Aspirin suppresses 1,2-dimethylhydrazine-induced alteration of proliferative parameters in rat colonic crypts

Human epidemiological reports and rodent experimental research data indicate a possible chemopreventive effect of regular aspirin use for decreasing risk of colon and rectum cancer incidence and mortality. We have previously demonstrated that aspirin can significantly suppress proliferative parameters in normal rat colonic epithelium when examined 24 h following an acute or chronic course of aspirin administration. To investigate whether aspirin would effectively suppress known carcinogen-induced changes in colonic epithelium, rats were given single s.c. injections of either aspirin (50 mg/kg bw) or saline on days 1-3 and either 1,2-dimethylhydrazine (DMH; 12 mg base/kg bw) or DMH vehicle on day 4 of each week for eight consecutive weeks. Rats were sacrificed 4 days after the last aspirin dose and 3 days after the last DMH or DMH vehicle dose. Using the proliferative biomarkers of proliferating cell nuclear antigen positive cells per midaxial crypt section (SCC), crypt proliferative zone height (PZ), crypt differentiated zone height (DZ), and total crypt height (CH), it was found that aspirin does suppress DMH-induced increases in SCC, PZ and CH. The findings demonstrate that aspirin has a long term (i.e. several days) protective effect against early carcinogen-induced proliferative changes in rat colonic crypts which may help account for aspirin's chemopreventive action against colon cancer.