Prospects for the Use of Intranasally Administered Insulin and Insulin-Like Growth Factor-1 in Cerebral Ischemia.

Current approaches to the treatment of stroke have significant limitations, and neuroprotective therapy is ineffective. In view of this, searching for effective neuroprotectors and developing new neuroprotective strategies remain a pressing topic in research of cerebral ischemia. Insulin and insulin-like growth factor-1 (IGF-1) play a key role in the brain functioning by regulating the growth, differentiation, and survival of neurons, neuronal plasticity, food intake, peripheral metabolism, and endocrine functions. Insulin and IGF-1 produce multiple effects in the brain, including neuroprotective action in cerebral ischemia and stroke. Experiments in animals and cell cultures have shown that under hypoxic conditions, insulin and IGF-1 improve energy metabolism in neurons and glial cells, promote blood microcirculation in the brain, restore nerve cell functions and neurotransmission, and produce the anti-inflammatory and antiapoptotic effects on brain cells. The intranasal route of insulin and IGF-1 administration is of particular interest in the clinical practice, since it allows controlled delivery of these hormones directly to the brain, bypassing the blood-brain barrier. Intranasally administered insulin alleviated cognitive impairments in elderly people with neurodegenerative and metabolic disorders; intranasally administered insulin and IGF-1 promoted survival of animals with ischemic stroke. The review discusses the published data and results of our own studies on the mechanisms of neuroprotective action of intranasally administered insulin and IGF-1 in cerebral ischemia, as well as the prospects of using these hormones for normalization of CNS functions and reduction of neurodegenerative changes in this pathology.

Hot Spots for the Use of Intranasal Insulin: Cerebral Ischemia, Brain Injury, Diabetes Mellitus, Endocrine Disorders and Postoperative Delirium.

A decrease in the activity of the insulin signaling system of the brain, due to both central insulin resistance and insulin deficiency, leads to neurodegeneration and impaired regulation of appetite, metabolism, endocrine functions. This is due to the neuroprotective properties of brain insulin and its leading role in maintaining glucose homeostasis in the brain, as well as in the regulation of the brain signaling network responsible for the functioning of the nervous, endocrine, and other systems. One of the approaches to restore the activity of the insulin system of the brain is the use of intranasally administered insulin (INI). Currently, INI is being considered as a promising drug to treat Alzheimer's disease and mild cognitive impairment. The clinical application of INI is being developed for the treatment of other neurodegenerative diseases and improve cognitive abilities in stress, overwork, and depression. At the same time, much attention has recently been paid to the prospects of using INI for the treatment of cerebral ischemia, traumatic brain injuries, and postoperative delirium (after anesthesia), as well as diabetes mellitus and its complications, including dysfunctions in the gonadal and thyroid axes. This review is devoted to the prospects and current trends in the use of INI for the treatment of these diseases, which, although differing in etiology and pathogenesis, are characterized by impaired insulin signaling in the brain.

Insulin and α-Tocopherol Enhance the Protective Effect of Each Other on Brain Cortical Neurons under Oxidative Stress Conditions and in Rat Two-Vessel Forebrain Ischemia/Reperfusion Injury.

Clinical trials show that insulin administered intranasally is a promising drug to treat neurodegenerative diseases, but at high doses its use may result in cerebral insulin resistance. Identifying compounds which could enhance the protective effects of insulin, may be helpful to reduce its effective dose. Our aim was thus to study the efficiency of combined use of insulin and α-tocopherol (α-T) to increase the viability of cultured cortical neurons under oxidative stress conditions and to normalize the metabolic disturbances caused by free radical reaction activation in brain cortex of rats with two-vessel forebrain ischemia/reperfusion injury. Immunoblotting, flow cytometry, colorimetric, and fluorometric techniques were used. α-T enhanced the protective and antioxidative effects of insulin on neurons in oxidative stress, their effects were additive. At the late stages of oxidative stress, the combined action of insulin and α-T increased Akt-kinase activity, inactivated GSK-3beta and normalized ERK1/2 activity in cortical neurons, it was more effective than either drug action. In the brain cortex, ischemia/reperfusion increased the lipid peroxidation product content and caused Na+,K+-ATPase oxidative inactivation. Co-administration of insulin (intranasally, 0.25 IU/rat) and α-T (orally, 50 mg/kg) led to a more pronounced normalization of the levels of Schiff bases, conjugated dienes and trienes and Na+,K+-ATPase activity than administration of each drug alone. Thus, α-T enhances the protective effects of insulin on cultured cortical neurons in oxidative stress and in the brain cortex of rats with cerebral ischemia/reperfusion injury.

The effect of metformin treatment on the basal and gonadotropin-stimulated steroidogenesis in male rats with type 2 diabetes mellitus.

Type 2 diabetes mellitus impairs reproductive functions in men, and important tasks are deciphering the mechanisms of testicular dysfunctions in diabetes and the search of effective approaches to their correction. The purpose was to study the effect of four-week metformin treatment (120 mg kg-1  day-1 ) of male Wistar rats with high-fat diet/low-dose streptozotocin-induced type 2 diabetes on basal and gonadotropin-stimulated steroidogenesis, intratesticular content of leptin and the leptin and luteinising hormone receptors and on spermatogenesis. Diabetic rats had hyperleptinaemia, androgen deficiency and reduced sperm count and quality, and in the testes, they had the increased leptin level and the decreased content of the leptin and luteinising hormone receptors and 17-hydroxyprogesterone. The stimulating effects of chorionic gonadotropin on testosterone production and expression of steroidogenic genes (Star, Cyp11a1) were decreased. Metformin restored basal and gonadotropin-stimulated blood testosterone levels. In the testes, it restored gonadotropin-stimulated 17-hydroxyprogesterone, androstenedione and testosterone levels, Star expression and the content of leptin and the leptin and luteinising hormone receptors. Metformin also improved epididymal sperm count and morphology. We concluded that metformin treatment normalises the testicular steroidogenesis in diabetic rats, which is due to restoration of the gonadotropin and leptin systems in the testes and is associated with an improvement in spermatogenesis.

The Protective Effect of Insulin on Rat Cortical Neurons in Oxidative Stress and Its Dependence on the Modulation of Akt, GSK-3beta, ERK1/2, and AMPK Activities.

Insulin is a promising drug for the treatment of diseases associated with brain damage. However, the mechanism of its neuroprotective action is far from being understood. Our aim was to study the insulin-induced protection of cortical neurons in oxidative stress and its mechanism. Immunoblotting, flow cytometry, colorimetric, and fluorometric techniques were used. The insulin neuroprotection was shown to depend on insulin concentration in the nanomolar range. Insulin decreased the reactive oxygen species formation in neurons. The insulin-induced modulation of various protein kinase activities was studied at eight time-points after neuronal exposure to prooxidant (hydrogen peroxide). In prooxidant-exposed neurons, insulin increased the phosphorylation of GSK-3beta at Ser9 (thus inactivating it), which resulted from Akt activation. Insulin activated ERK1/2 in neurons 5-30 min after cell exposure to prooxidant. Hydrogen peroxide markedly activated AMPK, while it was for the first time shown that insulin inhibited it in neurons at periods of the most pronounced activation by prooxidant. Insulin normalized Bax/Bcl-2 ratio and mitochondrial membrane potential in neurons in oxidative stress. The inhibitors of the PI3K/Akt and MEK1/2/ERK1/2 signaling pathways and the AMPK activator reduced the neuroprotective effect of insulin. Thus, the protective action of insulin on cortical neurons in oxidative stress appear to be realized to a large extent through activation of Akt and ERK1/2, GSK-3beta inactivation, and inhibition of AMPK activity increased by neuronal exposure to prooxidant.