CHEMOPREVENTIVE EFFECT OF ASPIRIN ON GROWTH OF ABERRANT CRYPT FOCI INRATS

Nonsteroidal anti-inflammatory drugs display a chemopreventive effect on polyps and cancer of the large bowel. This study evaluated the inhi bitory effect of aspirin on the distribution and growth of aberrant cr ypt foci (ACF), the earliest putative preneoplastic and early neoplast ic lesions in a rat model. For initiation of ACF, Sprague Dawley rats were injected with azoxymethane (30 mg/kg), a well-established rat car cinogen. After the second injection the rats were allocated to three g roups, which received 0.2% or 0.6% aspirin or the solvent only (contro l group). After 6 weeks the animals were killed, and their colons remo ved, fixed in formalin, and screened for distribution and size of ACF separately for middle and distal parts of the large intestine. The rat s injected with azoxymethane showed a 100% incidence of ACF. Administr ation of 0.2% and 0.6% aspirin resulted in 55% and 54% reduction, resp ectively, in overall frequency of ACF. Aspirin significantly reduced t he frequency of medium-sized (four tc, six crypts per focus) and large (three to six crypts per focus) but not the small (one to three crypt s per focus) ACF. In the control group the ACF of the same multiplicit y were larger than those in the aspirin-treated rats. No statistically significant difference in ACF-inhibiting effect was noted between 0.6 % and 0.2% aspirin solution, Aspirin given at a concentration of eithe r 0.2% of 0.6% thus has a chemopreventive effect on ACF acting on post initiation stage of azoxymethane-induced colonic carcinogenesis model in rats.