β-sitosterol: A novel molluscicidal agent from Liagora farinosa against Biomphalaria alexandrina snails with computational insights into its interaction with the retinoid X Receptor

Schistosomiasis is a tropical parasitic disease that presents significant public health concerns, occurring in both acute and chronic forms. In Egypt, the freshwater snail Biomphalaria alexandrina is the intermediate host of Schistosoma mansoni. This study evaluated the molluscicidal potential of β-sitosterol, isolated from the marine red alga Liagora farinosa, along with its methanolic extract, against B. alexandrina. Bioassay results demonstrated potent molluscicidal activity, with the methanolic extract exhibiting LC₅₀ and LC₉₀ values of 187.5 mg/L and 231.8 mg/L, respectively, and β-sitosterol showing enhanced potency with LC₅₀ and LC₉₀ values of 36.1 mg/L and 41.7 mg/L after 48 h of exposure. Sublethal concentrations of β-sitosterol significantly reduced snail survival and reproductive rates. Biochemical analyses revealed a marked decrease in total antioxidant capacity and superoxide dismutase (SOD) activity, accompanied by increased levels of malondialdehyde (MDA) and reduced glutathione (GSH), indicating oxidative stress. Histopathological examination of treated snails showed extensive damage in the digestive and hermaphrodite glands, including vacuolation, cellular rupture, and degeneration of reproductive cells. Ultrastructural alterations such as nuclear disintegration, cytoplasmic vacuolation, residual body accumulation, and microvilli loss were also observed. Computational studies suggested retinoid X receptor to be a plausible target for β-sitosterol in its molluscicidal activity. These findings highlight the potential of L. farinosa extracts and β-sitosterol as bioactive agents for Schistosoma mansoni intermediate host. However, further research is required to assess their impact on non-target aquatic organisms.