dc.description.abstract | 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 (TFPI<sup>BHK</sup>). Following intravenous administration, <sup>125</sup>I-TFPI<sup>BHK</sup> was cleared with a
biphasic elimination curve, and with a significantly slower t<sub>1/2</sub>α compared to recombinant human TFPI from <i>E.Coli</i> (TFPI<sup>E.Coli</sup>) (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 TFPI<sup>BHK</sup> and 81% of TFPI<sup>E.Coli</sup>, whereas the nonparenchymal cells (NPCs) were responsible for 4% and 19%, respectively. Pre-administration of excessive amounts of unlabeled TFPI<sup>BHK</sup> prolonged blood clearance of <sup>125</sup>I-TFPI<sup>BHK</sup>. Unlabelled TFPI<sup>BHK</sup> inhibited endocytosis of <sup>125</sup>I-TFPI<sup>BHK</sup> in PCs <i>in vitro</i>, whereas blocking
of LDL-receptor related protein-1 (LRP-1) by receptor-associated protein (RAP) affected
neither blood clearance nor endocytosis of <sup>125</sup>I-TFPI<sup>BHK</sup> in PCs. In addition, TFPI<sup>BHK</sup> 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 <sup>125</sup>I-m-TFPI by 1.5-fold (p<0.001). <i>In vitro</i>, ASOR and other ASGP-R antagonists significantly inhibited endocytosis of <sup>125</sup>I-TFPI<sup>BHK</sup> in PCs. Moreover, unlabelled TFPI<sup>BHK</sup> markedly decreased endocytosis of <sup>125</sup>I-asialofetuin. In conclusion, our findings
suggest that ASGP-R mediated endocytosis in the liver is involved in the clearance of
TFPI<sup>BHK</sup>. | en |