The Dependence of the Protective Effect of Insulin on Its Concentration and Modulation of ERK1/2 Activity under the Conditions of Oxidative Stress in Cortical Neurons

It has been recently shown that insulin has a neuroprotective effect. Experimental studies and clinical trials have demonstrated that insulin is a promising drug for treatment of neurodegenerative and other diseases associated with brain damage. However, the mechanism of the neuroprotective effect of insulin is far from being elucidated. The aim of this study was to examine the dependence of the protective effect of insulin in cortical neurons on its concentration and the involvement of the modulation of the activity of extracellular signal-regulated kinase (ERK1/2) by insulin in neuronal survival. Using the MTT method, we found that the protective effect of insulin in neurons treated with hydrogen peroxide varied in the concentration range of 1–100 nm (1 nM < 10 nM < 100 nM). There were no significant differences between the effects of 100 nM or 1 nM insulin. The literature data on the effects of insulin on the activity of ERK1/2 in neurons are controversial. We studied the modulatory effect of insulin on the activity of ERK1/2 in cortical neurons during development of oxidative stress using the immunoblotting method at eight time points after prooxidant application. We found that insulin increased the basal activity of ERK1/2 and the activity of the enzyme at the early stage of action of hydrogen peroxide, that is, 5–30 min after its addition. This may improve the protective effect of insulin.