Plasma obtained during human endotoxemia increases endothelial permeability in vitro

Objective

In order to gain insight into the pathogenesis of increased vascular permeability during sepsis, we studied the effect of plasma obtained during human experimental endotoxemia on the permeability of cultured endothelial monolayers in vitro.

Methods

Eight healthy subjects received an i.v. dose of 2 ng/kg Escherichia coli O:113 lipopolysaccharide (LPS). The concentration of various plasma mediators that supposedly induce vascular permeability was measured over time. Plasmas that were obtained prior to and 2 and 4 hours after the administration of LPS were added to human umbilical venular endothelial cells (HUVEC) that were cultured on semipermeable membranes.

The permeability of the endothelial monolayers to FITC-labeled bovine serum albumin was determined and expressed as the relative concentration of FITC-BSA when compared with that measured across empty Transwell-COL membranes (i.e. without endothelial monolayers). The permeability levels were correlated with the plasma concentrations of various mediators.

Results

Experimental endotoxemia resulted in elevated levels of TNF-α, IL-1β, IL-6, IL-8, IL-10 and VEGF, and a moderate increase of IL-12 and IFN-γ (all P < 0.01). Incubation of HUVEC with plasma obtained 2 and 4 hours after the administration of LPS increased the relative permeability from a baseline level of (median [range]) 17% [14–31%] to 23% ([12–39%], P = NS) and 28% ([11–40%], P < 0.05), respectively. Plasma levels of VEGF and IL-10, but not TNF-α, or any of the other mediators, significantly correlated with the increase in endothelial permeability (r = 0.47, P = 0.038 and r = 0.43, P = 0.038, respectively).

Conclusion

The data presented here demonstrate that plasmas obtained from experimental human endotoxemia increase endothelial permeability in vitro. This response was independent of the incubation time (45 min-6 hours) of endotoxic plasma on the endothelial monolayers. The increase in endothelial permeability was moderately correlated with VEGF and IL-10 levels in plasma. Our observations may facilitate future experiments that try to elucidate the pathophysiology of increased vascular permeability during systemic inflammation.