Insulin-degrading enzyme regulates the levels of insulin, amyloid beta-protein, and the beta-amyloid precursor protein intracellular domain in vivo

Krüppel-like factor 9 alleviates Alzheimer's disease via IDE-mediated Aβ degradation

The deposition of β-amyloid (Aβ) in the brain is a crucial factor in the pathogenesis of Alzheimer's disease (AD). Insulin-degrading enzyme (IDE) plays a critical role in the balance between Aβ production and degradation. However, the regulatory mechanisms of IDE are not yet fully understood. Therefore, uncovering additional IDE regulatory mechanisms will help elucidate the pathogenesis of AD and identify key therapeutic targets for this disease. This study revealed that global Krüppel-like factor 9-mutant (Klf9-/-) mice exhibited impaired cognitive function. Additionally, we found that Klf9 expression in hippocampal tissue was reduced in APPswe/PS1dE9 (APP/PS1) mice. This study also showed that Klf9 stimulates IDE expression and promotes the Aβ degradation process by directly binding to IDE and activating its transcription. Silencing IDE blocked the Klf9-induced Aβ degradation process. We stereotactically injected an adeno-associated virus to selectively overexpress IDE (AAV-IDE) in the hippocampal neurons of Klf9-/- mice and found that the overexpression of IDE in hippocampal neurons ameliorated cognitive deficits and reduced the Aβ content in Klf9-/- mice. Additionally, we also stereotactically injected AAV-Klf9 into the hippocampal neurons of APP/PS1 mice and found that overexpression of Klf9 in hippocampal neurons ameliorated cognitive deficits and reduced Aβ levels in APP/PS1 mice. These findings suggest that downregulation of Klf9 may be a key factor in AD progression, as it reduces Aβ clearance by decreasing IDE expression. Overexpression or activation of Klf9 may be a potential strategy for preventing the pathogenesis of AD.

Insulin resistance: fueling oxidative stress and neurodegeneration

The growing prevalence of age-related neurodegenerative diseases is a consequence of population aging and demands urgent treatment strategies. This literature review aims to provide a comprehensive overview of the contribution of oxidative stress and insulin resistance in neurodegenerative diseases, specifically Alzheimer's disease (AD). In addition, current therapeutic approaches to treat oxidative stress and insulin resistance in this age-related neurodegenerative disease will be discussed. AD is the most prevalent form of neurodegenerative disease and is marked at early stages by oxidative stress and insulin resistance. Results indicate that insulin resistance may be central in generating oxidative stress and exacerbating AD hallmarks. In turn, insulin resistance can be influenced by other factors, including amyloid beta (Aβ), impaired biliverdin-reductase A (BVR-A) activity, and the gut microbiota. Defective insulin signaling in the brain comes with consequences ranging from declined cognitive functions, impaired autophagy, mitochondrial dysfunction, hyperphosphorylation of Tau, and increased Aβ production. Multiple therapeutic approaches that target oxidative stress or brain insulin resistance, such as antioxidant supplementation and anti-diabetic drugs, have mostly been inconclusive, except for intranasal insulin. Positive results have been obtained in clinical trials using nasal delivery devices to administer insulin; however, results are inconsistent across studies likely due to inconsistencies in the delivery method. Future investigations should focus on investigating the molecular link between oxidative stress, insulin resistance, and AD to address current knowledge gaps. Moreover, more focus should be given to optimizing the reliability and efficacy of nasal delivery devices before considering such an approach viable to treat neurodegenerative diseases.

Glycation in Alzheimer's Disease and Type 2 Diabetes: The Prospect of Dual Drug Approaches for Therapeutic Interventions

As global life expectancy increases, the prevalence of neurodegenerative diseases like Alzheimer's disease (AD) continues to rise. Since therapeutic options are minimal, a deeper understanding of the pathophysiology is essential for improved diagnosis and treatments. AD is marked by the aggregation of Aβ proteins, tau hyperphosphorylation, and progressive neuronal loss, though its precise origins remain poorly understood. Meanwhile, type 2 diabetes mellitus (T2DM) is characterized by chronic hyperglycemia, leading to the formation of advanced glycation end products (AGEs), which are implicated in tissue damage and neurotoxicity. These AGEs can be resistant to proteolysis and, therefore, accumulate, exacerbating AD pathology and accelerating neurodegeneration. Insulin resistance, a hallmark of T2DM, further complicates AD pathogenesis by promoting tau hyperphosphorylation and Aβ plaque accumulation. Additionally, gut microbiome dysbiosis in T2DM fosters AGE accumulation and neuroinflammation, underscoring the intricate relationship between metabolic disorders, gut health, and neurodegenerative processes. This complex interplay presents both a challenge and a potential avenue for therapeutic intervention. Emerging evidence suggests that antidiabetic medications may offer cognitive benefits in AD, as well as in other neurodegenerative conditions, pointing to a shared pathophysiology. Thus, we posit that targeting AGEs, insulin signaling, and gut microbiota dynamics presents promising opportunities for innovative treatment approaches in AD and T2DM.

Impact of chronic hyperglycemia and high-fat diet on Alzheimer's disease-related pathology in CX3CR1 knockout mice

Diabetes mellitus (DM), obesity, and metabolic syndrome are related disorders with wide-ranging and devastating effects that are comorbid with many other diseases. Clinical and epidemiological studies have found that type II diabetes mellitus (T2DM), including chronic hyperglycemia and hyperinsulinemia, significantly increases the risk of Alzheimer's disease (AD) and other forms of dementia in the elderly. Insulin has slightly different functions in the peripheral body than in the central nervous system and the dysregulation of these functions may contribute to the onset and progression of late-life neurodegenerative disease. To investigate cognitive function and AD-related disease pathology, we utilized two different models of key features of diabetes, one model characterized by hyperglycemia resulting from a diabetogenic compound that selectively targets insulin-producing pancreatic β-cells, and the other model based on diet-induced obesity. Additionally, these diabetic models were combined with fractalkine receptor knockout mice (CX3CR1-/-), a genetic mouse model of inflammation, to explore the additive effects of multiple AD risk factors. The CX3CR1 receptor has been implicated in modulating neuroinflammation associated with AD, and its dysregulation can exacerbate metabolic disturbances and neurodegenerative markers. We found that diabetic-status, regardless of whether it was drug- or diet-induced, resulted in profound impairments in learning and memory and AD-related alterations within the hippocampus.

Chaperone-mediated autophagy, heat shock protein 70, and serotonin: novel targets of beta-hydroxybutyrate in HFFD/LPS-induced sporadic Alzheimer's disease model

Sporadic Alzheimer's disease (AD), which accounts for the majority of cases, is sturdily influenced by lifestyle factors such as dietary habits, obesity, and diabetes, leading to its classification as Type 3 diabetes. To model this pathological link, our AD-like model was developed by feeding Wistar male rats a high-fat diet with fructose in drinking water (HFFD) for 8 weeks, followed by a single dose of lipopolysaccharide (LPS). This group was compared with a normal control group fed a standard diet and a β-hydroxybutyrate (BHB)-treated group (125 mg/kg, p.o.), administered starting 3 h after LPS and continuing for 1 week. The results demonstrate that BHB treatment illuminated cognitive gains, as indicated by the Y-maze, Morris water maze, and novel object recognition tests. In addition, it preserved hippocampal cytoarchitecture, reduced neurodegeneration, and attenuated amyloid plaques and phosphorylated Tau deposition. Cellularly, BHB restored critical molecular mechanisms, including increased lysosomal-associated membrane protein 2A (LAMP2A) hippocampal content as the main marker of chaperone-mediated autophagy (CMA), along with the chaperon protein Hsp70. Moreover, BHB alleviated neuroinflammation by inhibiting the nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) inflammasome activation alongside the downstream targets cleaved caspase-1 and IL-1β/IL-18 cytokines. BHB also reduced pyroptotic markers, caspase-11 and gasdermin-N, and microglia-induced inflammation as it shifted microglial polarization toward the neuroprotective M2 phenotype. Finally, BHB normalized hippocampal neurotransmitter levels of the inhibited acetylcholine and serotonin. These findings support BHB as a promising, multifaceted treatment for AD, highlighting the roles of CMA, Hsp70, and 5-HT in slowing disease progression and improving cognitive function.

Alzheimer's Disease and Frontotemporal Dementia: A Review of Pathophysiology and Therapeutic Approaches

Alzheimer's disease (AD) is a devastating form of dementia, with the number of affected individuals rising sharply. The main hallmarks of the disease include amyloid-beta plaque deposits and neurofibrillary tangles consisting of hyperphosphorylated tau protein, besides other pathological features that contribute to the disease's complexity. The causes of sporadic AD are multifactorial and mostly age-related and involve risk factors such as diabetes and cardiovascular or cerebrovascular disorders. Frontotemporal dementia (FTD) is another type of dementia characterized by a spectrum of behaviors, memory, and motor abnormalities and associated with abnormal depositions of protein aggregation, including tau protein. Currently approved medications are symptomatic, and no disease-modifying therapy is available to halt the disease progression. Therefore, the development of multi-targeted therapeutic approaches could hold promise for the treatment of AD and other neurodegenerative disorders, including tauopathies. In this article, we will discuss the pathophysiology of AD and FTD, the proposed hypotheses, and current therapeutic approaches, highlighting the development of novel drug candidates and the progress of clinical trials in this field of research.

Anti-diabetic drug pioglitazone reduces Islet amyloid aggregation overload in the Drosophila neuronal cells

Amyloid-proteinopathy is observed in type 2 diabetes, where Islet amyloid polypeptide is secreted atypically and impedes cellular homeostasis. The thiazolidinediones family is reported to influence amyloid-beta aggregations. However, research on drug-based stimulation of insulin signaling to alleviate Islet amyloid aggregations is lacking. To understand the impact of pioglitazone on islet amyloid aggregation, we conducted an in vivo and in silico analysis. For in vivo analysis, we generated a transgenic Drosophila harboring the preproform of human Islet amyloid polypeptide (IAPP) that can be ectopically expressed in a spatio-temporal manner. We show that the unprocessed form of IAPP also has the propensity to form aggregates and cause degeneration. Pioglitazone feeding effectively reduces the burden of Islet amyloid aggregations in the larval brain. In silico analysis shows that there is a higher protein-ligand binding energy for IAPP with pioglitazone than amyloid-beta. These results suggests that pioglitazone might be repurposed as a drug to cure islet amyloidogenesis.

Peripheral Inflammation and Insulin Resistance: Their Impact on Blood-Brain Barrier Integrity and Glia Activation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory impairment, and synaptic dysfunction. The accumulation of amyloid beta (Aβ) plaques and hyperphosphorylated tau protein leads to neuronal dysfunction, neuroinflammation, and glial cell activation. Emerging evidence suggests that peripheral insulin resistance and chronic inflammation, often associated with type 2 diabetes (T2D) and obesity, promote increased proinflammatory cytokines, oxidative stress, and immune cell infiltration. These conditions further damage the blood-brain barrier (BBB) integrity and promote neurotoxicity and chronic glial cell activation. This induces neuroinflammation and impaired neuronal insulin signaling, reducing glucose metabolism and exacerbating Aβ accumulation and tau hyperphosphorylation. Indeed, epidemiological studies have linked T2D and obesity with an increased risk of developing AD, reinforcing the connection between metabolic disorders and neurodegeneration. This review explores the relationships between peripheral insulin resistance, inflammation, and BBB dysfunction, highlighting their role in glial activation and the exacerbation of AD pathology.

The Impact of Exercise Training on the Brain and Cognition in Type 2 Diabetes, and its Physiological Mediators: A Systematic Review

BACKGROUND

Type 2 diabetes (T2DM) affects brain structure and function, and is associated with an increased risk of dementia and mild cognitive impairment. It is known that exercise training has a beneficial effect on cognition and brain structure and function, at least in healthy people, but the impact of exercise training on these aspects remains to be fully elucidated in patients with T2DM.

OBJECTIVE

To determine the impact of exercise training on cognition and brain structure and function in T2DM, and identify the involved physiological mediators.

METHODS

This paper systematically reviews studies that evaluate the effect of exercise training on cognition in T2DM, and aims to indicate the most beneficial exercise modality for improving or preserving cognition in this patient group. In addition, the possible physiological mediators and targets involved in these improvements are narratively described in the second part of this review. Papers published up until the 14th of January 2025 were searched by means of the electronic databases PubMed, Embase, and Web of Science. Studies directly investigating the effect of any kind of exercise training on the brain or cognition in patients with T2DM, or animal models thereof, were included, with the exception of human studies assessing cognition only at one time point, and studies combining exercise training with other interventions (e.g. dietary changes, cognitive training, etc.). Study quality was assessed by means of the TESTEX tool for human studies, and the CAMARADES tool for animal studies.

RESULTS

For the systematic part of the review, 22 papers were found to be eligible. 18 out of 22 papers (81.8%) showed a significant positive effect of exercise training on cognition in T2DM, of which two studies only showed significant improvements in the minority of the cognitive tests. Four papers (18.2%) could not find a significant effect of exercise on cognition in T2DM. Resistance and endurance exercise were found to be equally effective for achieving cognitive improvement. Machine-based power training is seemingly more effective than resistance training with body weight and elastic bands to reach cognitive improvement. In addition, BDNF, lactate, leptin, adiponectin, GSK3β, GLP-1, the AMPK/SIRT1 pathway, and the PI3K/Akt pathway were identified as plausible mediators directly from studies investigating the effect of exercise training on brain structure and function in T2DM. Via these mediators, exercise training induces multiple beneficial brain changes, such as increased neuroplasticity, increased insulin sensitivity, and decreased inflammation.

CONCLUSION

Overall, exercise training beneficially affects cognition and brain structure and function in T2DM, with resistance and endurance exercise having similar effects. However, there is a need for additional studies, and more methodological consistency between different studies in order to define an exercise program optimal for improving cognition in T2DM. Furthermore, we were able to define several mediators involved in the effect of exercise training on cognition in T2DM, but further research is necessary to unravel the entire process.

Associations between triglyceride-glucose indices and delirium risk in critically ill patients with acute kidney injury: a retrospective study

Background

Delirium frequently occurs in individuals with acute kidney injury (AKI), leading to serious adverse outcomes. However, there are currently no predictors of early intervention for delirium in clinical practice. This study aims to investigate whether a correlation exists between TyG indices and the clinical symptoms of delirium in patients with AKI.

Methods

Eligible participants diagnosed with AKI from the Medical Information Mart for Intensive Care-IV (MIMIC-IV) database were categorised based on their TyG index. The primary outcome of this study was the incidence of delirium. The TyG indices were quartile and Kaplan-Meier (K-M) cumulative curve was conducted to compare the consequence of each group. Cox proportional hazards and restricted cubic spline (RCS) analyses were employed to explore the associations between TyG indices and outcomes. To mitigate potential biases, a no-replacement propensity score matching (PSM) approach was employed. Subgroup analyses were conducted to explore differences across various demographic and clinical categories.

Results

A positive correlation between the quartile groupings of TyG-AVG and an increased cumulative incidence of delirium in individuals with severe AKI, as demonstrated through K-M cumulative curves and Cox regression analysis. Regarding the TyG index, patients in the 4th group displayed the highest hazard of delirium in both of the methods mentioned above. Furthermore, RCS analysis indicated that the interaction between the two variables is approximately linear. Subgroup analyses revealed that the effects of both metrics remained consistent across most examined subgroups.

Conclusion

Higher TyG indices were clearly associated with the incidence of delirium in patients with severe AKI. These indices could serve as valuable tools for identifying delirium-prone individuals with AKI.

Ginsenoside CK modulates glucose metabolism via PPARγ to ameliorate SCOP-induced cognitive dysfunction

Ginsenoside compound K (CK) exhibits neuroprotective properties; however, the underlying mechanisms behind these effects have not been investigated thoroughly. CK is the primary active compound derived from ginseng and is metabolized in the gut. It enhances neuronal function by modulating the gut microflora. Therefore, the present study aimed to elucidate the mechanism through which CK enhances cognitive function, employing gut microbiome and microarray analyses. The results revealed that CK upregulated the expression of peroxisome proliferator-activated receptor gamma (PPARγ), suppressed amyloid-β (Aβ) aggregation in hippocampal neurons, and influenced the expression of cyclin-dependent kinase-5 (CDK5), (including insulin receptor substrate 2) IRS2, insulin-degrading enzyme (IDE), glycogen synthase kinase-3 beta (GSK-3β), glucose transporter type 1 (GLUT1), and glucose transporter type 3 (GLUT3) proteins. These proteins play crucial roles in regulating brain glucose metabolism, increasing neuronal energy, and reducing neuronal apoptosis, thereby ameliorating cognitive impairment in mice.

Amelioration of Astrocytic Dysfunction via AQP4/LRP1 Pathway by Zizania latifolia and Tricin in C6 Cells Exposed to Amyloid β and High-Dose Insulin and in Mice Treated with Scopolamine

Zizania latifolia and its bioactive compound tricin have been recognized for their anti-inflammatory, anti-allergic, and anti-aging properties. However, the impact of Z. latifolia extract (ZLE) and tricin on astrocyte dysfunction, particularly related to disruptions in the amyloid β (Aβ) clearance pathway, has not been extensively studied. This research aims to explore the regulatory effects of ZLE and tricin on astroglial dysfunction, utilizing astrocytic differentiated C6 cells (passages 75~85) subjected to Aβ and high-dose insulin, as well as scopolamine-induced mice. Results revealed that ZLE (500 μg/ml) and tricin (1 μg/ml) significantly upregulated the expression of astrocyte proteins GFAP and AQP4, brain-derived neurotrophic factor (BDNF), low-density lipoprotein receptor-related protein 1 (LRP1), and matrix metalloproteinases (MMPs) in C6 cells treated with Aβ and high-dose insulin. Furthermore, oral administration of ZLE (100 and 300 mg/kg) and tricin (0.3 mg/kg) in mice led to an increase in acetylcholine (ACh) levels and upregulation of insulin-degrading enzyme (IDE), LRP1, and MMPs, while reducing the levels of acetylcholinesterase (AChE), Aβ and ApoE4. These findings suggest that ZLE and tricin may ameliorate Aβ and high-dose insulin-induced astrocyte dysfunction in C6 cells and scopolamine-treated mice, potentially through the AQP4/LRP1 pathway.

Succinylation enables IDE to act as a hub of larval tissue destruction and adult tissue reconstruction during insect metamorphosis

Metamorphosis is an important way for insects to adapt to the environment. In this process, larval tissue destruction regulated by 20-hydroxyecdysone (20E) and adult tissue reconstruction regulated by insulin-like peptides (ILPs) occur simultaneously, but the detailed mechanism is still unclear. Here, the results of succinylome, subcellular localization, and protein interaction analysis show that non-succinylated insulin-degrading enzyme (IDE) localizes in the cytoplasm, binds to insulin-like growth factor 2 (IGF-2-like), and degrades it. When the metamorphosis is initiated, 20E up-regulated carnitine palmitoyltransferase 1A (Cpt1a) through transcription factor Krüppel-like factor 15 (KLF15), thus increasing the level of IDE succinylation on K179. Succinylated IDE translocated from cytoplasm to nucleus, combined with ecdysone receptor to promote 20E signaling pathway, causing larval tissue destruction, while IGF-2-like was released to promote adult tissue proliferation. That is, succinylation alters subcellular localization of IDE so that it can bind to different target proteins and act as a hub of metamorphosis.

Alterations of amino acids in older adults with Alzheimer's Disease and Vascular Dementia

Metabolomics provide a promising tool for understanding dementia pathogenesis and identifying novel biomarkers. This study aimed to identify amino acid biomarkers for Alzheimer's Disease (AD) and Vascular Dementia (VD). By amino acid metabolomics, the concentrations of amino acids were determined in the serum of AD and VD patients as well as age-matched healthy controls. Several differences in the concentration of amino acids were observed in AD patients compared to both healthy controls and VD patients. However, no significant distinction was found between healthy controls and VD patients. Considering comorbidities, cystine levels were higher in AD than in VD among non-diabetic patients, but not in those with diabetes. Notably, creatine, spermidine, cystine, and tyrosine demonstrated favorable results in decision curve analyses and good discriminative performances, suggesting their potential for clinical application. These fundings give novel perspectives of serum amino acids for predicting metabolic pathways in AD and VD pathogenesis.

Associations Between Diabetes Mellitus and Neurodegenerative Diseases

Diabetes mellitus (DM) and neurodegenerative diseases/disturbances are worldwide health problems. The most common chronic conditions diagnosed in persons 60 years and older are type 2 diabetes mellitus (T2DM) and cognitive impairment. It was found that diabetes mellitus is a major risk for cognitive decline, dementia, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Different mechanisms of associations between these diseases and diabetes mellitus have been suggested. For example, it is postulated that an impaired intracellular insulin signaling pathway, together with hyperglycemia and hyperinsulinemia, may cause pathological changes, such as dysfunction of the mitochondria, oxidative stress inflammatory responses, etc. The association between diabetes mellitus and neurodegenerative diseases, as well as the mechanisms of these associations, needs further investigation. The aim of this review is to describe the associations between diabetes mellitus, especially type 1 (T1DM) and type 2 diabetes mellitus, and selected neurodegenerative diseases, i.e., Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. Suggested mechanisms of these associations are also described.

Characterization and modulation of human insulin degrading enzyme conformational dynamics to control enzyme activity

Insulin degrading enzyme (IDE) is a dimeric 110 kDa M16A zinc metalloprotease that degrades amyloidogenic peptides diverse in shape and sequence, including insulin, amylin, and amyloid-β, to prevent toxic amyloid fibril formation. IDE has a hollow catalytic chamber formed by four homologous subdomains organized into two ~55 kDa N- and C- domains (IDE-N and IDE-C, respectively), in which peptides bind, unfold, and are repositioned for proteolysis. IDE is known to transition between a closed state, poised for catalysis, and an open state, able to release cleavage products and bind new substrate. Here, we present five cryoEM structures of the IDE dimer at 3.0-4.1 Å resolution, obtained in the presence of a sub-saturating concentration of insulin. Analysis of the heterogeneity within the particle populations comprising these structures combined with all-atom molecular dynamics (MD) simulations permitted a comprehensive characterization of IDE conformational dynamics. Our analysis identified the structural basis and key residues for these dynamics that were not revealed by IDE static structures. Notably arginine-668 serves as a molecular latch mediating the open-close transition and facilitates key protein motions through charge-swapping interactions at the IDE-N/C interface. Our size-exclusion chromatography-coupled small-angle X-ray scattering and enzymatic assays of an arginine-668 to alanine mutant indicate a profound alteration of conformational dynamics and catalytic activity. Taken together, this work highlights the power of integrating experimental and computational methodologies to understand protein dynamics, offers the molecular basis of unfoldase activity of IDE, and provides a new path forward towards the development of substrate-specific modulators of IDE activity.

Impaired insulin signaling and diet-induced type 3 diabetes pathophysiology increase amyloid β expression in the Drosophila model of Alzheimer's disease

Compelling evidence has strongly linked unregulated sugar levels to developing Alzheimer's disease, suggesting Alzheimer's to be 'diabetes of the brain or 'type 3 diabetes. Insulin resistance contributes to the pathogenesis of Alzheimer's disease due to uncontrolled and unchecked blood glucose, though the interrelatedness between Alzheimer's disease and type 2 diabetes is debatable. Here we describe the consequences of inducing type 3 diabetes by feeding Drosophila on a high sucrose diet, which effectively mimics the pathophysiology of diabetes. A high sucrose diet increases glycogen and lipid accumulation. Inducing type 3 diabetes worsened neurodegeneration and accelerated disease progression in Drosophila expressing the Alzheimer's Familial Arctic mutation. High sucrose milieu also negatively affected locomotor ability and reduced the lifespan in the Alzheimer's disease model of Drosophila. The results showed that creating diabetic conditions by using insulin receptor (InR) knockdown in the eyes of Drosophila led to a degenerative phenotype, indicating a genetic interaction between the insulin signaling pathway and Alzheimer's disease. The expression of PERK reflects disruption in the endoplasmic reticulum homeostasis due to amyloid-β (Aβ) under a high sucrose diet. These observations demonstrated an association between type 3 diabetes and Alzheimer's disease, and that a high sucrose environment has a degenerating effect on Alzheimer's disease condition.

PFOS sub-chronic exposure selectively activates Aβ clearance pathway to improve the cognitive ability of AD mice

Perfluorooctane sulfonate (PFOS), an emerging persistent organic pollutant, has been controversial in its impact on cognitive functions. Our previous research has confirmed that the sub-chronic PFOS exposure leads to neuronal apoptosis in the cerebral cortex, impairing cognitive functions in normal mice. However, our current study presents a surprising finding: sub-chronic exposure to PFOS effectively reduces cognitive impairments in Alzheimer's disease (AD) mice and significantly retards the disease's progression. Our results indicate that PFOS exposure upregulates the expression level of insulin-degrading enzyme (IDE) in the prefrontal cortex (PFC) of AD mice, thereby selectively enhancing the amyloid-beta (Aβ) clearance pathway without affecting the Aβ production. Moreover, PFOS exposure inhibits microglial proliferation and reduces inflammatory cytokines levels in the PFC of AD mice, providing further supporting for the pivotal role of IDE in attenuating AD progression under PFOS exposure. Collectively, our study is the first to demonstrate that sub-chronic PFOS exposure can alleviates cognitive impairments in AD pathology, with the IDE-mediated Aβ clearance pathway potentially playing a critical role.

Neprilysin-Mediated Amyloid Beta Clearance and Its Therapeutic Implications in Neurodegenerative Disorders

Neprilysin (NEP) is a neutral endopeptidase, important for the degradation of amyloid beta (Aβ) peptides and other neuropeptides, including enkephalins, substance P, and bradykinin, in the brain, that influences various physiological processes such as blood pressure homeostasis, pain perception, and neuroinflammation. NEP breaks down Aβ peptides into smaller fragments, preventing the development of detrimental aggregates such as Aβ plaques. NEP clears Aβ plaques predominantly by enzymatic breakdown in the extracellular space. However, NEP activity may be regulated by a variety of factors, including its expression and activity levels as well as interactions with other proteins or substances present in the brain. The Aβ de novo synthesis results from the amyloidogenic and nonamyloidogenic processing of the amyloid precursor protein (APP). In addition to Aβ synthesis, enzymatic degradation and various clearance pathways also contribute to the degradation of the monomeric form of Aβ peptides in the brain. Higher production, dysfunction of degradation enzymes, defective clearance mechanisms, intracellular accumulation of phosphorylated tau proteins, and extracellular deposition of Aβ are hallmarks of neurodegenerative diseases. Strategies for promoting NEP levels or activity, such as pharmaceutical interventions or gene therapy procedures, are being studied as possible therapies for neurodegenerative diseases including Alzheimer's disease. Therefore, in this perspective, we discuss the recent developments in NEP-mediated amyloidogenic and plausible mechanisms of nonamyloidogenic clearance of Aβ. We further highlight the current therapeutic interventions such as pharmaceutical agents, gene therapy, monoclonal antibodies, and stem-cell-based therapies targeting NEP for the management of neurodegenerative disorders.

The Promising Potency of Sodium-Glucose Cotransporter 2 Inhibitors in the Prevention of and as Treatment for Cognitive Impairment Among Type 2 Diabetes Patients

Type 2 diabetes mellitus (T2DM), accounting for the majority of diabetes mellitus prevalence, is associated with an increased risk of cognition decline and deterioration of cognition function in diabetic patients. The sodium-glucose cotransporter 2 (SGLT2), located in the renal proximal tubule, plays a role in urine glucose reabsorption. SGLT2 inhibitors (SGLT2i), have shown potential benefits beyond cardiac and renal improvement in preventing and treating cognitive impairment (CI), including mild cognitive impairment, Alzheimer's disease and vascular dementia in T2DM patients. Studies suggest that SGLT2i may ameliorate diabetic CI through metabolism pathways, inflammation, oxidative stress, neurotrophic factors and AChE inhibition. Clinical trials and meta-analyses have reported significant and insignificant results. Given their vascular effects, SGLT2i may offer unique protection against vascular CI. This review compiles mechanisms and clinical evidence, emphasizing the need for future analysis, evaluation, trials and meta-analyses to verify and recommend optimal SGLT2i selection and dosage for specific patients.

Dysregulation of energy metabolism in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Its etiology and associated mechanisms are still unclear, which largely hinders the development of AD treatment strategies. Many studies have shown that dysregulation of energy metabolism in the brain of AD is closely related to disease development. Dysregulation of brain energy metabolism in AD brain is associated with reduced glucose uptake and utilization, altered insulin signaling pathways, and mitochondrial dysfunction. In this study, we summarized the relevant pathways and mechanisms regarding the dysregulation of energy metabolism in AD. In addition, we highlight the possible role of mitochondrial dysfunction as a central role in the AD process. A deeper understanding of the relationship between energy metabolism dysregulation and AD may provide new insights for understanding learning memory impairment in AD patients and in improving AD prevention and treatment.

Does Metabolic Manager Show Encouraging Outcomes in Alzheimer's?: Challenges and Opportunity for Protein Tyrosine Phosphatase 1b Inhibitors

Protein tyrosine phosphatase 1b (PTP1b) is a member of the protein tyrosine phosphatase (PTP) enzyme group and encoded as PTP1N gene. Studies have evidenced an overexpression of the PTP1b enzyme in metabolic syndrome, anxiety, schizophrenia, neurodegeneration, and neuroinflammation. PTP1b inhibitor negatively regulates insulin and leptin pathways and has been explored as an antidiabetic agent in various clinical trials. Notably, the preclinical studies have shown that recuperating metabolic dysfunction and dyshomeostasis can reverse cognition and could be a possible approach to mitigate multifaceted Alzheimer's disease (AD). PTP1b inhibitor thus has attracted attention in neuroscience, though the development is limited to the preclinical stage, and its exploration in large clinical trials is warranted. This review provides an insight on the development of PTP1b inhibitors from different sources in diabesity. The crosstalk between metabolic dysfunction and insulin insensitivity in AD and type-2 diabetes has also been highlighted. Furthermore, this review presents the significance of PTP1b inhibition in AD based on pathophysiological facets, and recent evidences from preclinical and clinical studies.

Tyrosine modifications of insulin-degrading enzyme enable favorable control of substrate specificity for both Alzheimer's disease and type-2 diabetes mellitus

Insulin-degrading enzyme (IDE) cleaves amyloid beta (Aβ), insulin, and other bioactive peptides. Because Aβ and insulin are closely related to Alzheimer's disease (AD) and type-2 diabetes mellitus (T2DM), respectively, IDE is a candidate drug target for treating both AD and T2DM. However, the activity of IDE has opposing effects, including decreasing AD risk by degrading Aβ and increasing T2DM risk by degrading insulin. The opposed substrate specificity is associated with the exo- and active sites containing Tyr314 and Tyr831 residues, the plausible modification targets for controlling substrate specificity. In this study, we used a tyrosine-specific modification regent, Cookson reagent (4-phenyl-1,2,4-triazoline-3,5-dione, PTAD), for IDE and examined the degradation activities on Aβ40 and insulin. Fifteen tyrosine residues, including Tyr314 and Tyr831, were modified by PTAD. After incubation with PTAD-modified IDE for 3 days, insulin remained intact, whereas Aβ40 was completely degraded. This favorable change of substrate specificity was also observed in the mixture of Aβ40 and insulin, suggesting that tyrosine modification of IDE might be a therapeutic strategy for AD and T2DM.

Sleep deprivation leads to non-adaptive alterations in sleep microarchitecture and amyloid-β accumulation in a murine Alzheimer model

Impaired sleep is a common aspect of aging and often precedes the onset of Alzheimer's disease. Here, we compare the effects of sleep deprivation in young wild-type mice and their APP/PS1 littermates, a murine model of Alzheimer's disease. After 7 h of sleep deprivation, both genotypes exhibit an increase in EEG slow-wave activity. However, only the wild-type mice demonstrate an increase in the power of infraslow norepinephrine oscillations, which are characteristic of healthy non-rapid eye movement sleep. Notably, the APP/PS1 mice fail to enhance norepinephrine oscillations 24 h after sleep deprivation, coinciding with an accumulation of cerebral amyloid-β protein. Proteome analysis of cerebrospinal fluid and extracellular fluid further supports these findings by showing altered protein clearance in APP/PS1 mice. We propose that the suppression of infraslow norepinephrine oscillations following sleep deprivation contributes to increased vulnerability to sleep loss and heightens the risk of developing amyloid pathology in early stages of Alzheimer's disease.

The Icelandic Mutation (APP-A673T) Is Protective against Amyloid Pathology In Vivo

A previous epidemiological study in Northern Europe showed that the A673T mutation (Icelandic mutation) in the amyloid precursor protein gene (APP) can protect against Alzheimer's disease (AD). While the effect of the A673T mutation on APP processing has been investigated primarily in vitro, its in vivo impact has not been evaluated. This is mainly because most existing AD mouse models carry the Swedish mutation. The Swedish and Icelandic mutations are both located near the β-cleavage site, and each mutation is presumed to have the opposite effect on β-cleavage. Therefore, in the AD mouse models with the Swedish mutation, its effects could compete with the effects of the Icelandic mutation. Here, we introduced the A673T mutation into App knock-in mice devoid of the Swedish mutation (AppG-F mice) to avoid potential deleterious effects of the Swedish mutation and generated AppG-F-A673T mice. APP-A673T significantly downregulated β-cleavage and attenuated the production of Aβ and amyloid pathology in the brains of these animals. The Icelandic mutation also reduced neuroinflammation and neuritic alterations. Both sexes were studied. This is the first successful demonstration of the protective effect of the Icelandic mutation on amyloid pathology in vivo. Our findings indicate that specific inhibition of the APP-BACE1 interaction could be a promising therapeutic approach. Alternatively, the introduction of the disease-protective mutation such as APP-A673T using in vivo genome editing technology could be a novel treatment for individuals at high risk for AD, such as familial AD gene mutation carriers and APOE ε4 carriers.

Insulin-degrading enzyme regulates insulin-directed cellular autoimmunity in murine type 1 diabetes

Type 1 diabetes results from the destruction of pancreatic beta cells by autoreactive T cells. As an autoantigen with extremely high expression in beta cells, insulin triggers and sustains the autoimmune CD4+ and CD8+ T cell responses and islet inflammation. We have previously shown that deficiency for insulin-degrading enzyme (IDE), a ubiquitous cytosolic protease with very high affinity for insulin, induces endoplasmic reticulum (ER) stress and proliferation in islet cells and protects non-obese diabetic mice (NOD) from diabetes. Here we wondered whether IDE deficiency affects autoreactive CD8+ T cell responses to insulin and thereby immune pathogenesis in NOD mice. We find that Ide-/- NOD harbor fewer diabetogenic T cells and reduced numbers of CD8+ T cells recognizing the dominant autoantigen insulin and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP). Using in vitro digestions and cellular antigen presentation assays, we show that generation of the dominant insulin epitope B15-23 involves both the proteasome and IDE. IDE deficiency attenuates MHC-I presentation of the immunodominant insulin epitope by beta cells to cognate CD8+ T cells. Consequently, Ide-/- islets display reduced susceptibility to autoimmune destruction upon grafting, and to killing by insulin-specific CD8+ T cells. Moreover, Ide-/- mice are partly resistant to disease transfer by CD8+ T cells specific for insulin but not for IGRP. Thus, IDE has a dual role in beta cells, regulating ER stress and proliferation while at the same time promoting insulin-directed autoreactive CD8+ T cell responses.

Integrated in-silico and in-vitro assessments of HDAC6 inhibitor efficacy in mitigating amyloid beta pathology in Alzheimer's disease

Alzheimer's disease, marked by memory loss and cognitive decline, is associated with amyloid-beta (Aβ) peptide accumulation in the brain. The enzyme neprilysin (NEP), crucial for Aβ degradation, decreases with age and in sporadic Alzheimer's disease, leading to increased Aβ build-up. This study hypothesized the targeting of enzyme HDAC6, believed to influence NEP activity. An in-silico study was conducted using an FDA-approved drug database, with the focus on their interaction with the HDAC6 structure. Among tested ligands, Panobinostat showed the most favourable interaction with HDAC6. In-vitro experiments on the SH-SY5Y neuronal cell line confirmed these findings, with Panobinostat inhibiting HDAC6, enhancing NEP levels, and reducing Aβ load. The study suggests Panobinostat as a potential Alzheimer's therapeutic agent, mitigating Aβ accumulation via NEP upregulation. Further research is required for comprehensive understanding and validation.Communicated by Ramaswamy H. Sarma.

Farnesylthiosalicylic Acid Through Inhibition of Galectin-3 Improves Neuroinflammation in Alzheimer Disease via Multiple Pathways

AIMS

Many factors affect the neuroinflammatory response in patients with Alzheimer disease (AD). Galectin-3 (Gal-3) is closely related to microglial activation in the nervous system and can promote the aggregation of cancer cells in tumors. This study aimed to investigate the mechanism by which farnesylthiosalicylic acid (FTS) affects neuroinflammation in Aβ1-42 mice through Gal-3.

METHODS

We used the Morris water maze, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence to conduct our study.

RESULTS

FTS reduced the levels of proinflammatory factors and microglial activation in Aβ1-42 mice. FTS inhibited total and membrane expression levels of Gal-3 in Aβ1-42 mice, and the anti-inflammatory effect of FTS was reversed by Gal-3-adeno-associated viral (AAV). FTS reduced the expression levels of toll-like receptors (TLRs), effects that were reversed by Gal-3-AAV. Moreover, FTS ameliorated Aβ oligomerization and accumulation in Aβ1-42 mice, effects that were also reversed by Gal-3-AAV. FTS, through the inhibition of the Gal-3-c-Jun N-terminal kinase (JNK) pathway, reduced PS1 expression; in addition, inhibition of Gal-3 increased the Aβ-degrading enzymes in Aβ1-42 mice. FTS-induced improvements in cognition in Aβ1-42 mice were reversed by Gal-3-AAV.

CONCLUSION

FTS may through inhibiting Gal-3 reduce the expression of TLR4 and CD14 and alleviate Aβ pathology, downregulating Aβ-stimulated TLR2, TLR4, and CD14 expression, and thus alleviate neuroinflammation in Aβ1-42 mice.

Case report: Double mutations in a patient with early-onset Alzheimer's disease in China, PSEN2 and IDE variants

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by gradual cognitive decline. Early-onset Alzheimer's disease (EOAD) is defined as AD occurring before age 65. The main pathogenic gene variants associated with EOAD include PSEN1, PSEN2, and APP. IDE gene has been identified as a risk factor in the pathogenesis of AD. In this study, we report a 33-year-old male with mutations in the PSEN2 gene (c.640G > T, p.V214L) and IDE gene (c.782G > A, p.R261Q). PSEN2 V214L has been reported in five previous cases, and no reported cases have carried IDE R261Q. He had progressive memory decline, his sister carried the same gene mutations but had no clinical manifestations. Neuroimaging revealed mild cortical atrophy. The concentration of Aβ42 in cerebrospinal fluid (CSF) was obviously decreased. In silico predictive models suggested that these mutations are damaging. Our findings indicate that mutations in the PSEN2 and IDE genes may disrupt the normal functioning of their respective proteins, contributing to the pathogenesis of AD.

Somatostatin: Linking Cognition and Alzheimer Disease to Therapeutic Targeting

Over 4 decades of research support the link between Alzheimer disease (AD) and somatostatin [somatotropin-releasing inhibitory factor (SRIF)]. SRIF and SRIF-expressing neurons play an essential role in brain function, modulating hippocampal activity and memory formation. Loss of SRIF and SRIF-expressing neurons in the brain rests at the center of a series of interdependent pathological events driven by amyloid-β peptide (Aβ), culminating in cognitive decline and dementia. The connection between the SRIF and AD further extends to the neuropsychiatric symptoms, seizure activity, and inflammation, whereas preclinical AD investigations show SRIF or SRIF receptor agonist administration capable of enhancing cognition. SRIF receptor subtype-4 activation in particular presents unique attributes, with the potential to mitigate learning and memory decline, reduce comorbid symptoms, and enhance enzymatic degradation of Aβ in the brain. Here, we review the links between SRIF and AD along with the therapeutic implications. SIGNIFICANCE STATEMENT: Somatostatin and somatostatin-expressing neurons in the brain are extensively involved in cognition. Loss of somatostatin and somatostatin-expressing neurons in Alzheimer disease rests at the center of a series of interdependent pathological events contributing to cognitive decline and dementia. Targeting somatostatin-mediated processes has significant therapeutic potential for the treatment of Alzheimer disease.

The Dual Role of Amyloid Beta-Peptide in Oxidative Stress and Inflammation: Unveiling Their Connections in Alzheimer's Disease Etiopathology

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is currently the seventh leading cause of death worldwide. It is characterized by the extracellular aggregation of the amyloid β-peptide (Aβ) into oligomers and fibrils that cause synaptotoxicity and neuronal death. Aβ exhibits a dual role in promoting oxidative stress and inflammation. This review aims to unravel the intricate connection between these processes and their contribution to AD progression. The review delves into oxidative stress in AD, focusing on the involvement of metals, mitochondrial dysfunction, and biomolecule oxidation. The distinct yet overlapping concept of nitro-oxidative stress is also discussed, detailing the roles of nitric oxide, mitochondrial perturbations, and their cumulative impact on Aβ production and neurotoxicity. Inflammation is examined through astroglia and microglia function, elucidating their response to Aβ and their contribution to oxidative stress within the AD brain. The blood-brain barrier and oligodendrocytes are also considered in the context of AD pathophysiology. We also review current diagnostic methodologies and emerging therapeutic strategies aimed at mitigating oxidative stress and inflammation, thereby offering potential treatments for halting or slowing AD progression. This comprehensive synthesis underscores the pivotal role of Aβ in bridging oxidative stress and inflammation, advancing our understanding of AD and informing future research and treatment paradigms.

Insulin-degrading enzyme inhibition increases the unfolded protein response and favours lipid accumulation in the liver

BACKGROUND AND PURPOSE

Nonalcoholic fatty liver disease refers to liver pathologies, ranging from steatosis to steatohepatitis, with fibrosis ultimately leading to cirrhosis and hepatocellular carcinoma. Although several mechanisms have been suggested, including insulin resistance, oxidative stress, and inflammation, its pathophysiology remains imperfectly understood. Over the last decade, a dysfunctional unfolded protein response (UPR) triggered by endoplasmic reticulum (ER) stress emerged as one of the multiple driving factors. In parallel, growing evidence suggests that insulin-degrading enzyme (IDE), a highly conserved and ubiquitously expressed metallo-endopeptidase originally discovered for its role in insulin decay, may regulate ER stress and UPR.

EXPERIMENTAL APPROACH

We investigated, by genetic and pharmacological approaches, in vitro and in vivo, whether IDE modulates ER stress-induced UPR and lipid accumulation in the liver.

KEY RESULTS

We found that IDE-deficient mice display higher hepatic triglyceride content along with higher inositol-requiring enzyme 1 (IRE1) pathway activation. Upon induction of ER stress by tunicamycin or palmitate in vitro or in vivo, pharmacological inhibition of IDE, using its inhibitor BDM44768, mainly exacerbated ER stress-induced IRE1 activation and promoted lipid accumulation in hepatocytes, effects that were abolished by the IRE1 inhibitors 4μ8c and KIRA6. Finally, we identified that IDE knockout promotes lipolysis in adipose tissue and increases hepatic CD36 expression, which may contribute to steatosis.

CONCLUSION AND IMPLICATIONS

These results unravel a novel role for IDE in the regulation of ER stress and development of hepatic steatosis. These findings pave the way to innovative strategies modulating IDE to treat metabolic diseases.

Unraveling the mechanisms of hepatogenous diabetes and its therapeutic perspectives

The review focused mainly on the pathogenesis of hepatogenous diabetes (HD) in liver cirrhosis (LC). This review reveals parallels between the mechanisms of metabolic dysfunction observed in LC and type II diabetes (T2DM), suggesting a shared pathway leading to HD. It underscores the role of insulin in HD pathogenesis, highlighting key factors such as insulin signaling, glucose metabolism, insulin resistance (IR), and the influence of adipocytes. Furthermore, the impact of adipose tissue accumulation, fatty acid metabolism, and pro-inflammatory cytokines like Tumor necrosis factor-α (TNF-α) on IR are discussed in the context of HD. Altered signaling pathways, disruptions in the endocrine system, liver inflammation, changes in muscle mass and composition, and modifications to the gut microbiota collectively contribute to the complex interplay linking cirrhosis and HD. This study highlights how important it is to identify and treat this complex condition in cirrhotic patients by thoroughly analyzing the link between cirrhosis, IR, and HD. It also emphasizes the vitality of targeted interventions. Cellular and molecular investigations into IR have revealed potential therapeutic targets for managing and preventing HD.

Mechanisms Underlying Obesity-induced Aβ Accumulation in Alzheimer's Disease: A Qualitative Review

Epidemiological studies show that individuals with obesity are more likely to develop Alzheimer's disease (AD) than those who do not have obesity. However, the mechanisms underlying the relationship between obesity and AD are not entirely unclear. Here, we have reviewed and analyzed relevant articles published in the literature and found that obesity has correlation or potential increase in the levels of β-amyloid (Aβ) protein, which may explain why people with obesity are more likely to suffer from AD. Additionally, the published findings point to the roles of obesity-related metabolic disorders, such as diabetes, inflammation, oxidative stress, and imbalance in gut microbiota in Aβ accumulation caused by obesity. Therefore, in-depth experimental and clinical studies on these mechanisms in the future may help shed light on appropriate prevention and treatment strategies for AD, such as dietary changes and regular exercise to reverse or prevent obesity and related metabolic disorders.

Immunotherapy in Alzheimer's disease: focusing on the efficacy of gantenerumab on amyloid-β clearance and cognitive decline

Gantenerumab, a human monoclonal antibody (mAb), has been thought of as a potential agent to treat Alzheimer's disease (AD) by specifically targeting regions of the amyloid-β (Aβ) peptide sequence. Aβ protein accumulation in the brain leads to amyloid plaques, causing neuroinflammation, oxidative stress, neuronal damage, and neurotransmitter dysfunction, thereby causing cognitive decline in AD. Gantenerumab involves disrupting Aβ aggregation and promoting the breakdown of larger Aβ aggregates into smaller fragments, which facilitates the action of Aβ-degrading enzymes in the brain, thus slowing down the progression of AD. Moreover, Gantenerumab acts as an opsonin, coating Aβ plaques and enhancing their recognition by immune cells, which, combined with its ability to improve the activity of microglia, makes it an intriguing candidate for promoting Aβ plaque clearance. Indeed, the multifaceted effects of Gantenerumab, including Aβ disaggregation, enhanced immune recognition, and improved microglia activity, may position it as a promising therapeutic approach for AD. Of note, reports suggest that Gantenerumab, albeit its capacity to reduce or eliminate Aβ, has not demonstrated effectiveness in reducing cognitive decline. This review, after providing an overview of immunotherapy approaches that target Aβ in AD, explores the efficacy of Gantenerumab in reducing Aβ levels and cognitive decline.

Molecular mechanism and therapeutic strategy of bile acids in Alzheimer's disease from the emerging perspective of the microbiota-gut-brain axis

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β outside neurons and Tau protein inside neurons. Various pathological mechanisms are implicated in AD, including brain insulin resistance, neuroinflammation, and endocrinal dysregulation of adrenal corticosteroids. These factors collectively contribute to neuronal damage and destruction. Recently, bile acids (BAs), which are metabolites of cholesterol, have shown neuroprotective potential against AD by targeting the above pathological changes. BAs can enter the systematic circulation and cross the blood-brain barrier, subsequently exerting neuroprotective effects by targeting several endogenous receptors. Additionally, BAs interact with the microbiota-gut-brain (MGB) axis to improve immune and neuroendocrine function during AD episodes. Gut microbes impact BA signaling in the brain through their involvement in BA biotransformation. In this review, we summarize the role and molecular mechanisms of BAs in AD while considering the MGB axis and propose novel strategies for preventing the onset and progression of AD.

Insulin Resistance, a Risk Factor for Alzheimer's Disease: Pathological Mechanisms and a New Proposal for a Preventive Therapeutic Approach

Peripheral insulin resistance (IR) is a well-documented, independent risk factor for the development of type 2 diabetes, cardiovascular disease, cancer and cellular senescence. Recently, the brain has also been identified as an insulin-responsive region, where insulin acts as regulator of the brain metabolism. Despite the clear link between IR and the brain, the exact mechanisms underlying this relationship remain unclear. Therapeutic intervention in patients showing symptoms of neurodegenerative diseases has produced little or no results. It has been demonstrated that insulin resistance plays a significant role in the pathogenesis of neurodegenerative diseases, particularly cognitive decline. Peripheral and brain IR may represent a modifiable state that could be used to prevent major brain disorders. In this review, we will analyse the scientific literature supporting IR as a risk factor for Alzheimer's disease and suggest some therapeutic strategies to provide a new proposal for the prevention of brain IR and its consequences.

Trajectory of brain-derived amyloid beta in Alzheimer's disease: where is it coming from and where is it going?

Alzheimer's disease (AD) is a progressive neurological disorder that primarily impacts cognitive function. Currently there are no disease-modifying treatments to stop or slow its progression. Recent studies have found that several peripheral and systemic abnormalities are associated with AD, and our understanding of how these alterations contribute to AD is becoming more apparent. In this review, we focuse on amyloid‑beta (Aβ), a major hallmark of AD, summarizing recent findings on the source of brain-derived Aβ and discussing where and how the brain-derived Aβ is cleared in vivo. Based on these findings, we propose future strategies for AD prevention and treatment, from a novel perspective on Aβ metabolism.

State of the Science on Brain Insulin Resistance and Cognitive Decline Due to Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) is common and increasing in prevalence worldwide, with devastating public health consequences. While peripheral insulin resistance is a key feature of most forms of T2DM and has been investigated for over a century, research on brain insulin resistance (BIR) has more recently been developed, including in the context of T2DM and non-diabetes states. Recent data support the presence of BIR in the aging brain, even in non-diabetes states, and found that BIR may be a feature in Alzheimer's disease (AD) and contributes to cognitive impairment. Further, therapies used to treat T2DM are now being investigated in the context of AD treatment and prevention, including insulin. In this review, we offer a definition of BIR, and present evidence for BIR in AD; we discuss the expression, function, and activation of the insulin receptor (INSR) in the brain; how BIR could develop; tools to study BIR; how BIR correlates with current AD hallmarks; and regional/cellular involvement of BIR. We close with a discussion on resilience to both BIR and AD, how current tools can be improved to better understand BIR, and future avenues for research. Overall, this review and position paper highlights BIR as a plausible therapeutic target for the prevention of cognitive decline and dementia due to AD.

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

Comprehensive investigation of insulin-induced amyloidosis lesions in patients with diabetes at clinical and histological levels: A systematic review

INTRODUCTION

Insulin-derived amyloidosis (AIns), a skin complication in patients with diabetes, causes impaired insulin absorption. This systematic review aims to get a better understanding of this overlooked condition.

METHODS

Comprehensive literature searches were performed in Scopus, PubMed, EMBASE, and Web of Science databases until June 17, 2023. From 19,343 publications, duplicate and irrelevant records were eliminated by title, and the full texts of the remaining studies were examined for validity. Clinical, pathological, and therapeutic findings were extracted from 44 papers.

RESULTS

Forty-four articles were studied that covered 127 insulin-treated patients with diabetes. From the 62 patients with reported age and sex, males had a mean age of 58 years, and females 68.5 years. While AIns were twice as likely to develop in men (66.13 %) as in women (33.87 %), the administered insulin dose was significantly higher in males (p = 0.017). The most common insulin injection site was the abdominal wall (77.63 %). Histological findings showed the presence of amorphous material with the occasional presence of lymphocytes, plasma cells, macrophages, adipocytes, histocytes, and giant cells. The mean HbA1c level was 8.8 % and the need for receiving insulin was increased in AIns. Changing the site of insulin injections and/or surgically removing the nodules were the most common treatments to obtain better insulin uptake and controlled serum glucose levels.

CONCLUSION

This study highlights the importance of AIns, proper rotation of insulin injection site, and post-treatment patient follow-up to recognize and prevent the development of amyloid nodules.

Molecular basis of selective amyloid-β degrading enzymes in Alzheimer's disease

The accumulation of the small 42-residue long peptide amyloid-β (Aβ) has been proposed as a major trigger for the development of Alzheimer's disease (AD). Within the brain, the concentration of Aβ peptide is tightly controlled through production and clearance mechanisms. Substantial experimental evidence now shows that reduced levels of Aβ clearance are present in individuals living with AD. This accumulation of Aβ can lead to the formation of large aggregated amyloid plaques-one of two detectable hallmarks of the disease. Aβ-degrading enzymes (ADEs) are major players in the clearance of Aβ. Stimulating ADE activity or expression, in order to compensate for the decreased clearance in the AD phenotype, provides a promising therapeutic target. It has been reported in mice that upregulation of ADEs can reduce the levels of Aβ peptide and amyloid plaques-in some cases, this led to improved cognitive function. Among several known ADEs, neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), insulin degrading enzyme (IDE) and angiotensin-1 converting enzyme (ACE) from the zinc metalloprotease family have been identified as important. These ADEs have the capacity to digest soluble Aβ which, in turn, cannot form the toxic oligomeric species. While they are known for their amyloid degradation, they exhibit complexity through promiscuous nature and a broad range of substrates that they can degrade. This review highlights current structural and functional understanding of these key ADEs, giving some insight into the molecular interactions that leads to the hydrolysis of peptide substrates, the crucial tasks performed by them and the potential for therapeutic use in the future.

Bitter yet beneficial: The dual role of dietary alkaloids in managing diabetes and enhancing cognitive function

With the rising prevalence of diabetes and its association with cognitive impairment, interest in the use of dietary alkaloids and other natural products has grown significantly. Understanding how these compounds manage diabetic cognitive dysfunction (DCD) is crucial. This comprehensive review explores the etiology of DCD and the effects of alkaloids in foods and dietary supplements that have been investigated as DCD therapies. Data on how dietary alkaloids like berberine, trigonelline, caffeine, capsaicin, 1-deoxynojirimycin, nuciferine, neferine, aegeline, tetramethylpyrazine, piperine, and others regulate cognition in diabetic disorders were collected from PubMed, Research Gate, Web of Science, Science Direct, and other relevant databases. Dietary alkaloids could improve memory in behavioral models and modulate the mechanisms underlying the cognitive benefits of these compounds, including their effects on glucose metabolism, gut microbiota, vasculopathy, neuroinflammation, and oxidative stress. Evidence suggests that dietary alkaloids hold promise for improving cognition in diabetic patients and could open exciting avenues for future research in diabetes management.

Protein Tyrosine Phosphatase 1B (PTP1B): A Comprehensive Review of Its Role in Pathogenesis of Human Diseases

Overexpression of protein tyrosine phosphatase 1B (PTP1B) disrupts signaling pathways and results in numerous human diseases. In particular, its involvement has been well documented in the pathogenesis of metabolic disorders (diabetes mellitus type I and type II, fatty liver disease, and obesity); neurodegenerative diseases (Alzheimer's disease, Parkinson's disease); major depressive disorder; calcific aortic valve disease; as well as several cancer types. Given this multitude of therapeutic applications, shortly after identification of PTP1B and its role, the pursuit to introduce safe and selective enzyme inhibitors began. Regrettably, efforts undertaken so far have proved unsuccessful, since all proposed PTP1B inhibitors failed, or are yet to complete, clinical trials. Intending to aid introduction of the new generation of PTP1B inhibitors, this work collects and organizes the current state of the art. In particular, this review intends to elucidate intricate relations between numerous diseases associated with the overexpression of PTP1B, as we believe that it is of the utmost significance to establish and follow a brand-new holistic approach in the treatment of interconnected conditions. With this in mind, this comprehensive review aims to validate the PTP1B enzyme as a promising molecular target, and to reinforce future research in this direction.

Islet cell stress induced by insulin-degrading enzyme deficiency promotes regeneration and protection from autoimmune diabetes

Tuning of protein homeostasis through mobilization of the unfolded protein response (UPR) is key to the capacity of pancreatic beta cells to cope with variable demand for insulin. Here, we asked how insulin-degrading enzyme (IDE) affects beta cell adaptation to metabolic and immune stress. C57BL/6 and autoimmune non-obese diabetic (NOD) mice lacking IDE were exposed to proteotoxic, metabolic, and immune stress. IDE deficiency induced a low-level UPR with islet hypertrophy at the steady state, rapamycin-sensitive beta cell proliferation enhanced by proteotoxic stress, and beta cell decompensation upon high-fat feeding. IDE deficiency also enhanced the UPR triggered by proteotoxic stress in human EndoC-βH1 cells. In Ide-/- NOD mice, islet inflammation specifically induced regenerating islet-derived protein 2, a protein attenuating autoimmune inflammation. These findings establish a role of IDE in islet cell protein homeostasis, demonstrate how its absence induces metabolic decompensation despite beta cell proliferation, and UPR-independent islet regeneration in the presence of inflammation.

Therapeutic implications of glycogen synthase kinase-3β in Alzheimer's disease: a novel therapeutic target

Alzheimer's disease (AD) is an extremely popular neurodegenerative condition associated with dementia, responsible for around 70% of the cases. There are presently 50 million people living with dementia in the world, but this number is anticipated to increase to 152 million by 2050, posing a substantial socioeconomic encumbrance. Despite extensive research, the precise mechanisms that cause AD remain unidentified, and currently, no therapy is available. Numerous signalling paths related to AD neuropathology, including glycogen synthase kinase 3-β (GSK-3β), have been investigated as potential targets for the treatment of AD in current years.GSK-3β is a proline-directed serine/threonine kinase that is linked to a variety of biological activities, comprising glycogen metabolism to gene transcription. GSK-3β is also involved in the pathophysiology of sporadic as well as familial types of AD, which has led to the development of the GSK3 theory of AD. GSK-3β is a critical performer in the pathology of AD because dysregulation of this kinase affects all the main symbols of the disease such as amyloid formation, tau phosphorylation, neurogenesis and synaptic and memory function. The current review highlights present-day knowledge of GSK-3β-related neurobiology, focusing on its role in AD pathogenesis signalling pathways. It also explores the possibility of targeting GSK-3β for the management of AD and offers an overview of the present research work in preclinical and clinical studies to produce GSK-3β inhibitors.

Bacteroidota inhibit microglia clearance of amyloid-beta and promote plaque deposition in Alzheimer's disease mouse models

The gut microbiota and microglia play critical roles in Alzheimer's disease (AD), and elevated Bacteroides is correlated with cerebrospinal fluid amyloid-β (Aβ) and tau levels in AD. We hypothesize that Bacteroides contributes to AD by modulating microglia. Here we show that administering Bacteroides fragilis to APP/PS1-21 mice increases Aβ plaques in females, modulates cortical amyloid processing gene expression, and down regulates phagocytosis and protein degradation microglial gene expression. We further show that administering Bacteroides fragilis to aged wild-type male and female mice suppresses microglial uptake of Aβ1-42 injected into the hippocampus. Depleting murine Bacteroidota with metronidazole decreases amyloid load in aged 5xFAD mice, and activates microglial pathways related to phagocytosis, cytokine signaling, and lysosomal degradation. Taken together, our study demonstrates that members of the Bacteroidota phylum contribute to AD pathogenesis by suppressing microglia phagocytic function, which leads to impaired Aβ clearance and accumulation of amyloid plaques.

Insulin-like growth factor binding protein-2 in at-risk adults and autopsy-confirmed Alzheimer brains

Insulin, insulin-like growth factors (IGF) and their receptors are highly expressed in the adult hippocampus. Thus, disturbances in the insulin-IGF signalling pathway may account for the selective vulnerability of the hippocampus to nascent Alzheimer's disease (AD) pathology. In the present study, we examined the predominant IGF-binding protein in the CSF, IGFBP2. CSF was collected from 109 asymptomatic members of the parental history-positive PREVENT-AD cohort. CSF levels of IGFBP2, core AD and synaptic biomarkers were measured using proximity extension assay, ELISA and mass spectrometry. Cortical amyloid-beta (Aβ) and tau deposition were examined using 18F-NAV4694 and flortaucipir. Cognitive assessments were performed during up to 8 years of follow-up, using the Repeatable Battery for the Assessment of Neuropsychological Status. T1-weighted structural MRI scans were acquired, and neuroimaging analyses were performed on pre-specified temporal and parietal brain regions. Next, in an independent cohort, we allocated 241 dementia-free ADNI-1 participants into four stages of AD progression based on the biomarkers CSF Aβ42 and total-tau (t-tau). In this analysis, differences in CSF and plasma IGFBP2 levels were examined across the pathological stages. Finally, IGFBP2 mRNA and protein levels were examined in the frontal cortex of 55 autopsy-confirmed AD and 31 control brains from the Quebec Founder Population (QFP) cohort, a unique population isolated from Eastern Canada. CSF IGFBP2 progressively increased over 5 years in asymptomatic PREVENT-AD participants. Baseline CSF IGFBP2 was positively correlated with CSF AD biomarkers and synaptic biomarkers, and negatively correlated with longitudinal changes in delayed memory (P = 0.024) and visuospatial abilities (P = 0.019). CSF IGFBP2 was negatively correlated at a trend-level with entorhinal cortex volume (P = 0.082) and cortical thickness in the piriform (P = 0.039), inferior temporal (P = 0.008), middle temporal (P = 0.014) and precuneus (P = 0.033) regions. In ADNI-1, CSF (P = 0.009) and plasma (P = 0.001) IGFBP2 were significantly elevated in Stage 2 [CSF Aβ(+)/t-tau(+)]. In survival analyses in ADNI-1, elevated plasma IGFBP2 was associated with a greater rate of AD conversion (hazard ratio = 1.62, P = 0.021). In the QFP cohort, IGFBP2 mRNA was reduced (P = 0.049); however, IGFBP2 protein levels did not differ in the frontal cortex of autopsy-confirmed AD brains (P = 0.462). Nascent AD pathology may induce an upregulation in IGFBP2 in asymptomatic individuals. CSF and plasma IGFBP2 may be valuable markers for identifying CSF Aβ(+)/t-tau(+) individuals and those with a greater risk of AD conversion.

Correlations between insulin-degrading enzyme and metabolic markers in patients diagnosed with type 2 diabetes, Alzheimer's disease, and healthy controls: a comparative study

PURPOSE

This study aimed to explore correlations between insulin-degrading enzyme (IDE) and markers of metabolic function in a group of patients diagnosed with type 2 diabetes mellitus (T2DM) or Alzheimer's disease (AD) and metabolically healthy volunteers.

METHOD

We included 120 individuals (47 with T2DM, 9 with AD, and 64 healthy controls). Serum levels of IDE were measured with commercial kits for ELISA. Differences in IDE levels between groups were analyzed with non-parametric ANCOVA, and correlations were analyzed with Spearman's rank correlations. We also investigated the influence of age, sex, and the use of insulin on the correlation using a non-parametric version of partial correlation.

RESULTS

Patients diagnosed with T2DM had higher IDE levels than patients diagnosed with AD and healthy controls after adjustment for age and sex. IDE was increasingly associated with body mass index (BMI), fasting blood glucose, C-peptide, hemoglobin A1c (HbA1c), insulin resistance, and triglycerides. In stratified analyses, we found a decreasing partial correlation between IDE and HbA1c in patients diagnosed with AD and a decreasing partial correlation between IDE and C-peptide in healthy controls. In patients diagnosed with T2DM, we found no partial correlations.

CONCLUSION

These results indicate that IDE is essential in metabolic function and might reflect metabolic status, although it is not yet a biomarker that can be utilized in clinical practice. Further research on IDE in human blood may provide crucial insights into the full function of the enzyme.

Detection of insulin oligomeric forms by a novel surface plasmon resonance-diffusion coefficient based approach

Insulin is commonly used to treat diabetes and undergoes aggregation at the site of repeated injections in diabetic patients. Moreover, aggregation is also observed during its industrial production and transport and should be avoided to preserve its bioavailability to correctly adjust glucose levels in diabetic patients. However, monitoring the effect of various parameters (pH, protein concentration, metal ions, etc.) on the insulin aggregation and oligomerization state is very challenging. In this work, we have applied a novel Surface Plasmon Resonance (SPR)-based experimental approach to insulin solutions at various experimental conditions, monitoring how its diffusion coefficient is affected by pH and the presence of metal ions (copper and zinc) with unprecedented sensitivity, precision, and reproducibility. The reported SPR method, hereby applied to a protein for the first time, besides giving insight into the insulin oligomerization and aggregation phenomena, proved to be very robust for determining the diffusion coefficient of any biomolecule. A theoretical background is given together with the software description, specially designed to fit the experimental data. This new way of applying SPR represents an innovation in the bio-sensing field and expanding the potentiality of commonly used SPR instruments well over the canonical investigation of biomolecular interactions.