17 Beta-estradiol and not genistein modulates lacI mutant frequency and types of mutation induced in the heart of ovariectomized big blue rats treated with 7, 12-dimethylbenz[a]anthracene

Transgenic rat models for mutagenesis and carcinogenesis

Rats are a standard experimental animal for cancer bioassay and toxicological research for chemicals. Although the genetic analyses were behind mice, rats have been more frequently used for toxicological research than mice. This is partly because they live longer than mice and induce a wider variety of tumors, which are morphologically similar to those in humans. The body mass is larger than mice, which enables to take samples from organs for studies on pharmacokinetics or toxicokinetics. In addition, there are a number of chemicals that exhibit marked species differences in the carcinogenicity. These compounds are carcinogenic in rats but not in mice. Such examples are aflatoxin B1 and tamoxifen, both are carcinogenic to humans. Therefore, negative mutagenic/carcinogenic responses in mice do not guarantee that the chemical is not mutagenic/carcinogenic to rats or perhaps to humans. To facilitate research on in vivo mutagenesis and carcinogenesis, several transgenic rat models have been established. In general, the transgenic rats for mutagenesis are treated with chemicals longer than transgenic mice for more exact examination of the relationship between mutagenesis and carcinogenesis. Transgenic rat models for carcinogenesis are engineered mostly to understand mechanisms underlying chemical carcinogenesis. Here, we review papers dealing with the transgenic rat models for mutagenesis and carcinogenesis, and discuss the future perspective.

Neonatal exposure of 17β-estradiol has no effects on mutagenicity of 7,12-dimethylbenz [a] anthracene in reproductive tissues of adult mice

INTRODUCTION

Biological studies in animals and epidemiological findings in humans clearly demonstrate that estrogens including 17β-estradiol (E2) are weak carcinogens via both genetic and epigenetic mechanisms. Carcinogenesis analyses have indicated that female mice exposed to E2 as neonates develop more mammary and ovarian tumors when compared to adult exposures. In the present study, Big Blue transgenic mice were used to investigate the effects of E2 on mutagenicity of 7,12-dimethylbenz [a] anthracene (DMBA), a genotoxic carcinogen, in mammary gland and ovary following neonatal exposure.

RESULTS

DMBA treatment resulted in significant increases in cII mutant frequencies (MFs) in both mammary glands and ovaries, with A:T → T:A transversion as the predominant type of mutation. However, co-exposure to E2 daily for the first 5 days after birth and to DMBA at 6 months of age did not significantly increase cII MFs compared to DMBA treatment alone. Further, there were also no significant differences in mutational spectra between DMBA exposure alone and E2 + DMBA treatment.

CONCLUSION

These results suggest that early life exposures of mice to estrogens like E2 do not enhance mutagenicity by subsequent exposure to a chemical like DMBA in later life.

Oxidant/antioxidant status, paraoxonase activity, and lipid profile in plasma of ovariectomized rats under the influence of estrogen, estrogen combined with progesterone, and genistein

INTRODUCTION

The aim of this study was to investigate whether estradiol (E2), E2 combined with progesterone (Prog) (E2/Prog), and genistein (Gen) treatment had antioxidative and anti-hyperlipidemic effects in the plasma of ovariectomized (OVX) rats.

MATERIALS AND METHODS

Adult female Sprague-Dawley rats were divided into five groups. Rats in all groups, except for those in a sham group, underwent bilateral ovariectomy under general anesthesia. The groups were as follows: sham group; control OVX group; group treated with estrogen (0.014 mg/kg 17-β E2); group treated with a combination of E2 and Prog (0.014 mg/kg 17-β E2 plus 0.028 mg/kg drospirenone), and group treated with Gen (10 mg/kg/day). Plasma of rats of each treatment group was analyzed to determine the total antioxidant status, total oxidant status, paraoxonase activity, lipid profile, high-density lipoprotein (HDL-chol), low-density lipoprotein (LDL-chol), total cholesterol (Total-C), triacylglycerols, lipoprotein (a), and oxidative stress index.

RESULTS

Plasma Total-C levels and body weight increased in all the OVX groups compared with the sham group (P<0.005). The group treated with E2 had significantly elevated total oxidant status, oxidative stress index, LDL-chol, and Total-C compared with the control group (P<0.005). Gen treatment might lead to lower LDL-chol and Total-C levels compared with E2 treatment.

CONCLUSIONS

Gen treatment might be preferred to E2 treatment for treatment of menopausal symptoms in patients at risk for cardiovascular diseases. However, considering the small sample size of this study, larger studies are needed in this area.