Simultaneous effect of ursolic acid and oleanolic acid on epidermal permeability barrier function and epidermal keratinocyte differentiation via peroxisome proliferator‐activated receptor‐α

ABSTRACT Ursolic acid (UA) and oleanolic acid (ONA) are pentacyclic triterpenoids, which naturally occur in many medicinal herbs and plants. Recent research revealed that several pharmacological effects could be attributed to UA and ONA, such as anti‐tumor, anti‐inflammatory and anti‐microbial activities. To evaluate the effects of UA and ONA on epidermal permeability barrier recovery and normal skin, both flanks of hairless mice were topically treated with either 0.01~0.1 mg/mL UA or 0.1~1.0 mg/mL ONA after tape stripping and transepidermal water loss (TEWL) were assessed, and then hydration and TEWL were measured for 3 weeks with application of UA and ONA (2 mg/mL). We also investigated the morphological changes using light (LM) and electron microscopic (EM) examination. Finally, we observed that UA and ONA stimulated epidermal keratinocyte differentiation via peroxisome proliferator‐activated receptor (PPAR)‐α using Western immunoblotting. The recovery rate of epidermal permeability barrier after tape stripping increased in the UA‐ and ONA‐treated groups (0.1 mg/mL UA and 0.5 mg/mL ONA) at 6 h to more than 20% when compared to the vehicle‐treated group ( P < 0.05). In both groups, hydration was increased compared to the vehicle group from 1 week without TEWL alteration ( P < 0.05). An LM finding showed that epidermal thickening was frequently observed (UA > ONA > vehicle). EM examination revealed an increase in secretion and in the number of lamellar bodies in treated groups and that complete formation of lipid bilayers was also prominent (ONA > UA > vehicle). Protein expression of PPAR‐α, involucrin, loricrin and filaggrin increased twofold and threefold in HaCaT cells treated for 24 h with either ONA (10 µmol/L) or UA (10 µmol/L), respectively, reflecting that the UA and ONA can improve the recovery of skin barrier function and induce epidermal keratinocyte differentiation via PPAR‐α. Taken together, these results suggest that UA and ONA will be pertinent candidates for the improvement of epidermal permeability barrier function.