title: Cocoa flavonoids up-regulate antioxidant enzyme activity via the ERK1/2 pathway to protect against oxidative stress-induced apoptosis in HepG2 cells.
abstract: Oxidative stress is widely recognized as an important mediator of apoptosis in liver cells and plays a pivotal role in the pathogenesis of several diseases. Cocoa flavonoids have shown a powerful antioxidant activity providing protection against oxidation and helping prevent oxidative stress-related diseases. However, the molecular mechanisms responsible for this protection are not fully understood. Thus, in this study we investigated the protective effect of a cocoa polyphenolic extract (CPE) against tert-butyl hydroperoxide (t-BOOH)-induced apoptosis and the molecular mechanisms involved in this process. Incubation of HepG2 cells with t-BOOH induced apoptosis as evidenced by caspase-3 activation. This effect was accompanied by increased reactive oxygen species formation and by transient activation of the extracellular regulated kinases (ERKs) as well as sustained activation of the c-Jun N-terminal kinases (JNKs). On the contrary, pretreatment of HepG2 cells with CPE prevented apoptosis through the reduction of reactive oxygen species generation and the modulation of the apoptotic pathways activated by t-BOOH. CPE treatment also activated survival signaling proteins, such as protein kinase B (AKT) and ERKs, and increased the activities of two antioxidant enzymes, glutathione peroxidase (GPx) and glutathione reductase (GR). ERK's implication on GPx and GR induction and the protective effect of CPE against t-BOOH-induced oxidative stress and apoptosis were confirmed through experiments with selective inhibitors. These findings suggest that CPE is an effective inductor of GPx and GR activities via ERK activation and that this up-regulation seems to be required to attenuate t-BOOH-induced injury.
authors.affiliation: Department of Metabolism and Nutrition, Instituto de Ciencia y Tecnología de los Alimentos y Nutrición (formerly Instituto del Frío), CSIC, Ciudad Universitaria, 28040 Madrid, Spain. amartina@if.csic.es
authors.forename: María Angeles
authors.initials: MA
authors.lastname: Martín
authors.forename: Ana Belén Granado
authors.initials: AB
authors.lastname: Serrano
authors.forename: Sonia
authors.initials: S
authors.lastname: Ramos
authors.forename: María Izquierdo
authors.initials: MI
authors.lastname: Pulido
authors.forename: Laura
authors.initials: L
authors.lastname: Bravo
authors.forename: Luis
authors.initials: L
authors.lastname: Goya
mesh_terms: D000975:Antioxidants / Q000302:isolation & purification / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002099:Cacao / Q000737:chemistry*; D053148:Caspase 3 / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D019610:Cytoprotection; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005419:Flavonoids / Q000032:analysis / Q000302:isolation & purification / Q000494:pharmacology*; D005979:Glutathione Peroxidase / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D020122:tert-Butylhydroperoxide / Q000633:toxicity
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010936:Plant Extracts; D017382:Reactive Oxygen Species; D020122:tert-Butylhydroperoxide; D005979:Glutathione Peroxidase; D005980:Glutathione Reductase; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D053148:Caspase 3