Enhanced efflux of cholesterol from ABCA1-expressing macrophages to serum from type IV hypertriglyceridemic subjects

Since elevated plasma triglycerides (TGs) are an independent cardiovascular risk factor, we have compared the cholesterol efflux potential of sera from asymptomatic hypertriglyceridemic (HTG) type IIb, type IV or normolipidemic (NLP) individuals using two different cell systems. In both type IIb and IV HTG, the efflux of cholesterol from SR-BI-rich Fu5AH cells was similar to that obtained with NLP. The maintenance of efflux efficiency in spite of reduced HDL-cholesterol levels can be mainly attributed to the relative enrichment of HDL with phospholipid. In the J774 macrophage cell system, pretreatment with cAMP, which upregulates ABCA1, induced a markedly higher increase in efflux to type IV sera compared with type IIb or NLP. In addition, type IV sera exhibited two-fold higher pre-beta HDL relative concentration (percentage of total apo AI) compared with NLP. Moreover, positive correlations were established between ABCA1-mediated efflux and the serum pre-beta HDL levels or TG concentrations. Thus, the hyperTGemia is associated with a higher fraction of apo AI recovered as pre-beta HDL which appear to be partly responsible for enhanced efflux obtained upon the cAMP stimulation of J774 cells. In conclusion, we demonstrated for the first time that the ABCA1-expressing J774 cell system is responsive to the percent of apo AI present in human serum as pre-beta HDL. Our results suggest that high-plasma TG, accompanied by low HDL may not result in an impaired cholesterol efflux capacity.