Alkali supplementation as a therapeutic in chronic kidney disease: what mediates protection?

Metabolic acidosis in chronic kidney disease: mere consequence or also culprit?

Metabolic acidosis is a frequent complication in non-transplant chronic kidney disease (CKD) and after kidney transplantation. It occurs when net endogenous acid production exceeds net acid excretion. While nephron loss with reduced ammoniagenesis is the main cause of acid retention in non-transplant CKD patients, additional pathophysiological mechanisms are likely inflicted in kidney transplant recipients. Functional tubular damage by calcineurin inhibitors seems to play a key role causing renal tubular acidosis. Notably, experimental and clinical studies over the past decades have provided evidence that metabolic acidosis may not only be a consequence of CKD but also a driver of disease. In metabolic acidosis, activation of hormonal systems and the complement system resulting in fibrosis have been described. Further studies of changes in renal metabolism will likely contribute to a deeper understanding of the pathophysiology of metabolic acidosis in CKD. While alkali supplementation in case of reduced serum bicarbonate < 22 mmol/l has been endorsed by CKD guidelines for many years to slow renal functional decline, among other considerations, beneficial effects and thresholds for treatment have lately been under intense debate. This review article discusses this topic in light of the most recent results of trials assessing the efficacy of dietary and pharmacological interventions in CKD and kidney transplant patients.

NaHCO3 loading causes increased arterial pressure and kidney damage in rats with chronic kidney disease

Sodium bicarbonate (NaHCO3) is commonly utilized as a therapeutic to treat metabolic acidosis in people with chronic kidney disease (CKD). While increased dietary sodium chloride (NaCl) is known to promote volume retention and increase blood pressure, the effects of NaHCO3 loading on blood pressure and volume retention in CKD remain unclear. In the present study, we compared the effects of NaCl and NaHCO3 loading on volume retention, blood pressure, and kidney injury in both 2/3 and 5/6 nephrectomy remnant kidney rats, a well-established rodent model of CKD. We tested the hypothesis that NaCl loading promotes greater volume retention and increases in blood pressure than equimolar NaHCO3. Blood pressure was measured 24 h daily using radio telemetry. NaCl and NaHCO3 were administered in drinking water ad libitum or infused via indwelling catheters. Rats were housed in metabolic cages to determine volume retention. Our data indicate that both NaHCO3 and NaCl promote hypertension and volume retention in remnant kidney rats, with salt-sensitivity increasing with greater renal mass reduction. Importantly, while NaHCO3 intake was less pro-hypertensive than equimolar NaCl intake, NaHCO3 was not benign. NaHCO3 loading significantly elevated blood pressure and promoted volume retention in rats with CKD when compared with control rats receiving tap water. Our findings provide important insight into the effects of sodium loading with NaHCO3 in CKD and indicate that NaHCO3 loading in patients with CKD is unlikely to be benign.

Effect of sodium bicarbonate on cardiovascular outcome and mortality in patients with advanced chronic kidney disease

Background: Metabolic acidosis is a common complication in patients with chronic kidney disease (CKD). Oral sodium bicarbonate is often used to treat metabolic acidosis and prevent CKD progression. However, there is limited information about the effect of sodium bicarbonate on major adverse cardiovascular events (MACE) and mortality in patients with pre-dialysis advanced CKD. Method: 25599 patients with CKD stage V between January 1, 2001 and December 31, 2019 were identified from the Chang Gung Research Database (CGRD), a multi-institutional electronic medical record database in Taiwan. The exposure was defined as receiving sodium bicarbonate or not. Baseline characteristics were balanced using propensity score weighting between two groups. Primary outcomes were dialysis initiation, all-cause mortality, and major adverse cardiovascular events (MACE) (myocardial infarction, heart failure, stroke). The risks of dialysis, MACE, and mortality were compared between two groups using Cox proportional hazards models. In addition, we performed analyzes using Fine and Gray sub-distribution hazard models that considered death as a competing risk. Result: Among 25599 patients with CKD stage V, 5084 patients (19.9%) were sodium bicarbonate users while 20515 (80.1%) were sodium bicarbonate non-users. The groups had similar risk of dialysis initiation (hazard ratio (HR): 0.98, 95% confidence interval (CI): 0.95-1.02, p < 0.379). However, taking sodium bicarbonate was associated with a significantly lower risks of MACE (HR: 0.95, 95% CI 0.92-0.98, p < 0.001) and hospitalizations for acute pulmonary edema (HR: 0.92, 95% CI 0.88-0.96, p < 0.001) compared with non-users. The mortality risks were significantly lower in sodium bicarbonate users compared with sodium bicarbonate non-users (HR: 0.75, 95% CI 0.74-0.77, p < 0.001). Conclusion: This cohort study revealed that in real world practice, use of sodium bicarbonate was associated with similar risk of dialysis compared with non-users among patients with advanced CKD stage V. Nonetheless, use of sodium bicarbonate was associated with significantly lower rate of MACE and mortality. Findings reinforce the benefits of sodium bicarbonate therapy in the expanding CKD population. Further prospective studies are needed to confirm these findings.

The mechanisms of alkali therapy in targeting renal diseases

Chronic kidney disease (CKD) is characterized by progressive reduction in kidney function and treatments aiming at stabilizing or slowing its progression may avoid or delay the necessity of kidney replacement therapy and the increased mortality associated with reduced kidney function. Metabolic acidosis, and less severe stages of the acid stress continuum, are common consequences of CKD and some interventional studies support that its correction slows the progression to end-stage kidney disease. This correction can be achieved with mineral alkali in the form of bicarbonate or citrate salts, ingestion of diets with fewer acid-producing food components or more base-producing food components, or a pharmacological approach. In this mini-review article, we summarize the potential mechanisms involved in the beneficial effects of alkali therapy. We also discuss the perspectives in the field and challenges that must be overcome to advance our understanding of such mechanisms.

New mechanisms for the kidney-protective effect of alkali in chronic kidney disease

Worldwide, more than one in ten adults are estimated to have chronic kidney disease (CKD). As CKD progresses, both the cost of treatment and associated risk of morbidity and mortality increase exponentially. As such, there is a great need for therapies that effectively slow CKD progression. Evidence from several small clinical trials indicates that alkali therapy may slow the rate of CKD progression. The biological mechanisms underlying this protective effect, however, remain unknown. In their recently published manuscript, Pastor Arroyo et al. (Clin Sci (Lond) (2022) 136(8): https://doi.org/10.1042/CS20220095) demonstrate that the alkali sodium bicarbonate protects against loss of renal function in a crystal nephropathy model in mice. Using unbiased approaches in both mice and human tissue, the authors go on to identify two novel mechanisms that may underly this protection. The first pathway is through promoting pathways of cell metabolism, which they speculate helps the remaining functional nephrons adapt to the greater metabolic needs required to maintain kidney filtration. The second pathway is by restoration of α-Klotho levels, which may limit the expression of adhesion molecules in the injured kidney. This, the authors speculate, may prevent inflammation from driving the functional decline of the kidney. Identifying these novel pathways represents an important step forward harnessing the potential benefits of alkali therapy in CKD.

Adherence to multidisciplinary care in a prospective chronic kidney disease cohort is associated with better outcomes

INTRODUCTION

The Renal Healthcare Program Uruguay (NRHP-UY) is a national, multidisciplinary program that provides care to chronic kidney disease (CKD) patients. In this study, we report the global results of CKD patient outcomes and a comparison between those treated at the NRHP-UY Units, with those patients who were initially included in the program but did not adhere to follow up.

METHODS

A cohort of not-on dialysis CKD patients included prospectively in the NRHP-UY between October 1st 2004 and September 30th 2017 was followed-up until September 30th 2019. Two groups were compared: a) Nephrocare Group: Patients who had at least one clinic visit during the first year on NRHP-UY (n = 11174) and b) Non-adherent Group: Patients who were informed and accepted to be included but had no subsequent data registered after admission (n = 3485). The study was approved by the Ethics Committee and all patients signed an informed consent. Outcomes were studied with Logistic and Cox´s regression analysis, Fine and Gray competitive risk and propensity-score matching tests.

RESULTS

14659 patients were analyzed, median age 70 (60-77) years, 56.9% male. The Nephrocare Group showed improved achievement of therapeutic goals, ESKD was more frequent (HR 2.081, CI 95%1.722-2.514) as planned kidney replacement therapy (KRT) start (OR 2.494, CI95% 1.591-3.910), but mortality and the combined event (death and ESKD) were less frequent (HR 0.671, CI95% 0.628-0.717 and 0.777, CI95% 0.731-0.827) (p = 0.000) compared to the Non-adherent group. Results were similar in the propensity-matched group: ESKD (HR 2.041, CI95% 1.643-2.534); planned kidney replacement therapy (KRT) start (OR 2.191, CI95% 1.322-3.631) death (HR 0.692, CI95% 0.637-0.753); combined event (HR 0.801, CI95% 0.742-0.865) (p = 0.000).

CONCLUSION

Multidisciplinary care within the NRHP-UY is associated with timely initiation of KRT and lower mortality in single outcomes, combined analysis, and propensity-matched analysis.

Alkali therapy protects renal function, suppresses inflammation, and improves cellular metabolism in kidney disease

Chronic kidney disease (CKD) affects about 10-13 % of the population worldwide and halting its progression is a major clinical challenge. Metabolic acidosis is both a consequence and a possible driver of CKD progression. Alkali therapy counteracts these effects in CKD patients, but underlying mechanisms remain incompletely understood. Here we show that bicarbonate supplementation protected renal function in a murine CKD model induced by an oxalate-rich diet. Alkali therapy had no effect on the aldosterone-endothelin axis but promoted levels of the anti-aging protein klotho; moreover, it suppressed adhesion molecules required for immune cell invasion along with reducing T helper cell and inflammatory monocyte invasion. Comparing transcriptomes from the murine crystallopathy model and from human biopsies of kidney transplant recipients suffering from acidosis with or without alkali therapy unveils parallel transcriptome responses mainly associated with lipid metabolism and oxidoreductase activity. Our data reveal novel pathways associated with acidosis in kidney disease and sensitive to alkali therapy and identifies potential targets through which alkali therapy may act on CKD and that may be amenable for more targeted therapies.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

Effects of oral alkali drug therapy on clinical outcomes in pre-dialysis chronic kidney disease patients: a systematic review and meta-analysis

BACKGROUND

Metabolic acidosis accelerates the progression of chronic kidney disease (CKD) and increases the mortality rate. Whether oral alkali drug therapy benefits pre-dialysis CKD patients is controversial. We performed a meta-analysis of the effects of oral alkali drug therapy on major clinical outcomes in pre-dialysis CKD patients.

METHODS

We systematically searched MEDLINE using the Ovid, EMBASE, and Cochrane Library databases without language restriction. We included all eligible clinical studies that involved pre-dialysis CKD adults and compared those who received oral alkali drug therapy with controls.

RESULTS

A total of 18 eligible studies, including 14 randomized controlled trials and 4 cohort studies reported in 19 publications with 3695 participants, were included. Oral alkali drug therapy led to a 55% reduction in renal failure events (relative risk [RR]: 0.45; 95% confidence interval [CI]: 0.25-0.82), a rate of decline in the estimated glomerular filtration rate (eGFR) of 2.59 mL/min/1.73 m² per year (95% CI, 0.88-4.31). There was no significant effect on decline in eGFR events (RR: 0.34; 95% CI: 0.09-1.23), proteinuria (standardized mean difference: -0.32; 95% CI: -1.08 to 0.43), all-cause mortality events (RR: 0.90; 95% CI: 0.40-2.02) and cardiovascular (CV) events (RR: 1.03; 95% CI: 0.32-3.37) compared with the control groups.

CONCLUSION

Based on the available and low-to-moderate certainty evidence, oral alkali drug therapy might potentially reduce the risk of kidney failure events, but no benefit in reducing all-cause mortality events, CV events, decline in eGFR and porteninuria.

Acid-base effects of combined renal deletion of NBCe1-A and NBCe1-B

The molecular mechanisms regulating ammonia metabolism are fundamental to acid-base homeostasis. Deletion of the A splice variant of Na+-bicarbonate cotransporter, electrogenic, isoform 1 (NBCe1-A) partially blocks the effect of acidosis to increase urinary ammonia excretion, and this appears to involve the dysregulated expression of ammoniagenic enzymes in the proximal tubule (PT) in the cortex but not in the outer medulla (OM). A second NBCe1 splice variant, NBCe1-B, is present throughout the PT, including the OM, where NBCe1-A is not present. The purpose of the present study was to determine the effect of combined renal deletion of NBCe1-A and NBCe1-B on systemic and PT ammonia metabolism. We generated NBCe1-A/B deletion using Cre-loxP techniques and used Cre-negative mice as controls. As renal NBCe1-A and NBCe1-B expression is limited to the PT, Cre-positive mice had PT NBCe1-A/B deletion [PT-NBCe1-A/B knockout (KO)]. Although on a basal diet, PT-NBCe1-A/B KO mice had severe metabolic acidosis, yet urinary ammonia excretion was not changed significantly. PT-NBCe1-A/B KO decreased the expression of phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase and increased the expression of glutamine synthetase, an ammonia-recycling enzyme, in PTs in both the cortex and OM. Exogenous acid loading increased ammonia excretion in control mice, but PT-NBCe1-A/B KO prevented any increase. PT-NBCe1-A/B KO significantly blunted acid loading-induced changes in phosphate-dependent glutaminase, phosphoenolpyruvate carboxykinase, and glutamine synthetase expression in PTs in both the cortex and OM. We conclude that NBCe1-B, at least in the presence of NBCe1-A deletion, contributes to PT ammonia metabolism in the OM and thereby to systemic acid-base regulation.NEW & NOTEWORTHY The results of the present study show that combined deletion of both A and B splice variants of electrogenic Na+-bicarbonate cotransporter 1 from the proximal tubule impairs acid-base homeostasis and completely blocks changes in ammonia excretion in response to acidosis, indicating that both proteins are critical to acid-base homeostasis.

The Effects of Oral Sodium Bicarbonate on Renal Function and Cardiovascular Risk in Patients with Chronic Kidney Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

Oral sodium bicarbonate is often used to correct acid-base disturbance in patients with chronic kidney disease (CKD). However, there is little evidence on patient-level benign outcomes to support the practice.

METHODS

We conducted a systematic review and meta-analysis to examine the efficacy and safety of oral sodium bicarbonate in CKD patients. A total of 1853 patients with chronic metabolic acidosis or those with low-normal serum bicarbonate (22-24 mEq/L) were performed to compare the efficacy and safety of oral sodium bicarbonate in patients with CKD.

RESULTS

There was a significant increase in serum bicarbonate level (MD 2.37 mEq/L; 95% CI, 1.03 to 3.72) and slowed the decline in estimated glomerular filtration rate (eGFR) (MD -4.44 mL/min per 1.73 m2, 95% CI, -4.92 to -3.96) compared with the control groups. The sodium bicarbonate lowered T50-time, an indicator of vascular calcification (MD -20.74 min; 95% CI, -49.55 to 8.08); however, there was no significant difference between the two groups. In addition, oral sodium bicarbonate dramatically reduced systolic blood pressure (MD -2.97 mmHg; 95% CI, -5.04 to -0.90) and diastolic blood pressure (MD -1.26 mmHg; 95% CI, -2.33 to -0.19). There were no statistically significant body weight, urine pH and mean mid-arm muscle circumference.

CONCLUSION

Treatment of metabolic acidosis with sodium bicarbonate may slow the decline rate of kidney function and potentially significantly improve vascular endothelial function in patients with CKD.

PROSPERO REGISTRATION NUMBER

CRD42020207185.

Acidosis, cognitive dysfunction and motor impairments in patients with kidney disease

Metabolic acidosis, defined as a plasma or serum bicarbonate concentration <22 mmol/L, is a frequent consequence of chronic kidney disease (CKD) and occurs in ~10–30% of patients with advanced stages of CKD. Likewise, in patients with a kidney transplant, prevalence rates of metabolic acidosis range from 20% to 50%. CKD has recently been associated with cognitive dysfunction, including mild cognitive impairment with memory and attention deficits, reduced executive functions and morphological damage detectable with imaging. Also, impaired motor functions and loss of muscle strength are often found in patients with advanced CKD, which in part may be attributed to altered central nervous system (CNS) functions. While the exact mechanisms of how CKD may cause cognitive dysfunction and reduced motor functions are still debated, recent data point towards the possibility that acidosis is one modifiable contributor to cognitive dysfunction. This review summarizes recent evidence for an association between acidosis and cognitive dysfunction in patients with CKD and discusses potential mechanisms by which acidosis may impact CNS functions. The review also identifies important open questions to be answered to improve prevention and therapy of cognitive dysfunction in the setting of metabolic acidosis in patients with CKD.

A Role for SGLT-2 Inhibitors in Treating Non-diabetic Chronic Kidney Disease

In recent years, inhibitors of the sodium-glucose co-transporter 2 (SGLT2 inhibitors) have been shown to have significant protective effects on the kidney and the cardiovascular system in patients with diabetes. This effect is also manifested in chronic kidney disease (CKD) patients and is minimally due to improved glycaemic control. Starting from these positive findings, SGLT2 inhibitors have also been tested in patients with non-diabetic CKD or heart failure with reduced ejection fraction. Recently, the DAPA-CKD trial showed a significantly lower risk of CKD progression or death from renal or cardiovascular causes in a mixed population of patients with diabetic and non-diabetic CKD receiving dapagliflozin in comparison with placebo. In patients with heart failure and reduced ejection fraction, two trials (EMPEROR-Reduced and DAPA-HF) also found a significantly lower risk of reaching the secondary renal endpoint in those treated with an SGLT2 inhibitor in comparison with placebo. This also applied to patients with CKD. Apart from their direct mechanism of action, SGLT2 inhibitors have additional effects that could be of particular interest for patients with non-diabetic CKD. Among these, SGLT2 inhibitors reduce blood pressure and serum acid uric levels and can increase hemoglobin levels. Some safety issues should be further explored in the CKD population. SGLT2 inhibitors can minimally increase potassium levels, but this has not been shown by the CREDENCE trial. They also increase magnesium and phosphate reabsorption. These effects could become more significant in patients with advanced CKD and will need monitoring when these agents are used more extensively in the CKD population. Conversely, they do not seem to increase the risk of acute kidney injury.

Hyperkalemia in Chronic Kidney Disease in the New Era of Kidney Protection Therapies

Despite recent therapeutic advances, chronic kidney disease (CKD) is one of the fastest growing global causes of death. This illustrates limitations of current therapeutic approaches and, potentially, unidentified knowledge gaps. For decades, renin-angiotensin-aldosterone system (RAAS) blockers have been the mainstay of therapy for CKD. However, they favor the development of hyperkalemia, which is already common in CKD patients due to the CKD-associated decrease in urinary potassium (K⁺) excretion and metabolic acidosis. Hyperkalemia may itself be life-threatening as it may trigger potentially lethal arrhythmia, and additionally may limit the prescription of RAAS blockers and lead to low-K⁺ diets associated to low dietary fiber intake. Indeed, hyperkalemia is associated with adverse kidney, cardiovascular, and survival outcomes. Recently, novel kidney protective therapies, ranging from sodium/glucose cotransporter 2 (SGLT2) inhibitors to new mineralocorticoid receptor antagonists have shown efficacy in clinical trials. Herein, we review K⁺ pathophysiology and the clinical impact and management of hyperkalemia considering these developments and the availability of the novel K⁺ binders patiromer and sodium zirconium cyclosilicate, recent results from clinical trials targeting metabolic acidosis (sodium bicarbonate, veverimer), and an increasing understanding of the role of the gut microbiota in health and disease.

Acidosis and alkali therapy in patients with kidney transplant is associated with transcriptional changes and altered abundance of genes involved in cell metabolism and acid-base balance

BACKGROUND

Metabolic acidosis occurs frequently in patients with kidney transplant and is associated with higher risk for and accelerated loss of graft function. To date, it is not known whether alkali therapy in these patients improves kidney function and whether acidosis and its therapy is associated with altered expression of proteins involved in renal acid-base metabolism.

METHODS

We collected retrospectively kidney biopsies from 22 patients. Of these patients, 9 had no acidosis, 9 had metabolic acidosis (plasma HCO3- < 22 mmol/l), and 4 had acidosis and received alkali therapy. We performed transcriptome analysis and immunohistochemistry for proteins involved in renal acid-base handling.

RESULTS

We found the expression of 40 transcripts significantly changed between kidneys from non-acidotic and acidotic patients. These genes are mostly involved in proximal tubule amino acid and lipid metabolism and energy homeostasis. Three transcripts were fully recovered by alkali therapy: the Kir4.2 K+-channel, an important regulator of proximal tubule HCO3--metabolism and transport, ACADSB and SHMT1, genes involved in beta-oxidation and methionine metabolism. Immunohistochemistry showed reduced staining for the proximal tubule NBCe1 HCO3- transporter in kidneys from acidotic patients that recovered with alkali therapy. In addition, the HCO3-exchanger pendrin was affected by acidosis and alkali therapy.

CONCLUSIONS

Metabolic acidosis in kidney transplant recipients is associated with alterations in the renal transcriptome that are partly restored by alkali therapy. Acid-base transport proteins mostly from proximal tubule were also affected by acidosis and alkali therapy suggesting that the downregulation of critical players contributes to metabolic acidosis in these patients.

Update on Treatment of Hypertension After Renal Transplantation

PURPOSE OF REVIEW

To incorporate novel findings on pathophysiology and treatment of posttransplant hypertension.

RECENT FINDINGS

(1) The sodium retaining effects of CNIs are mediated by stimulation of the thiazide-sensitive sodium chloride co-transporter in the distal convoluted tubule and in this regard chlorthalidone was proven to be an effective antihypertensive drug in renal transplantation. (2) Local and not systemic activation of the renin-angiotensin-aldosterone system plays a crucial role in the pathogenesis of posttransplant hypertension. (3) Recent randomized controlled trials failed to prove the presumed superiority of renin-angiotensin blockers in kidney transplantation. (4) Steroid-free and mammalian target of rapamycin-based immunosuppressive drug combinations did not show favorable effects on blood pressure control. (5) In a recent report the risk of non-melanoma skin cancer was higher with thiazide diuretics. But the increased cancer risk in transplant recipients is mainly attributed to comorbidities, such as diabetes and hypertension and of course to the transplantation condition itself or the obligatory application of immunosuppression, and has little to do with the antihypertensive medication Actual recommendations about BP targets in adult renal transplant recipients are coming from a post hoc analysis of a large randomized trial with another primary endpoint. Unless convincing studies on treatment of hypertension after renal transplantation are available, the ESC/ESH Guidelines 2018 should apply for these patients.