Studies Of Factor VIII Inhibitor Bypassing Activity (FEIBA)

1981 ◽  
Author(s):  
T W Barrowcliffe ◽  
E Gray ◽  
G Kemball-Cook
Keyword(s):  
Factor Viii ◽  
Factor Xa ◽  
Factor Ix ◽  
Procoagulant Activity ◽  
Two Stage ◽  
Human Antibodies ◽  
One Stage ◽  
Viii And Ix ◽  
The One

The activities of an activated Factor IX concentrate (FEIBA, Immuno AG) were studied by two in vitro assays: a one-stage method using VUI-deficient plasma as substrate, and a two-stage assay based on the thrombin generation test. The nature of the active principle was explored by measuring the reduction in activity when FEIBA was incubated with specific antibodies.Incubation of FEIBA with human antibodies to Factor VIII reduced its activity by about 30% in the one-stage assay, and about 50% in the two-stage assay, suggesting that FEIBA contains Factor VIII procoagulant activity. Inactivation of the Factor VIII in FEIBA was somewhat slower than that of normal Factor VIII, indicating partial protection from inhibition. Human antibodies to Factor IX inhibited the one stage activity by about 30%, and incubation with both antibodies also produced a 30% reduction in activity. The remaining procoagulant activity decayed only slowly when incubated with non-inhibitor plasma. In contrast, purified human Factor Xa lost activity rapidly on incubation in normal plasma, as did a purified fraction from a Factor IX concentrate, which had high activity in the one-stage assay.These results suggest that the in vitro activity of FEIBA is due to at least two components. One component appears to be dependent on both Factors VIII and IX and may be a complex of VIII and IXa. The other component acts later than Factors VIII and IX in the coagulation cascade but, unlike purified Factor Xa, is relatively resistant to inactivation by plasma inhibitors such as antithrombin III. FEIBA was also found to contain phospholipid, and it may be that the phospholipid protects both the Factor VIII and activated enzymes from their inhibitors.

In Vivo Recovery of Factor VIII: A Comparison of One-Stage and Two-Stage Assay Methods

1979 ◽  
Vol 42 (04) ◽  
pp. 1230-1239 ◽  
Author(s):  
I M Nilsson ◽  
T B L Kirkwood ◽  
T W Barrowcliffe
Keyword(s):  
Factor Viii ◽  
Half Life ◽  
In Vitro Assays ◽  
Two Stage ◽  
One Stage ◽  
Significant Difference ◽  
Assay Methods ◽  
The One ◽  
Fraction I

SummaryThe recovery and half-life of VIII: C in the plasma of severely haemophilic patients was measured by one-stage and two-stage assays after injection of two Factor VIII concentrates (Hemofil, Hyland and Fraction I-O, Kabi). Plasma volumes were measured with an Evans� Blue technique, and both concentrates and post-infusion samples were measured against the same plasma standard.There was a highly significant difference in recoveries estimated by the two assay methods. The one-stage assays gave the most consistent results, in that the average recovery was 100%, whereas the two-stage assays gave only about 80% of the value expected from in vitro assays. There was no difference in recoveries between the two concentrates.The two-stage assays gave a slightly shorter half-life than the one-stage assays, and the half-life of Hemofil was also shorter than that of Fraction I-O.

Decreased Potency Of Factor VIII Concentrates

1981 ◽  
Author(s):  
C K Kasper
Keyword(s):  
Factor Viii ◽  
In Vitro Assays ◽  
Assay Method ◽  
Two Stage ◽  
One Stage ◽  
Plasma Factor ◽  
Factor Viii Concentrates ◽  
The One

Plasma factor VIII recoveries after infusions of factor VIII concentrates into patients with classic hemophilia have been measured in this laboratory for 14 years. Recently, we observed a decline in the in vivo recovery of factor VIII per factor VIII unit infused. In 1980, plasma factor VIII levels were measured by a one-stage APTT-based assay before and 10 min after 150 infusions of 46 lots of 3 brands of factor VIII concentrate produced in the U.S.A. Our pooled normal plasma reference was calibrated against WHO International Standard 2 and results expressed in International factor VIII units. Observed in vivo factor VIII recovery was compared to the value expected from calculations based on the unitage stated on the label. The ratio of observed/expected recovery averaged 56% per lot for brand A, 60% per lot for brand B, and 103% per lot for brand C. In vitro assays were performed on 22 lots on 36 occasions, and the ratio of observed/labelled units average 46% per lot for brand A, 53% for brand B and 75% for brand C. The two-stage factor VIII assay method of Pool and Robinson was also used to assay plasma samples from 18 infusions, and results averaged 135% of the one-stage values for infusions of brand A, 160% for brand B, and 109% for brand C. (Brand A is assayed by the manufacturer by a two-stage method, brands B and C by one-stage methods.)Decreased clinical efficacy was observed when postinfusion plasma factor VIII levels were lower than customary. The decline in potency of brands A and B has necessitated more frequent assay of patients and use of larger amounts of concentrate, with greatly-increased expense. Investigation of the effect of different assay methods and different factor VIII standards and references on the apparent factor VIII content of concentrates has begun.

Thrombin Potentiation of Factor VIII Procoagulant Activity: Assessment by the Two-Stage Assay

1982 ◽  
Vol 47 (02) ◽  
pp. 145-149 ◽  
Author(s):  
Robert G Kopitsky ◽  
Mary Ellen P Switzer ◽  
Patrick A McKee
Keyword(s):  
Factor Viii ◽  
Procoagulant Activity ◽  
Two Stage ◽  
Clotting System ◽  
One Stage ◽  
Fviii Activity ◽  
Thrombin Activation ◽  
The One ◽  
Dose Response Effect ◽  
Von Willebrand

SummaryFactor VIII (FVIII) procoagulant activity is the function of a plasma glycoprotein that is missing or inactive in patients with classic hemophilia. Numerous studies have shown that trace thrombin causes rapid enhancement followed by gradual inactivation of FVIII procoagulant activity. Recent evidence suggests that thrombin activation of the FVIII/von Willebrand factor (vWF) protein is required for inactivation to occur. All of these studies have used the one-stage partial thromboplastin time to assay FVIII activity. Other investigators have used the two-stage assay of FVIII activity and have been unable to demonstrate thrombin-induced enhancement of FVIII activity, although inactivation has consistently occurred. We performed experiments designed to help resolve this disagreement, using the two-stage assay specifically modified to detect thrombin potentiation of FVIII activity. The length of the first-stage incubation time was found to be critical in demonstrating the initial effect of thrombin on FVIII activity. Taking advantage of this finding we were able to show a 4.1 ± 0.5-fold enhancement of FVIII activity upon incubating purified FVin/vWF with 0.04 NIH unit thrombin per ml. The apparent enhancement of FVEQ activity declined with increasing thrombin concentration. Incubation with 0.08, 0.16, and 0.32 NIH unit thrombin per ml resulted in only 3.2 ± 0.5, 2.6 ± 0.5 and 1.5 ± 0.3-fold enhancement, respectively, of FVIII activity. As with results from the one-stage assay, activation was followed by slow inactivation of FVIH/vWF. Using the two-stage assay we also showed 100% inactivation and 100% inhibition of FVIII activity by plasmin and human anti-FVUI IgG, respectively. Plasmin inactivation of FVIII activity showed a dose-response effect. Thrombin was unable to activate plasmin-degraded FVin/vWF. Our results show that thrombin potentiation of FVni activity is easily demonstrable in the two-stage assay. These findings support the contention that activation of FVm activity by thrombin is prerequisite for inactivation and underscore the importance of thrombin activation of FVHI/vWF in the intrinsic clotting system.

Standardization of Factor VIII – IV. Establishment of the 3rd International Standard for Factor VIII: C Concentrate

1983 ◽  
Vol 50 (03) ◽  
pp. 697-702 ◽  
Author(s):  
T W Barrowcliffe ◽  
A D Curtis ◽  
D P Thomas
Keyword(s):  
Factor Viii ◽  
High Purity ◽  
Collaborative Study ◽  
World Health ◽  
Current Standard ◽  
Two Stage ◽  
International Standard ◽  
One Stage ◽  
The One ◽  
Health Organization

SummaryAn international collaborative study was carried out to establish a replacement for the current (2nd) international standard for Factor VIII: C, concentrate. Twenty-six laboratories took part, of which 17 performed one-stage assays, three performed two-stage assays and six used both methods. The proposed new standard, an intermediate purity concentrate, was assayed against the current standard, against a high-purity concentrate and against an International Reference Plasma, coded 80/511, previously calibrated against fresh normal plasma.Assays of the proposed new standard against the current standard gave a mean potency of 3.89 iu/ampoule, with good agreement between laboratories and between one-stage and two- stage assays. There was also no difference between assay methods in the comparison of high-purity and intermediate purity concentrates. In the comparison of the proposed standard with the plasma reference preparation, the overall mean potency was 4.03 iu/ampoule, but there were substantial differences between laboratories, and the two-stage method gave significantly higher results than the one stage method. Of the technical variables in the one-stage method, only the activation time with one reagent appeared to have any influence on the results of this comparison of concentrate against plasma.Accelerated degradation studies showed that the proposed standard is very stable. With the agreement of the participants, the material, in ampoules coded 80/556, has been established by the World Health Organization as the 3rd International Standard for Factor VIII :C, Concentrate, with an assigned potency of 3.9 iu/ampoule.

scholarly journals Inhibition of human coagulation factor VIII by monoclonal antibodies. Mapping of functional epitopes with the use of recombinant factor VIII fragments

1989 ◽  
Vol 263 (1) ◽  
pp. 187-194 ◽  
Author(s):  
A Leyte ◽  
K Mertens ◽  
B Distel ◽  
R F Evers ◽  
M J M De Keyzer-Nellen ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Factor Viii ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Procoagulant Activity ◽  
Coagulation Factor Viii ◽  
Coagulation Cascade ◽  
Restriction Enzyme Digestion ◽  
Proteolytic Activation

The epitopes of four monoclonal antibodies against coagulation Factor VIII were mapped with the use of recombinant DNA techniques. Full-length Factor VIII cDNA and parts thereof were inserted into the vector pSP64, permitting transcription in vitro with the use of a promoter specific for SP6 RNA polymerase. Factor VIII DNA inserts were truncated from their 3′-ends by selective restriction-enzyme digestion and used as templates for ‘run-off’ mRNA synthesis. Translation in vitro with rabbit reticulocyte lysate provided defined radiolabelled Factor VIII fragments for immunoprecipitation studies. Two antibodies are shown to be directed against epitopes on the 90 kDa chain of Factor VIII, between residues 712 and 741. The 80 kDa chain appeared to contain the epitopes of the other two antibodies, within the sequences 1649-1778 and 1779-1840 respectively. The effect of antibody binding to these sequences was evaluated at two distinct levels within the coagulation cascade. Both Factor VIII procoagulant activity and Factor VIII cofactor function in Factor Xa generation were neutralized upon binding to the region 1779-1840. The antibodies recognizing the region 713-740 or 1649-1778, though interfering with Factor VIII procoagulant activity, did not inhibit in Factor Xa generation. These findings demonstrate that antibodies that virtually inhibit Factor VIII in coagulation in vitro are not necessarily directed against epitopes involved in Factor VIII cofactor function. Inhibition of procoagulant activity rather than of cofactor function itself may be explained by interference in proteolytic activation of Factor VIII. This hypothesis is in agreement with the localization of the epitopes in the proximity of thrombin-cleavage or Factor Xa-cleavage sites.

scholarly journals Identification of Sources of Inter-Laboratory Variation in Factor VIII Assay

1977 ◽  
Author(s):  
T.B.L. Kirkwood ◽  
C.R. Rizza ◽  
T.J. Snape ◽  
I. Rhymes ◽  
D.E.G. Austen
Keyword(s):  
Factor Viii ◽  
Systematic Difference ◽  
Normal System ◽  
Two Stage ◽  
Initial Dilution ◽  
One Stage ◽  
Collaborative Studies ◽  
Freeze Dried ◽  
Sources Of Variation ◽  
The One

A repeated finding of national and international collaborative studies of standard Factor VIII preparations has been that systematic differences exist between laboratories in their measurement of the relative activities of the same pairs of Factor VIII preparations.A workshop meeting was held at the Oxford Haemophilia Centre (England) during 23rd-26th November 1976 to investigate which of the possible sources of variation between laboratories were responsible. Participants from 16 British laboratories (9 one-stage, 7 two-stage) performed a total of 273 assays using three freeze-dried preparations of differing purity (a plasma, an intermediate and a high purity concentrate). The results of assays with each participant using their normal system established that, if the participants were a representative cross-section, approximately one-third of one-stage laboratories would show a systematic difference from the overall mean of at least 16%, with a similar figure for the two-stage laboratories of 9%. Various features of the assay systems were then modified in a controlled series of experiments. The results showed conclusively that i) differences between reagents accounted for most of the variation between laboratories and, ii) the two-stage assays were, on average, detecting relatively more activity in the more purified preparations than the one-stage assays. The results also suggested that the use of buffer as opposed to haemophilic plasma for the initial dilution of concentrates did not affect the assay results.

scholarly journals Plasma Transfusions in Hemophilia

Blood ◽  
1952 ◽  
Vol 7 (7) ◽  
pp. 710-720 ◽  
Author(s):  
S. VAN CREVELD ◽  
M. M. P. PAULSSEN
Keyword(s):  
Two Stage ◽  
Coagulation Time ◽  
Prothrombin Activity ◽  
Lasting Effect ◽  
One Stage ◽  
The One ◽  
Rapid Appearance

Abstract Transfusions of heparinized plasma have a greater and more lasting effect on the coagulation time of hemophiliacs than transfusions of citrated plasma. Both in vitro and in vivo, heparinized plasma causes in hemophiliacs a far greater consumption of prothrombin as determined with the two-stage method than citrated plasma. In using the one-stage method no important differences in prothrombin activity are found after transfusions of heparinized and of citrated plasma respectively. This fact was thought to be connected with the more or less rapid appearance of an accelerator. Its a hemophiliac with a circulating anticoagulant, transfusions of heparinized plasma were unable to shorten the coagulation time to any important degree, nor did these transfusions cause an important decrease of serum prothrombin as determined by the two-stage method.

Binding To Phospholipid Protects Factor VIII From Inhibition By Human Antibodies

1981 ◽  
Author(s):  
T W Barrowcliffe ◽  
E Gray ◽  
G Kemball-Cook
Keyword(s):  
Factor Viii ◽  
Thrombin Generation ◽  
Total Phospholipid ◽  
Fluid Phase ◽  
Clinical Applications ◽  
Factor Ix ◽  
Two Stage ◽  
Human Antibodies ◽  
Thrombin Generation Assay ◽  
Detectable Antigen

Previous studies with activated Factor IX concentrates have suggested that they may contain a form of Factor VIII clotting activity (VIII:C) which is partly protected from inactivation by antibodies. A possible mechanism for such protection is binding to phospholipid. The interaction between Factor VIII, phospholipid and human antibodies to Factor VIII was studied by a two-stage clotting assay, and by a fluid-phase immunoradiometric assay for Factor VIII clotting antigen (VIII C:Ag).In the two-stage thrombin generation assay, Factor VIII:C was rapidly destroyed by human antibodies, even in the presence of optimal phospholipid. However, preincubation of Factor VIII with phospholipid before addition of antibody protected the Factor VIII from inactivation, resulting in the production of much more thrombin.In assays of VIII C:Ag, pre-incubation of Factor VIII with phospholipid before addition of labelled antibody reduced the amount of detectable antigen. The reduction was greater with increasing phospholipid concentration, up to 60% of the original antigen being ‘lost’ at a total phospholipid concentration of around 250 μg/i.u.These results suggest that human antibodies to Factor VIII are directed largely at its phospholipid binding site. The protection of Factor VIII from inactivation by complexing with phospholipid could have important clinical applications in treatment of haemophiliacs with inhibitors.

Validation of a Procedure for Potency Assessing of a High Purity Factor VIII Concentrate -Comparison of Different Factor VIII Coagulant Assays and Effect of Prediluent

1990 ◽  
Vol 64 (02) ◽  
pp. 251-255 ◽  
Author(s):  
Claudine Mazurier ◽  
Armelle Parquet-Gernez ◽  
Maurice Goudemand
Keyword(s):  
Factor Viii ◽  
Specific Activity ◽  
Assay Method ◽  
One Stage ◽  
Chromogenic Assay ◽  
Coagulant Activity ◽  
The One ◽  
In Vitro Data

SummaryThe assessment of factor VIII coagulant activity (FVTII: C) in recently available highly purified and concentrated FVTII therapeutic products calls for careful evaluation of assay methodologies. We assayed more than 130 batches of a concentrate with a specific activity of about 150 FVTII :C units/mg protein, using one-stage and two-stage clotting and chromogenic methods. There was good agreement between the potency estimates obtained with the different methods. We also compared the FVTII :C potencies obtained after predilution in buffer or FVIII-deficient plasma using either calibrated plasma or FVTII concentrate as references. With the one-stage assay we found a marked discrepancy between the potency values obtained with buffer and with FVTII-deficient plasma used as prediluents. In order to validate our “in vitro” data we performed 6 “in vivo” analyses in severe haemophilia A patients. On the basis of the overall data obtained we chose to label FVIII potency by using FVIII-deficient plasma as prediluent, reference plasma as standard and the chromogenic assay method.

In Vivo Recovery and Survival of Monoclonal-Antibody-Purified Factor VIII Concentrates

1991 ◽  
Vol 66 (06) ◽  
pp. 730-733 ◽  
Author(s):  
Carol K Kasper ◽  
Hugh C Kim ◽  
Edward D Gomperts ◽  
Kenneth J Smith ◽  
Phyllis M Salzman ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Factor Viii ◽  
In Vitro Assays ◽  
Two Stage ◽  
Double Blind ◽  
One Stage ◽  
Factor Viii Concentrates ◽  
In Vivo Recovery

SummaryIn response to reports of discrepant in vitro assays of high-purity concentrates, a double-blind crossover study of in vivo recovery and half-life of two brands of monoclonal-antibody-purified factor VIII concentrates (Monoclate and Hemofil-M) was performed in 23 patients with hemophilia A. In vivo recoveries were close to values predicted from the labelled unitage when plasma samples were assayed by a one-stage method. When a two-stage assay was used, lower recoveries were calculated and the recovery with Hemofil-M was slightly but significantly lower than that with Monoclate. The concentrates were re-assayed in vitro by the two-stage method. Monoclate (which is assayed by the manufacturer using a two-stage method) contained 97% of the labelled potency and Hemofil-M (which is assayed by the manufacturer using a one-stage method) contained 81% of the labelled potency. Differences in in vitro and in vivo assay methods contribute to disparities between expected and observed factor VIII recovery. Clearance of Hemofil-M was significantly faster than that of Monoclate, but volume of distribution at the steady state, mean residence time, and plasma half-disappearance times of the two concentrates were not significantly different.

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