Neuroprotective Effects of AMP-Activated Protein Kinase on Scopolamine Induced Memory Impairment

Empagliflozin and memantine combination ameliorates cognitive impairment in scopolamine + heavy metal mixture-induced Alzheimer's disease in rats: role of AMPK/mTOR, BDNF, BACE-1, neuroinflammation, and oxidative stress

One of the major consequences of diabetes mellitus that has gained attention due to its rising incidence is cognitive impairment. Recent research suggested that sodium-glucose cotransporter-2 (SGLT-2) inhibitors can mitigate memory impairment linked to Alzheimer's disease and are now being explored for their cognitive benefits. However, their mechanisms were not thoroughly studied. This research investigates the hypothesis of the neuroprotective effect of empagliflozin administration against scopolamine-heavy metal mixture (SCO + HMM)-treated Alzheimer's rat models in comparison with memantine as a reference drug and the impact of their combination. Yet, the neuroprotective effects of memantine and empagliflozin combination against cognitive impairment have not been previously explored. This study employed adult male albino rats categorized into five groups. The impact of empagliflozin, memantine, and their concomitant administration on cognitive performance was assessed in a scopolamine and heavy metal mixture-treated Alzheimer's disease model in rats. The assessment of rats' cognitive behavior, memory, and spatial learning was conducted, followed by an evaluation of hippocampal brain-derived neurotrophic factor (BDNF), beta-secretase (BACE-1), oxidative stress (OS), and inflammatory marker activity. And, a western blot analysis was conducted to detect phosphorylated 5' AMP-activated protein kinase (p-AMPK), phosphorylated mammalian target of rapamycin (p-mTOR), and heme oxygenase-1 (HO-1). Hippocampal and cerebellar histopathology were thoroughly examined, in addition to the expressions of amyloid β (Aβ). The current data demonstrate the involvement of the pAMPK/mTOR/HO-1 signaling pathway in empagliflozin neuroprotection against SCO + HMM-induced AD. In addition, it reduces AD hallmarks (Aβ and BACE1), neuro-inflammation, and oxidative stress sequelae, and enhances neurogenesis and synaptic density via BDNF. This study proposes that EMPA, especially when co-administered with other conventional anti-Alzheimer therapy, may be formulated into an innovative therapeutic strategy for the enhancement of cognitive impairments associated with neurodegenerative disorders.

Comparison of Malondialdehyde, Acetylcholinesterase, and Apoptosis-Related Markers in the Cortex and Hippocampus of Cognitively Dysfunctional Mice Induced by Scopolamine

Objectives: Until now, many researchers have conducted evaluations on hippocampi for analyses of cognitive dysfunction models using scopolamine. However, depending on the purposes of these analyses, there are differences in the experimental results for the hippocampi and cortexes. Therefore, this study intends to compare various analyses of cognitive dysfunction after scopolamine administration with each other in hippocampi and cortexes. Methods: Scopolamine was administered at three dosages in mice: 0.5, 1, and 3 mg/kg. And this study evaluates the differences in cognitive function and the expression of malondialdehyde (MDA), acetylcholinesterase (AChE), and brain-derived neurotrophic factor (BDNF) in mice's hippocampi and cortexes based on scopolamine dosages. Results: The Morris water maze test was conducted between 1 and 3 h after scopolamine injection to assess its duration. A significant decrease in behavioral ability was evaluated at 1 h, and we observed a similar recovery to the normal group at 3 h. And the Morris water maze escape latency showed differences depending on scopolamine concentration. While the escape waiting time in the control group and scop 0.5 administration group remained similar to that seen before administration, the administration of scop 1 and 3 increased it. In the experimental group administered scop 1 and 3, cerebral MDA levels in the cerebral cortex significantly increased. In the hippocampus, the MDA level in the scopolamine-administered groups slightly increased compared to the cortex. A Western blotting assay shows that Bax and Bcl-xl showed a tendency to increase or decrease depending on the concentration, but BDNF increased in scop 0.5, and scop 1 and 3 did not show a significant decrease compared to the control at the cerebral cortex. In the hippocampus, BDNF showed a concentration-dependent decrease in expression. Conclusions: This study's findings indicate that chemical analyses for MDA and AChE can be performed in the cerebral cortex, while the hippocampus is better suited for protein analysis of apoptosis and BDNF.

Butyric Acid Precursor Tributyrin Modulates Hippocampal Synaptic Plasticity and Prevents Spatial Memory Deficits: Role of PPARγ and AMPK

BACKGROUND

Short chain fatty acids (SCFA), such as butyric acid (BA), derived from the intestinal fermentation of dietary fiber and contained in dairy products, are gaining interest in relation to their possible beneficial effects on neuropsychological disorders.

METHODS

C57BL/6J male mice were used to investigate the effect of tributyrin (TB), a prodrug of BA, on hippocampus (HIP)-dependent spatial memory, HIP synaptic transmission and plasticity mechanisms, and the expression of genes and proteins relevant to HIP glutamatergic transmission.

RESULTS

Ex vivo studies, carried out in HIP slices, revealed that TB can transform early-LTP into late-LTP (l-LTP) and to rescue LTP-inhibition induced by scopolamine. The facilitation of l-LTP induced by TB was blocked both by GW9662 (a PPARγ antagonist) and C-Compound (an AMPK inhibitor), suggesting the involvement of both PPARγ and AMPK on TB effects. Moreover, 48-hour intake of a diet containing 1% TB prevented, in adolescent but not in adult mice, scopolamine-induced impairment of HIP-dependent spatial memory. In the adolescent HIP, TB upregulated gene expression levels of Pparg, leptin, and adiponectin receptors, and that of the glutamate receptor subunits AMPA-2, NMDA-1, NMDA-2A, and NMDA-2B.

CONCLUSIONS

Our study shows that TB has a positive influence on LTP and HIP-dependent spatial memory, which suggests that BA may have beneficial effects on memory.

Tadalafil Reversed H-89 - and Scopolamine - Induced Spatial Learning Impairments in Male Rats

Accumulated evidence shows that the cAMP and cGMP signaling pathway plays an important role in memory function and neuronal plasticity. Phosphodiesterase 5 (PDE5) is a hopeful therapeutic target in AD (Alzheimer disease), and PDE5 inhibition may be a good therapeutic strategy for the treatment of AD. In the present study, the four-day bilateral intra-hippocampal infusion of H-89 as a protein kinase AII inhibitor (10 µM/side) and intra-peritoneal injections of tadalafil (20 mg/kg) and scopolamine (0.5 mg/kg) alone and also on combination on spatial learning in Morris water maze (MWM) were investigated. DMSO and saline were used as controls for H-89 and other mentioned drugs, respectively. Rats were trained for 4 days; each day included one block of four trials. Post- training probe trial tests were performed on day 5. Administration of H-89 and scopolamine led to a significant impairment in spatial learning compared to their related controls. But, combination of tadalafil/H-89 or tadalafil/scopolamine reversed H-89 or scopolamine- induced spatial learning deficits in MWM. Taken together, these results showed the probable regulatory effects of cGMP on cholinergic and cAMP/PKA signaling pathways in co-administrations of these mentioned drugs on spatial learning in MWM.

The protective effect of metformin in scopolamine-induced learning and memory impairment in rats

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease in the world. One of the most commonly prescribed oral antidiabetic drug, metformin, has been shown to have beneficial effects on restoring impaired cognitive function. In the present study, we investigated the effects of metformin on spatial memory in terms of alleviating scopolamine-induced learning and memory impairments in rats by using the Morris water maze (MWM) test and the modified elevated plus-maze (mEPM) test. Furthermore, we investigated the possible mechanisms of action of metformin in preventing cognitive dysfunction.

METHODS

Male Wistar rats received metformin (50, 100, or 200 mg/kg/day) via gavage feeding for three weeks. Scopolamine was administered intraperitoneally before the probe step of the MWM test or the acquisition session of the mEPM test.

RESULTS

The learning and memory impairment induced by scopolamine was reversed by metformin. In addition, metformin improved the level of phosphorylated AMP-activated protein kinase and cAMP responsive element binding protein. However, metformin pretreatment had no impact on inhibiting the scopolamine-induced changes in acetylcholine levels. Furthermore, metformin exerted its antioxidant effect by significantly reversing scopolamine-induced changes in malondialdehyde, total antioxidant status, and superoxide dismutase levels in the hippocampus.

CONCLUSION

Our results indicate that one of the most commonly used antidiabetic drug, metformin, has the potential to prevent the development of dementia and be a novel therapeutic drug for the amelioration of cognitive dysfunction in AD.

Neuropathic Pain Creates an Enduring Prefrontal Cortex Dysfunction Corrected by the Type II Diabetic Drug Metformin But Not by Gabapentin

Chronic pain patients suffer from pain-related cognitive deficits, even when taking commonly prescribed analgesics. These deficits are likely related to pain-related maladaptive plasticity in the frontal cortex. We sought to model cognitive deficits in mice with neuropathic pain to examine maladaptive morphological plasticity in the mPFC and to assess the effects of several therapeutics. We used an attentional set-shifting task in mice with spared nerve injury (SNI) who received either a single intrathecal injection of an analgesic dose of clonidine, 7 d of 100 mg/kg gabapentin, or 7 d of 200 mg/kg metformin. Male SNI mice were significantly more impaired in the set-shifting task than females. This deficit correlated with a loss of parvalbumin (PV) and reductions in axon initial segment (AIS) length in layers 5/6 of the infralimbic (IL) cortex. Acute pain relief with clonidine had no effect on set-shifting performance, whereas pain relief via 7 day treatment with gabapentin worsened the impairment in both SNI and sham mice. Gabapentin reversed the PV loss in the IL but had no effect on AIS length. Treatment with the AMPK-activator metformin completely reversed the pain-related cognitive impairment and restored AIS length in the IL but had little effect on PV expression. Our findings reveal that neuropathic pain-related cognitive impairments in male mice are correlated to bilateral morphological changes in PV interneurons and layer 5/6 IL pyramidal neuron AIS. Pain relief with metformin can reverse some of the functional and anatomical changes.SIGNIFICANCE STATEMENT Cognitive impairments are a comorbidity of neuropathic pain but are inadequately addressed by existing therapeutics. We used a neuropathic pain model in mice to demonstrate that male (but not female) mice show a robust pain-related deficit in attentional set-shifting, which is associated with structural plasticity in axon initial segments in the infralimbic cortex. These deficits were completely reversed by 7 day treatment with the antidiabetic drug metformin, suggesting that this drug can be repurposed for the treatment of neuropathic pain and its cognitive comorbidities. Our findings have implications for our understanding of how neuropathic pain causes structural plasticity in the brain, and they point to a marked sexual dimorphism in neuropathic pain mechanisms in mice.

Canagliflozin prevents scopolamine-induced memory impairment in rats: Comparison with galantamine hydrobromide action

Canagliflozin (CAN) is a sodium-glucose co-transporter 2 (SGLT2) inhibitor indicated to improve glycemic control in adults with type 2 diabetes mellitus. There is a little information about its effect on the cholinergic system that proposed mechanism for memory improvement occurring by SGLT2 drugs. This study aimed to estimate the effect of CAN as compared to galantamine (GAL) treatments for two weeks on scopolamine hydrobromide (SCO)-induced memory dysfunction in experimental rats. Animals divided into six groups; control (CON), CAN, GAL, SCO, SCO + CAN and SCO + GAL. Results indicated significant decrease in body weights of the CAN groups as compared to control values. Moreover, in the SCO + CAN and SCO + GAL the number of arm entry and number of correct alternation in Y maze task increased and showed improvement in the water maze task, acetylcholinesterase (AChE) activities decreased significantly, while monoamines levels significantly increased compared with the SCO group values. Results also recorded acetylcholine M1 receptor (M1 mAChR) in SCO + CAN or SCO + GAL groups in comparison with the SCO group. The study suggested that canagliflozin might improve memory dysfunction induced by scopolamine hydrobromide via cholinergic and monoamines system.

Cannabis-induced Moto-Cognitive Dysfunction in Wistar Rats: Ameliorative Efficacy of Nigella Sativa

BACKGROUND

Cannabis is a widely used illicit drug with various threats of personality syndrome, and Nigella sativa has been widely implicated as having therapeutic efficacy in many neurological diseases. The present study investigates the ameliorative efficacy of Nigella sativa oil (NSO) on cannabis-induced moto-cognitive defects.

METHODS

Scopolamine (1 mg/kg i.p.) was given to induce dementia as a standard base line for cannabis (20 mg/kg)-induced cognitive impairment, followed by an oral administration of NSO (1 ml/kg) for 14 consecutive days. The Morris water maze (MWM) paradigm was used to assess the memory index, the elevated plus maze was used for anxiety-like behaviour, and the open field test was used for locomotor activities; thereafter, the rats were sacrificed and their brains were removed for histopathologic studies.

RESULTS

Cannabis-like Scopolamine caused memory impairment, delayed latency in the MWM, and anxiety-like behaviour, coupled with alterations in the cerebello-hippocampal neurons. The post-treatment of rats with NSO mitigated cannabis-induced cognitive dysfunction as with scopolamine and impaired anxiety-like behaviour by increasing open arm entry, line crossing, and histological changes.

CONCLUSIONS

The observed ameliorative effects of NSO make it a promising agent against moto-cognitive dysfunction and cerebelo-hippocampal alterations induced by cannabis.

Resveratrol attenuates lipopolysaccharide-induced dysfunction of blood-brain barrier in endothelial cells via AMPK activation

Resveratrol, a phytoalexin, is reported to activate AMP-activated protein kinase (AMPK) in vascular cells. The blood-brain barrier (BBB), formed by specialized brain endothelial cells that are interconnected by tight junctions, strictly regulates paracellular permeability to maintain an optimal extracellular environment for brain homeostasis. The aim of this study was to elucidate the effects of resveratrol and the role of AMPK in BBB dysfunction induced by lipopolysaccharide (LPS). Exposure of human brain microvascular endothelial cells (HBMECs) to LPS (1 µg/ml) for 4 to 24 hours week dramatically increased the permeability of the BBB in parallel with lowered expression levels of occluding and claudin-5, which are essential to maintain tight junctions in HBMECs. In addition, LPS significantly increased the reactive oxygen species (ROS) productions. All effects induced by LPS in HBVMCs were reversed by adenoviral overexpression of superoxide dismutase, inhibition of NAD(P) H oxidase by apocynin or gain-function of AMPK by adenoviral overexpression of constitutively active mutant (AMPK-CA) or by resveratrol. Finally, upregulation of AMPK by either AMPK-CA or resveratrol abolished the levels of LPS-enhanced NAD(P)H oxidase subunits protein expressions. We conclude that AMPK activation by resveratrol improves the integrity of the BBB disrupted by LPS through suppressing the induction of NAD(P)H oxidase-derived ROS in HBMECs.

HFS-Triggered AMPK Activation Phosphorylates GSK3β and Induces E-LTP in Rat Hippocampus In Vivo

BACKGROUND

The AMP-activated protein kinase (AMPK) is a sensor of cellular energy and nutrient status, with substantial amount of cross talk with other signaling pathways, including its phosphorylation by Akt, PKA, and GSK3β.

AIMS

Various signaling pathways and energy-consuming transport of glutamate receptors subunits are required in synaptic plasticity. However, it is unknown which energy sensors integrate the signaling pathways in these processes. In this article, we elucidated the role of AMPK activation and GSK3β phosphorylation after HFS during the inducement of early-phase long-term potentiation (E-LTP).

METHODS

Synaptic LTP in vivo was induced by high-frequency stimulation (HFS at 200 Hz at a 5-s interval). In addition, phosphorylation of AMPK and glycogen synthase kinase 3β (GSK3β) were measured using Western blotting. The amount of hippocampal AMP, ADP and ATP was measured by HPLC.

RESULTS

We showed that the phosphorylation of AMPK and GSK3β was significantly increased by HFS in vivo. HFS-induced AMPK activation occurred via increased (AMP + ADP)/ATP ratio and activation of Ca(2+) /calmodulin-dependent kinase kinase beta (CaMKKβ). Pharmacological inhibition of AMPK by compound C (CC) prevented HFS-induced inhibitory phosphorylation of GSK3β and the induction of LTP in dentate gyrus (DG) area in vivo.

CONCLUSIONS

Our findings reveal that HFS-triggered AMPK activation phosphorylates GSK3β and induces E-LTP in vivo.

AMPK Signaling in the Dorsal Hippocampus Negatively Regulates Contextual Fear Memory Formation

Both the formation of long-term memory (LTM) and dendritic spine growth that serves as a physical basis for the long-term storage of information require de novo protein synthesis. Memory formation also critically depends on transcription. Adenosine monophosphate-activated protein kinase (AMPK) is a transcriptional regulator that has emerged as a major energy sensor that maintains cellular energy homeostasis. However, still unknown is its role in memory formation. In the present study, we found that AMPK is primarily expressed in neurons in the hippocampus, and then we demonstrated a time-dependent decrease in AMPK activity and increase in mammalian target of rapamycin complex 1 (mTORC1) activity after contextual fear conditioning in the CA1 but not CA3 area of the dorsal hippocampus. Using pharmacological methods and adenovirus gene transfer to bidirectionally regulate AMPK activity, we found that increasing AMPK activity in the CA1 impaired the formation of long-term fear memory, and decreasing AMPK activity enhanced fear memory formation. These findings were associated with changes in the phosphorylation of AMPK and p70s6 kinase (p70s6k) and expression of BDNF and membrane GluR1 and GluR2 in the CA1. Furthermore, the prior administration of an mTORC1 inhibitor blocked the enhancing effect of AMPK inhibition on fear memory formation, suggesting that this negative regulation of contextual fear memory by AMPK in the CA1 depends on the mTORC1 signaling pathway. Finally, we found that AMPK activity regulated hippocampal spine growth associated with memory formation. In summary, our results indicate that AMPK is a key negative regulator of plasticity and fear memory formation.

EGCG Blocked Phenylephrin-Induced Hypertrophy in H9C2 Cardiomyocytes, by Activating AMPK-Dependent Pathway

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism. Previous studies have shown that activation of AMPK results in suppression of cardiac myocyte hypertrophy via inhibition of the p70S6 kinase (p70S6K) and eukaryotic elongation factor-2 (eEF2) signaling pathways. Epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea, possesses multiple protective effects on the cardiovascular system including cardiac hypertrophy. However, the molecular mechanisms has not been well investigated. In this study, we found that EGCG could significantly reduce natriuretic peptides type A (Nppa), brain natriuretic polypeptide (BNP) mRNA expression and decrease cell surface area in H9C2 cardiomyocytes stimulated with phenylephrine (PE). Moreover, we showed that AMPK is activated in H9C2 cardiomyocytes by EGCG, and AMPK-dependent pathway participates in the inhibitory effects of EGCG on cardiac hypertrophy. Taken together, our findings provide the first evidence that the effect of EGCG against cardiac hypertrophy may be attributed to its activation on AMPK-dependent signaling pathway, suggesting the therapeutic potential of EGCG on the prevention of cardiac remodeling in patients with pressure overload hypertrophy.

Activators of AMPK: not just for Type II diabetes

Recent discoveries of AMPK activators point to the large number of therapeutic candidates that can be transformed to successful designs of novel drugs. AMPK is a universal energy sensor and influences almost all physiological processes in the cells. Thus, regulation of the cellular energy metabolism can be achieved in selective tissues via the artificial activation of AMPK by small molecules. Recently, special attention has been given to direct activators of AMPK that are regulated by several nonspecific upstream factors. The direct activation of AMPK, by definition, should lead to more specific biological activities and as a result minimize possible side effects.

Ameliorative Effect of a Selective Endothelin ETA Receptor Antagonist in Rat Model of L-Methionine-induced Vascular Dementia

The present study was designed to investigate the efficacy of selective ET_A receptor antagonist, ambrisentan on hyperhomocysteinemia-induced experimental vascular dementia. L-methionine was administered for 8 weeks to induce hyperhomocysteinemia and associated vascular dementia in male rats. Ambrisentan was administered to L-methionine-treated effect rats for 4 weeks (starting from 5^th to 8^th week of L-methionine treatment). On 52^nd day onward, the animals were exposed to the Morris water maze (MWM) for testing their learning and memory abilities. Vascular endothelial function, serum nitrite/nitrate levels, brain thiobarbituric acid reactive species (TBARS), brain reduced glutathione (GSH) levels, and brain acetylcholinesterase (AChE) activity were also measured. L-methionine-treated animals showed significant learning and memory impairment, endothelial dysfunction, decrease in/serum nitrite/nitrate and brain GSH levels along with an increase in brain TBARS levels and AChE activity. Ambrisentan significantly improved hyperhomocysteinemia-induced impairment of learning, memory, endothelial dysfunction, and changes in various biochemical parameters. These effects were comparable to that of donepezil serving as positive control. It is concluded that ambrisentan, a selective ET_A receptor antagonist may be considered as a potential pharmacological agent for the management of hyperhomocysteinemia-induced vascular dementia.