Diosmetin ameliorates imiquimod-induced psoriasis by regulating apoptosis and inflammation via toll-like receptor 4/nuclear factor kappa B pathway

Background: Psoriasis is a common skin inflammatory disease. Dysregulated growth and differentiation of keratinocytes are the main characteristics of psoriasis. Diosmetin is a naturally occurring flavonoid with antioxidant, anti-inflammatory, and antibacterial properties. However, the anti-psoriatic role and mechanism of diosmetin remain unclear. Objectives: To investigate anti-psoriatic role and mechanism of diosmetin. Methods: Human immortalized epidermal cells (HaCaT) were treated with tumor necrosis factor-alpha (TNF-alpha) to establish the cell model of psoriasis. Mice were treated with imiquimod (IMQ) to establish the animal model of psoriasis. Cell viability and apoptosis were detected by methyl thiazolyl tetrazolium and flow cytometry, respectively. Reverse transcription-quantitative polymerase chain reaction and ELISA assays were performed to detect the expression of interleukin (IL)-6 and IL-8. Hematoxylin and eosin staining was used to detect the skin lesion. Results: Diosmetin reduced cell viability and promoted the apoptosis of TNF-alpha-induced HaCaT. Protein expression of Bax in TNF-alpha-induced HaCaT was up-regulated, while Bcl-2 was down-regulated by diosmetin. Diosmetin attenuated TNF-alpha-induced increase in IL-6 and IL-8 in HaCaT. The enhanced protein expression of toll-like receptor 4 (TLR 4) (toll-like receptor 4), p65 and I kappa B alpha phosphorylation, as well as reduced I kappa B alpha in TNF-alpha-induced HaCaT were restored by diosmetin. Diosmetin improved IMQ-induced skin lesion and attenuated inflammatory response in psoriasis-like mouse model. Conclusion: Diosmetin exerted anti-inflammatory and pro-apoptotic effects on TNF-alpha-induced HaCaT and IMQ-induced mice through inactivation of TLR4/nuclear factor kappa B pathway.