4.4. Cell Culture and Viability Assay

Moderately pigmented human epidermal melanocytes (HEMn-MP) were purchased from Cascade Biologics (Portland, OR, USA) and cultured in Medium 254 (#M254500) supplemented with Human Melanocyte Growth Supplement (Life Technologies, Carlsbad, CA, USA). Cells were incubated at 37 °C containing 5% CO₂. Cells from passages three to six were used for subsequent experiments. Cell viability was tested using a Cell Counting Kit-8 (CCK-8) according to manufacturer’s instruction (Dojindo, Tokyo, Japan).