Cisplatin impairs rat liver mitochondrial functions by inducing changes on membrane ion permeability: Prevention by thiol group protecting agents

Cisplatin (CisPt) is the most important platinum anticancer drug widely used in the treatment of head, neck, ovarian and testicular cancers. However, the mechanisms by which CisPt induces cytotoxicity, namely hepatotoxicity, are not completely understood. The goal of this study was to investigate the influence of CisPt on rat liver mitochondrial functions (Ca2+-induced mitochondrial permeability transition (MPT), mitochondrial bioenergetics, and mitochondrial oxidative stress) to better understand the mechanism underlying its hepatotoxicity. The effect of thiol group protecting agents and some antioxidants against CisPt-induced mitochondrial damage was also investigated. Treatment of rat liver mitochondria with CisPt (20 nmol/mg protein) induced Ca2+-dependent mitochondrial swelling, depolarization of membrane potential (ΔΨ), Ca2+ release, and NAD(P)H fluorescence intensity decay. These effects were prevented by cyclosporine A (CyA), a potent and specific inhibitor of the MPT. In the concentration range of up to 40 nmol/mg protein, CisPt slightly inhibited state 3 and stimulated state 2 and state 4 respiration rates using succinate as respiratory substrate. The respiratory indexes, respiratory control ratio (RCR) and ADP/O ratios, the ΔΨ, and the ADP phosphorylation rate were also depressed. CisPt induced mitochondrial inner membrane permeabilization to protons (proton leak) but did not induce significant changes on mitochondrial H2O2 generation. All the effects induced by CisPt on rat liver mitochondria were prevented by thiol group protecting agents namely, glutathione (GSH), dithiothreitol (DTT), N-acetyl-L-cysteine (NAC) and cysteine (CYS), whereas superoxide-dismutase (SOD), catalase (CAT) and ascorbate (ASC) were without effect. In conclusion, the anticancer drug CisPt: (1) increases the sensitivity of mitochondria to Ca2+-induced MPT; (2) interferes with mitochondrial bioenergetics by increasing mitochondrial inner membrane permeabilization to H+; (3) does not significantly affect H2O2 generation by mitochondria; (4) its mitochondrial damaging effects are protected by thiol group protecting agents. Based on these conclusions, it is possible to hypothesise that small changes on the redox-status of thiol groups, affecting membrane permeability to cations (Ca2+ and H+) underlie CisPt-induced liver mitochondrial damage, putatively responsible for its hepatotoxicity. Therefore, we propose that CisPt-induced mitochondrial damage and consequent hepatotoxicity could be prevented by using thiol group protecting agents as therapeutic adjuvants.