In silico insights into the molecular mechanisms of Eclipta alba leaf fractions enhancing nonspecific immune mechanisms and resistance to Aeromonas hydrophila in Oreochromis mossambicus (Peters)

The present study evaluated the impact of the water-soluble fraction (WSF) and hexane-soluble fraction (HSF) from Eclipta alba, a medicinal plant native to India, on nonspecific immune mechanisms and disease resistance in Oreochromis mossambicus (Mozambique tilapia) experimentally infected with Aeromonas hydrophila. Fish were intraperitoneally administered E. alba leaf fractions at doses of 0, 4, 40, or 400 mg kg−1. Immune parameters, including ROS and RNS production by leukocytes and serum lysozyme activity, were monitored at several time points (-2, 2, 4, 6, 8, and 10 days post-treatment). Both WSF and HSF significantly (p < 0.05) increased ROS levels across all days tested. The highest WSF dose (400 mg kg−1) notably induced RNS production (p < 0.05) on most days. Additionally, mid doses (40 mg kg−1) of both HSF and WSF significantly (p < 0.05) stimulated lysozyme activity on day 8. Disease resistance tests showed that the highest doses of HSF and WSF (400 mg kg−1), when administered as double doses, reduced mortality (p < 0.01) and increased relative percentage survival. These findings suggest that WSF and HSF fractions from E. alba, when administered at an optimal dose of 400 mg kg−1, stimulate the nonspecific immune mechanisms of O. mossambicus, improving resistance to A. hydrophila infection. Several compounds in the extracts were identified using GC-MS/MS, and their structures were retrieved. Molecular docking of the retrieved structures with NADPH oxidase (NOX) and Nitric oxide synthase (NOS), which are key enzymes involved in ROS and RNS production, was conducted using AutoDock software. Docking results showed that stigmasterol (WSF) and ethylcyclodocosane (HSF) bound to both NOX and NOS with high affinity. The observed immunostimulatory activity may be mediated through NOX and NOS activation, as supported by our in-silico docking studies.