Metformin regulates astrocyte reactivity in Parkinson's disease and normal aging

Glutamatergic dysfunction in neurodegenerative diseases focusing on Parkinson's disease: Role of glutamate modulators

Parkinson's disease (PD) is a prevalent neurodegenerative disorder resulting from the degeneration of dopamenergic neurons in the substantia nigra pars compacta (SNpc). Research has predominantly centered on understanding the dysfunction of dopaminergic neurotransmission in PD. Recently, more studies discussed the potential role of other neurotransmitters in PD neuropathology. One of the most important non-dopaminergic neurotransmitters involved in the pathogenesis of PD is glutamate, which is widely involved in glutamatergic neurotransmission in different brain regions, including SNpc. The development and progression of PD neuropathology and levodopa-induced dyskinesias (LID) are associated with glutamate neurotoxicity. Therefore, this review seeks to explore the possible involvement of glutamatergic signaling in PD development and assess the therapeutic potential of glutamate receptor antagonists in treating the disorder.

The Janus Face of Astrocytes in Multiple Sclerosis: Balancing Protection and Pathology

Multiple sclerosis (MS) is a chronic autoimmune disorder characterized by demyelination and neurodegeneration in the central nervous system (CNS), predominantly affecting young adults with a notable female predominance. While the pathogenesis of MS involves complex interactions between peripheral immune cells and CNS glia, astrocytes-the most abundant glial cells-play a dual role in disease progression. Traditionally classified into pro-inflammatory A1 and neuroprotective A2 phenotypes, recent single-cell and spatial transcriptomics reveal that human astrocytes exhibit a continuum of states beyond this binary paradigm. In MS, reactive astrocytes contribute to neurotoxicity by disrupting the blood-brain barrier (BBB), promoting glutamate excitotoxicity, and presenting antigens to autoreactive T cells. Conversely, they also support repair through neurotrophic factor release (e.g., BDNF, CNTF) and remyelination. Emerging therapies like dimethyl fumarate (DMF) and fingolimod modulate astrocyte reactivity, targeting oxidative stress and sphingosine-1-phosphate receptors to mitigate neuroinflammation. However, challenges persist in translating murine A1/A2 concepts to human MS, as human astrocytes display heterogeneous, context-dependent responses influenced by regional microenvironments and disease stages. Advanced techniques, including spatial multi-omics, highlight astrocyte-microglia crosstalk and metabolic reprogramming as key drivers of MS pathology. This review synthesizes current evidence on astrocyte heterogeneity, their Janus-faced roles in MS, and the therapeutic potential of astrocyte-targeted strategies, advocating for precision approaches that account for human-specific astrocyte biology. Future research must priorities human-centric biomarkers and dynamic modelling to bridge the gap between experimental findings and clinical applications.

Evaluating the Molecular Interactions between Type 2 Diabetes Mellitus and Parkinson's Disease: Role of Antidiabetic Drugs as Promising Therapeutics

Evidence from previous research demonstrates a relationship between diabetes mellitus (DM) and Parkinson's disease (PD). T2DM is associated with chronic glucose dysregulation, as an etiological factor. It inhibits neuronal function through disrupted insulin signaling and oxidative stress, which ultimately lead to the loss of dopaminergic neurons in the substantia nigra (SN). Interactions between T2DM and PD were analyzed by gene expression, coexpression, and gene set enrichment via NCBI and STRING databases following pathways like KEGG and Reactome. The study identified nine key gene interactions through published literature on different databases and search engines that are involved in the progression of these chronic diseases. Furthermore, some genetic and nongenetic risk factors, gene mutations and environmental factors, are also involved in the progression of T2DM and PD. This review highlights the limitations of currently available drug treatments for these diseases and examines modern therapeutic approaches to address neurodegenerative and metabolic abnormalities. We critically assess the current experimental methodologies aimed at unraveling the pathophysiological mechanisms linking PD and T2DM while addressing the key challenges impeding a comprehensive understanding of the concurrent emergence of these debilitating age-related conditions.

Sitagliptin attenuates L-dopa-induced dyskinesia by regulating mitochondrial proteins and neuronal activity in a 6-OHDA-induced mouse model of Parkinson's disease

L-dopa-induced dyskinesia (LID) is an incapacitating complication of long-term administration of L-dopa therapy that commonly affects patients with Parkinson's disease (PD) due to the widespread use of the causative drug. Herein, we investigated the therapeutic potential of sitagliptin, a drug used to treat type 2 diabetes mellitus, to treat LID. 6-hydroxydopamine (6-OHDA) was unilaterally injected into the left side of the substantia nigra pas compacta to induce a mouse model of PD. After four weeks of 6-OHDA induction, L-dopa was administered with or without sitagliptin for 11 consecutive days. LID was monitored using abnormal involuntary movement (AIM) scoring, conducted on days 5 and 10 of L-dopa treatment. Comparative proteomic analysis was performed on the 6-OHDA-lesioned striatum by comparing groups treated with vehicle + L-dopa and sitagliptin + L-dopa. Sitagliptin combined with L-dopa significantly attenuated AIM scores in 6-OHDA-lesioned mice. Proteomic analysis following sitagliptin treatment showed an increase in proteins involved in mitochondrial function regulation and a decrease in proteins associated with cytoskeleton function regulation. Changes in the expression of Ndufb2, a subunit of NADH: ubiquinone oxidoreductase (complex I), and Arc, an immediate early gene (IEG), which showed the most significant increase and decrease, respectively, were validated using western blotting and RT-PCR analysis. These findings suggest that sitagliptin may have therapeutic potential by enhancing mitochondrial functions and suppressing neuronal activity in the striatum, thereby mitigating the incapacitating complications associated with long-term L-dopa use in patients with PD.

Neuroprotective effects of semaglutide and metformin against rotenone-induced neurobehavioral changes in male diabetic rats

Pre-existing diabetes raises the likelihood of Parkinson's disease (PD), according to epidemiological and animal research. Our study aimed to investigating the likely neuroprotective effect of metformin (Met) and/or semaglutide (Sem) in model of PD in male diabetic rats and the possible underlying mechanism. Type 2 diabetes (T2DM) was induced by giving high-fat diet (HFD) for 3 weeks followed by a single streptozotocin (STZ) injection (40 mg/kg, i.p., once dose) followed by injection of 9 doses of rotenone every 48 ± 2 h for induction of PD. Met and/or Sema were administered to DM+PD via gastric gavage once daily for 4 weeks. In comparison with the DM+PD group, Met and/or Sem significantly lowered blood glucose levels, HOMA-IR, HbA1C, cholesterol, triglycerides, and LDL with significantly increased insulin and HDL levels. In addition, there was enhanced brain antioxidant status with lower oxidative-inflammatory stress biomarkers associated with improved rat cognitive, locomotor, and olfactory functions. A significant downregulation of caspase 3 and GFAP with concomitant upregulation of NRF2 protein expressions were observed in treated groups. Overall, co-treatment with Met and Sem elicited more efficacy than that of the individual regimen. When combined, the results of this study have demonstrated for the first time that Met and Sem work in concert to create neuroprotection in PD model of male diabetic rats compared to when taken separately. The study's findings indicate that Met and/or Sem have a restorative effect on T2DM and PD-induced changes in neurobehavioral and biochemical/molecular indices ascribed to the improvement of endogenous antioxidant systems, decreased lipid peroxidation, suppression of oxidative/inflammatory stress, and-most importantly-regulation of Nrf2 and caspase 3.

Advances in molecular mechanisms and therapeutic strategies for central nervous system diseases based on gut microbiota imbalance

BACKGROUD

Central nervous system (CNS) diseases pose a serious threat to human health, but the regulatory mechanisms and therapeutic strategies of CNS diseases need to be further explored. It has been demonstrated that the gut microbiota (GM) is closely related to CNS disease. GM structure disorders, abnormal microbial metabolites, intestinal barrier destruction and elevated inflammation exist in patients with CNS diseases and promote the development of CNS diseases. More importantly, GM remodeling alleviates CNS pathology to some extent.

AIM OF REVIEW

Here, we have summarized the regulatory mechanism of the GM in CNS diseases and the potential treatment strategies for CNS repair based on GM regulation, aiming to provide safer and more effective strategies for CNS repair from the perspective of GM regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The abundance and composition of GM is closely associated with the CNS diseases. On the basis of in-depth analysis of GM changes in mice with CNS disease, as well as the changes in its metabolites, therapeutic strategies, such as probiotics, prebiotics, and FMT, may be used to regulate GM balance and affect its microbial metabolites, thereby promoting the recovery of CNS diseases.

Metformin activates the PI3K/AKT/BDNF axis to attenuate postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a prevalent neurocognitive complication of anesthesia and surgery. Metformin, a widely used antidiabetic drug, has neuroprotective properties and improves cognitive impairment and memory deficits. However, the mechanisms underlying its action in improving cognitive dysfunction after anesthesia and surgery remain unclear. This study aimed to explore the effects of metformin on POCD and the underlying mechanisms at play. We established an in vivo POCD model using isoflurane inhalation anesthesia with exploratory laparotomy. We found that pretreatment with metformin significantly improved cognitive function and anxiety-like behaviors in mice. Additionally, metformin attenuated the impairment of synaptic plasticity induced by POCD and restored levels of synaptic proteins and dendritic density in the hippocampus. Furthermore, metformin attenuated neuroinflammation by downregulating the expression of interleukin (IL)-6, IL-1β, and tumor necrosis factor-α, and reducing neuronal apoptosis. It also activates the PI3K/AKT signaling pathway, resulting in increased expression of brain-derived neurotrophic factor (BDNF). Finally, the PI3K inhibitor, LY294002, reversed the effects of metformin on the levels of PI3K, AKT phosphorylation, and BDNF in vitro cultured HT-22 cells. Additionally, in an in vivo model of POCD, it was observed that cognitive function in mice was significantly suppressed by treatment with the PI3K inhibitor LY294002. These results reveal that metformin may alleviate POCD by modulating the PI3K/AKT/BDNF axis. Our study may provide a novel strategy for preventing and treating POCD with this medication.

Metformin's Effects on Cognitive Function from a Biovariance Perspective: A Narrative Review

This study examines the effects of metformin on brain functions focusing on the variability of the results reported in the literature. While some studies suggest that metformin may have neuroprotective effects in diabetic patients, others report an insignificant impact of metformin on cognitive function, or even a negative effect. We propose that this inconsistency may be due to intrinsic cellular-level variability among individuals, which we term "biovariance". Biovariance persists even in demographically homogeneous samples due to complex and stochastic biological processes. Additionally, the complex metabolic actions of metformin, including its influence on neuroenergetics and neuronal survival, may produce different effects depending on individual metabolic characteristics.

Targeting Ferroptosis in Parkinson's: Repurposing Diabetes Drugs as a Promising Treatment

This review explores the promising potential of repurposing type 2 diabetes (T2D) medications for the treatment of Parkinson's disease (PD), highlighting the shared pathophysiological mechanisms between these two age-related conditions, such as oxidative stress, mitochondrial dysfunction, and ferroptosis. The overlap suggests that existing diabetes drugs could target the common pathways involved in both conditions. Specifically, the review discusses how T2D medications, including metformin (Met), peroxisome-proliferator-activated receptor gamma (PPAR-γ) agonists, sodium-glucose cotransporter-2 (SGLT2) inhibitors, incretins, and dipeptidyl-peptidase 4 (DPP-4) inhibitors, can improve mitochondrial function, reduce neuroinflammation and oxidative stress, and potentially inhibit ferroptosis. The connection between ferroptosis and existing treatments, including diabetes medication, are only beginning to be explored. The limited data can be attributed also to the complexity of mechanisms involved in ferroptosis and Parkinson's disease and to the fact that the specific role of ferroptosis in Parkinson's disease pathogenesis has not been a primary focus until recent. Despite the promising preclinical evidence, clinical findings are mixed, underscoring the need for further research to elucidate these drugs' roles in neurodegeneration. Repurposing existing diabetes medications that have well-established safety profiles for Parkinson's disease treatment could significantly reduce the time and cost associated with drug development and could offer a more comprehensive approach to managing Parkinson's disease compared to treatments targeting a single mechanism.

Metformin and the PI3K/AKT signaling pathway: implications for cancer, cardiovascular, and central nervous system diseases

Recent findings have brought our understanding of diseases at the molecular level, highlighting upstream intracellular pathways as potential therapeutic targets. The PI3K/AKT pathway, a key regulator of cellular responses to environmental changes, is frequently altered in various diseases, making it a promising target for intervention. Metformin is the most known anti-diabetic agent that is known due to its effects on cancer, inflammatory-related diseases, oxidative stress, and other human diseases. It is clearly understood that metformin modulates the activity of the PI3K/AKT pathway leading to a wide variety of outcomes. This interaction has been well-studied in various diseases. Therefore, this review aims to examine PI3K/AKT-modulating properties of metformin in cancer, cardiovascular, and central nervous system diseases. Our findings indicate that metformin is effective in treating cancer and CNS diseases, and plays a role in both the prevention and treatment of cardiovascular diseases. These insights support the potential of metformin in comprehensive strategies for disease management.

Metabolism and metabolomics in senescence, aging, and age-related diseases: a multiscale perspective

The pursuit of healthy aging has long rendered aging and senescence captivating. Age-related ailments, such as cardiovascular diseases, diabetes, and neurodegenerative disorders, pose significant threats to individuals. Recent studies have shed light on the intricate mechanisms encompassing genetics, epigenetics, transcriptomics, and metabolomics in the processes of senescence and aging, as well as the establishment of age-related pathologies. Amidst these underlying mechanisms governing aging and related pathology metabolism assumes a pivotal role that holds promise for intervention and therapeutics. The advancements in metabolomics techniques and analysis methods have significantly propelled the study of senescence and aging, particularly with the aid of multiscale metabolomics which has facilitated the discovery of metabolic markers and therapeutic potentials. This review provides an overview of senescence and aging, emphasizing the crucial role metabolism plays in the aging process as well as age-related diseases.

Comparing psilocybin to metformin as neuroprotective agents against Parkinson's dementia: A systematic review of evidence and efficacy

BACKGROUND & AIM

Treatment of Parkinson's disease (PD) has remained largely unchanged and focuses primarily on symptomatic relief through activation of dopaminergic pathways. Currently, there are no proven prophylactic approaches to the prevention of PD. This systematic review seeks to compare two separate compounds, metformin (MTF) and psilocybin, as potential prophylactic therapeutics against the development of PD.

METHODS

The authors conducted a systematic review focusing on primary studies that test these compounds on cell and animal models to determine if they might have any neuroprotective or neuroplastic effects.

RESULTS

The results of this review found that MTF may halt the progression of diseases such as PD through multiple mechanisms including reduced oxidative stress at the level of the mitochondria, thereby reducing α-synuclein related damage. Psilocybin, on the other hand, may increase repair of damaged neurons through psychoplastogenic activation of serotonergic pathways, particularly 5-HT2A receptor activation, ultimately increasing the release of brain derived neurotropic factor (BDNF) and the reduction of α-synuclein accumulation.

CONCLUSION

Implications of this study include a need for further research in off-label use of MTF as well as further research into serotonergic compounds such as psilocybin for the treatment and prevention of neurodegenerative diseases.

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.

Too old for healthy aging? Exploring age limits of longevity treatments

It is well documented that aging elicits metabolic failures, while poor metabolism contributes to accelerated aging. Metabolism in general, and energy metabolism in particular are also effective entry points for interventions that extend lifespan and improve organ function during aging. In this review, we discuss common metabolic remedies for healthy aging from the angle of their potential age-specificity. We demonstrate that some well-known metabolic treatments are mostly effective in young and middle-aged organisms, while others maintain high efficacy independently of age. The mechanistic basis of presence or lack of the age limitations is laid out and discussed.

Metformin Lysosomal Targeting: A Novel Aspect to Be Investigated for Metformin Repurposing in Neurodegenerative Diseases?

Metformin is a widely employed drug in type 2 diabetes. In addition to warranting good short- and long-term glycemic control, metformin displays many intriguing properties as protection against cardiovascular and neurodegenerative diseases, anti-tumorigenic and longevity promotion. In addition to being a low-cost drug, metformin is generally well tolerated. However, despite the enthusiastic drive to aliment these novel studies, many contradictory results suggest the importance of better elucidating the complexity of metformin action in different tissues/cells to establish its possible employment in neurodegenerative diseases. This review summarises recent data identifying lysosomal-dependent processes and lysosomal targets, such as endosomal Na+/H+ exchangers, presenilin enhancer 2 (PEN2), the lysosomal pathway leading to AMP-activated protein kinase (AMPK) activation, and the transcription factor EB (TFEB), modulated by metformin. Lysosomal dysfunctions resulting in autophagic and lysosomal acidification and biogenesis impairment appear to be hallmarks of many inherited and acquired neurodegenerative diseases. Lysosomes are not yet seen as a sort of cellular dump but are crucial in determining key signalling paths and processes involved in the clearance of aggregated proteins. Thus, the possibility of pharmacologically modulating them deserves great interest. Despite the potentiality of metformin in this context, many additional important issues, such as dosing, should be addressed in the future.

Antidiabetic drugs in Parkinson's disease

This review explores the intricate connections between type 2 diabetes (T2D) and Parkinson's disease (PD), both prevalent chronic conditions that primarily affect the aging population. These diseases share common early biochemical pathways that contribute to tissue damage. This manuscript also systematically compiles potential shared cellular mechanisms between T2D and PD and discusses the literature on the utilization of antidiabetic drugs as potential therapeutic options for PD. This review encompasses studies investigating the experimental and clinical efficacy of antidiabetic drugs in the treatment of Parkinson's disease, along with the proposed mechanisms of action. The exploration of the benefits of antidiabetic drugs in PD presents a promising avenue for the treatment of this neurodegenerative disorder.

Angiotensin-converting enzyme inhibition prevents l-dopa-induced dyskinesia in a 6-ohda-induced mouse model of Parkinson's disease

Parkinson's disease (PD) is characterised by severe movement defects and the degeneration of dopaminergic neurones in the midbrain. The symptoms of PD can be managed with dopamine replacement therapy using L-3, 4-dihydroxyphenylalanine (L-dopa), which is the gold standard therapy for PD. However, long-term treatment with L-dopa can lead to motor complications. The central renin-angiotensin system (RAS) is associated with the development of neurodegenerative diseases in the brain. However, the role of the RAS in dopamine replacement therapy for PD remains unclear. Here, we tested the co-treatment of the angiotensin-converting enzyme inhibitor (ACEI) with L-dopa altered L-dopa-induced dyskinesia (LID) in a 6-hydroxydopamine (6-OHDA)-lesioned mouse model of PD. Perindopril, captopril, and enalapril were used as ACEIs. The co-treatment of ACEI with L-dopa significantly decreased LID development in 6-OHDA-lesioned mice. In addition, the astrocyte and microglial transcripts involving Ccl2, C3, Cd44, and Iigp1 were reduced by co-treatment with ACEI and L-dopa in the 6-OHDA-lesioned striatum. In conclusion, co-treatment with ACEIs and L-dopa, such as perindopril, captopril, and enalapril, may mitigate the severity of L-DOPA-induced dyskinesia in a mouse model of PD.

AMPK-mediated autophagy pathway activation promotes ΔFosB degradation to improve levodopa-induced dyskinesia

BACKGROUND

Parkinson's disease patients on chronic levodopa often suffer from motor complications, which tend to reduce their quality of life. Levodopa-induced dyskinesia (LID) is one of the most prevalent motor complications, often characterized by abnormal involuntary movements, and the pathogenesis of LID is still unclear but recent studies have suggested the involvement of autophagy.

METHODS

The onset of LID was mimicked by chronic levodopa treatment in a unilateral 6-hydroxydopamine (6-OHDA) -lesion rat model. Overexpression of ΔFosB in HEK293 cells to mimic the state of ΔFosB accumulation. The modulation of the AMP-activated protein kinase (AMPK)-mediated autophagy pathway using by metformin, AICAR (an AMPK activator), Compound C (an AMPK inhibitor) and chloroquine (an autophagy pathway inhibitor). The severity of LID was assessed by axial, limb, and orofacial (ALO) abnormal involuntary movements (AIMs) score and in vivo electrophysiology. The activity of AMPK pathway as well as autophagy markers and FosB-ΔFosB levels were detected by western blotting. RT-qPCR was performed to detect the transcription level of FosB-ΔFosB. The mechanism of autophagy dysfunction was further explored by immunofluorescence and transmission electron microscopy.

RESULTS

In vivo experiments demonstrated that chronic levodopa treatment reduced AMPK phosphorylation, impaired autophagosome-lysosomal fusion and caused FosB-ΔFosB accumulation in the striatum of PD rats. Long-term metformin intervention improved ALO AIMs scores as well as reduced the mean power of high gamma (hγ) oscillations and the proportion of striatal projection neurons unstable in response to dopamine for LID rats. Moreover, the intervention of metformin promoted AMPK phosphorylation, ameliorated the impairment of autophagosome-lysosomal fusion, thus, promoting FosB-ΔFosB degradation to attenuate its accumulation in the striatum of LID rats. However, the aforementioned roles of metformin were reversed by Compound C and chloroquine. The results of in vitro studies demonstrated the ability of metformin and AICAR to attenuate ΔFosB levels by promoting its degradation, while Compound C and chloroquine could block this effect.

CONCLUSIONS

In conclusion, our results suggest that long-term metformin treatment could promote ΔFosB degradation and thus attenuate the development of LID through activating the AMPK-mediated autophagy pathway. Overall, our results support the AMPK-mediated autophagy pathway as a novel therapeutic target for LID and also indicate that metformin is a promising therapeutic candidate for LID.

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.

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.

Clemastine and metformin extend the window of NMDA receptor surface expression in ageing oligodendrocyte precursor cells

In the central nervous system, oligodendrocyte precursor cells (OPCs) proliferate and differentiate into myelinating oligodendrocytes throughout life, allowing for ongoing myelination and myelin repair. With age, differentiation efficacy decreases and myelin repair fails; therefore, recent therapeutic efforts have focused on enhancing differentiation. Many cues are thought to regulate OPC differentiation, including neuronal activity, which OPCs can sense and respond to via their voltage-gated ion channels and glutamate receptors. However, OPCs' density of voltage-gated ion channels and glutamate receptors differs with age and brain region, and correlates with their proliferation and differentiation potential, suggesting that OPCs exist in different functional cell states, and that age-associated states might underlie remyelination failure. Here, we use whole-cell patch-clamp to investigate whether clemastine and metformin, two pro-remyelination compounds, alter OPC membrane properties and promote a specific OPC state. We find that clemastine and metformin extend the window of NMDAR surface expression, promoting an NMDAR-rich OPC state. Our findings highlight a possible mechanism for the pro-remyelinating action of clemastine and metformin, and suggest that OPC states can be modulated as a strategy to promote myelin repair.

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.

Dopamine in the Regulation of Glucose Homeostasis, Pathogenesis of Type 2 Diabetes, and Chronic Conditions of Impaired Dopamine Activity/Metabolism: Implication for Pathophysiological and Therapeutic Purposes

Dopamine regulates several functions, such as voluntary movements, spatial memory, motivation, sleep, arousal, feeding, immune function, maternal behaviors, and lactation. Less clear is the role of dopamine in the pathophysiology of type 2 diabetes mellitus (T2D) and chronic complications and conditions frequently associated with it. This review summarizes recent evidence on the role of dopamine in regulating insular metabolism and activity, the pathophysiology of traditional chronic complications associated with T2D, the pathophysiological interconnection between T2D and chronic neurological and psychiatric disorders characterized by impaired dopamine activity/metabolism, and therapeutic implications. Reinforcing dopamine signaling is therapeutic in T2D, especially in patients with dopamine-related disorders, such as Parkinson's and Huntington's diseases, addictions, and attention-deficit/hyperactivity disorder. On the other hand, although specific trials are probably needed, certain medications approved for T2D (e.g., metformin, pioglitazone, incretin-based therapy, and gliflozins) may have a therapeutic role in such dopamine-related disorders due to anti-inflammatory and anti-oxidative effects, improvement in insulin signaling, neuroinflammation, mitochondrial dysfunction, autophagy, and apoptosis, restoration of striatal dopamine synthesis, and modulation of dopamine signaling associated with reward and hedonic eating. Last, targeting dopamine metabolism could have the potential for diagnostic and therapeutic purposes in chronic diabetes-related complications, such as diabetic retinopathy.

Restoring autophagic function: a case for type 2 diabetes mellitus drug repurposing in Parkinson's disease

Parkinson's disease (PD) is a predominantly idiopathic pathological condition characterized by protein aggregation phenomena, whose main component is alpha-synuclein. Although the main risk factor is ageing, numerous evidence points to the role of type 2 diabetes mellitus (T2DM) as an etiological factor. Systemic alterations classically associated with T2DM like insulin resistance and hyperglycemia modify biological processes such as autophagy and mitochondrial homeostasis. High glucose levels also compromise protein stability through the formation of advanced glycation end products, promoting protein aggregation processes. The ability of antidiabetic drugs to act on pathways impaired in both T2DM and PD suggests that they may represent a useful tool to counteract the neurodegeneration process. Several clinical studies now in advanced stages are looking for confirmation in this regard.

Recent research progress on metabolic syndrome and risk of Parkinson's disease

Parkinson's disease (PD) is one of the most widespread neurodegenerative diseases. PD is associated with progressive loss of substantia nigra dopaminergic neurons, including various motor symptoms (e.g., bradykinesia, rigidity, and resting tremor), as well as non-motor symptoms (e.g., cognitive impairment, constipation, fatigue, sleep disturbance, and depression). PD involves multiple biological processes, including mitochondrial or lysosomal dysfunction, oxidative stress, insulin resistance, and neuroinflammation. Metabolic syndrome (MetS), a collection of numerous connected cerebral cardiovascular conditions, is a common and growing public health problem associated with many chronic diseases worldwide. MetS components include central/abdominal obesity, systemic hypertension, diabetes, and atherogenic dyslipidemia. MetS and PD share multiple pathophysiological processes, including insulin resistance, oxidative stress, and chronic inflammation. In recent years, MetS has been linked to an increased risk of PD, according to studies; however, the specific mechanism remains unclear. Researchers also found that some related metabolic therapies are potential therapeutic strategies to prevent and improve PD. This article reviews the epidemiological relationship between components of MetS and the risk of PD and discusses the potentially relevant mechanisms and recent progress of MetS as a risk factor for PD. Furthermore, we conclude that MetS-related therapies are beneficial for the prevention and treatment of PD.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Diabetes mellitus, prediabetes and the risk of Parkinson's disease: a systematic review and meta-analysis of 15 cohort studies with 29.9 million participants and 86,345 cases

A diagnosis of diabetes mellitus and prediabetes has been associated with increased risk of Parkinson's disease (PD) in several studies, but results have not been entirely consistent. We conducted a systematic review and meta-analysis of cohort studies on diabetes mellitus, prediabetes and the risk of PD to provide an up-to-date assessment of the evidence. PubMed and Embase databases were searched for relevant studies up to 6th of February 2022. Cohort studies reporting adjusted relative risk (RR) estimates and 95% confidence intervals (CIs) for the association between diabetes, prediabetes and Parkinson's disease were included. Summary RRs (95% CIs) were calculated using a random effects model. Fifteen cohort studies (29.9 million participants, 86,345 cases) were included in the meta-analysis. The summary RR (95% CI) of PD for persons with diabetes compared to persons without diabetes was 1.27 (1.20-1.35, I2 = 82%). There was no indication of publication bias, based on Egger's test (p = 0.41), Begg's test (p = 0.99), and inspection of the funnel plot. The association was consistent across geographic regions, by sex, and across several other subgroup and sensitivity analyses. There was some suggestion of a stronger association for diabetes patients reporting diabetes complications than for diabetes patients without complications (RR = 1.54, 1.32-1.80 [n = 3] vs. 1.26, 1.16-1.38 [n = 3]), vs. those without diabetes (pheterogeneity=0.18). The summary RR for prediabetes was 1.04 (95% CI: 1.02-1.07, I2 = 0%, n = 2). Our results suggest that patients with diabetes have a 27% increased relative risk of developing PD compared to persons without diabetes, and persons with prediabetes have a 4% increase in RR compared to persons with normal blood glucose. Further studies are warranted to clarify the specific role age of onset or duration of diabetes, diabetic complications, glycaemic level and its long-term variability and management may play in relation to PD risk.

Alpha synuclein post translational modifications: potential targets for Parkinson's disease therapy?

Parkinson's disease (PD) is the most common neurodegenerative disorder with motor symptoms. The neuropathological alterations characterizing the brain of patients with PD include the loss of dopaminergic neurons of the nigrostriatal system and the presence of Lewy bodies (LB), intraneuronal inclusions that are mainly composed of alpha-synuclein (α-Syn) fibrils. The accumulation of α-Syn in insoluble aggregates is a main neuropathological feature in PD and in other neurodegenerative diseases, including LB dementia (LBD) and multiple system atrophy (MSA), which are therefore defined as synucleinopathies. Compelling evidence supports that α-Syn post translational modifications (PTMs) such as phosphorylation, nitration, acetylation, O-GlcNAcylation, glycation, SUMOylation, ubiquitination and C-terminal cleavage, play important roles in the modulation α-Syn aggregation, solubility, turnover and membrane binding. In particular, PTMs can impact on α-Syn conformational state, thus supporting that their modulation can in turn affect α-Syn aggregation and its ability to seed further soluble α-Syn fibrillation. This review focuses on the importance of α-Syn PTMs in PD pathophysiology but also aims at highlighting their general relevance as possible biomarkers and, more importantly, as innovative therapeutic targets for synucleinopathies. In addition, we call attention to the multiple challenges that we still need to face to enable the development of novel therapeutic approaches modulating α-Syn PTMs.

Glucose Metabolism Impairment in Parkinson's Disease

Impairments in systematic and regional glucose metabolism exist in patients with Parkinson's disease (PD) at every stage of the disease course, and such impairments are associated with the incidence, progression, and special phenotypes of PD, which affect each physiological process of glucose metabolism including glucose uptake, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and pentose phosphate shunt pathway. These impairments may be attributed to various mechanisms, such as insulin resistance, oxidative stress, abnormal glycated modification, blood-brain-barrier dysfunction, and hyperglycemia-induced damages. These mechanisms could subsequently cause excessive methylglyoxal and reactive oxygen species production, neuroinflammation, abnormal aggregation of protein, mitochondrial dysfunction, and decreased dopamine, and finally result in energy supply insufficiency, neurotransmitter dysregulation, aggregation and phosphorylation of α-synuclein, and dopaminergic neuron loss. This review discusses the glucose metabolism impairment in PD and its pathophysiological mechanisms, and briefly summarized the currently-available therapies targeting glucose metabolism impairment in PD, including glucagon-likepeptide-1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory peptide receptor agonists, metformin, and thiazoledinediones.

Metformin Adherence Reduces the Risk of Dementia in Patients With Diabetes: A Population-based Cohort Study

OBJECTIVE

Metformin is widely used as the first-line drug for type 2 diabetes mellitus and has numerous benefits apart from lowering blood glucose. However, metformin-retained regimen is challenged by newly launching, powerful glucose-lowering antiglycemic agents. This population-based cohort study examined the association between metformin adherence and the risk of dementia and Parkinson's disease (PD).

METHODS

Diabetic patients with metformin-included combination antiglycemic therapy were identified from the National Health Insurance Research Database and categorized into metformin-adherent and -nonadherent groups according to the medical record of the first year prescription. Patients contraindicated with metformin, severe diabetic complications, and poor drug compliance were excluded. The study outcome was the diagnosis of dementia or PD.

RESULTS

A total of 31 384 matched pairs were included after using propensity score matching and both groups were followed up for an average of 5 years. Metformin adherence was associated with a significantly lower risk of dementia (adjusted hazard risk ratio = 0.72, P < .001) but not PD (adjusted hazard risk ratio = 0.97, P = .825). Subgroup analysis revealed that the risk of dementia was significantly reduced in metformin-adherent patients, both male and female, aged >65 or ≤ 65 years, and with or without concurrent insulin treatment. This effect was not influenced by concurrent insulin treatment, which may eliminate the bias caused by the severity of diabetes mellitus.

CONCLUSION

Despite the launching of numerous new oral antiglycemic agents, metformin may provide further benefit on lowering risk of dementia beyond conventional glycemic control according to the real-world evidence.

Onset and mortality of Parkinson's disease in relation to type II diabetes

OBJECTIVES

There is growing evidence that Parkinson's disease and diabetes are partially related diseases; however, the association between the two, and the impact of specific treatments, are still unclear. We evaluated the effect of T2D and antidiabetic treatment on age at PD onset and on all-cause mortality.

RESEARCH DESIGN AND METHODS

The standardized rate of T2D was calculated for PD patients using the direct method and compared with subjects with essential tremor (ET) and the general Italian population. Age at onset and survival were also compared between patients without T2D (PD-noT2D), patients who developed T2D before PD onset (PD-preT2D) and patients who developed T2D after PD onset (PD-postT2D).

RESULTS

We designed a retrospective and prospective study. The T2D standardized ratio of PD (N = 8380) and ET (N = 1032) patients was 3.8% and 6.1%, respectively, while in the Italian general population, the overall prevalence was 5.3%. In PD-preT2D patients, on antidiabetic treatment, the onset of PD was associated with a + 6.2 year delay (p < 0.001) while no difference was observed in PD-postT2D. Occurrence of T2D before PD onset negatively affected prognosis (adjusted hazard ratio = 1.64 [95% CI 1.33-2.02]; p < 0.001), while no effect on survival was found in PD-postT2D subjects (hazard ratio = 0.86, [95% CI 0.53-1.39]; p = 0.54).

CONCLUSIONS

T2D, treated with any antidiabetic therapy before PD, is associated with a delay in its onset. Duration of diabetes increases mortality in PD-preT2D, but not in PD-postT2D. These findings prompt further studies on antidiabetic drugs as a potential disease-modifying therapy for PD.

Type 2 diabetes mellitus augments Parkinson's disease risk or the other way around: Facts, challenges and future possibilities

About 10% of the adult population is living with type 2 diabetes mellitus (T2DM) and 1% of the population over 60 years of age is suffering from Parkinson's disease (PD). A school of thought firmly believes that T2DM, an age-related disease, augments PD risk. Such relationship is reflected from the severity of PD symptoms in drug naive subjects possessing T2DM. Onset of Parkinsonian feature in case controls possessing T2DM corroborates the role of hyperglycemia in PD. A few cohort, meta-analysis and animal studies have shown an increased PD risk owing to insulin resistance. High fat diet and role of insulin signaling in the regulation of sugar metabolism, oxidative stress, α-synuclein aggregation and accumulation, inflammatory response and mitochondrial function in PD models and sporadic PD further connect the two. Although little is reported about the implication of PD in hyperglycemia and T2DM, a few studies have also contradicted. Ameliorative effect of anti-diabetic drugs on Parkinsonian symptoms and vague outcome of anti-PD medications in T2DM patients also suggest a link. The article reviews the literature supporting augmented risk of one by the other, analysis of proof of the concept, facts, challenges, future possibilities and standpoint on the subject.

Agathobaculum butyriciproducens Shows Neuroprotective Effects in a 6-OHDA-Induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second-most prevalent neurodegenerative disease and is characterized by dopaminergic neuronal death in the midbrain. Recently, the association between alterations in PD pathology and the gut microbiota has been explored. Microbiota-targeted interventions have been suggested as a novel therapeutic approach for PD. Agathobaculum butyriciproducens SR79^T (SR79) is an anaerobic bacterium. Previously, we showed that SR79 treatment induced cognitive improvement and reduced Alzheimer's disease pathologies in a mouse model. In this study, we hypothesized that SR79 treatment may have beneficial effects on PD pathology. To investigate the therapeutic effects of SR79 on PD, 6-hydroxydopamine (6-OHDA)-induced mouse models were used. D-Amphetamine sulfate (d-AMPH)-induced behavioral rotations and dopaminergic cell death were analyzed in unilateral 6-OHDA-lesioned mice. Treatment with SR79 significantly decreased ipsilateral rotations induced by d-AMPH. Moreover, SR79 treatment markedly activated the AKT/GSK3β signaling pathway in the striatum. In addition, SR79 treatment affected the Nrf2/ARE signaling pathway and its downstream target genes in the striatum of 6-OHDA-lesioned mice. Our findings suggest a protective role of SR79 in 6-OHDA-induced toxicity by regulating the AKT/Nrf2/ARE signaling pathway and astrocyte activation. Thus, SR79 may be a potential microbe-based intervention and therapeutic strategy for PD.

Parkinson's Disease and Sugar Intake-Reasons for and Consequences of a Still Unclear Craving

Lately, studies have shown that patients with Parkinson’s disease (PD) report a strong craving for sweets and consume significantly more fast-acting carbohydrates than healthy controls. Consuming food with a high-sugar content is assumed to lead to an increase in insulin concentration, which could positively influence dopamine concentration in the brain and unconsciously be used by patients as kind of “self-medication” to compensate for a lack of dopamine in PD. On the other hand, high-sugar intake could also lead to insulin resistance and diabetes, which is discussed as a causative factor for progressive neurodegeneration in PD. In this critical appraisal, we discuss the role of sugar intake and insulin on dopamine metabolism in patients with PD and how this could influence the potential neurodegeneration mediated by insulin resistance.

Metformin alleviates prolonged isoflurane inhalation induced cognitive decline via reducing neuroinflammation in adult mice

With the widespread use of volatile anesthetic agents in the prolonged sedation for COVID-19 pneumonia and ARDS, there is an urgent need to investigate the effects and treatments of lengthy low-concentration inhaled anesthetics exposure on cognitive function in adults. Previous studies showed that general anesthetics dose- and exposure length-dependently induced neuroinflammatory response and cognitive decline in neonatal and aging animals. The anti-diabetes drug metformin has anti-neuroinflammation effects by modulating microglial polarization and inhibiting astrocyte activation. In this study, we demonstrated that the inhalation of 1.3% isoflurane (a sub-minimal alveolar concentration, sub-MAC) for 6 h impaired recognition of novel objects from Day 1 to Day3 in adult mice. Prolonged sub-MAC isoflurane exposure also triggered typically reactive microglia and A1-like astrocytes in the hippocampus of adult mice on Day 3 after anesthesia. In addition, prolonged isoflurane inhalation switched microglia into a proinflammatory M1 phenotype characterized by elevated CD68 and iNOS as well as decreased arginase-1 and IL-10. Metformin pretreatment before anesthesia enhanced cognitive performance in the novel object test. The positive cellular modifications promoted by metformin pretreatment included the inhibition of reactive microglia and A1-like astrocytes and the polarization of microglia into M2 phenotype in the hippocampus of adult mice. In conclusion, prolonged sub-MAC isoflurane exposure triggered significant hippocampal neuroinflammation and cognitive decline in adult mice which can be alleviated by metformin pretreatment via inhibiting reactive microglia and A1-like astrocytes and promoting microglia polarization toward anti-inflammatory phenotype in the hippocampus.

Actions of Metformin in the Brain: A New Perspective of Metformin Treatments in Related Neurological Disorders

Metformin is a first-line drug for treating type 2 diabetes mellitus (T2DM) and one of the most commonly prescribed drugs in the world. Besides its hypoglycemic effects, metformin also can improve cognitive or mood functions in some T2DM patients; moreover, it has been reported that metformin exerts beneficial effects on many neurological disorders, including major depressive disorder (MDD), Alzheimer’s disease (AD) and Fragile X syndrome (FXS); however, the mechanism underlying metformin in the brain is not fully understood. Neurotransmission between neurons is fundamental for brain functions, and its defects have been implicated in many neurological disorders. Recent studies suggest that metformin appears not only to regulate synaptic transmission or plasticity in pathological conditions but also to regulate the balance of excitation and inhibition (E/I balance) in neural networks. In this review, we focused on and reviewed the roles of metformin in brain functions and related neurological disorders, which would give us a deeper understanding of the actions of metformin in the brain.

Reduced microglia activation following metformin administration or microglia ablation is sufficient to prevent functional deficits in a mouse model of neonatal stroke

BACKGROUND

Neonatal stroke is a devastating insult that can lead to life-long impairments. In response to hypoxic-ischaemic injury, there is loss of neurons and glia as well as a neuroinflammatory response mediated by resident immune cells, including microglia and astrocytes, which can exacerbate damage. Administration of the antidiabetic drug metformin has been shown to improve functional outcomes in preclinical models of brain injury and the cellular basis for metformin-mediated recovery is unknown. Given metformin's demonstrated anti-inflammatory properties, we investigated its role in regulating the microglia activation and used a microglia ablation strategy to investigate the microglia-mediated outcomes in a mouse model of neonatal stroke.

METHODS

Hypoxia-ischaemia (H-I) was performed on post-natal day 8. Metformin was administered for one week, starting one day after injury. Immunohistochemistry was used to examine the spatiotemporal response of microglia and astrocytes after hypoxia-ischaemia, with or without metformin treatment. To evaluate the effects of microglia depletion after hypoxia-ischaemia, we delivered Plexxikon 5622 for 1 or 2 weeks post-injury. The regional pattern of microglia and astrocyte depletion was assessed through immunohistochemistry. Motor behaviour was assessed with the righting reflex, hindlimb suspension, grip strength and cylinder tests.

RESULTS

Herein, we revealed a spatiotemporally regulated response of microglia and astrocytes after hypoxia-ischaemia. Metformin treatment after hypoxia-ischaemia had no effect on microglia number and proliferation, but significantly reduced microglia activation in all regions examined, concomitant with improved behavioural outcomes in injured mice. Plexxikon 5622 treatment successfully ablated microglia, resulting in a > 90% depletion in microglia in the neonatal brain. Microglia rapidly repopulated upon treatment cessation of Plexxikon. Most interesting, microglia ablation was sufficient to reduce functional deficits after hypoxia-ischaemia, mimicking the effects of 1 week of metformin treatment post-injury.

CONCLUSION

These results highlight the importance of regulating the neuroinflammatory response after neonatal stroke to promote recovery.

Novel role of peroxisome proliferator activated receptor-α in valproic acid rat model of autism: Mechanistic study of risperidone and metformin monotherapy versus combination

Autism spectrum disorder (ASD) is a neurodevelopmental disorder of heterogenous etiology exhibiting a challenge in understanding its exact neuro-pathophysiology. Recently, peroxisome proliferator activated receptor (PPAR)-α activation was found to play a fundamental role in neuroprotection and improving autistic-like-behaviors in experimental animal models of ASD through alleviating neuroinflammation, oxidative-stress, astrocyte reactivity, tauopathy in addition to its favorable role in metabolic regulation, thus attracting attention as a possible target in treatment of ASD. This study aimed to investigate the role of PPAR-α, astrocytic dysfunction and tauopathy in ASD and detect the possible neuroprotective effects of metformin (MET), through PPAR-α activation, and risperidone (RIS) either monotherapy or in combination in alleviating autistic-like-changes at behavioral and neurobiological levels in male Wistar rats. Pregnant female Wistar rats received valproic-acid (VPA) to induce autistic-like-behavioral and neurobiological alterations in their offspring. Chronic intra-peritoneal MET (100 mg/kg/day) and RIS (1 mg/kg/day) either monotherapy or in combination started from postnatal day (PND) 24 till PND61 (38 days). Prenatal VPA exposure simulated the autistic core behaviors associated with neurochemical and histopathological neurodevelopmental degenerative changes. Both MET and RIS either monotherapy or in combination were able to reverse these changes. The effect of MET was comparable to RIS. Moreover, MET was able to alleviate the RIS induced weight gain and improve cognitive functions highlighting its promising adjunctive role in alleviating ASD pathophysiology. Our study highlighted the favorable effects of MET and RIS both in monotherapy and in combination in alleviating the autistic-like-changes and proposed PPAR-α activation along with restoring astrocytes homeostasis as promising targets in novel therapeutic strategies in ASD.

Type 2 diabetes mellitus-associated cognitive dysfunction: Advances in potential mechanisms and therapies

Type 2 diabetes (T2D) and its target organ injuries cause distressing impacts on personal health and put an enormous burden on the healthcare system, and increasing attention has been paid to T2D-associated cognitive dysfunction (TDACD). TDACD is characterized by cognitive dysfunction, delayed executive ability, and impeded information-processing speed. Brain imaging data suggest that extensive brain regions are affected in patients with T2D. Based on current findings, a wide spectrum of non-specific neurodegenerative mechanisms that partially overlap with the mechanisms of neurodegenerative diseases is hypothesized to be associated with TDACD. However, it remains unclear whether TDACD is a consequence of T2D or a complication that co-occurs with T2D. Theoretically, anti-diabetes methods are promising neuromodulatory approaches to reduce brain injury in patients with T2D. In this review, we summarize potential mechanisms underlying TDACD and promising neurotropic effects of anti-diabetes methods and some neuroprotective natural compounds. Constructing screening or diagnostic tools and developing targeted treatment and preventive strategies would be expected to reduce the burden of TDACD.

Repressing PTBP1 fails to convert reactive astrocytes to dopaminergic neurons in a 6-hydroxydopamine mouse model of Parkinson's disease

Lineage reprogramming of resident glial cells to dopaminergic neurons (DAns) is an attractive prospect of the cell-replacement therapy for Parkinson's disease (PD). However, it is unclear whether repressing polypyrimidine tract binding protein 1 (PTBP1) could efficiently convert astrocyte to DAns in the substantia nigra and striatum. Although reporter-positive DAns were observed in both groups after delivering the adeno-associated virus (AAV) expressing a reporter with shRNA or CRISPR-CasRx to repress astroglial PTBP1, the possibility of AAV leaking into endogenous DAns could not be excluded without using a reliable lineage-tracing method. By adopting stringent lineage-tracing strategy, two other studies show that either knockdown or genetic deletion of quiescent astroglial PTBP1 fails to obtain induced DAns under physiological condition. However, the role of reactive astrocytes might be underestimated because upon brain injury, reactive astrocyte can acquire certain stem cell hallmarks that may facilitate the lineage conversion process. Therefore, whether reactive astrocytes could be genuinely converted to DAns after PTBP1 repression in a PD model needs further validation. In this study, we used Aldh1l1-CreERT2-mediated specific astrocyte-lineage-tracing method to investigate whether reactive astrocytes could be converted to DAns in a 6-hydroxydopamine (6-OHDA) mouse model of PD. However, we found that no astrocyte-originated DAn was generated after effective and persistent knockdown of astroglial PTBP1 either in the substantia nigra or in striatum, while AAV 'leakage' to nearby neurons was easily observed. Our results confirm that repressing PTBP1 does not convert astrocytes to DAns, regardless of physiological or PD-related pathological conditions.

The α7 nAChR allosteric modulator PNU-120596 amends neuroinflammatory and motor consequences of parkinsonism in rats: Role of JAK2/NF-κB/GSk3β/ TNF-α pathway

Parkinson's disease (PD) is the second most common neurodegenerative disorder and a leading cause of disability. The current gold standard for PD treatment, L-Dopa, has limited clinical efficacy and multiple side effects. Evidence suggests that activation of α7 nicotinic acetylcholine receptors (α7nAChRs) abrogates neuronal and inflammatory insults. Here we tested whether PNU-120596 (PNU), a type II positive allosteric modulator of α7 nAChR, has a critical role in regulating motor dysfunction and neuroinflammation correlated with the associated PD dysfunction. Neuroprotective mechanisms were investigated through neurobehavioral, molecular, histopathological, and immunohistochemical studies. PNU reversed motor incoordination and hypokinesia induced via the intrastriatal injection of 6-hydroxydopamine and manifested by lower falling latency in the rotarod test, short ambulation time and low rearing incidence in open field test. Tyrosine hydroxylase immunostaining showed a significant restoration of dopaminergic neurons following PNU treatment, in addition to histopathological restoration in nigrostriatal tissues. PNU halted striatal neuroinflammation manifested as a suppressed expression of JAK2/NF-κB/GSk3β accompanied by a parallel decline in the protein expression of TNF-α in nigrostriatal tissue denoting the modulator anti-inflammatory capacity. Moreover, the protective effects of PNU were partially reversed by the α7 nAChR antagonist, methyllycaconitine, indicating the role of α7 nAChR modulation in the mechanism of action of PNU. This is the first study to reveal the positive effects of PNU-120596 on motor derangements of PD via JAK2/NF-κB/GSk3β/ TNF-α neuroinflammatory pathways, which could offer a potential therapeutic strategy for PD.

Geroscience-guided repurposing of FDA-approved drugs to target aging: A proposed process and prioritization

Common chronic diseases represent the greatest driver of rising healthcare costs, as well as declining function, independence, and quality of life. Geroscience-guided approaches seek to delay the onset and progression of multiple chronic conditions by targeting fundamental biological pathways of aging. This approach is more likely to improve overall health and function in old age than treating individual diseases, by addressing aging the largest and mostly ignored risk factor for the leading causes of morbidity in older adults. Nevertheless, challenges in repurposing existing and moving newly discovered interventions from the bench to clinical care have impeded the progress of this potentially transformational paradigm shift. In this article, we propose the creation of a standardized process for evaluating FDA-approved medications for their geroscience potential. Criteria for systematically evaluating the existing literature that spans from animal models to human studies will permit the prioritization of efforts and financial investments for translating geroscience and allow immediate progress on the design of the next Targeting Aging with MEtformin (TAME)-like study involving such candidate gerotherapeutics.

Neuron-glia (mis)interactions in brain energy metabolism during aging

Life expectancy in humans is increasing, resulting in a growing aging population, that is accompanied by an increased disposition to develop cognitive deterioration. Hypometabolism is one of the multiple factors related to inefficient brain function during aging. This review emphasizes the metabolic interactions between glial cells (astrocytes, oligodendrocytes, and microglia) and neurons, particularly, during aging. Glial cells provide support and protection to neurons allowing adequate synaptic activity. We address metabolic coupling from the expression of transporters, availability of substrates, metabolic pathways, and mitochondrial activity. In aging, the main metabolic exchange machinery is altered with inefficient levels of nutrients and detrimental mitochondrial activity that results in high reactive oxygen species levels and reduced ATP production, generating a highly inflammatory environment that favors deregulated cell death. Here, we provide an overview of the glial-to-neuron mechanisms, from the molecular components to the cell types, emphasizing aging as the crucial risk factor for developing neurodegenerative/neuroinflammatory diseases.

Metformin Alleviates Neuroinflammation Following Intracerebral Hemorrhage in Mice by Regulating Microglia/Macrophage Phenotype in a Gut Microbiota-Dependent Manner

The gut microbiota plays a key role in regulating intracerebral hemorrhage (ICH)-induced neuroinflammation. The anti-neuroinflammatory effects of metformin (Met) have been reported in many central nervous system (CNS) diseases. However, whether Met regulates neuroinflammation through the gut microbiota in ICH-induced brain injury remains unknown. We found that Met treatment substantially alleviated neurological dysfunction and reduced neuroinflammation by inhibiting pro-inflammatory polarization of microglia/macrophages in mice with ICH. Moreover, Met treatment altered the microbiota composition and improved intestinal barrier function. The expression of lipopolysaccharide-binding protein (LBP), a biomarker of intestinal barrier damage, was also significantly reduced by Met treatment. Neuroinflammation was also potently ameliorated after the transplantation of fecal microbiota from Met-treated ICH mice. The neuroprotective effects of fecal microbiota transplantation (FMT) were similar to those of oral Met treatment. However, suppression of the gut microbiota negated the neuroprotective effects of Met in ICH mice. Therefore, Met is a promising therapeutic agent for neuroinflammation owing to ICH-induced imbalance of the gut microbiota.

Parkinson's disease and diabetes mellitus: common mechanisms and treatment repurposing

In the last decade, attention has become greater to the relationship between neurodegeneration and abnormal insulin signaling in the central nervous system, as insulin in the brain is implicated in neuronal survival, plasticity, oxidative stress and neuroinflammation. Diabetes mellitus and Parkinson’s disease are both aging-associated diseases that are turning into epidemics worldwide. Diabetes mellitus and insulin resistance not only increase the possibility of developing Parkinson’s disease but can also determine the prognosis and progression of Parkinsonian symptoms. Today, there are no available curative or disease modifying treatments for Parkinson’s disease, but the role of insulin and antidiabetic medications in neurodegeneration opens a door to treatment repurposing to fight against Parkinson’s disease, both in diabetic and nondiabetic Parkinsonian patients. Furthermore, it is essential to comprehend how a frequent and treatable disease such as diabetes can influence the progression of neurodegeneration in a challenging disease such as Parkinson’s disease. Here, we review the present evidence on the connection between Parkinson’s disease and diabetes and the consequential implications of the existing antidiabetic molecules in the severity and development of Parkinsonism, with a particular focus on glucagon-like peptide-1 receptor agonists.

Metformin Repurposing for Parkinson Disease Therapy: Opportunities and Challenges

Parkinson disease (PD) is a severe neurodegenerative disorder that affects around 2% of the population over 65 years old. It is characterized by the progressive loss of nigrostriatal dopaminergic neurons, resulting in motor disabilities of the patients. At present, only symptomatic cures are available, without suppressing disease progression. In this frame, the anti-diabetic drug metformin has been investigated as a potential disease modifier for PD, being a low-cost and generally well-tolerated medication, which has been successfully used for decades in the treatment of type 2 diabetes mellitus. Despite the precise mechanisms of action of metformin being not fully elucidated, the drug has been known to influence many cellular pathways that are associated with PD pathology. In this review, we present the evidence in the literature supporting the neuroprotective role of metformin, i.e., autophagy upregulation, degradation of pathological α-synuclein species, and regulation of mitochondrial functions. The epidemiological studies conducted in diabetic patients under metformin therapy aimed at evaluating the correlation between long-term metformin consumption and the risk of developing PD are also discussed. Finally, we provide an interpretation for the controversial results obtained both in experimental models and in clinical studies, thus providing a possible rationale for future investigations for the repositioning of metformin for PD therapy.

Metformin and fluoxetine improve depressive-like behavior in a murine model of Parkinsońs disease through the modulation of neuroinflammation, neurogenesis and neuroplasticity

Thereabout 30-40% of patients with Parkinson's Disease (PD) also have depression contributing to the loss of quality of life. Among the patients who treat depression, about 50% do not show significant improvement due to the limited efficacy of the treatment. So far, there are no effective disease-modifying treatments that can impede its progression. The current clinical approach is based on symptom management. Nonetheless, the reuse of drugs with excellent safety profiles represents an attractive alternative strategy for treating of different clinical aspects of PD. In this study, we evaluated the effects of metformin separately and associated with fluoxetine on depressive like-behavior and motor alterations in experimental Parkinson's disease. C57BL6 mice were induced with rotenone (2.5 mg/kg/day) for 20 days and treated with metformin (200 mg/kg/day) and fluoxetine (10 mg/kg/day) from the 5th day of induction. The animals were submitted to Sucrose Preference, Tail Suspension, and rotarod tests. Hippocampus, prefrontal cortex, and substantia nigra were dissected for molecular and morphological analysis. Metformin and fluoxetine prevented depressive-like behavior and improved motor impairment and increased TH nigral positive cells. Metformin and fluoxetine also reduced IBA-1 and GFAP positive cells in the hippocampus. Moreover, metformin reduced the phospho-NF-kB, IL-1β in the prefrontal cortex and iNOS levels in the hippocampus. Both metformin and fluoxetine increased neurogenesis by increasing KI67, but only the combined treatment increased neuronal survival by NeuN positive cells in the hippocampus. In addition, fluoxetine reduced cell death, decreasing caspase-3 and PARP-1 levels. Lastly, metformin potentiated the effect of fluoxetine on neuroplasticity by increasing BDNF positive cells. Metformin has antidepressant and antiparkinsonian potential due to anti-inflammatory neurogenic, and neuroplasticity-inducing effects when combined with fluoxetine.

Astrocytes as Perspective Targets of Exercise- and Caloric Restriction-Mimetics

Enhanced mental and physical activity can have positive effects on the function of aging brain, both in the experimental animals and human patients, although cellular mechanisms underlying these effects are currently unclear. There is a growing evidence that pre-clinical stage of many neurodegenerative diseases involves changes in interactions between astrocytes and neurons. Conversely, astrocytes are strategically positioned to mediate the positive influence of physical activity and diet on neuronal function. Thus, development of therapeutic agents which could improve the astroglia-neuron communications in ageing brain is of crucial importance. Recent advances in studies of cellular mechanisms of brain longevity suggest that astrocyte-neuron communications have a vital role in the beneficial effects of caloric restriction, physical exercise and their pharmacological mimetics on synaptic homeostasis and cognitive function. In particular, our recent data indicate that noradrenaline uptake inhibitor atomoxetine can enhance astrocytic Ca2+-signaling and astroglia-driven modulation of synaptic plasticity. Similar effects were exhibited by caloric restriction-mimetics metformin and resveratrol. The emerged data also suggest that astrocytes could be involved in the modulatory action of caloric restriction and its mimetics on neuronal autophagy. Still, the efficiency of astrocyte-targeting compounds in preventing age-related cognitive decline is yet to be fully explored, in particular in the animal models of neurodegenerative diseases and autophagy impairment.