Compound-specific isotope analysis resolves the dietary origin of docosahexaenoic acid in the mouse brain

Abstract

DHA (22:6n-3) may be derived from two dietary sources, preformed dietary DHA or through synthesis from -linolenic acid (ALA; 18:3n-3). However, conventional methods cannot distinguish between DHA derived from either source without the use of costly labeled tracers. In the present study, we demonstrate the proof-of-concept that compound-specific isotope analysis (CSIA) by GC-isotope ratio mass spectrometry (IRMS) can differentiate between sources of brain DHA based on differences in natural13C enrichment. Mice were fed diets containing either purified ALA or DHA as the sole n-3 PUFA. Extracted lipids were analyzed by CSIA for natural abundance13C enrichment. Brain DHA from DHA-fed mice was significantly more enriched (23.32 to 21.92) compared with mice on the ALA diet (28.25 to 27.49). The measured13C enrichment of brain DHA closely resembled the dietary n-3 PUFA source, 21.86 and 28.22 for DHA and ALA, respectively. The dietary effect on DHA13C enrichment was similar in liver and blood fractions. Our results demonstrate the effectiveness of CSIA, at natural13C enrichment, to differentiate between the incorporation of preformed or synthesized DHA into the brain and other tissues without the need for tracers.—Lacombe, R. J. S., V. Giuliano, S. M. Colombo, M. T. Arts, and R. P. Bazinet. Compound-specific isotope analysis resolves the dietary origin of docosahexaenoic acid in the mouse brain. J. Lipid Res. 2017. 58: 2071–2081.