Luteolin Attenuates Imiquimod–induced Psoriasis-like Skin Lesions In BALB/c Mice And Its Immunomodulatory Mechanism

Psoriasis is a common chronic inflammatory skin disease mediated by the immune system.Because of its complex pathogenesis,long course and difficult to cure,and accompanied by a variety of complications,seriously affect the physical and mental health of patients.In recent years,with the development of psoriasis related studies,the exploration of multiple signaling pathways and targets found forth new drugs for the treatment of psoriasis.For example,tretinoins for epidermal cell proliferation,betamethasone for inflammatory reaction,and biological agents such as TNF-α inhibitors have achieved certain therapeutic effects.Although some drugs have achieved clinical efficacy,the side effects caused by longterm use of synthetic drugs and biological agents are still a challenge.Therefore,it is urgent to develop new,effective and less side effects anti-psoriasis drugs.In addition to the research and development of chemical and biological agents for the treatment of psoriasis,the natural products in herbal medicine have been widely studied in the form of chemical monomers or extracts.Luteolin,a representative natural flavonoid,exists in honeysuckle,perilla,chrysanthemum,pepper,orchid and other Chinese herbal medicines.It has attracted extensive attention because of its many and significant pharmacological activities such as anti-tumor,anti-inflammatory,antioxidant and immune regulation.With the deepening of research on luteolin,it is found that luteolin is mainly used to alleviate the immune and inflammation of diseases.It has been reported that luteolin can down regulate the expression levels of proinflammatory cytokines and inflammatory mediators,and reduce the virus induced inflammatory response by blocking the nuclear factor-κB(NF-κB)signaling pathway.In addition,previous studies have shown that luteolin and its analogues reduce the proliferation of keratinocytes.Luteolin glucoside is believed to reduce the skin damage of atopic dermatitis mouse model.Therefore,we speculate that luteolin may alleviate the silvery lesions by regulating the skin inflammatory response.We hypothesized that luteolin can alleviate psoriasis like skin damage by reducing inflammatory response.Therefore,in this project,we used imiquimod induced BALB/c mice to establish psoriasis like animal model,and LPS stimulated macrophages(RAW264.7 cells)to establish inflammatory cell model,to explore the alleviating effect of luteolin on psoriasis like symptoms and the inflammatory mechanism of luteolin in LPS stimulated macrophage system in vivo and in vitro,so as to provide a new idea for clinical treatment of psoriasis.The main research contents are as follows:(1)Objective to study the inhibitory effect of luteolin on imiquimod(IMQ)-induced psoriasis like mice model.Psoriasis like mice model was established by smearing imiquimod on the back of mice,and the changes of skin on the back of mice were evaluated by PASI score;H & E and immunohistochemical staining were used to complete the histopathological evaluation;enzyme linked immunosorbent assay(ELISA)was used to determine the inflammatory factors related to psoriasis to complete the immunological evaluation.(2)Objective to study the molecular mechanism of luteolin in relieving psoriasis like symptoms.LPS stimulated macrophages(RAW264.7)was used to establish in vitro inflammatory model.QPCR,ELISA,Western blot and other molecular biology experiments were used to detect the expression of inflammatory mediators and pathway proteins related to psoriasis,and completed the relevant mechanism research.The results showed that luteolin can improve the skin damage of psoriasis like mice model,inhibit the activation and infiltration of macrophages,T cells and neutrophils in psoriasis like skin lesions,and downregulate the expression of IL-6,IL-1 β,TNF-α and other inflammatory cytokines,and downregulate the expression of IL-17 A and IL-23 in the skin lesions and eyeball blood of psoriasis mice.In vitro,luteolin significantly inhibited the levels of proinflammatory cytokines such as IL-17 A,IL-6,TNF-α and IL-23,and inflammatory mediators such as NO,iNOS and COX-2 in RAW264.7 cells.At the same time,it down regulated the expression of NF-κB and inhibited the phosphorylation of NF-κB.Luteolin can alleviate inflammation and psoriasis like injury induced by imiquidine in vivo.In vitro,luteolin can inhibit NF-κB-mediated inflammatory signaling pathway and significantly reduce the release level of inflammatory factors,suggesting that luteolin is a potential molecule for further treatment of inflammation related skin diseases such as psoriasis.