Anti-inflammatory properties of Xylopia aethiopica leaves: Interference with pro-inflammatory cytokines in THP-1-derived macrophages and flavonoid profiling

Ethnopharmacological relevance: Ethnopharmacological surveys on Guinea-Bissauan flora reveal that several species are used to treat or ameliorate the symptomatology of conditions with an inflammatory background. As such, extracts obtained from a series of plants recorded in those surveys were screened for their anti-inflammatory properties, a hydroethanolic extract obtained from the leaves of Xylopia aethiopica (Dunal) A. Rich, (Annonaceae), used on the treatment of headache, muscular pain and rheumatic pain, scoring positively and being further investigated. Aim of the study: In order to identify species with anti-inflammatory properties, extracts were screened for their ability to interfere with LPS-induced TNF-alpha levels. Since significant effects were recorded upon treatment with the extract of the leaves obtained from X. aethiopica, further assays were conducted to elucidate additional mechanisms underlying its anti-inflammatory potential. Since little is known on the chemical composition of the plant, we also aimed to characterise its phenolic profile. Materials and methods: Interference with cytokines was evaluated by ELISA assay, through the quantification of TNF-alpha and IL-6 levels in the culture medium collected from LPS-activated THP-1-derived-macrophages. Inhibition of 5-lipoxygenase was assessed based on the oxidation of linoleic acid to 13-hydroperoxylinoleic acid. Characterization of the phenolic profile was attained by HPLC-DAD. Results: Evaluation of TNF-alpha levels in LPS-challenged THP-1 macrophages evidenced a significant inhibition (>90%) upon treatment with the hydroethanolic extract obtained from X. aethiopica leaves at a concentration of 500 mu g/mL. Additional anti-inflammatory effects were recorded, including a significant decrease on IL-6 levels at 250 and 500 mu g/mL. The extract proved to be active towards 5-LOX, leading to significant inhibition at concentrations ranging from 16 to 250 mu g/mL (IC50 = 85 mu g/mL). Phenolic profiling allowed the identification and quantitation of eight constituents, including caffeoylquinic acids (1-3), mono-O-glycosylated flavonols (5-8), and the mono-O-glycosyl flavone luteolin-7-O-glucoside (4). The main phenolic constituent, kaempferol-3-O-rutinoside (8), was found to significantly contribute to the anti-inflammatory effects, namely through the inhibition of 5-LOX. However, no effects on the decrease of TNF-alpha and IL-6 levels caused by this phenolic compound were found. Conclusion: The anti-inflammatory effects of X. aethiopica leaves are demonstrated experimentally, thus substantiating its use in folk Medicine. Relevantly, the observed anti-inflammatory properties can stimulate further studies in order to fully unveil the therapeutic potential of the plant, namely as a source of phenolic compounds with a significant ability to interfere with conventional inflammatory targets.