AQP1 Promoter Variant, Water Transport, and Outcomes in Peritoneal Dialysis.

BACKGROUND: Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1, the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability. METHODS: We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies. RESULTS: The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant. CONCLUSIONS: A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.).

Recent advances in the understanding of the peritoneal membrane.

PURPOSE OF REVIEW: The efficiency of peritoneal dialysis (PD) as a life-sustaining replacement therapy for patients with kidney failure relies on the integrity and function of the peritoneal membrane. Here, we review the most recent advances in the understanding of the peritoneal membrane and its role in PD. RECENT FINDINGS: A recent update of the ISPD guidelines proposed a revised definition of membrane dysfunction, emphasizing the importance of fluid balance in patients treated with PD and identified three main mechanisms leading to insufficient peritoneal ultrafiltration (UF). The Bio-PD study, the first genomewide association study in PD, demonstrated that 20% of the interindividual variability in the peritoneal solute transfer rate is genetically determined, and identified several loci of potential relevance for peritoneal transport. A candidate-gene approach identified and characterized a common and functional variant in the promoter of the AQP1 gene associated with water transport and clinical outcomes in PD. Innovative strategies to preserve the integrity of the peritoneal membrane and to enhance UF are also discussed, including the use of gliflozins; steady glucose concentration PD; modulation of GLUT proteins; and cytoprotective additives. SUMMARY: A comprehensive understanding of the peritoneal membrane and of the mechanisms driving UF may help individualizing PD prescription and improving outcomes in patients treated with PD.

Severe parental phenotype associates with hypertension in children with ADPKD.

BACKGROUND: Early detection of hypertension in children with autosomal polycystic kidney disease (ADPKD) may be beneficial, but screening children at risk of ADPKD remains controversial. We investigated determinants of hypertension in children with ADPKD to help identify a subgroup of children at risk of ADPKD for whom screening for the disease and/or its complications would be more relevant. METHODS: In a retrospective study including consecutive children with ADPKD aged 5-18 years and followed at Saint-Luc Hospital Brussels between 2006 and 2020, we investigated the potential association between genotype, clinical characteristics and parental phenotype, and presence of hypertension. Hypertension was defined as blood pressure > P95 during 24-h ambulatory monitoring or anti-hypertensive therapy use. Parental phenotype was considered severe based on age at kidney failure, Mayo Clinic Imaging Classification and rate of eGFR decline. RESULTS: The study enrolled 55 children with ADPKD (mean age 9.9 ± 2.2 years, 45% male), including 44 with a PKD1 mutation and 5 with no mutation identified. Nine (16%) children had hypertension. Hypertension in children was associated with parental phenotype severity (8/27 (30%) children with severe parental phenotype vs. 1/23 (4%) children with non-severe parental phenotype (p = 0.03)) and height-adjusted bilateral nephromegaly (6/9 (67%) children with bilateral nephromegaly vs. 3/44 (7%) children without bilateral nephromegaly (p < 0.001)). CONCLUSIONS: Severe parental phenotype is associated with higher prevalence of hypertension in children with ADPKD. Hence, children of parents with severe ADPKD phenotype may be those who will most benefit from screening of the disease and/or yearly BP measures. A higher resolution version of the Graphical abstract is available as Supplementary information.

Pathophysiology and Management of Hyperoxaluria and Oxalate Nephropathy: A Review.

Hyperoxaluria results from either inherited disorders of glyoxylate metabolism leading to hepatic oxalate overproduction (primary hyperoxaluria), or increased intestinal oxalate absorption (secondary hyperoxaluria). Hyperoxaluria may lead to urinary supersaturation of calcium oxalate and crystal formation, causing urolithiasis and deposition of calcium oxalate crystals in the kidney parenchyma, a condition termed oxalate nephropathy. Considerable progress has been made in the understanding of pathophysiological mechanisms leading to hyperoxaluria and oxalate nephropathy, whose diagnosis is frequently delayed and prognosis too often poor. Fortunately, novel promising targeted therapeutic approaches are on the horizon in patients with primary hyperoxaluria. Patients with secondary hyperoxaluria frequently have long-standing hyperoxaluria-enabling conditions, a fact suggesting the role of triggers of acute kidney injury such as dehydration. Current standard of care in these patients includes management of the underlying cause, high fluid intake, and use of calcium supplements. Overall, prompt recognition of hyperoxaluria and associated oxalate nephropathy is crucial because optimal management may improve outcomes.

Protocadherin 7-Associated Membranous Nephropathy.

BACKGROUND: Membranous nephropathy (MN) results from deposition of antigen-antibody complexes along the glomerular basement membrane (GBM). PLA2R, THSD7A, NELL1, and SEMA3B account for 80%-90% of target antigens in MN. METHODS: We performed laser microdissection and mass spectrometry (MS/MS) in kidney biopsies from 135 individuals with PLA2R-negative MN, and used immunohistochemistry/immunofluorescence and confocal microscopy to confirm the MS/MS finding, detect additional cases, and localize the novel protein. We also performed MS/MS and immunohistochemistry on 116 controls and used immunofluorescence microscopy to screen biopsy samples from two validation cohorts. Western blot and elution studies were performed to detect antibodies in serum and biopsy tissue. RESULTS: MS/MS studies detected a unique protein, protocadherin 7 (PCDH7), in glomeruli of ten (5.7%) PLA2R-negative MN cases, which also were negative for PLA2R, THSD7A, EXT1/EXT2, NELL1, and SEMA3B. Spectral counts ranged from six to 24 (average 13.2 [SD 6.6]). MS/MS did not detect PCDH7 in controls (which included 28 PLA2R-positive cases). In all ten PCDH7-positive cases, immunohistochemistry showed bright granular staining along the GBM, which was absent in the remaining cases of PLA2R-negative MN and control cases. Four of 69 (5.8%) cases in the validation cohorts (all of which were negative for PLA2R, THSD7A, EXT1, NELL1, and SEMA3B) were PCDH7-positive MN. Kidney biopsy showed minimal complement deposition in 12 of the 14 PCDH7-associated cases. Confocal microscopy showed colocalization of PCDH7 and IgG along the GBM. Western blot analysis using sera from six patients showed antibodies to nonreduced PCDH7. Elution of IgG from frozen tissue of PCDH7-associated MN showed reactivity against PCDH7. CONCLUSIONS: MN associated with the protocadherin PCDH7 appears to be a distinct, previously unidentified type of MN.

A genome-wide association study suggests correlations of common genetic variants with peritoneal solute transfer rates in patients with kidney failure receiving peritoneal dialysis.

Movement of solutes across the peritoneum allows for the use of peritoneal dialysis to treat kidney failure. However, there is a large inter-individual variability in the peritoneal solute transfer rate (PSTR). Here, we tested the hypothesis that common genetic variants are associated with variability in PSTR. Of the 3561 participants from 69 centers in six countries, 2850 with complete data were included in a genome-wide association study. PSTR was defined as the four-hour dialysate/plasma creatinine ratio from the first peritoneal equilibration test after starting PD. Heritability of PSTR was estimated using genomic-restricted maximum-likelihood analysis, and the association of PSTR with a genome-wide polygenic risk score was also tested. The mean four-hour dialysate/plasma creatinine ratio in participants was 0.70. In 2212 participants of European ancestry, no signal reached genome-wide significance but 23 single nucleotide variants at four loci demonstrated suggestive associations with PSTR. Meta-analysis of ancestry-stratified regressions in 2850 participants revealed five single-nucleotide variants at four loci with suggestive correlations with PSTR. Association across ancestry strata was consistent for rs28644184 at the KDM2B locus. The estimated heritability of PSTR was 19%, and a permuted model polygenic risk score was significantly associated with PSTR. Thus, this genome-wide association study of patients receiving peritoneal dialysis bolsters evidence for a genetic contribution to inter-individual variability in PSTR.

Serum uric acid, disease severity and outcomes in COVID-19.

BACKGROUND: The severity of coronavirus disease 2019 (COVID-19) is highly variable between individuals, ranging from asymptomatic infection to critical disease with acute respiratory distress syndrome requiring mechanical ventilation. Such variability stresses the need for novel biomarkers associated with disease outcome. As SARS-CoV-2 infection causes a kidney proximal tubule dysfunction with urinary loss of uric acid, we hypothesized that low serum levels of uric acid (hypouricemia) may be associated with severity and outcome of COVID-19. METHODS: In a retrospective study using two independent cohorts, we investigated and validated the prevalence, kinetics and clinical correlates of hypouricemia among patients hospitalized with COVID-19 to a large academic hospital in Brussels, Belgium. Survival analyses using Cox regression and a competing risk approach assessed the time to mechanical ventilation and/or death. Confocal microscopy assessed the expression of urate transporter URAT1 in kidney proximal tubule cells from patients who died from COVID-19. RESULTS: The discovery and validation cohorts included 192 and 325 patients hospitalized with COVID-19, respectively. Out of the 517 patients, 274 (53%) had severe and 92 (18%) critical COVID-19. In both cohorts, the prevalence of hypouricemia increased from 6% upon admission to 20% within the first days of hospitalization for COVID-19, contrasting with a very rare occurrence (< 1%) before hospitalization for COVID-19. During a median (interquartile range) follow-up of 148 days (50-168), 61 (12%) patients required mechanical ventilation and 93 (18%) died. In both cohorts considered separately and in pooled analyses, low serum levels of uric acid were strongly associated with disease severity (linear trend, P < 0.001) and with progression to death and respiratory failure requiring mechanical ventilation in Cox (adjusted hazard ratio 5.3, 95% confidence interval 3.6-7.8, P < 0.001) or competing risks (adjusted hazard ratio 20.8, 95% confidence interval 10.4-41.4, P < 0.001) models. At the structural level, kidneys from patients with COVID-19 showed a major reduction in urate transporter URAT1 expression in the brush border of proximal tubules. CONCLUSIONS: Among patients with COVID-19 requiring hospitalization, low serum levels of uric acid are common and associate with disease severity and with progression to respiratory failure requiring invasive mechanical ventilation.

Neural epidermal growth factor-like 1 protein (NELL-1) associated membranous nephropathy.

Membranous nephropathy is characterized by deposition of immune complexes along the glomerular basement membrane. PLA2R and THSD7A are target antigens in 70% and 1-5% of primary membranous nephropathy cases, respectively. In the remaining cases, the target antigen is unknown. Here, laser microdissection of glomeruli followed by mass spectrometry was used to identify novel antigen(s) in PLA2R-negative membranous nephropathy. An initial pilot mass spectrometry study in 35 cases of PLA2R-negative membranous nephropathy showed high spectral counts for neural tissue encoding protein with EGF-like repeats, NELL-1, in six cases. Mass spectrometry failed to detect NELL-1 in 23 PLA2R-associated membranous nephropathy and 88 controls. NELL-1 was localized by immunohistochemistry, which showed bright granular glomerular basement membrane staining for NELL-1 in all six cases. Next, an additional 23 NELL-1 positive cases of membranous nephropathy were identified by immunohistochemistry in a discovery cohort of 91 PLA2R-negative membranous nephropathy cases, 14 were confirmed by mass spectrometry. Thus, 29 of 126 PLA2R-negative cases were positive for NELL-1. PLA2R-associated membranous nephropathy and controls stained negative for NELL-1. We then identified five NELL-1 positive cases of membranous nephropathy out of 84 PLA2R and THSD7A-negative cases in two validation cohorts from France and Belgium. By confocal microscopy, both IgG and NELL-1 co-localized to the glomerular basement membrane. Western blot analysis showed reactivity to NELL-1 in five available sera, but no reactivity in control sera. Clinical and biopsy findings of NELL-1 positive membranous nephropathy showed features of primary membranous nephropathy. Thus, a subset of membranous nephropathy is associated with accumulation and co-localization of NELL-1 and IgG along the glomerular basement membrane, and with anti-NELL-1 antibodies in the serum. Hence, NELL-1 defines a distinct type of primary membranous nephropathy.

SARS-CoV-2 causes a specific dysfunction of the kidney proximal tubule.

Coronavirus disease 2019 (COVID-19) is commonly associated with kidney damage, and the angiotensin converting enzyme 2 (ACE2) receptor for SARS-CoV-2 is highly expressed in the proximal tubule cells. Whether patients with COVID-19 present specific manifestations of proximal tubule dysfunction remains unknown. To test this, we examined a cohort of 49 patients requiring hospitalization in a large academic hospital in Brussels, Belgium. There was evidence of proximal tubule dysfunction in a subset of patients with COVID-19, as attested by low-molecular-weight proteinuria (70-80%), neutral aminoaciduria (46%), and defective handling of uric acid (46%) or phosphate (19%). None of the patients had normoglycemic glucosuria. Proximal tubule dysfunction was independent of pre-existing comorbidities, glomerular proteinuria, nephrotoxic medications or viral load. At the structural level, kidneys from patients with COVID-19 showed prominent tubular injury, including in the initial part of the proximal tubule, with brush border loss, acute tubular necrosis, intraluminal debris, and a marked decrease in the expression of megalin in the brush border. Transmission electron microscopy identified particles resembling coronaviruses in vacuoles or cisternae of the endoplasmic reticulum in proximal tubule cells. Among features of proximal tubule dysfunction, hypouricemia with inappropriate uricosuria was independently associated with disease severity and with a significant increase in the risk of respiratory failure requiring invasive mechanical ventilation using Cox (adjusted hazard ratio 6.2, 95% CI 1.9-20.1) or competing risks (adjusted sub-distribution hazard ratio 12.1, 95% CI 2.7-55.4) survival models. Thus, our data establish that SARS-CoV-2 causes specific manifestations of proximal tubule dysfunction and provide novel insights into COVID-19 severity and outcome.

Clinical and genetic spectra of autosomal dominant tubulointerstitial kidney disease due to mutations in UMOD and MUC1.

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an increasingly recognized cause of end-stage kidney disease, primarily due to mutations in UMOD and MUC1. The lack of clinical recognition and the small size of cohorts have slowed the understanding of disease ontology and development of diagnostic algorithms. We analyzed two registries from Europe and the United States to define genetic and clinical characteristics of ADTKD-UMOD and ADTKD-MUC1 and develop a practical score to guide genetic testing. Our study encompassed 726 patients from 585 families with a presumptive diagnosis of ADTKD along with clinical, biochemical, genetic and radiologic data. Collectively, 106 different UMOD mutations were detected in 216/562 (38.4%) of families with ADTKD (303 patients), and 4 different MUC1 mutations in 72/205 (35.1%) of the families that are UMOD-negative (83 patients). The median kidney survival was significantly shorter in patients with ADTKD-MUC1 compared to ADTKD-UMOD (46 vs. 54 years, respectively), whereas the median gout-free survival was dramatically reduced in patients with ADTKD-UMOD compared to ADTKD-MUC1 (30 vs. 67 years, respectively). In contrast to patients with ADTKD-UMOD, patients with ADTKD-MUC1 had normal urinary excretion of uromodulin and distribution of uromodulin in tubular cells. A diagnostic algorithm based on a simple score coupled with urinary uromodulin measurements separated patients with ADTKD-UMOD from those with ADTKD-MUC1 with a sensitivity of 94.1%, a specificity of 74.3% and a positive predictive value of 84.2% for a UMOD mutation. Thus, ADTKD-UMOD is more frequently diagnosed than ADTKD-MUC1, ADTKD subtypes present with distinct clinical features, and a simple score coupled with urine uromodulin measurements may help prioritizing genetic testing.

The natural course of pregnancies in women with primary atypical haemolytic uraemic syndrome and asymptomatic relatives.

Pregnancy has been linked to various microangiopathies, including primary atypical haemolytic uraemic syndrome (aHUS). Complement dysregulation, often linked to rare variants in complement genes, is key for primary aHUS to manifest and may play a role in pregnancy complications of the mother and fetus. The burden of such complications is unknown, making counselling of women with primary aHUS and asymptomatic relatives difficult. We analyzed the maternal and fetal outcomes of 39 pregnancies from 17 women with primary aHUS and two asymptomatic relatives. Seven out of 39 pregnancies were complicated by pregnancy-associated aHUS. Five out of 32 pregnancies not linked to pregnancy-associated aHUS were complicated by pre-eclampsia or HELLP. Rare genetic variants were identified in 10 women (asymptomatic relatives, n = 2) who had a total of 14 pregnancies, including 10 uncomplicated pregnancies. Thirty-five out of 39 pregnancies resulted in live birth. Eight out of 19 women had progressed to end-stage kidney disease, with an incidence of 2·95 (95% confidence interval, 1·37-5·61) per 100 person-years after the first pregnancy. Thus, we emphasized the frequency of successful pregnancies in women with primary aHUS and asymptomatic relatives. Pregnancies should be monitored closely. Rare genetic variants cannot predict the risk of a given pregnancy.

mTORC Pathway Activation and Effect of Sirolimus on Native Kidney Antiphospholipid Syndrome Nephropathy: A Case Report.

Despite optimal anticoagulation and blood pressure control, patients with antiphospholipid syndrome (APS) nephropathy frequently progress to kidney failure, and recurrence after transplantation is common. The mTORC (mechanistic target of rapamycin complex) pathway was recently identified as a potential intermediate and a therapeutic target in vascular lesions associated with APS nephropathy. However, these results were derived from the retrospective analysis of a small cohort of patients receiving sirolimus after kidney transplantation. Therefore, they warranted external validation and the demonstration of the potential benefit of sirolimus in native kidney APS nephropathy. We report a patient with active APS nephropathy lesions occurring on native kidneys, in which endothelial mTORC activation was substantiated at the molecular level. Treatment with sirolimus was shown on a repeat kidney biopsy to successfully inhibit the AKT/mTORC pathway and was associated with significant improvement in kidney function and lesions of vasculopathy. Drug tolerance was excellent during the entire follow-up. This case validates and extends previous observations in kidney transplant recipients and demonstrates that endothelial activation of the AKT/mTORC pathway occurs in the damaged renal vasculature of native kidneys in APS nephropathy. These findings further support the potential of precision medicine and the use of mTORC activation as a biomarker of disease activity and as therapeutic target in patients with APS nephropathy.

Podocyte Antigen Staining to Identify Distinct Phenotypes and Outcomes in Membranous Nephropathy: A Retrospective Multicenter Cohort Study.

RATIONALE & OBJECTIVE: Membranous nephropathy (MN) is characterized by the deposition of immune complexes along glomerular basement membranes. M-Type phospholipase A2 receptor (PLA2R), thrombospondin type 1 domain-containing 7A (THSD7A), exostosin 1 and 2 (EXT1/2), and neural epidermal growth factor-like 1 protein (NELL-1) have been identified as established or potential podocyte antigens in MN. We investigated the association of podocyte antigen staining with MN clinical phenotype and outcomes. STUDY DESIGN: Multicenter retrospective cohort study. SETTING & PARTICIPANTS: 177 consecutive patients with MN unrelated to lupus erythematosus, identified after screening of 3,875 native kidney biopsies performed in the Belgian UCLouvain Kidney Disease Network from 2000 through 2018. PREDICTOR: Positive immunostaining for podocyte antigens on archived kidney biopsy samples. OUTCOMES: Association with different phenotypes (baseline characteristics of patients and pathologic findings on kidney biopsy), time to cancer and to kidney failure. ANALYTICAL APPROACH: Kaplan-Meier estimates and Cox regression analyses to assess time to cancer and kidney failure. RESULTS: 177 patients were followed up for a median of 4.0 (IQR, 1.3-8.0) years. Diagnosis of PLA2R-positive (PLA2R+), THSD7A+, and double-negative (PLA2R-/THSD7A-) MN was made in 117 (66.1%), 6 (3.4%), and 54 (30.5%) patients, respectively. Progression to kidney failure was similar in all groups. Although the number of patients with THSD7A+MN was small, they showed a higher incidence (50%) and increased risk for developing cancer during follow-up (adjusted HR, 5.0 [95% CI, 1.4-17.9]; P=0.01). 8% and 5% of patients with double-negative MN stained positively for EXT1/2 and NELL-1, respectively. Most patients with EXT1/2+MN were women, had features of systemic autoimmunity, and showed glomerular C1q deposits. LIMITATIONS: Retrospective design; small number of patients in the THSD7A group; lack of evaluation of immunoglobulin G subclasses deposition. CONCLUSIONS: Our real-world data describe the relative prevalence of subgroups of MN and support the hypothesis that a novel classification of MN based on podocyte antigen staining may be clinically relevant.

Mechanisms of kidney disease in Sneddon's syndrome: Case report and literature review
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Sneddon's syndrome is a rare, noninflammatory thrombotic vasculopathy characterized by the combination of livedo racemosa, recurrent stroke, and histopathological skin lesions of endarteritis obliterans. Although multiorgan involvement suggests its systemic nature, detailed pathological description of affected organs - including the kidney - is exceptional. We report a case of Sneddon's syndrome with chronic kidney disease, associated with features of endarteritis obliterans in the skin and the kidney. The clinical presentation of our patient is compared to previously reported cases of Sneddon's syndrome with biopsy-proven kidney disease. We also discuss the differential diagnosis, pathophysiological mechanisms, relationship with antiphospholipid syndrome, and management of patients with Sneddon's syndrome and kidney disease. This clinical observation supports the systemic nature of Sneddon's syndrome and provides insights into the mechanisms by which this rare but probably underdiagnosed disease alters kidney function.
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Mechanisms of Crystalloid versus Colloid Osmosis across the Peritoneal Membrane.

Background Osmosis drives transcapillary ultrafiltration and water removal in patients treated with peritoneal dialysis. Crystalloid osmosis, typically induced by glucose, relies on dialysate tonicity and occurs through endothelial aquaporin-1 water channels and interendothelial clefts. In contrast, the mechanisms mediating water flow driven by colloidal agents, such as icodextrin, and combinations of osmotic agents have not been evaluated.Methods We used experimental models of peritoneal dialysis in mouse and biophysical studies combined with mathematical modeling to evaluate the mechanisms of colloid versus crystalloid osmosis across the peritoneal membrane and to investigate the pathways mediating water flow generated by the glucose polymer icodextrin.ResultsIn silico modeling and in vivo studies showed that deletion of aquaporin-1 did not influence osmotic water transport induced by icodextrin but did affect that induced by crystalloid agents. Water flow induced by icodextrin was dependent upon the presence of large, colloidal fractions, with a reflection coefficient close to unity, a low diffusion capacity, and a minimal effect on dialysate osmolality. Combining crystalloid and colloid osmotic agents in the same dialysis solution strikingly enhanced water and sodium transport across the peritoneal membrane, improving ultrafiltration efficiency over that obtained with either type of agent alone.Conclusions These data cast light on the molecular mechanisms involved in colloid versus crystalloid osmosis and characterize novel osmotic agents. Dialysis solutions combining crystalloid and colloid particles may help restore fluid balance in patients treated with peritoneal dialysis.

Mechanisms of acid-base regulation in peritoneal dialysis.

Background: Peritoneal dialysis (PD) contributes to restore acid-base homeostasis in patients with end-stage renal disease. The transport pathways for buffers and carbon dioxide (CO2) across the peritoneal membrane remain poorly understood. Methods: Combining well-established PD protocols, whole-body plethysmography and renal function studies in mice, we investigated molecular mechanisms of acid-base regulation in PD, including the potential role of the water channel aquaporin-1 (AQP1). Results: After instillation in peritoneal cavity, the pH of acidic dialysis solutions increased within minutes to rapidly equilibrate with blood pH, whereas the neutral pH of biocompatible solutions remained constant. Predictions from the three-pore model of peritoneal transport suggested that local production of HCO3- accounts at least in part for the changes in intraperitoneal pH observed with acidic solutions. Carbonic anhydrase (CA) isoforms were evidenced in the peritoneal membrane and their inhibition with acetazolamide significantly decreased local production of HCO3- and delayed changes in intraperitoneal pH. On the contrary, genetic deletion of AQP1 had no effect on peritoneal transport of buffers and diffusion of CO2. Besides intraperitoneal modifications, the use of acidic dialysis solutions enhanced acid excretion both at pulmonary and renal levels. Conclusions: These findings suggest that changes in intraperitoneal pH during PD are mediated by bidirectional buffer transport and by CA-mediated production of HCO3- in the membrane. The use of acidic solutions enhances acid excretion through respiratory and renal responses, which should be considered in patients with renal failure.

The NLRP3 Inflammasome Has a Critical Role in Peritoneal Dialysis-Related Peritonitis.

Bacterial peritonitis remains the main cause of technique failure in peritoneal dialysis (PD). During peritonitis, the peritoneal membrane undergoes structural and functional alterations that are mediated by IL-1ß The NLRP3 inflammasome is a caspase-1-activating multiprotein complex that links sensing of microbial and stress products to activation of proinflammatory cytokines, including IL-1ß The potential roles of the NLRP3 inflammasome and IL-1ß in the peritoneal membrane during acute peritonitis have not been investigated. Here, we show that the NLRP3 inflammasome is activated during acute bacterial peritonitis in patients on PD, and this activation associates with the release of IL-1ß in the dialysate. In mice, lipopolysaccharide- or Escherichia coli-induced peritonitis led to IL-1ß release in the peritoneal membrane. The genetic deletion of Nalp3, which encodes NLRP3, abrogated defects in solute transport during acute peritonitis and restored ultrafiltration. In human umbilical vein endothelial cells, IL-1ß treatment directly enhanced endothelial cell proliferation and increased microvascular permeability. These in vitro effects require endothelial IL-1 receptors, shown by immunofluorescence to be expressed in peritoneal capillaries in mice. Furthermore, administration of the IL-1ß receptor antagonist, anakinra, efficiently decreased nitric oxide production and vascular proliferation and restored peritoneal function in mouse models of peritonitis, even in mice treated with standard-of-care antibiotherapy. These data demonstrate that NLRP3 activation and IL-1ß release have a critical role in solute transport defects and tissue remodeling during PD-related peritonitis. Blockade of the NLRP3/IL-1ß axis offers a novel method for rescuing morphologic alterations and transport defects during acute peritonitis.

Clinical and mutational spectrum of hypoparathyroidism, deafness and renal dysplasia syndrome.

BACKGROUND: Hypoparathyroidism, deafness and renal dysplasia (HDR) syndrome is a rare autosomal dominant disorder, secondary to mutations in the GATA-3 gene. Due to its wide range of penetrance and expressivity, the disease may not always be recognized. We herein describe clinical and genetic features of patients with HDR syndrome, highlighting diagnostic clues. METHODS: Medical records of eight patients from five unrelated families exhibiting GATA-3 mutations were reviewed retrospectively, in conjunction with all previously reported cases. RESULTS: HDR syndrome was diagnosed in eight patients between the ages of 18 and 60 years. Sensorineural deafness was consistently diagnosed, ranging from clinical hearing loss since infancy in seven patients to deafness detected only by audiometry in adulthood in one single patient. Hypoparathyroidism was present in six patients (with hypocalcaemia and inaugural seizures in two out of six). Renal abnormalities observed in six patients were diverse and of dysplastic nature. Three patients displayed nephrotic-range proteinuria and reached end-stage renal disease (ESRD) between the ages of 19 and 61 years, whilst lesions of focal and segmental glomerulosclerosis were histologically demonstrated in one of them. Interestingly, phenotype severity differed significantly between a mother and son within one family. Five new mutations of GATA-3 were identified, including three missense mutations affecting zinc finger motifs [NM_001002295.1: c.856A>G (p.N286D) and c.1017C>G (p.C339W)] or the conserved linker region [c.896G>A (p.R299G)], and two splicing mutations (c.924+4_924+19del and c.1051-2A>G). Review of 115 previously reported cases of GATA-3 mutations showed hypoparathyroidism and deafness in 95% of patients, and renal abnormalities in only 60%. Overall, 10% of patients had reached ESRD. CONCLUSIONS: We herein expand the clinical and mutational spectrum of HDR syndrome, illustrating considerable inter- and intrafamilial phenotypic variability. Diagnosis of HDR should be considered in any patient with hypoparathyroidism and deafness, whether associated with renal abnormalities or not. HDR diagnosis is established through identification of a mutation in the GATA-3 gene.