Hepatic Disposition Characteristics of 111In-Labeled Lactosaminated Bovine Serum Albumin in Rats

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Abstract
The hepatic disposition of lactosaminated bovine serum albumin (Lac-BSA) in rats was studied at the whole body, isolated liver, and isolated parenchymal cell levels. After intravenous injection, 111In-Lac-BSA (1 mg/kg) was rapidly eliminated from the plasma due to extensive uptake by liver parenchymal cells; however, a significant decrease in hepatic clearance was observed at high dose (50 mg/kg). In a single-pass, constant infusion experiment in the isolated liver, 111In-Lac-BSA was continuously extracted. The extraction ratio at steady state (Ess) for 111In-Lac-BSA was significantly decreased by coadministrating galactose, NH4Cl, or chloroquine, and at low temperature, suggesting that hepatic uptake of Lac-BSA proceeds via receptor-mediated endocytosis for asialoglycoprotein. Kinetic analysis of 111In-Lac-BSA binding with isolated parenchymal cells at 4°C yielded a dissociation constant (Kd) of 2.5 ×10−8M and a value of 3.5 × 105 maximal binding sites/cell (Bmax). The internalization rate constant (kint) for 111In-Lac-BSA was calculated to be 0.46 min−l in liver perfusion experiments using the EDTA-wash method.