Tamoxifen induces biochemical responses in Pacific oysters Magallana gigas (Thunberg, 1793) at environmentally relevant concentrations.

The activities of catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PDH), and glutathione-S-transferase (GST) were evaluated in the gills (GI) and digestive gland (DG) of Magallana gigas oysters exposed to tamoxifen (TAM) at environmental concentrations of 10 and 100 ng L-1 for 1 and 4 days. A higher CAT activity in the GI and DG and higher GPx activity only in the DG was observed of oysters exposed to both concentrations after 1 day. Furthermore, a significant increase in GR and G6PDH, was detected in the DG after 1 day of exposure to 10 ng L-1 and only G6PDH activity increase after 1 day of exposure to 10 ng L-1 in the GI. This suggests that the DG is a tissue more sensitive to TAM exposure and was confirmed with the individual Integrated Biomarker Response version 2 index (IBRv2i), highlighting the acute stress caused by TAM and a cellular adaptation.

Subchronic exposure to Tamoxifen modulates the hippocampal BDNF/ERK/Akt/CREB pathway and impairs memory in intact female rats.

Tamoxifen (TAM), a Selective Estrogen Receptor Modulator (SERM), is commonly used to treat and prevent breast cancer. Memory impairment has been noticed in patients who experience hormone therapy in the case of TAM and other SERMs. Animal studies that mimic the TAM longer exposure effects are needed to better elucidate the adverse effects of continuous treatment in humans. This study evaluated the effects of TAM subchronic administration on the memory performance and hippocampal neural plasticity of intact female Wistar rats. Animals were treated intragastrically with TAM (0.25 and 2.5 mg/kg) for 59 days. The rats were subjected to the Object Location Test (OLT) and Object Recognition Test (ORT) to evaluate memory performance. After euthanasia, the hippocampus samples were excised and the protein levels of the BDNF/ERK/Akt/CREB pathway were evaluated. The rat's locomotor activity and hippocampal TrkB levels were similar among the experimental groups. TAM at both doses reduced the memory performance of female rats in the OLT and short-term memory of ORT, and impaired hippocampal levels of mBDNF, proBDNF, and pCREB/CREB. TAM only at the dose of 2.5 mg/kg reduced the memory performance of rats in the long-term memory of ORT and hippocampal pERK/ERK and pAkt/Akt ratios. TAM subchronic administration induced amnesic effects and modulated the hippocampal BDNF/ERK/Akt/CREB pathway in intact young adult female Wistar rats.

Can maternal exposure to tamoxifen compromise sperm and behavioural parameters of male rat offspring?

Tamoxifen, a selective non-steroidal estrogen receptor modulator, is the standard adjuvant endocrine treatment for breast cancer. Since information on the risk of using tamoxifen during pregnancy is still scarce, this study evaluated whether the in utero and lactational treatment with this drug could compromise reproductive and behavioural parameters in male offspring. Pregnant Wistar rats were exposed to three doses of tamoxifen (0.12; 0.6; 3 µg/kg), by gavage, from gestational day 15 to lactational day 20. Tamoxifen exposure did not alter the anogenital distance in the male offspring; however, there was a significant increase in the body weight in the 0.12 µg/kg dose and a decrease in the 0.6 µg/kg dose. The male offspring treated with the highest dose exhibited a delay in the onset of puberty, evidenced by an increase in the age of preputial separation. Regarding sperm parameters, there was an increase in the sperm count in the cauda epididymis in the intermediate and highest dose groups, in addition to an increase in the number of static sperm and a decrease in the progressive sperm in the same groups. Moreover, an increase in the number of hyperplasia of the epithelial clear cells was observed in the epididymis. In conclusion, the present study demonstrated that maternal exposure to tamoxifen compromised the installation of puberty of the male offspring and the maturation of the epididymis, affecting sperm storage and motility in the adult life.

Diphenyl diselenide protects cultured MCF-7 cells against tamoxifen-induced oxidative DNA damage.

Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organoselenium compounds. Studies have shown its interesting pharmacodinamic properties, as antioxidant, antimutagenic and antitumoral effects. Here we report the antigenotoxic properties of DPDS against tamoxifen (TAM)-induced oxidative DNA damage in MCF-7 cultured cell line. We determined the cytotoxicity by lactate dehydrogenase (LDH) leakage assay and evaluated oxidative DNA damage by modified comet assay employing the enzymes formamidopyrimidine DNA-glycosylase (Fpg) and endonuclease III (Endo III). Our results demonstrate that the cellular effects of DPDS appear to be complex and concentration-dependent. The present findings show that DPDS is not genotoxic (at concentrations lower than 2.0µmol/L) in MCF-7 cells, as observed in the modified comet assay. Moreover, DPDS protects against TAM-induced oxidative DNA damage, probably by its antioxidant activity, without interfering with its cytotoxicity. In this manner, the treatment with low concentrations of DPDS, a synthetic organoselenium compound, could be used as a potent antigenotoxic agent to prevent the risk of cancer induction triggered by tamoxifen hormone therapy. Thereby, more studies concerning the toxicity of DPDS and its structural derivatives are still necessary for future safe therapeutic application and development of novel chemopreventive compounds for combined therapy in breast cancer.

Liver iron overload induced by tamoxifen in diabetic and non-diabetic female Wistar rats.

Tamoxifen (TX), a drug used in the treatment of breast cancer, may cause hepatic changes in some patients. The consequences of its use on the liver tissues of rats with or without diabetes mellitus (DM) have not been fully explored. The purpose of this study was to evaluate the correlation between plasma hepatic enzyme levels and the presence of iron overload in the hepatic tissue of female Wistar rats with or without streptozotocin-induced DM and using TX. Female rats were studied in control groups: C-0 (non-drug users), C-V (sorbitol vehicle only) and C-TX (using TX). DM (diabetic non-drug users) and DM-TX (diabetics using TX) were the test groups. Sixty days after induced DM, blood samples were collected for glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST) alkaline phosphatase (ALP) and bilirubin measures. Hepatic fragments were processed and stained with hematoxylin and eosin, Masson's trichrome, Perls. The hepatic iron content was quantified by atomic absorption spectrometry. AST, ALT and ALP levels were significantly elevated in the DM and DM-TX groups, with unchanged bilirubin levels. Liver iron overload using Perls stain and atomic absorption spectrometry were observed exclusively in groups C-TX and DM-TX. There was positive correlation between AST, ALT and ALP levels and microscopic hepatic siderosis intensity in group DM-TX. In conclusion, TX administration is associated with liver siderosis in diabetic and non-diabetic rats. In addition, TX induced liver iron overload with unaltered hepatic function in non-diabetic rats and may be a useful tool for investigating the biological control of iron metabolism.

Cytotoxicity of tamoxifen in normal and tumoral cell lines and its ability to induce cellular transformation in vitro.

Tamoxifen (TAM) is a non-steroidal anti-estrogen used to treat patients with estrogen receptor-positive breast cancer and as a chemopreventive agent against breast cancer in high risk pre- and post-menopausal women. However, recent studies have shown that tamoxifen causes endometrial and hepatic cancer. In this study, we examined the effects of tamoxifen (5, 10, 25 and 50 microM) on the growth and proliferation of nine tumoral cell lines (UACC62, MCF-7, NCI-460, K-562, OVCAR-03, PC-03, HT-29, 786-0, NCI-ADR) and non-tumoral cell lines (3T3, V79, MDCK, VERO). Chinese hamster lung fibroblasts (V79) were the most sensitive lineage to tamoxifen, with 21.6% of the cells showing apoptosis at 50 microM TAM. Microscopic analysis showed that, the cellular transformation caused by TAM in V79 cells was similar to that seen with 7,12-dimethylbenz(a)anthracene, thus indicating the carcinogenicity of TAM.

On the promoting action of tamoxifen in a model of hepatocarcinogenesis induced by p-dimethylaminoazobenzene in CF1 mice.

BACKGROUND AND AIMS: Tamoxifen (TMX) has proven to be an effective palliative treatment for advanced breast cancer with low reported incidence of side effects. TMX has been demonstrated to be an initiator and/or a promoter in the rat model of hepatocarcinogenesis. To document the long-term effect of TMX in mice treated with p-dimethylaminoazobenzene (DAB), we have investigated the time response action of these drugs on different biochemical parameters. METHODS: A group of animals was placed on dietary DAB (0.5%, w/w) during a period of 28 weeks. Control animals received a standard laboratory diet. Two other groups of non-treated and DAB-treated animals received TMX citrate (0.025%, w/w) in the diet since day 20. RESULTS: The activities of the enzymes involved in heme synthesis and degradation as evaluated in the DAB group was not further affected by TMX. DAB and/or TMX treatment significantly increased the content of total cytochrome P450 and also the activity of glutathione S-transferase indicating liver damage. In all treated groups oxidative stress and an adaptive response of the natural defense system (catalase and superoxide dismutase) were demonstrated. Histological and morphological studies revealed liver cell hyperplasia in DAB treated group; however, only in the DAB+TMX group solid, trabecular and acinar hepatocellular carcinoma was confirmed at the end of the experimental trial. CONCLUSION: We have demonstrated that TMX produced changes in hepatic enzyme activities which may be relevant for the metabolism and disposition of this and/or other drugs. Because liver tumors could be initiated and promoted by several agents which need to be activated, the possible hazard of TMX should be considered. This study reports that long-term treatment with TMX enhances hepatocarcinogenesis induced by DAB. The widespread use of TMX as an anticancer agent adds to the significance of this study.

Retinopatía tóxica en pacientes asintomáticos tratados con tamoxifén / Toxic retinopathy in asyntomathic patients treaty with tamoxifen

El tamoxifén es una droga antiestrogénica utilizada en el tratamiento de pacientes con cáncer de mama. Muchos estudios han reportado la toxicidad ocular causada por el tamoxifén en pacientes con síntomas visuales (disminución de la agudeza visual). Nuestro estudio determina la prevalencia de toxicidad ocular en pacientes visualmente asintomáticos que reciben tratamiento con tamoxifén a bajas dosis por tiempo prolongado (10 mg dos veces al día). Realizamos examen ocular a 30 pacientes asintomáticos visualmente. Dos pacientes (6,6 por ciento) presentaron cristales refráctiles en la retina, lo que se considera como la manifestación de la retinopatía por tamoxifén. Ninguno de los dos pacientes tuvieron disminución de la agudeza visual. Tampoco presentaron opacidades corneales, edema macular ni cambios a nivel del nervio óptico. La dosis total de tamoxifén en estos dos pacientes fue de 14,6 y 25,8 g. respectivamente. En los 30 pacientes estudiados, la dosis promedio fue de 19,92g. Un buen examen oftalmológico debe ser realizado a todos los pacientes que reciben terapia con tamoxifén