The endothelium and early immune activation: New perspective and interactions

Inflammatory Microenvironment of Skin Wounds

Wound healing is a dynamic and highly regulated process that can be separated into three overlapping and interdependent phases: inflammation, proliferation, and remodelling. This review focuses on the inflammation stage, as it is the key stage of wound healing and plays a vital role in the local immune response and determines the progression of wound healing. Inflammatory cells, the main effector cells of the inflammatory response, have been widely studied, but little attention has been paid to the immunomodulatory effects of wound healing in non-inflammatory cells and the extracellular matrix. In this review, we attempt to deepen our understanding of the wound-healing microenvironment in the inflammatory stage by focusing on the interactions between cells and the extracellular matrix, as well as their role in regulating the immune response during the inflammatory stage. We hope our findings will provide new ideas for promoting tissue regeneration through immune regulation.

Luteolin suppresses inflammation through inhibiting cAMP-phosphodiesterases activity and expression of adhesion molecules in microvascular endothelial cells

Luteolin, an anti-inflammatory ingredient found in the Chinese herb Folium perillae, can inhibit not only the cyclic adenosine monophosphate (cAMP)-phosphodiesterases (PDEs) activity of neutrophils, but also the expression of lymphocyte function-associated antigen-1 in neutrophils, both of which result in a decrease in the adhesion between neutrophils and microvascular endothelial cells. However, the effect of luteolin on the cAMP-PDEs activity and expression of adhesion molecules in endothelial cells are not clear. In the present study, primary rat pulmonary microvascular endothelial cells and a lipopolysaccharide-induced rat acute pneumonia model were used to explore the role of luteolin on cAMP-PDEs activity, expression of adhesion molecules, and leukocyte infiltration. We demonstrate that rat pulmonary microvascular endothelial cells expressed high levels of cAMP-PDEs, specifically PDE4, and further luteolin exhibited dose-dependent inhibition on the activity of cAMP-PDEs or PDE4 in endothelial cells. Luteolin also had a significant inhibitory effect on the expression of vascular cell adhesion molecule (VCAM)-1, but not intracellular cell adhesion molecule (ICAM)-1 in microvascular endothelial cells. Further, we show that luteolin decreased the levels of soluble ICAM-1 (sICAM-1), but not soluble E-selectin in the serum of rats subjected to acute pneumonia. We also show that luteolin treatment decreased the wet/dry weight ratio of lung tissue and reduced the total number of serum leukocytes in a dose-dependent manner in a rat acute pneumonia model. In conclusion, these results demonstrate that luteolin suppresses inflammation, at least in part, through inhibiting both cAMP-PDEs or PDE4 activity and the expression of VCAM-1 (in vitro) and sICAM-1 (in vivo) in endothelial cells.

Puerarin prevents vascular endothelial injury through suppression of NF-κB activation in LPS-challenged human umbilical vein endothelial cells

OBJECTIVE

In the present study, we aimed to explore the effects of puerarin on vascular endothelial cell injury induced by lipopolysaccharide (LPS) and its underlying mechanisms.

METHODS

The cell viability and morphological changes were assessed using the cell counting kit-8 (CCK-8) assay and 4´,6-diamidino-2-phenylindole (DAPI) staining, respectively. The levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), monocyte/macrophage chemotactic protein-1 (MCP-1), IL-8, intercellular cell adhesion molecule-1 (ICAM-1), thrombomodulin (TM) and plasminogen activator inhibitor-1 (PAI-1) in cell culture supernatant were determined by the enzyme-linked immunosorbent assay (ELISA). The neutrophils adhesion to endothelial cells were examined by myeloperoxidase activity assay. The nuclear translocation of nuclear factor-κB p65 (NF-κB p65) was assessed by immunofluorescence analysis.

RESULTS

Compared with the control group, LPS challenge significantly injured human umbilical vein endothelial cells (HUVECs) and increased the levels of TNF-α, IL-1β, MCP-1, IL-8, ICAM-1, TM and PAI-1 in the cell culture supernatants. The neutrophils adhesion to endothelial cells were significantly increased in LPS-challenged HUVECs. Moreover, LPS challenge increased the nuclear translocation of NF-κB p65. However, puerarin pre-treatment attenuated the vascular endothelial injury and reduced the levels of TNF-α, IL-1β, MCP-1, IL-8, ICAM-1, TM and PAI-1 in cell supernatants of LPS-challenged HUVECs. In addition, the neutrophils adhesion to HUVECs induced by LPS were also decreased by puerarin pre-treatment. Furthermore, puerarin pre-treatment reduced the nuclear translocation of NF-κB p65 elicited by LPS.

CONCLUSIONS

Puerarin prevented LPS-induced vascular endothelial injury, the mechanism of which might be related to the suppression of NF-κB activation and subsequently altered levels of inflammatory factors and coagulation-related factors.

Reperfusion Syndrome: Cellular Mechanisms of Microvascular Dysfunction and Potential Therapeutic Strategies

Reperfusion injury is the paradoxical and complex phenomenon of exacerbation of cellular dysfunction and increase in cell death after the restoration of blood flow to previously ischemic tissues. It involves biochemical and cellular changes causing oxidant production and complement activation, which culminates in an inflammatory response, mediated by neutrophil and platelet cell interactions with the endothelium and among the cells themselves. The mounted inflammatory response has both local and systemic manifestations. Despite improvements in imaging, interventional techniques, and pharmacological agents, morbidity from reperfusion remains high. Extensive research has furthered the understanding of the various pathophysiological mechanisms involved and the development of potential therapeutic strategies. Preconditioning has emerged as a powerful method of ameliorating ischemia reperfusion injury to the myocardium and in transplant surgery. More recently, postconditioning has been shown to provide a therapeutic counter to vasoocclusive emergencies. More research and well-designed trials are needed to bridge the gap between experimental evidence and clinical implementation.

Recent advances in understanding the roles of vascular endothelial cells in allergic inflammation

Allergic disorders commonly involve both chronic tissue inflammation and remodeling caused by immunological reactions to various antigens on tissue surfaces. Due to their anatomical location, vascular endothelial cells are the final responders to interact with various exogenous factors that come into contact with the epithelial surface, such as pathogen-associated molecular patterns (PAMPs) and antigens. Recent studies have shed light on the important roles of endothelial cells in the development and exacerbation of allergic disorders. For instance, endothelial cells have the greatest potential to produce several key molecules that are deeply involved in allergic inflammation, such as periostin and thymus and activation-regulated chemokine (TARC/CCL17). Additionally, endothelial cells were recently shown to be important functional targets for IL-33--an essential regulator of allergic inflammation. Notably, almost all endothelial cell responses and functions involved in allergic inflammation are not suppressed by corticosteroids. These corticosteroid-refractory endothelial cell responses and functions include TNF-α-associated angiogenesis, leukocyte adhesion, IL-33-mediated responses and periostin and TARC production. Therefore, these unique responses and functions of endothelial cells may be critically involved in the pathogenesis of various allergic disorders, especially their refractory processes. Here, we review recent studies, including ours, which have elucidated previously unknown pathophysiological roles of vascular endothelial cells in allergic inflammation and discuss the possibility of endothelium-targeted therapy for allergic disorders.

Endothelium and Regulatory Inflammatory Mechanisms During Organ Rejection

Endothelial integrity is mandatory for physiologic organ function; however, endothelium dysfunction can be caused by systemic inflammation, occurring during sepsis or organ rejection after transplantation. This article will address our current understanding of endothelial involvement in organ transplantation and rejection. Overall, more detailed studies focusing on the endothelial modulation after organ transplantation would be necessary to investigate the role of endothelium activation during organ rejection.

Impact of donor cause of death on transplant outcomes: UNOS registry analysis

Donor cause of death (DCOD) has been described to influence allograft survival. Whether this effect is independent of other donor characteristics and whether it is similar across different solid organ allografts is not known. The aim of our study was to determine the impact of DCOD on organ utilization and on transplantation outcomes-graft rejection, function, and survival. The registry data were provided by the United Network for Organ Sharing/Organ Procurement and Transplantation Network. Stroke, head trauma, and anoxia were the cause of brain death in 97% of the more than 86,000 donors whose data were recorded between 1989 and 2008. In univariate analysis, stroke DCOD was associated with worse graft survival across all organs. After adjustment in a multivariable analysis, modest differences persisted in survival of heart, kidney, and liver allografts. DCOD also appeared to affect the incidence of allograft rejection. Anoxia DCOD was associated with significantly less rejection relative to donor death caused by head trauma and stroke. In summary, this multi-institutional study confirms that DCOD is a modest predictor of survival and rejection of solid organ allografts of different types.

Immune regulation by microvascular endothelial cells: directing innate and adaptive immunity, coagulation, and inflammation

An effective immune response depends not only on the proper activation, regulation, and function of immune cells, but also on their distribution and retention in diverse tissue microenvironments where they encounter a number of stimuli and other cell types. These activities are mediated by endothelial cells, which form specialized microcirculatory networks used by immune cells under both physiological and pathological circumstances. Endothelial cells represent a highly heterogeneous population of cells with the ability to interact with and modulate the function of immune cells. This review is focused on the role of microvascular endothelial cells in innate and adaptive immunity, inflammation, coagulation, angiogenesis, and the therapeutic implications of targeting endothelial cells in selected autoimmune and chronic inflammatory disorders.