Lactoferrin catabolism in the rat liver.

Area of Science:

• Biochemistry
• Cell Biology
• Hepatology

Background:

• Lactoferrin (Lf) is an iron-binding glycoprotein with diverse biological functions.
• Understanding the hepatic metabolism of Lf is crucial for its physiological and therapeutic roles.

Purpose of the Study:

• To investigate the hepatic uptake, degradation, and intracellular trafficking of human diferric 125I-lactoferrin in rats.
• To explore the potential for repeated endo- and exocytosis (diacytosis) of Lf by the liver.

Main Methods:

• Intravenous injection of 125I-labeled human lactoferrin into intact rats.
• Analysis of tracer clearance, subcellular localization, and degradation rates.
• In vitro studies using lysosomal hydrolases.
• Investigation of fucoidin's effect on Lf release from the liver.

Main Results:

• Rapid hepatic clearance of 125I-Lf, likely via adsorptive pinocytosis.
• Delayed transfer of endocytosed Lf from light-density particles to lysosome-like organelles.
• Slow loss of protein-bound 125I from the liver (half-life 2.7 h), similar to asialotransferrin.
• Lf demonstrated poor susceptibility to lysosomal hydrolases in vitro.
• Fucoidin induced Lf release, suggesting potential diacytosis.

Conclusions:

• The liver efficiently uptakes and slowly degrades human lactoferrin.
• Evidence suggests a possible mechanism of repeated endo- and exocytosis (diacytosis) for a fraction of hepatic lactoferrin.
• Fucosylation of asialotransferrin did not fully replicate Lf's hepatic binding properties.