Screening of some Yemeni medicinal plants for inhibitory activity against peptidases.

Extracts of different polarities (dichloromethane, methanol, and aqueous extracts) from 5 Yemeni medicinal plants (Aspilia helianthoides, leaves; Ceropegia rupicola, whole plant; Kniphofia sumarae, whole plant; Pavetta longiflora, leaves; and Plectranthus cf barbatus, leaves) were screened for their inhibitory effects against angiotensin converting enzyme (ACE), neutral endopeptidase (NEP), and aminopeptidase N (APN) activities. Four extracts (methanol extracts of Ceropegia rupicola, Kniphofia sumarae, and Plectranthus cf barbatus, and the aqueous extract of Pavetta longiflora) were found able to inhibit the enzymatic activity of NEP. Significant reduction in the activity of NEP (p < 0.01) was observed at a concentration of 50 microg/ml, and above of all tested extracts. The most active extract was the methanolic extract of Ceropegia rupicola with IC50 of 111 microg/ml. Only the methanolic extract of Aspilia helianthoides was found to exhibit inhibitory effect against the ACE activity with IC50 = 133 microg/ml. None of the tested plant extracts was found active against the aminopeptidase N activity.