HDL Particle Concentration and Size Predict Incident Coronary Artery Disease Events in People with Type 1 Diabetes

Abstract

Background: Cholesterol efflux capacity (CEC) negatively correlates with cardiovascular disease risk. Small HDL particles account almost quantitively for CEC, perhaps mediated through efflux of outer leaflet plasma membrane phospholipids by ABCA1. People with type 1 diabetes (T1D) are at increased risk of coronary artery disease (CAD) despite normal levels of HDL-cholesterol (HDL-C). We therefore tested the hypotheses that small HDL particles (HDL-P)-rather than HDL-C levels-predict incident CAD in T1D.

Methods: Incident CAD (CAD death, myocardial infarction, and/or coronary revascularization) was determined in a cohort of 550 participants with childhood-onset T1D. HDL-P was quantified by calibrated ion mobility analysis. CEC and phospholipid efflux were quantified with validated assays.

Results: During a median follow-up of 26 years, 36.5% of the participants developed incident CAD. In multivariable Cox models, levels of HDL-C and apolipoprotein A-I (APOA1) did not predict CAD risk. In contrast, extra-small HDL particle levels strongly and negatively predicted risk (hazard ratio [HR]=0.25, 95% confidence interval [CI]=0.13-0.49). An increased concentration of total HDL particles (T-HDL-P) (HR=0.87, CI=0.82-0.92) and three other HDL sizes were weaker predictors of risk: small HDL (HR=0.80, 0.65-0.98), medium HDL (HR=0.78, CI=0.70-0.87) and large HDL (HR=0.72, CI=0.59-0.89). Although CEC negatively associated with incident CAD, that association disappeared after the model was adjusted for T-HDL-P. Isolated small HDLs strongly promoted ABCA1-dependent efflux of membrane outer leaflet phospholipids.

Conclusions: Low concentrations of T-HDL-P and all four sizes of HDL subpopulations predicted incident CAD independently of HDL-C, APOA1, and other common CVD risk factors. Extra-small HDL was a much stronger predictor of risk than the other HDLs. Our data are consistent with the proposal that small HDLs play a critical role in cardioprotection in T1D, which might be mediated by macrophage plasma membrane outer leaflet phospholipid export and cholesterol efflux by the ABCA1 pathway.

Keywords: calibrated ion mobility analysis; incident cardiovascular disease; prospective cohort study; type 1 diabetes mellitus.

Figure 1.. HDL particle concentration negatively predicts CAD risk in people with T1D. Hazard ratios (HR) and 95% confidence intervals (CI) from Cox proportional hazards models for predicting incident coronary artery disease.

Models allowed for diabetes duration, sex, BMI, smoking status, HbA1c, hypertension status (time-dependent variable and fixed term), T-HDL-P for the model with HDL-C as the main independent variable or HDL-C for models with HDL-P as the main independent variable, non-HDL-C, WBC, estimated glomerular filtration rate, and albumin excretion rate. HRs are per 1 unit increase for HDL-C and HDL-P and per SD for macrophage (SD=0.44) and ABCA1 (SD=0.31) CEC, respectively.

Figure 2.. ABCA1-dependent export of membrane outer leaflet PCs by different sizes of HDL.

(A) Phosphatidylcholine (PC) export and (B) cholesterol efflux capacity (CEC) by ABCA1 expressing cells were quantified using equimolar concentrations (80 nM) of each HDL subpopulation and lipid-free APOA1 (10 μg/mL). PC export and CEC were quantified with or without induction of ABCA1 expression with mifepristone. Radiolabeled outer leaflet phospholipids (PLs) were exchanged with unlabeled POPC and sphingomyelin with MαCD. PC efflux was calculated as the percentage of radiolabel in the medium of the cells divided by the total radioactivity of the medium and cells. PC export and CEC were quantified as described in Methods in cells with and without induced expression of ABCA1. Results are representative of triplicate analyses. The p-values were calculated by two-way ANOVA with Tukey’s post-hoc tests.