Dietary fat is known to enhance intestinal tumorigenesis during the promotional phase of the carcinogenic process. The actual tumor promoting agents responsible for this enhancement are unknown although suggestions include, bile acids, the caloric content of the fat, and oxidation products of polyunsaturated fatty acids. Structure-activity studies have shown the primary oxidation products of unsaturated fatty acids, in particular hydroperoxy-,hydroxy, and keto-derivatives are mitogenic to the colonic mucosa when instilled intra-rectally into animals. In that cell proliferation is an essential component of tumor promotion these findings are consistent with a role for oxidized fatty acids in the enhancement of tumorigenesis. The experiments in this proposal will investigate the colonic metabolism of 13- hydroperoxyoctadecadienoic acid (derived from linoleic acid) and related compounds in an effort to assess the production of active metabolites from the primary oxidation products of major dietary fatty acids. Metabolism of radiolabeled 13--hydroperoxyoctadecadienoic acid by colonic mucosal cell homogenates, particulate fractions, and tissue explants will be assessed. Special attention will be paid to the conversion of the hydroperoxy fatty acid to an alpha, beta- unsaturated ketone although the production of hydroxy-, epoxyhydroxy-, trihydroxy-, and other metabolites will also be evaluated. Metabolism, binding of metabolites to tissue constituents, and incorporation into lipid classes will be determined, and correlated with the stimulation of mitogenesis in the explants. The time course, dose response, and cofactor requirements for the reactions will be determined. These investigations will provide significant new information concerning the target tissue mediated metabolism of an important class of biologically active molecules, and may provide insight into the mechanism of carcinogenesis.
