Induction of apoptosis by conjugated linoleic acid in cultured mammary tumor cells and premalignant lesions of the rat mammary gland

Conjugated linoleic acid (CLA) is an effective agent in preventing mammary cancer in rats treated with a carcinogen. The appearance of a tumor mass is the net result of cell proliferation minus cell death. Thus, apoptosis cou ld be an important mechanism in controlling clonal expansion of the early p remalignant lesions. The overall objective of this report was to determine whether CLA stimulated apoptosis, In the first part of the study, CLA was f ound to increase chromatin condensation (visualized through fluorescent 4', 6-diamidino-2-phenglindole staining to DNA) and to induce DNA laddering, bo th evidence of apoptosis, in a rat mammary tumor cell line. The second part was to investigate the effect of CLA feeding on the development of histolo gically identifiable premalignant lesions in the rat mammary gland, as well as on the quantification of apoptosis (by terminal uridyltransferase nick end labeling assay) and the expression by immunohistochemistry of apoptosis regulatory proteins (bcl-2, bak, and bar) in normal versus premalignant ma mmary structures, CLA inhibited the formation of premalignant lesions by si milar to 50%. It also significantly increased apoptosis and reduced the exp ression of bcl-2 in these lesions, but it did not modulate the levels of ba k or bax, In contrast, neither apoptosis nor any of the apoptosis regulator y proteins was affected by CLA in normal mammary gland alveoli or terminal end buds. The data suggest that early pathological lesions may be particula rly sensitive to CLA. In addition to providing a molecular basis for elucid ating the mechanism of action of CLA in cancer prevention, the research on CLA-responsivc biomarkers also has a practical side because these assays ca n be applied biopsied human tissue samples in future CLA intervention trial s.