Modulation Of Lipoprotein Lipase Research Articles

Apolipoprotein CIII and Angiopoietin-like Protein 8 are Elevated in Lipodystrophy and Decrease after Metreleptin.

Lipodystrophy syndromes cause hypertriglyceridemia that improves with leptin treatment using metreleptin. Mechanisms causing hypertriglyceridemia and improvements after metreleptin are incompletely understood. Determine relationship of circulating lipoprotein lipase (LPL) modulators with hypertriglyceridemia in healthy controls and in patients with lipodystrophy before and after metreleptin. Cross-sectional comparison of patients with lipodystrophy (generalized lipodystrophy n = 3; partial lipodystrophy n = 11) vs age/sex-matched healthy controls (n = 28), and longitudinal analyses in patients before and after 2 weeks and 6 months of metreleptin. The study was carried out at the National Institutes of Health, Bethesda, Maryland. Outcomes were LPL stimulators apolipoprotein (apo) C-II and apoA-V and inhibitors apoC-III and angiopoietin-like proteins (ANGPTLs) 3, 4, and 8; ex vivo activation of LPL by plasma. Patients with lipodystrophy were hypertriglyceridemic and had higher levels of all LPL stimulators and inhibitors vs controls except for ANGPTL4, with >300-fold higher ANGPTL8, 4-fold higher apoC-III, 3.5-fold higher apoC-II, 1.9-fold higher apoA-V, 1.6-fold higher ANGPTL3 (P < .05 for all). At baseline, all LPL modulators except ANGPLT4 positively correlated with triglycerides. Metreleptin decreased apoC-II and apoC-III after 2 weeks and 6 months, and decreased ANGPTL8 after 6 months (P < 0.05 for all). Plasma from patients with lipodystrophy caused higher ex vivo LPL activation vs hypertriglyceridemic control plasma (P < .0001), which did not change after metreleptin. Elevations in LPL inhibitors apoC-III and ANGPTL8 may contribute to hypertriglyceridemia in lipodystrophy, and may mediate reductions in circulating and hepatic triglycerides after metreleptin. These therefore are strong candidates for therapies to lower triglycerides in these patients.

Abstract 16511: Isocaloric Fructose Restriction Improves Postprandial Chylomicron and VLDL Excursions in Adolescents With Obesity by Reducing Angiopoietin-Like Protein 3 and Apolipoprotein CIII

Introduction: Delayed postprandial triglyceride-rich lipoprotein (TRL) metabolism is associated with increased atherogenic risk. Dietary fructose is a preferred lipogenic substrate which contributes to NAFLD and dyslipoproteinemia. Hypothesis: Isocaloric fructose restriction reduces postprandial TRL excursions in part by affecting the modulation of lipoprotein lipase (LPL) activity and peripheral clearance rates. Methods: We determined the effect of 9 days of isocaloric fructose restriction on fasting and postprandial TRL metabolism markers in obese Latino and African American children (9-18 years old; n=30) with high habitual sugar consumption (&gt;50 g/d). Metabolic assessments were performed on day 0 and day 10 of isocaloric fructose restriction (starch substituted for sugar, same macronutrient composition). To follow postprandial TRL metabolism, after an initial double-sized meal, single-sized meals (providing 67% of daily calories, 15% protein, 35% fat, 50% carbohydrate) were fed every 30 minutes, with blood sampled every hour for 8 hours. Fructose content of meals reduced from 12% on day 0 to 4% on day 10. Paired t-tests compared change from day 0 to day 10 within each child. Results: Fasting TG, apoCIII, and ANGPTL3 reduced by 25%, 28% and 26% respectively (p &lt;0.01). Postprandial AUC of TG, apoCIII, ANGPTL3, VLDL, chylomicrons (apoB48) reduced by 35%, 34%, 40%, 17%, 19% (p &lt;0.01), while no changes were found in fasting or AUC for ANGPTL4, ANGPTL8 nor LPL mass. Conclusions: Short-term isocaloric fructose restriction improved postprandial chylomicron and VLDL metabolism in children with obesity. Specific and selective improvements in ANGPTL3 and apoCIII suggest differential modulation of LPL activity as a putative mechanism that deserves further exploration.

Lipoprotein lipase liberates free fatty acids to inhibit HCV infection and prevent hepatic lipid accumulation.

Lipoprotein lipase (LPL) has been identified as an anti-hepatitis C virus (HCV) host factor, but the cellular mechanism remains elusive. Here, we investigated the cellular mechanism of LPL involving in anti-HCV. The functional activation of peroxisome proliferator-activated receptor (PPAR) α signal by LPL transducing into hepatocytes was investigated in HCV-infected cells, primary human hepatocytes, and in HCV-core transgenic mice. The result showed that the levels of transcriptional transactivity and nuclear translocation of PPARα in Huh7 cells and primary human hepatocytes were elevated by physiologically ranged LPL treatment of either very-low density lipoprotein or HCV particles. The LPL-induced hepatic PPARα activation was weakened by blocking the LPL enzymatic activity, and by preventing the cellular uptake of free unsaturated fatty acids with either albumin chelator or silencing of CD36 translocase. The knockdowns of PPARα and CD36 reversed the LPL-mediated suppression of HCV infection. Furthermore, treatment with LPL, like the direct activation of PPARα, not only reduced the levels of apolipoproteins B, E, and J, which are involved in assembly and release of HCV virions, but also alleviated hepatic lipid accumulation induced by core protein. HCV-core transgenic mice exhibited more hepatic miR-27b, which negatively regulates PPARα expression, than did the wild-type controls. The induction of LPL activity by fasting in the core transgenic mice activated PPARα downstream target genes that are involved in fatty acid β-oxidation. Taken together, our study reveals dual beneficial outcomes of LPL in anti-HCV and anti-steatosis and shed light on the control of chronic hepatitis C in relation to LPL modulators.

Effect of Glycine on Adipocyte Hypertrophy in a Metabolic Syndrome Rat Model.

Glycine (Gly) lowers hypercholesterolemia, hypertriglyceridemia and hypertension but its role in preventing adipocyte hypertrophy and modulating enzymatic activity of adipocytes has not been studied. Here we evaluate the effect of 1% Gly in the diet on adipocyte hypertrophy and the modulation of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) in a metabolic syndrome (MS) rat model with intra-abdominal obesity. 32 Wistar rats were divided into 3 groups: control (C), MS, MS plus Gly (MS+Gly), and MS+Gly plus strychnine (MS+Gly+S). MS was induced by administering 30% sucrose in the drinking water for 16 weeks. In the MS+Gly and MS+Gly+S groups, the sucrose solution plus 1% Gly and 1 % Gly plus strychnine 10 μM were given during the last 4 weeks of the sucrose treatment. After 16 weeks of treatment, rats were sacrificed and the adipose tissue dissected. Gly in MS rats decreased body weight, intra-abdominal adipose tissue, adipocyte hypertrophy, blood pressure, triglycerides, insulin, HOMA-IR index, leptin, total fatty acids, non-esterified fatty acids and LPL activity. It increased fatty acids of the phospholipids, perilipin A expression and it decreased HSL expression, without changing LPL expression. The Gly receptor subunit-β was identified in adipocytes. In conclusion, Gly treatment regulates the activity of enzymes involved in the lipid metabolism of the adipocytes through the Gly receptor and it decreases the effects of the high sucrose diet.

Response of adipose tissue lipoprotein lipase to the cephalic phase of insulin secretion.

Modulation of lipoprotein lipase (LPL) allows a tissue-specific partitioning of triglyceride-derived fatty acids, and insulin is a major modulator of its activity. The present studies were aimed to assess in rats the contribution of insulin to the response of adipose tissue and muscle LPL to food intake. Epididymal and retroperitoneal adipose LPL rose 65% above fasting values as early as 1 h after the onset of a 30-min high-carbohydrate meal, with a second activity peak 1 h later that was maintained for an additional 2 h. Soleus muscle LPL was decreased by 25% between 0.5 and 4 h after meal intake. The essential contribution of insulin to the LPL response to food intake was determined by preventing the full insulin response to meal intake by administration of diazoxide (150 mg/kg body wt, in the meal). The usual postprandial changes in adipose and muscle LPL did not occur in the absence of an increase in insulinemia. However, the early (60 min) increase in adipose tissue LPL was not prevented by the drug, likely because of the maintenance of the early centrally mediated phase of insulin secretion. In a subsequent study, rats chronically implanted with a gastric cannula were used to demonstrate that the postprandial rise in adipose LPL is independent of nutrient absorption and can be elicited by the cephalic (preabsorptive) phase of insulin secretion. Obese Zucker rats were used because of their strong cephalic insulin response. After an 8-h fast, rats were fed a liquid diet ad libitum (orally, cannula closed), sham fed (orally, cannula opened), or fed directly into the stomach via the cannula during 4 h. Insulinemia increased 10-fold over fasting levels in ad libitum- and intragastric-fed rats and threefold in sham-fed rats. Changes in adipose tissue LPL were proportional to the elevation in plasma insulin levels, demonstrating that the cephalic-mediated rise in insulinemia, in the absence of nutrient absorption, stimulates adipose LPL. These results demonstrate the central role of insulin in the postprandial response of tissue LPL, and they show that cephalically mediated insulin secretion is able to stimulate adipose LPL.

Combined effects of sphingomyelin and cholesterol on the hydrolysis of emulsion particle triolein by lipoprotein lipase

Sphingomyelin (SM) is one of the major lipids in lipoproteins. However, its function in lipoprotein metabolism is unknown. In an attempt to understand the role that this lipid plays in modulation of lipoprotein lipase (LPL)-mediated hydrolysis, triolein-based emulsion particles containing 15% (physiological concentration) and 30% of the phospholipid content as SM together with phosphatidyl choline were used as substrate for the enzyme. Using a continuous fluorescence displacement assay to measure triglyceride (triolein) hydrolysis, it is shown that LPL activity was not modified by physiological concentrations of SM. However, under these assay conditions the presence of 30% SM inhibited LPL hydrolysis. SM and cholesterol (a normal component of the lipoprotein surface monolayer) become closely associated in phospholipid monolayers and bilayers. Incorporation of cholesterol into emulsion particles containing only PC increased LPL activity, but this increase was reduced by the additional presence of a physiological concentration (15%) of SM. These model studies suggest that the ratio, cholesterol : SM, in the monolayer may regulate the hydrolytic activity of the LPL. The production of ceramide by sphingomyelinase pre-treatment of emulsion particles containing SM leads to a two- to three-fold increase in LPL activity. This effect was dependent on sphingomyelinase concentration and time of pre-incubation and was not seen with cholesterol containing substrates. The ability of apolipoprotein CII to enhance LPL-catalysed triolein hydrolysis was not affected by the presence of SM; however, the stimulatory effect of this apolipoprotein was attenuated by pre-treatment of emulsion particles with sphingomyelinase. In summary, physiological concentrations of SM can inhibit the hydrolysis of cholesterol-containing emulsion particles; while pre-treatment of SM containing emulsion particles with sphingomyelinase in the absence of cholesterol can increase LPL-mediated triglyceride hydrolysis.

Failure of the nonselective beta-blocker propranolol to affect lipoprotein lipase gene expression in the rat.

Treatment with beta-blockers has been reported to be associated with the development of hypertriglyceridemia. The etiology, even the existence, of this phenomenon is controversial. The purpose of our study was to examine whether the nonselective beta-blocker propranolol causes hypertriglyceridemia in the rat and whether its action is mediated by the modulation of lipoprotein lipase (LPL) messenger RNA (mRNA) accumulation or activity. LPL activity was assayed in fresh tissue by incubation with tritiated triglycerides. LPL mRNA was quantified in total RNA by slot-blot analysis using a mouse LPL complementary DNA probe. We have conducted three series of experiments in unanaesthetized rats in order to study the effects of different single doses of propranolol (1.5 to 6 mg i.p.) and different durations of treatment (15 min to 4 wk). We measured triglyceride and cholesterol levels in plasma as well as the LPL activity and mRNA levels in the heart and adipose tissue before and after propranolol administration. In these experiments we did not find any significant decrease in either the activity or the amount of mRNA of lipoprotein lipase nor was there any change in plasma lipids following treatment. Our results lead us to the conclusion that the nonselective beta-blocker propranolol affects neither the activity nor the mRNA level of LPL in the rat.

Lipoprotein Lipase in Peripheral Tissues in Rats with Insulin Resistance Induced by Beef Tallow Diet.

The modulation of lipoprotein lipase (LPL) activity and mass was examined in rats with insulin resistance induced by a beef tallow diet. Male sprague-Dawley rats were meal-fed an isoenergetic diet based on either beef tallow or safflower oil for an 8-week period. Insulin resistance brought about by long-term feeding of a beef tallow diet was confirmed by an oral glucose tolerance test. Plasma glucose and insulin levels were higher at almost all times of day in the rats fed the beef tallow diet than in those fed the safflower oil one. LPL activities of the skeletal and cardiac muscles and brown adipose tissue before and after a meal were lower in the beef tallow diet group than in the safflower oil diet group, however those of the perirenal and subcutaneous adipose tissues were not different between the two dietary groups. The amounts of LPL proteins in the soleus muscle and perirenal adipose tissue corresponded to the enzyme activities in these tissues. These results suggest that the effect of dietary saturated fat on LPL activity and mass are different in muscles and adipose tissues and that generalized peripheral insulin resistance, induced by feeding rats a beef tallow diet for a sufficient duration, is not followed by an impairment of the modulation of LPL activities and protein amount.

Postprandial modulation of lipoprotein lipase in rats with insulin resistance

The purpose of this study was to determine whether the postprandial modulation of lipoprotein lipase (LPL) activity was altered in rats with resistance of glucose metabolism to insulin action induced by a high-fat diet. Relationships between serum insulin and tissue LPL activity were established in rats chronically fed a high-carbohydrate or high-fat diet, and the effects of fasting and intake of meals of habitual and alternate composition were contrasted. The feeding paradigm did not result in the development of obesity. Global resistance of glucose metabolism to insulin brought about by chronic high-fat feeding was confirmed by an intravenous glucose tolerance test. Fasting serum glucose and insulin concentrations were similar in both cohorts, as was LPL activity in retroperitoneal and inguinal white adipose tissues (WAT), the heart, and soleus. A high-carbohydrate meal brought about higher postprandial insulinemia in the cohort chronically fed the high-fat diet. This was associated with larger changes in LPL activity, that is, an increase in inguinal WAT and in brown adipose tissue and a decrease in soleus, red vastus lateralis, and the heart. Thus the established postprandial modulation of LPL, presumably by insulin, was potentiated in the presence of hyperinsulinemia induced by chronic high-fat feeding despite the concomitant impairment of glucose metabolism.

Modulation of lipoprotein lipase in the intact rat by cholera toxin - An irreversible agonist of cyclic AMP

Rats were injected intravenously with cholera toxin, a potent stimulator of adenylate cyclase, and lipoprotein lipase was determined in various organs and plasma. 16 h after cholera toxin injection, lipoprotein lipase activity increased 2–6-fold in heart, diaphragm and lung and decreased to one-third in adipose tissue. An increase in lipoprotein lipase activity was seen in the plasma and in the liver, as determined by antiserum to lipoprotein lipase. The increase in heart lipoprotein lipase was preceded by a rise in cyclic AMP and continued for 24 h when cyclic AMP returned to base-line levels. Both heparin-releasable and residual lipoprotein lipase increased in the heart, but to an unequal extent. The more pronounced rise in residual activity (up to 10-fold) could have contributed to an increase in the t 1 2 of heart lipoprotein lipase from 1.5 to 2.6 h. The relatively lower increase in heparin-releasable lipoprotein lipase could have been due to a loss of the enzyme from this compartment into the circulation. The effect of cholera toxin on heart and adipose tissue lipoprotien lipase was observed in fasted, fed and super-fed animals and thus appears to be independent of the nutritional state of the animal. Since cholera toxin not only mimics hormonal stimulation, but causes an exaggerated response to hormones, it made studies on some aspects of regulation of both the functional and storage forms of lipoprotein lipase in the intact organism possible.