Elevated Plasma High-density Lipoprotein Cholesterol Research Articles

Plasma HDL pattern, cholesterol efflux and cholesterol loading capacity of serum in carriers of a novel missense variant (Gly176Trp) of endothelial lipase

Loss of function variants of LIPG gene encoding endothelial lipase (EL) are associated with primary hyperalphalipoproteinemia (HALP), a lipid disorder characterized by elevated plasma levels of high density lipoprotein cholesterol (HDL-C). Aim of the study was the phenotypic and genotypic characterization of a family with primary HALP. HDL subclasses distribution was determined by polyacrylamide gradient gel electrophoresis. Serum content of preβ-HDL was assessed by (2D)-electrophoresis. Cholesterol efflux capacity (CEC) of serum mediated by ABCA1, ABCG1 or SR-BI was assessed using cells expressing these proteins. Cholesterol loading capacity (CLC) of serum was assayed using cultured human macrophages. Next generation sequencing was used for DNA analysis. Plasma EL mass was determined by ELISA. Three family members had elevated plasma HDL-C, apoA-I and total phospholipids, as well as a reduced content of preβ-HDL. These subjects were heterozygous carriers of a novel variant of LIPG gene [c.526 G>T, p.(Gly176Trp)] found to be deleterious in silico. Plasma EL mass in carriers was lower than in controls. CEC of sera mediated by ABCA1 and ABCG1 transporters was substantially reduced in the carriers. This effect was maintained after correction for serum HDL concentration. The sera of carriers were found to have a higher CLC in cultured human macrophages than control sera. The novel p.(Gly176Trp) variant of endothelial lipase is associated with changes in HDL composition and subclass distribution as well as with functional changes affecting cholesterol efflux capacity of serum which suggest a defect in the early steps of revere cholesterol transport.

Cholesterol efflux capacity of high-density lipoprotein particles is impaired in age-related macular degeneration patients with high plasma HDL-C levels

Background and Aims : Age-related macular degeneration (AMD) is a blinding disease initiated by the formation of fat globules, so-called drusen, in the retina. Epidemiological studies demonstrated an association between elevated plasma high-density lipoprotein-cholesterol (HDL-c) levels and AMD. This is in contrast to the risk of cardiovascular disease that is negatively associated with HDL-c levels. Among the genes linked with AMD, ABCA1, CETP, LIPC and APOE are related to the role of HDL in mediating cholesterol efflux from cells and consequently in reverse cholesterol transport.

Hyperalphalipoproteinemia and Beyond: The Role of HDL in Cardiovascular Diseases.

Hyperalphalipoproteinemia (HALP) is a lipid disorder characterized by elevated plasma high-density lipoprotein cholesterol (HDL-C) levels above the 90th percentile of the distribution of HDL-C values in the general population. Secondary non-genetic factors such as drugs, pregnancy, alcohol intake, and liver diseases might induce HDL increases. Primary forms of HALP are caused by mutations in the genes coding for cholesteryl ester transfer protein (CETP), hepatic lipase (HL), apolipoprotein C-III (apo C-III), scavenger receptor class B type I (SR-BI) and endothelial lipase (EL). However, in the last decades, genome-wide association studies (GWAS) have also suggested a polygenic inheritance of hyperalphalipoproteinemia. Epidemiological studies have suggested that HDL-C is inversely correlated with cardiovascular (CV) risk, but recent Mendelian randomization data have shown a lack of atheroprotective causal effects of HDL-C. This review will focus on primary forms of HALP, the role of polygenic inheritance on HDL-C, associated risk for cardiovascular diseases and possible treatment options.

CTRP12 ameliorates atherosclerosis by promoting cholesterol efflux and inhibiting inflammatory response via the miR-155-5p/LXR\u03b1 pathway

C1q tumor necrosis factor-related protein 12 (CTRP12), a conserved paralog of adiponectin, is closely associated with cardiovascular disease. However, little is known about its role in atherogenesis. The aim of this study was to examine the influence of CTRP12 on atherosclerosis and explore the underlying mechanisms. Our results showed that lentivirus-mediated CTRP12 overexpression inhibited lipid accumulation and inflammatory response in lipid-laden macrophages. Mechanistically, CTRP12 decreased miR-155-5p levels and then increased its target gene liver X receptor α (LXRα) expression, which increased ATP binding cassette transporter A1 (ABCA1)- and ABCG1-dependent cholesterol efflux and promoted macrophage polarization to the M2 phenotype. Injection of lentiviral vector expressing CTRP12 decreased atherosclerotic lesion area, elevated plasma high-density lipoprotein cholesterol levels, promoted reverse cholesterol transport (RCT), and alleviated inflammatory response in apolipoprotein E-deficient (apoE−/−) mice fed a Western diet. Similar to the findings of in vitro experiments, CTRP12 overexpression diminished miR-155-5p levels but increased LXRα, ABCA1, and ABCG1 expression in the aortas of apoE−/− mice. Taken together, these results suggest that CTRP12 protects against atherosclerosis by enhancing RCT efficiency and mitigating vascular inflammation via the miR-155-5p/LXRα pathway. Stimulating CTRP12 production could be a novel approach for reducing atherosclerosis.

Paeoniflorin regulates GALNT2-ANGPTL3-LPL pathway to attenuate dyslipidemia in mice

N-acetylgalactosaminyltransferase 2-Angiopoietin-like protein 3-lipoprotein lipase (GALNT2-ANGPTL3-LPL) pathway may be a useful pharmacologic objective for dyslipidemia. The present study was conducted to test the effect of paeoniflorin, a monoterpene Glycoside, on dyslipidemia in mice. Fifty mice were randomly divided into five groups (n = 10): three groups of apolipoprotein E-null (ApoE-/-) mice treated with paeoniflorin (10 or 20 or 30 mg/kg/day), untreated ApoE-/- mice group, and C57BL/6J control group. Six weeks after treatment, expression of hepatic ANGPTL3, hepatic GALNT2 and adipose tissue LPL, lipid levels in the liver and blood were quantified. Treatment with paeoniflorin (10 or 20 or 30 mg/kg) obviously down-regulated expression of ANGPTL3 and up-regulated expressions of GALNT2 and LPL concomitantly with elevated plasma high-density lipoprotein cholesterol level, reduced plasma concentrations of low-density lipoprotein cholesterol, total cholesterol, triglyceride, malonaldehyde, and 8-isoprostane. The present results suggest that paeoniflorin regulates GALNT2-ANGPTL3-LPL pathway to attenuate dyslipidemia in mice.

Apolipoprotein A-I interactions with insulin secretion and production.

Human population studies have established that an elevated plasma high-density lipoprotein cholesterol (HDL-C) level is associated with a decreased risk of developing cardiovascular disease. In addition to having several potentially cardioprotective functions, HDLs and apolipoprotein (apo)A-I, the main HDL apolipoprotein, also have antidiabetic properties. Interventions that elevate plasma HDL-C and apoA-I levels improve glycemic control in people with type 2 diabetes mellitus by enhancing pancreatic β-cell function and increasing insulin sensitivity. This review is concerned with recent advances in understanding the mechanisms by which HDLs and apoA-I improve pancreatic β-cell function. HDLs and apoA-I increase insulin synthesis and secretion in pancreatic β cells. The underlying mechanism of this effect is similar to what has been reported for intestinally derived incretins, such as glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, which both increase β-cell insulin secretion under high glucose conditions. This involves the activation of a heterotrimeric G protein Gαs subunit on the β-cell surface that leads to induction of a transmembrane adenylyl cyclase, increased intracellular cyclic adenosine monophosphate and Ca levels, and activation of protein kinase A. Protein kinase A increases insulin synthesis by excluding FoxO1 from the β-cell nucleus and derepressing transcription of the insulin gene.

JTT-130, a novel intestine-specific inhibitor of microsomal triglyceride transfer protein, ameliorates lipid metabolism and attenuates atherosclerosis in hyperlipidemic animal models

JTT-130 was developed as an intestine-specific MTP inhibitor designed to rapidly catabolize after absorption to avoid causing hepatotoxicity due to hepatic MTP inhibition. In previous reports, we have demonstrated that JTT-130 suppresses dietary lipid absorption in the small intestine without inducing hepatic steatosis. Thus, in this report, JTT-130 was administered to hyperlipidemic animals fed a Western diet to investigate the effect of intestinal MTP inhibition on lipid metabolism and progression of atherosclerosis.JTT-130 potently lowered plasma non-high density lipoprotein-cholesterol, and elevated plasma high density lipoprotein-cholesterol (HDL-C), indicating improvement in atherogenic index in hamsters. HDL fractions obtained after two weeks treatment with JTT-130 significantly increased the efflux of cholesterol from macrophages, as an index parameter of HDL function. Furthermore, long-term treatment with JTT-130 also improved the plasma lipid profile without inducing hepatic steatosis in rabbits, resulting in the suppression of atherosclerosis formation in aortas.From these results, JTT-130 ameliorates lipid metabolism accompanied with the enhancement of the anti-atherosclerotic function of HDL, and attenuates the progression of atherosclerosis in hyperlipidemic animals. These findings indicate that intestinal MTP inhibition may be atherogenic in vivo and that JTT-130 may be a useful compound for the treatment of dyslipidemia and a potential anti-atherogenic drug.

Quercetin-3-O-glucuronide induces ABCA1 expression by LXRα activation in murine macrophages

Reverse cholesterol transport (RCT) removes excess cholesterol from macrophages to prevent atherosclerosis. ATP-binding cassette, subfamily A, member 1 (ABCA1) is a crucial cholesterol transporter involved in RCT to produce high density lipoprotein-cholesterol (HDLC), and is transcriptionally regulated by liver X receptor alpha (LXRα), a nuclear receptor. Quercetin is a widely distributed flavonoid in edible plants which prevented atherosclerosis in an animal model. We found that quercetin-3-O-glucuronide (Q3GA), a major quercetin metabolite after absorption from the digestive tract, enhanced ABCA1 expression, in vitro, via LXRα in macrophages. In addition, leaf extracts of a traditional Asian edible plant, Nelumbo nucifera (NNE), which contained abundant amounts of quercetin glycosides, significantly elevated plasma HDLC in mice. We are the first to present experimental evidence that Q3GA induced ABCA1 in macrophages, and to provide an alternative explanation to previous studies on arteriosclerosis prevention by quercetin.

Anti-miR-33 Therapy Does Not Alter the Progression of Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient Mice

To determine the efficacy of long-term anti-miR-33 therapy on the progression of atherosclerosis in high-fat, high-cholesterol-fed Ldlr(-/-) mice. Ldlr(-/-) mice received saline, or control or anti-miR-33 oligonucleotides once a week for 14 weeks. The treatment was effective, as measured by reduced levels of hepatic miR-33 and increased hepatic expression of miR-33 targets. Analysis of plasma samples revealed an initial elevation in high-density lipoprotein cholesterol after 2 weeks of treatment that was not sustained by the end of the experiment. Additionally, we found a significant increase in circulating triglycerides in anti-miR-33-treated mice, compared with controls. Finally, examination of atheromata revealed no significant changes in the size or composition of lesions between the 3 groups. Prolonged silencing of miR-33 fails to maintain elevated plasma high-density lipoprotein cholesterol and does not prevent the progression of atherosclerosis in Ldlr(-/-) mice.

Pharmacological LXR activation reduces presence of SR-B1 in liver membranes contributing to LXR-mediated induction of HDL-cholesterol

ObjectivePharmacological LXR activation has anti-atherosclerotic actions in animal models. Part of these beneficial effects may be explained by accelerated reverse cholesterol transport since both plasma high density lipoprotein (HDL) cholesterol and fecal neutral sterol secretion are higher upon LXR activation. Mechanisms underlying these LXR-mediated effects have not been fully elucidated. MethodsWe investigated the roles of the isoforms LXRα and LXRβ and the HDL cholesterol uptake receptor SR-B1 in modulation of cholesterol metabolism upon treatment of mice with the LXR ligand T0901317. ResultsHDL cholesterol was maximally 60% increased in a time-dependent fashion due to appearance of more and larger HDL particles. Fecal neutral sterol secretion was maximally induced after 1week treatment. T0901317 treatment induced fecal neutral sterol secretion by ∼300% in wild-type but not in Lxrα deficient mice. Surprisingly, LXR activation reduced SR-B1 protein amount in hepatic membranes, suggesting that this might contribute to elevated HDL cholesterol. However, T0901317 still elevated plasma HDL cholesterol in Sr-b1 deficient mice, suggesting that SR-B1 is not the only step involved in LXR-mediated induction of plasma HDL cholesterol. In addition, SR-B1 is not essential for LXR-induced cholesterol removal from the body. ConclusionInduction of fecal neutral sterol secretion by T0901317 critically depends on LXRα but not on LXRβ. LXR activation reduces SR-B1 in hepatic membranes, probably partly contributing to elevated HDL cholesterol. SR-B1 is not required to enhance fecal neutral sterol secretion.

Heterozygosity for a Loss-of-Function Mutation in GALNT2 Improves Plasma Triglyceride Clearance in Man

Genome-wide association studies have identified GALNT2 as a candidate gene in lipid metabolism, but it is not known how the encoded enzyme ppGalNAc-T2, which contributes to the initiation of mucin-type O-linked glycosylation, mediates this effect. In two probands with elevated plasma high-density lipoprotein cholesterol and reduced triglycerides, we identified a mutation in GALNT2. It is shown that carriers have improved postprandial triglyceride clearance, which is likely attributable to attenuated glycosylation of apolipoprotein (apo) C-III, as observed in their plasma. This protein inhibits lipoprotein lipase (LPL), which hydrolyses plasma triglycerides. We show that an apoC-III-based peptide is a substrate for ppGalNAc-T2 while its glycosylation by the mutant enzyme is impaired. In addition, neuraminidase treatment of apoC-III which removes the sialic acids from its glycan chain decreases its potential to inhibit LPL. Combined, these data suggest that ppGalNAc-T2 can affect lipid metabolism through apoC-III glycosylation, thereby establishing GALNT2 as a lipid-modifying gene.

A novel homozygous mutation in CETP gene as a cause of CETP deficiency in a caucasian kindred

Objective To analyze the cholesteryl ester transfer protein (CETP) gene and the plasma HDL phenotype in a Caucasian subject with extremely elevated plasma high density lipoprotein-cholesterol (HDL-C). Methods and results The proband, a 63-year-old male of Swedish ancestry with elevated HDL-C (208 mg/dl) and apoA-I (and 272 mg/dl), was found to be homozygous for a point mutation in exon 2 of CETP gene (c.109 C > T) resulting in a premature termination codon (R37X). Plasma CETP mass and activity were undetectable. Plasma HDL were characterized by predominance of large HDL with enhanced preβ-HDL content. The proband's sons, heterozygotes for the mutation, had reduced plasma CETP activity and moderately elevated HDL-C. Serum of CETP deficient subjects showed a normal or enhanced cholesterol efflux capacity via ABCG1/SR-BI; cholesterol efflux via ABCA1 and macrophage cholesterol removal were lower than normal. The proband was healthy and had no atherosclerotic plaques in carotid or femoral arteries. Conclusion Complete CETP deficiency caused by mutations in CETP gene is exceedingly rare in Caucasians; the description of this single case indicates that CETP deficiency does not predispose to atherosclerosis in the absence of major cardiovascular risk factors.

Effects of Dietary Korean Proso-Millet Protein on Plasma Adiponectin, HDL Cholesterol, Insulin Levels, and Gene Expression in Obese Type 2 Diabetic Mice

We investigated the effect of dietary Korean proso-millet protein concentrate (PMP) on glycemic responses, plasma lipid levels, and the plasma level and gene expression of adiponectin in obese type 2 diabetic mice under normal and high-fat feeding conditions. The findings were that the feeding of PMP clearly elevated plasma high-density lipoprotein cholesterol (HDL cholesterol) and adiponectin levels and brought about effective reduction in the levels of glucose and insulin in mice under high-fat diet conditions as compared with a control diet. Gene expression study revealed that the diet up-regulated expression of adiponectin and down-regulated tumor necrosis factor-alpha (TNF-alpha). Considering the central role of adiponectin and HDL cholesterol in improving and ameliorating type 2 diabetes, obesity, and cardiovascular disease, our findings imply that PMP may have potential for therapeutic intervention in type 2 diabetes.

Simvastatin, an HMG-CoA reductase inhibitor, induces the synthesis and secretion of apolipoprotein AI in HepG2 cells and primary hamster hepatocytes

Clinical studies have recently suggested that statin treatment may beneficially elevate plasma concentrations of high density lipoprotein (HDL)–cholesterol in patients with hyperlipidemia. Here, we have investigated the effect of a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase on the synthesis and secretion of apolipoprotein AI (apoAI) in two model systems, HepG2 cells and primary hamster hepatocytes. Cultured cells were incubated with different doses of simvastatin (0.1–10 μM) for a period of 18 h. A dose-dependent increase in synthesis and secretion of apoAI was observed in both cell types. There was a significant increase in the synthesis of apoAI in HepG2 cells (44.3±12.1%), and hamster hepatocytes (212±2%) after treatment with 10 μM of the statin. The increase in apoAI synthesis appeared to result in a higher level of apoAI secreted into the culture media in both cell types (49.2±7.8% in HepG2, 197±0.2% in hamster hepatocytes). ApoAI mRNA levels were also significantly increased in both cell types in response to statin treatment. Control experiments with transferrin confirmed specificity of the effect on apoAI secretion. Analysis of a density fraction containing HDL particles in culture media revealed an increase in HDL-associated apoAI of 94.3±2.1% in HepG2 cells and 27.0±0.03% in hamster hepatocytes following 10 μM simvastatin-treatment. Comparative studies of simvastatin and lovastatin indicated a differential ability to induce apoAI synthesis and secretion, with simvastatin having a more significant effect. Thus, acute statin treatment of cultured hepatocytes (transformed as well as primary) resulted in a significant upregulation of apoAI mRNA and apoAI synthesis, causing oversecretion of apoAI and HDL extracellularly. The stimulatory effect on apoAI synthesis and secretion may thus explain the clinical observation of an elevated plasma HDL–cholesterol level in hyperlipidemic patients treated with certain statins.

Altered effect of 3% dietary cholestyramine on plasma lipids and biliary bile acid output in the pregnant rat

The effects of a diet containing 3% (ww) cholestyramine on plasma total, free, and high-density lipoprotein cholesterol and triglycerides and on bile flow and composition were compared between pregnant rats fed the resin from before mating until the twentieth day of gestation and virgin rats fed the resin for an equivalent length of time. Pregnant and virgin rats consuming a similar diet but not receiving cholestyramine were also studied. In the nonpregnant rat the usual response to cholestyramine was observed as a significantly elevated plasma high-density lipoprotein cholesterol level and biliary bile acid secretion. Plasma cholesterol levels and bile composition were not altered by cholestyramine in the pregnant rat. The inability of resin therapy to change plasma high-density lipoprotein cholesterol and bile composition during pregnancy is likely to be causally related to a reduced efficacy of cholestyramine treatment when administered during gestation.

Relationship between plasma high-density lipoprotein cholesterol and anticonvulsant levels in epileptics.

Plasma high-density lipoprotein (HDL) cholesterol is a recognized negative risk factor for coronary heart disease. In this study, therapy with phenytoin alone, carbamazepine alone, and phenytoin in combination with phenobarbital was associated with elevated plasma HDL cholesterol concentrations. The highest HDL cholesterol levels were seen in subjects treated with the combination of phenytoin and phenobarbital. Plasma HDL cholesterol levels were proportional to the serum phenobarbital and carbamazepine concentrations. In subjects treated with phenytoin alone, low plasma HDL cholesterol levels were associated with low drug concentrations. The results suggest direct links running from the serum anticonvulsant levels to the extent of hepatic microsomal enzyme induction, and further to the plasma HDL cholesterol concentrations.

Plasma HDL cholesterol and growth hormone in epileptics treated with anticonvulsants.

Plasma high density lipoprotein (HDL) cholesterol and serum growth hormone (GH) levels were determined in 166 epileptic patients undergoing anticonvulsant treatment in 54 healthy controls. HDL cholesterol and GH levels were high in epileptics when compared to the levels in controls. Nineteen out of 31 patients (61%) with elevated GH had elevated plasma HDL cholesterol concentration. This relationship in patients with normal GH was 34/135(25%). In female epileptics with elevated GH plasma HDL cholesterol was in positive relationship to serum GH level (r = 0.47, P less than 0.05). The increase in GH secretion in epileptics might be associated with an increase in hepatic production of HDL.

Plasma High-Density Lipoprotein Cholesterol in Epileptics Treated with Various Anticonvulsants

Plasma high-density lipoprotein (HDL) cholesterol in 97 epileptics on long-term anticonvulsant therapy was investigated. Therapy with phenytoin alone or in combination with carbamazepine or phenobarbital was associated with elevated plasma HDL cholesterol levels as compared with controls. HDL cholesterol in patients treated with carbamazepine did not diverge from control values. Patients treated with phenytoin and phenobarbital in combination showed higher HDL cholesterol levels than those treated with phenytoin alone. There was an inverse correlation between the HDL cholesterol and serum triglyceride levels. The results demonstrate that high plasma HDL cholesterol might be associated with therapy involving some anticonvulsants known to be potent enzyme inducers. This suggests that the elevation of HDL cholesterol during therapy is probably related to the drug-caused enzyme induction phenomenon.