Abnormal factor VIII coagulant antigen in patients with renal dysfunction and in those with disseminated intravascular coagulation.

Factor VIII antigen (VIII:CAg) exhibits molecular weight heterogeneity in normal plasma. We have compared the relative quantities of VIII:CAg forms present in normal individuals (n = 22) with VIII:CAg forms in renal dysfunction patients (n = 19) and in patients with disseminated intravascular coagulation (DIC; n = 7). In normal plasma, the predominant VIII: CAg form, detectable by sodium dodecyl sulfate polyacrylamide gel electrophoresis, was of molecular weight 2.4 X 10(5), with minor forms ranging from 8 X 10(4) to 2.6 X 10(5) D. A high proportion of VIII:CAg in renal dysfunction patients, in contrast, was of 1 X 10(5) mol wt. The patients' high 1 X 10(5) mol wt VIII: CAg level correlated with increased concentrations of serum creatinine, F1+2 (a polypeptide released upon prothrombin activation), and with von Willebrand factor. Despite the high proportion of the 1 X 10(5) mol wt VIII:CAg form, which suggests VIII:CAg proteolysis, the ratio of Factor VIII coagulant activity to total VIII:CAg concentration was normal in renal dysfunction patients. These results could be simulated in vitro by thrombin treatment of normal plasma, which yielded similar VIII:CAg gel patterns and Factor VIII coagulant activity to antigen ratios. DIC patients with high F1+2 levels but no evidence of renal dysfunction had an VIII:CAg gel pattern distinct from renal dysfunction patients. DIC patients had elevated concentrations of both the 1 X 10(5) and 8 X 10(4) mol wt VIII:CAg forms. We conclude that an increase in a particular VIII:CAg form correlates with the severity of renal dysfunction. The antigen abnormality may be the result of VIII:CAg proteolysis by a thrombinlike enzyme and/or prolonged retention of proteolyzed VIII:CAg fragments.

von Willebrand factor abnormalities and endothelial cell perturbation in a patient with acute thrombotic thrombocytopenic purpura.

The plasma of a 63-year-old patient with an initial acute, fatal episode of thrombotic thrombocytopenic purpura (TTP) contained agglutinated platelets and a factor VIII-related von Willebrand factor (vWF) antigen level that was elevated seven-fold above normal. Unusually large vWF multimers derived from endothelial cells were detected in her plasma at the onset of the TTP episode. This is the first patient in whom vWF abnormalities indicative of in vivo endothelial cell damage or perturbation have been found during an acute episode of TTP.

Direct radioimmune detection in human plasma of the association between factor VIII procoagulant protein and von Willebrand factor, and the interaction of von Willebrand factor-bound procoagulant VIII with platelets.

The predominant procoagulant factor VIII (VIII:C) form in normal human plasma containing various combinations of anticoagulants and serine/cysteine protease inhibitors is a protein with mol wt 2.6 +/- 0.2 X 10(5). This protein can be detected by 125I-anti-VIII:C Fab binding and gel electrophoresis in the presence and absence of sodium dodecylsulfate (SDS) and is distinct from the subunit of factor VIII/von Willebrand factor (VIII:vWF) multimers. No larger VIII:C form is present in plasma from patients with severe congenital deficiencies of each of the coagulation factors, other than VIII:C. The mol wt approximately 2.6 X 10(5) VIII:C form is, therefore, likely to be the in vivo procoagulant form of VIII:C, rather than a partially proteolyzed, partially activated derivative of a larger precursor. About 60% of this procoagulant mol wt approximately 2.6 X 10(5) VIII:C form in plasma is present in noncovalent complexes with larger VIII:vWF multimers, which attach reversibly to platelet surfaces in the presence of ristocetin. This VIII:vWF-bound protein of mol wt approximately 2.6 X 10(5) may be the plasma procoagulant form of VIII:C which, after proteolytic activation, accelerates the IXa-mediated cleavage and activation of X postulated to occur on platelet surfaces.

Interaction of platelets, von Willebrand factor, and ristocetin during platelet agglutination.

Ristocetin induces platelet agglutination in the presence of human factor VIII-associated ristocetin cofactor (vWF). The specificity, extent, and tenacity of binding among these reactants during agglutination and deagglutination were examined. Purified human vWF polymers were radioiodinated and reisolated. Radioiodinated vWF, a disulfide-linked polymer of 230,000 dalton subunits, attached to formalinized human platelets only in the presence of ristocetin. This binding reached equilibrium within 30 sec, and as ristocetin concentrations were raised from 0.2 mg/ml, the extent of attachment increased progressively to reach maximum at 0.5 to 0.6 mg/ml ristocetin. Ristocetin-induced binding was inhibited by vancomycin, unlabeled-purified vWF polymers, normal and hemophilia A plasma, and rabbit anti-human vWF. Binding was not impaired by plasma without detectable vWF or by naturally occurring human IgG antibodies to factor VIII coagulant activity. When formalinized platelets were pelleted from suspensions containing 125I-ristocetin, small quantities of radiolabeled ristocetin associated with platelets both in the presence or absence of vWF. About 95% of the attached 125I-ristocetin was removed by subsequent washes in buffered saline. The attachment of unmodified ristocetin or 125I-ristocetin to platelets, or the formation of complexes with vWF, could not be detected by agarose column chromatography, sucrose cushion ultracentrifugation, or equilibrium dialysis. These results indicate that (1) the initial binding of human vWF polymers to platelets is a specific interaction which requires the presence of ristocetin; (2) ristocetin and human vWF do not form persistent complexes in solution; and (3) the association of ristocetin and platelets is of low affinity.

Platelets, von Willebrand factor, and prostaglandin I2.

Depending on the time of addition, prostaglandin I2 (PGI2; greater than or equal to 10(-9) M) either inhibits or reverses platelet agglutination mediated by human factor VIII-related von Willebrand factor activity (FVIIIvWF) and ristocetin, or bovine FVIIIvWF alone. 6-Keto-PGF1 alpha, the inactive metabolite of PGI2, is without effect, PGI2 inhibition is potentiated by the phosphodiesterase inhibitor, theophylline, and is not the result of PGI2 suppression of ADP release. PGI2 (+/- theophylline) does not inhibit ristocetin-induced binding of purified human 125I-FVIIIvWF multimers to washed platelets or to platelets treated with PGI2 and then formalin fixed (although subsequent agglutination of these platelets is impaired). Washed platelets treated previously with 2-aminoethylisothiouronium bromide (AET), an agent that reduces disulfide bonds and alters platelet membranes, also bind human 125I-FVIIIvWF multimers without agglutinating. We conclude that FVIIIvWF-mediated agglutination requires both functional platelet FVIIIvWF binding sites and platelet-platelet cohesion sites, and that platelet surface cohesion sites are altered by AET and PGI2. PGI2 from adjacent intact endothelial cells may prevent excessive platelet accumulation on exposed subendothelium without suppressing an essential hemostatic process--the binding of platelets to subendothelial FVIIIvWF.

Abnormal VIII: von Willebrand factor patterns in the plasma of patients with the hemolytic-uremic syndrome.

Plasma VIII:von Willebrand factor antigen (VIII:vWF) levels were elevated approximately two- to eightfold in seven patients (three adults and four children) during acute episodes of thrombocytopenia, renal failure, and hemolytic anemia (the hemolytic-uremic syndrome, HUS). In all seven patients, there was an alteration in plasma VIII:vWF patterns during these acute HUS episodes, so that the largest VIII:vWF forms were relatively decreased. Plasma VIII:vWF multimer patterns returned to normal, or nearly to normal, as platelet counts returned to preexisting levels, even in the patients whose recovery of renal function was incomplete and whose plasma VIII:vWF antigen level remained above normal. The sister of one of the HUS patients had a similar clinical prodrome (gastroenteritis) that was not followed by thrombocytopenia or renal failure and was not accompanied by an elevated level or abnormal forms of plasma VIII:vWF. These results suggest that an alteration in VIII:vWF metabolism, distribution, or interaction with platelets is associated with acute HUS episodes. In contrast to patients with chronic relapsing thrombotic thrombocytopenic purpura, none of the HUS patients (either during or after the acute HUS episodes) had a defect in the conversion of unusually large VIII:vWF multimers derived from endothelial cells to the VIII:vWF forms found in normal plasma.

Therapy of chronic relapsing thrombotic thrombocytopenic purpura with prednisone and azathioprine.

As a 51-year-old woman recovered from an initial acute episode of thrombotic thrombocytopenic purpura (TTP), her plasma was found to contain unusually large von Willebrand factor (vWF) multimers. Clinical, hematological, and vWF studies of her siblings and children were normal. The unusually large vWF forms were presumably derived from endothelial cells, persisted in her plasma after recovery, and were associated with recurrent episodes of TTP during the subsequent 6 months. After the last episode of relapse they disappeared from her plasma following 3 1/2 weeks of therapy with prednisone and did not return during 17 months of treatment with prednisone and/or azathioprine. She is now receiving no drugs, has normal plasma vWF forms, and has not had any more episodes of TTP. We conclude that our patient had an acquired defect in the conversion of unusually large vWF multimers derived from endothelial cells to the somewhat smaller vWF forms usually present in circulation. The defect may have been immune-mediated, because it was eliminated during therapy with immunosuppressive drugs.

Effects of fresh-frozen plasma and its cryosupernatant fraction on von Willebrand factor multimeric forms in chronic relapsing thrombotic thrombocytopenic purpura.

Remission plasma samples of some patients with chronic relapsing thrombotic thrombocytopenic purpura (TTP) contain unusually large von Willebrand factor (vWF) multimers similar to those produced by normal human endothelial cells in culture. The infusion of the cryosupernatant fraction of normal plasma is as effective as normal fresh-frozen plasma (FFP) in the treatment or prevention of TTP episodes in patients with the chronic relapsing form of TTP. Three patients with chronic relapsing TTP during remission have unusually large vWF multimers present in their plasma. Two of the patients were transfused once with FFP, one of the two received cryosupernatant on three occasions, and the third patient was studied before and immediately after plasma exchange. Unusually large vWF multimers decreased or disappeared from patient plasma samples within 1/2 to 1 1/2 hours following the transfusion of FFP (on two occasions) or cryosupernatant (on two of three occasions), and immediately after plasma exchange (on one occasion). The patient who received cryosupernatant was studied serially after the infusions. Unusually large vWF multimers returned to her plasma within ten to 24 hours and persisted thereafter. Unusually large vWF multimers did not disappear from patient remission plasma samples, or from the culture medium removed from normal human endothelial cells, when these fluids were incubated in vitro with either normal FFP or cryosupernatant. We conclude that an activity in FFP, and its cryosupernatant fraction, promoted the rapid in vivo disappearance of unusually large vWF multimers from the plasma of two patients with chronic relapsing TTP in remission, and plasma exchange reversed the abnormality in a third patient who was in partial remission. Neither FFP nor cryosupernatant directly converted unusually large multimers to smaller vWF forms in vitro in the fluid phase. These results indicate that an activity in the cryosupernatant fraction of normal plasma is involved in vivo in controlling the metabolism of unusually large vWF multimers, and that this process is defective in some chronic relapsing TTP patients.