Role of the B domain for factor VIII and factor V expression and function

Factor V and factor VIII are homologous cofactors in the blood coagulation cascade that have the domain structure A1-A2-B-A3-C1-C2, of which the B domain has extensively diverged. In transfected COS-1 monkey cells, expression of factor VIII is approximately 10-fold less efficient than that of factor V, primarily because of inefficient protein secretion and, to a lesser extent, reduced mRNA expression. To study the functional significance and effect of the B domain on expression and activity, chimeric cDNAs were constructed in which the B domains of factor V and factor VIII were exchanged. Expression of a factor VIII chimera harboring the B-domain of factor V yielded a fully functional factor VIII molecule that was expressed twofold more efficiently than wild-type factor VIII because of increased mRNA expression. Thus, sequences within the factor VIII B domain were not responsible for the inefficient secretion of factor VIII compared with factor V. Expression of a factor V chimera harboring the B domain of factor VIII was slightly reduced compared with wild-type factor V, although the secreted molecule had significantly reduced procoagulant activity correlating with dissociated heavy and light chains and resistance to thrombin activation. Interestingly, the factor V chimera containing the factor VIII B domain was efficiently activated by Russell's viper venum (RVV). A factor V B domain deletion (residues 710- 1545) molecule also exhibited significantly reduced procoagulant activity caused by resistance to thrombin cleavage and activation, although this molecule was activatable by RVV. These results show that, in contrast to factor VIII, thrombin activation of factor V requires sequences within the B domain. In addition, thrombin activation of factor V occurs through a different mechanism than activation by RVV.     

von Willebrand factor released from Weibel-Palade bodies binds more avidly to extracellular matrix than that secreted constitutively

Large multimers of von Willebrand factor (vWf) are released from the Weibel-Palade bodies of cultured endothelial cells following treatment with a secretagogue (Sporn et al, Cell 46:185, 1986). These multimers were shown by immunofluorescent staining to bind more extensively to the extracellular matrix of human foreskin fibroblasts than constitutively secreted vWf, which is composed predominantly of dimeric molecules. Increased binding of A23187-released vWf was not due to another component present in the releasate, since releasate from which vWf was adsorbed, when added together with constitutively secreted vWf, did not promote binding. When iodinated plasma vWf was overlaid onto the fibroblasts, the large forms bound preferentially to the matrix. These results indicated that the enhanced binding of the vWf released from the Weibel-Palade bodies was likely due to its large multimeric size. It appears that multivalency is an important component of vWf interaction with the extracellular matrix, just as has been shown for vWf interaction with platelets. The pool of vWf contained within the Weibel-Palade bodies, therefore, is not only especially suited for platelet binding, but also for interaction with the extracellular matrix.     

Phage typing in dermatitis cruris pustulosa et atrophicans: does staphylococcal carrier status have a role?

Background Dermatitis cruris pustulosa et atrophicans (DCPA) is a form of chronic folliculitis of the legs with a multifactorial etiopathogenesis, seen primarily in tropical countries. Staphylococcus aureus has been isolated from the pustules in earlier studies, although the organisms isolated have not been further characterized. Materials and methods Patients with DCPA, who attended the Dermatology outpatient clinic at JIPMER, Pondicherry, India, during the study period (December 2006–June 2008) were included. Pus from the lesions as well as swabs from carrier sites (nares, axillae, and gluteal fold) were cultured. Staphylococcus aureus isolates were subjected to phage typing at the National Staphylococcal Phage Typing Center, Department of Microbiology, Maulana Azad Medical College, New Delhi, India. Results Thirty‐seven patients were included in the study. Pus from the folliculitic lesions grew S. aureus in 32 (86.49%) patients. Based on the comparison of antibiotic sensitivity patterns, isolates from pus and carrier sites were found to be similar in 15 patients. Phage typing established the organism to be identical in five of these patients. Conclusions Characterization of S. aureus in DCPA shows that there is no specific phage type that is uniformly responsible for the lesions in most patients. However, in view of the unclear etiology of this condition, the pathogenicity of a staphylococcal carrier state in individual patients needs to be addressed.     

The factor V B-domain provides two functions to facilitate thrombin cleavage and release of the light chain

Blood coagulation factors V and VIII are homologous proteins that have the domain organization A1-A2-B-A3-C1-C2. Upon thrombin activation, the B-domains of both molecules are released. Previous studies on factor VIII showed that the B-domain was not required for thrombin cleavage or activity. In contrast, deletion of the factor V B-domain (residues 709 to 1545) yielded a molecule with sevenfold reduced procoagulant activity that was not cleaved by thrombin. However, this factor V B- domain deletion molecule was activated by factor Xa, although the fold- activation was 85% that of wild-type factor V. Thrombin cleavage of factor V occurs initially after residue 709 and subsequently after residues 1018 and 1545. The requirement for thrombin cleavage within the B-domain at residue 1018 was evaluated by mutagenesis of Arg1018 to Ile. In the resultant R1018I mutant, the rate of thrombin activation and appearance of maximal cofactor activity was delayed and was consistent with delayed cleavage of the light chain at residue 1545. In contrast, the rate of factor Xa activation in the R1018I mutant was not altered. This finding suggests that thrombin cleavage at 1018 facilitates subsequent thrombin cleavage at 1545. Further mutagenesis was used to study the requirement for sequences within the factor V B- domain for thrombin cleavage at residue 1545. Whereas the factor V deletion molecule removing residues 709 to 1545 was not cleaved by thrombin, a smaller B-domain deletion molecule (residues 709 to 1476) containing an acidic amino acid-rich region (residues 1490 to 1520) was effectively cleaved by thrombin. These results show that residues 1476 to 1545, which contain an acidic amino acid-rich region, were required for thrombin cleavage of the light chain. Introduction of an acidic amino acid-rich region from factor VIII (residues 337 to 372) into the factor V 709 to 1545 deletion also restored thrombin cleavage of the light chain. In contrast, similar replacement with the acidic region from the factor VIII light chain (residues 1649 to 1689) was significantly less effective in promoting thrombin cleavage of the light chain. This finding suggests that the different acidic regions in factors V and VIII are not functionally equivalent in their interaction with thrombin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intrauterine growth retardation: evaluation by magnetic resonance. Work in progress

Eleven high risk fetuses between 32 and 37 menstrual weeks gestational age were examined by magnetic resonance (MR) imaging. Serial obstetrical sonograms, birth weights, and serial postnatal examinations were obtained in all subjects. Sagittal MR spin echo images obtained using TR = 0.5 sec and TE = 28 msec were useful for assessing subcutaneous fat. Prospective estimates of fetal fat stores correlated with neonatal outcome better than sonographic measurements of fetal growth parameters or actual birth weight. MR appears to be a safe and useful technique that offers information complementary to obstetrical sonography when IUGR is suspected.     

Allocation of health care resources in the neonatal and perinatal area �CCPS Symposium 1996

There have been publically expressed concerns about the costs and allocation of neonatal and perinatal health care resources in Canada and elsewhere for the past 15 years. This paper reports information from a symposium held during the 1996 Canadian Paediatric Society (CPS) annual meeting sponsored by the CPS Section on Perinatal Medicine. Experts in perinatal epidemiology, health care economics, public policy and finance, and consumer perspectives on the outcomes of neonatal and perinatal intensive care explored the following questions: How should the need for health care resources in the neonatal and perinatal area be objectively determined? When there are competing needs between the maternal-newborn area and other areas, how should these be rationalized? What evidence should be used (or should be available) to support the present use of resources? What evidence should be available (or is needed) to change or introduce new uses of resources? The conclusions indicated that there are no generally accepted methods to determine the allocation of health care resources but that considerations need to include population characteristics, desired outcomes, achievable results, values, ethics, legalities, cost-benefit analyses and political objectives. Information from families and adolescents who required the use of high technology and/or high cost programs will contribute individual, family and societal values that complement cost-efficacy analyses.     

国内六大行政区域六城市中老年人群膝关节骨性关节炎患病危险因素比较

目的：了解中国不同地区间中老年人群膝关节骨性关节炎患病危险因素。方法：调查时间为2005—07／08。①从中国六大行政区（西北，华北，华东。中南，东北，西南）选出六城市（西安，石家庄，上海。广州，哈尔滨市，成都），用分层多阶段整群抽样方法，抽取6218名40岁及以上具有正式户口常住男女人群进行膝关节骨性关节炎的流行病学问卷调查（包括一般情况、现病史、既往史、体格检查、X射线片检查情况和疾病诊断6个方面，共计94个问题141个变量指标），并对其中4808名有症状者进行X射线平片膝正侧位投照。②膝关节骨性关节炎诊断标准为临床症状阳性加X射线Kellgren ＆ Lawrence分级二级及以上者。③计算患病率，并采用Epilnf06．0和SPSS 10．0软件对其中83个变量进行多因素非条件Logistfc回归分析，表示疾病与暴露因素之间联系强度的指标用比值比（OR），若OR〉1，说明疾病发生危险性增加，与暴露因素呈正关联；若OR〈1，说明疾病发生危险性减少，与暴露因素呈负关联。 结果：①六城市膝关节骨性关节炎总患病率为15．6％，其中西安7．7％，石家庄11．2％，上海9．8％。广州30．5％，哈尔滨16．9％，成都17．5％，各城市患病率比较差异显著（P〈0．01）。②Logistic回归分析膝关节骨性关节炎在大部分城市有共同的危险因素如年龄大（OR=1．032—1．181），使用蹲坑排便年限长（OR=1．021-1．077），体质量高（OR=1．048—1．073），和开始饮酒年龄大（OR=1．008～1．028）；而从事专职体育运动（OR=1．651，西安），骨质疏松病史（OR=3．311，石家庄），吸烟（OR=2．654，石家庄），类风湿关节炎病史（OR=4．964，上海），文化程度高（OR=2．593，上海），女性（OR=2．510，广州），姐妹骨关节炎史（OR=13．251，哈尔滨），母亲骨关节炎史（OR=5．683，成都）等危险因素分别在不同地区出现． 结论：年龄大、使用蹲坑排便年限长、体质量高和开始饮酒年龄大是中国六地区膝关节骨性关节炎患病的共同危险因素，同时，不同地区主要危险因素又有一定差异。