Aims
This study aimed to evaluate in vitro antioxidant capacity of olive leaf extract (OLE), Olea europaea L., and its protective effect on peroxyl radical-induced oxidative damage in human erythrocytes. Main
Methods
The OLE was evaluated by the following assays: i) total phenolic and flavonoid content; ii) oleuropein content; iii) Ferric reducing antioxidant power (FRAP); iv) antioxidant activity against ABTS•+, DPPH• and reactive oxygen and nitrogen species: superoxide anion ( O2⋅−O2·-<math><mrow><msup><mrow><msub><mrow><mtext>O</mtext></mrow><mrow><mn>2</mn></mrow></msub></mrow><mrow><mo>·</mo><mo>-</mo></mrow></msup></mrow></math> ), hypochlorous acid (HOCl) and nitric oxide (NO•) and v) protective effect on peroxyl radical-induced oxidative damages in human erythrocytes as hemolysis, thiobarbituric acid reactive substances (TBARS) formation and oxyhemoglobin oxidation. Key findings: Total phenolic and flavonoid contents were 131.7 ± 9.4 mg gallic acid equivalents/g dry weight (dw) and 19.4 ± 1.3 mg quercetin equivalents/g dw, respectively. Oleuropein content was 25.5 ± 5.2 mg/g dw. FRAP analysis was 281.8 ± 22.8 mg trolox equivalent/g dw and OLE inhibited ABTS•+ (50% effective concentration (EC50) = 16.1 ± 1.2 μg/mL) and DPPH• (EC50 = 13.8 ± 0.8 μg/mL). The extract demonstrated effective ability to scavenge O2⋅−O2·-<math><mrow><msup><mrow><msub><mrow><mtext>O</mtext></mrow><mrow><mn>2</mn></mrow></msub></mrow><mrow><mo>·</mo><mo>-</mo></mrow></msup></mrow></math> (EC50 = 52.6 ± 2.1 μg/mL), NO• (EC50 = 48.4 ± 6.8 μg/mL) and HOCl (EC50 = 714.1 ± 31.4 μg/mL). The extract inhibited peroxyl radical-induced hemolysis (EC50 = 11.5 ± 1.5 μg/mL), TBARS formation (EC50 = 38.0 ± 11.7 μg/mL) and hemoglobin oxidation (EC50 = 186.3 ± 29.7 μg/mL) in erythrocytes. Significance: OLE is an important source of natural antioxidants; it has effective antioxidant activity against different reactive species and protects human erythrocytes against oxidative damage.
Significance
OLE is an important source of natural antioxidants; it has effective antioxidant activity against different reactive species and protects human erythrocytes against oxidative damage.