Anti-inflammatory, antimicrobial and antioxidant activities of Diospyros bipindensis (Gürke) extracts and its main constituents

Ethnopharmacological relevance: Diospyros bipindensis (Gürke) stem bark is used in Cameroon by Baka Pygmies for the treatment of respiratory disorders. Aim of the study: To assess the anti-inflammatory, antibacterial and antioxidant properties of constituents from the bark extracts through bioassay-guided fractionation. Materials and methods: The anti-inflammatory activity of extracts, fractions and pure compounds was assessed through the inhibition of the pro-inflammatory mediator nuclear factor-kappa B (NF-κB) transcriptional activity and nitric oxide (NO) production. DPPH, ABTS and ORAC assays were used for determining the antioxidant properties. The activity against Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Klebsiella pneumoniae, was evaluated on the basis of the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) by the macrodilution method. Results: The water extract showed antimicrobial activity against S. pneumoniae (MIC: 300 µg/ml) and S. pyogenes (MIC: 300 µg/ml). The dichloromethane extract efficiently inhibited NF-κB transcriptional activity and NO production and exhibited significant antioxidant activity in the ORAC assay. An interesting activity was also found against S. pneumoniae (MIC: 200 µg/ml), S. aureus (MIC: 400 µg/ml) and S. pyogenes (MIC: 200 µg/ml). The phytochemical investigation of the dichloromethane extract afforded plumbagin, canaliculatin, ismailin, betulinic acid and 4-hydroxy-5-methyl-coumarin as the main constituents. Plumbagin and ismailin were found to be responsible for the main biological activities observed.. Conclusions: These results may provide a rational support for the traditional use of Diospyros bipindensis stem bark in the treatment of respiratory disorders, since the anti-inflammatory, antimicrobial and antioxidant compounds isolated from the dichloromethane extract were also present in the traditional water extract.