Prepubertal resveratrol exposure accelerates N-methyl-N-nitrosourea-induced mammary carcinoma in female Sprague–Dawley rats

Abstract

The major object of this study was to characterize the effect of prepubertal trans-3,4′,5-trihydroxystilbene (resveratrol) exposure on N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in female Sprague–Dawley rats. Prepubertal rats (15 to 19 days of age) were treated daily with either 10 or 100 mg/kg resveratrol for 5 days, and were compared with resveratrol-untreated animals (30 rats in each group). Six rats in each group were autopsied at 49 days of age, and their growth was evaluated. All remaining rats were given 50 mg/kg MNU, followed by monitoring for occurrence of mammary carcinoma. A dose of 100 mg/kg (but not 10 mg/kg) resveratrol significantly increased incidence of rat with mammary carcinomas ≥1 cm and multiplicity (all histologically detected mammary carcinomas per rat), but did not affect latency, compared with untreated controls. Resveratrol did not affect body weight increase, but 100 mg/kg resveratrol caused slightly earlier vaginal opening. Although all rats cycled, resveratrol-treated animals exhibited significantly increased irregularity of estrous cycle, spending more time in the estrus phase. Thus, short resveratrol treatment of prepubertal female rats affected endocrine function, and accelerated development of MNU-induced mammary carcinomas.

Introduction

Geographical differences in the incidence of cancer indicate that diet and nutrition play a critical role in carcinogenesis [1], [2]. Epidemiological studies indicate that dietary factors influence the development of breast cancer, and experimental analysis suggests that natural products in the diet can act as modifying factors against breast cancer. Certain nonnutritive phytochemicals, particularly those in daily diets, have marked chemopreventive properties. For example, Asian women who consume a soy-rich diet have about 6-fold lower risk of developing breast cancer than their Western counterparts [3], [4]. Genistein, a flavonoid abundant in soy, shows anticancer activity [5]. One benefit of plant-derived bioactive agents is that they are less toxic.

Resveratrol is a naturally occurring phytochemical that is found in approximately 72 plant species, including grapes, peanuts and various herbs [6]. Resveratrol, a phytoalexin, may have roles in protecting plants against fungal infections and in conferring disease resistance. Resveratrol is highly concentrated in grape skin, and is also abundant in red wine [7]. The French have a lower incidence of coronary heart disease, despite having a diet relativity high in fat. This phenomenon, called the ‘French paradox’ [8], may be due to their high consumption of red wine. Resveratrol exerts anticarcinogenic activity in animal models of skin [6], esophageal [9] and mammary carcinogenesis [10], [11], when given to adults. In cell culture studies, resveratrol reportedly inhibits estrogen receptor (ER)-positive and -negative breast cancer cell growth [12], [13], [14]. Phytoestrogens are plant chemicals that resemble endogenous estrogens of humans and animals [15]. Resveratrol's stilbene structure shows structural similarity to estradiol and diethylstilbestrol [7]. Resveratrol is a phytoestrogen that binds to ER and induces various estrogenic effects [14], [16].

Estrogens have long been known to be important mitogens in the breast, and thus are associated with increased breast cancer risk. Estrogens and estrogenic compounds are a matter of considerable concern for human and animals during critical periods of development. The perinatal period of development is most sensitive to estrogenic chemicals, and human data indicate that high maternal exposure to estrogen during pregnancy increases the risk of breast cancer among daughters [17], [18]. Genistein, a phytoestrogen, accelerates mammary tumor development when administered to prenatal rats, and suppresses mammary tumor development when given to prepubertal rats [19], [20], [21], [22]. Zearalenone, a mycoestrogen used as an anabolic agent to enhance growth in cattle and lambs, reduces incidence of mammary tumors when a physiological dose is administered in the prepubertal period [19], and accelerates mammary tumor when a pharmacological dose is used [23]. The available experimental evidence regarding breast cancer risk and consumption of estrogenic chemicals during critical periods of development is inconsistent. The timing and level of exposure to estrogenic chemicals are apparently important. However, most resveratrol studies have been conducted using established cancer cell lines in culture, and few in vivo studies have been performed using adult animals [10], [11]. There has been no report of the effect of prepubertal administration of resveratrol on mammary carcinogenesis. In the present study, we examined the effects of prepubertal resveratrol exposure on N-methyl-N-nitrosourea (MNU)-induced mammary carcinomas in female Sprague–Dawley rats.