Insulin in the brain: its pathophysiological implications for States related with central insulin resistance, type 2 diabetes and Alzheimer's disease

Link Between Diabetes and Alzheimer's Disease due to the Shared Amyloid Aggregation and Deposition Involving both Neurodegenerative Changes and Neurovascular Damages

Diabetes and Alzheimer’s disease are two highly prevalent diseases among the aging population and have become major public health concerns in the 21st century, with a significant risk to each other. Both of these diseases are increasingly recognized to be multifactorial conditions. The terms “diabetes type 3” or “brain diabetes” have been proposed in recent years to provide a complete view of the potential common pathogenic mechanisms between these diseases. While insulin resistance or deficiency remains the salient hallmarks of diabetes, cognitive decline and non-cognitive abnormalities such as impairments in visuospatial function, attention, cognitive flexibility, and psychomotor speed are also present. Furthermore, amyloid aggregation and deposition may also be drivers for diabetes pathology. Here, we offer a brief appraisal of social impact and economic burden of these chronic diseases and provide insight into amyloidogenesis through considering recent advances of amyloid-β aggregates on diabetes pathology and islet amyloid polypeptide on Alzheimer’s disease. Exploring the detailed knowledge of molecular interaction between these two amyloidogenic proteins opens new opportunities for therapies and biomarker development.

Neonatal Exposure to Anesthesia Leads to Cognitive Deficits in Old Age: Prevention with Intranasal Administration of Insulin in Mice

Recent pre-clinical and clinical studies suggest that general anesthesia in infants and children may increase the risk of learning disabilities. Currently, there is no treatment for preventing anesthesia-induced neurotoxicity and potential long-term functional impairment. Animal studies have shown that neonatal exposure to anesthesia can induce acute neurotoxicity and long-term behavioral changes that can be detected a few months later. It is currently unknown whether neonatal exposure, especially repeated exposures, to general anesthesia can induce or increase the risk for cognitive impairment during aging. Here, we report that repeated exposures of neonatal mice (P7-9 days old) to anesthesia with sevoflurane (3 h/day for 3 days) led to cognitive impairment that was detectable at the age of 18-19 months, as assessed by using novel object recognition, Morris water maze, and fear conditioning tests. The repeated neonatal exposures to anesthesia did not result in detectable alterations in neurobehavioral development, in tau phosphorylation, or in the levels of synaptic proteins in the aged mouse brains. Importantly, we found that treatment with intranasal insulin prior to anesthesia exposure can prevent mice from anesthesia-induced cognitive impairment. These results suggest that neonatal exposure to general anesthesia could increase the risk for cognitive impairment during aging. This study also supports pre-treatment with intranasal administration of insulin to be a simple, effective approach to prevent infants and children from the increased risk for age-related cognitive impairment induced by neonatal exposure to general anesthesia.

Interlink Between Insulin Resistance and Neurodegeneration with an Update on Current Therapeutic Approaches

The interlink between diabetes mellitus and neurodegenerative diseases such as Alzheimer's Disease (AD) and Parkinson's Disease (PD) has been identified by several researchers. Patients with Type-2 Diabetes Mellitus (T2DM) are found to be affected with cognitive impairments leading to learning and memory deficit, while patients with Type-1 Diabetes Mellitus (T1DM) showed less severe levels of these impairments in the brain. This review aimed to discuss the connection between insulin with the pathophysiology of neurodegenerative diseases (AD and PD) and the current therapeutic approached mediated through insulin for management of neurodegenerative diseases. An extensive literature search was conducted using keywords "insulin"; "insulin resistance"; "Alzheimer's disease"; "Parkinson's disease" in public domains of Google scholar, PubMed, and ScienceDirect. Selected articles were used to construct this review. Studies have shown that impaired insulin signaling contributes to the accumulation of amyloid-β, neurofibrillary tangles, tau proteins and α-synuclein in the brain. Whereas, improvement in insulin signaling slows down the progression of cognitive decline. Various therapeutic approaches for altering the insulin function in the brain have been researched. Besides intranasal insulin, other therapeutics like PPAR-γ agonists, neurotrophins, stem cell therapy and insulin-like growth factor-1 are under investigation. Research has shown that insulin insensitivity in T2DM leads to neurodegeneration through mechanisms involving a variety of extracellular, membrane receptor, and intracellular signaling pathway disruptions. Some therapeutics, such as intranasal administration of insulin and neuroactive substances have shown promise but face problems related to genetic background, accessibility to the brain, and invasiveness of the procedures.

Neurodegeneration in type 2 diabetes: Alzheimer's as a case study

INTRODUCTION

Rigorous research in the last few years has shown that in addition to the classical mechanism of neurodegeneration, certain unconventional mechanisms may also lead to neurodegenerative disease. One of them is a widely studied metabolic disorder: type 2 diabetes mellitus (T2DM). We now have a clear understanding of glucose-mediated neurodegeneration, mostly from studies in Alzheimer's disease (AD) models. AD is recognized to be significantly associated with hyperglycemia, even earning the term "type 3 diabetes." Here, we review first the pathophysiology of AD, both from the perspective of classical protein accumulation, as well as the newer T2DM-dependent mechanisms supported by findings from patients with T2DM. Secondly, we review the different pathways through which neurodegeneration is aggravated in hyperglycemic conditions taking AD as a case study. Finally, some of the current advances in AD management as a result of recent research developments in metabolic disorders-driven neurodegeneration are also discussed.

METHODS

Relevant literatures found from PubMed search were reviewed.

RESULTS

Apart from the known causes of AD, type 2 diabetes opens a new window to the AD pathology in several ways. It is a bidirectional interaction, of which, the molecular and signaling mechanisms are recently studied. This is our attempt to connect all of them to draw a complete mechanistic explanation for the neurodegeneration in T2DM. Refer to Figure 3.

CONCLUSION

The perspective of AD as a classical neurodegenerative disease is changing, and it is now being looked at from a zoomed-out perspective. The correlation between T2DM and AD is something observed and studied extensively. It is promising to know that there are certain advances in AD management following these studies.

Evidence for altered insulin signalling in the brains of genetic absence epilepsy rats from Strasbourg

Insulin-mediated signalling in the brain is critical for neuronal functioning. Insulin resistance is implicated in the development of some neurological diseases, although changes associated with absence epilepsy have not been established yet. Therefore, we examined the major components of PI3K/Akt-mediated insulin signalling in cortical, thalamic, and hippocampal tissues collected from Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and Non-Epileptic Control (NEC) rats. Insulin levels were also measured in plasma and cerebrospinal fluid (CSF). For the brain samples, the nuclear fraction (NF) and total homogenate (TH) were isolated and investigated for insulin signalling markers including insulin receptor beta (IRβ), IR substrate-1 and 2 (IRS1 & 2), phosphatase and tensin homologue (PTEN), phosphoinositide 3-kinase phospho-85 alpha (PI3K p85α), phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol (3,4,5)-trisphosphate, protein kinase B (PKB/Akt1/2/3), glucose transporter-1 and 4 (GLUT1 & 4) and glycogen synthase kinase-3β (GSK3β) using western blotting. A significant increase in PTEN and GSK3β levels and decreased PI3K p85α and pAkt1/2/3 levels were observed in NF of GAERS cortical and hippocampal tissues. IRβ, IRS1, GLUT1, and GLUT4 levels were significantly decreased in hippocampal TH of GAERS compared to NEC. A non-significant increase in insulin levels was observed in plasma and CSF of GAERS rats. An insulin sensitivity assay showed decreased p-Akt level in cortical and hippocampal tissues. Together, altered hippocampal insulin signalling was more prominent in NF and TH compared to cortical and thalamic regions in GAERS. Restoring insulin signalling may improve the pathophysiology displayed by GAERS, including the spike-and-wave discharges that relate to absence seizures in patients.

Tau, Diabetes and Insulin

Tau protein which was discovered in 1975 [310] became of great interest when it was identified as the main component of neurofibrillary tangles (NFT), a pathological feature in the brain of patients with Alzheimer's disease (AD) [39, 110, 232]. Tau protein is expressed mainly in the brain as six isoforms generated by alternative splicing [46, 97]. Tau is a microtubule associated proteins (MAPs) and plays a role in microtubules assembly and stability, as well as diverse cellular processes such as cell morphogenesis, cell division, and intracellular trafficking [49]. Additionally, Tau is involved in much larger neuronal functions particularly at the level of synapses and nuclei [11, 133, 280]. Tau is also physiologically released by neurons [233] even if the natural function of extracellular Tau remains to be uncovered (see other chapters of the present book).

Glucose, glycolysis, and neurodegenerative diseases

Prolonged survival of a typical postmitotic neuron hinges on a balance between multiple processes, among these are a sustenance of ATP production and protection against reactive oxygen species. In neuropathological conditions, mitochondrial defects often lead to both a drop in ATP levels, as well as increase reactive oxygen species production from inefficient electron transport processes and NADPH-oxidases activities. The former often resulted in the phenomenon of compensatory aerobic glycolysis. The latter stretches the capacity of the cell's redox buffering capacity, and may lead to damages of key enzymes involved in energy metabolism. Several recent reports have indicated that enhancing glucose availability and uptake, as well as increasing glycolytic flux via pharmacological or genetic manipulation of glycolytic enzymes, could be protective in animal models of several major neurodegenerative diseases, including Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Activation of canonical Wnt signaling, which improves disease symptoms in mouse models of Alzheimer's disease also appears to work via an elevation of glycolytic enzymes and enhance glucose metabolism. Here, I discuss these findings and the possible underlying mechanisms of how an increase in glucose uptake and glycolysis could be neuroprotective. Increased glycolytic production of ATP would help alleviate energy deficiency, and ATP's hydrotropic effect may enhance solubility and clearance of toxic aggregates prevalent in many neurodegenerative diseases. Furthermore, channeling of glucose into the Pentose Phosphate Pathway would increase the redox buffering capacity of the cell.

Growth hormone receptor deficiency in humans associates to obesity, increased body fat percentage, a healthy brain and a coordinated insulin sensitivity

BACKGROUND

We have shown that subjects with Laron syndrome (LS) due to growth hormone receptor deficiency (GHRD) and their relatives have comparable brain structure and function; moreover, the brain of individuals affected with GHRD appears like those of younger people. While the functionally absent growth hormone receptor and the diminished concentrations of the insulin-like growth factor-I have been associated to these findings, the role of the insulin-glucose axis is emerging as an unavoidable consideration when determining the aetiology of these observations. In consequence, we decided to search for the potential and discrete associations between the neurological findings and several parameters of carbohydrate metabolism that might exist in the subjects affected with GHRD.

SUBJECTS AND METHODS

Individuals affected with GHRD were compared to relative controls. Besides standard measures of anthropometry, body composition and brain characteristics, the elements of the carbohydrate metabolism (CHO), including glucose, insulin, triacylglycerol and the free insulin growth factor binding protein 1 (IGFBP1) concentrations were determined. In addition, the correlations existing between the parameters of CHO and brain characteristics were established.

RESULTS

Besides the phenotypical characteristics of GHRD subjects, including those of brain structure and function, enhanced insulin sensitivity, and other minor, we observed that the insulin-regulated IGFBP1 had a consistent negative correlation with the main elements of the carbohydrate metabolism only in the individuals affected with the disease, and not in their relatives.

CONCLUSIONS

When compared to their relatives, subjects with GHRD who lack the counter-regulatory effects of GH on the insulin axis, despite their increased risk factor profile due to obesity and increased body fat percentage, have a healthy and younger looking brain associated to an enhanced and coordinated insulin sensitivity. Furthermore, it was observed that in the GHRD subjects IGFBP1 negatively correlates, in a constant and systematic manner, with the main elements of the CHO metabolism. These observations suggest a direct relationship between an efficient insulin sensitivity and a healthy brain.

ApoE and cerebral insulin: Trafficking, receptors, and resistance

Central nervous system (CNS) insulin resistance is associated with Alzheimer's disease (AD). In addition, the apolipoprotein E4 (apoE4) isoform is a risk factor for AD. The connection between these two factors in relation to AD is being actively explored. We summarize this literature with a focus on the transport of insulin and apoE across the blood-brain barrier (BBB) and into the CNS, the impact of apoE and insulin on the BBB, and the interactions between apoE, insulin, and the insulin receptor once present in the CNS. We highlight how CNS insulin resistance is apparent in AD and potential ways to overcome this resistance by repurposing currently approved drugs, with apoE genotype taken into consideration as the treatment response following most interventions is apoE isoform-dependent. This review is part of a special issue focusing on apoE in AD and neurodegeneration.

Role of c-Jun N-terminal Kinase (JNK) in Obesity and Type 2 Diabetes

Obesity has been described as a global epidemic and is a low-grade chronic inflammatory disease that arises as a consequence of energy imbalance. Obesity increases the risk of type 2 diabetes (T2D), by mechanisms that are not entirely clarified. Elevated circulating pro-inflammatory cytokines and free fatty acids (FFA) during obesity cause insulin resistance and ß-cell dysfunction, the two main features of T2D, which are both aggravated with the progressive development of hyperglycemia. The inflammatory kinase c-jun N-terminal kinase (JNK) responds to various cellular stress signals activated by cytokines, free fatty acids and hyperglycemia, and is a key mediator in the transition between obesity and T2D. Specifically, JNK mediates both insulin resistance and ß-cell dysfunction, and is therefore a potential target for T2D therapy.

Insulin mediated novel therapies for the treatment of Alzheimer's disease

Alzheimer's disease, a progressive neurodegenerative disorder, is one of the leading causes of death in the USA, along with cancer and cardiac disorders. AD is characterized by various neurological factors like amyloid plaques, tau hyperphosphorylation, mitochondrial dysfunction, acetylcholine deficiency, etc. Together, impaired insulin signaling in the brain is also observed as essential factor to be considered in AD pathophysiology. Hence, currently researchers focused on studying the effect of brain insulin metabolism and relation of diabetes with AD. Based on the investigations, AD is also considered as type 3 or brain diabetes. Besides the traditional view of correlating AD with aging, a better understanding of various pathological factors and effects of other physical ailments is necessary to develop a promising therapeutic approach. There is a vast scope of studying the relation of systemic insulin level, insulin signaling, its neuroprotective potency and effect of diabetes on AD progression. The present work describes worldwide status of AD and its relation with diabetes mellitus and insulin metabolism; pathophysiology of AD; different metabolic pathways associating insulin metabolism with AD; insulin receptor and signaling in the brain; glucose metabolism; insulin resistance; and various preclinical and clinical studies reported insulin-based therapies to treat AD via systemic route and through direct intranasal delivery to the brain.

Poor glucose regulation is associated with declines in well-being among older men, but not women

Glucose regulation is a key aspect of healthy aging and has been linked to brain functioning and cognition. Here we examined the role of glucose regulation for within-person longitudinal trajectories of well-being. We applied growth models to data from the Berlin Aging Study II (N = 955), using insulin resistance as an index of glucoregulatory capacity. We found that poor glucose regulation (higher insulin resistance) was consistently associated with lower levels of well-being among older men but not women. Our study provides novel evidence for the relevance of glucose regulation for well-being among older men. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Effect of amyloid toxicity or chronic cerebral hypoperfusion on brain insulin resistance in a rat model with intracerebroventricular streptozotocin

Sporadic Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder affected by amyloid and vascular pathogenesis. Brain insulin resistance (BIR) has been suggested as one of the pathomechanisms of sporadic AD. We investigated how the amyloid and vascular pathogenesis of AD interacts with BIR. We examined experimental groups mimicking amyloid pathogenesis following intracerebroventriculr (icv) injection of amyloid β or vascular pathogenesis following permanent ligation of the bilateral common carotid arteries in Wistar rats that had undergone icv injection of streptozotocin. Behavioral tests and pathologic studies were performed. Cognitive impairments were induced by BIR superimposed by amyloid or vascular pathogenesis. Neuroinflammation in the white matter and hippocampus was aggravated by an interaction between BIR and vascular pathogenesis. Amyloid-associated pathology in the white matter was enhanced by BIR and vascular pathogenesis. Tau-associated pathology in the hippocampus was altered by BIR in a relation with amyloid or vascular pathogenesis. Our study may provide useful experimental insights based on an integrated approach to the influence of amyloid and vascular pathogenesis on BIR, permitting better understanding of the heterogeneous pathogenesis of sporadic AD. Pathologic responses in sporadic AD may differ depending on amyloid and vascular pathogenesis and may sometimes be synergistically aggravated when combined with BIR.

Intranasal insulin administration may be highly effective in improving cognitive function in mice with cognitive dysfunction by reversing brain insulin resistance

It is well known in clinical practice that Alzheimer's disease (AD) is closely associated with brain insulin resistance, and the cerebral insulin pathway has been proven to play a critical role in the pathogenesis of AD. However, finding the most efficient way to improve brain insulin resistance remains challenging. Peripheral administration of insulin does not have the desired therapeutic effect and may induce adverse reactions, such as hyperinsulinemia, but intranasal administration may be an efficient way. In the present study, we established a brain insulin resistance model through an intraventricular injection of streptozotocin, accompanied by cognitive impairment. Following intranasal insulin treatment, the learning and memory functions of mice were significantly restored, the neurogenesis in the hippocampus was improved, the level of insulin in the brain increased, and the activation of the IRS-1-PI3K-Akt-GSK3β insulin signal pathway, but not the Ras-Raf-MEK-MAPK pathway, was markedly increased. The olfactory bulb-subventricular zone-subgranular zone (OB-SVZ-SGZ) axis might be the mechanism through which intranasal insulin regulates cognition in brain-insulin-resistant mice. Thus, intranasal insulin administration may be a highly efficient way to improve cognitive function by increasing cerebral insulin levels and reversing insulin resistance.

Brain insulin resistance triggers early onset Alzheimer disease in Down syndrome

Dysregulation of insulin signaling pathway with reduced downstream neuronal survival and plasticity mechanisms is a fundamental abnormality observed in Alzheimer's disease (AD) brain. This phenomenon, known as brain insulin resistance, is associated with poor cognitive performance and is driven by the uncoupling of insulin receptor (IR) from its direct substrate (IRS1). Considering that Down syndrome (DS) and AD neuropathology share many common features, we investigated metabolic aspects of neurodegeneration, i.e., brain insulin resistance, in DS and whether it would contribute to early onset AD in DS population. Changes of levels and activation of main brain proteins belonging to the insulin signaling pathway (i.e., IR, IRS1, PTEN, GSK3β, PKCζ, AS160, GLUT4) were evaluated. Furthermore, we analyzed whether changes of these proteins were associated with alterations of: (i) proteins regulating brain energy metabolism; (ii) APP cleavage; and (ii) regulation of synaptic plasticity mechanisms in post-mortem brain samples collected from people with DS before and after the development of AD pathology (DSAD) compared with their age-matched controls. We found that DS cases were characterized by key markers of brain insulin resistance (reduced IR and increased IRS1 inhibition) early in life. Furthermore, downstream from IRS1, an overall uncoupling among the proteins of insulin signaling was observed. Dysregulated brain insulin signaling was associated with reduced hexokinase II (HKII) levels and proteins associated with mitochondrial complexes levels as well as with reduced levels of syntaxin in DS cases. Tellingly, these alterations precede the development of AD neuropathology and clinical presentations in DS. We propose that markers of brain insulin resistance rise earlier with age in DS compared with the general population and may contribute to the cognitive impairment associated with the early development of AD in DS.

Association of Circulating Retinol and α-TOH Levels with Cognitive Function in Aging Subject with Type 2 Diabetes Mellitus

OBJECTIVES

Malnutrition of vitamin A (retinol) and vitamin E (α-tocopherol, α-TOH) was observed in type 2 diabetes mellitus (T2DM) or dementia patients. However, how these vitamins affect cognitive function of subjects with T2DM was seldom reported. The objective of this study was to determine the association of circulating retinol and α-TOH with cognition in aging subjects with T2DM.

METHODS

A total of 448 T2DM subjects and 448 age, gender and education matched control subjects (aged 55-75 years) were included in the study. Demographic characters of the participants were collected. Food frequency questionnaire (FFQ) method was used to collect dietary intake information. To assess the status of cognition, the MoCA test was used. Circulating retinol and α-TOH levels were compared between T2DM and non-T2DM subjects. Correlation of circulating retinol and α-TOH levels with cognitive function was analyzed in T2DM subjects. The effect of serum retinol and α-TOH levels on the risk of MCI in T2DM patients was explored.

RESULTS

We found that T2DM-MCI subjects demonstrate lower serum retinol level than T2DM-nonMCI subjects (P < 0.01). Serum retinol level was positively correlated to cognitive function in T2DM subject (P < 0.05). T2DM subjects with higher circulating retinol level demonstrate higher cognitive scores in visual and executive, attention, language, memory and delayed recall domains (P < 0.05).

CONCLUSION

Diminished circulating retinol predicts an increased risk of MCI in T2DM patients. Our findings provide suggestions that optimal retinol nutritional status might benefit cognition and decrease the risk of MCI in aging subjects with T2DM.

Curcumin in Depression: Potential Mechanisms of Action and Current Evidence-A Narrative Review

Major depressive disorder (MDD) is one of the most prevalent and debilitating disorders. Current available treatments are somehow limited, so alternative therapeutic approaches targeting different biological pathways are being investigated to improve treatment outcomes. Curcumin is the main active component in the spice turmeric that has been used for centuries in Ayurvedic medicine to treat a variety of conditions, including anxiety and depressive disorders. In the past decades, curcumin has drawn researchers' attention and displays a broad range of properties that seem relevant to depression pathophysiology. In this review, we break down the potential mechanisms of action of curcumin with emphasis on the diverse systems that can be disrupted in MDD. Curcumin has displayed, in a number of studies, a potency in modulating neurotransmitter concentrations, inflammatory pathways, excitotoxicity, neuroplasticity, hypothalamic-pituitary-adrenal disturbances, insulin resistance, oxidative and nitrosative stress, and endocannabinoid system, all of which can be involved in MDD pathophysiology. To date, a handful of clinical trials have been published and suggest a benefit of curcumin in MDD. With evidence that is progressively growing, curcumin appears as a promising alternative option in the management of MDD.

MicroRNA silencing: A promising therapy for Alzheimer's disease

Alzheimer's disease (AD) is a global health crisis currently afflicting ~6 million Americans (and ~40 million people worldwide). By the middle of the century, these numbers will stagger by ~16 million Americans (and ~152 million people worldwide) suffering from AD, if breakthrough disease-modifying treatments are not discovered. Currently, there are no treatments to prevent, halt or cure the disease. Multiple independent studies on brain gene expression patterns have indicated that in AD about 1/3rd of the genes are upregulated while the rest 2/3rd of the genes are downregulated. In that regard, AD therapeutics focused on antagomiR-mediated silencing of"upregulated"microRNAs (miRs) may be more feasible since upregulated miRs in AD continue to increase with the disease progression, as opposed to agomiR-mediated overexpression of down-regulated miRs with unpredictable reduced presence and relative short-life of 1-3h under pathological conditions in AD brain. Studies reported thus far indicate that most of the upregulated pathogenic genes in AD are regulated by pro-inflammatory microRNAs (miRs). Given the precedence of chronic neuroinflammation in triggering AD-like neurodegeneration and multifactorial nature of AD, silencing inflammation-specific micro-RNAs using antisense-microRNAs may be an effective adjuvant therapeutic strategy to prevent, halt or cure AD.

The Molecular Mechanisms Underlying Mitochondria-Associated Endoplasmic Reticulum Membrane-Induced Insulin Resistance

Mitochondria and the endoplasmic reticulum (ER) are connected at multiple sites via what are known as mitochondria-associated ER membranes (MAMs). These associations are known to play an important role in maintaining cellular homeostasis. Impaired MAM signaling has wide-ranging effects in many diseases, such as obesity, diabetes, and neurodegenerative disorders. Accumulating evidence has suggested that MAMs influence insulin signaling through different pathways, including those associated with Ca²⁺ signaling, lipid metabolism, mitochondrial function, ER stress responses, and inflammation. Altered MAM signaling is a common feature of insulin resistance in different tissues, including the liver, muscle, and even the brain. In the liver, MAMs are key glucose-sensing regulators and have been proposed to be a hub for insulin signaling. Impaired MAM integrity has been reported to disrupt hepatic responses to changes in glucose availability during nutritional transition and to induce hepatic insulin resistance. Meanwhile, these effects can be rescued by the reinforcement of MAM interactions. In contrast, several studies have proposed that enhanced ER-mitochondria connections are detrimental to hepatic insulin signaling and can lead to mitochondrial dysfunction. Thus, given these contradictory results, the role played by the MAM in the regulation of hepatic insulin signaling remains elusive. Similarly, in skeletal muscle, enhanced MAM formation may be beneficial in the early stage of diabetes, whereas continuous MAM enhancement aggravates insulin resistance. Furthermore, recent studies have suggested that ER stress may be the primary pathway through which MAMs induce brain insulin resistance, especially in the hypothalamus. This review will discuss the possible mechanisms underlying MAM-associated insulin resistance as well as the therapeutic potential of targeting the MAM in the treatment of type 2 diabetes.

Regulation of Diabetes: a Therapeutic Strategy for Alzheimer's Disease?

Accumulated evidence suggests that sporadic cases of Alzheimer's disease (AD) make up more than 95% of total AD patients, and diabetes has been implicated as a strong risk factor for the development of AD. Diabetes shares pathological features of AD, such as impaired insulin signaling, increased oxidative stress, increased amyloid-beta (Aβ) production, tauopathy and cerebrovascular complication. Due to shared pathologies between the two diseases, anti-diabetic drugs may be a suitable therapeutic option for AD treatment. In this article, we will discuss the well-known pathologies of AD, including Aβ plaques and tau tangles, as well as other mechanisms shared in AD and diabetes including reactive glia and the breakdown of blood brain barrier in order to evaluate the presence of any potential, indirect or direct links of pre-diabetic conditions to AD pathology. In addition, clinical evidence of high incidence of diabetic patients to the development of AD are described together with application of anti-diabetic medications to AD patients.

Mikania Micrantha Improved Memory Perform on Dementia Model

BACKGROUND:

The purpose of this research is to explore the existing natural resources in Jambi province which has potential as anti-dementia agent. So that will be many natural resources that can be a potential product in reducing the unwanted effects of dementia as a degenerative disorder that is currently an inevitable elderly disease. by investigating with various plants in Jambi that have activities as anti-dementia is expected more and more natural resources that can be used as neuron-protection and or neuron-curative.

AIM:

The purpose of this study is to find plants and / or compounds that are useful as neuroprotection

METHODS:

Dementia model is formed by diabetic test animals. The test group consisted of extract group, three fractions (hexane, ethyl acetate and butanol fraction at dose 500 mg/Kg BB p.o) and one group of antidiabetic drugs glibenclamide, and the group of normal animal test animals was tested with Radial arm maze (RAM) for seven days before alloxan induced to obtain dementia model.

RESULTS:

The results showed that extract and ethyl acetate fraction at dose 500 mg/Kg BW gave a positive effect on memory improvement based on animal performance on RAM tool during a testing time (P < 0, 05) with LSD statistical analysis.

CONCLUSION:

The extract and ethyl acetate fraction of Mikania micrantha showed good potential for improving the performance of animal memory in RAM devices representing dementia models.

Neuroendocrine Disturbances in Neurodegenerative Disorders: A Scoping Review

BACKGROUND

Neurodegenerative diseases cause progressive irreversible neuronal loss that has broad downstream effects. The neuroendocrine system regulates homeostasis of circuits that control critical functions such as the stress response, metabolism, reproduction, fluid balance, and glucose control. These systems are frequently disrupted in neurodegenerative disorders yet often overlooked in clinical practice.

OBJECTIVE

This review aims to gather the available data regarding these disturbances in Alzheimer's disease, Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis, and Huntington's disease and also to demonstrate the volume of literature in these individual arenas.

METHODS

Using the scoping review framework, a literature search was performed in PubMed to identify relevant articles published within the past 30 years (January 1988 to November 2018). The search criteria produced a total of 2022 articles, 328 of which were identified as relevant to this review.

RESULTS

Several major themes emerged from this review. These neuroendocrine disturbances may be a precursor to the illness, a part of the primary pathophysiology, or a direct consequence of the disease or independent of it. They have the potential to further understanding of the disease, exacerbate the underlying pathology, or provide therapeutic benefit.

CONCLUSIONS

By synthesizing the data from a systems' perspective, we aim to broaden how clinicians think about these illnesses and provide care.

Imaging of brain glucose uptake by PET in obesity and cognitive dysfunction: life-course perspective

The prevalence of obesity has reached epidemic proportions and keeps growing. Obesity seems implicated in the pathogenesis of cognitive dysfunction, Alzheimer's disease and dementia, and vice versa. Growing scientific efforts are being devoted to the identification of central mechanisms underlying the frequent association between obesity and cognitive dysfunction. Glucose brain handling undergoes dynamic changes during the life-course, suggesting that its alterations might precede and contribute to degenerative changes or signaling abnormalities. Imaging of the glucose analog 18F-labeled fluorodeoxyglucose (18FDG) by positron emission tomography (PET) is the gold-standard for the assessment of cerebral glucose metabolism in vivo. This review summarizes the current literature addressing brain glucose uptake measured by PET imaging, and the effect of insulin on brain metabolism, trying to embrace a life-course vision in the identification of patterns that may explain (and contribute to) the frequent association between obesity and cognitive dysfunction. The current evidence supports that brain hypermetabolism and brain insulin resistance occur in selected high-risk conditions as a transient phenomenon, eventually evolving toward normal or low values during life or disease progression. Associative studies suggest that brain hypermetabolism predicts low BDNF levels, hepatic and whole body insulin resistance, food desire and an unfavorable balance between anticipated reward from food and cognitive inhibitory control. Emerging mechanistic links involve the microbiota and the metabolome, which correlate with brain metabolism and cognition, deserving attention as potential future prevention targets.

The Dual Role of Kinin/Kinin Receptors System in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disease characterized by progressive spatial disorientation, learning and memory deficits, responsible for 60%–80% of all dementias. However, the pathological mechanism of AD remains unknown. Numerous studies revealed that kinin/kinin receptors system (KKS) may be involved in the pathophysiology of AD. In this review article, we summarized the roles of KKS in neuroinflammation, cerebrovascular impairment, tau phosphorylation, and amyloid β (Aβ) generation in AD. Moreover, we provide new insights into the mechanistic link between KKS and AD, and highlight the KKS as a potential therapeutic target for AD treatment.

Interplay between Alzheimer's disease and global glucose metabolism revealed by the metabolic profile alterations of pancreatic tissue and serum in APP/PS1 transgenic mice

Increasing evidence suggests that there is a correlation between type 2 diabetes mellitus (T2D) and Alzheimer's disease (AD). Increased Aβ polypeptide production in AD patients would promote metabolic abnormalities, insulin signaling dysfunction and perturbations in glucose utilization, thus leading to the onset of T2D. However, the metabolic mechanisms underlying the interplay between AD and its diabetes-promoting effects are not fully elucidated. Particularly, systematic metabolomics analysis has not been performed for the pancreas tissues of AD subjects, which play key roles in the glucose metabolism of living systems. In the current study, we characterized the dynamic metabolic profile alterations of the serum and the pancreas of APP/PS1 double-transgenic mice (an AD mouse model) using the untargeted metabolomics approaches. Serum and pancreatic tissues of APP/PS1 transgenic mice and wild-type mice were extracted and subjected to NMR analysis to evaluate the functional state of pancreas in the progress of AD. Multivariate analysis of principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were conducted to define the global and the local (pancreas) metabolic features associated with the possible initiation of T2D in the progress of AD. Our results showed the onset of AD-induced global glucose metabolism disorders in AD mice. Hyperglycemia and its accompanying metabolic disorders including energy metabolism down-regulation and oxidative stress were observed in the serum of AD mice. Meanwhile, global disturbance of branched-chain amino acid (BCAA) metabolism was detected, and the change of BCAA (leucine) was positively correlated to the alteration of glucose. Moreover, increased level of glucose and enhanced energy metabolism were observed in the pancreas of AD mice. The results suggest that the diabetes-promoting effects accompanying the progress of AD are achieved by down-regulating the global utilization of glucose and interfering with the metabolic function of pancreas. Since T2D is a risk factor for the pathogenesis of AD, our findings suggest that targeting the glucose metabolism dysfunctions might serve as a supplementary therapeutic strategy for Alzheimer's disease.

Diabetes drugs in the fight against Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, particularly in old age subjects. Hyperinsulinemia and insulin resistance, which are known as pathophysiological features of Type 2 Diabetes Mellitus (T2DM), have also been demonstrated to have a significant impact on cognitive impairment. Studies have shown that an altered insulin pathway may interact with amyloid-β protein deposition and tau protein phosphorylation, both leading factors for AD development. Drugs used for T2DM treatment from insulin and metformin through dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 receptor agonists may represent a promising approach to fight AD. With this review from animal to human studies, we aim at responding to the reasons why drugs for diabetes may represent potential treatments for AD.

Risk of dementia and cognitive dysfunction in individuals with diabetes or elevated blood glucose

AIMS

To determine the risk of dementia in patients with type 1 or type 2 diabetes and in individuals with glycosylated haemoglobin, type A1C (HbA1c) of ⩾48 mmol/mol, which is the diagnostic limit for diabetes.

METHODS

We included the following cohorts: all incident diabetes cases aged 15 or above registered in the National Diabetes Registry (NDR) from January 2000 through December 2012 (n = 148 036) and a reference population, adult participants from the Glostrup cohort (n = 16 801), the ADDITION Study (n = 26 586) and Copenhagen Aging and Midlife Biobank (CAMB) (n = 5408). Using these cohorts, we analysed if a diagnosis of type 1 or type 2 diabetes in the NDR or HbA1c level of ⩾ 6.5% (48 mmol/mol) in the cohorts increased risk of dementia in the Danish National Patient Registry or cognitive performance assessed by the Intelligenz-Struktur-Test 2000R (IST2000R).

RESULTS

A diagnosis of type 1 or type 2 diabetes in the NDR was associated with increased risk of dementia diagnosed both before or after age 65 as well as across different subtypes of dementia. Self-reported diabetes or high HbA1c levels were associated with lower cognitive performance (p = 0.004), while high HbA1c was associated with increased risk of dementia (HR 1.94 (1.10-3.44) in the Glostrup cohort but not in the ADDITION Study (HR 0.96 (0.57-1.61)).

CONCLUSIONS

Both type 1 and type 2 diabetes are associated with an increased risk of dementia, while the importance of screening-detected elevated HbA1c remains less clear.

The Relevance of Insulin Action in the Dopaminergic System

The advances in medicine, together with lifestyle modifications, led to a rising life expectancy. Unfortunately, however, aging is accompanied by an alarming boost of age-associated chronic pathologies, including neurodegenerative and metabolic diseases. Interestingly, a non-negligible interplay between alterations of glucose homeostasis and brain dysfunction has clearly emerged. In particular, epidemiological studies have pointed out a possible association between Type 2 Diabetes (T2D) and Parkinson’s Disease (PD). Insulin resistance, one of the major hallmark for etiology of T2D, has a detrimental influence on PD, negatively affecting PD phenotype, accelerating its progression and worsening cognitive impairment. This review aims to provide an exhaustive analysis of the most recent evidences supporting the key role of insulin resistance in PD pathogenesis. It will focus on the relevance of insulin in the brain, working as pro-survival neurotrophic factor and as a master regulator of neuronal mitochondrial function and oxidative stress. Insulin action as a modulator of dopamine signaling and of alpha-synuclein degradation will be described in details, too. The intriguing idea that shared deregulated pathogenic pathways represent a link between PD and insulin resistance has clinical and therapeutic implications. Thus, ongoing studies about the promising healing potential of common antidiabetic drugs such as metformin, exenatide, DPP IV inhibitors, thiazolidinediones and bromocriptine, will be summarized and the rationale for their use to decelerate neurodegeneration will be critically assessed.

Strain and sex-based glucocentric & behavioral differences between KK/HlJ and C57BL/6J mice

INTRODUCTION

Small-animal models are the most widely used preclinical model for studying the etiology, pathology and treatment of diabetes, prediabetes and diabetic comorbidities. Diabetic patients are burdened with higher rates of depression, anxiety and cognitive decline due to inadequate control of blood glucose levels, vascular damage and aberrant CNS insulin signaling. The C57BL/6J model is amongst the most widely used mouse model due to its susceptibility to diet-induced obesity (DIO). This strain has also been well-characterized in behavioral research studies. However the C57BL/6J model has a number of limitations: [1] overt fasting hyperglycemia can only be induced by dietary manipulation and/or chemical ablation of the pancreatic beta cells. [2] There is heterogeneity in the obesogenic response to hypercaloric feeding as well as sex-dependent differences, with males being more responsive. The KK inbred strain has been used to study aspects of the metabolic syndrome and prediabetes due to inherent glucose intolerance, hyperinsulinemia and insulin resistance. However KK/HlJ mice are less well-characterized and there have been fewer behavioral studies reported. The aim of this study was to examine differences in male and female glucocentric parameters between KK/HlJ and C57BL/6J mice, and to compare their performance in a variety of standard behavioral tests relating to general, anxiogenic and cognitive paradigms.

METHODS

Strain differences in male and female KK/HlJ and C57BL/6J mouse adiposity, glucose and insulin parameters were studied together with group differences in standard Open Field, Object Recognition, Elevated Plus Maze, Light-Dark Transition, Porsolt test, Marble Burying, Social Recognition and Morris Water Maze tests. Correlations between behavioral variables were analyzed.

RESULTS AND CONCLUSION

In addition to being uniformly larger, hyperinsulinemic and more insulin intolerant than C57BL/6J mice, we observed marked strain and sex-differences in KK/HlJ behavior. KK/HlJ mice exhibited less locomotor and vertical exploratory behavior in comparison to C57BL/6J, whereas object exploration and novel object discrimination were superior in KK/HlJ mice. Female KK/HlJ mice were faster swimmers, whereas the males exhibited greater spatial cognition and place-learning during the MWM test.

A Metabolic Obesity Profile Is Associated With Decreased Gray Matter Volume in Cognitively Healthy Older Adults

Obesity is a risk factor for cognitive decline and gray matter volume loss in aging. Studies have shown that different metabolic factors, e.g., dysregulated glucose metabolism and systemic inflammation, might mediate this association. Yet, even though these risk factors tend to co-occur, they have mostly been investigated separately, making it difficult to establish their joint contribution to gray matter volume structure in aging. Here, we therefore aimed to determine a metabolic profile of obesity that takes into account different anthropometric and metabolic measures to explain differences in gray matter volume in aging. We included 748 elderly, cognitively healthy participants (age range: 60 - 79 years, BMI range: 17 - 42 kg/m2) of the LIFE-Adult Study. All participants had complete information on body mass index, waist-to-hip ratio, glycated hemoglobin, total blood cholesterol, high-density lipoprotein, interleukin-6, C-reactive protein, adiponectin and leptin. Voxelwise gray matter volume was extracted from T1-weighted images acquired on a 3T Siemens MRI scanner. We used partial least squares correlation to extract latent variables with maximal covariance between anthropometric, metabolic and gray matter volume and applied permutation/bootstrapping and cross-validation to test significance and reliability of the result. We further explored the association of the latent variables with cognitive performance. Permutation tests and cross-validation indicated that the first pair of latent variables was significant and reliable. The metabolic profile was driven by negative contributions from body mass index, waist-to-hip ratio, glycated hemoglobin, C-reactive protein and leptin and a positive contribution from adiponectin. It positively covaried with gray matter volume in temporal, frontal and occipital lobe as well as subcortical regions and cerebellum. This result shows that a metabolic profile characterized by high body fat, visceral adiposity and systemic inflammation is associated with reduced gray matter volume and potentially reduced executive function in older adults. We observed the highest contributions for body weight and fat mass, which indicates that factors underlying sustained energy imbalance, like sedentary lifestyle or intake of energy-dense food, might be important determinants of gray matter structure in aging.

Combined dipeptidyl peptidase-4 inhibitor with low-dose testosterone exerts greater efficacy than monotherapy on improving brain function in orchiectomized obese rats

Both obesity and orchiectomy lead to the development of brain pathologies and cognitive decline. Testosterone replacement therapy (2 mg/kg/day TRT) and dipeptidyl peptidase-4 inhibitor (vildagliptin) improved cognition in orchiectomized rats, and obese rats. However, both had no beneficial effects in brain of orchiectomized-obese rats. TRT (>2 mg/kg/day) is possible to attenuate brain defects in those rats, but high dose of TRT causes adverse effects. Then, combined effect of low-dose TRT (1 mg/kg/day) and vildagliptin on brain and cognitive functions in orchiectomized-obese rats should be investigated. Sixty male rats were fed with either a normal diet (ND) or a high-fat diet (HFD) for 28 weeks. At week 13, both ND and HFD-fed rats had either a sham-operation or an orchiectomy. At week 25, orchiectomized rats were treated with either: a vehicle, 2 mg/kg/day TRT, vildagliptin (3 mg/kg/day) or a combined vildagliptin with 1 mg/kg/day TRT for 4 weeks. Then, metabolic parameters, brain and cognitive functions were determined. Hippocampal oxidative stress, apoptosis, dendritic spine loss, microglial hyperactivity, and cognitive decline were found in orchiectomized ND-fed rats and sham-operated HFD-fed rats. Interestingly, orchiectomy aggravated these brain pathologies and cognitive decline in HFD-fed rats. In orchiectomized ND-fed rats, all treatments restored brain and cognitive functions. In orchiectomized HFD-fed rats, monotherapies ameliorated these brain pathologies, while the combined therapies had the greatest beneficial effect on the brains. These findings suggest the combined therapies may be the best therapeutic approach for restoring brain functions in the orchiectomized-obese condition.

Insulin treatment increases brain nitric oxide and oxidative stress, but does not affect memory function in mice

Insulin increases brain nitric oxide (NO) level but the mechanism and the significance of the effect on memory are not fully understood. This study aimed to demonstrate the mechanism of insulin-induced increase in oxidative stress (OS) and its consequences on learning and memory. Twenty four mice were assigned to groups (n = 6) and treated daily for seven days with water (control), insulin, insulin+N^ω-nitro-L-arginine methyl ester hydrochloride (L-NAME) and L-NAME, respectively. Memory was assessed using Y-maze; NO, malondialdehyde (MDA) and glutathione peroxidase (GPx) in brain homogenate were also determined. There was no difference between the groups in the number of entries into the arms and time spent in them, and in number of and percentage alternations performed by the mice, indicating normal memory function of the control and treated mice. NO level in the insulin group was higher compared to the control (p = .018), while those of the other groups were statistically the same compared to the control group. MDA values in the insulin group were higher (p = .001) than those of the control, while those of the other groups were statistically the same compared to those of the control group. GPx activity in the insulin group was lower compared to control (p = .004), while that of the other groups was not significantly different compared to control. It was concluded that insulin treatment increased brain level of NO and OS through increased malondialdehyde level and glutathione peroxidase activity; insulin treatment did not affect long-term visuo-spatial and short-term working memory in the animals. Insulin treatment may have deleterious effects on the brain through increased NO and OS levels.

Dysglycemia, Not Altered Sex Steroid Hormones, Affects Cognitive Function in Polycystic Ovary Syndrome

Context

Polycystic ovary syndrome (PCOS) is a complex endocrine condition characterized by multiple reproductive and metabolic abnormalities. Because individual reproductive and metabolic abnormalities modulate working memory in the general population, there is growing interest in whether cognitive function is dually and negatively affected in PCOS.

Objective

To examine the association of reproductive and metabolic features with cognitive function in women with and without PCOS.

Design

An observational, cross-sectional study was conducted at an academic clinical research center in North America between 2006 and 2009. Common tests of working memory (i.e., manual dexterity, perceptual speed, and visuospatial ability) were performed by women with PCOS (n = 40) and control subjects (n = 40). Markers of sex steroid hormones, ovulatory function, and cardiometabolic health were also assessed.

Results

Reduced visuospatial ability was observed in women with PCOS compared with control subjects (P < 0.01). Reduced visuospatial ability was linked to higher levels of hemoglobin A1c in the entire study cohort, independent of body mass index or PCOS status. No associations were observed between visuospatial ability and reproductive features, after controlling for confounding variables.

Conclusion

Our findings support a role for glycemic control, and not PCOS per se, in cognitive dysfunction in women of reproductive age. Additional studies are needed to understand the short- and long-term effects of dysglycemia on brain health in women with PCOS, given their increased propensity for metabolic comorbidities, compared with control subjects.

Neurometabolic Evidence Supporting the Hypothesis of Increased Incidence of Type 3 Diabetes Mellitus in the 21st Century

The most recent evidence supports the existence of a link between type 2 diabetes (T2DM) and Alzheimer's Disease (AD), described by the new term: type 3 diabetes (T3D). The increasing incidence of T2DM in the 21st century and accompanying reports on the higher risk of AD in diabetic patients prompts the search for pathways linking glycemia disturbances and neurodegeneration. It is suggested that hyperglycemia may lead to glutamate-induced excitotoxicity, a pathological process resulting from excessive depolarization of membrane and uncontrolled calcium ion influx into neuronal cells. On the other hand, it has been confirmed that peripheral insulin resistance triggers insulin resistance in the brain, which may consequently contribute to AD by amyloid beta accumulation, tau phosphorylation, oxidative stress, advanced glycation end products, and apoptosis. Some literature sources suggest significant amylin involvement in additional amyloid formation in the central nervous system, especially under hyperamylinemic conditions. It is particularly important to provide early diagnostics in people with metabolic disturbances, especially including fasting insulin and HOMA-IR, which are necessary to reveal insulin resistance. The present review reveals the most recent and important evidence associated with the phenomenon of T3D and discusses the potential lacks of prevention and diagnostics for diabetes which might result in neurometabolic disorders, from a pharmacotherapy perspective.

DAF-16/FOXO promotes taste avoidance learning independently of axonal insulin-like signaling

The avoidance of starvation is critical for the survival of most organisms, thus animals change behavior based on past nutritional conditions. Insulin signaling is important for nutritional state-dependent behavioral plasticity, yet the underlying regulatory mechanism at the cellular level remains unclear. Previous studies showed that insulin-like signaling is required for taste avoidance learning, in which the nematode Caenorhabditis elegans avoids salt concentrations encountered under starvation conditions. DAF-2c, a splice isoform of the DAF-2 insulin receptor, functions in the axon of the ASER sensory neuron, which senses changes in salt concentrations. In addition, mutants of a major downstream factor of DAF-2, the forkhead transcription factor O (FOXO) homolog DAF-16, show defects in taste avoidance learning. Interestingly, the defect of the daf-2 mutant is not suppressed by daf-16 mutations in the learning, unlike those in other phenomena, such as longevity and development. Here we show that multiple DAF-16 isoforms function in ASER. By epistasis analysis using a DAF-2c isoform-specific mutant and an activated form of DAF-16, we found that DAF-16 acts in the nucleus in parallel with the DAF-2c-dependent pathway in the axon, indicating that insulin-like signaling acts both in the cell body and axon of a single neuron, ASER. Starvation conditioning induces nuclear translocation of DAF-16 in ASER and degradation of DAF-16 before starvation conditioning causes defects in taste avoidance learning. Forced nuclear localization of DAF-16 in ASER biased chemotaxis towards lower salt concentrtions and this effect required the Gq/PKC pathway and neuropeptide processing enzymes. These data imply that DAF-16/FOXO transmits starvation signals and modulates neuropeptide transmission in the learning.

Animals change behavior based on remembered experiences of hunger and appetite. Signaling by insulin and insulin-like peptides in the nervous system plays key roles in behavioral responses to hunger and satiety. In C. elegans, insulin-like signaling in the gustatory sensory neuron ASER regulates learned avoidance of salt concentrations experienced during fasting, which we call taste avoidance learning. DAF-2c, an isoform of the insulin receptor homolog, is localized to the axon of ASER and regulates taste avoidance learning. Here, we show that DAF-16, the forkhead transcription factor O (FOXO) homolog, translocates into the nucleus of ASER during fasting and promotes taste avoidance learning. DAF-16 is negatively regulated by insulin-like signaling independently of axonal DAF-2c signaling. This dual function of insulin-like signaling in the cell body and the axon ensures dynamic changes in behavioral responses after experience of hunger. By genetic analyses using constitutively nuclear-translocated DAF-16, we show that DAF-16 in ASER regulates taste avoidance learning via modulating neuropeptide signaling in the nervous system, which is reminiscent of the function of FOXO in the hypothalamus in the regulation of food-seeking behavior in mammals.

Intranasal Administration of Insulin Reduces Chronic Behavioral Abnormality and Neuronal Apoptosis Induced by General Anesthesia in Neonatal Mice

Children, after multiple exposures to general anesthesia, appear to be at an increased risk of developing learning disabilities. Almost all general anesthetics—including sevoflurane, which is commonly used for children—are potentially neurotoxic to the developing brain. Anesthesia exposure during development might also be associated with behavioral deficiencies later in life. To date, there is no treatment to prevent anesthesia-induced neurotoxicity and behavioral changes. In this study, we anesthetized 7-day-old neonatal mice with sevoflurane for 3 h per day for three consecutive days and found that the anesthesia led to mild behavioral abnormalities later in life that were detectable by using the novel object recognition test, Morris water maze, and fear conditioning test. Biochemical and immunohistochemical studies indicate that anesthesia induced a decrease in brain levels of postsynaptic density 95 (PSD95), a postsynaptic marker, and marked activation of neuronal apoptosis in neonatal mice. Importantly, insulin administered through intranasal delivery prior to anesthesia was found to prevent the anesthesia-induced long-term behavioral abnormalities, reduction of PSD95, and activation of neuronal apoptosis. These findings suggest that intranasal insulin administration could be an effective approach to prevent the increased risk of neurotoxicity and chronic damage caused by anesthesia in the developing brain.

High fructose diet induces early mortality via autophagy factors accumulation in the rostral ventrolateral medulla as ameliorated by pioglitazone

High fructose ingestion enhances mortality which has been linked to autonomic dysregulation. However, the underlying mechanisms are still largely unknown. In the present study, we demonstrated that 3 months of high fructose diet (HFD) ingestion induced mortality in 18-week-old Wistar Kyoto rats (WKY) during anesthesia. Concurrently, the low frequency (LF) and the high frequency (HF) elements of the power spectral analyses of SBP were increased. Of note, the decreased ratio of LF and HF (LF/HF), an index of sympathetic and parasympathetic balance, suggested an autonomic imbalance. In the rostral ventrolateral medulla (RVLM), a center of sympathetic outflow, the levels of presynaptic (synaptophysin) and postsynaptic (postsynaptic density protein 95 and phospho-Ca²⁺/calmodulin-dependent protein kinase II) proteins were increased. The down-regulation of insulin receptor β and insulin receptor substrate 1 suggested the status of insulin desensitization. Moreover, the up-regulation of AMP-activated protein kinase and sirtuin 1 suggested the enhancement of energy sensing to activate autophagy. Simultaneously, the accumulations of Beclin-1, ATG12 and LC3B were increased in RVLM. Pioglitazone (PIO), an insulin sensitizer, effectively relieved the accumulation of Beclin-1 and ATG12 as well as the synaptic proteins synchronized with the reverses of insulin and energy sensing signals. Moreover, the autonomic dysregulation and anesthesia-associated mortality were intervened. Together, these results suggested that the HFD-induced, anesthesia-associated mortality rate was related to the autonomic abnormality derived from the RVLM synaptic alteration, which is strongly related to insulin desensitization-associated autophagy. PIO intervened the HFD-induced mortality via reversal of the above-mentioned molecules.

Favorable impact of non-alcoholic fatty liver disease on the cerebral white matter hyperintensity in a neurologically healthy population

BACKGROUND AND PURPOSE

Although non-alcoholic fatty liver disease (NAFLD) shares common cardiovascular risk factors with cerebral white matter hyperintensity (WMH), few studies have reported the association between NAFLD and WMH. The association between the presence of NAFLD with its severity and the volume of WMH was investigated.

METHODS

This cross-sectional study was conducted for 2460 subjects who voluntarily participated in health screening check-ups including brain magnetic resonance imaging and liver ultrasonography at the Health Promotion Center at Seoul National University Hospital from 2009 to 2013. Ultrasonography was used to detect the presence and severity of NAFLD combined with the NAFLD fibrosis score and the FIB-4 index. The volume of WMH was measured using a semi-automated quantification method by a trained neurologist.

RESULTS

The prevalence of NAFLD was 36.5%, and the median volume of WMH in all the subjects was 1.1 ml (interquartile range 0.2-2.7 ml). The presence of NAFLD was associated with a smaller volume of WMH [β (standard error, SE) -0.051 (0.046); P = 0.012]. Moderate to severe NAFLD was associated with a smaller volume of WMH than was non-NAFLD [β (SE) -0.067 (0.061); P = 0.002]. The negative correlation observed between NAFLD severity and WMH volume was persistent only in those with low FIB-4 index and low NAFLD fibrosis scores, whereas there was a positive association in those with high FIB-4 index and NAFLD fibrosis scores.

CONCLUSIONS

Non-alcoholic fatty liver disease, and its severity, showed a favorable association with WMH volume. However, its causality and mechanism should be evaluated in further relevantly designed studies.

Chronic synaptic insulin resistance after traumatic brain injury abolishes insulin protection from amyloid beta and tau oligomer-induced synaptic dysfunction

Traumatic brain injury (TBI) is a risk factor for Alzheimer's disease (AD), although the mechanisms contributing to this increased risk are unknown. Insulin resistance is an additional risk factor for AD whereby decreased insulin signaling increases synaptic sensitivity to amyloid beta (Aβ) and tau. Considering this, we used rats that underwent a lateral fluid percussion injury at acute and chronic time-points to investigate whether decreased insulin responsiveness in TBI animals is playing a role in synaptic vulnerability to AD pathology. We detected acute and chronic decreases in insulin responsiveness in isolated hippocampal synaptosomes after TBI. In addition to assessing both Aβ and tau binding on synaptosomes, we performed electrophysiology to assess the dysfunctional impact of Aβ and tau oligomers as well as the protective effect of insulin. While we saw no difference in binding or degree of LTP inhibition by either Aβ or tau oligomers between sham and TBI animals, we found that insulin treatment was able to block oligomer-induced LTP inhibition in sham but not in TBI animals. Since insulin treatment has been discussed as a therapy for AD, this gives valuable insight into therapeutic implications of treating AD patients based on one's history of associated risk factors.

Fluoride exposure decreased learning ability and the expressions of the insulin receptor in male mouse hippocampus and olfactory bulb

Fluoride is one of the common environmental pollutants. Internal exposure to fluoride is related to the lowered cognitive function and intelligence, particularly for children. Determination of protein content in brain tissue is a means to reflect the functional development of the central nervous system. Insulin and insulin receptor (IR) signaling systems are associated with cognitive ability. The present research focused on the assessment of the expressions of IR protein and mRNA in hippocampus and olfactory bulb (OB), as well as learning and memory ability of male Kunming mice. Mice were exposed to 50, 100, and 150 mg/L NaF for 90 continuous days. The results showed that learning and memory abilities as well as protein content of male mice brain was significantly decreased by fluoride. Fluoride could inhibit the protein and mRNA expressions of the IR in the hippocampus and OB of mice. IRs mainly distributed in the olfactory nerve layer of the outermost layer of the OB, and most distributed in the hippocampal cornu ammon 3 (CA3) region, followed by the dentate gyrus (DG) and cornu ammon 1 (CA1) regions. These findings suggested that inhibition of the IR protein and mRNA expressions in the hippocampus and OB by fluoride might in part affect learning and memory ability in male mice.

Brain insulin action: Implications for the treatment of schizophrenia

Insulin action in the central nervous system is a major regulator of energy balance and cognitive processes. The development of central insulin resistance is associated with alterations in dopaminergic reward systems and homeostatic signals affecting food intake, glucose metabolism, body weight and cognitive performance. Emerging evidence has highlighted a role for antipsychotics (APs) to modulate central insulin-mediated pathways. Although APs remain the cornerstone treatment for schizophrenia they are associated with severe metabolic complications and fail to address premorbid cognitive deficits, which characterize the disorder of schizophrenia. In this review, we first explore how the hypothesized association between schizophrenia and CNS insulin dysregulation aligns with the use of APs. We then investigate the proposed relationship between CNS insulin action and AP-mediated effects on metabolic homeostasis, and different domains of psychopathology, including cognition. We briefly discuss a potential role of CNS insulin signaling to explain the hypothesized, but somewhat controversial association between therapeutic efficacy and metabolic side effects of APs. Finally, we propose how this knowledge might inform novel treatment strategies to target difficult to treat domains of schizophrenia. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Brain insulin action in schizophrenia: Something borrowed and something new

Insulin signaling in the central nervous system is at the intersection of brain and body interactions, and represents a fundamental link between metabolic and cognitive disorders. Abnormalities in brain insulin action could underlie the development of comorbid schizophrenia and type 2 diabetes. Among its functions, central nervous system insulin is involved in regulation of striatal dopamine levels, peripheral glucose homeostasis, and feeding regulation. In this review, we discuss the role and importance of central nervous system insulin in schizophrenia and diabetes pathogenesis from a historical and mechanistic perspective. We describe central nervous system insulin sites and pathways of action, with special emphasis on glucose metabolism, cognitive functioning, inflammation, and food preferences. Finally, we suggest possible mechanisms that may explain the actions of central nervous system insulin in relation to schizophrenia and diabetes, focusing on glutamate and dopamine signaling, intracellular signal transduction pathways, and brain energetics. Understanding the interplay between central nervous system insulin and schizophrenia is essential to disentangling this comorbid relationship and may provide novel treatment approaches for both neuropsychiatric and metabolic dysfunction. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Insulin Signaling Impairment in the Brain as a Risk Factor in Alzheimer's Disease

Type 2 diabetes is a risk factor for developing Alzheimer’s disease (AD). The underlying mechanism that links up the two conditions seems to be the de-sensitization of insulin signaling. In patients with AD, insulin signaling was found to be de-sensitized in the brain, even if they did not have diabetes. Insulin is an important growth factor that regulates cell growth, energy utilization, mitochondrial function and replacement, autophagy, oxidative stress management, synaptic plasticity, and cognitive function. Insulin desensitization, therefore, can enhance the risk of developing neurological disorders in later life. Other risk factors, such as high blood pressure or brain injury, also enhance the likelihood of developing AD. All these risk factors have one thing in common – they induce a chronic inflammation response in the brain. Pro-inflammatory cytokines block growth factor signaling and enhance oxidative stress. The underlying molecular processes for this are described in the review. Treatments to re-sensitize insulin signaling in the brain are also described, such as nasal insulin tests in AD patients, or treatments with re-sensitizing hormones, such as leptin, ghrelin, glucagon-like peptide 1 (GLP-1),and glucose-dependent insulinotropic polypeptide (GIP). The first clinical trials show promising results and are a proof of concept that utilizing such treatments is valid.

Curcumin Ameliorates the Impaired Insulin Signaling Involved in the Pathogenesis of Alzheimer's Disease in Rats

To date, dysregulation of the insulin signaling pathway in the brain has not been demonstrated unequivocally in Alzheimer's disease (AD). The purpose of the study was to examine the possible dysregulation of insulin signaling pathway in an AD rat model. Furthermore, the present study investigated the effect of Donepezil and Curcumin on insulin signaling, insulin, and glucose levels in AD rat brain. The rats were induced to develop AD by intraperitoneal administration of Scopolamine. We found that glucose levels in plasma and brain were decreased in AD rats, whereas the insulin levels was increased in plasma but decreased in brain in AD rats. In addition, insulin signaling proteins IR-β, IGF-1, IRS-1, IRS-2 p-Akt (Ser473), and Akt were markedly reduced in the AD rats. Furthermore, GLUT3 and GLUT4 levels in the brain were markedly reduced in AD rats. All these data were compared to Saline-treated control rats. Curcumin significantly increased glucose levels in plasma and in brain. However, insulin levels was decreased in plasma and was increased in AD rats' brain. Moreover, GLUT3 and GLUT4 levels were significantly increased in Curcumin-treated AD rats. All these data were compared to Scopolamine- induced AD rats. Thus amelioration of impaired insulin signaling and improved glucose regulation in AD rats by Curcumin may be beneficial in the management of AD.