Olive (Olea europaea L.) Biophenols: A Nutriceutical against Oxidative Stress in SH-SY5Y Cells

Plant biophenols have been shown to be effective in the modulation of Alzheimer's disease (AD) pathology resulting from free radical-induced oxidative stress and imbalance of the redox chemistry of transition metal ions (e.g., iron and copper). On the basis of earlier reported pharmacological activities, olive biophenols would also be expected to have anti-Alzheimer's activity. In the present study, the antioxidant activity of individual olive biophenols (viz. caffeic acid, hydroxytyrosol, oleuropein, verbascoside, quercetin, rutin and luteolin) were evaluated using superoxide radical scavenging activity (SOR), hydrogen peroxide (H₂O₂) scavenging activity, and ferric reducing ability of plasma (FRAP) assays. The identification and antioxidant activities in four commercial olive extracts-Olive leaf extract^TM (OLE), Olive fruit extract^TM (OFE), Hydroxytyrosol Extreme^TM (HTE), and Olivenol plus^TM (OLP)-were evaluated using an on-line HPLC-ABTS^•+ assay, and HPLC-DAD-MS analysis. Oleuropein and hydroxytyrosol were the predominant biophenols in all the extracts. Among the single compounds examined, quercetin (EC₅₀: 93.97 μM) and verbascoside (EC₅₀: 0.66 mM) were the most potent SOR and H₂O₂ scavengers respectively. However, OLE and HTE were the highest SOR (EC₅₀: 1.89 μg/mL) and H₂O₂ (EC₅₀: 115.8 μg/mL) scavengers among the biophenol extracts. The neuroprotection of the biophenols was evaluated against H₂O₂-induced oxidative stress and copper (Cu)-induced toxicity in neuroblastoma (SH-SY5Y) cells. The highest neuroprotection values (98% and 92%) against H₂O₂-induced and Cu-induced toxicities were shown by the commercial extract HTE^TM. These were followed by the individual biophenols, caffeic acid (77% and 64%) and verbascoside (71% and 72%). Our results suggest that olive biophenols potentially serve as agents for the prevention of neurodegenerative diseases such as AD, and other neurodegenerative ailments that are caused by oxidative stress.