Feeding filaggrin: effects of L-histidine supplementation in atopic dermatitis

Atopic dermatitis (AD), also known as eczema, is one of the most common chronic skin conditions worldwide, affecting up to 16% of children and 10% of adults. It is incurable and has significant psychosocial and economic impacts on the affected individuals. AD etiology has been linked to deficiencies in the skin barrier protein, filaggrin. In mammalian skin, L-histidine is rapidly incorporated into filaggrin. Subsequent filaggrin proteolysis releases L-histidine as an important natural moisturizing factor (NMF). In vitro studies were conducted to investigate the influence of L-histidine on filaggrin processing and barrier function in human skin-equivalent models. Our further aim was to examine the effects of daily oral L-histidine supplementation on disease severity in adult AD patients. We conducted a randomized, double-blind, placebo-controlled, crossover, nutritional supplementation pilot study to explore the effects of oral L-histidine in adult AD patients (n=24). In vitro studies demonstrated that L-histidine significantly increased both filaggrin formation and skin barrier function (P<0.01, respectively). Data from the clinical study indicated that once daily oral L-histidine significantly reduced (P<0.003) AD disease severity by 34% (physician assessment using the SCORingAD tool) and 39% (patient self-assessment using the Patient Oriented Eczema Measure tool) after 4 weeks of treatment. No improvement was noted with the placebo (P>0.32). The clinical effect of oral L-histidine in AD was similar to that of mid-potency topical corticosteroids and combined with its safety profile suggests that it may be a safe, nonsteroidal approach suitable for long-term use in skin conditions that are associated with filaggrin deficits such as AD.