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Insulin permeability across an in vitro dynamic model of endothelium
Francesca Salvetti1, Paolo Cecchetti, Damir Janigro
1Departimento di Psichiatria, Neurobiologia, Farmacologia e Biotechnologie, Facoltà di Farmacia, Università degli Studi di Pisa, Italy.
Purpose:
Endothelium insulin permeability was investigated using in vitro, dynamic culture of endothelial cells.
Methods:
Endothelial cells were cultured in a hollow fiber apparatus and continuously exposed to a flow. Transendothelial electrical resistance and permeability to [14C]sucrose and [14C]inulin were used to monitor the integrity of the endothelial monolayer.
Results:
Under these experimental conditions, measurements of insulin permeability, investigated at increasing hormone concentrations, suggested that the predominant transendothelial insulin fluxes were attributable to bidirectional convective transport rather than to a saturable transport mechanism, in agreement with in vivo experiment results published earlier. Analytical determinations of insulin catabolism demonstrated a low percent of insulin degradation by the endothelium, leading to production of insulin metabolites qualitatively identical to those produced by human monocytes.
Conclusions:
The findings of this paper indicated that (a) insulin crosses the endothelial monolayer by paracellular "leak" and endothelial insulin receptors have a minor (if any) role in insulin transport; (b) degradation of the hormone by BAEC is minimal; (c) the in vitro, dynamic culture of endothelial cells presented here should represent a valuable transport model system to study permeability mechanisms of insulin and many other drugs.