Increased risk of cognitive impairment in patients with diabetes is associated with metformin

Risk factors for mild cognitive impairment in type 2 diabetes mellitus older adult: a systematic review and meta-analysis

AIMS

Numerous of evidence suggest that older adults with diabetes are more likely to experience mild cognitive impairment (MCI), therefore identifying risk factors is crucial. Thus, the purpose of this study was to investigate the risk factors for the development of MCI in older diabetics.

METHODS

The MEDLINE, Web of Science, Scopus, and Embase databases were searched for pertinent research on the risk factors for the beginning of MCI. The remaining studies were assessed using predetermined inclusion and exclusion criteria after duplicate studies were eliminated. The Comprehensive Meta-Analysis software (version 2) was used to analyze the data. The Egger test was used to examine publication bias, while the I-square statistic was used to evaluate study heterogeneity. 95 % confidence limits and odds ratios were used in the analysis.

RESULTS

Thirty studies were authorized for assessment and statistical analysis using the systematic review procedure. These studies' findings indicate that, using both univariate and multivariate analyses, the odds ratio for the occurrence of MCI in older people with diabetes is higher for factors like low educational attainment (univariate analysis: OR = 0.706, CI95 %: 0.622-0.801, P ≤ 0.001 and multivariate analysis: OR = 0.753, CI95 %: 0.637-0.831, P = 0.001), duration of diabetes (univariate analysis: OR = 1.249, CI95 %: 1.111-1.405, P ≤ 0.001 and multivariate analysis: OR = 1.174, CI95 %: 1.006-1.370, P = 0.042), abnormal Hemoglobin A1c (HbA1C) levels (univariate analysis: OR = 1.744, CI95 %: 1.277-2.383, P ≤ 0.001 and multivariate analysis: OR = 1.248, CI95 %: 1.091-1.427, P ≤ 0.001), retinopathy(OR = 2.163, CI95 %: 1.686-2.776, P ≤ 0.001), nephropathy(OR = 1.568, CI95 %: 1.151-2.135, P = 0.004), neuropathy(OR = 1.334, CI95 %: 0.686-2.591, P = 0.396), depression(univariate analysis: OR = 1.649, CI95 %: 1.016-2.841, P = 0.046, and multivariate analysis: OR = 1.957, CI95 %: 1.322-2.856, P ≤ 0.001), and stroke(univariate analysis: OR = 1.820, CI95 %: 1.172-2.827, P = 0.008. multivariate analysis: OR = 1.496, CI95 %: 1.184-1.899, P = 0.001). Furthermore, univariate data analysis revealed that age(OR = 1.067, CI95 %: 1.011-1.126, P = 0.019), high total cholesterol(OR = 0.934, CI95 %: 0.866-1.008, P = 0.076), fasting blood sugar(OR = 1.129, CI95 %: 1.017-1.254, P = 0.023), the presence of hypertension(OR = 1.572, CI95 %: 1.147-2.155, P = 0.005), and kidney disease(OR = 1.676, CI95 %: 0.972-2.89, P = 0.063), all affect the odds ratio for the development of MCI in older adults with diabetes.

CONCLUSION

factors like low education, long-term diabetes, abnormal HbA1C levels, retinopathy, nephropathy, depression, and stroke, as well as high total cholesterol, fasting blood glucose, high blood pressure, and kidney disease, increase the risk of developing MCI in older diabetics. These cases in diabetic patients require special attention.

Risk factors for cognitive decline in type 2 diabetes mellitus adults: a systematic review and meta-analysis

Cognitive decline (CD) is a common disorder in patients with type 2 diabetes mellitus (T2DM), which is affected by various factors. The present study aimed to investigate the factors affecting its occurrence CD in patients T2DM. The PubMed, Web of Science, Scopus, and Embase databases were searched for pertinent research on the risk factors for the beginning of CD. The remaining studies were assessed using predetermined inclusion and exclusion criteria after duplicate studies were eliminated. The Comprehensive Meta-Analysis software (version 2) was used to analyze the data. The Egger test and Begg and Mazumdar test was used to examine publication bias, while the I-square statistic was used to evaluate study heterogeneity. 95% confidence limits and odds ratios were used in the analysis. 40 studies were authorized for assessment and statistical analysis using the systematic review procedure. These studies' findings indicate that, using both crude and adjusted analyses, the odds ratio for the occurrence of CD in people with diabetes is higher for factors like low educational attainment, men, abnormal Hemoglobin A1c (HbA1C) levels, physical inactivity, depression, and stroke. Factors like low education, abnormal HbA1C levels, depression, and stroke as well increase the risk of developing CD in diabetic patients. These cases in diabetic patients require special attention.

The overexpression of miR-146a in hippocampal microglia via IRAK1/TRAF6/NF-κB pathway improves cognitive function in diabetic mice

BACKGROUND AND OBJECTIVE

Diabetic encephalopathy (DEP), a central nervous system complication of diabetes, is primarily characterized by cognitive dysfunction. Despite its high prevalence and significant risks, the pathogenesis remains poorly understood. This study investigates the effects and mechanisms of miR-146a on cognitive function in DEP mice.

METHODS

Type 2 diabetic mice models were established by feeding a high-fat diet and administering a low-dose of streptozotocin. And the Morris water maze test was conducted to assess the learning and memory. The adeno-associated virus was delivered into hippocampus by stereotactic injection to overexpress miR-146a in microglia. The mRNA and protein expression levels were determined by quantitative real-time polymerase chain reaction, immunofluorescence, Western blot, and enzyme-linked immunosorbent assay.

RESULTS

DEP mice exhibited significantly reduced miR-146a expression in hippocampal microglia. This reduction was associated with elevated IRAK1, TRAF6, and NF-κB expression, increased markers of pro-inflammatory microglial phenotypes (CD86 and iNOS), and decreased markers of anti-inflammatory phenotypes (Arg-1 and CD206). Pro-inflammatory cytokines TNF-α and IL-6 were elevated, while anti-inflammatory IL-10 was reduced. Eventually, neuronal apoptosis and cognitive dysfunction were evident. Overexpression of miR-146a in hippocampal microglia reversed these molecular and phenotypic abnormalities, decreased neuronal apoptosis, and significantly improved cognitive performance in diabetic mice.

CONCLUSION

Downregulation of miR-146a in hippocampal microglia disrupts immune homeostasis through the IRAK1/TRAF6/NF-κB pathway, contributing to DEP. Targeted overexpression of miR-146a restores immune homeostasis, reduces neuronal apoptosis, and ameliorates cognitive impairment.

Exploring Metformin's Therapeutic Potential for Alzheimer's Disease: An In-Silico Perspective Using Well-Tempered Funnel Metadynamics

Alzheimer's disease (AD), often referred to as the "diabetes of the brain", is intricately linked to insulin resistance. Metformin, a first-line antidiabetic drug, has been anticipated as a potential treatment for AD and is currently undergoing phase 3 clinical trials. The potential success of metformin in treating AD could herald a new era in the management of this debilitating disease, providing hope for millions of people affected worldwide. Despite this fact, the precise molecular mechanisms underlying the therapeutic effects of metformin on AD remain poorly understood. To pursue this, in this present work, we implement a comprehensive computational approach combining classical molecular dynamics (MD) simulations and the advanced enhanced sampling technique funnel metadynamics (FM) to explore the dynamics and affinity of metformin and acetylcholinesterase (AChE), a novel target for AD. The MD and FM simulations suggest that metformin induces significant configurational changes within the AChE, resulting in weak and nonspecific binding. Furthermore, the presence of metformin alters the conformational landscape of AChE causing the emergence of metastable states and less rigid binding patterns. The binding energies for the metformin-AChE complex are -4.89 ± 1.2 kcal/mol and -1.68 ± 0.2 kcal/mol, as estimated through the molecular mechanics Poisson-Boltzmann surface area (MMPBSA) and FM approaches, respectively. To elucidate the binding energy relevance calculated by MMPBSA and FM approach with experimental inhibitory potency, ΔGexp is calculated using IC50 value reported in prior experimental studies. ΔGexp is estimated to be -3.59 kcal/mol. A comparison of these binding energy values with different methods highlights the moderate inhibitory potency of metformin toward AChE. This work provides molecular-level insights emphasizing the dynamic configurational changes induced by metformin within AChE and underscores its translational potential in the repurposing of AD.

Transcriptomics and proteomics characterizing the antioxidant mechanisms of semaglutide in diabetic mice with cognitive impairment

The aim of the present study was to investigate the neuroprotective effects of semaglutide in diabetes‑associated cognitive decline (DACD), while also exploring the underlying mechanisms targeting anti‑oxidative effects. The present study evaluated the antioxidant properties of semaglutide using a DACD model of inflammation. To investigate the underlying mechanisms, omics technologies were employed. Comprehensive transcriptomic and proteomic analysis of the cells was conducted to identify the pathways responsible for the observed antioxidant effects. Semaglutide demonstrated the potential to enhance learning and memory functions while mitigating hippocampal pathological damage. RNA‑sequencing and data‑independent acquisition proteomics analyses identified 13,511 differentially expressed genes and 588 differentially expressed proteins between the control and type 2 diabetes mellitus (T2DM) groups. In addition, 1,378 genes and 2,394 proteins exhibited a differential expression between the T2DM and semaglutide (10 µg/kg) treatment groups. A combined transcriptomic and proteomic analysis unveiled 40 common pathways. Acyl‑CoA oxidase 1 (ACOX1) was observed to be activated during oxidative stress and subsequently suppressed by semaglutide. Of note, the antioxidant and anti‑apoptotic properties of semaglutide in high glucose (HG) conditions were partially reversed upon ACOX1 overexpression. Overall, the present data provided molecular evidence to elucidate the physiological connections between semaglutide and neuronal function, and contribute to clarifying the role of semaglutide in combating oxidative stress and HG‑induced cognitive impairment.

The Possible Role of Metformin and Fibroblast Growth Factor-21 in Multiple Sclerosis Neuropathology: Birds of a Feather Flock Together

Multiple sclerosis (MS) is a progressive demyelinating disease of the CNS, characterized by inflammation, the formation of CNS plaques, and damage to the neuronal myelin sheath (Graphical abstract). Fibroblast growth factor 21 (FGF21) is involved in various metabolic disorders and neurodegenerative diseases. FGF21 and its co-receptor β-Kloth are essential in the remyelination process of MS. Metformin, an insulin-sensitizing drug that is the first-line treatment for type 2 diabetes mellitus (T2DM), may have a potential neuroprotective impact by up-regulating the production of FGF21, which may prevent the onset of neurodegenerative diseases including MS. The purpose of this review is to clarify how metformin affects MS neuropathology mechanistically via modifying FGF21. Metformin increases the expression of FGF21. Metformin also increases the expression of β-Klotho, modulates oxidative stress, reduces glutamate-induced excitotoxicity, and regulates platelet function and coagulation cascades. In conclusion, metformin can enhance the functional activity of FGF21 in counteracting the development and progression of MS. Preclinical and clinical studies are warranted in this regard.

Risk Factors, Pathological Changes, and Potential Treatment of Diabetes-Associated Cognitive Dysfunction

BACKGROUND

Diabetes is a prevalent public health issue worldwide, and the cognitive dysfunction and subsequent dementia caused by it seriously affect the quality of life of patients.

METHODS

Recent studies were reviewed to provide a comprehensive summary of the risk factors, pathogenesis, pathological changes and potential drug treatments for diabetes-related cognitive dysfunction (DACD).

RESULTS

Several risk factors contribute to DACD, including hyperglycemia, hypoglycemia, blood sugar fluctuations, hyperinsulinemia, aging, and others. Among them, modifiable risk factors for DACD include blood glucose control, physical activity, diet, smoking, and hypertension management, while non-modifiable risk factors include age, genetic predisposition, sex, and duration of diabetes. At the present, the pathogenesis of DACD mainly includes insulin resistance, neuroinflammation, vascular disorders, oxidative stress, and neurotransmitter disorders.

CONCLUSIONS

In this review, we provide a comprehensive summary of the risk factors, pathogenesis, pathological changes and potential drug treatments for DACD, providing information from multiple perspectives for its prevention and management.

Effect of diabetes medications on the risk of developing dementia, mild cognitive impairment, or cognitive decline: A systematic review and meta-analysis

Background: Diabetes is a risk factor for dementia, but we do not know whether specific diabetes medications ameliorate this risk. Objective: To systematically review and meta-analyze such medication's effect on the risk of developing dementia, mild cognitive impairment (MCI), or cognitive decline. Methods: We searched three databases until 21 November 2023. We included randomized controlled trials (RCT), cohort, and case-control studies assessing association between antidiabetic medication and future dementia, MCI, or cognitive decline. We meta-analyzed studies separately for individual drug classes and their comparators (no medication, placebo, or another drug). We appraised study quality using the Newcastle-Ottawa Scale and Physiotherapy Evidence Database Scale. Results: 42 studies fulfilled inclusion criteria. Glucagon-like peptide-1 receptor agonists (GLP-1 RA) versus placebo reduced dementia risk by 53% in three RCTs (n = 15,820, RR = 0.47[0.25, 0.86]) and 27% in three case-control studies (n = 312,856, RR = 0.73[0.54, 0.99], I2 = 96%). Repaglinide was superior to glibenclamide by 0.8 points on the Mini-Mental State Examination scale in another RCT. Meta-analysis of seven longitudinal studies showed glitazones (n = 1,081,519, RR = 0.78[0.76, 0.81], I2 = 0%) were associated with reduced dementia risk. Metformin (n = 999,349, RR = 0.94[0.79, 1.13], I2 = 98.4%), sulfonylureas (RR = 0.98[0.78, 1.22], I2 = 83.3%), dipeptidyl peptidase-IV inhibitors (DPP-1V) (n = 192,802, RR = 0.86[0.65, 1.15], I2 = 92.9%) and insulin (n = 571,274, RR = 1.09[0.95, 1.25], I2 = 94.8%) were not. Most studies were observational and limited by confounding by indication. Conclusions: In people with diabetes, RCTs consistently showed GLP-RAs reduce future dementia risk. Glitazones consistently showed protective effects, without heterogeneity, suggesting potential generalizability of these results. Metformin, sulfonylureas, insulin, and DPP-1V studies had inconsistent findings. If information is available future studies should consider dosage, severity, and duration.

Overview of Metformin and Neurodegeneration: A Comprehensive Review

This comprehensive review examines the therapeutic potential of metformin, a well-established diabetes medication, in treating neurodegenerative disorders. Originally used as a first-line treatment for type 2 diabetes, recent studies have begun investigating metformin's effects beyond metabolic disorders, particularly its neuroprotective capabilities against conditions like Parkinson's disease, Alzheimer's disease, Huntington's disease, and multiple sclerosis. Key findings demonstrate that metformin's neuroprotective effects operate through multiple pathways: AMPK activation enhancing cellular energy metabolism and autophagy; upregulation of antioxidant defenses; suppression of inflammation; inhibition of protein aggregation; and improvement of mitochondrial function. These mechanisms collectively address common pathological features in neurodegeneration and neuroinflammation, including oxidative stress, protein accumulation, and mitochondrial dysfunction. Clinical and preclinical evidence supporting metformin's association with improved cognitive performance, reduced risk of dementia, and modulation of pathological hallmarks of neurodegenerative diseases is critically evaluated. While metformin shows promise as a therapeutic agent, this review emphasizes the need for further investigation to fully understand its mechanisms and optimal therapeutic applications in neurodegenerative diseases.

Metformin Improves Spatial Memory and Reduces Seizure Severity in a Rat Model of Epilepsy and Alzheimer's Disease comorbidity via PI3K/Akt Signaling Pathway

Emerging evidence suggests a bidirectional relationship between Alzheimer's disease (AD) and epilepsy. In our previous studies, we identified a partial AD-like phenotype associated with central insulin resistance in the Wistar audiogenic rat (WAR), a genetic model of epilepsy. We also found that intracerebroventricular administration of streptozotocin, a compound used to model diabetes and AD, exacerbates seizure susceptibility. Given the role of insulin signaling in both AD and epilepsy, we hypothesized that metformin (MET), an anti-diabetic drug known for enhancing insulin sensitivity, could be a potential therapeutic agent for both conditions. Our objective was to investigate MET's effects on brain insulin signaling, seizure activity, and AD-like pathology in WARs. Adult male WARs received oral MET (250 mg/kg) for 21 days. Audiogenic seizures were assessed using the Categorized Severity Index and Racine's scale. Spatial memory was tested with the Morris water maze (MWM), followed by Western blot analysis of hippocampal proteins. MET significantly reduced seizure severity and improved MWM performance. Although MET did not affect insulin receptor levels or activation, it increased phosphoinositide 3-kinase (PI3K), activated Akt, and increased glycogen synthase kinase-3α/β (GSK-3α/β) levels. MET also decreased amyloid β precursor protein (AβPP) levels but did not affect Tau phosphorylation. These results suggest that chronic MET treatment alleviates behaviors related to both AD and epilepsy in WARs and modulates insulin signaling independently of insulin receptor activation. Our findings highlight MET's potential as a therapeutic agent for managing comorbid AD and epilepsy, warranting further investigation into its mechanisms of action.

Metformin and Cognitive Performance in Patients With Type 2 Diabetes: An Umbrella Review

Contradictory results for the association between metformin intake and changes in cognitive function have been reported. We attempted to overview systematic reviews and meta-analyses showing the role of metformin, as mono or combination therapy, in cognitive performance alterations among patients with type 2 diabetes mellitus (T2DM) and to determine the quality of the evidence as well. To find the English-written reviews, a literature search was conducted on PubMed, Web of Science, Scopus, Cochrane Library, Trip, and Google Scholar by May 1, 2023. The literature search unearthed 2672 records, 10 of which were included in the study. Metformin may provide cognitive benefits for patients with type 2 diabetes, as evidence suggests potential improvements in memory and a reduced risk of neurodegenerative diseases. Even though the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) score alterations correspond to raising concerns about cognitive decline, Mini-Mental State Examination (MMSE) and selective reminding test (SRT) score improvements support metformin's role in improving specific cognitive domains. As such, metformin may exert differential impacts on various aspects of cognitive performance in these patients. However, the inconsistency and low quality of current evidence point toward the need for accurate research to elucidate whether metformin's cognitive effects are protective, neutral, or context-dependent based on patient profiles.

An update on drug repurposing in Parkinson's disease: Preclinical and clinical considerations

The strategy of drug repositioning has historically played a significant role in the identification of new treatments for Parkinson's disease. Still today, numerous clinical and preclinical studies are investigating drug classes, already marketed for the treatment of metabolic disorders, for their potential use in Parkinson's disease patients. While drug repurposing offers a promising, fast, and cost-effective path to new treatments, these drugs still require thorough preclinical evaluation to assess their efficacy, addressing the specific neurodegenerative mechanisms of the disease. This review explores the state-of-the-art approaches to drug repurposing for Parkinson's disease, highlighting particularly relevant aspects. Preclinical studies still predominantly rely on traditional neurotoxin-based animal models, which fail to effectively replicate disease progression and are characterized by significant variability in model severity and timing of drug treatment. Importantly, for almost all the drugs analyzed here, there is insufficient data regarding the mechanism of action responsible for the therapeutic effect. Regarding drug efficacy, these factors may obviously render results less reliable or comparable. Accordingly, future preclinical drug repurposing studies in the Parkinson's disease field should be carried out using next-generation animal models like α-synuclein-based models that, unfortunately, have to date been used mostly for studies of disease pathogenesis and only rarely in pharmacological studies.

2-Hydroxyisobutyric acid targeted binding to MT-ND3 boosts mitochondrial respiratory chain homeostasis in hippocampus to rescue diabetic cognitive impairment

BACKGROUND

The prevalence of diabetic cognitive impairment (DCI) is significant, some studies have shown that it is related to mitochondrial respiratory chain homeostasis, but the specific mechanism is not clear. 2-hydroxyisobutyric acid (2-HIBA) is a novel short-chain fatty acid with potential applications in the treatment of metabolic diseases because it can regulate mitochondrial disorders. Our aim was to explore a novel mechanism of action for 2-HIBA in the treatment of DCI in mitochondrial respiratory chain homeostasis.

METHODS

Metabolic substances and differentially active metabolic pathways in the serum of diseased mice were identified based on multi-omics analysis. The nanoLC-Obitrap-MS technology was utilized to detect the content of selected small molecules with differential metabolic activity in the hippocampus and mitochondria of mice to evaluate their permeability through the blood-brain barrier (BBB) and outer mitochondrial membrane. A combination of behavioral, proteomic, and molecular biology approaches was used to explore specific regulatory mechanisms and identify potential pharmacological targets. Additionally, using techniques such as protein thermal shift, drug affinity responsive target stability (DARTS), hydrolase stability, and surface plasmon resonance (SPR) experiments, we demonstrated the direct binding effects of small molecule metabolites with protein targets.

RESULTS

2-HIBA was found to directly ameliorate cognitive dysfunction in db/db mice by penetrating the blood-brain barrier and reversing the decrease in the protein content of NADH dehydrogenase 3 (MT-ND3) in the hippocampus through direct binding to ND3. This action helps maintain the stability of NAD+/NADH and regulate the mitochondrial respiratory chain balance. Furthermore, a combined medication plant agonist of 2-HIBA can enhance the expression of MT-ND3, thereby improving cognitive dysfunction in mice.

CONCLUSION

MT-ND3 is a crucial target for improving diabetic cognitive dysfunction, and 2-HIBA can directly bind to the MT-ND3 protein to alleviate the functional impairment of the mitochondrial respiratory chain in mice to treat DCI.

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.

Mitochondria and the Repurposing of Diabetes Drugs for Off-Label Health Benefits

This review describes our current understanding of the role of the mitochondria in the repurposing of the anti-diabetes drugs metformin, gliclazide, GLP-1 receptor agonists, and SGLT2 inhibitors for additional clinical benefits regarding unhealthy aging, long COVID, mental neurogenerative disorders, and obesity. Metformin, the most prominent of these diabetes drugs, has been called the "Drug of Miracles and Wonders," as clinical trials have found it to be beneficial for human patients suffering from these maladies. To promote viral replication in all infected human cells, SARS-CoV-2 stimulates the infected liver cells to produce glucose and to export it into the blood stream, which can cause diabetes in long COVID patients, and metformin, which reduces the levels of glucose in the blood, was shown to cut the incidence rate of long COVID in half for all patients recovering from SARS-CoV-2. Metformin leads to the phosphorylation of the AMP-activated protein kinase AMPK, which accelerates the import of glucose into cells via the glucose transporter GLUT4 and switches the cells to the starvation mode, counteracting the virus. Diabetes drugs also stimulate the unfolded protein response and thus mitophagy, which is beneficial for healthy aging and mental health. Diabetes drugs were also found to mimic exercise and help to reduce body weight.

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

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

Repurposing antidiabetic drugs for Alzheimer's disease: A review of preclinical and clinical evidence and overcoming challenges

Repurposing antidiabetic drugs for the treatment of Alzheimer's disease (AD) has emerged as a promising therapeutic strategy. This review examines the potential of repurposing antidiabetic drugs for AD treatment, focusing on preclinical evidence, clinical trials, and observational studies. In addition, the review aims to explore challenges and opportunities in repurposing antidiabetic drugs for AD, emphasizing the importance of well-designed clinical trials that consider patient selection criteria, refined outcome measures, adverse effects, and combination therapies to enhance therapeutic efficacy. Preclinical evidence suggests that glucagon-like peptide-1 (GLP-1) analogs, dipeptidyl peptidase-4 (DPP4) inhibitors, metformin, thiazolidinediones, and sodium-glucose co-transporter-2 (SGLT2) inhibitors exhibit neuroprotective effects in AD preclinical models. In preclinical studies, antidiabetic drugs have demonstrated neuroprotective effects by reducing amyloid beta (Aβ) plaques, tau hyperphosphorylation, neuroinflammation, and cognitive impairment. Antidiabetic drug classes, notably GLP-1 analogs and SGLT2 inhibitors, and a reduced risk of dementia in patients with diabetes mellitus. While the evidence for DPP4 inhibitors is mixed, some studies suggest a potential protective effect. On the other hand, alpha-glucosidase inhibitors (AGIs) and sulfonylureas may potentially increase the risk, especially in those experiencing recurrent hypoglycemic events. Repurposing antidiabetic drugs for AD is a promising therapeutic strategy, but challenges such as disease heterogeneity, limited biomarkers, and benefits versus risk evaluation need to be addressed. Ongoing clinical trials in mild cognitive impairment (MCI) and early AD patients without diabetes will be crucial in determining the clinical efficacy and safety of the antidiabetic drugs, paving the way for potential treatments for AD.

Vitamin B12 Deficiency in Patients Taking Metformin: Pathogenesis and Recommendations

Metformin is a cornerstone therapy for type 2 diabetes mellitus due to its glucose-lowering efficacy and additional benefits such as reducing cardiovascular mortality. However, accumulating evidence suggests an association between long-term metformin use and vitamin B12 deficiency, which can lead to serious clinical consequences. This review aims to synthesize current knowledge on the pathogenesis, prevalence, clinical implications, and management of metformin-induced vitamin B12 deficiency. Given the significant clinical implications, it is crucial to monitor and manage vitamin B12 levels in patients using metformin. This review emphasizes the importance of early detection and supplementation to prevent adverse outcomes. By analyzing the current evidence, the review aims to inform healthcare professionals about best practices for managing vitamin B12 deficiency in patients on metformin, offering insights to guide future clinical practices and research directions.

Progress in the Pathogenesis of Diabetic Encephalopathy: The Key Role of Neuroinflammation

Diabetic encephalopathy (DE) is a severe complication that occurs in the central nervous system (CNS) and leads to cognitive impairment. DE involves various pathophysiological processes, and its pathogenesis is still unclear. This review summarised current research on the pathogenesis of diabetic encephalopathy, which involves neuroinflammation, oxidative stress, iron homoeostasis, blood-brain barrier disruption, altered gut microbiota, insulin resistance, etc. Among these pathological mechanisms, neuroinflammation has been focused on. This paper summarises some of the molecular mechanisms involved in neuroinflammation, including the Mammalian Target of Rapamycin (mTOR), Lipocalin-2 (LCN-2), Pyroptosis, Advanced Glycosylation End Products (AGEs), and some common pro-inflammatory factors. In addition, we discuss recent advances in the study of potential therapeutic targets for the treatment of DE against neuroinflammation. The current research on the pathogenesis of DE is progressing slowly, and more research is needed in the future. Further study of neuroinflammation as a mechanism is conducive to the discovery of more effective treatments for DE in the future.

Emerging role of Metformin in Alzheimer's disease: A translational view

Alzheimer's disease (AD) constitutes a major public-health issue of our time. Regrettably, despite our considerable understanding of the pathophysiological aspects of this disease, current interventions lead to poor outcomes. Furthermore, experimentally promising compounds have continuously failed when translated to clinical trials. Along with increased population ageing, Type 2 Diabetes Mellitus (T2DM) has become an extremely common condition, mainly due to unbalanced dietary habits. Substantial epidemiological evidence correlates T2DM with cognitive impairment as well. Considering that brain insulin resistance, mitochondrial dysfunction, oxidative stress, and amyloidogenesis are common phenomena, further approaching the common features among these pathological conditions. Metformin constitutes the first-choice drug to preclude insulin resistance in T2DM clinical management. Experimental evidence suggests that its functions might include neuroprotective effects, in addition to its hypoglycemic activity. This review aims to summarize and discuss current knowledge of experimental data on metformin on this path towards translational medicine. Finally, we discuss the controversial data of responses to metformin in vitro, and in vivo, animal models and human studies.

Effects of chronic treatment with metformin on brain glucose hypometabolism and central insulin actions in transgenic mice with tauopathy

Brain glucose hypometabolism and insulin alterations are common features of many neurological diseases. Herein we sought to corroborate the brain glucose hypometabolism that develops with ageing in 12-months old Tau-VLW transgenic mice, a model of tauopathy, as well as to determine whether this model showed signs of altered peripheral glucose metabolism. Our results demonstrated that 12-old months Tau mice exhibited brain glucose hypometabolism as well as basal hyperglycemia, impaired glucose tolerance, hyperinsulinemia, and signs of insulin resistance. Then, we further studied the effect of chronic metformin treatment (9 months) in Tau-VLW mice from 9 to 18 months of age. Longitudinal PET neuroimaging studies revealed that chronic metformin altered the temporal profile in the progression of brain glucose hypometabolism associated with ageing. Besides, metformin altered the content and/or phosphorylation of key components of the insulin signal transduction pathway in the frontal cortex leading to significant changes in the content of the active forms. Thus, metformin increased the expression of pAKT-Y474 while reducing pmTOR-S2448 and pGSK3β. These changes might be related, at least partially, to a slow progression of ageing, neurological damage, and cognitive decline. Metformin also improved the peripheral glucose tolerance and the ability of the Tau-VLW mice to maintain their body weight through ageing. Altogether our study shows that the tau-VLW mice could be a useful model to study the potential interrelationship between tauopathy and central and peripheral glucose metabolism alterations. More importantly our results suggest that chronic metformin treatment may have direct beneficial central effects by post-transcriptional modulation of key components of the insulin signal transduction pathway.

Current type 2 diabetes guidelines: Individualized treatment and how to make the most of metformin

Evidence-based guidelines provide the premise for the delivery of quality care to preserve health and prevent disabilities and premature death. The systematic gathering of observational, mechanistic and experimental data contributes to the hierarchy of evidence used to guide clinical practice. In the field of diabetes, metformin was discovered more than 100 years ago, and with 60 years of clinical use, it has stood the test of time regarding its value in the prevention and management of type 2 diabetes. Although some guidelines have challenged the role of metformin as the first-line glucose-lowering drug, it is important to point out that the cardiovascular-renal protective effects of sodium-glucose co-transporter-2 inhibitors and glucagon-like peptide-1 receptor agonists were gathered from patients with type 2 diabetes, the majority of whom were treated with metformin. Most national, regional and international guidelines recommend metformin as a foundation therapy with emphasis on avoidance of therapeutic inertia and early attainment of multiple treatment goals. Moreover, real-world evidence has confirmed the glucose-lowering and cardiovascular-renal benefits of metformin accompanied by an extremely low risk of lactic acidosis. In patients with type 2 diabetes and advanced chronic kidney disease (estimated glomerular filtration rate 15-30 mL/min/1.73m2), metformin discontinuation was associated with an increased risk of cardiovascular-renal events compared with metformin persistence. Meanwhile, it is understood that microbiota, nutrients and metformin can interact through the gut-brain-kidney axis to modulate homeostasis of bioactive molecules, systemic inflammation and energy metabolism. While these biological changes contribute to the multisystem effects of metformin, they may also explain the gastrointestinal side effects and vitamin B12 deficiency associated with metformin intolerance. By understanding the interactions between metformin, foods and microbiota, healthcare professionals are in a better position to optimize the use of metformin and mitigate potential side effects. The United Kingdom Prospective Diabetes Study and the Da Qing Diabetes Prevention Program commenced 40 years ago provided the first evidence that type 2 diabetes is preventable and treatable. To drive real-world impact from this evidence, payors, practitioners and planners need to co-design and implement an integrated, data-driven, metformin-based programme to detect people with undiagnosed diabetes and prediabetes (intermediate hyperglycaemia), notably impaired glucose tolerance, for early intervention. The systematic data collection will create real-world evidence to bring out the best of metformin and make healthcare sustainable, affordable and accessible.

True or false? Alzheimer's disease is type 3 diabetes: Evidences from bench to bedside

Globally, Alzheimer's disease (AD) is the most widespread chronic neurodegenerative disorder, leading to cognitive impairment, such as aphasia and agnosia, as well as mental symptoms, like behavioral abnormalities, that place a heavy psychological and financial burden on the families of the afflicted. Unfortunately, no particular medications exist to treat AD, as the current treatments only impede its progression.The link between AD and type 2 diabetes (T2D) has been increasingly revealed by research; the danger of developing both AD and T2D rises exponentially with age, with T2D being especially prone to AD. This has propelled researchers to investigate the mechanism(s) underlying this connection. A critical review of the relationship between insulin resistance, Aβ, oxidative stress, mitochondrial hypothesis, abnormal phosphorylation of Tau protein, inflammatory response, high blood glucose levels, neurotransmitters and signaling pathways, vascular issues in AD and diabetes, and the similarities between the two diseases, is presented in this review. Grasping the essential mechanisms behind this detrimental interaction may offer chances to devise successful therapeutic strategies.

Vitamin B12 deficiency in diabetic patients treated with metformin: A narrative review

Metformin is the most prescribed oral hypoglycemic drug and is considered by many health practitioners as the first-line treatment for non-insulin-dependent diabetes mellitus (T2DM). It is used either as a monotherapy or adjuvant to other anti-hyperglycemic agents. Most of its side effects are usually mild and self-limiting. However, several studies have shown an association between the use of metformin and low vitamin B12 levels in diabetic patients. The current review aimed to provide a literature review of the current published reports on the association, the possible mechanisms, and the related individualized risk factors that might lead to this incidence. The most accepted mechanism of the effect of metformin on vitamin B12 level is related to the absorption process where metformin antagonism of the calcium cation and interference with the calcium-dependent IF-vitamin B12 complex binding to the ileal cubilin receptor. In addition, many risk factors have been associated with the impact of metformin on vitamin B12 levels in diabetic patients such as dose and duration where longer durations showed a greater prevalence of developing vitamin B12 deficiency. Male patients showed lower levels of vitamin B12 compared to females. Black race showed a lower prevalence of vitamin B12 deficiency in metformin-treated patients. Moreover, chronic diseases including T2DM, hyperlipidemia, coronary artery disease, polycystic ovary disease (PCOD), obesity, and metformin therapy were significantly associated with increased risk of vitamin B12 deficiency.

Can exercise benefits be harnessed with drugs? A new way to combat neurodegenerative diseases by boosting neurogenesis

Adult hippocampal neurogenesis (AHN) is affected by multiple factors, such as enriched environment, exercise, ageing, and neurodegenerative disorders. Neurodegenerative disorders can impair AHN, leading to progressive neuronal loss and cognitive decline. Compelling evidence suggests that individuals engaged in regular exercise exhibit higher production of proteins that are essential for AHN and memory. Interestingly, specific molecules that mediate the effects of exercise have shown effectiveness in promoting AHN and cognition in different transgenic animal models. Despite these advancements, the precise mechanisms by which exercise mimetics induce AHN remain partially understood. Recently, some novel exercise molecules have been tested and the underlying mechanisms have been proposed, involving intercommunications between multiple organs such as muscle-brain crosstalk, liver-brain crosstalk, and gut-brain crosstalk. In this review, we will discuss the current evidence regarding the effects and potential mechanisms of exercise mimetics on AHN and cognition in various neurological disorders. Opportunities, challenges, and future directions in this research field are also discussed.

Impact of metformin on neocortical development during pregnancy: Involvement of ERK and p35/CDK5 pathways

Metformin, the most commonly prescribed drug for the treatment of diabetes, is increasingly used during pregnancy to address various disorders such as diabetes, obesity, preeclampsia, and metabolic diseases. However, its impact on neocortex development remains unclear. Here, we investigated the direct effects of metformin on neocortex development, focusing on ERK and p35/CDK5 regulation. Using a pregnant rat model, we found that metformin treatment during pregnancy induces small for gestational age (SGA) and reduces relative cortical thickness in embryos and neonates. Additionally, we discovered that metformin inhibits neural progenitor cell proliferation in the sub-ventricular zone (SVZ)/ventricular zone (VZ) of the developing neocortex, a process possibly mediated by ERK inactivation. Furthermore, metformin induces neuronal apoptosis in the SVZ/VZ area of the developing neocortex. Moreover, metformin retards neuronal migration, cortical lamination, and differentiation, potentially through p35/CDK5 inhibition in the developing neocortex. Remarkably, compensating for p35 through in utero electroporation partially rescues metformin-impaired neuronal migration and development. In summary, our study reveals that metformin disrupts neocortex development by inhibiting neuronal progenitor proliferation, neuronal migration, cortical layering, and cortical neuron maturation, likely via ERK and p35/CDK5 inhibition. Consequently, our findings advocate for caution in metformin usage during pregnancy, given its potential adverse effects on fetal brain development.

Novel targets and therapies of metformin in dementia: old drug, new insights

Dementia is a devastating disorder characterized by progressive and persistent cognitive decline, imposing a heavy public health burden on the individual and society. Despite numerous efforts by researchers in the field of dementia, pharmacological treatments are limited to relieving symptoms and fail to prevent disease progression. Therefore, studies exploring novel therapeutics or repurposing classical drugs indicated for other diseases are urgently needed. Metformin, a first-line antihyperglycemic drug used to treat type 2 diabetes, has been shown to be beneficial in neurodegenerative diseases including dementia. This review discusses and evaluates the neuroprotective role of metformin in dementia, from the perspective of basic and clinical studies. Mechanistically, metformin has been shown to improve insulin resistance, reduce neuronal apoptosis, and decrease oxidative stress and neuroinflammation in the brain. Collectively, the current data presented here support the future potential of metformin as a potential therapeutic strategy for dementia. This study also inspires a new field for future translational studies and clinical research to discover novel therapeutic targets for dementia.

Beneficial effects of metformin treatment on memory impairment

Memory issues are a prevalent symptom in different neurodegenerative diseases and can also manifest in certain psychiatric conditions. Despite limited medications approved for treating memory problems, research suggests a lack of sufficient options in the market. Studies indicate that a significant percentage of elderly individuals experience various forms of memory disorders. Metformin, commonly prescribed for type 2 diabetes, has shown neuroprotective properties through diverse mechanisms. This study explores the potential of metformin in addressing memory impairments. The current research gathered its data by conducting an extensive search across electronic databases including PubMed, Web of Science, Scopus, and Google Scholar. Previous research suggests that metformin enhances brain cell survival and memory function in both animal and clinical models by reducing oxidative stress, inflammation, and cell death while increasing beneficial neurotrophic factors. The findings of the research revealed that metformin is an effective medication for enhancing various types of memory problems in numerous studies. Given the rising incidence of memory disorders, it is plausible to utilize metformin, which is an affordable and accessible drug. It is often recommended as a treatment to boost memory.

Promising use of metformin in treating neurological disorders: biomarker-guided therapies

Neurological disorders are a diverse group of conditions that affect the nervous system and include neurodegenerative diseases (Alzheimer's disease, multiple sclerosis, Parkinson's disease, Huntington's disease), cerebrovascular conditions (stroke), and neurodevelopmental disorders (autism spectrum disorder). Although they affect millions of individuals around the world, only a limited number of effective treatment options are available today. Since most neurological disorders express mitochondria-related metabolic perturbations, metformin, a biguanide type II antidiabetic drug, has attracted a lot of attention to be repurposed to treat neurological disorders by correcting their perturbed energy metabolism. However, controversial research emerges regarding the beneficial/detrimental effects of metformin on these neurological disorders. Given that most neurological disorders have complex etiology in their pathophysiology and are influenced by various risk factors such as aging, lifestyle, genetics, and environment, it is important to identify perturbed molecular functions that can be targeted by metformin in these neurological disorders. These molecules can then be used as biomarkers to stratify subpopulations of patients who show distinct molecular/pathological properties and can respond to metformin treatment, ultimately developing targeted therapy. In this review, we will discuss mitochondria-related metabolic perturbations and impaired molecular pathways in these neurological disorders and how these can be used as biomarkers to guide metformin-responsive treatment for the targeted therapy to treat neurological disorders.

AMP-activated protein kinase activators have compound and concentration-specific effects on brain metabolism

AMP-activated protein kinase (AMPK) is a key sensor of energy balance playing important roles in the balancing of anabolic and catabolic activities. The high energy demands of the brain and its limited capacity to store energy indicate that AMPK may play a significant role in brain metabolism. Here, we activated AMPK in guinea pig cortical tissue slices, both directly with A769662 and PF 06409577 and indirectly with AICAR and metformin. We studied the resultant metabolism of [1-13C]glucose and [1,2-13C]acetate using NMR spectroscopy. We found distinct activator concentration-dependent effects on metabolism, which ranged from decreased metabolic pool sizes at EC50 activator concentrations with no expected stimulation in glycolytic flux to increased aerobic glycolysis and decreased pyruvate metabolism with certain activators. Further, activation with direct versus indirect activators produced distinct metabolic outcomes at both low (EC50) and higher (EC50 × 10) concentrations. Specific direct activation of β1-containing AMPK isoforms with PF 06409577 resulted in increased Krebs cycle activity, restoring pyruvate metabolism while A769662 increased lactate and alanine production, as well as labelling of citrate and glutamine. These results reveal a complex metabolic response to AMPK activators in brain beyond increased aerobic glycolysis and indicate that further research is warranted into their concentration- and mechanism-dependent impact.

Metformin role in Parkinson's disease: a double-sword effect

Parkinson's disease (PD) is a common neurodegenerative disease developed due to the degeneration of dopaminergic neurons in the substantia nigra. There is no single effective treatment in the management of PD. Therefore, repurposing effective and approved drugs like metformin could be an effective strategy for managing PD. However, the mechanistic role of metformin in PD neuropathology was not fully elucidated. Metformin is an insulin-sensitizing agent used as a first-line therapy in the management of type 2 diabetes mellitus (T2DM) and has the ability to reduce insulin resistance (IR). Metformin may have a beneficial effect on PD neuropathology. The neuroprotective effect of metformin is mainly mediated by activating adenosine monophosphate protein kinase (AMPK), which reduces mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation. As well, metformin mitigates brain IR a hallmark of PD and other neurodegenerative diseases. However, metformin may harm PD neuropathology by inducing hyperhomocysteinemia and deficiency of folate and B12. Therefore, this review aimed to find the potential role of metformin regarding its protective and detrimental effects on the pathogenesis of PD. The mechanistic role of metformin in PD neuropathology was not fully elucidated. Most studies regarding metformin and its effectiveness in PD neuropathology were observed in preclinical studies, which are not fully translated into clinical settings. In addition, metformin effect on PD neuropathology was previously clarified in T2DM, potentially linked to an increasing PD risk. These limitations hinder the conclusion concerning the therapeutic efficacy of metformin and its beneficial and detrimental role in PD. Therefore, as metformin does not cause hypoglycemia and is a safe drug, it should be evaluated in non-diabetic patients concerning PD risk.

Human trials exploring anti-aging medicines

Here, we summarize the current knowledge on eight promising drugs and natural compounds that have been tested in the clinic: metformin, NAD+ precursors, glucagon-like peptide-1 receptor agonists, TORC1 inhibitors, spermidine, senolytics, probiotics, and anti-inflammatories. Multiple clinical trials have commenced to evaluate the efficacy of such agents against age-associated diseases including diabetes, cardiovascular disease, cancer, and neurodegenerative diseases. There are reasonable expectations that drugs able to decelerate or reverse aging processes will also exert broad disease-preventing or -attenuating effects. Hence, the outcome of past, ongoing, and future disease-specific trials may pave the way to the development of new anti-aging medicines. Drugs approved for specific disease indications may subsequently be repurposed for the treatment of organism-wide aging consequences.

Impact of Different Diagnostic Measures on Drug Class Association with Dementia Progression Risk: A Longitudinal Prospective Cohort Study

Background

The Clinical Dementia Rating Scale Sum of Boxes (CDRSOB) score is known to be highly indicative of cognitive-functional status and is regularly employed for clinical and research purposes.

Objective

Our aim is to determine whether CDRSOB is consistent with clinical diagnosis in evaluating drug class associations with risk of progression to mild cognitive impairment (MCI) and dementia.

Methods

We employed weighted Cox regression analysis on longitudinal NACC data, to identify drug classes associated with disease progression risk, using clinical diagnosis and CDRSOB as the outcome.

Results

Aspirin (antiplatelet/NSAID), angiotensin II inhibitors (antihypertensive), and Parkinson's disease medications were significantly associated with reduced risk of progression to MCI/dementia and Alzheimer's disease medications were associated with increased MCI-to-Dementia progression risk with both clinical diagnosis and CDRSOB as the outcome. However, certain drug classes/subcategories, like anxiolytics, antiadrenergics, calcium (Ca2+) channel blockers, and diuretics (antihypertensives) were associated with reduced risk of disease progression, and SSRIs (antidepressant) were associated with increased progression risk only with CDRSOB. Additionally, metformin (antidiabetic medication) was associated with reduced MCI-to-Dementia progression risk only with clinical diagnosis as the outcome.

Conclusions

Although the magnitude and direction of the effect were primarily similar for both diagnostic outcomes, we demonstrate that choice of diagnostic measure can influence the significance of risk/protection attributed to drug classes and consequently the conclusion of findings. A consensus must be reached within the research community with respect to the most accurate diagnostic outcome to identify risk and improve reproducibility.

Metformin, age-related cognitive decline, and brain pathology

The objective of this study was to evaluate the relation of metformin with change in cognition and brain pathology. During a mean of 8 years (SD = 5.5) of annual follow-up visits, 262/3029 participants were using metformin at any time during the study. Using a linear-mixed effect model adjusted for age, sex, and education, metformin users had slower decline on a score of global cognition compared to non-users (estimate = 0.017, SE = 0.007, p = 0.027). Analyses of cognitive domains showed a slower decline in episodic memory and semantic memory specifically. In sensitivity analysis, when examining any diabetes medication use vs none, no association was observed of any diabetes medication use with cognitive function. In the autopsy subset of 1584 participants, there was no difference in the level of Alzheimer's disease (AD) pathology or the presence of infarcts (of any size or location) between groups of metformin users vs non-users. However, in additional analyses, metformin users had higher odds of subcortical infarcts, and lower odds of atherosclerosis and arteriosclerosis.

Role of Metalloproteinases in Diabetes-associated Mild Cognitive Impairment

Diabetes has been linked to an increased risk of mild cognitive impairment (MCI), a condition characterized by a subtle cognitive decline that may precede the development of dementia. The underlying mechanisms connecting diabetes and MCI involve complex interactions between metabolic dysregulation, inflammation, and neurodegeneration. A critical mechanism implicated in diabetes and MCI is the activation of inflammatory pathways. Chronic low-grade inflammation, as observed in diabetes, can lead to the production of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-1 beta (IL-1β), and interferon-gamma (IFNγ), each of which can exacerbate neuroinflammation and contribute to cognitive decline. A crucial enzyme involved in regulating inflammation is ADAM17, a disintegrin, and metalloproteinase, which can cleave and release TNF-α from its membrane-bound precursor and cause it to become activated. These processes, in turn, activate additional inflammation-related pathways, such as AKT, NF-κB, NLP3, MAPK, and JAK-STAT pathways. Recent research has provided novel insights into the role of ADAM17 in diabetes and neurodegenerative diseases. ADAM17 is upregulated in both diabetes and Alzheimer's disease, suggesting a shared mechanism and implicating inflammation as a possible contributor to much broader forms of pathology and pointing to a possible link between inflammation and the emergence of MCI. This review provides an overview of the different roles of ADAM17 in diabetes-associated mild cognitive impairment diseases. It identifies mechanistic connections through which ADAM17 and associated pathways may influence the emergence of mild cognitive impairment.

Metformin as a Potential Prevention Strategy for Alzheimer's Disease and Alzheimer's Disease Related Dementias

Background

Metformin is a safe and effective medication for type 2 diabetes (T2D) that has been proposed to decrease the risk of aging related disorders including Alzheimer's disease (AD) and Alzheimer's disease related disorders(ADRD).

Objective

This review seeks to summarize findings from studies examining the association of metformin with AD/ADRD related outcomes.

Methods

This is a narrative review of human studies, including observational studies and clinical trials, examining the association of metformin with cognitive and brain outcomes. We used PubMed as the main database for our literature search with a focus on English language human studies including observational studies and clinical trials. We prioritized studies published from 2013 until February 15, 2024.

Results

Observational human studies are conflicting, but those with better study designs suggest that metformin use in persons with T2D is associated with a lower risk of dementia. However, these observational studies are limited by the use of administrative data to ascertain metformin use and/or cognitive outcomes. There are few clinical trials in persons without T2D that have small sample sizes and short durations but suggest that metformin could prevent AD/ADRD. There are ongoing studies including large clinical trials with long duration that are testing the effect of metformin on AD/ADRD outcomes in persons without T2D at risk for dementia.

Conclusions

Clinical trial results are needed to establish the effect of metformin on the risk of AD and ADRD.

The Potential of a Stratified Approach to Drug Repurposing in Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative condition that is characterized by the build-up of amyloid-beta plaques and neurofibrillary tangles. While multiple theories explaining the aetiology of the disease have been suggested, the underlying cause of the disease is still unknown. Despite this, several modifiable and non-modifiable factors that increase the risk of developing AD have been identified. To date, only eight AD drugs have ever gained regulatory approval, including six symptomatic and two disease-modifying drugs. However, not all are available in all countries and high costs associated with new disease-modifying biologics prevent large proportions of the patient population from accessing them. With the current patient population expected to triple by 2050, it is imperative that new, effective, and affordable drugs become available to patients. Traditional drug development strategies have a 99% failure rate in AD, which is far higher than in other disease areas. Even when a drug does reach the market, additional barriers such as high cost and lack of accessibility prevent patients from benefiting from them. In this review, we discuss how a stratified medicine drug repurposing approach may address some of the limitations and barriers that traditional strategies face in relation to drug development in AD. We believe that novel, stratified drug repurposing studies may expedite the discovery of alternative, effective, and more affordable treatment options for a rapidly expanding patient population in comparison with traditional drug development methods.

A long-term ketogenic diet in young and aged rats has dissociable effects on prelimbic cortex and CA3 ensemble activity

Introduction

Age-related cognitive decline has been linked to distinct patterns of cellular dysfunction in the prelimbic cortex (PL) and the CA3 subregion of the hippocampus. Because higher cognitive functions require both structures, selectively targeting a neurobiological change in one region, at the expense of the other, is not likely to restore normal behavior in older animals. One change with age that both the PL and CA3 share, however, is a reduced ability to utilize glucose, which can produce aberrant neural activity patterns.

Methods

The current study used a ketogenic diet (KD) intervention, which reduces the brain's reliance on glucose, and has been shown to improve cognition, as a metabolic treatment for restoring neural ensemble dynamics in aged rats. Expression of the immediate-early genes Arc and Homer1a were used to quantify the neural ensembles that were active in the home cage prior to behavior, during a working memory/biconditional association task, and a continuous spatial alternation task.

Results

Aged rats on the control diet had increased activity in CA3 and less ensemble overlap in PL between different task conditions than did the young animals. In the PL, the KD was associated with increased activation of neurons in the superficial cortical layers, establishing a clear link between dietary macronutrient content and frontal cortical activity. The KD did not lead to any significant changes in CA3 activity.

Discussion

These observations suggest that the availability of ketone bodies may permit the engagement of compensatory mechanisms in the frontal cortices that produce better cognitive outcomes.

Metformin: The Winding Path from Understanding Its Molecular Mechanisms to Proving Therapeutic Benefits in Neurodegenerative Disorders

Metformin, a widely prescribed medication for type 2 diabetes, has garnered increasing attention for its potential neuroprotective properties due to the growing demand for treatments for Alzheimer's, Parkinson's, and motor neuron diseases. This review synthesizes experimental and clinical studies on metformin's mechanisms of action and potential therapeutic benefits for neurodegenerative disorders. A comprehensive search of electronic databases, including PubMed, MEDLINE, Embase, and Cochrane library, focused on key phrases such as "metformin", "neuroprotection", and "neurodegenerative diseases", with data up to September 2023. Recent research on metformin's glucoregulatory mechanisms reveals new molecular targets, including the activation of the LKB1-AMPK signaling pathway, which is crucial for chronic administration of metformin. The pleiotropic impact may involve other stress kinases that are acutely activated. The precise role of respiratory chain complexes (I and IV), of the mitochondrial targets, or of the lysosomes in metformin effects remains to be established by further research. Research on extrahepatic targets like the gut and microbiota, as well as its antioxidant and immunomodulatory properties, is crucial for understanding neurodegenerative disorders. Experimental data on animal models shows promising results, but clinical studies are inconclusive. Understanding the molecular targets and mechanisms of its effects could help design clinical trials to explore and, hopefully, prove its therapeutic effects in neurodegenerative conditions.

Diabetes: a tipping point in neurodegenerative diseases

Diabetes is associated with an increased risk and progression of Alzheimer's (AD) and Parkinson's (PD) diseases. Conversely, diabetes may confer neuroprotection against amyotrophic lateral sclerosis (ALS). It has been posited that perturbations in glucose and insulin regulation, cholesterol metabolism, and mitochondrial bioenergetics defects may underlie the molecular underpinnings of diabetes effects on the brain. Nevertheless, the precise molecular mechanisms remain elusive. Here, we discuss the evidence from molecular, epidemiological, and clinical studies investigating the impact of diabetes on neurodegeneration and highlight shared dysregulated pathways between these complex comorbidities. We also discuss promising antidiabetic drugs, molecular diagnostics currently in clinical trials, and outstanding questions and challenges for future pursuit.

The Roles of Caloric Restriction Mimetics in Central Nervous System Demyelination and Remyelination

The dysfunction of myelinating glial cells, the oligodendrocytes, within the central nervous system (CNS) can result in the disruption of myelin, the lipid-rich multi-layered membrane structure that surrounds most vertebrate axons. This leads to axonal degeneration and motor/cognitive impairments. In response to demyelination in the CNS, the formation of new myelin sheaths occurs through the homeostatic process of remyelination, facilitated by the differentiation of newly formed oligodendrocytes. Apart from oligodendrocytes, the two other main glial cell types of the CNS, microglia and astrocytes, play a pivotal role in remyelination. Following a demyelination insult, microglia can phagocytose myelin debris, thus permitting remyelination, while the developing neuroinflammation in the demyelinated region triggers the activation of astrocytes. Modulating the profile of glial cells can enhance the likelihood of successful remyelination. In this context, recent studies have implicated autophagy as a pivotal pathway in glial cells, playing a significant role in both their maturation and the maintenance of myelin. In this Review, we examine the role of substances capable of modulating the autophagic machinery within the myelinating glial cells of the CNS. Such substances, called caloric restriction mimetics, have been shown to decelerate the aging process by mitigating age-related ailments, with their mechanisms of action intricately linked to the induction of autophagic processes.

[The role of antidiabetic drugs in the treatment of Alzheimer's disease: systematic review]

Recent studies show that Alzheimer's disease (AD) has many common links with conditions associated with insulin resistance, including neuroinflammation, impaired insulin signaling, oxidative stress, mitochondrial dysfunction and metabolic syndrome. The authors conducted an electronic search for publications in the PubMed/MEDLINE and Google Scholar databases using the keywords "amyloid beta", "Alzheimer type-3-diabetes", "intranasal insulin", "metformin", "type 2 diabetes mellitus", "incretins" and "PPARy agonists». A systematic literature search was conducted among studies published between 2005 and 2022. The authors used the following inclusion criteria: 1) Subjects who received therapy for AD and/or DM2, if the expected result concerned the risk of cognitive decline or the development of dementia; 2) The age of the study participants is > 50 years; 3) The type of studies included in this review were randomized clinical trials, population-based observational studies or case-control studies, prospective cohort studies, as well as reviews and meta-analyses; 4) The included articles were written in English. In recent years, there has been considerable interest in identifying the mechanisms of action of antidiabetic drugs and their potential use in AD. Human studies involving patients with mild cognitive impairment and Alzheimer's disease have shown that the administration of certain antidiabetic drugs, such as intranasal insulin, metformin, incretins and thiazolidinediones, can improve cognitive function and memory. The purpose of this study is to evaluate the effectiveness of antidiabetic drugs in the treatment of AD. According to the results of the study, metformin, intranasal insulin, thiazolidinediones and incretins showed a positive effect both in humans and in animal models. Recent studies show that thiazolidinediones can activate pathways in the brain that are regulated by IGF-1; however, rosiglitazone may pose a significant risk of side effects. The results of clinical studies on the use of metformin in AD are limited and contradictory.

Insights from insulin resistance pathways: Therapeutic approaches against Alzheimer associated diabetes mellitus

Alzheimer Associated Diabetes Mellitus, commonly known as Type 3 Diabetes Mellitus (T3DM) is a distinct subtype of diabetes with a pronounced association with Alzheimer's disease (AD). Insulin resistance serves as a pivotal link between these two conditions, leading to diminished insulin sensitivity, hyperglycemia, and impaired glucose uptake. The brain, a vital organ in AD context, is also significantly impacted by insulin resistance, resulting in energy deficits and neuronal damage, which are hallmark features of the neurodegenerative disorder. To pave the way for potential therapeutic interventions targeting the insulin resistance pathway, it is crucial to comprehend the intricate pathophysiology of T3DM and identify the overlapped features between diabetes and AD. This comprehensive review article aims to explore various pathway such as AMPK, PPARγ, cAMP and P13K/Akt pathway as potential target for management of T3DM. Through the analysis of these complex mechanisms, our goal is to reveal their interdependencies and support the discovery of innovative therapeutic strategies. The review extensively discusses several promising pharmaceutical candidates that have demonstrated dual drug action mechanisms, addressing both peripheral and cerebral insulin resistance observed in T3DM. These candidates hold significant promise for restoring insulin function and mitigating the detrimental effects of insulin resistance on the brain. The exploration of these therapeutic options contributes to the development of innovative interventions that alleviate the burden of T3DM and enhance patient care.

Pharmacological profiling identifies divergent chemosensitivities of differentiating and maturing iPSC-derived human cortical neuron populations

Neuronal differentiation and maturation are extended developmental processes. To determine whether neurons at different developmental stages have divergent chemosensitivities, we screened differentiating and maturing neuronal populations using a small compound library comprising FDA-approved and investigational drugs. Using a neurotoxicity assay format, both respective neuronal population-based screening campaigns performed robustly (Z-factors = 0.7-0.8), although the hit rate for the differentiating neurons (2.8%) was slightly higher than for maturing neurons (1.9%). While the majority of hits were toxic to both neuronal populations, these hits predominantly represented promiscuous drugs. Other drugs were selectively neurotoxic, with receptor tyrosine kinase inhibitors disproportionally represented after confirmation. Ponatinib and amuvatinib were neuroinhibitory for differentiating and maturing neurons, respectively. Chemoinformatic analyses confirmed differences in potential drug targets that may be differentially expressed during neuronal development. Subsequent studies demonstrated neuronal expression of AXL, an amuvatinib target, in both neuronal populations. However, functional AXL activity was confirmed only in the maturing neuronal population as determined by AXL phosphorylation in response to GAS6, the cognate ligand of AXL, and concurrent STAT3Y705 phosphorylation. Differentiating neurons were unresponsive to the effects of GAS6 suggesting that the AXL-STAT3 signaling axis was nonfunctional. Amuvatinib treatment of maturing neuronal cultures significantly reduced pAXL levels. These studies indicate that neuronal developmental states may exhibit unique chemosensitivities and that drugs may have different neuro-inhibitory effects depending upon the developmental stage of the neuronal population.

Mitochondria and Oxidative Stress as a Link between Alzheimer's Disease and Diabetes Mellitus

This review is devoted to the problems of the common features linking metabolic disorders and type 2 diabetes with the development of Alzheimer's disease. The pathogenesis of Alzheimer's disease closely intersects with the mechanisms of type 2 diabetes development, and an important risk factor for both pathologies is aging. Common pathological mechanisms include both factors in the development of oxidative stress, neuroinflammation, insulin resistance, and amyloidosis, as well as impaired mitochondrial dysfunctions and increasing cell death. The currently available drugs for the treatment of type 2 diabetes and Alzheimer's disease have limited therapeutic efficacy. It is important to note that drugs used to treat Alzheimer's disease, in particular acetylcholinesterase inhibitors, show a positive therapeutic potential in the treatment of type 2 diabetes, while drugs used in the treatment of type 2 diabetes can also prevent a number of pathologies characteristic for Alzheimer's disease. A promising direction in the search for a strategy for the treatment of type 2 diabetes and Alzheimer's disease may be the creation of complex multi-target drugs that have neuroprotective potential and affect specific common targets for type 2 diabetes and Alzheimer's disease.

Baseline Profiles of Drug Prescriptions Prior to Diagnosis of Mild Cognitive Impairment (MCI) Obtained by Latent Class Analysis (LCA), and Assessment of Their Association with Conversion to Dementia

Polypharmacy has been linked to cognitive decline. However, interventions targeting modifiable risk factors, some of which are targets of the most commonly used drugs, could reduce the prevalence of dementia. Our aim was to determine the drug prescription regimen at baseline, prior to the diagnosis of mild cognitive impairment (MCI), and its possible association with progression to dementia. Data were collected from the electronic medical records of 342 MCI outpatients diagnosed during 2006-2017 at their first neurology consultation. We followed the classical three-step method of statistical analysis, starting with a Latent Class Analysis (LCA) to discover subgroups of drug prescription probability. Half of the patients were under polypharmacy (≥5 drugs), 17.5% had no recorded medication, 33.3% progressed to dementia (94.7% in ≤5 years), and 84.1% of them to Alzheimer's disease (AD). According to the LCA and based on 20 therapeutic indicators obtained from 240 substances and regrouped according the Anatomical Therapeutic Chemical Classification, we identified a four-profile model: (1) low (35.7% of patients); (2) mixed (28.7%); (3) cardio-metabolic (19.3%); and (4) psychotropic (16.4%). The binomial regression logistic model showed that profiles 2 and 3 (and 4 for AD), with a higher drug prescription conditioned probability against classic risk factors, were protective than profile 1 (OR = 0.421, p = 0.004; OR = 0.278, p = 0.000; OR = 0.457, p = 0.040, respectively), despite polypharmacy being significant in profiles 2 and 3 (mean > 7 drugs) vs. profile 1 (1.4 ± 1.6) (p = 0.000). Patients in the latter group were not significantly older, although being aged 65-79 years old quadrupled (OR = 4.217, p = 000) and being >79 tripled (OR = 2.945, p = 0.010) the conversion risk compared to patients <65 years old. According to the proposed analytical model, profiling the heterogeneous association of risk factors, which were taken prior to diagnosis, could be explored as an indicator of prior care and a predictor of conversion to dementia.

Analysis of Reports Sent to the Portuguese Pharmacovigilance System and Published Literature Regarding the Safety of Metformin in the Elderly

The first line medication for the treatment of type 2 diabetes is metformin. This study aims to investigate the safety profile of metformin and metformin combination medications in older adults using pharmacovigilance data. A literature search was used to identify published clinical studies reporting safety of metformin in older patients (age ≥ 65 years old), which were then thoroughly evaluated. Additionally, a deep analysis was performed, taking into account suspected adverse drug reaction (ADR) reports submitted to the Portuguese Pharmacovigilance System involving patients with 65 years old or older, with metformin or metformin combination as the suspected drug. The results suggest that metformin is safer when used in combination with other antidiabetics than when used in monotherapy. Metformin prolonged-release tablets have a lower incidence of adverse effects compared to treatment with immediate-release metformin tablets. The analysis of the reports showed that "gastrointestinal disorders" was one of the most common classes reported, and metformin alone was the drug most commonly associated with serious gastrointestinal reactions that resulted in hospitalization. In addition, it was the drug most commonly associated with the lactic acidosis ADR. Even though most ADRs in the reports were serious, the majority progressed to cure. According to the analysis performed, the results suggest that the patient's renal function should be considered in order to prevent ADRs associated with metformin, such as lactic acidosis. Therefore, monitoring the safety profile of metformin remains essential to prevent serious ADRs.

Association between Acid-Lowering Agents, Metformin, and Vitamin B12 among Boston-Area Puerto Ricans

BACKGROUND

Vitamin B12 involves several physiological functions, and malabsorption is reported with medication use.

OBJECTIVES

Studies have reported an inverse association between the use of metformin or acid-lowering agents (ALAs), such as proton pump inhibitors, histamine 2 receptor antagonists, and blood vitamin B12 concentration, because of malabsorption. The concomitant use of these medications is underreported. We sought to examine these associations in a cohort of Boston-area Puerto Rican adults.

METHODS

This analysis was conducted within the Boston Puerto Rican Health Study (BPRHS), an ongoing longitudinal cohort that enrolled 1499 Puerto Rican adults aged 45-75 y at baseline. Our study comprised 1428, 1155, and 782 participants at baseline, wave2 (2.2 y from baseline), and wave3 (6.2 y from baseline), respectively. Covariate-adjusted linear and logistic regression was used to examine the association between baseline medication use and vitamin B12 concentration or deficiency (vitamin B12 <148 pmol/L or methylmalonic acid >271 nmol/L), and long-term medication use (continuous use for ∼6.2 y) and wave3 vitamin B12 concentration and deficiency. Sensitivity analyses were done to examine these associations in vitamin B12 supplement users.

RESULTS

At baseline, we observed an association between metformin use (β = -0.069; P = 0.03) and concomitant ALA and metformin use (β = -0.112; P = 0.02) and vitamin B12 concentration, but not a deficiency. We did not observe associations between ALA, proton pump inhibitors, or histamine 2 receptor antagonists, individually, with vitamin B12 concentration or deficiency.

CONCLUSIONS

These results suggest an inverse relationship between metformin, concomitant ALA, metformin use, and serum vitamin B12 concentration.

Antidiabetic agents as a novel treatment for Alzheimer's and Parkinson's disease

Therapeutic strategies for neurodegenerative disorders have commonly targeted individual aspects of the disease pathogenesis to little success. Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by several pathological features. In AD and PD, there is an abnormal accumulation of toxic proteins, increased inflammation, decreased synaptic function, neuronal loss, increased astrocyte activation, and perhaps a state of insulin resistance. Epidemiological evidence has revealed a link between AD/PD and type 2 diabetes mellitus, with these disorders sharing some pathological commonalities. Such a link has opened up a promising avenue for repurposing antidiabetic agents in the treatment of neurodegenerative disorders. A successful therapeutic strategy for AD/PD would likely require a single or several agents which target the separate pathological processes in the disease. Targeting cerebral insulin signalling produces numerous neuroprotective effects in preclinical AD/PD brain models. Clinical trials have shown the promise of approved diabetic compounds in improving motor symptoms of PD and preventing neurodegenerative decline, with numerous further phase II trials and phase III trials underway in AD and PD populations. Alongside insulin signalling, targeting incretin receptors in the brain represents one of the most promising strategies for repurposing currently available agents for the treatment of AD/PD. Most notably, glucagon-like-peptide-1 (GLP-1) receptor agonists have displayed impressive clinical potential in preclinical and early clinical studies. In AD the GLP-1 receptor agonist, liraglutide, has been demonstrated to improve cerebral glucose metabolism and functional connectivity in small-scale pilot trials. Whilst in PD, the GLP-1 receptor agonist exenatide is effective in restoring motor function and cognition. Targeting brain incretin receptors reduces inflammation, inhibits apoptosis, prevents toxic protein aggregation, enhances long-term potentiation and autophagy as well as restores dysfunctional insulin signalling. Support is also increasing for the use of additional approved diabetic treatments, including intranasal insulin, metformin hydrochloride, peroxisome proliferator-activated nuclear receptor γ agonists, amylin analogs, and protein tyrosine phosphatase 1B inhibitors which are in the investigation for deployment in PD and AD treatment. As such, we provide a comprehensive review of several promising anti-diabetic agents for the treatment of AD and PD.