Dietary α-lipoic acid requirement and its effects on antioxidant status, carbohydrate metabolism, and intestinal microflora in oriental river prawn Macrobrachium nipponense (De Haan)

Alpha lipoic acid (alpha-LA) is not only a natural antioxidant, but also a key cofactor for the enzymes pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. The purpose of this study was to investigate the effects of dietary alpha-lipoic acid on the growth, antioxidant status, carbohydrate metabolism, and intestinal microflora of prawn, Macrobrachium nipponense. A total of 1250 juvenile M. nipponense with an average body weight of 0.050 +/- 0.003 g were randomly divided into five groups with three replicates (50 prawns per tank) for an 8-week feeding trial. The groups were fed with basal semi-purified diets containing alpha-lipoic acid at five different concentrations: 0 mg/kg (LA1), 500 mg/kg (LA2), 1000 mg/kg (LA3), 2000 mg/kg (LA4) and 4000 mg/kg (LA5). The results showed that the weight gain (WG), specific growth rate (SGR) and the survival rate were significantly lower in LA5 than in other groups. Dietary alpha-lipoic acid at a concentration below 2000 mg/kg (LA4) significantly reduced the malondialdehyde (MDA) content and increased the glutathione (GSH) content in the hepatopancreas of M. nipponense, and significantly increased the activities of glutathione reductase (GR), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD). However, the MDA content in the hepatopancreas was higher in LA5 than in LA1. The prawns in the LA3 group showed the highest activities of isocitrate dehydrogenase (ICDH) and key enzymes in glycolysis (pyruvate kinase, PK; 6-phosphofructokinase, PFK; Hexokinase, HK), but lower activity of lactate dehydmgenase (LDH) compared with those in LA1 and LA2. Analyses of gut micmflora at the operational taxonomic unit (OTU) level indicated that abundance (Chao index) and diversity (Simpson index) were lower in LA5 than in LA1 and LA3. The Shannon index's index was highest in LA5. The intestinal flora of M. nipponense comprised five main phyla and five main bacteria. The proportions of Proteobacteria and Citrobacter were higher in LA3 and LA5 than in LA1. The proportions of Actinobacteria, Bactemidetes Aeromonas, Tyzzerella 3 and Mycobacterium were significantly higher in LA5 than in LA3 and LA1. In summary, dietary a-lipoic acid at an appropriate level (<2000 mg/kg) can improve the antioxidant capacity and carbohydrate metabolism of M. nipponense and modulate its intestinal microbiota without reducing growth performance. Excessive alpha-lipoic acid (4000 mg/kg) negatively affected the growth performance and antioxidant activity of M. nipponense. Calculations based on WG and SGR indicate that the optimal addition amount of a-lipoic acid for juvenile M. nipponense is 1354.8 mg/kg and 1329.92 mg/kg, respectively.