Rooibos Extract Stimulates Exocrine Glands via M₃ Muscarinic Acetylcholine Receptor

Objectives: Various causes such as daily stress, aging, drugs' side effects, and Sjögren's syndrome can trigger dryness in the mouth, eyes, and skin by decreasing exocrine glandular secretion. We screened M₃ muscarinic acetylcholine receptor (M3R)-activating food materials because exocrine glandular secretion is controlled by M3R, and identified rooibos (Aspalathus linearis) extract as a positive candidate. In this study, we conducted cell culture experiments to find its active component and a clinical trial to examine the effects of rooibos extract on dryness in the mouth, eyes and skin.
Methods: Characteristic rooibos extract compounds were evaluated for their activity to stimulate the M3R in Chem-1 cells. In a double-blind placebo-controlled crossover clinical trial, subjects with daily dryness at multiple sites of the mouth, eyes or skin were tested for efficacy of the rooibos extract. Thirty-six subjects consumed either 100 mg of rooibos extract or placebo and were tested for resting saliva, tear volume, and stratum corneum moisture content after 60 and 120 min of consumption, as well as subjective dryness at the mouth, eyes and skin after 120 min.
Results: In the cell culture experiments, eriodictyol-6-C-glucoside (E6CG), characteristic rooibos extract compound, stimulated the M3R. The activity of E6CG was similar to that of the rooibos extract containing an equivalent amount of E6CG. In the clinical trial, moisture content of mouth, eyes and skin was significantly higher in the rooibos than in the placebo group, and subjective dryness at the mouth, eyes and skin was significantly reduced in the rooibos group.
Conclusions: We identified E6CG as the active component in rooibos extract, a food material that activates the M3R, and found that rooibos extract stimulates exocrine gland secretion and relieves dryness at the mouth, eyes and skin.