Platelets modulate the proteolysis of factor VIII:C protein by plasmin

Factor VIII coagulant protein (VIII:C) functions as a critical cofactor with factor IXa, calcium ions, and phospholipid during the activation of factor X. In the course of this reaction, the activity of VIII:C is first increased and then is destroyed by one or more serine proteases that are part of the coagulation sequence. In this study, we have investigated the influence of platelets on the inactivation of VIII:C by plasmin. Platelets were separated from plasma proteins in the presence of granule release inhibitors and were incubated with plasmin and isolated VIII:C or the complex of purified VIII:C/von Willebrand factor (vWF); VIII:C activity and antigen levels were assessed over time. In the presence of platelets, the isolated VIII:C showed an initial increase in VIII:C activity that was not present when platelets were absent, and the VIII:C/vWF showed an increase in VIII:C activity over that seen when platelets were absent. In addition, platelets stabilized VIII:C activity over a one-hour time course when compared with buffer. The VIII:C antigen did not increase and decreased slowly whether platelets were present or absent. Preincubating the platelets with ristocetin, collagen, or plasmin did not alter the results, and experiments using platelets from a patient with severe von Willebrand's disease also showed a pattern similar to that seen with normal platelets. Experiments using fixed platelets or phospholipid vesicles showed that they did not support the activation reaction or delay the inactivation reaction. These studies demonstrate that platelets modulate the activation and inactivation of VIII:C by plasmin, apparently by a mechanism that is independent of the platelet release reaction.     

QT-interval prolongation in right precordial leads: an additional electrocardiographic hallmark of Brugada syndrome

OBJECTIVES: The aim of this study was to evaluate whether the occurrence of the Brugada Syndrome typical electrocardiogram (ECG) pattern (i.e., right bundle branch block, coved-type ST-segment elevation, and T-wave inversion in the right precordial leads) is characterized by a concomitant lengthening of QT intervals in the right precordial leads. BACKGROUND: It has been suggested that the typical ECG pattern of Brugada syndrome is due to a decreased net inward current during phase 1 of the action potential, which also leads to its prolongation in the right epicardium. METHODS: Thirty-two subjects (19 males) age 37 +/- 15 years with a suspicious baseline ECG, or who were relatives of Brugada syndrome patients, underwent 12-lead ECG before and after the administration of flecainide. RESULTS: The flecainide test was negative in 14 and positive in 18 subjects. After flecainide administration, the positive ECGs were characterized by a greater QT interval corrected for heart rate (QTc) prolongation in the right precordial leads than that in the negative ECGs (78.2 +/- 35.5 ms vs. 22.0 +/- 28.4 ms in V(1) and 107.1 +/- 43.8 ms vs. 26.7 +/- 30.1 ms in V(2); p < 0.01), whereas there was no difference in the QTc prolongation in the left precordial leads (55.2 +/- 25.3 ms vs. 35.1 +/- 28.1 ms in V(5) and 53.1 +/- 32.8 ms vs. 27.3 +/- 22.4 ms in V(6); p = NS). CONCLUSIONS: In accordance with the electrophysiological background, the typical ECG pattern of Brugada syndrome is also characterized by a considerable prolongation of the QT interval in right precordial leads.     

Distal radial artery (snuffbox) access for carotid artery stenting – Technical pearls and procedural set-up

PurposeTo report use of distal radial artery (dRA) access for carotid artery stenting (CAS) and to discuss procedural setup and technical considerations for a successful intervention.MethodsA retrospective review of our prospective neurointerventional database of CAS was conducted between May 2019 and March 2020. All CAS cases via dRA in the anatomical snuffbox were identified. Patient demographics, clinical information, procedural and radiographic data was collected.Results22 CAS procedures in 20 patients via dRA were identified. Patients’ mean age was 69.4 years (range 53–87 years). 3 patients were female. Mean radial artery diameter was 2.1 mm (range 1.6–2.8 mm). dRA access was achieved in all cases. Conversion to femoral access was required in 2 cases (9.1%) due to persistent radial artery vasospasm resulting in patient discomfort despite multiple additional doses of intraarterial vasodilators and added intravenous sedation as well as tortuous vessel anatomy and limited support of the catheters in a type 3 aortic arch for left CAS.ConclusionOur preliminary experience with dRA access for CAS suggests this approach to be feasible and safe for patients. Technical considerations are important and preprocedural planning is necessary for a successful intervention. Catheter systems and devices specifically designed for radial access are needed to enable more interventionalists to safely perform neurointerventional procedures via wrist access.     

Platelet glycoproteins IIb and IIIa as a calcium channel in liposomes

Human platelet membrane glycoproteins IIb and IIIa (GPIIb and IIIa) were incorporated into phospholipid vesicles by the reverse-phase technique to assess the ability of GPIIb and IIIa to function as a Ca2+ channel. Movement of Ca2+ across the lipid bilayer was quantitated by injection of proteoliposomes with encapsulated Fura-2 into Ca2+ buffers and measurement of Fura-2 fluorescence as an indicator of Ca2+ influx. Reciprocally, to assess the function of proteins in an inside-out orientation, Ca2+-loaded vesicles were injected into Ca2+-free buffer and Ca2+ efflux monitored by a calcium electrode. Incorporation of the IIb-IIIa complex produced significant facilitation of Ca2+ movement across the lipid bilayer. No net transmembrane Ca2+ movement was seen with dissociated IIb and IIIa. Movement of Ca2+ was proportional to the transmembrane Ca2+ gradient. Ca2+ movement into the vesicles was inversely proportional to extravesicular NaCl from 25 to 150 mmol/L, analogous to several studies in the intact platelet. Adenosine triphosphate had no effect on Ca2+ movement into or out of the vesicles. Specific inhibition of a Ca2+ shift into the vesicles was seen with M148, a monoclonal antibody to IIb/IIIa, while no inhibition was observed with a panel of other anti-IIb/IIIa monoclonal antibodies. This suggests that a specific site on the complex or orientation of the complex is essential for calcium channel function. These data demonstrate that the GPIIb/IIIa complex can serve as a passive Ca2+ channel across a phospholipid bilayer and has the potential to play a role in Ca2+ flux across the platelet plasma membrane.     

Analysis of granulysin-mediated cytotoxicity in peripheral blood of patients with psoriatic arthritis

The objective of the present study was to investigate possible changes in granulysin (GNLY)-mediated cytotoxicity of peripheral blood lymphocytes in psoriatic arthritis (PsA) patients with respect to different phases of the disease. We prospectively enrolled 25 PsA patients in the active phase, 26 PsA patients in remission and 24 healthy controls. The simultaneous detection of intracellular GNLY and cell surface antigens (CD3 and CD56) was performed with flow cytometry. GNLY apoptotic protein was visualised by immunocytochemistry. Natural killer (NK) cell cytotoxicity was analysed with a cytotoxicity assay against human erythroleukaemia K-562 cells. The percentage of GNLY(+) cells did not differ significantly between PsA patients in the acute phase and those in remission; however, it was always higher than in healthy examinees due to the increased percentage of GNLY(+) cells within T cells, NKT cells, and both, and in the CD56(+dim) and CD56(+bright) NK subsets. The mean fluorescence intensity for GNLY was higher in all lymphocyte subpopulations in the acute phase than in remission and in healthy controls. Accordingly, GNLY-mediated NK cell cytotoxicity against K-562 cells of active phase PsA patients was significantly higher than that in patients in remission or in healthy controls. These findings demonstrated the involvement of GNLY in the worsening of PsA and suggested that GNLY mediated the development of joint lesions.     

《英国非酒精性脂肪性肝炎肝移植指南》导读

非酒精性脂肪性肝炎（non—alcoholicsteatohepatitis,NASH）现已成为肝移植愈来愈重要的基础肝病。鉴于晚期NASH患者常并存多种影响肝移植转归的临床问题,而至今尚无针对NASH患者进行肝移植的评估和治疗指南,为此英国移植学会（British Transplant Society,BTS）邀请相关专家制定了指南,以指导肝移植前后NASH患者的处理。