Selenite sensitizes mitochondrial permeability transition pore opening in vitro and in vivo: a possible mechanism for chemo-protection.

There is a known connection between selenium supplementation and chemo-protective anti-cancer activity. This biological phenomenon may be due to the ability of selenium to instigate cellular apoptosis. However, the mechanism by which selenium promotes cellular apoptosis is still obscure. The present study shows that sodium selenite, a common dietary form of selenium, promotes the mitochondrial permeability transition (MPT) in isolated rat liver mitochondria both in vitro and following in vivo supplementation. A low selenium concentration (0.1-10 microM) strongly induced cyclosporin A-sensitive mitochondrial swelling. Selenium also promoted both calcium release from the matrix of isolated mitochondria and uncoupled respiration. The MPT-inducing effect of selenium provoked the release of cytochrome c, a pro-apoptotic factor, into the incubation medium. Selenium did not increase intra-mitochondrial peroxide production, but did consume endogenous mitochondrial glutathione. Moreover, the effect of MPT induction was greatly potentiated in the presence of thiol-bearing antioxidants, e.g. N -acetylcysteine and lipoamide. During MPT progression, selenium induced NADH oxidation via electron acceptance from complex I. Supplementation for 20 days with 16 p.p.m. selenium in the drinking water of rats increased the propensity of mitochondria to undergo the MPT. More marked mitochondrial swelling in response to calcium and lower calcium-uptake capacity were observed, in the absence of liver damage or the intensive oxidation of reduced glutathione. Therefore selenite facilitates MPT pore opening via its thiol- and NADH/complex I-dependent reduction, and thereby may provide chemo-protection by potentiation of the capacity of the mitochondria to regulate programmed cell death. Data from the present study suggest that selenium can regulate important mitochondrial functions both in vivo and in vitro.

Membrane depolarization of isolated rat liver mitochondria attenuates permeability transition pore opening and oxidant production.

It has been suggested that one key feature of mitochondrial permeability transition (PT) regulation is its control by the proton electrochemical gradient and that depolarization favors pore opening, swelling, and reactive oxygen species (ROS) production. Moreover, ROS have been suggested to facilitate the process of mitochondrial PT pore opening. The aim of this study was to show that collapsing the mitochondrial membrane potential with the mitochondrial uncoupler, carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP), at concentrations of up to 10 microM, does not induce mitochondrial swelling and, in fact, stabilizes mitochondria exposed to oxidant, protecting them from tert-butyl hydroperoxide (TBH)-induced high-amplitude swelling. FCCP decreased polyethylene glycol-induced mitochondrial contraction following exposure to TBH, indicating closing of the PT mega-channel. In the presence of the calcium uniporter inhibitor ruthenium red, FCCP induced PT due to suppression of calcium efflux. Under PT-favorable conditions, ROS production was evaluated in mitochondria following treatments with TBH, inorganic phosphate, or FCCP (with or without ruthenium red). FCCP alone and in combination with ruthenium red attenuated mitochondria-derived ROS production. FCCP also decreased the augmented ROS production induced by inorganic phosphate. It is concluded that mitochondrial depolarization protects and prevents high-amplitude swelling and PT-derived ROS production.