Screening of a polar extract of Paeonia rockii: composition and antioxidant and antifungal activities

Abstract

Ethnopharmacological relevance: The genus Paeonia (Paeoniaceae), is one of the most important source of crude drugs in traditional Chinese medicine and investigation on many species is large. Up to now studies on Paeonia rockii, one of the eight species recognized in the section Moutan, are very limited.

Aim of the study: This research aimed to investigate the composition of Paeonia rockii roots and to evaluate the in vitro free-radical scavenging and antifungal activities of a polar extract (PPR) and its major constituents.

Materials and methods: PPR was obtained from defatted dried roots of Paeonia rockii using MeOH as extraction solvent. Its n-BuOH soluble portion (PPR-B) was purified by Sephadex LH-20 followed by RP-HPLC to give nineteen compounds belonging to the classes polyphenols, monoterpenes and triterpenes. Their structure were spectrally characterized (UV, 1D and 2D NMR, MS). The polyphenols content of PPR and PPR-B was examined by the Folin-Ciocalteau colorimetric assay and HPLC method. Both extracts (PPR and PPR-B) and their major constituents were tested for the free-radical scavenging activity by DPPH-test, and for the antifungal activity by three methods (micro-broth dilution method, XTT assay and Candida albicans morphological analysis).

Results: 5-Butylhydroxy-γ-lactone (1), and ethyl-arabinopyranoside (2) have been isolated for the first time as naturally occurring compounds and taxifolin (3) was reported for the first time in Paeonia spp. Nine polyphenols, four monoterpenes and three triterpenes were also identified. Both the extracts PPR and PPR-B had high polyphenol content, and high concentration of gallic acid derivatives and paeoniflorin, chemotaxonomic characteristic markers of the genus. PPR, gallic acid and methyl-gallate displayed high potency in scavenging free-radicals (DPPH test, EC(50) 13.3, 1.2, 1.9 μg/ml, respectively). Both the extracts and gallic acid individually showed an interesting antifungal property (MIC(50) at 24 h 25, 0.9 and 30 μg/ml, respectively) and notably, a combination of paeoniflorin/gallic acid (MIC(50)=0.5+20 μg/ml, respectively) was more active than the single compound in inhibiting Candida growth.

Conclusion: The polar methanolic extract (PPR), its n-BuOH soluble fraction and constituents of Paeonia rockii were extensively investigated. Both extracts and some of their compounds have the ability to scavenge free-radicals and to inhibit Candida albicans growth.