Remnant lipoproteins induce endothelial plasminogen activator inhibitor-1

Remnant-Like Particle Cholesterol and the Risk of Major Adverse Cardiovascular Events: A Systematic Review and Meta-Analysis

Background: The remnant-like particle cholesterol (RLP-C) has been demonstrated to be associated with residual cardiovascular risk. The meta-analysis aimed to evaluate the impact of baseline RLP-C on the incidence of major cardiovascular adverse events (MACEs) in patients with coronary artery disease (CAD). Methods: A systematic literature search was performed in PubMed and Embase electronic databases from the inception of the databases through 1 October 2022. Studies evaluating the association between baseline RLP-C and the risk of MACEs in patients with CAD were included. Hazard ratios (HRs) with 95% confidence intervals (CIs) were pooled by a random-effect method (RLP-C analyzed as a categorical variable) and a fixed-effects model (RLP-C analyzed as a continuous variable). Results: Ten studies including 18,053 subjects were finally included in this meta-analysis. In our pooled analysis, compared to CAD patients with the lowest RLP-C category, the CAD patients with the highest RLP-C category had a significantly higher risk of future MACEs during follow-up (HR 1.79, 95% CI, 1.42−2.26, I2 = 60.31%, p < 0.01), which was consistent with outcomes of meta-analysis with the RLP-C analyzed as a continuous variable (HR 1.40, 95% CI, 1.28−1.53, I2 = 38.20%, p < 0.01). The sensitivity analysis confirmed the robustness of the results, and no significant publication bias was identified. Conclusion: The present meta-analysis suggests that the RLP-C was associated with an increased risk of long-term MACEs in patients with CAD at baseline. It is necessary to conduct randomized controlled trials to explore whether reducing the RLP-C level is conducive to reducing residual cardiovascular risk, even coronary plaque regression.

Atherogenic Lipoproteins for the Statin Residual Cardiovascular Disease Risk

Randomized controlled trials (RCTs) show that decreases in low-density lipoprotein cholesterol (LDL-C) by the use of statins cause a significant reduction in the development of cardiovascular disease (CVD). However, one of our previous studies showed that, among eight RCTs that investigated the effect of statins vs. a placebo on CVD development, 56–79% of patients had residual CVD risk after the trials. In three RCTs that investigated the effect of a high dose vs. a usual dose of statins on CVD development, 78–87% of patients in the high-dose statin arms still had residual CVD risk. The risk of CVD development remains even when statins are used to strongly reduce LDL-C, and this type of risk is now regarded as statin residual CVD risk. Our study shows that elevated triglyceride (TG) levels, reduced high-density lipoprotein cholesterol (HDL-C), and the existence of obesity/insulin resistance and diabetes may be important metabolic factors that determine statin residual CVD risk. Here, we discuss atherogenic lipoproteins that were not investigated in such RCTs, such as lipoprotein (a) (Lp(a)), remnant lipoproteins, malondialdehyde-modified LDL (MDA-LDL), and small-dense LDL (Sd-LDL). Lp(a) is under strong genetic control by apolipoprotein (a), which is an LPA gene locus. Variations in the LPA gene account for 91% of the variability in the plasma concentration of Lp(a). A meta-analysis showed that genetic variations at the LPA locus are associated with CVD events during statin therapy, independent of the extent of LDL lowering, providing support for exploring strategies targeting circulating concentrations of Lp(a) to reduce CVD events in patients receiving statins. Remnant lipoproteins and small-dense LDL are highly associated with high TG levels, low HDL-C, and obesity/insulin resistance. MDA-LDL is a representative form of oxidized LDL and plays important roles in the formation and development of the primary lesions of atherosclerosis. MDA-LDL levels were higher in CVD patients and diabetic patients than in the control subjects. Furthermore, we demonstrated the atherogenic properties of such lipoproteins and their association with CVD as well as therapeutic approaches.

Dysbetalipoproteinemia: Two cases report and a diagnostic algorithm

Dysbetalipoproteinemia is a rare familial dyslipidemia characterized by approximately equally elevated serum cholesterol and triglyceride levels due to accumulated remnant lipoproteins in apolipoprotein E2/E2 homozygotes. It is associated with an increased risk for premature cardiovascular disease. Thus, making a diagnosis of dysbetalipoproteinemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up can be challenging. Diagnosis of dysbetalipoproteinemia should be considered in patients mixed dyslipidemia when the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated low density lipoprotein (LDL) and directly measured LDL cholesterol concentrations. Other indices are also informative in the diagnostic process. We present herein two phenotypically different cases (a 44-year-old man with severe hypertriglyceridemia and a 49-year-old woman with mixed dyslipidemia) of genotypically proven familial dysbetalipoproteinemia and a diagnostic algorithm of the disease.

Dysbetalipoproteinaemia: a mixed hyperlipidaemia of remnant lipoproteins due to mutations in apolipoprotein E

Atherosclerosis is strongly associated with dyslipoproteinaemia, and especially with increasing concentrations of low-density lipoprotein and decreasing concentrations of high-density lipoproteins. Its association with increasing concentrations of plasma triglyceride is less clear but, within the mixed hyperlipidaemias, dysbetalipoproteinaemia (Fredrickson type III hyperlipidaemia) has been identified as a very atherogenic entity associated with both premature ischaemic heart disease and peripheral arterial disease. Dysbetalipoproteinaemia is characterized by the accumulation of remnants of chylomicrons and of very low-density lipoproteins. The onset occurs after childhood and usually requires an additional metabolic stressor. In women, onset is typically delayed until menopause. Clinical manifestations may vary from no physical signs to severe cutaneous and tendinous xanthomata, atherosclerosis of coronary and peripheral arteries, and pancreatitis when severe hypertriglyceridaemia is present. Rarely, mutations in apolipoprotein E are associated with lipoprotein glomerulopathy, a condition characterized by progressive proteinuria and renal failure with varying degrees of plasma remnant accumulation. Interestingly, predisposing genetic causes paradoxically result in lower than average cholesterol concentration for most affected persons, but severe dyslipidaemia develops in a minority of patients. The disorder stems from dysfunctional apolipoprotein E in which mutations result in impaired binding to low-density lipoprotein (LDL) receptors and/or heparin sulphate proteoglycans. Apolipoprotein E deficiency may cause a similar phenotype. Making a diagnosis of dysbetalipoproteinaemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up may present some challenges. Diagnosis of dysbetalipoproteinaemia should be considered in mixed hyperlipidaemias for which the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated LDL and directly measured LDL cholesterol concentrations. Genetic tests are informative in predicting the risk of developing the disease phenotype and are diagnostic only in the context of hyperlipidaemia. Specialised lipoprotein studies in reference laboratory centres can also assist in diagnosis. Fibrates and statins, or even combination treatment, may be required to control the dyslipidaemia.

Endothelial cells as targets for chylomicron remnants

Endothelial dysfunction is characterised by pro-inflammatory/pro-coagulant changes in the endothelium and supports leukocyte adhesion and transmigration, key steps in early atherogenesis. There is emerging evidence that triacylglycerol-rich lipoproteins (TGRLs) present in the circulation during the postprandial phase influence vascular inflammation but the specific contribution of the remnant lipoprotein component of TGRLs is largely unexplored and the mechanistic basis of their actions poorly defined. This article provides a brief overview of the evidence supporting direct actions of these particles on endothelial cells and highlights the importance of their fatty acid composition and oxidative state as determinants of their cellular actions.

Remnant-like lipoprotein particles impair endothelial function: direct and indirect effects on nitric oxide synthase

Remnant-like lipoprotein particles (RLPs) have been implicated as potentially atherogenic lipoproteins. Endothelial dysfunction is known to be an early event in atherosclerosis and an important contributor to the pathogenesis of coronary artery disease. Moreover, there is considerable evidence linking increased RLP cholesterol levels with endothelial dysfunction, reflected by impaired endothelial vasodilatation and abnormal endothelial secretion. The underlying mechanisms by which RLPs may contribute to endothelial dysfunction are complex and have not been completely elucidated. Because the expression and activation of endothelial nitric oxide synthase (eNOS) are vital to endothelial function, and recent data have implied an association between RLPs and eNOS, this manuscript proposes the hypothesis that RLPs could impair endothelial function via direct and indirect effects on eNOS: RLPs may affect the autophosphorylation of focal adhesion kinase and its downstream phosphatidylinositol kinase/Akt (protein kinase B) signaling pathway, resulting in eNOS inactivation through induction of intracellular oxidative stress in endothelial cells; and RLPs could affect the expression or activation of eNOS indirectly by stimulating secretion of various inflammatory factors from multiple origins. The practical applications of this manuscript provide new insights for the future investigation of RLPs.

Atorvastatin markedly improves type III hyperlipoproteinemia in association with reduction of both exogenous and endogenous apolipoprotein B-containing lipoproteins

Remnant lipoproteins are known to promote atherosclerosis especially in patients with type III hyperlipoproteinemia (HLP). In the current study, the effects of atorvastatin were investigated with special reference to the exogenous and endogenous apolipoprotein (apo) B-containing lipoprotein metabolism in type III HLP. Four Japanese male patients with type III HLP associated with homozygous apoE2 were studied. One-month administration of atorvastatin (20 mg once daily), after a 4-week dietary run-in, strikingly reduced serum total cholesterol and triglyceride (TG) levels by 52 (P<0.01) and 56% (P<0.05), respectively. Atorvastatin further decreased remnant-like particle (RLP)-cholesterol by 73% and RLP-TG by 65% (P<0.05), respectively. Distribution analysis by polyacrylamide gel disc electrophoresis clearly showed that atorvastatin diminished very low-, intermediate- and low-density lipoprotein particles. The relative particle diameter of intermediate-density lipoprotein became smaller after atorvastatin treatment (P<0.01). Furthermore, ultracentrifugal analysis demonstrated that atorvastatin significantly decreased cholesterol, TG and phospholipid concentrations in all apoB-containing lipoprotein fractions and very low-density lipoprotein (VLDL)-cholesterol/serum TG ratio (P<0.05), implying atorvastatin-induced reduction of beta-VLDL. Finally, newly developed assays of apoB-48 and apoB-100 revealed that atorvastatin markedly reduced these apolipoproteins by 43 and 52%, respectively (P<0.01), suggesting that atorvastatin decreased the number of both exogenous and endogenous apoB-containing lipoproteins. Taken together, atorvastatin improves remnant lipoprotein metabolism in type III HLP both in quality and in quantity. Atorvastatin can be one of the optimal options for the treatment of patients with type III HLP.

The renin-angiotensin system is involved in the production of plasminogen activator inhibitor type 1 by cultured endothelial cells in response to chylomicron remnants

Triglyceride-rich lipoproteins have been suggested to promote atherosclerosis. Plasminogen activator inhibitor type 1 (PAI-1) plays an important role in the events of cardiovascular pathophysiology. The renin-angiotensin system influences various vascular functions, including PAI-1 production. We examined whether or not chylomicron remnants increased PAI-1 mRNA and protein production in endothelial cells and whether or not an inhibition of the renin-angiotensin system interfered with this effect. Chylomicron remnants were isolated from functionally hepatectomized rats injected with chylomicrons. Human umbilical vein endothelial cell cultures (HUVECs) were incubated with chylomicron remnants with or without an angiotensin-converting enzyme inhibitor (temocaprilat), an angiotensin II receptor type 1 antagonist (RNH-6270), or an angiotensin II receptor type 2 antagonist (PD123319). Chylomicron remnants increased PAI-1 secretion in HUVECs (0.5 microg/ml; 128.3 +/- 6.1%, the mean +/- SEM) as well as angiotensin II (10 nmol/l; 130.7 +/- 9.5%) in 18 h, as compared with the controls, as well as stimulated PAI-1 mRNA expression to a maximum level at 4 h. Temocaprilat and RNH-6270, but not PD123319, attenuated all of these effects. Chylomicron remnants enhanced nuclear extract binding to a very low-density lipoprotein response element in the PAI-1 promoter region and activated nuclear factor-kappaB. Extracellular signal-regulated kinase (ERK 1/2) was phosphorylated in response to chylomicron remnants. These effects were inhibited by temocaprilat or RNH-6270. In conclusion, chylomicron remnants increased protein secretion and mRNA expression of PAI-1 in HUVECs. Inhibition of the renin-angiotensin system reduced this stimulation.