Modifying Dietary Sodium and Potassium Intake: An End to the 'Salt Wars'?

Excessive salt intake raises blood pressure, but the implications of this observation for human health have remained contentious. It has also been recognized for many years that potassium intake may mitigate the effects of salt intake on blood pressure and possibly on outcomes such as stroke. Recent large randomized intervention trials have provided strong support for the benefits of replacing salt (NaCl) with salt substitute (75% NaCl, 25% KCl) on hard outcomes, including stroke. During the same period of time, major advances have been made in understanding how the body senses and tastes salt, and how these sensations drive intake. Additionally, new insights into the complex interactions between systems that control sodium and potassium excretion by the kidneys, and the brain have highlighted the existence of a potassium switch in the kidney distal nephron. This switch seems to contribute importantly to the blood pressure-lowering effects of potassium intake. In recognition of these evolving data, the United States Food and Drug Administration is moving to permit potassium-containing salt substitutes in food manufacturing. Given that previous attempts to reduce salt consumption have not been successful, this new approach has a chance of improving health and ending the 'Salt Wars'.

Evaluation of glomerular sirtuin-1 and claudin-1 in the pathophysiology of nondiabetic focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is the leading cause of nephrotic syndrome, which is characterized by podocyte injury. Given that the pathophysiology of nondiabetic glomerulosclerosis is poorly understood and targeted therapies to prevent glomerular disease are lacking, we decided to investigate the tight junction protein claudin-1 and the histone deacetylase sirtuin-1 (SIRT1), which are known to be involved in podocyte injury. For this purpose, we first examined SIRT1, claudin-1 and podocin expression in kidney biopsies from patients diagnosed with nondiabetic FSGS and found that upregulation of glomerular claudin-1 accompanies a significant reduction in glomerular SIRT1 and podocin levels. From this, we investigated whether a small molecule activator of SIRT1, SRT1720, could delay the onset of FSGS in an animal model of adriamycin (ADR)-induced nephropathy; 14 days of treatment with SRT1720 attenuated glomerulosclerosis progression and albuminuria, prevented transcription factor Wilms tumor 1 (WT1) downregulation and increased glomerular claudin-1 in the ADR + SRT1720 group. Thus, we evaluated the effect of ADR and/or SRT1720 in cultured mouse podocytes. The results showed that ADR [1 µM] triggered an increase in claudin-1 expression after 30 min, and this effect was attenuated by pretreatment of podocytes with SRT1720 [5 µM]. ADR [1 µM] also led to changes in the localization of SIRT1 and claudin-1 in these cells, which could be associated with podocyte injury. Although the use of specific agonists such as SRT1720 presents some benefits in glomerular function, their underlying mechanisms still need to be further explored for therapeutic use. Taken together, our data indicate that SIRT1 and claudin-1 are relevant for the pathophysiology of nondiabetic FSGS.

Acetyl-CoA is a key molecule for nephron progenitor cell pool maintenance

Nephron endowment at birth impacts long-term renal and cardiovascular health, and it is contingent on the nephron progenitor cell (NPC) pool. Glycolysis modulation is essential for determining NPC fate, but the underlying mechanism is unclear. Combining RNA sequencing and quantitative proteomics we identify 267 genes commonly targeted by Wnt activation or glycolysis inhibition in NPCs. Several of the impacted pathways converge at Acetyl-CoA, a co-product of glucose metabolism. Notably, glycolysis inhibition downregulates key genes of the Mevalonate/cholesterol pathway and stimulates NPC differentiation. Sodium acetate supplementation rescues glycolysis inhibition effects and favors NPC maintenance without hindering nephrogenesis. Six2Cre-mediated removal of ATP-citrate lyase (Acly), an enzyme that converts citrate to acetyl-CoA, leads to NPC pool depletion, glomeruli count reduction, and increases Wnt4 expression at birth. Sodium acetate supplementation counters the effects of Acly deletion on cap-mesenchyme. Our findings show a pivotal role of acetyl-CoA metabolism in kidney development and uncover new avenues for manipulating nephrogenesis and preventing adult kidney disease.

Characterizing post-branching nephrogenesis in the neonatal rabbit

Human nephrogenesis ends prior to birth in term infants (34-36 week gestation), with most (60%) nephrons forming in late gestation in two post-branching nephrogenesis (PBN) periods: arcading and lateral branch nephrogenesis. Preterm infants, however, must execute PBN postnatally. Extreme prematurity is associated with low nephron counts. Identifying additional model(s) that undergo PBN postnatally will help support postnatal PBN in preterm infants. The rabbit exhibits longer postnatal nephrogenesis than the mouse but whether it forms nephrons through PBN has not been determined. We performed morphologic and immunohistological assessments of rabbit nephrogenesis from birth (post-conceptual day 31 or 32) to PC49 using H&E and antibodies against SIX1, SIX2, WT1, ZO-1, and JAG1 in the postnatal period. We performed 3D rendering of the nephrogenic niche to assess for PBN, and supplemented the staining with RNAScope to map the expression of Six1, Six2 (nephron progenitors, NPC), and Ret (ureteric bud tip) transcripts to determine the nephrogenic niche postnatal lifespan. Unlike the mouse, rabbit SIX2 disappeared from NPC before SIX1, resembling the human niche. Active nephrogenesis as defined by the presence of SIX1 + naïve NPC/tip population persisted only until PC35-36 (3-5 postnatal days). 3D morphologic assessments of the cortical nephrons identified an elongated tubule with attached glomeruli extending below the UB tip, consistent with PBN arcades, but not with lateral branch nephrogenesis. We conclude that the rabbit shows morphologic and molecular evidence of PBN arcades continuing postnatally for a shorter period than previously thought. The rabbit is the first non-primate expressing SIX1 in the progenitor population. Our findings suggest that studies of arcading in postnatal nephrogenic niche should be performed within the first 5 days of life in the rabbit.

YAP nuclear translocation induced by HIF-1α prevents DNA damage under hypoxic conditions

Maladaptive repair of acute kidney injury (AKI) is associated with a high risk of developing chronic kidney disease deemed irremediable even in present days. When AKI arises from ischemia-reperfusion injury, hypoxia usually plays a major role. Although both hypoxia-inducible factor-1α (HIF-1α) and yes-associated protein (YAP) have been proven to promote renal cell survival under hypoxia, there is a lack of research that studies the crosstalk of the two and its effect on kidney repair. In studying the crosstalk, CoCl2 was used to create a mimetic hypoxic environment. Immunoprecipitation and proximity ligation assays were performed to verify protein interactions. The results show that HIF-1α interacts with YAP and promotes nuclear translocation of YAP at a high cell density under hypoxic conditions, suggesting HIF-1α serves as a direct carrier that enables YAP nuclear translocation. This is the first study to identify HIF-1α as a crucial pathway for YAP nuclear translocation under hypoxic conditions. Once translocated into a nucleus, YAP protects cells from DNA damage and apoptosis under hypoxic conditions. Since it is unlikely for YAP to translocate into a nucleus without HIF-1α, any treatment that fosters the crosstalk between the two holds the potential to improve cell recovery from hypoxic insults.

PACS-2 deficiency aggravates tubular injury in diabetic kidney disease by inhibiting ER-phagy

Autophagy of endoplasmic reticulum (ER-phagy) selectively removes damaged ER through autophagy-lysosome pathway, acting as an adaptive mechanism to alleviate ER stress and restore ER homeostasis. However, the role and precise mechanism of ER-phagy in tubular injury of diabetic kidney disease (DKD) remain obscure. In the present study, we demonstrated that ER-phagy of renal tubular cells was severely impaired in streptozocin (STZ)-induced diabetic mice, with a decreased expression of phosphofurin acidic cluster sorting protein 2 (PACS-2), a membrane trafficking protein which was involved in autophagy, and a reduction of family with sequence similarity 134 member B (FAM134B), one ER-phagy receptor. These changes were further aggravated in mice with proximal tubule specific knockout of Pacs-2 gene. In vitro, transfection of HK-2 cells with PACS-2 overexpression plasmid partially improved the impairment of ER-phagy and the reduction of FAM134B, both of which were induced in high glucose ambience; while the effect was blocked by FAM134B siRNA. Mechanistically, PACS-2 interacted with and promoted the nuclear translocation of transcription factor EB (TFEB), which was reported to activate the expression of FAM134B. Collectively, these data unveiled that PACS-2 deficiency aggravates renal tubular injury in DKD via inhibiting ER-phagy through TFEB/FAM134B pathway.

NGAL is a Novel Target in Hypertension by Modulating the NCC-Mediated Renal Na Balance

BACKGROUND

The expression of NGAL/lcn2 (neutrophil gelatinase-associated lipocalin) is directly modulated by mineralocorticoid receptor activation but its role in blood pressure control is unclear.

METHODS

a potential relationship between NGAL plasma levels, systolic blood pressure and urinary Na excretion was assessed in the STANISLAS cohort. The specific role of NGAL/lcn2 in salt-sensitive hypertension was studied using lcn2-knockout mice (lcn2 KO) fed with low-Na diet (0Na).

RESULTS

we show that NGAL plasma levels positively correlate with systolic blood pressure, whereas they negatively correlate with urinary Na excretion in subjects of the STANISLAS cohort. Prolonged feeding of lcn2 KO mice with a 0Na diet induced lower systolic blood pressure than that of the control group (wildtype), suggesting a role for NGAL/lcn2 in Na-balance homeostasis. Short-term or prolonged 0Na increased Na-Cl cotransporter (NCC) phosphorylation in the cortex of wildtype mice, which was prevented in lcn2 KO mice. Recombinant mouse lcn2 injections in lcn2 KO mice induced NCC phosphorylation in the kidney cortex, associated with decreased urinary Na excretion. Ex vivo experiments using kidney slices from lcn2 KO mice showed increased NCC phosphorylation by recombinant murine lcn2. In addition, recombinant murine lcn2 induced activation of CamK2β (calcium/calmodulin-dependent protein kinase II β subunit) phosphorylation in lcn2 KO mice and in kidney slices, providing an underlying mechanism involved in lcn2-induced NCC phosphorylation. Indeed, the inhibition of CamK2β prevented NCC phosphorylation induced by recombinant lcn2 in kidney slices.

CONCLUSIONS

we highlight a novel role of NGAL/lcn2 as a modulator of the activity of the renal sodium transporter NCC affecting salt-sensitive blood pressure.

Targeted deletion of von-Hippel-Lindau in the proximal tubule conditions the kidney against early diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease. Glomerular hyperfiltration and albuminuria subject the proximal tubule (PT) to a subsequent elevation of workload, growth, and hypoxia. Hypoxia plays an ambiguous role in the development and progression of DKD and shall be clarified in our study. PT-von-Hippel-Lindau (Vhl)-deleted mouse model in combination with streptozotocin (STZ)-induced type I diabetes mellitus (DM) was phenotyped. In contrary to PT-Vhl-deleted STZ-induced type 1 DM mice, proteinuria and glomerular hyperfiltration occurred in diabetic control mice the latter due to higher nitric oxide synthase 1 and sodium and glucose transporter expression. PT Vhl deletion and DKD share common alterations in gene expression profiles, including glomerular and tubular morphology, and tubular transport and metabolism. Compared to diabetic control mice, the most significantly altered in PT Vhl-deleted STZ-induced type 1 DM mice were Ldc-1, regulating cellular oxygen consumption rate, and Zbtb16, inhibiting autophagy. Alignment of altered genes in heat maps uncovered that Vhl deletion prior to STZ-induced DM preconditioned the kidney against DKD. HIF-1α stabilization leading to histone modification and chromatin remodeling resets most genes altered upon DKD towards the control level. These data demonstrate that PT HIF-1α stabilization is a hallmark of early DKD and that targeting hypoxia prior to the onset of type 1 DM normalizes renal cell homeostasis and prevents DKD development.

A spatially anchored transcriptomic atlas of the human kidney papilla identifies significant immune injury in patients with stone disease

Kidney stone disease causes significant morbidity and increases health care utilization. In this work, we decipher the cellular and molecular niche of the human renal papilla in patients with calcium oxalate (CaOx) stone disease and healthy subjects. In addition to identifying cell types important in papillary physiology, we characterize collecting duct cell subtypes and an undifferentiated epithelial cell type that was more prevalent in stone patients. Despite the focal nature of mineral deposition in nephrolithiasis, we uncover a global injury signature characterized by immune activation, oxidative stress and extracellular matrix remodeling. We also identify the association of MMP7 and MMP9 expression with stone disease and mineral deposition, respectively. MMP7 and MMP9 are significantly increased in the urine of patients with CaOx stone disease, and their levels correlate with disease activity. Our results define the spatial molecular landscape and specific pathways contributing to stone-mediated injury in the human papilla and identify associated urinary biomarkers.

Soluble Klotho protects against glomerular injury through regulation of ER stress response

αKlotho (Klotho) has well established renoprotective effects; however, the molecular pathways mediating its glomerular protection remain incompletely understood. Recent studies have reported that Klotho is expressed in podocytes and protects glomeruli through auto- and paracrine effects. Here, we examined renal expression of Klotho in detail and explored its protective effects in podocyte-specific Klotho knockout mice, and by overexpressing human Klotho in podocytes and hepatocytes. We demonstrate that Klotho is not significantly expressed in podocytes, and transgenic mice with either a targeted deletion or overexpression of Klotho in podocytes lack a glomerular phenotype and have no altered susceptibility to glomerular injury. In contrast, mice with hepatocyte-specific overexpression of Klotho have high circulating levels of soluble Klotho, and when challenged with nephrotoxic serum have less albuminuria and less severe kidney injury compared to wildtype mice. RNA-seq analysis suggests an adaptive response to increased endoplasmic reticulum stress as a putative mechanism of action. To evaluate the clinical relevance of our findings, the results were validated in patients with diabetic nephropathy, and in precision cut kidney slices from human nephrectomies. Together, our data reveal that the glomeruloprotective effects of Klotho is mediated via endocrine actions, which increases its therapeutic potential for patients with glomerular diseases.

Relationship between clinical phenotype and in vitro analysis of 13 NPT2c/SCL34A3 mutants

Biallelic pathogenic variants in the SLC34A3 gene, encoding for the NPT2c cotransporter, cause Hereditary Hypophosphatemic Rickets with Hypercalciuria (HHRH). However, the associated phenotype is highly variable. In addition, mice deleted for Slc34a3 exhibit a different phenotype compared to humans, without urinary phosphate leakage. The mechanisms by which SLC34A3 variants disrupt phosphate/calcium metabolism are un-completely understood. In this study we explored these mechanisms in vitro using SLC34A3 variants identified in patients with urinary phosphate leakage. We analyzed the consequences of these variants on NPT2c function and the link with the phenotype of the patients. We studied 20 patients with recurrent nephrolithiasis and low serum phosphate concentration harboring variants in the SLC34A3 gene. Half of the patients carried homozygous or composite heterozygous variants. Three patients had in addition variants in SLC34A1 and SLC9A3R1 genes. All these patients benefited from a precise analysis of their phenotype. We generated 13 of these mutants by site-directed mutagenesis. Then we carried out transient transfections of these mutants in HEK cells and measured their phosphate uptake capacity under different conditions. Among the 20 patients included, 3 had not only mutations in NPT2c but also in NPT2a or NHERF1 genes. Phosphate uptake was decreased in 8 NPT2c mutants studied and normal for 5. Four variants were initially categorized as variants of uncertain significance. Expression of the corresponding mutants showed that one did not modify phosphate transport, two reduced it moderately and one abolished it. Co-transfection of the NPT2c mutants with the wild-type plasmid of NPT2c or NPT2a did not reveal dominant negative effect of the mutants on NPT2c-mediated phosphate transport. A detailed analysis of patient phenotypes did not find a link between the severity of the disorder and the level of phosphate transport impairment. NPT2c mutations classified as ACMG3 identified in patients with renal phosphate leak should be characterized by in vitro study to check if they alter NPT2c-mediated phosphate transport since phosphate uptake capacity may not be affected. In addition, research for mutations in NHERF1 and NPT2a genes should always be associated to NPT2c sequencing.

Terlipressin combined with conservative fluid management attenuates hemorrhagic shock-induced acute kidney injury in rats

Hemorrhagic shock (HS), a major cause of trauma-related mortality, is mainly treated by crystalloid fluid administration, typically with lactated Ringer's (LR). Despite beneficial hemodynamic effects, such as the restoration of mean arterial pressure (MAP), LR administration has major side effects, including organ damage due to edema. One strategy to avoid such effects is pre-hospitalization intravenous administration of the potent vasoconstrictor terlipressin, which can restore hemodynamic stability/homeostasis and has anti-inflammatory effects. Wistar rats were subjected to HS for 60 min, at a target MAP of 30-40 mmHg, thereafter being allocated to receive LR infusion at 3 times the volume of the blood withdrawn (liberal fluid management); at 2 times the volume (conservative fluid management), plus terlipressin (10 µg/100 g body weight); and at an equal volume (conservative fluid management), plus terlipressin (10 µg/100 g body weight). A control group comprised rats not subjected to HS and receiving no fluid resuscitation or treatment. At 15 min after fluid resuscitation/treatment, the blood previously withdrawn was reinfused. At 24 h after HS, MAP was higher among the terlipressin-treated animals. Terlipressin also improved post-HS survival and provided significant improvements in glomerular/tubular function (creatinine clearance), neutrophil gelatinase-associated lipocalin expression, fractional excretion of sodium, aquaporin 2 expression, tubular injury, macrophage infiltration, interleukin 6 levels, interleukin 18 levels, and nuclear factor kappa B expression. In terlipressin-treated animals, there was also significantly higher angiotensin II type 1 receptor expression and normalization of arginine vasopressin 1a receptor expression. Terlipressin associated with conservative fluid management could be a viable therapy for HS-induced acute kidney injury, likely attenuating such injury by modulating the inflammatory response via the arginine vasopressin 1a receptor.

Immune-mediated tubule atrophy promotes acute kidney injury to chronic kidney disease transition

Incomplete repair after acute kidney injury can lead to development of chronic kidney disease. To define the mechanism of this response, we compared mice subjected to identical unilateral ischemia-reperfusion kidney injury with either contralateral nephrectomy (where tubule repair predominates) or contralateral kidney intact (where tubule atrophy predominates). By day 14, the kidneys undergoing atrophy had more macrophages with higher expression of chemokines, correlating with a second wave of proinflammatory neutrophil and T cell recruitment accompanied by increased expression of tubular injury genes and a decreased proportion of differentiated tubules. Depletion of neutrophils and T cells after day 5 reduced tubular cell loss and associated kidney atrophy. In kidney biopsies from patients with acute kidney injury, T cell and neutrophil numbers negatively correlated with recovery of estimated glomerular filtration rate. Together, our findings demonstrate that macrophage persistence after injury promotes a T cell- and neutrophil-mediated proinflammatory milieu and progressive tubule damage.

Alterations in fetal kidney development and increased risk for adult diseases

A low birth weight (LBW, < 2500 g), intrauterine growth restriction (IUGR), and preterm birth (PB, < 37 weeks of gestational age) are the most common clinical factors for an altered programming of nephron number and are associated with a greater risk for hypertension, proteinuria, and kidney disease later in life. At present, an indirect assessment of total nephron number based on postnatal markers is the most important approach to evaluate the risk for future kidney disorders in newborn infants with a LBW, IUGR or PB. Here we describe advances made in animal experiments and biochemical markers in humans, and the recommendations for the prevention of preconception kidney injury, including social factors and chronic diseases. According to the evidence, IUGR and prematurity alone can modulate nephrogenesis and kidney function, and, if occurring simultaneously, their effects tend to be cumulative.

Multiomic analysis of the Arabian camel (Camelus dromedarius) kidney reveals a role for cholesterol in water conservation

The Arabian camel (Camelus dromedarius) is the most important livestock animal in arid and semi-arid regions and provides basic necessities to millions of people. In the current context of climate change, there is renewed interest in the mechanisms that enable camelids to survive in arid conditions. Recent investigations described genomic signatures revealing evolutionary adaptations to desert environments. We now present a comprehensive catalogue of the transcriptomes and proteomes of the dromedary kidney and describe how gene expression is modulated as a consequence of chronic dehydration and acute rehydration. Our analyses suggested an enrichment of the cholesterol biosynthetic process and an overrepresentation of categories related to ion transport. Thus, we further validated differentially expressed genes with known roles in water conservation which are affected by changes in cholesterol levels. Our datasets suggest that suppression of cholesterol biosynthesis may facilitate water retention in the kidney by indirectly facilitating the AQP2-mediated water reabsorption.

Epithelial Sodium Channel and Salt-Sensitive Hypertension

The development of high blood pressure is influenced by genetic and environmental factors, with high salt intake being a known environmental contributor. Humans display a spectrum of sodium-sensitivity, with some individuals displaying a significant blood pressure rise in response to increased sodium intake while others experience almost no change. These differences are, in part, attributable to genetic variation in pathways involved in sodium handling and excretion. ENaC (epithelial sodium channel) is one of the key transporters responsible for the reabsorption of sodium in the distal nephron. This channel has an important role in the regulation of extracellular fluid volume and consequently blood pressure. Herein, we review the role of ENaC in the development of salt-sensitive hypertension, and present mechanistic insights into the regulation of ENaC activity and how it may accelerate sodium-induced damage and dysfunction. We discuss the traditional role of ENaC in renal sodium reabsorption and review work addressing ENaC expression and function in the brain, vasculature, and immune cells, and how this has expanded the implications for its role in the initiation and progression of salt-sensitive hypertension.

Nitric oxide signalling in kidney regulation and cardiometabolic health

The prevalence of cardiovascular and metabolic disease coupled with kidney dysfunction is increasing worldwide. This triad of disorders is associated with considerable morbidity and mortality as well as a substantial economic burden. Further understanding of the underlying pathophysiological mechanisms is important to develop novel preventive or therapeutic approaches. Among the proposed mechanisms, compromised nitric oxide (NO) bioactivity associated with oxidative stress is considered to be important. NO is a short-lived diatomic signalling molecule that exerts numerous effects on the kidneys, heart and vasculature as well as on peripheral metabolically active organs. The enzymatic L-arginine-dependent NO synthase (NOS) pathway is classically viewed as the main source of endogenous NO formation. However, the function of the NOS system is often compromised in various pathologies including kidney, cardiovascular and metabolic diseases. An alternative pathway, the nitrate-nitrite-NO pathway, enables endogenous or dietary-derived inorganic nitrate and nitrite to be recycled via serial reduction to form bioactive nitrogen species, including NO, independent of the NOS system. Signalling via these nitrogen species is linked with cGMP-dependent and independent mechanisms. Novel approaches to restoring NO homeostasis during NOS deficiency and oxidative stress have potential therapeutic applications in kidney, cardiovascular and metabolic disorders.

Endoscopic Treatment for Large Multifocal Upper Tract Urothelial Carcinoma

PURPOSE

We reviewed the oncologic and surgical outcomes of endoscopic treatments for low grade upper tract urothelial carcinoma, and assessed the prognostic significance of tumor size, location and multifocality.

MATERIALS AND METHODS

We retrospectively reviewed all patients who underwent endoscopic treatment for low grade upper tract urothelial carcinoma at our institution between 2014 and 2019. Tumors were treated with a dual laser generator, which alternately produces holmium and neodymium lasers. A stringent ureteroscopic followup protocol was conducted. We looked for an association between outcome and tumor size, location or multifocality, and for predictive factors for time to local recurrence and progression.

RESULTS

The cohort included 59 patients (62 renal units), 27% of tumors were multifocal and 40% were >2 cm. The median followup time was 22 months (IQR 11-41), and the median number of ureteroscopies was 5.5 (4-9). Local recurrence was observed in 46 renal units (74.1%) at a median of 6.5 months after initial surgery. Four patients (6.4%) developed disease progression and were referred for radical surgery: 2 had pathological progression and 2 had a rapid and high volume local recurrence, and 1 later developed metastatic disease. The progression-free rate was 93.2%. Tumor location in kidney (p=0.03, HR 1.95) and multifocality (p=0.005, HR 3.25) significantly predicted time to local recurrence. No factor predicted time to progression.

CONCLUSIONS

Ureteroscopic treatment of large, multifocal, low grade upper tract urothelial carcinoma is feasible, does not involve significant complications and has good short-term oncologic outcomes, with a 93.2% progression-free survival rate. Tumors located in the kidney and multifocality yielded shorter time to local recurrence but not progression.

High Salt Intake-Increased (Pro)renin Receptor Expression Is Exaggerated in the Kidney of Dahl Salt-Sensitive Rats

The (P)RR ([pro]renin receptor) was identified as a new component of the renin-angiotensin system. We previously reported that high salt (HS) intake increased the (P)RR expression in several nephron segments of Sprague-Dawley rats. Other studies reported HS intake increased the XO (xanthine oxidase) activity and an MR (mineralocorticoid receptor) antagonist inhibited HS intake-increased (P)RR expression in the kidneys of Dahl salt-sensitive (DS) rats. The present study examined the effects of HS intake on (P)RR expression in the kidney of DS rats. Male DS rats were fed a normal salt diet or an HS diet for 4 weeks. Some of the rats fed on the HS diet were treated with the XO inhibitor, febuxostat, and the MR antagonist, spironolactone. Immunoblot and immunohistochemical analyses showed that HS intake increased (P)RR expression in the renal cortex by 22.6-fold, the proximal tubules by 4.9-fold and the distal tubules, respectively. Both febuxostat and spironolactone inhibited HS intake-increased (P)RR expression in the renal cortex. Febuxostat inhibited HS intake-increased (P)RR expression in the proximal tubules, whereas spironolactone inhibited HS intake-increased (P)RR expression in the distal tubules. Additionally, deoxycorticosterone acetate increased (P)RR expression in the renal cortex and distal tubules but not in the proximal tubules of DS rats fed the normal salt diet. These results indicate that HS intake greatly increases (P)RR expression in the renal cortex of DS rats. The mechanisms of HS intake-increased (P)RR expression may work in an XO-dependent manner in the proximal tubules and an MR-dependent manner in the distal tubules.

A Primer on Congenital Anomalies of the Kidneys and Urinary Tracts (CAKUT)

Congenital anomalies of the kidneys and urinary tracts (CAKUT) are disorders caused by defects in the development of the kidneys and their outflow tracts. The formation of the kidneys begins at week 3 and nephrogenesis continues until week 36, therefore, the kidneys and outflow tracts are susceptible to environmental risk factors that perturb development throughout gestation. Many genes have been implicated in kidney and outflow tract development, and mutations have been identified in patients with CAKUT. In severe cases of CAKUT, when the kidneys do not form, the fetus will not survive. However, in less severe cases, the baby can survive with combined kidney and outflow tract defects or they may only be identified in adulthood. In this review, we will cover the clinical presentation of CAKUT, its epidemiology, and its long-term outcomes. We will then discuss risk factors for CAKUT, including genetic and environmental contributions. Although severe CAKUT is rare, low nephron number is a much more common disorder with its effect on kidney function increasingly apparent as a person ages. Low nephron number appears to arise by the same mechanisms as CAKUT, but it differs in terms of the magnitude of the insult and the timing of when it occurs during gestation. By understanding the causes of CAKUT and low nephron number, we can begin to identify preventive treatments and establish clinical guidelines for how these patients should be followed.

Alterations of Proximal Tubular Secretion in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES

In autosomal dominant polycystic kidney disease (ADPKD), the GFR often remains normal despite significant nephron loss. Proximal tubular secretory clearance may be reduced in ADPKD before detectable changes in GFR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We used targeted mass spectrometry to quantify secretory solutes from blood and urine samples from 31 patients with ADPKD and preserved GFR (mean eGFR =111±11 ml/min per 1.73 m²) and 25 healthy control individuals as well as from 95 patients with ADPKD and reduced GFR (mean eGFR =53±21 ml/min per 1.73 m²) and 92 individuals with non-ADPKD CKD. We used linear regression to compare the fractional excretion of each solute between ADPKD and control groups. Among 112 patients with ADPKD, we used linear regression to determine associations of solute fractional excretion with height-adjusted total kidney volume.

RESULTS

After adjusting for demographics, clinical characteristics, and kidney function measures, the fractional excretions of three secretory solutes were lower in patients with ADPKD and preserved GFR compared with healthy individuals: 52% lower cinnamoylglycine excretion (95% confidence interval, 24% to 70%), 53% lower tiglylglycine excretion (95% confidence interval, 23% to 71%), and 91% lower xanthosine excretion (95% confidence interval, 83% to 95%). In addition to lower excretions of tiglylglycine and xanthosine, patients with ADPKD and reduced GFR also demonstrated 37% lower dimethyluric acid excretion (95% confidence interval, 21% to 50%), 58% lower hippurate excretion (95% confidence interval, 48% to 66%), 48% lower isovalerylglycine excretion (95% confidence interval, 37% to 56%), and 31% lower pyridoxic acid excretion (95% confidence interval, 16% to 42%) compared with patients with non-ADPKD CKD and comparable eGFR. Among patients with ADPKD, solute fractional excretions were not associated with differences in kidney volume.

CONCLUSIONS

Patients with ADPKD and preserved and reduced GFR demonstrate lower tubular secretory solute excretion compared with healthy controls and patients with non-ADPKD CKD. Our results suggest that tubular secretion is impaired in ADPKD independent of GFR.

The Role of Volume Regulation and Thermoregulation in AKI during Marathon Running

BACKGROUND AND OBJECTIVES

Marathon runners develop transient AKI with urine sediments and injury biomarkers suggesting nephron damage.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

To investigate the etiology, we examined volume and thermoregulatory responses as possible mechanisms in runners' AKI using a prospective cohort of runners in the 2017 Hartford Marathon. Vitals, blood, and urine samples were collected in 23 runners 1 day premarathon and immediately and 1 day postmarathon. We measured copeptin at each time point. Continuous core body temperature, sweat sodium, and volume were assessed during the race. The primary outcome of interest was AKI, defined by AKIN criteria.

RESULTS

Runners ranged from 22 to 63 years old; 43% were men. Runners lost a median (range) of 2.34 (0.50-7.21) g of sodium and 2.47 (0.36-6.81) L of volume via sweat. After accounting for intake, they had a net negative sodium and volume balance at the end of the race. The majority of runners had increases in core body temperature to 38.4 (35.8-41)°C during the race from their baseline. Fifty-five percent of runners developed AKI, yet 74% had positive urine microscopy for acute tubular injury. Runners with more running experience and increased participation in prior marathons developed a rise in creatinine as compared with those with lesser experience. Sweat sodium losses were higher in runners with AKI versus non-AKI (median, 3.41 [interquartile range (IQR), 1.7-4.8] versus median, 1.4 [IQR, 0.97-2.8] g; P=0.06, respectively). Sweat volume losses were higher in runners with AKI versus non-AKI (median, 3.89 [IQR, 1.49-5.09] versus median, 1.66 [IQR, 0.72-2.84] L; P=0.03, respectively). Copeptin was significantly higher in runners with AKI versus those without (median, 79.9 [IQR, 25.2-104.4] versus median, 11.3 [IQR, 6.6-43.7]; P=0.02, respectively). Estimated temperature was not significantly different.

CONCLUSIONS

All runners experienced a substantial rise in copeptin and body temperature along with salt and water loss due to sweating. Sodium and volume loss via sweat as well as plasma copeptin concentrations were associated with AKI in runners.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_08_13_CJASNPodcast_19_09_.mp3.

Donor-Recipient Weight and Sex Mismatch and the Risk of Graft Loss in Renal Transplantation

BACKGROUND AND OBJECTIVES

Relatively smaller kidney donor to recipient size is proposed to result in higher graft loss due to nephron underdosing and hyperfiltration injury, but the potentially additive effect of sex and weight mismatch has not been explored in detail. The purpose of this study was to determine if concurrent donor and recipient absolute weight and sex mismatch was associated with graft loss in a cohort of deceased donor kidney transplant recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The association of kidney donor and recipient absolute weight and sex difference with death-censored graft loss was explored using a cohort of United States deceased donor recipients between 2000 and 2014 through the Scientific Registry of Transplants Recipients. Donor-recipient sex pairings (male donor-male recipient; female donor-female recipient; male donor-female recipient; female donor-male recipient) were further stratified by donor and recipient absolute weight difference (>30 or 10-30 kg [donorrecipient] or <10 kg [donor=recipient]) resulting in 20 weight and sex pairings. Time to death-censored graft loss for each pairing was evaluated using multivariable Cox proportional hazards models adjusting for donor, immunologic, surgical, and recipient predictors of graft loss compared with the reference group of male donor-male recipients with no weight mismatch (<10 kg difference).

RESULTS

Of 115,124 kidney transplant recipients, 21,261 developed death-censored graft failure (median graft survival time was 3.8 years; quartile 1 to 3, 0.0 to 14.8 years). After multivariable adjustment, the highest relative hazards for graft failure were observed for female recipients of male donor kidneys and male recipients of female donor kidneys in situations where the recipient was >30 kg larger than donor (hazard ratio, 1.50; 95% confidence interval, 1.32 to 1.70; hazard ratio, 1.35; 95% confidence interval, 1.25 to 1.45, respectively).

CONCLUSIONS

A concurrent mismatch in donor-recipient weight (donor Collapse

Key Words

• United States
• female
• graft failure
• graft survival
• kidney
• kidney transplantation
• male
• nephrons
• proportional hazards models
• registries
• sex characteristics
• sex mismatch
• size mismatch
• tissue donors
• transplant recipients

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MESH Headings

• Adult
• Body Weight
• Cohort Studies
• Female
• Graft Survival
• Humans
• Kidney Transplantation/statistics & numerical data
• Male
• Middle Aged
• Proportional Hazards Models
• Registries
• Risk Factors
• Sex Factors
• Tissue Donors
• Transplant Recipients
• United States

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Affiliation(s)

Amanda J. Miller Department of Medicine, Division of Nephrology, and
Bryce A. Kiberd Department of Medicine, Division of Nephrology, and
Ian P. Alwayn Department of General Surgery, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada; and
Ayo Odutayo Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, United Kingdom
Karthik K. Tennankore Department of Medicine, Division of Nephrology, and

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Glomerular Density and Volume in Renal Biopsy Specimens of Children with Proteinuria Relative to Preterm Birth and Gestational Age

BACKGROUND AND OBJECTIVES

A low total nephron number, which is associated with low birth weight (LBW), may indicate increased susceptibility to early-onset renal diseases in children. However, few studies have assessed renal biopsy findings in LBW children. We examined the relationship between LBW and glomerular density (GD) and/or glomerular volume (GV) in renal biopsy samples as a surrogate for total nephron number.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal biopsy findings of children of LBW were compared with those of age-matched control subjects of normal birth weight (NBW) who were histopathologically diagnosed with FSGS or minimal change nephrotic syndrome (MCNS) from 1995 to 2011. The GD and GV were estimated on the basis of measurements obtained by computerized image analysis.

RESULTS

A total of 31 subjects (mean age 11 years; eight with low birth weight-FSGS [LBW-FSGS], 10 with normal birth weight-FSGS [NBW-FSGS], and 13 with normal birth weight-minimal change nephrotic syndrome [NBW-MCNS]) were analyzed. The mean birth weight of each group was 777 g (629-1000), 3110 g (2888-3358), and 3120 g (2748-3398), respectively (median [25th-75th percentile]). Age, body mass index, BP, and degrees of globally sclerotic glomeruli at biopsy were comparable between the groups. The GD was lower (LBW-FSGS, 1.4±0.6/mm2; NBW-FSGS, 3.3±1.2/mm2; and NBW-MCNS, 3.6±1.1/mm2; P<0.05) and the GV was greater (LBW-FSGS, 4.1 [3.1-5.1]×106µm3; NBW-FSGS, 1.6 [1.5-2.1]×106µm3; and NBW-MCNS, 1.3 [1.1-1.8]×106µm3 [median, (25th-75th percentile)]; P<0.05) in patients with LBW-FSGS than in the other patient groups. The GD showed close positive correlations with birth weight (r=0.48) and gestational age (r=0.54), independent of renal function and degree of global glomerular sclerosis.

CONCLUSIONS

A low GD together with marked glomerular enlargement characterizes renal biopsy samples of children born with a LBW at an early stage of gestation.

Comparing Zero Ischemia Laparoscopic Radio Frequency Ablation Assisted Tumor Enucleation and Laparoscopic Partial Nephrectomy for Clinical T1a Renal Tumor: A Randomized Clinical Trial

PURPOSE

We evaluated the functional outcome, safety and efficacy of zero ischemia laparoscopic radio frequency ablation assisted tumor enucleation compared with conventional laparoscopic partial nephrectomy.

MATERIALS AND METHODS

A prospective randomized controlled trial was conducted from April 2013 to March 2015 in patients with cT1a renal tumor scheduled for laparoscopic nephron sparing surgery. All patients were followed for at least 12 months. Patients in the laparoscopic radio frequency ablation assisted tumor enucleation group underwent tumor enucleation after radio frequency ablation without hilar clamping. The primary outcome was the change in glomerular filtration rate of the affected kidney by renal scintigraphy at 12 months. Secondary outcomes included changes in estimated glomerular filtration rate, estimated blood loss, operative time, hospital stay, postoperative complications and oncologic outcomes. The Pearson chi-square or Fisher exact, Student t-test and Wilcoxon rank sum tests were used.

RESULTS

The trial ultimately enrolled 89 patients, of whom 44 were randomized to the laparoscopic radio frequency ablation assisted tumor enucleation group and 45 to the laparoscopic partial nephrectomy group. In the laparoscopic partial nephrectomy group 1 case was converted to radical nephrectomy. Compared with the laparoscopic partial nephrectomy group, patients in the laparoscopic radio frequency ablation assisted tumor enucleation group had a smaller decrease in glomerular filtration rate of the affected kidney at 3 months (10.2% vs 20.5%, p=0.001) and 12 months (7.6% vs 16.2%, p=0.002). Patients in the laparoscopic radio frequency ablation assisted tumor enucleation group had a shorter operative time (p=0.002), lower estimated blood loss (p <0.001) and a shorter hospital stay (p=0.029) but similar postoperative complications (p=1.000). There were no positive margins or local recurrence in this study.

CONCLUSIONS

Zero ischemia laparoscopic radio frequency ablation assisted tumor enucleation enables tumor excision with better renal function preservation compared to conventional laparoscopic partial nephrectomy. Less blood loss and a shorter operative time were achieved with similar postoperative complication rates.

The Fate of Nephrons in Congenital Obstructive Nephropathy: Adult Recovery is Limited by Nephron Number Despite Early Release of Obstruction

PURPOSE

Urinary tract obstruction and reduced nephron number often occur together as a result of maldevelopment of the kidneys and the urinary tract. We determined the role of nephron number on adaptation of the remaining nephrons of mice subjected to neonatal partial unilateral ureteral obstruction followed through adulthood.

MATERIALS AND METHODS

Wild-type and Os/+ mice (the latter with 50% fewer nephrons) underwent sham operation or partial unilateral ureteral obstruction in the first 2 days of life. Additional mice underwent release of unilateral ureteral obstruction at 7 days. All kidneys were harvested at 3 weeks (weaning) or 6 weeks (adulthood). Glomerular number and area, glomerulotubular junction integrity, proximal tubular volume fraction and interstitial fibrosis were measured by histomorphometry.

RESULTS

In the obstructed kidney unilateral ureteral obstruction caused additional nephron loss in Os/+ but not in wild-type mice. Glomerular growth from 3 to 6 weeks was impaired by ipsilateral obstruction and not preserved by release in wild-type or Os/+ mice. Proximal tubular growth was impaired and interstitial collagen was increased by ipsilateral obstruction in all mice. These conditions were attenuated by release of unilateral ureteral obstruction in wild-type mice but were not restored in Os/+ mice. Unilateral ureteral obstruction increased interstitial collagen in the contralateral kidney while release of obstruction enhanced tubular growth and reduced interstitial collagen.

CONCLUSIONS

Unilateral ureteral obstruction in early postnatal development impairs adaptation to reduced nephron number and induces additional nephron loss despite release of obstruction. Premature and low birth weight infants with congenital obstructive nephropathy are likely at increased risk for progression of chronic kidney disease.

Chronic angiotensin II infusion drives extensive aldosterone-independent epithelial Na+ channel activation

The inability of mineralocorticoid receptor (MR) blockade to reduce hypertension associated with high angiotensin (Ang) II suggests direct actions of Ang II to regulate tubular sodium reabsorption via the epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron. We used freshly isolated aldosterone-sensitive distal nephron from mice to delineate the synergism and primacy between aldosterone and Ang II in controlling functional ENaC activity. Inhibition of MR specifically prevented the increased number of functionally active ENaC, but not ENaC open probability elicited by a low sodium diet. In contrast, we found no functional role of glucocorticoid receptors in the regulation of ENaC activity by dietary salt intake. Simultaneous inhibition of MR and Ang II type 1 receptors ameliorated the enhanced ENaC activity caused by low dietary salt intake and produced significantly greater natriuresis than either inhibitor alone. Chronic systemic Ang II infusion induced more than 2 times greater increase in ENaC activity than observed during dietary sodium restriction. Importantly, ENaC activity remained greatly above control levels during maximal MR inhibition. We conclude that during variations in dietary salt intake both aldosterone and Ang II contribute complementarily to the regulation of ENaC activity in the aldosterone-sensitive distal nephron. In contrast, in the setting of Ang II-dependent hypertension, ENaC activity is upregulated well above the physiological range and is not effectively suppressed by inhibition of the aldosterone-MR axis. This provides a mechanistic explanation for the resistance to MR inhibition that occurs in hypertensive subjects having elevated intrarenal Ang II levels.

Prorenin receptor in distal nephron segments of 2-kidney, 1-clip goldblatt hypertensive rats

BACKGROUND

The prorenin receptor (PRR) is expressed in the kidneys and has been localized to mesangial cells, renal arterioles, and distal nephron segments. By binding renin or prorenin, this receptor increases renin catalytic activity and activates prorenin. The renin gene is expressed by the principal cells of collecting ducts and is enhanced in angiotensin II (AngII)-dependent hypertension and in both kidneys of 2-kidney, 1-clip (2K1C) Goldblatt hypertensive rats. Colocalization of PRR with prorenin and renin in distal nephron segments may contribute to increased local AngII formation.

METHODS

We examined the specific cell-type localization of PRR in distal nephron segments and the changes in PRR gene expression in both kidneys of 2K1C hypertensive rats (n=6) and sham-operated rats (n=5).

RESULTS

After 25 days, systolic blood pressure and plasma renin activity increased to 186 ± 8 mmHg and 12.8 ± 3 ng/AngI/mL/hr, respectively, in 2K1C rats compared to controls (133 ± 9 mmHg and 7.1 ± 1 ng/AngI/mL/hr, respectively). Immunohistochemistry of the PRR on fixed kidney sections showed intense positive staining in the apical aspects of intercalated cells in collecting ducts. PRR immunoreactivity (clipped kidney: 2.3 ± 1 IDU; nonclipped kidney: 1.3 ± 0 IDU; sham: 1.0 ± 0.0 IDU; P<0.05) and messenger RNA levels measured by quantitative real-time polymerase chain reaction (clipped kidney: 1.3 ± 0.1 au; nonclipped kidney: 0.9 ± 0.3 au; sham: 1 ± 0.0 au; P<0.05] were increased in collecting duct cells of clipped kidneys of 2K1C rats compared to nonclipped and sham kidneys.

CONCLUSION

The enhanced renin gene expression in the collecting ducts of hypertensive rats suggests that the renin secreted by principal cells is then anchored by the PRR on the intercalated cells, thus contributing to increased angiotensin peptide generation in distal nephron segments.