The negative impacts of dietary biotin deficiency on antioxidant status, apoptosis and tight junction protein transcription of immune organs in grass carp (Ctenopharyngodon idella)

Low-molecular-weight vitamin biotin is an essential nutrient substance for all animal normal growth. Previous exploration has documented that dietary biotin deficiency led to fish growth retardation and a decrease in immunity, whereas its detrimental impacts on fish other physiological status were still not revealed yet. Herein, further exploration was performed to excavate the latent influence of dietary biotin deficiency on antioxidant status, apoptosis and tight junction protein of immune organs (the skin, spleen and head kidney). In this research, grass carp (Ctenopharyngodon idella) (117.11 ± 0.48 g) as a model were fed six graded levels of biotin diets (0.012, 0.110, 0.214, 0.311, 0.427 and 0.518 mg/kg diet) in triplicate for 70 days, followed by a challenge with A. hydrophila for 6 days. Our data from above three immune organs manifested that biotin deficiency (0.012 mg/kg diet): (1) markedly increased oxidative damage degree as evidenced by the obtained highest value in all oxidative damage indicators and exhibited the lowest significant value in almost all antioxidant enzymes activities and corresponding gene expressions, where this action may be in part correlated with the modulation of Nrf2 signaling (P < 0.05); (2) signally aggravated cell apoptosis by altering the expression profiles of mitochondria and death receptor pathways involved genes (such as caspase-3,8 and FasL), where this mechanism may be partly connected with p38MAPK signaling (P < 0.05); (3) dramatically damaged tight junctions by regulating the expression profiles of a series of complexes (such as occludin and claudins), where the reason may be in part correlated with myosin light chain kinase (MLCK) signaling (P < 0.05). Differently, the transcriptional levels of MnSOD, GPx4, JNK and ZO-2 (only in spleen) were not regulated by dietary biotin in above three immune organs (P > 0.05). Furthermore, a broken line analysis showed that dietary biotin requirement levels for on-growing grass carp is 0.245–0.354 mg/kg diet for parameters (ROS content, caspase3 and claudin-3c expression levels).