Lipopolysaccharide-induced endothelial barrier breakdown is cyclic adenosine monophosphate dependent in vivo and in vitro*

Objectives: To determine whether cyclic adenosine monophosphate (cAMP) is critically involved in lipopolysaccharide (LPS)-induced breakdown of endothelial barrier functions in vivo and in vitro. Design: Experimental laboratory research. Setting: Research laboratory. Subjects: Wistar rats and cultured human microvascular endothelial cells. Intervention: Permeability measurements in single postcapillary venules in vivo and permeability measurements and cell biology techniques in vitro. Measurements and Results: We demonstrate that within 120 minutes LPS increased endothelial permeability in rat mesenteric postcapillary venules in vivo and caused a barrier breakdown in human dermal microvascular endothelial cells in vitro. This was associated with the formation of large intercellular gaps and fragmentation of vascular endothelial cadherin immunostaining. Furthermore, claudin 5 immunostaining at cell borders was drastically reduced after LPS treatment. Interestingly, activity of the small GTPase Rho A, which has previously been suggested to mediate the LPS-induced endothelial barrier breakdown, was not increased after 2 hours. However, activity of Rac 1, which is known to be important for maintenance of endothelial barrier functions, was significantly reduced to 64 ± 8% after 2 hours. All LPS-induced changes of endothelial cells were blocked by a forskolin-mediated or rolipram-mediated increase of cAMP. Consistently, enzyme-linked immunosorbent assay-based measurements demonstrated that LPS significantly decreased intracellular cAMP. Conclusion: In summary, our data demonstrate that LPS disrupts endothelial barrier properties by decreasing intracellular cAMP. This mechanism may involve inactivation of Rac 1 rather than activation of Rho A.