Comparative Oxidative Metabolism of Dietary Eicosapentaenoic Acid Hydroperoxide and Unoxidized Eicosapentaenoic Acid in Mice

Abstract

Abstract: Eicosapentaenoic acid hydroperoxides (EPA-OOH) are oxidized derivatives of eicosapentaenoic acid formed during lipid peroxidation and metabolism; however, their physio-logical fate remains unclear. Here, we investigated the in vivo fate of dietary EPA-OOH. We synthesized stable isotope (¹³C)-labeled EPA-ethyl ester hydroperoxide (*EPA-EE-OOH) and its unoxidized counterpart (*EPA-EE) and administered them orally to mice. Exhaled air was collected at defined time points and analyzed by isotope-ratio mass spectrometry to determine the ¹³C/¹²C ratio of expired ¹³CO₂. To evaluate gastric degradation, photo-oxidized EPA-EE-OOH was exposed to hydrochloric acid to simulate stomach conditions, and degradation products were characterized by gas chromatography-mass spectrometry and compared with those of unoxidized EPA-EE. Compared with *EPA-EE, *EPA-EE-OOH produced an earlier increase in expired ¹³CO₂ (Δ¹³C peak 28.6 ‰ at 30 min) than *EPA-EE (Δ¹³C peak 27.4 ‰ at 240 min); however, cumulative ¹³CO₂ excretion over 6 h did not differ significantly between treatments, indicating comparable overall catabolism. Under acidic conditions, EPA-EE-OOH underwent ac-id-catalyzed cleavage near the hydroperoxide moiety, yielding shorter-chain fatty acids and al-dehydes. These findings suggest that a fraction of dietary EPA-OOH is degraded in the gastroin-testinal tract into low-molecular-weight products that are rapidly catabolized, accounting for the early increase in expired ¹³CO₂. To the best of our knowledge, our study is the first to report the in vivo catabolic behavior of dietary EPA-OOH. These findings provide new insight into its physiological significance.