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Borrego Utiel FJ, Herrera Contreras I, Merino García E, Moriana Domínguez C, Ocaña Pérez E, García Cortés MJ. Hypocitraturia is present when renal function is impaired in diverse nephropathies and is not related with serum bicarbonate levels. Int Urol Nephrol 2021; 54:1261-1269. [PMID: 34546556 DOI: 10.1007/s11255-021-02992-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 08/02/2021] [Indexed: 12/01/2022]
Abstract
BACKGROUND In autosomal dominant polycystic kidney disease (ADPKD) it is frequently found a reduction in urinary citrate of unknown origin. It has been suggested that it could be a marker of acid retention in chronic kidney disease. Our aim was to compare urinary citrate in ADPKD with other nephropathies and to show its relation with serum bicarbonate. METHODS We determined urinary citrate in patients with several nephropathies and varied renal function. We included 291 patients, 119 with glomerular diseases, 116 with ADPKD, 21 with other nephropathies, and 35 patients with normal renal function. RESULTS Urinary citrate was higher in women and in patients with normal renal function. ADPKD patients showed similar values of urinary citrate to patients with glomerular diseases and with other nephropathies. We observed a progressive reduction in urinary citrate with renal impairment, in a comparable way among patients with ADPKD and glomerular diseases. We did not observe a relationship with serum bicarbonate. Serum uric acid levels were significantly higher in patients with glomerular diseases than in ADPKD patients, even after correction with the degree of renal function. CONCLUSIONS Hypocitraturia is not specific of ADPKD but it is also present in all tested nephropathies and is related with renal impairment and not with serum bicarbonate. It could be interesting to study urinary citrate as a marker of renal function and as a prognostic factor.
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Affiliation(s)
| | | | - Enoc Merino García
- Unidad de Gestión Clínica (UGC) de Nefrología, Hospital Universitario de Jaén, Jaén, Spain
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Urinary citrate as a marker of renal function in patients with autosomal dominant polycystic kidney disease. Int Urol Nephrol 2021; 54:873-881. [PMID: 34279821 DOI: 10.1007/s11255-021-02953-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 07/07/2021] [Indexed: 10/20/2022]
Abstract
INTRODUCTION Autosomal dominant polycystic kidney disease (ADPKD) is frequent to find low urinary citrate levels. Recently, it has been suggested that urinary citrate could be a marker of covert metabolic acidosis in chronic kidney disease. OBJECTIVE Our aim was to analyze relationship between urinary citrate levels, renal function, and serum bicarbonate in ADPKD patients. METHODS We determined citrate in 24-h collected urine from ADPKD patients and correlated with glomerular filtration rate (CKD-EPI equation) and serum bicarbonate concentration. RESULTS We included 120 patients, 60% men, eGFR was 71 ± 32 mL/min/1.73 m2. Urinary citrate/creatinine ratio was 195 ± 152 mg/gCr (range 1.2-689) with levels significantly higher in females. Urinary citrate lower than 300 mg/gCr was present in 75% of patients and when considering chronic kidney stages (CKD), we observed reduced levels in 48.8% in CKD1 stage, in 79.4% in CKD2 stage, in 96.2% in CKD3 stage, and in 94.7% of patients in CKD4 stage. Urinary citrate was correlated with serum creatinine (r = - 0.61, p < 0.001) and eGFR (r = 0.55, p < 0.001) in both gender. We did not find any correlation with serum bicarbonate. Using a general linear modeling analysis, we found as predictors of urinary citrate/creatinine ratio to glomerular filtration rate, gender, and age. Lower levels of urinary citrate were accompanied by a decline in urinary osmolality and in renal excretion of calcium and uric acid. In a subgroup of patients, we measured total kidney volume and we found an inverse correlation with urinary citrate levels that disappeared when it was corrected with glomerular filtration rate. CONCLUSIONS Urinary citrate is very frequently reduced in ADPKD patients being present from very early CKD stages. Their levels in urine are inversely correlated with glomerular filtration rate and it is not related with serum bicarbonate concentration. We think that it would be interesting to study urinary citrate as a marker of chronic kidney disease in ADPKD patients.
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Hering-Smith KS, Hamm LL. Acidosis and citrate: provocative interactions. ANNALS OF TRANSLATIONAL MEDICINE 2018; 6:374. [PMID: 30370301 DOI: 10.21037/atm.2018.07.37] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | - L Lee Hamm
- Department of Medicine, Tulane University School of Medicine, New Orleans, LA, USA
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Abstract
Distal renal tubular acidosis (DRTA) is defined as hyperchloremic, non-anion gap metabolic acidosis with impaired urinary acid excretion in the presence of a normal or moderately reduced glomerular filtration rate. Failure in urinary acid excretion results from reduced H+ secretion by intercalated cells in the distal nephron. This results in decreased excretion of NH4+ and other acids collectively referred as titratable acids while urine pH is typically above 5.5 in the face of systemic acidosis. The clinical phenotype in patients with DRTA is characterized by stunted growth with bone abnormalities in children as well as nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria, hypocitraturia, and relatively alkaline urine. Hypokalemia is a striking finding that accounts for muscle weakness and requires continued treatment together with alkali-based therapies. This review will focus on the mechanisms responsible for impaired acid excretion and urinary potassium wastage, the clinical features, and diagnostic approaches of hypokalemic DRTA, both inherited and acquired.
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Kurtz I. Renal Tubular Acidosis: H +/Base and Ammonia Transport Abnormalities and Clinical Syndromes. Adv Chronic Kidney Dis 2018; 25:334-350. [PMID: 30139460 PMCID: PMC6128697 DOI: 10.1053/j.ackd.2018.05.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Renal tubular acidosis (RTA) represents a group of diseases characterized by (1) a normal anion gap metabolic acidosis; (2) abnormalities in renal HCO3- absorption or new renal HCO3- generation; (3) changes in renal NH4+, Ca2+, K+, and H2O homeostasis; and (4) extrarenal manifestations that provide etiologic diagnostic clues. The focus of this review is to give a general overview of the pathogenesis of the various clinical syndromes causing RTA with a particular emphasis on type I (hypokalemic distal RTA) and type II (proximal) RTA while reviewing their pathogenesis from a physiological "bottom-up" approach. In addition, the factors involved in the generation of metabolic acidosis in both type I and II RTA are reviewed highlighting the importance of altered renal ammonia production/partitioning and new HCO3- generation. Our understanding of the underlying tubular transport and extrarenal abnormalities has significantly improved since the first recognition of RTA as a clinical entity because of significant advances in clinical acid-base chemistry, whole tubule and single-cell H+/base transport, and the molecular characterization of the various transporters and channels that are functionally affected in patients with RTA. Despite these advances, additional studies are needed to address the underlying mechanisms involved in hypokalemia, altered ammonia production/partitioning, hypercalciuria, nephrocalcinosis, cystic abnormalities, and CKD progression in these patients.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, and Brain Research Institute, UCLA, Los Angeles, CA.
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Walker RW, Zhang S, Coleman-Barnett JA, Hamm LL, Hering-Smith KS. Calcium receptor signaling and citrate transport. Urolithiasis 2018; 46:409-418. [PMID: 29383416 DOI: 10.1007/s00240-018-1035-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 01/10/2018] [Indexed: 01/22/2023]
Abstract
The calcium sensing receptor (CaSR) in the distal nephron decreases the propensity for calcium stones. Here we investigate if the apical CaSR in the proximal tubule also prevents stone formation acting via regulation of apical dicarboxylate and citrate transport. Urinary citrate, partially reabsorbed as a dicarboxylate in the proximal tubule lumen, inhibits stone formation by complexing calcium. We previously demonstrated a novel apical calcium-sensitive dicarboxylate transport system in OK proximal tubule cells. This calcium-sensitive process has the potential to modulate the amount of citrate available to complex increased urinary calcium. Using isotope labeled succinate uptake in OK cells along with various pharmacologic tools we examined whether the CaSR alters apical dicarboxylate transport and through which signal transduction pathways this occurs. Our results indicate that in the proximal tubule CaSR adjusts apical dicarboxylate transport, and does so via a CaSR → Gq → PKC signaling pathway. Thus, the CaSR may decrease the propensity for stone formation via actions in both proximal and distal nephron segments.
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Affiliation(s)
- Ryan W Walker
- Nephrology and Hypertension 8545, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA, 70112, USA
| | - Shijia Zhang
- Nephrology and Hypertension 8545, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA, 70112, USA
| | - Joycelynn A Coleman-Barnett
- Nephrology and Hypertension 8545, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA, 70112, USA
| | - L Lee Hamm
- Nephrology and Hypertension 8545, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA, 70112, USA
| | - Kathleen S Hering-Smith
- Nephrology and Hypertension 8545, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA, 70112, USA.
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Chung VY, Turney BW. A Drosophila genetic model of nephrolithiasis: transcriptional changes in response to diet induced stone formation. BMC Urol 2017; 17:109. [PMID: 29183349 PMCID: PMC5706311 DOI: 10.1186/s12894-017-0292-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 10/30/2017] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Urolithiasis is a significant healthcare issue but the pathophysiology of stone disease remains poorly understood. Drosophila Malpighian tubules were known to share similar physiological function to human renal tubules. We have used Drosophila as a genetic model to study the transcriptional response to stone formation secondary to dietary manipulation. METHODS Wild-type male flies were raised on standard medium supplemented with lithogenic agents: control, sodium oxalate (NaOx) and ethylene glycol (EG). At 2 weeks, Malpighian tubules were dissected under polarized microscope to visualize crystals. The parallel group was dissected for RNA extraction and subsequent next-generation RNA sequencing. RESULTS Crystal formation was visualized in 20%(±2.2) of flies on control diet, 73%(±3.6) on NaOx diet and 84%(±2.2) on EG diet. Differentially expressed genes were identified in flies fed with NaOx and EG diet comparing with the control group. Fifty-eight genes were differentially expressed (FDR <0.05, p < 0.05) in NaOx diet and 20 genes in EG diet. The molecular function of differentially expressed genes were assessed. Among these, Nervana 3, Eaat1 (Excitatory amino acid transporter 1), CG7912, CG5404, CG3036 worked as ion transmembrane transporters, which were possibly involved in stone pathogenesis. CONCLUSIONS We have shown that by dietary modification, stone formation can be manipulated and visualized in Drosophila Malpighian tubules. This genetic model could be potentially used to identify the candidate genes that influence stone risk hence providing more insight to the pathogenesis of human stone disease.
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Affiliation(s)
- Vera Y. Chung
- Oxford Stone Group, Department of Urology, Nuffield Department of Surgical Sciences, University of Oxford, Oxford, UK
| | - Benjamin W. Turney
- Oxford Stone Group, Department of Urology, Nuffield Department of Surgical Sciences, University of Oxford, Oxford, UK
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Lee HW, Handlogten ME, Osis G, Clapp WL, Wakefield DN, Verlander JW, Weiner ID. Expression of sodium-dependent dicarboxylate transporter 1 (NaDC1/SLC13A2) in normal and neoplastic human kidney. Am J Physiol Renal Physiol 2016; 312:F427-F435. [PMID: 27927654 PMCID: PMC5374311 DOI: 10.1152/ajprenal.00559.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 11/15/2016] [Accepted: 12/05/2016] [Indexed: 12/21/2022] Open
Abstract
Regulated dicarboxylate transport is critical for acid-base homeostasis, prevention of calcium nephrolithiasis, regulation of collecting duct sodium chloride transport, and the regulation of blood pressure. Although luminal dicarboxylate reabsorption via NaDC1 (SLC13A2) is believed to be the primary mechanism regulating renal dicarboxylate transport, the specific localization of NaDC1 in the human kidney is currently unknown. This study's purpose was to determine NaDC1's expression in normal and neoplastic human kidneys. Immunoblot analysis demonstrated NaDC1 expression with an apparent molecular weight of ~61 kDa. Immunohistochemistry showed apical NaDC1 immunolabel in the proximal tubule of normal human kidney tissue; well-preserved proximal tubule brush border was clearly labeled. Apical NaDC1 expression was evident throughout the entire proximal tubule, including the initial proximal convoluted tubule, as identified by origination from the glomerular tuft, and extending through the terminal of the proximal tubule, the proximal straight tubule in the outer medulla. We confirmed proximal tubule localization by colocalization with the proximal tubule specific protein, NBCe1. NaDC1 immunolabel was not detected other than in the proximal tubule. In addition, NaDC1 immunolabel was not detected in tumors of presumed proximal tubule origin, clear cell and papillary renal cell carcinoma, or in tumors of nonproximal tubule origin, oncocytoma and chromophobe carcinoma. In summary, 1) in the human kidney, apical NaDC1 immunolabel is present throughout the entire proximal tubule, and is not detectable in other renal cells; and 2) NaDC1 immunolabel is not present in renal tumors. These studies provide important information regarding NaDC1's role in human dicarboxylate metabolism.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - William L Clapp
- Department of Pathology, University of Florida College of Medicine, Gainesville, Florida; and
| | - Dara N Wakefield
- Department of Pathology, University of Florida College of Medicine, Gainesville, Florida; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; .,Nephrology and Hypertension Section, Gainesville Veterans Affairs Medical Center, Gainesville, Florida
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Osis G, Handlogten ME, Lee HW, Hering-Smith KS, Huang W, Romero MF, Verlander JW, Weiner ID. Effect of NBCe1 deletion on renal citrate and 2-oxoglutarate handling. Physiol Rep 2016; 4:e12778. [PMID: 27117802 PMCID: PMC4848728 DOI: 10.14814/phy2.12778] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Revised: 03/29/2016] [Accepted: 04/01/2016] [Indexed: 12/03/2022] Open
Abstract
UNLABELLED The bicarbonate transporter, NBCe1 (SLC4A4), is necessary for at least two components of the proximal tubule contribution to acid-base homeostasis, filtered bicarbonate reabsorption, and ammonia metabolism. This study's purpose was to determine NBCe1's role in a third component of acid-base homeostasis, organic anion metabolism, by studying mice with NBCe1 deletion. Because NBCe1 deletion causes metabolic acidosis, we also examined acid-loaded wild-type adult mice to determine if the effects of NBCe1 deletion were specific to NBCe1 deletion or were a non-specific effect of the associated metabolic acidosis. Both NBCe1 KO and acid-loading decreased citrate excretion, but in contrast to metabolic acidosis alone, NBCe1 KO decreased expression of the apical citrate transporter, NaDC-1. Thus, NBCe1 expression is necessary for normal NaDC-1 expression, and NBCe1 deletion induces a novel citrate reabsorptive pathway. Second, NBCe1 KO increased 2-oxoglutarate excretion. This could not be attributed to the metabolic acidosis as experimental acidosis decreased excretion. Increased 2-oxoglutarate excretion could not be explained by changes in plasma 2-oxoglutarate levels, the glutaminase I or the glutaminase II generation pathways, 2-oxoglutarate metabolism, its putative apical 2-oxoglutarate transporter, OAT10, or its basolateral transporter, NaDC-3. IN SUMMARY (1) NBCe1 is necessary for normal proximal tubule NaDC-1 expression; (2) NBCe1 deletion results in stimulation of a novel citrate reabsorptive pathway; and (3) NBCe1 is necessary for normal 2-oxoglutarate metabolism through mechanisms independent of expression of known transport and metabolic pathways.
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Affiliation(s)
- Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | | | - Weitao Huang
- Renal Division, Tulane University College of Medicine, New Orleans, Louisiana
| | - Michael F Romero
- Department of Physiology & Biomedical Engineering and Nephrology & Hypertension, Mayo Clinic College Of Medicine, Rochester, Minnesota
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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