Insulin on the brain: The role of central insulin signalling in energy and glucose homeostasis

The mitochondrial quality control system: a new target for exercise therapeutic intervention in the treatment of brain insulin resistance-induced neurodegeneration in obesity

Obesity is a major global health concern because of its strong association with metabolic and neurodegenerative diseases such as diabetes, dementia, and Alzheimer's disease. Unfortunately, brain insulin resistance in obesity is likely to lead to neuroplasticity deficits. Since the evidence shows that insulin resistance in brain regions abundant in insulin receptors significantly alters mitochondrial efficiency and function, strategies targeting the mitochondrial quality control system may be of therapeutic and practical value in obesity-induced cognitive decline. Exercise is considered as a powerful stimulant of mitochondria that improves insulin sensitivity and enhances neuroplasticity. It has great potential as a non-pharmacological intervention against the onset and progression of obesity associated neurodegeneration. Here, we integrate the current knowledge of the mechanisms of neurodegenration in obesity and focus on brain insulin resistance to explain the relationship between the impairment of neuronal plasticity and mitochondrial dysfunction. This knowledge was synthesised to explore the exercise paradigm as a feasible intervention for obese neurodegenration in terms of improving brain insulin signals and regulating the mitochondrial quality control system.

Hypothalamic NPFFR2 attenuates central insulin signaling and its knockout diminishes metabolic dysfunction in mouse models of diabetes mellitus

BACKGROUND

The hypothalamus is a crucial brain region that mediates the effects of insulin and leptin signals on peripheral metabolic functions. Previous research has shown that insulin signals in the hypothalamus act via multiple neuronal circuits and anabolic/catabolic pathways that converge on the vagus nerve and sympathetic fibers to coordinate energy metabolism in peripheral organs. Additionally, neuropeptide FF (NPFF) has been identified as a regulator of feeding behaviors and energy homeostasis in the hypothalamus, but the mechanisms underlying its involvement in metabolic control remain unclear. This study aims to explore the underlying mechanisms of NPFF in modulating metabolic disorders.

METHODS

In this study, we investigated the physiological role of NPFF in insulin-related energy homeostasis and metabolic health. First, we evaluated the effects of NPFF and its receptors on central insulin signaling using mouse hypothalamic cell lines and Npffr2-overexpressing mice. To further explore the effects of NPFFR2 on insulin-related metabolic disorders, such as diabetes mellitus, we used Npffr2-deleted mice in combination with the streptozotocin (STZ)-induced type 1 diabetes and high-fat diet/STZ-induced type 2 diabetic mouse models. The impacts of central NPFFR2 were demonstrated specifically through Npffr2 overexpression in the hypothalamic arcuate nucleus, which subsequently induced type 2 diabetes.

RESULTS

We found that stimulating NPFFR2 in the hypothalamus blocked hypothalamic insulin activity. Npffr2 deletion improved central and peripheral metabolic symptoms in both mouse models of diabetes mellitus, exerting effects on central and systemic insulin resistance, feeding behaviors, glucose and insulin intolerance, lipid metabolism, liver steatosis, and inflammation of white adipose tissues. The overexpression of ARC Npffr2 augmented the metabolic dysregulation in the mouse model of type 2 diabetes.

CONCLUSIONS

Our findings demonstrate that hypothalamic NPFFR2 negatively regulates insulin signaling in the central nervous system and plays an important role in maintaining systemic metabolic health, thereby providing valuable insights for potential clinical interventions targeting these health challenges.

Liraglutide restores impaired associative learning in individuals with obesity

Survival under selective pressure is driven by the ability of our brain to use sensory information to our advantage to control physiological needs. To that end, neural circuits receive and integrate external environmental cues and internal metabolic signals to form learned sensory associations, consequently motivating and adapting our behaviour. The dopaminergic midbrain plays a crucial role in learning adaptive behaviour and is particularly sensitive to peripheral metabolic signals, including intestinal peptides, such as glucagon-like peptide 1 (GLP-1). In a single-blinded, randomized, controlled, crossover basic human functional magnetic resonance imaging study relying on a computational model of the adaptive learning process underlying behavioural responses, we show that adaptive learning is reduced when metabolic sensing is impaired in obesity, as indexed by reduced insulin sensitivity (participants: N = 30 with normal insulin sensitivity; N = 24 with impaired insulin sensitivity). Treatment with the GLP-1 receptor agonist liraglutide normalizes impaired learning of sensory associations in men and women with obesity. Collectively, our findings reveal that GLP-1 receptor activation modulates associative learning in people with obesity via its central effects within the mesoaccumbens pathway. These findings provide evidence for how metabolic signals can act as neuromodulators to adapt our behaviour to our body's internal state and how GLP-1 receptor agonists work in clinics.

Can Allostery Be a Key Strategy for Targeting PTP1B in Drug Discovery? A Lesson from Trodusquemine

Protein tyrosine phosphatase 1B (PTP1B) is an enzyme crucially implicated in aberrations of various signaling pathways that underlie the development of different human pathologies, such as obesity, diabetes, cancer, and neurodegenerative disorders. Its inhibition can prevent these pathogenetic events, thus providing a useful tool for the discovery of novel therapeutic agents. The search for allosteric PTP1B inhibitors can represent a successful strategy to identify drug-like candidates by offering the opportunity to overcome some issues related to catalytic site-directed inhibitors, which have so far hampered the development of drugs targeting this enzyme. In this context, trodusquemine (MSI-1436), a natural aminosterol that acts as a non-competitive PTP1B inhibitor, appears to be a milestone. Initially discovered as a broad-spectrum antimicrobial agent, trodusquemine exhibited a variety of unexpected properties, ranging from antidiabetic and anti-obesity activities to effects useful to counteract cancer and neurodegeneration, which prompted its evaluation in several preclinical and clinical studies. In this review article, we provide an overview of the main findings regarding the activities and therapeutic potential of trodusquemine and their correlation with PTP1B inhibition. We also included some aminosterol analogues and related structure-activity relationships that could be useful for further studies aimed at the discovery of new allosteric PTP1B inhibitors.

Prevalence and clinical correlates of abnormal glucose metabolism in young, first- episode and medication-naïve outpatients with major depressive disorder

BACKGROUNDS

The high co-morbidity of abnormal glucose metabolism in depressed patients has been extensively studied, but few studies have explored abnormal glucose metabolism in young patients with major depressive disorder (MDD). This study aimed to examine the prevalence and clinical correlates of abnormal glucose metabolism in young patients with first-episode medication-naïve (FEMN) MDD.

METHODS

A cross-sectional study was conducted on 1289 young Chinese outpatients with FEMN MDD. All subjects were assessed on the Hamilton Depression Rating Scale, Hamilton Anxiety Rating Scale (HAMA), Positive and Negative Syndrome Scale, and their sociodemographic information was collected, and blood pressure, blood glucose, lipid and thyroid hormone levels were measured.

RESULTS

The prevalence of abnormal glucose metabolism was 12.57% in young FEMN MDD outpatients. Thyroid stimulating hormone (TSH) levels and HAMA scale scores were associated with fasting blood glucose levels in patients with FEMN MDD (P<0.05), and TSH could differentiate patients with abnormal normal glucose metabolism from those without abnormal glucose metabolism (Area Under Curve of 0.774).

CONCLUSIONS

Our study showed a high prevalence of comorbid glucose metabolism abnormalities in young FEMN MDD outpatients. TSH may be a promising biomarker of abnormal glucose metabolism in young patients with FEMN MDD.

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.

Could Naringenin Participate as a Regulator of Obesity and Satiety?

Obesity is a serious health problem worldwide, since it is associated with multiple metabolic disorders and complications such as cardiovascular disease, type 2 diabetes, fatty liver disease and overall metabolic dysfunction. Dysregulation of the hunger-satiety pathway, which includes alterations of central and peripheral signaling, explains some forms of obesity by favoring hyperphagia and weight gain. The present work comprehensively summarizes the mechanisms by which naringenin (NAR), a predominant flavanone in citrus fruits, could modulate the main pathways associated with the development of obesity and some of its comorbidities, such as oxidative stress (OS), inflammation, insulin resistance (IR) and dyslipidemia, as well as the role of NAR in modulating the secretion of enterohormones of the satiety pathway and its possible antiobesogenic effect. The results of multiple in vitro and in vivo studies have shown that NAR has various potentially modulatory biological effects against obesity by countering IR, inflammation, OS, macrophage infiltration, dyslipidemia, hepatic steatosis, and adipose deposition. Likewise, NAR is capable of modulating peptides or peripheral hormones directly associated with the hunger-satiety pathway, such as ghrelin, cholecystokinin, insulin, adiponectin and leptin. The evidence supports the use of NAR as a promising alternative to prevent overweight and obesity.

The changes in cognitive function following bariatric surgery considering the function of gut microbiome

Background

There is a correlation between gut microbiota and cognitive function. The mechanisms and pathways explain why the incidence of Alzheimer's disease in subjects undergoing bariatric surgery is lower than in other people with obesity.

Methods

In this review article, we aim to discuss the association of obesity, cognitive impairment, and physiological changes after bariatric surgery.

Results

Bariatric surgery has a series of physiological benefits which may lead to an improvement in cognitive functions in individuals who are prone to later developing Alzheimer's disease. Also, taxonomical change in the gut microbiome profile provides a healthy condition for living with better levels of cognition without neuropathological damages in older ages.

Conclusion

It can be concluded that there is a possible correlation between cognitive dysfunction and increased risk of cognitive dysfunction in people with a BMI higher than 40 kg/m2. Bariatric surgery may increase neurotransmitters and improve the gut bacteria, leading to a significant reduction in the risk of Alzheimer's disease.

Insulin Resistance in the Brain: Evidence Supporting a Role for Inflammation, Reactive Microglia, and the Impact of Biological Sex

Increased intake of highly processed, energy-dense foods combined with a sedentary lifestyle are helping fuel the current overweight and obesity crisis, which is more prevalent in women than in men. Although peripheral organs such as adipose tissue contribute to the physiological development of obesity, emerging work aims to understand the role of the central nervous system to whole-body energy homeostasis and development of weight gain and obesity. The present review discusses the impact of insulin, insulin resistance, free fatty acids, and inflammation on brain function and how these differ between the males and females in the context of obesity. We highlight the potential of microglia, the resident immune cells in the brain, as mediators of neuronal insulin resistance that drive reduced satiety, increased food intake, and thus, obesity.