Renal tubular acidosis: the clinical entity

Results of a Gene Panel Approach in a Cohort of Patients with Incomplete Distal Renal Tubular Acidosis and Nephrolithiasis

BACKGROUND

Distal renal tubular acidosis (dRTA) is characterized by an impairment of urinary acidification resulting in metabolic acidosis, hypokalemia, and inappropriately elevated urine pH. If not treated, this chronic condition eventually leads to nephrocalcinosis, nephrolithiasis, impaired renal function, and bone demineralization. dRTA is a well-defined entity that can be diagnosed by genetic testing of 5 genes known to be disease-causative. Incomplete dRTA (idRTA) is defined as impaired urinary acidification that does not lead to overt metabolic acidosis and therefore can be diagnosed if patients fail to adequately acidify urine after an ammonium chloride (NH4Cl) challenge or furosemide and fludrocortisone test. It is still uncertain whether idRTA represents a distinct entity or is part of the dRTA spectrum and whether it is caused by mutations in the same genes of overt dRTA.

METHODS

In this cross-sectional study, we investigated a group of 22 stone formers whose clinical features were suspicious of idRTA. They underwent an NH4Cl challenge and were found to have impaired urinary acidification ability. These patients were then analyzed by genetic testing with sequencing of 5 genes: SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, and WDR72.

RESULTS

Two unrelated individuals were found to have two different variants in SLC4A1 that had never been described before.

CONCLUSIONS

Our results suggest the involvement of other genes or nongenetic tubular dysfunction in the pathogenesis of idRTA in stone formers. However, genetic testing may represent a cost-effective tool to recognize, treat, and prevent complications in these patients.

Cystic fibrosis in the kidney: new lessons from impaired renal HCO3- excretion

PURPOSE OF REVIEW

A key role of cystic fibrosis transmembrane conductance regulator (CFTR) in the kidney has recently been uncovered. This needs to be integrated into the understanding of the developed phenotypes in cystic fibrosis (CF) patients.

RECENT FINDINGS

In the beta-intercalated cells of the collecting duct , CFTR functions in very similar terms as established in the exocrine pancreatic duct and both CFTR and SLC26A4 (pendrin) orchestrate regulated HCO3- secretion. Like in the pancreas, the hormone secretin is a key agonist to activate renal HCO3- secretion. In mice lacking CFTR or pendrin, acute and chronic base challenges trigger marked metabolic alkalosis because collecting duct base secretion is defective. Also in CF patients, the ability to acutely increase renal HCO3- excretion is markedly reduced.

SUMMARY

The now much enlarged understanding of CFTR in the kidney may permit the measurement of challenged urine HCO3- excretion as a new biomarker for CF. We suggest a new explanation for the electrolyte disorder in CF termed Pseudo-Bartter Syndrome. The hallmark electrolyte disturbance features of this can be well explained by a reduced function of collecting duct Cl-/HCO3- exchange. Eventually, we suggest the diagnostic term distal renal tubular alkalosis to cover those disturbances that causes metabolic alkalosis by a reduced collecting duct base secretion.

Distal Renal Tubular Acidosis: ERKNet/ESPN Clinical Practice Points

Distal renal tubular acidosis (dRTA) is characterised by an impaired ability of the distal tubule to excrete acid, leading to metabolic acidosis. Associated complications include bone disease, growth failure, urolithiasis and hypokalaemia. Due to its rarity, there is a limited evidence to guide diagnosis and management, however, available data strongly suggest that metabolic control of the acidosis by alkali supplementation can halt or revert almost all complications. Despite this, cohort studies show that adequate metabolic control is present in only about half of patients, highlighting problems with treatment provision or adherence. With these clinical practice points the authors, part of the working groups tubulopathies in the European Rare Kidney Disease Reference network (ERKnet) and inherited kidney diseases of the European Society for Paediatric Nephrology (ESPN) aim to provide guidance for the management of patients with dRTA to facilitate adequate treatment and establish an initial best practice standard against which treatment of patients can be audited.

Distal renal tubular acidosis: a systematic approach from diagnosis to treatment

Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO₃ is impaired, leading to chronic metabolic acidosis with normal anion gap. In the current review, the focus is placed on the most common type of RTA, Type 1 RTA or Distal RTA (dRTA), which is a rare chronic genetic disorder characterized by an inability of the distal nephron to secrete hydrogen ions in the presence of metabolic acidosis. Over the years, knowledge of the molecular mechanisms behind acid secretion has improved, thereby greatly helping the diagnosis of dRTA. The primary or inherited form of dRTA is mostly diagnosed in infancy, childhood, or young adulthood, while the acquired secondary form, as a consequence of other disorders or medications, can happen at any age, although it is more commonly seen in adults. dRTA is not as “benign” as previously assumed, and can have several, highly variable long-term consequences. The present review indeed reports and summarizes both clinical symptoms and diagnosis, long-term outcomes, genetic inheritance, epidemiology and current treatment options, with the aim of shedding more light onto this rare disorder. Being a chronic condition, dRTA also deserves attention in the transition between pediatric and adult nephrology care, and as a rare disease it has a place in the European and Italian rare nephrological diseases network.

Modulation of Tubular pH by Acetazolamide in a Ca2+ Transport Deficient Mice Facilitates Calcium Nephrolithiasis

Proximal tubular (PT) acidosis, which alkalinizes the urinary filtrate, together with Ca²⁺ supersaturation in PT can induce luminal calcium phosphate (CaP) crystal formation. While such CaP crystals are known to act as a nidus for CaP/calcium oxalate (CaOx) mixed stone formation, the regulation of PT luminal Ca²⁺ concentration ([Ca²⁺]) under elevated pH and/or high [Ca²⁺] conditions are unknown. Since we found that transient receptor potential canonical 3 (TRPC3) knockout (KO; -/-) mice could produce mild hypercalciuria with CaP urine crystals, we alkalinized the tubular pH in TRPC3-/- mice by oral acetazolamide (0.08%) to develop mixed urinary crystals akin to clinical signs of calcium nephrolithiasis (CaNL). Our ratiometric (λ340/380) intracellular [Ca²⁺] measurements reveal that such alkalization not only upsurges Ca²⁺ influx into PT cells, but the mode of Ca²⁺ entry switches from receptor-operated to store-operated pathway. Electrophysiological experiments show enhanced bicarbonate related current activity in treated PT cells which may determine the stone-forming phenotypes (CaP or CaP/CaOx). Moreover, such alkalization promotes reactive oxygen species generation, and upregulation of calcification, inflammation, fibrosis, and apoptosis in PT cells, which were exacerbated in absence of TRPC3. Altogether, the pH-induced alteration of the Ca²⁺ signaling signature in PT cells from TRPC3 ablated mice exacerbated the pathophysiology of mixed urinary stone formation, which may aid in uncovering the downstream mechanism of CaNL.

Phenotype and Genotype Profile of Children with Primary Distal Renal Tubular Acidosis: A 10-Year Experience from a North Indian Teaching Institute

Primary distal renal tubular acidosis (dRTA) or Type 1 RTA in children is caused by a genetic defect (involved genes ATP6V0A4, ATP6V1B1, SLC4A1, FOXI1, or WDR72), which causes tubular transport defects characterized by an inability to appropriately acidify urine with resultant persistent hyperchloremic metabolic acidosis. Retrospective analysis of 28 children (14 males) under the age of 14 years with dRTA seen from 2010 to 2019 was reviewed, and detailed clinic records were analyzed. The clinical features, investigations, and response to treatment were recorded. The median age of the children at presentation was 30 months (range: 9.25–72 months), and the median age at onset of symptoms was 2 months. All the children had growth failure, polyuria, and polydipsia at presentation. Mean serum potassium, pH, bicarbonate, and anion gap at presentation was 2.3 ± 0.5 mmol/L, 7.22 ± 0.09, 13.28 ± 4.37 mmol/L, and 9.3 ± 2.18, respectively. Mean serum potassium, pH, bicarbonate at follow-up was 3.88 ± 0.6 mmol/L, 7.35 ± 0.06, and 20.13 ± 4.17 mmol/L, respectively. The median z-score for the weight for age and height for age at initial presentation was −4.77 (–7.68 to –3.74) and –4.21 (–5.42 to –2.37) and at follow-up was –3.35 (–5.29 to –1.55) and –3.84 (–5.36 to –1.63), respectively. Twenty-two (78.6%) children had medullary nephrocalcinosis. Four children had sensorineural hearing loss. Seven children had genetic testing done, and six had pathogenic or likely pathogenic variants in ATP6V1B1 and ATP6V0A4 gene. Children with dRTA have a guarded prognosis and ATP6V1B1 and ATP6V0A4 mutations are the most common implicated genetic defect in Indian children with distal RTA.

Renal Tubular Acidosis and Management Strategies: A Narrative Review

Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid−base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.

Clinicopathological characteristics and long-term prognosis of monoclonal immunoglobulin light chain associated Fanconi syndrome

Background and aims:

Monoclonal immunoglobulin light chain associated Fanconi syndrome (LC-FS) is a rare disease that involves proximal tubules. As most of the reported cases came from western countries, we aimed to analyze the clinicopathological characteristics of Asian LC-FS and its treatment responses to chemotherapy.

Methods:

A total of 26 LC-FS patients in a single-center were retrospectively studied.

Results:

At diagnosis, the mean age of the 26 Asian LC-FS patients was 54.7 ± 14.7 years, with females accounting for 57.7%. They presented with different degrees of proximal tubular dysfunctions with normoglycemic glycosuria (88.0%), hyperphosphaturia (84.2%) and aminoaciduria (84.0%) as the most common features. The mean estimated glomerular filtration rate (eGFR) was (68.0 ± 26.4) ml/min per 1.73 m². After chemotherapy, renal response was achieved in 58.3% cases, which was accompanied by hematological response, and tubular response was acquired in 66.7% cases. During 3 years of follow-up, the eGFR levels significantly decreased in the monoclonal gammopathy of renal significance patients, few of whom (21.4%) had received chemotherapy.

Conclusion:

Asian LC-FS patients had mild renal function disorder. The chemotherapy could improve both renal and tubular functions, which may be related to the hematological response.

Severe Hypokalemia Secondary to Transient Distal Renal Tubular Acidosis in a Previously Healthy Woman

Normal anion gap (non-gap) hyperchloremic acidosis with hypokalemia is a medical emergency. There are several causes of this metabolic phenomenon, of which distal renal tubular acidosis is among the very rare causes. In this report, we present an unusual case of a previously healthy woman who was admitted to the intensive care unit with a short history of severe muscle weakness. She had no significant past medical history and was not taking any regular medication. There was also no history of recent drug or herb ingestion. Investigations demonstrated a combination of severe hypokalemia, hyperchloremia, hypobicarbonatemia (non-gap metabolic acidosis), and relatively raised urinary potassium and urinary pH in the presence of severe hypokalemia and metabolic acidosis. Results suggested a diagnosis of distal renal tubular acidosis. The patient responded rapidly to a short course of electrolyte replacement therapy and the condition resolved spontaneously thereafter. This case highlights the fact that distal renal tubular acidosis can occur as a transient phenomenon in previously healthy individuals.

Evaluating distal renal tubular acidification function in primary hyperparathyroidism and its effects on bone mineral density

Background

Primary hyperparathyroidism (PHPT) is a common endocrinopathy that may increase fracture risk and decrease bone mineral density (BMD). Some patients develop distal renal tubular acidification dysfunction under conditions of hyperchloraemia or hyperchloraemic acidosis. To examine whether this dysfunction influences the clinical outcome, we explored the distal renal tubular acidification function in patients with PHPT and its effects on the clinical manifestations of the disease.

Methods

We retrospectively analysed 75 PHPT patients with regard to renal tubular acidification and blood gas analysis. The patients were divided into two groups, the renal tubular acidification dysfunction group and normal function group.

Results

Serum phosphate level and total hip bone density were significantly decreased and 25OHD level was significantly increased in the renal tubular acidification dysfunction group in comparison to the normal function group. Female patients in the renal tubular acidification dysfunction group showed significantly decreased femoral neck and total hip BMD and increased susceptibility to fracture. However, there were no such differences in male patients between the two groups.

Conclusions

About 54.6 % of PHPT patients in our study population had abnormal distal renal tubular acidification. PHPT patients with abnormal distal renal tubular acidification may have lower hip bone density. Female PHPT patients with abnormal distal renal tubular acidification showed increased susceptibility to fractures and the development of osteoporosis.

Primary Sjögren's syndrome manifesting as sclerotic metabolic bone disease

Primary Sjögren's syndrome (pSS) is a chronic slowly progressive autoimmune disease characterised by lymphocytic infiltration of salivary and lacrimal glands with varying degree of systemic involvement. Renal involvement, a recognised extraglandular manifestation of pSS, is commonly related to tubular dysfunction and generally manifests as distal renal tubular acidosis (RTA), proximal RTA, tubular proteinuria and nephrogenic diabetes insipidus. Untreated long-standing RTA is known to cause metabolic bone disease. Here, we present the report of a patient with sclerotic metabolic bone disease related to pSS with combined distal and proximal RTA and negative workup for other causes of sclerotic bone disease. A significant clinical and biochemical improvement, including recovery of proximal tubular dysfunction, was noted with alkali therapy. This case suggests the need to consider pSS in the diagnostic algorithm of a patient presenting with sclerotic bone disease.

Efficacy and safety of an innovative prolonged-release combination drug in patients with distal renal tubular acidosis: an open-label comparative trial versus standard of care treatments

BACKGROUND

Distal renal tubular acidosis (dRTA), due to impaired acid secretion in the urine, can lead to severe long-term consequences. Standard of care (SoC) oral alkalizers, requiring several daily intakes, are currently used to restore normal plasma bicarbonate levels. A new prolonged-release formulation, ADV7103, has been developed to achieve a sustained effect with an improved dosing scheme.

METHODS

In a multicenter, open-label, non-inferiority trial (n = 37), patients with dRTA were switched from SoC to ADV7103. Mean plasma bicarbonate values and proportion of responders during steady state therapy with both treatments were compared, as were other blood and urine parameters, as well as acceptability, tolerability, and safety.

RESULTS

When switching from SoC to ADV7103, the number of daily intakes was reduced from a median of three to twice daily. Mean plasma bicarbonate was increased and non-inferiority of ADV7103 was demonstrated (p < 0.0001, per protocol), as was statistical superiority (p = 0.0008, intention to treat [ITT]), and the response rate increased from 43 to 90% with ADV7103 (p < 0.001, ITT). Urine calcium/citrate ratio was reduced below the threshold for risk of lithogenesis with ADV7103 in 56% of previously non-responders with SoC (p = 0.021, ITT). Palatability was improved (difference [95% CI] of 25 [10.7, 39.2] mm) and gastrointestinal discomfort was reduced (difference [95% CI] of - 14.2 [- 25.9, - 2.6] mm) with ADV7103.

CONCLUSIONS

Plasma bicarbonate levels and response rate were significantly higher with ADV7103 than with SoC. Urine calcium/citrate ratio, palatability, and gastrointestinal safety were significantly improved, supporting the use of ADV7103 as first-line treatment for dRTA.

TRIAL REGISTRATION

Registered as EudraCT 2013-002988-25 on the 1st July 2013 Graphical abstract.

Renal Tubular Acidosis Manifesting as Severe Metabolic Bone Disease

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Use of a carbonic anhydrase Ca17a knockout to investigate mechanisms of ion uptake in zebrafish (Danio rerio)

In fishes, branchial cytosolic carbonic anhydrase (CA) plays an important role in ion and acid-base regulation. The Ca17a isoform in zebrafish (Danio rerio) is expressed abundantly in Na⁺-absorbing/H⁺-secreting H⁺-ATPase-rich (HR) cells. The present study aimed to identify the role of Ca17a in ion and acid-base regulation across life stages using CRISPR/Cas9 gene editing. However, in preliminary experiments, we established that ca17a knockout is lethal with ca17a^-/- mutants exhibiting a significant decrease in survival beginning at ∼12 days postfertilization (dpf) and with no individuals surviving past 19 dpf. Based on these findings, we hypothesized that ca17a^-/- mutants would display alterations in ion and acid-base balance and that these physiological disturbances might underlie their early demise. Na⁺ uptake rates were significantly increased by up to 300% in homozygous mutants compared with wild-type individuals at 4 and 9 dpf; however, whole body Na⁺ content remained constant. While Cl^- uptake was significantly reduced in ca17a^-/- mutants, Cl^- content was unaffected. Reduction of CA activity by Ca17a morpholino knockdown or ethoxzolamide treatments similarly reduced Cl^- uptake, implicating Ca17a in the mechanism of Cl^- uptake by larval zebrafish. H⁺ secretion, O₂ consumption, CO₂ excretion, and ammonia excretion were generally unaltered in ca17a^-/- mutants. In conclusion, while the loss of Ca17a caused marked changes in ion uptake rates, providing strong evidence for a Ca17a-dependent Cl^- uptake mechanism, the underlying causes of the lethality of this mutation in zebrafish remain unclear.

Medical evaluation and pharmacotherapeutical strategies in management of urolithiasis

Treatment of urolithiasis depends on several important factors which include stone location, size, composition, and patient symptoms. Although significant advancements have been made in the surgical management of urolithiasis in the last decade, pharmacotherapy which can prevent the formation of new stones and decrease the recurrence of urolithiasis has not experienced the same level of success. Currently, urolithiasis is regarded as a complicated syndrome that is determined by numerous factors, and any treatment plan for urolithiasis should be individualized while considering any potential damage arising from stone-forming factors. This review introduces the most popular methods currently used to evaluate urolithiasis and the pharmacotherapy of urolithiasis based on patient-specific factors.

Safety, efficacy, and acceptability of ADV7103 during 24 months of treatment: an open-label study in pediatric and adult patients with distal renal tubular acidosis

BACKGROUND

A new prolonged-release formulation of potassium citrate and potassium bicarbonate, ADV7103, has been shown to improve metabolic control, palatability, and gastrointestinal safety in patients with distal renal tubular acidosis (dRTA) when compared to standard of care (SoC) treatments. The present work evaluates safety and efficacy of ADV7103 during 24 months.

METHODS

Thirty pediatric and adult patients were included in an open-label extension study after a phase II/III trial. Safety and tolerability were assessed. Plasma bicarbonate and potassium levels, as well as urine parameters, were evaluated over time. Acceptability, adherence, and quality of life were also assessed. The evolution of clinical consequences of dRTA in the cohort was explored.

RESULTS

There were 104 adverse events (AEs) reported, but only 9 gastrointestinal events observed in five patients (17%) were considered to be related to ADV7103 treatment. There were no AEs leading to treatment discontinuation. Plasma bicarbonate and potassium levels were in the normal ranges at the different visits, respectively, in 69-86% and 83-93% of patients. Overall adherence rates were ≥ 75% throughout the whole study in 79% patients. An average improvement of quality of life of 89% was reported at 24 months of study.

CONCLUSIONS

Common AEs concerned metabolism and gastrointestinal disorders; the former being related to the disease. Less than half of the gastrointestinal AEs were related to ADV7103 treatment and they were mostly mild in severity. Metabolic parameters were maintained in the normal ranges in most patients. Patient satisfaction was high and adherence to treatment was good and remained stable.

TRIAL REGISTRATION NUMBER

Registered as EudraCT 2013-003828-36 on the 3rd of September 2013.

Liddle Syndrome due to a Novel c.1713 Deletion in the Epithelial Sodium Channel β-Subunit in a Normotensive Adolescent

Objective

Liddle syndrome (LS) is a rare autosomal dominant condition secondary to a gain-of-function mutation affecting the epithelial sodium channels (ENaCs) in the distal nephron. It presents with early-onset hypertension, hypokalemia, and metabolic alkalosis in the face of hyporeninemia and hypoaldosteronism. We report a novel mutation affecting the ENaCs in a normotensive adolescent with LS.

Methods

We describe a pediatric case of LS with a novel mutation and review the condition’s presentation and management. To date, 31 different mutations in the β- or γ-subunit of ENaCs have been reported as associated with LS.

Results

We describe a 16-year-old girl presenting with muscle cramps with a strong family history of hypertension and hypokalemia. Initial investigations revealed hypokalemia together with hypoaldosteronism and hyporeninemia. Subsequent genetic testing revealed a novel mutation in SCNN1B (deletion: c.1713delC), leading to the premature termination of the sodium channel epithelial 1 subunit-β protein and the LS phenotype. Treatment with triamterene (50 mg, twice daily) and potassium chloride (20 mEq, once daily) normalized the serum potassium and led to resolution of her muscle cramps.

Conclusion

It is essential to consider investigating the presence of rare genetic syndromes, like LS, when a patient presents with hypokalemia. Further studies are needed to understand the variable presentation of this condition.

Evaluation of phenotypic and genotypic features of children with distal kidney tubular acidosis

BACKGROUND

The present study aimed to assess genotype-phenotype correlations with long-term prognosis in children with distal kidney tubular acidosis (dKTA). The kidney function of children with dKTA could be impaired in the long-term.

METHODS

Thirty-one children with dKTA from 23 families were included in the present study. Demographic features, growth parameters, clinical manifestations, follow-up results, and genetic analysis results of the patients were recorded.

RESULTS

Eighteen children (58.1%) were male. The median age at diagnosis was 3 months. The median follow-up period was 77 months and the longest was 23.5 years. Eight (28.8%) patients had chronic kidney disease (CKD) stage 2 or 3. Three patients aged 24, 23, and 19 years had CKD stage 3 with an estimated glomerular filtration rate of 54, 57, and 48 mL/min/1.73 m², respectively. Thirteen patients had mutations in the ATP6V0A4 gene, eight had mutations in the ATP6V1B1 gene, and three had mutations in the SLC4A1 gene. There was no significant correlation between molecular diagnosis and CKD. Growth retardation with a height below a standard deviation (SD) score of - 2 was found in 14 patients (45.1%) at the time of diagnosis. The mean height SD score at the last visit was significantly higher in patients who had adequate metabolic control at > 75% of all visits as compared with that in patients who did not.

CONCLUSION

Patients with dKTA usually have a good clinical prognosis in childhood with appropriate treatment; however, dRTA is characterized by deterioration of kidney function in adulthood, particularly after puberty.

Incomplete distal renal tubular acidosis in children

AIM

To describe incomplete distal renal tubular acidosis (iDRTA) in paediatric patients, a term used for the diagnosis of patients who do not develop spontaneous overt metabolic acidosis but are unable to acidify the urine in response to an ammonium chloride load.

METHODS

Tests used to explore urinary acidification were revised. In addition, publications in English extracted from 161 entries yielded by a PubMed database search, using 'incomplete distal renal tubular acidosis' as keyword, were reviewed.

RESULTS

Incomplete distal renal tubular acidosis has mostly been identified in adults with autoimmune diseases, nephrolithiasis, nephrocalcinosis and/or osteopenia. iDRTA has been reported in few paediatric patients with rickets, congenital abnormalities of kidney and urological tract and/or growth failure. The pathophysiological mechanisms potentially responsible for the defect of urinary acidification are discussed as well as the clinical and biochemical findings of iDRTA described in children.

CONCLUSION

The presentation of iDRTA in children differs from adults. The clinical and biochemical features of iDRTA are not well characterised in paediatric patients. The detection of iDRTA in groups of population such as heterozygous carriers of primary DRTA gene mutations and children with hypocitraturia or hypercalciuria might be of clinical interest to better know the pathophysiology and natural history of iDRTA.

The Effect of Acetylcysteine on Renal Function in Experimental Models of Cyclophosphamide-and Ifosfamide-Induced Cystitis

Introduction

Urotoxicity is a characteristic attribute of cy-clophosphamide and ifosfamide. Acetylcysteine is perceived as a uroprotective and possible nephroprotective compound. The purpose of the study was to assess the effect of acetylcysteine treatment on the morphology of the kidneys and the urinary bladder, and renal function in rats with cystitis induced by cyclophosphamide or ifosfamide.

Methods

Cystitis was induced in rats belonging to groups 2 and 3, as well as 4 and 5, by five administrations of cyclophosphamide (75 mg/kg) or ifosfamide (80 mg/kg) respectively. Additionally, groups 3 and 5 received acetylcysteine (200 mg/kg). Group 1 was "sham treated" as a control. Upon conclusion of the experiment, the animals were euthanized and their kidneys and urinary bladders were collected for histopathological analysis. The assessment of renal function was based on classic nitrogen blood parameters (urea, creatinine, and uric acid), as well as proteinuria and cystatin C (CysC) and kidney injury molecule-1 (KIM-1) urinary concentrations, and their 24-hour elimination with urine.

Results

Reduction of blood urea nitrogen and uric acid, and urinary pH with a significant increase of CysC and KIM-1 urinary concentrations, and their 24-hour elimination with urine were observed in groups 2 and 4. The acetylcysteine treatment did not cause a significant change of blood parameters, but significantly decreased 24-hour elimination of CysC and KIM-1 with urine, and accounted for alleviation of the histopathological abnormalities of urinary bladders, with no significant effects on the structure of the kidneys.

Conclusions

Acetylcysteine used in the experimental model of cyclophosphamide- and ifosfamide-induced cystitis had a uroprotective effect and also reduced renal dysfunction, which suggests its potential use as a nephroprotective compound in cyclophosphamide/ifosfamide therapy.

Severe metabolic acidosis due to acetazolamide intoxication in a dog

CASE REPORT

This case report describes the clinical signs and case management of a 1-year-old neutered male Siberian Husky that accidentally ingested 635 mg/kg of oral acetazolamide (a carbonic anhydrase inhibitor). The dog presented with severe tachypnoea due to the development of hyperchloraemic metabolic acidosis and associated hypokalaemia that persisted for 7 days. Clinical and biochemical changes resolved with intravenous and subsequent oral supplementation of sodium bicarbonate and potassium. Complete recovery occurred within 9 days of presentation.

CONCLUSION

To the authors' knowledge, this is the first case that reports overdosage of an oral carbonic anhydrase inhibitor in a dog and subsequent recovery with adequate supplementation and supportive care.

Mineralocorticoid Dysfunction during Critical Illness: A Review of the Evidence

The recent demonstration of the significant reduction in mortality in patients with septic shock treated with adjunctive glucocorticoids combined with fludrocortisone and the effectiveness of angiotensin II in treating vasodilatory shock have renewed interest in the role of the mineralocorticoid axis in critical illness. Glucocorticoids have variable interactions at the mineralocorticoid receptor. Similarly, mineralocorticoid receptor-aldosterone interactions differ from mineralocorticoid receptor-glucocorticoid interactions and predicate receptor-ligand interactions that differ with respect to cellular effects. Hyperreninemic hypoaldosteronism or selective hypoaldosteronism, an impaired adrenal response to increasing renin levels, occurs in a subgroup of hemodynamically unstable critically ill patients. The suggestion is that there is a defect at the level of the adrenal zona glomerulosa associated with a high mortality rate that may represent an adaptive response aimed at increasing cortisol levels. Furthermore, cross-talk exists between angiotensin II and aldosterone, which needs to be considered when employing therapeutic strategies.

Renal Tubular Acidosis

Renal tubular acidosis (RTA) comprises a group of disorders characterized by low capacity for net acid excretion and persistent hyperchloremic metabolic acidosis, despite preserved glomerular filtration rate. RTA are classified into chiefly three types (1, 2 and 4) based on pathophysiology and clinical and laboratory characteristics. Most patients have primary RTA that presents in infancy with polyuria, growth retardation, rickets and/or hypotonia. Diagnosis requires careful evaluation, including exclusion of other entities that can cause acidosis. A variety of tests, administered stepwise, are useful for the diagnosis and characterization of RTA. A genetic or acquired basis can be determined in majority of patients through focused evaluation. Management involves correction of acidosis and dyselectrolytemia; patients with proximal RTA with Fanconi syndrome and rickets require additional supplements of phosphate and vitamin D.

Renal Tubular Acidosis and Immune Checkpoint Inhibitor Therapy: An Immune-Related Adverse Event of PD-1 Inhibitor-A Report of 3 Cases

The main cause of acute kidney injury in patients receiving immune checkpoint inhibitors (ICIs) is acute interstitial nephritis. However, as their use continues to increase, other kidney manifestations are being described. We report 3 cases of patients treated with ICIs who developed predominantly electrolyte disorders secondary to renal tubular acidosis as an immune-related adverse event and discuss the potential mechanism. Nongap acidosis in combination with hypokalemia should raise suspicion for distal renal tubular acidosis in patients treated with ICIs.

A case series of distal renal tubular acidosis, Southeast Asian ovalocytosis and metabolic bone disease

BACKGROUND

Familial distal renal tubular acidosis (dRTA) associated with mutations of solute carrier family 4 membrane - 1 (SLC4A1) gene could co-exist with red cell membrane abnormality, Southeast Asian ovalocytosis (SAO). Although this association is well described in Southeast Asian countries, it is less frequently found in Sri Lanka.

CASE PRESENTATION

We describe six patients who had dRTA co-existing with SAO. All of them initially presented with severe hypokalemia and paralysis. They presented within a period of six months to the Teaching Hospital Anuradhapura, Sri Lanka. All had metabolic acidosis indicated by low serum bicarbonate. Three of them were having underlying chronic kidney disease as well. Those three patients had mixed high and normal anion gap metabolic acidosis indicated by low delta ratio. In all dRTA was confirmed by presence of normal anion gap, hyperchloraemia, high urine pH and positive urine anion gap. Examination of blood films of all of them revealed presence of stomatocytes and macro-ovalocytosis compatible with SAO. In relation to complications of dRTA, two patients had medullary nephrocalcinosis. Three patients had biochemical evidence of osteomalacia, with two of them having radiological evidence of diffuse osteosclerosis. One patient had secondary hyperparathyroidism and a pathological fracture.

CONCLUSIONS

Erythrocyte in SAO is exceptionally rigid and this abnormality is said to be evolved as it protects against Plasmodium vivax malaria and cerebral malaria cause by Plasmodium falciparum. Although two families of SAO was described earlier, SAO and dRTA combination was reported only once in a patient from Anuradhapura district. Distal renal tubular acidosis, SAO combination and its related complications including nephrocalcinosis, chronic kidney disease and metabolic bone disease was not described in Sri-Lankan literature. This case series emphasize the importance of investigating recurrent/ chronic hypokalemia to diagnose dRTA and its associations, as early correction of acidosis could prevent development of chronic kidney disease and metabolic bone disease.

A Novel Cyclic Mobile Transporter Can Induce Apoptosis by Facilitating Chloride Anion Transport into Cells

We report here the preparation of an aminoxy amide-based pseudopeptide-derived building block using furanoid sugar molecules. Through the cyclo-oligomerization reaction, we generate a hybrid triazole/aminoxy amide macrocycle using the as-prepared building block. The novel conformation of the macrocycle has been characterized using NMR and molecular modeling studies, which show a strong resemblance of our synthesized compound to d-,l-α-aminoxy acid-based cyclic peptides that contain uniform backbone chirality. We observe that the macrocycle can efficiently and selectively bind Cl^- ion and transport Cl^- ion across a lipid bilayer. ¹H NMR anion binding studies suggest a coherent relationship between the acidity of aminoxy amide N-H and triazole C-H proton binding strength. Using time-based fluorescence assay, we show that the macrocycle acts as a mobile transporter and follows an antiport mechanism. Our synthesized macrocycle imposes cancer cell death by disrupting ionic homeostasis through Cl^- ion transport. The macrocycle induced cytochrome c leakage and changes in mitochondrial membrane potential along with activation of family of caspases, suggesting that the cellular apoptosis occurs through a caspase-dependent intrinsic pathway. The present results suggest the possibility of using the macrocycle as a biological tool of high therapeutic value.

Renal disorders in rheumatologic diseases: the spectrum is changing (Part 1: connective tissue diseases)

The kidney is frequently involved by autoimmune rheumatic diseases. The renal manifestations may be variable, ranging from asymptomatic proteinuria and microscopic haematuria to nephrotic syndrome and rapidly progressive glomerulonephritis or vasculitis. In a number of cases the kidney involvement is related to the treatment of the original disease and may represent a major cause of morbidity and mortality. Thus, it is important for nephrologists and rheumatologists to remember that dysfunction of the kidney may be part of the primary systemic disorder or consequence of its pharmacotherapy. In the first part of this review we will analyse the kidney involvement in four autoimmune connective tissue diseases: systemic lupus erythematosus, Sjögren syndrome, polymyositis/dermatomyositis, and systemic sclerosis. Renal disease is common in lupus and is a main cause of morbidity and mortality. About 10% of patients with Sjögren syndrome may present interstitial nephritis or, more rarely, glomerulonephritis. Myoglobinuria and acute kidney injury is a frequent complication of polymyositis. Renal disease is one of the most serious complications of systemic sclerosis and may present with a dramatic renal crisis, characterized by malignant hypertension, oligo-anuria, and microangiopathic thrombocytopenic anaemia.

Primary Sjӧgren's syndrome with renal Fanconi syndrome: Good responses to treatment with glucocorticoids

BACKGROUND

Renal Fanconi syndrome (FS) is rare in primary Sjӧgren's syndrome (pSS). We aimed to describe the clinicopathological characteristics of pSS associated FS (pSS-FS) and its responses to treatment.

METHODS

We reported 25 cases of pSS-FS patients and retrospectively reviewed their clinical records, kidney pathology and follow-up data.

RESULTS

The 25 pSS-FS patients were mainly female (92.0%) and the mean age at diagnosis was 43.6±11.3 years. They showed different degrees of proximal tubular dysfunctions and eGFR decline (60.9±32.3 ml/min/1.73m²). Kidney pathology of pSS-FS patients showed tubulo-interstitial nephritis with defective brush border and lymphoplasmacytic infiltrates. After glucocorticoid treatment, the eGFR levels were significantly improved from 48.3±20.6 ml/min/1.73m² to 55.0±19.9 ml/min/1.73m² (P = 0.012) at the third month of follow-up. They also acquired good tubular (88.2%) and immunological (90.0%) responses. pSS-FS patients with young-onset pSS presented with a higher prevalence of positive anti-SSB antibody and hypocomplementemia, more severe hypokalemia, and better eGFR levels.

CONCLUSIONS

In pSS-FS patients, use of glucocorticoids could improve eGFR and tubular functions. The young-onset pSS group presented with a particular pattern in immunological features and kidney involvement.

Relapsing Tubulointerstitial Nephritis with Antimitochondrial M2 Antibody Accompanied by Pulmonary Involvement

We herein report a 50-year-old woman who suffered from tubulointerstitial nephritis with antimitochondrial M2 antibody, distal renal tubular acidosis, and Fanconi syndrome. Our case also had interstitial pneumonia. After initially successful glucocorticoid therapy, tubulointerstitial nephritis and interstitial pneumonia relapsed. After the second successful round of glucocorticoid therapy, tubulointerstitial nephritis relapsed again and responded to glucocorticoid and azathioprine. This case might indicate (1) the association between pulmonary involvement and tubulointerstitial nephritis with antimitochondrial antibodies and (2) the need for a maintenance dose of glucocorticoid and immunosuppressants in tubulointerstitial nephritis with antimitochondrial antibodies.

Hyponatremia Associated with Prophylactic Low-Dose Trimethoprim during Systemic Corticosteroid Therapy for AQP4-Positive Optic Neuritis in a Diabetic Patient

Hyponatremia associated with low-dose trimethoprim in patients on concomitant systemic corticosteroid therapy has rarely been reported. Here, we describe a 57-year-old woman with a history of diabetes mellitus and hypertension treated with telmisartan, who presented with progressive visual impairment of the left eye due to anti-aquaporin-4 antibody-positive optic neuritis. The patient received pulsed intravenous methylprednisolone followed by oral prednisolone at 30 mg/day and trimethoprim-sulfamethoxazole prophylaxis (160 mg and 800 mg daily). Her serum sodium level steadily decreased, and the potassium level was slightly elevated despite well-preserved renal function. This state persisted even after telmisartan discontinuation. In addition to hypotonic hyponatremia (125 mEq/L) with natriuresis, hyperkalemic renal tubular acidosis was diagnosed based on normal anion gap metabolic acidosis and hyperkalemia with low urinary potassium excretion. After trimethoprim-sulfamethoxazole cessation, electrolytes and acid-base imbalances swiftly recovered. We can conclude that caution must be exercised when treating such patients, because even low-dose trimethoprim may cause hyponatremia concomitant with hyperkalemic renal tubular acidosis, despite the mineralocorticoid effects of systemic corticosteroids.

Inhibitors of Calcium Oxalate Crystallization for the Treatment of Oxalate Nephropathies

Calcium oxalate (CaOx) crystal-induced nephropathies comprise a range of kidney disorders, for which there are no efficient pharmacological treatments. Although CaOx crystallization inhibitors have been suggested as a therapeutic modality already decades ago, limited progress has been made in the discovery of potent molecules with efficacy in animal disease models. Herein, an image-based machine learning approach to systematically screen chemically modified myo-inositol hexakisphosphate (IP6) analogues is utilized, which enables the identification of a highly active divalent inositol phosphate molecule. To date, this is the first molecule shown to completely inhibit the crystallization process in the nanomolar range, reduce crystal-cell interactions, thereby preventing CaOx-induced transcriptomic changes, and decrease renal CaOx deposition and kidney injury in a mouse model of hyperoxaluria. In conclusion, IP6 analogues based on such a scaffold may represent a new treatment option for CaOx nephropathies.

Renal aspects of metabolic acid-base disorders in neonates

Acid-base homeostasis is one of the most tightly regulated systems in the body. Maintaining the acid-base balance is particularly challenging for preterm infants and growing neonates. The kidney, which represents the crucial ultimate line of defense against disturbances of acid-base balance, undergoes a complex maturation process during the transition from a fetal to an extra-uterine environment. This review article summarizes the physiology of acid-base regulation by the immature human kidney and discusses disorders of acid-base balance, such as metabolic acidosis, respiratory acidosis, metabolic alkalosis, and respiratory alkalosis. In conditions of metabolic acidosis, the serum anion gap and the urinary anion gap can be useful tools to define the nature of the acidosis. Metabolic acidosis can reflect a decrease in glomerular filtration rate, or be the consequence of selective disorders of proximal or distal tubular function. Most tubulopathies associated with metabolic acidosis observed in neonates are primary, hereditary, isolated tubulopathies. Proximal renal tubular acidosis is characterized by bicarbonate wasting, while the distal types of renal tubular acidosis are secondary to distal acidification defects. All tubulopathies are associated with hypokalemia, with the exception of type 4 hyperkalemic distal renal tubular acidosis. The transporter defects in the various acid-base tubulopathies are now well defined. Treatment of the acidosis varies according to the site and mechanism of the defect. Chronic renal tubular acidosis or alkalosis severely impair growth and calcium metabolism. Early rational therapeutic intervention can prevent some of the consequences of the disorders and improves the prognosis.

Systematic review and case report: Systemic lupus erythematosus with renal tubular acidosis

Immune profile assessment-particularly for SLE-and subsequent specific therapy are beneficial in patients with persisting unexplained hyperkalemic or hypokalemic paralysis, especially in case of isolated RTA.

Unusual Presentation of Polyautoimmunity and Renal Tubular Acidosis in an Adolescent With Hashimoto's Thyroiditis and Central Pontine Myelinolysis

Background: Hashimoto's thyroiditis is frequently associated with other autoimmune diseases and may include renal involvement. Case description: A 17-year-old female with previously diagnosed Hashimoto's thyroiditis and vitiligo was admitted to a pediatric intensive care unit with hypokalemic paralysis and acidosis, after having suffered from recurrent muscular weakness for approximately one year. A few days later she developed central pontine myelinolysis. After initial stabilization she was also diagnosed with distal renal tubular acidosis (dRTA) and tubular proteinuria which can occur in Sjögren's syndrome. Extended screening for autoimmune diseases additionally revealed celiac disease. Treatment with Prednisone and substitution of potassium quickly lead to the resolution of proteinuria and dRTA, but unilateral paralysis of the sixth nerve as a result of central pontine myelinolysis was irreversible. Conclusions: This is the rare case of polyautoimmunity including autoimmune thyroiditis, Sjögren's syndrome, vitiligo and celiac disease in an adolescent with few disease-specific symptoms. The diagnoses were made via a complicating nephritis causing dRTA and proteinuria. Delay in diagnosis lead to permanent neurological damage. This case highlights the need for pediatricians to be aware of rare accompanying diseases and their complications in "common" pediatric autoimmune diseases like Hashimoto's thyroiditis and celiac disease.

Distal renal tubular acidosis: genetic causes and management

BACKGROUND

Distal renal tubular acidosis (dRTA) is a kidney tubulopathy that causes a state of normal anion gap metabolic acidosis due to impairment of urine acidification. This review aims to summarize the etiology, pathophysiology, clinical findings, diagnosis and therapeutic approach of dRTA, with emphasis on genetic causes of dRTA.

DATA SOURCES

Literature reviews and original research articles from databases, including PubMed and Google Scholar. Manual searching was performed to identify additional studies about dRTA.

RESULTS

dRTA is characterized as the dysfunction of the distal urinary acidification, leading to metabolic acidosis. In pediatric patients, the most frequent etiology of dRTA is the genetic alteration of genes responsible for the codification of distal tubule channels, whereas, in adult patients, dRTA is more commonly secondary to autoimmune diseases, use of medications and uropathies. Patients with dRTA exhibit failure to thrive and important laboratory alterations, which are used to define the diagnosis. The oral alkali and potassium supplementation can correct the biochemical defects, improve clinical manifestations and avoid nephrolithiasis and nephrocalcinosis.

CONCLUSIONS

dRTA is a multifactorial disease leading to several clinical manifestations. Clinical and laboratory alterations can be corrected by alkali replacement therapy.

Proximal renal tubular acidosis with and without Fanconi syndrome

Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO₃⁻) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO₃⁻ wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO₃⁻ not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO₃⁻ reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO₃⁻, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaP_i-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.

Rrm2b deletion causes mitochondrial metabolic defects in renal tubules

Renal diseases impose considerable health and economic burdens on health systems worldwide, and there is a lack of efficient methods for the prevention and treatment due to their complexity and heterogeneity. Kidneys are organs with a high demand for energy produced by mitochondria, in which Rrm2b has critical functions as reported. The Rrm2b kidney-specific knockout mice we generated exhibited age-dependent exacerbated features, including mitochondrial dysfunction and increased oxidative stress; additionally, resulted in severe disruption of mitochondria-related metabolism. Rrm2b is vital not only to supply dNTPs for DNA replication and repair, but also to maintain structural integrity and metabolic homeostasis in mitochondria. Thence, Rrm2b deletion might induce chronic kidney defects in mice. This model can facilitate exploration of novel mechanisms and targeted therapies in the kidney diseases and has important translational and clinical implications.

Interpreting clinical and laboratory tests: importance and implications of context

Clinical and laboratory tests in clinical medicine include a range of measurements that may be categorized as "normal range" tests, positive or negative tests, or contextual tests. Normal range test results are quantitative and are compared to a reference interval or range provided by the laboratory. Positive or negative tests are also quantitative tests and characteristically have a cutoff value that specifies the result. Contextual tests require a context, a physiological condition, to correctly interpret the result. A closer examination of reference intervals suggests that these also are contextual. The fact that there is a range of apparently normal values indicates the presence of cultural, biological, physiological and behavioral diversity in the population sampled to determine normality. As such, the reference interval describes the population from which it was determined and may have utility in this regard.

Hyperchloremic normal gap metabolic acidosis

Metabolic acidosis is defined as a pathologic process that, when unopposed, increases the concentration of hydrogen ions (H+) in the body and reduces the bicarbonate (HCO3-) concentration. Metabolic acidosis can be of a kidney origin or an extrarenal cause. Assessment of urinary ammonium excretion by calculating the urine anion gap or osmolal gap is a useful method to distinguish between these two causes. Extrarenal processes include increased endogenous acid production and accelerated loss of bicarbonate from the body. Metabolic acidosis of renal origin is due to a primary defect in renal acidification with no increase in extrarenal hydrogen ion production. This situation can occur because either the renal input of new bicarbonate is insufficient to regenerate the bicarbonate lost in buffering endogenous acid as with distal renal tubular acidosis (RTA) or the RTA of renal insufficiency, or the filtered bicarbonate is lost by kidney wasting as in proximal RTA. In either condition, because of loss of either NaHCO3 (proximal RTA) or NaA (distal RTA), effective extracellular volume is reduced and as a result the avidity for chloride reabsorption derived from the diet is increased and results in a hyperchloremic normal gap metabolic acidosis. The RTA of renal insufficiency is also characterized by a normal gap acidosis, however, with severe reductions in the glomerular filtration rate an anion gap metabolic acidosis eventually develops.

Prevalence of distal renal tubular acidosis in patients with calcium phosphate stones

INTRODUCTION AND PURPOSE

Distal renal tubular acidosis (DRTA) is a metabolic disorder that associates urolithiasis and urinary pH > 6. The prevalence of DRTA in patients with calcium phosphate stones is not well known. The objective is to determine the prevalence of DRTA in patients with calcium phosphate stones and urinary pH above 6 based on the furosemide test.

METHODS

A total of 54 patients with calcium phosphate stones and urinary pH above 6.0 were submitted to the furosemide test. The association of DRTA with age, sex, type of stone, stone recurrence, stone bilaterality, 24-h urine biochemistry, and adverse effects of the furosemide test were examined.

RESULTS

The furosemide test indicated that 19 of 54 patients (35.2%) had DRTA. The sex ratio was similar in the two groups (p < 0.776). The DRTA group was significantly younger (p < 0.001), and had a higher prevalence of bilateral stones (p < 0.001), a higher prevalence of recurrent stones (p < 0.04), a lower plasma potassium level (p < 0.001), a higher urinary Ca level (p ≤ 0.05), and a lower urinary citrate level (p < 0.001). None of the patients reported adverse effects from the furosemide test.

CONCLUSIONS

There was a high prevalence of DTRA in patients with urinary pH above 6 and calcium phosphate stones. Young age, bilateral stones, stone recurrence, hypercalciuria, hypocitraturia, and plasma hypokalemia were associated with DRTA. None of the patients reported adverse effects of the furosemide test.

The role of the clinical laboratory in diagnosing acid-base disorders

Acid-base homeostasis is fundamental for life. The body is exceptionally sensitive to changes in pH, and as a result, potent mechanisms exist to regulate the body's acid-base balance to maintain it in a very narrow range. Accurate and timely interpretation of an acid-base disorder can be lifesaving but establishing a correct diagnosis may be challenging. The underlying cause of the acid-base disorder is generally responsible for a patient's signs and symptoms, but laboratory results and their integration into the clinical picture is crucial. Important acid-base parameters are often available within minutes in the acute hospital care setting, and with basic knowledge it should be easy to establish the diagnosis with a stepwise approach. Unfortunately, many caveats exist, beginning in the pre-analytical phase. In the post-analytical phase, studies on the arterial reference pH are scarce and therefore many different reference values are used in the literature without any solid evidence. The prediction models that are currently used to assess the acid-base status are approximations that are mostly based on older studies with several limitations. The two most commonly used methods are the physiological method and the base excess method, both easy to use. The secondary response equations in the base excess method are the most convenient. Evaluation of acid-base disorders should always include the assessment of electrolytes and the anion gap. A major limitation of the current acid-base laboratory tests available is the lack of rapid point-of-care laboratory tests to diagnose intoxications with toxic alcohols. These intoxications can be fatal if not recognized and treated within minutes to hours. The surrogate use of the osmolal gap is often an inadequate substitute in this respect. This article reviews the role of the clinical laboratory to evaluate acid-base disorders.

Presence of serum autoantibodies to vacuolar H+ -ATPase in patients with renal tubular acidosis

OBJECTIVE

Concomitant presence of renal tubular acidosis (RTA) and autoimmune diseases is indicative of the potential role of immune factors in the pathogenesis of RTA. Our study aimed to detect the serum antibodies to renal tubular epithelial cells in RTA patients.

METHODS

We enrolled 11 RTA patients, eight primary Sjögren's syndrome (pSS) patients and eight healthy controls (HC). Serum biochemical test, urinary regular test, and 24 hours urinary protein quantification were measured using a fully automated analyzer. Immunofluorescence assay was performed to detect the antibodies to subunit B1 and subunit B2 of v-H+-ATPases (adenosine triphosphatases) in the serum of the participants.

RESULTS

Clinically, RTA patients showed hyperchloremia, acidosis and paradoxical alkaline urine. We detected the serum antibodies to renal tubular epithelial cells and there were 6/11 positive in RTA patients, much higher than that in the pSS group (0/8) and the HC group (0/8). Subsequently, we demonstrated that in normal renal tissue, the B1 subunit of v-H+-ATPase specifically expressed in intercalated cells, while the B2 subunit continuously expressed along the lumen of renal tubular epithelial cells. Moreover, the antibody to subunit B1/B2 of v-H+-ATPase was positive in the sera of 6 RTA patients (54%), while it was negative in both the pSS and HC group.

CONCLUSIONS

We detected the presence of serum autoantibodies to subunit B1 and subunit B2 of v-H⁺ -ATPase in RTA patients. Our findings may provide novel mechanism insights into the pathogenesis of RTA and the potential diagnostic utility of antibodies to v-H⁺ -ATPase in the classification of RTA.