Very Low Density Lipoprotein Apolipoprotein Research Articles

Mediterranean Diet, Energy Restriction, Physical Activity, and Atherogenicity of Very-Low Density Lipoproteins: Findings from Two Randomized Controlled Trials.

Some very-low density lipoprotein (VLDL) properties may render them more pro-atherogenic. We aimed to assess whether a Mediterranean diet (MedDiet) or an energy-reduced MedDiet with increased physical activity improves them. In a sample of the PREvención con DIeta MEDiterránea (PREDIMED) study, a 1-year intervention with MedDiet with extra-virgin olive oil (n = 89) or nuts (MedDiet-Nuts; n = 79) is compared with a low-fat diet (n=90). In the PREDIMED-Plus study, a 1-year intervention with energy-reduced MedDiet and physical activity (n = 103) is compared with an ad libitum MedDiet (n = 101). VLDL levels of apolipoprotein C-I, C-III, triglycerides, and cholesterol; the apolipoprotein E-/C-I ratio; and VLDL ex-vivo triglyceride transfer are measured. In PREDIMED participants in both MedDiet groups combined, VLDL apolipoprotein C-III levels are nominally reduced (-0.023 SD units, 95% CI -0.44 to -0.014, p = 0.037). VLDL triglyceride transfer is nominally increased in the MedDiet-Nuts group (+0.39 SD units, 95% CI 0.012-0.78, p = 0.045). In PREDIMED-Plus, no inter-group differences are detected. In older adults at high cardiovascular risk, MedDiet is associated with lower VLDL atherogenicity versus a low-fat diet. No differences are seen after an energy-reduced MedDiet with physical activity.

Cholesterol Content of Very-Low-Density Lipoproteins Is Associated with 1-Year Mortality in Acute Heart Failure Patients.

Considering the relationship between the extent of metabolic derangement and the disease severity in heart failure, we hypothesized that the lipid content of very-low-density lipoprotein (VLDL) may have prognostic value for 1 year mortality in acute heart failure (AHF). Baseline serum levels of VLDL cholesterol (VLDL-C), VLDL triglycerides (VLDL-TG), VLDL phospholipids (VLDL-PL), and VLDL apolipoprotein B (VLDL-apoB) were measured using NMR spectroscopy. We calculated the ratios of the respective VLDL lipids and VLDL apoB (VLDL-C/VLDL-apoB, VLDL-TG/VLDL-apoB, and VLDL-PL/VLDL-apoB), as estimators of the cholesterol, triglyceride, and phospholipid content of VLDL particles and tested their association with mortality. Out of 315 AHF patients, 118 (37.5%) patients died within 1 year after hospitalization for AHF. Univariable Cox regression analyses revealed a significant inverse association of VLDL-C/VLDL-apoB (hazard ratio (HR) 0.43, 95% confidence interval (CI) 0.29–0.64, p < 0.001), VLDL-TG/VLDL-apoB (HR 0.79, 95% CI 0.71–0.88, p < 0.001), and VLDL-PL/VLDL-apoB (HR 0.37, 95% CI 0.25–0.56, p < 0.001) with 1 year mortality. Of the tested parameters, only VLDL-C/VLDL-apoB remained significant after adjustment for age and sex, as well as other clinical and laboratory parameters that showed a significant association with 1 year mortality in the univariable analyses. We conclude that cholesterol content of circulating VLDL (VLDL-C/VLDL-apoB) might be of prognostic value in AHF.

Cyclodextrin-micellar electrokinetic chromatography of apolipoproteins on human very low-density lipoprotein.

The apolipoproteins (APOs) of human very low-density lipoprotein (VLDL) were investigated by an optimized cyclodextrin-micellar electrokinetic chromatography (CD-MEKC) method. The separation buffer consisted of 20mM sodium phosphate, 40mM bile salts (50% sodium cholate and 50% sodium deoxycholate), 25mM carboxymethyl-β-cyclodextrin (CM-β-CD) (pH 7.0). For CD-MEKC separation, a sample injection time of 12 s, a separation voltage of 15KV, and a capillary temperature of 15°C were chosen. The optimal CD-MEKC method showed good resolution and repeatability for VLDL APOs. Identification and quantitation of VLDL APOs CI, CIII, and E were based on comparison with human APO standards. Good linear relationships with correlation coefficient (R2 ) 0.99 were obtained for APOs CI, CIII, and E standards. For these three APOs, the linear ranges were within 0.01-0.54mg/mL, and the concentration limits of detection (LODs) were lower than 0.02mg/mL. Moreover, VLDL APOs from four uremic patients and four healthy subjects were compared. The uremic and healthy CD-MEKC profiles showed dramatic difference. The levels of APO CIII were significantly higher for two patients, and the level of APO E was significantly higher for one patient. This study might be helpful for following the disease development of uremia and cardiovascular disease (CVD) in the future.

DGAT2 Inhibition Alters Aspects of Triglyceride Metabolism in Rodents but Not in Non-human Primates

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step in triglyceride (TG) synthesis and has been shown to play a role in regulating hepatic very-low-density lipoprotein (VLDL) production in rodents. To explore the potential of DGAT2 as a therapeutic target for the treatment of dyslipidemia, we tested the effects of small-molecule inhibitors and gene silencing both invitro and invivo. Consistent with prior reports, chronic inhibition of DGAT2 in amurine model of obesity led to correction of multiple lipid parameters. In contrast, experiments in primary human, rhesus, and cynomolgus hepatocytes demonstrated that selective inhibition of DGAT2 has only a modest effect. Acute and chronic inhibition of DGAT2 in rhesus primates recapitulated the invitro data yielding no significant effects on production of plasma TG or VLDL apolipoprotein B. These results call into question whether selective inhibition of DGAT2 is sufficient for remediation of dyslipidemia.

Impact of phosphatidylcholine liposomes on the compositional changes of VLDL during lipoprotein lipase (LPL)-mediated lipolysis

Lipoprotein lipase (LPL)-mediated triacylglycerol (TAG) hydrolysis in very low density lipoprotein (VLDL) is accompanied by the release of surface material containing phospholipids (PL), free cholesterol (FC) and apolipoproteins, E (apoE) and Cs (apoCII, apoCIII). The released molecules are accepted by high density lipoprotein (HDL), and new HDL-sized apoE-containing particles are also generated. A decrease in the number of HDL particles or abnormalities in their structure is associated with unfavourable changes in the features of VLDL remnants. Phosphatidylcholine liposomes (PC-L) can also act as acceptors of surface material components released from lipoproteins. Thus, the aim of this study was to assess the impact of liposomes on compositional changes of VLDL during its LPL-mediated lipolysis.VLDL isolated from human sera was incubated with LPL (LPL:VLDLTAG; 24μg/ml:90mg/dl) and/or PC-L (VLDLPL:PC-LPL; 1:30 weight ratio). After incubation (2h, 37°C) VLDL was separated from other reaction products, and VLDL lipid and apolipoprotein content were analysed. Newly generated HDL-sized apoE-containing lipoproteins were separated by two-dimensional non-denaturing gradient gel electrophoresis (2D-PAGGE).The reaction of VLDL with PC-L in the presence or absence of LPL significantly affected the VLDL composition. The ratio of core (TAG+cholesteryl ester) to surface (PL+FC) lipids in VLDL decreased 1.8-fold with PC-L, 1.2-fold with LPL and 3-fold with PC-L+LPL. The reaction with PC-L and PC-L+LPL caused a 3.7-fold and 3.2-fold decrease of apoCs/apoE average weight ratio, respectively. Compositional changes in VLDL under the influence of PC-L were accompanied by an increase in the efficiency of VLDL lipolysis and the generation of apoE-containing HDL-sized particles, heterogeneous in size (from ∼9 to ∼18.8nm) and mobility (γ and preβ).We conclude that PL-rich particles, similarly to HDL, promote the release of surface material components from VLDL during LPL-mediated lipolysis and positively influence VLDL features which can facilitate VLDL metabolism. Such PC-L activity may impact on its antiatherogenic properties.

Diets naturally rich in polyphenols improve fasting and postprandial dyslipidemia and reduce oxidative stress: a randomized controlled trial

The postprandial triglyceride-rich lipoprotein (TRL) concentration is a recognized independent cardiovascular disease risk factor. Diet is the natural approach for these postprandial alterations. Dietary polyphenols and long chain n-3 polyunsaturated fatty acids (LCn3s) are associated with a lower cardiovascular disease risk. This randomized controlled study evaluated, in persons with a high risk of cardiovascular disease, the effects of diets naturally rich in polyphenols and/or marine LCn3s on plasma TRLs and urinary 8-isoprostane concentrations, a biomarker of oxidative stress. According to a 2 × 2 factorial design, 86 overweight/obese individuals with a large waist circumference and any other component of the metabolic syndrome were randomly assigned to an isoenergetic diet 1) poor in LCn3s and polyphenols, 2) rich in LCn3s, 3) rich in polyphenols, or 4) rich in LCn3s and polyphenols. The diets were similar in all other components. Before and after the 8-wk intervention, fasting and postmeal TRLs and 8-isoprostane concentrations in 24-h urine samples were measured. Dietary adherence was good in all participants. Polyphenols significantly reduced fasting triglyceride concentrations (2-factor ANOVA) in plasma (P = 0.023) and large very-low-density lipoproteins (VLDLs) (P = 0.016) and postprandial triglyceride total area under the curve in plasma (P = 0.041) and large VLDLs (P = 0.004). LCn3s reduced postprandial chylomicron cholesterol and VLDL apolipoprotein B-48. The concentrations of urinary 8-isoprostane decreased significantly with the polyphenol-rich diets. Lipoprotein changes induced by the intervention significantly correlated with changes in 8-isoprostane. Diets naturally rich in polyphenols positively influence fasting and postprandial TRLs and reduce oxidative stress. Marine LCn3s reduce TRLs of exogenous origin. Through their effects on postprandial lipemia and oxidative stress, polyphenols may favorably affect cardiovascular disease risk.

Endogenous Chronic Hyperinsulinemia Does Not Increase the Production Rate of VLDL Apolipoprotein B: Proof from a Kinetic Study in Patients with Insulinoma

It is currently suggested that chronic hyperinsulinemia is a causal factor for the increased production rate of very-low-density lipoproteins (VLDL) associated with metabolic syndrome. However, the involvement of hyperinsulinemia independently of the other abnormalities also observed in metabolic syndrome has never been proven in humans. We used patients with insulinoma showing hyperinsulinemia but no insulin resistance as a model and conducted an apolipoprotein B (apoB) kinetic study in seven patients with insulinoma, seven insulin-resistant (IR) obese patients, and 12 controls. Insulinemia was higher in patients with insulinoma or IR than in controls both in the fasting state [2.4-fold (P = 0.039) and 3.1-fold (P = 0.003), respectively] and in the fed state [3.5-fold (P = 0.006) and 2.6-fold (P = 0.05), respectively]. Patients with insulinoma were not IR (steady state plasma glucose = 80 ± 46 mg/dl, a value lower than in IR subjects (231 ± 75, P = 0.0013). In the fed state, triglyceridemia and VLDL apoB pool size were higher in IR subjects compared with controls and patients with insulinoma [208 ± 56 vs. 89 ± 30 mg/dl (P < 0.0001) and 96 ± 42 mg/dl (P < 0.0001), respectively, for triglyceridemia and 3.56 ± 0.60 vs. 1.85 ± 0.88 mg/kg (P = 0.004) and 2.32 ± 1.79 (P = 0.052) mg/kg for VLDL apoB pool size]. The production rate of VLDL apoB in subjects with insulinoma was not significantly different from that in controls (14.56 ± 7.43 vs. 16.40 ± 7.70 mg/kg · d) but was higher in IR subjects compared with these two groups [25.66 ± 12.84 mg/kg · d (P = 0.046 and 0.035, respectively)]. Chronic endogenous hyperinsulinemia is not directly responsible for any increase in the production rate of VLDL apoB in humans.

Relationships of Plasma and Very Low Density Lipoprotein Lipids and Subfractions with Abdominal Fat in Chickens

A study was conducted to determine the relationships between triacylglycerol (TAG) of plasma, very low density lipoprotein (VLDL) and fat deposition in two different breeds of chickens. The VLDL apolipoproteins of both breeds were also characterised. The breeds used were crossbred village chicken (AK) (Sasso crossed) and commercial broiler (CB) (Avian). They were housed in six pens with 30 female and 30 male birds of each breed per pen. Three male and three female birds from each pen were slaughtered and the blood was collected. The VLDL was isolated and sub-fractionated using Fast Protein Liquid Chromatography (FPLC). VLDL TAG of CB was significantly lower than AK. The particle size was negatively correlated with VLDL TAG and positively correlated with abdominal fat. Sub-fraction 2 contained more apo E that will enhance the lipolysis process of the VLDL TAG than sub-fraction 1. CB had a higher proportion of sub-fraction 2 than AK. The results showed that the proportion of sub-fraction 2 was negatively correlated with VLDL TAG concentration and positively correlated with abdominal fat.

Common CD36 SNPs reduce protein expression and may contribute to a protective atherogenic profile

Membrane CD36 functions in the uptake of fatty acids (FAs), oxidized lipoproteins and in signal transduction after binding these ligands. In rodents, CD36 is implicated in abnormal lipid metabolism, inflammation and atherosclerosis. In humans, CD36 variants have been identified to influence free FA and high-density lipoprotein (HDL) levels and to associate with the risk of the metabolic syndrome, coronary artery disease and stroke. In this study, 15 common lipid-associated CD36 single nucleotide polymorphisms (SNPs) were evaluated for the impact on monocyte CD36 expression (protein and transcript) in 104 African Americans. In a subset of subjects, the SNPs were tested for association with monocyte surface CD36 (n=65) and platelet total CD36 (n=57). The relationship between CD36 expression and serum HDL and very low-density lipoproteins (VLDLs) levels was also examined. After a permutation-based correction for multiple tests, four SNPs (rs1761667, rs3211909, rs3211913, rs3211938) influenced monocyte CD36 protein and two (rs3211909, rs3211938) platelet CD36. The effect of the HDL-associated SNPs on CD36 expression inversely related to the impact on serum HDL and potential causality was supported by Mendelian randomization analysis. Consistent with this, monocyte CD36 protein negatively correlated with total HDL and HDL subfractions. In contrast, positive correlations were documented between monocyte CD36 and VLDL lipid, particle number and apolipoprotein B. In conclusion, CD36 variants that reduce protein expression appear to promote a protective metabolic profile. The SNPs in this study may have predictive potential on CD36 expression and disease susceptibility in African Americans. Further studies are warranted to validate and determine whether these findings are population specific.

Hepatic and very low-density lipoprotein fatty acids in obese offspring of overfed dams

The combined effects of developmental programming and high-fat feeding at weaning on fatty acid metabolism of the offspring are not well known. In the present study, we aim at characterizing the influence of maternal and offspring's own diets on liver and very low-density lipoprotein (VLDL) lipids; fatty acid profiles of VLDL and liver phospholipids, triglycerides, and cholesteryl esters; and hepatic enzyme activities. Twenty obese male rats born to cafeteria diet–fed dams and 20 control rats born to control diet–fed dams were selected. At weaning, 10 rats of each group were fed control or cafeteria diet. Obese rats had a significant increase in serum glucose, insulin, leptin, VLDL apolipoprotein B100 and lipid levels, and hepatic fatty acid synthase and a reduction in acyl–coenzyme A oxidase and dehydrogenase activities compared with control pups at day 21 and day 90. Hepatic steatosis was apparent only at day 90. The proportions of saturated fatty acids and monounsaturated fatty acids and the oleic to stearic acid ratio were significantly increased, whereas polyunsaturated fatty acids and the arachidonic to linoleic acid ratio were decreased, in liver and VLDL lipids of obese pups compared with controls. The cafeteria diet at weaning induced more severe abnormalities in obese rats. In conclusion, maternal cafeteria diet induced a permanent reduction in hepatic β-oxidation and an increase in hepatic lipogenesis that caused liver steatosis and VLDL and fatty acid alterations in adult offspring. These preexisting alterations in offspring were worsened under a high-fat diet from weaning to adulthood. Nutritional recommendations in obesity must then target maternal and postnatal nutrition, especially fatty acid composition.

Effects of rosiglitazone and pioglitazone on lipoprotein metabolism in patients with Type 2 diabetes and normal lipids

Previous studies have suggested that plasma lipids are affected differently by the peroxisome proliferators-activated receptor (PPAR)-gamma agonists pioglitazone and rosiglitazone. The aim of this study was to perform a quantitative lipoprotein turnover study to determine the effects of PPAR-gamma agonists on lipoprotein metabolism. Twenty-four subjects with Type 2 diabetes treated with diet and/or metformin were randomized in a double-blind study to receive 30 mg pioglitazone, 8 mg rosiglitazone or placebo once daily for 3 months. Before and after treatment, absolute secretion rate (ASR) and fractional catabolic rate (FCR) of very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and low-density lipoprotein (LDL) apolipoprotein B100 were measured with a 10-h infusion of 1-13C leucine. There was a significant decrease in glycated haemoglobin (HbA(1c)) and non-esterified fatty acids with pioglitazone (P = 0.01; P = 0.02) and rosiglitazone (P = 0.04; P = 0.003), respectively, but no change in plasma triglyceride or high-density lipoprotein (HDL) cholesterol. Following rosiglitazone, there was a significant reduction in VLDL apolipoprotein B100 (apoB) ASR (P = 0.01) compared with baseline, a decrease in VLDL triglyceride/apoB (P = 0.01), an increase in LDL2 cholesterol (P = 0.02) and a decrease in LDL3 cholesterol (P = 0.02). There was a decrease in VLDL triglyceride/apoB (P = 0.04) in the pioglitazone group. There was no significant difference in change in VLDL ASR or FCR among the three groups. In patients with Type 2 diabetes and normal lipids, treatment with rosiglitazone or pioglitazone had no significant effect on lipoprotein metabolism compared with placebo.

PO3-79 UNIQUE CLINICAL PHENOTYPE IN A YOUNG BOY WITH TYPE I HYPERLIPOPROTEINEMIA ASSOCIATED WITH A COMBINED MUTATION ON THE LIPOPROTEIN LIPASE GENE

Familial hyperchylomicronemia (type 1 hyperlipoproteinemia) is a rare autosomal recessive disorder characterized by severe chylomicronemia secondary to a congenital deficiency of either lipoprotein lipase or apolipoprotein C-II.1 In 1983, the presence of a lipoprotein lipase inhibitor (which appears to be inherited as an autosomal dominant disease) as an additional cause of this disease was identified.1,2 Familial hyperchylomicronemia generally manifests itself in infancy or early childhood as repeated attacks of abdominal pain and as a creamy appearing (lipemic) plasma, both due to ingestion of dietary fats that have delayed clearance from the plasma. Complications due to hyperehylomicronemia include acute pancreatitis, eruptive xanthomas, lipemia retinalis, and hepatosplenomegaly. Plasma triglyceride concentrations generally range from 1,500 to 4,500 mg/ dl, but levels to 25,000 mg/dl have been reported. The plasma total cholesterol generally ranges from 160 to 400 mg/dl, but may be as high as 1,000 mg/dl when the triglyceride levels are severely elevated. Both low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol usually are exceedingly low, in the range of 20 to 40 mg/dl and 5 to 20 mg/dl, respectively. The fasting plasma very low density lipoprotein (VLDL) cholesterol is elevated, and it increases further after a low-fat, high-carbohydrate diet.3The diagnosis of familial hyperchylomicronemia is based on the presence of a creamy layer (chylomicrons) on the surface of plasma that has been stored in the cold (4 °C), and an elevated plasma triglyceride level. Demonstration of chylomicrons (fasting triglycerides > 1,500 mg/dl) after an overnight fast also may indicate familial hyperchylomicronemia. Analysis of lipoprotein lipase (assay of postheparin plasma) apolipoprotein C-II (gel electrophoresis of VLDL and chylomicron apolipoproteins or lipoprotein lipase activity, or both, in postheparin plasma), and lipoprotein lipase inhibitor activities establish the molecular defect in this disorder.1 Although many reports have appeared describing clinical and biochemical features of familial hyperchylomicronemia, morphologic features of this condition have received little attention. Some morphologic data have been reported in only 5 such patients.4–8 The present report describes clinical and necropsy findings in 4 men with familial hyperchylomicronemia with emphasis on cardiovascular observations.

Genes that affect cholesterol synthesis, cholesterol absorption, and chylomicron assembly: The relationship between the liver and intestine in control and streptozotosin diabetic rats

Chylomicrons and very low-density lipoproteins (VLDLs) are abnormal in diabetes. The aim of this study was to compare the expression of Niemann-Pick C1-like1 (NPC1L1), adenosine triphosphate–binding cassette (ABC) proteins G5 and G8, microsomal triglyceride transfer protein (MTP), and 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase in the fasting and fed states in nondiabetic Sprague-Dawley rats fed a high-fat/cholesterol diet and to examine the messenger RNA (mRNA) expression of these proteins in the liver and intestine of diabetic and control animals using streptozotosin diabetic cholesterol-fed rats. Chylomicron and VLDL concentrations were significantly lower after a 12-hour fast in fasted compared with fed rats ( P < .02). There was no change with fasting in mRNA expression of any of the genes in the intestine, but MTP level was significantly lower in the liver after the 12-hour fast ( P < .01). There was a positive correlation between intestinal NPC1L1 mRNA and chylomicron cholesterol ( P < .01) and between hepatic NPC1L1 mRNA and VLDL cholesterol ( P < .01). The diabetic rats had significantly higher chylomicron and VLDL cholesterol, triglyceride, and apolipoprotein B-48 and B-100 levels compared with control rats ( P < .0001). They had significantly increased NPC1L1 and MTP mRNA in both liver and intestine ( P < .05 and P < .0005, respectively), and ABCG5 and ABCG8 mRNA were significantly reduced ( P < .05). HMGCoA reductase mRNA was increased in diabetic animals ( P < .01). In conclusion, fasting intestinal gene expression reflects the fed state. In diabetes, intestinal and hepatic gene expression correlates with abnormalities in chylomicron and VLDL cholesterol.

Effects of long-term negative energy balance with exercise on plasma lipid and lipoprotein levels in identical twins

Plasma lipid and lipoprotein concentrations were measured before and after a 58,000 kcal (244 MJ) negative energy balance protocol induced entirely by supervised endurance exercise over a 93-day period in seven pairs of young sedentary and healthy male monozygotic twins. The negative energy balance induced significant changes in all measures of body weight and composition except fat free mass. The mean weight loss was 5.0±0.6 kg, and it was entirely accounted for by the loss of body fat. In response to the program, improvement in the plasma lipid profile was seen including decreases in plasma total ( P=0.028) and low density lipoprotein (LDL) ( P=0.004) cholesterol; total cholesterol/high density lipoprotein (HDL) cholesterol ratio ( P=0.002); and HDL apolipoprotein A–I concentration ( P=0.062). Statistically significant within-pair resemblance was found for the changes in total and very low density lipoprotein (VLDL) cholesterol; total, VLDL and LDL triglycerides, and total, VLDL and LDL apolipoprotein B. The findings suggest that favorable changes in the lipid profile can be obtained through chronic negative energy balance achieved by clamping daily energy intake and adding daily moderate intensity exercise even in persons with relatively normal lipid levels at baseline. Furthermore, within-pair resemblance among twin brothers strongly suggests that genetic differences partially account for the variation in the response of lipids and lipoproteins to the negative energy balance protocol.

Octanoate inhibits very low-density lipoprotein secretion in primary cultures of chicken hepatocytes

The effects of octanoate, a medium-chain fatty acid, on very low-density lipoprotein (VLDL) secretion in primary cultures of chicken hepatocytes were compared with those of palmitate. Palmitate added to the incubation media at concentrations up to 0.36 mM increased intracellular triacylglycerol (TG) accumulation and VLDL-TG secretion in a concentration-dependent manner, whereas the addition of octanoate alone (0.21–0.6 mM) did not change these parameters. VLDL-TG secretion from hepatocytes cultured in media to which 0.6 or 1.0 mM octanoate had been added in the presence of 0.21 mM palmitate was significantly lower than that obtained under control incubation conditions (0.21 mM palmitate only). The addition of 1.0 mM octanoate to the incubation media with or without 0.21 mM palmitate decreased VLDL apolipoprotein B (apoB) secretion. These results demonstrate that the addition of octanoate to primary cultures of chicken hepatocytes reduces VLDL secretion in respect of both TG and apoB secretion. It is suggested that medium-chain fatty acids are a factor modulating VLDL secretion, which plays a key role in fat deposition in chickens.

HOE 402 lowers serum cholesterol levels by reducing VLDL-lipid production, and not by induction of the LDL receptor, and reduces atherosclerosis in wild-type and LDL receptor-deficient mice

Previous rodent studies suggested that the potent hypolipidemic agent 4-amino-2-(4,4-dimethyl-2-oxo-1-imidazolidinyl)pyrimidine-5-N-(trifluoromethyl-phenyl) carboxamide monohydrochloride (HOE 402) is an inducer of the LDL receptor (LDLR). Using wild-type and heterozygous and homozygous LDLR-deficient (LDLR+/0 and LDLR0/0) mice, fed a low or high cholesterol diet, we investigated whether HOE 402 specifically induces the LDLR and whether other pathways are affected. Upon treatment with 0.05% (w/w) HOE 402, the serum cholesterol levels of wild-type, LDLR+/0 and LDLR0/0 mice, were maximally reduced by 53, 56, and 73%, respectively (P<0.05), by reducing levels in very low density-lipoprotein (VLDL), intermediate density-lipoprotein (IDL), and low density-lipoprotein (LDL) cholesterol, whereas high density-lipoprotein (HDL) cholesterol levels were increased. The observations that HOE 402 exhibited no effect on in vivo clearance of 125I-labeled LDL in wild-type mice, and clearly reduced serum cholesterol levels in LDLR0/0 mice, indicate that the LDLR is not the main target for the compound. In wild-type mice, production of VLDL-TG, and cholesterol were reduced by more than 50% by HOE 402 (P<0.05), whereas VLDL apolipoprotein B (ApoB) secretion was unaffected, indicating that HOE 402 treatment changes the size, rather than the number of the secreted VLDL particles. The reduced VLDL production was accompanied by a 22% decreased hepatic cholesterol ester concentration (P<0.05). Additionally, HOE 402 treatment strongly reduced the aortic content of atherosclerotic lesions by 90 and 72% in LDLR+/0 and LDLR0/0 mice, respectively (P<0.01). In conclusion, HOE 402 is a potent cholesterol-lowering compound, which inhibits VLDL production, and consequently attenuates atherosclerosis development.

Dietary Plant Stanol Esters Reduce VLDL Cholesterol Secretion and Bile Saturation in Apolipoprotein E*3-Leiden Transgenic Mice

Dietary plant stanols lower serum cholesterol levels in humans and in hyperlipidemic rodents, mainly by inhibition of the intestinal cholesterol absorption. We used female apolipoprotein E*3-Leiden transgenic mice to investigate the consequences of this effect on serum lipid levels and hepatic lipid metabolism. Five groups of 6 or 7 mice received for 9 weeks a diet containing 0.25% cholesterol and 0.0%, 0.25%, 0.5%, 0.75%, or 1.0% (wt/wt) plant stanols (sitostanol 88% [wt/wt], campestanol 10% [wt/wt]) esterified to fatty acids. Compared with the control diet, plant stanol ester treatment dose-dependently reduced serum cholesterol levels by 10% to 33% (P<0.05), mainly in very low density lipoproteins (VLDLs), intermediate density lipoproteins, and low density lipoproteins. Furthermore, 1.0% of the dietary plant stanols significantly decreased the liver contents of cholesteryl esters (-62%), free cholesterol (-31%), and triglycerides (-38%) but did not change the hepatic VLDL-triglyceride and VLDL-apolipoprotein B production rates. However, plant stanol ester feeding significantly decreased the amounts of cholesteryl esters and free cholesterol incorporated in nascent VLDLs by 72% and 30%, respectively, resulting in a net 2-fold decreased VLDL cholesterol output. Liver mRNA levels of low density lipoprotein receptors, 3-hydroxy-3-methylglutaryl coenzyme A synthase, cholesterol 7alpha-hydroxylase, and sterol 27-hydroxylase were not changed by plant stanol ester feeding. Nevertheless, the serum lathosterol-to-cholesterol ratio was significantly increased by 23%, indicating that dietary plant stanol esters increased whole-body cholesterol synthesis. Plant stanol esters also significantly decreased the cholesterol saturation index in bile by 55%. In conclusion, in apolipoprotein E*3-Leiden transgenic mice, plant stanol ester feeding dose-dependently lowered serum cholesterol levels as a result of a reduced secretion of VLDL cholesterol. This was caused by a decreased hepatic cholesterol content that also resulted in a lowered biliary cholesterol output, indicative of a reduced lithogenicity of bile in these mice.

Effects of growth hormone treatment on very-low-density lipoprotein apolipoprotein B100 turnover in adult hypopituitarism

Adult hypopituitarism is associated with hyperlipidemia, mainly due to an increase of very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) levels. Recent studies have shown that such patients exhibit increased hepatic secretion of VLDL apolipoprotein B100 (VLDL apo B100). To examine the effects of growth hormone (GH) replacement on VLDL apo B100 turnover, 13 GH-deficient hypopituitary patients (8 women and 5 men; aged 47 +/- 3 years, mean +/- SEM; body mass index [BMI], 30 +/- 2 kg/m2) entered a double-blind placebo-controlled study for 6 months (GH 0.125 IU/kg/wk for 4 weeks, and then 0.25 IU/kg/wk). GH was subsequently used in all patients for a further 6 months. A 6-hour [1-13C] leucine infusion was administered at baseline and at 6 months. The secretion rate of VLDL apo B100 was derived by kinetic analysis following quantitation of isotopic enrichment by gas chromatography/mass spectrometry. The GH-treated group (6 patients) demonstrated a similar fractional secretion rate (FSR) for VLDL apo B100 at 0 and 6 months. The pool size and absolute secretion rate (ASR) also were unaffected significantly by GH therapy. No significant changes were observed in the placebo group (7 patients). Treatment with GH for 6 months caused an increase in the high-density lipoprotein (HDL) cholesterol concentration (13 patients, 1.27 +/- 0.13 v 1.16 +/- 0.10 mmol/L, respectively, P = .05), whereas total cholesterol and triglyceride concentrations did not change. Nonesterified fatty acids (NEFAs) increased during GH therapy (471 +/- 43 micromol/L at 6 months v 349 +/- 49 micromol/L at baseline, P < .0005). The data suggest that GH does not affect VLDL apo B100 turnover in a significant way.

Genotypic associations of the hepatic secretion of VLDL apolipoprotein B-100 in obesity

AbstractWe examined the effect of genetic polymorphisms of proteins regulating intrahepatic processing of apolipoprotein B-100 (apoB) and the supply of neutral lipids to the liver on the hepatic secretion of very low density lipoprotein (VLDL) apoB in obesity. Hepatic secretion of very low density apolipoprotein B-100 (VLDL apoB) was measured using an infusion of [1-13C]leucine in 29 obese men. Isotopic enrichment and turnover of VLDL apoB was determined using gas chromatography–mass spectrometry and multi-compartmental modelling, respectively. Visceral fat was measured by magnetic resonance imaging. Genotypes for the apoB signal peptide (SP27/SP24 alleles), microsomal triglyceride transfer protein promoter (MTP, −493 G/T alleles), apoE (E2, E3, E4 alleles), hepatic lipase promoter (−514 C/T alleles), and cholesteryl ester transfer protein (CETP, Taq1B B1/B2 alleles) were determined using polymerase chain reaction. Statistically significant associations were found between hepatic secretion of apoB and allelic combinations of i) apoB SP with apoE (P = 0.02), hepatic lipase (P = 0.02), and CETP (P = 0.006) genes, ii) MTP promoter with CETP genes (P = 0.03); the association with apoBSP/MTP promoter allelic combinations just failed to reach significance (P = 0.06), however. The CETP/apoBSP allelic combination was the most significant predictor of apoB secretion, and this was independent of visceral fat, plasma lathosterol and insulin levels, and dietary fat. SP24 carriers who were homozygous for CETP B1 had 60% lower apoB secretion than B2 heterozygotes who were non-carriers of SP24 (10.5 ± 1.74 mg/kg fat free mass/day, n = 7 vs. 26.1 ± 3.16, n = 22). The data suggest that variation in both the apoB and CETP genes may be a major genetic determinant of the hepatic secretion of apoB in men with visceral obesity. —Watts, G. F., F. M. Riches, S. E. Humphries, P. J. Talmud, and F. M. Bockxmeer. Genotypic associations of the hepatic secretion of VLDL apolipoprotein B-100 in obesity. J. Lipid Res. 2000. 41: 481–488.

Hepatic overexpression of microsomal triglyceride transfer protein (MTP) results in increased in vivo secretion of VLDL triglycerides and apolipoprotein B

The microsomal triglyceride transfer protein (MTP) is essential for the hepatic secretion of apolipoprotein (apo) B-containing lipoproteins. Previous studies have indicated that inhibition of MTP results in decreased apoB plasma levels and decreased hepatic triglyceride secretion. However, the metabolic effects of overexpression of MTP have not been investigated. We constructed a recombinant adenovirus expressing MTP (AdhMTP) and used it to assess the effects of hepatic overexpression of MTP in mice. Injection of AdhMTP into C57BL/6 mice resulted in a 3-fold increase in hepatic microsomal triglyceride transfer activity compared to mice injected with Adnull. On day 4 after virus injection, AdhMTP-injected mice had significantly elevated plasma TG levels as compared to control virus (Adnull)-injected mice. Hepatic TG secretion rates were significantly greater in AdhMTP-injected mice (184 +/- 12 mg/kg/h) compared with Adnull-injected mice (65 +/- 9 mg/kg/h, P < 0.001). In addition, hepatic very low density lipoprotein (VLDL) apoB secretion in the AdhMTP-injected group was 74% higher than in the control virus group. Hepatic secretion of apoB-48 and apoB-100 contributed equally to this increase. These results provide the first data that hepatic overexpression of MTP results in increased secretion of VLDL-triglycerides as well as VLDL-apoB in vivo. These results suggest that MTP is rate-limiting for VLDL apoB secretion in wild-type mice under basal chow-fed conditions.