Researchers at Fox Chase Cancer Center in Philadelphia, US claim to have demonstrated that two plasticiser compounds, BPA and BBP, are environmental estrogens capable of affecting gene expression in the mammary glands of young female laboratory rats exposed to the compounds through their mothers' milk.

Plastic products used to wrap or contain food and beverages have therefore aroused concerns as possible cancer-causing agents because they can sometimes leach out of the plastic and migrate into the food.

The scientists found that this was especially true after heating or when the plastic is old or scratched.

"Development of breast cancer entails multiple events, in which estrogen appears to play an important role," said Jose Russo, director of the Breast Cancer and the Environment Research Center at Fox Chase.

"Estrogenic agents involved in breast development and possibly in breast cancer may include foreign estrogens, or xenoestrogens, that are used in manufacturing a number of products. The studies of BPA and BBP in young rats were designed to see whether exposure to these hormonally active biological compounds could alter the genomic signatures of the mammary gland during critical stages of development."

BPA (bisphenol A) is a synthetic resin used in food packaging and polycarbonate plastic products. BBP (n-butyl benzyl phthalate) is a widely used plasticiser used in food wraps and cosmetics.

"In exposing prepubescent female rats to BPA and BBP, our aim was to determine what effects, if any, each compound had on mammary gene expression during at different ages," said postdoctoral associate Raquel Moral.

"Our results showed that exposure to BPA changes the gene expression profile of mammary tissues as a function of age. That is, there was a significant increase in protein production governed by various genes at increasing ages from 21 to 100 days."

These included proteins regulating cell proliferation and differentiation, including tumour-suppressing proteins and a large number of unknown proteins. The exception was decreased expression of the GAD1 gene. It encodes a key enzyme of the GABA-ergic system, which could be involved in hormonal regulation and breast cancer development. GAD1 has consistently been overexpressed in primary breast cancer.

"In contrast, the BBP exposure modified the genomic signature of the mammary gland primarily at 21 days of age and had less effect later," said Moral.

However, future studies are needed to determine whether exposure to such xenoestrogens leads to breast cancer in rats and whether these estrogens bring about similar gene alterations in human breast tissue.