Renal cystinuria and immune cells (T lymphocytes) dysfunction, what we know about?

Cystinuria (CYS) is the most common monogenic kidney stone disease. Starting from an unusual case of CYS associated to Primary Sclerosing Cholangitis, inflammatory bowel disease (IBD) and autoimmune hepatitis in a young male, we carefully review the literature and propose here a working hypothesis regarding the potential risk of cystinuric patients to develop conditions due to immune system dysregulation. To corroborate this hypothesis, we retrospectively evaluate the frequency of dysimmunity in a cohort of cystinuric patients compared to healthy and disease controls. Further studies are needed to define the relationship between proximal tubular transport defect of CYS and dysregulated immunity.

Animal models to study cognitive impairment of chronic kidney disease

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD) and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives and society. However, the underlying pathomechanisms are poorly understood and current therapies mostly aim at supporting patients in their daily life. This illustrates the urgent need to elucidate the pathogenesis, and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modelling of cognitive disorders in CKD. We discuss the use of mice, rats and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving therapy of people with CKD and MCI.

Cyclosporin-induced hypertension is associated with the up-regulation of Na+-K+-2Cl- cotransporter (NKCC2)

BACKGROUND

The use of cyclosporin A (CsA) is hampered by the development of nephrotoxicity including hypertension, which is partially dependent on renal sodium retention. To address this issue, we have investigated in vivo sodium reabsorption in different nephron segments of CsA-treated rats through micropuncture study coupled to expression analyses of sodium transporters. To translate the findings in rats to human, kidney-transplanted patients having CsA treatment were enrolled in the study.

METHODS

Adult male Sprague-Dawley rats were treated with CsA (15 mg/kg/day) for 21 days, followed by micropuncture study and expression analyses of sodium transporters. CsA-treated kidney-transplanted patients with resistant hypertension were challenged with 50 mg furosemide.

RESULTS

CsA-treated rats developed hypertension associated with reduced glomerular filtration rate. In vivo microperfusion study demonstrated a significant decrease in rate of absolute fluid reabsorption in the proximal tubule but enhanced sodium reabsorption in the thick ascending limb of Henle's loop (TAL). Expression analyses of sodium transporters at the same nephron segments further revealed a reduction in Na+-H+ exchanger isoform 3 (NHE3) in the renal cortex, while TAL-specific, furosemide-sensitive Na+-K+-2Cl- cotransporter (NKCC2) and NHE3 were significantly upregulated in the inner stripe of outer medulla. CsA-treated patients had a larger excretion of urinary NKCC2 protein at basal condition, and higher diuretic response to furosemide, showing increased FeNa+, FeCl- and FeCa2+ compared with both healthy controls and FK506-treated transplanted patients.

CONCLUSION

Altogether, these findings suggest that up-regulation of NKCC2 along the TAL facilitates sodium retention and contributes to the development of CsA-induced hypertension.

The SGLT2 inhibitor dapagliflozin improves kidney function in glycogen storage disease XI

Glycogen storage disease XI, also known as Fanconi-Bickel syndrome (FBS), is a rare autosomal recessive disorder caused by mutations in the SLC2A2 gene that encodes the glucose-facilitated transporter type 2 (GLUT2). Patients develop a life-threatening renal proximal tubule dysfunction for which no treatment is available apart from electrolyte replacement. To investigate the renal pathogenesis of FBS, SLC2A2 expression was ablated in mouse kidney and HK-2 proximal tubule cells. GLUT2Pax8Cre+ mice developed time-dependent glycogen accumulation in proximal tubule cells and recapitulated the renal Fanconi phenotype seen in patients. In vitro suppression of GLUT2 impaired lysosomal autophagy as shown by transcriptomic and biochemical analysis. However, this effect was reversed by exposure to a low glucose concentration, suggesting that GLUT2 facilitates the homeostasis of key cellular pathways in proximal tubule cells by preventing glucose toxicity. To investigate whether targeting proximal tubule glucose influx can limit glycogen accumulation and correct symptoms in vivo, we treated mice with the selective SGLT2 inhibitor dapagliflozin. Dapagliflozin reduced glycogen accumulation and improved metabolic acidosis and phosphaturia in the animals by normalizing the expression of Napi2a and NHE3 transporters. In addition, in a patient with FBS, dapagliflozin was safe, improved serum potassium and phosphate concentrations, and reduced glycogen content in urinary shed cells. Overall, this study provides proof of concept for dapagliflozin as a potentially suitable therapy for FBS.

[Hyponatremia and Electrolyte Disorders in Cancer Patients]

Onconephrology is a rising and rapidly expanding field of medicine in which nephrology and oncology meet each other. Besides multidisciplinary meetings, oncologists and nephrologists often discuss on timing of the treatment, dosage, and side effects management. Cancer patients often encounter different electrolyte disorders. They are mostly secondary to the tumor itself or consequences of its treatment. In the last years, the great efforts to find new therapies like targeted, immune, and cell-based led us to many new side effects. Hyponatremia, hypokalemia, hyperkalemia, hypercalcemia, and hypomagnesemia are among the most common electrolyte disorders. Data have shown a worse prognosis in patients with electrolytic imbalances. Additionally, they cause a delay in chemotherapy or even an interruption. It is important to diagnose promptly these complications and treat them. In this review, we provide a special focus on hyponatremia and its treatment as the most common electrolytes disorder in cancer patients, but also on newly described cases of hypo- and hyperkalemia and metabolic acidosis.

RagD auto-activating mutations impair MiT/TFE activity in kidney tubulopathy and cardiomyopathy syndrome

Heterozygous mutations in the gene encoding RagD GTPase were shown to cause a novel autosomal dominant condition characterized by kidney tubulopathy and cardiomyopathy. We previously demonstrated that RagD, and its paralogue RagC, mediate a non-canonical mTORC1 signaling pathway that inhibits the activity of TFEB and TFE3, transcription factors of the MiT/TFE family and master regulators of lysosomal biogenesis and autophagy. Here we show that RagD mutations causing kidney tubulopathy and cardiomyopathy are "auto- activating", even in the absence of Folliculin, the GAP responsible for RagC/D activation, and cause constitutive phosphorylation of TFEB and TFE3 by mTORC1, without affecting the phosphorylation of "canonical" mTORC1 substrates, such as S6K. By using HeLa and HK-2 cell lines, human induced pluripotent stem cell-derived cardiomyocytes and patient-derived primary fibroblasts, we show that RRAGD auto-activating mutations lead to inhibition of TFEB and TFE3 nuclear translocation and transcriptional activity, which impairs the response to lysosomal and mitochondrial injury. These data suggest that inhibition of MiT/TFE factors plays a key role in kidney tubulopathy and cardiomyopathy syndrome.

Next-Generation Sequencing (NGS) Analysis Illustrates the Phenotypic Variability of Collagen Type IV Nephropathies

Mutations in COL4A3-A5 cause a spectrum of glomerular disorders, including thin basement membrane nephropathy (TBMN) and Alport syndrome (AS). The wide application of next-generation sequencing (NGS) in the last few years has revealed that mutations in these genes are not limited to these clinical entities. In this study, 176 individuals with a clinical diagnosis of inherited kidney disorders underwent an NGS-based analysis to address the underlying cause; those who changed or perfected the clinical diagnosis after molecular analysis were selected. In 5 out of 83 individuals reaching a molecular diagnosis, the genetic result was unexpected: three individuals showed mutations in collagen type IV genes. These patients showed the following clinical pictures: (1) familial focal segmental glomerulosclerosis; (2) end-stage renal disease (ESRD) diagnosed incidentally in a 49-year-old man, with diffuse cortical calcifications on renal imaging; and (3) dysmorphic and asymmetric kidneys with multiple cysts and signs of tubule-interstitial defects. Genetic analysis revealed rare heterozygote/compound heterozygote COL4A4-A5 variants. Our study highlights the key role of NGS in the diagnosis of inherited renal disorders and shows the phenotype variability in patients carrying mutations in collagen type IV genes.

miRNA-23a modulates sodium-hydrogen exchanger 1 expression: studies in medullary thick ascending limb of salt-induced hypertensive rats

BACKGROUND

The kidney is the main organ in the pathophysiology of essential hypertension. Although most bicarbonate reabsorption occurs in the proximal tubule, the medullary thick ascending limb (mTAL) of the nephron also maintains acid-base balance by contributing to 25% of bicarbonate reabsorption. A crucial element in this regulation is the sodium-hydrogen exchanger 1 (NHE1), a ubiquitous membrane protein controlling intracellular pH, where proton extrusion is driven by the inward sodium flux. MicroRNA (miRNA) expression of hypertensive patients significantly differs from that of normotensive subjects. The aim of this study was to determine the functional role of miRNA alterations at the mTAL level.

METHODS

By miRNA microarray analysis, we identified miRNA expression profiles in isolated mTALs from high sodium intake-induced hypertensive rats (HSD) versus their normotensive counterparts (NSD). In vitro validation was carried out in rat mTAL cells.

RESULTS

Five miRNAs involved in the onset of salt-sensitive hypertension were identified, including miR-23a, which was bioinformatically predicted to target NHE1 mRNA. Data demonstrated that miRNA-23a is downregulated in the mTAL of HSD rats while NHE1 is upregulated. Consistently, transfection of an miRNA-23a mimic in an mTAL cell line, using a viral vector, resulted in NHE1 downregulation.

CONCLUSION

NHE1, a protein involved in sodium reabsorption at the mTAL level and blood pressure regulation, is upregulated in our model. This was due to a downregulation of miRNA-23a. Expression levels of this miRNA are influenced by high sodium intake in the mTALs of rats. The downregulation of miRNA-23a in humans affected by essential hypertension corroborate our data and point to the potential role of miRNA-23a in the regulation of mTAL function following high salt intake.

Dapagliflozin Prevents Kidney Glycogen Accumulation and Improves Renal Proximal Tubule Cell Functions in a Mouse Model of Glycogen Storage Disease Type 1b

BACKGROUND

Mutations in SLC37A4, which encodes the intracellular glucose transporter G6PT, cause the rare glycogen storage disease type 1b (GSD1b). A long-term consequence of GSD1b is kidney failure, which requires KRT. The main protein markers of proximal tubule function, including NaPi2A, NHE3, SGLT2, GLUT2, and AQP1, are downregulated as part of the disease phenotype.

METHODS

We utilized an inducible mouse model of GSD1b, TM-G6PT-/-, to show that glycogen accumulation plays a crucial role in altering proximal tubule morphology and function. To limit glucose entry into proximal tubule cells and thus to prevent glycogen accumulation, we administered an SGLT2-inhibitor, dapagliflozin, to TM-G6PT-/- mice.

RESULTS

In proximal tubule cells, G6PT suppression stimulates the upregulation and activity of hexokinase-I, which increases availability of the reabsorbed glucose for intracellular metabolism. Dapagliflozin prevented glycogen accumulation and improved kidney morphology by promoting a metabolic switch from glycogen synthesis toward lysis and by restoring expression levels of the main proximal tubule functional markers.

CONCLUSION

We provide proof of concept for the efficacy of dapagliflozin in preserving kidney function in GSD1b mice. Our findings could represent the basis for repurposing this drug to treat patients with GSD1b.

MO675: A New in Vivo Multi-Photon Microscopy Based Approach to Study the Peritoneal Membrane Changes Induced by Peritoneal Dialysis

BACKGROUND AND AIMS

Peritoneal dialysis (PD) is a renal replacement therapy that allows the elimination of metabolic waste products and excess body fluid through the peritoneal membrane. The exposure to PD solution contributes to membrane aging and fibrosis resulting in ultrafiltration and clearance failure.

The glucose, used as an osmotic factor, in PD dialysate triggers several processes involved in the pathogenesis of peritoneal fibrosis, angiogenesis and epithelial to mesenchymal transition.

Studies on natural extracts, such as Oleuropein (Ole), a powerful antioxidant with remarkable antifibrotic and protective effects on the peritoneal membrane, are currently being validated.

This study aims to develop a method based on multi-photon microscopy to study the physiology of the peritoneal membrane during dialysis exchange and to validate in vivo the effects of the Ole in animal models of fibrosis undergoing dialysis treatment.

METHOD

Multi-photon microscopy allows in vivo evaluation of the microcirculation that supply the peritoneum and also to study the framework of mesothelial cells and their underlying layer of collagen fibers that contributes to the sub-mesothelial space.

We have implemented the surgical procedure in order to optimize the stability of a flap of parietal peritoneum to directly observe at the scope. With this approach the peritoneal membrane is evaluable at baseline condition and during exposure to dialysate solutions.

RESULTS

Our method allows building a three-dimensional render of the peritoneal membrane, with the evaluation of all the single layers without the use of specific markers. In this way we could assess specifically the phenomena induced by the fibrotic process: the thickening of the sub-mesothelial interstitium and the greater density of the vascular network.

Furthermore, in vivo measurements of flow in the vessels of microcirculation (arterioles, capillaries, post-capillary venules) determine that exposure to hypotonic solutions increases significantly the flow in large-diameter vessels due to better permeability and hemodilution.

Finally in order to evaluate the possibility to detect morphological and functional changes in pathogenic model we have used the well-established model of peritoneal fibrosis derived by 15 days’ long exposure of the peritoneal membrane with 3.86% glucose dialysate. Whth this approach we could detect the significant increase in the parameters of cellularity, vascularization, fibrosis and thickening of collagen fibers.

In order to test the sensibility of our approach to the evaluation of the peritoneal membrane senescence parameters, we tested the effect of Ole in preventing the damage induced by high glucose–containing dialysate. Ole reduced both the thickness and the organization of the collagen fibers and the vascular network, including the number of branch points.

CONCLUSION

The developed method has potential for a dynamic and reliable in vivo approach. Studies are ongoing to validate the effects of drugs and dialysates with different osmotic and electrolytic compositions on the dialysis capacities of the peritoneal membrane and on the blood flow in peritoneal capillaries.

This method offers great potential for testing new pharmacological approaches aimed at preserving the structural and functional integrity of the peritoneum and for the validation of substances, such as natural extracts with beneficial effects against the damage induced in the long term by conventional dialysis solutions.

MO068: Paraoxonase 2 Protects the Kidney Tissue from Aldosterone-Promoted Oxidative Stress in Milan Normotensive Rats Strain

BACKGROUND AND AIMS

Kidney plays a pivotal role on the maintenance of blood pressure by the regulation of sodium reabsorption. Aldosterone sensitive distal nephron finely tunes salt reabsorption through several transporters, including the epithelial sodium channel (ENaC). Alteration in ENaC function leads to clinical relevant conditions associated with high or low blood pressure when gain or loss of function mutations occur, respectively.

Recently, accumulating evidence suggests the putative role of renal Paraoxonase 2 (PON2) as regulator of ENaC function. PON2 is a membrane-associated enzyme showing hydrolytic activity against 3-oxo-C12 homoserine lactone, a signaling molecule produced by bacteria and mainly Pseudomonas aeruginosa. PON2 also exhibits antioxidant property. In the distal nephron, PON2 is expressed in principal cells, and in vitro it physically interacts with ENaC subunits and inhibits ENaC channel activity in Xenopus oocytes likely by modulating channel assembly in the endoplasmic reticulum. However, the role of PON2 in the kidney is still not known.

In the present study, we investigate whether PON2 is regulated by changes in aldosterone state and its role in aldosterone-induced oxidative stress in the kidneys.

METHOD

We addressed these issues utilizing both in vivo and in vitro approaches, such as

RESULTS

We first demonstrated that in Milan normotensive rats strain, PON2 is upregulated by low-salt state according with α-ENaC activation. This regulation is aldosterone sensitive since pretreatment with mineralocorticoid receptor antagonist spironolactone prevented the stimulatory effects of sodium restricted diet. Furthermore, low-sodium diet inducing PON2 upregulation was associated with reduced ROS levels, more specifically superoxide levels, but treatment with spironolactone prevented this beneficial effect, by increasing ROS level in kidney cortex.

Since antihypertensive drugs spironolactone and canrenone contain a lactone residue in their molecular structure, we tested whether they could directly interact with PON2. We demonstrated in vitro that spironolactone and canrenone were able to inhibit PON2 lactonase activity and so to directly interfere with PON2 function. Finally, Milan hypertensive rats, carrying a mutation of α-adducin as determinant of their hypertensive phenotype, presented with higher level of ROS while PON2 was upregulated.

CONCLUSION

These results demonstrate PON2 as a novel target of steroid hormone aldosterone. PON2 may serve as a potential ROS scavenger mechanism protecting the kidneys from aldosterone-promoted oxidative stress.

Single nephron glomerular filtration rate measured by linescan multiphoton microscopy compared to conventional micropuncture

Renal micropuncture, which requires the direct access to the renal tubules, has for long time been the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models. This approach is challenging by virtue of complex animal preparation and numerous technically difficult steps. The introduction of intravital multiphoton microscopy (MPM) offers another approach to the measure of the SNGFR by mean of the high laser-tissue penetration and the optical sectioning capacity. Previous MPM studies measuring SNGFR in vivo relied on fast full-frame acquisition during the filtration process obtainable with high performance resonant scanners. In this study, we describe an innovative linescan–based MPM method. The new method can discriminate SNGFR variations both in conditions of low and high glomerular filtration, and shows results comparable to conventional micropuncture both for rats and mice. Moreover, this novel approach has improved spatial and time resolution and is faster than previous methods, thus enabling the investigation of SNGFR from more tubules and improving options for data-analysis.

Uremic Toxin Lanthionine Induces Endothelial Cell Mineralization In Vitro

Vascular calcification (VC) is a pathological event caused by the unusual deposition of minerals in the vascular system, representing the leading cause of cardiovascular mortality in chronic kidney disease (CKD). In CKD, the deregulation of calcium and phosphate metabolism, along with the effect of several uremic toxins, act as key processes conveying altered mineralization. In this work, we tested the ability of lanthionine, a novel uremic toxin, to promote calcification in human endothelial cell cultures (Ea.hy926). We evaluated the effects of lanthionine, at a concentration similar to that actually detected in CKD patients, alone and under pro-calcifying culture conditions using calcium and phosphate. In pro-calcific culture conditions, lanthionine increased both the intracellular and extracellular calcium content and induced the expression of Bone Morphogenetic Protein 2 (BMP2) and RUNX Family Transcription Factor 2 (RUNX2). Lanthionine treatment, in pro-calcifying conditions, raised levels of tissue-nonspecific alkaline phosphatase (ALPL), whose expression also overlapped with Dickkopf WNT Signaling Pathway Inhibitor 1 (DKK1) gene expression, suggesting a possible role of the latter gene in the activation of ALPL. In addition, treatment with lanthionine alone or in combination with calcium and phosphate reduced Inorganic Pyrophosphate Transport Regulator (ANKH) gene expression, a protective factor toward the mineralizing process. Moreover, lanthionine in a pro-calcifying condition induced the activation of ERK1/2, which is not associated with an increase in DKK1 protein levels. Our data underscored a link between mineral disease and the alterations of sulfur amino acid metabolisms at a cell and molecular level. These results set the basis for the understanding of the link between uremic toxins and mineral-bone disorder during CKD progression.

Parathyroid hormone and phosphate homeostasis in patients with Bartter and Gitelman syndrome: an international cross-sectional study

BACKGROUND

Small cohort studies have reported high parathyroid hormone (PTH) levels in patients with Bartter syndrome and lower serum phosphate levels have anecdotally been reported in patients with Gitelman syndrome. In this cross-sectional study, we assessed PTH and phosphate homeostasis in a large cohort of patients with salt-losing tubulopathies.

METHODS

Clinical and laboratory data of 589 patients with Bartter and Gitelman syndrome were provided by members of the European Rare Kidney Diseases Reference Network (ERKNet) and the European Society for Paediatric Nephrology (ESPN).

RESULTS

A total of 285 patients with Bartter syndrome and 304 patients with Gitelman syndrome were included for analysis. Patients with Bartter syndrome type I and II had the highest median PTH level (7.5 pmol/L) and 56% had hyperparathyroidism (PTH >7.0 pmol/L). Serum calcium was slightly lower in Bartter syndrome type I and II patients with hyperparathyroidism (2.42 versus 2.49 mmol/L; P = .038) compared to those with normal PTH levels and correlated inversely with PTH (rs -0.253; P = .009). Serum phosphate and urinary phosphate excretion did not correlate with PTH. Overall, 22% of patients had low serum phosphate levels (phosphate-standard deviation score < -2), with the highest prevalence in patients with Bartter syndrome type III (32%). Serum phosphate correlated with tubular maximum reabsorption of phosphate/glomerular filtration rate (TmP/GFR) (rs 0.699; P < .001), suggesting renal phosphate wasting.

CONCLUSIONS

Hyperparathyroidism is frequent in patients with Bartter syndrome type I and II. Low serum phosphate is observed in a significant number of patients with Bartter and Gitelman syndrome and appears associated with renal phosphate wasting.

Drug toxicity in the proximal tubule: new models, methods and mechanisms

The proximal tubule (PT) reabsorbs most of the glomerular filtrate and plays an important role in the uptake, metabolism and excretion of xenobiotics. Some therapeutic drugs are harmful to the PT, and resulting nephrotoxicity is thought to be responsible for approximately 1 in 6 of cases of children hospitalized with acute kidney injury (AKI). Clinically, PT dysfunction leads to urinary wasting of important solutes normally reabsorbed by this nephron segment, leading to systemic complications such as bone demineralization and a clinical scenario known as the renal Fanconi syndrome (RFS). While PT defects can be diagnosed using a combination of blood and urine markers, including urinary excretion of low molecular weight proteins (LMWP), standardized definitions of what constitutes clinically significant toxicity are lacking, and identifying which patients will go on to develop progressive loss of kidney function remains a major challenge. In addition, much of our understanding of cellular mechanisms of drug toxicity is still limited, partly due to the constraints of available cell and animal models. However, advances in new and more sophisticated in vitro models of the PT, along with the application of high-content analytical methods that can provide readouts more relevant to the clinical manifestations of nephrotoxicity, are beginning to extend our knowledge. Such technical progress should help in discovering new biomarkers that can better detect nephrotoxicity earlier and predict its long-term consequences, and herald a new era of more personalized medicine.

Brain dysfunction in tubular and tubulointerstitial kidney diseases

Kidney function has two important elements: glomerular filtration and tubular function (secretion and reabsorption). A persistent decrease in glomerular filtration rate (GFR), with or without proteinuria, is diagnostic of chronic kidney disease (CKD). While glomerular injury or disease is a major cause of CKD and usually associated with proteinuria, predominant tubular injury, with or without tubulointerstitial disease, is typically non-proteinuric. CKD has been linked with cognitive impairment, but it is unclear how much this depends on a reduced GFR, altered tubular function or the presence of proteinuria. Since CKD is often accompanied by tubular and interstitial dysfunction, we explore here for the first time the potential role of the tubular and tubulointerstitial compartments in cognitive dysfunction. To help address this issue, we have selected a group of primary tubular diseases with preserved GFR, in which to review the evidence for any association with brain dysfunction. Cognition, mood, neurosensory, and motor disturbances are not well characterized in tubular diseases, possibly because they are subclinical and less prominent than other clinical manifestations. The available literature suggests that brain dysfunction in tubular and tubulointerstitial diseases is usually mild and is more often seen in disorders of water handling. Brain dysfunction may occur when severe electrolyte and water disorders in young children persist over a long period of time before the diagnosis is made. We have chosen as examples to highlight this topic, Bartter and Gitelman syndromes and nephrogenic diabetes insipidus. We discuss current published findings, some unanswered questions, and propose topics for future research.

Atorvastatin does not ameliorate nephrogenic diabetes insipidus induced by lithium or potassium depletion in mice

Acquired forms of nephrogenic diabetes insipidus (NDI) include lithium (Li)-induced and hypokalemia-induced NDI. Both forms are associated with AQP2 downregulation and collecting duct (CD) cellular remodeling. Statins are cholesterol-lowering drugs appearing to increase AQP2 membrane-translocation and improve urine concentration in other NDI models. We have investigated if statins are able to prevent or rescue the Li-induced changes in mice and in a mouse cortical CD cell line (mCCDc1l ). Biotinylation assays showed that acute (1hr) atorvastatin, simvastatin, or fluvastatin increased AQP2 membrane accumulation in mCCDc1l cells showing that the cell line responds to acute statin treatment. To see whether chronic statin treatment abolish the Li effects, mCCDc1l cells were treated with 48 h Li, combined Li/atorvastatin or combined Li/simvastatin. Li reduced AQP2, but combined Li/atorvastatin or Li/simvastatin did not prevent AQP2 downregulation. In mice, chronic (21 days) Li increased urine output and reduced urine osmolality, but combined Li/atorvastatin did not prevent these effects. In inner medulla (IM), Li reduced total AQP2 and increased pS261-AQP2. Combined Li/atorvastatin did not abolish these changes. Atorvastatin did not prevent a Li-induced increase in intercalated cells and proliferation in IM. In mice with already established NDI, atorvastatin had no effect on the Li-induced changes either. Mice subjected to 14 days of potassium-deficient diet developed polyuria and AQP2 downregulation in IM. Co-treatment with atorvastatin did not prevent this. In conclusion, atorvastatin does not appear to be able to prevent or rescue Li-NDI or to prevent hypokalemic-induced NDI.

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

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

The SGLT2-inhibitor dapagliflozin improves neutropenia and neutrophil dysfunction in a mouse model of the inherited metabolic disorder GSDIb

Glycogen Storage Disease type 1b (GSDIb) is a genetic disorder with long term severe complications. Accumulation of the glucose analog 1,5-anhydroglucitol-6-phosphate (1,5AG6P) in neutrophils inhibits the phosphorylation of glucose in these cells, causing neutropenia and neutrophil dysfunctions. This condition leads to serious infections and inflammatory bowel disease (IBD) in GSDIb patients. We show here that dapagliflozin, an inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2), improves neutrophil function in an inducible mouse model of GSDIb by reducing 1,5AG6P accumulation in myeloid cells.

Urine concentrating defect as presenting sign of progressive renal failure in Bardet-Biedl syndrome patients

BACKGROUND

Urine concentrating defect is a common dysfunction in ciliopathies, even though its underlying mechanism and its prognostic meaning are largely unknown. This study assesses renal function in a cohort of 54 Bardet-Biedl syndrome (BBS) individuals and analyses whether renal hyposthenuria is the result of specific tubule dysfunction and predicts renal disease progression.

METHODS

The estimated glomerular filtration rate (eGFR), urine albumin:creatinine ratio (ACR) and maximum urine osmolality (max-Uosm) were measured in all patients. Genetic analysis was conducted in 43 patients. Annual eGFR decline (ΔeGFR) was measured in patients with a median follow-up period of 6.5 years. Urine aquaporin-2 (uAQP2) excretion was measured and the furosemide test was performed in patients and controls.

RESULTS

At baseline, 33 (61.1%), 12 (22.2%) and 9 (16.7%) patients showed an eGFR >90, 60-90 and <60 mL/min/1.73 m2, respectively; 27.3% showed an ACR >30 mg/g and 55.8% of patients showed urine concentrating defect in the absence of renal insufficiency. Baseline eGFR, but not max-Uosm, correlated negatively with age. Conversely, truncating mutations affected max-Uosm and showed a trend towards a reduction in eGFR. Max-Uosm correlated with ΔeGFR (P < 0.005), suggesting that urine concentrating defect may predict disease progression. uAQP2 excretion and Na+ and Cl- fractional excretion after furosemide did not differ between hyposthenuric patients and controls, suggesting that specific collecting duct and thick ascending limb dysfunctions are unlikely to play a central role in the pathogenesis of hyposthenuria.

CONCLUSIONS

Hyposthenuria is a warning sign predicting poor renal outcome in BBS. The pathophysiology of this defect is most likely beyond defective tubular function.

Dysregulation of Principal Cell miRNAs Facilitates Epigenetic Regulation of AQP2 and Results in Nephrogenic Diabetes Insipidus

BACKGROUND

MicroRNAs (miRNAs), formed by cleavage of pre-microRNA by the endoribonuclease Dicer, are critical modulators of cell function by post-transcriptionally regulating gene expression.

METHODS

Selective ablation of Dicer in AQP2-expressing cells (Dicer^AQP2Cre+ mice) was used to investigate the role of miRNAs in the kidney collecting duct of mice.

RESULTS

The mice had severe polyuria and nephrogenic diabetes insipidus, potentially due to greatly reduced AQP2 and AQP4 levels. Although epithelial sodium channel levels were decreased in cortex and increased in inner medulla, amiloride-sensitive sodium reabsorption was equivalent in Dicer^AQP2Cre+ mice and controls. Small-RNA sequencing and proteomic analysis revealed 31 and 178 significantly regulated miRNAs and proteins, respectively. Integrated bioinformatic analysis of the miRNAome and proteome suggested alterations in the epigenetic machinery and various transcription factors regulating AQP2 expression in Dicer^AQP2Cre+ mice. The expression profile and function of three miRNAs (miR-7688-5p, miR-8114, and miR-409-3p) whose predicted targets were involved in epigenetic control (Phf2, Kdm5c, and Kdm4a) or transcriptional regulation (GATA3, GATA2, and ELF3) of AQP2 were validated. Luciferase assays could not demonstrate direct interaction of AQP2 or the three potential transcription factors with miR-7688-5p, miR-8114, and miR-409-3p. However, transfection of respective miRNA mimics reduced AQP2 expression. Chromatin immunoprecipitation assays demonstrated decreased Phf2 and significantly increased Kdm5c interactions at the Aqp2 gene promoter in Dicer^AQP2Cre+ mice, resulting in decreased RNA Pol II association.

CONCLUSIONS

Novel evidence indicates miRNA-mediated epigenetic regulation of AQP2 expression.

MO429A NOVEL METHOD LINESCAN-DRIVEN FOR SNGFR MEASUREMENTS AS ALTERNATIVE TO HIGH FULL FRAME MULTIPHOTON MICROSCOPY ACQUISITION

Background and Aims

Renal micropuncture, which requires the direct access to the renal tubules, has been for long time the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models, but this approach is challenging by virtue of complex animal preparation and numerous careful steps. The introduction of intravital multiphoton microscopy (MPM) permitted to improve the study of renal functions exploiting the high laser penetration and the optical sectioning capacity. Previous MPM studies measuring in vivo the SNGFR relied on fast full frame acquisition during the filtration process obtainable with microscope resonant scanners, which represent optional expensive equipment able to reach very high acquisition speed. In this work we propose an innovative linescan-based MPM method to calculate SNGFR in rodents doable without using the fast acquisition rate offered by resonant scanners.

Method

An in vivo MPM approach was used to measure the SNGFR in control Munich Wistar Frömter rats (MWF) and to test the feasibility of the innovative linescan approach. In order to validate this method in conditions known for reduced and increased SNGFR, it was applied to ischemia reperfusion injury (IRI) and low-dose dopamine treated conditions, respectively.

Results

The glomeruli connected to S1 proximal tubules extending at least 100 μm from the exit of the Bowman’s space were chosen for the measurement. A linescan path starting from the urinary pole and crossing many times the tubular lumen orthogonally to the cellular wall was hand drawn. The linescan was acquired soon after a i.v. bolus of low-molecular weight fluorescent marker was injected. The tubular length, the mean diameter and the transit time of the fluorescent marker within two lines of interest (called cross1 and cross2) were measured to obtain the SNGFR. SNGFR measured in control rats was comparable with previous reported data both at MPM and micropuncture. Significantly higher values compared to control were obtained in 3 μg/kg/min dopamine-treated rats. In IRI-treated rats the SNGFR was reduced about 35% compared to the controls.

Conclusion

The results achieved with our linescan method were quite similar to those obtained with conventional micropuncture, suggesting that the two methods overlap for the normal, dopamine and IRI treatment. Our results show that linescan approach is a promising and cheap alternative to the fast full frame acquisition for the investigation of SNGFR in health and disease, offering results comparable to conventional micropuncture with unprecedent temporal resolution.

MO036DAPAGLIFLOZIN RESCUES THE RENAL PHENOTYPE OF GLYCOGEN STORAGE DISEASE TYPE IB

Background and Aims

Glycogenosis I type b (GsdI-b) is a rare metabolic disease and immune disorder characterized by hepato-renal glycogen accumulation caused by a deficiency in the Glucose-6-phosphate transporter (G6PT). G6PT transports glucose-6-phosphate (G6P) from cytoplasm to endoplasmic reticulum (ER) where a G6Pase catalyses the hydrolysis of G6P in glucose and phosphate. G6PT deficiency lead to impaired glucose homeostasis, myeloid disfunction and long-term risk of hepatocellular adenomas. No causal therapy is so far available for GSDI-b patients besides a dietary approach to control glycemia and the use of Granulocyte Colony-Stimulating Factor (GCSF) to improve neutropenia. Over time, these supports increase the chronicity of GSDI-b with some complications. A mouse model recapitulating the GDSI-b has been recently generated by inducing G6PT suppression after tamoxifen injection. Here, we characterized the renal phenotype of TM-G6PT-/- mice model focusing on the molecular mechanisms that lead to renal dysfunction. Finally, we evaluated the efficiency of Dapagliflozin, a selective inhibitor of SGLT2, on kidney functions in terms of therapeutic effect.

Method

Machine learning approach to computer based evaluation of renal morphology was used to analyze the renal sections from TM-G6PT-/- treated with or without dapagliflozin.

Results: G6PT is expressed in all renal zones and a severe downregulation of G6PT mRNA expression in whole kidney of TM-G6PT-/- mice can be observed. TM-G6PT-/- mice show tubular vacuolization and overall cellular dysfunction of PT due to a high glycogen accumulation. TM-G6PT-/- mice manifest glycosuria, phosphaturia and polyuria associated with a down regulation of main transporters of PT cells. The urine concentrating defect is due to a primarily role of G6PT in CNT/CD cells confirmed by a downregulation of AQP2, main water channel along CD segments. This mouse model recapitulates the human GSD-Ib renal phenotype characterized by a disfunction of PT but also CNT/CD cells. In order to evaluate whether targeting the glucose metabolism would improve the renal phenotype of these mice we limited glucose flux across the apical membrane of PT cells, applying the SGLT2-inhibitor dapagliflozin to reduce new glycogen formation. After one month of treatment, Dapagliflozin prevents glycogen accumulation in TM-G6PT-/- mice and ameliorates the main dysregulated markers of PT function. This finding was paralleled by an improvement of the histological features of kidney morphology in dapagliflozin treated TM-G6PT-/- mice.

Conclusion

Our data provide evidence that treatment with dapagliflozin ameliorates intracellular glycogen storage and improves the renal functions in TM-G6PT-/- mice.

MO035COMPUTATIONAL MODELING APPROACH FOR THE COMPREHENSIVE INTERPRETATION OF RARE TUBULOPATHIES

Background and Aims

Kidney plays a central role on the maintenance of water homeostasis, acid-base and electrolytes balances through the activity of different types of ion channels/transporters expressed along the nephron segments. Mutations in genes encoding these transporters could subsequently lead to aberrant transporter activities, resulting in abnormal renal handling of electrolytes, thus represent monogenic form of rare kidney diseases.

Accumulating number of mutations identified in genes responsible for such monogenic disorders demonstrated that eventual disease phenotypes may vary according to the type and localization of the mutation within the gene. Thus, careful evaluation of gene variation would be crucial prior to designing the strategy for the therapy in each case.

Here we present various mutations from our patients, identified in genes including kcnj10, SLC12A1, SLC26A4 and clcn7 which are associated with rare tubulopathies EAST/SeSAME syndrome, Bartter’s syndrome, Pendred syndrome and Fanconi syndrome, respectively.

In order to explore molecular mechanisms underlying the observed disease conditions in our patients, we have performed computational modeling analyses of these mutations in comparison with wild-type models.

Method

Three-dimensional homology models of Kir4.1, NKCC2, Pendrin and CLC-7 proteins were generated by Swiss-Model protein structure homology-modelling server (http://swissmodel. expasy.org) and I-TASSER server (https://zhanglab.ccmb.med.umich.edu/I-TASSER/). Disease-related mutations including novel mutations identified from our patients were mapped onto the three-dimensional models and compared with wild-type models in terms of atomic interactions as well as secondary, tertiary and quaternary structures. Furthermore, we assessed possible effects of missense mutations on the function of ion channels/transporters using online bioinformatic prediction tools PolyPhen-2, Mutation taster, PROVEAN and SIFT.

Results

The three-dimensional model comparison between wild-type Kir4.1 and Ala167Val variant, which is related to EAST/SeSAME syndrome, revealed that Ala167Val located at the junction between transmembrane domain 2 (TM2) and C-terminus is predicted not to interrupt the sequence of the hydrogen bonds, thus not altering the TM2 alpha-helix structure. In addition, while PolyPhen-2 and Mutation taster evaluated Ala167Val as ‘probably damaging’, PROVEAN and SIFT predicted Ala167Val as ‘neutral’ and ‘tolerated’. These observations are in line with the clinical data demonstrating the milder phenotype in patients with Ala167Val mutation compared with the ones harboring frameshift mutations leading to truncated Kir4.1 channel (Figure. 1).

Furthermore, computational modeling of wild-type NKCC2 and frameshift mutation Arg302Glyfs*3 variant clearly demonstrated that Arg302Glyfs*3 results in a loss of large part of the protein, indicating that NKCC2-Arg302Glyfs*3 is practically nonfunctional (Figure. 2).

Conclusion

Computational modeling of disease-related mutations in various ion channels/transporters represents a novel, powerful approach for comprehensive interpretation of the disease phenotypes observed in patients with rare tubulopathies. In addition, combination of in silico modeling and clinical data could provide us with further insight into molecular mechanisms underlying the renal transporter activities. Furthermore, this in silico computational modeling approach can be applicable and suggestive for novel pharmacological intervention as well as the visual disease severity assessment.

A case series of adult patients affected by EAST/SeSAME syndrome suggests more severe disease in subjects bearing KCNJ10 truncating mutations

EAST/SeSAME syndrome is a rare disease affecting the Central Nervous System (CNS), inner ear, and kidney. The syndrome is due to loss-of-function mutations in the KCNJ10 gene encoding the inward-rectifying potassium channel Kir4.1. EAST/SeSAME syndrome is mainly diagnosed during childhood with a tonic-clonic seizure being the usual first symptom. Due to a limited number of patients and recent identification of the disease, few data are available on the clinical progress of this disease in adulthood. In particular, neurologic and nephrological outcomes have not been reported. We present a case series of 4 adult patients harbouring homozygous missense mutation p.Ala167Val and homozygous frameshift mutations p.Asn232Glnfs*14 and p.Gly275Valfs*7. Effects of these mutations were predicted by in silico modelling and bioinformatic tools. Patients with truncating mutations were associated with more severe outcomes, both in tubulopathy severity and neurological symptomatology. Conversely, either missense or truncating mutations were correlated with similar severity of epilepsy, with a long free-of-event period up to 20 years old. No eGFR decline was documented. Modelling predicted that truncating mutations lead to complete Kir4.1 dysfunction. Finally, all patients had a mild increase in urinary protein excretion. Our study indicates that the prognosis of patients suffering from EAST/SeSAME syndrome is related to the severity of the mutation causing the disease. As predicted by in silico modelling, truncating mutations of KCNJ10 are associated with more severe disease, with recurrence of symptomatic hypokalemia and more severe neurological phenotype. The type of mutation should be considered for the therapy tailored to patients' phenotype.

Distal Renal Tubular Acidosis: ERKNet/ESPN Clinical Practice Points

Distal renal tubular acidosis (dRTA) is characterised by an impaired ability of the distal tubule to excrete acid, leading to metabolic acidosis. Associated complications include bone disease, growth failure, urolithiasis and hypokalaemia. Due to its rarity, there is a limited evidence to guide diagnosis and management, however, available data strongly suggest that metabolic control of the acidosis by alkali supplementation can halt or revert almost all complications. Despite this, cohort studies show that adequate metabolic control is present in only about half of patients, highlighting problems with treatment provision or adherence. With these clinical practice points the authors, part of the working groups tubulopathies in the European Rare Kidney Disease Reference network (ERKnet) and inherited kidney diseases of the European Society for Paediatric Nephrology (ESPN) aim to provide guidance for the management of patients with dRTA to facilitate adequate treatment and establish an initial best practice standard against which treatment of patients can be audited.

Distal renal tubular acidosis: a systematic approach from diagnosis to treatment

Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO₃ is impaired, leading to chronic metabolic acidosis with normal anion gap. In the current review, the focus is placed on the most common type of RTA, Type 1 RTA or Distal RTA (dRTA), which is a rare chronic genetic disorder characterized by an inability of the distal nephron to secrete hydrogen ions in the presence of metabolic acidosis. Over the years, knowledge of the molecular mechanisms behind acid secretion has improved, thereby greatly helping the diagnosis of dRTA. The primary or inherited form of dRTA is mostly diagnosed in infancy, childhood, or young adulthood, while the acquired secondary form, as a consequence of other disorders or medications, can happen at any age, although it is more commonly seen in adults. dRTA is not as “benign” as previously assumed, and can have several, highly variable long-term consequences. The present review indeed reports and summarizes both clinical symptoms and diagnosis, long-term outcomes, genetic inheritance, epidemiology and current treatment options, with the aim of shedding more light onto this rare disorder. Being a chronic condition, dRTA also deserves attention in the transition between pediatric and adult nephrology care, and as a rare disease it has a place in the European and Italian rare nephrological diseases network.

Diagnosis and management of Bartter syndrome: executive summary of the consensus and recommendations from the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders

Bartter syndrome is a rare inherited salt-losing renal tubular disorder characterized by secondary hyperaldosteronism with hypokalemic and hypochloremic metabolic alkalosis and low to normal blood pressure. The primary pathogenic mechanism is defective salt reabsorption predominantly in the thick ascending limb of the loop of Henle. There is significant variability in the clinical expression of the disease, which is genetically heterogenous with 5 different genes described to date. Despite considerable phenotypic overlap, correlations of specific clinical characteristics with the underlying molecular defects have been demonstrated, generating gene-specific phenotypes. As with many other rare disease conditions, there is a paucity of clinical studies that could guide diagnosis and therapeutic interventions. In this expert consensus document, the authors have summarized the currently available knowledge and propose clinical indicators to assess and improve quality of care.

A double-blind, randomized, placebo-controlled pilot trial of atorvastatin for nephrogenic diabetes insipidus in lithium users

OBJECTIVE

Lithium remains an important treatment for mood disorders but is associated with kidney disease. Nephrogenic diabetes insipidus (NDI) is associated with up to 3-fold risk of incident chronic kidney disease among lithium users. There are limited randomized controlled trials (RCT) for treatments of lithium-induced NDI, and existing therapies can be poorly tolerated. Therefore, novel treatments are needed for lithium-induced NDI.

METHOD

We conducted a 12-week double-blind pilot RCT to assess the feasibility and efficacy of 20 mg/d atorvastatin vs placebo in the treatment of NDI in chronic lithium users. Patients, recruited between September 2017 and October 2018, were aged 18 to 85, currently on a stable dose of lithium, and determined to have NDI.

RESULTS

Urinary osmolality (UOsm) at 12 weeks adjusted for baseline was not statistically different between groups (+39.6 mOsm/kg [95% CI, -35.3, 114.5] in atorvastatin compared to placebo groups). Secondary outcomes of fluid intake and aquaporin-2 excretions at 12 weeks adjusted for baseline were -0.13 L [95% CI, -0.54, 0.28] and 98.68 [95% CI, -190.34, 387.70], respectively. A moderate effect size was observed for improvements in baseline UOsm by ≥100 mOsm/kg at 12 weeks in patients who received atorvastatin compared to placebo (38.45% (10/26) vs 22.58% (7/31); Cohen's d = 0.66).

CONCLUSION

Among lithium users with NDI, atorvastatin 20 mg/d did not significantly improve urinary osmolality compared to placebo over a 12-week period. Larger confirmatory trials with longer follow-up periods may help to further assess the effects of statins on NDI, especially within patients with more severe NDI.

Treatment and long-term outcome in primary nephrogenic diabetes insipidus

BACKGROUND

Primary nephrogenic diabetes insipidus (NDI) is a rare disorder and little is known about treatment practices and long-term outcome.

METHODS

Paediatric and adult nephrologists contacted through European professional organizations entered data in an online form.

RESULTS

Data were collected on 315 patients (22 countries, male 84%, adults 35%). Mutation testing had been performed in 270 (86%); pathogenic variants were identified in 258 (96%). The median (range) age at diagnosis was 0.6 (0.0-60) years and at last follow-up 14.0 (0.1-70) years. In adults, height was normal with a mean (standard deviation) score of -0.39 (±1.0), yet there was increased prevalence of obesity (body mass index >30 kg/m2; 41% versus 16% European average; P < 0.001). There was also increased prevalence of chronic kidney disease (CKD) Stage ≥2 in children (32%) and adults (48%). Evidence of flow uropathy was present in 38%. A higher proportion of children than adults (85% versus 54%; P < 0.001) received medications to reduce urine output. Patients ≥25 years were less likely to have a university degree than the European average (21% versus 35%; P = 0.003) but full-time employment was similar. Mental health problems, predominantly attention-deficit hyperactivity disorder (16%), were reported in 36% of patients.

CONCLUSION

This large NDI cohort shows an overall favourable outcome with normal adult height and only mild to moderate CKD in most. Yet, while full-time employment was similar to the European average, educational achievement was lower, and more than half had urological and/or mental health problems.

Regulation of urinary calcium excretion by vasopressin

Background

The antidiuretic hormone (ADH) or arginine vasopressin (AVP) regulates the body's water balance. Recently, modifications in AVP levels have been related to osteoporosis during ageing and microgravity/bed rest. Therefore the present study was devised to assess whether the absence of AVP, as in patients with central diabetes insipidus (CDI), modulates renal calcium excretion.

Methods

We retrospectively analysed data from 12 patients with CDI with measured 24-h urinary excretion levels of calcium. Data were available at the moment of the diagnosis when patients were drug-free and after therapy with dDAVP, an analog of AVP. Hypercalciuria was defined as 24-h urinary Ca²⁺ >275 mg/day in males and >250 mg/day in females and a urinary calcium (Ca):creatinine (Cr) ratio >0.20 mg/mg.

Results

Untreated CDI patients had a daily urinary Ca²⁺ excretion of 383 ± 47 mg/day and a urinary Ca:Cr ratio of 0.26 ± 0.38 mg/mg. The urine osmolarity significantly increased after the administration of dDAVP by 210% and the urinary flow decreased by 72%. Furthermore, the estimated glomerular filtration rate (eGFR) increased by 7%, which did not reach statistical significance. dDAVP treatment did not significantly modify the urinary Ca²⁺ concentration; however, the daily calcium excretion and the urinary Ca:Cr ratio were significantly decreased (160 ± 27 mg/day and 0.11 ± 0.02 mg/mg, respectively).

Conclusions

Patients with CDI show hypercalciuria even though urine is more diluted than normal controls, and dDAVP reverses this effect. These data support the intriguing relationship between AVP and osteoporosis in ageing and microgravity/bed rest.

Urinary Metabolic Profile of Patients with Transfusion-Dependent β-Thalassemia Major Undergoing Deferasirox Therapy

INTRODUCTION

Renal dysfunction is a frequent complication in patients suffering from β-thalassemia major (β-TM). The aim of this study was to analyze the renal function and urine metabolomic profile of β-TM patients undergoing transfusions and deferasirox (DFX) therapy, in order to better characterize and shed light on the pathogenesis of renal disease in this setting.

METHODS AND SUBJECTS

40 patients affected by β-TM treated with DFX and 35 age- and gender-matched healthy controls were enrolled in the study. Renal function was assessed. Glomerular filtration rate (GFR) was estimated with CKD-EPI and Schwartz formula for adults and children, respectively. Renal tubular function and maximal urine concentration ability were tested. Urine specimens were analyzed by nuclear magnetic resonance spectroscopy to identify the urinary metabolite profiles.

RESULTS

The study of renal function in β-TM patients revealed normal estimated (e)GFR mean values and the albumin-to-creatinine ratio was <30 mg/g. The analysis of tubular function showed normal basal plasma electrolyte levels; 60% of patients presented hypercalciuria and many subjects showed defective urine concentration. Several amino acids, N-methyl compounds, and organic acids were overexcreted in the urine of thalassemic patients compared with controls.

DISCUSSION

The major finding of this work is that β-TM patients and controls exhibit different concentrations of some metabolites in the urine. Early recognition of urinary abnormalities may be useful to detect and prevent kidney damage.

Treatment and long-term outcome in primary distal renal tubular acidosis

BACKGROUND

Primary distal renal tubular acidosis (dRTA) is a rare disorder, and we aimed to gather data on treatment and long-term outcome.

METHODS

We contacted paediatric and adult nephrologists through European professional organizations. Responding clinicians entered demographic, biochemical, genetic and clinical data in an online form.

RESULTS

Adequate data were collected on 340 patients (29 countries, female 52%). Mutation testing had been performed on 206 patients (61%); pathogenic mutations were identified in 170 patients (83%). The median (range) presentation age was 0.5 (0-54) years and age at last follow-up was 11.0 (0-70.0) years. Adult height was slightly below average with a mean (SD score) of -0.57 (±1.16). There was an increased prevalence of chronic kidney disease (CKD) Stage ≥2 in children (35%) and adults (82%). Nephrocalcinosis was reported in 88%. Nephrolithiasis was more common with SLC4A1 mutations (42% versus 21%). Thirty-six percent had hearing loss, particularly in ATP6V1B1 (88%). The median (interquartile range) prescribed dose of alkali (mEq/kg/day) was 1.9 (1.2-3.3). Adequate metabolic control (normal plasma bicarbonate and normocalciuria) was achieved in 158 patients (51%), more commonly in countries with higher gross domestic product (67% versus 23%), and was associated with higher height and estimated glomerular filtration rate.

CONCLUSION

Long-term follow-up from this large dRTA cohort shows an overall favourable outcome with normal adult height for most and no patient with CKD Stage 5. However, 82% of adult patients have CKD Stages 2-4. Importance of adequate metabolic control was highlighted by better growth and renal function but was achieved in only half of patients.

Potassium depletion induces cellular conversion in the outer medullary collecting duct altering Notch signaling pathway

Potassium depletion affects AQP2 expression and the cellular composition of the kidney collecting duct. This, in turn, contributes to the development of a secondary form of nephrogenic diabetes insipidus and hypokalemic nephropathy. Here we show that after 14 days of potassium depletion, the cellular fraction of A-type intercalated cells increases while the fraction of principal cells decreases along the outer medullary collecting duct in rats. The intercalated cells acquired a novel distribution pattern forming rows of cells attached to each other. These morphological changes occur progressively and reverse after 7 days of recovery on normal rat chow diet. The cellular remodeling mainly occurred in the inner stripe of outer medulla similar to the previously seen effect of lithium on the collecting duct cellular profile. The cellular remodeling is associated with the appearance of cells double labelled with both specific markers of principal and type-A intercalated cells. The appearance of this cell type was associated with the downregulation of the Notch signaling via the Hes1 pathways. These results show that the epithelium of the collecting duct has a high degree of plasticity and that Notch signaling likely plays a key role during hypokalemia.

COVID-19 and Extracellular Vesicles: An Intriguing Interplay

BACKGROUND

The outbreak of severe acute respiratory syndrome β-coronavirus 2 (SARS-CoV-2) has the potential to become a long-lasting global health crisis. The number of people infected with the novel coronavirus has surpassed 22 million globally, resulting in over 700,000 deaths with more than 15 million people having recovered (https://covid19.who.int). Enormous efforts are underway for rapid vaccine and treatment developments. Amongst the many ways of tackling the novel coronavirus disease 2019 (COVID-19) pandemic, extracellular vesicles (EVs) are emerging.

SUMMARY

EVs are lipid bilayer-enclosed structures secreted from all types of cells, including those lining the respiratory tract. They have established roles in lung immunity and are involved in the pathogenesis of various lung diseases, including viral infection. In this review, we point out the roles and possible contribution of EVs in viral infections, as well as ongoing EV-based approaches for the treatment of COVID-19, including clinical trials. Key Messages: EVs share structural similarities to viruses and recent findings demonstrate that viruses exploit EVs for cellular exit and EVs exploit viral entry mechanisms for cargo delivery. Moreover, EV-virus interplay could be exploited for future antiviral drug and vaccine development. EV-based therapies, especially the mesenchymal stem cell-derived EVs, are being intensively studied for the treatment of COVID-19.

ERA-EDTA fellowship, a 'bonne opportunité': the scientific and human experience of a fellow

As a fellow of the ERA-EDTA long-term fellowship programme, I spent two fantastic years as a post-doc in Prof. D. Eladari’s laboratory at Inserm U970, Paris-Cardiovascular Research Centre. It was a highly formative and productive scientific experience. On a personal level, immersion into the French society and the international environment of the laboratory were added bonuses that enriched my experience. I am honoured to report my experience here from the ERA-EDTA fellowship programme. I hope this will inspire young fellows to apply for such a programme and pursue their career in science. Good mentorship, a passion for scientific investigation and determination are required.

Uremic Toxin Lanthionine Interferes with the Transsulfuration Pathway, Angiogenetic Signaling and Increases Intracellular Calcium

(1) The beneficial effects of hydrogen sulfide (H2S) on the cardiovascular and nervous system have recently been re-evaluated. It has been shown that lanthionine, a side product of H2S biosynthesis, previously used as a marker for H2S production, is dramatically increased in circulation in uremia, while H2S release is impaired. Thus, lanthionine could be classified as a novel uremic toxin. Our research was aimed at defining the mechanism(s) for lanthionine toxicity. (2) The effect of lanthionine on H2S release was tested by a novel lead acetate strip test (LAST) in EA.hy926 cell cultures. Effects of glutathione, as a redox agent, were assayed. Levels of sulfane sulfur were evaluated using the SSP4 probe and flow cytometry. Protein content and glutathionylation were analyzed by Western Blotting and immunoprecipitation, respectively. Gene expression and miRNA levels were assessed by qPCR. (3) We demonstrated that, in endothelial cells, lanthionine hampers H2S release; reduces protein content and glutathionylation of transsulfuration enzyme cystathionine-β-synthase; modifies the expression of miR-200c and miR-423; lowers expression of vascular endothelial growth factor VEGF; increases Ca2+ levels. (4) Lanthionine-induced alterations in cell cultures, which involve both sulfur amino acid metabolism and calcium homeostasis, are consistent with uremic dysfunctional characteristics and further support the uremic toxin role of this amino acid.

The role of the intestinal microbiota in uremic solute accumulation: a focus on sulfur compounds

The gut microbiota is considered to be a novel important factor to take into account in the pathogenesis of chronic kidney disease and uremia. Much attention has been paid to specific uremic retention solutes of microbial origin, such as indoxyl sulfate, p-cresyl sulfate, and trimethylamine-N-oxide. However, other novel less well studied compounds, such as hydrogen sulfide and related sulfur metabolites (sulfane sulfur, lanthionine, etc.), should be included in a more comprehensive appraisal of this topic, in light of the potential therapeutic opportunities for the future.