Modulation of memory by insulin and glucose: neuropsychological observations in Alzheimer's disease

An integrative systems-biology approach defines mechanisms of Alzheimer's disease neurodegeneration

Despite years of intense investigation, the mechanisms underlying neuronal death in Alzheimer's disease, remain incompletely understood. To define relevant pathways, we conducted an unbiased, genome-scale forward genetic screen for age-associated neurodegeneration in Drosophila. We also measured proteomics, phosphoproteomics, and metabolomics in Drosophila models of Alzheimer's disease and identified Alzheimer's genetic variants that modify gene expression in disease-vulnerable neurons in humans. We then used a network model to integrate these data with previously published Alzheimer's disease proteomics, lipidomics and genomics. Here, we computationally predict and experimentally confirm how HNRNPA2B1 and MEPCE enhance toxicity of the tau protein, a pathological feature of Alzheimer's disease. Furthermore, we demonstrated that the screen hits CSNK2A1 and NOTCH1 regulate DNA damage in Drosophila and human stem cell-derived neural progenitor cells. Our study identifies candidate pathways that could be targeted to ameliorate neurodegeneration in Alzheimer's disease.

DJ-1-mediated repression of the RNA-binding protein FMRP is predicted to impact known Alzheimer's disease-related protein networks

BACKGROUND

RNA-binding proteins (RBPs) modulate the synaptic proteome and are instrumental in maintaining synaptic homeostasis. Moreover, aberrant expression of an RBP in a disease state would have deleterious downstream effects on synaptic function. While many underlying mechanisms of synaptic dysfunction in Alzheimer's disease (AD) have been proposed, the contribution of RBPs has been relatively unexplored.

OBJECTIVE

To investigate alterations in RBP-messenger RNA (mRNA) interactions in AD, and its overall impact on the disease-related proteome.

METHODS

We first utilized RNA-immunoprecipitation to investigate interactions between RBP, DJ-1 (Parkinson's Disease protein 7) and target mRNAs in controls and AD. Surface Sensing of Translation - Proximity Ligation Assay (SUnSET-PLA) and western blotting additionally quantified alterations in mRNA translation and protein expression of DJ-1 targets. Finally, we utilized an unbiased bioinformatic approach that connects AD-related pathways to two RBPs, DJ-1 and FMRP (Fragile X messenger ribonucleoprotein 1).

RESULTS

We find that oligomeric DJ-1 in AD donor synapses were less dynamic in their ability to bind and unbind mRNA compared to synapses from cognitively unimpaired, neuropathologically-verified controls. Furthermore, we find that DJ-1 associates with the mRNA coding for FMRP, Fmr1, leading to its reduced synaptic expression in AD. Through the construction of protein-protein interaction networks, aberrant expression of DJ-1 and FMRP are predicted to lead to the upregulation of key AD-related pathways, such as thyroid hormone stimulating pathway, autophagy, and ubiquitin mediated proteolysis.

CONCLUSIONS

DJ-1 and FMRP are novel targets that may restore established neurobiological mechanisms underlying AD.

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

An integrative systems-biology approach defines mechanisms of Alzheimer's disease neurodegeneration

Despite years of intense investigation, the mechanisms underlying neuronal death in Alzheimer's disease, the most common neurodegenerative disorder, remain incompletely understood. To define relevant pathways, we integrated the results of an unbiased, genome-scale forward genetic screen for age-associated neurodegeneration in Drosophila with human and Drosophila Alzheimer's disease-associated multi-omics. We measured proteomics, phosphoproteomics, and metabolomics in Drosophila models of Alzheimer's disease and identified Alzheimer's disease human genetic variants that modify expression in disease-vulnerable neurons. We used a network optimization approach to integrate these data with previously published Alzheimer's disease multi-omic data. We computationally predicted and experimentally demonstrated how HNRNPA2B1 and MEPCE enhance tau-mediated neurotoxicity. Furthermore, we demonstrated that the screen hits CSNK2A1 and NOTCH1 regulate DNA damage in Drosophila and human iPSC-derived neural progenitor cells. Our work identifies candidate pathways that could be targeted to ameliorate neurodegeneration in Alzheimer's disease.

Navigating the intersection: Diabetes and Alzheimer's intertwined relationship

Alzheimer's disease (AD) and Diabetes mellitus (DM) exhibit comparable pathophysiological pathways. Genetic abnormalities in APP, PS-1, and PS-2 are linked to AD, with diagnostic aid from CSF and blood biomarkers. Insulin dysfunction, termed "type 3 diabetes mellitus" in AD, involves altered insulin signalling and neuronal shrinkage. Insulin influences beta-amyloid metabolism, exacerbating neurotoxicity in AD and amyloid production in DM. Both disorders display impaired glucose transporter expression, hastening cognitive decline. Mitochondrial dysfunction and Toll-like receptor 4-mediated inflammation worsen neurodegeneration in both diseases. ApoE4 raises disease risk, especially when coupled with dyslipidemia common in DM. Targeting shared pathways like insulin-degrading enzyme activation and HSP60 holds promise for therapeutic intervention. Recognizing these interconnected mechanisms underscores the imperative for developing tailored treatments addressing the overlapping pathophysiology of AD and DM, offering potential avenues for more effective management of both conditions.

WNKs regulate mouse behavior and alter central nervous system glucose uptake and insulin signaling

Certain areas of the brain involved in episodic memory and behavior, such as the hippocampus, express high levels of insulin receptors and glucose transporter-4 (GLUT4) and are responsive to insulin. Insulin and neuronal glucose metabolism improve cognitive functions and regulate mood in humans. Insulin-dependent GLUT4 trafficking has been extensively studied in muscle and adipose tissue, but little work has demonstrated either how it is controlled in insulin-responsive brain regions or its mechanistic connection to cognitive functions. In this study, we demonstrate that inhibition of WNK (With-No-lysine (K)) kinases improves learning and memory in mice. Neuronal inhibition of WNK enhances in vivo hippocampal glucose uptake. Inhibition of WNK enhances insulin signaling output and insulin-dependent GLUT4 trafficking to the plasma membrane in mice primary neuronal cultures and hippocampal slices. Therefore, we propose that the extent of neuronal WNK kinase activity has an important influence on learning, memory and anxiety-related behaviors, in part, by modulation of neuronal insulin signaling.

A randomized feasibility trial of the modified Atkins diet in older adults with mild cognitive impairment due to Alzheimer's disease

Background

Alzheimer's disease (AD) is increasing in prevalence, but effective treatments for its cognitive impairment remain severely limited. This study investigates the impact of ketone body production through dietary manipulation on memory in persons with mild cognitive impairment due to early AD and explores potential mechanisms of action.

Methods

We conducted a 12-week, parallel-group, controlled feasibility trial of a ketogenic diet, the modified Atkins diet (MAD), compared to a control diet in patients with cognitive impairments attributed to AD. We administered neuropsychological assessments, including memory tests, and collected blood samples at baseline and after 12 weeks of intervention. We performed untargeted lipidomic and targeted metabolomic analyses on plasma samples to detect changes over time.

Results

A total of 839 individuals were screened to yield 38 randomized participants, with 20 assigned to receive MAD and 18 assigned to receive a control diet. Due to attrition, only 13 in the MAD arm and nine in the control arm were assessed for the primary endpoint, with two participants meeting ketosis levels used to define MAD adherence criteria. The average change from baseline in the Memory Composite Score was 1.37 (95% CI: -0.87, 4.90) points higher in the MAD group compared to the control group. The effect size of the intervention on baseline MAD change was moderate (Cohen's D = 0.57, 95% CI: -0.67, 1.33). In the 15 participants (nine MAD, six control) assessed for lipidomic and metabolomic-lipidomics and metabolomics, 13 metabolites and 10 lipids showed significant changes from baseline to 12 weeks, including triacylglycerols (TAGs, 50:5, 52:5, and 52:6), sphingomyelins (SM, 44:3, 46:0, 46:3, and 48:1), acetoacetate, fatty acylcarnitines, glycerol-3-phosphate, and hydroxy fatty acids.

Conclusions

Attrition was greatest between baseline and week 6. All participants retained at week 6 completed the study. Despite low rates of adherence by criteria defined a priori, lipidomic and metabolomic analyses indicate significant changes from baseline in circulating lipids and metabolites between MAD and control participants at 12-week postrandomization, and MAD participants showed greater, albeit nonsignificant, improvement in memory.

Association of cigarette smoking with cerebrospinal fluid biomarkers of insulin sensitivity and neurodegeneration

INTRODUCTION

Cigarette smoking increases both the risk for insulin resistance and amyloid-β (Aβ) aggregation, and impaired brain insulin/insulin-like growth factor 1 (IGF1) signaling might increase risk factors for Alzheimer's disease (AD). We aimed to investigate the association among cerebrospinal fluid (CSF) insulin sensitivity/IGF1, glucose/lactate, and Aβ42 and further explore whether insulin sensitivity contributed to the risk for AD in active smokers.

METHODS

In this cross-sectional study, levels of insulin, IGF1, and lactate/glucose of 75 active smokers and 78 nonsmokers in CSF were measured. Three polymorphisms regulating IGF1 were genotyped. Analysis of variance was used to compare differences of variables between groups. Partial correlation was performed to test the relationship between CSF biomarkers and smoking status. General linear models were applied to test the interaction of the effect of single nucleotide polymorphisms and cigarette smoking on CSF IGF1 levels.

RESULTS

In the CSF from active smokers, IGF1 and lactate levels were significantly lower (p = .016 and p = .010, respectively), whereas Aβ42 (derived from our earlier research) and insulin levels were significantly higher (p < .001 and p = .022, respectively) as compared to the CSF from nonsmokers. The AG + GG genotype of rs6218 in active smokers had a significant effect on lower CSF IGF1 levels (p = .004) and lower CSF insulin levels in nonsmokers (p = .016).

CONCLUSIONS

Cigarette smoking as the "at-risk" factor for AD might be due to lower cerebral insulin sensitivity in CSF, and the subjects with rs6218G allele seem to be more susceptible to the neurodegenerative risks for cigarette smoking.

Repurposing and clinical attributes of antidiabetic drugs for the treatment of neurodegenerative disorders

The risk of neurodegeneration was found to be increased among people with type 2 diabetes mellitus (T2DM). Brain disorders like Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis, and others are considered neurodegenerative diseases and can be characterized by progressive loss of neurons. The deficiency of insulin, impaired signaling, and its resistance lead to alteration in the neuronal functioning of the brain. Insulin degrading enzyme (IDE) plays a significant role in the amyloid β metabolism, aggregation, and deposition of misfolded proteins in the brain's hippocampal and cortical neuronal regions. The insulin signaling via IP3 activation upregulates the IDE and could be a promising approach to regulate neurodegeneration. The repurposing of existing antidiabetic drugs such as Metformin, DPP-4 inhibitors, thiazolidinediones, glucagon-like peptides (GLP-1), sodium-glucose co-transport-2 (SGCT-2) inhibitors, and insulin could be an alternative and effective strategy to treat neurodegeneration via modulating insulin signaling, insulin resistance, IDE activity, oxidative stress, mitochondrial dysfunction, serum lipid profile and neuroinflammation in the brain. Antidiabetic medications reduce the risk of neuroinflammation, oxidative stress, and Aβ deposition by enhancing their clearance rate. The downregulation of IDE alters the degradation of Aβ monomers in the Tg2576 APP mice. Also, the treatment with metformin activated the AMPK pathway and suppressed mTOR and BACE-1 protein expression in the APP/PS1-induced mice model. Thus, the primary intention of this review is to explore the link between T2DM and neurodegenerative disorders, and the possible role of various antidiabetic drugs in the management of neurodegenerative disorders.

The complex relationship between obesity and neurodegenerative diseases: an updated review

Obesity is a global epidemic, affecting roughly 30% of the world's population and predicted to rise. This disease results from genetic, behavioral, societal, and environmental factors, leading to excessive fat accumulation, due to insufficient energy expenditure. The adipose tissue, once seen as a simple storage depot, is now recognized as a complex organ with various functions, including hormone regulation and modulation of metabolism, inflammation, and homeostasis. Obesity is associated with a low-grade inflammatory state and has been linked to neurodegenerative diseases like multiple sclerosis (MS), Alzheimer's (AD), and Parkinson's (PD). Mechanistically, reduced adipose expandability leads to hypertrophic adipocytes, triggering inflammation, insulin and leptin resistance, blood-brain barrier disruption, altered brain metabolism, neuronal inflammation, brain atrophy, and cognitive decline. Obesity impacts neurodegenerative disorders through shared underlying mechanisms, underscoring its potential as a modifiable risk factor for these diseases. Nevertheless, further research is needed to fully grasp the intricate connections between obesity and neurodegeneration. Collaborative efforts in this field hold promise for innovative strategies to address this complex relationship and develop effective prevention and treatment methods, which also includes specific diets and physical activities, ultimately improving quality of life and health.

Drug Repositioning of Pioglitazone in Management and Improving the Cognitive Function among the Patients With Mild to Moderate Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background

Disease-modifying agents like Pioglitazone have shown promising effects on neuroinflammation and homeostasis of amyloid plaques, but there is a lack of research papers providing conclusive evidence.

Objectives

This study is aimed to determine the safety and efficacy of Pioglitazone in improving cognitive function in patients with mild-moderate Alzheimer's disease (AD).

Materials and Methods

Trials published in the last 12 years were identified from PubMed, Scopus, Cochrane Central, and other trial registries. Five hundred twenty-five records were obtained, from which five studies were included for quantitative analysis. Studies comparing Pioglitazone with a suitable placebo or other oral hypoglycemic agent were considered for review. Data was extracted using a pretested form, which was followed by a risk of bias assessment (ROB) with Cochrane's ROB assessment tool.

Results

This meta-analysis included studies where Pioglitazone (15-30 mg) was compared to other oral hypoglycemic agents, placebo, or diabetic diet for a minimum duration of 6 months. Pioglitazone did not show a statistically significant improvement in Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) scores [mean difference (MD): -1.16; 95% confidence interval (CI): -4.14-1.81]. By conducting sensitivity analysis with the removal of one study, significant efficacy was obtained [MD: -2.75; 95% CI: -4.84--0.66]. The Wechsler Memory Scale-Revised logical memory I (WMS-R) scores had a significant improvement in the Pioglitazone group [MD: 2.02; 95% CI: 0.09-3.95].

Conclusion

Pioglitazone is a safe medication that has a promising effect in slowing the advancement of AD.

Hypermethylation at CREBBP Is Associated with Cognitive Impairment in a Mexican American Cohort

BACKGROUND

The aging Mexican American (MA) population is the fastest growing ethnic minority group in the US. MAs have a unique metabolic-related risk for Alzheimer's disease (AD) and mild cognitive impairment (MCI), compared to non-Hispanic whites (NHW). This risk for cognitive impairment (CI) is multifactorial involving genetics, environmental, and lifestyle factors. Changes in environment and lifestyle can alter patterns and even possibly reverse derangement of DNA methylation (a form of epigenetic regulation).

OBJECTIVE

We sought to identify ethnicity-specific DNA methylation profiles that may be associated with CI in MAs and NHWs.

METHODS

DNA obtained from peripheral blood of 551 participants from the Texas Alzheimer's Research and Care Consortium was typed on the Illumina Infinium® MethylationEPIC chip array, which assesses over 850K CpG genomic sites. Within each ethnic group (N = 299 MAs, N = 252 NHWs), participants were stratified by cognitive status (control versus CI). Beta values, representing relative degree of methylation, were normalized using the Beta MIxture Quantile dilation method and assessed for differential methylation using the Chip Analysis Methylation Pipeline (ChAMP), limma and cate packages in R.

RESULTS

Two differentially methylated sites were significant: cg13135255 (MAs) and cg27002303 (NHWs) based on an FDR p < 0.05. Three suggestive sites obtained were cg01887506 (MAs) and cg10607142 and cg13529380 (NHWs). Most methylation sites were hypermethylated in CI compared to controls, except cg13529380 which was hypomethylated.

CONCLUSION

The strongest association with CI was at cg13135255 (FDR-adjusted p = 0.029 in MAs), within the CREBBP gene. Moving forward, identifying additional ethnicity-specific methylation sites may be useful to discern CI risk in MAs.

High-fat diet-induced diabetes couples to Alzheimer's disease through inflammation-activated C/EBPβ/AEP pathway

Diabetes is a risk factor for Alzheimer's disease (AD), which is also called type 3 diabetes with insulin reduction and insulin resistance in AD patient brains. However, the molecular mechanism coupling diabetes to AD onset remains incompletely understood. Here we show that inflammation, associated with obesity and diabetes elicited by high-fat diet (HFD), activates neuronal C/EBPβ/AEP signaling that drives AD pathologies and cognitive disorders. HFD stimulates diabetes and insulin resistance in neuronal Thy1-C/EBPβ transgenic (Tg) mice, accompanied with prominent mouse Aβ accumulation and hyperphosphorylated Tau aggregation in the brain, triggering cognitive deficits. These effects are profoundly diminished when AEP is deleted from C/EBPβ Tg mice. Chronic treatment with inflammatory lipopolysaccharide (LPS) facilitates AD pathologies and cognitive disorders in C/EBPβ Tg but not in wild-type mice, and these deleterious effects were substantially alleviated in C/EBPβ Tg/AEP -/- mice. Remarkably, the anti-inflammatory drug aspirin strongly attenuates HFD-induced diabetes and AD pathologies in neuronal C/EBPβ Tg mice. Therefore, our findings demonstrate that inflammation-activated neuronal C/EBPβ/AEP signaling couples diabetes to AD.

Regulation of Metabolic Health by an "Olfactory-Hypothalamic Axis" and Its Possible Implications for the Development of Therapeutic Approaches for Obesity and T2D

The olfactory system is responsible for the reception, integration and interpretation of odors. However, in the last years, it has been discovered that the olfactory perception of food can rapidly modulate the activity of hypothalamic neurons involved in the regulation of energy balance. Conversely, the hormonal signals derived from changes in the metabolic status of the body can also change the sensitivity of the olfactory system, suggesting that the bidirectional relationship established between the olfactory and the hypothalamic systems is key for the maintenance of metabolic homeostasis. In the first part of this review, we describe the possible mechanisms and anatomical pathways involved in the modulation of energy balance regulated by the olfactory system. Hence, we propose a model to explain its implication in the maintenance of the metabolic homeostasis of the organism. In the second part, we discuss how the olfactory system could be involved in the development of metabolic diseases such as obesity and type two diabetes and, finally, we propose the use of intranasal therapies aimed to regulate and improve the activity of the olfactory system that in turn will be able to control the neuronal activity of hypothalamic centers to prevent or ameliorate metabolic diseases.

Contributive Role of Hyperglycemia and Hypoglycemia Towards the Development of Alzheimer's Disease

Alzheimer's disease (AD) is one of the causes of dementia that results from several infections/biological conditions leading to either cell disruption or loss of neuronal communication. Studies have documented the accumulation of two proteins, beta-amyloid (Aβ), which accumulates on the exteriors of neurons, and tau (Tau), which assembles at the interiors of brain cells and is chiefly liable for the progression of the disease. Several molecular and cellular pathways account for the accumulation of amyloid-β and the formation of neurofibrillary tangles, which are phosphorylated variants of Tau protein. Moreover, research has revealed a potential connection between AD and diabetes. It has also been demonstrated that both hypoglycemia and hyperglycemia have a significant role in the development of AD. In addition, SUMO (small ubiquitin-like modifier protein) plays a crucial role in the pathogenesis of AD. SUMOylation is the process by which modification of amyloid precursor protein (APP) and Tau takes place. Furthermore, Drosophila melanogaster has proven to be an efficient model organism in studies to establish the relationship between AD and variations in blood glucose levels. In addition, the review successfully identifies the common pathway that links the effects of fluctuations in glucose levels on AD pathogenesis and advancements.

Chronic exposure of bisphenol-A impairs cognitive function and disrupts hippocampal insulin signaling pathway in male mice

Bisphenol-A (BPA), a well-known estrogenic endocrine disruptor, is generally applied to turn out plastic consumer products. Available data have manifested that exposure to BPA can trigger insulin resistance. Hence, the purpose of the actual study was to consider the impacts of BPA exposure on cognitive function and insulin signaling pathway in the hippocampus of male offspring mice. For this purpose, the pregnant female mice were treated either vehicle (0.1% ethanol) or BPA (0.01, 0.1, and 1µg/mL) via drinking water from day 1 of gestation until delactation (D1-PND21, newborn exposure). Afterward, the three-week-old male offspring mice took orally with the same doses of BPA for nine weeks (PND84). The behavioral tests, blood sugar level, histological observation, transcriptome sequencing, glucose transporter 4 (GLUT4), and hippocampal insulin signaling pathway were checked for the male offspring mice at 13 weeks of age (PND91). Our data indicated that BPA exposure impaired cognitive function, disrupted the hippocampal regular cell arrangement, increased blood glucose levels, disturbed the insulin signaling pathway including phosphorylated insulin receptor substrate1 (p-IRS1), protein kinase B (p-AKT), and glycogen synthase kinase 3β (p-GSK3β). At the same time, the mRNA and protein expressions of GLUT4 were markedly down-regulated in the BPA-exposed groups. To sum up, it has been suggested from these results that BPA has detrimental effects on the insulin signaling pathway, which might subsequently be conducive to the impairment of cognitive function in the adult male offspring mice. Therefore, BPA exposure might in part be an element of risk for the long-term neurodegeneration in male offspring mice.

Dysmetabolism and Neurodegeneration: Trick or Treat?

Accumulating evidence suggests the existence of a strong link between metabolic syndrome and neurodegeneration. Indeed, epidemiologic studies have described solid associations between metabolic syndrome and neurodegeneration, whereas animal models contributed for the clarification of the mechanistic underlying the complex relationships between these conditions, having the development of an insulin resistance state a pivotal role in this relationship. Herein, we review in a concise manner the association between metabolic syndrome and neurodegeneration. We start by providing concepts regarding the role of insulin and insulin signaling pathways as well as the pathophysiological mechanisms that are in the genesis of metabolic diseases. Then, we focus on the role of insulin in the brain, with special attention to its function in the regulation of brain glucose metabolism, feeding, and cognition. Moreover, we extensively report on the association between neurodegeneration and metabolic diseases, with a particular emphasis on the evidence observed in animal models of dysmetabolism induced by hypercaloric diets. We also debate on strategies to prevent and/or delay neurodegeneration through the normalization of whole-body glucose homeostasis, particularly via the modulation of the carotid bodies, organs known to be key in connecting the periphery with the brain.

Exercise Training Improves Memory Performance in Older Adults: A Narrative Review of Evidence and Possible Mechanisms

As human life expectancy increases, cognitive decline and memory impairment threaten independence and quality of life. Therefore, finding prevention and treatment strategies for memory impairment is an important health concern. Moreover, a better understanding of the mechanisms involved underlying memory preservation will enable the development of appropriate pharmaceuticals drugs for those who are activity limited. Exercise training as a non-pharmacological tool, has been known to increase the mean lifespan by maintaining general body health and improving the cardiovascular and nervous systems function. Among different exercise training protocols, aerobic exercise has been reported to prevent the progression of memory decline, provided adequate exertion level, duration, and frequency. Mechanisms underlying exercise training effects on memory performance have not been understood yet. Convergent evidence suggest several direct and indirect mechanisms at molecular and supramolecular levels. The supramolecular level includes improvement in blood circulation, synaptic plasticity and neurogenesis which are under controls of complex molecular signaling of neurotransmitters, neurotrophic factors, exerkines, and epigenetics factors. Among these various factors, irisin/BDNF signaling seems to be one of the important mediators of crosstalk between contracted skeletal muscles and the brain during exercise training. This review provides an affordable and effective method to improve cognitive function in old ages, particularly those who are most vulnerable to neurodegenerative disorders.

siRNA Mediated GSK3β Knockdown Targets Insulin Signaling Pathway and Rescues Alzheimer's Disease Pathology: Evidence from In Vitro and In Vivo Studies

Sporadic Alzheimer's disease (sAD) is a progressive neurodegenerative disorder with dysfunctional insulin signaling and energy metabolism. Emerging evidence suggests impairments in brain insulin responsiveness, glucose utilization, and energy metabolism may be major causes of amyloid precursor protein mishandling. The support for this notion comes from the studies wherein streptozotocin (STZ) induced brain insulin resistance in rodent model resulted in sAD-like neuropathology with cognitive decline. Our previous study showed a compromised insulin signaling pathway, glucose uptake, glucose metabolism, and energy homeostasis in STZ-induced glial-neuronal coculture and in vivo model of sAD. Various components of insulin signaling pathway were examined to understand the metabolic correlation, and GSK3β was selected for gene knockdown strategy to reverse sAD pathology based on the data. In the present study, we have synthesized carboxylated graphene oxide (GO) nanosheets functionalized with PEG and subsequently with polyethylenimine (PEI) to provide attachment sites for GSK3β siRNA. Our results showed that siRNA mediated knockdown of the GSK3β gene reduced expression of amyloid pathway genes (APP and BACE1), which was further confirmed by reduced amyloid beta (Aβ) levels in the in vitro STZ-induced sAD model. GSK3β knockdown also restored insulin signaling, AMPK and Mapk3 pathway by restoring the expression of corresponding candidate genes in these pathways (IR, Glut1/3, Prkaa1/2, Mapk3, BDNF) that reflected improved cellular energy homeostasis, neuronal proliferation, differentiation, maturation, and repair. Behavioral data from Morris water maze (MWM), open field (OF), novel object recognition (NOR), Y maze, and radial arm maze (RAM) tests showed that 0.5 μg nanoformulation (GOc-PP-siRNA^GSK3β) intranasally for 7 days improved spatial memory, rescued anxiety like behavior, improved visual and working memory, and rescued exploratory behavior in STZ-induced sAD rats. GSK3β silencing resulted in decreased BACE1 expression and prevented accumulation of Aβ in the cortex and hippocampus. These molecular findings with improved behavioral performances were further correlated with reduced amyloid beta (Aβ) and neurofibrillary tangle (NFTs) formation in the cortex and hippocampus of GOc-PP-siRNA^GSK3β administered sAD rats. Therefore, it is conceivable from the present study that nanoparticle-mediated targeting of GSK3β in the sAD appears to be a promising strategy to reverse sAD pathology.

Amino Acid Nanofibers Improve Glycemia and Confer Cognitive Therapeutic Efficacy to Bound Insulin

Diabetes poses a high risk for debilitating complications in neural tissues, regulating glucose uptake through insulin-dependent and predominantly insulin-independent pathways. Supramolecular nanostructures provide a flexible strategy for combinatorial regulation of glycemia. Here, we compare the effects of free insulin to insulin bound to positively charged nanofibers comprised of self-assembling amino acid compounds (AACs) with an antioxidant-modified side chain moiety (AAC2) in both in vitro and in vivo models of type 1 diabetes. Free AAC2, free human insulin (hINS) and AAC2-bound-human insulin (AAC2-hINS) were tested in streptozotocin (STZ)-induced mouse model of type 1 diabetes. AAC2-hINS acted as a complex and exhibited different properties compared to free AAC2 or hINS. Mice treated with the AAC2-hINS complex were devoid of hypoglycemic episodes, had improved levels of insulin in circulation and in the brain, and increased expression of neurotransmitter taurine transporter, Slc6a6. Consequently, treatment with AAC2-hINS markedly advanced both physical and cognitive performance in mice with STZ-induced and genetic type 1 diabetes compared to treatments with free AAC2 or hINS. This study demonstrates that the flexible nanofiber AAC2 can serve as a therapeutic platform for the combinatorial treatment of diabetes and its complications.

In situ growth of TiO2 nanowires on Ti3C2 MXenes nanosheets as highly sensitive luminol electrochemiluminescent nanoplatform for glucose detection in fruits, sweat and serum samples

A sensitive electrogenerated chemiluminescence (ECL) biosensor for glucose was developed based on in situ growth of TiO₂ nanowires on Ti₃C₂ MXenes (TiO₂-Ti₃C₂) as the nanoplatform. Via tuning the alkaline oxidation time, different amount of TiO₂ nanowires can be found on MXenes. An ECL biosensor for glucose was constructed by covalent immobilization of glucose oxidase (GODx) on the glycine functional TiO₂-Ti₃C₂ surface, with the ECL signal depending on the in-situ formation of H₂O₂ via the specifically catalysis of glucose by GODx, resulting in the apparent increase of ECL signal. The TiO₂-Ti₃C₂ can also act as the catalyst for the oxidation of H₂O₂ into O₂ to enhance the ECL of luminol. Based on this strategy, a highly sensitive ECL biosensor for glucose was obtained in wide concentration range of 20 nM-12 mM with a low detection limit of 1.2 nM (S/N = 3). The synergistic effects of large surface area, excellent conductivity, and high catalytic activity of the TiO₂-Ti₃C₂ make the sensor highly sensitive toward glucose; the specific enzyme catalysis reaction promises excellent selectivity of the ECL sensor. The proposed biosensor has been employed to detect glucose in human serum, fruits, and sweat samples with excellent performance, providing a universal approach for glucose in various samples, which shows great prospect in clinical diagnostics and wearable sensors.

The interplay among oxidative stress, brain insulin resistance and AMPK dysfunction contribute to neurodegeneration in type 2 diabetes and Alzheimer disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus (T2DM), characterized by chronic hyperglycemia and insulin resistance, as a risk factor for AD and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported in recent clinical and preclinical studies. Brain functions require continuous supply of glucose and oxygen and a tight regulation of metabolic processes. Loss of this metabolic regulation has been proposed to be a contributor to memory dysfunction associated with neurodegeneration. Within the above scenario, this review will focus on the interplay among oxidative stress (OS), insulin resistance and AMPK dysfunctions in the brain by highlighting how these neurotoxic events contribute to neurodegeneration. We provide an overview on the detrimental effects of OS on proteins regulating insulin signaling and how these alterations impact cell metabolic dysfunctions through AMPK dysregulation. Such processes, we assert, are critically involved in the molecular pathways that underlie AD.

Brain Glucose Transporters: Role in Pathogenesis and Potential Targets for the Treatment of Alzheimer's Disease

The most common cause of dementia, especially in elderly people, is Alzheimer’s disease (AD), with aging as its main risk factor. AD is a multifactorial neurodegenerative disease. There are several factors increasing the risk of AD development. One of the main features of Alzheimer’s disease is impairment of brain energy. Hypometabolism caused by decreased glucose uptake is observed in specific areas of the AD-affected brain. Therefore, glucose hypometabolism and energy deficit are hallmarks of AD. There are several hypotheses that explain the role of glucose hypometabolism in AD, but data available on this subject are poor. Reduced transport of glucose into neurons may be related to decreased expression of glucose transporters in neurons and glia. On the other hand, glucose transporters may play a role as potential targets for the treatment of AD. Compounds such as antidiabetic drugs, agonists of SGLT1, insulin, siRNA and liposomes are suggested as therapeutics. Nevertheless, the suggested targets of therapy need further investigations.

Towards development of a novel screening method for identifying Alzheimer's disease risk: Raman spectroscopy of blood serum and machine learning

There is an urgent clinical need for a fast and effective method for diagnosing Alzheimer's disease (AD). The identification of AD in its most initial stages, at which point treatment could provide maximum therapeutic benefits, is not only likely to slow down disease progression but to also potentially provide a cure. However, current clinical detection is complicated and requires a combination of several methods based on significant clinical manifestations due to widespread neurodegeneration. As such, Raman spectroscopy with machine learning is investigated as a novel alternative method for detecting AD in its earliest stages. Here, blood serum obtained from rats fed either a standard diet or a high-fat diet was analyzed. The high-fat diet has been shown to initiate a pre-AD state. Partial least squares discriminant analysis combined with receiver operating characteristic curve analysis was able to separate the two rat groups with 100% accuracy at the donor level during external validation. Although further work is necessary, this research suggests there is a potential for Raman spectroscopy to be used in the future as a successful method for identifying AD early on in its progression, which is essential for effective treatment of the disease.

Insulin Resistance as a Common Link Between Current Alzheimer's Disease Hypotheses

Almost 115 years ago, Alois Alzheimer described Alzheimer's disease (AD) for the first time. Since then, many hypotheses have been proposed. However, AD remains a severe health public problem. The current medical approaches for AD are limited to symptomatic interventions and the complexity of this disease has led to a failure rate of approximately 99.6%in AD clinical trials. In fact, no new drug has been approved for AD treatment since 2003. These failures indicate that we are failing in mimicking this disease in experimental models. Although most studies have focused on the amyloid cascade hypothesis of AD, the literature has made clear that AD is rather a multifactorial disorder. Therefore, the persistence in a single theory has resulted in lost opportunities. In this review, we aim to present the striking points of the long scientific path followed since the description of the first AD case and the main AD hypotheses discussed over the last decades. We also propose insulin resistance as a common link between many other hypotheses.

Some Candidate Drugs for Pharmacotherapy of Alzheimer's Disease

Alzheimer’s disease (AD; progressive neurodegenerative disorder) is associated with cognitive and functional impairment with accompanying neuropsychiatric symptoms. The available pharmacological treatment is of a symptomatic nature and, as such, it does not modify the cause of AD. The currently used drugs to enhance cognition include an N-methyl-d-aspartate receptor antagonist (memantine) and cholinesterase inhibitors. The PUBMED, Medical Subject Heading and Clinical Trials databases were used for searching relevant data. Novel treatments are focused on already approved drugs for other conditions and also searching for innovative drugs encompassing investigational compounds. Among the approved drugs, we investigated, are intranasal insulin (and other antidiabetic drugs: liraglitude, pioglitazone and metformin), bexarotene (an anti-cancer drug and a retinoid X receptor agonist) or antidepressant drugs (citalopram, escitalopram, sertraline, mirtazapine). The latter, especially when combined with antipsychotics (for instance quetiapine or risperidone), were shown to reduce neuropsychiatric symptoms in AD patients. The former enhanced cognition. Procognitive effects may be also expected with dietary antioxidative and anti-inflammatory supplements—curcumin, myricetin, and resveratrol. Considering a close relationship between brain ischemia and AD, they may also reduce post-brain ischemia neurodegeneration. An investigational compound, CN-105 (a lipoprotein E agonist), has a very good profile in AD preclinical studies, and its clinical trial for postoperative dementia is starting soon.

Does insulin resistance influence neurodegeneration in non-diabetic Alzheimer's subjects?

Background

Type 2 diabetes is a risk factor for Alzheimer’s disease (AD), and AD brain shows impaired insulin signalling. The role of peripheral insulin resistance on AD aetiopathogenesis in non-diabetic patients is still debated. Here we evaluated the influence of insulin resistance on brain glucose metabolism, grey matter volume and white matter lesions (WMLs) in non-diabetic AD subjects.

Methods

In total, 130 non-diabetic AD subjects underwent MRI and [18F]FDG PET scans with arterial cannula insertion for radioactivity measurement. T1 Volumetric and FLAIR sequences were acquired on a 3-T MRI scanner. These subjects also had measurement of glucose and insulin levels after a 4-h fast on the same day of the scan. Insulin resistance was calculated by the updated homeostatic model assessment (HOMA2). For [18F]FDG analysis, cerebral glucose metabolic rate (rCMRGlc) parametric images were generated using spectral analysis with arterial plasma input function.

Results

In this non-diabetic AD population, HOMA2 was negatively associated with hippocampal rCMRGlc, along with total grey matter volumes. No significant correlation was observed between HOMA2, hippocampal volume and WMLs.

Conclusions

In non-diabetic AD, peripheral insulin resistance is independently associated with reduced hippocampal glucose metabolism and with lower grey matter volume, suggesting that peripheral insulin resistance might influence AD pathology by its action on cerebral glucose metabolism and on neurodegeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00784-w.

Exploiting Common Aspects of Obesity and Alzheimer's Disease

Alzheimer’s disease (AD) is an example of age-related dementia, and there are still no known preventive or curative measures for this disease. Obesity and associated metabolic changes are widely accepted as risk factors of age-related cognitive decline. Insulin is the prime mediator of metabolic homeostasis, which is impaired in obesity, and this impairment potentiates amyloid-β (Aβ) accumulation and the formation of neurofibrillary tangles (NFTs). Obesity is also linked with functional and morphological alterations in brain mitochondria leading to brain insulin resistance (IR) and memory deficits associated with AD. Also, increased peripheral inflammation and oxidative stress due to obesity are the main drivers that increase an individual’s susceptibility to cognitive deficits, thus doubling the risk of AD. This enhanced risk of AD is alarming in the context of a rapidly increasing global incidence of obesity and overweight in the general population. In this review, we summarize the risk factors that link obesity with AD and emphasize the point that the treatment and management of obesity may also provide a way to prevent AD.

Insulin Resistance at the Crossroad of Alzheimer Disease Pathology: A Review

Insulin plays a major neuroprotective and trophic function for cerebral cell population, thus countering apoptosis, beta-amyloid toxicity, and oxidative stress; favoring neuronal survival; and enhancing memory and learning processes. Insulin resistance and impaired cerebral glucose metabolism are invariantly reported in Alzheimer's disease (AD) and other neurodegenerative processes. AD is a fatal neurodegenerative disorder in which progressive glucose hypometabolism parallels to cognitive impairment. Although AD may appear and progress in virtue of multifactorial nosogenic ingredients, multiple interperpetuative and interconnected vicious circles appear to drive disease pathophysiology. The disease is primarily a metabolic/energetic disorder in which amyloid accumulation may appear as a by-product of more proximal events, especially in the late-onset form. As a bridge between AD and type 2 diabetes, activation of c-Jun N-terminal kinase (JNK) pathway with the ensued serine phosphorylation of the insulin response substrate (IRS)-1/2 may be at the crossroads of insulin resistance and its subsequent dysmetabolic consequences. Central insulin axis bankruptcy translates in neuronal vulnerability and demise. As a link in the chain of pathogenic vicious circles, mitochondrial dysfunction, oxidative stress, and peripheral/central immune-inflammation are increasingly advocated as major pathology drivers. Pharmacological interventions addressed to preserve insulin axis physiology, mitochondrial biogenesis-integral functionality, and mitophagy of diseased organelles may attenuate the adjacent spillover of free radicals that further perpetuate mitochondrial damages and catalyze inflammation. Central and/or peripheral inflammation may account for a local flood of proinflammatory cytokines that along with astrogliosis amplify insulin resistance, mitochondrial dysfunction, and oxidative stress. All these elements are endogenous stressor, pro-senescent factors that contribute to JNK activation. Taken together, these evidences incite to identify novel multi-mechanistic approaches to succeed in ameliorating this pandemic affliction.

Preliminary Report on the Feasibility and Efficacy of the Modified Atkins Diet for Treatment of Mild Cognitive Impairment and Early Alzheimer's Disease

Ketone bodies, the products of fat metabolism, are a source of energy for the brain and are available even when glucose supplies are inadequate (such as with severe carbohydrate deprivation) or its metabolism is faulty (as it is in Alzheimer's disease). This phase I/II randomized clinical trial examined the feasibility of using a modified Atkins diet (MAD) to induce ketogenesis in persons with mild cognitive impairment (MCI) or early AD, and the effect of this diet on memory and other clinical outcomes. In the first 2.5 years of active recruitment, only 27 eligible and willing patients enrolled. After extensive assessment and education, they and their study partners were randomly assigned for 12 weeks to either the MAD or the National Institute on Aging (NIA) recommended diet for seniors. As of April 2018, 9 patients in the MAD arm and 5 in the NIA arm have completed the trial. In spite of extensive teaching, coaching, and monitoring, adherence to both diets was only fair. Among those in the MAD arm who generated at least trace amounts of urinary ketones, there was a large (effect size = 0.53) and statistically significant (p = 0.03) increase in Memory Composite Score between the baseline and week-6 assessment. MAD participants also reported increased energy between baseline and week-6 assessment. Despite challenges to implementing this trial, resulting in a small sample, our preliminary data suggest that the generation of even trace ketones might enhance episodic memory and patient-reported vitality in very early AD.

Healthy brain, healthy life: a review of diet and exercise interventions to promote brain health and reduce Alzheimer's disease risk

With the world's population aging at a rapid rate, the prevalence of Alzheimer's disease (AD) has significantly increased. These statistics are alarming given recent evidence that a third of dementia cases may be preventable. The role of lifestyle factors, such as diet and exercise, can directly alter the risk of disease development. However, an understanding of the effectiveness of dietary patterns and exercise strategies to reduce AD risk or improve brain function is not fully understood. The aim of this review is to discuss the effects of diet and exercise on AD risk. Key components of the Western and Mediterranean diets are discussed in relation to AD progression, as well as how physical activity promotes brain health. Components of the Western diet (saturated fatty acids and simple carbohydrates) are detrimental to the brain, impair cognition, and increase AD pathologies. While components of the Mediterranean diet (polyunsaturated fatty acids, polyphenols, and antioxidants) are considered to be neuroprotective. Exercise can significantly reduce the risk of AD; however, specific exercise recommendations for older adults are limited and optimal intensity, duration, and type remains unknown. This review highlights important modifiable risk factors for AD and points out potential avenues for future research. Novelty Diet and exercise are modifiable factors that can improve brain health and reduce the risk of AD. Polyunsaturated fatty acids, polyphenols, and antioxidants are neuroprotective. Exercise reduces neuroinflammation, improves brain insulin sensitivity, and increases brain derived neurotrophic factor.

Aging is not equal across memory systems

The present experiments compared the effects of aging on learning several hippocampus- and striatum-sensitive tasks in young (3-4 month) and old (24-28 month) male Fischer-344 rats. Across three sets of tasks, aging was accompanied not only by deficits on hippocampal tasks but also by maintained or even enhanced abilities on striatal tasks. On two novel object recognition tasks, rats showed impaired performance on a hippocampal object location task but enhanced performance on a striatal object replacement task. On a dual solution task, young rats predominately used hippocampal solutions and old rats used striatal solutions. In addition, on two maze tasks optimally solved using either hippocampus-sensitive place or striatum-sensitive response strategies, relative to young rats, old rats had impaired learning on the place version but equivalent learning on the response version. Because glucose treatments can reverse deficits in learning and memory across many tasks and contexts, levels of available glucose in the brain may have particular importance in cognitive aging observed across tasks and memory systems. During place learning, training-related rises in extracellular glucose levels were attenuated in the hippocampus of old rats compared to young rats. In contrast, glucose levels in the striatum increased comparably in young and old rats trained on either the place or response task. These extracellular brain glucose responses to training paralleled the impairment in hippocampus-sensitive learning and the sparing of striatum-sensitive learning seen as rats age, suggesting a link between age-related changes in learning and metabolic substrate availability in these brain regions.

Unbiased Proteomic Approach Identifies Pathobiological Profiles in the Brains of Preclinical Models of Repetitive Mild Traumatic Brain Injury, Tauopathy, and Amyloidosis

No concerted investigation has been conducted to explore overlapping and distinct pathobiological mechanisms between repetitive mild traumatic brain injury (r-mTBI) and tau/amyloid proteinopathies considering the long history of association between TBI and Alzheimer’s disease. We address this problem by using unbiased proteomic approaches to generate detailed time-dependent brain molecular profiles of response to repetitive mTBI in C57BL/6 mice and in mouse models of amyloidosis (with amyloid precursor protein KM670/671NL (Swedish) and Presenilin 1 M146L mutations [PSAPP]) and tauopathy (hTau). Brain tissues from animals were collected at different timepoints after injuries (24 hr–12 months post-injury) and at different ages for tau or amyloid transgenic models (3, 9, and 15 months old), encompassing the pre-, peri-, and post-“onset” of cognitive and pathological phenotypes. We identified 30 hippocampal and 47 cortical proteins that were significantly modulated over time in the r-mTBI compared with sham mice. These proteins identified TBI-dependent modulation of phosphatidylinositol-3-kinase/AKT signaling, protein kinase A signaling, and PPARα/RXRα activation in the hippocampus and protein kinase A signaling, gonadotropin-releasing hormone signaling, and B cell receptor signaling in the cortex. Previously published neuropathological studies of our mTBI model showed a lack of amyloid and tau pathology. In PSAPP mice, we identified 19 proteins significantly changing in the cortex and only 7 proteins in hTau mice versus wild-type littermates. When we explored the overlap between our r-mTBI model and the PSAPP/hTau models, a fairly small coincidental change was observed involving only eight significantly regulated proteins. This work suggests a very distinct TBI neurodegeneration and also that other factors are needed to drive pathologies such as amyloidosis and tauopathy postinjury.

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.

Amino acid-based compound activates atypical PKC and leptin receptor pathways to improve glycemia and anxiety like behavior in diabetic mice

Differences in glucose uptake in peripheral and neural tissues account for the reduced efficacy of insulin in nervous tissues. Herein, we report the design of short peptides, referred as amino acid compounds (AAC) with and without a modified side chain moiety. At nanomolar concentrations, a candidate therapeutic molecule, AAC2, containing a 7-(diethylamino) coumarin-3-carboxamide side-chain improved glucose control in human peripheral adipocytes and the endothelial brain barrier cells by activation of insulin-insensitive glucose transporter 1 (GLUT1). AAC2 interacted specifically with the leptin receptor (LepR) and activated atypical protein kinase C zeta (PKCς) to increase glucose uptake. The effects induced by AAC2 were absent in leptin receptor-deficient predipocytes and in Lepr^db mice. In contrast, AAC2 established glycemic control altering food intake in leptin-deficient Lep^ob mice. Therefore, AAC2 activated the LepR and acted in a cytokine-like manner distinct from leptin. In a monogenic Ins2^Akita mouse model for the phenotypes associated with type 1 diabetes, AAC2 rescued systemic glucose uptake in these mice without an increase in insulin levels and adiposity, as seen in insulin-treated Ins2^Akita mice. In contrast to insulin, AAC2 treatment increased brain mass and reduced anxiety-related behavior in Ins2^Akita mice. Our data suggests that the unique mechanism of action for AAC2, activating LepR/PKCς/GLUT1 axis, offers an effective strategy to broaden glycemic control for the prevention of diabetic complications of the nervous system and, possibly, other insulin insensitive or resistant tissues.

Effect of DPP-4 inhibitor on elderly patients with T2DM combined with MCI

The aim of this study was to investigate the effect of dipeptidyl peptidase-4 (DPP-4) inhibitor on blood sugar level and cognitive ability in elderly patients with type 2 diabetes mellitus (T2DM) combined with post-stroke mild cognitive impairment (MCI). Thirty patients received DPP-4 inhibitor (study group), while another thirty received sulfonylurea (control group). Six months after treatment, markers regarding blood sugar were improved in both groups (all P<0.05) without intergroup differences (all P>0.05); scores regarding cognitive ability improved in the study group (both P<0.05) and were higher versus the control group (both P<0.01); the study group had higher Aβ1-42/Aβ1-40 value versus the pretreatment value (P<0.001), which differed from the control group (P<0.05); tumor necrosis factor-α and interleukin-6 concentrations decreased in both groups, while the study group had greater reductions; C-reactive protein value decreased after treatment in the study group (all P<0.05). Using DPP-4 inhibitor in elderly patients with T2DM combined with post-stroke MCI can lower blood sugar and improve cognitive ability. The mechanism may be associated with the improvement of Aβ gathering and reduction in inflammatory response.

GluT4: A central player in hippocampal memory and brain insulin resistance

Insulin is now well-established as playing multiple roles within the brain, and specifically as regulating hippocampal cognitive processes and metabolism. Impairments to insulin signaling, such as those seen in type 2 diabetes and Alzheimer's disease, are associated with brain hypometabolism and cognitive impairment, but the mechanisms of insulin's central effects are not determined. Several lines of research converge to suggest that the insulin-responsive glucose transporter GluT4 plays a central role in hippocampal memory processes, and that reduced activation of this transporter may underpin the cognitive impairments seen as a consequence of insulin resistance.

Brain signalling systems: A target for treating type I diabetes mellitus

From early to later stages of Type I Diabetes Mellitus (TIDM), signalling molecules including brain indolamines and protein kinases are altered significantly, and that has been implicated in the Metabolic Disorders (MD) as well as impairment of retinal, renal, neuronal and cardiovascular systems. Considerable attention has been focused to the effects of diabetes on these signalling systems. However, the exact pathophysiological mechanisms of these signals are not completely understood in TIDM, but it is likely that hyperglycemia, acidosis, and insulin resistance play significant roles. Insulin maintains normal glycemic levels and it acts by binding to its receptor, so that it activates the receptor's tyrosine kinase activity, resulting in phosphorylation of several substrates. Those substrates provide binding/interaction sites for signalling molecules, including serine/threonine kinases and indolamines. For more than two decades, our research has been focused on the mechanisms of protein kinases, CaM Kinase and Serotonin transporter mediated alterations of indolamines in TIDM. In this review, we have also discussed how discrete areas of brain respond to insulin or some of the pharmacological agents that triggers or restores these signalling molecules, and it may be useful for the treatment of specific region wise changes/disorders of diabetic brain.

Stable Co-Cultivation of the Moss Physcomitrella patens with Human Cells in vitro as a New Approach to Support Metabolism of Diseased Alzheimer Cells

Alzheimer's disease (AD) is a devastating slowly progressive neurodegenerative disorder with no cure. While there are many hypotheses, the exact mechanism causing this pathology is still unknown. Among many other features, AD is characterized by brain hypometabolism and decreased sugar availability, to which neurons eventually succumb. In light of this aspect of the disease, we hypothesized that boosting fuel supply to neurons may help them survive or at least alleviate some of the symptoms. Here we demonstrate that live moss Physcomitrella patens cells can be safely co-cultured with human fibroblasts in vitro and thus have a potential for providing human cells with energy and other vital biomolecules. These data may form the foundation for the development of novel approaches to metabolic bioengineering and treatment of diseased cells based on live plants. In addition, by providing alternative energy sources to human tissues, the biotechnological potential of this interkingdom setup could also serve as a springboard to foster innovative dietary processes addressing current challenges of mankind such as famine or supporting long-haul space flight.

Differential Effects of BMI on Brain Response to Odor in Olfactory, Reward and Memory Regions: Evidence from fMRI

：Obesity has reached epidemic proportions, motivating research into the underlying mechanisms. Olfaction is a powerful mediator of food consumption, and obesity has been associated with altered olfactory sensitivity. The current study used an event-related functional magnetic resonance imaging (fMRI) to examine the central processing of odor in humans to gain insight into the effect of the body mass index (BMI) on the neural processes involved in rating the pleasantness of a food odor during a hunger state and in a satiety state. We hypothesized that, during the hedonic evaluation of food odor, BMI would be associated with differences in brain activation within olfactory and higher order processing areas important for perception, reward, and memory. We report novel findings of a dissociation between the relationship between BMI and activation in reward areas and in olfactory and odor memory areas, i.e., activation in reward areas decreased as BMI increased, whereas activation in primary olfactory and memory regions increased as BMI increased. A greater BMI is associated with decreased activation in the reward and frontal regions, supporting a blunted reward response in obesity. These findings have important potential implications for decision making, response inhibition, and reward-based behaviors that may play key roles as causal and maintenance factors in obesity. In contrast, a greater BMI is associated with an increased activation in the primary olfactory and memory areas, which was observed during a hunger state. These results raise the speculative hypothesis that high BMI may be associated with hyperactivation in the olfactory and memory areas, and that over time, the resulting excitotoxic effects may contribute to neurodegenerative changes in these areas.

In vitro models to study insulin and glucocorticoids modulation of trimethyltin (TMT)-induced neuroinflammation and neurodegeneration, and in vivo validation in db/db mice

Brain susceptibility to a neurotoxic insult may be increased in a compromised health status, such as metabolic syndrome. Both metabolic syndrome and exposure to trimethyltin (TMT) are known to promote neurodegeneration. In combination the two factors may elicit additive or compensatory/regulatory mechanisms. Combined effects of TMT exposure (0.5-1 μM) and mimicked metabolic syndrome-through modulation of insulin and glucocorticoid (GC) levels-were investigated in three models: tridimensional rat brain cell cultures for neuron-glia effects; murine microglial cell line BV-2 for a mechanistic analysis of microglial reactivity; and db/db mice as an in vivo model of metabolic syndrome. In 3D cultures, low insulin condition significantly exacerbated TMT's effect on GABAergic neurons and promoted TMT-induced neuroinflammation, with increased expression of cytokines and of the regulator of intracellular GC activity, 11β-hydroxysteroid dehydrogenase 1 (11β-Hsd1). Microglial reactivity increased upon TMT exposure in medium combining low insulin and high GC. These results were corroborated in BV-2 microglial cells where lack of insulin exacerbated the TMT-induced increase in 11β-Hsd1 expression. Furthermore, TMT-induced microglial reactivity seems to depend on mineralocorticoid receptor activation. In diabetic BKS db mice, a discrete exacerbation of TMT neurotoxic effects on GABAergic neurons was observed, together with an increase of interleukin-6 (IL-6) and of basal 11β-Hsd1 expression as compared to controls. These results suggest only minor additive effects of the two brain insults, neurotoxicant TMT exposure and metabolic syndrome conditions, where 11β-Hsd1 appears to play a key role in the regulation of neuroinflammation and of its protective or neurodegenerative consequences.

Evaluating the effects of the novel GLP-1 analogue liraglutide in Alzheimer's disease: study protocol for a randomised controlled trial (ELAD study)

BACKGROUND

Liraglutide is a glucagon-like peptide-1 (GLP-1) analogue currently approved for type 2 diabetes and obesity. Preclinical evidence in transgenic models of Alzheimer's disease suggests that liraglutide exerts neuroprotective effects by reducing amyloid oligomers, normalising synaptic plasticity and cerebral glucose uptake, and increasing the proliferation of neuronal progenitor cells. The primary objective of the study is to evaluate the change in cerebral glucose metabolic rate after 12 months of treatment with liraglutide in participants with Alzheimer's disease compared to those who are receiving placebo.

METHODS/DESIGN

ELAD is a 12-month, multi-centre, randomised, double-blind, placebo-controlled, phase IIb trial of liraglutide in participants with mild Alzheimer's dementia. A total of 206 participants will be randomised to receive either liraglutide or placebo as a daily injection for a year. The primary outcome will be the change in cerebral glucose metabolic rate in the cortical regions (hippocampus, medial temporal lobe, and posterior cingulate) from baseline to follow-up in the treatment group compared with the placebo group. The key secondary outcomes are the change from baseline to 12 months in z scores for clinical and cognitive measures (Alzheimer's Disease Assessment Scale-Cognitive Subscale and Executive domain scores of the Neuropsychological Test Battery, Clinical Dementia Rating Sum of Boxes, and Alzheimer's Disease Cooperative Study-Activities of Daily Living) and the incidence and severity of treatment-emergent adverse events or clinically important changes in safety assessments. Other secondary outcomes are 12-month change in magnetic resonance imaging volume, diffusion tensor imaging parameters, reduction in microglial activation in a subgroup of participants, reduction in tau formation and change in amyloid levels in a subgroup of participants measured by tau and amyloid imaging, and changes in composite scores using support machine vector analysis in the treatment group compared with the placebo group.

DISCUSSION

Alzheimer's disease is a leading cause of morbidity worldwide. As available treatments are only symptomatic, the search for disease-modifying therapies is a priority. If the ELAD trial is successful, liraglutide and GLP-1 analogues will represent an important class of compounds to be further evaluated in clinical trials for Alzheimer's treatment.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01843075 . Registration 30 April 2013.

Cachexia and advanced dementia

Cachexia is a complex metabolic process that is associated with several end-stage organ diseases. It is known to be also associated with advanced dementia, although the pathophysiologic mechanisms are still largely unknown. The present narrative review is aimed at presenting recent insights concerning the pathophysiology of weight loss and wasting syndrome in dementia, the putative mechanisms involved in the dysregulation of energy balance, and the interplay among the chronic clinical conditions of sarcopenia, malnutrition, and frailty in the elderly. We discuss the clinical implications of these new insights, with particular attention to the challenging question of nutritional needs in advanced dementia and the utility of tube feeding in order to optimize the management of end-stage dementia.

Associations of insulin resistance with cognition in individuals without diagnosed diabetes: Results from the Hispanic Community Health Study/Study of Latinos

AIMS

Insulin resistance (IR) adversely impacts memory and executive functioning in non-Hispanic whites without diabetes. Less is known in Hispanics/Latinos, despite the fact that Hispanics/Latinos have higher rates of insulin resistance than non-Hispanic whites. We investigated the association between IR and cognition and its variation by age.

METHODS

Data from 5987 participants 45-74 years old without diabetes from the Hispanic Community Health Study/Study of Latinos. IR was considered continuously using homeostasis model assessment for insulin resistance (HOMA-IR) and also dichotomized based on clinically relevant thresholds for hyperinsulinemia (fasting insulin > 84.73 pmol/L or HOMA-IR > 2.6) and sample-based norms (75th percentile of fasting insulin or HOMA-IR). Cognitive testing included the Brief Spanish English Verbal Learning Test (B-SEVLT), Verbal Fluency, and Digit Symbol Substitution.

RESULTS

There was 90% overlap in participant categorization comparing clinically relevant and sample-based thresholds. In separate fully-adjusted linear regression models, age modified the association between HOMA-IR and Digit Symbol Substitution (p = 0.02); advancing age combined with higher HOMA-IR levels resulted in higher scores. Age also modified the association between clinically relevant hyperinsulinemia and B-SEVLT recall (p = 0.03); with increasing age came worse performance for individuals with hyperinsulinemia.

CONCLUSION

The relationship of IR with cognition in Hispanics/Latinos without diabetes may reflect an age- and test-dependent state.

Longitudinal Changes in Serum Glucose Levels are Associated with Metabolic Changes in Alzheimer's Disease Related Brain Regions

BACKGROUND

The association between longitudinal changes in serum glucose level and longitudinal changes in [18F] Fluorodeoxyglucose-PET (FDG PET) measurements of Alzheimer's disease (AD) risk are unknown.

OBJECTIVE

To investigate whether variation in serum glucose levels across time are associated with changes in FDG PET measurements of cerebral metabolic rate for glucose (rCMRgl) in brain regions preferentially affected by Alzheimer's disease (AD).

METHODS

Participants are a subset of a prospective cohort study investigating FDG PET, apolipoprotein E (APOE) ɛ4, and risk for AD which includes data from baseline, interim, and follow up visits over 4.4±1.0-years. An automated brain-mapping algorithm was utilized to characterize and compare associations between longitudinal changes in serum glucose levels and longitudinal changes in rCMRgl.

RESULTS

This study included 80 adults aged 61.5±5 years, including 38 carriers and 42 non-carriers of the APOE ɛ4 allele. Longitudinal increases in serum glucose levels were associated with longitudinal CMRgl decline in the vicinity of parietotemporal, precuneus/posterior cingulate, and prefrontal brain regions preferentially affected by AD (p < 0.05, corrected for multiple comparisons). Findings remained significant when controlled for APOE ɛ4 status and baseline and advancing age.

CONCLUSIONS

Additional studies are needed to clarify and confirm the relationship between longitudinal changes in peripheral glucose and FDG PET measurements of AD risk. Future findings will set the stage on the use of FDG PET in the evaluation of possible interventions that target risk factors for the development of AD.

Differential Expression of Apoptotic and Low-Grade Inflammatory Markers in Alzheimer Disease Compared to Diabetes Mellitus Type 1 and 2

BACKGROUND

Neuroinflammation, impaired brain insulin signaling, and neuronal apoptosis may be interrelated in the pathophysiology of people with Alzheimer disease (AD) and diabetes, either type 1 or 2 diabetes (T1D or T2D, respectively).

METHODS

We studied 116 patients: 41 with AD, 20 with T1D, 21 with T2D, and 34 healthy controls. The number (n) of cytokine-secreting peripheral blood mononuclear cells (PBMCs) before and after mitogenic stimulation was determined for interleukin 1β (IL1β), interleukin 6 (IL6), tumor necrosis factor (TNF) by the enzyme-linked-immuno-spot assay. Serum concentrations of C-reactive protein (CRP) and Fas ligand (FASLG) were determined by ELISA.

RESULTS

The studied subgroups did not differ in sex but differed in age. Higher CRP concentrations were detected in the AD group than in the T1D group (P = 0.02) and lower in controls (P < 0.001). The nPBMCs was higher in AD patients after stimulation than in basal conditions: after stimulation in nTNF (P < 0.001 vs T2D; P < 0.001 vs T1D; P = 0.001 vs control), nIL6 (P = 0.039 vs T2D; P < 0.001 vs T1D; P = 0.007 vs control), and nIL1β (P = 0.03 vs control). The nPBMCs increased after stimulation with ΡΜA in all the subgroups (P < 0.001). FASLG in the AD group displayed statistically higher concentrations than in all other subgroups (P < 0.001 vs T2D; P < 0.001 vs T1D; P = 0.012 vs control). The nPBMCs was positively correlated with plasma concentrations of FASLG in the AD subgroup.

CONCLUSIONS

Patients with AD display a low-grade systemic inflammation compared to people with diabetes. The FAS-FASLG pathway has a potential role because FASLG concentrations are positively correlated with the inflammatory response in AD. However, this positive correlation cannot be seen in people with diabetes, at least not with the apoptotic markers used in the present study.

'Evolutionary medicine' perspectives on Alzheimer's Disease: Review and new directions

Evolution by natural selection eliminates maladaptive traits from a species, and yet Alzheimer's Disease (AD) persists with rapidly increasing prevalence globally. This apparent paradox begs an explanation within the framework of evolutionary sciences. Here, I summarize and critique previously proposed theories to explain human susceptibility to AD, grouped into 8 distinct hypotheses based on the concepts of novel extension of the lifespan; lack of selective pressure during the post-reproductive phase; antagonistic pleiotropy; rapid brain evolution; delayed neuropathy by selection for grandmothering; novel alleles selected to delay neuropathy; by-product of selection against cardiovascular disease; and thrifty genotype. Subsequently, I describe a new hypothesis inspired by the concept of mismatched environments. Many of the factors that enhance AD risk today may have been absent or functioned differently before the modern era, potentially making AD a less common affliction for age-matched individuals before industrialization and for the majority of human history. Future research is needed to further explore whether changes in environments and lifestyles across human history moderate risk factors and susceptibility to AD.