Activation of AMP-activated protein kinase by metformin protects against global cerebral ischemia in male rats: interference of AMPK/PGC-1α pathway

Neuroprotective effect of Apelin 13 on ischemic stroke by activating AMPK/GSK-3β/Nrf2 signaling

Background

Previous studies had showed that Apelin 13 could protect against apoptosis induced by ischemic/reperfusion (I/R). However, the mechanisms whereby Apelin 13 protected brain I/R remained to be elucidated. The present study was designed to determine whether Apelin 13 provided protection through AMPK/GSK-3β/Nrf2 pathway.

Methods

In vivo, the I/R model was induced and Apelin 13 was given intracerebroventricularly 15 min before reperfusion. The neurobehavioral scores, infarction volumes, and some cytokines in the brain were measured. For in vitro study, PC12 cells were used. To clarify the mechanisms, proteases inhibitors or siRNA were used. Protein levels were investigated by western blotting.

Results

The results showed that Apelin 13 treatment significantly reduced infarct size, improved neurological outcomes, decreased brain edema, and inhibited cell apoptosis, oxidative stress, and neuroinflammation after I/R. Apelin 13 significantly increased the expression of Nrf2 and the phosphorylation levels of AMPK and GSK-3β. Furthermore, in cultured PC12 cells, the same protective effects were also observed. Silencing Nrf2 gene with its siRNA abolished the Apelin 13’s prevention of I/R-induced PC12 cell injury, oxidative stress, and inflammation. Inhibition of AMPK by its siRNA decreased the level of Apelin 13-induced Nrf2 expression and diminished the protective effects of Apelin 13. The interplay relationship between GSK-3β and Nrf2 was also verified with relative overexpression. Using selective inhibitors, we further identified the upstream of AMPK/GSK-3β/Nrf2 is AR/Gα/PLC/IP3/CaMKK.

Conclusions

In conclusion, the previous results showed that Apelin 13 protected against I/R-induced ROS-mediated inflammation and oxidative stress through activating the AMPK/GSK-3β pathway by AR/Gα/PLC/IP3/CaMKK signaling, and further upregulated the expression of Nrf2-regulated antioxidant enzymes.

Regulation of mitochondrial biosynthesis and function by dietary carbohydrate levels and lipid sources in juvenile blunt snout bream Megalobrama amblycephala

This study aimed to investigate the effects of dietary non-protein energy adjustments on the mitochondrial biosynthesis and function of juvenile Megalobrama amblycephala. Fish (average weight: 37.98 ± 0.07 g) were fed eight diets containing two dietary carbohydrate levels (30% and 43%) and four lipid sources (fish oil, soybean oil, palm oil and the mixed oil) for 11 weeks. Liver mitochondrial respiratory chain complex V activity and ATP (adenosine triphosphate) content both increased significantly with increasing dietary carbohydrate levels, whereas the opposite was true for the AMP (adenosine 5'-monophosphate)/ATP ratio, hepatic transcripts of AMP-activated protein kinase α1 (AMPKα1), AMPKα2, peroxisome proliferators γ-activated receptor coativator-1α (PGC-1α), NADH dehydrogenase 1 and cytochrome c oxidase 1 (COX1) as well as the activities of Na⁺-K⁺-ATPase, succinate dehydrogenase (SDH), citrate synthase (CS) and mitochondrial respiratory chain complex I, III and IV. Additionally, hepatic ATP content, the transcripts of AMPKα, COX1 and ATP6 and the activities of Na⁺-K⁺-ATPase, SDH, CS and mitochondrial respiratory chain complex III were all significantly affected by lipid sources. Furthermore, an interaction between dietary carbohydrate levels and lipid sources was also observed in the activities of liver mitochondrial Na⁺-K⁺-ATPase and respiratory chain complex III as well as the transcripts of ATP6 and PGC-1α. Overall, these findings suggested that dietary carbohydrate levels and lipid sources remarkably affected the mitochondrial biosynthesis and function of M. amblycephala. A diet containing 30% carbohydrate and FO could boost its mitochondrial biosynthesis, while that of 30% carbohydrate and SO could enhance the mitochondrial function.

AMPK: Potential Therapeutic Target for Ischemic Stroke

5'-AMP-activated protein kinase (AMPK), a member of the serine/threonine (Ser/Thr) kinase group, is universally distributed in various cells and organs. It is a significant endogenous defensive molecule that responds to harmful stimuli, such as cerebral ischemia, cerebral hemorrhage, and, neurodegenerative diseases (NDD). Cerebral ischemia, which results from insufficient blood flow or the blockage of blood vessels, is a major cause of ischemic stroke. Ischemic stroke has received increased attention due to its '3H' effects, namely high mortality, high morbidity, and high disability. Numerous studies have revealed that activation of AMPK plays a protective role in the brain, whereas its action in ischemic stroke remains elusive and poorly understood. Based on existing evidence, we introduce the basic structure, upstream regulators, and biological roles of AMPK. Second, we analyze the relationship between AMPK and the neurovascular unit (NVU). Third, the actions of AMPK in different phases of ischemia and current therapeutic methods are discussed. Finally, we evaluate existing controversy and provide a detailed analysis, followed by ethical issues, potential directions, and further prospects of AMPK. The information complied here may aid in clinical and basic research of AMPK, which may be a potent drug candidate for ischemic stroke treatment in the future.

Dexmedetomidine pretreatment inhibits cerebral ischemia/reperfusion‑induced neuroinflammation via activation of AMPK

Focal ischemia/reperfusion (I/R) injury induced cerebral inflammation, aggravates brain damage. The aim of the present study was to investigate the protective mechanisms of dexmedetomidine (DEX) on I/R brain injury in rats. Sprague‑Dawley rats were divided to seven experimental groups (18 rats/group): Sham surgery; middle cerebral artery occlusion (MCAO) surgery (90 min); DEX10 [10 µg/kg intraperitoneal (i.p.) injection 30 min prior to MCAO]; DEX50 (50 µg/kg i.p. 30 min prior to MCAO); DEX100 (100 µg/kg i.p. 30 min prior to MCAO); DEX50+Yohimbine [YOH; 5 mg/kg 10 min prior to DEX (50 µg/kg i.p.) administration and MCAO] and YOH (5 mg/kg 40 min prior to MCAO). At 24 h post‑MCAO surgery, neurological deficit was examined by staining damaged brain tissues with 2,3,5‑triphenyltetrazolium chloride. Neuronal apoptosis in the cerebral cortex was histologically assessed by terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labeling staining, and the expression levels of phosphorylated (p)‑AMP‑activated protein kinase (AMPK; Thr172) was detected by western blotting. In addition, the expression levels of tumor necrosis factor (TNF)‑α and interleukin (IL)‑1β were assessed by ELISA. At days 1, 2 and 5 following I/R, motor functions were assessed by an observer blinded to the study. The brain infarct size, neurological deficit scores, number of apoptotic neurons, expression levels of pro‑inflammatory cytokines TNF‑α and IL‑1β were increased following MCAO, whereas the motor function scores were reduced. Pretreatment with DEX prior to MCAO can reverse the effects induced by I/R. Compared with rats in the Sham group, the expression levels of p‑AMPK were mildly increased in the MCAO group and highly increased in the three DEX‑treatment groups. Pretreatment with YOH reversed the above effects of DEX and produced a similar level of cerebral I/R injury. The results demonstrated that precondition with DEX exhibited anti‑inflammatory effects on brain ischemic injury mediated by AMPK signal pathway.

Effects of ischemic preconditioning on mitochondrial and metabolic neruoprotection: 5' adenosine monophosphate-activated protein kinase and sirtuins

Stroke and cardiac arrest result in cerebral ischemia, a highly prevalent medical issue around the world, which is characterized by a reduction or loss of blood flow to the brain. The loss of adequate nutrient supply in the brain during ischemia results in neuronal cell death contributing to cognitive and motor deficits that are usually permanent. Current effective therapies for cerebral ischemia are only applicable after the fact. Thus, the development of preventative therapies of ischemia is imperative. A field of research that continues to show promise in developing therapies for cerebral ischemia is ischemic preconditioning (IPC). IPC is described as exposure to sublethal ischemic events, which induce adaptive changes that provide tolerance to future ischemic events. Through either transient sub-lethal ischemic events, or the actions of a preconditioning molecular mimetic, IPC typically results in augmented gene expression and cellular metabolism. A pivotal target of such changes in gene expression and metabolism is the mitochondrion. Direct and indirect effects on mitochondria by IPC can result in the activation of 5’ adenosine monophosphate-activated protein kinase (AMPK), a master regulator of cellular metabolism. Changes in the activity of the posttranslational modifiers, SIRT1 and SIRT5, also contribute to the overall adaptive processes in cellular metabolism and mitochondrial functioning. In this review, we present recently collected evidence to highlight the neuroprotective interactions of mitochondria with AMPK, SIRT1, and SIRT5 in IPC. To produce this review, we utilized PubMed and previous reviews to target and to consolidate the relevant studies and lines of evidence.

Metformin Improves Neurologic Outcome Via AMP-Activated Protein Kinase-Mediated Autophagy Activation in a Rat Model of Cardiac Arrest and Resuscitation

BACKGROUND

Sudden cardiac arrest (CA) often results in severe injury to the brain, and neuroprotection after CA has proved to be difficult to achieve. Herein, we sought to investigate the effects of metformin pretreatment on brain injury secondary to CA and cardiopulmonary resuscitation.

METHODS AND RESULTS

Rats were subjected to 9-minute asphyxial CA after receiving daily metformin treatment for 2 weeks. Survival rate, neurologic deficit scores, neuronal loss, AMP-activated protein kinase (AMPK), and autophagy activation were assessed at indicated time points within the first 7 days after return of spontaneous circulation. Our results showed that metformin pretreatment elevated the 7-day survival rate from 55% to 85% and significantly reduced neurologic deficit scores. Moreover, metformin ameliorated CA-induced neuronal degeneration and glial activation in the hippocampal CA1 region, which was accompanied by augmented AMPK phosphorylation and autophagy activation in affected neuronal tissue. Inhibition of AMPK or autophagy with pharmacological inhibitors abolished metformin-afforded neuroprotection, and augmented autophagy induction by metformin treatment appeared downstream of AMPK activation.

CONCLUSIONS

Taken together, our data demonstrate, for the first time, that metformin confers neuroprotection against ischemic brain injury after CA/cardiopulmonary resuscitation by augmenting AMPK-dependent autophagy activation.

mTOR/AMPK signaling in the brain: Cell metabolism, proteostasis and survival

The mechanistic (or mammalian) target of rapamycin (mTOR) and the adenosine monophosphate-activated protein kinase (AMPK) regulate cell survival and metabolism in response to diverse stimuli such as variations in amino acid content, changes in cellular bioenergetics, oxygen levels, neurotrophic factors and xenobiotics. This Opinion paper aims to discuss the current state of knowledge regarding how mTOR and AMPK regulate the metabolism and survival of brain cells and the close interrelationship between both signaling cascades. It is now clear that both mTOR and AMPK pathways regulate cellular homeostasis at multiple levels. Studies so far demonstrate that dysregulation in these two pathways is associated with neuronal injury, degeneration and neurotoxicity, but the mechanisms involved remain unclear. Most of the work so far has been focused on their antagonistic regulation of autophagy, but recent findings highlight that changes in protein synthesis, metabolism and mitochondrial function are likely to play a role in the regulatory effects of both mTOR and AMPK on neuronal health. Understanding the role and relationship between these two master regulators of cell metabolism is crucial for future therapeutic approaches to counteract alterations in cell metabolism and survival in brain injury and disease.

Pre-Treatment with Metformin in Comparison with Post-Treatment Reduces Cerebral Ischemia Reperfusion Induced Injuries in Rats

Objective

To explore the effects of pre versus post ischemic treatment with metformin after global cerebral ischemia in rats.

Methods

Male Wister rats underwent forebrain ischemia by bilateral common carotid artery occlusion for 17 min. Metformin (200 mg/kg) or vehicle was given orally by gavage for 7-14 days. Rats were divided into: control, metformin pre-treatment, metformin post-treatment and metformin pre and post continuous treatment groups. Cerebral infarct size, histopathology, myeloperoxidase and serum malondialdehyde were measured 7 days after ischemia.

Results

Histopathological analysis showed that metformin pre-treatment significantly decreased leukocyte infiltration, myeloperoxidase activity and also malondialdehyde level. Metformin pre-treatment and metformin post-treatment reduced infarct size compared with the control group, but it was not significant in the pre and post continuous treatment group.

Conclusion

Our findings suggest that pre-treatment with metformin in comparison with post-treatment in experimental stroke can reduce the extent of brain damage and is more neuroprotective at least in part by inhibiting oxidative stress and inflammation.

AMP-activated protein kinase and adenosine are both metabolic modulators that regulate chloride secretion in the shark rectal gland ( Squalus acanthias)

The production of endogenous adenosine during secretagogue stimulation of CFTR leads to feedback inhibition limiting further chloride secretion in the rectal gland of the dogfish shark (Squalus acanthias). In the present study, we examined the role of AMP-kinase (AMPK) as an energy sensor also modulating chloride secretion through CFTR. We found that glands perfused with forskolin and isobutylmethylxanthine (F + I), potent stimulators of chloride secretion in this ancient model, caused significant phosphorylation of the catalytic subunit Thr172 of AMPK. These findings indicate that AMPK is activated during energy-requiring stimulated chloride secretion. In molecular studies, we confirmed that the activating Thr172 site is indeed present in the α-catalytic subunit of AMPK in this ancient gland, which reveals striking homology to AMPKα subunits sequenced in other vertebrates. When perfused rectal glands stimulated with F + I were subjected to severe hypoxic stress or perfused with pharmacologic inhibitors of metabolism (FCCP or oligomycin), phosphorylation of AMPK Thr172 was further increased and chloride secretion was dramatically diminished. The pharmacologic activation of AMPK with AICAR-inhibited chloride secretion, as measured by short-circuit current, when applied to the apical side of shark rectal gland monolayers in primary culture. These results indicate that that activated AMPK, similar to adenosine, transmits an inhibitory signal from metabolism, that limits chloride secretion in the shark rectal gland.

Targeting AMPK Signaling as a Neuroprotective Strategy in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder. It is characterized by the accumulation of intracellular α-synuclein aggregates and the degeneration of nigrostriatal dopaminergic neurons. While no treatment strategy has been proven to slow or halt the progression of the disease, there is mounting evidence from preclinical PD models that activation of 5'-AMP-activated protein kinase (AMPK) may have broad neuroprotective effects. Numerous dietary supplements and pharmaceuticals (e.g., metformin) that increase AMPK activity are available for use in humans, but clinical studies of their effects in PD patients are limited. AMPK is an evolutionarily conserved serine/threonine kinase that is activated by falling energy levels and functions to restore cellular energy balance. However, in response to certain cellular stressors, AMPK activation may exacerbate neuronal atrophy and cell death. This review describes the regulation and functions of AMPK, evaluates the controversies in the field, and assesses the potential of targeting AMPK signaling as a neuroprotective treatment for PD.

Design of Small Molecule Autophagy Modulators: A Promising Druggable Strategy

Autophagy is a lysosome-dependent mechanism of intracellular degradation for maintaining cellular homeostasis. Dysregulation of autophagy has been verified to be closely linked to a number of human diseases. Consequently, targeting autophagy has been highlighted as a novel therapeutic strategy for clinical utility. Mounting efforts have been done in recent years to elucidate the mechanisms of autophagy regulation and to identify potential modulators of autophagy. However, most of the compounds target complex and multifaceted pathway and proteins, which may limit the evaluation of therapeutic value and in depth studies as chemical tools. Therefore, the development of specific and active autophagy modulators becomes most desirable. Here, we briefly review the regulation of autophagy and then summarize the recent development of small molecules targeting the core autophagic machinery. Finally, we put forward our viewpoints on the current problems, with the aim to provide reference for future drug discovery and potential therapeutic perspectives on novel, potent, selective autophagy modulators.

Biochemical targets of drugs mitigating oxidative stress via redox-independent mechanisms

Acute or chronic oxidative stress plays an important role in many pathologies. Two opposite approaches are typically used to prevent the damage induced by reactive oxygen and nitrogen species (RONS), namely treatment either with antioxidants or with weak oxidants that up-regulate endogenous antioxidant mechanisms. This review discusses options for the third pharmacological approach, namely amelioration of oxidative stress by 'redox-inert' compounds, which do not inactivate RONS but either inhibit the basic mechanisms leading to their formation (i.e. inflammation) or help cells to cope with their toxic action. The present study describes biochemical targets of many drugs mitigating acute oxidative stress in animal models of ischemia-reperfusion injury or N-acetyl-p-aminophenol overdose. In addition to the pro-inflammatory molecules, the targets of mitigating drugs include protein kinases and transcription factors involved in regulation of energy metabolism and cell life/death balance, proteins regulating mitochondrial permeability transition, proteins involved in the endoplasmic reticulum stress and unfolded protein response, nuclear receptors such as peroxisome proliferator-activated receptors, and isoprenoid synthesis. The data may help in identification of oxidative stress mitigators that will be effective in human disease on top of the current standard of care.

Role of the AMPK pathway in promoting autophagic flux via modulating mitochondrial dynamics in neurodegenerative diseases: Insight into prion diseases

Neurons are highly energy demanding cells dependent on the mitochondrial oxidative phosphorylation system. Mitochondria generate energy via respiratory complexes that constitute the electron transport chain. Adenosine triphosphate depletion or glucose starvation act as a trigger for the activation of adenosine monophosphate-activated protein kinase (AMPK). AMPK is an evolutionarily conserved protein that plays an important role in cell survival and organismal longevity through modulation of energy homeostasis and autophagy. Several studies suggest that AMPK activation may improve energy metabolism and protein clearance in the brains of patients with vascular injury or neurodegenerative disease. Mild mitochondrial dysfunction leads to activated AMPK signaling, but severe endoplasmic reticulum stress and mitochondrial dysfunction may lead to a shift from autophagy towards apoptosis and perturbed AMPK signaling. Hence, controlling mitochondrial dynamics and autophagic flux via AMPK activation might be a useful therapeutic strategy in neurodegenerative diseases to reinstate energy homeostasis and degrade misfolded proteins. In this review article, we discuss briefly the role of AMPK signaling in energy homeostasis, the structure of AMPK, activation mechanisms of AMPK, regulation of AMPK, the role of AMPK in autophagy, the role of AMPK in neurodegenerative diseases, and finally the role of autophagic flux in prion diseases.

Therapeutic effects of baicalein on rotenone-induced Parkinson's disease through protecting mitochondrial function and biogenesis

Mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson’s disease (PD) for several decades, and disturbed mitochondrial biogenesis (mitobiogenesis) was recently found to be a common phenomenon in PD. Baicalein, a major bioactive flavone of Scutellaria baicalensis Georgi, exerted neuroprotective effects in several experimental PD models. However, the effects of baicalein in rotenone-induced PD rats and the possible mechanisms remain poorly understood. In this study, we evaluated the therapeutic effects of baicalein and explored its mechanism of action in rotenone-induced PD models. The results indicated that behavioural impairments and the depletion of dopaminergic neurons induced by rotenone were attenuated by baicalein. Furthermore, in rotenone-induced parkinsonian rats, baicalein treatment effectively restored mitochondrial function and improved mitobiogenesis, as determined by measuring the mitochondrial density and key regulators involved in mitobiogenesis. Additionally, we confirmed that baicalein enhanced mitobiogenesis through the cAMP-responsive element binding protein (CREB) and glycogen synthase kinase-3β (GSK-3β) pathways in rotenone-treated SH-SY5Y cells. Moreover, we demonstrated that the cytoprotective effects of baicalein could be attenuated by the mitobiogenesis inhibitor chloramphenicol as well as CREB siRNA transfection. Overall, our results suggested that baicalein partially enhanced mitobiogenesis to restore mitochondrial function, thus exerting therapeutic effects in rotenone-induced PD models.

Metformin ameliorates BSCB disruption by inhibiting neutrophil infiltration and MMP-9 expression but not direct TJ proteins expression regulation

Blood-spinal cord barrier (BSCB) disruption is a major process for the secondary injury of spinal cord injury (SCI) and is considered to be a therapeutic target for SCI. Previously, we demonstrated that metformin could improve functional recovery after SCI; however, the effect of metformin on BSCB is still unknown. In this study, we found that metformin could prevent the loss of tight junction (TJ) proteins at day 3 after SCI in vivo, but in vitro there was no significant difference of these proteins between control and metformin treatment in endothelial cells. This indicated that metformin-induced BSCB protection might not be mediated by up-regulating TJ proteins directly, but by inhibiting TJ proteins degradation. Thus, we investigated the role of metformin on MMP-9 and neutrophils infiltration. Neutrophils infiltration is the major source of the enhanced MMP-9 in SCI. Our results showed that metformin decreased MMP-9 production and blocked neutrophils infiltration at day 1 after injury, which might be related to ICAM-1 down-regulation. Also, our in vitro study showed that metformin inhibited TNF-α-induced MMP-9 up-regulation in neutrophils, which might be mediated via an AMPK-dependent pathway. Together, it illustrated that metformin prevented the breakdown of BSCB by inhibiting neutrophils infiltration and MMP-9 production, but not by up-regulating TJ proteins expression. Our study may help to better understand the working mechanism of metformin on SCI.

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.

Metformin ameliorates hypoxia/reoxygenation-induced cardiomyocyte apoptosis based on the SIRT3 signaling pathway

Myocardial hypoxia/reoxygenation (H/R) injury is one of the main causes of death and disability worldwide. However, a limited number of therapies are available to minimize the detrimental effects of this injury. Recently, researchers have demonstrated that metformin exerts direct cardioprotective effects against H/R. The aim of this study was to investigate the underlying mechanisms of how metformin affects myocardial hypoxia/reoxygenation (H/R) injury. In our study, the activities of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) as well as the levels of malondialdehyde (MDA) were measured. Following H/R injury, LDH activity and MDA levels were evidently increased, while SOD activity and cell viability significantly decreased. Surprisingly, metformin downregulated the levels of relative reactive oxygen species (ROS) and upregulated the levels of relative SOD following H/R injury. Furthermore, metformin-treated cells exhibited reduced cell death, which was demonstrated to be associated with increased SIRT3 expression compared to that in the control group, as evidenced by blocking of the protective effects of metformin on cell apoptosis by the SIRT3 inhibitor Nicotinamide (NAM). Therefore, our results demonstrate that metformin improves cells viability following H/R, and this cardioprotective effect is partly mediated by the SIRT3 signaling pathway.

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.

Involvement of arterial baroreflex and nicotinic acetylcholine receptor α7 subunit pathway in the protection of metformin against stroke in stroke-prone spontaneously hypertensive rats

Stroke is a leading cause of mortality and disability worldwide. There is growing evidence that metformin (Met) has potent neuroprotective effects; however, its mechanisms remain unclear. We examined the role of the arterial baroreflex and cholinergic-α7 nicotinic acetylcholine receptor (α7nAChR) anti-inflammory pathway in the beneficial effects of Met against stroke. Stroke-prone spontaneously hypertensive rats (SHRSP) were used to observe stroke development indicated by lifespan of SHRSP and the ischemic injury induced by permanent middle cerebral artery occlusion (MCAO). Sinoaortic denervation was used to inactivate the arterial baroreflex. MCAO were also performed in α7nAChR knockout (KO) mice. Briefly, Met increased the life span of SHRSP and reduced the infarct area induced by MCAO. Met also improved the function of arterial baroreflex. The beneficial effects of Met on stroke were markedly attenuated by blunting the arterial baroreflex. Met up-regulated the expression of vesicular acetylcholine transporter (VAChT) and α7nAChR, down-regulated the level of pro-inflammtory cytokines in serum and peri-infarct of ischemic brain. Arterial baroreflex dysfunction decreased the expression of VAchT and α7nAChR, showed upward tendency in the level of pro-inflammtory cytokines. Most importantly, arterial baroreflex dysfunction nearly abolished such effect of Met on cholinergic signaling. In addition, the α7nAChR KO mice also had significantly worse ischemic damage induced by MCAO, and neuroprotection of Met disappeared in α7nAChR KO mice. In conclusion, Met improved the arterial baroreflex function, and then enhancing cholinergic anti-inflammatory pathway in an α7nAChR-dependent manner, thereby effectively prevent ischemic induced brain injury and delayed stroke onset in SHRSP.

Metformin protects the brain against ischemia/reperfusion injury through PI3K/Akt1/JNK3 signaling pathways in rats

Although Metformin, a first-line antidiabetic drug, can ameliorate ischemia/reperfusion (I/R) induced brain damage, but how metformin benefits injured hippocampus and the mechanisms are still largely unknown. Therefore, the aim of this study was to investigate the neuroprotective mechanisms of metformin against ischemic brain damage induced by cerebral I/R and to explore whether the Akt-mediated down-regulation of the phosphorylation of JNK3 signaling pathway contributed to the protection provided by metformin. Transient global brain ischemia was induced by 4-vessel occlusion in adult male Sprague-Dawley rats. The open field tasks and Morris water maze were used to assess the effect of metformin on anxiety-like behavioral and cognitive impairment after I/R. Cresyl Violet staining was used to examine the survival of hippocampal CA1 pyramidal neurons. Immunoblotting was performed to measure the phosphorylation of Akt1, JNK3, c-Jun and the expression of cleaved caspase-3. Through ischemia/reperfusion (I/R) rat model, we found that metformin could attenuate the deficits of hippocampal related behaviors and inhibit cell apoptosis. The western blot data showed that metformin could promote the activation of Akt1 and reduce the phosphorylation of JNK3 and c-Jun as well as elevation of cleaved caspase-3 in I/R brains. PI3K inhibitor reversed all the protective effects, further indicating that metformin protect hippocampus from ischemic damage through PI3K/Akt1/JNK3/c-Jun signaling pathway.

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.

Inhibition of AMP-activated protein kinase alleviates focal cerebral ischemia injury in mice: Interference with mTOR and autophagy

Ischemic stroke is one of the most frequent acute cerebrovascular events worldwide. This study evaluated the variability of AMPK and mTOR and their relevance on LC3 and Beclin-1 expression, and further expounded the possible protective mechanism of inhibiting AMPK activity in the cerebral cortex after permanent focal cerebral ischemia injury in mice. Western blot and immunohistochemistry showed that p-AMPK expression was low in the cerebral cortex of the sham group; whereas it was significantly increased at 3h and 6h and peaked at 3h after pMCAO in the cerebral ischemic cortex, and was decreased at 12h and 24h. The expression patterns of LC3 and Beclin-1 were the same as that of p-AMPK after occlusion, and the variability pattern between p-AMPK and p-mTOR levels was completely inverted. After treatment with the AMPK inhibitor Compound C, p-AMPK/LC3/Beclin-1 expression was decreased significantly, whereas p-mTOR level was increased significantly. Deficiency of Nissl bodies was reduced compared with that in the vehicle group at all times points after occlusion. Neurological deficits, infarct areas, and brain water content were also significantly reduced 24h after occlusion with compound C treatment. The results suggested that the AMPK-autophagy pathway was activated, concomitant with mTOR inhibition in cerebral cortex after ischemic injury in mice. Moreover, inhibition of AMPK activity by Compound C inhibited autophagy and conferred protection against brain damage by restoring mTOR activity.

Neuropharmacological Actions of Metformin in Stroke

Increasing epidemiologic evidence suggests that metformin, a well-established AMPK activator and the most favorable first-line anti-diabetic drug, reduces stroke incidence and severity. However, the mechanism for this remains unclear. Moreover, previous experimental studies have reported controversial results about the effects of metformin on stroke outcomes during the acute phase. However, recent studies have consistently suggested that AMPK-mediated microglia/macrophage polarization and angioneurogenesis may play essential roles in metformin-promoted, long-term functional recovery following stroke. The present review summarizes the neuropharmacological actions of metformin in experimental stroke with an emphasis on the recent findings that the cell-specific effects and duration of AMPK activation are critical to the effects of metformin on stroke outcomes.

Sestrin2 Silencing Exacerbates Cerebral Ischemia/Reperfusion Injury by Decreasing Mitochondrial Biogenesis through the AMPK/PGC-1α Pathway in Rats

Sestrin2 (Sesn2) exerts neuroprotective properties in some neurodegenerative diseases. However, the role of Sesn2 in stroke is unclear. The AMP-activated protein kinase/peroxisome proliferator-activated receptor γ coactivator-1α (AMPK/PGC-1α) pathway plays an important role in regulating mitochondrial biogenesis, which helps prevent cerebral ischemia/reperfusion (I/R) injury. Here, we aimed to determine whether Sesn2 alleviated I/R damage by regulating mitochondrial biogenesis through the AMPK/PGC-1α signaling pathway. To be able to test this, Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO) for 1 h with Sesn2 silencing. At 24 h after reperfusion, we found that neurological deficits were exacerbated, infarct volume was enlarged, and oxidative stress and neuronal damage were greater in the Sesn2 siRNA group than in the MCAO group. To explore protective mechanisms, an AMPK activator was used. Expression levels of Sesn2, p-AMPK, PGC-1α, NRF-1, TFAM, SOD2, and UCP2 were significantly increased following cerebral I/R. However, upregulation of these proteins was prevented by Sesn2 small interfering RNA (siRNA). In contrast, activation of AMPK with 5′-aminoimidazole-4-carboxamide riboside weakened the effects of Sesn2 siRNA. These results suggest that Sesn2 silencing may suppress mitochondrial biogenesis, reduce mitochondrial biological activity, and finally aggravate cerebral I/R injury through inhibiting the AMPK/PGC-1α pathway.

Pre-stroke Metformin Treatment is Neuroprotective Involving AMPK Reduction

Long-term metformin treatment reduces the risk of stroke. However, the effective administration pattern and indications of metformin on acute cerebral ischemia are unclear. To investigate the neuroprotective treatment duration and dosage of metformin on focal ischemia mice and the association of neuroprotection with 5'-adenosine monophosphate-activated protein kinase (AMPK) regulations, male C57BL/6 mice were subjected to permanent or transient middle cerebral artery occlusion (MCAO) and metformin of 3, 10 and 30 mg/kg was intraperitoneally injected 1, 3 or 7 days prior to MCAO, or at the onset, or 1, 3 or 6 h after reperfusion, respectively. Infarct volumes, neurological deficit score, cell apoptosis, both total and phosphorylated AMPK expressions were assessed. Results showed that prolonged pretreatment to 7 days of metformin (10 mg/kg) significantly ameliorated brain infarct, neurological scores and cell apoptosis in permanent MCAO mice. Shorter (3 days or 1 day) or without pretreatment of metformin was not effective, suggesting a pretreatment time window. In transient MCAO mice, metformin showed no neuroprotection even with pretreatment. The expressions of total and phosphorylated AMPK were sharply decreased with effective metformin pretreatments in ischemic brains. Our data provided the first evidence that in acute ischemic injury, a 7-days pretreatment duration of 10 mg/kg metformin is necessary for its neuroprotection, and metformin may not be beneficial in the cases of blood reperfusion.

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

OBJECTIVE

I/R and its subsequent reactive hyperemia results in different adverse effects such as brain edema and BBB disruption. AMPK activation has been perceived as one of the target factors for I/R treatment. We investigated the effect of Met (an AMPK activator) on some physiological parameters including vascular responses, hyperemia, BBB disruption, and electrophysiological activity following tGCI.

METHODS

Rats were pretreated with Met for two weeks and CC was administered half an hour before tGCI. Brain vascular responses, hyperemia, BBB disruption, and electrophysiological activity were evaluated following the ischemia.

RESULTS

Met attenuated BBB disruption and reactive hyperemia in tGCI rats compared with the untreated I/R rats (p < 0.001). Met administration along with CC in the ischemic rats reversed the beneficial effects of Met on BBB disruption and reactive hyperemia (p < 0.001). Electrophysiological records indicated that Met increased spike rates in the ischemic rats comparing with I/R rats (p < 0.001), whereas, CC administration blocked the beneficial effects of Met on the neuronal discharges (p < 0.05).

CONCLUSION

We established a regulatory role for AMPK in vascular and electrophysiological responses to tGCI. Studies are ongoing to determine if activation of AMPK in the reperfusion period would offer similar protection.

Metformin preconditioning provide neuroprotection through enhancement of autophagy and suppression of inflammation and apoptosis after spinal cord injury

Spinal cord injury (SCI) is one of the most serious nervous system disorders characterised by high morbidity and disability. Inflammatory and autophagy responses play an important role in the development of SCI. Metformin, a first-line drug for type-2 diabetes, features autophagy promotion as well as anti-inflammatory and anti-apoptotic properties in the nervous system. In this study, we investigated the neuroprotection effects of metformin preconditioning on rats after SCI. Results of Basso, Beattie and Bresnahan scores, HE staining and Nissl staining showed that the function and quantity of motor neurons were protected by metformin after SCI. Western blot revealed that the expression of Beclin-1 and LC3B-II was enhanced, and the phosphorylation levels of the mammalian target of rapamycin (mTOR) protein and p70S6K were reduced by metformin after SCI. Metformin significantly reduced the expression of NF-κB. Moreover, Western blot and immunofluorescence results indicated that caspase 3 activation was reduced, whereas bcl-2 level was significantly increased by metformin. Hence, metformin attenuated SCI by inhibiting apoptosis and inflammation and enhancing the autophagy via the mTOR/p70S6K signalling pathway.

Metformin Improves Functional Recovery After Spinal Cord Injury via Autophagy Flux Stimulation

Spinal cord injury (SCI) is a severe neurological disease with few efficacious drugs. Autophagy is a cellular process to confront with stress after SCI and considered to be a therapeutic target of SCI. In this study, we investigated the therapeutic effect of metformin on functional recovery after SCI and its underlying mechanism of autophagy regulation. Using a rat model of traumatic SCI, we found improved function recovery which was paralleled by a reduction of apoptosis after metformin treatment. We further examined autophagy via detecting autophagosomes by transmission electron microscopy and immunofluorescence, as well as autophagy markers by western blot in each groups. The results showed that the number of autophagosomes and expression of autophagy markers such as LC3 and beclin1 were increased in SCI group, while autophagy substrate protein p62 as well as ubiquitinated proteins were found to accumulate in SCI group, indicating an impaired autophagy flux in SCI. But, metformin treatment attenuated the accumulation of p62 and ubiquitinated proteins, suggesting a stimulative effect of autophagy flux by metformin. Blockage of autophagy flux by chloroquine partially abolished the apoptosis inhibition and functional recovery effect of metformin on SCI, which suggested that the protective effect of metformin on SCI was through autophagy flux stimulation. Activation of AMPK as well as inhibition of its downstream mTOR signaling were detected under metformin treatment in vivo and in vitro; inhibition of AMPK signaling by compound C suppressed autophagy flux induced by metformin in vitro, indicating that AMPK signaling was involved in the effect of metformin on autophagy flux regulation. Together, these results illustrated that metformin improved functional recovery effect through autophagy flux stimulation and implied metformin to be a potential drug for SCI therapy.

An Orally Active Allosteric GLP-1 Receptor Agonist Is Neuroprotective in Cellular and Rodent Models of Stroke

Diabetes is a major risk factor for the development of stroke. Glucagon-like peptide-1 receptor (GLP-1R) agonists have been in clinical use for the treatment of diabetes and also been reported to be neuroprotective in ischemic stroke. The quinoxaline 6,7-dichloro-2-methylsulfonyl-3-N-tert- butylaminoquinoxaline (DMB) is an agonist and allosteric modulator of the GLP-1R with the potential to increase the affinity of GLP-1 for its receptor. The aim of this study was to evaluate the neuroprotective effects of DMB on transient focal cerebral ischemia. In cultured cortical neurons, DMB activated the GLP-1R, leading to increased intracellular cAMP levels with an EC50 value about 100 fold that of exendin-4. Pretreatment of neurons with DMB protected against necrotic and apoptotic cell death was induced by oxygen-glucose deprivation (OGD). The neuroprotective effects of DMB were blocked by GLP-1R knockdown with shRNA but not by GLP-1R antagonism. In C57BL/6 mice, DMB was orally administered 30 min prior to middle cerebral artery occlusion (MCAO) surgery. DMB markedly reduced the cerebral infarct size and neurological deficits caused by MCAO and reperfusion. The neuroprotective effects were mediated by activation of the GLP-1R through the cAMP-PKA-CREB signaling pathway. DMB exhibited anti-apoptotic effects by modulating Bcl-2 family members. These results provide evidence that DMB, a small molecular GLP-1R agonist, attenuates transient focal cerebral ischemia injury and inhibits neuronal apoptosis induced by MCAO. Taken together, these data suggest that DMB is a potential neuroprotective agent against cerebral ischemia.

Neuroprotective effects of metformin against Aβ-mediated inhibition of long-term potentiation in rats fed a high-fat diet

Metformin (Met) is used to treat neurodegenerative disorders such as Alzheimer's disease (AD). Conversely, high-fat diets (HFD) have been shown to increase AD risk. In this study, we investigated the neuroprotective effects of Met on β-amyloid (Aβ)-induced impairments in hippocampal synaptic plasticity in AD model rats that were fed a HFD. In this study, 32 adult male Wistar rats were randomly assigned to four groups: group I (control group, regular diet); group II (HFD+vehicle); group III (HFD+Aβ); or group IV (Met+HFD+Aβ). Rats fed a HFD were injected with Aβ to induce AD, allowed to recover, and treated with Met for 8 weeks. The rats were then anesthetized with intraperitoneal injections of urethane and placed in a stereotaxic apparatus for surgery, electrode implantation, and field potential recording. In vivo electrophysiological recordings were then performed to measure population spike (PS) amplitude and excitatory postsynaptic potential (EPSP) slope in the hippocampal dentate gyrus. Long-term potentiation (LTP) was induced by high-frequency stimulation of the perforant pathway. Blood samples were then collected to measure plasma levels of triglycerides, low-density lipoproteins, very low-density lipoprotein, and cholesterol. After induction of LTP, PS amplitude and EPSP slope were significantly decreased in Aβ-injected rats fed a HFD compared to vehicle-injected animals or untreated animals that were fed a normal diet. Met treatment of Aβ-injected rats significantly attenuated these decreases, suggesting that Met decreased the effects of Aβ on LTP. These findings suggest that Met treatment is neuroprotective against the detrimental effects of Aβ and HFDs on hippocampal synaptic plasticity.

Apelin-13 protects against apoptosis by activating AMP-activated protein kinase pathway in ischemia stroke

Apelin has been proved to be protective against apoptosis induced by ischemic reperfusion. However, mechanisms whereby apelin produces neuroprotection remain to be elucidated. AMP-activated protein kinase (AMPK) is a master energy sensor that monitors levels of key energy metabolites. It is activated via AMPKαThr172 phosphorylation during cerebral ischemia and appears to be neuroprotective. In this study, we investigated the effect of apelin on AMPKα and tested whether apelin protecting against apoptosis was associated with AMPK signals. Focal transient cerebral ischemia/reperfusion (I/R) model in male ICR mice was induced by 60 min of ischemia followed by reperfusion. Apelin-13 was injected intracerebroventricularly 15 min before reperfusion. AMPK inhibitor, compound C, was injected to mice intraperitoneally at the onset of ischemia. In experiment 1, the effect of apelin-13 on AMPKα was measured. In experiment 2, the relevance of AMPKα and apelin-13' effect on apoptosis was measured. Data showed that apelin-13 significantly increased AMPKα phosphorylation level after cerebral I/R. Apelin-13, with the co-administration of saline, reduced apoptosis cells, down-regulated Bax and cleaved-caspase3 and up-regulated Bcl2. However, with the co-administration of compound C, apelin-13 was inefficient in affecting apoptosis and Bax, Bcl2 and cleaved-caspase3. The study provided the evidence that apelin-13 up-regulated AMPKα phosphorylation level in cerebral ischemia insults and AMPK signals participated in the mechanism of apelin-mediated neuroprotection.

Prolonged metformin treatment leads to reduced transcription of Nrf2 and neurotrophic factors without cognitive impairment in older C57BL/6J mice

Long-term use of anti-diabetic agents has become commonplace as rates of obesity, metabolic syndrome and diabetes continue to escalate. Metformin, a commonly used anti-diabetic drug, has been shown to have many beneficial effects outside of its therapeutic regulation of glucose metabolism and insulin sensitivity. Studies on metformin's effects on the central nervous system are limited and predominantly consist of in vitro studies and a few in vivo studies with short-term treatment in relatively young animals; some provide support for metformin as a neuroprotective agent while others show evidence that metformin may be deleterious to neuronal survival. In this study, we examined the effect of long-term metformin treatment on brain neurotrophins and cognition in aged male C57Bl/6 mice. Mice were fed control (C), high-fat (HF) or a high-fat diet supplemented with metformin (HFM) for 6 months. Metformin decreased body fat composition and attenuated declines in motor function induced by a HF diet. Performance in the Morris water maze test of hippocampal based memory function, showed that metformin prevented impairment of spatial reference memory associated with the HF diet. Quantitative RT-PCR on brain homogenates revealed decreased transcription of BDNF, NGF and NTF3; however protein levels were not altered. Metformin treatment also decreased expression of the antioxidant pathway regulator, Nrf2. The decrease in transcription of neurotrophic factors and Nrf2 with chronic metformin intake, cautions of the possibility that extended metformin use may alter brain biochemistry in a manner that creates a vulnerable brain environment and warrants further investigation.

AMP-activated protein kinase: structure, function, and role in pathological processes

Recently, AMP-activated protein kinase (AMPK) has emerged as a key regulator of energy balance at cellular and whole-body levels. Due to the involvement in multiple signaling pathways, AMPK efficiently controls ATP-consuming/ATP-generating processes to maintain energy homeostasis under stress conditions. Loss of the kinase activity or attenuation of its expression leads to a variety of metabolic disorders and increases cancer risk. In this review, we discuss recent findings on the structure of AMPK, its activation mechanisms, as well as the consequences of its targets in regulation of metabolism. Particular attention is given to low-molecular-weight compounds that activate or inhibit AMPK; the perspective of therapeutic use of such modulators in treatment of several common diseases is discussed.

Metformin improves anxiety-like behaviors through AMPK-dependent regulation of autophagy following transient forebrain ischemia

Stroke is one of the main threats to the public health worldwide. Metformin, an anti-diabetic drug, is an activator of AMP-activated protein kinase (AMPK). Metformin plays an important role on improving behavior in neurodegenerative diseases through diverse pathways. In the current study we aimed to investigate the probable effects of metformin on anxiety and autophagy pathway in global cerebral ischemia. Rats were divided into seven groups; Sham, ischemia (I/R), metformin (met), compound c (CC), CC+ischemia, met+ischemia, met+CC+ischemia. Metformin was pretreated for 2 weeks and CC administrated half an hour before global cerebral ischemia. Blood glucose, body weight, sensorimotor scores, elevated plus maze and open field test were evaluated after ischemia. Autophagy related factors were measured by Western blot and immunofluorescent assay in hippocampus of rats. Based on our results, pretreatment of rats by metformin improved sensory motor signs, anxiolytic behavior and locomotion in ischemic rats. CC injection in I/R rats attenuated the therapeutic effects of metformin. Autophagy factors such as light chain 3B, Atg7, Atg5-12 and beclin-1 decreased in ischemic rats compared to the sham group (P < 0.001 in all proteins). Level of autophagic factors increased in metformin pretreated rats compared to global cerebral ischemia (P < 0.001 in all proteins). These data indicated that the beneficial role of metformin in behavior and autophagy flux mediates via AMPK. Our results recommended that metformin therapy could improve psychological disorders and movement disability following I/R and profound understanding of AMPK-dependent autophagy would enhance its development as a promising target for intracellular pathway.

Electroacupuncture preconditioning attenuates ischemic brain injury by activation of the adenosine monophosphate-activated protein kinase signaling pathway

Electroacupuncture has therapeutic effects on ischemic brain injury, but its mechanism is still poorly understood. In this study, mice were stimulated by electroacupuncture at the Baihui (GV20) acupoint for 30 minutes at 1 mA and 2/15 Hz for 5 consecutive days. A cerebral ischemia model was established by ligating the bilateral common carotid artery for 15 minutes. At 72 hours after injury, neuronal injury in the mouse hippocampus had lessened, and the number of terminal deoxynucleotide transferase-mediated dUTP nick-end labeling-positive cells reduced after electroacupuncture treatment. Moreover, expression of adenosine monophosphate-activated protein kinase α (AMPKα) and phosphorylated AMPKα was up-regulated. Intraperitoneal injection of the AMPK antagonist, compound C, suppressed this phenomenon. Our findings suggest that electroacupuncture preconditioning alleviates ischemic brain injury via AMPK activation.

Pre-treatment with metformin activates Nrf2 antioxidant pathways and inhibits inflammatory responses through induction of AMPK after transient global cerebral ischemia

Global cerebral ischemia arises in patients who have a variety of clinical conditions including cardiac arrest, shock and asphyxia. In spite of advances in understanding of the brain ischemia and stroke etiology, therapeutic approaches to improve ischemic injury still remain limited. It has been established that metformin can attenuate cell death in cerebral ischemia. One of the main functions of metformin is proposed to be conducted via AMP-activated protein kinase (AMPK)-dependent pathway in the experimental cerebral ischemia model. It is also established that metformin can suppress inflammation and activate Nuclear factor erythroid 2-related factor (Nrf2) pathways in neurons. In the current study, the role of metformin in regulating inflammatory and antioxidant pathways in the global cerebral ischemia was investigated. Our results indicated that pretreatment of rats by metformin attenuated cellular levels of nuclear factor-κB, Tumor Necrosis Factor alpha and Cyclooxygenase-2 which are considered as three important proteins involved in the inflammation pathway. Pretreatment by metformin increased the level of Nrf2 and heme oxygenase-1 in the hippocampus of ischemic rats compared with untreated ischemic group. Moreover, pretreatment by metformin enhanced the level of glutathione and catalase activities compared with them in ischemic group. Such protective changes detected by metformin pretreatment were reversed by injecting compound c, an AMPK inhibitor. These findings suggested that metformin might protect cells through modulating inflammatory and antioxidant pathways via induction of AMPK. However, more experimental and clinical trial studies regarding neuroprotective potential of metformin and the involved mechanisms, especially in the context of cerebral ischemic injuries, are necessary.

Pharmacological Interventions to Ameliorate Neuropathological Symptoms in a Mouse Model of Lafora Disease

Lafora disease (LD, OMIM 254780) is a rare fatal neurodegenerative disorder that usually occurs during childhood with generalized tonic-clonic seizures, myoclonus, absences, drop attacks, or visual seizures. Unfortunately, at present, available treatments are only palliatives and no curative drugs are available yet. The hallmark of the disease is the accumulation of insoluble polyglucosan inclusions, called Lafora bodies (LBs), within the neurons but also in heart, muscle, and liver cells. Mouse models lacking functional EPM2A or EPM2B genes (the two major loci related to the disease) recapitulate the Lafora disease phenotype: they accumulate polyglucosan inclusions, show signs of neurodegeneration, and have a dysregulation of protein clearance and endoplasmic reticulum stress response. In this study, we have subjected a mouse model of LD (Epm2b-/-) to different pharmacological interventions aimed to alleviate protein clearance and endoplasmic reticulum stress. We have used two chemical chaperones, trehalose and 4-phenylbutyric acid. In addition, we have used metformin, an activator of AMP-activated protein kinase (AMPK), as it has a recognized neuroprotective role in other neurodegenerative diseases. Here, we show that treatment with 4-phenylbutyric acid or metformin decreases the accumulation of Lafora bodies and polyubiquitin protein aggregates in the brain of treated animals. 4-Phenylbutyric acid and metformin also diminish neurodegeneration (measured in terms of neuronal loss and reactive gliosis) and ameliorate neuropsychological tests of Epm2b-/- mice. As these compounds have good safety records and are already approved for clinical uses on different neurological pathologies, we think that the translation of our results to the clinical practice could be straightforward.

Hypoglycemic effect of catalpol on high-fat diet/streptozotocin-induced diabetic mice by increasing skeletal muscle mitochondrial biogenesis

Catalpol, an iridoid glycoside, exists in the root of Radix Rehmanniae. Some studies have shown that catalpol has a remarkable hypoglycemic effect in the streptozotocin-induced diabetic model, but the underlying mechanism for this effect has not been fully elucidated. Because mitochondrial dysfunction plays a vital role in the pathology of diabetes and because improving mitochondrial function may offer a new approach for the treatment of diabetes, this study was designed. Catalpol was orally administered together with metformin to high-fat diet/streptozotocin (HFD/STZ)-induced diabetic mice daily for 4 weeks. Body weight (BW), fasting blood glucose (FBG) level, and glucose disposal (IPGTT) were measured during or after the treatment. The results showed a dose-dependent reduction of FBG level with no apparent changes in BW through four successive weeks of catalpol administration. Catalpol treatment substantially reduced serum total cholesterol and triglyceride levels in the diabetic mice. In addition, catalpol efficiently increased mitochondrial ATP production and reversed the decrease of mitochondrial membrane potential and mtDNA copy number in skeletal muscle tissue. Furthermore, catalpol (200 mg/kg) rescued mitochondrial ultrastructure in skeletal muscle, as detected with transmission electron microscopy. The relative mRNA level of peroxisome proliferator-activated receptor gamma co-activator 1 (PGC1) α was significantly decreased in muscle tissue of diabetic mice, while this effect was reversed by catalpol, resulting in a dose-dependent up-regulation. Taken together, we found that catalpol was capable of lowering FBG level via improving mitochondrial function in skeletal muscle of HFD/STZ-induced diabetic mice.

The biguanide metformin alters phosphoproteomic profiling in mouse brain

Metformin, a potent antihyperglycemic agent is recommended as the first-line oral therapy for type 2 diabetes (T2D). Recently, metformin has been reported to be beneficial to neurodegenerative disease models. However, the putative mechanisms underlying the neuroprotective effects of metformin in disease models are unknown. Thus, we applied LC-MS/MS-based pattern analysis and two-dimensional electrophoresis (2DE)-based proteomic approach to understand the global phosphoproteomic alteration in the brain of metformin-administrated mice. Collectively, LC-MS/MS-based pattern analysis reveals that 41 phosphoproteins were upregulated and 22 phosphoproteins were downregulated in the brain of metformin-administrated mice. In addition, 5 differentially expressed phosphoproteins were identified upon metformin administration by 2DE coupled with mass spectrometry. The phosphorylation status of metabolic enzymes was decreased while that of mitochondrial proteins was increased by metformin. Interestingly, phosphorylated α-synuclein was significantly decreased by metformin administration. Taken together, our results might provide potential pathways to understand the pharmacological effect of metformin on neuroprotection.