Discussion
Psoriasis is well recognized as a chronic inflammatory disease prone to recurrent attacks. Its typical symptoms are well-demarcated erythema and skin scales accompanied with systemic symptoms [12]. Curcumin, as a polyphenolic compound stemmed from turmeric, owns multiple pharmacological effects, comprising anti-inflammatory, anti-proliferative, antioxidant, and anti-angiogenic activities [13].
It is well known that the typical histological changes of psoriasis show excessive proliferation of keratinocytes and infiltration of inflammatory cells, increased PCNA in skin lesions, and elevation of various inflammatory factors, such as IL-6, IL-17A, IL-22, IL-23, IL-1β [14, 15]. We found that CUR could significantly alleviate IMQ-induced psoriasis-like dermatitis, decreasing lesion thickness of mice, inflammatory cell infiltration, dyskeratosis, and spinous layer hypertrophy. In additions, CUR could inhibit the levels of PCNA in the epidermis of IMQ-induced mice, and the epidermal expression of IL-6, IL-17A, IL-22, IL-23, TNF-α, TGF-β1. Thus, the results revealed a possible effective mechanism of CUR against psoriasis-like dermatitis induced by IMQ.
Recently, reports had shown that the occurrence and development of psoriasis were closely associated with intestinal microbiota, and some pro-inflammatory gut microbes promoted Th1/Th17 activation in psoriasis, which then could cause the expression of various inflammatory factors in the epidermis, such as IL-17 and TNF-α [16]. Therefore, the intestinal microbiota can be regarded as a potential therapeutic target for alleviating psoriasis. Meanwhile, it had been shown that CUR can participate in the regulation of intestinal microbiota [17]. Taken together, we reasoned that CUR reshaped the diversity of the mouse gut microbiota.
To further investigate the supposition, we detected the effect of CUR on intestinal flora by using 16S rRNA sequencing. Remarkably, we found that the abundances of genus Alistipes , Rikenella andMucispirillum were promoted in CUR group. The researchers found that Alistipes and Odorbacter were positively correlated with intestinal acetate and propionate production, which inhibits the inflammatory activity of inflammatory bowel diseases (IBD) [18].Rikenella had been shown to be associated with the formation of short-chain fatty acids (SCFAs). It had been reported that the intestinal microflora and its metabolites can catabolize polysaccharides to produce SCFAs. SCFAs can maintain the intestinal barrier function, which is important for intestinal homeostasis. SCFAs not only maintained the cellular barrier but also prevented the transfer of LPS from the intestinal barrier [19]. Moreover, the abundance ofMucispirillum positively correlated with the concentration of the inflammatory suppressor IL-10 in breast cancer model mice [20]. Interestingly, Lactobacillus at the genus level was increased, which was probably due to the decreased diversity of gut microbiota of mice in the IMQ group.
Taken together, although there was no direct evidence to demonstrate that the gut flora changes induced by CUR linked with psoriasis, these bacteria were associated with inflammation. Furthermore, Moreover, the correlation analysis further showed a significant association between the three picked gut microflora at genus level regulated by CUR and inflammatory factors. We thought that there was a close connection between them. Therefore, inflammation served as an important role to connect CUR, psoriasis, and intestinal microbiota together. To be brief, CUR could relief psoriasis-like lesions of mice by repressing Th-17 related inflammatory factors, and regulate intestinal microbiota associated with inflammation, showing CUR may be a promising drug for alleviating psoriasis.