Thrombolysis: the need for a critical review

Proteases as therapeutics

Proteases are an expanding class of drugs that hold great promise. The U.S. FDA (Food and Drug Administration) has approved 12 protease therapies, and a number of next generation or completely new proteases are in clinical development. Although they are a well-recognized class of targets for inhibitors, proteases themselves have not typically been considered as a drug class despite their application in the clinic over the last several decades; initially as plasma fractions and later as purified products. Although the predominant use of proteases has been in treating cardiovascular disease, they are also emerging as useful agents in the treatment of sepsis, digestive disorders, inflammation, cystic fibrosis, retinal disorders, psoriasis and other diseases. In the present review, we outline the history of proteases as therapeutics, provide an overview of their current clinical application, and describe several approaches to improve and expand their clinical application. Undoubtedly, our ability to harness proteolysis for disease treatment will increase with our understanding of protease biology and the molecular mechanisms responsible. New technologies for rationally engineering proteases, as well as improved delivery options, will expand greatly the potential applications of these enzymes. The recognition that proteases are, in fact, an established class of safe and efficacious drugs will stimulate investigation of additional therapeutic applications for these enzymes. Proteases therefore have a bright future as a distinct therapeutic class with diverse clinical applications.

Understanding the enzymology of fibrinolysis and improving thrombolytic therapy

Cardiovascular disease is responsible for 17 million deaths per year but acute myocardial infarction and stroke can be treated with thrombolytics ("clot busters"), which are plasminogen activators. However, despite many years of study and huge investment from the pharmaceutical industry, clinical trials of new drugs have often been disappointing. Part of the problem may be our incomplete understanding of the regulation of plasminogen activation in vivo. We have developed precise in vitro methods and with the application of computer simulations, we hope to improve our understanding of plasminogen activation to facilitate improvements in thrombolytic therapy.

Role of low-molecular-weight heparins in the management of patients with unstable angina pectoris and non-Q-wave acute myocardial infarction

The development of effective approaches to the management of the unstable coronary syndromes has resulted from an improved understanding of interactions between the vascular wall, platelets, and coagulation factors, and of their response to pharmacologic and mechanical interventions. Furthermore, the occurrence of frequent adverse events after discharge in patients with unstable coronary artery disease (CAD) treated with these therapies alone would argue that, for many of these patients, such stabilization is not the end of the therapeutic pathway; rather, these therapies are for many a preparation for ultimate revascularization, to preserve myocardium and minimize periprocedural complications. The low-molecular-weight heparins with their unique pharmacology offer a new option in the therapy of patients with unstable CAD. There is now extensive experience in the use of several of the low-molecular-weight heparins, particularly dalteparin and enoxaparin, in the management of patients with unstable angina. Several trials have investigated the questions raised by these observations, taking advantage of the unique pharmacologic properties of the low-molecular-weight heparins for both acute inpatient use and prolonged outpatient administration. Although differences in study design preclude direct comparison between the available low-molecular-weight heparins, in these trials low-molecular-weight heparins have been shown to be effective alternatives to conventional heparin for the management of patients with unstable angina and non-Q-wave infarction. These include several small-scale trials and the larger FRagmin during InStability in Coronary artery disease (FRISC), Fragmin in Unstable Coronary Artery Disease (FRIC), Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events (ESSENCE), FRISC II, and Thrombolysis in Myocardial Infarction (TIMI)-11B trials. Thus, the low-molecular-weight heparins appear to be a superior alternative to traditionally administered intravenous unfractionated heparin. They are more predictable in action, do not require frequent activated partial thromboplastin time (aPTT) measurements and dosage adjustments, are easier to administer, and are potentially more efficacious. With their proven efficacy, predictability of action, and convenience of administration and dosing, there are very good reasons for selecting them as first-line therapies for patients presenting with unstable angina and non-Q-wave myocardial infarction.

New strategy of thrombolysis. Conjunctive effect of plasminogen activators with different pharmacokinetic profile

Combined actions of native and prolonged thrombolytics allow the use of lower doses and simplified schemes of administration, thus yielding significant results in experimental therapy regarding the efficacy and safety of thrombolysis. Development of prolonged forms of plasminogen activators and testing their effect in combination with the thrombolysis trigger are well founded and of current interest. Thrombolytic compositions on the basis of short- and long-term-acting plasminogen activators appear to be promising and potentially eligible for bolus administration.

Intracerebral hemorrhage after fibrinolytic therapy for acute myocardial infarction

BACKGROUND AND PURPOSE

Intracerebral hematoma may complicate treatment of acute myocardial infarction in patients treated with fibrinolytic agents. We studied the clinical presentation and computed tomographic characteristics.

METHODS

We studied eight patients with lobar intracerebral hematomas after fibrinolytic treatment of acute coronary occlusion. All patients had electrocardiographic and laboratory evidence of acute myocardial infarction and were treated with tissue plasminogen activator or streptokinase followed by heparin infusion to prevent reocclusion. Computed tomography scans of 17 patients with cerebral hemorrhage from other causes were used for comparison.

RESULTS

For most patients, outcome was fatal within hours of the ictus. Computed tomography scans showed superficially large lobar hematomas in six patients. One patient had a putaminal hemorrhage, and one had a vermis hemorrhage. Multiple sites of intracerebral hemorrhage were noted in three patients. Fluid levels inside the hematoma suggesting continuing hemorrhage into multiple compartments were common. Radiologically, fluid levels in hematomas, multiple hematomas, and blood in multiple compartments served to differentiate fibrinolysis-induced hemorrhage from hemorrhage of other causes. Severe amyloid angiopathy was found in one patient who was operated on.

CONCLUSIONS

Hemorrhages in multiple compartments and the presence of fluid levels inside the hematoma suggest fibrinolysis-associated cerebral hematomas. Severe amyloid angiopathy may be a crucial factor in this clinical entity. Outcome is poor, and a high proportion of patients have rapid progression to brain death. Therefore, emergency neurosurgical evacuation will probably be unsuccessful.