| Psoriasis is an immunologically-mediated chronic inflammatory disease of the skin and joints affecting approximately 1-3% of the world's population. Traditionally, Chinese medicine has been extensively used both inside and outside China for treating psoriasis with promising clinical results. Based on the promising findings in our previous screening project on 61 psoriasis-treating Chinese medicines which showed the root of Rubia cordifolia L. (Rubiae Radix) to have potent anti-psoriatic action, the present study aimed to identify active anti-psoriatic chemical constituents derived from Rubiae Radix and another Chinese herb namely Celastrus orbiculatus Thunb. and to elucidate the underlying mechanisms of action.;Microplate MTT assay was performed to evaluate the anti-proliferative actions of 28 selected Rubiae Radix-derived anthraquinones and other chemical ingredients on cultured HaCaT keratinocytes. Among them, 1-hydroxy-3-methyl-anthraquinone (HMA) and 1,4-diamino-2,3-bis(2-phenoxyethoxy)anthraquinone (DBA), as well as celastrol, a Celastrus orbiculatus-derived triterpene, were found to possess significant anti-proliferative action on HaCaT cells, with IC50 value of 17.9, 15.8 and 1.1 muM, respectively. All DBA, HMA and celastrol showed only mild to moderate toxic effects on normal human keratinocyte HEK cells and human fibroblast Hs68 cells.;Mechanistically, celastrol and HMA was found to induce apoptosis in a dose-dependent manner in HaCaT cells as characterized by DNA fragmentation, phosphatidyl-serine externalization and activation of caspase 3. Further studies by flow cytometric and western blot analyses demonstrated that the celastrol-induced apoptosis on HaCaT cells was associated with the inhibition of NF-kappaB pathway and through caspase-related apoptotic pathway as characterized by activation of caspase proteins, regulation of Bcl-2 family proteins and depolarization of mitochondrial potential.;On the other hand, DBA showed an ability to induce terminal differentiation in cultured human keratinocytes and this capability is believed to be responsible for its growth inhibitory effects. DBA significantly accentuated the cornified envelope formation in HEK and HaCaT keratinocytes together with the augmentation of K1/K10, involucrin and transglutaminase 1 protein levels and decrease of expression of K5/K14 protein in DBA-treated cells. However, the subsequent in vivo study using a mouse tail model showed that HMA did not have significant effects on modulating keratinocyte terminal differentiation.;Taken together, our present PhD project successfully identified DBA, HMA and celastrol to have potent anti-psoriatic action on in vitro models, and the experimental findings render these naturally-occurring chemicals to be promising candidates for further development into anti-psoriatic pharmaceutical agents. |
