1
|
Kuhn C, Mohebbi N, Ritter A. Metabolic acidosis in chronic kidney disease: mere consequence or also culprit? Pflugers Arch 2024; 476:579-592. [PMID: 38279993 PMCID: PMC11006741 DOI: 10.1007/s00424-024-02912-5] [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] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 01/11/2024] [Accepted: 01/12/2024] [Indexed: 01/29/2024]
Abstract
Metabolic acidosis is a frequent complication in non-transplant chronic kidney disease (CKD) and after kidney transplantation. It occurs when net endogenous acid production exceeds net acid excretion. While nephron loss with reduced ammoniagenesis is the main cause of acid retention in non-transplant CKD patients, additional pathophysiological mechanisms are likely inflicted in kidney transplant recipients. Functional tubular damage by calcineurin inhibitors seems to play a key role causing renal tubular acidosis. Notably, experimental and clinical studies over the past decades have provided evidence that metabolic acidosis may not only be a consequence of CKD but also a driver of disease. In metabolic acidosis, activation of hormonal systems and the complement system resulting in fibrosis have been described. Further studies of changes in renal metabolism will likely contribute to a deeper understanding of the pathophysiology of metabolic acidosis in CKD. While alkali supplementation in case of reduced serum bicarbonate < 22 mmol/l has been endorsed by CKD guidelines for many years to slow renal functional decline, among other considerations, beneficial effects and thresholds for treatment have lately been under intense debate. This review article discusses this topic in light of the most recent results of trials assessing the efficacy of dietary and pharmacological interventions in CKD and kidney transplant patients.
Collapse
Affiliation(s)
- Christian Kuhn
- Clinic for Nephrology and Transplantation Medicine, Cantonal Hospital St. Gallen, St. Gallen, Switzerland
| | | | - Alexander Ritter
- Clinic for Nephrology and Transplantation Medicine, Cantonal Hospital St. Gallen, St. Gallen, Switzerland.
- Clinic for Nephrology, University Hospital Zurich, Zurich, Switzerland.
| |
Collapse
|
2
|
|
3
|
Affiliation(s)
- S Garella
- Department of Medicine, Michael Reese Hospital and Medical Center, University of Chicago, Ill
| |
Collapse
|
4
|
Abstract
Rickets is a condition in which there is failure of the normal mineralisation (osteomalacia) of growing bone. Whilst osteomalacia may be present in adults, rickets cannot occur. It is generally caused by a lack of mineral supply, which can either occur as a result of the deficiency of calcium (calciopaenic rickets, now known as parathyroid hormone-dependent rickets) or of phosphate (phosphopaenic rickets, now called FGF23-dependent rickets). Renal disorders may also interfere with the process of mineralisation and cause rickets. Only parathyroid hormone-dependent rickets and distal renal tubular disorders will be discussed in this chapter. The most common cause of rickets is still vitamin D deficiency, which is also responsible for other problems. Disorders of vitamin D metabolism or responsiveness may also cause similar issues. Distal renal tubular acidosis may also be caused by a variety of metabolic errors similar to those of osteoclasts. One form of distal renal tubular acidosis also causes a type of osteopetrosis. This chapter describes these conditions in detail and sets out a logical approach for treatment.
Collapse
|
5
|
Akin D, Ozmen S. Type 4 renal tubular acidosis in a patient with lupus nephritis. Iran J Kidney Dis 2014; 8:73-75. [PMID: 24413726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 07/05/2013] [Accepted: 07/13/2013] [Indexed: 06/03/2023]
Abstract
Although renal tubular acidosis (RTA) is a rare complication of systemic lupus erythematosus (SLE), type 4 RTA associated with lupus nephritis is extremely rare. A 20-year-old woman presented with malaise and edema in the lower extremities and face. She had multiple lymphadenopathies. There were 20% eosinophil in blood smear and 32% in bone marrow aspiration. Serology revealed positive antinuclear antibody at 1:1000 titer, positive double-stranded DNA antibodies, and low complements C3 and C4 levels. Urinary sediment was active and urinary protein excretion was 4.8 g/d. The SLE Disease Activity Index score was 23. A high SLE Disease Activity Index scores was proposed as a potential risk factor for type 4 RTA. Type 4 RTA may complicate SLE, and specifically, patients with high SLEDAI scores and lymphadenopathy may pose a high risk. Our patient responded successfully to immunomodulatory therapy.
Collapse
Affiliation(s)
- Davut Akin
- Department of Nephrology, Dicle University School of Medicine, Denizli, Turkey.
| | | |
Collapse
|
6
|
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
Collapse
Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
| | | |
Collapse
|
7
|
Golembiewska E, Ciechanowski K. Renal tubular acidosis--underrated problem? Acta Biochim Pol 2012; 59:213-217. [PMID: 22693689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 06/01/2012] [Accepted: 06/05/2012] [Indexed: 06/01/2023]
Abstract
Renal tubular acidosis (RTA) is a hyperchloremic metabolic acidosis characterized by a normal anion gap and normal (or near normal) glomerular filtration rate in the absence of diarrhoea. Inherited isolated forms of renal tubular acidosis are not common. However, they can also be a part of a more generalized tubule defect, like in Fanconi syndrome. In recent years more and more gene mutations have been found which are associated with RTA (mutations in the gene SLC4A4, encoding a Na(+)-HCO(3)(-) cotransporter (NBC-1); in the gene SLC4A1, encoding Cl(-)/HCO3(-) exchanger (AE1); in the gene ATP6B1, encoding B1 subunit of H(+)-ATPase; in the gene CA2 encoding carbonic anhydrase II; and others) and allow better understanding of underlying processes of bicarbonate and H(+) transport. Isolated renal tubular acidosis can be frequently acquired due to use of certain drug groups, autoimmune disease or kidney transplantation. As the prevalence of acquired forms of RTA is common, new therapeutic options for the currently used supplementation of oral alkali, are awaited.
Collapse
Affiliation(s)
- Edyta Golembiewska
- Department of Nephrology, Transplantology and Internal Medicine, Pomeranian Medical University, Szczecin, Poland.
| | | |
Collapse
|
8
|
Parker MD, Qin X, Williamson RC, Toye AM, Boron WF. HCO(3)(-)-independent conductance with a mutant Na(+)/HCO(3)(-) cotransporter (SLC4A4) in a case of proximal renal tubular acidosis with hypokalaemic paralysis. J Physiol 2012; 590:2009-34. [PMID: 22331414 PMCID: PMC3573318 DOI: 10.1113/jphysiol.2011.224733] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 02/07/2012] [Indexed: 12/14/2022] Open
Abstract
The renal electrogenic Na(+)/HCO(3)(−) cotransporter (NBCe1-A) contributes to the basolateral step of transepithelial HCO(3)(−) reabsorption in proximal tubule epithelia, contributing to the buffering of blood pH. Elsewhere in the body (e.g. muscle cells) NBCe1 variants contribute to, amongst other processes, maintenance of intracellular pH. Others have described a homozygous mutation in NBCe1 (NBCe1-A p.Ala799Val) in an individual with severe proximal renal tubular acidosis (pRTA; usually associated with defective HCO(3)(−) reabsorption in proximal tubule cells) and hypokalaemic periodic paralysis (hypoPP; usually associated with leaky cation channels in muscle cells). Using biotinylation and two-electrode voltage-clamp on Xenopus oocytes expressing NBCe1, we demonstrate that the mutant NBCe1-A (A(A799V)) exhibits a per-molecule transport defect that probably contributes towards the observed pRTA. Furthermore, we find that A(A799V) expression is associated with an unusual HCO(3)(−)-independent conductance that, if associated with mutant NBCe1 in muscle cells, could contribute towards the appearance of hypokalaemic paralysis in the affected individual. We also study three novel lab mutants of NBCe1-A: p.Ala799Ile, p.Ala799Gly and p.Ala799Ser. All three exhibit a per-molecule transport defect, but only A(A799I) exhibits an A(A799V)-like ion conductance. A(A799G) and A(A799S) exhibit unusual outward rectification in their HCO(3)(−)-dependent conductance and A(A799G) exhibits reduced sensitivity to both DIDS and tenidap. A799G is the first mutation shown to affect the apparent tenidap affinity of NBCe1. Finally we show that A(A799V) and A(A799I), which accumulate poorly in the plasma membrane of oocytes, exhibit signs of abnormal intracellular accumulation in a non-polarized renal cell-line.
Collapse
Affiliation(s)
- Mark D Parker
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
| | | | | | | | | |
Collapse
|
9
|
Affiliation(s)
- H U Rehman
- Department of Medicine, Regina Qu'Appelle Health Region, Regina General Hospital, Regina, SK, Canada S4P 0W5.
| |
Collapse
|
10
|
Kang SH, Kim J, Park JW. Biopsy-proven type 1 renal tubular acidosis in a patient with metabolic acidosis. Korean J Intern Med 2012; 27:119. [PMID: 22403514 PMCID: PMC3295982 DOI: 10.3904/kjim.2012.27.1.119] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 05/11/2011] [Accepted: 06/08/2011] [Indexed: 11/27/2022] Open
Affiliation(s)
- Seok Hui Kang
- Division of Nephrology, Department of Internal Medicine, Yeungnam University Hospital, Daegu, Korea
| | | | | |
Collapse
|
11
|
Khositseth S. Transient hyperkalemic distal renal tubular acidosis with bicarbonate wasting in a young child. J Med Assoc Thai 2011; 94 Suppl 7:S204-S207. [PMID: 22619931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Distal renal tubular acidosis is a clinical syndrome characterized by inability to acidify urine in the presence of metabolic acidosis. Classic dRTA patients exhibit failure to thrive, polyuria, metabolic acidosis and hypokalemia. Hyperkalemic dRTA without underlying disease is very rare. Transient bicarbonate wasting accompanied with hypokalemic dRTA was reported in infants. Herein, a transient hyperkalemic dRTA with bicarbonate wasting was reported in a young child.
Collapse
Affiliation(s)
- Sookkasem Khositseth
- Department of Pediatrics, Faculty of Medicine, Thammasat University, Klongloung, Pathumthani, Thailand.
| |
Collapse
|
12
|
Abstract
Renal tubular acidosis (RTA) is a group of disorders observed in patients with normal anion gap metabolic acidosis. There are three major forms of RTA: A proximal (type II) RTA and two types of distal RTAs (type I and type IV). Proximal (type II) RTA originates from the inability to reabsorb bicarbonate normally in the proximal tubule. Type I RTA is associated with inability to excrete the daily acid load and may present with hyperkalaemia or hypokalaemia. The most prominent abnormality in type IV RTA is hyperkalaemia caused by hypoaldosteronism. This article extensively reviews the mechanism of hydrogen ion generation from metabolism of normal diet and various forms of RTA leading to disruptions of normal acid-base handling by the kidneys.
Collapse
Affiliation(s)
- P Reddy
- Department of Medicine, University of Florida College of Medicine, Jacksonville, FL 32209, USA.
| |
Collapse
|
13
|
Malik SI, Naqvi R, Ahmed E, Zafar MN. Prevalence and risk factors of renal tubular acidosis after kidney transplantation. J PAK MED ASSOC 2011; 61:23-27. [PMID: 22368897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
OBJECTIVE To asses the prevalence of post-transplant renal tubular acidosis (RTA) and its associated risk factors. METHODS A cross-sectional study was conducted on 100 live related renal transplant recipients, with a transplant duration of more than one year and an estimated GFR > 40 ml/min/1.73m2. Patients with acute graft rejection within last 6 months, unstable graft function, acute urinary tract infection and diarrhoea were excluded. Renal Tubular Acidosis (RTA) was diagnosed on the basis of plasma bicarbonate, venous pH, urine and serum anion gap measurements. RESULTS Out of 100 patients (74 male, 26 female) RTA was observed in 40 (29 male, 11 female). Patients with RTA had a lower GFR (65.87 +/- 12.35 versus 74.23 +/- 14.8 ml/min/1.73m2, P = 0.004) and higher number of previous acute rejections. Lower bicarbonate was associated with higher serum chloride (108.2 +/- 3.19 versus 105.72 +/- 3.9 mEq/L, P = 0.001) and higher potassium concentration (3.95 +/- 0.53 vs 3.61 +/- 0.46 mg/dl, P = 0.001). Higher phosphorous level (3.46 +/- 0.71 in RTA vs 3.19 +/- 0.59 mg/dl in non-RTA, P = 0.045) but lower total serum calcium concentrations were found in patients with RTA. Intake of angiotensin converting enzyme inhibitors (ACE 1) was associated with the development of RTA. Calcineurin inhibitor (CNI) therapy was not associated with an increased likelihood of RTA. While no difference was noted in sex, age, pre-transplant dialysis duration, post transplant period, body mass index and serum albumin levels. CONCLUSION There is a high prevalence of RTA in renal transplant recipients. In most of the patients, this is subclinical and does not require treatment.
Collapse
Affiliation(s)
- Suhail Iqbal Malik
- Department of Nephrology, Sindh Institute of Urology and Transplantation (SIUT) Karachi, Pakistan
| | | | | | | |
Collapse
|
14
|
Abstract
Renal ammonia excretion is the predominant component of renal net acid excretion. The majority of ammonia excretion is produced in the kidney and then undergoes regulated transport in a number of renal epithelial segments. Recent findings have substantially altered our understanding of renal ammonia transport. In particular, the classic model of passive, diffusive NH3 movement coupled with NH4+ "trapping" is being replaced by a model in which specific proteins mediate regulated transport of NH3 and NH4+ across plasma membranes. In the proximal tubule, the apical Na+/H+ exchanger, NHE-3, is a major mechanism of preferential NH4+ secretion. In the thick ascending limb of Henle's loop, the apical Na+-K+-2Cl- cotransporter, NKCC2, is a major contributor to ammonia reabsorption and the basolateral Na+/H+ exchanger, NHE-4, appears to be important for basolateral NH4+ exit. The collecting duct is a major site for renal ammonia secretion, involving parallel H+ secretion and NH3 secretion. The Rhesus glycoproteins, Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg), are recently recognized ammonia transporters in the distal tubule and collecting duct. Rhcg is present in both the apical and basolateral plasma membrane, is expressed in parallel with renal ammonia excretion, and mediates a critical role in renal ammonia excretion and collecting duct ammonia transport. Rhbg is expressed specifically in the basolateral plasma membrane, and its role in renal acid-base homeostasis is controversial. In the inner medullary collecting duct (IMCD), basolateral Na+-K+-ATPase enables active basolateral NH4+ uptake. In addition to these proteins, several other proteins also contribute to renal NH3/NH4+ transport. The role and mechanisms of these proteins are discussed in depth in this review.
Collapse
Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, FL 32610, USA.
| | | |
Collapse
|
15
|
Xu J, Song P, Nakamura S, Miller M, Barone S, Alper SL, Riederer B, Bonhagen J, Arend LJ, Amlal H, Seidler U, Soleimani M. Deletion of the chloride transporter slc26a7 causes distal renal tubular acidosis and impairs gastric acid secretion. J Biol Chem 2009; 284:29470-9. [PMID: 19723628 PMCID: PMC2785580 DOI: 10.1074/jbc.m109.044396] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 08/18/2009] [Indexed: 11/06/2022] Open
Abstract
SLC26A7 (human)/Slc26a7 (mouse) is a recently identified chloride-base exchanger and/or chloride transporter that is expressed on the basolateral membrane of acid-secreting cells in the renal outer medullary collecting duct (OMCD) and in gastric parietal cells. Here, we show that mice with genetic deletion of Slc26a7 expression develop distal renal tubular acidosis, as manifested by metabolic acidosis and alkaline urine pH. In the kidney, basolateral Cl(-)/HCO3(-) exchange activity in acid-secreting intercalated cells in the OMCD was significantly decreased in hypertonic medium (a normal milieu for the medulla) but was reduced only mildly in isotonic medium. Changing from a hypertonic to isotonic medium (relative hypotonicity) decreased the membrane abundance of Slc26a7 in kidney cells in vivo and in vitro. In the stomach, stimulated acid secretion was significantly impaired in isolated gastric mucosa and in the intact organ. We propose that SLC26A7 dysfunction should be investigated as a potential cause of unexplained distal renal tubular acidosis or decreased gastric acid secretion in humans.
Collapse
Affiliation(s)
- Jie Xu
- From Research Services, Veterans Affairs Medical Center, Cincinnati, Ohio 45220
- the Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
| | - Penghong Song
- the Department of Gastroenterology, University of Hannover, 30625 Hannover, Germany
| | - Suguru Nakamura
- the Department of Biological Sciences, Murray State University, Murray, Kentucky 42071
| | | | - Sharon Barone
- the Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
- the Center on Genetics of Transport and Epithelial Biology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Seth L. Alper
- the Renal Division, Beth Israel Deaconess Medical Center, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115, and
| | - Brigitte Riederer
- the Department of Gastroenterology, University of Hannover, 30625 Hannover, Germany
| | - Janina Bonhagen
- the Department of Gastroenterology, University of Hannover, 30625 Hannover, Germany
| | - Lois J. Arend
- Pathology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Hassane Amlal
- the Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
- the Center on Genetics of Transport and Epithelial Biology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Ursula Seidler
- the Department of Gastroenterology, University of Hannover, 30625 Hannover, Germany
| | - Manoocher Soleimani
- From Research Services, Veterans Affairs Medical Center, Cincinnati, Ohio 45220
- the Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
- the Center on Genetics of Transport and Epithelial Biology, University of Cincinnati, Cincinnati, Ohio 45267
| |
Collapse
|
16
|
Abstract
Rickets is a condition in which there is failure of normal mineralisation (osteomalacia) of growing bone. Whilst osteomalacia may be present in adults, rickets cannot occur. It is generally caused by a lack of mineral supply which can either be as a result of deficiency of calcium (calciopaenic rickets) or of phosphate (phosphopaenic rickets) although, in addition, renal tubular acidosis may also interfere with the process of mineralisation and cause rickets. Only calciopaenic and distal renal tubular disorders will be discussed in this chapter. The commonest cause of rickets is still vitamin D deficiency which is also responsible for problems other than rickets. Disorders of vitamin D metabolism or responsiveness may also cause similar problems. Distal renal tubular acidosis may be caused by a variety of metabolic errors similar to those of osteoclasts. One form of DRTA also causes a form of osteopetrosis. This chapter describes these conditions in detail and sets out a logical approach to treatment.
Collapse
Affiliation(s)
- Jeremy Allgrove
- Department of Paediatric Endocrinology, Royal London Hospital, Whitechapel, London, UK.
| |
Collapse
|
17
|
|
18
|
Katzir Z, Dinour D, Reznik-Wolf H, Nissenkorn A, Holtzman E. Familial pure proximal renal tubular acidosis--a clinical and genetic study. Nephrol Dial Transplant 2007; 23:1211-5. [PMID: 17881426 DOI: 10.1093/ndt/gfm583] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Inherited proximal renal tubular acidosis (pRTA) is commonly associated with more generalized proximal tubular dysfunctions and occasionally with other organ system defects. Inherited combined pRTA and distal RTA with osteopetrosis and pure pRTA associated with ocular abnormalities, a rare disease which has been recently described. Only one family with pure isolated pRTA has been reported so far and the genetic cause for this disease is unknown. Objectives. We report a unique family with isolated pRTA. The aim of the project was to define the phenotype and to try to find the gene defect causing the disease. METHODS Clinical and metabolic evaluation of all family members was performed and a family pedigree was constructed. DNA was extracted from blood samples of affected and unaffected family members. We amplified by PCR and sequenced the coding areas and splice-sites of the genes that contribute to HCO(-)(3) reclamation in the proximal tubule. The genes studied were as follows: CA II, CA IV, CA XIV, NCB1, Na(+)/H(+) exchanger (NHE)-3, NHE-8, the regulatory proteins of NHE3, NHRF1 and NHRF2 and the Cl(-)/HCO(-)(3) exchanger, SLC26A6. RESULTS The father and all four children had RTA with blood HCO(-)(3) levels of 11-14 meq/l and urine pH of 5.3-5.4. Increased HCO(-)(3) fractional excretion after bicarbonate loading to 40-60% confirmed the diagnosis pRTA. No other tubular dysfunction was found, and no organ system dysfunction was detected, besides short stature. No mutation was found in all candidate genes studied. CONCLUSIONS We presented a second family in the literature with familial isolated pure pRTA. The mode of inheritance is compatible with an autosomal dominant disease. Because of the small size of the family, wide genome search was not applicable and the gene candidate approach was chosen. Nine important candidate genes were extensively studied but the molecular basis of the disease was not yet found and genotyping nine important gene candidates were negative.
Collapse
Affiliation(s)
- Ze'ev Katzir
- Ze'ev Katzir, Pediatric Nephrology Services, E. Wolfson Medical Center, Holon, Israel.
| | | | | | | | | |
Collapse
|
19
|
Abstract
PURPOSE OF REVIEW Metabolic acidosis is a severe disturbance of extracellular pH homeostasis that can be caused both by inborn or acquired defects in renal acid excretion or metabolic acid production. Chronic metabolic acidosis causes osteomalacia with nephrocalcinosis and urolithiasis. In the setting of end-stage renal disease, metabolic acidosis is often associated with increased peripheral insulin resistance, and represents an additional independent morbidity risk factor. This review summarizes recent insight, gained primarily from mouse models, into the mechanisms whereby the kidney regulates and adapts acid excretion. RECENT FINDINGS Human genetics and various mouse models have shed new light on mechanisms that contribute to the kidney's ability to excrete acid and adapt appropriately to metabolism. Progress in four specific areas will be highlighted: mechanisms contributing to the synthesis and excretion of ammonia; insights into adaptive processes during acidosis; mechanisms by which the kidney may sense acidosis; and the pathophysiology of acquired and inborn errors of renal acid handling. SUMMARY Genetic mouse models and various messenger RNA and proteome profiling and screening technologies demonstrate the importance of various acid-base transporting proteins and a metabolic and regulatory network that contributes to the kidney's ability to maintain the systemic acid-base balance.
Collapse
Affiliation(s)
- Carsten A Wagner
- Institute of Physiology and Zurich Center for Human Integrative Physiology (ZIHP), University of Zurich, Zurich, Switzerland.
| |
Collapse
|
20
|
Suzuki M, Vaisbich MH, Yamada H, Horita S, Li Y, Sekine T, Moriyama N, Igarashi T, Endo Y, Cardoso TP, de Sá LCF, Koch VH, Seki G, Fujita T. Functional analysis of a novel missense NBC1 mutation and of other mutations causing proximal renal tubular acidosis. Pflugers Arch 2007; 455:583-93. [PMID: 17661077 DOI: 10.1007/s00424-007-0319-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 07/03/2007] [Accepted: 07/03/2007] [Indexed: 10/23/2022]
Abstract
Mutations in the Na(+)-HCO(3)(-) cotransporter NBC1 cause severe proximal tubular acidosis (pRTA) associated with ocular abnormalities. Recent studies have suggested that at least some NBC1 mutants show abnormal trafficking in the polarized cells. This study identified a new homozygous NBC1 mutation (G486R) in a patient with severe pRTA. Functional analysis in Xenopus oocytes failed to detect the G486R activity due to poor surface expression. In ECV304 cells, however, G486R showed the efficient membrane expression, and its transport activity corresponded to approximately 50% of wild-type (WT) activity. In Madin-Darby canine kidney (MDCK) cells, G486R was predominantly expressed in the basolateral membrane domain as observed for WT. Among the previously identified NBC1 mutants that showed poor surface expression in oocytes, T485S showed the predominant basolateral expression in MDCK cells. On the other hand, L522P was exclusively retained in the cytoplasm in ECV304 and MDCK cells, and functional analysis in ECV304 cells failed to detect its transport activity. These results indicate that G486R, like T485S, is a partial loss of function mutation without major trafficking abnormalities, while L522P causes the clinical phenotypes mainly through its inability to reach the plasma membranes. Multiple experimental approaches would be required to elucidate potential disease mechanism by NBC1 mutations.
Collapse
Affiliation(s)
- Masashi Suzuki
- Department of Internal Medicine, Faculty of Medicine, Tokyo University, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Abstract
Inherited acidosis may result from a primary renal defect in acid-base handling, emphasizing the central role of the kidney in control of body pH; as a secondary phenomenon resulting from abnormal renal electrolyte handling; or from excess production of acid elsewhere in the body. Here, we review our current understanding of the inherited renal acidoses at a genetic and molecular level.
Collapse
Affiliation(s)
- Andrew C Fry
- Department of Medical Genetics and Division of Renal Medicine, University of Cambridge, Cambridge Institute for Medical Research, UK
| | | |
Collapse
|
22
|
Abstract
The role of the Na(+)-coupled HCO(3)(-) transporter (NBC) family is indispensable in acid-base homeostasis. Almost all tissues express a member of the NBC family. NBC has been studied extensively in the kidney and plays a role in proximal tubule HCO(3)(-) reabsorption. Although the exact function of this transporter family on other tissues is not very clear, the ubiquitous expression of NBC family suggests a role in cell pH regulation. Altered NBC activity caused by mutations of the gene responsible for NBC protein expression results in pathophysiologic conditions. Mutations of NBC resulting in important clinical disorders have been reported extensively on one member of the NBC family, the kidney NBC (NBC1). These mutations have led to several structural studies to understand the mechanism of the abnormal NBC1 activity.
Collapse
Affiliation(s)
- Angelito A Bernardo
- Department of Medicine, Section of Nephrology, University of Illinois at Chicago, 820 S. Wood Street, Chicago, IL 60612, USA
| | | | | | | |
Collapse
|
23
|
Disthabanchong S, Radinahamed P, Stitchantrakul W, Hongeng S, Rajatanavin R. Chronic metabolic acidosis alters osteoblast differentiation from human mesenchymal stem cells. Kidney Int 2007; 71:201-9. [PMID: 17183249 DOI: 10.1038/sj.ki.5002035] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Bone histology of distal renal tubular acidosis patients showed decreased bone formation with impaired bone matrix mineralization that is not entirely explained by an alteration in the mineral balance. Data from in vitro studies suggests a direct inhibitory effect of metabolic acidosis on osteoblast function. We investigated the effects of chronic metabolic acidosis on osteoblast differentiation from mesenchymal stem cells (MSCs). Human MSCs were allowed to differentiate into osteoblasts in culture. Concentrated hydrochloric acid was added to the medium to lower the bicarbonate concentration and pH. The expression of various osteoblastic genes and proteins and bone matrix mineralization were examined. Chronic metabolic acidosis enhanced the messenger RNA (mRNA) and protein expression of early osteoblast transcription factor, runx-2, whereas inhibiting osterix and having no effect on ATF-4. The expression of type I collagen, the most abundant bone matrix protein, was increased following the same pattern of runx-2. Likewise, metabolic acidosis slightly enhanced the expression of mature osteoblastic gene, osteocalcin. Study on mineralization revealed suppressed alkaline phosphatase mRNA and enzyme activity. Despite the augmented collagen deposit in acidic culture, bone matrix mineralization was impaired. In conclusion, chronic metabolic acidosis alters osteoblast differentiation from MSCs through its diverse effect on osteoblastic genes and proteins resulting in an impairment of bone formation.
Collapse
Affiliation(s)
- S Disthabanchong
- Division of Nephrology, Department of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
| | | | | | | | | |
Collapse
|
24
|
Keven K, Ozturk R, Sengul S, Kutlay S, Ergun I, Erturk S, Erbay B. Renal tubular acidosis after kidney transplantation--incidence, risk factors and clinical implications. Nephrol Dial Transplant 2007; 22:906-10. [PMID: 17210594 DOI: 10.1093/ndt/gfl714] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Renal tubular acidosis (RTA) is a non-anion gap metabolic acidosis and is generally mild and asymptomatic in kidney recipients. Although calcineurin inhibitors, suboptimal allograft function, donor age and acute rejection have been associated with RTA, no detailed study has been conducted to investigate the prevalence and clinical implications of RTA in long-term kidney recipients. METHODS In this cross-sectional study, we enrolled 109 patients (74 males, 35 females) for the study [patients with glomerular filtration rate (GFR) <30 ml/min/1.73 m(2), unstable allograft function, diarrhoea, and respiratory disease were excluded]. Thirty-six patients (33%) were found to have RTA on the basis of plasma bicarbonate, arterial pH, urine and serum anion gap measurements. RESULTS Deceased donor transplantation [P = 0.034, 95% confidence interval (CI): 1.10-13.27], female gender (P = 0.017, 95% CI: 1.23-8.50), and lower GFR (55.8 +/- 19.4 in RTA and 66.1 +/- 15.9 ml/min/1.73 m(2) in non-RTA, P = 0.002, 95% CI: 1.10-13.27) were independent risk factors for RTA. Also, C-reactive protein was found to be higher in the RTA group (2.7 +/- 1.5 vs 2.0 +/- 1.5 mg/dl, P = 0.03), while no difference was noticed in body mass index or serum albumin. Analysis of the prevalence of osteoporosis and osteopenia in patients with RTA and without RTA, respectively, revealed no difference in frequency of osteoporosis (33% vs 31%) or osteopenia (33% vs 47%). CONCLUSION Although long-term kidney recipients have a relatively high prevalence of RTA, it is usually mild and subclinical. Further studies are needed to clarify long-term effects of RTA in kidney recipients.
Collapse
Affiliation(s)
- Kenan Keven
- Department of Nephrology, Ankara University School of Medicine, Ibni Sina Hospital, Ankara 06100, Turkey.
| | | | | | | | | | | | | |
Collapse
|
25
|
Walsh S, Turner CM, Toye A, Wagner C, Jaeger P, Laing C, Unwin R. Immunohistochemical comparison of a case of inherited distal renal tubular acidosis (with a unique AE1 mutation) with an acquired case secondary to autoimmune disease. Nephrol Dial Transplant 2007; 22:807-12. [PMID: 17205967 DOI: 10.1093/ndt/gfl662] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Stephen Walsh
- Department of Physiology, Royal Free and University College Medical School, Rowland Hill Street, London, UK.
| | | | | | | | | | | | | |
Collapse
|
26
|
Abstract
Endothelin (ET) is a potent vasoconstrictor that is now known to modulate kidney tubule transport, including kidney tubule acidification. Animals undergoing an acid challenge to systemic acid-base status and with some models of chronic metabolic acidosis have increased kidney ET production. Increased ET production/activity contributes to enhanced kidney tubule acidification that facilitates kidney acid excretion in response to an acid challenge to systemic acid-base status. The data to date support a physiologic role for ET in mediating enhanced kidney acidification in response to acid challenges, but do not support an ET role in maintaining kidney tubule acidification in control, non-acid-challenged states. ET increases acidification in both the proximal and distal nephron and appears to exert its effects both directly and indirectly, the latter through modulating the levels and/or activity or other mediators of kidney tubule acidification. ET also contributes to enhanced kidney acidification in some pathophysiologic states and might contribute to some untoward outcomes associated with these conditions. Whether ET should be a therapeutic target in treating and/or preventing some of these untoward outcomes remains an open question. This review supports continued research into the physiologic and possibly pathophysiologic role of ET in settings of increased kidney tubule acidification.
Collapse
Affiliation(s)
- D E Wesson
- Division of Nephrology and Hypertension, Departments of Internal Medicine and Physiology, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
| |
Collapse
|
27
|
Cordat E, Reithmeier RAF. Expression and interaction of two compound heterozygous distal renal tubular acidosis mutants of kidney anion exchanger 1 in epithelial cells. Am J Physiol Renal Physiol 2006; 291:F1354-61. [PMID: 16849697 DOI: 10.1152/ajprenal.00015.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Kidney AE1 (kAE1) is a glycoprotein responsible for the electroneutral exchange of chloride for bicarbonate, promoting the reabsorption of bicarbonate into the blood by α-intercalated cells of the collecting tubule. Mutations occurring in the gene encoding kAE1 can induce defects in urinary acidification resulting in distal renal tubular acidosis (dRTA). We expressed two kAE1 dRTA mutants, A858D, a mild dominant mutation, and ΔV850, a recessive mutation, in epithelial Madin-Darby canine kidney (MDCK) cells. Individuals heterozygous with wild-type (WT) kAE1 either did not display any symptoms of dRTA (ΔV850/WT) or displayed a mild incomplete form of dRTA (A858D/WT), while compound heterozygotes (ΔV850/A858D) had dRTA. We found that the A858D mutant was slightly impaired in the endoplasmic reticulum (ER) exit but could target to the basolateral membrane of polarized MDCK cells. Despite an altered binding to an inhibitor affinity resin, anion transport assays showed that the A858D mutant was functional at the cell surface. The ΔV850 mutant showed altered binding to the affinity resin but was predominantly retained in the ER, resulting in undetectable AE1 expression at the basolateral membrane. When coexpressed in MDCK cells, the WT protein, and to a lesser extent the A858D mutant, enhanced the cell surface expression of the ΔV850 mutant. The ΔV850 mutant also affected the cell surface expression of the A858D mutant. Compound heterozygous (A858D/ΔV850) patients likely possess a decreased amount of functional anion exchangers at the basolateral membrane of their α-intercalated cells, resulting in impaired bicarbonate transport into the blood and defective acid transport into the urine.
Collapse
Affiliation(s)
- Emmanuelle Cordat
- Department of Biochemistry, Rm. 5216, Medical Sciences Bldg., Univ. of Toronto, Toronto, Ontario M5S 1A8, Canada.
| | | |
Collapse
|
28
|
Sawasdee N, Udomchaiprasertkul W, Noisakran S, Rungroj N, Akkarapatumwong V, Yenchitsomanus PT. Trafficking defect of mutant kidney anion exchanger 1 (kAE1) proteins associated with distal renal tubular acidosis and Southeast Asian ovalocytosis. Biochem Biophys Res Commun 2006; 350:723-30. [PMID: 17027918 DOI: 10.1016/j.bbrc.2006.09.113] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 09/21/2006] [Indexed: 01/01/2023]
Abstract
Compound heterozygous anion exchanger 1 (AE1) SAO/G701D mutations result in distal renal tubular acidosis with Southeast Asian ovalocytosis. Interaction, trafficking and localization of wild-type and mutant (SAO and G701D) kAE1 proteins fused with hemagglutinin, six-histidine, Myc, or green fluorescence protein (GFP) were examined in human embryonic kidney (HEK) 293 cells. When individually expressed, wild-type kAE1 was localized at cell surface while mutant kAE1 SAO and G701D were intracellularly retained. When co-expressed, wild-type kAE1 could form heterodimer with kAE1 SAO or kAE1 G701D and could rescue mutant kAE1 proteins to express on the cell surface. Co-expression of kAE1 SAO and kAE1 G701D also resulted in heterodimer formation but intracellular retention without cell surface expression, suggesting their trafficking defect and failure to rescue each other to the plasma membrane, most likely the molecular mechanism of the disease in the compound heterozygous condition.
Collapse
Affiliation(s)
- Nunghathai Sawasdee
- Division of Medical Molecular Biology and BIOTEC-Medical Biotechnology Unit, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
| | | | | | | | | | | |
Collapse
|
29
|
Abstract
Kidneys are essential for acid-base homeostasis, especially when organisms cope with changes in acid or base dietary intake. Because collecting ducts constitute the final site for regulating urine acid-base balance, we undertook to identify the gene network involved in acid-base transport and regulation in the mouse outer medullary collecting duct (OMCD). For this purpose, we combined kidney functional studies and quantitative analysis of gene expression in OMCDs, by transcriptome and candidate gene approaches, during metabolic acidosis. Furthermore, to better delineate the set of genes concerned with acid-base disturbance, the OMCD transcriptome of acidotic mice was compared with that of both normal mice and mice undergoing an adaptative response through potassium depletion. Metabolic acidosis, achieved through an NH4Cl-supplemented diet for 3 days, not only induced acid secretion but also stimulated the aldosterone and vasopressin systems and triggered cell proliferation. Accordingly, metabolic acidosis increased the expression of genes involved in acid-base transport, sodium transport, water transport, and cell proliferation. In particular, >25 transcripts encoding proteins involved in urine acidification (subunits of H-ATPase, kidney anion exchanger, chloride channel Clcka, carbonic anhydrase-2, aldolase) were co-regulated during acidosis. These transcripts, which cooperate to achieve a similar function and are co-regulated during acidosis, constitute a functional unit that we propose to call a "regulon".
Collapse
Affiliation(s)
- Lydie Cheval
- Laboratoire de Physiologie et Génomique Rénales, Unité mixte de recherche 7134, Centre National de la Recherche Scientifique/Université Pierre et Marie Curie, Institut Fédératif de Recherche 58, Paris cedex 6, France
| | | | | | | |
Collapse
|
30
|
Yang Q, Li G, Singh SK, Alexander EA, Schwartz JH. Vacuolar H+-ATPase B1 Subunit Mutations that Cause Inherited Distal Renal Tubular Acidosis Affect Proton Pump Assembly and Trafficking in Inner Medullary Collecting Duct Cells. J Am Soc Nephrol 2006; 17:1858-66. [PMID: 16769747 DOI: 10.1681/asn.2005121277] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Point mutations in the B1 subunit of vacuolar H+ -ATPase are associated with impaired ability of the distal nephron to secrete acid (distal renal tubular acidosis). For testing of the hypothesis that these mutations interfere with assembly and trafficking of the H+ -ATPase, constructs that mimic seven known point mutations in inherited distal renal tubular acidosis (M) or wild-type (WT) B1 were transfected into a rat inner medullary collecting duct cell line to express green fluorescence protein (GFP)-B1WT or GFP-B1M fusion proteins. In co-immunoprecipitation studies, GFP-B1WT formed complexes with other H+ -ATPase subunits (c, H, and E), whereas GFP-B1M did not. Proteins that were immunoprecipitated with anti-GFP antibody from GFP-B1WT cells had ATPase activity, whereas proteins from GFP-B1M cells did not. Proton pump-mediated intracellular pH transport was inhibited in GFP-B1M-transfected cells but not in GFP-B1WT cells. GFP-B1WT and GFP-B1M are present in the apical membrane and increased with cellular acidification. In GFP-B1WT cells, the apical membrane fraction of GFP-B1, endogenous B1, and the 31-kD subunits of the H+ -ATPase increased with cell acidification. In GFP-B1M cells, the endogenous B1 and 31-kD subunits did not increase with acidification. B1 point mutations prevent normal assembly of the H+ -ATPase and also may act as an inhibitor of H+ -ATPase function by competing with endogenous intact H+ -ATPase for trafficking in inner medullary collecting duct cells.
Collapse
Affiliation(s)
- Qiongqiong Yang
- Renal Section, 1st Affiliated Hospital of Zhongshan University, Guangzhou, China
| | | | | | | | | |
Collapse
|
31
|
Toye AM, Parker MD, Daly CM, Lu J, Virkki LV, Pelletier MF, Boron WF. The human NBCe1-A mutant R881C, associated with proximal renal tubular acidosis, retains function but is mistargeted in polarized renal epithelia. Am J Physiol Cell Physiol 2006; 291:C788-801. [PMID: 16707554 DOI: 10.1152/ajpcell.00094.2006] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human electrogenic renal Na-HCO(3) cotransporter (NBCe1-A; SLC4A4) is localized to the basolateral membrane of proximal tubule cells. Mutations in the SLC4A4 gene cause an autosomal recessive proximal renal tubular acidosis (pRTA), a disease characterized by impaired ability of the proximal tubule to reabsorb HCO(3)(-) from the glomerular filtrate. Other symptoms can include mental retardation and ocular abnormalities. Recently, a novel homozygous missense mutant (R881C) of NBCe1-A was reported from a patient with a severe pRTA phenotype. The mutant protein was described as having a lower than normal activity when expressed in Xenopus oocytes, despite having normal Na(+) affinity. However, without trafficking data, it is impossible to determine the molecular basis for the phenotype. In the present study, we expressed wild-type NBCe1-A (WT) and mutant NBCe1-A (R881C), tagged at the COOH terminus with enhanced green fluorescent protein (EGFP). This approach permitted semiquantification of surface expression in individual Xenopus oocytes before assay by two-electrode voltage clamp or measurements of intracellular pH. These data show that the mutation reduces the surface expression rather than the activity of the individual protein molecules. Confocal microscopy on polarized mammalian epithelial kidney cells [Madin-Darby canine kidney (MDCK)I] expressing nontagged WT or R881C demonstrates that WT is expressed at the basolateral membrane of these cells, whereas R881C is retained in the endoplasmic reticulum. In summary, the pathophysiology of pRTA caused by the R881C mutation is likely due to a deficit of NBCe1-A at the proximal tubule basolateral membrane, rather than a defect in the transport activity of individual molecules.
Collapse
Affiliation(s)
- Ashley M Toye
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
32
|
Abstract
BACKGROUND Neither the prevalence nor the associated risk factors of late post-transplant renal tubular acidosis (RTA) are known. METHODS We conducted a cross-sectional study with 576 patients for more than 12 months after kidney transplantation, and a glomerular filtration rate (GFR) >40 ml/min. RTA was diagnosed by measurement of the urine anionic gap, urine pH and plasma potassium during acidosis, and fractional bicarbonate excretion after bicarbonate loading. Uni- and multi-variable analysis were used to isolate factors associated with post-transplant RTA, and with the different RTA subtypes. RESULTS All patients (n = 76) had distal post-transplant RTA. A significant association with the presence of RTA was found for the intake of tacrolimus or renin-angiotensin-aldosterone blockers, the Parathyroid hormone level and the GFR. Type Ia (classic, distal), type Ib (hyperkalaemic, voltage-dependent), rate-limited and type IV RTA were present in 37, 14, 21 and 28% of the patients. Acute transplant rejection was the only significant different parameter between the RTA subtypes and more often present in patients with type Ia or Ib RTA. CONCLUSIONS We conclude that a significant fraction of stable long-term renal transplant recipients with adequate graft function develop post-transplant RTA, with a preponderance for type Ia and type IV, and absence of type II. In addition, acute transplant rejection seems to have an influence on the subtype of RTA present post-transplantation.
Collapse
Affiliation(s)
- Christoph Schwarz
- Department of Internal Medicine III, Division of Nephrology and Dialysis, University Hospital Vienna, Vienna, Austria
| | | | | | | | | |
Collapse
|
33
|
Cordat E, Kittanakom S, Yenchitsomanus PT, Li J, Du K, Lukacs GL, Reithmeier RAF. Dominant and recessive distal renal tubular acidosis mutations of kidney anion exchanger 1 induce distinct trafficking defects in MDCK cells. Traffic 2006; 7:117-28. [PMID: 16420521 DOI: 10.1111/j.1600-0854.2005.00366.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Distal renal tubular acidosis (dRTA), a kidney disease resulting in defective urinary acidification, can be caused by dominant or recessive mutations in the kidney Cl-/HCO3- anion exchanger (kAE1), a glycoprotein expressed in the basolateral membrane of alpha-intercalated cells. We compared the effect of two dominant (R589H and S613F) and two recessive (S773P and G701D) dRTA point mutations on kAE1 trafficking in Madin-Darby canine kidney (MDCK) epithelial cells. In contrast to wild-type (WT) kAE1 that was localized to the basolateral membrane, the dominant mutants (kAE1 R589H and S613F) were retained in the endoplasmic reticulum (ER) in MDCK cells, with a few cells showing in addition some apical localization. The recessive mutant kAE1 S773P, while misfolded and largely retained in the ER in non-polarized MDCK cells, was targeted to the basolateral membrane after polarization. The other recessive mutants, kAE1 G701D and designed G701E, G701R but not G701A or G701L mutants, were localized to the Golgi in both non-polarized and polarized cells. The results suggest that introduction of a polar mutation into a transmembrane segment resulted in Golgi retention of the recessive G701D mutant. When coexpressed, the dominant mutants retained kAE1 WT intracellularly, while the recessive mutants did not. Coexpression of recessive G701D and S773P mutants in polarized cells showed that these proteins could interact, yet no G701D mutant was detected at the basolateral membrane. Therefore, compound heterozygous patients expressing both recessive mutants (G701D/S773P) likely developed dRTA due to the lack of a functional kAE1 at the basolateral surface of alpha-intercalated cells.
Collapse
Affiliation(s)
- Emmanuelle Cordat
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | | | | | |
Collapse
|
34
|
Laing CM, Unwin RJ. Renal tubular acidosis. J Nephrol 2006; 19 Suppl 9:S46-52. [PMID: 16736441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Renal tubular acidosis (RTA) is a form of metabolic acidosis due to abnormal alkali (bicarbonate) loss by the kidneys or their failure to excrete net acid. While the latter does occur in chronic renal failure, the term RTA is usually applied only when the glomerular filtration rate is normal or near normal. As well as a cause of metabolic acidosis, RTA often presents as renal stone disease with nephrocalcinosis, rickets/osteomalacia, and growth retardation in children. In this brief review, we have summarized the classification, clinical features and the underlying cell and molecular pathophysiology of RTA. However, despite significant advances in our understanding of the mechanisms of RTA, its treatment is still empirical and based largely on alkali replacement therapy; but its wider significance in renal stone and bone disease is becoming increasingly recognized.
Collapse
Affiliation(s)
- C M Laing
- Centre for Nephrology and Department of Physiology, Royal Free and University College Medical School, Royal Free, London, UK.
| | | |
Collapse
|
35
|
Quigley R. Proximal renal tubular acidosis. J Nephrol 2006; 19 Suppl 9:S41-5. [PMID: 16736440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The proximal tubule reabsorbs approximately 80% of the filtered load of bicarbonate. Defects in the process of bicarbonate reabsorption result in loss of bicarbonate and proximal renal tubular acidosis. Global proximal tubule dysfunction is known as the Fanconi's syndrome. Both isolated proximal renal tubular acidosis and the Fanconi's syndrome can result from inherited defects or can be acquired. This review will discuss the mechanisms that cause defects in proximal tubule bicarbonate transport as well as the common causes of isolated proximal renal tubular acidosis and the Fanconi syndrome.
Collapse
Affiliation(s)
- R Quigley
- Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
| |
Collapse
|
36
|
Corey HE, Vallo A, Rodríguez-Soriano J. An analysis of renal tubular acidosis by the Stewart method. Pediatr Nephrol 2006; 21:206-11. [PMID: 16362393 DOI: 10.1007/s00467-005-2081-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Revised: 07/26/2005] [Accepted: 07/26/2005] [Indexed: 10/25/2022]
Abstract
Renal tubular acidosis (RTA) comprises a group of disorders characterized by a low capacity for net acid excretion and persistent hyperchloremic, metabolic acidosis. To investigate the role of chloride, we performed hypotonic (0.45%) saline-loading experiments in 12 children with alkali-treated distal RTA (dRTA) and compared the results with data obtained from 17 healthy control subjects. In patients, but not in controls, saline loading induced both hyperchloremia and metabolic acidosis. Hyperchloremia was associated with high total and high distal fractional reabsorption of chloride [C(H20)/(C(H20)+C(Cl))]. The increase in plasma chloride varied inversely with the fractional excretion of chloride (C(Cl)) and correlated with the decrease in blood pH. However, the urinary excretion of bicarbonate did not correlate with either changes in blood pH or plasma bicarbonate concentration. Our findings suggest that the mechanism of hyperchloremia was enhanced Cl(-)/HCO(3) (-) exchange by the distal tubule. The resulting metabolic acidosis is better explained by changes in the strong ion difference (the Stewart theory) than by changes in the urine bicarbonate excretion (the traditional theory).
Collapse
Affiliation(s)
- Howard E Corey
- The Children's Kidney Center of New Jersey, Goryeb Children's Hospital, Morristown Memorial Hospital, Morristown, New Jersey 07962, USA.
| | | | | |
Collapse
|
37
|
Abstract
The physiology and pathophysiology of renal H+ ion excretion and urinary buffer systems are reviewed. The main focus is on the two major conditions related to acid-base metabolism that cause kidney stone formation, i.e., distal renal tubular acidosis (dRTA) and abnormally low urine pH with subsequent uric acid stone formation. Both the entities can be seen on the background of disturbances of the major urinary buffer system, NH3+ <--> NH4+. On the one hand, reduced distal tubular secretion of H+ ions results in an abnormally high urinary pH and either incomplete or complete dRTA. On the other hand, reduced production/availability of NH4+ is the cause of an abnormally low urinary pH, which predisposes to uric acid stone formation. Most recent research indicates that the latter abnormality may be a renal manifestation of the increasingly prevalent metabolic syndrome. Despite opposite deviations from normal urinary pH values, both the dRTA and uric acid stone formation due to low urinary pH require the same treatment, i.e., alkali. In the dRTA, alkali is needed for improving the body's buffer capacity, whereas the goal of alkali treatment in uric acid stone formers is to increase the urinary pH to 6.2-6.8 in order to minimize uric acid crystallization.
Collapse
Affiliation(s)
- Bernhard Hess
- Internal Medicine and Nephrology, Klinik Im Park, Bellariastrasse 38, 8038, Zurich, Switzerland.
| |
Collapse
|
38
|
Bento LMA, Carvalheira JBC, Menegon LF, Saad MJA, Gontijo JAR. Effects of NH4Cl intake on renal growth in rats: role of MAPK signalling pathway. Nephrol Dial Transplant 2005; 20:2654-60. [PMID: 16169866 DOI: 10.1093/ndt/gfi133] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND There is a surprising lack of experimental data on the mechanisms of NH4Cl-induced chronic metabolic acidosis which causes kidney hypertrophy. The NH4Cl treatment results in an absolute increase in kidney mass. Despite findings to indicate a close interaction between NH4Cl-induced chronic metabolic acidosis and renal enlargement, the role of the stimulated serine kinase cascade, mediated by the stepwise activation of extracellular signal-regulated kinase (ERK) signalling, on kidney hypertrophy has not yet been investigated. METHODS To test this hypothesis, the present study was undertaken to further explore the possible involvement of mitogen-activated protein kinase (MAPK) signalling pathway in renal growth in chronic NH4Cl-treated rats by western blot analysis. RESULTS Our major findings are as follows: (1) Urinary sodium excretion significantly increased during the early phases of NH4Cl-induced acidosis, (2) This occurrence is associated with sustained renal hypertrophy, and (3) sustained basal phosphorylation of IRS-1, Shc, and MAPK/ERKs in acidotic kidneys. CONCLUSIONS The present study confirms that NH4Cl-induced acidosis causes disturbances in renal sodium handling. In addition, these findings demonstrate a sustained pre-stimuli activation of kidney MAPK/ERKs signalling pathways in the NH4Cl-treated rats that may correlate with an increased rate of kidney hypertrophy and a transient renal tubule inability to handle sodium. Thus, the altered renal electrolyte handling may result from a reciprocal relationship between the level of renal tubule metabolic activity and ion transport. In addition, the study shows that the appropriate regulation of tyrosine kinase protein phosphorylation, and its downstream signal transduction pathway, plays an important role on renal growth in the NH4Cl-treated rats.
Collapse
Affiliation(s)
- Leda M A Bento
- Departamento de Clínica Médica, Faculdade de Ciências Medicas, Universidade Estadual de Campinas, 13083-100 Campinas, SP, Brazil
| | | | | | | | | |
Collapse
|
39
|
Abstract
Plasmalemmal Cl- -HCO3- exchangers regulate intracellular pH and [Cl-] and cell volume. In polarized epithelial cells, they contribute also to transepithelial secretion and reabsorption of acid-base equivalents and of Cl-. Members of both the SLC4 and SLC26 mammalian gene families encode Na+-independent Cl- -HCO3- exchangers. Human SLC4A1/AE1 mutations cause either the erythroid disorders spherocytic haemolytic anaemia or ovalocytosis, or distal renal tubular acidosis. SLC4A2/AE2 knockout mice die at weaning. Human SLC4A3/AE3 polymorphisms have been associated with seizure disorder. Although mammalian SLC4/AE polypeptides mediate only electroneutral Cl- -anion exchange, trout erythroid AE1 also promotes osmolyte transport and increased anion conductance. Mouse AE1 is required for DIDS-sensitive erythroid Cl- conductance, but definitive evidence for mediation of Cl- conductance is lacking. However, a single missense mutation allows AE1 to mediate both electrogenic SO4(2-) -Cl- exchange or electroneutral, H+-independent SO4(2)- -SO4(2-) exchange. In the Xenopus oocyte, the AE1 C-terminal cytoplasmic tail residues reported to bind carbonic anhydrase II are dispensable for Cl- -Cl- exchange, but required for Cl- -HCO3- exchange. AE2 is acutely and independently inhibited by intracellular and extracellular H+, and this regulation requires integrity of the most highly conserved sequence of the AE2 N-terminal cytoplasmic domain. Individual missense mutations within this and adjacent regions identify additional residues which acid-shift pHo sensitivity. These regions together are modelled to form contiguous surface patches on the AE2 cytoplasmic domain. In contrast, the N-terminal variant AE2c polypeptide exhibits an alkaline-shifted pHo sensitivity, as do certain transmembrane domain His mutants. AE2-mediated anion exchange is also stimulated by ammonium and by hypertonicity by a mechanism sensitive to inhibition by chelation of intracellular Ca2+ and by calmidazolium. This growing body of structure-function data, together with increased structural information, will advance mechanistic understanding of SLC4 anion exchangers.
Collapse
MESH Headings
- Acidosis, Renal Tubular/genetics
- Acidosis, Renal Tubular/metabolism
- Amino Acid Sequence
- Animals
- Anion Exchange Protein 1, Erythrocyte/chemistry
- Anion Exchange Protein 1, Erythrocyte/genetics
- Anion Exchange Protein 1, Erythrocyte/metabolism
- Anion Transport Proteins/chemistry
- Anion Transport Proteins/genetics
- Anion Transport Proteins/metabolism
- Antiporters/chemistry
- Antiporters/genetics
- Antiporters/metabolism
- Carbonic Anhydrases/metabolism
- Chloride-Bicarbonate Antiporters/chemistry
- Chloride-Bicarbonate Antiporters/genetics
- Chloride-Bicarbonate Antiporters/metabolism
- Elliptocytosis, Hereditary/genetics
- Elliptocytosis, Hereditary/metabolism
- Humans
- Hydrogen-Ion Concentration
- Molecular Sequence Data
- Multigene Family
- Mutation
- Polymorphism, Genetic
- Protein Conformation
- SLC4A Proteins
- Spherocytosis, Hereditary/genetics
- Spherocytosis, Hereditary/metabolism
- Structure-Activity Relationship
Collapse
Affiliation(s)
- Seth L Alper
- Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
| |
Collapse
|
40
|
Seshadri RM, Klein JD, Kozlowski S, Sands JM, Kim YH, Han KH, Handlogten ME, Verlander JW, Weiner ID. Renal expression of the ammonia transporters, Rhbg and Rhcg, in response to chronic metabolic acidosis. Am J Physiol Renal Physiol 2005; 290:F397-408. [PMID: 16144966 DOI: 10.1152/ajprenal.00162.2005] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic metabolic acidosis induces dramatic increases in net acid excretion that are predominantly due to increases in urinary ammonia excretion. The current study examines whether this increase is associated with changes in the expression of the renal ammonia transporter family members, Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg). Chronic metabolic acidosis was induced in Sprague-Dawley rats by HCl ingestion for 1 wk; control animals were pair-fed. After 1 wk, metabolic acidosis had developed, and urinary ammonia excretion increased significantly. Rhcg protein expression was increased in both the outer medulla and the base of the inner medulla. Intercalated cells in the outer medullary collecting duct (OMCD) and in the inner medullary collecting duct (IMCD) in acid-loaded animals protruded into the tubule lumen and had a sharp, discrete band of apical Rhcg immunoreactivity, compared with a flatter cell profile and a broad band of apical immunolabel in control kidneys. In addition, basolateral Rhcg immunoreactivity was observed in both control and acidotic kidneys. Cortical Rhcg protein expression and immunoreactivity were not detectably altered. Rhcg mRNA expression was not significantly altered in the cortex, outer medulla, or inner medulla by chronic metabolic acidosis. Rhbg protein and mRNA expression were unchanged in the cortex, outer and inner medulla, and no changes in Rhbg immunolabel were evident in these regions. We conclude that chronic metabolic acidosis increases Rhcg protein expression in intercalated cells in the OMCD and in the IMCD, where it is likely to mediate an important role in the increased urinary ammonia excretion.
Collapse
Affiliation(s)
- Ramanathan M Seshadri
- University of Florida College of Medicine, P. O. Box 100224, Gainesville, FL 32610-0224, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
41
|
Abstract
dRTA (distal renal tubular acidosis) results from the failure of the a-intercalated cells in the distal tubule of the nephron to acidify the urine. A truncated form of AE1 (anion-exchanger 1; Band 3), kAE1 (kidney isoform of AE1), is located in the basolateral membrane of the intercalated cell. Mutations in the AE1 gene cause autosomal dominant and recessive forms of dRTA. All the dominant dRTA mutations investigated cause aberrant trafficking of kAE1, resulting in its intracellular retention or mistargeting to the apical plasma membrane. Therefore the intracellular retention of hetero-oligomers containing wild-type and dRTA mutants, or the mistargeted protein in the apical membrane neutralizing acid secretion, explains dominant dRTA. The kAE1 (Arg(901)-->stop) mutant has been studied in more detail, since the mistargeting kAE1 (Arg(901)-->stop) from the basolateral to the apical membrane is consistent with the removal of a basolateral localization signal. The C-terminal amino acids deleted by the Arg(901)-->stop mutation, contain a tyrosine motif and a type II PDZ interaction domain. The tyrosine residue (Tyr(904)), but not the PDZ domain, is critical for basolateral localization. In the absence of the N-terminus of kAE1, the C-terminus was not sufficient to localize kAE1 to the basolateral membrane. This suggests that a determinant within the kAE1 N-terminus co-operates with the C-terminus for kAE1 basolateral localization. Interestingly, Tyr(359), in the N-terminal domain, and Tyr(904) in the C-terminus of AE1 are phosphorylated in red blood cells. A potential scheme is suggested where successive phosphorylation of these residues is necessary for correct localization and recycling of kAE1 to the basolateral membrane.
Collapse
Affiliation(s)
- Ashley M Toye
- Department of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, U.K.
| |
Collapse
|
42
|
Li HC, Szigligeti P, Worrell RT, Matthews JB, Conforti L, Soleimani M. Missense mutations in Na+:HCO3- cotransporter NBC1 show abnormal trafficking in polarized kidney cells: a basis of proximal renal tubular acidosis. Am J Physiol Renal Physiol 2005; 289:F61-71. [PMID: 15713912 DOI: 10.1152/ajprenal.00032.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The kidney Na(+):HCO(3)(-) cotransporter NBC1 is located exclusively on the basolateral membrane of kidney proximal tubule cells and is responsible for the reabsorption of majority of filtered bicarbonate. Two well-described missense mutations in NBC1, R510H and S427L, are associated with renal tubular acidosis (RTA). However, the exact relationship between these mutations and NBC1 dysregulation remains largely unknown. To address this question, cDNAs for wild-type kidney NBC1 and its mutants R510H and S427L were generated, fused in frame with NH(2) terminally tagged GFP, and transiently expressed in Madin-Darby canine kidney cells. In parallel studies, oocytes were injected with the wild-type and mutant NBC1 cRNAs and studied for membrane expression and activity. In monolayer cells grown to polarity, the wild-type GFP-NBC1 was exclusively localized on the basolateral membrane domain. However, GFP-NBC1 mutant R510H was detected predominantly in the cytoplasm. GFP-NBC1 mutant S427L, on the other hand, was detected predominantly on the apical membrane with residual cytoplasmic retention and basolateral membrane labeling. In oocytes injected with the wild-type or mutant GFP-NBC1 cRNAs, Western blot analysis showed that wild-type NBC1 is predominantly localized in the membrane fraction, whereas NBC1-R510H mutant was predominantly expressed in the cytoplasm. NBC1-S427L mutant was mostly expressed in the membrane fraction. Functional analysis of NBC1 activity in oocytes by membrane potential recording demonstrated that compared with wild-type GFP-NBC1, the GFP-NBC1 mutants H510R and S427L exhibited significant reduction in activity. These findings suggest that the permanent isolated proximal RTA in patients with H510R or S427L mutation resulted from a combination of inactivation and mistargeting of kidney NBC1, with H510R mutant predominantly retained in the cytoplasm, whereas S427L mutant is mistargeted to the apical membrane.
Collapse
Affiliation(s)
- Hong C Li
- Dept. of Medicine, University of Cincinnati, Cincinnati, OH 45267-0585, USA
| | | | | | | | | | | |
Collapse
|
43
|
Abstract
INTRODUCTION Metabolic investigation in patients with urinary lithiasis is very important for preventing recurrence of disease. The objective of this work was to diagnose and to determine the prevalence of metabolic disorders, to assess the quality of the water consumed and volume of diuresis as potential risk factors for this pathology. PATIENTS AND METHODS We studied 182 patients older than 12 years. We included patients with history and/or imaging tests confirming at least 2 stones, with creatinine clearance > or = 60 mL/min and negative urine culture. The protocol consisted in the collection of 2, 24-hour urine samples, for dosing Ca, P, uric acid, Na, K, Mg, Ox and Ci, glycemia and serum levels of Ca, P, Uric acid, Na, K, Cl, Mg, U and Cr, urinary pH and urinary acidification test. RESULTS 158 patients fulfilled the inclusion criteria. Among these, 151 (95.5%) presented metabolic changes, with 94 (62.2%) presenting isolated metabolic change and 57 (37.8%) had mixed changes. The main disorders detected were hypercalciuria (74%), hypocitraturia (37.3%), hyperoxaluria (24.1%), hypomagnesuria (21%), hyperuricosuria (20.2%), primary hyperparathyroidism (1.8%), secondary hyperparathyroidism (0.6%) and renal tubular acidosis (0.6). CONCLUSION Metabolic change was diagnosed in 95.5% of patients. These results warrant the metabolic study and follow-up in patients with recurrent lithiasis in order to decrease the recurrence rate through specific treatments, modification in alimentary and behavioral habits.
Collapse
Affiliation(s)
- Carmen R Amaro
- General Hospital, Botucatu Medical School, Institute of Biosciences of Botucatu, State University of Sao Paulo, UNESP, Botucatu, Sao Paulo, Brazil.
| | | | | | | |
Collapse
|
44
|
Wołyniec W, Zdrojewski Z, Rutkowski B. [Metabolic acidosis after kidney transplantation]. Przegl Lek 2005; 62:68-71. [PMID: 16053226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Metabolic acidosis is a common complication in patients after kidney transplantation. It is caused by inability of transplanted kidney to regenerate bicarbonate buffer. Although every type of acidosis may be present in these patients, the most frequent are renal tubular acidosis and uremic acidosis. Both insufficiency of graft and tubular dysfunction can be caused by ischemic damage, episodes of rejection and cyclosporine A--induced nephrotoxicity. Ketoacidosis due to a post-transplant diabetes mellitus and bicarbonate loss in patients after simultaneous pancreas/kidney transplantation are rarely observed. Each type of acidosis is responsible for serious metabolic disturbances that influence graft and patient survival. The proper diagnosis and appropriate treatment with oral supplements are essential.
Collapse
Affiliation(s)
- Wojciech Wołyniec
- Klinika Nefrologii, Transplantologii i Chorób Wewnetrznych, Akademii Medycznej w Gdańsku
| | | | | |
Collapse
|
45
|
Abstract
In experimental animals, metabolic acidosis increases renal magnesium (Mg) excretion, whereas metabolic alkalosis reduces it. The objective of this study was to examine renal magnesium handling (U(Mg)) in children with primary distal renal tubular acidosis (DRTA). We measured U(Mg) in 11 children (3 females, 8 males, aged 6.9+/-4.9 years) with primary DRTA. They were studied either during spontaneous acidosis post treatment removal (3 patients) or after ammonium chloride (100 mmol/m2) induced acidosis (8 patients), and then following oral sodium bicarbonate load (4 g/1.73 m2). During acidosis (plasma pH 7.28+/-0.09, bicarbonate 13.2+/-4.3 mEq/l), U(Mg) was elevated (U(Mg/Cr) 0.18+/-0.06 mg/mg, normal values 0.1+/-0.06, P=0.003) although plasma Mg (P(Mg)) was in the normal range (1.93+/-0.31 mg/dl, controls 1.77+/-0.19, P=NS). After acute correction of metabolic acidosis (plasma pH 7.44+/-0.05, bicarbonate 25.6+/-1.6 mEq/l, P<0.001; urine pH 7.52+/-0.28, bicarbonate 86.9+/-39.1 mEq/l), U(Mg) decreased significantly (P=0.003), returning to control values after about 2 h (U(Mg/Cr) 0.09+/-0.06 mg/mg). Bicarbonate load resulted not only in reduction in U(Mg) but also in a decrease in urinary calcium excretion (U(Ca/Cr)) from 0.46+/-0.17 mg/mg to 0.14+/-0.12 mg/mg (P<0.001). We conclude that in children with primary DRTA, urinary Mg excretion is markedly increased and that this defect, like the hypercalciuric defect, is correctable by sodium bicarbonate administration.
Collapse
Affiliation(s)
- Gema Ariceta
- Division of Pediatric Nephrology, Department of Pediatrics, Hospital Clinico Universitario de Santiago de Compostela, Spain.
| | | | | |
Collapse
|
46
|
Dinour D, Chang MH, Satoh JI, Smith BL, Angle N, Knecht A, Serban I, Holtzman EJ, Romero MF. A novel missense mutation in the sodium bicarbonate cotransporter (NBCe1/SLC4A4) causes proximal tubular acidosis and glaucoma through ion transport defects. J Biol Chem 2004; 279:52238-46. [PMID: 15471865 DOI: 10.1074/jbc.m406591200] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In humans and terrestrial vertebrates, the kidney controls systemic pH in part by absorbing filtered bicarbonate in the proximal tubule via an electrogenic Na+/HCO3- cotransporter (NBCe1/SLC4A4). Recently, human genetics revealed that NBCe1 is the major renal contributor to this process. Homozygous point mutations in NBCe1 cause proximal renal tubular acidosis (pRTA), glaucoma, and cataracts (Igarashi, T., Inatomi, J., Sekine, T., Cha, S. H., Kanai, Y., Kunimi, M., Tsukamoto, K., Satoh, H., Shimadzu, M., Tozawa, F., Mori, T., Shiobara, M., Seki, G., and Endou, H. (1999) Nat. Genet. 23, 264-266). We have identified and functionally characterized a novel, homozygous, missense mutation (S427L) in NBCe1, also resulting in pRTA and similar eye defects without mental retardation. To understand the pathophysiology of the syndrome, we expressed wild-type (WT) NBCe1 and S427L-NBCe1 in Xenopus oocytes. Function was evaluated by measuring intracellular pH (HCO3- transport) and membrane currents using microelectrodes. HCO3- -elicited currents for S427L were approximately 10% of WT NBCe1, and CO2-induced acidification was approximately 4-fold faster. Na+ -dependent HCO3- transport (currents and acidification) was also approximately 10% of WT. Current-voltage (I-V) analysis reveals that S427L has no reversal potential in HCO3-, indicating that under physiological ion gradient conditions, NaHCO3 could not move out of cells as is needed for renal HCO3- absorption and ocular pressure homeostasis. I-V analysis without Na+ further shows that the S427L-mediated NaHCO3 efflux mode is depressed or absent. These experiments reveal that voltage- and Na+ -dependent transport by S427L-hkNBCe1 is unfavorably altered, thereby causing both insufficient HCO3- absorption by the kidney (proximal RTA) and inappropriate anterior chamber fluid transport (glaucoma).
Collapse
Affiliation(s)
- Dganit Dinour
- Department of Nephrology and Hypertension, Chaim Sheba Medical Center, Tel-Hashomer, and Tel-Aviv University, 52621 Israel
| | | | | | | | | | | | | | | | | |
Collapse
|
47
|
Shayakul C, Alper SL. Defects in processing and trafficking of the AE1 Cl-/HCO3- exchanger associated with inherited distal renal tubular acidosis. Clin Exp Nephrol 2004; 8:1-11. [PMID: 15067510 DOI: 10.1007/s10157-003-0271-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2003] [Accepted: 12/17/2003] [Indexed: 10/26/2022]
Abstract
Distal renal tubular acidosis (dRTA) results from impaired urinary acidification by the renal collecting duct. Acquired dRTA can be secondary to diverse pathological processes, including diabetic, ischemic, fibrosing, or immunological processes; less frequently it presents as a familial disorder with either an autosomal recessive or dominant pattern of transmission. Mutations in the SLC4A1/AE1/band 3 Cl(-)/HCO(3)(-) exchanger gene have been identified as causes for both dominant and recessive forms of dRTA. These mutations comprise a group almost entirely distinct from the SLC4A1 mutations that underlie the familial hemolytic anemia of hereditary spherocytosis. Why does one group of mutations express almost exclusively an isolated erythroid phenotype, whereas the second group of mutations expresses almost exclusively a phenotype explicable entirely by defective function of renal collecting duct type A intercalated cells? This review summarizes current research addressing this central question in the pathobiology of inherited dRTA associated with mutations in the SLC4A1 gene. Studying dRTA-associated mutant AE1 polypeptides can provide novel insights into the biology of the intercalated cell and the collecting duct as well as more generally into mechanisms by which epithelial cells generate and maintain functional polarity.
Collapse
Affiliation(s)
- Chairat Shayakul
- Renal Unit, Department of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | | |
Collapse
|
48
|
Watanabe S, Tsuruoka S, Vijayakumar S, Fischer G, Zhang Y, Fujimura A, Al-Awqati Q, Schwartz GJ. Cyclosporin A produces distal renal tubular acidosis by blocking peptidyl prolyl cis-trans isomerase activity of cyclophilin. Am J Physiol Renal Physiol 2004; 288:F40-7. [PMID: 15353404 DOI: 10.1152/ajprenal.00218.2004] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cyclosporin A (CsA), a widely used immunosuppressant, causes distal renal tubular acidosis (dRTA). It exerts its immunosuppressive effect by a calcineurin-inhibitory complex with its cytosolic receptor, cyclophilin A. However, CsA also inhibits the peptidyl prolyl cis-trans isomerase (PPIase) activity of cyclophilin A. We studied HCO(3)(-) transport and changes in beta-intercalated cell pH on luminal Cl(-) removal in isolated, perfused rabbit cortical collecting tubules (CCDs) before and after exposure to media pH 6.8 for 3 h. Acid incubation causes adaptive changes in beta-intercalated cells by extracellular deposition of hensin (J Clin Invest 109: 89, 2002). Here, CsA prevented this adaptation. The unidirectional HCO(3)(-) secretory flux, estimated as the difference between net flux and that after Cl(-) removal from the lumen, was -6.7 +/- 0.2 pmol.min(-1).mm(-1) and decreased to -1.3 +/- 0.2 after acid incubation. CsA in the bath prevented the adaptive decreases in HCO(3)(-) secretion and apical Cl(-):HCO(3)(-) exchange. To determine the mechanism, we incubated CCDs with FK-506, which inhibits calcineurin activity independently of the host cell cyclophilin. FK-506 did not prevent the acid-induced adaptive decrease in unidirectional HCO(3)(-) secretion. However, [AD-Ser](8) CsA, a CsA derivative, which does not inhibit calcineurin but inhibits PPIase activity of cyclophilin A, completely blocked the effect of acid incubation on apical Cl(-):HCO(3)(-) exchange. Acid incubation resulted in prominent "clumpy" staining of extracellular hensin and diminished apical surface of beta-intercalated cells [smaller peanut agglutinin (PNA) caps]. CsA and [AD-Ser](8) CsA prevented most hensin staining and the reduction of apical surface; PNA caps were more prominent. We suggest that hensin polymerization around adapting beta-intercalated cells requires the PPIase activity of cyclophilins. Thus CsA is able to prevent this adaptation by inhibition of a peptidyl prolyl cis-trans isomerase activity. Such inhibition may cause dRTA during acid loading.
Collapse
MESH Headings
- Acidosis, Renal Tubular/chemically induced
- Acidosis, Renal Tubular/enzymology
- Acidosis, Renal Tubular/metabolism
- Animals
- Chloride-Bicarbonate Antiporters/drug effects
- Cyclophilins/antagonists & inhibitors
- Cyclosporine/toxicity
- Extracellular Matrix/drug effects
- Extracellular Matrix/metabolism
- Extracellular Matrix/physiology
- Extracellular Matrix Proteins
- Female
- Hydrogen-Ion Concentration
- Immunosuppressive Agents/toxicity
- In Vitro Techniques
- Kidney Tubules, Collecting/drug effects
- Kidney Tubules, Collecting/physiology
- Kidney Tubules, Distal/drug effects
- Kidney Tubules, Distal/physiology
- Rabbits
- Receptors, Immunologic/metabolism
- Receptors, Immunologic/physiology
- Receptors, Scavenger
Collapse
Affiliation(s)
- Seiji Watanabe
- Department of Pediatrics, Strong Children's Research Center, University of Rochester School of Medicine, Rochester, NY 14642, USA
| | | | | | | | | | | | | | | |
Collapse
|
49
|
Disthabanchong S, Domrongkitchaiporn S, Sirikulchayanonta V, Stitchantrakul W, Karnsombut P, Rajatanavin R. Alteration of noncollagenous bone matrix proteins in distal renal tubular acidosis. Bone 2004; 35:604-13. [PMID: 15336595 DOI: 10.1016/j.bone.2004.04.028] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2003] [Revised: 04/01/2004] [Accepted: 04/30/2004] [Indexed: 11/15/2022]
Abstract
Our previous report on bone histomorphometry in patients with distal renal tubular acidosis (dRTA) revealed decreased bone formation rate (BFR) when compared to healthy subjects. The abnormality improved significantly after alkaline therapy. The modest increase in osteoblastic surface, after correction of metabolic acidosis, could not explain the striking improvement in bone formation, suggesting additional influence of metabolic acidosis on osteoblast function and/or bone matrix mineralization. Osteoblasts and, to a lesser extent, osteoclasts synthesize and secrete bone matrix including type I collagen and various noncollagenous proteins (NCPs). Substantial evidence suggested diverse functions of NCPs related to bone formation, resorption, and mineralization. Metabolic acidosis, through its effect on bone cells, may result in an alteration in the production of NCPs. Our study examined bone histomorphometry with detailed analysis on the mineralization parameters and NCPs expression within the bone matrix of patients with dRTA before and after treatment with alkaline. Seven dRTA patients underwent bone biopsy at their initial diagnosis and again 12 months after alkaline therapy. Bone mineral density (BMD) and bone histomorphometry were obtained at baseline and after the treatment. The expression of NCPs was examined by immunohistochemistry, quantitated by digital image analysis, and reported as a percentage of area of positive staining or mineralized trabecular bone area. Alkaline therapy normalized the low serum phosphate and PTH during acidosis. The reduction in BMD at baseline improved significantly by the treatment. Bone histomorphometry demonstrated the increase in osteoid surface and volume without significant alteration after acidosis correction. In comparison to the normal subjects, osteoid thickness was slightly but insignificantly elevated. Osteoblast and osteoclast populations and their activities were suppressed. The reduction in mineral apposition rate and adjusted apposition rate were observed in conjunction with the prolongation of mineralization lag time. Alkaline therapy improved the mineralization parameters considerably. In addition to the increase in BFR relative osteoblast number after acidosis correction, osteocalcin expression in the bone matrix increased significantly from 16.7% to 22.3%. Six of seven patients had decreased osteopontin expression. In conclusion, the abnormal bone remodeling in dRTA is characterized by low turnover bone disease with some degree of defective mineralization. Alteration of NCPs expression suggested the effect of metabolic acidosis on bone cells. Alkaline therapy increased bone mass through the restoration of bone mineral balance and, perhaps, improved osteoblast function.
Collapse
Affiliation(s)
- Sinee Disthabanchong
- Division of Nephrology, Department of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
| | | | | | | | | | | |
Collapse
|
50
|
Kittanakom S, Cordat E, Akkarapatumwong V, Yenchitsomanus PT, Reithmeier RAF. Trafficking defects of a novel autosomal recessive distal renal tubular acidosis mutant (S773P) of the human kidney anion exchanger (kAE1). J Biol Chem 2004; 279:40960-71. [PMID: 15252044 DOI: 10.1074/jbc.m405356200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Autosomal dominant and recessive distal renal tubular acidosis (dRTA) can be caused by mutations in the anion exchanger 1 (AE1 or SLC4A1) gene, which encodes the erythroid chloride/bicarbonate anion exchanger membrane glycoprotein (eAE1) and a truncated kidney isoform (kAE1). The biosynthesis and trafficking of kAE1 containing a novel recessive missense dRTA mutation (kAE1 S773P) was studied in transiently transfected HEK-293 cells, expressing the mutant alone or in combination with wild-type kAE1 or another recessive mutant, kAE1 G701D. The kAE1 S773P mutant was expressed at a three times lower level than wild-type, had a 2-fold decrease in its half-life, and was targeted for degradation by the proteasome. It could not be detected at the plasma membrane in human embryonic kidney cells and showed predominant endoplasmic reticulum immunolocalization in both human embryonic kidney and LLC-PK1 cells. The oligosaccharide on a kAE1 S773P N-glycosylation mutant (N555) was not processed to the complex form indicating impaired exit from the endoplasmic reticulum. The kAE1 S773P mutant showed decreased binding to an inhibitor affinity resin and increased sensitivity to proteases, suggesting that it was not properly folded. The other recessive dRTA mutant, kAE1 G701D, also exhibited defective trafficking to the plasma membrane. The recessive kAE1 mutants formed dimers like wild-type AE1 and could hetero-oligomerize with wild-type kAE1 or with each other. Hetero-oligomers of wild-type kAE1 with recessive kAE1 S773P or G701D, in contrast to the dominant kAE1 R589H mutant, were delivered to the plasma membrane.
Collapse
MESH Headings
- Acidosis, Renal Tubular/metabolism
- Anion Exchange Protein 1, Erythrocyte/chemistry
- Anion Exchange Protein 1, Erythrocyte/genetics
- Anions
- Biological Transport
- Biotinylation
- Blotting, Western
- Cell Line
- Cell Membrane/metabolism
- Cell Separation
- DNA, Complementary/metabolism
- Electrophoresis, Polyacrylamide Gel
- Endoplasmic Reticulum/metabolism
- Flow Cytometry
- Genes, Dominant
- Heterozygote
- Homozygote
- Humans
- Microscopy, Fluorescence
- Models, Biological
- Mutation
- Oligosaccharides/chemistry
- Plasmids/metabolism
- Polymorphism, Single-Stranded Conformational
- Precipitin Tests
- Protein Binding
- Protein Folding
- Protein Structure, Tertiary
- Time Factors
- Transfection
Collapse
Affiliation(s)
- Saranya Kittanakom
- Canadian Institutes of Health Research Group in Membrane Biology, Departments of Biochemistry and Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | |
Collapse
|