Effects of high dietary fat on the total DNA and receptor contents in rats with 7,12-dimethylbenz[a]anthracene-induced mammary carcinoma

Pre- and postpubertal irradiation induces mammary cancers with distinct expression of hormone receptors, ErbB ligands, and developmental genes in rats

Childhood exposure to carcinogens renders a higher risk of breast cancer. The molecular mechanisms underlying cancer development after such exposure are not, however, well understood. Here we examined how the mechanism of cancer development relates to the age at exposure to ionizing radiation (IR) or the carcinogen 1-methyl-1-nitrosourea (MNU). Pre- and postpubertal (3- and 7-wk-old, respectively) female Sprague-Dawley rats were whole-body γ-irradiated (2 Gy), injected intraperitoneally with MNU (20 mg/kg) or left untreated and were autopsied at 50 wk of age. Mammary carcinomas were examined for estrogen receptor (ER) α, progesterone receptor (PR) and ErbB ligand expression and for expression microarrays. Early histological changes of the ovaries were also evaluated. The incidence of mammary cancer was higher after postpubertal, rather than prepubertal, IR exposure; the inverse was true for MNU. Most cancers were positive for both ERα and PR except for the prepubertal IR group. Cancers of the prepubertal IR group expressed a different set of ErbB ligands from those of the other groups and did not overexpress Areg, which encodes an estrogen-regulated ErbB ligand, or other developmentally related genes including those for hormonally regulated mammary gland development. Prepubertal IR exposure resulted in ovarian dysfunction as revealed by a reduced follicular pool. Evidence thus suggests that mammary carcinogenesis induced by prepubertal IR exposure is independent of ovarian hormones but requires certain ErbB ligands; induction by postpubertal exposure depends on ovarian hormones and different ErbB ligands. In contrast, the mechanism of MNU-induced carcinogenesis was less influenced by the age at exposure.

Mammary gland carcinogenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Sprague-Dawley rats on high- and low-fat diets

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a carcinogenic heterocyclic amine derived from cooked meat. Mammary gland tumors were induced in female Sprague-Dawley rats given 10 doses of PhIP (75 mg/kg po) once per day from 43 days of age and then placed on a defined high-fat (23.5% corn oil) or low-fat (5% corn oil) diet for 25 weeks. Mammary tumor incidence was 49% (44 of 90 rats) and 31% (27 of 88 rats) in the high- and low-fat groups, respectively. No tumors were found in vehicle control rats on the high-or the low-fat diet (n = 44 and 43, respectively). The higher tumor incidence in the high-fat group was due to an increase specifically in carcinomas (classified as tubulopapillary carcinomas) rather than benign tumors (tubular adenomas and fibroadenomas). The incidence of carcinomas was 45% and 24% in PhIP-treated rats on the high- and low-fat diets, respectively. In addition, the percentage of carcinomas showing stromal invasion was highest in the high-fat diet group (22% vs. 8%, high- vs. low-fat diet). Proliferating cell nuclear antigen immunostaining (PCNA) index revealed six times more proliferation in carcinomas from rats on the high-fat diet than in rats on the low-fat diet. Adenomas from rats on different diets had similar PCNA indexes. The tumor apoptotic index, quantitated by immunohistochemical detection (terminal deoxynucleotidyl transferase nick end labeling), was twice as high in carcinomas from rats on the high-fat diet as in carcinomas from rats on the low-fat diet but was similar between the two groups of adenomas. The PCNA-to-apoptosis ratio was 43 and 17 in carcinomas from rats on the high- and low-fat diets, respectively, indicating that the growth rate of carcinomas was greater in rats on the high-fat diet. The results from this study show that the high-fat diet increases the incidence, invasiveness, and growth of PhIP-induced mammary gland carcinomas.

Influence of reducing luxury calories in the treatment of experimental mammary carcinoma

The aim of this study was to investigate the influence of dietary calorie intake at three different fat levels on (a) the growth of established methylnitrosourea (MNU)-induced mammary carcinoma, (b) the reappearance of mammary carcinomas after surgical removal, and (c) the growth of manifest lesions in animals treated with the cytostatic agent hexadecylphosphocholine (HPC). A reduction of calories by 30% significantly inhibited tumour growth of manifest mammary carcinomas in rats, without having a negative influence on body weight gain. After chemotherapeutic treatment no significant dietary influence was observed besides the high antineoplastic efficacy of HPC, but when feeding calorically restricted diets to surgically treated animals the number of reappearing tumours was considerably smaller (P = 0.06) than after feeding the diets ad libitum. The fat content of the diets did not influence the growth of manifest mammary carcinomas. No significant dietary effects were exerted on oestradiol or testosterone levels in untreated tumour bearing animals. An elevation of oestradiol levels was observed when animals were subjected to HPC and fed a high calorie diet. An elevation of testosterone levels was assessed after surgical treatment of the rats, irrespective of fat content and calorie level. Our results suggest that a reduction of calories can inhibit growth of manifest mammary carcinomas and has impeding effects on tumour development after surgical removal. After effective chemotherapeutic treatment the additional influence of dietary changes was of less relevance. Furthermore, our data do not establish any association between growth inhibition of mammary tumours, caused by the mild caloric restriction, and altered oestradiol or testosterone production.