Ethyl acetate fraction of Radix rubiae inhibits cell growth and promotes terminal differentiation in cultured human keratinocytes

Abstract

Ethnopharmacological relevanceIn Chinese medicine practice, Radix rubiae, the dry root of Rubia cordifolia L. is commonly used for the treatment of psoriasis. Aim of the studyPsoriasis is a chronic inflammatory skin disorder characterized by hyperproliferation and aberrant differentiation of epidermal keratinocytes. Our previous studies identified Radix rubiae to have potent antiproliferative action on cultured HaCaT keratinocytes and to induce keratinocyte differentiation in mouse tail model. The present study aimed to investigate whether Radix rubiae could also induce terminal differentiation in cultured human keratinocytes. Methods and resultsThe cornified envelope (CE) formation assay showed that ethyl acetate (EA) fraction of Radix rubiae significantly accentuated the CE formation, a well-recognized marker of terminal differentiation, in cultured HEK and HaCaT cells in a dose and time dependent manner. Western blot analyses demonstrated that EA fraction of Radix rubiae at a concentration of 3.2μg/ml significantly increased transglutaminase type I and involucrin expression in both HEK and HaCaT keratinocytes after 96h treatment, a response similar to that of Ca2+ positive control. Moreover, the expression level of cytokeratin 5/14, which is specifically related to cell proliferation, was significantly downregulated while terminal differentiation markers cytokeratin 1/10 were markedly increased by Radix rubiae treatment in both HEK and HaCaT cells. ConclusionThe present experimental findings unequivocally confirmed the keratinocyte terminal differentiation promoting capacity of Radix rubiae, and strongly suggest that Radix rubiae is a promising antipsoriatic agent warranting further clinical development for psoriasis treatment.