Heart Lipoprotein Lipase Research Articles

Loss of the lipoprotein lipase activating ability of rat serum after administration of some fatty liver inducing drugs.

The effects of the administration of different fatty liver inducing drugs on the serum lipoprotein lipase activating ability was investigated in rats. Addition of serum from 2-mercaptoethanol-, 2-mercaptoacetate-, ethionine- or D-galactosamine- treated rats failed to activate heart and adipose tissue lipoprotein lipase from control rats. The activating effect of serum was only slightly reduced in isopropanol-treated rats, whereas it was found unaffected in ethanol-treated ones. Electrophoresis of the lipoproteins and of the very low density lipoproteins (VLDL) fraction of sera from 2-mercaptoethanol-, 2-mercaptoacetate-, isopropanol-, ethionine- and D-galactosamine-treated rats suggest that the lack of lipoprotein lipase activation ability of these sera is most probably related to the impairing effects of these drugs upon VLDL metabolism, i.e. reduction of VLDL secretion in the case of 2-mercaptoethanol, 2-mercaptoacetate and isopropanol, production of abnormal VLDL in the case of D-galactosamine and both decreased VLDL secretion and production of abnormal VLDL in the case of ethionine.

Antibodies to lipoprotein lipase application to perfused heart

An antibody was prepared against purified rat heart lipoprotein lipase. 1. 1. This antibody showed marked species specificity. It inhibited almost totally the lipoprotein lipase activity from all rat tissues examined (i.e., heart, adipose, postheparin plasma, and mammary gland), while having no effect on the activity of lipoprotein lipase partially purified from rabbit, guinea pig and bovine heart and from bovine milk. The antibody also had no effect on the hepatic lipase activity of rat postheparin plasma. 2. 2. After antibody to rat heart lipoprotein lipase was recirculated for 5 min through isolated rat hearts, little or no lipoprotein lipase activity could be detected in the perfusate during 0–20 s of a subsequent non-recirculating perfusion with buffer containing 1 unit heparin/ml. 3. 3. Following recirculation of antibody to lipoprotein lipase for 10 min and a non-recirculating perfusion with buffer for 2 min, the hearts no longer oxidized any significant amounts of 14C-labelled palmitate chylomicron triacylglycerol fatty acid to 14CO 2 during a 15-min perfusion. The data give compelling evidence that the functional fraction of lipoprotein lipase in hearts is at the endothelial cell surface accessible to lipoprotein lipase antibody.

Rat heart in culture as a tool to elucidate the cellular origin of lipoprotein lipase

Lipoprotein lipase was determined in 5-day old cell cultures derived from hearts of newborn rats. With the help of the preplating method the cells were subdivided into cultures containing predominantly cardiac myocytes and into those composed mainly of mesenchymal cells. Lipoprotein lipase activity, associated with the mesenchymal cells was ten times higher than the activity found in the cultures containing mainly the myogenic cells. It is suggested that the mesenchymal cells are the progenitors of lipoprotein lipase in rat heart.

Tissue lipoprotein lipase in the hyperthyroid rat effect of growth and aging

The hydrolysis of lipoprotein triglycerides is catalyzed by lipoprotein lipase (LPL), an enzyme found in many tissues. We have examined tissue LPL activity (LPLA) in rats with experimentally-induced hyperthyroidism. In younger, lighter rats, hyperthyroidism was accompanied by a decrease in LPL in adipose tissue whereas heart and diaphragm muscle LPL activities were increased. These changes are consistent with the hypothesis that the hypercatabolism and increased ß-adrenergic activity of hyperthyroidism result in characteristic changes in tissue LPLA. In older, heavier hyperthyroid animals, however, adipose tissue LPLA was increased and heart and diaphragmatic LPLA were similar to control activities. Propranolol feeding abolished the thyroxine-induced increase in adipose tissue LPLA. In euthyroid animals of similar size the response of muscle LPLA to short-term starvation was also attenuated. These changes in tissue LPLA may provide a mechanism for shunting tri-glyceride fatty acids away from adipose tissue for utilization by muscle in the hyperthyroid state. During growth and aging, these adaptations are modified.

Diurnal Changes in Plasma and Liver Lipids and Lipoprotein Lipase Activity in Heart and Adipose Tissue in Rats Fed a High and Low Fat Diet

In order to evaluate a) the respective roles of adipose and muscle lipoprotein lipase (LPL) in the clearing of alimentary lipemia and b) the role of the resulting nonesterified fatty acids (NEFA) in controlling hepatic ketogenesis and liver triglyceride content, a number of parameters related to lipid metabolism were studied over the 24 hour period (the dark period being from 1930 to 0730 hours), in rats ad libitum fed either a low-fat (LF) or a high-fat (HF) diet containing respectively 1.1% and 41.5% lard. During spontaneous feeding (from 1500-1800 hours onwards), LPL activity in LF rats increased in adipose tissue and decreased in heart; in rats fed the HF diet for 3 weeks, the postprandial rise in adipose LPL was smaller and there was no decrease in heart LPL before 2100 hours. In HF rats, unlike the LF, feeding resulted in a large increase in circulating NEFA and total ketone concentrations, an increase in liver beta-hydroxybutyrate dehydrogenase activity, and a decrease in hepatic triglyceride content. The findings clearly indicate that in HF rats, muscle LPL controls the postprandial rise in plasma NEFA concentrations, which in turn appear to determine the extent of ketonemia and liver triglyceride changes. The possible control of these metabolic events by insulin is discussed.

Purification and characterization of lipoprotein lipase from human heart

Human heart lipoprotein lipase was purified by affinity chromatography on heparin-Sepharose 4B. When crude extracts of heart acetone powder were applied to columns, about 40% of total lipase activity was bound to the gel and then eluted with 1.5 M NaCl. At this stage the eluted enzyme was purified 1900-fold. Disc gel electrophoresis yielded a single protein band corresponding with lipolytic activity. Minimum molecular weight of the protein was 60,000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The purified enzyme was highly unstable; however, its activity could be partially stabilized at −20°C by bovine serum albumin, glycerol, or ethylene glycol. The activity of the purified enzyme (i) had a pH optimum between 7.8 and 8.0; (ii) required serum for full enzymatic activity; apoC-II could be substituted for serum; (iii) was inhibited by apoC-I in the presence of activated substrate; (iv) was markedly inhibited by NaCl; and (v) was stimulated by heparin.

Hydrolysis of tri- and monoacylglycerol by lipoprotein lipase: evidence for a common active site.

The relationship between triacylglycerol and monoacylglycerol hydrolyzing activities of purified rat heart lipoprotein lipase was studied using emulsified trioleoylglycerol and micellar or albumin-bound monooleoylglycerol as substrates. The maximal reaction rates obtained with the two substrates were similar (650 and 550 nmol of fatty acid released per min per mg of protein, respectively). Addition of apolipoprotein C-II or serum increased the maximal reaction rate for the trioleolyglycerol hydrolyzing activity about four-fold, but had no effect on the monooleolyglycerol hydrolyzing activity. Hydolysis of the two substrates apparently takes place at the same active site of the enzyme since (1) mutual competitive inhibition between the substrates could be demonstrated; (2) the rate of inactivation of enzymatic activity with the two substrates in 1.2 M NaCl was the same; (3) similar losses of hydrolytic activity with tri- and monooleoylglycerol were observed in the presence of low concentrations of n-butyl (p-nitrophenyl) carbamide; (4) inhibition of both hydrolytic activities by this compound could be prevented by prior exposure of lipoprotein lipase to either substrate.

Rat heart lipoprotein lipase

Rat heart lipoprotein lipase was highly purified by affinity chromatography using heparin-Sepharose 4B. When extracts of acetone powder were applied to columns, lipase activity was firmly bound to the gel matrix and was later eluted with 1.5 M NaCl. At this stage the eluted enzyme was purified 1500-fold. Dise gel electrophoresis yielded a single protein band corresponding with the enzyme activity. The apparent molecular weight was 60,000. The purified enzyme was highly unstable; however, its activity could be partially stabilized by glycerol or ethylene glycol. In studying the purified enzyme we observed: (i) a cofactor in serum was required for full enzymatic activity; ApoLp-Glu could be substituted for this cofactor; (ii) ApoLp-Ser was inhibitory to lipase activity; (iii) NaCl and protamine sulfate also markedly inhibited the lipase activity; (iv) heparin stimulated the enzymatic activity.

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.

Demonstration of endogenous heparin in rat blood.

Dr. Lindahl has referred to my concept of macromolecular heparin as a multichain, whose structural integrity depends on a polysaccharide core. In 1971, I postulated that macromolecular heparin must be depolymerized to become biologically active (6). Later, I found that macromolecular heparin is a potent inhibitor of heart lipoprotein lipase (LPL) in vitro (7). Injected macromolecular heparin has a relatively low potency as an initiator of LPL activity in the blood. This activity appears in the blood rather slowly, compared with that of low-molecular-weight heparin (i.e., commercial heparin or enzymatically depolymerized macromolecular heparin) (7). These facts support the concept that depolymerization precedes the release of biologically active heparin from the mast cells. Endogenous heparin in the blood should therefore be of low molecular weight, and I would now like to demonstrate that this is so.

Demonstration of endogenous heparin in rat blood

Dr. Lindahl has referred to my concept of macromolecular heparin as a multichain, whose structural integrity depends on a polysaccharide core. In 1971, I postulated that macromolecular heparin must be depolymerized to become biologically active (6). Later, I found that macromolecular heparin is a potent inhibitor of heart lipoprotein lipase (LPL) in vitro (7). Injected macromolecular heparin has a relatively low potency as an initiator of LPL activity in the blood. This activity appears in the blood rather slowly, compared with that of low-molecular-weight heparin (i.e., commercial heparin or enzymatically depolymerized macromolecular heparin) (7). These facts support the concept that depolymerization precedes the release of biologically active heparin from the mast cells. Endogenous heparin in the blood should therefore be of low molecular weight, and I would now like to demonstrate that this is so.

Regulation of rat heart lipoprotein lipase activity during cold exposure.

SummaryStarved thyroidectomized, ad-renalectomized, adrenal-demedullated and sham operated rats were exposed to 4° for 3 hr and their heart lipoprotein lipase activities compared to those of animals maintained at room temperature. The lipoprotein lipase activity in the hearts of the thyroidectomized rats was comparable to that of the sham operated animals when expressed as units/heart. The enzyme activities in the hearts of the adrenalectomized and adrenal-demedullated rats were about 50% lower than those of the controls. In all animals, exposure to cold temperature induced significant increases in the myo-cardial lipoprotein lipase activity. In normal rats this effect could not be reversed by the administration of insulin. It is concluded that the increases in lipoprotein lipase activity in the hearts of rats exposed to cold temperatures are not dependent on adrenal and thyroid hormones.

Post-heparin lipolytic activity and tissue lipoprotein lipase activity in the alloxan-diabetic rat.

1. Alloxan-diabetic rats showed raised plasma triglyceride levels and low adipose tissue lipoprotein lipase activity compared with controls. Heart lipoprotein lipase activity appeared unaltered by the diabetic state. 2. Plasma post-heparin lipolytic activity was slightly but not significantly increased in the diabetic group. The significance of these findings is discussed.

The role of glucagon in the regulation of myocardial lipoprotein lipase activity

The role of glucagon in regulating the lipoprotein lipase activities of rat heart and adipose tissue was examined. When starved rats were fed glucose, heart lipoprotein lipase activity decreased while that of adipose tissue increased. Glucagon administration to these animals at the time of glucose feeding prevented the decline in heart lipoprotein lipase activity, but had no effect on the adipose tissue enzyme. When glucagon was administered to fed rats, heart lipoprotein lipase activity increased to levels found in starved animals but there was no change in the adipose tissue enzyme. It is suggested that the reciprocal lipoprotein lipase activities in heart and adipose tissue of fed and starved animals may be regulated by the circulating plasma insulin and glucagon concentrations.

Dosage semi-automatique de la lipoproteine-lipase tissulaire, chez l'homme et chez l'animal

A semi-automatic method is used to measure the tissue lipoprotein lipase activity. This method includes an incubation of tissue extract of lipoprotein lipase with a triglyceride emulsion, whereafter the release of free fatty acids is measured automatically. This procedure has many advantages over previous manual methods, considering time consumption and accuracy. In animals, the adipose tissue and heart lipoprotein lipase activity depends upon the nutritional state. In human adipose tissue, the activity is 15 to 20 times lower than in animals.

Changes in adipose tissue and heart lipoprotein lipase activities and in serum glucose, insulin and corticosterone concentrations in rats adapted to a daily meal.

Changes in adipose tissue and heart lipoprotein lipase activities and in serum glucose, insulin and corticosterone concentrations in rats adapted to a daily meal.

The activity of lipoprotein lipase in rat heart after tourniquet stress.

Previously (1971) we found a considerable hyperlipaemia in rats subjected to sublethal tourniquet stress and 48–72 hr after stress the values returned to normal. Robinson and Jennings (1965 proved that perfusion of rat heart with heparinized McEwen-albumin solution by the Langendorf technique resulted in the release of clearing factor lipase into the perfusate. Later Gartner and Vahouny (1966) demonstrated the presence and heparin activation of lipoprotein lipase in the subcellular fractions of rat heart homogenate. To get a detailed answer to the changes in the lipoprotein lipase activity in rat heart we adopted the Gartner and Vahouny method (1966) as preferable to the acetone extracted powder method proposed by Korn (1955a, 1955b), The presence of the lipoprotein lipase in the cardiac muscle enables the heart to utilise circulating triglyceride fatty acids effectively as source of energy. The main purpose of the present study was to determine the pathophysiological significance of the heart lipoprotein lipase in sublethal tourniquet stress of rats.

Mechanism of triglyceridemia in hypercholesterolemic rabbits.

To elucidate mechanisms responsible for the increased plasma triglyceride (TG) which occurs in diet-induced hypercholesterolemia in rabbits, albino rabbits were fed a 3% cholesterol diet for various durations, and the following determinations were carried out: plasma lipid levels; turnover rate of plasma TG (labeled very low density lipoprotein, or glycerol-2- 3 H method); lipoprotein lipase activity of the heart and plasma; fatty acid and acetate incorporation into TG in the liver (homogenates and slices). Plasma levels of both free and esterified cholesterol and phospholipid increased rapidly, while TG increased relatively slowly during cholesterol feeding without change in hepatic TG synthesis. The fractional turnover was, on the other hand, depressed within a week. The decrease in plasma TG in response to a heparin injection was less in hypercholesterolemic rabbits than in normal animals. However, the measured activity of heart lipoprotein lipase of cholesterol-fed rabbits was higher than that of the control group. When the effects of two substrates (very low density lipoprotein from normo- and from hypercholesterolemic plasma) were compared, the apparent activity was lower with the latter. The Degrees of this inhibition was proportional to the amount of cholesterol in the lipoproteins. The inhibition of lipoprotein lipase activity was also observed with the addition of cholesterol to activated Ediol, but not with addition of esterified cholesterol. Lineweaver-Burk plots were constructed using partially purified plasma lipoprotein lipase, and Km values for Ediol, Ediol plus protamine sulphate, and Ediol plus cholesterol were calculated. The presence of cholesterol in the substrate of lipoprotein lipase competitively inhibits the enzyme activity, and this is the mechanism of hyperglyceridemia observed in diet-induced hypercholesterolemic rabbits.

Metabolic effects of ethanol on the rabbit heart.

Ethanol in saline solution (15%, v/v) was infused into anesthetized rabbits at a rate of 0.494 ml/min for the first 12 minutes and then at 0.247 ml/min for 108 minutes. Three hours after the infusion, heart triglyceride and lipoprotein lipase were assayed. Oxidation and esterification of fatty acids (palmitate -14 C as an indicator) were assessed by using either tissue homogenates or perfused hearts taken from the rabbits. Oxidation-reduction states of the perfused hearts were examined by measuring the tissue levels of dehydrogenase-linked substrates. The infusion of ethanol resulted in 180% increase in heart triglyceride content, but the infusion of norepinephrine (3 µg/kg/min) did not change the content. No change in plasma free fatty acids and triglyceride or heart lipoprotein lipase activity was detected. Addition of ethanol had little effect on the distribution of palmitate -14 C in the lipids of tissue slices and homogenates. On the other hand, prior infusion of ethanol resulted in depression of 14 CO 2 production (70 and 50%) and enhanced fatty acid esterification into triglyceride (270 and 170%) both in homogenates and perfused hearts. Mitochondrial and cytoplasmic redox states were shifted to more oxidized states by ethanol infusion. It is postulated from these results that an accumulation of triglyceride in the rabbit heart in response to ethanol administration is a result of decreased fatty acid oxidation rather than of increased triglyceride uptake or increased fatty acid synthesis.

EFFECTS OF HYPERTHYROIDISM, EPINEPHRINE, AND DIET ON HEART LIPOPROTEIN LIPASE ACTIVITY.

Rats were fasted for several days, placed on diets high in carbohydrate, fat, or containing iodinated casein so as to produce hyperthyroidism, or were chronically injected with epinephrine. Lipoprotein lipase (LPL) activities of homogenates of the hearts of these animals were determined. Significant increases in LPL activity occurred in thyrotoxic animals, in rats receiving epinephrine injections chronically, or after prolonged fasting, while significant lowering of cardiac LPL activity was observed in rats on the high-carbohydrate or high-fat diets. Single doses of fat or single injections of epinephrine had no effect. Addition of epinephrine or of triiodothyronine to heart slices or homogenates in vitro caused no LPL increases. It is postulated that adaptive changes in cardiac LPL activity may occur in response to altered needs for utilization of fatty acids by the heart. Microsomal fractions of heart cells had the highest specific LPL activities, suggesting synthesis of the enzyme by these cellular components, or activity of the enzyme at the endoplasmic reticulum.