α-Linolenic acid metabolism in human CD3+ T cells favours oxylipin production over polyunsaturated fatty acid synthesis

Abstract

The essential dietary fatty acid α-linolenic acid (ALA) can be converted into anti-inflammatory 18 carbon oxylipins or into longer chain n€‘3 polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The partitioning of ALA between these alternative metabolic fates is not understood. To address this, peripheral blood CD3+ T cells from healthy volunteers (18-30 years; n=10) were cultured for 48h, with or without concanavalin A (10µg/ml) in 10% (v/v) pooled donor plasma with low ALA (20 µM) or high ALA (40 µM) concentrations (1:10 [13C]€‘labelled/unlabelled). [13C]ALA metabolites were detected either by GC-isotope ratio mass spectrometry for intracellular PUFA or by LC-MS/MS for oxylipins in cell culture supernatant. The ratio of the labelled metabolites hydroxyoctatrienoic acid ([13C]HOTrE) and dihydroxyoctadecaenoic acid ([13C]DiHODE) to [13C]ALA were 1.8±0.2 / 7.2±1.1 and 0.9±0.2 / 4.3±0.6 for low / high ALA, respectively, compared to the eicosatrienoic acid ([13C]20:3n€‘3) to [13C]ALA ratio of 0.002±0.0001 / 0.02±0.003 in stimulated T cells. Results from unstimulated cells were similar. Furthermore, oxylipins from all PUFA precursors were analysed in the culture supernatant of the T cells. The ratio of oxylipin concentrations in high compared to low ALA cultures was 1.4±0.1 for EPA-derived dihydroxyeicosatetraenoic acid (DiHETE), 5.6±0.9 for DHA-derived dihydroxydocosapentaenoic acid (DiHDPE), 7.9±2.7 for resolvin RvE1 and 2.0±0.3 for resolvin RvD1. The total oxylipin profile was not altered significantly by mitogen stimulation. These findings show that ALA is used primarily by T cells for constitutive production of anti-inflammatory lipid mediators rather than synthesis of longer chain PUFA. Further, ALA addition changes the secreted oxylipins towards a less-inflammatory profile. This has implications for understanding the effects of dietary PUFA on immune function.