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PubMed1983

Activity of lipoprotein lipase in thyroidectomized rats.

Total plasma postheparin lipolytic activity as well as lipoprotein lipase activity in plasma was higher after heparin injection in thyroidectomized rats than in controls. In contrast, the activity of liver lipase was lower in thyroidectomized rats. Adipose tissue from thyroidectomized rats contained more lipoprotein lipase activity than adipose tissue from controls as measured both in extracts of tissue homogenates and medium from in vitro incubations of tissue pieces. There were no differences between control and hypothyroid rats in the disappearance of intravenously injected 125I-labeled lipoprotein lipase, but when a low dose of heparin was injected before the labeled enzyme, the disappearance of 125I-labeled lipoprotein lipase was more retarded in thyroidectomized rats. The elimination of heparin itself was slightly retarded by thyroidectomy.

Adipose Tissue↗
PubMed1984

Lipoprotein lipase- and phospholipase A2-catalyzed hydrolysis of phospholipid vesicles with an encapsulated fluorescent dye. Effects of apolipoproteins.

The self-quenching dye, 6-carboxyfluorescein, has been encapsulated into sonicated vesicles of egg phosphatidylcholine. Porcine pancreatic phospholipase A2 and bovine milk lipoprotein lipase catalyze the hydrolysis of the phosphatidylcholine resulting in the release of the encapsulated dye and a large increase in 6-carboxyfluorescein fluorescence. The fluorescence increase occurs in parallel with the formation of lysophosphatidylcholine and is strongly dependent on Ca2+ for phospholipase A2 catalysis and on apolipoprotein C-II for hydrolysis by lipoprotein lipase. Other apolipoproteins, including apolipoproteins C-III, C-I, and A-I, do not enhance lipoprotein lipase activity towards this substrate. We conclude that the enhancement of lipoprotein lipase activity by apolipoprotein C-II is a specific property of the activator protein due to its interaction with lipoprotein lipase or an enzyme/lipid interface and not a characteristic of lipid-binding proteins in general.

Animals↗
PubMed1984

Comparison of acyl-oxyester and acyl-thioester lipids as substrates for bovine milk lipoprotein lipase.

The dithioester analog of dihexanoylphosphatidylcholine, rac-1,2-S,S-dihexanoyl-3-phosphocholine-1,2-dimercapto-3-propanol was synthesized and compared to the corresponding acyl-oxyester lipid as a substrate for bovine milk lipoprotein lipase. The apparent maximal reaction velocity (Vmax) for dihexanoyldithiophosphatidylcholine was considerably lower than that for dihexanoylphosphatidylcholine (0.12 vs. 5.0 mumol product released/min per mg lipoprotein lipase, respectively). The apparent Km values were 1.9 and 4.0 mM, respectively. 3-Butyrylthio-1,2-dibutyryloxypropane was also compared to tributyrylglycerol as a substrate for lipoprotein lipase; hydrolysis of the acyl-thioester bond was insignificant when compared to the corresponding oxyester derivative. Apolipoprotein C-II, the activator protein of lipoprotein lipase for long-chain fatty acyl substrates, had no effect on the hydrolysis of either the thio- or oxyester short-chain substrates. The low lipoprotein lipase activity for the thioester substrates is discussed in relation to the structure of the lipid and the active site of the enzyme.

Animals↗
PubMed1984

Studies on chicken pancreatic lipase and colipase.

Lipase and colipase have been purified to homogeneity from chicken pancreatic tissue. The enzyme has a molecular weight (48 000) and catalytic properties similar to those of pancreatic lipase from higher mammals. Hydrolysis of triolein by chicken lipase is strongly inhibited by various bile salts, including sodium taurochenodeoxycholate, which is present in large proportion in chicken bile. Inhibition is reversed by colipase. With triolein as enzyme substrate, in the presence of sodium deoxycholate, no difference was observed in the ability of pure colipase from chicken, horse or pig to fully activate bile-salt-inhibited lipase from the same species. However, kinetic studies of the hydrolysis of a lecithin-stabilized emulsion of triacylglycerol (Intralipid) by chicken lipase show that the lag period is much longer in the presence of porcine colipase than with the chicken cofactor. This might reflect the higher ability of the avian enzyme to associate with colipase from the same species than with mammalian cofactors when the triacylglycerol substrate surface is covered with amphiphilic lecithin. From our study, the chicken pancreatic lipase/colipase system appears to be functionally similar to homologous lipolytic systems from higher mammals. It is then likely that they are of comparable physiological significance in fat digestion in avian and mammalian species.

Animals↗
PubMed1986

Lipoprotein lipases and stress hormones: studies with glucocorticoids and cholera toxin.

The intravenous injection of cholera toxin in rats 17 h prior to experimentation results in increased levels of insulin and corticosterone in the blood. This is accompanied by a rise in lipoprotein lipase activity in muscle and a decrease in adipose tissue. Pre- and postheparin blood levels of the enzyme are increased, representing the higher overall muscle activity. Hepatic lipase is decreased by cholera toxin treatment. These enzyme changes are accompanied by increased levels of non-esterified fatty acids, ketone bodies and unesterified cholesterol in the blood, whereas triacylglycerol levels are lowered. The lipoprotein triacylglycerol secretion is not affected by cholera toxin, suggesting increased triacylglycerol removal from the blood. On the other hand the unesterified cholesterol removal may be decreased due to the decreased hepatic lipase activity. Administration of excess glucocorticoid 2 days prior to blood and tissue sampling also resulted in a rise in lipoprotein lipase, a decrease in hepatic lipase activity and an increase of non-esterified fatty acids. In contrast to the effect of cholera toxin, the triacylglycerol levels were increased. Adrenalectomy, whether by inhibition of 11-beta-steroid hydroxylase or by surgical intervention, did not abolish the choleratoxin effects. It is concluded that corticosterone increase is not essential to the cholera toxin effects. Corticosterone itself probably causes an increase of cyclic AMP and/or Ca2+ levels, as is discussed.

Adipose Tissue↗
PubMed1986

Effect of phosphatidylcholine and free fatty acids on the activity of pancreatic lipase-colipase.

Mixed micelles of bile salt and phospholipids inhibit the lipase-colipase-catalysed hydrolysis of triacylglycerols. Free fatty acids can reverse this inhibition and reactivate lipase-colipase. This reactivation is either due to the formation of a high-affinity complex between lipase and colipase induced by free fatty acids and/or to a change of the quality of the interface. Lauric acid, oleic acid and linoleic acid are the most potent reactivators, while short-chain free fatty acids have no effect and long-chain, saturated free fatty acids inhibit the lipase-colipase activity further. The physiological relevance of these results is evident as the glyceride emulsion reaching the duodenum already contains free fatty acids due to the activity of lingual lipase in the stomach.

Animals↗
PubMed1986

Beta-adrenergic stimulation enhances translocation, processing and synthesis of lipoprotein lipase in rat heart cells.

Cells isolated from newborn rat hearts were cultured for 10-14 days, and lipoprotein lipase activity was present in an intracellular and heparin-releasable pool. Treatment of the cultures with 10(-7) M isoproterenol for 3 min resulted in a 3-fold increase in heparin-releasable lipoprotein lipase and a concomitant decrease in residual cellular enzyme activity. Similar results were obtained by treatment with dibutyryl cAMP. Treatment with isoproterenol or dibutyryl cAMP for 2 h affected glycosylation of immunoadsorbable lipoprotein lipase, so that the ratio of [3H]galactose to [14C]mannose in the heparin-releasable enzyme increased from 3.8 (control) to 13.0 (isoproterenol-treated). The change in the ratio of the sugars in the cellular fraction of the enzyme was from 3.1 to 9.9. 2 h treatment with isoproterenol did not enhance new enzyme synthesis, as determined by incorporation of [3H]leucine into immunoadsorbable lipoprotein lipase. 24 h after addition of either isoproterenol or dibutyryl cAMP to the culture medium, stimulation of enzyme synthesis was demonstrated. The present results permit three effects of isoproterenol on lipoprotein lipase to be distinguished: stimulation of translocation from a cellular to heparin-releasable pool; enhanced processing of mannose residues and terminal glycosylation; stimulation of synthesis of enzyme protein.

Animals↗
PubMed1986

Phospholipase C and diacylglycerol lipase activities associated with plasma membranes of chromaffin cells isolated from bovine adrenal medulla.

The plasma membranes of bovine adrenal chromaffin cells were isolated and the activities of enzymes involved in arachidonic acid liberation were investigated. Only a minute activity of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) could be detected using externally added phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as substrate. When membranes were treated with exogenous phospholipase C (orthophosphoric acid diester phosphohydrolase, EC 3.1.4.1) there was a liberation of free fatty acids from the sn-2 position of PC. The enzyme responsible for this effect could be demonstrated to be a diacylglycerol lipase (glycerol ester hydrolase, EC 3.1.1.3) localized in the plasma membrane. Using phosphatidylinositol (PI) as a substrate, it was found that an endogenous phospholipase C exists which co-purifies with the membrane preparation. The produced diacylglycerol is subsequently hydrolyzed by diacylglycerol lipase liberating arachidonic acid. The two enzymes, phospholipase C and diacylglycerol lipase were characterized. Phospholipase C was found to be calcium dependent and PI specific, showing an activity of 60 pmol/micrograms protein per h (1.2 mM Ca2+), whereas the diacylglycerol lipase was calcium independent hydrolyzing diacylglycerol at a rate of 7.2 pmol/micrograms protein per h. The lipase but not the phospholipase C was inhibited 50% by 1.7 mM para-bromophenacylbromide.

Adrenal Medulla↗
PubMed1986

Importance of human gastric lipase for intestinal lipolysis: an in vitro study.

Using soybean triacylglycerols emulsified with egg lecithin we have studied, in vitro, the influence of substrate prehydrolysis by human gastric lipase upon subsequent degradation by the pancreatic lipase-co-lipase system. Fatty acids liberated by pure human gastric lipase or juice trigger immediate activity of human pancreatic lipase. Gastric lipolysis appears to be of prime importance for dietary lipid digestion in human.

Emulsions↗
PubMed1986

Fatty acyl chain specificity of phosphatidylcholine hydrolysis catalyzed by lipoprotein lipase. Effect of apolipoprotein C-II and its (56-79) synthetic fragment.

Mixed acyl chain phosphatidylcholine molecules in Triton N-101 micelles were employed as substrates for lipoprotein lipase to test which substrate acyl chain has the greatest effect on activation of the enzyme by apolipoprotein C-II. The phospholipase A1 activity of lipoprotein lipase was measured by pH-stat. The activation factor (lipoprotein lipase activity plus apolipoprotein C-II/activity minus apolipoprotein C-II) increased monotonically with apolipoprotein C-II concentration up to 1 microM apolipoprotein C-II at an enzyme concentration of 0.01 microM. The maximal activation factor for phosphatidylcholine substrate molecules with sn-2 acyl chain lengths of 14 averages 14.8. By contrast, for sn-2 acyl chain lengths of 16 the activation factor was 29.2. Varying the sn-1 acyl chain length had no significant effect on the activation factor. The chain-length dependence of the activation factor is similar with the apolipoprotein C-II peptide fragment comprising residues 56-79, which does not include the lipid-binding region of apolipoprotein C-II. These data are consistent with a model for activation of lipoprotein lipase in which residues 56-79 bind to lipoprotein lipase and alter the interaction of the sn-2 acyl chain of the phosphatidylcholine (PC) substrate or the lysoPC product within the activated state complex.

Apolipoprotein C-II↗
PubMed1987

Diurnal variations of plasma lipids, tissue and plasma lipoprotein lipase, and VLDL secretion rates in the rat. A model for studies of VLDL metabolism.

Circadian rhythms of plasma lipids and lipoproteins, lipoprotein lipase activities and VLDL secretion rates were studied in fed and food-deprived (12 h) male rats after a light/dark synchronization of 14 days. In ad libitum fed rats, a circadian rhythm of plasma triacylglycerol, blood glucose and liver glycogen was clearly identified. A rhythm was also identified for plasma cholesterol, but not phospholipids. The peak of plasma triacylglycerol occurred 2 h after the beginning of the light period (7.00 a.m.), and the nadir, 2 h after the beginning of the dark period (7.00 p.m.). The differences of plasma triacylglycerol at these two circadian stages were even more pronounced in food-deprived rats and were confined to the very-low-density lipoprotein (VLDL) fraction. Plasma post-heparin and heart and muscle lipoprotein lipase activities were 50-100% higher at 7.00 p.m., the time when plasma triacylglycerol were lowest, as compared to 7.00 a.m. Plasma post-heparin hepatic lipase and adipose tissue lipoprotein lipase activities, in contrast, did not change. VLDL secretion rates were somewhat higher at 7.00 a.m. compared to 7.00 p.m., but this difference was not significant. It is concluded that physiological variation of heart and muscle lipoprotein lipase together with small differences of VLDL secretion rates are responsible for normal range oscillations of plasma VLDL triacylglycerol levels.

Animals↗
PubMed1987

Inhibition of purified bovine milk lipoprotein lipase by propranolol and other beta-adrenergic blockers in vitro.

Numerous clinical studies have shown that propranolol administration causes hypertriglyceridemia and a decrease in high-density lipoprotein in man. Although these findings have been attributed to diminution of triacylglycerol-rich lipoprotein catabolism by lipoprotein lipase, biochemical studies of the effects of propranolol on lipoprotein lipase activity in vitro have not been previously reported. We purified lipoprotein lipase from raw bovine skimmed milk and examined the effect of propranolol using as substrate phospholipid-stabilized, triolein emulsions containing purified human apolipoprotein C-II. These studies demonstrate that propranolol inhibits lipoprotein lipase activity. The inhibition was found to be noncompetitive with a Ki for propranolol of 0.55 mM. In addition, propranolol was shown to bind to phospholipid-stabilized triolein emulsions reaching local concentrations at the particle surface many times higher than its bulk concentration. Metoprolol, timolol and practolol, which are less hydrophobic than propranolol, were less inhibitory. Atenolol was the weakest inhibitor of purified bovine lipoprotein lipase in vitro.

Adrenergic beta-Antagonists↗
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↗
PubMed1989

Effects of tetrahydrolipstatin, a lipase inhibitor, on absorption of fat from the intestine of the rat.

Tetrahydrolipstatin (THL) derived by hydrogenation from lipstatin, a lipase inhibitor produced by Streptomyces toxytricini, has been shown to inhibit in vitro the activity of all three lipases secreted to the gastro-intestinal tract; gastric lipase, pancreatic lipase and carboxylester lipase (cholesterol ester hydrolase). The effects of THL on intestinal absorption of fat (transport to the thoracic duct chyle) has now been investigated after intraduodenal infusion in a rat model. Absorption of label from oleic acid when administered with monoolein in micellar bile salt solution was not affected by THL in concentrations up to 10(-4) M calculated on the volume of the aqueous phase. Absorption of free cholesterol in micellar bile salt solution of the lipolytic products of triolein; oleic acid and monoolein, is not significantly affected at a concentration of THL of 10(-4) M. Absorption of cholesterol from cholesteryl oleate under the same conditions is almost completely inhibited. The results indicate that absorption of free cholesterol is not dependent on the activity of pancreatic cholesterol ester hydrolase. The absorption of emulsified triolein was not significantly affected by 10(-5) M THL but decreased to around 30% of the controls by a concentration 10-times higher. There was no significant decrease of cholesterol absorption when administered in emulsified triolein while absorption of cholesteryl oleate was reduced at both concentrations of THL and almost completely at 10(-4) M. Radioactivity from [2-14C]THL when administered emulsified in triolein was recovered in urine, bile and thoracic duct lymph to 10-14, 8-13 and 1-3%, respectively, largely independent on dose administered. Label from [1"-14C] THL was recovered in the same amounts in lymph but much less in bile and urine indicating that the amino acid moiety has been split off early in the absorption process.

Animals↗
PubMed1991

Activation of hepatic lipase catalyzed phosphatidylcholine hydrolysis by apolipoprotein E.

The effect of apolipoproteins A-I, A-II, C-II, C-III and E on the hydrolysis of phosphatidylcholine and triacylglycerol by hepatic lipase was studied. Hepatic lipase catalyzed phospholipid hydrolysis was 1.8-fold activated by apolipoprotein E while the other apolipoproteins did not affect the hydrolysis by this enzyme. Triacylglycerol hydrolysis by hepatic lipase was 1.5-fold activated by apolipoprotein E while the other apolipoproteins inhibited hepatic lipase. These results suggest that lipoproteins containing apolipoprotein E may be preferred substrates for hepatic lipase.

Animals↗
PubMed1994

Dromedary pancreatic lipase: purification and structural properties.

Dromedary pancreatic lipase was purified from delipidated pancreases. Pure dromedary pancreatic lipase (glycerol ester hydrolase, EC 3.1.1.3) was obtained after ammonium sulfate fractionation, Sephadex G-100 gel filtration, anion-exchange (Mono Q Sepharose) and size exclusion column using high performance liquid chromatography (HPLC). The pure lipase is a monomer and has a molecular mass of about 45 kD and a pI of around 4.8. A specific activity of 5900 U/mg was measured on tributyrin as substrate at 37 degrees C in the presence of colipase and 2 mM NaTDC. The first 11 N-terminal amino acid residues and 10 peptides obtained by endoproteinase Glu-C digestion were sequenced. Dromedary pancreatic lipase is very similar to other pancreatic lipases as compared with their N-terminal and some peptides sequences. DrPL is activated by interfaces. The interfacial activation could be related to the presence of a lid and in fact one fragment of this lid domain (P9) was sequenced here: its' role will be discussed below.

Amino Acid Sequence↗
PubMed1983

RHC 80267 does not inhibit the diglyceride lipase pathway in intact platelets.

RHC 80267 inhibits diglyceride lipase activity in microsomes from canine platelets (1). Chau and Tai (2) reported that RHC 80267 prevents the transient accumulation of monoglyceride in thrombin-stimulated human platelets, while leaving arachidonate release unimpaired. In contrast, we find that while the drug inhibits both diglyceride lipase (I50 = 15 microM) and monoglyceride lipase (I50 = 11 microM) activities in platelet microsomes, it is ineffective when added to intact platelets. The transient intermediates in the diglyceride lipase pathway, 1,2-diglyceride and 2-monoglyceride, both accumulated after thrombin stimulation of intact platelets treated with RHC 80267, and arachidonate release was not inhibited. We conclude that RHC 80267 cannot be used to evaluate the diglyceride lipase pathway in intact platelets.

Arachidonic Acid↗
PubMed1992

Molecular cloning and characterization of rabbit pancreatic triglyceride lipase.

Pancreatic lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) has been cloned from a gt11 cDNA library made from poly A+ RNA of adult rabbit pancreas. Pancreatic lipase (PL) assists the absorption of dietary triglycerides by hydrolyzing them at 1 and 3 positions to free fatty acids and 2-monoacylglycerol in the presence of bile acids and colipase in the intestinal lumen. Since rabbits are classifically used for the study of the diet induced changes in the lipid metabolism, as a prelude to studying the diet and age dependent changes in the expression of this enzyme, a full length PL cDNA clone was obtained from its pancreas. The coding region of rabbit pancreatic lipase cDNA consists of 1407 base pairs contained in an open reading frame encoding 469 amino acids including the 16 that constitute the signal peptide. Northern blot analysis revealed a band around 1.5 kb. When rabbit enzyme is compared to other species, an over all homology of 70-80% was observed at the nucleotide level. High homology in the amino acid sequence and composition is also apparent between rabbit and other species like dog (65%), pig (76%) and rat (63%). Highest homology is found to be around active-site serine. The regions of homology with other species may help to define sites of interaction of lipase with co-lipase.

Amino Acid Sequence↗