Luteolin and Apigenin Attenuate 4-Hydroxy-2-Nonenal-Mediated Cell Death through Modulation of UPR, Nrf2-ARE and MAPK Pathways in PC12 Cells

The Role and Interactive Mechanism of Endoplasmic Reticulum Stress and Ferroptosis in Musculoskeletal Disorders

Endoplasmic reticulum (ER) stress is a cellular phenomenon that arises in response to the accumulation of misfolded proteins within the ER. This process triggers the activation of a signalling pathway known as the unfolded protein response (UPR), which aims to restore ER homeostasis by reducing protein synthesis, increasing protein degradation, and promoting proper protein folding. However, excessive ER stress can perturb regular cellular function and contribute to the development of diverse pathological conditions. As is well known, ferroptosis is a kind of programmed cell death characterized by the accumulation of lipid peroxides and iron-dependent reactive oxygen species (ROS), resulting in oxidative harm to cellular structures. In recent years, there has been increasing evidence indicating that ferroptosis occurs in musculoskeletal disorders (MSDs), with emerging recognition of the complex relationship between ER stress and ferroptosis. This review presents a summary of ER stress and the ferroptosis pathway. Most importantly, it delves into the significance of ER stress in the ferroptosis process within diverse skeletal or muscle cell types. Furthermore, we highlight the potential benefits of targeting the correlation between ER stress and ferroptosis in treating degenerative MSDs.

Idiopathic pulmonary fibrosis (IPF): disease pathophysiology, targets, and potential therapeutic interventions

Idiopathic pulmonary fibrosis (IPF) is a progressive, degenerative pulmonary condition. Transforming growth factor (TGF)-β, platelet-derived growth factor (PDGF), and tumor necrosis factor-α (TNF-α) are the major modulators of IPF that mediate myofibroblast differentiation and promote fibrotic remodeling of the lung. Cigarette smoke, asbestos fiber, drugs, and radiation are known to favor fibrotic remodeling of the lungs. Oxidative stress in the endoplasmic reticulum (ER) also leads to protein misfolding and promotes ER stress, which is predominant in IPF. This phenomenon further results in excess reactive oxygen species (ROS) aggregation, increasing oxidative stress. During protein folding in the ER, thiol groups on the cysteine residue are oxidized and disulfide bonds are formed, which leads to the production of hydrogen peroxide (H2O2) as a by-product. With the accumulation of misfolded proteins in the ER, multiple signaling cascades are initiated by the cell, collectively termed as the unfolded protein response (UPR). UPR also induces ROS production within the ER and mitochondria and promotes both pro-apoptotic and pro-survival pathways. The prevalence of post-COVID-19 pulmonary fibrosis (PCPF) is 44.9%, along with an alarming increase in "Coronavirus Disease 2019" (COVID-19) comorbidities. Fibrotic airway remodeling and declined lung function are the common endpoints of SARS-CoV-2 infection and IPF. Flavonoids are available in our dietary supplements and exhibit medicinal properties. Apigenin is a flavonoid found in plants, including chamomile, thyme, parsley, garlic, guava, and broccoli, and regulates several cellular functions, such as oxidative stress, ER stress, and fibrotic responses. In this study, we focus on the IPF and COVID-19 pathogenesis and the potential role of Apigenin in addressing disease progression.

Luteolin for neurodegenerative diseases: a review

Neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and multiple sclerosis affect millions of people around the world. In addition to age, which is a key factor contributing to the development of all neurodegenerative diseases, genetic and environmental components are also important risk factors. Current methods of treating neurodegenerative diseases are mostly symptomatic and do not eliminate the cause of the disease. Many studies focus on searching for natural substances with neuroprotective properties that could be used as an adjuvant therapy in the inhibition of the neurodegeneration process. These compounds include flavonoids, such as luteolin, showing significant anti-inflammatory, antioxidant, and neuroprotective activity. Increasing evidence suggests that luteolin may confer protection against neurodegeneration. In this review, we summarize the scientific reports from preclinical in vitro and in vivo studies regarding the beneficial effects of luteolin in neurodegenerative diseases. Luteolin was studied most extensively in various models of Alzheimer's disease but there are also several reports showing its neuroprotective effects in models of Parkinson's disease. Though very limited, studies on possible protective effects of luteolin against Huntington's disease and multiple sclerosis are also discussed here. Overall, although preclinical studies show the potential benefits of luteolin in neurodegenerative disorders, clinical evidence on its therapeutic efficacy is still deficient.

Luteolin: A promising multifunctional natural flavonoid for human diseases

Natural products are closely associated with human health. Luteolin (LUT), a flavonoid polyphenolic compound, is widely found in fruits, vegetables, flowers, and herbs. It is noteworthy that LUT exhibits a variety of beneficial pharmacological properties and holds significant potential for clinical applications, particularly in antitumor, anti-convulsion, diabetes control, anti-inflammatory, neuroprotection, anti-oxidation, anti-cardiovascular, and other aspects. The potential mechanism of action has been partially elucidated, including the mediation of NF-κB, toll-like receptor, MAPK, Wnt/β-catenin, PI3K/Akt, AMPK/mTOR, and Nrf-2, among others. The review that aimed to comprehensively consolidate essential information on natural sources, pharmacological effects, therapeutic and preventive potential, as well as potential mechanisms of LUT. The objective is to establish a theoretical basis for the continued development and application of LUT.

Polyphenols Targeting MAP Kinase Signaling Pathway in Neurological Diseases: Understanding Molecular Mechanisms and Therapeutic Targets

Polyphenols are a class of secondary metabolic products found in plants that have been extensively studied for how well they regulate biological processes, such as the proliferation of cells, autophagy, and apoptosis. The mitogen-activated protein kinase (MAPK)-mediated signaling cascade is currently identified as a crucial pro-inflammatory pathway that plays a significant role in the development of neuroinflammation. This process has been shown to contribute to the pathogenesis of several neurological conditions, such as Alzheimer's disease (AD), Parkinson's disease (PD), CNS damage, and cerebral ischemia. Getting enough polyphenols through eating habits has resulted in mitigating the effects of oxidative stress (OS) and lowering the susceptibility to associated neurodegenerative disorders, including but not limited to multiple sclerosis (MS), AD, stroke, and PD. Polyphenols possess significant promise in dealing with the root cause of neurological conditions by modulating multiple therapeutic targets simultaneously, thereby attenuating their complicated physiology. Several polyphenolic substances have demonstrated beneficial results in various studies and are presently undergoing clinical investigation to treat neurological diseases (NDs). The objective of this review is to provide a comprehensive summary of the different aspects of the MAPK pathway involved in neurological conditions, along with an appraisal of the progress made in using polyphenols to regulate the MAPK signaling system to facilitate the management of NDs.

Repaglinide Induces ATF6 Processing and Neuroprotection in Transgenic SOD1G93A Mice

The interaction of the activating transcription factor 6 (ATF6), a key effector of the unfolded protein response (UPR) in the endoplasmic reticulum, with the neuronal calcium sensor Downstream Regulatory Element Antagonist Modulator (DREAM) is a potential therapeutic target in neurodegeneration. Modulation of the ATF6-DREAM interaction with repaglinide (RP) induced neuroprotection in a model of Huntington's disease. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with no cure, characterized by the progressive loss of motoneurons resulting in muscle denervation, atrophy, paralysis, and death. The aim of this work was to investigate the potential therapeutic significance of DREAM as a target for intervention in ALS. We found that the expression of the DREAM protein was reduced in the spinal cord of SOD1G93A mice compared to wild-type littermates. RP treatment improved motor strength and reduced the expression of the ALS progression marker collagen type XIXα1 (Col19α1 mRNA) in the quadriceps muscle in SOD1G93A mice. Moreover, treated SOD1G93A mice showed reduced motoneuron loss and glial activation and increased ATF6 processing in the spinal cord. These results indicate that the modulation of the DREAM-ATF6 interaction ameliorates ALS symptoms in SOD1G93A mice.

Upregulation of Nrf2/HO-1 Signaling and Attenuation of Oxidative Stress, Inflammation, and Cell Death Mediate the Protective Effect of Apigenin against Cyclophosphamide Hepatotoxicity

Liver injury is among the adverse effects of the chemotherapeutic agent cyclophosphamide (CP). This study investigated the protective role of the flavone apigenin (API) against CP-induced liver damage, pointing to the involvement of Nrf2/HO-1 signaling. Rats were treated with API (20 and 40 mg/kg) for 15 days and received CP (150 mg/kg) on day 16. CP caused liver damage manifested by an elevation of transaminases, alkaline phosphatase (ALP), and lactate dehydrogenase (LDH), and histological alterations, including granular vacuolation, mononuclear cell infiltration, and hydropic changes. Hepatic reactive oxygen species (ROS), malondialdehyde (MDA), and nitric oxide (NO) were increased and glutathione (GSH) and antioxidant enzymes were decreased in CP-administered rats. CP upregulated the inflammatory markers NF-κB p65, TNF-α, IL-6, and iNOS, along with the pro-apoptotic Bax and caspase-3. Pre-treatment with API ameliorated circulating transaminases, ALP, and LDH, and prevented histopathological changes in CP-intoxicated rats. API suppressed ROS, MDA, NO, NF-κB p65, iNOS, inflammatory cytokines, oxidative DNA damage, Bax, and caspase-3 in CP-intoxicated rats. In addition, API enhanced hepatic antioxidants and Bcl-2 and boosted the Nrf2 and HO-1 mRNA abundance and protein. In conclusion, API is effective in preventing CP hepatotoxicity by attenuating oxidative stress, the inflammatory response, and apoptosis. The hepatoprotective efficacy of API was associated with the upregulation of Nrf2/HO-1 signaling.

Hydroxynonenal Causes Hepatocyte Death by Disrupting Lysosomal Integrity in Nonalcoholic Steatohepatitis

BACKGROUND & AIMS

The lipid oxidation is a key factor for damaging hepatocytes and causing cell death. However, the mechanisms underlying hepatocyte death and the role of the most popular lipid peroxidation product 4-hydroxy-2-nonenal (HNE) in nonalcoholic steatohepatitis (NASH) remains unclear.

METHODS

We demonstrated using hepatoma cell lines, a NASH mouse model, HNE-treated monkeys, and biopsy specimens from patients with NASH that HNE induced hepatocyte death by disintegrating the lysosomal limiting membrane.

RESULTS

The degree of HNE deposition in human NASH hepatocytes was more severe in cases with high lobular inflammation, ballooning, and fibrosis scores, and was associated with enlargement of the staining of lysosomes in hepatocytes. In in vitro experiments, HNE activated μ-calpain via G-protein coupled receptor (GPR) 120. The resultant rupture/permeabilization of the lysosomal limiting membrane induced the leakage of cathepsins from lysosomes and hepatocyte death. The blockade of G-protein coupled receptor 120 (GPR120) or μ-calpain expression suppressed lysosomal membrane damage and hepatocyte death by HNE. Alda-1, which activates aldehyde dehydrogenase 2 to degrade HNE, prevented HNE-induced hepatocyte death. Intravenous administration of HNE to monkeys for 6 months resulted in hepatocyte death by a mechanism similar to that of cultured cells. In addition, intraperitoneal administration of Alda-1 to choline-deficient, amino-acid defined treated mice for 8 weeks inhibited HNE deposition, decreased liver inflammation, and disrupted lysosomal membranes in hepatocytes, resulting in improvement of liver fibrosis.

CONCLUSIONS

These results provide novel insights into the mechanism of hepatocyte death in NASH and will contribute to the development of new therapeutic strategies for NASH.

ROS and Endoplasmic Reticulum Stress in Pulmonary Disease

Pulmonary diseases are main causes of morbidity and mortality worldwide. Current studies show that though specific pulmonary diseases and correlative lung-metabolic deviance own unique pathophysiology and clinical manifestations, they always tend to exhibit common characteristics including reactive oxygen species (ROS) signaling and disruptions of proteostasis bringing about accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER is generated by the unfolded protein response. When the adaptive unfolded protein response (UPR) fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis, which is called ER stress. The ER stress mainly includes the accumulation of misfolded and unfolded proteins in lumen and the disorder of Ca²⁺ balance. ROS mediates several critical aspects of the ER stress response. We summarize the latest advances in of the UPR and ER stress in the pathogenesis of pulmonary disease and discuss potential therapeutic strategies aimed at restoring ER proteostasis in pulmonary disease.

The Effect of Prosopis farcta and Its Bioactive Luteolin on the Hippocampus of Mice after Induced Ischemia Reperfusion

Background

Ischemia plays an important role in increasing damage to the nervous system. This study aimed to evaluate the effect of Prosopis farcta (PFE) and its bioactive luteolin (Lu) and forced swimming exercise on the hippocampus of mice after induced ischemia reperfusion.

Methods

The bioactive component of PFE (Lu) was identified by HPLC. Fifty-six male mice were divided into different groups. Ischemia was induced by ligation of the common carotid artery. After mice training (swimming exercise, 8 weeks) and consuming PFE and Lu, the mice's memory ability was evaluated in the shuttle box. Histological examination was performed by Nissel staining and immunohistochemistry.

Results

Results showed that the ischemic mice exercised and treated with PFE and Lu had higher step-through latency (STL) compared with the nonexercised mice, and this was confirmed with time spent in the dark compartment (TDC). The number of dark cells in the ischemic group exercising and receiving PFE and Lu decreased compared to that of the other groups in the hippocampus. DCX protein expression was increased in nonexercised groups compared to that of the exercised groups and those treated with PFE and Lu, while NeuN decreased.

Conclusions

Forced swimming exercise following ischemia, as well as consumption of PFE and Lu, has reduced cell death and increased neurogenesis in the hippocampus and thus may help improve memory in ischemia.

Reactive oxygen species: Key players in the anticancer effects of apigenin?

Reactive oxygen species (ROS) exhibit a double-edged sword in cancer-hence their modulation has been an attractive strategy in cancer prevention and therapy. The abundance of scientific information on the pro-oxidant effects of apigenin in cancer cells suggests the crucial role of ROS in its mechanisms of action. Although apigenin is known to enhance the cellular ROS levels to cytotoxic degrees in cancer cells in vitro, it remains to be determined if these pro-oxidant effects prevail or are relevant in experimental tumor models and clinical trials. Here, we critically examine the pro-oxidant and antioxidant effects of apigenin in cancer to provide insightful perspectives on the association between its ROS-modulating action and anticancer potential. We also discussed these effects in a cell/tissue type-specific context to highlight the factors influencing the switch between antioxidant and pro-oxidant effects. Finally, we raised some questions that need addressing for the potential translation of these studies into clinical applications. Further research into this duality in oxidant actions of apigenin, especially in vivo, may enable better exploitation of its anticancer potential. PRACTICAL APPLICATION: Apigenin is a naturally occurring compound found in chamomile flowers, parsley, celery, peppermint, and citrus fruits. Many human trials of dietary interventions with apigenin-containing herbs and flavonoid mixture on oxidative stress markers, for instance, point to their antioxidant effects and health benefits in many diseases. Preclinical studies suggest that apigenin alone or its combination with chemotherapeutics has a strong anti-neoplastic effect and can induce ROS-mediated cytotoxicity at concentrations in the micromolar (μM) range, which may not be feasible with dietary interventions. Enhancing the in vivo pharmacokinetic properties of apigenin may be indispensable for its potential cancer-specific pro-oxidant therapy and may provide relevant information for clinical studies of apigenin either as a single agent or an adjuvant to chemotherapeutics.

Functionality of apigenin as a potent antioxidant with emphasis on bioavailability, metabolism, action mechanism and in vitro and in vivo studies: A review

Numerous diseases such as cancer, diabetes, cardiovascular, neurodegenerative diseases, etc. are linked with overproduction of reactive oxygen species (ROS) and oxidative stress. Apigenin (5,7,4'-trihydroxyflavone) is a widely distributed flavonoid, responsible for antioxidant potential and chelating redox active metals. Being present as glycosides or polymers, the apigenin degrades to variable amount in the digestive tract; during processing, its activity is also reduced due to high temperature or Fe/Cu addition. Although its metabolism remains elusive, enteric absorption occurs sufficiently to reduce plasma indices of oxidant status. Delayed clearance in plasma and slow liver decomposition enhance its systematic bioavailability. Antioxidant mechanism of apigenin includes: oxidant enzymes inhibition, modulation of redox signaling pathways (NF-kB, Nrf2, MAPK, and P13/Akt), reinforcing enzymatic and nonenzymatic antioxidant, metal chelation, and free radical scavenging. DPPH, ORAC, ABTS, and FRAP are the major in vitro methods for determining the antioxidant potential of apigenin, whereas its protective effects in whole and living cells of animals are examined using in vivo studies. Due to limited information on antioxidant potential of apigenin, its in vitro and in vivo antioxidant effects are, therefore, discussed with action mechanism and interaction with the signaling pathways. This paper concludes that apigenin is a potent antioxidant compound to overcome the difficulties related to oxidative stress and other chronic diseases.

The Combination of Cigarette Smoking and Alcohol Consumption Synergistically Increases Reactive Carbonyl Species in Human Male Plasma

Cigarette smoking and alcohol consumption are major risk factors for lifestyle-related diseases. Although it has been reported that the combination of these habits worsens risks, the underlying mechanism remains elusive. Reactive carbonyl species (RCS) cause chemical modifications of biological molecules, leading to alterations in cellular signaling pathways, and total RCS levels have been used as a lipid peroxidation marker linked to lifestyle-related diseases. In this study, at least 41 types of RCS were identified in the lipophilic fraction of plasma samples from 40 subjects using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Higher levels of 10 alkanals, 5 trans-2-alkenals, 1 cis-4-alkenal, and 3 alkadienals were detected in the smoking/drinking group (N = 10) as compared to those with either habit (N = 10 each) or without both habits (N = 10) in the analysis of covariances adjusted for age and BMI. The levels of 3 alkanals, 1 trans-2-alkenal, 1 alkadienal, and 1 4-hydroxy-2-alkenal in the smoking/drinking group were significantly higher than those in the no-smoking/drinking and no-smoking/no-drinking groups. These results strongly indicate that the combination of cigarette smoking and alcohol drinking synergistically increases the level and variety of RCS in the circulating blood, and may further jeopardize cellular function.

A Shortage of FTH Induces ROS and Sensitizes RAS-Proficient Neuroblastoma N2A Cells to Ferroptosis

Ferroptosis, an iron-dependent form of programmed cell death, has excellent potential as an anti-cancer therapeutic strategy in different types of tumors, especially in RAS-mutated ones. However, the function of ferroptosis for inhibiting neuroblastoma, a common child malignant tumor with minimal treatment, is unclear. This study investigated the anti-cancer function of ferroptosis inducer Erastin or RSL3 in neuroblastoma N2A cells. Our results show that Erastin or RSL3 induces ROS level and cell death and, therefore, reduces the viability of RAS-proficient N2A cells. Importantly, inhibitors to ferroptosis, but not apoptosis, ameliorate the high ROS level and viability defect in Erastin- or RSL3-treated cells. In addition, our data also show that N2A cells are much more sensitive to ferroptosis inducers than primary mouse cortical neural stem cells (NSCs) or neurons. Moreover, a higher level of ROS and PARylation is evidenced in N2A, but not NSCs. Mechanically, ferritin heavy chain 1 (Fth), the ferroxidase function to oxidate redox-active Fe²⁺ to redox-inactive Fe³⁺, is likely responsible for the hypersensitivity of N2A to ferroptosis induction since its expression is lower in N2A compared to NSCs; ectopic expression of Fth reduces ROS levels and cell death, and induces expression of GPX4 and cell viability in N2A cells. Most importantly, neuroblastoma cell lines express a significantly low level of Fth than almost all other types of cancer cell lines. All these data suggest that Erastin or RSL3 induce ferroptosis cell death in neuroblastoma N2A cells, but not normal neural cells, regardless of RAS mutations, due to inadequate FTH. This study, therefore, provides new evidence that ferroptosis could be a promising therapeutic target for neuroblastoma.

Luteolin Orchestrates Porcine Oocyte Meiotic Progression by Maintaining Organelle Dynamics Under Oxidative Stress

Increasing evidence has demonstrated that oxidative stress impairs oocyte maturation, but the underlying mechanisms remain largely unknown. Here, for the first time, we examined the antioxidant role of luteolin in meiotic progression and the underlying mechanisms. Supplementation of 5 μM luteolin increased the rates of first polar body extrusion and blastocyst formation after parthenogenetic activation, and the expression levels of oocyte competence (BMP15 and GDF9)-, mitogen-activated protein kinase (MOS)-, and maturation promoting factor (CDK1 and Cyclin B)-related genes were also improved. Luteolin supplementation decreased intracellular reactive oxygen species levels and increased the expression levels of oxidative stress-related genes (SOD1, SOD2, and CAT). Interestingly, luteolin alleviated defects in cell organelles, including actin filaments, the spindle, mitochondria, the endoplasmic reticulum, and cortical granules, caused by H₂O₂ exposure. Moreover, luteolin significantly improved the developmental competence of in vitro-fertilized embryos in terms of the cleavage rate, blastocyst formation rate, cell number, cellular survival rate, and gene expression and markedly restored the competencies decreased by H₂O₂ treatment. These findings revealed that luteolin supplementation during in vitro maturation improves porcine meiotic progression and subsequent embryonic development by protecting various organelle dynamics against oxidative stress, potentially increasing our understanding of the underlying mechanisms governing the relationship between oxidative stress and the meiotic events required for successful oocyte maturation.

Protective effects of Lavandula stoechas L. methanol extract against 6-OHDA-induced apoptosis in PC12 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is a neurodegenerative disorder associated with oxidative stress-induced neuronal damage and death. In European and Persian Traditional Medicine, aerial parts (leaves, stems, and flowers) of Lavandula stoechas L. have been widely used for treating neurodegenerative disorders including PD.

AIM OF THE STUDY

Herein, the protective effects of L. stoechas methanol extract were investigated on 6-hydroxydopamine (6-OHDA)-induced cytotoxicity and oxidative damage in PC12 cells.

MATERIALS AND METHODS

The cells were pretreated with a standardized L. stoechas methanol extract (2.5-20 μg/mL) for 24 h and exposed to 6-OHDA (200 μM) thereafter. The cell viability percentage was determined by AlamarBlue test. Intracellular reactive oxygen species (ROS) production was determined by a fluorimetric method using 2',7'-dichlorodihydrofluorescein diacetate and cellular apoptosis was assessed by the fluorescent probe propidium iodide test. Finally, the expression of proteins involved in apoptosis pathway (Phospho SAPK/JNK, SAPK/JNK, p44/42 MAPK (ERK1/2) and Poly ADP ribose polymerase (PARP)) was measured via Western blot analysis.

RESULTS

Treatment of PC12 cells with 6-OHDA could significantly increase cytotoxicity, ROS level, and cell apoptosis. Pretreatment of PC12 cells with the extract could significantly decrease 6-OHDA cytotoxicity, ROS production, (2.5 and 5 μg/mL) and cell apoptosis (5 μg/mL). Western blot analysis showed that 6-OHDA exposure could increase the expression of proteins involved in apoptosis signaling, while pretreatment with L. stoechas (5 μg/mL) reduced apoptotic proteins.

CONCLUSIONS

The present study demonstrated that L. stoechas, which has been traditionally used in Persian Medicine for treating CNS diseases, is a valuable source of active compounds with neuroprotective, anti-oxidant, and anti-apoptotic activity.

Protective effects of apigenin against edifenphos-induced genotoxicity and cytotoxicity in rat hepatocytes

Edifenphos (EDF) is an organophosphorus pesticide with antifungal and anti-insecticidal properties. However, EDF accumulates in various agricultural products and causes potential hazards to human health. Although numerous reports have indicated EDF accumulation in agricultural products, toxic effects on cellular system is poorly understood. In the present study, we investigated the cytotoxicity and genotoxicity of EDF in rat hepatocytes and its amelioration by apigenin (a dietary flavonoid). Results showed that EDF inhibited the cell viability, induced oxidative stress, DNA damage, loss of mitochondrial membrane potential (ΔΨm) and caspase-9/-3 activation in rat hepatocytes. Incubation of hepatocytes with N-acetyl cysteine (ROS scavenger) significantly abrogated the ROS generation and apoptosis caused by EDF. In addition, this study also showed that apigenin significantly suppressed the toxic effects of EDF by quenching ROS production thereby abrogating the caspase-9/-3 and apoptosis activation in hepatocytes. Taken together, the findings of this study demonstrate that EDF induces cytotoxicity and DNA damage in hepatocytes, and apigenin can be considered as an effective dietary anti-oxidant regimen against EDF- induced toxicity in cellular system.Communicated by Ramaswamy H. Sarma.

Splicing reprogramming of TRAIL/DISC-components sensitizes lung cancer cells to TRAIL-mediated apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selective killing of cancer cells underlines its anticancer potential. However, poor tolerability and resistance underscores the need to identify cancer-selective TRAIL-sensitizing agents. Apigenin, a dietary flavonoid, sensitizes lung cancer cell lines to TRAIL. It remains unknown, however, whether apigenin sensitizes primary lung cancer cells to TRAIL and its underlying mechanisms. Here we show that apigenin reprograms alternative splicing of key TRAIL/death-inducing-signaling-complex (DISC) components: TRAIL Death Receptor 5 (DR5) and cellular-FLICE-inhibitory-protein (c-FLIP) by interacting with the RNA-binding proteins hnRNPA2 and MSI2, resulting in increased DR5 and decreased c-FLIP_S protein levels, enhancing TRAIL-induced apoptosis of primary lung cancer cells. In addition, apigenin directly bound heat shock protein 70 (Hsp70), promoting TRAIL/DISC assembly and triggering apoptosis. Our findings reveal that apigenin directs alternative splicing and inhibits Hsp70 enhancing TRAIL anticancer activity. These findings underscore impactful synergies between diet and cancer treatments opening new avenues for improved cancer treatments.

Vernonia patula (Dryand.) Merr. and Leucas chinensis (Retz.) R. Brown exert anti-inflammatory activities and relieve oxidative stress via Nrf2 activation

ETHNOPHARMACOLOGICAL RELEVANCE

Vernonia patula (Dryand.) Merr. and Leucas chinensis (Retz.) R. Brown have anti-inflammatory properties and are popularly used as complementary and alternative medicine in Asia.

AIM OF THE STUDY

To investigate the underlying molecular mechanism and active chemicals in the ethanol extracts of V. patula (VP) and L. chinensis (LC).

MATERIALS AND METHODS

The inhibitory activities of VP and LC on lipopolysaccharide (LPS)-stimulated nitric oxide (NO) and interleukin-6 (IL-6) production were investigated in RAW264.7 macrophages and BV2 microglia. Downregulation of pro-inflammatory genes and upregulation of Nrf2 (NF-E2 p45-related factor 2)-ARE (antioxidant response element) pathway were investigated using RT-Q-PCR and Western blotting. Direct antioxidant capacities were measured using free radical scavenging and Folin-Ciocalteu assays. The flavonoids and triterpenes in VP and LC were identified by HPLC-ESI-MS.

RESULTS

VP and LC inhibited NO and IL-6 production and suppressed iNOS, IL-6, IL-1β and CCL2 gene expression. VP and LC were potent direct antioxidants and effective indirect antioxidants assayed by Nrf2 activation and induction of heme oxygenase (HO)-1, glutamate-cysteine ligase modifier subunit (GCLM) and NAD(P)H quinone oxidoreductase 1 (NQO1). Three flavonoids including apigenin (1), luteolin (2) and chryseriol (3), and one triterpene betulinic acid (4) were found in VP; while compounds 1-4 and oleanolic acid (5) were in LC.

CONCLUSION

Anti-inflammatory and antioxidant activities of VP and LC may be in great part attributed to the identified Nrf2 activating compounds, which induce expression of Phase II enzymes and attenuate the upregulation of pro-inflammatory genes.

Lablab Purpureus Protects HaCaT Cells from Oxidative Stress-Induced Cell Death through Nrf2-Mediated Heme Oxygenase-1 Expression via the Activation of p38 and ERK1/2

Ultraviolet B (UV-B) radiation induces the extreme production of either reactive oxygen species (ROS) or inflammatory mediators. The aim of this study was to evaluate the antioxidant activities of 70% ethanolic extract of Lablab purpureus (LPE) and the underlying mechanisms using HaCaT cells exposed to UV-B. High-performance liquid chromatography (HPLC) confirmed the presence of gallic acid, catechin, and epicatechin in LPE. LPE was shown to have a very potent capacity to scavenge free radicals. The results showed that LPE prevented DNA damage and inhibited the generation of ROS in HaCaT cells without causing any toxicity. LPE increased the expression of endogenous antioxidant enzymes such as superoxide dismutase-1 and catalase. Furthermore, LPE treatment facilitates the nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), boosting the phase II detoxifying enzyme heme oxygenase-1 (HO-1) leading to the combatting of oxidative stress. However, pretreatment of LPE also caused the phosphorylation of mitogen-activated protein kinases (MAPK kinase) (p38 kinase) and extracellular signal-regulated kinase (ERK), whereas treatment with p38 and ERK inhibitors substantially suppressed LPE-induced Nrf2 and heme oxygenase (HO)-1 expression. These findings suggest that LPE exhibits antioxidant activity via Nrf-2-mediated HO-1 signaling through the activation of p38 and ERK, indicating that LPE can potentially be used as a remedy to combat oxidative stress-induced disorder.

Apigenin as a Candidate Prenatal Treatment for Trisomy 21: Effects in Human Amniocytes and the Ts1Cje Mouse Model

Human fetuses with trisomy 21 (T21) have atypical brain development that is apparent sonographically in the second trimester. We hypothesize that by analyzing and integrating dysregulated gene expression and pathways common to humans with Down syndrome (DS) and mouse models we can discover novel targets for prenatal therapy. Here, we tested the safety and efficacy of apigenin, identified with this approach, in both human amniocytes from fetuses with T21 and in the Ts1Cje mouse model. In vitro, T21 cells cultured with apigenin had significantly reduced oxidative stress and improved antioxidant defense response. In vivo, apigenin treatment mixed with chow was administered prenatally to the dams and fed to the pups over their lifetimes. There was no significant increase in birth defects or pup deaths resulting from prenatal apigenin treatment. Apigenin significantly improved several developmental milestones and spatial olfactory memory in Ts1Cje neonates. In addition, we noted sex-specific effects on exploratory behavior and long-term hippocampal memory in adult mice, and males showed significantly more improvement than females. We demonstrated that the therapeutic effects of apigenin are pleiotropic, resulting in decreased oxidative stress, activation of pro-proliferative and pro-neurogenic genes (KI67, Nestin, Sox2, and PAX6), reduction of the pro-inflammatory cytokines INFG, IL1A, and IL12P70 through the inhibition of NFκB signaling, increase of the anti-inflammatory cytokines IL10 and IL12P40, and increased expression of the angiogenic and neurotrophic factors VEGFA and IL7. These studies provide proof of principle that apigenin has multiple therapeutic targets in preclinical models of DS.

Neuroprotective Effects of Withania somnifera on 4-Hydroxynonenal Induced Cell Death in Human Neuroblastoma SH-SY5Y Cells Through ROS Inhibition and Apoptotic Mitochondrial Pathway

The antioxidant, anti-inflammatory, and anticancer activities of Withania somnifera (WS) are known for a long time. This study was aimed to examine whether WS also diminishes 4-hydroxy-trans-2-nonenal (HNE)-induced neurotoxicity in human neuroblastoma (SH-SY5Y) cell line. The cytotoxic response of HNE (0.1-50 μM) and WS (6.25-200 μg/ml) was measured by MTT assay after exposing SH-SY5Y cells for 24 h. Then neuroprotective potential was assessed by exposing the cells to biologically safe concentrations of WS (12.5, 25, and 50 μg/ml) then HNE (50 μM). Results showed a concentration-dependent protective effect of WS at 12.5, 25, and 50 μg/ml against HNE (50 μM) induced cytotoxicity and cell inhibition. Pre-exposure to WS resulted in a strong inhibition of 24, 55 and 83% in malondialdehyde (MDA) level; 5, 27 and 60% in glutathione (GSH) level; 12, 36 and 68% in catalase activity; 11, 33 and 67% in LDH leakage; and 40, 80 and 120% in cellular LDH activity at 12.5, 25, and 50 μg/ml, respectively, induced by 50 μM HNE in SH-SY5Y cells. The HNE-mediated cellular changes (cell shrinkage, rounded bodies, and inhibition of outgrowth) and increased caspase-3 activity were also prevented by WS. The HNE-induced upregulation of proapoptotic markers (p53, caspase-3, and -9, and Bax) and downregulation of antiapoptotic marker Bcl-2 genes were also blocked by pretreatment with WS. Altogether, our findings indicate that WS possesses a protective potential against HNE-induced neurotoxicity.

Cudratricusxanthone O Inhibits H2O2-Induced Cell Damage by Activating Nrf2/HO-1 Pathway in Human Chondrocytes

Osteoarthritis (OA) is a common joint degenerative disease induced by oxidative stress in chondrocytes. Although induced-heme oxygenase-1 (HO-1) has been found to protect cells against oxygen radical damage, little information is available regarding the use of bioactive compounds from natural sources for regulating the HO-1 pathway to treat OA. In this study, we explored the inhibitory effects of cudratricusxanthone O (CTO) isolated from the Maclura tricuspidata Bureau (Moraceae) on H₂O₂-induced damage of SW1353 chondrocytes via regulation of the HO-1 pathway. CTO promoted HO-1 expression by enhancing the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) into the nucleus without inducing toxicity. Pretreatment with CTO-regulated reactive oxygen species (ROS) production by inducing expression of antioxidant enzymes in H₂O₂-treated cells and maintained the functions of H₂O₂-damaged chondrocytes. Furthermore, CTO prevented H₂O₂-induced apoptosis by regulating the expression of anti-apoptotic proteins. Treatment with the HO-1 inhibitor tin-protoporphyrin IX revealed that these protective effects were exerted due to an increase in HO-1 expression induced by CTO. In conclusion, CTO protects chondrocytes from H₂O₂-induced damages-including ROS accumulation, dysfunction, and apoptosis through activation of the Nrf2/HO-1 signaling pathway in chondrocytes and, therefore, is a potential therapeutic agent for OA treatment.

Counteracting role of nuclear factor erythroid 2-related factor 2 pathway in Alzheimer's disease

A salient pathological features in Alzheimer's disease includes redox impairment and neuroinflammation. Nuclear factor erythroid 2-related factor 2 (Nrf2) and Nuclear factor kappa B (NF-ҡB) are the two key transcription factors that regulate cellular responses to redox impairment and neuroinflammation respectively. An effective way to confer neuroprotection in central nervous system (CNS) is the activation of a transcription factor i.e Nuclear factor erythroid 2-related factor 2 (Nrf2). An enhancer element known as Antioxidant Response Element (ARE) mediates the expression of phase II detoxification enzymes. Nrf2 is a nuclear transcription factor that binds to ARE thereby transcribing expression of several antioxidant genes. Kelch ECH associating protein-1 (Keap1), a culin 3-based E3 ligase, polyubiquitinates Nrf2 and targets it for its degradation. Disruption in the interaction between Keap1/Nrf2 can increase the brain's endogenous antioxidant capacity and thereby responsible for cell defence against oxidative stress and neuroinflammation in Alzheimer's disease (AD). The current review discusses about Keap1-Nrf2-ARE structure and function with special emphasis on the various pathways involved in positive and negative modulation of Nrf2, namely Phosphoinositide 3- kinase (PI3K), Glycogen synthase kinase-3β (GSK-3β), Nuclear factor kappa-b (NF-ҡb), Janus kinase/signal transducer and activator of transcription (JAK-STAT),Tumour Necrosis Factor- α (TNF-α), p38Mitogen-activated protein kinases (p38MAPK), Cyclic AMP response element binding protein (CREB) and intrinsic & extrinsic apoptotic pathway. Furthermore, this review highlights the miscellaneous Nrf2 activators as promising therapeutic agents for slowingdown the progression of AD.

Can Medicinal Plants and Bioactive Compounds Combat Lipid Peroxidation Product 4-HNE-Induced Deleterious Effects?

The toxic reactive aldehyde 4-hydroxynonenal (4-HNE) belongs to the advanced lipid peroxidation end products. Accumulation of 4-HNE and formation of 4-HNE adducts induced by redox imbalance participate in several cytotoxic processes, which contribute to the pathogenesis and progression of oxidative stress-related human disorders. Medicinal plants and bioactive natural compounds are suggested to be attractive sources of potential agents to mitigate oxidative stress, but little is known about the therapeutic potentials especially on combating 4-HNE-induced deleterious effects. Of note, some investigations clarify the attenuation of medicinal plants and bioactive compounds on 4-HNE-induced disturbances, but strong evidence is needed that these plants and compounds serve as potent agents in the prevention and treatment of disorders driven by 4-HNE. Therefore, this review highlights the pharmacological basis of these medicinal plants and bioactive compounds to combat 4-HNE-induced deleterious effects in oxidative stress-related disorders, such as neurotoxicity and neurological disorder, eye damage, cardiovascular injury, liver injury, and energy metabolism disorder. In addition, this review briefly discusses with special attention to the strategies for developing potential therapies by future applications of these medicinal plants and bioactive compounds, which will help biological and pharmacological scientists to explore the new vistas of medicinal plants in combating 4-HNE-induced deleterious effects.

Pathophysiological Alterations of Redox Signaling and Endocannabinoid System in Granulocytes and Plasma of Psoriatic Patients

Inflammatory granulocytes are characterized by an oxidative burst, which may promote oxidative stress and lipid modification both in affected tissues and on a systemic level. On the other hand, redox signaling involving lipid peroxidation products acting as second messengers of free radicals play important yet not fully understood roles in the pathophysiology of inflammation and various stress-associated disorders. Therefore, the aim of this study was to evaluate the onset of oxidative stress and alterations of enzyme-dependent lipid metabolism resulting from redox imbalance in granulocytes and plasma obtained from patients with psoriasis vulgaris or psoriatic arthritis in comparison to the healthy subjects. The results obtained revealed enhanced activity of pro-oxidant enzymes nicotinamide adenine dinucleotide phosphate (NADPH) and xanthine oxidases in granulocytes with a decrease of enzymatic and non-enzymatic antioxidants in the plasma of psoriatic patients. The nuclear factor erythroid 2–related factor 2 (Nrf2) and its regulators were increased in both forms of psoriasis while heme oxygenase 1 levels were increased only in psoriasis vulgaris. The redox imbalance was associated with decreased levels of phospholipids and of free polyunsaturated fatty acids but with enhanced activity of enzymes involved in lipid metabolism (phospholipase A2, acetylhydrolase PAF, cyclooxygenases 1 and 2) and increased lipid peroxidation products 4-hydroxynonenal, isoprostanes, and neuroprostanes. Increased endocannabinoids and G protein-coupled receptor 55 were observed in both forms of the disease while expression of the cannabinoid type 1 receptor (CB1) was increased only in patients with psoriatic arthritis, which is opposite to the cannabinoid type 2 receptor. This receptor was increased only in psoriasis vulgaris. Changes in protein expression promoted the apoptosis of granulocytes by increased caspases mainly in psoriasis vulgaris. This study indicates that inhibition of the Nrf2 pathway in psoriatic arthritis promotes a redox imbalance. In addition, increased expression of CB1 receptors leads to increased oxidative stress, lipid modifications, and inflammation, which, in turn, may promote the progression of psoriasis into the advanced, arthritic form of the disease.

Kaempferol induces autophagic cell death via IRE1-JNK-CHOP pathway and inhibition of G9a in gastric cancer cells

Kaempferol, a flavonoid, found in traditional medicine, fruits, and vegetables, and an HDAC inhibitor, is a powerful anti-cancer reagent against various cancer cell lines. However, detailed mechanisms involved in the treatment of gastric cancer (GC) using kaempferol are not fully understood. In our study, we investigated the biological activity and molecular mechanism involved in kaempferol-mediated treatment of GC. Kaempferol promoted autophagy and cell death, and increased LC3-I to LC3-II conversion and the downregulation of p62 in GC. Furthermore, our results showed that kaempferol induces autophagic cell death via the activation of the IRE1-JNK-CHOP signaling, indicating ER stress response. Indeed, the inhibition of ER stress suppressed kaempferol-induced autophagy and conferred prolonged cell survival, indicating autophagic cell death. We further showed that kaempferol mediates epigenetic change via the inhibition of G9a (HDAC/G9a axis) and also activates autophagic cell death. Taken together, our findings indicate that kaempferol activates the IRE1-JNK-CHOP signaling from cytosol to nucleus, and G9a inhibition activates autophagic cell death in GC cells.

Antioxidant mechanism of polyphenol-rich Nymphaea nouchali leaf extract protecting DNA damage and attenuating oxidative stress-induced cell death via Nrf2-mediated heme-oxygenase-1 induction coupled with ERK/p38 signaling pathway

This study investigates the polyphenolic composition and antioxidant mechanism of an ethyl acetate fraction of Nymphaea nouchali leaves (NNLE). Various in vitro assays were performed using RAW 264.7 cells to assess the antioxidant effects of NNLE and to understand the underlying molecular mechanism. High-performance liquid chromatography analysis revealed the presence of gallic acid, catechin, epigallocatechin, epicatechin gallate, caffeic acid, luteolin, and kaempferol as the key polyphenolic composition of NNLE. NNLE had a potent ability to scavenge numerous free radicals through hydrogen atom transfer and/or electron donation. In addition, NNLE prevented the damage of DNA and quenched t-BHP induced generation of ROS without showing toxicity. NNLE was found to combat oxidative stress by enhancing the transcription and translation of both primary antioxidant enzymes and phase-II detoxifying enzymes, especially heme-oxygenase-1 (HO-1). NNLE treatment enhanced Nrf2 accumulation in the nucleus and post-translational phosphorylation level of p38 kinase and extracellular signal-regulated kinase (ERK) in RAW 264.7 cells. Treatment with p38 and ERK inhibitors completely suppressed NNLE-induced Nrf2 and HO-1 expression. We also found that p38 and ERK inhibitors significantly antagonized the increase in cell viability and cellular ROS scavenging activity induced by NNLE. The findings of this study provide scientific evidence on the potential of NNLE as a cost-effective and readily available source of natural phytochemicals, along with the strategy to prevent diseases associated with oxidative stress through attenuating disease progression.

Oleuropein and rutin protect against 6-OHDA-induced neurotoxicity in PC12 cells through modulation of mitochondrial function and unfolded protein response

Parkinson’s disease (PD) is a highly prevalent neurodegenerative disorder, often associated with oxidative stress-induced transcriptional changes in dopaminergic neurons. Phenolic antioxidants, oleuropein (OLE) and rutin (RUT) have attracted a great interest due to their potential to counteract oxidative protein aggregation and toxicity. This study aimed at examining the effects of OLE and RUT against 6-OHDA-induced stress response in rat pheochromocytoma cells. When differentiated PC12 cells were exposed to oxidative stress composer 6-OHDA (100 μM, 8 h), a decreased mitochondrial membrane potential (ΔΨm) was observed along with a significant loss of cell viability and apoptotic nuclear changes. Exposure to 6-OHDA resulted in unfolded protein response (UPR) in differentiated PC12 cells as evidenced by an increased level of endoplasmic reticulum (ER)-localized transmembrane signal transducer IRE1α, adaptive response proteins ATF-4 and proapoptotic transcription factor CHOP. OLE or RUT pretreatment (24 h) at low doses (1–50 μM) protected the differentiated PC12 cells from 6-OHDA-induced cytotoxicity as assessed by increased viability, improved ΔΨm and inhibited apoptosis, whereas relatively high doses of OLE or RUT (>50 μM) inhibited cell growth and proliferation, indicating a typical hormetic effect. In hormetic doses, OLE and RUT up-regulated 6-OHDA-induced increase in IRE1α, ATF-4 and inhibited CHOP, PERK, BIP and PDI. 6-OHDA-activated XBP1 splicing was also inhibited by OLE or RUT. The presented results suggest that neuroprotection against 6-OHDA-induced oxidative toxicity may be attributable to neurohormetic effects of OLE or RUT at low doses through regulating mitochondrial functions, controlling persistent protein misfolding, activating and/or amplificating the adaptive response-related signaling pathways, leading to UPR prosurvival output.

Luteolin activates ERK1/2- and Ca2+-dependent HO-1 induction that reduces LPS-induced HMGB1, iNOS/NO, and COX-2 expression in RAW264.7 cells and mitigates acute lung injury of endotoxin mice

OBJECTIVE

Although luteolin has shown to have anti-inflammatory action, no report is available whether luteolin inhibits HMGB1 and protects acute lung injury (ALI) in endotoxin rodents. We hypothesized that HO-1 induction by luteolin might play a crucial role for inhibition of pro-inflammatory mediators including HMGB1 through MAPK signaling in LPS-induced RAW264.7 cells, and it ameliorates ALI of endotoxin mice.

METHODS

The effects of luteolin on the production of pro-inflammatory mediators in LPS-activated RAW264.7 cells and LPS-injected mice were evaluated. The mechanisms were investigated using various signal inhibitors.

RESULTS

Luteolin significantly increased HO-1 expression through ERK1/2 signaling in a time- and concentration-dependent manner. Indeed, luteolin inhibited pro-inflammatory mediators (HMGB1, iNOS/NO, COX-2, and NF-κB activity) in LPS-activated RAW264.7 cells. In addition, PD98059, an ERK1/2 inhibitor, treatment failed to inhibit production of these pro-inflammatory mediators by luteolin. Interestingly, luteolin augmented HO-1 induction through Ca²⁺ influx in RAW264.7 cells. Administration of luteolin significantly inhibited plasma HMGB1 level, and iNOS expression in the lung that resulted in a significant reduction of ALI in endotoxin mice that was reversed by a HO-1 inhibitor, ZnPPIX.

CONCLUSION

Therefore, we conclude that luteolin has a great potential for treatment of ALI and related diseases, where HMGB1 is a therapeutic target.

Luteolin Treatment Protects against Renal Ischemia-Reperfusion Injury in Rats

Renal ischemia-reperfusion (I/R) injury is a common but severe scientific problem. Luteolin has great anti-inflammatory and antioxidant effects. In this study, we studied the effect of luteolin on renal I/R injury in rats. Intragastric administration of luteolin or saline was performed in Sprague-Dawley rats before (40 mg/kg for three days) and after (one day) renal I/R modeling. Kidney and blood samples were harvested to detect the severity of renal injury 24 hours after operation. The results showed that luteolin-treated rats exhibited milder histomorphological changes with lower scores of renal histological lesions; lower blood urea nitrogen and creatinine levels; lower renal malondialdehyde (MDA), 8-oxo-deoxyguanosine (8-OHdG), and myeloperoxidase (MPO) levels; and higher superoxide dismutase (SOD) and catalase (CAT) activities in the kidney. Luteolin attenuated the increased levels of serum and renal tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, renal high mobility group box-1 (HMGB1), and nuclear factor kappa β (NF-κB) expression levels in I/R rats. Furthermore, luteolin treatment significantly reduced renal cell apoptosis and endoplasmic reticulum (ER) stress caused by renal I/R injury. In conclusion, luteolin improved renal function in I/R rats by reducing oxidative stress, neutrophil infiltration, inflammation, renal cell apoptosis, and expression of HMGB1 and NF-κB, and ER stress.

Apigenin in cancer therapy: anti-cancer effects and mechanisms of action

Apigenin is a common dietary flavonoid that is abundantly present in many fruits, vegetables and Chinese medicinal herbs and serves multiple physiological functions, such as strong anti-inflammatory, antioxidant, antibacterial and antiviral activities and blood pressure reduction. Therefore, apigenin has been used as a traditional medicine for centuries. Recently, apigenin has been widely investigated for its anti-cancer activities and low toxicity. Apigenin was reported to suppress various human cancers in vitro and in vivo by multiple biological effects, such as triggering cell apoptosis and autophagy, inducing cell cycle arrest, suppressing cell migration and invasion, and stimulating an immune response. In this review, we focus on the most recent advances in the anti-cancer effects of apigenin and their underlying mechanisms, and we summarize the signaling pathways modulated by apigenin, including the PI3K/AKT, MAPK/ERK, JAK/STAT, NF-κB and Wnt/β-catenin pathways. We also discuss combinatorial strategies to enhance the anti-cancer effect of apigenin on various cancers and its use as an adjuvant chemotherapeutic agent to overcome cancer drug resistance or to alleviate other adverse effects of chemotherapy. The functions of apigenin against cancer stem cells are also summarized and discussed. These data demonstrate that apigenin is a promising reagent for cancer therapy. Apigenin appears to have the potential to be developed either as a dietary supplement or as an adjuvant chemotherapeutic agent for cancer therapy.

DNA Protecting Activities of Nymphaea nouchali (Burm. f) Flower Extract Attenuate t-BHP-Induced Oxidative Stress Cell Death through Nrf2-Mediated Induction of Heme Oxygenase-1 Expression by Activating MAP-Kinases

This study was performed to investigate the antioxidant activities of Nymphaea nouchali flower (NNF) extract and the underlying mechanism using RAW 264.7 cells. The presence of gallic acid, catechin, epicatechin, epigallocatechin, epicatechin gallate, caffeic acid, quercetin, and apigenin in the NNF was confirmed by high-performance liquid chromatography (HPLC). The extract had a very potent capacity to scavenge numerous free radicals. NNF extract was also able to prevent DNA damage and quench cellular reactive oxygen species (ROS) generation induced by tert-Butyl hydroperoxide (t-BHP) with no signs of toxicity. The NNF extract was able to augment the expression of both primary and phase II detoxifying enzyme, resulting in combat the oxidative stress. This is accomplished by phosphorylation of mitogen-activated protein kinase (MAP kinase) (p38 kinase and extracellular signal-regulated kinase (ERK)) followed by enhancing the nuclear translocation of the nuclear factor erythroid 2-related factor 2 (Nrf2). This attenuates cellular ROS generation and confers protection from cell death. Altogether, the results of current study revealed that Nymphaea nouchali flower could be a source of natural phytochemicals that could lead to the development of new therapeutic agents for preventing oxidative stress associated diseases and attenuating disease progression.

Mulberry Anthocyanin Extract Ameliorates Oxidative Damage in HepG2 Cells and Prolongs the Lifespan of Caenorhabditis elegans through MAPK and Nrf2 Pathways

Mulberry anthocyanins possess many pharmacological effects including liver protection, anti-inflammation, and anticancer. The aim of this study was to evaluate whether mulberry anthocyanin extract (MAE) exerts beneficial effects against oxidative stress damage in HepG2 cells and Caenorhabditis elegans. In vitro, MAE prevented cytotoxicity, increased glucose consumption and uptake, and eliminated excessive intracellular free radicals in H₂O₂-induced cells. Moreover, MAE pretreatment maintained Nrf2, HO-1, and p38 MAPK stimulation and abolished upregulation of p-JNK, FOXO1, and PGC-1α that were involved in oxidative stress and insulin signalling modulation. In vivo, extended lifespan was observed in C. elegans damaged by paraquat in the presence of MAE, while these beneficial effects were disappeared in pmk-1 and daf-16 mutants. PMK-1 and SKN-1 were activated after exposure to paraquat and MAE suppressed PMK-1 activation but enhanced SKN-1 stimulation. Our findings suggested that MAE recovered redox status in HepG2 cells and C. elegans that suffered from oxidative stress, which might be by targeting MAPKs and Nrf2.

In Vitro and In Vivo Anti-tumoral Effects of the Flavonoid Apigenin in Malignant Mesothelioma

Malignant mesothelioma (MM) is a tumor arising from mesothelium. MM patients’ survival is poor. The polyphenol 4′,5,7,-trihydroxyflavone Apigenin (API) is a “multifunctional drug”. Several studies have demonstrated API anti-tumoral effects. However, little is known on the in vitro and in vivo anti-tumoral effects of API in MM. Thus, we analyzed the in vitro effects of API on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis, and autophagy of human and mouse MM cells. We evaluated the in vivo anti-tumor activities of API in mice transplanted with MM #40a cells forming ascites. API inhibited in vitro MM cells survival, increased reactive oxygen species intracellular production and induced DNA damage. API activated apoptosis but not autophagy. API-induced apoptosis was sustained by the increase of Bax/Bcl-2 ratio, increase of p53 expression, activation of both caspase 9 and caspase 8, cleavage of PARP-1, and increase of the percentage of cells in subG1 phase. API treatment affected the phosphorylation of ERK1/2, JNK and p38 MAPKs in a cell-type specific manner, inhibited AKT phosphorylation, decreased c-Jun expression and phosphorylation, and inhibited NF-κB nuclear translocation. Intraperitoneal administration of API increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of tumor growth. Our findings may have important implications for the design of MM treatment using API.

Apigenin ameliorates streptozotocin-induced diabetic nephropathy in rats via MAPK-NF-κB-TNF-α and TGF-β1-MAPK-fibronectin pathways

Diabetic nephropathy (DN), a microvascular complication of diabetes, has emerged as an important health problem worldwide. There is strong evidence to suggest that oxidative stress, inflammation, and fibrosis play a pivotal role in the progression of DN. Apigenin has been shown to possess antioxidant, anti-inflammatory, antiapoptotic, antifibrotic, as well as antidiabetic properties. Hence, we evaluated whether apigenin halts the development and progression of DN in streptozotocin (STZ)-induced diabetic rats. Male albino Wistar rats were divided into control, diabetic control, and apigenin treatment groups (5-20 mg/kg po, respectively), apigenin per se (20 mg/kg po), and ramipril treatment group (2 mg/kg po). A single injection of STZ (55 mg/kg ip) was administered to all of the groups except control and per se groups to induce type 1 diabetes mellitus. Rats with fasting blood glucose >250 mg/dl were included in the study and randomized to different groups. Thereafter, the protocol was continued for 8 mo in all of the groups. Apigenin (20 mg/kg) treatment attenuated renal dysfunction, oxidative stress, and fibrosis (decreased transforming growth factor-β1, fibronectin, and type IV collagen) in the diabetic rats. It also significantly prevented MAPK activation, which inhibited inflammation (reduced TNF-α, IL-6, and NF-κB expression) and apoptosis (increased expression of Bcl-2 and decreased Bax and caspase-3). Furthermore, histopathological examination demonstrated reduced inflammation, collagen deposition, and glomerulosclerosis in the renal tissue. In addition, all of these changes were comparable with those produced by ramipril. Hence, apigenin ameliorated renal damage due to DN by suppressing oxidative stress and fibrosis and by inhibiting MAPK pathway.

Fisetin Protects PC12 Cells from Tunicamycin-Mediated Cell Death via Reactive Oxygen Species Scavenging and Modulation of Nrf2-Driven Gene Expression, SIRT1 and MAPK Signaling in PC12 Cells

BACKGROUND

Fisetin (3,7,3',4'-tetrahydroxyflavone) is a dietary flavonol and exhibits antioxidant, anti-inflammatory, and neuroprotective activities. However, high concentration of fisetin is reported to produce reactive oxygen species (ROS), induce endoplasmic reticulum (ER) stress and cause cytotoxicity in cancer cells. The aim of this study is to investigate the cytoprotective effects of low concentration of fisetin against tunicamycin (Tm)-mediated cytotoxicity in neuronal-like catecholaminergic PC12 cells.

METHODS

Cell viability was assayed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and apoptotic and autophagic markers were analyzed by Western blot. Gene expression of unfolded protein response (UPR) and Phase II enzymes was further investigated using RT-Q-PCR or Western blotting. Intracellular ROS level was measured using 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) by a fluorometer. The effects of fisetin on mitogen activated protein kinases (MAPKs) and SIRT1 (Sirtuin 1) signaling pathways were examined using Western blotting and specific inhibitors.

RESULTS

Fisetin (<20 µM) restored cell viability and repressed apoptosis, autophagy and ROS production in Tm-treated cells. Fisetin attenuated Tm-mediated expression of ER stress genes, such as glucose-regulated proteins 78 (GRP78), C/EBP homologous protein (CHOP also known as GADD153) and Tribbles homolog 3 (TRB3), but induced the expression of nuclear E2 related factor (Nrf)2-targeted heme oxygenase (HO)-1, glutamate cysteine ligase (GCL) and cystine/glutamate transporter (xCT/SLC7A11), in both the presence and absence of Tm. Moreover, fisetin enhanced phosphorylation of ERK (extracellular signal-regulated kinase), JNK (c-JUN NH₂-terminal protein kinase), and p38 MAPK. Addition of JNK and p38 MAPK inhibitor significantly antagonized its cytoprotective activity and modulatory effects on UPR. Fisetin also restored Tm-inhibited SIRT1 expression and addition of sirtinol (SIRT1 activation inhibitor) significantly blocked fisetin-mediated cytoprotection. In conclusion, this result shows that fisetin activates Nrf2, MAPK and SIRT1, which may elicit adaptive cellular stress response pathways so as to protect cells from Tm-induced cytotoxicity.

Apigenin exhibits protective effects in a mouse model of d-galactose-induced aging via activating the Nrf2 pathway

The aim of the present research was to study the protective effects and underlying mechanisms of apigenin on d-galactose-induced aging mice.

Neurodegenerative Diseases: Might Citrus Flavonoids Play a Protective Role?

Neurodegenerative diseases (ND) result from the gradual and progressive degeneration of the structure and function of the central nervous system or the peripheral nervous system or both. They are characterized by deterioration of neurons and/or myelin sheath, disruption of sensory information transmission and loss of movement control. There is no effective treatment for ND, and the drugs currently marketed are symptom-oriented, albeit with several side effects. Within the past decades, several natural remedies have gained attention as potential neuroprotective drugs. Moreover, an increasing number of studies have suggested that dietary intake of vegetables and fruits can prevent or delay the onset of ND. These properties are mainly due to the presence of polyphenols, an important group of phytochemicals that are abundantly present in fruits, vegetables, cereals and beverages. The main class of polyphenols is flavonoids, abundant in Citrus fruits. Our review is an overview on the scientific literature concerning the neuroprotective effects of the Citrus flavonoids in the prevention or treatment of ND. This review may be used as scientific basis for the development of nutraceuticals, food supplements or complementary and alternative drugs to maintain and improve the neurophysiological status.

Luteolin inhibited proliferation and induced apoptosis of prostate cancer cells through miR-301

Luteolin is a falvonoid compound derived from Lonicera japonica Thunb. Numerous reports have demonstrated that luteolin has anticancer effects on many kinds of tumors. This study investigated the effects of luteolin on prostate cancer (PCa), assessing the PC3 and LNCaP cells. The cell viability and apoptosis were assessed by performing Cell Counting Kit-8 assay and Annexin V–fluorescein isothiocyanate/propidium iodide double staining. Luteolin was found to inhibit androgen-sensitive and androgen-independent PCa cell lines’ growth and induced apoptosis. To uncover the exact mechanisms and molecular targets, microRNA (miR) array analysis was performed. miR-301 was found to be markedly downregulated. Then, the expression of miR-301 was retrospectively analyzed in the primary PCa tissues by quantitative reverse transcription polymerase chain reaction and in situ hybridization methods. According to the quantitative reverse transcription polymerase chain reaction results of miR-301, the 54 PCa patients were divided into two groups: high and low miR-301 groups. The division indicator is a relative expression ≥5. Compared to the low-expression group, high miR-301 expression was associated with a significantly shorter overall survival (P=0.029). The proapoptotic gene, DEDD2, was predicted to be the direct target of miR-301. It was clarified in accordance with bioinformatics and luciferase activity analyses. The overexpression of miR-301 by plasmid decreased the luteolin effect. Taken together, these results suggest that luteolin inhibits PCa cell proliferation through miR-301, the poor predictive factor of PCa.

Molecular mechanisms of flavonoids in melanin synthesis and the potential for the prevention and treatment of melanoma

Flavonoids are becoming popular nutraceuticals. Different flavonoids show similar or distinct biological effects on different tissues or cell types, which may limit or define their usefulness in cancer prevention and/or treatment application. This review focuses on a few selected flavonoids and discusses their functions in normal and transformed pigment cells, including cyanidin, apigenin, genistein, fisetin, EGCG, luteolin, baicalein, quercetin and kaempferol. Flavonoids exhibit melanogenic or anti-melanogenic effects mainly via transcriptional factor MiTF and/or the melanogenesis enzymes tyrosinase, DCT or TYRP-1. To identify a direct target has been a challenge as most studies were not able to discriminate whether the effect(s) of the flavonoid were from direct targeting or represented indirect effects. Flavonoids exhibit an anti-melanoma effect via inhibiting cell proliferation and invasion and inducing apoptosis. The mechanisms are also multi-fold, via ROS-scavenging, immune-modulation, cell cycle regulation and epigenetic modification including DNA methylation and histone deacetylation. In summary, although many flavonoid compounds are extremely promising nutraceuticals, their detailed molecular mechanism and their multi-target (simultaneously targeting multiple molecules) nature warrant further investigation before advancement to translational studies or clinical trials.

Protective effects of Chaenomeles thibetica extract against carbon tetrachloride-induced damage via the MAPK/Nrf2 pathway

Chaenomeles thibetica extract possesses antioxidant and hepatoprotective effects against carbon tetrachloride-induced damage via the MAPK/Nrf2 pathway.