Significant difference was found in the beta diversity of gut microbiota between the AD group and the normal group (Bray-Curtis: p = 0.001, Jaccard: p = 0.001, unweighted-UniFrac: p = 0.025).
However, no significant difference was found in the alpha diversity between the two groups (Shannon diversity index: p = 0.285).
Alpha diversity refers to the observed richness and evenness of an average sample in a habitat type, while beta diversity refers to the variability among samples within a habitat.
Nine bacterial genera were found significantly enriched in the AD group, including Blautia, Butyricicoccus, Lachncoclostridium, Eubacterium_hallii_group, Erysipelatoclostridium, Megasphaera, Oscillibacter, Flavonifractor, and unclassified genera from the bacteria family of Oscillospiraceae.
Four genera, namely Romboutsia, Clostridium_sensu_stricto_1, and unclassified genera from two bacteria families, Butyricicoccacaeae and Erysipelotrichaceae, were enriched in the normal group.
Only two genera, namely Blautia and Butyricoccus, were significantly positively correlated with the severity of AD. Two genera, namely Romboutsia and Clostridium_sensu_strico_1, decreased significantly with the severity of AD.
Mechanism at work
Past research elicited the strong ability of the two genera lacking in the AD group, Romboutsia and Clostridium_sensu_strico_1, to produce short-chain fatty acids.
“Short-chain fatty acids, which play an important role in the gut–skin axis, can stamp out the immune responses by inhibiting the cytokine production, migration, proliferation, and adhesion of inflammatory cells.
“SCFAs can also regulate the apoptosis and activation of immune cells by deactivation of NF-κB signalling pathways and inhibiting histone deacetylase, which promotes the cell proliferation that regulates various skin physiological functions, for example, regulating the differentiation of hair follicle stem cells and wound healing
“Moreover, SCFAs can provide energy for the intestinal epithelium and improve the integrity of the intestinal epithelial barrier to prevent microorganisms and toxins from entering the body fluid circulation to trigger immunity, and further resulting in a disturbance of the skin homeostasis.”
Study design
The results were based on a clinical study conducted with 234 participants between the ages of 18 to 68 in Hong Kong.
130 participants with healthy skin were assigned to the normal group, and 104 patients with AD were assigned to the mild (n = 53) and severe (n = 51) groups based on a severity assessment.
The study is the General Research Fund from the Research Grants Council of Hong Kong, Research Impact Fund from Research Grants Council, the Health and Medical Research Fund from the Food and Health Bureau of Hong Kong, and the Hong Kong Society of Gut Microbiome.
The stool samples of the participants were collected, and their microbial DNA was isolated from the samples for analysis.
Alpha diversity was measured by the Shannon diversity index, Simpson diversity index, observed OTUs, Chao 1 richness index, abundance-based coverage estimator (ACE) index, and faith’s phylogenetic diversity index.
Beta diversity was measured based on the Jaccard distance metric, Bray-Curtis distance metric, weighted-UniFrac, and unweighted-UniFracdistance metrics.
“In summary, the composition, structure, and functional metabolic pathways of the gut bacterial community of AD patients were distinct from those of healthy people, but severe and mild AD patients had a similar overall structure of gut microbiome.
“Gut microbiome dysbiosis and metabolic abnormalities may have essential implications for the pathogenesis of the gut-skin axis in AD patients.
“Further studies of metagenomics and metabolomics are warranted in order to investigate the relationship between the gut microbiome and AD and further develop beneficial treatment methods for AD,” the researchers concluded.
Source: International Journal of Molecular Sciences
“Unique Gut Microbiome Signatures among Adult Patients with Moderate to Severe Atopic Dermatitis in Southern Chinese”
Authors: Wang, Y., et al.