title: 4-Hydroxytamoxifen induces slight uncoupling of mitochondrial oxidative phosphorylation system in relation to the deleterious effects of tamoxifen.
abstract: The use of tamoxifen (TAM) has been questioned on the chemotherapy and chemoprevention of breast cancer due to several estrogen receptor-independent cytotoxic effects. As an alternative, its more active metabolite 4-hydroxytamoxifen (OHTAM) has been proposed with presumed lower side effects. In this work, the potential OHTAM toxicity on rat liver mitochondrial bioenergetics in relation to the multiple deleterious effects of TAM was evaluated. OHTAM, at concentrations lower than those putatively reached in tissues following the administration of TAM, does not induce significant perturbations on the respiratory control ratio (RCR), ADP/O, transmembrane potential (DeltaPsi), phosphorylative capacity and membrane integrity of mitochondria. However, at high concentrations, OHTAM depresses the DeltaPsi, RCR and ADP/O, affecting the phosphorylation efficiency, as also inferred from the DeltaPsi fluctuations and pH changes associated with ADP phosphorylation. Moreover, OHTAM, at concentrations that stimulate the rate of state 4 respiration in parallel to the decrease in the DeltaPsi and phosphorylation rate, causes mitochondrial swelling and stimulates both ATPase and citrate synthase activities. However, the OHTAM-observed effects, at high concentrations, are not significant relatively to the damaging effects promoted by TAM and suggest alterations to mitochondrial functions due to proton leak across the mitochondrial inner membrane.
authors.affiliation: Laboratório de Bioqui;mica, Faculdade de Farmácia, Universidade de Coimbra, Couraça dos Apóstolos, 51 r/c 3000-295, Coimbra, Portugal.
authors.forename: Carla M P
authors.initials: CM
authors.lastname: Cardoso
authors.forename: António J M
authors.initials: AJ
authors.lastname: Moreno
authors.forename: Leonor M
authors.initials: LM
authors.lastname: Almeida
authors.forename: José B A
authors.initials: JB
authors.lastname: Custódio
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000187:drug effects; D000818:Animals; D002950:Citrate (si)-Synthase / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008933:Mitochondrial Swelling / Q000187:drug effects; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000633:toxicity*; D014475:Uncoupling Agents / Q000378:metabolism*
chemical_list: D000227:Adenine Nucleotides; D014475:Uncoupling Agents; D013629:Tamoxifen; C016601:afimoxifene; D002950:Citrate (si)-Synthase; D000251:Adenosine Triphosphatases