A maternal diet high in n - 6 polyunsaturated fats alters mammary gland development, puberty onset, and breast cancer risk among female rat offspring

Abstract

We hypothesized that feeding pregnant rats with a high-fat diet would increase both circulating 17beta-estradiol (E2) levels in the dams and the risk of developing carcinogen-induced mammary tumors among their female offspring. Pregnant rats were fed isocaloric diets containing 12% or 16% (low fat) or 43% or 46% (high fat) of calories from corn oil, which primarily contains the n - 6 polyunsaturated fatty acid (PUFA) linoleic acid, throughout pregnancy. The plasma concentrations of E2 were significantly higher in pregnant females fed a high n - 6 PUFA diet. The female offspring of these rats were fed with a laboratory chow from birth onward, and when exposed to 7,12-dimethylbenz(a)anthracene had a significantly higher mammary tumor incidence (60% vs. 30%) and shorter latency for tumor appearance (11.4 +/- 0.5 weeks vs. 14.2 +/- 0.6 weeks) than the offspring of the low-fat mothers. The high-fat offspring also had puberty onset at a younger age, and their mammary glands contained significantly higher numbers of the epithelial structures that are the targets for malignant transformation. Comparable changes in puberty onset, mammary gland morphology, and tumor incidence were observed in the offspring of rats treated daily with 20 ng of E2 during pregnancy. These data, if extrapolated to humans, may explain the link among diet, early puberty onset, mammary parenchymal patterns, and breast cancer risk, and indicate that an in utero exposure to a diet high in n - 6 PUFA and/or estrogenic stimuli may be critical for affecting breast cancer risk.

Figure 1

The plasma levels (mean ± SEM) of total E2 in pregnant females that were fed with isocaloric high (46% calories from fat) (n = 5) or low (12% calories from fat) n − 6 PUFA diet (n = 6) throughout gestation, and their 8-day-old offspring (high n − 6 PUFA: n = 10; low n − 6 PUFA: n = 15) that were kept on Purina laboratory chow immediately after birth. ∗ indicates statistical significance at the P < 0.05 level.

Figure 2

(A) Density of epithelial ducts and (B) TEBs and ABs in the fourth abdominal gland of 4-, 7-, and 11-week-old female rats exposed in utero to high-fat diet (43% calories from corn oil) or low-fat diet (16% calories from corn oil). Means ± SEM obtained from 3–8 female rats are shown. Significantly different from the controls: ∗, P < 0.05.

Figure 3

The epithelial density of the mammary whole-mount preparations (carmine staining) of the fourth abdominal glands obtained from 4- and 11-week-old female rats exposed in utero to high-fat diet (43% calories from corn oil) or low-fat diet (16% calories from corn oil) (magnification 2.5 × 25).

Figure 4

Density of epithelial ducts, TEBs, and ABs in the fourth abdominal gland of 4- and 7-week-old female rats exposed in utero to E2 or oil vehicle injections. Means ± SEM obtained from 2–6 female rats are shown. Significantly different from the controls: ∗, P < 0.05.

Figure 5

The proportion of DMBA-induced mammary tumors in offspring of mothers who were (A) fed with a high-fat diet containing 46% calories from corn oil (n = 60) or a low-fat diet containing 12% calories from corn oil (n = 60) during pregnancy, or (B) were injected with 20 ng E2 (n = 25) or oil vehicle (n = 26) daily between days 14 and 20 of gestation. Tumor incidence was significantly higher in the high than in the low n − 6 PUFA group (P < 0.0001) and in the E2 than in the vehicle control group (P < 0.02).

Figure 6

The proportion of female rats exposed in utero via their mother to (A) high (n = 31) or low n − 6 PUFA diets (n = 35) or (B) 20 ng E2 (n = 28) or oil vehicle (n = 28) between days 14 and 20 of gestation, with vaginal opening between postnatal days 33 and 38 days. Vaginal opening occurred significantly earlier in the high-fat vs. low-fat group (P < 0.0004) and in the E2 vs. oil group (P < 0.0001).