Apigenin induces hyperpigmentation in melanocytes. (A) Chemical structure of apigenin. (B) HEMCs were treated with various concentrations (0–20 μM) of apigenin for 48 h, and cell viability was assessed using the MTT assay. (C) HEMCs were treated with apigenin (0, 1, 5, or 10 μM) for 48 h, and melanin content was measured. (D) HEMCs were treated with apigenin (10 μM) or α-MSH (100 nM, positive control) for 48 h, followed by Masson-Fontana ammoniacal silver staining. Scale bar = 10 μm. The total dendrite length per cell was measured, and twenty cells per condition were analyzed in three independent experiments. (E) HEMCs were observed using TEM after 48 h of treatment with apigenin (10 μM). White and black arrows indicate stages I–II and III–IV melanosomes, respectively. The percentages of stages I–II and III–IV melanosomes relative to the total number of melanosomes are shown. Data are expressed as the mean ± SEM (n = 3). *p < 0.05, **p < 0.01, and ***p < 0.001 vs. untreated cells. HEMCs, human epidermal melanocytes; α-MSH, α-melanocyte-stimulating hormone; TEM, Transmission electron microscopy.
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