotein lipase activity. The partially purified human inhibitor decreased both the basal and the serum-stimulated activity of milk lipoprotein lipase. The inhibition was non-competitive with respect to serum. However, high levels of triglyceride substrate appeared to relieve the inhibitory effect. It is postulated that the inhibitor may be involved in an interaction with the emulsified lipid denying the enzyme access to its substrate.

Animals↗
PubMed1978

Decrease of lipase and esterase activities in intestinal contents of newborn infants during test meals.

Both lipase and esterase activities were present in intestinal contents of all newborns studied, from the first day of life. In adults given a test meal lipase activity increased and esterase activity remained unchanged. In contrast, both activities decreased markedly in infants on feeding. During the digestion of the test meal the lipase activity in intestinal contents of the infants was much lower than in adults (ratio of median values 1:27) and the esterase activity was also several fold lower (ratio of median values 1:1.3). Speculation Newborn infants often absorb lipids less efficiently than adults. One contributing factor may be that their incompletely developed pancreas responds to feedings with comparatively low outputs of lipolytic enzymes. The newborn may be more dependent than adults on auxiliary sources of lipase activity such as the pharyngeal lipase and/or the bile-stimulated lipase in human milk.

Adult↗
PubMed1977

Interaction of lipoprotein lipase with heparin-Sepharose. Evaluation of conditions for affinity binding.

Lipoprotein lipases from a variety of sources have been shown previously to bind to heparin and some related polysaccharides. For the present studies lipoprotein lipase purified from bovine milk was used. 1. In batch experiments binding of the enzyme activity to heparin-Sepharose occurred relatively slowly, so that 30min was required for the system to come to near-equilibrium. In contrast, release of the enzyme activity from heparin-Sepharose by addition of salt to the liquid phase occurred rapidly. 2. Some binding was observed also with unsubstituted Sepharose, but this binding had a low capacity compared with that observed with heparin-Sepharose. High salt concentrations, heparin or deoxycholate decreased the binding to unsubstituted Sepharose. These factors also increase the solubility of the enzyme, which is low. 3. Addition of heparin to the liquid phase caused a concentration-dependent release of enzyme activity from the gel. These results suggested that the binding of the enzyme to heparin-Sepharose was mainly through interaction with heparin. 4. The enzyme activity was also quantitatively displaced to the liquid phase at increased concentrations of salt. Among the positive ions tested the following order of effectiveness was noted: Cs(+) approximately K(+)>Na(+)>Li(+); and among the negative the following: SCN(-)>I(-)> NO(3) (-)>Br(-) approximately Cl(-). The differences were quite large. Thus addition of 0.16m-KSCN (in addition to the 0.32m-NaCl originally present) displaced one-half of the enzyme activity to the supernatant, whereas 0.8m-LiCl only displaced one-quarter. 5. The distribution of heparin in the gel also profoundly influenced the binding. Two series of gels were studied. One series was made by mixing heparin-Sepharose with unsubstituted Sepharose. Results obtained with these gels were those expected from a series of decreasing volumes of heparin-Sepharose. In contrast, a series of heparin-Sepharoses made with different degrees of substitution gave quite different results. With these gels the amount of enzyme activity bound per amount of heparin increased markedly, whereas the salt concentration needed to displace the enzyme activity from the gel decreased markedly with decreased concentration of heparin in the gel. 6. On stepwise elution of small columns of heparin-Sepharose the enzyme activity was eluted over a remarkably wide range of salt concentrations. When enzyme eluted at one salt concentration was re-applied, it gave the same elution profile as enzyme previously eluted at other salt concentrations or the entire enzyme preparation. These and other results suggested that, whereas the enzyme preparation was rather homogeneous in its binding to heparin, the heparin preparation was polydisperse in binding of lipoprotein lipase.

Animals↗
PubMed1977

Protein components of very low density lipoproteins from hen's egg yolk.

Egg yolk lipoproteins of very low density were found to contain proteins with cofactor activity for lipoprotein lipase. When delipidated very low density lipoproteins were dissolved in 10 mM HCl and fractionated by gel filtration about two thirds of the protein were in several components with estimated molecular weights of 60000 to more than 170000. The major low-molecular-weight proteins were the dimeric and monomeric forms of a previously characterized 9000-dalton peptide. The cofactor activity was not associated with any of these major proteins. A large-scale fractionation method was developed by which two proteins fractions with cofactor activity for lipoprotein lipase were purified more than thousand-fold. One fraction had a molecular size of about 9000 daltons and the other had a size of about 5000 daltons. Both these fractions could be further separated on the basis of charge into several fractions with cofactor activity. The cofactor proteins were relatively soluble both at high and at low pH. The retained their cofactor activity after denaturation in guanidinium hydrochloride and after reduction. During the initial steps in the purification of the cofactor proteins another low-molecular-weight protein followed the cofactors. It had a single 17500-dalton peptide chain and was present in four variants, three of which contained carbohydrate.

Amino Acids↗