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Goraya N, Wesson DE. Pathophysiology of Diet-Induced Acid Stress. Int J Mol Sci 2024; 25:2336. [PMID: 38397012 PMCID: PMC10888592 DOI: 10.3390/ijms25042336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Revised: 02/13/2024] [Accepted: 02/14/2024] [Indexed: 02/25/2024] Open
Abstract
Diets can influence the body's acid-base status because specific food components yield acids, bases, or neither when metabolized. Animal-sourced foods yield acids and plant-sourced food, particularly fruits and vegetables, generally yield bases when metabolized. Modern diets proportionately contain more animal-sourced than plant-sourced foods, are, thereby, generally net acid-producing, and so constitute an ongoing acid challenge. Acid accumulation severe enough to reduce serum bicarbonate concentration, i.e., manifesting as chronic metabolic acidosis, the most extreme end of the continuum of "acid stress", harms bones and muscles and appears to enhance the progression of chronic kidney disease (CKD). Progressive acid accumulation that does not achieve the threshold amount necessary to cause chronic metabolic acidosis also appears to have deleterious effects. Specifically, identifiable acid retention without reduced serum bicarbonate concentration, which, in this review, we will call "covert acidosis", appears to cause kidney injury and exacerbate CKD progression. Furthermore, the chronic engagement of mechanisms to mitigate the ongoing acid challenge of modern diets also appears to threaten health, including kidney health. This review describes the full continuum of "acid stress" to which modern diets contribute and the mechanisms by which acid stress challenges health. Ongoing research will develop clinically useful tools to identify stages of acid stress earlier than metabolic acidosis and determine if dietary acid reduction lowers or eliminates the threats to health that these diets appear to cause.
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Affiliation(s)
- Nimrit Goraya
- Department of Internal Medicine, Baylor Scott & White Health, Temple, TX 76508, USA;
- Department of Internal Medicine, Texas A&M Health Science Center College of Medicine, Temple, TX 76508, USA
| | - Donald E. Wesson
- Department of Internal Medicine, Dell Medical School, The University of Texas at Austin, Dallas, TX 78712, USA
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Misella Hansen N, Kamper AL, Rix M, Feldt-Rasmussen B, Leipziger J, Sørensen MV, Berg P, Astrup A, Salomo L. Health effects of the New Nordic Renal Diet in patients with stage 3 and 4 chronic kidney disease, compared with habitual diet: a randomized trial. Am J Clin Nutr 2023; 118:1042-1054. [PMID: 37598748 DOI: 10.1016/j.ajcnut.2023.08.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 08/14/2023] [Accepted: 08/16/2023] [Indexed: 08/22/2023] Open
Abstract
BACKGROUND Chronic kidney disease (CKD) leads to an accumulation of waste products and causes adverse cardiometabolic effects. OBJECTIVES We investigated the health effects of the New Nordic Renal Diet (NNRD), a novel meal pattern reduced in phosphorus, protein, and sodium. METHODS A 26-wk randomized trial compared the NNRD with a habitual diet. The NNRD group received weekly home deliveries of food and recipes. Monthly study visits included fasting blood samples, 24-h urine samples, blood pressure, and anthropometric measurements. Intention-to-treat analysis used linear mixed-effects models. RESULTS Sixty patients, mean estimated glomerular filtration rate (eGFR) 34 mL/min/1.73 m2 and body mass index of 25-27 kg/m2, were included and 58 completed. Metabolic syndrome was present in 53% (NNRD group) and 57% (control group). The NNRD group (n = 30) reduced their 24-h urine phosphorus excretion by 19% (-153 mg; 95% confidence interval [CI]: -210, -95), control group (n = 30) (no change), between-group difference -171 mg (95% CI: -233, -109; P < 0.001). Proteinuria was reduced by 39% in the NNRD group (-0.33 g/d; 95% CI: -0.47, -0.18), control group (no change), between-group difference -0.34 g/d (95% CI: -0.52, -0.17; P < 0.001). Plasma urea was reduced by -1.5 mmol/L in the NNRD group (95% CI: -2.1, -0.9), control group (no change), between-group difference -1.4 mmol/L (95% CI: -2.0, -0.7; P < 0.001). Systolic blood pressure fell by -5.2 mmHg in the NNRD group (95% CI: -8.4, -2.1), control group (no change), between-group difference -3.9 mmHg (95% CI; -7.6, -0.2; P = 0.04). The NNRD group lost -1.7 kg (95% CI: -2.6, -0.8), control group (no change), between-group difference -2.0 kg (95% CI: -3.0, -1.0; P < 0.001). There were no effects on eGFR during the 26-wk intervention. CONCLUSION NNRD in moderate CKD reduces phosphorus excretion, proteinuria, systolic blood pressure, and weight, mainly by reducing abdominal fat. This trial was registered at clinicaltrials.gov as NCT04579315.
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Affiliation(s)
- Nikita Misella Hansen
- Department of Nephrology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
| | - Anne-Lise Kamper
- Department of Nephrology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark
| | - Marianne Rix
- Department of Nephrology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark
| | - Bo Feldt-Rasmussen
- Department of Nephrology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Jens Leipziger
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Peder Berg
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Arne Astrup
- Department of Obesity and Nutritional Sciences, Novo Nordisk Foundation, Hellerup, Denmark
| | - Louise Salomo
- Department of Nephrology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark
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Yekymov E, Attia D, Levi-Kalisman Y, Bitton R, Yerushalmi-Rozen R. Effects of Non-Ionic Micelles on the Acid-Base Equilibria of a Weak Polyelectrolyte. Polymers (Basel) 2022; 14:polym14091926. [PMID: 35567095 PMCID: PMC9100363 DOI: 10.3390/polym14091926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2022] [Revised: 04/28/2022] [Accepted: 05/03/2022] [Indexed: 02/01/2023] Open
Abstract
Weak polyelectrolytes (WPEs) are widely used as pH-responsive materials, pH modulators and charge regulators in biomedical and technological applications that involve multi-component fluid environments. In these complex fluids, coupling between (often weak) interactions induced by micelles, nanoparticles and molecular aggregates modify the pKa as compared to that measured in single component solutions. Here we investigated the effect of coupling between hydrogen bonding and excluded volume interactions on the titration curves and pKa of polyacrylic acid (PAA) in solutions comprising PEO-based micelles (Pluronics and Brij-S20) of different size and volume fraction. Titration experiments of dilute, salt-free solutions of PAA (5 kDa, 30 kDa and 100 kDa) at low degree of polymer ionization (α < 0.25) drive spatial re-organization of the system, reduce the degree of ionization and consequentially increase the pKa by up to ~0.7 units. These findings indicate that the actual degree of ionization of WPEs measured in complex fluids is significantly lower (at a given pH) than that measured in single-component solutions.
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Affiliation(s)
- Evgenee Yekymov
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel; (E.Y.); (D.A.); (R.B.)
| | - David Attia
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel; (E.Y.); (D.A.); (R.B.)
| | - Yael Levi-Kalisman
- The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel;
- The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Ronit Bitton
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel; (E.Y.); (D.A.); (R.B.)
- The Ilse Katz Institute for Nanoscience and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Rachel Yerushalmi-Rozen
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel; (E.Y.); (D.A.); (R.B.)
- The Ilse Katz Institute for Nanoscience and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- Correspondence:
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4
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Abstract
One of the main functions of the kidney is to excrete an acid load derived from both dietary and endogenous sources, thus maintaining the pH of other fluids in the body. Urine pH is also of particular interest in stone formers, since it determines the presence of either calcium phosphate or uric acid content in stones. Others have noted in epidemiological studies a rise in incidence of low pH-dependent uric acid stones with age, coinciding with a decrease in the incidence of high pH-dependent phosphate stones. Taken together, these trends are suggestive of a longitudinal decline in urine pH in stone-forming patients, and, if true, this could explain the observed trends in stone incidence. We studied 7,891 stone formers, all of whom collected a 24-h urine sample and matching serum. Multivariate modeling revealed that urine pH did indeed fall with age and particularly between the ages of 20 and 50 yr old in both men and women. We sought to explain this trend through the inclusion of traditionally understood determinants of urine pH such as urinary buffers, estimates of glomerular filtration, and dietary acid load, but these, taken together, accounted for but a small fraction of the pH fall. Gastrointestinal anion absorption was the strongest predictor of urine pH in all age groups, as we have previously reported in middle-aged normal men and women. However, we found that, despite a decreasing urine pH, gastrointestinal anion absorption increased monotonically with age. In fact, after adjustment for gastrointestinal anion absorption, urine pH declined more markedly, suggesting that bicarbonate-producing anion absorption is regulated in a manner that offsets the decline of urine pH.
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Affiliation(s)
- Cameron J Menezes
- Department of Medicine, University of Chicago Medicine , Chicago, Illinois
| | - Elaine M Worcester
- Department of Medicine, University of Chicago Medicine , Chicago, Illinois
| | - Fredric L Coe
- Department of Medicine, University of Chicago Medicine , Chicago, Illinois
| | - John Asplin
- Litholink, Laboratory Corporation of America Holdings , Chicago, Illinois
| | | | - Benjamin Ko
- Department of Medicine, University of Chicago Medicine , Chicago, Illinois
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Martha SR, Collier LA, Davis SM, Goodwin SJ, Powell D, Lukins D, Fraser JF, Pennypacker KR. Early acid/base and electrolyte changes in permanent middle cerebral artery occlusion: Aged male and female rats. J Neurosci Res 2019; 98:179-190. [PMID: 30942522 DOI: 10.1002/jnr.24422] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 02/28/2019] [Accepted: 03/11/2019] [Indexed: 01/04/2023]
Abstract
BACKGROUND Early changes in acid/base and electrolyte concentrations could provide insights into the development of neuropathology at the onset of stroke. We evaluated associations between acid/base and electrolyte concentrations, and outcomes in permanent middle cerebral artery occlusion (pMCAO) model. METHODS 18-month-old male and female Sprague-Dawley rats underwent pMCAO. Pre-, post- (7 min after occlusion), and at 72 hr of pMCAO venous blood samples provided pH, carbon dioxide, oxygen, glucose, hematocrit, hemoglobin, and electrolyte values of ionized calcium, potassium, and sodium. Multiple linear regression determined predictors of infarct and edema volumes from these values, Kaplan-Meier curve analyzed morality between males and females at 72 hr, and a Cox regression model was used to determine predictors for mortality. RESULTS Analysis indicated significant differences in acid/base balance and electrolyte levels in aged rats not dependent on sex between the three time points in the pMCAO model. Changes in pH (from pre- to post and post- to 72 hr) and changes in sodium and ionized calcium (from post- to 72 hr) were predictors of infarct volume and edema volume, respectively. Cox Regression revealed there is a 3.25 times increased risk for mortality based on changes in bicarbonate (pre- to post-MCAO). CONCLUSIONS These early venous blood changes in acid/base balance and electrolytes can be used to predict stroke outcomes in our rat model of stroke. This study provides potential biomarkers to be examined in the human condition that could provide profound prognostic tools for stroke patients.
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Affiliation(s)
- Sarah R Martha
- College of Nursing, University of Kentucky, Lexington, Kentucky
| | - Lisa A Collier
- Department of Neurology, University of Kentucky, Lexington, Kentucky
| | - Stephanie M Davis
- Department of Neurology, University of Kentucky, Lexington, Kentucky
| | - Sarah J Goodwin
- Department of Neurology, University of Kentucky, Lexington, Kentucky
| | - David Powell
- Magnetic Resonance Imaging and Spectroscopy Center, University of Kentucky, Lexington, Kentucky.,Department of Biomedical Imaging, University of Kentucky, Lexington, Kentucky
| | - Doug Lukins
- Department of Neurosurgery, University of Kentucky, Lexington, Kentucky.,Department of Neuroscience, University of Kentucky, Lexington, Kentucky.,Department of Radiology, University of Kentucky, Lexington, Kentucky
| | - Justin F Fraser
- Department of Neurology, University of Kentucky, Lexington, Kentucky.,Department of Neurosurgery, University of Kentucky, Lexington, Kentucky.,Department of Neuroscience, University of Kentucky, Lexington, Kentucky.,Department of Radiology, University of Kentucky, Lexington, Kentucky
| | - Keith R Pennypacker
- Department of Neurology, University of Kentucky, Lexington, Kentucky.,Department of Neuroscience, University of Kentucky, Lexington, Kentucky
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Abstract
Topiramate is an anticonvulsant that is being increasingly used for a number of different off-label indications. Its inhibition of carbonic anhydrase isoenzymes can lead to metabolic acidosis, elevated urine pH, reduced urine citrate, and hypercalciuria, thereby creating a milieu that is ripe for calcium phosphate stone formation. In this review, we describe a case of topiramate-induced metabolic acidosis. We review the frequency of metabolic acidosis among children and adults, as well as the mechanism of hyperchloremic metabolic acidosis and renal tubular acidosis in topiramate users. Finally, we describe the long-term effects of topiramate-induced metabolic acidosis, including nephrolithiasis, nephrocalcinosis, and bone degradation. Patients who are prescribed topiramate should be carefully monitored for metabolic derangements, and they may benefit from alkali supplementation, or in extreme cases, discontinuation of the drug altogether.
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Affiliation(s)
- Shruti Gupta
- a Harvard Medical School , Massachusetts General Hospital , Boston , MA , USA
| | - Jennifer J Gao
- a Harvard Medical School , Massachusetts General Hospital , Boston , MA , USA
| | - Michael Emmett
- b Department of Internal Medicine , Baylor University Medical Center , Dallas , TX , USA
| | - Andrew Z Fenves
- a Harvard Medical School , Massachusetts General Hospital , Boston , MA , USA
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Weinberg L, Chiam E, Hooper J, Liskaser F, Hawkins AK, Massie D, Ellis A, Tan CO, Story D, Bellomo R. Plasma-Lyte 148 vs. Hartmann's solution for cardiopulmonary bypass pump prime: a prospective double-blind randomized trial. Perfusion 2017; 33:310-319. [PMID: 29144182 DOI: 10.1177/0267659117742479] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
BACKGROUND The mechanisms of acid-base changes during cardiopulmonary bypass (CPB) remain unclear. We tested the hypothesis that, when used as CPB pump prime solutions, Plasma-Lyte 148 (PL) and Hartmann's solution (HS) have differential mechanisms of action in their contribution to acid-base changes. METHODS We performed a prospective, double-blind, randomized trial in adult patients undergoing elective cardiac surgery with CPB. Participants received a CPB prime solution of 2000 mL, with either PL or HS. The primary endpoint was the standard base excess (SBE) value measured at 60 minutes after full CPB flows (SBE60min). Secondary outcomes included changes in SBE, pH, chloride, sodium, lactate, gluconate, acetate, strong ion difference and strong ion gap at two (T2min), five (T5min), ten (T10min), thirty (T30min) and sixty (T60min) minutes on CPB. The primary outcome was measured using a two-tailed Welch's t-test. Repeated measures ANOVA was used to test for differences between time points. RESULTS Twenty-five participants were randomized to PL and 25 to HS. Baseline characteristics, EURO and APACHE scores, biochemistry, hematology and volumes of cardioplegia were similar. Mean (SD) SBE at T60min was -1.3 (1.4) in the PL group and -0.1 (2.7) in the HS group; p=0.55. No significant differences in SBE between the groups was observed during the first 60 minutes (p=0.48). During CPB, there was hyperacetatemia and hypergluconatemia in the PL group and hyperlactatemia and hyperchloremia in the HS group. No significant difference between the groups in plasma bicarbonate levels and total weak acid levels were found. Complications and intensive care unit and hospital length of stays were similar. CONCLUSIONS During CPB, PL and HS did not cause a significant metabolic acidosis. There was hyperacetatemia and hypergluconatemia with PL and hyperchloremia and hyperlactatemia with HS. These physiochemical effects appear clinically innocuous.
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Affiliation(s)
- Laurence Weinberg
- 1 Department of Anesthesia, Austin Health, Heidelberg, Victoria, Australia.,2 Department of Surgery, The University of Melbourne, Austin Health, Victoria, Australia
| | - Elizabeth Chiam
- 2 Department of Surgery, The University of Melbourne, Austin Health, Victoria, Australia
| | - James Hooper
- 1 Department of Anesthesia, Austin Health, Heidelberg, Victoria, Australia
| | - Frank Liskaser
- 1 Department of Anesthesia, Austin Health, Heidelberg, Victoria, Australia
| | - Angela Kim Hawkins
- 1 Department of Anesthesia, Austin Health, Heidelberg, Victoria, Australia
| | - Denise Massie
- 3 Department of Clinical Pharmacology & Therapeutics, Austin Hospital, Heidelberg, Victoria, Australia
| | - Andrew Ellis
- 3 Department of Clinical Pharmacology & Therapeutics, Austin Hospital, Heidelberg, Victoria, Australia
| | - Chong O Tan
- 1 Department of Anesthesia, Austin Health, Heidelberg, Victoria, Australia
| | - David Story
- 4 Anesthesia, Perioperative and Pain Medicine Unit, Melbourne Medical School, University of Melbourne, Victoria, Australia
| | - Rinaldo Bellomo
- 5 Department of Intensive Care, The University of Melbourne, Victoria, Australia
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Elbers PWG, Van Regenmortel N, Gatz R. Over ten thousand cases and counting: acidbase.org is serving the critical care community. Anaesthesiol Intensive Ther 2015; 47:441-8. [PMID: 26459229 DOI: 10.5603/ait.a2015.0060] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 09/29/2015] [Indexed: 11/25/2022] Open
Abstract
Acidbase.org has been serving the critical care community for over a decade. The backbone of this online resource consists of Peter Stewart's original text "How to understand Acid-Base" which is freely available to everyone. In addition, Stewart's Textbook of Acid Base, which puts the theory in today's clinical context is available for purchase from the website. However, many intensivists use acidbase.org on a daily basis for its educational content and in particular for its analysis module. This review provides an overview of the history of the website, a tutorial and descriptive statistics of over 10,000 queries submitted to the analysis module.
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Affiliation(s)
- Paul W G Elbers
- Department of Intensive Care Medicine; Research VUmc Intensive Care; Institute for Cardiovascular Research Vrije Universiteit (ICaR-VU), VU University Medical Center Amsterdam, Amsterdam, Netherlands.
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Lee HW, Osis G, Handlogten ME, Guo H, Verlander JW, Weiner ID. Effect of dietary protein restriction on renal ammonia metabolism. Am J Physiol Renal Physiol 2015; 308:F1463-73. [PMID: 25925252 DOI: 10.1152/ajprenal.00077.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 04/20/2015] [Indexed: 11/22/2022] Open
Abstract
Dietary protein restriction has multiple benefits in kidney disease. Because protein intake is a major determinant of endogenous acid production, it is important that net acid excretion change in parallel during protein restriction. Ammonia is the primary component of net acid excretion, and inappropriate ammonia excretion can lead to negative nitrogen balance. Accordingly, we examined ammonia excretion in response to protein restriction and then we determined the molecular mechanism of the changes observed. Wild-type C57Bl/6 mice fed a 20% protein diet and then changed to 6% protein developed an 85% reduction in ammonia excretion within 2 days, which persisted during a 10-day study. The expression of multiple proteins involved in renal ammonia metabolism was altered, including the ammonia-generating enzymes phosphate-dependent glutaminase (PDG) and phosphoenolpyruvate carboxykinase (PEPCK) and the ammonia-metabolizing enzyme glutamine synthetase. Rhbg, an ammonia transporter, increased in expression in the inner stripe of outer medullary collecting duct intercalated cell (OMCDis-IC). However, collecting duct-specific Rhbg deletion did not alter the response to protein restriction. Rhcg deletion did not alter ammonia excretion in response to dietary protein restriction. These results indicate 1) dietary protein restriction decreases renal ammonia excretion through coordinated regulation of multiple components of ammonia metabolism; 2) increased Rhbg expression in the OMCDis-IC may indicate a biological role in addition to ammonia transport; and 3) Rhcg expression is not necessary to decrease ammonia excretion during dietary protein restriction.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hui Guo
- Division of Nephrology, Second Hospital of Shanxi Medical University, Yaiyuan, Shanxi, Peoples Republic of China; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida, Nephrology and Hypertension Section, Medical Service, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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Abstract
Mutations in the electrogenic Na(+)/HCO3(-) cotransporter (NBCe1) that cause proximal renal tubular acidosis (pRTA), glaucoma, and cataracts in patients are recessive. Parents and siblings of these affected individuals seem asymptomatic although their tissues should make some mutant NBCe1 protein. Biochemical studies with AE1 and NBCe1 indicate that both, and probably all, Slc4 members form dimers. However, the physiologic implications of dimerization have not yet been fully explored. Here, human NBCe1A dimerization is demonstrated by biomolecular fluorescence complementation (BiFC). An enhanced yellow fluorescent protein (EYFP) fragment (1-158, EYFP(N)) or (159-238, EYFP(C)) was fused to the NH2 or COOH terminus of NBCe1A and mix-and-matched expressed in Xenopus oocyte. The EYFP fluorescent signal was observed only when both EYFP fragments are fused to the NH2 terminus of NBCe1A (EYFP(N)-N-NBCe1A w/ EYFP(C)-N-NBCe1A), and the electrophysiology data demonstrated this EYFP-NBCe1A coexpressed pair have wild-type transport function. These data suggest NBCe1A forms dimers and that NH2 termini from the two monomers are in close proximity, likely pair up, to form a functional unit. To explore the physiologic significance of NBCe1 dimerization, we chose two severe NBCe1 mutations (6.6 and 20% wild-type function individually): S427L (naturally occurring) and E91R (for NH2-terminal structure studies). When we coexpressed S427L and E91R, we measured 50% wild-type function, which can only occur if the S427L-E91R heterodimer is the functional unit. We hypothesize that the dominant negative effect of heterozygous NBCe1 carrier should be obvious if the mutated residues are structurally crucial to the dimer formation. The S427L-E91R heterodimer complex allows the monomers to structurally complement each other resulting in a dimer with wild-type like function.
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Affiliation(s)
- Min-Hwang Chang
- Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55905.
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