The Influence of Intranasally Administered Insulin and C-peptide on AMP-Activated Protein Kinase Activity, Mitochondrial Dynamics and Apoptosis Markers in the Hypothalamus of Rats with Streptozotocin-Induced Diabetes

Abstract

Most important factors leading to the development of diabetic encephalopathy in type 1 diabetes mellitus (T1DM) are impaired energy metabolism and mitochondrial dynamics, as well as activation of apoptosis in brain neurons, which is largely due to insulin and C-peptide deficiency in the CNS. In T1DM, hypothalamic neuronal dysfunctions lead to disturb both feeding behavior and central regulation of energy metabolism. One of the approaches to compensate for insulin and C-peptide deficiency in the brain is their intranasal administration. However, its influence on the functional state of hypothalamic neurons has not yet been studied. The aim of the work was to study the effect of intranasally administered insulin and C-peptide on the activity of AMP-activated protein kinase (AMPK) and expression of Drp-1 and mitofusins (Mfn-1 and Mfn-2) responsible for the biogenesis of mitochondria, pro- and anti-apoptotic proteins Bax and Bcl-2, autophagy-associated protein Beclin-1, and melanocortin receptors (MCR) in the hypothalamus of male rats with T1DM induced by 50 mg/kg of streptozotocin. We studied a 7-day intranasal administration to diabetic rats (D) of insulin (20 µg/rat/day, DI), C-peptide (36 µg/rat/day, DC), and insulin combined with C-peptide at two doses of 12 and 36 µg/rat/day (DIC12, DIC36). In the hypothalamus of the DI and DIC36 rat groups, there were observed normalization of AMPK activity and the Bax/Bcl-2 ratio (typically increased in T1DM), restoration of Drp-1, Mfn-2 and Beclin-1 expression, and increased expression of type 4 MCR responsible for transduction of anorexigenic signals, with all changes being associated in these groups with attenuated hyperphagia. In the DIС12 and DС rat groups, the restorative effects of the intranasal treatment were less pronounced. Thus, intranasal administration of insulin and C-peptide, to the greatest extent at a 1:3 molar ratio, restores energetic balance and mitochondrial dynamics, as well as suppresses pro-apoptotic processes in the hypothalamus of rats with severe T1DM. These effects appear to underlie their neuroprotective action.