The in vitro inhibition of human neutrophil elastase activity by some Yemeni medicinal plants
Human neutrophil elastase (HNE) as a major contributor to inflammatory process is implicated in a number of diseases such as acute lung injury, cystic fibrosis, ischemic reperfusion injury, rheumatoid arthritis, atherosclerosis, psoriasis, and malignant tumors [1–4]. Moreover alpha-1 antitrypsin (α1- protease inhibitor) deficiency, an inherited disease, affects the lung and the liver . At present, a number of natural elastase inhibitors such as the human plasma derived α1- protease inhibitors (Aralast)  and synthetic elastase inhibitors for example Sivelestat,  have been used in the treatment of HNE associated diseases. Plants have been the targets of research to develop efficient elastase inhibitors. The aim of our study was therefore to test 15 extracts of different polarities (dichloromethane, methanol and aqueous extracts) from 5 Yemeni medicinal plants (Aspilia helianthoides C.D. Adams, leaves; Ceropegia rupicola, Defl. whole plant; Kniphofia sumarae Defler, whole plant; Pavetta longiflora, Vahl. leaves; and Plectranthus cf barbatus leaves)  for their inhibitory effects against the enzymatic activity of human neutrophil elastase in an in vitro human neutrophil elastase inhibitory 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 to treat wounds and indicate the presence of HNE inhibitory constituents in the active tested plants.
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