Background:
Coronary allograft vasculopathy (CAV) is an important cause of mortality after cardiac transplantation. High density lipoprotein (HDL) cholesterol efflux capacity has been inversely associated with coronary artery disease and is impaired in cardiac transplant recipients. We performed a single center case-cohort study to test the hypothesis that reduced efflux capacity is a risk factor for mortality and a second, multi-center retrospective study to test if efflux capacity is associated with CAV progression.
Methods:
We designed a single center case-cohort study in which we identified cardiac transplant patients who died between 2009-2012 (cases, n=34) and controls as cardiac transplant patients who were alive as of the fourth quarter of 2013 (n=57). Efflux capacity was measured by incubating apolipoprotein B-depleted serum with macrophages in a validated ex vivo system. In a second study, we utilized pre-transplant samples from the Clinical Trials in Organ Transplantation 5 (CTOT5) study to determine the association between ATP-binding-cassette (ABC) A1-dependent cholesterol efflux and CAV progression at 1 year.
Results:
In our single center study, the average time from transplant to study entry was well-matched between cases and controls (7.6±1.0 vs 7.7±0.8 years, respectively, p=0.48). Multivariable Cox proportional hazard ratios demonstrated that higher levels of HDL cholesterol efflux capacity were associated with survival (HR 0.61, 95% CI 0.43-0.85), even after adjustment for HDL cholesterol mass. To determine whether excess mortality observed in subjects with reduced efflux could be attributable to CAV progression, we tested the relationship between intravascular ultrasound (IVUS) progression of CAV and cholesterol efflux capacity using linear regression. ABCA1-dependent efflux and IVUS progression were significantly associated (β = -0.90, 95% CI [-1.73 - -0.07], p = 0.037, R2 = 0.37).
Conclusion:
Reduced efflux capacity is an important mediator of CAV progression and mortality in cardiac transplant recipients. This finding suggests that interventions to increase HDL cholesterol efflux capacity may provide clinical benefit in cardiac transplant recipients.
