Cationic charge-dependent hepatic delivery of amidated serum albumin.

To obtain a quantitative correlation between the physicochemical properties of amidated bovine serum albumin (BSA) and their tissue distribution characteristics for the development of targeted delivery of proteins, BSA was amidated with hexamethylenediamine (HMD) or ethylenediamine (ED) to obtain cationized BSAs. Their structural changes were examined by spectroscopic and electrophoretic techniques then their tissue distribution was studied in mice. Circular dichroism (CD) and fluorescence measurements showed that spectroscopic changes occurred as the number of free NH2 groups increased. Capillary electrophoresis revealed a linear relationship between the mobility and the increased number of free NH2 groups. 111In-cationized BSAs were rapidly taken up by liver, but HMD-BSA showed a faster uptake than ED-BSA with a similar number of free NH2 groups, suggesting that the diamine reagent with a longer carboxyl side chain results in more efficient hepatic targeting. The hepatic uptake clearance (CL(liver)) of both derivatives increased significantly with a decrease in electrophoretic mobility (mu(ep)) towards the anode and reached a plateau at low electrophoretic mobility. The electrophoretic mobility is an appropriate indicator of the degree of amidation, which was closely correlated with the hepatic uptake clearance. The correlation between the mobility and the clearance shows that a low degree of amidation is sufficient for efficient hepatic targeting of proteins.