Spatiotemporal Landscape of Kidney Tubular Responses to Glomerular Proteinuria

BACKGROUND

Large increases in glomerular protein filtration induce major changes in body homeostasis and increase risk of kidney functional decline and cardiovascular disease. We investigated how elevated protein exposure modifies the landscape of tubular function along the entire nephron, to understand the cellular changes that mediate these important clinical phenomena.

METHODS

We conducted single nuclei RNA sequencing, functional intravital imaging, and antibody staining to spatially map transport processes along the mouse kidney tubule. We then delineated how these were altered in a transgenic mouse model of inducible glomerular proteinuria (POD-ATTAC) at 7 and 28 days.

RESULTS

Glomerular proteinuria activated large-scale and pleotropic changes in gene expression in all major nephron sections. Extension of protein uptake from early (S1) to later (S2) parts of the proximal tubule initially triggered dramatic expansion of a hybrid S1/2 population, followed by injury and failed repair, with the cumulative effect of loss of canonical S2 functions. Proteinuria also induced acute injury in S3. Meanwhile, overflow of luminal proteins to the distal tubule caused transcriptional convergence between specialized regions and generalized dedifferentiation.

CONCLUSIONS

Proteinuria modulated cell signaling in tubular epithelia and causes distinct patterns of remodeling and injury in a segment specific manner.

The role of hypoxia in chronic kidney disease: a nuanced perspective

PURPOSE OF REVIEW

This review critically examines the role of hypoxia in chronic kidney disease (CKD). While traditionally viewed as detrimental, recent insights suggest a more nuanced understanding of hypoxia's role during renal disease.

RECENT FINDINGS

Emerging evidence challenges the traditional view that hypoxia is universally harmful in CKD context. We review here the recent evidence about hypoxia and HIF activation in CKD. We also discuss the effect of hypoxia on the renal tissue, and the relative inhibition of different HIF isoforms. Recent advancements in therapies, such as HIF prolyl hydroxylase inhibitors (HIF-PHIs) and sodium-glucose cotransporter 2 (SGLT2) inhibitors seem to target the HIF pathway. These drugs impact anemia associated with CKDbut also renoprotection, hinting at a more complex interplay between hypoxia, HIF activation, and renal health.

SUMMARY

A certain level of hypoxia and specific HIF pathway activation, especially HIF-α, can be beneficial in CKD progression. Therapeutic strategies targeting HIF stabilization, such as with HIF-PHIs and SGLT2 inhibitors, offer promising avenues for enhancing renal protection. Future investigations should aim at better understanding the precise effects on HIF pathway and optimize their clinical application to improve outcomes for CKD patients.

A transfer learning framework to elucidate the clinical relevance of altered proximal tubule cell states in kidney disease

The application of single-cell technologies in clinical nephrology remains elusive. We generated an atlas of transcriptionally defined cell types and cell states of human kidney disease by integrating single-cell signatures reported in the literature with newly generated signatures obtained from 5 patients with acute kidney injury. We used this information to develop kidney-specific cell-level information ExtractoR (K-CLIER), a transfer learning approach specifically tailored to evaluate the role of cell types/states on bulk RNAseq data. We validated the K-CLIER as a reliable computational framework to obtain a dimensionality reduction and to link clinical data with single-cell signatures. By applying K-CLIER on cohorts of patients with different kidney diseases, we identified the most relevant cell types associated with fibrosis and disease progression. This analysis highlighted the central role of altered proximal tubule cells in chronic kidney disease. Our study introduces a new strategy to exploit the power of single-cell technologies toward clinical applications.

Short-term hypercaloric carbohydrate loading increases surgical stress resilience by inducing FGF21

Dietary restriction promotes resistance to surgical stress in multiple organisms. Counterintuitively, current medical protocols recommend short-term carbohydrate-rich drinks (carbohydrate loading) prior to surgery, part of a multimodal perioperative care pathway designed to enhance surgical recovery. Despite widespread clinical use, preclinical and mechanistic studies on carbohydrate loading in surgical contexts are lacking. Here we demonstrate in ad libitum-fed mice that liquid carbohydrate loading for one week drives reductions in solid food intake, while nearly doubling total caloric intake. Similarly, in humans, simple carbohydrate intake is inversely correlated with dietary protein intake. Carbohydrate loading-induced protein dilution increases expression of hepatic fibroblast growth factor 21 (FGF21) independent of caloric intake, resulting in protection in two models of surgical stress: renal and hepatic ischemia-reperfusion injury. The protection is consistent across male, female, and aged mice. In vivo, amino acid add-back or genetic FGF21 deletion blocks carbohydrate loading-mediated protection from ischemia-reperfusion injury. Finally, carbohydrate loading induction of FGF21 is associated with the induction of the canonical integrated stress response (ATF3/4, NF-kB), and oxidative metabolism (PPARγ). Together, these data support carbohydrate loading drinks prior to surgery and reveal an essential role of protein dilution via FGF21.

Evolution of hypoxia and hypoxia-inducible factor asparaginyl hydroxylase regulation in chronic kidney disease

BACKGROUND

The roles of hypoxia and hypoxia inducible factor (HIF) during chronic kidney disease (CKD) are much debated. Interventional studies with HIF-α activation in rodents have yielded contradictory results. The HIF pathway is regulated by prolyl and asparaginyl hydroxylases. While prolyl hydroxylase inhibition is a well-known method to stabilize HIF-α, little is known about the effect asparaginyl hydroxylase factor inhibiting HIF (FIH).

METHODS

We used a model of progressive proteinuric CKD and a model of obstructive nephropathy with unilateral fibrosis. In these models we assessed hypoxia with pimonidazole and vascularization with three-dimensional micro-computed tomography imaging. We analysed a database of 217 CKD biopsies from stage 1 to 5 and we randomly collected 15 CKD biopsies of various severity degrees to assess FIH expression. Finally, we modulated FIH activity in vitro and in vivo using a pharmacologic approach to assess its relevance in CKD.

RESULTS

In our model of proteinuric CKD, we show that early CKD stages are not characterized by hypoxia or HIF activation. At late CKD stages, some areas of hypoxia are observed, but these are not colocalizing with fibrosis. In mice and in humans, we observed a downregulation of the HIF pathway, together with an increased FIH expression in CKD, according to its severity. Modulating FIH in vitro affects cellular metabolism, as described previously. In vivo, pharmacologic FIH inhibition increases the glomerular filtration rate of control and CKD animals and is associated with decreased development of fibrosis.

CONCLUSIONS

The causative role of hypoxia and HIF activation in CKD progression is questioned. A pharmacological approach of FIH downregulation seems promising in proteinuric kidney disease.

Gluconeogenesis in the kidney: in health and in chronic kidney disease

Chronic kidney disease (CKD) is a global health issue with increasing prevalence. Despite large improvements in current therapies, slowing CKD progression remains a challenge. A better understanding of renal pathophysiology is needed to offer new therapeutic targets. The role of metabolism alterations and mitochondrial dysfunction in tubular cells is increasingly recognized in CKD progression. In proximal tubular cells, CKD progression is associated with a switch from fatty acid oxidation to glycolysis. Glucose synthesis through gluconeogenesis is one of the principal physiological functions of the kidney. Loss of tubular gluconeogenesis in a stage-dependent manner is a key feature of CKD and contributes to systemic and possibly local metabolic complications. The local consequences observed may be related to an accumulation of precursors, such as glycogen, but also to the various physiological functions of the gluconeogenesis enzymes. The basic features of metabolism in proximal tubular cells and their modifications during CKD will be reviewed. The metabolic modifications and their influence on kidney disease will be described, as well as the local and systemic consequences. Finally, therapeutic interventions will be discussed.

Calcification Propensity (T50) Predicts a Rapid Decline of Renal Function in Kidney Transplant Recipients

BACKGROUND

Serum creatinine level, proteinuria, and interstitial fibrosis are predictive of renal prognosis. Fractional excretion of phosphate (FEP)/FGF23 ratio, tubular reabsorption of phosphate (TRP), serum calcification propensity (T50), and Klotho's serum level are emerging as determinants of poor kidney outcomes in CKD patients. We aimed at analysing the use of FGF23, FEP/FGF23, TRP, T50, and Klotho in predicting the rapid decline of renal function in kidney allograft recipients.

METHODS

We included 103 kidney allograft recipients in a retrospective study with a prospective follow-up of 4 years. We analysed the predictive values of FGF23, FEP/FGF23, TRP, T50, and Klotho for a rapid decline of renal function defined as a drop of eGFR > 30%.

RESULTS

During a follow-up of 4 years, 23 patients displayed a rapid decline of renal function. Tertile of FGF23 (p value = 0.17), FEP/FGF23 (p value = 0.78), TRP (p value = 0.62) and Klotho (p value = 0.31) were not associated with an increased risk of rapid decline of renal function in kidney transplant recipients. The lower tertile of T50 was significantly associated with eGFR decline >30% with a hazard ratio of 3.86 (p = 0.048) and remained significant in multivariable analysis.

CONCLUSION

T50 showed a strong association with a rapid decline of renal function in kidney allograft patients. This study underlines its role as an independent biomarker of loss of kidney function. We found no association between other phosphocalcic markers, such as FGF23, FEP/FGF23, TRP and Klotho, with a rapid decline of renal function in kidney allograft recipients.

PCK1 is a key regulator of metabolic and mitochondrial functions in renal tubular cells

Phosphoenolpyruvate carboxykinase 1 (PCK1 or PEPCK-C) is a cytosolic enzyme converting oxaloacetate to phosphoenolpyruvate, with a potential role in gluconeogenesis, ammoniagenesis, and cataplerosis in the liver. Kidney proximal tubule cells display high expression of this enzyme, whose importance is currently not well defined. We generated PCK1 kidney-specific knockout and knockin mice under the tubular cell-specific PAX8 promoter. We studied the effect of PCK1 deletion and overexpression at the renal level on tubular physiology under normal conditions and during metabolic acidosis and proteinuric renal disease. PCK1 deletion led to hyperchloremic metabolic acidosis characterized by reduced but not abolished ammoniagenesis. PCK1 deletion also resulted in glycosuria, lactaturia, and altered systemic glucose and lactate metabolism at baseline and during metabolic acidosis. Metabolic acidosis resulted in kidney injury in PCK1-deficient animals with decreased creatinine clearance and albuminuria. PCK1 further regulated energy production by the proximal tubule, and PCK1 deletion decreased ATP generation. In proteinuric chronic kidney disease, mitigation of PCK1 downregulation led to better renal function preservation. PCK1 is essential for kidney tubular cell acid-base control, mitochondrial function, and glucose/lactate homeostasis. Loss of PCK1 increases tubular injury during acidosis. Mitigating kidney tubular PCK1 downregulation during proteinuric renal disease improves renal function.NEW & NOTEWORTHY Phosphoenolpyruvate carboxykinase 1 (PCK1) is highly expressed in the proximal tubule. We show here that this enzyme is crucial for the maintenance of normal tubular physiology, lactate, and glucose homeostasis. PCK1 is a regulator of acid-base balance and ammoniagenesis. Preventing PCK1 downregulation during renal injury improves renal function, rendering it an important target during renal disease.

Validation of automatically measured T1 map cortico-medullary difference (ΔT1) for eGFR and fibrosis assessment in allograft kidneys

MRI T1-mapping is an important non-invasive tool for renal diagnosis. Previous work shows that ΔT1 (cortex-medullary difference in T1) has significant correlation with interstitial fibrosis in chronic kidney disease (CKD) allograft patients. However, measuring cortico-medullary values by manually drawing ROIs over cortex and medulla (a gold standard method) is challenging, time-consuming, subjective and requires human training. Moreover, such subjective ROI placement may also affect the work reproducibility. This work proposes a deep learning-based 2D U-Net (RCM U-Net) to auto-segment the renal cortex and medulla of CKD allograft kidney T1 maps. Furthermore, this study presents a correlation of automatically measured ΔT1 values with eGFR and percentage fibrosis in allograft kidneys. Also, the RCM U-Net correlation results are compared with the manual ROI correlation analysis. The RCM U-Net has been trained and validated on T1 maps from 40 patients (n = 2400 augmented images) and tested on 10 patients (n = 600 augmented images). The RCM U-Net segmentation results are compared with the standard VGG16, VGG19, ResNet34 and ResNet50 networks with U-Net as backbone. For clinical validation of the RCM U-Net segmentation, another set of 114 allograft kidneys patient's cortex and medulla were automatically segmented to measure the ΔT1 values and correlated with eGFR and fibrosis. Overall, the RCM U-Net showed 50% less Mean Absolute Error (MAE), 16% better Dice Coefficient (DC) score and 12% improved results in terms of Sensitivity (SE) over conventional CNNs (i.e. VGG16, VGG19, ResNet34 and ResNet50) while the Specificity (SP) and Accuracy (ACC) did not show significant improvement (i.e. 0.5% improvement) for both cortex and medulla segmentation. For eGFR and fibrosis assessment, the proposed RCM U-Net correlation coefficient (r) and R-square (R2) was better correlated (r = -0.2, R2 = 0.041 with p = 0.039) to eGFR than manual ROI values (r = -0.19, R2 = 0.037 with p = 0.051). Similarly, the proposed RCM U-Net had noticeably better r and R2 values (r = 0.25, R2 = 0.065 with p = 0.007) for the correlation with the renal percentage fibrosis than the Manual ROI results (r = 0.3, R2 = 0.091 and p = 0.0013). Using a linear mixed model, T1 was significantly higher in the medulla than in the cortex (p<0.0001) and significantly lower in patients with cellular rejection when compared to both patients without rejection and those with humoral rejection (p<0.001). There was no significant difference in T1 between patients with and without humoral rejection (p = 0.43), nor between the types of T1 measurements (Gold standard manual versus automated RCM U-Net) (p = 0.7). The cortico-medullary area ratio measured by the RCM U-Net was significantly increased in case of cellular rejection by comparison to humoral rejection (1.6 +/- 0.39 versus 0.99 +/- 0.32, p = 0.019). In conclusion, the proposed RCM U-Net provides more robust auto-segmented cortex and medulla than the other standard CNNs allowing a good correlation of ΔT1 with eGFR and fibrosis as reported in literature as well as the differentiation of cellular and humoral transplant rejection. Therefore, the proposed approach is a promising alternative to the gold standard manual ROI method to measure T1 values without user interaction, which helps to reduce analysis time and improves reproducibility.

Variability of 24-Hour Sodium Urinary Excretion in Young Healthy Males Based on Consecutive Urine Collections: Impact on Categorization of Salt Intake

OBJECTIVE

Several nonconsecutive 24-h urinary collections are considered the gold standard for estimating dietary salt intake. As those samples are logistically demanding, we aimed to describe the variability of 24-h sodium urinary excretion over consecutive days and report its adequacy with sodium intake.

METHODS

We enrolled 16 healthy male volunteers in a prospective controlled study. All participants randomly received a low salt diet (LSD) (3 g/day of NaCl), a normal salt diet (NSD) (6 g/day of NaCl), and a high salt diet (HSD) (15 g/day of NaCl) for 7 days in a crossover design without wash-out period.

RESULTS

On day 6, median sodium urinary excretion was 258 (216-338), 10 (8-18), and 87 (69-121) mmol/day for HSD, LSD, and NSD, respectively (P < .001). When considering days 4-6, sodium urinary excretion was in steady state as models with and without interaction term "diet type X sample day" were not significantly different (P = .163). On day 6, area under the curve (AUC) of receiver operating characteristic for urinary sodium excretion to detect HSD was 1.0 (1.0-1.0) and a cut-point of 175 mmol/day was 100% sensitive and specific to detect HSD. On day 6, receiver operating characteristic AUC to detect LSD was 0.993 (0.978-1.0) and a cut-point of 53 mmol/day was 96.4% sensitive and 100% specific to detect LSD.

CONCLUSION

A steady state of sodium balance, where sodium intake is proportional to its excretion, is reached within a few days under a constant diet in the real-life setting. Categorization of salt consumption into low (3 g/day), normal (6 g/day), or high (15 g/day) based on a single 24-h urine collection is nearly perfect. Based on these results, repeated nonconsecutive urine collection might prove unnecessary to estimate sodium intake in daily clinical practice provided that diet is rather constant over time.

NADPH oxidase 4 is dispensable for skin myofibroblast differentiation and wound healing

Differentiation of fibroblasts to myofibroblasts is governed by the transforming growth factor beta (TGF-β) through a mechanism involving redox signaling and generation of reactive oxygen species (ROS). Myofibroblasts synthesize proteins of the extracellular matrix (ECM) and display a contractile phenotype. Myofibroblasts are predominant contributors of wound healing and several pathological states, including fibrotic diseases and cancer. Inhibition of the ROS-generating enzyme NADPH oxidase 4 (NOX4) has been proposed to mitigate fibroblast to myofibroblast differentiation and to offer a therapeutic option for the treatment of fibrotic diseases. In this study, we addressed the role of NOX4 in physiological wound healing and in TGF-β-induced myofibroblast differentiation. We explored the phenotypic changes induced by TGF-β in primary skin fibroblasts isolated from Nox4-deficient mice by immunofluorescence, Western blotting and RNA sequencing. Mice deficient for Cyba, the gene coding for p22^phox, a key subunit of NOX4 were used for confirmatory experiments as well as human primary skin fibroblasts. In vivo, the wound healing was similar in wild-type and Nox4-deficient mice. In vitro, despite a strong upregulation following TGF-β treatment, Nox4 did not influence skin myofibroblast differentiation although a putative NOX4 inhibitor GKT137831 and a flavoprotein inhibitor diphenylene iodonium mitigated this mechanism. Transcriptomic analysis revealed upregulation of the mitochondrial protein Ucp2 and the stress-response protein Hddc3 in Nox4-deficient fibroblasts, which had however no impact on fibroblast bioenergetics. Altogether, we provide extensive evidence that NOX4 is dispensable for wound healing and skin fibroblast to myofibroblast differentiation, and suggest that another H₂O₂-generating flavoprotein drives this mechanism.

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.

Kidney-targeted irradiation triggers renal ischaemic preconditioning in mice

Renal ischemia/reperfusion (I/R) causes acute kidney injury (AKI). Ischemic preconditioning (IPC) attenuates I/R-associated AKI. Whole-body irradiation induces renal IPC in mice. Still, the mechanisms remain largely unknown. Furthermore, the impact of kidney-centered irradiation on renal resistance against I/R has not been studied. Renal irradiation (8.5Gy) was done in male 8-12-week-old C57bl/6 mice using Small Animal Radiation Therapy (SmART) device. Left renal I/R was performed by clamping the renal pedicles for 30 minutes, with simultaneous right nephrectomy, at 7, 14, and 28 days post-irradiation. The renal reperfusion lasted 48 hours. Following I/R, blood urea nitrogen (BUN) and creatinine (SCr) levels were lower in pre-irradiated mice compared to controls, so was the histological Jablonski score of AKI. The metabolomics signature of renal I/R was attenuated in pre-irradiated mice. The numbers of PCNA-, CD11b-, and F4-80-positive cells in the renal parenchyma post-I/R were reduced in pre-irradiated versus control groups. Such an IPC was significantly observed as early as D14 post-irradiation. RNA-Seq showed an up-regulation of angiogenesis- and stress response-related signaling pathways in irradiated non-ischemic kidneys at D28. RT-qPCR confirmed the increased expression of VEGF, ALK5, HO1, PECAM1, NOX2, HSP70, and HSP27 in irradiated kidneys compared to controls. In addition, irradiated kidneys showed an increased CD31-positive vascular area compared to controls. A 14-day gavage of irradiated mice with the anti-angiogenic drug Sunitinib before I/R abrogated the irradiation-induced IPC at both functional and structural levels. Our observations suggest that kidney-centered irradiation activates pro-angiogenic pathways and induces IPC, with preserved renal function and attenuated inflammation post-I/R.

MO886: Outcomes in Incident Patients Treated With Incremental Haemodialysis as Compared With Thrice-Weekly Haemodialysis and Peritoneal Dialysis: The Geneva Experience

BACKGROUND AND AIMS

Preservation of residual kidney function (RKF) in maintenance haemodialysis (HD) patients is associated with better survival and quality of life. RKF may be better preserved with an incremental HD (frequency &lt; 3x/week) regimen in patients starting HD. Since 2013, incremental HD is routinely used at our centre.

METHOD

Incremental HD was implemented in incident HD patients with a urine output of &gt;600 mL/day,  a urea clearance (KRU) ≥2 mL/min and an interdialytic weight gain &lt; 2.5 kg. Patients were clinically assessed every week and a 24-h urine collection was ordered every other month in order to measure RKF.

RESULTS

From January 2013 to December 2020, 296 patients started chronic dialysis, with 162 on thrice-weekly HD, 63 on incremental HD and 71 on peritoneal dialysis (PD). Patients on incremental HD did not differ from those on thrice-weekly HD or PD in terms of age, gender and comorbidity score. Diuresis, eGFR and KRU at incremental HD initiation were 1842 ± 749 mL/day, 6.7 ± 3.1 mL/min and 4.0 ± 1.8 mL/min, respectively. Among patients on incremental HD, four could retrieve a sufficient RKF to become dialysis-independent and two were transplanted. Among the 57 remaining patients on incremental HD, median duration until transition to a thrice-weekly HD regimen or death was 10 (6–20) months. Within the first year of dialysis, median survival and hospital-free days were higher in patients starting with incremental HD as compared with thrice-weekly HD: 91% versus 77%, P = 0.02 and 348 (316–362) versus 338 (295–354) days; P = 0.03.

CONCLUSION

These preliminary results show that incremental HD can be implemented in incident HD patients as long as regular clinical and RKF assessments are found adequate. A median duration of 10 months before transition to thrice-weekly HD can be expected in this setting. Results of randomised clinical trials assessing long-term survival and quality of life in incremental HD are awaited prior to its large-scale implementation.

MO457: Diffusion-MRI Predicts Decline of Renal Function in Chronic Kidney Diseases and Kidney Allograft Patients

BACKGROUND AND AIMS

Kidney cortical interstitial fibrosis is highly predictive of renal prognosis and is currently assessed by the evaluation of a biopsy. Diffusion-weighted magnetic resonance imaging is a promising non-invasive tool to evaluate kidney fibrosis. We recently adapted a diffusion-weighted imaging sequence, allowing for the discrimination between the kidney cortex and medulla. The cortico-medullary difference in apparent diffusion coefficient (ΔADC) correlated to histological interstitial fibrosis. The aim of this study was to assess whether ΔADC as measured with diffusion-weighted magnetic resonance imaging is predictive of renal function decline and dialysis in chronic kidney diseases (CKD) and kidney allograft patients.

METHOD

We performed a prospective study including 197 patients. We measured ΔADC in 43 CKD patients [estimated glomerular filtration rate (eGFR) 55 mL/min/1.73m2] and 154 kidney allograft patients (eGFR 53 ml/min/1.73m2). Patients underwent a renal biopsy and diffusion-weighted magnetic resonance imaging, within 1 week of biopsy. Follow-up was 2.2 years in median. During follow-up, laboratory parameters were measured. Primary outcome was defined as rapid decline of renal function (eGFR decline &gt; 30% or dialysis initiation) during follow-up.

RESULTS

Patients with low ΔADC (&lt;0 x10-6mm2/s) had 5.4 times more risk of rapid decline of renal function or dialysis [95% confidence interval (CI): 2.29–12.58; P &lt; 0.001]. After correction for renal function at baseline and proteinuria, low ADC still predict renal function loss with a hazard ratio (HR) of 4.62 (P &lt; 0.001, 95% CI 1.56–13.67).

CONCLUSION

We demonstrate in this study that low ΔADC is a predictor of renal function decline and dialysis initiation in CKD and kidney allograft patients, independent of baseline renal function and proteinuria.

Decreased Renal Gluconeogenesis Is a Hallmark of Chronic Kidney Disease

INTRODUCTION

CKD is associated with alterations of tubular function. Renal gluconeogenesis is responsible for 40% of systemic gluconeogenesis during fasting, but how and why CKD affects this process and the repercussions of such regulation are unknown.

METHODS

We used data on the renal gluconeogenic pathway from more than 200 renal biopsies performed on CKD patients and from 43 kidney allograft patients, and studied three mouse models, of proteinuric CKD (POD-ATTAC), of ischemic CKD, and of unilateral urinary tract obstruction. We analyzed a cohort of patients who benefitted from renal catheterization and a retrospective cohort of patients hospitalized in the intensive care unit.

RESULTS

Renal biopsies of CKD and kidney allograft patients revealed a stage-dependent decrease in the renal gluconeogenic pathway. Two animal models of CKD and one model of kidney fibrosis confirm gluconeogenic downregulation in injured proximal tubule cells. This shift resulted in an alteration of renal glucose production and lactate clearance during an exogenous lactate load. The isolated perfused kidney technique in animal models and renal venous catheterization in CKD patients confirmed decreased renal glucose production and lactate clearance. In CKD patients hospitalized in the intensive care unit, systemic alterations of glucose and lactate levels were more prevalent and associated with increased mortality and a worse renal prognosis at follow-up. Decreased expression of the gluconeogenesis pathway and its regulators predicted faster histologic progression of kidney disease in kidney allograft biopsies.

CONCLUSION

Renal gluconeogenic function is impaired in CKD. Altered renal gluconeogenesis leads to systemic metabolic changes with a decrease in glucose and increase in lactate level, and is associated with a worse renal prognosis.

Diffusion-Magnetic Resonance Imaging predicts decline of kidney function in chronic kidney disease and in patients with a kidney allograft

Kidney cortical interstitial fibrosis is highly predictive of kidney prognosis and is currently assessed by evaluation of a biopsy. Diffusion-weighted magnetic resonance imaging is a promising non-invasive tool to evaluate kidney fibrosis. We recently adapted diffusion-weighted imaging sequence for discrimination between the kidney cortex and medulla and found that the cortico-medullary difference in apparent diffusion coefficient (ΔADC) correlated with histological interstitial fibrosis. Here, we assessed whether ΔADC as measured with diffusion-weighted magnetic resonance imaging is predictive of kidney function decline and dialysis initiation in chronic kidney disease (CKD) and patients with a kidney allograft in a prospective study encompassing 197 patients. We measured ΔADC in 43 patients with CKD (estimated GFR (eGFR) 55ml/min/1.73m²) and 154 patients with a kidney allograft (eGFR 53ml/min/1.73m²). Patients underwent a kidney biopsy and diffusion-weighted magnetic resonance imaging within one week of biopsy; median follow-up of 2.2 years with measured laboratory parameters. The primary outcome was a rapid decline of kidney function (eGFR decline over 30% or dialysis initiation) during follow up. Significantly, patients with a negative ΔADC had 5.4 times more risk of rapid decline of kidney function or dialysis (95% confidence interval: 2.29-12.58). After correction for kidney function at baseline and proteinuria, low ADC still predicted significant kidney function loss with a hazard ratio of 4.62 (95% confidence interval 1.56-13.67) independent of baseline age, sex, eGFR and proteinuria. Thus, low ΔADC can be a predictor of kidney function decline and dialysis initiation in patients with native kidney disease or kidney allograft, independent of baseline kidney function and proteinuria.

Estimated Renal Metabolomics at Reperfusion Predicts One-Year Kidney Graft Function

Renal transplantation is the gold-standard procedure for end-stage renal disease patients, improving quality of life and life expectancy. Despite continuous advancement in the management of post-transplant complications, progress is still needed to increase the graft lifespan. Early identification of patients at risk of rapid graft failure is critical to optimize their management and slow the progression of the disease. In 42 kidney grafts undergoing protocol biopsies at reperfusion, we estimated the renal metabolome from RNAseq data. The estimated metabolites' abundance was further used to predict the renal function within the first year of transplantation through a random forest machine learning algorithm. Using repeated K-fold cross-validation we first built and then tuned our model on a training dataset. The optimal model accurately predicted the one-year eGFR, with an out-of-bag root mean square root error (RMSE) that was 11.8 ± 7.2 mL/min/1.73 m2. The performance was similar in the test dataset, with a RMSE of 12.2 ± 3.2 mL/min/1.73 m2. This model outperformed classic statistical models. Reperfusion renal metabolome may be used to predict renal function one year after allograft kidney recipients.

Tubular Cell Glucose Metabolism Shift During Acute and Chronic Injuries

Acute and chronic kidney disease are responsible for large healthcare costs worldwide. During injury, kidney metabolism undergoes profound modifications in order to adapt to oxygen and nutrient shortage. Several studies highlighted recently the importance of these metabolic adaptations in acute as well as in chronic phases of renal disease, with a potential deleterious effect on fibrosis progression. Until recently, glucose metabolism in the kidney has been poorly studied, even though the kidney has the capacity to use and produce glucose, depending on the segment of the nephron. During physiology, renal proximal tubular cells use the beta-oxidation of fatty acid to generate large amounts of energy, and can also produce glucose through gluconeogenesis. In acute kidney injury, proximal tubular cells metabolism undergo a metabolic shift, shifting away from beta-oxidation of fatty acids and gluconeogenesis toward glycolysis. In chronic kidney disease, the loss of fatty acid oxidation is also well-described, and data about glucose metabolism are emerging. We here review the modifications of proximal tubular cells glucose metabolism during acute and chronic kidney disease and their potential consequences, as well as the potential therapeutic implications.

Impact of Hyponatremia after Renal Transplantation on Decline of Renal Function, Graft Loss and Patient Survival: A Prospective Cohort Study

Background: Hyponatremia is one of the most common electrolyte disorders observed in hospitalized and ambulatory patients. Hyponatremia is associated with increased falls, fractures, prolonged hospitalisation and mortality. The clinical importance of hyponatremia in the renal transplant field is not well established, so the aim of this study was to determine the relationships between hyponatremia and mortality as main outcome and renal function decline and graft loss as secondary outcome among a prospective cohort of renal transplant recipients. Methods: This prospective cohort study included 1315 patients between 1 May 2008 and 31 December 2014. Hyponatremia was defined as sodium concentration below 136 mmol/L at 6 months after transplantation. The main endpoint was mortality. A secondary composite endpoint was also defined as: rapid decline in renal function (≥5 mL/min/1.73 m² drop of the eGFR/year), graft loss or mortality. Results: Mean sodium was 140 ± 3.08 mmol/L. 97 patients displayed hyponatremia with a mean of 132.9 ± 3.05 mmol/L. Hyponatremia at 6 months after transplantation was associated neither with mortality (HR: 1.02; p = 0.97, 95% CI: 0.47–2.19), nor with the composite outcome defined as rapid decline in renal function, graft loss or mortality (logrank test p = 0.9). Conclusions: Hyponatremia 6 months after transplantation is not associated with mortality in kidney allograft patients.

Increased oxytocin release precedes hyponatremia after pituitary surgery

PURPOSE

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a well-known complication of transsphenoidal pituitary surgery, related to inappropriate secretion of arginine vasopressin (AVP). Its diagnosis is based on hyponatremia, with a peak of occurrence around day 7 after surgery and, to date, no early marker has been reported. In particular, copeptin levels are not predictive of hyponatremia in this case. Oxytocin (OXT) is secreted into the peripheral blood by axon terminals adjacent to those of AVP neurons in the posterior pituitary. Besides its role in childbirth and lactation, recent evidences suggested a role for OXT in sodium balance. The contribution of this hormone in the dysnatremias observed after pituitary surgery has however never been investigated.

METHODS

We analyzed the urinary output of OXT in patients subjected to transsphenoidal pituitary surgery.

RESULTS

While OXT excretion remained stable in patients who presented a normonatremic postoperative course, patients who were later diagnosed with SIADH-related hyponatremia presented with a significantly increased urinary secretion of OXT 4 days after surgery.

CONCLUSION

Taken together, these results show for the first time that urinary OXT output remains normally stable after transsphenoidal pituitary surgery. OXT excretion however becomes abnormally high on or around 4 days after surgery in patients later developing hyponatremia, suggesting that this abnormal dynamics of OXT secretion might serve as an early marker for transsphenoidal surgery-related hyponatremia attributed to SIADH.

Measured and Estimated Glomerular Filtration Rate in the ICU: A Prospective Study

OBJECTIVES

To compare estimated glomerular filtration rate using classical static and kinetic equations with measured glomerular filtration rate assessed by plasma iohexol clearance in a mixed population of critical care patients.

PATIENTS

Unselected patients older than 18 and admitted to a general ICU.

DESIGN

Interventional prospective single center study.

INTERVENTION

Measurement of glomerular filtration rate by the plasma clearance of an IV single dose of iohexol and estimation of glomerular filtration rate with creatinine or cystatin C-based standard and kinetic equations as well as urinary creatinine clearance.

MEASUREMENTS AND MAIN RESULTS

Sixty-three patients were included with a median age of 66 years old. The median measured glomerular filtration rate was 51 mL/min/1.73 m (interquartile range, 19-85 mL/min/1.73 m). All used equations displayed significant biases, high errors, and poor accuracy when compared with measured glomerular filtration rate, overestimating renal function. The highest accuracy and lowest error were observed with cystatin C-based chronic kidney disease epidemiology collaboration equations. Both modification of diet in renal disease and Cockcroft-Gault equations displayed the lowest performance. Kinetic models did not improve performances, except in patients with unstable creatinine levels. Creatinine- but not cystatin C-based estimations largely derived over ICU stay, which appeared more related to sarcopenia than fluid balance. Finally, estimated glomerular filtration rate misclassified patients according to classical glomerular filtration rate categories in approximately half of the studied cases.

CONCLUSIONS

All known estimated glomerular filtration rate equations displayed high biases and unacceptable errors when compared with measured glomerular filtration rate in a mixed ICU population, with the lowest performance related to creatinine-based equations compared with cystatin C. In the ICU, we advocate for caution when using creatinine based estimated glomerular filtration rate equations. Drifting of serum creatinine levels over time should also be taken into consideration when assessing renal function in the ICU.

Differential role of nicotinamide adenine dinucleotide deficiency in acute and chronic kidney disease

BACKGROUND

Nicotinamide adenine dinucleotide (NAD+) is a ubiquitous coenzyme involved in electron transport and a co-substrate for sirtuin function. NAD+ deficiency has been demonstrated in the context of acute kidney injury (AKI).

METHODS

We studied the expression of key NAD+ biosynthesis enzymes in kidney biopsies from human allograft patients and patients with chronic kidney disease (CKD) at different stages. We used ischaemia-reperfusion injury (IRI) and cisplatin injection to model AKI, urinary tract obstruction [unilateral ureteral obstruction (UUO)] and tubulointerstitial fibrosis induced by proteinuria to investigate CKD in mice. We assessed the effect of nicotinamide riboside (NR) supplementation on AKI and CKD in animal models.

RESULTS

RNA sequencing analysis of human kidney allograft biopsies during the reperfusion phase showed that the NAD+de novo synthesis is impaired in the immediate post-transplantation period, whereas the salvage pathway is stimulated. This decrease in de novo NAD+ synthesis was confirmed in two mouse models of IRI where NR supplementation prevented plasma urea and creatinine elevation and tubular injury. In human biopsies from CKD patients, the NAD+de novo synthesis pathway was impaired according to CKD stage, with better preservation of the salvage pathway. Similar alterations in gene expression were observed in mice with UUO or chronic proteinuric glomerular disease. NR supplementation did not prevent CKD progression, in contrast to its efficacy in AKI.

CONCLUSION

Impairment of NAD+ synthesis is a hallmark of AKI and CKD. NR supplementation is beneficial in ischaemic AKI but not in CKD models.

Dietary sodium intake does not alter renal potassium handling and blood pressure in healthy young males

Background

The effects of sodium (Na⁺) intakes on renal handling of potassium (K⁺) are insufficiently studied.

Methods

We assessed the effect of Na⁺ on renal K⁺ handling in 16 healthy males assigned to three 7-day periods on low salt diet [LSD, 3 g sodium chloride (NaCl)/day], normal salt diet (NSD, 6 g NaCl/day) and high salt diet (HSD, 15 g NaCl/day), with constant K⁺ intake. Contributions of distal NaCl co-transporter and epithelial Na⁺ channel in the collecting system on K⁺ and Na⁺ handling were assessed at steady state by acute response to 100 mg oral hydrochlorothiazide and with addition of 10 mg of amiloride to hydrochlorothiazide, respectively.

Results

Diurnal blood pressure slightly increased from 119.30 ± 7.95 mmHg under LSD to 123.00 ± 7.50 mmHg (P = 0.02) under HSD, while estimated glomerular filtration rate increased from 133.20 ± 34.68 mL/min under LSD to 187.00 ± 49.10 under HSD (P = 0.005). The 24-h K⁺ excretion remained stable on all Na⁺ intakes (66.28 ± 19.12 mmol/24 h under LSD; 55.91 ± 21.17 mmol/24 h under NSD; and 66.81 ± 20.72 under HSD, P = 0.9). The hydrochlorothiazide-induced natriuresis was the highest under HSD (30.22 ± 12.53 mmol/h) and the lowest under LSD (15.38 ± 8.94 mmol/h, P = 0.02). Hydrochlorothiazide increased kaliuresis and amiloride decreased kaliuresis similarly on all three diets.

Conclusions

Neither spontaneous nor diuretic-induced K⁺ excretion was influenced by Na⁺ intake in healthy male subjects. However, the respective contribution of the distal convoluted tubule and the collecting duct to renal Na⁺ handling was dependent on dietary Na⁺ intake.

Contribution of Genetic Background and Data Collection on Adverse Events of Anti-human Immunodeficiency Virus (HIV) Drugs (D:A:D) Clinical Risk Score to Chronic Kidney Disease in Swiss HIV-infected Persons With Normal Baseline Estimated Glomerular Filtration Rate

BACKGROUND

In human immunodeficiency virus (HIV), the relative contribution of genetic background, clinical risk factors, and antiretrovirals to chronic kidney disease (CKD) is unknown.

METHODS

We applied a case-control design and performed genome-wide genotyping in white Swiss HIV Cohort participants with normal baseline estimated glomerular filtration rate (eGFR >90 mL/minute/1.73 m2). Univariable and multivariable CKD odds ratios (ORs) were calculated based on the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) score, which summarizes clinical CKD risk factors, and a polygenic risk score that summarizes genetic information from 86 613 single-nucleotide polymorphisms.

RESULTS

We included 743 cases with confirmed eGFR drop to <60 mL/minute/1.73 m2 (n = 144) or ≥25% eGFR drop to <90 mL/minute/1.73 m2 (n = 599), and 322 controls (eGFR drop <15%). Polygenic risk score and D:A:D score contributed to CKD. In multivariable analysis, CKD ORs were 2.13 (95% confidence interval [CI], 1.55-2.97) in participants in the fourth (most unfavorable) vs first (most favorable) genetic score quartile; 1.94 (95% CI, 1.37-2.65) in the fourth vs first D:A:D score quartile; and 2.98 (95% CI, 2.02-4.66), 1.70 (95% CI, 1.29-2.29), and 1.83 (95% CI, 1.45-2.40), per 5 years of exposure to atazanavir/ritonavir, lopinavir/ritonavir, and tenofovir disoproxil fumarate, respectively. Participants in the first genetic score quartile had no increased CKD risk, even if they were in the fourth D:A:D score quartile.

CONCLUSIONS

Genetic score increased CKD risk similar to clinical D:A:D score and potentially nephrotoxic antiretrovirals. Irrespective of D:A:D score, individuals with the most favorable genetic background may be protected against CKD.

Renal gluconeogenesis: an underestimated role of the kidney in systemic glucose metabolism

Glucose levels are tightly regulated at all times. Gluconeogenesis is the metabolic pathway dedicated to glucose synthesis from non-hexose precursors. Gluconeogenesis is critical for glucose homoeostasis, particularly during fasting or stress conditions. The renal contribution to systemic gluconeogenesis is increasingly recognized. During the post-absorptive phase, the kidney accounts for ∼40% of endogenous gluconeogenesis, occurring mainly in the kidney proximal tubule. The main substrate for renal gluconeogenesis is lactate and the process is regulated by insulin and cellular glucose levels, but also by acidosis and stress hormones. The kidney thus plays an important role in the maintenance of glucose and lactate homoeostasis during stress conditions. The impact of acute and chronic kidney disease and proximal tubular injury on gluconeogenesis is not well studied. Recent evidence shows that in both experimental and clinical acute kidney injury, impaired renal gluconeogenesis could significantly participate in systemic metabolic disturbance and thus alter the prognosis. This review summarizes the biochemistry of gluconeogenesis, the current knowledge of kidney gluconeogenesis, its modifications in kidney disease and the clinical relevance of this fundamental biological process in human biology.

Exploring blood alterations in chronic kidney disease and haemodialysis using metabolomics

Chronic kidney disease (CKD) is characterized by retention of uremic solutes. Compared to patients with non-dialysis dependent CKD, those requiring haemodialysis (HD) have increased morbidity and mortality. We wished to characterise metabolic patterns in CKD compared to HD patients using metabolomics. Prevalent non-HD CKD KDIGO stage 3b-4 and stage 5 HD outpatients were screened at a single tertiary hospital. Various liquid chromatography approaches hyphenated with mass spectrometry were used to identify 278 metabolites. Unsupervised and supervised data analyses were conducted to characterize metabolic patterns. 69 patients were included in the CKD group and 35 in the HD group. Unsupervised data analysis showed clear clustering of CKD, pre-dialysis (preHD) and post-dialysis (postHD) patients. Supervised data analysis revealed qualitative as well as quantitative differences in individual metabolites profiles between CKD, preHD and postHD states. An original metabolomics framework could discriminate between CKD stages and highlight HD effect based on 278 identified metabolites. Significant differences in metabolic patterns between CKD and HD patients were found overall as well as for specific metabolites. Those findings could explain clinical discrepancies between patients requiring HD and those with earlier stage of CKD.

Author Correction: Altered proximal tubular cell glucose metabolism during acute kidney injury is associated with mortality

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Altered proximal tubular cell glucose metabolism during acute kidney injury is associated with mortality

Acute kidney injury (AKI) is strongly associated with mortality, independently of its cause. The kidney contributes to up to 40% of systemic glucose production by gluconeogenesis during fasting and under stress conditions. Whether kidney gluconeogenesis is impaired during AKI and how this might influence systemic metabolism remain unknown. Here we show that glucose production and lactate clearance are impaired during human and experimental AKI by using renal arteriovenous catheterization in patients, lactate tolerance testing in mice and glucose isotope labelling in rats. Single-cell transcriptomics reveal that gluconeogenesis is impaired in proximal tubule cells during AKI. In a retrospective cohort of critically ill patients, we demonstrate that altered glucose metabolism during AKI is a major determinant of systemic glucose and lactate levels and is strongly associated with mortality. Thiamine supplementation increases lactate clearance without modifying renal function in mice with AKI, enhances glucose production by renal tubular cells ex vivo and is associated with reduced mortality and improvement of the metabolic pattern in a retrospective cohort of critically ill patients with AKI. This study highlights an unappreciated systemic role of renal glucose and lactate metabolism under stress conditions, delineates general mechanisms of AKI-associated mortality and introduces a potential intervention targeting metabolism for a highly prevalent clinical condition with limited therapeutic options.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

Impact of superimposed nephrological care to guidelines-directed management by primary care physicians of patients with stable chronic kidney disease: a randomized controlled trial

BACKGROUND

Optimal clinical care of patients with chronic kidney disease (CKD) requires collaboration between primary care physicians (PCPs) and nephrologists. We undertook a randomised trial to determine the impact of superimposed nephrologist care compared to guidelines-directed management by PCPs in CKD patients after hospital discharge.

METHODS

Stage 3b-4 CKD patients were enrolled during a hospitalization and randomised in two arms: Co-management by PCPs and nephrologists (interventional arm) versus management by PCPs with written instructions and consultations by nephrologists on demand (standard care). Our primary outcome was death or rehospitalisation within the 2 years post-randomisation. Secondary outcomes were: urgent renal replacement therapy (RRT), decline of renal function and decrease of quality of life at 2 years.

RESULTS

From November 2009 to the end of June 2013, we randomised 242 patients. Mean follow-up was 51 + 20 months. Survival without rehospitalisation, GFR decline and elective dialysis initiation did not differ between the two arms. Quality of life was also similar in both groups. Compared to randomised patients, those who either declined to participate in the study or were previously known by nephrologists had a worse survival.

CONCLUSION

These results do not demonstrate a benefit of a regular renal care compared to guided PCPs care in terms of survival or dialysis initiation in CKD patients. Increased awareness of renal disease management among PCPs may be as effective as a co-management by PCPs and nephrologists in order to improve the prognosis of moderate-to-severe CKD.

TRIAL REGISTRATION

This study was registered on June 29, 2009 in clinicaltrials.gov (NCT00929760) and adheres to CONSORT 2010 guidelines.

Case report: a 58 -year -old man with small kidneys and elevated liver enzymes

BACKGROUND

The conjunction of hepatitis and renal disease can be seen in several clinical context, including karyomegalic nephritis (KIN). Karyomegalic nephritis (KIN) is a rare genetic disease, with less than 50 cases reported, which incidence is probably underestimated. We report here an unusual case presentation of KIN with obtention of several organ biopsies and a novel mutation leading to the disease.

CASE PRESENTATION

A 58 year old Caucasian without relevant family history presents with advanced chronic kidney disease, elevated liver enzymes and recurrent pulmonary infection. Familial history was negative. Renal biopsy revealed a chronic tubulo-intertsitial nephritis with enlarged and irregular hyperchromatic nuclei. Karyomegalic nephritis (KIN) was confirmed by genetic testing with a non-sense mutation and a deletion in the Fanconi anemia associated nuclease 1 (FAN1) gene.

CONCLUSIONS

KIN is rare disease to be suspected in the presence of renal disease, biological hepatitis and recurrent pulmonary infections, even without a familial history. Diagnosis of this condition is crucial to perform family screening, avoid progression factors, and adapt post transplantation immunosuppression. Finally, avoiding familial heterozygote donors appears of major importance in this condition.

[Ethylene glycol intoxication requires a multidisciplinary approach]

Cheap and easy to access, ethylene glycol is used in the synthesis of antifreezes. Intoxication has potentially irreversible morbid consequences. Ingestion of a small amount can lead to death. Due to its ubiquitous distribution and potential complications, it is of paramount importance for the practitioner to recognize its manifestations and metabolic complications in order to implement its therapy in partnership with the nephrologist and the intensivist. A successful treatment depends on rapid and multidisciplinary management, as reviewed in this article.

Potential benefits and harms of NADPH oxidase type 4 in the kidneys and cardiovascular system

The main function of NADPH oxidases is to catalyse the formation of reactive oxygen species (ROS). NADPH oxidase 4 (NOX4) is expressed at high levels in kidney tubular cells, and at lower levels in endothelial cells, cardiomyocytes and other cell types under physiological conditions. NOX4 is constitutively active producing hydrogen peroxide (H2O2) as the prevalent ROS detected, whereas other NOX isoforms present in the renal and cardiovascular systems (i.e. NOX1, NOX2 and NOX5) generate superoxide radical anions as main products. Pharmacological inhibition of NOX4 has received enormous attention for its potential therapeutic benefit in fibrotic disease and nephropathologies. Ongoing clinical trials are testing this approach in humans. Diabetes elevates NOX4 expression in podocytes and mesangial cells, which was shown to damage glomeruli leading to podocyte loss, mesangial cell hypertrophy and matrix accumulation. Consequently, NOX4 represents an interesting therapeutic target in diabetic nephropathy. On the contrary, experiments using NOX4-deficient mice have shown that NOX4 is cytoprotective in tubular cells, cardiomyocytes, endothelial cells and vascular smooth muscle cells, and has a metabolism-regulating role when these cells are subjected to injury. Mice with systemic NOX4 deletion are more susceptible to acute and chronic tubular injury, heart failure and atherosclerosis. Overall, the current literature suggests a detrimental role of increased NOX4 expression in mesangial cells and podocytes during diabetic nephropathy, but a cytoprotective role of this enzyme in other cellular types where it is expressed endogenously. We review here the recent evidence on the role of NOX4 in the kidneys and cardiovascular system. With the emergence of pharmacological NOX4 inhibitors in clinical trials, caution should be taken in identifying potential side effects in patients prone to acute kidney injury and cardiovascular disease.

Time-course of sodium transport along the nephron in nephrotic syndrome: The role of potassium

The mechanism of sodium retention and its location in kidney tubules may vary with time in nephrotic syndrome (NS). We studied the mechanisms of sodium retention in transgenic POD-ATTAC mice, which display an inducible podocyte-specific apoptosis. At day 2 after the induction of NS, the increased abundance of NHE3 and phosphorylated NCC in nephrotic mice compared with controls suggest that early sodium retention occurs mainly in the proximal and distal tubules. At day 3, the abundance of NHE3 normalized, phosphorylated NCC levels decreased, and cleavage and apical localization of γ-ENaC increased in nephrotic mice. These findings indicate that sodium retention shifted from the proximal and distal tubules to the collecting system. Increased cleavage and apical localization of γ-ENaC persisted at day 5 in nephrotic mice when hypovolemia resolved and steady-state was reached. Sodium retention and γ-ENaC cleavage were independent of the increased plasma levels of aldosterone. Nephrotic mice displayed decreased glomerular filtration rate and urinary potassium excretion associated with hyperkaliemia at day 3. Feeding nephrotic mice with a low potassium diet prevented hyperkaliemia, γ-ENaC cleavage, and led to persistent increased phosphorylation of NCC. These results suggest that potassium homeostasis is a major determinant of the tubular site of sodium retention in nephrotic mice.

Klotho regulation by albuminuria is dependent on ATF3 and endoplasmic reticulum stress

Proteinuria is associated with renal function decline and cardiovascular mortality. This association may be attributed in part to alterations of Klotho expression induced by albuminuria, yet the underlying mechanisms are unclear. The presence of albumin decreased Klotho expression in the POD-ATTAC mouse model of proteinuric kidney disease as well as in kidney epithelial cell lines. This downregulation was related to both decreased Klotho transcription and diminished protein half-life, whereas cleavage by ADAM proteases was not modified. The regulation was albumin specific since it was neither observed in the analbuminemic Col4α3^-/- Alport mice nor induced by exposure of kidney epithelial cells to purified immunoglobulins. Albumin induced features of ER stress in renal tubular cells with ATF3/ATF4 activation. ATF3 and ATF4 induction downregulated Klotho through altered transcription mediated by their binding on the Klotho promoter. Inhibiting ER stress with 4-PBA decreased the effect of albumin on Klotho protein levels without altering mRNA levels, thus mainly abrogating the increased protein degradation. Taken together, albuminuria decreases Klotho expression through increased protein degradation and decreased transcription mediated by ER stress induction. This implies that modulating ER stress may improve proteinuria-induced alterations of Klotho expression, and hence renal and extrarenal complications associated with Klotho loss.

Dialysis initiation improves calcification propensity

Background

Cardiovascular morbidity and mortality is high in patients starting dialysis and could be related to modifications of calcification inducers and inhibitors by dialysis, promoting cardiovascular events. The impact of dialysis initiation on serum calcification propensity evolution and arterial stiffness is unknown. We therefore prospectively determined the evolution of the one-half maximal transition time (T50) value and its main determinants as well as pulse wave velocity over the first 3 months of dialysis initiation.

Methods

We analysed the evolution of T50, fetuin-A and mineral metabolism parameters before dialysis initiation (M0) and monthly until Month 3 (M3) in incident patients starting haemodialysis (HD) or peritoneal dialysis (PD) in two tertiary Swiss university hospitals. Arterial stiffness was assessed by pulse tonometry at M0 and M3 and biological parameters were compared between M0 and M3 and before/after HD. Linear mixed models were used to assess parameter evolution over time, taking into account repeated measures and other influencing variables.

Results

Forty-six patients on HD and 12 on PD were followed. Among them, 45 were male (78%) with a median age of 67 years (25th–75th quartile range 54–77). T50 significantly increased between M0 and M3 from 183 (120–266) to 246 min (175–330) (P &lt; 0.001). Fetuin-A, calcium and magnesium also increased while phosphate decreased. Factors associated with T50 changes over time were fetuin-A, phosphate and magnesium (P &lt; 0.001). Fetuin-A changes were associated with inflammation-related factors (albumin, C-reactive protein) but not calcium and phosphate levels. Arterial stiffness was not significantly modified over 3 months. PD and HD initiation showed similar trends.

Conclusions

Dialysis initiation significantly improves calcification propensity and fetuin-A levels. These modifications do not explain the high mortality related to dialysis initiation. The clinical relevance of using T50 values to initiate dialysis awaits further studies.

Tubular NOX4 expression decreases in chronic kidney disease but does not modify fibrosis evolution

Background

NADPH oxidase 4 (NOX4) catalyzes the formation of hydrogen peroxide (H₂O₂). NOX4 is highly expressed in the kidney, but its role in renal injury is unclear and may depend on its specific tissue localization.

Methods

We performed immunostaining with a specific anti-NOX4 antibody and measured NOX4 mRNA expression in human renal biopsies encompassing diverse renal diseases. We generated transgenic mice specifically overexpressing mouse Nox4 in renal tubular cells and subjected the animals to the unilateral ureteral obstruction (UUO) model of fibrosis.

Results

In normal human kidney, NOX4 protein expression was at its highest on the basolateral side of proximal tubular cells. NOX4 expression increased in mesangial cells and podocytes in proliferative diabetic nephropathy. In tubular cells, NOX4 protein expression decreased in all types of chronic renal disease studied. This finding was substantiated by decreased NOX4 mRNA expression in the tubulo-interstitial compartment in a repository of 175 human renal biopsies. Overexpression of tubular NOX4 in mice resulted in enhanced renal production of H₂O₂, increased NRF2 protein expression and decreased glomerular filtration, likely via stimulation of the tubulo-glomerular feedback. Tubular NOX4 overexpression had no obvious impact on kidney morphology, apoptosis, or fibrosis at baseline. Under acute and chronic tubular injury induced by UUO, overexpression of NOX4 in tubular cells did not modify the course of the disease.

Conclusions

NOX4 expression was decreased in tubular cells in all types of CKD tested. Tubular NOX4 overexpression did not induce injury in the kidney, and neither modified microvascularization, nor kidney structural lesions in fibrosis.

Validation of the corticomedullary difference in magnetic resonance imaging-derived apparent diffusion coefficient for kidney fibrosis detection: a cross-sectional study

Background

Kidney cortical interstitial fibrosis (IF) is highly predictive of renal prognosis and is currently assessed by the evaluation of a biopsy. Diffusion magnetic resonance imaging (MRI) is a promising tool to evaluate kidney fibrosis via the apparent diffusion coefficient (ADC), but suffers from inter-individual variability. We recently applied a novel MRI protocol to allow calculation of the corticomedullary ADC difference (ΔADC). We here present the validation of ΔADC for fibrosis assessment in a cohort of 164 patients undergoing biopsy and compare it with estimated glomerular filtration rate (eGFR) and other plasmatic parameters for the detection of fibrosis.

Methods

This monocentric cross-sectional study included 164 patients undergoing renal biopsy at the Nephrology Department of the University Hospital of Geneva between October 2014 and May 2018. Patients underwent diffusion-weighted imaging, and T1 and T2 mappings, within 1 week after biopsy. MRI results were compared with gold standard histology for fibrosis assessment.

Results

Absolute cortical ADC or cortical T1 values correlated poorly to IF assessed by the biopsy, whereas ΔADC was highly correlated to IF (r=−0.52, P &lt; 0.001) and eGFR (r = 0.37, P &lt; 0.01), in both native and allograft patients. ΔT1 displayed a lower, but significant, correlation to IF and eGFR, whereas T2 did not correlate to IF nor to eGFR. ΔADC, ΔT1 and eGFR were independently associated with kidney fibrosis, and their combination allowed detection of extensive fibrosis with good specificity.

Conclusion

ΔADC is better correlated to IF than absolute cortical or medullary ADC values. ΔADC, ΔT1 and eGFR are independently associated to IF and allow the identification of patients with extensive IF.

Red blood cell volume is not decreased in ESA-naive anemic chronic kidney disease patients

Anemia is defined according to decreased blood hemoglobin concentration ([Hb]), which is considered a marker of low total red blood cell volume (RBCV). Alterations of plasma volume (PV) may also modify [Hb] without concomitant changes in RBCV. Since anemia and fluid retention are frequent complications of chronic kidney disease (CKD), we hypothesized that anemia during CKD may in part be related to expanded PV without a simultaneous decrease in RBCV. We quantified hemoglobin mass, RBCV, PV, and total blood volume (BV) using an automated carbon monoxide device in 40 consecutive stage 3-5 CKD patients not on dialysis and in seven healthy male controls of the same age range. These were compared within and to predicted volumes according to Nadler's formula. Arterial stiffness and NT-proBNP were measured. RBCV was similar to predicted values range in anemic CKD patients 2073 (1818-2704) versus, 2061 (1725-2473) mL, P > 0.05. In contrast, PV was largely increased in anemic CKD patients (3881 (3212-4352) vs. 2916 (2851-3201)), P = 0.01. Of 26 anemic patients, only six had a >20% decrease in RBCV as the cause for their anemia, whereas 14 had a >20% increase of PV as a cause for their anemia. NT-pro BNP correlated with eGFR but neither with PV nor BV, whereas arterial stiffness was not correlated to blood volumes. Anemia in CKD as diagnosed by low [Hb] is not necessarily associated to low RBCV but may reflect increased PV. This finding has implications for the treatment of CKD patients and may refrain from normalizing [Hb] levels in all CKD patients.

De novo NAD+ synthesis enhances mitochondrial function and improves health

Nicotinamide adenine dinucleotide (NAD⁺) is a cosubstrate for several enzymes, including the sirtuin family of NAD⁺-dependent protein deacylases. Beneficial effects of increased NAD⁺ levels and sirtuin activation on mitochondrial homeostasis, organismal metabolism and lifespan have been established across species. Here we show that α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), the enzyme that limits the proportion of ACMS able to undergo spontaneous cyclisation in the de novo NAD⁺ synthesis pathway, controls cellular NAD⁺ levels via an evolutionary conserved mechanism from C. elegans to the mouse. Genetic and pharmacological inhibition of ACMSD boosts de novo NAD⁺ synthesis and SIRT1 activity, ultimately enhancing mitochondrial function. We furthermore characterized a series of potent and selective ACMSD inhibitors, which, given the restricted ACMSD expression in kidney and liver, are of high therapeutic interest to protect these tissues from injury. ACMSD hence is a key modulator of cellular NAD⁺ levels, sirtuin activity, and mitochondrial homeostasis in kidney and liver.