ARTICLE: Inhibition of sodium/hydrogen exchanger 3 in the gastrointestinal tract by tenapanor reduces paracellular phosphate permeability
AUTHORS: Andrew J. King1, Matthew Siegel, Ying He, Baoming Nie, Ji Wang, Samantha Koo-McCoy, Natali A. Minassian, Qumber Jafri, Deng Pan, Jill Kohler, Padmapriya Kumaraswamy, Kenji Kozuka, Jason G. Lewis, Dean Dragoli, David P. Rosenbaum, Debbie O’Neill, Allein Plain, Peter J. Greasley, Ann-Cathrine Jönsson-Rylander, Daniel Karlsson, Margareta Behrendt, Maria Strömstedt, Tina Ryden-Bergsten, Thomas Knöpfel, Eva M. Pastor Arroyo, Nati Hernando, Joanne Marks, Mark Donowitz, Carsten A. Wagner , R. Todd Alexander, Jeremy S. Caldwell
JOURNAL: Sci Transl Med. 2018 Aug 29;10(456). pii: eaam6474. doi: 10.1126/scitranslmed.aam6474.
Hyperphosphatemia is common in patients with chronic kidney disease and is increasingly associated with poor clinical outcomes. Current management of hyperphosphatemia with dietary restriction and oral phosphate binders often proves inadequate. Tenapanor, a minimally absorbed, small-molecule inhibitor of the sodium/hydrogen exchanger isoform 3 (NHE3), acts locally in the gastrointestinal tract to inhibit sodium absorption. Because tenapanor also reduces intestinal phosphate absorption, it may have potential as a therapy for hyperphosphatemia. We investigated the mechanism by which tenapanor reduces gastrointestinal phosphate uptake, using in vivo studies in rodents and translational experiments on human small intestinal stem cell-derived enteroid monolayers to model ion transport physiology. We found that tenapanor produces its effect by modulating tight junctions, which increases transepithelial electrical resistance (TEER) and reduces permeability to phosphate, reducing paracellular phosphate absorption. NHE3-deficient monolayers mimicked the phosphatephenotype of tenapanor treatment, and tenapanor did not affect TEER or phosphate flux in the absence of NHE3. Tenapanor also prevents active transcellular phosphate absorption compensation by decreasing the expression of NaPi2b, the major active intestinal phosphatetransporter. In healthy human volunteers, tenapanor (15 mg, given twice daily for 4 days) increased stool phosphorus and decreased urinary phosphorus excretion. We determined that tenapanor reduces intestinal phosphate absorption predominantly through reduction of passive paracellular phosphate flux, an effect mediated exclusively via on-target NHE3 inhibition.
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