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Effects of all-trans-retinoic acid on the permeability transition and bioenergetic functions of rat liver mitochondria in combination with endoxifen

Ribeiro, Mariana P.C., Santos, Armanda E., Santos, Maria S., Custódio, José B.A.
Life sciences 2013 v.93 no.2-3 pp. 96-107
adenosine diphosphate, adverse effects, anticarcinogenic activity, breast neoplasms, calcium, energy metabolism, energy-dispersive X-ray analysis, fluorescence, hepatotoxicity, liver, membrane potential, mitochondria, mitochondrial membrane, oxidative stress, oxygen consumption, permeability, phosphorylation, protons, rats, specific ion electrodes, synergism, thiobarbituric acid
AIMS: The clinical utilization of the combinations of all-trans-retinoic acid (RA) with antiestrogens, which present synergism of action in breast cancer, has been limited by RA adverse effects, including hepatotoxicity, which may be related with mitochondrial damage. This work evaluated the effects of RA alone and in combination with the antiestrogen endoxifen (EDX) on liver mitochondria. MAIN METHODS: Mitochondrial permeability transition (MPT) was assessed by using Calcium Green-5N fluorescence and a tetraphenylphosphonium selective electrode. Oxidative stress was evaluated by oxygen consumption and thiobarbituric acid method. Mitochondrial bioenergetic was monitored by measuring oxygen consumption and mitochondrial membrane potential (ΔΨ). Osmotic volume changes of mitochondria were followed at 540nm. KEY FINDINGS: EDX prevents the MPT induced by RA, allowing mitochondria pre-incubated with RA to accumulate Ca²⁺ and inhibiting the depolarization of ΔΨ. RA above 10nmol/mg protein depresses the phosphorylation capacity of mitochondria, as shown by the increase in the time required for ADP phosphorylation as well as by the decrease in state 3 respiration. At 20nmol/mg protein, RA decreases the ΔΨ and increases the state 4 respiration, suggesting that high concentrations of RA permeabilize the membrane to protons, possibly due to a proton leak through the Fo fraction of complex V. Moreover, the effects of RA on mitochondrial bioenergetics are not changed by EDX. SIGNIFICANCE: RA-induced hepatotoxicity may be related with induction of MPT and alterations in bioenergetic parameters; the combination with EDX, which reduces mitochondrial dysfunction and synergistically potentiates the anticancer activity, may provide a safer therapeutic strategy.