Lipoprotein Components in Bile

We tried to prove the hypothesis that apolipoproteins, the protein constituents of plasma lipoproteins, are secreted into bile. We examined human gallbladder bile obtained at surgery (N=54) from subjects with (N=44) and without (N=10) gallstones and hepatic bile collected by T-tube drainage (N=9) after cholecystectomy.<br>Using specific radioimmunoassays for human apolipoproteins A-I and A-II, the major apolipo-proteins of high density lipoproteins, for apolipo-proteins C-II and C-III, major apolipoproteins of very low density lipoproteins, we found immuno-reactivity for these four apolipoproteins in every bile samples.<br>Using immunodiffusion technique, we observed complete lines of identity between bile samples and purified apolipoproteins A-I and A-II, or C-II.<br>Using molecular sieve chromatography, we found identical elution profiles of biliary apolipo-proteins A-I and A-II, as those of apolipoproteins A-I and A-II purified from human plasma.<br>When we added high density lipoproteins purified from human plasma to lipoprotein-free solutions perfusing through isolated rat livers, we detected apolipoproteins A-I and A-II in bile.<br>These data indicate that apolipoproteins can be transported across the hepatocyte and secreted into bile.