Protective effects of Debo on zinc-induced apoptosis of C6 glial cells via modulation of intracellular antioxidant, reduced glutathione

Transition metal-induced apoptosis in lymphocytes via hydroxyl radical generation, mitochondria dysfunction, and caspase-3 activation: an in vitro model for neurodegeneration

BACKGROUND

Redox transition metals have been implicated as crucial players in pathogenesis of neurodegenerative diseases. Intracellular signaling mechanism(s) responsible for oxidative stress and death in single-cell model exposed to metals has not yet been fully elucidated. The objective of the study was to determine the mechanism by which metals induced apoptosis in human peripheral blood lymphocytes (PBL).

METHODS

PBL were exposed to 50, 100, 250, 500, and 1,000 microM (Fe2+), (Mn2+), (Cu2+), and (Zn2+)-(SO4). Apoptotic/necrotic morphology was assessed with acridine orange/ethidium bromide staining. Further evaluations comprised production of H2O2, generation of hydroxyl radical (.OH), disruption of mitochondrial transmembrane potential (DeltaPsim), caspase-3 activation, and activation of NF-kappaB and p53 transcriptional factors.

RESULTS

Morphologic analysis showed that 500 microM provoked maximal percentage of apoptosis (22-30% AO/EB) and minimal necrosis (3-7%), whereas low concentrations were innocuous but 1,000 microM induced mainly necrosis (>40% AO/EB). Metals generated both H2O2 and (.OH) by Fenton reaction. Hydroxyl scavengers protected PBL from metal-induced apoptosis. All metals induced mitochondrial depolarization (17-62% nonfluorescent cells) and activated caspase-3 concomitantly with apoptotic morphology (25-32% AO/EB) at 24 h, and neither NF-kappaB nor p53 transcription factor showed activation.

CONCLUSIONS

This study provides evidence that redox-active (Fe2+), (Mn2+), (Cu2+), and (Zn2+) ion-induced apoptosis in PBL by (H2O2)/(.OH) generation, resulting in mitochondria depolarization, caspase-3 activation, and nuclear fragmentation independent of NF-kappaB and p53 transcription factors activation. Our data highlight the potential use of lymphocytes as a model to screen antioxidant strategies designed to remove H2O2/.OH associated with metal-catalyzed reactions in neurodegenerative disorders.

The role of NF-kappaB in the regulation of cell stress responses

Nuclear factor-kappaB (NF-kappaB) is one of the key regulatory molecules in oxidative stress-induced cell activation. NF-kappaB is normally sequestered in the cytoplasm of nonstimulated cells and must translocate into the nucleus to regulate effector gene expression. A family of inhibitory proteins, IKBs, binds to NF-kappaB and masks its nuclear localization signal domain and therefore controls the translocation of NF-kappaB. Exposure of cells to extracellular stimuli that perturb redox balance results in rapid phosphorylation, ubiquitination, and proteolytic degradation of IkappaBs. This process frees NF-kappaB from the NF-KB/IKB complexes and enables NF-kappaB to translocate to the nucleus where it regulates gene transcription. Many effector genes including those encoding cytokines and adhesion molecules are in turn regulated by NF-kappaB. NF-kappaB is also an essential component of ionizing radiation (IR)-triggered signal transduction pathways that can lead to cell death or survival. The purpose of this review is to briefly summarize the recent progress in the studies of the role of reactive oxygen species (ROS), cytokines and ionizing radiation in NF-kappaB activation.

Protective effects of Debo on serum-deprived apoptosis of PC12 cells via inhibition of H2O2 generation and caspase 3-like protease activity

Oxidative stress can be induced neurotoxic insults by increasing intracellular H2O2, which has been implicated in various neurodegenerative diseases in aging. We investigated the mechanism by which Debo protects PC12 cells from serum deprivation-induced apoptosis. PC12 cells underwent apoptotic death in association with increase in caspase 3-like activity, DNA fragmentation, H2O2 production, GSH depletion, and NF-kappaB activation after 24 hr of serum withdrawal. Debo protected cells from a serum deprivation-induced cytotoxicity in a dose dependent manner. Debo recovered the intracellular GSH level decreased by serum deprivation in PC12 cells. Also, Debo inhibited the activation of caspase 3-like protease of serum-deprived PC12 cells in a dose dependent manner. Furthermore, Debo inhibited the transcriptional activation of NF-kappaB by serum deprivation. These findings indicate that Debo may protect PC12 cells against apoptosis by serum deprivation via generation of intracellular GSH to scavenge oxidative radicals including H2O2.