IkappaB-alpha expression following transient focal cerebral ischemia is modulated by nitric oxide

The role of nitric oxide (NO) in cerebral ischemia/reperfusion (IR) has been intensively investigated. In general NO is regarded as a mediator of ischemia-associated neuronal damage, as inhibitors of NO synthesis ameliorate neuronal injury during permanent focal cerebral ischemia, however the exact role of NO in ischemia remains controversial. It has been previously shown that NO-donors can directly inhibit the DNA binding activity of NF-kappaB family proteins and strong evidence supports that activation of NF-κB contributes to ischemia-induced neuronal injury. In this study, we have investigated whether NO production by nNOS, eNOS and iNOS modulates IkB-alpha expression in cerebral ischemia, by using various inhibitors of NOS, in rats subjected to transient (1 h) middle cerebral artery occlusion (tMCAo). Male Wistar rats were treated intraperitoneally (i.p.) with 3 mg/kg of NG-nitro-l-arginine methyl ester (l-NAME, a non-selective NOS inhibitor), 5 mg/kg of l-N6-(1-iminoethyl)- lysine (l-NIL, an inducible NOS inhibitor), 25 mg/kg of 7-Nitroindazole (7-NI, a neuronal NOS inhibitor) and 10 mg/Kg of l-N-(1-iminoethyl)ornithine (l-NIO, a selective eNOS inhibitor) 15 min before the induction of tMCAo. Cortical IkB-alpha expression was evaluated by western blotting and its decrease was considered as an indicator of NF-κB activation. IkB-alpha expression decreased in ischemic cortices when compared with the cortices of the sham group, thus confirming the activation of NF-κB in ischemic conditions. Pre-treatment with l-NAME, l-NIL and 7-NI significantly reduced the infarct volume and prevented ischemia-induced reduction in IkB-alpha expression. Conversely, pretreatment with l-NIO was associated with a significant increase in infarct volume and a reduction in IkB-alpha expression. These findings suggest that NO of neuronal and inducible origin promotes NF-κB activation via IkB-alpha modulation and mediates ischemic-related damage in the brain following ischemia.