The role of renal proximal tubular cells in diabetic nephropathy

Avasopasem manganese (GC4419) protects against cisplatin-induced chronic kidney disease: An exploratory analysis of renal metrics from a randomized phase 2b clinical trial in head and neck cancer patients

Head and neck squamous cell carcinoma (HNSCC) patients treated with high-dose cisplatin concurrently with radiotherapy (hdCis-RT) commonly suffer kidney injury leading to acute and chronic kidney disease (AKD and CKD, respectively). We conducted a retrospective analysis of renal function and kidney injury-related plasma biomarkers in a subset of HNSCC subjects receiving hdCis-RT in a double-blinded, placebo-controlled clinical trial (NCT02508389) evaluating the superoxide dismutase mimetic, avasopasem manganese (AVA), an investigational new drug. We found that 90 mg AVA treatment prevented a significant reduction in estimated glomerular filtration rate (eGFR) three months as well as six and twelve months after treatment compared to 30 mg AVA and placebo. Moreover, AVA treatment may have allowed renal repair in the first 22 days following cisplatin treatment as evidenced by an increase in epithelial growth factor (EGF), known to aid in renal recovery. An upward trend was also observed in plasma iron homeostasis proteins including total iron (Fe-blood) and iron saturation (Fe-saturation) in the 90 mg AVA group versus placebo. These data support the hypothesis that treatment with 90 mg AVA mitigates cisplatin-induced CKD by inhibiting hdCis-induced renal changes and promoting renal recovery.

Platycodin D regulates high glucose-induced ferroptosis of HK-2 cells through glutathione peroxidase 4 (GPX4)

Diabetic nephropathy (DN) is associated with inflammation. Platycodin D (PD) demonstrates anti-inflammatory activity. However, whether PD affects DN remains to be explored. Here, we aimed to discuss the role of PD in DN and its underlying mechanisms. High glucose (HG)-induced HK-2 cells were treated with PD, and cell viability was assessed using the Thiazolyl Blue Tetrazolium Bromide (MTT) assay. Ferroptosis-related factors such as lactate dehydrogenase (LDH) activity, lipid reactive oxygen species (ROS), iron (Fe²⁺) level, GSH level, and malondialdehyde (MDA) level were evaluated. Cell death was evaluated using the TUNEL assay. GPX4 expression was evaluated using Quantitative Real-time PCR (qRT-PCR) and Western blotting analysis. The results indicated that HG increased LDH activity, lipid ROS production, Fe²⁺ levels, and MDA levels and decreased GSH levels, suggesting that the HG condition induced ferroptosis. PD treatment inhibited ferroptosis in HG-induced cells, downregulated ACSL4 and TFR1 expression, and upregulated FTH-1 and SLC7A11 expression. PD reversed the effects of HG condition on cell death. Moreover, GPX4 expression was downregulated in HG-stimulated cells. Furthermore, we substantiated that PD suppressed ferroptosis by modulating GPX4 expression. In conclusion, PD inhibited ferroptosis in HG-induced HK-2 cells by upregulating GPX4 expression, suggesting that PD may be an effective drug for the clinical treatment of DN.

Long Term Culture of Human Kidney Proximal Tubule Epithelial Cells Maintains Lineage Functions and Serves as an Ex vivo Model for Coronavirus Associated Kidney Injury

The mechanism of how SARS-CoV-2 causes severe multi-organ failure is largely unknown. Acute kidney injury (AKI) is one of the frequent organ damage in severe COVID-19 patients. Previous studies have shown that human renal tubule cells could be the potential host cells targeted by SARS-CoV-2. Traditional cancer cell lines or immortalized cell lines are genetically and phenotypically different from host cells. Animal models are widely used, but often fail to reflect a physiological and pathogenic status because of species tropisms. There is an unmet need for normal human epithelial cells for disease modeling. In this study, we successfully established long term cultures of normal human kidney proximal tubule epithelial cells (KPTECs) in 2D and 3D culture systems using conditional reprogramming (CR) and organoids techniques. These cells had the ability to differentiate and repair DNA damage, and showed no transforming property. Importantly, the CR KPTECs maintained lineage function with expression of specific transporters (SLC34A3 and cubilin). They also expressed angiotensin-converting enzyme 2 (ACE2), a receptor for SARS-CoV and SARS-CoV-2. In contrast, cancer cell line did not express endogenous SLC34A3, cubilin and ACE2. Very interestingly, ACE2 expression was around twofold higher in 3D organoids culture compared to that in 2D CR culture condition. Pseudovirion assays demonstrated that SARS-CoV spike (S) protein was able to enter CR cells with luciferase reporter. This integrated 2D CR and 3D organoid cultures provide a physiological ex vivo model to study kidney functions, innate immune response of kidney cells to viruses, and a novel platform for drug discovery and safety evaluation.

Interstitial HIF1A induces an estimated glomerular filtration rate decline through potentiating renal fibrosis in diabetic nephropathy

AIMS

This study aimed to identify interstitial molecules that were responsible for the deterioration of the esiantimated glomerular filtration rate (eGFR) in diabetic nephropathy (DN).

MATERIALS AND METHODS

Weighted gene co-expression network analysis (WGCNA) was used to link the tubulointerstitial gene expression profile of DN to eGFR values. The relationship of eGFR with each sub-domain regulator in the network was analyzed with the linear regression model. Gene sets enrichment analysis (GSEA) was applied to detect the molecular changes mostly relating to the essential regulators.

KEY FINDINGS

Four co-expression modules were found strongly correlating with eGFR values. Genes from these modules were over-represented in fibrosis-related biological processes (extracellular matrix (ECM) organization and cell adhesion) and pathways (integrin signaling and ECM-receptor interaction). Of sub-domains in the gene interaction network, the expression of hypoxia-inducible factor 1A (HIF1A) was most negatively correlated with eGFR (R² = 0.417, P = 0.026). The positive correlations between HIF1A and its target genes were found, indicating an enhanced transcriptional activity of HIF1A. We also found that HIF1A positively correlated with CCAAT enhancer binding protein delta (CEBPD) (r = 0.731, P = 0.011), an activator of HIF1A transcription. Moreover, GSEA showed that samples with high HIF1A expression were enriched with fibrosis associated signaling, like ECM-receptor interaction and cell adhesion. Intriguingly, vascular epithelial growth factor A (VEGFA) expression decreased while HIF1A increased (R² = 0.733, P = 0.001), suggesting VEGFA loss may exacerbate hypoxia and stimulate HIF1A induction.

SIGNIFICANCE

The present study suggested that interstitial HIF1A may be involved in renal interstitial fibrosis in DN.

Association of neutrophil-gelatinase-associated lipocalin with microvascular complications in patients with type 2 diabetes: a cross-sectional study

Diabetic nephropathy and diabetic retinopathy are serious microvascular complications of diabetes mellitus. Recent studies have demonstrated that neutrophil-gelatinase-associated lipocalin (NGAL) may be accompanied by these complications during and before the appearance of microalbuminuria. In this study, we set out to research the role of NGAL in patients with diabetic nephropathy and diabetic retinopathy.

Material and methods

Eighty-two patients with type 2 diabetes were enrolled in our study. Urinary microalbumine and NGAL levels were measured in urine samples over 24 hours. We also studied NGAL levels in serum. All patients went through an ophthalmologic examination. The results were evaluated based on the presence of microalbuminuria and retinopathy.

Results

There were no significant differences in serum and urine NGAL levels between normoalbuminuric (n = 66) and microalbuminuric (n = 16) patients. We also did not find any significant difference in patients with retinopathy (n = 16) or without retinopathy (n = 66).

Conclusion

There are controversial findings about the role of NGAL in diabetic patients in medical literature. Standard values of urine and serum NGAL levels have yet to be determined. Our study suggests that NGAL is not a useful marker to differentiate microalbuminuric patients from normoalbuminuric subjects. We also did not find a relationship between NGAL levels and the presence of retinopathy. Additional studies with larger sample sizes will be required to confirm or refute these findings.

Microparticles as Potential Mediators of High Glucose-Induced Renal Cell Injury

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease worldwide. Activation of signaling pathways such as the mammalian target of rapamycin (mTOR), extracellular signal-regulated kinases (ERK), endoplasmic reticulum (ER) stress, transforming growth factor-beta (TGF-β), and epithelial-mesenchymal transition (EMT), are thought to play a significant role in the etiology of DN. Microparticles (MPs), the small membrane vesicles containing bioactive signals shed by cells upon activation or during apoptosis, are elevated in diabetes and were identified as biomarkers in DN. However, their exact role in the pathophysiology of DN remains unclear. Here, we examined the effect of MPs shed from renal proximal tubular cells (RPTCs) exposed to high glucose conditions on naïve RPTCs in vitro. Our results showed significant increases in the levels of phosphorylated forms of 4E-binding protein 1 and ERK1/2 (the downstream targets of mTOR and ERK pathways), phosphorylated-eIF2α (an ER stress marker), alpha smooth muscle actin (an EMT marker), and phosphorylated-SMAD2 and nuclear translocation of SMAD4 (markers of TGF-β signaling). Together, our findings indicate that MPs activate key signaling pathways in RPTCs under high glucose conditions. Pharmacological interventions to inhibit shedding of MPs from RPTCs might serve as an effective strategy to prevent the progression of DN.

Establishment of renal proximal tubule cell lines derived from the kidney of p53 knockout mice

The human cell line HK-2 is most commonly used as a model of renal proximal tubular epithelial cells (PTECs) for various studies despite the absence or low expression of transporters characteristic of parental PTECs. In an effort to develop reliable PTEC models, several human cell lines have been newly established over the last decade. In contrast, reliable mouse PTEC models are still unavailable. In this study, we established immortalized renal cortex tubule cell lines derived from p53 knockout mice and evaluated various PTEC characteristics toward the development of reliable mouse PTEC models. Here, we focus on MuRTE61, one of 13 newly established clonal cell lines. Albumin uptake in MuRTE61 cells was verified by incubation with fluorescent dye-labeled albumin. RT-PCR confirmed the expression of efflux transporter genes characteristic of PTECs in the MuRTE61 cells. MuRTE61 cells exhibited high sensitivity to treatment with cisplatin, a nephrotoxic agent, accompanied by upregulated expression of the uptake transporter Slc22a2 gene. Furthermore, MuRTE61 cells consistently formed spheroids with a lumen and apicobasal polarity in three-dimensional Matrigel cultures. Apical brush border microvilli were also observed in the spheroids by transmission electron microscopy. These data validate that MuRTE61 can be characterized as a reliable mouse PTEC line. In future, detailed analysis of reliable mouse and human PTEC lines will provide an accurate extrapolation of results of experiments using mice and humans, and may help resolve apparent inconsistencies between mouse and human nephrotoxicity.

Plasma Neutrophil Gelatinase-Associated Lipocalin as a Marker of Tubular Damage in Diabetic Nephropathy

Background

An increase in neutrophil gelatinase-associated lipocalin (NGAL) indicates tubular injury. Diabetic nephropathy causes typical changes in the kidney, characterized by glomerulosclerosis and eventual tubular damage. We validated the usefulness of plasma NGAL (pNGAL) as a biomarker of tubular damage in patients with diabetic nephropathy.

Methods

We included 376 patients with diabetes mellitus (260 patients with chronic renal insufficiency who had not received hemodialysis and 116 hemodialyzed due to diabetic nephropathy) and 24 healthy controls. Patients with chronic renal insufficiency were divided into three groups according to urinary albumin excretion (UAE) levels. pNGAL levels were measured using the Triage NGAL test (Alere, San Diego, CA, USA) and were compared between groups. We also examined whether pNGAL level was related to the degree of albuminuria and cystatin C-based glomerular filtration rate (GFR).

Results

Mean pNGAL levels of the healthy controls, chronic renal insufficiency patients with diabetes mellitus, and hemodialyzed patients were 61.9±5.3 ng/mL, 93.4±71.8 ng/mL, and 1,536.9±554.9 ng/mL, respectively. pNGAL level increased significantly in patients with severe albuminuria (P<0.001) and had a moderate correlation with the degree of albuminuria (r=0.467; P<0.001) and GFR (r=0.519; P<0.001). Multivariate regression analysis showed that the pNGAL level was associated with tubular damage independent of patient age, sex, and GFR.

Conclusions

pNGAL level independently reflects the degree of tubular damage in patients with diabetic nephropathy. Measurement of pNGAL, combined with UAE, would enable simultaneous, highly reliable assessments of tubular damage for such patients.

Composite urinary biomarkers to predict pathological tubulointerstitial lesions in lupus nephritis

Objective This study aimed to evaluate the clinical value of urinary biomarkers including kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and monocyte chemoattractant protein-1 (MCP-1) in lupus nephritis. Methods A total of 109 biopsy-proven lupus nephritis patients were included and 50 healthy individuals were used as normal controls. Urinary KIM-1, NGAL, and MCP-1 levels were measured by ELISA and their correlations with clinical and histological features were assessed. Receiver operating characteristic curves were performed and the Cox regression model was applied to identify prognostic factors associated with renal outcomes. Results Active lupus nephritis patients exhibited elevated urinary levels of KIM-1, NGAL, and MCP-1 compared with lupus nephritis patients in remission ( P < 0.001) and normal controls ( P < 0.001). The urinary KIM-1 level was correlated with pathological tubular atrophy ( r = 0.208, P < 0.05) and increased significantly in the presence of interstitial inflammatory lesions ( P = 0.031). Urinary KIM-1, NGAL, and MCP-1 levels were higher in patients with active tubulointerstitial lesions than in those with only chronic lesions ( P = 0.015, P = 0.230, and P = 0.086, respectively). A combination of KIM-1, NGAL, and MCP-1 was a good indicator for diagnosing active tubulointerstitial lesions (area under the curve: 0.796). The combination of KIM-1 and NGAL was identified as an independent risk factor for renal outcomes (hazard ratio = 7.491, P < 0.05). Conclusion Urinary KIM-1, NGAL, and MCP-1 levels were associated with kidney injury indices in lupus nephritis. The combination of the three biomarkers showed increased power in predicting tubulointerstitial lesions and renal outcomes.

Neutrophil Gelatinase-associated Lipocalin: As a Predictor of Early Diabetic Nephropathy in Type 2 Diabetes Mellitus

This study was carried out to look for diagnostic and prognostic role of neutrophil gelatinase-associated lipocalin (NGAL) in early diabetic nephropathy (DN) in type 2 diabetes individuals. NGAL was measured in both urinary and serum sample of 144 type 2 diabetes individuals stratified into three categories based on urinary albumin-creatinine ratio and 54 control populations with estimated glomerular filtration rate >60 mL/min/1.73 m² and serum creatinine <1.2 mg/dl. The serum NGAL (sNGAL), urine NGAL (uNGAL), and uNGAL/urine creatinine were significantly higher in diabetic individuals than in the control populations with significant difference in between the groups (P < 0.05). Difference of above values between control value and normoalbuminuria was also statistically significant (P < 0.05). Again, sNGAL and uNGAL correlate positively with albuminuria (P < 0.05). Tubular injury may precede glomerular injury in diabetic individuals, and NGAL can be used as a biomarker to diagnose DN even earlier to incipient nephropathy. Both sNGAL and uNGAL can predict albuminuria and be used as a noninvasive tool for diagnosis, staging, and progression of DN.

New biomarkers defining a novel early stage of Fabry nephropathy: A diagnostic test study

BACKGROUND

Renal involvement in Fabry disease is a major determinant of overall disease prognosis and early enzyme replacement therapy seems effective in preventing progression of kidney injury. Gb3 storage, glomerular sclerosis and tubulo-interstitial fibrosis may occur with minimal or no changes on standard renal tests, hence alternative markers of renal dysfunction are crucial. In this study we compared several biomarkers with albuminuria in the identification of incipient Fabry nephropathy and their diagnostic accuracy to identify chronic kidney disease (CKD) stage≥2.

METHODS

In this multicentre, prospective, cross-sectional and diagnostic test study, a cohort of 78 Fabry patients and 25 healthy controls was consecutively recruited. Patients were grouped by severity of nephropathy: 1) albuminuria<30mg/g; 2) albuminuria 30-299mg/g; 3) albuminuria>300mg/g; 4) glomerular filtration rate (GFR)<60mL/min/1.73m². Several index tests, namely biomarkers of glomerular (transferrin and type IV collagen) and tubular (α1-microglobulin, N-acetyl-β-glucosaminidase and alanine aminopeptidase) dysfunction were compared with the reference standard (albuminuria).

RESULTS

Significant increase of all tested biomarkers in Fabry patients, even in the subgroup of patients without evidence of nephropathy. We also found inverse significant correlations between estimated GFR and collagen type IV (ρ=-0.289; p=0.003) or N-acetyl-β-glucosaminidase (ρ=-0.448; p<0.001), which were stronger than with albumin (ρ=-0.274; p=0.019). There was also better diagnostic accuracy of N-acetyl-β-glucosaminidase to predict CKD stage≥2.

CONCLUSIONS

These results suggest that studied biomarkers may overcome the limitations of albuminuria as sensitive marker of early renal dysfunction and as marker for CKD progression risk. These biomarkers may also define novel early stages of nephropathy characterized by mesangial expansion and/or tubular damage.

Associations between urinary kidney injury biomarkers and cardiovascular mortality risk in elderly men with diabetes

AIM

Three urinary biomarkers, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and cystatin C, have been suggested as clinically relevant highly specific biomarkers of acute kidney tubular damage. Yet, the utility of these biomarkers in the prognostication of diabetic nephropathy has been less studied. Therefore, we aimed to investigate the longitudinal association between these urinary biomarkers and cardiovascular mortality in patients with diabetes.

METHODS

The study sample consisted of participants with diabetes in the community-based Uppsala Longitudinal Study of Adult Men (n = 91; mean age 77.8 years). During follow-up (median 8.3 years, interval 0.7-13.4 years), 33 participants died of cardiovascular causes.

RESULTS

In a multivariable Cox regression model adjusting for age, glomerular filtration rate, and urinary albumin/creatinine ratio, higher urinary KIM-1/creatinine was associated with an increased risk for cardiovascular mortality (HR per SD increase 1.51, 95% confidence intervals 1.03-2.24, P = 0.03). Neither urinary NGAL/creatinine nor urinary cystatin C/creatinine were independently associated with an increased cardiovascular mortality risk.

CONCLUSION

In elderly men with diabetes, higher urinary KIM-1/creatinine was associated with an increased long-term risk of cardiovascular mortality independently of established markers of diabetic nephropathy. Our data provide support for kidney tubular damage as an important aspect of diabetic nephropathy that merits further investigation.

Neutrophil gelatinase-associated lipocalin as a biomarker of disease progression in patients with chronic kidney disease

Chronic kidney disease (CKD) is associated with early mortality, decreased quality of life and increased health care expenditures. The aim of this study was to determine whether or not urinary NGAL (uNGAL) level is associated with renal damage and kidney disease progression in patients with CKD and to evaluate the predictive value of uNGAL in progression of CKD. Totally, 91 cases of CKD stage II, III, IV, and 50 age-matched healthy controls were enrolled. The follow-up end-point was 18 months; end-point of the study was progression to an estimated glomerular filtration rate (eGFR) of <15 ml/min and/or CKD stage V. Forty-five cases (49.4%) were progressors and 46 were nonprogressors. uNGAL levels were significantly higher in CKD subjects as compared to healthy controls (log 1.09 ± 0.22 μg/ml in controls versus log 1.22 ± 2.08 μg/ml in stage II, log 3.34 ± 2.74 μg/ml in stage III and log 3.70 ± 0.18 μg/ml in stage IV). Univariate Cox proportional hazards model showed that only eGFR (hazard ratio [HR]: 0.95; 95% confidence interval [CI]: 0.93–0.96; P < 0.001) and uNGAL (HR: 1.11; 95% CI: 1.01–1.20; P < 0.001) were significantly associated with end-point of CKD stage V, but multiple Cox proportional regression model showed significant association of uNGAL (HR: 1.11; 95% CI: 1.01–1.20; P < 0.001) and eGFR (HR: 0.962, 95% CI: 0.95–0.98; P < 0.001) with end-point of CKD stage V. This suggests that uNGAL would not be a simple surrogate index of baseline eGFR, but a marker of CKD progression beyond the information provided by eGFR estimation.

myo-Inositol Oxygenase Overexpression Accentuates Generation of Reactive Oxygen Species and Exacerbates Cellular Injury following High Glucose Ambience: A NEW MECHANISM RELEVANT TO THE PATHOGENESIS OF DIABETIC NEPHROPATHY

Diabetic nephropathy (DN) is characterized by perturbations in metabolic/cellular signaling pathways with generation of reactive oxygen species (ROS). The ROS are regarded as a common denominator of various pathways, and they inflict injury on renal glomerular cells. Recent studies indicate that tubular pathobiology also plays a role in the progression of DN. However, the mechanism(s) for how high (25 mm) glucose (HG) ambience induces tubular damage remains enigmatic. myo-Inositol oxygenase (MIOX) is a tubular enzyme that catabolizes myo-inositol to d-glucuronate via the glucuronate-xylulose (G-X) pathway. In this study, we demonstrated that G-X pathway enzymes are expressed in the kidney, and MIOX expression/bioactivity was up-regulated under HG ambience in LLC-PK1 cells, a tubular cell line. We further investigated whether MIOX overexpression leads to accentuation of tubulo-interstitial injury, as gauged by some of the parameters relevant to the progression of DN. Under HG ambience, MIOX overexpression accentuated redox imbalance, perturbed NAD(+)/NADH ratios, increased ROS generation, depleted reduced glutathione, reduced GSH/GSSG ratio, and enhanced adaptive changes in the profile of the antioxidant defense system. These changes were also accompanied by mitochondrial dysfunctions, DNA damage and induction of apoptosis, accentuated activity of profibrogenic cytokine, and expression of fibronectin, the latter two being the major hallmarks of DN. These perturbations were largely blocked by various ROS inhibitors (Mito Q, diphenyleneiodonium chloride, and N-acetylcysteine) and MIOX/NOX4 siRNA. In conclusion, this study highlights a novel mechanism where MIOX under HG ambience exacerbates renal injury during the progression of diabetic nephropathy following the generation of excessive ROS via an unexplored G-X pathway.

Plasma neutrophil gelatinase-associated lipocalin as a potential predictor of adverse renal outcomes in immunoglobulin A nephropathy

BACKGROUND/AIMS

Neutrophil gelatinase-associated lipocalin (NGAL) is a well-known biomarker of acute kidney injury. We evaluated the value of plasma NGAL (pNGAL) as an independent predictor of prognosis in immunoglobulin A nephropathy (IgAN).

METHODS

In total, 91 patients with biopsy-proven IgAN at a single center were evaluated. pNGAL was measured using a commercial enzyme-linked immunosorbent assay kit (R&D Systems). Adverse renal outcome was defined as chronic kidney disease (CKD) stage 3 or above at the last follow-up. Pearson correlation coefficient and Cox regression were used for analyses.

RESULTS

The mean age of all patients (male:female, 48:43) was 35 years (range, 18 to 77). pNGAL ranged between 21.68 and 446.40 ng/mL (median, 123.97) and showed a correlation with age (r = 0.332, p = 0.001), creatinine (r = 0.336, p = 0.001), estimated glomerular filtration rate (r = -0.397, p < 0.001), uric acid (r = 0.289, p = 0.006), and the protein-to-creatinine ratio (r = 0.288, p = 0.006). During a mean follow-up period of 37.6 months, 11 patients (12.1%) had CKD stage 3 or above. In a multivariate Cox regression model, hypertension (hazard ratio [HR], 8.779; 95% confidence interval [CI], 1.526 to 50.496; p = 0.015), proteinuria > 1 g/day (HR, 5.184; 95% CI, 1.124 to 23.921; p = 0.035), and pNGAL (HR, 1.012; 95% CI, 1.003 to 1.022; p = 0.013) were independent predictors associated with adverse renal outcome.

CONCLUSIONS

pNGAL showed strong correlations with other clinical prognostic factors and was also an independent predictor of adverse renal outcome. We suggest pNGAL as a potential predictor for prognosis in IgAN, while further studies are needed to confirm the clinical value.

Plasma neutrophil gelatinase-associated lipocalin and kidney function decline and kidney disease-related clinical events in older women

BACKGROUND

It is still unclear whether serum neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of renal tubular injury, is a prognostic marker for the progression of chronic kidney disease (CKD) in the general population.

METHODS

A prospective-cohort study of 1,245 women aged ≥70 from the general population. Associations between plasma NGAL and change in 5-year estimated glomerular filtration rate (eGFR), rapid renal decline and 10-year risk of acute or chronic renal disease-related hospitalisations and/or mortality were examined.

RESULTS

Compared to women with above-median plasma NGAL of 76.5 ng/l, women with below-median plasma NGAL had a 9.3% reduction in eGFR over a 5-year period. Among women with above-median plasma NGAL, there was over a 1.7-fold increased risk of rapid renal decline (eGFR decline of >3 ml/min/year) (adjusted odds ratio 1.76, 95% CI 1.003, 3.102, p = 0.049). Compared to women with baseline eGFR of <60 ml/min/1.73 m(2), women with above-median plasma NGAL experienced over a 2.5-fold increased risk of renal disease events at 10 years (hazard ratio 2.55, 95% CI 1.13, 5.78, p = 0.025) after adjustment of age, hypertension and diabetes. Addition of plasma NGAL in participants with eGFR of <60 ml/min/1.73 m(2) significantly improved the accuracy in predicting the 10-year risk of renal disease events (adjusted area-under-curve receiver operator characteristics without and with NGAL 0.64 and 0.71, respectively; p = 0.027) and reclassified 13% of women who experienced renal disease events into the higher risk categories (p = 0.03).

CONCLUSION

Plasma NGAL is of modest clinical utility in predicting the renal function decline and risk of renal disease-related clinical events, particularly those with mild to moderate CKD.

Thioredoxin-interacting protein mediates dysfunction of tubular autophagy in diabetic kidneys through inhibiting autophagic flux

Thioredoxin-interacting protein (TXNIP) expression is ubiquitous and is induced by a variety of cellular stresses, including high intracellular glucose. TXNIP is associated with activation of oxidative stress and tubulointerstitial fibrosis in diabetic nephropathy. Autophagy is a major pathway that delivers damaged proteins and organelles to lysosomes to maintain cellular homeostasis. This study aimed to investigate the dysregulation of autophagy and the regulation of TXNIP on autophagy in renal proximal tubular cells (PTCs) under diabetic conditions. The formation of autophagosomes was measured using transmission electron microscopy, and LC3-II, and the effectiveness of autophagic clearance was determined by p62 expression in diabetic kidney and in human PTCs exposed to high glucose (HG). The results collectively demonstrated increased expression of TXNIP, LC3/LC3-II and p62 in renal tubular cells of mice with diabetic nephropathy and in cultured human PTCs exposed to HG (30 mM/l) for 48 h compared with control. The formation of autophagic vacuoles was increased in HG-induced cells. Furthermore, silencing of TXNIP by siRNA transfection reduced autophagic vacuoles and the expression of LC3-II and p62 in human PTCs exposed to HG compared with control and partially reversed the accumulation of LC3-II and p62 induced by bafilomycin A1 (50 nM/l), a pharmacological inhibitor of autophagy which blocks the fusion of autophagosomes with lysosomes and impairs the degradation of LC3-II and p62. Collectively, these results suggest that hyperglycemia leads to dysfunction of autophagy in renal tubular cells and decreases autophagic clearance. HG-induced overexpression of TXNIP may contribute to the dysfunction of tubular autophagy in diabetes.

"Normoalbuminuric" diabetic nephropathy: tubular damage and NGAL

The aim of this study was to demonstrate that neutrophil gelatinase-associated lipocalin (NGAL) increased before the onset of microalbuminuria in patients with type 1 diabetes mellitus (T1DM), representing an important biochemical parameter with high sensitivity and specificity to make a precocious diagnosis of "normoalbuminuric" diabetic nephropathy (DN). Serum NGAL (sNGAL) and urinary NGAL (uNGAL) levels were evaluated in a cohort of fifty patients affected by T1DM. They had no signs of clinical nephropathy. Thirty-five healthy subjects (HS) were recruited. sNGAL levels were significantly higher compared with those measured in HS [193.7 (103.2-405.4) vs. 46.4 (39.8-56.2) ng/ml; p < 0.0001], as were uNGAL levels [25.5 (14.2-40.2) vs. 6.5 (2.9-8.5) ng/ml; p < 0.0001]. sNGAL was found to be directly correlated with glycated hemoglobin. uNGAL also positively correlated with albuminuria, whereas an inverse correlation was found with uric acid. After multivariate analysis, significance was maintained for the correlation between uNGAL and microalbuminuria. In ROC analysis, sNGAL showed a good diagnostic profile such as uNGAL. NGAL increases in patients with T1DM, even before diagnosis of microalbuminuria representing an early biomarker of "normoalbuminuric" DN with a good sensitivity and specificity. NGAL measurement could be useful for the evaluation of early renal involvement in the course of diabetes.

Serum cystatin C and tubular urinary enzymes as biomarkers of renal dysfunction in type 2 diabetes mellitus

Renal tubulointerstitium plays an important role in the development and progression of diabetic nephropathy. The aim of this study was to assess serum cystatin C and 2 renal tubular enzymes, neutrophil gelatinase associated lipocalin (NGAL) and N-acetyl-beta-D-glucosaminidase (NAG), as screening markers for early renal dysfunction in patients with type 2 diabetes mellitus (T2DM). ROC curve analysis showed that urinary NAG is the most sensitive marker of microalbuminuria and early renal damage with sensitivity of 83.3%, while serum cystatin C was the most sensitive and specific marker of macroalbuminuria and damage progress with sensitivity of 70.8% and specificity of 83.3% versus 70.6% and 83.3% for uNGAL; and 64.7% and 66.7% for NAG, respectively. Our data indicate that urinary NAG is the most sensitive marker for early renal damage in diabetic patients. However, for damage progress, serum cystatin C is the most sensitive and specific marker for follow-up and monitoring renal dysfunction.

Role of guanine-nucleotide exchange factor Epac in renal physiology and pathophysiology

Exchange proteins directly activated by cAMP [Epac(s)] were discovered more than a decade ago as new sensors for the second messenger cAMP. The Epac family members, including Epac1 and Epac2, are guanine nucleotide exchange factors for the Ras-like small GTPases Rap1 and Rap2, and they function independently of protein kinase A. Given the importance of cAMP in kidney homeostasis, several molecular and cellular studies using specific Epac agonists have analyzed the role and regulation of Epac proteins in renal physiology and pathophysiology. The specificity of the functions of Epac proteins may depend upon their expression and localization in the kidney as well as their abundance in the microcellular environment. This review discusses recent literature data concerning the involvement of Epac in renal tubular transport physiology and renal glomerular cells where various signaling pathways are known to be operative. In addition, the potential role of Epac in kidney disorders, such as diabetic kidney disease and ischemic kidney injury, is discussed.

Glucose-induced down regulation of thiamine transporters in the kidney proximal tubular epithelium produces thiamine insufficiency in diabetes

Increased renal clearance of thiamine (vitamin B(1)) occurs in experimental and clinical diabetes producing thiamine insufficiency mediated by impaired tubular re-uptake and linked to the development of diabetic nephropathy. We studied the mechanism of impaired renal re-uptake of thiamine in diabetes. Expression of thiamine transporter proteins THTR-1 and THTR-2 in normal human kidney sections examined by immunohistochemistry showed intense polarised staining of the apical, luminal membranes in proximal tubules for THTR-1 and THTR-2 of the cortex and uniform, diffuse staining throughout cells of the collecting duct for THTR-1 and THTR-2 of the medulla. Human primary proximal tubule epithelial cells were incubated with low and high glucose concentration, 5 and 26 mmol/l, respectively. In high glucose concentration there was decreased expression of THTR-1 and THTR-2 (transporter mRNA: -76% and -53% respectively, p<0.001; transporter protein -77% and -83% respectively, p<0.05), concomitant with decreased expression of transcription factor specificity protein-1. High glucose concentration also produced a 37% decrease in apical to basolateral transport of thiamine transport across cell monolayers. Intensification of glycemic control corrected increased fractional excretion of thiamine in experimental diabetes. We conclude that glucose-induced decreased expression of thiamine transporters in the tubular epithelium may mediate renal mishandling of thiamine in diabetes. This is a novel mechanism of thiamine insufficiency linked to diabetic nephropathy.

Novel carbocyclic nucleoside analogs suppress glomerular mesangial cells proliferation and matrix protein accumulation through ROS-dependent mechanism in the diabetic milieu

The synthesis of a series of novel 3,4-cis- and 3,4-trans-substituted carbocyclic nucleoside analogs from protected uracil and thymine is described. The key reaction in the followed synthetic protocols utilized the Mitsunobu reaction to couple 3,4-substituted cyclopentanols to (3)N-benzoyl uracil or (3)N-benzoyl thymine. These molecules were evaluated with regard to their ability to treat diabetic nephropathy. Our results show that two analogs significantly reduced high-glucose induced glomerular mesangial cells proliferation and matrix protein accumulation in vitro and, more interestingly, exhibited an anti-oxidative effect suggesting that the activity may be mediated through ROS-dependent mechanism.

Effects of lipid-lowering therapy with rosuvastatin on kidney function and oxidative stress in patients with diabetic nephropathy

AIM

We aimed to assess the effects of rosuvastatin treatment on lipid levels, a biomarker of oxidative stress, albuminuria, and kidney function in patients with diabetic nephropathy.

METHODS

We conducted a prospective, open-label, parallel group, controlled study of 104 patients with diabetic nephropathy, low-density lipoprotein cholesterol (LDL-C) levels of > 120 mg/dL, and well-controlled blood pressure who were undergoing treatment with renin angiotensin system inhibitors. Patients were randomly assigned to two groups: the rosuvastatin group (n = 52; 2.5 mg/day rosuvastatin, increased to 10 mg/day) and the control group (n = 52; no rosuvastatin administered). We determined the efficacy of rosuvastatin by monitoring serum lipid profiles, high sensitivity C-reactive protein (hs-CRP), malondialdehyde-modified LDL (MDA-LDL), and cystatin C levels. In addition, urinary albumin, 8-hydroxydeoxyguanosine (8-OHdG) and liver-type fatty acid-binding protein (L-FABP) levels were measured before and 6 months after rosuvastatin was added to the treatment.

RESULTS

Rosuvastatin effectively reduced total cholesterol, LDL-C, triglycerides, non-high-density lipoprotein cholesterol (non-HDL-C) levels, and the LDL-C/ HDL-C ratio in the rosuvastatin group. These parameters remained unchanged in patients who were not treated with rosuvastatin. Although there was no significant change in the estimated glomerular filtration rate level, serum cystatin C levels and urinary albumin excretion rates were significantly decreased in the rosuvastatin group. In addition, rosuvastatin significantly reduced hs-CRP and MDA-LDL levels. Moreover, urinary 8-OHdG and L-FABP levels at baseline (13.5±5.1 and 41.7±26.1 ng/mgCr, respectively) decreased significantly at 6 months (11.5±4.0 and 26.9±13.4 ng/mgCr, respectively), and there was a significant correlation (r = 0.48, p < 0.01). Multivariate analysis revealed that albuminuria was significantly correlated with only rosuvastatin use (p = 0.0006, R(2)= 0.53).

CONCLUSION

Rosuvastatin administration reduced albuminuria, oxidative stress, and serum cystatin C levels, independent of blood pressure and lipid levels.

Autocrine modulation of glucose transporter SGLT2 by IL-6 and TNF-α in LLC-PK(1) cells

We determined in cultured kidney epithelial cells (LLC-PK(1)) the effects of high glucose, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) on mRNA and protein expression of the renal glucose transporters SGLT1 and SGLT2. Cultured monolayers were incubated with similar concentrations of IL-6 and TNF-α to those produced by LLC-PK(1) in the presence of 20 mM glucose. Confluent monolayers with either 5 (controls, C) or 20 mM glucose (high glucose, HG) were incubated in the presence of 5 mM glucose, 20 mM glucose, 10 pg/ml IL-6, or TNF-α alone or in combination. Separate groups with IL-6 and TNF-α were incubated with antibodies to their respective receptors. HG induced an increased SGLT1 mRNA at 48 h (p<0.05 vs. C) and protein expression in 120 h (p<0.05 vs. C). HG also induced an increased SGLT2 mRNA at 72 and 96 h (P<0.05 vs. C) and SGLT2 protein expression at 120 h (p<0.05 vs. C). In C, 10 pg/ml IL-6 or TNF-α did not modify SGLT1 mRNA (n.s vs. in the absence of cytokines). In contrast, cytokines induced an increased expression of SGLT1 protein at 120 h (p<0.05 vs. in the absence of cytokines), and SGLT2 mRNA and protein were increased at 96 and 120 h, respectively (p<0.05 vs. in absence of cytokines). No changes were observed when cells were incubated with cytokines and HG (n.s vs. C). In conclusion, this study showed that SGLT2 increased in the presence of IL-6 and TNF-α, indicating an autocrine modulation of the expression of this transporter by cytokines.

Epac1-mediated, high glucose-induced renal proximal tubular cells hypertrophy via the Akt/p21 pathway

The mechanisms involved in tubular hypertrophy in diabetic nephropathy are unclear. We investigated the role of exchange protein activated by cAMP 1(Epac1), which activates Rap-family G proteins in cellular hypertrophy. Epac1 is expressed in heart, renal tubules, and in the HK-2 cell line. In diabetic mice, increased Epac1 expression was observed, and under high glucose ambience (HGA), HK-2 cells also exhibited increased Epac1 expression. We isolated a 1614-bp DNA fragment upstream of the initiation codon of Epac1 gene, inclusive of glucose response elements (GREs). HK-2 or COS7 cells transfected with the Epac1 promoter revealed a dose-dependent increase in its activity under HGA. Mutations in GRE motifs resulted in decreased promoter activity. HK-2 cells exhibited a hypertrophic response and increased protein synthesis under HGA, which was reduced by Epac1-siRNA or -mutants, whereas the use of a protein kinase A inhibitor had minimal effect. Epac1 transfection led to cellular hypertrophy and increased protein synthesis, which was accentuated by HGA. HGA increased the proportion of cells in the G0/G1 cell-cycle phase, and the expression of pAkt and the cyclin-dependent kinase inhibitors p21 and p27 was increased while the activity of cyclin-dependent kinase 4 decreased. These effects were reversed following transfection of cells with Epac1-siRNA or -mutants. These data suggest that HGA increases GRE-dependent Epac1 transcription, leading to cell cycle arrest and instigation of cellular hypertrophy.

Transcriptional and post-translational modulation of myo-inositol oxygenase by high glucose and related pathobiological stresses

Renal-specific oxidoreductase/myo-inositol oxygenase (RSOR/MIOX) catabolizes myo-inositol and is implicated in the pathogenesis of diabetic nephropathy. How high glucose (HG) ambience up-regulates its expression and enzyme activity was investigated. MIOX up-regulation was associated with an increase in enzyme activity, which was reduced to basal levels with phosphatase treatment. Using phosphothreonine, protein kinase A (PKA), and PKC substrate antibodies, analyses of kidney lysates of diabetic animals and LLC-PK1/HK-2 cells subjected to HG ambience indicated MIOX to be a phosphoprotein. Kinase phosphorylated recombinant RSOR/MIOX proteins had increased activity confined to exons 2-5. Mutants with substituted phosphorylation sites had a minimal increase in activity. Treatment of cells with PKC, PKA, and PDK1 kinase activators increased activity, whereas inhibitors reduced it. Inhibitors also reduced the phosphorylation and activity of MIOX induced by HG. Besides HG, exposure of cells to oxidants H(2)O(2) and methylglyoxal up-regulated MIOX expression and its phosphorylation and activity, whereas antioxidants N-acetylcysteine, β-naphthoflavone, and tertiary butyl hydroquinone reduced MIOX expression. Treatment with HG or oxidants or overexpression of MIOX induced nuclear translocation of redox-sensitive transcription factor Nrf2, which binds to antioxidant response elements of various promoters. Promoter analyses revealed an increase in luciferase activity with HG and oxidants. Analyses of antioxidant response elements and carbohydrate response elements revealed an accentuation of DNA-protein interactions with oxidants and under HG ambience. ChIP-PCR and immunofluorescence studies revealed nuclear translocation of carbohydrate response element-binding protein. These findings suggest that phosphorylation of RSOR/MIOX enhances its activity, which is augmented by HG via transcriptional/translational events that are also modulated by diabetes-related pathobiological stresses.

Regulation of heparanase by albumin and advanced glycation end products in proximal tubular cells

Diabetic nephropathy is one of the main causes of end-stage renal disease, in which the development of tubular damage depends on factors such as high glucose levels, albuminuria and advanced glycation end-product. In this study, we analyzed the involvement of heparanase, a heparan sulfate glycosidase, in the homeostasis of proximal tubular epithelial cells in the diabetic milieu. In vitro studies were performed on a wild-type and stably heparanase-silenced adult tubular line (HK2) and HEK293. Gene and protein expression analyses were performed in the presence and absence of diabetic mediators. Albumin and advanced glycation end-product, but not high glucose levels, increased heparanase expression in adult tubular cells via the AKT/PI3K signaling pathway. This over-expression of heparanase is then responsible for heparan sulfate reduction via its endoglycosidase activity and its capacity to regulate the heparan sulfate-proteoglycans core protein. In fact, heparanase regulates the gene expression of syndecan-1, the most abundant heparan sulfate-proteoglycans in tubular cells. We showed that heparanase is a target gene of the diabetic nephropathy mediators albumin and advanced glycation end-product, so it may be relevant to the progression of diabetic nephropathy. It could take part in several processes, e.g. extracellular-matrix remodeling and cell-cell crosstalk, via its heparan sulfate endoglycosidase activity and capacity to regulate the expression of the heparan sulfate-proteoglycan syndecan-1.

A glimpse of various pathogenetic mechanisms of diabetic nephropathy

Diabetic nephropathy is a well-known complication of diabetes and is a leading cause of chronic renal failure in the Western world. It is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments and by the thickening and hyalinization of intrarenal vasculature. The various cellular events and signaling pathways activated during diabetic nephropathy may be similar in different cell types. Such cellular events include excessive channeling of glucose intermediaries into various metabolic pathways with generation of advanced glycation products, activation of protein kinase C, increased expression of transforming growth factor β and GTP-binding proteins, and generation of reactive oxygen species. In addition to these metabolic and biochemical derangements, changes in the intraglomerular hemodynamics, modulated in part by local activation of the renin-angiotensin system, compound the hyperglycemia-induced injury. Events involving various intersecting pathways occur in most cell types of the kidney.

Urinary cystatin C as a potential risk marker for cardiovascular disease and chronic kidney disease in patients with obesity and metabolic syndrome

BACKGROUND AND OBJECTIVES

Obesity and metabolic syndrome (MS) increase the risk of cardiovascular disease (CVD), chronic kidney disease (CKD), and all-cause mortality. Serum cystatin C (S-CysC), a marker of GFR, has been shown to be associated with CVD and CKD. This study was designed to elucidate the association of urinary CysC (U-CysC), a marker of renal tubular dysfunction, with CVD and CKD risk factors in patients with obesity and MS.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The U-CysC-creatinine ratio (UCCR) was examined in 343 Japanese obese outpatients enrolled in the multi-centered Japan Obesity and Metabolic Syndrome Study.

RESULTS

UCCR was positively correlated with urine albumin-creatinine ratio (UACR) and S-CysC and negatively correlated with estimated GFR (eGFR). Among obese patients, UCCR was significantly higher in MS patients than in non-MS patients. UCCR had significant correlations with the number of components of MS and arterial stiffness, all of which are CVD predictors, similarly to UACR (P<0.05). Interestingly, diet- and exercise-induced weight reduction for 3 months significantly decreased only UCCR among all of the renal markers examined (P<0.01), in parallel with the decrease in BMI, HbA1c, and arterial stiffness, suggesting the beneficial effect of weight reduction on renal tubular dysfunction.

CONCLUSIONS

This study demonstrates that UCCR is significantly associated with renal dysfunction, the severity of MS, arterial stiffness, and weight change in obese patients. The data of this study suggest that U-CysC could serve as a CVD and CKD risk factor in patients with obesity and MS.

Cannabinoid receptor 1 mediates palmitic acid-induced apoptosis via endoplasmic reticulum stress in human renal proximal tubular cells

The endocannabinoid system (ECS) is activated at the onset of obesity and diverse metabolic diseases. Endocannabinoids mediate their physiological and behavioral effects by activating specific cannabinoid receptors, mainly cannabinoid receptor 1 (CB(1)R). Diabetic nephropathy (DN) is induced by hyperlipidemia, and renal proximal tubule cells are an important site for the onset of DN. However, the pathophysiology of CB(1)R, especially in the hyperlipidemia of DN, has not been elucidated. Therefore, we examined the effect of palmitic acid (PA) on CB(1)R expression and its related signal pathways in human renal proximal tubular cells (HK-2 cells). PA significantly increased CB(1)R mRNA and protein levels and induced CB(1)R internalization. PA-induced activation of CB(1)R is prevented by the treatment of AACOCF(3) (a cPLA(2) inhibitor), indomethacin and NS398 (a COX 2 inhibitors). Indeed, PA increased cPLA(2), and COX-2 but not COX-1. We also investigated whether the PA-induced activation of CB(1)R is linked to apoptosis. As a result, AM251 (a CB(1)R antagonist) attenuated PA-mediated apoptosis in a concentration-dependent manner. Furthermore, PA decreased GRP78 expression and induced increases in the endoplasmic reticulum (ER) stress signaling pathways p-PERK, p-eIF2α, p-ATF4, and CHOP, which were blocked by AM251 treatment. Moreover, PA increased the Bax/Bcl-2 ratio, cleaved PARP, and caspase-3 levels. The PA-induced apoptotic effects were decreased with CB(1)R-specific antagonist (AM251) treatment and CB1 si-RNA transfection. In conclusion, PA induced apoptosis through ER stress via CB(1)R expression in human proximal tubule cells. Our results provide evidence that CB(1)R blockade may be a potential anti-diabetic therapy for the treatment of DN.

Normal-range albuminuria does not exclude nephropathy in diabetic children

Clinically detectable diabetic nephropathy (DN) begins with the development of microalbuminuria (MA). However, early renal dysfunction may be overlooked despite using that method. On the other hand, the gold standard in DN detection-that is, renal biopsy-is highly invasive. The aim of this study was to evaluate the level of neutrophil-gelatinase-associated lipocalin (NGAL) and interleukin (IL)-18 and their relations to albumin excretion rate (AER) in children with normal-range albuminuria, e.g. in those considered as not presenting diabetic nephropathy. The study group consisted of 22 children (age 12.7 +/- 3.5 years) with type 1 diabetes mellitus (T1DM). Long-term glycemic control was assessed on hemoglobin A1c (HbA1c) levels (8.52 +/- 1.78%). All patients presented normal estimated glomerular filtration rate (eGFR) (141 +/- 23 ml/min/1.73 m(2)) and normal urinary albumin excretion (13.09 +/- 7.63 mg/24 h). Fourteen healthy children served as a control group. Children with T1DM showed increased NGAL values with respect to controls-interestingly, both in serum (sNGAL) (867.43 +/- 341.98 vs. 655.29 +/- 196.17 ng/ml; p = 0.04) and in urine (uNGAL) (420.04 +/- 374.16 vs. 156.53 +/- 185.18 ng/ml, p = 0.04). IL-18 levels were not different in both groups both in serum (58.52 +/- 20.11 vs. 69.79 +/- 58.76 ng/ml; NS) and in urine (14.53 +/- 12.74 vs. 14.60 +/- 10.92 ng/ml; NS). Despite the relatively small study group, the positive correlation between sNGAL and AER was found [AER (mg/24 h) = 3.1893 + 0.01141 x sNGAL (ng/ml); r = 0.51; p = 0.014] as well as between uNGAL and AER [AER (mg/24 h) = 8.7538 + 0.01032 x uNGAL (ng/ml); r = 0.51; p = 0.016]. No relationship between sNGAL and uNGAL, and GFR and HbA1c were found. Normal-range albuminuria does not exclude diabetic nephropathy defined as increased sNGAL and uNGAL concentration. NGAL measurement can be more sensitive than MA and may become a useful tool for evaluating renal involvement in diabetic children.

Neutrophil gelatinase-associated lipocalin (NGAL) and progression of chronic kidney disease

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) has recently assumed epidemic proportion, becoming a troubling emerging cause of morbidity, especially if it progresses to terminal stage (ESRD). The authors aimed to evaluate whether neutrophil gelatinase-associated lipocalin (NGAL), a novel specific biomarker of acute kidney injury, could predict the progression of CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Serum and urinary NGAL levels, together with a series of putative progression factors, were evaluated in a cohort of 96 patients (mean age: 57 +/- 16 years) affected by nonterminal CKD (eGFR > or =15 ml/min/1.73 m(2)) of various etiology. Progression of CKD, assessed as doubling of baseline serum creatinine and/or onset of ESRD, was evaluated during follow-up.

RESULTS

At baseline, both serum and urinary NGAL were inversely, independently, and closely related to eGFR. After a median follow-up of 18.5 mo (range 1.01 to 20), 31 patients (32%) reached the composite endpoint. At baseline, these patients were significantly older and showed increased serum creatinine, calcium-phosphate product, C-reactive protein, fibrinogen, daily proteinuria, and NGAL levels, whereas eGFR values were significantly lower. Univariate followed by multivariate Cox proportional hazard regression analysis showed that urinary NGAL and sNGAL predicted CKD progression independently of other potential confounders, including eGFR and age.

CONCLUSION

In patients with CKD, NGAL closely reflects the entity of renal impairment and represents a strong and independent risk marker for progression of CKD.

Neutrophil gelatinase-associated lipocalin (NGAL) and progression of chronic kidney disease

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) has recently assumed epidemic proportion, becoming a troubling emerging cause of morbidity, especially if it progresses to terminal stage (ESRD). The authors aimed to evaluate whether neutrophil gelatinase-associated lipocalin (NGAL), a novel specific biomarker of acute kidney injury, could predict the progression of CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Serum and urinary NGAL levels, together with a series of putative progression factors, were evaluated in a cohort of 96 patients (mean age: 57 +/- 16 years) affected by nonterminal CKD (eGFR > or =15 ml/min/1.73 m(2)) of various etiology. Progression of CKD, assessed as doubling of baseline serum creatinine and/or onset of ESRD, was evaluated during follow-up.

RESULTS

At baseline, both serum and urinary NGAL were inversely, independently, and closely related to eGFR. After a median follow-up of 18.5 mo (range 1.01 to 20), 31 patients (32%) reached the composite endpoint. At baseline, these patients were significantly older and showed increased serum creatinine, calcium-phosphate product, C-reactive protein, fibrinogen, daily proteinuria, and NGAL levels, whereas eGFR values were significantly lower. Univariate followed by multivariate Cox proportional hazard regression analysis showed that urinary NGAL and sNGAL predicted CKD progression independently of other potential confounders, including eGFR and age.

CONCLUSION

In patients with CKD, NGAL closely reflects the entity of renal impairment and represents a strong and independent risk marker for progression of CKD.

Rap1b GTPase ameliorates glucose-induced mitochondrial dysfunction

The role of tubular injury in diabetic nephropathy is relatively unknown, despite that apoptosis of tubular epithelial cells is commonly observed in human renal biopsies. The GTPase Ras-proximate-1 (Rap1b) is upregulated in the hyperglycemic state and is known to increase B-Raf, an antiapoptotic effector protein. In this study, the effects of high glucose on renal tubular apoptosis and the potential ability for Rap1b to ameliorate these effects were investigated. In the kidneys of diabetic mice, apoptotic tubular cells and dysmorphic mitochondria were observed, Bcl-2 expression was decreased, and Bax expression was increased. Total Rap1b expression was slightly increased, but its associated GTPase activity was significantly decreased. In vitro, high extracellular glucose led to decreased Bcl-2 expression, reduced Rap1b GTPase activity, and increased levels of both Bax and GTPase activating protein in a proximal tubular cell line (HK-2). These changes were accompanied by increased DNA fragmentation, decreased high molecular weight mitochondrial DNA, altered mitochondrial morphology and function, disrupted Bcl-2-Bax and Bcl-2-Rap1b interactions, and reduced cell survival. Overexpression of Rap1b partially prevents these abnormalities. Furthermore, the BH4 domain of Bcl-2 was found to be required for successful protein-protein interaction between Bcl-2 and Rap1b. In summary, these data suggest that Rap1b ameliorates glucose-induced mitochondrial dysfunction in renal tubular cells.

hTERT alone immortalizes epithelial cells of renal proximal tubules without changing their functional characteristics

Telomere-dependent replicative senescence is one of the mechanisms that limit the number of population doublings of normal human cells. By overexpression of telomerase, cells of various origins have been successfully immortalized without changing the phenotype. While a limited number of telomerase-immortalized cells of epithelial origin are available, none of renal origin has been reported so far. Here we have established simple and safe conditions that allow serial passaging of renal proximal tubule epithelial cells (RPTECs) until entry into telomere-dependent replicative senescence. As reported for other cells, senescence of RPTECs is characterized by arrest in G1 phase, shortened telomeres, staining for senescence-associated beta-galactosidase, and accumulation of gamma-H2AX foci. Furthermore, ectopic expression of the catalytic subunit of telomerase (TERT) was sufficient to immortalize these cells. Characterization of immortalized RPTEC/TERT1 cells shows characteristic morphological and functional properties like formation of tight junctions and domes, expression of aminopeptidase N, cAMP induction by parathyroid hormone, sodium-dependent phosphate uptake, and the megalin/cubilin transport system. No genomic instability within up to 90 population doublings has been observed. Therefore, these cells are proposed as a valuable model system not only for cell biology but also for toxicology, drug screening, biogerontology, as well as tissue engineering approaches.

NOX enzymes and diabetic complications

Several molecular mechanisms have been identified that mediate the tissue-damaging effects of hyperglycemia. These are increased flux through the polyol and hexosamine pathways, increased formation of advanced glycation end products, activation of protein kinase C, and augmented generation of reactive oxygen species (ROS). Increased production of ROS not only causes cellular damage but also activates the signal transduction cascade that activates specific target genes. Based on recent experimental data, it is now accepted that increased NADPH oxidase activity in tissues vulnerable to hyperglycemia takes place downstream of the advanced glycation end products and protein kinase C pathways, two of the primary mechanisms involved in the pathogenesis of diabetic complications. Thus, compounds that suppress NADPH oxidase activity may offer therapeutic benefits to ameliorate diabetic complications, highlighting the significance of NADPH oxidase as a new therapeutic target.

Diabetic nephropathy: mechanisms of renal disease progression

Diabetic nephropathy is characterized by excessive amassing of extracellular matrix (ECM) with thickening of glomerular and tubular basement membranes and increased amount of mesangial matrix, which ultimately progress to glomerulosclerosis and tubulo-interstitial fibrosis. In view of this outcome, it would mean that all the kidney cellular elements, i.e., glomerular endothelia, mesangial cells, podocytes, and tubular epithelia, are targets of hyperglycemic injury. Conceivably, high glucose activates various pathways via similar mechanisms in different cell types of the kidney except for minor exceptions that are related to the selective expression of a given molecule in a particular renal compartment. To begin with, there is an obligatory excessive channeling of glucose intermediaries into various metabolic pathways with generation of advanced glycation products (AGEs), activation of protein kinase C (PKC), increased expression of transforming growth factor-beta (TGF-beta), GTP-binding proteins, and generation of reactive oxygen species (ROS). The ROS seem to be the common denominator in various pathways and are central to the pathogenesis of hyperglycemic injury. In addition, there are marked alterations in intraglomerular hemodynamics, i.e., hyperfiltration, and this along with metabolic derangements adversely compounds the hyperglycemia-induced injury. Here, the information compiled under various subtitles of this article is derived from an enormous amount of data summarized in several excellent literature reviews, and thus their further reading is suggested to gain in-depth knowledge of each of the subject matter.

17beta-Estradiol attenuates diabetic kidney disease by regulating extracellular matrix and transforming growth factor-beta protein expression and signaling

We previously showed that supplementation with 17beta-estradiol (E2) from the onset of diabetes attenuates the development of diabetic renal disease. The aim of the present study was to examine whether E2 can also attenuate the disease process once it has developed. The present study was performed in nondiabetic and streptozotocin-induced diabetic Sprague-Dawley rats. E2 supplementation began after 9 wk of diabetes and continued for 8 wk. Diabetes was associated with an increase in urine albumin excretion, glomerulosclerosis, tubulointerstitial fibrosis, renal cortical collagen type I and IV, laminin, plasminogen activator inhibitor-1, tissue inhibitors of metalloproteinase-1 and -2, transforming growth factor (TGF)-beta, TGF-beta receptor type I and II, Smad2/3, phosphorylated Smad2/3, and Smad4 protein expression, and CD68-positive cell abundance. Decreases in matrix metalloproteinase (MMP)-2 protein expression and activity and decreases in Smad6 and Smad7 protein expression were also associated with diabetes. E2 supplementation completely or partially attenuated all these changes, except Smad4 and fibronectin, on which E2 supplementation had no effect. These data suggest that E2 attenuates the progression of diabetic renal disease once it has developed by regulating extracellular matrix, TGF-beta, and expression of its downstream regulatory proteins. These findings support the notion that sex hormones in general, and E2 in particular, are important regulators of renal function and may be novel targets for the treatment and prevention of diabetic renal disease.

Damage of tubule cells in diabetic nephropathy type 2: urinary N-acetyl-beta-D-glucosaminidasis and gamma-glutamil-transferasis

BACKGROUND/AIM

A damage of tubular epithelial cells is followed by the release of cell enzymes and production of proinflammatory compounds, which lead to the tubulointerstitial damage. The aim of this study was to examine the function of renal tubules in the patients with diabetes mellitus type 2 (DM type 2) and the various proteinuria degrees, to establish the damage of the proximal tubule cells caused by DM type 2 by determining urinary N-acetyl-beta-D-glucosaminidasis (beta-NAG) and gamma-glutamil-transferasis (gamma-GT) activity in urine, as well as to compare the obtained results in the examined groups of patients with the values in the healthy examinees.

METHODS

A complete examination of renal function and selective enzymuria was performed in 37 patients with DM type 2, and 14 healthy examinees as the controls. The patients were divided in three groups according to the degree of proteinuria. The first group consisted of the patients with diabetes without microalbuminuria; the second one consisted of the patients with proteinuria of < 300 mg/24 h, and microalbuminuria of > 20 mg/24 h, while the third one included the patients with proteinuria of > 300 mg/24 h.

RESULTS

In the patients with DM type 2 and the preserved global renal function, fractional excretion of sodium, potassium and phosphates, as well as renal threshold of phosphates concentration, were not sensitive parameters for discovering the damage of the renal tubule function. The determination of beta-NAG activity proved to be the most sensitive parameter for early discovering of tubule cells damages. The difference among the examined groups was statistically highly significant.

CONCLUSION

The increased presence of beta-NAG in the urine of DM type 2 patients, pointed out an early tubular disorder and damage of cells, while gamma-GT was a less sensitive indicator of this damage.

Effect of pioglitazone on urinary liver-type fatty acid-binding protein concentrations in diabetes patients with microalbuminuria

BACKGROUND

Urinary liver-type fatty acid-binding protein (L-FABP) is a useful marker for renal tubulointerstitial injury. Pioglitazone is reported to be effective in early diabetic nephropathy. The aim of the present study was to determine whether pioglitazone affects urinary L-FABP levels in diabetic nephropathy patients with microalbuminuria.

METHODS

Sixty-eight patients with type 2 diabetes and microalbuminuria were randomized to a 12-month treatment with pioglitazone (30 mg/d, n = 17), glibenclamide (5 mg/d, n = 18), voglibose (0.6 mg/d, n = 17), or nateglinide (270 mg/d, n = 16). Pre- and posttreatment urinary albumin excretion (UAE) and urinary L-FABP concentrations were compared between the four treatment groups and 40 age-matched healthy subjects.

RESULTS

Pretreatment UAE and urinary L-FABP levels differed little between the four groups. UAE and urinary L-FABP levels were significantly greater in the diabetes patients than in the healthy subjects (UAE: p < 0.001; L-FABP: p < 0.01). After 6 and 12 months, UAE and urinary L-FABP were significantly lower in the pioglitazone treatment group than in the other treatment groups (UAE: 6 months, p < 0.01 and 12 months, p < 0.001; L-FABP: 6 months, p < 0.05 and 12 months, p < 0.01).

CONCLUSIONS

Pioglitazone, but not glibenclamide, voglibose, or nateglinide, appears to be effective in reducing UAE and the urinary L-FABP level, suggesting that pioglitazone has a specific role in ameliorating both glomerular and tubulointerstitial lesions associated with early diabetic nephropathy.

Upregulation of osteopontin gene expression in diabetic rat proximal tubular cells revealed by microarray profiling

Progression of diabetic nephropathy appears directly related to renal tubulointerstitial injury, but the involved genes are incompletely delineated. To identify such genes, DNA microarray analysis was performed with RNA from renal proximal tubules (RPTs) of streptozotocin-induced diabetic Wistar rats, spontaneously diabetic BioBreeding rats, and rat immortalized renal proximal tubular cells (IRPTCs) exposed to high glucose (25 mM) medium for 2 weeks. Osteopontin (OPN) mRNA expression was quantified by real time-quantitative polymerase chain reaction (RT-qPCR) or conventional reverse transcriptase-polymerase chain reaction (RT-PCR). OPN mRNA expression was upregulated (5-70-fold increase) in diabetic rat RPTs and in IRPTCs chronically exposed to high glucose compared to control RPTs and IRPTCs. High glucose, angiotensin II, phorbol 12-myristate 13-acetate and transforming growth factor-beta 1 (TGF-beta1) stimulated OPN mRNA expression in IRPTCs in a dose- and time-dependent manner. This effect was inhibited by tiron, taurine, diphenylene iodinium, losartan, perindopril, calphostin C, or LY 379196 but not PD123319. IRPTCs overexpressing dominant-negative protein kinase C-beta 1 (PKC-beta1) cDNA or antisense TGF-beta1 cDNA prevented the high glucose effect on OPN mRNA expression. We concluded that high glucose-mediated increases in OPN gene expression in diabetic rat RPTs and IRPTCs are mediated, at least in part, via reactive oxygen species generation, intrarenal rennin-angiotensin system activation, TGF-beta1 expression, and PKC-beta1 signaling.

Renal-specific oxidoreductase biphasic expression under high glucose ambience during fetal versus neonatal development

BACKGROUND

Renal-specific oxidoreductase (RSOR) has been recently identified in mice kidneys of diabetic animals, and it is developmentally regulated. Its expression during fetal, neonatal, and postnatal periods was assessed under high glucose ambience.

METHODS

Whole-mount immunofluorescence and confocal microscopy were performed to assess the effect of high glucose on the morphogenesis of mice fetal kidneys. RSOR mRNA and protein expression was assessed by competitive polymerase chain reaction (PCR) and immunoprecipitation methods in embryonic kidneys (day E13 to E17) subjected to high glucose ambience and by Northern and Western blot analyses of kidneys of newborn and 1-week-old mice with hyperglycemia. The spatiotemporal changes in the RSOR expression were assessed by in situ hybridization analyses and immunofluorescence microscopy. In addition, the extent of apoptosis in the kidneys was determined by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) assay.

RESULTS

Whole-mount microscopy of the embryonic metanephroi revealed a dose-dependent disruption in the ureteric bud iterations with reduced population of the nascent nephrons. Both gene and protein expressions were reduced in day E13 to E17 metanephroi, while increased in kidneys of newborn and 1-week-old mice. In day E13 and day E15 kidneys, the RSOR was expressed in the ureteric bud branches and some of the immature tubules, and its expression was reduced with high glucose treatment. In day E17 kidneys the RSOR was expressed in the tubules of the deeper cortex, and its expression was marginally decreased. In newborn kidneys, this enzyme was expressed in the subcortical tubules and it spread to the entire width of the renal cortex in hyperglycemic state. In 1-week-old mice kidneys, the RSOR was localized to the entire cortex, and in animals with blood glucose above 300 mg/dL, its intensity increased with extension of expression into the outer medullary tubules. A dose-dependent fulminant apoptosis was observed in day E13 to E17 kidneys subjected to high glucose ambience. In newborn and 1-week-old mice control kidneys, the apoptosis was minimal although slightly increased during hyperglycemia.

CONCLUSION

High glucose has a differential effect on the RSOR expression in kidneys during the embryonic versus neonatal/postnatal period. This may partly be related to the differential degree of apoptosis, a process reflective of oxidant stress that is seen in diabetic milieu, which as previously has been shown to adversely effect the modulators of fetal development and thereby the morphogenesis of the kidney and RSOR expression.