Dermatologic photoprotective potential of Sutherlandia frutescens extracts

Abstract

This work explores the dermatologic photoprotective potential of the phenolic acids and antioxidant activity of the plant Sutherlandia frutescens subspecies microphylla commonly known as the cancer bush (CB). The medicinal value of CB and its reported role in the management of chronic ailments like HIV/AIDS generates interest for the identification and quantitation of the total phenolic acid content. The antioxidant properties of phenolic acids are known to reduce the risk of chronic diseases including cancer and heart sicknesses linked to oxidative stress. Phenolic acids were extracted from the leaves of the CB by Soxhlet (SXE) and ultrasonication (USE) extraction methods. These extracts were analysed by ultraviolet (UV) spectroscopy, high performance liquid chromatography (HPLC), and liquid chromatographymass

spectrometry (RP-HPLC-PDA-ESI-MS). Six phenolic acids were identified and quantitated by RPHPLC-PDA,

under isocratic elution conditions with an external standard method. The identified phenolic acids were: gallic, p-hydroxybenzoic, vanillic, caffeic, syringic and p-coumaric acids. The concentration of pcoumaric

acid was the highest in all the extracts. RPHPLC-PDA-ESI-MS was used to characterise three novel

phenolic

acids: 5-hydroxy-2-vinylbenzoic acid, an isomer of p-coumaric acid (C-1); (Z)-3-(4-hydroxy-2methoxyphenyl)acrylic

acid (C-2); and (Z)-2-hydroxy3-(4-methoxyphenyl)acrylic

acid (C-3) ferulic acid isomers. The Folin-Ciocalteu protocol was used to determine the total phenolic content of the extracts. The ultrasonication-diethyl ether (USDE) fraction gave GAE = 0.1247 mg g and ultrasonication-ethyl acetate (USEA) GAE = 0.0769 mg g -1 as the highest and lowest total phenolic content respectively. Antioxidant activity was investigated by the DPPH free radical scavenging assay and the FRAP assay. The USDE extract (EC 50 = 30.38µg mL -1 )and the Soxhlet-diethyl ether extract (SXDE) (EC 50 -1 = 48.63µg mL )exhibited the highest and lowest antioxidant activity by DPPH assay respectively. The FRAP assay showed higher activity for USDE (EC 1 = 41.53 µg mL -1 -1 ) and lower value for SXDE extract (EC 1 = 33.05 µg mL ). The CB extracts with higher phenolic content had higher antioxidant activity and are thus a suitable remedy for free radical mediated ailments. Also the UV-vis spectra of the CB extracts had significant absorption in the UV region, and hence are viable ingredients in sunscreen preparations.