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ADPKD is characterized by progressive cyst formation and enlargement leading to kidney failure. Tolvaptan is currently the only FDA-approved treatment for ADPKD; however, it can cause serious adverse effects including hepatotoxicity. There remains an unmet clinical need for effective and safe treatments for ADPKD. The extracellular Ca 2+ -sensing receptor (CaSR) is a regulator of epithelial ion transport. FDA-approved CaSR activator cinacalcet can reduce cAMP-induced Cl - and fluid secretion in various epithelial cells by activating phosphodiesterases (PDE) that hydrolyze cAMP. Since elevated cAMP is a key mechanism of ADPKD progression by promoting cell proliferation, cyst formation and enlargement (via Cl - and fluid secretion), here we tested efficacy of cinacalcet in cell and animal models of ADPKD. Cinacalcet treatment reduced cAMP-induced Cl - secretion and CFTR activity in MDCK cells as suggested by ∼70 % lower short-circuit current (I sc ) changes in response to forskolin and CFTR inh -172, respectively. Cinacalcet treatment inhibited forskolin-induced cAMP elevation by 60 % in MDCK cells, and its effect was completely reversed by IBMX (PDE inhibitor). In MDCK cells treated with forskolin, cinacalcet treatment concentration-dependently reduced cell proliferation, cyst formation and cyst enlargement by up to 50 % without affecting cell viability. Cinacalcet treatment (20 mg/kg/day for 7 days, subcutaneous) reduced renal cyst index in a mouse model of ADPKD (Pkd1 flox/flox ;Ksp-Cre) by 20 %. Lastly, cinacalcet treatment reduced cyst enlargement and cell proliferation in human ADPKD cells by 60 %. Considering its efficacy as shown here, and favorable safety profile including extensive post-approval data, cinacalcet can be repurposed as a novel ADPKD treatment., Competing Interests: Declaration of Competing Interest All authors have read the journal's policy on disclosure of potential conflicts of interest and have none to declare., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Cholera is a global health problem with no targeted therapies. The Ca2+-sensing receptor (CaSR) is a regulator of intestinal ion transport and a therapeutic target for diarrhea, and Ca2+ is considered its main agonist. We found that increasing extracellular Ca2+ had a minimal effect on forskolin-induced Cl- secretion in human intestinal epithelial T84 cells. However, extracellular Mg2+, an often-neglected CaSR agonist, suppressed forskolin-induced Cl- secretion in T84 cells by 65% at physiological levels seen in stool (10 mM). The effect of Mg2+ occurred via the CaSR/Gq signaling that led to cAMP hydrolysis. Mg2+ (10 mM) also suppressed Cl- secretion induced by cholera toxin, heat-stable E. coli enterotoxin, and vasoactive intestinal peptide by 50%. In mouse intestinal closed loops, luminal Mg2+ treatment (20 mM) inhibited cholera toxin-induced fluid accumulation by 40%. In a mouse intestinal perfusion model of cholera, addition of 10 mM Mg2+ to the perfusate reversed net fluid transport from secretion to absorption. These results suggest that Mg2+ is the key CaSR activator in mouse and human intestinal epithelia at physiological levels in stool. Since stool Mg2+ concentrations in patients with cholera are essentially zero, oral Mg2+ supplementation, alone or in an oral rehydration solution, could be a potential therapy for cholera and other cyclic nucleotide-mediated secretory diarrheas.

Background: Dengue is a mosquito-borne viral disease with a wide spectrum of presentations ranging from subclinical disease to severe dengue. Dengue is endemic to the Terai of Nepal. Interestingly, an increasing incidence has been reported from hilly areas like Kathmandu valley. This study explored the clinicopathological profile of dengue infection., Methods: A total of 84 serologically confirmed dengue cases from September to November 2019 at KIST Medical College were recruited in a cross-sectional study after obtaining ethical approval. Dengue was categorized as dengue without warning signs, dengue with warning signs, and severe dengue. Clinicopathological information was recorded in the proforma by reviewing patients' records. A descriptive statistical tool and chi-square test were carried out., Results: Out of 84 patients, 76% (64) were dengue without warning signs, 21.4% (18) were dengue with warning signs and 2.4% (2) were severe dengue. About 97.6% (82) presented with fever. During the course of illness, anemia was identified in 38.1% (32), thrombocytopenia in 65.5% (55), hemoconcentration in 6% (5), and leucopenia in 82.1% (69). Similarly, elevated aspartate transaminase and alanine transaminase (ALT) was observed in 67.7% (42) and 53.2% (33) respectively. The severity of dengue on presentation to hospital was significantly associated with thrombocytopenia, leucopenia, and elevated ALT. Similarly, the severity during course of illness in hospital was significantly associated with hemoconcentration, thrombocytopenia, leucopenia, and elevated ALT., Conclusions: Most common presentation of dengue infection was fever. The most common laboratory abnormalities were leucopenia, thrombocytopenia, hemoconcentration, anemia, and elevated liver enzymes. Awareness of these clinical and laboratory parameters is important for the prompt diagnosis, severity estimation, and overall management of dengue infection.

Loss of prosecretory Cl - channel CFTR activity is considered as the key cause of gastrointestinal disorders in cystic fibrosis including constipation and meconium ileus. Clc-2 is proposed as an alternative Cl - channel in intestinal epithelia that can compensate for CFTR loss-of-function. Lubiprostone is an FDA-approved drug with Clc-2 activation as its presumed mechanism of action. However, relative contribution of Clc-2 in intestinal Cl - secretion and the mechanism of action of lubiprostone remain controversial due to lack of selective Clc-2 inhibitors. Using recently identified selective Clc-2 inhibitor AK-42, we characterized the roles of Clc-2 in Cl - secretion in human intestinal epithelial T84 cells. Clc-2 inhibitor AK-42 had minimal (15%) inhibitory effect on secretory short-circuit current (I sc ) induced by cAMP agonists, where subsequently applied CFTR inhibitor (CFTR inh -172) caused 2-3 fold greater inhibition. Similarly, AK-42 inhibited lubiprostone-induced secretory I sc by 20%, whereas CFTR inh -172 caused 2-3 fold greater inhibition. In addition to increasing CFTR and Clc-2-mediated apical Cl - conductance, lubiprostone increased basolateral membrane K + conductance, which was completely reversed by cAMP-activated K + channel inhibitor BaCl 2 All components of lubiprostone-induced secretion (Clc-2, CFTR and K + channels) were inhibited by ~65% with the extracellular Ca 2+ -sensing receptor (CaSR) activator cinacalcet that stimulates cAMP hydrolysis. Lastly, EP4 prostaglandin receptor inhibitor GW627368 pretreatment inhibited lubiprostone-induced secretion by 40% without any effect on forskolin response. Our findings suggest that Clc-2 has minor role in cAMP-induced intestinal Cl - secretion; and lubiprostone is not a selective Clc-2 activator, but general activator of cAMP-gated ion channels in human intestinal epithelial cells. Significance Statement Cl- channel Clc-2 activation is the proposed mechanism of action of the FDA-approved constipation drug lubiprostone. Using first-in-class selective Clc-2 inhibitor AK-42, we showed that Clc-2 has minor contribution in intestinal Cl- secretion induced by lubiprostone and cAMP agonists. We also found that lubiprostone is a general activator of cAMP-gated ion channels in human intestinal epithelial cells (via EP4 receptors). Our findings clarify the roles of Clc-2 in intestinal Cl- secretion and elucidate the mechanism of action of approved-drug lubiprostone., (Copyright © 2020 American Society for Pharmacology and Experimental Therapeutics.)

Diarrhea is a major cause of global mortality, and outbreaks of secretory diarrhea such as cholera remain an important problem in the developing world. Current treatment of secretory diarrhea primarily involves supportive measures, such as fluid replacement. The calcium-sensing receptor (CaSR) regulates multiple biological activities in response to changes in extracellular Ca2+. The FDA-approved drug cinacalcet is an allosteric activator of CaSR used for treatment of hyperparathyroidism. Here, we found by short-circuit current measurements in human colonic T84 cells that CaSR activation by cinacalcet reduced forskolin-induced Cl- secretion by greater than 80%. Cinacalcet also reduced Cl- secretion induced by cholera toxin, heat-stable E. coli enterotoxin, and vasoactive intestinal peptide (VIP). The cinacalcet effect primarily involved indirect inhibition of cystic fibrosis transmembrane conductance regulator-mediated (CFTR-mediated) Cl- secretion following activation of CaSR and downstream phospholipase C and phosphodiesterases. In mice, cinacalcet reduced fluid accumulation by more than 60% in intestinal closed loop models of cholera and traveler's diarrhea. The cinacalcet effect involved both inhibition of CFTR-mediated secretion and stimulation of sodium-hydrogen exchanger 3-mediated absorption. These findings support the therapeutic utility of the safe and commonly used drug cinacalcet in CFTR-dependent secretory diarrheas, including cholera, traveler's diarrhea, and VIPoma.