A diet rich in cocoa attenuates N-nitrosodiethylamine-induced liver injury in rats

The effects of cocoa feeding against N-nitrosodiethylamine (DEN)-induced liver injury were studied in rats. Animals were divided into five groups. Groups 1 and 2 were fed with standard and cocoa-diet, respectively. Groups 3 and 4 were injected with DEN at 2 and 4 weeks, and fed with standard and cocoa-diet, respectively. Group 5 was treated with DEN, received the standard diet for 4 weeks and then it was replaced by the cocoa-diet. DEN-induced hepatic damage caused a significant increase in damage markers, as well as a decrease in the hepatic glutathione, diminished levels of p-ERK and enhanced protein carbonyl content, caspase-3 activity and values of p-AKT and p-JNK. The cocoa-rich diet prevented the reduction of hepatic glutathione concentration and catalase and GPx activities in DEN-injected rats, as well as diminished protein carbonyl content, caspase-3 activity, p-AKT and p-JNK levels, and increased GST activity. However, cocoa administration did not abrogate the DEN-induced body weight loss and the increased levels of hepatic-specific enzymes and LDH. These results suggested that cocoa-rich diet attenuates the DEN-induced liver injury. © 2009 Elsevier Ltd. All rights reserved.This work was supported by the grants 200870I198, AGL2004-302, AGL2007-64042 and CSD2007-00063 from the Spanish Ministry of Science and Innovation. A.B. Granado-Serrano is a predoctoral fellow of the Spanish Ministry of Science and Education.Peer Reviewe

Molecular targets of quercetin in cancer chemoprevention

Prevention of cancer through dietary intervention has received increasing interest recently, and dietary polyphenols have become important potential chemopreventive natural agents. Quercetin, among polyphenols, has been reported to interfere with the initiation, promotion and progression of cancer. It might lead to the modulation of proteins in diverse pathways and require the integration of different signals for the final chemopreventive effect. Quercetin has been demonstrated to act on multiple key elements in signal transduction pathways related to cellular proliferation, differentiation, apoptosis and inflammation; however, these molecular mechanisms of action are not completely characterized and many features remain to be elucidated. The aim of this review is to provide insights into the molecular basis of the potential chemopreventive activity of quercetin with an emphasis on its ability to control intracellular signalling cascades considered as relevant targets in a cancer-preventive approach.Peer Reviewe

Quercetin modulates Nrf2 and glutathione-related defenses in HepG2 cells: Involvement of p38

Dietary flavonoid quercetin has been suggested as a cancer chemopreventive agent, but the mechanisms of action remain unclear. This study investigated the influence of quercetin on p38-MAPK and the potential regulation of the nuclear transcription factor erythroid-2p45-related factor (Nrf2) and the cellular antioxidant/detoxifying defense system related to glutathione (GSH) by p38 in HepG2 cells. Incubation of HepG2 cells with quercetin at a range of concentrations (5-50 οM) for 4 or 18 h induced a differential effect on the modulation of p38 and Nrf2 in HepG2 cells, 50 οM quercetin showed the highest activation of p38 at 4h of treatment and values of p38 similar to those of control cells after 18 h of incubation, together with the inhibition of Nrf2 at both incubation times. Quercetin (50 οM) induced a time-dependent activation of p38, which was in concert with a transient stimulation of Nrf2 to provoke its inhibition afterward. Quercetin also increased GSH content, mRNA levels of glutamylcysteine-synthetase (GCS) and expression and/or activity of glutathione-peroxidase, glutathione-reductase and GCS after 4 h of incubation, and glutathione-S-transferase after 18 h of exposure. Further studies with the p38 specific inhibitor SB203580 showed that the p38 blockage restored the inhibited Nrf2 transcription factor and the enzymatic expression and activity of antioxidant/detoxificant enzymes after 4 h exposure. In conclusion, p38-MAPK is involved in the mechanisms of the cell response to quercetin through the modulation of Nrf2 and glutathione-related enzymes in HepG2 cells. © 2011 Elsevier Ireland Ltd. All rights reserved.This work was supported by the Grants 200870I198 (CSIC), and AGL2004-302, AGL2007-64042 and CSD2007-00063 from the Spanish Ministry of Science and Innovation (CICYT). A.B. Granado-Serrano was a predoctoral fellow of the Spanish Ministry of Science and Education.Peer Reviewe

Quercetin attenuates TNF-induced inflammation in Hepatic cells by inhibiting the NF-κB pathway

The dietary flavonoid quercetin is an antioxidant that possesses antiinflammatory and anticarcinogenic properties and may modulate signaling pathways. Inflammation is considered to play a pivotal role in carcinogenesis by triggering activation of transcription factors such as nuclear factor kappa B (NF-κB), functionally dependent on cellular redox status. This study aims to investigate the antiinflammatory effect of quercetin and its role on the NF-κB pathway, and cyclooxygenase-2 (COX-2) and mitogen-activated protein kinases modulation in a human hepatoma cell line (HepG2). Quercetin alone did not modify any of the parameters analyzed but protected cells against activation of the NF-κB route induced by tumor necrosis factor-α. This inhibitory effect of quercetin was mediated, at least in part, by extracellular regulated kinase, c-jun amino-terminal kinase, and reactive oxygen species, and it was accompanied by reduced COX-2 levels. These observations suggest that quercetin may contribute as an antiinflammatory agent in the liver and provide evidences about its role in the prevention of diseases associated with inflammation, including cancer.This work was supported by the grants 200870I198 (CSIC) and CSD2007-00063 from the Spanish Ministry of Science and Innovation (CICYT). A.B. Granado-Serrano was a predoctoral fellow of the Spanish Ministry of Science and Education.Peer Reviewe

Epicatechin induces NF-κB, activator protein-1 (AP-1) and nuclear transcription factor erythroid 2p45-related factor-2 (Nrf2) via phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) and extracellular regulated kinase (ERK) signalling in HepG2 cells

The dietary flavonoid epicatechin has been reported to exhibit a wide range of biological activities. The objective of the present study was to investigate the time-dependent regulation by epicatechin on the activity of the main transcription factors (NF-κB, activator protein-1 (AP-1) and nuclear transcription factor erythroid 2p45-related factor (Nrf2)) related to antioxidant defence and survival and proliferation pathways in HepG2 cells. Treatment of cells with 10m-epicatechin induced the NF-κB pathway in a time-dependent manner characterised by increased levels of IB kinase (IKK) and phosphorylated inhibitor of κB subunit-α(p-IB) and proteolytic degradation of IκB, which was consistent with an up-regulation of the NκF-B-binding activity. Time-dependent activation of the AP-1 pathway, in concert with enhanced c-Jun nuclear levels and induction of Nrf2 translocation and phosphorylation were also demonstrated. Additionally, epicatechin-induced NκF-B and Nrf2 were connected to reactive oxygen species intracellular levels and to the activation of cell survival and proliferation pathways, being phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) and extracellular regulated kinase (ERK) associated to Nrf2 modulation and ERK to NF-κB induction. These data suggest that the epicatechin-induced survival effect occurs by the induction of redox-sensitive transcription factors through a tight regulation of survival and proliferation pathways. © 2009 The Authors.The present study was supported by the grants AGL2004-302, AGL2007-64042 and CSD2007-00063 from the Spanish Ministry of Science and Innovation (CICYT) and 200870 I198 (CSIC). A. B. G.-S. is a predoctoral fellow of the Spanish Ministry of Science and Education.Peer Reviewe

Time-course regulation of survival pathways by epicatechin on HepG2 cells

Polyphenols, such as epicatechin, have been reported to exhibit a wide range of biological activities. The objective of the present study was to investigate the time-dependent regulation by epicatechin of survival/proliferation pathways in HepG2 cells. Treatment of HepG2 cells with 10 μmol/L epicatechin did not result in any cell damage up to 18 h, as evaluated by the lactate dehydrogenase assay. Moreover, the enhanced cell death evoked by an oxidative stress induced with tert-butyl hydroperoxide was prevented in the cells pretreated 4 or 18 h with epicatechin. Epicatechin-induced survival was a rapid event that was accompanied by early and sustained activation of major survival signaling proteins, such as AKT/phosphatidylinositol 3-kinase and extracellular-regulated kinase (activated from 5 min to 18 h), as well as protein kinase C (PKC)-α (30 min to 18 h), in concert with unaltered c-jun N-amino terminal kinase levels and early inactivation of key death-related signals like PKC-δ (5 min to 18 h). Additionally, reactive oxygen species generation was transiently reduced when cells were treated with 10 μmol/L epicatechin (15-240 min). These data suggest that epicatechin induces cellular survival through a tight regulation of survival/proliferation pathways that requires the integration of different signals and persists over time, the ultimate effect on HepG2 cells being regulated by the balance among these signals.A.B. Granado-Serrano is a predoctoral fellow of the Spanish Ministry of Science and Education, and S. Ramos has a Ramón y Cajal contract from the Spanish Ministry of Science and Technology.Peer Reviewe

Time-course regulation of quercetin on cell survival/ proliferation pathways in human hepatoma cells

Quercetin, a dietary flavonoid, has been shown to possess anticarcinogenic properties, but the precise molecular mechanisms of action are not thoroughly elucidated. This study was aimed at investigating the time-course regulation effect of quercetin on survival/proliferation pathways in a human hepatoma cell line (HepG2). Quercetin induced a significant time-dependent inactivation of the major survival signaling proteins, i. e., phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (AKT), extracellular regulated kinase (ERK), protein kinase C-α (PKC-α), in concert with a time-dependent activation of key death-related signals: c-jun amino-terminal kinase (JNK) and PKC-δ. These data suggest that quercetin exerts a tight regulation of survival/proliferation pathways that requires the integration of different signals and persists over time, being the balance of these regulatory signals what determines the fate of HepG2 cells. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.This work was sup-ported by the grants AGL2004-302 from the Spanish Ministry of Science and Technology (CICYT), and 200570M050from the Comunidad de Madrid (CAM). A. B. G.–S. is a pre-doctoral fellow of the Spanish Ministry of Science and Edu-cation and S. R. has a Ramón y Cajal contract from theSpanish Ministry of Science and Technology.Peer reviewe

Quercetin modulates NF-κB and AP-1/JNK pathways to induce cell death in human hepatoma cells

Quercetin, a dietary flavonoid, has been shown to possess anticarcinogenic properties, but the precise molecular mechanisms of action are not thoroughly elucidated. The aim of this study was to investigate the regulatory effect of quercetin (50 μM) on two main transcription factors (NF-κB and AP-1) related to survival/proliferation pathways in a human hepatoma cell line (HepG2) over time. Quercetin induced a significant time-dependent inactivation of the NF-κB pathway consistent with a downregulation of the NF-κB binding activity (from 15 min onward). These features were in concert with a time-dependent activation (starting at 15 min and maintained up to 18 h) of the AP-1/JNK pathway, which played an important role in the control of the cell death induced by the flavonoid and contributed to the regulation of survival/proliferation (AKT, ERK) and death (caspase-3, p38, unbalance of Bcl-2 proapoptotic and antiapoptotic proteins) signals. These data suggest that NF-κB and AP-1 play a main role in the tight regulation of survival/proliferation pathways exerted by quercetin and that the sustained JNK/AP-1 activation and inhibition of NF-κB provoked by the flavonoid induced HepG2 death. Copyright © 2010, Taylor & Francis Group, LLC.This work was supported by the grants AGL2004-302 and CSD2007-00063 from the Spanish Ministry of Science and Technology (CICYT). A. B. Granado-Serrano is a predoctoral fellow of the Spanish Ministry of Science and Education.Peer Reviewe

Quercetin induces apoptosis via caspase activation, regulation of Bcl-2, and inhibition of PI-3-kinase/Akt and ERK pathways in a human hepatoma cell line (HepG2)

Dietary polyphenols have been associated with the reduced risk of chronic diseases such as cancer, but the precise underlying mechanism of protection remains unclear. The aim of this study was to investigate the effect of quercetin on the activation of the apoptotic pathway in ahumanhepatoma cell line (HepG2). Treatment of cells for 18 h with quercetin induced cell death in a dose-dependent manner; however, a shorter treatment (4 h) had no effect on cell viability. Incubation of HepG2 cells with quercetin for 18 h induced apoptosis by the activation of caspase-3 and -9, but not caspase-8. Moreover, this flavonoid decreased the Bcl-xL:Bcl-xS ratio and increased translocation of Bax to the mitochondrial membrane. A sustained inhibition of the major survival signals, Akt and extracellular regulated kinase (ERK), also occurred in quercetin-treated cells. These data suggest that quercetin may induce apoptosis by direct activation of caspase cascade (mitochondrial pathway) and by inhibiting survival signaling in HepG2. © 2006 American Society for Nutrition.This work was supported by grants AGL2004-302 from the Spanish Ministry of Science and Technology and 200570M050 from the Comunidad de Madrid; A. B. G-S. is a predoctoral fellow of the Spanish Ministry of Science and Education; S. R. has a Ramón y Cajal contract from the Spanish Ministry of Science and Technology.Peer Reviewe

Quercetin protects human hepatoma HepG2 against oxidative stress induced by tert-butyl hydroperoxide

Flavonols such as quercetin, have been reported to exhibit a wide range of biological activities related to their antioxidant capacity. The objective of the present study was to investigate the protective effect of quercetin on cell viability and redox status of cultured HepG2 cells submitted to oxidative stress induced by tert-butyl hydroperoxide. Concentrations of reduced glutathione and malondialdehyde, generation of reactive oxygen species and activity and gene expression of antioxidant enzymes were used as markers of cellular oxidative status. Pretreatment of HepG2 with 10 μM quercetin completely prevented lactate dehydrogenase leakage from the cells. Pretreatment for 2 or 20 h with all doses of quercetin (0.1-10 μM) prevented the decrease of reduced glutathione and the increase of malondialdehyde evoked by tert-butyl hydroperoxide in HepG2 cells. Reactive oxygen species generation induced by tert-butyl hydroperoxide was significantly reduced when cells were pretreated for 2 or 20 h with 10 μM and for 20 h with 5 μM quercetin. Finally, some of the quercetin treatments prevented the significant increase of glutathione peroxidase, superoxide dismutase, glutathione reductase and catalase activities induced by tert-butyl hydroperoxide. Gene expression of antioxidant enzymes was also affected by the treatment with the polyphenol. The results of the biomarkers analyzed clearly show that treatment of HepG2 cells in culture with the natural dietary antioxidant quercetin strongly protects the cells against an oxidative insult. © 2005 Elsevier Inc. All rights reserved.This work was supported by the grant AGL2000-1314 from the Spanish Ministry of Science and Technology (CICYT). S. Ramos has a contract from the Ramon y Cajal program from the Ministerio de Educación y Ciencia. R. Mateos is a postdoctoral fellow from the Ministerio de Educación y Ciencia.Peer Reviewe