Abstract
Crofelemer, a purified proanthocyanidin oligomer extracted from the bark latex of Croton lechleri, is in clinical trials for secretory diarrheas of various etiologies. We investigated the antisecretory mechanism of crofelemer by determining its effect on the major apical membrane transport and signaling processes involved in intestinal fluid transport. Using cell lines and measurement procedures to isolate the effects on individual membrane transport proteins, crofelemer at 50 μM had little or no effect on the activity of epithelial Na+ or K+ channels or on cAMP or calcium signaling. Crofelemer inhibited the cystic fibrosis transmembrane regulator (CFTR) Cl− channel with maximum inhibition of ∼60% and an IC50 ∼7 μM. Crofelemer action at an extracellular site on CFTR produced voltage-independent block with stabilization of the channel closed state. Crofelemer did not affect the potency of glycine hydrazide or thiazolidinone CFTR inhibitors. Crofelemer action resisted washout, with <50% reversal of CFTR inhibition after 4 h. Crofelemer was also found to strongly inhibit the intestinal calcium-activated Cl− channel TMEM16A by a voltage-independent inhibition mechanism with maximum inhibition >90% and IC50 ∼6.5 μM. The dual inhibitory action of crofelemer on two structurally unrelated prosecretory intestinal Cl− channels may account for its intestinal antisecretory activity.
Footnotes
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This work was supported by the National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases [Grants DK72517, DK35124, DK86125]; the National Institutes of Health National Heart, Lung, and Blood Institute [Grant HL73856]; the National Institutes of Health National Eye Institute [Grant EY13574]; the National Institutes of Health National Institute of Biomedical Imaging and Bioengineering [Grant EB00415]; the Cystic Fibrosis Foundation [Grant R613]; and an unrestricted gift from Napo Pharmaceuticals.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.061051
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ABBREVIATIONS:
- CFTR
- cystic fibrosis transmembrane conductance regulator
- CaCC
- calcium-activated chloride channel
- CFTRinh-172
- thiazolidinone cystic fibrosis transmembrane conductance regulator inhibitor
- CPT-cAMP
- chlorophenylthio-cAMP
- FRT
- Fisher rat thyroid
- GlyH-101
- glycine hydrazide cystic fibrosis transmembrane conductance regulator inhibitor
- IBMX
- 3-isobutyl-1-methylxanthine
- NMDG-Cl
- N-methyl-d-glucamine chloride.
- Received September 15, 2009.
- Accepted October 5, 2009.
- © 2010 The American Society for Pharmacology and Experimental Therapeutics
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