Screening for free radical scavenging and cell aggregation inhibitory activities by secondary metabolites from Turkish Verbascum species

Free radical scavenging and cell aggregation inhibitory activities of 36 secondary metabolites isolated from the methanolic extracts of Verbascum cilicicum Boiss., V. lasianthum Boiss. ex Bentham, V. pterocalycinum var. mutense Hub.-Mor., and V. salviifolium Boiss. (Scrophulariaceae) were investigated. The isolated compounds, 6-O-vaniloyl ajugol (1), ilwensisaponin A (2), ilwensisaponin C (3), verbascoside (4), β-hydroxyacteoside (5), martynoside (6), poliumoside (7), forsythoside B (8), angoroside A (9), dehydrodiconiferyl alcohol-9-O-β-D-glucopyranoside (10), dehydrodiconiferyl alcohol-9′-O-β-D-glucopyranoside (11), apigenin 7-O-β- glucopyranoside (12), luteolin 7-O-β-glucopyranoside (13), luteolin 3′-O-β-glucopyranoside (14) and chrysoeriol 7-O-β- glucopyranoside (15), exhibited a dose-dependent inhibition of bioautographic and spectrophotometric DPPH activities. Verbascoside (4) was the most active (IC₅₀ 4.0 μg/ml) comparing it to vitamin C (IC₅₀ 4.4 μg/ml) to inhibit phorbol 12-myristate 13-acetate (PMA)-induced peroxide-catalyzed oxidation of 2′,7′-dichlorofluorescein (DCFH) by reactive oxygen species (ROS) within human promyelocytic HL-60 cells. Ilwensisaponin A (2) (MIC 6.9 μg/ml) showed moderate in vitro activity on lymphocyte-associated antigen-1 (LFA-1)/intercellular adhesion molecule-1 (ICAM-1)-mediated aggregation using the HL-60 cell line [positive control was cytochalasin B (MIC 2.3 μg/ml)]. None of the other compounds showed free radical scavenging and cell aggregation inhibitory activities.