Effect of olive oil on early and late events of colon carcinogenesis in rats: modulation of arachidonic acid metabolism and local prostaglandin E-2 synthesis

Background--Animal model studies have shown that the colon tumour promoting effect of dietary fat depends not only on the amount but on its fatty acid composition. With respect to this, the effect of n9 fatty acids, present i n olive oil, on colon carcinogenesis has been scarcely investigated. Aims-To assess the effect of an n9 fat diet on precancer events, carcinoma development, and changes in mucosal fatty acid composition and prostaglandi n (PG)E-2 formation in male Sprague-Dawley rats with azoxymethane induced c olon cancer. Methods--Rats were divided into three groups to receive isocaloric diets (5 % of the energy as fat) rich in n9, n3, or n6 fat, and were administered az oxymethane subcutaneously once a week for 11 weeks at a dose rate of 7.4 mg /kg body weight. Vehicle treated groups received an equal volume of normal saline. Groups of animals were colectomised at weeks 12 and 19 after the fi rst dose of azoxymethane or saline. Mucosal fatty acids were assessed at 12 and 19 weeks. Aberrant crypt foci and the in vivo intracolonic release of PGE, were assessed at week 12, and tumour formation at week 19. Results--Rats on the n6 diet were found to have colonic aberrant crypt foci and adenocarcinomas more often than those consuming either the n9 or n3 di et. There were no differences between the rats on the n9 and n3 diets. On t he other hand, administration of both n9 and n3 diets was associated with a decrease in mucosal arachidonate concentrations as compared with the n6 di et. Carcinogen treatment induced an appreciable increase in PGE, formation in rats fed the n6 diet, but not in those fed the n3 and n9 diets. Conclusions-Dietary olive oil prevented the development of aberrant crypt f oci and colon carcinomas in rats, suggesting that olive oil may have chemop reventive activity against colon carcinogenesis. These effects may be partl y due to modulation of arachidonic acid metabolism and local PGE, synthesis .