Postprandial remnant lipoproteins as targets for the prevention of atherosclerosis

Association between the remnant cholesterol to high-density lipoprotein cholesterol ratio and the risk of coronary artery disease

BACKGROUND

The purpose of this study was to evaluate the relationship between remnant cholesterol (RC) to high-density lipoprotein cholesterol (HDL-C) ratio and the risk of coronary artery disease (CAD). We also investigated the clinical value of RC/HDL-C ratio in evaluating the severity of CAD and in predicting the short-term prognosis of CAD patients.

METHODS

In total, 615 patients were enrolled and they were classified into a CAD group (418 cases) and a normal group (197 cases) according to the results of coronary angiography. Serum RC/HDL-C ratio and Gensini score were calculated. Multivariate logistic regression and receiver operating characteristic (ROC) curves were employed to evaluate the association between RC/HDL-C ratio and CAD. The effect of RC/HDL-C ratio on the progression of major adverse cardiovascular events (MACEs) was also explored.

RESULTS

Increased RC/HDL-C ratio was associated with an increased risk of CAD (OR: 11.122; 95% CI: 5.903-20.954; P  < 0.001). When stratified by CAD subtypes, increased RC/HDL-C ratio was correlated with a greater risk of acute coronary syndrome (ACS) (OR:1.549; 95% CI: 1.014-2.364; P  < 0.05). Compared with the first quartile, the 4th quartile of RC/HDL-C ratio had a 9.774-fold ( P  = 0.000) increase in the odds ratio for CAD, and a 2.241-fold ( P  = 0.017) increase in the odds ratio for ACS. RC/HDL-C ratio was an independent determinant of Gensini score ≥32 (OR: 2.138, 95% CI:1.389-3.292, P  < 0.01), and multi-branch (MVD) (OR: 2.245; 95% CI: 1.468-3.443; P  < 0.001). The prevalence of Gensini score ≥32 and MVD in the 4th quartile of RC/HDL-C ratio group were much higher than that of other quartile groups ( P  < 0.01). Moreover, the areas under the ROC for the predictive value of RC/HDL-C ratio for CAD, ACS, Gensini score ≥32, and MVD were 0.702, 0.563, 0.602, and 0.669, respectively. Furthermore, the incidence of MACEs was significantly increased in CAD patients with levels of RC/HDL-C ratio ( P  < 0.05).

CONCLUSION

RC/HDL-C ratio plays an important role in the progression and severity of CAD.

The chylomicron saga: time to focus on postprandial metabolism

Since statins have had such tremendous therapeutic success over the last three decades, the field of atherosclerosis has become somewhat LDL-centric, dismissing the relevance of triglycerides (TG), particularly chylomicrons, in atherogenesis. Nonetheless, 50% of patients who take statins are at risk of developing atherosclerotic cardiovascular disease (ASCVD) and are unable to achieve their goal LDL-C levels. This residual risk is mediated, in part by triglyceride rich lipoproteins (TRL) and their remnants. Following his seminal investigation on the subject, Zilversmit proposed that atherosclerosis is a postprandial event in 1979 (1-4). In essence, the concept suggests that remnant cholesterol-rich chylomicron (CM) and very-low density lipoprotein (VLDL) particles play a role in atherogenesis. Given the foregoing, this narrative review addresses the most recent improvements in our understanding of postprandial dyslipidemia. The primary metabolic pathways of chylomicrons are discussed, emphasizing the critical physiological role of lipoprotein lipase and apoCIII, the importance of these particles' fluxes in the postprandial period, their catabolic rate, the complexities of testing postprandial metabolism, and the role of angiopoietin-like proteins in the partition of CM during the fed cycle. The narrative is rounded out by the dysregulation of postprandial lipid metabolism in insulin resistance states and consequent CVD risk, the clinical evaluation of postprandial dyslipidemia, current research limits, and potential future study directions.

Triglyceride and Triglyceride-Rich Lipoproteins in Atherosclerosis

Cardiovascular disease (CVD) is still the leading cause of death globally, and atherosclerosis is the main pathological basis of CVDs. Low-density lipoprotein cholesterol (LDL-C) is a strong causal factor of atherosclerosis. However, the first-line lipid-lowering drugs, statins, only reduce approximately 30% of the CVD risk. Of note, atherosclerotic CVD (ASCVD) cannot be eliminated in a great number of patients even their LDL-C levels meet the recommended clinical goals. Previously, whether the elevated plasma level of triglyceride is causally associated with ASCVD has been controversial. Recent genetic and epidemiological studies have demonstrated that triglyceride and triglyceride-rich lipoprotein (TGRL) are the main causal risk factors of the residual ASCVD. TGRLs and their metabolites can promote atherosclerosis via modulating inflammation, oxidative stress, and formation of foam cells. In this article, we will make a short review of TG and TGRL metabolism, display evidence of association between TG and ASCVD, summarize the atherogenic factors of TGRLs and their metabolites, and discuss the current findings and advances in TG-lowering therapies. This review provides information useful for the researchers in the field of CVD as well as for pharmacologists and clinicians.

Mechanisms of Atherosclerosis Induced by Postprandial Lipemia

Postprandial lipemia plays an important role in the formation, occurrence, and development of atherosclerosis, and it is closely related to coronary heart disease and other diseases involving endothelial dysfunction, oxidative stress, inflammation, and other mechanisms. Therefore, it has become a focus area for further research. The studies on postprandial lipemia mainly include TG, TRL, VLDL, CM, and remnant cholesterol. Diurnal triglyceride patterns and postprandial hyperlipidemia are very relevant and are now insufficiently covered. The possible mechanisms between postprandial lipemia and cardiovascular disease have been reviewed in this article by referring to relevant literature in recent years. The research progress on the effects of postprandial lipemia on endothelial function, oxidative stress, and inflammation is highlighted. The intervention of postprandial lipemia is discussed. Non-medicinal intervention such as diet and exercise improves postprandial lipemia. As medicinal intervention, statin, fibrate, ezetimibe, omega-3 fatty acids, and niacin have been found to improve postprandial lipid levels. Novel medications such as pemafibrate, PCSK9, and apoCIII inhibitors have been the focus of research in recent years. Gut microbiota is closely related to lipid metabolism, and some studies have indicated that intestinal microorganisms may affect lipid metabolism as environmental factors. Whether intervention of gut microbiota can reduce postprandial lipemia, and therefore against AS, may be worthy of further study.

Association between postprandial lipoprotein subclasses and Framingham cardiovascular disease risk stratification

OBJECTIVE

To determine the ability of postprandial lipoprotein subclass concentrations to stratify patients with respect to their risk for cardiovascular disease (CVD).

METHODS

Using the Framingham cardiovascular disease risk score (FRS) algorithm, a total of 112 consecutive patients referred for community health screening were stratified into two groups: (a) low-risk (FRS < 10%) and (b) intermediate/high-risk (FRS ≥ 10%). Serum lipoprotein subclass concentrations were determined by Vertical Auto Profile (VAP-II).

RESULTS

Fasting and postprandial levels of LDL4, HDL2, VLDL1 + 2, VLDL3, and RLP, as well as fasting levels of ApoB and postprandial levels of LDL3 and IDL1, were significantly different in the intermediate/high risk FRS group vs. the low-risk group (P < 0.05). Correlations between Framingham CVD risk and LDL3, LDL4, IDL1, VLDL1 + 2, VLDL3, RLP, and ApoB were positive while negative for HDL2 in both the fasting and postprandial states. Intermediate/high risk for CVD was shown to be significantly associated with both fasting and postprandial levels of VLDL1 + 2 and RLP, as well as with postprandial LDL4 and VLDL3, as determined using forward conditional logistic regression analysis. Postprandial levels of VLDL1 + 2 were better at identifying patients in the intermediate/high-risk FRS group than fasting levels, although the differences were not significant due to overlapping reference intervals. In addition, the association between RLP and VLDL subclasses relative to Framingham CVD risk increased significantly in the postprandial state (ΔR² = 0.023; ΔF = 7.178; ΔP = 0.025) but not in the fasting state.

CONCLUSIONS

The use of postprandial lipoprotein subclass concentrations is not inferior to the use of fasting levels in identifying intermediate/high-risk FRS individuals. In addition, changes in RLP and VLDL subclass concentrations in fasting vs. postprandial states may reveal lipid metabolic mechanisms associated with CVD.

Lipoprotein removal mechanisms and aging: implications for the cardiovascular health of the elderly

PURPOSE OF REVIEW

The speed of removal from the plasma of apolipoprotein B-containing lipoproteins, for example, chylomicrons, VLDL and LDL is determinant of the plasma concentration of these lipoproteins, is influenced by genetic features and ambient factors, and has implications in atherogenesis. As aging increases the clinical complications of atherosclerosis, it is important to appraise the status of the removal mechanisms in elderly individuals.

RECENT FINDINGS

Removal of triglyceride-rich lipoproteins remnants is delayed but the triglyceride breakdown is unchanged in elderly individuals. The discovery of PCSK9, enzyme that degrades LDL receptors, and the recent observation that PCSK9 is elevated in the elderly raises another hypothesis to account for the increased LDL-cholesterol levels in the elderly. The removal of cholesterol from cells by HDL, the first step of cholesterol reverse transport is also less efficient in the elderly, which may compromise the body cholesterol homeostasis.

SUMMARY

Aging determines reduction of the efficiency of lipoprotein plasma removal mechanisms, which is implicated in increased incidence of cardia complications. Moreover, aging is frequently accompanied by physical activity reduction, weight gain, and metabolic disturbances that can further decrease the efficacy of the removal mechanisms. This knowledge is important for promoting cardiovascular health in the elderly and prolonging survival.

Comparing remnant lipoprotein cholesterol measurement methods to evaluate efficacy of ezetimibe/statin vs statin therapy

BACKGROUND

Elevated remnant lipoprotein cholesterol (RLP-C) levels increase cardiovascular disease risk. However, RLP-C measurement methods are not standardized, leading to variations across studies.

OBJECTIVE

To evaluate the effect of ezetimibe (Eze) + statins vs statin monotherapy on RLP-C using immunoseparation (IM), vertical auto profile (VAP) ultracentrifugation, and calculated RLP-C measurement methods.

METHODS

This post hoc analysis evaluated data pooled from 3 first-line (all-statin [simvastatin 10/20/40/80 mg] vs Eze + statin [Eze 10 mg + simvastatin]) and 2 second-line (statin [atorvastatin uptitrated to 40/80 mg] vs statin + Eze [atorvastatin 20/40 mg + Eze 10 mg]) studies. Similarity of RLP-C methods was evaluated using Pearson correlation coefficients and Bland-Altman plots. RLP-C changes and percent changes from baseline were measured by all 3 methods in first-line and VAP and calculated methods in second-line studies.

RESULTS

Correlations between methods were generally moderate to strong for RLP-C levels, changes, and percent changes across treatment groups (r = 0.29-0.79) but with little evidence of agreement by Bland-Altman plots. Baseline RLP-C levels for Eze + statin vs all-statin groups were lower by IM (14.0 vs 14.0) compared with VAP (36.9 vs 35.9) and calculated (32.8 vs 33.3) methods. RLP-C changes (mg/dL) and percent changes from baseline were significantly greater (P < .01) with Eze + statins vs statins by VAP, calculated, and IM methods (between-treatment differences: -5.0 and -12.0, -2.0 and -5.4, and -1.5 and -12.1, respectively) in first-line, and VAP and calculated methods (between-treatment differences: -5.0 and -19.9 and -2.0 and -7.3) in second-line studies.

CONCLUSION

Although the 3 methods showed little agreement, each supported Eze + statins for achieving greater RLP-C reductions vs statin monotherapy; variability of results reinforces urgent need to standardize RLP-C measurements.

The VLDL receptor plays a key role in the metabolism of postprandial remnant lipoproteins

A new concept to account for the process of postprandial remnant lipoprotein metabolism is proposed based on the characteristics of lipoprotein particles and their receptors. The characteristics of remnant lipoprotein (RLP) were investigated using an immuno-separation method. The majority of the postprandial lipoproteins increased after fat intake was shown to be VLDL remnants, not chylomicron (CM) remnants, based on the significantly high ratio of apoB100/apoB48 in the RLP and the high degree of similarity in the particle size of the apoB48 and apoB100 carrying lipoproteins, which fluctuate in parallel during a 6 h period after fat intake. The VLDL receptor was discovered as a receptor for TG-rich lipoprotein metabolism and is located in peripheral tissues such as skeletal muscle, adipose tissue, etc., but not in the liver. Postprandial VLDL particles are strongly bound and internalized into cells expressing the VLDL receptor. Ligands that bind to VLDL receptor, such as LPL and Lp(a), present in RLP. The presence of various specific ligands in VLDL remnants may enhance the capacity for binding to the VLDL receptor, which play the role primarily for energy delivery to the peripheral tissues, but is also a causal factor in atherogenic diseases when excessively and/or continuously remained in plasma.

Hypothesis II: The majority of VLDL-apoB48 remnants in postprandial plasma are derived from the liver, not from the intestine

We have long thought that remnant lipoproteins (RLP) in the postprandial plasma contain CM remnants (exogenous remnants; RLP-apoB48) and VLDL remnants (endogenous remnants; RLP-apoB100) of different origin, i.e. produced in the intestine and liver, respectively. However, the majority of CM remnants incorporated into liver from the circulation are degraded in liver and may be reused for the remodeling of VLDL. Namely, the most of the apoB48 in CM remnants are smoothly incorporated into the liver after fat intake along with lipids and other apolipoproteins via the LDL receptor and LDL-receptor-related protein (LRP). Subsequently, apoB48 may be reconstituted in VLDL as VLDL apoB48 through an essential physiological pathway similar or the same to that of VLDL apoB100 formation in the liver and secreted into the circulation as VLDL apoB48 to form their remnants. Because those particles are newly reconstituted in liver as a portion of VLDL, we propose that both RLP-apoB100 and RLP-apoB48 are endogenous VLDL remnants produced in liver after fat intake. Also we predict the presence of a new pathway for the formation of VLDL apoB48 along with VLDL apoB100 in liver in humans similar in mice and rats.