A recent study finds that the inflammatory disease psoriasis is clearly associated with lower microbial diversity in the gut. A researcher says that studies are needed to show whether treatment of psoriasis can improve the composition of gut bacteria or whether re-establishing gut microbiota with higher functional potential can reduce the symptoms of psoriasis.
Many diseases are associated with alterations in the composition of gut bacteria.
These include cardiovascular disease, obesity, type 2 diabetes and Alzheimer’s disease, all of which are associated with lower microbial diversity in the gut’
A new study shows that psoriasis is yet another disease associated with changes in the gut microbiota.
“Psoriasis is a chronic systemic inflammatory disease. It is also associated with other inflammatory diseases such as inflammatory bowel disease, cardiovascular disease and metabolic disorders. We know that chronic inflammation and the immune system play a role in all these diseases and that gut bacteria can affect the immune system. It is therefore important that we have now found that psoriasis is associated with lower microbial diversity in composition and in functional potential,” explains Lone Skov, professor and senior physician in the Department of Dermatology and Allergy, Herlev and Gentofte Hospital, and a professor at the Department of Clinical Medicine at the University of Copenhagen.
The results have been published in the British Journal of Dermatology.
Previous studies of poor quality
Researchers have tried to find associations between psoriasis and gut bacteria. However, in a review of these studies, the first author of the new study, Tanja Todberg, and colleagues found that the previous studies have had major methodological problems that have made definite conclusions difficult.
The majority of the studies included very few people, and they were not adequately controlled for confounding factors that could affect psoriasis and gut bacteria, including smoking, obesity and use of antibiotics.
In the new study, the researchers therefore took a more thorough approach and considered as many factors as possible that could affect the composition of the gut microbiota. The study included 53 people with psoriasis, 52 healthy controls and 21 partners of people with psoriasis.
The participants were matched for sex, age and body-mass-index with the controls, and the researchers also ensured that the participants had not been treated with systemic anti-inflammatory treatment or with antibiotics in the previous 3 months.
“Antibiotics strongly affects the composition of the gut microbiota, and we therefore excluded people treated with antibiotics and laid down several other criteria,” says Lone Skov.
Examined faecal samples from people with psoriasis and controls
The participants, including patients, their healthy partners and healthy controls, submitted faecal samples, and in a subgroup for up to a year, and the researchers analysed the samples for their microbial profile.
The total bacteria in a faecal sample can be characterised in different ways. The researchers used shotgun metagenomic sequencing analysis providing detailed information about the gut microbiota.
The results showed very clearly that the composition of the gut bacteria differed between people with psoriasis and their partners and healthy controls.
Lone Skov explains that the microbial diversity especially differed.
“We found lower microbial richness in function. suggesting that people with psoriasis do not have the same functional potential as other people,” she adds.
Functional richness indicates the health-promoting effect of having great variation in the composition of gut bacteria, since the bacteria produce health-promoting molecules that can affect many body functions, including metabolism and the immune response by regulating the production of anti-inflammatory cytokines.
Lower variation in microbial profile is probably associated with poorer health and an increased risk of developing many diseases.
The chicken or the egg?
Lone Skov emphasises that the results do not determine whether lower diversity in the gut microbiota leads to psoriasis or psoriasis causes the lower diversity.
In parallel studies, the researchers tried to improve understanding of this issue by treating people intensively for psoriasis and then determining how this affected the composition of gut bacteria.
However, they found no shifts in composition among people with psoriasis who received thorough treatment.
“We did not see any difference in gut microbiota after 3 months of treatment despite an excellent clinical response on psoriasis. We also carried out a study in which we examined seasonal differences, because people with psoriasis often have fewer symptoms in the summer, but we did not find anything there either,” explains Lone Skov.
The big question is whether improving the functional richness of the gut bacteria will help people with psoriasis or whether keeping this inflammatory disease in check can improve functional richness.
Lone Skov thinks that psoriasis causes changes in the gut microbiota and that improving functional richness will not help psoriasis symptoms.
“But this is speculative and must be examined in future studies before we can make conclusions,” she concludes.