Diacerein Alone and in Combination with Infliximab Suppresses the Combined Proinflammatory Effects of IL-17A, IL-22, Oncostatin M, IL-1A, and TNF-alpha in Keratinocytes: A Potential Therapeutic Option in Psoriasis

Psoriasis is a chronic disorder characterized by a complex interplay between keratinocytes and inflammatory mediators. In a previous study, we evaluated diacerein's ability to diminish interleukin (IL)-1's proinflammatory effects on cultured primary human keratinocytes. In this study, we evaluated diacerein's ability to diminish the inflammatory effects of a cytokine mixture (CM) consisting of IL-17A, IL-22, oncostatin M, IL-1A, and tumor necrosis factor (TNF)-alpha on cultured primary human keratinocytes. These five cytokines have been previously shown to induce an in vivo-equivalent cell culture psoriasis model. We also evaluated diacerein's anti-inflammatory effects in comparison to and in combination with infliximab, a TNF-alpha inhibitor currently used in the treatment of psoriasis. We found 81 genes that were significantly (P < 0.05) dysregulated by CM compared to medium control. All three treatment groups (diacerein alone, infliximab alone, and diacerein plus infliximab) diminished the effects of CM on these genes, with the greatest effect seen with diacerein plus infliximab. Using enzyme-linked immunosorbent assay method on cell culture supernatant, we determined the protein concentration for five genes (IL-19, IL-6, CSF3, S100A8, and NAP-2) significantly (P < 0.05) upregulated by CM at the gene level. Diacerein alone diminished the effect of CM on the protein concentration of two genes, whereas diacerein plus infliximab diminished the effect of CM on the protein concentration of all the five genes. Based on these results, we conclude that diacerein alone or in combination with infliximab may have a therapeutic role in psoriasis by downregulating key inflammatory mediators.

A molecular mechanism for IL-4 suppression of loricrin transcription in epidermal keratinocytes: implication for atopic dermatitis pathogenesis

Skin barrier defects play an important role in atopic dermatitis (AD) pathogenesis. Loricrin, an important barrier protein suppressed in human AD, is down-regulated by IL-4 in keratinocytes. However, the molecular mechanism is unknown. Since loricrin transcription requires p300/CBP, and Stat6 also recruits this common coactivator for its stimulated factors, we hypothesize that IL-4-activated Stat6 competes for the available endogenous p300/CBP, leading to loricrin transcription inhibition. First, we showed that loricrin is suppressed in the skin of IL-4 transgenic mice, an AD mouse model. In human keratinocytes, IL-4 down-regulation of loricrin is abrogated by a pan-Jak inhibitor, suggesting that the Jak-Stat pathway is involved. To further investigate the downstream molecular mechanism, we transfected HaCat cells with a loricrin promoter and then treated them with either IL-4 or vehicle. Not surprisingly, IL-4 greatly suppressed the promoter activity. Interestingly, this suppression was prevented when we knocked down Stat6, indicating that Stat6 participates in IL-4 regulation of loricrin. A Stat6-specific inhibitor confirmed the knockdown study. Finally, IL-4 suppression of loricrin was reversed with transfection of a CBP expression vector in a dose-dependent manner. Taken together, for the first time, we delineate a molecular mechanism for IL-4 down-regulation of loricin expression in human keratinocytes, which may play an important role in AD pathogenesis.