Structural Characterization and Anti-Inflammatory Properties of an Alginate Extracted from the Brown Seaweed Ericaria amentacea

Brown algae of the Cystoseira genus are recognized as valuable sources of bioactive compounds, including polysaccharides. Within the framework of current restoration efforts regarding damaged <i>Ericaria amentacea</i> populations in the Mediterranean Sea, the valorization of apices derived from ex situ cultivation waste represents a sustainable opportunity for industrial and biomedical applications. In this study, sodium alginate (SA) was extracted from <i>E. amentacea</i> apex by-products using a hydrothermal-alkaline method and subsequently chemically characterized. FTIR analysis showed O-H, C-H, and COO- stretching compatible with commercial alginates, while 1H-NMR spectroscopy indicated high β-D-mannuronic acid content, with an M/G ratio of 2.33. The extracted SA displayed a molecular weight of 1 × 10⁴ g/mol and a polydispersity index of 3.5. The bioactive properties of the SA extract were investigated in chemico and in vitro. SA exhibited remarkable antioxidant activity, showing significant DPPH and nitric oxide-radical-scavenging capacity. Furthermore, SA demonstrated a strong anti-inflammatory effect in LPS-stimulated macrophages through modulation of several inflammatory mediators (i.e., IL-6, IL-8/CXCL5, MCP-1, and TNF-α). In particular, SA promoted a striking iNOS gene expression inhibition, which, paired with its direct NO-scavenging ability, paves the way for future pharmacological use of <i>E. amentacea</i> derivatives, particularly if sustainably obtained from restoration activity waste.