Complement membrane attack complex (C5b-9) mediates interstitial disease in experimental nephrotic syndrome

Lactobacillus acidophilus KBL409 protects against kidney injury via improving mitochondrial function with chronic kidney disease

PURPOSE

Recent advances have led to greater recognition of the role of mitochondrial dysfunction in the pathogenesis of chronic kidney disease (CKD). There has been evidence that CKD is also associated with dysbiosis. Here, we aimed to evaluate whether probiotic supplements can have protective effects against kidney injury via improving mitochondrial function.

METHODS

An animal model of CKD was induced by feeding C57BL/6 mice a diet containing 0.2% adenine. KBL409, a strain of Lactobacillus acidophilus, was administered via oral gavage at a dose of 1 × 109 CFU daily. To clarify the underlying mechanisms by which probiotics exert protective effects on mitochondria in CKD, primary mouse tubular epithelial cells stimulated with TGF-β and p-cresyl sulfate were administered with butyrate.

RESULTS

In CKD mice, PGC-1α and AMPK, key mitochondrial energy metabolism regulators, were down-regulated. In addition, mitochondrial dynamics shifted toward fission, the number of fragmented cristae increased, and mitochondrial mass decreased. These alterations were restored by KBL409 administration. KBL409 supplementation also improved defects in fatty acid oxidation and glycolysis and restored the suppressed enzyme levels involved in TCA cycle. Accordingly, there was a concomitant improvement in mitochondrial respiration and ATP production assessed by mitochondrial function assay. These favorable effects of KBL409 on mitochondria ultimately decreased kidney fibrosis in CKD mice. In vitro analyses with butyrate recapitulated the findings of animal study.

CONCLUSIONS

This study demonstrates that administration of the probiotic Lactobacillus acidophilus KBL409 protects against kidney injury via improving mitochondrial function.

Amiloride Reduces Urokinase/Plasminogen-Driven Intratubular Complement Activation in Glomerular Proteinuria

SIGNIFICANCE STATEMENT

Proteinuria predicts accelerated decline in kidney function in CKD. The pathologic mechanisms are not well known, but aberrantly filtered proteins with enzymatic activity might be involved. The urokinase-type plasminogen activator (uPA)-plasminogen cascade activates complement and generates C3a and C5a in vitro / ex vivo in urine from healthy persons when exogenous, inactive, plasminogen, and complement factors are added. Amiloride inhibits uPA and attenuates complement activation in vitro and in vivo . In conditional podocin knockout (KO) mice with severe proteinuria, blocking of uPA with monoclonal antibodies significantly reduces the urine excretion of C3a and C5a and lowers tissue NLRP3-inflammasome protein without major changes in early fibrosis markers. This mechanism provides a link to proinflammatory signaling in proteinuria with possible long-term consequences for kidney function.

BACKGROUND

Persistent proteinuria is associated with tubular interstitial inflammation and predicts progressive kidney injury. In proteinuria, plasminogen is aberrantly filtered and activated by urokinase-type plasminogen activator (uPA), which promotes kidney fibrosis. We hypothesized that plasmin activates filtered complement factors C3 and C5 directly in tubular fluid, generating anaphylatoxins, and that this is attenuated by amiloride, an off-target uPA inhibitor.

METHODS

Purified C3, C5, plasminogen, urokinase, and urine from healthy humans were used for in vitro / ex vivo studies. Complement activation was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and ELISA. Urine and plasma from patients with diabetic nephropathy treated with high-dose amiloride and from mice with proteinuria (podocin knockout [KO]) treated with amiloride or inhibitory anti-uPA antibodies were analyzed.

RESULTS

The combination of uPA and plasminogen generated anaphylatoxins C3a and C5a from intact C3 and C5 and was inhibited by amiloride. Addition of exogenous plasminogen was sufficient for urine from healthy humans to activate complement. Conditional podocin KO in mice led to severe proteinuria and C3a and C5a urine excretion, which was attenuated reversibly by amiloride treatment for 4 days and reduced by >50% by inhibitory anti-uPA antibodies without altering proteinuria. NOD-, LRR- and pyrin domain-containing protein 3-inflammasome protein was reduced with no concomitant effect on fibrosis. In patients with diabetic nephropathy, amiloride reduced urinary excretion of C3dg and sC5b-9 significantly.

CONCLUSIONS

In conditions with proteinuria, uPA-plasmin generates anaphylatoxins in tubular fluid and promotes downstream complement activation sensitive to amiloride. This mechanism links proteinuria to intratubular proinflammatory signaling. In perspective, amiloride could exert reno-protective effects beyond natriuresis and BP reduction.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Increased Activity of a Renal Salt Transporter (ENaC) in Diabetic Kidney Disease, NCT01918488 and Increased Activity of ENaC in Proteinuric Kidney Transplant Recipients, NCT03036748 .

Urine Proteomics Link Complement Activation with Interstitial Fibrosis/Tubular Atrophy in Lupus Nephritis Patients

BACKGROUND

Intrarenal complement activation has been implicated in the pathogenesis of tubulointerstitial fibrosis in lupus nephritis (LN) based on prior animal studies. The assembly of the membrane attack complex (MAC) by complement C5b to C9 on the cell membrane leads to cytotoxic pores and cell lysis, while CD59 inhibits MAC formation by preventing C9 from joining the complex. We hypothesize that complement activation and imbalance between complement activation and inhibition, as defined by increased production of individual complement components and uncontrolled MAC activation relative to CD59 inhibition, are associated with interstitial fibrosis and tubular atrophy (IFTA) in LN and correlate with the key mediators of kidney fibrosis- transforming growth factor receptors beta (TGFRβ), platelet-derived growth factor beta (PDGFβ) and platelet-derived growth factor receptor beta (PDGFRβ).

METHODS

We included urine samples from 46 adults and pediatric biopsy-proven lupus nephritis patients who underwent clinically indicated kidney biopsies between 2010 and 2019. We compared individual urinary complement components and the urinary C9-to-CD59 ratio between LN patients with moderate/severe IFTA and none/mild IFTA. IFTA was defined as none/mild (<25% of interstitium affected) versus moderate/severe (≥ 25% of interstitium affected). Proteomics analysis was performed using mass spectrometry (Orbitrap Fusion Lumos, Thermo Scientific) and processed by the Proteome Discoverer. Urinary complement proteins enriched in LN patients with moderate/severe IFTA were correlated with serum creatinine, TGFβR1, TGFβR2, PDGFβ, and PDGFRβ.

RESULTS

Of the 46 LN patients included in the study, 41 (89.1%) were women, 20 (43.5%) self-identified as Hispanic or Latino, and 26 (56.5%) self-identified as Black or African American. Ten of the 46 (21.7%) LN patients had moderate/severe IFTA on kidney biopsy. LN patients with moderate/severe IFTA had an increased urinary C9-to-CD59 ratio [median 0.91 (0.83-1.05) vs 0.81 (0.76-0.91), p=0.01]. Urinary C3 and CFI levels in LN patients with moderate/severe IFTA were higher compared to those with none/mild IFTA [C3 median (IQR) 24.4(23.5-25.5) vs. 20.2 (18.5-22.2), p= 0.02], [CFI medium (IQR) 28.8 (21.8-30.6) vs. 20.4 (18.5-22.9), p=0.01]. Complement C9, CD59, C3 and CFI correlated with TGFβR1, PDGFβ, and PDGFRβ, while C9, CD59 and C3 correlated with TGFβR2.

CONCLUSION

This study is one of the first to compare the urinary complement profile in LN patients with moderate/severe IFTA and none/mild IFTA in human tissues. This study identified C3, CFI, and C9-to-CD59 ratio as potential markers of tubulointerstitial fibrosis in LN.

Nutritional Treatment as a Synergic Intervention to Pharmacological Therapy in CKD Patients

Nutritional and pharmacological therapies represent the basis for non-dialysis management of CKD patients. Both kinds of treatments have specific and unchangeable features and, in certain cases, they also have a synergic action. For instance, dietary sodium restriction enhances the anti-proteinuric and anti-hypertensive effects of RAAS inhibitors, low protein intake reduces insulin resistance and enhances responsiveness to epoetin therapy, and phosphate restriction cooperates with phosphate binders to reduce the net phosphate intake and its consequences on mineral metabolism. It can also be speculated that a reduction in either protein or salt intake can potentially amplify the anti-proteinuric and reno-protective effects of SGLT2 inhibitors. Therefore, the synergic use of nutritional therapy and medications optimizes CKD treatment. Quality of care management is improved and becomes more effective when compared to either treatment alone, with lower costs and fewer risks of unwanted side effects. This narrative review summarizes the established evidence of the synergistic action carried out by the combination of nutritional and pharmacological treatments, underlying how they are not alternative but complementary in CKD patient care.

Nicorandil protects podocytes via modulation of antioxidative capacity in acute puromycin aminonucleoside-induced nephrosis in rats

Nephrotic syndrome, characterized by proteinuria and hypoalbuminemia, results from the dysregulation of glomerular podocytes and is a significant cause of end-stage kidney disease. Patients with idiopathic nephrotic syndrome are generally treated with immunosuppressive agents; however, these agents produce various adverse effects. Previously, we reported the renoprotective effects of a stimulator of the mitochondrial ATP-dependent K⁺ channel (MitK_ATP), nicorandil, in a remnant kidney model. Nonetheless, the cellular targets of these effects remain unknown. Here, we examined the effect of nicorandil on puromycin aminonucleoside-induced nephrosis (PAN) rats, a well-established model of podocyte injury and human nephrotic syndrome. PAN was induced using a single intraperitoneal injection. Nicorandil was administered orally at 30 mg/kg/day. We found that proteinuria and hypoalbuminemia in PAN rats were significantly ameliorated following nicorandil treatment. Immunostaining and ultrastructural analysis under electron microscopy demonstrated that podocyte injury in PAN rats showed a significant partial attenuation following nicorandil treatment. Nicorandil ameliorated the increase in the oxidative stress markers nitrotyrosine and 8-hydroxy-2-deoxyguanosine in glomeruli. Conversely, nicorandil prevented the decrease in levels of the antioxidant enzyme manganese superoxide dismutase in PAN rats. We found that mitochondrial Ca²⁺ uniporter levels in glomeruli were higher in PAN rats than in control rats, and this increase was significantly attenuated by nicorandil. We conclude that stimulation of MitK_ATP by nicorandil reduces proteinuria by attenuating podocyte injury in PAN nephrosis, which restores mitochondrial antioxidative capacity, possibly through mitochondrial Ca²⁺ uniporter modulation. These data indicate that MitK_ATP may represent a novel target for podocyte injury and nephrotic syndrome.NEW & NOTEWORTHY Our findings suggest that the mitochondrial Ca²⁺ uniporter may be an upstream regulator of manganese superoxide dismutase and indicate a biochemical basis for the interaction between the ATP-sensitive K⁺ channel and Ca²⁺ signaling. We believe that our study makes a significant contribution to the literature because our results indicate that the ATP-sensitive K⁺ channel may be a potential therapeutic target for podocyte injury and nephrotic syndrome.

Membrane attack complex (MAC) deposition in renal tubules is associated with interstitial fibrosis and tubular atrophy: a pilot study

INTRODUCTION

Treatment failures for lupus nephritis (LN) are high with 10%-30% of patients progressing to end-stage renal disease (ESRD) within 10 years. Interstitial fibrosis/tubular atrophy (IFTA) is a predictor of progression to ESRD. Prior studies suggest that tubulointerstitial injury secondary to proteinuria in LN is mediated by complement activation in the tubules, specifically through the membrane attack complex (MAC). This study aimed to investigate the associations between tubular MAC deposition with IFTA and proteinuria.

METHODS

In this cross-sectional study, LN kidney biopsies were assessed for MAC deposition by staining for Complement C9, a component of the MAC. Chromogenic immunohistochemistry was performed on paraffin-embedded human renal biopsy sections using unconjugated, murine anti-human Complement C9 (Hycult Biotech, clone X197). Tubular C9 staining intensity was analysed as present versus absent. IFTA was defined as minimal (<10%), mild (10%-24%), moderate (25%-50%) and severe (>50%).

RESULTS

Renal biopsies from 30 patients with LN were studied. There were 24 (80%) female sex, mean age (SD) was 33 (12) years old and 23 (77%) had pure/mixed proliferative LN. Tubular C9 staining was present in 7 (23%) biopsies. 27 patients had minimal-to-mild IFTA and 3 patients had moderate IFTA. Among the C9 + patients, 3 (43%) had moderate IFTA as compared with none in the C9- group, p=0.009. C9 + patients had higher median (IQR) proteinuria as compared with C9- patients: 6.2 g (3.3-13.1) vs 2.4 g (1.3-4.6), p=0.001 at the time of biopsy. There was no difference in estimated glomerular filtration rate (eGFR) between the C9 + and C9- groups.

CONCLUSION

This study demonstrated that tubular MAC deposition is associated with higher degree of IFTA and proteinuria, which are predictors of progression to ESRD. These results suggest that tubular MAC deposition may be useful in classification of LN. Understanding the role of complement in tubulointerstitial injury will also identify new avenues for LN treatment.

Inhibition of EZH2 ameliorates hyperoxaluria-induced kidney injury through the JNK/FoxO3a pathway

AIMS

Enhancer of zeste homolog 2 (EZH2), a histone H3 lysine 27 methyltransferase, has been shown to play a role in kidney diseases. However, its role in hyperoxaluria-induced renal tubular epithelial cells (TECs) injury remains unclear.

MATERIALS AND METHODS

A hyperoxaluria rat model was established by providing 0.5% ammonium chloride and drinking water containing 1% ethylene glycol. TECs were exposed to oxalate stress. The 3-DZNeP, a selective EZH2 inhibitor, was administered in vivo and in vitro. Cell viability, ROS production, and apoptosis ratio were evaluated. Crystal deposition was detected by Von Kossa staining and kidney tissue injury was detected by HE staining and TUNEL. EZH2, H3K27me3, cleaved-caspase3, IL-6, and MCP-1 were examined by western blot or immunohistochemistry.

KEY FINDINGS

Inhibition of EZH2 by 3-DZNeP significantly attenuated hyperoxaluria-induced oxidative and inflammatory injury and CaOx crystal deposition in vivo. Similarly, inhibition of EZH2 using 3-DZNeP or shRNA restored cell viability, suppressed LDH release and the production of intracellular ROS in vitro. Furthermore, the MAPK signaling pathway and FoxO3a levels were activated or elevated in TECs exposed to oxalate. EZH2 inhibition using 3-DZNeP blocked these effects. CC90003 (ERK inhibitor) or SB203580 (p38 inhibitor) did not significantly affect the expression of FoxO3a in TECs treated with 3-DZNeP and oxalate; only SP600125 (JNK inhibitor) significantly decreased FoxO3a expression.

SIGNIFICANCE

EZH2 inhibition protects against oxalate-induced TECs injury and reduces CaOx crystal deposition in the kidney may by modulating the JNK/FoxO3a pathway; EZH2 may be a promising therapeutic target in TECs injury.

Proteinuria is accompanied by intratubular complement activation and apical membrane deposition of C3dg and C5b-9 in kidney transplant recipients

Proteinuria predicts accelerated decline in kidney function in kidney transplant recipients (KTRs). We hypothesized that aberrant filtration of complement factors causes intraluminal activation, apical membrane attack on tubular cells, and progressive injury. Biobanked samples from two previous studies in albuminuric KTRs were used. The complement-activation split products C3c, C3dg, and soluble C5b-9-associated C9 neoantigen were analyzed by ELISA in urine and plasma using neoepitope-specific antibodies. Urinary extracellular vesicles (uEVs) were enriched by lectin and immunoaffinity isolation and analyzed by immunoblot analysis. Urine complement excretion increased significantly in KTRs with an albumin-to-creatinine ratio of ≥300 mg/g compared with <30 mg/g. Urine C3dg and C9 neoantigen excretion correlated significantly to changes in albumin excretion from 3 to 12 mo after transplantation. Fractional excretion of C9 neoantigen was significantly higher than for albumin, indicating postfiltration generation. C9 neoantigen was detected in uEVs in six of the nine albuminuric KTRs but was absent in non-albuminuric controls (n = 8). In C9 neoantigen-positive KTRs, lectin affinity enrichment of uEVs from the proximal tubules yielded signal for iC3b, C3dg, C9 neoantigen, and Na⁺-glucose transporter 2 but only weakly for aquaporin 2. Coisolation of podocyte markers and Tamm–Horsfall protein was minimal. Our findings show that albuminuria is associated with aberrant filtration and intratubular activation of complement with deposition of C3 activation split products and C5b-9-associated C9 neoantigen on uEVs from the proximal tubular apical membrane. Intratubular complement activation may contribute to progressive kidney injury in proteinuric kidney grafts.

NEW & NOTEWORTHY The present study proposes a mechanistic coupling between proteinuria and aberrant filtration of complement precursors, intratubular complement activation, and apical membrane attack in kidney transplant recipients. C3dg and C5b-9-associated C9 neoantigen associate with proximal tubular apical membranes as demonstrated in urine extracellular vesicles. The discovery suggests intratubular complement as a mediator between proteinuria and progressive kidney damage. Inhibitors of soluble and/or luminal complement activation with access to the tubular lumen may be beneficial.

Pre-operative proteinuria, postoperative acute kidney injury and mortality: A systematic review and meta-analysis

OBJECTIVE

To investigate the association of pre-operative proteinuria with postoperative acute kidney injury (AKI) development as well as the requirement for a renal replacement therapy (RRT) and mortality at short-term and long-term follow-up.

BACKGROUND

Postoperative AKI is associated with surgical morbidity and mortality. Pre-operative proteinuria is potentially a risk factor for postoperative AKI and mortality. However, the results in literature are conflicting.

METHODS

We searched PubMed, Embase, Scopus, Web of Science and Cochrane Library from the inception through to 3 June 2020. Observational cohort studies investigating the association of pre-operative proteinuria with postoperative AKI development, requirement for RRT, and all-cause mortality at short-term and long-term follow-up were considered eligible. Using inverse variance method with a random-effects model, the pooled effect estimates and 95% confidence interval (CI) were calculated.

RESULTS

Twenty-eight studies were included. Pre-operative proteinuria was associated with postoperative AKI development [odds ratio (OR) 1.74, 95% CI, 1.45 to 2.09], in-hospital RRT (OR 1.70, 95% CI, 1.25 to 2.32), requirement for RRT at long-term follow-up [hazard ratio (HR) 3.72, 95% CI, 2.03 to 6.82], and long-term all-cause mortality (hazard ratio 1.50, 95% CI, 1.30 to 1.73). In the subgroup analysis, pre-operative proteinuria was associated with increased odds of postoperative AKI in both cardiovascular (OR 1.77, 95% CI, 1.47 to 2.14) and noncardiovascular surgery (OR 1.63, 95% CI, 1.01 to 2.63). Moreover, there is a stepwise increase in OR of postoperative AKI development when the quantity of proteinuria increases from trace to 3+.

CONCLUSION

Pre-operative proteinuria is significantly associated with postoperative AKI and long-term mortality. Pre-operative anaesthetic assessment should take into account the presence of proteinuria to identify high-risk patients.

PROSPERO REGISTRATION

CRD42020190065.

Generation and characterization of a novel rat model of primary hyperoxaluria type 1 with a nonsense mutation in alanine-glyoxylate aminotransferase gene

Primary hyperoxaluria type 1 (PH1) is a severe inherited disorder caused by a genetic defect in alanine-glyoxylate aminotransferase (AGXT), which results in recurrent urolithiasis and renal failure. Animal models that precisely reflect human PH1 phenotypes are lacking. We aimed to develop a novel PH1 rat model and study the mechanisms involved in PH1 deterioration. One cell stage Sprague-Dawley embryos were injected with the CRISPR/Cas9 system to introduce a Q84X mutation in Agxt. Liver tissues were harvested to determine Agxt expression. Urine oxalate, crystals, and electrolyte levels in Agxt^Q84X and wild-type (WT) littermates were evaluated. Kidney tissues were used for Pizzolato staining and kidney injury evaluation. Data showed that Agxt mRNA and protein were absent in Agxt^Q84X rats. At 4 and 24 wk, Agxt^Q84X rats displayed 2.1- and 2.9-fold higher urinary oxalate levels, respectively, compared with WT littermates. As a result, calcium oxalate (CaOx) crystals in urine were revealed in all Agxt^Q84X rats but in none of the WT rats. We also observed bladder stones in 36.4% of Agxt^Q84X rats, of which 44.4% had renal CaOx deposition. Moreover, the elevated serum urea and creatinine levels indicated the impaired renal function in Agxt^Q84X rats. Further investigation revealed significantly increased expression of inflammation-, necroptosis-, and fibrosis-related genes in the kidneys of Agxt^Q84X rats with spontaneous renal CaOx deposition, indicating that these pathways are involved in PH1 deterioration. Collectively, these results suggest that this rat model has broad applicability in mechanistic studies and innovative therapeutics development for PH1 and other kidney stone diseases.NEW & NOTEWORTHY Primary hyperoxaluria type 1 is a severe inherited disorder that results in recurrent urolithiasis and renal failure. We generated an alanine-glyoxylate aminotransferase (Agxt)^Q84X nonsense mutant rat model that displayed an early onset of hyperoxaluria, spontaneous renal CaOx precipitation, bladder stone, and kidney injuries. Our results suggest an interaction of renal CaOx crystals with the activation of inflammation-, fibrosis-, and necroptosis-related pathways. In all, the Agxt^Q84X rat strain has broad applicability in mechanistic studies and the development of innovative therapeutics.

Complement C6 deficiency exacerbates pathophysiology after spinal cord injury

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

AhR activation attenuates calcium oxalate nephrocalcinosis by diminishing M1 macrophage polarization and promoting M2 macrophage polarization

Calcium oxalate (CaOx) crystal can trigger kidney injury, which contributes to the pathogenesis of nephrocalcinosis. The phenotypes of infiltrating macrophage may impact CaOx-mediated kidney inflammatory injury as well as crystal deposition. How aryl hydrocarbon receptor (AhR) regulates inflammation and macrophage polarization is well understood; however, how it modulates CaOx nephrocalcinosis remains unclear.

Methods: Mice were intraperitoneally injected with glyoxylate to establish CaOx nephrocalcinosis model with or without the treatment of AhR activator 6-formylindolo(3,2-b)carbazole (FICZ). Positron emission tomography computed tomography (PET-CT) imaging, Periodic acid-Schiff (PAS) staining, and polarized light optical microscopy were used to evaluate kidney injury and crystal deposition in mice kidney. Western blotting, immunofluorescence, chromatin immunoprecipitation, microRNA-fluorescence in situ hybridization, and luciferase reporter assays were applied to analyze polarization state and regulation mechanism of macrophage.

Results: AhR expression was significantly upregulated and negatively correlated with interferon-regulatory factor 1 (IRF1) and hypoxia inducible factor 1-alpha (HIF-1α) levels in a murine CaOx nephrocalcinosis model following administration of FICZ. Moreover, AhR activation suppressed IRF1 and HIF-1α levels and decreased M1 macrophage polarization in vitro. In terms of the mechanism, bioinformatics analysis and chromatin immunoprecipitation assay confirmed that AhR could bind to miR-142a promoter to transcriptionally activate miR-142a. In addition, luciferase reporter assays validated that miR-142a inhibited IRF1 and HIF-1α expression by directly targeting their 3'-untranslated regions.

Conclusions: Our results indicated that AhR activation could diminish M1 macrophage polarization and promote M2 macrophage polarization to suppress CaOx nephrocalcinosis via the AhR-miR-142a-IRF1/HIF-1α pathway.

Systems Analysis of Biliary Atresia Through Integration of High-Throughput Biological Data

Biliary atresia (BA), blockage of the proper bile flow due to loss of extrahepatic bile ducts, is a rare, complex disease of the liver and the bile ducts with unknown etiology. Despite ongoing investigations to understand its complex pathogenesis, BA remains the most common cause of liver failure requiring liver transplantation in children. To elucidate underlying mechanisms, we analyzed the different types of high-throughput genomic and transcriptomic data collected from the blood and liver tissue samples of children suffering from BA. Through use of a novel integrative approach, we identified potential biomarkers and over-represented biological functions and pathways to derive a comprehensive network showing the dysfunctional mechanisms associated with BA. One of the pathways highlighted in the integrative network was hypoxia signaling. Perturbation with hypoxia inducible factor activator, dimethyloxalylglycine, induced the biliary defects of BA in a zebrafish model, serving as a validation for our studies. Our approach enables a systems-level understanding of human BA biology that is highlighted by the interaction between key biological functions such as fibrosis, inflammation, immunity, hypoxia, and development.

Sulforaphane elicts dual therapeutic effects on Renal Inflammatory Injury and crystal deposition in Calcium Oxalate Nephrocalcinosis

Intrarenal calcium oxalate (CaOx) crystals induce renal tubular epithelial cells (TECs) injury and inflammation, which involve Toll-like receptor 4 (TLR4)/interferon regulatory factor 1 (IRF1) signaling. Additionally, infiltrating macrophages (Mϕs) might influence intrarenal CaOx crystals and CaOx-induced renal injury. Although the roles of nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating inflammation and macrophage polarization are well characterized, its potential mechanisms in regulating CaOx nephrocalcinosis remain undefined.

Methods: We used a Gene Expression Omnibus dataset to analyze gene-expression profiles. Luciferase reporter, western blot, quantitative polymerase chain reaction, immunofluorescence staining, fluorescence in situ hybridization, positron emission tomography computed tomography imaging, flow cytometry, and chromatin immunoprecipitation assays were employed to study the mechanism of miR-93-TLR4/IRF1 regulation by Nrf2. Anti-inflammatory activity and regulation of macrophage polarization by Nrf2 were investigated in vitro and in vivo.

Results: We found that stone-mediated kidney inflammation significantly affected stone growth, and that sulforaphane attenuated CaOx nephrocalcinosis-induced kidney injury and renal CaOx crystals deposition. Additionally, Nrf2 levels significantly increased and negatively correlated with TLR4 and IRF1 levels in a mouse model of CaOx nephrocalcinosis following sulforaphane treatment. Moreover, Nrf2 suppressed TLR4 and IRF1 levels and decreased M1-macrophage polarization which induced by supernatants from COM-stimulated TECs in vitro. In terms of mechanism, transcription factor analyses, microRNA microarray, and chromatin immunoprecipitation assays showed that Nrf2 exhibited positive transcriptional activation of miR-93-5p. In addition, Luciferase reporter, qRT-PCR, and western blot validated that miR-93-5p targets TLR4 and IRF1 mRNA. Furthermore, suppressed miR-93-5p expression partially reversed Nrf2-dependent TLR4/IRF1 downregulation.

Conclusions: The results suggested that sulforaphane might promote M2Mϕ polarization and inhibit CaOx nephrocalcinosis-induced inflammatory injury to renal tubular epithelial cells via the Nrf2-miR-93-TLR4/IRF1 pathway in vitro and in vivo.

New therapeutic targets in chronic kidney disease progression and renal fibrosis

INTRODUCTION

The current therapeutic armamentarium to prevent chronic kidney disease (CKD) progression is limited to the control of blood pressure and in diabetic patients, the strict control of glucose levels. Current research is primarily focused on the reduction of inflammation and fibrosis at different levels.

AREAS COVERED

This article examines the latest progress in this field and places an emphasis on inflammation, oxidative stress, and fibrosis. New therapeutic targets are described and evidence from experimental and clinical studies is summarized. We performed a search in Medline for articles published over the last 10 years.

EXPERT OPINION

The search for therapeutic targets of renal inflammation is hindered by an incomplete understanding of the pathophysiology. The determination of the specific inducers of inflammation in the kidney is an area of heightened potential. Prevention of the progression of renal fibrosis by blocking TGF-β signaling has been unsuccessful, but the investigation of signaling pathways involved in late stages of fibrosis progression could yield improved results. Preventive strategies such as the modification of microbiota-inducers of uremic toxins involved in CKD progression is a promising field because of the interaction between the gut microbiota and the renal system.

Urinary Properdin and sC5b-9 Are Independently Associated With Increased Risk for Graft Failure in Renal Transplant Recipients

The pathophysiology of late kidney-allograft failure remains complex and poorly understood. Activation of filtered or locally produced complement may contribute to the progression of renal failure through tubular C5b-9 formation. This study aimed to determine urinary properdin and sC5b-9 excretion and assess their association with long-term outcome in renal transplant recipients (RTR). Methods: We measured urinary properdin and soluble C5b-9 in a well-defined cross-sectional cohort of RTR. Urinary specimens were taken from a morning urine portion, and properdin and sC5b-9 were measured using an enzyme-linked-immunosorbent assay (ELISA). Cox proportional hazard regression analyses were used to investigate prospective associations with death-censored graft failure. Results: We included 639 stable RTR at a median [interquartile range] 5.3 (1.8-12.2) years after transplantation. Urinary properdin and sC5b-9 excretion were detectable in 161 (27%) and 102 (17%) RTR, respectively, with a median properdin level of 27.6 (8.6-68.1) ng/mL and a median sC5b-9 level of 5.1 (2.8-12.8) ng/mL. In multivariable-adjusted Cox regression analyses, including adjustment for proteinuria, urinary properdin (HR, 1.12; 95% CI 1.02-1.28; P = 0.008) and sC5b-9 excretion (HR, 1.34; 95% CI 1.10-1.63; P = 0.003) were associated with an increased risk of graft failure. If both urinary properdin and sC5b-9 were detectable, the risk of graft failure was further increased (HR, 3.12; 95% CI 1.69-5.77; P < 0.001). Conclusions: Our findings point toward a potential role for urinary complement activation in the pathogenesis of chronic allograft failure. Urinary properdin and sC5b-9 might be useful biomarkers for complement activation and chronic kidney allograft deterioration, suggesting a potential role for an alternative pathway blockade in RTR.

Nephrotic syndrome is associated with increased plasma K+ concentration, intestinal K+ losses, and attenuated urinary K+ excretion: a study in rats and humans

The present study tested the hypotheses that nephrotic syndrome (NS) leads to renal K⁺ loss because of augmented epithelial Na⁺ channel (ENaC) activity followed by downregulation of renal K⁺ secretory pathways by suppressed aldosterone. The hypotheses were addressed by determining K⁺ balance and kidney abundance of K⁺ and Na⁺ transporter proteins in puromycin aminonucleoside (PAN)-induced rat nephrosis. The effects of amiloride and angiotensin II type 1 receptor and mineralocorticoid receptor (MR) antagonists were tested. Glucocorticoid-dependent MR activation was tested by suppression of endogenous glucocorticoid with dexamethasone. Urine and plasma samples were obtained from pediatric patients with NS in acute and remission phases. PAN-induced nephrotic rats had ENaC-dependent Na⁺ retention and displayed lower renal K⁺ excretion but elevated intestinal K⁺ secretion that resulted in less cumulated K⁺ in NS. Aldosterone was suppressed at day 8. The NS-associated changes in intestinal, but not renal, K⁺ handling responded to suppression of corticosterone, whereas angiotensin II type 1 receptor and MR blockers and amiloride had no effect on urine K⁺ excretion during NS. In PAN-induced nephrosis, kidney protein abundance of the renal outer medullary K⁺ channel and γ-ENaC were unchanged, whereas the Na⁺-Cl^- cotransporter was suppressed and Na⁺-K⁺-ATPase increased. Pediatric patients with acute NS displayed suppressed urine Na⁺-to-K⁺ ratios compared with remission and elevated plasma K⁺ concentration, whereas fractional K⁺ excretion did not differ. Acute NS is associated with less cumulated K⁺ in a rat model, whereas patients with acute NS have elevated plasma K⁺ and normal renal fractional K⁺ excretion. In NS rats, K⁺ balance is not coupled to ENaC activity but results from opposite changes in renal and fecal K⁺ excretion with a contribution from corticosteroid MR-driven colonic secretion.

Complement Activation in Progression of Chronic Kidney Disease

Chronic kidney disease (CKD) is a public health problem worldwide, with increasing incidence and prevalence. The mechanisms underlying the progression to end-stage renal disease (ESRD) is not fully understood. The complement system was traditionally regarded as an important part of innate immunity required for host protection against infection and for maintaining host hemostasis. However, compelling evidence from both clinical and experimental studies has strongly incriminated complement activation as a pivotal pathogenic mediator of the development of multiple renal diseases and progressive replacement of functioning nephrons by fibrosis. Both anaphylatoxins, i.e., C3a and C5a, and membrane attack complex (MAC) contribute to the damage that occurs during chronic renal progression through various mechanisms including direct proinflammatory and fibrogenic activity, chemotactic effect, activation of the renal renin-angiotensin system, and enhancement of T-cell immunity. Evolving understanding of the mechanisms of complement-mediated renal injury has led to the emergence of complement-targeting therapeutics. A variety of specific antibodies and inhibitors targeting complement components have shown efficacy in reducing disease in animal models. Moreover, building on these advances, targeting complement has gained encouraging success in treating patients with renal diseases such as atypical hemolytic uremic syndrome (aHUS). Nevertheless, it still requires a great deal of effort to develop inhibitors that can be applied to treat more patients effectively in routine clinical practice.

Lysosomal dysfunction induced by changes in albumin's tertiary structure: Potential key factor in protein toxicity during diabetic nephropathy

AIMS

Increased amounts of protein, in particular albumin within renal tubular cells (TBCs), induce the expression of inflammatory and fibrogenic mediators, which are adverse prognostic factors in tubulointerstitial fibrosis and diabetic nephropathy (DN). We sought to assess the participation of the thiol-linked tertiary structure of albumin in the mechanism of protein toxicity in a model of TBCs.

MATERIALS AND METHODS

Cultured human renal proximal tubular cells, HK-2, were exposed to isolated albumin from patients with and without DN (Stages 0, 1 and 4). The magnitude of change of the albumin tertiary structure, cell viability (LDH leakage), apoptosis (Annexin V), transdifferentiation and reticulum endoplasmic stress (Western blot and flow cytometry) and lysosomal enzyme activity were assessed.

KEY FINDINGS

We found that albumin from Stage 4 patients presented >50% higher thiol-dependent changes of tertiary structure compared to Stages 0 and 1. Cells incubated with Stage 4 albumin displayed 5 times less viability, accompanied by an increased number of apoptotic cells; evidence of profibrogenic markers E-cadherin and vimentin and higher expression of epithelial-to-mesenchymal transition markers α-SMA and E-cadherin and of endoplasmic reticulum stress protein GRP78 were likewise observed. Moreover, we found that cathepsin B activity in isolated lysosomes showed a significant inhibitory effect on albumin from patients in advanced stages of DN and on albumin that was intentionally modified.

SIGNIFICANCE

Overall, this study showed that thiol-dependent changes in albumin's tertiary structure interfere with the lysosomal proteolysis of renal TBCs, inducing molecular changes associated with interstitial fibrosis and DN progression.

Clinical Value of Complement Activation Biomarkers in Overt Diabetic Nephropathy

Background

Experimental studies support a role of complement activation in diabetic nephropathy (DN), yet few clinical correlates exist. We evaluated urinary levels of sC5b-9 membrane attack complex (MAC) in patients with overt DN, and examined its association with the glomerular filtration rate (GFR) decline, proteinuria, and inflammatory biomarkers. We explored different complement pathways and compared our findings to autoimmune glomerulonephritis.

Methods

We prospectively followed 83 patients with DN and obtained repeated measurements of proteinuria, complement fragments (sC5b-9, C4a, C1q, mannose-binding lectin–associated serine protease [MASP]-1, and factor Bb), monocyte chemoattractant protein-1 (MCP-1), and transforming growth factor (TGF)-β1. We assessed independence and interactions using general linear models and repeated measures analyses and compared levels with subjects with active focal and segmental glomerulosclerosis, ANCA-associated vasculitis, and membranous and IgA nephropathies (n = 63).

Results

The diabetic cohort had an initial GFR of 25 ± 9 ml/min per 1.73 m² and a renal function decline of 2.9 ± 3.0 ml/min per 1.73 m² per year. All complement biomarkers were strongly intercorrelated and associated with biomarker inflammation and fibrosis, proteinuria, and the rate of renal function decline. There was a significant interaction (P = 0.03) between the level of proteinuria and urinary sC5b-9: in individuals with higher levels of urinary MAC, the relationship between proteinuria and the rate of renal function decline was more pronounced than in those with low urinary MAC. Finally, patients with DN had levels of urinary sC5b-9 comparable to autoimmune glomerulonephritis, when stratified by the level of proteinuria.

Conclusion

Urinary MAC is present in patients with overt DN at levels comparable to autoimmune glomerulonephritis and correlates with the GFR decline, supporting that complement activation and its measurement are clinically relevant in DN.

Urine Complement Proteins and the Risk of Kidney Disease Progression and Mortality in Type 2 Diabetes

OBJECTIVE

We examined the association of urine complement proteins with progression to end-stage renal disease (ESRD) or death in people with type 2 diabetes and proteinuric diabetic kidney disease (DKD).

RESEARCH DESIGN AND METHODS

Using targeted mass spectrometry, we quantified urinary abundance of 12 complement proteins in a predominantly Mexican American cohort with type 2 diabetes and proteinuric DKD (n = 141). The association of urine complement proteins with progression to ESRD or death was evaluated using time-to-event analyses.

RESULTS

At baseline, median estimated glomerular filtration rate (eGFR) was 54 mL/min/1.73 m² and urine protein-to-creatinine ratio 2.6 g/g. Sixty-seven participants developed ESRD or died, of whom 39 progressed to ESRD over a median of 3.1 years and 40 died over a median 3.6 years. Higher urine CD59, an inhibitor of terminal complement complex formation, was associated with a lower risk of ESRD (hazard ratio [HR] [95% CI per doubling] 0.50 [0.29-0.87]) and death (HR [95% CI] 0.56 [0.34-0.93]), after adjustment for demographic and clinical covariates, including baseline eGFR and proteinuria. Higher urine complement components 4 and 8 were associated with lower risk of death (HR [95% CI] 0.57 [0.41-0.79] and 0.66 [0.44-0.97], respectively); higher urine factor H-related protein 2, a positive regulator of the alternative complement pathway, was associated with greater risk of death (HR [95% CI] 1.61 [1.05-2.48]) in fully adjusted models.

CONCLUSIONS

In a largely Mexican American cohort with type 2 diabetes and proteinuric DKD, urine abundance of several complement and complement regulatory proteins was strongly associated with progression to ESRD and death.

Preparation and renoprotective effects of carboxymethyl chitosan oligosaccharide on adriamycin nephropathy

Carboxymethyl chitosan oligosaccharide (CMCOS), the hydrolytic product of carboxymethyl chitosan, is nontoxic, easily absorbable and good antioxidant. In this study, CMCOS was prepared and its properties in adriamycin nephropathy therapy were investigated. Our results showed that CMCOS had good curative effects on renal function and parenchymal injury induced by adriamycin. CMCOS administration significantly relieved symptoms of proteinuria, hypoalbuminemia, hyperlipidemia, renal hyperplasia and histological lesions in rats (P < 0.01). Further exploration for the underlying mechanisms indicated that CMCOS treatment reduced macrophage accumulation, myofibroblast transdifferentiation and podocyte apoptosis. CMCOS treatment could regulate secretions of cytokines (IL-1β, TNF-ɑ and TGF-β1) and improve activities of antioxidative enzymes (SOD, GSH-Px) (P < 0.01). In conclusion, therapeutic effects of CMCOS on renal injury mediated by inflammation, fibrosis and oxidative stress made it a good kidney health product and a promising candidate in clinical treatment of human chronic kidney disease.

The role of the complement system in diabetic nephropathy

The development of type 1 and type 2 diabetes mellitus has a substantial negative impact on morbidity and mortality and is responsible for substantial individual and socioeconomic costs worldwide. One of the most serious consequences of diabetes mellitus is the development of diabetic angiopathy, which manifests clinically as microvascular and macrovascular complications. One microvascular complication, diabetic nephropathy, is the most common cause of end-stage renal disease in developed countries. Although several available therapeutic interventions can delay the onset and progression of diabetic nephropathy, morbidity associated with this disease remains high and new therapeutic approaches are needed. In addition, not all patients with diabetes mellitus will develop diabetic nephropathy and thus new biomarkers are needed to identify individuals who will develop this life-threatening disease. An increasing body of evidence points toward a role of the complement system in the pathogenesis of diabetic nephropathy. For example, circulating levels of mannose-binding lectin (MBL), a pattern recognition molecule of the innate immune system, have emerged as a robust biomarker for the development and progression of this disease, and evidence suggests that MBL, H-ficolin, complement component C3 and the membrane attack complex might contribute to renal injury in the hyperglycaemic mileu. New approaches to modulate the complement system might lead to the development of new agents to prevent or slow the progression of diabetic nephropathy.

The Tubulointerstitial Pathophysiology of Progressive Kidney Disease

Accumulating evidence suggests that the central locus for the progression of CKD is the renal proximal tubule. As injured tubular epithelial cells dedifferentiate in attempted repair, they stimulate inflammation and recruit myofibroblasts. At the same time, tissue loss stimulates remnant nephron hypertrophy. Increased tubular transport workload eventually exceeds the energy-generating capacity of the hypertrophied nephrons, leading to anerobic metabolism, acidosis, hypoxia, endoplasmic reticulum stress, and the induction of additional inflammatory and fibrogenic responses. The result is a vicious cycle of injury, misdirected repair, maladaptive responses, and more nephron loss. Therapy that might be advantageous at one phase of this progression pathway could be deleterious during other phases. Thus, interrupting this downward spiral requires narrowly targeted approaches that promote healing and adequate function without generating further entry into the progression cycle.

Albuminuria is associated with an increased prostasin in urine while aldosterone has no direct effect on urine and kidney tissue abundance of prostasin

The proteinase prostasin is a candidate mediator for aldosterone-driven proteolytic activation of the epithelial sodium channel (ENaC). It was hypothesized that the aldosterone-mineralocorticoid receptor (MR) pathway stimulates prostasin abundance in kidney and urine. Prostasin was measured in plasma and urine from type 2 diabetic patients with resistant hypertension (n = 112) randomized to spironolactone/placebo in a clinical trial. Prostasin protein level was assessed by immunoblotting in (1) human and rat urines with/without nephrotic syndrome, (2) human nephrectomy tissue, (3) urine and kidney from aldosterone synthase-deficient (AS^-/-) mice and ANGII- and aldosterone-infused mice, and in (4) kidney from adrenalectomized rats. Serum aldosterone concentration related to prostasin concentration in urine but not in plasma. Plasma prostasin concentration increased significantly after spironolactone compared to control. Urinary prostasin and albumin related directly and were reduced by spironolactone. In patients with nephrotic syndrome, urinary prostasin protein was elevated compared to controls. In rat nephrosis, proteinuria coincided with increased urinary prostasin, unchanged kidney tissue prostasin, and decreased plasma prostasin while plasma aldosterone was suppressed. Prostasin protein abundance in human nephrectomy tissue was similar across gender and ANGII inhibition regimens. Prostasin urine abundance was not different in AS^-/- and aldosterone-infused mice. Prostasin kidney level was not different from control in adrenalectomized rats and AS^-/- mice. We found no evidence for a direct relationship between mineralocorticoid receptor signaling and kidney and urine prostasin abundance. The reduction of urinary prostasin in spironolactone-treated patients is most likely the result of an improved glomerular filtration barrier function and generally reduced proteinuria.

Proteinuria can predict prognosis after liver transplantation

Background

Proteinuria is a manifestation of renal dysfunction and it has been demonstrated to be a significant prognostic factor in various clinical situations. The study was designed to analyze prognosis of patients receiving liver transplantation as well as to determine predictive performance of perioperative proteinuria.

Methods

We retrospectively reviewed data of patients who had received a liver transplant in a medical center between 2002 and 2010. Demographic information and clinical characteristic parameters were recorded on the day of intensive care unit admission before operation and on postoperative days 1, 7, and 14.

Results

Among a total of 323 patients, in-hospital mortality and 90-day mortality rates were 13.0 % (42/323) and 14.2 % (46/323), respectively. Patients with proteinuria on admission had higher rates of acute kidney injury (26.8 % vs. 8.8 %, p < 0.001), severe infection episodes (48.8 % vs. 30.7 %, p = 0.023), hospital death (31.1 % vs. 10.1 %, p < 0.001), and 90-day mortality (37.7 % vs. 10.9 %, p < 0.001). Multivariate analysis showed that proteinuria on admission and Sequential Organ Failure Assessment (SOFA) score were independent predictors of in-hospital mortality. The discriminatory ability of proteinuria plus SOFA was even better than that of SOFA alone, especially on postoperative day 1.

Conclusions

The presence of proteinuria before liver transplantation is supposed to be recognized as a negative predictor for in-hospital survival. Moreover, the presence of proteinuria after liver transplantation can assist in the early prediction of poor short-term prognosis for patients receiving liver transplantation.

Monomeric C-reactive protein inhibits renal cell-directed complement activation mediated by properdin

Previous studies have shown that complement activation on renal tubular cells is involved in the induction of interstitial fibrosis and cellular injury. Evidence suggests that the tubular cell damage is initiated by the alternative pathway (AP) of complement with properdin having an instrumental role. Properdin is a positive regulator of the AP, which can bind necrotic cells as well as viable proximal tubular epithelial cells (PTECs), inducing complement activation. Various studies have indicated that in the circulation there is an unidentified inhibitor of properdin. We investigated the ability of C-reactive protein (CRP), both in its monomeric (mCRP) and pentameric (pCRP) form, to inhibit AP activation and injury in vitro on renal tubular cells by fluorescent microscopy, ELISA, and flow cytometry. We demonstrated that preincubation of properdin with normal human serum inhibits properdin binding to viable PTECs. We identified mCRP as a factor able to bind to properdin in solution, thereby inhibiting its binding to PTECs. In contrast, pCRP exhibited no such binding and inhibitory effect. Furthermore, mCRP was able to inhibit properdin-directed C3 and C5b-9 deposition on viable PTECs. The inhibitory ability of mCRP was not unique for viable cells but also demonstrated for binding to necrotic Jurkat cells, a target for properdin binding and complement activation. In summary, mCRP is an inhibitor of properdin in both binding to necrotic cells and viable renal cells, regulating complement activation on the cell surface. We propose that mCRP limits amplification of tissue injury by controlling properdin-directed complement activation by damaged tissue and cells.

Complement Activation in Patients with Focal Segmental Glomerulosclerosis

Background

Recent pre-clinical studies have shown that complement activation contributes to glomerular and tubular injury in experimental FSGS. Although complement proteins are detected in the glomeruli of some patients with FSGS, it is not known whether this is due to complement activation or whether the proteins are simply trapped in sclerotic glomeruli. We measured complement activation fragments in the plasma and urine of patients with primary FSGS to determine whether complement activation is part of the disease process.

Study Design

Plasma and urine samples from patients with biopsy-proven FSGS who participated in the FSGS Clinical Trial were analyzed.

Setting and Participants

We identified 19 patients for whom samples were available from weeks 0, 26, 52 and 78. The results for these FSGS patients were compared to results in samples from 10 healthy controls, 10 patients with chronic kidney disease (CKD), 20 patients with vasculitis, and 23 patients with lupus nephritis.

Outcomes

Longitudinal control of proteinuria and estimated glomerular filtration rate (eGFR).

Measurements

Levels of the complement fragments Ba, Bb, C4a, and sC5b-9 in plasma and urine.

Results

Plasma and urine Ba, C4a, sC5b-9 were significantly higher in FSGS patients at the time of diagnosis than in the control groups. Plasma Ba levels inversely correlated with the eGFR at the time of diagnosis and at the end of the study. Plasma and urine Ba levels at the end of the study positively correlated with the level of proteinuria, the primary outcome of the study.

Limitations

Limited number of patients with samples from all time-points.

Conclusions

The complement system is activated in patients with primary FSGS, and elevated levels of plasma Ba correlate with more severe disease. Measurement of complement fragments may identify a subset of patients in whom the complement system is activated. Further investigations are needed to confirm our findings and to determine the prognostic significance of complement activation in patients with FSGS.

Custom 4-Plex DiLeu Isobaric Labels Enable Relative Quantification of Urinary Proteins in Men with Lower Urinary Tract Symptoms (LUTS)

The relative quantification of proteins using liquid chromatography mass spectrometry (LC-MS) has allowed researchers to compile lists of potential disease markers. These complex quantitative workflows often include isobaric labeling of enzymatically-produced peptides to analyze their relative abundances across multiple samples in a single LC-MS run. Recent efforts by our lab have provided scientists with cost-effective alternatives to expensive commercial labels. Although the quantitative performance of these dimethyl leucine (DiLeu) labels has been reported using known ratios of complex protein and peptide standards, their potential in large-scale proteomics studies using a clinically relevant system has never been investigated. Our work rectifies this oversight by implementing 4-plex DiLeu to quantify proteins in the urine of aging human males who suffer from lower urinary tract symptoms (LUTS). Protein abundances in 25 LUTS and 15 control patients were compared, revealing that of the 836 proteins quantified, 50 were found to be differentially expressed (>20% change) and statistically significant (p-value <0.05). Gene ontology (GO) analysis of the differentiated proteins showed that many were involved in inflammatory responses and implicated in fibrosis. While confirmation of individual protein abundance changes would be required to verify protein expression, this study represents the first report using the custom isobaric label, 4-plex DiLeu, to quantify protein abundances in a clinically relevant system.

Urinary proteomics in chronic kidney disease: diagnosis and risk of progression beyond albuminuria

BACKGROUND

The contrast between a high prevalence of chronic kidney disease (CKD) and the low incidence of end-stage renal disease highlights the need for new biomarkers of progression beyond albuminuria testing. Urinary proteomics is a promising method, but more studies focusing on progression rate and patients with hypertensive nephropathy are needed.

RESULTS

We analyzed urine samples with capillary electrophoresis coupled to a mass-spectrometer from 18 well characterized patients with CKD stage 4-5 (of whom six with hypertensive nephropathy) and 17 healthy controls. Classification scores based on a previously developed panel of 273 urinary peptides were calculated and compared to urine albumin dipstick results. Urinary proteomics classified CKD with a sensitivity of 0.95 and specificity of 1.00. Overall diagnostic accuracy (area under ROC curve) was 0.98, which was better than for albuminuria (0.85, p = 0.02). Results for hypertensive nephropathy were similar to other CKD diagnoses. Adding the proteomic score to an albuminuria model improved detection of rapid kidney function decline (>4 ml/min/1.73 m(2) per year) substantially: area under ROC curve increased from 0.762 to 0.909 (p = 0.042), and 38% of rapid progressors were correctly reclassified to a higher risk and 55% of slow progressors were correctly reclassified to a lower risk category. Reduced excretion of collagen types I-III, uromodulin, and other indicators of interstitial inflammation, fibrosis and tubular dysfunction were associated with CKD diagnosis and rapid progression. Patients with hypertensive nephropathy displayed the same findings as other types of CKD.

CONCLUSIONS

Urinary proteomic analyses had a high diagnostic accuracy for CKD, including hypertensive nephropathy, and strongly improved identification of patients with rapid kidney function decline beyond albuminuria testing.

Inhibition of Rho-associated kinase relieves C5a-induced proteinuria in murine nephrotic syndrome

Childhood nephrotic syndrome is mainly caused by minimal change disease which is named because only subtle ultrastructural alteration could be observed at electron microscopic level in the pathological kidney. Glomerular podocytes are presumed to be the target cells whose protein sieving capability is compromised by a yet unidentified permeability perturbing factor. In a cohort of children with non-hereditary idiopathic nephrotic syndrome, we found the complement fragment C5a was elevated in their sera during active disease. Administration of recombinant C5a induced profound proteinuria and minimal change nephrotic syndrome in mice. Purified glomerular endothelial cells, instead of podocytes, were demonstrated to be responsible for the proteinuric effect elicited by C5a. Further studies depicted a signaling pathway involving Rho/Rho-associated kinase/myosin activation leading to endothelial cell contraction and cell adhesion complex breakdown. Significantly, application of Rho-associated kinase inhibitor, Y27632, prevented the protein leaking effects observed in both C5a-treated purified endothelial cells and mice. Taken together, our study identifies a previously unknown mechanism underlying nephrotic syndrome and provides a new insight toward identifying Rho-associated kinase inhibition as an alternative therapeutic option for nephrotic syndrome.

Urine proteomic analysis in cystinuric children with renal stones

INTRODUCTION

The gene mutations responsible for cystinuria do not fully explain kidney stone activity, suggesting that specific proteins may serve as promoters of cystine precipitation, aggregation or epithelial adherence. In this study we assessed (1) the differences in the urinary proteins between children with cystinuria and kidney stones (CYS) and healthy controls (HC), with particular attention to the fibrosis-related proteins, and (2) the presence of diagnostic biomarkers for CYS.

MATERIAL AND METHODS

We conducted a pilot study comparing individual urinary proteomes of 2 newly diagnosed children with CYS and 2 age- and gender-matched HC, using liquid chromatography-mass spectrometry. Relative protein abundance was estimated using spectral counting. Proteins of interest in both CYS and HC were selected using the following criteria: i) ≥5 spectral counts; ii) ≥2-fold difference in spectral counts; and iii) ≤0.05 p-value for the Fisher's Exact Test.

DISCUSSION

This study demonstrates a different urinary polypeptide profile in two children with CYS compared to two HC. Of the 623 proteins identified by proteomic analysis, 180 exhibited at least a 2-fold increased relative abundance in CYS compared to HC. Of these, 39 were involved in response to stress, 26 in response to wounding, 21 in inflammatory response, 18 in immune response, and 4 in cellular response to oxidative stress. 133 proteins were found only in children with CYS, 33 of which met the selection criteria. Of these 33 unique proteins, six are known to be associated with fibrosis pathways (Table). The major limitation of this study is the small number of samples that were analyzed. Validation using highly specific methods such as ELISA is needed.

CONCLUSION

We provide proteomic evidence of oxidative injury, inflammation, wound healing and fibrosis in two children with CYS. We speculate that oxidative stress and inflammation may cause remodeling via actin and vimentin pathways, leading to fibrosis. Additionally, we identified ITIH and MMP-9 as potential diagnostic biomarkers and novel therapeutic targets in CYS. These proteins merit further investigation.

High (≥6.5) Spontaneous and Persistent Urinary pH Is Protective of Renal Function at Baseline and during Disease Course in Idiopathic Membranous Nephropathy

Metabolic acidosis correction in advanced renal failure slows renal function decline attributed to tubulointerstitial damage (TID) reduction. No study evaluated if spontaneous baseline high urinary pH (UpH) is renoprotective in patients with normal renal function and without metabolic acidosis. The study tested this hypothesis in idiopathic membranous nephropathy (IMN). Eighty-five patients (follow-up 81 ± 54 months) measured UpH, serum creatinine, eGFR, protein/creatinine ratio, fractional excretion of albumin, IgG, α1-microglobulin, and urinary N-acetyl-β-D-glucosaminidase (β-NAG)/creatinine ratio. Twenty-eight patients (33%) had UpH ≥ 6.5 and 57 (67%) pH < 6.5; high versus low UpH patients had significantly lower values of the tubulointerstitial damage (TID) markers FE α1m and β-NAG and significantly better baseline renal function. These differences persisted over time in a subset of 38 patients with 5 measurements along 53 ± 26 months. In 29 patients with nephrotic syndrome (NS) treated with supportive therapy (follow-up: 80 ± 52 months) renal function was stable in 10 high and significantly worse in 19 low UpH patients. Steroids + cyclophosphamide treatment in 35 NS patients masks the renoprotection of high UpH. Conclusions. In IMN high and persistent UpH is associated with reduction of the proteinuric markers of tubulointerstitial damage and baseline better renal function in all patients and in NS patients treated only with supportive therapy during disease course. The factors associated with high pH-dependent renoprotection were lower values of TID markers, eGFR ≥ 60 mL/min, BP < 140/90 mmHg, and age < 55 years.

Nephrotic range proteinuria as a strong risk factor for rapid renal function decline during pre-dialysis phase in type 2 diabetic patients with severely impaired renal function

BACKGROUND

Proteinuria is an established risk factor for progression of renal disease, including diabetic nephropathy. The predictive power of proteinuria, especially nephrotic range proteinuria, for progressive renal deterioration has been well demonstrated in diabetic patients with normal to relatively preserved renal function. However, little is known about the relationship between severity of proteinuria and renal outcome in pre-dialysis diabetic patients with severely impaired renal function.

METHODS

125 incident dialysis patients with type 2 diabetes were identified. This study was aimed at retrospectively evaluating the impact of nephrotic range proteinuria (urinary protein-creatinine ratio above 3.5 g/gCr) on renal function decline during the 3 months just prior to dialysis initiation.

RESULTS

In total, 103 patients (82.4 %) had nephrotic range proteinuria. The median rate of decline in estimated glomerular filtration rate (eGFR) in this study population was 0.98 (interquartile range 0.51-1.46) ml/min/1.73 m(2) per month. Compared to patients without nephrotic range proteinuria, patients with nephrotic range proteinuria showed significantly faster renal function decline (0.46 [0.24-1.25] versus 1.07 [0.64-1.54] ml/min/1.73 m(2) per month; p = 0.007). After adjusting for gender, age, systolic blood pressure, serum albumin, calcium-phosphorus product, hemoglobin A1c, and use of an angiotensin-converting enzyme inhibitor or an angiotensin II receptor blocker, patients with nephrotic range proteinuria showed a 3.89-fold (95 % CI 1.08-14.5) increased risk for rapid renal function decline defined as a decline in eGFR ≥0.5 ml/min/1.73 m(2) per month.

CONCLUSION

Nephrotic range proteinuria is the predominant renal risk factor in type 2 diabetic patients with severely impaired renal function receiving pre-dialysis care.

Properdin has an ascendancy over factor H regulation in complement-mediated renal tubular damage

Background

Urinary (U)-complement components have been detected in patients with proteinuric renal diseases, and complement activation via the alternative pathway (AP) is believed to play a role in renal tubular damage. The present study aimed to examine the regulation of complement AP activation in patients with renal tubular damage by focusing on the balance between properdin (P) and factor H (fH).

Methods

In the in vivo studies, U concentrations of P, fH and membrane attack complex (MAC) were measured in patients with renal diseases using an enzyme-linked immunosorbent assay (ELISA), and their relationships with the clinical data were evaluated. In the in vitro studies, human proximal tubular epithelial cells (PTECs) were incubated with normal human serum (NHS), P-depleted serum (PDS), purified P and/or fH. Changes in cell morphology and phenotype were assessed by microscopy, real-time polymerase chain reaction (PCR), immunostaining and a cell viability assay.

Results

The U-P, fH and MAC concentrations were significantly higher in patients with renal disease than in normal controls and correlated with the U-protein and tubular damage markers. Furthermore, multivariate analysis revealed a relationship between P levels and tubular damage markers. There were no significant changes in morphology and mRNA expression in the AP components (P, fH, fB, C3, C5 and C9) after the addition of up to 25% NHS. Dose-dependent depositions of P or fH were observed after the addition of P or fH on PTECs. Depositions of P were not inhibited by fH in a mixture of a fixed concentration of P and a variable concentration of fH, and vice versa. Preincubation with the fixed concentration of P before the addition of NHS or PDS increased the depositions of P, C3 and MAC compared with incubation with intact NHS or intact PDS only; the depositions of C3 and MAC showed a serum-dependent trend. Preincubation with P before NHS addition significantly suppressed cell viability without causing morphological changes.

Conclusions

In the pathogenesis of renal tubular damage, P can directly bind to PTECs and may accelerate AP activation by surpassing fH regulation.

Pathophysiology of proteinuria and its value as an outcome measure in chronic kidney disease

Chronic kidney diseases share common pathogenic mechanisms that, independently from the initial injury, lead to glomerular hyperfiltration, proteinuria, and progressive renal scarring and function loss. Consistent experimental evidence supports the crucial role of proteinuria in accelerating kidney disease progression to end-stage renal failure through multiple pathways, including induction of tubular chemokine expression and complement activation. These events, in turn, lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis. The extent of proteinuria is widely recognized as a marker of the severity of chronic kidney disease and as a predictor of future decline in glomerular filtration rate. More importantly, a reduction in proteinuria invariably translates into a protection from renal function decline in patients with diabetic and non-diabetic renal disease. Recent evidence also showed the existence of a relationship between proteinuria levels and cardiovascular risk, which extends to the range of urinary albumin excretion that was previously thought 'normal'. Thus, proteinuria should be considered a valuable surrogate end point for clinical trials in patients with chronic renal diseases and a target for reno- and cardioprotecive strategies.

An update on the pathomechanisms and future therapies of Alport syndrome

Alport Syndrome (AS) is an inherited progressive disease that is caused by mutations of the genes encoding the key collagen chains, α3, α4, and α5, which are necessary for the composition of collagen type IV to form a robust glomerular basement membrane (GBM), capable of withstanding the significant biomechanical strain to which the glomerulus is subjected. Progressive loss of the filtration barrier allows excessive proteinuria, which ultimately leads to end-stage kidney disease (ESKD). The evidence for a beneficial renoprotective effect of renin-angiotensin-aldosterone system (RAAS) blockade by angiotensin-converting enzyme (ACE) inhibition and/or angiotensin receptor blockers (ARBs) is well established in AS and recent evidence has shown that it can significantly delay the time to onset of renal replacement therapy and ESKD. Future potential treatments of AS disease progression are evaluated in this review.

Blood pressure, proteinuria, and phosphate as risk factors for progressive kidney disease: a hypothesis

Chronic kidney disease (CKD) affects approximately 500 million people worldwide and is increasingly common in both industrialized and emerging countries. Although the mechanisms underlying the inexorable progression of CKD are incompletely defined, recent discoveries may pave the way to a more comprehensive understanding of the pathophysiology of CKD progression and the development of new therapeutic strategies. In particular, there is accumulating evidence indicating a key role for the complex and yet incompletely understood system of divalent cation regulation, which includes phosphate metabolism and the recently discovered fibroblast growth factor 23 (FGF-23)/klotho system, which seems inextricably associated with vitamin D deficiency. The aim of this review is to discuss the links between high blood pressure, proteinuria, phosphate levels, and CKD progression and explore new therapeutic strategies to win the fight against CKD.

Immune and inflammatory role in renal disease

Chronic and acute renal diseases, irrespective of the initiating cause, have inflammation and immune system activation as a common underlying mechanism. The purpose of this review is to provide a broad overview of immune cells and inflammatory proteins that contribute to the pathogenesis of renal disease, and to discuss some of the physiological changes that occur in the kidney as a result of immune system activation. An overview of common forms of acute and chronic renal disease is provided, followed by a discussion of common therapies that have anti-inflammatory or immunosuppressive effects in the treatment of renal disease.

Renoprotective effect of human umbilical cord-derived mesenchymal stem cells in immunodeficient mice suffering from acute kidney injury

It is unknown whether human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) can improve the renal function of patients suffering from acute kidney injury. Moreover, before beginning clinical trials, it is necessary to investigate this renoprotective effect of hUC-MSCs in a xenogeneic model of acute kidney injury. However, no previous studies have examined the application of hUC-MSCs to immunodeficient mice suffering from acute kidney injury. The objectives of this study were to examine whether hUC-MSCs could improve renal function in nonobese diabetic-severe combined immune deficiency (NOD-SCID) mice suffering from acute kidney injury, and to investigate the mechanism(s) for hUC-MSCs to improve renal function in this xenogeneic model. Early (3 hr) and late (12 hr) administrations of hUC-MSCs (10⁶ cells) were performed via the external jugular vein into NOD-SCID mice suffering from either folic acid (FA) (250 mg/kg body weight) or vehicle. The results showed that early administration of hUC-MSCs improved the renal function of NOD-SCID mice suffering from FA-induced acute kidney injury, as evidenced by decreased serum urea nitrogen and serum creatinine levels, as well as a reduced tubular injury score. The beneficial effects of hUC-MSCs were through reducing apoptosis and promoting proliferation of renal tubular cells. These benefits were independent of inflammatory cytokine effects and transdifferentiation. Furthermore, this study is the first one to show that the reduced apoptosis of renal tubular cells by hUC-MSCs in this xenogeneic model is mediated through the mitochondrial pathway, and through the increase of Akt phosphorylation.

Therapeutic regulation of complement in patients with renal disease - where is the promise?

Numerous renal diseases are characterized by complement activation within the kidney, and several lines of evidence implicate complement activation as an important part of the pathogenesis of these diseases. Investigators have long anticipated that complement inhibitors would be important and effective therapies for renal diseases. Eculizumab is a monoclonal antibody to the complement protein C5 that has now been administered to patients with several types of renal disease. The apparent efficacy of this agent may herald a new era in the treatment of renal disease, but many questions about the optimal use of therapeutic complement inhibitors remain. Herein we review the rationale for using complement inhibitors in patients with renal disease and discuss several drugs and approaches that are currently under development.

Proteinuria should be used as a surrogate in CKD

Surrogate end points of renal failure are instrumental to the testing of new treatments in patients with chronic kidney disease, the natural history of which is characterized by a slow, asymptomatic decline in renal function. The magnitude of proteinuria is widely recognized as a marker of the severity of glomerulopathy. Population-based studies have identified proteinuria as a predictor of future decline in glomerular filtration rate and of the development of end-stage renal disease. More importantly, a reduction in proteinuria invariably translates into a protection from renal function decline in patients with diabetic and nondiabetic renal disease with overt proteinuria. Thus, proteinuria should be considered a valuable surrogate end point for clinical trials in patients with proteinuric renal diseases.

Complement in glomerular disease

The role of the complement system in renal disease has long been recognized, but there have been major advances in our understanding of its role over the past decade. Complement plays a critical role not only in host's defense against infection and preventing damage to "self" tissues but also mediates tissue injury, both in the glomerulus and tubulointerstitium. Although injury may originate in the glomerulus, resulting proteinuria and complement activation within the tubular lumen may lead to tubulointerstitial damage and progressive renal disease. Recent advances in our understanding of the mechanisms by which complement mediates renal injury have led to the development of promising strategies with which complement may be targeted to prevent renal injury and its associated complications.

Complement involvement in neovascular ocular diseases

Pathological neovascularization (NV) is a hallmark of late stage neovascular age-related macular degeneration (AMD), diabetic retinopathy (DR), and retinopathy of prematurity (ROP). There is accumulating evidence that alterations in inflammatory and immune system pathways that arise from genetic differences, injury, and disease can predispose individuals to retinal neovascular eye diseases. Yet the mechanism of disease progression with respect to the complement system in these maladies is not fully understood. Recent studies have implicated the complement system as an emerging player in the etiology of several retinal diseases. We will summarize herein several of the complement system pathways known to be involved in ocular neovascular pathologies. Current treatment for many neovascular eye diseases focuses on suppression of NV with laser ablation, photodynamic therapy, or anti-VEGF angiogenic inhibitors. However, these treatments do not address the underlying cause of many of these diseases. A clear understanding of the cellular and molecular mechanisms could bring a major shift in our approach to disease treatment and prevention.

Effects of dietary salt restriction on puromycin aminonucleoside nephrosis: preliminary data

Proteinuria is a major promoter that induces tubulointerstitial injury in glomerulopathy. Dietary salt restriction may reduce proteinuria, although the mechanism is not clear. We investigated the effects of dietary salt restriction on rat kidneys in an animal model of glomerular proteinuria. Male Sprague-Dawley rats were used and divided into 3 groups: vehicle-treated normal-salt controls, puromycin aminonucleoside (PA)-treated normal-salt rats, and PA-treated low-salt rats. PA was given at a dose of 150 mg/kg BW at time 0, followed by 50 mg/kg BW on days 28, 35, and 42. Sodium-deficient rodent diet with and without additional NaCl (0.5%) were provided for normal-salt rats and low-salt rats, respectively. On day 63, kidneys were harvested for histopathologic examination and immunohistochemistry. PA treatment produced overt proteinuria and renal damage. Dietary salt restriction insignificantly reduced proteinuria in PA-treated rats, and PA-treated low-salt rats had lower urine output and lower creatinine clearance than vehicle-treated normal-salt controls. When tubulointerstitial injury was semiquantitatively evaluated, it had a positive correlation with proteinuria. The tubulointerstitial injury score was significantly increased by PA treatment and relieved by low-salt diet. ED1-positive infiltrating cells and immunostaining for interstitial collagen III were significantly increased by PA treatment. These changes appeared to be less common in PA-treated low-salt rats, although the differences in PA-treated normal-salt versus low-salt rats did not reach statistical significance. Our results suggest that renal histopathology in PA nephrosis may potentially be improved by dietary salt restriction. Non-hemodynamic mechanisms induced by low-sodium diet might contribute to renoprotection.

Significance of glomerular activation of the alternative pathway and lectin pathway in lupus nephritis

The objective of the present study was to elucidate the association between glomerular complement depositions belonging to the alternative (AP) and lectin (LP) pathways, and clinical findings of lupus nephritis (LN). Immunofluorescence (IF) was performed on 17 LN patients using antibodies against factor B, factor H, properdin, mannose-binding lectin (MBL) and L-ficolin. Compared with factor B/factor H negative patients (n = 9), positive patients (n = 8) showed longer duration of LN (p < 0.05) and more severe interstitial fibrosis (p < 0.05). Eleven patients had properdin deposition in glomeruli, and in three of them, with a duration of LN of less than 1 month, factor B was undetectable. Compared with properdin negative patients (n = 6), positive patients (n = 11) showed significantly higher urinary protein excretion (p < 0.01). MBL/L-ficolin positive patients (n = 11) also had significantly higher urinary protein excretion (p < 0.05) compared with negative patients (n = 6). An independent association was found between glomerular deposition of properdin and that of MBL/L-ficolin (p < 0.01) in addition to factor B/factor H. Traces of glomerular activation of AP and LP reflected the clinical status of LN. It appears that glomerular deposition of each complement component, especially properdin, may be an index of the histological activity of LN.