Citrate Excretion Research Articles

The membrane protein ANKH is crucial for bone mechanical performance by mediating cellular export of citrate and ATP.

The membrane protein ANKH was known to prevent pathological mineralization of joints and was thought to export pyrophosphate (PPi) from cells. This did not explain, however, the presence of ANKH in tissues, such as brain, blood vessels and muscle. We now report that in cultured cells ANKH exports ATP, rather than PPi, and, unexpectedly, also citrate as a prominent metabolite. The extracellular ATP is rapidly converted into PPi, explaining the role of ANKH in preventing ankylosis. Mice lacking functional Ank (Ankank/ank mice) had plasma citrate concentrations that were 65% lower than those detected in wild type control animals. Consequently, citrate excretion via the urine was substantially reduced in Ankank/ank mice. Citrate was even undetectable in the urine of a human patient lacking functional ANKH. The hydroxyapatite of Ankank/ank mice contained dramatically reduced levels of both, citrate and PPi and displayed diminished strength. Our results show that ANKH is a critical contributor to extracellular citrate and PPi homeostasis and profoundly affects bone matrix composition and, consequently, bone quality.

GhMATE1 expression regulates Aluminum tolerance of cotton and overexpression of GhMATE1 enhances acid soil tolerance of Arabidopsis

The ionic form of Aluminum (Al3+) is one of the dangerous metals to the plants under acid soil condition. A principal functional tool of plant Al tolerance encompasses Al-induced stimulation of membrane transporters, which accelerates the organic acid release from the root region. The released organic acid (usually citrate, oxalate and malate) form stable and nontoxic complexes with Al in the rhizosphere. Several genes were characterized to understand the acid soil tolerance mechanisms of plants. In particular, Al-activated malate and citrate discharge from the roots are effectively involved in acid soil stress tolerance mechanisms. Based on the above mechanisms, in this present work, the cotton citrate (GhMATE1 [Multidrug and Toxic compound Extrusion]) transporters has been cloned and characterized in Cotton. Down-regulation of GhMATE1 (GhMATE1-RNAi) system increased the sensitivity to Al and proton. Moreover, plants lacking GhMATE1 released negligible amount of citrate when compared with control plants. The primary and secondary root growth of GhMATE1-RNAi-lines was significantly inhibited under Al stress conditions. Besides, Al stress responsive genes like GhALMT1 (Aluminum-activated Malate Transporter 1), GhSTOP1 (Sensitive to Proton toxicity 1) and GhALS3 (Aluminum Sensitive 3) were not affected in GhMATE1-RNAi lines. In addition, transgenic Arabidopsis plants overexpressing GhMATE1 exhibited Al tolerant phenotypes and these transgenic plants displayed accelerated root growth and enhanced citrate excretion when compared with control plants. The results pointed out that the GhMATE1 expression is Al inducible and controls the citrate-mediated Al3+ sequestration. These observations indicated that GhMATE1 is a key gene which is involved in Al induced citrate release and lateral root growth arrest.

Effect of citrate on ionized calcium levels during plateletpheresis procedures

Plateletpheresis procedures are generally well tolerated by most of the donors and adverse reactions due to citrate are generally mild and easily managed. The most common apheresis‐related reaction is hypocalcemia due to citrate anticoagulation which reduces ionized calcium and magnesium levels. The levels of ionized calcium levels decrease continuously from the baseline levels till end of the procedure and restore to baseline values post‐procedure. Symptoms of citrate toxicity are dependent on various factors like rate of citrate administration, duration of citrate infusion, dilution of citrate in extracellular fluid, redistribution, rate of citrate metabolism and the rate of citrate excretion. Citrate metabolism occurs in the liver, kidney, and skeletal muscle. Donors generally tolerate up to 20% decreases in ionized calcium levels. Citrate related reactions are generally transient and selflimiting. Citrate reactions can be differentiated into mild, moderate and severe. Management of citrate reactions includes mostly procedural modifications and/or oral calcium supplementation and rarely may require intravenous calcium supplementation. In donors with citrate related hypocalcemic symptoms, unresponsive to calcium supplementation, measurement of ionized magnesium should be considered as citrate decreased the ionized magnesium levels too. Management of such donors should be done with supplementation with magnesium sulfate. Management of donor reactions will make donors experience more pleasant, thereby increasing donor return rate and maintain the donor pool.

SO010URINARY LITHOGENIC RISK PROFILE IN ADPKD PATIENTS TREATED WITH TOLVAPTAN

Abstract Background and Aims Nephrolithiasis is a common health problem in autosomal dominant polycystic kidney disease (ADPKD) and significantly contributes to patient morbidity. In observational studies, prevalence rates of up to 36% have been reported. Kidney stones of ADPKD patients are typically composed of uric acid (UA) or calcium oxalate (CaOx), and hypocitraturia and low urinary pH have been reported as the main prolithogenic abnormalities. Recently, Tolvaptan has been introduced for the treatment of ADPKD, but its impact on the lithogenic risk profile in ADPKD patients remains unknown. Method We conducted a retrospective analysis of patients enrolled in the Bern ADPKD registry, an observational cohort study. Inclusion criteria were age ≥ 18 years, clinical diagnosis of ADPKD, and informed consent. The main exclusion criterion was need for renal replacement therapy. 24-h urine analyses were performed at baseline and then at yearly follow-ups. Relative supersaturation ratios (RSS) for CaOx, calcium phoshate (CaP) and UA were calculated with EQUIL2. Univariate and multivariate mixed-effects linear regression models, adjusted for age, sex, BMI, eGFR and endogenous acid production, estimated by net acid excretion, were used to assess the impact of Tolvaptan treatment on urinary composition. Results 38 patients received Tolvaptan treatment (39.5% females) and were included in the analysis. Six patients (15.8%) had a history of symptomatic stone events. In multivariate analysis, Tolvaptan treatment was significantly associated with reductions of CaOx, CaP and UA RSS (p < 0.01) and increased urinary citrate (p = 0.015) and calcium (p < 0.01) excretion. In contrast, Tolvaptan treatment was not associated with alterations in urinary oxalate excretion or urinary pH. Conclusion Tolvaptan significantly reduces RSS for CaOx, CaP and UA. Future studies are needed to assess the impact of Tolvaptan treatment on stone recurrence in ADPKD patients.

P0077A NEW MUTATION OF DNAJB11 AS A CAUSE OF CYSTIC KYDNEY DISEASE: THE FOURTH GENE OF ADPKD

Abstract Background and Aims Monogenic inherited diseases are an underestimated but important cause of chronic kidney disease (CKD). Despite the increasing knowledge about their inheritance, they are identified in fewer than 10% of CKD patients. Among monogenic causes of CKD, polycystic kidney diseases (PKD) represent a group of disorders with a clinical and genetic heterogeneity and a variable phenotype (from early manifestations during pregnancy or childhood to the absence of clinical manifestations until adulthood). We here present a PKD family with 5 members displaying the disease (Figure 1). Method We revised patients clinical history, laboratory data and imaging exams. An accurate family history was recovered. Blood samples were collected from living patients to perform an exome analysis using next generation sequencing to analyze all possible genes involved in PKD. Results Each patient presented a clinical history of nephrolithiasis, a variable degree of CKD (from normal kidney function to renal transplant), urinary and blood parameters compatible with distal renal tubular acidosis (hypercalciuria, low urinary citrate excretion and hypokalemia). Imaging exams showed several renal cysts in the medulla or at the cortico-medullary junction with intracystic calcifications (Figure 2). Some patients displayed also large cortical renal cysts and also hepatic and pancreatic cysts. The genetic analysis performed using next generation sequencing in four patients showed a new mutation on the gene DNAJB11; the mutation introduced a stop codon and was identified as pathogenic by prediction programs. It was present in heterozygosity in all subjects and had an autosomal dominant pattern of inheritance. Conclusion DNAJB11 mutations were reported as a cause of PKD for the first time in 2018 by Cornec-Le-Gall and colleagues. The nephropathy derived from these mutations need to be differentiated from ADPKD (autosomal dominant polycystic kidney disease), from ADTKD (autosomal dominant tubulointerstitial kidney disease) and from medullary sponge kidney. DNAJB11 encodes a co-chaperone of the endoplasmic reticulum (ER) also called ERdj3. It is part of the HSP40 protein family and plays a central role in both intracellular and extracellular proteomic homeostasis (proteostasis). In the intracellular compartment it acts as a co-chaperone in the pathway of the unfolded protein response (UPR) in which it binds misfolded proteins which have to be secreted and activates BiP an HSP70 of ER whose function is to correct the misfolding. In the kidney it is mainly expressed in the thick ascending limb of Henle’s loop, in the distal tubule and in the collecting duct justifying the clinical presentation of nephropathy and differentiating the disease from ADPKD (Figure 3).

P0064RENAL PHENOTYPES IN A GROUP OF PATIENTS WITH MITOCHONDRIAL DISEASES

Abstract Background and Aims Mitochondrial diseases (MDs) are one of the most common inherited metabolic disorders caused by mutations of either mitochondrial or nuclear genes involved in the oxidative phosphorylation pathway. Tissues with high energy demand (i.e. brain and skeletal muscle) are preferentially affected, and MDs are not rarely referred to as mitochondrial encephalomyopathies. However, one of the hallmarks of MDs is multisystemic involvement, with large clinical variability and severity due to different mitochondrial DNA heteroplasmy levels. Given the possibility of multisystemic phenotype of MDs, renal involvement has been suggested, based on renal cells vulnerability to poor energy supply. A specific mitochondrial kidney disease is thought to underlie renal manifestations, therefore theoretically every district of the nephron might be affected by MDs. Regarding tubular involvement, we suggested a possible association between nephrolithiasis and MDs, based on data of 3 related stone formers with reduced urinary citrate excretion and MELAS syndrome. The aim of this study is to provide a clinical description of the renal phenotypes of patients with MDs. Method In 2019, 6 patients with MDs routinely followed by the Neurology outpatient clinic of our Institution were randomly asked to perform renal screening. Genetic tests, blood and 24-hour urine analyses were assessed in the whole population. The main comorbidities were recorded. Glomerular filtration rate (GFR) was estimated using creatinine clearance. Results Half of the patients were female, the average age at renal evaluation was 48±15 years; diabetes, hypertension and neurosensorial hypoacusia occurred in 4, 1 and 2 subjects, respectively. Five patients had m.3243A>G mutation, responsible for more than 85% of maternal inherited diabetes and deafness (MIDD) and syndrome of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS). The remaining patient carried the m.8363G>A variant, reported to be associated with a multisystem MDs known as Leigh syndrome (subacute necrotizing encephalomyelopathy). Median serum creatinine was 0.6 mg/dL (IQR: 0.5-1.1) with median GFR of 92 mL/min/1.73 m2 (IQR: 40-117). Three patients exhibited signs of kidney disease: one had both reduced GFR and proteinuria (eGFR 37 mL/min/1.73 m2 and 750 mg/day respectively), one had renal impairment (58 mL/min/1.7 3m2) and severe hypocitraturia (22 mg/day), one showed increased urinary calcium excretion (348 mg/day). In one patient, evaluation of the type of proteinuria has not been performed yet. Serum lactate was 3.1±1.9 mmol/L, urinary pH 5.8±0.3 and median urinary citrate excretion 593 mg/24h (IQR: 310-923). No relevant results were found on serum and/or urinary levels of sodium, potassium, magnesium, phosphorus, urate, chloride, oxalate, parathyroid hormone and 25-OH vitamin D. Conclusion These results confirmed the presence of renal disease and its heterogeneity in patients with MDs. A complete renal screening is necessary in these subjects in order to early recognize renal involvement and carefully select candidates for further diagnostic work-up including renal biopsy. A consensus on the optimal renal screening for these patients has yet to be established.

SO014CHANGES IN CHARACTERISTICS OF CRYSTALLURIA IN PATIENTS WITH RECURRENT NEPHROLITHIASIS

Abstract Background and Aims The study of crystals in the urinary sediment finds application in the diagnosis of hereditary or metabolic nephrolithiasis and in the identification of crystals from drugs. Method We conducted a thorough microscopic urine examination, focused on the determination of crystalluria, associated with the metabolic study at baseline and about 6 months after the start of a metaphylactic therapy, in 21 patients with recurrent nephrolithiasis, followed at the Metabolic Stone Clinic of our Institution. The analysis of the crystals was performed in parallel and blind through direct microscopic examination (MD) and automated instrumentation (SA) (SediMax analyzer - Menarini Diagnostics) of our institution. We used a semi-quantitative approach for both methods. Results We examined 42 sediments (21 at baseline and 21 after an average follow-up of 196±88 days) from 21 patients (8 females, 13 males), all of them showing calcium oxalate crystalluria. The analysis on baseline evaluation and follow-up on both Crystalluria MD and crystalluria SA through spaghetti plots showed a tendency to reduction of severity for the first one only. This trend is consistent with the data obtained from the metabolic studies: urinary oxalate and calcium excretions, the main drivers of calcium oxalate crystallization, which showed decreasing levels. The same examination for urinary citrate excretion showed a rising trend, again in accordance with the on-going changes in urine lithogenic profile. Conclusion The study of crystals in the urinary sediment, repeated over time, may represent a further indicator of the effectiveness of metaphylactic therapy and an indicator of patient adherence to the prescription in metabolic calcium oxalate nephrolithiasis.

Khella induced nephropathy: a case report and review of literature

Khella (Ammi visnagais) was used in Ancient Egypt as a herbal remedy for renal colic. Khella contains group of coumarins, xanthotoxin, ammidin, furoquinoline alkaloids and, dihydroseselins with varying cytotoxic activity. The most common is Khellin and visnagin. Khellin was found to be a smooth muscle relaxant, induces diuresis, increases excretion of citrate and decreases the excretion of oxalate in urine, which improves nephrolithiasis and passage of ureteric stones. Synthetic derivatives of khellin include amiodarone, the anti-arrhythmic drug, and cromolyn, an anti-asthma drug. Khellin is not as safe as it seems to be. Its oral use is limited by its potential toxicity (eg, elevated liver enzymes, phototoxicity, dermatitis). In experimental animals, the median lethal dose (LD50) was 3.6 g/kg for intra-peritoneal administration and 10.1 g/kg for oral administration. In humans, nausea and vomiting were observed frequently in 29% and transaminitis in 7-14% of the patients. Other potential adverse reactions include dizziness, constipation, headache, itching, insomnia, photosensitivity and lack of appetite. We report for the first-time, acute kidney injury following use of khella in a CKD patient with a 5-fold increase in his serum creatinine level from 1.9 to 9.2 mg/dl. His renal biopsy revealed eosinophilic interstitial nephritis. He responded well to pulse methylprednisolone followed by short course of oral steroids. We believe this is the first case describing Khella nephropathy. Herbal nephropathy is not uncommon and herbal remedies are not as safe as it is believed. Accurate diagnosis and early management are the key in improving the renal outcome.

Association of Impaired Renal Function With Changes in Urinary Mineral Excretion and Stone Composition

ObjectiveTo investigate the effect of kidney function on stone composition and urinary mineral excretion in patients undergoing surgical intervention for nephrolithiasis. MethodsUsing our institutional kidney stone database, we performed a retrospective review of stone patients who underwent surgical intervention between 2004 and 2015. Patients’ demographic information, 24-hour urinary mineral excretion, and stone characteristics were reported. The patients’ estimated glomerular filtration rates (eGFR) were compared with their stone compositions and 24-hour urine mineral excretions. ResultsA statistically significant difference was noted between the groups, with uric acid stones being associated with lower eGFR and calcium phosphate stones associated with higher eGFR. No relationship could be demonstrated between eGFR and calcium oxalate or struvite stones. Patients with lower eGFR also demonstrated a statistically significant association with lower urinary pH as well as lower urinary excretion of calcium and citrate. ConclusionWhile various factors have been found to play significant roles in kidney stone formation and composition, our findings demonstrate a definite relationship between these and renal function. This paper highlights the fact that renal function evaluation should be considered an important component in the evaluation, counseling, and management of patients with nephrolithiasis.

MP43-06 BAKING SODA EXERTS A SIGNIFICANT ALKALINIZING EFFECT IN PATIENTS WITH UROLITHIASIS WITHOUT INCREASING URINARY CALCIUM EXCRETION

You have accessJournal of UrologyStone Disease: Medical & Dietary Therapy (MP43)1 Apr 2020MP43-06 BAKING SODA EXERTS A SIGNIFICANT ALKALINIZING EFFECT IN PATIENTS WITH UROLITHIASIS WITHOUT INCREASING URINARY CALCIUM EXCRETION Kristina Penniston*, Scott Quarrier, Shuang Li, and R. Allan Jhagroo Kristina Penniston*Kristina Penniston* More articles by this author , Scott QuarrierScott Quarrier More articles by this author , Shuang LiShuang Li More articles by this author , and R. Allan JhagrooR. Allan Jhagroo More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000898.06AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Baking soda (sodium bicarbonate, NaHCO3) has been used for decades as an alkalinizing agent. When taken orally, NaHCO3 increases urine pH and citrate. Despite rising prices of prescriptive urinary alkalinizing agents, urologists may be reluctant to recommend NaHCO3 due to fear of Na-induced hypercalciuria. To assess this potential adverse event, we reviewed our recent clinical experience with baking soda as alkali treatment. METHODS: A convenience sample of patients from our metabolic stone prevention clinic who used baking soda within the past year was assembled from an IRB-approved prospectively maintained database. In addition to taking 1/4 tsp baking soda BID (dissolved in water or other liquid), providing approximately 25 mEq alkali, most patients were counseled to increase intake of bicarbonate precursors from fruits and vegetables. Results from patients’ 24-h urine collections before and during treatment were retrospectively reviewed. The primary outcome was change in urinary calcium (UCa) excretion. Patients were excluded for urine creatinine variation >40% and/or no follow-up urine collection. In order to assess only patients compliant with treatment, those with no increases in either urine citrate or pH and/or 24-h urine Na:Cl ratio <0.9 while on treatment were excluded. RESULTS: Patients (n=21) were mostly male (71%) and were 60±10 y. Urine collections were 9.1±2.1 months apart. Overall, significant increases were observed in urinary citrate excretion (523 to 822 mg/d), pH (5.83 to 6.26), and 24-h urine Na:Cl ratio (1.03 to 1.17); p≤0.003 for all comparisons (paired t-tests). The increase in urinary Na excretion (40±102 mEq) was >3-fold higher than change in Cl excretion, confirming higher Na intake from NaHCO3 vs. dietary salt (NaCl). UCa excretion was not different before and during treatment (191 mg and 217 mg respectively; p=0.18, paired t-test). Before treatment, 4 patients had UCa>250 mg; 2 of these resolved on treatment. Of 5 patients with new-onset hypercalciuria, higher dietary NaCl intake, suggested by higher post-treatment Cl excretion (delta >200 mEq), was deemed to have explained the rise in UCa in a subset of these. CONCLUSIONS: Treatment with baking soda providing 25 mEq alkali daily in patients who achieved increases in urinary citrate excretion and/or urine pH was not associated with higher UCa. Moreover, treatment with baking soda did not exacerbate hypercalciuria in patients with high pre-treatment urine calcium. A prospective trial to confirm these results is currently underway. Source of Funding: none © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e649-e649 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Kristina Penniston* More articles by this author Scott Quarrier More articles by this author Shuang Li More articles by this author R. Allan Jhagroo More articles by this author Expand All Advertisement PDF downloadLoading ...

Exploring the Potential Relationship Between Phytate Ingestion, Urinary Phytate Excretion, and Renal Stone Risk in a Unique Human Model: No Hard Evidence in Support of Phytate as a Stone Inhibitor

Dietary phytate (IP6) enjoys a reputation as an inhibitor of calcium renal stone formation, although there are very few human studies to support this notion. In South Africa, urolithiasis occurs in the white (W) but is rare in the black (B) population. We undertook this unique human model to further investigate the IP6 theory. Healthy W and B males completed baseline food-frequency recall questionnaires. Dietary intake of IP6 was restricted for 18 days. An IP6 dietary supplement was ingested on days 15-18. Twenty-four-hour urinary phytate and other urinary components were determined. Relative supersaturations of calcium salts were calculated. The urinary metastable limit (MSL) of calcium oxalate (CaOx) and its crystallisation kinetics were determined experimentally. Habitual dietary intake of IP6 and its urinary excretion were significantly higher in B than in W (1650 ± 202 vs. 640 ± 134 mg/d, P = .0002 and 1.13 ± 0.12 vs. 0.75 ± 0.13 μM, P <.05, respectively). In B, urinary phytate decreased significantly after 15 days of IP6 restriction, but in W, its excretion remained constant. After supplementation, urinary IP6 increased significantly in both groups reaching levels commensurate with the baseline value in B. No significant differences occurred in B in any of the routine urinary risk factors throughout the trial. However, in W, urinary citrate excretion increased on day 18 relative to day 0. There were no significant intragroup or intergroup changes in relative supersaturation, metastable limit, or crystallization kinetics. Despite notable differences in the renal handling of ingested IP6, there were no changes in any of the well-established urinary risk factors for calcium renal stone formation in either of our uniquely different test groups. We conclude that, in the absence of hard evidence, claims that IP6 is a stone inhibitor remain unproven.

Cortisol and 11 beta-hydroxysteroid dehydrogenase type 2 as potential determinants of renal citrate excretion in healthy children.

In patients with Cushing disease, renal citrate excretion is reduced. A low urinary citrate concentration is a risk factor for nephrolithiasis. Since higher acid loading is one major determinant of reduced citrate excretion, we aimed to examine whether glucocorticoids still within the physiological range may already impact on urinary citrate excretion independently of acid-base status. Overall, 132 healthy prepubertal participants of the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study who had collected two successive 24-h urine samples (at 1 and 2 years) before the start of their pubertal growth spurt were included in the study. Net acid excretion capacity (NAEC), urinary potential renal acid load (PRAL), creatinine, calcium, and various cortisol metabolites were measured in all samples. Glucocorticoid quantification was done by GC-MS and radioimmunoassay. In regression models multivariable-adjusted for 24-h urinary PRAL, NAEC, creatinine and calcium, urinary free cortisol (UFF), 6β-hydroxycortisol, and 20α-dihydrocortisol showed significant inverse relationships (P ≤ 0.02) with 24-h renal citrate output. By contrast, the estimate of renal 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), i.e., the ratio of urinary free cortisone/UFF, associated positively with urinary citrate (P = 0.04). In line with studies in hypercortisolic state, even moderately high cortisol levels in healthy children, still within the physiological range, may negatively impact on the kidney's citrate excretion. Besides, a higher 11β-HSD2 activity, favoring cortisol inactivation, is paralleled by an increased citrate excretion.

Crystal deposition triggers tubule dilation that accelerates cystogenesis in polycystic kidney disease.

The rate of disease progression in autosomal-dominant (AD) polycystic kidney disease (PKD) exhibits high intra-familial variability suggesting that environmental factors may play a role. We hypothesized that a prevalent form of renal insult may accelerate cystic progression and investigated tubular crystal deposition. We report that calcium oxalate (CaOx) crystal deposition led to rapid tubule dilation, activation of PKD-associated signaling pathways, and hypertrophy in tubule segments along the affected nephrons. Blocking mTOR signaling blunted this response and inhibited efficient excretion of lodged crystals. This mechanism of "flushing out" crystals by purposefully dilating renal tubules has not previously been recognized. Challenging PKD rat models with CaOx crystal deposition, or inducing calcium phosphate deposition by increasing dietary phosphorous intake, led to increased cystogenesis and disease progression. In a cohort of ADPKD patients, lower levels of urinary excretion of citrate, an endogenous inhibitor of calcium crystal formation, correlated with increased disease severity. These results suggest that PKD progression may be accelerated by commonly occurring renal crystal deposition which could be therapeutically controlled by relatively simple measures.

Impact of potassium citrate on urinary risk profile, glucose and lipid metabolism of kidney stone formers in Switzerland.

BackgroundHypocitraturia and hypercalciuria are the most prevalent risk factors in kidney stone formers (KSFs). Citrate supplementation has been introduced for metaphylaxis in KSFs. However, beyond its effects on urinary parameters and stone recurrence, only a few studies have investigated the impact of citrate on other metabolic pathways such as glucose or lipid metabolism.MethodsWe performed an observational study using data from the Swiss Kidney Stone Cohort. Patients were subdivided into two groups based on treatment with potassium citrate or not. The outcomes were changes of urinary risk parameters, haemoglobin A1c (HbA1c), fasting glucose, cholesterol and body mass index (BMI).ResultsHypocitraturia was present in 19.3% of 428 KSFs and potassium citrate was administered to 43 patients (10.0%) at a mean dosage of 3819 ± 1796 mg/day (corresponding to 12.5 ± 5.9 mmol/ day). Treatment with potassium citrate was associated with a significantly higher mean change in urinary citrate (P = 0.010) and urinary magnesium (P = 0.020) compared with no potassium citrate treatment. Exogenous citrate administration had no effect on cholesterol, fasting glucose, HbA1c and BMI. Multiple linear regression analysis demonstrated no significant association of 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3] levels with urinary citrate excretion.ConclusionPotassium citrate supplementation in KSFs in Switzerland resulted in a beneficial change of the urinary risk profile by particularly increasing anti-lithogenic factors. Fasting glucose, HbA1c, cholesterol levels and BMI were unaffected by potassium citrate therapy after 3 months, suggesting that potassium citrate is safe and not associated with unfavourable metabolic side effects. Lastly, 1,25(OH)2 D3 levels were not associated with urinary citrate excretion.

Contrasting effects of isocitrate dehydrogenase deletion on fluxes through enzymes of central metabolism in Escherichia coli.

Flux analysis is central to understanding cellular metabolism and successful manipulation of metabolic fluxes in microbial cell-factories. Isocitrate dehydrogenase (ICDH) deletion conferred contrasting effects on fluxes through substrate-level phosphorylation (SLP) reactions. While significantly increasing flux through pyruvate kinase, it diminishes flux through succinyl CoA synthetase and upregulates phosphotransacetylase (PTA) and acetate kinase (AK). In addition to acetate, the ICDH-less strain excretes pyruvate, citrate and isocitrate. While efflux to acetate excretion by the Escherichia coli parental strain and its ICDH-less derivative is a reflection of high throughput of glycolytic intermediates, excretion of pyruvate is a reflection of high throughput via pyruvate kinase. On the other hand, citrate and isocitrate excretion is a reflection of truncating the Krebs cycle at the level of ICDH. Furthermore, another striking finding is the inability of the ICDH-less cultures to utilize acetate as a source of carbon despite the availability of an adequate supply of extracellular glutamate (for biosynthesis) and elevated levels of AK and PTA (for acetate uptake). This striking observation is now explicable in the light of the newly proposed hypothesis that the expression of the ace operon enzymes is controlled in response to a minimum threshold signal (ATP), which could not be achieved in the ICDH-less strain.

Urine citrate excretion identifies changes in acid retention as eGFR declines in patients with chronic kidney disease.

Previous studies have shown that acid (H+) retention in patients with chronic kidney disease (CKD) but without metabolic acidosis increases as the estimated glomerular filtration rate (eGFR) decreases over time. The present study examined whether changes in urine excretion of the pH-sensitive metabolite citrate predicted changes in H+ retention over time in similar patients with CKD that were followed for 10 yr. We randomized 120 CKD2 nondiabetic, hypertension-associated nephropathy patients with plasma total CO2 of >24 mM to receive 0.5 meq·kg body wt-1·day-1 NaHCO3 ([Formula: see text]; n = 40), 0.5 meq·kg body wt-1·day-1 NaCl (NaCl; n = 40), or usual care (UC; n = 40). We assessed eGFR (CKD-EPI) and H+ retention by comparing the observed with expected plasma total CO2 increase 2 h after an oral NaHCO3 bolus (0.5 meq/kg body wt). Although 10 yr versus baseline eGFR was lower for each group, 10-yr eGFR was higher (P < 0.01) in [Formula: see text] (59.6 ± 4.8 ml·min-1·1.73 m-2) than NaCl and UC (52.1 ± 5.9 and 52.3 ± 4.1 ml·min-1·1.73 m-2, respectively) groups. Less eGFR preservation was associated with higher 10-yr versus baseline H+ retention in the NaCl group (26.5 ± 13.1 vs. 18.2 ± 15.3 mmol, P < 0.01) and UC group (24.8 ± 11.3 vs. 17.7 ± 10.9 mmol, P < 0.01) and with lower 10-yr versus baseline 8-h urine citrate excretion (UcitrateV) for the NaCl group (162 ± 47 vs. 196 ± 52 mg, respectively, P < 0.01) and UC group (153 ± 41 vs. 186 ± 42 mg, respectively, P < 0.01). Conversely, better eGFR preservation in the [Formula: see text] group was associated with no differences in 10-yr versus baseline H+ retention (14.2 ±13.5 vs. 16.1 ± 15.1 mmol, P = 1.00) or UcitrateV (212 ± 45 vs. 203 ± 49 mg, respectively, P = 0.74). An overall generalized linear model for repeated measures showed that UcitrateV predicted H+ retention (P < 0.01). Less eGFR preservation in patients with CKD2 without metabolic acidosis was associated with increased H+ retention that was predicted by decreased UcitrateV.

Dietary vinegar prevents kidney stone recurrence via epigenetic regulations.

BackgroundEpidemiological evidence of over 9000 people suggests that daily intake of vinegar whose principal bioactive component is acetic acid is associated with a reduced risk of nephrolithiasis. The underlying mechanism, however, remains largely unknown.MethodsWe examined the in vitro and in vivo anti-nephrolithiasis effects of vinegar and acetate. A randomized study was performed to confirm the effects of vinegar in humans.FindingsWe found individuals with daily consumption of vinegar compared to those without have a higher citrate and a lower calcium excretion in urine, two critical molecules for calcium oxalate (CaOx) kidney stone in humans. We observed that oral administration of vinegar or 5% acetate increased citrate and reduced calcium in urinary excretion, and finally suppressed renal CaOx crystal formation in a rat model. Mechanism dissection suggested that acetate enhanced acetylation of Histone H3 in renal tubular cells and promoted expression of microRNAs-130a-3p, −148b-3p and -374b-5p by increasing H3K9, H3K27 acetylation at their promoter regions. These miRNAs can suppress the expression of Nadc1 and Cldn14, thus enhancing urinary citrate excretion and reducing urinary calcium excretion. Significantly these mechanistic findings were confirmed in human kidney tissues, suggesting similar mechanistic relationships exist in humans. Results from a pilot clinical study indicated that daily intake of vinegar reduced stone recurrence, increased citrate and reduced calcium in urinary excretion in CaOx stone formers without adverse side effects.InterpretationVinegar prevents renal CaOx crystal formation through influencing urinary citrate and calcium excretion via epigenetic regulations. Vinegar consumption is a promising strategy to prevent CaOx nephrolithiasis occurrence and recurrence.FundNational Natural Science Foundations of China and National Natural Science Foundation of Guangdong Province.

Regulation of renal NaDC1 expression and citrate excretion by NBCe1-A.

Citrate is critical for acid-base homeostasis and to prevent calcium nephrolithiasis. Both metabolic acidosis and hypokalemia decrease citrate excretion and increase expression of Na+-dicarboxylate cotransporter 1 (NaDC1; SLC13A2), the primary protein involved in citrate reabsorption. However, the mechanisms transducing extracellular signals and mediating these responses are incompletely understood. The purpose of the present study was to determine the role of the Na+-coupled electrogenic bicarbonate cotransporter (NBCe1) A variant (NBCe1-A) in citrate metabolism under basal conditions and in response to acid loading and hypokalemia. NBCe1-A deletion increased citrate excretion and decreased NaDC1 expression in the proximal convoluted tubules (PCT) and proximal straight tubules (PST) in the medullary ray (PST-MR) but not in the PST in the outer medulla (PST-OM). Acid loading wild-type (WT) mice decreased citrate excretion. NaDC1 expression increased only in the PCT and PST-MR and not in the PST-MR. In NBCe1-A knockout (KO) mice, the acid loading change in citrate excretion was unaffected, changes in PCT NaDC1 expression were blocked, and there was an adaptive increase in PST-MR. Hypokalemia in WT mice decreased citrate excretion; NaDC1 expression increased only in the PCT and PST-MR. NBCe1-A KO blocked both the citrate and NaDC1 changes. We conclude that 1) adaptive changes in NaDC1 expression in response to metabolic acidosis and hypokalemia occur specifically in the PCT and PST-MR, i.e., in cortical proximal tubule segments; 2) NBCe1-A is necessary for normal basal, metabolic acidosis and hypokalemia-stimulated citrate metabolism and does so by regulating NaDC1 expression in cortical proximal tubule segments; and 3) adaptive increases in PST-OM NaDC1 expression occur in NBCe1-A KO mice in response to acid loading that do not occur in WT mice.

Hydroxycitrate: a potential new therapy for calcium urolithiasis.

Alkali supplements are used to treat calcium kidney stones owing to their ability to increase urine citrate excretion which lowers stone risk by inhibiting crystallization and complexing calcium. However, alkali increases urine pH, which may reduce effectiveness for patients with calcium phosphate stones and alkaline urine. Hydroxycitrate is a structural analog of citrate, widely available as an over-the-counter supplement for weight reduction. In vitro studies show hydroxycitrate has the capacity to complex calcium equivalent to that of citrate and that it is an effective inhibitor of calcium oxalate monohydrate crystallization. In fact, hydroxycitrate was shown to dissolve calcium oxalate crystals in supersaturated solution in vitro. Hydroxycitrate is not known to be metabolized by humans, so it would not be expected to alter urine pH, as opposed to citrate therapy. Preliminary studies have shown orally ingested hydroxycitrate is excreted in urine, making it an excellent candidate as a stone therapeutic. In this article, we detail the crystal inhibition activity of hydroxycitrate, review the current knowledge of hydroxycitrate use in humans, and identify gaps in knowledge that require appropriate research studies before hydroxycitrate can be recommended as a therapy for kidney stones.

Urine citrate excretion as a marker of acid retention in patients with chronic kidney disease without overt metabolic acidosis

Acid (H+) retention appears to contribute to progressive decline in glomerular filtration rate (GFR) in patients with chronic kidney disease (CKD), including some patients without metabolic acidosis. Identification of patients with H+ retention but without metabolic acidosis could facilitate targeted alkali therapy; however, current methods to assess H+ retention are invasive and have little clinical utility. We tested the hypothesis that urine excretion of the pH-sensitive metabolite citrate can identify H+ retention in patients with reduced GFR but without overt metabolic acidosis. H+ retention was assessed based on the difference between observed and expected plasma total CO2 after an oral sodium bicarbonate load. The association between H+ retention and urine citrate excretion was evaluated in albuminuric CKD patients with eGFR 60-89 ml/min/1.73m2 (CKD 2, n=40) or >90 ml/min/1.73m2 (CKD 1, n= 26) before and after 30 days of base-producing fruits and vegetables. Baseline H+ retention was higher in CKD 2, while baseline urine citrate excretion was lower in CKD 2 compared to CKD 1. Base-producing fruits and vegetables decreased H+ retention in CKD 2 and increased urine citrate excretion in both groups. Thus, H+ retention is associated with lower urine citrate excretion, and reduction of H+ retention with a base-producing diet is associated with increased urine citrate excretion. These results support further exploration of the utility of urine citrate excretion to identify H+ retention in CKD patients with reduced eGFR but without metabolic acidosis, to determine their candidacy for kidney protection with dietary H+ reduction or alkali therapy.