Insulin Diminishes Superoxide Increase in Cytosol and Mitochondria of Cultured Cortical Neurons Treated with Toxic Glutamate

Abstract

Glutamate excitotoxicity is involved in the pathogenesis of many disorders, including stroke, traumatic brain injury, and Alzheimer’s disease, for which central insulin resistance is a comorbid condition. Neurotoxicity of glutamate (Glu) is primarily associated with hyperactivation of the ionotropic N-methyl-D-aspartate receptors (NMDARs), causing a sustained increase in intracellular free calcium concentration ([Ca2+]i) and synchronous mitochondrial depolarization and an increase in intracellular superoxide anion radical (O2–•) production. Recently, we found that insulin protects neurons against excitotoxicity by decreasing the delayed calcium deregulation (DCD). However, the role of insulin in O2–• production in excitotoxicity still needs to be clarified. The present study aims to investigate insulin’s effects on glutamate-evoked O2–• generation and DCD using the fluorescent indicators dihydroethidium, MitoSOX Red, and Fura-FF in cortical neurons. We found a linear correlation between [Ca2+]i and [O2–•] in primary cultures of the rat neuron exposed to Glu, with insulin significantly reducing the production of intracellular and mitochondrial O2–• in the primary cultures of the rat neuron. MK 801, an inhibitor of NMDAR-gated Ca2+ influx, completely abrogated the glutamate effects in both the presence and absence of insulin. In experiments in sister cultures, insulin diminished neuronal death and O2 consumption rate (OCR).

Keywords

• insulin
• glutamate (Glu) excitotoxicity
• intracellular free Ca²⁺ concentration ([Ca²⁺]_i)
• intracellular superoxide (O₂^–•)
• mitochondrial superoxide production
• primary cortical neurons