Antitumorigenic Effect of a High Protein Diet in Mouse Skin

The recent increase of colon, breast, and prostate cancer incidence in Korea has been attributed to a diet pattern change to a more Western style, in which the foods eaten are higher in protein and fat. Whether high protein intake itself stimulates tumor cell growth and exacerbates disease status has been investigated, however, many epidemiological studies have inconsistent results between meat intake and the risk of certain cancers. These inconsistent results are partly because of the difficulty of studying the effects of just the meat intake. Other factors, such as overall meal context, could not be completely excluded in the study. To address the question of whether high protein itself is independently associated with carcinogenesis, we initiated ICR mice with 200 nmol ($50{\mu}g$) 7,12-dimethylbenz[a]anthracene (DMBA) and fed animals either a normal diet (ND, 14% casein) or a high protein diet (HPD, 50% casein) for 15 weeks with 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion in two-stage skin carcinogenesis protocol. There was no significant difference between ND and HPD group in food intake and body weight throughout the experiment. However, tumor multiplicity of the HPD group was decreased by 75.5% compared to that of the ND group. In addition, HPD inhibited skin hyperplasia and epidermal cell proliferation. Western analyses with whole skin lysates showed that HPD inhibited TPA-induced Akt (S473), S6K (T389), 4E-BP1 (Thr 37/46) and Erk1/2 (Thr202/Tyr204) phosphorylation as well as COX-2 expression. Taken together, these data suggest that a high protein diet has an anticarcinogenic effect by inhibiting the TPA-induced Akt signaling pathway.