Increased serum midkine levels during hemodialysis using heparin in chronic renal failure

The heparin-binding growth factor midkine (MK) has been implicated in neuron growth, angiogenesis, and inflammation. In this study, to elucidate the involvement of MK in the development of pathologies associated with uremia, we examined the serum MK levels in patients receiving hemodialysis (HD) by a highly sensitive enzyme-linked immunoassay. Although no significant difference was found between control serum and serum before dialysis in HD patients, serum MK levels increased significantly at the early stage of HD sessions using heparin and gradually decreased after dialysis. In normal controls, intravenous administration of heparin induced a similar sudden increase of MK, but the subsequent decrease was also rapid. In an in vitro study, MK was released in time- and heparin-dose dependent manner from cultured vessels, but not from peripheral leukocytes. These results indicate that, in HD patients, MK is released mainly from endothelial cells immediately after administration of heparin during HD and disappears gradually from blood due to renal impairment. This phenomenon might affect some complications associated with HD.