Streptokinase—the drug of choice for thrombolytic therapy

Maggot Kinase and Natural Thrombolytic Proteins

Thrombolytic enzymes constitute a class of proteases with antithrombotic functions. Derived from natural products and abundant in nature, certain thrombolytic enzymes, such as urokinase, earthworm kinase, and streptokinase, have been widely used in the clinical treatment of vascular embolic diseases. Fly maggots, characterized by their easy growth and low cost, are a traditional Chinese medicine recorded in the Compendium of Materia Medica. These maggots can also be used as raw material for the extraction and preparation of thrombolytic enzymes (maggot kinase). In this review, we assembled global research reports on natural thrombolytic enzymes through a literature search and reviewed the functions and structures of natural thrombolytic enzymes to provide a reference for natural thrombophilic drug screening and development.

Targeted drug delivery to the thrombus by fusing streptokinase with a fibrin-binding peptide (CREKA): an in silico study

Aim: Streptokinase has poor selectivity and provokes the immune response. In this study, we used in silico studies to design a fusion protein to achieve targeted delivery to the thrombus. Materials & methods: Streptokinase was analyzed computationally for mapping. The fusion protein modeling and quality assessment were carried out on several servers. The enzymatic activity and the stability of the fusion protein and its complex with plasminogen were assessed through molecular docking analysis and molecular dynamics simulation respectively. Results: Physicochemical properties analysis, protein quality assessments, protein-protein docking and molecular dynamics simulations predicted that the designed fusion protein is functionally active. Conclusion: Our results showed that this fusion protein might be a prospective candidate as a novel thrombolytic agent with better selectivity.

Antarctic Krill Oil from Euphausia superba Ameliorates Carrageenan-Induced Thrombosis in a Mouse Model

FJH-KO obtained from Antarctic krill, especially Euphausia superba, has been reported to contain high amounts of omega-3 polyunsaturated fatty acids (n-3 PUFA) and to exhibit anticancer and anti-inflammatory properties. However, its antithrombotic effects have not yet been reported. This study aimed to investigate the antithrombotic effects of FJH-KO in carrageenan-induced thrombosis mouse models and human endothelial cells. Thrombosis was induced by carrageenan injection, whereas the mice received FJH-KO pretreatment. FJH-KO attenuated carrageenan-induced thrombus formation in mouse tissue vessels and prolonged tail bleeding. The inhibitory effect of FJH-KO was associated with decreased plasma levels of thromboxane B2, P-selectin, endothelin-1, β-thromboglobulin, platelet factor 4, serotonin, TNF-α, IL-1β, and IL-6. Meanwhile, FJH-KO induced plasma levels of prostacyclin I2 and plasminogen. In vitro, FJH-KO decreased the adhesion of THP-1 monocytes to human endothelial cells stimulated by TNF-α via eNOS activation and NO production. Furthermore, FJH-KO inhibited the expression of TNF-α-induced adhesion molecules such as ICAM-1 and VCAM-1 by suppressing the NF-κB signaling pathway. Taken together, our study demonstrates that FJH-KO protects against carrageenan-induced thrombosis by regulating endothelial cell activation and has potential as an antithrombotic agent.

Efficiency of targeted delivery of streptokinase based on fibrin-specific liposomes in the in vivo experiment

Acute thrombosis has a narrow therapeutic window and remains the leading cause of morbidity and mortality, while thrombolytic therapy has limited efficacy and risk of side effects. We have developed and investigated new fibrin-specific systems for local drug delivery to increase efficiency while minimizing the side effects of streptokinase. The experiment was carried out on dogs with 2-h thrombi in the femoral artery received intravenous injections of streptokinase, liposome-bound and free streptokinase at 40/60% ratio, and immunoliposomes. The completeness of the vessel lumen restoration affected by the thrombus, and the risks of side effects were assessed. Fibrinolytic parameters (plasminogen, fibrinogen, alpha2-antiplasmin, and D-dimers levels) were measured at several time points after thrombus induction and the administration of the drug. There was a strong activation of fibrinolysis and consumption of fibrinolysis inhibitors after therapy with all liposomal forms of streptokinase. According to the ultrasound data, immunoliposomal form of streptokinase significantly reduces the degree of residual stenosis to 32% [30.5; 33.7] in 180 min after injection. The high fibrinolytic effect of liposomal forms of streptokinase is not accompanied by a sharp drop in the fibrinogen concentration in the blood compared to the native streptokinase by 60 min. The morphometric evaluation of the artery samples showed that immunoliposomal form of streptokinase induces a significant increase in the degree of free vascular lumen compared to the native streptokinase (71.3% (62.7; 77.5) vs. 47.7% (39.6; 55.7), p < 0.001). Thus, the study shows the efficacy of streptokinase-induced thrombolysis using immunoliposomal form of drug delivery system. Mechanism of action of the immunoliposomal delivery system.

Use of thrombolytic agents to treat neonatal thrombosis in clinical practice

Among children, neonates have the highest incidence of thrombosis. Thrombolytic agents are used for the management of life and/or organ-threatening thrombosis. Literature on the efficacy and safety of thrombolytic agents in neonates is limited. We reviewed the evidence on dosing, administration, monitoring and treatment duration of tissue plasminogen activator (tPA), streptokinase and urokinase (URK) in neonates (≤ 28days). A systematic literature search was conducted of current databases from inception until 31 March 2021. The initial search yielded 6881 articles and 18 were retained for review. tPA, streptokinase and URK was utilized in 12, seven and four studies on 115, 51 and 16 patients, respectively. The dose range for tPA, streptokinase and URK was 0.01 -0.6 mg/kg/h, 50-2000 and 1000-0 000 units/kg/h, respectively, and treatment duration ranged from 30 min to 30 days. This is the first study to objectively summarize the efficacy and safety of thrombolytic agents in neonates. Overall, thrombolysis was associated with 87.9% complete or partial thrombus resolution and 7.4% recurrence risk. The bleeding risk associated with thrombolytic agents was 23.1% on pooled analysis, which is higher than other anticoagulants. Larger prospective studies are required to determine effective dosing regimens of these therapeutic drugs and further clarify their efficacy and safety. Blood Coagul Fibrinolysis 33:000-000 Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.

Thrombolytic Agents: Nanocarriers in Targeted Release

A thrombus, known as a blood clot, may form within the vascular system of the body and impede blood flow. Thrombosis is the most common underlying pathology of cardiovascular diseases, contributing to high morbidity and mortality. However, the main thrombolytic drugs (urokinase, streptokinase, etc.) have shortcomings, including a short half-life, serious side effects and a lack of targeting, that limit their clinical application. The use of nano-drug delivery systems is expected to address these problems and a variety of approaches, including biological and physical responsive systems, have been explored. In this report, recent advances in the development of targeted nano-drug delivery systems are thoroughly reviewed.

Leonurine Ameliorates Oxidative Stress and Insufficient Angiogenesis by Regulating the PI3K/Akt-eNOS Signaling Pathway in H2O2-Induced HUVECs

Thrombus is considered to be the pathological source of morbidity and mortality of cardiovascular disease and thrombotic complications, while oxidative stress is regarded as an important factor in vascular endothelial injury and thrombus formation. Therefore, antioxidative stress and maintaining the normal function of vascular endothelial cells are greatly significant in regulating vascular tension and maintaining a nonthrombotic environment. Leonurine (LEO) is a unique alkaloid isolated from Leonurus japonicus Houtt (a traditional Chinese medicine (TCM)), which has shown a good effect on promoting blood circulation and removing blood stasis. In this study, we explored the protective effect and action mechanism of LEO on human umbilical vein endothelial cells (HUVECs) after damage by hydrogen peroxide (H₂O₂). The protective effects of LEO on H₂O₂-induced HUVECs were determined by measuring the cell viability, cell migration, tube formation, and oxidative biomarkers. The underlying mechanism of antioxidation of LEO was investigated by RT-qPCR and western blotting. Our results showed that LEO treatment promoted cell viability; remarkably downregulated the intracellular generation of reactive oxygen species (ROS), malondialdehyde (MDA) production, and lactate dehydrogenase (LDH); and upregulated the nitric oxide (NO) and superoxide dismutase (SOD) activity in H₂O₂-induced HUVECs. At the same time, LEO treatment significantly promoted the phosphorylation level of angiogenic protein PI3K, Akt, and eNOS and the expression level of survival factor Bcl2 and decreased the expression level of death factor Bax and caspase3. In conclusion, our findings suggested that LEO can ameliorate the oxidative stress damage and insufficient angiogenesis of HUVECs induced by H₂O₂ through activating the PI3K/Akt-eNOS signaling pathway.

Purification and Characterization of a Thrombolytic Enzyme Produced by a New Strain of Bacillus subtil

Fibrinolytic enzymes with a direct mechanism of action and safer properties are currently requested for thrombolytic therapy. This paper reports on a new enzyme capable of degrading blood clots directly without impairing blood coagulation. This enzyme is also non-cytotoxic and constitutes an alternative to other thrombolytic enzymes known to cause undesired side effects. Twenty-four Bacillus isolates were screened for production of fibrinolytic enzymes using a fibrin agar plate. Based on produced activity, isolate S127e was selected and identified as B. subtilis using the 16S rDNA gene sequence. This strain is of biotechnological interest for producing high fibrinolytic yield and consequently has potential in the industrial field. The purified fibrinolytic enzyme has a molecular mass of 27.3 kDa, a predicted pI of 6.6, and a maximal affinity for Ala-Ala-Pro-Phe. This enzyme was almost completely inhibited by chymostatin with optimal activity at 48°C and pH 7. Specific subtilisin features were found in the gene sequence, indicating that this enzyme belongs to the BPN group of the S8 subtilisin family and was assigned as AprE127. This subtilisin increased thromboplastin time by 3.7% (37.6 to 39 s) and prothrombin time by 3.2% (12.6 to 13 s), both within normal ranges. In a whole blood euglobulin assay, this enzyme did not impair coagulation but reduced lysis time significantly. Moreover, in an in vitro assay, AprE127 completely dissolved a thrombus of about 1 cc within 50 min and, in vivo, reduced a thrombus prompted in a rat tail by 11.4% in 24 h compared to non-treated animals.

A critical review on marine serine protease and its inhibitors: A new wave of drugs?

Marine organisms are rich sources of enzymes and their inhibitors having enormous therapeutic potential. Among different proteolytic enzymes, serine proteases, which can be obtained from various marine organisms show a potential to biomedical application as thrombolytic agents. Although this type of proteases plays a crucial role in almost all biological processes, their uncontrolled activity often leads to several diseases. Accordingly, the actions of these types of proteases are regulated by serine protease inhibitors (SPIs). Marine SPIs control complement activation and various other physiological functions, such as inflammation, immune function, fibrinolysis, blood clotting, and cancer metastasis. This review highlights the potential use of serine proteases and their inhibitors as the new wave of promising drugs.

Streptokinase: An Efficient Enzyme in Cardiac Medicine

An imbalance in oxygen supply to cardiac tissues or formation of thrombus leads to deleterious results like pulmonary embolism, coronary heart disease and acute cardiac failure. The formation of thrombus requires clinical encounter with fibrinolytic agents including streptokinase, urokinase or tissue plasminogen activator. Irrespective to urokinase and tissue plasminogen activator, streptokinase is still a significant agent in treatment of cardiovascular diseases. Streptokinase, being so economical, has an important value in treating cardiac diseases in developing countries. This review paper will provide the maximum information to enlighten all the pros and cons of streptokinase up till now. It has been concluded that recent advances in structural/synthetic biology improved SK with enhanced half-life and least antigenicity. Such enzyme preparations would be the best thrombolytic agents.

Plasma metabonomics and proteomics studies on the anti-thrombosis mechanism of aspirin eugenol ester in rat tail thrombosis model

Aspirin eugenol eater (AEE), a new drug compound, was synthesized through the combination of aspirin and eugenol. Antithrombotic effects of AEE have been confirmed in carrageenan-induced rat tail thrombosis model. However, its mechanism is unclear. With the application of integrated approach combining proteomics and metabolomics, the profilings of protein and metabolite in plasma were examined in thrombosis rat pretreated with AEE, aspirin and eugenol, respectively. A clear separation of the plasma metabolic profiles from different groups was found in score plots. 15 metabolites related with the metabolism of fatty acid, energy and amino acid were found. A total of 144, 38, 41 and 54 differentially abundant proteins (DAPs) were identified in control, AEE, aspirin and eugenol group, respectively. Proteomic results showed that aspirin modulated 7 proteins in amino acid metabolism and 4 proteins in complement system; eugenol regulated the 8 proteins related with coagulation cascades and fibrinogen; AEE improved 3 proteins in TCA cycle and 3 in lipid metabolism. Integrated analysis suggested that AEE improved fatty acid, energy and lipid metabolism to against thrombosis. Results of this study indicated AEE had different action mechanism on thrombosis from aspirin and eugenol, and contribute to understanding the mechanisms of AEE on thrombosis. SIGNIFICANCE: Thrombosis is a threat to human health, and there is an urgent need for new drug. In this study, compared with the model group, plasma metabolic profiles in AEE-treated rats were clearly separated; 15 metabolites and 38 proteins were picked out. These metabolites and proteins may assist in understanding the action mechanism of AEE on thrombosis. The results of plasma metabonomics and proteomics also revealed the different action mechanism among AEE, aspirin and eugenol on thrombosis. This study established the foundation to further evaluate the druggability of AEE on thrombosis treatment.

LongShengZhi Capsule reduces carrageenan-induced thrombosis by reducing activation of platelets and endothelial cells

Formation of thrombosis is associated with activation of platelets and endothelial cells. The effect of LongShengZhi Capsule (LSZ), a traditional Chinese medicine used for treatment of vascular diseases, on thrombosis was investigated in this study. BALB/c mice were induced thrombosis by injection of carrageenan while receiving pre or simultaneous LSZ treatment. We also compared the therapeutic effects of LSZ and clopidogrel on formed thrombi. LSZ inhibited carrageenan-induced thrombi in mouse tissue vessels. In addition, LSZ but not clopidogrel reduced formed thrombi with a short time window. The reduction of thrombi by LSZ was associated with reduced serum P-selectin, reduced expression of TNF-α and P-selectin and activated matrix metalloproteinase 2 expression in tissues. In vitro, LSZ decreased thrombin-induced human platelet clot retraction which was associated with inactivation of AKT and ERK1/2. LSZ also reduced adhesion of platelets or THP-1 monocytes to human umbilical vein endothelial cells (HUVECs) induced by oxidized low-density lipoprotein or lipopolysaccharide. The anti-adherent actions of LSZ was attributed to reduction of oxidative stress, expression of platelet receptors (P2Y₁₂, PAR4 and CD36) and AKT activity in platelets. LSZ also reduced adhesion molecules or tissue factor but activated tissue factor pathway inhibitor expression in HUVECs. Taken together, our study demonstrates the antithrombotic properties of LSZ by reducing activation of platelets and endothelial cells, and suggests its potential application in clinics.

In-vitro assessment of the thrombolytic efficacy of therapeutic ultrasound

BACKGROUND

Ultrasound is mainly used as a diagnostic tool. Several studies demonstrated that therapeutic ultrasound (TUS) can enhance thrombolysis, but the optimal mechanical parameters to achieve this biological effect are still unknown.

METHODS

We assembled 46 blood clots in a closed in-vitro circulatory model. Clots were randomly divided into 7 groups, control group and six TUS groups of three frequencies (0.3, 0.5, 0.7 MHz) and six intensities (0.75, 1.5, 3, 237.7, 475, 950 W/cm²). Treatment was composed of 12 repetitions, 5 min US application and 3 min pause, lasting 93 min in total. Clots' weight and flow rate were measured before and after the treatment.

RESULTS

Mean initial clot weight (0.318 ± 0.129 g) and flow (0.53 ± 0.31 ml/min) were comparable among the experimental groups. We found a final clot weights reduction (0.15 ± 0.05, 0.16 ± 0.06, 0.09 ± 0.07, 0.21 ± 0.09, 0.17 ± 0.09, 0.17 ± 0.07 and 0.18 ± 0.02 g in groups 1 through 6, respectively) and a flow increase (30.61 ± 19.76, 52.1 ± 25.44, 28.78 ± 8.15, 43.93 ± 20.03, 40.86 ± 18.25 and 45.10 ± 22.20 ml/min in groups 1-6, respectively) in all TUS groups. Clot weight change (%) and flow increase reveals that the TUS profile f = 0.5 MHz I = 1.5 W/cm² was most efficacious. In the control group, clot weight change was +6.3% of baseline and flow increase of 4.4% of baseline, whereas -75.4% of baseline and 209.3% of baseline in the f = 0.5 MHz I = 1.5 W/cm² profile were noted, respectively.

CONCLUSIONS

Our study proved that TUS at low frequency (0.5 MHz) is most effective, whereas changing the intensity of TUS has only a minor effect on clot lysis magnitude.

Liposomes for the delivery of streptokinase

Streptokinase is an efficient thrombolytic agent used to treat thromboembolic disorders. Conventional streptokinase formulations have limited thrombolytic activity and several shortcomings because of their immunogenicity and dose-related side effects including short half-life, lack of tissue targeting and peripheral bleeding. Different liposomal formulations have been explored by researchers in order to improve thrombolytic activity of streptokinase. Liposomal formulations could improve plasma stability, retain drug for longer periods of time in the circulation and promote selective delivery to the thrombus. Side effects of conventional streptokinase formulations, such as immunogenicity and hemorrhage, can also be reduced by using liposomal carriers. In vivo therapeutic efficacy of the liposomal streptokinase has been demonstrated well in animal models. In the present review, we will discuss the potential of different liposomal carriers to improve thrombolytic efficacy of streptokinase.

Elongated Plant Virus-Based Nanoparticles for Enhanced Delivery of Thrombolytic Therapies

Thrombotic cardiovascular disease, including acute myocardial infarction, ischemic stroke, and venous thromboembolic disease, is the leading cause of morbidity and mortality worldwide. While reperfusion therapy with thrombolytic agents reduces mortality from acute myocardial infarction and disability from stroke, thrombolysis is generally less effective than mechanical reperfusion and is associated with fatal intracerebral hemorrhage in up to 2-5% of patients. To address these limitations, we propose the tobacco mosaic virus (TMV)-based platform technology for targeted delivery of thrombolytic therapies. TMV is a plant virus-based nanoparticle with a high aspect ratio shape measuring 300 × 18 nm. These soft matter nanorods have favorable flow and margination properties allowing the targeting of the diseased vessel wall. We have previously shown that TMV homes to thrombi in a photochemical mouse model of arterial thrombosis. Here we report the synthesis of TMV conjugates loaded with streptokinase (STK). Various TMV-STK formulations were produced through bioconjugation of STK to TMV via intervening PEG linkers. TMV-STK was characterized using SDS-PAGE and Western blot, transmission electron microscopy, cryo-electron microscopy, and cryo-electron tomography. We investigated the thrombolytic activity of TMV-STK in vitro using static phantom clots, and in a physiologically relevant hydrodynamic model of shear-induced thrombosis. Our findings demonstrate that conjugation of STK to the TMV surface does not compromise the activity of STK. Moreover, the nanoparticle conjugate significantly enhances thrombolysis under flow conditions, which can likely be attributed to TMV's shape-mediated flow properties resulting in enhanced thrombus accumulation and dissolution. Together, these data suggest TMV to be a promising platform for the delivery of thrombolytics to enhance clot localization and potentially minimize bleeding risk.

Analysis of streptokinase by validated liquid chromatography methods and correlation with an in vitro bioassay

Reversed-phase and size-exclusion liquid chromatography methods were validated for the assessment of streptokinase. The reversed-phase method was carried out on a Jupiter C₄ column (250 mm × 4.6 mm id) maintained at 25°C. The mobile phase consisted of 50 mM sodium sulfate solution pH 7.0 and methanol (90:10, v/v), run isocratically at a flow rate of 0.8 mL/min. The size-exclusion method was carried out on a Protein KW 802.5 column (300 mm × 8.0 mm id), at 25°C. The mobile phase consisted of 40 mM sodium acetate solution pH 7.0, run isocratically at a flow rate of 1.0 mL/min. Retention times were 19.3 min, and 14.1 min, and calibration curves were linear over the concentration range of 0.25-250 μg/mL (25.75-25 750 IU/mL) (r² = 0.9997) and 5-80 μg/mL (515-8240 IU/mL) (r² = 0.9996), respectively, for reversed-phase and size exclusion, with detection at 220 and 204 nm. Chromatographic methods were employed in conjunction with the in vitro bioassay for the content/potency assessment of Streptokinase, contributing to improve the quality control and ensure the efficacy of the biotherapeutic.

The evolution of recombinant thrombolytics: Current status and future directions

Cardiovascular disorders are on the rise worldwide due to alcohol abuse, obesity, hypertension, raised blood lipids, diabetes and age-related risks. The use of classical antiplatelet and anticoagulant therapies combined with surgical intervention helped to clear blood clots during the inceptive years. However, the discovery of streptokinase and urokinase ushered the way of using these enzymes as thrombolytic agents to degrade the fibrin network with an issue of systemic hemorrhage. The development of second generation plasminogen activators like anistreplase and tissue plasminogen activator partially controlled this problem. The third generation molecules, majorly t-PA variants, showed desirable properties of improved stability, safety and efficacy with enhanced fibrin specificity. Plasmin variants are produced as direct fibrinolytic agents as a futuristic approach with targeted delivery of these drugs using liposome technlogy. The novel molecules from microbial, plant and animal origin present the future of direct thrombolytics due to their safety and ease of administration.

Understanding the immunogenicity and antigenicity of nanomaterials: Past, present and future

Nanoparticle immunogenicity and antigenicity have been under investigation for many years. During the past decade, significant progress has been made in understanding what makes a nanoparticle immunogenic, how immune cells respond to nanoparticles, what consequences of nanoparticle-specific antibody formation exist and how they challenge the application of nanoparticles for drug delivery. Moreover, it has been recognized that accidental contamination of therapeutic protein formulations with nanosized particulate materials may contribute to the immunogenicity of this type of biotechnology products. While the immunological properties of engineered nanomaterials and their application as vaccine carriers and adjuvants have been given substantial consideration in the current literature, little attention has been paid to nanoparticle immuno- and antigenicity. To fill in this gap, we herein provide an overview of this subject to highlight the current state of the field, review past and present research, and discuss future research directions.

Streptococcus agalactiae mural infective endocarditis in a structurally normal heart

A 38-year-old Caucasian man with uncontrolled diabetes mellitus type 2 was admitted with a 1-week duration of fevers, chills, and a non-productive cough. He had a left ischiorectal abscess 1 month prior to admission. Physical examination revealed caries on a left upper molar and a well-healed scar on the left buttock, but no heart murmur or evidence of micro-emboli. Blood cultures grew Streptococcus agalactiae. A transesophageal echocardiogram revealed a mobile mass in the right ventricle that attached to chordae tendineae without valvular disease or dysfunction. A computed tomography (CT) with contrast revealed the mass within the right ventricle, a left lung cavitary lesion, and a splenic infarction. He was initially treated with penicillin G for a week. Subsequently, ceftriaxone was continued for a total of 8 weeks. A follow-up CT showed no evidence of right ventricular mass 8 weeks after discharge. This is the first reported case of S. agalactiae mural infective endocarditis in a structurally normal heart.

An In Vitro Thrombolysis Study Using a Mixture of Fast-Acting and Slower Release Microspheres

PURPOSE

To test the hypothesis that a mixture combining fast and slower release rate microspheres can restore blood flow rapidly and prevent formation of another blockage in thrombolysis.

METHODS

We used polyethylene glycol (PEG) microspheres which provide the release of the encapsulated streptokinase (SK) on the scale of minutes, and Eudragit FS30D (Eud), a polymethacrylate polymer, for development of delayed release microspheres which were desirable to prevent a putative second thrombus. Eud microspheres were coated with chitosan (CS) to further extend half-life. Experiments included the development, characterization of Eud/SK and CS-Eud/SK microspheres, and in vitro thrombolytic studies of the mixtures of PEG/SK and Eud /SK microspheres and of PEG/SK and CS-Eud/SK microspheres.

RESULTS

CS-Eud/SK microspheres have slightly lower encapsulation efficiency, reduced activity of SK, and a much slower release of SK when compared with microspheres of Eud/SK microspheres. Counter-intuitively, slower release leads to faster thrombolysis after reocclusion as a result of greater retention of agent and the mechanism of distributed intraclot thrombolysis.

CONCLUSIONS

A mixture of PEG/SK and CS-Eud/SK microspheres could break up the blood clot rapidly while providing clot-lytic efficacy in prevention of a second blockage up to 4 h.

A fibrinolytic protease AfeE from Streptomyces sp. CC5, with potent thrombolytic activity in a mouse model

Fibrinolytic proteases have potential applications in cardiovascular disease therapy. A novel fibrinolytic protease, AfeE, with strong thrombolytic activity was purified from Streptomyces sp. CC5. AfeE displayed maximum activity at 40°C in the pH range of 7.0-12.0. It was strongly inhibited by serine protease inhibitor phenylmethanesulfonylfluoride, soybean trypsin inhibitor, tosyl-l-lysine chloromethyl ketone and tosyl-l-phenylalanine chloromethyl ketone. The activity of the enzyme was partially inhibited by Cu(2+), Co(2+) and Zn(2+). AfeE exhibited higher substrate specificity for fibrin than fibrinogen, which has rarely been reported in fibrinolytic enzymes. AfeE also showed high thrombolytic activity in a carrageenan-induced mouse tail thrombosis model. AfeE prolonged prothrombin time, activated partial thromboplastin time, and thrombin time in rat blood. A bleeding time assay revealed that AfeE did not prolong bleeding time in mice at a dose of 1mg/kg. No acute cytotoxicity was observed for AfeE at 320μg/well in human umbilical vein endothelial cells. The afeE gene was cloned from the genome of Streptomyces sp. CC5. Full-length AFE-CC5E contained 434 amino acids and was processed into a mature form consisting 284 amino acids by posttranslational modification, as revealed by high-resolution mass spectrometry analysis. These results indicate that AfeE is a prospective candidate for antithrombotic drug development.

Nanomedicine as a strategy to fight thrombotic diseases

This review highlights the preclinical and clinical research based on the use of nano- and micro-carriers in thrombolytic drug delivery. Ischemic heart and stroke caused by thrombosis are the main causes of death in the world. Because of their inactivation in the blood, high doses of thrombolytics are administered to patients, increasing the risk of intracranial hemorrhage. Preclinical research conducted with lipid, polymer or magnetic nanoparticles loaded with thrombolytic drugs showed an enhancement of thrombolysis and a reduction of undesirable side effects. Targeted nanocarriers exhibited an increased accumulation into clot. Clinical trials were already conducted with lipid-based microbubbles combined with ultrasound and thrombolytic drug and showed thrombolysis improvement. Future validation of nanosystems is awaited in clinic. This research opens new strategies for the management of thrombotic diseases.

To dissolve a thrombus, thrombolytic drugs are administered, but they are rapidly inactivated in the blood. High amounts are thus injected to patients with the risk to develop intracranial hemorrhages. Nanocarriers and microbubbles have been tested in preclinical models to deliver thrombolytic drugs. These systems have the advantage to protect the drug from the degradation. In clinical trials, galactose and lipid-based microbubbles associated to ultrasound and thrombolytic drugs showed an enhancement of thrombolysis. Other systems are also expected with new drugs combined or not with endovascular intervention to treat ischemic heart or stroke.

Cytotoxicity of chitosan/streptokinase nanoparticles as a function of size: An artificial neural networks study

Predicting the size and toxicity of chitosan/streptokinase nanoparticles at various values of processing parameters was the aim of this study. For the first time, a comprehensive model could be developed to determine the cytotoxicity of the nanoparticles as a function of their size. Then, artificial neural networks were used for identifying main factors influencing self-assembly prepared nanoparticles size and cytotoxicity. Three variables included polymer concentration; pH and stirring time were used for a modeling study. A second modeling was performed to evaluate the influence of particles' size on toxicity. Experimentally data modeled using ANNs was validated against unseen data. The response surfaces generated from the software demonstrated that chitosan concentration is the dominant factor with a direct effect on size. Results also showed that the most important factor in determining the particles' toxicity is size--smaller particles showed more toxic effects, regardless of the effect of other input parameters. From the Clinical Editor: The understanding of toxicity of nanoparticles is of prime importance. In this article, the authors generated a model to visualize the relationship between nanoparticle size and its cellular toxicity, using chitosan/streptokinase nanoparticles. The data generated here would help the design of future nanoparticles of appropriate sizes for the application in the clinical setting.

Shaping bio-inspired nanotechnologies to target thrombosis for dual optical-magnetic resonance imaging

Arterial and venous thrombosis are among the most common causes of death and hospitalization worldwide. Nanotechnology approaches hold great promise for molecular imaging and diagnosis as well as tissue-targeted delivery of therapeutics. In this study, we developed and investigated bioengineered nanoprobes for identifying thrombus formation; the design parameters of nanoparticle shape and surface chemistry, i.e. incorporation of fibrin-binding peptides CREKA and GPRPP, were investigated. Two nanoparticle platforms based on plant viruses were studied - icosahedral cowpea mosaic virus (CPMV) and elongated rod-shaped tobacco mosaic virus (TMV). These particles were loaded to carry contrast agents for dual-modality magnetic resonance (MR) and optical imaging, and both modalities demonstrated specificity of fibrin binding in vitro with the presence of targeting peptides. Preclinical studies in a carotid artery photochemical injury model of thrombosis confirmed thrombus homing of the nanoprobes, with the elongated TMV rods exhibiting significantly greater attachment to thrombi than icosahedral (sphere-like) CPMV. While in vitro studies confirmed fibrin-specificity conferred by the peptide ligands, in vivo studies indicated the nanoparticle shape had the greatest contribution toward thrombus targeting, with no significant contribution from either targeting ligand. These results demonstrate that nanoparticle shape plays a critical role in particle deposition at the site of vascular injury. Shaping nanotechnologies opens the door for the development of novel targeted diagnostic and therapeutic strategies (i.e., theranostics) for arterial and venous thrombosis.

Antiplatelet and antithrombotic activity of a fibrin(ogen)olytic protease from Bacillus cereus strain FF01

Fibrin(ogen)olytic enzymes offer great promise for the treatment of thrombosis associated disorders. The present study describes the characterization of an extracellular fibrin(ogen)olytic serine protease (named Bacethrombase) purified from the Bacillus cereus strain FF01. The molecular mass of the Bacethrombase was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and matrix assisted laser desorption/ionization-time-of-flight-mass spectroscopy analyses at 39.5 kDa and 38,450.51 Da, respectively. The peptide mass fingerprinting and analyses of the composition of the amino acids revealed the similarity of the Bacethrombase to the bacterial serine proteases. The secondary structure of the Bacethrombase was composed of 14% helix, 6.6% beta-sheet, and 79.4% random coil. Bacethrombase was found to contain 48% sialic acid and it preferentially degraded the Aα-chain of fibrinogen, as well as fibrin. The anticoagulant potency of the Bacethrombase was comparable with that of warfarin and heparin, and was corroborated by its fibrinogenolytic activity rather than the inhibition of thrombin, prothrombin or FXa. Bacethrombase demonstrated antiplatelet activity, and dose-dependently inhibited the ADP-induced platelet aggregation. Bacethrombase (10 mg/kg) did not show toxicity after i.v. administration in Wistar rats; however, it revealed an in vivo anticoagulant effect and significantly inhibited the carrageenan-induced in vivo thrombus formation in rats.

Effects of organic extracts and their different fractions of five Bangladeshi plants on in vitro thrombolysis

Background

The increasingly high incidence of ischemic stroke caused by thrombosis of the arterial vessels is one of the major factors that threaten people’s health and lives in the world. The present treatments for thrombosis are still unsatisfactory. Herbal preparations have been used since ancient times for the treatment of several diseases. The aim of this study was to investigate whether herbal preparations possess thrombolytic activity or not.

Methods

An in vitro thrombolytic model was used to check the clot lysis effect of the crude extracts and fractions of five Bangladeshi plant viz., Trema orientalis L., Bacopa monnieri L., Capsicum frutescens L., Brassica oleracea L. and Urena sinuata L. using streptokinase as a positive control and water as a negative control. Briefly, venous blood drawn from twenty healthy volunteers was allowed to form clots which were weighed and treated with the test plant materials to disrupt the clots. Weight of clot after and before treatment provided a percentage of clot lysis.

Results

Using an in vitro thrombolytic model, different fractions of five Bangladeshi medicinal plants namely T. orientalis, B. monnieri, C. frutescens, B. oleracea and U. sinuata showed various range of clot lysis activity. Chloroform fractions of T. orientalis, B. monnieri, C. frutescens, B. oleracea and U. sinuata showed highest significant (P < 0.05 and P < 0.001) clot lysis activity viz., 46.44 ± 2.44%, 48.39 ± 10.12%, 36.87 ± 1.27%, 30.24 ± 0.95% and 47.89 ± 6.83% respectively compared with positive control standard streptokinase (80.77 ± 1.12%) and negative control sterile distilled water (5.69 ± 3.09%). Other fractions showed moderate to low clot lysis activity. Order of clot lysis activity was found to be: Streptokinase > Chloroform fractions > Methanol (crude) extract > Hydro-methanol fractions > Ethyl acetate fractions > n-hexane fractions > Water.

Conclusions

Our study suggests that thrombolytic activity of T. orientalis, B. monnieri and U. sinuata could be considered as very promising and beneficial for the Bangladeshi traditional medicine. Lower effects of other extracts might suggest the lack of bio-active components and/or insufficient quantities in the extract. In vivo clot dissolving property and active component(s) of T. orientalis and B. monnieri for clot lysis could lead the plants for their therapeutic uses. However, further work will establish whether or not, chloroform soluble phytochemicals from these plants could be incorporated as a thrombolytic agent for the improvement of the patients suffering from atherothrombotic diseases.

[Covalent stretokinase-polyethylene glycol conjugates with increased stability and decreased side effects]

By variation of incubation time of streptokinase (SK) with activated polyethylene glycol (M 2 and 5 kDa, PEG2 and PEG5) it was obtained covalent SK-PEG2 and SK-PEG5 conjugates with different modification degrees of amino groups of protein and their properties were studied in vitro as compared with free SK. It was shown, that maximal stable and retaining 80% fibrinolytic activity SK-PEG2 and SK-PEG5 conjugates are formed when the modification degrees of amino groups of protein are 54 and 52%, respectively. At interaction of the given conjugates with equimolar plasminogen concentration it were formed the plasmin (Pm)·SK-PEG2 and Pm·SK-PEG5 activator complexes, the maximal amidase activity of which is equal to activity of unmodified Pm·SK complex. It was found, that the catalytic efficiency of plasminogen activation (kPg/KPg) by Pm·SK-PEG2 complex is some higher (2.84 min(-1) μM(-1)) and by Pm·SK-PEG5 complex is lower (1.17 min(-1) μM(-1)), than that by unmodified Pm·SK complex (2.1 min(-1) μM(-1)). Investigation of lysis kinetics of human plasma clots and depletion of plasminogen and fibrinogen in plasma under the action of free SK and SK-PEG2 and SK-PEG5 conjugates showed, that the latter's have high thrombolytic activity (89 and 72%, respectively) and cause 3.5-4 fold lower side effects, than free SK. Obtained by us SK-PEG2 and SK-PEG5 conjugates with increased stability and decreased side effects may be used in the therapy of thrombotic disorders.

In Vivo Anticoagulant and Thrombolytic Activities of a Fibrinolytic Serine Protease (Brevithrombolase) With the k-Carrageenan-Induced Rat Tail Thrombosis Model

In the present study, in vivo thrombolysis efficiency of Brevithrombolase, a nontoxic fibrinolytic enzyme purified from Brevibacillus brevis strain FF02B, was affirmed by significant inhibition of thrombus formation in the k-carrageenan-induced rat tail, in a dose-dependent manner. Brevithrombolase at a dose of 600 µg/kg showed an efficacy that was comparable to streptokinase and plasmin, in dissolving in vivo thrombus of k-carrageenan-treated rats under identical conditions. The in vivo anticoagulant property of Brevithrombolase was demonstrated by its prolongation of activated partial thromboplastin time, prothrombin time, and thrombin time in Wistar rats. However, the Brevithrombolase-treated rats demonstrated an insignificant decrease in fibrinogen (Fg) level of plasma compared with Fg level of control group of rats corroborating in vivo as well as in vitro anticoagulant activity of Brevithrombolase is due to its hydrolytic action on thrombin. These findings unequivocally suggest that Brevithrombolase may serve a promising alternative to the commercial thrombolytic drugs.

Production of recombinant streptokinase from Streptococcus pyogenes isolate and its potential for thrombolytic therapy

Objectives:

To produce an effective recombinant streptokinase (rSK) from pathogenic Streptococcus pyogenes isolate in yeast, and evaluate its potential for thrombolytic therapy.

Methods:

This study was conducted from November 2012 to December 2013 at King Khalid University, Abha, Kingdom of Saudi Arabia (KSA). Throat swabs collected from 45 pharyngitis patients in Asser Central Hospital, Abha, KSA were used to isolate Streptococcus pyogenes. The bacterial DNA was used for amplification of the streptokinase gene (1200 bp). The gene was cloned and in vitro transcribed in an eukaryotic expression vector that was transformed into yeast Pichia pastoris SMD1168, and the rSK protein was purified and tested for its thrombolytic activity.

Results:

The Streptococcus pyogenes strain was isolated and its DNA nucleotide sequence revealed similarity to other Streptococcus pyogenes in the Gene bank. Sequencing of the amplified gene based on DNA nucleotide sequence revealed a SK gene closely related to other SK genes in the Gene bank. However, based on deduced amino acids sequence, the gene formed a separate cluster different from clusters formed by other examined genes, suggesting a new bacterial isolate and accordingly a new gene. The purified protein showed 82% clot lysis compared to a commercial SK (81%) at an enzyme concentration of 2000 U/ml.

Conclusion:

The present yeast rSK showed similar thrombolytic activity in vitro as that of a commercial SK, suggesting its potential for thrombolytic therapy and large scale production.

Targeted thrombolysis strategies for neuroprotective effect

Stroke is usually treated by systemic thrombolytic therapy if the patient presents within an appropriate time window. There is also widespread interest in the development of thrombolytic agents that can be used in cases of delayed presentation. Current agents that can be used in cases of delayed presentation of nerve damage by thrombus. Current systemic thrombolytic therapy is associated with adverse effects such as fibrinogenolysis and bleeding. In an attempt to increase the efficacy, safety, and specificity of thrombolytic therapy, a number of targeted thrombolytic agents have been studied in recent years. This review focuses on the concepts underlying targeted thrombolytic therapy and describes recent drug developments in this field.

[Properties of streptokinase included in polyetylenglycol microcapsules]

Thrombolytic therapy by high doses of streptokinase (SK) that are stipulated by its rapid clearance is accompanied by side effects. In this work for the purpose of lifetime prolongation in bloodstream and decrease in side effects SK was included in microcapsules from water-soluble polyethyleneglygol (PEG) using the double emulsification method. By variation of the emulsification conditions, molecular weight of PEG (20 or 40 kDa) and PEG/SK ratio (12 or 8 mg PEG/1000 IU SK) it was obtained four preparations of PEG-microcapsules with high percent of SK inclusion (approximately 90-91%), which has completely preserved its fibrinolytic activity and released from microcapsules with different rates. The time of SK full release from obtained PEG-microcapsules was varied from 45 to 90 min (pH 7.4; 37 degrees C). The comparative in vitro study ofthrombolytic and side effects of free SK and SK*PEG-microcapsules was conducted. It was found that at equal doses (500 IU/mL) the lysis rates of human plasma clots under the action of encapsulated preparations of SK (with the exception of a small lag period) were equal to the lysis rate induced by free SK. Besides, SK*PEG-microcapsules caused a less exhaustion of plasminogen and fibrinogen in plasma than free SK.

Pentoxifylline Increases Antiadhesion Effect of Streptokinase on Postoperative Adhesion Formation: Involvement of Fibrinolytic Pathway

Pentoxifylline reduces peritoneal adhesions and increases peritoneal fibrinolysis in rodents. Furthermore, the activation of the fibrinolytic system by streptokinase leading to degradation of fibrin is effective in the prevention of adhesion formation. We have investigated the effects of pentoxifylline and streptokinase alone and/or coadministration on postoperative intra-abdominal adhesion formation in adult female NMRI mice. Drugs were administered from the day of surgery until 10 days after surgery. At relaparotomy 11 days after surgery, the abdomen was opened, and the adhesions were graded in a blinded fashion utilizing the classification system described. Oral gavage administration of lower doses of pentoxifylline (3.125, 6.25, and 12.5 mg/kg) had no significant effect on postsurgical adhesion formation, while the higher doses of pentoxifylline (25 and 50 mg/kg) significantly decreased postsurgical adhesion formation. Moreover, intraperitoneal injection of lower doses of streptokinase (9.375, 18.75, and 37.5 unit/kg, i.p.) had no significant effect on postsurgical adhesion formation, while the higher doses of streptokinase (75 and 150 unit/kg) significantly decreased postsurgical adhesion formation. In other series of experiments, coadministration of lower doses of pentoxifylline and streptokinase doses, which were ineffective when given alone, significantly decreased postsurgical intra-abdominal adhesion formation compared with streptokinase control group. The results suggest that pentoxifylline may interfere with streptokinase in the reduction of postoperative intra-abdominal adhesion formation by enhancing local fibrinolytic activity.

Pitfalls in screening streptococci for retrieving superior streptokinase (SK) genes: no activity correlation for streptococcal culture supernatant and recombinant SK

Streptokinase (SK), the heterogeneous protein family secreted by some groups of β-hemolytic streptococci (βHS), is a plasminogen activator and well-known drug for thrombolytic therapy. Differences in plasminogen activation property of streptococcal culture supernatants (SCS) have been traditionally used to identify superior producer strains and SK genes (skc) for recombinant SK (rSK) production. However, the role of SK heterogeneity and whether SK activities in SCS correlate with that of their corresponding rSK is a matter of debate. To address these concerns, SCS of nine group C streptococci (GCS) screened among 252 βHS clinical isolates were compared for plasminogen activation using S-2251 chromogenic assay. The GCS (Streptococcus equisimilis) showing the highest (GCS-S87) and lowest (GCS-S131) activities were selected for PCR-based isolation of skc, cloning and rSK production in Escherichia coli. The 6×His-tagged rSK proteins were purified by NI–NTA chromatography, analyzed by SDS-PAGE and Western blotting and their activities were determined. While SCS of GCS-S87 and GCS-S131 showed different plasminogen activations (95 and 35 %, respectively) compared to that of the reference strain (GCS-9542), but interestingly rSK of all three strains showed close specific activities (1.33, 1.70, and 1.55 × 104 IU mg−1). Accordingly, SKS87 and SKS131 had more than 90 % sequence identity at the amino acids level compared to SK9542. Therefore, SK heterogeneity by itself may not contribute to the differences in plasminogen activation properties of SCS and evaluation of this activity in SCS might not be a proper assay for screening superior skc.

PCR/RFLP-based allelic variants of streptokinase and their plasminogen activation potencies

PCR-restriction fragment length polymorphism (PCR/RFLP)-based analysis of β-domain variable region of streptokinase genes (sk) has previously identified 14 sk alleles (sk1-sk14) in group A (GAS), C (GCS) and G (GGS) streptococci isolates from a few geographically distinct regions. However, the relation of sk allelic variants to their plasminogen activation potencies remained as a matter of debate. Herein, employing the same PCR/RFLP assay, we analysed sk allelic variants of GAS and GCS/GGS isolates from Iranian patients. In total, 21 sk allelic variants including 14 new alleles (sk14-sk28) were identified. Results implied the horizontal gene transfer of sk fragments between GAS and GCS/GGS strains and did not prove the specificity of particular sk alleles to GCS/GGS or GAS groups. Measurement of streptokinase (SK) activity in streptococcal culture supernatants by colorimetric assay (S2251 substrate) ranged from 9 to 182 IU mL(-1). Although some strains with the highest SK activity were detected in definite variants, no significant correlation between sk alleles and plasminogen activation was detected (P value > 0.05). Analysis of DNA sequences and restriction site mapping of selective sk variants with similar SK activity pointed to the inadequacy of the currently available PCR/RFLP method for differentiation of critical/silent nucleotides to precisely categorize sk alleles for their functional properties.

Platelet-derived growth factor-C (PDGF-C) activation by serine proteases: implications for breast cancer progression

The PDGF (platelet-derived growth factor) family members are potent mitogens for cells of mesenchymal origin and serve as important regulators of cell migration, survival, apoptosis and transformation. Tumour-derived PDGF ligands are thought to function in both autocrine and paracrine manners, activating receptors on tumour and surrounding stromal cells. PDGF-C and -D are secreted as latent dimers, unlike PDGF-A and -B. Cleavage of the CUB domain from the PDGF-C and -D dimers is required for their biological activity. At present, little is known about the proteolytic processing of PDGF-C, the rate-limiting step in the regulation of PDGF-C activity. In the present study we show that the breast carcinoma cell line MCF7, engineered to overexpress PDGF-C, produces proteases capable of cleaving PDGF-C to its active form. Increased PDGF-C expression enhances cell proliferation, anchorage-independent cell growth and tumour cell motility by autocrine signalling. In addition, MCF7-produced PDGF-C induces fibroblast cell migration in a paracrine manner. Interestingly, PDGF-C enhances tumour cell invasion in the presence of fibroblasts, suggesting a role for tumour-derived PDGF-C in tumour-stromal interactions. In the present study, we identify tPA (tissue plasminogen activator) and matriptase as major proteases for processing of PDGF-C in MCF7 cells. In in vitro studies, we also show that uPA (urokinase-type plasminogen activator) is able to process PDGF-C. Furthermore, by site-directed mutagenesis, we identify the cleavage site for these proteases in PDGF-C. Lastly, we provide evidence suggesting a two-step proteolytic processing of PDGF-C involving creation of a hemidimer, followed by GFD-D (growth factor domain dimer) generation.

Serine-proteases as plasminogen activators in terms of fibrinolysis

OBJECTIVES

This review should give an overview about the natural human plasminogen activators and their various modified variants as well as similar substances isolated from animals, microorganisms and plants. When a blood clot is formed in a blood vessel, it avoids the oxygen supply of the surrounding tissue. A fast fibrinolytic therapy should redissolve the blood vessel and reduce the degradation of the tissue. All proteases that are part of the human blood coagulation and fibrinolytic system belong to the serine protease family. t-PA (tissue plasminogen activator) and u-PA (urokinase plasminogen activator) are the naturally occurring fibrinolytic agents that are also used in therapy.

KEY FINDINGS

Despite many years of research, t-PA is still the gold standard in fibrinolytic therapy. But it has to be given as an infusion, which needs time. Modified fibrinolytic substances are, were, or perhaps will be in the market. They have different advantages over t-PA, but often the disadvantages predominate.

CONCLUSION

Many substances have been developed but an optimal fibrinolytic agent combined with a simple administration is not in therapeutic use to date.