Thermal Therapy Modulation of the Psoriasis-Associated Skin and Gut Microbiome

IntroductionPsoriasis is a systemic immune-mediated disease primarily manifesting as skin redness and inflammation. Balneotherapy proved to be a successful non-pharmacological option to reduce the skin areas affected by the disease, but the specific mechanisms underlying this effect have not been elucidated yet. Here we test the hypothesis that the effect of thermal treatments on psoriatic lesions could be partially mediated by changes in the resident microbial population, i.e., the microbiome.MethodsIn this study, we enrolled patients with psoriasis and monitored changes in their skin and gut microbiome after a 12-bath balneotherapy course with a combination of 16S rRNA amplicon sequencing and metagenomics. Changes in the resident microbiome were then correlated with thermal therapy outcomes evaluated as changes in Psoriasis Area and Severity Index (PASI) and Body Surface Area index (BSA).ResultsThe amplicon sequencing analysis of the skin microbiome showed that after thermal treatment the microbiome composition of affected areas improved to approach that typical of unaffected skin. We moreover identified some low-abundance bacterial biomarkers indicative of disease status and treatment efficacy, and we showed via metagenomic sequencing that thermal treatments and thermal water drinking affect the fecal microbiome to host more species associated with favorable metabolic health.ConclusionsChanges in lower-abundance microbial taxa presence and abundance could be the basis for the positive effect of thermal water treatment and drinking on the cutaneous and systemic symptomatology of psoriasis. Psoriasis is an immune-mediated disease primarily manifesting as skin redness and inflammation that affects 2-3% of the world's population. No cure is currently available for this condition, and patients are offered pharmacological and non-pharmacological options to alleviate the discomfort. Previous studies and clinical practice have shown that thermal water treatment can be a non-pharmacological option to reduce the areas affected by the disease. However, the specific mechanisms causing this reduction have not been clarified yet. Given that neither the chemical nor the physical composition of thermal water can explain this beneficial effect, recent studies have suggested that it might be due to the effect of thermal water on the microbial communities living on the skin (i.e., the skin microbiome).In this work carried out at Terme di Comano, Northern Italy, we describe the effect of thermal water treatment on the skin microbiome of patients with psoriasis and we highlight the potentially beneficial effect of thermal water drinking on the microbial communities living in the gut, namely the gut microbiome. Specifically, we show that after balneotherapy the areas affected by psoriasis have a higher diversity of microbes usually present on healthy skin, potentially explaining the reduction in disease severity after treatment, and we describe how the gut microbiome of patients who drank thermal water changes to host more species linked with favorable metabolic health. These findings highlight that thermal water treatment and drinking could reduce both the skin and systemic symptomatology of psoriasis by affecting the skin and gut microbiome.