The Beneficial Role of CLA in Breast Cancer
Professor and Member, Department of Pharmacology and Therapeutics
Roswell Park Cancer Institute
Conjugated linoleic acid (CLA), found naturally in dairy products and ruminant meats, refers to isomers of C18 fatty acids with conjugated double bonds. CLA inhibits the development of mammary tumors induced in rats by carcinogen treatment. Both the predominant natural isomer cis-9, trans-11-CLA and the synthetically produced trans-10, cis-12-CLA are equally effective. Butter fat—naturally enriched with cis-9, trans-11-CLA and vaccenic acid – has been shown to be similarly protective. CLA is incorporated into, and stored in, mammary adipose tissue. Additionally, dietary t10,c12-CLA, but not c9,t11-CLA, alters the composition of the mammary gland. This effect is species specific, with a marked loss of fat-storing cells (adipocytes) and an increase in the fibrous material surrounding the epithelial cells (the site where cancer develops) observed in the mammary gland of the mouse, but not the rat. A decrease in leptin — a hormone that has a central role in fat metabolism — is also seen with t10,c12-CLA. Both isomers, however, inhibit the development of new blood vessels, an important mechanism by which CLA may inhibit mammary tumor growth.
Importantly, since adipose tissue (including that within the breast) acts as an endocrine organ by synthesizing and secreting growth factors, it has an impact on the growth of the epithelium within the breast. Although there is no information to date on how each of these CLA isomers may modify the supportive framework of the human breast, a mixture of the two isomers was reported to depress milk fat levels in lactating women, an effect attributed to t10,c12-CLA. (Thus, although an equal mixture of the two CLA isomers is readily available in health food stores, CLA supplements containing t10,c12-CLA should not be used by nursing mothers.) Finally, given the demonstrated effects of both CLA isomers in carcinogen-induced rat models, future studies are needed to examine their efficacy in mouse models which are designed to mimic subsets of breast cancers in which the expression of specific genes is altered (gene expression is the translation of information encoded in a gene into protein or RNA).
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