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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

A Natural Plant-Derived Dihydroisosteviol Prevents Cholera Toxin-Induced Intestinal Fluid Secretion

Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.P., C.M., V.C.); and Division of Physical Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn, Thailand (S.H.)

Stevioside and its major metabolite, steviol, have been reported to affect ion transport in many types of tissues, such as the kidney, pancreas, and intestine. The effect of stevioside, steviol, and its analogs on intestinal Cl^- secretion was investigated in a human T84 epithelial cell line. Short-circuit current measurements showed that steviol and analogs isosteviol, dihydroisosteviol, and isosteviol 16-oxime inhibited in a dose-dependent manner forskolin-induced Cl^- secretion with IC₅₀ values of 101, 100, 9.6, and 50 µM, respectively, whereas the parent compound stevioside had no effect. Apical Cl^- current measurement indicated that dihydroisosteviol targeted the cystic fibrosis transmembrane regulator (CFTR). The inhibitory action of dihydroisosteviol was reversible and was not associated with changes in the intracellular cAMP level. In addition, dihydroisosteviol did not affect calcium-activated chloride secretion and T84 cell viability. In vivo studies using a mouse closed-loop model of cholera toxin-induced intestinal fluid secretion showed that intraluminal injection of 50 µM dihydroisosteviol reduced intestinal fluid secretion by 88.2% without altering fluid absorption. These results indicate that dihydroisosteviol and similar compounds could be a new class of CFTR inhibitors that may be useful for further development as antidiarrheal agents.

Address correspondence to: Dr. Varanuj Chatsudthipong, Department of Physiology, Faculty of Science, Mahidol University, Rama 6 Rd., Phayathai, Bangkok 10400, Thailand. E-mail: scvcs{at}mahidol.ac.th