Interactions of Cr(VI) and Cr(III) with isolated rat liver mitochondria

Abstract

The mechanism of interaction of Cr(VI) with isolated rat liver mitochondria was investigated in this study. The results suggest that Cr(VI) induces the opening of the membrane permeability transition pore (MPT). The phenomenon is cyclosporine-sensitive and is in agreement with the cyclosporine-sensitive apoptosis observed in the cells incubated with this compound. Moreover the action of Cr(III), that is formed in the cells by a reduction of Cr(VI), has been also analysed. The results obtained demonstrated that the Cr(III) does not induce the opening of the MPT in isolated mitochondria, but it has a protective effect in preventing Cr(VI) MPT opening. Therefore, these results suggest that apoptosis is regulated by a balance between Cr(VI) accumulation in the cytoplasm and Cr(III) formation.Many "in vitro" studies regarding the interactions of Cr(VI) with cellular and sub-cellular structures have been performed directed to discover the biological-molecular mechanism responsible for the high toxicity of this element [1-10].Among the numerous cellular investigations carried out, two significant findings stand out:-Cr(VI) enters into the cell (by means of a carrier-mediated mechanism). Cell apoptosis is subsequently induced and the phenomenon is inhibited by cyclosporine A [1,4,6,9,39,41]; -Once inside the cell, the Cr(VI) is reduced to Cr(III) [2,3,5,8].However, these experiments do not clarify whether the apoptosis is induced by Cr(VI) or by Cr(III) since both compounds are present in the cell. In order to clarify this point, the interactions of both Cr(VI) and Cr(III) with isolated mitochondria were investigated in the present study since mitochondria are involved in all apoptosis mechanisms, and the cyclosporine-sensitive cell apoptosis is correlated with the opening of a mitochondrial pore (a MPT cyclosporinesensitive pore) [11,12].The interactions of chromium as Cr(VI) with isolated plants and animal mitochondria were previously studied [7,10], but the conclusions did not clarify the above cited problem. In particular, the opening of the membrane pore and the cyclosporine-sensitivity of this phenomenon, which is the key experiment for determining the involvement of mitochondria, has never been taken into account [7,10]. This study intends to demonstrate that only Cr(VI) form induces the opening of the mitochondrial cyclosporine-sensitive pore, while Cr(III) has no effect on this process, but, conversely, it seems to have a protective effect against the opening of the pore induced by Cr (VI).In mitochondria, the free energy arising from the oxidation of the substrates by molecular oxygen is utilized to form ATP from ADP. The oxidation of the substrates leads to the production of NADH and FADH 2 which triggers the electron flux along the mitochondrial respiratory chain (RC). The electron flow in the RC gives rise to a proton extrusion, that in turn gives rise to a ΔΨ (electrical gradient) and to a ΔpH (chemical gradient) which constitute the proton-motive force (p.m.f. = ΔΨ + ΔpH), driving the ATP synthesis [15]. T...

Development and application of vanadium oxide/polyaniline composite as a novel cathode catalyst in microbial fuel cell

“…The structure of the supporting materials can also affect the performance of the oxygen reduction reaction (ORR) as well as the catalyst. Vanadium is one of the most abundant metals on Earth (widely distributed within the Earth's crust) . Both the pure and composite forms of vanadium are used in many chemical reactions as a catalyst to obtain promising yields and reduce environmental problems .…”