Combined effects of dietary quercetin and resveratrol on growth performance, antioxidant capability and innate immunity of blunt snout bream (Megalobrama amblycephala)

This study was conducted to investigate the effects of resveratrol (R) and quercetin (Q) supplementation on growth performance, antioxidant capability and hepatic apoptosis of juvenile blunt snout bream (average initial weight 4.6 +/- 0.10 g) fed a high-fat diet (HFD). Eight experimental diets were formulated to contain normal fat diet (NFD, 5% fat), a HFD (11% fat), or a HFD supplemented with three resveratrol levels (0, 0.5% and 1.0%) and two quercetin levels (0.4% and 0.8%), designated diets as Dl, D2, D3, D4, D5, D6, D7, and D8, respectively. After an 8-week feeding trial, the results showed that fish fed a HFD developed hepatic steatosis, as shown by elevated hepatic and plasma triglycerides (TG), total cholesterol (TC), and by increased plasma glucose (GLU), apoptosis index (AI) and liver fat content. Also, hepatocyte mRNA expressions of sirtuin-1 (SIRT1), copperezinc superoxide dismutase (Cu/Zn-SOD) and catalase (CAT) in fish fed a HFD were significantly decreased compared to fish fed a NFD (P < 0.05). Tumor necrosis factor-alpha (TNF-alpha) level was significantly increased in fish fed D2 compared to those fed D1. Dietary resveratrol and quercetin supplementation decreased plasma GLU, TG and TC, increased nitric oxide (NO) content, upregulated the mRNA expressions of SIRT1, Cu/Zn-SOD, CAT and glutathione peroxidase (GPx), and downregulated Caspase8 and TNF-alpha mRNA expressions. Weight gain rate (WGR) significantly increased in fish fed a HFD supplemented with 0.8% quercetin alone compared to other treatments (except for fish fed HFD supplemented with 0.4% quercetin alone). At the same quercetin concentration, the growth performance decreased with increasing resveratrol. Compared with D2 (HFD) and D7 (HFD supplemented with 0.8% quercetin and 0.5% resveratrol), the combination of 0.4% quercetin and 1.0% resveratrol supplementation significantly decreased hepatic TG and TC (P < 0.05). Additionally, compared with D2, the combination of 0.8% quercetin and 1.0% resveratrol supplementation significantly increased hepatic endothelial nitric oxide synthase (e-NOS) and inducible nitric oxide synthase (i-NOS) contents (P < 0.05). The results of this study indicated that dietary quercetin and resveratrol association could improve immunity, antioxidant capability and lipid metabolism of blunt snout bream, and high concentration of resveratrol would inhibit the growth of this species, while relatively high concentration of quercetin alone could promote its growth.