RESISTANCE OF ABERRANT CRYPT FOCI TO APOPTOSIS INDUCED BY AZOXYMETHANE IN RATS CHRONICALLY FED CHOLIC-ACID

We have previously shown that chronic feeding of cholic acid to carcinogen treated rats reduces the number of putative preneoplastic lesions of colonic cancer, aberrant crypt foci (ACF), but enhances the growth of remaining ACF and the incidence of colonic tumors. The following study was conducted to further explore the effects of cholic acid on ACF growth by determining if ACF in cholic acid-fed animals display resistance to apoptotic cell death. ACF were induced in male Sprague- Dawley rats with two injections of azoxymethane (20 mg/kg body wt). Rats were divided into two groups and fed either the control AIN-76 diet or the AIN-76 diet containing 0.2% cholic acid. After 18 weeks, colonic apoptotic cell death was induced with an acute low dose of azoxymethane (10 mg/kg body wt). The number of cells, apoptotic bodies and bromodeoxyuridine (BUdR)-labeled cells were determined in colonic crypts comprising ACF and surrounding normal crypts in rats from each diet group. The number of apoptotic bodies per 100 cells was lower in ACF crypts than in normal-appearing crypts (P = 0.0034). Both normal and ACF crypts from rats fed the cholic acid diet had fewer apoptotic bodies per 100 cells than crypts from rats fed the control diet (P = 0.0102). These data suggest that ACF harbor resistance to induction of apoptosis. Chronic feeding of a diet containing 0.2% cholic acid results in the development of increased resistance to apoptosis. The lower rate of cell death in ACF may contribute to the enhanced growth of ACP and higher tumor incidence previously observed in cholic acid-fed animals.