The crucial roles of apolipoproteins E and C-III in apoB lipoprotein metabolism in normolipidemia and hypertriglyceridemia

Apolipoproteins E and CIII interact to regulate HDL metabolism and coronary heart disease risk

BACKGROUND

Subspecies of HDL contain apolipoprotein E (apoE) and/or apoCIII. Both proteins have properties that could affect HDL metabolism. The relation between HDL metabolism and risk of coronary heart disease (CHD) is not well understood.

METHODS

Eighteen participants were given a bolus infusion of [D3]L-leucine to label endogenous proteins on HDL. HDL was separated into subspecies containing apoE and/or apoCIII and then into 4 sizes. Metabolic rates for apoA-I in HDL subspecies and sizes were determined by interactive modeling. The concentrations of apoE in HDL that contain or lack apoCIII were measured in a prospective study in Denmark including 1,949 incident CHD cases during 9 years.

RESULTS

HDL containing apoE but not apoCIII is disproportionately secreted into the circulation, actively expands while circulating, and is quickly cleared. These are key metabolic steps in reverse cholesterol transport, which may protect against atherosclerosis. ApoCIII on HDL strongly attenuates these metabolic actions of HDL apoE. In the epidemiological study, the relation between HDL apoE concentration and CHD significantly differed depending on whether apoCIII was present. HDL apoE was associated significantly with lower risk of CHD only in the HDL subspecies lacking apoCIII.

CONCLUSIONS

ApoE and apoCIII on HDL interact to affect metabolism and CHD. ApoE promotes metabolic steps in reverse cholesterol transport and is associated with lower risk of CHD. ApoCIII, when coexisting with apoE on HDL, abolishes these benefits. Therefore, differences in metabolism of HDL subspecies pertaining to reverse cholesterol transport are reflected in differences in association with CHD.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01399632.

FUNDING

This work was supported by NIH grant R01HL095964 to FMS and by a grant to the Harvard Clinical and Translational Science Center (8UL1TR0001750) from the National Center for Advancing Translational Science.

Duality of statin action on lipoprotein subpopulations in the mixed dyslipidemia of metabolic syndrome: Quantity vs quality over time and implication of CETP

BACKGROUND

Statins impact the metabolism, concentrations, composition, and function of circulating lipoproteins.

OBJECTIVE

We evaluated time course relationships between statin-mediated reduction in atherogenic apolipoprotein B (ApoB)-containing particles and dynamic intravascular remodeling of ApoAI-containing lipoprotein subpopulations in the mixed dyslipidemia of metabolic syndrome.

METHODS

Insulin-resistant, hypertriglyceridemic, hypercholesterolemic, obese males (n = 12) were treated with pitavastatin (4 mg/d) and response evaluated at 6, 42, and 180 days.

RESULTS

Reduction in low-density lipoprotein (LDL) cholesterol, ApoB, and triglycerides (TGs) was essentially complete at 42 days (-38%, -32%, and -35%, respectively); rapid reduction equally occurred in remnant cholesterol, ApoCII, CIII, and E levels (day 6; -35%, -50%, -23%, and -26%, respectively). Small dense LDLs (LDL4 and LDL5 subpopulations) predominated at baseline and were markedly reduced on treatment (-29% vs total LDL mass). Cholesteryl ester (CE) transfer protein activity and mass decreased progressively (-18% and -16%, respectively); concomitantly, TG depletion (up to -49%) and CE enrichment occurred in all high-density lipoprotein (HDL) particle subpopulations with normalization of CE/TG mass ratio at 180 days. ApoAI was redistributed from LpAI to LpAI:AII particles in HDL2a and HDL3a subpopulations; ApoCIII was preferentially depleted from LpAI:AII-rich particles on treatment.

CONCLUSION

Overall, statin action exhibits duality in mixed dyslipidemia, as CE transfer protein-mediated normalization of the HDL CE/TG core lags markedly behind subacute reduction in elevated levels of atherogenic ApoB-containing lipoproteins. Normalization of the HDL neutral lipid core is consistent with enhanced atheroprotective function. The HDL CE/TG ratio constitutes a metabolomic marker of perturbed HDL metabolism in insulin-resistant states, equally allowing monitoring of statin impact on HDL metabolism, structure, and function.

From High-Density Lipoprotein Cholesterol to Measurements of Function: Prospects for the Development of Tests for High-Density Lipoprotein Functionality in Cardiovascular Disease

The evidence is strong that biological functions contained in high-density lipoproteins (HDL) are antiatherogenic. These functions may track with HDL cholesterol or apolipoprotein A1 concentration to explain the strongly inverse risk curve for cardiovascular disease. Moreover, there are harmful as well as protective HDL subspecies in regard to cardiovascular disease, which could be responsible for paradoxical responses to HDL-directed treatments. Recent metabolic studies show that apolipoprotein A1-containing HDL is secreted into the circulation as mostly spherical cholesterol ester-rich lipoproteins that span the HDL size range. Most of the flux of apolipoprotein A1 HDL into and out of the circulation occurs in these spherical cholesterol-replete particles. Discoidal cholesterol-poor HDL comprises a minority of HDL secretion. We propose that much cholesterol in reverse cholesterol transport enters and exits medium and large size HDL without changing a size category, and its flux may be estimated provisionally from holoparticle clearance of cholesterol ester-rich HDL. An accurate framework for metabolism of HDL is essential to finding steady-state biomarkers that reflect HDL function in vivo. Whereas cholesterol efflux from cells to mainly discoidal HDL, mediated by ABCA1 (ATP-binding cassette transporter ABCA1), predicts cardiovascular disease, cholesterol transfers to spherical HDL also can be measured and may be relevant to protection against atherosclerosis. We propose several investigative paths on which human HDL biology may be investigated leading to convenient biomarkers of HDL quality and function having potential not only to improve risk prediction but also to more accurately target drug treatments.

Lipid core nanoparticles resembling low-density lipoprotein and regression of atherosclerotic lesions: effects of particle size

Particles are usually polydispersed and size is an important feature for lipid-based drug delivery systems in order to optimize cell-particle interactions as to pharmacologic action and toxicity. Lipid nanoparticles (LDE) with composition similar to that of low-density lipoprotein carrying paclitaxel were shown to markedly reduce atherosclerosis lesions induced in rabbits by cholesterol feeding. The aim of this study was to test whether two LDE fractions, one with small (20-60 nm) and the other with large (60-100 nm) particles, had different actions on the atherosclerotic lesions. The two LDE-paclitaxel fractions, prepared by microfluidization, were separated by density gradient ultracentrifugation and injected (4 mg/body weight, intravenously once a week) into two groups of rabbits previously fed cholesterol for 4 weeks. A group of cholesterol-fed animals injected with saline solution was used as control to assess lesion reduction with treatment. After the treatment period, the animals were euthanized for analysis. After treatment, both the small and large nanoparticle preparations of LDE-paclitaxel had equally strong anti-atherosclerosis action. Both reduced lesion extension in the aorta by roughly 50%, decreased the intima width by 75% and the macrophage presence in the intima by 50%. The two preparations also showed similar toxicity profile. In conclusion, within the 20-100 nm range, size is apparently not an important feature regarding the LDE nanoparticle system and perhaps other solid lipid-based systems.

High-Density Lipoprotein Subspecies Defined by Presence of Apolipoprotein C-III and Incident Coronary Heart Disease in Four Cohorts

BACKGROUND

The causal role of high-density lipoprotein (HDL) cholesterol in cardioprotection has been questioned by genetic and randomized studies. Novel measures that relate to HDL function may contribute new information to the prediction of cardiovascular risk. Apolipoprotein C-III (apoC-III) is a key regulator of lipoprotein metabolism. We investigated whether subspecies of HDL defined by apoC-III are associated with coronary heart disease (CHD).

METHODS

We used immunoaffinity chromatography to measure the apoA-I concentrations of HDL that contains and lacks apoC-III in 2 prospective studies of adults free of CHD. In MESA (Multi-Ethnic Study of Atherosclerosis), 5657 participants (52% women, 52-72 years of age) were followed for risk of CHD from 2000 to 2002 through 2013. In a case-cohort study nested within the DCH study (Danish Diet, Cancer, and Health), 3642 participants (47% women, 51-64 years of age) were followed from 1994 to 1997 through 2010. Subsequently, we conducted a meta-analysis that combined these results with the previously published findings from 2 cohort studies that used similar laboratory methodology to measure lipoproteins, totaling 2997 incident cases.

RESULTS

ApoC-III was found on 6% to 8% of apoA-I. The 2 HDL subspecies showed opposing associations, with risk of CHD in each of the individual cohorts and in the meta-analysis (P heterogeneity between the 2 subspecies <0.01). HDL that contains apoC-III was associated with a higher risk of CHD (pooled relative risk per standard deviation, 1.09; 95% confidence interval, 1.01-1.18), whereas HDL that lacks apoC-III was associated with lower risk (relative risk, 0.76; 95% confidence interval, 0.70-0.83). The relative risk for HDL lacking apoC-III was even more negative than the relative risk for total HDL (relative risk, 0.80; 95% confidence interval, 0.74-0.87).

CONCLUSIONS

Our findings from 4 prospective studies support the hypothesis that apoC-III may mark a subfraction of HDL that is associated with higher risk of CHD. New measures reflecting HDL structure and function may provide novel insights for cardiovascular risk that extend beyond traditional plasma HDL cholesterol concentrations.

ANGPTL3 serum concentration and rare genetic variants in Finnish population

Genetic variants of angiopoietin-like protein 3 (ANGPTL3) are associated with serum triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C) concentration in GWASs. ANGPTL3 deficiency causes declined TG, total cholesterol (TC), LDL-C, high-density lipoprotein cholesterol (HDL-C), apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I) serum concentration, a phenotype defined as familial combined hypolipidaemia (FHBL2). Our aim is to establish whether ANGPTL3 serum protein concentration correlates with lipoproteins and lipids in hyper- or hypolipidaemic subjects, and whether ANGPTL3 sequence variants are associated with untypical lipid profiles. Additionally, 10 subjects with very low lipoprotein concentrations were sequenced for ANGPTL3 for possible loss-of-function (LOF) variants. Study subjects were selected from Finnish FINRISK and Health 2000 surveys. ANGPTL protein concentrations were measured by ELISA method. As a result, ANGPTL3 serum concentration correlated positively with age, phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) activities, but not with any of the lipid or lifestyle attributes. No ANGPTL3 variants were found among sequenced samples. Subjects who carried ANGPTL3 sequence variants rs12563308 (n = 4) and rs199772471 (n = 1) had abnormally high TC and LDL-C concentrations. Whole exome sequencing data of these five subjects were further analyzed for rare and deleterious missense variants in genes associated with cholesterol metabolism. In conclusion, ANGPTL3 serum protein concentration did not predict lipid concentrations, unlike apolipoprotein C-III (apoC-III) which positively correlated with most of the lipid attributes. ANGPTL3 variant screen yielded five carriers with abnormally high TC concentration; the actual genetic causality, however, could not be verified.

Triglyceride-Rich Lipoproteins and Remnants: Targets for Therapy?

It is now evident that elevated circulating levels of triglycerides in the non-fasting state, a marker for triglyceride (TG)-rich remnant particles, are associated with increased risk of premature cardiovascular disease (CVD). Recent findings from basic and clinical studies have begun to elucidate the mechanisms that contribute to the atherogenicity of these apoB-containing particles. Here, we review current knowledge of the formation, intravascular remodelling and catabolism of TG-rich lipoproteins and highlight (i) the pivotal players involved in this process, including lipoprotein lipase, glycosylphosphatidylinositol HDL binding protein 1 (GPIHBP1), apolipoprotein (apo) C-II, apoC-III, angiopoietin-like protein (ANGPTL) 3, 4 and 8, apoA-V and cholesteryl ester transfer protein; (ii) key determinants of triglyceride (TG) levels and notably rates of production of very-low-density lipoprotein 1 (VLDL1) particles; and (iii) the mechanisms which underlie the atherogenicity of remnant particles. Finally, we emphasise the polygenic nature of moderate hypertriglyceridemia and briefly discuss modalities for its clinical management. Several new therapeutic strategies to attenuate hypertriglyceridemia have appeared recently, among which those targeted to apoC-III appear to hold considerable promise.

Apolipoprotein C-III and High-Density Lipoprotein Subspecies Defined by Apolipoprotein C-III in Relation to Diabetes Risk

Apolipoprotein C-III (apoC-III) is a potentially novel biomarker that may play an important role in the pathogenesis of diabetes, particularly when present on the surface of high-density lipoprotein (HDL). In a case-cohort study carried out among 434 incident diabetes cases occurring before 2007 and 3,101 noncases in the Danish Diet, Cancer, and Health Study, we examined associations of baseline (1993-1997) plasma concentrations of apoC-III and subspecies of HDL defined by the presence or absence of apoC-III with risk of diabetes using Cox regression. ApoC-III was strongly associated with risk of diabetes (for top quintile vs. bottom quintile, hazard ratio (HR) = 3.43, 95% confidence interval (CI): 1.75, 6.70; P-trend < 0.001). The cholesterol concentration of HDL (HDL cholesterol (HDL-C)) without apoC-III was inversely associated with risk of diabetes (HR = 0.48, 95% CI: 0.27, 0.85; P-trend = 0.002), more so than total HDL-C (HR = 0.60, 95% CI: 0.35, 1.03; P-trend = 0.04), whereas HDL-C with apoC-III was not associated (HR = 1.05, 95% CI: 0.50, 2.21; P-trend = 0.44) (for HDL-C with apoC-III vs. HDL-C without apoC-III, P-heterogeneity = 0.002). ApoC-III itself is a strong risk marker for diabetes, and its presence on HDL may impair the antidiabetogenic properties of HDL. ApoC-III has potential to be a therapeutic target for the prevention of diabetes.

Why Is Apolipoprotein CIII Emerging as a Novel Therapeutic Target to Reduce the Burden of Cardiovascular Disease?

ApoC-III was discovered almost 50 years ago, but for many years, it did not attract much attention. However, as epidemiological and Mendelian randomization studies have associated apoC-III with low levels of triglycerides and decreased incidence of cardiovascular disease (CVD), it has emerged as a novel and potentially powerful therapeutic approach to managing dyslipidemia and CVD risk. The atherogenicity of apoC-III has been attributed to both direct lipoprotein lipase-mediated mechanisms and indirect mechanisms, such as promoting secretion of triglyceride-rich lipoproteins (TRLs), provoking proinflammatory responses in vascular cells and impairing LPL-independent hepatic clearance of TRL remnants. Encouraging results from clinical trials using antisense oligonucleotide, which selectively inhibits apoC-III, indicate that modulating apoC-III may be a potent therapeutic approach to managing dyslipidemia and cardiovascular disease risk.

Very-Low-Density Lipoprotein-Associated Apolipoproteins Predict Cardiovascular Events and Are Lowered by Inhibition of APOC-III

Background

Routine apolipoprotein (apo) measurements for cardiovascular disease (CVD) are restricted to apoA-I and apoB. Here, the authors measured an unprecedented range of apolipoproteins in a prospective, population-based study and relate their plasma levels to risk of CVD.

Objectives

This study sought to measure apolipoproteins directly by mass spectrometry and compare their associations with incident CVD and to obtain a system-level understanding of the correlations of apolipoproteins with the plasma lipidome and proteome.

Methods

Associations of 13 apolipoproteins, 135 lipid species, and 211 other plasma proteins with incident CVD (91 events), defined as stroke, myocardial infarction, or sudden cardiac death, were assessed prospectively over a 10-year period in the Bruneck Study (N = 688) using multiple-reaction monitoring mass spectrometry. Changes in apolipoprotein and lipid levels following treatment with volanesorsen, a second-generation antisense drug targeting apoC-III, were determined in 2 human intervention trials, one of which was randomized.

Results

The apolipoproteins most significantly associated with incident CVD were apoC-II (hazard ratio per 1 SD [HR/SD]: 1.40; 95% confidence interval [CI]: 1.17 to 1.67), apoC-III (HR/SD: 1.38; 95% CI: 1.17 to 1.63), and apoE (HR/SD: 1.31; 95% CI: 1.13 to 1.52). Associations were independent of high-density lipoprotein (HDL) and non-HDL cholesterol, and extended to stroke and myocardial infarction. Lipidomic and proteomic profiles implicated these 3 very-low-density lipoprotein (VLDL)-associated apolipoproteins in de novo lipogenesis, glucose metabolism, complement activation, blood coagulation, and inflammation. Notably, apoC-II/apoC-III/apoE correlated with a pattern of lipid species previously linked to CVD risk. ApoC-III inhibition by volanesorsen reduced plasma levels of apoC-II, apoC-III, triacylglycerols, and diacylglycerols, and increased apoA-I, apoA-II, and apoM (all p < 0.05 vs. placebo) without affecting apoB-100 (p = 0.73).

Conclusions

The strong associations of VLDL-associated apolipoproteins with incident CVD in the general community support the concept of targeting triacylglycerol-rich lipoproteins to reduce risk of CVD.

Crossroads between peripheral atherosclerosis, western-type diet and skeletal muscle pathophysiology: emphasis on apolipoprotein E deficiency and peripheral arterial disease

Atherosclerosis is a chronic inflammatory process that, in the presence of hyperlipidaemia, promotes the formation of atheromatous plaques in large vessels of the cardiovascular system. It also affects peripheral arteries with major implications for a number of other non-vascular tissues such as the skeletal muscle, the liver and the kidney. The aim of this review is to critically discuss and assimilate current knowledge on the impact of peripheral atherosclerosis and its implications on skeletal muscle homeostasis. Accumulating data suggests that manifestations of peripheral atherosclerosis in skeletal muscle originates in a combination of increased i)-oxidative stress, ii)-inflammation, iii)-mitochondrial deficits, iv)-altered myofibre morphology and fibrosis, v)-chronic ischemia followed by impaired oxygen supply, vi)-reduced capillary density, vii)- proteolysis and viii)-apoptosis. These structural, biochemical and pathophysiological alterations impact on skeletal muscle metabolic and physiologic homeostasis and its capacity to generate force, which further affects the individual's quality of life. Particular emphasis is given on two major areas representing basic and applied science respectively: a)-the abundant evidence from a well-recognised atherogenic model; the Apolipoprotein E deficient mouse and the role of a western-type diet and b)-on skeletal myopathy and oxidative stress-induced myofibre damage from human studies on peripheral arterial disease. A significant source of reactive oxygen species production and oxidative stress in cardiovascular disease is the family of NADPH oxidases that contribute to several pathologies. Finally, strategies targeting NADPH oxidases in skeletal muscle in an attempt to attenuate cellular oxidative stress are highlighted, providing a better understanding of the crossroads between peripheral atherosclerosis and skeletal muscle pathophysiology.

Short-term cooling increases serum triglycerides and small high-density lipoprotein levels in humans

BACKGROUND

Cold exposure and β3-adrenergic receptor agonism, which both activate brown adipose tissue, markedly influence lipoprotein metabolism by enhancing lipoprotein lipase-mediated catabolism of triglyceride-rich lipoproteins and increasing plasma high-density lipoprotein (HDL) levels and functionality in mice. However, the effect of short-term cooling on human lipid and lipoprotein metabolism remained largely elusive.

OBJECTIVE

The objective was to assess the effect of short-term cooling on the serum lipoprotein profile and HDL functionality in men.

METHODS

Body mass index-matched young, lean men were exposed to a personalized cooling protocol for 2 hours. Before and after cooling, serum samples were collected for analysis of lipids and lipoprotein composition by ¹H-nuclear magnetic resonance. Adenosine triphosphate-binding cassette A1 (ABCA1)-mediated cholesterol efflux capacity of HDL was measured using [³H]cholesterol-loaded ABCA1-transfected Chinese hamster ovary cells.

RESULTS

Short-term cooling increased serum levels of free fatty acids, triglycerides, and cholesterol. Cooling increased the concentration of large very low-density lipoprotein (VLDL) particles accompanied by increased mean size of VLDL particles. In addition, cooling enhanced the concentration of small LDL and small HDL particles as well as the cholesterol levels within these particles. The increase in small HDL was accompanied by increased ABCA1-dependent cholesterol efflux in vitro.

CONCLUSIONS

Our data show that short-term cooling increases the concentration of large VLDL particles and increases the generation of small LDL and HDL particles. We interpret that cooling increases VLDL production and turnover, which results in formation of surface remnants that form small HDL particles that attract cellular cholesterol.

Monosialyl Ganglioside GM3 Decreases Apolipoprotein B-100 Secretion in Liver Cells

Some sialic acid-containing glycolipids are known to regulate development of atherosclerosis with accumulated plasma apolipoprotein B-100 (Apo-B)-containing lipoproteins, because Apo-B as an atherogenic apolipoprotein is assembled mainly in VLDL and LDL. Previously, we have elucidated that disialyl GD3 promotes the microsomal triglyceride transfer protein (MTP) gene expression and secretion of triglyceride (TG)-assembled ApoB, claiming the GD3 role in ApoB lipoprotein secretion in liver cells. In the synthetic pathway of gangliosides, GD3 is synthesized by addition of a sialic acid residue to GM3. Thus, there should be some regulatory links between GM3 and GD3. In this study, exogenous and endogenous monosialyl GM3 has been examined how GM3 plays a role in ApoB secretion in Chang liver cells in a view point of MTP and ApoB degradation in the same cells. The level of GM3 ganglioside in the GM3 synthase gene-transfected cells was increased in the cell extract, but not in the medium. In addition, GM3 synthase gene-transfected cells showed a diminished secretion of TG-enriched ApoB with a lower content of TG in the medium. Exogenous GM3 treatment for 24 h exerted a dose dependent inhibitory effect on ApoB secretion together with TG, while a liver-specific albumin was unchanged, indicating that GM3 effect is limited to ApoB secretion. GM3 decreased the mRNA level of MTP gene, too. ApoB protein assembly dysregulated by GM3 indicates the impaired ApoB secretion is caused by a proteasome-dependent pathway. Treatment with small interfering RNAs (siRNAs) decreased ApoB secretion, but GM3-specific antibody did not. These results indicate that plasma membrane associated GM3 inhibits ApoB secretion, lowers development of atherosclerosis by decreasing the secretion of TG-enriched ApoB containing lipoproteins, suggesting that GM3 is an inhibitor of ApoB and TG secretion in liver cells. J. Cell. Biochem. 118: 2168-2181, 2017. © 2017 Wiley Periodicals, Inc.

Metabolism and proteomics of large and small dense LDL in combined hyperlipidemia: effects of rosuvastatin

Small dense LDL (sdLDL) has been reported to be more atherogenic than large buoyant LDL (lbLDL). We examined the metabolism and protein composition of sdLDL and lbLDL in six subjects with combined hyperlipidemia on placebo and rosuvastatin 40 mg/day. ApoB-100 kinetics in triglyceride-rich lipoproteins (TRLs), lbLDL (density [d] = 1.019-1.044 g/ml), and sdLDL (d = 1.044-1.063 g/ml) were determined in the fed state by using stable isotope tracers, mass spectrometry, and compartmental modeling. Compared with placebo, rosuvastatin decreased LDL cholesterol and apoB-100 levels in TRL, lbLDL, and sdLDL by significantly increasing the fractional catabolic rate of apoB-100 (TRL, +45%; lbLDL, +131%; and sdLDL, +97%), without a change in production. On placebo, 25% of TRL apoB-100 was catabolized directly, 37% was converted to lbLDL, and 38% went directly to sdLDL; rosuvastatin did not alter these distributions. During both phases, sdLDL apoB-100 was catabolized more slowly than lbLDL apoB-100 (P < 0.01). Proteomic analysis indicated that rosuvastatin decreased apoC-III and apoM content within the density range of lbLDL (P < 0.05). In our view, sdLDL is more atherogenic than lbLDL because of its longer plasma residence time, potentially resulting in more particle oxidation, modification, and reduction in size, with increased arterial wall uptake. Rosuvastatin enhances the catabolism of apoB-100 in both lbLDL and sdLDL.

Effects of Multiple Freeze/Thaw Cycles on Measurements of Potential Novel Biomarkers Associated With Adverse Pregnancy Outcomes

World-wide, millions of women enter preterm labor or have small newborns. Effective biomarkers are needed to identify women at risk for these adverse outcomes. A time and cost effective way to examine any potentially new biomarkers in samples collected during prior studies or trials that had been assayed for other metabolites would be highly useful. Thus, the current study aimed to determine if samples that had been previously thawed and re-frozen could be re-assayed for novel biomarkers, those being lipoprotein composition (sizing, proteome, lipids) and combined cholesterol and cytokine concentrations. Fasting blood was collected from 51 young non-pregnant women and plasma was analyzed for lipoprotein composition and cytokine concentrations after multiple freeze/thaw cycles in the cold or at room temperature and after being stored for 18 months. Plasma LDL-C, HDL-C, total cholesterol, and triglyceride concentrations decreased <6-7% (cholesterols) or <20% (triglyceride) after 7 thaws in the cold, 3 thaws at room temperature, and after 18 months of storage. As these decreases were less than day-to-day reported variation of lipids, they do not appear to be physiologically significant. Cytokine (IL-6, TNF α, IL-8, IL-1β) and hsCRP concentrations decreased by 22%, 8%, 8%, 22%, and 35%, respectively; only IL-6, IL-1β and hsCRP concentrations showed significant decreases greater than day-to-day variations of 20%. For measured triglyceride and cytokine, but not cholesterol concentrations, decreases with freeze/thaw cycles were greater when concentrations were elevated. Multiple thaws also led to changes in lipoprotein sizing, specifically to a shift from medium- and large-sized HDL particles to small-sized HDL particles and from large LDL to IDL. No changes occurred for VLDL particle numbers. Though particle sizes changed, the HDL proteome did not change with multiple thaw cycles or after long term storage. Overall, the results demonstrate that it is possible to use previously obtained frozen samples for plasma cholesterol and triglyceride levels and the lipoprotein proteome, and lipoprotein sizing and cytokine concentrations if one knows the history of the sample as changes should be relative to one another.

Kinetics of plasma triglycerides in abdominal obesity

PURPOSE OF REVIEW

Abdominal obesity is associated with a number of important metabolic abnormalities including liver steatosis, insulin resistance and an atherogenic lipoprotein profile (termed dyslipidemia). The purpose of this review is to highlight recent progress in understanding the pathogenesis of this dyslipidemia.

RECENT FINDINGS

Recent results from kinetic studies using stable isotopes indicate that the hypertriglyceridemia associated with abdominal obesity stems from dual mechanisms: (1) enhanced secretion of triglyceride-rich lipoproteins and (2) impaired clearance of these lipoproteins. The over-secretion of large triglyceride-rich VLDLs from the liver is linked to hepatic steatosis and increased visceral adiposity. The impaired clearance of triglyceride-rich lipoproteins is linked to increased levels of apolipoprotein C-III, a key regulator of triglyceride metabolism.

SUMMARY

Elucidation of the pathogenesis of the atherogenic dyslipidemia in abdominal obesity combined with the development of novel treatments based on apolipoprotein C-III may in the future lead to better prevention, diagnosis and treatment of the atherogenic dyslipidemia in abdominal obesity.

Acetoacetic acid induces oxidative stress to inhibit the assembly of very low density lipoprotein in bovine hepatocytes

Dairy cows with fatty liver or ketosis exhibit hyperketonemia, oxidative stress, and a low rate of very low density lipoprotein (VLDL) assembly, and there may be a potential link among these characteristics. Therefore, the objective of this study was to determine the effect of acetoacetic acid (AcAc) on the assembly of VLDL in cow hepatocytes. Cultured cow hepatocytes were treated with different concentrations of AcAc with or without N-acetylcysteine (NAC, an antioxidant). AcAc treatment decreased the mRNA expression and activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), and significantly increased malondialdehyde (MDA) content, indicative of oxidative stress. Furthermore, AcAc treatment significantly down-regulated the mRNA expression of apolipoprotein B100 (ApoB100), apolipoprotein E (ApoE), and low density lipoprotein receptor (LDLR), which thus decreased VLDL assembly and increased triglyceride (TG) accumulation in these bovine hepatocytes. Importantly, NAC relieved AcAc-induced oxidative stress and increased VLDL assembly. In summary, these results suggest that AcAc-induced oxidative stress affects the assembly of VLDL, which increases TG accumulation in bovine hepatocytes.

Fasting and nonfasting triglycerides in cardiovascular and other diseases

Moderately elevated plasma/serum triglycerides (2-10 mmol/l) signalize increased risk for cardiovascular disease or presence of non-alcoholic steatohepatitis. Extremely elevated triglycerides (more than 10 mmol/l) signalize increased risk for pancreatitis and lipemia retinalis. The concentration of triglycerides is regulated by many genetic and nongenetic factors. Extremely elevated triglycerides not provoked by nutritional factors, especially inappropriate alcohol intake are more likely to have a monogenic cause. On the contrary, mildly to moderately elevated triglycerides are often caused by polygenic disorders; these could be also associated with central obesity, insulin resistance, and diabetes mellitus. Concentration of triglycerides is also closely interconnected with presence of atherogenic remnant lipoproteins, impaired reverse cholesterol transport and more atherogenic small LDL particles. In general, there is tight association between triglycerides and many other metabolic factors including intermediate products of lipoprotein metabolism which are frequently atherogenic. Therefore, reliable evaluation of the independent role of triglycerides especially in atherosclerosis and cardiovascular disease is difficult. In individual cases values of HDL cholesterol, non-HDL cholesterol (total minus HDL cholesterol), non-HDL/nonLDL cholesterol (total minus HDL minus LDL cholesterol, especially in nonfasting status), atherogenic index of plasma and/or apolipoprotein B could help in decisions regarding aggressiveness of treatment.

An APOC3 3'UTR variant associated with plasma triglycerides levels and coronary heart disease by creating a functional miR-4271 binding site

Apolipoprotein C-III (APOC3) is a key regulator of plasma triglycerides levels. Increasing evidence has shown that loss-of-function mutations in APOC3 is associated with reduction in plasma triglycerides levels and will confer a benefit in patients at high risk for cardiovascular disease. However, these favorable mutations were extremely distribution discrepant among different ethnics. In this study, the APOC3 gene was resequenced and we identified a common variant which located in the microRNA-binding site in APOC3 and would affect its expression and the risk of coronary heart disease (CHD). The molecular mechanism was explored. We found that the T allele of rs4225 suppressed APOC3 translation by facilitating miR-4271 binding, but not the G allele. Subjects carrying the GG genotype had higher plasma APOC3 levels (p for trend = 0.03) than those with the TT genotype. Furthermore, the T allele was significantly associated with decreased triglyceride levels [Beta (SE): -0.024 (0.020), P = 0.03]. Finally, the case-control study suggested that the TT genotype resulted in a significant reduction in overall CHD risk [OR, 0.89 (95% confidence interval, 0.77-0.98), P = 0.009]. In conclusion, our results provide evidence that the rs4225 in the 3'-UTR of APOC3 might contribute to the risk of CHD by interfering with miR-4271 binding.

Low-Density Lipoprotein Receptor-Dependent and Low-Density Lipoprotein Receptor-Independent Mechanisms of Cyclosporin A-Induced Dyslipidemia

OBJECTIVE

Cyclosporin A (CsA) is an immunosuppressant commonly used to prevent organ rejection but is associated with hyperlipidemia and an increased risk of cardiovascular disease. Although studies suggest that CsA-induced hyperlipidemia is mediated by inhibition of low-density lipoprotein receptor (LDLr)-mediated lipoprotein clearance, the data supporting this are inconclusive. We therefore sought to investigate the role of the LDLr in CsA-induced hyperlipidemia by using Ldlr-knockout mice (Ldlr(-/-)).

APPROACH AND RESULTS

Ldlr(-/-) and wild-type (wt) C57Bl/6 mice were treated with 20 mg/kg per d CsA for 4 weeks. On a chow diet, CsA caused marked dyslipidemia in Ldlr(-/-) but not in wt mice. Hyperlipidemia was characterized by a prominent increase in plasma very low-density lipoprotein and intermediate-density lipoprotein/LDL with unchanged plasma high-density lipoprotein levels, thus mimicking the dyslipidemic profile observed in humans. Analysis of specific lipid species by liquid chromatography-tandem mass spectrometry suggested a predominant effect of CsA on increased very low-density lipoprotein-IDL/LDL lipoprotein number rather than composition. Mechanistic studies indicated that CsA did not alter hepatic lipoprotein production but did inhibit plasma clearance and hepatic uptake of [(14)C]cholesteryl oleate and glycerol tri[(3)H]oleate-double-labeled very low-density lipoprotein-like particles. Further studies showed that CsA inhibited plasma lipoprotein lipase activity and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9.

CONCLUSIONS

We demonstrate that CsA does not cause hyperlipidemia via direct effects on the LDLr. Rather, LDLr deficiency plays an important permissive role for CsA-induced hyperlipidemia, which is associated with abnormal lipoprotein clearance, decreased lipoprotein lipase activity, and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9. Enhancing LDLr and lipoprotein lipase activity and decreasing apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9 levels may therefore provide attractive treatment targets for patients with hyperlipidemia receiving CsA.

Icosapent ethyl (eicosapentaenoic acid ethyl ester): Effects on plasma apolipoprotein C-III levels in patients from the MARINE and ANCHOR studies

BACKGROUND

Apolipoprotein C-III (ApoC-III) regulates lipoprotein and triglyceride (TG) metabolism and may have a causal role in cardiovascular disease. In the Multi-Center, Placebo-Controlled, Randomized, Double-Blind, 12-Week Study With an Open-Label Extension (MARINE) and ANCHOR studies, icosapent ethyl, a high-purity prescription eicosapentaenoic acid ethyl ester, reduced TG, and other atherogenic lipid parameters without increasing low-density lipoprotein cholesterol (LDL-C) compared with placebo.

OBJECTIVE

To evaluate the effects of icosapent ethyl on plasma ApoC-III levels in patients from 2 phase 3 studies.

METHODS

MARINE and ANCHOR were 12-week double-blind studies of icosapent ethyl in adult patients. Patients in MARINE had very high TG levels (≥500 and ≤2000 mg/dL) and patients in ANCHOR had high TG levels (≥200 and <500 mg/dL) despite statin control of LDL-C. This post hoc analysis of MARINE and ANCHOR assessed the median percent change from baseline in plasma ApoC-III levels vs placebo and includes subgroup analyses by statin use/efficacy and median ApoC-III levels.

RESULTS

We assessed ApoC-III levels in 148 and 612 patients in the MARINE and ANCHOR studies, respectively. In MARINE, the approved prescription dose of icosapent ethyl (4 g/day) significantly reduced ApoC-III levels by 25.1% (P < .0001) vs placebo. In ANCHOR, icosapent ethyl 4 g/day significantly reduced ApoC-III levels by 19.2% (P < .0001) vs placebo; subanalysis by statin efficacy revealed significant reductions vs placebo in the higher-efficacy and medium-efficacy groups (24.6% and 17.2%, respectively; both P < .0001).

CONCLUSION

Icosapent ethyl 4 g/day significantly reduced plasma ApoC-III levels in patients with elevated TGs from the MARINE and ANCHOR studies.

Reduction in lipoprotein-associated apoC-III levels following volanesorsen therapy: phase 2 randomized trial results

Elevated apoC-III levels predict increased cardiovascular risk when present on LDL and HDL particles. We developed novel high-throughput chemiluminescent ELISAs that capture apoB, lipoprotein (a) [Lp(a)], and apoA-I in plasma and then detect apoC-III on these individual lipoproteins as apoCIII-apoB, apoCIII-Lp(a), and apoCIII-apoAI complexes, respectively. We assessed the effects on these complexes of placebo or 100-300 mg volanesorsen, a generation 2.0+ antisense drug that targets apoC3 mRNA in patients with hypertriglyceridemia, including familial chylomicronemia syndrome (n = 3), volanesorsen monotherapy (n = 51), and as add-on to fibrate (n = 26), treated for 85 days and followed for 176 days. Compared with placebo, volanesorsen was associated with an 82.3 ± 11.7%, 81.3 ± 15.7%, and 80.8 ± 13.6% reduction in apoCIII-apoB, apoCIII-Lp(a), and apoCIII-apoA-I, respectively (300 mg dose;P< 0.001 for all), at day 92. Strong correlations in all assay measures were noted with total plasma apoC-III, chylomicron-apoC-III, and VLDL-apoC-III. In conclusion, novel high-throughput ELISAs were developed to detect lipoprotein-associated apoC-III, including for the first time on Lp(a). Volanesorsen uniformly lowers apoC-III on apoB-100, Lp(a), and apoA-I lipoproteins, and may be a potent agent to reduce triglycerides and cardiovascular risk mediated by apoC-III.

Apolipoprotein CIII overexpression exacerbates diet-induced obesity due to adipose tissue higher exogenous lipid uptake and retention and lower lipolysis rates

Background

Hypertriglyceridemia is a common type of dyslipidemia found in obesity. However, it is not established whether primary hyperlipidemia can predispose to obesity. Evidences have suggested that proteins primarily related to plasma lipoprotein transport, such as apolipoprotein (apo) CIII and E, may significantly affect the process of body fat accumulation. We have previously observed an increased adiposity in response to a high fat diet (HFD) in mice overexpressing apoCIII. Here, we examined the potential mechanisms involved in this exacerbated response of apoCIII mice to the HFD.

Methods

We measured body energy balance, tissue capacity to store exogenous lipids, lipogenesis and lipolysis rates in non-transgenic and apoCIII overexpressing mice fed a HFD during two months.

Results

Food intake, fat excretion and whole body CO₂ production were similar in both groups. However, the adipose tissue mass (45 %) and leptin plasma levels (2-fold) were significantly greater in apoCIII mice. Lipogenesis rates were similar, while exogenous lipid retention was increased in perigonadal (2-fold) and brown adipose tissues (40 %) of apoCIII mice. In addition, adipocyte basal lipolysis (55 %) and in vivo lipolysis index (30 %) were significantly decreased in apoCIII mice. A fat tolerance test evidenced delayed plasma triglyceride clearance and greater transient availability of non-esterified fatty acids (NEFA) during the post-prandial state in the apoCIII mice plasma. Thus, apoCIII overexpression resulted in increased NEFA availability to adipose uptake and decreased adipocyte lipolysis, favoring lipid enlargement of adipose depots.

Conclusion

We propose that plasma apoCIII levels represent a new risk factor for diet-induced obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-015-0058-6) contains supplementary material, which is available to authorized users.

Kinetic and Related Determinants of Plasma Triglyceride Concentration in Abdominal Obesity: Multicenter Tracer Kinetic Study

OBJECTIVES

Patients with obesity and diabetes mellitus have increased risk of cardiovascular disease. A major cause is an atherogenic dyslipidemia related primarily to elevated plasma concentrations of triglyceride-rich lipoproteins. The aim of this study was to clarify determinants of plasma triglyceride concentration. We focused on factors that predict the kinetics of very-low density lipoprotein 1 (VLDL1) triglycerides.

APPROACH AND RESULTS

A multicenter study using dual stable isotopes (deuterated leucine and glycerol) and multicompartmental modeling was performed to elucidate the kinetics of triglycerides and apoB in VLDL1 in 46 subjects with abdominal obesity and additional cardiometabolic risk factors. Results showed that plasma triglyceride concentrations were dependent on both the secretion rate (r=0.44, P<0.01; r=0.45, P<0.01) and fractional catabolism (r=0.49, P<0.001; r=0.55, P<0.001) of VLDL1-triglycerides and VLDL1-apoB. Liver fat mass was independently and directly associated with secretion rates of VLDL1-triglycerides (r=0.56, P<0.001) and VLDL1-apoB (r=0.53, P<0.001). Plasma apoC-III concentration was independently and inversely associated with the fractional catabolisms of VLDL1-triglycerides (r=0.48, P<0.001) and VLDL1-apoB (r=0.51, P<0.001).

CONCLUSIONS

Plasma triglyceride concentrations in abdominal obesity are determined by the kinetics of VLDL1 subspecies, catabolism being mainly dependent on apoC-III concentration and secretion on liver fat content. Reduction in liver fat and targeting apoC-III may be an effective approach for correcting triglyceride metabolism atherogenic dyslipidemia in obesity.

Sirtuin regulation in aging and injury

Sirtuins or Sir2 family of proteins are a class of NAD(+) dependent protein deacetylases which are evolutionarily conserved from bacteria to humans. Some sirtuins also exhibit mono-ADP ribosyl transferase, demalonylation and desuccinylation activities. Originally identified in the yeast, these proteins regulate key cellular processes like cell cycle, apoptosis, metabolic regulation and inflammation. Humans encode seven sirtuin isoforms SIRT1-SIRT7 with varying intracellular distribution. Apart from their classic role as histone deacetylases regulating transcription, a number of cytoplasmic and mitochondrial targets of sirtuins have also been identified. Sirtuins have been implicated in longevity and accumulating evidence indicate their role in a spectrum of diseases like cancer, diabetes, obesity and neurodegenerative diseases. A number of studies have reported profound changes in SIRT1 expression and activity linked to mitochondrial functional alterations following hypoxic-ischemic conditions and following reoxygenation injury. The SIRT1 mediated deacetylation of targets such as PGC-1α, FOXO3, p53 and NF-κb has profound effect on mitochondrial function, apoptosis and inflammation. These biological processes and functions are critical in life-span determination and outcome following injury. Aging is reported to be characterized by declining SIRT1 activity, and its increased expression or activation demonstrated prolonged life-span in lower forms of animals. A pseudohypoxic state due to declining NAD(+) has also been implicated in aging. In this review we provide an overview of studies on the role of sirtuins in aging and injury.

Antisense Inhibition of Apolipoprotein C-III in Patients with Hypertriglyceridemia

BACKGROUND

Apolipoprotein C-III (APOC3) is a key regulator of plasma triglyceride levels. Elevated triglyceride levels are associated with a risk of adverse cardiovascular events and pancreatitis. ISIS 304801 is a second-generation antisense inhibitor of APOC3 synthesis.

METHODS

We conducted a randomized, double-blind, placebo-controlled, dose-ranging, phase 2 study to evaluate ISIS 304801 in untreated patients with fasting triglyceride levels between 350 mg per deciliter (4.0 mmol per liter) and 2000 mg per deciliter (22.6 mmol per liter) (ISIS 304801 monotherapy cohort), as well as in patients receiving stable fibrate therapy who had fasting triglyceride levels between 225 mg per deciliter (2.5 mmol per liter) and 2000 mg per deciliter (ISIS 304801-fibrate cohort). Eligible patients were randomly assigned to receive either ISIS 304801, at doses ranging from 100 to 300 mg, or placebo, once weekly for 13 weeks. The primary outcome was the percentage change in APOC3 level from baseline.

RESULTS

A total of 57 patients were treated in the ISIS 304801 monotherapy cohort (41 received active agent, and 16 received placebo), and 28 patients were treated in the ISIS 304801-fibrate cohort (20 received active agent, and 8 received placebo). The mean (±SD) baseline triglyceride levels in the two cohorts were 581±291 mg per deciliter (6.6±3.3 mmol per liter) and 376±188 mg per deciliter (4.2±2.1 mmol per liter), respectively. Treatment with ISIS 304801 resulted in dose-dependent and prolonged decreases in plasma APOC3 levels when the drug was administered as a single agent (decreases of 40.0±32.0% in the 100-mg group, 63.8±22.3% in the 200-mg group, and 79.6±9.3% in the 300-mg group, vs. an increase of 4.2±41.7% in the placebo group) and when it was administered as an add-on to fibrates (decreases of 60.2±12.5% in the 200-mg group and 70.9±13.0% in the 300-mg group, vs. a decrease of 2.2±25.2% in the placebo group). Concordant reductions of 31.3 to 70.9% were observed in triglyceride levels. No safety concerns were identified in this short-term study.

CONCLUSIONS

We found that treatment with ISIS 304801 was associated with significant lowering of triglyceride levels, among patients with a broad range of baseline levels, through selective antisense inhibition of APOC3 synthesis. (Funded by Isis Pharmaceuticals; ClinicalTrials.gov number, NCT01529424.).

Saturated Fats Versus Polyunsaturated Fats Versus Carbohydrates for Cardiovascular Disease Prevention and Treatment

The effects of saturated fatty acids (SFAs) on cardiovascular disease (CVD) risk are modulated by the nutrients that replace them and their food matrices. Replacement of SFAs with polyunsaturated fatty acids has been associated with reduced CVD risk, although there is heterogeneity in both fatty acid categories. In contrast, replacement of SFAs with carbohydrates, particularly sugar, has been associated with no improvement or even a worsening of CVD risk, at least in part through effects on atherogenic dyslipidemia, a cluster of traits including small, dense low-density lipoprotein particles. The effects of dietary SFAs on insulin sensitivity, inflammation, vascular function, and thrombosis are less clear. There is growing evidence that SFAs in the context of dairy foods, particularly fermented dairy products, have neutral or inverse associations with CVD. Overall dietary patterns emphasizing vegetables, fish, nuts, and whole versus processed grains form the basis of heart-healthy eating and should supersede a focus on macronutrient composition.