Thrombolytic therapy: a review of its use in acute myocardial infarction

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.

Biomimetic nanoparticle technology for cardiovascular disease detection and treatment

Cardiovascular disease (CVD), which encompasses a number of conditions that can affect the heart and blood vessels, presents a major challenge for modern-day healthcare. Nearly one in three people has some form of CVD, with many suffering from multiple or intertwined conditions that can ultimately lead to traumatic events such as a heart attack or stroke. While the knowledge obtained in the past century regarding the cardiovascular system has paved the way for the development of life-prolonging drugs and treatment modalities, CVD remains one of the leading causes of death in developed countries. More recently, researchers have explored the application of nanotechnology to improve upon current clinical paradigms for the management of CVD. Nanoscale delivery systems have many advantages, including the ability to target diseased sites, improve drug bioavailability, and carry various functional payloads. In this review, we cover the different ways in which nanoparticle technology can be applied towards CVD diagnostics and treatments. The development of novel biomimetic platforms with enhanced functionalities is discussed in detail.

In vitro Simulation of Therapeutic Plasmatic Fibrinolysis

One type of therapy for thromboembolism is plasmatic thrombolysis. Several plasminogen activators (PA) are clinically available, including urokinase (u-PA), tissue plasminogen activator (t-PA), streptokinase (SK), plasminogen-streptokinase-activator-complex (PSAC), or mutants of t-PA such as reteplase (RP) or tenecteplase (TP). Therapeutic plasmatic fibrinolysis was simulated, using the PA at relevant plasma concentrations, and plasmin (Pli) and PA activities were determined. Normal citrated plasma was supplemented with 31 to 1,000 IU/mL u-PA, 0.31 to 20 μg/mL t-PA, 125 to 4,000 IU/mL SK, 12.5 to 400 U/mL PSAC, 125 to 4,000 U/mL RP, or 0.31 to 10,μg/mL TP. Ten IU/mL urokinase was also incubated with pooled plasma of stroke patients, that was previously oxidized with the singlet oxygen (1O2) donor chloramine T® (CT), to destroy plasmatic PAI-1 and a2-antiplasmin. After 0 to 80 minutes (37°C), 50-μL samples were withdrawn and added to 100 μL 1.5 M arginine, pH 8.7, and oxidized with 50 μL of 20 mM CT. For determination of plasmin activity, 10 μL thereof was incubated with 150 μL 1.5 M arginine, pH 8.7, and 100 μL 20 mM CT preoxidized (15 minutes 37°C) pooled normal citrate buffered EDTA-plasma for 30 minutes (37°C). For determination of [PA+Pli]-activity, arginine was added after this incubation. 25-μL 6 mM Val-Leu-Lys-pNA were added and AA/h at room temperature (RT) was monitored, using a microtiterplate reader. [PA+Pli]-Pli = PA. The PA concentration required to induce 25% [ED25] of the maximally inducible Pli-activity in plasma (= 1 U/mL = 45 mg/L = 0.53 Amol/L active Pli; AA = 363 + 8 mA/h RT) after 10 minutes (37°C) were 320 IU/mL u-PA, 8 μg/mL t-PA, 140 U/mL PSAC, 6,000 IU/mL SK, 720 U/mL RP, and approximately 150 μg/mL TP. The approximate activity half-lives of the PA in plasma were 30 minutes for u-PA, 30 minutes for t-PA, greater than 80 minutes for SK, greater than 80 minutes for PSAC, 50 minutes for RP, and 80 minutes for TP. The present study shows-for the first time-a combined kinetic in vitro simulation of the plasmatic activity of six different PAs. At clinically used concentrations, RP induces the highest plasmatic Pli activity. Due to unselective generation of plasmin in plasma, all PA are of some danger in inducing severe hemorrhagias. Clinical thrombolysis might be improved by usage of more physiologic activators of thrombolysis, such as activators of polymorphonuclear neutrophils.

A review of current agents for anticoagulation for the critical care practitioner

There has been a tremendous boom in the arena of anticoagulant therapy recently. Although the indications for these agents reside in the noncritical care environment, over time, the impact of these agents have infiltrated the critical care environment particularly due to devastating complications with associated use. With so many newer agents on the market or coming down the pipeline, it is easy to become overwhelmed. It is important that the critical care practitioner does not ignore these agents but becomes familiar with them to better prepare for the management of patients on one or more anticoagulant agents in the intensive care unit. To equip the critical care practitioners with the knowledge about commonly used anticoagulants, we provide an extensive review of the pharmacology, indications, and adverse effects related to these agents as well as suggestions on preventing or managing complications.

Recent advances in the treatment of thromboembolic diseases: Venous thromboembolism

Venous thromboembolic diseases are the major concern of rising cost of healthcare and are commonest health problem across the globe. Both genetic and acquired risk factors are believed to be strongly linked with these diseases. Commonly encountered problems to the therapy include dose fixing and routine monitoring, yet some serious problems of bleeding also necessitate the immediate need to develop new agents. The review is primarily concerned with the new developments in the treatment of thromboembolic diseases. Therapeutic applications of anticoagulants, antiplatelets, and thrombolytics have been discussed in enough detail.

In vitro simulation of therapeutic thrombolysis with microtiter plate clot-lysis assay

Only limited comparable data are available on the clot lysis power of the clinically used plasminogen activators (PA). Here the PA were used at different clinically relevant concentrations, and the lysis of the microclots was determined. A microclot lysis assay was used to study thrombolysis by urokinase, tissue-PA (t-PA), streptokinase, plasminogen-streptokinase activator complex (PSAC), reteplase, or tenecteplase. The clot turbidity served as a tool to determine clot mass: 100 microL fresh microclots were incubated with 25 microL PA in 6% bovine serum albumin (BSA)-phosphate-buffered saline (PBS) and 100 microL BSA-PBS or pooled normal human plasma; that is, the PA were in the liquid supernatant of a plasma clot and were not entrapped in the clot, an assay system comparable to normal physiology. The turbidity was determined after 0 to 5 hours (37 degrees C) by a microtiter plate reader. The lysable clot turbidity (clot mass) was expressed in percent of 100% lysable clot control. The clot lysis activity is 100% minus the clot mass in percent. The effective doses at 50% (ED(50)) of lysis of fresh clots after 4 hours (37 degrees C) with 6% BSA or pooled normal human plasma in the clot-supernatant were urokinase 128 or 180 IU/mL; t-PA 0.3 or 0.2 microg/mL; streptokinase 215 or 1371 IU/mL; PSAC 60 or 91 U/mL; reteplase 664 or 996 U/mL; tenecteplase 0.2 or 0.2 microg/mL. The presence of a plasma thrombus with plasma supernatant increases the activity of t-PA approximately 20-fold and that of tenecteplase approximately 400-fold after 4 hours (37 degrees C), when compared to urokinase; in contrast, the lytic activity induced by reteplase decreases; i.e., the plasmin generated by reteplase is hampered on its lytic action against a thrombus. When comparing the clot lysability of microclots of 29 different donors, the only correlation (r > 0.6) was that between u-PA and t-PA. The lysability of individual clots by PA can be measured with the present routine-suited technique. It is suggested that different thrombolytic agents or concentrations thereof would have a different clinical outcome in different individuals.

Changes in the management of acute myocardial infarction in Southern Tasmania

BACKGROUND

In recent years, the management of acute myocardial infarction (AMI) has been the subject of many clinical trials. These studies have clearly established the value of using pharmacological agents, including aspirin, beta-blockers, thrombolytics and angiotensin converting enzyme (ACE) inhibitors. There have been suggestions, however, that practice has been slow to change in light of the findings of these trials.

AIM

To review cases of AMI at the major teaching hospital in Tasmania, Australia, to determine whether the recommendations from the results of the trials had been translated into local clinical practice, and to examine temporal changes in drug usage and clinical outcomes.

METHODS

A retrospective review of the medical records of patients admitted to the hospital with an AMI during 1996 and for the first four months of 1998 was performed. An extensive range of demographic and clinical variables was recorded, and differences between the 1996 and 1998 patients and between recipients and non-recipients of the different pharmacological agents were statistically evaluated.

RESULTS

The patients had a mean age of 65.9 +/- 12.3 years in 1996 (n = 205) and 66.8 +/- 12.3 years in 1998 (n = 71), with males accounting for 64.4% of cases in 1996 and 64.8% of cases in 1998. There were no significant demographic or medical history differences between the two groups. The median time of presentation after the onset of chest pain was 3.5 h in 1996 and 4 h in 1998. The rates of use of major therapeutic interventions post-AMI for 1996 and 1998, respectively, were: aspirin (89.1%, 90.3%), streptokinase (18.5%, 9. 9%), r-tPA (14.1%, 21.1%), intravenous beta-blockers (11.2%, 7.0%), oral beta-blockers (67.2%, 49.3%; P < 0.01), ACE inhibitors (44.4%, 59.2%; P < 0.05), intravenous nitrate (94.1%, 91.6%), oral nitrate (22.9%, 26.8%), calcium channel antagonists (19.5%, 35.2%; P < 0.05), cholesterol lowering agents (26.3%, 40.9%; P < 0.05), antiarrhythmics (21.5%, 25.4%) and warfarin (8.3%, 9.9%). Patients who received therapy with each of aspirin, r-tPA, intravenous beta-blockers, oral beta-blockers, intravenous nitrate and cholesterol lowering agents were significantly younger than the non-recipients (all P < 0.01), while patients treated with ACE inhibitors and antiarrhythmics were significantly older than the non-recipients (both P < 0.001). Non-recipients of thrombolytics presented to hospital significantly later, on average, than recipients. The hospital mortality rate was 15.1% in 1996 and 12.7% in 1998, and adverse drug reactions occurred in 21.5% of patients in 1996 and 15.5% in 1998.

CONCLUSION

Although there have been substantial increases in the use of ACE inhibitors and cholesterol lowering agents post-AMI in recent years, reductions in the use of thrombolytics and beta-blockers and their possible underuse in the elderly are of concern and warrant intervention.

Ebselen: prospective therapy for cerebral ischaemia

Stroke occurs due to haemorrhage or occlusive injury and results in ischaemia and reperfusion injury. A variety of destructive mechanisms are involved including oxygen radical generation, calcium overload, cytotoxicity and apoptosis as well as the generation of inflammatory mediators. Ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one (PZ 51, DR3305), is a mimic of GSH peroxidase which also reacts with peroxynitrite and can inhibit enzymes such as lipoxygenases, NO synthases, NADPH oxidase, protein kinase C and H(+)/K(+)-ATPase. Ebselen is in a late stage of development for the treatment of stroke. The molecular actions of ebselen contribute to its anti-inflammatory and anti-oxidant properties, which have been demonstrated in a variety of in vivo models. Numerous in vitro experiments using isolated LDL, liposomes, microsomes, isolated cells and organs have established that ebselen protects against oxidative challenge. Unlike many inorganic and aliphatic selenium compounds, ebselen has low toxicity as metabolism of the compound does not liberate the selenium moiety, which remains within the ring structure. Subsequent metabolism involves methylation, glucuronidation and hydroxylation. Experimental studies in rats and dogs have revealed that ebselen is able to inhibit both vasospasm and tissue damage in stroke models, which correlates with its inhibitory effects on oxidative processes. Results from randomised, placebo-controlled, double-blind clinical studies on the neurological consequences of acute ischaemic stroke, subarachnoid haemorrhage and acute middle cerebral artery occlusion, have revealed that ebselen significantly enhances outcome in patients who have experienced occlusive cerebral ischaemia of limited duration. The benefit achieved with ebselen is closely related to the rapidity with which the treatment is initiated, following the onset of the stroke attack. Safety and tolerability are good and no adverse effects have become apparent. Ebselen is currently at the pre-registration stage for subarachnoid haemorrhage and stroke in Japan.