Retroconversion and metabolism of [13C]22:6n−3 in humans and rats after intake of a single dose of [13C]22:6n−3-triacylglycerols

• Published in: The American journal of clinical nutrition 1996-10, Vol.64 (4), p.577-586
• Main Authors: Brossard, N, Croset, M, Pachiaudi, C, Riou, JP, Tayot, JL, Lagarde, M
• Format: Article
• Language: English
• Subjects: Administration, Oral; Animals; Biological and medical sciences; Carbon Isotopes; Chromatography, Gas; Docosahexaenoic Acids - metabolism; Eicosapentaenoic Acid - blood; Fatty Acids, Unsaturated - blood; Fundamental and applied biological sciences. Psychology; Humans; Lipids. Glycolipids; Male; Metabolisms and neurohumoral controls; Rats; Rats, Sprague-Dawley; Species Specificity; Triglycerides - administration & dosage; Triglycerides - blood; Triglycerides - metabolism; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/64.4.577

The apparent retroconversion of docosahexaenoic acid (22:6n−3) to eicosapentaenoic acid (20:5n−3) and docosapentaenoic acid (22:5n−3) was studied in vivo, in rats and humans, after they ingested a single dose of triacylglycerols containing [13C]22:6n−3 ([13C]22:6-triacylglycerol), without 22:6n−3 dietary supplementation. The amount of apparent retroconversion and the distribution of the three n−3 polyunsaturated fatty acids (PUFAs) in plasma lipid classes were followed as a function of time by measuring the appearance of 13C in these PUFAs with gas-chromatography combustion-isotope ratio mass spectrometry. This [13C]22:6n−3 retroconversion, calculated by summing the amounts of [13C]22:5n−3 and [13C]20:5n−3 in plasma lipids, was lower in humans than in rats, reaching a maximum of approximately 9% of the total plasma [13C]22:6n−3 in rats, but only 1.4% in humans. The incorporation of [13C]22:6n−3 and [13C]22:5n−3 in lipid classes followed their endogenous distribution with a maximal accumulation in phospholipids, but a low incorporation into cholesterol esters (CEs), whereas [13C]20:5n−3 was equally present in phospholipids and CEs. The ratio of the amount of HDL-CE to HDL-phosphatidylcholine for [13C]20:5n−3 was higher than for [13C]22:6n−3, indicating a selectivity of the lecithin-cholesterol acyltransferase enzyme with regard to these PUFAs, which may be related to the differences in their biological properties after fish oil feeding. The occurrence of a weak basal 22:6n−3 retroconversion in humans supports feeding this pure PUFA in cases in which 20:5n−3 presents undesirable side effects and when specific alterations of blood lipids are expected.