Tc-99m galactosyl-neoglycoalbumin: in vitro characterization of receptor-mediated binding.
Hepatic binding protein (HBP) is a membrane receptor that binds and transports plasma glycoproteins from hepatic blood to hepatocellular lysosomes. We have characterized the in vitro binding of Tc-99m galactosyl-neoglycoalbumin (Tc-NGA), a synthetic HBP ligand, to liver membrane. Structural modifications of NGA resulted in the alteration of the equilibrium constant, KA, and the forward-binding rate constant, kb. Binding was second-order; the relative amount of membrane-bound NGA depended on the initial concentrations of ligand and membrane. Membrane displacement studies, using carrier ligands in contrast to previously bound Tc-NGA or I-NGA, correlated with the binding characteristics of a native HBP ligand, asialo-orosomucoid. We used computer simulation to study the detectability of the changes in HBP concentration at different values of kb. The simulations indicated that radiopharmacokinetic sensitivity to alterations in [HBP] should be possible using a neoglycoalbumin preparation with a carbohydrate density within the range of 15 to 25 galactose units per albumin molecule.
D000418:Albumins / Q000378:metabolism*; D000818:Animals; D037263:Asialoglycoprotein Receptor; D002352:Carrier Proteins / Q000378:metabolism*; D003201:Computers; D008954:Models, Biological; D015609:Organotechnetium Compounds; D011485:Protein Binding; D011817:Rabbits; D013667:Technetium / Q000378:metabolism*
D000418:Albumins; D037263:Asialoglycoprotein Receptor; D002352:Carrier Proteins; D015609:Organotechnetium Compounds; C027122:hepatic sialoglycoprotein receptor; C036586:technetium Tc 99m neogalactoalbumin; D013667:Technetium