The circadian metabolome of atopic dermatitis

Background Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by dry, pruritic skin. Several studies have described nocturnal increases in itching behavior, suggesting a role for the circadian rhythm in modulating symptom severity. However, the circadian rhythm of metabolites in the skin and serum of patients with AD has yet to be described. Objective This study sought to assess circadian patterns of skin and serum metabolism in patients with AD. Methods 12 patients with moderate to severe AD and 5 healthy volunteers were monitored for 28 hours in a controlled environment. Serum was collected every 2 hours and tape strips every 4 hours from both lesional and non-lesional skin in participants with AD and location-, sex-, and age-matched, healthy skin of controls. We then performed an untargeted metabolomics analysis, examining the circadian peaks of metabolism in AD. Results Distinct metabolic profiles were observed in AD vs. control samples. When accounting for time of collection, the greatest differences in serum metabolic pathways were observed in the arachidonic acid, steroid biosynthesis, and terpenoid backbone biosynthesis. We identified 42 circadian peaks in AD or control serum and 17 in the skin. Pathway enrichment and serum-skin metabolite correlation varied throughout the day. Differences were most evident in the late morning and immediately after sleep onset. Conclusion Although limited by a small sample size and observational design, our findings suggest that accounting for sample collection time could improve biomarker detection studies in AD and highlight that metabolic changes may be associated with nocturnal differences in symptom severity.