Diverse origins of fibrinolytic enzymes: A comprehensive review

Fibrinolytic enzymes cleave fibrin which plays a crucial role in thrombus formation which otherwise leads to cardiovascular diseases. While different fibrinolytic enzymes have been purified, only a few have been utilized as clinical and therapeutic agents; hence, the search continues for a fibrinolytic enzyme with high specificity, fewer side effects, and one that can be mass-produced at a lower cost with a higher yield. In this context, this review discusses the physiological mechanism of thrombus formation and fibrinolysis, and current thrombolytic drugs in use. Additionally, an overview of the optimization, production, and purification of fibrinolytic enzymes and the role of Artificial Intelligence (AI) in optimization and the patents granted is provided. This review classifies microbial as well as non-microbial fibrinolytic enzymes isolated from food sources, including fermented foods and non-food sources, highlighting their advantages and disadvantages. Despite holding immense potential for the discovery of novel fibrinolytic enzymes, only a few fermented food sources limited to Asian countries have been studied, necessitating the research on fibrinolytic enzymes from fermented foods of other regions. This review will aid researchers in selecting optimal sources for screening fibrinolytic enzymes and is the first one to provide insights and draw a link between the implication of source selection and in vivo application.

C-terminal lysine residues enhance plasminogen activation by inducing conformational flexibility and stabilization of activator complex of staphylokinase with plasmin

Staphylokinase (SAK), a potent fibrin-specific plasminogen activator secreted by Staphylococcus aureus, carries a pair of lysine at the carboxy-terminus that play a key role in plasminogen activation. The underlaying mechanism by which C-terminal lysins of SAK modulate its function remains unknown. This study has been undertaken to unravel role of C-terminal lysins of SAK in plasminogen activation. While deletion of C-terminal lysins (Lys135, Lys136) drastically impaired plasminogen activation by SAK, addition of lysins enhanced its catalytic activity 2-2.5-fold. Circular dichroism analysis revealed that C-terminally modified mutants of SAK carry significant changes in their beta sheets and secondary structure. Structure models and RING (residue interaction network generation) studies indicated that the deletion of lysins has conferred extensive topological alterations in SAK, disrupting vital interactions at the interface of SAK.plasmin complex, thereby leading significant impairment in its functional activity. In contrast, addition of lysins at the C-terminus enhanced its conformational flexibility, creating a stronger coupling at the interface of SAK.plasmin complex and making it more efficient for plasminogen activation. Taken together, these studies provided new insights on the role of C-terminal lysins in establishment of precise intermolecular interactions of SAK with the plasmin for the optimal function of activator complex.

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.

Programmable antibiotic delivery to combat methicillin-resistant Staphylococcus aureus through precision therapy

The rapid dissemination of life-threatening multidrug-resistant bacterial pathogens calls for the development of new antibacterial agents and alternative strategies. The virulence factor secreted by bacteria plays a crucial role in the sophisticated processes during infections. Inspired by the unique capacity of many bacteria inducing clotting of plasma to initiate colonization, we propose a programmable antibiotic delivery system for precision therapy using methicillin-resistant S. aureus (MRSA) as a model. Coagulase utilized by MRSA to directly cleave fibrinogen into fibrin, is an ideal target not only for tracking bacterial status but for triggering the collapse of fibrinogen functionalized porous microspheres. Subsequently, staphylokinase, another virulence factor of MRSA, catalyzed hydrolysis of fibrin to further release the encapsulated antibiotics from microspheres. Our sequential triggered-release system exhibits high selectivity to distinguish live or dead MRSA from other pathogenic bacteria. Furthermore, such programmable microspheres clear 99% MRSA in 4 h, and show increased efficiency in a wound healing model in rats. Our study provides a programmable drug delivery system to precisely target bacterial pathogens using their intrinsic enzymatic cascades. This programmable platform with reduced selective stress of antibiotics on microbiota sheds light on the potential therapy for future clinical applications.

Construction of a novel Staphylokinase (SAK) mutant with low immunogenicity and its evaluation in rhesus monkey

The heterologous nature of SAK, a thrombolytic drug, elicits high titers of neutralizing antibodies, which limits its clinical use. Here, we aim to establish a SAK mutant with equivalent activity to the wild type but reduced antigenicity, which may allow for multiple injections. Biosun software was used to predict SAK antigenic epitopes, and several main epitopes were modified by gene deletion and mutation. Ten SAK mutants were constructed, and their thrombolytic activity and immunogenicity were analyzed in vitro. SAK6, with a high expression level (45%), similar thrombolytic activity, and lower antibody reaction, was chosen for in vivo analysis in rhesus monkey. In the nearly 8-month experimental period, the antibody level of the SAK6 group was significantly lower than that of the SAK group. Moreover, only 5% of SAK activity was retained, whereas 75.6% of SAK6 activity was retained after incubating with respective antiserum. Overall, these results demonstrated that SAK6, established through comprehensive site-directed mutagenesis program, had identical thrombolytic activity to SAK, low immunogenicity, and less side effects, demonstrating its efficient clinical potential for thrombus disease.

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.

Designing a multifunctional staphylokinase variant (SAK-2RGD-TTI) with appropriate thrombolytic activity in vitro

OBJECTIVE

Thrombin, platelets, and plasmin are three key factors involved in hemostasis and thrombolysis. Thrombolytic therapy with clinically approved drugs is often followed by recurrent thrombosis caused by thrombin-induced platelet aggregation from the clot debris. In order to minimize these problems, new constructs were designed for the expression of recombinant staphylokinase (rSAK) and also a fusion protein composed of staphylokinase, 20 amino acids containing 2 RGD followed by tsetse thrombin Inhibitor (SAK-2RGD-TTI) in Pichia pastoris.

RESULT

Modeling the tertiary structure of SAK-2RGD-TTI showed that the linker containing RGD and TTI did not interfere with proper folding of SAK. In laboratory testing, the purified SAK-2RGD-TTI (420 μg/mL) dissolved an average of 45% of the blood clot. The activity of the SAK-2RGD-TTI was also confirmed in various tests including human plasminogen activation assay, fibrin clot lysis assay, well diffusion method, activated partial thromboplastin time and platelet rich clot lysis assay.

CONCLUSION

Our findings suggest that SAK-2RGD-TTI has improved therapeutic properties preventing reocclussion. It further confirms that it is practicable to assemble and produce a hybrid multifunctional protein that targets hemostatic process at various stages.

Bacterial staphylokinase as a promising third-generation drug in the treatment for vascular occlusion

Vascular occlusion is one of the major causes of mortality and morbidity. Blood vessel blockage can lead to thrombotic complications such as myocardial infarction, stroke, deep venous thrombosis, peripheral occlusive disease, and pulmonary embolism. Thrombolytic therapy currently aims to rectify this through the administration of recombinant tissue plasminogen activator. Research is underway to design an ideal thrombolytic drug with the lowest risk. Despite the potent clot lysis achievable using approved thrombolytic drugs such as alteplase, reteplase, streptokinase, tenecteplase, and some other fibrinolytic agents, there are some drawbacks, such as high production cost, systemic bleeding, intracranial hemorrhage, vessel re-occlusion by platelet-rich and retracted secondary clots, and non-fibrin specificity. In comparison, bacterial staphylokinase, is a new, small-size plasminogen activator, unlike bacterial streptokinase, it hinders the systemic degradation of fibrinogen and reduces the risk of severe hemorrhage. A fibrin-bound plasmin-staphylokinase complex shows high resistance to a₂-antiplasmin-related inhibition. Staphylokinase has the potential to be considered as a promising thrombolytic agent with properties of cost-effective production and the least side effects.

Structural Biology and Protein Engineering of Thrombolytics

Myocardial infarction and ischemic stroke are the most frequent causes of death or disability worldwide. Due to their ability to dissolve blood clots, the thrombolytics are frequently used for their treatment. Improving the effectiveness of thrombolytics for clinical uses is of great interest. The knowledge of the multiple roles of the endogenous thrombolytics and the fibrinolytic system grows continuously. The effects of thrombolytics on the alteration of the nervous system and the regulation of the cell migration offer promising novel uses for treating neurodegenerative disorders or targeting cancer metastasis. However, secondary activities of thrombolytics may lead to life-threatening side-effects such as intracranial bleeding and neurotoxicity. Here we provide a structural biology perspective on various thrombolytic enzymes and their key properties: (i) effectiveness of clot lysis, (ii) affinity and specificity towards fibrin, (iii) biological half-life, (iv) mechanisms of activation/inhibition, and (v) risks of side effects. This information needs to be carefully considered while establishing protein engineering strategies aiming at the development of novel thrombolytics. Current trends and perspectives are discussed, including the screening for novel enzymes and small molecules, the enhancement of fibrin specificity by protein engineering, the suppression of interactions with native receptors, liposomal encapsulation and targeted release, the application of adjuvants, and the development of improved production systems.

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.

Lipid modification of staphylokinase and its implications on stability and activity

Thrombolytic agents are routinely used to dissolve blood clot by activating fibrinolytic system. Among different thrombolytic agents available, staphylokinase (SAK) is gaining much attention because of their fibrin specificity and reduced inhibition by α2 antiplasmin. Though SAK had exhibited less circulatory half life, they are equipotent to tissue plasminogen activator and streptokinase and had shown more potency for clot dissolution during retracted thrombi. In this study, SAK was lipid modified at the N-terminal by a protein engineering approach to enhance its stability and activity. Native SAK as well as the gene encoding SAK with lipobox was cloned into E. coli GJ1158 using pRSET-B expression vector for higher expression. The lipid modification of SAK was confirmed by a mobility shift of 1.3 kDa against the 15.5 kDa of native SAK using tricine SDS-PAGE. Lipid modification of SAK was confirmed by LC MS/MS. The secondary structure analysis was carried out using circular dichroism and deconvoluted fourier transform infrared spectroscopy. LMSAK was found to have a slightly higher denaturation temperature compared to SAK. The improved stablility and activity of lipid modified SAK was studied by heated plasma agar plate assay and mouse tail bleeding test.

Staphylokinase Enzyme: An Overview of Structure, Function and Engineered Forms

BACKGROUND

One of the most important causes of death in the modern lifestyle is acute ischemic stroke, which is related to thrombosis in the blood vessels. Staphylokinase (SAK), a fibrinolytic agent, which is produced mainly by Staphylococcus aureus, is an indirect activator of plasminogen and belongs to the third generation of fibrinolytic enzymes.

METHODS

Considering the very low level of production and immunogenicity concerns of natural SAK produced by Staphylococcus aureus, attempts have been made to produce recombinant SAKs with high production levels, more fibrinolytic activities and low immunogenicity.

RESULTS AND CONCLUSION

In this review, we summarized a number of expression systems based on recombinant DNA technology and protein-engineering approaches, which have been developed for the production of engineered recombinant SAK molecules with higher fibrinolytic activities and lower antigenicity.

Structure-based antigenic epitope and PEGylation improve the efficacy of staphylokinase

Staphylokinase (Sak) holds promise for use in thrombolytic therapy for acute myocardial infarction. However, its immunogenicity is a major disadvantage under clinical conditions. PEGylation has become a sophisticated method to decrease that immunogenicity. In this report, according predicted epitope from the active center, five residues, including Gly79, Leu82, Lys84, Ala97, and Arg104 have been mutant as cysteine for mono PEGylation, respectively. According to the relative immunogenicity of Sak or its PEGylation derivatives, the amount of specific anti-Sak IgG antibodies elicited by PEGylation proteins, including C79G, C82L, C84K, C97A, and C104R in BALB/c mice decreased by approximately 15–75% each. PEGylated Sak derivatives showed a decrease of up to 75% in the immune reactivity in PEG-Sak-C104R. Thrombelastography experiments showed that two PEG-conjugated derivatives, PEG-Sak-C97A (Ly30, 68.14 ± 2.51%) and PEG-Sak-C104R (Ly30, 66.49 ± 5.97%), the LY30 of PEG-Sak-C97A, and PEG-Sak-C104R produced values very similar to those of wild-type Sak. The fibrin plate assays showed the bioactivity of PEG-Sak-C104R to exhibit the most activity approximately as much as urokinase (diameter of halo pattern, 18.6 ± 1.06 mm) and tPA (diameter of halo pattern, 17.2 ± 0.49 mm). The Sak PEGylation derivative PEG-Sak-C104R was also selected for further in vivo activity experimentation. The thrombolytic ability of PEG-Sak-C104R is a little lower than wild-type Sak, whereas, this PEGylated protein retained high activity suitable for thrombolytic therapy. Collectively, with the in vivo and in vitro experiments, the present study suggests that site mutant PEGylation, PEG-Sak-C104R, is a suitable type of PEGylation for clinical applications. Further optimization would help maintain the bioactivity and decrease the immunogenicity of staphylokinase.

Genome comparisons of two Taiwanese community-associated methicillin-resistant Staphylococcus aureus ST59 clones support the multi-origin theory of CA-MRSA

Sequence type (ST) 59 is an epidemic lineage of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Asia. Two ST59 clones are prevalent in Taiwan: the Taiwan clone (TW) causes severe infections, whereas the Asian-Pacific clone (AP) is usually commensal. In this study, we sequenced the genome and transcriptome of the representative strains of these two clones and found their differences to focus on three mobile genetic elements: TW carries SCCmec Type V_T, Panton-Valentine leucocidin (PVL)-encoding prophage ΦSa2, whereas AP carries SCCmec Type IV and staphylokinase (SAK)-encoding prophage ΦSa3. The anti-virulent role of SAK was confirmed using murine skin and bloodstream infection models. ΦSa3 usually integrates into the hlb gene, but in AP was found to be integrated at the genomic island νSaβ. The mutation of the attB site "TGTATCCAAACTGG" to "TGTATCCGAATTGG" led to a failure in the integration of ΦSa3 in hlb, prompting atypical integration at other sites. The sak gene possessed remarkably different patterns of distribution among the different STs of S. aureus. We conclude that the atypical integration of ΦSa3 may help S. aureus adapt to the human host habitat and that the subsequent loss of ΦSa3 contributes toward the development of a virulent CA-MRSA lineage for wider horizontal transmission.

The pharmaceutics from the foreign empire: the molecular pharming of the prokaryotic staphylokinase in Arabidopsis thaliana plants

Here, we present the application of microbiology and biotechnology for the production of recombinant pharmaceutical proteins in plant cells. To the best of our knowledge and belief it is one of few examples of the expression of the prokaryotic staphylokinase (SAK) in the eukaryotic system. Despite the tremendous progress made in the plant biotechnology, most of the heterologous proteins still accumulate to low concentrations in plant tissues. Therefore, the composition of expression cassettes to assure economically feasible level of protein production in plants remains crucial. The aim of our research was obtaining a high concentration of the bacterial anticoagulant factor—staphylokinase, in Arabidopsis thaliana seeds. The coding sequence of staphylokinase was placed under control of the β-phaseolin promoter and cloned between the signal sequence of the seed storage protein 2S2 and the carboxy-terminal KDEL signal sequence. The engineered binary vector pATAG-sak was introduced into Arabidopsis thaliana plants via Agrobacterium tumefaciens-mediated transformation. Analysis of the subsequent generations of Arabidopsis seeds revealed both presence of the sak and nptII transgenes, and the SAK protein. Moreover, a plasminogen activator activity of staphylokinase was observed in the protein extracts from seeds, while such a reaction was not observed in the leaf extracts showing seed-specific activity of the β-phaseolin promoter.

Pseudoaneurysm of Left Ventricle following Staphylococcal Pericarditis in a Child

Formation of pseudo-aneurysm of the left ventricle is a rare entity particularly in the pediatric age group. We report a case of a pseudo-aneurysm of the left ventricle in a 6-year-old boy who initially presented to us with staphylococcus aureus septicemia. The left ventricular pseudo-aneurysm was surgically resected and the boy was discharged in a healthy condition.

Bilobed shape of PadA reveals the connectivity from single to multi-domain bacterial plasminogen activators

The bacterial plasminogen activator, PadA activates bovine, ovine and caprine plasminogen but remains inert toward human plasminogen. It shows high sequence homology with human plasminogen activator, staphylokinase (SAK) but generates active-site in bovine plasminogen non-proteolytically, similar to streptokinase (SK). To examine the structural requirements for the function of this unique cofactor, attempts were made to visualize solution structure of the PadA using small-angle X-ray scattering (SAXS) data and compare its shape profile with structural models based on crystal structures of staphylokinase and streptokinase domains. The bilobal shape solved for the PadA matched closely with the structural model of α-domain of SK rather than its sequence homolog, SAK. The SAXS based solution structure of the PadA exhibited an extra volume and high mobility around Y(90)DKAEK(95) and P(104)ITES(108) loop regions that were found to play a crucial role in its cofactor function. Structure and sequence analysis of bacterial cofactors and mammalian plasminogens displayed evolutionary conservation of crucial complimentary amino acids required for making a functional binary activator complex between bacterial plasminogen activators and their cognate partner plasminogen. These studies highlighted the importance of structure-function related evolutionary strategies adopted by bacteria for exploiting mammalian plasminogen activation system and its understanding may help in designing and the development of new thrombolytic agents for clinical interventions.

Temperature-sensitive liposome-mediated delivery of thrombolytic agents

BACKGROUND

Clinical efficacy of thrombolytic drugs is limited by lack of specific delivery and requires large therapeutic doses which increase toxicity. Encapsulating these drugs in temperature-sensitive liposomes and applying hyperthermia to deliver thrombolytic agents locally to thrombus might theoretically favourably alter the therapeutic window. The objectives of this study were to formulate liposomes encapsulating thrombolytics and assess thrombolytic activity following hyperthermia.

METHODS

Three liposome formulations were investigated: temperature-sensitive liposome (TSL, DPPC:DSPE-PEG2000 (mol% 95:5)), low temperature-sensitive liposome (LTSL, DPPC:MSPC:DSPE-PEG2000 (mol% 85.3:9.7:5)), and traditional temperature-sensitive liposome (TTSL, DPPC:HSPC:Chol:DSPE-PEG2000 (mol% 55:25:15:5)). To characterise temperature-dependent release of high molecular weight cargo from each formulation, fluorescein-conjugated dextrans (70 kDa) were loaded and release was quantified via spectrophotometry. Staphylokinase (SAK), urokinase, and tissue-type plasminogen activator were also loaded individually into each liposome formulation. Leakage at 37 °C and release at 38-44 °C were quantified via chromogenic enzymatic activity assay. Clot lysis was evaluated by measuring mass of blood clots before and after thrombolytic liposome treatment.

RESULTS

The LTSL formulation had optimal release characteristics with maximum release at 41.3 °C. Release of dextrans from LTSLs was observed to be 11.5 ± 1.5%, 79.7 ± 1.6%, and 93.6 ± 3.7% after 15 min in plasma at 37°, 39°, and 41.3 °C, respectively. The SAK LTSL had the highest release/leakage ratio and demonstrated greater clot lysis.

CONCLUSIONS

The SAK LTSL achieves significant clot lysis in vitro. When combined with local hyperthermia, the SAK LTSL potentially produces sufficient thrombolysis while minimising systemic side effects.