von Willebrand Factor Activity Detected in a Monoclonal Antibody-based ELISA: an Alternative to the Ristocetin Cofactor Platelet Agglutination Assay for Diagnostic Use

The monoclonal antibody RFF-VIII:R/1 recognises an epitope on von Willebrand factor involved in its interaction with GPIbα. A two-site, solid phase ELISA has been established using RFF-VIII:R/1 as the solid-phase, capture antibody and an enzyme-conjugated, polyclonal antibody to human VWF, which provides an assay for VWF functional activity with a detection limit of 0.5 U/dl VWF and an interassay %CV<10. Plasma from 192 VWD patients (48 studied retrospectively; 144 prospectively) showed VWF levels of <50 U/dl in type 1 patients (n = 156), <25 U/dl in type 2A (n = 26) and <35 U/dl in type 2B (n = 8) which, in type 1 and 2A patients, correlated with RiCoF activity (r >0.82). In plasma from patients with type 1 VWD values of VWF in the Mab-based ELISA were similar to levels of VWF:Ag measured in a polyclonal antibody-based ELISA (r >0.87) but were significantly lower than VWF:Ag in type 2A and 2B plasmas (p <0.0005), allowing discrimination of variant VWD. The Mab-based ELISA has advantages of sensitivity and reproducibility over the RiCoF assay to measure VWF activity and can be used to analyse stored samples. In conjunction with an ELISA for VWF:Ag and VWF multimer analysis, it provides a reliable method, for the laboratory diagnosis of VWD.

Fish as bioreactors: transgene expression of human coagulation factor VII in fish embryos

A plasmid containing human coagulation factor VII (hFVII) complementary DNA regulated by a cytomegalovirus promoter was microinjected into fertilized eggs of zebrafish, African catfish, and tilapia. The active form of hFVll was detected in the fish embryos by various assays. This positive expression of human therapeutic protein in fish embryos demonstrates the possibility of exploitation of transgenic fish as bioreactors.

Simple shifts in redox/thiol balance that perturb blood coagulation

The biological chemistry that underlies and regulates the blood coagulation cascade is not fully understood. To begin to understand this, we performed clotting assays under various redox conditions. By varying the amount of oxidant and/or antioxidant in these assays, we observed that both the intrinsic/tenase complex and the extrinsic pathways were susceptible to shifts in the thiol/redox balance. We established a dichotomy where blood clotting via the intrinsic pathway was sensitive to oxidation whereas the tissue factor or extrinsic pathway was more sensitive to reduction. These differential inhibitory effects present a conceptual mechanism for selective modulation of the activities of clotting factors specific for the respective pathways. These data also suggest that blood clotting may be influenced by unidentified redox or thiol equilibria.

Thrombotic risk factors associated with transurethral prostatectomy

OBJECTIVE

To ascertain the potential thrombotic risk associated with transurethral prostatectomy (TURP).

PATIENTS AND METHODS

The changes in coagulation variables were assessed in a prospective study of 40 patients undergoing TURP.

RESULTS

There was a significant increase in thrombin-antithrombin complexes 6 h after TURP (anova, P=0.01) combined with a significant decrease in activated partial thromboplastin time (anova, P=0.006), suggesting a postoperative hypercoagulable state. The significant increase in d-dimer 24 h after TURP (anova, P=0.015) in the absence of any significant rise in tissue plasminogen activator antigen levels perioperatively (anova, P=0.737) suggests a physiological fibrinolytic response to the developing procoagulant state. The absence of any significant increase in plasminogen activator inhibitor-1 antigen perioperatively (anova, P=0.348) suggests the observed hypercoagulability is not due to a 'fibrinolytic shutdown' reported in other forms of surgery.

CONCLUSION

TURP is associated with a hypercoagulable prothrombotic state; aspirin withdrawal perioperatively may be hazardous, and low-dose heparin prophylaxis for venous thrombosis should be considered.

von Willebrand factor activity detected in a monoclonal antibody-based ELISA: an alternative to the ristocetin cofactor platelet agglutination assay for diagnostic use

The monoclonal antibody RFF-VIII:R/1 recognises an epitope on von Willebrand factor involved in its interaction with GPIb alpha. A two-site, solid phase ELISA has been established using RFF-VIII:R/1 as the solid-phase, capture antibody and an enzyme-conjugated, polyclonal antibody to human VWF, which provides an assay for VWF functional activity with a detection limit of 0.5 U/dl VWF and an interassay %CV < 10. Plasma from 192 VWD patients (48 studied retrospectively; 144 prospectively) showed VWF levels of < 50 U/dl in type 1 patients (n = 156), < 25 U/dl in type 2A (n = 26) and < 35 U/dl in type 2B (n = 8) which, in type 1 and 2A patients, correlated with RiCoF activity (r > or = 0.82). In plasma from patients with type 1 VWD values of VWF in the Mab-based ELISA were similar to levels of VWF:Ag measured in a polyclonal antibody-based ELISA (r > or = 0.87) but were significantly lower than VWF:Ag in type 2A and 2B plasmas (p < or = 0.0005), allowing discrimination of variant VWD. The Mab-based ELISA has advantages of sensitivity and reproducibility over the RiCoF assay to measure VWF activity and can be used to analyse stored samples. In conjunction with an ELISA for VWF:Ag and VWF multimer analysis, it provides a reliable method for the laboratory diagnosis of VWD.

A simple monoclonal antibody based ELISA for free protein S. Comparison with PEG precipitation

A simple monoclonal antibody based ELISA for free Protein S, compatible with out existing ELISA for total Protein S has been developed, and its performance compared with the conventional PEG precipitation method of free Protein S assay. The normal range (mean +/- 2 SD) was 0.19-0.54 iu/ml free Protein S. The mean intra assay variation was 5.24% and the mean inter assay variation was 5.50%. A total of 102 routine diagnostic samples from patients referred for prothrombotic investigation (six assays for each method) were assayed by PEG precipitation (mean 0.32 iu/ml, SD 10.60), and the monoclonal ELISA (mean 0.34, SD 0.9). Paired t-test analysis of the two data sets indicated no significant difference between them (P < 0.001). In this sample population, there was no significant difference in free Protein S values when assayed by monoclonal based ELISA or by PEG precipitation. The monoclonal assay has proved to be reliable, accurate and precise. The monoclonal ELISA is simpler, quicker and easier to perform in routine use. Data generated is directly comparable to that generated by PEG precipitation. This methodology would be suitable for laboratories currently measuring Protein S by ELISA.

Thrombelastographic evaluation of coagulation in transurethral prostatectomy

OBJECTIVE

To assess the changes in overall coagulation status and define the degree of systemic fibrinolysis occurring in patients undergoing transurethral prostatectomy (TURP).

PATIENTS AND METHODS

Thirty patients undergoing TURP, 23 for benign prostatic hyperplasia and seven for prostatic carcinoma, were studied prospectively. Serial venous blood samples were taken using the two-syringe technique. Samples were taken before, during and at intervals up to 72 h and 10-14 days after surgery. Thrombelastography (TEG) was performed on native whole blood samples. Peri-operative blood loss was assessed, until the catheter was removed, by photometric estimation of the haemoglobin content of the irrigant fluid and the measurement of clot volume.

RESULTS

There was no evidence of fibrinolysis (TEG Percentage Clot Lysis Ly60 > 15%) in any patient over the whole peri-operative period. There was a significant change in the mean TEG variables towards hypercoagulation from 3 h until 10-14 days postoperatively, compared with the pre-operative values (P < 0.05). There was a significant correlation between blood loss and clot volume.

CONCLUSION

These results question the role of systemic fibrinolysis in primary and secondary haemorrhage following TURP and thus the rationale of using antifibrinolytics in these patients. The persistent hypercoagulable state post-operatively indicates a possible role of hypercoagulability in clot retention.

Expression of factor VII by muscle cells in vitro and in vivo following direct gene transfer: modelling gene therapy for haemophilia

Direct injection of plasmid DNA into skeletal muscle has been proposed as a method of effecting somatic gene therapy. This article describes the construction and testing of a plasmid derived expression cassette believed to confer skeletal muscle specific expression. Expression constructs were designed containing the full-length cDNAs for both coagulation factor VIII and factor VII. The engineered genes were flanked by two muscle specific regulatory elements from different myosin isoforms and by an artificial polyadenylation signal sequence. In vitro transfection of C2-myoblasts led to expression of the factor VIII gene, shown by reverse transcription and polymerase chain reaction, upon differentiation of the myoblasts. The expression of the FVII construct was tested in a C2 cell culture system and also when injected directly into mouse muscle. It was found that in cell culture the level of factor VII antigen outside the cell, ie in the cell culture medium was two- to three-fold higher than inside the cell, ie in the cell lysate. This level of expression was found to continue for the duration of cell culture maintenance and a fully functional protein was produced. In vivo transfection experiments in mice showed a substantial increase in factor VII antigen compared with the background level 4-5 days after injection. An anti-human factor VII antibody was detected 7-10 days after injection. We conclude that muscle cells in vitro secrete and efficiently carry out post-translational modifications of the engineered gene product and in vivo secrete the gene product resulting in elevation of systemic levels. The data provide the basis for the use of muscle cells as an in vivo expression system for coagulation proteins in the treatment of inherited haemostatic and thrombotic disorders.

Development and evaluation of ELISAs for factor XIIIA and XIIIB subunits in plasma

Severe, congenital deficiency of factor XIII is extremely rare. However, a moderate reduction in the plasma level of the functional subunit (factor XIIIA) and also to a lesser extent of the carrier subunit (factor XIIIB), and a decrease in the XIIIA:B subunit ratio, have recently been reported in patients with the inflammatory bowel disorder Crohn's disease, particularly during clinical relapse. In order to accurately monitor patients, sensitive, reliable assays for the two subunits of factor XIII are required. We report here the development and validation of ELISAs for these components. The assays are identical except in respect of the specificity of the polyclonal antiserum used as starting material, both of which are commercially available. The antisera are purified by n-octanoic acid precipitation and portions of these purified immunoglobulins are used as coating antibodies. The remaining portions are biotinylated and used with streptavidin and horse-radish peroxidase as tracer antibodies. A normal range (n = 24) was established for factor XIIIA (mean 95 range 60-130 U/dl) and for factor XIIIB (mean 99 range 60-130 U/dl). There were no significant differences between the ELISA and electroimmunodiffusion assays either for factor XIIIA (means +/- 1 standard deviation 95 +/- 15.9 and 89 +/- 22.7 respectively) or for factor XIIIB (99 +/- 18.3 and 106 +/- 23.4 respectively). These assays have been in routine use for six months, during which time two further antisera purifications and biotinylations have been carried out without significant problems of reproducibility or stability.