Vitamin E inhibits inflammation and improves immune response of mud crabs (Scylla paramamosain) by activating an antioxidant enzyme system and apoptosis mechanism

An 8-week feeding trial was conducted to evaluate the effects of dietary vitamin E levels on growth, antioxidant status and immune response for mud crabs (<i>Scylla paramamosain</i>). A total of 180 mud crabs (initial weight: 24.16 ± 1.08 g) were fed six different dietary vitamin E levels, where the analyzed vitamin E were 9.65, 34.70, 58.50, 76.30, 102.00 and 199.00 mg/kg, respectively. The results showed that crabs fed with the 76.30 mg/kg vitamin E diet exhibited significantly higher final weight (<i>P</i> = 0.007), percent weight gain (PWG) (<i>P</i> = 0.008) and specific growth rate (<i>P</i> = 0.010) than those fed the diets with 9.65 and 34.70 mg/kg vitamin E. The highest activities of total antioxidant capacity in hemolymph (<i>P</i> = 0.006) and hepatopancreas (<i>P</i> = 0.017), and superoxide dismutase (SOD) (<i>P</i> = 0.037) in hemolymph were observed in crabs fed the 76.30 mg/kg vitamin E diet, and crabs fed the diet with 102.00 mg/kg vitamin E showed higher activities of peroxidase (POD) (<i>P</i> = 0.006) and α-tocopherol transfer protein (<i>P</i> = 0.024) in hemolymph than those fed the other diets. Dietary 76.30 mg/kg vitamin E significantly up-regulated the expression of <i>cat</i>, <i>gpx</i>, <i>prx</i> and <i>CytMn-sod</i> in hepatopancreas (<i>P</i> < 0.01). The expression levels of genes related to pro-inflammatory factor (<i>il-16</i>, <i>litaf</i>, <i>rab6a</i> and <i>relish</i>) in hepatopancreas were significantly down-regulated and the expression level of anti-inflammatory factor related gene (<i>tgf</i>) significantly up-regulated in crabs fed diet with 199.00 mg/kg vitamin E (<i>P</i> < 0.05). Crabs fed the diet with 76.30 mg/kg vitamin E exhibited the highest percentage of survival cells in hemocytes (<i>P</i> = 0.026). The mRNA expression level of genes related to pro-apoptotic cytokines (<i>bax</i> and <i>bok</i>) significantly down-regulated, and the mRNA expression level of anti-apoptotic cytokines related genes (<i>pi3k</i>, <i>akt</i> and <i>bcl-2</i>) significantly up-regulated with dietary vitamin E levels increasing from 9.65 to 76.30 mg/kg (<i>P</i> < 0.05). In conclusion, the quadratic regression model based on PWG indicated that the optimal requirement of vitamin E was 99.13 mg/kg for the mud crab. Moreover, dietary 58.50 and 76.30 mg/kg vitamin E inhibited the inflammatory response and improved the immune response.