Activation of Intestinal Cl- Secretion by Lubiprostone Requires the Cystic Fibrosis Transmembrane Conductance Regulator
Background & Aims: Lubiprostone alleviates constipation by stimulating intestinal fluid secretion, purportedly through activation of ClC-2-type Cl-channels. Intestinal obstruction is also a recurrent cause of distress in cystic fibrosis (CF) patients, caused by loss of CF transmembrane conductance regulator (CFTR) Cl-channel activity. Because ClC-2 recruitment might be beneficial to CF patients, we investigated lubiprostone's mode of action. Methods: Cl-transport was measured in an Ussing chamber, in 3 model systems: (1) T84 colonocytes, (2) intestinal epithelium of wild-type and CF mice, and (3) intestinal epithelium of CF patients and controls. Results: In T84 monolayers, lubiprostone induced a robust secretory response. Selective permeabilization of the basolateral plasma membrane revealed that lubiprostone activated an apical Cl-conductance. The lubiprostone response was attenuated by H89, an inhibitor of the cAMP-dependent protein kinase, and lubiprostone precluded responsiveness to the cAMP agonist forskolin. CFTR blockage by CFTRinh172, but not ClC-2 blockage by CdCl2, inhibited the lubiprostone response. Lubiprostone induced a CdCl2-insensitive secretory response in mouse intestine, but failed to induce intestinal Cl-secretion in Cftr-null mice. Correspondingly, lubiprostone induced a secretory response in human intestinal epithelium, but not in tissue of CF patients. The EP4-type prostanoid receptor antagonist L-161,982 blocked the lubiprostone response in all 3 models studied. In T84 cells, lubiprostone induced a rise in cAMP levels that was sensitive to EP4-receptor blockage. Conclusions: Lubiprostone enhances intestinal Cl-and fluid secretion via prostanoid receptor signaling, triggering activation of CFTR. Therefore, it is of limited use for treatment of CF-related intestinal disease.