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Infusion studies of recombinant factor VIII were performed in hemophilic (factor VIII-deficient) animals. Functional activity was determined using a standardized model of bleeding and kinetic characteristics charted by performing assays of factor VIII functional and antigenic activities over time. To obtain an adequate comparison with plasma-derived factor VIII, a crossover study in two animals was performed in which each animal received either recombinant factor VIII or a highly purified plasma-derived factor VIII on day 1 and the alternative three days later (day 4). Both factor VIII preparations were functionally effective with complete correction of the cuticle bleeding time occurring one hour after infusion. The observed recovery was full and close to predicted for both preparations. The survival curves obtained for both functional and antigenic activities for both preparations were virtually identical and within the anticipated range determined from previous experiments using infusions of conventional factor VIII preparations. The plasma half-disappearance time (T 1/2) for recombinant factor VIII and plasma-derived factor VIII was 9.2 and 7.9 hours, respectively. Plasma samples obtained following infusion were subjected to chromatography on Sepharose 4B. The elution profile of factor VIII antigen activity was compared with that obtained with the infusates. A clear shift in profile was observed with the plasma samples, suggesting complexing of the infused factor VIII material with circulating canine von Willebrand factor (vWF). The elution profile of vWF antigen was superimposable, thus providing further evidence in support of this assumption. The study provided evidence that recombinant factor VIII possesses full functional activity in vivo, binds to circulating vWF, and exhibits normal recovery and survival characteristics.

The effect of both congenital and acquired factor VII deficiency on the cuticle bleeding time (CBT) was evaluated in dogs. The CBT has been previously documented to be a sensitive indicator of factor VIII:C deficiency in hemophilic dogs. Serial CBT determinations were made on normal dogs treated with high-dose warfarin. At 48 hours post- treatment, the CBT was normal, although the factor VII level was less than 1%, whereas the levels of factors II, IX, and X were 44%, 25%, and 17%, respectively. At 120 hours the CBT became abnormal when all vitamin K-dependent clotting factors had dropped to less than 18%. Administration of a plasma concentrate of factors II, IX, and X corrected the CBT, despite the factor VII level remaining at less than 1%. Similar studies in a congenitally factor VII-deficient dog (factor VII less than 2%) confirmed that this deficiency state was not associated with an abnormality of the CBT. Administration of heparin to both normal and factor VII-deficient animals was associated with prolongation of the CBT, but the heparin dose required in the normal animals was substantially higher than in the factor VII-deficient animals. These data do not suggest that factor VII/VIIa has an exclusive role in generating factor Xa, either directly or indirectly, by way of factor IXa generation, in vivo. However, the increase in heparin sensitivity of the factor VII-deficient animals does suggest that factor VII/VIIa may, in some circumstances, present a significant alternative pathway of factor X activation, although the activation pathway involved cannot be determined from the studies performed.

Classic hemophilia A (factor VIII:C deficiency) was diagnosed in a miniature Schnauzer dog and a breeding program established. Inbreeding and crossbreeding produced 16 hemophilic animals. All were initially treated with canine cryoprecipitate, as required, for sporadic hemorrhagic events. Five animals developed potent antibodies to canine factor VIII:C. All were the offspring of obligate carriers, resulting from the mating of a hemophilic purebred miniature Schnauzer male to a normal female Brittany spaniel. The mean age at first treatment and factor VIII exposure at the time of inhibitor development was 10.3 wk and 286.3 U, respectively. The remaining hemophilic animals have not developed antibodies, despite receiving a mean factor VIII dosage of 1.5 X 10(3) U. This group includes animals derived from a mating between the same purebred miniature Schnauzer hemophilic male and a purebred miniature Schnauzer carrier female. In each case, the antibodies recognize both canine and human but not porcine VIII:C. They are non-precipitating IgG immunoglobulins. Following inhibitor development, infusion of canine cryoprecipitate was hemostatically ineffective and factor VIII:C recovery at 30 min was negligible. Infusion of a concentrate of porcine factor VIII resulted in a correction of the hemostatic defect and optimal factor VIII:C recovery. All animals receiving porcine factor VIII:C subsequently developed antibodies to this protein. The chance occurrence of this complication should facilitate further studies directed at elucidating the pathogenesis and management of hemophilia complicated by the development of antibodies to factor VIII:C.

In previous studies using a nonhuman primate model of Protein C (PC) activation in vivo, immunoblotting showed substantial amounts of activated PC (APC) in a high molecular weight complex with what was presumed to be a previously unrecognized APC binding protein. This APC complex can also be formed in citrated plasma in vitro. It is of low electrophoretic mobility, sodium dodecyl sulfate (SDS) stable, with an apparent Mr of 320 Kd. Its purification from human plasma was accomplished using barium citrate adsorption, sequential polyethylene glycol (PEG) precipitations, diethylaminoethyl sepharose chromatography, AcA-34 gel filtration, and zinc-chelate affinity chromatography. This was monitored by subjecting the fractions to nondenaturing polyacrylamide gel electrophoresis (PAGE), transfer to polyvinyl idene-difIuoride membranes, and probing with 125I-labeled human APC. The purified APC-binding protein was homogeneous by SDS-PAGE with an Mr of 275 Kd. Its identity as α2-macroglobulin (α2M) was demonstrated immu- nochemically. Complex formation between α 2M and APC was found to be almost completely inhibited by EDTA, but to a lesser extent by citrate. Complex formation could also be prevented by active site inhibition with D-Phenylalanyl-L-Prolyl-L-Arginine-Chloromethyl Ketone (PPACK) or pretreatment of α2M with methylamine. Incubation of APC (33 nmol/ L) with α2M (1 μmol/L) resulted in time-dependent inhibition of APC anticoagulant activity when measured using an activated partial thromboplastin time based APC assay. These data show that α2M binds and inhibits APC in vitro and the interaction is both metal-ion and active-site dependent, requiring functionally intact α2M. As the complexes formed in vitro comigrate electrophoretically with those observed in vivo after PC activation, it is suggested that α2M is a physiologically relevant inhibitor involved in the processing of APC in vivo.

In vitro evaluation of prothrombin complex concentrates in a thrombin generation assay, using DAPA and purified components of the prothrombinase complex, demonstrated significant levels of coagulant- active “phospholipid replacing” activity. Quantification of this activity showed a significant correlation (r = 0.8747, p less than 0.01) with thrombogenicity measured in vivo in a stasis model in rabbits. Extracted lipid material retained full phospholipid replacing activity in the vitro assay. Thin-layer chromatographic characterization confirmed the presence of phospholipids with known coagulant activity in vitro. In vivo, the extracted material was nonthrombogenic but augmented the thrombogenicity of purified factor Xa. Substitution of a synthetic coagulant-active phospholipid (phosphatidylcholine-phosphatidylserine lipid vesicles) for the extracted phospholipid produced a similar augmentation of a factor-Xa- induced thrombogenicity in vivo. It is concluded that the coagulant- active phospholipid content of prothrombin complex concentrates is a major determinant of thrombogenicity but requires the presence of activated clotting factors for its expression in vivo.

Streptococcus mutans NCTC 10499 was cultured under glucose limitation in a chemostat at varying oxygen supply. The rates of oxygen uptake and hydrogen peroxide degradation by cells from the cultures were measured polarographically using a Clark electrode. Oxygenation of the chemostat culture led to adaptation of the organism to oxygen, in that the maximum oxygen uptake rate of the cells was higher when the cells were grown at higher rate of oxygen supply. It is noted that anaerobically grown cells still exhibited significant oxygen uptake. The rate of oxygen uptake followed saturation-type kinetics and Ks values of cells for oxygen were in the micromole range. Hydrogen peroxide accumulation was not observed in aerated chemostat cultures. However, anaerobically grown cells accumulated H2O2 when exposed to oxygen. Cells from aerated cultures did not accumulate hydrogen peroxide. This may be explained by the fact that the rate of hydrogen peroxide degradation was consistently higher than the rate of oxygen uptake.