Mechanisms in hyperkalemic renal tubular acidosis

Revisiting voltage-coupled H+ secretion in the collecting duct

Experimental studies have shown that V-type ATPase-driven H+ secretion is dependent on transepithelial voltage. On this basis, the "voltage hypothesis" of urinary acidification by the collecting duct was derived. Accordingly, it has been supposed that the lumen-negative potential created by the reabsorption of Na+ via the epithelial Na+ channel (ENaC) enhances electrogenic H+ secretion via V-type H+-ATPase. This concept continues to be widely used to explain acid/base disorders. Importantly, however, a solid proof of principle for the voltage hypothesis in physiologically relevant situations has not been reached. Rather, it has been challenged by recent in vivo functional studies. In this review, we outline the arguments and experimental observations explaining why voltage-coupled H+ secretion in the collecting duct often appears poorly applicable for rationalizing changes in H+ secretion as a function of more or less ENaC function in the collecting duct.

Sodium-glucose cotransporter-2 inhibitors and abnormal serum potassium: a real-world, pharmacovigilance study

BACKGROUND

New trials indicated a potential of sodium-glucose cotransporter-2 inhibitors (SGLT2i) to reduce hyperkalemia, which might have important clinical implications, but real-world data are limited. Therefore, we examined the effect of SGLT2i on hyper- and hypokalemia occurrence using the FDA adverse event reporting system (FAERS).

METHODS

The FAERS database was retrospectively queried from 2004q1 to 2021q3. Disproportionality analyses were performed based on the reporting odds ratio (ROR) and 95% confidence interval (CI).

RESULTS

There were 84 601 adverse event reports for SGLT2i and 1 321 186 reports for other glucose-lowering medications. The hyperkalemia reporting incidence was significantly lower with SGLT2i than with other glucose-lowering medications (ROR, 0.83; 95% CI, 0.79-0.86). Reductions in hyperkalemia reports did not change across a series of sensitivity analyses. Compared with that with renin-angiotensin-aldosterone system inhibitors (RAASi) alone (ROR, 4.40; 95% CI, 4.31-4.49), the hyperkalemia reporting incidence was disproportionally lower among individuals using RAASi with SGLT2i (ROR, 3.25; 95% CI, 3.06-3.45). Compared with that with mineralocorticoid receptor antagonists (MRAs) alone, the hyperkalemia reporting incidence was also slightly lower among individuals using MRAs with SGLT-2i. The reporting incidence of hypokalemia was lower with SGLT2i than with other antihyperglycemic agents (ROR, 0.79; 95% CI, 0.75-0.83).

CONCLUSION

In a real-world setting, hyperkalemia and hypokalemia were robustly and consistently reported less frequently with SGLT2i than with other diabetes medications. There were disproportionally fewer hyperkalemia reports among those using SGLT-2is with RAASi or MRAs than among those using RAASi or MRAs alone.

Real-Life Experience on the Effect of SGLT2 Inhibitors vs. Finerenone vs. Combination on Albuminuria in Chronic Kidney Disease

BACKGROUND

There have been several recent advances in the care of patients with chronic kidney disease (CKD), including the use of sodium glucose cotransporter 2 (SGLT2) inhibitors and selective mineralocorticoid receptor antagonists (MRAs). There are very few data reporting the outcomes of these treatments in real-world experience. The aim of this retrospective study is to report the effects of SGLT2 inhibitors, finerenone, and their combination in CKD patients in our community-based setting.

METHODS

Ninety-eight patients with CKD with an estimated glomerular filtration rate (eGFR) between 25 and 90 mL/min per 1.73 m2 and a urine albumin-to-creatinine ratio (UACR) ≥ 30 mg/g were included. Patients were divided into three groups: two monotherapy groups of SGLT2 inhibitors or finerenone and a third combination group of therapy with SGLT2 inhibitors for the first 4 months and SGLT2 inhibitors and finerenone subsequently. The primary outcomes were the timing and percentage of patients achieving a >50% reduction in UACR from baseline.

RESULTS

Group 1 comprised 52 patients on SGLT2i, group 2 had 22 patients on finerenone, and group 3 had 24 patients on combination therapy. The baseline median UACR and mean eGFR were 513 mg/g and 47.9 mL/min per 1.73 m2 in group 1, 548.0 mg/g and 50.5 mL/min per 1.73 m2 in group 2, and 800 mg/g and 60 mL/min per 1.73 m2 in group 3. At baseline, 71 (72.4%) patients were on the angiotensin-converting enzyme inhibitor (ACEi) or the angiotensin receptor blocker (ARB), and 78 (79.5%) patients had type 2 diabetes. After 8 months of follow-up, a >50% decrease in albuminuria was achieved in 96% of patients in group 3, compared to 50% in group 1 and 59% in group 2 (p-values were <0.01 and <0.01, respectively). There was a statistically but not clinically significant change in mean potassium levels in group 2 (+0.4 mmol/L) compared to either group 1 (0.0 mmol/L with p-value: <0.01) or group 3 (-0.01 mmol/L with p-value: <0.01). However, there was no difference in potassium levels when comparing groups 1 and 3. At the end of the follow-up, the average difference in eGFR was -3.4 (8.8), -5.3(10.1), and -7.8 (11.2) mL/min per 1.73 m2 in groups 1, 2, and 3, respectively, without a statistically significant difference between groups.

CONCLUSIONS

In this real-world experience in our community setting, the combination of SGLT2 inhibitors and finerenone in our adult patients with CKD was associated with a very significant and clinically relevant reduction in UACR, without an increased risk of hyperkalemia. Combination therapy of SGLT2 inhibitor and finerenone regarding background use of ACEi/ARB is feasible and should be encouraged for further albuminuria reductions in CKD patients.

Sodium Zirconium Cyclosilicate in CKD, Hyperkalemia, and Metabolic Acidosis: NEUTRALIZE Randomized Study

Key Points

Sodium zirconium cyclosilicate effectively lowers serum potassium and maintains normokalemia in patients with CKD with concomitant hyperkalemia and metabolic acidosis. Despite high screen failure and small sample size, a nominally significant increase in sHCO3– was seen for sodium zirconium cyclosilicate versus placebo. Further studies on the basis of an appropriate cohort size may help validate the trend observed in sHCO3– levels, supporting these clinically relevant findings.

Background

Metabolic acidosis and hyperkalemia are common in CKD. A potential dual effect of sodium zirconium cyclosilicate (SZC), a selective binder of potassium in the gastrointestinal tract, on serum potassium (sK+) and serum bicarbonate (sHCO3−) was evaluated in patients with hyperkalemia and metabolic acidosis associated with CKD.

Methods

In the NEUTRALIZE study (NCT04727528 ), non-dialysis patients with stage 3–5 CKD, hyperkalemia (sK+>5.0 to ≤5.9 mmol/L), and metabolic acidosis (sHCO3− 16–20 mmol/L) received open-label SZC 10 g three times daily for ≤48 hours. Patients achieving normokalemia (sK+ 3.5–5.0 mmol/L) were randomized 1:1 to SZC 10 g or placebo daily for 4 weeks. The primary end point was patients (%) maintaining normokalemia at the end of treatment (EOT) without rescue. Secondary end points included mean change in sHCO3− at EOT (day 29) and patients (%) with normokalemia with a ≥3-mmol/L increase in sHCO3− without rescue.

Results

Of 229 patients screened, 37 were randomized (SZC, n =17; placebo, n =20). High screen failure led to early study termination. At EOT, 88.2% (SZC) versus 20.0% (placebo) of patients maintained normokalemia (odds ratio, 56.2; P = 0.001). Low enrollment rendered secondary end point P values nominal. SZC treatment provided nominally significant increases in sHCO3– versus placebo from day 15 onward. Patients with normokalemia with a ≥3-mmol/L increase in sHCO3− without rescue were 35.3% (SZC) and 5.0% (placebo; P < 0.05). No new safety concerns were reported.

Conclusions

SZC effectively lowered sK+ and maintained normokalemia, with nominally significant increases in sHCO3– observed for SZC versus placebo.

Variables Associated With Hyperkalemic Renal Tubular Acidosis in Solid Organ Transplant Recipients

INTRODUCTION

The occurrence of hyperkalemic renal tubular acidosis (RTA) in the post-transplantation period is likely underestimated, and its identification remains important to offer adequate medical management. Transplant recipients frequently present with clinical and biological characteristics that may be associated with the occurrence of this complication.

METHODS

This was a single-center retrospective study that compared transplanted patients with hyperkalemic RTA and a control group to identify variables associated with the occurrence of this complication. Fisher's exact test and the Mann-Whitney test, followed by multivariate logistic regression, were applied to test whether there was a significant association between hyperkalemic RTA and different variables.

RESULTS

Kidney and heart transplant recipients were at greater risk of developing RTA than lung transplant recipients (p = 0.016). There was also a significant association between the development of RTA and kalemia (p < 0.01), chloremia (p < 0.01), and bicarbonatemia (p < 0.01). The significant impact of these last three variables was confirmed by the results of the multivariate logistic regression. Residual serum tacrolimus levels (p = 0.13) and creatinine levels (p = 0.17) of renal transplant patients were not significantly associated with hyperkalemic RTA.

CONCLUSION

The type of transplanted organ, kalemia, chloremia, and bicarbonatemia were significantly associated with the occurrence of hyperkalemic RTA. This study calls into question certain approaches to managing this complication proposed in a number of case reports, such as reducing the target serum residual of tacrolimus or discontinuing trimethoprim-sulfamethoxazole (TMP-SMX) in favor of another antibiotic prophylactic agent, potentially exposing patients to graft rejection and opportunistic infections.

Phosphate Restriction Prevents Metabolic Acidosis and Curbs Rise in FGF23 and Mortality in Murine Folic Acid-Induced AKI

SIGNIFICANCE STATEMENT

Patients with AKI suffer a staggering mortality rate of approximately 30%. Fibroblast growth factor 23 (FGF23) and phosphate (P i ) rise rapidly after the onset of AKI and have both been independently associated with ensuing morbidity and mortality. This study demonstrates that dietary P i restriction markedly diminished the early rise in plasma FGF23 and prevented the rise in plasma P i , parathyroid hormone, and calcitriol in mice with folic acid-induced AKI (FA-AKI). Furthermore, the study provides evidence for P i -sensitive osseous Fgf23 mRNA expression and reveals that P i restriction mitigated calciprotein particles (CPPs) formation, inflammation, acidosis, cardiac electrical disturbances, and mortality in mice with FA-AKI. These findings suggest that P i restriction may have a prophylactic potential in patients at risk for AKI.

BACKGROUND

In AKI, plasma FGF23 and P i rise rapidly and are independently associated with disease severity and outcome.

METHODS

The effects of normal (NP) and low (LP) dietary P i were investigated in mice with FA-AKI after 3, 24, and 48 hours and 14 days.

RESULTS

After 24 hours of AKI, the LP diet curbed the rise in plasma FGF23 and prevented that of parathyroid hormone and calcitriol as well as of osseous but not splenic or thymic Fgf23 mRNA expression. The absence of Pth prevented the rise in calcitriol and reduced the elevation of FGF23 in FA-AKI with the NP diet. Furthermore, the LP diet attenuated the rise in renal and plasma IL-6 and mitigated the decline in renal α -Klotho. After 48 hours, the LP diet further dampened renal IL-6 expression and resulted in lower urinary neutrophil gelatinase-associated lipocalin. In addition, the LP diet prevented the increased formation of CPPs. Fourteen days after AKI induction, the LP diet group maintained less elevated plasma FGF23 levels and had greater survival than the NP diet group. This was associated with prevention of metabolic acidosis, hypocalcemia, hyperkalemia, and cardiac electrical disturbances.

CONCLUSIONS

This study reveals P i -sensitive FGF23 expression in the bone but not in the thymus or spleen in FA-AKI and demonstrates that P i restriction mitigates CPP formation, inflammation, acidosis, and mortality in this model. These results suggest that dietary P i restriction could have prophylactic potential in patients at risk for AKI.

Re-Thinking Hyperkalaemia Management in Chronic Kidney Disease-Beyond Food Tables and Nutrition Myths: An Evidence-Based Practice Review

Potassium dysregulation can be life-threatening. Dietary potassium modification is a management strategy for hyperkalaemia. However, a 2017 review for clinical guidelines found no trials evaluating dietary restriction for managing hyperkalaemia in chronic kidney disease (CKD). Evidence regarding dietary hyperkalaemia management was reviewed and practice recommendations disseminated. A literature search using terms for potassium, hyperkalaemia, and CKD was undertaken from 2018 to October 2022. Researchers extracted data, discussed findings, and formulated practice recommendations. A consumer resource, a clinician education webinar, and workplace education sessions were developed. Eighteen studies were included. Observational studies found no association between dietary and serum potassium in CKD populations. In two studies, 40-60 mmol increases in dietary/supplemental potassium increased serum potassium by 0.2-0.4 mmol/L. No studies examined lowering dietary potassium as a therapeutic treatment for hyperkalaemia. Healthy dietary patterns were associated with improved outcomes and may predict lower serum potassium, as dietary co-factors may support potassium shifts intracellularly, and increase excretion through the bowel. The resource recommended limiting potassium additives, large servings of meat and milk, and including high-fibre foods: wholegrains, fruits, and vegetables. In seven months, the resource received > 3300 views and the webinar > 290 views. This review highlights the need for prompt review of consumer resources, hospital diets, and health professionals' knowledge.

The pathophysiology of distal renal tubular acidosis

The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease.

Type 4 renal tubular acidosis and uric acid nephrolithiasis: two faces of the same coin?

PURPOSE OF REVIEW

The present review summarizes findings of recent studies examining the epidemiology, pathophysiology, and treatment of type 4 renal tubular acidosis (RTA) and uric acid nephrolithiasis, two conditions characterized by an abnormally acidic urine.

RECENT FINDINGS

Both type 4 RTA and uric acid nephrolithiasis disproportionately occur in patients with type 2 diabetes and/or chronic kidney disease. Biochemically, both conditions are associated with reduced renal ammonium excretion resulting in impaired urinary buffering and low urine pH. Reduced ammoniagenesis is postulated to result from hyperkalemia in type 4 RTA and from insulin resistance and fat accumulation in the renal proximal tubule in uric acid nephrolithiasis. The typical biochemical findings of hyperkalemia and systemic acidosis of type 4 RTA are rarely reported in uric acid stone formers. Additional clinical differences between the two conditions include findings of higher urinary uric acid excretion and consequent urinary uric acid supersaturation in uric acid stone formers but not in type 4 RTA.

SUMMARY

Type 4 RTA and uric acid nephrolithiasis share several epidemiological, clinical, and biochemical features. Although both conditions may be manifestations of diabetes mellitus and thus have a large at-risk population, the means to the shared biochemical finding of overly acidic urine are different. This difference in pathophysiology may explain the dissimilarity in the prevalence of kidney stone formation.

Diet and Metabolism in CKD-Related Metabolic Acidosis

Metabolic acidosis is a common complication in patients with chronic kidney disease that occurs when the daily nonvolatile acid load produced in metabolism cannot be excreted fully by the kidney. A reduction in urine net acid excretion coupled with a high nonvolatile acid load may play a role in its pathogenesis. Diet is important in generation of the nonvolatile acid load. Acids are produced from metabolism of dietary protein and from the endogenous production of organic anions from neutral precursors. Acids can be balanced by alkali precursors ingested in the diet in the form of combustible organic anions. These typically are reflected indirectly by the excess of mineral cations to mineral anions in a food or diet. These principles underscore widely used methods to estimate the nonvolatile acid load from dietary intake using formulas such as the net endogenous acid production equation and the potential renal acid load equation. Empiric data largely validate these paradigms with high net endogenous acid production and potential renal acid load contributed by foods such as protein, grains, and dairy, and low net endogenous acid production and potential renal acid load contributed by fruits and vegetables along with corresponding dietary patterns. Although further studies are needed to understand the health benefits of altering nonvolatile acid load via diet, this review provides a detailed assessment on our current understanding of the role of diet in chronic kidney disease-related acidosis, providing an updated resource for researchers and clinicians.

Sodium zirconium cyclosilicate and metabolic acidosis: Potential mechanisms and clinical consequences

Metabolic acidosis is frequent in chronic kidney disease (CKD) and is associated with accelerated progression of CKD, hypercatabolism, bone disease, hyperkalemia, and mortality. Clinical guidelines recommend a target serum bicarbonate ≥ 22 mmol/L, but metabolic acidosis frequently remains undiagnosed and untreated. Sodium zirconium cyclosilicate (SZC) binds potassium in the gut and is approved to treat hyperkalemia. In clinical trials with a primary endpoint of serum potassium, SZC increased serum bicarbonate, thus treating CKD-associated metabolic acidosis. The increase in serum bicarbonate was larger in patients with more severe pre-existent metabolic acidosis, was associated to decreased serum urea and was maintained for over a year of SZC therapy. SZC also decreased serum urea and increased serum bicarbonate after switching from a potassium-binding resin in normokalemic individuals. Mechanistically, these findings are consistent with SZC binding the ammonium ion (NH₄⁺) generated from urea by gut microbial urease, preventing its absorption and, thus, preventing the liver regeneration of urea and promoting the fecal excretion of H⁺. This mechanism of action may potentially result in benefits dependent on corrected metabolic acidosis (e.g., improved well-being, decreased catabolism, improved CKD mineral bone disorder, better control of serum phosphate, slower progression of CKD) and dependent on lower urea levels, such as decreased protein carbamylation. A roadmap is provided to guide research into the mechanisms and clinical consequences of the impact of SZC on serum bicarbonate and urate.

Sodium-Glucose Cotransporter 2 Inhibitors and Risk of Hyperkalemia in People With Type 2 Diabetes: A Meta-Analysis of Individual Participant Data From Randomized, Controlled Trials

BACKGROUND

Hyperkalemia increases risk of cardiac arrhythmias and death and limits the use of renin-angiotensin-aldosterone system inhibitors and mineralocorticoid receptor antagonists, which improve clinical outcomes in people with chronic kidney disease or systolic heart failure. Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the risk of cardiorenal events in people with type 2 diabetes at high cardiovascular risk or with chronic kidney disease. However, their effect on hyperkalemia has not been systematically evaluated.

METHODS

A meta-analysis was conducted using individual participant data from randomized, double-blind, placebo-controlled clinical outcome trials with SGLT2 inhibitors in people with type 2 diabetes at high cardiovascular risk or with chronic kidney disease in whom serum potassium levels were routinely measured. The primary outcome was time to serious hyperkalemia, defined as central laboratory-determined serum potassium ≥6.0 mmol/L, with other outcomes including investigator-reported hyperkalemia events and hypokalemia (serum potassium ≤3.5 mmol/L). Cox regression analyses were performed to estimate treatment effects from each trial with hazards ratios and corresponding 95% CIs pooled with random-effects models to obtain summary treatment effects, overall and across key subgroups.

RESULTS

Results from 6 trials were included comprising 49 875 participants assessing 4 SGLT2 inhibitors. Of these, 1754 participants developed serious hyperkalemia, and an additional 1119 investigator-reported hyperkalemia events were recorded. SGLT2 inhibitors reduced the risk of serious hyperkalemia (hazard ratio, 0.84 [95% CI, 0.76-0.93]), an effect consistent across studies (P_{heterogeneity}=0.71). The incidence of investigator-reported hyperkalemia was also lower with SGLT2 inhibitors (hazard ratio, 0.80 [95% CI, 0.68-0.93]; P_{heterogeneity}=0.21). Reductions in serious hyperkalemia were observed across a range of subgroups, including baseline kidney function, history of heart failure, and use of renin-angiotensin-aldosterone system inhibitor, diuretic, and mineralocorticoid receptor antagonist. SGLT2 inhibitors did not increase the risk of hypokalemia (hazard ratio, 1.04 [95% CI, 0.94-1.15]; P_{heterogeneity}=0.42).

CONCLUSIONS

SGLT2 inhibitors reduce the risk of serious hyperkalemia in people with type 2 diabetes at high cardiovascular risk or with chronic kidney disease without increasing the risk of hypokalemia.

Albuminuria-Lowering Effect of Dapagliflozin, Eplerenone, and their Combination in Patients with Chronic Kidney Disease: A Randomized Cross-over Clinical Trial

Background: SGLT2 inhibitors and MRAs reduce the urinary albumin-to-creatinine ratio (UACR) and confer kidney and cardiovascular protection in patients with chronic kidney disease (CKD). We assessed efficacy and safety of the SGLT2 inhibitor dapagliflozin and mineralocorticoid receptor antagonists (MRA) eplerenone alone and in combination in patients with CKD. Methods: We conducted a randomized open-label cross-over trial in patients with urinary albumin excretion ≥100 mg/24-hour, eGFR 30-90 mL/min/1.73m², who had been receiving maximum tolerated stable doses of an ACE inhibitor (ACEi) or angiotensin receptor blocker (ARB). Patients were assigned to 4-week treatment periods with dapagliflozin 10 mg/day, eplerenone 50 mg/day, or their combination in random order, separated by 4-week wash-out periods. Primary outcome was the correlation in UACR changes between treatments. Secondary outcome was the percent change in 24-hour UACR from baseline. Results: Of 57 patients screened, 46 were randomly assigned (mean eGFR 58.1 mL/min/1.73m², median UACR 401 mg/g) to the three groups. Mean percentage change from baseline in UACR after 4 weeks treatment with dapagliflozin, eplerenone, and dapagliflozineplerenone was -19.6% (95%CI -34.3, -1.5), -33.7% (95%CI -46.1, -18.5), and -53.0% (95%CI -61.7, -42.4; p<0.001 vs dapagliflozin; p=0.0127 vs eplerenone). UACR change during dapagliflozin or eplerenone treatment did not correlate with UACR change during dapagliflozineplerenone (r=-0.13; p=0.473; r=-0.08; p=0.658 respectively). Hyperkalemia was more frequently reported with eplerenone (N=8, [17.4%]) compared to dapagliflozin (N=0, [0%]) or dapagliflozin-eplerenone (N=2, [4.3%]; P_{between-groups}=0.0033). Conclusion: Albuminuria changes in response to dapagliflozin and eplerenone did not correlate, supporting systematic rotation of these therapies to optimize treatment. Combining dapagliflozin with eplerenone resulted in a robust additive UACR lowering effect. A larger trial in this population is required to confirm long-term efficacy and safety of combined SGLT2 inhibitor and MRA treatment.

Effect of Sodium Zirconium Cyclosilicate on Serum Potassium and Bicarbonate in Patients with Hyperkalemia and Metabolic Acidosis Associated with Chronic Kidney Disease: Rationale and Design of the NEUTRALIZE Study

INTRODUCTION

Sodium zirconium cyclosilicate (SZC) is a selective potassium (K+) binder for hyperkalemia management that provides rapid and sustained correction of hyperkalemia. The NEUTRALIZE study is investigating whether SZC, in addition to correcting hyperkalemia and maintaining normal serum K+, can provide sustained increases in serum bicarbonate (HCO3-) in patients with hyperkalemia and metabolic acidosis associated with chronic kidney disease (CKD).

METHODS

This is a prospective, randomized, double-blind, placebo-controlled phase 3b study of US adults with stage 3-5 CKD not on dialysis with hyperkalemia (K+ >5.0-≤5.9 mmol/L) and low-serum HCO3- (16-20 mmol/L). In the open-label correction phase, all eligible patients receive SZC 10 g three times daily for up to 48 h. Patients who achieve normokalemia (K+ ≥3.5-≤5.0 mmol/L) are then randomized 1:1 to once-daily SZC 10 g or placebo for a 4-week, double-blind, placebo-controlled maintenance phase. The primary endpoint is the proportion of patients with normokalemia at the end of treatment (EOT) without rescue therapy for hyperkalemia. Key secondary endpoints include mean change in serum HCO3-, the proportion of patients with an increase in serum HCO3- of ≥2 or ≥3 mmol/L without rescue therapy for metabolic acidosis, and the proportion of patients with serum HCO3- ≥22 mmol/L at EOT.

CONCLUSIONS

NEUTRALIZE will establish whether SZC can provide sustained increases in serum HCO3- while lowering serum K+ in patients with hyperkalemia and CKD-associated metabolic acidosis and may provide insights on the mechanism(s) underlying the increased serum HCO3- with SZC treatment.

Interpretation of network-based integration from multi-omics longitudinal data

Multi-omics integration is key to fully understand complex biological processes in an holistic manner. Furthermore, multi-omics combined with new longitudinal experimental design can unreveal dynamic relationships between omics layers and identify key players or interactions in system development or complex phenotypes. However, integration methods have to address various experimental designs and do not guarantee interpretable biological results. The new challenge of multi-omics integration is to solve interpretation and unlock the hidden knowledge within the multi-omics data. In this paper, we go beyond integration and propose a generic approach to face the interpretation problem. From multi-omics longitudinal data, this approach builds and explores hybrid multi-omics networks composed of both inferred and known relationships within and between omics layers. With smart node labelling and propagation analysis, this approach predicts regulation mechanisms and multi-omics functional modules. We applied the method on 3 case studies with various multi-omics designs and identified new multi-layer interactions involved in key biological functions that could not be revealed with single omics analysis. Moreover, we highlighted interplay in the kinetics that could help identify novel biological mechanisms. This method is available as an R package netOmics to readily suit any application.

Fludrocortisone Is an Effective Treatment for Hyperkalaemic Metabolic Acidosis in Kidney Transplant Recipients on Tacrolimus: A Case Series

BACKGROUND

Hyperkalaemia with metabolic acidosis is common but under-reported following kidney transplantation. Calcineurin inhibitors, such as tacrolimus, are widely used in the management of transplant patients and are associated with the development of hyperkalaemia. We report on 10 renal transplant patients, treated with fludrocortisone, following identification of hyperkalaemic metabolic acidosis.

RESULTS

All 10 patients were male aged (mean ± SD) 53.0 ± 13.2 years; 7 were Caucasian and 3 South Asian. Before and after fludrocortisone administration, respective (mean ± SD) serum potassium was 6.1 ± 0.4 mmol/L and 5.3 ± 0.3 mmol/L (p = 0.0002); serum bicarbonate 18.5 ± 1.6 mmol/L and 20.5 ± 2.3 mmol/L (p = 0.002); serum sodium 135 ± 4.6 mmol/L and 137 ± 2.2 mmol/L (p = 0.0728); serum creatinine 181 ± 61 μmol/L and 168 ± 64 μmol/L (p = 0.1318); eGFR 42 ± 18 mL/min and 46 ± 18 mL/min (p = 0.0303); blood tacrolimus 10.1 ± 2.9 ng/mL and 10.4 ± 1.4 ng/mL (p = 0.7975); and blood pressure 129 ± 15/79 ± 25 mm Hg and 126 ± 24/75 ± 7 mm Hg. Pre-fludrocortisone, there were 7 episodes of serum potassium ≥6.5 mEq/L, with 4 patients requiring admission for the treatment of hyperkalaemia. Following fludrocortisone, no patients had hyperkalaemia requiring inpatient management.

CONCLUSIONS

Treatment of hyperkalaemic metabolic acidosis in transplant patients on tacrolimus with low-dose fludrocortisone resulted in rapid correction of hyperkalaemia and acidosis without significant effects on blood pressure or serum sodium. Fludrocortisone can be an effective short-term option for the treatment of hyperkalaemic metabolic acidosis in kidney transplant recipients on tacrolimus; however, patient selection remains important in order to reduce to risk of potential adverse effects.

Prevalence of Metabolic Acidosis Among Patients with Chronic Kidney Disease and Hyperkalemia

INTRODUCTION

Although hyperkalemia and metabolic acidosis often co-occur in patients with chronic kidney disease (CKD), the prevalence of metabolic acidosis among patients with CKD and hyperkalemia is understudied. Therefore, we used medical record data from the Research Action for Health Network to estimate this prevalence.

METHODS

Adult patients with CKD stage 3-5, ≥ 1 outpatient potassium value > 5.0 mEq/l, and ≥ 1 outpatient bicarbonate value available were identified. Patients with end stage kidney disease (ESKD) in the prior year were excluded. The prevalence of metabolic acidosis in each calendar year from 2014 to 2017 among patients with CKD and hyperkalemia was estimated using two definitions of hyperkalemia (potassium > 5.0 mEq/l and > 5.5 mEq/l) and metabolic acidosis (bicarbonate < 18 mEq/l and < 22 mEq/l).

RESULTS

In the 2017 patient cohort and among patients with CKD and hyperkalemia, patients with metabolic acidosis were younger (69 versus 74 years), more likely to have advanced CKD (35% versus 13%), and use oral sodium bicarbonate (21% versus 4%) than patients without metabolic acidosis. The prevalence of metabolic acidosis (< 22 mEq/l) ranged from 25 to 29% when hyperkalemia was defined by potassium > 5.0 mEq/l and ranged from 33 to 39% when hyperkalemia was defined by potassium > 5.5 mEq/l.

CONCLUSION

Results demonstrated that prevalence estimates of metabolic acidosis varied based on the definition of hyperkalemia and metabolic acidosis utilized.

Prevalence and clinical correlates of hyperkalemia in stable kidney transplant recipients

Although hyperkalemia (HK) is often associated with adverse clinical outcomes in renal patients, few studies are available in the setting of kidney transplantation. Therefore, we evaluated prevalence and clinical correlates of HK in stable kidney transplant recipients (KTRs) on standard of care immunosuppressive therapy. We studied 160 stable KTRs (post-transplant vintage 46.6 ± 16.6 months), most of whom (96.2%) on calcineurin inhibitor (CNI)-based immunosuppressive therapy. HK was defined as plasma potassium levels above 5 mEq/L, confirmed in two consecutive samples. Office blood pressure was measured, and renal graft function was expressed by estimated glomerular filtration rate (eGFR), calculated according to the CKD-EPI formula. HK prevalence was 8.8%, and plasma K above 5.5 mEq/L was found in 2.5% of all KTRs. In the univariate logistic regression analysis HK was significantly associated with serum urea concentration (OR 1.03, 95% CI 1.01-1.05 for each 1 mg/dL increase), tCO₂ (OR 0.77, 95% CI 0.66-0.90 for each 1 mmol/L increase), the presence of arterial hypertension (OR 4.01, 95% CI 1.3-12.64), the use of RAAS inhibitors (OR 5.26, 95% CI 1.6-17.7), and eGFR less than 30 ml/min/1.73 m² (OR 7.51, 95% CI 2.37-23.77). By multivariable backward stepwise regression analysis, the presence of metabolic acidosis (OR 0.83, 95% CI 0.69-0.99, P = 0.04), arterial hypertension (OR 4.65 95% CI 1.01-17.46 P = 0.03), and to be administered RAAS inhibitors (OR 6.11, 95% CI 1.03-25.96 P = 0.03) remained significantly associated with HK. We conclude that in stable KTRs the prevalence of HK is about 9%, slightly lower than previously reported. Moreover, it is not associated with eGFR, but with metabolic acidosis, arterial hypertension, and the use of RAAS inhibitors.

Incidence of hyperkalemic RTA in pediatric post-renal transplant patients and the role of fludrocortisone

BACKGROUND

One of the most common forms of post-transplant tubulopathy is hyperkalemic (RTA). The true incidence of hyperkalemic RTA in pediatric patients has not yet been studied. (CNIs) remain mostly blamed. Most cases are managed with sodium bicarbonate and potassium binding resins. Few studies have addressed the role of fludrocortisone in managing such patients. This study aimed to assess the efficacy and safety of fludrocortisone in the treatment of post-transplant hyperkalemic RTA.

METHOD

This is a retrospective cohort study of all pediatric (aged ≤16 years) post-kidney transplant patients who were followed up in KFSH-D, Saudi Arabia from January 2015 until September 2019. A total of 136 pediatric post-renal transplant patients were reviewed, of these, 39 patients who were commenced on fludrocortisone post-transplant treatment and were followed up for at least 6 months after fludrocortisone initiation were included in this study.

RESULTS

The incidence of hyperkalemic RTA in our center was 60.6%. The medication requirements decreased significantly after fludrocortisone initiation. The median sodium bicarbonate dose decreased from 1.2 mEq/kg/day (range, 0.0-4.7) prior to fludrocortisone treatment to 0.0 mEq/kg/day (range, 0.0-4.3) at 6-month follow-up (p < .001). Similarly, the median (SPS) dose decreased from 1.2 g/kg/day (range, 0.0-4.0) before fludrocortisone treatment to 0.0 g/kg/day (range, 0.0-3.6) (p < .001) at 6-month follow-up. The initial mean potassium level 5.17 mmol/L ± 0.61SD dropped to 4.60 mmol/L ± 0.46SD at 6-month follow-up (p < .001). The initial mean serum bicarbonate level 22.31 mmol/L ± 3.67SD increased to 24.5 mmol/L ± 2.8SD at 6-month follow-up (p < .01). No effect on systolic and diastolic blood pressure was observed during follow-up.

CONCLUSION

Hyperkalemic RTA incidence was high in our cohort. Fludrocortisone is safe and effective drug in the treatment of post-kidney transplant hyperkalemic RTA.

Effects of canagliflozin on serum potassium in people with diabetes and chronic kidney disease: the CREDENCE trial

AIMS

Hyperkalaemia is a common complication of type 2 diabetes mellitus (T2DM) and limits the optimal use of agents that block the renin-angiotensin-aldosterone system, particularly in patients with chronic kidney disease (CKD). In patients with CKD, sodium‒glucose cotransporter 2 (SGLT2) inhibitors provide cardiorenal protection, but whether they affect the risk of hyperkalaemia remains uncertain.

METHODS AND RESULTS

The CREDENCE trial randomized 4401 participants with T2DM and CKD to the SGLT2 inhibitor canagliflozin or matching placebo. In this post hoc analysis using an intention-to-treat approach, we assessed the effect of canagliflozin on a composite outcome of time to either investigator-reported hyperkalaemia or the initiation of potassium binders. We also analysed effects on central laboratory-determined hyper- and hypokalaemia (serum potassium ≥6.0 and <3.5 mmol/L, respectively) and change in serum potassium. At baseline, the mean serum potassium in canagliflozin and placebo arms was 4.5 mmol/L; 4395 (99.9%) participants were receiving renin-angiotensin system blockade. The incidence of investigator-reported hyperkalaemia or initiation of potassium binders was lower with canagliflozin than with placebo [occurring in 32.7 vs. 41.9 participants per 1000 patient-years; hazard ratio (HR) 0.78, 95% confidence interval (CI) 0.64-0.95, P = 0.014]. Canagliflozin similarly reduced the incidence of laboratory-determined hyperkalaemia (HR 0.77, 95% CI 0.61-0.98, P = 0.031), with no effect on the risk of hypokalaemia (HR 0.92, 95% CI 0.71-1.20, P = 0.53). The mean serum potassium over time with canagliflozin was similar to that of placebo.

CONCLUSION

Among patients treated with renin-angiotensin-aldosterone system inhibitors, SGLT2 inhibition with canagliflozin may reduce the risk of hyperkalaemia in people with T2DM and CKD without increasing the risk of hypokalaemia.

Potassium Metabolism and Management in Patients with CKD

Potassium (K), the main cation inside cells, plays roles in maintaining cellular osmolarity and acid-base equilibrium, as well as nerve stimulation transmission, and regulation of cardiac and muscle functions. It has also recently been shown that K has an antihypertensive effect by promoting sodium excretion, while it is also attracting attention as an important component that can suppress hypertension associated with excessive sodium intake. Since most ingested K is excreted through the kidneys, decreased renal function is a major factor in increased serum levels, and target values for its intake according to the degree of renal dysfunction have been established. In older individuals with impaired renal function, not only hyperkalemia but also hypokalemia due to anorexia, K loss by dialysis, and effects of various drugs are likely to develop. Thus, it is necessary to pay attention to K management tailored to individual conditions. Since abnormalities in K metabolism can also cause lethal arrhythmia or sudden cardiac death, it is extremely important to monitor patients with a high risk of hyper- or hypokalemia and attempt to provide early and appropriate intervention.

Sodium zirconium cyclosilicate increases serum bicarbonate concentrations among patients with hyperkalaemia: exploratory analyses from three randomized, multi-dose, placebo-controlled trials

BACKGROUND

Sodium zirconium cyclosilicate (SZC) binds potassium and ammonium in the gastrointestinal tract. In addition to serum potassium reduction, Phase 2 trial data have shown increased serum bicarbonate with SZC, which may be clinically beneficial because maintaining serum bicarbonate ≥22 mmol/L preserves kidney function. This exploratory analysis examined serum bicarbonate and urea, and urine pH data from three SZC randomized, placebo-controlled Phase 3 studies among patients with hyperkalaemia [ZS-003 (n = 753), HARMONIZE (n = 258) and HARMONIZE-Global (n = 267)].

METHODS

In all studies, patients received ≤10 g SZC 3 times daily (TID) for 48 h to correct hyperkalaemia, followed by randomization to maintenance therapy with SZC once daily (QD) versus placebo for ≤29 days among those achieving normokalaemia.

RESULTS

Significant dose-dependent mean serum bicarbonate increases from baseline of 0.3 to 1.5 mmol/L occurred within 48 h of SZC TID in ZS-003 (all P < 0.05), which occurred regardless of chronic kidney disease (CKD) stage. Similar acute increases in HARMONIZE and HARMONIZE-Global were maintained over 29 days. With highest SZC maintenance doses, patient proportions with serum bicarbonate <22 mmol/L fell from 39.4% at baseline to 4.9% at 29 days (P = 0.005) in HARMONIZE and from 87.9% to 70.1%, (P = 0.006) in HARMONIZE-Global. Path analyses demonstrated that serum urea decreases (but not serum potassium or urine pH changes) were associated with SZC effects on serum bicarbonate.

CONCLUSIONS

SZC increased serum bicarbonate concentrations and reduced patient proportions with serum bicarbonate <22 mmol/L, likely due to SZC-binding of gastrointestinal ammonium. These SZC-induced serum bicarbonate increases occurred regardless of CKD stage and were sustained during ongoing maintenance therapy.

Familial distal renal tubular acidosis

We report the case of a family in which two sisters have distal renal tubular acidosis (dRTA). Familial dRTA is a rare disorder, with both autosomal dominant and recessive transmission. This is a report of familial dRTA from China.

Cotrimoxazole-induced hyperkalaemia in a patient with known hypoaldosteronism

A70-year-old man, with established hypoadrenalism due to a previous bilateral adrenalectomy, was admitted with recurrent episodes of postural dizziness and presyncope. He had been discharged from hospital 3 weeks earlier on a 1-month course of cotrimoxazole following a diagnosis of prostatitis. His electrolytes on admission showed new onset hyponatraemia and hyperkalaemia.His usual glucocorticoid replacement dose was doubled in view of a presumed diagnosis of hypocortisolaemia. However, the hyperkalaemia persisted. On rereviewing his treatment, we suspected a possible diagnosis of cotrimoxazole-induced hyperkalaemia. Cotrimoxazole was stopped and ciprofloxacin started instead. His fludrocortisone replacement was doubled for 3 days after stopping treatment to decrease his postural symptoms. His postural symptoms improved, his serum potassium decreased to normal levels and he was safely discharged.It is essential to remember that cotrimoxazole, a commonly used antibiotic, can induce a potentially fatal hyperkalaemia especially in patients with known hypoadrenalism.

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.

Type IV RTA in Chronic Adrenal Insufficiency and Concomitant Lisinopril Treatment

Type IV renal tubular acidosis (RTA) is the only RTA characterized by hyperkalemia, and it is caused by a true aldosterone deficiency or renal tubular aldosterone hyporesponsiveness. It is frequent among hospitalized patients as it is related to type 2 diabetes mellitus (T2DM) and common medications such as ACE-inhibitors (ACE-is) and trimethoprim-sulfamethoxazole (TMP-SMX). Drug-induced RTA commonly manifests in patients with predisposing conditions such as mild renal insufficiency and certain pharmacological therapies. ACE-i use and chronic adrenal insufficiency (cAI) are other significant risk factors. Chronic ACTH suppression is thought to induce global adrenal atrophy, including the zona glomerulosa, thus affecting aldosterone secretion as well. Furthermore, in the setting of cAI, treatment with ACE-is further suppresses aldosterone production. This case report describes a patient with cAI secondary to corticosteroid use for years who developed type IV RTA in the setting of lisinopril use. Potassium (K) elevation persisted despite removing underlying conditions and metabolic acidosis correction. The patient required long-term treatment with mineralocorticoids in addition to sodium bicarbonate to maintain normal K levels and acid-base status. Mineralocorticoid administration is a second-line treatment for type IV RTA, but it might be necessary for a subgroup of high-risk patients. In fact, it is important to consider patients with chronic adrenal insufficiency and on ACE-is treatment at increased risk for refractory hyperkalemia in the setting of type IV RTA. Indeed, this subgroup of patients can have severe hypoaldosteronism.

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.

Hyperkalemia: pathophysiology, risk factors and consequences

There have been significant recent advances in our understanding of the mechanisms that maintain potassium homoeostasis and the clinical consequences of hyperkalemia. In this article we discuss these advances within a concise review of the pathophysiology, risk factors and consequences of hyperkalemia. We highlight aspects that are of particular relevance for clinical practice. Hyperkalemia occurs when renal potassium excretion is limited by reductions in glomerular filtration rate, tubular flow, distal sodium delivery or the expression of aldosterone-sensitive ion transporters in the distal nephron. Accordingly, the major risk factors for hyperkalemia are renal failure, diabetes mellitus, adrenal disease and the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers or potassium-sparing diuretics. Hyperkalemia is associated with an increased risk of death, and this is only in part explicable by hyperkalemia-induced cardiac arrhythmia. In addition to its well-established effects on cardiac excitability, hyperkalemia could also contribute to peripheral neuropathy and cause renal tubular acidosis. Hyperkalemia-or the fear of hyperkalemia-contributes to the underprescription of potentially beneficial medications, particularly in heart failure. The newer potassium binders could play a role in attempts to minimize reduced prescribing of renin-angiotensin inhibitors and mineraolocorticoid antagonists in this context.

Mechanisms of Metabolic Acidosis-Induced Kidney Injury in Chronic Kidney Disease

Retrospective analyses and single-center prospective studies identify chronic metabolic acidosis as an independent and modifiable risk factor for progression of CKD. In patients with CKD, untreated chronic metabolic acidosis often leads to an accelerated reduction in GFR. Mechanisms responsible for this reduction include adaptive responses that increase acid excretion but lead to a decline in kidney function. Metabolic acidosis in CKD stimulates production of intrakidney paracrine hormones including angiotensin II, aldosterone, and endothelin-1 (ET-1) that mediate the immediate benefit of increased kidney acid excretion, but their chronic upregulation promotes inflammation and fibrosis. Chronic metabolic acidosis also stimulates ammoniagenesis that increases acid excretion but also leads to ammonia-induced complement activation and deposition of C3 and C5b-9 that can cause tubule-interstitial damage, further worsening disease progression. These effects, along with acid accumulation in kidney tissue, combine to accelerate progression of kidney disease. Treatment of chronic metabolic acidosis attenuates these adaptive responses; reduces levels of angiotensin II, aldosterone, and ET-1; reduces ammoniagenesis; and diminishes inflammation and fibrosis that may lead to slowing of CKD progression.

Defective bicarbonate reabsorption in Kir4.2 potassium channel deficient mice impairs acid-base balance and ammonia excretion

The kidneys excrete the daily acid load mainly by generating and excreting ammonia but the underlying molecular mechanisms are not fully understood. Here we evaluated the role of the inwardly rectifying potassium channel subunit Kir4.2 (Kcnj15 gene product) in this process. In mice, Kir4.2 was present exclusively at the basolateral membrane of proximal tubular cells and disruption of Kcnj15 caused a hyperchloremic metabolic acidosis associated with a reduced threshold for bicarbonate in the absence of a generalized proximal tubule dysfunction. Urinary ammonium excretion rates in Kcnj15- deleted mice were inappropriate to acidosis under basal and acid-loading conditions, and not related to a failure to acidify urine or a reduced expression of ammonia transporters in the collecting duct. In contrast, the expression of key proteins involved in ammonia metabolism and secretion by proximal cells, namely the glutamine transporter SNAT3, the phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase enzymes, and the sodium-proton exchanger NHE-3 was inappropriate in Kcnj15-deleted mice. Additionally, Kcnj15 deletion depolarized the proximal cell membrane by decreasing the barium-sensitive component of the potassium conductance and caused an intracellular alkalinization. Thus, the Kir4.2 potassium channel subunit is a newly recognized regulator of proximal ammonia metabolism. The kidney consequences of its loss of function in mice support the proposal for KCNJ15 as a molecular basis for human isolated proximal renal tubular acidosis.

Renal Tubular Acidosis

Renal tubular acidosis should be suspected in poorly thriving young children with hyperchloremic and hypokalemic normal anion gap metabolic acidosis, with/without syndromic features. Further workup is needed to determine the type of renal tubular acidosis and the presumed etiopathogenesis, which informs treatment choices and prognosis. The risk of nephrolithiasis and calcinosis is linked to the presence (proximal renal tubular acidosis, negligible stone risk) or absence (distal renal tubular acidosis, high stone risk) of urine citrate excretion. New formulations of slow-release alkali and potassium combination supplements are being tested that are expected to simplify treatment and lead to sustained acidosis correction.

Life-threatening Hyperkalemia Associated with Axitinib Treatment in Patients with Recurrent Renal Carcinoma

Axitinib has emerged as a promising antineoplastic agent for the treatment of advanced renal cell carcinoma. Although the administration of axitinib was well-tolerated in clinical trials, the real-world safety and tolerability remain unverified. We herein report a patient with metastatic renal cell carcinoma who suddenly developed life-threatening hyperkalemia following the initiation of axitinib treatment. Although hyperkalemia has been reported with an incidence of <10%, acute severe hyperkalemia may be a considerably critical adverse event of axitinib therapy, especially in patients with risk factors for hyperkalemia. An abundance of caution for unusual and unpredictable toxicities is warranted when using axitinib.

Can ACE-I Be a Silent Killer While Normal Renal Functions Falsely Secure Us?

The current case report represents a warning against serious hyperkalaemia and acidosis induced by ACE-I during surgical stress while normal renal function could deceive the attending anaesthetist. Arterial gas analysis for follow-up of haemoglobin loss accidentally discovered hyperkalaemia and acidosis. Glucose-insulin and furosemide successfully corrected hyperkalaemia after 25 minutes and acidosis after 3 hours. These complications could be explained by a deficient steroid stress response to surgery secondary to suppression by ACE-I. Event analysis and database search found that ACE-I induced aldosterone deficiency aggravated by surgical stress response with an inadequate increase in aldosterone secretion due to angiotensin II deficiency as a sequel of ACE-I leading to defective secretion of H+ and K+. Furosemide is recommended to secrete H+ and K+ compensating for aldosterone deficiency in addition to other antihyperkalaemia measures. Anaesthetising an ACE-I treated patient requires considering ACE-I as a potential cause of hyperkalaemia and acidosis.

A physiology-based approach to a patient with hyperkalemic renal tubular acidosis

Hyperkalemic renal tubular acidosis is a non-anion gap metabolic acidosis that invariably indicates an abnormality in potassium, ammonium, and hydrogen ion secretion. In clinical practice, it is usually attributed to real or apparent hypoaldosteronism caused by diseases or drug toxicity. We describe a 54-year-old liver transplant patient that was admitted with flaccid muscle weakness associated with plasma potassium level of 9.25 mEq/L. Additional investigation revealed type 4 renal tubular acidosis and marked hypomagnesemia with high fractional excretion of magnesium. Relevant past medical history included a recent diagnosis of Paracoccidioidomycosis, a systemic fungal infection that is endemic in some parts of South America, and his outpatient medications contained trimethoprim-sulfamethoxazole, tacrolimus, and propranolol. In the present acid-base and electrolyte case study, we discuss a clinical approach for the diagnosis of hyperkalemic renal tubular acidosis and review the pathophysiology of this disorder.

Renal Tubular Acidosis: H+/Base and Ammonia Transport Abnormalities and Clinical Syndromes

Renal tubular acidosis (RTA) represents a group of diseases characterized by (1) a normal anion gap metabolic acidosis; (2) abnormalities in renal HCO3- absorption or new renal HCO3- generation; (3) changes in renal NH4+, Ca2+, K+, and H2O homeostasis; and (4) extrarenal manifestations that provide etiologic diagnostic clues. The focus of this review is to give a general overview of the pathogenesis of the various clinical syndromes causing RTA with a particular emphasis on type I (hypokalemic distal RTA) and type II (proximal) RTA while reviewing their pathogenesis from a physiological "bottom-up" approach. In addition, the factors involved in the generation of metabolic acidosis in both type I and II RTA are reviewed highlighting the importance of altered renal ammonia production/partitioning and new HCO3- generation. Our understanding of the underlying tubular transport and extrarenal abnormalities has significantly improved since the first recognition of RTA as a clinical entity because of significant advances in clinical acid-base chemistry, whole tubule and single-cell H+/base transport, and the molecular characterization of the various transporters and channels that are functionally affected in patients with RTA. Despite these advances, additional studies are needed to address the underlying mechanisms involved in hypokalemia, altered ammonia production/partitioning, hypercalciuria, nephrocalcinosis, cystic abnormalities, and CKD progression in these patients.

Mechanism of Hyperkalemia-Induced Metabolic Acidosis

Background Hyperkalemia in association with metabolic acidosis that are out of proportion to changes in glomerular filtration rate defines type 4 renal tubular acidosis (RTA), the most common RTA observed, but the molecular mechanisms underlying the associated metabolic acidosis are incompletely understood. We sought to determine whether hyperkalemia directly causes metabolic acidosis and, if so, the mechanisms through which this occurs.Methods We studied a genetic model of hyperkalemia that results from early distal convoluted tubule (DCT)-specific overexpression of constitutively active Ste20/SPS1-related proline-alanine-rich kinase (DCT-CA-SPAK).Results DCT-CA-SPAK mice developed hyperkalemia in association with metabolic acidosis and suppressed ammonia excretion; however, titratable acid excretion and urine pH were unchanged compared with those in wild-type mice. Abnormal ammonia excretion in DCT-CA-SPAK mice associated with decreased proximal tubule expression of the ammonia-generating enzymes phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase and overexpression of the ammonia-recycling enzyme glutamine synthetase. These mice also had decreased expression of the ammonia transporter family member Rhcg and decreased apical polarization of H⁺-ATPase in the inner stripe of the outer medullary collecting duct. Correcting the hyperkalemia by treatment with hydrochlorothiazide corrected the metabolic acidosis, increased ammonia excretion, and normalized ammoniagenic enzyme and Rhcg expression in DCT-CA-SPAK mice. In wild-type mice, induction of hyperkalemia by administration of the epithelial sodium channel blocker benzamil caused hyperkalemia and suppressed ammonia excretion.Conclusions Hyperkalemia decreases proximal tubule ammonia generation and collecting duct ammonia transport, leading to impaired ammonia excretion that causes metabolic acidosis.

Distal renal tubular acidosis in a Libyan patient: Evidence for digenic inheritance

AIM OF THE STUDY

Recent advances in understanding the underlying molecular mechanism for distal renal tubular acidosis (dRTA), led to an increased attention towards the primary and the familial forms of the disease. Mutations in ATP6V1B1 and ATP6V0A4 are usually responsible for the recessive form of the disease. Mutations in gene AE1 encoding the Cl-/HCO3- exchanger, usually present as dominant dRTA, but a recessive pattern has been recently described. Our objective is to identify the mutational spectrum responsible of dRTA in a consanguineous Libyan family.

MATERIALS AND METHODS

Both ATP6V0A4 and ATP6V1B1 genes were preferentially screened in our patient. Additional whole exome sequencing (WES) in the same patient, offered a wider view on potential chromosomal rearrangements as well as the mutational spectrum of other genes involved in this disease.

RESULTS

The patient is a heterozygote for two different mutations, one in each of the genes ATP6V0A4 and ATP6V1B1, while no deleterious variation was detected in the remaining genes responsible for the recessive form of dRTA. Homozygosity mapping and WES confirmed our findings and supported the hypothesis of a digenic inheritance model existing as an explanation for dRTA.

CONCLUSIONS

To our knowledge, this is the first report describing a Libyan patient with dRTA who suffered from early-onset sensorineural hearing loss, with a digenic mode of inheritance, supported by the identification of two novel mutations. This study increases the understanding of how dRTA is genetically transmitted, while offers a good outline towards the molecular diagnostics and genetic counseling for dRTA in Lybians.

Tacrolimus-Induced Type IV Renal Tubular Acidosis following Liver Transplantation

Calcineurin inhibitors remain an integral component of immunosuppressive therapy regimens following solid organ transplantation. Although nephrotoxicity associated with these agents is well documented, type IV renal tubular acidosis is a rare and potentially underreported complication following liver transplantation. Hepatologists must be able to recognize this adverse effect as it can lead to fatal hyperkalemia. We describe a case of tacrolimus-induced hyperkalemic type IV renal tubular acidosis in a patient following an orthotopic liver transplant for alcoholic cirrhosis.

Transient pseudohypoaldosteronism in infancy secondary to urinary tract infection

AIM

Hyponatraemia with hyperkalaemia in infancy is a typical presentation of congenital adrenal hyperplasia. In the presence of pyelonephritis, the same biochemical picture can occur with transient type 1 pseudohypoaldosteronism (PHA-1) also termed type 4 renal tubular acidosis. Recognition of PHA-1 enables appropriate management thus avoiding unnecessary investigations and treatment. To improve awareness of this condition, we present a case series to highlight the clinical and biochemical features of PHA-1.

METHODS

A retrospective chart review of patients diagnosed with transient PHA-1 at a tertiary children's hospital in Western Australia was conducted.

RESULTS

Five male infants (32 days to 6 months) with transient PHA-1 were identified. Failure to thrive was the most common symptom with hyponatraemia on presentation. Two infants had antenatally diagnosed bilateral hydronephrosis and urinary tract infection (UTI) on admission. Two infants were treated for congenital adrenal hyperplasia and received hydrocortisone. All infants had UTI and required parenteral antibiotics. The condition was transient and hyponatraemia corrected by day 4 in all infants. There was no correlation between plasma sodium and aldosterone levels. The severity of PHA-1 was independent of the underlying renal anomaly. Four infants had hydronephrosis and vesicoureteric reflux. Surgical intervention was required in two infants.

CONCLUSIONS

PHA-1 may be precipitated by UTI or urinary tract anomalies in early infancy. Urine analysis should be performed in infants with hyponatraemia. Diagnosis of PHA-1 facilitates appropriate renal investigations to reduce long-term morbidity.

Role of Acid-Base Homeostasis in Diabetic Kidney Disease

PURPOSE OF REVIEW

Acid-base homeostasis is impaired in chronic kidney disease (CKD) and may contribute to disease progression. Diabetes, a major cause of CKD worldwide, may exacerbate acidosis further due to differences in acid production and excretion. Here, we review the role of abnormal acid-base homeostasis in the pathogenesis and progression of diabetes and diabetic kidney disease.

RECENT FINDINGS

Acidosis and dietary acid loading may contribute to the development and worsening of insulin resistance and hypertension, thereby promoting diabetes and diabetic CKD. However, although metabolic acidosis associates with progression of CKD generally, the results in diabetic CKD are mixed. Data suggests that metabolic acid production in diabetes may be higher than would be predicted based on dietary intake alone, and new observational data suggests that this higher diet-independent acid production could potentially be protective. The role of acid-base homeostasis in diabetic CKD progression is complex and must consider differences in endogenous acid production and excretion in diabetes. Ongoing observational and interventional studies in this field should consider the unique physiology of diabetes.

Ammonia Transporters and Their Role in Acid-Base Balance

Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH₃ and NH₄⁺, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.