Phytochemical screening and arginase inhibitory activity of extracts from several Tunisian medicinal plants

Abstract Arginase has been the focus of a particular interest since it has been shown that the increase of its activity is involved in various pathologies for which the inhibition of this enzyme could be a promising treatment. The several existing synthetic inhibitors of arginase are not suitable for a use in human therapeutics. Hence, interest has been initiated to explore natural resources, in particular medicinal plants for the search for new arginase inhibitors. Tunisia is famous for its great flora diversity, as well as a centuries-old tradition of medicinal plants used to treat many diseases including cardiovascular disorders. Therefore, seven Tunisian plants belonging to various families: Retama raetam (Forssk.) Webb & Berthel ., Rhus tripartita (Ucria) Grande , Artemisia campestris L., Artemisia herba-alba Asso , Myrtus communis L., Crataegus azarolus L., Rubus ulmifolius Schott, were selected to be screened on arginase using an in vitro inhibition test. Fifty-one crude extracts obtained from different parts of these plants showed inhibition percentages ranging from 2.66 ± 7.57% to 90.00 ± 1.53% at 100 μg/mL. Five extracts were identified as the most active and their IC 50 were determined, as well as their phenolic and flavonoid contents. Results showed that the methanolic extract from Crataegus azarolus stems is the most interesting crude material with the lowest IC 50 (41.99 ± 1.53 μg/mL). This extract also shows the richest polyphenolic content (161.02 ± 1.24 μg GAE/mg CE). The analyses of total flavonoid content revealed that flavonoids represent only a small part of this polyphenolic content (22.32 ± 0.24 μg RE/mg CE) and cannot be considered as fully responsible for the observed activity. Further, bio-guided fractionations and structural elucidation will aim to identify secondary metabolites responsible for the bioactivity observed on arginase.