The role of Akt signaling in oxidative stress mediates NF-kappaB activation in mild transient focal cerebral ischemia

Inhibition of nuclear factor-κB by 6-O-acetyl shanzhiside methyl ester protects brain against injury in a rat model of ischemia and reperfusion

BACKGROUND

Recent studies have demonstrated an inflammatory response associated with the pathophysiology of cerebral ischemia. The beneficial effects of anti-inflammatory drugs in cerebral ischemia have been documented. When screening natural compounds for drug candidates in this category, we isolated 6-O-acetyl shanzhiside methyl ester (ND02), an iridoid glucoside compound, from the leaves of Lamiophlomis rotata (Benth.) Kudo. The objectives of this study were to determine the effects of ND02 on a cultured neuronal cell line, SH-SY5Y, in vitro, and on experimental ischemic stroke in vivo.

METHODS

For TNF-α-stimulated SH-SY5Y cell line experiments in vitro, SH-SY5Y cells were pre-incubated with ND02 (20 μM or 40 μM) for 30 min and then incubated with TNF-α (20 ng/ml) for 15 min. For in vivo experiments, rats were subjected to middle cerebral artery occlusion (MCAO) for 1 h followed by reperfusion for 23 h.

RESULTS

ND02 treatment of SH-SY5Y cell lines blocked TNF-α-induced nuclear factor-κB (NF-κB) and IκB-α phosphorylation and increased Akt phosphorylation. LY294002 blocked TNF-α-induced phosphorylation of Akt and reduced the phosphorylation of both IκB-α and NF-κB. At doses higher than 10 mg/kg, ND02 had a significant neuroprotective effect in rats with cerebral ischemia and reperfusion (I/R). ND02 (25 mg/kg) demonstrated significant neuroprotective activity even after delayed administration 1 h, 3 h and 5 h after I/R. ND02, 25 mg/kg, attenuated histopathological damage, decreased cerebral Evans blue extravasation, inhibited NF-κB activation, and enhanced Akt phosphorylation.

CONCLUSION

These data show that ND02 protects brain against I/R injury with a favorable therapeutic time-window by alleviating cerebral I/R injury and attenuating blood-brain barrier (BBB) breakdown, and that these protective effects may be due to blocking of neuronal inflammatory cascades through an Akt-dependent NF-κB signaling pathway.

Ischemic preconditioning mediates cyclooxygenase-2 expression via nuclear factor-kappa B activation in mixed cortical neuronal cultures

Nuclear factor-kappaB (NF-κB) activation occurs following ischemic preconditioning (IPC) in brain. However, the upstream signaling messengers and down-stream targets of NF-κB required for induction of IPC remain undefined. In a previous study, we demonstrated that epsilon protein kinase c (εPKC) was a key mediator of IPC in brain. Activation of εPKC induced cyclooygenase-2 (COX-2) expression and conferred ischemic tolerance in the neuronal and hippocampal slice models. Here, we hypothesized that IPC-mediated COX-2 expression was mediated by NF-κB. We tested this hypothesis in mixed cortical neuron/astrocyte cell cultures. To simulate IPC or ischemia, cell cultures were exposed to 1 or 4 h of oxygen-glucose deprivation, respectively. Our results demonstrated translocation of p65 and p50 subunits of NF-κB into nucleus following IPC or εPKC activation. NF-κB inhibition with pyrrolidine dithiocarbamate (10 μM) abolished IPC or εPKC activator-mediated neuroprotection indicating that NF-κB activation was involved in ischemic tolerance. In parallel studies, inhibition of either εPKC or the extracellular signal-regulated kinase (ERK 1/2) pathway reduced IPC-induced NF-κB activation. Finally, inhibition of NF-κB blocked IPC-induced COX-2 expression. In conclusion, we demonstrated that IPC-signaling cascade comprises εPKC activation→ERK1/2 activation→NF-κB translocation to nucleus→COX-2 expression resulting in neuroprotection in mixed neuronal culture.

Akt inhibitor Akt-IV blocks virus replication through an Akt-independent mechanism

Many viruses activate the phosphatidylinositol 3'-kinase (PI3k)/Akt intracellular signaling pathway to promote viral replication. We have analyzed whether a rapidly replicating rhabdovirus, vesicular stomatitis virus (VSV), requires the PI3k/Akt signaling pathway for its replication. Through the use of chemical inhibitors of PI3k and Akt, we show that VSV replication and cytopathic effects do not require activation of these kinases. Inhibitors that block the activating phosphorylations of Akt at threonine 308 (Thr308) and serine 473 (Ser473) did not inhibit VSV protein expression or the induction of the cytopathic effects of VSV. One compound, Akt inhibitor Akt-IV, inhibited the replication of VSV, respiratory syncytial virus, and vaccinia virus but increased the phosphorylation of Akt at positions Thr308 and Ser473 and did not inhibit Akt kinase activity in vitro. Together, our data suggest that the PI3k/Akt pathway is of limited relevance to the replication of VSV but that Akt inhibitor Akt-IV is a novel broad-spectrum antiviral compound with a mechanism differing from that of its previously reported effect on the PI3k/Akt pathway. Identification of other targets for this compound may define a new approach for blocking virus replication.

Long-term neuroprotection from a potent redox-modulating metalloporphyrin in the rat

Sustained oxidative stress is a known sequel to focal cerebral ischemia. This study examined the effects of treatment with a single dose or sustained infusion of the redox-modulating MnPorphyrin Mn(III)TDE-2-ImP(5+) on outcome from middle cerebral artery occlusion (MCAO) in the rat. Normothermic rats were subjected to 90 min MCAO followed by 90 min reperfusion and then were treated with a single intracerebroventricular dose of Mn(III)TDE-2-ImP(5+). Neurologic and histologic outcomes were assessed at 1 or 8 weeks postischemia. A single dose of Mn(III)TDE-2-ImP(5+) caused a dose-dependent improvement in histologic and neurologic outcome when assessed 1 week postischemia. Mn(III)TDE-2-ImP(5+) afforded preservation of brain aconitase activity at 5.5 h after reperfusion onset, consistent with its known antioxidant properties. Mn(III)TDE-2-ImP(5+) also attenuated postischemic NF-kappaB activation. Evidence for effects on cerebral infarct size and neurologic function had completely dissipated when rats were allowed to survive for 8 weeks postischemia. In contrast, a 1-week continuous intracerebroventricular Mn(III)TDE-2-ImP(5+) infusion caused persistent and substantive reduction in both cerebral infarct size and neurologic deficit at 8 weeks postischemia. Pharmacologic modulation of postischemic oxidative stress is likely to require sustained intervention for enduring efficacy in improving neurologic and histologic outcome from a transient focal ischemic insult.