Involvement of Nrf2-Keap1 and NF-κB signaling pathways in alleviation of Aeromonas sobria pathogenicity in Botia rostrata by Ceratophyllum demersum ethanol extract.

The present study aims to investigate the functional mechanism by which Ceratophyllum demersum ethanol extract (CE) acts as an antibacterial agent against Aeromonas sobria infection in Botia rostrata. Healthy, juvenile B. rostrata males (Weight: 2.7 ± 0.5 g; Length: 4.9 ± 0.8 cm) were administered intraperitoneal (i.p.) injection with a single dose of 96 h LD50 (1∗107.261 CFU/ml) A. sobria suspension (working volume: 25 μl) and fed diet fortified with ethanol extract of C. demersum at 0.4 g/kg feed for 30 days. Bacteria-exposed fish fed the CE-fortified diet showed significantly (P < 0.05) lower mortality, serum cortisol (η2 = 0.983), cytokines [IL-1β (η2 = 0.872), IL-2 (η2 = 0.769), IL-6 (η2 = 0.796), IL-10 (η2 = 0.798), TNF-α (η2 = 0.823), IFN-γ (η2 = 0.726)], gill and liver reactive oxygen species (ROS) levels and nuclear Nrf2, NF-κB protein expression compared to bacteria-exposed fish fed the basal diet. Significantly (P < 0.05) higher respiratory burst activity (η2 = 0.983), serum lysozyme (η2 = 0.997), phagocytic activity (η2 = 0.753), and cytosolic Keap 1, IκB protein expression compared to basal diet-fed fish were also observed. Moreover, alterations in gill and liver histoarchitecture induced by A. sobria infection were minimized by the plant extract dietary treatment. The principal bioactive compounds in the plant extract may quench ROS, reduce oxidative stress, and subsequently restore the endogenous antioxidant system and bring down the proinflammatory cytokine levels. Thus, the present results elucidate how C. demersum and its constituent phytochemicals interact with key host signaling pathways, specifically the Keap1-Nrf2 antioxidant pathway and the NF-κB inflammatory pathway, to restore redox homeostasis, modulate cytokine responses, and thereby enhance pathogen resistance in fish.