Toxicity Study of Bisphenol A, Nonylphenol, and Genistein in Rats Neonatally Exposed to Low Doses

Abstract

Due to reports that a considerable number of compounds may have endocrine-disrupting activity in humans and animals, the Organization for Economic Co-operation and Development (OECD) revised the original OECD Test Guideline No. 407 assay and introduced in vivo screening tests in 2008 to detect endocrine-mediated effects. These effects are one of the important parameters in assessing the risk assessment of chemicals in the REACH program. Recently, risk assessments of Bisphenol A (BPA) have conducted [1,2], and several countries such as Canada, Denmark and France have adopted a national ban on baby bottles made from polycarbonate plastic [3]. On the other hand, neonatal exposure assay has been reported as an assay for detection of endocrine effects in the early life stages of rats and mice, and the endocrine effects of estrogenic compounds, such as clomiphene, diethylbestrol, ethynylestradiol, 17β-estradiol, tamoxifen, BPA, and some phytoestrogens have been detected by this assay [4][5][6][7][8][9][10][11]. Therefore, this assay is considered to be a useful method of detecting endocrine-mediated effects. However, since few studies have been reported to detect endocrine effects of weakly estrogenic compounds designed, we performed the neonatal exposure assays of the weakly estrogenic compounds, BPA, nonylphenol, and genistein.Pregnant female rats on 13 days after mating were purchased from Charles River Japan, Inc. (Shiga, Japan), and the pups that were subsequently born were used in this study. All animals were cared for according to the principles outlined in the guide for animal experimentation prepared by the Japanese Association for Laboratory Animal Science. Rats were subcutaneously injected with 0, 0.1, 1 or 10 µg/rat/day of each chemical for 5 days starting on Postnatal Day 1 (PND 1). A positive control group injected with diethylstilbestrol was also established. Animals were killed by exsanguination under ether anesthesia on PND 50. The following were assessed: clinical signs, body weight changes, ano-genital distance, vaginal opening, preputial separation, estrous cycling, organ weight changes, and histological changes.No abnormities were detected in clinical signs, body weights, anogenital distance, vaginal opening, preputial separation, estrous cycling, and histological changes. Seminal vesicle weight was significantly lower in all genistein groups, and ventral prostate weight was higher in the 10 µg BPA group. No changes were observed in rats given nonylphenol. On the other hand, various endocrine-mediated effects in each parameter were detected in the diethylstilbestrol groups.The estrogenic compounds DES, ethynylestradiol, clomiphen, tamoxifen, BPA, and 17β-estradiol, all of which except BPA appear to be strongly estrogenic compounds based on their receptor binding affinities and the results of uterotrophic assays [12][13][14], were administered to neonatal rats for a short time, and endocrinemediated effects were detected [4][5][6][8][9][10][11]. Although there are few neonatal exposure data for wea...