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PubMed1998

Genetic polymorphisms and mutations of the lipoprotein lipase gene in Japanese schoolchildren with hypoalphalipoproteinemia.

Lipoprotein lipase (LPL) is an important enzyme for the hydrolysis of TG on lipoproteins, and its activity is positively correlated with the plasma levels of high density lipoprotein cholesterol (HDL-C). To investigate the association between the LPL gene and low HDL-C levels, we studied two polymorphisms (Hind III and Pvu II) and three mutations (Asn291Ser, Gly188Glu and LPL(Arita)) of the LPL gene in 114 children with low HDL-C levels (<40 mg/dl) and 194 control children using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques (PCR-RFLP). The frequency of the Pvu II +/+ genotype was significantly higher in the children with low-HDL/high-TG (TG>100 mg/dl, 90th percentile level among Japanese schoolchildren) than in the other children (vs the low-HDL/normal-TG children, chi2 = 7.49, p < 0.01; vs control children, chi2 = 7.23, p < 0.01). Pvu II+ allele of the LPL gene was associated with elevated TG levels in low HDL-C groups. In addition, we found one heterozygote of LPL(Arita) (deletion of G at base 916 in exon 5, the most common mutation of LPL deficiency in Japanese), among the low-HDL/high-TG subjects. The other two variants were not detected in either the low-HDL children or control children. LPL Asn291Ser and Gly188Glu have been presumed to be rare in the Japanese population. In conclusion, our results suggest that hypoalphalipoproteinemia with elevated TG level may be associated with genetic variations of the LPL gene.

Adolescent↗

PubMed1972

Lipoprotein lipase activity in the adipose tissue of rats adapted to controlled feeding schedules.

1. The relationships between nutritional state, lipoprotein lipase activity in epididymal fat-pads, and the concentrations of glucose, insulin and unesterified fatty acids in the plasma were studied in rats that had been adapted for 3 weeks to one of two controlled feeding schedules. In one of these, rats had access to food for 14h during each 24h period, and in the other, they had access to food for 14h during each 48h period. Groups of animals were killed at different times during the 14h when they had access to food and during the following period when they were deprived of food. 2. Low lipoprotein lipase activity, low concentrations of plasma glucose and insulin and high concentrations of plasma unesterified fatty acids were found in rats deprived of food for 34h. Feeding resulted in increases in lipoprotein lipase activity and in the concentrations of glucose and insulin in the plasma. Enzyme activity continued to increase during the first 6-9h of the feeding period. 3. After adapted rats had been deprived of food for 12-16h there was a marked and unexpected increase in lipoprotein lipase activity; this occurred even when the rats were kept in an isolated environment. 4. The findings suggest that factors other than the absolute concentrations of insulin and glucose in the blood can exert a considerable influence on lipoprotein lipase activity in the epididymal fat-pad of a rat.

Adipose Tissue↗

PubMed2005

Correlation between the activities of lipoprotein lipase and paraoxonase in type 2 diabetes mellitus.

UNLABELLED: In type 2 diabetes mellitus the decreased catabolism of triglyceride-rich lipoproteins as a consequence of mainly the decreased lipoprotein lipase activity results in hypertriglyceridaemia and other lipoprotein alterations promoting atherosclerosis. The high-density lipoprotein-associated enzyme, paraoxonase, prevents the oxidation of low-density lipoprotein, which is an antiatherogenic effect. AIM: to examine the relation between the activities of enzymes influencing HDL remodelling- LPL and PON- in type 2 diabetes mellitus. METHODS: 56 newly diagnosed type 2 diabetic patients and 39 healthy controls were involved in the study. The serum PON activity was measured spectrophotometrically using paraoxone as substrate. PON phenotype was determined by the dual substrate method, PON mass was measured by ELISA. The determination of lipoprotein lipase activity was performed using 3H-triolein. RESULTS: We noticed smaller PON activity decrease in our newly diagnosed diabetic subjects compared to the previous studies which investigated the alteration of enzyme activity after a longer duration of diabetes mellitus. The lipoprotein lipase activity showed a positive correlation with PON activity (r=0.43; P<0.02). Interestingly, the PON activity of the homozygous-low activity group did not correlate with the LPL activity, while in the heterozygous and homozygous-high activity groups there was a significantly positive correlation (r=0.51; P<0.05) between PON and LPL activity. CONCLUSION: Besides lipid alterations, the metabolic changes of type 2 diabetes mellitus influence the reduction of the antioxidant capacity of HDL by remodelling HDL and decreasing PON activity via modification of lipoprotein lipase activity, which might contribute to accelerated atherosclerosis.

Aryldialkylphosphatase↗

PubMed1999

Lipoprotein lipase mutations and Alzheimer's disease.

Lipoprotein lipase (LPL) helps transfer lipids from lipoprotein particles to cells. In the brain, LPL is present in Alzheimer's disease (AD) amyloid plaques. LPL binds apolipoprotein E (ApoE) lipoprotein particles and low-density lipoprotein receptor-related protein (LRP), an ApoE receptor. Since polymorphisms in both ApoE and LRP influence AD risk, we sought to determine whether LPL mutations also affect AD risk. In a case-control study, the frequencies of two of the most common known LPL mutations were measured in European-Americans either clinically diagnosed or pathologically confirmed as AD or normal control (N) subjects. In clinically diagnosed subjects, the Ser447Ter mutation comprised 9.8% (62/630) of alleles in N and 3.8% (9/238) in AD, a significant difference (P = 0.0057), while the Asn291Ser mutation comprised 1.1% (5/460) of alleles in N and 5.1% (8/158) in AD, also a significant difference (P = 0.0073), though in pathologically confirmed subjects the allele frequencies for AD did not significantly differ from N for either mutation. In clinically diagnosed subjects, LPL mutations were associated with altered AD risk, suggesting a potential role for LPL in the causation of AD. Further studies in different populations should help clarify the questions raised by these results.

Aged↗

PubMed2003

Mice expressing only covalent dimeric heparin binding-deficient lipoprotein lipase: muscles inefficiently secrete dimeric enzyme.

Lipoprotein lipase (LpL) hydrolyzes triglycerides of circulating lipoproteins while bound as homodimers to endothelial cell surface heparan sulfate proteoglycans. This primarily occurs in the capillary beds of muscle and adipose tissue. By creating a mouse line that expresses covalent dimers of heparin-binding deficient LpL (hLpLHBM-Dimer) in muscle, we confirmed in vivo that linking two LpL monomers in a head to tail configuration creates a functional LpL. The hLpLHBM-Dimer transgene produced abundant activity and protein in muscle, and the LpL was the expected size of a dimer (approximately 110 kDa). Unlike the heparin-binding mutant monomer, hLpLHBM-Dimer had the same stability as nonmutated LpL. The hLpLHBM-Dimer transgene prevented the neonatal demise of LpL knockout mice; however, these mice were hypertriglyceridemic. Postheparin plasma LpL activity was lower than expected with the robust expression in muscle and was no longer covalently linked. Studies in transfected cells showed that Chinese hamster lung cells, but not COS cells, also degraded tandem repeated LpL into monomers. Thus, although muscle can synthesize tethered, dimeric LpL, efficient production of this enzyme leading to secretion, and physiological function appears to favor secretion of a noncovalent dimer composed of monomeric subunits.

Amino Acid Sequence↗

PubMed1982

The storage and synthetic pools of heparin-releasable lipoprotein lipase and hepatic triacylglycerol lipase in the growing puppy.

Age-related changes in the activities of extrahepatic lipoprotein lipase and hepatic triacylglycerol lipase were determined during a primed/constant-rate infusion of heparin for 2 h in puppies between birth and 18 weeks of age. The early (storage) and late (synthetic) phases were measured. Both phases of hepatic triacylglycerol lipase activity were well developed in the first week, reflecting the metabolic maturity of the liver at birth. During the 18 weeks of study, the activity remained relatively unchanged except for a sharp peak at 12 weeks. Extrahepatic lipoprotein lipase activity was low in the first 4 weeks of suckling. Its storage pool increased 6-fold in the next 14 weeks, with a less marked rise in its late (synthetic) pool. Sustained increases in the activity of this enzyme were first noticed during weaning, when the insulin-secretory response matured. Endogenous insulin-secretory capacity rather than the fat content of the feed appeared significant in the postnatal development of lipoprotein lipase (Clearing-factor lipase) activity.

Animals↗

PubMed2005

Apoa5 Q139X truncation predisposes to late-onset hyperchylomicronemia due to lipoprotein lipase impairment.

While type 1 hyperlipidemia is associated with lipoprotein lipase or apoCII deficiencies, the etiology of type 5 hyperlipidemia remains largely unknown. We explored a new candidate gene, APOA5, for possible causative mutations in a pedigree of late-onset, vertically transmitted hyperchylomicronemia. A heterozygous Q139X mutation in APOA5 was present in both the proband and his affected son but was absent in 200 controls. It was subsequently found in 2 of 140 cases of hyperchylomicronemia. Haplotype analysis suggested the new Q139X as a founder mutation. Family studies showed that 5 of 9 total Q139X carriers had hyperchylomicronemia, 1 patient being homozygote. Severe hypertriglyceridemia in 8 heterozygotes was strictly associated with the presence on the second allele of 1 of 2 previously described triglyceride-raising minor APOA5 haplotypes. Furthermore, ultracentrifugation fraction analysis indicated in carriers an altered association of Apoa5 truncated and WT proteins to lipoproteins, whereas in normal plasma, Apoa5 associated with VLDL and HDL/LDL fractions. APOB100 kinetic studies in 3 severely dyslipidemic patients with Q139X revealed a major impairment of VLDL catabolism. Lipoprotein lipase activity and mass were dramatically reduced in dyslipidemic carriers, leading to severe lipolysis defect. Our observations strongly support in humans a role for APOA5 in lipolysis regulation and in familial hyperchylomicronemia.

Amino Acid Sequence↗

PubMed1988

Biochemical indicators of fatness in meat-type chickens: lack of correlation between lipoprotein lipase activity in post-heparin plasma and body fat.

1. Possible relationships between fatness and lipoprotein lipase activity in adipose tissue and plasma from heparinised birds were examined in 7-week-old male and female broilers. 2. Total lipoprotein lipase activity in abdominal fat was significantly correlated (r = 0.5) with fat pad weight, but there was no correlation between specific activity of the enzyme and fat pad weight. 3. Lipoprotein lipase activity in post-heparin plasma showed no correlation with either abdominal fat or total body fat content. 4. The results indicate that measurements of lipoprotein lipase activity in biopsy samples or in post-heparin plasma are of no value in predicting the fat content of live birds.

Adipose Tissue↗

PubMed1997

Heterozygous lipoprotein lipase deficiency: frequency in the general population, effect on plasma lipid levels, and risk of ischemic heart disease.

BACKGROUND: Patients with mutations on both alleles of the lipoprotein lipase gene resulting in complete lipoprotein lipase deficiency exhibit the chylomicronemia syndrome with severe hypertriglyceridemia and increased risk of pancreatitis and possibly of ischemic heart disease. This study examined frequency, lipid levels, and risk of ischemic heart disease for heterozygous carriers of lipoprotein lipase mutations known to cause the chylomicronemia syndrome in the homozygous state. METHODS AND RESULTS: Two mutations were screened for in 9259 individuals in a general population sample and in 948 patients with verified ischemic heart disease. The percent frequencies of heterozygous individuals with the Gly188-->Glu and Ile194-->Thr substitutions in the general population were 0.06% (95% CI, 0.04% to 0.23%) and 0% (95% CI, 0.00% to 0.12%), respectively. The Gly188-->Glu substitution was associated with an increase in plasma triglycerides of 0.8+/-0.3 mmol/L (mean+/-SEM) and a decrease in plasma HDL cholesterol, apo A-I, and glucose levels of 0.45+/-0.07 mmol/L, 17+/-6 mg/dL, and 1.1+/-0.2 mmol/L, respectively. On multiple logistic regression analysis allowing for age, sex, plasma cholesterol, plasma lipoprotein (a), hypertension, diabetes mellitus, smoking, and body mass index, both plasma triglycerides and HDL cholesterol levels were independent predictors of ischemic heart disease. Finally, the Gly188-->Glu substitution was more common among patients with verified ischemic heart disease (percent frequency of heterozygous individuals, 0.32%) than among individuals from the general population (odds ratio, 4.9; 95% CI, 1.2 to 19.6). The effects of the Gly188-->Glu substitution were more pronounced than those of the common Asn291-->Ser substitution. CONCLUSIONS: Heterozygous lipoprotein lipase deficiency due to the Gly188-->Glu substitution appears to increase plasma triglycerides and reduce HDL levels and may thereby predispose carriers to ischemic heart disease.

Adult↗

PubMed1987

Effects of doxazosin and propranolol administration on lipoprotein lipases in cholesterol-fed rats.

The effects of alpha 1-adrenergic receptor inhibition with doxazosin, and beta-blockade with propranolol on tissue lipoprotein lipases and plasma lipids were studied in rats. In rats fed a normal lab chow, doxazosin increased heart lipoprotein lipase activity (+14%), while propranolol had the opposite effect (-20%). These effects were not statistically significant when compared with nontreated controls, although the difference between the doxazosin and propranolol groups was significant (p less than 0.05). There were no significant effects on adipose tissue lipoprotein lipase activity or hepatic lipase activity. In rats fed a cholesterol-enriched diet there were similar but smaller effects on heart lipoprotein lipase activity (+5% and -12%, respectively). In these rats alpha 1-inhibition also tended to increase adipose tissue lipoprotein lipase (+14%) and hepatic lipase (+13%), while beta-blockade had the opposite effect (-20% and -9%, respectively). The lipase activities were significantly different between the treatment groups in liver and heart but not in adipose tissue. Doxazosin and propranolol did not affect plasma triglyceride or total cholesterol, but high-density lipoprotein cholesterol was increased during alpha 1-blockade (+24%).

Adipose Tissue↗

PubMed1996

Common DNA polymorphisms at the lipoprotein lipase gene. Association with severity of coronary artery disease and diabetes.

BACKGROUND: DNA variants of the lipoprotein lipase gene are associated with changes in lipid metabolism similar to those in diabetes and may relate to the development of atherosclerotic lesions, particularly premature lesions. METHODS AND RESULTS: To determine whether lipoprotein lipase gene variants are relevant to ongoing atherogenesis, we explored relationships between two common lipoprotein lipase gene polymorphic markers, Pvu II at intron 6 and HindIII at intron 8; the severity of coronary artery disease (CAD); and lipid variables in 475 white patients 65 years of age or younger. We assessed CAD severity as the number of significantly stenosed (> 50% luminal obstruction) major coronary arteries at angiography and by the Green Lane coronary score. We found a significant association between the Pvu II polymorphism and the number of significantly diseased vessels (P = .0099) and coronary score (P = .028), with the Pvu II(-) alleles associated with less severe disease. The HindIII polymorphism was not associated with severity but had an additive effect with the Pvu II polymorphism. There was a close relationship between the Pvu II(+/+) genotype and the presence of diabetes (P = .0025), with an OR of 3.12 (95% CI, 1.30 to 7.49) compared with the Pvu II(-/-) genotype. The interaction between these polymorphisms and CAD severity (rather than occurrence) was independent of the levels of triglycerides and HDL cholesterol and of other lipid variables. There was also a dosage-dependent relationship between the Pvu II polymorphism and levels of triglyceride. The Pvu II(-) allele was associated with low levels and variances of triglycerides. CONCLUSIONS: We conclude that the lipoprotein lipase Pvu II polymorphism is significantly associated with CAD severity and with type II diabetes in CAD patients, independent of changes in circulating lipid levels. These findings may be relevant to mechanisms mediating atherogenesis.

Aged↗

PubMed2002

Analysis of lipoprotein lipase activity using high-performance liquid chromatography.

Lipoprotein lipase (LPL) is a key enzyme which regulates the plasma triglyceride concentration by hydrolyzing triglycerides in chylomicrons and very-low-density lipoprotein (VLDL). The activity of LPL was conventionally analyzed using radio-labeled residues or direct sandwich-ELISA. An assay for lipoprotein lipase activity which used a nonradioactive substrate, tri-olein, is described. In this method, LPL activity was detected fluorometrically by reacting 9-anthryldiazomethane (ADAM) with the oleic acid generated from tri-olein by enzyme activity and separated by reversed-phase HPLC. This method has been optimized and the optimum enzyme incubation time and reaction time of the generated oleic acid with ADAM were both at 20 min. The method correlated well with the conventional method.

Chromatography, High Pressure Liquid↗

PubMed1995

Influence of lipoprotein lipase and hepatic lipase on the transformation of VLDL and HDL during lipolysis of VLDL.

In order to study the relative effects of lipolytic enzymes on the removal of lipids and apolipoproteins, in particular apolipoprotein (apo) E and cholesteryl ester, from human very low density lipoprotein (VLDL) during its conversion to product lipoproteins, the action of lipoprotein lipase (LPL) and the combined action of lipoprotein lipase and hepatic lipase (HL) were studied in the presence of physiological proportions of high density lipoprotein (HDL) (10 mg protein), VLDL (2 mg protein) and albumin in an amount sufficient for the binding of all released fatty acids. The HDL used in the incubation was free of apo E in order to facilitate assessment of apo E transfer from VLDL to HDL. The redistribution of lipid and apolipoprotein mass and the movement of labeled cholesteryl ester from VLDL to other lipoprotein fractions was assessed by density gradient ultracentrifugation. Following 90%-95% lipolysis of VLDL triglycerides by rat heart LPL in 2 h, there was an almost complete transfer of apo C-II and apo C-III to HDL but only 20% of VLDL apo E was transferred to HDL. There was significant augmentation of HDL unesterified cholesterol and phospholipid mass during LPL action despite a substantial overall phospholipid hydrolysis (30%). The transfer of cholesteryl ester mass to HDL was variable (0%-13%) with a mean transfer of 7% of VLDL cholesteryl ester. Transfer of labeled VLDL cholesteryl ester to HDL was 3%-6%. A considerable amount of the VLDL lipid mass appeared in the light fraction of the low density lipoprotein (LDL) region, but a substantial amount remained in the VLDL/intermediate density lipoprotein (IDL) region. The post-lipolysis particles that were isolated in the VLDL-LDL density range were larger than LDL and contained a high ratio of surface lipids relative to core lipids as compared to plasma LDL. The inclusion of human HL with LPL did not alter the redistribution of apolipoproteins proteins or lipids from VLDL to LDL or to HDL. The major effect of HL, relative to that observed with LPL alone, was a marked hydrolysis of HDL triglycerides (68%). Despite the combined action of LPL and HL on VLDL in the presence of HDL and over 90% lipolysis of triglycerides, a major portion of residual VLDL mass remained in fractions lighter than normal LDL density and retained apo E. It is concluded that lipoprotein lipase of LPL in combination with HL are ineffective in bringing about the complete conversion of plasma VLDL to LDL. Lipoprotein lipase was effective in substantially augmenting the HDL mass including cholesteryl while the major effect of HL was the selective hydrolysis of HDL triglycerides.

Animals↗

PubMed1975

Interference with the transport of heparin-releasable lipoprotein lipase in the perfused rat heart by colchicine and vinblastine.

The effect of pretreatment with colchicine or vinblastine on the lipoprotein lipase activity of rat heart was studied. Administration of colchicine or vinblastine 4 h prior to perfusion of the heart caused a very marked reduction in lipoprotein lipase activity released into the perfusate within 1 min of heparin perfusion. At the same time an increase in residual heart lipase occurred so that total lipoprotein lipase content of the heart (heparin releasable plus residual) did not change. The colchicine effect was dose and time dependent; no decrease in heparin-releasable enzyme activity occurred after only 30 min of pretreatment or upon addition of colchicine into the perfusate. These results indicate that colchicine did not impede enzyme synthesis or its release from the cell surface, but may have interfered with the transport of lipoprotein lipase from the site of its synthesis to the endothelial cell surface.

Animals↗

PubMed1995

Lipoprotein lipase enhances removal of chylomicrons and chylomicron remnants by the perfused rat liver.

Lipoprotein lipase has been found to efficiently mediate binding of lipoproteins to cell surfaces and to the low density lipoprotein (LDL) receptor-related protein (LRP) under cell culture conditions (Beisiegel et al. 1991. Proc. Natl. Acad. Sci. USA. 88: 8242-8346). This supports the previously proposed idea that the lipase could have a role in receptor-mediated uptake of chylomicron remnants in the liver. We have investigated the effects of lipoprotein lipase on the clearance of chylomicrons during perfusions of rat livers. The chylomicrons were doubly labeled in vivo with [14C]retinol (in retinyl esters) and with [3H]oleic acid (in triacylglycerols) and were collected from lymph. In the absence of any lipase the clearance of chylomicron label from the perfusion medium was slow. Addition of lipoprotein lipase caused lipolysis of chylomicron triacylglycerols as evidenced by increased levels of 14C-labeled fatty acids in the perfusate. Simultaneously, the level of [14C]retinyl esters in the perfusate decreased dramatically, indicating core-particle removal. Similar effects were seen with an unrelated lipase from Pseudomonas fluorescens. To discriminate between the effects of lipolysis and a true liganding effect of the lipoprotein lipase protein, the active site inhibitors tetrahydrolipstatinR and hexadecylsulfonylfluoride were used to reduce or totally inhibit the catalytical activity. With lipase covalently inhibited by the latter inhibitor, lipolysis during perfusions was low or absent. Nonetheless, the inhibited enzyme had a clear effect on the removal of chylomicrons by the liver. With 1.2 micrograms of inhibited lipase/ml perfusate, about 70% of the core label had been removed after 15 min as compared to about 20% in perfusions without lipase. With identical amounts of active lipoprotein lipase protein, more than 90% of the label was removed. We conclude that any lipase causing lipolysis of chylomicrons can stimulate their clearance by the liver, but that lipoprotein lipase has an additional effect on the removal, which is not dependent on its catalytic activity.

Animals↗

PubMed1995

Human triacylglycerol-rich lipoprotein subfractions as substrates for lipoprotein lipase.

In order to test the hypothesis that lipoprotein lipase (LPL) acts preferentially on larger lipoprotein particles, we determined the susceptibility of triacylglycerol-rich lipoprotein (TRL) subfractions to hydrolysis by LPL in vitro. Chylomicrons (Sf > 400), very low density lipoproteins (VLDL)1 (Sf 60-400) and VLDL2 (Sf 20-60) were isolated from six subjects with a range of plasma-triacylglycerol (TAG) concentrations following an overnight fast and for up to 6 h after the consumption of a mixed meal (41% fat). The percent of TRL-TAG hydrolysed by LPL in subfractions isolated following overnight fast was VLDL1 > VLDL2 (46.8 +/- 10.2 vs. 25.9 +/- 7.4%, P = 0.006) and 3 h after the meal it was chylomicrons > VLDL1 > VLDL2 (81.0 +/- 12.6 vs. 52.8 +/- 10.2 vs. 27.7 +/- 6.2%, chylomicrons vs. VLDL1 and VLDL1 vs. VLDL2, both P < or = 0.005). The percent of VLDL1-TAG hydrolysed increased both within and between subjects as VLDL1-TAG concentrations increased. This relationship could be explained by the positive correlation observed between VLDL1-TAG and VLDL1-TAG:apolipoprotein B. In conclusion, increasing the size and TAG content of a lipoprotein particle increases its susceptibility to hydrolysis by LPL.

Adult↗

PubMed1992

Lipoprotein lipase release from BFC-1 beta adipocytes. Effects of triglyceride-rich lipoproteins and lipolysis products.

Lipoprotein lipase (LPL), synthesized by adipocytes and myocytes, must be transported to the luminal endothelial cell surface where it then interacts with circulating lipoproteins. The first step in this extracellular LPL transport pathway is LPL release from the surface of LPL-synthesizing cells. Because hydrolysis of triglyceride (TG)-rich lipoproteins releases LPL from the apical surface of endothelial cells, we hypothesized that the same substances dissociate LPL from adipocytes. 125I-LPL was bound to the surface of brown adipocytes (BFC-1 beta). LPL binding to the adipocyte surface was greater than to endothelial cell surfaces. Using low concentrations of heparin, more LPL was released from endothelial cells than BFC-1 beta, suggesting that the affinity of LPL binding to the adipocytes was greater than LPL affinity for endothelial cells. Greater than 3-fold more LPL was released from the cell surface when very low density lipoproteins (VLDL) were added to culture medium containing 3% bovine serum albumin. LPL remaining on the cell surface decreased with VLDL addition. Endogenously produced LPL activity was also released from the cells by VLDL. Low and high density lipoproteins did not release 125I-LPL or LPL activity from the adipocytes. To assess whether lipolysis was necessary for LPL release, BFC-1 beta were incubated with TG-rich lipoproteins from a patient with apoCII deficiency. The apoCII-deficient lipoproteins did not release LPL unless an exogenous source of apoCII was added. Apolipoproteins E and Cs and high molar ratios of oleic acid:bovine serum albumin did not release surface-associated LPL. Lysolecithin (25 and 100 microM), but not lecithin, monoglycerides, or diglycerides, released adipocyte surface LPL. Because lysolecithin also released LPL during a 4 degrees C incubation, cellular metabolic functions are not required for LPL dissociation from the cells. Lysolecithin also inhibited LPL binding to endothelial cells; however, this effect was abrogated by addition of bovine serum albumin. We hypothesize that lipolysis products from TG-rich lipoproteins release adipocyte surface LPL, which can then be transported to the luminal endothelial cell surface.

Adipose Tissue, Brown↗

PubMed1993

Lipid droplet accumulation and lipoprotein lipase activity in the rat salivary gland during the perinatal period.

The submandibular and sublingual glands of foetal and newborn rats aged 21 days in utero to 7 days after birth were examined morphologically and biochemically. Lipid droplets tended to be localized in secretory cells, especially in their basal cytoplasm. The degree of droplet accumulation varied with the age of the rat. No droplets were observed before and immediately after birth. The number of accumulated droplets peaked 24-48 h after birth, then gradually decreased and reached normal levels by 5 days. In the salivary glands of fasted newborn rats, no lipid droplets were observed throughout the experiment. The amount of triacylglycerol reached its maximum level 1 day after birth; it then decreased gradually until 5 days and after that did not change. The amount of cholesterol did not change during postnatal development. Lipase activity attained its maximum level in the salivary glands immediately after birth and then decreased rapidly. It was higher in the glands of fasted than fed 1-day-old rats. Antiserum against lipoprotein lipase inhibited the salivary gland lipase activity in a dose-dependent manner, with 5 microliters of antiserum producing 60-70% inhibition. Non-immune serum had little effect. It was concluded that (1) accumulated lipid in the secretory cell cytoplasm of the salivary glands originates from ingested milk; (2) the principal component of accumulated lipid droplets is triacylglycerol; (3) 60-70% of the total lipase activity represents lipoprotein lipase; (4) an increase of lipoprotein lipase activity is recognizable before the accumulation of triacylglycerol.

Animals↗