Ultraviolet radiation induces DNA damage and oxidative stress which can result in
skin inflammation, photoaging and photocarcinogenesis. The flavonoid luteolin that
is present in high amounts in the dyers weld, Reseda luteola, is one of the most potent antioxidative plant polyphenols that has also ultraviolet-absorbing
properties.
The aim of this study was to determine whether tocopherol and ubiquinone add synergistic
antioxidative values to luteolin. None of the substances showed cytotoxic effects
in concentrations from 0.25 to 4 µg/ml. The photoprotective and antioxidant effect
of equivalent concentrations of luteolin, tocopherol and ubiquinone and their combination
in a ratio of 4:1:4 were studied in solar simulator irradiated human skin fibroblasts.
Luteolin had a strong radical scavenging effect at a concentration of 2 µg/ml whereas
tocopherol and ubiquinone were not effective at this concentration. None of the substances
showed a phototoxic effect and only luteolin had a moderate photoprotective effect
at 2 µg/ml. However, the combination of luteolin, tocopherol and ubiquinone exerted
a synergistic radical scavenging effect already at a concentration of 0.25 µg/ml and
a complete photoprotection at 2 µg/ml.
In summary, our findings suggest that the potent antioxidant and photoprotective effect
of flavonoids like luteolin may be further increased by the addition of low concentrations
of other antioxidants such as tocopherol and ubiquinone.
