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PubMed1986

Effects of different skim milk fractions on activity of cow milk purified lipoprotein lipase.

Hydrolysis of a long-chain triglyceride substrate by purified cow milk lipoprotein lipase, in the absence of blood serum, was changed by adding heated skim milks. Preincubation of the substrate with small amounts of several skim milks increased (+50 to 300%) lipoprotein lipase activity. By contrast, greater amounts of skim milk increased further or decreased lipoprotein lipase activity (+ 300 to -90%). The inhibitory effect was due to substrate surface protection. Results obtained after removal of casein (by isoelectric precipitation or by ultracentrifugation) and of whey proteins (by heat treatment) showed that the effect of skim milk was due to the proteose-peptone fraction. Fractionation of the proteose-peptone fraction into component 5-enriched fraction and component 3-enriched fractions suggested that the activating effect was due partially to proteose-peptone component 5, and the inhibitory effect resulted from component 3. These effects were overcome by blood serum.

Animals↗
PubMed1997

Marked changes of lipid levels during puberty in a patient with lipoprotein lipase deficiency.

UNLABELLED: Clinical and biochemical characteristics of a female patient with familial lipoprotein lipase deficiency have been followed in short intervals before and during puberty. The proband is compound heterozygote for two missense mutations in the lipoprotein lipase gene. One mutation occurs in codon 250 (Asp250-->Asn), the other is in codon 410 (Glu410-->Lys). The residual lipoprotein lipase activity in the proband is less than 10% of controls. Before puberty the proband usually presented with moderate isolated hypertriglyceridaemia. During the initial phase of puberty a dramatic increase in the plasma concentration of both cholesterol and triglycerides was observed. During the second half of puberty a reduction of cholesterol but not of triglycerides was noticed. CONCLUSION: These findings show that the phenotypic expression of familial chylomicronaemia can be modified to a large extent by hormones. Furthermore they demonstrate the need for a closer clinical observation of type I patients during puberty.

Adolescent↗
PubMed1990

Lipoprotein ApoC-II activation of lipoprotein lipase. Modulation by apolipoprotein A-IV.

Lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides (TG) contained in chylomicrons requires the presence of a cofactor, apolipoprotein (apo) C-II. The physiological mechanism by which chylomicrons gain apoC-II necessary for LPL activation in whole plasma is not known. Using a gum arabic stabilized TG emulsion, activation of LPL by lipoprotein apoC-II was studied. Hydrolysis of TG by LPL was greater in the presence of serum than with addition of either high density lipoproteins (HDL) or very low density lipoproteins (VLDL). LPL activation by either VLDL or HDL increased with addition of the lipoprotein-free fraction of plasma. A similar increase in LPL activity by addition of the lipoprotein-free fraction together with HDL or VLDL was observed when another TG emulsion (Intralipid) or TG-rich lipoproteins from an apoC-II deficient subject were used as a substrate. Human apoA-IV, apoA-I, apoE, and cholesteryl ester transfer protein were assessed for their ability to increase LPL activity in the presence of VLDL. At and below physiological concentrations, only apoA-IV increased LPL activity. One hundred percent of LPL activity measured in the presence of serum was achieved using VLDL plus apoA-IV. In the absence of an apoC-II source, apoA-IV had no effect on LPL activity. Removal of greater than 80% of the apoA-IV from the nonlipoprotein-containing fraction of plasma by incubation with Intralipid markedly reduced its ability to activate LPL in the presence of VLDL or HDL. Gel filtration chromatography demonstrated that incubation of the nonlipoprotein-containing fraction of plasma with HDL and the TG emulsion caused increased transfer of apoC-II to the emulsion and association of apoA-IV with HDL. Our studies demonstrate that apoA-IV increases LPL activation in the presence of lipoproteins. We hypothesize that apoA-IV is required for efficient release of apoC-II from either HDL or VLDL, which then allows for LPL-mediated hydrolysis of TG in nascent chylomicrons.

Apolipoprotein C-II↗
PubMed1981

The activities of lipoprotein lipase and of enzymes involved in triacylglycerol synthesis in rat adipose tissue. Effects of starvation, dietary modification and of corticotropin injection.

1. The effects of dietary modification, including starvation, and of corticotropin injection on the activities of acyl-CoA synthetase, glycerol phosphate acyltransferase, dihydroxyacetone phosphate acyltransferase, phosphatidate phosphohydrolase, diacylglycerol acyltransferase and lipoprotein lipase were measured in adipose tissue. 2. Lipoprotein lipase activities in heart were increased and those in adipose tissue were decreased when rats were fed on diets enriched with corn oil or beef tallow rather than with sucrose or starch. The lipoprotein lipase activity was lower in the adipose tissue of rats fed on the sucrose rather than on the starch diet. 3. Rats fed on the beef tallow diet had slightly higher activities of the total glycerol phosphate acyltransferase in adipose tissue than did rats fed on the sucrose or starch diet. The diacylglycerol acyltransferase and the mitochondrial glycerol phosphate acyltransferase activities were higher for the rats fed on the tallow diet than for those fed on the corn-oil diet. 4. Starvation significantly decreased the activities of lipoprotein lipase (after 24 and 48 h), acyl-CoA synthetase (after 24 h) and of the mitochondrial glycerol phosphate acyltransferase and the N-ethylmaleimide-insensitive dihydroxyacetone phosphate acyltransferase (after 48 h) in adipose tissue. The activities of the microsomal glycerol phosphate acyltransferase, diacylglycerol acyltransferase and the soluble phosphatidate phosphohydrolase were not significantly changed after 24 or 48 h of starvation. 5. The activities of lipoprotein lipase and phosphatidate phosphohydrolase in adipose tissue were decreased 15 min after corticotropin was injected into rats during November to December. No statistically significant differences were found when these experiments were performed during March to September. These differences may be related to the seasonal variation in acute lipolytic responses. 6. These results are discussed in relation to the control of triacylglycerol synthesis and lipoprotein metabolism.

Adipose Tissue↗
PubMed1978

Changes in the lipoprotein lipase (clearing-factor lipase) activity of white adipose tissue during development of the rat.

The lipoprotein lipase (clearing-factor lipase) activity of the white adipose tissue from rats aged between 1 and 145 days was determined. Five adipose-tissue sites (epididymal, uterine, subcutaneous, perirenal and intramuscular) together with serum concentrations of triacylglycerol, cholesterol and glucose were studied. The pattern of enzyme-activity change was remarkably similar in all the sites studied, although the growth of the tissues proceeded non-uniformly. After a peak of activity early in suckling, lipoprotein lipase activity fell to low values by 20 days of age. At weaning (21 days) the activity increased sharply and within 5 days high values were regained. The serum triacylglycerol and cholesterol concentrations were low at birth and reached peaks of concentration coincidentally with the minima of white-adipose-tissue lipoprotein lipase activities, seen late in suckling. The changes in enzyme activity were related to other metabolic changes in adipose tissue and with the known changes in plasma insulin concentrations occurring during development.

Adipose Tissue↗
PubMed1995

Binding to heparan sulfate is a major event during catabolism of lipoprotein lipase by HepG2 and other cell cultures.

Lipoprotein lipase (LPL) is rapidly and efficiently cleared from the circulation by the liver through an as yet unclear mechanism. In the present study, we determined the nature of LPL interactions with the liver parenchimal cell line HepG2 as compared to other cells in culture. Binding, cell association and degradation of 125I-labelled bovine milk LPL by HepG2 cells, normal and low density lipoprotein (LDL) receptor-negative human fibroblasts and Chinese hamster ovary (CHO) cells show similar values irrespective of source and origin. LPL metabolism in HepG2 cells was characterized by a high capacity to degrade the enzyme, an extremely high sensitivity to heparin and was inhibited by 60%-70% after treatment of the cells with sodium chlorate and heparinase (but not chondroitinase). These findings suggested an important role for heparan sulfate in the process of cell interaction and metabolism of LPL. To further clarify the role of heparan sulfate in determining the LPL-cell interactions, we compared the metabolism of LPL in wild type and mutant heparan sulfate-deficient CHO cells. Heparan sulfate-deficient CHO cells show a low capacity to bind and degrade LPL, about 10%-20% that of the wild type cells. In another set of experiments, we sought to determine whether LPL interactions with HepG2 cells are affected by triglyceride-rich lipoproteins. The results clearly show that whereas unlabeled LPL dramatically enhanced the metabolism of radioiodinated very low density lipoprotein (VLDL), unlabeled VLDL had no effect on radioiodinated LPL metabolism in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Monoclonal antibodies against bovine milk lipoprotein lipase. Characterization of an antibody specific for the apolipoprotein C-II binding site.

Ten murine monoclonal antibodies have been produced that are specific for bovine milk lipoprotein lipase. One monoclonal antibody, bLPL-mAb-7, inhibited completely the apolipoprotein C-II (apo-C-II)-dependent enzymic hydrolysis of trioleoylglycerol in a phospholipid-stabilized emulsion, but had no effect on the hydrolysis of the water-soluble substrate p-nitro-phenylacetate. Four times more bLPL-mAb-7 was required to achieve 50% inactivation of lipoprotein lipase activity when the enzyme was preincubated with excess apo-C-II. Disruption of the binding of a dansyl-labeled apo-C-II peptide to lipoprotein lipase by bLPL-mAb-7 was demonstrated by resonance energy transfer, both in the presence and absence of lipid. This antibody thus appears to recognize the apo-C-II binding site of lipoprotein lipase. In addition, bLPL-mAb-7 also inhibited the lipoprotein lipase activity of human post-heparin plasma.

Animals↗
PubMed1988

Increased lipoprotein lipase content in the adipose tissue of suckling and weaning obese Zucker rats.

The aim of this study was to determine whether the increase in lipoprotein lipase activity displayed by the adipose tissue of obese (fa/fa) rats as compared with that of lean (Fa/fa) rats could be ascribed to a change in the content or in the catalytic properties of the enzyme. The question was addressed in rats of two ages: in 7-day-old suckling and in 30-day-old post-weaning pups. Inguinal fat-pads were removed surgically (7 days of age) or after killing (30 days of age), and acetone-extract powders were prepared. The relative quantity of enzyme was assessed by immunotitration using an antiserum raised in goat against purified lipoprotein lipase from rat adipose tissue. The results indicate that increases in enzyme activity in obese animals were strictly paralleled by increases in the amount of enzyme in suckling as well as in post-weaning pups. Moreover, the apparent Km values of lipoprotein lipase for its substrate triacylglycerol were identical in the two genotypes. In conclusion, the genotype-mediated increase in lipoprotein lipase activity in adipose tissue of obese Zucker rats was fully accounted for by an increase in the content of the enzyme. In addition, this work documents the mechanism of the increase in lipoprotein lipase activity during weaning, which is mediated mainly through changes in the adipose-tissue enzyme content.

Adipose Tissue↗
PubMed1997

Uptake of chylomicrons by the liver, but not by the bone marrow, is modulated by lipoprotein lipase activity.

We have shown that chylomicrons are catabolized by the liver and bone marrow in rabbits and marmosets. In the present investigation, we studied the role of various apolipoproteins and lipoprotein lipase in the clearance of these particles by the liver and bone marrow in rabbits. Incubation of chylomicrons with purified apolipoprotein (apo) E or C-II resulted in more rapid clearance of these particles from the plasma, whereas incubation of chylomicrons with apoA-I, apoC-I, apoC-III1, or apoC-III2, did not affect their clearance rates. Analysis of tissue uptake revealed that the increased plasma clearance rate of chylomicrons enriched with apoE or apoC-II was primarily due to enhanced uptake by the liver. The uptake of chylomicrons by the bone marrow increased after their enrichment with apoA-I but decreased after their enrichment with apoC-II. Because apoC-II is a cofactor for lipoprotein lipase, we hypothesized that the increased clearance rates were due to faster hydrolysis of chylomicrons and rapid generation of chylomicron remnants. To test this hypothesis, lipoprotein lipase activity was inhibited by injection of an antilipoprotein lipase monoclonal antibody. Inhibition of lipoprotein lipase retarded clearance of chylomicrons from the plasma and decreased their uptake by the liver but did not affect their uptake by the bone marrow. These studies suggest that bone marrow can take up chylomicrons in the absence of lipoprotein lipase activity and provide an explanation for the presence of foam cells in the bone marrow of type I hyperlipoproteinemic patients.

Animals↗
PubMed1993

Metabolism of apolipoprotein B-100 and of triglyceride-rich lipoprotein particles in the absence of functional lipoprotein lipase.

Cholesterol and triglyceride in the various lipoprotein fractions were determined in five patients without functional lipoprotein lipase (LPL) while on their habitual therapeutic diet of 'low fat' content (20-25 g/day). They were also studied following 3 days on either a 'minimal fat' diet (< 15 g/day) or a 'moderate fat' diet (45-50 g/day). Values obtained were compared with the respective levels measured in five control subjects on a 'normal fat' (70-90 g/day) diet. The patients had hypertriglyceridaemia (type V hyperlipoproteinaemia) under all dietary conditions. Cholesterol and triglyceride levels in plasma and in the chylomicron fraction increased in the patients with increasing dietary fat. In the very low density lipoprotein (VLDL) fraction from the patients, triglyceride levels also increased with the dietary fat intake, but cholesterol levels were similar under all dietary conditions. In the patients, cholesterol concentrations in the low (LDL) and high density (HDL) lipoprotein fractions were significantly lower than the respective levels in controls, but the ratio of cholesterol to triglyceride levels in both of these lipoprotein fractions decreased with the dietary fat intake. VLDL apolipoprotein B-100 (apo B-100) pool size was similar in the patients on the two test diets (P = 0.95) and 3.5-fold higher than in five healthy volunteers on a normal fat diet. Using a stable isotope enrichment method, the kinetics of apo B-100 were investigated in the patients under the last two dietary conditions. The fractional and absolute secretion rates of the apolipoprotein in the patients did not vary with fat intake, but fractional secretion rates were significantly lower and the absolute secretion rates were significantly higher in the patients than the respective values in the controls. These results are consistent with the hypothesis that in the absence of LPL activity the metabolism of chylomicron and VLDL particles in the circulation results in triglyceride-rich LDL and HDL particles that are taken up by the liver at increased rates, thus reducing the plasma LDL and HDL cholesterol concentrations, whereas the products of hydrolysis of these particles induce an increased rate of synthesis of triglyceride and an increased rate of secretion of VLDL apo B-100.

Adult↗
PubMed2001

Effects of the heparin-mimicking compound RG-13577 on lipoprotein lipase and on lipase mediated binding of LDL to cells.

Lipoprotein lipase (LPL) has high affinity for heparin and heparin-like compounds. In vivo the enzyme is attached to heparan sulfate proteoglycans on the endothelium of capillaries and larger blood vessels. The enzyme is released from these sites after intravenous injection of heparin. One has here investigated the effects of RG-13577 on LPL, both after intravenous injection to rats and under cell culture conditions. RG-13577 is a heparin-mimicking compound known to prevent angiogenesis by interference with binding of growth factors to cells. It has therefore been considered for use in cancer therapy as well as for prevention of atherosclerosis and restenosis. It was found that intravenously injected RG-13577 released both LPL and hepatic lipase (HL) to the blood. Binding of LPL in extrahepatic tissues was prevented and clearance of radiolabeled LPL from the circulation was delayed. Furthermore, RG-13577 released LPL from extracellular matrix (ECM) produced by endothelial cells and from THP-1 monocyte-derived macrophages. Lipase-mediated binding and uptake of human LDL in these cells was also prevented by RG-13577. Thus, in the test systems RG-13577 had the same effects as heparin, but on a molar basis RG-13577 was in all cases less effective.

Animals↗
PubMed1983

Measurement of lipoprotein lipase and hepatic triacylglycerol lipase in post-heparin plasma of the cynomolgus monkey.

Conditions for measurement of the lipolytic activities, lipoprotein lipase and hepatic triacylglycerol lipase in cynomolgus monkey postheparin plasma are described. The two activities are separable by heparin-Sepharose chromatography. Goat anti-human hepatic triacylglycerol lipase serum inhibits monkey hepatic triacylglycerol lipase activity and allows direct measurement of lipoprotein lipase in post-heparin plasma. While both human and homologous serum can be used as a source of activator apolipoprotein, homologous serum produces a much greater activation.

Animals↗
PubMed1980

Activation of the phospholipase A1 activity of lipoprotein lipase by apoprotein C-II.

The effect of apo very low density lipoprotein (apo VLDL) and apoprotein C-II on the phospholipase A1 activity associated with lipoprotein lipase (E.C.3.1.1.3) was studied using purified bovine milk lipoprotein lipase. The enzyme degraded 14C phosphatidylcholine (PC) to 14C 2-acyl lysophosphatidylcholine at a rate of 0.28 +/- 0.01 nmol/min/ml and triolein at a rate of 20.3 +/- 0.4 nmol/min/ml in mixed emulsions of PC and triolein. The phospholipase activity and triacylglycerol lipase activity were both increased by the addition of apo VLDL and apoprotein C-II. After maximal activation, the rate of PC degradation was 1.19 +/- 0.02 nmol/min/ml and triolein degradation 64.4 +/- 0.4 nmol/min/ml. Activation of phospholipase A1 activity and triacylglycerol lipase activity occurred in parallel.

Animals↗
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↗
PubMed1977

A comparison of lipoprotein lipase activity and adipocyte differentiation in growing male rats.

During adipose tissue development changes in lipoprotein lipase activity per adipocyte precede significant changes in fat cell size. Lipoprotein lipase activity per adipocyte increases fourfold from the second to seventh postnatal week. Furthermore, when isolated adipocytes and stromal--vascular cells are prepared by collagenase digestion of adipose tissue, there is a progressive shift in enzyme activity during development from the stromal-vascular compartment to the adipocyte fraction. The data support the concept that during normal development a "bed" of preadipocytes is synthesized during the suckling period. The data further suggest a regulatory role for lipoprotein lipase in the control of "lipid-filling" during early postnatal development.

Adipose Tissue↗
PubMed1982

The characterization of lipoprotein lipase isolated from the post-heparin plasma of the rainbow trout, Salmo gairdneri Richardson.

1. Intravenous injection of heparin into the trout resulted in the appearance in the plasma of a lipase with the properties of lipoprotein lipase. 2. The enzyme was purified to apparent electrophoretic homogeneity by means of heparin-Sepharose affinity chromatography. The enzyme was eluted with 1.5 M-NaCl and had a specific activity approx. 450-fold that of the post-heparin plasma. 3. The activity of the purified enzyme was inhibited by 1.0 M-NaCl and protamine sulphate and was stimulated between 3- and 8.8-fold by the addition of trout plasma. 4. The activity was strongly stimulated by trout very low density lipoproteins and to a lesser extent by high density lipoproteins. 5. The isolated enzyme fraction gave a single band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and had an apparent subunit M4 of 63 000. 6. These results suggest that the uptake of lipid by the tissues in the trout can occur by a process similar to that in mammals.

Animals↗
PubMed1976

Chylomicron protein content and the rate of lipoprotein lipase activity.

Chylomicrons isolated form rat intestinal lymph were incubated with plasma. Protein transfer to chylomicrons, reaction rate with purified lipoprotein lipase, and content of lipase cofactor were determined. While the overall protein content of chylomicrons was increased 3--4-fold, and the content of lipase cofactor increase 4-fold, reaction velocity of the activated particles with lipoprotein lipase was increased only 1.3-fold. Maximal rate of hydrolysis was achieved in the presence of much smaller quantities of activator than the lipoprotein particles were capable of binding, and chylomicrons were fully activated for triclyceride hydrolysis in the presence of only 10% plasma for triglyceride concentrations of up to 3 mg/ml. Cofactor protein was not rate-limiting for hydrolysis of triglyceride from chylomicrons. These results are discussed in the light of recent concepts of the regulation of lipoprotein lipase activity.

Animals↗