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 <i>Saccharomyces cerevisiae</i> (BG40 and BG60), laminarin extracted from <i>Laminaria hyperborea</i> (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 (<i>il6</i>, <i>il8</i>, <i>il1b</i> and <i>tnfa</i>; <i>p</i> < 0.05). All ingredients except carnosine significantly reduced TEER (<i>p</i> < 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 <i>il6</i> expression (<i>p</i> < 0.05). High-dose salmon hydrolysate also tended to reduce <i>il6</i> (<i>p</i> = 0.05) and increased <i>pcna</i> expression (<i>p</i> < 0.001), suggesting tissue recovery. Low-dose laminarin and both carnosine concentrations upregulated <i>cldn3</i> post-challenge (<i>p</i> < 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.