J. Biol. Chem., Vol. 261, Issue 20, 9294-9299, Jul, 1986
Enhanced catabolism of low density lipoproteins in rat by lactosaminated Fab fragment. A new carrier of macromolecules to the liver
F Bernini, SR Tanenbaum, BC Sherrill, AM Gotto Jr and LC Smith
Proteins conjugated with lactose residues exhibit enhanced hepatic uptake
mediated by the galactose receptor. In this study, we demonstrate that
lactosaminated Fab fragments (lac-Fab) of IgG can induce hepatic catabolism
of specific antigens, especially low density lipoproteins (LDL). lac-Fab
and human LDL-lac-Fab complex exhibited specific uptake in isolated rat
hepatocytes. In vivo in the rat, lactosamination enhanced plasma clearance
of Fab fragments 2-fold and hepatic localization 20-fold. Fab fragments
retained their affinity after lactosamination. Hepatic uptake of rat
125I-IgG complexed in vitro with anti-rat lac-Fab was increased almost
5-fold, compared to rat 125I-IgG alone. Injection of rats with anti-LDL
lac-Fab induced plasma clearance and hepatic uptake of tracer amounts of
previously injected human 125I-LDL, which decreased 50% 10 min after
injection of lac-Fab, with 30% present in the liver. Asialofetuin
completely inhibited these processes. After a bolus of 6 mg of human LDL,
administration of anti-LDL lac-Fab reduced the serum cholesterol of rats to
basal values within 2.5 h. These findings suggest that lactosaminated Fab
fragments of specific IgGs are effective reagents for inducing hepatic
uptake of macromolecules through the galactose receptor. lac-Fab specific
for LDL may be an effective hypocholesterolemic agent in vivo.