Plasma Lipoprotein Lipase Research Articles

Homozygosity for a partial deletion of apoprotein A-V signal peptide results in intracellular missorting of the protein and chylomicronemia in a breast-fed infant

Deficiency of apoprotein A-V (apoA-V) can cause hypertriglyceridemia. In an 11 months old boy presenting with a severe hypertriglyceridemia, a formerly unknown 24 nucleotide deletion in exon 2 of the APOA5 gene was detected. The homozygous mutation results in an eight amino acid loss in the signal peptide sequence (c.16_39del; p.Ala6_Ala13del). Screening of control persons proved that this deletion is a rare mutation. Hypertriglyceridemia in the patient was only found at the time when he was breast fed, while after weaning, triglyceride levels were close to normal. Under both dietary conditions, apoA-V protein was undetectable in plasma while post-heparin plasma lipoprotein lipase activity was normal.Expression analysis of normal and mutated protein by Western blot and immunofluorescence in apoA-V deficient primary hepatocytes revealed that, due to changes in the signal peptide, mutated apoA-V was intracellularly missorted to lipid droplets and not secreted. Wild type apoA-V, instead, was not targeted to lipid droplets but transported via endosomal compartments to the plasma membrane for secretion.It is concluded that the c.16_39del mutation in the APOA5 gene leads to hepatic missorting and impaired secretion, which consequently results in undetectable apoA-V plasma levels. The absence of apoA-V in plasma leads under conditions of fat-rich diets to severe chylomicronemia, suggestive for a modulatory role of apoA-V for lipoprotein lipase mediated intravascular triglyceride lipolysis.

Lagenaria siceraria ameliorates atheromatous lesions by modulating HMG–CoA reductase and lipoprotein lipase enzymes activity in hypercholesterolemic rats

ObjectiveTo investigate the antiatherosclerotic potential of Lagenaria siceraria (L. siceraria) by calculating percentage plaque area in aorta and grade of atheromatous lesions modulated by HMG–CoA reductase enzyme and lipoprotein lipase enzymes levels in hyperlipidemic rats. MethodsRats were divided into different groups, fed with high cholesterol atherogenic diet and in addition supplemented with ethanolic extract of fruits of L. siceraria and standard drug atorvastatin. At the end of the treatment schedule, the atherosclerotic lesion area was measured in cross-sections of the aortic root and grading of atherosclerotic lesions was done. The blood samples from animals of different groups were evaluated for serum lipid profile determination and plasma lipoprotein lipase activity and the hepatic HMG-CoA activity was also determined. ResultsTreatment of rats with ethanolic extract of fruits of L. siceraria significantly lowers the risk of atherosclerosis by lowering percentage plaque area in aorta and grade of atheromatous lesions in hypercholesterolemic rats and also serum cholesterol, triglyceride, LDL–c, VLDL–c and increased HDL–c levels as well. The extract also induced lipoprotein lipase activity and significantly decreased cholesterogenesis in liver by reducing HMG-CoA reductase activity in hypercholeaterolemic rats. ConclusionIt can be concluded that ethanolic extract of fruits of L. siceraria contains active components which ameliorates the atheromatous lesions in rat aorta and lowers the risk of atherosclerosis in hypercholesterolemic rats.

Lipid-lowering effect of molluscan (Katelysia opima) glycosaminoglycan (GAG) in hypercholesterolemic induced rats

Identifying pharmacologically safe lipid-lowering 'deliverables' could potentiate therapeutic outcome for diet-induced atherogenesis. Accordingly, we investigated the potential of molluscan (Katelysia opima) glycosaminoglycan (GAG) in modulating the early lipid changes in atherogenesis. Wistar rats were fed a diet with (n=24) or without (n=6) hypercholesterolemic atherogenic CCT (rat chow supplemented with 4% cholesterol, 1% cholic acid, and 0.5% thiouracil) for 17 days. CCT-fed rates were (i) treated with isolated molluscan GAG (40 mg/kg/day, s.c.) for 10 days after the introduction of CCT diet, (ii) cotreated with GAG (40 mg/kg/day, s.c.) for 17 days, or (iii) treated with heparin (200 units/kg/day, s.c.) for 10 days after the introduction of CCT. The increases induced by CCT diet in the plasma levels of cholesterol, triglycerides, high-density lipoprotein, very-low-density lipoprotein, and low-density lipoprotein were completely attenuated with GAG treatment. Consistently, alterations induced by CCT diet in the levels of plasma lecithin cholesterol acyltransferase and lipoprotein lipase activities were restored to baseline levels with GAG treatment. Coherently, histology revealed a decrease associated with GAG treatment in the CCT-diet-induced foam cells (in aorta), tubular damages (kidney), and lipid accumulations (liver). Together, these results suggest that GAG may exert antiatherogenesis potential by significantly attenuating lipid modulations derived by a high-fat diet. Further, the data imply that the GAG extracts may comprehensively prevent hypercholesterolemia-associated tissue damage and could thus serve as a therapeutic deliverable for hypercholesterolemia.

Leu452His Mutation in Lipoprotein Lipase Gene Transfer Associated with Hypertriglyceridemia in Mice in vivo

Mutated mouse lipoprotein lipase (LPL) containing a leucine (L) to histidine (H) substitution at position 452 was transferred into mouse liver by hydrodynamics-based gene delivery (HD). Mutated-LPL (MLPL) gene transfer significantly increased the concentrations of plasma MLPL and triglyceride (TG) but significantly decreased the activity of plasma LPL. Moreover, the gene transfer caused adiposis hepatica and significantly increased TG content in mouse liver. To understand the effects of MLPL gene transfer on energy metabolism, we investigated the expression of key functional genes related to energy metabolism in the liver, epididymal fat, and leg muscles. The mRNA contents of hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), fatty acid-binding protein (FABP), and uncoupling protein (UCP) were found to be significantly reduced. Furthermore, we investigated the mechanism by which MLPL gene transfer affected fat deposition in the liver, fat tissue, and muscle. The gene expression and protein levels of forkhead Box O3 (FOXO3), AMP-activated protein kinase (AMPK), and peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) were found to be remarkably decreased in the liver, fat and muscle. These results suggest that the Leu452His mutation caused LPL dysfunction and gene transfer of MLPL in vivo produced resistance to the AMPK/PGC-1α signaling pathway in mice.

The effects of VEGF-A on atherosclerosis, lipoprotein profile, and lipoprotein lipase in hyperlipidaemic mouse models

The role of vascular endothelial growth factor (VEGF-A) in atherogenesis has remained controversial. We addressed this by comparing the effects of adenoviral VEGF-A gene transfer on atherosclerosis and lipoproteins in ApoE(-/-), LDLR(-/-), LDLR(-/-)ApoE(-/-), and LDLR(-/-)ApoB(100/100) mice. After 4 weeks on western diet, systemic adenoviral gene transfer was performed with hVEGF-A or control vectors. Effects on atherosclerotic lesion area and composition, lipoprotein profiles, and plasma lipoprotein lipase (LPL) activity were examined. On day 4, VEGF-A induced alterations in lipoprotein profiles and a significant negative correlation was observed between plasma LPL activity and VEGF-A levels. One month after gene transfer, no changes in atherosclerosis were observed in LDLR(-/-) and LDLR(-/-)ApoB(100/100) models, whereas both ApoE(-/-) models displayed increased en face lesion areas in thoracic and abdominal aortas. VEGF-A also reduced LPL mRNA in heart and white adipose tissue, whereas Angptl4 was increased, potentially providing further mechanistic explanation for the findings. VEGF-A gene transfer induced pro-atherogenic changes in lipoprotein profiles in all models. As a novel finding, VEGF-A also reduced LPL activity, which might underlie the observed changes in lipid profiles. However, VEGF-A was observed to increase atherosclerosis only in the ApoE(-/-) background, clearly indicating some mouse model-specific effects.

Macrophage lipoprotein lipase modulates the development of atherosclerosis but not adiposity

The role of macrophage lipoprotein lipase (LpL) in the development of atherosclerosis and adiposity was examined in macrophage LpL knockout (MLpLKO) mice. MLpLKO mice were generated using cre-loxP gene targeting. Loss of LpL in macrophages did not alter plasma LpL activity or lipoprotein levels. Incubation of apolipoprotein E (ApoE)-deficient β-VLDL with peritoneal macrophages from ApoE knockout mice lacking macrophage LpL (MLpLKO/ApoEKO) led to less cholesteryl ester formation than that found with ApoEKO macrophages. MLpLKO/ApoEKO macrophages had reduced intracellular triglyceride levels, with decreased CD36 and carnitine palmitoyltransferase-1 mRNA levels compared with ApoEKO macrophages, when incubated with VLDL. Although both MLpLKO/ApoEKO and ApoEKO mice developed comparable hypercholesterolemia in response to feeding with a Western-type diet for 12 weeks, atherosclerosis was less in MLpLKO/ApoEKO mice. Epididymal fat mass and gene expression levels associated with inflammation did not differ between the two groups. In conclusion, macrophage LpL plays an important role in the development of atherosclerosis but not adiposity.

Correction

HomeArteriosclerosis, Thrombosis, and Vascular BiologyVol. 32, No. 11Correction Free AccessCorrectionPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessCorrectionPDF/EPUBCorrection Originally published1 Nov 2012https://doi.org/10.1161/ATV.0b013e3182730081Arteriosclerosis, Thrombosis, and Vascular Biology. 2012;32:e147This article corrects the followingHuman ATP–Binding Cassette G1 Controls Macrophage Lipoprotein Lipase Bioavailability and Promotes Foam Cell FormationIn the article by Olivier et al, which appeared in the September issue of the journal (Arterioscler Thromb Vasc Biol. 2012;32:2223–2231. DOI: 10.1161/ATVBAHA.111.243519), Figure 1 appeared distorted. The correct representation of the figure is below and the online version of the article has been corrected.Download figureDownload PowerPointFigure 1. Reduced plasma lipoprotein lipase (LPL) activity in Abcg1−/− mice. A, LPL activity was measured in preheparin and postheparin plasmas (100 U/Kg) from Abcg1+/+ and Abcg1−/− mice after an overnight fast. One mU represents 1 nmol of free fatty acid released per minute. n=5 mice per group. B, LPL protein in preheparin and postheparin plasmas from Abcg1+/+ and Abcg1−/− mice. Each sample corresponds to pooled plasmas from 5 to 7 mice. C, Quantification of LPL fluorescence intensity detected in postheparin plasmas from Abcg1+/+ and Abcg1−/− mice. Abcg1 indicates ATP–binding cassette G1. Ns indicates non significant. Previous Back to top Next FiguresReferencesRelatedDetailsRelated articlesHuman ATP–Binding Cassette G1 Controls Macrophage Lipoprotein Lipase Bioavailability and Promotes Foam Cell FormationMaryline Olivier, et al. Arteriosclerosis, Thrombosis, and Vascular Biology. 2012;32:2223-2231 November 2012Vol 32, Issue 11 Advertisement Article InformationMetrics © 2012 American Heart Association, Inc.https://doi.org/10.1161/ATV.0b013e3182730081 Originally publishedNovember 1, 2012 PDF download Advertisement

Hepatic lipase activity is decreased in Japanese patients with type III hyperlipoproteinemia

BackgroundType III hyperlipoproteinemia (HLP), a disorder associated with a high incidence of premature cardiovascular diseases, is characterized by the accumulation of remnant lipoproteins in the plasma. The primary genetic defect in patients with type III HLP is the presence of apolipoprotein E2 (apoE2), an isoform of apoE, and accumulation of remnant lipoproteins in the plasma has been thought to be attributable to the presence of apoE2, which bind poorly to low density lipoprotein receptors, resulting in defective remnant lipoprotein clearance. On the other hand, the activity of hepatic lipase (HL), the enzyme that plays a pivotal role in the removal of remnant lipoproteins, in type III HLP has not been investigated. MethodsWe examined post-heparin plasma lipoprotein lipase (LPL) and HL activities in 7 patients with type III HLP. The activities of HL and LPL in post-heparin plasma were measured separately by an immunochemical method using antiserum specifically directed against HL. ResultsThe post-heparin plasma HL activity was significantly reduced, while the LPL activity was normal. ConclusionsReduced HL activity may account, at least in part, for the accumulation of remnant lipoproteins in the plasma, a characteristic feature of type III HLP.

Human ATP–Binding Cassette G1 Controls Macrophage Lipoprotein Lipase Bioavailability and Promotes Foam Cell Formation

The physiological function of the ATP-binding cassette G1 (ABCG1) transporter in humans is not yet elucidated, as no genetic disease caused by ABCG1 mutations has been documented. The goal of our study was, therefore, to investigate the potential role(s) of ABCG1 in lipid metabolism in humans. Here we report that among the 104 polymorphisms present in the ABCG1 gene, the analysis of the frequent functional rs1893590 and rs1378577 single nucleotide polymorphisms located in the regulatory region of ABCG1 in the Regression Growth Evaluation Statin Study population revealed that both ABCG1 single nucleotide polymorphisms were significantly associated with plasma lipoprotein lipase (LPL) activity. Moreover, we observed that plasma LPL activity was modestly reduced in Abcg1(-/-) mice as compared with control mice. Adipose tissue and skeletal muscle are the major tissues accounting for levels and activity of plasma LPL in the body. However, beyond its lipolytic action in the plasma compartment, LPL was also described to act locally at the cellular level. Thus, macrophage LPL was reported to promote foam cell formation and atherosclerosis in vivo. Analysis of the relationship between ABCG1 and LPL in macrophages revealed that the knockdown of ABCG1 expression (ABCG1 knockdown) in primary cultures of human monocyte-derived macrophages using small interfering RNAs led to a marked reduction of both the secretion and activity of LPL. Indeed, LPL was trapped at the cell surface of ABCG1 knockdown human monocyte-derived macrophages, likely in cholesterol-rich domains, thereby reducing the bioavailability and activity of LPL. As a consequence, LPL-mediated lipid accumulation in human macrophage foam cells in the presence of triglyceride-rich lipoproteins was abolished when ABCG1 expression was repressed. We presently report that ABCG1 controls LPL activity and promotes lipid accumulation in human macrophages in the presence of triglyceride-rich lipoproteins, thereby suggesting a potential deleterious role of macrophage ABCG1 in metabolic situations associated with high levels of circulating triglyceride-rich lipoproteins together with the presence of macrophages in the arterial wall.

Biological and functional characteristics of a novel low–molecular weight antagonist of glucose‐dependent insulinotropic polypeptide receptor, SKL‐14959, in vitro and in vivo

We recently discovered a glucose-dependent insulinotropic polypeptide (GIP) receptor antagonist, SKL-14959. GIP plays a role in the glucose and lipid metabolism, and is associated with obesity and insulin resistance. Therefore, we aimed to ascertain the inhibitory potency and glucose and lipid metabolism of SKL-14959. SKL-14959 was evaluated for its binding affinity to each GIP, glucagon-like peptide-1 (GLP-1) and glucagon receptors by each labelled and non-labelled ligand; GIP-stimulated cyclic AMP (cAMP) production in CHO cells expressing human GIP receptor in vitro. Oral and intraperitoneal glucose tolerance tests (OGTT and IPGTT) were performed to examine the insulinotropic effect on endogenous and exogenous GIP. Oil tolerance tests were also conducted to examine the lipid metabolism and the postheparin plasma lipase activity, lipoprotein lipase (LPL) and hepatic lipase (HL). SKL-14959 selectively bound to GIP receptor and inhibited GIP-stimulated cAMP production with the Ki value of 55 nM and an IC(50) value of 2.9 µM, respectively. SKL-14959·Na significantly increased blood glucose levels, inhibited insulin secretion in OGTT and inhibited the plasma glucose lowering of exogenous GIP in IPGTT. Furthermore, SKL-14959 increased plasma triacylglycerol (TG) levels as well as suppressed the postheparin plasma lipase activity in an oil load test. These data indicate that SKL-14959 is distinguished in the physiological phenotype of GIP following direct binding to the receptor.

Effects of NO-1886, a Lipoprotein Lipase Promoting Agent, on Homozygous and Heterozygous Watanabe Heritable Hyperlipidaemic Rabbits

The novel compound NO-1886 ([4-(4-bromo-2-cyano-phenylcarbamoyl)-benzyl]-phosphonic acid diethyl ester, CAS 133208-93-2) is a lipoprotein lipase (LPL) activator, and long term administration of NO-1886 protects against the development of experimental atherosclerosis in rats and rabbits. In the present experiments, the effects of this compound were examined in Watanabe heritable hyperlipidaemic (WHHL) rabbits, an animal model for familial hypercholesterolemia lacking low density lipoprotein (LDL) receptors. NO-1886 increased postheparin plasma LPL activity, resulting in a reduction of plasma triglycerides with concomitant elevation of HDL cholesterol in heterozygous WHHL rabbits. However, the compound did not cause any changes in plasma lipids and postheparin plasma LPL activity in homozygous WHHL rabbits. The different responses suggest that the effects of NO-1886 may be either mediated by LDL receptors, or that persistent exposure to extreme hypercholesterolemia might affect the cellular response to this particular compound in homozygous WHHL rabbits.

EFFECT OF NARINGENIN (CITRUS FLAVANONE) ON LIPID PROFILE IN ETHANOL-INDUCED TOXICITY IN RATS

ABSTRACT Our aim was to investigate the effect of naringenin on hyperlipidemia induced by ethanol. Groups 1 and 2 rats received isocaloric glucose and 0.5% carboxymethyl cellulose (CMC); groups 3 and 4 received 20% (6 g/kg body weight p.o.) ethanol everyday for 60 days. Groups 2 and 4 rats received naringenin (50 mg/kg body weight/day in 0.5% CMC) everyday during the last 30 days of the experiment. There were increased levels of plasma total cholesterol (TC), triglycerides (TG), free fatty acids (FFA), very low density lipoproteins (VLDL), low density lipoproteins (LDL) and tissue TC, TG, FFA, HMG CoA reductase and alterations in collagen content of ethanol-fed rats, which on naringenin supplementation showed decreased levels of plasma and tissue TC, TG and FFA, HMG CoA reductase and collagen content. There was a significant decrease in the levels of plasma high density lipoprotein (HDL), lipoprotein lipase (LPL) and lecithin cholesterol acyltransferase (LCAT) of ethanol-fed rats, which on naringenin supplementation showed an increase in the levels of HDL and LPL with ethanol alone–fed rats. Naringenin can efficiently prevent the accumulation of plasma lipids and lipoproteins. PRACTICAL APPLICATIONS Alcohol abuse, alcohol intolerance, alcohol dependence and other alcohol related disabilities are some of the most challenging public health problems. A phytotherapeutic approach in the new drug development can provide many valuable drugs from traditional plant sources. The use of herbal medicines for the treatment of hepatotoxicity has gained importance throughout the world. Renewed attention to alternative medicine and natural therapies has stimulated new wave of research interest in traditional practice, and there is a need to look for more potent agents with lesser side effects. The present study is aimed to identify the efficacy of naringenin by uncovering its underlying mechanism of action against alcohol-induced liver disease for effective therapy. Naringenin, an important flavonoid, is widely present in fruits and vegetables. Naringenin is known to possess a number of significant beneficial properties. If the biochemical and histological findings are positive, indicating the marked hepatoprotective efficacy of naringenin, it could be subjected to human trials in the future.

ATP-binding cassette G5/G8 deficiency causes hypertriglyceridemia by affecting multiple metabolic pathways

Mutations in ABCG5 or ABCG8 transporters are responsible for sitosterolemia, an autosomal recessive disease characterized by the accumulation of plant sterols. The aim of this study was to investigate the effects of ABCG5 and ABCG8 deficiency on TG metabolism in mice. Experiments were carried out in wild-type (G5/G8+/+) mice, mice heterozygous for ABCG5 and ABCG8 deficiency (G5/G8+/−) and ABCG5/G8-deficient (G5/G8−/−) mice fed a chow diet. Plasma TG were 2.6 and 4.3-fold higher in fasted G5/G8+/− and G5/G8−/− mice, respectively, than in G5/G8+/+ mice. Postprandial TG were 5-fold higher in G5/G8−/− mice. TG metabolism studies indicate that: first, the fractional catabolic rate was significantly lower in G5/G8+/− (1.3-fold) and G5/G8−/− mice (1.5-fold) compared to G5/G8+/+ and postheparin plasma lipoprotein lipase activities were significantly lower in G5/G8+/− (1.8-fold) and G5/G8−/− mice (5.4-fold) than in G5/G8+/+. Second, liver TG secretion was 1.3-fold higher in G5/G8+/− and G5/G8−/− than in G5/G8+/+ mice and this was associated with an increase in liver LXR, FAS, ACAC and CD36 gene expression. Third, TG intestinal secretion, determined after an oral fat gavage of glycerol tri[9,10(n)-3H] oleate, was 5.8-fold higher in G5/G8−/− than in G5/G8+/+ mice. Also, the HOMA index was 2.6-fold higher in G5/G8−/− than in G5/G8+/+ mice, reflecting a degree of insulin resistance. In conclusion, ABCG5/G8 deficiency in mice fed a chow diet markedly raises TG levels by impairing TG catabolism and by increasing liver and intestinal TG secretion.

Genetic variations at the lipoprotein lipase gene influence plasma lipid concentrations and interact with plasma n-6 polyunsaturated fatty acids to modulate lipid metabolism

ObjectiveTo investigate whether seven common single nucleotide polymorphisms (SNPs) at the lipoprotein lipase (LPL) locus interact with total plasma fatty acids to modulate plasma lipid metabolism in metabolic syndrome (MetS) patients. MethodsPlasma fatty acid composition, plasma lipid concentrations and LPL SNPs were determined in 452 subjects with the MetS in the European LIPGENE human study and were repeated in 1754 subjects from the LIPGENE-SU.VI.MAX Study. ResultsTriglycerides (TG) were lower, and HDL higher in the carriers of rs328 and rs1059611 in the SUVIMAX cohort (all P<0.001), and these findings showed a similar, non-significant trend in LIPGENE cohort. In this last cohort, we found a gene–fatty acids interaction, as the carriers of the minor allele displayed a lower fasting TG and triglyceride rich lipoproteins-TG (TRL-TG) concentrations only when they had n-6 polyunsaturated fatty acids below the median (all P<0.05). Moreover, subjects carrying the minor allele for rs328 SNP and with a low level of n-6 PUFA displayed higher nonesterified fatty acid (NEFA) plasma concentrations as compared with homozygous for the major allele (P=0.034). Interestingly, the n-6 PUFA-dependent associations between those SNPs and TG metabolism were also replicated in subjects without MetS from the SU.VI.MAX cohort. ConclusionTwo genetic variations at the LPL gene (rs328 and rs1059611) influence plasma lipid concentrations and interact with plasma n-6 PUFA to modulate lipid metabolism. The knowledge of new genetic factors together with the understanding of these gene–nutrient interactions could help to a better knowledge of the pathogenesis in the MetS.

Preventive effect of Ibrolipim on suppressing lipid accumulation and increasing lipoprotein lipase in the kidneys of diet-induced diabetic minipigs

BackgroundThe role of renal lipoprotein lipase (LPL) per se in kidney diseases is still controversial and obscure. The purpose of this study was to observe the preventive effects of Ibrolipim, a LPL activator, on lipid accumulation and LPL expression in the kidneys of minipigs fed a high-sucrose and high-fat diet (HSFD).MethodsMale Chinese Bama minipigs were fed a control diet or HSFD with or without 0.1 g/kg/day Ibrolipim for 5 months. Body weight, plasma glucose, insulin, lipids, LPL activity, and urinary microalbumin were measured. Renal tissue was obtained for detecting LPL activity and contents of triglyceride and cholesterol, observing the renal lipid accumulation by Oil Red O staining, and examining the mRNA and protein expression of LPL by real time PCR, Western Blot and immunohistochemistry.ResultsFeeding HSFD to minipigs caused weight gain, hyperglycemia, hyperinsulinemia, hyperlipidemia and microalbuminuria. HSFD increased plasma LPL activity while it decreased the mRNA and protein expression and activity of LPL in the kidney. The increases in renal triglyceride and cholesterol contents were associated with the decrease in renal LPL activity of HSFD-fed minipigs. In contrast, supplementing Ibrolipim into HSFD lowered body weight, plasma glucose, insulin, triglyceride and urinary albumin concentrations while it increased plasma total cholesterol and HDL-C. Ibrolipim suppressed the renal accumulation of triglyceride and cholesterol, and stimulated the diet-induced down-regulation of LPL expression and activity in the kidney.ConclusionsIbrolipim exerts renoprotective and hypolipidemic effects via the increase in renal LPL activity and expression, and thus the increased expression and activity of renal LPL play a vital role in suppressing renal lipid accumulation and ameliorating proteinuria in diet-induced diabetic minipigs.

Activation of lipoprotein lipase increases serum high density lipoprotein 2 cholesterol and enlarges high density lipoprotein 2 particles in rats

It is known that postheparin plasma lipoprotein lipase (LPL) activity correlates with serum high density lipoprotein cholesterol (HDL-C) levels in humans and animals. Furthermore, LPL has been reported to cause enlargement of HDL particle size in vitro. However, these effects have not yet been experimentally proven. The aim of this study was to determine whether LPL has a role in increase in HDL-C and enlargement of HDL particle by activating the LPL function with NO-1886, the LPL promoting agent. NO-1886 administration increased postheparin plasma LPL activity without influencing hepatic triglyceride lipase activity. NO-1886 increased serum HDL2-cholesterol (HDL2-C) concentration and enlarged HDL2 particle size, but did not increase serum HDL3-cholesterol concentration or enlarge HDL3 particle size. Also, serum HDL2-C concentrations were positively correlated with HDL2 particle size (r=0.910). Our study demonstrates that the LPL activation induced with NO-1886 may cause production of HDL2-C by catabolism of triglyceride-rich lipoproteins and enlarges HDL2 particle size in rats.

The Effect of Diet on the Response of Low-density Lipoprotein Receptor Knockout Mice to the Liver X Receptor Agonist T1317

It has been previously observed that low-density lipoprotein receptor knockout (LDLR--/--) mice fed a Western-type diet without cholate and given the liver X receptor agonist T1317 develop a persistent and enhanced hypertriglyceridemia. In contrast, LDLR--/-- mice fed a Paigen diet with cholate exhibit only a transient increase in plasma triglycerides when given T1317. Cholate as an activator of farnesoid X receptor may attenuate T1317-induced triglyceridemia. To determine if cholate was responsible for this transient nature of the hypertriglyceridemia, we orally administered T1317 to LDLR--/-- mice fed a modified Paigen diet without cholate. T1317 transiently elevated plasma triglycerides by increasing plasma very-low-density lipoprotein. Cholesterol and triglyceride levels in plasma very-low-density lipoprotein in T1317-treated mice decreased from peak levels to levels found in vehicle-treated mice after 8 weeks of treatment. A gradual decline of hepatic cholesterol and a transient increase in hepatic triglycerides were also observed in T1317-treated mice. T1317 only transiently activated the expression of genes related to liver de novo lipogenesis, whereas genes related to lipid metabolism were induced in T1317-treated mice, including a gradual increase in plasma lipoprotein lipase activity. Atheroprotective effects of T1317 were observed in the innominate artery and aortic arch but not in the aortic sinus. This work indicates that some component(s) in the Paigen diet other than cholate affect the T1317-induced gene expression profile and ameliorate its effects on lipid synthesis, which lead to hypertriglyceridemia and fatty liver. These findings are important for liver X receptor-related pharmaceutical development for the treatment of cardiovascular disease.

163 OLD MYTHS AND NEW INSIGHTS: INTERACTION OF LDL-SUBCLASSES WITH HUMAN FIBROBLASTS

A comparison of post-heparin and pre-heparin plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) on the metabolism of remnant lipoproteins (RLPs) has not been reported yet.Healthy volunteers were injected with heparin for LPL and HTGL determination in the fasting (8:00) and postprandial (20:00) plasma on the same day. Plasma total cholesterol (TC), triglycerides (TG), LDL-C, HDL-C, small dense LDL (sdLDL)-C, remnant lipoprotein (RLP)-C, RLP-TG, the RLP-TG/RLP-C ratio, adiponectin and apoCIII were measured.LPL activity and concentration in the post-heparin plasma exhibited a significant inverse correlation with TG, RLP-C, RLP-TG, and RLP particle size estimated as RLP-TG/RLP-C ratio and sdLDL-C, and positively correlated with HDL-C. HTGL was only inversely correlated with HDL-C. LPL concentration in the pre-heparin plasma was also inversely correlated with the RLP-TG/RLP-C ratio and other lipoprotein parameters. Adiponectin was inversely correlated with RLP-TG/RLP-C ratio and apoC III was positively correlated with RLP-TG/RLP-C ratio, but not correlated with LPL activity.LPL activity and concentration were inversely and significantly correlated with the particle size of RLP in both the post-heparin and pre-heparin plasma. Those results suggest that LPL concentration in pre-heparin plasma can take the place of LPL activity in the post-heparin plasma.

Determination of lipoprotein lipase activity using a novel fluorescent lipase assay

A novel, real-time, homogeneous fluorogenic lipoprotein lipase (LPL) assay was developed using a commercially available substrate, the EnzChek lipase substrate, which is solubilized in Zwittergent. The triglyceride analog substrate does not fluoresce, owing to apposition of fluorescent and fluorescent quenching groups at the sn-1 and sn-2 positions, respectively, fluorescence becoming unquenched upon release of the sn-1 BODIPY FA derivative following hydrolysis. Increase in fluorescence intensity at 37°C was proportional to LPL concentration. The assay was more sensitive than a similar assay using 1,2-O-dilauryl-rac-glycero-3-glutaric acid-(6-methylresorufin ester) and was validated in biological samples, including determination of LPL-specific activity in postheparin mouse plasma. The simplicity and reproducibility of the assay make it ideal for in vitro, high-throughput screening for inhibitors and activators of LPL, thus expediting discovery of drugs of potential clinical value.

Evidence for a Shift to Anaerobic Metabolism in Adipose Tissue in Efavirenz-Containing Regimens for HIV with Different Nucleoside Backbones

Antiretroviral (ARV) treatment has been associated with abnormalities in lipid and mitochondrial metabolism. We compared patterns of gene expression in the subcutaneous adipose tissue (SAT) of HIV-positive subjects before and after 18-24 months of ARV therapy with HIV-negative controls. HIV patients naive to ARV were randomized to receive zidovudine (AZT), lamivudine (3TC) with efavirenz (EFV) or tenofovir disoproxil fumarate (TDF) with emtricitabine (FTC) and EFV. Healthy controls (n=15) were matched for age, ethnicity and gender. Patients on a regimen containing abacavir (ABC), 3TC and EFV for 18-24 months were also tested. Genes involved in adipocyte glucocorticoid, lipid and mitochondrial metabolism, and adipocyte differentiation, were profiled with real-time PCR. AZT led to increased visceral adipose tissue (VAT; P=0.012) and VAT:SAT ratio (P=0.036), whereas TDF increased SAT (P=0.047) and peripheral fat/lean body mass ratio (P=0.017). HIV treatment-naive patients had lower plasma lipoprotein lipase (LPL) activity (P=0.0001) versus controls (remaining below controls after ARV; P=0.038-0.0001). The overall pattern of gene expression was similar across all treatment groups, being most marked with AZT and least with TDF. There was up-regulation of peroxisome proliferator-activated receptor-γ coactivator-1α, uncoupling protein-2 and hexose 6-phosphate dehydrogenase, and down-regulation of nuclear respiratory factor-1, cytochrome oxidase B, cytochrome c oxidase-4, uncoupling protein-3, 11β-hydroxysteroid dehydrogenase type-1, glucocorticoid receptor-α, fatty acid synthase, fatty acid binding protein-4, LPL and hormone sensitive lipase (18-24 months post-treatment versus pretreatment levels and controls; P<0.05 to <0.0001). The decreased expression of genes involved in lipid and mitochondrial metabolism 18-24 months post-ARV treatment in SAT of HIV patients, in conjunction with the increase in uncoupling protein-2 and decrease in cytochrome oxidase B gene expression, provides evidence of mitochondrial dysfunction and a shift to anaerobic metabolism within SAT in EFV-containing ARV regimens.