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At least 19 recordsLinked to original sources
PubMed1975

Serum-stimulated lipases (lipoprotein lipases). Immunological crossreaction between the bovine and the human enzymes.

A rabbit antiserum prepared against the serum-stimulated lipase (lipoprotein lipase) from bovine milk crossreacted with serum-stimulated lipases from human milk and from human postheparin plasma, but not with bile salt-stimulated lipase from human milk or with salt-resistant lipase from human postheparin plasma. Thus, the serum-stimulated lipase in bovine milk has immunological determinants in common with the serum-stimulated lipases in human milk and in human postheparin plasma. The time-courses for the appearance of serum-stimulated lipase and salt-resistant lipase activities in human plasma after heparin injection were different. The two activities were separated by heparin-Sepharose chromatography. After treatment of postheparin plasma with the antiserum only the salt-resistant lipase activity could be eluted from the column. Thus, these two enzyme activities in postheparin plasma reside in two different enzyme molecules.

Animals↗
PubMed1976

Clearing factor lipase (lipoprotein lipase) activator. A method for the measurement of the net activating ability of human sera.

The hydrolysis of an emulsified triglyceride substrate by clearing factor lipase (lipoprotein lipase) normally requires the presence of particular activating polypeptide species. These are present in serum, together with other inhibitory species, as part of the serum lipoproteins. The paper describes a method whereby the net activating ability of individual human sera may be measured routinely. In a normal population, this activating ability is shown to be correlated positively with the fasting serum triglyceride concentration. As the fasting triglyceride concentration increases, there is a rise in the proportion of the total activating ability that is associated with the very low density lipoproteins. A dietary fat load does not raise the total activating ability but does increase the proportion of the total that is associated with the serum lipoproteins of lowest density.

Animals↗
PubMed1976

Effects of clofibrate treatment on plasma triglyceride concentration, plasma post-heparin clearing factor lipase (lipoprotein lipase) activity and serum clearing factor lipase activating ability in maturity-onset diabetes.

The effects of clofibrate on plasma triglyceride concentration, plasma post-heparin clearing factor lipase activity and serum clearing factor lipase activating ability were studied in a group of maturity-onset diabetic patients. Significant falls in both triglyceride concentration and in activating ability occurred within 2 weeks of beginning clofibrate treatment and, when treatment was stopped after 4 weeks, these changes were reversed within a further 4 weeks. Plasma post-heparin clearing factor lipase activity, on the other hand, was significantly increased during clofibrate administration and fell again when the treatment was stopped. The possible interrelationships of these findings are discussed.

Blood Proteins↗
PubMed1979

Rapid removal to the liver of intravenously injected lipoprotein lipase.

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

Animals↗
PubMed1977

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.

Animals↗
PubMed1979

A new method for the measurement of lipoprotein lipase in postheparin plasma using sodium dodecyl sulfate for the inactivation of hepatic triglyceride lipase.

Lipoprotein lipase (LPL) and hepatic triglyceride lipase (H-TGL) are lipolytic activities found in postheparin plasma. A simple and precise method for the direct determination of LPL in postheparin plasma is described. Pre-incubations of this plasma (45--60 min at 26 degrees C) with sodium dodecyl sulfate (35--50 mM) in 0.2 M Tris-HCl buffer, pH 8.2, results in the inactivation of H-TGL, while leaving LPL fully active. Direct determination of H-TGL is done in a separate aliquot of the same postheparin plasma sample using previously reported assay conditons that do not measure LPL. The sodium dodecyl sulfate-resistant lipolytic activity has the characteristics of LPL as judged by a) its activation by serum and by apolipoprotein C-II; b) its inactivation (over 90%) by 0.75 M NaCl; and c) its inactivation by a specific antiserum. No sodium dodecyl sulfate-resistant activity was found in postheparin plasma from a patient with LPL deficiency (primary type I hyperlipoproteinemia). An excellent correlation of values was obtained (r = 0.99) for 30 samples assayed after sodium dodecyl sulfate treatment and after immuno-inactivation of H-TGL. The intra-assay coefficient of variation was +/- 11% and 4% before and after normalization of values, respectively.

Female↗
PubMed1976

Estrogen treatment and gonadal function in the regulation of lipoprotein lipase.

Lipoprotein lipase (LPL) activity was measured in adipose tissue, heart and diaphragm in Sprague--Dawley rats after estrogen therapy or orchiectomy. Enzyme activity was measured by incubation of tissue fragments with a triolein emulsion in the presence of serum and heparin. In confirmation of other work, depression of adipose tissue LPL followed estradiol treatment in pharmacologic or near-physiologic doses. Cardiac and diaphragmatic muscle LPL were increased. Estrogen-treated male animals showed growth retardation. However, they gained weight steadily and did not show significant differences in serum insulin, glucose of D-beta-hydroxybutyrate. The effects of estradiol in male animals were reversed by sequential fasting and re-feeding. At times during growth and aging in normal female rats, adipose tissue activity was decreased while cardiac and skeletal muscle activities were increased relative to males of the same age or body weight. Castration of male rats failed to reproduce the effect of estrogens on tissue lipoprotein lipase. These in vitro data suggest that exogenous estrogens may shift the flux of triglyceride fatty acids from storage in the adipose organ toward incorporation by muscle. These, and other data, raise the possibility that physiological estrogen secretion exerts a tonic influence over the synthesis and ultimate destination of triglyceride fatty acids.

Adipose Tissue↗
PubMed1992

The low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor binds and mediates catabolism of bovine milk lipoprotein lipase.

Lipoprotein lipase (LPL), the major lipolytic enzyme involved in the conversion of triglyceride-rich lipoproteins to remnants, was found to compete with binding of activated alpha 2-macroglobulin (alpha 2M*) to the low density lipoprotein receptor-related protein (LRP)/alpha 2-macroglobulin receptor. Bovine milk LPL displaced both 125I-labeled alpha 2M* and 39-kDa alpha 2M receptor-associated protein (RAP) from the surface of cultured mutant fibroblasts lacking LDL receptors with apparent KI values at 4 degrees C of 6.8 and 30 nM, respectively. Furthermore, LPL inhibited the cellular degradation of 125I-alpha 2M* at 37 degrees C. Because both alpha 2M* and RAP interact with LRP, these data suggest that LPL binds specifically to this receptor. This was further supported by observing that an immunoaffinity-isolated polyclonal antibody against LRP blocked cellular degradation of 125I-LPL in a dose-dependent manner. In addition, 125I-LPL bound to highly purified LRP in a solid-phase assay with a KD of 18 nM, and this binding could be partially displaced with alpha 2M* (KI = 7 nM) and RAP (KI = 3 nM). Taken together, these data establish that LPL binds with high affinity to LRP and undergoes LRP-mediated cellular uptake. The implication of these findings for lipoprotein catabolism in vivo may be important if LRP binding is preserved when LPL is attached to lipoproteins. If so, LPL might facilitate LRP-mediated clearance of lipoproteins.

Animals↗
PubMed1979

Properties of salt-resistant lipase and lipoprotein lipase purified from human post-heparin plasma.

Lipoprotein lipase and salt-resistant lipase were isolated from human post-heparin plasma. The proteins of human post-plasma lipoprotein lipase and salt-resistant lipase were identified and demonstrated to be immunologically different. Significant differences between the two enzymes in their relative amino acid composition were demonstrated, which indicates that the two enzymes are different proteins. When analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the enzymes seemed to have monomer molecular weights similar to that of lipoprotein lipase purified from bovine milk.

Amino Acids↗
PubMed1976

Properties of purified bovine milk lipoprotein lipase.

Lipoprotein lipase has been purified from bovine milk by affinity chromatography on Sepharose containing covalently linked heparin. In addition to an enzyme eluted by salt, further activity could be eluted with detergent. Rechromatography experiments suggested that the two activities were due to the same enzyme. This assumption was further verified by several other criteria as follows: (a) both require a serum activator, (b) their apparent molecular weights (55 000), their amino acid compositions and amino sugar contents were similar and (c) they had identical immunological reactivities. Thus, the enzyme appears to be bound to the heparin-Sepharose matrix by both salt-reversed and detergent-reversed interactions. Sodium deoxycholate stimulated the activity eluted by high salt, but had no effect on the detergent-eluted enzyme.

Amino Acids↗
PubMed1978

A comparison of molecular properties of hepatic triglyceride lipase and lipoprotein lipase from human post-heparin plasma.

Hepatic triglyceride lipase was isolated from human post-heparin plasma by the method of Ehnholm et al. using modifications which increased the specific activity 12-fold to approximately 3,000 mumol of free fatty acid/h/mg of protein. Lipoprotein lipase with similar specific activity was prepared from the same plasma samples using heparin and concanavalin A affinity chromatography. The molecular weight of hepatic triglyceride lipase (69,000) was slightly greater than that of lipoprotein lipase (67,000) as determined by polyacrylamide electrophoresis in sodium dodecyl sulfate-containing buffers. These proteins had identical amino acid compositions, terminal amino acid residues, and tryptic peptide maps. However, the differences previously described regarding optima of pH and ionic strength and the requirement for apolipoprotein CII (only for lipoprotein lipase) were maintained in the highly purified state. It was found that both proteins contain approximately 8% carbohydrate. Antisera prepared in goats selectively precipitated each activity. Other antisera prepared in chickens reacted with both enzymes, suggesting a common antigenic determinant.

Adult↗
PubMed1978

Activation of adipose tissue lipoprotein lipase by lipoprotein fractions from normals and patients with type v hyperlipoproteinemia.

The effects of the main lipoprotein density classes on the human adipose tissue lipoprotein lipase activity were studied. A dose-dependent stimulation of lipoprotein lipase activity was obtained for HDL and, to a lesser extent, for VLDL on a constant weight basis. LDL exerted virtually no effect. At higher concentrations, HDL as well as VLDL inhibited the stimulated lipolytic activity. In type V hyperlipoproteinemia, the stimulating effect of VLDL and of HDL was significantly lower, whereas the inhibiting action of HDL was markedly increased.

Adipose Tissue↗
PubMed1978

Hepatic lipase and lipoprotein lipase in postheparin plasma in liver disease. relations to plasma proteins.

Hepatic lipase (HL) and lipoprotein lipase (LPL) in postheparin plasma have been studied in patients with different liver disorders and in a reference group. The dose of heparin (100 I.U./kg body weight) used intravenously to get maximal release of both HL and LPL was the same in patients and in healthy individuals. The release of HL was maximal in healthy controls after 2-5 min, but in patients with liver disease the maximum was not reached until 15 min after heparin administration. The time course of the release of LPL showed the same pattern in patients and controls. The activity of HL was below the lowest observation in the reference group in 8 out of 20 patients with liver diseases, and was not measurable in 3 of them (2 with chronic active hepatitis and 1 with alcoholic cirrhosis). The activity of hepatic lipase was positively correlated with the levels of coagulation factors and with the concentration of prealbumin in the total patient material. The results indicate that low activity of hepatic lipase is a sign of liver parenchymatous injury, and out study gives indirect evidence of the hepatic origin of this enzyme in man.

Blood Proteins↗
PubMed1977

Differential characteristics of purified hepatic triglyceride lipase and lipoprotein lipase from human postheparin plasma.

Evidence is presented that hepatic triglyceride lipase (H-TGL) and lipoprotein lipase (LPL), purified from human postheparin plasma, can each hydrolyze both glyceryl trioleate and palmitoyl-CoA. The average ratio of glyceryl trioleate/palmitoyl-CoA hydrolase activities, obtained with enzyme preparations from 15 human postheparin plasma samples was 1.30 (1.18-1.52) for H-TGL and 8.75 (7.45-10.25) for LPL. Albumin was identified as the serum cofactor required for the hydrolysis of palmitoyl-CoA by H-TGL. It protected this enzyme from inactivation by this substrate. In contrast, palmitoyl-CoA activated and protected LPL from denaturation by dilution and incubation at 25 degrees C. The effects of other detergents were investigated on glyceryl trioleate hydrolase activities of both enzymes. Sodium dodecyl sulfate (0.4 mM) and Trisoleate (0.4 mM), which also effectively activated and protected LPL against inactivation, had only moderate protective effect on H-TGL. Sodium dodecyl sulfate at a higher concentration (1 mM) produced little or no inhibition of LPL, while completely inactivating H-TGL. Conversely, sodium taurodeoxycholate (0.4 mM) protected and activated H-TGL, but had only moderate protective effect on LPL. Triton X-100 (0.1-0.8 mM) and egg lysolecithin (0.05-2 mM) also protected H-TGL, but not LPL. The very dissimilar effects of detergents on preparations on H-TGL and LPL may form the basis for the direct assay of each enzyme in the presence of the other.

Apolipoproteins↗
PubMed1976

Glucocorticoids and triglyceride transport: effects on triglyceride secretion rates, lipoprotein lipase, and plasma lipoproteins in the rat.

In order to elucidate the mechanism(s) of hyperlipidemia following glucocorticoid administration, dexamethasone (0.125 mg/Kg) was administered daily intramuscularly for 2 wk to male Sprague-Dawley rats and the effects on plasma triglyceride (TG) and cholesterol (Chol), lipoprotein neutral lipids, hepatic triglyceride secretion rates (TGSR; Triton), and epididymal fat lipoprotein lipase (LPL) were determined. Special measures were taken to maintain positive caloric balance and keep the weights of control and dexamethasone-treated animals comparable. Significant increases (p less than 0.001) in TG and very-low density lipoprotein (VLDL) triglyceride associated with no change in Chol and actual reduction in both triglyceride and cholesterol in low density lipoprotein (ldl) were observed in the steroid-treated animals. Dexamethasone treatment was associated with increased basal insulin and glucose levels, an insignificant increment in TGSR, and a highly significant reduction (p less than 0.001) in LPL. These findings suggest that glucocorticoid treatment increases splanchnic triglyceride production rates, but the resulting hypertriglyceridemia is primarily a consequence of impaired VLDL removal due to low adipose tissue LPL activity.

Animals↗