PLATSAK, a potent antithrombotic and fibrinolytic protein, inhibits arterial and venous thrombosis in a baboon model

Thrombogenicity assessment of perfusable tissue engineered constructs: a systematic review

Vascular surgery faces a critical demand for novel vascular grafts that are biocompatible and thromboresistant. This urgency particularly applies to bypass operations involving small caliber vessels. In the realm of tissue engineering, the development of fully vascularized organs holds great promise as a solution to organ shortage for transplantation. To achieve this, it is imperative to (re-)construct a biocompatible and non-thrombogenic vascular network within these organs. In this systematic review, we identify, classify and discuss basic principles and methods used to perform in vitro/ex vivo dynamic thrombogenicity testing of perfusable tissue engineered organs and tissues. We conducted a pre-registered systematic review of studies published in the last 23 years according to PRISMA-P Guidelines, comprising a systematic data extraction, in-depth analysis and risk of bias assessment of 116 included studies. We identified shaking (n=28), flow loop (n=17), ex vivo (arterio-venous shunt, n=33) and dynamic in vitro models (n=38) as main approaches for thrombogenicity assessment. This comprehensive review unveils a prevalent lack of standardization and serves as a valuable guide in the design of standardized experimental setups.

Thrombolytic and anticoagulant effects of a recombinant staphylokinase-hirudin fusion protein

A pure recombinant staphylokinase-hirudin fusion protein (SFH) was obtained by recombinant genetic engineering and purification techniques. The thrombolytic and anticoagulant activities of SFH were investigated using in vitro coagulation models and chromogenic assays. The results showed that intact SFH had targeted thrombolytic activity, and gained anticoagulant activity when cleaved by FXa. In addition, we investigated the pharmacodynamics of SFH in vivo using a variety of animal models, including a rat inferior vena cava thrombosis model, a rat coronary thrombosis model, a rabbit carotid artery thrombosis model and a canine coronary thrombosis model. We found that SFH had an obvious thrombolytic effect and could prevent and reduce re-embolization after thrombolysis and reduce the serious bleeding side effects caused by the combination of thrombolytic and anticoagulant drugs. The results suggest that SFH can be used for thrombolytic therapy in thromboembolic diseases.

Oriented Immobilization on Gold Nanoparticles of a Recombinant Therapeutic Zymogen

Direct immobilization of functional proteins on gold nanoparticles (AuNPs) affects their structure and function. Changes may vary widely and range from strong inhibition to the enhancement of protein function. More often though the outcome of direct protein immobilization results in protein misfolding and the loss of protein activity. Additional complications arise when the protein being immobilized is a zymogen which requires and relies on additional protein-protein interactions to exert its function. Here we describe molecular design of a glutathione-S-transferase-Staphylokinase fusion protein (GST-SAK) and its conjugation to AuNPs. The multivalent AuNP-(GST-SAK)n complexes generated show plasminogen activation activity in vitro. The methods described are transferable and could be adapted for conjugation and functional analysis of other plasminogen activators, thrombolytic preparations or other functional enzymes.

Cloning and purification of an anti-thrombotic, chimeric Staphylokinase in Pichia pastoris

There has been an increasing prevalence of cardiovascular diseases such as myocardial infarction and stroke in modern societies because of multiple lifestyle related issues like sedentariness and obesity, alcohol consumption and many more "life-style"factors. The FDA-approved thrombolytics such as Tissue Plasminogen Activator, Streptokinase etc. are used to lyse the clots in thrombotic disorders such as myocardial infarction, stroke etc. but re-occlusion and bleeding that are co-incident to their clinical usage are not addressed. Hence, there is need to develop thrombolytics having properties like increased fibrin clot specificity and thrombin inhibition capability to prevent re-occlusion. In the present work, a fusion protein construct containing two components i.e. Staphylokinase (SAK) and Epidermal Growth Factor (EGF) 4, 5, 6-like domains of human thrombomodulin (THBD) was expressed in Pichia pastoris after genetic optimization. SAK isolated from Staphylococcus aureus is a fibrin-specific plasminogen activator while EGF 4, 5, 6-like domains are reported to be responsible for imparting thrombin inhibition to human thrombomodulin, and therefore, expected could help prevent re-occlusion in the novel construct - SAK_EGF, which is a 43 kDa protein. After expression, it was purified (approx. 13-fold) using two-step purification protocol involving ion-exchange followed by Gel Filtration Chromatography (GFC). The functional characterization including plasminogen activation and thrombin inhibition showed that both the fusion partners viz. SAK and 4,5,6 EGF-like domains retained their respective activities after fusion, confirming it to be a bio-active construct. Thus, this engineered protein could be clinically promising due to the combinatorial effect of fibrin-specific thrombus lysis and prevention of re-occulusion.

Thrombolytic and Antiplatelet Effects of a Novel Plasminogen Activator from the Venom of Gloydius Brevicaudus Viper

AIM

To investigate the thrombolytic and antiplatelet effects of a novel plasminogen activator from the venom of the Gloydius brevicaudus viper (GBV-PA) in vitro and in vivo.

METHODS

Thrombolytic experiments were performed in rabbit models of ear vein thrombosis and carotid artery thrombosis and in dog model of acute cerebral infarction. Inhibition of thrombus formation was evaluated in rat inferior vena cava thrombosis model and ferric chloride-induced arterial thrombosis. In vitro, we assayed the antithrombotic effect of GBV-PA on rabbit blood clots, euglobulin lysis time (ELT) of rabbit plasma, and ADP-induced platelet aggregation.

RESULTS

GBV-PA intravenous administration significantly reduced vascular recanalization times of rabbit ear veins thrombosis and thrombus weight of rabbit carotid artery thrombosis. The arterial recanalization rates were dose- and time-dependently improved after the administration of GBV-PA in canine acute cerebral infarction model. Thrombus length and weight were significantly reduced by GBV-PA both in rat inferior vena cava and ferric chloride-induced arterial thrombosis models. Thrombus formation in the blood of rabbits that were administered of GBV-PA was also inhibited. GBV-PA radically reduced plasma ELT of the rabbit's blood clots. ADP-induced platelet aggregation was inhibited by GBV-PA in a dose-dependent manner with a half-maximal inhibitory concentration of 19.9 μg/mL.

CONCLUSION

This study demonstrates that GBV-PA is a thrombolytic and antiplatelet agent. It has significant antithrombotic effects on various in vitro and in vivo experimental models of thrombosis. The mechanisms that underline its antithrombotic effects were related to GBV-PA's capabilities of increasing fibrinolytic activity and inhibition of platelet aggregation.

The use of antithrombotic therapies in reducing synthetic small-diameter vascular graft thrombosis

BACKGROUND

Thrombosis of synthetic small-diameter bypass grafts remains a major problem. The aim of this article is to review the antithrombotic strategies that have been used in an attempt to reduce graft thrombogenicity.

METHODS

A PubMed/MEDLINE search was performed using the search terms "vascular graft thrombosis," "small-diameter graft thrombosis," "synthetic graft thrombosis" combined with "antithrombotic," "antiplatelet," "anticoagulant," "Dacron," "PTFE," and "polyurethane."

RESULTS

The majority of studies on antithrombotic therapies have used either in vitro models or in vivo animal experiments. Many of the therapies used in these settings do show antithrombotic efficacy against synthetic graft materials. There is however, a distinct lack of human in vivo studies to further delineate the performance and limitations of therapies displaying good antithrombotic characteristics.

CONCLUSION

Very few antithrombotic therapies have translated into clinical use. More human in vivo studies are required to assess the efficacy and safety of such therapies.

Trombectomia com cateter de Fogarty no tratamento da tromboflebite jugular experimental em eqüinos

Trombose da veia jugular é problema freqüente na medicina eqüina, implicando muitas vezes em conseqüências fatais. O objetivo deste trabalho foi avaliar em eqüinos a aplicabilidade da trombectomia com cateter de Fogarty, técnica rotineiramente empregada pela medicina humana, no restabelecimento da perviedade vascular. Foram utilizados 10 eqüinos divididos em dois grupos de cinco animais, em que se induziu a trombose da veia jugular direita, através do acesso cirúrgico à veia e aplicação de sutura estenosante e injeção de glicose a 50%. No grupo controle avaliou-se a evolução da tromboflebite sem qualquer tipo de intervenção terapêutica. Os animais do grupo tratado foram submetidos à trombectomia com cateter de Fogarty. Foram avaliados os parâmetros clínicos gerais, regionais, ultra-sonográficos e angiográficos, nos momentos pré-indução (M-PRÉ), indução da trombose (MTI) e 10 dias de evolução da trombose (M10). A técnica empregada induziu a tromboflebite, que obstruiu completamente um segmento da veia jugular de todos os animais. Os animais do grupo controle mantiveram os trombos obstruindo totalmente o lume vascular até o final do período de avaliação, sendo que avaliações regionais mostraram principalmente o edema parotídeo e o ingurgitamento vascular, cranial à tromboflebite da veia jugular. O grupo tratado apresentou as veias jugulares pérvias ao final do experimento, confirmadas pelos exames ultra-sonográficos e angiográficos, com remissão total dos sinais clínicos. Concluiu-se que a técnica da trombectomia com cateter de Fogarty foi eficiente na desobstrução da veia jugular submetida à trombose experimental.

Characterization of a novel bifunctional mutant of staphylokinase with platelet-targeted thrombolysis and antiplatelet aggregation activities

Background

Although staphylokianse (SAK) is among the most promising blood dissolving agents, it is far from ideal. It is interesting to hypothesize that the clot lysis efficacy of SAK can be enhanced with direct active platelet binding ability, and at the same time the rethrombosis complication after successful recanalization can be minimized with an antiplatelet aggregation activity. The present study was performed to characterize the functional properties of RGD-SAK, a novel mutant of staphylokinase (SAK).

Results

By using site-directed mutagenesis, an Arg-Gly-Asp (RGD) motif was engineered in the staphylokinase (SAK). This mutant of SAK designated RGD-SAK was expressed, purified and characterized. Biochemical analysis indicated that RGD-SAK maintained the similar structure and the fibrinolytic function of SAK. Measurement of platelet binding activity in vitro demonstrated that RGD-SAK had a much higher affinity with platelets than SAK. In vitro platelet-rich clot lysis assay demonstrated that the engineered mutant outperformed the non-manipulated SAK. The time required for 50% platelet-rich clot lysis and the concentration required to obtain 50% clot lysis (C₅₀) were reduced significantly across different concentrations of RGD-SAK comparing with SAK. Meanwhile, RGD-SAK was found to inhibit ADP-induced platelet aggregation in a concentration-dependent manner while SAK had negligible effect on platelet aggregation.

Conclusion

RGD-SAK possessed the bifunction to target platelet-rich clots and to block platelets aggregation, and thus may serve as a more potential thrombolytic agent with platelet-targeted thrombolytic and antiplatelet aggregation activities in compared with SAK.

Functional properties of a novel mutant of staphylokinase with platelet-targeted fibrinolysis and antiplatelet aggregation activities

The present study was performed to characterize the functional properties of RGD-SAK, a novel mutant of staphylokinase (SAK). Biochemical analysis indicated that RGD-SAK maintained the similar structure and the fibrinolytic function of SAK. Measurement of platelet binding activity in vitro demonstrated that RGD-SAK had a much higher affinity with platelets than SAK. In vitro platelet-rich clot lysis assay demonstrated that the engineered mutant outperformed the non-manipulated SAK. The time required for 50% platelet-rich clot lysis was reduced significantly across different concentrations of RGD-SAK comparing with SAK. Meanwhile, RGD-SAK was found to inhibit ADP-induced platelet aggregation in a concentration-dependent manner while SAK had negligible effect on platelet aggregation. In concordance, further study in a porcine coronary balloon injury model demonstrated the efficacy of RGD-SAK for the lysis of platelet-rich coronary blood clots and for the prevention of reocclusion after thrombolysis. These results suggested that RGD-SAK may serve as a potential thrombolytic agent with platelet-targeted fibrinolysis and antiplatelet aggregation activities.

A new recombinant thrombolytic and antithrombotic agent with higher fibrin affinity--a staphylokinase variant. I. In vitro study

We attempted to construct a new recombinant protein characterized by fibrin-specific properties of plasminogen activation combined with antithrombin and antiplatelet activities. To the C-terminal part of recombinant staphylokinase (r-SAK), which is a promising profibrinolytic agent, we assembled: (i) the Kringle 2 domain (K2) of tissue-type plasminogen activator (t-PA), containing a fibrin-specific binding site, (ii) the RGD sequence (Arg-Gly-Asp) for the prevention of platelet aggregation and (iii) the antithrombotic agent - hirudin. The cDNA for hybrid protein SAK-RGD-K2-Hir was cloned into pESP-3 yeast protein expression vector. The introduction of K2 t-PA, RGD sequence and hirudin into r-SAK molecule did not alter the SAK activity. The plasminogen activation rate (determined by K(M) and K(cat)) of SAK-RGD-K2-Hir was not significantly different from that of r-SAK. Affinity and binding strength of the recombinant protein to fibrin immobilized on the biosensor were higher than to r-SAK. We observed a higher clot lysis potency of SAK-RGD-K2-Hir as evidenced by a faster and more profound lysis of 125I-labeled human fibrin clots. The potency of thrombin inhibition by the hirudin part of the recombinant fusion protein SAK-RGD-K2-Hir was the same as that of r-Hir alone. In conclusion, the results of the in vitro study suggest that the SAK-RGD-K2-Hir construct can be a more potent and faster-acting thrombolytic agent with antithrombin and antiplatelet properties compared with standard r-SAK.

Engineering of a staphylokinase-based fibrinolytic agent with antithrombotic activity and targeting capability toward thrombin-rich fibrin and plasma clots

Current clinically approved thrombolytic agents have significant drawbacks including reocclusion and bleeding complications. To address these problems, a staphylokinase-based thrombolytic agent equipped with antithrombotic activity from hirudin was engineered. Because the N termini for both staphylokinase and hirudin are required for their activities, a Y-shaped molecule is generated using engineered coiled-coil sequences as the heterodimerization domain. This agent, designated HE-SAKK, was produced and assembled from Bacillus subtilis via secretion using an optimized co-cultivation approach. After a simple in vitro treatment to reshuffle the disulfide bonds of hirudin, both staphylokinase and hirudin in HE-SAKK showed biological activities comparable with their parent molecules. This agent was capable of targeting thrombin-rich fibrin clots and inhibiting clot-bound thrombin activity. The time required for lysing 50% of fibrin clot in the absence or presence of fibrinogen was shortened 21 and 30%, respectively, with HE-SAKK in comparison with staphylokinase. In plasma clot studies, the HE-SAKK concentration required to achieve a comparable 50% clot lysis time was at least 12 times less than that of staphylokinase. Therefore, HE-SAKK is a promising thrombolytic agent with the capability to target thrombin-rich fibrin clots and to minimize clot reformation during fibrinolysis.

Fusion proteins with anticoagulant and fibrinolytic properties: functional studies and structural considerations

In an effort to combine the benefits of fibrinolytics, such as staphylokinase, with those of thrombin inhibitors for the prevention of vessel reocclusion after vascular injury, we have produced several chimeric proteins with plasminogen-activating and thrombin-inhibiting properties. Fusion proteins were constructed consisting of the modules staphylokinase (Sak), the factor Xa cleavage site, and various dipetalin (Dip) domains (H(6)-Sak-Dip-I+II, H(6)-Sak-Dip-I, and H(6)-Sak-Dip-II). Sak stimulates fibrinolysis via activation of plasminogen, whereas dipetalin is a two-domain, Kazal-type inhibitor of thrombin. NMR spectroscopy of the fusion proteins revealed that the molecular structures of the modules are retained in the fusion protein and that no significant interactions occur between the modules in terms of their functionally relevant regions. In enzymatic thrombin inhibition tests and blood coagulation assays (thrombin, prothrombin, and activated partial thromboplastin times), no significant differences in anticoagulant capacity were observed between the fusion protein H(6)-Sak-Dip-I+II and isolated Dip-I+II, even at nanomolar concentrations. Similar results (i.e., the inhibition of thrombin-induced platelet aggregation and the inhibition of thrombin-induced vascular relaxation) were obtained when the cellular thrombin effects were studied. The fusion protein containing Dip-I has less but still significant thrombin inhibitory effects compared with those of H(6)-Sak-Dip-I+II. In contrast, the H(6)-Sak-Dip-II protein failed to inhibit thrombin in each of the assays used. The plasminogen-activating and fibrinolytic activities of the fusion proteins are similar to those of wild-type Sak. The individual dipetalin domains do not activate plasminogen. In conclusion, the fusion protein H(6)-Sak-Dip-I+II is a bifunctional molecule able to activate fibrinolysis via plasminogen activation and inhibit blood coagulation via direct inhibition of thrombin.