High dietary arachidonic acid produces excess eicosanoids, and induces hepatic inflammatory responses, oxidative stress and apoptosis in juvenile Acanthopagrus schlegelii

Abstract

As a functional fatty acid, Arachidonic acid (ARA) plays an important role in immunity due to its metabolites in mammals, which have been extensively studied in mammals. However, studies on the function of metabolites produced by dietary ARA in aquatic animals are not comprehensive and in-depth. Hence, an eight-week feeding trial was conducted to evaluated the regulatory effects of dietary ARA and its metabolites-eicosanoids on inflammation, oxidative stress and apoptosis in the liver of Acanthopagrus schlegelii with an initial weight of 0.99 ± 0.10 g. Six isonitrogenous and isolipidic (41% protein, 14% lipid) diets were formulated with gradient levels of ARA: 0% (ARA0.10), 0.5% (ARA0.59), 1.0% (ARA1.04), 1.5% (ARA1.42), 2.0% (ARA1.94), 2.5% (ARA2.42), respectively, and palmitic acid was used to regulate lipid levels. Results showed that the key enzyme contents of ARA metabolic pathway such as phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), lipoxygenase (LOX) cytochrome P450 (CYP450), prostaglandin E2 (PGE2), leukotriene C4 (LTC4) and 20-hydroxyeicosatetraenoic acid (20-HETE) in the liver were increased with dietary ARA levels increased. High levels of dietary ARA (1.94% and 2.42%) activated the gene expression levels of nuclear factor kappa B (nf-κb), which were confirmed by the results of immunofluorescence assay. Likewise, the expression levels of pro-inflammatory cytokines (tnf-α and il-1β) were up-regulated by ARA1.94 and ARA2.42 groups. Fish fed with excess ARA level has significantly low antioxidant capacity by decreasing the activity of related antioxidant parameters and down-regulating the expression level of related genes. The pro-apoptotic related genes (bax and caspase 7/9) were markedly up-regulated as dietary ARA levels increased from 1.04% to 2.42%. Collectively, excess dietary ARA levels (1.92% and 2.42%) produced excess eicosanoids, triggering inflammation via activating NF-κB expression and promoting its nuclear translocation, resulting in oxidative stress by reducing antioxidant parameters (SOD, GSH and GPX), inducing cell apoptosis through up-regulating pro-apoptotic gene expression levels.