Inhibitory spectrum of alpha 2-plasmin inhibitor.

205

A B S T R A C T a2-Plasmin inhibitor (a2PI) is a recently characterized, fast-reacting plasmin inhibitor in human plasma that appears to play an important role in regulation of in vivo fibrinolysis. We report here a case of complete deficiency of a2PI in man. The patient, a 25-yr-old Japanese man, had a life-long severe bleeding tendency (hemarthrosis and excessive bleeding after trauma). The following tests were within normal limits: platelet count, bleeding time, thrombin time, prothrombin time, partial thromboplastin time, titers of known clotting factors, platelet glass bead retention, Factor VIII-related antigen, platelet aggregation by ADP, collagen and ristocetin, and clot retraction. Routine liver function tests were also normal. The only abnormal finding was that whole blood clot lysis was extemely rapid and was complete in 4-8 h. The concentration of plasma protease inhibitors, including a2-macroglobulin, antithrombin III, a,-antitrypsin, and C1INH, were all normal. The concentration of a2-PI in the patient's plasma, assayed by immunological methods, was <0.1 mg/100 ml (normal concentration, 6.1+0.88 mg/100 ml [mean±SE]) and functional assays showed a complete deficiency of a2PI. Addition of purified a2PI to the patient's whole blood completely corrected the accelerated fibrinolysis. The patient's parents, four siblings, and four other members of this family were asymptomatic, but the titers of a2PI in their plasmas were-50% of normal pooled plasma. There were three

Section: Resultsmentioning

confidence: 99%

Congenital Deficiency of α2-Plasmin Inhibitor Associated with Severe Hemorrhagic Tendency *

Aoki¹,

Saito²,

Kamiya³

et al. 1979

205

“…4) (I). The values for k' were tabulated for a1-protease inhibitor, antithrombin III, and Cl-inhibitor from this study, and for a2-plasmin inhibitor from the report of Saito et al (7). From these data we predicted that al-protease inhibitor would be responsible for 68% of the inhibitory activity in plasma against Factor XIa.…”

Section: Resultsmentioning

confidence: 99%

Inactivation of Factor XIa by Plasma Protease Inhibitors

Scott¹,

Schapira²,

James³

et al. 1982

127

A B S T R A C T Factor XIa is a plasma protease that, by activating Factor IX, plays an important role in the early phase of the intrinsic pathway of blood coagulation. Four plasma protease inhibitors, a1-protease inhibitor, antithrombin III, Cl-inhibitor, and a2-plasmin inhibitor, have been reported to inactivate human Factor XIa, but their quantitative contribution to the inactivation of Factor XIa in plasma has not been fully assessed. Using purified systems, we observed that the second-order rate constants for the reaction of Factor XIa with a1-protease inhibitor, antithrombin III, and Cl-inhibitor were 4.08, 10, and 14.6 M`min-' X 103, respectively. The pseudo-first-order rate constants, at plasma concentration of the inhibitors, were 1.86 X 10-1, 4.68 X 10-2, and 2.4 X 10-2 min-', respectively. These kinetic data predict that al-protease inhibitor should account for 68%, antithrombin III for 16%, and Cl-inhibitor and the equipotent a2-plasmin inhibitor each for 8% of the total inhibitory activity of plasma against Factor XIa. The rate of inactivation of Factor XIa in various plasma samples specifically deficient in inhibitors was consistent with these predictions.Factor XI, the zymogen form of Factor XIa, circulates in plasma associated with the contact system cofactor, high molecular weight kininogen (HMW kininogen). Kinetic analysis indicated the existence of a reversible bimolecular Factor XIa-HMW kininogen complex with a dissociation constant (Kd) = 0.17 ,M. The light chain derived from HMW kininogen decreased the inactivation rate of Factor XIa by Cl-in-hibitor with a Kd of 0.08 AM for a complex of Factor XIa and the light chain derived from HMW kininogen. The protective effect of HMW kininogen was confirmed by the finding that the inactivation rate of Fac-

“…The clot formed was suspended in normal plasma and incubated at 370C. At 2 (-), 6 (0), and 24 (A) h of incubation, release of radiolabel from the clot into the suspending plasma milieu was measured and expressed as a percentage of the total radioactivity. The concentrations of a2PI in the clot at the time of clotting are given on the abscissa.…”

Section: Resultsmentioning

confidence: 99%

Significance of Cross-Linking of α2-Plasmin Inhibitor to Fibrin in Inhibition of Fibrinolysis and in Hemostasis

Sakata¹,

Aoki²

1982

290

180

A B S T R A C T When blood is clotted, a2-plasmin inhibitor (a2PI) is cross-linked to fibrin by activated fibrin-stabilizing factor (activated coagulation Factor XIII, plasma transglutaminase). The amount of crosslinked a2-PI is proportional to the amount of a2PI present at the time of clotting. Plasma from a patient with congenital deficiency of a2PI was supplemented with various amounts of purified a2PI. Clots were prepared from these plasmas and were suspended in plasma containing a normal concentration of a2PI, and spontaneous clot lysis was observed. When the clot was formed in the presence of calcium ions and thereby allowing cross-linking to occur, the rate and extent of fibrinolysis were found to be inversely proportional to the concentrations of a2PI present in the clot at the time of clotting. When the clot was formed in the absence of calcium ions so that no cross-linking occurred, the clot underwent fibrinolysis at similar rates, regardless of the concentrations of a2PI in the clot. When the clot formed in the presence of calcium ions was squeezed and washed to remove unbound proteins before being suspended in plasma, the extent of fibrinolysis was also inversely proportional to the amount of a2PI cross-linked to fibrin. Similar results were obtained when the clot was suspended in buffered saline instead of plasma. These observations suggest that spontaneous fibrinolysis is mainly carried out by plasminogen/plasminogen activator bound to fibrin, and this fibrinolysis caused by fibrin-associated activation of plasminogen was mainly inhibited by a2PI crosslinked to fibrin. To further support this concept, a2PI treated with activated fibrin-stabilizing factor and that had lost most of its cross-linking capacity was used in similar experiments. This modified a2PI had the same inhibitory activity on plasmin as the native inhibitor, but gave significantly less inhibition of fibrinolysis in