Catabolism and Accumulation of Dietary <i>cis</i>- and <i>trans</i>-Epoxy Octadecanoic Acids in Mice

<i>In vivo</i> 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 <i>cis-</i> and <i>trans-</i>epoxy octadecanoic acids (epoxy-C18:0) with those of oleic acid (<i>cis-</i>C18:1) in mice using stable isotope-labeled compounds. Both epoxy isomers were catabolized more rapidly than <i>cis-</i>C18:1, with <i>trans-</i>epoxy-C18:0 exhibiting a slightly faster rate than <i>cis-</i>epoxy-C18:0. The concentrations of <i>cis-</i> and <i>trans-</i>epoxy-C18:0 were significantly lower than those of <i>cis-</i>C18:1 in the plasma, small intestine, and liver, with <i>trans-</i>epoxy-C18:0 accumulation being lower than <i>cis-</i>epoxy-C18:0 accumulation. These results indicate that epoxy-C18:0 isomers are preferentially catabolized and accumulate less in the body than <i>cis-</i>C18:1. The structural differences between <i>cis-</i> and <i>trans-</i>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.