title: Tissue-plasminogen activator-induced ischemic brain injury is reversed by melatonin: role of iNOS and Akt.
abstract: 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.
authors.affiliation: Department of Neurology, University Hospital Zürich, Zürich, Switzerland. ertugrul.kilic@usz.ch
authors.forename: Ertugrul
authors.initials: E
authors.lastname: Kilic
authors.forename: Ulkan
authors.initials: U
authors.lastname: Kilic
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.forename: Claudio L
authors.initials: CL
authors.lastname: Bassetti
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Hermann
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002545:Brain Ischemia / Q000139:chemically induced / Q000188:drug therapy*; D007150:Immunohistochemistry; D017078:Laser-Doppler Flowmetry; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D019001:Nitric Oxide Synthase / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D010959:Tissue Plasminogen Activator / Q000494:pharmacology
chemical_list: D011518:Proto-Oncogene Proteins; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D010959:Tissue Plasminogen Activator; D008550:Melatonin