Alzheimer's disease is type 3 diabetes-evidence reviewed

The landscape of metabolic brain alterations in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is accompanied by metabolic alterations both in the periphery and the central nervous system. However, so far, a global view of AD-associated metabolic changes in the brain has been missing.

METHODS

We metabolically profiled 500 samples from the dorsolateral prefrontal cortex. Metabolite levels were correlated with eight clinical parameters, covering both late-life cognitive performance and AD neuropathology measures.

RESULTS

We observed widespread metabolic dysregulation associated with AD, spanning 298 metabolites from various AD-relevant pathways. These included alterations to bioenergetics, cholesterol metabolism, neuroinflammation, and metabolic consequences of neurotransmitter ratio imbalances. Our findings further suggest impaired osmoregulation as a potential pathomechanism in AD. Finally, inspecting the interplay of proteinopathies provided evidence that metabolic associations were largely driven by tau pathology rather than amyloid beta pathology.

DISCUSSION

This work provides a comprehensive reference map of metabolic brain changes in AD that lays the foundation for future mechanistic follow-up studies.

The Effects of Momordica charantia on Type 2 Diabetes Mellitus and Alzheimer's Disease

T2DM is a complex metabolic disorder characterized by hyperglycemia and glucose intolerance. It is recognized as one of the most common metabolic disorders and its prevalence continues to raise major concerns in healthcare globally. Alzheimer's disease (AD) is a gradual neurodegenerative brain disorder characterized by the chronic loss of cognitive and behavioral function. Recent research suggests a link between the two diseases. Considering the shared characteristics of both diseases, common therapeutic and preventive agents are effective. Certain bioactive compounds such as polyphenols, vitamins, and minerals found in vegetables and fruits can have antioxidant and anti-inflammatory effects that allow for preventative or potential treatment options for T2DM and AD. Recently, it has been estimated that up to one-third of patients with diabetes use some form of complementary and alternative medicine. Increasing evidence from cell or animal models suggests that bioactive compounds may have a direct effect on reducing hyperglycemia, amplifying insulin secretion, and blocking the formation of amyloid plaques. One plant that has received substantial recognition for its numerous bioactive properties is Momordica charantia (M. charantia), otherwise known as bitter melon, bitter gourd, karela, and balsam pear. M. charantia is utilized for its glucose-lowering effects and is often used as a treatment for diabetes and related metabolic conditions amongst the indigenous populations of Asia, South America, India, and East Africa. Several pre-clinical studies have documented the beneficial effects of M. charantia through various postulated mechanisms. Throughout this review, the underlying molecular mechanisms of the bioactive components of M. charantia will be highlighted. More studies will be necessary to establish the clinical efficacy of the bioactive compounds within M. charantia to effectively determine its pertinence in the treatment of metabolic disorders and neurodegenerative diseases, such as T2DM and AD.

Unlocking Modifiable Risk Factors for Alzheimer's Disease: Does the Oral Microbiome Hold Some of the Keys?

Advancing age is recognized as the primary risk factor for Alzheimer's disease (AD); however approximately one third of dementia cases are attributable to modifiable risk factors such as hypertension, diabetes, smoking, and obesity. Recent research also implicates oral health and the oral microbiome in AD risk and pathophysiology. The oral microbiome contributes to the cerebrovascular and neurodegenerative pathology of AD via the inflammatory, vascular, neurotoxic, and oxidative stress pathways of known modifiable risk factors. This review proposes a conceptual framework that integrates the emerging evidence regarding the oral microbiome with established modifiable risk factors. There are numerous mechanisms by which the oral microbiome may interact with AD pathophysiology. Microbiota have immunomodulatory functions, including the activation of systemic pro-inflammatory cytokines. This inflammation can affect the integrity of the blood-brain barrier, which in turn modulates translocation of bacteria and their metabolites to brain parenchyma. Amyloid-β is an antimicrobial peptide, a feature which may in part explain its accumulation. There are microbial interactions with cardiovascular health, glucose tolerance, physical activity, and sleep, suggesting that these modifiable lifestyle risk factors of dementia may have microbial contributors. There is mounting evidence to suggest the relevance of oral health practices and the microbiome to AD. The conceptual framework presented here additionally demonstrates the potential for the oral microbiome to comprise a mechanistic intermediary between some lifestyle risk factors and AD pathophysiology. Future clinical studies may identify specific oral microbial targets and the optimum oral health practices to reduce dementia risk.

Metabolic Syndrome as a Risk Factor for Alzheimer's Disease: A Focus on Insulin Resistance

Alzheimer's disease (AD) is the main type of dementia and is a disease with a profound socioeconomic burden due to the lack of effective treatment. In addition to genetics and environmental factors, AD is highly associated with metabolic syndrome, defined as the combination of hypertension, hyperlipidemia, obesity and type 2 diabetes mellitus (T2DM). Among these risk factors, the connection between AD and T2DM has been deeply studied. It has been suggested that the mechanism linking both conditions is insulin resistance. Insulin is an important hormone that regulates not only peripheral energy homeostasis but also brain functions, such as cognition. Insulin desensitization, therefore, could impact normal brain function increasing the risk of developing neurodegenerative disorders in later life. Paradoxically, it has been demonstrated that decreased neuronal insulin signalling can also have a protective role in aging and protein-aggregation-associated diseases, as is the case in AD. This controversy is fed by studies focused on neuronal insulin signalling. However, the role of insulin action on other brain cell types, such as astrocytes, is still unexplored. Therefore, it is worthwhile exploring the involvement of the astrocytic insulin receptor in cognition, as well as in the onset and/or development of AD.

Using Optogenetics to Model Cellular Effects of Alzheimer's Disease

Across the world a dementia case is diagnosed every three seconds. Alzheimer's disease (AD) causes 50-60% of these cases. The most prominent theory for AD correlates the deposition of amyloid beta (Aβ) with the onset of dementia. Whether Aβ is causative remains unclear due to findings such as the recently approved drug Aducanumab showing effective clearance of Aβ, but not improving cognition. New approaches for understanding Aβ function, are therefore necessary. Here we discuss the application of optogenetic techniques to gain insight into AD. Optogenetics, or genetically encoded, light-dependent on/off switches, provides precise spatiotemporal control to regulate cellular dynamics. This precise control over protein expression and oligomerization or aggregation could provide a better understanding of the etiology of AD.

How Can Insulin Resistance Cause Alzheimer's Disease?

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.

Imaging Methods Applicable in the Diagnostics of Alzheimer's Disease, Considering the Involvement of Insulin Resistance

Alzheimer's disease (AD) is an incurable neurodegenerative disease and the most frequently diagnosed type of dementia, characterized by (1) perturbed cerebral perfusion, vasculature, and cortical metabolism; (2) induced proinflammatory processes; and (3) the aggregation of amyloid beta and hyperphosphorylated Tau proteins. Subclinical AD changes are commonly detectable by using radiological and nuclear neuroimaging methods such as magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), and single-photon emission computed tomography (SPECT). Furthermore, other valuable modalities exist (in particular, structural volumetric, diffusion, perfusion, functional, and metabolic magnetic resonance methods) that can advance the diagnostic algorithm of AD and our understanding of its pathogenesis. Recently, new insights into AD pathoetiology revealed that deranged insulin homeostasis in the brain may play a role in the onset and progression of the disease. AD-related brain insulin resistance is closely linked to systemic insulin homeostasis disorders caused by pancreas and/or liver dysfunction. Indeed, in recent studies, linkages between the development and onset of AD and the liver and/or pancreas have been established. Aside from standard radiological and nuclear neuroimaging methods and clinically fewer common methods of magnetic resonance, this article also discusses the use of new suggestive non-neuronal imaging modalities to assess AD-associated structural changes in the liver and pancreas. Studying these changes might be of great clinical importance because of their possible involvement in AD pathogenesis during the prodromal phase of the disease.

GSK3α phosphorylates dynamin-2 to promote GLUT4 endocytosis in muscle cells

Insulin-stimulated translocation of glucose transporter 4 (GLUT4) to plasma membrane of skeletal muscle is critical for postprandial glucose uptake; however, whether the internalization of GLUT4 is also regulated by insulin signaling remains unclear. Here, we discover that the activity of dynamin-2 (Dyn2) in catalyzing GLUT4 endocytosis is negatively regulated by insulin signaling in muscle cells. Mechanistically, the fission activity of Dyn2 is inhibited by binding with the SH3 domain of Bin1. In the absence of insulin, GSK3α phosphorylates Dyn2 to relieve the inhibition of Bin1 and promotes endocytosis. Conversely, insulin signaling inactivates GSK3α and leads to attenuated GLUT4 internalization. Furthermore, the isoform-specific pharmacological inhibition of GSK3α significantly improves insulin sensitivity and glucose tolerance in diet-induced insulin-resistant mice. Together, we identify a new role of GSK3α in insulin-stimulated glucose disposal by regulating Dyn2-mediated GLUT4 endocytosis in muscle cells. These results highlight the isoform-specific function of GSK3α on membrane trafficking and its potential as a therapeutic target for metabolic disorders.

Gut-brain axis through the lens of gut microbiota and their relationships with Alzheimer's disease pathology: Review and recommendations

Alzheimer's disease (AD) is a neurodegenerative disorder that affects millions of people worldwide. Growing evidence suggests that the gut microbiome (GM) plays a pivotal role in the pathogenesis of AD through the microbiota-gut-brain axis (MGB). Alterations in GM composition and diversity have been observed in both animal models and in human patients with AD. GM dysbiosis has been implicated in increased intestinal permeability, blood-brain barrier (BBB) impairment, neuroinflammation and the development of hallmarks of AD. Further elucidation of the role of GM in AD could pave way for the development of holistic predictive methods for determining AD risk and progression of disease. Furthermore, accumulating evidence suggests that GM modulation could alleviate adverse symptoms of AD or serve as a preventive measure. In addition, increasing evidence shows that Type 2 Diabetes Mellitus (T2DM) is often comorbid with AD, with common GM alterations and inflammatory response, which could chart the development of GM-related treatment interventions for both diseases. We conclude by exploring the therapeutic potential of GM in alleviating symptoms of AD and in reducing risk. Furthermore, we also propose future directions in AD research, namely fecal microbiota transplantation (FMT) and precision medicine.

How does apolipoprotein E genotype influence the relationship between physical activity and Alzheimer's disease risk? A novel integrative model

BACKGROUND

Wide evidence suggests that physical activity (PA) confers protection against Alzheimer's disease (AD). On the other hand, the apolipoprotein E gene (APOE) ε4 allele represents the greatest genetic risk factor for developing AD. Extensive research has been conducted to determine whether frequent PA can mitigate the increased AD risk associated with APOE ε4. However, thus far, these attempts have produced inconclusive results. In this context, one possible explanation could be that the influence of the combined effect of PA and APOE ε4 carriage might be dependent on the specific outcome measure utilised.

MAIN BODY

In order to bridge these discrepancies, the aim of this theoretical article is to propose a novel model on the interactive effects of PA and APOE ε4 carriage on well-established mechanisms underlying AD. Available literature was searched to investigate how PA and APOE ε4 carriage, independently and in combination, may alter several molecular pathways involved in AD pathogenesis. The reviewed mechanisms include amyloid beta (Aβ) and tau deposition and clearance, neuronal resilience and neurogenesis, lipid function and cerebrovascular alterations, brain immune response and glucose metabolism. Finally, combining all this information, we have built an integrative model, which includes evidence-based and theoretical synergistic interactions across mechanisms. Moreover, we have identified key knowledge gaps in the literature, providing a list of testable hypotheses that future studies need to address.

CONCLUSIONS

We conclude that PA influences a wide array of molecular targets involved in AD neuropathology. A deeper understanding of where, when and, most importantly, how PA decreases AD risk even in the presence of the APOE ε4 allele will enable the creation of new protocols using exercise along pharmaceuticals in combined therapeutic approaches.

Relationship between glycemic control and cognitive impairment: A systematic review and meta-analysis

Background

Diabetes mellitus, or hyperglycemia, is an independent risk factor for cognitive impairment. Here we systematically analyzed whether glycemic control could improve cognitive impairment in patients with diabetes mellitus (DM), hyperglycemia, or insulin resistance.

Methods

Three databases (PubMed, EMBASE, and Cochrane Library) and ClinicalTrials.gov were searched for randomized controlled trials analyzing the relationship between glycemic control and cognitive function assessments, published from database inception to June 2022. Patients in experimental groups were treated with antidiabetic drugs, while control groups were treated with a placebo or alternative antidiabetic drugs. Data analysis was conducted using RevMan 5.3 and StataSE-64, and standardized mean difference (SMD) and 95% confidence intervals (CIs) were calculated.

Results

Thirteen studies comprising 19,314 participants were included. Analysis revealed that glycemic control significantly attenuated the degree of decline in cognitive function assessment scores (SMD  =  0.15; 95% CI 0.05, 0.26; p  <  0.00001), and funnel plots confirmed no publication bias. Seven studies used Mini-Mental State Examination as the primary cognitive function assessment, showing that glycemic control significantly delayed the degree of decline in cognitive function assessment scores (SMD  =  0.18; 95% CI 0.03, 0.34; p  =  0.02). Similar results were seen in two studies using the Montreal Cognitive Assessment scale, but without significant difference (SMD  =  0.05; 95% CI-0.10, 0.21; p  =  0.51). One study using Auditory Word Learning Test (AVLT) showed that glycemic control significantly delayed the decline in cognitive function assessment scores (SMD  =  0.52; 95% CI 0.11,0.93; p  =  0.01), and another used Wechsler Memory Scale Revised, showing similar results (SMD  =  1.45; 95% CI 0.86, 2.04; p  <  0.00001). Likewise, a study that used Modified Mini-Mental State scale showed that glycemic control significantly delayed the decline in cognitive function assessment scores (SMD  =  -0.10; 95% CI-0.16, -0.03; p  =  0.005). Lastly, one study used AVLT subtests to show that glycemic control delayed the decline in cognitive function assessment scores, although not statistically significant (SMD  =  0.09; 95% CI-0.53, 0.71; p  =  0.78).

Conclusion

Glycemic control through antidiabetic treatment correlates with the improvement of cognitive impairment in patients with DM, hyperglycemia or insulin resistance. However, further studies are needed to validate the results of this study.

Systematic Review Registration

PROSPERO, identifier CRD42022342260.

Multi-Targeting Intranasal Nanoformulation as a Therapeutic for Alzheimer's Disease

Melatonin, insulin, and Δ9-tetrahydrocannabinol (THC) have been shown to reverse cognitive deficits and attenuate neuropathologies in transgenic mouse models of Alzheimer's disease (AD) when used individually. Here, we evaluated the therapeutic properties of long-term intranasal treatment with a novel nanoformulation containing melatonin, insulin, and THC in aged APPswe/PS1ΔE9 (APP/PS1) mice, a transgenic model of AD. Transgenic mice at the age of 12 months were intranasally administered with a new nanoformulation containing melatonin, insulin, and THC at doses of 0.04, 0.008, and 0.02 mg/kg, respectively, once daily for 3 months. The spatial memory of the mice was assessed using the radial arm water maze (RAWM) test before and after drug treatment. Brain tissues were collected at the end of the treatment period for the assessment of Aβ load, tauopathy state, and markers of mitochondrial function. The RAWM test revealed that the treatment with the melatonin-insulin-THC (MIT) nasal spray improved the spatial learning memory of APP/PS1 mice significantly. Results of protein analyses of brain homogenates indicated that MIT treatment significantly decreased the tau phosphorylation implicated in tau toxicity (p < 0.05) and the expression of CKMT1 associated with mitochondrial dysfunction. Moreover, MIT significantly decreased the expression of two mitochondrial fusion-related proteins, Mfn2 and Opa1 (p < 0.01 for both), while increasing the expression of a mitophagy regulator, Parkin, suggesting a compensatory enhancement of mitophagy due to MIT-promoted mitochondrial fusion. In conclusion, this study was the first to demonstrate the ability of an MIT nanoformulation to improve spatial memory in AD mice through its multi-targeting effects on Aβ production, tau phosphorylation, and mitochondrial dynamics. Thus, MIT may be a safe and effective therapeutic for AD.

Type 2 Diabetes and Alzheimer's Disease: The Emerging Role of Cellular Lipotoxicity

Type 2 diabetes (T2D) and Alzheimer's diseases (AD) represent major health issues that have reached alarming levels in the last decades. Although growing evidence demonstrates that AD is a significant comorbidity of T2D, and there is a ~1.4-2-fold increase in the risk of developing AD among T2D patients, the involvement of possible common triggers in the pathogenesis of these two diseases remains largely unknown. Of note, recent mechanistic insights suggest that lipotoxicity could represent the missing ring in the pathogenetic mechanisms linking T2D to AD. Indeed, obesity, which represents the main cause of lipotoxicity, has been recognized as a major risk factor for both pathological conditions. Lipotoxicity can lead to inflammation, insulin resistance, oxidative stress, ceramide and amyloid accumulation, endoplasmic reticulum stress, ferroptosis, and autophagy, which are shared biological events in the pathogenesis of T2D and AD. In the current review, we try to provide a critical and comprehensive view of the common molecular pathways activated by lipotoxicity in T2D and AD, attempting to summarize how these mechanisms can drive future research and open the way to new therapeutic perspectives.

Alzheimer's Disease: A Systems View Provides a Unifying Explanation of Its Development

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder affecting 50 million people globally. It is characterized by the presence of extracellular senile plaques and intracellular neurofibrillary tangles, consisting of amyloid-β and hyperphosphorylated tau proteins, respectively. Despite global research efforts, there is currently no cure available, due in part to an incomplete understanding of the disease pathogenesis. Numerous possible mechanisms, or hypotheses, explaining the origins of sporadic or late-onset AD have been proposed, including the amyloid-β, inflammatory, vascular, and infectious hypotheses. However, despite ample evidence, the failure of multiple trial drugs at the clinical stage illuminates the possible pitfalls of these hypotheses. Systems biology is a strategy which aims to elucidate the interactions between parts of a whole. Using this approach, the current paper shows how the four previously mentioned hypotheses of AD pathogenesis can be intricately connected. This approach allows for seemingly contradictory evidence to be unified in a system-focused explanation of sporadic AD development. Within this view, it is seen that infectious agents, such as P. gingivalis, may play a central role. The data presented here shows that when present, P. gingivalis or its virulence factors, such as gingipains, may induce or exacerbate pathologies underlying sporadic AD. This evidence supports the view that infectious agents, and specifically P. gingivalis, may be suitable treatment targets in AD.

Discovery of an evodiamine derivative for PI3K/AKT/GSK3β pathway activation and AD pathology improvement in mouse models

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive neurodegeneration and cognitive decline. Evodiamine, a main component in Chinese medicine, was found to improve cognitive impairment in AD model mice based on several intensive studies. However, evodiamine has high cytotoxicity and poor bioactivity. In this study, several evodiamine derivatives were synthesized via heterocyclic substitution and amide introduction and screened for cytotoxicity and antioxidant capacity. Under the same concentrations, compound 4c was found to exhibit lower cytotoxicity and higher activity against H₂O₂ and amyloid β oligomers (AβOs) than evodiamine in vitro and significantly improve the working memory and spatial memory of 3 x Tg and APP/PS1 AD mice. Subsequent RNA sequencing and pathway enrichment analysis showed that 4c affected AD-related genes and the AMPK and insulin signaling pathways. Furthermore, we confirmed that 4c recovered PI3K/AKT/GSK3β/Tau dysfunction in vivo and in vitro. In conclusion, 4c represents a potential lead compound for AD therapy based on the recovery of PI3K/AKT/GSK3β pathway dysfunction.

Carotid Body Resection Prevents Short-Term Spatial Memory Decline in Prediabetic Rats Without Changing Insulin Signaling in the Hippocampus and Prefrontal Cortex

Individuals who develop type 2 diabetes (T2D) at an early age are at higher risk of developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease. A shared dysfunctional characteristic between T2D and these neurodegenerative disorders is insulin resistance. Recently, it was shown that prediabetes animals and patients exhibited increased carotid body (CB) activity. Moreover, these organs are deeply involved in the development of metabolic diseases, since upon abolishment of their activity via carotid sinus nerve (CSN) resection, several dysmetabolic features of T2D were reverted. Herein, we investigated if CSN resection may also prevent cognitive impairment associated with brain insulin resistance. We explored a diet-induced prediabetes animal model where Wistar rats are kept in a high fat-high sucrose (HFHSu) diet for 20 weeks. We evaluated CSN resection effects on behavioral parameters and on insulin signaling-related proteins levels, in the prefrontal cortex and the hippocampus. HFHSu animals exhibited impaired short-term memory evaluated by the y-maze test. Remarkably, CSN resection prevented the development of this phenotype. HFHSu diet or CSN resection did not promote significant alterations in insulin signaling-associated proteins levels. Our findings suggest that CBs modulation might have a role in preventing short-term spatial memory deficits associated with peripheral dysmetabolic states.

Fructose diet ameliorate effects of macrophage migration inhibitory factor deficiency on prefrontal cortex inflammation, neural plasticity, and behavior in male mice

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that represents a link between diet-induced inflammation and insulin resistance. Our aim was to examine whether fructose diet affects inflammation and insulin signaling in the prefrontal cortex (PFC) of Mif knockout mice (MIF-KO), and their possible link to neural plasticity and behavior. We analyzed nuclear factor κB (NF-κB) and glucocorticoid signaling, expression of F4/80, IL-1β, TNF-α, TLR-4, MyD88, arginase 1 (Arg-1), mannose receptor (Mrc-1), and leukemia inhibitory factor (Lif) to assess inflammation in the PFC of C57/BL6J and MIF-KO mice consuming 20% fructose solution for 9 weeks. Insulin receptor (IR), IRS-1 serine phosphorylations (307 and 1101) and activity of PKCα, Akt, GSK-3β and AMPKα were used to analyze insulin signaling. Brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) mRNA levels, together with synapthophysin and PSD-95 protein level and calcium calmodulin-dependent kinase 2 (CaMKII) activity, were used as plasticity markers. Behavior was examined in elevated plus maze, light dark box and novel object recognition test. The results showed concomitant increase of Tnf-α, Tlr-4, MyD88 and M2 microglia markers (Arg-1, Mrc-1, Lif) in the PFC of MIF-KO, paralleled with unchanged glucocorticoid and insulin signaling. Increase of BDNF and IGF-1 was paralleled with increased CaMKII activity, decreased PSD-95 protein level, anxiogenic behavior, and impaired memory in MIF-KO mice. Fructose feeding restored these parameters in the PFC to the control level and mitigated behavioral changes, suggesting that ameliorating effects of fructose on neuroinflammation and behavior depend on the presence of MIF.

Probiotic supplement as a promising strategy in early tau pathology prevention: Focusing on GSK-3β?

Neurofibrillary tangles (NFT) is one of the hallmarks of Alzheimer's disease (AD). Recent research suggests that pretangle tau, the soluble precursor of NFT, is an initiator for AD pathogenesis, thus targeting pretangle tau pathology may be a promising early intervention focus. The bidirectional communications between the gut and the brain play a crucial role in health. The compromised gut-brain axis is involved in various neurodegenerative diseases including AD. However, most research on the relationship between gut microbiome and AD have focused on amyloid-β. In this mini review, we propose to target preclinical pretangle tau stages with gut microbiota interventions such as probiotic supplementation. We discuss the importance of targeting pretangle tau that starts decades before the onset of clinical symptoms, and potential intervention focusing on probiotic regulation of tau hyperphosphorylation. A particular focus is on GSK-3β, a protein kinase that is at the interface between tau phosphorylation, AD and diabetes mellitus.

Mitochondrial defects in pancreatic beta-cell dysfunction and neurodegenerative diseases: Pathogenesis and therapeutic applications

Mitochondria malfunction is linked to the development of β-cell failure and a variety of neurodegenerative disorders. Pancreatic β-cells are normally configured to detect glucose and other food secretagogues in order to adjust insulin exocytosis and maintain glucose homeostasis. As a result of the increased glucose level, mitochondria metabolites and nucleotides are produced, which operate in concert with cytosolic Ca2+ to stimulate insulin secretion. Furthermore, mitochondria are the primary generators of adenosine triphosphate (ATP), reactive oxygen species (ROS), and apoptosis regulation. Mitochondria are concentrated in synapses, and any substantial changes in synaptic mitochondria location, shape, quantity, or function might cause oxidative stress, resulting in faulty synaptic transmission, a symptom of various degenerative disorders at an early stage. However, a greater understanding of the role of mitochondria in the etiology of β-cell dysfunction and neurodegenerative disorder should pave the way for a more effective approach to addressing these health issues. This review looks at the widespread occurrence of mitochondria depletion in humans, and its significance to mitochondria biogenesis in signaling and mitophagy. Proper understanding of the processes might be extremely beneficial in ameliorating the rising worries about mitochondria biogenesis and triggering mitophagy to remove depleted mitochondria, therefore reducing disease pathogenesis.

Malignant Brain Aging: The Formidable Link Between Dysregulated Signaling Through Mechanistic Target of Rapamycin Pathways and Alzheimer's Disease (Type 3 Diabetes)

Malignant brain aging corresponds to accelerated age-related declines in brain functions eventually derailing the self-sustaining forces that govern independent vitality. Malignant brain aging establishes the path toward dementing neurodegeneration, including Alzheimer's disease (AD). The full spectrum of AD includes progressive dysfunction of neurons, oligodendrocytes, astrocytes, microglia, and the microvascular systems, and is mechanistically driven by insulin and insulin-like growth factor (IGF) deficiencies and resistances with accompanying deficits in energy balance, increased cellular stress, inflammation, and impaired perfusion, mimicking the core features of diabetes mellitus. The underlying pathophysiological derangements result in mitochondrial dysfunction, abnormal protein aggregation, increased oxidative and endoplasmic reticulum stress, aberrant autophagy, and abnormal post-translational modification of proteins, all of which are signature features of both AD and dysregulated insulin/IGF-1-mechanistic target of rapamycin (mTOR) signaling. This article connects the dots from benign to malignant aging to neurodegeneration by reviewing the salient pathologies associated with initially adaptive and later dysfunctional mTOR signaling in the brain. Effective therapeutic and preventive measures must be two-pronged and designed to 1) address complex and shifting impairments in mTOR signaling through the re-purpose of effective anti-diabetes therapeutics that target the brain, and 2) minimize the impact of extrinsic mediators of benign to malignant aging transitions, e.g., inflammatory states, obesity, systemic insulin resistance diseases, and repeated bouts of general anesthesia, by minimizing exposures or implementing neuroprotective measures.

Prevailing Antagonistic Risks in Pleiotropic Associations with Alzheimer's Disease and Diabetes

BACKGROUND

The lack of efficient preventive interventions against Alzheimer's disease (AD) calls for identifying efficient modifiable risk factors for AD. As diabetes shares many pathological processes with AD, including accumulation of amyloid plaques and neurofibrillary tangles, insulin resistance, and impaired glucose metabolism, diabetes is thought to be a potentially modifiable risk factor for AD. Mounting evidence suggests that links between AD and diabetes may be more complex than previously believed.

OBJECTIVE

To examine the pleiotropic architecture of AD and diabetes mellitus (DM).

METHODS

Univariate and pleiotropic analyses were performed following the discovery-replication strategy using individual-level data from 10 large-scale studies.

RESULTS

We report a potentially novel pleiotropic NOTCH2 gene, with a minor allele of rs5025718 associated with increased risks of both AD and DM. We confirm previously identified antagonistic associations of the same variants with the risks of AD and DM in the HLA and APOE gene clusters. We show multiple antagonistic associations of the same variants with AD and DM in the HLA cluster, which were not explained by the lead SNP in this cluster. Although the ɛ2 and ɛ4 alleles played a major role in the antagonistic associations with AD and DM in the APOE cluster, we identified non-overlapping SNPs in this cluster, which were adversely and beneficially associated with AD and DM independently of the ɛ2 and ɛ4 alleles.

CONCLUSION

This study emphasizes differences and similarities in the heterogeneous genetic architectures of AD and DM, which may differentiate the pathogenic mechanisms of these diseases.

Gold nanoparticles application to the treatment of brain dysfunctions related to metabolic diseases: evidence from experimental studies

Nanotechnology is an emerging and expanding technology worldwide. The manipulation of materials on a nanometric scale generates new products with unique properties called nanomaterials. Due to its significant expansion, nanotechnology has been applied in several fields of study, including developing materials for biomedical applications, i.e., nanomedicine. The use of nanomaterials, including nanoparticles, in nanomedicine, is promising and has been associated with pharmacokinetics, bioavailability, and therapeutic advantages. In this regard, it is worth mentioning the Gold Nanoparticles (AuNPs). AuNPs' biomedical application is extensively investigated due to their high biocompatibility, simple preparation, catalytic, and redox properties. Experimental studies have pointed out critical therapeutic actions related to AuNPs in different pathophysiological contexts, mainly due to their anti-inflammatory and antioxidant effects. Thus, in this review, we will discuss the main experimental findings related to the therapeutic properties of AuNPs in metabolic, neurodegenerative diseases, and ultimately brain dysfunctions related to metabolic diseases.

Advances in Anti-Diabetic Cognitive Dysfunction Effect of Erigeron Breviscapus (Vaniot) Hand-Mazz

Diabetic cognitive dysfunction (DCD) is the decline in memory, learning, and executive function caused by diabetes. Although its pathogenesis is unclear, molecular biologists have proposed various hypotheses, including insulin resistance, amyloid β hypothesis, tau protein hyperphosphorylation hypothesis, oxidative stress and neuroinflammation. DCD patients have no particular treatment options and current pharmacological regimens are suboptimal. In recent years, Chinese medicine research has shown that herbs with multi-component, multi-pathway and multi-target synergistic activities can prevent and treat DCD. Yunnan is home to the medicinal herb Erigeron breviscapus (Vant.) Hand-Mazz. (EBHM). Studies have shown that EBHM and its active components have a wide range of pharmacological effects and applications in cognitive disorders. EBHM's anti-DCD properties have been seldom reviewed. Through a literature study, we were able to evaluate the likely pathophysiology of DCD, prescribe anti-DCD medication and better grasp EBHM's therapeutic potential. EBHM's pharmacological mechanism and active components for DCD treatment were also summarized.

The Role of PPARs in Breast Cancer

Breast cancer is a malignant tumor with high morbidity and lethality. Its pathogenesis is related to the abnormal expression of many genes. The peroxisome proliferator-activated receptors (PPARs) are a class of ligand-dependent transcription factors in the nuclear receptor superfamily. They can regulate the transcription of a large number of target genes, which are involved in life activities such as cell proliferation, differentiation, metabolism, and apoptosis, and regulate physiological processes such as glucose metabolism, lipid metabolism, inflammation, and wound healing. Further, the changes in its expression are associated with various diseases, including breast cancer. The experimental reports related to "PPAR" and "breast cancer" were retrieved from PubMed since the discovery of PPARs and summarized in this paper. This review (1) analyzed the roles and potential molecular mechanisms of non-coordinated and ligand-activated subtypes of PPARs in breast cancer progression; (2) discussed the correlations between PPARs and estrogen receptors (ERs) as the nuclear receptor superfamily; and (3) investigated the interaction between PPARs and key regulators in several signaling pathways. As a result, this paper identifies PPARs as targets for breast cancer prevention and treatment in order to provide more evidence for the synthesis of new drugs targeting PPARs or the search for new drug combination treatments.

Research progress of fibroblast growth factor in nervous system diseases

Fibroblast growth factors (FGF) are a group of structurally related polypeptides which constitute an elaborate signaling system with their receptors. Evidence accumulated in the years suggests that the FGF family plays a key role in the repair of central nervous system injury. The main protective mechanisms include activating the expression of PI3K-Akt, peroxisome proliferator-activated receptor (PPARγ) and other signals; inhibiting NF-κB-mediated inflammatory response, oxidative stress and apoptosis; regulating neuronal differentiation and neuronal excitability as well as participating in protection of neurovascular units and nerve function repair. This paper comprehensively summarizes the latest research progress in FGF signaling related to diseases of the central nervous system such as cerebral infarction, cerebral hemorrhage, traumatic brain injury, Alzheimer's disease, Parkinson's disease, epilepsy and depression, aiming to provide scientific basis and reference for the development of innovative FGF drugs for the prevention and treatment of neurological diseases.

Ranolazine Attenuates Brain Inflammation in a Rat Model of Type 2 Diabetes

Recent studies suggest a pathogenetic association between metabolic disturbances, including type 2 diabetes (T2DM), and cognitive decline and indicate that T2DM may represent a risk factor for Alzheimer's disease (AD). There are a number of experimental studies presenting evidence that ranolazine, an antianginal drug, acts as a neuroprotective drug. The aim of the present study was to evaluate the effects of ranolazine on hippocampal neurodegeneration and astrocytes activation in a T2DM rat model. Diabetes was induced by a high fat diet (HFD) and streptozotocin (STZ) injection. Animals were divided into the following groups: HFD/STZ + Ranolazine, HFD/STZ + Metformin, HFD/STZ + Vehicle, NCD + Vehicle, NCD + Ranolazine and NCD + Metformin. The presence of neurodegeneration was evaluated in the hippocampal cornus ammonis 1 (CA1) region by cresyl violet staining histological methods, while astrocyte activation was assessed by western blot analysis. Staining with cresyl violet highlighted a decrease in neuronal density and cell volume in the hippocampal CA1 area in diabetic HFD/STZ + Vehicle rats, while ranolazine and metformin both improved T2DM-induced neuronal loss and neuronal damage. Moreover, there was an increased expression of GFAP in the HFD/STZ + Vehicle group compared to the treated diabetic groups. In conclusion, in the present study, we obtained additional evidence supporting the potential use of ranolazine to counteract T2DM-associated cognitive decline.

Degradation of Bone Quality in a Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) patients present with symptoms such as impairment of insulin signaling, chronic inflammation, and oxidative stress. Furthermore, there are comorbidities associated with AD progression. For example, osteoporosis is common with AD wherein patients exhibit reduced mineralization and a risk for fragility fractures. However, there is a lack of understanding on the effects of AD on bone beyond loss of bone density. To this end, we investigated the effects of AD on bone quality using the 5XFAD transgenic mouse model in which 12-month-old 5XFAD mice showed accumulation of amyloid-beta (Aβ42) compared with wild-type (WT) littermates (n = 10/group; 50% female, 50% male). Here, we observed changes in cortical bone but not in cancellous bone quality. Both bone mass and bone quality, measured in femoral samples using imaging (micro-CT, confocal Raman spectroscopy, X-ray diffraction [XRD]), mechanical (fracture tests), and chemical analyses (biochemical assays), were altered in the 5XFAD mice compared with WT. Micro-CT results showed 5XFAD mice had lower volumetric bone mineral density (BMD) and increased endocortical bone loss. XRD results showed decreased mineralization with smaller mineral crystals. Bone matrix compositional properties, from Raman, showed decreased crystallinity along with higher accumulation of glycoxidation products and glycation products, measured biochemically. 5XFAD mice also demonstrated loss of initiation and maximum toughness. We observed that carboxymethyl-lysine (CML) and mineralization correlated with initiation toughness, whereas crystal size and pentosidine (PEN) correlated with maximum toughness, suggesting bone matrix changes predominated by advanced glycation end products (AGEs) and altered/poor mineral quality explained loss of fracture toughness. Our findings highlight two pathways to skeletal fragility in AD through alteration of bone quality: (i) accumulation of AGEs; and (ii) loss of crystallinity, decreased crystal size, and loss of mineralization. We observed that the accumulation of amyloidosis in brain correlated with an increase in several AGEs, consistent with a mechanistic link between elevated Aβ42 levels in the brain and AGE accumulation in bone. © 2022 American Society for Bone and Mineral Research (ASBMR).

The effect of chronic stress and its preconditioning on spatial memory as well as hippocampal LRP1 and RAGE expression in a streptozotocin-induced rat model of Alzheimer's disease

According to available evidence, prolonged or chronic exposure to stress is detrimental to various brain structures, including the hippocampus. The current study examined the expression of two critical blood-brain barrier receptors required for amyloid-beta clearance to understand better the mechanism by which chronic stress impairs learning and memory in patients with Alzheimer's disease (AD). Rats were randomly assigned to one of two groups in this study: experiment 1 and experiment 2. Each main group was then divided into four subgroups. Rats were bilaterally injected with streptozotocin (STZ, 3 mg/kg, twice) using the intracerebroventricular (ICV) technique to induce the Alzheimer's model. Additionally, they were subjected to foot shock (1 mA, 1 Hz) for 10 s every 60 s (1 h/day) for ten consecutive days prior to and following STZ injection. The Morris Water Maze (MWM) test was used to assess spatial learning and memory. Real-time PCR was used to determine Low-density lipoprotein receptor-related protein-1 (LRP1) and receptor for advanced glycation end-products (RAGE) mRNA levels in the hippocampus. Moreover, the animals' body weights were determined as physiological parameters in all groups. The results indicated that 10-day chronic electric foot shock stress reduced body weight, impaired spatial learning and memory, decreased hippocampal LRP1 mRNA expression, and increased hippocampal RAGE mRNA expression in a rat AD model. It can be concluded that chronic stress in conjunction with AD alters the expression of LRP1 and RAGE in the hippocampus. The findings pave the way for scientists to develop novel treatment strategies for AD.

Brain insulin resistance and cognitive function: influence of exercise

Exercise has systemic health benefits in people, in part, through improving whole body insulin sensitivity. The brain is an insulin-sensitive organ that is often underdiscussed relative to skeletal muscle, liver, and adipose tissue. Although brain insulin action may have only subtle impacts on peripheral regulation of systemic glucose homeostasis, it is important for weight regulation as well as mental health. In fact, brain insulin signaling is also involved in processes that support healthy cognition. Furthermore, brain insulin resistance has been associated with age-related declines in memory and executive function as well as Alzheimer's disease pathology. Herein, we provide an overview of brain insulin sensitivity in relation to cognitive function from animal and human studies, with particular emphasis placed on the impact exercise may have on brain insulin sensitivity. Mechanisms discussed include mitochondrial function, brain growth factors, and neurogenesis, which collectively help combat obesity-related metabolic disease and Alzheimer's dementia.

The Role of Ketogenic Diet in the Treatment of Neurological Diseases

Over a hundred years of study on the favourable effect of ketogenic diets in the treatment of epilepsy have contributed to a long-lasting discussion on its potential influence on other neurological diseases. A significant increase in the number of scientific studies in that field has been currently observed. The aim of this paper is a widespread, thorough analysis of the available scientific evidence in respect of the role of the ketogenic diet in the therapy of neurological diseases such as: epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A wide range of the mechanisms of action of the ketogenic diet has been demonstrated in neurological diseases, including, among other effects, its influence on the reduction in inflammatory conditions and the amount of reactive oxygen species (ROS), the restoration of the myelin sheath of the neurons, the formation and regeneration of mitochondria, neuronal metabolism, the provision of an alternative source of energy for neurons (ketone bodies), the reduction in glucose and insulin concentrations, the reduction in amyloid plaques, the induction of autophagy, the alleviation of microglia activation, the reduction in excessive neuronal activation, the modulation of intestinal microbiota, the expression of genes, dopamine production and the increase in glutamine conversion into GABA. The studies discussed (including randomised controlled studies), conducted in neurological patients, have stressed the effectiveness of the ketogenic diet in the treatment of epilepsy and have demonstrated its promising therapeutic potential in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A frequent advantage of the diet was demonstrated over non-ketogenic diets (in the control groups) in the therapy of neurological diseases, with simultaneous safety and feasibility when conducting the nutritional model.

Nutritional intervention for diabetes mellitus with Alzheimer's disease

The combined disease burden of diabetes mellitus (DM) and Alzheimer's disease (AD) is increasing, and the two diseases share some common pathological changes. However, the pharmacotherapeutic approach to this clinical complexity is limited to symptomatic rather than disease-arresting, with the possible exception of metformin. Whether nutritional intervention might extend or synergize with these effects of metformin is of interest. In particular, dietary patterns with an emphasis on dietary diversity shown to affect cognitive function are of growing interest in a range of food cultural settings. This paper presents the association between diabetes and AD. In addition, the cross-cultural nutritional intervention programs with the potential to mitigate both insulin resistance (IR) and hyperglycemia, together with cognitive impairment are also reviewed. Both dietary patterns and nutritional supplementation showed the effects of improving glycemic control and reducing cognitive decline in diabetes associated with AD, but the intervention specificity remained controversial. Multi-nutrient supplements combined with diverse diets may have preventive and therapeutic potential for DM combined with AD, at least as related to the B vitamin group and folate-dependent homocysteine (Hcy). The nutritional intervention has promise in the prevention and management of DM and AD comorbidities, and more clinical studies would be of nutritional scientific merit.

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.

Advances of neurovascular protective potential of 3-N-butylphthalide and its derivatives in diabetic related diseases

3-N-butylphthalide (NBP) is a component isolated from seeds of Chinese celery, and it was firstly approved for the treatment of ischemic stroke. With the gradual in-depth understanding of its pharmacological action, it was found that it may have potential effects on treating diabetes and its complications. This review aims to illustrate the researches on the properties of NBP and its therapeutic efficacy in diabetic related diseases. This review will discuss the results of experiments in vitro and in vivo to make progress in understanding the beneficial effects of NBP and its derivatives on diabetic complications including diabetic vascular diseases, diabetic peripheral neuropathy, diabetic brain related diseases and diabetic cataract. We will also demonstrate NBP's numerous molecular targets and interactions with multiple cellular signaling pathways such as oxidative stress, inflammatory responses, apoptosis and autophagy. NBP is proved to be a potential therapeutic approach for treating diabetic complications.

Metabolic Regulation of Glia and Their Neuroinflammatory Role in Alzheimer's Disease

Alzheimer's disease (AD) is an aging-related neurodegenerative disorder. It is characterized clinically by progressive memory loss and impaired cognitive function. Its progression occurs from neuronal synapse loss to amyloid pathology and Tau deposit which eventually leads to the compromised neuronal function. Neurons in central nervous tissue work in a composite and intricate network with the glia and vascular cells. Microglia and astrocytes are becoming the prime focus due to their involvement in various aspects of neurophysiology, such as trophic support to neurons, synaptic modulation, and brain surveillance. AD is also often considered as the sequela of prolonged metabolic dyshomeostasis. The neuron and glia have different metabolic profiles as cytosolic glycolysis and mitochondrial-dependent oxidative phosphorylation (OXPHOS), especially under dyshomeostasis or with aging pertaining to their unique genetic built-up. Various efforts are being put in to decipher the role of mitochondrial dynamics regarding their trafficking, fission/fusion imbalance, and mitophagy spanning over both neurons and glia to improve aging-related brain health. The mitochondrial dysfunction may lead to activation in various signaling mechanisms causing metabolic reprogramming in glia cells, further accelerating AD-related pathogenic events. The glycolytic-dominant astrocytes switch to the neurotoxic phenotype, i.e., disease-associated astrocyte under metabolic stress. The microglia also transform from resting to reactive phenotype, i.e., disease-associated microglia. It may also exist in otherwise a misconception an M1, glycolytic, or M2, an OXPHOS-dependent phenotype. Further, glial transformation plays a vital role in regulating hallmarks of AD pathologies like synapse maintenance, amyloid, and Tau clearance. In this updated review, we have tried to emphasize the metabolic regulation of glial reactivity, mitochondrial quality control mechanisms, and their neuroinflammatory response in Alzheimer's progression.

Treadmill Exercise Modulates Intestinal Microbes and Suppresses LPS Displacement to Alleviate Neuroinflammation in the Brains of APP/PS1 Mice

Neuroinflammation occurs throughout the pathogenesis of Alzheimer’s disease (AD). Here, we investigated the effects of treadmill exercise on neuroinflammation in APP/PS1 transgenic AD mice and the potential involvement of microbe–gut–brain axis (MGB) mechanisms based on growing evidence that AD’s pathogenesis is correlated with a deterioration in the function of gut microbiota. APP/PS1 transgenic AD mice were subjected to 12 weeks of treadmill exercise, followed by spatial memory tests. After the behavioral study, the amyloid (Aβ) pathology, gut microbes and metabolites, bacterial lipopolysaccharide (LPS) displacement, and degree of neuroinflammation were analyzed. We found that this strategy of exercise enriched gut microbial diversity and alleviated neuroinflammation in the brain. Notably, exercise led to reductions in pathogenic bacteria such as intestinal Allobaculum, increases in probiotic bacteria such as Akkermansia, increased levels of intestine–brain barrier proteins, and attenuated LPS displacement. These results suggest that prolonged exercise can effectively modulate gut microbes and the intestinal barrier and thereby reduce LPS displacement and ultimately alleviate AD-related neuroinflammation.

Insulin signaling in the central nervous system, a possible pathophysiological mechanism of anesthesia-induced delayed neurocognitive recovery/postoperative neurocognitive disorder: a narrative review

INTRODUCTION

Impairment in neurocognitive functions ranges between delayed neurocognitive recovery (DNR) and postoperative neurocognitive disorders (pNCD). Incidence varies from 11% after noncardiac surgery to 60% after cardiac surgery.

AREAS COVERED

Insulin receptors (IRs) signaling pathway in the central nervous system (CNS) could be a possible pathophysiological mechanism of anesthesia-induced DNR/pNCD and perioperative intranasal insulin administration could be a preventive approach. This hypothesis is supported by the following evidence: effects of IRs-CNS signaling pathway on neuromodulation; higher incidence of DNR/pNCD in patients with insulin resistance; neurotoxicity of IRs signaling pathways after anesthetic exposure; improvement of neurocognitive impairment after insulin exposure. This narrative review was conducted after a literature search of PubMed, EMBASE and SCOPUS online medical data performed in May 2022.

EXPERT OPINION

Perioperative intranasal insulin is shown to be protective and future studies should address: the role of insulin as a neuromodulator; its integration into neuroprotection approaches; patient populations that might benefit from this approach; a well-defined protocol of intranasal insulin administration in a perioperative background and other disciplines; and possible collateral effects.

A Low-Molecular-Weight BDNF Mimetic, Dipeptide GSB-214, Prevents Memory Impairment in Rat Models of Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF) is known to be involved in the pathogenesis of Alzheimer's disease (AD). However, the pharmacological use of full-length neurotrophin is limited, because of its macromolecular protein nature. A dimeric dipeptide mimetic of the BDNF loop 1, bis-(N-monosuccinyl-L-methionyl-L-serine) heptamethylene diamide (GSB-214), was designed at the Zakusov Research Institute of Pharmacology. GSB-214 activates TrkB, PI3K/AKT, and PLC-γ1 in vitro. GSB-214 exhibited a neuroprotective activity during middle cerebral artery occlusion in rats when administered intraperitoneally (i.p.) at a dose of 0.1 mg/kg and improved memory in the novel object recognition test (0.1 and 1.0 mg/kg, i.p.). In the present study, we investigated the effects of GSB-214 on memory in the scopolamine- and steptozotocin-induced AD models, with reference to activation of TrkB receptors. AD was modeled in rats using a chronic i.p. scopolamine injection or a single streptozotocin injection into the cerebral ventricles. GSB-214 was administered within 10 days after the exposure to scopolamine at doses of 0.05, 0.1, and 1 mg/kg (i.p.) or within 14 days after the exposure to streptozotocin at a dose of 0.1 mg/kg (i.p.). The effect of the dipeptide was evaluated in the novel object recognition test; K252A, a selective inhibitor of tyrosine kinase receptors, was used to reveal a dependence between the mnemotropic action and Trk receptors. GSB-214 at doses of 0.05 and 0.1 mg/kg statistically significantly prevented scopolamine-induced long-term memory impairment, while not affecting short-term memory. In the streptozotocin-induced model, GSB-214 completely eliminated the impairment of short-term memory. No mnemotropic effect of GSB-214 was registered when Trk receptors were inhibited by K252A.

A Pathophysiological Intersection of Diabetes and Alzheimer's Disease

Diabetes is among the most prevalent diseases of the modern world and is strongly linked to an increased risk of numerous neurodegenerative disorders, although the exact pathophysiological mechanisms are not clear yet. Insulin resistance is a serious pathological condition, connecting type 2 diabetes, metabolic syndrome, and obesity. Recently, insulin resistance has been proven to be connected also to cognitive decline and dementias, including the most prevalent form, Alzheimer's disease. The relationship between diabetes and Alzheimer's disease regarding pathophysiology is so significant that it has been proposed that some presentations of the condition could be termed type 3 diabetes.

Dysfunctional Glucose Metabolism in Alzheimer’s Disease Onset and Potential Pharmacological Interventions

Alzheimer’s disease (AD) is the most common age-related dementia. The alteration in metabolic characteristics determines the prognosis. Patients at risk show reduced glucose uptake in the brain. Additionally, type 2 diabetes mellitus increases the risk of AD with increasing age. Therefore, changes in glucose uptake in the cerebral cortex may predict the histopathological diagnosis of AD. The shifts in glucose uptake and metabolism, insulin resistance, oxidative stress, and abnormal autophagy advance the pathogenesis of AD syndrome. Here, we summarize the role of altered glucose metabolism in type 2 diabetes for AD prognosis. Additionally, we discuss diagnosis and potential pharmacological interventions for glucose metabolism defects in AD to encourage the development of novel therapeutic methods.

Ketones: potential to achieve brain energy rescue and sustain cognitive health during ageing

Alzheimer’s disease (AD) is the most common major neurocognitive disorder of ageing. Although largely ignored until about a decade ago, accumulating evidence suggests that deteriorating brain energy metabolism plays a key role in the development and/or progression of AD-associated cognitive decline. Brain glucose hypometabolism is a well-established biomarker in AD but was mostly assumed to be a consequence of neuronal dysfunction and death. However, its presence in cognitively asymptomatic populations at higher risk of AD strongly suggests that it is actually a pre-symptomatic component in the development of AD. The question then arises as to whether progressive AD-related cognitive decline could be prevented or slowed down by correcting or bypassing this progressive ‘brain energy gap’. In this review, we provide an overview of research on brain glucose and ketone metabolism in AD and its prodromal condition – mild cognitive impairment (MCI) – to provide a clearer basis for proposing keto-therapeutics as a strategy for brain energy rescue in AD. We also discuss studies using ketogenic interventions and their impact on plasma ketone levels, brain energetics and cognitive performance in MCI and AD. Given that exercise has several overlapping metabolic effects with ketones, we propose that in combination these two approaches might be synergistic for brain health during ageing. As cause-and-effect relationships between the different hallmarks of AD are emerging, further research efforts should focus on optimising the efficacy, acceptability and accessibility of keto-therapeutics in AD and populations at risk of AD.

Sleeve Gastrectomy Reduces Glycemia but Does Not Affect Cognitive Impairment in Lean 5xFAD Mice

Obesity and hyperglycemia are risk factors for cognitive decline and for the development of Alzheimer’s Disease (AD). Bariatric surgery is an effective treatment for obesity that was shown to improve cognitive decline in obese patients. Bariatric surgery was shown to exert weight loss independent effects on metabolic diseases such as type 2 diabetes. We tested whether sleeve gastrectomy (SG), a common bariatric surgery, can affect the cognitive impairment in lean, normoglycemic female 5xFAD mice, a genetic model for AD. 5xFAD mice and wild-type (WT) littermates underwent SG or sham surgery at the age of 5 months and were tested for metabolic, behavioral, and molecular phenotypes 90 days later. SG led to a reduction in blood glucose levels and total plasma cholesterol levels in 5xFAD mice without inducing weight loss. However, the surgery did not affect the outcomes of long-term spatial memory tests in these mice. Analysis of β-Amyloid plaques corroborated the behavioral studies in showing no effect of surgery on the molecular phenotype of 5xFAD mice. In conclusion, SG leads to an improved metabolic profile in lean female 5xFAD mice without inducing weight loss but does not affect the brain pathology or behavioral phenotype. Our results suggest that the positive effects of bariatric surgery on cognitive decline in obese patients are likely attributed to weight loss and improvement in obesity sequelae, and not to weight loss independent effects of surgery.

The AICD fragment of APP initiates a FoxO3a mediated response via FANCD2

The amyloid precursor protein (APP) is a cell surface protein of uncertain function that is notable for being the parent protein of beta-amyloid. Research around this protein has focussed heavily on the link to Alzheimer's disease and neurodegeneration. However, there is increasing evidence that APP may be linked to neuronal loss through mechanisms independent of beta-amyloid. FoxO3a is a transcription factor associated with neuronal longevity and apoptosis. In neurons, FoxO3a is associated with cell death through pathways that include BIM, a BCL-2 family member. In this study we have shown that APP overexpression increased the cellular levels and activity of FoxO3a. This increased expression and activity is not a result of decreased phosphorylation but is more likely a result of increased nuclear stability due to increased levels of FANCD2, a binding partner of FoxO3a. The changes caused by APP overexpression were shown to be due to the AICD fragment of APP possibly directly inducing transcription increase in FANCD2. These findings strengthen the link between APP metabolism and FoxO3a neuronal activity. This link may be crucial in better understanding the cellular role of APP and its link to neurodegeneration and aging.

Peroxisomal Proliferator-Activated Receptor β/δ Deficiency Induces Cognitive Alterations

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ), the most PPAR abundant isotype in the central nervous system, is involved in microglial homeostasis and metabolism, whose disturbances have been demonstrated to play a key role in memory impairment. Although PPARβ/δ function is well-established in metabolism, its contribution to neuronal and specifically memory process is underexplored. Therefore, the aim of the study is to determine the role of PPARβ/δ in the neuropathological pathways involved in memory impairment and as to whether a risk factor implicated in memory loss such as obesity modulates neuropathological markers. To carry out this study, 6-month-old total knock-out for the Ppard gene male mice with C57BL/6X129/SV background (PPARβ/δ-/-) and wild-type (WT) littermates with the same genetic background were used. Animals were fed, after the weaning (at 21 days old), and throughout their growth, either conventional chow (CT) or a palmitic acid-enriched diet (HFD). Thus, four groups were defined: WT CT, WT HFD, PPARβ/δ-/- CT, and PPARβ/δ-/- HFD. Before sacrifice, novel object recognition test (NORT) and glucose and insulin tolerance tests were performed. After that, animals were sacrificed by intracardiac perfusion or cervical dislocation. Different techniques, such as GolgiStain kit or immunofluorescence, were used to evaluate the role of PPARβ/δ in memory dysfunction. Our results showed a decrease in dendritic spine density and synaptic markers in PPARβ/δ-/- mice, which were corroborated in the NORT. Likewise, our study demonstrated that the lack of PPARβ/δ receptor enhances gliosis in the hippocampus, contributing to astrocyte and microglial activation and to the increase in neuroinflammatory biomarkers. Additionally, alterations in the hippocampal insulin receptor pathway were found. Interestingly, while some of the disturbances caused by the lack of PPARβ/δ were not affected by feeding the HFD, others were exacerbated or required the combination of both factors. Taken together, the loss of PPARβ/δ-/- affects neuronal and synaptic structure, contributing to memory dysfunction, and they also present this receptor as a possible new target for the treatment of memory impairment.

Effect of Selenium Treatment on Central Insulin Sensitivity: A Proteomic Analysis in β-Amyloid Precursor Protein/Presenilin-1 Transgenic Mice

Prior studies have demonstrated a close association between brain insulin resistance and Alzheimer’s disease (AD), while selenium supplementation was shown to improve insulin homeostasis in AD patients and to exert neuroprotective effects in a mouse model of AD. However, the mechanisms underlying the neuroprotective actions of selenium remain incompletely understood. In this study, we performed a label-free liquid chromatography-tandem mass spectrometry (LC–MS/MS) quantitative proteomics approach to analyze differentially expressed proteins (DEPs) in the hippocampus and cerebral cortex of Aβ precursor protein (APP)/presenilin-1 (PS1) mice following 2 months of treatment with sodium selenate. A total of 319 DEPs (205 upregulated and 114 downregulated proteins) were detected after selenium treatment. Functional enrichment analysis revealed that the DEPs were mainly enriched in processes affecting axon development, neuron differentiation, tau protein binding, and insulin/insulin-like growth factor type 1 (IGF1)-related pathways. These results demonstrate that a number of insulin/IGF1 signaling pathway-associated proteins are differentially expressed in ways that are consistent with reduced central insulin resistance, suggesting that selenium has therapeutic value in the treatment of neurodegenerative and metabolic diseases such as AD and non-alcoholic fatty liver disease (NAFLD).

Neurovascular Coupling in Type 2 Diabetes With Cognitive Decline. A Narrative Review of Neuroimaging Findings and Their Pathophysiological Implications

Type 2 diabetes causes substantial long-term damage in several organs including the brain. Cognitive decline is receiving increased attention as diabetes has been established as an independent risk factor along with the identification of several other pathophysiological mechanisms. Early detection of detrimental changes in cerebral blood flow regulation may represent a useful clinical marker for development of cognitive decline for at-risk persons. Technically, reliable evaluation of neurovascular coupling is possible with several caveats but needs further development before it is clinically convenient. Different modalities including ultrasound, positron emission tomography and magnetic resonance are used preclinically to shed light on the many influences on vascular supply to the brain. In this narrative review, we focus on the complex link between type 2 diabetes, cognition, and neurovascular coupling and discuss how the disease-related pathology changes neurovascular coupling in the brain from the organ to the cellular level. Different modalities and their respective pitfalls are covered, and future directions suggested.

Asian Best Practices for Care of Diabetes in Elderly (ABCDE)

The elderly population with diabetes is diverse with the majority experiencing a decline in physical and mental capabilities, impacting the entire diabetes management process. Therefore, a need for geriatric-specific guidelines, especially for the Asian population, was identified and subsequently developed by an expert panel across government and private institutions from several Asian countries. The panel considered clinical evidence (landmark trials, position papers, expert opinions), recommendations from several important societies along with their decades of clinical experience and expertise, while meticulously devising thorough geriatric-specific tailored management strategies. The creation of the ABCDE best practices document underscores and explores the gaps and challenges and determines optimal methods for diabetes management of the elderly population in the Asian region.

d-Pinitol promotes tau dephosphorylation through a cyclin-dependent kinase 5 regulation mechanism: A new potential approach for tauopathies?

Background and Purpose

Recent evidence links brain insulin resistance with neurodegenerative diseases, where hyperphosphorylated tau protein contributes to neuronal cell death. In the present study, we aimed to evaluate if d‐pinitol inositol, which acts as an insulin sensitizer, affects the phosphorylation status of tau protein.

Experimental Approach

We studied the pharmacological effect of d‐pinitol on insulin signalling and tau phosphorylation in the hippocampus of Wistar and Zucker rats. To this end, we evaluated by western blotting the Akt pathway and its downstream proteins as being one of the main insulin‐mediator pathways. Also, we explored the functional status of additional kinases phosphorylating tau, including PKA, ERK1/2, AMPK and CDK5. We utilized the 3xTg mouse model as a control for tauopathy, since it carries tau mutations that promote phosphorylation and aggregation.

Key Results

Surprisingly, we discovered that oral d‐pinitol treatment lowered tau phosphorylation significantly, but not through the expected kinase GSK‐3 regulation. An extensive search for additional kinases phosphorylating tau revealed that this effect was mediated through a mechanism dependent on the reduction of the activity of the CDK5, affecting both its p35 and p25 subunits. This effect disappeared in leptin‐deficient Zucker rats, uncovering that the association of leptin deficiency, obesity, dyslipidaemia and hyperinsulinaemia abrogates d‐pinitol actions on tau phosphorylation. The 3xTg mice confirmed d‐pinitol effectiveness in a genetic AD‐tauopathy.

Conclusion and Implications

The present findings suggest that d‐pinitol, by regulating CDK5 activity through a decrease of CDK5R1, is a potential drug for developing treatments for neurological disorders such as tauopathies.