Metabolism of linoleic and linolenic acids in hepatocytes of two freshwater fish with different n-3 or n-6 fatty acid requirements

Abstract

The requirements of essential fatty acids (EFAs) varies among fish species, however, the possible different cellular metabolism patterns of EFAs among fish species have not been well addressed. In the present study, we compared activities of cellular FA uptake, β-oxidation and esterification towards [1–14C]-labeled linoleic acid (LA, 18:2n-6) and linolenic acid (LNA, 18:3n-3) in the primary hepatocytes between grass carp (GCH) and Nile tilapia (NTH), which are two freshwater fish but have specific requirement of LNA or LA, respectively. The results showed that LNA had a higher FA-serum binding efficiency than LA in both GCH and NTH. GCH preferentially took up LNA, while NTH primarily took up LA. Both GCH and NTH had higher β-oxidation activity to LA than to LNA. LNA caused higher esterification than LA in GCH, but LA and LNA caused similar esterification effects in NTH. In GCH, LNA tended to induce higher expressions of the genes related to lipid transportation and lipogenesis, but lowered expressions of the lipid catabolism-related genes. However, the regulation of LNA or LA on gene expressions in NTH was marginal. Taken together, GCH had specific preference to take up and esterify LNA, while NTH preferentially took up LA. These differences are in accordance with the specific EFA requirements of grass carp and Nile tilapia. Our study provides new information for understanding the relationships between the specific EFA requirements and cellular metabolism of EFAs in fish.