title: Effects of all-trans-retinoic acid on the permeability transition and bioenergetic functions of rat liver mitochondria in combination with endoxifen.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  RESULTS
  EDX prevents the MPT induced by RA, allowing mitochondria pre-incubated with RA to accumulate Ca(2+) and inhibiting the depolarization of ΔΨ. RA above 10 nmol/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 20 nmol/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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Center for Neuroscience and Cell Biology, University of Coimbra, 3000-354 Coimbra, Portugal. marianaponte@msn.com
authors.forename: Mariana P C
authors.initials: MP
authors.lastname: Ribeiro
authors.forename: Armanda E
authors.initials: AE
authors.lastname: Santos
authors.forename: Maria S
authors.initials: MS
authors.lastname: Santos
authors.forename: José B A
authors.initials: JB
authors.lastname: Custódio
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004734:Energy Metabolism / Q000187:drug effects; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D005260:Female; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000187:drug effects; D000083162:Mitochondrial Permeability Transition Pore; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000494:pharmacology; D014212:Tretinoin / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D020847:Estrogen Receptor Modulators; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D013629:Tamoxifen; C055492:4-hydroxy-N-desmethyltamoxifen; D014212:Tretinoin; D002118:Calcium
keywords: All-trans-retinoic acid; Bioenergetic functions; Endoxifen; Hepatotoxicity; Mitochondrial permeability transition; Oxidative stress