Effects of a gel containing the defined microalgae extract Spiralin® on the skin microbiome and clinical activity in atopic dermatitis - a double-blind, intraindividual vehicle-controlled proof-of-concept study.

Introduction: Changes in the skin microbiome in atopic dermatitis include a reduced bacterial diversity and increased abundance of Staphylococcus aureus. Topical antibiotics and antiseptics may decrease bacterial pathogens, but lack positive effects on microbiome diversity.

Methods: In this double-blind, intraindividual vehicle-controlled pilot study, n = 20 patients received a gel containing a defined extract (Spiralin®) of the microalgae Spirulina platensis, previously shown to exert anti-microbial effects, or vehicle on target lesions of similar size and clinical activity. The Shannon index reflecting -diversity and the abundance of S. aureus were calculated from the analysis of 16s rRNA gene libraries with untreated non-lesional skin serving as control. Clinical activity was determined by the Target Lesion Severity Score (TLSS) and lesion size.

Results: Positive effects of the active gel on the microbiome after 4 weeks of treatment were indicated by a significant increase of the Shannon index in areas treated with verum (mean increase 16.7%; p<0.01 vs. baseline), but not in areas treated with vehicle. This increase in verum-treated lesions was more pronounced in lesions with an at least 50% (26.3%) or an at least 75% reduction of the TLSS (33.3%). There was also a stronger decrease of the abundance of S. aureus in lesions treated with active gel compared to those treated with vehicle (25.5% vs. 9.4%), but significance was not met. There were several trends indicating clinical effects of the active gel. For example, vehicle-treated areas showed no reduction in area size (77.8 cm2 at week 4 compared to 77.0 cm2 at baseline), while verum-treated lesion area decreased on average by 6.9 cm2. Active and vehicle gel were well tolerated and very few local side effects were noted.

Conclusion: These preliminary results indicate a positive effect of a gel containing Spiralin® on the skin microbiome in patients with active atopic dermatitis (AD) lesions combined with reductions in clinical disease activity supporting further investigations of the active gel alone or in combination with anti-inflammatory treatments in larger AD studies.