Dietary Ala-Gln ameliorated growth suppression and intestinal injury induced by soya saponin in zebrafish

Our previous study showed that dietary soybean saponin (SA) consumption reduced growth performance and damaged the morphology of the intestinal mucosa in zebrafish (Danio rerio). Glutamine (Gln) plays an important role in ameliorating intestinal atrophy. Therefore, the present study tested the hypothesis that dietary alanine-glutamine (Ala-Gln) supplementation ameliorates the growth suppression and intestinal injury induced by dietary SA in zebrafish. Five experimental diets were prepared by supplementing the basal diet with either SA at 0, 5 or 10 g/kg, and Ala-Gln at 0 or 10 g/kg, with adjustment of Ala-Ala to maintain equal nitrogen levels among all diets. Fish with average initial body weight of (9.00 +/- 0.13) mg were fed five diets for 4 weeks. The growth performance increased significantly and intestinal morphology was improved by supplementation of Ala-Gln at 10 g/kg. Ala-Gln supplementation improved growth via regulation of the growth hormone (GH)-insulin like growth factor I (IGF-I) axis. The experimental diets significantly affected the mRNA expression levels of amino acid and peptide transporters. Dietary Ala-Gln upregulated the mRNA expression levels of glycolysis and fat synthesis-related factors, significantly reduced the activity of AMP-activated protein kinase (AMPK), but stimulated the activity of target of rapamycin (TOR). Overall, Ala-Gln might be broken down into free amino acids, with Gln being absorbed by the intestinal mucosa cells. Dietary Ala-Gln supplementation ameliorated the intestinal injury induced by SA, and promoted the breakdown of carbohydrates and fats for energy, thereby improving the growth performance of zebrafish.