Neuroprotective effects of (–)-epigallocatechin gallate after hypoxia-ischemia-induced brain damage: novel mechanisms of action

(–)-Epigallocatechin gallate (EGCG) is a potent antioxidant that is neuroprotective against ischemia-induced brain damage. However, the neuroprotective effects and possible mechanisms of action of EGCG after hypoxia-ischemia (HI) have not been investigated. Therefore, we used a modified “Levine” model of HI to determine the effects of EGCG. Wistar rats were treated with either 0.9% saline or 50 mg/kg EGCG daily for 1 day and 1 h before HI induction and for a further 2 days post-HI. At 26-days-old, both groups underwent permanent left common carotid artery occlusion and exposure to 8% oxygen/92% nitrogen atmosphere for 1 h. Histological assessment showed that EGCG significantly reduced infarct volume (38.0±16.4 mm3 ) in comparison to HI + saline (99.6±15.6 mm3 ). In addition, EGCG significantly reduced total (622.6±85.8 pmol L-[3 H]citrulline/30 min/mg protein) and inducible nitric oxide synthase (iNOS) activity (143.2±77.3 pmol L-[3 H]citrulline/30 min/mg protein) in comparison to HI+saline controls (996.6±113.6 and 329.7±59.6 pmol L-[3 H]citrulline/30 min/mg protein for total NOS and iNOS activity, respectively). Western blot analysis demonstrated that iNOS protein expression was also reduced. In contrast, EGCG significantly increased endothelial and neuronal NOS protein expression compared with HI controls. EGCG also significantly preserved mitochondrial energetics (complex I-V) and citrate synthase activity. This study demonstrates that the neuroprotective effects of EGCG are, in part, due to modulation of NOS isoforms and preservation of mitochondrial complex activity and integrity. We therefore conclude that the in vivo neuroprotective effects of EGCG are not exclusively due to its antioxidant effects but involve more complex signal transduction mechanisms.