Cardoso Carla M P, Moreno António J M, Almeida Leonor M, Custódio José B A
Laboratório de Bioquímica, Faculdade de Farmácia, Couraça dos Apóstolos, 51 r/c, 3000-295 Coimbra, Portugal.
Toxicol In Vitro. 2003 Oct-Dec;17(5-6):663-70. doi: 10.1016/s0887-2333(03)00106-1.
The antiestrogen tamoxifen (TAM) inhibits the growth of different estrogen receptor (ER)-negative cells. Recently, multiple effects of TAM on mitochondrial bioenergetic functions have been pointed to explain its ER-independent cell death mechanisms. We have shown that TAM and its major active metabolite 4-hydroxytamoxifen (OHTAM) induce depolarization of the mitochondrial membrane potential (DeltaPsi) and uncouple the mitochondrial respiration, depressing the oxidative phosphorylation efficiency. To clarify the biochemical mechanisms underlying the changes in the regulation of ATP synthesis and yield, in this work we evaluated the alterations of mitochondrial adenine nucleotides induced by both drugs and ascertained whether such changes could reflect a specific inhibition of either the adenine nucleotide translocase (ANT) or the phosphate carrier, as well as the activation of ATP hydrolysis due to DeltaPsi depolarization. We found that both antiestrogens caused a concentration-dependent decrease in mitochondrial ATP levels. Mitochondrial ADP and AMP were concomitantly increased with a subsequent decrease in the ATP/ADP or ATP/AMP ratios. The total concentration of adenine nucleotides also changed. Additionally, both drugs decreased the ANT content of mitochondria, inhibited the phosphate carrier and induced ATP hydrolysis. However, the effects of TAM were more drastic than those induced by OHTAM. Therefore, the depletion of ATP might result from an activation of ATP catabolism, as well as from a decrease in the mitochondrial content of ANT and partial inhibition of the phosphate carrier. Our data may explain the ER-independent effects and cytotoxicity of both drugs and, in agreement with other previous studies, suggest that OHTAM is much less toxic to mitochondria than TAM.
抗雌激素他莫昔芬（TAM）可抑制不同雌激素受体（ER）阴性细胞的生长。最近，人们指出TAM对线粒体生物能量功能具有多种作用，以解释其不依赖ER的细胞死亡机制。我们已经表明，TAM及其主要活性代谢物4-羟基他莫昔芬（OHTAM）可诱导线粒体膜电位（ΔΨ）去极化，并使线粒体呼吸解偶联，降低氧化磷酸化效率。为了阐明ATP合成和产量调节变化背后的生化机制，在这项工作中，我们评估了两种药物诱导的线粒体腺嘌呤核苷酸的变化，并确定这种变化是否可能反映对腺嘌呤核苷酸转位酶（ANT）或磷酸载体的特异性抑制，以及由于ΔΨ去极化导致的ATP水解激活。我们发现两种抗雌激素均导致线粒体ATP水平呈浓度依赖性下降。线粒体ADP和AMP随之增加，随后ATP/ADP或ATP/AMP比值下降。腺嘌呤核苷酸的总浓度也发生了变化。此外，两种药物均降低了线粒体的ANT含量，抑制了磷酸载体并诱导了ATP水解。然而，TAM的作用比OHTAM更显著。因此，ATP的消耗可能是由于ATP分解代谢的激活，以及线粒体中ANT含量的减少和磷酸载体的部分抑制。我们的数据可以解释两种药物不依赖ER的作用和细胞毒性，并且与之前的其他研究一致，表明OHTAM对线粒体的毒性远低于TAM。
