LACK OF BUTYRATE IS ASSOCIATED WITH INDUCTION OF BAX AND SUBSEQUENT APOPTOSIS IN THE PROXIMAL COLON OF GUINEA-PIG

Background & Aims: Butyrate stimulates proliferation and suppresses di fferentiation in normal colonic epithelial cells. Because the involved intracellular signaling mechanisms are unclear, this study investigat ed certain molecular effects of butyrate. Methods: Tissue sheets from guinea pig proximal colon were incubated in Ussing chambers in the pre sence and absence of butyrate. Colonic tissues were examined by scanni ng and transmission electron microscopy, DNA laddering, Western blots, and immunohistochemistry. Results: After incubation of the colonic mu cosa for 150 minutes without butyrate, morphological studies showed ma ssive apoptosis of colonocytes. Simultaneously, these colonocytes exhi bited a significant oligonucleosomal DNA fragmentation. In contrast, a ddition of physiological concentrations of butyrate (10 mmol/L) to col onic sheets showed no detectable DNA fragmentation within 150 minutes. Western blot analysis showed little if any difference in the level of Bcl-2 expression in colonocytes incubated with or without butyrate up to 150 minutes. In contrast, expression of Bar proteins continuously increased after 45 minutes without butyrate and reached a fivefold ind uction after 150 minutes compared with cells incubated in the presence of butyrate. Moreover, immunohistochemistry using an anti-Bax antibod y system showed enhanced labeling of the epithelial colonocytes in the absence of butyrate. Conclusions: Removal of butyrate induces increas ed expression of Bar proteins paralleled by rapid apoptosis of colonoc ytes in vitro.