Anti-inflammatory Effects of Rainbow Trout (<em>Oncorhynchus mykiss</em>) Spleen Extract via Modulation of the NF-κB Pathway in LPS-Stimulated RAW264.7 Macrophages

Natural products have contributed significantly to anti-inflammatory drug development, but the therapeutic potential of fish visceral extracts has yet to be fully investigated. In this study, we investigated the anti-inflammatory properties of a crude spleen extract from rainbow trout (Oncorhynchus mykiss). The extract significantly reduced nitric oxide (NO) production and downregulated iNOS and COX-2 expression at both mRNA and protein levels. Among four fractions derived from the extract, the OSB fraction showed the strongest and most consistent activity. OSB suppressed LPS-induced expression of iNOS, COX-2, and pro-inflammatory cytokines, while enhancing anti-inflammatory cytokine expression. Mechanistic studies revealed that OSB inhibited NF-κB activation by blocking nuclear translocation of the p65 subunit. Additionally, OSB reduced M1 macrophage markers and LPS-induced ROS generation, indicating inhibition of M1 polarization. These findings suggest that OSB exerts anti-inflammatory effects by modulating the NF-κB pathway and highlight its potential as a natural therapeutic agent for inflammatory diseases.