The effects of dietary oxidized konjac glucomannan and its acidolysis products on the immune response, expression of immune related genes and disease resistance of Schizothorax prenanti

In the present study, KGM was degraded by H2O2 and HCl to obtain two products with different molecular weights: oxidized konjac glucomannan (OKGM, 4.7 × 105 Da) and low-molecular-weight oxidized konjac glucomannan (L-OKGM, 9.2 × 103 Da). The effects of the two OKGM products on IL-1β, TNF-α, and TLR22 gene expression, and immune parameters and the resistance to Aeromonas hydrophila of Schizothorax prenanti were determined. The results showed that the lysozyme activity was significantly enhanced by the L-OKGM diets. The SOD activity was significantly increased by both OKGM and L-OKGM diets. The MDA level of fish fed the OKGM and L-OKGM diets was significantly lower than the control group. IL-1β mRNA level in the spleen significantly increased in all L-OKGM fed groups. The 8.0 g kg−1 L-OKGM diet also significantly up-regulated IL-1β gene expression in the head kidney. In the gut, IL-1β mRNA levels were significantly higher in fish fed with the 8.0 g kg−1 OKGM and 16.0 g kg−1 L-OKGM diets. The TNF-α mRNA level of L-OKGM group significantly increased in the spleen, head kidney and gut. High dosing of OKGM significantly up-regulated TNF-α transcription in the head kidney, while only the 8.0 g kg−1 OKGM group showed significantly higher TNF-α mRNA expression in the mesonephros. Fish fed the L-OKGM diets showed significantly higher expression of TLR22 in the spleen, head kidney and mesonephros. After the injection of A. hydrophila, the 8.0 g kg−1 L-OKGM group showed a significantly higher survival rate than did the control group. Present study suggests that OKGM and L-OKGM can up-regulate immune-related gene expression and enhance disease resistance in S. prenanti, and L-OKGM exhibits higher immunomodulatory activity. •We prepared two oxidative degradation products of KGM (9.2×103 Da and 4.7×105 Da).•Dietary OKGM and L-OKGM enhanced the immune capacity.•OKGM and L-OKGM diet up-regulated the expression of IL-1β，TNF-α and TLR22.•Fish fed 8.0 g kg−1 L-OKGM diet showed the highest survival rate.