Tamoxifen and Estradiol Interact with the Flavin Mononucleotide Site of Complex I Leading to Mitochondrial Failure

Abstract

This study evaluated the action of tamoxifen and estradiol on the function of isolated liver mitochondria. We observed that although tamoxifen and estradiol per se did not affect mitochondrial complexes II, III, or IV, complex I is affected, this effect being more drastic (except for state 4 of respiration) when mitochondria were coincubated with both drugs. Furthermore, using two respiratory chain inhibitors, rotenone and diphenyliodonium chloride, we identified the flavin mononucleotide site of complex I as the target of tamoxifen and/or estradiol action(s). Tamoxifen (25 M) per se induced a significant increase in hydrogen peroxide production and state 4 of respiration. Additionally, a significant decrease in respiratory control ratio, transmembrane, and depolarization potentials were observed. Estradiol per se decreased carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)-stimulated respiration, state 3 of respiration, and respiratory control ratio and increased lag phase of repolarization. With the exception of state 4 of respiration whose increase induced by tamoxifen was reversed by the presence of estradiol, the effects of tamoxifen were highly exacerbated when estradiol was present. We observed that 10 M tamoxifen in the presence of estradiol affected mitochondria significantly by decreasing FCCP-stimulated respiration, state 3 of respiration, respiratory control ratio, and ADP depolarization and increasing the lag phase of repolarization. All of the deleterious effects induced by 25 M tamoxifen were highly exacerbated in the presence of estradiol. Furthermore, we observed that the effects of both compounds were independent of estrogen receptors because the pure estrogen antagonist ICI 182,780 did not interfere with tamoxifen and/or estradiol detrimental effects. Altogether, our data provide a mechanistic explanation for the multiple cytotoxic effects of tamoxifen including its capacity to destroy tamoxifen-resistant breast cancer cells in the presence of estradiol. This new piece of information provides a basis for the development of new and promising anticancer therapeutic strategies.Selective estrogen receptor modulators, also known as tissue selective estrogens, are a class of drugs with mixed estrogen agonist/antagonist actions (1). They were originally classified as antiestrogens because of their ability to antagonize the proliferative effects of estrogens (2). It was later discovered that these compounds could antagonize the action of estrogen by binding to the estrogen receptor (ER) 2 to thereby block estradiol (E2) access (1, 3). It is now known that under certain circumstances and in certain tissues, in addition to acting as competitive inhibitors of endogenous estrogen, these same estrogen antagonists can exert estrogenic agonist properties (4 -6). These findings indicate that the mechanisms regulating ER function are not the same in all cells and that a compound can only be classified as an ER agonist or antagonist in relation to a specific cell type or process.It is known for a long ti...

Estradiol affects liver mitochondrial function in ovariectomized and tamoxifen-treated ovariectomized female rats

“…Similarly, Wang and collaborators (2006) using human neuroblastoma SK-N-SH cells as experimental model, reported that E2 effectively reduce lipid peroxidation induced by 5-min H 2 O 2 exposure. Moreover, the authors observed that the estrogen receptor antagonist fulvestrant (ICI 182,780) did not block the effects of E2 (Wang et al, 2006) supporting previous findings from our laboratory indicating that the effects of E2 on liver mitochondria are estrogen-receptor independent (Moreira et al, 2006). Although we observed that E2 exerts a strong protective effect against lipid peroxidation (Figs.…”

“…These data are supported by a previous in vitro study from our laboratory that showed that lower concentrations of TAM that do not interfere with mitochondrial function, in the presence of E2 significantly affect the function of these organelles. Furthermore, we were able to show that TAM and E2 act directly on the flavin mononucleotide (FMN) site of complex I leading to mitochondrial failure (Moreira et al, 2006). Although these results were obtained with liver mitochondria isolated from male rats, preliminary results from our laboratory show the same effects in mitochondria isolated from female rats though less pronounced.…”

“…From the bioenergetics point of view, the choice of succinate as substrate tends to provide the most consistent results because succinate oxidation does not require matrix pyridine nucleotides, which can be lost via the PTP during storage or incubation even when swelling is undetectable (Vinogradov et al, 1972). Furthermore, our previous in vitro study with liver mitochondria isolated from male rats (Moreira et al, 2006) as well as our preliminary results obtained from female rats show that E2 affects mitochondrial complex I. To avoid interferences in Ca 2+ fluxes induced by E2 on mitochondrial complex I, we used succinate as mitochondrial substrate.…”

Chemo-resistant melanoma sensitized by tamoxifen to low dose curcumin treatment through induction of apoptosis and autophagy

“…Tamoxifen alone destabilizes the mitochondria to generate ROS, which agrees with previous studies that state that the drug can directly target the mitochondria. 14,15 In a previous study, we have shown that the mitochondria of melanoma A375 cells are vulnerable to tamoxifen treatment, thereby sensitizing these cells to co-treatment. 16 curcumin promoted rapid dissipation of the mitochondrial membrane potential in HeLa cells.…”

Mitochondrial respiratory chain complexes: apoptosis sensors mutated in cancer?

“…Different inhibitors of complex I (for example, tamoxifen; Moreira et al, 2006), complex II (for example, fenretinide; Cuperus et al, 2010) or complex III (for example, adaphostin; Le et al, 2007) markedly induce ROS and apoptosis in tumour cells. One of the most promising drugs in this field is the vitamin E derivative a-tocopheryl succinate (Dong et al, 2007(Dong et al, , 2008(Dong et al, , 2009) and its mitochondrial targeted analogue mitoVES (Dong et al, 2011a, b) developed by the Neuzil group.…”