Cholesterol efflux from Fu5AH cells to the serum of patients with Alagillesyndrome: importance of the HDL-phospholipids free cholesterol ratio and of the HDL size distribution

We have previously described the lipoprotein abnormalities in cholestatic c hildren with paucity of interlobular bile ducts (PILBD), and we have shown that two different profiles emerged among these patients, depending on the level of lecithin:cholesterol acyltransferase (LCAT) activity. Reduced LCAT activity was associated with hypo-alpha-lipoproteinemia (group I) whereas normal LCAT activity was associated with hyper-alpha-lipoproteinemia (group II). In both groups, high density lipoproteins (HDL) were enriched with ph ospholipids and LpA-I particles were predominant. Here, we have investigate d the ability of serum and of isolated HDL, obtained from PILBD and control subjects, to promote cellular cholesterol efflux, from Fu5AH rat hepatoma cells. The mean fractional efflux to 5% serum in each group was, on average , following the differences in HDL concentrations (control: 30.1 +/- 4.2%; group I: 23.7 +/- 7.9%, ns; group II: 44.2 +/- 6.5%, P < 0.001). The variat ions in efflux values in group II were positively correlated to the variati ons in HDL-PL concentrations (P < 0.0001) and in HDL-PL to serum apo-AI rat io (P < 0.003). By contrast, the variation in efflux in group I was only po sitively related to the large range of HDL-PL to free cholesterol (FC) rati o values (P < 0.0004). Fractional efflux to isolated HDL, measured at a con stant HDL-PL amount, confirmed this relationship (P < 0.0001). Two-dimensio nal gel electrophoresis of the HDL size and apo A-I distribution in serum, revealed that small size HDL3 and pre-beta HDL were predominant in the seru m of patients from group I, especially those exhibiting low HDL-PL to FC ra tio, whereas in the serum of patients from group II, both small HDL3 and la rge HDL2 were present. These results suggest that a combination of an imbal ance between phospholipids and free cholesterol in the HDL particles and a deficit in large accepters of cholesterol will be responsible for an impair ment of cellular cholesterol efflux in PILBD patients with reduced lecithin :cholesterol acyltransferase activity.