Phenylpropanoid glycosides from plant cell cultures induce heme oxygenase 1 gene expression in a human keratinocyte cell line by affecting the balance of nrf2/bach1 transcription factors

The identification of natural antioxidants for effective photoprotection and suppression of inflammatory reactions in the skin is now a major concern for investigative dermatology. The present results strongly suggest that the phenylpropanoid glycosides (PPGs), forsythoside B, echinacoside, verbascoside and partially campneoside I, may represent natural substances of special dermatological interest for the protection of the skin from environmental induced oxidative stress and inflammatory insults. Indeed, using real time PCR, we found that, in a human keratinocytes cell line (HaCaT), these compounds induce the expression of an important detoxifying phase II gene, heme oxygenase-1 (HO-1), in a dose- and time-dependent manner. 24 hours of treatment with PPGs was required to increase HO-1 gene expression. A single administration of verbascoside, forsythoside B and echinacoside (200 µM) to cell cultures caused a further increase in the amount of HO-1 mRNA after 48 and 72 hours, showing that these PPGs had late onset but long lasting effects. Furthermore, we demonstrated, by western blot analyses, that the increase of HO-1 mRNA by PPGs might be dependent on the increase of Nrf2 transcription activator and the reduction of nuclear protein levels of Bach1 repressor. Moreover, experimental evidences suggest that hydroxytyrosol could be the major bioactive moiety of PPGs since we demonstrated that hydroxytyrosol, added alone to cell cultures in equimolar amounts to PPGs, was able to both increase HO-1 gene expression and affect Nrf2 and Bach1 nuclear protein levels. The understanding of their molecular mechanism on HO-1 expression could promote the innovative use of these compounds in dermatology to slow down aging or alleviate diseases in which oxidative stress is a primary cause.