Expression of zinc-deficient human superoxide dismutase in Drosophila neurons produces a locomotor defect linked to mitochondrial dysfunction.

More than 130 different mutations in the Cu/Zn superoxide dismutase (SOD1) gene have been associated with amyotrophic lateral sclerosis but the mechanism of this toxicity remains controversial. To gain insight into the importance of the zinc site in the pathogenesis of SOD1 in vivo, we generated a Drosophila model with transgenic expression of a zinc-deficient human SOD1. Expression of zinc-deficient SOD1 in Drosophila resulted in a progressive movement defect with associated mitochondrial cristae vacuolization and reductions in adenosine triphosphate (ATP) levels. Furthermore, these flies are sensitized to mitochondrial toxins, paraquat, and zinc. Importantly, we show that the zinc-deficient SOD1-induced motor defect can be ameliorated by supplementing the endogenous fly respiratory chain machinery with the single-subunit NADH-ubiquinone oxidoreductase from yeast (NADH is nicotinamide adenine dinucleotide, reduced form.). These results demonstrate that zinc-deficient SOD1 is neurotoxic in vivo and suggest that mitochondrial dysfunction plays a critical role in this toxicity. The robust behavioral, pathological, and biochemical phenotypes conferred by zinc-deficient SOD1 in Drosophila have general implications for the role of the zinc ion in familial and sporadic amyotrophic lateral sclerosis.

Antioxidant therapy attenuates oxidative stress in the blood of subjects exposed to occupational airborne contamination from coal mining extraction and incineration of hospital residues.

Coal mining and incineration of solid residues of health services (SRHS) generate several contaminants that are delivered into the environment, such as heavy metals and dioxins. These xenobiotics can lead to oxidative stress overgeneration in organisms and cause different kinds of pathologies, including cancer. In the present study the concentrations of heavy metals such as lead, copper, iron, manganese and zinc in the urine, as well as several enzymatic and non-enzymatic biomarkers of oxidative stress in the blood (contents of lipoperoxidation = TBARS, protein carbonyls = PC, protein thiols = PT, α-tocopherol = AT, reduced glutathione = GSH, and the activities of glutathione S-transferase = GST, glutathione reductase = GR, glutathione peroxidase = GPx, catalase = CAT and superoxide dismutase = SOD), in the blood of six different groups (n = 20 each) of subjects exposed to airborne contamination related to coal mining as well as incineration of solid residues of health services (SRHS) after vitamin E (800 mg/day) and vitamin C (500 mg/day) supplementation during 6 months, which were compared to the situation before the antioxidant intervention (Ávila et al., Ecotoxicology 18:1150-1157, 2009; Possamai et al., Ecotoxicology 18:1158-1164, 2009). Except for the decreased manganese contents, heavy metal concentrations were elevated in all groups exposed to both sources of airborne contamination when compared to controls. TBARS and PC concentrations, which were elevated before the antioxidant intervention decreased after the antioxidant supplementation. Similarly, the contents of PC, AT and GSH, which were decreased before the antioxidant intervention, reached values near those found in controls, GPx activity was reestablished in underground miners, and SOD, CAT and GST activities were reestablished in all groups. The results showed that the oxidative stress condition detected previously to the antioxidant supplementation in both directly and indirectly subjects exposed to the airborne contamination from coal dusts and SRHS incineration, was attenuated after the antioxidant intervention.

Inactivation of cytochrome c oxidase by mutant SOD1s in mouse motoneuronal NSC-34 cells is independent from copper availability but is because of nitric oxide.

The copper-enzyme cytochrome c oxidase (Cytox) has been indicated as a primary molecular target of mutant copper, zinc superoxide dismutase (SOD1) in familial amyotrophic lateral sclerosis (fALS); however, the mechanism underlying its inactivation is still unclear. As the toxicity of mutant SOD1s could arise from their selective recruitment to mitochondria, it is conceivable that they might compete with Cytox for the mitochondrial copper pool causing Cytox inactivation. To investigate this issue, we used mouse motoneuronal neuroblastoma x spinal cord cell line-34, stably transfected for the inducible expression of low amounts of wild-type or mutant (G93A, H46R, and H80R) human SOD1s and compared the effects observed on Cytox with those obtained by copper depletion. We demonstrated that all mutants analyzed induced cell death and decreased the Cytox activity, but not the protein content of the Cytox subunit II, at difference with copper depletion that also affected subunit II protein. Copper supplementation did not counteract mutant hSOD1s toxicity. Otherwise, the treatment of neuroblastoma x spinal cord cell line-34 expressing G93A, H46R, or H80R hSOD1 mutants, and showing constitutive expression of iNOS and nNOS, with either a NO scavenger, or NOS inhibitors prevented the inhibition of Cytox activity and rescued cell viability. These results support the involvement of NO in mutant SOD1s-induced Cytox damage, and mitochondrial toxicity.

The toxicity of high-dose superoxide dismutase suggests that superoxide can both initiate and terminate lipid peroxidation in the reperfused heart.

Recently, we described an anomalous bell-shaped dose-response curve for the protection of the reoxygenated isolated myocardium by superoxide dismutase (SOD). SOD is dramatically protective up to a point (5 micrograms/ml in the perfusate) beyond which it loses its ability to protect and, at very high doses (50 micrograms/ml), exacerbates the injury. We proposed that O2-. may serve as both initiator and terminator of lipid peroxidation, such that over scavenging the radical may increase net lipid peroxidation via increased chain length. We examined the ability of U74389F, a lipid peroxidation inhibitor, to ameliorate the toxicity of high-dose SOD in the isolated perfused rabbit heart preparation. The results show a significant improvement in the percent recovery of developed tension of hearts treated with U74389F and overdosed with MnSOD, as well as a decrease in thiobarbituric acid reactive substances.

Safety evaluation of free radical scavengers PEG-catalase and PEG-superoxide dismutase.

Treatment with catalase and SOD (superoxide dismutase) could diminish the damage due to oxygen free radical formation, but these enzymes are rapidly removed from circulation. The covalent attachment of monomethoxypolyethylene glycol (PEG) to catalase and SOD extended their plasma half-lives. Toxicity of PEG-catalase and PEG-SOD was evaluated in mice and rats prior to their use as free radical scavengers. Rodents used in acute, subacute, and subchronic toxicologic studies could tolerate large doses of PEG-catalase and PEG-SOD without developing toxic signs. The conjugates did not affect survival rate, appearance, behavior, food intake, blood chemistry, hematology, or urinalysis. In general, body weight gains, organ weights, and histomorphology were also unaffected. Massive doses of PEG-catalase caused slight weight loss, splenic hypertrophy, and generalized splenic stimulation in mice. Massive doses of PEG-SOD resulted in vacuolation in splenic macrophages in rats. PEG-catalase and PEG-SOD circulated for 3 days and 8 days, respectively, in mice following i.v. or i.m. administration.

Chromosomal aberrations in V79 cells induced by superoxide radical generated by the hypoxanthine-xanthine oxidase system.

The effect of the superoxide radical, generated by the hypoxanthine-xanthine oxidase system, on chromosomal mutation was examined in Chinese hamster V79 cells. When cells were treated with this system for 1 h in Hanks' solution, the incidence of metaphases with chromosomal aberrations was increased with hypoxanthine at concentrations of 2.5 to 10 micrograms/ml. On the other hand, in Eagle's minimum essential medium (MEM) or MEM supplemented with 10% fetal bovine serum, only hypoxanthine at 5 micrograms/ml plus xanthine oxidase induced chromosomal aberrations and higher concentrations of hypoxanthine were cytotoxic to V79 cells. The increased frequency of chromosomal aberrations and the cytotoxicity of hypoxanthine plus xanthine oxidase were not affected by superoxide dismutase, but were strongly inhibited by catalase.