p-Synephrine: a novel agonist for neuromedin U2 receptor.

In the brain, Neuromedin U2 receptor (NMU2R) is prominent in the hypothalamic regions and is known to be associated with regulation of several important physiological functions, including food intake, energy balance, stress response, and nociception. In this article, by random screening of compounds using the model of high-throughput screening for NMU2R stable expression, NMU2R negative and NMU2R short hairpin RNA (shRNA) knockdown HEK293 cell lines, for the first time, we discovered that p-synephrine, which is the primary protoalkaloid in Citrus aurantium (bitter orange) and is widely used in weight loss and weight management products, is a highly potent and selective NMU2R agonist. In NMU2R activating ability experiments, p-synephrine was found binding to NMU2R with high efficacy and potency; the efficacy, 50% of the maximum possible effect (EC50) and potency values were determined to be 7.207, 6.604 and 0.227 µmol/L for the NMU2R, respectively. Our researches have important theoretical value for elucidating the mechanisms of p-synephrine in body weight and energy balance regulation. These data provide further evidence for widespread roles for p-synephrine and its receptors in the brain.