Introduction: Tissue plasminogen activator (tPA) remains the only approved pharmacologic treatment for patients with ischemic stroke. Although intravenous thrombolysis improves outcome in a subset of patients, tPA also increases symptomatic hemorrhage and worsens brain edema, thus limiting its clinical applicability. Among several putative mechanisms, plasmin-meditated complement cascade activation likely plays a critical role in the deleterious effects of tPA.
Hypothesis: tPA administration promotes C3 cleavage and complement activation in ischemic brain, and pharmacologic inhibition of the C3a receptor abrogates tPA-mediated hemorrhage and brain edema following reperfused stroke.
Methods: C3a concentrations were assessed using ELISA. Transient focal cerebral ischemia was induced in mice by 60 minutes of middle cerebral artery occlusion (MCAO), with tPA (10mg/kg) or saline injected intravenously at reperfusion. C3a receptor antagonist (1mg/kg) or vehicle was administered 45 minutes prior to MCAO. Infarct volume was determined at 24 hours by TTC staining, neurological function was assessed on a 5-point scale, and brain hemorrhage was quantified using a spectrophotometric assay. Cerebral edema was determined by calculating the difference in volume between ischemic and non-ischemic hemispheres and normalized to infarct volume.
Results: The incubation of tPA with native C3 as well as plasma promotes the generation of C3a. Similarly, intravenous tPA administration dramatically increases cerebral C3a levels in the ischemic hemisphere following MCAO. Intravenous tPA significantly reduces infarct volume (p<0.05) and improves neurological function (p<0.05) in our stroke model. However, tPA also dramatically increases cerebral hemorrhage (p<0.05) and relative cerebral edema (p<0.05). Administration of a C3a receptor antagonist abrogates this hemorrhagic conversion (p<0.05) and brain edema (p<0.05).
Conclusions: Intravenous tPA administration promotes complement activation through C3 cleavage in ischemic brain. Pharmacologic inhibition of the C3a receptor protects against the deleterious side effects of tPA and represents a promising therapeutic strategy for stroke patients.