“What's new about our work is that we're showing that the diet itself can increase your susceptibility to psoriatic inflammation, both in the joints and in the skin,” Dr. Hwang says.
Using a mouse model, Dr. Hwang, in collaboration with University of California Davis School of Medicine colleagues Satya Dandekar, Ph.D., Department of Medical Microbiology and Immunology, and Yu-Jui Yvonne Wan, Ph.D., Department of Medical Pathology and Laboratory Medicine, and others, examined the effects of diet on intestinal dysbiosis for evidence of impact on skin and joint inflammation.
First, the researchers looked at the impact of the Western diet on susceptibility to IL-23-mediated skin inflammation. The researchers fed mice either a chow or standard diet, or a Western diet for 6 weeks, at which time the mice were injected with either IL-23 minicircle (MC) DNA to induce systemic IL-23 overexpression or control green fluorescent protein (GFP) MC DNA. After another 4 weeks, the mice injected with IL-23 MC DNA showed a significant elevation of serum IL-23. Additionally, they developed skin changes consisting of erythema and scaling. However, the mice fed the chow diet had much milder changes while the mice injected with the GFP MC DNA showed no changes.
“Short-term Western diet intake appears sufficient to enhance susceptibility to IL-23‒mediated psoriasis-like skin inflammation,” the authors wrote.
In characterizing the immunological features observed in the mice injected with the IL-23 MC DNA, the authors noted that mice fed the Western diet appeared to have worse skin inflammation. What this means, Dr. Hwang explains is that while a Western diet alone may result in changes that can lead to psoriatic inflammation, if you have other factors that might trigger psoriasis, a Western diet can make it worse.
The researchers also discovered the Western diet appeared to predispose mice to IL-23‒mediated joint inflammation.
A critical finding of their study was establishing the gut microbiome as a pathogenic link between diet and psoriatic inflammation. The researchers observed significant differences in bacterial abundance between groups. Mice fed the Western diet had a lower microbial diversity than the chow-fed mice, including a loss of beneficial bacteria, and the changes in microbial diversity were exacerbated in the group injected with IL-23 MC DNA.
Are the changes reversible? This was the final question Dr. Hwang and colleagues examined. They fed a group of mice a Western diet for 6 weeks and then injected them with IL-23 MC DNA to initiate psoriatic-like disease. These mice were then divided into two groups: one which continued the Western diet and one which switched to the chow diet. After 4 weeks, the mice that switched to the chow diet showed less scaling, reduced ear thickness, as well as other molecular changes such as diminished epidermal thickness and cellular infiltrates than those which maintained the Western diet. In addition, the researchers observed a beneficial change in gut microbiota composition in the mice switched to the chow diet.
“We know that psoriasis is a systemic disease,” Dr. Hwang says. “But I think we're now understanding that environmental contributions such as diet can make a difference — and sometimes a pretty striking difference.”
Psoriasis results from predisposing genetic factors and the influence of external triggers, so while you cannot change your genetics, you can modify your diet, Dr. Hwang says. And possibly, by implementing changes at the first sign of psoriatic skin inflammation, it may be possible to reduce the risk of joint disease, he adds. Further, by combining weight loss, which often involves dietary changes or caloric restriction, with other treatments, we may get a better outcome.
He says he now advises patients that this is a lifestyle change, but it does not have to be onerous. Modifying a Western diet to something like a Mediterranean diet does not mean you are just eating lettuce every day, he says. There are different ways to modify the balance of one’s diet to get a beneficial effect and this work suggests that’s possible, he adds. Working with an experienced dietician or certified nutritionist as part of your collaborative care team can be beneficial.
I hope that gives patients hope, Dr. Hwang says. Even for those with other pro-inflammatory stimuli or other triggers that are not easily changed. If you can change your diet, it may be enough to mitigate these other factors enough that it lessens disease severity, he says.
Dr. Hwang says his team continues to explore the possible connection with the gut microbiome and its impact on psoriatic disease as they examine the particular roles of bacterial species and the role of bacterial metabolites in skin inflammation.