Cytotoxicity and cellular anti-tyrosinase activity of the isolated constituents of H. pogonocalyx in human epidermal melanocytes (HEMn cells). HEMn cells (1 × 105) were treated with the positive control arbutin (Ar) and the isolated compounds (100 μM) for 24 h. Afterward, (A) the supernatant was removed and incubated with WST-8 cell counting reagent for 4 h at 37°C. The absorbance was measured using a microplate reader at 450 nm. (B) The lysates (equal amount of proteins) were incubated with l-dopa at a final concentration 2.5 mM for 1 h at 37°C. Each determination was made in triplicate, and the data shown represent means ± SD. *P-value < 0.05 when compared with control.