Rosmarinic acid downregulates the oxLDL-induced interaction between monocytes and endothelial cells, in addition to monocyte diapedesis, under high glucose conditions

Endothelial dysfunction during diabetes has been previously reported to be at least in part attributed to increased oxidized low-density lipoprotein (oxLDL) levels mediated by high glucose (HG) levels. Endothelial inflammation increases the adhesiveness of monocytes to the endothelium in addition to increasing vascular permeability, promoting diabetic atherogenesis. In a previous study, it was reported that oxLDL treatment induced nucleotide-binding domain and leucine-rich repeat containing family, pyrin domain-containing 3 inflammasome activation in endothelial cells (ECs) under HG conditions, in a manner that could be effectively reversed by rosmarinic acid. However, it remains unclear whether oxLDL-mediated inflammasome activation can regulate the interaction between monocytes and ECs. The effects of oxLDL-mediated inflammasome activation on endothelial permeability under HG conditions, in addition to the effects of rosmarinic acid on these oxLDL-mediated processes, also remain poorly understood. Therefore, the present study aimed to elucidate the mechanisms involved in oxLDL-induced endothelial permeability and monocyte diapedesis under HG conditions, in addition to the potential effects of rosmarinic acid. ECs were treated with oxLDL under HG conditions in the presence or absence of ROS scavengers mitoTEMPO and NAC, p38 inhibitor SB203580, FOXO1 inhibitor AS1842856 or transfected with the TXNIP siRNA, before protein expression levels of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), phosphorylated vascular endothelial-cadherin (VE-cadhedrin), VE-cadherin and zonula occludens-1 (ZO-1) were measured by western blotting. In addition, adhesion assay and Transwell assays were performed. oxLDL was found to significantly increase the expression of ICAM-1 and VCAM-1 in ECs under HG conditions whilst also enhancing the adhesion of monocytes to ECs. This was found to be dependent on the reactive oxygen species (ROS)/p38 MAPK/forkhead box O1 (FOXO1)/thioredoxin interacting protein (TXNIP) signaling pathway. In addition, oxLDL-stimulated ECs under HG conditions exhibited increased phosphorylated VE-cadherin protein levels and decreased ZO-1 protein expression levels compared with those in untreated ECs, suggesting increased endothelial permeability. Furthermore, monocyte transmigration through the endothelial monolayer was significantly increased by oxLDL treatment under HG conditions. These oxLDL-mediated effects under HG conditions were also demonstrated to be dependent on this ROS/p38 MAPK/FOXO1/TXNIP signaling pathway. Subsequently, rosmarinic acid treatment significantly reversed oxLDL-induced overexpression of adhesion molecules and monocyte-EC adhesion, oxLDL-induced endothelial junction hyperpermeability and monocyte transmigration through the endothelial monolayer under HG conditions, in a dose-dependent manner. These results suggest that rosmarinic acid can exert a protective effect against oxLDL-mediated endothelial dysfunction under HG conditions by reducing the interaction between monocytes and ECs in addition to preventing monocyte diapedesis.