AJP - Endocrinology and Metabolism, Vol 272, Issue 6 E1089-E1098, Copyright © 1997 by American Physiological Society
Fate of insulin analogs in intact and nephrectomized rats determined by their receptor binding constants
V. Kruse, I. Jensen, L. Permin and A. Heding
Novo Nordisk, Bagsvaerd, Denmark.
After intravenous injection of 125I-labeled human insulin and analogs in
normal and nephrectomized rats, we examined their kinetic fate by
Q-Sepharose separation into intact ligand, "fragments" (genuine fragments
and protein-bound radioactivity), and iodide. Receptor binding association
and dissociation constants (kass and kdis, respectively) of the analogs
were estimated dynamically in vitro by BIAcore. The very fast disappearance
of intact ligand from serum was found to be determined by 1) both kass and
kdis of receptor-bearing tissue, thus substantiating our primary
hypothesis; 2) elimination by kidneys, and 3) fast extravascularization.
The rate of appearance of degradation products from receptor-mediated
intracellular processing seems determined by kdis. With the possible
exception of a truncated analog, ligand appears protected against
degradation while the intracellular receptor-ligand complex remains intact.
Non-receptor-mediated processing in kidneys is slow, compared with the
receptor-mediated uptake and degradation of ligands with rate constants
comparable to those of insulin. We observed binding of insulin and analogs
putatively to serum proteins; binding capacity and affinity appeared
insignificant for insulin but considerable for some analogs.
