title: Recognition of lactoferrin and aminopeptidase M-modified lactoferrin by the liver: involvement of the remnant receptor.
abstract: Lactoferrin inhibits the hepatic uptake of lipoprotein remnants, and we showed earlier that arginine residues of lactoferrin are involved. In this study, lactoferrin was treated with aminopeptidase-M (APM), which resulted in removal of 14 N-terminal amino acids, including 4 clustered arginines at positions 2-5 (APM-lactoferrin). After i.v. injection into rats, 125I-APM-lactoferrin was cleared within 10 min by the liver parenchymal cells (74.7% of the dose). Binding of APM-lactoferrin to isolated parenchymal liver cells was saturable with a Kd of 186 nM (750.000 sites/cell). This is in striking contrast to the binding of lactoferrin (Kd 10 microM; 20 x 10(6) sites/cell). Preinjection of rats with 20 mg of APM-lactoferrin/kg body weight reduced the liver association of beta-VLDL by 50%, whereas lactoferrin had no effect at this dose. With isolated parenchymal liver cells, APM-lactoferrin was a more effective competitor for beta-VLDL binding than native lactoferrin (50% inhibition at 0.5 mg/ml vs. 8.0 mg/ml). We conclude that the 4-arginine cluster of lactoferrin at position 2-5 involved in the massive association of lactoferrin with the parenchymal liver cell, but is not essential for the inhibition of the lipoprotein remnant uptake. The Arg/Lys sequence at position 25-30, which resembles the binding site of apoE, may mediate the high affinity binding of lactoferrin and block the binding of beta-VLDL to the remnant receptor efficiently.
authors.affiliation: Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, University of Leiden, Sylvius Laboratory, The Netherlands.
authors.forename: G J
authors.initials: GJ
authors.lastname: Ziere
authors.forename: J K
authors.initials: JK
authors.lastname: Kruijt
authors.forename: M K
authors.initials: MK
authors.lastname: Bijsterbosch
authors.forename: T J
authors.initials: TJ
authors.lastname: Berkel
mesh_terms: D000626:Aminopeptidases / Q000097:blood*; D000818:Animals; D001665:Binding Sites; D004705:Endocytosis / Q000502:physiology; D007781:Lactoferrin / Q000097:blood*; D008079:Lipoproteins, VLDL / Q000097:blood*; D008099:Liver / Q000378:metabolism*; D008297:Male; D063208:Methionyl Aminopeptidases; D051381:Rats; D017208:Rats, Wistar
chemical_list: D008079:Lipoproteins, VLDL; D000626:Aminopeptidases; D063208:Methionyl Aminopeptidases; D007781:Lactoferrin