Examination of the Catabolic Rates of 13C-Labeled Fatty Acids Bound to the α and β Positions of Triacylglycerol Using 13CO2 Expired from Mice

Fatty acids in triacylglycerol (TAG) are catabolized after digestion. However, the catabolic rates of several fatty acids bound to the alpha (sn-1, 3) or beta (sn-2) position of TAG have not been thoroughly compared. In this study, the catabolic rates of C-13-labeled palmitic acid, oleic acid, linoleic acid, alpha-linolenic acid, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) bound to the alpha and beta position of TAG were compared using isotope ratio mass spectrometry. The catabolic rates of the studied fatty acids were evaluated using the ratio of C-13 and C-12 in carbon dioxide expired from mice. The results indicated that palmitic acid, oleic acid, or alpha-linolenic acid bound to the beta position was slowly catabolized for a long duration compared to that when bound to the a position. In contrast, EPA bound to the beta position was quickly catabolized, and EPA bound to the a position was slowly catabolized for a long time. For linoleic acid or DHA, no difference in the catabolic rates was detected between the binding positions in TAG. Furthermore, EPA and DHA were less catabolized than the other fatty acids. These results indicate that the catabolic rates of fatty acids are influenced by their binding positions in TAG and that this influence on the catabolic rate differed depending on the fatty acid species.