Abstract: OBJECTIVES: To evaluate the capacity of serum from carriers of LCAT gene mutations to promote cell cholesterol efflux through the ABCA1, ABCG1, and SR-BI pathways. METHODS: Serum was obtained from 41 carriers of mutant LCAT alleles (14 carriers of two mutant LCAT alleles and 27 heterozygotes) and 10 non-carrier relatives (controls). The capacity of serum to promote cholesterol efflux was tested in pathway-specific cell models. RESULTS: LCAT deficient sera were significantly more efficient than control sera in promoting cell cholesterol efflux via ABCA1 (3.1+/-0.3% for carriers of two mutant LCAT alleles and 2.6+/-0.2% for heterozygotes vs. 1.5+/-0.4% for controls), and less efficient in promoting ABCG1- and SR-BI-mediated cholesterol efflux. The enhanced capacity of LCAT deficient serum for ABCA1 efflux is explained by the increased content of prebeta-HDL, as indicated by the significant positive correlation between ABCA1 efflux and serum prebeta-HDL content (R=0.468, P<0.001). Moreover, chymase treatment of LCAT deficient serum selectively degraded prebeta-HDL and completely abolished ABCA1 efflux. Despite the remarkable reductions in serum HDL levels, LCAT deficient sera were as effective as control sera in removing mass cholesterol from cholesterol-loaded macrophages. CONCLUSIONS: Serum from carriers of LCAT gene mutations has the same capacity of control serum to decrease the cholesterol content of cholesterol-loaded macrophages due to a greater cholesterol efflux capacity via ABCA1.

Abstract: The liver X receptors (LXRs) have been shown to affect lipoprotein plasma profile, lipid metabolism, and reverse cholesterol transport (RCT). In the present study, we investigated whether a short-term administration of the synthetic LXR agonist T0901317 (T0) to mice may affect RCT by modulating the capacity of plasma to promote cellular lipid efflux. Consistent with previous data, the pharmacological treatment of mice caused a significant increase of macrophage-derived [3H]cholesterol content in plasma, liver, and feces and resulted in improved capacity of plasma to promote cellular cholesterol release through passive diffusion and scavenger receptor class B type I (SR-BI)-mediated mechanisms. Differently, plasma from treated mice possessed similar or reduced capacity to drive lipid efflux via ABCA1. Consistent with these data, the analysis of plasma HDL fractions revealed that T0 caused the formation of larger, lipid-enriched particles. These results suggest that T0 promotes in vivo RCT from macrophages at least in part by inducing an enrichment of those HDL subclasses that increase plasma capacity to promote cholesterol efflux by passive diffusion and SR-BI-mediated mechanisms.