Dietary Gamma-Tocopherol Rich Mixture Inhibits Estrogen-Induced Mammary Tumorigenesis by Modulating Estrogen Metabolism, Antioxidant Response and PPARγ
Menée sur deux modèles murins, cette étude montre qu'une préparation riche en tocophérol gamma peut inhiber la tumorigenèse mammaire induite par les estrogènes en agissant sur le métabolisme de ces hormones, l'expression du récepteur PPARgamma et le stress oxydant
This study evaluated the anti-cancer activity and mechanism of action of a γ-tocopherol rich tocopherol mixture, γ-TmT, in two different animal models of estrogen-induced breast cancer. The chemopreventive effect of γ-TmT at early (6 weeks), intermediate (18 weeks) and late (31 weeks) stages of mammary tumorigenesis was determined using the ACI rat model. Female rats receiving 17β-estradiol (E2) implants were administered with different doses (0, 0.05%, 0.1%, 0.3% and 0.5%) of γ-TmT diet. Treatment with 0.3% and 0.5% γ-TmT decreased tumor volume and multiplicity. At 31 weeks, serum concentrations of E2 were significantly decreased by γ-TmT. γ-TmT preferentially induced expression of the E2 metabolizing enzyme CYP1A1, over CYP1B1 in the rat mammary tissues. Nrf2-dependent antioxidant response was stimulated by γ-TmT, as evident from enhanced expression of its downstream targets, NQO1, GCLM and HMOX1. Serum concentrations of the oxidative stress marker, 8-isoprostane, were also decreased in the γ-TmT treated groups. Treatment with γ-TmT increased expression of PPARγ and its downstream genes, PTEN and p27, while the cell proliferation marker, PCNA, was significantly reduced in γ-TmT treated mammary tumors. In an orthotopic model in which human MCF-7 breast cancer cells were injected into the mammary fat pad of immunodeficient mice, γ-TmT inhibited E2-dependent tumor growth at all the doses tested. In conclusion, γ-TmT reduced mammary tumor development, in part through decreased E2 availability and reduced oxidative stress in mammary tissues; γ-TmT could thus be an effective agent for the prevention and treatment of E2-induced breast cancer.