Functional feed ingredients modulate the immune response of RTgutGC cells to LPS-induced inflammation

Functional feed ingredients can enhance the fish gut integrity and immune resilience during challenging situations in the aquaculture industry. This study used the RTgutGC cell line - derived from rainbow trout intestinal epithelium, to evaluate the immunomodulatory and barrier effects of selected ingredients. These included β-glucan from Saccharomyces cerevisiae (BG40 and BG60), laminarin extracted from Laminaria hyperborea (Lam60 and Lam90), and bioactive peptides with antioxidative and immunomodulatory potential; carnosine (Carn100 and Carn120) and salmon hydrolysate (FPH300 and FPH600). Cells were exposed for 24 hours at two concentrations (maintaining 100 % and 80 % viability), and effects on transepithelial resistance (TEER), permeability (P_app) and gene expression (qPCR) were assessed before and after a 6-hour lipopolysaccharide (LPS) challenge. High-dose laminarin and both salmon hydrolysate concentrations elevated mRNA encoding for pro-inflammatory cytokines (il6, il8, il1b and tnfa; p < 0.05). All ingredients except carnosine significantly reduced TEER (p < 0.05) often with downregulation of barrier genes. Low-dose carnosine and laminarin reduced P_app of Lucifer yellow, indicating less barrier disruption. LPS induced inflammation, barrier dysfunction and reduced proliferation. These effects were modulated by high-dose β-glucan and both laminarin concentrations, which significantly reduced il6 expression (p < 0.05). High-dose salmon hydrolysate also tended to reduce il6 (p = 0.05) and increased pcna expression (p < 0.001), suggesting tissue recovery. Low-dose laminarin and both carnosine concentrations upregulated cldn3 post-challenge (p < 0.05). These findings support the RTgutGC model as a valuable screening tool and provides new insights into the biological activity and immunomodulatory effects of various functional feed ingredients.