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PubMed1975

Modifications of plasma post-heparin lipolytic activity and tissue lipoprotein lipase activity induced in the rat by acute administration of ethanol or propan-2-ol.

1. The oral administration of propan-2-ol [isopropanol; 100 mmol (6 g)/kg body weight] or ethanol [130 mmol (6 g)/kg body weight] to starved rats produced no change in plasma post-heparin lipase activity (PHLA) compared with that observed in 154 mmol/1 sodium chloride (saline)-treated rats. 2. An increase of adipose tissue lipoprotein lipase (LLA) and a decrease of heart LLA occurred in isopropanol-treated animals, whereas no significant changes were found in these activities after ethanol administration. 3. Since administration of isopropanol produces hyperglycaemia, observations were also made in rats receiving glucose infusion rather than saline. In these animals a rise in PHLA and adipose tissue LLA, and a fall in heart LLA, occurred. 4. It is suggested that the changes in tissue LLA produced by isopropanol are mediated by the rise in blood glucose.

1-Propanol↗
PubMed1992

The regulation of lipoprotein lipase gene expression by dexamethasone in isolated rat adipocytes.

Lipoprotein lipase (LPL) is an enzyme found in adipose tissue that is important in the hydrolysis of triglyceride rich lipoproteins, and in the uptake of FFA lipid into the adipocyte. To examine the effects of glucocorticoids on adipose tissue LPL, male Sprague-Dawley rats were injected with dexamethasone (1 mg/kg) every other day for 10 days, followed by measurement of LPL in epididymal adipose tissue. Compared to sham-injected controls, heparin-releasable LPL activity and LPL mass in the dexamethasone-treated rats were 44% and 62% of those in control rats, respectively. Adipocytes were prepared from the fat pads and pulse labeled with [35S]methionine, demonstrating a decrease in the LPL synthetic rate in the treated rats to 57% of the rate in control rats. In addition, LPL mRNA was quantitated by Northern blotting, demonstrating a decrease in LPL mRNA in the dexamethasone-treated rats. A simultaneous decrease in the message for gamma-actin was also noted. To examine the effects of dexamethasone on LPL in vitro, adipocytes were prepared from normal rats and treated with dexamethasone for 24 h in vitro. Dexamethasone decreased heparin-releasable LPL activity in cultured adipocytes to 40 +/- 6% of the control value (P less than 0.01). This decrease in LPL activity was accompanied by a decrease in the LPL synthetic rate using [35S]methionine labeling, to 33% of the control value, and no specific change in LPL turnover or secretion. In addition, dexamethasone added to adipocytes decreased LPL mRNA levels. Because the combination of insulin plus dexamethasone has been shown to yield synergistic increases in LPL in adipose tissue pieces, insulin was added to isolated adipocytes in combination with dexamethasone. Whereas insulin and dexamethasone individually had opposite effects on LPL, the combination of insulin plus dexamethasone resulted in no change in any aspect of LPL gene expression. Thus, dexamethasone resulted in a decrease in adipocyte LPL mRNA levels both when added to cultured adipocytes in vitro as well as when injected into rats. This decreased LPL mRNA level yielded corresponding changes in the LPL synthetic rate and LPL activity.

Actins↗
PubMed1994

Kinetics of lipolysis of very low density lipoproteins by lipoprotein lipase. Importance of particle number and noncompetitive inhibition by particles with low triglyceride content.

Our objective was to identify the major compositional factor(s) of very low density lipoprotein which determines its properties as a substrate for lipoprotein lipase. Human very low density lipoprotein was fractionated by preparative electrophoresis. The apparent Km was significantly lower for pre-beta very low density lipoprotein compared with beta very low density lipoprotein when calculated on the basis of triglyceride concentration. When the triglyceride concentration was adjusted for the triglyceride/apolipoprotein B ratio, the apparent Km was not different among very low density lipoprotein fractions. This implied that very low density lipoprotein particle number was of primary importance. To test this hypothesis further, rabbit cholesterol-rich very low density lipoprotein and human intermediate density lipoprotein and low density lipoprotein, from a patient with hepatic lipase deficiency, were added to the incubations. Each of these fractions functioned as noncompetitive inhibitors of lipolysis. We speculate that the saturation of lipoprotein lipase by an excess number of particles is a characteristic of human hyperlipoproteinemias that predispose to coronary heart disease and that are commonly classified as familial combined hyperlipoproteinemia or hyperapobetalipoproteinemia.

Animals↗
PubMed2000

A common mutation in lipoprotein lipase confers a 2-fold increase in risk of ischemic cerebrovascular disease in women but not in men.

BACKGROUND: We previously showed that the common Asn291Ser substitution in lipoprotein lipase is associated with elevated plasma triglyceride levels and a 2-fold increase in the risk of ischemic heart disease in women but not men. In this study, we tested the hypothesis that this substitution is also associated with an increased risk of ischemic cerebrovascular disease (ICVD). METHODS AND RESULTS: We compared 260 patients who had nonfatal ICVD and carotid stenosis >/=50% with 1560 age-matched controls and also compared 205 Copenhagen City Heart Study cases who had nonfatal ICVD with 1210 age-matched controls. All subjects were white and from Denmark. Overall, no significant difference was observed between carrier frequencies among those with and without ICVD; however, sex interacted with genotype in predicting ICVD in the ICVD and carotid stenosis cases (P=0.02). In Copenhagen City Heart Study cases, sex was not significant (P=0.18). Odds ratios for ICVD in female mutation carriers were 2.9 (95% confidence interval [CI], 1.3 to 6. 4) and 1.9 (95% CI, 0.8 to 4.6) in ICVD plus carotid stenosis cases and Copenhagen City Heart Study cases, respectively. Equivalent values in male mutation carriers were 0.8 (95% CI, 0.3 to 1.8) and 0.8 (95% CI, 0.3 to 2.0), respectively. These results were similar in analyses that also allowed for other conventional cardiovascular risk factors. CONCLUSIONS: These results suggest that the Asn291Ser substitution in lipoprotein lipase is not associated with nonfatal ICVD in men but that it possibly confers a 2-fold risk in women.

Adult↗
PubMed1990

Metabolism of endothelial cell-bound lipoprotein lipase. Evidence for heparan sulfate proteoglycan-mediated internalization and recycling.

Lipoprotein lipase (LPL) hydrolyzes triglyceride in plasma lipoprotein primarily while bound to vascular endothelial cells. LPL metabolism by cultured endothelial cells was studied. Purified radioiodinated bovine LPL bound to porcine aortic endothelial cells at 4 degrees C with an association constant of 0.18 x 10(7) m-1. Analysis of the time course of LPL dissociation from endothelial cells at 4 degrees C yielded a dissociation rate constant of 3.9 x 10(-6)s-1. After 1 h at 37 degrees C, 28% of the LPL initially bound to the cell surface was no longer releasable by heparin or trypsin treatments, suggesting that LPL was internalized by the cells. Addition of heparin to the medium or pretreatment of the cells with heparinase markedly reduced the amount of LPL internalized, establishing a requirement for cell surface heparan sulfate proteoglycans in the process. When cells containing internalized LPL were incubated at 37 degrees C, a time-dependent increase in the amount of LPL in the medium and a corresponding decrease in LPL associated with the cells was found. This suggested that internalized LPL was released back into the medium. The catalytic activity, molecular size, and heparin-binding characteristics of the released LPL was similar to native LPL. Addition of either heparin, heparinase, or excess unlabeled LPL to prevent the rebinding of released 125I-LPL to the cell surface increased the amount of 125I-LPL present in the medium, suggesting that there is a process of recycling of 125I-LPL bound to the cell surface. Studies examining the effect of pH on dissociation of LPL from its binding site showed less dissociation of cell surface bound LPL at pH 5.5 compared with pH 7.4 and 8.5. These results suggest that even at acidic pH as in endocytotic vesicles, LPL remains bound to proteoglycans and this may facilitate the recycling of internalized LPL molecules.

Animals↗
PubMed1985

Lipoprotein metabolism in patients with elevated lipoprotein-lipase activity in adipose tissue.

We have evaluated the relationships between adipose tissue lipoprotein-lipase activity (AT-LPL) or post-heparin plasma lipolytic activity (PHLA) and the composition of circulating lipoproteins in 7 patients with multiple symmetric lipomatosis (MSL). In addition we have investigated the behaviour of serum triglycerides after an oral fat load (1 g triglycerides/kg body weight) in 5 MSL patients and in 5 age and sex matched controls. We found significantly higher values of HDL, HDL2 and HDL3 cholesterol in MSL patients than in controls. Moreover, HDL2/HDL3 cholesterol ratio was higher in MSL patients than in controls, which indicate a predominant increase in HDL2 subfraction. The mean values of AT-LPL in lipomatous tissue was significantly higher than in control tissue. A positive statistically significant correlation was found between AT-LPL activity and HDL, HDL2 and HDL3 cholesterol values. After the fat load the maximal increments of serum triglyceride levels and the triglyceride areas over 8 and 12 h are lower in MSL patients than in controls; there was an inverse, statistically significant correlation between the total PHLA or the extrahepatic PHLA values and the triglyceride areas after lipid load. We conclude that MSL represents a useful naturally occurring model for the study of the role of AT-LPL in the metabolism of triglyceride-rich lipoproteins and in the clearance of lipoproteins in the post-prandial phase.

Adipose Tissue↗
PubMed2001

Inactive lipoprotein lipase (LPL) alone increases selective cholesterol ester uptake in vivo, whereas in the presence of active LPL it also increases triglyceride hydrolysis and whole particle lipoprotein uptake.

We have previously shown that transgenic expression of catalytically inactive lipoprotein lipase (LPL) in muscle (Mck-N-LPL) enhances triglyceride hydrolysis as well as whole particle lipoprotein and selective cholesterol ester uptake. In the current study, we have examined whether these functions can be performed by inactive LPL alone or require the presence of active LPL expressed in the same tissue. To study inactive LPL in the presence of active LPL in the same tissue, the Mck-N-LPL transgene was bred onto the heterozygous LPL-deficient (LPL1) background. At 18 h of age, Mck-N-LPL reduced triglycerides by 35% and markedly increased muscle lipid droplets. In adult mice, it reduced triglycerides by 40% and increased lipoprotein particle uptake into muscle by 60% and cholesterol ester uptake by 110%. To study inactive LPL alone, the Mck-N-LPL transgene was bred onto the LPL-deficient (LPL0) background. These mice die at approximately 24 h of age. At 18 h of age, in the absence of active LPL, inactive LPL expression did not diminish triglycerides nor did it result in the accumulation of muscle lipid droplets. To study inactive LPL in the absence of active LPL in the same tissue in adult animals, the Mck-N-LPL transgene was bred onto mice that only expressed active LPL in the heart (LPL0/He-LPL). In this case, Mck-N-LPL did not reduce triglycerides or increase the uptake of lipoprotein particles but did increase muscle uptake of chylomicron and very low density lipoprotein cholesterol ester by 40%. Thus, in the presence of active LPL in the same tissue, inactive LPL augments triglyceride hydrolysis and increases whole particle triglyceride-rich lipoprotein and selective cholesterol ester uptake. In the absence of active LPL in the same tissue, inactive LPL only mediates selective cholesterol ester uptake.

Animals↗
PubMed1989

Lipolysis of polyenoic fatty acid esters of human chylomicrons by lipoprotein lipase.

Human chylomicrons, obtained from chylous pleural fluid of a patient with mesothelioma, were incubated with bovine milk lipoprotein lipase. No difference in the release of different C16-C18 fatty acids as unesterified fatty acids, or in their appearance in diacylglycerols, was observed. The rate of lipolysis of arachidonic (20:4), and eicosapentaenoic (20:5) acid ester bonds of chylomicron triacylglycerols was slower, and a larger proportion of these fatty acids accumulated in mono- and diacylglycerols. The hydrolysis pattern for docosahexaenoic acid (22:6) was intermediary between that of the C16-C18 fatty acids and that of 20:4 and 20:5. The data suggest that the presence of a double bond at position 5 in the eicosanoid precursors may be important for the rate of lipolysis. The relative resistance of the 20:4- and 20:5- esters of chylomicrons to lipoprotein lipase may be important for the tissue distribution of these fatty acids.

Arachidonic Acid↗
PubMed1999

Plasma triglyceride reduction in mice after direct injections of muscle-specific lipoprotein lipase DNA.

The present study was conducted to determine if direct injections of plasmid pMCKhLPL DNA would lead to sufficient overexpression of lipoprotein lipase (LPL) to reduce plasma triglycerides in mice. After single intramuscular (i.m.) injections, human lipoprotein lipase (hLPL) mRNA was detectable in the quadriceps muscle for at least 21 days. Repeated intraperitoneal (i.p.) and i.m. DNA administration increased the LPL activity in skeletal muscle by 58% (i.p.) and 36% (i.m.) when compared with control-injected mice. A concomitant reduction of plasma triglycerides by 38% (i.p.) and 26% (i.m.) was obtained. Also, repeated measures of plasma triglycerides indicate that the triglyceride-lowering effect of pMCKhLPL can be noted early after DNA injections. Thus, the injection of pMCKhLPL into the peritoneum or quadriceps muscle results in plasma triglyceride reduction in mice.

Animals↗
PubMed2004

Overexpression of lipoprotein lipase in transgenic rabbits leads to increased small dense LDL in plasma and promotes atherosclerosis.

Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of triglyceride-rich lipoproteins. Previous studies using transgenic mice and rabbits have demonstrated that high level of LPL activity in adipose and skeletal muscle protects against diet-induced hypercholesterolemia and subsequently prevents aortic atherosclerosis. However, it is unknown, per se, whether increased LPL activity itself is antiatherogenic, or whether the antiatherogenic effect of LPL is dependent upon the LPL lipid-lowering effect. To address this issue, we fed LPL transgenic and littermate rabbits diets containing different amounts of cholesterol (0.3-0.6%) adjusted to maintain their plasma cholesterol concentrations at similarly high levels for 16 weeks. We analyzed their lipoprotein profiles and compared their susceptibility to atherosclerosis. The results showed that the overexpression of LPL in transgenic rabbits reduced remnant lipoproteins (beta-VLDL, d<1.006 g/ml) but concomitantly led to a significant increase of the large (d=1.02-1.04 g/ml) and small LDLs (d=1.04-1.06 g/ml) compared to the amounts in control rabbits. Furthermore, we found that with equally high hypercholesterolemia, transgenic rabbits developed 1.8-fold more extensive aortic atherosclerosis than control rabbits. To examine the hypothesis that altered lipoprotein profiles may be responsible for the enhanced atherosclerosis in transgenic rabbits, we studied the atherogenic properties of apoB-containing lipoproteins in vitro. These studies revealed that small-sized LDLs of transgenic rabbits were more susceptible to copper-induced oxidation and had higher affinity to biglycan than large remnant lipoproteins. We conclude, therefore, that LPL exerts a dual function in terms of its atherogenicity, namely antiatherogenicity, through enhancing receptor-mediated remnant lipoprotein catabolism and proatherogenicity via the generation of a large amount of small-sized LDLs. At an equal atherogenic-cholesterol level, small and dense LDLs are more atherogenic than large remnant lipoproteins.

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↗
PubMed1996

Endothelial binding sites for lipoprotein lipase are not diminished in perfused hearts from diabetic rats.

The possibility that diabetes reduces functional, heparin-releasable lipoprotein lipase (HR-LPL) activity on the coronary vasculature of perfused hearts by altering endothelial binding sites for the enzyme was examined by measuring the binding and subsequent heparin-induced release of exogenous lipoprotein lipase purified from bovine milk (mLPL). Rat hearts were first perfused with heparin (5 U/mL) for 5 min to displace endogenous HR-LPL into the perfusate. The subsequent perfusion of control hearts with 0.05-2 micrograms/mL mLPL resulted in a progressive increase in bound exogenous enzyme that could be released by a second heparin perfusion. Induction of an acute, insulin-deficient model of diabetes (100 mg/kg streptozotocin 4-5 days prior to heart perfusions) reduced endogenous HR-LPL activity, but the binding and heparin-induced release of mLPL (0.5 microgram/mL) were the same as measured in control hearts. Therefore, diabetes does not alter low-affinity, high-capacity proteoglycan binding sites for mLPL on the endothelium of perfused hearts.

Animals↗
PubMed1989

Effects of doxazosin on lipids, lipoprotein lipases, and cholesterol synthesis in the golden hamster.

The effects of treatment with adrenoceptor blockers on sites regulating lipid metabolism were studied in golden hamsters. In hamsters fed a standard chow, doxazosin, propranolol, and atenolol did not affect plasma cholesterol or triglycerides. After hypercholesterolemia was induced by feeding a cholesterol-enriched diet, doxazosin lowered plasma cholesterol by 12%. Lipoprotein lipase activity in adipose tissue and in the heart was not changed by any of the treatments. Hepatic lipase activity in the liver and blood was lowered by 31% in the doxazosin-treated animals. Hepatic cholesterol synthesis, measured as acetate incorporation into cholesterol and hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase activity, was also lowered in the doxazosin-treated hamsters. After norepinephrine administration to cholesterol-fed hamsters, atenolol increased (+8%) and doxazosin decreased (-35%) plasma triglycerides. Plasma cholesterol levels and hepatic cholesterol synthesis were no longer significantly affected by doxazosin. In norepinephrine-treated animals, adipose tissue lipoprotein lipase activity was enhanced (+30%) by doxazosin. Hepatic lipase activity in plasma and liver, which was lowered by norepinephrine, was increased by doxazosin. In hamsters not treated with norepinephrine, adrenoceptor blockers had no effect on plasma insulin or thyroid hormone, but with norepinephrine, levels of both insulin and thyroid hormone were increased by doxazosin. These data indicate that selective alpha 1-inhibition with doxazosin may interfere with lipid metabolism at several regulatory sites. The effects depend to a large extent on nutritional and hormonal status. Doxazosin might exert these effects partly via influences on other hormones.

Adrenergic alpha-Antagonists↗
PubMed1989

Epinephrine-activation of heparin-nonreleasable lipoprotein lipase in 3 skeletal muscle fiber types of the rat.

Epinephrine was used to activate the heparin non-releasable lipoprotein lipase (LPL) in the 3 skeletal muscle fiber types of the perfused rat hindlimb. Following a 9 min washout of the capillary-bound lipoprotein lipase, the hindquarter of the rat was perfused with a buffer containing 10 nM of epinephrine. Activity of the residual LPL in soleus, red vastus lateralis, and white vastus lateralis muscles increased 75%, 96%, and 102% respectively, following epinephrine perfusion. These results suggest that skeletal muscle LPL is under hormonal control possibly through protein phosphorylation by cyclic AMP dependent protein kinase.

Animals↗
PubMed1989

Lipoprotein lipase in rat heart--I. Characterization of tri-, di- and monoacylglycerol lipase activities in post-heparin effluents.

1. The lipolytic activities that sequentially hydrolyze tri-, di- and monoacylglycerol in rat post-heparin heart effluents were examined. 2. Properties of triacylglycerol lipase (TAGL) activity were typical of lipoprotein lipase. Diacylglycerol lipase (DAGL) behaved similarly to TAGL, suggesting that both activities refer to the same catalytic entity. 3. Differences, particularly in thermal stability, between TAGL and DAGL activities on one hand, and monoacylglycerol lipase (MAGL) activity on the other, may reflect different intrinsic molecular properties. 4. TAGL, DAGL and MAGL activities could not be separated by physical means and appeared to belong to a single unit at the same site on the capillary wall.

Animals↗
PubMed1996

Lack of association of the apolipoprotein A-I-C-III-A-IV gene XmnI and SstI polymorphisms and of the lipoprotein lipase gene mutations in familial combined hyperlipoproteinemia in French Canadian subjects.

Familial combined hyperlipoproteinemia (FCH) is a common familial lipoprotein disorder characterized by elevated plasma cholesterol and triglyceride levels with segregation in first-degree relatives. Most affected subjects with FCH have elevated plasma levels of apolipoprotein (apo) B. The disorder results from oversecretion of hepatic apoB-containing lipoprotein particles. The genetic defect(s) are unknown. Previous work has suggested that genetic polymorphisms of the apoA-I gene and functional abnormalities of the lipoprotein lipase (LPL) gene are associated with FCH. We investigated the XmnI and SstI restriction fragment length polymorphisms (RFLP) of the apoA-I gene in FCH subjects of French Canadian descent. We also investigated three common functional mutations of the lipoprotein lipase (LPL) gene (LPLGly188Glu, LPLPro207Leu, and LPLAsp250Asn) in French Canadians that account for approximately 97% of cases of complete LPL deficiency in the province of Québec, Canada. We identified and characterized 54 FCH probands in lipid clinics and examined at least one first-degree relative. There were 37 men and 17 women (mean age 48 +/- 9 and 58 +/- 8 years, respectively). None of the probands had diabetes mellitus; mean plasma glucose was 5.5 mmol/L. High blood pressure was diagnosed in 32% of men and 29% of women. The body mass index (weight (kg)/height(m2)) was elevated in probands (27 +/- 4 for men and 26 +/- 4 for women). Mean plasma levels of cholesterol (C) was 7.6 +/- 1.5 mmol/L, triglycerides 3.5 +/- 1.6 mmol/L, LDL-C 4.9 +/- 1.2 mmol/L, HDL-C 1.0 +/- 0.3 mmol/L, and apoB 1.83 +/- 0.67 g/L in the probands. Allele frequency of the rare alleles of the XmnI and SstI RFLP was not significantly different from a healthy reference group. In several families studied, the XmnI and SstI RFLP did not unequivocally segregate with the FCH phenotype. There was no significant effect of the presence or absence of the XmnI or SstI RFLP's on plasma lipids, lipoprotein cholesterol or apoB levels. Only one FCH proband was found to have a mutation of the LPL gene (Gly188Glu), and this did not segregate with the FCH phenotype in the family. We conclude that in our highly selected group of FCH subjects of French Canadian descent, the XmnI and SstI RFLPs of the apoA-I gene and common functional mutations of the LPL gene resulting in complete LPL deficiency are not associated with FCH.

Adult↗
PubMed1984

Lipoproteins, lipoprotein lipase, and glycogen after prolonged physical activity.

The effect of strenuous exercise on lipoprotein level and composition as well as on lipoprotein lipase activity (LPLA) and glycogen stores in skeletal muscle was studied in 16 healthy young men after military field maneuvers. Body weight was reduced by 1 kg after the maneuvers and was gradually restored during a 5-day recovery phase. Glycogen levels were reduced by 50% and LPLA increased threefold immediately after the exercise, and neither were restored until 3-5 days of recovery. Serum triglycerides were decreased by about 50% after 1 day of recovery and the cholesterol concentration in high-density lipoproteins increased but only immediately after exercise. In contrast, the apolipoproteins A-I and A-II, the main protein constituents, were both decreased and remained so for 3-5 days. The results indicate that significant alterations of plasma lipoprotein level and composition as well as of muscle metabolism occur after prolonged physical exertion and that some changes are still evident after 5 days of recovery.

Adult↗
PubMed1983

Clofibrate decreases jejunal cholesterol synthesis and activity of postheparin plasma lipoprotein lipase in the rat.

Clofibrate treatment decreased drastically the activity of serum postheparin lipoprotein lipase of rats fed with fat-free test diet but had no effect on hepatic lipase. 3 weeks' treatment was followed by a significant fall in serum cholesterol caused by a marked decrease in HDL-cholesterol. Clofibrate decreased in vitro synthesis of cholesterol and fatty acids in jejunal villous cells but not in the crypt cells.

Animals↗