From Coastal Residue to Bioactive Resource: Antioxidant and Anti-Inflammatory Potential of Beach-Cast Posidonia oceanica

Beach-cast Posidonia oceanica represents an abundant Mediterranean marine biomass that is commonly perceived as coastal waste, despite its potential value within circular bioeconomy strategies. This study investigated the antioxidant and anti-inflammatory potential of a hydroethanolic extract obtained from beach-cast P. oceanica biomass (POE). The extract was chemically profiled by UHPLC-ESI-MS/MS and evaluated through spectrophotometric antioxidant assays, including total phenolic content, total flavonoid content, reducing power, ABTS and DPPH radical-scavenging assays. Its ability to protect plasmid DNA from oxidative damage was also assessed. Anti-inflammatory activity was investigated in LPS-stimulated RAW 264.7 macrophages by evaluating cell viability, intracellular ROS production, NO release, iNOS and COX-2 expression, NF-κB p65 nuclear translocation and MAPK phosphorylation. POE showed measurable phenolic and flavonoid contents, moderate antioxidant capacity and protection against H2O2/Fe2+-induced plasmid DNA damage. UHPLC-ESI-MS/MS analysis revealed a complex metabolite profile, with 156 annotated compounds distributed across 20 chemical classes. In macrophages, POE was not cytotoxic at 50 and 100 µg/mL and significantly reduced LPS-induced ROS and NO production. These effects were accompanied by decreased iNOS and COX-2 expression, inhibition of NF-κB p65 nuclear translocation and reduced phosphorylation of p38, ERK and JNK. In addition, POE showed no detectable cytotoxicity in NIH3T3 fibroblasts up to 10 mg/mL and no mutagenic activity in the Ames MPF™ assay using TA98 and TA100 strains, either in the absence or presence of metabolic activation. Overall, this exploratory study suggests that beach-cast P. oceanica retains bioactive properties, although further studies incorporating standardized collection protocols and quantitative chemical characterization will help clarify its potential for sustainable valorisation.