Neuroprotective efficacy of nimesulide against hippocampal neuronal damage following transient forebrain ischemia

Abstract

Cyclooxygenase-2 is involved in the inflammatory component of the ischemic cascade, playing an important role in the delayed progression of the brain damage. The present study evaluated the pharmacological effects of the selective cyclooxygenase-2 inhibitor nimesulide on delayed neuronal death of hippocampal CA1 neurons following transient global cerebral ischemia in gerbils. Administration of therapeutically relevant doses of nimesulide (3, 6 and 12 mg/kg; i.p.) 30 min before ischemia and at 6, 12, 24, 48 and 72 h after ischemia significantly (P<0.01) reduced hippocampal neuronal damage. Treatment with a single dose of nimesulide given 30 min before ischemia also resulted in a significant increase in the number of healthy neurons in the hippocampal CA1 sector 7 days after ischemia. Of interest is the finding that nimesulide rescued CA1 pyramidal neurons from ischemic death even when treatment was delayed until 24 h after ischemia (34±9% protection). Neuroprotective effect of nimesulide is still evident 30 days after the ischemic episode, providing the first experimental evidence that cyclooxygenase-2 inhibitors confer a long-lasting neuroprotection. Oral administration of nimesulide was also able to significantly reduce brain damage, suggesting that protective effects are independent of the route of administration. The present study confirms the ability of cyclooxygenase-2 inhibitors to reduce brain damage induced by cerebral ischemia and indicates that nimesulide can provide protection when administered for up to 24 h post-ischemia.

Introduction

Transient global cerebral ischemia is produced when the brain is deprived temporarily of oxygen and glucose. In humans, after cardiac arrest with resuscitation or cardiopulmonary bypass surgery, cerebral ischemia can lead to problems with cognition and memory, to serious neurological problems such as sensorimotor deficits and seizures and to death Levy et al., 1985, Petito et al., 1987.

In humans and in animals subjected to transient forebrain ischemia, specific neurons degenerate following the ischemic episode Kirino, 1982, Kirino, 2000, Pulsinelli et al., 1982, Petito et al., 1987. The cornu ammonis 1 (CA1) neurons of the hippocampus are widely regarded as among the most vulnerable in the mammalian brain to ischemia Pulsinelli et al., 1982, Kirino, 1982. Delayed hippocampal damage is observed 3 to 7 days after the insult in CA1 pyramidal neurons (Kirino, 1982), suggesting that mechanisms that develop slowly after ischemia have an important role in ischemic neuronal demise.

Several lines of recent evidences have shown that several pro-inflammatory genes or mediators, such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 and cytokines (e.g., tumor necrosis factor α and interleukin-1β), are strongly expressed in the ischemic brain Ohtsuki et al., 1996, Koistinaho and Hokfelt, 1997, Barone and Feuerstein, 1999. Inflammation is now recognized as a significant contributing mechanism in cerebral ischemia because anti-inflammatory compounds or inhibitors of iNOS and cyclooxygenase-2 have been proven to reduce ischemic brain damage Nogawa et al., 1997, Iadecola, 1997, Nagayama et al., 1998a, Nakayama et al., 1998b.

Nimesulide (N-(4-nitro-2-phenoxyphenyl)-methanesulfonamide) is a nonsteroidal anti-inflammatory drug with potent effects, showing a high affinity and selectivity for cyclooxygenase-2 Rabasseda, 1996, Cullen et al., 1998, but other mechanisms have been proposed to explain its mode of action: (1) inhibition of tumor necrosis factor α production (Azab et al., 1998), (2) antioxidant properties (Facino et al., 1993), (3) inhibition of the production of platelet activating factor (Tool and Verhoeven, 1995) and (4) reduction of the release of superoxide anions and other toxic substances from neutrophils (Bevilacqua et al., 1994). Nimesulide readily crosses the intact blood–brain barrier in both humans and rodents Taniguchi et al., 1997, Cullen et al., 1998.

Recently, several studies have demonstrated a marked neuroprotective effect of nimesulide on chronic cerebral hypoperfusion (Wakita et al., 1999), kainate-induced excitotoxicity (Candelario-Jalil et al., 2000) and quisqualic acid-induced neurodegeneration in rats (Scali et al., 2000).

In the light of these evidences, the present study was undertaken to investigate the effects of clinically relevant doses of nimesulide on the delayed neuronal death of CA1 pyramidal cells in the gerbil hippocampus following global ischemia. To our knowledge, there is no previous study on the effects of nimesulide against neuronal damage after focal or global cerebral ischemia.