Lipoprotein distribution of apolipoprotein C-III and its relationship to the presence in plasma of triglyceride-rich remnant lipoproteins

Fasting, non-fasting and postprandial triglycerides for screening cardiometabolic risk

Fasting triacylglycerols have long been associated with cardiovascular disease (CVD) and other cardiometabolic conditions. Evidence suggests that non-fasting triglycerides (i.e. measured within 8 h of eating) better predict CVD than fasting triglycerides, which has led several organisations to recommend non-fasting lipid panels as the new clinical standard. However, unstandardised assessment protocols associated with non-fasting triglyceride measurement may lead to misclassification, with at-risk individuals being overlooked. A third type of triglyceride assessment, postprandial testing, is more controlled, yet historically has been difficult to implement due to the time and effort required to execute it. Here, we review differences in assessment, the underlying physiology and the pathophysiological relevance of elevated fasting, non-fasting and postprandial triglycerides. We also present data suggesting that there may be a distinct advantage of postprandial triglycerides, even over non-fasting triglycerides, for early detection of CVD risk and offer suggestions to make postprandial protocols more clinically feasible.

Correlation between estimated plasma remnant-like particle cholesterol and vegetable fat intake in Uku town, Japan

Background

Remnant-like particle cholesterol (RLP-C) is highly atherogenic, which is associated with atherosclerosis. However, RLP-C has not been routinely measured in the clinical practice. We estimated RLP-C levels using conventional lipid profiles and examined the association between estimated RLP-C and related factors including nutrient intake.

Methods

This study was performed in Uku town, Nagasaki prefecture, Japan in 2019. A total of 225 subjects were enrolled and directly measured RLP-C levels. Estimated RLP-C levels were defined as the following formula [total cholesterol − (LDL-cholesterol) − (HDL-cholesterol)]. Multivariate analyses were used to assess the relationship between estimated RLP-C and atherogenic factors. We calculated cut-off values on dichotomized RLP-C (< 7.5 mg/dL vs. ≥ 7.5 mg/dL) by receiver operating characteristic (ROC) curve.

Results

The mean values of directly measured RLP-C levels and estimated RLP-C were 4.0 mg/dL and 16.4 mg/dL, respectively. In the multiple stepwise linear regression analysis, directly measured and estimated RLP-C levels were independently and commonly associated with apolipoprotein E, triglycerides, and vegetable fat intake (inversely). Using ROC curves, we found the cut-off value of estimated RLP-C was 22.0 mg/dL.

Conclusion

We demonstrated that the estimated RLP-C levels using conventional lipid profiles may substitute for directly measured RLP-C and these levels were independently and inversely associated with vegetable fat intake in the community-dwelling Japanese population.

Triglyceride-Rich Lipoprotein Remnants and Cardiovascular Disease

BACKGROUND

Triglycerides, cholesterol, and their metabolism are linked due to shared packaging and transport within circulating lipoprotein particles. While a case for a causal role of cholesterol-carrying low-density lipoproteins (LDLs) in atherosclerosis is well made, the body of scientific evidence for a causal role of triglyceride-rich lipoproteins (TRLs) is rapidly growing, with multiple lines of evidence (old and new) providing robust support.

CONTENT

This review will discuss current perspectives and accumulated evidence that an overabundance of remnant lipoproteins stemming from intravascular remodeling of nascent TRLs-chylomicrons and very low-density lipoproteins (VLDL)-results in a proatherogenic milieu that augments cardiovascular risk. Basic mechanisms of TRL metabolism and clearance will be summarized, assay methods reviewed, and pivotal clinical studies highlighted.

SUMMARY

Remnant lipoproteins are rendered highly atherogenic by their high cholesterol content, altered apolipoprotein composition, and physicochemical properties. The aggregate findings from multiple lines of evidence suggest that TRL remnants play a central role in residual cardiovascular risk.

Triglycerides and cardiovascular disease

PURPOSE OF REVIEW

Triglycerides (TGs) are measured as part of routine lipid profiles but their relationship to cardiovascular disease (CVD) risk has been controversial and overshadowed by high-density lipoprotein cholesterol (HDL-C).

RECENT FINDINGS

Epidemiological studies show a clear relationship of TG-containing lipoproteins including remnant particles with CVD risk with the effect being most clearly demonstrated through the excess risk captured by non-HDL-C compared with low-density lipoprotein-cholesterol (LDL-C). Mendelian randomisation studies show a consistent relationship of gene variants linked to TG metabolism with rates of CVD. Furthermore, meta-analyses of intervention trials with statins and other nonstatin drugs also suggest that reducing TGs is associated with benefits on rates of CVD events. Historical subgroup data from fibrate trials suggest benefits in patients with high TG:HDL ratios but seem to add little to optimized statin therapy. Recent trials with omega-3 fatty acids (specifically eicosapentaenoic acid) have suggested that high-dose formulations in contrast to low dose formulations have benefits on CVD outcomes.

SUMMARY

Further studies with newer agents are required to determine the place of TG-lowering drugs in therapeutic pathways. Trials with agents such as pemafibrate and vupanorsen may finally answer these questions.

Hypertriglyceridemia and Atherosclerosis: Using Human Research to Guide Mechanistic Studies in Animal Models

Human studies support a strong association between hypertriglyceridemia and atherosclerotic cardiovascular disease (CVD). However, whether a causal relationship exists between hypertriglyceridemia and increased CVD risk is still unclear. One plausible explanation for the difficulty establishing a clear causal role for hypertriglyceridemia in CVD risk is that lipolysis products of triglyceride-rich lipoproteins (TRLs), rather than the TRLs themselves, are the likely mediators of increased CVD risk. This hypothesis is supported by studies of rare mutations in humans resulting in impaired clearance of such lipolysis products (remnant lipoprotein particles; RLPs). Several animal models of hypertriglyceridemia support this hypothesis and have provided additional mechanistic understanding. Mice deficient in lipoprotein lipase (LPL), the major vascular enzyme responsible for TRL lipolysis and generation of RLPs, or its endothelial anchor GPIHBP1, are severely hypertriglyceridemic but develop only minimal atherosclerosis as compared with animal models deficient in apolipoprotein (APO) E, which is required to clear TRLs and RLPs. Likewise, animal models convincingly show that increased clearance of TRLs and RLPs by LPL activation (achieved by inhibition of APOC3, ANGPTL3, or ANGPTL4 action, or increased APOA5) results in protection from atherosclerosis. Mechanistic studies suggest that RLPs are more atherogenic than large TRLs because they more readily enter the artery wall, and because they are enriched in cholesterol relative to triglycerides, which promotes pro-atherogenic effects in lesional cells. Other mechanistic studies show that hepatic receptors (LDLR and LRP1) and APOE are critical for RLP clearance. Thus, studies in animal models have provided additional mechanistic insight and generally agree with the hypothesis that RLPs derived from TRLs are highly atherogenic whereas hypertriglyceridemia due to accumulation of very large TRLs in plasma is not markedly atherogenic in the absence of TRL lipolysis products.

Serum apolipoprotein C3 levels are negatively associated with hepatitis B virus DNA in HBeAg-negative chronic hepatitis B patients

Background

Hepatitis B virus (HBV) infection remains a global health issue associated with substantial morbidity and mortality. Serum apolipoprotein C3 (ApoC3) and apolipoprotein A5 (ApoA5) levels were decreased in chronic hepatitis B (CHB) patients, however the relationship between ApoC3 or ApoA5 and HBV DNA load remains elusive.

Methods

A total of 384 CHB patients including 194 HBsAg(+) HBeAg(−) and 190 HBsAg(+) HBeAg(+) and 154 healthy individuals were recruited in our study. Serum levels of alanine aminotransferase (ALT), aspartate transaminase (AST), total cholesterol (Chol), triglycerides (TG), apolipoprotein A1 (ApoA1), apolipoprotein B (ApoB), high-density lipoproteins cholesterol (HDL-C), low-density lipoproteins cholesterol (LDL-C) and lipoprotein a (Lpa) were examined in an automatic biochemical analyzer. Apolipoprotein A5 (ApoA5) and apolipoprotein C3 (ApoC3) were detected via ELISA.

Results

Serum ApoA1, ApoB, ApoC3 and ApoA5 levels were reduced in CHB patients. In HBeAg(−) CHB patients, plasma ApoC3 levels were negatively associated with HBV DNA load (r = 0.219, P < 0.001). But no correlation between ApoA5 and HBV DNA load was observed in CHB patients.

Conclusions

These data showed that HBV infection inhibits lipid metabolism and ApoC3 is negatively associated with HBV DNA load in HBeAg (−) CHB patients. These findings provided new evidence about the link between ApoC3-related lipid metabolism and immune response.

The role of antisense oligonucleotide therapy against apolipoprotein-CIII in hypertriglyceridemia

Increased triglyceride levels (higher than ∼1000 mg/dL) are associated with an increased risk for pancreatitis. Apolipoprotein-CIII (apo-CIII) plays a key role in the metabolism of triglycerides and triglyceride-rich lipoproteins. While loss of function mutations in the gene encoding apo-CIII (APOC3) are associated with low triglyceride levels and a decreased risk for cardiovascular disease (CVD), overexpression of APOC3 is associated with hypertriglyceridemia. Although many drugs such as fibrates, statins and omega-3 fatty acids modestly decrease triglyceride levels (and apo-CIII concentrations), there are many patients who still have severe hypertriglyceridemia and are at risk for pancreatitis and potentially CVD. The antisense oligonucleotide (ASO) against APOC3 mRNA volanesorsen (previously called ISIS 304801, ISIS-ApoCIIIRx and IONIS-ApoCIIIRx) robustly decreases both, apo-CIII production and triglyceride concentrations and is being currently evaluated in phase 3 trials. In this narrative review we present the currently available clinical evidence on the efficacy and safety of volanesorsen for the treatment of hypertriglyceridemia.

ApoCIII enrichment in HDL impairs HDL-mediated cholesterol efflux capacity

Apolipoprotein CIII (apoCIII) has been reported to be tightly associated with triglyceride metabolism and the susceptibility to coronary artery disease (CAD). Besides, apoCIII has also been found to affect the anti-apoptotic effects of HDL. However, the effect of apoCIII on HDL-mediated cholesterol efflux, the crucial function of HDL, has not been reported. A hospital-based case-control study was conducted to compare the apoCIII distribution in lipoproteins between CAD patients and nonCAD controls and to explore the relationship between HDL-associated apoCIII (apoCIII_HDL) and HDL-mediated cholesterol efflux. One hundred forty CAD patients and nighty nine nonCAD controls were included. Plasma apoCIII, apoCIII_HDL and cholesterol efflux capacity was measured. The apoCIII_HDL ratio (apoCIII_HDL over plasma apoCIII) was significantly higher in CAD patients than that in control group (0.52 ± 0.24 vs. 0.43 ± 0.22, P = 0.004). Both apoCIII_HDL and apoCIII_HDL ratio were inversely correlated with cholesterol efflux capacity (r = −0.241, P = 0.0002; r = −0.318, P < 0.0001, respectively). Stepwise multiple regression analysis revealed that the apoCIII_HDL ratio was an independent contributor to HDL-mediated cholesterol efflux capacity (standardized β = −0.325, P < 0.001). This study indicates that the presence of apoCIII in HDL may affect HDL-mediated cholesterol efflux capacity, implying the alternative role of apoCIII in the atherogenesis.

Tryptophan probes reveal residue-specific phospholipid interactions of apolipoprotein C-III

Apolipoproteins are essential human proteins for lipid metabolism. Together with phospholipids, they constitute lipoproteins, nm to μm sized particles responsible for transporting cholesterol and triglycerides throughout the body. To investigate specific protein-lipid interactions, we produced and characterized three single-Trp containing apolipoprotein C-III (ApoCIII) variants (W42 (W54F/W65F), W54 (W42F/W65F), W65 (W42F/W54F)). Upon binding to phospholipid vesicles, wild-type ApoCIII adopts an α-helical conformation (50% helicity) as determined by circular dichroism spectroscopy with an approximate apparent partition constant of 3×10(4) M(-1). Steady-state and time-resolved fluorescence measurements reveal distinct residue-specific behaviors with W54 experiencing the most hydrophobic environment followed by W42 and W65. Interestingly, time-resolved anisotropy measurements show a converse trend for relative Trp mobility with position 54 being the least immobile. To determine the relative insertion depths of W42, W54, and W65 in the bilayer, fluorescence quenching experiments were performed using three different brominated lipids. W65 had a clear preference for residing near the headgroup while W54 and W42 sample the range of depths ~8-11 Å from the bilayer center. On average, W54 is slightly more embedded than W42. Based on Trp spectral differences between ApoCIII binding to phospholipid vesicles and sodium dodecyl sulfate micelles, we suggest that ApoCIII adopts an alternate helical conformation on the bilayer which could have functional implications.

Isoelectric Focusing of Serum Apolipoprotein C-III as a Sensitive Screening Method for the Detection of O-glycosylation Disturbances

Apolipoprotein C-III (ApoC-III) is a glycoprotein carrying the most common O-linked glycan structure and is abundantly present in serum, what renders it a suitable marker for analysis of O-glycosylation abnormalities. Isoelectric focusing followed by a Western blot of ApoC-III, using PhastSystem™ Electrophoresis System (GE Healthcare), was introduced as a rather simple and rapid method for screening of certain subtypes of inherited glycosylation disorders. The study's aim was to establish this method in our laboratory, what included performing the analysis in a group of 170 healthy individuals to set the reference range of detected relative amounts of sialylated ApoC-III isoforms and to evaluate the gender- and age-dependent differences. A significant relative increase of asialo-ApoC-III with growing age was found. Secondly, we examined serum from patients with selected metabolic disorders and detected minor O-glycosylation changes in diseases such as Prader-Willi syndrome, PGM1 (phosphoglucomutase 1) or MAN1B (class 1B alpha-1,2-mannosidase) deficiency. Our results show that this method allows for a sensitive detection of ApoC-III O-glycosylation status, however this might be modulated by several factors (i.e. nutrition, medication) whose exact role remains to be determined.

New insights into the pathophysiology of dyslipidemia in type 2 diabetes

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality for patients with type 2 diabetes, despite recent significant advances in management strategies to lessen CVD risk factors. A major cause is the atherogenic dyslipidemia, which consists of elevated plasma concentrations of both fasting and postprandial triglyceride-rich lipoproteins (TRLs), small dense low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) cholesterol. The different components of diabetic dyslipidemia are not isolated abnormalities but closely linked to each other metabolically. The underlying disturbances are hepatic overproduction and delayed clearance of TRLs. Recent results have unequivocally shown that triglyceride-rich lipoproteins and their remnants are atherogenic. To develop novel strategies for the prevention and treatment of dyslipidaemia, it is essential to understand the pathophysiology of dyslipoproteinaemia in humans. Here, we review recent advances in our understanding of the pathophysiology of diabetic dyslipidemia.

FoxO6 integrates insulin signaling with MTP for regulating VLDL production in the liver

Excessive production of triglyceride-rich very low-density lipoproteins (VLDL-TG) contributes to hypertriglyceridemia in obesity and type 2 diabetes. To understand the underlying mechanism, we studied hepatic regulation of VLDL-TG production by (forkhead box O6) FoxO6, a forkhead transcription factor that integrates insulin signaling to hepatic metabolism. We showed that transgenic mice expressing a constitutively active FoxO6 allele developed hypertriglyceridemia, culminating in elevated VLDL-TG levels and impaired postprandial TG clearance. This effect resulted in part from increased hepatic VLDL-TG production. We recapitulated these findings in cultured HepG2 cells and human primary hepatocytes, demonstrating that FoxO6 promoted hepatic VLDL-TG secretion. This action correlated with the ability of FoxO6 to stimulate hepatic production of microsomal triglyceride transfer protein (MTP), a molecular chaperone that catalyzes the rate-limiting step in VLDL-TG assembly and secretion. FoxO6 was shown to bind to the MTP promoter and stimulate MTP promoter activity in HepG2 cells. This effect was inhibited by insulin, consistent with the ability of insulin to promote FoxO6 phosphorylation and disable FoxO6 DNA-binding activity. Mutations of the FoxO6 target site within the MTP promoter abrogated FoxO6-mediated induction of MTP promoter activity. Hepatic FoxO6 expression became deregulated in insulin-resistant mice with obesity and type 2 diabetes. FoxO6 inhibition in insulin-resistant liver suppressed hepatic MTP expression and curbed VLDL-TG overproduction, contributing to the amelioration of hypertriglyceridemia in obese and diabetic db/db mice. These results characterize FoxO6 as an important signaling molecule upstream of MTP for regulating hepatic VLDL-TG production.

Factor II activity is similarly increased in patients with elevated apolipoprotein CIII and in carriers of the factor II 20210A allele

Background

Few studies have so far investigated the relationship between apolipoprotein CIII (Apo CIII) and coagulation pathway in subjects with or without coronary artery disease (CAD).

Methods and Results

Serum Apo CIII concentrations and plasma coagulant activities of factor II (FII:c), factor V (FV:c), and factor VIII (FVIII:c), and activated factor VII (FVIIa) were analyzed in a total of 933 subjects, with (n=687) or without (n=246) angiographically demonstrated CAD and not taking anticoagulant drugs. Activated factor X (FXa) generation assay was performed on plasma from subgroups of subjects with low and high levels of Apo CIII. A statistical incremental concentration of FII:c, FV:c, and FVIIa levels was observed through the quartiles of Apo CIII distribution in the population considered as a whole. Significant results were confirmed for FII:c in CAD and CAD‐free subgroup when separately considered. Subjects within the highest Apo CIII quartile (>12.6 mg/dL) had high FII:c levels not statistically different from those of carriers of 20210A allele (n=40; 4.28%). In a multiple linear model, Apo CIII was the best predictor of FII:c variability, after adjustment for age, gender, plasma lipids, CRP, creatinine, diagnosis, and carriership of 20210A allele. FXa generation was increased and its lag time shortened in plasmas with high Apo CIII levels. However, after thrombin inhibition by hirudin, differences between low and high Apo C‐III samples disappeared.

Conclusions

Elevated concentrations of Apo CIII are associated with an increase of thrombin activity to an extent comparable with the carriership of G20210A gene variant and mainly modulating the thrombin generation.

ATF4 protein deficiency protects against high fructose-induced hypertriglyceridemia in mice

Hypertriglyceridemia is the most common lipid disorder in obesity and type 2 diabetes. It results from increased production and/or decreased clearance of triglyceride-rich lipoproteins. To better understand the pathophysiology of hypertriglyceridemia, we studied hepatic regulation of triglyceride metabolism by the activating transcription factor 4 (ATF4), a member of the basic leucine zipper-containing protein subfamily. We determined the effect of ATF4 on hepatic lipid metabolism in Atf4(-/-) mice fed regular chow or provided with free access to fructose drinking water. ATF4 depletion preferentially attenuated hepatic lipogenesis without affecting hepatic triglyceride production and fatty acid oxidation. This effect prevented excessive fat accumulation in the liver of Atf4(-/-) mice, when compared with wild-type littermates. To gain insight into the underlying mechanism, we showed that ATF4 depletion resulted in a significant reduction in hepatic expression of peroxisome proliferator-activated receptor-γ, a nuclear receptor that acts to promote lipogenesis in the liver. This effect was accompanied by a significant reduction in hepatic expression of sterol regulatory element-binding protein 1c (SREBP-1c), acetyl-CoA carboxylase, and fatty-acid synthase, three key functions in the lipogenic pathway in Atf4(-/-) mice. Of particular significance, we found that Atf4(-/-) mice, as opposed to wild-type littermates, were protected against the development of steatosis and hypertriglyceridemia in response to high fructose feeding. These data demonstrate that ATF4 plays a critical role in regulating hepatic lipid metabolism in response to nutritional cues.

Identification of the HDL-ApoCIII to VLDL-ApoCIII ratio as a predictor of coronary artery disease in the general population: the Chin-Shan Community Cardiovascular Cohort (CCCC) study in Taiwan

Background

Apolipoprotein (Apo) levels are considered more reliable than plasma lipoprotein levels for predicting coronary artery disease (CAD). However, a unanimous Apo marker for CAD has not been identified. In the Chin-Shan Community Cardiovascular Cohort (CCCC), we sought to identify a common Apo marker for predicting CAD in the general population.

Methods

We examined the cross-sectional association between Apo markers and CAD in the CCCC from 1990 to 2001. Among 3,602 subjects, 90 had angiographically proven CAD (>50% stenosis in ≥1 vessel), and 200 did not have CAD. These subjects were divided into the following 4 groups for analysis: normolipidemic (total cholesterol [TC] <200 mg/dL, triglyceride [TG] <150 mg/dL), hypertriglyceridemic (TC <200 mg/dL, TG ≥150 mg/dL), hypercholesterolemic (TC ≥200 mg/dL, TG <150 mg/dL), and hyperlipidemic (TC ≥200 mg/dL, TG ≥150 mg/dL).

Results

Compatible with findings in other populations, our results showed that CAD patients in the CCCC had higher ApoB and lower high-density lipoprotein (HDL) cholesterol and ApoAI concentrations than non-CAD subjects, but the differences were not significant in all groups. Plasma concentrations of ApoE and lipoprotein (a) were not consistently correlated with CAD. In contrast, the ratio of HDL-ApoCIII to very-low-density lipoprotein (VLDL)-ApoCIII was the only universal determinant for CAD in the normolipidemic group (P=0.0018), the hypertriglyceridemic group (P=0.0001), the hypercholesterolemic group (P=0.0001), and the hyperlipidemic group (P=0.0001). Overall, a high HDL-ApoCIII/VLDL-ApoCIII ratio was observed in all CAD patients, including those with a normal lipid profile. In multivariate analyses, the HDL-ApoCIII/VLDL-ApoCIII ratio was the strongest predictor for CAD among all lipid factors investigated (odds ratio, 2.04; 95% confidence interval, 1.46–2.84; P<0.0001).

Conclusions

A high HDL-ApoCIII to VLDL-ApoCIII ratio is a better marker for predicting CAD than are the conventional lipid markers or ApoAI and ApoB. High HDL-ApoCIII and low VLDL-ApoCIII values in CAD, irrespective of lipid variations, suggest that ApoCIII is markedly transported from VLDL to HDL in this disease. Measurement of plasma ApoCIII may improve CAD prediction in the general population.

Serum apolipoprotein C-III in high-density lipoprotein: a key diabetogenic risk factor in Turks

AIMS

We studied determinants of serum apolipoprotein C-III (apoC-III) and whether levels of apoC-III or its fractions predict metabolic syndrome (MetS), Type 2 diabetes and coronary heart disease (CHD).

METHODS

The predictive value of apoC-III, measured by immunoturbimetric immunoassay in 802 tracked individuals of a Turkish general population in determining cardiometabolic risk was assessed over 4.4 +/- 1.2 years' follow-up. Patients with MetS, Type 2 diabetes and CHD at baseline were excluded.

RESULTS

Total apoC-III, as well as both fractions, was significantly, linearly and inversely related to smoking status, positively to alcohol usage and to levels of complement C3. Mid and high tertiles of total or non-high density lipoprotein (HDL) apoC-III predicted significantly and independently incident MetS; they predicted CHD with risk ratios of 1.6 [95% confidence intervals (CI) 1.02-2.5], for 1 sd increment, after adjustments that included HDL cholesterol and body mass index (BMI). The highest tertile of HDL apoC-III was a major independent predictor of new-onset diabetes with a 2.5-fold risk ratio for 1 sd increment (95% CI 1.5-4.0) in combined sexes, after adjustment for waist circumference, HDL cholesterol and other confounders and was a better predictor than waist girth.

CONCLUSIONS

Serum total apoC-III or its fractions are linearly and inversely associated with smoking, positively with alcohol usage and serum complement C3. The presumably dysfunctional HDL apoC-III is a stronger predictor of Type 2 diabetes than waist girth in Turks. Non-HDL apoC-III predicts strongly the development of MetS as well as incident CHD, independent of HDL cholesterol, BMI and non-lipid factors. The atherogenicity of apoC-III and dysfunctionality of HDL apoC-III carry huge public health implications in Turks.

A proteomic study of the apolipoproteins in LDL subclasses in patients with the metabolic syndrome and type 2 diabetes

The exchangeable apolipoproteins present in small, dense LDL (sdLDL) and large, buoyant LDL subclasses were evaluated with a quantitative proteomic approach in patients with the metabolic syndrome and with type 2 diabetes, both with subclinical atherosclerosis and the B LDL phenotype. The analyses included surface-enhanced laser adsorption/ionization, time-of-flight mass spectrometry, and subsequent identification by mass spectrometry or immunoblotting and were carried out in LDL subclasses isolated by ultracentrifugation in deuterium oxide gradients with near physiological salt concentrations. The sdLDLs of both types of patients were enriched in apolipoprotein C-III (apoC-III) and were depleted of apoC-I, apoA-I, and apoE compared with matched healthy controls with the A phenotype. The LDL complexes formed in serum from patients with diabetes with the arterial proteoglycan (PG) versican were also enriched in apoC-III. In addition, there was a significant correlation between the apoC-III content in sdLDL in patients and the apparent affinity of their LDLs for arterial versican. The unique distribution of exchangeable apolipoproteins in the sdLDLs of the patients studied, especially high apoC-III, coupled with the augmented affinity with arterial PGs, may contribute to the strong association of the dyslipidemia of insulin resistance with increased risk for cardiovascular disease.

Alterations of lipids and apolipoprotein CIII in very low density lipoprotein subspecies in type 2 diabetes

AIMS/HYPOTHESIS

Very low density lipoprotein (VLDL) particles are heterogeneous, comprising two main subspecies, VLDL 1 (Sf 60-400) and VLDL 2 (Sf 20-60). The aim of the study was to examine the distribution and composition of VLDL subspecies in type 2 diabetes.

SUBJECTS, MATERIALS AND METHODS

We studied the composition and concentration of triglyceride-rich lipoproteins (TRLs) in 217 type 2 diabetic patients and 93 control subjects between 50 and 75 years of age. Lipoprotein subspecies were separated by density-gradient ultracentrifugation. Apolipoprotein (apo) CIII and apo E in plasma and apo CIII in TRL subspecies were measured by nephelometry and apo CII in serum by a commercial kit using a single radial immunodiffusion method.

RESULTS

The concentrations of VLDL 1, VLDL 2 and intermediate density lipoprotein were significantly increased in type 2 diabetes subjects, the change being most marked for VLDL 1. There was a strong linear correlation between VLDL 1 triglycerides and plasma triglycerides in both groups (r = 0.879, p < 0.001 and r = 0.899, p < 0.001). Diabetic subjects had markedly higher plasma ratios of apo CII:apo CIII and apo CIII:apo E. Despite elevated plasma apo CIII, type 2 diabetic subjects had a relative deficiency of apo CIII in all TRL subspecies, suggesting profound disturbances of apo CIII metabolism.

CONCLUSIONS/INTERPRETATION

The elevation of VLDL 1 triglycerides is the major determinant of plasma triglyceride concentration in normal subjects and in type 2 diabetic individuals. Both apo CIII and apo E metabolism are disturbed in type 2 diabetes.

Grape seed procyanidins improve atherosclerotic risk index and induce liver CYP7A1 and SHP expression in healthy rats

Moderate consumption of red wine reduces risk of death from cardiovascular disease. The polyphenols in red wine are ultimately responsible for this effect, exerting antiatherogenic actions through their antioxidant capacities and modulating intracellular signaling pathways and transcriptional activities. Lipoprotein metabolism is crucial in atherogenesis, and liver is the principal organ controlling lipoprotein homeostasis. This study was intended to identify the primary effects of procyanidins, the most abundant polyphenols in red wine, on both plasma lipoprotein profile and the expression of genes controlling lipoprotein homeostasis in the liver. We show that procyanidins lowered plasma triglyceride, free fatty acids, apolipoprotein B (apoB), LDL-cholesterol and nonHDL:nonLDL-cholesterol levels and slightly increased HDL-cholesterol. Liver mRNA levels of small heterodimer partner (SHP), cholesterol 7alpha-hydroxylase (CYP7A1), and cholesterol biosynthetic enzymes increased, whereas those of apoAII, apoCI, and apoCIII decreased. Lipoprotein lipase (LPL) mRNA levels increased in muscle and decreased in adipose tissue. In conclusion, procyanidins improve the atherosclerotic risk index in the postprandial state, inducing in the liver the overexpression of CYP7A1 (suggesting an increase of cholesterol elimination via bile acids) and SHP, a nuclear receptor emerging as a key regulator of lipid homeostasis at the transcriptional level. These results could explain, at least in part, the beneficial long-term effects associated with moderate red wine consumption.

Association of serum apolipoprotein C III levels and apolipoprotein C III gene Sst I polymorphism with carotid intima-media thickness in Chinese type 2 diabetic patients

Apolipoprotein C III (apo C III) plays a central role in regulating plasma metabolism of triglyceride-rich lipoprotein (TRL). The G3238C allele (Sst I) in the 3'-untranslated region has been found to be associated with raised apo C III levels and hypertriglyceridemia (HTG). Some studies suggest that apo C III and the S(2) allele of apo C III gene are independent risk factors for atherosclerotic diseases. To study the potential association between these factors we analyzed the clinical data and their correlations with serum apo C III levels, apo C III gene Sst I polymorphism, and carotid intima-media thickness (IMT) in 78 unrelated Chinese patients with type 2 diabetes. Apo C III gene Sst I polymorphism was examined using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). Carotid IMT was measured by color doppler ultrasound examination. Serum apo C III levels were found to be positively associated with plasma TG ( r = 0.527, P < 0.001), TC (r = 0.424, P < 0.001), LDL-C (r = 0.308, P < 0.01) concentrations, and carotid IMT (r =0.359, P < 0.01 ). Multivariate analysis (backward) showed that diastolic blood pressure, apo C III, and fasting insulin levels were independent risk factors of carotid IMT. However, the results did not show the association between S(2) allele and carotid IMT in our diabetic patients. Thus, our study suggested that apo C III is an independent risk factor for atherosclerotic diseases in Chinese type 2 diabetes.

Storage of human plasma samples leads to alterations in the lipoprotein distribution of apoC-III and apoE

The effect of frozen storage on lipoprotein distribution of apolipoprotein C-III (apoC-III) and apoE was investigated by measuring apoC-III and apoE by ELISA in HDL and apoB-containing lipoproteins of human plasma samples (n = 16) before and after 2 weeks of frozen storage (-20 degrees C). HDLs were separated by heparin-manganese precipitation (HMP) or by fast-protein liquid chromatography (FPLC). Total plasma apoC-III and apoE levels were not affected by frozen storage. HDL-HMP apoC-III and apoE levels were significantly higher in frozen versus fresh samples: 7.7 +/- 0.7 versus 6.7 +/- 0.7 mg/dl (P < 0.05) and 2.0 +/- 0.1 versus 1.2 +/- 0.1 mg/dl (P < 0.001), respectively. HDL-FPLC apoC-III and apoE, but not triglyceride (TG) or cholesterol, levels were also higher in frozen samples: 12.0 +/- 1.2 versus 7.5 +/- 0.6 mg/dl (P < 0.001) and 2.7 +/- 0.2 versus 1.6 +/- 0.2 mg/dl (P < 0.001), respectively. Frozen storage led to a decrease in apoC-III (-17 +/- 9%) and apoE (-19 +/- 9%) in triglyceride-rich lipoprotein. Redistribution of apoC-III and apoE was most evident in samples with high TG levels. HDL apoC-III and apoE levels were also significantly higher when measured in plasma stored at -80 degrees C. Our results demonstrate that lipoprotein distribution of apoC-III and apoE is affected by storage of human plasma, suggesting that analysis of frozen plasma should be avoided in studies relating lipoprotein levels of apoC-III and/or apoE to the incidence of coronary artery disease.

Apolipoprotein CIII deficiency prevents the development of hypertriglyceridemia in streptozotocin-induced diabetic mice

To explore the role of apolipoprotein (apo) CIII in the development of hypertriglyceridemia associated with diabetes mellitus, we examined triglyceride (TG) kinetics in apo CIII - deficient mice (apo CIII - null) and wild-type (WT) (C57BL/6J) mice with diabetes induced by the injection of streptozotocin (STZ). Plasma TG levels increased significantly in WT mice after diabetes was induced (102 +/- 29 v 65 +/- 33 mg/dL, P <.01). Apo CIII-null mice had a significantly lower TG level (35 +/- 9 mg/dL) that remained unchanged even when diabetes was induced (35 +/- 8 mg/dL). The TG secretion rate (TGSR) measured by the Triton WR1339 method tended to decrease in diabetic WT, indicating that catabolism of TG was impaired. Apo CIII-null mice showed 2-fold higher TG production than WT mice, indicating markedly faster clearance of TG. The high TGSR was halved when diabetes was induced in apo CIII-null mice, and the fractional catabolic rate (FCR) of TG was also halved, although it was still significantly higher than in WT mice. Lipoprotein lipase (LPL) activity in postheparin plasma was not significantly altered in WT or apo CIII-null mice regardless of the presence or absence of diabetes. [(3)H] very-low-density lipoprotein (VLDL)-TG from WT or apo CIII-null mice showed similar clearance by WT recipients, and this was also observed when VLDL was obtained from diabetic counterparts. In contrast, VLDL-TG was cleared faster by apo CIII-null recipients compared with WT recipients, regardless of the VLDL donors. These results suggest that apo CIII deficiency prevents the development of hypertriglyceridemia associated with diabetes by stimulating TG removal, possibly by promoting the interaction of VLDL with the TG removal system.

Apolipoprotein C-III, a strong discriminant of coronary risk in men and a determinant of the metabolic syndrome in both genders

AIMS

Apolipoprotein C-III (apoC-III) has been recognized as a useful marker of triglyceride-rich lipoproteins (TRLs) metabolism and proposed as an indicator of prognosis for coronary risk in healthy subjects. We studied cross-sectionally in a population having low cholesterol levels, but a high prevalence of the metabolic syndrome, whether serum levels of total apoC-III or its sub-fractions were independent markers of prevalent coronary heart disease (CHD) or were related to variables reflecting the metabolic syndrome.

METHODS AND RESULTS

In 857 unselected participants of the representative population sample of the Turkish Adult Risk Factor Survey in 2001, apoC-III as well as other risk variables were evaluated, and CHD was diagnosed based on clinical findings and Minnesota coding of resting electrocardiograms. The sample consisted of men and women, aged 33-82 years, having a mean waist circumference of 89.4 and 92.9 cm, respectively, 42% of whom had the metabolic syndrome identified by criteria of the ATP III. ApoC-III values were measured by turbidimetric immunoassay. Mean concentrations for non-high-density lipoprotein (nonHDL) apoC-III in men and women were 6.4 and 6.2 mg/dl, respectively, and for apoC-III in HDL were 6.2 and 6.3 mg/dl, respectively. NonHDL apoC-III was similar to, and apoC-III in HDL was higher than that in Western populations. Both fractions of apoC-III were significantly correlated with lipids, lipoproteins, apoB, anthropometric measures, and blood pressures in both genders. Correlations for both were high with serum triglycerides (r(s)=around 0.70) and apoB (r(p)=around 0.37). Total apoC-III as well as both fractions were significantly correlated in women also with levels of inflammatory risk markers: strongly (r=0.40-0.45, P<0.001) with complement C3, and weakly (r(s)=around 0.20, P<0.001) with C-reactive protein. A cutoff of >7.0 mg/dl as opposed to lower levels of nonHDL apoC-III indicated the presence of hypertriglyceridemic hyperapo B with an age-adjusted odds ratio (OR) of 13.8; it indicated the presence of metabolic syndrome with 4.66-fold likelihood. Total apoC-III and nonHDL apoC-III proved to be significantly (P-trend <0.05 and 0.002) and strongly associated with prevalent CHD in men even after adjustment for age, low-density lipoprotein-cholesterol (LDL-C) and high-density lipoprotein-cholesterol (HDL-C): OR gradients across upper and lower quartiles were 3.88-fold (CI: 1.3; 11.4) and 8.8-fold (CI: 2.6; 29.8), respectively.

CONCLUSIONS

In a population among whom the metabolic syndrome prevails, total- and nonHDL apoC-III are each a determinant in both genders of the metabolic syndrome and of hypertriglyceridemic hyperapo B. Each is a powerful significant marker of prevalent CHD in men independent of LDL- and HDL-C levels. In women, despite being correlated with inflammatory risk markers, the significant association of elevated levels of apoC-III with CHD did not prove to be independent of age.

Approach to lipoprotein management in 2001 National Cholesterol Guidelines

In 2001 the National Cholesterol Education Program (NCEP) released its Adult Treatment Panel (ATP) III report. This was an evidence-based report that upgraded cholesterol management guidelines. The update was made possible by a series of large, cholesterol-lowering clinical trials. These trials demonstrated strongly the efficacy and safety of cholesterol reduction in both primary and secondary prevention of coronary heart disease (CHD). The major recommendations of the report were several. Low-density lipoprotein (LDL) cholesterol continued to be identified as the major target of cholesterol-lowering therapy. However, more emphasis was given to HDL cholesterol and triglycerides as important targets for management. The concept of CHD risk equivalents was introduced. A CHD risk equivalent represents an absolute risk for future CHD events equal to that in persons with established CHD. Diabetes was identified as a CHD risk equivalent, requiring more intensive LDL-lowering therapy. Finally, the report placed more emphasis on the metabolic syndrome as a major, multiplex risk factor requiring increased clinical attention.

Orphan nuclear hormone receptor Rev-erbalpha regulates the human apolipoprotein CIII promoter

Apolipoprotein CIII (apoCIII) plays an important role in plasma triglyceride and remnant lipoprotein metabolism. Because hypertriglyceridemia is an independent risk factor in coronary artery disease and the presence in plasma of triglyceride-rich remnant lipoproteins is correlated with atherosclerosis, considerable research efforts have been focused on the identification of factors regulating apoCIII gene expression to decrease its production. Here we report that the orphan nuclear hormone receptor Rev-erbalpha regulates the human apoCIII gene promoter. In apoCIII expressing human hepatic HepG2 cells, transfection of Rev-erbalpha specifically repressed apoCIII gene promoter activity. We determined by deletion and site-directed mutagenesis experiments that Rev-erbalpha dependent repression is mainly due to an element present in the proximal promoter of the apoCIII gene. In contrast, we found no functional Rev-erbalpha response elements in the convergently transcribed human apoAI gene or the common regulatory enhancer. The identified Rev-erbalpha response element coincides with a RORalpha1 element, and in the present study we provide evidence that functional cross-talk between these orphan receptors modulates the apoCIII promoter. In vitro binding analysis showed that monomers of Rev-erbalpha bound this element but not another upstream RORalpha1 response element. In addition, we showed that the closely related nuclear orphan receptor RVR also specifically repressed the human apoCIII gene. These studies underscore a novel physiological role for members of the Rev-erb family of nuclear receptors in the regulation of genes involved in triglyceride metabolism and the pathogenesis of atherosclerosis.