In vivo studies showed that
tissue-plasminogen activator (t-PA) may aggravate neuronal injury after focal
cerebral ischemia. We hypothesized that t-PA impairs survival-promoting cell signaling in the ischemic brain, which may be reversed by a
neuroprotectant, i.e.
melatonin. We examined the effects of t-
PA (10 mg/kg, i.v.), administered alone or in combination with
melatonin (4 mg/kg, i.p.), on ischemic injury,
inducible nitric oxide synthase (iNOS) expression as well as Akt, Bcl-X(L) and
caspase-3 signaling following 90 min of intraluminal middle cerebral artery (MCA) occlusion in mice. t-PA, delivered immediately after reperfusion onset, increased
infarct volume at 24 hr 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 that t-PA treatment was associated with an accumulation of iNOS positive cells in ischemic brain areas, which was abolished after co-delivery of
melatonin. Western blots revealed that t-PA decreased phosphorylated Akt levels, but did not influence Bcl-X(L) expression and
caspase-3 activity in ischemic brain lysates. Co-treatment with
melatonin restored phosphorylated Akt levels, increased Bcl-X(L) expression and reduced
caspase-3 activity. We provide evidence that t-PA-induced
brain injury is accompanied by an activation of iNOS and inhibition of phosphatidylinositol-3
kinase/Akt. That
melatonin reversed these signaling changes and the t-PA-induced
brain injury makes this
indole attractive as an add-on treatment with thrombolytics.