Purpose
In vivo studies showed that t-PA may aggravate neuronal injury after focal cerebral ischemia1, 2 and 3. We hypothesized that therapeutically delivered t-PA might impair survival-promoting cell signalling in the ischemic brain, which may be reversed by an anti-oxidative neuroprotectant, the neurohormone melatonin.
Methods
We examined the effects of t-PA (10 mg/kg, i. v.), administered alone or in combination with melatonin (4 mg/kg, i.p.) immediately after reperfusion onset, on ischemic injury, inducible NO synthase (iNOS) expression and Akt, Bcl-XL and caspase-3 signalling following 90 minutes of intraluminal middle cerebral artery (MCA) occlusion in mice, followed by 24 hours of reperfusion.
Results
t-PA, delivered immediately after reperfusion onset, increased infarct volume at 24 hours after MCA occlusion, in accordance with previous findings. Melatonin reduced infarct size, when administered alone, and reversed the t-PA-induced brain injury. Immunohistochemical studies showed an accumulation of iNOS+ cells in ischemic brain areas after t-PA treatment, which was abolished after co-delivery of melatonin. Western blots revealed that t-PA decreased phosphorylated Akt levels, but did not influence Bcl-XL expression and caspase-3 activity in ischemic brain lysates. Co-treatment with melatonin restored phosphorylated Akt levels, increased Bcl-XL expression and reduced caspase-3 activity.
Conclusions
We provide evidence that t-PA-induced brain injury is accompanied by an activation of iNOS and inhibition of phosphatidylinositol-3 kinase/ Akt. Our observation that melatonin reverses the signalling changes and brain injury evoked by t-PA makes this indole attractive as add-on treatment with thrombolytics.