In Vitro Tyrosinase Inhibitory and Antioxidant Activities of Extracts and Constituents of Paeonia lactiflora Pall. Flowers

Abstract : Background: In recent years researchers have undertaken the search for antioxidant compounds that can delay or inhibit the initiation or propagation of oxidative chain reaction and thus prevent or repair oxidative damage done to the body's cells by reactive oxygen species. Currently, a variety of synthetic antioxidant supplements are available. However, antioxidants derived from natural sources have attracted many interests for use in foods or pharmaceutical preparations. Various dermatological disorders such as freckling, age spots and sites of actinic damage are caused by the accumulation of dermal melanin pigment, which is synthesized in melanocytes via the action of tyrosinase. Therefore, there is a large demand for developing antityrosinase and antioxidant products to treat and protect against hyperpigmentation and ageing of the skin caused by ultraviolet rays, ROS, free radicals and other insults. Method: Ethanol 70% extract of Paeonia lactiflora flowers was partitioned in water and ethyl acetate extracts by liquid/liquid chromatography. These two extracts were purified by combination of chromatographic methods. The chemical structures of the isolated compounds were elucidated on the basis of 1D and 2D NMR spectra and Mass spectrometry. HPLC analysis was used to quantify the major compounds of the ethanol 70% extract. The in vitro fungal tyrosinase assay, using 3,4- dihydroxyphenylalanine (L-DOPA) as substrate, was used to evaluate the antityrosinase potential of these extracts and isolated compounds. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was used to quantifying the antioxidant activity. Results: Twenty-six compounds were isolated from the flowers of Paeonia lactiflora. The HPLC fingerprint of the ethanol 70% extract of this plant was established. The antioxidant assays revealed that ethanol 70% and ethyl acetate extracts had significant antioxidant abilities in DPPH scavenging activity. The most active compound was identified as methyl gallate. Through the in vitro fungal tyrosinase inhibition screening, we found, that ethanol, ethyl acetate and H2O extracts and three isolated compounds [1,2,3,6-tetra-O-galloyl-β-D-glucopyranoside, 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranoside and kaempferol 3-O-(6-O-galloyl)-β-D-glucopyranoside] inhibit the target protein activities with good IC50 values. Conclusion: These results demonstrate the antioxidant and antityrosinase activities of ethanol extract of Paeonia lactiflora flowers. A simple, accurate, and reliable method was developed to evaluate the quality of P. lactiflora extracts by using the established HPLC fingerprint and the determination of sixteen compounds. It is interesting that the tetra- and penta-galloylglucoses and the flavonoid have bi-functionality, not just have antioxidative abilities, but also had the inhibitory effects on fungal tyrosinase. These constituents from P. lactiflora exhibited potential applications in medical cosmetology and food supplementation, simultaneously.