Rooibos (Aspalathus linearis) extract, containing eriodictyol-6-C-β-d-glucoside as the active component, stimulates exocrine glands via the M3 muscarinic acetylcholine receptor

Abstract

Abstract We previously discovered that rooibos extract activates the M3 muscarinic acetylcholine receptor (M3R), a key component of exocrine secretion. In this study, we examined the rooibos extract for active components in vitro and monitored its fast-acting effects against dryness in humans. Our in vitro analysis demonstrated that the M3R-stimulating effect of rooibos extract was similar to that of eriodictyol-6-C-β- d -glucoside (E6CG), whereas other rooibos constituents (aspalathin, orientin, isoorientin or eriodictyol-8-C-β- d -glucoside) were not active. In a placebo-controlled, double-blinded crossover clinical trial, 36 subjects with dryness at the mouth, eyes, and skin consumed a daily dose of either 100 mg rooibos or placebo tablets for three days. Rooibos extract ingestion increased resting-saliva content, tear volume, and stratum corneum moisture content, and reduced the dryness symptoms. In conclusion, rooibos extract contains E6CG as an M3R activator and stimulates exocrine gland secretion, which relieves dryness at the mouth, eyes, and skin in humans.