Production of functional coagulation factor VIII from iPSCs using a lentiviral vector

The use of induced pluripotent stem cells (iPSCs) as an autologous cell source has shed new light on cell replacement therapy with respect to the treatment of numerous hereditary disorders. We focused on the use of iPSCs for cell-based therapy of haemophilia. We generated iPSCs from mesenchymal stem cells that had been isolated from C57BL/6 mice. The mouse iPSCs were generated through the induction of four transcription factor genes Oct3/4, Klf-4, Sox-2 and c-Myc. The derived iPSCs released functional coagulation factor VIII (FVIII) following transduction with a simian immunodeficiency virus vector. The subcutaneous transplantation of iPSCs expressing FVIII into nude mice resulted in teratoma formation, and significantly increased plasma levels of FVIII. The plasma concentration of FVIII was at levels appropriate for human therapy at 2-4 weeks post transplantation. Our data suggest that iPSCs could be an attractive and prospective autologous cell source for the production of coagulation factor, and that engineered iPSCs expressing coagulation factor might provide a cell-based therapeutic strategy appropriate for haemophilia.

Intra-articular injection of mesenchymal stem cells expressing coagulation factor ameliorates hemophilic arthropathy in factor VIII-deficient mice

BACKGROUND

Transplantation of cells overexpressing a target protein represents a viable gene therapeutic approach for treating hemophilia. Here, we focused on the use of autologous mesenchymal stem cells (MSCs) expressing coagulation factor for the treatment of coagulation factor VIII (FVIII) deficiency in mice.

METHODS AND RESULTS

Analysis of luciferase gene constructs driven by different promoters revealed that the plasminogen activator inhibitor-1 (PAI-1) gene promoter coupled with the cytomegalovirus promoter enhancer region was one of the most effective promoters for producing the target protein. MSCs transduced with the simian immunodeficiency virus (SIV) vector containing the FVIII gene driven by the PAI-1 promoter expressed FVIII for several months, and this expression was maintained after multiple mesenchymal lineage differentiation. Although intravenous injection of cell supernatant derived from MSCs transduced with an SIV vector containing the FVIII gene driven by the PAI-1 promoter significantly increased plasma FVIII levels, subcutaneous implantation of the MSCs resulted in a transient and weak increase in plasma FVIII levels in FVIII-deficient mice. Interestingly, intra-articular injection of the transduced MSCs significantly ameliorated the hemarthrosis and hemophilic arthropathy induced by knee joint needle puncture in FVIII-deficient mice. The therapeutic effects of a single intra-articular injection of transduced MSCs to inhibit joint bleeding persisted for at least 8 weeks after administration.

CONCLUSIONS

MSCs provide a promising autologous cell source for the production of coagulation factor. Intra-articular injection of MSCs expressing coagulation factor may offer an attractive treatment approach for hemophilic arthropathy.

Induction of factor VIII-specific unresponsiveness by intrathymic factor VIII injection in murine hemophilia A

SUMMARY BACKGROUND

Hemophilia A is a congenital bleeding disorder caused by a deficiency of coagulation factor VIII. Approximately 30% of hemophilia A patients develop inhibitors against FVIII following replacement therapy. We have reported that neonatal exposure of FVIII antigen can induce antigen-specific immune tolerance by interferon-gamma (IFN-gamma)-dependent T-cell anergy in hemophilia A mice.

OBJECTIVE

The thymus plays crucial roles in self-tolerance, with negative selection of self-reactive effector T cells and positive selection of self-reactive regulatory T cells. We investigated the possibility of the induction of antigen-specific immune tolerance by intrathymic injection of FVIII in hemophilia A mice.

METHODS

Hemophilia A mice were injected with recombinant FVIII into the thymus under real-time high-resolution image guidance.

RESULTS

Anti-FVIII inhibitory antibody titers in mice challenged with intravenous administration of FVIII were significantly lower in mice (n = 22) that had received thymic FVIII injection than in mice (n = 18) without thymic injection (9.4 +/- 2.3 vs. 122.5 +/- 27.6 BU mL(-1), respectively, P = 0.00078). The CD4(+) T cells from thymic-injected mice could not proliferate or produce interleukin (IL)-2, IL-12 and IFN-gamma in response to FVIII. The CD4(+)CD25(+) T cells generated from thymic-treated mice but not from naïve mice efficiently suppressed the in vitro proliferative response of CD4(+) T cells and blocked the in vivo development of anti-FVIII antibodies in the adoptive transfer.

CONCLUSION

These data suggest that intrathymic administration of FVIII could result in immune tolerance by induction of FVIII-specific regulatory T cells.

A classification of the fibrin network structures formed from the hereditary dysfibrinogens

OBJECTIVE

The main objective was to study the relationships of the molecular defects in 38 dysfibrinogens with their fibrin networks.

METHODS AND RESULTS

Scanning electron microscopic analyses revealed that all the fibrins formed under the same conditions had networks composed of either normal thickness fibers or thin fibers, accompanied by a variety of alterations in the network structure and characteristics. We classified these fibrin networks into five classes, designated normal, less-ordered, porous A, porous B and lace-like networks. The dysfibrinogens with defects in fibrinopeptide A release or the E:D binding sites formed normal or less-ordered networks, while those with defects in the D:D association formed porous A networks composed of many tapered terminating fibers, despite having fibers of normal width, and containing many pores or spaces. The porous B and lace-like networks were composed of highly branched thin fibers because of defects in the lateral association among protofibrils, and the major difference between them was the porosity of the porous B networks. All the porous B networks were easily damaged by mechanical stress, whereas the lace-like networks retained high resistance to such stress, indicating that the network strength was not dependent on the fiber width, but on the porosity that led to fragility of the network.

CONCLUSION

Impairment of the D:D association is the major disturbing factor that leads to the formation of porous fibrin networks. The porosity may be introduced by severe impairment of the D:D association, as well as the lateral association, as has often been observed by extra glycosylation or defects in Ca2+ binding.

Aspirin resistance detected with aggregometry cannot be explained by cyclooxygenase activity: involvement of other signaling pathway(s) in cardiovascular events of aspirin-treated patients

OBJECTIVES

Although the concept of aspirin resistance is extensively reported in medical literature, its precise mechanisms and clinical outcomes are largely unknown. In this study, we examined individual thromboxane biosynthesis and platelet aggregation in aspirin-treated patients, and whether the results of a platelet aggregation test influenced clinical outcomes.

RESULTS

Subjects taking 81 mg of aspirin (n = 50) and controls (n = 38) were evaluated for platelet aggregation and platelet cyclooxygenase-1 (COX-1) activity by measuring collagen-induced thromboxane B2 production. For aggregometry, both light transmission (LT) and laser-light scattering methods were employed to quantitatively evaluate aggregate sizes and numbers. Aspirin treatment resulted in the inhibition of collagen-induced platelet aggregation, particularly the transition from small to large platelet aggregates. Although platelet COX-1 activity seemed to be uniformly inhibited in all patients, platelet aggregation studies showed great inter-individual differences; variation in platelet COX-1 activity only accounted for 6-20% of the individual aggregations. Factor analysis revealed the existence of a common factor (other than platelet COX-1) that explained 48.4% of the variations in platelet aggregation induced by collagen, adenosine diphosphate (ADP), and collagen-related peptide. We then prospectively enrolled 136 aspirin-treated patients in our study, and we found that being in the upper quartile level of LT, or with large aggregate formation induced by collagen, was an independent risk factor for developing cardiovascular events within 12 months [hazard ratio (HR) = 7.98, P = 0.008 for LT; HR = 7.76, P = 0.007 for large aggregates]. On the other hand, the existence of diabetes mellitus was an independent risk factor for overall outcomes (HR 1.30-11.9, P = 0.015-0.033).

CONCLUSIONS

Aspirin resistance expressed as unsuppressed platelet COX-1 activity is a rare condition in an out-patient population. Other factor(s) affecting collagen-induced platelet aggregation may influence early outcomes in aspirin-treated patients.

Induction of immune tolerance by neonatal intravenous injection of human factor VIII in murine hemophilia A

Inhibitory antibody formation is the most serious complication of factor (F)VIII replacement therapy in hemophilia A patients. FVIII-deficient mice were used to study new approaches for induction of immune tolerance. Neither antiFVIII inhibitory antibodies nor antiFVIII IgGs were observed in 13 of 14 adult mice that received 0.05 U g(-1) body weight of human FVIII intravenously within 24 h after birth and repeated injections as adults. In contrast, high FVIII antibody titers (>50 Bethesda Units mL(-1)) developed in seven of 13 mice injected on day 3 postpartum and in all adult mice not treated neonatally. One of nine mice and three of 17 mice developed high-titer antiFVIII inhibitory antibody when they were treated initially with 2-fold (0.1 U g(-1) body weight) and 10-fold higher doses (0.5 U g(-1) body weight) FVIII on day 0, respectively. A human FVIII-specific T-cell proliferative response was absent in splenocytes from neonatally treated mice. The tolerance was FVIII specific because antitoxoid antibodies developed after immunization with tetanus toxoid. Splenocytes failed to proliferate or produce interferon (IFN)-gamma in response to FVIII stimulation, yet still secreted interleukin-2. A proliferative response was restored with exogenous IFN-gamma or interleukin-12, suggesting that lack of inhibitor to FVIII was due to IFN-gamma-dependent anergy. Thus, exposure on day 0 to physiological levels of FVIII antigen might be important for induction of immune tolerance. This immune tolerance model may provide a basis for new approaches to prevention of FVIII inhibitors during replacement therapy.

Specific detection of human coagulation factor IX in cynomolgus macaques

After screening for species-specific antihuman factor (F)IX monoclonal antibodies, we found that antibody 3A6 did not bind to cynomolgus FIX. The 3A6 epitope was found to include Ala262 of human FIX. The 3A6 antibody was used as a catching antibody in an enzyme immunoassay (EIA) for specific detection of human FIX in cynomolgus macaque plasma. No significant increase of substrate hydrolysis was observed when EIA buffer containing cynomolgus macaque plasma was subjected to the 3A6-based EIA. Addition of up to 30% cynomolgus macaque plasma or canine plasma to the assay did not alter detection of human FIX. Three cynomolgus macaques were injected with human FIX (10 U kg-1; i.v.) and the circulating human FIX was quantified in the macaque plasma. The FIX level in the circulation increased to 470 +/- 37.6 ng mL-1 at 1 h after the injection and gradually decreased to 1.79 +/- 1.1 ng mL-1 by day 5, which is approximately 0.06% of the normal human plasma FIX concentration. These data suggest that the cynomolgus macaque can be used as a primate model for studying hemophilia B gene therapy by transduction of macaque organs with vectors to express human FIX in vivo and detection of human FIX using the 3A6 monoclonal antibody.

Expression of human coagulation factor VIII in adipocytes transduced with the simian immunodeficiency virus agmTYO1-based vector for hemophilia A gene therapy

We demonstrate that transduction of adipocytes with a simian immunodeficiency virus agm TYO1 (SIVagm)-based lentiviral vector carrying the human coagulation factor VIII gene (SIVhFVIII) resulted in expression of the human FVIII transgene in vitro and in db/db mice in vivo. Cultured human adipocytes were transduced with the SIVagm vector carrying the GFP gene in a dose-dependent manner and transduction of adipocytes with SIVhFVIII resulted in efficient expression of human coagulation factor VIII (hFVIII; 320 +/- 39.8 ng/10(6) adipocytes/24 h) in vitro. Based upon successful transduction of adipocytes by SIV vectors carrying the lacZ gene in vivo in mice, the adipose tissue of db/db mice was transduced with SIVhFVIII. There was a transient appearance of human FVIII in mouse plasma (maximum 1.8 ng/ml) on day 11 after the injection. Transcripts of human FVIII transgene and human FVIII antigen also were detected in the adipose tissue by RT-PCR and immunofluorescence, respectively, on day 14. Emergence of anti-human FVIII antibodies 14 days after the injection of SIVhFVIII may explain the disappearance of human FVIII from the circulation. These results suggest that transduction of the adipocytes with vectors carrying the human FVIII gene may be potentially applicable for gene therapy of hemophilia A.

Recombinant adeno-associated virus vector-transduced vascular endothelial cells express the thrombomodulin transgene under the regulation of enhanced plasminogen activator inhibitor-1 promoter

We were able to facilitate plasminogen activator inhibitor 1 (PAI-1) promoter activity approximately by 14-fold using an enhancer element. This enhanced PAI-1 promoter has a strong basal activity, comparable to CAG promoter activity, and has a response similar to the PAI-1 promoter with respect to TGFbeta 1 and TNFalpha stimulation. The characteristics of the enhanced PAI-1 promoter are thought to be suited to timely and tissue-specific expression of anticoagulant molecules in the vascular cells. Thus, we developed recombinant adeno-associated virus (rAAV) vectors using the enhanced PAI-1 promoter and were successful in transducing vascular endothelial cells to express the thrombomodulin transgene under the regulation of the enhanced PAI-1 promoter in vitro. Thromobomodulin transgene expression driven by the enhanced PAI-1 promoter in rAAV vector-transduced cultured endothelial cells was between 600- and 1000-fold higher than constitutive thrombomodulin gene expression in cultured human umbilical vein endothelial cells and was up-regulated by TGFbeta1 and TNFalpha stimulation which may down-regulate endogenous thrombomodulin gene expression in endothelial cells. The brain vascular endothelial cells of Mongolian gerbils could also be transduced by the same rAAV vector in vivo. Transduction of endothelial cells by rAAV vectors to express enhanced PAI-1 promoter-driven transgenes may be a useful gene therapy approach for vascular diseases.

Autoantibody against prothrombin aberrantly alters the proenzyme to facilitate formation of a complex with its physiological inhibitor antithrombin III without thrombin conversion

Acquired coagulation factor inhibitors include pathologic immunoglobulins that specifically bind to coagulation factors and either neutralize their procoagulant activity, accelerate their clearance from the circulation, or have proteolytic activity to degrade them into inactive polypeptides. Here, an autoantibody against prothrombin is described in a patient with serious hemorrhagic diatheses. The autoantibody exerts its influence by a previously unknown mechanism in which it inhibits coagulation through aberrant activation of the proenzyme in a catalytic manner. The antibody-bound prothrombin formed a stable stoichiometric complex with antithrombin III, consisting of intact prothrombin and an antithrombin III molecule cleaved at the (393)Arg-(394)Ser bond. The antibody dissociated from prothrombin after the complex formation with antithrombin III. Although the bound antibody elicited protease activity from prothrombin, the complex was not able to convert fibrinogen to fibrin or to activate protein C. Thus, this is the first description of an autoantibody that induces protease-like activity from a human proenzyme, permitting subsequent neutralization by its physiological inhibitor. (Blood. 2001;97:3783-3789)

A novel strategy for the tumor angiogenesis-targeted gene therapy: generation of angiostatin from endogenous plasminogen by protease gene transfer

When NIH 3T3 fibroblasts were transduced with a retroviral vector containing a cDNA for porcine pancreatic elastase 1 and cultured in the presence of affinity-purified human plasminogen, the exogenously added plasminogen was digested to generate the kringle 1-3 segment known as angiostatin, a potent angiogenesis inhibitor. This was evidenced by immunoblot analysis of the plasminogen digests using a monoclonal antibody specifically reacting with the kringle 1-3 segment, and by efficient inhibition of proliferation of human umbilical vein endothelial cells by the plasminogen digests isolated from the culture medium of 3T3 fibroblasts. However, when Lewis lung carcinoma cells were transduced with the same vector and injected subcutaneously into mice in their back or via the tail vein, their growth at the injection sites or in the lungs was markedly suppressed compared with the growth of similarly treated nontransduced Lewis lung carcinoma cells. Nevertheless, the transduced cells were able to grow as avidly as the control cells in vitro. Assuming that the elastase 1 secreted from the transduced cells is likely to be exempt from rapid inhibition by its physiological inhibitor, alpha1-protease inhibitor, as shown in the inflammatory tissues, the elastase 1 secreted from the tumor cells may effectively digest the plasminogen that is abundantly present in the extravascular spaces and generate the kringle 1-3 segment in the vicinity of implanted tumor cell clusters. Although the selection of more profitable virus vectors and cells to be transduced awaits further studies, such a protease gene transfer strategy may provide us with a new approach to anti-angiogenesis gene therapy for malignant tumors and their metastasis in vivo.

Developmental expression of plasminogen activator inhibitor-1 associated with thrombopoietin-dependent megakaryocytic differentiation

Plasminogen activator inhibitor-1 (PAI-1) is present in the platelet alpha-granule and is released on activation. However, there is some debate as to whether the megakaryocyte and platelet synthesize PAI-1, take it up from plasma, or both. We examined the expression of PAI-1 in differentiating megakaryocytic progenitor cells (UT-7) and in CD34(+)/CD41(-) cells from cord blood. UT-7 cells differentiated with thrombopoietin (TPO) resembled megakaryocytes (UT-7/TPO) with respect to morphology, ploidy, and the expression of glycoprotein IIb-IIIa. PAI-1 messenger RNA (mRNA) expression was upregulated and PAI-1 protein synthesized in the UT-7/TPO cells accumulated in the cytoplasm without being released spontaneously. In contrast, erythropoietin (EPO)-stimulated UT-7 cells (UT-7/EPO) did not express PAI-1 mRNA after stimulation with TPO because they do not have endogenous c-Mpl. After cotransfection with human wild-type c-mpl, the cells (UT-7/EPO-MPL) responded to phorbol 12-myristate 13-acetate (PMA), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) with enhanced PAI-1 mRNA expression within 24 to 48 hours. However, induction of PAI-1 mRNA in UT-7/EPO-MPL cells by TPO required at least 14-days stimulation. UT-7/EPO cells expressing c-Mpl changed their morphology and the other characteristics similar to the UT-7/TPO cells. TPO also differentiated human cord blood CD34(+)/CD41(-) cells to CD34(-)/CD41(+) cells, generated morphologically mature megakaryocytes, and induced the expression of PAI-1 mRNA. These results suggest that both PAI-1 mRNA and de novo PAI-1 protein synthesis is induced after differentiation of immature progenitor cells into megakaryocytes by TPO.

A new type of Ser substitution for gamma Arg-275 in fibrinogen Kamogawa I characterized by impaired fibrin assembly

A new type of substitution, Arg to Ser at gamma275, has been found in a heterozygous dysfibrinogen derived from a 23-year-old woman with no major bleeding or thrombosis. By sequence analyses of the affected gamma-chain and its gene. we found a single amino acid substitution of gamma Arg-275 to Ser in an aberrant gamma (274-302) residue peptide isolated from lysyl endopeptidase-digests of the patient's fibrinogen. In agreement with this amino acid substitution, we identified a single nucleotide exchange of A for C at position 5728 in the gamma-chain gene creating a codon (AGC) encoding Ser instead of the codon (CGC) encoding Arg at position gamma 275. Like two other known types of mutants with a His or Cys substitution at this position, the functional abnormality was characterized by delayed fibrin polymerization, most likely due to impaired abutting of two D domains of adjacent fibrin monomers in the same strand of fibrin protofibrils. The structural derangement that affects the D:D association may not be so severe as compared with those of Cys and His mutants, possessing an additional disulfide-linked Cys molecule and an imidazole ring at the mutation site, respectively.

Structural studies of the interactions of normal and abnormal human plasmins with bovine basic pancreatic trypsin inhibitor

Catalytic activity of human plasmin is inhibited by bovine basic pancreatic trypsin inhibitor (BPTI, also known as aprotinin). In spite of increased interest in the function of BPTI as an inhibitor of plasmin, the 3-D structure of the plasmin-BPTI complex has not yet been determined. Therefore, in the present paper, the structure of the plasmin-BPTI complex was constructed by the homology modeling method, which provided information about the high affinity of plasmin for BPTI. Moreover, normal mode analyses of free plasmin, free BPTI and the plasmin-BPTI complex were carried out to investigate the changes in dynamics following complex formation. After study of the plasmin-BPTI interaction, we also investigated the binding of BPTI with abnormal plasmin, theoretically and experimentally. The result showing that BPTI binds to abnormal plasmin in the same way as it does to normal plasmin supports the previous finding that the difference between normal and abnormal plasmins is very small and that the abnormality is localized to the catalytic site.

Role of the kringle domain in plasminogen activation with staphylokinase

We have evaluated the effect of lysine binding sites in kringle structures on the activation of plasminogen with plasmin and staphylokinase (SAK) complex and on the binding of plasminogen to SAK. Activation of native plasminogen (Glu-plasminogen) by a catalytic amount of plasmin-SAK complex increased in the presence of epsilon-amino-n-caproic acid (EACA) and then decreased with higher concentrations of EACA. By contrast, activation of modified plasminogen (Lys-plasminogen) decreased in an EACA-concentration-dependent manner. This decrease was explained by a more than 10-fold higher Km for activation of Lys-plasminogen with a catalytic amount of plasmin-SAK complex in the presence of EACA. EACA was a competitive inhibitor with Ki 0.23 mM. In addition, the Km for activation of mini-plasminogen, which lacks first four kringle structures (K1+2+3+4), was at least 3.5-fold higher than that for the activation of Lys-plasminogen. Furthermore, EACA showed a negligible inhibitory effect on the activation of mini-plasminogen by the plasmin-SAK complex. We observed a similar biphasic effect of EACA on the binding of Glu-plasminogen to SAK and a dose-dependent effect on the Lys-plasminogen binding to SAK by gel filtration methods. Since EACA binds to plasminogen via lysine binding sites in the kringle structure, we propose that the lysine binding site in K1+2+3+4 domain plays a role in the activation of plasminogen by plasmin SAK complex, and in the binding of plasminogen to SAK.

Fibroblasts spread on immobilized fibrin monomer by mobilizing a beta1-class integrin, together with a vitronectin receptor alphavbeta3 on their surface

Human and murine fibroblasts were found to spread far more avidly on fibrin monomer monolayers than on immobilized fibrinogen, indicating that removal of fibrinopeptides by thrombin is a prerequisite for the fibrin-mediated augmentation of cell spreading. In fact, cell spreading was not efficiently augmented on monolayers of a thrombin-treated dysfibrinogen lacking the release of fibrinopeptide A due to an Aalpha Arg-16 --> Cys substitution. Since a synthetic Arg-Gly-Asp (RGD)-containing peptide inhibited the fibrin-mediated cell spreading, subsequent dissociation of the carboxyl-terminal globular domain of the Aalpha-chains appears to render the RGD segments accessible to the cell-surface integrins. In support of this, fibrin-augmented cell spreading was inhibited by an antibody recognizing a 12-kDa peptide segment with gamma Met-89 at its amino terminus, which is located in close association with the RGD segment at Aalpha 95-97 in the helical coiled-coil interdomainal connector. The fibrin-mediated augmentation of cell spreading was inhibited not only by an antibody against human vitronectin receptor (LM 609) but also by an antibody against the beta1 subunit of integrin (mAb13), suggesting that the beta1-class integrin together with a vitronectin receptor, alphavbeta3, is mobilized onto the surface of fibroblasts upon contact with the fibrin monomer monolayer.

A battery of monoclonal antibodies that induce unique conformations to evolve cryptic but constitutive functions of plasminogen

Two groups of anti-plasminogen monoclonal antibodies, whose epitope was either in the kringle 1 + 2 + 3 domain (F3P2, F11P5, F11P6, and F12P18) or the kringle 5 domain (F1P6 and F12P16), were isolated and their effects on the conformation of plasminogen were explored. All antibodies except F1P6 had 3- to 10-fold higher affinity toward Lys-plasminogen than Glu-plasminogen. F1P6 exhibited a comparable affinity to Glu- and Lys-plasminogen. Among these, only F11P5 binding was inhibited by epsilon-amino-nu-caproic acid (EACA) in a concentration-dependent manner, with half maximal inhibition at 3 mM. From a competition assay, we concluded that the epitopes of F11P5, F11P6, and F12P18 should be very close, and located at or near the low affinity lysine binding site on the kringle 2 + 3. These three antibodies dramatically enhanced the binding of Glu-plasminogen to the other antibodies, except to F1P6. Interestingly, F3P2, whose non-overlapping epitope was in the kringle 2 + 3 domain, also augmented the binding of Glu-plasminogen to the other antibodies. In contrast, we did not observe enhanced binding of Lys-plasminogen to one antibody in the presence of the other antibodies, and the binding of Glu-plasminogen to these antibodies did not increase in the presence of 10 mM EACA. In the presence of these antibodies, including F1P6, Glu-plasminogen bound more efficiently to immobilized degraded fibrin, with a binding profile similar to Lys-plasminogen. All antibodies except F1P6 enhanced the conversion rate of plasminogen to plasmin remarkably. Taken together, we propose that these two groups of monoclonal antibodies can dissociate the intramolecular interactions of Glu-plasminogen and induce the conformational transition of Glu-plasminogen to Lys-plasminogen. In addition, the kringle 2 + 3 and kringle 5 structures of Glu-plasminogen liganded with EACA are distinct from the Lys-plasminogen structure.

Effect of staphylokinase concentration of plasminogen activation

Activation of Glu- and Lys-plasminogen by various concentrations of recombinant staphylokinase (SAK) were studied by the generation of amidolytic activity from the chromogenic substrate S-2251(H-D-Val-Leu-Lys-pNA) and by SDS-PAGE analysis. Surprisingly, excess SAK decreased and fixed the rate of S-2251 hydrolysis in a mixture of Lys-plasminogen and SAK. Since the effect of SAK on S-2251 hydrolysis by plasma was similar, the hydrolysis kinetics by free plasmin and plasmin-SAK complex were studied. Hydrolysis by either enzyme form followed Michaelis-Menten kinetics with a Km of 0.38 mM for plasma and 3.74 mM for SAK-plasmin complex. The catalytic rate constant was 22.7 s-1 for plasmin and 21.0 s-1 for the SAK-plasmin complex. With excess SAK and vigorous removal of plasmin activity from plasminogen, the pre-activation lag period differed greatly between Glu- and Lys-plasminogen. Based on the different substrate specificity of plasmin and plasmin-SAK complex, we analyzed the Glu-plasminogen activation with either catalytic or excess SAK. With excess SAK, almost no Lys-plasminogen was detectable and whole Glu-plasminogen was converted directly to Glu-plasmin, then gradually to Lys-plasmin. In contrast, Lys-plaminogen appeared rapidly with catalytic amount of SAK. These results suggest that inhibition of Glu-plasminogen to Lys-plasminogen to Lys-plasminogen conversion in the plasminogen-SAK complex in the presence of excess SAK prolonged the initial lag phase of activation.