Antioxidant and Anti-Osteoclastogenic Potential of Olive Oil Dregs Extracts

The agri-food industry generates substantial amounts of waste, which are increasingly regarded as valuable resources within the framework of the circular economy. Among the recoverable bioactive molecules, phenolic compounds are of particular interest for nutraceutical and biomedical applications. Olive oil production by-products, such as olive oil dregs (OOD), represent a rich source of polyphenols, especially hydroxytyrosol (3,4-DHPEA). In this study, we investigated the in vitro biological properties of OOD extracts obtained through methanolic or eco-friendly aqueous extraction methods, both characterized by a high 3,4-DHPEA content. The antioxidant potential of the extracts was evaluated together with their activity in murine peritoneal macrophages, while their ability to counteract osteoclastogenesis was assessed using RAW 264.7 cells stimulated with receptor activator of nuclear factor kappa-B ligand (RANKL). Our results demonstrated that both extracts showed a total antioxidant effect and significantly reduced intracellular reactive oxygen species (ROS) levels. Notably, this antioxidant activity was accompanied by a marked inhibition of RANKL-induced osteoclast formation, as evidenced by a reduction in tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells together with fewer mature osteoclasts displaying well-structured F-actin rings and bone-resorbing activity as demonstrated by the pit formation assay. Taken together, these findings suggest that OOD extract, through its dual antioxidant and anti-osteoclastogenic properties, may represent a promising strategy for the prevention of inflammation-driven pathological bone loss.