Evaluation of the Immunomodulatory Effect of Fish Protein Hydrolysates Obtained From Atlantic Salmon (Salmo salar) by-Products Using Dicentrarchus labrax Brain Cell Line

This study investigates the immunomodulatory effects of fish protein hydrolysates (FPHs) derived from Atlantic salmon (Salmo salar) by-products using the Dicentrarchus labrax brain (DLB-1) cell line. Utilizing aquaculture by-products for FPH production offers significant potential in aquaculture, providing both economic benefits and a reduction on environmental impact. FPHs contain bioactive peptides with several biological properties, including health-promoting, antioxidant, anti-inflammatory, and antimicrobial activities. This study focused on the immunological properties of three FPHs, namely SS1, SS4, and SS5, obtained from salmon skin by-products using enzymatic hydrolysis with trypsin, α chymotrypsin, and bromelain, respectively. Cytotoxicity assays showed that SS5 hydrolysate exhibited no toxic effects on DLB-1 cells, even at high concentrations (up to 80 µg/mL), unlike SS1 and SS4 that showed a 50% cytotoxic concentration (CC₅₀) of 7.0 and 11.8 µg/mL, respectively. Gene expression analysis revealed that SS1, SS4, and SS5 hydrolysates significantly upregulated the proinflammatory gene IL-1β (p  < 0.05), especially after LPS stimulation, indicating their potential to activate macrophages and modulate immune responses after bacterial infections. Interestingly, SS5 also significantly upregulated the anti-inflammatory gene IL-10 when treated with LPS (p  < 0.05), suggesting its ability to regulate inflammation and balance immune responses. These results highlight the role of hydrolysis conditions, such as enzyme selection and peptide molecular weight, in determining the bioactivity of FPH. Moreover, the study suggests that smaller peptides with mass >1.0 and <2.0 kDa, particularly those produced with the bromelain enzyme in SS5, exhibit enhanced anti-inflammatory properties. This research supports the use of FPH in promoting fish health by improving immune responses, and it contributes to sustainable aquaculture practices by transforming waste into valuable bioactive compounds, offering insights for future applications in functional feeds.