What’s salt got to do with atopic dermatitis?
Patients with atopic dermatitis (AD) have elevated levels of sodium chloride or salt in their skin compared with those with nonlesional atopic and healthy skin, according to a new study finding which experts described as “provocative.”
“It is fantastic … this is so new and so old at the same time,” commented ISDS session co-chair Dr Tove Agner from the University of Copenhagen in Copenhagen, Denmark. However, she cautioned that the hypothesis needs a lot more work.
In the study, sodium chloride levels were higher at 39 μg/mg in AD patients with skin lesions. By contrast, there was no appreciable sodium accumulation in nonlesional skin and in healthy skin, said lead investigator Dr Christina Zielinski from the Technical University of Munich in Munich, Germany. [ISDS 2018, abstract 21]
“Here, we demonstrated that sodium chloride potently promoted Th2 cell responses on multiple regulatory levels,” Zielinski said. “Sodium chloride enhanced IL‐4 and IL‐13 production while suppressing IFN‐g production in effector T cells. It diverted alternative T cell fates into the Th2 cell phenotype and induced de novo Th2 cell polarization from naïve T cell precursors. Mechanistically, it exerted effects via the osmosensitive transcription factor NFAT5 and the kinase SGK‐1, which regulated Th2 signature cytokines and master transcription factors in hyperosmolar salt conditions.”
In patients with psoriasis, there was a nonsignificant increase of 8 μg/mg in sodium chloride level in their skin.
Early studies had provided proof of concept that dietary salt reduction could help improve eczema. This notion was given a new twist in recent studies which showed that sodium had an impact on the functional changes of multiple sclerosis (MS). Current knowledge also suggests that a low-salt diet (<5 g/day) may be beneficial for the prevention and treatment of autoimmune diseases, including MS.
The nature of environmental factors and the mode of action by which sodium induces the type 2 immune deviation characteristic of atopic diseases remain to be fully elucidated though.
Considering that salt accumulation was highest in the skin and the kidneys, as demonstrated in the current study, clinicians should evaluate sodium chloride consumption in patients with AD, said Zielinski. “Sodium chloride represents a so far overlooked cutaneous microenvironmental factor in AD that can induce Th2 cell responses, the orchestrators of allergic diseases. Together, our data propose ionic signaling through sodium chloride as a novel checkpoint and potential therapeutic target for type 2 immunity and its associated allergic diseases,” she added.