Insulin prevents mitochondrial generation of H2O2 in rat brain

Abstract The mitochondrial electron transport system (ETS) is a main source of cellular ROS, including hydrogen peroxide (H 2 O 2 ). The production of H 2 O 2 also involves the mitochondrial membrane potential (ΔΨ m ) and oxygen consumption. Impaired insulin signaling causes oxidative neuronal damage and places the brain at risk of neurodegeneration. We evaluated whether insulin signaling cross-talks with ETS components (complexes I and F o F 1 ATP synthase) and ΔΨ m to regulate mitochondrial H 2 O 2 production, in tissue preparations from rat brain. Insulin (50 to 100 ng/mL) decreased H 2 O 2 production in synaptosomal preparations in high Na + buffer (polarized state), stimulated by glucose and pyruvate, without affecting the oxygen consumption. In addition, insulin (10 to 100 ng/mL) decreased H 2 O 2 production induced by succinate in synaptosomes in high K + (depolarized state), whereas wortmannin and LY290042, inhibitors of the PI3K pathway, reversed this effect; heated insulin had no effect. Insulin decreased H 2 O 2 production when complexes I and F o F 1 ATP synthase were inhibited by rotenone and oligomycin respectively suggesting a target effect on complex III. Also, insulin prevented the generation of maximum level of ∆Ψ m induced by succinate. The PI3K inhibitors and heated insulin maintained the maximum level of ∆Ψ m induced by succinate in synaptosomes in a depolarized state. Similarly, insulin decreased ROS production in neuronal cultures. In mitochondrial preparations, insulin neither modulated H 2 O 2 production or oxygen consumption. In conclusion, the normal downstream insulin receptor signaling is necessary to regulate complex III of ETS avoiding the generation of maximal ∆Ψ m and increased mitochondrial H 2 O 2 production.