Intravenous administration of MEK inhibitor U0126 affords brain protection against forebrain ischemia and focal cerebral ischemia

Abstract

Brain subjected to acute ischemic attack caused by an arterial blockage needs immediate arterial recanalization. However, restoration of cerebral blood flow can cause tissue injury, which is termed reperfusion injury. It is important to inhibit reperfusion injury to achieve greater brain protection. Because oxidative stress has been shown to activate mitogen-activated protein kinases (MAPKs), and because oxidative stress contributes to reperfusion injury, MAPK may be a potential target to inhibit reperfusion injury after brain ischemia. Here, we demonstrate that reperfusion after forebrain ischemia dramatically increases phosphorylation level of extracellular signal-regulated kinase 2 (ERK2) in the gerbil hippocampus. In addition, i.v. administration of U0126 (100 -200 mg͞kg), a specific inhibitor of MEK (MAPK͞ERK kinase), protects the hippocampus against forebrain ischemia. Moreover, treatment with U0126 at 3 h after ischemia significantly reduces infarct volume after transient (3 h) focal cerebral ischemia in mice. This protection is accompanied by reduced phosphorylation level of ERK2, substrates for MEK, in the damaged brain areas. Furthermore, U0126 protects mouse primary cultured cortical neurons against oxygen deprivation for 9 h as well as nitric oxide toxicity. These results provide further evidence for the role of MEK͞ERK activation in brain injury resulting from ischemia͞reperfusion, and indicate that MEK inhibition may increase the resistance of tissue to ischemic injury. C ardiac arrest or cerebral arterial occlusion can cause a brain attack. Quickly restoring the cerebral blood flow is needed to stop brain injury. The most exciting new development in the field of stroke research is the recent approval of i.v. injection of tissue plasminogen activator that dissolves the blood clot (1, 2). Restoration of blood flow not only brings oxygen and nutrients into the damaged brain, but also produces free radicals such as reactive oxygen and reactive nitrogen species. These free radicals have been shown to contribute to oxidative injury. The tissue damage by the restoration of blood flow is termed reperfusion injury (3, 4). Thus, inhibition of reperfusion injury may be important to achieve greater brain protection.Mitogen-activated protein kinase (MAPK) family members, including extracellular signal-regulated kinases (ERK1͞2), p38 MAPK, and c-Jun N-terminal kinase (JNK), respond to various extracellular stimuli, thereby transmitting extracellular signals into the nucleus. ERK1͞2 are activated by MAPK͞ERK kinase1͞2 (MEK1͞2) by phosphorylating these MAPKs (5). The MEK͞ERK pathway plays a crucial role in cell growth and differentiation (6, 7). ERK1͞2 are constitutively expressed in the adult brain (8); however, little is known about the function of ERK1͞2 in postmitotic, terminally differentiated neurons. The MEK͞ERK pathway is also activated by reactive oxygen and reactive nitrogen species (9-11). Several in vivo studies showed that ERK1͞2 are phosphorylated in the damaged brain after ischemia, hypoglycemia, a...

Early Release of HMGB-1 from Neurons after the Onset of Brain Ischemia

“…High-mobility group box 1 proinflammatory signaling might begin early, possibly in the first hour after focal ischemia, but may continue for hours thereafter (Faraco et al, 2007). Consistent with a more protracted HMGB-1 signaling, we have previously reported neuroprotection through ERK inhibition, even when the treatment had been initiated 3 h after MCAO (Namura et al, 2001).…”

MEK1/2 inhibition attenuates vascular ETA and ETB receptor alterations after cerebral ischaemia

“…The effect of MEK1/2 inhibition on infarct volume has been studied by Namura and colleagues. However, they used a different species (mouse), time point (7 days) and did not examine the cerebral vasculature (Namura et al 2001). In the present study, the question of whether the decrease of the infarct volume is a direct effect of MEK1/2 inhibition in neurons or a more indirect effect due to the normalization of the vascular receptor responses remains to be answered.…”

“…Several studies have shown an involvement of the MEK/ERK1/2 signalling pathway in focal cerebral ischaemia, and inhibitors towards this pathway are able to diminish the ischaemic area (Alessandrini et al 1999;Namura et al 2001). In addition, Lennmyr and colleagues showed that ERK1/2 is activated in both the ipsilateral and contralateral cerebral blood vessels (Lennmyr et al 2002).…”

Central role of the MEK/ERK MAP kinase pathway in a mouse model of rheumatoid arthritis: Potential proinflammatory mechanisms

“…In a mouse model of 12-Otetradecanoylphorbol-13-acetate-induced ear edema, topical administration of U0126 effectively blocked both swelling and tissue ERK phosphorylation (44). When administered intravenously, U0126 blocked IL-1␤ production and focal ischemic injury in mice (45), as well as the inflammation associated with cisplatin-induced renal injury (46).…”