Growth features of aberrant crypt foci that resist modulation by cholic acid.

Previously, we demonstrated that feeding rats a diet containing 0.2% cholic acid (CHA-diet) resulted in the elimination or remodelling of a number of aberrant crypt foci (ACF) in their primal stages (1-3 crypts/focus). The present investigation was conducted to determine if ACF with advanced growth features will respond differently than their primal counterparts to the CHA-diet. Sprague-Dawley male rats were injected with azoxymethane (20 mg/ kg) and were maintained on a control diet for 21 weeks. At week 21, three rats were killed and their colons were assessed for ACE. The remaining animals were randomly divided into two groups, which were fed a control diet or a CHA-diet respectively, After 3 weeks of feeding, the rats (n = 5) were killed and their colons were assessed for the number, size (area occupied by each focus) and crypt multiplicity (number of crypts/focus). The CHA-diet resulted in a significant (P 4 crypts/focus, a 50.4% reduction. Treatment with CHA resulted in a marked reduction in the population of ACF with 1-2 or 3-4 crypt multiplicity with area >5-1Ox10(-2) mm2. These findings demonstrate that ACF with advanced growth features are phenotypically different from their primal counterparts in resisting the responses elicited by the CHA-diet even at a late time point, and that morphological heterogeneity among ACF may represent different biological states.

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 ACF and higher tumor incidence previously observed in cholic acid-fed animals.