Comparison of catabolic rates of ¹³C‐labeled palmitic acid bound to the alpha and beta positions of triacylglycerol using CO₂ expired from mice

Abstract

We investigated the catabolic rate of 13 C-labeled palmitic acid ( à P) bound to a (sn-1) or b (sn-2) position of triacylglycerol (TAG) using isotope-ratio mass spectrometry. Specifically, we measured the 13 C-to-12 C ratio in CO 2 expired from mice. After 30-75 min, à P bound to the a position was catabolized faster than that bound to the b position. Thereafter, the catabolic rate of à P bound to the b position increased and surpassed that bound to the a position. This indicated that binding position affected the catabolic rate of à P, possibly due to the different specificities of pancreatic lipase, lipoprotein lipase, and hepatic lipase. Next, we measured the catabolic rate of à P bound to TAG in combination with one of three unsaturated fatty acids (oleic acid, linoleic acid, or a-linolenic acid). When à P was bound to the b position and Ln was bound to the a position, the catabolism of TAG was significantly higher than for other TAGs. This result suggests that fatty acid structure might affect the catabolism of counterpart fatty acids in TAG.Practical applications: Binding position to TAG affects fatty acid catabolism. The fatty acid desired to change to energy such as saturated fatty acid should be bound to the b position of TAG. In contrast, fatty acid desired to accumulate in our body such as polyunsaturated fatty acid should be bound at the a position of TAG because catabolism does not continue for a long time even though the fatty acid is catabolized quickly at first period. Our results can be applied to the design of structured lipid used for enteral nutrients, enteric nutrient, sports nutrients, etc.

Comparison of Catabolic Rates of <i>sn</i>-1, <i>sn</i>-2, and <i>sn</i>-3 Fatty Acids in Triacylglycerols Using ¹³CO₂ Breath Test in Mice

“…A similar trend was observed in Fig. 3 and our previous study using *P 7 . We previously thought that the difference is attributable to the difference in the characteristics of the two lipases 7 .…”

“…3 and our previous study using *P 7 . We previously thought that the difference is attributable to the difference in the characteristics of the two lipases 7 . As mentioned above, the fatty acid at the sn-2 position is absorbed by the epithelial cells of the small intestine in the form of 2-MAG, which is then resynthesized to TAG.…”

“…Owing to this preferential hydrolysis, the fatty acid at β position sn-2 position is not released from the glycerol backbone, resulting in the formation of 2-monoacyl glycerol 2-MAG , which is absorbed by the epithelial cells of the small intestine, where the TAG gets resynthesized. The catabolic rate of mediumchain fatty acids at the sn-2 position is lower than that of fatty acids at the sn-1 and sn-3 positions 7 . This is consistent with our results.…”

“…The relationship between the fatty acid position in TAGs and the function or catabolic rate of fatty acids has been studied. For example, the catabolic rate of stable isotope-labeled palmitic acid *P bound at α or β position was compared using a CO 2 breath test in mice 7 . The results suggested that the catabolic rate was different between the α and β positions and that in the first stage, the fatty acid at α position was catabolized faster than that at the β position.…”

Homochiral Asymmetric Triacylglycerol Isomers in Egg Yolk

“…Egg yolk may also play the same role as milk fat and acts as a source of energy and nutrients to babies. FAs at the α position are more rapidly β-oxidized to produce energy as compared to those at the β-position 22 .…”