Activation of AMPK/aPKCζ/CREB pathway by metformin is associated with upregulation of GDNF and dopamine

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.

Metformin Treatment Leads to Increased HIV Transcription and Gene Expression through Increased CREB Phosphorylation and Recruitment to the HIV LTR Promoter

Antiretroviral therapy has effectively suppressed HIV infection and replication and prolonged the lifespan of HIV-infected individuals. In the meantime, various complications including type 2 diabetes associated with the long-term antiviral therapy have shown steady increases. Metformin has been the front-line anti-hyperglycemic drug of choice and the most widely prescribed medication for the treatment of type 2 diabetes. However, little is known about the effects of Metformin on HIV infection and replication. In this study, we showed that Metformin treatment enhanced HIV gene expression and transcription in HIV-transfected 293T and HIV-infected Jurkat and human PBMC. Moreover, we demonstrated that Metformin treatment resulted in increased CREB expression and phosphorylation, and TBP expression. Furthermore, we showed that Metformin treatment increased the recruitment of phosphorylated CREB and TBP to the HIV LTR promoter. Lastly, we showed that inhibition of CREB phosphorylation/activation significantly abrogated Metformin-enhanced HIV gene expression. Taken together, these results demonstrated that Metformin treatment increased HIV transcription, gene expression, and production through increased CREB phosphorylation and recruitment to the HIV LTR promoter. These findings may help design the clinical management plan and HIV cure strategy of using Metformin to treat type 2 diabetes, a comorbidity with an increasing prevalence, in people living with HIV.

Effect of Metformin on Epidermal Neural Crest Stem Cells and Their Potential Application in Ameliorating Paclitaxel-induced Neurotoxicity Phenotype

AIMS

Epidermal Neural Crest Stem Cells (EPI-NCSCs) have emerged as prospective ideal candidates to meet the fundamental requirements of cell-based therapies in neurodegenerative disorders. The present study aimed to identify the potential of metformin in driving EPI-NCSCs to neuronal/glial differentiation and express neurotrophic factors as well as assess their therapeutic potential for mitigating the main behavioral manifestations of chemotherapy-induced neurotoxicity (CIN).

MAIN METHODS

EPI-NCSCs were extracted from the bulge region of hair follicle. Following expansion, transcript and protein expression profiles of key markers for stemness (Nestin, EGR-1, SOX-2 and 10), neurotrophic activity (BDNF, GDNF, NGF, FGF-2, and IL-6), and neuronal (TUB3, DCX, NRF and NeuN) and glial (PDGFRα, NG2, GFAP, and MBP) differentiation were determined on days 1 and 7 post-treatment with 10 and 100 μM metformin using real time-PCR and immunocytochemistry methods. Then, the in vivo function of metformin-treated stem cells was evaluated in the context of paclitaxel CIN. To do so, thermal hyperalgesia, mechanical allodynia, and spatial learning and memory tests were evaluated by Hotplate, Von Frey, and Morris water maze tests.

KEY FINDINGS

Our result indicated that exposure of EPI-NCSCs to metformin was associated with progressive decline in stemness markers and enhanced expression levels of several neurotrophic, neuron and oligodendrocyte-specific markers. Further, it was observed that intranasal metformin-treated EPI-NCSCs improved the cognitive impairment, and mechanical and thermal hypersensitivity induced by paclitaxel in rats.

SIGNIFICANCE

Collectively, we reasoned that metformin pretreatment of EPI-NCSCs might further enhance their therapeutic benefits against CIN.

Metformin antagonizes nickel-refining fumes-induced cell pyroptosis via Nrf2/GOLPH3 pathway in vitro and in vivo

Nickel compounds, an international carcinogen in the industrial environment, increased the risk of lung inflammation even lung cancer in Ni refinery workers. Metformin has displayed the intense anti-inflammation and anti-cancer properties through regulating pyroptosis. This study was designed to explore whether Nickel-refining fumes (NiRF) can induce cell pyroptosis and how AMPK/CREB/Nrf2 mediated the protection afforded by metformin against Ni particles-induced lung impairment. Our results represented that Ni fumes exposure evoked pyroptosis via GOLPH3 and induced oxidative stress, while, metformin treatment alleviated Ni particles-mediated above changes. Moreover, nuclear factor erythroid 2-related factor 2 (Nrf2) involved in the protection of metformin, and the deficiency of Nrf2 attenuated the beneficial protection. We also determined that Nrf2 was a downstream molecule of AMPK/CREB pathway. Furthermore, male C57BL/6 mice were administered with Ni at a dose of 2 mg/kg by non-exposed endotracheal instillation and metformin (100, 200 and 300 mg/kg) via oral gavage for 4 weeks. The results indicated that NiRF promoted GOLPH3 and pyroptosis by stimulating NLRP3, caspase-1, N-GSDMD, IL-18 and IL-1β expression. However, various doses of metformin reduced GOLPH3 and the above protein levels of pyroptosis, also improved AMPK/CREB/Nrf2 expression. In summary, we found that metformin suppressed NiRF-connected GOLPH3-prompted pyroptosis via AMPK/CREB/Nrf2 signaling pathway to confer pulmonary protection.

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.

Targeting Macroautophagy as a Therapeutic Opportunity to Treat Parkinson's Disease

Macroautophagy, an evolutionary conserved catabolic process in the eukaryotic cell, regulates cellular homeostasis and plays a decisive role in self-engulfing proteins, protein aggregates, dysfunctional or damaged organelles, and invading pathogens. Growing evidence from in vivo and in vitro models shows that autophagy dysfunction plays decisive role in the pathogenesis of various neurodegenerative diseases, including Parkinson's disease (PD). PD is an incurable and second most common neurodegenerative disease characterised by neurological and motor dysfunction accompanied of non-motor symptoms that can also reduce the life quality of patients. Despite the investment in research, the aetiology of the disease is still unknown and the therapies available are aimed mostly at ameliorating motor symptoms. Hence, therapeutics regulating the autophagy pathway might play an important role controlling the disease progression, reducing neuronal loss and even ameliorating non-motor symptoms. In this review, we highlight potential therapeutic opportunities involved in different targeting options like an initiation of autophagy, Leucine-rich repeat kinase 2 (LRRK2) inhibition, mitophagy, lysosomes, lipid metabolism, immune system, gene expression, biomarkers, and also non-pharmacological interventions. Thus, strategies to identify therapeutics targeting the pathways modulating autophagy might hold a future for therapy development against PD.

Methanolic Extract of Boswellia serrata Gum Protects the Nigral Dopaminergic Neurons from Rotenone-Induced Neurotoxicity

Boswellia serrata gum is a natural product that showed beneficial effects on neurodegenerative diseases in recent studies. In this study, we investigated the effects of Boswellia serrata resin on rotenone-induced dopaminergic neurotoxicity. Firstly, we attempted to see if the resin can induce AMP-activated protein kinase (AMPK) signaling pathway which has been known to have broad neuroprotective effects. Boswellia increased AMPK phosphorylation and reduced phosphorylation of mammalian target of rapamycin (p-mTOR) and α-synuclein (p-α-synuclein) in the striatum while increased the expression level of Beclin1, a marker for autophagy and brain-derived neurotrophic factor. Next, we examined the neuroprotective effects of the Boswellia extract in the rotenone-injected mice. The results showed that Boswellia evidently attenuated the loss of the nigrostriatal dopaminergic neurons and microglial activation caused by rotenone. Moreover, Boswellia ameliorated rotenone-induced decrease in the striatal dopamine and impairment in motor function. Accumulation of α-synuclein meditated by rotenone was significantly ameliorated by Boswellia. Also, we showed that β-boswellic acid, the active constituents of Boswellia serrata gum, induced AMPK phosphorylation and attenuated α-synuclein phosphorylation in SHSY5 cells. These results suggest that Boswellia protected the dopaminergic neurons from rotenone neurotoxicity via activation of the AMPK pathway which might be associated with attenuation of α-synuclein aggregation and neuroinflammation. Further investigations are warranted to identify specific molecules in Boswellia which are responsible for the neuroprotection.

Neurogenic effects of rotarod walking exercise in subventricular zone, subgranular zone, and substantia nigra in MPTP-induced Parkinson's disease mice

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, and its incidence is predicted to increase worldwide. Striatal dopamine depletion caused by substantia nigra (SN) degeneration is a pathological hallmark of PD and is strongly associated with cardinal motor and non-motor symptoms. Previous studies have reported that exercise increases neuroplasticity and promotes neurorestoration by increasing neurotrophic factors and synaptic strength and stimulating neurogenesis in PD. In the present study, we found that rotarod walking exercise, a modality of motor skill learning training, improved locomotor disturbances and reduced nigrostriatal degeneration in the subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In addition, our exercise regimen improved MPTP-induced perturbation of adult neurogenesis in some areas of the brain, including the subventricular zone, subgranular zone, SN, and striatum. Moreover, rotarod walking activated the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and induced brain-derived neurotrophic factor (BDNF) expression in these regions. The results suggest that motor skill learning training using rotarod walking improves adult neurogenesis and restores motor performance by modulating the AMPK/BDNF pathway. Therefore, our findings provide evidence for neuroprotective effects and improved neuroplasticity in PD through motor skill learning training.

Metformin and the risk of neurodegenerative diseases in patients with diabetes: A meta-analysis of population-based cohort studies

AIMS

The association between metformin use and neurodegenerative disease (ND) onset remains controversial. In this systematic review and meta-analysis, we aimed to determine the relationship between metformin use and ND risk based on data from population-based cohort studies.

METHODS

Articles were systematically searched in PubMed, EMBASE and Cochrane Library databases. Pooled relative risks (RRs) with 95% CIs were obtained using a random-effects model. Subgroup analyses, sensitivity analyses and meta-regression were performed to identify the sources of heterogeneity and strengthen the results.

RESULTS

Twelve population-based cohort studies involving 194,792 participants (94,462 metformin users and 100,330 metformin non-users) were eligible for inclusion in this meta-analysis. The pooled RR of NDs reached 0.77 (95% CI 0.67-0.88) when comparing metformin users with non-users. The effects were more prominent in long-term metformin users (≥4 years) (RR 0.29, 95% CI 0.13-0.44) and studies from Asian countries (RR 0.69, 95% CI 0.64-0.74). The effect estimates were stable when stratified by subtypes of NDs, study designs, and control definitions (p for interaction >0.05). Meta-regression did not identify the coefficients as the sources of heterogeneity (all p > 0.05).

CONCLUSIONS

This systematic review and meta-analysis found that metformin use, especially long-term use, was associated with lower ND risk. However, because there was substantial heterogeneity among studies, high-quality randomized controlled trials are still needed to confirm this finding.

Exploring the Pharmacological Potential of Metformin for Neurodegenerative Diseases

Metformin, one of the first-line of hypoglycemic drugs, has cardioprotective, anti-inflammatory and anticancer activities, in addition to its proven hypoglycemic effects. Furthermore, the preventive and therapeutic potential of metformin for neurodegenerative diseases has become a topic of concern. Increasing research suggests that metformin can prevent the progression of neurodegenerative diseases. In recent years, many studies have investigated the neuroprotective effect of metformin in the treatment of neurodegenerative diseases. It has been revealed that metformin can play a neuroprotective role by regulating energy metabolism, oxidative stress, inflammatory response and protein deposition of cells, and avoiding neuronal dysfunction and neuronal death. On the contrary, some have hypothesized that metformin has a two-sided effect which may accelerate the progression of neurodegenerative diseases. In this review, the results of animal experiments and clinical studies are reviewed to discuss the application prospects of metformin in neurodegenerative diseases.

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.

Targeting autophagy using small-molecule compounds to improve potential therapy of Parkinson's disease

Parkinson's disease (PD), known as one of the most universal neurodegenerative diseases, is a serious threat to the health of the elderly. The current treatment has been demonstrated to relieve symptoms, and the discovery of new small-molecule compounds has been regarded as a promising strategy. Of note, the homeostasis of the autolysosome pathway (ALP) is closely associated with PD, and impaired autophagy may cause the death of neurons and thereby accelerating the progress of PD. Thus, pharmacological targeting autophagy with small-molecule compounds has been drawn a rising attention so far. In this review, we focus on summarizing several autophagy-associated targets, such as AMPK, mTORC1, ULK1, IMPase, LRRK2, beclin-1, TFEB, GCase, ERRα, C-Abelson, and as well as their relevant small-molecule compounds in PD models, which will shed light on a clue on exploiting more potential targeted small-molecule drugs tracking PD treatment in the near future.

Metformin a Potential Pharmacological Strategy in Late Onset Alzheimer's Disease Treatment

Alzheimer's disease (AD) is one of the most devastating brain disorders. Currently, there are no effective treatments to stop the disease progression and it is becoming a major public health concern. Several risk factors are involved in the progression of AD, modifying neuronal circuits and brain cognition, and eventually leading to neuronal death. Among them, obesity and type 2 diabetes mellitus (T2DM) have attracted increasing attention, since brain insulin resistance can contribute to neurodegeneration. Consequently, AD has been referred to "type 3 diabetes" and antidiabetic medications such as intranasal insulin, glitazones, metformin or liraglutide are being tested as possible alternatives. Metformin, a first line antihyperglycemic medication, is a 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) activator hypothesized to act as a geroprotective agent. However, studies on its association with age-related cognitive decline have shown controversial results with positive and negative findings. In spite of this, metformin shows positive benefits such as anti-inflammatory effects, accelerated neurogenesis, strengthened memory, and prolonged life expectancy. Moreover, it has been recently demonstrated that metformin enhances synaptophysin, sirtuin-1, AMPK, and brain-derived neuronal factor (BDNF) immunoreactivity, which are essential markers of plasticity. The present review discusses the numerous studies which have explored (1) the neuropathological hallmarks of AD, (2) association of type 2 diabetes with AD, and (3) the potential therapeutic effects of metformin on AD and preclinical models.

FOXO and related transcription factors binding elements in the regulation of neurodegenerative disorders

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and others, are characterized by progressive loss of neuronal cells, which causes memory impairment and cognitive decline. Mounting evidence demonstrated the possible implications of diverse biological processes, namely oxidative stress, mitochondrial dysfunction, aberrant cell cycle re-entry, post-translational modifications, protein aggregation, impaired proteasome dysfunction, autophagy, and many others that cause neuronal cell death. The condition worsens as there is no effective treatment for such diseases due to their complex pathogenesis and mechanism. Mounting evidence demonstrated the role of regulatory transcription factors, such as NFκβ, FoxO, Myc, CREB, and others that regulate the biological processes and diminish the disease progression and pathogenesis. Studies demonstrated that forkhead box O (FoxO) transcription factors had been implicated in the regulation of aging and longevity. Further, the functions of FoxO proteins are regulated by different post-translational modifications (PTMs), namely acetylation, and ubiquitination. Various studies concluded that FoxO proteins exert both neuroprotective and neurotoxic properties depending on their regulation mechanism and activity in the brain. Thus, understanding the nature of FoxO expression and activity in the brain will help develop effective therapeutic strategies. Herein, firstly, we discuss the role of FoxO protein in cell cycle regulation and cell proliferation, followed by the regulation of FoxO proteins through acetylation and ubiquitination. We also briefly explain the activity and expression pattern of FoxO proteins in the neuronal cells and explain the mechanism through which FoxO proteins are rescued from oxidative stress-induced neurotoxicity. Later on, we present a detailed view of the implication of FoxO proteins in neurodegenerative disease and FoxO proteins as an effective therapeutic target.