Volume 88, Issue 4, October (2002), pp. 355-364 © The Author 2002
doi:10.1079/BJN2002662

Eicosapentaenoic and docosapentaenoic acids are the principal products of α-linolenic acid metabolism in young men

Graham C. Burdge, Amanda E. Jones and Stephen A. Wootton
Institute of Human Nutrition, Level C, West Wing, Southampton General Hospital, Tremona Road, Southampton SO16 6YD, UK

 (Received 6 July 2001–Revised 3 April 2002–Accepted 17 May 2002)

The capacity for conversion of α-linolenic acid (ALNA) to n-3 long-chain polyunsaturated fatty acids was investigated in young men. Emulsified [U-¹³C]ALNA was administered orally with a mixed meal to six subjects consuming their habitual diet. Approximately 33 % of administered [¹³C]ALNA was recovered as ¹³CO₂ on breath over the first 24 h. [¹³C]ALNA was mobilised from enterocytes primarily as chylomicron triacylglycerol (TAG), while [¹³C]ALNA incorporation into plasma phosphatidylcholine (PC) occurred later, probably by the liver. The time scale of conversion of [¹³C]ALNA to eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) suggested that the liver was the principal site of ALNA desaturation and elongation, although there was some indication of EPA and DPA synthesis by enterocytes. [¹³C]EPA and [¹³C]DPA concentrations were greater in plasma PC than TAG, and were present in the circulation for up to 7 and 14 d, respectively. There was no apparent ¹³C enrichment of docosahexaenoic acid (DHA) in plasma PC, TAG or non-esterified fatty acids at any time point measured up to 21 d. This pattern of ¹³C n-3 fatty acid labelling suggests inhibition or restriction of DHA synthesis downstream of DPA. [¹³C]ALNA, [¹³C]EPA and [¹³C]DPA were incorporated into erythrocyte PC, but not phosphatidylethanolamine, suggesting uptake of intact plasma PC molecules from lipoproteins into erythrocyte membranes. Since the capacity of adult males to convert ALNA to DHA was either very low or absent, uptake of pre-formed DHA from the diet may be critical for maintaining adequate membrane DHA concentrations in these individuals.

Abbreviations: ALNA; α-linolenic acid; AUC; area under the curve; CRF; chylomicron-enriched fraction; DHA; docosahexaenoic acid; DPA; docosapentaenoic acid; EPA; eicosapentaenoic acid; FAME; fatty acid methyl esters; GC-C-IRMS; gas chromatography-combustion-isotope ratio mass spectrometry; LCPUFA; long-chain polyunsaturated fatty acid; NEFA; non-esterified fatty acids; PC; phosphatidylcholine; PE; phosphatidylethanolamine; TAG; triacylglycerol

Keywords:
alpha-Linolenic acid: Polyunsaturated fatty acids: Metabolism