Ethyl pyruvate inhibits HMGB1 phosphorylation and secretion in activated microglia and in the postischemic brain

Abstract

Ethyl pyruvate (EP) has been shown to have anti-inflammatory effects and confer protective effects in various pathological conditions. For example, EP inhibits secretion of high mobility group box 1 (HMGB1), which is known to be released from activated or dying cells and aggravate inflammatory pathways. In the present study, we investigated whether EP reduces HMGB1 phosphorylation and release in ischemic brain and in cultured microglia. In the postischemic brains (60min middle cerebral artery occlusion (MCAO)), HMGB1 was released extracellularly, generating dual peaks in cerebrospinal fluid (CSF) around 1 and 7 days after ischemic insult, which were probably generated from damaged neurons and activated inflammatory cells, respectively. We showed that treatment with EP 30min post-MCAO (5mg/kg, i.v.), which has been shown to confer a robust neuroprotective effect in the postischemic brain, reduced both peaks. In addition, delayed EP treatment from 4 days post-MCAO reduced HMGB1 accumulation in CSF at 7 day post-MCAO in the absence of accompanying amelioration of ischemic brain damage, indicating that the suppression of HMGB1 release is a direct effect. We also found that EP markedly suppressed the LPS-induced nuclear translocations of protein kinase C alpha and calcium/calmodulin-dependent protein kinase IV, HMGB1 phosphorylation, and subsequent secretion of HMGB1 induced by LPS in BV2 cells and EP-mediated above-mentioned effects were also independent of cell death or survival. These results indicate that EP inhibits HMGB1 phosphorylation and release in activated microglia, which might be responsible for EP-mediated suppression of HMGB1 release in the postischemic brain.