Heparin-hepatocyte growth factor complex with low plasma clearance and retained hepatocyte proliferating activity

Because hepatocyte growth factor is known to have affinity for heparin, we studied the binding isotherm and found that hepatocyte growth factor has a high-affinity binding site for 35S-heparin with an equilibrium dissociation constant of approximately 0.6 nmol/L. We then analyzed the pharmacokinetic behavior of the heparin-hepatocyte growth factor complex in rats. The area under the plasma concentration-time profiles of trichloroacetic acid-precipitable radioactivities from 0 to 30 min after the intravenous administration of the heparin-125I-hepatocyte growth factor complex was approximately three times that after the administration of 125I-hepatocyte growth factor only. Because we previously demonstrated that the liver is the major clearance organ for hepatocyte growth factor, the hepatic uptake of 125I-hepatocyte growth factor and the heparin-125I-hepatocyte growth factor complex was compared. The liver-to-plasma concentration ratio after the intravenous administration of the complex was half that after the administration of 125I-hepatocyte growth factor only. Furthermore, the steady state hepatic extraction ratio of 125I-hepatocyte growth factor in perfused rat liver decreased depending on the heparin concentration. In addition, the biological activity of the complex was examined by assessing the 125I-deoxyuridine incorporation in cultured rat hepatocytes. Although the half-effective concentration of hepatocyte growth factor increased slightly--namely, two to three times in the presence of heparin compared with that in its absence--the maximal activity was not changed. We conclude that the heparin-hepatocyte growth factor complex, which retains biological activity, exhibits much lower clearances for hepatic uptake and plasma disappearance than hepatocyte growth factor itself.(ABSTRACT TRUNCATED AT 250 WORDS)