Lactoferrin enhances Fas expression and apoptosis in the colon mucosa of azoxymethane-treated rats

Bovine lactoferrin, a multifunctional glycoprotein, has been shown to strongly inhibit development of azoxymethane (AOM)-induced rat colon tumors. Little, however, is known about the inhibitory mechanisms. We have demonstrated recently that lactoferrin enhances the expression of a member of the tumor necrosis factor receptor family, Fas, in the colon mucosa during both early and late stages of carcinogenesis. Thus, Fas could be involved in bovine lactoferrin-mediated inhibition of tumor development. To investigate this possibility, we studied the influence of bovine lactoferrin on Fas-mediated apoptosis with regard to expression of Fas, activation of caspase-8 and caspase-3, and DNA fragmentation in the colon mucosa of AOM-treated rats. Western blot analysis demonstrated a >2.5-fold increase in Fas protein expression, as well as elevation of the active forms of both caspase-8 and caspase-3. Immunohistochemical analysis revealed Fas-positive cells and apoptotic cells preferentially within the proximal colon region, clearly at the site of bovine lactoferrin-mediated tumor inhibition. These results suggest that apoptosis caused by elevated expression of Fas is involved in chemoprevention by lactoferrin of colon carcinogenesis.