The effects of genistein on nmu-induced tumorigenesis and mammary tumor growth in adult female rats

Abstract

This study aimed to determine the effects of genistein on NMU-induced tumorigenesis and mammary tumor growth in adult female rats and its mechanism of action comparing to tamoxifen. The experiment was divided into 2 sets. Experimental 1: Study the effects of genistein on tumorigenesis. Forty-five-day old female Sprague-Dawley rats were induced to develop the mammary tumors by a single injection of 40 mg / kg BW of NMU via tail vein. The rats were divided into 2 groups, treatment and control, and daily subcutaneously injected with Img / kg BW of genistein and vehicle (2% DMSO in peanut oil), respectively, for 20 weeks. The rat estrous cycles were checked daily. The body weight, food intake and mammary tumorigenesis parameters were monitored weekly. The blood samples were collected monthly for E, and genistein assays. After 20 weeks or when the tumor diameter was 3.5 cm, the rats were euthanized and the tumor tissues were dissected for histology study. The results showed that genistein increased tumor cross sectional area and tumor multiplicity, which is related to the high levels of serum total genistein, but no changes in tumor incidence, latency period and mammary tumor types. There were no significant differences in the length of estrous cycle, food consumption and weights of body, uterus and ovary between genistein and vehicle groups. The results were congruent with the non-difference of E, levels between those two groups. Experimental 2: Study the mechanism of action of genistein comparing to tamoxifen, an estrogen antagonist, on mammary tumor growth. The induction of tumor development in rats was similar to the Experiment 1. After 8-10 weeks or when the tumor diameter was 1 cm, rats were randomized into four groups, and daily subcutaneously injected with vehicle, genistein (1 mg / kg BW). tamoxifen (100 ug) and tamoxifen (100 g) plus genistein (1 mg / kg BW). respectively, for 10 weeks. After 10 weeks or when the tumor diameter was 3.5 cm, the rats were euthanized and the tumor tissues were dissected for gene expression determination The mRNA expression levels of the estrogen responsive related genes (ERa, ERB and pS2), growth factor related genes (IGF-1 and new) and metastasis suppressor gene (GPR54) were determined using RT-PCR techniques. It was found that genistein stimulated the mammary tumor growth, while tamoxifen, alone or in combination with genistein, reduced the tumor growth. At the molecular level, tamoxifen treatments, alone or in combination with genistein, suppressed the expression of ERa gent, and the genistein treatment increased the IGF-I mRNA levels. In addition, genistein treatment increased the tumor metastases to the liver and uterus, together with the decrease of the GPR 54 gene expression. There were no significant differences in the levels of neu mRNA among four treatment groups. In agreement with the Experiment 1. genistein at dosage of 1 mg / kg BW did not exhibit the reproductive effects, both on the reproductive organs and E, levels, and toxicity effect on livers. Tamoxifen showed the estrogen antagonistic effect on reproductive organs and increased E₂ levels. From this study, it can conclude that the supplementation of genistein at dosage of 1 mg / kg BW, in comparable to the human consumption dose, has no effect on reproductive organs, but it can enhance the tumorigenesis and tumor growth, via the growth factor related gene (IGF-1). Tamoxifen can show the estrogen antagonistic effect by reduction of tumor growth, via the estrogen responsive related gene (ERa), and inhibit the reproductive organs and functions.