antioxidant activity of olive leaf extract ( L.) and its protective effect on oxidative damage in human erythrocytes.

Aims: This study aimed to evaluate antioxidant capacity of olive leaf extract (OLE), 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 ( ), 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 (EC) = 16.1 ± 1.2 μg/mL) and DPPH (EC = 13.8 ± 0.8 μg/mL). The extract demonstrated effective ability to scavenge  (EC = 52.6 ± 2.1 μg/mL), NO (EC = 48.4 ± 6.8 μg/mL) and HOCl (EC = 714.1 ± 31.4 μg/mL). The extract inhibited peroxyl radical-induced hemolysis (EC = 11.5 ± 1.5 μg/mL), TBARS formation (EC = 38.0 ± 11.7 μg/mL) and hemoglobin oxidation (EC = 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.