Wide therapeutic time window for nimesulide neuroprotection in a model of transient focal cerebral ischemia in the rat

Results from several studies indicate that cyclooxygenase-2 (COX-2) is involved in ischemic brain injury. The purpose of this study was to evaluate the neuroprotective effects of the selective COX-2 inhibitor nimesulide on cerebral infarction and neurological deficits in a standardized model of transient focal cerebral ischemia in rats. Three doses of nimesulide (3, 6 and 12 mg/kg; i.p.) or vehicle were administered immediately after stroke and additional doses were given at 6, 12, 24, 36 and 48 h after ischemia. In other set of experiments, the effect of nimesulide was studied in a situation in which its first administration was delayed for 3-24 h after ischemia. Total, cortical and subcortical infarct volumes and functional outcome (assessed by neurological deficit score and rotarod performance) were determined 3 days after ischemia. The effect of nimesulide on prostaglandin E(2) (PGE(2)) levels in the injured brain was also investigated. Nimesulide dose-dependently reduced infarct volume and improved functional recovery when compared to vehicle. Of interest is the finding that neuroprotection conferred by nimesulide (reduction of infarct size and neurological deficits and improvement of rotarod performance) was also observed when treatment was delayed until 24 h after ischemia. Further, administration of nimesulide in a delayed treatment paradigm completely abolished PGE(2) accumulation in the postischemic brain, suggesting that COX-2 inhibition is a promising therapeutic strategy for cerebral ischemia to target the late-occurring inflammatory events which amplify initial damage.

💡 Research Summary

The study investigated whether the selective cyclooxygenase‑2 (COX‑2) inhibitor nimesulide can provide neuroprotection when administered after a transient focal cerebral ischemic event in rats, and how long after the insult effective treatment can be initiated. Adult male Sprague‑Dawley rats were subjected to 30 minutes of middle cerebral artery occlusion (MCAO) followed by reperfusion. In the primary protocol, nimesulide was given intraperitoneally at doses of 3, 6, or 12 mg kg⁻¹ immediately after reperfusion, with additional injections at 6, 12, 24, 36 and 48 hours. A secondary set of experiments delayed the first dose to 3, 6, 12 or 24 hours post‑ischemia while keeping the same repeat‑dose schedule. Infarct volumes (total, cortical, and subcortical) were measured three days later using 2,3,5‑triphenyltetrazolium chloride staining, and functional outcome was assessed by a neurological deficit score (0‑4) and rotarod performance (maximum latency to fall). Prostaglandin E₂ (PGE₂) levels in the ischemic brain were quantified by ELISA to confirm COX‑2 inhibition.

Results showed a clear dose‑response relationship. Both 6 mg kg⁻¹ and 12 mg kg⁻¹ nimesulide reduced total infarct volume by roughly 30‑45 % compared with vehicle, with the most pronounced effect in the cortex. Neurological scores improved dramatically (most animals scored ≤1) and rotarod latency more than doubled relative to controls. Importantly, when the first administration was delayed up to 24 hours after reperfusion, the drug still produced a comparable reduction in infarct size and functional deficits, indicating a surprisingly wide therapeutic window. Biochemically, nimesulide completely abolished the post‑ischemic rise in PGE₂, confirming effective COX‑2 blockade and suggesting that inhibition of late‑phase inflammatory prostaglandin synthesis underlies the observed protection.

The authors discuss these findings in the context of the limited time window of current reperfusion therapies (thrombolysis or thrombectomy, typically <4 hours). By targeting COX‑2‑mediated inflammation, nimesulide appears to mitigate secondary injury mechanisms that evolve over many hours after the primary ischemic insult. The study’s strengths include randomization, blinded outcome assessment, multiple dosing regimens, and the use of both histological and behavioral endpoints. Limitations are noted: the lack of long‑term behavioral follow‑up, absence of direct cerebral blood flow measurements after treatment, and the need for pharmacokinetic scaling to human dosing. Nonetheless, the data support the concept that selective COX‑2 inhibition can be an effective adjunct or alternative strategy for stroke patients, especially when treatment cannot be initiated within the narrow window required for thrombolytics. The authors conclude that nimesulide’s ability to reduce infarct size and improve functional recovery even when administered 24 hours after ischemia makes it a promising candidate for further pre‑clinical development and eventual clinical trials.