Suppression of azoxymethane-induced rat colon carcinoma development by a fish oil component, docosahexaenoic acid (DHA)

The effects of intragastric gavage administration of docosahexaenoic acid (DNA), a major component of fish oil, on azoxymethane (AOM)-induced colon carcinogenesis in rats was investigated. Male F344 rats were treated with 15 mg/kg body wt of AOM once a week, for two weeks. The animals were given either 1 ml of DHA or water intragastrically 5 times a week, starting the day before the first carcinogen treatment. The numbers of AOM-induced aberrant crypt foci in the rats given DHA were 76% and 62% of the control values, at 4 and 12 weeks, respectively. After 36 weeks of DHA treatment, colon tumors were counted and examined histologically. The blood plasma levels of prostaglandin E2 (PGE₂) and polyunsaturated fatty acids were also quantified. The incidences of colon cancer did not differ, being 96% and 92% in the AOM and AOM + DHA groups, respectively. Colon cancer multiplicity was, however, significantly decreased by the DHA treatment; 3.65 ± 2.18 in the AOM group and 2.41 ± 1.58 in the AOM + DHA group (P < 0.01). Notably, the numbers of moderately differentiated adenocarcinomas in the middle and distal colon in the DHA-treated group were lower than in the AOM group. The levels of PGE₂ and arachidonic acid in the blood plasma of DHA-treated rats were also significantly lower than in the AOM group. These results suggest that DHA exerts its inhibitory effect on colon carcinogenesis by modulating lipid metabolism and inhibiting the arachidonic cascade.