Tubular Injury Markers Research Articles

Anti-Renal Fibrosis Effect of Urolithin B, Ellagitannin-Gut Microbial-Derived Metabolites, via TGF-β1/Smad and TLR4/NF-κb Signaling Pathways in a Rat Model of Unilateral Ureteral Obstruction

Background: Urolithin B, gut microbiota metabolite of ellagitannins, contributes toward multiple health benefits attributed to ellagitannin-rich foods, has various bioactivities such as anti-inflammatory and anti-aging effects. This study was to investigate the effect of urolithin B on renal fibrosis and the underlying mechanism. Methods: In vivo, unilateral ureteral obstruction (UUO) model was established with or without urolithin B treatment for three weeks. Then, changes in the kidney function and renal pathology were investigated. In vitro, the HK-2 cells were treated with TGF-β1 (10 ng/ml) for 24 h with or without urolithin B administration. Next cell damage and proliferation was evaluated. Findings: In vivo, after urolithin B treatment, UUO-induced kidney injury was significantly ameliorated as shown by the improvement of renal function (BUN and serum creatinine), kidney morphology and the suppression of renal tubular injury markers of TGF-β1, Ang II, α-SMA and Col IV. Meanwhile, the renal inflammatory induced by UUO were also strikingly attenuated in urolithin B-treated rats (TNF-α, IL-6 and MCP-1). In vitro, urolithin B treatment markedly inhibited TGF-β1-induced HK-2 cells fibrosis and proliferation, suppressed TGF-β1 and NF-κB activation. Interpretation: This works suggested that urolithin B contributes critically to the development of chronic kidney pathologies induced by UUO, and modulating TGF-β/Smad and TLR4/NF-κB signaling possibly represent a potential therapeutic strategy to impede renal fibrosis transition. Funding: This work was supported by a grant from the National Natural Science Foundation of China (no. 31770381). Declaration of Interest: The authors declare that there are no conflicts of interest. Ethical Approval: All animal experiment were approved by the ethics committee of Wu Han University, Wu Han, China, and carried in accordance with National institutes of health guide for the care and use of laboratory animals.

Using Collaborative Cross Mouse Population to Fill Data Gaps in Risk Assessment: A Case Study of Population-Based Analysis of Toxicokinetics and Kidney Toxicodynamics of Tetrachloroethylene.

Background:Interindividual variability in susceptibility remains poorly characterized for environmental chemicals such as tetrachloroethylene (PERC). Development of population-based experimental models provide a potential approach to fill this critical need in human health risk assessment.Objectives:In this study, we aimed to better characterize the contribution of glutathione (GSH) conjugation to kidney toxicity of PERC and the degree of associated interindividual toxicokinetic (TK) and toxicodynamic (TD) variability by using the Collaborative Cross (CC) mouse population.Methods:Male mice from 45 strains were intragastrically dosed with PERC () or vehicle (5% Alkamuls EL-620 in saline), and time-course samples were collected for up to 24 h. Population variability in TK of S-(1,2,2-trichlorovinyl)GSH (TCVG), S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC), and N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine (NAcTCVC) was quantified in serum, liver, and kidney, and analyzed using a toxicokinetic model. Effects of PERC on kidney weight, fatty acid metabolism–associated genes [Acot1 (Acyl-CoA thioesterase 1), Fabp1 (fatty acid-binding protein 1), and Ehhadh (enoyl-coenzyme A, hydratase/3-hydroxyacyl coenzyme A dehydrogenase)], and a marker of proximal tubular injury [KIM-1 (kidney injury molecule-1)/Hepatitis A virus cellular receptor 1 (Havcr1)] were evaluated. Finally, quantitative data on interstrain variability in both formation of GSH conjugation metabolites of PERC and its kidney effects was used to calculate adjustment factors for the interindividual variability in both TK and TD.Results:Mice treated with PERC had significantly lower kidney weight, higher kidney-to-body weight (BW) ratio, and higher expression of fatty acid metabolism–associated genes (Acot1, Fabp1, and Ehhadh) and a marker of proximal tubular injury (KIM-1/Havcr1). Liver levels of TCVG were significantly correlated with KIM-1/Havcr1 in kidney, consistent with kidney injury being associated with GSH conjugation. We found that the default uncertainty factor for human variability may be marginally adequate to protect 95%, but not more, of the population for kidney toxicity mediated by PERC.Discussion:Overall, this study demonstrates the utility of the CC mouse population in characterizing metabolism–toxicity interactions and quantifying interindividual variability. Further refinement of the characterization of interindividual variability can be accomplished by incorporating these data into in silico population models both for TK (such as a physiologically based pharmacokinetic model), as well as for toxicodynamic responses. https://doi.org/10.1289/EHP5105

Renal Effects of Intensive Volume Removal in Heart Failure Patients With Preexisting Worsening Renal Function.

Background The relationship between intensive volume removal in acute decompensated heart failure patients with preexisting worsening renal function (WRF) and renal tubular injury, postdischarge renal function, and clinical outcomes is unknown. Methods and Results We used data from the multicenter CARRESS-HF trial (Cardiorenal Rescue Study in Acute Decompensated Heart Failure) that randomized patients with acute decompensated heart failure and preexisting WRF to intensive volume removal with stepped pharmacological therapy or fixed rate ultrafiltration. Patients in the urinary renal tubular injury biomarker substudy (NAG [N-acetyl-b-D-glucosaminidase], KIM-1 [kidney injury molecule-1], and NGAL [neutrophil gelatinase-associated lipocalin]) were evaluated (N=105). The severity of prerandomization WRF was unrelated to baseline renal tubular injury biomarkers ( r=0.14; P=0.17). During randomized intensive volume removal, creatinine further worsened in 53% of patients. Despite a small to moderate magnitude increase in creatinine in most of these patients, postrandomization WRF was strongly associated with worsening in renal tubular injury biomarkers (odds ratio, 12.6; P=0.004). This observation did not differ by mode of volume removal (stepped pharmacological therapy versus ultrafiltration, Pinteraction=0.46). Increase in renal tubular injury biomarkers was associated with a higher incidence of hemoconcentration (odds ratio, 3.1; P=0.015), and paradoxically, better recovery of creatinine at 60 days ( P=0.01). Conclusions In acute decompensated heart failure patients with preexisting WRF, intensive volume removal resulted in a further worsening of creatinine approximately half of the time, a finding associated with a rise in tubular injury biomarkers. However, decongestion and renal function recovery at 60 days were superior in patients with increased tubular injury markers. These data suggest that the benefits of decongestion may outweigh any modest or transient increases in serum creatinine or tubular injury markers that occur during intensive volume removal. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT00608491.

Neonatal hyperamonemia as a consequence of a defect of the urea cycle

Propionic acidemia (PA) is a severe metabolic disorder characterized by multiorgan pathology, including renal disease. The prevalence of chronic kidney disease (CKD) in PA patients and factors associated with CKD in PA are not known.Thirty-one subjects diagnosed with PA underwent laboratory and clinical evaluations through a dedicated natural history study at the National Institutes of Health (ClinicalTrials.gov identifier: NCT02890342).Cross-sectional analysis of the creatinine-based estimated glomerular filtration rate (eGFR) in subjects with native kidneys revealed an age-dependent decline in renal function (P < 0.002). Among adults with PA, 4/8 (50%) had eGFR <60 mL/min/1.73 m2. There was a significant discrepancy between eGFRs calculated using estimating equations based on serum creatinine compared with serum cystatin C (P < 0.0001). The tubular injury marker, plasma lipocalin-2, and plasma uric acid were strongly associated with CKD (P < 0.0001). The measured 24-hour creatinine excretion was below normal, even after adjusting for age, height, and sex.CKD is common in adults with PA and is associated with age. The poor predictive performance of standard eGFR estimating equations, likely due to reduced creatine synthesis in kidney and liver, could delay the recognition of CKD and management of ensuing complications in this population.

Tubular Injury and Dendritic Cell Activation Are Integral Components of Light Chain-Associated Acute Tubulointerstitial Nephritis.

Light chain-associated acute tubulointerstitial nephritis (LC-ATIN) is a variant of light chain proximal tubulopathy (LCPT). It is characterized by interstitial inflammation with tubulitis and deposition of monoclonal light chains in the tubulointerstitium. LC-ATIN is a rather poorly recognized pattern of LCPT and not much is known about this entity. To determine the clinicopathologic features of patients with LC-ATIN and investigate the proximal tubular injury and mechanism of interstitial inflammation in LC-ATIN. A total of 38 cases of LC-ATIN were identified from the archives of 5043 renal biopsy specimens. In all cases, routine light microscopic examination, immunofluorescence, and electron microscopic examination were performed. In selected cases, immunofluorescent staining of dendritic cells and immunohistochemical staining for 4 tubular injury markers-KIM-1, p53, bcl-2, and Ki-67-were performed. A characteristic finding in LC-ATIN cases was immunofluorescence staining of monoclonal light chains along tubular basement membranes in linear fashion and inside proximal tubular cells with a granular pattern. No monoclonal light chains were present in glomerular or vascular compartments confirmed with immunofluorescence, electron microscopy, and ultrastructural gold labeling. Ten of 15 LC-ATIN cases (67%) were concurrently positive for the 4 tubular injury markers. Dendritic cells were identified within the tubulointerstitium in the renal biopsy specimens, interacting with surrounding tubules with light-chain deposits and inflammatory cells. Significant proximal tubular injury occurs associated with LC-ATIN, and the monoclonal light chains accumulated in proximal tubular cells contribute to the injury. Dendritic cells are involved in the pathogenesis of interstitial inflammation in LC-ATIN.

The SPRINT trial suggests that markers of tubule cell function in the urine associate with risk of subsequent acute kidney injury while injury markers elevate after the injury

Urine markers can quantify tubular function including reabsorption (α-1 microglobulin [α1m]) and β-2-microglobulin [β2m]) and protein synthesis (uromodulin). Individuals with tubular dysfunction may be less able to compensate to insults than those without, despite similar estimated glomerular filtration rate (eGFR) and albuminuria. Among Systolic Blood Pressure Intervention Trial (SPRINT) participants with an eGFR under 60 ml/min/1.73m2, we measured urine markers of tubular function and injury (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule-1 [KIM-1], interleukin-18 [IL-18], monocyte chemoattractant protein-1, and chitinase-3-like protein [YKL-40]) at baseline. Cox models evaluated associations with subsequent acute kidney injury (AKI) risk, adjusting for clinical risk factors, baseline eGFR and albuminuria, and the tubular function and injury markers. In a random subset, we remeasured biomarkers after four years, and compared changes in biomarkers in those with and without intervening AKI. Among 2351 participants, 184 experienced AKI during 3.8 years mean follow-up. Lower uromodulin (hazard ratio per two-fold higher (0.68, 95% confidence interval [0.56, 0.83]) and higher α1m (1.20; [1.01, 1.44]) were associated with subsequent AKI, independent of eGFR and albuminuria. None of the five injury markers were associated with eventual AKI. In the random subset of 947 patients with repeated measurements, the 59 patients with intervening AKI versus without had longitudinal increases in urine NGAL, IL-19, and YKL-40 and only 1 marker of tubule function (α1m). Thus, joint evaluation of tubule function and injury provided novel insights to factors predisposing to AKI, and responses to kidney injury.

Rapid decline of kidney function in diabetic kidney disease is associated with high soluble Klotho levels

BackgroundKlotho is found in two forms: a transmembrane form and a soluble form (s-Klotho). In order to be excreted, s-Klotho, that is too large to be filtered, will probably reach the proximal convoluted tubule by a transcytosis process. The aim of our study was to show the relationship between the levels of s-Klotho and tubular injury in patients with diabetic kidney disease (DKD), using as tubular injury marker the kidney injury molecule-1 (KIM-1). MethodsOur study included 63 DKD patients (stages 1–5, mean eGFR 65.15±32.45ml/min) with a mean age 58.13±12 years. In all patients we determined serum levels of: KIM-1 and s-Klotho using ELISA, urinary albumin/creatinine ratio (UACR) and reduction in the estimated glomerular filtration rate (eGFR) per year. ResultsWe found a strong statistically significant correlation of s-Klotho with the rate of reduction of eGFR/year (r=0.714, p=0.0004) and with the tubular injury marker KIM-1 (r=0.758, p=0.005) and strong correlations of UACR with the rate of reduction of eGFR/year (r=0.53, p<0.01), KIM-1 (r=0.49, p<0.05) and s-Klotho (r=0.52, p<0.01). ConclusionDespite previous published data, that shows a decrease of s-Klotho in chronic kidney disease, in our study the rapid annual decline of kidney function but not the level of eGFR was associated with increased s-Klotho. A possible explanation could be a more severe proximal tubule injury that could lead to a reduction of tubular excretion of s-Klotho as suggested by the correlation of s-Klotho levels with the serum levels of KIM-1.

Gene deletion of the Na+-glucose cotransporter SGLT1 ameliorates kidney recovery in a murine model of acute kidney injury induced by ischemia-reperfusion.

Renal Na+-glucose cotransporter SGLT1 mediates glucose reabsorption in the late proximal tubule, a hypoxia-sensitive tubular segment that enters the outer medulla. Gene deletion in mice (Sglt1-/-) was used to determine the role of the cotransporter in acute kidney injury induced by ischemia-reperfusion (IR), including the initial injury and subsequent recovery phase. On days 1 and 16 after IR, absolute and fractional urinary glucose excretion remained greater in Sglt1-/- mice versus wild-type (WT) littermates, consistent with a sustained contribution of SGLT1 to tubular glucose reabsorption in WT mice. Absence of SGLT1 did not affect the initial kidney impairment versus WT mice, as indicated by similar increases on day 1 in plasma concentrations of creatinine and urinary excretion of the tubular injury marker kidney injury molecule-1 as well as a similar rise in plasma osmolality and fall in urine osmolality as indicators of impaired urine concentration. Recovery of kidney function on days 14/16, however, was improved in Sglt1-/- versus WT mice, as indicated by lower plasma creatinine, higher glomerula filtration rate (by FITC-sinistrin in awake mice), and more completely restored urine and plasma osmolality. This was associated with a reduced tubular injury score in the cortex and outer medulla, better preserved renal mRNA expression of tubular transporters (Sglt2 and Na+-K+-2Cl- cotransporter Nkcc2), and a lesser rise in renal mRNA expression of markers of injury, inflammation, and fibrosis [kidney injury molecule-1, chemokine (C-C motif) ligand 2, fibronectin 1, and collagen type I-α1] in Sglt1-/- versus WT mice. These results suggest that SGLT1 activity in the late proximal tubule may have deleterious effects during recovery of IR-induced acute kidney injury and identify SGLT1 as a potential therapeutic target.

The combination of a neprilysin inhibitor (sacubitril) and angiotensin-II receptor blocker (valsartan) attenuates glomerular and tubular injury in the Zucker Obese rat

ObjectiveDiabetic nephropathy (DN) is characterized by glomerular and tubulointerstitial injury, proteinuria and remodeling. Here we examined whether the combination of an inhibitor of neprilysin (sacubitril), a natriuretic peptide-degrading enzyme, and an angiotensin II type 1 receptor blocker (valsartan), suppresses renal injury in a pre-clinical model of early DN more effectively than valsartan monotherapy.MethodsSixty-four male Zucker Obese rats (ZO) at 16 weeks of age were distributed into 4 different groups: Group 1: saline control (ZOC); Group 2: sacubitril/valsartan (sac/val) (68 mg kg−1 day−1; ZOSV); and Group 3: valsartan (val) (31 mg kg−1 day−1; ZOV). Group 4 received hydralazine, an anti-hypertensive drug (30 mg kg−1 day−1, ZOH). Six Zucker Lean (ZL) rats received saline (Group 5) and served as lean controls (ZLC). Drugs were administered daily for 10 weeks by oral gavage.ResultsMean arterial pressure (MAP) increased in ZOC (+ 28%), but not in ZOSV (− 4.2%), ZOV (− 3.9%) or ZOH (− 3.7%), during the 10 week-study period. ZOC were mildly hyperglycemic, hyperinsulinemic and hypercholesterolemic. ZOC exhibited proteinuria, hyperfiltration, elevated renal resistivity index (RRI), glomerular mesangial expansion and podocyte foot process flattening and effacement, reduced nephrin and podocin expression, tubulointerstitial and periarterial fibrosis, increased NOX2, NOX4 and AT1R expression, glomerular and tubular nitroso-oxidative stress, with associated increases in urinary markers of tubular injury. None of the drugs reduced fasting glucose or HbA1c. Hypercholesterolemia was reduced in ZOSV (− 43%) and ZOV (− 34%) (p < 0.05), but not in ZOH (− 13%) (ZOSV > ZOV > ZOH). Proteinuria was ameliorated in ZOSV (− 47%; p < 0.05) and ZOV (− 30%; p > 0.05), but was exacerbated in ZOH (+ 28%; p > 0.05) (ZOSV > ZOV > ZOH). Compared to ZOC, hyperfiltration was improved in ZOSV (p < 0.05 vs ZOC), but not in ZOV or ZOH. None of the drugs improved RRI. Mesangial expansion was reduced by all 3 treatments (ZOV > ZOSV > ZOH). Importantly, sac/val was more effective in improving podocyte and tubular mitochondrial ultrastructure than val or hydralazine (ZOSV > ZOV > ZOH) and this was associated with increases in nephrin and podocin gene expression in ZOSV (p < 0.05), but not ZOV or ZOH. Periarterial and tubulointerstitial fibrosis and nitroso-oxidative stress were reduced in all 3 treatment groups to a similar extent. Of the eight urinary proximal tubule cell injury markers examined, five were elevated in ZOC (p < 0.05). Clusterin and KIM-1 were reduced in ZOSV (p < 0.05), clusterin alone was reduced in ZOV and no markers were reduced in ZOH (ZOSV > ZOV > ZOH).ConclusionsCompared to val monotherapy, sac/val was more effective in reducing proteinuria, renal ultrastructure and tubular injury in a clinically relevant animal model of early DN. More importantly, these renoprotective effects were independent of improvements in blood pressure, glycemia and nitroso-oxidative stress. These novel findings warrant future clinical investigations designed to test whether sac/val may offer renoprotection in the setting of DN.

Bioinformatics-based discovery of the urinary BBOX1 mRNA as a potential biomarker of diabetic kidney disease

BackgroundDiabetic kidney disease (DKD) is the leading cause of end-stage kidney disease (ESKD) in the world. Emerging evidence has shown that urinary mRNAs may serve as early diagnostic and prognostic biomarkers of DKD. In this article, we aimed to first establish a novel bioinformatics-based methodology for analyzing the “urinary kidney-specific mRNAs” and verify their potential clinical utility in DKD.MethodsTo select candidate mRNAs, a total of 127 Affymetrix microarray datasets of diabetic kidney tissues and other tissues from humans were compiled and analyzed using an integrative bioinformatics approach. Then, the urinary expression of candidate mRNAs in stage 1 study (n = 82) was verified, and the one with best performance moved on to stage 2 study (n = 80) for validation. To avoid potential detection bias, a one-step Taqman PCR assay was developed for quantification of the interested mRNA in stage 2 study. Lastly, the in situ expression of the selected mRNA was further confirmed using fluorescent in situ hybridization (FISH) assay and bioinformatics analysis.ResultsOur bioinformatics analysis identified sixteen mRNAs as candidates, of which urinary BBOX1 (uBBOX1) levels were significantly upregulated in the urine of patients with DKD. The expression of uBBOX1 was also increased in normoalbuminuric diabetes subjects, while remained unchanged in patients with urinary tract infection or bladder cancer. Besides, uBBOX1 levels correlated with glycemic control, albuminuria and urinary tubular injury marker levels. Similar results were obtained in stage 2 study. FISH assay further demonstrated that BBOX1 mRNA was predominantly located in renal tubular epithelial cells, while its expression in podocytes and urothelium was weak. Further bioinformatics analysis also suggested that tubular BBOX1 mRNA expression was quite stable in various types of kidney diseases.ConclusionsOur study provided a novel methodology to identify and analyze urinary kidney-specific mRNAs. uBBOX1 might serve as a promising biomarker of DKD. The performance of the selected urinary mRNAs in monitoring disease progression needs further validation.

Serial assessment of spot urine sodium predicts effectiveness of decongestion and outcome in patients with acute heart failure.

The clinical significance of the measurement of urine sodium concentration (UNa+ ) in response to loop diuretic administration in patients with acute heart failure (AHF) is still unsettled. We studied the association of serial measurements of spot UNa+ during the first 48 h of AHF treatment with the indices of decongestion, renal function, and prognosis. We enrolled 111 AHF patients, all of whom received intravenous furosemide on admission. The mean spot UNa+ significantly increased in the 6 h sample (P< 0.05 vs. baseline) and returned to baseline values in the 24 and 48 h samples. Based on the increase or decrease/no change of UNa+ in the 6 and 48 h samples vs. baseline, patients were divided into two groups at each time point, respectively. Patients did not differ in baseline clinical and laboratory characteristics. Patients with a decrease/no change of UNa+ in the 6 and 48 h samples had a lower weight loss during hospitalization. Patients with a decrease/no change of UNa+ in the 48 h sample had a poorer diuretic response and a significant increase in the urinary levels of the tubular biomarkers: kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin. Low UNa+ and decrease/no change in UNa+ in the 6 and 48 h samples were independent predictors of higher risk of all-cause mortality during 1-year follow-up (all P< 0.05). In AHF, low spot UNa+ and lack to increase UNa+ in response to intravenous diuretics are associated with poor diuretic response, markers of tubular injury and high risk of 1-year mortality.

The Role of Extracellular Phosphate Levels on Kidney Disease Progression in a Podocyte Injury Mouse Model

Background: Hyperphosphatemia is a major accelerator of complications in chronic kidney disease and dialysis, and phosphate (Pi) binders have been shown to regulate extracellular Pi levels. Research on hyperphosphatemia in mouse models is scarce, and few models display hyperphosphatemia induced by glomerular injury, despite its relevance to human glomerular disease conditions. In this study, we investigated the involvement of hyperphosphatemia in kidney disease progression using a mouse model in which hyperphosphatemia is induced by focal segmental glomerulosclerosis (FSGS). Methods: We established the NEP25 mouse model in which FSGS-hyperphosphatemia is induced by podocyte injury and evaluated the effect of a Pi binder, sevelamer. Results: After disease induction, we confirmed a gradual increase in serum Pi accompanied by reduced renal function and observed increases in serum FGF23 and PTH. Treatment with sevelamer significantly reduced serum Pi and urinary Pi fractional excretion and suppressed increases in serum FGF23 and PTH. A high dose improved serum creatinine and tubular injury markers, and pathological analysis confirmed amelioration of glomerular and tubular damage. Gene expression and marker analysis suggested protective effects on tubular epithelial cells in the diseased kidney. Compared to disease control, NEP25 mice treated with sevelamer retained their mRNA expression of Klotho, a known FGF23 co-receptor and renoprotective factor. Conclusions: Hyperphosphatemia caused by renal function decline was observed in a FSGS-induced NEP25 mouse model. Studies using this model showed that Pi regulation had a positive impact on kidney disease progression, and notably on tubular epithelial cell injury, which indicates the importance of Pi regulation in the treatment of kidney disease progression.

Urine markers of renal tubular injury in idiopathic membranous nephropathy: A cross sectional study

IntroductionIdiopathic membranous nephropathy (IMN) is a primary glomerular disease and a major cause of adult nephrotic syndrome. Presently, little is known about the capabilities of the urine markers to reflect the severity of IMN. We aimed at establishing whether urinary N-acetyl-β-glucosaminidase (NAG), Retinol binding protein (RBP), Kidney injury molecule-1 (KIM-1) and Neutrophil gelatianse-associated lipocalin (NGAL) are related with renal parameters and the histological grades tubular injury. MethodsThe levels of urinary NAG, RBP, KIM-1 and NGAL were determined in 165 biopsy-proven patients and 64 healthy controls. Their levels were then compared between patients and healthy subjects, and between patients with and without nephrotic syndrome. Their linearity with renal parameters and associations with histological grades of renal tubular injury were also assessed. ResultsAll biomarkers were significantly increased in patients (p < .001). However, no significant increase was observed between patients exhibiting moderate and severe grades tubular injury and those exhibiting mild histological grade. With exception of RBP, all biomarkers were higher in patients with nephrotic syndrome (p < .001) and significantly correlated with majority of renal parameters including proteinuria. ConclusionOur findings suggest that although urine markers of tubular injury are increased in IMN, they may not offer a reflection of histological grades.

Myofibroblasts acquire retinoic acid–producing ability during fibroblast-to-myofibroblast transition following kidney injury

Tubular injury and interstitial fibrosis are the hallmarks of chronic kidney disease. While recent studies have verified that proximal tubular injury triggers interstitial fibrosis, the impact of fibrosis on tubular injury and regeneration remains poorly understood. We generated a novel mouse model expressing diphtheria toxin receptor on renal fibroblasts to allow for the selective disruption of renal fibroblast function. Administration of diphtheria toxin induced upregulation of the tubular injury marker Ngal and caused tubular proliferation in healthy kidneys, whereas administration of diphtheria toxin attenuated tubular regeneration in fibrotic kidneys. Microarray analysis revealed down-regulation of the retinol biosynthesis pathway in diphtheria toxin-treated kidneys. Healthy proximal tubules expressed retinaldehyde dehydrogenase 2 (RALDH2), a rate-limiting enzyme in retinoic acid biosynthesis. After injury, proximal tubules lost RALDH2 expression, whereas renal fibroblasts acquired strong expression of RALDH2 during the transition to myofibroblasts in several models of kidney injury. The retinoic acid receptor (RAR) RARγ was expressed in proximal tubules both with and without injury, and αB-crystallin, the product of an RAR target gene, was strongly expressed in proximal tubules after injury. Furthermore, BMS493, an inverse agonist of RARs, significantly attenuated tubular proliferation invitro. In human biopsy tissue from patients with IgA nephropathy, detection of RALDH2 in the interstitium correlated with older age and lower kidney function. These results suggest a role of retinoic acid signaling and cross-talk between fibroblasts and tubular epithelial cells during tubular injury and regeneration, and may suggest a beneficial effect of fibrosis in the early response to injury.

Iron handling by the human kidney: glomerular filtration and tubular reabsorption both contribute to urinary iron excretion.

In physiological conditions, circulating iron can be filtered by the glomerulus and is almost completely reabsorbed by the tubular epithelium to prevent urinary iron wasting. Increased urinary iron concentrations have been associated with renal injury. However, it is not clear whether increased urinary iron concentrations in patients are the result of increased glomerular iron filtration and/or insufficient tubular iron reabsorption and if these processes contribute to renal injury. We measured plasma and urine iron parameters and urinary tubular injury markers in healthy human subjects ( n = 20), patients with systemic iron overload ( n = 20), and patients with renal tubular dysfunction ( n = 18). Urinary iron excretion parameters were increased in both patients with systemic iron overload and tubular dysfunction, whereas plasma iron parameters were only increased in patients with systemic iron overload. In patients with systemic iron overload, increased urinary iron levels were associated with elevated circulating iron, as indicated by transferrin saturation (TSAT), and increased body iron, as suggested by plasma ferritin concentrations. In patients with tubular dysfunction, enhanced urinary iron and transferrin excretion were associated with distal tubular injury as indicated by increased urinary glutathione S-transferase pi 1-1 (GSTP1-1) excretion. In systemic iron overload, elevated urinary iron and transferrin levels were associated with increased injury to proximal tubules, indicated by increased urinary kidney injury marker 1 (KIM-1) excretion. Our explorative study demonstrates that both glomerular filtration of elevated plasma iron levels and insufficient tubular iron reabsorption could increase urinary iron excretion and cause renal injury.

Urinary Biomarkers of Renal Fibrosis.

Renal fibrosis is the common pathological pathway of progressive CKD. The commonly used biomarkers in clinical practice are not optimal to detect injury or predict prognosis. Therefore, it is crucial to develop novel biomarkers to allow prompt intervention. Urine serves as a valuable resource of biomarker discovery for kidney diseases. Owing to the rapid development of omics platforms and bioinformatics, research on novel urinary biomarkers for renal fibrosis has proliferated in recent years. In this chapter, we discuss the current status and provide basic knowledge in this field. We present novel promising biomarkers including tubular injury markers, proteins related to activated inflammation/fibrosis pathways, CKD273, transcriptomic biomarkers, as well as metabolomic biomarkers. Furthermore, considering the complex nature of the pathogenesis of renal fibrosis, we also highlight the combination of biomarkers to further improve the diagnostic and prognostic performance.

Effects of short-term atorvastatin use in patients with calcium stones: A randomized placebo-controlled clinical trial.

PurposeA few experimental and observational studies have reported that atorvastatin prevents calcium oxalate stone formation. Our study is the first to investigate the effect of atorvastatin on 24-hour urinary metabolites, urinary malondialdehyde (U-MDA) (an oxidative stress marker) and urinary neutrophil gelatinase-associated lipocalin (U-NGAL) (a renal tubular injury marker) in patients with calcium stones and hyperoxaluria.Materials and MethodsThis randomized, double-blind, placebo-controlled, parallel-group clinical trial included 32 adults with recurrent calcium stone formation and hyperoxaluria. All participants received a 3-month course of either atorvastatin (20 mg/d) or placebo of an identical shape. Both groups received the usual nutritional care based on the European Association of Urology guidelines.ResultsTwenty-eight participants completed the study. Serum levels of total and low-density lipoprotein cholesterol decreased in the atorvastatin group, and these changes were significantly different between groups (p<0.001). No statistically significant differences were observed between intergroup changes of the 24-hour urinary metabolite analysis, the U-MDA to creatinine ratio and the U-NGAL to creatinine ratio.ConclusionsAtorvastatin administration at a dose of 20 mg/d for 3 months did not affect 24-hour urinary metabolite, U-MDA and U-NGAL levels in recurrent calcium stone formers. However, this study could not disprove the preventive role of atorvastatin in kidney stone formation. Future studies should consider a larger sample size, longer follow-up, different drug doses, and measurements of multiple biomarkers of oxidative stress and tubular injury.

Inhibition of Mitochondrial Complex I Aggravates Folic Acid-Induced Acute Kidney Injury

Background: Some researches revealed that mitochondrial dysfunction is associated with various kidney injury. However, the role of mitochondrial dysfunction in the pathogenesis of acute kidney injury (AKI) still needs evidence. Methods: We evaluated the effect of mitochondrial complex I inhibitor rotenone on folic acid (FA)-induced AKI in mice. Results: Strikingly, the mice pretreated with rotenone at a dose of 200 ppm in food showed exacerbated kidney injury as shown by higher levels of blood urea nitrogen and creatinine compared with FA alone group. Meanwhile, both renal tubular injury score and the expression of renal tubular injury marker neutrophil gelatinase-associated lipocalin were further elevated in rotenone-pretreated mice, suggesting the deteriorated renal tubular injury. Moreover, the decrements of mitochondrial DNA copy number and the expressions of mitochondrial Cytochrome c oxidase subunit 1, mitochondrial NADH dehydrogenase subunit 1, and mitochondria-specific superoxide dismutase (SOD2) in the kidneys of FA-treated mice were further reduced in rotenone-pretreated mice, indicating the aggravated mitochondrial damage. In parallel with the SOD2 reduction, the oxidative stress markers of malondialdehyde and HO-1 displayed greater increment in AKI mice with rotenone pretreatment in line with the deteriorated apoptotic response and inflammation. Conclusion: Our results suggested that the inhibition of mitochondrial complex I activity aggravated renal tubular injury, mitochondrial damage, oxidative stress, cell apoptosis, and inflammation in FA-induced AKI.

Abemaciclib Inhibits Renal Tubular Secretion Without Changing Glomerular Filtration Rate.

Abemaciclib, an inhibitor of cyclin dependent kinases 4 and 6, is indicated for metastatic breast cancer treatment. Reversible increases in serum creatinine levels of ~15–40% over baseline have been observed following abemaciclib dosing. This study assessed the in vitro and clinical inhibition of renal transporters by abemaciclib and its metabolites using metformin (a clinically relevant transporter substrate), in a clinical study that quantified glomerular filtration and iohexol clearance. In vitro, abemaciclib inhibited metformin uptake by organic cation transporter 2, multidrug and toxin extrusion (MATE)1, and MATE2‐K transporters with a half‐maximal inhibitory concentration of 0.4–3.8 μM. Clinically, abemaciclib significantly increased metformin exposure but did not significantly affect measured glomerular filtration rate, serum neutrophil gelatinase‐associated lipocalin (NGAL), serum cystatin‐C, or the urinary markers of kidney tubular injury, NGAL and kidney injury molecule‐1.

Tauroursodeoxycholic acid (TUDCA) abolishes chronic high salt-induced renal injury and inflammation.

Chronic high salt intake exaggerates renal injury and inflammation, especially with the loss of functional ETB receptors. Tauroursodeoxycholic acid (TUDCA) is a chemical chaperone and bile salt that is approved for the treatment of hepatic diseases. Our aim was to determine whether TUDCA is reno-protective in a model of ETB receptor deficiency with chronic high salt-induced renal injury and inflammation. ETB -deficient and transgenic control rats were placed on normal (0.8% NaCl) or high salt (8% NaCl) diet for 3weeks, receiving TUDCA (400mg/kg/d; ip) or vehicle. Histological and biochemical markers of kidney injury, renal cell death and renal inflammation were assessed. In ETB -deficient rats, high salt diet significantly increased glomerular and proximal tubular histological injury, proteinuria, albuminuria, excretion of tubular injury markers KIM-1 and NGAL, renal cortical cell death and renal CD4+ T cell numbers. TUDCA treatment increased proximal tubule megalin expression as well as prevented high salt diet-induced glomerular and tubular damage in ETB -deficient rats, as indicated by reduced kidney injury markers, decreased glomerular permeability and proximal tubule brush border restoration, as well as reduced renal inflammation. However, TUDCA had no significant effect on blood pressure. TUDCA protects against the development of glomerular and proximal tubular damage, decreases renal cell death and inflammation in the renal cortex in rats with ETB receptor dysfunction on a chronic high salt diet. These results highlight the potential use of TUDCA as a preventive tool against chronic high salt induced renal damage.