Synergism of plant-derived polyphenols in adipogenesis: perspectives and implications.

Dietary polyphenols may exert their pharmacological effect via synergistic interactions with multiple targets. Putative effects of polyphenols in the management of obesity should be primarily evaluated in adipose tissue and consequently in well-documented cell model. We used Hibiscus sabdariffa (HS), a widely recognised medicinal plant, as a source of polyphenols with a number of salutary effects previously reported. We present here the full characterisation of bioactive components of HS aqueous extracts and document their effects in a model of adipogenesis from 3T3-L1 cells and in hypertrophic and insulin-resistant adipocytes. Aqueous extracts were up to 100 times more efficient in inhibiting triglyceride accumulation when devoid of fibre and polysaccharides. Significant differences were also observed in reactive oxygen species generation and adipokine secretion. We also found that, when polyphenols were fractionated and isolated, the benefits of the whole extract were greater than the sum of its parts, which indicated a previously unnoticed synergism. In conclusion, polyphenols have interactive and complementary effects, which suggest a possible application in the management of complex diseases and efforts to isolate individual components might be irrelevant for clinical medicine and/or human nutrition.

Trastuzumab plus tamoxifen: anti-proliferative and molecular interactions in breast carcinoma.

HER2 overexpression has been associated with anti-estrogen resistance in human breast cancer, and it has been suggested that the combined treatment of an anti-HER2 antibody plus tamoxifen has enhanced anti-cancer efficacy in breast cancer. The detailed anti-proliferative interactions between trastuzumab and tamoxifen were analyzed with the isobologram and Chou and Talalay methods, which assess the presence of synergy, addition or antagonism. We used the breast cancer cell lines that are estrogen receptor (ER)-positive and HER2-positive. We also analyzed the molecular changes on the HER2 and (ER) signaling pathways that are induced by trastuzumab plus tamoxifen. In terms of cancer cell proliferation, the simultaneous combination of trastuzumab and tamoxifen on BT-474 cells was more growth inhibitory (44%) than the treatment with trastuzumab (24%) or tamoxifen (31%) alone. Isobologram analysis of simultaneous trastuzumab plus tamoxifen exposure showed, however, that there were antagonistic interactions at an effect level of 30% (IC30). Using Chou and Talalay analysis we also observed antagonistic interactions at lower levels of cell kill, although there were additive effects at highest levels of cell kill. Trastuzumab followed by tamoxifen showed antagonism at all effects levels. Tamoxifen followed by trastuzumab showed antagonism at lower levels of cell kill, and additivity at higher levels of cell kill. Similar interactions were observed using T47D cells. The molecular effects of the combined treatment with trastuzumab plus tamoxifen on the levels of HER2 and ER signaling showed that, with respect to HER2 protein levels, trastuzumab downregulated HER2 by 27%, tamoxifen upregulated HER2 by 40%, and the combination of trastuzumab plus tamoxifen did not induce changes in HER2 respect to control. With respect to HER2 mRNA, trastuzumab upregulated HER2 mRNA to 367%, tamoxifen to 166%, and the combination to 401%. With respect to HER2 phosphorylation, trastuzumab upregulated HER2 phosphorylation to 352%, tamoxifen to 202% and the combination to 633%. Epidermal growth factor receptor levels were not changed by trastuzumab or tamoxifen alone, and were upregulated to 138% by the combination. The protein levels and activity of extracellular recptor kinase were not modified by trastuzumab, tamoxifen or the combination. Finally, estrogen receptor protein and mRNA levels were downregulated to about 50% by trastuzumab, tamoxifen or the combination. Taken together, our results show that in ER-positive breast cancer cells overexpressing HER2, trastuzumab plus tamoxifen have antagonistic interactions when used in combination, and that this antagonism may be related with an increase in HER2 signaling pathways that occurs when tamoxifen is added to trastuzumab.

Omega-6 polyunsaturated fatty acid gamma-linolenic acid (18:3n-6) enhances docetaxel (Taxotere) cytotoxicity in human breast carcinoma cells: Relationship to lipid peroxidation and HER-2/neu expression.

The omega-6 polyunsaturated fatty acid gamma-linolenic acid (GLA; 18:3n-6) has raised recent interest as novel anti-cancer agent as it possesses effective tumoricidal properties while not inducing damage to normal cells or creating harmful systemic side effects. The taxane docetaxel (Taxotere) is currently one of the most active microtubule-interfering agents for breast cancer. Despite this encouraging therapeutical potential, the clinical use of taxanes involves problems related to the solubility, toxicity and development of drug resistance, which may be partially dependent on the expression of HER-2/neu oncogene. Current trends in the treatment of human tumors are for drug combinations that result in improved responses as well as the ability to use less toxic concentrations of the drugs. Here, we examined the cytotoxic effects of GLA in combination with docetaxel against estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-231 and SK-Br3) human breast carcinoma cell lines. The cells were exposed simultaneously to GLA and docetaxel or sequentially to GLA followed by docetaxel for 24 h. Cytotoxicity was evaluated by the MTT assay, and the nature of the interactions between GLA and docetaxel (antagonism, additivity, and synergism) was analyzed by median effect and isobologram analyses. Interaction assessment showed that concurrent exposure to GLA plus docetaxel for 24 h resulted in synergism for MCF-7 and MDA-MB-231 cells, whereas an additive effect was observed in SK-Br3 cells. When exposure to GLA (24 and 48 h) was followed sequentially by docetaxel (24 h) a synergistic effect was observed in MDA-MB-231 and SK-Br3 cells, whereas an additive effect was found in MCF-7 cells. GLA-mediated increase in docetaxel cytotoxicity was only marginally abolished by Vitamin E, a lipid peroxidation inhibitor. Moreover, simultaneous exposure to GLA and docetaxel in the presence of the anti-oxidant Vitamin E also resulted in synergism, suggesting a limited influence of the oxidative status of GLA in achieving potentiation of docetaxel-induced cytotoxicity. Further experiments showed that GLA markedly decreased the expression of p185HER-2/neu oncoprotein in MCF-7 breast cancer cells (

Effects of a high olive oil diet on the clinical behavior and histopathological features of rat DMBA-induced mammary tumors compared with a high corn oil diet.

Effects of a high virgin olive oil diet on the promotion stage of dimethylbenz(alpha)anthracene-induced mammary carcinogenesis in rats were investigated in comparison with those of a high corn oil diet. Animals were randomly placed into 4 groups: control, fed a normolipidic control diet (3% corn oil); M, fed a high corn oil diet (20%); O, fed a high olive oil diet (3% corn oil plus 17% olive oil); and MO, fed the high olive oil diet after 33 days of high corn oil diet. Whereas the high corn oil diet clearly stimulated the mammary carcinogenesis, reducing the latency time and increasing the tumor incidence, multiplicity and volume, the high olive oil diet led to a lower tumor incidence than in the former group, a latency time similar to that of the control and lower tumor multiplicity and volume even than in the control group. Moreover, the histopathological features of the adenocarcinomas in olive oil groups were compatible with a greater degree of differentiation. These data suggest that the high virgin olive oil diet would have acted as a negative modulator of the experimental mammary carcinogenesis conferring to the tumors a more benign clinical behavior and a lower histopathological malignancy in comparison with the control and high corn oil diets.

Synergistic interaction between vinorelbine and gamma-linolenic acid in breast cancer cells.

It has been suggested that exogenous unsaturated fatty acids (UFAs) may increase the cytotoxic activity of cancer chemotherapeutic agents. We examined how y-linolenic acid (GLA; 18: 3n-6), the most promising UFA in the treatment of human tumors, affects the effectiveness of the lipophilic drug vinorelbine (VNR) on human breast carcinoma cell lines. Cells were exposed simultaneously to VNR and GLA or sequentially to GLA followed by VNR. Cell viability was determined by MTT assay. The increase in VNR-induced cell growth inhibition was measured by dividing the IC50 and IC70 values (50 and 70% inhibitory concentrations, respectively) that were obtained when the cells were exposed to VNR alone with those with VNR plus GLA. We found that GLA enhanced in a dose-dependent manner the cell growth inhibitory activity of VNR on MCF-7 cells (up to 9-fold). As GLA by itself showed anti-proliferative effects, possible GLA-VNR interactions at the cellular level were assessed employing the isobologram analysis and the combination index (CI) method of Chou-Talalay. Both methods showed an overall synergism between GLA and VNR in MCF-7 cells. At a high level of cell kill, the synergism was greater when a 24 h GLA pre-exposure or co-exposures were tested. Synergy was likewise observed with the GLA-VNR combination in MDA-MB-231, T47D, and SK-Br3 breast cancer cells. In all cell lines, the synergism was independent of the treatment schedule and the exposure time. Under conditions inhibiting lipid peroxidation using Vitamin E (dl-alpha-tocopherol), the enhancing effect of GLA (an easily oxidizable UFA) on VNR activity was partially abolished. However, when Vitamin E was used in combination, a similar synergistic increase in growth inhibition was obtained. These latter observations strongly implies that the synergistic effects of GLA with VNR are not mediated through a mechanism involving a generation of lipoperoxides. For comparison, the effects of other UFAs were examined on VNR chemosensitivity: GLA was the most potent at enhancing VNR activity, followed by docosahexaenoic acid (22: 6n-3), eicosapentaenoic acid (20: 5n-3) and alpha-linolenic acid (18: 3n-3), whereas linoleic acid (18: 2n-6) and arachidonic acid (20: 4n-6) did not increase VNR chemosensitivity. Very high concentrations of oleic acid (OA; 18:1 n-9), an UFA inversely correlated with breast cancer risk, also enhanced VNR effectiveness. Thus, various types of UFAs were not equivalent with respect to their actions on VNR effectiveness. In conclusion, our results give experimental support to the hypothesis that some UFAs can be used as modulators of tumor cell chemosensitivity and provide the rationale for in vivo preclinical investigation.