Olive leaf waste valorization: Mitigation of contaminant-induced cellular, biochemical, and physiological alterations in Mytilus galloprovincialis

The circular bioeconomy promotes the use of agro-industrial by-products as sustainable sources of bioactive compounds with potential applications in the healthcare sector. In this context, olive leaves represent a promising source rich in phenolic compounds. This study provides novel evidence into the potential use of an olive leaf extract (OLE), isolated from a Sicilian cultivar (Olea europaea L. cv. Ogliarola). The protective capacity of OLE was assessed following subchronic exposure to the neonicotinoid insecticide thiacloprid (THCP) in the Mediterranean mussel Mytilus galloprovincialis. Chemical characterisation by HPLC-PDA-MS revealed a phytochemical profile dominated by oleuropein, along with other phenolic compounds and pigments. Mussels were exposed for 14 days to THCP, OLE or a combination of the two (MIX), and a multi-marker approach was used to assess cellular, physiological and biochemical responses. THCP significantly impaired the parameters analysed, causing disruption to cellular functions, oxidative stress and changes in enzymatic activities in the gonadal tissue. In contrast, OLE alone did not induce evident cytotoxic effects in cellular and physiological endpoints, although it significantly modulated selected gonadal biochemical parameters. Co-exposure partially mitigated several alterations induced by THCP, particularly at the cellular and physiological levels. These findings support the sustainable valorization of olive leaf waste and encourage further investigation of OLE-derived products in environmental and aquaculture-related applications.