The steroid glycoside H.g.-12 from Hoodia gordonii

21 Steroid glycosides extracted from the succulent plant Hoodia gordonii are suggested to have 22 appetite suppressant effects both in animals and humans. Yet, the mechanisms underlying the 23 putative satiety action of Hoodia steroid glycosides are not fully understood. We found that 24 H.g.-12, a steroid glycoside purified from Hoodia gordonii extract, initiated cholecystokinin 25 (CCK) secretion both ex vivo in rat intestine and in vitro in the human enteroendocrine (EC) 26 cell line HuTu-80. CCK is known to exert central effects on appetite suppression via the 27 vagus nerve which afferents terminate in the gut wall. Recent data show that G-protein28 coupled receptors signalling bitter taste (T2Rs) are expressed in both rodent and human 29 gastrointestinal tract. It was further demonstrated that bitter sensing is functional in mouse 30 STC-1 enteroendocrine cells and leads to CCK secretion via increased intracellular Ca 31 concentrations. Based on the bitter taste of Hoodia gordonii purified extracts, we assessed 32 whether H.g.-12 could activate human bitter receptors. The steroid glycoside activated 33 selectively TAS2R7 and TAS2R14, both heterologously expressed in HEK 293 cells. 34 Removing an essential structural feature from the steroid glycoside inhibited H.g.-12-induced 35 Ca increase in TAS2R14-expressing HEK cells and abolished H.g.-12-induced CCK 36 secretion from human EC cells. Similarly, a non-specific bitter receptor antagonist abolished 37 H.g.-12-induced CCK secretion in HuTu-80 cells. 38 These results point to a potential route of action by which components of Hoodia might 39 influence appetite control. Our data also provide additional evidence that bitter taste sensing 40 mechanisms are coupled to hormone release from enteroendocrine cells in the intestine. 41 Moreover, we identified a natural agonist of TAS2R7 and TAS2R14 for further studies on the 42 role of bitter receptors in satiety control and food intake. 43