Bioengineering contributions in vascular biology at the cellular and molecular level

Insulin permeability across an in vitro dynamic model of endothelium

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.

Delivery and expression of fluid shear stress-inducible promoters to the vessel wall: applications for cardiovascular gene therapy

In atherosclerosis, endothelial cells at sites of stenosis experience elevated levels of shear stress. We have constructed a series of shear stress-inducible transcription units (SITUs) expressing the luciferase reporter gene and determined their activation by fluid shear stress in transfected endothelial cells. Chimeric promoters were constructed that comprised basal transcription factor-binding sites coupled to a shear stress response element (SSRE). We have used consensus binding sites for transcription factors NF-kappaB, Ap1, Sp1, Oct1, and Egr-1/Sp1 in either the presence or absence of the previously defined "GAGACC" SSRE. The response of the promoters to shear stress was determined after transfection into human umbilical vein endothelial cells (HUVECs). After transient transfection into HUVECs, fluid shear stress activated the promoters by between two- and eightfold. The most responsive SITUs comprised an overlapping Sp1/Egr-1-binding site linked to a TATA box with (SP5) or without (SP7) the GAGACC SSRE. Instillation of SP5 DNA in vivo into the left carotid artery of rabbit and subsequent generation of a stenosis using a mechanical wire occluder caused a 10-fold upregulation of luciferase reporter gene expression at the site of vessel occlusion. These vectors show promise for therapeutic gene expression at sites of occlusive vascular disease.