LONG-TERM FEEDING OF FIELD BEAN PROTEIN CONTAINING PROTEASE INHIBITORS SUPPRESSES VIRUS-INDUCED MAMMARY-TUMORS IN MICE

Protease inhibitors (PIs) of synthetic, bacterial or soybean origin ha ve been shown to suppress carcinogen or radiation-induced rat mammary carcinogenesis. We report, for the first time, the effect of year-long feeding of Field bean meal, a rich source of Pls with a 24% protein c ontent, at different protein levels in the diet, on mouse mammary tumo r virus (MMTV)induced mammary tumorigenesis in C3H/Jax mice. Weanling female mice were randomized and divided into groups and fed chow or ch ow with 2%, 4%, 8% FB protein (FBP) or autoclaved 2% FBP (AFBP) until 49 weeks and the incidence of mammary tumors was recorded until 58 wee ks when they were sacrificed. Mice fed 2% FBP showed significant (P < 0.001) reduction (68%) in tumor incidence and delay (P < 0.02) in tumo r appearance compared to controls. This suppressive effect on mammary tumorigenesis increased with increased FBP intake with values of tumor suppression being 75% and 81% in mice groups fed 4% and 8% FBP, respe ctively. Incidentally, the tumors appeared earlier (P < 0.05) in the 8 % FBP-treated mice compared to other groups. Moreover, this suppressiv e effect on mammary tumorigenesis was related to the PI activity of th e FB meal, since mice fed 2% AFBP showed no reduction in tumor inciden ce. Heat treatment, which had destroyed the PI activity, apparently di d not affect other chemopreventive agents known to be present in plant material. This possibility is supported by our observation that prolo nged feeding of 2% FBP or 2% AFBP increased the liver glutathione cont ent of mice, suggesting the presence of a highly heat-stable factor, o ther than PIs, in the FBP, which brought about this elevation. Further , while 2% or 4% FBP- and 2% AFBP- treated mice showed no adverse grow th effects, only the 8% FBP-fed group showed a significant lower growt h curve compared to control mice, with some of them showing pancreatic lesions. Published by Elsevier Science Ireland Ltd.