Dabigatran reduces endothelial permeability through inhibition of thrombin-induced cytoskeleton reorganization

Distinct pleiotropic effects of direct oral anticoagulants on cultured endothelial cells: a comprehensive review

Direct Oral Anticoagulants (DOACs) have simplified the treatment of thromboembolic disease. In addition to their established anticoagulant effects, there are indications from clinical and preclinical studies that DOACs exhibit also non-anticoagulant actions, such as anti-inflammatory and anti-oxidant actions, advocating overall cardiovascular protection. In the present study, we provide a comprehensive overview of the existing knowledge on the pleiotropic effects of DOACs on endothelial cells (ECs) in vitro and their underlying mechanisms, while also identifying potential differences among DOACs. DOACs exhibit pleiotropic actions on ECs, such as anti-inflammatory, anti-atherosclerotic, and anti-fibrotic effects, as well as preservation of endothelial integrity. These effects appear to be mediated through inhibition of the proteinase-activated receptor signaling pathway. Furthermore, we discuss the potential differences among the four drugs in this class. Further research is needed to fully understand the pleiotropic effects of DOACs on ECs, their underlying mechanisms, as well as the heterogeneity between various DOACs. Such studies can pave the way for identifying biomarkers that can help personalize pharmacotherapy with this valuable class of drugs.

Pterostilbene alleviated cerebral ischemia/reperfusion-induced blood-brain barrier dysfunction via inhibiting early endothelial cytoskeleton reorganization and late basement membrane degradation

Pterostilbene, an important analogue of the star molecule resveratrol and a novel compound naturally occurring in blueberries and grapes, exerts a significant neuroprotective effect on cerebral ischemia/reperfusion (I/R), but its mechanism is still unclear. This study aimed to follow the molecular mechanisms behind the potential protective effect of pterostilbene against I/R induced injury. For fulfilment of our aim, we investigated the protective effects of pterostilbene on I/R injury caused by middle cerebral artery occlusion (MCAO) in vivo and oxygen-glucose deprivation (OGD) in vitro. Machine learning models and molecular docking were used for target exploration and validated by western blotting. Pterostilbene significantly reduced the cerebral infarction volume, improved neurological deficits, increased cerebral microcirculation and improved blood-brain barrier (BBB) leakage. Machine learning models confirmed that the stroke target MMP-9 bound to pterostilbene, and molecular docking demonstrated the strong binding activity. We further found that pterostilbene could depolymerize stress fibers and maintain the cytoskeleton by effectively increasing the expression of the non-phosphorylated actin depolymerizing factor (ADF) in the early stage of I/R. In the late stage of I/R, pterostilbene could activate the Wnt pathway and inhibit the expression of MMP-9 to decrease the degradation of the extracellular basement membrane (BM) and increase the expression of junction proteins. In this study, we explored the protective mechanisms of pterostilbene in terms of both endothelial cytoskeleton and extracellular matrix. The early and late protective effects jointly maintain BBB stability and attenuate I/R injury, showing its potential to be a promising drug candidate for the treatment of ischemic stroke.

Amplification of protease-activated receptors signaling in sporadic cerebral cavernous malformation endothelial cells

In the central nervous system, thrombin-mediated activation of protease-activated receptors (PARs) results in neuroinflammation and increased vascular permeability. These events have been linked to cancer and neurodegeneration. Endothelial cells (ECs) isolated from sporadic cerebral cavernous malformation (CCM) specimens showed dysregulation of genes involved in "thrombin-mediated PAR-1 activation" signaling. CCM is a vascular disease involving brain capillaries. In CCM, ECs show defective cell junctions. Oxidative stress and neuroinflammation play a key role in disease onset and progression. In order to confirm the possible role of thrombin pathway in sporadic CCM pathogenesis, we evaluated PARs expression in CCM-ECs. We found that sporadic CCM-ECs overexpress PAR1, PAR3 and PAR4, together with other coagulation factor encoding genes. Moreover, we investigated about expression of the three familial CCM genes (KRIT1, CCM2 and PDCD10) in human cerebral microvascular ECs, following thrombin exposure, as well as protein level. Thrombin exposure affects EC viability and results in dysregulation of CCM gene expression and, then, in decreased protein level. Our results confirm amplification of PAR pathway in CCM suggesting, for the first time, the possible role of PAR1-mediated thrombin signaling in sporadic CCM. Thrombin-mediated PARs over activation results in increased blood-brain barrier permeability due to loss of cell junction integrity and, in this context, also the three familial CCM genes may be involved.

Purinergic signaling: A gatekeeper of blood-brain barrier permeation

This review outlined evidence that purinergic signaling is involved in the modulation of blood-brain barrier (BBB) permeability. The functional and structural integrity of the BBB is critical for maintaining the homeostasis of the brain microenvironment. BBB integrity is maintained primarily by endothelial cells and basement membrane but also be regulated by pericytes, neurons, astrocytes, microglia and oligodendrocytes. In this review, we summarized the purinergic receptors and nucleotidases expressed on BBB cells and focused on the regulation of BBB permeability by purinergic signaling. The permeability of BBB is regulated by a series of purinergic receptors classified as P2Y₁, P2Y₄, P2Y₁₂, P2X4, P2X7, A₁, A_2A, A_2B, and A₃, which serve as targets for endogenous ATP, ADP, or adenosine. P2Y₁ and P2Y₄ antagonists could attenuate BBB damage. In contrast, P2Y₁₂-mediated chemotaxis of microglial cell processes is necessary for rapid closure of the BBB after BBB breakdown. Antagonists of P2X4 and P2X7 inhibit the activation of these receptors, reduce the release of interleukin-1 beta (IL-1β), and promote the function of BBB closure. In addition, the CD39/CD73 nucleotidase axis participates in extracellular adenosine metabolism and promotes BBB permeability through A₁ and A_2A on BBB cells. Furthermore, A_2B and A₃ receptor agonists protect BBB integrity. Thus, the regulation of the BBB by purinergic signaling is complex and affects the opening and closing of the BBB through different pathways. Appropriate selective agonists/antagonists of purinergic receptors and corresponding enzyme inhibitors could modulate the permeability of the BBB, effectively delivering therapeutic drugs/cells to the central nervous system (CNS) or limiting the entry of inflammatory immune cells into the brain and re-establishing CNS homeostasis.

Dabigatran: its protective effect against endothelial cell damage by oxysterol

Recent data showed that dabigatran can reduce not only procoagulatory effects but also block proinflammatory stimuli by inhibiting the expression of cytokines and chemokines and reducing thrombin-induced endothelial permeability. The aim of our study was to assess the effect of dabigatran on the integrity and inflammatory properties of endothelial cells stimulated by 25-hydroxycholesterol (25-OHC, oxysterol). HUVECs (Human Umbilical Vein Endothelial Cells) were stimulated with 25-hydroxycholesterol 10 µg/ml, dabigatran 100 ng/ml or 500 ng/ml and 25-hydroxycholesterol + dabigatran (100 ng/ml, 500 ng/ml). HUVEC integrity and permeability was measured in the RTCA-DP xCELLigence system and by the paracellular flux system. The mRNA expression of ICAM-1, VEGF, IL-33, MCP-1 and TNF-α was analyzed by Real-time PCR. Cell apoptosis and viability was measured by flow cytometry. VEGF protein concentration was assessed in supernatants by ELISA. VE-cadherin expression in endothelial cells was evaluated by confocal microscopy. Pre-stimulation of HUVECs with 25-OHC decreased endothelial cell integrity (p < 0.001) and increased the expression of IL-33, ICAM-1, MCP-1, VEGF, TNF-α mRNA (p < 0.01) compared to unstimulated controls. Following stimulation of HUVECs with dabigatran 100 ng/ml or 500 ng/ml restored HUVEC integrity interrupted by 25-OHC (p < 0.001). In HUVECs pre-stimulated with oxysterol, dabigatran stimulation decreased mRNA expression of the proinflammatory cytokines IL-33 and TNF-α, chemokines MCP-1 ICAM-1 and VEGF (p < 0.01). Dabigatran 500 mg/ml+ 25-OHC increased the endothelial expression of VE-cadherin as compared to 25-OHC (p < 0.01). Our findings suggest that dabigatran stabilizes the endothelial barrier and inhibits the inflammation caused by oxysterol.

Ca2+ homeostasis in brain microvascular endothelial cells

Blood brain barrier (BBB) is formed by the brain microvascular endothelial cells (BMVECs) lining the wall of brain capillaries. Its integrity is regulated by multiple mechanisms, including up/downregulation of tight junction proteins or adhesion molecules, altered Ca²⁺ homeostasis, remodeling of cytoskeleton, that are confined at the level of BMVECs. Beside the contribution of BMVECs to BBB permeability changes, other cells, such as pericytes, astrocytes, microglia, leukocytes or neurons, etc. are also exerting direct or indirect modulatory effects on BBB. Alterations in BBB integrity play a key role in multiple brain pathologies, including neurological (e.g. epilepsy) and neurodegenerative disorders (e.g. Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis etc.). In this review, the principal Ca²⁺ signaling pathways in brain microvascular endothelial cells are discussed and their contribution to BBB integrity is emphasized. Improving the knowledge of Ca²⁺ homeostasis alterations in BMVECa is fundamental to identify new possible drug targets that diminish/prevent BBB permeabilization in neurological and neurodegenerative disorders.

Effects of Thrombin on the Neurovascular Unit in Cerebral Ischemia

Cerebral ischemia is a cerebrovascular disease with high morbidity and mortality that poses a significant burden on society and the economy. About 60% of cerebral ischemia is caused by thrombus, and the formation of thrombus proceeds from insoluble fibrin, following its transformation from liquid fibrinogen. In thrombus-induced ischemia, increased permeability of the blood-brain barrier (BBB), followed by the extravasation of blood components into the brain results in an altered brain microenvironment. Changes in the brain microenvironment affect brain function and the neurovascular unit (NVU), the working unit of the brain. Recent studies have reported that coagulation factors interact with the NVU and its components, but the specific function of this interaction is highly speculative and warrants further investigations. In this article, we reviewed the role of coagulation factors in cerebral ischemia and the role of coagulation factors in thrombosis. Additionally, the influence of thrombin on the NVU is introduced, as well as in the function of NVU, which may help to explore part of brain injury mechanism during ischemia. Lastly, we propose some novel therapeutic approaches on ischemic stroke by reducing the risk of coagulation.

The Role of Thrombin in Brain Injury After Hemorrhagic and Ischemic Stroke

Thrombin is increased in the brain after hemorrhagic and ischemic stroke primarily due to the prothrombin entry from blood either with a hemorrhage or following blood-brain barrier disruption. Increasing evidence indicates that thrombin and its receptors (protease-activated receptors (PARs)) play a major role in brain pathology following ischemic and hemorrhagic stroke (including intracerebral, intraventricular, and subarachnoid hemorrhage). Thrombin and PARs affect brain injury via multiple mechanisms that can be detrimental or protective. The cleavage of prothrombin into thrombin is the key step of hemostasis and thrombosis which takes place in every stroke and subsequent brain injury. The extravascular effects and direct cellular interactions of thrombin are mediated by PARs (PAR-1, PAR-3, and PAR-4) and their downstream signaling in multiple brain cell types. Such effects include inducing blood-brain-barrier disruption, brain edema, neuroinflammation, and neuronal death, although low thrombin concentrations can promote cell survival. Also, thrombin directly links the coagulation system to the immune system by activating interleukin-1α. Such effects of thrombin can result in both short-term brain injury and long-term functional deficits, making extravascular thrombin an understudied therapeutic target for stroke. This review examines the role of thrombin and PARs in brain injury following hemorrhagic and ischemic stroke and the potential treatment strategies which are complicated by their role in both hemostasis and brain.

Thrombin inhibition by dabigatran attenuates endothelial dysfunction in diabetic mice

Diabetic patients have coagulation abnormalities, in which thrombin plays a key role. Whereas accumulating evidence suggests that it also contributes to the development of vascular dysfunction through the activation of protease-activated receptors (PARs). Here we investigated whether the blockade of thrombin attenuates endothelial dysfunction in diabetic mice. Induction of diabetes by streptozotocin (STZ) increased the expression of PAR1, PAR3, and PAR4 in the aorta. STZ-induced diabetic mice showed impairment of endothelial function, while the administration of dabigatran etexilate, a direct thrombin inhibitor, significantly attenuated endothelial dysfunction in diabetic mice with no alteration of metabolic parameters including blood glucose level. Dabigatran did not affect endothelium-independent vasodilation. Dabigatran decreased the expression of inflammatory molecules (e.g., MCP-1 and ICAM-1) in the aorta of diabetic mice. Thrombin increased the expression of these inflammatory molecules and the phosphorylation of IκBα, and decreased the phosphorylation of eNOS^Ser1177 in human umbilical endothelial cells (HUVEC). Thrombin significantly impaired the endothelium-dependent vascular response of aortic rings obtained from wild-type mice. Inhibition of NF-κB attenuated thrombin-induced inflammatory molecule expression in HUVEC and ameliorated thrombin-induced endothelial dysfunction in aortic rings. Dabigatran attenuated the development of diabetes-induced endothelial dysfunction. Thrombin signaling may serve as a potential therapeutic target in diabetic condition.

The Research Progress of Direct Thrombin Inhibitors

Blood coagulation is the process of changing the blood from the flowing state to the gel state. It is an important part of the hemostatic function. Coagulation is a process by which a series of coagulation factors are sequentially activated, and finally thrombin is formed to form fibrin clot. Direct thrombin inhibitors are important anticoagulant drug. These drugs can selectively bind to the active site of thrombin, inhibit thrombin activity, have strong action and high specificity, and have important significance in the clinical treatment of thrombus diseases. Some of them come from natural products of animals or plants, and many of them have been applied in the clinic. The other part is derived from the design, synthesis and activity studies of small molecule inhibitors. This review discusses the progress of direct thrombin inhibitors in recent years.

Effects of Oral Anticoagulant Therapy on Gene Expression in Crosstalk between Osteogenic Progenitor Cells and Endothelial Cells

Direct oral anti-coagulants (DOACs) are employed in clinical practice for the prevention and treatment of recurrent venous thromboembolism and for the prevention of stroke in non-valvular atrial fibrillation. DOACs directly and reversibly inhibit activated factor X or thrombin and can interfere with other pathophysiological processes such as inflammation, lipid metabolism, and bone turnover. We aimed to evaluate the possible effects of DOACs on osteogenesis and angiogenesis. We treated 34 patients affected by cardiovascular disorders with DOACs; biochemical and molecular analyses were performed before and after three months of treatment. Circulating progenitors (CPs; CD34⁻, CD45⁻, CD14⁻, CD73⁺, CD105⁺), which share typical bone marrow stem cell (MSCs) features, were harvested from peripheral blood of the study subjects to monitor the expression of osteogenesis-related genes RUNX2 and SPARC. Human umbilical vein endothelial cells (HUVECs) were used to probe angiogenesis-related VEGF, CD31, and CD105 gene expression. We performed co-culture experiments using a commercial human mesenchymal stem cells line (hMSCs) obtained from bone marrow and HUVECs. Clinical parameters related to bone metabolism, coagulation, renal and liver function, and the lipid profile were evaluated. Values of the C-terminal telopeptide type I collagen (CTX) increased after the treatment. We found a significant increase in osteogenesis marker gene expression in CPs after three months of anticoagulant therapy. An increase in the RUNX2 expression determinant alone was detected instead in hMSCs co-cultured with HUVECs in the presence of treated patients’ sera. The VEGF, CD31, and CD105 marker genes appeared to be significantly upregulated in HUVECs co-cultured with hMSCs in the presence of treated patients’ sera. Under these conditions, new vessel formation increased as well. Our results highlight an unexpected influence of DOAC therapy on osteogenic commitment and vascular endothelial function promotion.