Damiana (Turnera diffusa), of the family Passifloraceae, has been widely studied for its pharmacological effects, especially for antioxidant and antibacterial actions. However, there are limited scientific findings describing its antiphotoaging effects on the skin. In the present study, the underlying molecular mechanisms of the protective effect of Damiana were investigated in keratinocytes (HaCaTs) and normal human dermal fibroblasts (HDFs) subject to UVB irradiation. The mRNA expression of matrix metalloproteinases (MMPs) and procollagen type I was determined by reverse transcription-polymerase chain reaction. The protein expression of antiphotoaging-related signaling molecules in the activator protein-1 (AP-1) and nuclear factor erythroid 2-related factor 2 (NRF2)/antioxidant response element (ARE) pathways was assessed by Western blotting. We observed that Damiana blocked the upregulated production of reactive oxygen species induced in UVB-irradiated HaCaTs and HDFs in a dose-dependent manner. Treatment with Damiana also significantly ameliorated the mRNA expression of MMPs and procollagen type I. In addition, the phosphorylation level of c-Jun and c-Fos was also decreased through the attenuated expression of p-38, p-ERK, and p-JNK after treatment with Damiana. Furthermore, the treatment of cells with Damiana resulted in the inhibition of Smad-7 expression in the TGF-β/Smad pathway and upregulated the expression of the Nrf2/ARE signaling pathway. Hence, the synthesis of procollagen type I, a precursor of collagen I, was promoted. Collectively, these results provide us with the novel insight that Damiana is a potential source of antiphotoaging compounds.
Keywords: activator protein-1 (AP-1); damiana leaves; nuclear factor erythroid 2–related factor 2 (NRF2); oxidative stress; skin photoaging.