Flavonoids protect neurons from oxidized low-density-lipoprotein-induced apoptosis involving c-Jun N-terminal kinase (JNK), c-Jun and caspase-3.
Oxidative stress has been associated with neuronal loss in neurodegenerative diseases and during age-associated cognitive decline. Flavonoids have been proposed to play a useful role in protecting the central nervous system against oxidative and excitotoxic stress, although the mechanism of action is unknown. Using oxidized low-density lipoprotein (oxLDL) as the oxidative insult we investigated the mechanism of neurotoxicity and attempted to identify possible sites of action of two of the most potent protective flavonoids, epicatechin and kaempferol, in cultured primary neurons. Using cultured striatal neurons and selective phosphospecific antibodies we addressed the potential role of extracellular signal-regulated kinases 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). OxLDL stimulated a Ca(2+)-dependent activation of both ERK1/2 and JNK that was strongly inhibited by pre-treatment with low micromolar concentrations of epicatechin. Neurotoxicity induced by oxLDL, however, was neither reduced nor enhanced by inhibiting ERK1/2 activation with mitogen-activated protein kinase kinase (MEK) inhibitors, suggesting that this cascade is unlikely to be involved in either oxLDL toxicity or the protective effects of flavonoids. oxLDL caused a sustained activation of JNK that resulted in the phosphorylation of the transcription factor c-Jun, which was abolished in neurons pre-treated with flavonoids. Furthermore, oxLDL induced the cleavage of procaspase-3 and increased caspase-3-like protease activity in neurons, an effect which was strongly inhibited by pre-exposure to either epicatechin or kaempferol. In addition, a caspase-3 inhibitor reduced oxLDL-induced neuronal death, implicating an apoptotic mechanism. A major in vivo metabolite of epicatechin, 3'-O-methyl-epicatechin was as effective as epicatechin in protecting neurons. Thus dietary flavonoids might have potential as protective agents against neuronal apoptosis through selective actions within stress-activated cellular responses, including protein kinase signalling cascades.
Schroeter
H
H
Centre for Neuroscience Research, Guy's, King's and St. Thomas' School of Biomedical Sciences, Hodgkin Building, Guy's Campus, London SE1 1UL, UK.
Spencer
J P
JP
Rice-Evans
C
C
Williams
R J
RJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001692:Biological Transport / Q000187:drug effects; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002392:Catechin / Q000494:pharmacology; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000166:cytology; D004622:Embryo, Mammalian; D004789:Enzyme Activation; D005419:Flavonoids / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases; D044949:Kaempferols; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects; D008077:Lipoproteins, LDL / Q000493:pharmacokinetics / Q000633:toxicity*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D018696:Neuroprotective Agents; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D011794:Quercetin / Q000031:analogs & derivatives / Q000494:pharmacology
D005419:Flavonoids; D044949:Kaempferols; D008077:Lipoproteins, LDL; D018696:Neuroprotective Agents; D016755:Proto-Oncogene Proteins c-jun; C099252:oxidized low density lipoprotein; C006552:kaempferol; D002392:Catechin; D011794:Quercetin; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases