Dietary Arachidonic Acid Has a Time-Dependent Differential Impact on Adipogenesis Modulated via COX and LOX Pathways in Grass Carp Ctenopharyngodon idellus

In this study, we explored the function of arachidonic acid (ARA) in adipogenesis in the grass carp (Ctenopharyngodon idellus) using in vivo and in vitro models. An 8-week feeding trial was performed using three isonitrogenous and isoenergetic purified diets: ARA-free, ARA, and ARA + acetylsalicylic acid [ASA, a cyclooxygenase (COX) inhibitor]. Fish were sampled after 4 and 8 weeks of feeding. Results showed that ARA-fed fish had a significantly lower intraperitoneal fat index (IPFI) and smaller adipocytes; these decreases were reversed by ASA after 8 weeks of feeding. Nevertheless, at week 4, the IPFI and adipocyte size were higher in the ARA group, and they were comparable to those of fish fed ARA + ASA. To further investigate the influence of ARA on adipocyte differentiation, confluent pre-adipocytes of grass carp were incubated with ARA for 3 days. This in vitro experiment demonstrated that ARA promoted adipogenesis in a dose-dependent manner. Pre-treatment with the lipoxygenase (LOX) inhibitor nordihydroguaiaretic acid attenuated the pro-adipogenic function of ARA. However, after treatment with ARA for 8 days, adipocytes had a lower lipid content than cells treated with oleic acid, and ASA could suppress this effect. We thus revealed the dual function of ARA in adipogenesis in grass carp. The LOX pathway may play a key role in pro-adipogenesis after short-term treatment with ARA, whereas the COX pathway is possibly responsible for the inhibition of adipogenesis after long-term treatment.