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At least 739 records · Page 41Linked to original sources
PubMed1984

Fat digestion by lingual lipase: mechanism of lipolysis in the stomach and upper small intestine.

Ten to 30% of dietary fat is hydrolyzed in the stomach by lingual lipase, an enzyme secreted from lingual serous glands. We investigated the substrate specificity of this enzyme as well as the potential of lingual lipase to act in the upper small intestine i.e., in the presence of bile salts and lecithin. The data presented show that partially purified preparations of rat lingual lipase and the lipase in gastric aspirates of newborn infants have identical substrate specificity: medium-chain triglycerides were hydrolyzed at rates 5-8-fold higher than long-chain triglycerides; the rat and human enzymes do not hydrolyze the ester bond of lecithin or cholesteryl-ester. In contrast to pancreatic lipase, the hydrolysis of triglycerides by lingual lipase is not inhibited by lecithin. But, similar to pancreatic lipase the activity of lingual lipase is inhibited by bile salts, the extent of inhibition varying with its nature and concentration. This inactivation is not prevented by colipase but is partially averted by lipids and protein, suggesting that lingual lipase can remain active in the duodenum. The pH optimum of the enzyme (2.2-6.5 in the rat and 3.5-6.0 in human gastric aspirates) is compatible with continued activity in the upper small intestine, especially during the neonatal period, when the luminal pH is under 6.5. The marked variation in lipase activity levels in gastric aspirates of newborn infants is probably due to individual variations in enzyme amounts. The characteristics of the lipase are however identical in infants with low, intermediate or high activity levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed2006

Acidolysis and glyceride synthesis reactions using fatty acids with two Pseudomonas lipases having different substrate specificities.

Enzymatic acidolysis and glyceride synthesis using polyunsaturated fatty acids (PUFAs) with lipases from Pseudomonas fluorescens HU380 (HU-lipase), P. fluorescens AK102 (AK-lipase), and Candida rugosa (CR-lipase) were studied. The acidolysis of triolein with eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in n-hexane was evaluated with lipases immobilized on Celite 545. HU-lipase showed the highest incorporation rate at a low temperature (10 degrees C) with either EPA or DHA as the acyl donor, and the rate decreased with increasing reaction temperature. At 45 degrees C, the rates for EPA and DHA were 7.1 and 0.5 relative to those at 10 degrees C, respectively. The EPA incorporation rate was even higher at a low temperature (10 degrees C), and the DHA incorporation rate increased with decreasing temperature. Although AK-lipase showed the reverse tendency for incorporation rate, the DHA incorporation rate increased with increasing reaction temperature with both PUFAs. HU-lipase reacted well with PUFAs such as DHA, EPA, arachidonic acid (AA), mead acid (MA), and dihomo-gamma-linolenic acid (DGLA) on acidolysis and glyceride synthesis. The reactivities of AK-lipase toward these PUFAs except for DGLA, i.e., MA, AA, EPA, and DHA, were low for both reactions. The unique substrate specificities of the lipases from the Pseudomonas strains will enable us to use these lipases for the modification of fats and oils containing PUFAs such as fish oil.

Bacterial Proteins↗
PubMed1996

Ginsenosides increase secretion of lipoprotein lipase by 3T3-L1 adipocytes.

Treatment of 3T3-L1 adipocytes with either an oleanolic acid glycoside or a 20(S)-protopanaxatriol glycoside increased the secretion of lipoprotein lipase activity into the medium dose-dependently. At a concentration of 100 micrograms/ml, ginsenosides Ro, Re, Rg1, and Rh1 increased the secretion of lipase activity into the medium by 119, 107, 56, and 32%, respectively. The ratio of lipase activity in the medium to cellular lipase activity was 4.7% in control cells and 8.6% in ginsenoside Ro-treated cells, 8.3% in ginsenoside Re-treated cells, 7.0% in ginsenoside Rg1-treated cells, and 6.3% in ginsenoside Rh1-treated cells. Ginsenoside Rb2, which is a 20(S)-protopanaxadiol glycoside, increased the secretion of lipase activity by 16% at 25 micrograms/ml, and the ratio of lipase activity in the medium to cellular lipase activity was higher in ginsenoside Rb2-treated cells than in control cells. However, at 100 and 200 micrograms/ml, ginsenoside Rb2 decreased the secretion of lipase activity in parallel with cellular lipase activity. Ginsenoside Rd also decreased the secretion of lipase activity in the same dose-dependent manner. Thus, the effective dose for the secretion of lipoprotein lipase activity with ginsenosides varies with their aglycone structure.

3T3 Cells↗
PubMed2001

Kinetic studies of lipase from Candida rugosa: a comparative study between free and immobilized enzyme onto porous chitosan beads.

The search for an inexpensive support has motivated our group to undertake this work dealing with the use of chitosan as matrix for immobilizing lipase. In addition to its low cost, chitosan has several advantages for use as a support, including its lack of toxicity and chemical reactivity, allowing easy fixation of enzymes. In this article, we describe the immobilization of Candida rugosa lipase onto porous chitosan beads for the enzymatic hydrolysis of olive oil. The binding of the lipase onto the support was performed by physical adsorption using hexane as the dispersion medium. A comparative study between free and immobilized lipase was conducted in terms of pH, temperature, and thermal stability. A slightly lower value for optimum pH (6.0) was found for the immobilized form in comparison with that attained for the soluble lipase (7.0). The optimum reaction temperature shifted from 37 degrees C for the free lipase to 50 degrees C for the chitosan lipase. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. The half-life of the soluble free lipase at 55 degrees C was equal to 0.71 h (Kd = 0.98 h(-1)), whereas for the immobilized lipase it was 1.10 h (Kd = 0.63 h(-1)). Kinetics was tested at 37 degrees C following the hydrolysis of olive oil and obeys the Michaelis-Menten type of rate equation. The Km was 0.15 mM and the Vmax was 51 micromol/(min x mg), which were lower than for free lipase, suggesting that the apparent affinity toward the substrate changes and that the activity of the immobilized lipase decreases during the course of immobilization.

Candida↗
PubMed1983

Influence of colipase on the turbidimetric determination of pancreatic lipase catalytic activity.

The influence of colipase on the turbidimetric measurement of the catalytic activity of pure human pancreatic lipase (EC 3.1.1.3) and of sera from pancreatitis patients was studied. A deoxycholate-stabilized triolein emulsion served as substrate. It was found that the activity of the pure, colipase-free lipase is strongly inhibited by deoxycholate, and can be blocked completely if normal serum, pure human albumin, or the globulin fraction of normal serum is present. The inhibition by serum is competitive. This finding largely excludes the existence of a specific lipase inhibitor in human serum and explains the non-linear response of activity to the amount of serum added, a frequently observed problem with various turbidimetric lipase methods. A high molar excess of colipase (greater than 250-fold) completely abolishes the inhibition of lipase, irrespective of the inhibitory factor studied. Sera of pancreatitis patients, when measured turbidimetrically without addition of colipase, exhibit elevated lipase activity only if they contain colipase. However, the activity measured is not a function of the serum lipase concentration alone but of the molar ratio of colipase to lipase. Since this ratio varies considerably and is usually too low to ensure complete activation of lipase, erroneously low or even false negative results are obtained. For this reason it is strongly recommended that an excess of colipase is used in turbidimetric lipase assays. It therefore also appears important to study the influence of the serum colipase level on non-turbidimetric lipase methods.

Blood Proteins↗
PubMed2001

Calibration, specificity and trueness of a postheparin plasma lipoprotein lipase assay.

Measurement of lipoprotein lipase activity in postheparin plasma is generally accompanied by moderate within-run variation CV(W-R) (<10%) and higher between-run variation CV(B-R) (5-25%). A calibration system was introduced in order to improve the reproducibility of measurements and to compare lipoprotein lipase activities from different days. Every day a calibration curve for lipoprotein lipase activity was constructed. Fifteen calibration curves designed over 2 years, show linearity over the whole biological spectrum and a considerable reduction of between-run variation in lipoprotein lipase activity, from 42% to 5.3% as estimated from two control postheparin plasma samples. The lipoprotein lipase calibration system is an easy and very cheap arrangement, which makes it possible to compare lipoprotein lipase activities achieved over years. When the lipoprotein lipase control values are compared with reference lipoprotein lipase samples determined in other lipase laboratories, the calibration-control system becomes an important tool for reducing analytical bias. The article reviews the original analytical criteria of catalytic measurement of lipoprotein lipase activity and describes the implementation of the calibration-control system. We describe a model for reduction of the analytical variability in the measurement of lipoprotein lipase activity. Other standardization efforts need to be made in the future, especially to define the reference material for calibration.

Animals↗
PubMed1992

Retention of glucose by N-linked oligosaccharide chains impedes expression of lipoprotein lipase activity: effect of castanospermine.

The effect of castanospermine (CSTP), an inhibitor of glucosidase I, on processing, activity, and secretion of lipoprotein lipase was studied in 3T3-L1 adipocytes. Processing was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of endoglycosidase H (endo H)-digested subunits of lipoprotein lipase from cells incubated 1-2 h with [35S]methionine. Lipoprotein lipase in untreated cells consisted of two groups of subunits, M(r) = 55,000-58,000 and M(r) = 53,000-55,000. The heavier subunits were endo H-resistant, whereas the others were either totally or partially endo H-sensitive. The lipase secreted by untreated cells contained primarily endo H-resistant subunits. Immunofluorescent studies showed that lipoprotein lipase accumulated in Golgi in untreated cells. CSTP, 100 micrograms/ml for 18 h, decreased intracellular lipase activity by 80% and decreased secretion of lipase activity by 91%. Most of the lipase subunits in CSTP-treated cells were totally endo H-sensitive with M(r) = 57,000, some were partially endo H-sensitive, and a trace was endo-H resistant. Totally endo H-sensitive subunits in CSTP-treated cells had a M(r) 2,000-4,000 larger than that in untreated cells, indicating impaired trimming of sugar residues from oligosaccharide chains of the lipase in CSTP-treated cells. The small amount of lipase secreted by CSTP-treated cells consisted primarily of partially endo H-sensitive subunits, with one sensitive and one resistant chain per subunit. Immunofluorescent studies showed that lipoprotein lipase was excluded from Golgi in CSTP-treated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1991

Expression of rat hepatic lipase in heterologous systems: evidence for different sites for interface binding and catalysis.

Rat hepatic triglyceride lipase was expressed as a bacterial fusion protein and as a secreted protein in eukaryotic cells. The bacterial fusion construct coded for seven amino acids at the N-terminus which are not present in the hepatic lipase cDNA, but otherwise consisted of only the complete mature lipase sequence. Fusion protein was isolated as an insoluble product which did not have lipase or phospholipase activities; it was, however, active as an esterase when solubilized after preparative gel electrophoresis. The fusion protein was used to raise polyclonal antibodies that recognize native rat hepatic lipase and inhibit its activity. For eukaryotic expression, a full-length rat hepatic lipase cDNA clone was inserted into the metallothionein promoter expression vector pMTSV40polyA.Bam. Transfected CHO cells, induced with ZnSO4, secreted an immunoreactive protein of Mr approximately 57,000. A lipase-producing clonal cell line was isolated and used to characterize the enzyme. The protein was purified from serum-free medium by heparin-Sepharose and DEAE-Trisacryl M column chromatography. It was apparently identical to native rat hepatic lipase, with the exception of the conformation of the linkage of the sialic acids which form part of the N-linked carbohydrate complexes. The bacterial fusion protein, the CHO-produced lipase, and native rat hepatic lipase were all inhibited by phenylmethylsulfonyl fluoride, implying that they function catalytically as serine esterases. Substrate competition studies indicated that the esterase and lipase activities use the same active site; thus, the major defect in the fusion protein was probably in triglyceride substrate binding. These results suggest that interface binding and catalysis occur at different sites in the protein.

Animals↗
PubMed1986

[Lipases of the digestive system].

Studies on gastrointestinal lipolysis have underestimated several important points. In view of recent in vitro data obtained in our laboratories, this review focuses on the role of gastric lipolysis during fat digestion. Polyclonal antibodies generated from purified rat lingual lipase were used to screen a cDNA library prepared from mRNA isolated from the serous glands of rat tongue cloned in E. coli expression vectors. A cDNA clone was isolated and the nucleotide and predicted amino acid sequences obtained. Comparison with the N-terminal amino acid sequence of the purified enzyme confirmed the identity of the cDNA. The amino acid sequence of rat lingual lipase consisted of 377 residues and showed little homology with porcine pancreatic lipase, apart from a short region containing a serine residue at an analogous position to the Ser 152 of the porcine enzyme. Human gastric lipase activity on tributyrin emulsion was detected only in the presence of amphiphiles. This behaviour was in sharp contrast with the strong inhibitory effect of amphiphiles observed on pure pancreatic lipase. To reveal human gastric lipase activity, amphiphiles must be added to human gastric lipase in order to prevent irreversible interfacial denaturation. Human gastric lipase activity was found to be restricted to triacylglycerol/water surface tensions ranging from 8 to 13 dynes/cm. All amphiphiles which decrease interfacial tension to less than 8 dynes/cm act as irreversible inhibitors of human gastric lipase in the absence or presence of bile salts. Our results confirm that human gastric lipase is capable of hydrolysing triacylglycerol in the presence of the bile salts concentration prevailing in the upper small intestine and in the presence of alimentary proteins. These observations could explain the high dietary lipid absorption observed under pancreatic lipase deficiency.

Amino Acid Sequence↗
PubMed1983

Evidence for independent genetic regulation of heart and adipose lipoprotein lipase activity.

The relationship between the genes controlling heart and adipose lipoprotein lipase in fasted animals has been studied. 32 inbred mouse strains were tested for variations in heart or adipose specific activity and thermolability. The survey revealed that specific activity of heart and adipose lipoprotein lipase varied as much as 3-fold and 20-fold, respectively. In thermolability, up to a 2-fold variation was observed in the lipase in each tissue. The correlation coefficient between variations in heart and adipose lipase was apparently not significant for both parameters studied. Additional studies were performed in two strains, BALB/c and C57BL/6, along with the recombinant inbred set derived from them. The two strains did not show genetic variation for lipoprotein lipase thermolability, although the inactivation rate of heart lipase was higher than that of adipose lipase. However, BALB/c and C57BL/6 displayed significant differences in their levels of lipoprotein lipase specific activity. Thus, strain C57BL/6 showed higher heart activity when compared to BALB/c, whereas the latter showed higher adipose lipase activity when compared to C57BL/6, i.e. an inverse relationship. The specific activity levels of heart and adipose lipoprotein lipase in the recombinant inbred strains derived from BALB/c and C57BL/6 exhibited independent inheritance. Thus, in adipose tissue, a single major gene seems to control the variation observed, while the inheritance pattern of heart activity could imply involvement of more than one gene. Moreover, two out of the seven recombinant strains showed distinct recombinant phenotypes, indicating that separate unlinked genes control the variations found in heart and adipose activity. We conclude that the expression of heart and adipose lipoprotein lipase activity is under independent genetic control.

Adipose Tissue↗
PubMed1993

Hepatic lipase treatment of chylomicron remnants increases exposure of apolipoprotein E.

The consequences of hepatic lipase treatment of chylomicron remnants were studied. Rats were fed corn oil to induce production and secretion of chylomicrons and were then injected with polyclonal antiserum raised against hepatic lipase to specifically and quantitatively inhibit hepatic lipase activity in vivo. A fraction enriched in chylomicron remnants was isolated from rat plasma by a brief centrifugation step that preferentially isolates triglyceride-rich apolipoprotein (apo) B-48-containing lipoproteins. The chylomicron remnants were then treated with hepatic lipase in vitro, or incubated under identical conditions in the absence of enzyme (control incubations). Hepatic lipase-treated and control chylomicron remnants were isolated by a second brief centrifugation step using discontinuous salt gradients. Control lipoproteins were collected from one discrete band at d < 1.02 g/ml. Hepatic lipase-treated chylomicron remnants formed two discrete bands and were collected at two densities: d < 1.02 g/ml and 1.02 < d < 1.04 g/ml. The buoyant (d < 1.02 g/ml) subfraction of hepatic lipase-treated chylomicron remnants was depleted of 62% of the total phospholipid when compared to control d < 1.02 g/ml lipoproteins. The dense (1.02 < d < 1.04 g/ml) subfraction of hepatic lipase-treated chylomicron remnants was depleted of 65% of particle phospholipid content and 90% of particle triglyceride content when compared to control d < 1.02 g/ml lipoproteins. The dense (1.02 < d < 1.04 g/ml) subfraction of hepatic lipase-treated chylomicron remnants showed 5- to 7-fold greater immunoreactivity of apoE when compared to control lipoproteins in competitive displacement immunoassays. These data suggest that extensive hydrolysis of chylomicron remnant phospholipid and triglyceride leads to the formation of a dense remnant particle that contains highly exposed apoE. This increased exposure of apoE may be the key to the previously observed increased degradation of chylomicron remnants treated with hepatic lipase because more exposed apoE may bind better to cell surface lipoprotein receptors. Furthermore, the data imply that hepatic lipase cleaves chylomicron remnant phospholipid and triglyceride in a sequential fashion; hydrolytic intermediates depleted only of phospholipid precede the formation of a smaller dense remnant particle depleted of phospholipid and triglyceride.

Animals↗
PubMed1990

Biomodulator-mediated susceptibility of endogenous lipid droplets from rat adipocytes to hormone-sensitive lipase.

The amount of fatty acid release by a fat cell homogenate without pretreatment with epinephrine was found to be slightly more than that released from fat cells by epinephrine, suggesting that fat cells contain high lipolytic activity even in the absence of lipolytic agents. Fat cells contain high hormone-sensitive lipase activity (1383 mumole free fatty acids/g/hr) in the absence of epinephrine, and addition of epinephrine to the cells did not increase the activity, significantly. Like epinephrine, DBcAMP and/or theophylline also elicited marked release of glycerol from fat cells without activating the hormone-sensitive lipase activity. However, although fat cells contain a large amount of hormone-sensitive lipase, lipolysis was negligible in the absence of these lipolytic agents. These results suggest that lipolytic agents such as epinephrine, DBcAMP, and theophylline induce lipolysis in fat cells through some mechanism other than activation of hormone-sensitive lipase and that in the absence of lipolytic agents, some system in fat cells inhibits lipolysis of endogenous lipid droplets by hormone-sensitive lipase. The lipid droplets in fat cells consist mainly of triglyceride with phospholipids, cholesterol, carbohydrate, and protein as minor constituents. The phospholipid fraction was found to consist of 75% phosphatidylcholine and 25% phosphatidylethanolamine. Of the minor constituents of endogenous lipid droplets, only phosphatidylcholine strongly inhibited hormone-sensitive lipase activity in a [3H]triolein emulsion. These results suggest that phosphatidylcholine in endogenous lipid droplets may be responsible for inhibition of hormone-sensitive lipase. Then, a cell-free system was established in which epinephrine, DBcAMP, and theophylline stimulated lipolysis of endogenous lipid droplets from fat cells by lipase solution. In this system, these lipolytic agents did not induce lipolysis in the absence of added lipase. Lipolysis in the mixture of the endogenous lipid droplets and lipase solution was accelerated by phospholipase C with concomitant loss of epinephrine-induced lipolysis. After pretreatment of the endogenous lipid droplets with phospholipase C, these lipolytic agents no longer induced lipolysis. Pretreatment of the endogenous lipid droplets with phospholipase C reduced their phospholipid content with the formation of phosphorylcholine, but did not affect their triglyceride and cholesterol contents. Treatment of the endogenous lipid droplets with phospholipase D did not affect lipolysis in the cell-free system. These results suggest that phosphatidylcholine in the endogenous lipid droplets may inhibit their lipolysis by hormone-sensitive lipase in fat cells and also be involved in the mechanisms of the stimulatory effects of epinephrine, DBcAMP, and theophylline on lipolysis.

Adipose Tissue↗
PubMed2000

The lipolytic stimulation of 3T3-L1 adipocytes promotes the translocation of hormone-sensitive lipase to the surfaces of lipid storage droplets.

Hormone-sensitive lipase catalyzes the rate-limiting step in the release of fatty acids from triacylglycerol-rich lipid storage droplets of adipocytes, which contain the body's major energy reserves. Hormonal stimulation of cAMP formation and the activation of cAMP-dependent protein kinase leads to the phosphorylation of hormone-sensitive lipase and a large increase in lipolysis in adipocytes. By contrast, phosphorylation of hormone-sensitive lipase by the kinase in vitro results in a comparatively minor increase in catalytic activity. In this study, we investigate the basis for this discrepancy by using immunofluorescence microscopy to locate hormone-sensitive lipase in lipolytically stimulated and unstimulated 3T3-L1 adipocytes. In unstimulated cells, hormone-sensitive lipase is diffusely distributed throughout the cytosol. Upon stimulation of cells with the beta-adrenergic receptor agonist, isoproterenol, hormone-sensitive lipase translocates from the cytosol to the surfaces of intracellular lipid droplets concomitant with the onset of lipolysis, as measured by the release of glycerol to the culture medium. Both hormone-sensitive lipase translocation and lipolysis are reversed by the incubation of cells with the beta-adrenergic receptor antagonist, propranolol. The treatment of cells with cycloheximide fails to inhibit lipase translocation or lipolysis, indicating that the synthesis of nascent proteins is not required. Cytochalasin D and nocodazole used singly and in combination also failed to have a major effect, thus suggesting that the polymerization of microfilaments and microtubules and the formation of intermediate filament networks is unnecessary. Hormone-sensitive lipase translocation and lipolysis were inhibited by N-ethylmaleimide and a combination of deoxyglucose and sodium azide. We propose that the major consequence of the phosphorylation of hormone-sensitive lipase following the lipolytic stimulation of adipocytes is the translocation of the lipase from the cytosol to the surfaces of lipid storage droplets.

3T3 Cells↗
PubMed1984

Lingual lipase in cystic fibrosis. Quantitation of enzyme activity in the upper small intestine of patients with exocrine pancreatic insufficiency.

We have measured the level of lingual lipase activity in gastric and duodenal aspirates of five patients with cystic fibrosis (CF) and pancreatic insufficiency. Lingual lipase activity (measured in vitro by the hydrolysis of long-chain triglyceride, tri-[3H]olein, at pH 4.2 and expressed in nanomoles FFA released per milliliter aspirate per minute) and pH in gastric and duodenal aspirates were measured at 10-min intervals during a a 30-min basal period and at 15-min intervals during a 2-h period after the ingestion of a test meal. In gastric aspirates, lingual lipase activity decreased from basal levels of 200 +/- 34 nmol FFA released per milliliter per minute (similar to values reported previously in normal subjects (Hamosh M., H. L. Klaeveman, R. O. Wolf, and R. O. Scow, 1975, J. Clin. Invest., 55:908-913) to 79 +/- 15 nmol FFA/ml per min during the first postprandial hour and returned to basal levels during the second postprandial hour, (206 +/- 39 nmol FFA/ml per min). Duodenal aspirates, obtained during basal conditions, had lingual lipase activity similar to that in the stomach, 178 +/- 63 nmol FFA/ml per min. Enzyme activity levels were 56 +/- 14 and 113 +/- 29 during the first and second postprandial hours. Measurements of total lipase activity delivered to the ligament of Treitz showed that lingual lipase amounted to 91.22 +/- 4.06% of the total lipase activity in the upper small intestine during the 150-min study period. The basal and postprandial gastric pH levels in the five CF patients studied (3.2 +/- 0.44, 4.0 +/- 0.16, and 4.4 +/- 0.4 for basal and first and second postprandial hours, respectively) did not differ from previously reported values for normal subjects. The pH of duodenal aspirates was however significantly lower (P less than 0.001) in CF patients, both under basal conditions (5.0 +/- 0.26) and during the first and second postprandial hours (4.9 +/- 0.13 and 4.4 +/- 0.36, respectively), than in normal subjects. The low postprandial duodenal pH enables lingual lipase to act not only in the stomach but to continue the hydrolysis of dietary fat in the upper small intestine of CF patients. The data presented show that lingual lipase remains fully active in CF and accounts for greater than 90% of total lipase activity in the upper small intestine. We suggest that, because of low intestinal pH in CF, enzyme replacement therapy containing lingual lipase could improve fat absorption in CF patients to a greater extent than the pancreatic preparations now in use.

Adult↗
PubMed1987

Relationship between postheparin plasma lipases and high-density lipoprotein cholesterol in different types of diabetes.

We measured serum lipids, lipoproteins and post-heparin plasma lipases, lipoprotein lipase and hepatic lipase, in 12 female patients with Type 1 (insulin-dependent) diabetes (postglucagon C-peptide undetectable), in 11 female insulin-treated patients with Type 2 (non-insulin-dependent) diabetes (postglucagon C-peptide greater than 0.60 nmol/l) and in 16 non-diabetic female control subjects. These three groups of subjects were similar with respect to age and obesity. Insulin dose was similar in patients with Type 1 and with Type 2 diabetes. HDL and HDL2 cholesterol were lower in patients with Type 2 diabetes than in non-diabetic control subjects (p less than 0.05) but did not differ between patients with Type 1 diabetes and non-diabetic control subjects. No difference in lipoprotein lipase activity was seen between the groups. The highest levels of lipoprotein lipase and hepatic lipase activities were observed in patients with Type 2 diabetes. Lipoprotein lipase activity correlated significantly with HDL cholesterol in patients with Type 1 diabetes (p less than 0.01) and in patients with Type 2 diabetes (p less than 0.001) but not in control subjects. Hepatic lipase activity did not correlate significantly with HDL cholesterol in any of the groups. In conclusion, postheparin plasma lipoprotein lipase and hepatic lipase activities do not seem to explain the difference in HDL cholesterol concentration between patients with Type 1 and Type 2 diabetes.

Apoproteins↗
PubMed1980

Properties of binding of lipases to non-parenchymal rat liver cells.

The binding of a heparin-releasable acylglycerol hydrolase from rat liver (liver lipase) to non-parenchymal liver cells was studied in vitro. The binding of the partially purified liver lipase to the cells was found to be rapid. Within 1 min 80% of the maximal binding occurred at either 4 or 25 degrees C. The binding capacity of the cells was saturable, with a maximal binding of 46 mU lipase activity per mg cell protein. Albumin did not prevent the binding and neither did glucose, galactose or methyl-alpha-mannoside. Mg2+, but not Ca2+, promoted the binding of the lipase to the cells. The in vitro bound enzyme activity was releasable from the cells by heparin. Both the soluble and bound liver lipase could be completely inhibited by an antibody against liver lipase. Lipoprotein lipase, derived from rat adipose tissue, was also found to bind preferentially to non-parenchymal liver cells. The presented results show that non-parenchymal liver cells contain 10(5) binding sites per cell for heparin-releasable lipases. Lipase secreted from parenchymal cells in vitro was also bound to the non-parenchymal cells. The data suggest that in vivo the liver lipase bound to endothelial liver cells can be derived from parenchymal cells.

Animals↗
PubMed1988

Lipoprotein lipase in liver. Release by heparin and immunocytochemical localization.

We have previously demonstrated that infusion of Intralipid to rats causes a pronounced increase of the lipoprotein lipase activity in the liver. In this paper we study where in the liver this lipoprotein lipase is located. When isolated livers from Intralipid-treated rats were perfused with heparin, substantial amounts of lipoprotein lipase were released into the perfusate. The identity of the lipase activity was demonstrated by specific inhibition with antisera to lipoprotein lipase, and to hepatic lipase, respectively, and by separation of the two lipase activities by chromatography on heparin-Sepharose. We have also studied the localization of both enzymes by an immunostaining procedure based on post-embedding incubation of ultrathin tissue sections with specific antibodies which were then visualized using protein A-colloidal gold complexes. There was no marked difference in localization for the two enzymes which were both seen at the luminal side of endothelial cells, at the interdigitations of the space of Disse and inside both hepatocytes and endothelial cells. Thus, lipoprotein lipase is present in the liver in positions similar to where the functional pool of hepatic lipase is located and analogous to where lipoprotein lipase is found in extrahepatic tissues. These results raise the possibility that the enzyme has a functional role in the liver.

Animals↗
PubMed1995

Characterization of a partially purified diacylglycerol lipase from bovine aorta.

A partially-purified diacylglycerol (DG) lipase from bovine aorta has been characterized with respect to the effects of lipid metabolites and two lipase inhibitors, phenylboronic acid and tetrahydrolipstatin (THL). DG lipase activity was determined by the hydrolysis of the sn-1 position of 1-[1-14C]palmitoyl-2-oleoyl-sn-glycerol. The products of the lipase reaction, 2-monoacylglycerol (2-monoolein) and non-esterified fatty acids (oleate, archidonate) produced a concentration-dependent (20-200 microM) inhibition of DG lipase activity. Oleoyl-CoA and dioleoylphosphatidic acid also inhibited aortic DG lipase activity, but lysophosphatidylcholine had little or no effect. The inhibition of aortic DG lipase by phenylboronic acid was competitive, with a Ki of approx. 4 mM. THL was a very potent inhibitor of aortic DG lipase; the concentration required for inhibition to 50% of control was 2-6 nM. THL inhibition was reduced when the concentration of substrate in the assay was increased. Attempts to identify the aortic DG lipase by covalent-labelling with [14C]THL were unsuccessful. Immunoblotting experiments revealed that hormone-sensitive triacylglycerol lipase (HSL) could not be detected in bovine aorta.

Animals↗