Isoflavone and its metabolite equol inhibit the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumours in ovariectomised rats

Abstract

Studies have yet to determine whether or not equol can explain the chemopreventive effect of soy. In the present study, a single oral dose of 5mg 7,12-dimethylbenz(a)anthracene (DMBA) was administered to 120 rats. After ovariectomy, these rats were divided into eight different treatment groups: control group (CG); high isoflavone (HI); middle isoflavone (MI); low isoflavone (Li); high equol (HE); middle equol (ME); low equol (LE); and oestrogen group (EG). At week 24 after DMBA was administered, tumour incidences were 60% (9/15) in CG, 13.3% (2/15) in the MI group, 13.3% (2/15) in the Li group, 6.7% (1/15) in the LE group, and 73.3% (11/15) in EG. Isoflavone/equol groups exhibited significantly lower incidences of tumour and longer mean latent period compared with CG and EG. Thiobarbituric acid reactive substances were significantly decreased in the plasma of the rats in HI and MI groups as well as in equol treatment groups compared with CG. Moreover, RT-PCR and western blotting show that the mRNA and protein expression levels of ERα and ERβ were significantly higher in isoflavone/equol treatment groups than in CG. In conclusion, isoflavone/equol intake can significantly inhibit the development of post-menopausal mammary tumours by antioxidant activities and oestrogenic activities.