Mechanism of the defect in cholesteryl ester clearance from macrophages of atherosclerosis-susceptible White Carneau pigeons.

Recent studies from our laboratory (Yancey, P.G., and R. W. St. Clair. 1992. Arterioscler. Thromb. 12: 1291-1304) have shown that cultured peritoneal macrophages from White Carneau (WC) pigeons clear cholesteryl esters at a slower rate than do macrophages from Show Racer (SR) pigeons (9% per 24 h vs. 42% per 24 h, respectively) when incubated in the presence of a cholesterol acceptor apo high density lipoprotein/phosphatidylcholine (apoHDL/PC) at concentrations that are not rate-limiting for cholesterol efflux. In the present studies we have examined some potential mechanisms for this difference in cholesterol efflux. The desorption of [3H]cholesterol from the plasma membranes of non-cholesterol-loaded cells was log-linear with half-times of 24-31 h, and was not different for WC and SR macrophages. As this rate of cholesterol desorption was 2- to 3-times faster than the rate of cholesteryl ester clearance, it is unlikely to be rate-limiting. In cells loaded with cholesteryl esters, the re-esterification of cholesterol was equally low in both WC and SR macrophages when incubated with apoHDL/PC. The addition of the acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, Sandoz 58,035, reduced esterification approximately 50%, but did not affect the clearance of cholesteryl ester mass from either WC or SR macrophages. Thus, differences in cholesteryl re-esterification could not explain the differences in cholesteryl ester clearance. The rate of hydrolysis of radiolabeled cellular cholesteryl esters was log-linear for up to 36 h in WC and SR macrophages. The half-time for hydrolysis of cholesteryl ester was 89 h in WC macrophages, compared to only 37 h in the SR macrophages, and paralleled the rate of clearance of cholesteryl esters in these cells (133 h and 51 h, respectively). Cyclic AMP stimulated cholesterol ester hydrolysis in WC macrophages and increased by 5-fold the clearance of cholesteryl esters in the presence of apoHDL/PC and Sandoz 58,035. These data are consistent with the conclusion that the rate-limiting step in the clearance of cholesteryl esters from pigeon macrophages is the hydrolysis of cholesteryl esters, and that the slow rate of cholesteryl ester clearance in WC macrophages is due, at least in part, to a defect in cholesteryl ester hydrolysis. It is tempting to speculate that this defect in cholesteryl ester hydrolysis may play a role in the difference in susceptibility to atherosclerosis between WC and SR pigeons.