Atopic dermatitis, otherwise known as eczema, is an inflammatory autoimmune response of the skin. Today in the United States it affects around 25% of children, and as many as 3% of adults, with its incidences increasing each year. Like many other allergies, the microbiome is now being implicated in the cause of this disease. A few months back evidence was published linking atopic dermatitis to the skin bacteria Staphylococcus aureus. Other work, however, has shown that the gut microbiome may be critically important to this disease as well, especially because gut bacteria are more likely to control and elicit certain inflammatory responses seen in dermatitis, such as the release of specific cytokines. A group of Korea recently compared the gut bacteria in atopic dermatitis patients and healthy controls and identified a specific organism that may be important to the disease. They published their results last week in the Journal of Allergy and Clinical Immunology.

The researchers measured the gut microbiomes of 132 people, including 90 of which had atopic dermatitis and were seeking medical treatment. They also measured gene expression by bacteria in the gut, and short chained fatty acids (SCFAs) in the guts of all the individuals. They discovered that one particular bacterial species was much more abundant in dermatitis patients compared to controls, Faecalibacterium prausnitzii. After, they measured SCFA production, and noted that a decrease in butyrate and propionate was directly linked with the presence of F. prausnitzii, suggesting an important link between this bug, SCFAs, and the disease state. In addition, they noted that the overall diversity of bacteria was similar in all microbiomes measured. Finally, the scientists investigated the gene expression, and observed an increase in bacteria that are capable of breaking down gut mucins, or mucous, in the guts of atopic dermatitis individuals. For example, these bugs were expressing proteins that break down fucose and N-acetylgalactosamine (GalNAc), two monosaccharides that are normally derived from mucins rather than food.

This study presents a number of differences in the gut microbiomes of individuals with an without atopic dermatitis. The scientists suggest that an important species associated with this disease may be F. prausnitzii, and perhaps it may even be influencing the disease through a lack of SCFA production, and the breakdown of gut mucins. Atopic dermatitis is a complex disease, and certainly cannot be explained by the presence of an individual bug. However, this paper does support the notion that diseased individuals, who present rashes on their skin, may have disruptions to gut, and that changes in the gut microenvironment create a niche for specific bacteria to grow. This, in turn, may inform new therapeutic strategies that target the gut microbiome, rather than topical treatments.

New microbiome based drug may cause people to eat less!

Many people have heard that eating fiber is good for your health and helps to prevent weight gain. One of the reasons for this, as we have blogged about before, is thought to be related to the short chained fatty acids (SCFAs) that are produced by the microbiome from fiber. In mouse models, mice that receive a fecal transplant containing a microbiome with a high capacity for generating SCFAs show reduced weight gain. The SCFAs appear to induce the production of certain hormones associated with appetite control. The problem with human interventions of fiber-based diets is that an unpalatable amount of fiber is normally required, and very little of it is eventually converted into SCFAs. Scientists from England recently tried to tackle this problem by introducing one type of SCFA, propionate, into the colons of obese humans to investigate its effects on weight gain. The results of their study were published in the journal Gut.

The researchers chemically modified propionate so that after it was eaten it would only be released in the colon. They then performed a double blind trial with 60 obese participants that took either the propionate or a placebo every day for 24 weeks. The scientists discovered that, as hypothesized, ingesting the propionate increased the production of the appetite control hormones in the colon. In addition, people who took the propionate tended to have a suppressed appetite and ate less overall food than their placebo counterparts. Overall, the propionate prevented weight gain in the individuals who ingested it compared to the placebo group.

Recent advances in microbiome research have shown hormones produced by the gut are critical to managing hunger and food intake, and that research has allowed these scientists to create a new drug that stimulates the microbiome into producing those hormones. In addition, the scientists show a new method of drug delivery to the colon which may have applications for other therapies. At the AMI, we hope that their research continues to be as fruitful as it is promising.

Atopic dermatitis associated gut microbe identified

Microbiome based therapy prevents weight gain in obese individuals