Ameliorative effect of dietary lipopolysaccharides on Oreochromis niloticus juveniles submitted to aflatoxin B1‐induced oxidative stress and bacterial challenge

The current study was designed to evaluate the ameliorative effect of lipopolysaccharides (LPS) (a portion of the Gram –ve bacteria cell wall) on aflatoxin (AFB1)‐persuaded changes in the cytokine expression, heat‐shock protein 70 (HSP70), antioxidant genes, different haematological and biochemical parameters in Nile Tilapia along with the infection by Aeromonas hydrophila and the immune‐stimulant efficiency of LPS on the growth pattern. For this study, two hundred and forty O. niloticus (35 ± 1.5 g) were used. The fish were randomly allocated into four experimental groups, four replicates for each group (15 fish/replicate). Group 1 was the negative control group fed on a basal diet, and group 2 was the positive control group fed on the basal diet with aflatoxins (AFB1) 200 µg/kg feed. Group 3 has fed the lipopolysaccharides 20 mg/100 gm diets. Group 4, besides the AFB1‐contaminated basal diet, was provided with lipopolysaccharides 20 mg/100 gm diet. At the end of the 12 weeks, each group was injected with A. hydrophila. The analysis revealed that LPS‐treated AFB1‐supplemented fish showed improvement in haematological, lysosomal and phagocytic activities and total protein and significantly decreased liver enzyme exaggerated by aflatoxin; alongside, the LPS‐treated aflatoxin‐supplemented fish revealed a significant effect on the haematological and the immunity markers after 24 h, 48 h and 1 week post challenged with A. hydrophila. Concerning the gene expression, AFB1 group showed significant up‐regulation of HSP70 and interferon gamma gene mRNA expression, which is significantly down‐regulated by LPS treatment, besides LPS showed up‐regulation of catalase and superoxide dismutase genes markedly alongside with interleukins (IL), IL‐8 and IL‐1B; the binding effect of LPS markedly appears after A. hydrophila which significantly modulates the HSP70 and immunity marker genes in addition to the antioxidant‐related genes, CAT and SOD. Histopathological findings reflected a marked increase in intestinal villi length in LPS‐treated groups. Our view illuminates for the first time the pathways of molecular wellness for the role of LPS in AFB1 toxicity and bacterial infection. Our observation illuminates the molecular fitness pathways for the LPS that can aide to the development of a bacterial disease tolerance strategy and potentially boost immune response in O. niloticus fish.