The effect of PPT on skin barrier function and hydration. (A) Chemical structure of PPT. (B) Cytotoxicity of PPT was measured using a 3-(4-5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in HaCaT cells. (C) The morphology shooting of HaCaT cells under PPT (25 μM) treatment. (D) The expression levels of skin barrier-related genes [filaggrin (FLG), transglutaminase (TGM)-1, claudin, and occludin] were measured by RT-PCR in HaCaT cells after treatment with PPT (12.5 and 25 μM) or retinol (10 μg/mL) for 24 h. (E) The expression levels of hydration factors [hyaluronic acid synthase (HAS)-1, −2, −3, and aquaporin (AQP)-3] were determined by RT-PCR in HaCaT cells treated with PPT (12.5 and 25 μM) or retinol (10 μg/mL) for 24 h. (F) The levels of HAS-2 protein expression were measured by immunoblot analysis under PPT (12.5 and 25 μM) and retinol (10 μg/mL) treatment conditions in HaCaT cells. (G) The expression levels of hydration factors hyaluronic acid synthase (HAS)-1, −2 were determined by RT-PCR in HaCaT cells treated with PPT (12.5 and 25 μM) or retinol (10 μg/mL) for 12 h under UVB (30 mJ/cm2) irradiation.