Fatty acids and colon cancer in experimental models

Experimental models have several advantages in the study of colon cancer. They can be used to tightly control diet, examine putative intermediate markers, test hypotheses about mechanisms of carcinogenesis, and quantify development of tumors in a short time. Dietary issues that have been studied in animal models but are unresolved include the concept of the effects of total fat compared with energy intake, composition of the basal diet, linoleic acid requirements, and interactions of fat with other nutrients. Intermediate markers that have been probed in animal or in vitro studies include cytokinetics, aberrant crypt foci, eicosanoids and hydroxyoctadecadienoic acids, ornithine decarboxylase, tyrosine kinase, protein kinase C, and gene expression. Colon cancer is studied in animals primarily with use of chemicals that are relatively specific inducers of these tumors, but transplantable models and transgenic animals are also used. Total dietary fat is generally thought to affect colon tumorigenesis, but there does not appear to be any specific fatty acid that promotes the development of colon cancer. Several studies indicate that n-3 fatty acids from marine sources alter a variety of biological intermediates and inhibit colonic tumorigenesis; this is probably mediated via the eicosanoid pathway. Although there are undoubtedly multiple cellular changes elicited by certain fatty acids, our current knowledge of this area suggests that specific fatty acid metabolites or their targets are the likely mediators in this sequence.