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, EC₅₀ 13.3, 1.2, 1.9 μg/ml, respectively). Both the extracts and gallic acid individually showed an interesting antifungal property (MIC₅₀ at 24 h 25, 0.9 and 30 μg/ml, respectively) and notably, a combination of paeoniflorin/gallic acid (MIC₅₀ = 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.

Introduction

Paeonia comprises shrubs and perennial herbs distributed in Asia and Mediterranean region, known for the ornamental and economic value as well as for the medicinal properties of their roots. As a matter of fact, tree peonies, commonly called “King of Flowers” in China, are one of the most important crude drugs in traditional Chinese medicine (Zhao et al., 2008). They have been used as analgesic, sedative, antinflammatory and antimicrobial agents, and as remedy for cardiovascular and female genital diseases (Duan et al., 2009, Wu et al., 2010). The biological properties may be primarily attributed to the characteristic chemotaxonomic markers, paeoniflorin and its derivatives, which are monoterpenes with a “cage-like” pinane skeleton (Duan et al., 2009). Recent reviews on the genus have reported polyphenols such as paeonol and gallic acid derivatives, monoterpenoids, triterpenoids, and steroids as the main components (He et al., 2010, Wu et al., 2010) and have summarized the main biological activities (anti-oxidant, anti-inflammatory, anticancer, cardioprotective) of Paeonia spp. Moreover, studies reported on the antigenotoxic effect of Paeonia lactiflora ethanol extract containing gallic acid and methyl gallate (Lee et al., 2005), and antioxidant properties of monoterpene galactosides (Paeonins A–C) from Paeonia emodi (Riaz et al., 2004). Volatiles constituents from roots of Greek Paeonia taxa (Papandreou et al., 2002), and Paeonia peregrina and Paeonia tenuifolia of Bulgarian origin (Ivanova et al., 2002) showed antimicrobial activity.

Paeonia rockii (S.G. Haw & Lauener) T. Hong & J.J. Li (Paeoniaceae) is a rare woody shrub wildly distributed in the northwestern of China which belongs to the section Moutan DC (Zhao et al., 2008). Up to now only anthocyanins, flavones and flavonols, have been described from the flowers (Wang et al., 2004), and nutritional components (lipids, proteins, mineral elements and amino acids) (Xiaoyong, 2003) from the seeds. Its medical application has not been so far documented; however, extracts and oils from the fruits and root bark are the components of moisturizing cosmetic preparations and health-care capsules (Qianlong et al., 2010, Qianlong and Aixia, 2010). As a consequence, other species of Paeonia have been chemically and biologically investigated (He et al., 2010, Wu et al., 2010); however, such knowledge of Paeonia rockii is very limited. This paper reports on the composition and biological activity of a crude methanolic extract (PPR) from the roots of Paeonia rockii. Alkoxy-γ-lactone (1), and ethyl-arabinopyranose (2) as naturally occurring compounds as well as the dihydroflavonol, taxifolin (3), have been isolated for the first time from Paeonia rockii together with sixteen constituents characteristic of the genus. The polar extract and its n-BuOH soluble portion (PPR-B) were both examined for their polyphenols content using the Folin–Ciocalteau colorimetric and HPLC methods. Finally, the in vitro free-radical scavenging effect was assayed by the DPPH test, and antifungal activity of the extracts and their major constituents was evaluated by three methods: micro-broth dilution method, XTT assay and Candida albicans morphological analysis.