Protective effect of indigo naturalis extract against oxidative stress in cultured human keratinocytes

Ethnopharmacological relevance: Indigo naturalis is used in traditional Chinese medicine to treat various skin disorders. Aim of the study: The aims were to explore the effect of indigo naturalis on suppressing oxidative stress and protein modifications by hydrogen peroxide (H ₂O ₂) and 4-hydroxy-2-nonenal (HNE), a lipid peroxidation product, in cultured primary human keratinocytes. Materials and methods: Indigo naturalis extract at a dose that did not cause cytotoxicity was added to cultured keratinocytes in the absence or the presence of H ₂O ₂ or HNE. The degree of cytotoxicity, levels of reactive oxygen species (ROS), and amount of protein carbonyl groups were evaluated. Results: Indigo naturalis extract at the concentration of 10 μg/ml had no protective effect against H ₂O ₂ or HNE-induced cytotoxicity, but decreased intracellular levels of ROS after H ₂O ₂ treatment and suppressed the increase of protein carbonyl groups induced by HNE. Conclusion: Indigo naturalis possesses an inhibitory effect on formation of intracellular ROS induced by exogenous ROS and protein modification induced by HNE in human keratinocytes, which is relevant to the alleviation of inflammatory skin diseases.