Abstract
DHA (22:6n-3) may be derived from two dietary sources, preformed dietary DHA or through synthesis from α-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 natural 13C 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 abundance 13C 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 measured 13C 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 DHA 13C enrichment was similar in liver and blood fractions. Our results demonstrate the effectiveness of CSIA, at natural 13C enrichment, to differentiate between the incorporation of preformed or synthesized DHA into the brain and other tissues without the need for tracers.
Highlights
DHA (22:6n-3) may be derived from two dietary sources, preformed dietary DHA or through synthesis from -linolenic acid (ALA; 18:3n-3)
FA tissue concentrations After feeding mice purified ALA and DHA diets over two generations, there were no significant diet × generation (F1 and F2) interaction effects (P > 0.05) in brain, liver, and red blood cell (RBC) with respect to DHA concentrations (Fig. 3); serum concentrations did trend toward significance (P = 0.0614)
DHA concentrations were between 40% and 60% lower across serum, RBCs, and liver tissues in mice maintained on the ALA diet when compared with the DHA-fed group
Summary
DHA (22:6n-3) may be derived from two dietary sources, preformed dietary DHA or through synthesis from -linolenic acid (ALA; 18:3n-3). 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 natural 13C enrichment. Our results demonstrate the effectiveness of CSIA, at natural 13C enrichment, to differentiate between the incorporation of preformed or synthesized DHA into the brain and other tissues without the need for tracers.—Lacombe, R. One study by Lefkowitz et al [9] presented a novel approach whereby dietary ALA was replaced in its entirety with a 2H-labeled analog and fed to Abbreviations: ALA, -linolenic acid; ARA, arachidonic acid; CSIA, compound-specific isotope analysis; EA, elemental analyzer; FAME, fatty acid methyl ester; IRMS, isotope ratio mass spectrometry; LNA, linoleic acid; RBC, red blood cell; VPDB, Vienna PeeDee Belemnite. Due to exorbitant costs associated with custom formulating a diet exclusively with an isotopically labeled tracer, it is reasonable to assume this approach is not likely to be replicated; thereby highlighting a demand for alternative cost effective techniques to study FA metabolism
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