The hawthorn special extract WS® 1442 protects against endothelial barrier dysfunction – elucidation of the underlying molecular mechanisms

Due to its profound cardiac effects, the hawthorn (Crataegus spp.) extract WS® 1442 (Dr. Willmar Schwabe GmbH & Co. KG, Karlsruhe, Germany) is an approved drug against heart failure stage NYHA II. Heart failure is accompanied by inflammatory processes leading to endothelial hyperpermeability and edema formation. However, data about an effect of Crataegus on endothelial barrier dysfunction and the underlying molecular mechanisms are lacking. In vivo, WS® 1442 abrogated the histamine-induced extravasation of FITC-dextran from venules of the mouse cremaster muscle. In cultured human endothelial cells, Crataegus inhibited thrombin-induced macromolecular permeability. By applying biochemical and microscopic techniques, we revealed that WS® 1442 abrogates the detrimental effects of thrombin on crucial subcellular regulator systems of endothelial barrier stability: adhesion junctions, the F-actin cytoskeleton, and the contractile apparatus. Mechanistically, we found that Crataegus inhibits the thrombin-induced rise of intracellular calcium, which is accompanied by an inactivation of PKC, and reduces RhoA activation. Moreover, Crataegus activated barrier-protecting mechanisms: it increased endothelial cAMP levels, which consequently activated Rap1 and PKA. However, PKA was not crucially involved in barrier protection. Rac1 and cortactin were activated by WS® 1442 leading to enhanced cortical F-actin bundles. By using Epac1-targeting siRNA, we found that the Crataegus-induced Epac/Rap1 activity is important for the activation of cortactin. Taken together, our study provides evidence that Crataegus effectively inhibits endothelial hyperpermeability in vitro and in vivo. Mechanistically, we elucidated a dual role of action of WS® 1442, since it inhibited the barrier-stabilizing Ca2+/PKC/RhoA pathway and activated the barrier-protecting cAMP/Rap1/Rac1 signaling network.