Cryopreservation of human kidney organoids.

Recent advances in stem cell research have led to the creation of organoids, miniature replicas of human organs, offering innovative avenues for studying diseases. Kidney organoids, with their ability to replicate complex renal structures, provide a novel platform for investigating kidney diseases and assessing drug efficacy, albeit hindered by labor-intensive generation and batch variations, highlighting the need for tailored cryopreservation methods to enable widespread utilization. Here, we evaluated cryopreservation strategies for kidney organoids by contrasting slow-freezing and vitrification methods. 118 kidney organoids were categorized into five conditions. Control organoids followed standard culture, while two slow-freezing groups used 10% DMSO (SF1) or commercial freezing media (SF2). Vitrification involved V1 (20% DMSO, 20% Ethylene Glycol with sucrose) and V2 (15% DMSO, 15% Ethylene Glycol). Assessment of viability, functionality, and structural integrity post-thawing revealed notable differences. Vitrification, particularly V1, exhibited superior viability (91% for V1, 26% for V2, 79% for SF1, and 83% for SF2 compared to 99.4% in controls). 3D imaging highlighted distinct nephron segments among groups, emphasizing V1's efficacy in preserving both podocytes and tubules in kidney organoids. Cisplatin-induced injury revealed a significant reduction in regenerative capacities in organoids cryopreserved by flow-freezing methods, while the V1 method did not show statistical significance compared to the unfrozen controls. This study underscores vitrification, especially with high concentrations of cryoprotectants, as an effective approach for maintaining kidney organoid viability and structure during cryopreservation, offering practical approaches for kidney organoid research.

Advancements in therapeutic development: kidney organoids and organs on a chip.

The use of animal models in therapeutic development has long been the standard practice. However, ethical concerns and the inherent species differences have prompted a reevaluation of the experimental approach in human disease studies. The urgent need for alternative model systems that better mimic human pathophysiology has led to the emergence of organoids, innovative in vitro models, to simulate human organs in vitro. These organoids have gained widespread acceptance in disease models and drug development research. In this mini review, we explore the recent strides made in kidney organoid differentiation and highlight the synergistic potential of incorporating organ-on-chip systems. The emergent use of microfluidic devices reveals the importance of fluid flow in the maturation of kidney organoids and helps decipher pathomechanisms in kidney diseases. Recent research has uncovered their potential applications across a wide spectrum of kidney research areas, including hemodynamic forces at stake in kidney health and disease, immune cell infiltration, or drug delivery and toxicity. This convergence of cutting-edge technologies not only holds promise for expediting therapeutic development but also reflects an acknowledgment of the need to embrace innovative and more human-centric research models.

Low exposition to lithium prevents nephrogenic diabetes insipidus but not microcystic dilations of the collecting ducts in long-term rat model.

Lithium induces nephrogenic diabetes insipidus (NDI) and microcystic chronic kidney disease (CKD). As previous clinical studies suggest that NDI is dose-dependent and CKD is time-dependent, we investigated the effect of low exposition to lithium in a long-term experimental rat model. Rats were fed with a normal diet (control group), with the addition of lithium (Li+ group), or with lithium and amiloride (Li+/Ami group) for 6 months, allowing obtaining low plasma lithium concentrations (0.25 ± 0.06 and 0.43 ± 0.16 mmol/L, respectively). Exposition to low concentrations of plasma lithium levels prevented NDI but not microcystic dilations of kidney tubules, which were identified as collecting ducts (CDs) on immunofluorescent staining. Both hypertrophy, characterized by an increase in the ratio of nuclei per tubular area, and microcystic dilations were observed. The ratio between principal cells and intercalated cells was higher in microcystic than in hypertrophied tubules. There was no correlation between AQP2 messenger RNA levels and cellular remodeling of the CD. Additional amiloride treatment in the Li+/Ami group did not allow consistent morphometric and cellular composition changes compared to the Li+ group. Low exposition to lithium prevented overt NDI but not microcystic dilations of the CD, with differential cellular composition in hypertrophied and microcystic CDs, suggesting different underlying cellular mechanisms.

Navigating the kidney organoid: insights into assessment and enhancement of nephron function.

Kidney organoids are three-dimensional structures generated from pluripotent stem cells (PSCs) that are capable of recapitulating the major structures of mammalian kidneys. As this technology is expected to be a promising tool for studying renal biology, drug discovery, and regenerative medicine, the functional capacity of kidney organoids has emerged as a critical question in the field. Kidney organoids produced using several protocols harbor key structures of native kidneys. Here, we review the current state, recent advances, and future challenges in the functional characterization of kidney organoids, strategies to accelerate and enhance kidney organoid functions, and access to PSC resources to advance organoid research. The strategies to construct physiologically relevant kidney organoids include the use of organ-on-a-chip technologies that integrate fluid circulation and improve organoid maturation. These approaches result in increased expression of the major tubular transporters and elements of mechanosensory signaling pathways suggestive of improved functionality. Nevertheless, continuous efforts remain crucial to create kidney tissue that more faithfully replicates physiological conditions for future applications in kidney regeneration medicine and their ethical use in patient care.NEW & NOTEWORTHY Kidney organoids are three-dimensional structures derived from stem cells, mimicking the major components of mammalian kidneys. Although they show great promise, their functional capacity has become a critical question. This review explores the advancements and challenges in evaluating and enhancing kidney organoid function, including the use of organ-on-chip technologies, multiomics data, and in vivo transplantation. Integrating these approaches to further enhance their physiological relevance will continue to advance disease modeling and regenerative medicine applications.

Mechanistic insights into the primary and secondary alterations of renal ion and water transport in the distal nephron.

The kidneys, by equilibrating the outputs to the inputs, are essential for maintaining the constant volume, pH, and electrolyte composition of the internal milieu. Inability to do so, either because of internal kidney dysfunction (primary alteration) or because of some external factors (secondary alteration), leads to pathologies of varying severity, leading to modification of these parameters and affecting the functions of other organs. Alterations of the functions of the collecting duct (CD), the most distal part of the nephron, have been extensively studied and have led to a better diagnosis, better management of the related diseases, and the development of therapeutic tools. Thus, dysfunctions of principal cell-specific transporters such as ENaC or AQP2 or its receptors (mineralocorticoid or vasopressin receptors) caused by mutations or by compounds present in the environment (lithium, antibiotics, etc.) have been demonstrated in a variety of syndromes (Liddle, pseudohypoaldosteronism type-1, diabetes insipidus, etc.) affecting salt, potassium, and water balance. In parallel, studies on specific transporters (H+ -ATPase, anion exchanger 1) in intercalated cells have revealed the mechanisms of related tubulopathies like distal renal distal tubular acidosis or Sjögren syndrome. In this review, we will recapitulate the mechanisms of most of the primary and secondary alteration of the ion transport system of the CD to provide a better understanding of these diseases and highlight how a targeted perturbation may affect many different pathways due to the strong crosstalk and entanglements between the different actors (transporters, cell types).

MRI-based kidney radiomic analysis during chronic lithium treatment.

BACKGROUND: Lithium therapy during bipolar disorder is associated with an increased risk of chronic kidney disease (CKD) that is slowly progressive and undetectable at early stages. We aimed at identifying kidney image texture features as possible imaging biomarkers of decreased measured glomerular filtration rate (mGFR) using radiomics of T2-weighted magnetic resonance imaging (MRI). METHODS: One hundred and eight patients treated with lithium were evaluated including mGFR and kidney MRI, with T2-weighted sequence single-shot fast spin-echo. Computed radiomic analysis was performed after kidney segmentation. Significant features were selected to build a radiomic signature using multivariable Cox analysis to detect an mGFR <60 ml/min/1.73 m². The texture index was validated using a training and a validation cohort. RESULTS: Texture analysis index was able to detect an mGFR decrease, with an AUC of 0.85 in the training cohort and 0.71 in the validation cohort. Patients with a texture index below the median were older (59 [42-66] vs. 46 [34-54] years, p = .001), with longer treatment duration (10 [3-22] vs. 6 [2-10] years, p = .02) and a lower mGFR (66 [46-84] vs. 83 [71-94] ml/min/1.73m², p < .001). Texture analysis index was independently and negatively associated with age (ß = -.004 ± 0.001, p < .001), serum vasopressin (-0.005 ± 0.002, p = .02) and lithium treatment duration (-0.01 ± 0.003, p = .001), with a significant interaction between lithium treatment duration and mGFR (p = .02). CONCLUSIONS: A renal texture index was developed among patients treated with lithium associated with a decreased mGFR. This index might be relevant in the diagnosis of lithium-induced renal toxicity.

The risk of medically uncontrolled secondary hyperparathyroidism depends on parathyroid hormone levels at haemodialysis initiation.

BACKGROUND: Optimal parathyroid hormone (PTH) control during non-dialysis chronic kidney disease (ND-CKD) might decrease the subsequent risk of parathyroid hyperplasia and uncontrolled secondary hyperparathyroidism (SHPT) on dialysis. However, the evidence for recommending PTH targets and therapeutic strategies is weak for ND-CKD. We evaluated the patient characteristics, treatment patterns and PTH control over the first year of haemodialysis (HD) by PTH prior to HD initiation. METHODS: We studied 5683 incident HD patients from 21 countries in Dialysis Outcomes and Practice Patterns Study Phases 4-6 (2009-18). We stratified by PTH measured immediately prior to HD initiation and reported the monthly prescription prevalence of active vitamin D and calcimimetics over the first year of HD and risk of PTH >600 pg/mL after 9-12 months on HD. RESULTS: The 16% of patients with PTH >600 pg/mL prior to HD initiation were more likely to be prescribed active vitamin D and calcimimetics during the first year of HD. The prevalence of PTH >600 pg/mL 9-12 months after start of HD was greater for patients who initiated HD with PTH >600 (29%) versus 150-300 (7%) pg/mL (adjusted risk difference: 19%; 95% confidence interval : 15%, 23%). The patients with sustained PTH >600 pg/mL after 9-12 months on HD were younger, more likely to be black, and had higher serum phosphorus and estimated glomerular filtration rates at HD initiation. CONCLUSIONS: Increased PTH before HD start predicted a higher PTH level 9-12 months later, despite greater use of active vitamin D and calcimimetics. More targeted PTH control during ND-CKD may influence outcomes during HD, raising the need for PTH target guidelines in these patients.

Evaluation of glomerular filtration rate using iohexol plasma clearance in critically ill patients with augmented renal creatinine clearance: A single-centre retrospective study.

BACKGROUND: Augmented renal creatinine clearance (ARC) (≥130 ml min-1 1.73 m-2) is frequent in intensive care unit (ICU) patients and may impact patient outcome. OBJECTIVES: To compare glomerular filtration rate (GFR) measured with iohexol plasma clearance and creatinine clearance in critically ill patients with augmented renal clearance. DESIGN: Single-centre, retrospective study. SETTING: French University Hospital ICU from November 2016 to May 2019. PATIENTS: Adult patients with augmented renal clearance who had a measurement of iohexol plasma clearance. MAIN OUTCOME MEASURE: Agreement between 6 h creatinine clearance (6 h CrCl) and iohexol plasma clearance (GFRio). RESULTS: Twenty-nine patients were included. The median 6 h creatinine clearance was 195 [interquartile range (IQR) 162 to 251] ml min-1 1.73 m-2 and iohexol clearance was 133 [117 to 153] ml min-1 1.73 m-2. Sixteen patients (55%) had hyperfiltration (clearance >130 ml min-1 1.73 m-2) measured with iohexol clearance. Mean bias between iohexol and creatinine clearance was -80 [limits of agreement (LoA) -216 to 56 ml min-1 1.73 m-2]. For Cockcroft and Gault Modification of Diet in Renal Disease equation (MDRD), Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) formulae, mean biases were, respectively -27 (LoA -99 to 45), -14 (LoA -86 to 59) and 15 (LoA -33 to 64) ml min-1 1.73 m-2. CONCLUSION: In the present study, we found that in patients with augmented renal creatinine clearance, half of the patients do not have hyperfiltration using iohexol clearance measurements. We observed an important bias between 6 h CrCl and GFRio with large LoA. In critically patients with ARC, 6 h CrCl does not reliably estimate GFR and 6 h CrCl nearly systematically overestimates renal function. Comparison of creatinine-based GFR estimations and GFRio show acceptable bias but wide LoA.

Knowledge self-monitoring, efficiency, and determinants of self-confidence statement in multiple choice questions in medical students.

BACKGROUND: Multiple-choice question (MCQ) tests are commonly used to evaluate medical students, but they do not assess self-confidence nor penalize lucky guess or harmful behaviors. Based on a scoring method according to the appropriateness of confidence in answers, the study aimed at assessing knowledge self-monitoring and efficiency, and the determinants of self-confidence. METHODS: A cross-sectional study of 842 s- and third-year medical students who were asked to state their level of confidence (A: very confident, B: moderately confident and C: not confident) during 12 tests (106,806 events). A bonus was applied if the level of confidence matched with the correctness of the answer, and a penalty was applied in the case of inappropriate confidence. RESULTS: Level A was selected more appropriately by the top 20% students whereas level C was selected more appropriately by the lower 20% students. Efficiency of higher-performing students was higher when correct (among correct answers, rate of A statement), but worse when incorrect compared to the bottom 20% students (among incorrect answers, rate of C statement). B and C statements were independently associated with female and male gender, respectively (OR for male vs female = 0.89 [0.82-0.96], p = 0.004, for level B and 1.15 [1.01-1.32], p = 0.047, for level C). CONCLUSION: While both addressing the gender confidence gap, knowledge self-monitoring might improve awareness of students' knowledge whereas efficiency might evaluate appropriate behavior in clinical practice. These results suggest differential feedback during training in higher versus lower-performing students, and potentially harmful behavior in decision-making during clinical practice in higher-performing students.

Fasting Urinary Osmolality, CKD Progression, and Mortality: A Prospective Observational Study.

RATIONALE & OBJECTIVE: Chronic kidney disease (CKD) characterized by decreased glomerular filtration rate (GFR) is often accompanied by various degrees of impaired tubular function in the cortex and medulla. Assessment of tubular function may therefore be useful in establishing the severity of kidney disease and identifying those at greater risk for CKD progression. We explored reductions in urinary concentrating ability, a well-known feature of CKD, as a risk factor for GFR decline and end-stage renal disease (ESRD). STUDY DESIGN: Prospective longitudinal cohort study. SETTING & PARTICIPANTS: 2,084 adult patients with CKD stages 1 to 4 from the French NephroTest Cohort Study. PREDICTOR: Fasting urinary osmolality measured using delta cryoscopy. OUTCOMES: ESRD, mortality before ESRD, and measured GFR (mGFR) assessed using 51Cr-EDTA renal clearance. ANALYTICAL APPROACH: Cause-specific hazards models were fit to estimate crude and adjusted associations of urinary osmolality with ESRD and death before ESRD. Linear mixed models with random intercepts were fit to evaluate the association of urinary osmolality with slope of decline in mGFR. RESULTS: At baseline, mean age was 58.7±15.2 (SD) years with a median mGFR of 40.2 (IQR, 29.1-54.5) mL/min/1.73m2 and a median fasting urinary osmolality of 502.7±151.7mOsm/kg H2O. Baseline fasting urinary osmolality was strongly associated with mGFR (R=0.54; P < 0.001). 380 ESRD events and 225 deaths before ESRD occurred during a median follow-up of 5.9 (IQR, 3.8-8.2) years. Patients with lower baseline fasting urinary osmolality had higher adjusted risk for ESRD but not for mortality (HRs of 1.97 [95% CI, 1.26-3.08] and 0.99 [95% CI, 0.68-1.44], respectively, for the lowest vs highest tertile). Based on a mixed linear model adjusted for baseline mGFR and clinical characteristics, patients in the lowest tertile of baseline urinary osmolality had a steeper decline in kidney function (-4.9% ± 0.9% per year; P < 0.001) compared with patients in the highest tertile. LIMITATIONS: Fasting was self-reported. CONCLUSIONS: Fasting urinary osmolality may be a useful tool, in addition to GFR and albuminuria, for assessing nonglomerular damage in patients with CKD who are at higher risk for CKD progression.

Differential Determinants of Tubular Phosphate Reabsorption: Insights on Renal Excretion of Phosphates in Kidney Disease.

We assessed the tubular reabsorption of phosphate (TRP) and maximal renal threshold for phosphate reabsorption to glomerular filtration rate (TmPi/GFR) and their determinants in 64 stages 2-4 chronic kidney disease (CKD) patients in order to define the early changes in phosphate metabolism in CKD. In multivariable analysis, TmPi/GFR correlates were estimated GFR (eGFR), intact parathyroid hormone (iPTH), and hemoglobin (R2 = 0.417), while TRP correlates were eGFR, iPTH, 24-h phosphaturia, and calcitriol (R2 = 0.72). This suggests that TmPi/GFR and TRP, respectively, assess hemoglobin-phosphate and bowel-kidney phosphate regulation axis. Iron supplementation based on TmPi/GFR or earlier phosphate restriction based on TRP should be investigated in view of modifying clinical outcomes in CKD.

Ly6Chigh Monocytes Protect against Kidney Damage during Sepsis via a CX3CR1-Dependent Adhesion Mechanism.

Monocytes have a crucial role in both proinflammatory and anti-inflammatory phenomena occurring during sepsis. Monocyte recruitment and activation are orchestrated by the chemokine receptors CX3CR1 and CCR2 and their cognate ligands. However, little is known about the roles of these cells and chemokines during the acute phase of inflammation in sepsis. Using intravital microscopy in a murine model of polymicrobial sepsis, we showed that inflammatory Ly6C(high) monocytes infiltrated kidneys, exhibited altered motility, and adhered strongly to the renal vascular wall in a chemokine receptor CX3CR1-dependent manner. Adoptive transfer of Cx3cr1-proficient monocyte-enriched bone marrow cells into septic Cx3cr1-depleted mice prevented kidney damage and promoted mouse survival. Modulation of CX3CR1 activation in septic mice controlled monocyte adhesion, regulated proinflammatory and anti-inflammatory cytokine expression, and was associated with the extent of kidney lesions such that the number of lesions decreased when CX3CR1 activity increased. Consistent with these results, the pro-adhesive I249 CX3CR1 allele in humans was associated with a lower incidence of AKI in patients with sepsis. These data show that inflammatory monocytes have a protective effect during sepsis via a CX3CR1-dependent adhesion mechanism. This receptor might be a new therapeutic target for kidney injury during sepsis.

Long-term outcome after early cyclosporine withdrawal in kidney transplantation: ten years after.

BACKGROUND: Despite long-term side effects, calcineurin inhibitors (CNI) remain a cornerstone of immunosuppression in renal transplantation. Few trials assessed the long-term outcome after early CNI withdrawal. METHODS: This intention-to-treat study assessed the 10-year outcome of 108 patients randomly converted from a cyclosporine (CsA)-mycophenolate mofetil (MMF)-prednisone regimen to a dual therapy (CsA-prednisone or MMF-prednisone) at 3 months postgraft. RESULTS: At 10 years, 3.7% in the CsA group and 35.2% in the MMF group remained on the protocol regimen (P<.001). eGFR was higher in the MMF group (64.4±21 vs 49.7±14.7 mL/min/1.73 m², P<.001), although acute rejection (12 vs 4 in the CsA group, P=.03) and Class II DSA incidences were increased. CNI-related toxicity (P=.019) and moderate-to-severe IF/TA (P=.004) were higher in the CsA group. Ten-year graft and patient survivals were not different. In multivariate analysis, acute rejection remained the strongest predictor of graft loss (HR=11.64, 95% CI [5.05-26.79], P<.0001). CONCLUSIONS: MMF withdrawal largely failed due to CNI toxicity, while CsA withdrawal led to increased graft failure due to uncontrolled acute rejection without increasing graft survival. From this study, it remains unclear which patients could benefit from limiting CNI exposure.

Advancing preclinical drug evaluation through automated 3D imaging for high-throughput screening with kidney organoids.

High-throughput drug screening is crucial for advancing healthcare through drug discovery. However, a significant limitation arises from availablein vitromodels using conventional 2D cell culture, which lack the proper phenotypes and architectures observed in three-dimensional (3D) tissues. Recent advancements in stem cell biology have facilitated the generation of organoids-3D tissue constructs that mimic human organsin vitro. Kidney organoids, derived from human pluripotent stem cells, represent a significant breakthrough in disease representation. They encompass major kidney cell types organized within distinct nephron segments, surrounded by stroma and endothelial cells. This tissue allows for the assessment of structural alterations such as nephron loss, a characteristic of chronic kidney disease. Despite these advantages, the complexity of 3D structures has hindered the use of organoids for large-scale drug screening, and the drug screening pipelines utilizing these complexin vitromodels remain to be established for high-throughput screening. In this study, we address the technical limitations of kidney organoids through fully automated 3D imaging, aided by a machine-learning approach for automatic profiling of nephron segment-specific epithelial morphometry. Kidney organoids were exposed to the nephrotoxic agent cisplatin to model severe acute kidney injury. An U.S. Food and Drug Administration (FDA)-approved drug library was tested for therapeutic and nephrotoxicity screening. The fully automated pipeline of 3D image acquisition and analysis identified nephrotoxic or therapeutic drugs during cisplatin chemotherapy. The nephrotoxic potential of these drugs aligned with previousin vivoand human reports. Additionally, Imatinib, a tyrosine kinase inhibitor used in hematological malignancies, was identified as a potential preventive therapy for cisplatin-induced kidney injury. Our proof-of-concept report demonstrates that the automated screening process, using 3D morphometric assays with kidney organoids, enables high-throughput screening for nephrotoxicity and therapeutic assessment in 3D tissue constructs.

Predictors of daytime blood pressure, nighttime blood pressure, and nocturnal dipping in patients with chronic kidney disease.

Increasing attention has recently been paid to discrepancies between office and ambulatory blood pressure (BP) control in patients with chronic kidney disease (CKD), but information on mechanisms underlying circadian BP variations in CKD remains scarce. We described circadian BP patterns and their predictors in patients with CKD stages 1 to 5 referred for kidney function testing in a French tertiary hospital: 1122 ambulatory BP measurements from 635 participants. Factors associated with daytime and nighttime systolic BP (SBP) as well as with nocturnal SBP dipping (ratio of average nighttime to daytime SBP) were analyzed with linear mixed regression models. Participants (mean age 55 ± 16 years; 36% female, mean GFR 51 ± 22 mL/min/1.73m2) had a mean daytime and nighttime SBP of 130 ± 17 and 118 ± 18 mm Hg, respectively. The prevalence of impaired dipping (nighttime over daytime SBP ratio ≥ 0.9) increased from 32% in CKD stage 1 to 68% in CKD stages 4-5. After multivariable adjustment, measured GFR, diabetes, and sub-Saharan African origin were more strongly associated with nighttime than with daytime SBP, which led to significant associations with altered nocturnal BP dipping. For a 1 SD decrease in measured GFR, nighttime BP was 2.87 mmHg (95%CI, 1.44-4.30) higher and nocturnal SBP dipping ratio was 1.55% higher (95%CI, 0.85-2.26%). In conclusion, the prevalence of impaired nocturnal BP dipping increases substantially across the spectrum of CKD. Along with sub-Saharan African origin and diabetes, lower measured GFR was a robust and specific predictor of higher nighttime BP and blunted nocturnal BP decline.

Diuretic prescriptions in the first year of haemodialysis: international practice patterns and associations with outcomes.

Background: The use of diuretics in patients on haemodialysis (HD) is thought to maintain diuresis. However, this assumption and the optimal dose are based on little scientific evidence, and associations with clinical outcomes are unclear. Methods: We reported international variations in diuretic use and loop diuretic dose across 27 759 HD patients with dialysis vintage <1 year in the Dialysis Outcomes and Practice Patterns Study phases 2-5 (2002-2015), a prospective cohort study. Doses of torsemide (4:1) and bumetanide (80:1) were converted to oral furosemide-equivalent doses. Adjusted Cox, logistic and linear regressions were used to investigate the association of diuretic use and dose with outcomes. Results: Diuretic utilization varied widely by country at vintage <3 months, ranging from >80% in Germany and Sweden to <35% in the USA, at a median dose ranging from 400-500 mg/day in Germany and Sweden to <100 mg/day in Japan and the USA. Neither diuretic use nor higher doses were associated with a lower risk of all-cause mortality, a higher risk of hospitalization for fracture or elevated parathyroid hormone levels, but the prescription of higher doses (>200 mg/day) was associated with a higher risk of all-cause hospitalization. Conclusions: Substantial international differences exist in diuretic prescriptions, with use and doses much higher in some European countries than the USA. The prescription and higher doses of loop diuretics was not associated with improved outcomes.