Fibrinolytic activity of endothelial cells from different venous beds

Viral coagulation: pushing the envelope

Many virus types affect the blood clotting system with correlations to pathology that range widely from thrombosis to hemorrhage linking to inflammation. Here we overview the intricate crosstalk induced by infection between proteins on the virus encoded by either the host or virus genomes, coagulation proteins, platelets, leukocytes, and endothelial cells. For blood-borne viruses with an outer covering acquired from the host cell, the envelope, a key player may be the cell-derived trigger of coagulation on the virus surface, tissue factor (TF). TF is a multifunctional transmembrane cofactor that accelerates factor (F)VIIa-dependent activation of FX to FXa, leading to clot formation. However, the nascent TF/FVIIa/FXa complex also facilitates G protein-coupled modulation of cells via protease-activated receptor 2. As a viral envelope constituent, TF can bypass the physiological modes of regulation, thereby initiating the activation of neighboring platelets, leukocytes, and endothelial cells. A thromboinflammatory environment is predicted due to feedback amplification in response to cellular release of cytokines, procoagulant proteins, neutrophil extracellular traps, and stimulus-induced accessibility of adhesive receptors, resulting in cellular aggregates. The pathobiological effects of thromboinflammation ultimately contribute to innate and adaptive immunity for viral clearance. In contrast, the preceding stages of viral infection may be enhanced via the TF-protease axis.

Endothelial cell dysfunction, coagulation, and angiogenesis in coronavirus disease 2019 (COVID-19)

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been led to a pandemic emergency. So far, different pathological pathways for SARS-CoV-2 infection have been introduced in which the excess release of pro-inflammatory cytokines (such as interleukin 1 β [IL-1β], IL-6, and tumor necrosis factor α [TNFα]) has earned most of the attentions. However, recent studies have identified new pathways with at least the same level of importance as cytokine storm in which endothelial cell (EC) dysfunction is one of them. In COVID-19, two main pathologic phenomena have been seen as a result of EC dysfunction: hyper-coagulation state and pathologic angiogenesis. The EC dysfunction-induced hypercoagulation state seems to be caused by alteration in the levels of different factors such as plasminogen activator inhibitor 1 (PAI-1), von Willebrand factor (vWF) antigen, soluble thrombomodulin, and tissue factor pathway inhibitor (TFPI). As data have shown, these thromboembolic events are associated with severity of disease severity or even death in COVID-19 patients. Other than thromboembolic events, pathologic angiogenesis is among the recent findings. Furthermore, over-expression/higher levels of different proangiogenic factors such as vascular endothelial growth factor (VEGF), hypoxia-inducible factor 1 α (HIF-1α), IL-6, TNF receptor super family 1A and 12, and angiotensin-converting enzyme 2 (ACE2) have been found in the lung biopsies/sera of both survived and non-survived COVID-19 patients. Also, there are some hypotheses regarding the role of nitric oxide in EC dysfunction and acute respiratory distress syndrome (ARDS) in SARS-CoV-2 infection. It has been demonstrated that different pathways involved in inflammation are generally common with EC dysfunction and angiogenesis. Altogether, considering the common possible upstream pathways in cytokine storm, pathologic angiogenesis, and EC dysfunction, it seems that targeting these molecules (such as nuclear factor κB) could be more effective in the management of patients with COVID-19.

Drospirenone Effects on the Plasminogen Activator System in Immortalized Human Endometrial Endothelial Cells

Drospirenone (DRSP) is a fourth-generation progestin that interacts with the progesterone receptor (PR) and androgen receptor (AR) in addition to uniquely interacting to the mineralocorticoid receptor (MR). The known effects of DRSP via the mineralocorticoid receptor (MR) are limited. This study seeks to determine if DRSP alters plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (tPA) in human immortalized endometrial endothelial cells (HEEC) and if such changes in the plasminogen activator system (PAS) are mediated through the MR or AR. The in vitro cell culture experiments utilizing an immortalized human endometrial endothelial cell line evaluated two concentrations of DRSP on PAI-1 and tPA levels in the culture media using specific enzyme-linked immunoassays (ELISA). Experiments adding DRSP with an androgen receptor blocker, flutamide, or a mineralocorticoid receptor agonist, aldosterone, were performed to elucidate which receptor(s) mediated the PAS effects. DRSP 10 μM significantly decreased both HEEC levels of PAI-1 and tPA to 0.75 ± 0.04 and 0.82 ± 0.05 of control, respectively. These direct effects were blunted by flutamide, an AR antagonist. PAI-1 and tPA were not changed by the MR agonist, aldosterone. DRSP significantly decreased both PAI-1 and tPA in the HEECs via the androgen receptor.

Pulmonary Artery Thrombosis: A Diagnosis That Strives for Its Independence

According to a widespread theory, thrombotic masses are not formed in the pulmonary artery (PA) but result from migration of blood clots from the venous system. This concept has prevailed in clinical practice for more than a century. However, a new technologic era has brought forth more diagnostic possibilities, and it has been shown that thrombotic masses in the PA could, in many cases, be found without any obvious source of emboli. Chronic obstructive pulmonary disease, asthma, sickle cell anemia, emergency and elective surgery, viral pneumonia, and other conditions could be complicated by PA thrombosis development without concomitant deep vein thrombosis (DVT). Different pathologies have different causes for local PA thrombotic process. As evidenced by experimental results and clinical observations, endothelial and platelet activation are the crucial mechanisms of this process. Endothelial dysfunction can impair antithrombotic function of the arterial wall through downregulation of endothelial nitric oxide synthase (eNOS) or via stimulation of adhesion receptor expression. Hypoxia, proinflammatory cytokines, or genetic mutations may underlie the procoagulant phenotype of the PA endothelium. Both endotheliocytes and platelets could be activated by protease mediated receptor (PAR)- and receptors for advanced glycation end (RAGE)-dependent mechanisms. Hypoxia, in particular induced by high altitudes, could play a role in thrombotic complications as a trigger of platelet activity. In this review, we discuss potential mechanisms of PA thrombosis in situ.

An Unusually Rare but Interesting Co-Occurrence of Idiopathic Pulmonary Artery and Pulmonary Vein Thrombosis: A Case Report

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Concomitant in situ pulmonary artery and vein thrombosis is a unique event.

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This situation can lead to chronic severe and life-threatening respiratory failure.

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Surgical removal of clots can be lifesaving in severe cases.

Thrombin stimulates increased plasminogen activator inhibitor-1 release from liver compared to lung endothelium

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) is a major regulator of the fibrinolytic system, covalently binding to tissue plasminogen activator and blocking its activity. Fibrinolysis shutdown is evident in the majority of severely injured patients in the first 24 h and is thought to be due to PAI-1. The source of this PAI-1 is thought to be predominantly endothelial cells, but there are known organ-specific differences, with higher levels thought to be in the liver. Thrombin generation is also elevated in injured patients and is a potent stimulus for PAI-1 release in human umbilical endothelial cells. We hypothesize that thrombin induces liver endothelial cells to release increased amounts of PAI-1, versus pulmonary endothelium, consisting of both stored PAI-1 and a larger contribution from de novo PAI-1 synthesis.

METHODS

Human liver sinusoidal endothelial cells (LSECs) and human microvascular lung endothelial cells (HMVECs) were stimulated in vitro ± thrombin (1 and 5 IU/mL) for 15-240 min, the supernatants were collected, and PAI-1 was measured by enzyme-linked immunosorbent assays. To elucidate the PAI-1 contribution from storage versus de novo synthesis, cycloheximide (10 μg/mL) was added before thrombin in separate experiments.

RESULTS

While both LSECs and HMVECs rapidly stimulated PAI-1 release, LSECs released more PAI-1 than HMVECs in response to high-dose thrombin, whereas low-dose thrombin did not provoke immediate release. LSECs continued to release PAI-1 over the ensuing 240 min, whereas HMVECs did not. Cycloheximide did not inhibit early PAI-1 release from LSECs but did at the later time points (30-240 min).

CONCLUSIONS

Thrombin elicits increased amounts of PAI-1 release from liver endothelium compared with lung, with a small presynthesized stored contribution and a later, larger increase in PAI-1 release via de novo synthesis. This study suggests that the liver may be an important therapeutic target for inhibition of the hypercoagulable surgical patient and the associated complications that result.

Protective, repairing and fibrinolytic effects of rivaroxaban on vascular endothelium

AIMS

Rivaroxaban, a direct inhibitor of activated factor X (FXa), is the only new oral anticoagulant approved for secondary prevention after acute coronary syndrome. Our objective was to identify the possible molecular mechanisms of rivaroxaban that contribute to endothelial function.

METHODS

Cell viability and growth of human umbilical vein endothelial cells (HUVEC) were registered. Gene expression studies comparing the effects of rivaroxaban and FXa were conducted by a selective RNA array and confirmed by protein quantification. Wound-healing experiments on HUVEC, platelet adhesion, enzymatic activity, and cell-based assays for fibrin formation were performed with rivaroxaban.

RESULTS

Rivaroxaban (50 nM) only altered (>2 fold change) the expression of matrix metallopeptidase 2 and urokinase plasminogen activator (u-PA), but counteracted the FXa (9 nM)-induced upregulation of several pro-inflammatory genes (P < 0.05) and FXa-enhanced platelet adhesion over HUVEC. Rivaroxaban increased u-PA protein expression in HUVEC supernatants and enhanced u-PA activity (up to 4 IU ng^-1 of u-PA). Rivaroxaban (1 nM-1 μM) showed a significant and dose-dependent positive effect on HUVEC growth that was inhibited by BC-11-hydroxibromide, an inhibitor of u-PA. Healing properties after a wound on HUVEC cultures, and fibrinolytic properties were also shown by rivaroxaban. Both effects were reversed by BC-11-hydroxibromide.

CONCLUSIONS

Rivaroxaban enhanced viability, growth and migration of HUVEC, mainly by u-PA activation and upregulation, which also participate in the rivaroxaban-induced fibrinolytic activity at endothelial level. Rivaroxaban also protected from the pro-inflammatory effects of FXa on HUVEC. Altogether may improve endothelial functionality and could contribute to the cardiovascular benefits of rivaroxaban.