Asialoglycoprotein Receptor (ASGP-R) is Liver Parenchymal Cells is Involved in Elimination of Recombinant Human TFPI
We here report on a study carried out to determine the early clearance kinetics, and organ, cell(s) and receptor(s) responsible for the clearance of full length TFPI purified from BHK cells (TFPIBHK). Following intravenous administration, 125I-TFPIBHK was cleared with a biphasic elimination curve, and with a significantly slower t1/2α compared to recombinant human TFPI from E.Coli (TFPIE.Coli) (1.95±0.10 versus 1.42±0.07 min, respectively, p<0.001). Studies on organ and cell distribution revealed that liver parenchymal cells (PCs) were responsible for 96% of the uptake of TFPIBHK and 81% of TFPIE.Coli, whereas the nonparenchymal cells (NPCs) were responsible for 4% and 19%, respectively. Pre-administration of excessive amounts of unlabeled TFPIBHK prolonged blood clearance of 125I-TFPIBHK. Unlabelled TFPIBHK inhibited endocytosis of 125I-TFPIBHK in PCs in vitro, whereas blocking of LDL-receptor related protein-1 (LRP-1) by receptor-associated protein (RAP) affected neither blood clearance nor endocytosis of 125I-TFPIBHK in PCs. In addition, TFPIBHK was also found in the kidneys and this could be reduced in the presence of RAP. Asialoorosomucoid (ASOR), a potent inhibitor of the asialoglycoprotein receptor (ASGP-R), prolonged the circulatory survival of 125I-m-TFPI by 1.5-fold (p<0.001). In vitro, ASOR and other ASGP-R antagonists significantly inhibited endocytosis of 125I-TFPIBHK in PCs. Moreover, unlabelled TFPIBHK markedly decreased endocytosis of 125I-asialofetuin. In conclusion, our findings suggest that ASGP-R mediated endocytosis in the liver is involved in the clearance of TFPIBHK.
This article is part of Cristina Ionica Øie's doctoral thesis, which is available in Munin at http://hdl.handle.net/10037/2910
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