Rhealba® Oat Plantlet Extract: Evidence of Protein-Free Content and Assessment of Regulatory Activity on Immune Inflammatory Mediators

Owing to their high content of flavonoids and saponins, plantlets of Avena sativa L. (Poaceae) are likely to possess anti-inflammatory and immunoregulatory properties of value in the treatment of atopic dermatitis (AD). With a view to its potential use in atopic subjects at risk of developing sensitisation to dietary proteins, we prepared a plantlet extract without proteins and isolated 2 flavonoids, isoorientin-2 ''-O-arabinoside (1) and isovitexin-2 ''-O-arabinoside (2), and two saponins, avenacosides A (3) and B (4). The absence of protein in this extract was evidenced by electrophoresis and Western immunoblotting. Furthermore, Western immunoblotting demonstrated the absence of cross-reaction between grain and plantlet proteins. We evaluated the anti-inflammatory activity of the plantlet extract and its compounds in vitro in a model of keratinocyte inflammation: 6-keto prostaglandin F1 alpha production was inhibited by the plantlet extract (-35% and -57% at 10 and 30 mu g/mL, respectively; p < 0.001) and isoorientin-2 '''-O-arabinoside (-31%, -51%, and -56% at 3, 10, and 30 mu g/mL, respectively; p < 0.001). Intracellular interleukin- 2 production in activated T lymphocytes was also inhibited by 16%, 27%, and 31% with 3, 10, and 30 mu g/mL plantlet extract, respectively, and by 23% and 32% with 3 and 10 mu g/mL avenacoside A, respectively, (p < 0.001), demonstrating their immunoregulatory activity in vitro. The plantlet extract was also effective on the phenotype and function of dendritic cells (DC) differentiated from monocytes. It decreased the expression of major histocompatibility complex class II molecules on DC and significantly impaired their stimulatory activity on autologous T-cell proliferation (-25%, p < 0.05). In conclusion, this protein-free oat plantlet extract exhibits anti-inflammatory and immunoregulatory activities in vitro.