Dichloromethane extraction from Piper nigrum L. and P. longum L. to mitigate ischemic stroke by activating the AKT/mTOR signaling pathway to suppress autophagy

Tetrahydropiperine, a natural alkaloid with neuroprotective effects in ischemic stroke

BACKGROUND

Ischemic stroke (IS) is a life-threatening neurological disease with various pathological mechanisms. Tetrahydropiperine (THP) is a natural alkaloid with protective effects against multiple diseases, such as seizure, and pain. This study was to examine the impact of THP on IS and investigate its potential mechanism.

MATERIAL AND METHODS

We employed network pharmacology and molecular docking techniques to identify the target proteins of THP for intervention in IS. Adult male Sprague-Dawley rats were used to create a permanent middle cerebral artery occlusion model. PC-12 cells were chosen to establish an oxygen-glucose deprivation (OGD) cell model. Disease modeling followed by nimodipine (NIMO); 3-methyladenine (3-MA) and rapamycin (RAP) interventions. Open field test, Longa score, balance beam test, and forelimb grip test were used to measure motor and neurological functions. The degree of neurological damage recovery was assessed through behavioral analysis, and cerebral infarction volume was determined using TTC staining. Morphological changes were examined through HE and Nissl staining, and ultrastructural changes in neurons were observed using transmission electron microscopy. The protein expression of autophagy and related pathways was analyzed through Western blot (WB). The appropriate hypoxia time and drug concentration were determined using CCK-8 assay, which also measured cell survival rate.

RESULTS

The network pharmacology findings indicated that the impact of THP on IS was enhanced in the PI3K/Akt signaling pathway. THP demonstrated robust docking capability with proteins associated with the autophagy and PI3K/Akt/mTOR, as indicated by the molecular docking outcomes. THP significantly improved behavioral damage, reduced the area of cerebral infarction, ameliorated histopathological damage from ischemia, increase neuronal survival, and alleviated ultrastructural damage in neurons (P < 0.05). THP enhanced the survival of PC-12 cells induced by OGD and ameliorated the morphological harm to the cells (P < 0.05). THP was found to elevate the quantities of P62, LC3-Ⅰ, PI3K, P-AKt/Akt, and P-mTOR/mTOR proteins while reducing the levels of Atg7 and Beclin1 proteins. The results of transmission electron microscopy showed no autophagosomes in the THP, 3-MA, and 3-MA + THP groups.

CONCLUSION

The activation of the PI3K/Akt/mTOR signaling pathway by THP inhibits autophagy and provides relief from neurological damage in IS.

Akt/mTOR Pathway Agonist SC79 Inhibits Autophagy and Apoptosis of Oligodendrocyte Precursor Cells Associated with Neonatal White Matter Dysplasia

White matter dysplasia (WMD) in preterm infants due to intrauterine inflammation is caused by excessive apoptosis of oligodendrocyte precursor cells (OPCs). In recent years, studies have found that excessive autophagy and apoptosis are highly interconnected and important in infection and inflammatory diseases in general. Therefore, in this study, we aimed to confirm whether regulation of autophagy by using the Akt phosphorylation agonist SC79 can inhibit abnormal apoptosis of OPCs and promote myelin maturation and white matter development in neonatal rats with WMD. We investigated the effect of inflammation on oligodendrocyte development in P0 neonatal rats by intracerebellar injection of LPS, and collected brain tissue at P2 and P5. Immunohistochemical and immunofluorescence staining were used to evaluate white matter damage, while immunofluorescence staining, terminal deoxynucleotidyl transferase dUTP nick end labeling analysis (TUNEL), and western blotting were used to evaluate autophagy and apoptosis. First, we observed that white matter development was arrested and white matter fiber maturation was impaired in LPS-inflicted pups compared with those in the sham-operated group. Second, treatment with SC79 reduced the levels of LC3II, caspase 3, caspase 9, and Bax/Bcl-2 and increased the levels of p62, p-Akt, and p-mTOR in the brain tissue of neonatal rats. Finally, SC79 treatment inhibited OPC apoptosis by increasing the binding of Beclin 1 to Bcl-2, which promoted OPC differentiation and maturation. However, the opposite results were observed after rapamycin administration. Taken together, our results suggest that SC79 can inhibit the abnormal apoptosis of OPCs caused by excessive autophagy through the Akt/mTOR pathway and that SC79 is a potential therapeutic agent for WMD in preterm infants.

Identification of ligustrazine-based analogs of piperlongumine as potential anti-ischemic stroke agents

Piper longum has a specific aroma and spicy taste. In addition to edible value, current studies have shown that piper longum also has pharmacological activities such as anti-platelet aggregation, anti-inflammation, anti-cancer, anti-diabetes and anti-depression. Piperlongumine is an alkaloid isolated from Piper longum. Based on our previous studies, four Piperlongumine analogs were synthesized, and their anti-platelet aggregation activities were evaluated. Among them, compound 8 has the strongest anti-platelet aggregation activity. Therefore, compound 8 was docked with stroke-related protein targets, and it was found that compound 8 had good binding affinity to MRTF-A complex and Bcl-2. Through animal experiments, it was found that compound 8 could significantly improve the pathological damage of brain tissue after ischemia and could increase the expression of MRTF-A and Bcl-2 in cerebral cortex in rats. These results suggest that compound 8 may have a good inhibitory effect on apoptosis and tissue structurel disorders induced by cerebral ischemia-reperfusion, so as to reduce the injury caused by ischemic stroke.

Effects of dichloromethane extraction from Piper nigrum L. and P. longum L. on the expression of autophagy-related proteins in ischemic stroke

Piper nigrum L. and P. longum L. are widely used in various medicinal formulations. The dichloromethane fraction of Piper nigrum L. and P. longum L. (DF) can prevent cerebral ischemic injury although the underlying mechanisms are obscure. The aim of this study was to evaluate the potential neuroprotective effects of DF on a rat model of permanent middle cerebral artery occlusion (pMCAO) and assess the molecular mechanisms. Animals were administered with DF (50, 100, and 150 mg/kg) or nimodipine (12 mg/kg) 6 h after pMCAO for 14 consecutive days via intragastric gavage. In the vitro this study identified that DF reduced neurological severity scores and improved survival rate. Results showed that DF markedly inhibited the percentage of apoptotic cells as well as neuronal autophagy and mitigated the overall neuronal and vascular damage in the ischemic region. Western blot testing showed that at the molecular level, DF significantly suppressed ischemia-induced activated expression of LC3, Beclin1, Atg12, and Atg5. Overall, our study indicated that DF attenuated neuronal autophagy by suppressing the expression of autophagy-related proteins to generate neuroprotection effect for ischemic stroke.

Piperine ameliorates ischemic stroke-induced brain injury in rats by regulating the PI3K/AKT/mTOR pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Piperine (PIP), a main active component isolated from Piper nigrum L., exerts neuroprotective effects in a rat model of ischemic stroke (IS). However, studies on the effects of PIP on neuroprotection and autophagy after IS are limited.

AIM OF THE STUDY

This study aimed to prove the protective effects of PIP against brain IS and elucidate its underlying mechanisms.

MATERIALS AND METHODS

Specific pathogen-free male Sprague-Dawley rats were selected to establish a permanent middle cerebral artery occlusion model. The experiment was randomly divided into six groups: sham group, model group, PIP intervention group (10, 20, and 30 mg/kg group), and nimodipine group (Nimo group, 12 mg/kg). Neurological function score, postural reflex score, body swing score, balance beam test, and grip strength test were used to detect behavioral changes of rats. The area of cerebral infarction was detected by TTC staining, and the number and morphological changes of neurons were observed by Nissl and HE staining. In addition, the ultrastructure of hippocampal dentate gyrus neurons was observed using a transmission electron microscope. Western blot was used to detect the expression of PI3K/AKT/mTOR signaling pathway proteins and autophagy-related proteins, namely, Beclin1 and LC3, in the hippocampus and cortex. Cell experiments established an in vitro model of oxygen-glucose deprivation (OGD) with the HT22 cell line to verify the mechanism. The experiment was divided into five groups: control group, OGD group, OGD + PIP 20 μg/mL group, OGD + PIP 30 μg/mL group, and OGD + PIP 40 μg/mL group. CCK-8 was used to measure cell activity, and Western blot was used to measure the expression of PI3K/AKT/mTOR signaling pathway proteins and autophagy-related proteins (Beclin1 and LC3).

RESULTS

Compared with the model group, the neurological function scores, body swing scores, and postural reflex scores of rats in the 10, 20, and 30 mg/kg PIP intervention groups and Nimo groups decreased, whereas the balance beam score and grip test scores increased (all p < 0.05). After 10, 20, and 30 mg/kg PIP and Nimo intervention, the cerebral infarction area of pMCAO rats was reduced (p < 0.01), and Nissl and HE staining results showed that the number of neurons survived in the 30 mg/kg PIP and Nimo intervention groups increased. Cell morphology and structure were significantly improved (p < 0.05). Most of the hippocampal dentate gyrus neurons and their organelles gradually returned to normal in the 30 mg/kg PIP and Nimo intervention groups, with less neuronal damage. The expression levels of p-mTOR, p-AKT, and p-PI3K in the hippocampus and cortex of the 30 mg/kg PIP and Nimo intervention groups decreased, whereas the expression level of PI3K increased (all p < 0.05). In addition, the expression level of autophagy-related proteins, namely, Beclin1 and LC3-II, in the 30 mg/kg PIP and Nimo intervention groups decreased (all p < 0.05). Results of CCK-8 showed that after 1 h of OGD, the 30 and 40 μg/mL PIP intervention groups had higher cell viability than the OGD group (p < 0.01). Western blot results showed that compared with the OGD group, the expression level of p-mTOR, p-AKT, and p-PI3K in the 30 and 40 μg/mL PIP intervention groups decreased, and the expression level of PI3K increased (all p < 0.05). Moreover, the expression level of autophagy-related proteins, namely, Beclin1 and LC3-II, in the 30 and 40 μg/mL PIP intervention groups decreased (all p < 0.05).

CONCLUSIONS

This study shows that PIP is a potential compound with neuroprotective effects. PIP can inhibit the PI3K/AKT/mTOR pathway and autophagy. Its inhibition of autophagy is possibly related to modulating the PI3K/AKT/mTOR pathway. These findings provide new insights into the use of PIP for the treatment of IS and its underlying mechanism.

EGCG protects the mouse brain against cerebral ischemia/reperfusion injury by suppressing autophagy via the AKT/AMPK/mTOR phosphorylation pathway

Stroke remains one of the leading reasons of mortality and physical disability worldwide. The treatment of cerebral ischemic stroke faces challenges, partly due to a lack of effective treatments. In this study, we demonstrated that autophagy was stimulated by transient middle cerebral artery occlusion/reperfusion (MCAO/R) and oxygen-glucose deprivation/reoxygenation (OGD/R). Treatment with (−)-epigallocatechin-3-gallate (EGCG), a bioactive ingredient in green tea, was able to mitigate cerebral ischemia/reperfusion injury (CIRI), given the evidence that EGCG administration could reduce the infarct volume and protect poststroke neuronal loss in MCAO/R mice in vivo and attenuate cell loss in OGD/R-challenged HT22 cells in vitro through suppressing autophagy activity. Mechanistically, EGCG inhibited autophagy via modulating the AKT/AMPK/mTOR phosphorylation pathway both in vivo and in vitro models of stroke, which was further confirmed by the results that the administration of GSK690693, an AKT/AMPK inhibitor, and rapamycin, an inhibitor of mTOR, reversed aforementioned changes in autophagy and AKT/AMPK/mTOR signaling pathway. Overall, the application of EGCG relieved CIRI by suppressing autophagy via the AKT/AMPK/mTOR phosphorylation pathway.

Glutamate excitotoxicity: Potential therapeutic target for ischemic stroke

Glutamate-mediated excitotoxicity is an important mechanism leading to post ischemic stroke damage. After acute stroke, the sudden reduction in cerebral blood flow is most initially followed by ion transport protein dysfunction and disruption of ion homeostasis, which in turn leads to impaired glutamate release, reuptake, and excessive N-methyl-D-aspartate receptor (NMDAR) activation, promoting neuronal death. Despite extensive evidence from preclinical studies suggesting that excessive NMDAR stimulation during ischemic stroke is a central step in post-stroke damage, NMDAR blockers have failed to translate into clinical stroke treatment. Current treatment options for stroke are very limited, and there is therefore a great need to develop new targets for neuroprotective therapeutic agents in ischemic stroke to extend the therapeutic time window. In this review, we highlight recent findings on glutamate release, reuptake mechanisms, NMDAR and its downstream cellular signaling pathways in post-ischemic stroke damage, and review the pathological changes in each link to help develop viable new therapeutic targets. We then also summarize potential neuroprotective drugs and therapeutic approaches for these new targets in the treatment of ischemic stroke.

Neuroprotective Effect of Daidzein Extracted From Pueraria lobate Radix in a Stroke Model Via the Akt/mTOR/BDNF Channel

Daidzein is a plant isoflavonoid primarily isolated from Pueraria lobate Radix as the dry root of P. lobata (Wild.) Ohwi, have long been used as nutraceutical and medicinal herb in China. Despite the report that daidzein can prevent neuronal damage and improve outcome in experimental stroke, the mechanisms of this neuroprotective action have been not fully elucidated. The aim of this study was to determine whether the daidzein elicits beneficial actions in a stroke model, namely, cerebral ischemia/reperfusion (I/R) injury, and to reveal the underlying neuroprotective mechanisms associated with the regulation of Akt/mTOR/BDNF signal pathway. The results showed that I/R, daidzein treatment significantly improved neurological deficits, infarct volume, and brain edema at 20 and 30 mg/kg, respectively. Meanwhile, it was found out that the pretreatment with daidzein at 20 and 30 mg/kg evidently improved striatal dopamine and its metabolite levels. In addition, daidzein treatment reduced the cleaved Caspase-3 level but enhanced the phosphorylation of Akt, BAD and mTOR. Moreover, daidzein at 30 mg/kg treatment enhanced the expression of BDNF and CREB significantly. This protective effect of daidzein was ameliorated by inhibiting the PI3K/Akt/mTOR signaling pathway using LY294002. To sum up, our results demonstrated that daidzein could protect animals against ischemic damage through the regulation of the Akt/mTOR/BDNF channel, and the present study may facilitate the therapeutic research of stroke.

Neuroprotective Effects of Black Pepper and Its Bioactive Compounds in Age-Related Neurological Disorders

Age-related neurological disorders (ANDs), including neurodegenerative diseases, are multifactorial disorders whose risk increases with age. The main pathological hallmarks of ANDs include behavioral changes, excessive oxidative stress, progressive functional declines, impaired mitochondrial function, protein misfolding, neuroinflammation, and neuronal cell death. Recently, efforts have been made to overcome ANDs because of their increased age-dependent prevalence. Black pepper, the fruit of Piper nigrum L. in the family Piperaceae, is an important food spice that has long been used in traditional medicine to treat various human diseases. Consumption of black pepper and black pepper-enriched products is associated with numerous health benefits due to its antioxidant, antidiabetic, anti-obesity, antihypertensive, anti-inflammatory, anticancer, hepatoprotective, and neuroprotective properties. This review shows that black pepper's major bioactive neuroprotective compounds, such as piperine, effectively prevent AND symptoms and pathological conditions by modulating cell survival signaling and death. Relevant molecular mechanisms are also discussed. In addition, we highlight how recently developed novel nanodelivery systems are vital for improving the efficacy, solubility, bioavailability, and neuroprotective properties of black pepper (and thus piperine) in different experimental AND models, including clinical trials. This extensive review shows that black pepper and its active ingredients have therapeutic potential for ANDs.

Targeting autophagy in ischemic stroke: From molecular mechanisms to clinical therapeutics

Stroke constitutes the second leading cause of death and a major cause of disability worldwide. Stroke is normally classified as either ischemic or hemorrhagic stroke (HS) although 87% of cases belong to ischemic nature. Approximately 700,000 individuals suffer an ischemic stroke (IS) in the US each year. Recent evidence has denoted a rather pivotal role for defective macroautophagy/autophagy in the pathogenesis of IS. Cellular response to stroke includes autophagy as an adaptive mechanism that alleviates cellular stresses by removing long-lived or damaged organelles, protein aggregates, and surplus cellular components via the autophagosome-lysosomal degradation process. In this context, autophagy functions as an essential cellular process to maintain cellular homeostasis and organismal survival. However, unchecked or excessive induction of autophagy has been perceived to be detrimental and its contribution to neuronal cell death remains largely unknown. In this review, we will summarize the role of autophagy in IS, and discuss potential strategies, particularly, employment of natural compounds for IS treatment through manipulation of autophagy.

Autophagy Inhibition by ATG3 Knockdown Remits Oxygen-Glucose Deprivation/Reoxygenation-Induced Injury and Inflammation in Brain Microvascular Endothelial Cells

Autophagy participates in the development of cerebral ischemia stroke. Autophagy-related 3 (ATG3), an important autophagy regulator, was reported to be upregulated in a rat model of cerebral ischemia/reperfusion (CI/R) injury and an oxygen-glucose deprivation/reoxygenation (OGD/R) cell model. However, the detailed role of ATG3 in CI/R injury remains elusive. An in vitro cellular model was established to mimic CI/R injury by exposing hBMECs and bEnd.3 cells to OGD/R. OGD/R-induced injury were evaluated by cell counting kit-8 (CCK-8), LDH release assay, caspase-3 activity assay and TUNEL assay. Inflammation was assessed by detecting mRNA expression and concentrations of interleukin-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α) using qRT-PCR and ELISA, respectively. The protein levels of ATG3, light chain 3 (LC3)-I, LC3-II, p62, protein kinase B (Akt), and phosphorylated Akt (p-Akt) were determined by western blot analysis. We successfully established an in vitro OGD/R injury model using hBMECs and bEnd.3 cells. ATG3 was time-dependently upregulated and ATG3 knockdown inhibited autophagy in OGD/R-challenged brain microvascular endothelial cells. Moreover, autophagy inhibition by ATG3 interference attenuated OGD/R-induced viability inhibition and increase of LDH release, caspase-3 activity, programmed cell death, and production of IL-1β, IL-6 and TNF-α. Inhibition of autophagy by ATG3 silencing activated the phosphoinositide 3-kinase (PI3K)/Akt pathway in OGD/R-challenged brain microvascular endothelial cells. Furthermore, inhibition of the PI3K/Akt pathway reversed the protective effects of ATG3 silencing on OGD/R-induced injury and inflammation. In conclusion, autophagy inhibition by ATG3 knockdown remitted OGD/R-induced injury and inflammation in brain microvascular endothelial cells via activation of the PI3K/Akt pathway.