Postheparin Plasma Lipoprotein Lipase Research Articles

Significant but partial lipoprotein lipase functional loss caused by a novel occurrence of rare LPL biallelic variants

BackgroundLipoprotein lipase (LPL) plays a crucial role in triglyceride hydrolysis. Rare biallelic variants in the LPL gene leading to complete or near-complete loss of function cause autosomal recessive familial chylomicronemia syndrome. However, rare biallelic LPL variants resulting in significant but partial loss of function are rarely documented. This study reports a novel occurrence of such rare biallelic LPL variants in a Chinese patient with hypertriglyceridemia-induced acute pancreatitis (HTG-AP) during pregnancy and provides an in-depth functional characterization.MethodsThe complete coding sequences and adjacent intronic regions of the LPL, APOC2, APOA5, LMF1, and GPIHBP1 genes were analyzed by Sanger sequencing. The aim was to identify rare variants, including nonsense, frameshift, missense, small in-frame deletions or insertions, and canonical splice site mutations. The functional impact of identified LPL missense variants on protein expression, secretion, and activity was assessed in HEK293T cells through single and co-transfection experiments, with and without heparin treatment.ResultsTwo rare LPL missense variants were identified in the patient: the previously reported c.809G > A (p.Arg270His) and a novel c.331G > C (p.Val111Leu). Genetic testing confirmed these variants were inherited biallelically. Functional analysis showed that the p.Arg270His variant resulted in a near-complete loss of LPL function due to effects on protein synthesis/stability, secretion, and enzymatic activity. In contrast, the p.Val111Leu variant retained approximately 32.3% of wild-type activity, without impacting protein synthesis, stability, or secretion. Co-transfection experiments indicated a combined activity level of 20.7%, suggesting no dominant negative interaction between the variants. The patient’s post-heparin plasma LPL activity was about 35% of control levels.ConclusionsThis study presents a novel case of partial but significant loss-of-function biallelic LPL variants in a patient with HTG-AP during pregnancy. Our findings enhance the understanding of the nuanced relationship between LPL genotypes and clinical phenotypes, highlighting the importance of residual LPL function in disease manifestation and severity. Additionally, our study underscores the challenges in classifying partial loss-of-function variants in classical Mendelian disease genes according to the American College of Medical Genetics and Genomics (ACMG)’s variant classification guidelines.

A novel homozygous nonsense variant of LMF1 in pregnancy-induced hypertriglyceridemia with acute pancreatitis

Hypertriglyceridemia (HTG)-induced pancreatitis during pregnancy could lead to maternal and fetal death. However, its genetic bases are not fully understood, and its treatment strategies are yet to be established.Here we report a case with a novel homozygous nonsense variant of LMF1 in pregnancy-associated HTG with acute pancreatitis.Our patient had childhood-onset severe HTG that had been well-controlled by dietary management in the non-pregnant period with plasma triglyceride (TG) levels at around 200 mg/dL. Milky plasma was noted at the first-trimester pregnancy checkup, followed by a severe increase in plasma TG (10,500 mg/dL) that resulted in pancreatitis in the last trimester. The implementation of strict dietary fat restriction (less than 4 grams per day) reduced plasma TG levels and led to successful delivery. Exome sequencing revealed a novel homozygous nonsense variant in LMF1 (c.697C>T, p.Arg233Ter). The activities of lipoprotein lipase (LPL) and hepatic lipase in post-heparin plasma were not abolished but reduced. The use of pemafibrate decreased plasma TG levels with a concomitant increase in LPL activity.HTG in childhood or early pregnancy is commonly assumed to be polygenic in origin but should be regarded as a feature suggestive of monogenic hyperchylomicronemia. Adequate TG monitoring and dietary fat restriction should be implemented to prevent potentially lethal events of pancreatitis.

Corn Oil, Palm Oil and Butterfat Fractions Affect Postprandial Lipemia and Lipoprotein Lipase in Meal-Fed Rats

Our objective was to investigate the time course of postprandial lipemia and lipolytic activity in male Sprague-Dawley rats trained to eat meals containing butterfat fractions, palm oil or corn oil. Baseline and postprandial blood samples were obtained via a carotid cannula in rats fed the experimental diets for 4 wk. Rats fed saturated fats compared with corn oil showed a significantly greater peak increase in postprandial triacylglycerol concentrations. Corn oil ingestion resulted in significantly lower concentrations of cholesterol and triacylglycerol in plasma and significantly less triacylglycerol accumulation (millimoles per liter per 24 h) compared with ingestion of saturated fats. Postheparin plasma lipoprotein lipase activity and plasma insulin concentration were generally greater with ingestion of corn oil compared with palm oil or butterfat. Palm oil ingestion resulted in a biphasic plasma triacylglycerol response curve and greater postheparin plasma lipoprotein lipase activity compared with butterfat ingestion, suggesting differential effects of saturated fats on postprandial lipemia. Our results indicate that greater postprandial lipemia with ingestion of saturated fats compared with corn oil may be due in part to slower plasma triacylglycerol clearance.

Correlation between chylomicronemia diagnosis scores and post-heparin lipoprotein lipase activity

IntroductionSustained chylomicronemia is a defect in post-prandial triglyceride management characterized by severe hypertriglyceridemia (triglyceride > 10 mmol/L) due to functional or genetic defects in lipoprotein lipase (LPL)-mediated triglyceride-rich lipoprotein lipolysis. Familial chylomicronemia syndrome (FCS) is a rare mendelian form of chylomicronemia caused by loss-of–function variants in LPL or LPL-related genes. Most individuals with chylomicronemia however present multifactorial chylomicronemia (MCS), in which LPL bio-availability and activity are variable. FCS and MCS differ in terms of clinical characteristics and risk of disease, and diagnosis scoring systems have been proposed to accurately distinguish FCS from MCS. ObjectiveThe aim of this study was to assess the strength of the relationship between plasma post-heparin LPL activity and two published chylomicronemia diagnosis scoring systems. Design and MethodsPost-heparin plasma LPL activity was measured using colorimetric assays in a sample of 29 subjects with sustained chylomicronemia (20 FCS and 9 MCS).Chylomicronemia diagnosis scores were obtained for all subjects using the scoring system A (model A), which integrates apolipoprotein B and free glycerol, a surrogate marker of triglyceride hydrolysis, and the scoring system B (model B). Correlation analyses were conducted to estimate the linear relationship between LPL activity and the two diagnosis scoring systems. ResultsThere was a significant (p < 0.001) difference in post-heparin LPL activity between FCS and MCS. Both scoring systems significantly correlated with post-heparin LPL activity (model A: rs = −0.64, p < 0.001; model B: rs = −0.54, p = 0.002). ConclusionsThese result suggest that chylomicronemia diagnosis scoring systems correlate with LPL activity and adequately contribute to distinguish FCS from MCS.

Role of lipoprotein lipase activity measurement in the diagnosis of familial chylomicronemia syndrome

Activity assays for lipoprotein lipase (LPL) are not standardised for use in clinical settings. This study sought to define and validate a cut-off points based on a ROC curve for the diagnosis of patients with familial chylomicronemia syndrome (FCS). We also evaluated the role of LPL activity in a comprehensive FCS diagnostic workflow. A derivation cohort (including an FCS group (n=9), a multifactorial chylomicronemia syndrome (MCS) group (n=11)), and an external validation cohort (including an FCS group (n=5), a MCS group (n=23) and a normo-triglyceridemic (NTG) group (n=14)), were studied. FCS patients were previously diagnosed by the presence of biallelic pathogenic genetic variants in the LPL and GPIHBP1 genes. LPL activity was also measured. Clinical and anthropometric data were recorded, and serum lipids and lipoproteins were measured. Sensitivity, specificity and cut-offs for LPL activity were obtained from a ROC curve and externally validated. All post-heparin plasma LPL activity in the FCS patients were below 25.1 mU/mL, that was cut-off with best performance. There was no overlap in the LPL activity distributions between the FCS and MCS groups, conversely to the FCS and NTG groups. We conclude that, in addition to genetic testing, LPL activity in subjects with severe hypertriglyceridemia is a reliable criterium in the diagnosis of FCS when using a cut-off of 25.1 mU/mL (25% of the mean LPL activity in the validation MCS group). We do not recommend the NTG patient based cut-off values due to low sensitivity.

An automated method for measuring lipoprotein lipase and hepatic triglyceride lipase activities in post-heparin plasma

BackgroundLipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) play a central role in triglyceride-rich lipoprotein metabolism by catalyzing the hydrolysis of triglycerides. Quantification of LPL and HTGL activity is useful for diagnosing lipid disorders, but there has been no automated method for measuring these lipase activities. MethodsThe automated kinetic colorimetric method was used for assaying LPL and HTGL activity in the post-heparin plasma using the natural long-chain fatty acid 2-diglyceride as a substrate. LPL activity was determined with apoCII and HTGL activity was determined without apoCII with 2 channel of auto-analyzer. ResultsThe calibration curve for dilution tests of the LPL and HTGL activity assay ranged from 0.0 to 500 U/L. Within-run CV was obtained within a range of 5%. No interference was observed in the testing of specimens containing potentially interfering substances. The measurement range of LPL activity in the post-heparin plasma was 30–153 U/L, while HTGL activity was 135–431 U/L in normal controls. ConclusionsThe L PL and HTGL activity assays are applicable to quantitating the LPL and HTGL activity in the post-heparin plasma. This assay is more convenient and faster than radiochemical assay and highly suitable for the detection of lipid disorders.

Molecular basis of the familial chylomicronemia syndrome in patients from the National Dyslipidemia Registry of the Spanish Atherosclerosis Society

Familial chylomicronemia syndrome (FCS) is an extremely rare lipoprotein disorder caused by mutations in at least 5 genes of the lipoprotein lipase (LPL) complex. This work shows the molecular analysis of patients diagnosed with FCS, who attended the Spanish Arteriosclerosis Society lipid units and were included in the National Dyslipidemia Registry. Among the 238 patients registered with severe hypertriglyceridemia (fasting triglycerides>1000mg/dL), 26 were diagnosed with FCS as they had confirmed postheparin plasma LPL activity deficiency and/or homozygosity for loss-of-function mutations in LPL, GPIHBP1, APOC2, LMF1, or Apolipoprotein A5 (APOA5). Among the 26 FCS cases, 23 had mutations in the homozygous state: 19 in LPL and 4 in the GPIHBP1 gene. The molecular analysis revealed 3 novel mutations: 2 in LPL, in 2 unrelated patients (c.312delA; p.Asp105Thrfs*66 and c.629A>G; p.His210Arg), and 1 in GPHIBP1 in a third patient (c.502delC; p.Leu168Serfs*83). These 3 patients had confirmed lack of LPL activity. Three additional patients with confirmed LPL activity deficiency were heterozygous carriers of mutations in the genes analyzed. Among these, we found 2 novel mutations in APOA5 (c.50-1G>A and c.326_327insC; p.Tyr110Leufs*158). We have identified 5 novel pathogenic mutations: 2 in LPL, 1 in GPIHBP1, and 2 in the APOA5 gene. The genetic defaults accounting for the LPL activity deficiency of 23 of them have been clearly identified and 3 patients, who harbored mutations in heterozygosity, were diagnosed based on LPL activity deficiency, which raises the question of the involvement of new genes in the manifestation of FCS.

Chylomicrons against light scattering: The battle for characterization.

Chylomicrons (CMs) are lipoprotein particles circulating in blood and transporting dietary lipids. Optically speaking, CMs are small compared to the wavelength of visible light and widely distributed by the size and refractive index (RI). Consequently, intensity of light scattered by the CMs scales with up to the sixth power of their size, hampering simultaneous analysis of 60 and 600 nm CMs. We present an accurate method for quantitative characterization of large-size CM subpopulation by the distributions over size and RI. For the first time the CM characteristics have been determined at a single particle level based on angle-resolved light-scattering measurements. We applied the developed method to 2 key processes relating to CM metabolism, namely in vivo dynamics of CMs in blood plasma after a meal and in vitro lipolysis of CMs by the lipoprotein lipase in postheparin plasma. We have observed the substantial variations in CM concentration, size and RI distributions. This opens the way for a multitude of medical applications involving screening of CM metabolism, which we exemplified by revealing large differences in CM characteristics after a 12-hour fast between a healthy volunteer and a patient with atherosclerosis.

Inulin Improves Postprandial Hypertriglyceridemia by Modulating Gene Expression in the Small Intestine.

Postprandial hyperlipidemia is an important risk factor for cardiovascular diseases in the context of obesity. Inulin is a non-digestible carbohydrate, known for its beneficial properties in metabolic disorders. We investigated the impact of inulin on postprandial hypertriglyceridemia and on lipid metabolism in a mouse model of diet-induced obesity. Mice received a control or a western diet for 4 weeks and were further supplemented or not with inulin for 2 weeks (0.2 g/day per mouse). We performed a lipid tolerance test, measured mRNA expression of genes involved in postprandial lipid metabolism, assessed post-heparin plasma and muscle lipoprotein lipase activity and measured lipid accumulation in the enterocytes and fecal lipid excretion. Inulin supplementation in western diet-fed mice decreases postprandial serum triglycerides concentration, decreases the mRNA expression levels of Cd36 (fatty acid receptor involved in lipid uptake and sensing) and apolipoprotein C3 (Apoc3, inhibitor of lipoprotein lipase) in the jejunum and increases fecal lipid excretion. In conclusion, inulin improves postprandial hypertriglyceridemia by targeting intestinal lipid metabolism. This work confirms the interest of using inulin supplementation in the management of dyslipidemia linked to obesity and cardiometabolic risk.

Striated muscle gene therapy for the treatment of lipoprotein lipase deficiency.

Excessive circulating triglycerides due to reduction or loss of lipoprotein lipase activity contribute to hypertriglyceridemia and increased risk for pancreatitis. The only gene therapy treatment for lipoprotein lipase deficiency decreases pancreatitis but minimally reduces hypertriglyceridemia. Synthesized in multiple tissues including striated muscle and adipose tissue, lipoprotein lipase is trafficked to blood vessel endothelial cells where it is anchored at the plasma membrane and hydrolyzes triglycerides into free fatty acids. We conditionally knocked out lipoprotein lipase in differentiated striated muscle tissue lowering striated muscle lipoprotein lipase activity causing hypertriglyceridemia. We then crossed lipoprotein lipase striated muscle knockout mice with mice possessing a conditional avian retroviral receptor gene and injected mice with either a human lipoprotein lipase retrovirus or an mCherry control retrovirus. Post-heparin plasma lipoprotein lipase activity increased for three weeks following human lipoprotein lipase retroviral infection compared to mCherry infected mice. Human lipoprotein lipase infected mice had significantly lower blood triglycerides compared to mCherry controls and were comparable to wild-type blood triglyceride levels. Thus, targeted delivery of human lipoprotein lipase into striated muscle tissue identifies a potential therapeutic target for lipoprotein lipase deficiency.

Streptozotocin-Treated High Fat Fed Mice: A New Type 2 Diabetes Model Used to Study Canagliflozin-Induced Alterations in Lipids and Lipoproteins.

The pharmacological effects of type 2 diabetes (T2DM) medications on lipoprotein metabolism are difficult to assess in preclinical models because those created failure to replicate the human condition in which insulin deficiency is superimposed on obesity-related insulin resistance. To create a better model, we fed mice with high fat (HF) diet and treated the animals with low dose streptozotocin (STZ) to mimic T2DM. We used this model to evaluate the effects of canagliflozin (CANA), a drug that reduces plasma glucose by inhibiting the sodium-glucose transporter 2 (SGLT2), which mediates ~90% of renal glucose reabsorption] on lipid and lipoprotein metabolism. After 6 weeks of CANA (30 mg/kg/day) treatment, the increase in total plasma cholesterol in HF-STZ diabetic mice was reversed, but plasma triglycerides were not affected. Lipoprotein fractionation and cholesterol distribution analysis showed that CANA kept HDL-Cholesterol, LDL-Cholesterol, and IDL-Cholesterol levels steady while these lipoprotein species were increased in placebo- and insulin-treated control groups. CANA treatment of HF-STZ mice reduced post-heparin plasma lipoprotein lipase (LPL) activity at 2 (-40%) and 5 (-30%) weeks compared to placebo. Tissue-specific LPL activity following CANA treatment showed similar reduction. In summary, CANA prevented the total cholesterol increase in HF-STZ mice without effects on plasma lipids or lipoproteins, but did decrease LPL, implying a potential role of LPL-dependent lipoprotein metabolism in CANA action. These effects did not recapitulate the effect of SGLT2 inhibitors on lipids and lipoproteins in human, suggesting that a better murine T2DM model (such as the ApoB100 humanized CETP-overexpressing mouse) is needed next.

Comparison of the effect of post-heparin and pre-heparin lipoprotein lipase and hepatic triglyceride lipase on remnant lipoprotein metabolism

BackgroundA 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. MethodsHealthy 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. ResultsLPL 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. ConclusionLPL 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.

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.

The ddY mouse: a model of postprandial hypertriglyceridemia in response to dietary fat

Postprandial hyperlipidemia (lipemia) is a risk factor for atherosclerosis. However, mouse models of postprandial hyperlipidemia have not been reported. Here, we report that ddY mice display marked postprandial hypertriglyceridemia in response to dietary fat. In ddY mice, the fasting serum total triacylglyceride (TG) concentration was 134 mg/dl, which increased to 571 mg/dl after an intragastric safflower oil load (0.4 ml/mouse). In C57BL/6J mice, these concentrations were 57 and 106 mg/dl, respectively. By lipoprotein analysis, ddY mice showed increases in chylomicron- and VLDL-sized TG fractions (remnants and VLDL) after fat load. In C57BL/6J mice, post-heparin plasma LPL activity after fat load was increased 4.8-fold relative to fasting. However, in ddY mice, the increase of LPL activity after fat load was very small (1.2-fold) and not significant. High fat feeding for 10 weeks led to obesity in ddY mice. A difference in LPL amino acid composition between C57BL/6J and ddY mice was detected but was deemed unlikely to cause hypertriglyceridemia because hypertriglyceridemia was not evident in other strains harboring the ddY-type LPL sequence. These findings indicate that postprandial hypertriglyceridemia in ddY mice is induced by decreased LPL activity after fat load and is associated with obesity induced by a high-fat diet.

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.

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.

The lipid-lowering effect of dietary proanthocyanidins in rats involves both chylomicron-rich and VLDL-rich fractions

Proanthocyanidins have been shown to improve postprandial hypertriacylglycerolaemia. The present study aims to determine the actual contribution of chylomicrons (CM) and VLDL in the hypotriacylglycerolaemic action of grape seed proanthocyanidin extract (GSPE) in the postprandial state and to characterise the mechanisms by which the GSPE treatment reduces TAG-rich lipoproteins in vivo. A plasma lipid tolerance test was performed on rats fasted for 14 h and orally loaded with lard containing either GSPE or not. GSPE (250 mg/kg body weight) markedly blocked the increase in plasma TAG induced by lard, with a statistically significant reduction of 22 % in the area under the curve. The VLDL-rich fraction was the major contributor (72 %) after 1 h, whereas the CM-rich fraction was the major contributor (85 %) after 3 h. At 5 and 7 h after treatment, CM-rich and VLDL-rich fractions showed a similar influence. Plasma post-heparin lipoprotein lipase (LPL) activity and LPL mRNA levels in white adipose tissue and muscle were not affected by GSPE. On the contrary, GSPE treatment significantly repressed (30 %) the secretion of VLDL-TAG. In the liver, GSPE treatment induced different effects on the expression of acyl-coenzyme A synthetase long-chain family member 1, Apoc3 and 3-hydroxy-3-methylglutaryl-coenzyme A reductase at 1 h and Cd36 at 5 h, compared to those induced by lard. Furthermore, GSPE treatment significantly increased the activity of carnitine palmitoyltransferase 1a at 1 h. In conclusion, both CM-rich and VLDL-rich fractions contributed to the hypotriacylglycerolaemic action of GSPE, but their influence depended on time. GSPE induces hypotriacylglycerolaemic actions by repressing lipoprotein secretion and not by increasing LPL activity.

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.

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.