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

Intrarenal pH-Responsive Self-Assembly of Luminescent Gold Nanoparticles for Diagnosis of Early Kidney Injury

Metabolic acidosis-induced kidney injury (MAKI) is asymptomatic and lack of clinical biomarkers in early stage, but rapidly progresses to severe renal fibrosis and ultimately results in end-stage kidney failure. Therefore, developing rapid and noninvasive strategies direct responsive to renal tubular acidic microenvironment rather than delayed biomarkers are essential for timely renoprotective interventions. Herein, we develop pH-responsive luminescent gold nanoparticles (p-AuNPs) in the second near-infrared emission co-coated with 2,3-dimethylaleic anhydride conjugated β-mercaptoethylamine and cationic 2-diethylaminoethanethiol hydrochloride, which showed sensitive pH-induced charge reversal and intrarenal self-assembly for highly sensitive and long-time (~24 h) imaging of different stages of MAKI. By integrating advantages of pH-induced intrarenal self-assembly and enhanced interactions between pH-triggered positively charged p-AuNPs and renal tubular cells, the early- and late-stage MAKI could be differentiated rapidly within 10 min post-injection (p.i.) with contrast index (CI) of 3.5 and 4.3, respectively. The corresponding maximum CI could reach 5.1 and 9.2 at 12 h p.i., respectively. Furthermore, p-AuNPs were demonstrated to effectively real-time monitor progressive recovery of kidney injury in MAKI mice after therapy, and also exhibit outstanding capabilities for drug screening. This pH-responsive strategy showed great promise for feedback on kidney dysfunction progression, opening new possibilities for early-stage diagnosis of pH-related diseases.

Association between serum chloride levels and estimated glomerular filtration rate among US adults: evidence from NHANES 1999-2018

PURPOSE

Chloride, the predominant anion in extracellular fluid from humans, is essential to maintaining homeostasis. One important metric for thoroughly assessing kidney function is the estimated glomerular filtration rate (eGFR). However, the relationship between variations in serum chloride concentration and eGFR in general populations has been poorly studied. Therefore, the purpose of this study is to elucidate the correlation between serum chloride levels and eGFR within the United States' adult population.

METHODS

This cohort study was conducted using data from the National Health and Nutrition Examination Survey (NHANES), which covered the years 1999-2018. We employed multiple linear regression analysis and subgroup analysis to evaluate the correlation between serum chloride concentration and eGFR. To examine the nonlinear association between serum chloride levels and eGFR, restricted cubic spline analyses were employed.

RESULTS

Data from 49,008 participants in this cohort study were used for the chloride analysis. In the comprehensively adjusted model, a noteworthy inverse relationship was discovered between chloride plasma concentration and eGFR. Restricted cubic spline analyses revealed a significant nonlinear relationship between chloride levels and eGFR (P for overall < 0.001 and P for nonlinear < 0.001). A significant interaction was observed between eGFR and plasma chloride concentration (all P < 0.001 for interaction) among the subgroups characterized by sex, household income to poverty ratio, BMI, hypertension, and diabetes.

CONCLUSION

Our findings suggest that higher levels of chloride plasma concentration were linked to decreased eGFR. These findings underscore the significance of monitoring chloride plasma concentration as a potential indicator for identifying individuals at risk of developing chronic kidney disease (CKD).

Metabolic Acidosis Is Associated With an Accelerated Decline of Allograft Function in Pediatric Kidney Transplantation

Introduction

We investigated the relationship between metabolic acidosis over time and allograft outcome in pediatric kidney transplantation (KTx).

Methods

This registry study collected data up to 10 years posttransplant. Survival analysis for a composite end point of graft loss or estimated glomerular filtration rate (eGFR) ≤ 30 ml/min per 1.73 m2 or ≥50% decline from eGFR at month 3 posttransplant was performed. The association of serum bicarbonate concentration (HCO3 -) < 22 mmol/l (metabolic acidosis) and HCO3 - < 18 mmol/l (severe metabolic acidosis) with allograft outcome was investigated using stratified Cox models and marginal structural models. Secondary analyses included the identification of risk factors for metabolic acidosis and the relationship between alkali supplementation and allograft outcome.

Results

We report on 1911 patients, of whom 347 reached the composite end point. The prevalence of metabolic acidosis over time ranged from 20.4% to 38.9%. In the adjusted Cox models, metabolic acidosis (hazard ratio [HR], 2.00; 95% confidence interval [CI], 1.54-2.60) and severe metabolic acidosis (HR, 2.49; 95% CI, 1.56-3.99) were associated with allograft dysfunction. Marginal structural models showed similar results (HR, 1.75; 95% CI, 1.32-2.31 and HR, 2.09; 95% CI, 1.23-3.55, respectively). Older age was associated with a lower risk of metabolic acidosis (odds ratio [OR] 0.93/yr older; 95% CI, 0.91-0.96) and severe metabolic acidosis (OR, 0.89; 95% CI, 0.84-0.95). Patients with uncontrolled metabolic acidosis had the worst outcome compared to those without metabolic acidosis and without alkali (HR, 3.70; 95% CI, 2.54-5.40).

Conclusion

The degree of metabolic acidosis is associated with allograft dysfunction.

Sex-specific Stone-forming Phenotype in Mice During Hypercalciuria/Urine Alkalinization

Sex differences in kidney stone formation are well known. Females generally have slightly acidic blood and higher urine pH when compared with males, which makes them more vulnerable to calcium stone formation, yet the mechanism is still unclear. We aimed to examine the role of sex in stone formation during hypercalciuria and urine alkalinization through acetazolamide and calcium gluconate supplementation, respectively, for 4 weeks in wild-type (WT) and moderately hypercalciuric [TRPC3 knockout [KO](-/-)] male and female mice. Our goal was to develop calcium phosphate (CaP) and CaP+ calcium oxalate mixed stones in our animal model to understand the underlying sex-based mechanism of calcium nephrolithiasis. Our results from the analyses of mice urine, serum, and kidney tissues show that female mice (WT and KO) produce more urinary CaP crystals, higher [Ca2+], and pH in urine compared to their male counterparts. We identified a sex-based relationship of stone-forming phenotypes (types of stones) in our mice model following urine alkalization/calcium supplementation, and our findings suggest that female mice are more susceptible to CaP stones under those conditions. Calcification and fibrotic and inflammatory markers were elevated in treated female mice compared with their male counterparts, and more so in TRPC3 KO mice compared with their WT counterparts. Together these findings contribute to a mechanistic understanding of sex-influenced CaP and mixed stone formation that can be used as a basis for determining the factors in sex-related clinical studies.

State of knowledge on ammonia handling by the kidney

The disposal of ammonia, the main proton buffer in the urine, is important for acid-base homeostasis. Renal ammonia excretion is the predominant contributor to renal net acid excretion, both under basal condition and in response to acidosis. New insights into the mechanisms of renal ammonia production and transport have been gained in the past decades. Ammonia is the only urinary solute known to be produced in the kidney and selectively transported through the different parts of the nephron. Both molecular forms of total ammonia, NH3 and NH4+, are transported by specific proteins. Proximal tubular ammoniagenesis and the activity of these transport processes determine the eventual fate of total ammonia produced and excreted by the kidney. In this review, we summarized the state of the art of ammonia handling by the kidney and highlighted the newest processes described in the last decade.

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.

Sodium citrate versus sodium bicarbonate for metabolic acidosis in patients with chronic kidney disease: A randomized controlled trial

BACKGROUND

Metabolic acidosis (MA) is frequently associated with chronic kidney disease (CKD) progression. Our aim was to compare the effect of oral sodium citrate (SC) with that of oral sodium bicarbonate (SB) on renal function and serum bicarbonate correction, as well as to evaluate their safety profile in patients with MA of CKD.

METHODS

We conducted a prospective, single-center, randomized 1:1, parallel, controlled, unblinded clinical trial of 124 patients with MA and CKD stages 3b and 4. The primary outcome was the mean change in estimated glomerular filtration rate (eGFR). The secondary outcomes were mean change in serum bicarbonate level, eGFR decrease by 30%, eGFR decrease by 50%, dialysis, death or prolonged hospitalization, and a combined endpoint.

RESULTS

No significant difference was found between the groups in terms of mean eGFR change [adjusted mean difference = -0.99 mL/min/1.73 m2 (95% CI: -2.51 to 0.93, P = .20)]. We observed a mean serum bicarbonate change of 6.15 mmol/L [(95% CI: 5.55-6.74), P < .001] in the SC group and of 6.19 mmol/L [(95% CI: 5.54-6.83), P < .001] in the SB group, but no significant difference between the 2 groups [adjusted mean difference = 0.31 mmol/L (-0.22 to 0.85), P = .25]. Cox proportional hazard analysis showed similar risks regarding eGFR decrease by 30% (P = .77), eGFR decrease by 50% (P = .50), dialysis (P = .85), death or prolonged hospitalization (P = .29), and combined endpoint (P = .57). Study drug discontinuation due to adverse events was significantly more common in the SB group (17.7% vs 4.8%, P = .02).

CONCLUSIONS

SC and SB have a similar effect on kidney function decline, both improve serum bicarbonate level, but SB is associated with higher rates of medication discontinuation due to adverse events.

Effects of Alterations in Acid-Base Effects on Insulin Signaling

Insulin tightly regulates glucose levels within a narrow range through its action on muscle, adipose tissue and the liver. The activation of insulin receptors activates multiple intracellular pathways with different functions. Another tightly regulated complex system in the body is acid-base balance. Metabolic acidosis, defined as a blood pH < 7.35 and serum bicarbonate < 22 mmol/L, has clear pathophysiologic consequences including an effect on insulin action. With the ongoing intake of typical acid-producing Western diets and the age-related decline in renal function, there is an increase in acid levels within the range considered to be normal. This modest increase in acidosis is referred to as "acid stress" and it may have some pathophysiological consequences. In this article, we discuss the effects of acid stress on insulin actions in different tissues.

Crosstalk with renal proximal tubule cells drives acidosis-induced inflammatory response and dedifferentiation of fibroblasts via p38-singaling

BACKGROUND

Tubulointerstitial kidney disease associated microenvironmental dysregulation, like acidification, inflammation and fibrosis, affects tubule cells and fibroblasts. Micromilieu homeostasis influences intracellular signaling and intercellular crosstalk. Cell-cell communication in turn modulates the interstitial microenvironment. We assessed the impact of acidosis on inflammatory and fibrotic responses in proximal tubule cells and fibroblasts as a function of cellular crosstalk. Furthermore, cellular signaling pathways involved were identified.

METHODS

HK-2 (human proximal tubule) and CCD-1092Sk (human fibroblasts), in mono and coculture, were exposed to acidic or control media for 3 or 48 h. Protein expression of inflammation markers (TNF, TGF-ß and COX-2), dedifferentiation markers (N-cadherin, vinculin, ß-catenin and vimentin), fibrosis markers (collagen III and fibronectin) and phospho- as well as total MAPK levels were determined by western blot. Secreted collagen III and fibronectin were measured by ELISA. The impact of MAPK activation was assessed by pharmacological intervention. In addition, necrosis, apoptosis and epithelial permeability were determined.

RESULTS

Independent of culture conditions, acidosis caused a decrease of COX-2, vimentin and fibronectin expression in proximal tubule cells. Only in monoculture, ß-Catenin expression decreased and collagen III expression increased in tubule cells during acidosis. By contrast, in coculture collagen III protein expression of tubule cells was reduced. In fibroblasts acidosis led to an increase of TNF, COX-2, vimentin, vinculin, N-cadherin protein expression and a decrease of TGF-ß expression exclusively in coculture. In monoculture, expression of COX-2 and fibronectin was reduced. Collagen III expression of fibroblasts was reduced by acidosis independent of culture conditions. In coculture, acidosis enhanced phosphorylation of ERK1/2, JNK1/2 and p38 transiently in proximal tubule cells. In fibroblasts, acidosis enhanced phosphorylation of p38 in a sustained and very strong manner. ERK1/2 and JNK1/2 were not affected in fibroblasts. Inhibition of JNK1/2 and p38 under coculture conditions reduced acidosis-induced changes in fibroblasts significantly.

CONCLUSIONS

Our data show that the crosstalk between proximal tubule cells and fibroblasts is crucial for acidosis-induced dedifferentiation of fibroblasts into an inflammatory phenotype. This dedifferentiation is at least in part mediated by p38 and JNK1/2. Thus, cell-cell communication is essential for the pathophysiological impact of tubulointerstitial acidosis.

The Role of the Endocrine System in the Regulation of Acid-Base Balance by the Kidney and the Progression of Chronic Kidney Disease

Systemic acid-base status is primarily determined by the interplay of net acid production (NEAP) arising from metabolism of ingested food stuffs, buffering of NEAP in tissues, generation of bicarbonate by the kidney, and capture of any bicarbonate filtered by the kidney. In chronic kidney disease (CKD), acid retention may occur when dietary acid production is not balanced by bicarbonate generation by the diseased kidney. Hormones including aldosterone, angiotensin II, endothelin, PTH, glucocorticoids, insulin, thyroid hormone, and growth hormone can affect acid-base balance in different ways. The levels of some hormones such as aldosterone, angiotensin II and endothelin are increased with acid accumulation and contribute to an adaptive increase in renal acid excretion and bicarbonate generation. However, the persistent elevated levels of these hormones can damage the kidney and accelerate progression of CKD. Measures to slow the progression of CKD have included administration of medications which inhibit the production or action of deleterious hormones. However, since metabolic acidosis accompanying CKD stimulates the secretion of several of these hormones, treatment of CKD should also include administration of base to correct the metabolic acidosis.

Dietary acid load and the risk of events of mortality and kidney replacement therapy in people with chronic kidney disease: the Progredir Cohort Study

BACKGROUND/OBJECTIVES

The association between dietary acid load (DAL) and chronic kidney disease (CKD) progression remains controversial. Also, there is a gap in the literature on the association between DAL and mortality. In this study, we evaluated the association between NEAP (net endogenous acid production) and PRAL (potential renal acid load) and the risk of events of all-cause mortality and kidney replacement therapy (KRT) in people with CKD.

SUBJECTS/METHODS

We included 442 patients (250 diabetics) from the Progredir Cohort Study, based in São Paulo, Brazil. We estimated NEAP and PRAL from dietary intake. Events of death before KRT and KRT were ascertained after a median follow-up of 5.8 and 5.1 years, respectively. Cox proportional hazards regression, Weibull regression, and competing risk models were performed.

RESULTS

Median NEAP and PRAL were 49.5 and 4.8 mEq/d. There were 200 deaths and 75 KRT events. Neither NEAP nor PRAL were associated with mortality or KRT when all participants were analyzed. After stratification for diabetes, both estimates were positively related to the risk of KRT even after adjustment for age, sex, weight status, glomerular filtration rate, serum bicarbonate, and intakes of protein, phosphorus, and energy (HR 1.31; 95% CI 1.07, 1.60 for NEAP, and HR 1.27; 95% CI 1.04, 1.57 for every 10 mEq/d increments). Competing risk analyses confirmed these findings.

CONCLUSIONS

DAL estimates were associated with the risk of KRT in people with CKD and diabetes but not in non-diabetics. There was no association between all-cause mortality and DAL.

Higher Renal Net Acid Excretion, but Not Higher Phosphate Excretion, during Childhood and Adolescence Associates with the Circulating Renal Tubular Injury Marker Interleukin-18 in Adulthood

High dietary phosphorus intake (P-In) and high acid loads may adversely affect kidney function. In animal models, excessive phosphorus intake causes renal injury, which, in humans, is also inducible by chronic metabolic acidosis. We thus examined whether habitually high P-In and endogenous acid production during childhood and adolescence may be early indicators of incipient renal inflammatory processes later in adulthood. P-In and acid-base status were longitudinally and exclusively determined by biomarker-based assessment in 277 healthy children, utilizing phosphate and net acid excretion (NAE) measurements in 24 h urine samples repeatedly collected between the ages of 3 and 17 years. Standard deviation scores (by sex and age) were calculated for anthropometric data and for the urinary biomarkers available within age range 3-17 years. Multivariable linear regression was used to analyze the relations of phosphate excretion and NAE with the adulthood outcome circulating interleukin-18 (IL-18), a marker of inflammation and kidney dysfunction. After adjusting for growth- and adulthood-related covariates and pro-inflammatory biomarkers to rule out confounding by non-renal inflammatory processes, regression models revealed a significant positive relationship of long-term NAE (p = 0.01), but not of long-term phosphate excretion with adult serum IL-18. Similar significant positive regression results were obtained after replacing NAE with 24 h urinary ammonium excretion as the exposition variable. Our results suggest that even moderate elevations in renal ammonia production, as caused by habitually higher acid loading during growth, may affect the intrarenal pro-inflammatory system in the long-term, known to be boosted by acidosis-induced raised ammoniagenesis.

The metabolic pathway regulation in kidney injury and repair

Kidney injury and repair are accompanied by significant disruptions in metabolic pathways, leading to renal cell dysfunction and further contributing to the progression of renal pathology. This review outlines the complex involvement of various energy production pathways in glucose, lipid, amino acid, and ketone body metabolism within the kidney. We provide a comprehensive summary of the aberrant regulation of these metabolic pathways in kidney injury and repair. After acute kidney injury (AKI), there is notable mitochondrial damage and oxygen/nutrient deprivation, leading to reduced activity in glycolysis and mitochondrial bioenergetics. Additionally, disruptions occur in the pentose phosphate pathway (PPP), amino acid metabolism, and the supply of ketone bodies. The subsequent kidney repair phase is characterized by a metabolic shift toward glycolysis, along with decreased fatty acid β-oxidation and continued disturbances in amino acid metabolism. Furthermore, the impact of metabolism dysfunction on renal cell injury, regeneration, and the development of renal fibrosis is analyzed. Finally, we discuss the potential therapeutic strategies by targeting renal metabolic regulation to ameliorate kidney injury and fibrosis and promote kidney repair.

The synergism of cytosolic acidosis and reduced NAD+/NADH ratio is responsible for lactic acidosis-induced vascular smooth muscle cell impairment in sepsis

BACKGROUND

During sepsis, serve vascular dysfunctions lead to life-threatening multiple organ failure, due to vascular smooth muscle cells (VSMC) impairments, resulting in vasoplegia, hypotension and hypoperfusion. In addition, septic patients have an altered cell metabolism that leads to lactic acidosis. Septic patients suffering from lactic acidosis have a high risk of mortality. In addition, septic survivors are at risk of secondary vascular disease. The underlying mechanisms of whether and how lactic acidosis leads to the changes in VSMCs is not well understood. The aim of this study was to comprehensively investigate the effect of lactic acidosis on VSMCs and additionally compare the effects with those induced by pure acidosis and sodium lactate.

METHODS

Primary human aortic smooth muscle cells (HAoSMCs) were treated for 48 h with lactic acidosis (LA_pH 6.8), hydrochloric acid (HCl_pH 6.8), sodium lactate (Na+-lactate_pH 7.4) and the respective controls (ctrl._pH 7.4; hyperosmolarity control: mannitol_pH 7.4) and comparatively analyzed for changes in (i) transcriptome, (ii) energy metabolism, and (iii) phenotype.

RESULTS

Both types of acidosis led to comparable and sustained intracellular acidification without affecting cell viability. RNA sequencing and detailed transcriptome analysis revealed more significant changes for lactic acidosis than for hydrochloric acidosis, with lactate being almost ineffective, suggesting qualitative and quantitative synergism of acidosis and lactate. Bioinformatic predictions in energy metabolism and phenotype were confirmed experimentally. Lactic acidosis resulted in strong inhibition of glycolysis, glutaminolysis, and altered mitochondrial respiration which reduced cellular ATP content, likely due to increased TXNIP expression and altered NAD+/NADH ratio. Hydrochloric acidosis induced significantly smaller effects without changing the NAD+/NADH ratio, with the ATP content remaining constant. These metabolic changes led to osteo-/chondrogenic/senescent transdifferentiation of VSMCs, with the effect being more pronounced in lactic acidosis than in pure acidosis.

CONCLUSIONS

Overall, lactic acidosis exerted a much stronger effect on energy metabolism than pure acidosis, whereas lactate had almost no effect, reflecting the qualitative and quantitative synergism of acidosis and lactate. As a consequence, lactic acidosis may lead to acute functional impairments of VSMC, sustained perturbations of the transcriptome and cellular dedifferentiation. Moreover, these effects may contribute to the acute and prolonged vascular pathomechanisms in septic patients.

Pharmacological functions of salidroside in renal diseases: facts and perspectives

Rhodiola rosea is a valuable functional medicinal plant widely utilized in China and other Asian countries for its anti-fatigue, anti-aging, and altitude sickness prevention properties. Salidroside, a most active constituent derived from Rhodiola rosea, exhibits potent antioxidative, hypoxia-resistant, anti-inflammatory, anticancer, and anti-aging effects that have garnered significant attention. The appreciation of the pharmacological role of salidroside has burgeoned over the last decade, making it a beneficial option for the prevention and treatment of multiple diseases, including atherosclerosis, Alzheimer's disease, Parkinson's disease, cardiovascular disease, and more. With its anti-aging and renoprotective effects, in parallel with the inhibition of oxidative stress and inflammation, salidroside holds promise as a potential therapeutic agent for kidney damage. This article provides an overview of the microinflammatory state in kidney disease and discuss the current therapeutic strategies, with a particular focus on highlighting the recent advancements in utilizing salidroside for renal disease. The potential mechanisms of action of salidroside are primarily associated with the regulation of gene and protein expression in glomerular endothelial cells, podocytes, renal tubule cells, renal mesangial cells and renal cell carcinoma cell, including TNF-α, TGF-β, IL-1β, IL-17A, IL-6, MCP-1, Bcl-2, VEGF, ECM protein, caspase-3, HIF-1α, BIM, as well as the modulation of AMPK/SIRT1, Nrf2/HO-1, Sirt1/PGC-1α, ROS/Src/Cav-1, Akt/GSK-3β, TXNIP-NLRP3, ERK1/2, TGF-β1/Smad2/3, PI3K/Akt, Wnt1/Wnt3a β-catenin, TLR4/NF-κB, MAPK, JAK2/STAT3, SIRT1/Nrf2 pathways. To the best of our knowledge, this review is the first to comprehensively cover the protective effects of salidroside on diverse renal diseases, and suggests that salidroside has great potential to be developed as a drug for the prevention and treatment of metabolic syndrome, cardiovascular and cerebrovascular diseases and renal complications.

Heart Failure With Preserved Ejection Fraction With CKD: A Narrative Review of a Multispecialty Disorder

Heart failure with preserved ejection fraction (HFpEF) is a heterogenous syndrome with varying phenotypic expression. The phenotype chronic kidney disease (CKD) associated HFpEF is increasing in prevalence globally and is associated with increased morbidity and mortality compared to other HFpEF variants. These 2 conditions share common risk factors, including obesity, diabetes, and metabolic syndrome, as well as similar pathophysiology, including systemic inflammation, oxidative stress, elevated neurohormones, mineralocorticoid-receptor activation, and venous congestion. Given the coexistence of CKD and HFpEF, the diagnosis of HFpEF can be difficult. Moreover, treatment options for HFpEF have remained limited despite the success seen in its counterpart, heart failure with reduced ejection fraction. HFpEF encompasses complex multisystem pathophysiological perturbations beyond neurohormones, it is unlikely that a single agent can have significant benefit in this population. Recent data on sodium-glucose cotransporter 2 (SGLT2) inhibitors in HFpEF and CKD, and on glucagon-like peptide-1 (GLP-1) agonists and mineralocorticoid-receptor antagonists in metabolic syndrome, which target multiple pathways simultaneously, have led to promising therapeutics for HFpEF and CKD. In this perspective, our goal is to increase awareness of HFpEF as a multisystem disorder that shares the same disease processes seen in CKD and to emphasize that its management in individuals with CKD warrants a collective and multidisciplinary approach.

Curcumenol improves renal function in 5/6 nephrectomy-induced chronic renal failure rats via the SIRT1/NF-κB pathway

The present work aimed to explore the protective effects of curcumenol and evaluate its pharmacological mechanisms in 5/6 nephrectomy-induced chronic renal failure (CRF). Rats with CRF were administrated curcumenol and the effects on renal functions were investigated. Renal function examinations were carried out, whereas serum levels of inflammatory mediators, including NF-κB, MCP-1 and IL-1β were analyzed by ELISA. The mRNA expression levels of SIRT1, p65 and IκBα were measured by qRT-PCR, and the SIRT1 protein levels were analyzed by western blot and immunohistochemistry. Our results indicated that curcumenol significantly improved the renal functions in the CRF rats. Compared to the sham group, serum levels of NF-κB, MCP-1, IL-1β, and the mRNA expression levels of p65 were significantly increased (p < 0.01), whereas the mRNA expression level of IκBα was significantly decreased (p < 0.01) and the SIRT1 levels were dramatically down-regulated (p < 0.05) in the CRF groups. Treatment with curcumenol remarkably inhibited inflammatory responses as reflected by the reduced levels of inflammatory mediators (p < 0.01) and SIRT1 up-regulation (p < 0.05). Our findings suggested that curcumenol could improve the renal function in 5/6 nephrectomy-induced CRF rats, and the mechanisms might involve suppressing the associated inflammation and modulating the SIRT1 and NF-κB signaling pathways.

A Counterion-Free Strategy for Chronic Metabolic Acidosis Based on an Orally Administered Gut-Restricted Inorganic Adsorbent

Chronic metabolic acidosis, arising as a complication of chronic kidney disease (CKD), not only reduces patients' quality of life but also aggravates renal impairment. The only available therapeutic modality, involving intravenous infusion of NaHCO3 , engenders undesirable sodium retention, thereby increasing hemodynamic load and seriously exacerbating the primary disease. This deleterious cascade extends to the development of cardiovascular diseases. Herein, an orally administered, gut-restricted inorganic adsorbent that can effectively alleviate chronic metabolic acidosis without causing any electrolytic derangement or superfluous cardiovascular strain is developed. The genesis of ABC-350 entails the engineering of bismuth subcarbonate via annealing, thereby yielding a partially β-Bi2 O3 -doped (BiO)2 CO3 biphasic crystalline structure framework enriched with atomic vacancies. ABC-350 can selectively remove chloride ions and protons from the gastrointestinal tract, mimicking the physiological response to gastric acid removal and resulting in increased serum bicarbonate. Owing to its gut-restricted nature, ABC-350 exhibits commendable biosafety, averting undue systemic exposure. In two rat models of metabolic acidosis, ABC-350 emerges not only as a potent mitigator of acidosis but also effects discernible amelioration concerning proximal tubular morphology, interstitial fibrosis, and the incendiary cascades incited by metabolic acidosis. ABC-350, as the translationally relevant material, provides a promising strategy for the treatment of metabolic acidosis.

An Overview of Chronic Kidney Disease Pathophysiology: The Impact of Gut Dysbiosis and Oral Disease

Chronic kidney disease (CKD) is a severe condition and a significant public health issue worldwide, carrying the burden of an increased risk of cardiovascular events and mortality. The traditional factors that promote the onset and progression of CKD are cardiometabolic risk factors like hypertension and diabetes, but non-traditional contributors are escalating. Moreover, gut dysbiosis, inflammation, and an impaired immune response are emerging as crucial mechanisms in the disease pathology. The gut microbiome and kidney disease exert a reciprocal influence commonly referred to as "the gut-kidney axis" through the induction of metabolic, immunological, and endocrine alterations. Periodontal diseases are strictly involved in the gut-kidney axis for their impact on the gut microbiota composition and for the metabolic and immunological alterations occurring in and reciprocally affecting both conditions. This review aims to provide an overview of the dynamic biological interconnections between oral health status, gut, and renal pathophysiology, spotlighting the dynamic oral-gut-kidney axis and raising whether periodontal diseases and gut microbiota can be disease modifiers in CKD. By doing so, we try to offer new insights into therapeutic strategies that may enhance the clinical trajectory of CKD patients, ultimately advancing our quest for improved patient outcomes and well-being.

Plant-based diets: a fad or the future of medical nutrition therapy for children with chronic kidney disease?

Plant-based diets are growing in popularity worldwide due to the importance of reducing the population's ecological footprint as well as an emerging role in the prevention and treatment of chronic human diseases. In adults, plant-based diets have been shown to be beneficial for preventing and controlling conditions that are common in patients with chronic kidney disease (CKD), such as obesity, hypertension, type 2 diabetes, dyslipidemia, and metabolic acidosis. Emerging evidence suggests that the higher fiber content of plant-based diets may help to modulate production of uremic toxins through beneficial shifts in the gut microbiome. The effects of the plant-based diet on progression of CKD remain controversial, and there are no data to support this in children. However, knowledge that the bioavailability of potassium and phosphorus from plant-based foods is reduced has led to recent changes in international kidney-friendly diet recommendations for children with CKD. The new guidelines advise that high potassium fruits and vegetables should no longer be automatically excluded from the kidney-friendly diet. In fact, a plant-based diet can be safely implemented in children with CKD through building the diet around whole, high fiber foods, avoiding processed foods and using recommended cooking methods to control potassium. The health benefits of the plant-based diet compared to omnivorous diets in children with CKD need investigation.

Health effects of the New Nordic Renal Diet in patients with stage 3 and 4 chronic kidney disease, compared with habitual diet: a randomized trial

BACKGROUND

Chronic kidney disease (CKD) leads to an accumulation of waste products and causes adverse cardiometabolic effects.

OBJECTIVES

We investigated the health effects of the New Nordic Renal Diet (NNRD), a novel meal pattern reduced in phosphorus, protein, and sodium.

METHODS

A 26-wk randomized trial compared the NNRD with a habitual diet. The NNRD group received weekly home deliveries of food and recipes. Monthly study visits included fasting blood samples, 24-h urine samples, blood pressure, and anthropometric measurements. Intention-to-treat analysis used linear mixed-effects models.

RESULTS

Sixty patients, mean estimated glomerular filtration rate (eGFR) 34 mL/min/1.73 m2 and body mass index of 25-27 kg/m2, were included and 58 completed. Metabolic syndrome was present in 53% (NNRD group) and 57% (control group). The NNRD group (n = 30) reduced their 24-h urine phosphorus excretion by 19% (-153 mg; 95% confidence interval [CI]: -210, -95), control group (n = 30) (no change), between-group difference -171 mg (95% CI: -233, -109; P < 0.001). Proteinuria was reduced by 39% in the NNRD group (-0.33 g/d; 95% CI: -0.47, -0.18), control group (no change), between-group difference -0.34 g/d (95% CI: -0.52, -0.17; P < 0.001). Plasma urea was reduced by -1.5 mmol/L in the NNRD group (95% CI: -2.1, -0.9), control group (no change), between-group difference -1.4 mmol/L (95% CI: -2.0, -0.7; P < 0.001). Systolic blood pressure fell by -5.2 mmHg in the NNRD group (95% CI: -8.4, -2.1), control group (no change), between-group difference -3.9 mmHg (95% CI; -7.6, -0.2; P = 0.04). The NNRD group lost -1.7 kg (95% CI: -2.6, -0.8), control group (no change), between-group difference -2.0 kg (95% CI: -3.0, -1.0; P < 0.001). There were no effects on eGFR during the 26-wk intervention.

CONCLUSION

NNRD in moderate CKD reduces phosphorus excretion, proteinuria, systolic blood pressure, and weight, mainly by reducing abdominal fat. This trial was registered at clinicaltrials.gov as NCT04579315.

The effects of oral sodium bicarbonate supplementation on anthropometric measures in patients with chronic kidney disease: A systematic review and meta-analysis of randomized clinical trials

Metabolic acidosis (MA) may play a key role in the pathogenesis of protein-energy wasting (PEW) in patients with chronic kidney disease (CKD). To present a comprehensive synthesis of the effect of oral sodium bicarbonate (SB) supplementation on anthropometric measures in patients with CKD, a systematic review was undertaken in PubMed/MEDLINE, Web of Science, Cochrane CENTRAL, and Google Scholar, of relevant articles published prior to September 2022. The summary statistics of effect size, nonstandardized weighted mean difference (WMD), and 95% confidence interval (CI) were used to compare the effects of SB supplementation on anthropometric parameters vs. control group. To detect probable sources of heterogeneity, a series of predefined subgroup analyses were conducted. In total, 17 studies with 21 treatment arms, including 2203 participants (1149 cases, 1054 controls), met our inclusion criteria and were included in the meta-analysis. SB supplementation had no significant effect on body weight (BW), midarm muscle circumference (MAMC), or lean body mass (LBM) in patients with CKD. There was a significant increase in body mass index (BMI) (MD: 0.59 kg/m2, 95% CI: 0.25 to 0.93, p = 0.001) after SB supplementation in the overall analysis. In subgroup analysis, LBM was increased in studies that were ≥ 24-week duration (MD: 1.81 kg, 95% CI: 0.81 to 2.81) and in participants with BMI lower than 27 kg/m2 (MD: 1.81 mg/L, 95% CI: 0.81 to 2.81). SB supplementation may yield increases in BMI in predialysis CKD patients. However, our findings did not support the beneficial effects of SB supplementation on other anthropometric outcomes. There is an evident need for long-term high-quality interventions to confirm these findings.

Small Ceria Nanoclusters with High ROS Scavenging Activity and Favorable Pharmacokinetic Parameters for the Amelioration of Chronic Kidney Disease

The over production of reactive oxygen species (ROS) plays a critical role in the progression of chronic kidney disease (CKD). Organic ROS scavengers currently used for CKD treatment do not satisfy low dosage and high efficiency requirements. Ceria nanomaterials featured with renewable ROS scavenging activity are potential candidates for CKD treatment. Herein, a method for the synthesis of ceria nanoclusters (NCs) featured with small size of ≈1.2 nm is reported. The synthesized NCs are modified by three hydrophilic ligands with different molecular weights, including succinic acid (SA), polyethylene glycol diacid 600 (PEG600), and polyethylene glycol diacid 2000 (PEG2000). The surface modified NCs exhibit excellent ROS scavenging activity due to the high Ce3+ /Ce4+ ratio in their crystal structures. Compared with bigger-sized ceria nanoparticles (NPs) (≈45 nm), NCs demonstrate smoother blood concentration-time curve, lower organ accumulation, and faster metabolic rate superiorities. The administration of NCs to CKD mice, especially PEG600 and PEG2000 modified NCs, can effectively inhibit oxidative stress, inflammation, renal fibrosis, and apoptosis in their kidneys. Due to these benefits, the constructed NCs can ameliorate the progression of CKD. These findings suggest that NCs is a potential redox nanomedicine for future clinical treatment of CKD.

Dietary anions control potassium excretion: it is more than a poorly absorbable anion effect

The urinary potassium (K+) excretion machinery is upregulated with increasing dietary K+, but the role of accompanying dietary anions remains inadequately characterized. Poorly absorbable anions, including [Formula: see text], are thought to increase K+ secretion through a transepithelial voltage effect. Here, we tested if they also influence the K+ secretion machinery. Wild-type mice, aldosterone synthase (AS) knockout (KO) mice, or pendrin KO mice were randomized to control, high-KCl, or high-KHCO3 diets. The K+ secretory capacity was assessed in balance experiments. Protein abundance, modification, and localization of K+-secretory transporters were evaluated by Western blot analysis and confocal microscopy. Feeding the high-KHCO3 diet increased urinary K+ excretion and the transtubular K+ gradient significantly more than the high-KCl diet, coincident with more pronounced upregulation of epithelial Na+ channels (ENaC) and renal outer medullary K+ (ROMK) channels and apical localization in the distal nephron. Experiments in AS KO mice revealed that the enhanced effects of [Formula: see text] were aldosterone independent. The high-KHCO3 diet also uniquely increased the large-conductance Ca2+-activated K+ (BK) channel β4-subunit, stabilizing BKα on the apical membrane, the Cl-/[Formula: see text] exchanger, pendrin, and the apical KCl cotransporter (KCC3a), all of which are expressed specifically in pendrin-positive intercalated cells. Experiments in pendrin KO mice revealed that pendrin was required to increase K+ excretion with the high-KHCO3 diet. In summary, [Formula: see text] stimulates K+ excretion beyond a poorly absorbable anion effect, upregulating ENaC and ROMK in principal cells and BK, pendrin, and KCC3a in pendrin-positive intercalated cells. The adaptive mechanism prevents hyperkalemia and alkalosis with the consumption of alkaline ash-rich diets but may drive K+ wasting and hypokalemia in alkalosis.NEW & NOTEWORTHY Dietary anions profoundly impact K+ homeostasis. Here, we found that a K+-rich diet, containing [Formula: see text] as the counteranion, enhances the electrogenic K+ excretory machinery, epithelial Na+ channels, and renal outer medullary K+ channels, much more than a high-KCl diet. It also uniquely induces KCC3a and pendrin, in B-intercalated cells, providing an electroneutral KHCO3 secretion pathway. These findings reveal new K+ balance mechanisms that drive adaption to alkaline and K+-rich foods, which should guide new treatment strategies for K+ disorders.

Hypothesis-generating analysis of the impact of non-damaging metabolic acidosis on the transcriptome of different cell types: Integrated stress response (ISR) modulation as general transcriptomic reaction to non-respiratory acidic stress?

Extracellular pH is an important parameter influencing cell function and fate. Microenvironmental acidosis accompanies different pathological situations, including inflammation, hypoxia and ischemia. Research focussed mainly on acidification of the tumour micromilieu and the possible consequences on proliferation, migration and drug resistance. Much less is known regarding the impact of microenvironmental acidosis on the transcriptome of non-tumour cells, which are exposed to local acidosis during inflammation, hypoxia, ischemia or metabolic derailment. In the present hypothesis-generating study, we investigated the transcriptional impact of extracellular acidosis on five non-tumour cell types of human and rat origin, combining RNA-Sequencing and extensive bioinformatics analyses. For this purpose, cell type-dependent acidosis resiliences and acidosis-induced transcriptional changes within these resilience ranges were determined, using 56 biological samples. The RNA-Sequencing results were used for dual differential-expression analysis (DESeq and edgeR) and, after appropriate homology mapping, Gene Ontology enrichment analysis (g:Profiler), Ingenuity Pathway Analysis (IPA®), as well as functional enrichment analysis for predicted upstream regulators, were performed. Extracellular acidosis led to substantial, yet different, quantitative transcriptional alterations in all five cell types. Our results identify the regulator of the transcriptional activity NCOA5 as the only general acidosis-responsive gene. Although we observed a species- and cell type-dominated response regarding gene expression regulation, Gene Ontology enrichment analysis and upstream regulator analysis predicted a general acidosis response pattern. Indeed, they suggested the regulation of four general acidosis-responsive cellular networks, which comprised the integrated stress response (ISR), TGF-β signalling, NFE2L2 and TP53. Future studies will have to extend the results of our bioinformatics analyses to cell biological and cell physiological validation experiments, in order to test the refined working hypothesis here.

Discovery of Biomarkers Related to Interstitial Fibrosis and Tubular Atrophy among Kidney Transplant Recipients by mRNA-Sequencing

Interstitial fibrosis and tubular atrophy (IF/TA) after kidney transplantation causes a chronic deterioration of graft function. IF/TA can be diagnosed by means of a graft biopsy, which is a necessity as non-invasive diagnostic methods are unavailable. In this study, we identified IF/TA-related differentially expressed genes (DEGs) through next-generation sequencing using peripheral blood mononuclear cells. Blood samples from kidney transplant recipients undergoing standard immunosuppressive therapy (tacrolimus/mycophenolate mofetil or mycophenolate sodium/steroid) and diagnosed as IF/TA (n = 41) or normal (controls; n = 41) at their one-year protocol biopsy were recruited between January of 2020 and August of 2020. DEGs were derived through mRNA sequencing and validated by means of a quantitative real-time polymerase chain reaction. We identified 34 DEGs related to IF/TA. ADAMTS2, PLIN5, CLDN9, and KCNJ15 demonstrated a log2(fold change) of >1.5 and an area under the receiver operating characteristic curve (AUC) value of >0.6, with ADAMTS2 showing the largest AUC value and expression levels, which were 3.5-fold higher in the IF/TA group relative to that observed in the control group. We identified and validated DEGs related to IF/TA progression at one-year post-transplantation. Specifically, we identified ADAMTS2 as a potential IF/TA biomarker.

Loss of the Secretin Receptor Impairs Renal Bicarbonate Excretion and Aggravates Metabolic Alkalosis in Mice during Acute Base-Loading

SIGNIFICANCE STATEMENT

During acute base excess, the renal collecting duct β -intercalated cells ( β -ICs) become activated to increase urine base excretion. This process is dependent on pendrin and cystic fibrosis transmembrane regulator (CFTR) expressed in the apical membrane of β -ICs. The signal that leads to activation of this process was unknown. Plasma secretin levels increase during acute alkalosis, and the secretin receptor (SCTR) is functionally expressed in β -ICs. We find that mice with global knockout for the SCTR lose their ability to acutely increase renal base excretion. This forces the mice to lower their ventilation to cope with this challenge. Our findings suggest that secretin is a systemic bicarbonate-regulating hormone, likely being released from the small intestine during alkalosis.

BACKGROUND

The secretin receptor (SCTR) is functionally expressed in the basolateral membrane of the β -intercalated cells of the kidney cortical collecting duct and stimulates urine alkalization by activating the β -intercalated cells. Interestingly, the plasma secretin level increases during acute metabolic alkalosis, but its role in systemic acid-base homeostasis was unclear. We hypothesized that the SCTR system is essential for renal base excretion during acute metabolic alkalosis.

METHODS

We conducted bladder catheterization experiments, metabolic cage studies, blood gas analysis, barometric respirometry, perfusion of isolated cortical collecting ducts, immunoblotting, and immunohistochemistry in SCTR wild-type and knockout (KO) mice. We also perfused isolated rat small intestines to study secretin release.

RESULTS

In wild-type mice, secretin acutely increased urine pH and pendrin function in isolated perfused cortical collecting ducts. These effects were absent in KO mice, which also did not sufficiently increase renal base excretion during acute base loading. In line with these findings, KO mice developed prolonged metabolic alkalosis when exposed to acute oral or intraperitoneal base loading. Furthermore, KO mice exhibited transient but marked hypoventilation after acute base loading. In rats, increased blood alkalinity of the perfused upper small intestine increased venous secretin release.

CONCLUSIONS

Our results suggest that loss of SCTR impairs the appropriate increase of renal base excretion during acute base loading and that SCTR is necessary for acute correction of metabolic alkalosis. In addition, our findings suggest that blood alkalinity increases secretin release from the small intestine and that secretin action is critical for bicarbonate homeostasis.

Association of serum bicarbonate with the development of kidney stones in patients with chronic kidney disease: a retrospective cohort study

BACKGROUND

Epidemiological studies demonstrate an association between kidney stones and risk of chronic kidney disease (CKD) and CKD progression. Metabolic acidosis, as a consequence of CKD, results in a reduced urine pH which promotes the formation of some types of kidney stones and inhibits the formation of others. While metabolic acidosis is a risk factor for CKD progression, the association of serum bicarbonate with risk of incident kidney stones is not well understood.

METHODS

We used an Integrated Claims-Clinical dataset of US patients to generate a cohort of patients with non-dialysis-dependent CKD with two serum bicarbonate values of 12 to <22 mmol/L (metabolic acidosis) or 22 to <30 mmol/L (normal serum bicarbonate). Primary exposure variables were baseline serum bicarbonate and change in serum bicarbonate over time. Cox proportional hazards models evaluated time to first occurrence of kidney stones during a median 3.2-year follow-up.

RESULTS

A total of 142 884 patients qualified for the study cohort. Patients with metabolic acidosis experienced post-index date kidney stones at greater frequency than patients with normal serum bicarbonate at the index date (12.0% vs 9.5%, P < .0001). Both lower baseline serum bicarbonate [hazard ratio (HR) 1.047; 95% confidence interval (CI) 1.036-1.057] and decreasing serum bicarbonate over time (HR 1.034; 95% CI 1.026-1.043) were associated with increased risk of kidney stone development.

CONCLUSIONS

Metabolic acidosis was associated with a higher incidence of kidney stones and shorter time to incident stone formation in patients with CKD. Future studies may investigate the role of correcting metabolic acidosis to prevent stone formation.

Hidden Acid Retention with Normal Serum Bicarbonate Level in Chronic Kidney Disease

Management of metabolic acidosis is crucial for preserving bone, muscle, and renal health, as evidenced by the results of several interventional studies conducted on patients with chronic kidney disease (CKD). Considering the continuity of CKD progression over time, it is reasonable to deduce that a subclinical form of metabolic acidosis may exist prior to the manifestation of overt metabolic acidosis. Covert H⁺ retention with normal serum bicarbonate level in patients with CKD may result in maladaptive responses that contribute to kidney function deterioration, even in the early stages of the disease. The loss of adaptive compensatory mechanisms of urinary acid excretion may be a key factor in this process. Early modulation of these responses could be an important therapeutic strategy in preventing CKD progression. However, to date, the optimal approach for alkali therapy in subclinical metabolic acidosis in CKD remains uncertain. There is a lack of established guidelines on when to initiate alkali therapy, potential side effects of alkali agents, and the optimal blood bicarbonate levels based on evidence-based practices. Therefore, further research is necessary to address these concerns and establish more robust guidelines for the use of alkali therapy in patients with CKD. Herein, we provide an overview of recent developments on this subject and examine the potential therapeutic approaches that interventional treatments may present for patients with hidden H⁺ retention, exhibiting normal serum bicarbonate levels - commonly described as subclinical or eubicarbonatemic metabolic acidosis in patients with CKD.

Endothelial Cell Dysfunction and Increased Cardiovascular Risk in Patients With Chronic Kidney Disease

The endothelium is considered to be the gatekeeper of the vessel wall, maintaining and regulating vascular integrity. In patients with chronic kidney disease, protective endothelial cell functions are impaired due to the proinflammatory, prothrombotic and uremic environment caused by the decline in kidney function, adding to the increase in cardiovascular complications in this vulnerable patient population. In this review, we discuss endothelial cell functioning in healthy conditions and the contribution of endothelial cell dysfunction to cardiovascular disease. Further, we summarize the phenotypic changes of the endothelium in chronic kidney disease patients and the relation of endothelial cell dysfunction to cardiovascular risk in chronic kidney disease. We also review the mechanisms that underlie endothelial changes in chronic kidney disease and consider potential pharmacological interventions that can ameliorate endothelial health.

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.

Effect of Sodium Bicarbonate on Systolic Blood Pressure in CKD: A Systematic Review and Meta-Analysis

BACKGROUND

Individuals with CKD are at a higher risk of cardiovascular morbidity and mortality. Acidosis is positively correlated with CKD progression and elevated systolic BP. Sodium bicarbonate is an efficacious treatment of acidosis, although this may also increase systolic BP. In this systematic review and meta-analysis, we summarize the evidence evaluating systolic BP and antihypertensive medication change (which may indicate systolic BP change) in response to sodium bicarbonate therapy in individuals with CKD.

METHODS

Medical Literature Analysis and Retrieval System Online, Excerpta Medica database, Cumulative Index to Nursing and Allied Health Literature, Allied and Complementary Medicine Database, Cochrane Central Register of Controlled Trials, and World Health Organization (WHO) trials registry databases were searched for randomized control trials where sodium bicarbonate was compared with placebo/usual care in CKD stage G1-5 non-dialysis-dependent populations. Random effects meta-analyses were used to evaluate changes in systolic BP and BP-modifying drugs after sodium bicarbonate intervention.

RESULTS

Fourteen randomized control trials (2110 individuals, median follow-up 27 [interquartile range 97] weeks, mean age 60 [SD 10] years, mean systolic BP 136 [SD 17] mm Hg, mean eGFR 38 [SD 10] ml/min, mean serum bicarbonate 22 [SD 4] mmol/L) were eligible for inclusion. Meta-analysis suggested that sodium bicarbonate did not influence systolic BP in individuals with CKD stage G1-5. Results were consistent when stratifying by dose of sodium bicarbonate or duration of intervention. Similarly, there was no significant increase in the use of antihypertensive medication or diuretics in individuals taking sodium bicarbonate, whereas there was a greater decrease in antihypertensive medication use in individuals taking sodium bicarbonate compared with controls.

CONCLUSIONS

Our results suggest, with moderate certainty, that sodium bicarbonate supplementation does not adversely affect systolic BP in CKD or negatively influence antihypertensive medication requirements.

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.

Acidosis Activates the Nrf2 Pathway in Renal Proximal Tubule-Derived Cells through a Crosstalk with Renal Fibroblasts

Crosstalk of renal epithelial cells with interstitial fibroblasts plays an important role in kidney pathophysiology. A previous study showed that crosstalk between renal epithelial cells and renal fibroblasts protects against acidosis-induced damage. In order to gain further mechanistic insight into this crosstalk, we investigated the effect of acidosis on the transcriptome of renal epithelial cells (NRK-52E) and renal fibroblasts (NRK-49F) in co-culture by RNASeq, bioinformatics analysis and experimental validation. Cells were exposed to acidic media or control media for 48 h. RNA and protein from whole cell lysate were isolated. In addition, cells were fractionated into cytosol, nucleus and chromatin. RNASeq data were analyzed for differential expression and pathway enrichment (ingenuity pathway analysis, IPA, QIAGEN). Total and phosphorylated protein expression was assessed by Western blot (WB). Transcription factor activity was assessed by luciferase reporter assay. Bioinformatic analysis using differentially expressed genes according to RNASeq (7834 for NRK-52E and 3197 for NRK-49F) predicted the antioxidant and cell-protective Nrf2 pathway as acidosis-induced in NRK-52E and NRK-49F cells. Activation of Nrf2 comprises enhanced Nrf2 phosphorylation, nuclear translocation, DNA binding and initiation of a cell protective transcriptional program. Our data show that acidosis enhances chromatin-associated Nrf2 expression and the abundance of phosphorylated Nrf2 in the chromatin fraction of NRK-52E cells in co-culture but not in monoculture. Furthermore, acidosis enhances the activity of a reporter for Nrf2 (ARE-luciferase). Despite the bioinformatics prediction, NRK-49F cells did not respond with Nrf2 activation. Transketolase (TKT) is an important regulator of antioxidant and homeostatic responses in the kidney and a canonical Nrf2 target gene. We show that protein and mRNA expression of TKT is increased in NRK-52E cells under co-culture but not under monoculture conditions. In conclusion, our data show that extracellular acidosis activates the cytoprotective transcription factor Nrf2 in renal epithelial cells co-cultivated with renal fibroblasts, thereby enhancing the expression of cytoprotective TKT. This protective response is not observed in monoculture. Activation of the Nrf2 pathway represents a co-operative cellular strategy of protection against acidosis.

Increasing Serum Bicarbonate is Associated with Reduced Risk of Adverse Kidney Outcomes in Patients with CKD and Metabolic Acidosis

Introduction

Low serum bicarbonate at a single point in time is associated with accelerated kidney decline in patients with chronic kidney disease (CKD). We modeled how changes in serum bicarbonate over time affect incidence of adverse kidney outcomes.

Methods

We analyzed data from Optum's deidentified Integrated Claims-Clinical data set of US patients (2007-2019) with ≥1 year of prior medical record data, CKD stages G3 to G5, and metabolic acidosis (i.e., index serum bicarbonate 12 to <22 mmol/l). The primary predictor of interest was the change in serum bicarbonate, evaluated at each postindex outpatient serum bicarbonate test as a time-dependent continuous variable. The primary outcome was a composite of either a ≥40% decline in estimated glomerular filtration rate (eGFR) from index or evidence of dialysis or transplantation, evaluated using Cox proportional hazards models.

Results

A total of 24,384 patients were included in the cohort with median follow-up of 3.7 years. A within-patient increase in serum bicarbonate over time was associated with a lower risk of the composite kidney outcome. The unadjusted hazard ratio (HR) per 1-mmol/l increase in serum bicarbonate was 0.911 (95% confidence interval [CI]: 0.905-0.917; P < 0.001). After adjustment for baseline eGFR and serum bicarbonate, the time-adjusted effect of baseline eGFR and other covariates, the HR per 1-mmol/l increase in serum bicarbonate was largely unchanged (0.916 [95% CI: 0.910-0.922; P < 0.001]).

Conclusion

In a real-world population of US patients with CKD and metabolic acidosis, a within-patient increase in serum bicarbonate over time independent of changes in eGFR, was associated with a lower risk of CKD progression.

Blood pH and COVID-19

The coronavirus disease 2019 (COVID-19) pandemic is a worldwide war. Raising the blood pH might be a crucial strategy to chase COVID-19. The human blood is slightly alkaline, which is essential for cell metabolism, normal physiology, and balanced immunity since all of these biological processes are pH-dependent. Varieties of physiologic derangements occur when the blood pH is disrupted. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) proliferates in acidic blood that magnifies the severity of COVID-19. On the other side, blood acidemia is linked to increased morbidity and mortality because of its complications on immunity, especially in the elderly and in critical diseases such as cancer, musculoskeletal degradation, renal, cardiac, and pulmonary disorders, which result in many pathological disorders such as osteomalacia, and disturbing the hematopoiesis. Additionally, acidemia of the blood facilitates viral infection and progression. Thus, correcting the acid-base balance might be a crucial strategy for the treatment of COVID-19, which might be attributed to the distraction of the viral spike protein to its cognate receptor angiotensin-converting enzyme 2 and supporting the over-taxed immunity.

Diabetic kidney disease in type 2 diabetes: a consensus statement from the Swiss Societies of Diabetes and Nephrology

Diabetic kidney disease is highly prevalent in patients with type 2 diabetes and is a major cause of end-stage renal disease in Switzerland. Patients with diabetic kidney disease are among the most complex patients in diabetes care. They require a multifactorial and multidisciplinary approach with the goal to slow the decline in glomerular filtration rate (GFR) and cardiovascular morbidity. With this consensus we propose an evidence-based guidance to health care providers involved in the care of type 2 diabetic patients with diabetic kidney disease.First, there is a need to increase physician awareness and improve screening for diabetic kidney disease as early intervention may improve clinical outcomes and the financial burden. Evaluation of estimated GFR (eGFR) and spot urine albumin/creatinine ratio is recommended at least annually. Once it is diagnosed, glucose control and optimisation of blood pressure control with renin-angiotensin system blockers have been recommended as mainstay management of diabetic kidney disease for more than 20 years. Recent, high quality randomised controlled trials have shown that sodium-glucose cotransporter-2 (SGLT2) inhibition slows eGFR decline and cardiovascular events beyond glucose control. Likewise, mineralocorticoid receptor antagonism with finerenone has cardiorenal protective effects in diabetic kidney disease. Glucagon-like peptide-1 (GLP1) receptor agonists improve weight loss if needed, and decrease albuminuria and cardiovascular morbidity. Lipid control is also important to decrease cardiovascular events. All these therapies are included in the treatment algorithms proposed in this consensus. With advancing kidney failure, other challenges may rise, such as hyperkalaemia, anaemia and metabolic acidosis, as well as chronic kidney disease-mineral and bone disorder. These different topics and treatment strategies are discussed in this consensus. Finally, an update on diabetes management in renal replacement therapy such as haemodialysis, peritoneal dialysis and renal transplantation is provided. With the recent developments of efficient therapies for diabetic kidney disease, it has become evident that a consensus document is necessary. We are optimistic that it will significantly contribute to a high-quality care for patients with diabetic kidney disease in Switzerland in the future.

Paradigm shift in lifestyle modification for solitary kidney after donor nephrectomy

PURPOSE OF REVIEW

Living donor kidney transplantation potentially leads to long-term complications including chronic kidney disease, end-stage kidney disease, elevated blood pressure, and pregnancy-associated hypertension. Given living donors generally do not have underlying medical conditions, lifestyle modifications, particularly dietary interventions may prevent those complications and improve their health outcomes.

RECENT FINDINGS

Glomerular hyperfiltration occurs as physiologic adaptation during an initial postdonor nephrectomy period. In the long-term, these adaptations may become pathologic consequences resulting from hyperfiltration-mediated kidney injury and ultimately secondary focal segmental glomerulosclerosis in the solitary kidney. Dietary interventions to slow a decline in kidney function include low protein intake of <0.8 g/kg/day and low sodium consumption of 2-4 g/day as well as certain health dietary patterns. There is no evidence regarding the quantity and quality of protein that can be recommended for living kidney donors and the same for sodium. Plant Dominant (PLADO) diets, Dietary Approaches to Stop Hypertension (DASH), Mediterranean, and vegetarian diets may be favorable for living kidney donors with solitary kidney but the evidence is still lacking.

SUMMARY

Although dietary interventions may provide benefits and kidney health for living kidney donors, further studies including clinical trials are required to incorporate them into clinical practice guidelines.

Serum Bicarbonate and Graft and Patient Outcomes Among Kidney Transplant Recipients: A Retrospective Cohort Study Evaluating Changes in Serum Bicarbonate Over Time

Rationale & Objective

Identification of treatable risk factors for kidney allograft failure is necessary to improve graft longevity. Metabolic acidosis with either low serum bicarbonate or normal serum bicarbonate (eubicarbonatemic metabolic acidosis) is implicated in native kidney disease progression but its effects in kidney transplant recipients are unclear.

Study Design

Retrospective cohort study.

Setting & Participants

An Integrated Claims-Clinical dataset of US patients with chronic kidney disease (estimated glomerular filtration rates <60 mL/min/1.73 m²) and serum bicarbonate data were used to generate a cohort of kidney transplant recipients with data from ≥1 year before and after transplantation.

Primary Predictor

The primary independent variable was a change in serum bicarbonate from baseline.

Outcomes

The primary outcomes were graft failure and all-cause mortality. The secondary outcomes were major adverse cardiac events and all-cause hospitalization.

Analytical Approach

We used adjusted time-dependent Cox proportional hazards models to assess the risk of graft failure, all-cause mortality, major adverse cardiac events, and time to first hospitalization.

Results

In this US community-based cohort of 1,915 kidney transplant recipients with a median follow-up of ∼2.5 years, each 1-mEq/L increase in serum bicarbonate was associated with significantly lower hazard of graft loss, death, major adverse cardiac events, and hospitalization by 10%, 8%, 4%, and 8%, respectively.

Limitations

Possible residual confounding.

Conclusions

In a US community-based population of kidney transplant recipients, even small incremental increases in serum bicarbonate (1 mEq/L) were significantly associated with reduced hazard of graft loss, all-cause mortality, cardiovascular events, and hospitalization. Interventional trials evaluating the potential benefits of treating metabolic acidosis in kidney transplant recipients are warranted.

Tipping the balance between erythroid cell differentiation and induction of anemia in response to the inflammatory pathology associated with chronic trypanosome infections

Infection caused by extracellular single-celled trypanosomes triggers a lethal chronic wasting disease in livestock and game animals. Through screening of 10 Trypanosoma evansi field isolates, exhibiting different levels of virulence in mice, the current study identifies an experimental disease model in which infection can last well over 100 days, mimicking the major features of chronic animal trypanosomosis. In this model, despite the well-controlled parasitemia, infection is hallmarked by severe trypanosomosis-associated pathology. An in-depth scRNA-seq analysis of the latter revealed the complexity of the spleen macrophage activation status, highlighting the crucial role of tissue resident macrophages (TRMs) in regulating splenic extramedullary erythropoiesis. These new data show that in the field of experimental trypanosomosis, macrophage activation profiles have so far been oversimplified into a bi-polar paradigm (M1 vs M2). Interestingly, TRMs exert a double-sided effect on erythroid cells. On one hand, these cells express an erythrophagocytosis associated signature. On another hand, TRMs show high levels of Vcam1 expression, known to support their interaction with hematopoietic stem and progenitor cells (HSPCs). During chronic infection, the latter exhibit upregulated expression of Klf1, E2f8, and Gfi1b genes, involved in erythroid differentiation and extramedullary erythropoiesis. This process gives rise to differentiation of stem cells to BFU-e/CFU-e, Pro E, and Baso E subpopulations. However, infection truncates progressing differentiation at the orthochromatic erythrocytes level, as demonstrated by scRNAseq and flow cytometry. As such, these cells are unable to pass to the reticulocyte stage, resulting in reduced number of mature circulating RBCs and the occurrence of chronic anemia. The physiological consequence of these events is the prolonged poor delivery of oxygen to various tissues, triggering lactic acid acidosis and the catabolic breakdown of muscle tissue, reminiscent of the wasting syndrome that is characteristic for the lethal stage of animal trypanosomosis.

Beyond the Urine Anion Gap: In Support of the Direct Measurement of Urinary Ammonium

Ammonium is a major urinary buffer that is necessary for the normal excretion of the daily acid load. Its urinary rate of excretion (UNH₄) may be increased several fold in the presence of extrarenal metabolic acidosis. Therefore, measurement of UNH₄ can provide important clues about causes of metabolic acidosis. Because UNH₄ is not commonly measured in clinical laboratories, the urinary anion gap (UAG) was proposed as its surrogate about 4 decades ago, and it is still frequently used for that purpose. Several published studies strongly suggest that UAG is not a good index of UNH₄ and support the concept that direct measurement of UNH₄ is an important parameter to define in clinical nephrology. Low UNH₄ levels have recently been found to be associated with a higher risk of metabolic acidosis, loss of kidney function, and death in persons with chronic kidney disease, while surrogates like the UAG do not recapitulate this risk. In order to advance the field it is necessary for the medical community to become more familiar with UNH₄ levels in a variety of clinical settings. Herein, we review the literature, searching for available data on UNH₄ under normal and various pathological conditions, in an attempt to establish reference values to interpret UNH₄ results if and when UNH₄ measurements become available as a routine clinical test. In addition, we present original data in 2 large populations that provide further evidence that the UAG is not a good predictor of UNH₄. Measurement of urine NH₄ holds promise to aid clinicians in the care of patients, and we encourage further research to determine its best diagnostic usage.

Associations between local acidosis induced by renal LDHA and renal fibrosis and mitochondrial abnormalities in patients with diabetic kidney disease

During the progression of diabetic kidney disease (DKD), renal lactate metabolism is rewired. The relationship between alterations in renal lactate metabolism and renal fibrosis in patients with diabetes has only been partially established due to a lack of biopsy tissues from patients with DKD and the intricate mechanism of lactate homeostasis. The role of lactate dehydrogenase A (LDHA)-mediated lactate generation in renal fibrosis and dysfunction in human and animal models of DKD was explored in this study. Measures of lactate metabolism (urinary lactate levels and LDHA expression) and measures of DKD progression (estimated glomerular filtration rate and Wilms' tumor-1 expression) were strongly negatively correlated in patients with DKD. Experiments with streptozotocin-induced DKD rat models and the rat renal mesangial cell model confirmed our findings. We found that the pathogenesis of DKD is linked to hypoxia-mediated lactic acidosis, which leads to fibrosis and mitochondrial abnormalities. The pathogenic characteristics of DKD were significantly reduced when aerobic glycolysis or LDHA expression was inhibited. Further studies will aim to investigate whether local acidosis caused by renal LDHA might be exploited as a therapeutic target in patients with DKD.

Effects of Short-Term Potassium Chloride Supplementation in Patients with CKD

BACKGROUND

Observational studies suggest that adequate dietary potassium intake (90-120 mmol/day) may be renoprotective, but the effects of increasing dietary potassium and the risk of hyperkalemia are unknown.

METHODS

This is a prespecified analysis of the run-in phase of a clinical trial in which 191 patients (age 68±11 years, 74% males, 86% European ancestry, eGFR 31±9 ml/min per 1.73 m2, 83% renin-angiotensin system inhibitors, 38% diabetes) were treated with 40 mmol potassium chloride (KCl) per day for 2 weeks.

RESULTS

KCl supplementation significantly increased urinary potassium excretion (72±24 to 107±29 mmol/day), plasma potassium (4.3±0.5 to 4.7±0.6 mmol/L), and plasma aldosterone (281 [198-431] to 351 [241-494] ng/L), but had no significant effect on urinary sodium excretion, plasma renin, BP, eGFR, or albuminuria. Furthermore, KCl supplementation increased plasma chloride (104±3 to 105±4 mmol/L) and reduced plasma bicarbonate (24.5±3.4 to 23.7±3.5 mmol/L) and urine pH (all P<0.001), but did not change urinary ammonium excretion. In total, 21 participants (11%) developed hyperkalemia (plasma potassium 5.9±0.4 mmol/L). They were older and had higher baseline plasma potassium.

CONCLUSIONS

In patients with CKD stage G3b-4, increasing dietary potassium intake to recommended levels with potassium chloride supplementation raises plasma potassium by 0.4 mmol/L. This may result in hyperkalemia in older patients or those with higher baseline plasma potassium. Longer-term studies should address whether cardiorenal protection outweighs the risk of hyperkalemia.Clinical trial number: NCT03253172.

Metabolic Acidosis is Associated With Acute Kidney Injury in Patients With CKD

Introduction

Metabolic acidosis in patients with chronic kidney disease (CKD) results from a loss of kidney function. It has been associated with CKD progression, all-cause mortality, and other adverse outcomes. We aimed to determine whether metabolic acidosis is associated with a higher risk of acute kidney injury (AKI).

Methods

This was a retrospective cohort study. Using electronic health records and administrative data, we enrolled 2 North American cohorts of patients with CKD Stages G3-G5 as follows: (i) 136,067 patients in the US electronic medical record (EMR) based cohort; and (ii) 34,957 patients in the Manitoba claims-based cohort. The primary exposure was metabolic acidosis (serum bicarbonate between 12 mEq/l and <22 mEq/l). The primary outcome was the development of AKI (defined using ICD-9 and 10 codes at hospital admission or a laboratory-based definition based on Kidney Disease: Improving Global Outcomes guidelines). We applied Cox proportional hazards regression models adjusting for relevant demographic and clinical characteristics.

Results

In both cohorts, metabolic acidosis was associated with AKI: hazard ratio (HR) 1.57 (95% confidence interval [CI] 1.52-1.61) in the US EMR cohort, and HR 1.65 (95% CI 1.58-1.73) in the Manitoba claims cohort. The association was consistent when serum bicarbonate was treated as a continuous variable, and in multiple subgroups, and sensitivity analyses including those adjusting for albuminuria.

Conclusion

Metabolic acidosis is associated with a higher risk of AKI in patients with CKD. AKI should be considered as an outcome in studies of treatments for patients with metabolic acidosis.

Short chain fatty acids for the risk of diabetic nephropathy in type 2 diabetes patients

AIMS

This study aimed to explore relationships short chain fatty acids with diabetic nephropathy (DN) in type 2 diabetes (T2D) patients.

METHODS

We extracted the clinical and omics data of 100 T2D patients and 100 DN patients from April 2018 to April 2019 from a tertiary hospital. Restricted cubic splines were used to examine full-range associations of short chain fatty acids with DN in T2D.Query Logistic regression was used to obtain odds ratio (OR) and confidence interval (CI).

RESULTS

Acetate, butyrate and isovalerate were negatively correlated with DN. Isobutyrate was positively correlated with DN. Propionate ≥ 4.4 μg/mL and isobutyrate ≥ 1.4 μg/mL had threshold effects and their increasing levels above the cutoff points were associated with rapid rises in the risk of DN. The additive interaction between high propionate and high isobutyrate in serum significantly increased the risk of DN (OR34.35; 95%CI 7.11 to 166.08). Presence of hypertension further increased the OR of high propionate for DN to 8.27(95%CI 1.82 to 37.57) with a significant additive interaction. The additive interaction of the high isobutyrate and hypertension was not significant.

CONCLUSIONS

Acetate, butyrate and isovalerate were negatively associated with DN. Isobutyrate was positively associated with DN. Serum high propionate and high isobutyrate worked independently and synergistically to increase the risk of DN in T2D. Presence of hypertension further amplified the effect of copresence of high propionate on DN risk.

Acid-Mediated Kidney Injury Across the Spectrum of Metabolic Acidosis

Metabolic acidosis affects about 15% of patients with chronic kidney disease. As kidney function declines, the kidneys progressively fail to eliminate acid, primarily reflected by a decrease in ammonium and titratable acid excretion. Several studies have shown that the net acid load remains unchanged in patients with reduced kidney function; the ensuing acid accumulation can precede overt metabolic acidosis, and thus, indicators of urinary acid or potential base excretion, such as ammonium and citrate, may serve as early signals of impending metabolic acidosis. Acid retention, with or without overt metabolic acidosis, initiates compensatory responses that can promote tubulointerstitial fibrosis via intrarenal complement activation and upregulation of endothelin-1, angiotensin II, and aldosterone pathways. The net effect is a cycle between acid accumulation and kidney injury. Results from small- to medium-sized interventional trials suggest that interrupting this cycle through base administration can prevent further kidney injury. While these findings inform current clinical practice guidelines, large-scale clinical trials are still necessary to prove that base therapy can limit chronic kidney disease progression or associated adverse events.

Importance of Metabolic Acidosis as a Health Risk in Chronic Kidney Disease

Human kidneys are well adapted to excrete the daily acid load from diet and metabolism in order to maintain homeostasis. In approximately 30% of patients with more advanced stages of CKD, these homeostatic processes are no longer adequate, resulting in metabolic acidosis. Potential deleterious effects of chronic metabolic acidosis in CKD, including muscle wasting, bone demineralization, hyperkalemia, and more rapid progression of CKD, have been well cataloged. Based primarily upon concerns related to nutrition and bone disease, early Kidney Disease Outcomes Quality Initiative guidelines recommended treating metabolic acidosis with alkali therapy targeting a serum bicarbonate ≥22 mEq/L. More recent guidelines have suggested similar targets based upon potential slowing of CKD progression. However, appropriately powered, long-term, randomized controlled trials to study efficacy and safety of alkali therapy for these outcomes are largely lacking. As a result, practice among physicians varies, underscoring the complexity of treatment of chronic metabolic acidosis in real-world CKD practice. Novel treatment approaches and rigorous phase 3 trials may resolve some of this controversy in the coming years. Metabolic acidosis is an important complication of CKD, and where it "falls" in the priority schema of CKD care will depend upon the generation of strong clinical evidence.

Single-cell RNA sequencing data analysis suggests the cell-cell interaction patterns of the pituitary-kidney axis

Kidney functions, including electrolyte and water reabsorption and secretion, could be influenced by circulating hormones. The pituitary gland produces a variety of hormones and cytokines; however, the influence of these factors on the kidney has not been well explained and explored. To provide more in-depth information and insights to support the pituitary–kidney axis connection, we used mouse pituitary and kidney single-cell transcriptomics data from the GEO database for further analysis. Based on a ligand–receptor pair analysis, cell–cell interaction patterns between the pituitary and kidney cell types were described. Key ligand–receptor pairs, such as GH-GHR, PTN-SDC2, PTN-SDC4, and DLK1-NOTCH3, were relatively active in the pituitary–kidney axis. These ligand–receptor pairs mainly target proximal tubule cells, principal cells, the loop of Henle, intercalated cells, pericytes, mesangial cells, and fibroblasts, and these cells are related to physiological processes, such as substance reabsorption, angiogenesis, and tissue repair. Our results suggested that the pituitary gland might directly regulate kidney function by secreting multiple hormones or cytokines and indicated that the above ligand–receptor pairs might represent a new research focus for studies on kidney function or kidney disease.