Effect of milk on the 7,12-dimethylbenz[a]-anthracene-induced mammary tumor model in rat

Comparison of estrone and 17β-estradiol levels in commercial goat and cow milk

Increased levels of estrogen metabolites are believed to be associated with cancers of the reproductive system. One potential dietary source of these metabolites that is commonly consumed worldwide is milk. In North America, dairy cows are the most common source of milk; however, goats are the primary source of milk worldwide. In this study, the absolute concentrations of unconjugated and total (unconjugated plus conjugated) estrone (E(1)) and 17β-estradiol (E(2)) were compared in a variety of commercial cow milks (regular and organic) and goat milk. A lower combined concentration of E(1) and E(2) was found in goat milk than in any of the cow milk products tested. The differences in E(1) and E(2) levels between regular and organic cow milks were not as significant as the differences between goat milk and any of the cow milk products. Goat milk represents a better dietary choice for individuals concerned with limiting their estrogen intake.

Milk stimulates growth of prostate cancer cells in culture

Concern has been expressed about the fact that cows' milk contains estrogens and could stimulate the growth of hormone-sensitive tumors. In this study, organic cows' milk and two commercial substitutes were digested in vitro and tested for their effects on the growth of cultures of prostate and breast cancer cells. Cows' milk stimulated the growth of LNCaP prostate cancer cells in each of 14 separate experiments, producing an average increase in growth rate of over 30%. In contrast, almond milk suppressed the growth of these cells by over 30%. Neither cows' milk nor almond milk affected the growth of MCF-7 breast cancer cells or AsPC-1 pancreatic cancer cells significantly. Soy milk increased the growth rate of the breast cancer cells. These data indicate that prostate and breast cancer patients should be cautioned about the possible promotional effects of commercial dairy products and their substitutes.

Proliferative effect of whey from cows' milk obtained at two different stages of pregnancy measured in MCF-7 cells

Dietary estrogens may play a role in the etiology of hormone-dependent cancers like breast cancer. Cow's milk contains various endogenous estrogens and feed derived phytoestrogens that potentially contribute to an estrogenic effect of milk in consumers, and therefore we evaluated the effect of milk (whey) in a proliferation assay with estrogen-sensitive MCF-7 human breast cancer cells. Milk samples were obtained from 22 cows representing different stages of pregnancy (first and second half) and whey was produced from the milk. 0·1, 0·25 or 0·5% whey was included in the cell culture medium and after 6 days of treatment cell proliferation was assessed by a colorimetric method with a fluorometer. Whey induced significant (P<0·05) proliferative effects compared with control cells with no added whey at all concentrations tested. There was no difference in the proliferative effect of whey depending on the stage of pregnancy from which the milk was obtained. We did not observe anti-proliferative effects when whey was tested in the presence of 10 pm estradiol in the medium. In conclusion, these results indicate that whey, irrespective of the pregnancy stage from which the milk was obtained induced a significant proliferative response in MCF-7 cells and no anti-proliferative effect, which may be caused, at least in part, by estrogens present in milk. The implications of our findings in relation to for example breast cancer will have to be studied further in other model systems preferentially in vivo.

Maternal obesity and developmental programming of metabolic disorders in offspring: evidence from animal models

The incidence of obesity and overweight has reached epidemic proportions in the developed world as well as in those countries transitioning to first world economies, and this represents a major global health problem. Concern is rising over the rapid increases in childhood obesity and metabolic disease that will translate into later adult obesity. Although an obesogenic nutritional environment and increasingly sedentary lifestyle contribute to our risk of developing obesity, a growing body of evidence links early life nutritional adversity to the development of long-term metabolic disorders. In particular, the increasing prevalence of maternal obesity and excess maternal weight gain has been associated with a heightened risk of obesity development in offspring in addition to an increased risk of pregnancy-related complications. The mechanisms that link maternal obesity to obesity in offspring and the level of gene-environment interactions are not well understood, but the early life environment may represent a critical window for which intervention strategies could be developed to curb the current obesity epidemic. This paper will discuss the various animal models of maternal overnutrition and their importance in our understanding of the mechanisms underlying altered obesity risk in offspring.

Prepubertal exposure to cow's milk reduces susceptibility to carcinogen-induced mammary tumorigenesis in rats

Cow's milk contains high levels of estrogens, progesterone and insulin-like growth factor 1 (IGF-1), all of which are associated with breast cancer. We investigated whether prepubertal milk exposure affects mammary gland development and carcinogenesis in rats. Sprague-Dawley rats were given either whole milk or tap water to drink from postnatal day (PND) 14 to PND 35, and thereafter normal tap water. Mammary tumorigenesis was induced by administering 7,12-dimethylbenz[a]anthracene on PND 50. Milk exposure increased circulating E2 levels on PND 25 by 10-fold (p < 0.001) and accelerated vaginal opening, which marks puberty onset, by 2.5 days (p < 0.001). However, rats exposed to milk before puberty exhibited reduced carcinogen-induced mammary carcinogenesis; that is, their tumor latency was longer (p < 0.03) and incidence was lower (p < 0.05) than in the controls. On PND 25 and 50, mammary glands of the milk-exposed rats had significantly less terminal end buds (TEBs) than the tap water-exposed controls (p < 0.019). ER-α protein levels were elevated in the TEBs and lobules of milk rats, compared to rats given tap water (p < 0.019), but no changes in cyclin D1 expression, cell proliferation or apoptosis were seen. IGF-1 mRNA levels were reduced on PND 50 in the mammary glands of rats exposed to milk at puberty. Our results suggest that drinking milk before puberty reduces later risk of developing mammary cancer in rats. This might be mediated by a reduction in the number of TEBs and lower expression of IGF-1 mRNA in the mammary glands of milk-exposed animals.

Uterotrophic effects of cow milk in immature ovariectomized Sprague-Dawley rats

OBJECTIVES

Milk contains considerable quantities of estrogens and progesterone and as such may be one of the risk factors for hormone-related cancers. To determine the hormonal effects of commercial and traditional types of milk, we performed uterotrophic tests.

METHODS

Forty-five rats were ovariectomized and divided into three groups of 15 animals each. The animals were kept for 7 days on powdered chow and one of three different liquids: commercial milk (C), traditional milk (T), or water. At autopsy, wet and dry uterine weights were determined. The cell heights of the uterine epithelium and endometrium were determined. The uterine 5-bromo-2-deoxyuridine (BrdU) labeling index of the epithelium and endometrium gland epithelium was also assessed.

RESULTS

The weights of wet and dry uterus were 142 ± 13 and 112 ± 10 mg in the C group, 114 ± 30 and 91 ± 24 mg in the T group, and 87 ± 6 and 69 ± 5 mg in the W group. Significant differences in wet and dry uterus weights were found between all pairs of groups. The ratio of the wet uterine weight to body weight was significantly higher in the C and T groups than in the W group. The heights of the uterine epithelium and endometrium were higher and BrdU labeling index was greater in the C group than in the T and W groups.

CONCLUSIONS

Commercially available milk and traditional milk have uterotrophic effects on young ovariectomized rats. Our findings indicate that these uterotrophic effects in the milk groups were partly due to the estrogen and progesterone in the milk.