Is Apo-CIII the new cardiovascular target? An analysis of its current clinical and dietetic therapies

AIMS

Recently, Apolipoprotein CIII (Apo-CIII) has gained remarkable attention since its overexpression has been strongly correlated to cardiovascular disease (CVD) occurrence. The aim of this review was to summarize the latest findings of Apo-CIII as a CVDs and diabetes risk factor, as well as the plausible mechanisms involved in the development of these pathologies, with particular emphasis on current clinical and dietetic therapies.

DATA SYNTHESIS

Apo-CIII is a small protein (∼8.8 kDa) that, among other functions, inhibits lipoprotein lipase, a key enzyme in lipid metabolism. Apo-CIII plays a fundamental role in the physiopathology of atherosclerosis, type-1, and type-2 diabetes. Apo-CIII has become a potential clinical target to tackle these multifactorial diseases. Dietetic (omega-3 fatty acids, stanols, polyphenols, lycopene) and non-dietetic (fibrates, statins, and antisense oligonucleotides) therapies have shown promising results to regulate Apo-CIII and triglyceride levels. However, more information from clinical trials is required to validate it as a new target for atherosclerosis and diabetes types 1 and 2.

CONCLUSIONS

There are still several pathways involving Apo-CIII regulation that might be affected by bioactive compounds that need further research. The mechanisms that trigger metabolic responses following bioactive compounds consumption are mainly related to higher LPL expression and PPARα activation, although the complete pathways are yet to be elucidated.

The Positive Association between Plasma Myristic Acid and ApoCIII Concentrations in Cardiovascular Disease Patients Is Supported by the Effects of Myristic Acid in HepG2 Cells

BACKGROUND

In the settings of primary and secondary prevention for coronary artery disease (CAD), a crucial role is played by some key molecules involved in triglyceride (TG) metabolism, such as ApoCIII. Fatty acid (FA) intake is well recognized as a main determinant of plasma lipids, including plasma TG concentration.

OBJECTIVES

The aim was to investigate the possible relations between the intakes of different FAs, estimated by their plasma concentrations, and circulating amounts of ApoCIII.

METHODS

Plasma samples were obtained from 1370 subjects with or without angiographically demonstrated CAD (mean ± SD age: 60.6 ± 11.0 y; males: 75.8%; BMI: 25.9 ± 4.6 kg/m2; CAD: 73.3%). Plasma lipid, ApoCIII, and FA concentrations were measured. Data were analyzed by regression models adjusted for FAs and other potential confounders, such as sex, age, BMI, diabetes, smoking, and lipid-lowering therapies. The in vitro effects of FAs were tested by incubating HepG2 hepatoma cells with increasing concentrations of selected FAs, and the mRNA and protein contents in the cells were quantified by real-time RT-PCR and LC-MS/MS analyses.

RESULTS

Among all the analyzed FAs, myristic acid (14:0) showed the most robust correlations with both TGs (R = 0.441, P = 2.6 × 10-66) and ApoCIII (R = 0.327, P = 1.1 × 10-31). By multiple regression analysis, myristic acid was the best predictor of both plasma TG and ApoCIII variability. Plasma TG and ApoCIII concentrations increased progressively at increasing concentrations of myristic acid, independently of CAD diagnosis and gender. Consistent with these data, in the in vitro experiments, an ∼2-fold increase in the expression levels of the ApoCIII mRNA and protein was observed after incubation with 250 μM myristic acid. A weaker effect (∼30% increase) was observed for palmitic acid, whereas incubation with oleic acid did not affect ApoCIII protein or gene expression.

CONCLUSIONS

Plasma myristic acid is associated with increased ApoCIII concentrations in cardiovascular patients. In vitro experiments indicated that myristic acid stimulates ApoCIII expression in HepG2 cells.

Familial Chylomicronemia Syndrome (FCS): Recent Data on Diagnosis and Treatment

PURPOSE OF REVIEW

Familial chylomicronemia syndrome (FCS) is a rare recessive genetic disorder often underdiagnosed with potentially severe clinical consequences. In this review, we describe the clinical and biological characteristics of the disease together with its main complication, i.e., acute pancreatitis. We focused the paper on new diagnostic tools, progress in understanding the role of two key proteins (apolipoprotein CIII (apo CIII) and angiopoietin-like3 (ANGPTL-3)), and new therapeutic options.

RECENT FINDINGS

Recently, a new diagnostic tool has been proposed by European experts to help identify these patients. This tool with two recently identified parameters (low LDL and low body mass index) can help identify patients who should be genetically tested or who may have the disease when genetic testing is not available. FCS is caused by homozygous or compound heterozygous mutations of lipoprotein lipase, apolipoprotein C-II, apolipoprotein A-V, glycosylphosphatidylinositol anchored high-density lipoprotein-binding protein 1, and lipase maturation factor. Two proteins have been identified as important player in the metabolism of triglyceride-rich lipoprotein and its regulation. These two proteins are therapeutic target. Antisense oligonucleotide targeting apo CIII has been shown to significantly decrease triglyceride levels even in FCS and is the first available treatment for these patients. Further development might identify new compounds with reduced risk to develop severe thrombocytopenia. ANGPTL-3 inhibitors have not yet been tested in FCS patients but exert significant hypotriglyceridemic effect in the more frequent and less severe polygenic forms. Beyond these two new targets, microsomal triglyceride transfer protein (MTTP) inhibitors could also be part of the armamentarium, if on-going trials confirm their efficacy. New clinical tools and simple criteria can help select patients with possible FCS and identify patients who should have a genetic testing. Identifying patients with FCS is a major issue since these patients have a high risk to suffer severe episodes of acute pancreatitis and may now benefit from new therapeutic options including antisense oligonucleotide targeting apo CIII.

Apolipoprotein CIII predicts cardiovascular events in patients with coronary artery disease: a prospective observational study

Background

Apolipoprotein CIII (apoCIII) is associated with triglyceride-rich lipoprotein metabolism and has emerged as independent marker for risk of cardiovascular disease. The objective was to test whether apoCIII is regulated postprandially and whether apoCIII concentrations in native and chylomicron-free serum predict future cardiovascular events in patients with stable coronary artery disease (CAD).

Methods

ApoCIII concentrations were measured in native and chylomicron-free serum in the fasting state and after a standardized oral fat load test in 195 patients with stable CAD. Clinical follow-up was 48 months. Chylomicron-free serum was prepared by ultracentrifugation (18,000 rpm, 3 h). The log-rank test and Cox regression analyses were used to investigate the association of apoCIII with recurrent cardiovascular events.

Results

Of the 195 patients included, 92 had a cardiovascular event, and 103 did not. 97% were treated with a statin. No significant changes in apoCIII concentration were observed after the oral fat load test. The apoCIII concentration was associated with event-free survival independent of conventional risk factors. This association reached statistical significance only for apoCIII concentration measured in chylomicron-free serum (hazard ratio [95% confidence interval] for apoCIII above the mean: postprandial: 1.67 (1.06–2.29), P = 0.028, fasting: 2.09 (1.32–3.32), P = 0.002), but not for apoCIII concentration measured in native serum (postprandial: 1.47 [0.89–2.43], P = 0.133, fasting: 1.56 [0.95–2.58], P = 0.081). The effects were independent of other risk factors.

Conclusions

ApoCIII concentrations in chylomicron-free serum are independently associated with event-free survival in patients with CAD both in fasting and postprandial state. This findings support considering apoCIII for risk assessment and attempting to test the hypothesis that lowering apoCIII reduces residual cardiovascular risk.

Take home message

Apolipoprotein CIII concentration measured in chylomicron-free serum predicts recurrent cardiovascular events in patients with stable coronary artery disease.

Trial registration

The trial which included the participants of this study was registered at https://clinicaltrials.gov (NCT00628524) on March 5, 2008.

Human apolipoprotein CIII levels; evaluation of three assay methods

Apolipoprotein CIII (apoCIII) is associated with triglyceride (TG)-rich particles like VLDL and exerts an inhibitory effect of lipoprotein lipase. Increased levels are related to cardiovascular diseases and diabetes and therefore apoCIII has been proposed as a useful biomarker. Even if several commercial assays for measuring apoCIII in human plasma/serum are available, data is scarce concerning their reliability and none is used clinically. In the present study a comparative investigation has been done. Two ELISA-based methods (Cusabio Biotech and Assay Pro) and one nephelometric assay (Siemens Healthcare) were investigated. Serum and plasma samples were obtained from healthy volunteers and from samples sent to the Laboratory of Clinical Chemistry, preferably with higher levels of TGs. The Cusabio Biotech assay did not yield any valid results. However, both the methods from Assay Pro and Siemens Healthcare showed good performance with similar dynamic ranges. The latter assay had lower CV and required less work. In healthy individuals, apoCIII levels were not affected by fasting, freezing or thawing, nor did we find any gender differences. Individuals with elevated levels of TG displayed higher apoCIII values. Females with oral intake of contraceptives had higher levels. In conclusion, the nephelometric assay showed the best performance with the lowest CV, was less labor intensive than an assay based on ELISA and could therefore be suitable for clinical use.

Contribution of ApoCIII to Diabetic Dyslipidemia and Treatment With Volanesorsen

Diabetic dyslipidemia in type 2 diabetes (T2DM) is characterized by elevated levels of triglycerides (TG), decreased levels of high density lipoprotein-cholesterol (HDL-C), elevated levels of low density lipoprotein-cholesterol (LDLC), and the predominance of small and dense LDL particles (sdLDL). The mechanism underlying diabetic dyslipidemia remains unclear. Insulin resistance is believed to be an important determinant. Mechanisms underlying insulin resistance-induced diabetic dyslipidemia seem to be related to apolipoprotein CIII (ApoCIII), a known inhibitor of lipoprotein lipase. The concentration of very low density lipoprotein1 (VLDL₁) with a higher TG content and abundant ApoCIII was found to be significantly elevated in patients with T2DM. Recently, volanesorsen as a promising ApoIII inhibitor was shown to improve the lipid profile in patients with diabetic dyslipidemia. Herein, this paper will review recent advance in pathophysiology of diabetic dyslipidemia and the role of ApoCIII in this condition, with focus on describing a novel drug volanesorsen as potential treatment strategy.

Neither polyphenol-rich red wine nor fenofibrate affects the onset of type-1 diabetes mellitus in the BB rat

Serum levels of the pro-inflammatory apolipoprotein CIII (apoCIII) are increased in type-1 diabetic (T1D) patients and when β-cells are exposed to apoCIII they undergo apoptosis, which can be prevented by an antibody against apoCIII. We have previously investigated the BB rat, an animal model that develops a human-like T1D at the age of around 60 days, and found that apoCIII was also increased in sera from pre-diabetic rats and this promoted β-cell death. Lowering apoCIII with an oligonucleotide antisense during a phase of the pre-diabetic period prolonged the time to onset of T1D. In order to find other ways to lower apoCIII we in this study tested non-alcoholic red wine with medium and high concentrations of polyphenols and the lipid-lowering drug, fenofibrate, both reported to decrease the expression of apoCIII by activating peroxisome proliferator-activated receptors. Pre-diabetic BB-rats were treated orally for one month prior to the expected onset of diabetes with the two different wines or fenofibrate. None of the treatments prevented or prolonged the time to onset of diabetes and the expression of apoCIII was unaffected in this animal model for T1D. However, it must be emphasized that this does not exclude that other species can show a response to these substances.

Increased inflammation, endoplasmic reticulum stress and oxidative stress in endothelial and macrophage cells exacerbate atherosclerosis in ApoCIII transgenic mice

Background

Overexpression of apolipoprotein CIII (ApoCIII) leads to hypertriglyceridemia (HTG) which promotes atherosclerosis development. However, it remains unclear whether ApoCIII affects the atherosclerosis alone by promoting the inflammation and endoplasmic reticulum (ER) stress, or in combination with HTG.

Methods

Transgenic (ApoCIIItg) mouse models were used to investigate the atherogenic role of ApoCIII. Since endothelial cells and macrophages play crucial roles in atherosclerosis, we examined whether triglyceride-rich lipoproteins (TRLs), the major lipoproteins, in plasma of ApoCIIItg mice affect inflammation and ER stress levels in these cells. To further investigate the role of ApoCIII and triglyceride, we incubated HUVECs cells and peritoneal macrophages with TRLs with or without ApoCIII.

Results

Increased inflammation and ER stress were found in the aorta of ApoCIIItg mice. TRLs increased ER stress and oxidative stress in HUVECs and macrophages in a dose dependent. Moreover, TRLs together with ApoCIII could induce a higher inflammation level than TRLs alone in these cells.

Conclusions

Both TRLs and ApoCIII contribute to the progression of atherosclerosis, and the modulation of TRLs and ApoCIII may represent a novel therapeutic approach against HTG induced atherosclerosis.

Effect of statin therapy on plasma apolipoprotein CIII concentrations: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Statins are well-established low-density lipoprotein cholesterol-lowering drugs. Elevated apolipoprotein CIII (Apo CIII) levels are associated with elevated triglyceride-rich particles, which are also considered to be a possible risk factor for cardiovascular disease.

OBJECTIVE

The aim of this meta-analysis of randomized placebo-controlled clinical trials was to assess the effect of statins on Apo CIII concentrations.

METHODS

Randomized placebo-controlled trials investigating the impact of statin treatment on cholesterol lowering that include lipoprotein measurement were searched in PubMed, MEDLINE, Scopus, Web of Science, and Google Scholar databases (up to July 31, 2017). A random-effects model and generic inverse variance method were used for quantitative data synthesis. Sensitivity analysis was conducted using the leave-one-out method. A weighted random-effects meta-regression was performed to evaluate the impact of potential confounders on Apo CIII concentrations.

RESULTS

This meta-analysis of data from 6 randomized placebo-controlled clinical trials (10 statin arms) involving 802 subjects showed that statin therapy significantly decreased circulating Apo CIII concentrations (weighted mean difference [WMD]: -2.71, 95% confidence interval [CI]: -3.74 to -1.68, P < .001; I²: 73.83%). The effect size was robust in the leave-one-out sensitivity analysis and not driven by any single study. Subgroup analysis showed a reduction of Apo CIII concentrations by atorvastatin (WMD: -4.74, 95% CI: -3.74 to -1.68, P = .002; I²: 84.02%), rosuvastatin (WMD: -2.68, 95% CI: -4.52 to -0.84, P = .004; I²: 0%), and lovastatin (WMD: -1.64, 95% CI: -2.22 to -1.07, P < .001; I²: 0%).

CONCLUSION

This meta-analysis suggests that statin treatment significantly reduces plasma Apo CIII levels.

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

ApoCIII as a Cardiovascular Risk Factor and Modulation by the Novel Lipid-Lowering Agent Volanesorsen

PURPOSE OF REVIEW

Apolipoprotein CIII (ApoCIII) is now recognized as a key regulator in severe hypertriglyceridemia, chylomicronemia, and conditions of triglyceride-rich lipoprotein (TRL) remnant excess due to its inhibition of lipoprotein lipase (LPL) and hepatic lipase, leading to decreased hepatic reuptake of TRLs, as well as enhanced synthesis and secretion of VLDL from the liver. ApoCIII gain-of-function mutations are associated with atherosclerosis and coronary heart disease (CHD), and contribute to the development of cardiometabolic syndrome, hypertriglyceridemia, and type 2 diabetes mellitus. Conversely, loss-of-function mutations in ApoCIII are associated with lower levels of plasma triglycerides (TG), attenuation of vascular inflammatory processes such as monocyte adhesion and endothelial dysfunction, and potentially, a reduction in the incidence and progression of atherosclerosis and cardioprotection.

RECENT FINDINGS

Evidence is now emerging that volanesorsen, a second-generation antisense oligonucleotide drug targeting ApoCIII messenger RNA resulting in decreases in TG in patients with familial chylomicronemia syndrome, severe hypertriglyceridemia, and metabolic dyslipidemia with type 2 diabetes giving support to the hypothesis that ApoCIII is a powerful inhibitor of LPL, and when reduced, endogenous clearance of TRLs can result in substantial reductions in TG levels. Discovery of the ApoCIII inhibitor volanesorsen opens a new era of lipid-lowering drugs for reduction in TG and potentially for reduction in LDL-C. Herein, this review will provide an update on the pathophysiology of ApoCIII-linked atherosclerosis and the development of the first drug to target ApoCIII, volanesorsen, as a promising lipid-lowering agent.

Omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and their mechanisms of action on apolipoprotein B-containing lipoproteins in humans: a review

Background

Epidemiological and genetic studies suggest that elevated triglyceride (TG)-rich lipoprotein levels in the circulation increase the risk of cardiovascular disease. Prescription formulations of omega-3 fatty acids (OM3FAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), reduce plasma TG levels and are approved for the treatment of patients with severe hypertriglyceridemia. Many preclinical studies have investigated the TG-lowering mechanisms of action of OM3FAs, but less is known from clinical studies.

Methods

We conducted a review, using systematic methodology, of studies in humans assessing the mechanisms of action of EPA and DHA on apolipoprotein B-containing lipoproteins, including TG-rich lipoproteins and low-density lipoproteins (LDLs). A systematic search of PubMed retrieved 55 articles, of which 30 were used in the review; 35 additional arrticles were also included.

Results

In humans, dietary DHA is retroconverted to EPA, while production of DHA from EPA is not observed. Dietary DHA is preferentially esterified into TGs, while EPA is more evenly esterified into TGs, cholesterol esters and phospholipids. The preferential esterification of DHA into TGs likely explains the higher turnover of DHA than EPA in plasma. The main effects of both EPA and DHA are decreased fasting and postprandial serum TG levels, through reduction of hepatic very-low-density lipoprotein (VLDL)-TG production. The exact mechanism for reduced VLDL production is not clear but does not include retention of lipids in the liver; rather, increased hepatic fatty acid oxidation is likely. The postprandial reduction in TG levels is caused by increased lipoprotein lipase activity and reduced serum VLDL-TG concentrations, resulting in enhanced chylomicron clearance. Overall, no clear differences between the effects of EPA and DHA on TG levels, or on turnover of TG-rich lipoproteins, have been observed. Effects on LDL are complex and may be influenced by genetics, such as APOE genotype.

Conclusions

EPA and DHA diminish fasting circulating TG levels via reduced production of VLDL. The mechanism of reduced VLDL production does not involve hepatic retention of lipids. Lowered postprandial TG levels are also explained by increased chylomicron clearance. Little is known about the specific cellular and biochemical mechanisms underlying the TG-lowering effects of EPA and DHA in humans.

Plasma apoCIII Levels in Relation to Inflammatory Traits and Metabolic Syndrome in Patients not Treated with Lipid-lowering Drugs Undergoing Coronary Angiography

OBJECTIVE

Assessment of the comprehensive relationship among apolipoprotein CIII (apoCIII) levels, inflammation, and metabolic disorders is rare.

METHODS

A total of 1455 consecutive patients not treated with lipid-lowering drugs and undergoing coronary angiography were enrolled in this cross-sectional study. A mediation analysis was used to detect the underlying role of apoCIII in the association of inflammation with metabolic syndrome (MetS).

RESULTS

Patients with MetS showed higher levels of apoCIII [95.1 (73.1-131.4) vs. 81.7 (58.6-112.4) μg/mL, P < 0.001] and inflammatory markers [high sensitivity C-reactive protein, 1.7 (0.8-3.4) vs. 1.1 (0.5-2.2) mg/L; white blood cell count, (6.48 ± 1.68) vs. (6.11 ± 1.67) × 109/L]. The levels of apoCIII and inflammatory markers increased with the number of metabolic risk components (all P < 0.001). Furthermore, apoCIII levels were associated with virtually all individual MetS risk factors and inflammatory markers (all P < 0.05). Importantly, the prevalence of MetS in each metabolic disorder rose as apoCIII levels increased (all P < 0.05). Mediation analysis showed that apoCIII partially mediated the effect of inflammation on MetS independently from triglycerides.

CONCLUSION

Plasma apoCIII levels were significantly associated with the development and severity of MetS, and a role of apoCIII in the effect of inflammation on the development of MetS was identified.

Mass spectrometry-based approaches to targeted quantitative proteomics in cardiovascular disease

Mass spectrometry-based proteomics methodology has become an important tool in elucidating some of the underlying mechanisms involved in cardiovascular disease. The present review provides details on selected important protein targets where highly selective and specific mass spectrometry-based approaches have led to important new findings and provided new mechanistic information. The role of six proteins involved in the etiology of cardiovascular disease (acetylated platelet cyclooxygenase-1, serum apolipoprotein A1, apolipoprotein C-III, serum C-reactive protein, serum high mobility group box-1 protein, insulin-like growth factor I) and their quantification has been discussed. There are an increasing number of examples where highly selective mass spectrometry-based quantification has provided new important data that could not be obtained with less labor intensive and cheaper immunoassay-based procedures. It is anticipated that these findings will lead to significant advances in a number of important issues related to the role of specific proteins in cardiovascular disease. The availability of a new generation of high-resolution high-sensitivity mass spectrometers will greatly facilitate these studies so that in the future it will be possible to analyze serum proteins of relevance to cardiovascular disease with levels of specificity and/or sensitivity that cannot be attained by immunoassay-based procedures.

18O proteomics reveal increased human apolipoprotein CIII in Hispanic HIV-1+ women with HAART that use cocaine

PURPOSE

Drug abuse is a major risk factor in the development and progression of HIV-1. This study defines the alterations in the plasma proteome of HIV-1-infected women that use cocaine.

EXPERIMENTAL DESIGN

Plasma samples from 12 HIV-seropositive Hispanic women under antiretroviral therapy were selected for this study. Six sample pairs were matched between nondrug users and cocaine users. After IgG and albumin depletion, SDS-PAGE, and in-gel digestion, peptides from nondrug users and cocaine users were labeled with (16) O and (18) O, respectively, and subjected to LC-MS/MS and quantitation using Proteome Discover and QuiXoT softwares and validated by ELISA.

RESULTS

A total of 1015 proteins were identified at 1% false discovery rates (FDR). Statistical analyses revealed 13 proteins with significant changes between the two groups, cocaine and noncocaine users (p < 0.05). The great majority pertained to protection defense function and the rest pertained to transport, homeostatic, regulation, and binding of ligands. Apolipoprotein CIII was increased in plasma of HIV+ Hispanic women positive for cocaine compared to HIV+ nondrug users (p ≤ 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

Increased human apolipoprotein CIII warrants that these patients be carefully monitored to avoid the increased risk of cardiovascular events associated with HIV, HAART, and cocaine use.

Reduced high density lipoprotein cholesterol in severe hypertriglyceridemic ApoCIII transgenic mice via lowered hepatic ApoAI synthesis

Clinical and epidemiological investigations confirm that patients with loss-of-function mutations (R19X, etc.) in Apolipoprotein CIII (ApoCIII) showed beneficial lipid profile including decreased plasma triglyceride and increased high density lipoprotein (HDL) levels. However, whether HDL level would be reduced in hypertriglyceridemia (HTG) induced by high ApoCIII expression has not been demonstrated yet. Here we showed, ApoCIII transgenic mice (ApoCIIItg) displayed severe HTG and had significantly lower HDL level. Analysis of apolipoproteins in lipoprotein fractions by SDS-PAGE revealed marked decrease of apolipoprotein AI (ApoAI) in HDL in transgenic mice compared with the wild type mice (WT) as controls. Further examination demonstrated that hepatic but not intestinal ApoAI mRNA was significantly reduced. Therefore, the decreased ApoAI synthesis might be accounted for the lower plasma HDL level in ApoCIII transgenic mice.

Maternal inheritance of severe hypertriglyceridemia impairs glucose metabolism in offspring

Maternally inherited familial hypercholesterolemia (FH) impairs glucose metabolism and increases cardiovascular risks in the offspring to a greater degree than paternal inherited FH. However, it remains unknown whether hypertriglyceridemia affects glucose metabolism via inheritance. In this study, we sought to compare the impact of maternally and paternally inherited hypertriglyceridemia on glucose and lipid metabolism in mice. ApoCIII transgenic mice with severe hypertriglyceridemia were mated with non-transgenic control mice to obtain 4 types of offspring: maternal non-transgenic control and maternal transgenic offspring, and paternal control and paternal transgenic offspring. Plasma triglycerides (TG), total cholesterol (TC), fasting plasma glucose (FPG) and fasting insulin (FINS) were measured. ApoCIII overexpression caused severe hypertriglyceridemia, but the transgenic female mice had unaltered fertility with normal pregnancy and birth of pups. The 4 groups of offspring had similar birth weight and growth rate. The plasma TG of maternal and paternal transgenic offspring were nearly 40-fold higher than maternal and paternal control mice, but there was no difference in plasma TG between maternal and paternal transgenic offspring. Although the FPG of the 4 groups of animals had no difference, the maternal transgenic mice showed impaired glucose tolerance, increased FINS levels and higher homeostasis model assessment insulin resistance index (HOMA-IR) than the other 3 groups. In conclusion, maternally inherited hypertriglyceridemia in ApoCIII transgenic mice displayed impaired glucose tolerance, hyperinsulinemia and increased HOMA-R, while paternally inherited hypertriglyceridemia did not have such impacts.

Apolipoprotein CIII regulates lipoprotein-associated phospholipase A2 expression via the MAPK and NFκB pathways

Apolipoprotein CIII (apo CIII), a small glycoprotein that binds to the surfaces of certain lipoproteins, is associated with inflammatory and atherogenic responses in vascular cells. Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) has been proposed as an inflammatory biomarker and potential therapeutic target for cardiovascular disease (CVD). Here, we report that apo CIII increases Lp-PLA₂ mRNA and protein levels in dose- and time- dependent manner in human monocytic THP-1 cells, and the increase can be abolished by MAPK and NFκB pathway inhibitors. Lp-PLA₂ inhibitor, 1-linoleoyl glycerol attenuates the inflammation induced by apo CIII. In turn, exogenous Lp-PLA₂ expression upregulates apo CIII and the upregulation can be inhibited by 1-linoleoyl glycerol in HepG2 cells. Moreover, plasma Lp-PLA₂ level is correlated with apo CIII expression in pig liver. In vivo, Lp-PLA₂ expression in monocytes and its activity in serum were significantly increased in human apo CIII transgenic porcine models compared with wild-type pigs. Our results suggest that Lp-PLA₂ and apo CIII expression level is correlated with each other in vitro and in vivo.

Determinants of VLDL composition and apo B-containing particles in familial combined hyperlipidemia

BACKGROUND

In familial combined hyperlipidemia (FCHL) the severity of the dyslipidemia is determined by an overproduction of VLDL (very low density lipoprotein) particles and by its abnormal lipid composition. However, few are known regarding the metabolic factors that determine these abnormalities. We investigated the impact of metabolic factors on the number of atherogenic particles (apolipoprotein B level (apoB)) and the triglyceride content of very low-density lipoproteins (VLDLs-TG).

METHODS

A cross-sectional study done in FCHL subjects and gender and age-matched healthy subjects. A clinical assessment, lipid profile and plasma concentrations of insulin, apolipoprotein CIII (apo CIII), apolipoprotein AII (apo AII), high sensitive C-reactive protein (HS-CRP), adiponectin and leptin were documented in 147 FCHL patients and 147 age-matched healthy subjects. Multivariate regression models were performed to investigate the independent determinants of VLDL-TG and apo B levels adjusting for confounding factors.

RESULTS

The variables that determined the VLDL-triglyceride content as a surrogate of VLDL composition were apo CIII (β=0.365, p<0.001), insulin (β=0.281, p<0.001), Apo AII (β=0.145, p<0.035), and adiponectin levels (β=-0.255, p<0.001). This model explained 34% of VLDL composition (VLDL-TG) variability. However, none of these variables were independent contributors of apo B-containing particles.

CONCLUSIONS

In patients with FCHL apo CIII, apo AII and adiponectin are major novel factors determining the VLDL particle composition. However, such factors do not explain apo B-containing particles.