4The gut microbiome in psoriasis and psoriatic arthritis
Introduction
The human microbiome refers to the total diversity of microorganisms and their genomes that live in association with our own bodies, existing in, on, and within us. This community is made up of bacteria, eukaryotes, viruses, and archaea. Different anatomical sites harbor distinct microbial communities that play important roles in modulating local host physiology. Thanks to recent advances in high-throughput sequencing, researchers have been able to inexpensively and rapidly evaluate the taxonomic composition and functional activities of microbial communities at different body sites [1]. Since the gut microbiota is influenced by numerous factors, including age, genetics, dietary habits, geographic location, and antibiotic use, a great deal of interpersonal variability exists [2].
Host-microbe interactions are crucial for human health. Intestinal microbes carry out a multitude of important functions, including educating the immune system and synthesizing necessary vitamins in host survival [3]. While the gut microbiome of an adult is relatively stable over time, it can be influenced by a wide variety of environmental factors. Disruption of microbial community homeostasis can result in an aberrant host-microbe relationship and increased disposition of developing disease. More recently, evidence has accumulated supporting the pathogenic role of the gut microbiome in various autoimmune and inflammatory diseases, including diabetes mellitus [4], inflammatory bowel disease (IBD) [5], spondyloarthritis (SpA) [6], cardiovascular disease [7], and anxiety and depression [8], many of which are well-established comorbidities of psoriasis and psoriatic arthritis (PsA) [9]. With respect to dermatology, more extensive research has been done describing how the skin microbiome is involved in disease pathogenesis, including that of atopic dermatitis [10], hidradenitis suppurativa [11], and psoriasis [12]. The importance of the gut microbiome in these inflammatory conditions, however, is just beginning to be explored in greater depth.
Psoriasis is a chronic immune-mediated inflammatory condition reported to affect roughly 2–4% of the global population [13], although prevalence varies with geographic location. While it is defined by its skin involvement, psoriasis can manifest as inflammation in many other organ systems, including the gastrointestinal, cardiovascular, and musculoskeletal systems [14]. It has a profound effect on patient health-related and psychosocial quality of life, and it is associated with high morbidity and mortality [15]. The principal comorbidity associated with psoriasis is PsA, a chronic inflammatory musculoskeletal disease. PsA affects more than 500,000 individuals within the United States alone, and millions more are affected globally [16]. PsA can be significantly disabling for patients [17] and can add to the severity of morbidity and mortality that is associated with psoriasis [16]. In spite of accumulating research on psoriasis and PsA, the etiologies of these diseases are still being investigated. They are both known to be multifactorial in nature, with genetic, immunologic, and environmental factors playing critical roles as evidenced by an increase in psoriasis and PsA incidence in developed countries over the past few decades [18]. Similar pathogenesis is also seen in IBD, in terms of genetic susceptibility and Th17-predominant immune activity [19]. IBD is an established comorbidity of psoriasis, and the role of the gut microbiome in this disease's development is already well-supported [5].
In this review, we summarize previous studies examining the gut microbiome composition and function in psoriasis and PsA and discuss proposed mechanisms by which observed patterns of dysbiosis yield local and systemic inflammation with skin and joint involvement. A better understanding of the gut microbiome's role in these diseases offers the potential for novel targets in psoriatic management. However, research evaluating the clinical application and therapeutic benefits of these targets is still in its early stages.
Section snippets
Methods
A literature search of PubMed and Embase databases was conducted for the terms ‘psoriasis’ or ‘psoriatic arthritis,’ ‘microbiome,’ ‘microbiota,’ or ‘metagenome,’ and ‘gastrointestinal flora,’ ‘intestinal flora,’ or ‘gut flora.’ Our search was limited to English-language articles and those published prior to November 20, 2019. For review, the authors manually identified the relevant articles discussing the gut microbiome specifically. Duplicate articles were excluded. In total, we identified
The gut microbiome in psoriasis
To date, eight studies investigating the gut microbiome composition in psoriasis patients have been performed, all of which report distinct and unique characteristics pertaining to the gut microbiome in psoriasis versus control subjects. Three out of the eight studies revealed either a slight or significant decrease in overall bacterial diversity within the fecal microbiome samples of psoriasis patients versus control subjects [[20], [21], [22]]. However, one study by Codoñer et al. found a
The gut microbiome in psoriatic arthritis
Upon literature review, we found only one study that specifically investigated the gut microbiome in PsA [21], as most of the research on this topic exists within the broader context of SpA and inflammatory arthropathies [38]. In this study, Scher et al. compared the gut microbiome composition of never-treated and recent-onset PsA patients versus PsO patients and healthy controls. In regard to the PsA fecal microbiomes, they noted a decrease in overall diversity as compared to healthy fecal
Impact of diet and medications on the gut microbiome in psoriasis and psoriatic arthritis
Given the strong evidence for gut dysbiosis in psoriasis and psoriatic arthritis, and the roles of microbes in modulating the host's immune system, targeting the microbiome and microbiome-derived compounds is a potentially effective strategy for developing novel therapies in psoriatic disease. Moreover, microbiome profiling may also lead to identification of promising biomarkers assisting in earlier diagnosis and more personalized, efficacious treatment recommendations. For example, in
Discussion
While studies investigating the gut microbiome in psoriasis and PsA demonstrate variability in their findings, this body of research has revealed several distinct and compelling patterns of dysbiosis that may be discriminative of these diseases. Already, these findings are showing promise in helping us to better understand the pathogenic series of events connecting the gut microbiome to psoriasis and psoriatic arthritis (see Fig. I). They also provide compelling evidence to suggest that shifts
Funding
No funding sources were used for the purposes of this manuscript.
Declaration of Competing Interest
The authors have none to disclose.
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Cited by (0)
- 1
UCSF Psoriasis and Skin Treatment Center, 515 Spruce Street, San Francisco, CA 94118, USA.
- 2
2340 Sutter Street San Francisco, CA 94115, USA.