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Jiang Y, Zhang R, Fang Y, Zhao R, Fu Y, Ren P, Zhan Q, Shao M. P-CAB versus PPI in the eradication of Helicobacter pylori: a systematic review and network meta-analysis. Therap Adv Gastroenterol 2024; 17:17562848241241223. [PMID: 38751605 PMCID: PMC11095192 DOI: 10.1177/17562848241241223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 03/06/2024] [Indexed: 05/18/2024] Open
Abstract
Background The efficacy and safety of potassium-competitive acid blockers (P-CABs) in the eradication of Helicobacter pylori (Hp) remains controversial when compared with proton pump inhibitors (PPIs). Objectives The current study set out to compare the differences in the eradication rate and adverse reactions between eradication regimens based on P-CAB or PPI drugs and the differences between the vonoprazan-based and the tegoprazan-based regimens to explore the efficacy and safety of different Hp eradication regimens. Data sources and methods Databases including PubMed, EMBASE, Cochrane Library, and WOS were searched from the inception of these databases up to July 2023, and eligible randomized controlled trials (RCTs) were included. The outcome measures were the eradication rate and the incidence of adverse reactions of different regimens in treating Hp. The results were estimated as relative risk (RR) and its 95% confidence interval (CI), and R 4.2.1 software was used to perform the network meta-analysis (NMA). Results A total of 20 studies were included in the analysis, involving 5815 patients with Hp. In terms of eradication rate, the 2-week vonoprazan-based triple regimen (V-Tri-2w) was the best, which was superior to the 2-week PPI-based quadruple regimen [P-Qua-2w, RR = 0.9, 95% CI: (0.85-0.95)] and the 1-week tegoprazan-based triple regimen [T-Tri-1w, RR = 0.79, 95% CI: (0.64-0.97)]; the 2-week tegoprazan-based quadruple regimen (T-Qua-2w) was superior to the 1-week PPI-based triple regimen [P-Tri-1w, RR = 0.82, 95% CI: (0.67-0.99)], and there was no difference between the remaining tegoprazan-based regimens and the PPI-based or vonoprazan-based regimens. In terms of the incidence of adverse reactions, the 2-week vonoprazan-based binary regimen (V-Bi-2w) was lower than that of the 2-week PPI-based quadruple regimen [P-Qua-2w, RR = 1.98, 95% CI: (1.57-2.52)]; there was no significant difference between 1 and 2 weeks for each regimen, such as the vonoprazan-based triple regimen [RR = 1.11, 95% CI: (0.82-1.52)]. Conclusion In the eradication treatment of Hp, the efficacy and safety of vonoprazan-based regimens are generally better than those of PPI-based regimens. Among them, the V-Tri-2w regimen has the highest eradication rate and may be the preferred choice for Hp eradication.
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Affiliation(s)
- Yutong Jiang
- The First Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, Henan, China
- The First Clinical Medical College of Henan University of Chinese Medicine, Zhengzhou, China
| | - Rongrong Zhang
- The First Clinical Medical College of Henan University of Chinese Medicine, Zhengzhou, China
| | - Yuxuan Fang
- The First Clinical Medical College of Henan University of Chinese Medicine, Zhengzhou, China
| | - Ruixia Zhao
- The First Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, Henan, China
| | - Yu Fu
- The First Affiliated Hospital of Henan University of Chinese Medicine, Zhengzhou, Henan, China
| | - Pingping Ren
- The First Clinical Medical College of Henan University of Chinese Medicine, Zhengzhou, China
| | - Qingqing Zhan
- The First Clinical Medical College of Henan University of Chinese Medicine, Zhengzhou, China
| | - Mingyi Shao
- The First Affiliated Hospital of Henan University of Chinese Medicine, 19 Renmin Road, Jinshui District, Zhengzhou, Henan 450000, China
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Akhter S, Concepcion O, Fernández de la Torre A, Ali A, Rauf Raza A, Eman R, Khalid M, Fayyaz ur Rehman M, Safwan Akram M, Ali HM. Synthesis, Spectroscopic Characterization, DFT and Molecular Dynamics of Quinoline-based Peptoids. ARAB J CHEM 2023. [DOI: 10.1016/j.arabjc.2023.104570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
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3
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Tanaka S, Morita M, Yamagishi T, Madapally HV, Hayashida K, Khandelia H, Gerle C, Shigematsu H, Oshima A, Abe K. Structural Basis for Binding of Potassium-Competitive Acid Blockers to the Gastric Proton Pump. J Med Chem 2022; 65:7843-7853. [PMID: 35604136 DOI: 10.1021/acs.jmedchem.2c00338] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
As specific inhibitors of the gastric proton pump, responsible for gastric acidification, K+-competitive acid blockers (P-CABs) have recently been utilized in the clinical treatment of gastric acid-related diseases in Asia. However, as these compounds have been developed based on phenotypic screening, their detailed binding poses are unknown. We show crystal and cryo-EM structures of the gastric proton pump in complex with four different P-CABs, tegoprazan, soraprazan, PF-03716556 and revaprazan, at resolutions reaching 2.8 Å. The structures describe molecular details of their interactions and are supported by functional analyses of mutations and molecular dynamics simulations. We reveal that revaprazan has a novel binding mode in which its tetrahydroisoquinoline moiety binds deep in the cation transport conduit. The mechanism of action of these P-CABs can now be evaluated at the molecular level, which will facilitate the rational development and improvement of currently available P-CABs to provide better treatment of acid-related gastrointestinal diseases.
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Affiliation(s)
- Saki Tanaka
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan
| | - Mikio Morita
- Discovery Research, RaQualia Pharma Inc., 1-21-19 Meieki Minami, Nakamura, Nagoya 450-0003, Japan.,RaQualia Pharma Industry-Academia Collaborative Research Center, Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-8601, Japan
| | - Tatsuya Yamagishi
- Discovery Research, RaQualia Pharma Inc., 1-21-19 Meieki Minami, Nakamura, Nagoya 450-0003, Japan.,RaQualia Pharma Industry-Academia Collaborative Research Center, Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-8601, Japan
| | - Hridya Valia Madapally
- PHYLIFE: Physical Life Science, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Kenichi Hayashida
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
| | - Himanshu Khandelia
- PHYLIFE: Physical Life Science, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Christoph Gerle
- RIKEN SPring-8 Center, Kouto, Sayo-gun, Hyogo 679-5148, Japan.,Laboratory for Protein Crystallography, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | | | - Atsunori Oshima
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan.,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan.,Institute for Glyco-core Research (iGCORE), Nagoya University, Nagoya, 464-8601, Japan
| | - Kazuhiro Abe
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan.,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
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4
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Goswami S. Interplay of potassium channel, gastric parietal cell and proton pump in gastrointestinal physiology, pathology and pharmacology. Minerva Gastroenterol (Torino) 2021; 68:289-305. [PMID: 34309336 DOI: 10.23736/s2724-5985.21.02964-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Gastric acid secretion plays a pivotal role in the physiology of gastrointestinal tract. The functioning of the system encompasses a P2 ATPase pump (which shuttles electroneutral function at low pH) along with different voltage sensitive/neutral ion channels, cytosolic proteins, acid sensor receptors as well hormonal regulators. The increased acid secretion is a pathological marker of several diseases like peptic ulcer, gastroesophageal reflux disease (GERD), chronic gastritis, and the bug Helicobacter pylori (H. pylori) has also a critical role, which altogether affects the patient's quality of life. This review comprehensively describes about the nature of potassium ion channel and its mediators, the different clinical strategy to control acid rebound, and some basic experimental observations performed to study the interplay of ion channels, pumps, as well as mediators during acid secretion. Different aspects of regulation of gastric acid secretion have been focused either in terms of physiology of secretion or molecular interactions. The importance of H pylori infection and its treatment have also been discussed. Furthermore, the relevance of calcium signaling during acid secretion has been reviewed. The entire theme will make anyone to understand in details about the gastric secretion machinery in general.
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Affiliation(s)
- Suchandra Goswami
- Smt. Vidyawati College of Pharmacy, Gora Machhiya, Jhansi, Uttar Pradesh, India -
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5
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Taxifolin and gastro-adhesive microparticles containing taxifolin promotes gastric healing in vivo, inhibits Helicobacter pylori in vitro and proton pump reversibly in silico. Chem Biol Interact 2021; 339:109445. [PMID: 33741339 DOI: 10.1016/j.cbi.2021.109445] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 02/22/2021] [Accepted: 03/10/2021] [Indexed: 01/02/2023]
Abstract
Taxifolin (3,5,7,3,4-pentahydroxy flavanone or dihydroquercetin, Tax) was identified as a gastroprotective compound and a gastroadhesive formulation was recently developed to prolong its residence time and release in the stomach. So, the gastric healing effectiveness of Tax and gastro-mucoadhesive microparticles containing Tax (MPTax) against the acetic acid induced-gastric ulcer in rats was investigated in this study. Moreover, the interactions between Tax and H+/K+-ATPase were investigated in silico, and its anti- H. pylori activity was determined in vitro. The oral treatment with MPTax (81.37 mg/kg, containing 12.29% of Tax) twice a day for seven days reduced the ulcer area by 63%, compared to vehicle-treated group (Veh: 91.9 ± 10.3 mm2). Tax (10 mg/kg, p.o) reduced the ulcer by 40% but with a p = 0.07 versus Veh group. Histological analysis confirmed these effects. Tax and MPTax increased the gastric mucin amount, reduced the myeloperoxidase activity, and increased the glutathione reduced content at ulcer site. However, only MPTax decreased the lipoperoxide accumulation at ulcer site. Besides, Tax and MPTax normalize the catalase and glutathione S-transferase activity. Tax showed reversible interaction with H+/K+-ATPase in silico and its anti-H. pylori effects was confirmed (MIC = 625 μg/mL). These results suggest that the antiulcer property of Tax involves the strengthening of the gastric protective factors in parallel to its inhibitory interaction with H+/K+-ATPase and H. pylori. Considering that ulcer healing action displayed by Tax was favored by gastroadhesive microparticles, this approach seems to be promising for its oral delivery to treat acid-peptic diseases.
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6
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Engevik AC, Kaji I, Goldenring JR. The Physiology of the Gastric Parietal Cell. Physiol Rev 2020; 100:573-602. [PMID: 31670611 PMCID: PMC7327232 DOI: 10.1152/physrev.00016.2019] [Citation(s) in RCA: 101] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 10/10/2019] [Accepted: 10/13/2019] [Indexed: 12/11/2022] Open
Abstract
Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.
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Affiliation(s)
- Amy C Engevik
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - Izumi Kaji
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - James R Goldenring
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
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7
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Eftekhari M, Hoseinsalari A, Mansourian M, Farjadmand F, Shams Ardekani MR, Sharifzadeh M, Hassanzadeh G, Khanavi M, Gholami M. Trachyspermum ammi (L.) Sprague, superb essential oil and its major components on peptic ulcers: in vivo combined in silico studies. ACTA ACUST UNITED AC 2019; 27:317-327. [PMID: 31218527 DOI: 10.1007/s40199-019-00279-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 06/05/2019] [Indexed: 11/30/2022]
Abstract
BACKGROUND Trachyspermum ammi (L.) Sprague is used for treating gastrointestinal disorders. Several studies indicated gastric antiulcer activity of T. ammi extract, yet the effect of its essential oil has not been studied on. OBJECTIVES The present study evaluates chemical composition of T. ammi essential oil and anti-peptic ulcer effect of the essential oil as well as its three major components in ethanol induced-gastric ulcers in rats. METHODS Primarily chemical composition of the essential oil was analyzed by gas chromatography-mass spectrometry (GC/MS). Rats received the essential oil (500, 250, 125, 62.5, 31.25 mg/kg), thymol (30, 100 mg/kg), para-cymene (100, 150 mg/kg) and gamma-terpinene (100, 150 mg/kg) using gavage tube along with ethanol 80%. Finally, dissected stomachs were assessed both macroscopically and microscopically to evaluate anti-ulcerative effect of the essential oil and the pure compounds. Moreover, molecular docking was utilized to explore the interactive behavior of the main components with active site residues of H+/K+ ATPase. RESULTS Analysis of the essential oil indicated that para-cymene (37.18%), gamma-terpinene (35.36%) and thymol (20.51%) are the main components. Administration of different doses of the essential oil noticeably diminished the number of peptic ulcers in a dose-dependent manner. Among the main components, thymol was more potent than para-cymene and gamma-terpinene. Administration of the essential oil (500 mg/kg) and thymol (100 mg/kg) observed maximum inhibition percentage (98.58% and 79.37%, respectively). Molecular docking study provides the evidence of thymol ability to inhibit H+/K+ ATPase. CONCLUSIONS The findings revealed that T. ammi essential oil can be applied to treat gastric ulcer as a natural agent. Graphical abstract.
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Affiliation(s)
- Mahdieh Eftekhari
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Afsaneh Hoseinsalari
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Mahboubeh Mansourian
- Medicinal Plants Research Center, Yasuj University of Medical Sciences, Yasuj, Iran.,Department of Pharmacology, Faculty of Medicine, Yasuj University of Medical Sciences, Yasuj, Iran
| | - Fatemeh Farjadmand
- Food and Drug Organization, Ministry of Health and Medical Education of Iran, Tehran, Iran
| | | | - Mohammad Sharifzadeh
- Department of Toxicology and Pharmacology, Tehran University of Medical Sciences, Tehran, Iran.,The institute of Pharmaceutical Sciences, Tehran University of Medical Sciences, Tehran, Iran
| | - Gholamreza Hassanzadeh
- Department of Anatomy, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Mahnaz Khanavi
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. .,Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada.
| | - Mahdi Gholami
- Department of Toxicology and Pharmacology, Tehran University of Medical Sciences, Tehran, Iran
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8
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Assessment of the risk of acute kidney injury associated with the use of pantoprazole and esomeprazole. DRUGS & THERAPY PERSPECTIVES 2018. [DOI: 10.1007/s40267-018-0503-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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9
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Abe K, Shimokawa J, Naito M, Munson K, Vagin O, Sachs G, Suzuki H, Tani K, Fujiyoshi Y. The cryo-EM structure of gastric H +,K +-ATPase with bound BYK99, a high-affinity member of K +-competitive, imidazo[1,2-a]pyridine inhibitors. Sci Rep 2017; 7:6632. [PMID: 28747707 PMCID: PMC5529566 DOI: 10.1038/s41598-017-06698-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 06/21/2017] [Indexed: 12/13/2022] Open
Abstract
The gastric proton pump H+,K+-ATPase acidifies the gastric lumen, and thus its inhibitors, including the imidazo[1,2-a]pyridine class of K+-competitive acid blockers (P-CABs), have potential application as acid-suppressing drugs. We determined the electron crystallographic structure of H+,K+-ATPase at 6.5 Å resolution in the E2P state with bound BYK99, a potent P-CAB with a restricted ring structure. The BYK99 bound structure has an almost identical profile to that of a previously determined structure with bound SCH28080, the original P-CAB prototype, but is significantly different from the previously reported P-CAB-free form, illustrating a common conformational change is required for P-CAB binding. The shared conformational changes include a distinct movement of transmembrane helix 2 (M2), from its position in the previously reported P-CAB-free form, to a location proximal to the P-CAB binding site in the present BYK99-bound structure. Site-specific mutagenesis within M2 revealed that D137 and N138, which face the P-CAB binding site in our model, significantly affect the inhibition constant (Ki) of P-CABs. We also found that A335 is likely to be near the bridging nitrogen at the restricted ring structure of the BYK99 inhibitor. These provide clues to elucidate the binding site parameters and mechanism of P-CAB inhibition of gastric acid secretion.
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Affiliation(s)
- Kazuhiro Abe
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan. .,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan. .,Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Chiyoda, Tokyo, 100-0004, Japan.
| | - Jun Shimokawa
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan
| | - Mao Naito
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan.,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
| | | | | | | | - Hiroshi Suzuki
- Laboratory of Molecular Electron Microscopy, Rockefeller University, New York, 10065, USA
| | - Kazutoshi Tani
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
| | - Yoshinori Fujiyoshi
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan.,Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Chiyoda, Tokyo, 100-0004, Japan.,CeSPIA Inc., 2-1-1, Otemachi, Chiyoda, Tokyo, 100-0004, Japan
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10
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Sakai H, Fujii T, Takeguchi N. Proton-Potassium (H+/K+) ATPases: Properties and Roles in Health and Diseases. Met Ions Life Sci 2016; 16:459-83. [DOI: 10.1007/978-3-319-21756-7_13] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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11
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Scott DR, Munson KB, Marcus EA, Lambrecht NWG, Sachs G. The binding selectivity of vonoprazan (TAK-438) to the gastric H+, K+ -ATPase. Aliment Pharmacol Ther 2015; 42:1315-26. [PMID: 26423447 PMCID: PMC4626316 DOI: 10.1111/apt.13414] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Revised: 08/09/2015] [Accepted: 09/03/2015] [Indexed: 12/14/2022]
Abstract
BACKGROUND The gastric H(+) ,K(+) -ATPase is the preferred target for acid suppression. Until recently, the only drugs that effectively inhibited this ATPase were the proton pump inhibitors (PPIs). PPIs are acid-activated prodrugs that require acid protection. Once acid-activated, PPIs bind to cysteines of the ATPase, resulting in covalent, long-lasting inhibition. The short plasma half-life of PPIs and continual de novo synthesis of the H(+) ,K(+) -ATPase result in difficulty controlling night-time acid secretion. A new alternative to PPIs is the pyrrolo-pyridine, vonoprazan (TAK-438), a potassium-competitive acid blocker (PCAB) that does not require acid protection. In contrast to other PCABs, vonoprazan has a long duration of action, resulting in 24-h control of acid secretion, a high pKa of 9.37 and high affinity (Ki = 3.0 ηmol/L). AIM To determine binding selectivity of vonoprazan for the gastric H(+) ,K(+) -ATPase and to explain its slow dissociation. METHODS Gastric gland and parietal cell binding of vonoprazan was determined radiometrically. Molecular modelling explained the slow dissociation of vonoprazan from the H(+) ,K(+) -ATPase. RESULTS Vonoprazan binds selectively to the parietal cell, independent of acid secretion. Vonoprazan binds in a luminal vestibule between the surfaces of membrane helices 4, 5 and 6. Exit of the drug to the lumen is hindered by asp137 and asn138 in the loop between TM1 and TM2, which presents an electrostatic barrier to movement of the sulfonyl group of vonoprazan. This may explain its slow dissociation from the H(+) ,K(+) -ATPase and long-lasting inhibition. CONCLUSION The binding model provides a template for design of novel potassium-competitive acid blockers.
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Affiliation(s)
- David R. Scott
- Department of Physiology, DGSOM at UCLA, Los Angeles, CA,VA GLAHS, Los Angeles, CA
| | - Keith B. Munson
- Department of Medicine, DGSOM at UCLA, Los Angeles, CA,VA GLAHS, Los Angeles, CA
| | - Elizabeth A. Marcus
- Department of Pediatrics, DGSOM at UCLA, Los Angeles, CA,VA GLAHS, Los Angeles, CA
| | - Nils W. G. Lambrecht
- Pathology and Laboratory Medicine Service, VA Long Beach Healthcare System, Long Beach, CA
| | - George Sachs
- Department of Physiology, DGSOM at UCLA, Los Angeles, CA,Department of Medicine, DGSOM at UCLA, Los Angeles, CA,VA GLAHS, Los Angeles, CA
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12
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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13
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ATP4A gene regulatory network for fine-tuning of proton pump and ion channels. SYSTEMS AND SYNTHETIC BIOLOGY 2013; 7:23-32. [PMID: 24432139 DOI: 10.1007/s11693-012-9103-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 12/31/2012] [Accepted: 12/31/2012] [Indexed: 12/11/2022]
Abstract
The ATP4A encodes α subunit of H(+), K(+)-ATPase that contains catalytic sites of the enzyme forming pores through cell membrane which allows the ion transport. H(+), K(+)-ATPase is a membrane bound P-type ATPase enzyme which is found on the surface of parietal cells and uses the energy derived from each cycle of ATP hydrolysis that can help in exchanging ions (H(+), K(+) and Cl(-)) across the cell membrane secreting acid into the gastric lumen. The 3-D model of α-subunit of H(+), K(+)-ATPase was generated by homology modeling. It was evaluated and validated on the basis of free energies and amino acid residues. The inhibitor binding amino acid active pockets were identified in the 3-D model by molecular docking. The two drugs Omeprazole and Rabeprazole were found more potent interactions with generated model of α-subunit of H(+), K(+)-ATPase on the basis of their affinity between drug-protein interactions. We have generated ATP4A gene regulatory networks for interactions with other proteins which involved in regulation that can help in fine-tuning of proton pump and ion channels. These findings provide a new dimension for discovery and development of proton pump inhibitors and gene regulation of the ATPase. It can be helpful in better understanding of human physiology and also using synthetic biology strategy for reprogramming of parietal cells for control of gastric ulcers.
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14
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Shin JM, Kim N. Pharmacokinetics and pharmacodynamics of the proton pump inhibitors. J Neurogastroenterol Motil 2013; 19:25-35. [PMID: 23350044 PMCID: PMC3548122 DOI: 10.5056/jnm.2013.19.1.25] [Citation(s) in RCA: 251] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 12/20/2012] [Accepted: 12/21/2012] [Indexed: 12/13/2022] Open
Abstract
Proton pump inhibitor (PPI) is a prodrug which is activated by acid. Activated PPI binds covalently to the gastric H+, K+-ATPase via disulfide bond. Cys813 is the primary site responsible for the inhibition of acid pump enzyme, where PPIs bind. Omeprazole was the first PPI introduced in market, followed by pantoprazole, lansoprazole and rabeprazole. Though these PPIs share the core structures benzimidazole and pyridine, their pharmacokinetics and pharmacodynamics are a little different. Several factors must be considered in understanding the pharmacodynamics of PPIs, including: accumulation of PPI in the parietal cell, the proportion of the pump enzyme located at the canaliculus, de novo synthesis of new pump enzyme, metabolism of PPI, amounts of covalent binding of PPI in the parietal cell, and the stability of PPI binding. PPIs have about 1hour of elimination half-life. Area under the plasmic concentration curve and the intragastric pH profile are very good indicators for evaluating PPI efficacy. Though CYP2C19 and CYP3A4 polymorphism are major components of PPI metabolism, the pharmacokinetics and pharmacodynamics of racemic mixture of PPIs depend on the CYP2C19 genotype status. S-omeprazole is relatively insensitive to CYP2C19, so better control of the intragastric pH is achieved. Similarly, R-lansoprazole was developed in order to increase the drug activity. Delayed-release formulation resulted in a longer duration of effective concentration of R-lansoprazole in blood, in addition to metabolic advantage. Thus, dexlansoprazole showed best control of the intragastric pH among the present PPIs. Overall, PPIs made significant progress in the management of acid-related diseases and improved health-related quality of life.
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15
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New pharmacologic approaches in gastroesophageal reflux disease. Thorac Surg Clin 2011; 21:557-74. [PMID: 22040637 DOI: 10.1016/j.thorsurg.2011.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.
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16
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Shin JM, Inatomi N, Munson K, Strugatsky D, Tokhtaeva E, Vagin O, Sachs G. Characterization of a novel potassium-competitive acid blocker of the gastric H,K-ATPase, 1-[5-(2-fluorophenyl)-1-(pyridin-3-ylsulfonyl)-1H-pyrrol-3-yl]-N-methylmethanamine monofumarate (TAK-438). J Pharmacol Exp Ther 2011; 339:412-20. [PMID: 21828261 DOI: 10.1124/jpet.111.185314] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Inhibition of the gastric H,K-ATPase by the potassium-competitive acid blocker (P-CAB) 1-[5-(2-fluorophenyl)-1-(pyridin-3-ylsulfonyl)-1H-pyrrol-3-yl]-N-methylmethanamine (TAK-438), is strictly K(+)-competitive with a K(i) of 10 nM at pH 7. In contrast to previous P-CABs, this structure has a point positive charge (pK(a) 9.06) allowing for greater accumulation in parietal cells compared with previous P-CABs [e.g., (8-benzyloxy-2-methyl-imidazo(1,2-a)pyridin-3-yl)acetonitrile (SCH28080), pK(a) 5.6]. The dissociation rate of the compound from the isolated ATPase is slower than other P-CABs, with the t(1/2) being 7.5 h in 20 mM KCl at pH 7. The stoichiometry of binding of TAK-438 to the H,K-ATPase is 2.2 nmol/mg in the presence of Mg-ATP, vanadate, or MgP(i). However, TAK-438 also binds enzyme at 1.3 nmol/mg in the absence of Mg(2+). Modeling of the H,K-ATPase to the homologous Na,K-ATPase predicts a close approach and hydrogen bonding between the positively charged N-methylamino group and the negatively charged Glu795 in the K(+)-binding site in contrast to the planar diffuse positive charge of previous P-CABs. This probably accounts for the slow dissociation and high affinity. The model also predicts hydrogen bonding between the hydroxyl of Tyr799 and the oxygens of the sulfonyl group of TAK-438. A Tyr799Phe mutation resulted in a 3-fold increase of the dissociation rate, showing that this hydrogen bonding also contributes to the slow dissociation rate. Hence, this K(+)-competitive inhibitor of the gastric H,K-ATPase should provide longer-lasting inhibition of gastric acid secretion compared with previous drugs of this class.
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Affiliation(s)
- Jai Moo Shin
- Department of Physiology and Medicine, David Geffen School of Medicine, University of California at Los Angeles, and VA Greater Los Angeles Healthcare System, Los Angeles, 11301 Wilshire Blvd., Bldg. 113, CA 90073, USA.
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17
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Abe K, Tani K, Fujiyoshi Y. Conformational rearrangement of gastric H(+),K(+)-ATPase induced by an acid suppressant. Nat Commun 2011; 2:155. [PMID: 21224846 PMCID: PMC3105306 DOI: 10.1038/ncomms1154] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Accepted: 12/01/2010] [Indexed: 12/12/2022] Open
Abstract
Acid-related gastric diseases are associated with disorder of digestive tract acidification. The gastric proton pump, H(+),K(+)-ATPase, exports H(+) in exchange for luminal K(+) to generate a highly acidic environment in the stomach, and is a main target for acid suppressants. Here, we report the three-dimensional structure of gastric H(+),K(+)-ATPase with bound SCH28080, a representative K(+)-competitive acid blocker, at 7 Å resolution based on electron crystallography of two-dimensional crystals. The density of the bound SCH28080 is found near transmembrane (TM) helices 4, 5 and 6, in the luminal cavity. The SCH28080-binding site is formed by the rearrangement of TM helices, which is in turn transmitted to the cytoplasmic domains, resulting in a luminal-open conformation. These results represent the first structural evidence for a binding site of an acid suppressant on H(+),K(+)-ATPase, and the conformational change induced by this class of drugs.
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Affiliation(s)
- Kazuhiro Abe
- Department of Biophysics, Faculty of Science, Kyoto University, Oiwake, Kitashirakawa, Sakyo-ku, Kyoto 606-0852, Japan
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18
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Abstract
This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.
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19
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20
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Gumz ML, Lynch IJ, Greenlee MM, Cain BD, Wingo CS. The renal H+-K+-ATPases: physiology, regulation, and structure. Am J Physiol Renal Physiol 2009; 298:F12-21. [PMID: 19640897 DOI: 10.1152/ajprenal.90723.2008] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The H(+)-K(+)-ATPases are ion pumps that use the energy of ATP hydrolysis to transport protons (H(+)) in exchange for potassium ions (K(+)). These enzymes consist of a catalytic alpha-subunit and a regulatory beta-subunit. There are two catalytic subunits present in the kidney, the gastric or HKalpha(1) isoform and the colonic or HKalpha(2) isoform. In this review we discuss new information on the physiological function, regulation, and structure of the renal H(+)-K(+)-ATPases. Evaluation of enzymatic functions along the nephron and collecting duct and studies in HKalpha(1) and HKalpha(2) knockout mice suggest that the H(+)-K(+)-ATPases may function to transport ions other than protons and potassium. These reports and recent studies in mice lacking both HKalpha(1) and HKalpha(2) suggest important roles for the renal H(+)-K(+)-ATPases in acid/base balance as well as potassium and sodium homeostasis. Molecular modeling studies based on the crystal structure of a related enzyme have made it possible to evaluate the structures of HKalpha(1) and HKalpha(2) and provide a means to study the specific cation transport properties of H(+)-K(+)-ATPases. Studies to characterize the cation specificity of these enzymes under different physiological conditions are necessary to fully understand the role of the H(+)-K(+) ATPases in renal physiology.
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Affiliation(s)
- Michelle L Gumz
- Research Service, North Florida/South Georgia Veterans Health System, Gainesville, Florida, USA
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21
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Bamford M. 3 H+/K+ ATPase Inhibitors in the Treatment of Acid-Related Disorders. PROGRESS IN MEDICINAL CHEMISTRY 2009; 47:75-162. [DOI: 10.1016/s0079-6468(08)00203-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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22
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Shin JM, Munson K, Vagin O, Sachs G. The gastric HK-ATPase: structure, function, and inhibition. Pflugers Arch 2008; 457:609-22. [PMID: 18536934 DOI: 10.1007/s00424-008-0495-4] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Revised: 03/07/2008] [Accepted: 03/11/2008] [Indexed: 02/06/2023]
Abstract
The gastric H,K-ATPase, a member of the P(2)-type ATPase family, is the integral membrane protein responsible for gastric acid secretion. It is an alpha,beta-heterodimeric enzyme that exchanges cytoplasmic hydronium with extracellular potassium. The catalytic alpha subunit has ten transmembrane segments with a cluster of intramembranal carboxylic amino acids located in the middle of the transmembrane segments TM4, TM5,TM6, and TM8. Comparison to the known structure of the SERCA pump, mutagenesis, and molecular modeling has identified these as constituents of the ion binding domain. The beta subunit has one transmembrane segment with N terminus in cytoplasmic region. The extracellular domain of the beta subunit contains six or seven N-linked glycosylation sites. N-glycosylation is important for the enzyme assembly, maturation, and sorting. The enzyme pumps acid by a series of conformational changes from an E(1) (ion site in) to an E(2) (ion site out) configuration following binding of MgATP and phosphorylation. Several experimental observations support the hypothesis that expulsion of the proton at 160 mM (pH 0.8) results from movement of lysine 791 into the ion binding site in the E(2)P configuration. Potassium access from the lumen depends on activation of a K and Cl conductance via a KCNQ1/KCNE2 complex and Clic6. K movement through the luminal channel in E(2)P is proposed to displace the lysine along with dephosphorylation to return the enzyme to the E(1) configuration. This enzyme is inhibited by the unique proton pump inhibitor class of drug, allowing therapy of acid-related diseases.
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Affiliation(s)
- Jai Moo Shin
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles and VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA
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23
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Morii M, Yamauchi M, Ichikawa T, Fujii T, Takahashi Y, Asano S, Takeguchi N, Sakai H. Involvement of the H3O+-Lys-164 -Gln-161-Glu-345 charge transfer pathway in proton transport of gastric H+,K+-ATPase. J Biol Chem 2008; 283:16876-84. [PMID: 18403373 DOI: 10.1074/jbc.m800563200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Gastric H(+),K(+)-ATPase is shown to transport 2 mol of H(+)/mol of ATP hydrolysis in isolated hog gastric vesicles. We studied whether the H(+) transport mechanism is due to charge transfer and/or transfer of hydronium ion (H(3)O(+)). From transport of [(18)O]H(2)O, 1.8 mol of water molecule/mol of ATP hydrolysis was found to be transported. We performed a molecular dynamics simulation of the three-dimensional structure model of the H(+),K(+)-ATPase alpha-subunit at E(1) conformation. It predicts the presence of a charge transfer pathway from hydronium ion in cytosolic medium to Glu-345 in cation binding site 2 (H(3)O(+)-Lys-164 -Gln-161-Glu-345). No charge transport pathway was formed in mutant Q161L, E345L, and E345D. Alternative pathways (H(3)O(+)-Gln-161-Glu-345) in mutant K164L and (H(3)O(+)-Arg-105-Gln-161-Gln-345) in mutant E345Q were formed. The H(+),K(+)-ATPase activity in these mutants reflected the presence and absence of charge transfer pathways. We also found charge transfer from sites 2 to 1 via a water wire and a charge transfer pathway (H(3)O(+)-Asn-794 -Glu-797). These results suggest that protons are charge-transferred from the cytosolic side to H(2)O in sites 2 and 1, the H(2)O comes from cytosolic medium, and H(3)O(+) in the sites are transported into lumen during the conformational transition from E(1)PtoE(2)P.
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Affiliation(s)
- Magotoshi Morii
- Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
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24
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Zies DL, Gumz ML, Wingo CS, Cain BD. The renal H+, K+-ATPases as therapeutic targets. Expert Opin Ther Targets 2007; 11:881-90. [PMID: 17614757 DOI: 10.1517/14728222.11.7.881] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The kidney is an important regulatory organ responsible for maintaining constant blood volume and composition despite wide variations in the intake of food and water. Throughout the nephron, the functional unit of the kidney, there is a wide variety of proteins that function to add additional waste products and to recover needed materials from the lumen filtrate. The collecting duct of the nephron is the primary renal location for the H+, K+-ATPases, a group of ion pumps that function in both acid/base balance and potassium homeostasis. This review summarizes the present understanding of the structure and functions for the different subtypes of the H+, K+-ATPases under specific physiologic conditions. The obstacles in determining the pharmacologic properties of the different subtypes are considered and future directions for the inhibition and/or stimulation of the H+, K+-ATPases are evaluated.
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Affiliation(s)
- Deborah L Zies
- University of Mary Washington, Department of Biology, Fredericksburg, VA 22401, USA
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25
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Abstract
Since it was discovered 3 decades ago the H,K-ATPase has come to be recognized as the key both to the generation and pharmacologic suppression of gastric acid secretion. Although 30 years of concerted research has answered many questions, it is perhaps not surprising that these efforts have raised many new and crucial issues that await elucidation. These can be divided into 5 broad categories that relate to structure, mechanism, regulation, trafficking, and macromolecular interactions. It is probably safe to predict that the growing sophistication of x-ray crystallographic techniques will yield a picture of the pump's molecular structure in the near future. These insights will, in turn, illuminate the details of the process through which enzymatic hydrolysis is coupled to ion translocation with unprecedented clarity. The gastric parietal cell employs an extremely complicated system of receptors, kinases, and second messengers to maintain tight control over pump function. Upon activation, this cell also performs a massive and elegant membrane trafficking transformation that plays a critical role in the regulatory process. Finally, it is becoming clear that every ion transport protein is a component in a large macromolecular complex whose constituents help to determine all of the transport system's fundamental physiologic properties. These are the major topics that will drive H,K pump research in the future, and it is likely that their resolution will create the foundations for the next generation of therapies aimed at controlling gastric acid secretion and its clinical consequences.
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Affiliation(s)
- Michael J Caplan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8026, USA.
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26
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Munson K, Law RJ, Sachs G. Analysis of the gastric H,K ATPase for ion pathways and inhibitor binding sites. Biochemistry 2007; 46:5398-417. [PMID: 17425287 PMCID: PMC2837483 DOI: 10.1021/bi062305h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
New models of the gastric H,K ATPase in the E1K and E2P states are presented as the first structures of a K+ counter-transport P2-type ATPase exhibiting ion entry and exit paths. Homology modeling was first used to generate a starting conformation from the srCa ATPase E2P form (PDB code 1wpg) that contains bound MgADP. Energy minimization of the model showed a conserved adenosine site but nonconserved polyphosphate contacts compared to the srCa ATPase. Molecular dynamics was then employed to expand the luminal entry sufficiently to allow access of the rigid K+ competitive naphthyridine inhibitor, Byk99, to its binding site within the membrane domain. The new E2P model had increased separation between transmembrane segments M3 through M8, and addition of water in this space showed not only an inhibitor entry path to the luminal vestibule but also a channel leading to the ion binding site. Addition of K+ to the hydrated channel with molecular dynamics modeling of ion movement identified a pathway for K+ from the lumen to the ion binding site to give E2K. A K+ exit path to the cytoplasm operating during the normal catalytic cycle is also proposed on the basis of an E1K homology model derived from the E12Ca2+ form of the srCa ATPase (PDB code 1su4). Autodock analyses of the new E2P model now correctly discriminate between high- and low-affinity K+ competitive inhibitors. Finally, the expanded luminal vestibule of the E2P model explains high-affinity ouabain binding in a mutant of the H,K ATPase [Qiu et al. (2005) J. Biol. Chem. 280, 32349-32355].
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Affiliation(s)
- Keith Munson
- Laboratory of Membrane Biology, David Geffen School of Medicine at UCLA, and VA GLAHS, Los Angeles, California 90073, USA.
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27
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Gedda K, Briving C, Svensson K, Maxvall I, Andersson K. Mechanism of action of AZD0865, a K+-competitive inhibitor of gastric H+,K+-ATPase. Biochem Pharmacol 2007; 73:198-205. [PMID: 17081503 DOI: 10.1016/j.bcp.2006.09.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2006] [Revised: 09/20/2006] [Accepted: 09/20/2006] [Indexed: 01/28/2023]
Abstract
AZD0865 is a member of a drug class that inhibits gastric H(+),K(+)-ATPase by K(+)-competitive binding. The objective of these experiments was to characterize the mechanism of action, selectivity and inhibitory potency of AZD0865 in vitro. In porcine ion-leaky vesicles at pH 7.4, AZD0865 concentration-dependently inhibited K(+)-stimulated H(+),K(+)-ATPase activity (IC(50) 1.0+/-0.2 microM) but was more potent at pH 6.4 (IC(50) 0.13+/-0.01 microM). The IC(50) values for a permanent cation analogue, AR-H070091, were 11+/-1.2 microM at pH 7.4 and 16+/-1.8 microM at pH 6.4. These results suggest that the protonated form of AZD0865 inhibits H(+),K(+)-ATPase. In ion-tight vesicles, AZD0865 inhibited H(+),K(+)-ATPase more potently (IC(50) 6.9+/-0.4 nM) than in ion-leaky vesicles, suggesting a luminal site of action. AZD0865 inhibited acid formation in histamine- or dibutyryl-cAMP-stimulated rabbit gastric glands (IC(50) 0.28+/-0.01 and 0.26+/-0.003 microM, respectively). In ion-leaky vesicles at pH 7.4, AZD0865 (3 microM) immediately inhibited H(+),K(+)-ATPase activity by 88+/-1%. Immediately after a 10-fold dilution H(+),K(+)-ATPase inhibition was 41%, indicating reversible binding of AZD0865 to gastric H(+),K(+)-ATPase. In contrast to omeprazole, AZD0865 inhibited H(+),K(+)-ATPase activity in a K(+)-competitive manner (K(i) 46+/-3 nM). AZD0865 inhibited the process of cation occlusion concentration-dependently (IC(50) 1.7+/-0.06 microM). At 100 microM, AZD0865 reduced porcine renal Na(+),K(+)-ATPase activity by 9+/-2%, demonstrating a high selectivity for H(+),K(+)-ATPase. Thus, AZD0865 potently, K(+)-competitively, and selectively inhibits gastric H(+),K(+)-ATPase activity and acid formation in vitro, with a fast onset of effect.
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28
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Parsons ME, Keeling DJ. Novel approaches to the pharmacological blockade of gastric acid secretion. Expert Opin Investig Drugs 2006; 14:411-21. [PMID: 15882117 DOI: 10.1517/13543784.14.4.411] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Research into new methods of controlling acid secretion is driven by existing medical needs in gastro-oesophageal reflux disease treatment. Histamine receptor subtype 3 agonists offer one approach for acid inhibition but no agent is yet undergoing clinical testing. Other, as yet unrealized strategies include preventing the fusion of the tubulovesicular elements that contain H+/K+-ATPase with the parietal cell membrane, or blocking channels that recycle K+ in the parietal cell. Of more promise are gastrin (cholecystokinin) receptor antagonists and potassium-competitive acid blockers; examples of both are in clinical development. It is probable that gastrin receptor antagonists would be used adjunctively with proton pump inhibitors, possibly for meal-induced reflux. The potassium-competitive acid blockers have attributes that may facilitate use as monotherapy for the treatment of gastro-oesophageal reflux disease. The early promise of gastrin receptor antagonists and potassium-competitive acid blockers remains to be defined in large-scale trials.
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Affiliation(s)
- Michael E Parsons
- Department of Biosciences, University of Hertfordshire, Hatfield, Hertfordshire AL10 9AB, UK.
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29
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Kirchhoff P, Andersson K, Socrates T, Sidani S, Kosiek O, Geibel JP. Characteristics of the K+-competitive H+,K+-ATPase inhibitor AZD0865 in isolated rat gastric glands. Am J Physiol Gastrointest Liver Physiol 2006; 291:G838-43. [PMID: 16798725 DOI: 10.1152/ajpgi.00120.2006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The gastric H+,K+-ATPase of the parietal cell is responsible for acid secretion in the stomach and is the main target in the pharmacological treatment of acid-related diseases. Omeprazole and other benzimidazole drugs, although having delayed efficacy if taken orally, have high success rates in the treatment of peptic ulcer disease. Potassium competitive acid blockers (P-CAB) compete with K+ for binding to the H+,K+-ATPase and thereby they inhibit acid secretion. In this study, the in vitro properties of AZD0865, a reversible H+,K+-ATPase inhibitor of gastric acid secretion, are described. We used a digital-imaging system and the pH sensitive dye BCECF to observe proton efflux from hand-dissected rat gastric glands. Glands were stimulated with histamine (100 microM) and exposed to a bicarbonate- and Na+-free perfusate to induce an acid load. H+,K+-ATPase inhibition was determined by calculating pHi recovery (dpH/dT) in the presence of omeprazole (10-200 microM) or AZD0865 (0.01-100 microM). The efficacies of both drugs were compared. Our data show that acid secretion is inhibited by both the proton pump inhibitor omeprazole and the P-CAB AZD0865. Complete inhibition of acid secretion by AZD0865 had a rapid onset of activation, was reversible, and occurred at a 100-fold lower dose than omeprazole (1 microM AZD0865 vs. 100 microM omeprazole). This study demonstrates that AZD0865 is a potent, fast-acting inhibitor of gastric acid secretion, effective at lower concentrations than drugs of the benzimidazole class. Therefore, these data strongly suggest that AZD0865 has great potential as a fast-acting, low-dose inhibitor of acid secretion.
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Affiliation(s)
- P Kirchhoff
- Department of Surgery, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520, USA
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30
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Reyes N, Gadsby DC. Ion permeation through the Na+,K+-ATPase. Nature 2006; 443:470-4. [PMID: 17006516 DOI: 10.1038/nature05129] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Accepted: 07/26/2006] [Indexed: 11/09/2022]
Abstract
P-type ATPase pumps generate concentration gradients of cations across membranes in nearly all cells. They provide a polar transmembrane pathway, to which access is strictly controlled by coupled gates that are constrained to open alternately, thereby enabling thermodynamically uphill ion transport (for example, see ref. 1). Here we examine the ion pathway through the Na+,K+-ATPase, a representative P-type pump, after uncoupling its extra- and intracellular gates with the marine toxin palytoxin. We use small hydrophilic thiol-specific reagents as extracellular probes and we monitor their reactions, and the consequences, with cysteine residues introduced along the anticipated cation pathway through the pump. The distinct effects of differently charged reagents indicate that a wide outer vestibule penetrates deep into the Na+,K+-ATPase, where the pathway narrows and leads to a charge-selectivity filter. Acidic residues in this region, which are conserved to coordinate pumped ions, allow the approach of cations but exclude anions. Reversing the charge at just one of those positions converts the pathway from cation selective to anion selective. Close structural homology among the catalytic subunits of Ca2+-, Na+,K+- and H+,K+-ATPases argues that their extracytosolic cation exchange pathways all share these physical characteristics.
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Affiliation(s)
- Nicolás Reyes
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, New York 10021, USA
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31
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Piche T, Galmiche JP. Pharmacological targets in gastro-oesophageal reflux disease. Basic Clin Pharmacol Toxicol 2006; 97:333-41. [PMID: 16364047 DOI: 10.1111/j.1742-7843.2005.pto_273.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Although proton pump inhibitors have become the mainstay of treatment in gastro-oesophageal reflux disease (GORD), there are still unmet needs in the management of this very common disorder. For example, all current proton pump inhibitors have a relatively slow onset of action and their activity is limited mainly to the post-prandial period with far less effective inhibition of nocturnal acid secretion. In order to achieve more potent, rapid and sustained acid inhibition several compounds are currently under development, such as new proton pump inhibitors with a prolonged plasma half-life, potassium competitive ATPase blockers (PCABs), histamine H3 agonists, and gastrin antagonists. Acid suppression does not, however, cure the disease and relapses are frequently observed after discontinuation of proton pump inhibitor therapy. Among the different abnormalities involved in the pathophysiology of this multifactorial disease, transient lower oesophageal sphincter relaxations represent the major mechanism responsible for episodes of reflux. Baclofen, the prototype GABA(B) receptor agonist, is one of the most potent inhibitors of transient lower oesophageal sphincter relaxations identified. To date the transfer of these relaxation-controlling pharmacological agents into clinical practice has however been hampered by the occurrence of unacceptable side effects. Beside "anti-relaxation therapy", the potential of novel prokinetics such as motilin agonists has been explored, especially since the motilin receptor has been cloned. Thus far the broad therapeutic value of prokinetics in GORD does, however, seem very limited in terms of efficacy with respect to oesophageal motility and acid exposure. Lastly, further research is necessary to better understand the complex mechanisms involved in oesophageal sensitivity and mucosal defence.
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32
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Hibino T, Ishii Y, Levin M, Nishino A. Ion flow regulates left-right asymmetry in sea urchin development. Dev Genes Evol 2006; 216:265-76. [PMID: 16534626 DOI: 10.1007/s00427-005-0051-6] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2005] [Accepted: 12/06/2005] [Indexed: 11/29/2022]
Abstract
The degree of conservation among phyla of early mechanisms that pattern the left-right (LR) axis is poorly understood. Larvae of sea urchins exhibit consistently oriented LR asymmetry. The main part of the adult rudiment is formed from the left coelomic sac of larvae, the left hydrocoel. Although this left preference is conserved among all echinoderm larvae, its mechanism is largely not understood. Using two marker genes, HpNot and HpFoxFQ-like, which are asymmetrically expressed during larval development of the sea urchin Hemicentrotus pulcherrimus, we examined in this study the possibility that the recently discovered ion flux mechanism controls asymmetry in sea urchins as it does in several vertebrate species. Several ion-transporter inhibitors were screened for the ability to alter the expression of the asymmetric marker genes. Blockers of the H(+)/K(+)-ATPase (omeprazole, lansoprazole and SCH28080), as well as a calcium ionophore (A23187), significantly altered the normal sidedness of asymmetric gene expression. Exposure to omeprazole disrupted the consistent asymmetry of adult rudiment formation in larvae. Immuno-detection revealed that H(+)/K(+)-ATPase-like antigens in sea urchin embryos were present through blastula stage and exhibited a striking asymmetry being present in a single blastomere in 32-cell embryos. These results suggest that, as in vertebrates, endogenous spatially-regulated early transport of H(+) and/or K(+), and also of Ca(2+), functions in the establishment of LR asymmetry in sea urchin development.
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Affiliation(s)
- Taku Hibino
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
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33
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Abstract
Gastric acid secretion is a complex process that requires hormonal, neuronal, or calcium-sensing receptor activation for insertion of pumps into the apical surface of the parietal cell. Activation of any or all these pathways causes the parietal cell to secrete concentrated acid with a pH at or close to 1. This acidic fluid combines with enzymes that are secreted from neighbouring chief cells and passes out of the gland up through a mucous gel layer covering the surface of the stomach producing a final intragastric pH of less than 4 during the active phase of acid secretion. Defects in either the mucosal barrier or in the regulatory mechanisms that modulate the secretory pathways will result in erosion of the barrier and ulcerations of the stomach or esophagus. The entire process of acid secretion relies on activation of the catalytic cycle of the gastric H+,K+-ATPase, resulting in the secretion of acid into the parietal cell canaliculus, with K+ being the important and rate-limiting ion in this activation process. In addition to K+ as a rate limiter for acid production, Cl- secretion via an apical channel must also occur. In this review we present a discussion of the mechanics of acid secretion and a discussion of recently identified transporter proteins and receptors. Included is a discussion of some of the recent candidates for the apical K' recycling channel, as well as two recently identified apical proteins (NHE-3, PAT-1), and the newly characterized calcium-sensing receptor (CaSR). We hope that this review will give additional insight into the complex process of acid secretion.
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Affiliation(s)
- J P Geibel
- Yale University School of Medicine, Department of Surgery, BML 265, New Haven, 06520 CT, USA.
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34
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Abstract
Potassium (K+) ions are critical for the activation and catalytic cycle of the gastric H+,K+-ATPase, resulting in the secretion of hydrochloric acid into the parietal cell canaliculus. As both symptom, severity and esophageal mucosal damage in gastro-esophageal reflux disease (GERD) are related to the degree of acid exposure, K+ is a logical target for approaches to inhibit acid production. The probable K+ binding site on the gastric H+,K+-ATPase has recently been described and studies are elucidating how K+ activates the enzyme. K+ channels in the apical membrane of the parietal cell are implicated in the recycling of K+ and, to date, three potential K+ channels (KCNQ1, Kir2.1 and Kir4.1) have been identified. The channels represent theoretical sites for agents to control acid secretion but it will be difficult to develop selective blockers. An alternative strategy is to prevent K+ from activating gastric H+,K+-ATPase; the potassium-competitive acid blocker (P-CAB) class inhibits acid secretion by binding at or near the K+ binding site. Ongoing research is further defining the role of K+ in the functioning of the gastric H+,K+-ATPase, as well as determining the clinical utility of agents directed toward this important cation.
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Affiliation(s)
- John-P Geibel
- Department of Surgery, Yale University School of Medicine, BML 265, New Haven, CT 06520, USA.
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Andersson K, Carlsson E. Potassium-competitive acid blockade: a new therapeutic strategy in acid-related diseases. Pharmacol Ther 2005; 108:294-307. [PMID: 16000224 DOI: 10.1016/j.pharmthera.2005.05.005] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Accepted: 05/04/2005] [Indexed: 02/06/2023]
Abstract
Current therapies to treat gastroesophageal reflux disease (GERD), peptic ulcer disease (PUD), and other acid-related diseases either prevent stimulation of the parietal cell (H2 receptor antagonists, H2RAs) or inhibit gastric H+,K+-ATPase (e.g., proton pump inhibitors, PPIs). Of the 2 approaches, the inhibition of the final step in acid production by PPIs provides more effective relief of symptoms and healing. Despite the documented efficacy of the PPIs, therapeutic doses have a gradual onset of effect and do not provide complete symptom relief in all patients. There is scope for further improvements in acid suppressive therapy to maximize healing and offer more complete symptom relief. It is unlikely that cholecystokinin2 (CCK2, gastrin) receptor antagonists, a class in clinical trials, will be superior to H2RAs or PPIs. However, a new class of acid suppressant, the potassium-competitive acid blockers (P-CABs), is undergoing clinical trials in GERD and other acid-related diseases. These drugs block gastric H+,K+-ATPase by reversible and K+-competitive ionic binding. After oral doses, P-CABs rapidly achieve high plasma concentrations and have linear, dose-dependent pharmacokinetics. The pharmacodynamic properties reflect the pharmacokinetics of this group (i.e., the effect on acid secretion is correlated with plasma concentrations). These agents dose dependently inhibit gastric acid secretion with a fast onset of action and have similar effects after single and repeated doses (i.e., full effect from the first dose). Animal studies comparing P-CABs with PPIs suggest some important pharmacodynamic differences (e.g., faster and better control of 24-hr intragastric acidity). Studies in humans comparing PPIs with P-CABs will help to define the place of this new class in the management of acid-related diseases.
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36
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Abstract
The gastric H,K-ATPase catalyzes electroneutral exchange of H(+) for K(+) as a function of enzyme phosphorylation and dephosphorylation during transition between E(1)/E(1)-P (ion site in) and E(2)-P/E(2) (ion site out) conformations. Here we present homology modeling of the H,K-ATPase in the E(2)-P conformation as a means of predicting the interaction of the enzyme with two known classes of specific inhibitors. All known proton pump inhibitors, PPIs, form a disulfide bond with cysteine 813 that is accessible from the luminal surface. This allows allocation of the binding site to a luminal vestibule adjacent to Cys813 enclosed by part of TM4 and the loop between TM5 and TM6. K(+) competitive imidazo-1,2alpha-pyridines also bind to the luminal surface of the E(2)-P conformation, and their binding excludes PPI reaction. This overlap of the binding sites of the two classes of inhibitors combined with the results of site-directed mutagenesis and cysteine cross-linking allowed preliminary assignment of a docking mode for these reversible compounds in a position close to Glu795 that accounts for the detailed structure/activity relationships known for these compounds. The new E(2)-P model is able to assign a possible mechanism for acid secretion by this P(2)-type ATPase. Several ion binding side chains identified in the sr Ca-ATPase by crystallography are conserved in the Na,K- and H,K-ATPases. Poised in the middle of these, the H,K-ATPase substitutes lysine in place of a serine implicated in K(+) binding in the Na,K-ATPase. Molecular models for hydronium binding to E(1) versus E(2)-P predict outward displacement of the hydronium bound between Asp824, Glu820, and Glu795 by the R-NH(3)(+) of Lys791 during the conformational transition from E(1)P and E(2)P. The site for luminal K(+) binding at low pH is proposed to be between carbonyl oxygens in the nonhelical part of the fourth membrane span and carboxyl oxygens of Glu795 and Glu820. This site of K(+) binding is predicted to destabilize hydrogen bonds between these carboxylates and the -NH(3)(+) group of Lys791, allowing the Lys791 side chain to return to its E(1) position.
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Affiliation(s)
- Keith Munson
- Geffen School of Medicine, University of California at Los Angeles, and VAGLAHS, Los Angeles, California 90073, USA. kmunson@ ucla.edu
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