Design for Cell-Specific Targeting of Proteins Utilizing Sugar-Recognition Mechanism: Effect of Molecular Weight of Proteins on Targeting Efficiency

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Abstract
Hepatic targeting of proteins utilizing the sugar-recognition mechanism was investigated in mice after intravenous injection. Five proteins with different molecular weights, i.e., bovine γ-globulins (IgG), bovine serum albumin (BSA), recombinant human superoxide dismutase (SOD), soybean trypsin inhibitor (STI), and chicken egg white lysozyme (LZM), were modified with 2-imino-2-methoxyethyl 1-thiogalactoside to obtain galactosylated proteins (Gal-IgG, Gal-BSA, Gal-SOD, Gal-STI, and Gal-LZM). The numbers of galactose residues were 38, 20, 11, 6, and 5 for Gal-IgG, Gal-BSA, Gal-SOD, Gal-STI, and Gal-LZM, respectively. All galactosylated proteins were dose-dependently taken up by the liver and the relative amount accumulated in the liver was decreased with an increase of the administered dose. At low doses (0.05 and 0.1 mg/kg), Gal-IgG, Gal-BSA, and Gal-SOD could be taken up by the liver up to more than 70–80% of dose within 10 min after intravenous injection, but the maximum amounts accumulated in the liver were approximately 40 and 30% of the dose for Gal-STI and Gal-LZM, respectively. Pharmacokinetic analysis revealed that the hepatic uptake clearance (CLliver) was quite different around the molecular weight of 32 kDa and correlated with the amount delivered to the liver; Gal-IgG, Gal-BSA, and Gal-SOD has a large CLliver that is close to the hepatic plasma flow rate (85 ml/hr), whereas those of Gal-STI and Gal-LZM were approximately 10 ml/hr at low doses. As for the total amount accumulated in the liver, high glomerular filtration rate of Gal-STI and Gal-LZM was also shown to cause insufficient delivery to the liver apart from being caused by their low CLliver.