3',4'-didemethylnobiletin induces phase II detoxification gene expression and modulates PI3K/Akt signaling in PC12 cells

Protective effect of dexmedetomidine against delayed bone healing caused by morphine via PI3K/Akt mediated Nrf2 antioxidant defense system

Background

As a class of analgesics, opioids are frequently used to treat both acute and chronic moderate to severe pain. Patients frequently receive opioid painkillers after orthopedic accidents or surgeries. Evidence suggests that opioid drug users have a 55.1% higher risk of fracture and poor bone repair than non-users of opioid drugs. The key pathogenic alterations in the incidence and progression of poor bone repair are over apoptosis and aging of osteoblasts due to the stress caused by oxidation. Dexmedetomidine (Dex) has been proven to protect against a variety of degenerative illnesses by reducing oxidative stress. However, nothing is known about how it affects bone repair.

Methods

PI3K/Akt/Nrf2 pathway was detected by immunofluorescence and Western blot. SOD, CAT, JC-1, dihydroethidium and mitosox were used in the Oxidative Stress. Micro-CT, H&E and Masson's staining, immunohistochemically were performed to evaluate the therapeutic effects of DEX on calvarial defects in the morphine-induced rat model.

Results

We found that morphine-induced an imbalance in the metabolism and catabolism of primary rat Osteoblasts. However, these conditions could be inhibited by DEX treatment. In the meantime, DEX induced the expression of Nrf2-regulated antioxidant enzymes such as NQO1, HO-1, GCLm, GCLc, and TrxR1. DEX-mediated Nrf2 activation is linked to the PI3K/Akt signaling system. Furthermore, it has been established that intravenous DEX enhanced the growth of bone healing in a model of a surgically produced rat cranial lesion.

Conclusion

This is the first description of the unique DEX mechanism acting as a Nrf2 activator against morphine-mediated oxidative harm, raising the possibility that the substance may be used to prevent bone defects.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

Mechanisms of action of non-enzymatic antioxidants to control oxidative stress during in vitro follicle growth, oocyte maturation, and embryo development

In vitro follicle growth and oocyte maturation still has a series of limitations, since not all oocytes matured in vitro have the potential to develop in viable embryos. One of the factors associated with low oocyte quality is the generation of reactive oxygen species (ROS) during in vitro culture. Therefore, this review aims to discuss the role of non-enzymatic antioxidants in the control of oxidative stress during in vitro follicular growth, oocyte maturation and embryonic development. A wide variety of non-enzymatic antioxidants (melatonin, resveratrol, L-ascorbic acid, L-carnitine, N-acetyl-cysteine, cysteamine, quercetin, nobiletin, lycopene, acteoside, mogroside V, phycocyanin and laminarin) have been used to supplement culture media. Some of them, like N-acetyl-cysteine, cysteamine, nobiletin and quercetin act by increasing the levels of glutathione (GSH), while melatonin and resveratrol increase the expression of antioxidant enzymes and minimize oocyte oxidative stress. L-ascorbic acid reduces free radicals and reactive oxygen species. Lycopene positively regulates the expression of many antioxidant genes. Additionally, L-carnitine protects DNA against ROS-induced damage, while acteoside and laminarin reduces the expression of proapoptotic genes. Mogrosides increases mitochondrial function and reduces intracellular ROS levels, phycocyanin reduces lipid peroxidation, and lycopene neutralizes the adverse effects of ROS. Thus, it is very important to know their mechanisms of actions, because the combination of two or more antioxidants with different activities has great potential to improve in vitro culture systems.

Biosynthesis of 6- and 7-Mono-Demethylated Nobiletins by a Newly Isolated Strain of Yeast

Demethylated nobiletins (DMNs), which are generally recognized as the metabolites of orally administered nobiletin, are widely investigated. However, studies related to 8-demethylated-nobiletin, 7-demethylated-nobiletin (7DMN), and 6-demethylated-nobiletin (6DMN) are limited due to the lack of a synthesis method. In this study, a strain of microbe able to metabolize nobiletin was isolated from aged orange peel. Internal transcribed spacers (ITS) rRNA sequencing analysis showed it belonged to the yeast family, Filobasidium magnum specie. High-performance liquid chromatography (HPLC), HPLC-MS, and ¹³C NMR results proved that the metabolites were 7DMN and 6DMN. Growth curves of the isolated yeast were studied at different temperatures, media pH, NaCl, and glucose concentrations. Meanwhile, factors that influence the demethylation efficiencies were also investigated. This study lays the groundwork for the investigation of the biological functions of these two compounds and opens a new window for further research of the metabolic fate of nobiletin in the human body.

Protective Effect of Flavonoids against Methylglyoxal-Induced Oxidative Stress in PC-12 Neuroblastoma Cells and Its Structure-Activity Relationships

Methylglyoxal-induced oxidative stress and cytotoxicity are the main factors causing neuronal death-related, diabetically induced memory impairment. Antioxidant and anti-apoptotic therapy are potential intervention strategies. In this study, 25 flavonoids with different substructures were assayed for protecting PC-12 cells from methylglyoxal-induced damage. A structure-activity relationship (SAR) analysis indicated that the absence of the double bond at C-2 and C-3, substitutions of the gallate group at the 3 position, the pyrogallol group at the B-ring, and the R configuration of the 3 position enhanced the protection of flavan-3-ols, and a hydroxyl substitution at the 4' and meta-positions were important for the protection of flavonol. These SARs were further confirmed by molecular docking using the active site of the Keap1-Nrf2 complex as the receptor. The mechanistic study demonstrated that EGCG with the lowest EC₅₀ protected the PC-12 cells from methylglyoxal-induced damage by reducing oxidative stress via the Nrf2/Keap1/HO-1 and Bcl-2/Bax signaling pathways. These results suggested that flavan-3-ols might be a potential dietary supplement for protection against diabetic encephalopathy.

Nobiletin-induced partial abrogation of deleterious effects of AKT inhibition on preimplantation bovine embryo development in vitro

During preimplantational embryo development, PI3K/AKT regulates cell proliferation and differentiation and nobiletin modulates this pathway to promote cell survival. Therefore, we aimed to establish whether, when the AKT cascade is inhibited using inhibitors III and IV, nobiletin supplementation to in vitro culture media during the minor (2 to 8-cell stage, MNEGA) or major (8 to 16-cell stage, MJEGA) phases of EGA is able to modulate the development and quality of bovine embryos. In vitro zygotes were cultured during MNEGA or MJEGA phase in SOF + 5% FCS or supplemented with: 15 μM AKT-InhIII; 10 μM AKT-InhIV; 10 μM nobiletin; nobiletin+AKT-InhIII; nobiletin+AKT-InhIV; 0.03% DMSO. Embryo development was lower in treatments with AKT inhibitors, while combination of nobiletin with AKT inhibitors was able to recover their adverse developmental effect and also increase blastocyst cell number. The mRNA abundance of GPX1, NFE2L2, and POU5F1 was partially increased in 8- and 16-cell embryos from nobiletin with AKT inhibitors. Besides, nobiletin increased the p-rpS6 level whether or not AKT inhibitors were present. In conclusion, nobiletin promotes bovine embryo development and quality and partially recovers the adverse developmental effect of AKT inhibitors which infers that nobiletin probably uses another signalling cascade that PI3K/AKT during early embryo development in bovine.

Flavonoids with Potential Anti-Amyloidogenic Effects as Therapeutic Drugs for Treating Alzheimer's Disease

Alzheimer's disease (AD) is a central neurodegenerative disease generally among the elderly; it accounts for approximately 50-75%of total cases of dementia patients and poses a serious threat to physical and mental health. Currently available treatments for AD mainly relieves its symptoms, and effective therapy is urgently needed. Deposition of amyloid-β protein in the brain is an early and invariant neuropathological feature of AD. Currently the main efforts in developing anti-AD drugs focus on anti-amyloidogenic therapeutics that prevent amyloid-β production or aggregation and decrease the occurrence of neurotoxic events. The results of an increasing number of studies suggest that natural extracts and phytochemicals have a positive impact on brain aging. Flavonoids belong to the broad group of polyphenols and recent data indicate a favorable effect of flavonoids on brain aging. In this review, we collect relevant discoveries from 1999 to 2021, discuss 75 flavonoids that effectively influence AD pathogenesis, and summarize their functional mechanisms in detail. The data we have reviewed show that, these flavonoids belong to various subclasses, including flavone, flavanone, biflavone, etc. Our results provide a reference for further study of the effects of flavonoids on AD and the progress of anti-AD therapy.

Dietary 5-demethylnobiletin modulates xenobiotic-metabolizing enzymes and ameliorates colon carcinogenesis in benzo[a]pyrene-induced mice

The intake of common polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (BaP), is strongly correlated to the initiation of colon cancer. BaP is a well-known pro-carcinogen that is metabolically activated by xenobiotic-metabolizing enzymes. Studies indicate that polymethoxyflavones, including 5-demethylnobiletin (5-DMNB), exhibit anti-inflammatory and anti-carcinogenic properties. However, the effects of 5-DMNB on xenobiotic-metabolizing enzymes and BaP-induced carcinogenesis remain unclear. The combination of BaP and a promoting agent-dextran sulfate sodium (DSS)-has been demonstrated to induce tumors in mouse models. Thus, this study aimed to determine the protective effect of 5-DMNB on carcinogen biotransformation and BaP/DSS-induced colon carcinogenesis. Our results showed that 5-DMNB had a substantial inhibitory effect on CYP1B1 induced by BaP and upregulated the detoxification enzymes UDP-glucuronosyltransferases (UGTs) and glutathione S-transferases (GSTs). Furthermore, subsequent analyses confirmed that the dietary administration of 5-DMNB markedly ameliorated tumor formation in BaP/DSS-treated mice. Exposure to BaP/DSS also significantly elevated TNF-α levels, and the administration of 5-DMNB reversed this increase. Taken together, we determined that 5-DMNB attenuates BaP/DSS-induced colon cancer through the regulation of inflammation and xenobiotic-metabolizing enzymes. These results indicate that 5-DMNB has significant potential as a novel chemopreventive agent for preventing carcinogen activation and inflammation-associated carcinogenesis.

Citrus flavonoids and their antioxidant evaluation

The antioxidant ability is the link and bridge connecting a variety of biological activities. Citrus flavonoids play an essential role in regulating oxidative stress and are an important source of daily intake of antioxidant supplements. Many studies have shown that citrus flavonoids promote health through antioxidation. In this review, the biosynthesis, composition and distribution of citrus flavonoids were concluded. The detection methods of antioxidant capacity of citrus flavonoids were divided into four categories: chemical, cellular, animal and clinical antioxidant capacity evaluation systems. The modeling methods, applicable scenarios, and their relative merits were compared based on these four systems. The antioxidant functions of citrus flavonoids under different evaluation systems were also discussed, especially the regulation of the Nrf2-antioxidases pathway. Some shortcomings in the current research were pointed out, and some suggestions for progress were put forward.

Nobiletin Regulates ROS/ADMA/DDAHII/eNOS/NO Pathway and Alleviates Vascular Endothelium Injury by Iron Overload

Iron overload is harmful to health and associates with intracellular excessive reactive oxygen species (ROS) generation. Nobiletin (Nob) is known to be antioxidant and anti-inflammatory. However, whether Nob can protect endothelial cells against iron overload has not been studied, and the specific mechanism has not yet been elucidated. In this study, we have identified the protective effects of Nob, and its underlying molecular mechanism in human umbilical vein endothelial cells (HUVECs) suffered from iron overload via ROS/ADMA/DDAHII/eNOS/NO pathway. We found that compared with 50 μM iron dextran treatment, co-treatment with 20 μM Nob increased cell viability and decreased lactate dehydrogenase activity. Besides, Nob could upregulate DDAHII expression and activity, promote eNOS phosphorylation to produce more NO, reduce ADMA content, and therefore increase superoxide dismutase, catalase, and glutathione peroxidase activities, and decrease malondialdehyde level and ROS generation. Nob also inhibited mitochondrial permeability transition pore (mPTP) openness and cleaved caspase-3 expression, and decreased apoptosis induced by iron overload. These results were consistent when Nob was replaced by the positive control reagents L-arginine (a competitive substrate of ADMA), cyclosporin A (an mPTP closing agent), or edaravone (a free radical scavenger). The addition of pAD/DDAHII-shRNA adenovirus reversed the above effects of Nob. These data suggested that the protective mechanism of Nob was to inhibit ROS burst, upregulate DDAHII expression and activity, promote eNOS phosphorylation, produce NO, reduce ADMA content, and ultimately alleviate iron overload damage in vascular endothelium.

In-vivo biotransformation of citrus functional components and their effects on health

Citrus, one of the most popular fruits worldwide, contains various functional components, including flavonoids, dietary fibers (DFs), essential oils (EOs), synephrines, limonoids, and carotenoids. The functional components of citrus attract special attention due to their health-promoting effects. Food components undergo complex biotransformation by host itself and the gut microbiota after oral intake, which alters their bioaccessibility, bioavailability, and bioactivity in the host body. To better understand the health effects of citrus fruits, it is important to understand the in-vivo biotransformation of citrus functional components. We reviewed the biotransformation of citrus functional components (flavonoids, DFs, EOs, synephrines, limonoids, and carotenoids) in the body from their intake to excretion. In addition, we described the importance of biotransformation in terms of health effects. This review would facilitate mechanistic understanding of the health-promoting effect of citrus and its functional components, and also provide guidance for the development of health-promoting foods based on citrus and its functional components.

Synergistic anticancer effects of curcumin and 3',4'-didemethylnobiletin in combination on colon cancer cells

Chemoprevention strategies employing the use of multiple dietary bioactive components and their metabolites in combination offer advantages due to their low toxicity and potential synergistic interactions. Herein, for the first time, we studied the combination of curcumin and 3',4'-didemethylnobiletin (DDMN), a primary metabolite of nobiletin, to determine their combinatory effects in inhibiting growth of human colon cancer cells. Isobologram analysis revealed a synergistic interaction between curcumin and DDMN in the inhibition of cell growth of HCT116 colon cancer cells. The combination treatment induced significant G₂ -M cell-cycle arrest and extensive apoptosis, which greatly exceeded the effects of individual treatments with curcumin or DDMN. Proteins associated with these heightened anticarcinogenic effects were p53, p21, HO-1, c-poly(ADP-ribose) polymerase, Cdc2, and Cdc25c; each of the proteins was confirmed to be substantially impacted by the combination treatment, more than by individual treatments alone. Interestingly, an increase in the stability of curcumin was also observed with the presence of DDMN in cell culture medium, which could offer an explanation in part for the synergistic interaction between curcumin and DDMN. This newly identified synergy between curcumin and DDMN should be explored further to determine its chemopreventive potential against colon cancer in vivo. PRACTICAL APPLICATION: This study identifies for the first time the synergistic inhibition of colon cancer cell growth by the dietary component curcumin present in turmeric, in combination with a metabolite of nobiletin, a unique citrus flavonoid. The synergism of the combination may be due to cell-cycle arrest and apoptosis induced by the combination as well as an improvement in the stability of curcumin as a result of the antioxidant property of the nobiletin metabolite. These significant findings of synergism between curcumin and the nobiletin metabolite could offer potential chemopreventive value against colon cancer.

Inhibiting the PI3K/AKT/NF-κB signal pathway with nobiletin for attenuating the development of osteoarthritis: in vitro and in vivo studies

Osteoarthritis (OA), an age-related degenerative disease, is characterized by progressive degradation of the articular cartilage. There is increasing evidence that nobiletin (NOB) exerts special biological functions in a variety of diseases. However, whether it protects against OA remains unknown. In this study, we investigated the anti-inflammatory and chondroprotective effects of NOB on IL-1β-induced human OA chondrocytes and in the surgical DMM mice OA models. In vitro, NOB treatment completely suppressed the overproduction of pro-inflammatory mediators, including PGE2, NO, COX-2, iNOS, TNF-α and IL-6 in IL-1β-induced human OA chondrocytes. Moreover, NOB exerted a potent inhibitory effect on the expression of MMP-13 and ADAMTS-5 as well as the degradation of aggrecan and collagen-II, which leads to the degradation of the extracellular matrix. Furthermore, NOB dramatically suppressed the IL-1β-stimulated phosphorylation of PI3K/Akt and activation of NF-κB in human OA chondrocytes. In addition, treatment with NOB not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in mice OA models. In conclusion, our study suggests that NOB holds novel therapeutic potential for the treatment of OA.

Potential Benefits of Nobiletin, A Citrus Flavonoid, against Alzheimer's Disease and Parkinson's Disease

Alzheimer’s disease (AD), which is characterized by the presence of amyloid-β (Aβ) plaques and neurofibrillary tangles, accompanied by neurodegeneration, is the most common form of age-related neurodegenerative disease. Parkinson’s disease (PD) is the second most common neurodegenerative disease after AD, and is characterized by early prominent loss of dopaminergic neurons in the substantia nigra pars compacta. As currently available treatments are not able to significantly alter the progression of these diseases, successful therapeutic and preventive interventions are strongly needed. In the course of our survey of substances from natural resources having anti-dementia and neuroprotective activity, we found nobiletin, a polymethoxylated flavone from the peel of Citrus depressa. Nobiletin improved cognitive deficits and the pathological features of AD, such as Aβ pathology, hyperphosphorylation of tau, and oxidative stress, in animal models of AD. In addition, nobiletin improved motor and cognitive deficits in PD animal models. These observations suggest that nobiletin has the potential to become a novel drug for the treatment and prevention of neurodegenerative diseases such as AD and PD.

Inhibitory effects of nobiletin and its major metabolites on lung tumorigenesis

The present study demonstrated that the oral administration of nobiletin significantly inhibited lung carcinogenesis in mice, and these chemopreventive effects could be attributed to its metabolites that showed potent anti-cancer effects.

Effects of low dose of aliskiren on isoproterenol-induced acute myocardial infarction in rats

This study examined the effects of aliskiren (Ali) (direct renin inhibitor) on serum cardiac enzymes (LDH and CK-MB), electrocardiography (ECG) changes, myocardial oxidative stress markers (MDA, CAT, and GSH) and the expression of Bcl2, HO-1, and Nrf2 genes in isoproterenol (ISO)-induced myocardial infarction (MI). A total of 40 male albino rats were allocated into four groups, (1) normal control (NC) group, (2) Ali group (rats received Ali at 10 mg/kg/day p.o. for 5 days), (3) ISO group (rats received ISO 150 mg/kg i.p. for two consecutive days at 24 h intervals), and (4) Ali + ISO group (rats received ISO + Ali at 10 mg/kg/day p.o. for 5 days from the 2^nd dose of ISO). ISO group showed significant rise in serum cardiac enzymes (CK-MB and LDH), myocardial damage scores, myocardial MDA, HO-1, myocardial Nrf2 expression with significant reduction in myocardial antioxidants (CAT and GSH), and Bcl2 expression compared to the normal group (p < 0.05). ECG showed ST segment elevation, prolonged QT interval and QRS complex, and increased heart rate in ISO group. Co-administration of Ali and ISO caused significant increase in cardiac enzymes and morphology with increase in MDA, serum K, and creatinine with significant decrease in Bcl2, HO-1, and Nrf2 without significant changes in ECG parameters compared to ISO group. We concluded that low dose of Ali seems to exacerbate the myocardial injury in ISO-MI, which might be due to the enhanced oxidative stress and apoptosis.

Two sesquiterpene aminoquinones protect against oxidative injury in HaCaT keratinocytes via activation of AMPKα/ERK-Nrf2/ARE/HO-1 signaling

AIMS

To investigate the cytoprotective effects of two sesquiterpene aminoquinones isolated from the marine sponge Dysidea fragilis, Dysidaminone H (DA8) and 3'-methylamino-avarone (DA14), we examined their effects against hydrogen peroxide (H₂O₂)-induced oxidative injury in human keratinocyte cell line and elucidated the underlying mechanisms.

MAIN METHODS

Cell viability was detected using a CCK-8 assay kit. Intracellular reactive oxygen species (ROS) production was measured by fluorescence of 2, 7-Dichlorodi-hydrofluorescein diacetate (DCFH-DA). Messenger RNA and protein expression were measured by real-time quantitative PCR and western blotting analysis. Immunocytochemistry was performed to determine the intracellular location of nuclear factorerythroid 2 p45 related factor 2 (Nrf2). The antioxidant response element (ARE)-luciferase reporter gene assay and RNA interference were used to establish the role of ARE and Nrf2.

KEY FINDINGS

DA8 and DA14 (DAs) resisted H₂O₂induced decline of cell viability by inhibiting the accumulation of ROS. Meanwhile, DAs increased HO-1 expression and ARE activity and induced Nrf2 expression, as well as the accumulation of Nrf2 in the cell nucleus. However, silencing of Nrf2 abolished DAs-induced HO-1 expression and ARE luciferase activation. In addition, DAs induced the phosphorylation of both cyclic AMP-activated protein kinase-α (AMPKα) and extracellular signal-regulated kinase (ERK), while specific inhibitors of AMPKα and ERK abrogated HO1 upregulation and Nrf2 activation.

SIGNIFICANCE

DAs provided cytoprotective effects against H₂O₂-induced cytotoxicity by activation of the Nrf2/ARE/HO-1 pathway via phosphorylation of AMPKα and ERK. The findings suggested that DA8 and DA14 might be the candidate therapeutic agents for skin diseases caused by oxidative injury.

Diallyl trisulfide, a garlic polysulfide protects against As-induced renal oxidative nephrotoxicity, apoptosis and inflammation in rats by activating the Nrf2/ARE signaling pathway

BACKGROUND

Arsenic (As) contamination is an extremely dangerous global environmental problem as it can enter into the food chain and become bio-accumulated, endangering human health. Chronic As intoxication leads to undesirable toxic effects in various organ systems of the body, especially the kidney. Diallyl trisulfide (DATS) is an organosulfur compound which has been widely known for its uses as antibacterial, antitumorogenic, antioxidant agent and has been also reported to have anti-apoptotic and anti-inflammatory properties.

PURPOSE

In the present work, we intend to investigate the protective role of DATS, a garlic organosulfur compound in preventing the As-induced oxidative stress mediated renal injury in rats. Study design The activity of DATS to antagonize As-induced renal oxidative toxicity was analyzed using rats as an in vivo model.

METHODS

We investigated the nephroprotective effect of DATS on As treated rats by performing various serological, biochemical, molecular and histological studies. The activation of Nrf2 was investigated using western blot.

RESULTS

The data showed that As exposure significantly increased the serum and urine nephritic, oxidative stress, apoptosis and inflammatory markers in the renal tissue of rats. As intoxication also decreased the antioxidant status of the renal tissue along with the disturbances in the membrane bound ATPases. As nephrotoxicity was further confirmed with the altered morphological and ultrastructural changes in the renal tissue. Conversely, the DATS pre-administration effectively recuperate the altered renal variables by As, which has been further supported by the histological and ultrastructural observations. This counteraction was achieved partially via the activation of Nrf2-ARE pathway through the activation of Akt.

CONCLUSION

These findings explicate the prospective use of DATS as a promising organosulfur compound against As-induced renal oxidative dysfunction in rats.

NGF Attenuates High Glucose-Induced ER Stress, Preventing Schwann Cell Apoptosis by Activating the PI3K/Akt/GSK3β and ERK1/2 Pathways

Diabetic peripheral neuropathy (DPN) is one of the most common and troublesome complications of diabetes mellitus. It has been demonstrated that nerve growth factor (NGF) exerts a pivotal role in the regulation of neuronal growth and the promotion of DPN recovery. However, the exact molecular mechanisms are not well understood. Recent studies have indicated that as a novel therapeutic target, endoplasmic reticulum (ER) stress participates in the onset and progression of DPN. In the present study, it has been demonstrated that NGF prevents the sciatic nerve from degeneration and demyelination in DPN rats. Thus, RSC 96 cells, which retain the characteristic features of Schwann cells (SCs), were cultured in medium containing 30 mM glucose (high glucose, HG) to mimic SCs in DPN mice. The 50-ng/ml dose of NGF was identified to be the optimal concentration for treating an excessive ER stress level under HG conditions for 24 h. We found that NGF treatment significantly inhibits HG-induced ER stress and subsequently suppresses ER-related apoptosis. Further, NGF administration also activates the upstream signaling pathway of ER stress, PI3K/Akt/GSK3β signaling and ERK1/2 signaling. Co-treatment with the PI3K inhibitor LY294002 or ERK1/2 inhibitor U0126 significantly reverses the protective role of NGF on HG-induced excessive ER stress and subsequent apoptosis. These observations suggest that the neuroprotective role of NGF in DPN is mediated by the inhibition of excessive ER stress via the activation of the PI3K/Akt/GSK3β and ERK1/2 signaling pathways.

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.

The Multifunctional Effects of Nobiletin and Its Metabolites In Vivo and In Vitro

Nobiletin (NOB) chemically known as 5,6,7,8,3′,4′-hexamethoxyflavone is a dietary polymethoxylated flavonoid found in Citrus fruits. Recent evidences show that NOB is a multifunctional pharmaceutical agent. The various pharmacological activities of NOB include neuroprotection, cardiovascular protection, antimetabolic disorder, anticancer, anti-inflammation, and antioxidation. These events may be underpinned by modulation of signaling cascades, including PKA/ERK/MEK/CREB, NF-κB, MAPK, Ca²⁺/CaMKII, PI3K/Akt1/2, HIF-1α, and TGFβ signaling pathways. The metabolites may exhibit stronger beneficial effects than NOB on diseases pathogenesis. The biological activities of NOB have been clarified on many systems. This review aims to discuss the pharmacological effects of NOB with specific mechanisms of actions. NOB may become a promising candidate for potential drug development. However, further investigations of NOB on specific intracellular targets and clinical trials are still needed, especially for in vivo medical applications.

[A new strategy for preventive and functional therapeutic methods for dementia--approach using natural products]

Alzheimer's disease (AD) has become a serious social problem in Japan. However, effective preventive and fundamental therapeutic methods for AD have not yet been developed. Using a new strategy in the course of our survey of numerous natural resouces having neurotrophic activity, we isolated a variety of active constituents and proved their pharmacological properties. As a result, we successfully found nobiletin, a compound with anti-dementia activity that comes from citrus peels. Also, we have demonstrated that nobiletin ameliorates cognitive impairment in several dementia model animals such as chronically amyloid β(Aβ) infused rats, amyloid precursor protein transgenic (APPTg) mice, olfactory-bulbectomized (OBX) mice, N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801)-treated mice, senescence-accelated mice and bilaterial common carotid arteries occlusion mice. In a APPTg mouse of AD, nobiletin greatly improved memory impairment, and this was accompanied by a marked decrease in Aβ deposition. Also, in OBX mice memory impairment was markedly recoverd by nobiletin, accompanied by improvement of a decrease indensity of cholinergic neurons. Interestingly, nobiletin improves age-related congnitive impairment and decreased hyperphosphorylation of tau as well as oxidative stress in senescence-accelerated mice. In cultured cells, nobiletin reversed the Aβ-induced inhibition of glutamate-induced increases in cAMP response element binding protein (CREB) phosphorylation and modulated gen expression of thioredoxin-interacting protein and NMDA resceptor subunits. These results suggest that nobiletin prevents memory impairment and exhibits a protecting action against neurodgeneration in AD model animals. Nobiletin and citrus peels thus have potential as functional foods for prevention of dementia.

Paeonol and danshensu combination attenuates apoptosis in myocardial infarcted rats by inhibiting oxidative stress: Roles of Nrf2/HO-1 and PI3K/Akt pathway

Paeonol and danshensu is the representative active ingredient of traditional Chinese medicinal herbs Cortex Moutan and Radix Salviae Milthiorrhizae, respectively. Paeonol and danshensu combination (PDSS) has putative cardioprotective effects in treating ischemic heart disease (IHD). However, the evidence for the protective effect is scarce and the pharmacological mechanisms of the combination remain unclear. The present study was designed to investigate the protective effect of PDSS on isoproterenol (ISO)-induced myocardial infarction in rats and to elucidate the potential mechanism. Assays of creatine kinase-MB, cardiac troponin I and T and histopathological analysis revealed PDSS significantly prevented myocardial injury induced by ISO. The ISO-induced profound elevation of oxidative stress was also suppressed by PDSS. TUNEL and caspase-3 activity assay showed that PDSS significantly inhibited apoptosis in myocardia. In exploring the underlying mechanisms of PDSS, we found PDSS enhanced the nuclear translocation of Nrf2 in myocardial injured rats. Furthermore, PDSS increased phosphorylated PI3K and Akt, which may in turn activate antioxidative and antiapoptotic signaling events in rat. These present findings demonstrated that PDSS exerts significant cardioprotective effects against ISO-induced myocardial infarction in rats. The protective effect is, at least partly, via activation of Nrf2/HO-1 signaling and involvement of the PI3K/Akt cell survival signaling pathway.

Safflower yellow B suppresses HepG2 cell injury induced by oxidative stress through the AKT/Nrf2 pathway

Oxidative stress plays an important role in the pathogenesis of various liver diseases. Safflower yellow B (SYB) has been reported to protect the brain against damage induced by oxidative stress; however, whether SYB can also protect hepatocytes from oxidative stress remains unknown. In the present study, to determine whether pre-treatment with SYB reduces hydrogen peroxide (H2O2)‑induced oxidative stress in HepG2 cells, we investigated H2O2-induced oxidative damage to HepG2 cells treated with or without SYB. Cell viability was measured by MTT assay and cytotoxicity was evaluated by lactate dehydrogenase (LDH) assay. The activities of the antioxidant enzymes, glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were determined using respective kits. Intracellular reactive oxygen species (ROS) accumulation in the HepG2 cells was monitored using the fluorescent marker, 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA). Cell apoptosis was evaluated by determining the activity of caspase-3 and by Annexin V/propidium iodide (PI) double staining. Protein expression levels were measured by western blot analysis, and the levels of related cellular kinases were also determined. H2O2 induced pronounced injury to the HepG2 cells, as evidenced by increased levels of malondialdehyde (MDA) and ROS, the decreased activity of SOD and GSH-Px, the increased activitation of caspase-3 and cell apoptosis, and the loss of mitochondrial membrane potential. SYB significantly inhibited the damaging effects of H2O2, indicating that it protected the cells against H2O2-induced oxidative damage. Moreover, pre-treatment with SYB increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1) and NAD(P)H dehydrogenase, quinone 1 (NQO1) which are peroxiredoxins. SYB also significantly increased the phosphorylation of AKT. However, this inductive effect was blunted in the presence of the AKT inhibitor, LY294002. The findings of our study suggest that the activation of the AKT/Nrf2 pathway is involved in the cytoprotective effects of SYB against oxidative stress. Our findings provide new insight into the cytoprotective effects of SYB and the possible mechanisms underlying these effects. Thus, SYB may prove to be of therapeutic value for the treatment of various liver diseases.

Disease chemopreventive effects and molecular mechanisms of hydroxylated polymethoxyflavones

Recent increasing attention in research of polymethoxyflavones (PMFs) from Citrus genus because of their wide range of biological properties has been reported in various studies. Hydroxylated PMFs are unique flavones and recognized as the methoxy group of PMFs that is substituted for hydroxyl one. Hydroxylated PMFs are naturally existed in citrus peel and other plants as well as occurred as metabolites of their PMFs counterparts. Several in vitro and in vivo studies have documented the chemopreventive effects of hydroxylated PMFs including anti-cancer, anti-inflammation, anti-atherosclerosis, and neuroprotection. They function to regulate cell death, proliferation, differentiation, repair, and metabolism through acting on modulation of signaling cascade, gene transcription, and protein function and enzyme activity. The mechanisms of action of hydroxylated PMFs in disease chemoprevention depend on their structure, the number, and position of hydroxyl group. Although the efficacy of hydroxylated PMFs in chemoprevention and the oral bioavailability requires further investigation, they still provide great promise for improving human health. This review highlights the recent published data of hydroxylated PMFs with chemopreventive potential and the underlying mechanism involved.

Protective efficacy of carnosic acid against hydrogen peroxide induced oxidative injury in HepG2 cells through the SIRT1 pathway

Carnosic acid (CA), found in rosemary, has been reported to have antioxidant and antiadipogenic properties. Here, we investigate the molecular mechanism by which CA inhibits hydrogen peroxide (H2O2)-induced injury in HepG2 cells. Cells were pretreated with 2.5–10 μmol/L CA for 2 h and then exposed to 3 mmol/L H2O2 for an additional 4 h. CA dose-dependently increased cell viability and decreased lactate dehydrogenase activities. Pretreatment with CA completely attenuated the inhibited expression of manganese superoxide dismutase (MnSOD) and the B-cell lymphoma-extra large (Bcl-xL), and reduced glutathione activity caused by H2O2, whereas it reversed reactive oxygen species accumulation and the increase in cleaved caspase-3. Importantly, sirtuin 1 (SIRT1), a NAD+-dependent deacetylase, was significantly increased by CA. Considering the above results, we hypothesized that SIRT1 may play important roles in the protective effects of CA in injury induced by H2O2. As expected, SIRT1 suppression by Ex527 (6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide) and siRNA-mediated SIRT1 silencing (si-SIRT1) significantly aggravated the H2O2-induced increased level of cleaved caspase-3 but greatly reduced the decreased expression of MnSOD and Bcl-xL. Furthermore, the positive regulatory effect of CA was inhibited by si-SIRT1. Collectively, the present study indicated that CA can alleviate H2O2-induced hepatocyte damage through the SIRT1 pathway.

Retino-protective effect of Bucida buceras against oxidative stress induced by H2O2 in human retinal pigment epithelial cells line

BACKGROUND

Reactive Oxygen Species (ROS) impair the physiological functions of Retinal Pigment Epithelial (RPE) cells, which are known as one major cause of age-related macular degeneration and retinopathy diseases. The purpose of this study is to explore the cytoprotective effects of the antioxidant Bucida buceras extract in co-treatment with hydrogen peroxide (H2O2) delivery as a single addition or with continuous generation using glucose oxidase (GOx) in ARPE-19 cell cultures. The mechanism of Bucida buceras extract is believed to be associated with their antioxidant capacity to protect cells against oxidative stress.

METHODS

A comparative oxidative stress H2O2-induced was performed by addition and enzymatic generation using glucose oxidase on human retinal pigment epithelial cells line. H2O2-induced injury was measured by toxic effects (cell death and apoptotic pathway) and intracellular redox status: glutathione (GSH), antioxidant enzymes (catalase and glutathione peroxidase) and reducing power (FRAP). The retino-protective effect of co-treatment with Bucida buceras extract on H2O2-induced human RPE cell injury was investigated by cell death (MTT assay) and oxidative stress biomarkers (H2O2, GSH, CAT, GPx and FRAP).

RESULTS

Bucida buceras L. extract is believed to be associated with the ability to prevent cellular oxidative stress. When added as a pulse, H2O2 is rapidly depleted and the cytotoxicity analyses show that cells can tolerate short exposure to high peroxide doses delivered as a pulse but are susceptible to lower chronic doses. Co-treatment with Bucida buceras was able to protect the cells against H2O2-induced injury. In addition to preventing cell death treatment with antioxidant plant could also reverse the significant decrease in GSH level, catalase activity and reducing power caused by H2O2.

CONCLUSION

These findings suggest that Bucida buceras could protect RPE against ocular pathogenesis associated with oxidative stress induced by H2O2-delivered by addition and enzymatic generation.

Peroxynitrite-mediated glyoxalase I epigenetic inhibition drives apoptosis in airway epithelial cells exposed to crystalline silica via a novel mechanism involving argpyrimidine-modified Hsp70, JNK, and NF-κB

Glyoxalase I (Glo1) is a cellular defense enzyme involved in the detoxification of methylglyoxal (MG), a cytotoxic by-product of glycolysis, and MG-derived advanced glycation end products (AGEs). Argpyrimidine (AP), one of the major AGEs coming from MG modification of protein arginines, is a proapoptotic agent. Crystalline silica is a well-known occupational health hazard, responsible for a relevant number of pulmonary diseases. Exposure of cells to crystalline silica results in a number of complex biological responses, including apoptosis. The present study was aimed at investigating whether, and through which mechanism, Glo1 was involved in Min-U-Sil 5 crystalline silica-induced apoptosis. Apoptosis, by TdT-mediated dUTP nick-end labeling assay, and transcript and protein levels or enzymatic activity, by quantitative real-time PCR, Western blot, and spectrophotometric methods, respectively, were evaluated in human bronchial BEAS-2B cells exposed or not (control) to crystalline silica and also in experiments with appropriate inhibitors. Reactive oxygen species were evaluated by coumarin-7-boronic acid or Amplex red hydrogen peroxide/peroxidase methods for peroxynitrite (ONOO(-)) or hydrogen peroxide (H2O2) measurements, respectively. Our results showed that Min-U-Sil 5 crystalline silica induced a dramatic ONOO(-)-mediated inhibition of Glo1, leading to AP-modified Hsp70 protein accumulation that, in a mechanism involving JNK and NF-κB, triggered an apoptotic mitochondrial pathway. Inhibition of Glo1 occurred at both functional and transcriptional levels, the latter occurring via ERK1/2 MAPK and miRNA 101 involvement. Taken together, our data demonstrate that Glo1 is involved in the Min-U-Sil 5 crystalline silica-induced BEAS-2B cell mitochondrial apoptotic pathway via a novel mechanism involving Hsp70, JNK, and NF-κB. Because maintenance of an intact respiratory epithelium is a critically important determinant of normal respiratory function, the knowledge of the mechanisms underlying its disruption may provide insight into the genesis, and possibly the prevention, of a number of pathological conditions commonly occurring in silica dust occupational exposure.

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

Luteolin and apigenin are dietary flavones and exhibit a broad spectrum of biological activities including antioxidant, anti-inflammatory, anti-cancer and neuroprotective effects. The lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE) has been implicated as a causative agent in the development of neurodegenerative disorders. This study investigates the cytoprotective effects of luteolin and apigenin against 4-HNE-mediated cytotoxicity in neuronal-like catecholaminergic PC12 cells. Both flavones restored cell viability and repressed caspase-3 and PARP-1 activation in 4-HNE-treated cells. Luteolin also mitigated 4-HNE-mediated LC3 conversion and reactive oxygen species (ROS) production. Luteolin and apigenin up-regulated 4-HNE-mediated unfolded protein response (UPR), leading to an increase in endoplasmic reticulum chaperone GRP78 and decrease in the expression of UPR-targeted pro-apoptotic genes. They also induced the expression of Nrf2-targeted HO-1 and xCT in the absence of 4-HNE, but counteracted their expression in the presence of 4-HNE. Moreover, we found that JNK and p38 MAPK inhibitors significantly antagonized the increase in cell viability induced by luteolin and apigenin. Consistently, enhanced phosphorylation of JNK and p38 MAPK was observed in luteolin- and apigenin-treated cells. In conclusion, this result shows that luteolin and apigenin activate MAPK and Nrf2 signaling, which elicit adaptive cellular stress response pathways, restore 4-HNE-induced ER homeostasis and inhibit cytotoxicity. Luteolin exerts a stronger cytoprotective effect than apigenin possibly due to its higher MAPK, Nrf2 and UPR activation, and ROS scavenging activity.

Anti-dementia Activity of Nobiletin, a Citrus Flavonoid: A Review of Animal Studies

Alzheimer's disease (AD), the most common form of dementia among the elderly, is characterized by the progressive decline of cognitive function and has a detrimental impact worldwide. Despite intensive laboratory and clinical research over the last three decades, pharmacological options for the prevention and effective long-term treatment of AD are not currently available. Consequently, successful therapeutic and preventive treatments for AD are needed. When researching materials from natural resources having anti-dementia drug activity, we identified nobiletin, a polymethoxylated flavone from the peel of Citrus depressa. Nobiletin exhibited memory-improving effects in various animal models of dementia and exerted a wide range of beneficial effects against pathological features of AD including amyloid-β (Aβ) pathology, tau hyperphosphorylation, oxidative stress, cholinergic neurodegeneration and dysfunction of synaptic plasticity-related signaling, suggesting this natural compound could become a novel drug for the treatment and prevention of AD.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

Photosensitive fluorescent dye contributes to phototoxicity and inflammatory responses of dye-doped silica NPs in cells and mice

Dye-doped fluorescent silica nanoparticles provide highly intense and photostable fluorescence signals. However, some dopant dye molecules are photosensitive. A widely-used photosensitive fluorescent dopant, RuBpy, was chosen to systematically investigate the phototoxicity of the dye-doped silica nanoparticles (NPs). We investigated cell viability, DNA damage, and Reactive Oxygen Species (ROS) levels in alveolar macrophages using the dye-doped NPs with or without irradiation. Our results showed that the RuBpy-doped silica NPs could induce significant amount of ROS, DNA damage, apoptosis and impaired proliferation in MH-S cells. In vivo studies in mice showed that RuBpy-doped silica NPs induced significant inflammatory cytokine production and lowered expression in signaling proteins such as ERK1/2 and NF-κB as well as increased lung injury determined by myeloperoxidase and lipid peroxidation. Strikingly, we also found that both RuBpy alone and NPs induced systemic signaling activation in the kidney compared to the liver and lung where showed highly selective signaling patterns, which is more pronounced than RuBpy-doped silica NPs. Moreover, we discovered a critical biomarker (e.g., HMGB1) for silica NPs-induced stress and toxicity and demonstrated differentially-regulated response patterns in various organs. Our results indicate for the first time that the RuBpy-doped silica NPs may impose less inflammatory responses but stronger thermotherapeutic effects on target cells in animals than naked NPs in a time- and dose-dependent manner.

Lipid peroxidation end product 4-hydroxy-trans-2-nonenal triggers unfolded protein response and heme oxygenase-1 expression in PC12 cells: Roles of ROS and MAPK pathways

This study investigates the roles of ROS overproduction and MAPK signaling pathways in the induction of unfolded protein response (UPR) and the expression of Phase II enzymes in response to 4-hydroxy-trans-2-nonenal (4-HNE) in a neuronal-like catecholaminergic PC12 cells. Our results showed that 4-HNE triggered three canonical pathways of UPR, namely IRE1-XBP1, PERK-eIF2α-ATF4 and ATF6, and induced the expression of UPR-targeted genes, GRP78, CHOP, TRB3, PUMA, and GADD34, as well as Phase II enzymes, HO-1 and GCLC. 4-HNE also induced apoptosis, intracellular calcium accumulation, caspase-3 activation, and G0/G1 cell cycle arrest, which was correlated with the increased expression of GADD45α. The addition of tiron, a cellular permeable superoxide scavenger, scavenged 4-HNE-mediated ROS formation, but did not alleviate cytotoxicity, or the expression of UPR-targeted genes or Phase II enzymes, indicating that ROS overproduction per se did not play a major role in 4-HNE-caused deleterious effects. HO-1 expression was attenuated by Nrf2 siRNA and chemical chaperone 4-phenylbutyrate (4-PBA), suggesting HO-1 expression was regulated by Nrf2-ARE, which may work downstream of ER stress. 4-HNE treatment promptly induced ERK, JNK and p38 MAPK activation. Addition of p38 MAPK specific inhibitor SB203580 attenuated HO-1 upregulation, but enhanced expression of CHOP, PUMA and TRB3, and cytotoxicity. These results indicate that 4-HNE-induced transient p38 MAPK activation may serve as an upstream negative regulator of ER stress and confer adaptive cytoprotection against 4-HNE-mediated cell injury.

Antioxidant effects of diallyl trisulfide on high glucose-induced apoptosis are mediated by the PI3K/Akt-dependent activation of Nrf2 in cardiomyocytes

BACKGROUND

Hyperglycemia-induced reactive oxygen species (ROS) generation contributes to development of diabetic cardiomyopathy. Nuclear factor E2-related factor 2 (Nrf2), a redox-sensing transcription factor, induces the antioxidant enzyme expressions. Diallyl trisulfide (DATS) is the most powerful antioxidant among the sulfur-containing compounds in garlic oil. We investigated whether DATS inhibits hyperglycemia-induced ROS production via Nrf2-mediated activation of antioxidant enzymes in cardiac cells exposed to high glucose (HG).

METHODS AND RESULTS

Treatment of H9c2 cells with HG resulted in an increase in intracellular ROS level and caspase-3 activity, which were markedly reduced by the administration of DATS (10 μM). DATS treatment significantly increased Nrf2 protein stability and nuclear translocation, upregulated downstream gene HO-1, and suppressed its repressor Keap1. However, apoptosis was not inhibited by DATS in cells transfected with Nrf2-specific siRNA. Inhibition of PI3K/Akt signaling by LY294002 (PI3K inhibitor) or PI3K-specific siRNA not only decreased the level of DATS-induced Nrf2-mediated HO-1 expression, but also diminished the protective effects of DATS. Similar results were also observed in high glucose-exposed neonatal primary cardiomyocytes and streptozotocin-treated diabetic rats fed DATS at a dose of 40 mg/kg BW.

CONCLUSIONS

Our findings indicate that DATS protects against hyperglycemia-induced ROS-mediated apoptosis by upregulating the PI3K/Akt/Nrf2 pathway, which further activates Nrf2-regulated antioxidant enzymes in cardiomyocytes exposed to HG.

Dietary flavonoid genistein induces Nrf2 and phase II detoxification gene expression via ERKs and PKC pathways and protects against oxidative stress in Caco-2 cells

SCOPE

Flavonoids have well-known antioxidant, anti-inflammatory, and anti-cancer activities. Isoflavone genistein is considered a potent antioxidant agent against oxidative stress. Although several mechanisms have been proposed, a clear antioxidant mechanism of genistein is still remained to be answered.

METHODS AND RESULTS

In this study, we focused on the concerted effects on expression of Nrf2 and phase II enzyme pathway components. Transient transfection assays, RT-PCR and immunoblot analysis were performed to study its molecular mechanisms of action. In Caco-2 cells, treatment with genistein markedly attenuated H(2)O(2) -induced peroxide formation; this amelioration was reversed by buthionine sulfoximine(GCLC inhibitor) and zinc protoporphyrin(HO-1 inhibitor). Genistein increased HO-1 and GCLC mRNA and protein expression. Genistein treatment activated the ERK1/2 and PKC signaling pathway; therefore increased Nrf2 mRNA and protein expression. The roles of the ERK1/2 and PKC signaling pathway were determined using PD98059 (ERK1/2 inhibitor) and GF109203X (PKC inhibitor) and RNA interference directed against Nrf2. Both inhibitors and siNrf2 abolished genistein-induced HO-1 and GCLC protein expression. These results suggest the involvement of ERK1/2, PKC, and Nrf2 in inducing HO-1 and GCLC by genistein.

CONCLUSION

Our studies show that genistein up-regulated HO-1 and GCLC expression through the EKR1/2 and PKC /Nrf2 pathways during oxidative stress.

Luteolin induces microRNA-132 expression and modulates neurite outgrowth in PC12 cells

Luteolin (3′,4′,5,7-tetrahydroxyflavone), a food-derived flavonoid, has been reported to exert neurotrophic properties that are associated with its capacity to promote neuronal survival and neurite outgrowth. In this study, we report for the first time that luteolin induces the persistent expression of microRNA-132 (miR-132) in PC12 cells. The correlation between miR-132 knockdown and a decrease in luteolin-mediated neurite outgrowth may indicate a mechanistic link by which miR-132 functions as a mediator for neuritogenesis. Furthermore, we find that luteolin led to the phosphorylation and activation of cAMP response element binding protein (CREB), which is associated with the up-regulation of miR-132 and neurite outgrowth. Moreover, luteolin-induced CREB activation, miR-132 expression and neurite outgrowth were inhibited by adenylate cyclase, protein kinase A (PKA) and MAPK/ERK kinase 1/2 (MEK1/2) inhibitors but not by protein kinase C (PKC) or calcium/calmodulin-dependent protein kinase II (CaMK II) inhibitors. Consistently, we find that luteolin treatment increases ERK phosphorylation and PKA activity in PC12 cells. These results show that luteolin induces the up-regulation of miR-132, which serves as an important regulator for neurotrophic actions, mainly acting through the activation of cAMP/PKA- and ERK-dependent CREB signaling pathways in PC12 cells.

bFGF inhibits ER stress induced by ischemic oxidative injury via activation of the PI3K/Akt and ERK1/2 pathways

Extensive research has focused on finding effective strategies to prevent or improve recovery from brain ischemia and reperfusion (I/R) injury. The basic fibroblast growth factor (bFGF) has been shown to have therapeutic potential in some central nervous system (CNS) disorders, including ischemic injury. In this study, we demonstrate that bFGF administration can improve locomotor activity and inhibit the ER stress induced in the CA1 region of the hippocampus in a mouse model of I/R injury. In vitro, bFGF exerts a protective effect by inhibiting the ER stress response proteins CHOP, XBP-1, ATF-6 and caspase-12 that are induced by H(2)O(2) treatment. Both of these in vivo and in vitro effects are related to the activation of two downstream signaling pathways, PI3K/Akt and ERK1/2. Inhibition of the PI3K/Akt and ERK1/2 pathways by specific inhibitors, LY294002 and U0126, respectively, partially reduce the protective effect of bFGF. Taken together, our results indicate that the neuroprotective role of bFGF involves the suppression of ER stress in the ischemic oxidative damage models and oxidative stress-induced PC12 cell injury, and these effects is underlying the activation of the PI3K/Akt and ERK1/2 signal pathway.