Remnant-Like Particle Cholesterol, Low-Density Lipoprotein Triglycerides, and Incident Cardiovascular Disease

Abstract

Background: Hypertriglyceridemia is associated with increased remnant-like particle cholesterol (RLP-C) and triglycerides in low-density lipoprotein (LDL-TG). Recent studies have focused on atherogenicity of RLP-C, with few data on LDL-TG.

Objectives: The aim of this study was to examine associations of RLP-C and LDL-TG with incident cardiovascular disease (CVD) events and genetic variants in the ARIC (Atherosclerosis Risk In Communities) study.

Methods: Fasting plasma RLP-C and LDL-TG levels were measured in 9,334 men and women without prevalent CVD. Participants were followed for incident CVD events (coronary heart disease and ischemic stroke) for up to 16 years. Associations between LDL-TG and RLP-C levels and genetic variants were assessed by whole-exome sequencing using single-variant analysis for common variants and gene-based burden tests for rare variants; both an unbiased and a candidate gene approach were explored.

Results: RLP-C and LDL-TG levels were correlated with triglyceride levels (r = 0.85 and r = 0.64, p < 0.0001). In minimally adjusted analyses, RLP-C and LDL-TG were associated with CVD risk, but in models adjusted for traditional risk factors including lipids, only LDL-TG was associated with incident CHD (hazard ratio: 1.28; 95% confidence interval: 1.10 to 1.50) and stroke (hazard ratio: 1.47; 95% confidence interval: 1.13 to 1.92). A common APOE variant, rs7412, had the strongest association with LDL-TG and RLP-C (p < 5 × 10^-8).

Conclusions: RLP-C and LDL-TG levels were predictive of CVD and associated with APOE variants. LDL-TG may represent a marker of dysfunctional remnant lipoprotein metabolism associated with increased CVD risk. Further research is needed to determine whether LDL-TG plays a causal role in CVD and may be a target for therapy.

Keywords: coronary heart disease; remnant lipoproteins; risk; stroke; triglyceride-rich lipoproteins.

Figure 1. Study population

The Atherosclerosis Risk in Communities study (ARIC) is a prospective study of cardiovascular disease (CVD) in 15,792 middle-aged adults recruited from four US communities in 1987–1989. The current study was conducted among participants in ARIC visit 4 (1996–1998). Of 11,656 eligible individuals, we excluded those with self-reported race neither white nor black (n=31) and African American participants at the Minnesota and Washington County field centers (n=38) because of small enrollment numbers, individuals missing data for low-density lipoprotein triglyceride (LDL-TG), remnant-like particle cholesterol (RLP-C), or other covariates (n=1524), and those with prevalent coronary heart disease (CHD) (n=632) or ischemic stroke (n=97) at visit 4. Therefore, 9334 individuals were included in this analysis.

Figure 2. Kaplan–Meier survival analyses

A) Incident ischemic stroke and RLP-C; B) incident CVD and RLP-C; C) incident ischemic stroke and LDL-TG; D) incident CVD and LDL-TG. P-values from logrank tests.

Figure 2. Kaplan–Meier survival analyses

A) Incident ischemic stroke and RLP-C; B) incident CVD and RLP-C; C) incident ischemic stroke and LDL-TG; D) incident CVD and LDL-TG. P-values from logrank tests.

Figure 2. Kaplan–Meier survival analyses

A) Incident ischemic stroke and RLP-C; B) incident CVD and RLP-C; C) incident ischemic stroke and LDL-TG; D) incident CVD and LDL-TG. P-values from logrank tests.

Figure 2. Kaplan–Meier survival analyses

A) Incident ischemic stroke and RLP-C; B) incident CVD and RLP-C; C) incident ischemic stroke and LDL-TG; D) incident CVD and LDL-TG. P-values from logrank tests.

Figure 3. Associations of apoE haplotypes with log LDL-TG (left) and RLP-C (right)

Associations between LDL-TG and RLP-C levels and genetic variants were assessed by whole exome sequencing. A common APOE variant, rs7412, had the strongest association with LDL-TG and RLP-C (p<5×10⁻⁸). Since rs7412 defines APOE e2 allele status, we assessed APOE haplotypes and found that APOE e2/2 was associated with reduced LDL-TG and increased RLP-C (p<0.0001 vs any other haplotype). The different relationships of RLP-C and LDL-TG with APOE ε2/2 may be partly explained by the low affinity of apoE2 for the LDL (apoB/E) receptor, potentially leading to delayed clearance of remnant particles. This delayed clearance may lead to increased RLP-C levels, while simultaneously lowering LDL and LDL-TG levels via upregulation of cellular LDL receptors in these individuals.

Central Illustration. Remnant lipoprotein metabolism

Chylomicrons secreted from the intestine and very low density lipoprotein (VLDL) secreted from the liver are lipolyzed by lipoprotein lipase (LPL), leading to triglyceride-rich lipoprotein (TGRL) remnants. Chylomicron secretion is largely regulated by food intake, whereas VLDL secretion is controlled by insulin. Remnant particles undergo remodeling via the enzymatic action of cholesteryl ester transfer protein (CETP) with high-density lipoprotein (HDL), hepatic lipase (HL), and the exchange of soluble apolipoproteins such as E, C-I, C-II, and C-III. TGRL remnants are cleared from the circulation via receptor-mediated uptake involving the low-density lipoprotein (LDL) receptor (LDLR), LDL receptor–like protein (LRP), and heparan sulfate proteoglycans (HSPG). Chylomicron remnants and VLDL remnants compete for the same lipolytic pathway, a process mediated by apoE. While chylomicron remnant clearance may be mediated by LDLR-, LRP-, or HSPG, VLDL remnants are believed to be predominantly cleared via LDLR. Individuals with apoE2 isoforms have reduced remnant clearance and are postulated to have compensatory upregulation of cellular LDLR expression that may lead to decreased LDL-TG and LDL-C levels. The purported role of HL in the lipolytic conversion of IDL to LDL may at least partly explain why individuals with decreased HL activity due to genetic variation in the LIPC gene (e.g., rs 2070895) have elevated LDL-TG levels.