The interaction of von Willebrand factor-A1 domain with collagen: mutation G1324S (type 2M von Willebrand disease) impairs the conformational change in A1 domain induced by collagen

BACKGROUND: It is established that the A3 domain in von Willebrand factor (VWF) contains the major collagen-binding site. However, there are conflicting reports describing the capacity of the A1 domain to interact with collagen types I and III. METHODS: In this study, we have used recombinant VWF-A1 polypeptides, as well as conformation-specific monoclonal antibodies (mAb), to analyze the A1-collagen interaction. RESULTS: The A1 domain bound to collagen with K(d) approximately 8.0 nm and this binding was blocked by the mAb 6G1, which blocks the interaction between ristocetin and VWF. In addition, collagen-bound A1 protein was able to support flow-dependent adhesion of platelets, demonstrating that the binding sites for collagen and glycoprotein (GP)Ib are different. Analysis with two conformation-specific mAb demonstrated that the structure of the A1 domain changed as a result of the binding to collagen. In contrast, the antibodies failed to detect conformational change in the G1324S mutant (type 2M von Willebrand disease). Thus, direct binding to collagen induces a change in the structural conformation within the VWF-A1 domain, and the G1324S substitution prevents this conformational change. CONCLUSION: This study has shown that the isolated A1 domain can simultaneously bind to collagen and platelet GPIb, supporting platelet adhesion under high-flow conditions. In addition, this study has used mAb to demonstrate that the binding of the isolated A1 domain or full-length VWF to collagen is accompanied by a conformational change in A1 domain.     

A comparative study of plateletpheresis using Baxter Autopheresis C and Haemonetics PCS Plus

SUMMARY. This study compared plateletpheresis on the Haemonetics PCS Plus (PCS Plus) and the Baxter Autopheresis C (Auto C) using the same 100 selected donors. The number of packs meeting UK BTS/NIBSC specification (>2.2 times 10¹¹ platelets per pack) was achieved by 99% of PCS Plus and 82% of Auto C procedures. The positive correlation found between donor precount and final platelet yield was better for the PCS Plus. Both machines met U.K. specification for white-cell contamination but this was significantly greater for the Auto C. Plasma yields were similar.
As a result of this study we chose to use the PCS Plus for routine plateletpheresis in our unit. This has enabled us not only to comply with UK BTS/NIBSC specifications for apheresis platelets easily and cost effectively but also to meet our own higher specification (2.75 times 10¹¹ platelets per pack) using existing staff and without extending the working day.     

Platelet aggregation,disc haemorrhage and progressive loss of visual fields in glaucoma

Platelet aggregationin vitro, deterioration of visual field defects (VFD) and the prevalence of disc haemorrhages (DH) were assessed in 49 patients with primary open angle glaucoma (POAG) and compared with the findings for 67 individuals with suspected glaucoma (GS) in a seven-year follow-up study (range 5.8 to 8.2 years). The percentage patients with spontaneous platelet aggregation (SPA) was higher for POAG patients with visual field deterioration (60%) than both POAG patients without progressive loss of visual fields (12.5%; P<0.005) and those with suspected glaucoma (22.4%; P<0.005). The occurrence of DH was higher among POAG patients with progressive loss of visual field (28%) compared to the GS group (8.4%; P<0.025) and the group of patients consisting of POAG patients without deterioration of VFD and GS (9.9%; P<0.05). DH also occurred more often in patients with low tension glaucoma (41.6%) than in the remaining POAG patients (13.5%; P<0.05). No relation between the patients with SPA and the patients with DH was observed.Abbreviations NPB normal platelet behavior - SPA spontaneous platelet aggregation - DH disc haemorrhage     

水蛭注射液对大白鼠血小板粘附和血小板聚集功能的影响

目的　探讨水蛭注射液对大白鼠血小板粘附性和聚集性的影响。方法　采用大白鼠 2 4只 ,随机分成两组 ,实验组给药 ,对照组以实验组同样的方法和剂量给予生理盐水 ,5d后由颈总动脉取血 ,做血小板粘附性和聚集性试验。结果　水蛭注射液对大鼠血小板粘附性和聚集性具有显著的抑制作用 ,实验组与对照组抑制率有显著的统计学意义 (P <0 0 0 1)。结论　水蛭注射液能够抑制大白鼠血小板的粘附和聚集。     

海风藤酚、甲基海风藤酚、海风藤醇A和海风藤醇B对兔血小板聚集的影响

海风藤酚、甲基海风藤酚、海风藤醇Ａ和海风藤醇Ｂ均有抑制血小板激活因子（ＰＡＦ）诱导的兔血小板聚集作用，ＩＣ_（５０）分别为１７．９、９．２、１４２．０、１４．０μｍｏｌ·Ｌ~（－１）。经阿司匹林（ＡＳＡ）、磷酸肌酸／磷酸肌酸激酶（ＣＰ／ＣＰＫ）预处理的兔洗涤血小板，甲基海风藤酚和海风藤醇Ｂ仍能抑制ＰＡＦ诱导的兔血小板聚集，ＩＣ_（５０）为９．０、１６．５μｍｏｌ·Ｌ~（－１）。同时，４种成分对于二磷酸腺苷（ＡＤＰ），花生四烯酸（ＡＡ）诱导的血小板聚集抑制作用较弱，海风藤Ｂ能使ＰＡＦ诱导血小板聚集量－效曲线平行右移，ＥＣ_（５０）由１．５９ｎｍｏｌ·Ｌ~（－１）升为２０．６ｎｍｏｌ·Ｌ~（－１）。结果表明：４种成分能选择性拮抗ＰＡＦ对兔血小板的聚集作用。     

Inhibitory effect of activated protein C on platelet aggregation induced by the prothrombin-converting reaction

The present study was undertaken to elucidate the effect on platelet aggregation of the prothrombin-converting reaction on platelets with or without activated protein C (APC). A reaction mixture of washed platelets from human individuals, Factor Xa and prothrombin markedly induced platelet aggregation; maximum aggregation rates, 31.3–92.5%, and times to reach to maximum aggregation, 11.6 to 20.1 min. This aggregation was inhibited by the addition of APC with 50% inhibition concentration (IC₅₀) value of 14.4 U/ml. APC also inhibited thrombin generation in the reaction mixture in a dose-dependent manner with IC50 value of 0.96 U/ml. However, APC did not inhibit the thrombin (0.1 CU/ml)-induced platelet aggregation at concentrations of up to 30 U/ml. These findings suggest that APC has no direct inhibitory effect on platelet aggregation and that APC inhibits platelet aggregation through inhibition of thrombin generation.     

尿毒症患者的血小板聚集功能变化及血液透析的影响

本文应用 ADP、肾上腺素及复合诱聚剂对30例慢性肾功能不全(尿毒症期)病人的血小板聚集功能进行了检测,其中5例在血液透析前后分别测定。结果表明尿毒症患者血小板聚集功能障碍,血液透析有助于改善血小板功能。通过相关性检验,发现尿毒症病人的血小板聚集率与血肌酐值呈负相关性,其意义尚需进一步探讨。     

苏州地区汉族人血小板糖蛋白Ⅲa基因TaqI多态性与脑梗死的相关性研究

目的　研究苏州地区汉族人血小板糖蛋白Ⅲa基因TaqⅠ多态性与脑梗死发生的相关性。 方法　应用PCR技术结合TaqⅠ酶切分析、聚丙烯酰胺凝胶电泳 ,研究了苏州地区汉族正常人与脑梗死患者血小板糖蛋白Ⅲa基因TaqⅠ多态性特点。 结果　正常对照组TaqⅠ等位基因的频率分别为C 5 3.8%、A 4 6 .2 %。脑梗死组TaqⅠ等位基因频率分别为C 5 0 .6 %、A 4 9.4 %。脑梗死组和对照组之间无显著性差异 (P >0 .0 5 )。结论　苏州地区汉族人血小板糖蛋白Ⅲa基因TaqⅠ多态性与脑梗死发生无关。     

血小板活化与冠心病关系的研究进展

病理性血小板活化与血栓性疾病密切相关,在心血管疾病中,这一病理生理过程不仅与冠心病的发生、发展有着非常重要的联系,而且对于该病的治疗策略的优化和近、远期预后等方面都有直接的影响。