Investigating biomechanical determinants of endothelial permeability in a hollow fibre bioreactor

The effect of haemodynamic stresses on endothelial permeability to macromolecules is important to normal physiology and in the pathogenesis of atherosclerosis. I developed and applied novel methods to evaluate effects on such transport of acute or chronic exposure to flow along and across cultured endothelium. Porcine aortic endothelial cells were isolated and cultured at passage 1-3 within the porous capillaries of a FiberCell bioreactor. At confluence they were exposed to acute (4 h) or chronic (3-10 day) steady or pulsatile luminal flow (mean shear 3.75 dyne/cm2), with or without transendothelial flow (4 x 10-7 cm/s). Permeability to rhodamine-labelled albumin was assessed by fluorimetry. Confluence of monolayers was confirmed by confocal and scanning electron microscopy and by demonstrating established effects of vasoactive agents on permeability: 10 U/ml thrombin increased permeability, as did 500 μM Nω-nitro-Larginine methyl ester, compared to controls. Permeability was increased by acute pulsatile shear and decreased by chronic pulsatile shear compared to static controls. A decrease in PECAM-1 expression under chronic pulsatile flow was demonstrated by flow cytometry. Steady flow gave higher permeability than pulsatile flow. The introduction of transendothelial flow increased apparent permeability more than could be explained by the addition of the convective transport itself. Preliminary studies suggested that albumin transport may partially be an active process and demonstrated the potential for engineered fibre walls that would allow effects of cyclic strain to be investigated. In conclusion, the hollow fibre bioreactor allowed endothelial permeability to be measured with or without exposure to luminal flow and transendothelial flow over 30 days, permitting the investigation of effects of mechanical stresses. Effects of shear stress varied with duration, pulsatility and direction relative to the endothelial surface.Open Acces