From Sea to Cell: Ascophyllum nodosum and Fucus vesiculosus Extracts Attenuate NF-κB-Mediated Inflammation and Protect Intestinal Barrier Integrity—A Comprehensive Analysis Applying In Vitro and In Vivo Models

The restriction of antimicrobial growth promoters in livestock production has intensified the search for nutritional strategies that support intestinal health while modulating inflammatory processes. Chronic or dysregulated inflammation can impair gut function and animal performance, highlighting the need for functional feed additives. Brown macroalgae are rich in bioactive compounds with immunomodulatory properties, though their mechanisms remain incompletely understood. In this study, the anti-inflammatory and barrier-protective effects of aqueous extracts from Ascophyllum nodosum (AN) and Fucus vesiculosus (FV) were investigated using complementary in vitro and in vivo models. Extracts were prepared by aqueous solid–liquid extraction and tested in lipopolysaccharide (LPS)-stimulated RAW264.7 and THP-1 macrophages, HEK-Blue TLR4 reporter cells, and Drosophila melanogaster models of intestinal inflammation and infection. Both extracts significantly reduced LPS-induced nitric oxide production in RAW264.7 macrophages in a concentration-dependent manner. In THP-1 macrophages, AN and FV attenuated secretion of inflammatory mediators, including TNF-α, IL-6, IL-33, CXCL9, CXCL10, CXCL11, and CCL7. Reporter assays demonstrated selective inhibition of TLR4-dependent NF-κB activation. In Drosophila melanogaster, supplementation reduced intestinal barrier disruption, mortality, and infection-induced immune activation. Overall, AN and FV attenuate inflammatory signaling and protect intestinal integrity via TLR4-dependent NF-κB inhibition, supporting their potential as functional feed additives to enhance gut health and resilience in livestock.