Dabigatran abrogates brain endothelial cell permeability in response to thrombin

Atrial fibrillation (AF) increases the risk and severity of thromboembolic stroke. Generally, antithrombotic agents increase the hemorrhagic risk of thromboembolic stroke. However, significant reductions in thromboembolism and intracerebral hemorrhage have been shown with the antithrombin dabigatran compared with warfarin. As thrombin has been implicated in microvessel injury during cerebral ischemia, we hypothesized that dabigatran decreases the risk of intracerebral hemorrhage by direct inhibition of the thrombin-mediated increase in cerebral endothelial cell permeability. Primary murine brain endothelial cells (mBECs) were exposed to murine thrombin before measuring permeability to 4-kDa fluorescein isothiocyanate-dextran. Thrombin increased mBEC permeability in a concentration-dependent manner, without significant endothelial cell death. Pretreatment of mBECs with dabigatran completely abrogated the effect of thrombin on permeability. Neither the expressions of the endothelial cell β1-integrins nor the tight junction protein claudin-5 were affected by thrombin exposure. Oxygen-glucose deprivation (OGD) also increased permeability; this effect was abrogated by treatment with dabigatran, as was the additive effect of thrombin and OGD on permeability. Taken together, these results indicate that dabigatran could contribute to a lower risk of intracerebral hemorrhage during embolism-associated ischemia from AF by protection of the microvessel permeability barrier from local thrombin challenge.     

心房颤动口服药物治疗的新选择

近年来,尽管导管消融和外科手术在心房颤动(房颤)的治疗中取得了令人瞩目的进展,但并未广泛应用,药物治疗依然处于首要地位。由于传统抗凝药和抗心律失常药的自身局限性,该领域新型药物的开发成为研究热点,而近年来多种新型口服药物的开发研制和临床试验的成功,为房颤的药物治疗带来新的希望。本文对此加以综述。     

Laboratory Measurement of the Anticoagulant Activity of the Non–Vitamin K Oral Anticoagulants

Background

Non–vitamin K oral anticoagulants (NOACs) do not require routine laboratory monitoring. However, laboratory measurement may be desirable in special situations and populations.

Objectives

This study’s objective was to systematically review and summarize current evidence regarding laboratory measurement of the anticoagulant activity of dabigatran, rivaroxaban, and apixaban.

Methods

We searched PubMed and Web of Science for studies that reported a relationship between drug levels of dabigatran, rivaroxaban, and apixaban and coagulation assay results. Study quality was evaluated using QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2).

Results

We identified 17 eligible studies for dabigatran, 15 for rivaroxaban, and 4 for apixaban. For dabigatran, a normal thrombin time excludes clinically relevant drug concentrations. The activated partial thromboplastin time (APTT) and prothrombin time (PT) are less sensitive and may be normal at trough drug levels. The dilute thrombin time (R² = 0.92 to 0.99) and ecarin-based assays (R² = 0.92 to 1.00) show excellent linearity across on-therapy drug concentrations and may be used for drug quantification. For rivaroxaban and apixaban, anti-Xa activity is linear (R² = 0.89 to 1.00) over a wide range of drug levels and may be used for drug quantification. Undetectable anti-Xa activity likely excludes clinically relevant drug concentrations. The PT is less sensitive (especially for apixaban); a normal PT may not exclude clinically relevant levels. The APTT demonstrates insufficient sensitivity and linearity for quantification.

Conclusions

Dabigatran, rivaroxaban, and apixaban exhibit variable effects on coagulation assays. Understanding these effects facilitates interpretation of test results in NOAC-treated patients. More information on the relationship between drug levels and clinical outcomes is needed.     

Inhibition of staphylothrombin by dabigatran reduces Staphylococcus aureus virulence

Summary. Background: Staphylocoagulase and von Willebrand binding protein (VWbp) bind to prothrombin to form the staphylothrombin complex that converts fibrinogen into fibrin. Objectives: To study the role of staphylothrombin and its inhibition by dabigatran on Staphylococcus aureus virulence. Methods: We studied the effect of staphylothrombin inhibition on bacterial attachment to polystyrene surfaces, leukocyte activation and bactericidal activity for S. aureus ATCC 25923, S. aureus Newman, and staphylocoagulase‐ and VWbp‐negative S. aureus Newman mutants in the presence or absence of prothrombin and fibrinogen. We measured the abscess size after subcutaneous (s.c.) injection of S. aureus ATCC 25923 and S. aureus Newman, as well as an S. aureus Newman mutant strain lacking staphylocoagulase and VWbp, in mice treated with either dabigatran or placebo. Results: Staphylothrombin‐mediated fibrin increased the association of S. aureus to polystyrene surfaces and reduced the bactericidal activity of leukocytes. The absence or inhibition of staphylothrombin decreased the bacterial association, enhanced leukocyte activation and reduced bacterial survival in vitro. Abscess size was smaller in mice treated with dabigatran or infected with a coagulase‐negative mutant. Conclusion: Inhibition or the absence of staphylothrombin reduced S. aureus virulence in in vitro and in vivo models.     

达比加群对凝血酶诱导的人气道平滑肌细胞收缩和增殖的影响

目的 探讨这比加群对凝血酶诱导的人气道平滑肌(HASM)细胞收缩和增殖的影响.方法 将原代培养的HASM细胞用于实验.用免疫荧光的方法观察细胞收缩的形态学变化;用Western blot法分析α-actin蛋白相对表达量;用cck8法检测平滑肌细胞增殖能力.结果 达比加群能显著抑制凝血酶诱导的HASM细胞骨架重组和收缩蛋白α-actin的表达(P＜0.05).对血管紧张素Ⅱ(AngⅡ)、转化生长因子-β1、血小板源性生长因子、乙酰甲胆碱、凝血酶的促增殖能力进行比较,凝血酶显著强于AngⅡ,仅次于10％胎牛血清(P＜0.05).达比加群呈浓度依赖性和时间依赖性地抑制了凝血酶诱导的HASM细胞增殖(P＜0.05).结论 达比加群能够显著抑制凝血酶诱导的HASM细胞收缩和增殖.