Whole-Body β-Oxidation of Docosahexaenoic Acid Is Decreased under n-3 Polyunsaturated Fatty Acid Insufficiency as Assessed by a ¹³CO₂ Breath Test Using [U-¹³C]Fatty Acids

Abstract

We applied a continuous ¹³CO₂ breath test to examination of the effects of n-3 polyunsaturated fatty acid (PUFA) insufficiency on fatty acid β-oxidation. Fischer rats were divided into two groups, and were reared on two different regimens of diet for multiple successive generations. One diet was adequate with respect to n-3 PUFA and the other was insufficient in n-3 PUFA. Rats (the F18 generation) were given [U-¹³C]docosahexaenoic acid or [U-¹³C]palmitic acid by intravenous injection, and expired ¹³CO₂ was continuously measured using a mass spectrometer. Fatty acid oxidation was evaluated by two parameters, the half-life of ¹³CO₂ in the breath and cumulative ¹³CO₂ recovery from the labeled fatty acids. When [U-¹³C] docosahexaenoic acid was administered, cumulative ¹³CO₂ recovery was 40% lower in the n-3 PUFA-insufficient diet group than in the n-3 PUFA-adequate diet group. The half-life appeared to be the same for the two diet groups. In the case of [U-¹³C]palmitic acid, neither the half-life nor cumulative ¹³CO₂ recovery significantly differed between the two diet groups. These results suggest that overall β-oxidation of DHA in a whole-body system is decreased under n-3 PUFA insufficiency. Our finding shows that the ¹³CO₂ breath test can be used to assess n-3 PUFA insufficiency. The test provides a useful and invasive method for evaluation of fatty acid β-oxidation.