Mitochondrial dysfunction induced by different organochalchogens is mediated by thiol oxidation and is not dependent of the classical mitochondrial permeability transition pore opening

Ebselen (Ebs) and diphenyl diselenide [(PhSe)₂] readily oxidize thiol groups. Here we studied mitochondrial swelling changes in mitochondrial potential (ΔΨm), NAD(P)H oxidation, reactive oxygen species production, protein aggregate formation, and oxygen consumption as ending points of their in vitro toxicity. Specifically, we tested the hypothesis that organochalchogens toxicity could be associated with mitochondrial dysfunction via oxidation of vicinal thiol groups that are known to be involved in the regulation of mitochondrial permeability (Petronilli et al. J. Biol. Chem., 269; 16638; 1994). Furthermore, we investigated the possible mechanism(s) by which these organochalchogens could disrupt liver mitochondrial function. Ebs and (PhSe)₂ caused mitochondrial depolarization and swelling in a concentrationdependent manner. Furthermore, both organochalchogens caused rapid oxidation of the mitochondrial pyridine nucleotides (NAD(P)H) pool, likely reflecting the consequence and not the cause of increased mitochondrial permeability (Costantini, P., Chernyak, B. V., Petronilli, V., and Bernardi, P. (1996). Modulation of the mitochondrial permeability transition pore (PTP) by pyridine nucleotides and dithiol oxidation at two separate sites. J. Biol. Chem. 271, 6746-6751). The organochalchogens-induced mitochondrial dysfunction was prevented by the reducing agent dithiothreitol (DTT). Ebsand (PhSe)₂-induced mitochondrial depolarization and swelling were unchanged by ruthenium red (4μM), butylated hydroxytoluene (2.5μM), or cyclosporine A(1μM). N-ethylmaleimide enhanced the organochalchogensinduced mitochondrial depolarization, without affecting the magnitude of the swelling response. In contrast, iodoacetic acid did not modify the effects of Ebs or (PhSe)₂ on the mitochondria. Additionally, Ebs and (PhSe)₂ decreased the basal 2' 7' dichlorofluorescin diacetate (H₂-DCFDA) oxidation and oxygen consumption rate in state 3 and increased it during the state 4 of oxidative phosphorylation and induced the formation of protein aggregates, which were prevented by DTT. However, DTT failed to reverse the formation of protein aggregates, when it was added after a preincubation of liver mitochondria with Ebs or (PhSe)₂.Similarly, DTT did not reverse the Ebsor (PhSe)₂-induced ΔΨm collapse or swelling, when it was added after a preincubation period of mitochondria with chalcogenides. These results show that Ebs and (PhSe)₂ can effectively induce mitochondrial dysfunction and suggest that effects of these compounds are associated with mitochondrial thiol groups oxidation. The inability of cyclosporine A to reverse the Ebs-and (PhSe)₂-induced mitochondrial effects suggests that the redox-regulated mitochondrial permeability transition (MPT) pore was mechanistically regulated in a manner that is distinct from the classical MPT pore.