Brain insulin dysregulation: implication for neurological and neuropsychiatric disorders

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

A computational model of Alzheimer's disease at the nano, micro, and macroscales

Introduction

Mathematical models play a crucial role in investigating complex biological systems, enabling a comprehensive understanding of interactions among various components and facilitating in silico testing of intervention strategies. Alzheimer's disease (AD) is characterized by multifactorial causes and intricate interactions among biological entities, necessitating a personalized approach due to the lack of effective treatments. Therefore, mathematical models offer promise as indispensable tools in combating AD. However, existing models in this emerging field often suffer from limitations such as inadequate validation or a narrow focus on single proteins or pathways.

Methods

In this paper, we present a multiscale mathematical model that describes the progression of AD through a system of 19 ordinary differential equations. The equations describe the evolution of proteins (nanoscale), cell populations (microscale), and organ-level structures (macroscale) over a 50-year lifespan, as they relate to amyloid and tau accumulation, inflammation, and neuronal death.

Results

Distinguishing our model is a robust foundation in biological principles, ensuring improved justification for the included equations, and rigorous parameter justification derived from published experimental literature.

Conclusion

This model represents an essential initial step toward constructing a predictive framework, which holds significant potential for identifying effective therapeutic targets in the fight against AD.

Intranasal insulin intake and exercise improve memory function in amyloid-β induced Alzheimer's-like disease in rats: Involvement of hippocampal BDNF-TrkB receptor

The most prevalent type of dementia, Alzheimer's disease (AD), is a compelling illustration of the link between cognitive deficits and neurophysiological anomalies. We investigated the possible protective effect of intranasal insulin intake with exercise on amyloid-β (Aβ)-induced neuronal damage. The level of hippocampal brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB) were analyzed to understand the involvement of BDNF-TrkB pathway in this modulation. In this study, we induced AD-like pathology by amyloid-β (Aβ) administration. Then, we examined the impact of a 4-week pretreatment of moderate treadmill exercise and intranasal intake of insulin on working and spatial memory in male Wistar rats. We also analyzed the mechanisms of improved memory and anxiety through changes in the protein level of BDNF and TrkB. Results showed that animals received Aβ had impaired working memory, increased anxiety which were accompanied by lower protein levels of BDNF and TrkB in the hippocampus. The exercise training and intranasal insulin improved working memory deficits, decreased anxiety, and increased BDNF, and TrkB levels in the hippocampus of animals received Aβ. Our finding of improved memory performance after intranasal intake of insulin and exercise may be of significance for the treatment of memory impairments and anxiety-like behavior in AD.

The GLP-1 receptor agonist exenatide improves recovery from spinal cord injury by inducing macrophage polarization toward the M2 phenotype

Although a wide variety of mechanisms take part in the secondary injury phase of spinal cord injury (SCI), inflammation is the most important factor implicated in the sequelae after SCI. Being central to the inflammation reaction, macrophages and their polarization are a topic that has garnered wide interest in the studies of SCI secondary injury. The glucagon-like peptide 1 (GLP-1) receptor agonist exenatide has been shown to enhance the endoplasmic reticulum stress response and improve motor function recovery after spinal cord injury (SCI). Since exenatide has also been reported to induce the production of M2 cells in models of cerebral infarction and neurodegenerative diseases, this study was conducted to examine the effects of exenatide administration on the inflammation process that ensues after spinal cord injury. In a rat contusion model of spinal cord injury, the exenatide group received a subcutaneous injection of 10 μg exenatide immediately after injury while those in the control group received 1 mL of phosphate-buffered saline. Quantitative RT-PCR and immunohistochemical staining were used to evaluate the effects of exenatide administration on the macrophages infiltrating the injured spinal cord, especially with regard to macrophage M1 and M2 profiles. The changes in hind limb motor function were assessed based on Basso, Beattie, Bresnahan locomotor rating scale (BBB scale) scores. The improvement in BBB scale scores was significantly higher in the exenatide group from day 7 after injury and onwards. Quantitative RT-PCR revealed an increase in the expression of M2 markers and anti-inflammatory interleukins in the exenatide group that was accompanied by a decrease in the expression of M1 markers and inflammatory cytokines. Immunohistochemical staining showed no significant difference in M1 macrophage numbers between the two groups, but a significantly higher number of M2 macrophages was observed in the exenatide group on day 3 after injury. Our findings suggest that exenatide administration promoted the number of M2-phenotype macrophages after SCI, which may have led to the observed improvement in hind limb motor function in a rat model of SCI.

Involvement of the Receptor for Advanced Glycation End Products (RAGE) in high fat-high sugar diet-induced anhedonia in rats

Clinical and basic science investigation indicates a link between insulin resistance and anhedonia. Previous results of this laboratory point to impaired nucleus accumbens (NAc) insulin signaling as an underpinning of diet-induced anhedonia, based on use of a glucose lick microstructure assay. The present study evaluated whether advanced glycation end products (AGEs) and their receptor (RAGE), known to mediate obesogenic diet-induced inflammation and pathological metabolic conditions, are involved in this behavioral change. Six weeks maintenance of male and female rats on a high fat-high sugar liquid diet (chocolate Ensure) increased body weight gain, and markedly increased circulating insulin and leptin, but induced anhedonia (decreased first minute lick rate and lick burst size) in males only. In these subjects, anhedonia correlated with plasma concentrations of insulin. Although the diet did not alter plasma or NAc AGEs, or the expression of RAGE in the NAc, marginally significant correlations were seen between anhedonia and plasma content of several AGEs and NAc RAGE. Importantly, a small molecule RAGE antagonist, RAGE229, administered twice daily by oral gavage, prevented diet-induced anhedonia. This beneficial effect was associated with improved adipose function, reflected in the adiponectin/leptin ratio, and increased pCREB/total CREB in the NAc, and a shift in the pCREB correlation with pThr34-DARPP-32 from near-zero to strongly positive, such that both phospho-proteins correlated with the rescued hedonic response. This set of findings suggests that the receptor/signaling pathway and cell type underlying the RAGE229-mediated increase in pCREB may mediate anhedonia and its prevention. The possible role of adipose tissue as a locus of diet-induced RAGE signaling, and source of circulating factors that target NAc to modify hedonic reactivity are discussed.

The concept of "metabolic jet lag" in the pathophysiology of bipolar disorder: implications for research and clinical care

Bipolar disorder (BD) is a potentially chronic mental disorder marked by recurrent depressive and manic episodes, circadian rhythm disruption, and changes in energetic metabolism. "Metabolic jet lag" refers to a state of shift in circadian patterns of energy homeostasis, affecting neuroendocrine, immune, and adipose tissue function, expressed through behavioral changes such as irregularities in sleep and appetite. Risk factors include genetic variation, mitochondrial dysfunction, lifestyle factors, poor gut microbiome health and abnormalities in hunger, satiety, and hedonistic function. Evidence suggests metabolic jet lag is a core component of BD pathophysiology, as individuals with BD frequently exhibit irregular eating rhythms and circadian desynchronization of their energetic metabolism, which is associated with unfavorable clinical outcomes. Although current diagnostic criteria lack any assessment of eating rhythms, technological advancements including mobile phone applications and ecological momentary assessment allow for the reliable tracking of biological rhythms. Overall, methodological refinement of metabolic jet lag assessment will increase knowledge in this field and stimulate the development of interventions targeting metabolic rhythms, such as time-restricted eating.

Combination of UHPLC-Q Exactive-Orbitrap MS, Bioinformatics and Molecular Docking to Reveal the Mechanism of Huan-Lian-Jie-Du Decoction in the Treatment of Diabetic Encephalopathy

Diabetic encephalopathy (DE) is a serious complication of diabetes, which affects patients' quality of life. We aimed to explore HLJDD in the treatment of DE by LC/MS and bioinformatics. UPLC-Q Exactive-Orbitrap MS was employed to clarify the compounds. The modules and hub targets of DE were gained from WGCNA. Subsequently, an Herb-Compound-Target network was constructed and enrichment analysis was used. In addition, a protein-protein interaction (PPI) network was constructed and molecular docking was used to verify the above analysis. As result, 138 compounds and 10 prototypes in brain were identified. In network pharmacology, 8 modules and 5692 hub targets were obtained from WGCNA. An Herb-Compound-Target network was constructed by 4 herbs, 10 compounds and 56 targets. The enrichment analysis showed that the treatment of DE with HLJDD involve oxidative stress and neuroprotection. Beside, SRC, JUN, STAT3, MAPK1 and PIK3R1 were identified and as hub targets of HLJDD in treating DE. Moreover, Molecular docking showed that five hub targets had strong affinity with the corresponding alkaloids. Therefore, we explored the underlying mechanisms of HLJDD in the treatment of DE and to provide the theoretical and scientific basis for subsequent experimental studies and clinical applications.

Apigetrin-enriched Pulmeria alba extract prevents assault of STZ on pancreatic β-cells and neuronal oxidative stress with concomitant attenuation of tissue damage and suppression of inflammation in the brain of diabetic rats

In the present study, in vitro, in vivo, and in silico models were used to evaluate the therapeutic potential of Pulmeria alba methanolic (PAm) extract, and we identified the major phytocompound, apigetrin. Our in vitro studies revealed dose-dependent increased glucose uptake and inhibition of α-amylase (50% inhibitory concentration (IC₅₀)= 217.19 µg/mL), antioxidant (DPPH, ferric-reducing activity of plasma (FRAP), and lipid peroxidation (LPO) [IC₅₀ = 103.23, 58.72, and 114.16 µg/mL respectively]), and anti-inflammatory potential (stabilizes human red blood cell (HRBC) membranes, and inhibits proteinase and protein denaturation [IC₅₀ = 143.73, 131.63, and 198.57 µg/mL]) by the PAm extract. In an in vivo model, PAm treatment reversed hyperglycemia and attenuated insulin deficiency in rats with streptozotocin (STZ)-induced diabetes. A post-treatment tissue analysis revealed that PAm attenuated neuronal oxidative stress, neuronal inflammation, and neuro-cognitive deficiencies. This was evidenced by increased levels of antioxidants enzymes (superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH)), and decreased malondialdehyde (MDA), proinflammatory markers (cyclooxygenase 2 (COX2), nuclear factor (NF)-κB and nitric oxide (NOx)), and acetylcholinesterase (AChE) activities in the brain of PAm-treated rats compared to the STZ-induced diabetic controls. However, no treatment-related changes were observed in levels of neurotransmitters, including serotonin and dopamine. Furthermore, STZ-induced dyslipidemia and alterations in serum biochemical markers of hepatorenal dysfunction were also reversed by PAm treatment. Extract characterization identified apigetrin (retention time: 21,227 s, 30.48%, m/z: 433.15) as the major bioactive compound in the PAm extract. Consequently, we provide in silico insights into the potential of apigetrin to target AChE/COX-2/NOX/NF-κB Altogether the present study provides preclinical evidence of the therapeutic potential of the apigetrin-enriched PAm extract for treating oxidative stress and neuro-inflammation associated with diabetes.

A novel protective modality against rotenone-induced Parkinson's disease: A pre-clinical study with dulaglutide

Parkinson's disease (PD) drugs treat symptoms without inhibiting progression. In recent years, finding novel therapeutic medications that can halt disease progression has become crucial. Research on antidiabetic medicines is valuable in these investigations because of the parallels between the two disorders. Using Rotenone (ROT), a frequently used PD model, the possible neuroprotective benefits of Dulaglutide (DUL), an extended-acting glucagon-like peptide-1 agonist, were considered. Twenty-four rats were randomly assigned to 4 groups to complete this experiment (n = 6). 0.2 ml of the vehicle (1 ml of dimethyl sulfoxide (DMSO) diluted in sunflower oil) was administered to the standard control group subcutaneously with a 48-hour pause. The second group was administered ROT 2.5 mg/kg SC every 48 h for 20 days as a positive control group. The third and fourth groups were administered one dose of DUL each week (0.05 and 0.1 mg/kg SC, respectively) to their regimens. The mice received ROT (2.5 mg/kg SC) every 48 h for 20 days after receiving DUL for the initial dose (96 h later). The current study focused on the DUL's ability to preserve usual behavioral function, enhance antioxidant and anti-inflammatory pathways, inhibit alpha-synuclein (α-syn), and increase parkin levels. It is concluded that DUL acts as an antioxidant and an anti-inflammatory to protect against ROT-induced PD. However, more studies are required to support this finding.

Neurotransmitters in Type 2 Diabetes and the Control of Systemic and Central Energy Balance

Efficient signal transduction is important in maintaining the function of the nervous system across tissues. An intact neurotransmission process can regulate energy balance through proper communication between neurons and peripheral organs. This ensures that the right neural circuits are activated in the brain to modulate cellular energy homeostasis and systemic metabolic function. Alterations in neurotransmitters secretion can lead to imbalances in appetite, glucose metabolism, sleep, and thermogenesis. Dysregulation in dietary intake is also associated with disruption in neurotransmission and can trigger the onset of type 2 diabetes (T2D) and obesity. In this review, we highlight the various roles of neurotransmitters in regulating energy balance at the systemic level and in the central nervous system. We also address the link between neurotransmission imbalance and the development of T2D as well as perspectives across the fields of neuroscience and metabolism research.

Virgin coconut oil reverses behavioral phenotypes of letrozole-model of PCOS in Wistar rats via modulation of NRF2 upregulation

Objectives

Polycystic ovarian syndrome (PCOS) is an endocrine disorder associated with insulin resistance, hyperandrogenism, and sub-infertility. Virgin coconut oil (VCO) has been reported to have health benefits, such as anti-inflammatory, anti-oxidant, and antiviral properties. This study investigated the effects of dietary VCO supplementation on memory and cognitive impairment in female rats with letrozole induced PCOS.

Methods

Thirty female rats were randomly divided into five groups. All rats except controls were treated with letrozole for 21 days to induce PCOS and were subsequently treated for 14 days with 10% VCO, clomiphene (CLO), or VCO + CLO. Three neurobehavioral tests were conducted: elevated plus maze, Y maze, and novel object recognition tests.

Results

Our results indicated statistically elevated serum concentrations of sex hormones in rats with PCOS, compared with the control and treated groups. In addition, all treated groups showed significant reversal of the low serum concentrations of catalase and down-regulated gene expression of Nrf2 in the hippocampus seen in the PCOS rats. In addition, gene expression of acetylcholine esterase was up-regulated in PCOS rats, and was statistically reverted in the VCO treated groups.

Conclusion

Anxiety-like behavior and impaired short-term memory were observed in PCOS rats; however, VCO supplementation reversed these effects by modulating the gene expression of Nrf2 and AchE.

The identities of insulin signaling pathway are affected by overexpression of Tau and its phosphorylation form

Introduction

Hyperphosphorylated Tau formed neurofibrillary tangles was one of the major neuropathological hallmarks of Alzheimer's disease (AD). Dysfunctional insulin signaling in brain is involved in AD. However, the effect of Tau pathology on brain insulin resistance remains unclear. This study explored the effects of overexpressing wild-type Tau (WTau) or Tau with pseudo-phosphorylation at AT8 residues (PTau) on the insulin signaling pathway (ISP).

Methods

293T cells or SY5Y cells overexpressing WTau or PTau were treated with or without insulin. The elements in ISP or the regulators of IPS were analyzed by immunoblotting, immunofluorescent staining and co-immunoprecipitation. Akt inhibitor MK2206 was used for evaluating the insulin signaling to downstream of mTOR in Tau overexpressing cells. The effects of anti-aging drug lonafarnib on ISP in WTau or PTau cells were also analyzed with immunoblotting. Considering lonafarnib is an inhibitor of FTase, the states of Rhes, one of FTase substrate in WTau or PTau cells were analyzed by drug affinity responsive target stability (DARTS) assay and the cellular thermal shift assay (CETSA).

Results

WTau or PTau overexpression in cells upregulated basal activity of elements in ISP in general. However, overexpression of WTau or PTau suppressed the ISP signaling transmission responses induced by insulin simulation, appearing relative higher response of IRS-1 phosphorylation at tyrosine 612 (IRS-1 p612) in upstream IPS, but a lower phosphorylation response of downstream IPS including mTOR, and its targets 4EPB1 and S6. This dysregulation of insulin evoked signaling transmission was more obvious in PTau cells. Suppressing Akt with MK2206 could compromise the levels of p-S6 and p-mTOR in WTau or PTau cells. Moreover, the changes of phosphatases detected in WTau and PTau cells may be related to ISP dysfunction. In addition, the effects of lonafarnib on the ISP in SY5Y cells with WTau and PTau overexpression were tested, which showed that lonafarnib treatment resulted in reducing the active levels of ISP elements in PTau cells but not in WTau cells. The differential effects are probably due to Tau phosphorylation modulating lonafarnib-induced alterations in Rhes, as revealed by DARTS assay.

Conclusion and discussion

Overexpression of Tau or Tau with pseudo-phosphorylation at AT8 residues could cause an upregulation of the basal/tonic ISP, but a suppression of insulin induced the phasic activation of ISP. This dysfunction of ISP was more obvious in cells overexpressing pseudo-phosphorylated Tau. These results implied that the dysfunction of ISP caused by Tau overexpression might impair the physiological fluctuation of neuronal functions in AD. The different effects of lonafarnib on ISP between WTau and PTau cells, indicating that Tau phosphorylation mediates an additional effect on ISP. This study provided a potential linkage of abnormal expression and phosphorylation of Tau to the ISP dysfunction in AD.

Intranasal Peptide Therapeutics: A Promising Avenue for Overcoming the Challenges of Traditional CNS Drug Development

The central nervous system (CNS) has, among all organ systems in the human body, the highest failure rate of traditional small-molecule drug development, ranging from 80-100% depending on the area of disease research. This has led to widespread abandonment by the pharmaceutical industry of research and development for CNS disorders, despite increased diagnoses of neurodegenerative disorders and the continued lack of adequate treatment options for brain injuries, stroke, neurodevelopmental disorders, and neuropsychiatric illness. However, new approaches, concurrent with the development of sophisticated bioinformatic and genomic tools, are being used to explore peptide-based therapeutics to manipulate endogenous pathways and targets, including "undruggable" intracellular protein-protein interactions (PPIs). The development of peptide-based therapeutics was previously rejected due to systemic off-target effects and poor bioavailability arising from traditional oral and systemic delivery methods. However, targeted nose-to-brain, or intranasal (IN), approaches have begun to emerge that allow CNS-specific delivery of therapeutics via the trigeminal and olfactory nerve pathways, laying the foundation for improved alternatives to systemic drug delivery. Here we review a dozen promising IN peptide therapeutics in preclinical and clinical development for neurodegenerative (Alzheimer's, Parkinson's), neuropsychiatric (depression, PTSD, schizophrenia), and neurodevelopmental disorders (autism), with insulin, NAP (davunetide), IGF-1, PACAP, NPY, oxytocin, and GLP-1 agonists prominent among them.

Cinnamaldehyde Regulates Insulin and Caspase-3 Signaling Pathways in the Sporadic Alzheimer's Disease Model: Involvement of Hippocampal Function via IRS-1, Akt, and GSK-3β Phosphorylation

Insulin signaling disruption and caspase-3 cleavage play a pathologic role in Alzheimer's disease (AD). Evidence suggested that cinnamaldehyde (Cin), the major component of cinnamon, has the ability to act as a neuroprotective agent. However, little evidence is available to demonstrate its effectiveness in regulating the insulin and caspase-3 signaling pathways and underlying molecular mechanisms. Therefore, the present study was conducted to correlate the molecular mechanisms of these signaling pathways and Cin treatment on animal behavioral performance in an intracerebroventricular (ICV)-streptozotocin (STZ, 3 mg/kg) model. The sporadic AD rat model was treated with Cin (10 and 100 mg/kg; intraperitoneal, i.p) daily for 2 weeks. Novel object recognition (NOR), Morris water maze (MWM), and elevated plus maze (EPM) tests were performed to assess recognition/spatial memory and anxiety-like behavior, respectively. Hippocampal Aβ aggregation was assessed using Congo red staining. The activity of hippocampal caspase-3 and IRS-1/Akt/GSK-3β signaling pathways were analyzed using the Western blot technique. The results revealed that Cin (100 mg/kg, effective dose) improved recognition/spatial memory deficits and anxiety-like behavior. In addition, Cin negated the effects of STZ on Aβ aggregation and caspase-3 cleavage in the hippocampus. Furthermore, the Western blot method showed that hippocampal IRS-1/AKT/GSK-3β phosphorylation was altered in ICV-STZ animal model, while Cin modulated this signaling pathway through decreasing Phospho.IRS-1_Ser307/Total.IRS-1 ratio and also increasing Phospho.Akt_Ser473/Total.Akt and Phospho.GSK-3β_Ser9/Total.GSK-3β ratios. These findings suggest that Cin is involved in the regulation of hippocampal IRS-1/AKT/GSK-3β and caspase-3 pathways in a sporadic AD model, and modulation of these signaling pathways also influences the animal behavioral performance.

Learning and memory impairment and transcriptomic profile in hippocampus of offspring after maternal fructose exposure during gestation and lactation

Increased fructose intake is a global issue, especially in mothers. Maternal fructose exposure during gestation and lactation can affect learning and memory in offspring; however, the detailed mechanism is still unknown. The hippocampus is a mind locale liable for learning and memory. Here, we established a maternal high-fructose diet model by administering 13% and 40% fructose water, applied the Morris Water Maze test on postnatal day 60 offspring, and performed full-length RNA sequencing using the Oxford Nanopore Technologies platform to explore the changes in gene expression in the hippocampus. The results showed that learning and memory in offspring were negatively affected. Compared with the control group, 369 differentially expressed transcripts (DETs) were identified in the 13% fructose group, and 501 DETs were identified in the 40% fructose group. Gene Ontology enriched term and Kyoto Encyclopedia of Genes and Genomes enriched pathway analyses identified several terms and pathways related to brain development and cognitive function. Furthermore, we confirmed that the Wnt/β-catenin signaling pathway was down-regulated and neuron degeneration was enhanced. In summary, our results indicate that maternal fructose exposure during gestation and lactation can impair learning and memory in offspring and affect brain function at the transcriptome level.

New Therapeutic Approaches to and Mechanisms of Ginsenoside Rg1 against Neurological Diseases

Neurological diseases, including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), stroke, cerebral infarction, ischemia-reperfusion injury, depression and, stress, have high incidence and morbidity and often lead to disability. However, there is no particularly effective medication against them. Therefore, finding drugs with a suitable efficacy, low toxicity and manageable effects to improve the quality of life of patients is an urgent problem. Ginsenoside Rg1 (Rg1) is the main active component of ginseng and has a variety of pharmacological effects. In this review, we focused on the therapeutic potential of Rg1 for improving neurological diseases. We introduce the mechanisms of Ginsenoside Rg1 in neurological diseases, including apoptosis, neuroinflammation, the microRNA (miRNA) family, the mitogen-activated protein kinase (MAPK) family, oxidative stress, nuclear factor-κB (NF-κB), and learning and memory of Rg1 in neurological diseases. In addition, Rg1 can also improve neurological diseases through the interaction of different signal pathways. The purpose of this review is to explore more in-depth ideas for the clinical treatment of neurological diseases (including PD, AD, HD, stroke, cerebral infarction, ischemia–reperfusion injury, depression, and stress). Therefore, Rg1 is expected to become a new therapeutic method for the clinical treatment of neurological diseases.

Long term high fat diet induces metabolic disorders and aggravates behavioral disorders and cognitive deficits in MAPT P301L transgenic mice

Most Alzheimer disease (AD) patients present as sporadic late onset AD, with metabolic factors playing an important role in the occurrence and development of AD. Given the link between peripheral insulin resistance and tau pathology in streptozotocin-injected and db/db mouse models of diabetes, we fed high fat diet (HFD) to pR5 mice expressing P301L mutant human tau, with the aim of developing a new model with characteristics of obesity, T2DM and AD to mimic AD patients exacerbated by obesity and T2DM, an increasing trend in modern society. In our study, pR5 and C57BL/6 (WT) mice were randomly allocated to a standard diet (STD) or HFD for 30 weeks starting at 8 weeks of age. Food intake was measured weekly, body weight and fasting glucose levels were measured fortnightly, and a comprehensive behavioral test battery was performed to assess anxiety, depression and cognitive dysfunction. Glucose and insulin tolerance tests were performed after 30 weeks of HFD. We also investigated the effect of long term HFD on tau pathology in the brains of WT and P301L mice by performing western blotting of whole brain homogenates for total tau, phosphorylated tau at Ser396 and Thr231. Our results show that pR5 mice fed with HFD are more vulnerable to diet induced obesity compared to WT, especially with increasing age. In addition, pR5 mice on HFD developed glucose intolerance and insulin resistance. It was identified that long term HFD significantly aggravates depression like behavior and impairs cognitive function in pR5 mice, and also induces anxiety like behavior in both pR5 and WT mice. Long term HFD was also shown to aggravate tau hyperphosphorylation in pR5 transgenic mice, and increase total and hyperphosphorylated tau in WT mice. These results indicate that diet induced obesity of pR5 transgenic mice expressing P301L mutant human tau generates T2DM, and aggravates tau phosphorylation, and is therefore a model useful for investigations that seek to understand the relationships between AD, T2DM and obesity, and the underlying biochemical changes and mechanisms associated with metabolic disorders and AD tauopathy.

Type 2 Diabetes Mellitus as a Risk Factor for Alzheimer’s Disease: Review and Meta-Analysis

Alzheimer’s disease is the most common type of dementia, reaching 60–80% of case totals, and is one of the major global causes of the elderly population’s decline in functionality concerning daily life activities. Epidemiological research has already indicated that, in addition to several others metabolic factors, diabetes mellitus type 2 is a risk factor of Alzheimer’s disease. Many molecular pathways have been described, and at the same time, there are clues that suggest the connection between type 2 diabetes mellitus and Alzheimer’s disease, through specific genes, autophagy, and even inflammatory pathways. A systematic review with meta-analysis was conducted, and its main goal was to reveal the multilevel connection between these diseases.

Significance of Brain Glucose Hypometabolism, Altered Insulin Signal Transduction, and Insulin Resistance in Several Neurological Diseases

Several neurological diseases share pathological alterations, even though they differ in their etiology. Neuroinflammation, altered brain glucose metabolism, oxidative stress, mitochondrial dysfunction and amyloidosis are biological events found in those neurological disorders. Altered insulin-mediated signaling and brain glucose hypometabolism are characteristic signs observed in the brains of patients with certain neurological diseases, but also others such as type 2 diabetes mellitus and vascular diseases. Thus, significant reductions in insulin receptor autophosphorylation and Akt kinase activity, and increased GSK-3 activity and insulin resistance, have been reported in these neurological diseases as contributing to the decline in cognitive function. Supporting this relationship is the fact that nasal and hippocampal insulin administration has been found to improve cognitive function. Additionally, brain glucose hypometabolism precedes the unmistakable clinical manifestations of some of these diseases by years, which may become a useful early biomarker. Deficiencies in the major pathways of oxidative energy metabolism have been reported in patients with several of these neurological diseases, which supports the hypothesis of their metabolic background. This review remarks on the significance of insulin and brain glucose metabolism alterations as keystone common pathogenic substrates for certain neurological diseases, highlighting new potential targets.

Effects of apolipoprotein E isoform, sex, and diet on insulin BBB pharmacokinetics in mice

Age, apolipoprotein E (apoE) isoform, sex, and diet can independently affect the risk for the development of Alzheimer’s disease (AD). Additionally, synergy between some of these risk factors have been observed. However, the relation between the latter three risk factors has not been investigated. Central nervous system (CNS) insulin resistance is commonly involved in each of these risk factors. CNS insulin is primarily derived from the periphery in which insulin must be transported across the blood–brain barrier (BBB). Additionally, insulin can bind the brain endothelial cell to affect intracellular signaling. Therefore, we hypothesized CNS access to insulin could be affected by the combination of apoE isoform, sex, and diet. We analyzed insulin BBB pharmacokinetics in aged apoE targeted replacement (E3 and E4) male and female mice on a low-fat and high-fat diet. There were differences within males and females due to apoE genotype and diet in insulin interactions at the BBB. These sex-, diet-, and apoE isoform-dependent differences could contribute to the cognitive changes observed due to altered CNS insulin signaling.

Insulin and Insulin Resistance in Alzheimer's Disease

Insulin plays a range of roles as an anabolic hormone in peripheral tissues. It regulates glucose metabolism, stimulates glucose transport into cells and suppresses hepatic glucose production. Insulin influences cell growth, differentiation and protein synthesis, and inhibits catabolic processes such as glycolysis, lipolysis and proteolysis. Insulin and insulin-like growth factor-1 receptors are expressed on all cell types in the central nervous system. Widespread distribution in the brain confirms that insulin signaling plays important and diverse roles in this organ. Insulin is known to regulate glucose metabolism, support cognition, enhance the outgrowth of neurons, modulate the release and uptake of catecholamine, and regulate the expression and localization of gamma-aminobutyric acid (GABA). Insulin is also able to freely cross the blood–brain barrier from the circulation. In addition, changes in insulin signaling, caused inter alia insulin resistance, may accelerate brain aging, and affect plasticity and possibly neurodegeneration. There are two significant insulin signal transduction pathways: the PBK/AKT pathway which is responsible for metabolic effects, and the MAPK pathway which influences cell growth, survival and gene expression. The aim of this study is to describe the role played by insulin in the CNS, in both healthy people and those with pathologies such as insulin resistance and Alzheimer’s disease.

Linsitinib (OSI-906) modulates brain energy metabolism and seizure activity in the lithium-pilocarpine rat model

Background

Epileptic seizure is a process of energy accumulation, bursting, and depletion accompanied by the production, spread, and termination of epileptic discharges. The energy required for a seizure is mainly provided through mitochondrial production of ATP. Mitochondrial diseases often lead to epileptic seizures, and energy depletion caused by seizures can lead to mitochondrial dysfunction. The energy metabolism has become a key target for treatment of epileptic diseases.

Method

The effect of OSI-906, an insulin receptor (IR)/ insulin-like growth factor 1 receptor (IGF-1R) inhibitor, on behaviors and electroencephalographic activity in the lithium-pilocarpine rats were tested. 18F-FDG positron emission tomography (PET)/ computed tomography (CT) was performed to detect the relative whole-brain glucose uptake values. Electron microscopy was performed to observe the ultrastructure of neuronal and mitochondrial damage. The changes in blood glucose at different time points before and after the intervention were tested and the effects of OSI-906 on IR/IGF-1R and downstream Akt signaling in the context of seizures were evaluated.

Results

The OSI-906 treatment applied 3 days before the pilocarpine-induced seizures significantly reduced the seizure severity, prolonged the seizure latency and decreased the EEG energy density. MicroPET/CT revealed that 50 mg/kg of OSI-906 inhibited the 18F-FDG glucose uptake after epileptic seizures, suggesting that OSI-906, through inhibiting IR/IGF-1R and the downstream AKT signaling, may regulate the excessive energy consumption of the epileptic brain. The OSI-906 treatment also reduced the mitochondrial damage caused by epileptic seizures.

Conclusion

The IR/IGF-1R inhibitor OSI-906 can significantly reduce the sensitivity and severity of pilocarpine-induced seizures by inhibiting the IR/IGF-1R and the downstream Akt signaling pathway.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

Evaluation of Effect of Ninjin'yoeito on Regional Brain Glucose Metabolism by 18F-FDG Autoradiography With Insulin Loading in Aged Mice

Introduction: A recent clinical study revealed that Ninjin'yoeito (NYT) may potentially improve cognitive outcome. However, the mechanism by which NYT exerts its effect on elderly patients remains unclear. The aim of this study is to evaluate the effect of Ninjin'yoeito on regional brain glucose metabolism by ¹⁸F-FDG autoradiography with insulin loading in aged wild-type mice.

Materials and Methods: After 12 weeks of feeding NYT, mice were assigned to the control and insulin-loaded groups and received an intraperitoneal injection of human insulin (2 U/kg body weight) 30 min prior to ¹⁸F-FDG injection. Ninety minutes after the injection, brain autoradiography was performed.

Results: After insulin loading, the ¹⁸F-FDG accumulation showed negative changes in the cortex, striatum, thalamus, and hippocampus in the control group, whereas positive changes were observed in the NYT-treated group.

Conclusions: Ninjin'yoeito may potentially reduce insulin resistance in the brain regions in aged mice, thereby preventing age-related brain diseases.

Protective properties of GLP-1 and associated peptide hormones in neurodegenerative disorders

Type 2 diabetes mellitus and the associated desensitisation of insulin signalling has been identified as a risk factor for progressive neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and others. Glucagon-like peptide 1 (GLP-1) is a hormone that has growth factor-like and neuroprotective properties. Several clinical trials have been conducted, testing GLP-1 receptor agonists in patients with Alzheimer's disease, Parkinson's disease or diabetes-induced memory impairments. The trials showed clear improvements in Alzheimer's disease, Parkinson's disease and diabetic patients. Glucose-dependent insulinotropic polypeptide/gastric inhibitory peptide (GIP) is the 'sister' incretin hormone of GLP-1. GIP analogues have shown neuroprotective effects in animal models of disease and can improve on the effects of GLP-1. Novel dual GLP-1/GIP receptor agonists have been developed that can enter the brain at an enhanced rate. The improved neuroprotective effects of these drugs suggest that they are superior to single GLP-1 receptor agonists and could provide disease-modifying care for Alzheimer's disease and Parkinson's disease patients.

Imipramine alleviates memory impairment and hippocampal apoptosis in STZ-induced sporadic Alzheimer's rat model: Possible contribution of MAPKs and insulin signaling

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, associated with several pathophysiological complaints. Impaired insulin signaling in the brain, is one of the important characteristic features of AD which is accompanied by cognitive deficits. According to the multifactorial and complicated pathology of AD, no modifying therapy has been approved yet. Imipramine is a kind of tricyclic antidepressant with reported anti-inflammatory and anti-oxidant effects in the brain. There are controversial studies about the effect of this drug on spatial memory. This study investigates the effect of imipramine on streptozotocin (STZ) induced memory impairment in rats. Pursuing this objective, rats were treated with imipramine 10 or 20 mg/kg i.p. once a day for 14 days. 24 h after the last injection, memory function was evaluated by the Morris water maze (MWM) test in 4 consecutive days. Then, hippocampi were removed and the activity of caspase-3, mitogen activated protein kinases (MAPKs) family and inhibitory phosphorylation of insulin receptor substrate-1 (IRS-1_ser307) were analyzed using Western blotting. Results showed that imipramine prevents memory impairment in STZ induced rats and this improvement was accompanied with an increase in ERK activity, reduction of caspase-3 and JNK activity, as well as partial restoration of P38 and IRS-1 activity. In conclusion, our study demonstrated that at least some members of the MAPK family are involved in the neuroprotective effect of imipramine.

The Burden of Antipsychotic-Induced Weight Gain and Metabolic Syndrome in Children

Antipsychotic medications are critical to child and adolescent psychiatry, from the stabilization of psychotic disorders like schizophrenia, bipolar disorder, and psychotic depression to behavioral treatment of autism spectrum disorder, tic disorders, and pediatric aggression. While effective, these medications carry serious risk of adverse events-most commonly, weight gain and cardiometabolic abnormalities. Negative metabolic consequences affect up to 60% of patients and present a major obstacle to long-term treatment. Since antipsychotics are often chronically prescribed beginning in childhood, cardiometabolic risk accumulates. An increased susceptibility to antipsychotic-induced weight gain (AIWG) has been repeatedly documented in children, particularly rapid weight gain. Associated cardiometabolic abnormalities include central obesity, insulin resistance, dyslipidemia, and systemic inflammation. Lifestyle interventions and medications such as metformin have been proposed to reduce risk but remain limited in efficacy. Furthermore, antipsychotic medications touted to be weight-neutral in adults can cause substantial weight gain in children. A better understanding of the biological underpinnings of AIWG could inform targeted and potentially more fruitful treatments; however, little is known about the underlying mechanism. As yet, modest genetic studies have nominated a few risk genes that explain only a small percentage of the risk. Recent investigations have begun to explore novel potential mechanisms of AIWG, including a role for gut microbiota and microbial metabolites. This article reviews the problem of AIWG and AP metabolic side effects in pediatric populations, proposed mechanisms underlying this serious side effect, and strategies to mitigate adverse impact. We suggest future directions for research efforts that may advance the field and lead to improved clinical interventions.

Mechanisms of Insulin Resistance at the Crossroad of Obesity with Associated Metabolic Abnormalities and Cognitive Dysfunction

Obesity mediates most of its direct medical sequelae through the development of insulin resistance (IR). The cellular effects of insulin occur through two main postreceptor pathways that are the phosphatidylinositol 3-kinase (PI3-K) and the mitogen-activated protein kinase (MAP-K) pathways. Obesity-related IR implicates the PI3-K pathway that confers the metabolic effects of insulin. Numerous and complex pathogenic pathways link obesity with the development of IR, including chronic inflammation, mitochondrial dysfunction (with the associated production of reactive oxygen species and endoplasmic reticulum stress), gut microbiota dysbiosis and adipose extracellular matrix remodelling. IR itself plays a key role in the development of metabolic dysfunction, including hypertension, dyslipidaemia and dysglycaemia. Furthermore, IR promotes weight gain related to secondary hyperinsulinaemia, with a resulting vicious cycle of worsening IR and its metabolic sequelae. Ultimately, IR underlies obesity-related conditions such as type 2 diabetes mellitus (T2D) and polycystic ovary syndrome (PCOS). IR also underlies many obesity-related malignancies, through the effects of compensatory hyperinsulinaemia on the relatively intact MAP-K insulin pathway, which controls cellular growth processes and mitoses. Furthermore, the emergent data over recent decades support an important role of obesity- and T2D-related central IR in the development of cognitive dysfunction, including effects on hippocampal synaptic plasticity. Importantly, IR is largely reversible through the optimisation of lifestyle factors that include regular engagement in physical activity with the avoidance of sedentariness, improved diet including increased fibre intake and sleep sufficiency. IR lies at the key crossroad between obesity and both metabolic and cognitive dysfunction. Given the importance of IR in the pathogenesis of many 21st century chronic diseases and its eminent reversibility, it is important that we all embrace and facilitate optimised lifestyles to improve the future health and wellbeing of the populace.

Glucagon-like peptide-1/glucose-dependent insulinotropic polypeptide dual receptor agonist DA-CH5 is superior to exendin-4 in protecting neurons in the 6-hydroxydopamine rat Parkinson model

Patients with Parkinson's disease (PD) have impaired insulin signaling in the brain. Incretin hormones, including glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), can re-sensitize insulin signaling. In a recent phase II clinical trial, the first GLP-1 mimic, exendin-4, has shown reliable curative effect in patients with PD. DA-CH5 is a novel GLP-1/GIP receptor unimolecular co-agonist with a novel peptide sequence added to cross the blood-brain barrier. Here we showed that both exendin-4 and DA-CH5 protected against 6-hydroxydopamine (6-OHDA) cytotoxicity, inhibited apoptosis, improved mitogenesis and induced autophagy flux in SH-SY5Y cells via activation of the insulin receptor substrate-1 (IRS-1)/alpha serine/threonine-protein kinase (Akt)/cAMP response element-binding protein (CREB) pathway. We also found that DA-CH5 (10 nmol/kg) daily intraperitoneal administration for 30 days post-lesion alleviated motor dysfunction in rats and prevented stereotactic unilateral administration of 6-OHDA induced dopaminergic neurons loss in the substantia nigra pars compacta. However, DA-CH5 showed curative effects in reducing the levels of α-synuclein and the levels of pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-1β). It was also more effective than exendin-4 in inhibiting apoptotic process and protecting mitochondrial functions. In addition, insulin resistance was largely alleviated and the expression of autophagy-related proteins was up-regulated in PD model rats after DA-CH5 treatment. These results in this study indicate DA-CH5 plays a therapeutic role in the 6-OHDA-unilaterally lesioned PD rat model and is superior to GLP-1 analogue exendin-4. The study was approved by the Animal Ethics Committee of Shanxi Medical University of China.

Determination of Neurodegeneration in Polycystic Ovary Syndrome with Retinal Segmentation Analysis

Purpose: To compare the thickness of each retinal layer in patients with polycystic ovary syndrome (PCOS) versus healthy, age-matched controls by using retinal segmentation analysis.Methods: In our cross-sectional study, 37 patients with PCOS (i.e., patient group) and 35 healthy individuals (i.e., control group) underwent spectral-domain optical coherence tomography imaging. Using built-in automatic retinal segmentation software to analyze the images collected, we compared the thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, outer plexiform layer, outer nuclear layer, photoreceptor layer (PRL), retinal pigment epithelium (RPE), inner retinal layers, and outer retinal layers between the groups. To analyze the measurements, we used a traditional Early Treatment Diabetic Retinopathy Study (ETDRS) grid.Results: In ETDRS subfields, 6-mm nasal RNFL thickness; 3- and 6-mm nasal GCL thickness; 3-mm superior and 6-mm nasal IPL thickness; 1-mm central, 3-mm nasal, superior, and inferior, and 6-mm nasal and inferior PRL thickness; and 6-mm inferior RPE thickness were significantly thinner in patients with PCOS than that of healthy controls.Conclusion: The results of our retinal segmentation analysis indicate that patients with PCOS tend to have thinner GCL, IPL, and PRL than healthy, age-matched controls due to neurodegeneration likely caused by insulin resistance, or subclinical retinal inflammation.

Type 3 Diabetes Mellitus: A Link Between Alzheimer's Disease and Type 2 Diabetes Mellitus

Chronic diseases, as their name suggests, are progressive and can have overlapping features. Similar to this, Alzheimer's disease (AD) and diabetes mellitus (DM) fall into the category of chronic degenerative diseases. The global burden of these two ailments is manifold; hence, it seems important to view the pathophysiologic mechanisms of DM in the worsening of AD. Genetic as well as environmental factors are seen to play a role in the disease pathogenesis. Several genes, metabolic pathways, electrolytes, and dietary habits are seen to hasten brain atrophy. Lying behind this is the accumulation of amyloid precursor and tau - the misfolded proteins - within the brain substance. This mechanism is usually innate to AD itself, but the impact of insulin resistance, disturbing the homeostatic milieu, is seen as a powerful contributing factor aggravating the neuronal loss impairing an individual's memory. Since this neuronal loss is permanent, it may lead to complications as seen with AD. To reach a consensus, we conducted an electronic literature review search using different databases. This aided us in understanding the common aspects between AD and DM on genetic, molecular, cellular levels, as well as the impact of minerals and diet on the disease manifestation. We also found that despite exceptional work, additional efforts are needed to explore the relationship between the two entities. This will help physicians, researchers, and pharmaceuticals to frame remedies targeting the cause and avoid the progression of AD.

Brain uptake pharmacokinetics of incretin receptor agonists showing promise as Alzheimer's and Parkinson's disease therapeutics

Among the more promising treatments proposed for Alzheimer's disease (AD) and Parkinson's disease (PD) are those reducing brain insulin resistance. The antidiabetics in the class of incretin receptor agonists (IRAs) reduce symptoms and brain pathology in animal models of AD and PD, as well as glucose utilization in AD cases and clinical symptoms in PD cases after their systemic administration. At least 9 different IRAs are showing promise as AD and PD therapeutics, but we still lack quantitative data on their relative ability to cross the blood-brain barrier (BBB) reaching the brain parenchyma. We consequently compared brain uptake pharmacokinetics of intravenous 125I-labeled IRAs in adult CD-1 mice over the course of 60 min. We tested single IRAs (exendin-4, liraglutide, lixisenatide, and semaglutide), which bind receptors for one incretin (glucagon-like peptide-1 [GLP-1]), and dual IRAs, which bind receptors for two incretins (GLP-1 and glucose-dependent insulinotropic polypeptide [GIP]), including unbranched, acylated, PEGylated, or C-terminally modified forms (Finan/Ma Peptides 17, 18, and 20 and Hölscher peptides DA3-CH and DA-JC4). The non-acylated and non-PEGylated IRAs (exendin-4, lixisenatide, Peptide 17, DA3-CH and DA-JC4) had significant rates of blood-to-brain influx (Ki), but the acylated IRAs (liraglutide, semaglutide, and Peptide 18) did not measurably cross the BBB. The brain influx of the non-acylated, non-PEGylated IRAs were not saturable up to 1 μg of these drugs and was most likely mediated by adsorptive transcytosis across brain endothelial cells, as observed for exendin-4. Of the non-acylated, non-PEGylated IRAs tested, exendin-4 and DA-JC4 were best able to cross the BBB based on their rate of brain influx, percentage reaching the brain that accumulated in brain parenchyma, and percentage of the systemic dose taken up per gram of brain tissue. Exendin-4 and DA-JC4 thus merit special attention as IRAs well-suited to enter the central nervous system (CNS), thus reaching areas pathologic in AD and PD.

Role of Insulin in Neurotrauma and Neurodegeneration: A Review

Insulin is a hormone typically associated with pancreatic release and blood sugar regulation. The brain was long thought to be “insulin-independent,” but research has shown that insulin receptors (IR) are expressed on neurons, microglia and astrocytes, among other cells. The effects of insulin on cells within the central nervous system are varied, and can include both metabolic and non-metabolic functions. Emerging data suggests that insulin can improve neuronal survival or recovery after trauma or during neurodegenerative diseases. Further, data suggests a strong anti-inflammatory component of insulin, which may also play a role in both neurotrauma and neurodegeneration. As a result, administration of exogenous insulin, either via systemic or intranasal routes, is an increasing area of focus in research in neurotrauma and neurodegenerative disorders. This review will explore the literature to date on the role of insulin in neurotrauma and neurodegeneration, with a focus on traumatic brain injury (TBI), spinal cord injury (SCI), Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Insulin resistance and bioenergetic manifestations: Targets and approaches in Alzheimer's disease

AIM

Insulin has a well-established role in cognition, neuronal detoxification and synaptic plasticity. Insulin transduction affect neurotransmitter functions, influence bioenergetics and regulate neuronal survival through regulating glucose energy metabolism and downward pathways.

METHODS

A systematic literature review of PubMed, Medline, Bentham, Scopus and EMBASE (Elsevier) databases was carried out with the help of the keywords like "Alzheimer's disease; Hypometabolism; Oxidative stress; energy failure in AD, Insulin; Insulin resistance; Bioenergetics" till June 2020. The review was conducted using the above keywords to collect the latest articles and to understand the nature of the extensive work carried out on insulin resistance and bioenergetic manifestations in Alzheimer's disease.

KEY FINDINGS

The article sheds light on insulin resistance mediated hypometabolic state on pathological progression of AD. The disrupted insulin signaling has pathological outcome in form of disturbed glucose homeostasis, altered bioenergetic state which increases build-up of senile plaques (Aβ), neurofibrillary tangles (τ), decline in transportation of glucose and activation of inflammatory pathways. The mechanistic link of insulin resistant state with therapeutically explorable potential transduction pathways is the focus of the reviewed work.

SIGNIFICANCE

The present work opines that the mechanism by which the insulin resistance mediates dysregulation of bioenergetics and progresses to neurodegenerative state holds the tangible potential to succeed in the development of novel dementia therapies. Further, hypometabolic complications and altered insulin signaling may be explored as a mechanistic relation between bioenergetic deficits and AD.

GLP-1 receptor agonists for Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a progressive disorder characterised by both motor and non-motor problems. Glucagon-like peptide-1 (GLP-1) receptor agonists, licensed for treatment of type 2 diabetes, work by stimulating GLP-1 receptors in the pancreas, which triggers the release of insulin. GLP-1 receptors have been found in the brain. Insulin signalling in the brain plays a key role in neuronal metabolism and repair and in synaptic efficacy, but insulin signalling is desensitised in the brain of people with PD. Researchers are exploring the neuroprotective effects of GLP-1 receptor agonists in neurodegenerative disorders such as PD.

OBJECTIVES

To evaluate the effectiveness and safety of GLP-1 receptor agonists for Parkinson's disease.

SEARCH METHODS

We searched the Cochrane Movement Disorders Group trials register; the Cochrane Central Register of Controlled Trials (CENTRAL), in the Cochrane Library; and Ovid MEDLINE and Embase. We also searched clinical trials registries, and we handsearched conference abstracts. The most recent search was run on 25 June 2020.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of adults with PD that compared GLP-1 receptor agonists with conventional PD treatment, placebo, or no treatment.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion, extracted data, and assessed risk of bias. We rated the quality of evidence using GRADE. We resolved discrepancies between the two data extractors by consultation with a third review author.

MAIN RESULTS

Through our searches, we retrieved 99 unique records, of which two met our inclusion criteria. One double-blind study of exenatide versus placebo randomised 62 participants, who self-administered exenatide or placebo for 48 weeks and were followed up at 60 weeks after a 12-week washout. One single-blind study of exenatide versus no additional treatment randomised 45 participants; participants in the intervention group self-administered exenatide for 12 months, and all participants were followed up at 14 months and 24 months following absence of exenatide for 2 months and 12 months, respectively. These trials had low risk of bias, except risk of performance bias was high for Aviles-Olmos 2013. Exenatide versus placebo Primary outcomes We found low-certainty evidence suggesting that exenatide improves motor impairment as assessed by the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III in the off-medication state (mean difference (MD) -3.10, 95% confidence interval (CI) -6.11 to -0.09). The difference in scores was slightly greater when scores were adjusted for baseline severity of the condition (as reported by study authors) (MD -3.5, 95% CI -6.7 to -0.3), exceeding the minimum clinically important difference (MCID). We found low-certainty evidence suggesting that exenatide has little or no effect on health-related quality of life (HRQoL) as assessed by the Parkinson's Disease Questionnaire (PDQ)-39 Summary Index (SI) (MD -1.80, 95% CI -6.95 to 3.35), the EuroQol scale measuring health status in five dimensions (EQ5D) (MD 0.07, 95% CI -0.03 to 0.16), or the EQ5D visual analogue scale (VAS) (MD 5.00, 95% CI -3.42 to 13.42). Eight serious adverse events (SAEs) were recorded, but all were considered unrelated to the intervention. Low-certainty evidence suggests that exenatide has little or no effect on weight loss (risk ratio (RR) 1.25, 95% CI 0.89 to 1.76). Exenatide versus no treatment Primary outcomes at 14 months We found very low-certainty evidence suggesting that exenatide improves motor impairment as assessed by MDS-UPDRS Part III off medication (MD -4.50, 95% CI -8.64 to -0.36), exceeding the MCID. We are uncertain whether exenatide improves HRQoL as assessed by the PDQ-39 SI (MD 3.50, 95% CI -2.75 to 9.75; very low-quality evidence). We found very low-certainty evidence suggesting that exenatide has little or no effect on the number of SAEs (RR 1.60, 95% 0.40 to 6.32). We found very low-certainty evidence suggesting that exenatide may lead to weight loss (MD -2.40 kg, 95% CI -4.56 to -0.24). Primary outcomes at 24 months We found evidence as reported by study authors to suggest that exenatide improves motor impairment as measured by MDS-UPDRS Part III off medication (MD 5.6 points, 95% CI 2.2 to 9.0). Exenatide may not improve HRQoL as assessed by the PDQ-39 SI (P = 0.682) and may not result in weight loss (MD 0.1 kg, 95% CI 3.0 to 2.8).

AUTHORS' CONCLUSIONS

Low- or very low-certainty evidence suggests that exenatide may improve motor impairment for people with PD. The difference in motor impairment observed between groups may persist for some time following cessation of exenatide. This raises the possibility that exenatide may have a disease-modifying effect. SAEs were unlikely to be related to treatment. The effectiveness of exenatide for improving HRQoL, non-motor outcomes, ADLs, and psychological outcomes is unclear. Ongoing studies are assessing other GLP-1 receptor agonists.

Central nervous pathways of insulin action in the control of metabolism and food intake

Insulin acts on the CNS to modulate behaviour and systemic metabolism. Disturbances in brain insulin action represent a possible link between metabolic and cognitive health. Current findings from human research suggest that boosting central insulin action in the brain modulates peripheral metabolism, enhancing whole-body insulin sensitivity and suppressing endogenous glucose production. Moreover, central insulin action curbs food intake by reducing the salience of highly palatable food cues and increasing cognitive control. Animal models show that the mesocorticolimbic circuitry is finely tuned in response to insulin, driven mainly by the dopamine system. These mechanisms are impaired in people with obesity, which might increase their risk of developing type 2 diabetes and associated diseases. Overall, current findings highlight the role of insulin action in the brain and its consequences on peripheral metabolism and cognition. Hence, improving central insulin action could represent a therapeutic option for people at an increased risk of developing metabolic and cognitive diseases.

Insulin BBB pharmacokinetics in young apoE male and female transgenic mice

In addition to age, apolipoprotein E4 (E4), female sex, or a combination of both synergistically increase the risk for the development of Alzheimer’s disease (AD). Why these risk factors predispose an individual to developing AD later in life is the target of the current investigation. Central nervous system (CNS) insulin resistance is associated with cognitive impairment and AD. CNS insulin is acquired primarily from the circulation and therefore must negotiate the blood-brain barrier (BBB). Thus, changes in BBB transport of insulin could lead to alterations in CNS insulin signaling and resistance, which would then lead to changes in cognition. There has been recent evidence suggesting the relationship between CNS insulin; E4, a risk factor to develop AD as compared to E3; and the female sex in aged individuals and in pre-clinical models. However, this relationship has been largely unexplored at a younger age, in which some of these risk factors could predispose an individual to dysregulation of CNS insulin later in life. Here, we present the first findings of BBB insulin pharmacokinetics in young E3 and E4 male and female targeted replacement (TR) mice. We found that levels of insulin binding the vasculature at the BBB are different due to genotype and sex which could impact the function of the brain endothelial cell. These early alterations could contribute to or fully explain the age-related cognitive changes observed due to CNS insulin signaling in E4 and/or female individuals.

Variants in the Upstream Region of the Insulin Receptor Substrate-1 Gene Is Associated with Major Depressive Disorder in the Han Chinese Population

INTRODUCTION

Major depressive disorder (MDD) is one of the most prevalent and disabling mental disorders, although its underlying genetic mechanism remains unknown. Insulin receptor substrate-1 (IRS-1) is one of the critical downstream molecules in the insulin resistance signaling pathway, linking depression and diabetes. Therefore, we hypothesized that IRS-1 would be a susceptible gene for MDD, and we aimed to examine the genetic association between IRS-1 and MDD.

METHODS

This case-control study included 583 patients with MDD and 564 controls, and the genotypic and allelic distributions of the IRS-1 gene's four single nucleotide polymorphisms (SNPs) were detected by TaqMan SNP genotyping technology. Of the 583 patients, 191 underwent a further detailed interview about symptom severity and family history of mental illness. The chi-square or t test was used to analyze the data, and analyses were performed using SPSS19.0 software.

RESULTS

A haplotype in the 5'-upstream region of IRS-1 consisting of rs13411764 and rs3820926 was a risk factor of MDD. Patients with a family history of mental illness were more likely to have a GG genotype in rs13411764 and a G-T haplotype containing rs13411714-rs3820926.

DISCUSSION

The findings imply that the haplotype consisting of rs13411764 and rs3820926 in the upstream of IRS-1 is a risk factor for MDD. This haplotype could affect IRS-1 expression levels, and it is mostly inherited from parents. Thus, the presence of variants in the upstream region of IRS-1 is a risk factor of MDD, and this study could serve as a convincing reference for further studies.

Brain Metabolic Alterations in Rats Showing Depression-Like and Obesity Phenotypes

Current data suggest an important role of brain metabolic disturbances in the pathogenesis of depression and obesity, diseases that frequently co-occur. Our aim was to determine whether there are changes in markers characterizing glucose metabolism in prenatal stress (PS; animal model of depression), in rats fed a high-fat diet (HFD), and especially in the model of depression and obesity co-occurrence. The changes in glucose-6-phosphate, glycogen, glucose transporters (GLUT1, GLUT4), glucagon-like peptide-1 receptor (GLP-1R), and mitochondrial complexes levels in the frontal cortex and/or hippocampus were observed. In the case of the coexistence of depression and obesity, the most important changes were (1) the decrease in the membrane form of GLUT4, which may suggest weaker insulin action in the frontal cortex, and (2) the diminished GLP-1R, which could cause neurodegenerative changes in the hippocampus. However, presented results suggested that HFD weakened the PS effect of uncoupling oxidative phosphorylation in the frontal cortex.

Effects of hypertension on cerebral cortical thickness alterations in patients with type 2 diabetes

AIMS

Although hypertension (HTN) is the high comorbidity of Type 2 diabetes mellitus (T2DM) and known to be a vascular risk factor for brain damage, the effects of HTN on brain function in T2DM patients are not well understood. Present study was performed to investigate whether HTN might accelerate the Cerebral cortical thickness (CT) alterations in patients with T2DM.

METHODS

We enrolled 35 participants with only T2DM, 25 T2DM patients with HTN (HT2DM) and 28 healthy controls (HCs). The cognitive function was assessed and brain image data was collected then the CT was calculated for each participant. Partial correlations between the CT of each brain region and standard laboratory testing data and neuropsychological scale scores were also analyzed. Multivariable regression analysis was performed to evaluated the vascular risk factors and brain regions with different CT in HT2DM patients.

RESULTS

Cognitive impairment is associated with thinning of the cerebral cortical thickness reduction in T2DM patients. CT thinning in the left inferior parietal lobe, left posterior cingulate and right precuneus were observed in HT2DM group relative to only T2DM group. Furthermore, the CT decreasing in the right precuneus was negatively correlated with duration of HTN.

CONCLUSION

The current study revealed that coexistent HTN may accelerate the CT reduction in T2DM patients.

Current and emerging avenues for Alzheimer's disease drug targets

Alzheimer's disease (AD), the most frequent cause of dementia, is escalating as a global epidemic, and so far, there is neither cure nor treatment to alter its progression. The most important feature of the disease is neuronal death and loss of cognitive functions, caused probably from several pathological processes in the brain. The main neuropathological features of AD are widely described as amyloid beta (Aβ) plaques and neurofibrillary tangles of the aggregated protein tau, which contribute to the disease. Nevertheless, AD brains suffer from a variety of alterations in function, such as energy metabolism, inflammation and synaptic activity. The latest decades have seen an explosion of genes and molecules that can be employed as targets aiming to improve brain physiology, which can result in preventive strategies for AD. Moreover, therapeutics using these targets can help AD brains to sustain function during the development of AD pathology. Here, we review broadly recent information for potential targets that can modify AD through diverse pharmacological and nonpharmacological approaches including gene therapy. We propose that AD could be tackled not only using combination therapies including Aβ and tau, but also considering insulin and cholesterol metabolism, vascular function, synaptic plasticity, epigenetics, neurovascular junction and blood-brain barrier targets that have been studied recently. We also make a case for the role of gut microbiota in AD. Our hope is to promote the continuing research of diverse targets affecting AD and promote diverse targeting as a near-future strategy.

Low-dose intranasal insulin improves cognitive function and suppresses the development of epilepsy

Intranasal insulin exerts neuroprotective effects in a variety of neurological diseases. Whether intranasal insulin affects epileptic activity and whether it has neuroprotective effects in epileptic diseases is however still unknown. In this study we show that low-dose intranasal insulin inhibited kainic acid (KA)- or pentylenetetrazole (PTZ)-induced acute seizures and reduced epileptic discharge activities in mice, potentially by alleviating the increase in seizure-induced glutamate in the hippocampus. Meanwhile, intranasal insulin increased GABA levels and the activities of hippocampal theta, which may affect the excitability of the hippocampus. In chronic KA-induced epilepsy, low-dose intranasal insulin reduces the frequency of spontaneous recurrent seizures and epileptic discharges, while it increases theta energy and thereby improves spatial memory. Larger doses of intranasal insulin increased the frequency of seizures but did not aggravate cognitive impairment, suggesting that the frequency of seizures may not be related to impaired cognitive function. Overall, our findings show that low-dose intranasal insulin inhibits epileptic events and improves cognitive impairment in epileptic mice, suggesting that learning and memory can be improved by intranasal insulin. However, larger doses might increase the risk of epileptic seizures.

To be or not to be: PP2A as a dual player in CNS functions, its role in neurodegeneration, and its interaction with brain insulin signaling

Accumulating evidence has reached the consensus that the balance of phosphorylation state of signaling molecules is a pivotal point in the regulation of cell signaling. Therefore, characterizing elements (kinases-phosphatases) in the phosphorylation balance are at great importance. However, the role of phosphatase enzymes is less investigated than kinase enzymes. PP2A is a member of serine/threonine protein phosphatase that its imbalance has been reported in neurodegenerative diseases. Therefore, we reviewed the superfamily of phosphatases and more specifically PP2A, its regulation, and physiological functions participate in CNS. Thereafter, we discussed the latest findings about PP2A dysregulation in Alzheimer and Parkinson diseases and possible interplay between this phosphatase and insulin signaling pathways. Finally, activating/inhibitory modulators for PP2A activity as well as experimental methods for PP2A study have been reviewed.

The Effect of Intrahippocampal Insulin Injection on Scopolamine-induced Spatial Memory Impairment and Extracellular Signal-regulated Kinases Alteration

Introduction

It is well documented that insulin has neuroprotective and neuromodulator effects and can protect against different models of memory loss. Furthermore, cholinergic activity plays a significant role in memory, and scopolamine-induced memory loss is widely used as an experimental model of dementia. The current study aimed at investigating the possible effects of insulin against scopolamine-induced memory impairment in Wistar rat and its underlying molecular mechanisms.

Methods

Accordingly, animals were bilaterally cannulated in CA1, hippocampus. Intrahippocampal administration of insulin 6 MU and 12 MU in CA1 per day was performed during first 6 days after surgery. During next four days, the animal's spatial learning and memory were assessed in Morris water maze test (three days of learning and one day of retention test). The animals received scopolamine (1 mg/kg) Intraperitoneally (IP) 30 minutes before the onset of behavioral tests in each day. In the last day, the hippocampi were dissected and the levels of MAPK (mitogen-activated protein kinases) and caspase-3 activation were analyzed by Western blot technique.

Results

The behavioral results showed that scopolamine impaired spatial learning and memory without activating casapase-3, P38, and JNK, but chronic pretreatment by both doses of insulin was unable to restore this spatial memory impairment. In addition, scopolamine significantly reduced Extracellular signal-Regulated Kinases (ERKs) activity and insulin was unable to restore this reduction. Results revealed that scopolamine-mediated memory loss was not associated with hippocampal damage.

Conclusion

Insulin as a neuroprotective agent cannot restore memory when there is no hippocampal damage. In addition, the neuromodulator effect of insulin is not potent enough to overwhelm scopolamine-mediated disruptions of synaptic neurotransmission.

Ablating astrocyte insulin receptors leads to delayed puberty and hypogonadism in mice

Insulin resistance and obesity are associated with reduced gonadotropin-releasing hormone (GnRH) release and infertility. Mice that lack insulin receptors (IRs) throughout development in both neuronal and non-neuronal brain cells are known to exhibit subfertility due to hypogonadotropic hypogonadism. However, attempts to recapitulate this phenotype by targeting specific neurons have failed. To determine whether astrocytic insulin sensing plays a role in the regulation of fertility, we generated mice lacking IRs in astrocytes (astrocyte-specific insulin receptor deletion [IRKOGFAP] mice). IRKOGFAP males and females showed a delay in balanopreputial separation or vaginal opening and first estrous, respectively. In adulthood, IRKOGFAP female mice also exhibited longer, irregular estrus cycles, decreased pregnancy rates, and reduced litter sizes. IRKOGFAP mice show normal sexual behavior but hypothalamic-pituitary-gonadotropin (HPG) axis dysregulation, likely explaining their low fecundity. Histological examination of testes and ovaries showed impaired spermatogenesis and ovarian follicle maturation. Finally, reduced prostaglandin E synthase 2 (PGES2) levels were found in astrocytes isolated from these mice, suggesting a mechanism for low GnRH/luteinizing hormone (LH) secretion. These findings demonstrate that insulin sensing by astrocytes is indispensable for the function of the reproductive axis. Additional work is needed to elucidate the role of astrocytes in the maturation of hypothalamic reproductive circuits.

Distribution of insulin in trigeminal nerve and brain after intranasal administration

In the brain, insulin acts as a growth factor, regulates energy homeostasis, and is involved in learning and memory acquisition. Many central nervous system (CNS) diseases are characterized by deficits in insulin signaling. Pre-clinical studies have shown that intranasal insulin is neuroprotective in models of Alzheimer’s disease, Parkinson’s disease, and traumatic brain injury. Clinical trials have also shown that intranasal insulin elicits beneficial cognitive effects in patients with Alzheimer’s disease. It is known that insulin can be detected in the CNS within minutes following intranasal administration. Despite these advances, the anatomical pathways that insulin utilizes to reach the CNS and the cellular CNS targets after intranasal administration are not fully understood. Here, we intranasally administered fluorescently labeled insulin and imaged its localization within the brain and trigeminal nerves. Our data indicates that intranasal insulin can reach cellular CNS targets along extracellular components of the trigeminal nerve. Upon CNS entry, we found insulin significantly increased levels of an activated form of the insulin receptor. These findings suggest that the intranasal route of administration is able to effectively deliver insulin to CNS targets in a biologically active form.