Phenylpropanoid glycosides from plant cell cultures induce heme oxygenase 1 gene expression in a human keratinocyte cell line by affecting the balance of NRF2 and BACH1 transcription factors.

Phenylpropanoids have several highly significant biological properties in both plants and animals. Four phenylpropanoid glycosides (PPGs), verbascoside (VB), forsythoside B (FB), echinacoside (EC) and campneoside I (CP), were purified and tested for their capability to activate NRF2 and induce phase II cyto-protective enzymes in a human keratinocyte cell line (HaCaT). All four substances showed similar strong antioxidant and radical-scavenging activities as determined by diphenylpicrylhydrazyl assay. Furthermore, in HaCaT cells, FB and EC are strong activators of NRF2, the nuclear transcription factor regulating many phase II detoxifying and cytoprotective enzymes, such as heme oxygenase 1 (HMOX1). InHaCaT cells, FB and EC (200 microM) induced nuclear translocation of NRF2 protein after 24 h and reduced nuclear protein levels of BACH1, a repressor of the antioxidant response element. FB and EC greatly HMOX1mRNA levels by more than 40-fold in 72 h. Cytoplasmic HMOX1 protein levels were also increased at 48 h after treatment. VB was less active compared to FB and EC, and CP was slightly active only at later times of treatment.We suggest that hydroxytyrosol (HYD) could be a potential bioactivemetabolite of PPGs since HYD, in equimolar amounts to PGGs, is able to both activateHO-1 transcription andmodifyNrf2/Bach1 nuclear protein levels. This is in agreementwith the poor activity of CP,which contains aHYDmoietymodified by an O-methyl group. In conclusion, FB and EC fromplant cell culturesmay provide long-lasting skin protection by induction of phase II cytoprotective capabilities.