Introduction
Psoriasis is a chronic, immune-mediated skin disease that can be accompanied by joint involvement. For its high prevalence and the complexity of causative mechanisms, psoriasis has caused great concern worldwide [1]. Its typical clinical manifestations are scales, erythema, and epidermal thickening. Currently, it is well recognized that psoriasis results from the complex interaction between keratinocytes and immune cells [2]. Many inflammatory factors (e. g. TNF- α, IL-1 β, IL-23, and IL-12) secreted by Th17 cells, Th1 cells, and keratinocytes played crucial effects in their pathogenesis [3]. A growing body of evidence suggests that psoriasis is closely linked to multiple co-morbidities, such as systemic inflammation and cardiovascular comorbidity [4]. Therefore, psoriasis has gained significant attention worldwide. However, there are no effective measures to achieve a cure for psoriasis.
Curcumin is a polyphenolic compound purified and isolated from Curcuma longa. Since ancient times, turmeric had been considered an herbal remedy for the treatment of skin and gastrointestinal disorders [5]. Now, it is clear that its widespread use in medicine stems from its many properties, such as antioxidant, anti-inflammatory, anti-proliferative, anti-cancer and anti-bacterial effects [6]. It had been demonstrated that curcumin can reduce various inflammatory factors such as TNF-α, IFN-γ, IL-22 and IL-23 in mouse serum, which are closely involved in the pathogenic mechanism of psoriasis [7]. Meanwhile, curcumin was also considered as a protective compound that can regulate the intestinal microflora. Currently, increasing evidence had found that gut microbes were potentially involved in regulating the progression of a variety of diseases closely related to inflammation, such as psoriasis, psoriatic arthritis, inflammatory bowel diseases (IBD) [8, 9].
To further confirm our speculation, we found that curcumin could significantly improve the IMQ-induced mouse model, and reduce the expression of multiple pathogenic factors in its skin lesions, such as TNF- α, IL-17, IL-1 β, etc. Furthermore, we analyzed the changes of intestinal microbiota in mice after curcumin treatment. By using 16s rRNA technology, this study investigated whether curcumin could exert its therapeutic effect in psoriasis, which was in relation to the regulation of intestinal flora.