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We recently reported a cardioselective and cumulative oxidation of cardiac mitochondrial DNA (mtDNA) following subchronic administration of doxorubicin to rats. The mtDNA adducts persist for up to 5 weeks after cessation of doxorubicin treatment. Since the evidence suggests that this persistence of mtDNA adducts cannot be attributed to a lack of repair and replication, we investigated whether it might reflect a long-lasting stimulation of free radical-mediated adduct formation. Male Sprague-Dawley rats received weekly s.c. injections of either doxorubicin (2 mg/kg) or an equivalent volume of saline. Cardiac myocytes isolated from rats following 6 weekly injections of doxorubicin expressed a much higher rate of reactive oxygen species (ROS) formation compared to saline controls. This higher rate of ROS formation persisted for 5 weeks following the last injection. Associated with this was a persistent depression of GSH in heart tissue, while protein-thiol content was not markedly altered. These data suggest that the accumulation and persistence of oxidized mtDNA may be due, not to the stability of the adducts, but to some as yet undefined toxic lesion that causes long-lasting stimulation of ROS generation by doxorubicin. This persistent generation of ROS may contribute to the cumulative and irreversible cardiotoxicity observed clinically with the drug. http://www.sciencedirect.com/science/article/B6TCR-430NR94-2/1/6f6f519d5a0b8b4e5b7cef8e0ed6c7f0

This report is an extension and complement of a previous study reporting the effect of three herbicides (paraquat, dinoseb and 2,4-D) on cell viability, GSH oxidation, NADH and ATP depletion (Arch. Toxicol. 68: 24–31, 1994). Here we report additional data and findings aimed at a better understanding of the toxicity mechanisms induced by these herbicides. Biochemical mechanisms of cytotoxicity induced by the herbicides paraquat (1,1′-dimethyl-4,4′-bipyridylium dichloride), dinoseb (2-sec-butyl-4,6-dinitrophenol) and 2,4-D (2,4-dichlorophenoxyacetic acid) were investigated in freshly isolated rat hepatocytes. Herbicide metabolism, especially paraquat and 2,4-D, rapidly depletes GSH and protein thiols. Paraquat and 2,4-D (1–10 mM) decrease the GSH/GSSG ratio, promote loss of protein thiol contents and induce lipid peroxidation. Dinoseb, the most effective cytotoxic compound under study (used in concentrations 1000-fold lower than paraquat and 2,4-D), had moderate effects upon the GSH/GSSG ratio and lipid peroxidation, causing a depletion of protein thiols of about 20%. The results indicate that the herbicides paraquat and 2,4-D are hepatotoxic and may induce cell death by decreasing cellular GSH/GSSG ratio and protein thiols, and by inducing lipid peroxidation. The eytotoxic action of dinoseb is likely to be related with the uncoupling of oxidative phosphorylation in mitochondria. Therefore, it is likely that liver damage observed during the first phase of herbicide-intoxication is related to these metabolic processes.

Environmental pollutants, such as dioxins and furans, are extremely toxic and related with pulmonary disease development. Exposure of A549 human lung cells to dibenzofuran showed both time- and concentration-dependent decreases in cell proliferation and MTT reduction, but no alterations in cell viability. No differences were observed in the number of apoptotic nuclei, which can be due to the energetic failure caused by dibenzofuran-induced ATP depletion. Moreover, cells in culture exposed to the pollutant showed an increase in the conversion of LC3, a protein involved in the autophagic process. Incubation of A549 lung cells with dibenzofuran caused an increase in Lysotracker Red staining, indicating an increase in lysosomal vacuoles content. These results suggest that exposure to dibenzofuran affects lung mitochondrial phosphorylative function, causing an increase in the population of dysfunctional mitochondria and an impairment in the energetic status maintenance, therefore stimulating autophagy as a possible rescue mechanism in this cell line.