Background Increasing evidence suggests that FXI is an attractive target for antithrombotic therapy because it reduces thrombosis without increasing bleeding risk. Patients with decreased levels of FXI are at reduced risk of cardiovascular diseases and thromboembolic events. We have already revealed that depletion of FXI inhibits the vascular coagulation-inflammatory circuit in angiotensin II-induced arterial hypertension. However, the effect of FXI depletion on cardiac inflammation and vascular function in ischemia/reperfusion (I/R) injury is unknown. Purpose Using FXI-depleted mice to investigate the role of FXI in inflammation response post cardiac I/R injury. Methods 8–12 weeks old C57BL/6J male mice were injected intraperitoneally with FXI antisense oligonucleotide (FXI ASO) or scrambled controls for a period of 2 weeks. Then we temporarily ligated the left anterior descending (LAD) for 45 minutes to induce myocardial ischemia, followed by the reperfusion for 72 hours (ischemia/reperfusion injury, IRI). Myocardial inflammation and vascular function were analyzed by flow cytometry, real-time PCR, vascular relaxation studies from isolated aortic segment in organ chamber and chemiluminescence photon counting of oxidative burst in whole blood. Results FXI ASO treatment reduced hepatic FXI mRNA levels and prolonged activated partial thromboplastin time. Compared to scrambled ASO injected mice, oxidative burst from whole blood and endothelial dysfunction were decreased in FXI ASO injected mice with IRI. Compared to control groups, depletion of FXI attenuated cardiac infiltration of CD45+CD11b+ cells, especially LyG-LyChigh monocytes and LyG+ neutrophils at day 3 in I/R injury. Furthermore, the expression levels of adhesion molecules and expression of pro-inflammatory cytokines, such as Vcam-1, CCL2, IL-6 and IL-1b, in ischemic myocardium were significantly decreased in the FXI depleted mice of I/R injury. Conclusion Our results suggest that Inhibition of FXI leads to reduction of vascular dysfunction and ROS production in I/R injury, as well as attenuation of the inflammatory response and the influx of inflammatory cells in ischemic myocardium. This indicates that FXI could be a potential target for further treatment in cardiac IRI. Funding Acknowledgement Type of funding sources: Public grant(s) – EU funding. Main funding source(s): TICARDIO project has received funding from the European Union's Horizon 2020 research and Innovation programme under the Marie Skłodowska-Curie grant agreement No 813409.

Background Arterial hypertension is one of the most important modifiable risk factors for all-cause morbidity and mortality worldwide. Angiotensin II (Ang II) plays a pathogenic role in the development of hypertension, vascular dysfunction, inflammation and tissue damage. In the context of hypertension, heme-oxygenase 1 (HO-1) gene expression is upregulated as an antioxidant defense system in response to AngII through its action on heme catabolism, which generates carbon monoxide (CO), ferritin and biliverdin, which is reduced to bilirubin by biliverdin reductase A (BLVRA). Previous studies have shown the important role of HO-1 in the maturation and migration of immune cells. Myeloid HO-1 modulates macrophage polarization and protects against ischemia-reperfusion damage. However, the role of myeloid cell specific HO-1 in the detrimental effects of AngII induced vascular dysfunction has not yet been explored. Objectives To investigate the potential vascular protection of myeloid cell specific overexpression of HO-1 in AngII-induced arterial hypertension. Methods Hypertension was induced in 8–13 weeks old male mice with selective over-expression of HO-1 (HO-1indLysMcre) in myelomonocytic cells versus LysMCre/wt by AngII infusion (1mg/kg/d). Blood pressure was recorded by tail-cuff. Bilirubin levels were quantified in plasma by High Performance Liquid Chromatography (HPLC). The quantification of adherent and rolling leukocytes in carotid arteries was detected by intravital video microscopy (IVM). Endogenuos Thrombin potential (ETP) was measured in platelet rich plasma (PRP) and platelets poor plasma (PPP) by Calibrated Automated Thrombogram (CAT) assay. Endothelium-dependent vasodilation was assessed in isolated aortic rings by concentration-relaxation curves in response to acetylcholine (ACh). Results AngII-infused HO-1indLysMcre had decreased blood pressure values and improved endothelial function as compared to LysMcre controls. IVM revealed reduced leukocyte rolling and adhesion to the vascular endothelium in AngII infused HO-1indLysMcre mice compared to controls, paralleled by reduced expression of NOX-2 mediated oxidative stress and vascular inflammation in AngII-induced arterial hypertension by decreasing VCAM-1, CCR2 and MCP-1 expression. mRNA analysis revealed an increased expression of BLVRA in liver, spleen, heart and aortic tissues in response to AngII, which was higher in HO-1indLysMcre mice than in controls. By CAT assay we registered a decrease ETP in PPP and PRP in HO-1ind mice infused with AngII compatible with less abundance of inflammatory platelets, potentially regulated by BLVRA activity. This was supported by increased in bilirubin levels in response to AngII, which was higher in HO-1indLysMcre mice than in controls. Conclusion Myeloid cell specific overexpression of HO-1 confers anti-inflammatory protection to the vasculature in AngII induced hypertension. This effect is, at least in part, mediated by BLVRA. Funding Acknowledgement Type of funding sources: None.