cytochrome-c-t and methylmercuric-chloride

The involvement of oxidative stress has been suggested as a mechanism for toxicity caused by methylmercury (MeHg). One of the major critical sites for oxidative stress is the mitochondria. In this research, to clarify the target site in mitochondria affected by MeHg, the individual activities of the mitochondrial electron transport chain (ETC) (I∼IV) were examined in the liver, cerebrum and cerebellum of MeHg-intoxicated rats. In addition, to elucidate the mechanism underlying MeHg toxicity, cytochrome c release, caspase 3 activity and histological study were examined in the cerebrum and cerebellum. The cerebellum was found to be an exclusive tissue in which significant MeHg-induced alterations were observed. The complex II activity in the cerebellum mitochondria significantly decreased after MeHg exposure. Cytochrome c release from mitochondria increased only in the cerebellum by MeHg exposure. However, no significant alterations in caspase 3 activity or histological structure were found in brain tissues. These results suggest that MeHg acts on the constituents of complex II in the cerebellum, and induces mitochondrial dysfunction, leading to a release of cytochrome c from mitochondria. These events were considered to occur at the early stage of MeHg intoxication.

Topics: Animals; Apoptosis; Caspase 3; Cerebellum; Cerebrum; Cytochromes c; Electron Transport Chain Complex Proteins; Liver; Male; Methylmercury Compounds; Mitochondria; Oxidative Stress; Rats; Rats, Wistar

Mangiferin (MGN), a C-glucosylxanthone was investigated for its ability to protect against methylmercury (MeHg) induced neurotoxicity by employing IMR-32 (human neuroblastoma) cell line. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] and clonogenic cell survival assays confirmed the efficacy of MGN supplementation in attenuating MeHg-induced cytotoxicity. Pre-treatment with MGN significantly (p<0.01) inhibited MeHg-induced DNA damage (micronuclei, olive tail moment and % tail DNA) thereby demonstrating MGN's antigenotoxic potential. Also, pre-treatment with MGN significantly reduced MeHg-induced oxidative stress, intra-cellular Ca(2+) influx and inhibited depolarization of mitochondrial membrane. MGN pre-treated cells demonstrated a significant (p<0.05) increase in the GSH and GST levels followed by a significant (p<0.05) decrease in malondialdehyde (MDA) formation. In addition, inhibition of MeHg induced apoptotic cell death by MGN was demonstrated by microscopic, Annexin-V FITC and DNA fragmentation assays and further confirmed by western blot analysis. The present findings indicated the protective effect of MGN against MeHg induced toxicity, which may be attributed to its anti-genotoxic, anti-apoptotic and anti-lipid peroxidative potential plausibly because of its free radical scavenging ability, which reduced the oxidative stress and in turn facilitated the down-regulation of mitochondrial apoptotic signalling pathways.

Topics: Annexin A5; Antioxidants; Apoptosis; bcl-2-Associated X Protein; Calcium; Caspase 3; Cell Line, Tumor; Cell Nucleus; Cell Survival; Comet Assay; Cytochromes c; Cytokinesis; Cytoprotection; DNA Damage; DNA Fragmentation; Dose-Response Relationship, Drug; Drug Interactions; Free Radical Scavengers; Humans; Inhibitory Concentration 50; Intracellular Space; Membrane Potential, Mitochondrial; Metallothionein; Methylmercury Compounds; Micronucleus Tests; Necrosis; Neuroblastoma; NF-E2-Related Factor 2; Oxidative Stress; Proto-Oncogene Proteins c-bcl-2; Reactive Oxygen Species; Tubulin; Tubulin Modulators; Tumor Stem Cell Assay; Xanthones