Dietary conjugated linoleic acid (CLA) induces apoptosis of colonic mucosa in 1,2-dimethylhydrazine-treated rats: a possible mechanism of the anticarcinogenic effect by CLA

One of the objectives of the present study was to investigate whether 1% conjugated linoleic acid (CLA) in the diet reduced tumour incidence in the colon of 1,2-dimethylhydrazine (DMH)-treated rats. Colon cancer was induced by injecting 6-week-old, male, Sprague-Dawley rats with 15 mg/kg DMH twice per week for 6 weeks. They were fed either 1% CLA or a control diet ad libitum for 30 weeks. Dietary CLA significantly decreased colon tumour incidence (P <0.05). Our second objective was to investigate whether apoptosis in the colon mucosa of DMH-treated rats was affected by the amount of dietary CLA and whether the changes in apoptosis were related to those in fatty acid-responsive biomarkers. For this purpose, rats were killed after being fed a diet containing 0 %, 0.5%, 1% or 1.5% CLA for 14 weeks. CLA was undetected in the mucosa of rats fed the 0 % CLA diet and increased to 5.9 mg/g phospholipid in rats fed the 0.5% diet. The apoptotic index estimated by the terminal deoxynucleotidyl transferase-mediated dUTP nick and labelling technique was increased by 251% and the 1,2-diacylglycerol content was decreased by 57% in rats fed 0.5% CLA. No further changes in these variables were observed when CLA in the diet was raised to 1.0% or 1.5 %. However, dietary CLA decreased mucosal levels of prostaglandin E-2, thromboxane B-2 and arachidonic acid in a dose-dependent manner. The present data indicate that dietary CLA can inhibit DMH-induced colon carcinogenesis by mechanisms probably involving increased apoptosis.