Plasma Levels of Bioactive Vitamin D and A5 Ligands Positively Correlate with Clinical Atopic Dermatitis Markers.

BACKGROUND: Over the past decade, several controversial studies described a relationship between vitamin D and atopic diseases. Low plasma vitamin D levels or even vitamin D deficiency was associated with an increased incidence of atopic disease, postulating that a higher dietary intake of vitamin D may be a beneficial strategy against atopic diseases such as atopic dermatitis (AD). OBJECTIVE: Our aim was to determine the relationship between plasma 25-hydroxyvitamin D3 (25(OH)D3) levels, the levels of the ligand of the vitamin D receptor (VDR) heterodimerization partner as well as the retinoid X receptor (RXR) and the active vitamin A5 derivative 9-cis-13,14-dihydroretinoic acid (9CDHRA) and AD severity. METHODS/RESULTS: Samples from AD patients (n = 20) and healthy volunteers (n = 20) were assessed. In our study, the frequently measured VDR ligand precursor 25(OH)D3 in addition to the VDR-ligand 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 9CDHRA displayed no different levels when compared with the plasma of AD patients and healthy volunteers. When performing further correlation studies focusing on AD patients, plasma 25(OH)D3 levels showed a negative correlation with eosinophils in blood (EOS) and SCORing Atopic Dermatitis (SCORAD) values, while 1,25(OH)2D3 and 9CDHRA levels correlated positively with plasma IgE, EOS, and SCORAD values. CONCLUSION: In consequence, the metabolic activation of vitamin D from 25(OH)D3 towards 1,25(OH)2D3 as well as the co-liganding of the RXR by 9CDHRA may be an important signalling mechanism, an important marker for AD development and severity as well as the basis for novel nutritional and pharmaceutical AD treatment options.