Journal of Lipid Research, Vol 24, 391-401, Copyright © 1983 by Lipid Research, Inc.
Apolipoproteins of high, low, and very low density lipoproteins in human bile
RB Sewell, SJ Mao, T Kawamoto and NF LaRusso
We tested 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. Using specific radioimmunoassays for human
apolipoproteins A-I and A-II, the major apoproteins of high density
lipoproteins, for apolipoproteins C-II and C-III, major apoproteins of very
low density lipoproteins, and for apolipoprotein B, the major apoprotein of
low density lipoproteins, we found immunoreactivity for these five
apolipoproteins in every bile sample studied in concentrations up to 10% of
their plasma values. Using double immunodiffusion, we observed complete
lines of identity between bile samples and purified apolipoproteins A-I,
A-II, or C-II. Using molecular sieve chromatography, we found identical
elution profiles for biliary apolipoproteins A-I, A-II and B and these same
apolipoproteins purified from human plasma. When we added high density
lipoproteins purified from human plasma to lipoprotein-free solutions
perfusing isolated rat livers, we detected apolipoproteins A-I and A-II in
bile. Similarly, when we added low density lipoproteins purified from human
plasma to lipoprotein-free solutions perfusing isolated livers of rats
treated with ethinyl estradiol in order to enhance hepatic uptake of
low-density lipoproteins, we found apolipoprotein B in bile. These data
indicate that apolipoproteins can be transported across the hepatocyte and
secreted into bile.