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.