Japan Oil Chemists' Society Acta Medica Okayama 1345-8957 74 11 2025 Bioconversion and Metabolic Fate of the n-1 Polyunsaturated Fatty Acids, 6,9,12,15- Hexadecatetraenoic (C16:4 n-1) and 8,11,14,17- Octadecatetraenoic (C18:4 n-1) Acids, in HepG2 Cells 1023 1032 EN Koki Sugimoto Faculty of Food and Nutritional Sciences, Toyo University Hideto Nishiguchi Faculty of Chemistry, Materials, and Bioengineering, Kansai University Ryota Hosomi Faculty of Chemistry, Materials, and Bioengineering, Kansai University Toshifumi Tanizaki Bizen Chemical Co., Ltd. Tadahiro Tsushima Bizen Chemical Co., Ltd. Naomichi Baba Bizen Chemical Co., Ltd. Yoshihisa Misawa Bizen Chemical Co., Ltd. Ziyi Wang Department of Molecular Biology and Biochemistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Mitsuaki Ono Department of Oral Rehabilitation and Regenerative Medicine, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Yuki Murakami Department of Hygiene and Public Health, Kansai Medical University Seiji Kanda Department of Hygiene and Public Health, Kansai Medical University Kenji Fukunaga Faculty of Chemistry, Materials, and Bioengineering, Kansai University Fish oil contains not only major fatty acids with double bonds at the n-3, n-6, n-7, and n-9 positions but also those with a double bond at the n-1 position, such as 6,9,12,15-hexadecatetraenoic acid (C16:4 n-1; HDTA). However, intracellular bioconversion and metabolic fate of n-1 polyunsaturated fatty acids (PUFA) remain unclear. Therefore, in this study, we aimed to assess the intracellular bioconversion and metabolic fate of HDTA and its metabolite, 8,11,14,17- octadecatetraenoic acid (C18:4 n-1; ODTA), using HepG2 cells. Based on the results of cell viability and cytotoxicity assays for HDTA and ODTA, the concentration of each fatty acid supplemented in the experiments was set at 10 ƒÊM. HepG2 cell culture with HDTA revealed C20:4 n-1 as a new HDTA metabolite, along with previously reported ODTA. Our findings suggest that the HDTA taken up by HepG2 cells undergoes elongation to form ODTA and C20:4 n-1. Following supplementation with HDTA, ODTA, and 5,8,11,14,17-eicosapentaenoic acid (C20:5 n-3; EPA), fatty acids disappeared from the culture medium within 24 h. Notably, the total relative level of HDTA and its metabolites, including ODTA and C20:4 n-1 in HDTA- and ODTA-supplemented cells were significantly lower than the total relative level of EPA and its metabolites, including 7,10,13,16,19-docosapentaenoic acid (C22:5 n-3), C24:6 n-3, and 4,7,10,13,16,19-docosahexaenoic acid (C22:6 n-3) in the EPA-supplemented cells. Except for a portion that was intracellularly elongated, most HDTA was taken up by HepG2 cells and may undergo rapid fatty acid ƒÀ-oxidation. However, RNA-sequencing and real-time polymerase chain reaction analysis revealed no significant changes in fatty acid ƒÀ-oxidation–related gene expression levels in HDTA-supplemented cells. Collectively, these results provide novel insights into the intracellular bioconversion mechanisms and metabolic fate of HDTA and ODTA in HepG2 cells, suggesting that the metabolic fate of n-1 PUFA is distinct from that of common PUFA. No potential conflict of interest relevant to this article was reported.