Study Of Prenatal N-3 Polyunsaturated Fatty Acids And Genistein Exposure On Occurrences And Progression Of N-methyl-N-nitrosourea (MNU)-induced Mammary Carcinoma In Female Sprague-Dawley (SD) Rats And Its Mechanism

Human breast cancer is the second leading cause of cancer death in women, but the etiology of human breast cancer is largely unknown. Genetic susceptibility, hormonal effects and environmental factors appear to be major determinants. Many dietary components have been evaluated for their influence on breast cancer in epidemiological and experimental studies. In the last several decades, increasing attention has been paid to the intake of n-3 polyunsaturated fatty acid (n-3 PUFA) and the risk of cancers, which has indicated that dietary fat intake can influence incidence of the hormone-related cancers(e.g., breast cancer, prostate cancer and colon cancer). The dietary isoflavones may be playing very important role in the decreasing cancer occurrence, people whose diets are rich in soy products have low incidence of breast cancer, prostate cancer and colon cancer.It also showed in epidemiological and experimental studies that high fish consumption and genistein in people's diet resulted in low incidence of breast cancer, prostate cancer and colon cancer. Studies suggest that dietary fat and dietary phytochemicals affect the etiology of breast cancer. Somebody reports that dietary of high dose n-3 PUFA could increase the concentration of 17-β-estradiol in pregnancy rats ( higher than the n-6 PUFA group), and the mammary gland cell divided more well in high n-3 PUFA pregnancy mouse offspring, whose offspring reveals in occurrence rate guided by the carcinogens raise a group obviously lower than n-6 PUFA.Epidemiological studies indicate that incidence and mortality of breast cancer is higher in Western countries than in some Asian countries. It is generally thought that Asian people whose diets are rich in soy products have low incidence of clinically manifested carcinoma. Genistein can postpone cancer occurrence in animal experiment. It also found that genistein maybe the most anticancer component, and it can suppress many cancer cell lines. Such findings suggest that estrogens play an important role in the etiology of breast cancer. Estrogen exposure early in life, when endogenous estrogen levels are low, may have profound effects, including effects on breast carcinogenesis. Relationships between dietary factors and breast cancer may result from effects that occur before maturity when the breasts are still developing. For example, it was increased the incidences of DMBA-induced breast cancer when genistein was injected to pregnancy rats. However, it can decrease the incidences of DMBA-induced breast cancer when genistein exposed on puberty mice. Genistein maybe effected the mammary cell differentiation. Fielden et al reported that genistein at the dose of dietary intake at gestation and lactation have no harmful effects, furthermore, it can protect from chemical carcinogens.Both n-3 PUFA and genistein can anticancer, and the same method was that both of them are closely link with body hormone. Genistein can be direct compete with body inner estrogen acceptor, lighten estrogen's thereby urging the tumour proliferation of cells effect, reduce the cancer morbidity danger being related to estrogen. However, n-3 PUFA is the sex hormone effect possibility reaction. Both of them can effect hormone and effect the reaction to chemical carcinogens.Based on the above analysis, combining the progress of research both at home and abroad, in vivo study, fetus were exposed to n-3 PUFA and genistein in uterus. Then, using MNU-induced breast cancer models on female offspring, RT-PCR, immunohistochemistry, western blotting methods were used to study the effects of n-3 PUFA and genistein onMNU-induced mammary tumors. In vitro study, using MCF-7 and MDA-MB-231 breast cancer cells study the effects of n-3 PUFA and genistein on the proliferation and apoptosis. Further, we focused on the influence of MNU-induced breast cancer on female offspring which exposed to n-3 PUFA and genstein in uterus and its mechanism.The results and conclusions are as followed:1. N-3 PUFA and genistein developed no harmful effects on the pregnancy rats and their offspring. N-3 PUFA and genistein have no abnormally influence on the gestation period, weight increasing, and sex ratio of offspring. N-3 PUFA increased the E2 and P4 concentrations in the serum on ablation rats, but genistein decreased the E2 and P4 concentrations in the serum on ablation rats, both of them decreased the concentration. It can help the male offspring's growth at the lactation and prepubescence period. The male offspring's AGD was affected between the genistein group and the n-3 PUFA and genistein group. The results suggested that the influence of exponential to male offspring was more obvious than to the female offspring. N-3 PUFA and genstein can affect the fetus, but the effects display later. The mammary gland tissues of the female offspring were better differentiation than the control group. It can urge the mammary gland to be in charge of mature time of differentiation, boosting the mammary gland cell developing ahead of time.2. Fifty-day-old female Sprangue-Dawley rats were received intraperitoneal injection of methyl-nitrosourea (MNU) at 50 mg/kg body weight one time to establish the female F1 rat model of mammary carcinogenesis. The breast tumors induced by MNU were confirmed to be mammary ductal carcinomas by histopathological evaluation of hematoxylin and eosin (HE) staining. Meanwhile, the study showed that exposing to n-3 PUFA and genistein treatment in utero could diversely influence incidence of MNU-induced breast tumors in F1 female rats. There was a longer latency period, less tumor incidence and tumor multiplicity on exposing to n-3 PUFA and genstein. Because of MNU-induced breast cancer, the E2 and P4 concentrations in F1 female serum were different with it in their mother serum.3. Both DHA and geinistein inhibited the proliferation of MCF-7, MDA-MB-231 breast cancer cell. The inhibitions were the same in 24 hours, but time-effect relationship was just on MDA-MB-231 cell line. DHA and genistein can postpone cell cycle on G0/G1 of MCF-7 cell line, but they block the MDA-MB-231 cell line at G2/M. This can inhibit the cell cycle and suppress the proliferation of MCF-7 and MDA-MB-231.4. Compared with the MNU-induced breast cancer model group, n-3 PUFA and genistein inhibited the expression of C-erbB2, ERαmRNA and protein, reduced the level of PR, PCNA, Ki-67 and increased the expression of BRCA1 mRNA and protein in mammary tumor tissues. The results suggested that n-3 PUFA and genistein reduced ERαexpression by directly inhibiting the expressions of ERαmRNA in karyoplast. On the other hand, n-3 PUFA and genistein can also reduced mutation and tumor formation by increasing the expressions of BRCA mRNA and protein.In summary, when female offspring were exposed to n-3 PUFA and genistein treatment in utero, latency period of MNU-induced breast cancer was prolonged and the incidence, invasion of MNU-induced breast tumors were decreased. It suggested that the mammary gland tissues of the female offspring were better differentiation than the control group if the pregnancy rats exposed to n-3 PUFA and genistein. N-3 PUFA and genistein decreases the formation of breast cancer by inhibiting the ERαgene and protein. N-3 PUFA and genistein can inhibit the proliferation of breast cancer cell, change the expressions of PCNA, C-erbB-2, BRCA1, and ERαare correlated to ERαpathway.