Catabolism and Accumulation of Dietary cis- and trans-Epoxy Octadecanoic Acids in Mice

In vivo metabolism of epoxy fatty acids, the unsaturated fatty acid oxidation products formed upon heating of edible oils, remains unclear. Here, we compared the catabolic rates and accumulation of dietary cis- and trans-epoxy octadecanoic acids (epoxy-C18:0) with those of oleic acid (cis-C18:1) in mice using stable isotope-labeled compounds. Both epoxy isomers were catabolized more rapidly than cis-C18:1, with trans-epoxy-C18:0 exhibiting a slightly faster rate than cis-epoxy-C18:0. The concentrations of cis- and trans-epoxy-C18:0 were significantly lower than those of cis-C18:1 in the plasma, small intestine, and liver, with trans-epoxy-C18:0 accumulation being lower than cis-epoxy-C18:0 accumulation. These results indicate that epoxy-C18:0 isomers are preferentially catabolized and accumulate less in the body than cis-C18:1. The structural differences between cis- and trans-epoxy-C18:0 isomers may influence their metabolic fate. This is the first comprehensive elucidation of the catabolism and body accumulation of dietary epoxy fatty acids, providing insights for food safety assessment.