To clarify the role of mitochondrial electron transport chain (mtETC) in heavy-metal-induced neurotoxicity, we studied action of Cd2+, Hg2+, and Cu2+ on cell viability, intracellular reactive oxygen species formation, respiratory function, and mitochondrial membrane potential of rat cell line PC12. As found, the metals produced, although in a different way, dose- and time-dependent changes of all these parameters. Importantly, Cd2+ beginning from 10 [mu]M and already at short incubation time (3 h) significantly inhibited the FCCP-uncoupled cell respiration; besides, practically the complete inhibition of the respiration was reached after 3 h incubation with 50 [mu]M Hg2+ or 500 [mu]M Cd2+, whereas even after 48 h exposure with 500 [mu]M Cu2+, only a 50% inhibition of the respiration occurred. Against the Cd2+-induced cell injury, not only different antioxidants and mitochondrial permeability transition pore inhibitors were protective but also such mtETC effectors as FCCP and stigmatellin (complex III inhibitor). However, all mtETC effectors used did not protect against the Hg2+- or Cu2+-induced cell damage. Notably, stigmatellin was shown to be one of the strongest protectors against the Cd2+-induced cell damage, producing a 15–20% increase in the cell viability. The mechanisms of the mtETC involvement in the heavy-metal-induced mitochondrial membrane permeabilization and cell death are discussed.

Abstract:Oxidative stress may contribute to many pathophysiologic changes that occur after traumatic brain injury. In the current study, contemporary methods of detecting oxidative stress were used in a rodent model of traumatic brain injury. The level of the stable product derived from peroxidation of arachidonyl residues in phospholipids, 8-epi-prostaglandin F 2␣ , was increased at 6 and 24 h after traumatic brain injury. Furthermore, relative amounts of fluorescent end products of lipid peroxidation in brain extracts were increased at 6 and 24 h after trauma compared with sham-operated controls. The total antioxidant reserves of brain homogenates and water-soluble antioxidant reserves as well as tissue concentrations of ascorbate, GSH, and protein sulfhydryls were reduced after traumatic brain injury. A selective inhibitor of cyclooxygenase-2, SC 58125, prevented depletion of ascorbate and thiols, the two major water-soluble antioxidants in traumatized brain. Electron paramagnetic resonance (EPR) spectroscopy of rat cortex homogenates failed to detect any radical adducts with a spin trap, 5,5-dimethyl-1-pyrroline N-oxide, but did detect ascorbate radical signals. The ascorbate radical EPR signals increased in brain homogenates derived from traumatized brain samples compared with sham-operated controls. These results along with detailed model experiments in vitro indicate that ascorbate is a major antioxidant in brain and that the EPR assay of ascorbate radicals may be used to monitor production of free radicals in brain tissue after traumatic brain injury. Key Words: Traumatic brain injury-Oxidative stress-Ascorbate -Spin traps-Thiols-8-epi-Prostaglandin F 2␣ .

Ganglioside GM1 was shown to increase the viability of PC12 cells exposed to hydrogen peroxide or amyloid beta-peptide (Abeta(25-35)). The PC12 cells transfected with mutant gene (expressing APP(SW)) were found to be more sensitive to oxidative stress than the cells transfected with wild type gene (expressing APP(WT)) or vector-transfected cells, GM1 being effective in enhancing the viability of the cells transfected with mutant gene. The exposure to hydrogen peroxide or Abeta(25-35) results in a partial inactivation of Na(+),K(+)-ATPase in PC12 cells, H(2)O(2) increases MDA accumulation in these cells. But these effects could be partially prevented or practically abolished by GM1 ganglioside. In the presence of the inhibitor of tyrosine kinase of Trk receptors (K-252a) the protective and metabolic effects of GM1 on PC12 cells in conditions of oxidative stress caused by hydrogen peroxide are not observed or are markedly diminished.

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