Metabolic conversion of C20 polymethylene-interrupted polyunsaturated fatty acids to essential fatty acids.

Polymethylene-interrupted (PMI)-polyunsaturated fatty acids (PUFA) are fatty acids present largely in gymnosperm. Sciadonic acid (SciA, 20:3 Δ-5,11,14) and juniperonic acid (JA, 20:4 Δ-5,11,14,17) are typical C20 PMI-PUFA with an isolated double bond at Δ5. Previously, we found that SciA and JA are converted to linoleic acid (LNA) and α-linolenic acid (ΑLA), respectively. The conversion process includes chain-shortening step by peroxisomal β-oxidation for elimination a double bond at Δ5, and subsequent chain-elongation step in microsomes. In this study, we examined the substrate specificity of this metabolism in rodent and human cells. Supplementation of SciA, eicosadienoic acid (EDA, 20:2 Δ-11,14) or JA to CHO-K1 cells (wild type) induced an accumulation of LNA, LNA or ALA, respectively, in cellular lipids. These changes were not observed in the peroxisomes-deficient CHO cells, indicating involvement of peroxisomes in the metabolism. Two types of human cells (MKN74 and HepG2) also converted the C20 PMI-PUFA and EDA to the respective essential fatty acids. In contrast, no chain-shortened metabolite of pinolenic acid (18:3 Δ-5,9,12) was detected in any cell lines tested. From these results, C20 PMI-PUFA and EDA, but not C18 PMI-PUFA, are suggested as being effectively converted to essential fatty acids by the fatty acid remodeling system in rodent and human cells.