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PubMed1983

Regulation of liver lipase. I. Evidence for several regulatory sites, studied in corticotrophin-treated rats.

The activity of liver lipase, an enzyme that can be released from the liver by heparin, varies under several hormonal conditions. The site(s) at which regulation of the enzyme activity may occur was investigated in vitro. As a model, rats were used which had been treated with a corticotrophin analogue, to induce hypercortisolism, a condition in which liver lipase activity is lowered. Lipases isolated from heparin-containing perfusates of livers from ACTH or control rats were identical with respect to heat stability and specific activity as determined by immunotitration and binding to isolated non-parenchymal liver cells, indicating that the enzyme structure was not affected by the treatment. The secretion of liver lipase by isolated parenchymal liver cells was studied. During incubation of parenchymal cells derived from ACTH rats, less enzyme activity was found to be secreted when compared with hepatocytes isolated from control rats (ACTH rats, 2.30 +/- 0.2 mU/10(6) cells; control rats, 3.3 +/- 0.3 mU/10(6) cells). Liver lipase partially purified from control rats could be bound specifically to saturation by non-parenchymal cells, isolated from ACTH or control rats. Non-parenchymal cells from ACTH rats bound less lipase activity (29 mU/mg cell protein) than cells from control rats (50 mU/mg cell protein). This reduction in binding capacity seems to be due to a diminished number of binding sites, since the affinity based on Scatchard analysis and half-maximal binding was not different. These results suggest that the lowered liver lipase activity found during hypercortisolism may be due to an impaired synthesis and/or secretion of the enzyme by the parenchymal cells and to a reduced binding capacity of the non-parenchymal cells for liver lipase.

Adrenocorticotropic Hormone↗
PubMed1984

Inhibition of pancreatic and microbial lipases by proteins.

We have compared the effect of several proteins, including melittin, beta-lactoglobulin A, serum albumin, ovalbumin and myoglobin, on the hydrolysis of tributyrin and triolein by lipases from various origins. All proteins tested inactivate pancreatic lipase in absence of colipase and bile salt. Inhibition is not significantly reversed by colipase in absence of bile salt except in systems containing tributyrin and melittin or triolein and beta-lactoglobulin A. In all other cases, activation of pancreatic lipase by colipase in presence of inhibitory protein requires the presence of bile salt. Lipase from Rhizopus delemar is also inhibited by the proteins that inactivate pancreatic lipase. In contrast, the activity of lipase from Rhizopus arrhizus is not affected by the proteins in the same concentration range. Inhibition of lipase activity by amphiphiles such as proteins or detergents appears to be a general phenomenon not directly related to a decrease in tension at the triacylglycerol-water interface. Inhibition could be the result of desorption of lipase from its substrate due to a change in interfacial quality.

Animals↗
PubMed1986

The activity and properties of an acidic triacylglycerol lipase from adult and fetal rat lung.

Triacylglycerol lipase with maximal activity at pH 5 was present in adult and fetal lung. The activity was inhibited by serum concentrations used to measure lipoprotein lipase and by 0.5 M NaCl. The activity in homogenates from fetal lung was about 40% of the activity in adult lung homogenates. The activity increased to 80% of the adult levels during the first 24-48 h following birth. Acidic triacylglycerol lipase was present in all subcellular fractions from adult lung. However, the major amount of activity appeared to be associated with lysosomes. Fetal lung contained significantly more activity in the cytosolic fraction compared to the adult. The reaction produced free fatty acids (65%), 1,2(2,3)-diacylglycerol (22%) and 2-monoacylglycerol (12%). Minimal amounts of 1,3-diacylglycerol and 1(3)-monoacylglycerol were formed. Diacylglycerol lipase and monoacylglycerol hydrolase activities at pH 5 were independently determined and both were higher than the triacylglycerol lipase activity. The subcellular distribution of diacylglycerol lipase and monoacylglycerol hydrolase differed from that of triacylglycerol lipase. Overall, the results indicated that the lung has considerable intracellular lipase activity and therefore could readily hydrolyze intracellular triacylglycerol to free fatty acids. The reaction also produced significant amounts of 1,2-diacylglycerol which suggests that triacylglycerol could be a direct source of diacylglycerol for phospholipid synthesis.

Aging↗
PubMed1986

Comparison of apolipoprotein C-II-deficient triacylglycerol-rich lipoproteins and trioleoylglycerol/phosphatidylcholine-stabilized particles as substrates for lipoprotein lipase.

The effect of apolipoproteins C-II and C-III on the lipoprotein lipase-catalyzed hydrolysis of apolipoprotein C-II-deficient triacylglycerol-rich lipoproteins and particles of trioleoylglycerol stabilized with a phosphatidylcholine monolayer was investigated. For both triacylglycerol-rich lipoproteins and artificial lipid particles, maximal lipoprotein lipase activity occurred at a constant apolipoprotein C-II/phospholipid mol ratio of 2.0 X 10(-4) and was independent of particle size, indicating that the amount of apolipoprotein C-II bound to the surface of the substrate is important for enzyme activation. The effect of apolipoprotein C-II on lipoprotein lipase activity with apolipoprotein C-II-deficient lipoproteins as substrate was to decrease the apparent Michaelis constant (Kmapp) from 7.1 to 1.0 mM with minor changes on the apparent maximal velocity (Vmax) (22.2 mmol free fatty acid released/h per mg enzyme). In contrast, apolipoprotein C-II increased the apparent Vmax from 2.4 to 20.0 mmol free fatty acid/h per mg enzyme for the lipoprotein lipase-catalyzed hydrolysis of trioleoylglycerol/phospholipid particles with little change in Kmapp (1.0 mM). Addition of apolipoprotein C-II-deficient triacylglycerol-rich lipoproteins or high-density lipoproteins to trioleoylglycerol/phospholipid particles in the presence of apolipoprotein C-II inhibited lipoprotein lipase activity. Lipoprotein lipase activity was also inhibited by the addition of a large excess of lipid-free apolipoprotein C-III to the artificial particles. The decrease in lipoprotein lipase activity correlated with the amount of bound apolipoprotein C-II. We suggest that the reported discrepancies on the effect of apolipoproteins C-II and C-III on lipoprotein lipase catalysis is related to differences in substrates and to the amount of added apolipoproteins.

Apolipoprotein C-II↗
PubMed1986

Maturation and secretion of lipoprotein lipase in cultured adipose cells. II. Effects of tunicamycin on activation and secretion of the enzyme.

The effects of N-linked glycosylation on the activation and secretion of lipoprotein lipase were studied in Ob17 cells. The cells were first depleted of any activity and enzyme content by cycloheximide treatment and of precursors of oligosaccharide chains by tunicamycin. The repletion of lipoprotein lipase content was studied in these cells maintained in the presence of tunicamycin after cycloheximide removal. During the repletion phase, the EC50 values of inhibition by tunicamycin (approx. 0.2 microgram/ml) of the incorporation of labeled glucose, mannose or galactose into trichloroacetic acid-insoluble material were found to be identical. Under these conditions, the rate of protein synthesis was maximally decreased by 30%. The results showed clearly that the recovery in lipoprotein lipase activity was parallel to the recovery in hexose incorporation, no activity being recovered in the absence of glycosylation. An inactive form of lipoprotein lipase from tunicamycin-treated cells was detected by competition experiments with mature active lipoprotein lipase for the binding to immobilized antilipoprotein lipase antibodies, as well as by immunofluorescence staining. SDS-polyacrylamide gel electrophoresis and Western blots of cellular extracts and of extracellular media, obtained after tunicamycin-treated cells were exposed to heparin, revealed a single immunodetectable Mr 52 000 protein, whereas a single Mr 57 000 protein was detected in control cells. Therefore, the results indicate that the acquisition by lipoprotein lipase of a catalytically active conformation is linked directly or indirectly to glycosylation. Despite this lack of activation, the lipoprotein lipase molecule was able to migrate intracellularily and to undergo secretion after heparin stimulation of the tunicamycin-treated cells.

Adipose Tissue↗
PubMed1986

Lipoprotein lipase in guinea pig tissues: molecular size and rates of synthesis.

Lipoprotein lipase was immunoprecipitated from guinea pig tissues which had been pulse labeled with [35S]methionine. The apparent size of the product (on SDS gels) was 55 kDa in all tissues studied. Lipoprotein lipase released by heparin from adipocytes and from perfused hearts had the same apparent size. No significant amounts of immunoreactive protein with smaller size were found on immunoblotting of tissue homogenates, or in preparations partially purified by heparin-Sepharose chromatography. Lipoprotein lipase accounted for only a small proportion of total protein synthesis. The highest value was in adipose tissue (0.3-0.8%). In lactating mammary gland lipoprotein lipase accounted for about 0.1%, a figure similar to that previously estimated for the proportion of lipoprotein lipase protein in milk. This suggests that lipoprotein lipase is secreted into milk as efficiently as other milk proteins are, in contrast to the previous opinion that the enzyme appears in milk because small amounts leak out from tissue sites. Relative synthesis of lipoprotein lipase was the same in adipocytes from fed or fasted animals, whereas relative synthesis of several other proteins changed dramatically. This indicates that some proteins in guinea pig adipose tissue are under transcriptional control in response to feeding-fasting, but that lipoprotein lipase is not.

Adipose Tissue↗
PubMed1986

Nutritional regulation of lipoprotein lipase in guinea pig tissues.

Glucose transport in guinea pig adipocytes has been shown to be markedly resistant to stimulation by insulin. Lipoprotein lipase is another transport catalyst in adipose tissue which is believed to be regulated by insulin. We have therefore studied how feeding-fasting affects lipoprotein lipase activity in guinea pig tissues. There was an even more marked decrease in adipose tissue lipoprotein lipase activity on fasting in guinea pigs (10-20 fold) than in rats or mice (4-5 fold). In adipocytes, the activity decreased only 2.5-4.5 fold; most of the change was in extracellular lipoprotein lipase. On glucose refeeding, the activity was rapidly restored. In the first 4 hours after glucose administration extracellular lipoprotein lipase activity increased to more than 10 times the amount present in adipocytes. After cycloheximide, lipoprotein lipase activity decreased with a half-life of 22 min. It is concluded that lipoprotein lipase is rapidly produced and turned over in guinea pig adipose tissue, and that the system is quite sensitive to feeding-fasting. In contrast to adipose tissue, there was no significant change in lipoprotein lipase activity in any other tissue on fasting. There was a strong correlation between the activities in heart and diaphragm muscle, but this correlation was independent of feeding-fasting.

Adipose Tissue↗
PubMed1988

Mode of action of tetrahydrolipstatin: a derivative of the naturally occurring lipase inhibitor lipstatin.

Tetrahydrolipstatin is a specific lipase inhibitor derived from lipstatin, a lipid produced by Streptomyces toxytricini. In addition to pancreatic lipase, it is shown in the present study that tetrahydrolipstatin also inhibits human gastric lipase, carboxyl ester lipase (cholesterol esterase) of pancreatic origin and the closely related bile-salt-stimulated lipase of human milk. It does not inhibit the exocellular lipase from Rhizopus arrhizus or a lipase recently isolated from Staphylococcus aureus. In the presence of a water-insoluble substrate, such as tributyrin, the inhibition has the characteristics of an irreversible inactivation of the uncompetitive type, thus indicating that an enzyme.substrate.inhibitor complex is formed, which cannot undergo further reaction to yield the normal product. This reaction probably takes place at the aqueous/oil interface of the substrate. In aqueous solution, in the absence of substrate, the inhibition of carboxyl ester lipase by tetrahydrolipstatin has the characteristics of being reversible, and finally becomes of a temporary nature analogues to the trypsin-trypsin inhibitor system. It is suggested that an enzyme-inhibitor complex of an acyl-enzyme type is formed that is slowly hydrolysed, with water as the final acceptor, leaving an intact enzyme and an inactive form of the inhibitor. The enzyme thus consumes the inhibitor, which undergoes a chemical conversion, as indicated by a change in mobility in an appropriate thin-layer chromatographic system, indicating an increase in hydrophilicity. Evidence is presented that the reaction product is an acid and that the functional group of tetrahydrolipstatin is the beta-lactone reacting with the active site of the enzyme.

Bile Acids and Salts↗
PubMed1989

Phosphatidylcholine and triacylglycerol hydrolysis in HDL as induced by hepatic lipase: modulation of the phospholipase activity by changes in the particle surface or in the lipid core.

(1) Human HDL2 (d 1.063-1.125) and HDL3 (d 1.125-1.210), labelled with 2-[14C]oleoylphosphatidylcholine (PC), and with/without tri[3H]oleoylglycerol, were incubated with a partially purified human hepatic triacylglycerol lipase, at pH 8.5. PC hydrolysis was linear up to 90-120 min incubation and within a range of lipase activities, from 50 to 500 mIU/ml. At low degrees of lipolysis, the hydrolysis of triacylglycerol was linearly related to that of PC, but the relative degradation rate was 10-fold higher for the former, which was thus very rapidly consumed. HDL subfractions were then differentiated in terms of PC hydrolysis. Km values were 0.32 and 0.43 mM for HDL2 PC and HDL3 PC, respectively. The corresponding Vmax values expressed for 200 mIU/ml hepatic lipase activity were 41.0 nmol PC hydrolysed/ml per h (HDL2) and 28.6 nmol PC/ml per h (HDL3). (2) HDL3 were modified in the presence of VLDL by inducing triacylglycerol lipolysis in VLDL with a semi-purified human plasma or bovine milk lipoprotein lipase (LPL). Lipolysis-modified HDL3 (LIP-HDL3) were mostly enriched in free cholesterol (+80%, P less than 0.05) and to a lesser extent in triacylglycerol (+33%). As a consequence, 45% of the LIP-HDL3 was reisolated in the HDL2-density interval, and is referred to as light LIP-HDL3. LIP-HDL3 displayed a 65% increase in its reactivity towards hepatic lipase compared to control HDL3. The light LIP-HDL3 showed the lowest Km (0.19 mM PC) and the highest Vmax (69 nmol/ml per h) of all HDL tested. Coincubation of HDL3 with VLDL and albumin did not alter the further reactivity of HDL3 towards hepatic lipase. Cholesterol loading of HDL3 by celite-cholesterol dispersions also led to an enhanced reactivity, though less important than with the lipolysis modification. (3) HDL3 were also modified by coincubation with VLDL and the lecithin-cholesterol acyltransferase-inhibited plasma fraction of d greater than 1.21 g/ml, thus allowing the cholesteryl ester transfer reaction to occur. The modified HDL3 (CET-HDL3) were depleted in esterified cholesterol (-25%, P less than 0.05) and enriched in triacylglycerol (+70%, P less than 0.05). However, these particles behaved like control HDL3 in their reactivity towards hepatic triacylglycerol lipase. Thus, the hydrolysis of HDL PC mediated by hepatic triacylglycerol lipase appears to be influenced by changes occurring in the particle's surface rather than in the lipid core.

Humans↗
PubMed1993

Purification and characterization of Pseudomonas fluorescens SIK W1 lipase expressed in Escherichia coli.

Pseudomonas fluorescens SIK W1 lipase was expressed as a form of inclusion bodies in Escherichia coli, which was equivalent to 46% of total cell protein. The inclusion bodies isolated from other cell components were solubilized in the buffer containing 8 M urea and then refolded by diluting urea. The lipase with active conformation was purified by hydrophobic interaction chromatography, gel filtration, anion-exchange chromatography and hydroxyapatite chromatography from the refolded sample. By these purification steps, a single band for active lipase was detected on non-reducing SDS-PAGE and 10-fold purification was attained on the basis of specific activity. Specific activity of the purified lipase toward olive oil emulsion was found to be 7395 units per mg protein. The optimum pH and temperature of the lipase were pH 8.5 and 45-55 degrees C, respectively. The lipase showed higher lipolytic activity toward tricaproin (C6) and tricaprylin (C8) among the triacylglycerols examined and preferentially hydrolyzed ester bond of 1- and 3-position of triolein. Lipase activity was greatly increased by approx. 6-fold and stability for pH was shifted to alkaline pH by Ca2+ ion. The lipase was inhibited by Hg2+, Ag2+, p-chloromercuribenzoate, diethylpyrocarbonate and sodium dodecyl sulfate.

Amino Acid Sequence↗
PubMed1994

Screening, purification and properties of a thermophilic lipase from Bacillus thermocatenulatus.

By screening of 15 thermophilic Bacillus strains, five strains exhibiting lipase activity were found. Among these the strain Bacillus thermocatenulatus (DSM 730) produced the highest lipase activity. The lipase proved to be inducible and extracellular and was purified 67-fold to homogenous state by hexane extraction, methanol precipitation and ion-exchange chromatography on Q-Sepharose. The molecular weight of the lipase determined by SDS-PAGE is 16 kDa. However, the lipase forms very large aggregates (> 750 kDa) as observed after native PAGE, which makes handling of the lipase very difficult. The lipase binds almost irreversibly on different chromatography matrices, e.g., Amberlite and Serolite, and is very stable in the immobilised form. The N-terminal sequence consists of 53% apolar amino acids and shows no significant homology towards other known lipase sequences. Maximum activity was found at pH 7.5-8.0 and 60-70 degrees C with pNPP and olive oil as substrates.

Amino Acid Sequence↗
PubMed1994

The activation of porcine pancreatic lipase by cis-unsaturated fatty acids.

In the presence of taurodeoxycholate, cis-unsaturated fatty acids increase porcine pancreatic lipase activity 15-fold at pH 7.5. This effect is saturable with a low proportion of fatty acid to substrate. The overall angle of the fatty acid, the position of its double bond and the presence of a carboxyl group were critical factors in whether the fatty acid effectively increased lipase activity. When the substrate is emulsified by taurodeoxycholate, the pH optimum for lipase ranges from 6.2 to 7.0. In the presence of cis-unsaturated fatty acids, the overall activity of lipase increases, the pH optimum shifts, and the pH-activity curve becomes biphasic, with one optimum around pH 7.7, and the other around pH 8.8. Fluorescence studies indicate that fatty acids bind near aromatic residues in lipase, particularly tryptophan. Using the fluorescent fatty acid cis-parinaric acid, it was determined that multiple binding sites are present with Kd values of approx. 10(-6) M. Far-UV circular dichroism (CD) studies indicate that in addition to a high affinity fatty acid binding site with a Kd of approx. 10(-6) M, there is also a low affinity binding site with a Kd of approx. 10(-4) M. The far-UV CD data also show that cis-unsaturated fatty acids change the conformation of lipase. It is calculated that the percentage of alpha helix decreases, and the amount of beta sheet and beta turn structure increases. Because the three-dimensional crystal structure of lipase is known, a model is proposed to describe how cis-unsaturated fatty acids increase lipase activity.

Animals↗
PubMed1986

Assay of human pancreatic lipase in biological fluids using a non-competitive enzyme immunoassay.

A sandwich enzyme immunoassay has been developed for human pancreatic lipase using polystyrene balls coated with specific IgG as the first antibody and peroxidase-labelled IgG as the second antibody. The detection limit was 0.5 microgram/l. Good parallelism was observed with the curves obtained from standard lipase and lipase present in serum, pancreatic juice and duodenal contents, demonstrating that the assay may be used to measure the level of the protein in different biological fluids. Mean values of lipase in human sera were 12.3 +/- 6.8 micrograms/l in adults and 4.5 +/- 2.7 in newborns. In all cases a good correlation was found in serum between the catalytic activity and the enzyme immunoassay. Lipase is detectable in amniotic fluids at the 18th week of pregnancy but at a very low level (0.95 +/- 0.32 microgram/l). In pancreatic juices, lipase concentration was 14.6% of the total protein content. A study on cystic fibrosis patients showed a poor correlation between blood pancreatic lipase concentration and fat malabsorption underlying the difficulty in assessing pancreatic function by the measurement of serum pancreatic enzymes. The use of the lipase assay in duodenal contents would permit better assessment of pancreatic function in patients presenting a severe or borderline defect in fat digestion and absorption.

Amniotic Fluid↗
PubMed1986

Release of hepatic lipase and very low density lipoprotein by cultured rat hepatocytes.

Primary cultures of rat hepatocytes were used to study the release of hepatic lipase and very low density lipoprotein (VLDL). The presence of hepatic lipase activity was proved by salt-resistance, affinity chromatography and inactivation by a hepatic lipase antibody. Cellular rate of hepatic lipase release increased by prolonged time in culture, whereas VLDL secretion decreased. Oleic acid and dextran-70 had no effect on release of hepatic lipase, whereas VLDL secretion was increased and decreased, respectively. Calcium antagonists (cobalt and verapamil), monensin and cycloheximide inhibited both the release of hepatic lipase and VLDL. Colchicine and chloroquine, which decreased VLDL secretion, had no effect on release of hepatic lipase. The present results suggest that release of hepatic lipase and secretion of VLDL are not coordinated and exhibit different sensitivity towards certain compounds altering secretory functions.

Animals↗
PubMed1996

Inhibition of lipoprotein lipase induced cholesterol ester accumulation in human hepatoma HepG2 cells.

It has been suggested previously that lipoprotein lipase may act as a ligand to enhance binding and uptake of lipoprotein particles. In the present study we have examined the capacity of bovine milk lipoprotein lipase to induce intracellular accumulation of triglyceride and cholesterol ester by VLDL (Sr 60-400) isolated from Type IV hypertriglyceridemic subject (HTg-VLDL) in HepG2 cells, independent of its lipolytic activity. We have also attempted to elucidate the cellular receptor mechanisms responsible for these effects. HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester were dependent on the presence of an active lipase. Bovine milk lipoprotein lipase (LPL) increases triglyceride mass by 301% +/- 28% (P < 0.0005) and cholesterol ester mass by 176% +/- 12% (P < 0.0005). These HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester did not occur when heat-inactivated lipase was used. Rhizopus lipase could replace LPL and cause equivalent increases in intracellular triglyceride and cholesterol ester (472% +/- 61%(P < 0.005) and 202% +/- 25% (P < 0.025) respectively vs. control). HTg-VLDL treated with LPL and reisolated also caused equivalent increases (274% +/- 18%(P < 0.01) and 177% +/- 12% (P < 0.005) for triglyceride and cholesterol ester). LDL also caused increases in intracellular cholesterol ester (189% +/- 20%(P < 0.005)), although three times more LDL cholesterol had to be added to achieve the same effect. These LDL-induced increases were effectively blocked by monoclonal antibodies directed against the B,E receptor binding domains of apo B (-97% +/- 13% (P < 0.0005) with anti-apo B 5E11 and -68% +/- 13% (P < 0.05) for anti-apo B B1B3) or by anti-B,E receptor antibodies (-77% +/- 7% (P < 0.01) antibody C7). These same antibodies had little effect on the HTg-VLDL+LPL-induced increases in cholesterol ester (+21%, +15% and -22% for 5E11, B1B3 and C7, respectively). Monoclonal anti-apo E antibodies also had no effect on LDL-mediated increases in intracellular cholesterol ester, but had a small and significant effect on VLDL-mediated increases in cholesterol ester. However, heparin, which interferes with cell surface proteoglycan interaction, was very effective at blocking HTg-VLDL-mediated increases in cholesterol ester in the presence of LPL (-86% +/- 8% P < 0.0005). Heparin was also effective in the presence of Rhizopus lipase (-79%) or lipolyzed re-isolated HTg-VLDL (-95%). These results suggest that lipoprotein lipase may enhance the uptake process beyond its role in lipolytic remodelling but does not appear to be an absolute requirement. In contrast, heparin had no effect on LDL-mediated cholesterol ester accumulation. Lactoferrin, which inhibits interaction with the low density lipoprotein receptor-related protein (LRP), was also very effective at inhibiting HTg-VLDL increases in intracellular cholesterol ester (-95% +/- 6%, P < 0.01). However, there was no effect of either heparin or lactoferrin on HTg-VLDL-mediated triglyceride accumulation. Thus cell surface heparin sulphate may facilitate intracellular lipid acquisition by providing a stabilizing bridge with the lipoproteins and enhance uptake through receptor-mediated processes such as LRP.

Animals↗
PubMed1984

Hypertriglyceridemia and its relation to tissue lipoprotein lipase activity in endotoxemic, Escherichia coli bacteremic, and polymicrobial septic rats.

Hypertriglyceridemia, commonly observed in septic patients, may result from a decreased ability of tissues to remove plasma triacylglycerol due to depressed lipoprotein lipase activity. While endotoxin administration results in substantial decreases in muscle lipoprotein lipase activity, enzyme activity is increased in animals subjected to other forms of stress and trauma. The present study was initiated to compare changes in plasma triacylglycerol concentrations and tissue lipoprotein lipase activities in rats challenged with endotoxin or live Escherichia coli (iv or ip) or rats subjected to polymicrobial peritoneal sepsis. Sixteen hours post-treatment plasma triacylglycerol levels were increased 200 to 300% in endotoxin- and E. coli-treated rats but did not differ from control animals subjected to peritoneal sepsis. At the same time, endotoxin administration resulted in significant decreases in heart (71-80%), soleus muscle (52-74%), and adipose tissue (21-32%) lipoprotein lipase activity regardless of the route injected. Intravenous E. coli also lead to a decrease in the three tissues examined while ip administration of E. coli reduced muscle and adipose tissue but not heart lipoprotein lipase activity. In contrast to endotoxemic and E. coli bacteremic rats, polymicrobial peritonitis resulted in significant increases in heart (46-89%) and skeletal muscle (18-39%) lipoprotein lipase activity. Thus, hypertriglyceridemia is not necessarily a consequence of sepsis but occurred in endotoxemic and bacteremic states when muscle and adipose tissue lipoprotein lipase activities were reduced. These findings support the postulate that sepsis-induced hypertriglyceridemia is likely to be associated with a decreased ability of lipoprotein lipase-containing tissues to clear circulating triacylglycerol.

Animals↗
PubMed1995

The effects of a selective alpha-1 adrenergic blockade on the activity of adipose tissue lipoprotein lipase in female hamsters.

Lipoprotein lipase, is an enzyme responsible for the hydrolysis of triacylglycerols at the surface of endothelial cells. Its regulation is not completely elucidated and seems, among other things, under the influence of the sympathetic nervous system. The adrenergic regulation of lipoprotein lipase activity is complex and the alpha 1 adrenergic pathway appears involved in this regulation. In the present study, adipose tissues of female hamsters are investigated following a single injection of doxazosin and phenylephrine and are compared to controls for the activity of lipoprotein lipase. After an acute treatment with a selective alpha 1 antagonist (doxazosin), lipoprotein lipase activity was decreased in the parametrial white adipose tissue and increased in brown adipose tissue (p < or = 0.05). Moreover, a treatment with phenylephrine, an alpha 1 adrenergic agonist, increased the activity of lipoprotein lipase, in the parametrial fat pad only. On the other hand, the activity of lipoprotein lipase in heart and in skeletal muscle was not modified by an alpha 1 stimulation or blockade. In this study, calcium and norepinephrine did not appear involved in the regulation of lipoprotein lipase activity. On the contrary, the increase of plasma glycerol after an acute treatment with doxazosin suggests that the lipolytic activity of white adipose tissue could be involved in the decrease of lipoprotein lipase activity in the parametrial white adipose tissue.

Adipose Tissue↗
PubMed1987

Brain lipoprotein lipase is responsive to nutritional and hormonal modulation.

Functional lipoprotein lipase activity was recently described in rat brain. The present study was performed to further characterize the biologic significance of brain lipoprotein lipase (heparin releasable component) and elucidate regulatory factors. Comparative studies were performed on tissue (brain, adipose, and heart) heparin releasable lipoprotein lipase in the fasted and diabetic (streptozotocin 100 mg/kg BW IP) rat. Both fasting (96 hours) and diabetes (ten days) significantly decreased brain (cortical) (P less than .05) and adipose (epididymal fat pad) (P less than .001) lipoprotein lipase activity. In contrast, heart muscle enzyme activity was significantly increased (P less than .001) in response to fasting and diabetes. Refeeding (Purina chow 96 hours) and insulin replacement (96 hours) reversed these changes in tissue lipoprotein lipase consequent to fasting and diabetes, respectively. There was a positive correlation between the changes in serum insulin concentration and adipose lipoprotein lipase, but there was no correlation between this parameter and brain or heart lipoprotein lipase. In addition, although T3 therapy normalized the low T3 state associated with both fasting and diabetes, it had no effect on the enzyme activity in the studied tissues. However, subsequent studies demonstrated that hypothyroidism (2 weeks post thyroidectomy) significantly decreased brain lipoprotein lipase activity (P less than .001) and increased both the adipose (P less than .025) and heart (P less than .025) enzyme activity. T3 replacement (0.8 micrograms/100 BW/d for 1 week) reversed the effects of hypothyroidism. However, the relationship between brain enzyme activity and serum T3 was nonlinear as hyperthyroidism tended to reduce brain LPL activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗