Modulation of mitochondrial membrane potential and reactive oxygen species production by copper in astrocytes

Abstract

In monolayers of cultured rat astrocytes a number of agents that induce oxidative stress act synergistically with exposure to copper leading to rapid depolarization of the mitochondrial membrane potential (Y m ) and increased reactive oxygen species (ROS) production. Copper sensitized astrocytes to the action of menadione, an intracellular generator of superoxide anion radical, exogenous hydrogen peroxide (H 2 O 2 ) and rotenone, an inhibitor of mitochondrial electron transport chain complex I. However, significant differences were observed in the ability to modulate the copper-enhanced oxidative stress depending on which stressor was used. The inhibitor of mitochondrial permeability transition cyclosporin A attenuated the effect of copper and rotenone, but had no protective action in the case of H 2 O 2 /copper and menadione/copper combinations. The H 2 O 2 scavenger pyruvate was effective at protecting mitochondria against damage associated with the combined exposure to H 2 O 2 /copper and menadione/copper but not to the rotenone/copper combination. The antioxidant Trolox was ineffective at protecting against any of these actions and indeed had a damaging effect when combined with copper. The membrane-permeable copper chelator neocuproine combined with sensitizing concentrations of menadione caused a decrease in Y m , mimicking the action of copper. Penicillamine, a membrane-impermeable copper chelator, was effective at reducing copper sensitization. Endogenous copper, mobilized during periods of oxidative stress, may play a role in the pathophysiology of brain injury. Our results suggest that this might be particularly dangerous in dysfunctional conditions in which the mitochondrial electron transport chain is compromised. Keywords: antioxidants, astrocytes, copper, copper chelators, mitochondrial membrane potential, reactive oxygen species. J. Neurochem. Astrocytes are one of the major cell types in the brain; they protect neurons from various external insults, including reactive oxygen species (ROS) (Desagher et al. 1996;Tanaka et al. 1999). Alterations in astroglial cell function during oxidative stress may thus play a key role in the pathophysiology of brain injury. Mitochondria are highly sensitive to oxidative stress, and ROS production by mitochondria can in turn disturb mitochondrial function causing a vicious cycle. Damage to mitochondria in brain cells may compromise their ability to protect against ROS and indeed lead them to become sources of ROS production (Lenaz 1998;Montal 1998;Sullivan et al. 1999;Beal 2000;Chan 2001).Copper is a transition metal that plays an important functional role in many biological processes (Camakaris et al. 1999;Rinaldi 2000). However, even in a bound form copper is dangerous owing to its ability to increase oxidative stress through conversion of H 2 O 2 to more reactive ROS such as the hydroxyl radical (OHAE) (the Fenton-Haber-Weiss reaction) (Halliwell and Gutteridge 1999). There is evidence that copper can be mobilized and redistributed from cell storage poo...

The mitochondrial permeability transition, and oxidative and nitrosative stress in the mechanism of copper toxicity in cultured neurons and astrocytes

“…Although our investigation demonstrates that copper induces mPT in cultured astrocytes, an earlier study failed to identify it, 41 although in that study copper potentiated the dissipation of DCm caused by menadione, rotenone, and H 2 O 2 . A likely explanation for this discrepancy may be that the investigators employed very high concentration of copper (100 mM) for only a short time period (40 min).…”

Tumor Necrosis Factor-α-Induced Cytokine-Induced Neutrophil Chemoattractant-1 (CINC-1) Production by Rat Gastric Epithelial Cells: Role of Reactive Oxygen Species and Nuclear Factor-κB

“…Two sites of the mitochondrial respiratory chain have been identified as sources of ROS: complex 1 (NADH ubiquinone oxidoreductase) and complex 3 (the ubiquinone reductase site) (Liu et al, 2002). In the mitochondrial membrane, the ubiquinone reductase activity of complex 1 is sensitive to rotenone (Ko et al, 2001;Gyulkhandanyan et al, 2003). DPI inhibits the mitochondrial complex 1, especially between NADH and ferritin-sulfur clusters (Majander et al, 1994).…”

Hydrogen peroxide alters membrane and cytoskeleton properties and increases intercellular connections in astrocytes

“…dependent kinases (proteases, phospholipases and nucleases), leading to mitochondrial dysfunction and activation of apoptotic pathways (Butterfield and Lauderback, 2002;Gyulkhandanyan et al, 2003;Jacobson and Duchen, 2002;Robb et al, 1999). Despite the metabolic changes, little is known about the direct effects of H 2 O 2 on membrane properties of astrocytes.…”