No abstract

Sciadonic acid (20:3 Δ‐5,11,14) is an n‐6 series trienoic acid that lacks the Δ8 double bond of arachidonic acid. This fatty acid is not converted to arachidonic acid in higher animals. In this study, we characterized the metabolic behavior of sciadonic acid in the process of acylation to phospholipid of HepG2 cells. One of the characteristics of fatty acid compositions of phospholipids in sciadonic acid‐supplemented cells is a higher proportion of sciadonic acid in phosphatidylinositol (PtdIns) (27.4%) than in phosphatidylethanolamine (PtdEtn) (23.2%), phosphatidylcholine (PtdCho) (17.3%) and phosphatidylserine (PtdSer) (20.1%). Similarly, the proportion of arachidonic acid was higher in PtdIns (35.8%) than in PtdEtn (29.1%), PtdSer (18.2%) and PtdCho (20.2%) in arachidonic‐acid‐supplemented cells. The extensive accumulation of sciadonic acid in PtdIns resulted in the enrichment of newly formed 1‐stearoyl‐2‐sciadonoyl molecular species (38%) in PtdIns and caused the reduction in the level of pre‐existing arachidonic‐acid‐containing molecular species. The kinetics of incorporation of sciadonic acid to PtdEtn, PtdSer and PtdIns of cells were similar to those of arachidonic acid. In contrast to sciadonic acid, neither eicosapentaenoic acid (20:5 Δ‐5,8,11,14,17) nor juniperonic acid (20:4 Δ‐5,11,14,17) accumulated in the PtdIns fraction. Rather, these n‐3 series polyunsaturated fatty acids, once incorporated into PtdIns, tended to be excluded from PtdIns. In addition, the level of arachidonic‐acid‐containing PtdIns molecular species remained unchanged by eicosapentaenoic‐acid‐supplementation. These results suggest that sciadonic acid or sciadonic‐acid‐containing glycerides are metabolized in a similar manner to arachidonic acid or arachidonic‐acid‐containing glyceride in the biosynthesis of PtdIns and that sciadonic acid can effectively modify the molecular species composition of PtdIns in HepG2 cells. In this regard, sciadonic acid will be an interesting experimental tool to clarify the significance of arachidonic acid‐residue of PtdIns‐origin bioactive lipids.

Previously, we showed that lowering the growth temperature increased the level of eicosapentaenoic acid (EPA) in the phosphatidylcholine (PtdCho) of Caenorhabditis elegans. In this study, we investigated the molecular species composition of PtdCho of C. elegans, with an emphasis on EPA-containing species. C. elegans contained a substantial amount of 1,2-dipolyunsaturated fatty acid-containing PtdCho (1,2-diPUFA-PtdCho) species, such as arachidonic acid/EPA and EPA/EPA, which are unusual phospholipids in higher animals. The EPA/EPAPtdCho content was significantly increased in C. elegans grown at a low temperature. To examine the possibility that the acyltransferase activity involved in the remodeling of phospholipids accounts for the production of 1,2-diPUFA-PtdCho, we investigated the substrate specificity of this enzyme in C. elegans and found that it did not exhibit a preference for saturated fatty acid for acylation to the sn-1 position of PtdCho. The efficacy of the esterification of EPA to the sn-1 position was almost equal to that of stearic acid. The lack of preference for a saturated fatty acid for acylation to the sn-1 position of PtdCho is thought to result in the existence of the unusual 1,2-diEPA-PtdCho in C. elegans.