The In Vitro Inhibition of Human Neutrophil Elastase Activity by some Yemeni Medicinal Plants

15 extracts of different polarities (dichloromethane, methanol and aqueous extracts) from 5 Yemeni medicinal plants (Aspilia helianthoides, (Schumach. & Thonn.) Oliv. & Hiern subsp. ciliate (Schumach.) C.D. Adams leaves; Ceropegia rupicola, Defl. var. rupicola whole plant; Kniphofia sumarae, Defler whole plant; Pavetta longiflora, Vahl. subsp. longifloraleaves; and Plectranthus cf barbatus (Thulin & Gifri) leaves) were tested for their inhibitory effects against the enzymatic activity of human neutrophil elastase (HNE) (EC 3.4.21.37) in an in vitro human neutrophil elastase inhibition assay. 14 extracts at various concentrations were found able to inhibit the activity of HNE. Among the plants tested,A. helianthoides was the most active inhibitor of HNE. The dichloromethane extracts of all tested plants, exhibited more inhibitory effect on HNE activity than the methanolic and aqueous extracts. The dichloromethane extract of A. helianthoides showed the most active inhibitory effect on the HNE activity (IC₅₀ = 0.4μg/ml). Within the HNE inhibitory active methanolic extracts, those of A. helianthoides and P. cf barbatus were the most active inhibitors with IC₅₀ of about 3μg/ml. These results provide some scientific justification for the use of A. helianthoides in traditional medicine and indicate the presence of HNE inhibitory constituents in the active tested plants.