Biomarkers in serum and epidermis overlap across anatomical locations in patients with atopic dermatitis

Immunoinflammatory biomarkers and skin barrier function in atopic dermatitis (AD) may be crucial for monitoring disease activity and patient stratification. Commonly, biomarkers are determined from blood or stratum corneum (SC), but comparative studies between biomarker levels in blood and SC tape strips are scarce. SC biomarkers have showed great potential in recent studies, though little is known about differences between anatomical sites and how it might influence the relationship between biomarker levels and disease severity. This study investigated the difference in biomarker levels in serum and SC, collected from lesional and non-lesional skin on different anatomical locations. Also, the association between these biomarkers and disease severity on a global and local level in adult patients with AD was explored. Adult outpatients with AD referred to the Department of Dermatology, Bispebjerg Hospital, Copenhagen were included. SC samples of non-lesional and lesional skin sites were collected from three different anatomical sites. Cytokine concentrations in serum and SC were measured by multiplex immunoassay, and natural moisturizing levels (NMF) by liquid chromatography. In all patients, transepidermal water loss (TEWL) and pH were determined. Disease severity was assessed by global and local SCORAD (global, ranging 0-103 and local, ranging 0-18, with high score indicating severe disease). A total of 25 adult patients with AD were included ; 10 (40.0%) with mild and 15 (60.0%) with moderate-severe disease. The mean age was 34.8 years (range 22-62 years) and 11 (44.0%) were females. Positive correlations between serum and epidermal biomarker levels was seen for IL-18 and CTACK, whereas IL-17A and IL-31 correlated negatively across anatomical locations. Epidermal levels of TEWL, pH, TARC, CTACK, TSLP, IL-22 and IL-18 were significantly higher in lesional compared to non-lesional skin, NMF was highest in non-lesional skin. Global SCORAD correlated with lesional levels of TEWL, IL-1β and Eotaxin. Local SCORAD correlated with lesional levels of NMF and several immunoinflammatory cytokines. Serum and epidermal biomarkers levels overlap to some extent, with no apparent differences observed between anatomical sites. Lesional-skin showed upregulation of central inflammatory markers, suggesting that determination of biomarkers from lesional skin could be of relevance for monitoring topical therapy. Disease severity, global and local, was associated with impaired barrier function and expression of numerous immunoinflammatory markers in both lesional and non-lesional skin.