Streptokinase—a clinically useful thrombolytic agent

Proteases, a powerful biochemical tool in the service of medicine, clinical and pharmaceutical

Proteases, enzymes that hydrolyze peptide bonds, have various applications in medicine, clinical applications, and pharmaceutical development. They are used in cancer treatment, wound debridement, contact lens cleaning, prion degradation, biofilm removal, and fibrinolytic agents. Proteases are also crucial in cardiovascular disease treatment, emphasizing the need for safe, affordable, and effective fibrinolytic drugs. Proteolytic enzymes and protease biosensors are increasingly used in diagnostic and therapeutic applications. Advanced technologies, such as nanomaterials-based sensors, are being developed to enhance the sensitivity, specificity, and versatility of protease biosensors. These biosensors are becoming effective tools for disease detection due to their precision and rapidity. They can detect extracellular and intracellular proteases, as well as fluorescence-based methods for real-time and label-free detection of virus-related proteases. The active utilization of proteolytic enzymatic biosensors is expected to expand significantly in biomedical research, in-vitro model systems, and drug development. We focused on journal articles and books published in English between 1982 and 2024 for this study.

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.

Evaluation of clinical efficacy of streptokinase by comparison with the thrombolytic agent on animal model

Cardiovascular disorders, including acute myocardial infarction (AMI), often lead to blood clot formation, impacting blood circulation. Streptokinase, a cost-effective and widely available thrombolytic agent, is crucial in treating thrombosis. This study aimed to produce streptokinase from Streptococcus pyogenes EBL-48 and compare its efficacy with heparin in an animal model. We evaluated the clot-lysing effectiveness of streptokinase produced from Streptococcus pyogenes EBL-48, emphasizing its low cost and ease of production. Streptokinase was produced using pre-optimized fermentation media and purified through ion exchange and gel-filtration chromatography. In vivo analysis involved inducing clots in a trial animal model using ferric chloride, comparing streptokinase with heparin. Ultrasonography assessed the clot-lysing activity of streptokinase. Streptokinase (47 kDa) effectively lysed clots, proving its low cost, easy production, and minimal adverse effects. Ultrasonography confirmed its fibrinolytic efficacy. These findings highlight potential as an affordable and easily produced thrombolytic agent, particularly relevant in resource-limited settings. Streptokinase efficacy and minimal adverse effects make it a promising option for thrombolytic therapy, especially in economically constrained regions. Future studies could optimize production techniques, explore different strains, and conduct clinical trials for human validation. Comparative studies with other thrombolytic agents would enhance understanding of their advantages and limitations.

Cell-free protein synthesis system: A new frontier for sustainable biotechnology-based products

Cell-free protein synthesis (CFPS) system is an innovative technology with a wide range of potential applications that could challenge current thinking and provide solutions to environmental and health issues. CFPS system has been demonstrated to be a successful way of producing biomolecules in a variety of applications, including the biomedical industry. Although there are still obstacles to overcome, its ease of use, versatility, and capacity for integration with other technologies open the door for it to continue serving as a vital instrument in synthetic biology research and industry. In this review, we mainly focus on the cell-free based platform for various product productions. Moreover, the challenges in the bio-therapeutic aspect using cell-free systems and their future prospective for the improvement and sustainability of the cell free systems.

Fibrin and Fibrinolytic Enzyme Cascade in Thrombosis: Unravelling the Role

Blood clot formation in blood vessels (thrombosis) is a major cause of life-threatening cardiovascular diseases. These clots are formed by αA-, βB-, and ϒ-peptide chains of fibrinogen joined together by isopeptide bonds with the help of blood coagulation factor XIIIa. These clot structures are altered by various factors such as thrombin, platelets, transglutaminase, DNA, histones, and red blood cells. Various factors are used to dissolve the blood clot, such as anticoagulant agents, antiplatelets drugs, fibrinolytic enzymes, and surgical operations. Fibrinolytic enzymes are produced by microorganisms (bacteria, fungi, etc.): streptokinase of Streptococcus hemolyticus, nattokinase of Bacillus subtilis YF 38, bafibrinase of Bacillus sp. AS-S20-I, longolytin of Arthrobotrys longa, versiase of Aspergillus versicolor ZLH-1, etc. They act as a thrombolytic agent by either enhancing the production of plasminogen activators (tissue or urokinase types), which convert inactive plasminogen to active plasmin, or acting as plasmin-like proteins themselves, forming fibrin degradation products which cause normal blood flow again in blood vessels. Fibrinolytic enzymes may be classified in two groups, as serine proteases and metalloproteases, based on their catalytic properties, consisting of a catalytic triad responsible for their fibrinolytic activity having different physiochemical properties (such as molecular weight, pH, and temperature). The analysis of fibrinolysis helps to detect hyperfibrinolysis (menorrhagia, renal failure, etc.) and hypofibrinolysis (diabetes, obesity, etc.) with the help of various fibrinolytic assays such as a fibrin plate assay, fibrin microplate assay, the viscoelastic method, etc. These fibrinolytic activities serve as a key aspect in the recognition of numerous cardiovascular diseases and can be easily produced on a large scale with a short generation time by microbes and are less expensive.

Reevaluation of lock solutions for Central venous catheters in hemodialysis: a narrative review

BACKGROUND

A significant proportion of incident and prevalent hemodialysis patients have central venous catheters for vascular access. No consensus is available on the prevention of catheter dysfunction or catheter-related bloodstream infections in patients undergoing hemodialysis by means of catheter lock solutions.

METHOD

We reviewed the effects of single and combined anticoagulants with antibacterial catheter lock solutions or other antimicrobials for the prevention of thrombosis or infections in hemodialysis patients. Relative risks with 95% confidence intervals for trials of the same type of catheter locking solution were pooled.

SOURCES OF INFORMATION

We included original research articles in English from PubMed, EMBASE, SpringerLink, Elsevier and Ovid using the search terms 'hemodialysis,' 'central venous catheter,' 'locking solution,' 'UFH,' 'low molecular weight heparin,' 'EDTA,' 'citrate,' 'rt-PA,' 'urokinase,' 'gentamicin,' 'vancomycin', 'taurolidine,' 'sodium bicarbonate,' 'hypertonic saline' and 'ethanol' and 'catheter'.

FINDINGS

Low-dose heparin lock solution (< 5000 U/ml) can efficiently achieve anticoagulation and will not increase the risk of bleeding. Low-concentration citrate (< 5%) combined with rt-PA can effectively prevent catheter infection and dysfunction. Catheter-related infections may be minimized by choosing the appropriate antibiotic and dose.

LIMITATIONS

There is a lack of follow-up validation data for LMWH, EDTA, taurolidine, sodium bicarbonate, ethanol, and other lock solutions.

IMPLICATIONS

Since catheterization is common in hemodialysis units, studies on long-term treatment and preventative strategies for catheter dysfunction and catheter-related infection are warranted.

Evolution of ischemic stroke drug clinical trials in mainland China from 2005 to 2021

Background

To assess the temporal changes in the characteristics of ischemic stroke drug clinical trials conducted in mainland China in 2005–2021.

Methods

A statistical analysis of registered clinical trials on ischemic stroke was performed using the platform of the Center for Drug Evaluation of China National Medical Products Administration, the Chinese Clinical Trial Registry, and ClinicalTrials.gov websites.

Results

From January 1, 2005 to August 1, 2021, a total of 384 registered drug clinical trials on ischemic stroke were identified in mainland China. Over time, the number of trials gradually increased each year, with a significant growth in 2014, from 16 in 2013 to 42 in 2014. Phase IV trials (31.8%) accounted for the majority, followed by phase II (16.4%), phase I (10.9%), and phase III (8.6%). In terms of sponsorship, the proportion of investigator‐initiated trials (IITs) (60.7%) was higher than industry‐sponsored trials (ISTs) (39.3%). Additionally, trials involving traditional Chinese medicines (TCMs) (36.2%) accounted for the largest proportion, followed by trials involving antithrombotic therapy (19.5%) and cerebral protection agents (16.7%). Furthermore, over the past 17 years, the number of leading drug clinical trial units for ischemic stroke in mainland China has continuously increased. The leading principal units from Beijing, Shanghai, Guangdong, Jiangsu, and Liaoning accounted for the majority of the trials (67.4%).

Conclusion

In the past 17 years, great progress has been made in the research and development (R&D) of drugs and clinical trials for ischemic stroke in mainland China. The most extensive progress was observed in TCMs, antithrombotic therapy, and cerebral protection agents. More clinical trials are needed to confirm whether the newly developed drugs can improve the clinical efficacy of ischemic stroke. Simultaneously, more pharmaceutical R&D efforts of innovative drugs are warranted.

Fibrinolytic Enzyme - An Overview

Cardiovascular diseases, like coronary heart disease or artery disorders (arteriosclerosis, including artery solidification), heart failure (myocardial infarction), arrhythmias, congestive heart condition, stroke, elevated vital signs (hypertension), rheumatic heart disorder, and other circulatory system dysfunctions are the most common causes of death worldwide. Cardiovascular disorders are treated with stenting, coronary bypass surgery grafting, anticoagulants, antiplatelet agents, and other pharmacological and surgical procedures; however, these have limitations due to their adverse effects. Fibrinolytic agents degrade fibrin through enzymatic and biochemical processes. There are various enzymes that are currently used as a treatment for CVDs, like Streptokinase, Nattokinase, Staphylokinase, Urokinase, etc. These enzymes are derived from various sources like bacteria, fungi, algae, marine organisms, plants, snakes, and other organisms. This review deals with the fibrinolytic enzymes, their mechanisms, sources, and their therapeutic potential.

Phytochemical and pharmacological investigation of the ethanol extract of Byttneria pilosa Roxb

Background

Traditionally, the herb Byttneria pilosa Roxb. is used for bone fractures, boils, scabies, rheumatalgia, snake bites, syphilis, elephantiasis, poisoning, and eye infection. Scientific reports suggest that it has significant anti-inflammatory, analgesic, anti-diarrheal, anxiolytic, locomotion, sedative and anti-obesity effects. This study aims at the investigation of the phytochemical and pharmacological properties of the ethanol extract of this herb.

Methods

Fresh whole plant was extracted with absolute ethanol. A preliminary phytochemical investigation was followed by the evaluation of thrombolytic, anti-inflammatory, and anti-nociceptive activities by applying human clotted blood lysis, egg albumin, and acetic acid-induced writhing models, respectively.

Results

Phytochemical investigation suggests that B. pilosa possesses alkaloids, flavonoids, glycosides, terpenoids, tannins, saponins, and reducing sugars. The extract exhibited clot lysis and anti-inflammatory effects in a concentration-dependent manner. B. pilosa extract at 250 and 500 mg/kg also showed significant (p < 0.05) dose-dependent anti-nociceptive activity in Swiss albino mice.

Conclusion

The B. pilosa ethanol extract contains many important secondary metabolites and has thrombolytic, anti-inflammatory, and anti-nociceptive activities. More research is necessary on this hopeful medicinal herb.

Microbial Fibrinolytic Enzymes as Anti-Thrombotics: Production, Characterisation and Prodigious Biopharmaceutical Applications

Cardiac disorders such as acute myocardial infarction, embolism and stroke are primarily attributed to excessive fibrin accumulation in the blood vessels, usually consequential in thrombosis. Numerous methodologies including the use of anti-coagulants, anti-platelet drugs, surgical operations and fibrinolytic enzymes are employed for the dissolution of fibrin clots and hence ameliorate thrombosis. Microbial fibrinolytic enzymes have attracted much more attention in the management of cardiovascular disorders than typical anti-thrombotic strategies because of the undesirable after-effects and high expense of the latter. Fibrinolytic enzymes such as plasminogen activators and plasmin-like proteins hydrolyse thrombi with high efficacy with no significant after-effects and can be cost effectively produced on a large scale with a short generation time. However, the hunt for novel fibrinolytic enzymes necessitates complex purification stages, physiochemical and structural-functional attributes, which provide an insight into their mechanism of action. Besides, strain improvement and molecular technologies such as cloning, overexpression and the construction of genetically modified strains for the enhanced production of fibrinolytic enzymes significantly improve their thrombolytic potential. In addition, the unconventional applicability of some fibrinolytic enzymes paves their way for protein hydrolysis in addition to fibrin/thrombi, blood pressure regulation, anti-microbials, detergent additives for blood stain removal, preventing dental caries, anti-inflammatory and mucolytic expectorant agents. Therefore, this review article encompasses the production, biochemical/structure-function properties, thrombolytic potential and other surplus applications of microbial fibrinolytic enzymes.

Thrombolytic Enzymes of Microbial Origin: A Review

Enzyme therapies are attracting significant attention as thrombolytic drugs during the current scenario owing to their great affinity, specificity, catalytic activity, and stability. Among various sources, the application of microbial-derived thrombolytic and fibrinolytic enzymes to prevent and treat vascular occlusion is promising due to their advantageous cost-benefit ratio and large-scale production. Thrombotic complications such as stroke, myocardial infarction, pulmonary embolism, deep venous thrombosis, and peripheral occlusive diseases resulting from blood vessel blockage are the major cause of poor prognosis and mortality. Given the ability of microbial thrombolytic enzymes to dissolve blood clots and prevent any adverse effects, their use as a potential thrombolytic therapy has attracted great interest. A better understanding of the hemostasis and fibrinolytic system may aid in improving the efficacy and safety of this treatment approach over classical thrombolytic agents. Here, we concisely discuss the physiological mechanism of thrombus formation, thrombo-, and fibrinolysis, thrombolytic and fibrinolytic agents isolated from bacteria, fungi, and algae along with their mode of action and the potential application of microbial enzymes in thrombosis therapy.

Phytochemical and pharmacological investigations of different extracts of leaves and stem barks of Macropanax dispermus (Araliaceae): a promising ethnomedicinal plant

Background

Macropanax dispermus is traditionally used to treat various diseases by ethnic people. The present research reports the pharmacological properties with phytochemical profiling of the crude extracts of M. dispermus leaves (MDML), its n-hexane (MDHL), carbon tetrachloride (MDTL), chloroform (MDCL), ethyl acetate (MDEL), and aqueous (MDAL) fractions, and crude methanol extracts of its stem barks (MDMS). The in vitro thrombolytic activity was done on human erythrocytes whereas the cytotoxic activity was done by brine shrimp lethality assay. The in vivo analgesic activity was examined by acetic acid-induced writhing, tail immersion, and formalin-induced paw licking method. In contrast, antipyretic activity was done by the brewer’s yeast-induced pyrexia method.

Results

MDHL and MDMS showed 37.05% and 42.21% of significant (p < 0.01) thrombolytic activity, respectively. MDCL and MDMS showed the lower LC50 values of 23.15 and 37.11 µg/ml during cytotoxicity test, respectively. In acetic acid writhing method, MDTL and MDEL showed significant (p < 0.001) inhibition of writhing by 79.34% and 80.17%, respectively. MDMS showed significant (p < 0.001) maximal possible effect (%MPE) of 45.95%, 62.26%, 65.79%, 89.69% and elongation of time in pain reaction of 48.53%, 60.28%, 58.76%, and 70.14% at 30, 60, 90, and 120 min intervals, respectively. MDML at 400 mg/kg exhibited significant (p < 0.001) 82.72% of inhibition of pain at the late phases. MDEL at 400 mg/kg of dose exhibited significant (p < 0.001) reduction of rectal temperature by 36.31%, 62.42%, 89.81%,, and 96.82% at 1, 2, 3, and 4 h intervals, respectively.

Conclusion

The current research suggests that the plant extracts possess potential thrombolytic, cytotoxic, analgesic, and antipyretic activities.

Fibrinolytic enzymes from extremophilic microorganisms in the development of new thrombolytic therapies: Technological Prospecting

BACKGROUND

Extremophilic microorganisms from a wide variety of extreme natural environments have been researched, and many biotechnological applications have been carried out, due to their capacity to produce biomolecules resistant to extreme conditions, such as fibrinolytic proteases. The search for new fibrinolytic enzymes is important in the development of new therapies against cardiovascular diseases.

OBJECTIVE

This article aimed to evaluate the patents filed about protease with fibrinolytic activity produced by extremophilic microorganisms whose use is aimed at the development of new drugs for the treatment of cardiovascular diseases.

METHODS

The prospecting was carried out using data on deposits and patent concessions made available on the technological bases: European Patent Office (EPO), United States Patent and Trademark Office (USPTO), World Intellectual Property Organization (WIPO), Instituto Nacional de Propriedade Industrial - Brazil (INPI), The LENS and Patent Inspiration. The International Patent Classification and subclasses and groups for each document were also evaluated.

RESULTS

Although 382 patents were selected using terms related to extreme environments, such as "thermophile" and "acidophiles", few were related to clinical use and were mainly performed using Bacillus subtilis and Streptomyces megasporus strains. A highlight of nattokinase was produced by Bacillus subtilis GDN and actinokinase by Streptomyces megasporus SD5.

CONCLUSION

The low number of patents on enzymes with this profile (extreme environments) revealed a little-explored field, promising in the development of new microbial thrombolytic drugs, such as fibrinolytic enzymes with less adverse effects.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.

Nitrogen supplementation ameliorates product quality and quantity during high cell density bioreactor studies of Pichia pastoris: A case study with proteolysis prone streptokinase

Streptokinase is a well-established cost-effective therapeutic molecule for thrombo-embolic complications. In the current study, a tag-free variant of streptokinase with a native N-terminus (N-rSK) was developed using the Pichia expression system. A three-copy clone was screened that secreted 1062 mg/L of N-rSK in the complex medium at shake flask level. The biologically active (67,552.61 IU/mg) N-rSK recovered by anion exchange chromatography was predicted to contain 15.43% α-helices, 26.43% β-sheets. The fermentation run in a complex medium yielded a poor quality product due to excessive N-rSK degradation. Therefore, modified basal salt medium was also employed during fermentation operations to reduce the proteolytic processing of the recombinant product. The concomitant feeding of 1 g/L/h soya flour hydrolysate with methanol during the protein synthesis phase reduced the proteolysis and yielded 2.29 g/L of N-rSK. The fermentation medium was also supplemented with urea during growth and induction phases. The combined feeding approach of nitrogen-rich soya flour hydrolysate and urea during bioreactor operations showed significant improvement in protein stability and resulted in a 4-fold increase in N-rSK concentration to a level of 4.03 g/L over shake flask. Under optimized conditions, the volumetric productivity and specific product yield were 52.33 mg/L/h and 33.24 mg/g DCW, respectively.

Thrombolytic Agents: Nanocarriers in Controlled Release

Thrombosis is a life-threatening pathological condition in which blood clots form in blood vessels, obstructing or interfering with blood flow. Thrombolytic agents (TAs) are enzymes that can catalyze the conversion of plasminogen to plasmin to dissolve blood clots. The plasmin formed by TAs breaks down fibrin clots into soluble fibrin that finally dissolves thrombi. Several TAs have been developed to treat various thromboembolic diseases, such as pulmonary embolisms, acute myocardial infarction, deep vein thrombosis, and extensive coronary emboli. However, systemic TA administration can trigger non-specific activation that can increase the incidence of bleeding. Moreover, protein-based TAs are rapidly inactivated upon injection resulting in the need for large doses. To overcome these limitations, various types of nanocarriers have been introduced that enhance the pharmacokinetic effects by protecting the TA from the biological environment and targeting the release into coagulation. The nanocarriers show increasing half-life, reducing side effects, and improving overall TA efficacy. In this work, the recent advances in various types of TAs and nanocarriers are thoroughly reviewed. Various types of nanocarriers, including lipid-based, polymer-based, and metal-based nanoparticles are described, for the targeted delivery of TAs. This work also provides insights into issues related to the future of TA development and successful clinical translation.

Deciphering the Pharmacological Properties of Methanol Extract of Psychotria calocarpa Leaves by In Vivo, In Vitro and In Silico Approaches

The present study explores the neuropharmacological, antinociceptive, antidiarrheal, antioxidant, thrombolytic and cytotoxic activity of methanol extract of Psychotria calocarpa leaves (MEPC). In anxiolytic activity testing of MEPC by elevated plus maze test, hole-board test and light-dark test, the extract exhibited a dose-dependent reduction of anxiety while the open field test observed a decreased locomotion. The administration of MEPC revealed a significant dose-dependent reduction of depressant behavior in forced swimming and tail suspension test. Additionally, the antinociceptive and antidiarrheal activity exposed a significant reduction of nociception and diarrheal behavior at the highest dose. In addition, a strong antioxidant activity was observed in DPPH-free radical-scavenging assay (IC50 = 461.05 μg/mL), total phenol content (118.31 ± 1.12 mg) and total flavonoid content (100.85 ± 0.97 mg). The significant clot-lysis activity was also observed with moderate toxicity (LC50 = 247.92 μg/mL) level in the lethality assay of brine shrimp. Moreover, in silico molecular docking study showed that the compound Psychotriasine could offer promising active site interactions for binding proteins. Furthermore, ADME/T and toxicological properties of the compound satisfied the Lipinski's rule of five and Veber rules for drug-like potential and toxicity level. Overall, MEPC had a potential neuropharmacological, antinociceptive, antidiarrheal and antioxidant activity that warranted further investigation.

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.

Kringles of substrate plasminogen provide a 'catalytic switch' in plasminogen to plasmin turnover by Streptokinase

To understand the role of substrate plasminogen kringles in its differential catalytic processing by the streptokinase - human plasmin (SK-HPN) activator enzyme, Fluorescence Resonance Energy Transfer (FRET) model was generated between the donor labeled activator enzyme and the acceptor labeled substrate plasminogen (for both kringle rich Lys plasminogen - LysPG, and kringle less microplasminogen - µPG as substrates). Different steps of plasminogen to plasmin catalysis i.e. substrate plasminogen docking to scissile peptide bond cleavage, chemical transformation into proteolytically active product, and the decoupling of the nascent product from the SK-HPN activator enzyme were segregated selectively using (1) FRET signal as a proximity sensor to score the interactions between the substrate and the activator during the cycle of catalysis, (2) active site titration studies and (3) kinetics of peptide bond cleavage in the substrate. Remarkably, active site titration studies and the kinetics of peptide bond cleavage have shown that post docking chemical transformation of the substrate into the product is independent of kringles adjacent to the catalytic domain (CD). Stopped-flow based rapid mixing experiments for kringle rich and kringle less substrate plasminogen derivatives under substrate saturating and single cycle turnover conditions have shown that the presence of kringle domains adjacent to the CD in the macromolecular substrate contributes by selectively speeding up the final step, namely the product release/expulsion step of catalysis by the streptokinase-plasmin(ogen) activator enzyme.

Preparation of PEG-grafted chitosan/streptokinase nanoparticles to improve biological half-life and reduce immunogenicity of the enzyme

Streptokinase, as a thrombolytic drug, is widely used in treatment of cardiovascular disorders and deep vein thrombosis. Streptokinase is immunogenic due to its prokaryotic source, having short biological half-life (i.e. 15 to 30 min) that is not enough for an efficient therapy. In this study, nanoparticles (NPs) of chitosan/streptokinase and polyethylene glycol (PEG)-grafted chitosan/streptokinase were prepared by polyelectrolyte complex method. Particle size of chitosan and PEG-grafted chitosan NPs were 154 ± 42 and 211 ± 47 nm, respectively. Results showed that using PEG in preparation of nanoparticles leads to ~24% decrease in encapsulation efficiency. Encapsulation of streptokinase in the NPs also resulted in a slight reduction in enzymatic activity. However, in vivo findings indicated that response of the immune system was delayed for 20 days and blood circulation time of the enzyme increased up to 120 min by using PEG. Biological half-life of the drug also increased up to twice in PEG-grafted chitosan. In conclusion, PEG-grafted chitosan NPs could be an alternative for delivery of streptokinase to reduce its clinical limitations.

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.

Near-Infrared Light Activated Thermosensitive Ion Channel to Remotely Control Transgene System for Thrombolysis Therapy

Current antithrombotic therapeutic strategies often suffer from severe post-thrombotic syndromes (PTS), inconvenient daily subcutaneous injections for a long time and short circulation times accompanied by a dose-dependent risk of intracranial hemorrhage. Aiming at noninvasive, on-demand, and sustained antithrombotic therapy, a new thrombolysis approach based on the transgene system has been developed to remotely and precisely control the expression of urokinase plasminogen activator (uPA) by bioengineered cells for antithrombotic therapy both in vitro and in vivo. In this design, the near-infrared (NIR) light could activate the expression of the thermosensitive TRPV1 channel in response to photothermal responsive nanotransducers to trigger the synthetic signaling pathway to secret uPA. By encapsulating bioengineered cells in injectable hydrogel to ensure long-term survival and convenience for injection, the engineered cells could noninvasively and precisely control the production of uPA protein in situ via an NIR laser to significantly enhance the thrombolysis therapeutic effects by spatiotemporally controlling the local temperature, in both the microfluidic blood circulation mimic and the murine tail thrombus model. This novel thrombolysis approach could overcome some key limitations that are associated with conventional antithrombotic therapy, thus opening a new direction for developing remotely and precisely controllable continuous thrombolysis through artificially designed signaling.

Evaluation of Activity Kinetic Parameters of SK319cys, As a New Cysteine Variant of Streptokinase: A Comparative Study

BACKGROUND

Despite the extensive use of streptokinase in thrombolytic therapy, its administration may have some shortcomings like allergic reactions and relatively low half life. Specific PEGylation on cysteine at desired sites of streptokinase may alleviate these deficiencies and improve the quality of treatment.

OBJECTIVE

This study was carried out to create a new cystein variant of streptokinase and compare its activity with formerly mutated SK263cys, SK45cys and intact streptokinase (Ski) to introduce superior candidates for specific PEGylation.

METHOD

In silico study was carried out to select appropriate amino acid for cysteine substitution and accordingly mutagenesis was carried out by SOEing PCR. The mutated gene was cloned in E. coli, expressed, and purified by affinity chromatography. Activity of the purified proteins was assayed and kinetic parameters of enzymatic reaction were analyzed.

RESULTS

According to in silico data, Arginine319 was selected for substitution with cysteine. SK319cys was achieved with 98% purity after cloning, expression and purification. It was shown that the enzymatic efficiency of SK319Cys and SK263cys was increased 18 and 21%, respectively, when compared to SKi (79.4 and 81.3 vs. 67.1µM-1min-1), while SK45cys showed 7% activity decrease (62.47µM-1min-1) compared to SKi. According to time-based activity assay, SK319Cys and SK263cys exhibited higher activity at lower substrate concentrations (100 and 200 µM), but at higher concentrations of substrate (400 and 800 µM), the proteins showed a very close trend of activity.

CONCLUSION

SK319cys, as the new cysteine variant of streptokinase, together with SK263cys and SK45cys can be considered as appropriate molecules for specific PEGylation.

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.

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.

On-Chip Preparation of Streptokinase Entrapped in Chitosan Nanoparticles Used in Thrombolytic Therapy Potentially

The objective of this work was to prepare the streptokinase (SK) entrapped in chitosan nanoparticles (CS NPs) using bulk mixing (BM) and microfluidic (MF) techniques. The physicochemical properties of the samples were characterized by means of scanning electron microscopy and dynamic light scattering analysis for optimizing CS and SK solution concentrations as well as pH values. The obtained results showed that CS NPs fabricated using MF chip have the most uniform morphology, spherical shape, and average diameter of 67 ± 13 nm along with a narrow polydispersity. Conversely, the NP samples prepared via BM method have an irregular and disordered morphology as well as a broad distribution in their particle size (452 ± 300 nm). The in vitro drug release from microfluidically generated CS NPs depicted the controlled release of SK without plateau regime compared to those samples prepared using BM method during 48 h. Also, the drug release kinetic followed Higuchi model which revealed that the Fickian diffusion was the predominant mechanism. Subsequently, in in vivo animal model test, the performance of SK in blood plasma exhibited higher amidolytic activity for SK entrapped in CS NP samples fabricated via MF technique compared to those NPs prepared using BM and also SK alone.

Preparation, Optimization and Activity Evaluation of PLGA/Streptokinase Nanoparticles Using Electrospray

Purpose: PLGA nanoparticles (NPs) have been extensively investigated as carriers of different drug molecules to enhance their therapeutic effects or preserve them from the aqueous environment. Streptokinase (SK) is an important medicine for thrombotic diseases. Methods: In this study, we used electrospray to encapsulate SK in PLGA NPs and evaluate its activity. This is the first paper which investigates activity of an electrosprayed enzyme. Effect of three input parameters, namely, voltage, internal diameter of needle (nozzle) and concentration ratio of polymer to protein on size and size distribution (SD) of NPs was evaluated using artificial neural networks (ANNs). Optimizing the SD has been rarely reported so far in electrospray. Results: From the results, to obtain lowest size of nanoparticles, ratio of polymer/enzyme and needle internal diameter (ID) should be low. Also, minimum SD was obtainable at high values of voltage. The optimum preparation had mean (SD) size, encapsulation efficiency and loading capacity of 37 (12) nm, 90% and 8.2%, respectively. Nearly, 20% of SK was released in the first 30 minutes, followed by cumulative release of 41% during 72 h. Activity of the enzyme was also checked 30 min after preparation and 19.2% activity was shown. Conclusion: Our study showed that electrospraying could be an interesting approach to encapsulate proteins/enzymes in polymeric nanoparticles. However, further works are required to assure maintaining the activity of the enzyme/protein after electrospray.

Microbubble-Based Sonothrombolysis Using a Planar Rectangular Ultrasonic Transducer

BACKGROUND

The aim of the proposed study was to evaluate in an in vitro flow model the ability of small planar rectangular (2 × 10 mm²) ultrasonic transducer to enhance thrombolysis induced by the thrombolytic agent tenecteplase (TNK-tPA).

METHODS

To provide a more realistic clinical environment of stroke, the study was conducted under realistic flow conditions and TNK-tPA concentrations. Fully retracted porcine blood clots were used to determine the thrombolytic efficacy of ultrasound (US) waves as an adjunct to TNK-tPA or in combination with microbubbles (MBs). Two ultrasonic flat rectangular transducers were used in the experiments, operating at 3.7 and 5.2 MHz respectively. A pulsed US protocol that maintained temperature elevation at the target of 1°C was applied. Thrombolysis efficacy was measured in milligrams of mass clot removed.

RESULTS

The effect of experimental parameters, such as power, frequency, and MBs administration, on thrombolysis efficacy was explored.

CONCLUSIONS

The results revealed that thrombolysis efficacy decreases at higher frequency, and therefore, the possibility of using lower frequency to improve efficacy should be further investigated. Additionally, study findings demonstrated that the combination of 3.7 MHz with MBs as an adjunct to TNK-tPA strongly enhanced thrombolysis efficacy, because with 30 minutes of treatment, 700 mg of clot was removed through nonthermal mechanisms. As a final point, this study has shown that MBs dose influences thrombolysis enhancement, because higher thrombolytic efficacy was observed with higher doses of MBs.

Preparation and antithrombotic activity identification of Perinereis aibuhitensis extract: a high temperature and wide pH range stable biological agent

In this work, a thermal and wide pH range stable biological agent was extracted from Perinereis aibuhitensis, whose antithrombotic activity was investigated.

Intrapleural Fibrinolytic Therapy for Residual Coagulated Hemothorax After Lung Surgery

BACKGROUND

Many studies have described the use of intrapleural fibrinolytics for the treatment of complex pleural processes and traumatic hemothorax, but data are scarce regarding their use for hemothorax after lung surgery.

OBJECTIVE

To evaluate the utility of intrapleural fibrinolytic therapy with urokinase for residual coagulated hemothorax (blood clot accumulation in the pleural cavity) after lung surgery.

METHODS

From July 2009 to November 2013, 46 patients (33 males; mean age, 56.9 ± 10.7 years) were treated with intrapleural urokinase (250,000 IU per dose) for residual hemothorax after lung surgery. Complete response was defined as clinical improvement with complete drainage of the retained collection shown by chest X-ray, and partial response as substantial resolution with minimal residual opacity (<25 % of the thorax). Follow-up was at least 30 days.

RESULTS

The procedure was successful in 42 patients (91.3 %), with complete response observed in 35/46 patients (76.1 %) and partial response in 7/46 (15.2 %). These 42 patients did not require re-intervention for fluid accumulation in the pleural cavity. Treatment failed in 4 patients (8.7 %): one developed bronchopleural fistula that later resolved spontaneously and three (6.5 %) required thoracoscopic drainage for pleural cavity fluid accumulation and lung collapse. No patient required thoracotomy for total decortication. Intrapleural urokinase administration was not associated with serious adverse events, including bleeding complications or allergic reactions.

CONCLUSIONS

Intrapleural fibrinolytic agents should be considered a useful therapeutic option for the treatment of postoperative residual hemothorax. This method appears to be safe and effective in >90 % of patients with postoperative hemothorax.

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.

Streptokinase@alumina nanoparticles as a promising thrombolytic colloid with prolonged action

The present study is devoted to the development of a new class of thrombolytic systems - nanocolloids. A non-direct plasminogen activator, streptokinase, was entrapped in a sol-gel matrix based on boehmite nanoparticles used in medical practice as the most common vaccine adjuvant. It is shown that when the enzyme content in the composite is less than 10%, only minor release is observed, while thrombolytic properties are maintained at a relatively high level, demonstrating the prolonged effect. Based on the obtained composites, thrombolytic nanocolloids containing nanoparticles of less than 500 nm size and suitable for parenteral administration were produced. The thrombolytic properties were studied using the plasminogen activation tests, human plasma clots and a model thrombus made from a whole human blood. Based on the obtained results, the structure of the composites and the mechanism of their action are suggested.

Engineering, expression and purification of a chimeric fibrin-specific streptokinase

Streptokinase is a valuable fibrinolytic agent used to cope with myocardial infarction and brain stroke. Despite its high efficiency in dissolving blood clots, streptokinase (SK) has no specificity in binding fibrin, causing some problems such as internal bleedings following its administration. To make streptokinase fibrin specific and limit the fibrinolytic process to the clot location, we engineered a chimeric streptokinase by fusing the fibrin binding Kringle 2 domain of tissue plasminogen activator (TPA) to the streptokinase N-terminal end. The chimeric SK construct (KSK) with inserted Kringle 2 domain was cloned into pET28a expression vector. The expression of recombinant protein was carried out in Escherichia coli origami (DE3) and confirmed by SDS-PAGE and Western blotting analyses. We used the chromogenic substrate S-2251 method to assess the specific activities of the chimeric and control wild-type proteins. Then, the two proteins were added in amounts with equal activity to fibrin clots of identical size. Finally, the supernatant above the fibrin clots was collected and subjected to the chromogenic assay to analyze the specificity of the chimeric protein. The specific activities of the chimeric and wild-type proteins were found to be 0.06 U/mg and 0.07 U/mg, respectively. Because of the binding of the chimeric protein to fibrin, the mean specific activity was significantly lower in the KSK supernatant (0.01) compared with the control (approximately 0.06) (p < 0.05). Our in vitro results indicate that the chimeric streptokinase protein has strong fibrin-specific activity compared to the wild-type protein. However, further in vivo studies are needed to evaluate its potential fibrinolytic effects.

Cow Dung Is a Novel Feedstock for Fibrinolytic Enzyme Production from Newly Isolated Bacillus sp. IND7 and Its Application in In Vitro Clot Lysis

Bacterial fibrinolytic enzymes find great applications to treat and prevent cardiovascular diseases. The novel fibrinolytic enzymes from food grade organisms are useful for thrombolytic therapy. This study reports fibrinolytic enzyme production by Bacillus sp. IND7 in solid-state fermentation (SSF). In this study, cow dung was used as the cheap substrate for the production of fibrinolytic enzyme. Enzyme production was primarily improved by optimizing the nutrient and physical factors by one-variable-at-a-time approach. A statistical method (two-level full factorial design) was applied to investigate the significant variables. Of the different variables, pH, starch, and beef extract significantly influenced on the production of fibrinolytic enzyme (p < 0.05). The optimum levels of these significant factors were further investigated using response surface methodology. The optimum conditions for enhanced fibrinolytic enzyme production were 1.23% (w/w) starch and 0.3% (w/w) beef extract with initial medium pH 9.0. Under the optimized conditions, cow dung substrate yielded 8,345 U/g substrate, and an overall 2.5-fold improvement in fibrinolytic enzyme production was achieved due to its optimization. This is the first report of fibrinolytic enzyme production using cow dung substrate from Bacillus sp. in SSF. The crude enzyme displayed potent activity on zymography and digested goat blood clot completely in in vitro condition.

Liposomal nanocarriers for plasminogen activators

Several plasminogen activators (PAs) have been found effective in treating different thromboembolic diseases. However, administration of conventional thrombolytic therapy is limited by a low efficacy of present formulations of PAs. Conventional treatments using these therapeutic proteins are associated with several limitations including rapid inactivation and clearance, short half-life, bleeding complications or non-specific tissue targeting. Liposome-based formulations of PAs such as streptokinase, tissue-plasminogen activator and urokinase have been developed to improve the therapeutic efficacy of these proteins. Resulting liposomal formulations were found to preserve the original activity of PAs, promote their selective delivery and improve thrombus targeting. Therapeutic potential of these liposome-based PAs has been demonstrated successfully in various pre-clinical models in vivo. Reductions in unwanted side effects (e.g., hemorrhage or immunogenicity) as well as enhancements of efficacy and safety were achieved in comparison to currently existing treatment options based on conventional formulations of PAs. This review summarizes present achievements in: (i) preparation of liposome-based formulations of various PAs, (ii) development of PEGylated and targeted liposomal PAs, (iii) physico-chemical characterization of these developed systems, and (iv) testing of their thrombolytic efficacy. We also look to the future and the imminent arrival of theranostic liposomal formulations to move this field forward.

Targeted thrombolysis of tissue plasminogen activator and streptokinase with extracellular biosynthesis nanoparticles using optimized Streptococcus equi supernatant

Extracellular biosynthesis of nanoparticles have many important advantages such as well dispersed in aqueous solutions, low energy requirements, ecofriendly, non-toxic, low-costs and non-flocculate. This technique have shown significant promise as targeted drug delivery applications. In this investigation, for the first time, we examine the efficacy of targeted therapeutic delivery with t-PA and SK immobilized to biosynthesis of nanoparticles (CuNP) by using Streptococcus equi strains isolated from the horses of Iran and their ability to produce metallic nanoparticles. Also we compared them with their chemical synthesis. The S. equi was screened for its ability to produce MNPs. The minimum size and shapes (23-89 nm) are presented in the formation with good dispersion and high stability. Response Surface methodology was applied for the optimized production of biological CuNPs. The growth factors like pH, temperature and incubation time was changed. The optimum conditions to obtain CuNPs were found with the culture conditions of pH 7.5 in 120 h at 35 °C. To determine some of MNPs structural properties UV-vis absorption spectrophotometer, FTIR, XRD and SEM has characterized. The results provided some parameters may impact on the formation of biological MNPs. Lastly, these MNPs were conjugated with t-PA and SK, as a drug carrier. In addition, effective thrombolysis with magnet-guided SiO2CuNPs-tPA-SK is demonstrated in rat embolism model where 18.6% of the regular t-PA dose and 15.78% of SK dose restored and 15-25 min reductions in blood clot lysis time were observed compared with runs with free t-PA and without magnet-guided and using the same drug dosage. The comparison between CuNPs with MNPs shows that thrombolysis had not been directed to the type of magnetic carrier under the magnetic guide.

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.