Acta Dermato-Venereologica 99-1CompleteContent | Page 9

REVIEW ARTICLE 5 Role of the Gut Microbiota in Atopic Dermatitis: A Systematic Review Elisabeth B. M. PETERSEN, Lone SKOV, Jacob P. THYSSEN and Peter JENSEN Copenhagen Research Group for Inflammatory Skin (CORGIS), Department of Dermatology and Allergy, Herlev and Gentofte Hospital, University of Copenhagen, Hellerup, Denmark The immune mechanisms involved in atopic derma- titis (AD) are complex and little is known about the possible role of the gut microbiota in the aetiopatho- genesis of AD. A systematic review of the literature was performed according to PRISMA guidelines, and included 44 of 2,199 studies (26 observational and 18 interventional studies). Detection of gut microbiota was performed by either 16s rRNA PCR, or by culture. Observational studies were diverse regarding the age of study participants and the bacterial species investi- gated. Overall, the results were conflicting with regard to diversity of the gut microbiota, specific bacterial colonization, and subsequent risk of AD. Nearly half of the included interventional studies showed that an altered gut microbial colonization due to use of pro- biotics had a positive effect on the severity of AD. The remaining studies did not show an effect of probiotics on the severity of AD despite an alteration in the gut microbial composition. The role of the gut microbiome for the onset and severity of pre-existing AD remains controversial. Key words: atopic dermatitis; gut; microbiome. Accepted Jul 27, 2018; Epub ahead of print Aug 7, 2018 Acta Derm Venereol 2019; 99: 5–11. Corr: Peter Jensen, Department of Dermatology and Allergy, Herlev and Gentofte Hospital, University of Copenhagen, Kildegårdsvej 28, DK-2900 Hellerup, Denmark. E-mail: [email protected] A topic dermatitis (AD) is a common chronic inflam- matory skin disease with a worldwide prevalence of approximately 20% in children and 2–5% in adults (1). In recent years, there has been an increasing interest in the role of the intestinal microbiota in the aetiopathogenesis of AD. The gut microbiota increases in diversity over time, especially during the first 5 years of life, and the gut bacterial composition is unique at the individual level (2). The adult gastrointestinal tract houses several tril- lion microbial cells. Studies in humans have identified a total of 9.9 million microbial genes in the adult intestine. The gut microbiota is involved in the regulation of a wide range of physiological processes, such as intestinal endocrine function, cell proliferation, vascularization, biosynthesis of various compounds, and elimination of toxins (2). Cell-mediated immune pathways, and development and maintenance of the gut mucosa are also influenced by the gut microbiota (3). Imbalance or dysbiosis of the human gut microbiota during early childhood may be a risk factor for a wide range of SIGNIFICANCE Atopic dermatitis (AD) a chronic inflammatory skin disease with complex immune mechanisms. Research interest in the role of the intestinal microbiome in the regulation of cell- mediated immune pathways is increasing. We performed a systemic review summarizing studies investigating the role of the gut microbiota in AD. We included 44 studies, 26 observational, and 18 interven- tional studies. Overall, the results were conflicting. Nearly half of the included interventional studies showed that an altered gut microbial colonization by use of probiotics had a positive effect on the severity of AD. The role of the gut microbiome in AD remains controversial. lifestyle-related and immune-mediated diseases, such as asthma, metabolic diseases, and inflammatory bo- wel disease (4–6). Also, studies examining the effect of an altered gut microbial composition, i.e. through faecal transplantation, have shown promising results in atherosclerosis, intestinal infection, and certain cancers (2). Studies on germ-free mice suggest that the absence of intestinal bacteria may lead to immune dysfunction, which may increase the risk of disease later in life (7–9). The immune mechanisms in AD are complex and little is known about the role of the gut microbiome in the pathogenesis of AD. The aim of this study was to review the existing literature on the role of the gut microbiota in the aetiopathogenesis and severity of AD. METHODS A systematic review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta- Analyses) guidelines (10). Prior to study start, the search string, objectives and study protocol methods were defined. Search strategy PubMed was searched (on 13 June 2017) for studies and trials that aimed to investigate the role of the gut microbiota in AD. The following search string was used: ((Atopic Dermatitis OR Atopic Eczema) AND (Intestine OR Microbiota OR Intestinal Micro- biome OR Intestinal microflora OR Gastrointestinal microbiome OR Gut microbiome)). Additional studies were identified from the reference lists of already included studies. Eligibility criteria Articles in English, which included patients diagnosed with AD and/or healthy controls, were included. The studies were either interventional or observational and had to evaluate the gut micro- This is an open access article under the CC BY-NC license. www.medicaljournals.se/acta Journal Compilation © 2019 Acta Dermato-Venereologica. doi: 10.2340/00015555-3008 Acta Derm Venereol 2019; 99: 5–11