Asiatic Acid Prevents Cognitive Deficits by Inhibiting Calpain Activation and Preserving Synaptic and Mitochondrial Function in Rats with Kainic Acid-Induced Seizure

Stabilization of mitochondrial function by chlorogenic acid protects against kainic acid-induced seizures and neuronal cell death in rats

The current study investigated the effect of chlorogenic acid, a polyphenolic compound found in numerous plant products, on a kainic acid-induced seizure rat model and its potential mechanism. Rats were administered chlorogenic acid (10 and 50 mg/kg) intraperitoneally for 30 min before kainic acid (15 mg/kg) intraperitoneal administration. Pretreatment with chlorogenic acid decreased the seizure score, increased the latency to onset of the first seizure, and decreased the mortality rate. Chlorogenic acid pretreatment also resulted in a significant reduction in glutamate elevation and neuronal death in the hippocampus of kainic acid-treated rats. In addition, electron microscopy revealed that kainic acid-induced changes in hippocampal mitochondrial structure were prevented by chlorogenic acid pretreatment. Additionally, the levels of mitochondrial function-related proteins, including sirtuin 3, Complex I, glutamate dehydrogenase 1 and ATP synthase, were increased, and the level of the mitochondrial damage marker cytochrome C was decreased in the hippocampus of chlorogenic acid/kainic acid rats. Furthermore, the expression of mitochondrial biogenesis-related proteins [AMP-activated protein kinase (AMPK), sirtuin1, and peroxisome proliferator-activated receptor γ-coactivator-1α (PGC-1α)] and mitophagy-related proteins [phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), Parkin, and microtubule-associated protein 1 light chain 3 (LC3)] was decreased in the hippocampus of kainic acid-treated rats, which was reversed by chlorogenic acid pretreatment. These observations reveal the marked neuroprotective potential of chlorogenic acid against kainic acid-induced neurotoxicity and seizures through prevention of glutamate increase and preservation of AMPK/sirtuin 1/PGC-1α-mediated mitochondrial biogenesis and PINK1/Parkin-induced mitophagy to maintain adequate mitochondrial homeostasis and function.

Neuroprotective mechanisms of Asiatic acid

Asiatic acid (AA) is the most crucial component of Asiaticoside in many edible and medicinal plants. It has diverse biological activities such as anti-inflammatory, antioxidant, anti-infective, and anti-tumor. Additionally, AA has been intensively studied in the last decades. It has shown great potential in the treatment of various neurological diseases such as spinal cord injury (SCI), cerebral ischemia, epilepsy, traumatic brain injury (TBI), neural tumors, Alzheimer's disease (AD), and Parkinson's disease (PD). Moreover, AA provides pertinent data for neuroprotective signaling pathways, and its substantial neuroprotective ability makes it a novel candidate for developing drugs that target the central nervous system.

Natural products regulate mitochondrial function in cognitive dysfunction-A scoping review

Medicines from natural products can not only treat neurodegenerative diseases but also improve the cognitive dysfunction caused by treatments with western medicines. This study reviews the literature related to the regulation of mitochondrial participation in cognitive function by natural products. In this study, we focused on English articles in PubMed, Web of Science, and Google Scholar, from 15 October 2017, to 15 October 2022. Fourteen studies that followed the inclusion criteria were integrated, analyzed, and summarized. Several studies have shown that natural products can improve or reduce cognitive dysfunction by ameliorating mitochondrial dysfunction. These results suggest that natural products may serve as new therapeutic targets for neurodegenerative diseases.

Calpain Inhibitor Calpeptin Improves Alzheimer's Disease-Like Cognitive Impairments and Pathologies in a Diabetes Mellitus Rat Model

Diabetes mellitus (DM) has been considered an accelerator of Alzheimer's disease (AD), but the cellular and molecular mechanisms underlying this effect are not fully understood. Here, we attempted to determine the role and regulatory mechanism of calpain in the AD-like cognitive decline and pathological changes in rats caused by DM. In the initial stages, our results verified that DM model rats showed cognitive impairment, as well as a loss of neurons, decreased pericyte marker (PDGFR-β and α-SMA), and calpain-2 expression and amyloid-β (Aβ) deposition in the hippocampal tissues. In high glucose-induced primary pericytes, the cell apoptotic rate was increased, and cell proliferation was inhibited in a time-dependent manner. The protein level of calpain-2 was also upregulated by HG induction, but the level of calpain-1 did not change with HG treatment, which was also observed in DM model rats. Subsequently, some DM model rats were administered calpeptin, an inhibitor of calpain. Our data revealed that calpeptin treatment significantly suppressed calpain-1 and calpain-2 expression in the hippocampal tissues and effectively improved the cognitive impairments of DM model rats. Neuronal loss, Aβ accumulation, pericyte loss, inflammation, and oxidative stress injury in the hippocampal tissues of DM model rats were also partly rescued by calpeptin administration. Our work demonstrated that the calpain inhibitor calpeptin could alleviate DM-induced AD-like cognitive impairments and pathological changes in rats, and this effect may be associated with pericytes. Calpeptin may become a promising drug to treat the AD-like complications of DM.

Recent Advances Regarding the Molecular Mechanisms of Triterpenic Acids: A Review (Part I)

Triterpenic acids are phytocompounds with a widespread range of biological activities that have been the subject of numerous in vitro and in vivo studies. However, their underlying mechanisms of action in various pathologies are not completely elucidated. The current review aims to summarize the most recent literature, published in the last five years, regarding the mechanism of action of three triterpenic acids (asiatic acid, oleanolic acid, and ursolic acid), corelated with different biological activities such as anticancer, anti-inflammatory, antidiabetic, cardioprotective, neuroprotective, hepatoprotective, and antimicrobial. All three discussed compounds share several mechanisms of action, such as the targeted modulation of the PI3K/AKT, Nrf2, NF-kB, EMT, and JAK/STAT3 signaling pathways, while other mechanisms that proved to only be specific for a part of the triterpenic acids discussed, such as the modulation of Notch, Hippo, and MALAT1/miR-206/PTGS1 signaling pathway, were highlighted as well. This paper stands as the first part in our literature study on the topic, which will be followed by a second part focusing on other triterpenic acids of therapeutic value.

Anticonvulsive and Neuroprotective Effects of Eupafolin in Rats Are Associated with the Inhibition of Glutamate Overexcitation and Upregulation of the Wnt/β-Catenin Signaling Pathway

Several plant compounds have been found to possess neuroactive properties. The aim of this study was to investigate the anticonvulsant effect of eupafolin, a major active component extracted from Salvia plebeia, a herb used in traditional medicine for its anti-inflammatory properties. To this end, we assessed the anticonvulsant effects of eupafolin in rats intraperitoneally (i.p.) injected with kainic acid (KA) to elucidate this mechanism. Treatment with eupafolin (i.p.) for 30 min before KA administration significantly reduced behavioral and electrographic seizures induced by KA, similar to carbamazepine (i.p.), a widely used antiepileptic drug. Eupafolin treatment also significantly decreased KA seizure-induced neuronal cell death and glutamate elevation in the hippocampus. In addition, eupafolin notably reversed KA seizure-induced alterations in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit GluR2, glutamate decarboxylase 67 (GAD67, GABAergic enzyme), and Wnt signaling-related proteins, including porcupine, Wnt1, phosphorylated-glycogen synthase kinase-3β, β-catenin, and Bcl-2 in the hippocampus. Furthermore, the increased level of Dickkopf-related protein 1 (Dkk-1, a Wnt signaling antagonist) and the decreased level of Disheveled1 (Dvl-1, a Wnt signaling activator) in the hippocampus of KA-treated rats were reversed by eupafolin. This study provides evidence of the anticonvulsant and neuroprotective properties of eupafolin and of the involvement of regulation of glutamate overexcitation and Wnt signaling in the mechanisms of these properties. These findings support the benefits of eupafolin in treating epilepsy.

Piperine Provides Neuroprotection against Kainic Acid-Induced Neurotoxicity via Maintaining NGF Signalling Pathway

The neuroprotective properties of piperine, the major alkaloid extracted from black pepper, have been under investigation, but its mechanism of action in excitotoxicity is still poorly understood. This study aimed to evaluate the protective effects of piperine with a focus on nerve growth factor (NGF) signalling in a kainic acid (KA) rat model of excitotoxicity. Rats were administered intraperitoneally (i.p.) piperine (10 or 50 mg/kg) before KA injection (15 mg/kg, i.p.). Our results show that KA exposure in rats caused seizure behaviour, intrinsic neuronal hyperactivity, glutamate elevation, hippocampal neuronal damage, and cognitive impairment. These KA-induced alterations could be restored to the normal state by piperine treatment. In addition, piperine decreased the expression of the NGF precursor proNGF and NGF-degrading protease matrix metalloproteinase 9, whereas it increased the expression of proNGF processing enzyme matrix metalloproteinase 7, NGF, and NGF-activated receptor TrkA in the hippocampus of KA-treated rats. Furthermore, KA decreased phosphorylation of the protein kinase B (Akt) and glycogen synthase kinase 3β (GSK3β) in the hippocampus, and piperine reversed these changes. Our data suggest that piperine protects hippocampal neurons against KA-induced excitotoxicity by upregulating the NGF/TrkA/Akt/GSK3β signalling pathways.

Neferine, an Alkaloid from Lotus Seed Embryos, Exerts Antiseizure and Neuroprotective Effects in a Kainic Acid-Induced Seizure Model in Rats

Current anti-seizure drugs fail to control approximately 30% of epilepsies. Therefore, there is a need to develop more effective anti-seizure drugs, and medicinal plants provide an attractive source for new compounds. This study aimed to evaluate the possible anti-seizure and neuroprotective effects of neferine, an alkaloid from the lotus seed embryos of Nelumbo nucifera, in a kainic acid (KA)-induced seizure rat model and its underlying mechanisms. Rats were intraperitoneally (i.p.) administrated neferine (10 and 50 mg/kg) 30 min before KA injection (15 mg/kg, i.p.). Neferine pretreatment increased seizure latency and reduced seizure scores, prevented glutamate elevation and neuronal loss, and increased presynaptic protein synaptophysin and postsynaptic density protein 95 expression in the hippocampi of rats with KA. Neferine pretreatment also decreased glial cell activation and proinflammatory cytokine (interleukin-1β, interleukin-6, tumor necrosis factor-α) expression in the hippocampi of rats with KA. In addition, NOD-like receptor 3 (NLRP3) inflammasome, caspase-1, and interleukin-18 expression levels were decreased in the hippocampi of seizure rats pretreated with neferine. These results indicated that neferine reduced seizure severity, exerted neuroprotective effects, and ameliorated neuroinflammation in the hippocampi of KA-treated rats, possibly by inhibiting NLRP3 inflammasome activation and decreasing inflammatory cytokine secretion. Our findings highlight the potential of neferine as a therapeutic option in the treatment of epilepsy.

Soybean Meal Extract Preserves Memory Ability by Increasing Presynaptic Function and Modulating Gut Microbiota in Rats

Age-related degenerative brain diseases frequently manifest as memory deficits. Dietary interventions or nutraceuticals may provide efficacious treatments through prevention and cure. Soybean meal, a byproduct of soy oil refining, has health benefits, but its effect on memory function is unknown. Therefore, we evaluated the effect of the oral administration of soybean meal extract (SME) for 2 weeks on memory function using the Morris water maze (MWM) test in healthy rats and investigated the possible underlying mechanisms. First, analysis of the composition revealed that SME is rich in isoflavones; SME did not exhibit hepatotoxicity or renal toxicity at the different doses tested. The MWM results revealed that the escape latency and movement distance of rats were significantly shorter in the SME group than in the control group, indicating that SME can help in memory preservation. In addition, SME increased the levels of presynaptic proteins such as synaptophysin, synaptobrevin, synaptotagmin, syntaxin, synapsin I, and 25-kDa synaptosome-associated protein as well as protein kinases and their phosphorylated expression, including extracellular signal-regulated kinases 1 and 2 (ERK1/2), protein kinase C (PKC), and Ca2+/calmodulin-dependent protein kinase II (CaMKII) in the hippocampal nerve terminals (synaptosomes). Transmission electron microscopy also indicated that SME increased the number of synaptic vesicles in hippocampal synaptosomes. Furthermore, SME rats exhibited altered microbiota composition compared with control rats. Therefore, our data suggest that SME can increase presynaptic function and modulate gut microbiota, thus aiding in memory preservation in rats.

Kaempferol 3-Rhamnoside on Glutamate Release from Rat Cerebrocortical Nerve Terminals Involves P/Q-Type Ca2+ Channel and Ca2+/Calmodulin-Dependent Protein Kinase II-Dependent Pathway Suppression

Excess synaptic glutamate release has pathological consequences, and the inhibition of glutamate release is crucial for neuroprotection. Kaempferol 3-rhamnoside (KR) is a flavonoid isolated from Schima superba with neuroprotective properties, and its effecton the release of glutamate from rat cerebrocortical nerve terminals was investigated. KR produced a concentration-dependent inhibition of 4-aminopyridine (4-AP)-evoked glutamate release with half-maximal inhibitory concentration value of 17 µM. The inhibition of glutamate release by KR was completely abolished by the omission of external Ca²⁺ or the depletion of glutamate in synaptic vesicles, and it was unaffected by blocking carrier-mediated release. In addition, KR reduced the 4-AP-evoked increase in Ca²⁺ concentration, while it did not affect 4-AP-evoked membrane potential depolarization. The application of selective antagonists of voltage-dependent Ca²⁺ channels revealed that the KR-mediated inhibition of glutamate release involved the suppression of P/Q-type Ca²⁺ channel activity. Furthermore, the inhibition of release was abolished by the calmodulin antagonist, W7, and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) inhibitor, KN62, but not by the protein kinase A (PKA) inhibitor, H89, or the protein kinase C (PKC) inhibitor, GF109203X. We also found that KR reduced the 4-AP-induced increase in phosphorylation of CaMKII and its substrate synapsin I. Thus, the effect of KR on evoked glutamate release is likely linked to a decrease in P/Q-type Ca²⁺ channel activity, as well as to the consequent reduction in the CaMKII/synapsin I pathway.

Anti-excitotoxicity and neuroprotective action of asiaticoside encapsulated polymeric nanoparticles in pilocarpine rodent seizure model

Asiaticoside (ASI), an ursane-type triterpenoid saponin, isolated from the memory enhancing herb Centella asiatica, is known for its neuroprotective activities. Here the anti-excitotoxicity and neuro protective effects of ASI encapsulated alginate chitosan nanoparticles (ACNPs) were evaluated in pilocarpine (PC) induced seizure in mice model. ACNPs were prepared by ionic gelation-polyelectrolyte complex method and their physicochemical characterization was carried out by TEM, SEM, DLS, XRD and FT-IR. Subsequently their encapsulation efficiency (EE), in vitro drug release, cell viability, seizure score, DNA fragmentation and mRNA expression of regulatory stress markers were evaluated. Membrane permeability of ACNPs in brain, histopathology and biological TEM and SEM analyses were also carried out. TEM of ACNPs showed spherical morphology with a particle size of 200-400 nm. DLS of ACNPs displayed an average size of 486.2 nm with polydispersity index (PDI) of 0.567 and zeta potential of -14.1 mV. ACNPs achieved high EE (> 90%) and controlled release (10%). Biological evaluation studies revealed ACNPs as non-toxic to mouse neural stem cells (mNSCs). They displayed enhanced brain permeability and attenuated seizure. Our results confirmed ACNPs as effective in crossing the brain membrane barrier and mitigating seizure severity induced by PC.

Enmein Decreases Synaptic Glutamate Release and Protects against Kainic Acid-Induced Brain Injury in Rats

This study investigated the effects of enmein, an active constituent of Isodon japonicus Hara, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes) and evaluated its neuroprotective potential in a rat model of kainic acid (KA)-induced glutamate excitotoxicity. Enmein inhibited depolarization-induced glutamate release, FM1-43 release, and Ca²⁺ elevation in cortical nerve terminals but had no effect on the membrane potential. Removing extracellular Ca²⁺ and blocking vesicular glutamate transporters, N- and P/Q-type Ca²⁺ channels, or protein kinase C (PKC) prevented the inhibition of glutamate release by enmein. Enmein also decreased the phosphorylation of PKC, PKC-α, and myristoylated alanine-rich C kinase substrates in synaptosomes. In the KA rat model, intraperitoneal administration of enmein 30 min before intraperitoneal injection of KA reduced neuronal cell death, glial cell activation, and glutamate elevation in the hippocampus. Furthermore, in the hippocampi of KA rats, enmein increased the expression of synaptic markers (synaptophysin and postsynaptic density protein 95) and excitatory amino acid transporters 2 and 3, which are responsible for glutamate clearance, whereas enmein decreased the expression of glial fibrillary acidic protein (GFAP) and CD11b. These results indicate that enmein not only inhibited glutamate release from cortical synaptosomes by suppressing Ca²⁺ influx and PKC but also increased KA-induced hippocampal neuronal death by suppressing gliosis and decreasing glutamate levels by increasing glutamate uptake.

Chlorogenic Acid Decreases Glutamate Release from Rat Cortical Nerve Terminals by P/Q-Type Ca2+ Channel Suppression: A Possible Neuroprotective Mechanism

The glutamatergic neurotransmitter system has received substantial attention in research on the pathophysiology and treatment of neurological disorders. The study investigated the effect of the polyphenolic compound chlorogenic acid (CGA) on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). CGA inhibited 4-aminopyridine (4-AP)-induced glutamate release from synaptosomes. This inhibition was prevented in the absence of extracellular Ca²⁺ and was associated with the inhibition of 4-AP-induced elevation of Ca²⁺ but was not attributed to changes in synaptosomal membrane potential. In line with evidence observed through molecular docking, CGA did not inhibit glutamate release in the presence of P/Q-type Ca²⁺ channel inhibitors; therefore, CGA-induced inhibition of glutamate release may be mediated by P/Q-type Ca²⁺ channels. CGA-induced inhibition of glutamate release was also diminished by the calmodulin and Ca²⁺/calmodilin-dependent kinase II (CaMKII) inhibitors, and CGA reduced the phosphorylation of CaMKII and its substrate, synapsin I. Furthermore, pretreatment with intraperitoneal CGA injection attenuated the glutamate increment and neuronal damage in the rat cortex that were induced by kainic acid administration. These results indicate that CGA inhibits glutamate release from cortical synaptosomes by suppressing P/Q-type Ca²⁺ channels and CaMKII/synapsin I pathways, thereby preventing excitotoxic damage to cortical neurons.

Natural products attenuate PI3K/Akt/mTOR signaling pathway: A promising strategy in regulating neurodegeneration

BACKGROUND

As common, progressive, and chronic causes of disability and death, neurodegenerative diseases (NDDs) significantly threaten human health, while no effective treatment is available. Given the engagement of multiple dysregulated pathways in neurodegeneration, there is an imperative need to target the axis and provide effective/multi-target agents to tackle neurodegeneration. Recent studies have revealed the role of phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) in some diseases and natural products with therapeutic potentials.

PURPOSE

This is the first systematic and comprehensive review on the role of plant-derived secondary metabolites in managing and/or treating various neuronal disorders via the PI3K/Akt/mTOR signaling pathway.

STUDY DESIGN AND METHODS

A systematic and comprehensive review was done based on the PubMed, Scopus, Web of Science, and Cochrane electronic databases. Two independent investigators followed the PRISMA guidelines and included papers on PI3K/Akt/mTOR and interconnected pathways/mediators targeted by phytochemicals in NDDs.

RESULTS

Natural products are multi-target agents with diverse pharmacological and biological activities and rich sources for discovering and developing novel therapeutic agents. Accordingly, recent studies have shown increasing phytochemicals in combating Alzheimer's disease, aging, Parkinson's disease, brain/spinal cord damages, depression, and other neuronal-associated dysfunctions. Amongst the emerging targets in neurodegeneration, PI3K/Akt/mTOR is of great importance. Therefore, attenuation of these mediators would be a great step towards neuroprotection in such NDDs.

CONCLUSION

The application of plant-derived secondary metabolites in managing and/or treating various neuronal disorders through the PI3K/Akt/mTOR signaling pathway is a promising strategy towards neuroprotection.

Mitoprotective Effects of Centella asiatica (L.) Urb.: Anti-Inflammatory and Neuroprotective Opportunities in Neurodegenerative Disease

Natural products remain a crucial source of drug discovery for accessible and affordable solutions for healthy aging. Centella asiatica (L.) Urb. (CA) is an important medicinal plant with a wide range of ethnomedicinal uses. Past in vivo and in vitro studies have shown that the plant extract and its key components, such as asiatic acid, asiaticoside, madecassic acid and madecassoside, exhibit a range of anti-inflammatory, neuroprotective, and cognitive benefits mechanistically linked to mitoprotective and antioxidant properties of the plant. Mitochondrial dysfunction and oxidative stress are key drivers of aging and neurodegenerative disease, including Alzheimer’s disease and Parkinson’s disease. Here we appraise the growing body of evidence that the mitoprotective and antioxidative effects of CA may potentially be harnessed for the treatment of brain aging and neurodegenerative disease.