New insights into the role of (2-Carboxyethyl) dimethylsulfonium Bromide (Br-DMPT) in enhancing the structural integrity of immune organs of on-growing grass carp (Ctenopharyngodon idella)

The immune function operation of fish immune organs depends tightly on the immune organs' structural integrity which is mainly regulated by various biological respects such as oxidative status, apoptosis and tight junctions. Previous explorations have documented that dietary (2-carboxyethyl) dimethylsulfonium Bromide (BrDMPT) intervention boosted fish growth in association with the strengthened immune function of the head kidney, spleen and skin. Here, further exploration was performed to better decipher the primary action mechanisms by which Br-DMPT maintains the immune organs' integrity of fish. In this research, grass carp (Ctenopharyngodon idella) (216.49 +/- 0.29 g) as a model were fed five graded levels of Br-DMPT diets (0-520.0 mg/kg) in triplicate for 60 days, followed by a challenge with Aeromonas hydrophila for 2 weeks. Subsequently, immune organ samples were selectively collected to investigate oxidative status, apoptosis and tight junctions associated parameters. Our data from above three immune organs manifested that compared to the control group, 260.0 mg/kg Br-DMPT diet group: (1) markedly decreased oxidative damage degree as evidenced by the obtained lowest value in all oxidative damage indicators and exhibited the highest 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 signalling (P < 0.05); (2) signally alleviated 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 and JNK signalling (P < 0.05); (3) dramatically elevated 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) signalling (P < 0.05). Noticeably, no statistical distinction was examined between all Br-DMPT diet groups with respect to the gene expressions of GPx4a, GPx4b, GSTP2, Bcl-2, claudin-b and claudin-7 in above diverse immune organs (P > 0.05). Overall, for the first time, our present results confirm that the enhanced structural integrity of immune organs in Br-DMPT- supplemented fish appears to partly be associated with the increased antioxidant status and the inhibited cell apoptosis, as well as the elevated tight junctions, which provides groundbreaking insight into the undiscovered role of Br-DMPT in accelrating fish growth and increases Br-DMPT more potential to be popularly Table 1 applied in future fishery productin. Composition and nutrients content of the basal diet.