Epigoitrin decreases synaptosomal glutamate release and protects neurons from glutamate excitotoxicity in rats

Abstract

Excessive synaptic glutamate levels can lead to excitotoxicity, which is implicated in various neuropathologies. This study investigates whether epigoitrin, an alkaloid abundantly found in Radix isatidis, affects glutamate release in rat cortical nerve terminals (synaptosomes) and its impact on excitotoxicity induced by the glutamate analogue kainic acid in rats. In rat cortical synaptosomes, epigoitrin reduced glutamate release induced by 4-aminopyridine in a dose-dependent manner, with an IC₅₀ value of 3 μM. Removal of extracellular Ca²⁺ or blockade of P/Q-type Ca²⁺ channels prevented epigoitrin's effect on synaptosomal glutamate release, while the N-type Ca²⁺ channel inhibitor did not. In an in vivo rat model of glutamate excitotoxicity induced by kainic acid, epigoitrin pretreatment significantly mitigated neuronal injury, glutamate elevation, and the upregulation of excitotoxicity-related proteins (DAPK1 and NMDA receptor subunit GluN2B) in the cortex of kainic acid-treated rats. Additionally, epigoitrin pretreatment reduced reactive oxygen species (ROS) production, glial activation, and levels of inflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), while increasing the anti-inflammatory cytokine interleutin-10 in the cortex of kainic acid-treated rats. These results suggest that epigoitrin inhibits glutamate release from cortical synaptosomes by reducing P/Q-type Ca²⁺ channel activity and provides neuroprotection against kainic acid-induced neurotoxicity by preventing oxidative stress, neuroinflammation, and glutamate elevation. This study is the first to reveal the impact of epigoitrin on the glutamatergic system.