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

Abstract

Fatty acids in triacylglycerol (TAG) are catabolized after digestion. However, the catabolic rates of several fatty acids bound to the α (sn-1, 3) or β (sn-2) position of TAG have not been thoroughly compared. In this study, the catabolic rates of ¹³C-labeled palmitic acid, oleic acid, linoleic acid, α-linolenic acid, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) bound to the α and β position of TAG were compared using isotope ratio mass spectrometry. The catabolic rates of the studied fatty acids were evaluated using the ratio of ¹³C and ¹²C in carbon dioxide expired from mice. The results indicated that palmitic acid, oleic acid, or α-linolenic acid bound to the β position was slowly catabolized for a long duration compared to that when bound to the α position. In contrast, EPA bound to the β position was quickly catabolized, and EPA bound to the α 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.

graphical abstract