β‐Ionone suppresses mammary carcinogenesis, proliferative activity and induces apoptosis in the mammary gland of the Sprague‐Dawley rat

β‐Ionone demonstrates potent anticancer activity both in vitro and in vivo. We determined tumor incidence and the number of rats bearing tumors as well as cell proliferation and apoptosis in a rat mammary cancer model induced by 7, 12‐dimethylbenz[a]anthracene (DMBA). Rats were fed an AIN‐76A diet containing β‐ionone (0, 9, 18 or 36 mmol/kg), starting 2 weeks before DMBA administration and continuing for 24 weeks. A dose‐dependent inhibition of mammary carcinogenesis by dietary β‐ionone was observed. Corresponding tumor incidence values were 82.1, 53.3, 25.9 and 10.0% (p < 0.01 or 0.05). Time to tumor appearance increased and tumor multiplicity decreased with increasing dietary β‐ionone. Histopathological and immunohistochemical evaluations of tumors were performed on the 64, 31, 15 and 3 tumors, respectively, identified in rats from the respective groups of 30. The proportions of adenocarcinomas, adenomas and benign masses were equally distributed in the latter group. In proportions within the other groups, the proportions of adenocarcinomas and benign masses decreased and increased with increasing dietary β‐ionone. Proliferating cell nuclear antigen (PCNA), cyclin D1 and Bcl‐2 expression decreased, and Bax expression and nuclear fragmentation increased with increasing dietary β‐ionone. These results demonstrate the potent capacity of dietary β‐ionone to suppress DMBA‐initiated mammary cancer in rats. © 2008 Wiley‐Liss, Inc.