Heterologous expression, purification and single step efficient refolding of recombinant tissue plasminogen activator (Reteplase) from E. coli.

Reteplase (recombinant plasminogen activator, rPA) is a mutant non-glycosylated tissue-type plasminogen activator (tPA) containing 355 amino acids with longer half-life and promising thrombolytic activity than its original counterpart, full length tPA. In this study, we aimed to produce and optimize the purification process of recombinant tissue-type plasminogen activator (tPA) known as Reteplase (rPA). Reteplase cDNA synthesized from total mRNA isolated from human placenta was PCR amplified, cloned into a pET-28a(+) E. coli expression vector and expressed in Rosetta-gami 2 E. coli (NovagenⓇ) host. rPA was expressed as an inclusion body in E. coli and its biological activity was achieved after single step solubilization, purification and refolding. We exploited the strategy of Slow Refolding using Gradual Dialysis (SRGD) in which a refolding buffer containing glutathione oxidized (1 mM GSSG) and glutathione reduced (3 mM GSH) and pH 9.0 was used. Using the SRGD method, we were able to successfully obtain the protein in its active form. We obtained 4.26 mg of active refolded protein from a 50 mL culture that was scaled up in a bioreactor. The purity and homogeneity of rPA was evaluated by SDS-PAGE, Western blotting and mass spectrometry. Circular dichroism spectroscopy was conducted to evaluate the refolding and stability of the refolded rPA in comparison to reference standard rPA. The thrombolytic potential of rPA was assessed by fibrin plate assay and In Vitro clot lysis assay. The presented protocol offers a viable approach for enhancing both the yield and refolding efficiency of reteplase, potentially resulting in an increase in yield.

Comparison of the effect of heparin, reteplase, and taurolock in the prevention of thrombosis in hemodialysis catheters.

Background and Aim: One of the complications of using catheters is the occurrence of thrombosis, which can be dangerous for patients. The main objective of this study is to compare the effect of heparin, reteplase, and taurolock in the prevention of thrombosis in hemodialysis catheters. Methods: The present study is a clinical trial, in which the effect of three drugs, heparin, reteplase, and taurolock, in the prevention of thrombosis in hemodialysis catheters, has been investigated. The research units were studied in two intervention and control groups. The stratified random allocation method was used to assign patients to five groups (control, Heparin 50, Heparin 1000, reteplase, and taurolock), with strata based on the patient's age (20-70 years), gender, and duration of dialysis. Within each stratum, patients were also assigned to groups using the randomized block permutation method and a random number table tool. To prevent bias, this study is triple-blinded. This means that the patient, the thrombosis assessor, and the statistical analyst are unaware of the type of intervention received by the patient. Results: Gender (p < 0.999), age distribution (p = 0.774), and duration of dialysis (p = 0.875) showed no statistically significant relationship with thrombosis. However, significant differences were observed among the five groups regarding thrombosis incidence. The relative risk of thrombosis in the Heparin 50, Heparin 1000, reteplase, and taurolock groups compared to the control group was 92.5%, 92.2%, 98.2%, and 89% lower, respectively. Conclusion: Our study underscores the efficacy of heparin, reteplase, and taurolock in preventing thrombosis in hemodialysis catheters. While all three drugs demonstrated efficacy, the Heparin 50 group exhibited the highest relative risk reduction. These findings suggest that heparin, particularly at a low dose, should be considered a standard prophylactic treatment in hemodialysis patients.

An in vitro comparative study on clot lysis efficiency of urokinase and reteplase with the synergy of ultrasound needle.

Objectives: Ultrasound Needle, which is an improved ultrasonic horn device, has shown great potential for promoting the diffusion of thrombolytic drugs within clots and enhancing clot lysis efficiency. However, the clot lysis efficiency of different thrombolytic drugs with the synergy of Ultrasound Needle remains unknown. In this study, we aimed to compare the lysis efficiency of the non-fibrin-specific drug urokinase and fibrin-specific drug reteplase with the synergy of Ultrasound Needle. Materials and methods: Twenty-five milliliters of human blood was incubated for 1.5 h to form in vitro clots and then received the corresponding treatment protocols: control group (normal saline), US group (10 min of Ultrasound Needle treatment), UK group (30000IU of urokinase), r-PA group (2 mg of reteplase), US + UK group, and US + r-PA group. After treatment, the morphological changes of the clots were analyzed by B-mode ultrasound imaging and hematoxylin and eosin (H&E) staining. Lysis efficiency was evaluated based on the relative end weight (final weight/initial weight). The fibrin density of the different groups after treatment was assessed by immunofluorescence staining. Results: Morphological examination and relative end weight analysis showed that combination therapies induced a more thorough dissolution of clots compared with single therapies, and the US + r-PA group exhibited higher lysis efficiency than the US + UK group. In addition, immunofluorescence staining showed that the US + r-PA group had fewer remaining thrombus fibrins than the US + UK group after treatment. Conclusions: The Ultrasound Needle can significantly improve the clot lysis efficiency of both fibrinolytic drugs, and fibrin-specific reteplase exhibited superior lysis efficiency over non-fibrin-specific urokinase with the synergy of the Ultrasound Needle.

Prehospital Fibrinolysis Therapy in Acute Myocardial Infarction: A Narrative Review.

Acute myocardial infarction is a fatal condition. Acute myocardial infarction requires appropriate timely reperfusion therapy to improve the outcomes. Fibrinolysis and percutaneous coronary intervention are the cornerstone strategies for managing such cases. In this review, our objective is to summarize the available evidence concerning the administration of prehospital fibrinolysis and its impact on patient outcomes in patients with acute myocardial infarction. We conducted a comprehensive literature search across PubMed, Cochrane Library, Scopus, and Web of Science databases. Our search strategy included the following terms: "Prehospital," "EMS," "Emergency Medical Services," "ambulance," "Fibrinolytic Therapy," "alteplase," "streptokinase," "reteplase," "tenecteplase," "Acute Myocardial Infarction," and "patient outcomes." We found prehospital administration of fibrinolysis may improve the outcomes and decrease the mortality rate. We found that some recommendations were to use prehospital fibrinolysis only if the percutaneous coronary intervention was not accessible within two hours. Additionally, we discussed recommendations to use newer prehospital fibrinolysis as they have better efficacy and safety outcomes. In conclusion, prehospital fibrinolysis decreases the total ischemic time and improves outcomes in acute myocardial infarction patients when timely percutaneous coronary intervention is not available. The guidelines strongly recommend it when the anticipated time for percutaneous coronary intervention exceeds two hours. Ongoing research optimizes patient selection, treatment tools, and prehospital systems of care.

The effect of mutation on neurotoxicity reduction of new chimeric reteplase, a computational study.

Background and purpose: Excitotoxicity in nerve cells is a type of neurotoxicity in which excessive stimulation of receptors (such as N-methyl-d-aspartate glutamate receptors (NMDAR)) leads to the influx of high-level calcium ions into cells and finally cell damage or death. This complication can occur after taking some of the plasminogen activators like tissue plasminogen activator and reteplase. The interaction of the kringle2 domain in such plasminogen activator with the amino-terminal domain (ATD) of the NR1 subunit of NMDAR finally leads to excitotoxicity. In this study, we assessed the interaction of two new chimeric reteplase, mutated in the kringle2 domain, with ATD and compared the interaction of wild-type reteplase with ATD, computationally. Experimental approach: Homology modeling, protein docking, molecular dynamic simulation, and molecular dynamics trajectory analysis were used for the assessment of this interaction. Findings/Results: The results of the free energy analysis between reteplase and ATD (wild reteplase: -2127.516 ± 0.0, M1-chr: -1761.510 ± 0.0, M2-chr: -521.908 ± 0.0) showed lower interaction of this chimeric reteplase with ATD compared to the wild type. Conclusion and implications: The decreased interaction between two chimeric reteplase and ATD of NR1 subunit in NMDAR which leads to lower neurotoxicity related to these drugs, can be the start of a way to conduct more tests and if the results confirm this feature, they can be considered potential drugs in acute ischemic stroke treatment.

Combining Molecular Dynamics Simulations and Biophysical Characterization to Investigate Protein-Specific Excipient Effects on Reteplase during Freeze Drying.

We performed molecular dynamics simulations of Reteplase in the presence of different excipients to study the stabilizing mechanisms and to identify the role of excipients during freeze drying. To simulate the freeze-drying process, we divided the process into five distinct steps: (i) protein-excipient formulations at room temperature, (ii) the ice-growth process, (iii)-(iv) the partially solvated and fully dried formulations, and (v) the reconstitution. Furthermore, coarse-grained (CG) simulations were employed to explore the protein-aggregation process in the presence of arginine. By using a coarse-grained representation, we could observe the collective behavior and interactions between protein molecules during the aggregation process. The CG simulations revealed that the presence of arginine prevented intermolecular interactions of the catalytic domain of Reteplase, thus reducing the aggregation propensity. This suggests that arginine played a stabilizing role by interacting with protein-specific regions. From the freeze-drying simulations, we could identify several protein-specific events: (i) collapse of the domain structure, (ii) recovery of the drying-induced damages during reconstitution, and (iii) stabilization of the local aggregation-prone region via direct interactions with excipients. Complementary to the simulations, we employed nanoDSF, size-exclusion chromatography, and CD spectroscopy to investigate the effect of the freeze-drying process on the protein structure and stability.

Response Surface Methodology to Optimize the Expression Efficiency of Recombinant Reteplase.

Background: Over expression of Reteplase enzyme has already been studies in the periplasmic space of Escherichia coli (E. coli). However, the role different factors in its expresssin rate remained to be elucidated. Objectives: Optical cell density (OD), IPTG concentration, and expression time are highly effective in the protein expression rates. Therefore, we aimed to determine the optimum levels of these factors for reteplase expression using response surface methodology (RSM). Materials and Methods: The pET21b plasmid was used to sub-clone the designed reteplase gene. Then, the gene was transformed into E. coli BL21 strain. Induction of expression was done by IPTG and analyzed by the SDS page. experiments were designed using the RMS, while the effects of different conditions were evaluated using the Real time-PCR. Results: Sequence optimization removed all undesirable sequences of the designed gene. Transformation into E. coli BL21 was confirmed with an 1152 bp band on the agarose gel. A 39 kDa expression band on the SDS gel confirmed the gene expression. Performing 20 RSM-designed experiments, the optimum levels for IPTG concentration and OD were determined as 0.34mM and 5.6, respectively. Moreover, the optimum level of expression time was demonstrated to be 11.91 hours. The accuracy of the regression model for reteplase overexpression was confirmed by an F-value equal to 25.31 and a meager probability value [(Prob > F) < 0.0001]. The real-time-PCR results indicated that the performed calculations were highly accurate. Conclusion: The obtained results indicate that IPTG concentration, OD, and expression time are significantly involved in the augmentation of recombinant reteplase expression. To the best of our knowledge, this is the first study to assess the combined effect of these factors on reteplase expression. Further RSM-based experiments would bring about new insights regarding the best conditions for reteplase expression.

Hemorrhagic stroke as a rare complication of opening the permanent dialysis catheter by Reteplase: A case report study.

INTRODUCTION AND IMPORTANCE: Thrombosis of permanent hemodialysis catheters is one of the most important problems in hemodialysis centers. Drug methods such as heparin, aspirin and warfarin along with urokinase are used to keep these catheters open. CASE PRESENTATION: The present case report is of a 52-year-old Kurdish patient with a 7-year history of type 2 diabetes and hypertension leading to end-stage renal disease (ESRD). The patient has been undergoing hemodialysis for two months with two 3-h sessions per week. After several dialysis sessions, the patient is referred to Imam Khomeini Hospital in Urmia to open the catheter due to dysfunction. Because of catheter dysfunction, Reteplase (Retavase; Centocor, Malvern, PA) was administered at a dose of 3 U/lm (total dose 6 U). After administration of reteplase, the patient experienced sudden onset of headache and arterial hypertension. A computed tomography scan (CT) was immediately performed and revealed hemorrhagic stroke. Unfortunately, due to the extensive hemorrhagic stroke, the patient died one day later. CLINICAL DISCUSSION: Retavase (reteplase) is a thrombolytic drug used to dissolve blood clots. Reteplase increases your risk for bleeding, which can be severe or life-threatening. CONCLUSION: Thrombolysis with tissue plasminogen activator has been shown to be useful in some conditions. However, reteplase has a narrow therapeutic window and serious side effects, such as an increased risk of bleeding.

In Silico Study of Different Thrombolytic Agents for Fibrinolysis in Acute Ischemic Stroke.

Alteplase is the only FDA-approved drug for thrombolysis in acute ischemic stroke (AIS). Meanwhile, several thrombolytic drugs are deemed to be promising candidates to substitute alteplase. This paper evaluates the efficacy and safety of urokinase, ateplase, tenecteplase, and reteplase for intravenous AIS therapy by computational simulations of the pharmacokinetics and pharmacodynamics combined with a local fibrinolysis model. The performances of the drugs are evaluated by comparing clot lysis time, plasminogen activator inhibitor (PAI) inhibition resistance, intracranial hemorrhage (ICH) risk, and activation time from drug administration to clot lysis. Our results reveal that urokinase has the quickest lysis completion but the highest ICH risk due to excess fibrinogen depletion in systemic plasma. While tenecteplase and alteplase have very similar thrombolysis efficacy, tenecteplase has a lower risk of ICH and better resistance to PAI-1. Among the four simulated drugs, reteplase has the slowest fibrinolysis rate, but fibrinogen concentration in systemic plasma is unaffected during thrombolysis.

Insights Into The Effects of Amino Acid Substitutions on The Stability of Reteplase Structure: A Molecular Dynamics Simulation Study.

Background: Reteplase (recombinant plasminogen activator, r-PA) is a recombinant protein designed to imitate the endogenous tissue plasminogen activator and catalyze the plasmin production. It is known that the application of reteplase is limited by the complex production processes and protein's stability challenges. Computational redesign of proteins has gained momentum in recent years, particularly as a powerful tool for improving protein stability and consequently its production efficiency. Hence, in the current study, we implemented computational approaches to improve r-PA conformational stability, which fairly correlates with protein's resistance to proteolysis. Objectives: The current study was developed in order to evaluate the effect of amino acid substitutions on the stability of reteplase structure using molecular dynamic simulations and computational predictions. Materials and Methods: Several web servers designed for mutation analysis were utilized to select appropriate mutations. Additionally, the experimentally reported mutation, R103S, converting wild type r-PA into non-cleavable form, was also employed. Firstly, mutant collection, consisting of 15 structures, was constructed based on the combinations of four designated mutations. Then, 3D structures were generated using MODELLER. Finally, 17 independent 20-ns molecular dynamics (MD) simulations were conducted and different analysis were performed like root-mean-square deviation (RMSD), root-mean-square fluctuations (RMSF), secondary structure analysis, number of hydrogen bonds, principal components analysis (PCA), eigenvector projection, and density analysis. Results: Predicted mutations successfully compensated the more flexible conformation caused by R103S substitution, so, improved conformational stability was analyzed from MD simulations. In particular, R103S/A286I/G322I indicated the best results and remarkably enhanced the protein stability. Conclusion: The conformational stability conferred by these mutations will probably lead to more protection of r-PA in protease-rich environments in various recombinant systems and potentially enhance its production and expression level.

Fibrinolytic Therapy in Thrombosis of Mechanical Valves: Outcomes and Complications.

INTRODUCTION: Valvular heart disease presents a significant and escalating global health challenge. Prosthetic valve thrombosis (PVT) following surgical valve replacement is a primary cause of valve failure. The aim of this study was to ascertain the outcomes and complications of fibrinolytic therapy in patients diagnosed with PVT. METHOD: This cross-sectional study enrolled 81 patients diagnosed with PVT who underwent fibrinolytic therapy between 2008 and 2018. Streptokinase was administered to 87.6% of patients, while 12.4% received reteplase. All demographic and clinical data were gathered from the patients' medical records. The incidence of successful recovery and complications were assessed. RESULTS: The records of 81 patients (43.2% male, mean age: 51.6 ± 13.9 years) were examined. The findings revealed that 59% and 35% of the patients had mitral and aortic PVT, respectively. While 12% of the patients experienced drug complications, 90% achieved successful recovery. Stroke and severe hemorrhage were complications frequently reported by the patients treated with streptokinase (8% and 4% respectively). The patients treated with reteplase demonstrated a 100% recovery rate. Conversely, 89% of the patients treated with streptokinase achieved successful recovery, and 7% of the patients experienced a partial recovery. CONCLUSION: Fibrinolytic agents can serve as an effective treatment with an excellent success rate for managing PVT in patients post-surgical valve replacement.

Impact of intracoronary reteplase during primary percutaneous coronary intervention on infarct size in large anterior myocardial infarction: rationale and design of the RECOVER II trial.

Background: Thrombus embolization and microvascular obstruction during percutaneous coronary intervention (PCI) in ST-segment elevation myocardial infarction (STEMI) is commonly detected, which causes inadequate myocardial perfusion and elevated infarct size. An approach with low-dose intracoronary fibrinolytic treatment for reducing distal embolization and improving myocardial reperfusion in high-risk STEMI cases remains controversial. Methods: The RECOVER II study represents a multicenter, randomized, double-blind, parallel-group trial assessing low-dose adjunctive intracoronary reteplase during primary PCI in individuals with large anterior myocardial infarction and thrombus determined by angiography. The trial will enroll 306 cases who present within 12 h following STEMI for proximal or mid left anterior descending artery occlusion undergoing primary PCI. Cases will be randomized to receive a bolus intracoronary reteplase at 9 mg or 18 mg vs. placebo. The drug will be delivered over 2 minutes proximal to culprit lesions with an intracoronary catheter early after wire-crossing and before thrombus aspiration or balloon dilation. Results: The primary outcome will be infarct size assessed by late gadolinium-enhanced magnetic resonance imaging (MRI) (% of left ventricular mass) on day 7 after enrollment. Secondary outcomes will include the amount of microvascular obstruction and myocardial salvage index examined via MRI on day 7, angiographic measures of reperfusion [Thrombolysis in Myocardial Infarction (TIMI) coronary flow grade, TIMI frames count and myocardial blush grade], incidence of complete ST-segment resolution at 2 hours after reperfusion, area under the curve for troponin T, and rates of major adverse cardiovascular events at 30 days. Conclusions: RECOVER II will determine whether the addition of low-dose intracoronary reteplase early after wire-crossing as an adjunct to reperfusion treatment reduces infarct size in individuals with large anterior myocardial infarction. Trial Registration: ClinicalTrials.gov Identifier: NCT04571580.

Rational design of a new variant of Reteplase with optimized physicochemical profile and large-scale production in Escherichia coli.

Structural engineering of the recombinant thrombolytic drug, Reteplase, and its cost-effective production are important goals in the pharmaceutical industry. In this study, a single-point mutant of the protein was rationally designed and evaluated in terms of physicochemical characteristics, enzymatic activity, as well as large-scale production settings. An accurate homology model of Reteplase was used as the input to appropriate tools to identify the aggregation-prone sites, while considering the structural stability. Selected variants underwent extensive molecular dynamic simulations (total 540 ns) to assess their solvation profile and their thermal stability. The Reteplase-fibrin interaction was investigated by docking. The best variant was expressed in E. coli, and Box-Behnken design was used through response surface methodology to optimize its expression conditions. M72R mutant demonstrated appropriate stability, enhanced enzymatic activity (p < 0.05), and strengthened binding to fibrin, compared to the wild type. The optimal conditions for the variant's production in a bioreactor was shown to be 37 ºC, induction with 0.5 mM IPTG, for 2 h of incubation. Under these conditions, the final amount of the produced enzyme was increased by about 23 mg/L compared to the wild type, with an increase in the enzymatic activity by about 2 IU/mL. This study thus offered a new Reteplase variant with nearly all favorable properties, except solubility. The impact of temperature and incubation time on its large-scale production were underlined as well.

Enhanced clot lysis by a single point mutation in a reteplase variant.

Recombinant tissue-type plasminogen activator (rtPA) is the clot lysis drug approved for clinical use, and is characterised by a short half-life and substantial inactivation by plasminogen activator inhibitor-1 (PAI-1). We previously discovered that a tPA mutation (A419Y) at the protease domain led to enhanced fibrinolysis activity. In the present study, we studied the mechanism of such mutation in enhancing the proteolytic activity, and whether such enhancement persists in reteplase, an United States Food and Drug Administration-approved tPA truncated variant. We constructed and expressed a series of reteplase-based mutants, including rPAG (glycosylated rPA), rPAG -Y (with A419Y mutant at rPAG ), rPAG -A4 (tetra-alanine mutation at 37-loop of rPAG ), and rPAG -A4/Y (with both) and evaluated their plasminogen activation and PAI-1 resistance. Surface plasmon resonance analysis showed that the rPAG had fibrin affinity comparable to full-length tPA. Moreover, rPAG -Y had 8·5-fold higher plasminogen activation and stronger tolerance to PAI-1 compared to rPAG . We also found that the mutations containing tetra-alanine (rPAG -A4 and rPAG -A4/Y) had dramatically reduced plasminogen activation and impaired clot lysis. In a pulmonary embolism murine model, rPAG -Y displayed a more efficient thrombolytic effect than rPAG . These results identified a novel mutant reteplase variant of tPA with increased fibrinolytic activity, laying the foundation for the development of a new potent fibrinolytic agent.

Recombinant Expression of Thrombolytic Agent Reteplase in Marine Microalga Tetraselmis subcordiformis (Chlorodendrales, Chlorophyta).

Tetraselmis subcordiformis, a unicellular marine green alga, is used widely in aquaculture as an initial feeding for fish, bivalve mollusks, penaeid shrimp larvae, and rotifers because of its rich content of amino acids and fatty acids. A stable nuclear transformation system using the herbicide phosphinothricin (PPT) as a selective reagent was established previously. In this research, the recombinant expression in T. subcordiformis was investigated by particle bombardment with the rt-PA gene that encodes the recombinant human tissue-type plasminogen activator (Reteplase), which is a thrombolytic agent for acute myocardial infarction treatment. Transgenic algal strains were selected by their resistance to PPT, and expression of rt-PA was validated by PCR, Southern blotting, and Western blotting, and bioactivity of rt-PA was confirmed by the fibrin agarose plate assay for bioactivity. The results showed that rt-PA was integrated into the genome of T. subcordiformis, and the expression product was bioactive, indicating proper post-transcriptional modification of rt-PA in T. subcordiformis. This report contributes to efforts that take advantage of marine microalgae as cell factories to prepare recombinant drugs and in establishing a characteristic pathway of oral administration in aquaculture.

Modulation of Early Neutrophil Granulation: The Circulating Tumor Cell-Extravesicular Connection in Pancreatic Ductal Adenocarcinoma.

Tumor cells dissociate from the primary site and enter into systemic circulation (circulating tumor cells, CTCs) either alone or as tumor microemboli (clusters); the latter having an increased predisposition towards forming distal metastases than single CTCs. The formation of clusters is, in part, created by contacts between cell-cell junction proteins and/or cytokine receptor pairs with other cells such as neutrophils, platelets, fibroblasts, etc. In the present study, we provide evidence for an extravesicular (EV) mode of communication between pancreatic cancer CTCs and neutrophils. Our results suggest that the EV proteome of CTCs contain signaling proteins that can modulate degranulation and granule mobilization in neutrophils and, also, contain tissue plasminogen activator and other proteins that can regulate cluster formation. By exposing naïve neutrophils to EVs isolated from CTCs, we further show how these changes are modulated in a dynamic fashion indicating evidence for a deeper EV based remodulatory effect on companion cells in clusters.

Fusion Expression and Fibrinolytic Activity of rPA/SP-B.

BACKGROUND: Pulmonary surfactant dysfunction is an important pathological factor in acute respiratory distress syndrome (ARDS) and pulmonary fibrosis (PF). OBJECTIVE: In this study, the characteristics of recombinant mature surfactant protein B (SP-B) and reteplase (rPA) fusion protein maintaining good pulmonary surface activity and rPA fibrinolytic activity in acute lung injury cell model were studied. METHODS: We studied the characteristics of SP-B fusion expression, cloned rPA gene and N-terminal rPA/C-terminal SP-B co-expression gene, and constructed them into eukaryotic expression vector pEZ-M03 to obtain recombinant plasmids pEZ-rPA and pEZ-rPA/SP-B. The recombinant plasmids was transfected into Chinese hamster ovary (CHO) K1 cells and the expression products were analyzed by Western Blot. Lipopolysaccharide (LPS) was used to induce CCL149 (an alveolar epithelial cell line) cell injury model. Fluorescence staining of rPA and rPA/SP-B was carried out with the enhanced green fluorescent protein (eGFP) that comes with pEZ-M03; the cell Raman spectroscopy technique was used to analyze the interaction between rPA/SP-B fusion protein and the phospholipid structure of cell membrane in CCL149 cells. The enzyme activity of rPA in the fusion protein was determined by fibrin-agarose plate method. RESULTS: The rPA/SP-B fusion protein was successfully expressed. In the CCL149 cell model of acute lung injury (ALI), the green fluorescence of rPA/SP-B is mainly distributed on the CCL149 cell membrane. The rPA/SP-B fusion protein can reduce the disorder of phospholipid molecules and reduce cell membrane damage. The enzyme activity of rPA/SP-B fusion protein was 3.42, and the fusion protein still had good enzyme activity. CONCLUSION: The recombinant eukaryotic plasmid pEZ-rPA/SP-B is constructed and can be expressed in the eukaryotic system. Studies have shown that rPA/SP-B fusion protein maintains good SP-B lung surface activity and rPA enzyme activity in acute lung injury cell model.

Design and production of new chimeric reteplase with enhanced fibrin affinity: a theoretical and experimental study.

Plasminogen activators (PAs) are widely used for treatment of disorders caused by clot formation. Fibrin specific PAs are safe drugs from this group because of reducing the incidence of hemorrhage. The newer generation of PAs like tenecteplase, reteplase and desmoteplase were designed with the aim of achieving desirable properties such as improving specificity and affinity to fibrin and increasing half-life. Protein engineering and using of theoretical methods can help to rational and reliable design of new PAs with a set of favorable properties. In the present study, two new chimeric reteplase named M1-chr and M2-chr were designed with the aim of enhancing fibrin affinity also some potential properties include of increasing resistance to plasminogen activator inhibitor-1 and decreasing neurotoxicity. So, finger domain of desmoteplase was added to reteplase as a high fibrin specific domain. Some other point mutations were considering to achieve other mentioned properties. Three dimensional structure of wild-type reteplase and mutants were created by homology modeling and were evaluated by molecular dynamic simulation. Then, mutants docked to fibrin by HADDOCK web tools. Result of theoretical section verified the stability of mutants' structures. Also showed better interaction between M1-chr with fibrin than M2-chr. Wild-type and mutants were produced in bacterial expression system. Experimental assessment showed both mutants have appropriate enzymatic activity also 1.9-fold fibrin binding ability compared to wild-type. Therefore, this study offers new thrombolytic drugs with desirable properties specially enhanced fibrin affinity so they can represent a promising future in cost-effective production of favorable thrombolytic drugs.Communicated by Ramaswamy H. Sarma.

FTIR Investigation of Secondary Structure of Reteplase Inclusion Bodies Produced in Escherichia coli in Terms of Urea Concentration.

Recent studies suggest that reducing the induction temperature would improve the quality of some recombinant inclusion bodies (IB) by providing a native-like secondary structure and leading to an improvement in protein recovery. This study focused on optimizing the solubilization condition of Reteplase, a recombinant protein with 9 disulfide bonds. The influence of lowering induction temperature and urea concentration was investigated on the secondary structure of the recombinant protein through FTIR analysis. Induction temperature reduction decreased the percentage of helixes and loops from 49 to 8. In addition, FTIR spectroscopy corroborates the drastic impact of this parameter on Reteplase secondary structure. Even though lowering urea concentration tripled the solubility of IBs expressed at lower induction temperature, the final yield is still quite low to be considered as optimum. On the other hand, the percentage of beta strands and turns in secondary structure of dissolved proteins were proportional to urea concentration. Therefore, in case of Reteplase, protein expression at low temperature (25 °C) was not efficient to improve the protein recovery yield. Future studies need to focus on using other methods of solubilizing IBs to improve protein recovery.

Efficient refolding of recombinant reteplase expressed in Escherichia coli strains using response surface methodology.

Reteplase is a deleted variant of human tissue plasminogen activator with a complex structure containing nine disulfide bonds. Reteplase is expressed as inclusion bodies in Escherichia coli and needs the additional step of refolding for activation. In this study an experimental design was performed to find the optimal refolding condition for reteplase. The influence of 14 chemical additives was assessed by one factor at a time method and then Taguchi design followed by response surface methodology was employed to find compounds with most significant effects on reteplase refolding and their optimum concentration. We found that 0.13 M histidine, 1.64 M methionine, 0.33 M cysteine, and 0.34 M arginine in addition to the GSH/GSSG is the optimal condition for refolding of reteplase. We also investigated the refolding yield for inclusion bodies obtained from different E. coli strains and found that BL21 (DE3) has the best recovery yield in comparison to Rosetta-gami and Shuffle T7.