Conjugated Linoleic Acid and Cancer

Abstract

1. Conjugated linoleic acid (CLA) contains conjugated double bonds and is known as a family of isomers of linoleic acid that can be found in the meat and dairy products. 2. In vitro studies have shown that CLA can inhibit the growth of mammary, colon, colorectal, gastric, prostate, and malignant liver cell lines and has also been shown to induce the expression of apoptotic genes. 3. The incidence of mammary tumors induced by methylnitrosourea and forestomach tumors induced by benzo[a]pyrene was decreased by CLA in rodent models. CLA isomers may regulate tumorigenesis through different mechanisms by altering lipid metabolism, regulation of oncogene expression, regulation of cyclooxygenase-2 expression, and lipooxygenase metabolic pathways. 4. The specific effects of CLA appear to be dependent on which isomer is assessed. The effects of various isomers in vitro and in vivo have recently been reviewed. With respect to breast cancer, the t10, c12-CLA isomer was shown to enhance tumorigenesis in a transgenic mouse mammary tumor model when compared to the c9, t11-CLA isomer. In a parallel study, increased polyp diameter was associated with supplementation of the t10, c12-CLA diet compared to the c9, t11-CLA diet, which decreased colonic polyp number in the mouse MIN model of colon cancer. 5. Future studies should investigate the effects of CLA on developing cancer tissues, their progenitor cells, and stem cells. Moreover, animal studies should use models that better recapitulate human cancers in an effort to shorten the time for the development of clinical studies. Therefore, no recommendations for CLA consumption in the context of prevention or therapy can be made until such studies are undertaken.