Crofelemer, an Antisecretory Antidiarrheal Proanthocyanidin Oligomer Extracted from Croton lechleri, Targets Two Distinct Intestinal Chloride Channels

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 M had little or no effect on the activity of epithelial Na ϩ or K ϩ channels or on cAMP or calcium signaling. Crofelemer inhibited the cystic fibrosis transmembrane regulator (CFTR) Cl Ϫ channel with maximum inhibition of ϳ60% and an IC 50 ϳ7 M. 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 Ͻ50% reversal of CFTR inhibition after 4 h. Crofelemer was also found to strongly inhibit the intestinal calcium-activated Cl Ϫ channel TMEM16A by a voltage-independent inhibition mechanism with maximum inhibition Ͼ90% and IC 50 ϳ6.5 M. The dual inhibitory action of crofelemer on two structurally unrelated prosecretory intestinal Cl Ϫ channels may account for its intestinal antisecretory activity.

Effects of Grape Seed Proanthocyanidin on 5-Hydroxytryptamine3 Receptors in NCB-20 Neuroblastoma Cells

“…Our data and the above reports 22,23) suggest that proanthocyanidin inhibits 5-HT 3 receptors in a noncompetitive manner, and that there exits the possibility that proanthocyanidin acts as an open channel blocker at 5-HT 3 receptors. Therefore, we tested the voltage dependency of the inhibition by proanthocyanidin by measuring its effect on current-voltage relationships.…”

“…Prior studies suggested that proanthocyanidin is membrane-impermeable because of its size and polarity and that it seems unlikely that it is transported across the membrane at a sufficient rate to reach a potential intracellular target. 22,23) Thus, the noncompetitive inhibition of 5-HT 3 receptor channel activity by proanthocyanidin indicates that proanthocyanidin has different binding or interaction sites through which it modulates the 5-HT 3 ion channel from the extracellular side.…”

Profile of crofelemer for the symptomatic treatment of diarrhea in HIV-infected persons

“…Thus, the antisecretory properties of crofelemer are based on a dual mechanism of action. 15 Finally, the chloride channel type-2 channels are located on the lateral membranes of enterocytes, and their role in chloride-ion secretion is not well understood.…”

“…The two chloride channels are cAMPstimulated cystic fibrosis transmembrane conductance regulator (CFTR) and CaCC. 15 Inhibition of chloride-ion secretion results in decreased efflux of sodium and water and, therefore, improvement in diarrheal symptoms. 15 In the study performed by Tradtrantip et al, 15 crofelemer demonstrated a concentration-dependent inhibition on both the luminal CFTR channels, as well as an even stronger inhibition of the CACCs.…”

“…15 Inhibition of chloride-ion secretion results in decreased efflux of sodium and water and, therefore, improvement in diarrheal symptoms. 15 In the study performed by Tradtrantip et al, 15 crofelemer demonstrated a concentration-dependent inhibition on both the luminal CFTR channels, as well as an even stronger inhibition of the CACCs. Regarding the CFTR channels, increasing concentrations of crofelemer produced more rapid, although partial, inhibition of CFTR, with maximal inhibition being 60% and a half maximal inhibitory concentration (IC 50 ) value of 7 µM.…”