Regulation of solute carriers oct2 and OAT1/3 in the kidney: a phylogenetic, ontogenetic, and cell dynamic perspective.

Over the course of more than 500 million years, the kidneys have undergone a remarkable evolution from primitive nephric tubes to intricate filtration-reabsorption systems that maintain homeostasis and remove metabolic end products from the body. The evolutionarily conserved solute carriers organic cation transporter 2 (OCT2) and organic anion transporters 1 and 3 (OAT1/3) coordinate the active secretion of a broad range of endogenous and exogenous substances, many of which accumulate in the blood of patients with kidney failure despite dialysis. Harnessing OCT2 and OAT1/3 through functional preservation or regeneration could alleviate the progression of kidney disease. Additionally, it would improve current in vitro test models that lose their expression in culture. With this review, we explore OCT2 and OAT1/3 regulation from different perspectives: phylogenetic, ontogenetic, and cell dynamic. Our aim is to identify possible molecular targets both to help prevent or compensate for the loss of transport activity in patients with kidney disease and to enable endogenous OCT2 and OAT1/3 induction in vitro in order to develop better models for drug development.

A comprehensive transcriptome characterization of individual nuclear receptor pathways in the human small intestine.

Nuclear receptors (NRs) are widely expressed transcription factors that bind small, lipophilic compounds and regulate diverse biological processes. In the small intestine, NRs are known to act as sensors that control transcriptional responses to endogenous and exogenous signals, yet their downstream effects have not been characterized extensively. Here, we investigate the activation of six different NRs individually in human intestinal organoids using small molecules agonists. We observe changes in key enterocyte functions such as lipid, glucose, and amino acid absorption, the regulation of electrolyte balance, and drug metabolism. Our findings reinforce PXR, LXR, FXR, and PPARα as regulators of lipid absorption. Furthermore, known hepatic effects of AHR and VDR activation were recapitulated in the human small intestine. Finally, we identify unique target genes for intestinal PXR activation (ERG28, TMEM97, and TM7SF2), LXR activation (RAB6B), and VDR activation (CA12). This study provides an unbiased and comprehensive transcriptomic description of individual NR pathways in the human small intestine. By gaining a deeper understanding of the effects of individual NRs, we might better harness their pharmacological and therapeutic potential.

Tubuloid culture enables long-term expansion of functional human kidney tubule epithelium from iPSC-derived organoids.

Kidney organoids generated from induced pluripotent stem cells (iPSC) have proven valuable for studies of kidney development, disease, and therapeutic screening. However, specific applications have been hampered by limited expansion capacity, immaturity, off-target cells, and inability to access the apical side. Here, we apply recently developed tubuloid protocols to purify and propagate kidney epithelium from d7+18 (post nephrogenesis) iPSC-derived organoids. The resulting 'iPSC organoid-derived (iPSCod)' tubuloids can be exponentially expanded for at least 2.5 mo, while retaining expression of important tubular transporters and segment-specific markers. This approach allows for selective propagation of the mature tubular epithelium, as immature cells, stroma, and undesirable off-target cells rapidly disappeared. iPSCod tubuloids provide easy apical access, which enabled functional evaluation and demonstration of essential secretion and electrolyte reabsorption processes. In conclusion, iPSCod tubuloids provide a different, complementary human kidney model that unlocks opportunities for functional characterization, disease modeling, and regenerative nephrology.

Atherosclerosis on a Chip: A 3-Dimensional Microfluidic Model of Early Arterial Events in Human Plaques.

BACKGROUND: Realistic reconstruction of the in vivo human atherosclerotic environment requires the coculture of different cell types arranged in atherosclerotic vessel-like structures with exposure to flow and circulating cells, presenting challenges for disease modeling. This study aimed to develop a 3-dimensional tubular microfluidic model with quadruple coculture of human aortic smooth muscle cells, human umbilical cord vein endothelial cells, and foam cells to recreate a complex human atherosclerotic vessel in vitro to study the effects of flow and circulating immune cells. METHODS: We developed a coculture protocol utilizing BFP (blue fluorescent protein)-labeled human aortic smooth muscle cells, GFP (green fluorescent protein)-labeled human umbilical cord vein endothelial cells, and THP-1 macrophage-derived, Dil-labeled oxidized LDL (low-density lipoprotein) foam cells within a fibrinogen/collagen I-based 3-dimensional ECM (extracellular matrix). Perfusion experiments were conducted for 24 hours on both atherosclerotic vessels and healthy vessels (BFP-labeled human aortic smooth muscle cells and GFP-labeled human umbilical cord vein endothelial cells without foam cells). Additionally, perfusion with circulating THP-1 monocytes was performed to observe cell extravasation and recruitment. RESULTS: The resulting vessels displayed early lesion morphology, with a layered composition including an endothelium and media, and foam cells accumulating in the subendothelial space. The layered wall composition of both atherosclerotic and healthy vessels remained stable under perfusion. Circulating THP-1 monocytes demonstrated cell extravasation into the atherosclerotic vessel wall and recruitment to the foam cell core. The qPCR analysis indicated increased expression of atherosclerosis markers in the atherosclerotic vessels and adaptation of vascular smooth muscle cell migration in response to flow and the plaque microenvironment, compared with control vessels. CONCLUSIONS: The human 3-dimensional atherosclerosis model demonstrated stability under perfusion and allowed for the observation of immune cell behavior, providing a valuable tool for the atherosclerosis research field.

Discrepancies between transcutaneous and estimated glomerular filtration rates in rats with chronic kidney disease.

Accurate assessment of the glomerular filtration rate (GFR) is crucial for researching kidney disease in rats. Although validation of methods that assess GFR is crucial, large-scale comparisons between different methods are lacking. Both transcutaneous GFR (tGFR) and a newly developed estimated GFR (eGFR) equation by our group provide a low-invasive approach enabling repeated measurements. The tGFR is a single bolus method using FITC-labeled sinistrin to measure GFR based on half-life of the transcutaneous signal, whilst the eGFR is based on urinary sinistrin clearance. Here, we retrospectively compared tGFR, using both 1- and 3- compartment models (tGFR_1c and tGFR_3c, respectively) to the eGFR in a historic cohort of 43 healthy male rats and 84 male rats with various models of chronic kidney disease. The eGFR was on average considerably lower than tGFR-1c and tGFR-3c (mean differences 855 and 216 µL/min, respectively) and only 20 and 47% of measurements were within 30% of each other, respectively. The relative difference between eGFR and tGFR was highest in rats with the lowest GFR. Possible explanations for the divergence are problems inherent to tGFR, such as technical issues with signal measurement, description of the signal kinetics, and translation of half-life to tGFR, which depends on distribution volume. The unknown impact of isoflurane anesthesia used in determining mGFR remains a limiting factor. Thus, our study shows that there is a severe disagreement between GFR measured by tGFR and eGFR, stressing the need for more rigorous validation of the tGFR and possible adjustments to the underlying technique.

Editor's Choice - Prognostic Factors and Models to Predict Mortality Outcomes in Patients with Peripheral Arterial Disease: A Systematic Review.

OBJECTIVE: Predicting adverse outcomes in patients with peripheral arterial disease (PAD) is a complex task owing to the heterogeneity in patient and disease characteristics. This systematic review aimed to identify prognostic factors and prognostic models to predict mortality outcomes in patients with PAD Fontaine stage I - III or Rutherford category 0 - 4. DATA SOURCES: PubMed, Embase, and Cochrane Database of Systematic Reviews were searched to identify studies examining individual prognostic factors or studies aiming to develop or validate a prognostic model for mortality outcomes in patients with PAD. REVIEW METHODS: Information on study design, patient population, prognostic factors, and prognostic model characteristics was extracted, and risk of bias was evaluated. RESULTS: Sixty nine studies investigated prognostic factors for mortality outcomes in PAD. Over 80 single prognostic factors were identified, with age as a predictor of death in most of the studies. Other common factors included sex, diabetes, and smoking status. Six studies had low risk of bias in all domains, and the remainder had an unclear or high risk of bias in at least one domain. Eight studies developed or validated a prognostic model. All models included age in their primary model, but not sex. All studies had similar discrimination levels of > 70%. Five of the studies on prognostic models had an overall high risk of bias, whereas two studies had an overall unclear risk of bias. CONCLUSION: This systematic review shows that a large number of prognostic studies have been published, with heterogeneity in patient populations, outcomes, and risk of bias. Factors such as sex, age, diabetes, hypertension, and smoking are significant in predicting mortality risk among patients with PAD Fontaine stage I - III or Rutherford category 0 - 4.

Sex Differences in Mortality Risk after the First Hospitalisation with Lower Extremity Peripheral Arterial Disease.

OBJECTIVE: Lower extremity peripheral arterial disease (PAD) is a severe condition that increases the risk of major adverse cardiovascular events, major adverse limb events, and all cause mortality. This study aimed to investigate the mortality risk among females and males hospitalised for the first time with lower extremity PAD. METHODS: Three cohorts of patients who were admitted for the first time with lower extremity PAD in 2007 - 2010, 2011 - 2014, and 2015 - 2018 were constructed. For the 2007 - 2010 and 2011 - 2014 cohorts, the 28 day, one year, and five year mortality rates were calculated, assessing survival time from date of hospital admission until date of death, end of study period, or censoring. For the 2015 - 2018 cohort, only 28 day and one year mortality were investigated due to lack of follow up data. Mortality rates of these cohorts were compared with the general population using standardised mortality rates (SMRs), and the risk of death between sexes was evaluated using Cox proportional hazards models. Cox models were adjusted for age, cardiovascular disease, and diabetes mellitus to account for potential confounding factors. RESULTS: In total, 7 950, 9 670, and 13 522 patients were included in the 2007 - 2010, 2011 - 2014, and 2015 - 2018 cohorts, respectively. Over 60% of individuals in each cohort were males. Mortality rates at 28 day and one year remained stable across all cohorts, while the five year mortality rate increased for both males and females in the 2011 - 2014 cohort. The SMRs both of females and males with PAD were significantly higher than in the general population. Multivariable regression analyses found no significant differences in mortality risk between sexes at 28 day and one year. However, the five year mortality risk was lower in females, with a hazard ratio of 0.89 (95% confidence interval [CI] 0.83 - 0.97) in the 2007 - 2010 cohort and 0.88 (95% CI 0.82 - 0.94) in the 2011 - 2014 cohort. CONCLUSION: The five year mortality risk has increased, and females face a lower mortality risk than males. Lower extremity PAD still carries unfavourable long term consequences compared with the general population.

Advances and potential of regenerative medicine in pediatric nephrology.

The endogenous capacity of the kidney to repair is limited, and generation of new nephrons after injury for adequate function recovery remains a need. Discovery of factors that promote the endogenous regenerative capacity of the injured kidney or generation of transplantable kidney tissue represent promising therapeutic strategies. While several encouraging results are obtained after administration of stem or progenitor cells, stem cell secretome, or extracellular vesicles in experimental kidney injury models, very little data exist in the clinical setting to make conclusions about their efficacy. In this review, we provide an overview of the cutting-edge knowledge on kidney regeneration, including pre-clinical methodologies used to elucidate regenerative pathways and describe the perspectives of regenerative medicine for kidney patients.

Renal injury in relation to obesity and the additive effect of hypertension in female and male obese and lean ZSF1 rats.

Heart failure with preserved ejection fraction (HFpEF) is characterized by obesity, hypertension, diabetes mellitus, and chronic kidney disease. Obese ZSF1 rats, a model of HFpEF, exhibit multiple such comorbidities that can disturb cardiac function. Little attention has been paid to how these comorbidities affect renal disease in ZSF1 rats. HFpEF is found predominantly in women in whom obesity and hypertension are particularly prevalent. Therefore, we characterized the renal phenotype in female and male lean and obese ZSF1 rats and investigated additional effects of worsened hypertension on disease severity. Systolic blood pressure and renal function were assessed biweekly from 12 to 26 wk. From 19 wk, rats were implanted with either a deoxycorticosterone acetate pellet and fed a high-salt diet (DS) or a placebo pellet and fed a normal-salt diet. At 26 wk of age, terminal glomerular filtration rate was assessed via inulin clearance under isoflurane. Renal sections were processed for histological analysis. Lean and obese ZSF1 rats, both female and male, were mildly hypertensive (systolic blood pressure: 140-150 mmHg). All obese ZSF1 rats showed HFpEF. In female normoglycemic ZSF1 rats, obesity associated with mild proteinuria, decreased glomerular filtration rate, and glomerular hypertrophy. DS-worsened hypertension enhanced proteinuria and triggered glomerulosclerosis. Male obese ZSF1 rats were hyperglycemic and showed proteinuria, glomerular hypertrophy and sclerosis, and tubulointerstitial damage. DS-worsened hypertension aggravated this phenotype in male ZSF1 rats. In conclusion, female obese ZSF1 rats develop mild renal dysfunction and DS-worsened hypertension compromises renal function and structure in normoglycemic female obese ZSF1 rats as in hyperglycemic male obese ZSF1 rats.NEW & NOTEWORTHY Chronic kidney disease coexists with heart failure with a preserved ejection fraction (HFpEF), which is associated with multiple comorbidities and the female sex. We showed that obese, mildly hypertensive female ZSF1 rats, an animal model for HFpEF, simultaneously develop renal disease with diastolic dysfunction. Exacerbation of their hypertension, a comorbidity highly prevalent in HFpEF, compromised renal function and structure similarly in normoglycemic obese female ZSF1 rats and hyperglycemic obese male ZSF1 rats.

Antioxidants for adults with chronic kidney disease.

BACKGROUND: Chronic kidney disease (CKD) is a significant risk factor for cardiovascular disease (CVD) and death. Increased oxidative stress in people with CKD has been implicated as a potential causative factor. Antioxidant therapy decreases oxidative stress and may consequently reduce cardiovascular morbidity and death in people with CKD. This is an update of a Cochrane review first published in 2012. OBJECTIVES: To examine the benefits and harms of antioxidant therapy on death and cardiovascular and kidney endpoints in adults with CKD stages 3 to 5, patients undergoing dialysis, and kidney transplant recipients. SEARCH METHODS: We searched the Cochrane Kidney and Transplant Register of Studies until 15 November 2022 using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal, and ClinicalTrials.gov. SELECTION CRITERIA: We included all randomised controlled trials investigating the use of antioxidants, compared with placebo, usual or standard care, no treatment, or other antioxidants, for adults with CKD on cardiovascular and kidney endpoints. DATA COLLECTION AND ANALYSIS: Titles and abstracts were screened independently by two authors who also performed data extraction using standardised forms. Results were pooled using random effects models and expressed as risk ratios (RR) or mean difference (MD) with 95% confidence intervals (CI). Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. MAIN RESULTS: We included 95 studies (10,468 randomised patients) that evaluated antioxidant therapy in adults with non-dialysis-dependent CKD (31 studies, 5342 patients), dialysis-dependent CKD (41 studies, 3444 patients) and kidney transplant recipients (21 studies, 1529 patients). Two studies enrolled dialysis and non-dialysis patients (153 patients). Twenty-one studies assessed the effects of vitamin antioxidants, and 74 assessed the effects of non-vitamin antioxidants. Overall, the quality of included studies was moderate to low or very low due to unclear or high risk of bias for randomisation, allocation concealment, blinding, and loss to follow-up. Compared with placebo, usual care, or no treatment, antioxidant therapy may have little or no effect on cardiovascular death (8 studies, 3813 patients: RR 0.94, 95% CI 0.64 to 1.40; I² = 33%; low certainty of evidence) and probably has little to no effect on death (any cause) (45 studies, 7530 patients: RR 0.95, 95% CI 0.82 to 1.11; I² = 0%; moderate certainty of evidence), CVD (16 studies, 4768 patients: RR 0.79, 95% CI 0.63 to 0.99; I² = 23%; moderate certainty of evidence), or loss of kidney transplant (graft loss) (11 studies, 1053 patients: RR 0.88, 95% CI 0.67 to 1.17; I² = 0%; moderate certainty of evidence). Compared with placebo, usual care, or no treatment, antioxidants had little to no effect on the slope of urinary albumin/creatinine ratio (change in UACR) (7 studies, 1286 patients: MD -0.04 mg/mmol, 95% CI -0.55 to 0.47; I² = 37%; very low certainty of evidence) but the evidence is very uncertain. Antioxidants probably reduced the progression to kidney failure (10 studies, 3201 patients: RR 0.65, 95% CI 0.41 to 1.02; I² = 41%; moderate certainty of evidence), may improve the slope of estimated glomerular filtration rate (change in eGFR) (28 studies, 4128 patients: MD 3.65 mL/min/1.73 m², 95% CI 2.81 to 4.50; I² = 99%; low certainty of evidence), but had uncertain effects on the slope of serum creatinine (change in SCr) (16 studies, 3180 patients: MD -13.35 µmol/L, 95% CI -23.49 to -3.23; I² = 98%; very low certainty of evidence). Possible safety concerns are an observed increase in the risk of infection (14 studies, 3697 patients: RR 1.30, 95% CI 1.14 to 1.50; I² = 3%; moderate certainty of evidence) and heart failure (6 studies, 3733 patients: RR 1.40, 95% CI 1.11 to 1.75; I² = 0; moderate certainty of evidence) among antioxidant users. Results of studies with a low risk of bias or longer follow-ups generally were comparable to the main analyses. AUTHORS' CONCLUSIONS: We found no evidence that antioxidants reduced death or improved kidney transplant outcomes or proteinuria in patients with CKD. Antioxidants likely reduce cardiovascular events and progression to kidney failure and may improve kidney function. Possible concerns are an increased risk of infections and heart failure among antioxidant users. However, most studies were of suboptimal quality and had limited follow-up, and few included people undergoing dialysis or kidney transplant recipients. Furthermore, the large heterogeneity in interventions hampers drawing conclusions on the efficacy and safety of individual agents.

Bioengineered Kidney Tubules Efficiently Clear Uremic Toxins in Experimental Dialysis Conditions.

Patients with end-stage kidney disease (ESKD) suffer from high levels of protein-bound uremic toxins (PBUTs) that contribute to various comorbidities. Conventional dialysis methods are ineffective in removing these PBUTs. A potential solution could be offered by a bioartificial kidney (BAK) composed of porous membranes covered by proximal tubule epithelial cells (PTECs) that actively secrete PBUTs. However, BAK development is currently being hampered by a lack of knowledge regarding the cytocompatibility of the dialysis fluid (DF) that comes in contact with the PTECs. Here, we conducted a comprehensive functional assessment of the DF on human conditionally immortalized PTECs (ciPTECs) cultured as monolayers in well plates, on Transwell® inserts, or on hollow fiber membranes (HFMs) that form functional units of a BAK. We evaluated cell viability markers, monolayer integrity, and PBUT clearance. Our results show that exposure to DF did not affect ciPTECs' viability, membrane integrity, or function. Seven anionic PBUTs were efficiently cleared from the perfusion fluid containing a PBUTs cocktail or uremic plasma, an effect which was enhanced in the presence of albumin. Overall, our findings support that the DF is cytocompatible and does not compromise ciPTECs function, paving the way for further advancements in BAK development and its potential clinical application.

Lifestyle changes and kidney function: A 10-year follow-up study in patients with manifest cardiovascular disease.

BACKGROUND: Patients with cardiovascular disease (CVD) are at higher risk of kidney function decline. The current study aimed to examine the association of lifestyle changes with kidney function decline in patients with manifest CVD. METHODS: A total of 2260 patients from the Utrecht Cardiovascular Cohort-Second Manifestations of ARTerial disease cohort with manifest CVD who returned for a follow-up visit after a median of 9.9 years were included. The relation between change in lifestyle factors (smoking, alcohol consumption, physical activity and obesity) and change in kidney function (eGFR and uACR) was assessed using linear regression models. RESULTS: An increase in body mass index (ß -2.81; 95% CI -3.98; -1.63 per 5 kg/m2 ) and for men also an increase in waist circumference (ß -0.87; 95% CI -1.28; -0.47 per 5 cm) were significantly associated with a steeper decline in eGFR over 10 years. Continuing smoking (ß -2.44, 95% CI -4.43; -0.45) and recent smoking cessation during follow-up (ß -3.27; 95% CI -5.20; -1.34) were both associated with a steeper eGFR decline compared to patients who remained as non- or previous smokers from baseline. No significant association was observed between physical exercise or alcohol consumption and kidney function decline. No significant relation between any lifestyle factor and change in uACR was observed. CONCLUSIONS: In patients with CVD, continuing smoking, recent smoking cessation and an increase in obesity markers were related to a steeper kidney function decline. Although no definite conclusions from this study can be drawn, the results support the importance of encouraging weight loss and smoking cessation in high-risk patients as a means of slowing down kidney function decline.

Differences in hospitalisation between peritoneal dialysis and haemodialysis patients.

BACKGROUND: Dialysis is associated with frequent hospitalisations. Studies comparing hospitalisations between peritoneal dialysis (PD) and haemodialysis (HD) report conflicting results and mostly analyse data of patients that remain on their initial dialysis modality. This cohort study compares hospitalisations between PD and HD patients taking into account transitions between modalities. METHODS: The Dutch nOcturnal and hoME dialysis Study To Improve Clinical Outcomes collected hospitalisation data of patients who started dialysis between 2012 and 2017. Primary outcome was hospitalisation rate, analysed with a multi-state model that attributed each hospitalisation to the current dialysis modality. RESULTS: In total, 695 patients (252 PD, 443 HD) treated in 31 Dutch hospitals were included. The crude hospitalisation rate for PD was 2.3 ( ± 5.0) and for HD 1.4 ( ± 3.2) hospitalisations per patient-year. The adjusted hazard ratio for hospitalisation rate was 1.1 (95%CI 1.02-1.3) for PD compared with HD. The risk for first hospitalisation was 1.3 times (95%CI 1.1-1.6) higher for PD compared with HD during the first year after dialysis initiation. The number of hospitalisations and number of hospital days per patient-year were significantly higher for PD. The most common causes of PD and HD hospitalisations were peritonitis (23%) and vascular access-related problems (33%). CONCLUSION: PD was associated with higher hospitalisation rate, higher risk for first hospitalisation and higher number of hospitalisations compared with HD. Since the PD hospitalisations were mainly caused by peritonitis, more attention to infection prevention is necessary for reducing the number of hospitalisations in the future.

Evidence on continuous flow peritoneal dialysis: A review.

Clinical application of continuous flow peritoneal dialysis (CFPD) has been explored since the 1960s, but despite anticipated clinical benefits, CFPD has failed to gain a foothold in clinical practice, among others due to the typical use of two catheters (or a dual-lumen catheter) and large dialysate volumes required per treatment. Novel systems applying CFPD via the existing single-lumen catheter using rapid dialysate cycling may solve one of these hurdles. Novel on-demand peritoneal dialysate generation systems and sorbent-based peritoneal dialysate regeneration systems may considerably reduce the storage space for peritoneal dialysate and/or the required dialysate volume. This review provides an overview of current evidence on CFPD in vivo. The available (pre)clinical evidence on CFPD is limited to case reports/series with inherently nonuniform study procedures, or studies with a small sample size, short follow-up, and no hard endpoints. Small solute clearance appears to be higher in CFPD compared to conventional PD, in particular at dialysate flows ≥100 mL/min using two single-lumen catheters or a double-lumen catheter. Results of CFPD using rapid cycling via a single-lumen catheter are too preliminary to draw any conclusions. Continuous addition of glucose to dialysate with CFPD appears to be effective in reducing the maximum intraperitoneal glucose concentration while increasing ultrafiltration efficiency (mL/g absorbed glucose). Patient tolerance may be an issue since abdominal discomfort and sterile peritonitis were reported with continuous circulation of the peritoneal dialysate. Thus, well-designed clinical trials of longer duration and larger sample size, in particular applying CFPD via the existing catheter, are urgently required.

Differentiated kidney tubular cell-derived extracellular vesicles enhance maturation of tubuloids.

The prevalence of end-stage kidney disease (ESKD) is rapidly increasing with the need for regenerative therapies. Adult stem cell derived kidney tubuloids have the potential to functionally mimic the adult kidney tubule, but still lack the expression of important transport proteins needed for waste removal. Here, we investigated the potential of extracellular vesicles (EVs) obtained from matured kidney tubular epithelial cells to modulate in vitro tubuloids functional maturation. We focused on organic anion transporter 1 (OAT1), one of the most important proteins involved in endogenous waste excretion. First, we show that EVs from engineered proximal tubule cells increased the expression of several transcription factors and epithelial transporters, resulting in improved OAT1 transport capacity. Next, a more in-depth proteomic data analysis showed that EVs can trigger various biological pathways, including mesenchymal-to-epithelial transition, which is crucial in the tubular epithelial maturation. Moreover, we demonstrated that the combination of EVs and tubuloid-derived cells can be used as part of a bioartificial kidney to generate a tight polarized epithelial monolayer with formation of dense cilia structures. In conclusion, EVs from kidney tubular epithelial cells can phenotypically improve in vitro tubuloid maturation, thereby enhancing their potential as functional units in regenerative or renal replacement therapies.

Remote sensing and signaling in kidney proximal tubules stimulates gut microbiome-derived organic anion secretion.

Membrane transporters and receptors are responsible for balancing nutrient and metabolite levels to aid body homeostasis. Here, we report that proximal tubule cells in kidneys sense elevated endogenous, gut microbiome-derived, metabolite levels through EGF receptors and downstream signaling to induce their secretion by up-regulating the organic anion transporter-1 (OAT1). Remote metabolite sensing and signaling was observed in kidneys from healthy volunteers and rats in vivo, leading to induced OAT1 expression and increased removal of indoxyl sulfate, a prototypical microbiome-derived metabolite and uremic toxin. Using 2D and 3D human proximal tubule cell models, we show that indoxyl sulfate induces OAT1 via AhR and EGFR signaling, controlled by miR-223. Concomitantly produced reactive oxygen species (ROS) control OAT1 activity and are balanced by the glutathione pathway, as confirmed by cellular metabolomic profiling. Collectively, we demonstrate remote metabolite sensing and signaling as an effective OAT1 regulation mechanism to maintain plasma metabolite levels by controlling their secretion.

A plasma creatinine- and urea-based equation to estimate glomerular filtration rate in rats.

Monitoring renal function is a vital part of kidney research involving rats. The laborious measurement of glomerular filtration rate (GFR) with administration of exogenous filtration markers does not easily allow serial measurements. Using an in-house database of inulin clearances, we developed and validated a plasma creatinine- and plasma urea-based equation to estimate GFR in a large cohort of male rats [development cohort n = 325, R2 = 0.816, percentage of predictions that fell within 30% of the true value (P30) = 76%] that had high accuracy in the validation cohort (n = 116 rats, R2 = 0.935, P30 = 79%). The equation was less accurate in rats with nonsteady-state creatinine, in which the equation should therefore not be used. In conclusion, applying this equation facilitates easy and repeatable estimates of GFR in rats.NEW & NOTEWORTHY This is the first equation, that we know of, which estimates glomerular filtration rate in rats based on a single measurement of body weight, plasma creatinine, and plasma urea.

A systematic review and meta-analysis of COVID-19 in kidney transplant recipients: Lessons to be learned.

Kidney transplant recipients (KTR) may be at increased risk of adverse COVID-19 outcomes, due to prevalent comorbidities and immunosuppressed status. Given the global differences in COVID-19 policies and treatments, a robust assessment of all evidence is necessary to evaluate the clinical course of COVID-19 in KTR. Studies on mortality and acute kidney injury (AKI) in KTR in the World Health Organization COVID-19 database were systematically reviewed. We selected studies published between March 2020 and January 18th 2021, including at least five KTR with COVID-19. Random-effects meta-analyses were performed to calculate overall proportions, including 95% confidence intervals (95% CI). Subgroup analyses were performed on time of submission, geographical region, sex, age, time after transplantation, comorbidities, and treatments. We included 74 studies with 5559 KTR with COVID-19 (64.0% males, mean age 58.2 years, mean 73 months after transplantation) in total. The risk of mortality, 23% (95% CI: 21%-27%), and AKI, 50% (95% CI: 44%-56%), is high among KTR with COVID-19, regardless of sex, age and comorbidities, underlining the call to accelerate vaccination programs for KTR. Given the suboptimal reporting across the identified studies, we urge researchers to consistently report anthropometrics, kidney function at baseline and discharge, (changes in) immunosuppressive therapy, AKI, and renal outcome among KTR.

Reduced nitric oxide bioavailability impairs myocardial oxygen balance during exercise in swine with multiple risk factors.

In the present study, we tested the hypothesis that multiple risk factors, including diabetes mellitus (DM), dyslipidaemia and chronic kidney disease (CKD) result in a loss of nitric oxide (NO) signalling, thereby contributing to coronary microvascular dysfunction. Risk factors were induced in 12 female swine by intravenous streptozotocin injections (DM), a high fat diet (HFD) and renal artery embolization (CKD). Female healthy swine (n = 13) on normal diet served as controls (Normal). After 5 months, swine were chronically instrumented and studied at rest and during exercise. DM + HFD + CKD swine demonstrated significant hyperglycaemia, dyslipidaemia and impaired kidney function compared to Normal swine. These risk factors were accompanied by coronary microvascular endothelial dysfunction both in vivo and in isolated small arteries, due to a reduced NO bioavailability, associated with perturbations in myocardial oxygen balance at rest and during exercise. NO synthase inhibition caused coronary microvascular constriction in exercising Normal swine, but had no effect in DM + HFD + CKD animals, while inhibition of phosphodiesterase 5 produced similar vasodilator responses in both groups, indicating that loss of NO bioavailability was principally responsible for the observed coronary microvascular dysfunction. This was associated with an increase in myocardial 8-isoprostane levels and a decrease in antioxidant capacity, while antioxidants restored the vasodilation to bradykinin in isolated coronary small arteries, suggesting that oxidative stress was principally responsible for the reduced NO bioavailability. In conclusion, five months of combined exposure to DM + HFD + CKD produces coronary endothelial dysfunction due to impaired NO bioavailability, resulting in impaired myocardial perfusion at rest and during exercise.

Multiparametric Renal MRI: An Intrasubject Test-Retest Repeatability Study.

BACKGROUND: Renal multiparametric magnetic resonance imaging (MRI) is a promising tool for diagnosis, prognosis, and treatment monitoring in kidney disease. PURPOSE: To determine intrasubject test-retest repeatability of renal MRI measurements. STUDY TYPE: Prospective. POPULATION: Nineteen healthy subjects aged over 40 years. FIELD STRENGTH/SEQUENCES: T1 and T2 mapping, R2 * mapping or blood oxygenation level-dependent (BOLD) MRI, diffusion tensor imaging (DTI), and intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI), 2D phase contrast, arterial spin labelling (ASL), dynamic contrast enhanced (DCE) MRI, and quantitative Dixon for fat quantification at 3T. ASSESSMENT: Subjects were scanned twice with ~1 week between visits. Total scan time was ~1 hour. Postprocessing included motion correction, semiautomated segmentation of cortex and medulla, and fitting of the appropriate signal model. STATISTICAL TEST: To assess the repeatability, a Bland-Altman analysis was performed and coefficients of variation (CoVs), repeatability coefficients, and intraclass correlation coefficients were calculated. RESULTS: CoVs for relaxometry (T1 , T2 , R2 */BOLD) were below 6.1%, with the lowest CoVs for T2 maps and highest for R2 */BOLD. CoVs for all diffusion analyses were below 7.2%, except for perfusion fraction (FP ), with CoVs ranging from 18-24%. The CoV for renal sinus fat volume and percentage were both around 9%. Perfusion measurements were most repeatable with ASL (cortical perfusion only) and 2D phase contrast with CoVs of 10% and 13%, respectively. DCE perfusion had a CoV of 16%, while single kidney glomerular filtration rate (GFR) had a CoV of 13%. Repeatability coefficients (RCs) ranged from 7.7-87% (lowest/highest values for medullary mean diffusivity and cortical FP , respectively) and intraclass correlation coefficients (ICCs) ranged from -0.01 to 0.98 (lowest/highest values for cortical FP and renal sinus fat volume, respectively). DATA CONCLUSION: CoVs of most MRI measures of renal function and structure (with the exception of FP and perfusion as measured by DCE) were below 13%, which is comparable to standard clinical tests in nephrology. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.