Metabolite Profile of Athrixia phylicoides DC. (Bush Tea) and Determination of Inhibitory Mechanism against Tyrosinase Enzyme from Mushroom

Athrixia phylicoides DC. (Bush tea) is a shrub harvested in the north-eastern mountain regions of South Africa and belongs to the Asteraceae family. Generally, A. phylicoides is consumed as a hot tea beverage for its associated health benefits. The use of bush tea extracts for beauty enhancement has not been investigated even though several ethnobotanical reports have indicated its usage against skin imperfections. Therefore, the aim of the study was to assess plant metabolites of A. phylicoides for their inhibition of tyrosinase from mushroom and determine their inhibitory mechanism. Methanolic extracts (80% v/v) of A. phylicoides were evaluated using a tyrosinase-based TLC (thin-layer chromatography) autography technique. The inhibitory mechanism of active metabolites against the enzyme was determined using Lineweaver–Burk plots. Quercetin and an unknown metabolite with a retention factor (Rf) value of 0.73 inhibited melanogenesis. However, the IC50 value for Quercetin was reported as 51.07 ± 2.43 µg/mL higher than that of kojic acid of 5.22 ± 1.44 µg/mL. Chlorogenic acid was reported to have a similar Rf value as kojic acid, suggesting similarities in polarity and affinity towards the adsorbent material. However, chlorogenic acid with an IC50 value of 15.25 ± 1.18 µg/mL and an inhibitory strength of 2.92 could not inhibit melanogenesis with a similar intensity as kojic acid. The inhibitory mechanism for A. phylicoides extract was reported to be mixed inhibition (competitive/uncompetitive). The IC50 value for A. phylicoides was recorded as 20.65 ± 0.14 µg/mL with an inhibitory strength of 3.96. These results suggest that A. phylicoides extracts could be used against dark spots associated with scarring and ageing through modulation of tyrosinase activity.