Targeting Adenosine Monophosphate-Activated Protein Kinase by Metformin Adjusts Post-Ischemic Hyperemia and Extracellular Neuronal Discharge in Transient Global Cerebral Ischemia

Neuroprotective Effects of Metformin Through AMPK Activation in a Neurotoxin-Based Model of Cerebellar Ataxia

Cerebellar ataxia is a heterogeneous group of neural disorders clinically characterized by cerebellar dysfunction. The diagnosis of patients with progressive cerebellar ataxia is complex due to the direct correlation with other neuron diseases. Although there is still no cure for this pathological condition, some metabolic, hereditary, inflammatory, and immunological factors affecting cerebellar ataxia are being studied and may become therapeutic targets. Advances in studying the neuroanatomy, pathophysiology, and molecular biology of the cerebellum (CE) contribute to a better understanding of the mechanisms behind the development of this disorder. In this study, Wistar rats aged 30 to 35 days were injected intraperitoneally with 3-acetylpyridine (3-AP) and/or metformin (for AMP-activated protein kinase (AMPK) enzyme activation) and euthanized in 24 hours and 4 days after injection. We analyzed the neuromodulatory role of the AMPK on cerebellar ataxia induced by the neurotoxin 3-AP in the brain stem (BS) and CE, after pre-treatment for 7 and 15 days with metformin, a pharmacological indirect activator of AMPK. The results shown here suggest that AMPK activation in the BS and CE leads to a significant reduction in neuroinflammation in these regions. AMPK was able to restore the changes in fatty acid composition and pro-inflammatory cytokines caused by 3-AP, suggesting that the action of AMPK seems to result in a possible neuroprotection on the cerebellar ataxia model.

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.

Rhoa/ROCK, mTOR and Secretome-Based Treatments for Ischemic Stroke: New Perspectives

Ischemic stroke triggers a complex cascade of cellular and molecular events leading to neuronal damage and tissue injury. This review explores the potential therapeutic avenues targeting cellular signaling pathways implicated in stroke pathophysiology. Specifically, it focuses on the articles that highlight the roles of RhoA/ROCK and mTOR signaling pathways in ischemic brain injury and their therapeutic implications. The RhoA/ROCK pathway modulates various cellular processes, including cytoskeletal dynamics and inflammation, while mTOR signaling regulates cell growth, proliferation, and autophagy. Preclinical studies have demonstrated the neuroprotective effects of targeting these pathways in stroke models, offering insights into potential treatment strategies. However, challenges such as off-target effects and the need for tissue-specific targeting remain. Furthermore, emerging evidence suggests the therapeutic potential of MSC secretome in stroke treatment, highlighting the importance of exploring alternative approaches. Future research directions include elucidating the precise mechanisms of action, optimizing treatment protocols, and translating preclinical findings into clinical practice for improved stroke outcomes.

Human iPS-derived blood-brain barrier model exhibiting enhanced barrier properties empowered by engineered basement membrane

The basement membrane (BM) of the blood-brain barrier (BBB), a thin extracellular matrix (ECM) sheet underneath the brain microvascular endothelial cells (BMECs), plays crucial roles in regulating the unique physiological barrier function of the BBB, which represents a major obstacle for brain drug delivery. Owing to the difficulty in mimicking the unique biophysical and chemical features of BM in in vitro systems, current in vitro BBB models have suffered from poor physiological relevance. Here, we describe a highly ameliorated human BBB model accomplished by an ultra-thin ECM hydrogel-based engineered basement membrane (nEBM), which is supported by a sparse electrospun nanofiber scaffold that offers in vivo BM-like microenvironment to BMECs. BBB model reconstituted on a nEBM recapitulates the physical barrier function of the in vivo human BBB through ECM mechano-response to physiological relevant stiffness (∼500 kPa) and exhibits high efflux pump activity. These features of the proposed BBB model enable modelling of ischemic stroke, reproducing the dynamic changes of BBB, immune cell infiltration, and drug response. Therefore, the proposed BBB model represents a powerful tool for predicting the BBB permeation of drugs and developing therapeutic strategies for brain diseases.

Repurposing metformin to treat age-related neurodegenerative disorders and ischemic stroke

Aging is a risk factor for major central nervous system (CNS) disorders. More specifically, aging can be inked to neurodegenerative diseases (NDs) because of its deteriorating impact on neurovascular unit (NVU). Metformin, a first line FDA-approved anti-diabetic drug, has gained increasing interest among researchers for its role in improving aging-related neurodegenerative disorders. Additionally, numerous studies have illustrated metformin's role in ischemic stroke, a cerebrovascular disorder in which the NVU becomes dysfunctional which can lead to permanent life-threatening disabilities. Considering metformin's beneficial preclinical actions on various disorders, and the drug's role in alleviating severity of these conditions through involvement in commonly characterized cellular pathways, we discuss the potential of metformin as a suitable drug candidate for repurposing in CNS disorders.

Neuroprotective effects of metformin on traumatic brain injury in rats is associated with the AMP-activated protein kinase signaling pathway

Metformin is an activator of AMP-activated protein kinase (AMPK). Thus, it has the potential to restore energy in damaged neurons and attenuate secondary brain damage due to traumatic brain injury (TBI). This study aims to investigate the potential neuroprotective effects of metformin through the energy balance reestablishment in acute severe brain injury after TBI and explore the underlying mechanisms. Male Wistar rats were divided into eight groups. The veterinary coma scale (VCS) was used to assess short-term neurological deficits. Blood-Brain barrier (BBB) disruption was evaluated by Evans Blue method 6 h post-injury. Vestibulomotor function was evaluated by beam-walk and beam-balance methods. Brain water content and brain tissue phosphorylated and total AMPK were assessed by the wet/dry method and enzyme-linked immunosorbent assay (ELISA), respectively. In order to eliminate the effect of AMPK, compound C was used as an AMPK inhibitor. The presented study showed that TBI has led to significant brain edema, BBB disruption, neurological deficit, vestibulomotor dysfunction and decrease AMPK phosphorylation in the rat brain. Metformin (100 and 200 mg/kg doses) attenuated brain edema, improved BBB and vestibulomotor dysfunction compared to TBI or Vehicle groups (P < 0.001). Furthermore, the p-AMPK/AMPK ratio was increased by metformin administration compare to TBI or Vehicle groups (p < 0.0001). Inhibition of AMPK by compound C abolished Metformin neuroprotective effects (P < 0.05 compared to Met 200 group). This study suggests that metformin inhibits TBI-mediated secondary injury via phosphorylation of AMPK and improves neurobehavioral function following TBI, which provides a potential therapeutic opportunity in the treatment of TBI.

Long-term metformin therapy improves neurobehavioral functions and antioxidative activity after cerebral ischemia/reperfusion injury in rats

Metformin (MET),an antidiabetic drug, has shown antioxidative and neuroprotective effects. In the present investigation, we aimed to study the probable effects of MET on cerebral ischemia/reperfusion in rats. Rats underwent cerebral ischemia/reperfusion and MET was administered orally at doses of 100 and 200 mg/kg for 56 days. Anxiety- and depressive-like behaviors were evaluated by elevated plus-maze or forced swimming tests, respectively. was assessed by. Cognitive functions were assessed by Y-maze continuous alternation task and morris water maze. The activity of SOD and the level of BDNF were measured in brains samples. Our results showed that administration of 200 mg/kg MET reduced the percent of brain edema (84.00 ± 2.13) in comparison with the ischemic animals (91.25 ± 2.25) (p < 0.05). Administration of 200 mg/kg MET in ischemic animals improved anxiety-like behavior by increasing the percentage of the open arms entries (46.51 ± 3.13) and the percentage of the open arms time (32.70 ± 2.49) in comparison with the cerebral ischemia group (26.35 ± 7.02 and 15.32 ± 5.78, respectively) (all p < 0.001). MET treatment (200 mg/kg) increased the cognition index of correct alternations (90.20 ± 4.95) in comparison with the cerebral ischemia group (59.50 ± 8.01) (p < 0.05). MET at the both doses reduced escape latency compared to the cerebral ischemia animals (all p < 0.05). In addition, 200 mg/kg MET increased the time spent in the target quadrant (16.06 ± 0.58) in comparison with the ischemic animals (9.84 ± 0.92) (p < 0.001) and the both doses of the drug increased the number of crossing (5.42 ± 0.36 and 6.5 ± 0.42, respectively) compared to the cerebral ischemia group (3.75 ± 0.31) (p < 0.05 and p < 0.001, respectively). Moreover, 200 mg/kg MET reduced the immobility time (47.50 ± 9.00) in comparison with the cerebral ischemia group (93.43 ± 8.28) (p < 0.001). Furthermore, the both doses of MET increased the BDNF levels (4590 ± 197.6 and 4767 ± 44.10, respectively) in comparison with the ischemic animals (3807 ± 42.56) (p < 0.01 and p < 0.001, respectively). Also, the both doses of the drug increased the SOD activity of brain (52.67 ± 0.33 and 55.00 ± 0.57, respectively) compared to the ischemic animals (49.33 ± 0.33) (p < 0.01 and p < 0.001, respectively). Based on our data, long-term MET therapy may improve behavioral disorders following cerebral ischemia/reperfusion and can be considered as a novel therapeutic approach for the treatment of brain ischemic conditions.

Protective effects of Chrysin against memory impairment, cerebral hyperemia and oxidative stress after cerebral hypoperfusion and reperfusion in rats

Stroke is devastating and a leading cause of morbidity and mortality worldwide. Cerebral ischemia-reperfusion and its subsequent reactive hyperemia lead to neuronal damage in the hippocampus and cognitive decline. Chrysin (5, 7-dihydroxyflavone) is a well-known member of the flavonoid family with antioxidant and neuroprotective effects. Therefore, in the present study, the aim was to investigate whether chrysin will be able to recover the brain function caused by ischemia-reperfusion (I/R) in rats. Adult male Wistar rats (250-300 g) were randomly divided into five groups: and submitted to cerebral I/R or a sham surgery after three-weeks of pretreatment with chrysin (CH; 10, 30 and 100 mg/kg; P.O.) and/or normal saline containing %5 DMSO. Subsequently, sensorimotor scores, cognition, local cerebral blood flow, extracellular single unit, and histological parameters were evaluated following I/R. Hippocampus was used to evaluate biomarkers including: oxidative stress parameters and prostaglandin E2 (PGE2) using ELISA kits. Data showed that pretreatment with chrysin significantly improved sensorimotor signs, passive avoidance memory, and attenuated reactive hyperemia, and increased the average number of spikes/bin (p < 0.001). Furthermore, chrysin pre-treatment significantly decreased the levels of MDA, NO, and PGE2 (p < 0. 001), while increased the levels of GPX and the number of surviving cells in the hippocampal CA1 region (p < 0.01, p < 0.001; respectively). This study demonstrates that chrysin may have beneficial effects in the treatment of cognitive impairment and help recover the brain dysfunction induced by I/R.

Inhibition of microRNA-148b-3p alleviates oxygen-glucose deprivation/reoxygenation-induced apoptosis and oxidative stress in HT22 hippocampal neuron via reinforcing Sestrin2/Nrf2 signalling

MicroRNAs (miRNAs) have emerged as crucial regulators of neuronal injury during cerebral ischaemia/reperfusion injury. Various miRNAs are dysregulated during this pathological process; however, the precise role of these miRNAs in regulating neuronal injury remains largely unknown. In the current study, we explored the potential function of microRNA-148b-3p (miR-148b-3p) in regulating neuronal injury induced by oxygen-glucose deprivation/reoxygenation (OGD/R) in vitro, a cellular model for mimicking cerebral ischaemia/reperfusion injury. We found that miR-148b-3p expression was significantly decreased in neurons in response to OGD/R exposure. Importantly, miR-148b-3p overexpression decreased cell viability and exacerbated apoptosis and reactive oxygen species (ROS) production in OGD/R-exposed neurons. By contrast, miR-148b-3p inhibition improved cell viability and decreased apoptosis and ROS production in OGD/R-exposed neurons. Notably, Sestrin2, a cytoprotective gene, was identified as a miR-148b-3p target gene. miR-148b-3p inhibition markedly increased Sestrin2 expression as well as the activation of nuclear factor erythroid-2-related factor 2 (Nrf2) antioxidant signalling. Moreover, silencing of Sestrin2 or Nrf2 significantly reversed the miR-148-3p-inhibition-mediated protective effect in OGD/R-injured neurons. Overall, these results demonstrate that miR-148b-3p inhibition protects neurons from OGD/R-induced apoptosis and ROS production through reinforcing Nrf2 antioxidant signalling via upregulation of Sestrin2. Our study indicates that the miR-148b-3p/Sestrin2/Nrf2 axis plays an important role in regulating neuronal injury and may serve as a potential therapeutic target for providing neuroprotection during cerebral ischaemia/reperfusion injury.

Reciprocal Association between the Apical Junctional Complex and AMPK: A Promising Therapeutic Target for Epithelial/Endothelial Barrier Function?

Epithelial/endothelial cells adhere to each other via cell–cell junctions including tight junctions (TJs) and adherens junctions (AJs). TJs and AJs are spatiotemporally and functionally integrated, and are thus often collectively defined as apical junctional complexes (AJCs), regulating a number of spatiotemporal events including paracellular barrier, selective permeability, apicobasal cell polarity, mechano-sensing, intracellular signaling cascades, and epithelial morphogenesis. Over the past 15 years, it has been acknowledged that adenosine monophosphate (AMP)-activated protein kinase (AMPK), a well-known central regulator of energy metabolism, has a reciprocal association with AJCs. Here, we review the current knowledge of this association and show the following evidences: (1) as an upstream regulator, AJs activate the liver kinase B1 (LKB1)–AMPK axis particularly in response to applied junctional tension, and (2) TJ function and apicobasal cell polarization are downstream targets of AMPK and are promoted by AMPK activation. Although molecular mechanisms underlying these phenomena have not yet been completely elucidated, identifications of novel AMPK effectors in AJCs and AMPK-driven epithelial transcription factors have enhanced our knowledge. More intensive studies along this line would eventually lead to the development of AMPK-based therapies, enabling us to manipulate epithelial/endothelial barrier function.

The beneficial roles of metformin on the brain with cerebral ischaemia/reperfusion injury

Cerebral ischaemia/reperfusion (I/R) injury is the transient loss, followed by rapid return, of blood flow to the brain. This condition is often caused by strokes and heart attacks. The underlying mechanisms resulting in brain damage during cerebral I/R injury include mitochondrial dysregulation, increased oxidative stress/reactive oxygen species, blood-brain-barrier breakdown, inflammation of the brain, and increased neuronal apoptosis. Metformin is the first-line antidiabetic drug which has recently been shown to be capable of acting through the aforementioned pathways to improve recovery following cerebral I/R injury. However, some studies have suggested that metformin therapy may have no effect or even worsen recovery following cerebral I/R injury. The present review will compile and examine the available in vivo, in vitro, and clinical data concerning the neuroprotective effects of metformin following cerebral I/R injury. Any contradictory evidence will also be assessed and presented to determine the actual effectiveness of metformin treatment in stroke recovery.

The evidence of metabolic-improving effect of metformin in Ay/a mice with genetically-induced melanocortin obesity and the contribution of hypothalamic mechanisms to this effect

In diet-induced obesity, metformin (MF) has weight-lowering effect and improves glucose homeostasis and insulin sensitivity. However, there is no information on the efficiency of MF and the mechanisms of its action in melanocortin-type obesity. We studied the effect of the 10-day treatment with MF at the doses of 200, 400 and 600 mg/kg/day on the food intake and the metabolic and hormonal parameters in female C57Bl/6J (genotype A^y/a) agouti-mice with melanocortin-type obesity, and the influence of MF on the hypothalamic signaling in obese animals at the most effective metabolic dose (600 mg/kg/day). MF treatment led to a decrease in food intake, the body and fat weights, the plasma levels of glucose, insulin and leptin, all increased in agouti-mice, to an improvement of the lipid profile and glucose sensitivity, and to a reduced fatty liver degeneration. In the hypothalamus of obese agouti-mice, the leptin and insulin content was reduced and the expression of the genes encoding leptin receptor (LepR), MC₃- and MC₄-melanocortin receptors and pro-opiomelanocortin (POMC), the precursor of anorexigenic melanocortin peptides, was increased. The activities of AMP-activated kinase (AMPK) and the transcriptional factor STAT3 were increased, while Akt-kinase activity did not change from control C57Bl/6J (a/a) mice. In the hypothalamus of MF-treated agouti-mice (10 days, 600 mg/kg/day), the leptin and insulin content was restored, Akt-kinase activity was increased, and the activities of AMPK and STAT3 were reduced and did not differ from control mice. In the hypothalamus of MF-treated agouti-mice, the Pomc gene expression was six times higher than in control, while the gene expression for orexigenic neuropeptide Y was decreased by 39%. Thus, we first showed that MF treatment leads to an improvement of metabolic parameters and a decrease of hyperleptinemia and hyperinsulinaemia in genetically-induced melanocortin obesity, and the specific changes in the hypothalamic signaling makes a significant contribution to this effect of MF.

The protective effect of betulinic acid on microvascular responsivity and protein expression in alzheimer disease induced by cerebral micro-injection of beta-amyloid and streptozotocin

OBJECTIVE

Alzheimer's disease (AD) is mainly caused by accumulation of β-amyloid (Aβ) in vessels or parenchyma of the brain. Accordingly, natural compounds such as betulinic acid (BA) might improve the AD signs by increase in blood flow and through reduction in amyloid plaques.

METHODS

Intra-hippocampal injection of BA (0.2 and 0.4 μmol/L /10 μL DMSO /rat) was done at intervals of 180 and 10 min before co-microinjection of 0.1 μmol/L Aβ dissolved in PBS (5 μL/rat, hippocampi) and 1.5 mg/kg Streptozotocin dissolved in aCSF (10 μL/rat, lateral ventricles). Cerebro-vascular responsivity tested by Laser Doppler, BBB leakage, Elisa assays of cytokines (TNF-α and IL-10), and Western blot analysis of proteins (BDNF and AchE) in the hippocampus were assessed 1 month after the injections.

RESULTS

Microvascular reaction and BBB function were significantly impaired in AD rats, which were improved via BA pretreatment. BA could increase BDNF expression and decrease cytokine levels in the hippocampus of AD rats (especially 0.1 μmol/L Aβ: 0.4 μmol/L BA); however, no significant changes were detected in the blotting of AchE among the groups.

CONCLUSIONS

Betulinic acid could have a role in AD through protecting microcirculation, alleviating inflammation, and up-regulating BDNF expression which is clearer toward 1:4 molar ratios of Aβ to BA.

Vanillic acid attenuates cerebral hyperemia, blood-brain barrier disruption and anxiety-like behaviors in rats following transient bilateral common carotid occlusion and reperfusion

Transient bilateral common carotid artery occlusion (tBCCAO), followed by reperfusion, is a model of transient global hypoperfusion. In the present study we aimed to investigate the probable effects of Vanillic acid (VA) on some physiological parameters including cerebral hyperemia, blood-brain barrier (BBB) disruption, anxiety behaviors and neurological deficits induced by bilateral occlusion of the common carotid arteries and reperfusion (BCCAO/R) in rats. Rats were randomly divided into four groups; Sham, BCCAO/R, VA and VA+ BCCAO/R. Chronic cerebral hypoperfusion was induced after 2 weeks of pretreatment by VA. Subsequently, sensorimotor scores, elevated plus maze tests, cerebral hyperemia, and BBB disruption were evaluated 72 h after 30 min of BCCAO. Pretreatment of rats by VA improved sensory motor signs, anxiolytic behavior in BCCAO/R rats compared with untreated rats (p < 0.05). Further, VA attenuated reactive hyperemia and BBB disruption in BCCAO/R rats compared with untreated rats (p < 0.01). To our knowledge, this study is the first to reveal VA could attenuate reactive hyperemia and improve BBB disruption following BCCAO/R, and could improve neurological scores and anxiety like behaviors in this model of cerebral hypoperfusion. These results suggest that VA could be a promising pretreatment agent in cerebral hypoperfusion.

Is the Nociception Mechanism Altered in Offspring of Morphine-Abstinent Rats?

To investigate the effect of parental drug abuse on children, nociception, electrophysiological alteration, mRNA expression of opioid receptors, and expression of certain intracellular proteins in offspring of morphine-abstinent rats were studied. Adult male and female animals received water-soluble morphine for 21 days. Ten days after the last morphine administration, animals were placed for mating in 4 groups as follows: healthy (drug naive) female and male, morphine-abstinent female and healthy male, morphine-abstinent male and healthy female, morphine-abstinent male and morphine-abstinent female. Their adult male offspring were tested for nociception, neuronal discharge in nucleus accumbens (NAC) and prefrontal cortex (PFC). Our results showed that nociception in male offspring of all morphine-abstinent parent(s) groups was significantly reduced, compared with the control group. In the offspring of morphine-abstinent parent(s) groups, sensitivity to the antinociceptive effect of morphine was enhanced in chronic as well as in acute phases of the formalin test. Neuronal electrical activity reduced in the offspring of the morphine-exposed parent(s) in NAC as well as PFC regions. Moreover, our findings show that opioid receptors' expressions (µ, κ, and δ) increased in NAC of the litter of morphine-abstinent parent(s), compared with the control group. In addition, the expression of κ receptors was remarkably increased in the PFC in morphine-abstinent parent group, relative to the control group. The phosphorylated levels of extracellular regulated kinase 1/2 and cyclic adenosine monophosphate responsive element binding protein were significantly higher in the offspring of the morphine-abstinent parent(s) than the control group in the NAC. Our results indicated that endogenous opioid is altered in offspring of the morphine-exposed parent(s) and that heritage has a major role.

PERSPECTIVE

This study showed that nociception was reduced in offspring of morphine-abstinent rat(s) and also these litters had a low level of neuronal firing rate, and enhanced opioid receptors expression, especially in the NAC. Because these offspring are more sensitive to the analgesic effect of morphine, clinicians should consider this issue to manage the dosage of morphine for treating pain in children with an abstinent parent(s).

The stress polarity pathway: AMPK 'GIV'-es protection against metabolic insults

Loss of cell polarity impairs organ development and function; it can also serve as one of the first triggers for oncogenesis. In 2006-2007 two groups simultaneously reported the existence of a special pathway for maintaining epithelial polarity in the face of environmental stressors. In this pathway, AMPK, a key sensor of metabolic stress stabilizes tight junctions, preserves cell polarity, and thereby, maintains epithelial barrier functions. Accumulating evidence since has shown that pharmacologic activation of AMPK by Metformin protects the epithelial barrier against multiple environmental and pathological stressful states and suppresses tumorigenesis. How AMPK protects the epithelium remained unknown until recently Aznar et al. identified GIV/Girdin as a novel effector of AMPK at the cell-cell junctions; phosphorylation of GIV at a single site by AMPK appears to be both necessary and sufficient for strengthening tight junctions and preserving cell polarity and epithelial barrier function in the face of energetic stress. Here we review the fundamentals of this specialized signaling pathway that buttresses cell-cell junctions against stress-induced collapse and discuss its pathophysiologic relevance in the context of a variety of diseases, including cancers, diabetes, aging, and the growing list of beneficial effects of the AMPK-activator, Metformin.

To Use or Not to Use Metformin in Cerebral Ischemia: A Review of the Application of Metformin in Stroke Rodents

Ischemic strokes are major causes of death and disability. Searching for potential therapeutic strategies to prevent and treat stroke is necessary, given the increase in overall life expectancy. Epidemiological reports indicate that metformin is an oral antidiabetic medication that can reduce the incidence of ischemic events in patients with diabetes mellitus. Its mechanism of action has not been elucidated, but metformin pleiotropic effects involve actions in addition to glycemic control. AMPK activation has been described as one of the pharmacological mechanisms that explain the action of metformin and that lead to neuroprotective effects. Most experiments done in the cerebral ischemia model, via middle cerebral artery occlusion in rodents (MCAO), had positive results favoring metformin's neuroprotective role and involve several cellular pathways like oxidative stress, endothelial nitric oxide synthase activation, activation of angiogenesis and neurogenesis, autophagia, and apoptosis. We will review the pharmacological properties of metformin and its possible mechanisms that lead to neuroprotection in cerebral ischemia.

Subchronic metformin pretreatment enhances novel object recognition memory task in forebrain ischemia: behavioural, molecular, and electrophysiological studies

Metformin exerts its effect via AMP-activated protein kinase (AMPK), which is a key sensor for energy homeostasis that regulates different intracellular pathways. Metformin attenuates oxidative stress and cognitive impairment. In our experiment, rats were divided into 8 groups; some were pretreated with metformin (Met, 200 mg/kg) and (or) the AMPK inhibitor Compound C (CC) for 14 days. On day 14, rats underwent transient forebrain global ischemia. Data indicated that pretreatment of ischemic rats with metformin reduced working memory deficits in a novel object recognition test compared to group with ischemia–reperfusion (I–R) (P < 0.01). Pretreatment of the I–R animals with metformin increased phosphorylated cyclic-AMP response element-binding protein (pCREB) and c-fos levels compared to the I–R group (P < 0.001 for both). The level of CREB and c-fos was significantly lower in ischemic rats pretreated with Met + CC compared to the Met + I–R group. Field excitatory postsynaptic potential (fEPSP) amplitude and slope was significantly lower in the I–R group compared to the sham operation group (P < 0.001). Data showed that fEPSP amplitude and slope was significantly higher in the Met + I–R group compared to the I–R group (P < 0.001). Treatment of ischemic animals with Met + CC increased fEPSP amplitude and slope compared to the Met + I–R group (P < 0.01). We unravelled new aspects of the protective role of AMPK activation by metformin, further emphasizing the potency of metformin pretreatment against cerebral ischemia.

Metformin pretreatment enhanced learning and memory in cerebral forebrain ischaemia: the role of the AMPK/BDNF/P70SK signalling pathway

Context Metformin induced AMP-activated protein kinase (AMPK) and protected neurons in cerebral ischaemia. Objective This study examined pretreatment with metformin and activation of AMPK in molecular and behavioral levels associated with memory. Materials and methods Rats were pretreated with metformin (200 mg/kg) for 2 weeks and 4-vessels occlusion global cerebral ischaemia was induced. Three days after ischaemia, memory improvement was done by passive avoidance task and neurological scores were evaluated. The amount of Brain-Derived Neurotropic Factor (BDNF) and phosphorylated and total P70S6 kinase (P70S6K) were measured. Results Pretreatment with metformin (met) in the met + ischaemia/reperfusion (I/R) group reduced latency time for enter to dark chamber compared with the sham group (p < 0.001) and increased latency time compared with the I/R group (p < 0.001). Injection of Compound C (CC) (as an AMPK inhibitor) concomitant with metformin reduced latency time in I/R rats compared with the I/R + met group (p < 0.05). Neurological scores were reduced in met treated rats compared with the sham group. Pretreatment with metformin in I/R animals reduced levels of pro-BDNF compared with the I/R group (p < 0.001) but increased that compared with the sham group (p < 0.001). The level of pro-BDNF decreased in the met + CC + I/R group compared with the met + I/R group (p < 0.01). Pretreatment with metformin in I/R animals significantly increased P70S6K compared with the I/R group (p < 0.001). Conclusion Short-term memory in ischaemic rats treated with metformin increased step-through latency; sensory-motor evaluation was applied and a group of ischaemia rats that were pretreated with metformin showed high levels of BDNF, P70S6K that seemed to be due to increasing AMPK.

The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes

Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.