Uptake Characteristics of Anionized and Cationized Proteins in Brain Microvessel Endothelial Cells

Abstract

We previously reported that proteins anionized by succinylation or maleylation were taken up by brain microvessel endothelial cells (BMECs), as an in-vitro model of the blood-brain barrier (BBB), via a scavenger receptor-mediated mechanism for polyanions. The present study was conducted for further characterization of the cellular uptake of anionized proteins by BMECs in comparison with that of cationized proteins. Internalization of FITC-labelled succinylated bovine serum albumin (BSA; molecular weight 67 kDa, Suc-BSA) and cationized BSA (Cat-BSA) was confirmed using confocal laser microscopy. In uptake experiments using radiolabelled proteins, both Cat-superoxide dismutase (SOD, molecular weight 32 kDa) and Cat-BSA showed significant uptake by BMECs. Suc-BSA was taken up by the cells to a great extent whereas no significant uptake was observed for Suc-SOD, suggesting the importance of the molecular weight of anionized protein in the uptake by BMECs. The concentration dependency experiments showed that the uptake of Suc-BSA by BMECs was characterized by a high affinity and a low capacity compared with Cat-BSA. These results extended the characterization of the uptake of anionized proteins by BMECs. The present study suggested that direct anionization of protein drugs may be useful for drug delivery across the blood-brain barrier.