THE EFFECT OF CHENODEOXYCHOLIC ACID ON THE DEVELOPMENT OF ABERRANT CRYPT FOCI IN THE RAT COLON

Bile acids are reported to enhance experimentally-induced colonic tumorigenesis. Previously we have reported that cholic acid, a known tumor promoter, actually reduced the number of aberrant crypt foci (ACF), purported preneoplastic lesions (B.A. Magnuson and R.P. Bird, Cancer Lett., 68 (1993), 15-23). This observation was unexpected and has prompted us to explore the effect of other bile acids on the development of ACF. The primary objective of this investigation was to evaluate the effect of feeding varying dosages of chenodeoxycholic acid (CDC) on the induction and growth of ACF and on the proliferative indices of the colonic epithelium. Sprague-Dawley male rats were injected with azoxymethane (+AOM, 20 mg/kg) or saline (-AOM). One week later they were randomly allocated to five groups and were fed diets containing CDC at varying levels (0.0, 0.025, 0.05, 0.1 and 0.2% by weight) for 2 weeks. After completion of the feeding period the number and crypt multiplicity of ACF were quantified, and three different proliferative indices, including mitotic index, BUDR labelling index (percentage S-phase cells) and proliferating cell nuclear antigen labelling index (percentage cycling cells) were determined. CDC at all dosages increased the number of ACF having the maximum effect at the 0.1% CDC level. A significant dose-related increase in crypt height was noted in CDC-fed +AOM groups when compared with the +AOM control groups. The mitotic indices of colonic crypts were higher (P less than or equal to 0.05) only in the 0.025% CDC -AOM group when compared with the 0% CDC -AOM group (5.97 +/- 0.63 vs. 3.92 +/- 0.79). The BUDR labelling indices were not altered by CDC feeding (P greater than or equal to 0.05). PCNA labelling indices increased consistently among the CDC-fed groups. Among the -AOM group the 0.05% CDC group had the maximum value, which was significantly different from the control value(19.21 +/- 1.92 vs. 10.93 +/- 0.56, respectively). Among the +AOM groups the PCNA labelling indices increased with increasing levels of CDC. It was concluded that CDC stimulated the development of ACF and altered cell cycle associated events in colonic crypts undergoing neoplastic changes.