Neuroprotective effects of liquiritigenin isolated from licorice roots on glutamate-induced apoptosis in hippocampal neuronal cells

Interpreting the Mechanism of Active Ingredients in Polygonati Rhizoma in Treating Depression by Combining Systemic Pharmacology and In Vitro Experiments

Polygonati Rhizoma (PR) has certain neuroprotective effects as a homology of medicine and food. In this study, systematic pharmacology, molecular docking, and in vitro experiments were integrated to verify the antidepressant active ingredients in PR and their mechanisms. A total of seven compounds in PR were found to be associated with 45 targets of depression. Preliminarily, DFV docking with cyclooxygenase 2 (COX2) showed good affinity. In vitro, DFV inhibited lipopolysaccharide (LPS)-induced inflammation of BV-2 cells, reversed amoeba-like morphological changes, and increased mitochondrial membrane potential. DFV reversed the malondialdehyde (MDA) overexpression and superoxide dismutase (SOD) expression inhibition in LPS-induced BV-2 cells and decreased interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-6 mRNA expression levels in a dose-dependent manner. DFV inhibited both mRNA and protein expression levels of COX2 induced by LPS, and the activation of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) and caspase1 was suppressed, thus exerting an antidepressant effect. This study proves that DFV may be an important component basis for PR to play an antidepressant role.

Calcium Modulating Effect of Polycyclic Cages: A Suitable Therapeutic Approach Against Excitotoxic-induced Neurodegeneration

Neurodegenerative disorders pose a significant challenge to global healthcare systems due to their progressive nature and the resulting loss of neuronal cells and functions. Excitotoxicity, characterized by calcium overload, plays a critical role in the pathophysiology of these disorders. In this review article, we explore the involvement of calcium dysregulation in neurodegeneration and neurodegenerative disorders. A promising therapeutic strategy to counter calcium dysregulation involves the use of calcium modulators, particularly polycyclic cage compounds. These compounds, structurally related to amantadine and memantine, exhibit neuroprotective properties by attenuating calcium influx into neuronal cells. Notably, the pentacycloundecylamine NGP1-01, a cage-like structure, has shown efficacy in inhibiting both N-methyl-D-aspartate (NMDA) receptors and voltage- gated calcium channels (VGCCs), making it a potential candidate for neuroprotection against excitotoxic-induced neurodegenerative disorders. The structure-activity relationship of polycyclic cage compounds is discussed in detail, highlighting their calcium-inhibitory activities. Various closed, open, and rearranged cage compounds have demonstrated inhibitory effects on calcium influx through NMDA receptors and VGCCs. Additionally, these compounds have exhibited neuroprotective properties, including free radical scavenging, attenuation of neurotoxicities, and reduction of neuroinflammation. Although the calcium modulatory activities of polycyclic cage compounds have been extensively studied, apart from amantadine and memantine, none have undergone clinical trials. Further in vitro and in vivo studies and subsequent clinical trials are required to establish the efficacy and safety of these compounds. The development of polycyclic cages as potential multifunctional agents for treating complex neurodegenerative diseases holds great promise.

Modified Erchen decoction ameliorates cognitive dysfunction in vascular dementia rats via inhibiting JAK2/STAT3 and JNK/BAX signaling pathways

BACKGROUND

Vascular dementia (VaD) is one of the most common clinical syndromes of progressive neurocognitive dysfunction with uncertain mechanisms. Modified Erchen decoction (MECD), developed from "Erchen decoction (ECD)" recorded in "Taiping Huimin Heji Jufang", showed a good effect in the treatment of VaD. However, its therapeutic mechanism is still unclear.

PURPOSE

This study aimed to elucidate the multi-target mechanisms of MECD against VaD in vivo and in vitro.

METHODS

VaD model was established by two-vessel obstruction (2-VO) in Sprague-Dawley rats. Six groups, including the control, 2-VO operation, MECD treatment (2.5, 5.0 and 10.0 g kg^-1 d^-1), donepezil hydrochloride (positive control, 0.45 g kg^-1 d^-1) were designed in the whole experiment. After oral administration for 4 weeks, the effects of MECD were verified by behavioral experiments, histological observation, and biochemical index analysis. The chemical profiling of MECD was performed by UHPLC-Orbitrap Fusion-HRMS, and a "compound-target-pathway" multivariate network was constructed to validate and elucidate its pharmacological mechanisms.

RESULTS

Compared with 2-VO group, MECD treatment significantly alleviated anxiety and improved spatial memory in VaD rats according to the open field test (OFT) and Y-maze test. A significant increase in neuron number was observed from hematoxylin and eosin (H&E) stained images in cornu ammonis 1 (CA1) of the hippocampal region after MECD treatment. On the one hand, MECD reduced the plasma levels of triglyceride (TG), low-density lipoprotein (LDL), malondialdehyde (MDA), and amyloid-beta 42 (Aβ42), and inhibited mRNA expression of interleukin-1 beta (Il-1β) and Il-6 in the hippocampus. On the other hand, superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) were significantly increased after treatment with MECD. Moreover, MECD reduced the mRNA expression and protein expression of janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), c-Jun N-terminal kinase (JNK), and BCL2-associated X (BAX) in the brain of 2-VO rats. Furthermore, 71 compounds were identified from the extract of MECD. Among them, liquiritin and isochlorogenic acid C gave inhibiting effects on the mRNA expression of Jnk. In addition, liquiritin and hesperetin were conformed with the inhibition of Jak2 transcription level in vitro experiments.

CONCLUSION

MECD has demonstrated a significant amelioration effect on cognitive dysfunction in VaD rats via JAK2/STAT3 and JNK/BAX signaling pathways, which represents an innovative insight into the "activate blood and eliminate phlegm" theory.

Targeting Estrogen Signaling in the Radiation-induced Neurodegeneration: A Possible Role of Phytoestrogens

Radiation for medical use is a well-established therapeutic method with an excellent prognosis rate for various cancer treatments. Unfortunately, a high dose of radiation therapy comes with its own share of side effects, causing radiation-induced non-specific cellular toxicity; consequently, a large percentage of treated patients suffer from chronic effects during the treatment and even after the post-treatment. Accumulating data evidenced that radiation exposure to the brain can alter the diverse cognitive-related signaling and cause progressive neurodegeneration in patients because of elevated oxidative stress, neuroinflammation, and loss of neurogenesis. Epidemiological studies suggested the beneficial effect of hormonal therapy using estrogen in slowing down the progression of various neuropathologies. Despite its primary function as a sex hormone, estrogen is also renowned for its neuroprotective activity and could manage radiation-induced side effects as it regulates many hallmarks of neurodegenerations. Thus, treatment with estrogen and estrogen-like molecules or modulators, including phytoestrogens, might be a potential approach capable of neuroprotection in radiation-induced brain degeneration. This review summarized the molecular mechanisms of radiation effects and estrogen signaling in the manifestation of neurodegeneration and highlighted the current evidence on the phytoestrogen mediated protective effect against radiationinduced brain injury. This existing knowledge points towards a new area to expand to identify the possible alternative therapy that can be taken with radiation therapy as adjuvants to improve patients' quality of life with compromised cognitive function.

Liquiritin Attenuates Pathological Cardiac Hypertrophy by Activating the PKA/LKB1/AMPK Pathway

Background: Liquiritin (LQ) is one of the main flavonoids extracted from the roots of Glycyrrhiza spp., which are widely used in traditional Chinese medicine. Studies in both cellular and animal disease models have shown that LQ attenuates or prevents oxidative stress, inflammation, and apoptosis. However, the potential therapeutic effects of LQ on pressure overload-induced cardiac hypertrophy have not been so far explored. Therefore, we investigated the cardioprotective role of LQ and its underlying mechanisms in the aortic banding (AB)-induced cardiac hypertrophy mouse model.

Methods and Results: Starting 3 days after AB surgery, LQ (80 mg/kg/day) was administered daily over 4 weeks. Echocardiography and pressure-volume loop analysis indicated that LQ treatment markedly improved hypertrophy-related cardiac dysfunction. Moreover, hematoxylin and eosin, picrosirius red, and TUNEL staining showed that LQ significantly inhibited cardiomyocyte hypertrophy, interstitial fibrosis, and apoptosis. Western blot assays further showed that LQ activated LKB1/AMPKα2/ACC signaling and inhibited mTORC1 phosphorylation in cardiomyocytes. Notably, LQ treatment failed to prevent cardiac dysfunction, hypertrophy, and fibrosis in AMPKα2 knockout (AMPKα2^−/−) mice. However, LQ still induced LKB1 phosphorylation in AMPKα2^−/− mouse hearts. In vitro experiments further demonstrated that LQ inhibited Ang II-induced hypertrophy in neonatal rat cardiomyocytes (NRCMs) by increasing cAMP levels and PKA activity. Supporting the central involvement of the cAMP/PKA/LKB1/AMPKα2 signaling pathway in the cardioprotective effects of LQ, inhibition of Ang II-induced hypertrophy and induction of LKB1 and AMPKα phosphorylation were no longer observed after inhibiting PKA activity.

Conclusion: This study revealed that LQ alleviates pressure overload-induced cardiac hypertrophy in vivo and inhibits Ang II-induced cardiomyocyte hypertrophy in vitro via activating cAMP/PKA/LKB1/AMPKα2 signaling. These findings suggest that LQ might be a valuable adjunct to therapeutic approaches for treating pathological cardiac remodeling.

Glycyrrhiza uralensis Fisch. and its active components mitigate Semen Strychni-induced neurotoxicity through regulating high mobility group box 1 (HMGB1) translocation

Semen Strychni has long been used for the treatment of rheumatoid arthritis, facioplegia and myasthenia gravis due to its anti-inflammation and anti-nociceptive properties in China. However, the fatal neurotoxicity of Semen Strychni has limited its wider clinical application. To investigate the acute toxicity induced by Semen Strychni and the detoxification of liquorice, we evaluated inflammation, oxidative stress and the translocation of high mobility group box 1 (HMGB1) in rats. As a result, there were obvious oxidative stress and inflammation in hippocampus after the Semen Strychni extracts (STR) treatment in rats. Liquorice extracts (LE) and its three active monomers - glycyrrhizic acid (GA), liquiritigenin (LIQ), isoliquiritigenin (ISL) showed the potential for mitigating STR-induced neurotoxicity. HMGB1 levels in cytoplasm and serum and the levels of two downstream receptors RAGE and TLR4 were significantly increased after STR treatment. Through using LE and the monomers, the nucleocytoplasmic transport and release of HMGB1 were inhibited. In addition, the binding between HMGB1 and TLR4 was weakened in detoxification groups comparing with the STR group. Taken together, these findings indicated that liquorice and its active components alleviated acute neurotoxicity induced by Semen Strychni partly via HMGB1-related pathway.

Glycyrrhiza glabra (Licorice): A Comprehensive Review on Its Phytochemistry, Biological Activities, Clinical Evidence and Toxicology

There are more than 30 species of Glycyrrhiza genus extensively spread worldwide. It was the most prescribed herb in Ancient Egyptian, Roman, Greek, East China, and the West from the Former Han era. There are various beneficial effects of licorice root extracts, such as treating throat infections, tuberculosis, respiratory, liver diseases, antibacterial, anti-inflammatory, and immunodeficiency. On the other hand, traditional medicines are getting the attraction to treat many diseases. Therefore, it is vital to screen the medicinal plants to find the potential of new compounds to treat chronic diseases such as respiratory, cardiovascular, anticancer, hepatoprotective, etc. This work comprehensively reviews ethnopharmacological uses, phytochemistry, biological activities, clinical evidence, and the toxicology of licorice, which will serve as a resource for future clinical and fundamental studies. An attempt has been made to establish the pharmacological effect of licorice in different diseases. In addition, the focus of this review article is on the molecular mechanism of licorice extracts and their four flavonoids (isoliquiritigenin, liquiritigenin, lichalocone, and glabridin) pharmacologic activities. Licorice could be a natural alternative for current therapy to exterminate new emerging disorders with mild side effects. This review will provide systematic insights into this ancient drug for further development and clinical use.

New Autophagy-Ferroptosis Gene Signature Predicts Survival in Glioma

Background: Ferroptosis plays an important role in glioma and significantly affects the prognosis, but the specific mechanism has not yet been elucidated. Recent studies suggest that autophagy regulates the process of ferroptosis. This study aimed to find potential autophagy-ferroptosis genes and explore the prognostic significance in glioma.

Methods: Ferroptosis and autophagy genes were obtained from two online databases (zhounan.org/ferrdb and autophagy.lu/). The RNAseq data and clinical information were obtained from the Chinese Glioma Genome Atlas (CGGA) database (http://www.cgga.org.cn/). Univariate, multivariate, lasso and Cox regression analysis screened out prognosis-related genes, and a risk model was constructed. Receiver operating characteristic (ROC) curve analysis evaluated the predictive efficiency of the model. Finally, a nomogram was constructed to more accurately predict the prognosis of glioma.

Results: We developed a Venn diagram showing 23 autophagy-ferroptosis genes. A total of 660 cases (including RNA sequences and complete clinical information) from two different cohorts (training group n = 413, verification group n = 247) of the CGGA database was acquired. Cohorts were screened to include five prognosis-related genes (MTOR, BID, HSPA5, CDKN2A, GABARAPLA2). Kaplan-Meier curves showed that the risk model was a good prognostic indicator (p < 0.001). ROC analysis showed good efficacy of the risk model. Multivariate Cox analysis also revealed that the risk model was suitable for clinical factors related to prognosis, including type of disease (primary, recurrence), grade (III-IV), age, temozolomide treatment, and 1p19q state. Using the five prognosis-related genes and the risk score, we constructed a nomogram assessed by C-index (0.7205) and a calibration plot that could more accurately predict glioma prognosis.

Conclusion: Using a current database of autophagy and ferroptosis genes, we confirmed the prognostic significance of autophagy-ferroptosis genes in glioma, and we constructed a prognostic model to help guide treatment for high grade glioma in the future.

Recent Progress on Biological Activity of Amaryllidaceae and Further Isoquinoline Alkaloids in Connection with Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive age-related neurodegenerative disease recognized as the most common form of dementia among elderly people. Due to the fact that the exact pathogenesis of AD still remains to be fully elucidated, the treatment is only symptomatic and available drugs are not able to modify AD progression. Considering the increase in life expectancy worldwide, AD rates are predicted to increase enormously, and thus the search for new AD drugs is urgently needed. Due to their complex nitrogen-containing structures, alkaloids are considered to be promising candidates for use in the treatment of AD. Since the introduction of galanthamine as an antidementia drug in 2001, Amaryllidaceae alkaloids (AAs) and further isoquinoline alkaloids (IAs) have been one of the most studied groups of alkaloids. In the last few years, several compounds of new structure types have been isolated and evaluated for their biological activity connected with AD. The present review aims to comprehensively summarize recent progress on AAs and IAs since 2010 up to June 2021 as potential drugs for the treatment of AD.

Herbal drugs and natural bioactive products as potential therapeutics: A review on pro-cognitives and brain boosters perspectives

Memory, one of the most vital aspects of the human brain, is necessary for the effective survival of an individual. 'Memory' can be defined in various ways but in an overall view, memory is the retention of the information that the brain grasps. Different factors are responsible for the disbalance in the brain's hippocampus region and the acetylcholine level, which masters the memory and cognitive functions. Plants are a source of pharmacologically potent drug molecules of high efficacy. Recently herbal medicine has evolved rapidly, gaining great acceptance worldwide due to their natural origin and fewer side effects. In this review, the authors have discussed the mechanisms and pharmacological action of herbal bioactive compounds to boost memory. Moreover, this review presents an update of different herbs and natural products that could act as memory enhancers and how they can be potentially utilized in the near future for the treatment of severe brain disorders. In addition, the authors also discuss the differences in biological activity of the same herb and emphasize the requirement for a higher standardization in cultivation methods and plant processing. The demand for further studies evaluating the interactions of herbal drugs is mentioned.

Characterization of Novel Diphenylamine Compounds as Ferroptosis Inhibitors

Ferroptosis is a form of oxidative cell death that is increasingly recognized as a key mechanism not only in neurodegeneration but also in regulated cell death, causing disease in other tissues. In neurons, major hallmarks of ferroptosis involve the accumulation of lipid reactive oxygen species (ROS) and impairment of mitochondrial morphology and function. Compounds that interfere with ferroptosis could provide novel treatment options for neurodegenerative disorders and other diseases involving ferroptosis. In the present study, we developed new compounds by refining structural elements of the BH3 interacting-domain death agonist inhibitor BI-6c9, which was previously demonstrated to block ferroptosis signaling at the level of mitochondria. Here, we inserted an antioxidative diphenylamine (DPA) structure to the BI-6c9 structure. These DPA compounds were then tested in models of erastin, and Ras-selective lethal small molecule 3 induced ferroptosis in neuronal HT22 cells. The DPA compounds showed an increased protective potency against ferroptotic cell death compared with the scaffold molecule BI-6c9. Moreover, hallmarks of ferroptosis such as lipid, cytosolic, and mitochondrial ROS formation were abrogated in a concentration- and time-dependent manner. Additionally, mitochondrial parameters such as mitochondrial morphology, mitochondrial membrane potential, and mitochondrial respiration were preserved by the DPA compounds, supporting the conclusion that lipid ROS toxicity and mitochondrial impairment are closely related in ferroptosis. Our findings confirm that the DPA compounds are very effective agents in preventing ferroptotic cell death by blocking ROS production and, in particular, via mitochondrial protection. SIGNIFICANCE STATEMENT: Preventing neuronal cells from different forms of oxidative cell death was previously described as a promising strategy for treatment against several neurodegenerative diseases. This study reports novel compounds based on a diphenylamine structure that strongly protects neuronal HT22 cells from ferroptotic cell death upon erastin and Ras-selective lethal small molecule 3 induction by preventing the development of different reactive oxygen species and by protecting mitochondria from ferroptotic impairments.

Liquiritigenin promotes osteogenic differentiation and prevents bone loss via inducing auto-lysosomal degradation and inhibiting apoptosis

Osteoporosis (OP) is a debilitating skeletal abnormality involving bone remodeling and bone cell homeostasis characterized by decreased bone strength and high fracture risk. A novel therapeutic intervention for OP by manipulating cellular autophagy-apoptosis processes to promote skeletal homeostasis is presented. Protective effects of the naturally occurring plant extract Liquiritigenin (LG) were demonstrated in an ovariectomy (OVX)-OP mouse model and preosteoblast MC3T3-E1 cells. Micro-CT and histological staining assessments of skeletal phenotype were applied alongside detection of autophagy activity in osteocytes and MC3T3-E1 cells by transmission electron microscopy (TEM). The effects of LG on chloroquine (CQ)- and the apoptosis-inducing TS-treated osteogenic differentiations and status of lysosomes within MC3T3-E1 cells were analyzed by Neutral red, Alizarin red S and alkaline phosphatase (ALP) staining and Western blot assays. Treatment with LG prevented bone loss, increased osteogenic differentiation in vivo and in vitro, and inhibited osteoclast formation to some extent. TEM analyses revealed that LG can improve auto-lysosomal degradation within osteocytes from OVX mice and MC3T3-E1 cells. The abnormal status of lysosomes associated with CQ and TS treatments was notably alleviated by LG which also reduced levels of apoptosis-induced inhibition of osteogenic differentiation and averted abnormal osteogenic differentiation as a consequence of a blockage in autolysosome degradation. Overall, LG stimulates bone growth in OVX mice through increased osteogenic differentiation and regulation of autophagy-apoptosis mechanisms, presenting an auspicious natural therapy for OP.

Natural products targeting mitochondria: emerging therapeutics for age-associated neurological disorders

Mitochondria are the primary source of energy production in the brain thereby supporting most of its activity. However, mitochondria become inefficient and dysfunctional with age and to a greater extent in neurological disorders. Thus, mitochondria represent an emerging drug target for many age-associated neurological disorders. This review summarizes recent advances (covering from 2010 to May 2020) in the use of natural products from plant, animal, and microbial sources as potential neuroprotective agents to restore mitochondrial function. Natural products from diverse classes of chemical structures are discussed and organized according to their mechanism of action on mitochondria in terms of modulation of biogenesis, dynamics, bioenergetics, calcium homeostasis, and membrane potential, as well as inhibition of the oxytosis/ferroptosis pathway. This analysis emphasizes the significant value of natural products for mitochondrial pharmacology as well as the opportunities and challenges for the discovery and development of future neurotherapeutics.

Xiaoyaosan Alleviates Hippocampal Glutamate-Induced Toxicity in the CUMS Rats via NR2B and PI3K/Akt Signaling Pathway

Purpose: It is revealed that Xiaoyaosan could reduce glutamate level in the hippocampus of depressed rats, whose metabolism leads to the pathophysiology of depression. However, the underlying mechanism remains unclear. This study aims to explore the effect of Xiaoyaosan on glutamate metabolism, and how to regulate the excitatory injury caused by glutamate. Methods: Rats were induced by chronic unpredictable mild stress, then divided into control, vehicle (distilled water), Xiaoyaosan, fluoxetine, vehicle (DMSO), Xiaoyaosan + Ly294002 and Ly294002 groups. Ly294002 was microinjected into the lateral ventricular catheterization at 5 mM. Xiaoyaosan (2.224 g/kg) and fluoxetine (2.0 mg/kg) were orally administered for three weeks. The open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT) were used to assess depressive behavior. The glutamate and corticosterone (CORT) levels were detected by ELISA. Western blot, immunochemistry or immunofluorescence were used to detect the expressions of NR2B, MAP2, PI3K and P-AKT/Akt in the hippocampal CA1 region. The mRNA level of MAP2, NR2B and PI3K were detected by RT-qPCR. Results: Compared to the rats in control group, body weight and food intake of CUMS rats was decreased. CUMS rats also showed depression-like behavior as well as down regulate the NR2B and PI3K/Akt signaling pathway. Xiaoyaosan treatments could increase food intake and body weight as well as improved time spent in the central area, total distance traveled in the OFT. Xiaoyaosan could also decrease the immobility time as well as increase the sucrose preference in SPT. Moreover, xiaoyaosan decreased the level of glutamate in the hippocampal CA1 region and serum CORT in CUMS rats. Furthermore, xiaoyaosan improved the expression of MAP2 as well as increased the expression of NR2B, PI3K and the P-AKT/AKT ratio in the hippocampal CA1 region in the CUMS rats. Conclusion: Xiaoyaosan treatment can exert the antidepressant effect by rescuing hippocampal neurons loss induced by the glutamate-mediated excitotoxicity in CUMS rats. The underlying pathway maybe through NR2B and PI3K/Akt signaling pathways. These results may suggest the potential of Xiaoyaosan in preventing the development of depression.

Analgesic Efficacy of a Combination of Fentanyl and a Japanese Herbal Medicine "Yokukansan" in Rats with Acute Inflammatory Pain

Background: Fentanyl can induce acute opioid tolerance and postoperative hyperalgesia when administered at a single high dose; thus, this study examined the analgesic efficacy of a combination of fentanyl and Yokukansan (YKS). Methods: Rats were divided into control, formalin-injected (FOR), YKS-treated+FOR (YKS), fentanyl-treated+FOR (FEN), and YKS+FEN+FOR (YKS+FEN) groups. Acute pain was induced via subcutaneous injection of formalin into the paw. The time engaged in pain-related behavior was measured. Results: In the early (0–10 min) and intermediate (10–20 min) phases, pain-related behavior in the YKS+FEN group was significantly inhibited compared with the FOR group. In the late phase (20–60 min), pain-related behavior in the FEN group was the longest and significantly increased compared with the YKS group. We explored the influence on the extracellular signal-regulated kinase (ERK) pathway in the spinal cord, and YKS suppressed the phosphorylated ERK expression, which may be related to the analgesic effect of YKS in the late phase. Conclusions: These findings suggest that YKS could reduce the use of fentanyl and combined use of YKS and fentanyl is considered clinically useful.

Neuroprotective effects of natural compounds on neurotoxin-induced oxidative stress and cell apoptosis

OBJECTIVES

Overproduction of reactive species, notably reactive oxygen (ROS) and nitrogen (RNS) species, along with the failure of balancing effects of endogenous antioxidant defenses result in destruction of cellular structures, lipids, proteins, and genetic material, which lead to oxidative stress. Oxidative stress-induced neuronal apoptosis plays a pivotal role in pathogenesis of neurodegeneration. Antioxidants represent one of the medical choice strategies for protecting against this unbalanced oxidation-antioxidation status. Recently, natural compounds with neuroprotective potential that can scavenge free radicals and protect cells from oxidative damage have received extensive attention.

METHODS

In this review, we summarized the detailed research progress on the medicinal plants-derived natural compounds with potential anti-oxidation effects and their molecular mechanisms on modulating the neurotoxin (6-OHDA, H₂O₂, glutamate, Aβ)-induced oxidative stress and cell apoptosis.

RESULTS

The natural compounds that efficacious in modulating reactive species production and mitochondrial function include flavonoids, glucosides, alkaloids, polyphenols, lignans, coumarins, terpenoids, quinones and others. They decreased the neurotoxin-induced oxidative damage and apoptosis by (1) decreasing ROS/RNS generation, lipid peroxidation, caspase-3 and caspase-9 activities, LDH release, the ratio of Bax/Bcl-2, Ca²⁺ influx and cytochrome c release, (2) elevating MMP, and (3) restoring endogenous antioxidant enzymatic activities (CAT, GSH-Px, GSR, SOD). And they exerted neuroprotective effects against cell damages and apoptosis by modulating the oxidative cascades of different signaling pathways (Nrf2/HO-1, NF-κB, MAPKs, PI3K/Akt, GSK-3β) and preventing mitochondria-dependent apoptosis pathways.

DISCUSSION

The present work reviews the role of oxidative stress in neurodegeneration, highlighting the potential anti-oxidation effects of natural compounds as a promising approach to develop innovative neuroprotective strategy.

Isoliquiritigenin Attenuates Anxiety-Like Behavior and Locomotor Sensitization in Rats after Repeated Exposure to Nicotine

As important components of positive and negative reinforcement, locomotor sensitization and withdrawal anxiety following repeated exposure to nicotine (NIC) constitute crucial risk factors for relapse to NIC use after abstinence. Glycyrrhiza radix (G. radix), an important tonic used in traditional Oriental medicine, has not only anxiolytic effects but also reduces NIC-induced locomotor sensitization. Isoliquiritigenin (ISL), a bioactive ingredient of G. radix, also exhibits neuropharmacological effects, including anxiolytic action. Previously, we reported that ISL suppressed cocaine-induced extracellular dopamine release in the nucleus accumbens shell (NaccSh) and attenuated methamphetamine-induced neurotoxicity. The present study was performed to evaluate the effects of ISL on both NIC withdrawal anxiety and locomotor sensitization. Adult male rats received subcutaneous administration of NIC hydrogen tartrate (0.4 mg/kg, twice a day) for 7 days followed by 4 days of withdrawal. During the period of NIC withdrawal, the rats received four intragastric treatments with ISL (3, 10, or 30 mg/kg/day). All three doses of ISL significantly inhibited NIC withdrawal-induced anxiety-like behaviors in the elevated plus maze (EPM) test, but only the 10 mg/kg/day and 30 mg/kg/day ISL doses attenuated locomotor sensitization induced by a challenge dose of NIC. Intracerebroventricular ISL also inhibited both NIC-induced withdrawal anxiety and locomotor sensitization, but intra-NaccSh injection of ISL blocked only NIC locomotor sensitization, which was abolished by post-ISL infusion of tert-butyl hydroperoxide (an oxidant) or N-methyl-d-aspartate (NMDA) into the NaccSh. Moreover, there was increased protein expression of phosphorylated Erk1/2 in the NIC-sensitized NaccSh, which was suppressed by ISL. Taken together, these results suggest that ISL can inhibit repeated NIC-induced withdrawal anxiety and locomotor sensitization, and the latter is mediated by antagonizing accumbal reactive oxygen species and NMDA receptor signaling.

Synergistic Neuroprotective Effect of Endogenously-Produced Hydroxytyrosol and Synaptic Vesicle Proteins on Pheochromocytoma Cell Line Against Salsolinol

Oxidative stress triggers a lethal cascade, leading to Parkinson's disease by causing degeneration of dopaminergic neurons. In this study, eight antioxidants were screened for their neuroprotective effect on PC12 cells (pheochromocytoma cell line) under oxidative stress induced by salsolinol (OSibS). Hydroxytyrosol was found to be the strongest neuroprotective agent; it improved viability of PC12 cells by up to 81.69% under OSibS. Afterward, two synaptic vesicle proteins, synapsin-1 and septin-5, were screened for their neuroprotective role; the overexpression of synapsin-1 and the downregulation of septin-5 separately improved the viability of PC12 cells by up to 71.17% and 67.00%, respectively, compared to PC12 cells only treated with salsolinol (PoTwS) under OSibS. Subsequently, the PC12+syn++sep- cell line was constructed and pretreated with 100 µM hydroxytyrosol, which improved its cell viability by up to 99.03% and led to 14.71- and 6.37-fold reductions in the levels of MDA and H2O2, respectively, and 6.8-, 12.97-, 10.57-, and 7.57-fold increases in the activity of catalase, glutathione reductase, superoxide dismutase, and glutathione peroxidase, respectively, compared to PoTwS under OSibS. Finally, alcohol dehydrogenase-6 from Saccharomyces cerevisiae was expressed in PC12+syn++sep- cells to convert 3,4-dihydroxyphenylacetaldehyde (an endogenous neurotoxin) into hydroxytyrosol. The PC12+syn++sep-+ADH6+ cell line also led to 22.38- and 12.33-fold decreases in the production of MDA and H2O2, respectively, and 7.15-, 13.93-, 12.08-, and 8.11-fold improvements in the activity of catalase, glutathione reductase, superoxide dismutase, and glutathione peroxidase, respectively, compared to PoTwS under OSibS. Herein, we report the endogenous production of a powerful antioxidant, hydroxytyrosol, from 3,4-dihydroxyphenylacetaldehyde, and evaluate its synergistic neuroprotective effect, along with synapsin-1 and septin-5, on PC12 cells under OSibS.

Anti-inflammatory secondary metabolites from the stems of Millettia dielsiana Harms ex Diels

A phytochemical investigation for the constituents of the stems of Millettia dielsiana Harms ex Diels resulted in the isolation of a new isoflavone glycoside, mildiside A (1), and 14 known compounds (2-15). Their chemical structures were determined using a combination of IR, NMR, MS, and optical rotation analysis, as well as comparison with the literature data. The ethanolic (EtOH) extract and several isolated compounds exert the inflammatory effect of nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated murine RAW264.7 macrophage cells.

Herbal medicine (Hepad) prevents dopaminergic neuronal death in the rat MPTP model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra. The purpose of this study was to examine neuroprotective effects of Hepad S1, an herbal medicine used for the treatment of PD, in in vitro and in vivo models of PD.

METHODS

Differentiated neuronal PC12 cells underwent a cytotoxicity assay and oxidative stress analysis including DCF-DA staining, glutathione, and malondialdehyde, after exposure to 1-methyl-4-phenylpyridium (MPP+). Male Sprague-Dawley rats were used as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD models. After 4-week oral administration of Hepad S1 (200, 300, 400, and 500 mg/kg/day), the levels of complex enzyme I activity and dopamine, and dopaminergic neuronal cell number in substantia nigra were measured by enzyme linked immune-sorbent assay (ELISA) and microscopic observation, respectively. Circulating serotonin and orexin A were also examined by ELISA.

RESULTS

Hepad S1 pretreatment prevented the ability of MPP+ challenge to decrease glutathione and increase lipid peroxidation in cells, indicating antioxidant activity. Hepad S1 recovered MPTP-induced decreases in complex I enzyme activity and enhanced dopamine availability in substantia nigra. Serum levels of serotonin and orexin A were increased by Hepad S1 treatment in model animals. Hepad S1 treatment was associated with the preservation of tyrosine hydroxylase-positive cells in the substantia nigra of MPTP-treated rats.

CONCLUSIONS

Hepad S1 exerts antioxidant and neuroprotective effects on neurons of the substantia nigra in a rodent model of PD.

A metabolic perspective of late onset Alzheimer's disease

After decades of research, the molecular neuropathology of Alzheimer's disease (AD) is still one of the hot topics in biomedical sciences. Some studies suggest that soluble amyloid β (Aβ) oligomers act as causative agents in the development of AD and could be initiators of its complex neurodegenerative cascade. On the other hand, there is also evidence pointing to Aβ oligomers as mere aggravators, with an arguable role in the origin of the disease. In this line of research, the relative contribution of soluble Aβ oligomers to neuronal damage associated with metabolic disorders such as Type 2 Diabetes Mellitus (T2DM) and obesity is being actively investigated. Some authors have proposed the endoplasmic reticulum (ER) stress and the induction of the unfolded protein response (UPR) as important mechanisms leading to an increase in Aβ production and the activation of neuroinflammatory processes. Following this line of thought, these mechanisms could also cause cognitive impairment. The present review summarizes the current understanding on the neuropathological role of Aβ associated with metabolic alterations induced by an obesogenic high fat diet (HFD) intake. It is believed that the combination of these two elements has a synergic effect, leading to the impairement of ER and mitochondrial functions, glial reactivity status alteration and inhibition of insulin receptor (IR) signalling. All these metabolic alterations would favour neuronal malfunction and, eventually, neuronal death by apoptosis, hence causing cognitive impairment and laying the foundations for late-onset AD (LOAD). Moreover, since drugs enhancing the activation of cerebral insulin pathway can constitute a suitable strategy for the prevention of AD, we also discuss the scope of therapeutic approaches such as intranasal administration of insulin in clinical trials with AD patients.

Liquiritin and Liquiritigenin Induce Melanogenesis via Enhancement of p38 and PKA Signaling Pathways

Background: Liquiritin (LQ) and its aglycone, liquiritigenin (LQG), are major flavonoids in licorice root (Glycyrrhiza spp.). Our preliminary screening identified LQ and LQG, which promote melanin synthesis in the melanoma cells. In this study, we investigated the molecular mechanism of melanin synthesis activated by LQ and LQG. Methods: Murine (B16-F1) and human (HMVII) melanoma cell lines were treated with LQ or LQG. After incubation, melanin contents, intracellular tyrosinase activity, and cell viability were evaluated. Protein levels were determined using Western blotting. Results: LQ and LQG activated melanin synthesis and intracellular tyrosinase activity. The induction of melanin and intracellular tyrosinase activity by LQG was higher than that by LQ. LQ and LQG induced the expression of tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2. LQ and LQG also enhanced microphthalmia-associated transcription factor (MITF) expression, and cyclic AMP-responsive element-binding protein (CREB) phosphorylation. The phosphorylation of p38 and extracellular signal-regulated kinase (ERK), but not Akt, was significantly increased by LQ or LQG. Furthermore, LQ- or LQG-mediated melanin synthesis was partially blocked by p38 inhibitor (SB203580) and protein kinase A (PKA) inhibitor (H-89); however, ERK kinase (MEK) inhibitor (U0126) and phosphatidylinositol-3-kinase (PI3K) inhibitor (LY294002) had no effect. Conclusions: The results suggest that LQ and LQG enhance melanin synthesis by upregulating the expression of melanogenic enzymes, which were activated by p38 and PKA signaling pathways, leading to MITF expression and CREB phosphorylation.

Prevention of ochratoxin A-induced oxidative stress-mediated apoptotic processes and impairment of embryonic development in mouse blastocysts by liquiritigenin

Ochratoxin A (OTA), a mycotoxin constituent of a range of food commodities, including coffee, wine, beer, grains, and spices, exerts toxicological and pathological effects in vivo, such as nephrotoxicity, hepatotoxicity, and immunotoxicity. In a previous report, we highlighted the potential of OTA to induce apoptosis via reactive oxygen species (ROS) generation in mouse blastocysts that led to impaired preimplantation and postimplantation embryo development in vitro and in vivo. Here, we have shown that liquiritigenin (LQ), a type of flavonoid isolated from Glycyrrhiza radix, effectively protects against OTA-mediated apoptosis and inhibition of cell proliferation in mouse blastocysts. Preincubation of blastocysts with LQ clearly prevented OTA-triggered impairment of preimplantation and postimplantation embryonic development and fetal weight loss, both in vitro and in vivo. Detailed investigation of regulatory mechanisms revealed that OTA mediated apoptosis and embryotoxicity through ROS generation, loss of mitochondrial membrane potential (MMP), and activation of caspase-9 and caspase-3, which were effectively prevented by LQ. The embryotoxic effects of OTA were further validated in an animal model in vivo. Intravenous injection of dams with OTA (3 mg/kg/day) led to apoptosis of blastocysts, impairment of embryonic development from zygote to blastocyst stage and decrease in day 18 fetal weight. Notably, preinjection of dams with LQ (5 mg/kg/day) effectively prevented OTA-induced apoptosis and toxic effects on embryo development. Our collective results clearly demonstrate that OTA exposure via injection has the potential to damage preimplantation and postimplantation embryonic development against which LQ has a protective effect.

Pregabalin affords retinal neuroprotection in diabetic rats: Suppression of retinal glutamate, microglia cell expression and apoptotic cell death

Pregabalin is the first drug to receive FDA approval for treating diabetic neuropathic pain. This study investigated the neuroprotective effect of pregabalin in an experimental model of diabetic retinopathy and tested some possible mechanisms underlying the putative neuroprotective effect. Male Wistar rats received streptozotocin (45 mg/kg) to induce type 1 diabetes mellitus. After two weeks, a course of pregabalin (3, 10 and 30 mg/kg) has been launched for five consecutive weeks. Retinal expression of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was estimated by real-time PCR and retinal glutamate content was also estimated. Further, retinal caspase-3 immunoblotting and DNA fragmentation assays determined the degree of apoptosis. Pregabalin improved histopathological abnormalities in diabetic retinas and suppressed the diabetes-enhanced retinal expression of IL-1β, TNF-α, CD₁₁b (a surface marker for microglia) while attenuated expression of caspase-3 and DNA fragmentation versus the diabetic group. In addition, diabetic rats treated with pregabalin displayed reductions in retinal glutamate, nitric oxide and malondialdehyde (MDA) and enhanced reduced glutathione (GSH) content versus the diabetic controls. Furthermore, pregabalin enhanced the histopathological picture and reduced fibrosis in the optic nerve of diabetic rats in addition to suppression of the content of the glia fibrillary acidic protein. The findings provide the first evidence demonstrating that pregabalin alleviates retinal neuroinflammation, apoptosis and oxidative stress in an experimental type 1 diabetes mellitus. Therefore, pregabalin might serve as a potential therapy for retinopathy after adequate clinical research.

OPFRs and BFRs induced A549 cell apoptosis by caspase-dependent mitochondrial pathway

Organophosphate flame retardants (OPFRs) and brominated flame retardants (BFRs) are frequently detected in indoor environment at high levels, posing health risks to humans. However, the potential cytotoxicity mediated by OPFRs and BFRs in relevant human cell models is limited. In current study, non-small cell lung cancer A549 cell was employed to investigate toxicity mechanisms of typical OPFRs (i.e., tris (2-chloroethyl) phosphate (TCEP), tris-(2-chloropropyl) phosphate (TCPP), tricresy phosphate (TCP), triphenyl phosphate (TPHP) and BFRs (i.e., 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), 3,3', 5,5'-tetrabromobisphenol A (TBBPA)). It was found that BDE-47 exhibited the strongest cytotoxicity, followed by TBBPA, TPHP, TCP, TCPP and TCEP. OPFRs and BFRs could cause the reduction of cell viability of A549 cell in both dose- and time-dependent manner after exposure for 24 and 48 h. Simultaneously, excessive generation of reactive oxygen species (ROS), mitochondrial membrane potential (MMP) dysfunction, cell apoptosis and overload of intracellular free Ca²⁺ demonstrated that cytotoxicity induced by OPFRs and BFRs were mediated by oxidative stress. Of note, the survival rate of cell significantly increased when pretreated with Ac-DEVD-CHO, suggesting that caspase-3 dependent mitochondrial pathway may have played a primary role in the process of A549 cell apoptosis.

Epicatechin Prevents Methamphetamine-Induced Neuronal Cell Death via Inhibition of ER Stress

Methamphetamine (METH) acts strongly on the nervous system and damages neurons and is known to cause neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Flavonoids, polyphenolic compounds present in green tea, red wine and several fruits exhibit antioxidant properties that protect neurons from oxidative damage and promote neuronal survival. Especially, epicatechin (EC) is a powerful flavonoid with antibacterial, antiviral, antitumor and antimutagenic effects as well as antioxidant effects. We therefore investigated whether EC could prevent METH-induced neurotoxicity using HT22 hippocampal neuronal cells. EC reduced METH-induced cell death of HT22 cells. In addition, we observed that EC abrogated the activation of ERK, p38 and inhibited the expression of CHOP and DR4. EC also reduced METH-induced ROS accumulation and MMP. These results suggest that EC may protect HT22 hippocampal neurons against METH-induced cell death by reducing ER stress and mitochondrial damage.

Liquiritigenin Inhibits Colorectal Cancer Proliferation, Invasion, and Epithelial-to-Mesenchymal Transition by Decreasing Expression of Runt-Related Transcription Factor 2

Inhibition of tumor metastasis is one of the most important purposes in colorectal cancer (CRC) treatment. This study aimed to explore the effects of liquiritigenin, a flavonoid extracted from the roots of Glycyrrhiza uralensis Fisch, on HCT116 cell proliferation, invasion, and epithelial-to-mesenchymal transition (EMT). We found that liquiritigenin significantly inhibited HCT116 cell proliferation, invasion, and the EMT process, but had no influence on cell apoptosis. Moreover, liquiritigenin remarkably reduced the expression of runt-related transcription factor 2 (Runx2) in HCT116 cells. Overexpression of Runx2 obviously reversed the liquiritigenin-induced invasion and EMT inhibition. Furthermore, liquiritigenin inactivated the phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathway in HCT116 cells. Upregulation of Runx2 reversed the liquiritigenin-induced PI3K/AKT pathway inactivation. In conclusion, our research verified that liquiritigenin exerted significant inhibitory effects on CRC invasion and EMT process by downregulating the expression of Runx2 and inactivating the PI3K/AKT signaling pathway. Liquiritigenin could be an effective therapeutic and preventative medicine for CRC treatment.

Reversal of Multidrug Resistance in Human Colon Cancer and Human Leukemia Cells by Three Plant Extracts and Their Major Secondary Metabolites

Background: We studied the effect of three plant extracts (Glycyrrhiza glabra, Paeonia lactiflora, Eriobotrya japonica) and six of their major secondary metabolites (glycyrrhizic acid, 18β glycyrrhetinic acid, liquiritigenin, isoliquiritigenin, paeoniflorin, ursolic acid) on the multidrug resistant human colon cancer cell line Caco-2 and human leukemia cell line CEM/ADR 5000 as compared to the corresponding sensitive cell line CCRF-CEM, and human colon cancer cells HCT-116, which do not over-express ATP-binding cassette (ABC) transporters. Methods: The cytotoxicity of single substances in sensitive and resistant cells was investigated by MTT assay. We also applied combinations of extracts or single compounds with the chemotherapeutic agent doxorubicin or doxorubicin plus the saponin digitonin. The intracellular retention of the ABC transporter substrates rhodamine 123 and calcein was examined by flow cytometry to explore the effect of the substances on the activity of ABC transporters P-glycoprotein and MRP1. Real-time PCR was applied to analyse the gene expression changes of ABCB1, ABCC1, caspase 3, caspase 8, AhR, CYP1A1, and GSTP1 in resistant cells under the treatment of the substances. Results: All the substances moderately inhibited cell growth in sensitive and resistant cells to some degree. Whereas ursolic acid showed IC50 of 14 and 22 µM in CEM/ADR 5000 and Caco-2 cells, respectively, glycyrrhizic acid and paeoniflorin were inactive with IC50 values above 400 μM. Except for liquiritigenin and isoliquiritigenin, all the other substances reversed MDR in CEM/ADR 5000 and Caco-2 cells to doxorubicin. Ue, ga, 18ga, and urs were powerful reversal agents. In CEM/ADR 5000 cells, high concentrations of all the substances, except Paeonia lactiflora extract, increased calcein or rhodamine 123 retention in a dose-dependent manner. In Caco-2 cells, all the substances, except liquiritigenin, retained rhodamine 123 in a dose-dependent manner. We also examined the effect of the plant secondary metabolite (PSM) panel on the expression of ABCB1, ABCC1, caspase 3, caspase 8, AhR, CYP1A1, and GSTP1 genes in MDR cells. Conclusions: The extracts and individual PSM could reverse MDR in CEM/ADR 5000 and Caco-2 cells, which overexpress ABC transporters, in two- and three-drug combinations. Most of the PSM also inhibited the activity of ABC transporters to some degree, albeit at high concentrations. Ue, ga, 18ga, and urs were identified as potential multidrug resistance (MDR) modulator candidates, which need to be characterized and validated in further studies.

Phytochemical and Pharmacological Role of Liquiritigenin and Isoliquiritigenin From Radix Glycyrrhizae in Human Health and Disease Models

The increasing lifespan in developed countries results in age-associated chronic diseases. Biological aging is a complex process associated with accumulated cellular damage by environmental or genetic factors with increasing age. Aging results in marked changes in brain structure and function. Age-related neurodegenerative diseases and disorders (NDDs) represent an ever-growing socioeconomic challenge and lead to an overall reduction in quality of life around the world. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are most common degenerative neurological disorders of the central nervous system (CNS) in aging process. The low levels of acetylcholine and dopamine are major neuropathological feature of NDDs in addition to oxidative stress, intracellular calcium ion imbalance, mitochondrial dysfunction, ubiquitin-proteasome system impairment and endoplasmic reticulum stress. Current treatments minimally influence these diseases and are ineffective in curing the multifunctional pathological mechanisms. Synthetic neuroprotective agents sometimes have negative reactions as an adverse effect in humans. Recently, numerous ethnobotanical studies have reported that herbal medicines for the treatment or prevention of NDDs are significantly better than synthetic drug treatment. Medicinal herbs have traditionally been used around the world for centuries. Radix Glycyrrhizae (RG) is the dried roots and rhizomes of Glycyrrhiza uralensis or G. glabra or G. inflata from the Leguminosae/Fabaceae family. It has been used for centuries in traditional medicine as a life enhancer, for the treatment of coughs and influenza, and for detoxification. Diverse chemical constituents from RG have reported including flavanones, chalcones, triterpenoid saponins, coumarines, and other glycosides. Among them, flavanone liquiritigenin (LG) and its precursor and isomer chalcone isoliquiritigenin (ILG) are the main bioactive constituents of RG. In the present review, we summarize evidence in the literature on the structure and phytochemical properties and pharmacological applications of LG and ILG in age-related diseases to establish new therapeutics to improve human health and lifespan.

Total Flavonoids from Radix Glycyrrhiza Exert Anti-Inflammatory and Antitumorigenic Effects by Inactivating iNOS Signaling Pathways

Inducible nitric oxide synthase (iNOS) plays an important role in inflammation, which has also been considered as a major driver of breast cancer disease progression. Radix Glycyrrhiza (RG) has been broadly used for its anti-inflammatory and antitumorigenic effects. However, the mechanisms of regulation of iNOS in inflammation and cancer have not been fully explored. Total flavonoids isolated from RG (TFRG) exhibited anti-inflammatory activity through the regulation of ERK/NF-κB/miR-155 signaling and suppression of iNOS expression in LPS/IFN-γ stimulated RAW264.7 macrophages without cytotoxicity. TFRG also markedly reduced tumor mass of breast cancer cell MDA-MB-231 xenografts with suppression of iNOS expression, formation of 3-nitrotyrosine (3-NT), and inactivation of protumorigenic JAK2/STAT3 signaling pathway. These results suggested that TFRG limited the development of breast cancer and inflammation due to its property of iNOS inhibition.

Calpain and JNK pathways participate in isoflurane - induced nucleus translocation of apoptosis-inducing factor in the brain of neonatal rats

Recent studies have demonstrated that volatile anesthetic causes caspase-dependent neuroapoptosis and persistent cognitive deficits in young animals. Apoptosis-inducing factor (AIF) can trigger apoptosis by caspase-independent pathway. Whether isoflurane induces neuroapoptosis by activation of AIF and its possible mechanism are underdetermined. Rats at postnatal day 7 were exposed to 1.1% isoflurane for 4 h and the expression of AIF, cytochrome c, caspase-3, μ-calpain, m-calpain, Bcl-2 and Bax in the mitochondrial, cytosolic, and nuclear fraction, as well as the number of both AIF and TUNEL positive neurons in the cortices of rats were measured. Moreover, the effects of calpain inhibitor MDL-28170 or JNK inhibitor SP600125 on isoflurane-induced AIF release, caspase activation and cognitive deficits were assessed. We found isoflurane activated CytC-caspase-3 dependent apoptosis pathway mainly in the early phase (0-6 h after exposure). Moreover, isoflurane activated mitochondrial μ-calpain, induced AIF truncation during early phase and activated m-calpain, induced AIF release from the mitochondria to cytosol and translocation into the nucleus in the late phase (6-24 h after exposure). MDL-28170 attenuated the isoflurane-induced mitochondrial AIF truncation, release and nuclear translocation, but did not change the expression of cleaved-caspase-3 and mitochondrial Bax and Bcl-2 proteins. SP600125 attenuated isoflurane-induced neuroapoptosis by inhibiting both AIF and caspase-3 pathways and reduced cognitive impairment in neonatal rats. This is the first study to provide the evidence that isoflurane induced AIF-dependent neuroapoptosis by activation of mitochondrial μ-calpain and m-calpain in neonatal rats. JNK inhibition reversed isoflurane-induced neuroapoptosis and subsequent long-term neurocognitive impairment, acting via inhibiting activation of both AIF and caspase-3 pathways.

Neuroprotective effect of licochalcone A against oxygen-glucose deprivation/reperfusion in rat primary cortical neurons by attenuating oxidative stress injury and inflammatory response via the SIRT1/Nrf2 pathway

Perinatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of neonatal death and neurological disability. Oxidative stress and neuroinflammation are typical pathogenic factors of HIE. Licochalcone A (LCA) exerts various biological properties, including anti-inflammatory and antioxidant activities. However, no data have been reported to elucidate the role of LCA in the development of HIE. In the present study, primary cultured rat cortical neurons were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) in vitro to simulate the in vivo situation of neonatal HIE. Interestingly, LCA significantly antagonized cell injury under OGD/R by increasing cell survival, inhibiting lactate dehydrogenase (LDH) release and cell apoptosis. Furthermore, treatment with LCA suppressed oxidative stress by decreasing reactive oxygen species (ROS) production and malondialdehyde (MDA) content, and increasing superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in primary rat cortical neurons after OGD/R. LCA stimulation also restrained OGD/R-triggered increase in pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production. Importantly, LCA treatment effectively counteracts OGD/R-mediated downregulation of silent information regulator 1 (SIRT1), nuclear factor erythroid2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1), and upregulation of nuclear factor kappa B p65 (NF-κB p65). Moreover, administration with SIRT1 inhibitor EX527 partly abolished LCA-induced neuroprotective effects on rat cortical neurons exposed to OGD/R. In conclusion, our study indicates that LCA exerts a neuroprotective effect against OGD/R-induced neuronal injury in rat primary cortical neurons, suggesting that LCA might act as a candidate therapeutic target drug used for HIE and related diseases.

Protective Effects of Liquiritigenin against Citrinin-Triggered, Oxidative-Stress-Mediated Apoptosis and Disruption of Embryonic Development in Mouse Blastocysts

The mycotoxin citrinin (CTN), a natural contaminant in foodstuffs and animal feeds, exerts cytotoxic and genotoxic effects on various mammalian cells and embryos. A previous investigation by our group revealed potentially hazardous effects of CTN on mouse oocyte maturation and pre- and post-implantation embryo development via the induction of apoptosis. The present study showed that CTN induces apoptosis and inhibits cell proliferation in the inner cell mass of mouse blastocysts. Notably, we observed for the first time that both these effects are suppressed by liquiritigenin (LQ). LQ is a type of flavonoid isolated from Glycyrrhiza radix with several biochemical and pharmacological activities, including antioxidant and anti-inflammatory properties. The preincubation of blastocysts with LQ clearly prevented CTN-induced disruption of pre- and post-implantation embryonic development and fetal weight loss, both in vitro and in vivo. CTN-induced damage processes directly promoted reactive oxygen species (ROS) generation, loss of mitochondrial membrane potential (MMP) and activation of caspase-9 and caspase-3, which were effectively blocked by LQ. Moreover, in an animal model, intravenous injection of dams with CTN (3 mg/kg/day) triggered apoptosis of blastocysts, disruption of embryonic development from the zygote to the blastocyst stage and a decrease in fetal weight. Pre-injection with LQ (5 mg/kg/day) effectively reduced apoptosis and impaired the cytotoxic effects of CTN on development. Our in vivo findings further confirm that CTN exposure via injection has the potential to impair pre- and post-implantation development, leading to apoptosis and the suppression of sequent embryonic development, which can be effectively prevented by LQ.

Estrogen receptor activation contributes to RNF146 expression and neuroprotection in Parkinson's disease models

RNF146 is an E3 ubiquitin ligase that specifically recognizes and polyubiquitinates poly (ADP-ribose) (PAR)-conjugated substrates for proteasomal degradation. RNF146 has been shown to be neuroprotective against PAR polymerase-1 (PARP1)-induced cell death during stroke. Here we report that RNF146 expression and RNF146 inducers can prevent cell death elicited by Parkinson’s disease (PD)-associated and PARP1-activating stimuli. In SH-SY5Y cells, RNF146 expression conferred resistance to toxic stimuli that lead to PARP1 activation. High-throughput screen using a luciferase construct harboring the RNF146 promoter identified liquiritigenin as an RNF146 inducer. We found that RNF146 expression by liquiritigenin was mediated by estrogen receptor activation and contributed to cytoprotective effect of liquiritigenin. Finally, RNF146 expression by liquiritigenin in mouse brains provided dopaminergic neuroprotection in a 6-hydroxydopamine PD mouse model. Given the presence of PARP1 activity and RNF146 deficits in PD, it could be a potential therapeutic strategy to restore RNF146 expression by natural compounds or estrogen receptor activation.

Protective effect of isoliquiritin against corticosterone-induced neurotoxicity in PC12 cells

Isoliquiritin, a flavonoid glycoside compound from licorice, possesses a broad spectrum of pharmacological activities including antioxidant, anti-inflammatory and anti-depression activities. However, the neuroprotective mechanisms of antidepressant effects remain unclear. In this study, the aim was to investigate the cytoprotective efficiency and potential mechanisms of isoliquiritin in corticosterone-damaged PC12 cells. The results of this study showed that pretreatment of PC12 cells with isoliquiritin significantly prevented corticosterone-induced cell apoptosis. In addition, isoliquiritin increased the activity of dismutase (SOD) and catalase (CAT), decreased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA). These findings suggest that isoliquiritin provides protective action against corticosterone-induced cell damage by reducing oxidative stress. Furthermore, pretreatment with isoliquiritin reduced corticosterone-induced mitochondrial dysfunction by preventing mitochondrial membrane potential dissipation. Our findings indicate that isoliquiritin might exert its therapeutic effects via regulating mitochondrial dysfunction. Moreover, isoliquiritin strongly attenuated intracellular calcium ([Ca²⁺]i) overload and down-regulation of Bax, caspase-3 and cytochrome C (Cyt-C) protein expression, and up-regulation of Bcl protein expression. In conclusion, isoliquiritin has a cytoprotective effect on corticosterone-induced neurotoxicity in PC12 cells, which may be related to its antioxidant action, inhibition of [Ca²⁺]i overload and inhibition of the mitochondrial apoptotic pathway.

N-stearoyltyrosine protects primary cortical neurons against oxygen-glucose deprivation-induced apoptosis through inhibiting anandamide inactivation system

N-stearoylthrosine (NST), a synthesized anandamide (AEA) analogue, plays a neuroprotective role in neurodegenerative diseases and cerebrovascular diseases. Several studies have demonstrated that the endocannabinoids systems (ECS) are involved in the neuroprotective effects against cerebral ischemic injury. Oxygen-glucose deprivation (OGD)-induced neuronal injury elevated the levels of endocannabinoids and activated ECS. This research was conducted to investigate the neuroprotective effect of NST against OGD-induced neuronal injury in cultured primary cortical neurons and the potential mechanism involved. Cortical neurons were treated with NST at indicate concentrations for 30min prior to injury and OGD injured neurons were incubated with normal conditions for 0-24h. The best neuroprotective effect of NST against OGD-induced injury occurred at 10μM. All data indicated that the neuroprotective effect of NST against OGD-induced injury resulted from blocking anandamide membrane transporter (AMT) (IC₅₀=11.74nM) and inhibiting fatty acid amide hydrolase activity (FAAH) (IC₅₀=16.54nM). Our findings demonstrated that NST has an important role in cerebral ischemic injury pathological progression through activating cannabinoid receptors by inhibiting AEA inactivation system. These data suggested a potential role for NST in the therapeutic consideration of cerebral ischemic injury. However, inhibition of AEA inactivation system may provide a neuroprotective effect during cerebral ischemic injury.

Astaxanthin attenuates glutamate-induced apoptosis via inhibition of calcium influx and endoplasmic reticulum stress

Astaxanthin (AST) is a carotenoid that has been shown to have neuroprotective effects. In this study, it was found that AST significantly inhibited glutamate-induced loss of cell viability and apoptosis. AST pretreatment attenuated glutamate-induced activation of caspase-3, reduction of anti-apoptotic protein Bcl-2, and increase of pro-apoptotic protein Bak. In addition, AST pretreatment suppressed the production of intracellular reactive oxygen species. AST treatment also prevented glutamate-induced increase of the level of activated p38 mitogen-activated protein kinase (MAPK), which has been shown to promote apoptotic events. Furthermore, AST treatment greatly reduced the elevation of intracellular calcium level induced by glutamate and inhibited the activity of calpain, a calcium-dependent protease that plays an important role in mediating apoptosis stimulated by calcium overload in cytoplasm. Both oxidative stress and calcium overload can lead to endoplasmic reticulum (ER) stress. C/EBP-homologous protein (CHOP) is a bZIP transcription factor that can be activated by ER stress and promotes apoptosis. Here we found that AST attenuated glutamate-induced elevation of CHOP and ER chaperone glucose-regulated protein (GRP78). Overall, these results suggested that AST might protect cells against glutamate-induced apoptosis through maintaining redox balance and inhibiting glutamate-induced calcium influx and ER stress.

The comparison of neuroprotective effects of isoliquiritigenin and its Phase I metabolites against glutamate-induced HT22 cell death

It is becoming increasingly important to investigate drug metabolites to evaluate their toxic or preventive effects after administration of the parent compound. In our previous study, isoliquiritigenin isolated from Glycyrrhizae Radix effectively protected mouse-derived hippocampal neuronal cells (HT22) against 5mM glutamate-induced oxidative stress. However, there is little information on the protective effects of the metabolites of isoliquiritigenin on HT22 cells. In this study, isoliquiritigenin and its Phase I metabolites were prepared and their neuroprotective activities on glutamate-treated HT22 cells were compared. The prepared metabolites were liquiritigenin (1), 2',4,4',5'-tetrahydroxychalcone (2), sulfuretin (3), butein (4), davidigenin (5), and cis-6,4'-dihydroxyaurone (6). Among the six metabolites, 4 showed better neuroprotective effects than the parent compound, isoliquiritigenin. Our study suggests that the neuroprotective effect of isoliquiritigenin could be elevated by its active metabolite 4, which is a chalcone containing a catechol group in the B ring.

In vitro Study of the Antagonistic Effect of Low-dose Liquiritigenin on Gemcitabine-induced Capillary Leak Syndrome in Pancreatic Adenocarcinoma via Inhibiting ROS- Mediated Signalling Pathways

BACKGROUND

To investigate in-vitro antagonistic effect of low-dose liquiritigenin on gemcitabine-induced capillary leak syndrome (CLS) in pancreatic adenocarcinoma via inhibiting reactive oxygen species (ROS)- mediated signalling pathways.

MATERIALS AND METHODS

Human pancreatic adenocarcinoma Panc-1 cells and human umbilical vein endothelial cells (HUVECs) were pre-treated using low-dose liquiritigenin for 24 h, then added into gemcitabine and incubated for 48 h. Cell viability, apoptosis rate and ROS levels of Panc-1 cells and HUVECs were respectively detected through methylthiazolyldiphenyl-tetrazoliumbromide (MTT) and flow cytometry. For HUVECs, transendothelial electrical resistance (TEER) and transcellular and paracellular leak were measured using transwell assays, then poly (ADP-ribose) polymerase 1 (PARP-1) and metal matrix proteinase-9 (MMP9) activity were assayed via kits, mRNA expressions of p53 and Rac-1 were determined through quantitative polymerase chain reaction (qPCR); The expressions of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and PARP-1 were measured via western blotting.

RESULTS

Low-dose liquiritigenin exerted no effect on gemcitabine-induced changes of cell viability, apoptosis rate and ROS levels in Panc-1 cells, but for HUVECs, liquiritigenin (3 μM) could remarkably elevate gemcitabine- induced decrease of cell viability, transepithelial electrical resistance (TEER), pro-MMP9 level and expression of ICAM-1 and VCAM-1 (p<0.01). Meanwhile, it could also significantly decrease gemcitabine-induced increase of transcellular and paracellular leak, ROS level, PARP-1 activity, Act-MMP9 level, mRNA expressions of p53 and Rac-1, expression of PARP-1 and apoptosis rate (p<0.01).

CONCLUSIONS

Low-dose liquiritigenin exerts an antagonistic effect on gemcitabine-induced leak across HUVECs via inhibiting ROS-mediated signalling pathways, but without affecting gemcitabine-induced Panc-1 cell apoptosis. Therefore, low-dose liquiritigenin might be beneficial to prevent the occurrence of gemcitabine-induced CLS in pancreatic adenocarcinoma.

Polyozellin, a key constituent of the edible mushroom Polyozellus multiplex, attenuates glutamate-induced mouse hippocampal neuronal HT22 cell death

Polyozellus multiplex (PM), a Korean edible mushroom, has biological activities such as chemoprevention of stomach cancer, inhibition of lipid peroxidation, and reduction of prolyl endopeptidase activity. However, there are little reports on the protective effects of PM or its constituents against glutamate-induced mouse hippocampal neuronal cell (HT22) death. In this study, polyozellin (PZ), a key constituent of PM, was applied to glutamate-treated HT22 cells to evaluate its neuroprotective mechanisms. PZ (25 μM) dramatically increased the HT22 cell viability when the cell death was induced by 5 mM glutamate for 12 h, which was mediated by inhibition of Ca(2+) influx, intracellular reactive oxygen species (ROS) production, and lipid peroxidation. PZ also regulated expression of Bid, Bcl-2, and apoptosis-inducing factor (AIF), as well as phosphorylation of mitogen-activated protein kinases (MAPKs). These data suggest that PM and its constituent PZ might be useful for prevention and treatment of neurodegenerative disorders.

Sevoflurane post-conditioning protects primary rat cortical neurons against oxygen-glucose deprivation/resuscitation via down-regulation in mitochondrial apoptosis axis of Bid, Bim, Puma-Bax and Bak mediated by Erk1/2

Temporal post-conditioning helps provide neuroprotection against brain injury secondary to ischemia-reperfusion and is considered an effective intervention, but the exact mechanism of sevoflurane post-conditioning is unclear. The essential axis involves activator Bid, Bim, Puma (BH3s), Bax, and Bak; activates the mitochondrial death program; and might be involved in a cell death signal. Extracellular signal-related kinases 1/2 (Erk1/2) play a pivotal role in cell growth and proliferation. We hypothesized that sevoflurane post-conditioning might inhibit Bid, Bim, Puma, Bax, and Bak expression and is activated by phosphor-Erk1/2 to decrease neuronal death. To test this hypothesis, we exposed primary cortical neuron cultures to oxygen-glucose deprivation for 1h, along with resuscitation for 24h (OGD/R). MTT assays, propidium iodide uptake (PI), JC-1 fluorescence, and Western blot indicated the following: decreased cell viability (P<0.05); increased cell death (P<0.05); decreased mitochondrial membrane potential (P<0.05); and decreased Bid, Bim, Puma, Bax, and Bak expression with OGD/R exposure. Inhibition of Erk1/2 phosphorylation could attenuate sevoflurane post-conditioning that mediated an increase in neuronal viability and mitochondrial membrane potential, as well as a decrease in cell death and Bid, Bim, Puma, Bax, and Bak expression after OGD/R treatment. The results demonstrated that sevoflurane post-conditioning caused a marked decrease in cortical neuronal death secondary to OGD/R exposure through the downregulation of the mitochondrial apoptosis axis involving Bid, Bim, Puma, Bax, and Bak that was mediated by the phosphorylation/activation of Erk1/2.

Neuroprotection and spatial memory enhancement of four herbal mixture extract in HT22 hippocampal cells and a mouse model of focal cerebral ischemia

BACKGROUND

Four traditional Korean medicinal herbs which act in retarding the aging process, Polygonum multiflorum Thunb., Rehmannia glutinosa (Gaertn) Libosch., Polygala tenuifolia Willd., and Acorus gramineus Soland., were prepared by systematic investigation of Dongeuibogam (Treasured Mirror of Eastern Medicine), published in the early 17th century in Korea. This study was performed to evaluate beneficial effects of four herbal mixture extract (PMC-12) on hippocampal neuron and spatial memory.

METHODS

High performance liquid chromatography (HPLC) analysis was performed for standardization of PMC-12. Cell viability, lactate dehydrogenase, flow cytometry, reactive oxygen species (ROS), and Western blot assays were performed in HT22 hippocampal cells and immunohistochemistry and behavioral tests were performed in a mouse model of focal cerebral ischemia in order to observe alterations of hippocampal cell survival and subsequent memory function.

RESULTS

In the HPLC analysis, PMC-12 was standardized to contain 3.09% 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside, 0.35% 3',6-disinapoyl sucrose, and 0.79% catalpol. In HT22 cells, pretreatment with PMC-12 resulted in significantly reduced glutamate-induced apoptotic cell death. Pretreatment with PMC-12 also resulted in suppression of ROS accumulation in connection with cellular Ca(2+) level after exposure to glutamate. Expression levels of phosphorylated p38 mitogen-activated protein kinases (MAPK) and dephosphorylated phosphatidylinositol-3 kinase (PI3K) by glutamate exposure were recovered by pretreatment with either PMC-12 or anti-oxidant N-acetyl-L-cysteine (NAC). Expression levels of mature brain-derived neurotrophic factor (BDNF) and phosphorylated cAMP response element binding protein (CREB) were significantly enhanced by treatment with either PMC-12 or NAC. Combination treatment with PMC-12, NAC, and intracellular Ca(2+) inhibitor BAPTA showed similar expression levels. In a mouse model of focal cerebral ischemia, we observed higher expression of mature BDNF and phosphorylation of CREB in the hippocampus and further confirmed improved spatial memory by treatment with PMC-12.

CONCLUSIONS

Our results suggest that PMC-12 mainly exerted protective effects on hippocampal neurons through suppression of Ca(2+)-related ROS accumulation and regulation of signaling pathways of p38 MAPK and PI3K associated with mature BDNF expression and CREB phosphorylation and subsequently enhanced spatial memory.

Estrogen receptor β agonist enhances temozolomide sensitivity of glioma cells by inhibiting PI3K/AKT/mTOR pathway

Glioma is the most common primary brain tumor among adults. Temozolomide (TMZ) is widely used as the first‑line postsurgical drug for malignant glioma. However, the therapeutic efficacy of TMZ remains ineffective as inherited or acquired drug resistance is frequently observed. Estrogen receptor β (ERβ) has emerged as a tumor suppressor and a key regulator of signal transduction in glioma cells. However, little is known about the role of ERβ in regulating the chemotherapeutic response to TMZ. In the current study, the TMZ‑resistant U138 glioma cells were treated with the novel ERβ agonist liquiritigenin (Liq). It was observed that Liq significantly enhanced ERβ expression and sensitized glioma cells to TMZ‑induced proliferation inhibition. As a potential mechanism, it was noted that Liq treatment significantly inhibited the activity of the PI3K/AKT/mTOR pathway, which played a protective role against the TMZ‑induced cytotoxicity. In addition, it was demonstrated that ERβ knockdown or activation of the phosphatidylinositol‑4,5‑bisphosphate 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway by insulin‑like growth factor 1 both eradicated the function of Liq. These results suggest that Liq treatment enhances glioma cell susceptibility to TMZ by inhibiting the PI3K/AKT/mTOR pathway. As hyperactivation of the PI3K/AKT/mTOR pathway is frequently observed in gliomas, the combined use of ERβ agonists may become a feasible therapy option to overcome chemoresistance to TMZ.