Aspalathin, a key flavonoid in rooibos, restores STAT6-mediated immune dysregulation in atopic dermatitis

Abstract

Atopic dermatitis (AD), a chronic inflammatory skin disease whose incidence is increasing worldwide, requires the development of alternative treatments due to limited treatment options and concerns about side effects of therapeutic agents. Aspalathin (ASP) is the primary flavonoid found in rooibos, an herb traditionally used for allergies and eczema, accounting for over 40 % of the total flavonoid content, especially in its unfermented state (Green rooibos). This research conducted a thorough investigation into the pharmacological properties of ASP on AD, emphasizing local responses via activated keratinocytes, systemic responses involving T cells and basophils, and an integrated assessment using an AD mouse model. Topical application of ASP significantly reduced AD phenotypes, including erythema, scaling, and increased skin thickness, in AD mouse model. Histological analysis indicated a decrease in the infiltration of immune cells in skin lesions. Moreover, ASP down-regulated inflammatory markers, including T helper (Th)1 and Th2 cytokines, in both skin tissues and activated mouse T cells. In particular, ASP significantly reduced serum immunoglobulin (Ig)E and IgG2a levels. ASP suppressed the expression of cytokines linked to allergy and inflammation in T cells, basophils, and keratinocytes. Mechanistically, ASP exhibited anti-inflammatory properties by inhibiting STAT6 and NFAT1 activation in AD mouse skin and in activated T cells, basophils, and keratinocytes. In conclusion, ASP displayed pronounced effectiveness in relieving AD by sophisticated modulation of immune responses across both local and systemic domains. These findings highlight ASP's promise as a therapeutic intervention for AD, providing a solid scientific basis for future exploration and development.