Sinusoidal obstruction syndrome, also known as veno-occlusive disease (SOS/VOD), is a potentially life-threatening complication that can develop after hematopoietic cell transplantation (HCT). A new definition for diagnosis, and a severity grading system for SOS/VOD in adult patients, was reported a few years ago on behalf of the European Society for Blood and Marrow Transplantation (EBMT). The aim of this work is to update knowledge regarding diagnosis and severity assessment of SOS/VOD in adult patients, and also its pathophysiology and treatment. In particular, we now propose to refine the previous classification and distinguish probable, clinical and proven SOS/VOD at diagnosis. We also provide an accurate definition of multiorgan dysfunction (MOD) for SOS/VOD severity grading based on Sequential Organ Failure Assessment (SOFA) score.

Background: COVID-19 presents a spectrum of signs and symptoms in pregnant women that might resemble preeclampsia. Differentiation between severe COVID-19 and preeclampsia is difficult in some cases. Objective: To study biomarkers of endothelial damage, coagulation, innate immune response and angiogenesis in preeclampsia and COVID-19 in pregnancy in addition to in vitro alterations in endothelial cells exposed to sera from pregnant women with preeclampsia and COVID-19. Methods: Plasma and sera samples were obtained from pregnant women with COVID-19 infection classified into mild (n=10) or severe (n=9) in addition to normotensive pregnancies as controls (n=10) and patients with preeclampsia (n=13). A panel of plasmatic biomarkers was assessed including vascular cell adhesion molecule-1 (VCAM-1), soluble TNF-receptor I (sTNFRI), heparan sulfate (HS), von Willebrand factor (VWF) antigen, activity and multimeric pattern, α2-antiplasmin (α2AP), C5b9, neutrophil extracellular traps (NETS), placental growth factor (PlGF), fms-like tyrosine kinase-1 (sFlt-1) and angiopoietin 2 (Ang2). Additionally, microvascular endothelial cells were exposed patient's serum, and changes in the cell expression of intercellular adhesion molecule 1 (ICAM-1) on cell membrane and VWF release to the extracellular matrix were evaluated through immunofluorescence. Changes in inflammation cell signaling pathways were also assessed by of P38MAPK phosphorylation. Statistical analysis included univariate and multivariate methods. Results: Biomarker profiles in mild COVID-19 were similar to controls. Both preeclampsia and severe COVID-19 showed significant alterations in the majority of circulating biomarkers with distinctive profiles. While severe COVID-19 exhibited higher concentrations of VCAM-1, sTNFR-I, HS, VWF antigen and NETS with a significant reduction of PlGF as compared to controls; preeclampsia presented a marked increase in VCAM-1, sTNFR-I (significantly increased compared to controls and to severe COVID-19) with a striking reduction in VWF antigen, VWF activity and α2AP. As expected, reduced PlGF, increased sFlt-1 and Ang2 and a very high sFlt-1/PlGF ratio were also observed in preeclampsia. In addition, a significant increase in C5b9 and NETS was also detected in preeclampsia compared to controls. The principal component analysis demonstrated a clear separation between preeclampsia and the rest of groups (first and second components explained 42.2% and 13.5% of the variance), mainly differentiated by variables related to VWF, sTNFRI, HS and sFlt-1. VWF multimeric analysis revealed the absence of VWF high-molecular-weight multimers in preeclampsia (similar profile to von Willebrand disease type 2A) whereas in healthy pregnancies and COVID-19 patients, VWF multimeric pattern was normal. Sera from both preeclampsia and severe COVID-19 patients induced an overexpression of ICAM-1 and VWF in endothelial cells in culture compared to controls. However, the effect of preeclampsia was less pronounced than the one triggered by severe COVID-19. Immunoblots of lysates from endothelial cells exposed to mild and severe COVID-19, and preeclampsia sera showed an increase in p38MAPK phosphorylation. Severe COVID-19 and preeclampsia were statistically different from controls, suggesting that both severe COVID-19 and preeclampsia sera can activate inflammatory signaling pathways. Conclusion: While similar in vitro endothelial dysfunction, preeclampsia and severe COVID-19 exhibit distinctive profiles of circulating biomarkers related to endothelial damage, coagulopathy and angiogenic imbalance that could aid in the differential diagnosis of these entities.

Hepatic veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS), a potentially life-threatening complication of hematopoietic cell transplantation (HCT), results from prolonged sinusoidal endothelial cell activation and profound endothelial cell damage, with sequelae. Defibrotide, the only drug approved in the United States and Europe for treating VOD/SOS post-HCT, has European Commission orphan drug designation for preventing graft-versus-host disease (GvHD), associated with endothelial dysfunction. This endothelial cell protector and stabilizing agent restores thrombo-fibrinolytic balance and preserves endothelial homeostasis through antithrombotic, fibrinolytic, anti-inflammatory, anti-oxidative, and anti-adhesive activity. Defibrotide also preserves endothelial cell structure by inhibiting heparanase activity. Evidence suggests that downregulating p38 mitogen-activated protein kinase (MAPK) and histone deacetylases (HDACs) is key to defibrotide's endothelial protective effects; phosphatidylinositol 3-kinase/Akt (PI3K/AKT) potentially links defibrotide interaction with the endothelial cell membrane and downstream effects. Despite defibrotide's being most extensively studied in VOD/SOS, emerging preclinical and clinical data support defibrotide for treating or preventing other conditions driven by endothelial cell activation, dysfunction, and/or damage, such as GvHD, transplant-associated thrombotic microangiopathy, or chimeric antigen receptor T-cell (CAR-T) therapy-associated neurotoxicity, underpinned by cytokine release syndrome and endotheliitis. Further preclinical and clinical studies will explore defibrotide's potential utility in a broader range of disorders resulting from endothelial cell activation and dysfunction.

Patients with COVID-19 present a wide spectrum of disease severity, from asymptomatic cases in the majority to serious disease leading to critical care and even death. Clinically, four different scenarios occur within the typical disease timeline: first, an incubation and asymptomatic period; second, a stage with mild symptoms due mainly to the virus itself; third, in up to 20% of the patients, a stage with severe symptoms where a hyperinflammatory response with a cytokine storm driven by host immunity induces acute respiratory distress syndrome; and finally, a post-acute sequelae (PASC) phase, which present symptoms that can range from mild or annoying to actually quite incapacitating. Although the most common manifestation is acute respiratory failure of the lungs, other organs are also frequently involved. The clinical manifestations of the COVID-19 infection support a key role for endothelial dysfunction in the pathobiology of this condition. The virus enters into the organism via its interaction with angiotensin-converting enzyme 2-receptor that is present prominently in the alveoli, but also in endothelial cells, which can be directly infected by the virus. Cytokine release syndrome can also drive endothelial damage independently. Consequently, a distinctive feature of SARS-CoV-2 infection is vascular harm, with severe endothelial injury, widespread thrombosis, microangiopathy, and neo-angiogenesis in response to endothelial damage. Therefore, endothelial dysfunction seems to be the pathophysiological substrate for severe COVID-19 complications. Biomarkers of endothelial injury could constitute strong indicators of disease progression and severity. In addition, the endothelium could represent a very attractive target to both prevent and treat these complications. To establish an adequate therapy, the underlying pathophysiology and corresponding clinical stage should be clearly identified. In this review, the clinical features of COVID-19, the central role of the endothelium in COVID-19 and in other pathologies, and the potential of specific therapies aimed at protecting the endothelium in COVID-19 patients are addressed.

Background: The vascular endothelium plays a key role in sepsis pathophysiology and the associated organ dysfunction. Methods: We evaluated endothelial function in an experimental in-vitro model of sepsis, using endothelial cells grown in the presence of serum from patients with septic syndromes (sepsis, severe sepsis, and septic shock), non-infectious systemic inflammatory response syndrome (NI-SIRS) and healthy volunteers. Experiments were performed in the absence and presence of defibrotide (DF) (100µg/mL) to evaluate its potential protective effect. Results: After exposure to patients' sera, there was a progressive endothelial cell activation in correlation with sepsis severity, with a proinflammatory and prothrombotic phenotype, exhibiting significantly increased expression of adhesion receptors at the surface (ICAM-1, p< 0.05 and VCAM-1, p< 0.05); higher production and release to the extracellular matrix (ECM) of Von Willebrand factor (p< 0.001); augmented thrombogenicity of the ECM towards platelets (p< 0.001); and increased phosphorylation of intracellular p38MAPK. DF prevented these changes in all groups. Conclusions: Markers of endothelial damage increased progressively in association with the severity of septic syndromes. The endothelium is therefore an important therapeutic target to prevent complications of sepsis. DF shows promising potential to modulate the endothelial damage associated with sepsis and may constitute a pharmacological tool to decrease its sequelae including multiorgan failure.

Carfilzomib has been associated with the development of thrombotic microangiopathy (TMA) in relapsed/refractory multiple myeloma patients, a severe disease with no currently available aetiological treatment. We evaluated the potential role of terminal complement pathway in four patients with carfilzomib-induced TMA. Membrane attack complex (C5b-9) deposition on endothelial cells in culture exposed to plasma from patients during the acute phase of the disease suggests complement overactivation as a mechanism of potential endothelial damage in three out of four patients. If confirmed in larger cohorts, C5b-9 evaluation will allow early identification of patients who could benefit from complement blockade and treatment monitoring.

Multiple myeloma induction treatment includes proteasome inhibitors (PI) and immunomodulatory agents at present. The incidence of engraftment syndrome, a transplant complication potentially related to endothelium, has increased in the last years. Our aim was to investigate whether bortezomib (Velcade, V), thalidomide (T), and dexamethasone (D) affect the endothelium, and explore defibrotide (DF) as protective agent. Endothelial cells (ECs) in culture were exposed to the compounds separately or in combination, without (VTD) and with DF (VTD + DF). Changes in markers of: (i) inflammation (ICAM-1 expression and leukocyte adhesion), (ii) VWF production, (iii) cell permeability (VE-cadherin expression and cell monolayer integrity), and (iv) oxidative stress (ROS production and eNOS expression) were measured. ICAM-1 and VWF expression increased significantly in VTD but were similar to controls in VTD + DF. Separately, bortezomib was the main deleterious agent whereas dexamethasone showed no harmful effect. Leukocyte adhesion showed similar trends. VE-cadherin expression was lower in VTD and normalized in VTD + DF. EC permeability increased only with bortezomib. No changes were observed in oxidative stress markers. Our results demonstrate that bortezomib damages the endothelium, and DF prevents this effect. A better knowledge of the induction drugs impact will allow the design of measures to protect the endothelium.

The aim of the present article is to review the role of endothelial damage and dysfunction in the vaso-occlusive episodes associated with sickle cell disease (SCD). This inherited hematological disorder leads to irreversible damage of multiple organs through a wide variety of mechanisms, such as sickling of red cells, oxidative state due to ischemic-reperfusion episodes, inflammation, hypercoagulation state, and platelet activation, among others. In SCD, the endothelium arises as the key entity where most of these processes, which eventually lead to increased morbidly and mortality, interact. This review begins with the already accepted idea that organ-specific vasculopathy precedes clinical manifestation, and briefly explains one of the main triggers of vaso-occlusive episodes, the complex interplay between blood cells and the dysfunctional endothelium. Endothelial protective strategies emerge as a potential tool for the prevention of organ-specific disease in SCD. Actually, this knowledge is currently used for the development of potential pharmacologic interventions to improve the lives of SCD patients.

Endothelial dysfunction is an earlier contributor to the development of atherosclerosis in chronic kidney disease (CKD), in which the role of epigenetic triggers cannot be ruled out. Endothelial protective strategies, such as defibrotide (DF), may be useful in this scenario. We evaluated changes induced by CKD on endothelial cell proteome and explored the effect of DF and the mechanisms involved. Human umbilical cord vein endothelial cells were exposed to sera from healthy donors (n = 20) and patients with end-stage renal disease on haemodialysis (n = 20). Differential protein expression was investigated by using a proteomic approach, Western blot and immunofluorescence. HDAC1 and HDAC2 overexpression was detected. Increased HDAC1 expression occurred at both cytoplasm and nucleus. These effects were dose-dependently inhibited by DF. Both the HDACs inhibitor trichostatin A and DF prevented the up-regulation of the endothelial dysfunction markers induced by the uraemic milieu: intercellular adhesion molecule-1, surface Toll-like receptor-4, von Willebrand Factor and reactive oxygen species. Moreover, DF down-regulated HDACs expression through the PI3/AKT signalling pathway. HDACs appear as key modulators of the CKD-induced endothelial dysfunction as specific blockade by trichostatin A or by DF prevents endothelial dysfunction responses to the CKD insult. Moreover, DF exerts its endothelial protective effect by inhibiting HDAC up-regulation likely through PI3K/AKT.

Atypical hemolytic uremic syndrome is a form of thrombotic microangiopathy caused by dysregulation of the alternative complement pathway. There is evidence showing complement activation in other thrombotic microangiopathies. The aim of this study was to evaluate complement activation in different thrombotic microangiopathies and to monitor treatment response.