Conjugated linoleic acid does not inhibit development of aberrant crypt foci in colons of male Sprague-Dawley rats

Conjugated linoleic acid (CLA) is a potent inhibitor of the initiation and promotion of mammary carcinogenesis in animal models, but its role in colon carcinogenesis remains unclear. The objective of this study was to determine whether CLA inhibits the promotion of colon carcinogenesis. Forty male Sprague-Dawley rats were given a single dose of azoxymethane (20 mg/kg body wt i.p.). After 1 wk, the animals were randomized into two groups (n = 20) and fed a control AIN-93G diet or the control diet supplemented with 1% CLA at the expense of the soybean oil. After 12 wk, the animals were killed, and their colons were stained with methylene blue for aberrant crypt foci (ACF) analysis by light microscopy. The total number of ACF per animal did not differ between the control (174 +/- 11) and CLA (170 +/- 10) groups. Furthermore, CLA did not affect the average crypt multiplicity (crypts/ACF) or the average number of ACF in any size category. However, rats fed the 1% CLA diet had significantly higher serum insulin levels at the time of sacrifice than those fed the control diet. Thus it is possible that the promoting effects of elevated serum insulin on colon carcinogenesis may have counteracted an inhibitory effect of CLA.