Neuroprotective Effect of Physiological Circulating Phenolic Metabolites Against Oxidative Stress- and...

Growing evidence indicates that circulating phenolic metabolites can reach brain tissue and exert neuroprotective effects; however, their combined activity at physiological concentrations remains poorly understood. This study evaluated three metabolite mixtures designed according to previously reported plasma and brain metabolite profiles following a Mediterranean (poly)phenol-rich intervention (Mix Eq, Mix %C, and Mix %T), together with their individual constituent metabolites, in human cellular models of oxidative stress, neuroinflammation, and blood-brain barrier (BBB) dysfunction. All physiological mixtures significantly protected SH-SY5Y neuroblastoma cells against H₂O₂-induced oxidative stress by improving cell viability and reducing intracellular ROS production in a concentration-dependent manner, with cotreatment showing greater efficacy than pretreatment. Individual metabolites also showed protective effects, although none matched the overall efficacy of the mixtures. In HMC3 cells, the mixtures moderately attenuated LPS- and TNF-α-induced inflammatory responses, reducing IL-6 and IL-8. Finally, in HBMECs, TNF-α increased BBB permeability and cytokine release, whereas Mix %C significantly attenuated TNF-α-induced sodium fluorescein permeability. However, none of the mixtures significantly reduced IL-6 or IL-8 secretion in this BBB model. Overall, physiologically relevant combinations of circulating phenolic metabolites showed greater neuroprotective activity than individual metabolites, supporting the contribution of additive or cooperative interactions to the benefits associated with Mediterranean diet-derived phenolics.