The physiology of urinary concentration: an update

Prevalence of canine renal crest hyperattenuation in precontrast computed tomography

Normal canine kidneys are relatively homogeneous soft tissue attenuating structures on nonenhanced CT images. However, visible differences in attenuation between the renal crest and medulla are occasionally observed. This finding and its potential clinical implications have not been previously investigated. This study aimed to estimate the prevalence of renal crest hyperattenuation (RCH) and investigate possible associations with signalment and laboratory parameters. Abdominal CT studies from 100 dogs, with biochemistry and urinalysis data obtained within 48 h before the CT acquisition, were categorized by two radiologists into those with and without visible RCH. The attenuation in Hounsfield units (HU) of the renal crest and renal medulla were measured. Signalment, biochemical, and urinalysis data were analyzed for associations with RCH. Correlation coefficients were calculated for measured HU and associated continuous parameters. Prevalence of RCH was 42.42% (42/99 dogs, 95% CI, 33-52%). Urinary specific gravity (USG) was significantly different between dogs with and without RCH (P = .034). Weak positive correlations were identified between left and right renal crest attenuation and USG (r = 0.233 and 0.253, respectively; P = .05). Renal crest hyperattenuation is a common finding in dogs undergoing abdominal CT. Although the correlation between the USG and renal crest HU is weak, the dogs with RCH have significantly higher USG. Renal crest hyperattenuation might, therefore, not be associated with renal insufficiency. No other specific associations of RCH were identified with parameters typically altered in a variety of diseases. Further investigation may be warranted for its relevance to specific diseases or if it indeed represents a physiological variant.

Vasopressin, protein metabolism, and water conservation

PURPOSE OF REVIEW

Highlight the mechanisms through which vasopressin and hypertonic stress regulate protein metabolism.

RECENT FINDINGS

Mammals have an 'aestivation-like' response in which hypertonic stress increases muscle catabolism and urea productionVasopressin can directly regulate ureagenesis in the liver and the kidneyIn humans chronic hypertonic stress is associated with premature aging, diabetes, cardiovascular disease, and premature mortality.

SUMMARY

There is an evolutionarily conserved 'aestivation-like' response in humans in which hypertonic stress results in activation of the vasopressin system, muscle catabolism, and ureagenesis in order to promote water conservation.

The EFLM European Urinalysis Guideline 2023

BACKGROUND

The EFLM Task and Finish Group Urinalysis has updated the ECLM European Urinalysis Guidelines (2000) on urinalysis and urine bacterial culture, to improve accuracy of these examinations in European clinical laboratories, and to support diagnostic industry to develop new technologies.

RECOMMENDATIONS

Graded recommendations were built in the following areas.

MEDICAL NEEDS AND TEST REQUISITION

Strategies of urine testing are described to patients with complicated or uncomplicated urinary tract infection (UTI), and high or low-risk to kidney disease.

SPECIMEN COLLECTION

Patient preparation, and urine collection are supported with two quality indicators: contamination rate (cultures), and density of urine (chemistry, particles).

CHEMISTRY

Measurements of both urine albumin and α1-microglobulin are recommended for sensitive detection of kidney disease in high-risk patients. Performance specifications are given for urine protein measurements and quality control of multiproperty strip tests.

PARTICLES

Procedures for microscopy are reviewed for diagnostic urine particles, including urine bacteria. Technologies in automated particle counting and visual microscopy are updated with advice how to verify new instruments with the reference microscopy.

BACTERIOLOGY

Chromogenic agar is recommended as primary medium in urine cultures. Limits of significant growth are reviewed, with an optimised workflow for routine specimens, using leukocyturia to reduce less important antimicrobial susceptibility testing. Automation in bacteriology is encouraged to shorten turn-around times. Matrix assisted laser desorption ionization time-of-flight mass spectrometry is applicable for rapid identification of uropathogens. Aerococcus urinae, A. sanguinicola and Actinotignum schaalii are taken into the list of uropathogens. A reference examination procedure was developed for urine bacterial cultures.

Influence of previous plane of nutrition on molecular mechanisms regulating the expression of urea and water metabolism related genes in the rumen and kidney of finishing crossbred Angus steers

This study aimed to understand how molecular mechanisms controlling water and urea metabolism at the finishing phase can be affected by previous plane of nutrition of crossbred Angus beef steers. Twenty-four (n = 24) animals were randomly distributed into either a moderate (MP) or high plane of nutrition during the background phase for 85 d. Animals were then blocked by their previous plane and were moved onto a 105-d finishing phase in a 2 × 2 factorial arrangement. The forage-finished group received only high-quality alfalfa hay, whereas the grain-fed group received a high grain diet (80% whole corn and 20% alfalfa hay). By the end of the finishing phase, animals were harvested and tissue samples from the rumen and kidney were collected. Changes in gene expression of aquaporins (AQP)-2, -3, -4, -7, ATP1A1, ATP1B1, SGK1, CLIC1 (kidney and rumen), UT-A1 (kidney only) and UT-B (rumen only), were assayed via real-time qPCR; 18S rRNA was used as an endogenous control. One-way ANOVA followed by Tukey's post hoc analysis was conducted. When animals were from MP, forage-finishing increased the relative abundance of AQP3 (P ≤ 0.05), AQP7 (P ≤ 0.05), ATP1B1 (P ≤ 0.05), and SGK1 (P ≤ 0.05) in the kidney when compared to grain-fed animals. In the rumen, for the MP group, AQP7 was differentially expressed in both treatments at the finishing phase (P ≤ 0.01), with forage-finished steers having the highest expression of AQP7. For the MP group, UT-B had a tendency of presenting a higher expression on grain-fed animals (P = 0.075). Overall, these results suggest that previous plane can impact expression of genes associated with water and urea metabolism during the finishing phase, namely AQP3, AQP7, ATP1B1, and SGK1 in the kidney, and AQP7 and UT-B in the rumen. The greatest impact observed on gene expression changes of investigated genes at the finishing phase was reflective of animals backgrounded on the moderate previous plane.

Incretin and glucagon receptor polypharmacology in chronic kidney disease

Chronic kidney disease is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have a direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influencing volume and electrolyte handling, and improving systemic risk factors.

Protein Quality Control of NKCC2 in Bartter Syndrome and Blood Pressure Regulation

Mutations in NKCC2 generate antenatal Bartter syndrome type 1 (type 1 BS), a life-threatening salt-losing nephropathy characterized by arterial hypotension, as well as electrolyte abnormalities. In contrast to the genetic inactivation of NKCC2, inappropriate increased NKCC2 activity has been associated with salt-sensitive hypertension. Given the importance of NKCC2 in salt-sensitive hypertension and the pathophysiology of prenatal BS, studying the molecular regulation of this Na-K-2Cl cotransporter has attracted great interest. Therefore, several studies have addressed various aspects of NKCC2 regulation, such as phosphorylation and post-Golgi trafficking. However, the regulation of this cotransporter at the pre-Golgi level remained unknown for years. Similar to several transmembrane proteins, export from the ER appears to be the rate-limiting step in the cotransporter's maturation and trafficking to the plasma membrane. The most compelling evidence comes from patients with type 5 BS, the most severe form of prenatal BS, in whom NKCC2 is not detectable in the apical membrane of thick ascending limb (TAL) cells due to ER retention and ER-associated degradation (ERAD) mechanisms. In addition, type 1 BS is one of the diseases linked to ERAD pathways. In recent years, several molecular determinants of NKCC2 export from the ER and protein quality control have been identified. The aim of this review is therefore to summarize recent data regarding the protein quality control of NKCC2 and to discuss their potential implications in BS and blood pressure regulation.

Long-term health outcomes associated with hydration status

Body water balance is determined by fundamental homeostatic mechanisms that maintain stable volume, osmolality and the composition of extracellular and intracellular fluids. Water balance is maintained by multiple mechanisms that continuously match water losses through urine, the skin, the gastrointestinal tract and respiration with water gains achieved through drinking, eating and metabolic water production. Hydration status is determined by the state of the water balance. Underhydration occurs when a decrease in body water availability, due to high losses or low gains, stimulates adaptive responses within the water balance network that are aimed at decreasing losses and increasing gains. This stimulation is also accompanied by cardiovascular adjustments. Epidemiological and experimental studies have linked markers of low fluid intake and underhydration - such as increased plasma concentration of vasopressin and sodium, as well as elevated urine osmolality - with an increased risk of new-onset chronic diseases, accelerated aging and premature mortality, suggesting that persistent activation of adaptive responses may be detrimental to long-term health outcomes. The causative nature of these associations is currently being tested in interventional trials. Understanding of the physiological responses to underhydration may help to identify possible mechanisms that underlie potential adverse, long-term effects of underhydration and inform future research to develop preventative and treatment approaches to the optimization of hydration status.

Genetic Appraisal of RAAS-Associated SNPs: REN (rs16853055), AGT (rs3789678) and ACE (rs4305) in Preeclamptic Women Living with HIV Infection

PURPOSE OF REVIEW

The primary goal of this review article was to determine whether the three RAAS-associated SNPs, Renin-rs16853055, AGT-rs3789678 and ACE-rs4305 are genetically linked to the development of hypertension in preeclampsia. The secondary goal was to establish if there was a link between these SNPs and HIV infection.

RECENT FINDINGS

There is a paucity of findings related to the aforementioned SNPs and preeclampsia. There are no recent findings on the rs16853055 renin polymorphism. The rs3789678 angiotensinogen polymorphism correlated significantly with gestational hypertension. The rs4305 ACE polymorphism showed no significant association with the development of pregnancy-induced hypertension. There are conflicting findings when determining the relationship between ethnicity and the predisposition of preeclampsia and hypertension in relation to the discussed RAAS-associated SNPs. To date, the association between RAAS-associated SNPs and preeclamptic women co-morbid with HIV in South Africa has revealed that certain alleles of the AGT gene are more prominent in HIV-infected PE compared to normotensive pregnant HIV-infected women.

Is mild dehydration a risk for progression of childhood chronic kidney disease?

Children with chronic kidney disease (CKD) can have an inherent vulnerability to dehydration. Younger children are unable to freely access water, and CKD aetiology and stage can associate with reduced kidney concentrating capacity, which can also impact risk. This article aims to review the risk factors and consequences of mild dehydration and underhydration in CKD, with a particular focus on evidence for risk of CKD progression. We discuss that assessment of dehydration in the CKD population is more challenging than in the healthy population, thus complicating the definition of adequate hydration and clinical research in this field. We review pathophysiologic studies that suggest mild dehydration and underhydration may cause hyperfiltration injury and impact renal function, with arginine vasopressin as a key mediator. Randomised controlled trials in adults have not shown an impact of improved hydration in CKD outcomes, but more vulnerable populations with baseline low fluid intake or poor kidney concentrating capacity need to be studied. There is little published data on the frequency of dehydration, and risk of complications, acute or chronic, in children with CKD. Despite conflicting evidence and the need for more research, we propose that paediatric CKD management should routinely include an assessment of individual dehydration risk along with a treatment plan, and we provide a framework that could be used in outpatient settings.

Fractional excretion of urea nitrogen can identify true worsening renal function in patients with heart failure

AIMS

Fractional excretion of urea nitrogen (FEUN), used to differentiate the cause of acute kidney injury, has emerged as a useful fluid index in patients with heart failure (HF). We hypothesized that FEUN could be useful in identifying worsening renal function (WRF) associated with poor outcomes in patients with acute HF (AHF).

METHODS AND RESULTS

Overall, 1103 patients with AHF (median age, 78 years; male proportion, 60%) were categorized into six groups according to the presence of WRF and FEUN values (low, ≤32.1%; medium, >32.1% and ≤38.0%; and high, >38.0%) at discharge. WRF was defined as an increase of ≥0.3 mg/dL in the serum creatinine level from admission to discharge. FEUN was calculated by the following formula: (urinary urea × serum creatinine) × 100/(serum urea × urinary creatinine). The cut-off values for low, medium, and high FEUN were based on a previous study. The primary outcome of this study was HF readmission after hospital discharge. During the 1 year follow-up, 170 HF readmissions occurred. Kaplan-Meier analysis revealed significantly higher HF readmission rates in patients with WRF than in those without WRF (log-rank test, P < 0.001). Additionally, among patients with WRF, HF readmission rates were lowest in those with medium FEUN values, followed by those with low FEUN values and those with high FEUN values. On multivariable analysis, the presence of WRF with low or high FEUN values was independently associated with increased HF readmission, as compared with the absence of WRF with medium FEUN values. Notably, no association was noted between WRF with medium FEUN values and HF readmission.

CONCLUSIONS

The prognostic impact of WRF was significantly mediated by the FEUN values and was associated with worse outcomes only when the FEUN values were either low or high. Our study suggests that FEUN can identify prognostically relevant WRF in patients with AHF.

[Features of water-electrolyte balance in persons of the older age group]

Age-related changes have a great influence on the regulation of water and electrolyte homeostasis in the body, which is regulated by a complex interaction of environmental factors, drinking behavior, the secretion of a number of hormones and hormone-like substances, as well as the innervation and functional state of the kidneys. It is well known that the changes that are part of physiological aging underlie fluid and electrolyte imbalances, exacerbated by the presence of age-related diseases, medications, or a number of external factors such as malnutrition, fluid intake, and the presence of dementia. This review considers literature data on the effect of normal aging on the development of pathology of the water-sodium balance, including dehydration of senile patients, hyponatremia, hypernatremia, changes in the secretion of antidiuretic hormone and the activity of elements of the renin-angiotensin-aldosterone system.

Renal macrophages monitor and remove particles from urine to prevent tubule obstruction

When the filtrate of the glomerulus flows through the renal tubular system, various microscopic sediment particles, including mineral crystals, are generated. Dislodging these particles is critical to ensuring the free flow of filtrate, whereas failure to remove them will result in kidney stone formation and obstruction. However, the underlying mechanism for the clearance is unclear. Here, using high-resolution microscopy, we found that the juxtatubular macrophages in the renal medulla constitutively formed transepithelial protrusions and "sampled" urine contents. They efficiently sequestered and phagocytosed intraluminal sediment particles and occasionally transmigrated to the tubule lumen to escort the excretion of urine particles. Mice with decreased renal macrophage numbers were prone to developing various intratubular sediments, including kidney stones. Mechanistically, the transepithelial behaviors of medulla macrophages required integrin β1-mediated ligation to the tubular epithelium. These findings indicate that medulla macrophages sample urine content and remove intratubular particles to keep the tubular system unobstructed.

Impact assessment of metabolite instability in the development and validation of LC-MS/MS bioanalytical assays for measurement of rosuvastatin in human plasma and urine samples

During bioanalytical assay development and validation, maintaining the stability of the parent drug and metabolites of interest is critical. While stability of the parent drug has been thoroughly investigated, the stability of unanalyzed metabolites is often overlooked. When an unstable metabolite is known or suspected to interfere with measurement of the parent drug or other metabolites of interest through back-conversion or other routes, additional tests with these unstable metabolites should be conducted. Here, the development and validation of two assays for quantification of rosuvastatin, one in human plasma and one in human urine, was reported. To this end, additional sets of quality control samples were added during assay validation to ensure the reliability of the assays. Acid treatment of samples is shown to be necessary for rosuvastatin quantification. In this regard, stability issues caused by the metabolite, rosuvastatin lactone, may have been overlooked if assay development and validation had only considered the parent drug, rosuvastatin. These assays represent a case study for how to develop and validate assays with unstable metabolites. Taken together, unstable metabolites should be included in all applicable stability tests.

Comparing Effects of Tolvaptan and Instruction to Increase Water Consumption in ADPKD: Post Hoc Analysis of TEMPO 3:4

Key Points

In a post hoc analysis, short-term reduction in spot urine osmolality (Uosm) was associated with decreased kidney volume growth in autosomal dominant polycystic kidney disease for both tolvaptan and instruction to increase hydration alone. For the same spot Uosm reduction, however, the kidney volume benefit was greater with tolvaptan, possibly because of greater cumulative 24-hour Uosm suppression by tolvaptan.

Background

In addition to decreasing water excretion and increasing urinary concentration, the antidiuretic hormone vasopressin plays a role in the pathophysiology of autosomal dominant polycystic kidney disease. It has been hypothesized that by suppressing vasopressin release, drinking large amounts of water might exert therapeutic effects in autosomal dominant polycystic kidney disease similar to those of tolvaptan, an antagonist of the vasopressin type 2 receptor, but evidence is lacking. We analyzed data from tolvaptan clinical trials to evaluate relationships among water intake, urine osmolality (Uosm), and change in total kidney volume (TKV).

Methods

Analysis of the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes 3:4 clinical trial in which participants were randomized to tolvaptan or placebo and instructed to drink large amounts of water. The relationship between change in spot Uosm from baseline to week 3 and change in TKV to month 12 was assessed using linear regression modeling. Two short-term tolvaptan trials were analyzed to explore relationships between intermittent Uosm sampling and 24-hour Uosm suppression.

Results

With both tolvaptan and placebo (i.e. , mandated high water intake alone), Uosm reduction at week 3 was associated with reduction in TKV growth at month 12. However, for the same decrease in spot Uosm, the corresponding reduction in TKV growth was greater for tolvaptan (e.g. , a −250 mOsm/kg reduction in Uosm at week 3 was associated with a −1% change in TKV at month 12 for tolvaptan versus +4.5% for placebo). In short-term trials, similar reductions in spot or trough Uosm values were achievable with tolvaptan and high water intake, but cumulative 24-hour suppression was greater with tolvaptan.

Conclusions

This analysis supports a relationship between effects on Uosm and inhibition of disease progression by tolvaptan and high water intake alone. The findings further suggest that 24-hour Uosm measurement is superior to spot Uosm for assessing suppression of vasopressin activity by tolvaptan.

A better explanation of countercurrent multiplication in the formation of the corticopapillary osmotic gradient in the outer medulla

Countercurrent multiplication (CCM) is widely accepted as the mechanism for the generation of the corticopapillary osmotic gradient in the outer medulla of mammalian kidneys. However, several issues in the literature cause the current explanations of CCM to be inefficient and incomplete. As a result, it is challenging to clearly explain CCM in physiology education. The goal of this article is to share a modified version of CCM with more understandable explanation in the hopes of motivating peer discussion, further improvement, and future research. To reach this goal, the logical processes leading to CCM are first analyzed, which results in a set of formulas that serve as the principles governing CCM. Next, the cessation of CCM is addressed to provide a complete picture of the modified version of CCM. Throughout these two steps, the issues mentioned above are identified and addressed so that how the modified version of CCM eliminates these issues becomes clear. The formulas mentioned above are provided in the Tables S1, S2, and S3 (all Supplemental material is available in the Supplemental Excel File at https://doi.org/10.6084/m9.figshare.23515614) to explain how the interstitial and intrathick ascending limb osmotic concentration (OC) values used in the figures in this article are simulated and how alternative OC values can be generated from Tables S1 and S2 to illustrate CCM.NEW & NOTEWORTHY Countercurrent multiplication is widely accepted as the mechanism for the generation of the corticopapillary osmotic gradient in the outer medulla of mammalian kidneys, but the current explanations of it in textbooks and the literature are inefficient and incomplete, leading to confusion for students. This article shares a modified version of countercurrent multiplication with more understandable explanation as a way of motivating peer discussion, further improvement, and future research.

Obesity and renal cell carcinoma: Biological mechanisms and perspectives

Obesity, defined by body mass index (BMI), is an established risk factor for specific renal cell carcinoma (RCC) subtypes such as clear cell RCC, the most common RCC histology. Many studies have identified an association between obesity and improved survival after diagnosis of RCC, a potential "obesity paradox." Clinically, there is uncertainty whether improved outcomes observed after diagnosis are driven by stage, type of treatment received, or artifacts of longitudinal changes in weight and body composition. The biological mechanisms underlying obesity's influence on RCC are not fully established, but multiomic and mechanistic studies suggest an impact on tumor metabolism, particularly fatty acid metabolism, angiogenesis, and peritumoral inflammation, which are known to be key biological hallmarks of clear cell RCC. Conversely, high-intensity exercise associated with increased muscle mass may be a risk factor for renal medullary carcinoma, a rare RCC subtype that predominantly occurs in individuals with sickle hemoglobinopathies. Herein, we highlight methodologic challenges associated with studying the influence of obesity on RCC and review the clinical evidence and potential underlying mechanisms associating RCC with BMI and body composition.

The Integral Role of Chloride & With-No-Lysine Kinases in Cell Volume Regulation & Hypertension

Chloride anions are the most abundant in humans. For many years, it has been believed that chloride is simply a counterion of all other cations, ensuring the electroneutrality of the extracellular space. Recent data suggests that chloride anions possess a broad spectrum of important activities that regulate vital cellular functions. It is now evident that, apart from its contribution to the electroneutrality of the extracellular space, it acts as an osmole and contributes to extracellular and intracellular volume regulation. Its anionic charge also contributes to the generation of cell membrane potential. The most interesting action of chloride anions is their ability to regulate the activity of with-no-lysine kinases, which in turn regulate the activity of sodium chloride and potassium chloride cotransporters and govern the reabsorption of salt and excretion of potassium by nephron epithelia. Chloride anions seem to play a crucial role in cell functions, such as cell volume regulation, sodium reabsorption in the distal nephron, potassium balance, and sodium sensitivity, which lead to hypertension. All of these functions are accomplished on a molecular level via complicated metabolic pathways, many of which remain poorly defined. We attempted to elucidate some of these pathways in light of recent advances in our knowledge, obtained mainly from experimental studies.

Dynamics of differentiated-renal epithelial cell monolayer after calcium oxalate injury: The role of cyclooxygenase-2

AIMS

Calcium oxalate (Oxa), constituent of most common kidney stones, damages renal tubular epithelial cells leading to kidney disease. Most in vitro studies designed to evaluate how Oxa exerts its harmful effects were performed in proliferative or confluent non-differentiated renal epithelial cultures; none of them considered physiological hyperosmolarity of renal medullary interstitium. Cyclooxygenase 2 (COX2) has been associated to Oxa deleterious actions; however, up to now, it is not clear how COX2 acts. In this work, we proposed an in vitro experimental system resembling renal differentiated-epithelial cells that compose medullary tubular structures which were grown and maintained in a physiological hyperosmolar environment and evaluated whether COX2 → PGE2 axis (COX2 considered a cytoprotective protein for renal cells) induces Oxa damage or epithelial restitution.

MAIN METHODS

MDCK cells were differentiated with NaCl hyperosmolar medium for 72 h where cells acquired the typical apical and basolateral membrane domains and a primary cilium. Then, cultures were treated with 1.5 mM Oxa for 24, 48, and 72 h to evaluate epithelial monolayer restitution dynamics and COX2-PGE2 effect.

KEY FINDINGS

Oxa completely turned the differentiated phenotype into mesenchymal one (epithelial-mesenchymal transition). Such effect was partially and totally reverted after 48 and 72 h, respectively. Oxa damage was even deeper when COX2 was blocked by NS398. PGE2 addition restituted the differentiated-epithelial phenotype in a time and concentration dependence.

SIGNIFICANCE

This work presents an experimental system that approaches in vitro to in vivo renal epithelial studies and, more important, warns about NSAIDS use in patients suffering from kidney stones.

Brain-specific biomarkers in urine as a non-invasive approach to monitor neuronal and glial damage

BACKGROUND AND PURPOSE

This study evaluates the quantitative measurability of glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL), ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) and total tau (t-tau) in urine of patients with acute cerebral damage.

METHODS

Serum and urine samples were prospectively collected from patients with an acute ischemic stroke or intracerebral hemorrhage (target group) and compared to healthy subjects (control group); samples were measured using ultrasensitive single-molecule arrays (Simoa®). Glomerular barrier function was assessed based on albumin-creatinine ratio (ACR); biomarker-creatinine ratios were calculated for correction of urine dilution.

RESULTS

Ninety-three urine-serum pairs in the target group and 10 urine-serum pairs in the control group were measured. The mean absolute concentration ± standard deviation in urine of the target and control groups were 184.7 ± 362.4 pg/ml and 27.3 ± 24.1 pg/ml for GFAP (r = 0.3 [Wilcoxon effect size], p = 0.007), 17.5 ± 38.6 pg/ml and 0.9 ± 0.3 pg/ml for NfL (r = 0.4, p < 0.005), 320.2 ± 443.3 pg/ml and 109.6 ± 116.8 pg/ml for UCH-L1 (r = 0.26, p = 0.014), and 219.5 ± 255.8 pg/ml and 21.1 ± 27.1 pg/ml for t-tau (r = 0.37, p < 0.005), respectively, whereas biomarker-creatinine ratio was significantly different only for NfL (r = 0.29, p = 0.015) and t-tau (r = 0.32, p < 0.01). In patients with intact glomerular barrier (ACR < 30 mg/g), only NfL in urine was significantly different between the target and control group and showed a significant correlation with the respective serum concentrations (r = 0.58 [Pearson's correlation-coefficient], p < 0.005).

CONCLUSION

All four investigated biomarkers could be measured in urine, with NfL and t-tau showing the strongest effect size after correction for urine dilution. NfL revealed the most accurate relation between serum and urine concentrations in patients with intact kidney function.

Utility of fractional excretion of urea nitrogen in heart failure patients with chronic kidney disease

AIMS

Maintenance of euvolaemia with diuretics is critical in heart failure (HF) patients with chronic kidney disease (CKD); however, it is challenging because no reliable marker of volume status exists. Fractional excretion of urea nitrogen (FEUN) is a useful index of volume status in patients with renal failure. We aimed to examine whether FEUN is a surrogate marker of volume status for risk stratification in HF patients with CKD.

METHODS AND RESULTS

We examined 516 HF patients with CKD (defined as discharge estimated glomerular filtration rate < 60 mL/min/1.73 m² ) whose FEUN was measured at discharge (median age, 80 years; 58% male). The patients were divided into four groups according to quartile FEUN value at discharge: low-FEUN, FEUN ≤ 32.1; medium-FEUN, 32.1 < FEUN ≤ 38.0; high-FEUN, 38.0 < FEUN ≤ 43.7; and extremely-high-FEUN, FEUN > 43.7. FEUN was calculated by the following formula: (urinary urea × serum creatinine) × 100/(serum urea × urinary creatinine). During the 3 year follow-up, 131 HF readmissions occurred. Kaplan-Meier analysis showed that the HF readmission rate was significantly lower in the medium-FEUN group than in the other three groups (log-rank test, P = 0.029). Multivariate Cox regression analysis identified the low-FEUN, high-FEUN, and extremely-high-FEUN values as independent factors associated with post-discharge HF readmission. In the analysis of 130 patients who underwent right heart catheterization during hospitalization, a significant correlation between FEUN value and right atrial pressure was observed (R = 0.243, P = 0.005). Multivariate linear regression analysis revealed that FEUN value at discharge decreased in a dose-dependent manner with loop diuretics.

CONCLUSIONS

In HF patients with CKD, FEUN is a potential marker of volume status for risk stratification of post-discharge HF readmission. Low FEUN value (FEUN ≤ 32.1) may represent intravascular dehydration, whereas high FEUN value (FEUN > 38.0) may represent residual congestion; both of them were independent risk factors for HF readmission. FEUN may be useful to determine euvolaemia and guide fluid management in HF patients with CKD.

Fibrosis imaging with multiparametric proton and sodium MRI in pig injury models

Chronic kidney disease (CKD) is common and has huge implications for health and mortality. It is aggravated by intrarenal fibrosis, but the assessment of fibrosis is limited to kidney biopsies, which carry a risk of complications and sampling errors. This calls for a noninvasive modality for diagnosing and staging intrarenal fibrosis. The current, exploratory study evaluates a multiparametric MRI protocol including sodium imaging (²³ Na-MRI) to determine the opportunities within this modality to assess kidney injury as a surrogate endpoint of fibrosis. The study includes 43 pigs exposed to ischemia-reperfusion injury (IRI) or unilateral ureteral obstruction (UUO), or serving as healthy controls. Fibrosis was determined using gene expression analysis of collagen. The medulla/cortex ratio of ²³ Na-MRI decreased in the injured kidney in the IRI pigs, but not in the UUO pigs (p = 0.0180, p = 0.0754). To assess the combination of MRI parameters in estimating fibrosis, we created a linear regression model consisting of the cortical apparent diffusion coefficient, ΔR2*, ΔT1, the ²³ Na medulla/cortex ratio, and plasma creatinine (R²  = 0.8009, p = 0.0117). The ²³ Na medulla/cortex ratio only slightly improved the fibrosis prediction model, leaving ²³ Na-MRI in an ambiguous place for evaluation of intrarenal fibrosis. Use of multiparametric MRI in combination with plasma creatinine shows potential for the estimation of fibrosis in human kidney disease, but more translational and clinical work is warranted before MRI can contribute to earlier diagnosis and evaluation of treatment for acute kidney injury and CKD.

The nuclear factor of activated T cells 5 (NFAT5) contributes to the renal corticomedullary differences in gene expression

The corticomedullary osmotic gradient between renal cortex and medulla induces a specific spatial gene expression pattern. The factors that controls these differences are not fully addressed. Adaptation to hypertonic environment is mediated by the actions of the nuclear factor of activated T-cells 5 (NFAT5). NFAT5 induces the expression of genes that lead to intracellular accumulation of organic osmolytes. However, a systematical analysis of the NFAT5-dependent gene expression in the kidneys was missing. We used primary cultivated inner medullary collecting duct (IMCD) cells from control and NFAT5 deficient mice as well as renal cortex and inner medulla from principal cell specific NFAT5 deficient mice for gene expression profiling. In primary NFAT5 deficient IMCD cells, hyperosmolality induced changes in gene expression were abolished. The majority of the hyperosmolality induced transcripts in primary IMCD culture were determined to have the greatest expression in the inner medulla. Loss of NFAT5 altered the expression of more than 3000 genes in the renal cortex and more than 5000 genes in the inner medulla. Gene enrichment analysis indicated that loss of NFAT5 is associated with renal inflammation and increased expression of kidney injury marker genes, like lipocalin-2 or kidney injury molecule-1. In conclusion we show that NFAT5 is a master regulator of gene expression in the kidney collecting duct and in vivo loss of NFAT function induces a kidney injury like phenotype.

Langerhans Cell Histiocytosis Manifests with Acute Severe Hypernatremia during Hospitalization

Central diabetes insipidus (DI) is characterized by a deficiency in arginine vasopressin (AVP), an antidiuretic hormone leading to excessive free water loss in the urine and hypernatremia. Central DI can be the first presentation of several occult diseases. However, patients with central DI who have functioning thirst mechanisms and access to water may initially exhibit normal sodium levels. We report a 57-year-old woman who was admitted to the hospital due to cholangitis. Her initial serum sodium was normal and she rapidly developed severe hypernatremia after fluid restriction. The results of the laboratory workup indicated DI, which dramatically responded to desmopressin. MRI showed an ill-defined faint hyper signal intensity in T1, T2/FLAIR lesions involving the bilateral hypothalamus. The histopathological findings confirmed the diagnosis of Langerhans cell histiocytosis (LCH) with multiorgan involvement. Serum sodium returned to normal after receiving desmopressin and water replacement therapy.

A critical analysis of urea transporter B inhibitors: molecular fingerprints, pharmacophore features for the development of next-generation diuretics

Urea transporter is a membrane transport protein. It is involved in the transferring of urea across the cell membrane in humans. Along with urea transporter A, urea transporter B (UT-B) is also responsible for the management of urea concentration and blood pressure of human. The inhibitors of urea transporters have already generated a huge attention to be developed as alternate safe class of diuretic. Unlike conventional diuretics, these inhibitors are suitable for long-term therapy without hampering the precious electrolyte imbalance in the human body. In this study, UT-B inhibitors were analysed by using multi-chemometric modelling approaches. The possible pharmacophore features along with favourable and unfavourable sub-structural fingerprints for UT-B inhibition are extracted. This information will guide the medicinal chemist to design potent UT-B inhibitors in future.

Urinary sodium excretion is low prior to acute kidney injury in patients in the intensive care unit

Background

The incidence of acute kidney injury (AKI) is high in intensive care units (ICUs), and a better understanding of AKI is needed. Early chronic kidney disease is associated with urinary concentration inability and AKI recovery with increased urinary solutes in humans. Whether the inability of the kidneys to concentrate urine and excrete solutes at appropriate levels could occur prior to the diagnosis of AKI is still uncertain, and the associated mechanisms have not been studied.

Methods

In this single-center prospective observational study, high AKI risk in ICU patients was followed up for 7 days or until ICU discharge. They were grouped as "AKI" or "No AKI" according to their AKI status throughout admission. We collected daily urine samples to measure solute concentrations and osmolality. Data were analyzed 1 day before AKI, or from the first to the fifth day of admission in the "No AKI" group. We used logistic regression models to evaluate the influence of the variables on future AKI diagnosis. The expression of kidney transporters in urine was evaluated by Western blotting.

Results

We identified 29 patients as "No AKI" and 23 patients as "AKI," the latter being mostly low severity AKI. Urinary sodium excretion was lower in "AKI" patients prior to AKI diagnosis, particularly in septic patients. The expression of Na+/H+ exchanger (NHE3), a urinary sodium transporter, was higher in "AKI" patients.

Conclusions

Urinary sodium excretion is low before an AKI episode in ICU patients, and high expressions of proximal tubule sodium transporters might contribute to this.

Holistic care of patients with diabetic foot ulcers during the COVID-19 era: integration of Henderson's Need Theory

The COVID-19 pandemic has inhibited the practice of diabetic foot ulcer care, particularly in the community. Comprehensive theory-based nursing care is needed to prevent further complications. Unfortunately, a study combining theory with nursing care in diabetic foot ulcer care has not been explored. When caring for patients with diabetic foot ulcers, who are also at increased risk of severe complications from COVID-19, it is important to take a holistic view of the patient and consider all of their needs and the factors affecting them. Henderson's Need Theory and the 14 basic needs contained within it was chosen to be integrated in the care of patients with diabetic foot ulcers during the pandemic, with the hope that the findings will help nurses to optimise care in both hospital-based and community practice.

Renal Deletion of LRRC8/VRAC Channels Induces Proximal Tubulopathy

BACKGROUND

Volume-regulated anion channels (VRACs) are heterohexamers of LRRC8A with LRRC8B, -C, -D, or -E in various combinations. Depending on the subunit composition, these swelling-activated channels conduct chloride, amino acids, organic osmolytes, and drugs. Despite VRACs' role in cell volume regulation, and large osmolarity changes in the kidney, neither the localization nor the function of VRACs in the kidney is known.

METHODS

Mice expressing epitope-tagged LRRC8 subunits were used to determine the renal localization of all VRAC subunits. Mice carrying constitutive deletions of Lrrc8b-e, or with inducible or cell-specific ablation of Lrrc8a, were analyzed to assess renal functions of VRACs. Analysis included histology, urine and serum parameters in different diuresis states, and metabolomics.

RESULTS

The kidney expresses all five VRAC subunits with strikingly distinct localization. Whereas LRRC8C is exclusively found in vascular endothelium, all other subunits are found in the nephron. LRRC8E is specific for intercalated cells, whereas LRRC8A, LRRC8B, and LRRC8D are prominent in basolateral membranes of proximal tubules. Conditional deletion of LRRC8A in proximal but not distal tubules and constitutive deletion of LRRC8D cause proximal tubular injury, increased diuresis, and mild Fanconi-like symptoms.

CONCLUSIONS

VRAC/LRRC8 channels are crucial for the function and integrity of proximal tubules, but not for more distal nephron segments despite their larger need for volume regulation. LRRC8A/D channels may be required for the basolateral exit of many organic compounds, including cellular metabolites, in proximal tubules. Proximal tubular injury likely results from combined accumulation of several transported molecules in the absence of VRAC channels.

Potential Influence of Age and Diabetes Mellitus Type 1 on MSH2 (MutS homolog 2) Expression in a Rat Kidney Tissue

Background: Homeostasis of proliferating tissues is strongly dependent on intact DNA. Both neoplastic and non-neoplastic diseases have been associated with MSH2 (MutS homolog 2, a mismatch repair protein) deficiency. In this study, we examined how age and diabetes mellitus influence the expression of MSH2 in the kidney. Methods: To study the effect of age, three groups of healthy rats were formed: 2 months, 8 months, and 14 months old. Two groups of diabetic rats were formed: 8 months old and 14 months old. Expression of MSH2 in the kidney was studied by quantifying immunofluorescent staining. Results: Age was identified as the main factor that influences MSH2 expression in kidneys. The effect of age followed parabolic dynamics, with peak expression at 8 months of age and similar levels at 2 and 14 months. Diabetes had an age-dependent effect, which manifested as the increase of MSH2 expression in 14-month-old diabetic rats in comparison to healthy animals. Conclusions: Age influences MSH2 expression in the kidney more than diabetes mellitus. Since ageing is a risk factor for kidney neoplasia, downregulation of MSH2 in older rats might represent one of the pro-oncogenic mechanisms of ageing at a molecular level.

Coughing Can Be Modulated by the Hydration Status in Adolescents with Asthma

A lower thirst sensitivity frequently characterizes children and adolescents. The daily water intake can be frequently insufficient for the homeostasis and the integrity of their airway epithelium. Little is known about the real-life relationship between dehydration and coughing in young students with asthma. The aim was to investigate the effect of dehydration on coughing in asthmatic students aged ≤16 years. A validated questionnaire aimed to investigate their respiratory history and cough incidence was used. Urine samples were also collected for assessing osmolality. Wilcoxon test, the Pearson Chi Square and the Fisher Exact Test were used; p < 0.05 was assumed as significant. Valid data were obtained from 305 healthy and 56 asthmatic students. Mean urine osmolality was significantly higher in asthmatic than in healthy students (1012 ± 197.7 vs. 863.0 ± 223.0 mOsm/kg, respectively; p < 0.001), particularly in symptomatic asthmatic students (1025 ± 191.6 mOsm/kg, p < 0.01). Both the incidence and duration of coughing episodes were directly related to the degree of urine osmolality (both p < 0.001). Dehydration affects the prevalence and the duration of a cough in asthmatic students aged ≤16 years. Adequate daily water intake should be stimulated in these subjects in order to contain their basic cough attitude.

Kidney Microcirculation as a Target for Innovative Therapies in AKI

Acute kidney injury (AKI) is a serious multifactorial conditions accompanied by the loss of function and damage. The renal microcirculation plays a crucial role in maintaining the kidney’s functional and structural integrity for oxygen and nutrient supply and waste product removal. However, alterations in microcirculation and oxygenation due to renal perfusion defects, hypoxia, renal tubular, and endothelial damage can result in AKI and the loss of renal function regardless of systemic hemodynamic changes. The unique structural organization of the renal microvasculature and the presence of autoregulation make it difficult to understand the mechanisms and the occurrence of AKI following disorders such as septic, hemorrhagic, or cardiogenic shock; ischemia/reperfusion; chronic heart failure; cardiorenal syndrome; and hemodilution. In this review, we describe the organization of microcirculation, autoregulation, and pathophysiological alterations leading to AKI. We then suggest innovative therapies focused on the protection of the renal microcirculation and oxygenation to prevent AKI.

A meta-analytical evaluation of the effects of high-salt water intake on beef cattle

Adequate drinking water is essential to maintain acceptable production levels in beef cattle operations. In the context of global climate change, the water scarcity forecasted for the future is a growing concern and it would determine an increase in the use of poorer quality water by the agricultural sector in many parts of the world. However, consumption of high-salt water by cattle has consequences often overlooked. A meta-analysis was carried out to assess the impact of utilizing high-salt water on dry matter (DMI) and water intake (WI), and performance in beef cattle. The dataset was collected from 25 studies, which were conducted between 1960 and 2020. Within the dataset, the water quality was divided into three categories according to the ratio of sulfates (SO4) or sodium chloride (NaCl) to total dissolved solids (TDS): 1) TDS = all studies included (average SO4:TDS = 0.4); 2) NaCl = considered studies in which water salinity was dominated by NaCl (average SO4:TDS = 0.1); and 3) SO4 = considered studies in which water salinity was dominated by SO4 (average SO4:TDS = 0.8). Results showed that DMI and WI were negatively affected by high-salt water consumption, although the magnitude of the effect is dependent on the type of salt dissolved in the water. There was a quadratic effect (P < 0.01) for the WI vs. TDS, WI vs. NaCl, DMI vs. TDS, and DMI vs. NaCl, and a linear effect (P < 0.01) for WI vs. SO4 and WI vs. SO4. Average daily gain (ADG) and feed efficiency (FE) were quadratically (P < 0.01) affected by high-salt water, respectively. This study revealed significant negative effects of high-salt water drinking on beef cattle WI, DMI, and performance. However, the negative effects are exacerbated when cattle drink high-sulfate water when compared with high-chloride water. To the best of our knowledge, this is the first approach to evaluate animal response to high-salt water consumption and could be included in the development of future beef cattle models to account for the impact of water quality on intake and performance. In addition, this meta-analysis highlights the need for research on management strategies to mitigate the negative effects of high-salt water in cattle.

Prognostic Value of Fractional Excretion of Urea Nitrogen at Discharge in Acute Decompensated Heart Failure

Background

Maintaining euvolemia is crucial for improving prognosis in acute decompensated heart failure (ADHF). Although fractional excretion of urea nitrogen (FEUN) is used as a body fluid volume index in patients with acute kidney injury, the clinical impact of FEUN in patients with ADHF remains unclear. This study aimed to investigate whether FEUN can determine the long‐term prognosis in patients with ADHF.

Methods and Results

We retrospectively identified 466 patients with ADHF who had FEUN measured at discharge between April 2011 and December 2018. The primary endpoint was post‐discharge all‐cause death. Patients were divided into two groups according to a FEUN cut‐off value of 35%, commonly used in pre‐renal failure. The FEUN <35% (low‐FEUN) group included 224 patients (48.1%), and the all‐cause mortality rate for the total cohort was 37.1%. The log‐rank test revealed that the low‐FEUN group had a significantly higher rate of all‐cause death compared to the FEUN equal to or greater than 35% (high‐FEUN) group (P<0.001). Multivariate Cox proportional hazards model analysis revealed that low‐FEUN was associated with post‐discharge all‐cause death, independently of other heart failure risk factors (hazard ratio, 1.467; 95% CI, 1.030–2.088, P=0.033). The risk of low‐FEUN compared to high‐FEUN in post‐discharge all‐cause death was consistent across all subgroups; however, the effects tended to be modified by renal function (threshold: 60 mL/min/1.73 m², interaction P=0.069).

Conclusions

Our study suggests that FEUN may be a novel surrogate marker of volume status in patients with ADHF requiring diuretics.

Hydration Marker Diagnostic Accuracy to Identify Mild Intracellular and Extracellular Dehydration

Identifying mild dehydration (≤2% of body mass) is important to prevent the negative effects of more severe dehydration on human health and performance. It is unknown whether a single hydration marker can identify both mild intracellular dehydration (ID) and extracellular dehydration (ED) with adequate diagnostic accuracy (≥0.7 receiver-operating characteristic-area under the curve [ROC-AUC]). Thus, in 15 young healthy men, the authors determined the diagnostic accuracy of 15 hydration markers after three randomized 48-hr trials; euhydration (water 36 ml·kg-1·day-1), ID caused by exercise and 48 hr of fluid restriction (water 2 ml·kg-1·day-1), and ED caused by a 4-hr diuretic-induced diuresis begun at 44 hr (Furosemide 0.65 mg/kg). Body mass was maintained on euhydration, and dehydration was mild on ID and ED (1.9% [0.5%] and 2.0% [0.3%] of body mass, respectively). Urine color, urine specific gravity, plasma osmolality, saliva flow rate, saliva osmolality, heart rate variability, and dry mouth identified ID (ROC-AUC; range 0.70-0.99), and postural heart rate change identified ED (ROC-AUC 0.82). Thirst 0-9 scale (ROC-AUC 0.97 and 0.78 for ID and ED) and urine osmolality (ROC-AUC 0.99 and 0.81 for ID and ED) identified both dehydration types. However, only the thirst 0-9 scale had a common dehydration threshold (≥4; sensitivity and specificity of 100%; 87% and 71%, 87% for ID and ED). In conclusion, using a common dehydration threshold ≥4, the thirst 0-9 scale identified mild intracellular and ED with adequate diagnostic accuracy. In young healthy adults', thirst 0-9 scale is a valid and practical dehydration screening tool.

Multiomic analysis of the Arabian camel (Camelus dromedarius) kidney reveals a role for cholesterol in water conservation

The Arabian camel (Camelus dromedarius) is the most important livestock animal in arid and semi-arid regions and provides basic necessities to millions of people. In the current context of climate change, there is renewed interest in the mechanisms that enable camelids to survive in arid conditions. Recent investigations described genomic signatures revealing evolutionary adaptations to desert environments. We now present a comprehensive catalogue of the transcriptomes and proteomes of the dromedary kidney and describe how gene expression is modulated as a consequence of chronic dehydration and acute rehydration. Our analyses suggested an enrichment of the cholesterol biosynthetic process and an overrepresentation of categories related to ion transport. Thus, we further validated differentially expressed genes with known roles in water conservation which are affected by changes in cholesterol levels. Our datasets suggest that suppression of cholesterol biosynthesis may facilitate water retention in the kidney by indirectly facilitating the AQP2-mediated water reabsorption.

Paper spray ionization-high-resolution mass spectrometry (PSI-HRMS) of peroxide explosives in biological matrices

Mitigation of the peroxide explosive threat, specifically triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD), is a priority among the law enforcement community, as scientists and canine (K9) units are constantly working to improve detection. We propose the use of paper spray ionization-high-resolution mass spectrometry (PSI-HRMS) for detection of peroxide explosives in biological matrices. Occurrence of peroxide explosives and/or their metabolites in biological samples, obtained from urine or blood tests, give scientific evidence of peroxide explosives exposure. PSI-HRMS promote analysis of samples in situ by eliminating laborious sample preparation steps. However, it increases matrix background issues, which were overcome by the formation of multiple alkali metal adducts with the peroxide explosives. Multiple ion formation increases confidence when identifying these peroxide explosives in direct sample analysis. Our previous work examined aspects of TATP metabolism. Herein, we investigate the excretion of a TATP glucuronide conjugate in the urine of bomb-sniffing dogs and demonstrate its detection using PSI from the in vivo sample.

Kidney Single-cell Transcriptomes Predict Spatial Corticomedullary Gene Expression and Tissue Osmolality Gradients

BACKGROUND

Single-cell transcriptomes from dissociated tissues provide insights into cell types and their gene expression and may harbor additional information on spatial position and the local microenvironment. The kidney's cells are embedded into a gradient of increasing tissue osmolality from the cortex to the medulla, which may alter their transcriptomes and provide cues for spatial reconstruction.

METHODS

Single-cell or single-nuclei mRNA sequencing of dissociated mouse kidneys and of dissected cortex, outer, and inner medulla, to represent the corticomedullary axis, was performed. Computational approaches predicted the spatial ordering of cells along the corticomedullary axis and quantitated expression levels of osmo-responsive genes. In situ hybridization validated computational predictions of spatial gene-expression patterns. The strategy was used to compare single-cell transcriptomes from wild-type mice to those of mice with a collecting duct-specific knockout of the transcription factor grainyhead-like 2 (Grhl2^CD-/-), which display reduced renal medullary osmolality.

RESULTS

Single-cell transcriptomics from dissociated kidneys provided sufficient information to approximately reconstruct the spatial position of kidney tubule cells and to predict corticomedullary gene expression. Spatial gene expression in the kidney changes gradually and osmo-responsive genes follow the physiologic corticomedullary gradient of tissue osmolality. Single-nuclei transcriptomes from Grhl2^CD-/- mice indicated a flattened expression gradient of osmo-responsive genes compared with control mice, consistent with their physiologic phenotype.

CONCLUSIONS

Single-cell transcriptomics from dissociated kidneys facilitated the prediction of spatial gene expression along the corticomedullary axis and quantitation of osmotically regulated genes, allowing the prediction of a physiologic phenotype.

Verification of UriSed 3 PRO automated urine microscope in regional laboratory environment

BACKGROUND AND AIMS

Ten UriSed 3 PRO automated microscopes (77 Elektronika, Hungary) were verified for nine HUSLAB laboratories with 160 000 annual urine samples.

MATERIALS AND METHODS

Particle counting of the primary UriSed 3 PRO instrument (77 Elektronika, Hungary) was verified against reference visual microscopy with 463 urine specimens, and against urine culture on chromogenic agar plates with parallel 396 specimens. Nine secondary instruments were compared pairwise with the primary instrument.

RESULTS

Relative imprecisions compared to Poisson distribution, R(CV), were estimated to be 1.0 for white blood cell (WBC) and 1.5 for red blood cell (RBC) counts, respectively. Spearman's correlations against visual microscopy were r_S = 0.94 for WBC, r_S = 0.87 for RBC, and r_S = 0.82 for squamous epithelial cell (SEC) counts. Agreement with visual microscopy (Cohen's weighted kappa) was 0.94 for WBC, 0.89 for RBC, 0.88 for SEC, 0.59 for combined casts, and 0.49 for non-squamous epithelial cells (NEC). Bacteria were detected with a sensitivity of 90% and specificity of 39 against culture at 10⁷ CFB/L (10⁴ CFU/mL). Created flagging limits allowed automated reporting for 70-75% of patient results.

CONCLUSIONS

UriSed 3 PRO instruments were adopted into routine use after acceptance of the verification.

Phenotypic diversity and metabolic specialization of renal endothelial cells

Complex multicellular life in mammals relies on functional cooperation of different organs for the survival of the whole organism. The kidneys play a critical part in this process through the maintenance of fluid volume and composition homeostasis, which enables other organs to fulfil their tasks. The renal endothelium exhibits phenotypic and molecular traits that distinguish it from endothelia of other organs. Moreover, the adult kidney vasculature comprises diverse populations of mostly quiescent, but not metabolically inactive, endothelial cells (ECs) that reside within the kidney glomeruli, cortex and medulla. Each of these populations supports specific functions, for example, in the filtration of blood plasma, the reabsorption and secretion of water and solutes, and the concentration of urine. Transcriptional profiling of these diverse EC populations suggests they have adapted to local microenvironmental conditions (hypoxia, shear stress, hyperosmolarity), enabling them to support kidney functions. Exposure of ECs to microenvironment-derived angiogenic factors affects their metabolism, and sustains kidney development and homeostasis, whereas EC-derived angiocrine factors preserve distinct microenvironment niches. In the context of kidney disease, renal ECs show alteration in their metabolism and phenotype in response to pathological changes in the local microenvironment, further promoting kidney dysfunction. Understanding the diversity and specialization of kidney ECs could provide new avenues for the treatment of kidney diseases and kidney regeneration.

Purinergic signaling is enhanced in the absence of UT-A1 and UT-A3

ATP is an important paracrine regulator of renal tubular water and urea transport. The activity of P2Y2 , the predominant P2Y receptor of the medullary collecting duct, is mediated by ATP, and modulates urinary concentration. To investigate the role of purinergic signaling in the absence of urea transport in the collecting duct, we studied wild-type (WT) and UT-A1/A3 null (UT-A1/A3 KO) mice in metabolic cages to monitor urine output, and collected tissue samples for analysis. We confirmed that UT-A1/A3 KO mice are polyuric, and concurrently observed lower levels of urinary cAMP as compared to WT, despite elevated serum vasopressin (AVP) levels. Because P2Y2 inhibits AVP-stimulated transport by dampening cAMP synthesis, we suspected that, similar to other models of AVP-resistant polyuria, purinergic signaling is increased in UT-A1/A3 KO mice. In fact, we observed that both urinary ATP and purinergic-mediated prostanoid (PGE2 ) levels were elevated. Collectively, our data suggest that the reduction of medullary osmolality due to the lack of UT-A1 and UT-A3 induces an AVP-resistant polyuria that is possibly exacerbated by, or at least correlated with, enhanced purinergic signaling.

Organ protection by SGLT2 inhibitors: role of metabolic energy and water conservation

Therapeutic inhibition of the sodium-glucose co-transporter 2 (SGLT2) leads to substantial loss of energy (in the form of glucose) and additional solutes (in the form of Na⁺ and its accompanying anions) in urine. However, despite the continuously elevated solute excretion, long-term osmotic diuresis does not occur in humans with SGLT2 inhibition. Rather, patients on SGLT2 inhibitor therapy adjust to the reduction in energy availability and conserve water. The metabolic adaptations that are induced by SGLT2 inhibition are similar to those observed in aestivation - an evolutionarily conserved survival strategy that enables physiological adaptation to energy and water shortage. Aestivators exploit amino acids from muscle to produce glucose and fatty acid fuels. This endogenous energy supply chain is coupled with nitrogen transfer for organic osmolyte production, which allows parallel water conservation. Moreover, this process is often accompanied by a reduction in metabolic rate. By comparing aestivation metabolism with the fuel switches that occur during therapeutic SGLT2 inhibition, we suggest that SGLT2 inhibitors induce aestivation-like metabolic patterns, which may contribute to the improvements in cardiac and renal function observed with this class of therapeutics.

Water transport mediated by murine urea transporters: implications for urine concentration mechanisms

Urea transporters (UTs) facilitate urea diffusion across cell membranes and play an important role in the urinary concentration mechanisms in the kidney. Herein, we injected cRNAs encoding for c-Myc-tagged murine UT-B, UT-A2 or UT-A3 (versus water-injected control) in Lithobates oocytes and evaluated oocyte surface protein expression with biotinylation and immunoblotting, urea uptake using [14C] counts and water permeability (P f ) by video microscopy. Immunoblots of UT-injected oocyte membranes revealed bands with a molecular weight consistent with that of a UT monomer (34 kDa), and UT-injected oocytes displayed significantly increased and phloretin-sensitive urea uptake and P f when compared to day-matched control oocytes. Subtracting the water-injected urea uptake or P f values from those of UT-injected oocytes yielded UT-dependent values*. We demonstrate for the first time that UT-A2 and UT-A3 can transport water, and we confirm that UT-B is permeable to water. Moreover, the [14C] urea*/P f * ratios fell in the sequence mUT-B>mUT-A2>mUT-A3, indicating that UTs can exhibit selectivity to urea and/or water. It is likely that specific kidney regions with high levels of UTs will exhibit increased urea and/or water permeabilities, directly influencing urine concentration. Furthermore, UT-mediated water transport activity must be considered when developing UT-inhibitors as novel diuretics.This article has an associated First Person interview with the first author of the paper.

Gut Microbiota and Cardiovascular Disease

Fecal microbial community changes are associated with numerous disease states, including cardiovascular disease (CVD). However, such data are merely associative. A causal contribution for gut microbiota in CVD has been further supported by a multitude of more direct experimental evidence. Indeed, gut microbiota transplantation studies, specific gut microbiota-dependent pathways, and downstream metabolites have all been shown to influence host metabolism and CVD, sometimes through specific identified host receptors. Multiple metaorganismal pathways (involving both microbe and host) both impact CVD in animal models and show striking clinical associations in human studies. For example, trimethylamine N-oxide and, more recently, phenylacetylglutamine are gut microbiota-dependent metabolites whose blood levels are associated with incident CVD risks in large-scale clinical studies. Importantly, a causal link to CVD for these and other specific gut microbial metabolites/pathways has been shown through numerous mechanistic animal model studies. Phenylacetylglutamine, for example, was recently shown to promote adverse cardiovascular phenotypes in the host via interaction with multiple ARs (adrenergic receptors)-a class of key receptors that regulate cardiovascular homeostasis. In this review, we summarize recent advances of microbiome research in CVD and related cardiometabolic phenotypes that have helped to move the field forward from associative to causative results. We focus on microbiota and metaorganismal compounds/pathways, with specific attention paid to short-chain fatty acids, secondary bile acids, trimethylamine N-oxide, and phenylacetylglutamine. We also discuss novel therapeutic strategies for directly targeting the gut microbiome to improve cardiovascular outcomes.

DHHC7-mediated palmitoylation of the accessory protein barttin critically regulates the functions of ClC-K chloride channels

Barttin is the accessory subunit of the human ClC-K chloride channels, which are expressed in both the kidney and inner ear. Barttin promotes trafficking of the complex it forms with ClC-K to the plasma membrane and is involved in activating this channel. Barttin undergoes post-translational palmitoylation that is essential for its functions, but the enzyme(s) catalyzing this post-translational modification is unknown. Here, we identified zinc finger DHHC-type containing 7 (DHHC7) protein as an important barttin palmitoyl acyltransferase, whose depletion affected barttin palmitoylation and ClC-K-barttin channel activation. We investigated the functional role of barttin palmitoylation in vivo in Zdhhc7 ^-/- mice. Although palmitoylation of barttin in kidneys of Zdhhc7 ^-/- animals was significantly decreased, it did not pathologically alter kidney structure and functions under physiological conditions. However, when Zdhhc7 ^-/- mice were fed a low-salt diet, they developed hyponatremia and mild metabolic alkalosis, symptoms characteristic of human Bartter syndrome (BS) type IV. Of note, we also observed decreased palmitoylation of the disease-causing R8L barttin variant associated with human BS type IV. Our results indicate that dysregulated DHHC7-mediated barttin palmitoylation appears to play an important role in chloride channel dysfunction in certain BS variants, suggesting that targeting DHHC7 activity may offer a potential therapeutic strategy for reducing hypertension.

Medullary and cortical thick ascending limb: similarities and differences

The thick ascending limb of the loop of Henle (TAL) is the first segment of the distal nephron, extending through the whole outer medulla and cortex, two regions with different composition of the peritubular environment. The TAL plays a critical role in the control of NaCl, water, acid, and divalent cation homeostasis, as illustrated by the consequences of the various monogenic diseases that affect the TAL. It delivers tubular fluid to the distal convoluted tubule and thereby affects the function of the downstream tubular segments. The TAL is commonly considered as a whole. However, many structural and functional differences exist between its medullary and cortical parts. The present review summarizes the available data regarding the similarities and differences between the medullary and cortical parts of the TAL. Both subsegments reabsorb NaCl and have high Na+-K+-ATPase activity and negligible water permeability; however, they express distinct isoforms of the Na+-K+-2Cl−cotransporter at the apical membrane. Ammonia and bicarbonate are mostly reabsorbed in the medullary TAL, whereas Ca2+and Mg2+are mostly reabsorbed in the cortical TAL. The peptidic hormone receptors controlling transport in the TAL are not homogeneously expressed along the cortical and medullary TAL. Besides this axial heterogeneity, structural and functional differences are also apparent between species, which underscores the link between properties and role of the TAL under various environments.

Single-Cell RNA Sequencing Reveals Renal Endothelium Heterogeneity and Metabolic Adaptation to Water Deprivation

BACKGROUND

Renal endothelial cells from glomerular, cortical, and medullary kidney compartments are exposed to different microenvironmental conditions and support specific kidney processes. However, the heterogeneous phenotypes of these cells remain incompletely inventoried. Osmotic homeostasis is vitally important for regulating cell volume and function, and in mammals, osmotic equilibrium is regulated through the countercurrent system in the renal medulla, where water exchange through endothelium occurs against an osmotic pressure gradient. Dehydration exposes medullary renal endothelial cells to extreme hyperosmolarity, and how these cells adapt to and survive in this hypertonic milieu is unknown.

METHODS

We inventoried renal endothelial cell heterogeneity by single-cell RNA sequencing >40,000 mouse renal endothelial cells, and studied transcriptome changes during osmotic adaptation upon water deprivation. We validated our findings by immunostaining and functionally by targeting oxidative phosphorylation in a hyperosmolarity model in vitro and in dehydrated mice in vivo.

RESULTS

We identified 24 renal endothelial cell phenotypes (of which eight were novel), highlighting extensive heterogeneity of these cells between and within the cortex, glomeruli, and medulla. In response to dehydration and hypertonicity, medullary renal endothelial cells upregulated the expression of genes involved in the hypoxia response, glycolysis, and-surprisingly-oxidative phosphorylation. Endothelial cells increased oxygen consumption when exposed to hyperosmolarity, whereas blocking oxidative phosphorylation compromised endothelial cell viability during hyperosmotic stress and impaired urine concentration during dehydration.

CONCLUSIONS

This study provides a high-resolution atlas of the renal endothelium and highlights extensive renal endothelial cell phenotypic heterogeneity, as well as a previously unrecognized role of oxidative phosphorylation in the metabolic adaptation of medullary renal endothelial cells to water deprivation.

Claudin 19 Is Regulated by Extracellular Osmolality in Rat Kidney Inner Medullary Collecting Duct Cells

The inner medullary collecting duct (IMCD) is subject to severe changes in ambient osmolality and must either allow water transport or be able to seal the lumen against a very high osmotic pressure. We postulate that the tight junction protein claudin-19 is expressed in IMCD and that it takes part in epithelial adaptation to changing osmolality at different functional states. Presence of claudin-19 in rat IMCD was investigated by Western blotting and immunofluorescence. Primary cell culture of rat IMCD cells on permeable filter supports was performed under different osmotic culture conditions and after stimulation by antidiuretic hormone (AVP). Electrogenic transepithelial transport properties were measured in Ussing chambers. IMCD cells cultivated at 300 mosm/kg showed high transepithelial resistance, a cation selective paracellular pathway and claudin-19 was mainly located in the tight junction. Treatment by AVP increased cation selectivity but did not alter transepithelial resistance or claudin-19 subcellular localization. In contrast, IMCD cells cultivated at 900 mosm/kg had low transepithelial resistance, anion selectivity, and claudin-19 was relocated from the tight junctions to intracellular vesicles. The data shows osmolality-dependent transformation of IMCD epithelium from tight and sodium-transporting to leaky, with claudin-19 expression in the tight junction associated to tightness and cation selectivity under low osmolality.

Regulation of Epithelial Cell Functions by the Osmolality and Hydrostatic Pressure Gradients: A Possible Role of the Tight Junction as a Sensor

Epithelia act as a barrier to the external environment. The extracellular environment constantly changes, and the epithelia are required to regulate their function in accordance with the changes in the environment. It has been reported that a difference of the environment between the apical and basal sides of epithelia such as osmolality and hydrostatic pressure affects various epithelial functions including transepithelial transport, cytoskeleton, and cell proliferation. In this paper, we review the regulation of epithelial functions by the gradients of osmolality and hydrostatic pressure. We also examine the significance of this regulation in pathological conditions especially focusing on the role of the hydrostatic pressure gradient in the pathogenesis of carcinomas. Furthermore, we discuss the mechanism by which epithelia sense the osmotic and hydrostatic pressure gradients and the possible role of the tight junction as a sensor of the extracellular environment to regulate epithelial functions.

Discovery and optimization of thienopyridine derivatives as novel urea transporter inhibitors

Urea transporters (UTs) play an important role in the urine concentrating mechanism and are recognized as novel targets for developing small molecule inhibitors with salt-sparing diuretic activity. Thienoquinoline derivatives, a class of novel UT-B inhibitors identified by our group, play a significant diuresis in animal model. However, the poor solubility and low bioavailability limited its further development. To overcome these shortcomings, the structure modification of thienoquinoline was carried out in this study, which led to the discovery of novel thienopyridine derivatives as specific urea transporter inhibitors. Further optimization obtained the promising preclinical candidate 8n with not only excellent inhibition effect on urea transporters and diuretic activity on rat model, but also suitable water solubility and Log P value.

High-Precision Quantitation of Biofluid Samples Using Direct Mass Spectrometry Analysis

The transition of mass spectrometry for clinical analysis is highly desirable, and major progress has been made with direct sampling ionization for operation simplification. High-precision quantitation, however, remains a major challenge in this transition. Herein, a novel method was developed for direct quantitation of biofluid samples, using an extremely simplified procedure for incorporation of internal standards selected against the traditional rules. Slug flow microextraction was used for the development, with conditions predicted by a theoretical model, viz., using internal standards of partition coefficients very different from the analytes and large sample-to-extraction solvent volume ratios. Direct quantitation of drug compounds in urine and blood samples was demonstrated. This development enabled an extremely simplified protocol that is expected to have a significant impact on on-site or clinical analysis.