Perturbation of red blood cell membrane rigidity by extracellular ligands

It is known that binding of extracellular antibodies against the major sialoglycoprotein, glycophorin A, reduced the deformability of the red blood cell membrane. This has been taken to result from new or altered interactions between the glycophorin A and the membrane skeleton. We have shown by means of the micropipette aspiration technique that antibodies against the preponderant transmembrane protein, band 3, induce similar effects. A definite but much smaller reduction in elasticity of the membrane is engendered by univalent Fab fragments of the anti-band 3 antibodies. By examining cells genetically devoid of glycophorin A or containing a variant of this constituent, truncated at the inner membrane surface, we have shown that the anti-band 3 antibodies do not act through the band 3-associated glycophorin A. We examined the effect of anti-glycophorin A antibodies on homozygous Wr(a+b-) cells, in which an amino acid replacement in band 3 annihilates the Wright b (Wrb) epitope (comprising sequence elements of glycophorin A and band 3) and thus, by implication disrupts or perturbs the band 3-glycophorin A interaction; these cells show a much smaller response to an anti-glycophorin A antibody than do normal controls. We infer that in this case anti-glycophorin A antibodies exert their rigidifying effect through the associated band 3. Another anti- glycophorin A antibody, directed against an epitope remote from the membrane surface, however, increases the rigidity of both Wr(a+b-) and normal cells. This implies that not all antibodies act in the same manner in modifying the membrane mechanical properties. The effect exerted by anti-band 3 antibodies appears not to be transmitted through the band 3-ankyrin-spectrin pathway because the rigidifying effect of the intact antibody persists at alkaline pH, at which there is evidence that the ankyrin-band 3 link is largely dissociated. The large difference between the effects of saturating concentrations of the divalent and univalent anti-band 3 antibodies implies the existence of an overriding effect on rigidity, resulting from the bifunctionality of the intact antigen. Freeze-fracture electron microscopy shows that the anti-band 3 promotes the formation of small clusters of intra-membrane proteins. Extracellular ligands may in general act by promoting strong or transient interactions between integral membrane proteins, thereby impeding local distortion of the membrane skeletal network in response to shear.     

ADP causes subsecond changes in protein phosphorylation of platelets

We developed a general quenched-flow approach to study platelet function as early as 0.3 seconds after stimulation. Phosphorylation of 20- and 47-kiloDalton (kD) proteins was analyzed during the first 5 seconds of platelet response to ADP from 0.5 to 10.0 mumol/L and compared with the progress of aggregation. The onset time for aggregation and phosphorylation of both proteins was less than 1 second; 20-K phosphorylation was increased greater than 200% and 47-K phosphorylation was increased 50%. The ADP sensitivity of 20-K phosphorylation was greater than that of 47-K phosphorylation (P less than .025), and of that of aggregation (P less than .01), with Ka values of 0.7, 1.0, and 1.2 mumol/L of ADP, respectively. The cyclooxygenase inhibitor indomethacin had no effect on aggregation, but inhibited both phosphorylations. Its inhibition of 20-K phosphorylation was greater than that of 47-K phosphorylation. Platelet activation by ADP thus induced biochemical changes well before 1 second. The quenched- flow approach may help to reveal relationships between phospholipase activation, calcium fluxes, and protein phosphorylation during these early periods of platelet activation.     

Impaired responsiveness to B cell growth factor in a patient with common variable hypogammaglobulinemia

Common variable hypogammaglobulinemia (CVH) is a clinical syndrome that includes a diverse group of patients with heterogeneous defects resulting in impaired B cell proliferation and terminal differentiation into mature plasma cells capable of normal immunoglobulin synthesis and secretion. In this study, we report our identification of a previously undescribed intrinsic B cell defect in a patient with CVH. This patient's B cells showed a marked impairment in hemolytic plaque- forming cell (HePFC) formation compared with control B cells (15 v 80 HePFCs per culture, respectively). In addition, this patient's B cells displayed decreased B cell colony formation compared with control B cells (5 +/- 2 v 93 +/- 8, respectively). When examined for their responsiveness to phytohemagglutinin-T cell conditioned media (PHA- TCM), the patient's B cells displayed impaired B cell proliferation compared with control B cells (stimulation index [SI] 1.3 +/- 0.20 v 26 +/- 1.4 with 20% control PHA-TCM [vol/vol]). Impaired proliferation by the patient's B cells persisted with increasing concentrations of B cell growth factor (BCGF). Additionally, PHA-TCM prepared from the patient's T cells when compared with control PHA-TCM consistently showed less support for control B cell proliferation (SI 1.27 +/- 0.21 v 26 +/- 1.4, respectively). In coculture studies of B cell proliferation and immunoglobulin synthesis, patient's T cells showed no evidence of an enhanced suppressive effect or decreased helper effect. This patient's immune defects involve, first, an intrinsic B cell defect characterized by an impaired responsiveness to BCGF's proliferation signal and, second, impaired production of BCGF by the patient's T cells.     

Paroxysmal AF Catheter Ablation With a Contact Force Sensing Catheter : Results of the Prospective,Multicenter SMART-AF Trial

Background

Catheter ablation is important for treatment of paroxysmal atrial fibrillation (PAF). Limited animal and human studies suggest a correlation between electrode-tissue contact and radiofrequency lesion generation.

Objectives

The study sought to assess the safety and effectiveness of an irrigated, contact force (CF)-sensing catheter in the treatment of drug refractory symptomatic PAF.

Methods

A prospective, multicenter, nonrandomized study was conducted. Enrollment criteria included: ≥3 symptomatic episodes of PAF within 6 months of enrollment and failure of ≥1 antiarrhythmic drug (Class I to IV). Ablation included pulmonary vein isolation with confirmed entrance block as procedural endpoint.

Results

A total of 172 patients were enrolled at 21 sites, where 161 patients had a study catheter inserted and 160 patients underwent radiofrequency application. Procedural-related serious adverse events occurring within 7 days of the procedure included tamponade (n = 4), pericarditis (n = 3), heart block (n = 1, prior to radiofrequency application), and vascular access complications (n = 4). By Kaplan-Meier analyses, 12-month freedom from atrial fibrillation/atrial flutter/atrial tachycardia recurrence was 72.5%. The average CF per procedure was 17.9 ± 9.4 g. When the CF employed was between investigator selected working ranges ≥80% of the time during therapy, outcomes were 4.25 times more likely to be successful (p = 0.0054; 95% confidence interval: 1.53 to 11.79).

Conclusions

The SMART-AF trial demonstrated that this irrigated CF-sensing catheter is safe and effective for the treatment of drug refractory symptomatic PAF, with no unanticipated device-related adverse events. The increased percent of time within investigator-targeted CF ranges correlates with increased freedom from arrhythmia recurrence. Stable CF during radiofrequency application increases the likelihood of 12-month success. (THERMOCOOL® SMARTTOUCH® Catheter for Treatment of Symptomatic Paroxysmal Atrial Fibrillation; NCT01385202)     

Rationale and design of VENTURE-AF: a randomized,open-label,active-controlled multicenter study to evaluate the safety of rivaroxaban and vitamin K antagonists in subjects undergoing catheter ablation for atrial fibrillation

Purpose

To evaluate the safety of uninterrupted rivaroxaban, a novel oral anticoagulant that directly inhibits factor Xa, and a vitamin K antagonist (VKA) in eligible adult patients with nonvalvular AF (NVAF) who are scheduled for a catheter ablation.

Methods/design

This is a prospective, randomized, open-label, active-controlled, global multicenter safety study of up to 250 randomized patients. Eligible patients with paroxysmal or persistent NVAF, a left ventricular ejection fraction >40 %, and a creatinine clearance >50 mL/min will be randomized 1:1 to rivaroxaban 20 mg orally once daily or to dose-adjusted oral VKA (recommended international normalized ratio (INR) 2.0–3.0) and stabilized on anticoagulation therapy for 1–7 days (if no intracardiac thrombus on transesophageal echocardiogram (TEE) immediately prerandomization/post-randomization or if 3 weeks of sufficient anticoagulation is documented) or for 4–5 weeks (if no TEE, no documented 3 weeks of sufficient anticoagulation, or by patient choice). During catheter ablation, heparin will be administered (ACT-targeted range?=?300–400 s) after catheter ablation, and VKA will be managed per usual care. The next dose of rivaroxaban will be provided at least 6 h after establishment of hemostasis. The primary endpoint will be the incidence of post-procedure major bleeding events observed during the first 30?±?5 days post-ablation. Secondary endpoints will include post-procedure thromboembolic events, additional bleeding, time-to-event, and medication adherence.

Relevance

This study is intended to provide information about the safety characteristics of rivaroxaban in patients with NVAF undergoing catheter ablation.     

瘦素受体基因Gln223Arg多态性与上海地区人群肥胖的相关性

目的:瘦素的体质量调节作用是通过瘦素受体介导的,分析瘦素受体基因Gln223Arg多态性与上海地区人群肥胖的相关性。方法:于2003-09/2004-05选择解放军第二军医大学长海医院内分泌科门诊的超重和单纯性肥胖患者130例(诊断按照WHO标准:体质量指数≥25kg/m2为超重,体质量指数≥30kg/m2为肥胖),为肥胖组。选择同期参加门诊体检的正常对照者102例,为对照组。所有观察对象均为上海籍、汉族、无亲缘关系,且有完整临床资料。实验经医院伦理委员会批准,受试者均知情同意。采用聚合酶链反应-限制性片段长度多态性方法测定受试者瘦素受体基因Gln223Arg多态性的基因型。结果:①肥胖组和对照组瘦素受体基因Gln223Arg基因型的频率分布差异无显著性。②在肥胖组中,瘦素受体基因Gln223Arg多态性与体质量指数相关(P=0.036),携带G等位基因的肥胖患者体质量指数较高。③Logistic回归分析显示,该多态性与体质量指数独立相关(P=0.046)。结论:实验结果提示,瘦素受体基因Gln223Arg多态性与上海地区人群肥胖相关。     

FK506 (Tacrolimus) monotherapy for prevention of graft-versus-host disease after histocompatible sibling allogenic bone marrow transplantation

FK506 (Tacrolimus) is an immunosuppressive drug that blocks the activation of antigen-specific T lymphocytes, a major component in the pathogenesis of graft-versus-host disease (GVHD). This study was designed to obtain first estimates of the safety and efficacy of FK506 monotherapy in the prevention of GVHD following HLA-identical sibling marrow transplantation. Additionally, a subset of patients was studied to define the pharmacokinetic profile of FK506. Twenty-seven adult patients with leukemia or myelodysplasia received FK506 starting the day before transplant at a dose of 0.04 mg/kg/d by continuous intravenous infusion. When clinically possible, FK506 was given orally in two divided doses starting at five times the daily intravenous dose. FK506 doses were adjusted to target a steady state or trough blood level between 10 to 30 ng/mL. These patients were followed for 6 months posttransplant. All patients had sustained marrow engraftment. Frequently noted adverse events included reversible renal dysfunction, diarrhea, fever, nausea, vomiting, and headache. Most patients required FK506 dose reductions associated with elevated serum creatinine. Two (7%) patients relapsed, one of whom died of the disease within the 6- month study period. A second patient died due to pulmonary mucor. Whole blood pharmacokinetic parameters indicated a half-life of 18.2 +/- 12.1 hours; volume of distribution of 1.67 +/- 1.02 L/kg; clearance of 71 +/- 34 mL/h/kg; and bioavailability of 32 +/- 24%. Eleven of 27 (41%) patients developed grade II to IV acute GVHD, including 10 grade II and one grade III. Six of 24 (25%) evaluable patients developed chronic GVHD. These data indicate that FK506 monotherapy has activity in preventing GVHD. Further studies of FK506 with lower doses to improve tolerability and in combination with other immunosuppressants to augment efficacy are warranted.     

Inhibition of malarial parasite invasion by monoclonal antibodies against glycophorin A correlates with reduction in red cell membrane deformability

The effect of well-characterized monoclonal antibodies to red cell surface molecules on the invasion of human red cells by the malarial parasites Plasmodium falciparum and Plasmodium knowlesi was examined. Antibodies to glycophorin A (GP alpha) inhibit invasion for both parasite species, and this is highly correlated with the degree to which they decrease red cell membrane deformability as measured by ektacytometry. This effect on rigidity and invasion was also seen with monovalent Fab fragments. The closer the antibody binding site was to the membrane bilayer, the greater was its effect on inducing membrane rigidity and decreasing parasite invasion. Antibodies to the Wright determinant in particular were the most inhibitory. This differential effect of the various antibodies was not correlated with their binding affinities or the number of sites bound per cell. Antibodies to surface molecules other than GP alpha were without effect. A novel mechanism is described whereby monoclonal antibodies and their Fab fragments directed at determinants on the external surface of red cells might act to inhibit invasion by malarial parasites by altering membrane material properties.