Quercetin activates AMP-activated protein kinase by reducing PP2C expression protecting old mouse brain against high cholesterol-induced neurotoxicity

Digitoflavone provokes mitochondrial biogenesis in PC12 cells: A protective approach to oxidative stress

CONTEXT

Reactive oxygen species (ROS) are known to be one of the main causes of neurodegenerative disorders, and flavonoids play characteristic roles in a variety of biological activities, and specially are known to be antioxidant reagents.

OBJECTIVE

In this study, we investigated neuroprotective effects of digitoflavone to suppress H2O2 -induced cell death in neuron-like PC12 cells.

MATERIAL AND METHODS

PC12 cells were pre-treated with digitoflavone for 2 h and then cells were exposed to H2O2 for 18 h. The cells' viability was evaluated by MTT assay. Rhodamine 123 staining was used for the determination of mitochondrial membrane potential (ΔΨm). The intracellular ROS aggregation was determined by using 2',7'-dichlorofluorescein diacetate. Also, the level of mitochondrial biogenesis factors was measured by western blot. The antioxidant capacity of digitoflavone was also determined by measuring reduced glutathione (GSH) level and catalase (CAT) activity quantification.

RESULTS

Digitoflavone significantly elevated cells' viability at concentrations of 10 and 20 µM. Also, digitoflavone attenuated intracellular level of ROS, and stabilized ΔΨm. Moreover, digitoflavone increased phosphorylation of AMP-activated protein kinase (AMPK) and, consequently, elevated mitochondrial biogenesis factors which were reduced after H2O2 exposure. We emphasized on the protective effect of digitoflavone through increasing mitochondrial biogenesis by specifically inhibiting AMPK. Antioxidant ability of digitoflavone was indicated by the elevation of GSH level and CAT activity.

CONCLUSION

As a result, digitoflavone stabilize ΔΨm, enhanced cell viability through inducing mitochondrial biogenesis pathway, and increased antioxidant capacity of the cells which lead to better combating the oxidative stress.

Modulation of nitric oxide by flavonoids

One of the main mechanisms by which dietary flavonoids are thought to influence cardiovascular disease is via protection of the bioactivity of the endothelium-derived nitric oxide (NO). Additionally, flavonoids may also interfere with the signalling cascades of inflammation and prevent overproduction of NO and its deleterious consequences in shock and ischemia-reperfusion injury. In the present paper we review the evidence of the effects of flavonoids on NO. Flavonoids exert complex actions on the synthesis and bioavailability of NO which may result both in enhanced or decreased NO levels: (1) in cell free systems, several flavonoids may scavenge NO via its pro-oxidant properties by increasing superoxide. However, under conditions of oxidative stress, flavonoids may also protect NO from superoxide-driven inactivation. (2) In intact healthy tissues, some flavonoids increase eNOS activity in endothelial cells. Paradoxically this effect involves a pro-oxidant effect which results in Ca(2+)-dependent activation of eNOS. As inhibitors of PI3K, flavonoids may potentially inhibit the PI3K/Akt-dependent activation of eNOS. (3) Under conditions of inflammation and oxidative stress, flavonoids may prevent the inflammatory signalling cascades via inhibition of NFκB and thereby downregulate iNOS. On the other hand, they also prevent the overexpression of ROS generating enzymes, reducing superoxide and peroxynitrite levels, and hence preventing superoxide-induced NO inactivation and eNOS uncoupling. Therefore, the final effect of flavonoids on NO levels will depend on the flavonoid structure and the concentrations used, on the cell type under study and particularly on the presence of inflammatory/oxidative conditions.

Effect of quercetin and rutin in some acute seizure models in mice

Quercetin is one of the most widely occurring flavonoid which is also often present in plants as glycosidic form - rutin. These compounds are ingredients of plant diet and are also present in numerous pharmaceutical preparations and diet supplements which are taken by patients suffering from epilepsy and treating with antiepileptic drugs (AEDs). Influence of these compounds on central nervous system-related effects was proved both in experimental and clinical studies. Their influence on anxiety, depression, memory processes and convulsant activity was reported. The aim of the present study was to investigate the effect of quercetin and rutin in some models of seizures, i.e., in the model of psychomotor seizures induced by 6Hz stimulation, in the maximal electroshock seizure threshold and intravenous pentylenetetrazole tests in mice. We also examined a possible mechanism of anticonvulsant activity of quercetin and its influence on action of two AEDs, i.e., valproic acid and levetiracetam, in the 6Hz seizure test. Our results revealed only a weak anticonvulsant potential of the studied flavonoids because they showed anticonvulsant action at doses from 10 to 200mg/kg only in the 6Hz test and did not change seizure thresholds in the remaining tests. Moreover, anticonvulsant action of the studied flavonoids was short-term, noted only at pretreatment time ranging between 30 and 60min. The highest anticonvulsant activity of quercetin was correlated with its high plasma and brain concentration, which was revealed in a pharmacokinetic study. We did not note changes in the anticonvulsant action of the used AEDs combined with quercetin in the model of psychomotor seizures in mice. Neither quercetin and rutin nor combinations of quercetin with the studied AEDs produced any significant impairments of motor coordination (assessed in the chimney test), muscular strength (investigated in the grip-strength test) and long-term memory (evaluated in the passive avoidance test) in mice. The results of the present study suggest that quercetin and rutin have only weak and short-term anticonvulsant potential. These flavonoids seem to be safe for patients with epilepsy because they neither changed activity of the studied AEDs nor produced any adverse effects.

Autophagy in microglia degrades extracellular β-amyloid fibrils and regulates the NLRP3 inflammasome

Accumulation of β-amyloid (Aβ) and resultant inflammation are critical pathological features of Alzheimer disease (AD). Microglia, a primary immune cell in brain, ingests and degrades extracellular Aβ fibrils via the lysosomal system. Autophagy is a catabolic process that degrades native cellular components, however, the role of autophagy in Aβ degradation by microglia and its effects on AD are unknown. Here we demonstrate a novel role for autophagy in the clearance of extracellular Aβ fibrils by microglia and in the regulation of the Aβ-induced NLRP3 (NLR family, pyrin domain containing 3) inflammasome using microglia specific atg7 knockout mice and cell cultures. We found in microglial cultures that Aβ interacts with MAP1LC3B-II via OPTN/optineurin and is degraded by an autophagic process mediated by the PRKAA1 pathway. We anticipate that enhancing microglial autophagy may be a promising new therapeutic strategy for AD.

Quercetin attenuates renal ischemia/reperfusion injury via an activation of AMP-activated protein kinase-regulated autophagy pathway

Renal ischemia/reperfusion (I/R) is a major cause of acute renal failure. Quercetin, a flavonoid antioxidant, presents in many kinds of food. The molecular mechanism of quercetin on renal protection during I/R is still unclear. Here, we investigated the role of AMP-activated protein kinase (AMPK)-regulated autophagy in renal protection by quercetin. To investigate whether quercetin protects renal cells from I/R-induced cell injury, an in vitro model of I/R and an in vivo I/R model were used. Cell apoptosis was determined by propidium iodide/annexin V staining. Western blotting and immunofluorescence were used to determine the autophagy. AMPK expression was inhibited with appropriate short hairpin RNA (shRNA). In cultured renal tubular cell I/R model, quercetin decreased the cell injury, up-regulated the AMPK phosphorylation, down-regulated the mammalian target of rapamycin (mTOR) phosphorylation and activated autophagy during I/R. Knockdown of AMPK by shRNA transfection decreased the quercetin-induced autophagy but did not affect the mTOR phosphorylation. In I/R mouse model, quercetin decreased the increased serum creatinine level and altered renal histological score. Quercetin also increased AMPK phosphorylation, inhibited the mTOR phosphorylation and activated autophagy in the kidneys of I/R mice. These results suggest that quercetin activates an AMPK-regulated autophagy signaling pathway, which offers a protective effect in renal I/R injury.

Activators of AMPK: not just for Type II diabetes

Recent discoveries of AMPK activators point to the large number of therapeutic candidates that can be transformed to successful designs of novel drugs. AMPK is a universal energy sensor and influences almost all physiological processes in the cells. Thus, regulation of the cellular energy metabolism can be achieved in selective tissues via the artificial activation of AMPK by small molecules. Recently, special attention has been given to direct activators of AMPK that are regulated by several nonspecific upstream factors. The direct activation of AMPK, by definition, should lead to more specific biological activities and as a result minimize possible side effects.

Calcineurin suppresses AMPK-dependent cytoprotective autophagy in cardiomyocytes under oxidative stress

Calcineurin signalling plays a critical role in the pathogenesis of many cardiovascular diseases. Calcineurin has been proven to affect a series of signalling pathways and to exert a proapoptotic effect in cardiomyocytes. However, whether it is able to regulate autophagy remains largely unknown. Here, we report that prolonged oxidative stress-induced activation of calcineurin contributes to the attenuation of adaptive AMP-activated protein kinase (AMPK) signalling and inhibits autophagy in cardiomyocytes. Primary cardiomyocytes exhibited rapid formation of autophagosomes, microtubule-associated protein 1 light chain 3 (LC3) expression and phosphorylation of AMPK in response to hydrogen peroxide (H₂O₂) treatment. However, prolonged (12 h) H₂O₂ treatment attenuated these effects and was accompanied by a significant increase in calcineurin activity and apoptosis. Inhibition of calcineurin by FK506 restored AMPK function and LC3 expression, and decreased the extent of apoptosis caused by prolonged oxidative stress. In contrast, overexpression of the constitutively active form of calcineurin markedly attenuated the increase in LC3 induced by short-term (3 h) H₂O₂ treatment and sensitised cells to apoptosis. In addition, FK506 failed to induce autophagy and alleviate apoptosis in cardiomyocytes expressing a kinase-dead K45R AMPK mutant. Furthermore, inhibition of autophagy by 3-methylanine (3-MA) or by knockdown of the essential autophagy-related gene ATG7 abrogated the protective effect of FK506. These findings suggest a novel role of calcineurin in suppressing adaptive autophagy during oxidative stress by downregulating the AMPK signalling pathway. The results also provide insight into how altered calcineurin and autophagic signalling is integrated to control cell survival during oxidative stress and may guide strategies to prevent cardiac oxidative damage.

Quercetin improves behavioral deficiencies, restores astrocytes and microglia, and reduces serotonin metabolism in 3-nitropropionic acid-induced rat model of Huntington's Disease

AIM

Huntington's disease (HD) is an autosomal dominant disorder, for which clinically available drugs offer only symptomatic relief. These prescription drugs are not free of side effects, and the patients usually suffer from anxiety and depression. We investigated quercetin, a dietary flavonoid with free radical scavenging properties, for its beneficial potential if any, in 3-nitropropionic acid (3-NP)-induced HD in rats where both drugs were administered simultaneously.

METHODS

Performance of rats on beam balancing, elevated plus maze and gait traits were investigated following 3-NP and/or quercetin treatments for 4 days. Striatal biogenic amine levels and monoamine oxidase activity were assayed. Striatal sections were examined for Cd11B and glial fibrillary acidic protein immunoreactivity, and for evidences of neuronal lesion.

RESULTS

Quercetin significantly attenuated 3-NP-induced anxiety, motor coordination deficits, and gait despair. While the dopaminergic hyper-metabolism was unaffected, quercetin provided a significant reduction of 3-NP mediated increase in serotonin metabolism. Quercetin failed to affect 3-NP-induced striatal neuronal lesion, but decreased microglial proliferation, and increased astrocyte numbers in the lesion core.

CONCLUSION

These results taken together suggest that quercetin could be of potential use not only for correcting movement disturbances and anxiety in HD, but also for addressing inflammatory damages.

Quercetin enhances hypoxia-mediated apoptosis via direct inhibition of AMPK activity in HCT116 colon cancer

Tumor hypoxia is considered the best validated target in clinical oncology because of its significant contribution to chemotherapy failure and drug resistance. As an approach to target hypoxia, we assessed the potential of quercetin, a flavonoid widely distributed in plants, as a anticancer agent under hypoxic conditions and examined its pharmacological mechanisms by primarily focusing on the role of AMP-activated protein kinase (AMPK). Quercetin significantly attenuated tumor growth in an HCT116 cancer xenograft in vivo model with a substantial reduction of AMPK activity. In a cell culture system, quercetin more dramatically induced apoptosis of HCT116 cancer cells under hypoxic conditions than normoxic conditions, and this was tightly associated with inhibition of hypoxia-induced AMPK activity. An in vitro kinase assay demonstrated that quercetin directly inhibits AMPK activity. Inhibition of AMPK by expressing a dominant-negative form resulted in an increase of apoptosis under hypoxia, and a constitutively active form of AMPK effectively blocked quercetin-induced apoptosis under hypoxia. Collectively, our data suggest that quercetin directly inhibits hypoxia-induced AMPK, which plays a protective role against hypoxia. Quercetin also reduced the activity of hypoxia-inducible factor-1 (HIF-1), a major transcription factor for adaptive cellular response to hypoxia. Moreover, quercetin sensitized HCT116 cancer cells to the anticancer drugs cisplatin and etoposide under hypoxic conditions. Our findings suggest that AMPK may serve as a novel target for overcoming tumor hypoxia-associated negative aspects.

Aspirin attenuates vinorelbine-induced endothelial inflammation via modulating SIRT1/AMPK axis

Vinorelbine (VNR), a semisynthetic vinca alkaloid acquired from vinblastine, is frequently used as the candidate for intervention of solid tumors. Nevertheless, VNR-caused endothelial injuries may lead a mitigative effect of clinical treatment efficiency. A growing body of evidence reveals that aspirin is a potent antioxidant and anti-inflammation drug. We investigated whether aspirin attenuate VNR-induced endothelial dysfunction. Human endothelial cells (EA.hy 926) were treated with VNR to cause endothelial inflammation. Western blotting, ROS assay, ELISA were used to confirm the anti-inflammatory effect of aspirin. We confirmed that VNR suppresses SIRT1 expression, reduced LKB1 and AMPK phosphorylation as well as enriched PKC activation in treated endothelial cells. Furthermore, the membrane translocation assay displayed that the levels of NADPH oxidase subunits p47phox and Rac-1 in membrane fractions of endothelial cells were higher in cells that had been treated with VNR for than in untreated cells. We corroborated that treatment of Aspirin significantly diminishes VNR-repressed SIRT1, LKB1 and AMPK phosphorylation and VNR-promoted NADPH oxidase activation, however, those findings were vanished by SIRT1 and AMPK siRNAs. Our data also shown that Aspirin represses VNR-activated TGF-beta-activated kinase-1 (TAK1) activation, inhibited the interaction of TAK1/TAK-binding protein1 (TAB1), suppressed NF-kappa B activation and pro-inflammatory cytokine secretion. We demonstrated a novel connection between VNR-caused oxidative damages and endothelial dysfunction, and provide further insight into the protective effects of aspirin in VNR-caused endothelial dysfunction.

Synaptic activity and bioenergy homeostasis: implications in brain trauma and neurodegenerative diseases

Powered by glucose metabolism, the brain is the most energy-demanding organ in our body. Adequate ATP production and regulation of the metabolic processes are essential for the maintenance of synaptic transmission and neuronal function. Glutamatergic synaptic activity utilizes the largest portion of bioenergy for synaptic events including neurotransmitter synthesis, vesicle recycling, and most importantly, the postsynaptic activities leading to channel activation and rebalancing of ionic gradients. Bioenergy homeostasis is coupled with synaptic function via activities of the sodium pumps, glutamate transporters, glucose transport, and mitochondria translocation. Energy insufficiency is sensed by the AMP-activated protein kinase (AMPK), a master metabolic regulator that stimulates the catalytic process to enhance energy production. A decline in energy supply and a disruption in bioenergy homeostasis play a critical role in multiple neuropathological conditions including ischemia, stroke, and neurodegenerative diseases including Alzheimer’s disease and traumatic brain injuries.

The aqueous extract from Toona sinensis leaves inhibits microglia-mediated neuroinflammation

The leaves of Toona sinensis, a well‐known traditional oriental medicine, have been prescribed for the treatment of enteritis and infection. Recently, aqueous extracts of Toona sinensis leaves (TSL‐1) have demonstrated many biological effects both in vitro and in vivo. In the central nervous system, microglial activation and their proinflammatory responses are considered an important therapeutic strategy for neuroinflammatory disorders such as cerebral ischemia, Alzheimer's disease, and Parkinson's disease. The present study attempted to validate the effect of TSL‐1 on microglia‐mediated neuroinflammation stimulated by lipopolysaccharide (LPS). As inflammatory parameters, the production of nitric oxide (NO), inducible NO synthase, and tumor necrosis factor‐α were evaluated. Our results demonstrate that TSL‐1 suppresses LPS‐induced NO production, tumor necrosis factor‐α secretion, and inducible NO synthase protein expression in a concentration‐dependent manner, without causing cytotoxicity. In addition, the inhibitory effects of TSL‐1 in LPS‐stimulated BV‐2 microglia were extended to post‐treatment suggesting the therapeutic potential of TSL‐1. Therefore, this work provides the future evaluation of the role of TSL‐1 in the treatment of neurodegenerative diseases by inhibition of inflammatory mediator production in activated microglia.

TSG (2,3,4' ,5-tetrahydroxystilbene 2-O-β-D-glucoside) suppresses induction of pro-inflammatory factors by attenuating the binding activity of nuclear factor-κB in microglia

BACKGROUND

Induction of pro-inflammatory factors is one of the characteristics of microglia activation and can be regulated by numerous active components of Chinese traditional herbs. Suppression of pro-inflammatory factors is beneficial to alleviate microglia-mediated cell injury. The present study aims to investigate the effect and possible mechanism of 2,3,4',5-tetrahydroxystilbene 2-O-β-D-glucoside (TSG) on LPS-mediated induction of pro-inflammatory factors in microglia.

METHODS

Western blot, ELISA, and Hoechst 33258 were used to measure the protein expression, TNF-α/IL-6 content, and apoptotic nuclei, respectively. The mRNA level was measured by real time-PCR. Nitric oxide (NO) content, lactate dehydrogenase (LDH) content, and NF-κB binding activity were assayed by commercial kits.

RESULTS

TSG reduced iNOS protein expression as well as TNF-α, IL-6, and NO content in LPS-stimulated BV-2 cells. TSG attenuated the increase in apoptotic nuclei, caspase-3 cleavage, and LDH content induced by BV-2 cell-derived conditioned medium in primary hippocampal neurons. Mechanistic studies showed that TSG reduced the mRNA level of iNOS, TNF-α, and IL-6. TSG failed to suppress IκB-α degradation, NF-κB phosphorylation and nuclear translocation, and ERK1/2, JNK, and p38 phosphorylation. TSG, however, markedly reduced the binding of NF-κB to its DNA element. Chromatin immunoprecipitation (ChIP) assays confirmed that TSG reduced NF-κB binding to the iNOS promoter. These findings were ascertained in primary microglia where the LPS-induced increase in iNOS expression, NO content, apoptotic nuclei, and NF-κB binding to its DNA element were diminished by TSG.

CONCLUSIONS

These studies demonstrate that TSG attenuates LPS-mediated induction of pro-inflammatory factors in microglia through reducing the binding activity of NF-κB. This might help us to further understand the pharmacological role of TSG in inflammatory response in the central nervous system.

Potential synergy between tau aggregation inhibitors and tau chaperone modulators

Tau is a soluble, microtubule-associated protein known to aberrantly form amyloid-positive aggregates. This pathology is characteristic for more than 15 neuropathies, the most common of which is Alzheimer’s disease. Finding therapeutics to reverse or remove this non-native tau state is of great interest; however, at this time only one drug is entering phase III clinical trials for treating tauopathies. Generally, tau manipulation by therapeutics can either directly or indirectly alter tau aggregation and stability. Drugs that bind and change the conformation of tau itself are largely classified as aggregation inhibitors, while drugs that alter the activity of a tau-effector protein fall into several categories, such as kinase inhibitors, microtubule stabilizers, or chaperone modulators. Chaperone inhibitors that have proven effective in tau models include heat shock protein 90 inhibitors, heat shock protein 70 inhibitors and activators, as well as inducers of heat shock proteins. While many of these compounds can alter tau levels and/or aggregation states, it is possible that combining these approaches may produce the most optimal outcome. However, because many of these compounds have multiple off-target effects or poor blood–brain barrier permeability, the development of this synergistic therapeutic strategy presents significant challenges. This review will summarize many of the drugs that have been identified to alter tau biology, with special focus on therapeutics that prevent tau aggregation and regulate chaperone-mediated clearance of tau.

Ursolic acid improves domoic acid-induced cognitive deficits in mice

Our previous findings suggest that mitochondrial dysfunction is the mechanism underlying cognitive deficits induced by domoic acid (DA). Ursolic acid (UA), a natural triterpenoid compound, possesses many important biological functions. Evidence shows that UA can activate PI3K/Akt signaling and suppress Forkhead box protein O1 (FoxO1) activity. FoxO1 is an important regulator of mitochondrial function. Here we investigate whether FoxO1 is involved in the oxidative stress-induced mitochondrial dysfunction in DA-treated mice and whether UA inhibits DA-induced mitochondrial dysfunction and cognitive deficits through regulating the PI3K/Akt and FoxO1 signaling pathways. Our results showed that FoxO1 knockdown reversed the mitochondrial abnormalities and cognitive deficits induced by DA in mice through decreasing HO-1 expression. Mechanistically, FoxO1 activation was associated with oxidative stress-induced JNK activation and decrease of Akt phosphorylation. Moreover, UA attenuated the mitochondrial dysfunction and cognitive deficits through promoting Akt phosphorylation and FoxO1 nuclear exclusion in the hippocampus of DA-treated mice. LY294002, an inhibitor of PI3K/Akt signaling, significantly decreased Akt phosphorylation in the hippocampus of DA/UA mice, which weakened UA actions. These results suggest that UA could be recommended as a possible candidate for the prevention and therapy of cognitive deficits in excitotoxic brain disorders.

Diphenyl diselenide prevents cortico-cerebral mitochondrial dysfunction and oxidative stress induced by hypercholesterolemia in LDL receptor knockout mice

Recent studies have indicated a causal link between high dietary cholesterol intake and brain oxidative stress. In particular, we have previously shown a positive correlation between elevated plasma cholesterol levels, cortico-cerebral oxidative stress and mitochondrial dysfunction in low density lipoprotein receptor knockout (LDLr(-/-)) mice, a mouse model of familial hypercholesterolemia. Here we show that the organoselenium compound diphenyl diselenide (PhSe)2 (1 mg/kg; o.g., once a day for 30 days) significantly blunted the cortico-cerebral oxidative stress and mitochondrial dysfunction induced by a hypercholesterolemic diet in LDLr(-/-) mice. (PhSe)2 effectively prevented the inhibition of complex I and II activities, significantly increased the reduced glutathione (GSH) content and reduced lipoperoxidation in the cerebral cortex of hypercholesterolemic LDLr(-/-) mice. Overall, (PhSe)2 may be a promising molecule to protect against hypercholesterolemia-induced effects on the central nervous system, in addition to its already demonstrated antiatherogenic effects.

Protein folding and aggregation into amyloid: the interference by natural phenolic compounds

Amyloid aggregation is a hallmark of several degenerative diseases affecting the brain or peripheral tissues, whose intermediates (oligomers, protofibrils) and final mature fibrils display different toxicity. Consequently, compounds counteracting amyloid aggregation have been investigated for their ability (i) to stabilize toxic amyloid precursors; (ii) to prevent the growth of toxic oligomers or speed that of fibrils; (iii) to inhibit fibril growth and deposition; (iv) to disassemble preformed fibrils; and (v) to favor amyloid clearance. Natural phenols, a wide panel of plant molecules, are one of the most actively investigated categories of potential amyloid inhibitors. They are considered responsible for the beneficial effects of several traditional diets being present in green tea, extra virgin olive oil, red wine, spices, berries and aromatic herbs. Accordingly, it has been proposed that some natural phenols could be exploited to prevent and to treat amyloid diseases, and recent studies have provided significant information on their ability to inhibit peptide/protein aggregation in various ways and to stimulate cell defenses, leading to identify shared or specific mechanisms. In the first part of this review, we will overview the significance and mechanisms of amyloid aggregation and aggregate toxicity; then, we will summarize the recent achievements on protection against amyloid diseases by many natural phenols.

Inflammatory role of AMP-activated protein kinase signaling in an experimental model of toxic smoke inhalation injury

OBJECTIVE

The molecular mechanisms underlying lung inflammation in toxic smoke inhalation injury are unknown. We investigated the signaling pathway responsible for the induction of interleukin 8 by wood smoke extract in lung epithelial cells and lung inflammation induced by wood smoke exposure in mice.

DESIGN

A randomized, controlled study.

SETTING

A research laboratory.

INTERVENTIONS AND MAIN RESULTS

Exposure of primary human bronchial epithelial cells to wood smoke extract sequentially activated NADPH oxidase and increased intracellular reactive oxygen species level; activated AMP-activated protein kinase, extracellular signal-regulated kinase and Jun N-terminal kinase (two mitogen-activated protein kinases), and nuclear factor-κB and signal transducer and activator of transcription protein 3 (two transcription factors); and induced interleukin-8. Inhibition of NADPH oxidase activation with apocynin or siRNA targeting p47(phox ) (a subunit of NADPH oxidase) attenuated the increased intracellular reactive oxygen species level, AMP-activated protein kinase activation, and interleukin-8 induction. Removal of intracellular reactive oxygen species by N-acetyl-cysteine reduced the activation of AMP-activated protein kinase, extracellular signal-regulated kinase and Jun N-terminal kinase, and interleukin-8 induction. Prevention of AMP-activated protein kinase activation by Compound C or AMP-activated protein kinase siRNA lessened the activation of Jun N-terminal kinase, extracellular signal-regulated kinase, nuclear factor-κB, signal transducer and activator of transcription protein 3 and interleukin-8 induction. Inhibition of Jun N-terminal kinase and extracellular signal-regulated kinase activation by inhibitors reduced the activation of nuclear factor-κB and signal transducer and activator of transcription protein 3 and interleukin-8 induction. Abrogation of nuclear factor-κB and signal transducer and activator of transcription protein 3 activation by inhibitors attenuated the interleukin-8 induction. Additionally, acute exposure of mice to wood smoke promoted AMP-activated protein kinase phosphorylation and expression of macrophage inflammatory protein 2 (an interleukin-8 homolog) in lung epithelial cells and lungs and lung inflammation, all of which were reduced by Compound C treatment.

CONCLUSIONS

Interleukin-8 induction by wood smoke extract in lung epithelial cells is mediated by novel NADPH oxidase-dependent, reactive oxygen species-sensitive AMP-activated protein kinase signaling with Jun N-terminal kinase and extracellular signal-regulated kinase as the downstream kinases and nuclear factor-κB and signal transducer and activator of transcription protein 3 as the downstream transcription factors. This AMP-activated protein kinase signaling is likely important for inducing lung inflammation with toxic smoke exposure in mice.

Inhibition of AMP-activated protein kinase accentuates lipopolysaccharide-induced lung endothelial barrier dysfunction and lung injury in vivo

The aim of this study was to determine the role of AMP-activated protein kinase (AMPK) in lipopolysaccharide (LPS)-induced lung endothelial barrier dysfunction and lung injury in vivo. Both cultured human pulmonary artery endothelial cells (HPAECs) and experimental animals [AMPK subunit α-deficient mice and wild-type (WT) control mice (C57BL/6J)] were used. In cultured HPAECs, LPS increased endothelial permeability in parallel with a decrease in AMPK activity. Consistent with this observation, AMPK activation with the potent AMPK activator 5-aminoimidazole-4-carboxamide-1-d-ribofuranoside (AICAR) attenuated LPS-induced endothelial hyperpermeability in vitro. Intratracheal administration of LPS (1 mg/kg) in WT mice reduced AMPK phosphorylation at Thr172 in lung tissue extracts, increased protein content and cell count in bronchial alveolar lavage fluid, and increased Evans Blue dye infiltration into the lung. These same attributes were similarly enhanced in AMPKα-knockout mice, compared with WT mice. Pretreatment with AICAR reduced these lung injury indicators in LPS-treated WT mice. AMPK activation with AICAR attenuated LPS-induced endothelial hyperpermeability by activating the Rac/Cdc42/PAK pathway, with concomitant inhibition of the Rho pathway, and decreased VE-cadherin phosphorylation at Tyr658. We conclude that AMPK activity supports normal endothelial barrier function and that LPS exposure inhibits AMPK, thereby contributing to endothelial barrier dysfunction and lung injury.

Molecular mechanisms of the cardiovascular protective effects of polyphenols

Epidemiological studies have reported a greater reduction in cardiovascular risk and metabolic disorders associated with diets rich in polyphenols. The antioxidant effects of polyphenols are attributed to the regulation of redox enzymes by reducing reactive oxygen species production from mitochondria, NADPH oxidases and uncoupled endothelial NO synthase in addition to also up-regulating multiple antioxidant enzymes. Although data supporting the effects of polyphenols in reducing oxidative stress are promising, several studies have suggested additional mechanisms in the health benefits of polyphenols. Polyphenols from red wine increase endothelial NO production leading to endothelium-dependent relaxation in conditions such as hypertension, stroke or the metabolic syndrome. Numerous molecules contained in fruits and vegetables can activate sirtuins to increase lifespan and silence metabolic and physiological disturbances associated with endothelial NO dysfunction. Although intracellular pathways involved in the endothelial effects of polyphenols are partially described, the molecular targets of these polyphenols are not completely elucidated. We review the novel aspects of polyphenols on several targets that could trigger the health benefits of polyphenols in conditions such as metabolic and cardiovascular disturbances.

PPM1B and P-IKKβ expression levels correlated inversely with rat gastrocnemius atrophy after denervation

Activated inhibitor of nuclear factor-κB kinase β (IKKβ) is necessary and sufficient for denervated skeletal muscle atrophy. Although several studies have shown that Mg(2+)/Mn(2+)-dependent protein phosphatase 1B (PPM1B) inactivated IKKβ, few studies have investigated the role of PPM1B in denervated skeletal muscle. In this study, we aim to explore the expression and significance of PPM1B and phosphorylated IKKβ (P-IKKβ) during atrophy of the denervated gastrocnemius. Thirty young adult female Wistar rats were subjected to right sciatic nerve transection and were sacrificed at 0 (control), 2, 7, 14, and 28 days after denervation surgery. The gastrocnemius was removed from both the denervated and the contralateral limb. The muscle wet weight ratio was calculated as the ratio of the wet weight of the denervated gastrocnemius to that of the contralateral gastrocnemius. RT-PCR and Western blot analysis showed that mRNA and protein levels of PPM1B were significantly lower than those of the control group at different times after the initiation of denervation, while P-IKKβ showed the opposite trends. PPM1B protein expression persistently decreased while P-IKKβ expression persistently increased for 28 days after denervation. PPM1B expression correlated negatively with P-IKKβ expression by the Spearman test, whereas decreasing PPM1B expression correlated positively with the muscle wet weight ratio. The expression levels of PPM1B and P-IKKβ were closely associated with atrophy in skeletal denervated muscle. These results suggest that PPM1B and P-IKKβ could be markers in skeletal muscle atrophy.

Small interfering RNA-mediated knockdown of protein kinase C zeta attenuates domoic acid-induced cognitive deficits in mice

Accumulated evidence indicates that domoic acid (DA)-induced excitatory neuronal injury is associated with excessive reactive oxygen species (ROS) production. Protein kinase C zeta (PKC-ζ)/nicotinamide adenine dinucleotide phosphate (NOX) signaling regulates ROS levels and is involved in various neurodegenerative disorders including excitoneurotoxicity. Our previous studies have demonstrated that ROS-induced activation of the stress-activated protein kinase/c-jun-N-terminal kinase (SAPK/JNK) pathway plays a key role in the pathogenesis of cognitive deficits induced by DA. However, the precise biological mechanisms underlying these effects are not well understood. In this study, we investigate whether the PKC-ζ mediates DA-induced cognitive deficits and further explored the potential molecular processes. DA treatment significantly increased the expression of PI3K p85α, and PKC-ζ in the hippocampus of mice, which promoted the p47phox phosphorylation and expression, enhanced NOX activity, and increased the levels of ROS and protein carbonyls. In turn, the abnormal ROS levels in the hippocampus of DA-treated mice activated SAPK/JNK pathway, decreased FoxO1 phosphorylation, stimulated the nuclear translocation of FoxO1, activated FasL/Fas signaling, and promoted the activation of caspase-8 and caspase-3, which resulted in neuron apoptosis and cognitive deficits in mice. However, PKC-ζ knockdown reversed these changes in mice. It was further demonstrated that FoxO1 was a downstream target of SAPK/JNK signaling by FoxO1 small interfering RNA and SP600125 (an inhibitor of SAPK/JNK pathway) treatment. Additionally, SP600125 treatment or FoxO1 knockdown also blocked FasL/Fas signaling-dependent apoptosis and improved DA-induced cognitive deficits in the hippocampus of mice. These results suggest that PKC-ζ could be a possible target for the prevention or treatment of cognitive deficits in excitotoxic and other brain disorders.

Roles of AMP-activated protein kinase in Alzheimer's disease

AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis and a central player in glucose and lipid metabolism, is potentially implicated in the pathogenesis of Alzheimer's disease (AD). AMPK activity decreases in AD brain, indicating decreased mitochondrial biogenesis and function. Emerging evidence demonstrates that AMPK activation is a potential target for improving perturbed brain energy metabolism that is involved in the pathogenesis of AD. The roles of AMPK in the pathogenesis of AD include β-amyloid protein (Aβ) generation and tau phosphorylation. In particular, AMPK may regulate Aβ generation through modulating neuronal cholesterol and sphingomyelin levels and through regulating APP distribution in the lipid rafts. AMPK is activated by phosphorylation of Thr-172 by LKB1 complex in response to increase in the AMP/ATP ratio and by calmodulin-dependent protein kinase kinase-beta in response to elevated Ca(2+) levels, which contributes to regulating Aβ generation. AMPK is a physiological tau kinase and can increase the phosphorylation of tau at Ser-262. AMPK can also directly phosphorylate tau at Thr-231 and Ser-396/404. Furthermore, AMPK activation decreases mTOR signaling activity to facilitate autophagy and promotes lysosomal degradation of Aβ. However, AMPK activation has non-neuroprotective property and may lead to detrimental outcomes, including Aβ generation and tau phosphorylation. Therefore, it is still unclear whether AMPK could serve a potential therapeutic target for AD, and hence, further studies will be needed to clarify the role of AMPK in AD.

AMPK and gastrointestinal carcinoma

Activation of adenosine monophosphate activated protein kinase (AMPK) not only affects gastrointestinal cancer cell growth and proliferation by regulating cholesterol metabolism, fatty acid synthesis and protein synthesis, but also promotes gastrointestinal cancer cell cycle arrest by regulating cell cycle progression. Moreover, activation of AMPK activates caspase-9 and then induces the apoptosis of gastrointestinal cancer cells. In addition, AMPK is closely related with angiogenesis, invasion and metastasis of gastrointestinal cancer. This review aims to elucidate the relationship between AMPK and gastrointestinal cancer.

Purple sweet potato color attenuates domoic acid-induced cognitive deficits by promoting estrogen receptor-α-mediated mitochondrial biogenesis signaling in mice

Recent findings suggest that endoplasmic reticulum stress may be involved in the pathogenesis of domoic acid-induced neurodegeneration. Purple sweet potato color, a class of naturally occurring anthocyanins, has beneficial health and biological effects. Recent studies have also shown that anthocyanins have estrogenic activity and can enhance estrogen receptor-α expression. In this study, we evaluated the effect of purple sweet potato color on cognitive deficits induced by hippocampal mitochondrial dysfunction in domoic acid-treated mice and explored the potential mechanisms underlying this effect. Our results showed that the oral administration of purple sweet potato color to domoic acid-treated mice significantly improved their behavioral performance in a step-through passive avoidance task and a Morris water maze task. These improvements were mediated, at least in part, by a stimulation of estrogen receptor-α-mediated mitochondrial biogenesis signaling and by decreases in the expression of p47phox and gp91phox. Decreases in reactive oxygen species and protein carbonylation were also observed, along with a blockade of the endoplasmic reticulum stress pathway. Furthermore, purple sweet potato color significantly suppressed endoplasmic reticulum stress-induced apoptosis, which prevented neuron loss and restored the expression of memory-related proteins. However, knockdown of estrogen receptor-α using short hairpin RNA only partially blocked the neuroprotective effects of purple sweet potato color in the hippocampus of mice cotreated with purple sweet potato color and domoic acid, indicating that purple sweet potato color acts through multiple pathways. These results suggest that purple sweet potato color could be a possible candidate for the prevention and treatment of cognitive deficits in excitotoxic and other brain disorders.

Neuroinflammation: modulation by flavonoids and mechanisms of action

Neuroinflammatory processes are known to contribute to the cascade of events culminating in the neuronal damage that underpins neurodegenerative disorders such as Parkinson's and Alzheimer's disease. Recently, there has been much interest in the potential neuroprotective effects of flavonoids, a group of plant secondary metabolites known to have diverse biological activity in vivo. With respect to the brain, flavonoids, such as those found in cocoa, tea, berries and citrus, have been shown to be highly effective in preventing age-related cognitive decline and neurodegeneration in both animals and humans. Evidence suggests that flavonoids may express such ability through a multitude of physiological functions, including an ability to modulate the brains immune system. This review will highlight the evidence for their potential to inhibit neuroinflammation through an attenuation of microglial activation and associated cytokine release, iNOS expression, nitric oxide production and NADPH oxidase activity. We will also detail the current evidence indicting that their regulation of these immune events appear to be mediated by their actions on intracellular signaling pathways, including the nuclear factor-κB (NF-κB) cascade and mitogen-activated protein kinase (MAPK) pathway. As such, flavonoids represent important precursor molecules in the quest to develop of a new generation of drugs capable of counteracting neuroinflammation and neurodegenerative disease.

The effect of cyclosporine A on the phosphorylation of the AMPK pathway in the rat hippocampus

Cyclosporine A (CsA), an immunosuppressant and calcineurin inhibitor, induces hyperlipidemia in humans and animals. AMP-activated protein kinase (AMPK) is involved in metabolic homeostasis and lipid metabolism through modulating downstream molecules acetyl CoA carboxylase (ACC) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoAR). AMPK activity is regulated by the phosphorylation at the Thr-172 residue by its upstream liver kinase B 1 (LKB1), Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) or transforming growth-factor-β-activated kinase 1 (TAK1). AMPK can be deactivated through dephosphorylation by protein phosphatase 2Cα (PP2Cα). In this study, we demonstrated that phosphorylation at Thr-172-AMPK increased with a concurrent increase in the phosphorylation of Ser-431-LKB1 and Thr-184/187-TAK1 in the rat hippocampus at 5 h after an intraperitoneal CsA (50 mg/kg) injection. CsA did not affect the phosphorylation of Thr-196-Ca(2+)/calmodulin-dependent protein kinase 4 (CaMK4) and the amount of PP2Cα. An increased phosphorylation of Ser-79-ACC and Ser-872-HMG-CoAR was also observed. In conclusion, our data indicate that CsA activates the AMPK pathway in the rat hippocampus, which suggests that CsA affects the regulatory signaling pathway of lipid metabolism in the rat brain.

Oxidative stress in neurodegenerative diseases: mechanisms and therapeutic perspectives

The incidence and prevalence of neurodegenerative diseases (ND) increase with life expectancy. This paper reviews the role of oxidative stress (OS) in ND and pharmacological attempts to fight against reactive oxygen species (ROS)-induced neurodegeneration. Several mechanisms involved in ROS generation in neurodegeneration have been proposed. Recent articles about molecular pathways involved in ROS generation were reviewed. The progress in the development of neuroprotective therapies has been hampered because it is difficult to define targets for treatment and determine what should be considered as neuroprotective. Therefore, the attention was focused on researches about pharmacological targets that could protect neurons against OS. Since it is necessary to look for genes as the ultimate controllers of all biological processes, this paper also tried to identify gerontogenes involved in OS and neurodegeneration. Since neurons depend on glial cells to survive, recent articles about the functioning of these cells in aging and ND were also reviewed. Finally, clinical trials testing potential neuroprotective agents were critically reviewed. Although several potential drugs have been screened in in vitro and in vivo models of ND, these results were not translated in benefit of patients, and disappointing results were obtained in the majority of clinical trials.

Molecular mechanisms for anti-aging by natural dietary compounds

Aging is defined as a normal decline in survival with advancing age; however, the recent researches have showed that physiological functions of the body change during the aging process. Majority of the changes are often subject to a higher risk of developing diseases, such as cardiovascular disease, type II diabetes, Alzheimer's disease, Parkinson's disease, as well as the dysregulated immune and inflammatory disorders. Aging process is controlled by a complicated and precise signaling network that involved in energy homeostasis, cellular metabolism and stress resistance. Over the past few decades, research in natural dietary compounds by various organism and animal models provides a new strategy for anti-aging. Natural dietary compounds act through a variety mechanisms to extend lifespan and prevent age-related diseases. This review summarizes the current understanding on signaling pathways of aging and knowledge and underlying mechanism of natural dietary compounds that provide potential application on anti-aging and improve heath in human.

Ursolic acid improves high fat diet-induced cognitive impairments by blocking endoplasmic reticulum stress and IκB kinase β/nuclear factor-κB-mediated inflammatory pathways in mice

Evidence suggests that obesity-induced cognitive impairments are driven by in brain inflammatory responses and inflammation-mediated brain insulin resistance. Ursolic acid (UA), a triterpenoid compound, has many important biological functions, including antioxidant and anti-inflammatory activities. Here, we evaluated the effect of UA on cognitive impairment induced by a high-fat diet (HFD), and we explored the potential mechanisms mediating this effect. Results showed that UA administration significantly improved the behavioral performance of C57/BL6J mice fed a HFD in both the step-through test and the Morris water maze task. These results were associated with the inhibition of endoplasmic reticulum stress and IκB kinase β/nuclear factor-κB-mediated inflammatory signaling and the restoration of insulin signaling and phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. UA administration also increased memory-related protein expression in the hippocampus of mice given a HFD. However, the neuroprotective effects of UA were blocked by an intracerebroventricular (i.c.v.) injection of PI-103, a specific PI3K 110α inhibitor. These results suggest that UA may be a potent candidate for the prevention and treatment of cognitive deficits caused by type 2 diabetes.

Selective recruitment of regulatory T cell through CCR6-CCL20 in hepatocellular carcinoma fosters tumor progression and predicts poor prognosis

BACKGROUND

Regulatory T cells (Tregs) are highly prevalent in tumor tissue and can suppress effective anti-tumor immune responses. However, the source of the increased tumor-infiltrating Tregs and their contribution to cancer progression remain poorly understood.

METHODOLOGY/PRINCIPAL FINDING

We here investigated the frequency, phenotype and trafficking property of Tregs and their prognostic value in patients with hepatocellular carcinoma (HCC). Our results showed that FoxP3(+) Tregs highly aggregated and were in an activated phenotype (CD69(+)HLA-DR(high)) in the tumor site, where they can suppress the proliferation and INF-γ secretion of CD4(+)CD25(-) T cells. These tumor-infiltrating Tregs could be selectively recruited though CCR6-CCL20 axis as illustrated by (a) high expression of CCR6 on circulating Tregs and their selective migration to CCR6 ligand CCL20, and (b) correlation of distribution and expression between tumor-infiltrating Tregs and intratumoral CCL20. In addition, we found that the number of tumor-infiltrating Tregs was associated with cirrhosis background (P = 0.011) and tumor differentiation (P = 0.003), and was an independent prognostic factor for overall survival (HR = 2.408, P = 0.013) and disease-free survival (HR = 2.204, P = 0.041). The increased tumor-infiltrating Tregs predicted poorer prognosis in HCC patients.

CONCLUSIONS

The CCL20-CCR6 axis mediates the migration of circulating Tregs into tumor microenvironment, which in turn results in tumor progression and poor prognosis in HCC patients. Thus, blocking CCL20-CCR6 axis-mediated Treg migration may be a novel therapeutic target for HCC.

AMP-activated protein kinase: a potential player in Alzheimer's disease

AMP-activated protein kinase (AMPK) stimulates energy production via glucose and lipid metabolism, whereas it inhibits energy consuming functions, such as protein and cholesterol synthesis. Increased cytoplasmic AMP and Ca(2+) levels are the major activators of neuronal AMPK signaling. Interestingly, Alzheimer's disease (AD) is associated with several abnormalities in neuronal energy metabolism, for example, decline in glucose uptake, mitochondrial dysfunctions and defects in cholesterol metabolism, and in addition, with problems in maintaining Ca(2+) homeostasis. Epidemiological studies have also revealed that many metabolic and cardiovascular diseases are risk factors for cognitive impairment and sporadic AD. Emerging studies indicate that AMPK signaling can regulate tau protein phosphorylation and amyloidogenesis, the major hallmarks of AD. AMPK is also a potent activator of autophagic degradation which seems to be suppressed in AD. All these observations imply that AMPK is involved in the pathogenesis of AD. However, the responses of AMPK activation are dependent on stimulation and the extent of activating stress. Evidently, AMPK signaling can repress and delay the appearance of AD pathology but later on, with increasing neuronal stress, it can trigger detrimental effects that augment AD pathogenesis. We will outline the potential role of AMPK function in respect to various aspects affecting AD pathogenesis.

Novel role of AMP-activated protein kinase signaling in cigarette smoke induction of IL-8 in human lung epithelial cells and lung inflammation in mice

Cigarette smoke (CS) increases chemokine production in lung epithelial cells (LECs), but the pathways involved are not completely understood. AMP-activated protein kinase (AMPK), a crucial regulator of energy homeostasis, may modulate inflammation. Here, we show that cigarette smoke extract sequentially activated NADPH oxidase; increased intracellular reactive oxygen species (ROS) level; activated AMPK, NF-κB, and STAT3; and induced interleukin 8 (IL-8) in human LECs. Inhibition of NADPH oxidase activation by apocynin or siRNA targeting p47(phox) (a subunit of NADPH oxidase) attenuated the increased intracellular ROS level, AMPK activation, and IL-8 induction. Removal of intracellular ROS by N-acetylcysteine reduced the AMPK activation and IL-8 induction. Prevention of AMPK activation by Compound C or AMPK siRNA lessened the activation of both NF-κB and STAT3 and the induction of IL-8. Abrogation of the activation of NF-κB and STAT3 by BAY11-7085 and AG490, respectively, attenuated the IL-8 induction. We additionally show that chronic CS exposure in mice promoted AMPK phosphorylation and expression of MIP-2α (an IL-8 homolog) in LECs and lungs, as well as lung inflammation, all of which were reduced by Compound C treatment. Thus, a novel NADPH oxidase-dependent, ROS-sensitive AMPK signaling is important for CS-induced IL-8 production in LECs and possibly lung inflammation.

The role of LKB1 and AMPK in cellular responses to stress and damage

The LKB1 and AMPK proteins participate in an energy sensing cascade that responds to depletion of ATP, serving as a master regulator of metabolism that inhibits anabolic processes and stimulates catabolic processes. However in recent years, LKB1 and AMPK have been implicated in a variety of other cellular processes, both cytoplasmic and nuclear, such as control of cell polarity and regulation of gene transcription. In this review, we summarize the most recent discoveries regarding participation of LKB1 and AMPK in signaling pathways that respond to cellular stress and damage, and the relevance of this signaling for disease and therapy.