Retroconversion is a minor contributor to increases in eicosapentaenoic acid following docosahexaenoic acid feeding as determined by compound specific isotope analysis in rat liver

• Published in: Nutrition & metabolism 2017-11, Vol.14 (1), p.75-75, Article 75
• Main Authors: Metherel, Adam H, Chouinard-Watkins, Raphaël, Trépanier, Marc-Olivier, Lacombe, R J Scott, Bazinet, Richard P
• Format: Article
• Language: English
• Subjects: Alpha-linolenic acid; Brief Communication; Docosahexaenoic acid; Eicosapentaenoic acid; Linolenic acids; Liver; Metabolism; Omega-3 fatty acids; Physiological aspects; Retroconversion
• ISSN: 1743-7075; 1743-7075
• DOI: 10.1186/s12986-017-0230-2

Dietary docosahexaenoic acid (DHA, 22:6n-3) not only increases blood and tissue levels of DHA, but also eicosapentaenoic acid (EPA, 20:5n-3). It is generally believed that this increase is due to DHA retroconversion to EPA, however, a slower conversion of α-linolenic acid (ALA, 18:3n-3) derived EPA to downstream metabolic products (i.e. slower turnover of EPA) is equally plausible. In this study, 21-day old Long Evans rats were weaned onto an ALA only or DHA + ALA diet for 12 weeks. Afterwards, livers were collected and the natural abundance C-enrichment was determined by compound specific isotope analysis (CSIA) of liver EPA by isotope ratio mass-spectrometry and compared to dietary ALA and DHA C-enrichment. Isotopic signatures (per mil, ‰) for liver EPA were not different (  > 0.05) between the ALA only diet (-25.89 ± 0.39 ‰, mean ± SEM) and the DHA + ALA diet (-26.26 ± 0.40 ‰), suggesting the relative contribution from dietary ALA and DHA to liver EPA did not change. However, with DHA feeding estimates of absolute EPA contribution from ALA increased 4.4-fold (147 ± 22 to 788 ± 153 nmol/g) compared to 3.2-fold from DHA (91 ± 14 to 382 ± 13 nmol/g), respectively. In conclusion, CSIA of liver EPA in rats following 12-weeks of dietary DHA suggests that retroconversion of DHA to EPA is a relatively small contributor to increases in EPA, and that this increase in EPA is largely coming from elongation/desaturation of ALA.