An aqueous extract of Poncirus fructus activates the prokinetic activity of 5-HT receptor subtype 4 without hERG interaction.
OBJECTIVE
Poncirus fructus (PF)--also known as the dried, immature fruit of Poncirus trifoliata (L.) Raf. (Rutaceae)--is a natural substance that has long been used for various gastrointestinal disorders in eastern Asia. An aqueous extract of PF (PF-W) has particularly potent gastroprokinetic effects, but its molecular mechanism was not well understood. Identification of the underlying prokinetic mechanism of PF-W was pursued in the present study.


METHODS
Changes in in vitro cAMP levels and in vivo intestinal transit rate (ITR) caused by PF-W were measured after pretreatment with GR125487, an antagonist for serotonin receptor subtype 4 (5-HT4R). An [(3)H] astemizole binding assay and electrophysiology experiments were performed to determine if PF-W has any interaction with the human ether-à-go-go related gene (hERG) potassium channel.


RESULTS
PF-W induced an increase in intracellular cAMP in 5-HT4R-expressing HEK293T cells, indicating that PF-W does activate 5-HT4R. Moreover, pretreatment with GR125487 successfully blocked the increase, suggesting that the response was 5-HT4R-specific. More importantly, pretreatment of GR125487 in rats inhibited the elevation of ITR by PF-W, indicating that the prokinetic effect of PF-W was indeed exerted via 5-HT4R. On the other hand, both [(3)H]-astemizole binding assay and electrophysiological experiments revealed that PF-W did not interfere at all with the hERG channel.


CONCLUSIONS
It was found that PF-W exerts its prokinetic activity through a 5-HT4R-mediated pathway, with no interaction with hERG channels. Therefore, PF-W is a good candidate that might be developed as a prokinetic agent with fewer expected cardiac side effects.
Shim
Won-Sik
WS
National Research Laboratory for Transporters Targeted Drug Design & Research Institute of Pharmaceutical Sciences and Department of Pharmaceutics, College of Pharmacy, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul 151-742, Republic of Korea.
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Heejung
H
Jung
Sang-Won
SW
Kim
Jun-Woo
JW
Jang
Yongwoo
Y
Lee
Byeongjun
B
Seo
Eun-Kyoung
EK
Oh
Uhtaek
U
Shim
Chang-Koo
CK
D000818:Animals; D016589:Astemizole / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D005638:Fruit / Q000737:chemistry; D005772:Gastrointestinal Transit / Q000187:drug effects*; D006801:Humans; D018408:Patch-Clamp Techniques; D010936:Plant Extracts / Q000009:adverse effects / Q000302:isolation & purification / Q000494:pharmacology*; D032104:Poncirus / Q000737:chemistry*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D044422:Receptors, Serotonin, 5-HT4 / Q000235:genetics / Q000378:metabolism*; D058828:Serotonin 5-HT4 Receptor Agonists / Q000009:adverse effects / Q000302:isolation & purification / Q000494:pharmacology*; D058832:Serotonin 5-HT4 Receptor Antagonists / Q000494:pharmacology; D014162:Transfection
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D010936:Plant Extracts; D026902:Potassium Channel Blockers; D058828:Serotonin 5-HT4 Receptor Agonists; D058832:Serotonin 5-HT4 Receptor Antagonists; D044422:Receptors, Serotonin, 5-HT4; D016589:Astemizole; D000242:Cyclic AMP