Impaired glomerular and tubular antioxidative defense mechanisms in nephrotic syndrome

Biomarkers of acute kidney injury in patients with nephrotic syndrome

Introduction:

Emergence of acute kidney injury (AKI) in patients with nephrotic syndrome (NS) requires prompt diagnosis and differentiation between acute tubular necrosis (ATN) and proliferative glomerulonephritis. We studied the potential use of commercial urinary biomarkers' tests in the diagnosis of AKI in patients with NS.

Methods:

A cross sectional estimate of urinary concentrations of KIM-1 and NGAL was performed in 40 patients with NS: 9 with proliferative glomerulopathy, being 4 with AKI and 31 without proliferative glomerulopathy, being 15 with AKI. AKI was defined using the KDIGO criteria.

Results:

The mean age was 35 ± 16 years. The main diagnoses were focal and segmental glomerulosclerosis (10, 25%), membranous glomerulopathy (10, 25%), minimal change disease (7, 18%), lupus nephritis (6, 15%), and proliferative glomerulonephritis (3, 8%). Patients with ATN had higher levels of urinary KIM-1 (P = 0.0157) and NGAL (P = 0.023) than patients without ATN. The urinary concentrations of KIM-1 (P= 0.009) and NGAL (P= 0.002) were higher in patients with AKI than in patients without AKI. Urinary NGAL and KIM-1 levels were significantly higher in patients with ATN without proliferative glomerulonephritis than in patients with proliferative glomerulonephritis (P = 0.003 and P=0.024, respectively).

Conclusions:

Neutrophil gelatinase associated lipocalin (NGAL) and kidney injury molecule 1 (KIM-1) estimates correlated with histological signs of ATN and were able to discriminate patients with AKI even in conditions of NS. Furthermore, urinary levels of NGAL and KIM-1 may be useful in the differential diagnosis of acute tubular necrosis and exudative glomerulonephritis in patients with nephrotic syndrome.

Impaired thiol/disulphide homoeostasis in children with steroid-sensitive nephrotic syndrome

BACKGROUND

Abnormal thiol/disulphide homoeostasis (TDH) is responsible for the pathogenesis of various diseases. We aimed to examine the TDH in children with steroid-sensitive nephrotic syndrome (SSNS).

METHODS

A total of 131 children, 60 with SSNS and 71 healthy controls, participated in the study. Plasma total thiol (TT), native thiol (SH) and disulphide (SS) levels in the SSNS during remission and control groups were estimated using a new method developed by Erel and Neselioglu.

RESULTS

Albumin, TT, SH levels and SH/TT ratio were decreased, whereas SS/SH and SS/TT ratios were elevated in SSNS group compared with control group. However, there was no significant difference in SS levels between the two groups. Albumin level was positively correlated with TT, SH and SS levels in the SSNS group.

CONCLUSIONS

We found that TDH shifts in favour of oxidants in children with SSNS in remission. This shift indicates that SSNS patients are exposed to augmented oxidative stress.

Increased ischemia-modified albumin levels in children with steroid-sensitive nephrotic syndrome

Objective:

Growing evidence shows that oxidative stress plays an important role in the development and progression of nephrotic syndrome (NS). In this study, we aimed to examine serum IMA levels as an indicator of oxidative stress in children with steroid-sensitive NS (SSNS) in remission and relapse.

Methods:

This cross-sectional study was carried out at the Pediatric Nephrology Unit of Sanliurfa Training and Research Hospital, Sanliurfa, Turkey, from April 2019 to December 2019. In this study Serum IMA and albumin levels were determined in 70 children with SSNS and 45 healthy controls. Among the children with SSNS, 50 were in remission and 20 were in relapse. Then, adjusted IMA levels were calculated from the IMA/albumin ratio.

Results:

IMA and adjusted IMA levels significantly increased and albumin significantly decreased in children with SSNS in relapse and remission compared with those of the healthy controls. Moreover, these alterations were more prominent in the relapse group than in the remission group. IMA was inversely correlated with albumin in children with SSNS (r= −0.881, p= <0.001).

Conclusions:

Our findings demonstrated that elevated IMA and adjusted IMA levels observed in patients with SSNS were associated with increased oxidative stress and could indirectly reflect the degree of oxidative damage in glomerular structures.

Kidney-derived c-kit+ progenitor/stem cells contribute to podocyte recovery in a model of acute proteinuria

Kidney-derived c-kit⁺ cells exhibit progenitor/stem cell properties and can regenerate epithelial tubular cells following ischemia-reperfusion injury in rats. We therefore investigated whether c-kit⁺ progenitor/stem cells contribute to podocyte repair in a rat model of acute proteinuria induced by puromycin aminonucleoside (PAN), the experimental prototype of human minimal change disease and early stages of focal and segmental glomerulosclerosis. We found that c-kit⁺ progenitor/stem cells accelerated kidney recovery by improving foot process effacement (foot process width was lower in c-kit group vs saline treated animals, P = 0.03). In particular, these cells engrafted in small quantity into tubules, vessels, and glomeruli, where they occasionally differentiated into podocyte-like cells. This effect was related to an up regulation of α-Actinin-4 and mTORC2-Rictor pathway. Activation of autophagy by c-kit⁺ progenitor/stem cells also contributed to kidney regeneration and intracellular homeostasis (autophagosomes and autophagolysosomes number and LC3A/B-I and LC3A/B-II expression were higher in the c-kit group vs saline treated animals, P = 0.0031 and P = 0.0009, respectively). Taken together, our findings suggest that kidney-derived c-kit⁺ progenitor/stem cells exert reparative effects on glomerular disease processes through paracrine effects, to a lesser extent differentiation into podocyte-like cells and contribution to maintenance of podocyte cytoskeleton after injury. These findings have clinical implications for cell therapy of glomerular pathobiology.

Taurine Supplementation Alleviates Puromycin Aminonucleoside Damage by Modulating Endoplasmic Reticulum Stress and Mitochondrial-Related Apoptosis in Rat Kidney

Taurine (TAU) is a sulfur-containing beta amino acid that is not involved in protein composition and anabolism, conditionally essential in mammals provided through diet. Growing evidence supports a protective role of TAU supply in osmoregulation, calcium flux, and reduction of inflammation and oxidant damage in renal diseases like diabetes. Endoplasmic reticulum (ER) stress, due to abnormal proteostasis, is a contributor to nephrotic syndrome and related renal damage. Here, we investigated the effect of dietary TAU (1.5% in drinking water for 15 days) in an established rat model that mimics human minimal change nephrosis, consisting of a single puromycin aminonucleoside (PAN) injection (intraperitoneally 15 mg/100 g body weight), with sacrifice after eight days. TAU limited proteinuria and podocytes foot processes effacement, and balanced slit diaphragm nephrin and glomerular claudin 1 expressions. In cortical proximal tubules, TAU improved lysosomal density, ER perimeter, restored proper ER-mitochondria tethering and mitochondrial cristae, and decreased inflammation. Remarkably, TAU downregulated glomerular ER stress markers (GRP78, GRP94), pro-apoptotic C/EBP homologous protein, activated caspase 3, tubular caspase1, and mitochondrial chaperone GRP75, but maintained anti-apoptotic HSP25. In conclusion, TAU, by targeting upstream ER stress separate from mitochondria dysfunctions at crucial renal sites, might be a promising dietary supplement in the treatment of the drug-resistant nephrotic syndrome.

Nitric oxide synthase inhibition causes acute increases in glomerular permeability in vivo, dependent upon reactive oxygen species

There is increasing evidence that the permeability of the glomerular filtration barrier (GFB) is partly regulated by a balance between the bioavailability of nitric oxide (NO) and that of reactive oxygen species (ROS). It has been postulated that normal or moderately elevated NO levels protect the GFB from permeability increases, whereas ROS, through reducing the bioavailability of NO, have the opposite effect. We tested the tentative antagonism between NO and ROS on glomerular permeability in anaesthetized Wistar rats, in which the left ureter was cannulated for urine collection while simultaneously blood access was achieved. Rats were systemically infused with either l-NAME or l-NAME together with the superoxide scavenger Tempol, or together with l-arginine or the NO-donor DEA-NONOate, or the cGMP agonist 8-bromo-cGMP. To measure glomerular sieving coefficients (theta, θ) to Ficoll, rats were infused with FITC-Ficoll 70/400 (mol/radius 10-80 Å). Plasma and urine samples were analyzed by high-performance size-exclusion chromatography (HPSEC) for determination of θ for Ficoll repeatedly during up to 2 h. l-NAME increased θ for Ficoll_70Å from 2.27 ± 1.30 × 10^-5 to 8.46 ± 2.06 × 10^-5 (n = 6, P < 0.001) in 15 min. Tempol abrogated these increases in glomerular permeability and an inhibition was also observed with l-arginine and with 8-bromo-cGMP. In conclusion, acute NO synthase inhibition in vivo by l-NAME caused rapid increases in glomerular permeability, which could be reversed by either an ROS antagonist or by activating the guanylyl cyclase-cGMP pathway. The data strongly suggest a protective effect of NO in maintaining normal glomerular permeability in vivo.

Blood concentration of aminothiols in children with relapse of nephrotic syndrome

BACKGROUND

The role of idiopathic nephrotic syndrome (INS) in the pathogenesis of atherosclerosis in childhood has not been clearly elucidated. However, antioxidative defense in INS is thought to be imbalanced. This study aimed to assess the changes of plasma concentration of selected aminothiols in the blood of children with INS at various stages of the disease.

METHODS

This cross-sectional study was conducted in 125 children aged 2-18 years. The children were divided into 4 groups: group A, early relapse (n=37); group B, early remission for 4-6 weeks from the onset (n=37); group C, late steroid-free remission (n=31); and group D, long-term remission for 2-5 years (n=20). Control group (E) consisted of 30 age- and gender-matched healthy children. The study protocol comprised an analysis of plasma concentrations of glutathione, homocysteine, cysteine and cysteinylglycine by high-performance liquid chromatography. Fractions of protein-bound and free aminothiols were measured. Endothelial injury was assessed by thrombomodulin, PAI-1 concentration, and von Willebrand factor activity.

RESULTS

The children with INS had unbalanced aminothiol metabolism only in relapse and early remission, that shifted towards increased oxidative processes. Administration of cyclosporine A caused a significant increase in homocysteine and cysteine concentration. Changes in aminothiol metabolism were significantly related to endothelial injury.

CONCLUSIONS

The findings of this study may be helpful in elucidating the pathogenesis of premature atherosclerosis in patients with INS refractory to the treatment or in the case of frequent relapse.

Oxidative Stress and Nuclear Factor κB (NF-κB) Increase Peritoneal Filtration and Contribute to Ascites Formation in Nephrotic Syndrome

Water accumulation in the interstitium (edema) and the peritoneum (ascites) of nephrotic patients is classically thought to stem from the prevailing low plasma albumin concentration and the decreased transcapillary oncotic pressure gradient. However, several clinical and experimental observations suggest that it might also stem from changes in capillary permeability. We addressed this hypothesis by studying the peritoneum permeability of rats with puromycin aminonucleoside-induced nephrotic syndrome. The peritoneum of puromycin aminonucleoside rats displayed an increase in the water filtration coefficient of paracellular and transcellular pathways, and a decrease in the reflection coefficient to proteins. It also displayed oxidative stress and subsequent activation of NF-κB. Scavenging of reactive oxygen species and inhibition of NF-κB prevented the changes in the water permeability and reflection coefficient to proteins and reduced the volume of ascites by over 50%. Changes in water permeability were associated with the overexpression of the water channel aquaporin 1, which was prevented by reactive oxygen species scavenging and inhibition of NF-κB. In conclusion, nephrotic syndrome is associated with an increased filtration coefficient of the peritoneum and a decreased reflection coefficient to proteins. These changes, which account for over half of ascite volume, are triggered by oxidative stress and subsequent activation of NF-κB.

Melanocortin 1 receptor agonist protects podocytes through catalase and RhoA activation

Drugs containing adrenocorticotropic hormone have been used as therapy for patients with nephrotic syndrome. We have previously shown that adrenocorticotropic hormone and a selective agonist for the melanocortin 1 receptor (MC1R) exert beneficial actions in experimental membranous nephropathy with reduced proteinuria, reduced oxidative stress, and improved glomerular morphology and function. Our hypothesis is that MC1R activation in podocytes elicits beneficial effects by promoting stress fibers and maintaining podocyte viability. To test the hypothesis, we cultured podocytes and used highly specific agonists for MC1R. Podocytes were subjected to the nephrotic-inducing agent puromycin aminonucleoside, and downstream effects of MC1R activation on podocyte survival, antioxidant defense, and cytoskeleton dynamics were studied. To increase the response and enhance intracellular signals, podocytes were transduced to overexpress MC1R. We showed that puromycin promotes MC1R expression in podocytes and that activation of MC1R promotes an increase of catalase activity and reduces oxidative stress, which results in the dephosphorylation of p190RhoGAP and formation of stress fibers through RhoA. In addition, MC1R agonists protect against apoptosis. Together, these mechanisms protect the podocyte against puromycin. Our findings strongly support the hypothesis that selective MC1R-activating agonists protect podocytes and may therefore be useful to treat patients with nephrotic syndromes commonly considered as podocytopathies.

Homocysteine in Chronic Kidney Disease

Hyperhomocysteinemia occurs in chronic- and end-stage kidney disease at the time when dialysis or transplant becomes indispensable for survival. Excessive accumulation of homocysteine (Hcy) aggravates conditions associated with imbalanced homeostasis and cellular redox thereby resulting in severe oxidative stress leading to oxidation of reduced free and protein-bound thiols. Thiol modifications such as N-homocysteinylation, sulfination, cysteinylation, glutathionylation, and sulfhydration control cellular responses that direct complex metabolic pathways. Although cysteinyl modifications are kept low, under Hcy-induced stress, thiol modifications persist thus surpassing cellular proteostasis. Here, we review mechanisms of redox regulation and show how cysteinyl modifications triggered by excess Hcy contribute development and progression of chronic kidney disease. We discuss different signaling events resulting from aberrant cysteinyl modification with a focus on transsulfuration.

Glomerular IgG subclasses in idiopathic and malignancy-associated membranous nephropathy

Background

In idiopathic membranous nephropathy (MN), antibodies directed towards the glomerular phospholipase A₂ receptor (PLA₂R) have mainly been reported to be of IgG4 subclass. However, the role of the different IgG subclasses in the pathogenesis of MN, both in idiopathic MN and in secondary cases, is still unclear. In this retrospective study, we test the hypothesis that the absence of glomerular IgG4 and PLA₂R in patients with MN indicates malignant disease.

Methods

The distribution pattern of glomerular IgG subclasses and PLA₂R was studied in 69 patients with idiopathic MN and 16 patients with malignancy-associated MN who were followed up for a mean of 83 months.

Results

A significant correlation between the absence of IgG4 and PLA₂R and malignancy-associated MN was found. Thus, IgG4 was positive in 45 of 69 patients (65%) with idiopathic MN but only in 5 of 16 patients (31%) with malignancy-associated MN. The other IgG subclasses did not differ statistically between the groups, IgG2-positivity being present in more than 94% of patients in both groups. Thirty-five of 63 patients (56%) with idiopathic MN and 3 of 16 (19%) patients with malignancy-associated MN had glomerular deposits of PLA₂R.

Conclusions

We have found that the absence of glomerular IgG4 and PLA₂R is common in patients with malignancy-associated MN. In our material, IgG2 could not be used as a marker of underlying malignant disease. Finally, neither IgG1 nor IgG3 seems to be involved in the pathogenesis of MN.

Oedema in kwashiorkor is caused by hypoalbuminaemia

It has been argued that the oedema of kwashiorkor is not caused by hypoalbuminaemia because the oedema disappears with dietary treatment before the plasma albumin concentration rises. Reanalysis of this evidence and a review of the literature demonstrates that this was a mistaken conclusion and that the oedema is linked to hypoalbuminaemia. This misconception has influenced the recommendations for treating children with severe acute malnutrition. There are close pathophysiological parallels between kwashiorkor and Finnish congenital nephrotic syndrome (CNS) pre-nephrectomy; both develop protein-energy malnutrition and hypoalbuminaemia, which predisposes them to intravascular hypovolaemia with consequent sodium and water retention, and makes them highly vulnerable to develop hypovolaemic shock with diarrhoea. In CNS this is successfully treated with intravenous albumin boluses. By contrast, the WHO advise the cautious administration of hypotonic intravenous fluids in kwashiorkor with shock, which has about a 50% mortality. It is time to trial intravenous bolus albumin for the treatment of children with kwashiorkor and shock.

mTOR inhibition with temsirolimus causes acute increases in glomerular permeability, but inhibits the dynamic permeability actions of puromycin aminonucleoside

Inhibitors of the mammalian target of rapamycin (mTORi) can produce de novo proteinuria in kidney transplant patients. On the other hand, mTORi has been shown to suppress disease progression in several animal models of kidney disease. In the present study, we investigated whether glomerular permeability can be acutely altered by the mTORi temsirolimus and whether mTORi can affect acute puromycin aminonucleoside (PAN) or angiotensin II (ANG II)-induced glomerular hyperpermeability. In anesthetized Wistar rats, the left ureter was cannulated for urine collection, while simultaneously blood access was achieved. Temsirolimus was administered as a single intravenous dose 30 min before the start of the experiments in animals infused with PAN or ANG II or in nonexposed animals. Polydispersed FITC-Ficoll-70/400 (molecular radius 10-80 Å) and (51)Cr-EDTA infusion was given during the whole experiment. Measurements of Ficoll in plasma and urine were performed sequentially before the temsirolimus injection (baseline) and at 5, 15, 30, 60, and 120 min after the start of the experiments. Urine and plasma samples were analyzed by high-performance size-exclusion chromatography (HPSEC) to assess glomerular sieving coefficients (θ) for Ficoll10-80Å. Temsirolimus per se increased baseline glomerular permeability to Ficoll50-80Å 45 min after its administration, a reactive oxygen species (ROS)-dependent phenomenon. PAN caused a rapid and reversible increase in glomerular permeability, peaking at 5 min, and again at 60-120 min, which could be blocked by the ROS scavenger tempol. mTORi abrogated the second permeability peak induced by PAN. However, it had no effect on the immediate ANG II- or PAN-induced increases in glomerular permeability.

Overexpression of Mafb in podocytes protects against diabetic nephropathy

We previously showed that the transcription factor Mafb is essential for podocyte differentiation and foot process formation. Podocytes are susceptible to injury in diabetes, and this injury leads to progression of diabetic nephropathy. In this study, we generated transgenic mice that overexpress Mafb in podocytes using the nephrin promoter/enhancer. To examine a potential pathogenetic role for Mafb in diabetic nephropathy, Mafb transgenic mice were treated with either streptozotocin or saline solution. Diabetic nephropathy was assessed by renal histology and biochemical analyses of urine and serum. Podocyte-specific overexpression of Mafb had no effect on body weight or blood glucose levels in either diabetic or control mice. Notably, albuminuria and changes in BUN levels and renal histology observed in diabetic wild-type animals were ameliorated in diabetic Mafb transgenic mice. Moreover, hyperglycemia-induced downregulation of Nephrin was mitigated in diabetic Mafb transgenic mice, and reporter assay results suggested that Mafb regulates Nephrin directly. Mafb transgenic glomeruli also overexpressed glutathione peroxidase, an antioxidative stress enzyme, and levels of the oxidative stress marker 8-hydroxydeoxyguanosine decreased in the urine of diabetic Mafb transgenic mice. Finally, Notch2 expression increased in diabetic glomeruli, and this effect was enhanced in diabetic Mafb transgenic glomeruli. These data indicate Mafb has a protective role in diabetic nephropathy through regulation of slit diaphragm proteins, antioxidative enzymes, and Notch pathways in podocytes and suggest that Mafb could be a therapeutic target.

Serum levels of malondialdehyde, vitamin C and E in idiopathic nephrotic syndrome: a meta-analysis

It is well documented that oxidative stress is involved in the pathogenesis of idiopathic nephrotic syndrome (INS). Malondialdehyde (MDA) is a measurement of lipid oxidation; vitamin C and E are important components of antioxidants. However, the association between MDA, vitamin C or E levels and INS remains elusive. A meta-analysis was performed to investigate the alteration of serum levels of MDA, vitamin C and E in INS compared with controls. Eight studies were included in our meta-analysis according to predefined criteria. Active INS patients demonstrated significantly higher level of serum MDA (SMD: 2.13, 95% CI: 1.511 to 2.749, p < 10(-4)), markedly lower levels of serum vitamin C (SMD: -1.449, 95% CI: -2.616 to -0.281, p = 0.015) and E (SMD: -1.45, 95% CI: -2.544 to -0.356, p = 0.009) compared with those in controls. Active steroid-sensitive nephrotic syndrome (SSNS) patients showed comparable levels of serum vitamin C and E to those in controls. INS subjects in the remission stage demonstrated significantly higher level of serum MDA (SMD: 1.028, 95% CI: 0.438 to 1.617, p < 10(-4)), markedly lower level of serum vitamin C (SMD: -2.235, 95% CI: -3.048 to -1.421, p < 10(4)) and similar level of serum vitamin E compared with those in controls. No significant publication bias was observed. In conclusion, the disorder of MDA and vitamin C persists in the remission stage of INS. It seems that the serum levels of vitamin C and E is associated with the responsiveness of INS to steroids. However, more studies should be performed in the future.

Gene expression analysis and urinary biomarker assays reveal activation of tubulointerstitial injury pathways in a rodent model of chronic proteinuria (Doxorubicin nephropathy)

BACKGROUND

Tubular atrophy and interstitial fibrosis are well-recognized sequelae of chronic proteinuria; however, little is known regarding the molecular pathways activated within tubulointerstitium in chronic proteinuric nephropathies.

METHODS

To investigate the molecular mechanisms of proteinuria-associated tubulointerstitial (TI) disease, doxorubicin nephropathy was induced in rats. Progression of disease was monitored with weekly urinary biomarker assays. Because histopathology revealed multifocal TI injury, immunodirected laser capture microdissection was used to identify and isolate injured proximal tubules, as indicated by kidney injury molecule-1 immunolabeling. Adjacent interstitial cells were harvested separately. Gene expression microarray, manual annotation of gene lists, and Gene Set Enrichment Analysis were performed. A subset of the regulated transcripts was validated by quantitative PCR and immunohistochemistry.

RESULTS

Severe proteinuria preceded tubular injury biomarkers by 1 week. Histology revealed multifocal, mild TI damage at 3 weeks, which progressed in severity at 5 weeks. Affymetrix microarray analysis revealed tissue-specific regulation of gene expression. Manual annotation of gene lists, gene set enrichment analysis, and urinary biomarker assays revealed similarities to pathways activated in direct TI injuries. This suggests commonalities amongst the molecular mechanisms of TI injury secondary to proteinuria, ischemia-reperfusion, and nephrotoxicity. © 2013 S. Karger AG, Basel.