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Li N, Zhang H, Wang S, Xu Y, Ying Y, Li J, Li X, Li M, Yang B. Urea transporter UT-A1 as a novel drug target for hyponatremia. FASEB J 2024; 38:e23760. [PMID: 38924449 DOI: 10.1096/fj.202400555rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 06/06/2024] [Accepted: 06/13/2024] [Indexed: 06/28/2024]
Abstract
Hyponatremia is the most common disorder of electrolyte imbalances. It is necessary to develop new type of diuretics to treat hyponatremia without losing electrolytes. Urea transporters (UT) play an important role in the urine concentrating process and have been proved as a novel diuretic target. In this study, rat and mouse syndromes of inappropriate antidiuretic hormone secretion (SIADH) models were constructed and analyzed to determine if UTs are a promising drug target for treating hyponatremia. Experimental results showed that 100 mg/kg UT inhibitor 25a significantly increased serum osmolality (from 249.83 ± 5.95 to 294.33 ± 3.90 mOsm/kg) and serum sodium (from 114 ± 2.07 to 136.67 ± 3.82 mmol/L) respectively in hyponatremia rats by diuresis. Serum chemical examination showed that 25a neither caused another electrolyte imbalance nor influenced the lipid metabolism. Using UT-A1 and UT-B knockout mouse SIADH model, it was found that serum osmolality and serum sodium were lowered much less in UT-A1 knockout mice than in UT-B knockout mice, which suggest UT-A1 is a better therapeutic target than UT-B to treat hyponatremia. This study provides a proof of concept that UT-A1 is a diuretic target for SIADH-induced hyponatremia and UT-A1 inhibitors might be developed into new diuretics to treat hyponatremia.
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Affiliation(s)
- Nannan Li
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Hang Zhang
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Shuyuan Wang
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yue Xu
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, Ohio, USA
| | - Yi Ying
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Jing Li
- The State Key Laboratory of Anti-Infective Drug Development, Sunshine Lake Pharma Co., Ltd., Dongguan, China
| | - Xiaowei Li
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Min Li
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Baoxue Yang
- State Key Laboratory of Vascular Homeostasis and Remodeling, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
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Bankir L, Crambert G, Vargas-Poussou R. The SLC6A18 Transporter Is Most Likely a Na-Dependent Glycine/Urea Antiporter Responsible for Urea Secretion in the Proximal Straight Tubule: Influence of This Urea Secretion on Glomerular Filtration Rate. Nephron Clin Pract 2024:1-27. [PMID: 38824912 DOI: 10.1159/000539602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Accepted: 05/25/2024] [Indexed: 06/04/2024] Open
Abstract
BACKGROUND Urea is the major end-product of protein metabolism in mammals. In carnivores and omnivores, a large load of urea is excreted daily in urine, with a concentration that is 30-100 times above that in plasma. This is important for the sake of water economy. Too little attention has been given to the existence of energy-dependent urea transport that plays an important role in this concentrating activity. SUMMARY This review first presents functional evidence for an energy-dependent urea secretion that occurs exclusively in the straight part of the proximal tubule (PST). Second, it proposes a candidate transmembrane transporter responsible for this urea secretion in the PST. SLC6A18 is expressed exclusively in the PST and has been identified as a glycine transporter, based on findings in SLC6A18 knockout mice. We propose that it is actually a glycine/urea antiport, secreting urea into the lumen in exchange for glycine and Na. Glycine is most likely recycled back into the cell via a transporter located in the brush border. Urea secretion in the PST modifies the composition of the tubular fluid in the thick ascending limb and, thus, contributes, indirectly, to influence the "signal" at the macula densa that plays a crucial role in the regulation of the glomerular filtration rate (GFR) by the tubulo-glomerular feedback. KEY MESSAGES Taking into account this secondary active secretion of urea in the mammalian kidney provides a new understanding of the influence of protein intake on GFR, of the regulation of urea excretion, and of the urine-concentrating mechanism.
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Affiliation(s)
- Lise Bankir
- Laboratoire de Physiologie Rénale et Tubulopathies, Centre de Recherche des Cordeliers, INSERM UMRS 1138, Sorbonne Université, Université Paris Cité, Paris, France
- CNRS EMR 8228, Unité Métabolisme et Physiologie Rénale, Centre de Recherche des Cordeliers, Paris, France
| | - Gilles Crambert
- Laboratoire de Physiologie Rénale et Tubulopathies, Centre de Recherche des Cordeliers, INSERM UMRS 1138, Sorbonne Université, Université Paris Cité, Paris, France
- CNRS EMR 8228, Unité Métabolisme et Physiologie Rénale, Centre de Recherche des Cordeliers, Paris, France
| | - Rosa Vargas-Poussou
- CNRS EMR 8228, Unité Métabolisme et Physiologie Rénale, Centre de Recherche des Cordeliers, Paris, France
- Service de Médecine Génomique des Maladies Rares, Assistance Publique-Hôpitaux de Paris, Université Paris Cité, Paris, France
- Centre de Référence des Maladies Rénales Héréditaires de l'Enfant et de l'Adulte, MARHEA, Hôpital Européen Georges Pompidou, Paris, France
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Ying Y, Li N, Wang S, Zhang H, Zuo Y, Tang Y, Qiao P, Quan Y, Li M, Yang B. Urea Transporter Inhibitor 25a Reduces Ascites in Cirrhotic Rats. Biomedicines 2023; 11:biomedicines11020607. [PMID: 36831143 PMCID: PMC9953117 DOI: 10.3390/biomedicines11020607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 02/03/2023] [Accepted: 02/15/2023] [Indexed: 02/22/2023] Open
Abstract
Ascites is a typical symptom of liver cirrhosis that is caused by a variety of liver diseases. Ascites severely affects the life quality of patients and needs long-term treatment. 25a is a specific urea transporter inhibitor with a diuretic effect that does not disturb the electrolyte balance. In this study, we aimed to determine the therapeutic effect of 25a on ascites with a dimethylnitrosamine (DMN)-induced cirrhotic rat model. It was found that 100 mg/kg of 25a significantly increased the daily urine output by 60% to 97% and reduced the daily abdominal circumference change by 220% to 260% in cirrhotic rats with a water intake limitation. The 25a treatment kept the serum electrolyte levels within normal ranges in cirrhotic rats. The H&E and Masson staining of liver tissue showed that 25a did not change the cirrhotic degree. A serum biochemical examination showed that 25a did not improve the liver function in cirrhotic rats. A Western blot analysis showed that 25a did not change the expression of fibrosis-related marker protein α-SMA, but significantly decreased the expressions of type I collagen in the liver of cirrhotic rats, indicating that 25a did not reverse cirrhosis, but could slow the cirrhotic progression. These data indicated that 25a significantly reduced ascites via diuresis without an electrolyte imbalance in cirrhotic rats. Our study provides a proof of concept that urea transporter inhibitors might be developed as novel diuretics to treat cirrhotic ascites.
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Affiliation(s)
- Yi Ying
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Nannan Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Shuyuan Wang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Hang Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Yinglin Zuo
- The State Key Laboratory of Anti-Infective Drug Development, Sunshine Lake Pharma Co., Ltd., Dongguan 523871, China
| | - Yiwen Tang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Panshuang Qiao
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Yazhu Quan
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Min Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
| | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing 100191, China
- Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing 100191, China
- Correspondence:
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4
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Zhang S, Zhao Y, Wang S, Li M, Xu Y, Ran J, Geng X, He J, Meng J, Shao G, Zhou H, Ge Z, Chen G, Li R, Yang B. Discovery of novel diarylamides as orally active diuretics targeting urea transporters. Acta Pharm Sin B 2021; 11:181-202. [PMID: 33532188 PMCID: PMC7838058 DOI: 10.1016/j.apsb.2020.06.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Revised: 05/14/2020] [Accepted: 05/26/2020] [Indexed: 12/17/2022] Open
Abstract
Urea transporters (UT) play a vital role in the mechanism of urine concentration and are recognized as novel targets for the development of salt-sparing diuretics. Thus, UT inhibitors are promising for development as novel diuretics. In the present study, a novel UT inhibitor with a diarylamide scaffold was discovered by high-throughput screening. Optimization of the inhibitor led to the identification of a promising preclinical candidate, N-[4-(acetylamino)phenyl]-5-nitrofuran-2-carboxamide (1H), with excellent in vitro UT inhibitory activity at the submicromolar level. The half maximal inhibitory concentrations of 1H against UT-B in mouse, rat, and human erythrocyte were 1.60, 0.64, and 0.13 μmol/L, respectively. Further investigation suggested that 8 μmol/L 1H more powerfully inhibited UT-A1 at a rate of 86.8% than UT-B at a rate of 73.9% in MDCK cell models. Most interestingly, we found for the first time that oral administration of 1H at a dose of 100 mg/kg showed superior diuretic effect in vivo without causing electrolyte imbalance in rats. Additionally, 1H did not exhibit apparent toxicity in vivo and in vitro, and possessed favorable pharmacokinetic characteristics. 1H shows promise as a novel diuretic to treat hyponatremia accompanied with volume expansion and may cause few side effects.
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Key Words
- AQP1, aquaporin 1
- BCRP, breast cancer resistance protein
- CCK-8, cell counting kit-8
- CMC-Na, carboxymethylcellulose sodium
- DMF, N,N-dimethylformamide
- Diuretic
- Fa, fraction absorbance
- GFR, glomerular filtration rate
- HDL-C and LDL-C, high- and low-density lipoprotein
- IC50, half maximal inhibitory concentration
- IMCD, inner medulla collecting duct
- Oral administration
- P-gp, P-glycoprotein
- PBS, phosphate buffered saline
- Papp, apparent permeability
- Structure optimization
- THF, tetrahydrofuran
- UT, urea transporter
- Urea transporter inhibitor
- r.t., room temperature
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Kabutomori J, Pina-Lopes N, Musa-Aziz R. Water transport mediated by murine urea transporters: implications for urine concentration mechanisms. Biol Open 2020; 9:bio051805. [PMID: 32661130 PMCID: PMC7438002 DOI: 10.1242/bio.051805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 06/30/2020] [Indexed: 12/01/2022] Open
Abstract
Urea transporters (UTs) facilitate urea diffusion across cell membranes and play an important role in the urinary concentration mechanisms in the kidney. Herein, we injected cRNAs encoding for c-Myc-tagged murine UT-B, UT-A2 or UT-A3 (versus water-injected control) in Lithobates oocytes and evaluated oocyte surface protein expression with biotinylation and immunoblotting, urea uptake using [14C] counts and water permeability (P f ) by video microscopy. Immunoblots of UT-injected oocyte membranes revealed bands with a molecular weight consistent with that of a UT monomer (34 kDa), and UT-injected oocytes displayed significantly increased and phloretin-sensitive urea uptake and P f when compared to day-matched control oocytes. Subtracting the water-injected urea uptake or P f values from those of UT-injected oocytes yielded UT-dependent values*. We demonstrate for the first time that UT-A2 and UT-A3 can transport water, and we confirm that UT-B is permeable to water. Moreover, the [14C] urea*/P f * ratios fell in the sequence mUT-B>mUT-A2>mUT-A3, indicating that UTs can exhibit selectivity to urea and/or water. It is likely that specific kidney regions with high levels of UTs will exhibit increased urea and/or water permeabilities, directly influencing urine concentration. Furthermore, UT-mediated water transport activity must be considered when developing UT-inhibitors as novel diuretics.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- J Kabutomori
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil 05508-900
| | - N Pina-Lopes
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil 05508-900
| | - R Musa-Aziz
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil 05508-900
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Geng X, Zhang S, He J, Ma A, Li Y, Li M, Zhou H, Chen G, Yang B. The urea transporter UT-A1 plays a predominant role in a urea-dependent urine-concentrating mechanism. J Biol Chem 2020; 295:9893-9900. [PMID: 32461256 PMCID: PMC7380188 DOI: 10.1074/jbc.ra120.013628] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 05/22/2020] [Indexed: 12/12/2022] Open
Abstract
Urea transporters are a family of urea-selective channel proteins expressed in multiple tissues that play an important role in the urine-concentrating mechanism of the mammalian kidney. Previous studies have shown that knockout of urea transporter (UT)-B, UT-A1/A3, or all UTs leads to urea-selective diuresis, indicating that urea transporters have important roles in urine concentration. Here, we sought to determine the role of UT-A1 in the urine-concentrating mechanism in a newly developed UT-A1-knockout mouse model. Phenotypically, daily urine output in UT-A1-knockout mice was nearly 3-fold that of WT mice and 82% of all-UT-knockout mice, and the UT-A1-knockout mice had significantly lower urine osmolality than WT mice. After 24-h water restriction, acute urea loading, or high-protein (40%) intake, UT-A1-knockout mice were unable to increase urine-concentrating ability. Compared with all-UT-knockout mice, the UT-A1-knockout mice exhibited similarly elevated daily urine output and decreased urine osmolality, indicating impaired urea-selective urine concentration. Our experimental findings reveal that UT-A1 has a predominant role in urea-dependent urine-concentrating mechanisms, suggesting that UT-A1 represents a promising diuretic target.
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Affiliation(s)
- Xiaoqiang Geng
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Shun Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Jinzhao He
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Ang Ma
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yingjie Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Min Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Hong Zhou
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Guangping Chen
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Baoxue Yang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
- Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing, China
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7
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Li M, Zhao Y, Zhang S, Xu Y, Wang SY, Li BW, Ran JH, Li RT, Yang BX. A thienopyridine, CB-20, exerts diuretic activity by inhibiting urea transporters. Acta Pharmacol Sin 2020; 41:65-72. [PMID: 31213671 PMCID: PMC7468274 DOI: 10.1038/s41401-019-0245-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/28/2019] [Indexed: 01/08/2023] Open
Abstract
Urea transporters (UTs) are transmembrane proteins selectively permeable to urea and play an important role in urine concentration. UT-knockout mice exhibit the urea-selective urine-concentrating defect, without affecting electrolyte balance, suggesting that UT-B inhibitors have the potential to be developed as novel diuretics. In this study, we characterized a novel compound 5-ethyl-2-methyl-3-amino-6-methylthieno[2,3-b]pyridine-2,5-dicarboxylate (CB-20) with UT inhibitory activity as novel diuretics with excellent pharmacological properties. This compound was discovered based on high-throughput virtual screening combined with the erythrocyte osmotic lysis assay. Selectivity of UT inhibitors was assayed using transwell chambers. Diuretic activity of the compound was examined in rats and mice using metabolic cages. Pharmacokinetic parameters were detected in rats using LC-MS/MS. Molecular docking was employed to predict the potential binding modes for the CB-20 with human UT-B. This compound dose-dependently inhibited UT-facilitated urea transport with IC50 values at low micromolar levels. It exhibited nearly equal inhibitory activity on both UT-A1 and UT-B. After subcutaneous administration of CB-20, the animals showed polyuria, without electrolyte imbalance and abnormal metabolism. CB-20 possessed a good absorption and rapid clearance in rat plasma. Administration of CB-20 for 5 days did not cause significant morphological abnormality in kidney or liver tissues of rats. Molecular docking showed that CB-20 was positioned near several residues in human UT-B, including Leu364, Val367, and so on. This study provides proof of evidence for the prominent diuretic activity of CB-20 by specifically inhibiting UTs. CB-20 or thienopyridine analogs may be developed as novel diuretics.
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Affiliation(s)
- Min Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Yan Zhao
- State Key Laboratory of Natural and Biomimetic Drugs, School of pharmaceutical Sciences, Peking University, Beijing, 100191, China
- College of Pharmacy, Inner Mongolia Medical University, Hohhot, 010110, China
| | - Shun Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Yue Xu
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Shu-Yuan Wang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Bo-Wen Li
- State Key Laboratory of Natural and Biomimetic Drugs, School of pharmaceutical Sciences, Peking University, Beijing, 100191, China
| | - Jian-Hua Ran
- Chongqing Medical University, Chongqing, 400016, China
| | - Run-Tao Li
- State Key Laboratory of Natural and Biomimetic Drugs, School of pharmaceutical Sciences, Peking University, Beijing, 100191, China.
| | - Bao-Xue Yang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China.
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9
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Nawata CM, Pannabecker TL. Mammalian urine concentration: a review of renal medullary architecture and membrane transporters. J Comp Physiol B 2018; 188:899-918. [PMID: 29797052 PMCID: PMC6186196 DOI: 10.1007/s00360-018-1164-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 04/23/2018] [Accepted: 05/14/2018] [Indexed: 01/10/2023]
Abstract
Mammalian kidneys play an essential role in balancing internal water and salt concentrations. When water needs to be conserved, the renal medulla produces concentrated urine. Central to this process of urine concentration is an osmotic gradient that increases from the corticomedullary boundary to the inner medullary tip. How this gradient is generated and maintained has been the subject of study since the 1940s. While it is generally accepted that the outer medulla contributes to the gradient by means of an active process involving countercurrent multiplication, the source of the gradient in the inner medulla is unclear. The last two decades have witnessed advances in our understanding of the urine-concentrating mechanism. Details of medullary architecture and permeability properties of the tubules and vessels suggest that the functional and anatomic relationships of these structures may contribute to the osmotic gradient necessary to concentrate urine. Additionally, we are learning more about the membrane transporters involved and their regulatory mechanisms. The role of medullary architecture and membrane transporters in the mammalian urine-concentrating mechanism are the focus of this review.
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Affiliation(s)
- C Michele Nawata
- Department of Physiology, Banner University Medical Center, University of Arizona, 1501 N. Campbell Avenue, Tucson, AZ, 85724-5051, USA.
| | - Thomas L Pannabecker
- Department of Physiology, Banner University Medical Center, University of Arizona, 1501 N. Campbell Avenue, Tucson, AZ, 85724-5051, USA
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10
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Pharmacokinetics, Tissue Distribution and Excretion of a Novel Diuretic (PU-48) in Rats. Pharmaceutics 2018; 10:pharmaceutics10030124. [PMID: 30096833 PMCID: PMC6160999 DOI: 10.3390/pharmaceutics10030124] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 07/21/2018] [Accepted: 07/27/2018] [Indexed: 01/02/2023] Open
Abstract
Methyl 3-amino-6-methoxythieno [2,3-b] quinoline-2-carboxylate (PU-48) is a novel diuretic urea transporter inhibitor. The aim of this study is to investigate the profile of plasma pharmacokinetics, tissue distribution, and excretion by oral dosing of PU-48 in rats. Concentrations of PU-48 within biological samples are determined using a validated high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. After oral administration of PU-48 (3, 6, and 12 mg/kg, respectively) in self-nanomicroemulsifying drug delivery system (SNEDDS) formulation, the peak plasma concentrations (Cmax), and the area under the curve (AUC0⁻∞) were increased by the dose-dependent and linear manner, but the marked different of plasma half-life (t1/2) were not observed. This suggests that the pharmacokinetic profile of PU-48 prototype was first-order elimination kinetic characteristics within the oral three doses range in rat plasma. Moreover, the prototype of PU-48 was rapidly and extensively distributed into thirteen tissues, especially higher concentrations were detected in stomach, intestine, liver, kidney, and bladder. The total accumulative excretion of PU-48 in the urine, feces, and bile was less than 2%. This research is the first report on disposition via oral administration of PU-48 in rats, and it provides important information for further development of PU-48 as a diuretic drug candidate.
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11
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Zhang ZY, Wang X, Liu D, Zhang H, Zhang Q, Lu YY, Li P, Lou YQ, Yang BX, Lu C, Lou YX, Zhang GL. Development and validation of an LC-MS/MS method for the determination of a novel thienoquinolin urea transporter inhibitor PU-48 in rat plasma and its application to a pharmacokinetic study. Biomed Chromatogr 2018; 32. [PMID: 29193233 DOI: 10.1002/bmc.4157] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 10/05/2017] [Accepted: 11/20/2017] [Indexed: 01/25/2023]
Abstract
A specific, sensitive and stable high-performance liquid chromatographic-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantitative determination of methyl 3-amino-6-methoxythieno [2,3-b]quinoline-2-carboxylate (PU-48), a novel diuretic thienoquinolin urea transporter inhibitor in rat plasma. In this method, the chromatographic separation of PU-48 was achieved with a reversed-phase C18 column (100 × 2.1 mm, 3 μm) at 35°C. The mobile phase consisted of acetonitrile and water with 0.05% formic acid added with a gradient elution at flow rate of 0.3 mL/min. Samples were detected with the triple-quadrupole tandem mass spectrometer with multiple reaction monitoring mode via electrospray ionization source in positive mode. The retention time were 6.2 min for PU-48 and 7.2 min for megestrol acetate (internal standard, IS). The monitored ion transitions were mass-to-charge ratio (m/z) 289.1 → 229.2 for PU-48 and m/z 385.3 → 267.1 for the internal standard. The calibration curve for PU-48 was linear over the concentration range of 0.1-1000 ng/mL (r2 > 0.99), and the lower limit of quantitation was 0.1 ng/mL. The precision, accuracy and stability of the method were validated adequately. The developed and validated method was successfully applied to the pharmacokinetic study of PU-48 in rats.
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Affiliation(s)
- Zhi-Yuan Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Xin Wang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Dan Liu
- Proteomics Laboratory, Medical and Health Analysis Center, Peking University, Beijing, China
| | - Hua Zhang
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Peking University, Beijing, China
| | - Qiang Zhang
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Peking University, Beijing, China
| | - Ying-Yuan Lu
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Pu Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Ya-Qing Lou
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Bao-Xue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Chuang Lu
- Department of Drug Metabolism and Pharmacokinetics, Biogen, Cambridge, Massachusetts, USA
| | - Ya-Xin Lou
- Proteomics Laboratory, Medical and Health Analysis Center, Peking University, Beijing, China
| | - Guo-Liang Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
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12
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Cheng CJ, Rodan AR, Huang CL. Emerging Targets of Diuretic Therapy. Clin Pharmacol Ther 2017; 102:420-435. [PMID: 28560800 DOI: 10.1002/cpt.754] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 05/15/2017] [Accepted: 05/21/2017] [Indexed: 12/14/2022]
Abstract
Diuretics are commonly prescribed for treatment in patients with hypertension, edema, or heart failure. Studies on hypertensive and salt-losing disorders and on urea transporters have contributed to better understanding of mechanisms of renal salt and water reabsorption and their regulation. Proteins involved in the regulatory pathways are emerging targets for diuretic and aquaretic therapy. Integrative high-throughput screening, protein structure analysis, and chemical modification have identified promising agents for preclinical testing in animals. These include WNK-SPAK inhibitors, ClC-K channel antagonists, ROMK channel antagonists, and pendrin and urea transporter inhibitors. We discuss the potential advantages and side effects of these potential diuretics.
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Affiliation(s)
- C-J Cheng
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, 114, Taiwan
| | - A R Rodan
- Department of Medicine, Division of Nephrology, University of Utah, Salt Lake City, Utah, USA
| | - C-L Huang
- Department of Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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13
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Jiang T, Li Y, Layton AT, Wang W, Sun Y, Li M, Zhou H, Yang B. Generation and phenotypic analysis of mice lacking all urea transporters. Kidney Int 2017; 91:338-351. [PMID: 27914708 PMCID: PMC5423716 DOI: 10.1016/j.kint.2016.09.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 08/30/2016] [Accepted: 09/08/2016] [Indexed: 01/22/2023]
Abstract
Urea transporters (UT) are a family of transmembrane urea-selective channel proteins expressed in multiple tissues and play an important role in the urine concentrating mechanism of the mammalian kidney. UT inhibitors have diuretic activity and could be developed as novel diuretics. To determine if functional deficiency of all UTs in all tissues causes physiological abnormality, we established a novel mouse model in which all UTs were knocked out by deleting an 87 kb of DNA fragment containing most parts of Slc14a1 and Slc14a2 genes. Western blot analysis and immunofluorescence confirmed that there is no expression of urea transporter in these all-UT-knockout mice. Daily urine output was nearly 3.5-fold higher, with significantly lower urine osmolality in all-UT-knockout mice than that in wild-type mice. All-UT-knockout mice were not able to increase urinary urea concentration and osmolality after water deprivation, acute urea loading, or high protein intake. A computational model that simulated UT-knockout mouse models identified the individual contribution of each UT in urine concentrating mechanism. Knocking out all UTs also decreased the blood pressure and promoted the maturation of the male reproductive system. Thus, functional deficiency of all UTs caused a urea-selective urine-concentrating defect with little physiological abnormality in extrarenal organs.
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Affiliation(s)
- Tao Jiang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yingjie Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Anita T Layton
- Department of Mathematics, Duke University, Durham, North Carolina, USA
| | - Weiling Wang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yi Sun
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Min Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Hong Zhou
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Baoxue Yang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China; Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing, China.
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14
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Abstract
PURPOSE OF REVIEW Urea is transported by urea transporter proteins in kidney, erythrocytes, and other tissues. Mice in which different urea transporters have been knocked out have urine-concentrating defects, which has led to the development and testing of urea transporters Slc14A2 (UT-A) and Slc14A1 (UT-B) inhibitors as urearetics. This review summarizes the knowledge gained during the past year on urea transporter regulation and investigations into the clinical potential of urearetics. RECENT FINDINGS UT-A1 undergoes several posttranslational modifications that increase its function by increasing UT-A1 accumulation in the apical plasma membrane. UT-A1 is phosphorylated by protein kinase A, exchange protein activated by cyclic AMP, protein kinase Cα, and AMP-activated protein kinase, all at different serine residues. UT-A1 is also regulated by 14-3-3, which contributes to UT-A1 removal from the membrane. UT-A1 is glycosylated with various glycan moieties in animal models of diabetes mellitus. Transgenic expression of UT-A1 into UT-A1/UT-A3 knockout mice restores urine-concentrating ability. UT-B is present in descending vasa recta and urinary bladder, and is linked to bladder cancer. Inhibitors of UT-A and UT-B have been developed that result in diuresis with fewer abnormalities in serum electrolytes than conventional diuretics. SUMMARY Urea transporters play critical roles in the urine-concentrating mechanism. Urea transport inhibitors are a promising new class of diuretic agent.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA
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15
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Klein JD, Wang Y, Mistry A, LaRocque LM, Molina PA, Rogers RT, Blount MA, Sands JM. Transgenic Restoration of Urea Transporter A1 Confers Maximal Urinary Concentration in the Absence of Urea Transporter A3. J Am Soc Nephrol 2016; 27:1448-55. [PMID: 26407594 PMCID: PMC4849813 DOI: 10.1681/asn.2014121267] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Accepted: 08/09/2015] [Indexed: 11/03/2022] Open
Abstract
Urea has a critical role in urinary concentration. Mice lacking the inner medullary collecting duct (IMCD) urea transporter A1 (UT-A1) and urea transporter A3 (UT-A3) have very low levels of urea permeability and are unable to concentrate urine. To investigate the role of UT-A1 in the concentration of urine, we transgenically expressed UT-A1 in knockout mice lacking UT-A1 and UT-A3 using a construct with a UT-A1 gene that cannot be spliced to produce UT-A3. This construct was inserted behind the original UT-A promoter to yield a mouse expressing only UT-A1 (UT-A1(+/+)/UT-A3(-/-)). Western blot analysis demonstrated UT-A1 in the inner medulla of UT-A1(+/+)/UT-A3(-/-) and wild-type mice, but not in UT-A1/UT-A3 knockout mice, and an absence of UT-A3 in UT-A1(+/+)/UT-A3(-/-) and UT-A1/UT-A3 knockout mice. Immunohistochemistry in UT-A1(+/+)/UT-A3(-/-) mice also showed negative UT-A3 staining in kidney and other tissues and positive UT-A1 staining only in the IMCD. Urea permeability in isolated perfused IMCDs showed basal permeability in the UT-A1(+/+)/UT-A3(-/-) mice was similar to levels in wild-type mice, but vasopressin stimulation of urea permeability in wild-type mice was significantly greater (100% increase) than in UT-A1(+/+)/UT-A3(-/-) mice (8% increase). Notably, basal urine osmolalities in both wild-type and UT-A1(+/+)/UT-A3(-/-) mice increased upon overnight water restriction. We conclude that transgenic expression of UT-A1 restores basal urea permeability to the level in wild-type mice but does not restore vasopressin-stimulated levels of urea permeability. This information suggests that transgenic expression of UT-A1 alone in mice lacking UT-A1 and UT-A3 is sufficient to restore urine-concentrating ability.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia
| | | | | | | | | | | | - Mitsi A Blount
- Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia
| | - Jeff M Sands
- Renal Division, Department of Medicine, and Department of Physiology, Emory University, Atlanta, Georgia
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16
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Song W, Qi X, Zhang W, Zhao CY, Cao Y, Wang F, Yang C. Abnormal Expression of Urea Transporter Protein in a Rat Model of Hepatorenal Syndrome Induced by Succinylated Gelatin. Med Sci Monit 2015; 21:2905-11. [PMID: 26414230 PMCID: PMC4591985 DOI: 10.12659/msm.894232] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 05/25/2015] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Hepatorenal syndrome (HRS) is a serious complication of advanced chronic liver disease. Abdominal compartment syndrome (ACS) occurs with dysfunction of multiple organs when abdominal pressure increases. Here, we report on a novel model of ACS with ascites and a model of HRS in rats to observe the urea transporter protein (UT) expression in the 2 models. MATERIAL AND METHODS A liver cirrhosis model was induced by CCl4. After changes of liver histopathology were observed, rats were injected intraperitoneally with succinylated gelatin to establish a model of ACS and HRS. Then, changes in BUN, Cr, and renal histopathology were detected. Moreover, the UT in ACS and HRS were also quantified. RESULTS The surfaces of liver in the cirrhotic group became coarse, with visible small nodules and became yellow and greasy. The normal structure of the hepatic lobules were destroyed, and hyperplasia of fibrotic tissue and pseudo-lobe was observed. The levels of BUN and Cr were significantly increased in rats suffering from ACS and HRS, respectively, compared to their control groups. In addition, the mRNA levels of UT-A2 and UT-A3 decreased in rats with HRS compared to cirrhotic rats. However, there was no significant difference between the mRNA levels of UT-A2, UT-A3, and UT-B in rats with ACS vs. normal rats. CONCLUSIONS It is feasible to model ACS in rats by injecting succinylated gelatin into the abdominal cavity. Increasing the intra-abdominal pressure by succinylated gelatin is also a novel approach for modeling HRS in cirrhotic rats. Compared with control rats, there is an abnormal mRNA expression of UT in ACS rats and HRS rats.
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Affiliation(s)
- Weiping Song
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
| | - Xiaolong Qi
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
| | - Wenhui Zhang
- Liver Cirrhosis Diagnosis and Therapeutic Center, 302 Hospital of the People’s Liberation Army, Beijing, P.R. China
| | - C Yingying Zhao
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
| | - Yan Cao
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
| | - Fei Wang
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
| | - Changqing Yang
- Division of Gastroenterology and Hepatology, Institute of Digestive Disease, Tongji Hospital, Tongji University School of Medicine, Shanghai, P.R. China
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Guo L, Meng J, Xuan C, Ge J, Sun W, O'Rourke ST, Sun C. High salt-diet reduces SLC14A1 gene expression in the choroid plexus of Dahl salt sensitive rats. Biochem Biophys Res Commun 2015; 461:254-9. [PMID: 25869070 PMCID: PMC4428960 DOI: 10.1016/j.bbrc.2015.04.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 04/02/2015] [Indexed: 01/11/2023]
Abstract
Elevated Na(+) concentration ([Na(+)]) in the cerebrospinal fluid (CSF) contributes to the development of salt-sensitive hypertension. CSF is formed by the choroid plexus (CP) in cerebral ventricles, and [Na(+)] in CSF is controlled by transporters in CP. Here, we examined the effect of high salt diet on the expression of urea transporters (UTs) in the CP of Dahl S vs Dahl R rats using real time PCR. High salt intake (8%, for 2 weeks) did not alter the mRNA levels of UT-A (encoded by SLC14A2 gene) in the CP of either Dahl S or Dahl R rats. In contrast, the mRNA levels of UT-B (encoded by SLC14A1 gene) were significantly reduced in the CP of Dahl S rats on high salt diet as compared with Dahl R rats or Dahl S rats on normal salt diet. Reduced UT-B expression was associated with increased [Na(+)] in the CSF and elevated mean arterial pressure (MAP) in Dahl S rats treated with high salt diet, as measured by radiotelemetry. High salt diet-induced reduction in UT-B protein expression in the CP of Dahl S rats was confirmed by Western blot. Immunohistochemistry using UT-B specific antibodies demonstrated that UT-B protein was expressed on the epithelial cells in the CP. These data indicate that high salt diet induces elevations in CSF [Na(+)] and in MAP, both of which are associated with reduced UT-B expression in the CP of Dahl S rats, as compared with Dahl R rats. The results suggest that altered UT-B expression in the CP may contribute to an imbalance of water and electrolytes in the CSF of Dahl S rats on high salt diet, thereby leading to alterations in MAP.
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Affiliation(s)
- Lirong Guo
- Department of Pathophysiology, College of Basic Medical Sciences, and Second Hospital of Jilin University, Jilin University, Changchun, Jilin 130021, China; Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA.
| | - Jie Meng
- Department of Pathophysiology, College of Basic Medical Sciences, and Second Hospital of Jilin University, Jilin University, Changchun, Jilin 130021, China
| | - Chengluan Xuan
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA
| | - Jingyan Ge
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA
| | - Wenzhu Sun
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA
| | - Stephen T O'Rourke
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA
| | - Chengwen Sun
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, ND 58105, USA.
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18
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Esteva-Font C, Anderson MO, Verkman AS. Urea transporter proteins as targets for small-molecule diuretics. Nat Rev Nephrol 2015; 11:113-23. [PMID: 25488859 PMCID: PMC4743986 DOI: 10.1038/nrneph.2014.219] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Conventional diuretics such as furosemide and thiazides target salt transporters in kidney tubules, but urea transporters (UTs) have emerged as alternative targets. UTs are a family of transmembrane channels expressed in a variety of mammalian tissues, in particular the kidney. UT knockout mice and humans with UT mutations exhibit reduced maximal urinary osmolality, demonstrating that UTs are necessary for the concentration of urine. Small-molecule screening has identified potent and selective inhibitors of UT-A, the UT protein expressed in renal tubule epithelial cells, and UT-B, the UT protein expressed in vasa recta endothelial cells. Data from UT knockout mice and from rodents administered UT inhibitors support the diuretic action of UT inhibition. The kidney-specific expression of UT-A1, together with high selectivity of the small-molecule inhibitors, means that off-target effects of such small-molecule drugs should be minimal. This Review summarizes the structure, expression and function of UTs, and looks at the evidence supporting the validity of UTs as targets for the development of salt-sparing diuretics with a unique mechanism of action. UT-targeted inhibitors may be useful alone or in combination with conventional diuretics for therapy of various oedemas and hyponatraemias, potentially including those refractory to treatment with current diuretics.
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Affiliation(s)
- Cristina Esteva-Font
- Departments of Medicine and Physiology, University of California, 513 Parnassus Avenue, San Francisco, CA 94143, USA
| | - Marc O Anderson
- Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA
| | - Alan S Verkman
- Departments of Medicine and Physiology, University of California, 513 Parnassus Avenue, San Francisco, CA 94143, USA
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19
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Hyodo S, Kakumura K, Takagi W, Hasegawa K, Yamaguchi Y. Morphological and functional characteristics of the kidney of cartilaginous fishes: with special reference to urea reabsorption. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1381-95. [PMID: 25339681 DOI: 10.1152/ajpregu.00033.2014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
For adaptation to high-salinity marine environments, cartilaginous fishes (sharks, skates, rays, and chimaeras) adopt a unique urea-based osmoregulation strategy. Their kidneys reabsorb nearly all filtered urea from the primary urine, and this is an essential component of urea retention in their body fluid. Anatomical investigations have revealed the extraordinarily elaborate nephron system in the kidney of cartilaginous fishes, e.g., the four-loop configuration of each nephron, the occurrence of distinct sinus and bundle zones, and the sac-like peritubular sheath in the bundle zone, in which the nephron segments are arranged in a countercurrent fashion. These anatomical and morphological characteristics have been considered to be important for urea reabsorption; however, a mechanism for urea reabsorption is still largely unknown. This review focuses on recent progress in the identification and mapping of various pumps, channels, and transporters on the nephron segments in the kidney of cartilaginous fishes. The molecules include urea transporters, Na(+)/K(+)-ATPase, Na(+)-K(+)-Cl(-) cotransporters, and aquaporins, which most probably all contribute to the urea reabsorption process. Although research is still in progress, a possible model for urea reabsorption in the kidney of cartilaginous fishes is discussed based on the anatomical features of nephron segments and vascular systems and on the results of molecular mapping. The molecular anatomical approach thus provides a powerful tool for understanding the physiological processes that take place in the highly elaborate kidney of cartilaginous fishes.
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Affiliation(s)
- Susumu Hyodo
- Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kawshiwa, Chiba, Japan
| | - Keigo Kakumura
- Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kawshiwa, Chiba, Japan
| | - Wataru Takagi
- Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kawshiwa, Chiba, Japan
| | - Kumi Hasegawa
- Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kawshiwa, Chiba, Japan
| | - Yoko Yamaguchi
- Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, Kawshiwa, Chiba, Japan
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20
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Li C, Xue H, Lei Y, Zhu J, Yang B, Gai X. Clinical significance of the reduction of UT-B expression in urothelial carcinoma of the bladder. Pathol Res Pract 2014; 210:799-803. [PMID: 25445116 DOI: 10.1016/j.prp.2014.09.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 07/09/2014] [Accepted: 09/24/2014] [Indexed: 02/07/2023]
Abstract
Urea transporter B (UT-B) is a membrane protein and plays an important role in regulating urea concentration in bladder urothelial cells. It has been reported that UT-B gene mutations were related to bladder carcinogenesis, and UT-B deletion could induce DNA damage and apoptosis in bladder urothelium. However, the functions and clinical significance of UT-B in human bladder cancer remain unknown. The most common type of bladder cancer is urothelial carcinoma (UC). We hypothesized that UT-B expression was related to bladder UC progress. In this study, UT-B was detected using immunohistochemistry in 52 paraffin-embedded specimens of bladder UC and 10 normal urothelium specimens. The results showed that UT-B protein expression in UC tumor cells was significantly lower as compared with normal urothelial cells (P = 0.021). UT-B protein expression was significantly reduced with increasing histological grade (P = 0.010). UT-B protein expression in muscle-invasive stage was significantly lower than in non-muscle-invasive stage (P = 0.014). Taken together, our data suggest that the reduction or loss of UT-B expression may be related to the incidence, progression and invasiveness of bladder UC. UT-B may be a novel diagnostic or prognostic biomarker, as well as a potential therapeutic target in UC of the bladder.
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Affiliation(s)
- Chun Li
- Department of Immunology, School of Basic Medical Sciences, Beihua University, Jilin, China
| | - Haogang Xue
- Department of Immunology, School of Basic Medical Sciences, Beihua University, Jilin, China
| | - Yanming Lei
- Department of Pathology, The General Hospital of CNPC in Jilin, Jilin, China
| | - Jianqiang Zhu
- Department of Immunology, School of Basic Medical Sciences, Beihua University, Jilin, China
| | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, and State Key Laboratory of Natural and Biomimetic Drugs, Beijing, China
| | - Xiaodong Gai
- Department of Immunology, School of Basic Medical Sciences, Beihua University, Jilin, China.
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Ren H, Wang Y, Xing Y, Ran J, Liu M, Lei T, Zhou H, Li R, Sands JM, Yang B. Thienoquinolins exert diuresis by strongly inhibiting UT-A urea transporters. Am J Physiol Renal Physiol 2014; 307:F1363-72. [PMID: 25298523 DOI: 10.1152/ajprenal.00421.2014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Urea transporters (UT) play an important role in the urine concentration mechanism by mediating intrarenal urea recycling, suggesting that UT inhibitors could have therapeutic use as a novel class of diuretic. Recently, we found a thienoquinolin UT inhibitor, PU-14, that exhibited diuretic activity. The purpose of this study was to identify more potent UT inhibitors that strongly inhibit UT-A isoforms in the inner medullary collecting duct (IMCD). Efficient thienoquinolin UT inhibitors were identified by structure-activity relationship analysis. Urea transport inhibition activity was assayed in perfused rat terminal IMCDs. Diuretic activity of the compound was determined in rats and mice using metabolic cages. The results show that the compound PU-48 exhibited potent UT-A inhibition activity. The inhibition was 69.5% with an IC50 of 0.32 μM. PU-48 significantly inhibited urea transport in perfused rat terminal IMCDs. PU-48 caused significant diuresis in UT-B null mice, which indicates that UT-A is the target of PU-48. The diuresis caused by PU-48 did not change blood Na(+), K(+), or Cl(-) levels or nonurea solute excretion in rats and mice. No toxicity was detected in cells or animals treated with PU-48. The results indicate that thienoquinolin UT inhibitors induce a diuresis by inhibiting UT-A in the IMCD. This suggests that they may have the potential to be developed as a novel class of diuretics with fewer side effects than classical diuretics.
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Affiliation(s)
- Huiwen Ren
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yanhua Wang
- Renal Division, Departments of Medicine and Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Yongning Xing
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Jianhua Ran
- Department of Anatomy, Neuroscience Research Center, Basic Medical College, Chongqing Medical University, Chongqing, China; and
| | - Ming Liu
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Tianluo Lei
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Hong Zhou
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Runtao Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Jeff M Sands
- Renal Division, Departments of Medicine and Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Baoxue Yang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China; Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing, China
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22
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Esteva-Font C, Cil O, Phuan PW, Su T, Lee S, Anderson MO, Verkman AS. Diuresis and reduced urinary osmolality in rats produced by small-molecule UT-A-selective urea transport inhibitors. FASEB J 2014; 28:3878-90. [PMID: 24843071 PMCID: PMC4139901 DOI: 10.1096/fj.14-253872] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 05/05/2014] [Indexed: 11/11/2022]
Abstract
Urea transport (UT) proteins of the UT-A class are expressed in epithelial cells in kidney tubules, where they are required for the formation of a concentrated urine by countercurrent multiplication. Here, using a recently developed high-throughput assay to identify UT-A inhibitors, a screen of 50,000 synthetic small molecules identified UT-A inhibitors of aryl-thiazole, γ-sultambenzosulfonamide, aminocarbonitrile butene, and 4-isoxazolamide chemical classes. Structure-activity analysis identified compounds that inhibited UT-A selectively by a noncompetitive mechanism with IC50 down to ∼1 μM. Molecular modeling identified putative inhibitor binding sites on rat UT-A. To test compound efficacy in rats, formulations and administration procedures were established to give therapeutic inhibitor concentrations in blood and urine. We found that intravenous administration of an indole thiazole or a γ-sultambenzosulfonamide at 20 mg/kg increased urine output by 3-5-fold and reduced urine osmolality by ∼2-fold compared to vehicle control rats, even under conditions of maximum antidiuresis produced by 1-deamino-8-D-arginine vasopressin (DDAVP). The diuresis was reversible and showed urea > salt excretion. The results provide proof of concept for the diuretic action of UT-A-selective inhibitors. UT-A inhibitors are first in their class salt-sparing diuretics with potential clinical indications in volume-overload edemas and high-vasopressin-associated hyponatremias.
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Affiliation(s)
- Cristina Esteva-Font
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
| | - Onur Cil
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
| | - Puay-Wah Phuan
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
| | - Tao Su
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
| | - Sujin Lee
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
| | - Marc O Anderson
- Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, California, USA
| | - A S Verkman
- Department of Medicine and Department of Physiology, University of California, San Francisco, California, USA and
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23
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Pannabecker TL, Layton AT. Targeted delivery of solutes and oxygen in the renal medulla: role of microvessel architecture. Am J Physiol Renal Physiol 2014; 307:F649-55. [PMID: 25056344 DOI: 10.1152/ajprenal.00276.2014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Renal medullary function is characterized by corticopapillary concentration gradients of various molecules. One example is the generally decreasing axial gradient in oxygen tension (Po2). Another example, found in animals in the antidiuretic state, is a generally increasing axial solute gradient, consisting mostly of NaCl and urea. This osmolality gradient, which plays a principal role in the urine concentrating mechanism, is generally considered to involve countercurrent multiplication and countercurrent exchange, although the underlying mechanism is not fully understood. Radial oxygen and solute gradients in the transverse dimension of the medullary parenchyma have been hypothesized to occur, although strong experimental evidence in support of these gradients remains lacking. This review considers anatomic features of the renal medulla that may impact the formation and maintenance of oxygen and solute gradients. A better understanding of medullary architecture is essential for more clearly defining the compartment-to-compartment flows taken by fluid and molecules that are important in producing axial and radial gradients. Preferential interactions between nephron and vascular segments provide clues as to how tubular and interstitial oxygen flows contribute to safeguarding active transport pathways in renal function in health and disease.
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Affiliation(s)
- Thomas L Pannabecker
- Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona; and
| | - Anita T Layton
- Department of Mathematics, Duke University, Durham, North Carolina
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24
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Li M, Tou WI, Zhou H, Li F, Ren H, Chen CYC, Yang B. Developing hypothetical inhibition mechanism of novel urea transporter B inhibitor. Sci Rep 2014; 4:5775. [PMID: 25047372 PMCID: PMC5376056 DOI: 10.1038/srep05775] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Accepted: 06/27/2014] [Indexed: 02/03/2023] Open
Abstract
Urea transporter B (UT-B) is a membrane channel protein that specifically transports urea. UT-B null mouse exhibited urea selective urine concentrating ability deficiency, which suggests the potential clinical applications of the UT-B inhibitors as novel diuretics. Primary high-throughput virtual screening (HTVS) of 50000 small-molecular drug-like compounds identified 2319 hit compounds. These 2319 compounds were screened by high-throughput screening using an erythrocyte osmotic lysis assay. Based on the pharmacological data, putative UT-B binding sites were identified by structure-based drug design and validated by ligand-based and QSAR model. Additionally, UT-B structural and functional characteristics under inhibitors treated and untreated conditions were simulated by molecular dynamics (MD). As the result, we identified four classes of compounds with UT-B inhibitory activity and predicted a human UT-B model, based on which computative binding sites were identified and validated. A novel potential mechanism of UT-B inhibitory activity was discovered by comparing UT-B from different species. Results suggest residue PHE198 in rat and mouse UT-B might block the inhibitor migration pathway. Inhibitory mechanisms of UT-B inhibitors and the functions of key residues in UT-B were proposed. The binding site analysis provides a structural basis for lead identification and optimization of UT-B inhibitors.
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Affiliation(s)
- Min Li
- The State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
- These authors contributed equally to this work
| | - Weng Ieong Tou
- School of Medicine, College of Medicine, China Medical University, Taichung, 40402, Taiwan
- These authors contributed equally to this work
| | - Hong Zhou
- The State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Fei Li
- The State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
- School of Pharmaceutical Sciences, Hubei University of Medicine, Shiyan, 442000, China
| | - Huiwen Ren
- The State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - Calvin Yu-Chian Chen
- School of Medicine, College of Medicine, China Medical University, Taichung, 40402, Taiwan
- Human Genetic Center, Department of Medical Research, China Medical University Hospital, Taichung, Taiwan
- Department of Biomedical Informatics, Asia University, Taichung, 41354, Taiwan
- Research Center for Chinese Medicine & Acupuncture, China Medical University, Taichung 40402, Taiwan
| | - Baoxue Yang
- The State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
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25
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Abstract
The renal medulla produces concentrated urine through the generation of an osmotic gradient that progressively increases from the cortico-medullary boundary to the inner medullary tip. In the outer medulla, the osmolality gradient arises principally from vigorous active transport of NaCl, without accompanying water, from the thick ascending limbs of short- and long-looped nephrons. In the inner medulla, the source of the osmotic gradient has not been identified. Recently, there have been important advances in our understanding of key components of the urine-concentrating mechanism, including (a) better understanding of the regulation of water, urea, and sodium transport proteins; (b) better resolution of the anatomical relationships in the medulla; and (c) improvements in mathematical modeling of the urine-concentrating mechanism. Continued experimental investigation of signaling pathways regulating transepithelial transport, both in normal animals and in knockout mice, and incorporation of the resulting information into mathematical simulations may help to more fully elucidate the mechanism for concentrating urine in the inner medulla.
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Affiliation(s)
- Jeff M. Sands
- Renal Division, Department of Medicine, and Department of Physiology,Emory University School of Medicine, Atlanta, Georgia 30322
| | - Harold E. Layton
- Department of Mathematics, Duke University, Durham, North Carolina 27708-0320
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26
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Abstract
Urea transporter gene knockout mice have been created for the study of the urine-concentrating mechanism. The major findings in studies of the renal phenotype of these mice are as follows: (1) Urea accumulation in the inner medullary interstitium is dependent on intrarenal urea recycling mediated by urea transporters; (2) urea transporters are essential for preventing urea-induced osmotic diuresis and thus for water conservation; (3) NaCl concentration in the inner medullary interstitium is not significantly affected by the absence of IMCD, descending limb of Henle and descending vasa recta urea transporters. Studies in urea transporter knockout mouse models have highlighted the essential role of urea for producing maximally concentrated urine.
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Affiliation(s)
- Robert A Fenton
- Department of Biomedicine, Interpret Center, Aarhus University, Aarhus, Building 233/234, 8000, Aarhus, Denmark,
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27
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Verkman AS, Esteva-Font C, Cil O, Anderson MO, Li F, Li M, Lei T, Ren H, Yang B. Small-molecule inhibitors of urea transporters. Subcell Biochem 2014; 73:165-77. [PMID: 25298345 PMCID: PMC4306426 DOI: 10.1007/978-94-017-9343-8_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Urea transporter (UT) proteins, which include isoforms of UT-A in kidney tubule epithelia and UT-B in vasa recta endothelia and erythrocytes, facilitate urinary concentrating function. Inhibitors of urea transporter function have potential clinical applications as sodium-sparing diuretics, or 'urearetics,' in edema from different etiologies, such as congestive heart failure and cirrhosis, as well as in syndrome of inappropriate antidiuretic hormone (SIADH). High-throughput screening of drug-like small molecules has identified UT-A and UT-B inhibitors with nanomolar potency. Inhibitors have been identified with different UT-A versus UT-B selectivity profiles and putative binding sites on UT proteins. Studies in rodent models support the utility of UT inhibitors in reducing urinary concentration, though testing in clinically relevant animal models of edema has not yet been done.
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Affiliation(s)
- Alan S Verkman
- Departments of Medicine and Physiology, University of California, San Francisco, CA, 94143-0521, USA,
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28
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Esteva-Font C, Phuan PW, Anderson MO, Verkman AS. A small molecule screen identifies selective inhibitors of urea transporter UT-A. CHEMISTRY & BIOLOGY 2013; 20:1235-44. [PMID: 24055006 PMCID: PMC3890325 DOI: 10.1016/j.chembiol.2013.08.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2013] [Revised: 08/05/2013] [Accepted: 08/15/2013] [Indexed: 01/24/2023]
Abstract
Urea transporter (UT) proteins, including UT-A in kidney tubule epithelia and UT-B in vasa recta microvessels, facilitate urinary concentrating function. A screen for UT-A inhibitors was developed in MDCK cells expressing UT-A1, water channel aquaporin-1, and YFP-H148Q/V163S. An inwardly directed urea gradient produces cell shrinking followed by UT-A1-dependent swelling, which was monitored by YFP-H148Q/V163S fluorescence. Screening of ~90,000 synthetic small molecules yielded four classes of UT-A1 inhibitors with low micromolar half-maximal inhibitory concentration that fully and reversibly inhibited urea transport by a noncompetitive mechanism. Structure-activity analysis of >400 analogs revealed UT-A1-selective and UT-A1/UT-B nonselective inhibitors. Docking computations based on homology models of UT-A1 suggested inhibitor binding sites. UT-A inhibitors may be useful as diuretics ("urearetics") with a mechanism of action that may be effective in fluid-retaining conditions in which conventional salt transport-blocking diuretics have limited efficacy.
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Affiliation(s)
- Cristina Esteva-Font
- Departments of Medicine and Physiology, University of California, San Francisco, San Francisco, CA 94143-0521, USA
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29
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Layton AT, Bankir L. Impacts of Active Urea Secretion into Pars Recta on Urine Concentration and Urea Excretion Rate. Physiol Rep 2013; 1. [PMID: 24058732 PMCID: PMC3777697 DOI: 10.1002/phy2.34] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
It has been observed experimentally that early distal tubular urea flow exceeds urea delivery by the proximal convoluted tubule to the pars recta and loop of Henle. Moreover, the fractional excretion of urea in the urine may exceed values compatible with the reabsorption known to occur in the proximal convoluted tubule in the cortex. A likely explanation for these observations is that urea may be actively secreted into the pars recta, as proposed in a few studies. However, this hypothesis has yet to be demonstrated experimentally. In this study, we used a mathematical model of the renal medulla of the rat kidney to investigate the impacts of active urea secretion in the intrarenal handling of urea and in the urine concentrating ability. The model represents only the outer and inner medullary zones, with the actions taking place in the cortex incorporated via boundary conditions. Blood flow in the model vasculature is divided into plasma and red blood cell compartments. We compared urea flow rates and other related model variables without and with the hypothetical active urea secretion in the pars recta. The simulation suggests that active urea secretion induces a “urea-selective” improvement in urine concentrating ability by enhancing the efficiency of urea excretion without requiring a higher urine flow rate, and with only modest changes in the excretion of other solutes. These results should encourage experimental studies in order to assess the existence of an active urea secretion in the rodent kidney.
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Affiliation(s)
- Anita T Layton
- Department of Mathematics, Duke University, Durham, NC 27708-0320, USA
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30
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Li F, Lei T, Zhu J, Wang W, Sun Y, Chen J, Dong Z, Zhou H, Yang B. A novel small-molecule thienoquinolin urea transporter inhibitor acts as a potential diuretic. Kidney Int 2013; 83:1076-86. [PMID: 23486518 DOI: 10.1038/ki.2013.62] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Urea transporters (UTs) are a family of membrane channel proteins that are specifically permeable to urea and play an important role in intrarenal urea recycling and in urine concentration. Using an erythrocyte osmotic lysis assay, we screened a small-molecule library for inhibitors of UT-facilitated urea transport. A novel class of thienoquinolin UT-B inhibitors were identified, of which PU-14 had potent inhibition activity on human, rabbit, rat, and mouse UT-B. The half-maximal inhibitory concentration of PU-14 on rat UT-B-mediated urea transport was ∼0.8 μmol/l, and it did not affect urea transport in mouse erythrocytes lacking UT-B but inhibited UT-A-type urea transporters, with 36% inhibition at 4 μmol/l. PU-14 showed no significant cellular toxicity at concentrations up to its solubility limit of 80 μmol/l. Subcutaneous delivery of PU-14 (at 12.5, 50, and 100 mg/kg) to rats caused an increase of urine output and a decrease of the urine urea concentration and subsequent osmolality without electrolyte disturbances and liver or renal damages. This suggests that PU-14 has a diuretic effect by urea-selective diuresis. Thus, PU-14 or its analogs might be developed as a new diuretic to increase renal fluid clearance in diseases associated with water retention without causing electrolyte imbalance. PU-14 may establish 'chemical knockout' animal models to study the physiological functions of UTs.
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Affiliation(s)
- Fei Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
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31
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Shayakul C, Clémençon B, Hediger MA. The urea transporter family (SLC14): physiological, pathological and structural aspects. Mol Aspects Med 2013; 34:313-22. [PMID: 23506873 DOI: 10.1016/j.mam.2012.12.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 12/12/2012] [Indexed: 11/27/2022]
Abstract
Urea transporters (UTs) belonging to the solute carrier 14 (SLC14) family comprise two genes with a total of eight isoforms in mammals, UT-A1 to -A6 encoded by SLC14A2 and UT-B1 to -B2 encoded by SLC14A1. Recent efforts have been directed toward understanding the molecular and cellular mechanisms involved in the regulation of UTs using transgenic mouse models and heterologous expression systems, leading to important new insights. Urea uptake by UT-A1 and UT-A3 in the kidney inner medullary collecting duct and by UT-B1 in the descending vasa recta for the countercurrent exchange system are chiefly responsible for medullary urea accumulation in the urinary concentration process. Vasopressin, an antidiuretic hormone, regulates UT-A isoforms via the phosphorylation and trafficking of the glycosylated transporters to the plasma membrane that occurs to maintain equilibrium with the exocytosis and ubiquitin-proteasome degradation pathways. UT-B isoforms are also important in several cellular functions, including urea nitrogen salvaging in the colon, nitric oxide pathway modulation in the hippocampus, and the normal cardiac conduction system. In addition, genomic linkage studies have revealed potential additional roles for SLC14A1 and SLC14A2 in hypertension and bladder carcinogenesis. The precise role of UT-A2 and presence of the urea recycling pathway in normal kidney are issues to be further explored. This review provides an update of these advances and their implications for our current understanding of the SLC14 UTs.
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Affiliation(s)
- Chairat Shayakul
- Renal Unit, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
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32
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Klein JD, Blount MA, Sands JM. Molecular mechanisms of urea transport in health and disease. Pflugers Arch 2012; 464:561-72. [PMID: 23007461 PMCID: PMC3514661 DOI: 10.1007/s00424-012-1157-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 09/05/2012] [Accepted: 09/06/2012] [Indexed: 10/27/2022]
Abstract
In the late 1980s, urea permeability measurements produced values that could not be explained by paracellular transport or lipid phase diffusion. The existence of urea transport proteins were thus proposed and less than a decade later, the first urea transporter was cloned. The family of urea transporters has two major subgroups, designated SLC14A1 (or UT-B) and Slc14A2 (or UT-A). UT-B and UT-A gene products are glycoproteins located in various extra-renal tissues however, a majority of the resulting isoforms are found in the kidney. The UT-B (Slc14A1) urea transporter was originally isolated from erythrocytes and two isoforms have been reported. In kidney, UT-B is located primarily in the descending vasa recta. The UT-A (Slc14A2) urea transporter yields six distinct isoforms, of which three are found chiefly in the kidney medulla. UT-A1 and UT-A3 are found in the inner medullary collecting duct (IMCD), while UT-A2 is located in the thin descending limb. These transporters are crucial to the kidney's ability to concentrate urine. The regulation of urea transporter activity in the IMCD involves acute modification through phosphorylation and subsequent movement to the plasma membrane. UT-A1 and UT-A3 accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation of the urea transporters in the IMCD involves altering protein abundance in response to changes in hydration status, low protein diets, or adrenal steroids. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new genetically engineered mouse models are being developed to study these transporters.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA
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33
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Levin EJ, Cao Y, Enkavi G, Quick M, Pan Y, Tajkhorshid E, Zhou M. Structure and permeation mechanism of a mammalian urea transporter. Proc Natl Acad Sci U S A 2012; 109:11194-9. [PMID: 22733730 PMCID: PMC3396522 DOI: 10.1073/pnas.1207362109] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
As an adaptation to infrequent access to water, terrestrial mammals produce urine that is hyperosmotic to plasma. To prevent osmotic diuresis by the large quantity of urea generated by protein catabolism, the kidney epithelia contain facilitative urea transporters (UTs) that allow rapid equilibration between the urinary space and the hyperosmotic interstitium. Here we report the first X-ray crystal structure of a mammalian UT, UT-B, at a resolution of 2.36 Å. UT-B is a homotrimer and each protomer contains a urea conduction pore with a narrow selectivity filter. Structural analyses and molecular dynamics simulations showed that the selectivity filter has two urea binding sites separated by an approximately 5.0 kcal/mol energy barrier. Functional studies showed that the rate of urea conduction in UT-B is increased by hypoosmotic stress, and that the site of osmoregulation coincides with the location of the energy barrier.
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Affiliation(s)
- Elena J. Levin
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032
| | - Yu Cao
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032
| | - Giray Enkavi
- Center for Biophysics and Computational Biology, Department of Biochemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801; and
| | - Matthias Quick
- Department of Psychiatry and Center for Molecular Recognition, Columbia University, 650 West 168th Street, New York, NY 10032
| | - Yaping Pan
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032
| | - Emad Tajkhorshid
- Center for Biophysics and Computational Biology, Department of Biochemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801; and
| | - Ming Zhou
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032
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34
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Li X, Chen G, Yang B. Urea transporter physiology studied in knockout mice. Front Physiol 2012; 3:217. [PMID: 22745630 PMCID: PMC3383189 DOI: 10.3389/fphys.2012.00217] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 05/31/2012] [Indexed: 01/09/2023] Open
Abstract
In mammals, there are two types of urea transporters; urea transporter (UT)-A and UT-B. The UT-A transporters are mainly expressed in kidney epithelial cells while UT-B demonstrates a broader distribution in kidney, heart, brain, testis, urinary tract, and other tissues. Over the past few years, multiple urea transporter knockout mouse models have been generated enabling us to explore the physiological roles of the different urea transporters. In the kidney, deletion of UT-A1/UT-A3 results in polyuria and a severe urine concentrating defect, indicating that intrarenal recycling of urea plays a crucial role in the overall capacity to concentrate urine. Since UT-B has a wide tissue distribution, multiple phenotypic abnormalities have been found in UT-B null mice, such as defective urine concentration, exacerbated heart blockage with aging, depression-like behavior, and earlier male sexual maturation. This review summarizes the new insights of urea transporter functions in different organs, gleaned from studies of urea transporter knockout mice, and explores some of the potential pharmacological prospects of urea transporters.
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Affiliation(s)
- Xuechen Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, and Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education Beijing, China
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35
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Bankir L, Yang B. New insights into urea and glucose handling by the kidney, and the urine concentrating mechanism. Kidney Int 2012; 81:1179-98. [PMID: 22456603 DOI: 10.1038/ki.2012.67] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The mechanism by which urine is concentrated in the mammalian kidney remains incompletely understood. Urea is the dominant urinary osmole in most mammals and may be concentrated a 100-fold above its plasma level in humans and even more in rodents. Several facilitated urea transporters have been cloned. The phenotypes of mice with deletion of the transporters expressed in the kidney have challenged two previously well-accepted paradigms regarding urea and sodium handling in the renal medulla but have provided no alternative explanation for the accumulation of solutes that occurs in the inner medulla. In this review, we present evidence supporting the existence of an active urea secretion in the pars recta of the proximal tubule and explain how it changes our views regarding intrarenal urea handling and UT-A2 function. The transporter responsible for this secretion could be SGLT1, a sodium-glucose cotransporter that also transports urea. Glucagon may have a role in the regulation of this secretion. Further, we describe a possible transfer of osmotic energy from the outer to the inner medulla via an intrarenal Cori cycle converting glucose to lactate and back. Finally, we propose that an active urea transporter, expressed in the urothelium, may continuously reclaim urea that diffuses out of the ureter and bladder. These hypotheses are all based on published findings. They may not all be confirmed later on, but we hope they will stimulate further research in new directions.
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Affiliation(s)
- Lise Bankir
- INSERM Unit 872/Equipe 2, Centre de Recherche des Cordeliers, Paris, France.
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36
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He X. Functional MR imaging of kidney--novel approaches to monitoring renal physiology. Am J Physiol Renal Physiol 2012; 303:F639-40. [PMID: 22573377 DOI: 10.1152/ajprenal.00224.2012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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