Affinity of binding of radiolabeled (125I) heparin and low molecular weight heparin fraction CY 222 to endothelium in culture

Abstract

Binding of radiolabeled (125I) heparin and its low molecular weight fraction CY 222 (Choay) to human and porcine cultured endothelium was investigated. The binding was measured over a wide range of heparin or CY 222 concentration in culture medium, from less than 20-time up to more than 30-times of the therapeutic heparin level. A relatively small fraction (less than 1%) of tested products was bound to endothelium. The process of binding was temperature-independent. A comparable number of endothelial binding sites (approx. 10(12)/cm2) for both 125I-heparin and 125I-CY 222 was calculated. About 40% totally bound 125I-heparin and 30% of 125I-CY 222 was found in extracellular matrix of cultured endothelium. The endothelium exhibited a 2.4-times lower affinity for 125I-CY 222 (Kd = 5.59 +/- 1.77 microM) than that for 125I-heparin (Kd = 2.35 +/- 0.78 microM). A similar affinity of human (venous) and porcine (aortic) endothelium for 125I-heparin was demonstrated. Cultured endothelium exhibited the same affinity for unlabeled heparin as for 125I-heparin. The endothelium depleted of sialic acid residues bound 1.5-times more of 125I-CY 222 than the control endothelium in culture.