How does proteinuria cause progressive renal damage?

The Association Between GFR Evaluated by Serum Cystatin C and Proteinuria During Pregnancy

Introduction

Physiological changes in pregnancy result in increased cardiac output and renal blood flow, with a consequential increase in proteinuria. Data from studies of the relationship between proteinuria caused by isolated proteinuria and glomerular filtration rate (GFR) are still limited. The objective of this study was to investigate the effects of isolated proteinuria on the cystatin C–based GFR in the third trimester of pregnancy.

Methods

Data were collected from pregnant women in their third trimester whose serum creatinine levels were normal. The GFR of each participant was measured using serum cystatin C levels, and proteinuria was measured using urine protein–creatinine ratios. The participants were divided into 3 groups according to their level of proteinuria: normal (<150 mg/d), physiological (150–300 mg/d), and gestational (>300 mg/d). Changes in GFR were recorded for each group.

Results

The study included 89 participants, of whom 66.3% had levels of proteinuria that did not differ from that of the normal population (<150 mg/d). The incidence of physiological and gestational proteinuria was 21.4% and 12.4%, respectively. The results demonstrate that proteinuria >101.50 mg/d was significantly associated with declined estimated glomerular filtration rate (eGFR) (r = –0.34, P = 0.01). The analysis found that proteinuria >491.27 mg/d led to a risk of GFR <90 ml/min with an odds ratio of 12.69, P = 0.02 when adjusted for systolic blood pressure (SBP), diastolic blood pressure (DBP), and body mass index.

Conclusion

This study suggests that the term “physiological proteinuria” is a misnomer. When used in the traditional manner, creatinine level has inadequate sensitivity to estimate GFR in pregnant women. We found that there is a significant decline in GFR when urine protein > 101.5 mg/d, which could be an early biomarker for renal pathology rather than pregnancy physiology, suggesting that further workup and precaution is required.

The Association of Serum hsCRP and Urinary Alpha1-Microglobulin in Patients with Type 2 Diabetes Mellitus

This study aimed to investigate the association of serum hsCRP and urinary A1MG in patients with T2DM. Numerous investigations have proven that serum hypersensitive C-reactive protein (hsCRP) concentration in patients with type 2 diabetes mellitus (T2DM) is increased. Also, increased urinary alpha-1 microglobulin (A1MG) can be an early sign of renal damage, primarily on the proximal tubules in T2DM. Little information is available with respect to the associations of serum hsCRP levels and urinary A1MG in T2DM. A total of 520 patients with T2DM were recruited to participate in this study. Serum hsCRP and UA1MG (urinary alpha1-microglobulin to creatinine ratio), UACR (urinary microalbumin to creatinine ratio), UIGG (urinary immunoglobulin G to creatinine ratio), and UTRF (urinary transferrin to creatinine ratio) were obtained. The association of serum hsCRP level and each urinary protein parameter was analyzed by using the regression analysis, respectively. LnhsCRP was positively associated with the lnUA1MG in all three linear regression models (adjusted β in model 3=0.122, SE=0.027, P<0.001). Furthermore, the high hsCRP group (hsCRP > 3mg/L) was associated with increasing risk of high UA1MG (adjusted OR in model 3=1.610, 95% CI 1.037-2.499, P=0.034) by logistic regression. This study suggests that serum hsCRP levels independently associate with UA1MG in patients with T2DM. Further research is warranted to elucidate these interactions.

Extracellular Vesicles from Albumin-Induced Tubular Epithelial Cells Promote the M1 Macrophage Phenotype by Targeting Klotho

Albumin absorbed by renal tubular epithelial cells induces inflammation and plays a key role in promoting diabetic kidney disease (DKD) progression. Macrophages are prominent inflammatory cells in the kidney, and their role there is dependent on their phenotypes. However, whether albuminuria influences macrophage phenotypes and underlying mechanisms during the development of DKD is still unclear. We found that M1 macrophage-related markers were increased in diabetes mellitus (DM) mouse renal tissues with the development of DKD, and coculture of extracellular vesicles (EVs) from human serum albumin (HSA)-induced HK-2 cells with macrophages induced macrophage M1 polarization in the presence of lipopolysaccharide (LPS). Through a bioinformatic analysis, miR-199a-5p was selected and found to be increased in EVs from HSA-induced HK-2 cells and in urinary EVs from DM patients with macroalbuminuria. Tail-vein injection of DM mice with EVs from HSA-induced HK-2 cells induced kidney macrophage M1 polarization and accelerated the progression of DKD through miR-199a-5p. miR-199a-5p exerted its effect by targeting Klotho, and Klotho induced macrophage M2 polarization through the Toll-like receptor 4 (TLR4) pathway both in vivo and in vitro. In summary, miR-199a-5p from HSA-stimulated HK-2 cell-derived EVs induces M1 polarization by targeting the Klotho/TLR4 pathway and further accelerates the progression of DKD.

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.

Dipeptidyl peptidase-4 plays a pathogenic role in BSA-induced kidney injury in diabetic mice

Diabetic kidney disease (DKD) is appeared to be higher risk of declining kidney function compared to non-diabetic kidney disease with same magnitude of albuminuria. Epithelial-mesenchymal transition (EMT) program of tubular epithelial cells (TECs) could be important for the production of the extracellular matrix in the kidney. Caveolin-1 (CAV1), dipeptidyl peptidase-4 (DPP-4) and integrin β1 have shown to be involved in EMT program. Here, we found diabetic kidney is prone for albuminuria-induced TECs damage and DPP-4 plays a vital role in such parenchymal damages in diabetic mice. The bovine serum albumin (BSA) injection induced severe TECs damage and altered expression levels of DPP-4, integrin β1, CAV1, and EMT programs including relevant microRNAs in type 1 diabetic CD-1 mice when compared to non-diabetic mice; teneligliptin (TENE) ameliorated these alterations. TENE suppressed the close proximity among DPP-4, integrin β1 and CAV1 in a culture of HK-2 cells. These findings suggest that DPP-4 inhibition can be relevant for combating proteinuric DKD by targeting the EMT program induced by the crosstalk among DPP-4, integrin β1 and CAV1.

Albumin induces CD44 expression in glomerular parietal epithelial cells by activating extracellular signal-regulated kinase 1/2 pathway

De novo expression of CD44 in glomerular parietal epithelial cells (PECs) leads to a prosclerotic and migratory PEC phenotype in glomerulosclerosis. However, the regulatory mechanisms underlying CD44 expression by activated PECs remain largely unknown. This study was performed to examine the mediators responsible for CD44 induction in glomerular PECs in association with diabetes. CD44 expression and localization were evaluated in the glomeruli of Zucker diabetic rat kidneys and primary cultured PECs upon albumin stimulation. Real-time polymerase chain reaction confirmed an albuminuria-associated upregulation of the CD44 gene in the glomeruli of diabetic rats. Immunostaining analysis of diabetic kidneys further revealed an increase in CD44 in hypertrophic PECs, which often contain albumin-positive vesicles. Losartan treatment significantly attenuated albuminuria and lowered CD44 protein levels in the diabetic kidneys. In primary cultured rat PECs, rat serum albumin (0.25-1 mg/ml) caused a dose-dependent upregulation of CD44, claudin-1, and megalin protein expression, which was accompanied by an activation of extracellular signal-regulated kinase1/2 (ERK1/2) signaling. Albumin-induced CD44 and claudin-1 expression were greatly suppressed in the presence of the ERK1/2 inhibitor, U0126. In addition, knockdown of megalin by small interfering RNA interference in PECs resulted in a significant reduction of albumin-induced CD44 and claudin-1 proteins. Taken together, our results demonstrate that albumin induces CD44 expression by PECs via the activation of the ERK signaling pathway, which is partially mediated by endocytic receptor megalin.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Lithium ameliorates tubule-interstitial injury through activation of the mTORC2/protein kinase B pathway

Tubule-interstitial injury (TII) is a critical step in the progression of renal disease. It has been proposed that changes in proximal tubule (PT) albumin endocytosis plays an important role in the development of TII. Some reports have shown protective effects of lithium on kidney injury animal models that was correlated to proteinuria. We tested the hypothesis that lithium treatment ameliorates the development of TII due to changes in albumin endocytosis. Two experimental models were used: (1) TII induced by albumin overload in an animal model; (2) LLC-PK1 cells, a PT cell line. Lithium treatment ameliorates TII induced by albumin overload measured by (1) proteinuria; (2) collagen deposition; (3) area of tubule-interstitial space, and (4) macrophage infiltration. Lithium treatment increased mTORC2 activity leading to the phosphorylation of protein kinase B (PKB) at Ser473 and its activation. This mechanism enhanced albumin endocytosis in PT cells, which decreased the proteinuria observed in TII induced by albumin overload. This effect did not involve changes in the expression of megalin, a PT albumin receptor. In addition, activation of this pathway decreased apoptosis in LLC-PK1 cells, a PT cell line, induced by higher albumin concentration, similar to that found in pathophysiologic conditions. Our results indicate that the protective role of lithium treatment on TII induced by albumin overload involves an increase in PT albumin endocytosis due to activation of the mTORC2/PKB pathway. These results open new possibilities in understanding the effects of lithium on the progression of renal disease.

[Laboratory tests for kidney disease]

Kidney diseases are among the most frequently reported diseases with a poor prognosis that are diagnosed too late. According to current Kidney Disease Improving Global Outcomes (KDIGO) guidelines, diagnosis and risk stratification are mainly based on functional markers (creatinine and cystatin C), which are used to determine the estimated glomerular filtration rate (eGFR) and the analysis of urinary albumin excretion as a marker of kidney damage. These methods have limitations that can complicate the interpretation of the results and can lead to a delay of the diagnosis as well as to a misinterpretation of the prognosis. Therefore, new damage markers are required that sensitively and specifically detect kidney damage and enable targeted treatment. Urinalysis complements the laboratory diagnostic spectrum of diseases of the kidneys and urinary tract. It is mainly used for screening and provides important information on localization (renal/postrenal) and differentiation of kidney diseases (glomerular/tubulointerstitial).

Differential trafficking of albumin and IgG facilitated by the neonatal Fc receptor in podocytes in vitro and in vivo

Proteinuria is strongly associated with kidney disease progression but the mechanisms underlying podocyte handling of serum proteins such as albumin and IgG remain to be elucidated. We have previously shown that albumin and IgG are transcytosed by podocytes in vitro. In other epithelial cells, the neonatal Fc receptor (FcRn) is required to salvage albumin and IgG from the degradative pathway thereby allowing these proteins to be transcytosed or recycled. Here we directly examine the role of FcRn in albumin and IgG trafficking in podocytes by studying handling of these proteins in FcRn knockout (KO) podocytes in vitro and in a podocyte-specific FcRn knockout mice in vivo. In vitro, we find that knockout of FcRn leads to IgG accumulation in podocytes but does not alter albumin trafficking. Similarly, in vivo, podocyte-specific knockout of FcRn does not result in albumin accumulation in podocytes in vivo as measured by mean albumin fluorescence intensity whereas these mice demonstrate significant intraglomerular accumulation of IgG over time. In addition we find that podocyte-specific FcRn KO mice demonstrate mesangial expansion as they age and activation of mesangial cells as demonstrated by increased expression of α-smooth muscle actin. Taken together, these results suggest that trafficking pathways for albumin and IgG differ in podocytes and that sustained disruption of trafficking of plasma proteins alters glomerular structure.

Change in albuminuria as a surrogate endpoint for progression of kidney disease: a meta-analysis of treatment effects in randomised clinical trials

BACKGROUND

Change in albuminuria has strong biological plausibility as a surrogate endpoint for progression of chronic kidney disease, but empirical evidence to support its validity is lacking. We aimed to determine the association between treatment effects on early changes in albuminuria and treatment effects on clinical endpoints and surrograte endpoints, to inform the use of albuminuria as a surrogate endpoint in future randomised controlled trials.

METHODS

In this meta-analysis, we searched PubMed for publications in English from Jan 1, 1946, to Dec 15, 2016, using search terms including "chronic kidney disease", "chronic renal insufficiency", "albuminuria", "proteinuria", and "randomized controlled trial"; key inclusion criteria were quantifiable measurements of albuminuria or proteinuria at baseline and within 12 months of follow-up and information on the incidence of end-stage kidney disease. We requested use of individual patient data from the authors of eligible studies. For all studies that the authors agreed to participate and that had sufficient data, we estimated treatment effects on 6-month change in albuminuria and the composite clinical endpoint of treated end-stage kidney disease, estimated glomerular filtration rate of less than 15 mL/min per 1·73 m², or doubling of serum creatinine. We used a Bayesian mixed-effects meta-regression analysis to relate the treatment effects on albuminuria to those on the clinical endpoint across studies and developed a prediction model for the treatment effect on the clinical endpoint on the basis of the treatment effect on albuminuria.

FINDINGS

We identified 41 eligible treatment comparisons from randomised trials (referred to as studies) that provided sufficient patient-level data on 29 979 participants (21 206 [71%] with diabetes). Over a median follow-up of 3·4 years (IQR 2·3-4·2), 3935 (13%) participants reached the composite clinical endpoint. Across all studies, with a meta-regression slope of 0·89 (95% Bayesian credible interval [BCI] 0·13-1·70), each 30% decrease in geometric mean albuminuria by the treatment relative to the control was associated with an average 27% lower hazard for the clinical endpoint (95% BCI 5-45%; median R² 0·47, 95% BCI 0·02-0·96). The association strengthened after restricting analyses to patients with baseline albuminuria of more than 30 mg/g (ie, 3·4 mg/mmol; R² 0·72, 0·05-0·99]). For future trials, the model predicts that treatments that decrease the geometric mean albuminuria to 0·7 (ie, 30% decrease in albuminuria) relative to the control will provide an average hazard ratio (HR) for the clinical endpoint of 0·68, and 95% of sufficiently large studies would have HRs between 0·47 and 0·95.

INTERPRETATION

Our results support a role for change in albuminuria as a surrogate endpoint for the progression of chronic kidney disease, particularly in patients with high baseline albuminuria; for patients with low baseline levels of albuminuria this association is less certain.

FUNDING

US National Kidney Foundation.

A scrutiny of circulating microRNA biomarkers for drug-induced tubular and glomerular injury in rats

Drug-induced acute kidney injury (AKI) is a frequent cause of adverse drug reaction. Serum creatinine (CRE) and blood urea nitrogen (BUN) are widely used as standard biomarkers for kidney injury; however, the sensitivity and specificity are considered to be low. In recent years, circulating microRNA (miRNAs) have been attracting considerable attention as novel biomarkers for organ injury, but there are currently no established miRNA biomarkers for drug-induced AKI. The present study aimed to identify plasma miRNAs that may enable early and specific detection of drug-induced tubular and glomerular injury through next-generation sequencing analysis. Six-week old male Sprague-Dawley (SD) rats were intravenously administered cisplatin (CSP, 6 mg/kg) and gentamicin (GEN, 120 mg/kg) to induce tubular injury. To create glomerular injury models, puromycin (PUR, 120 mg/kg) and doxorubicin (DOX, 7.5 mg/kg) were intravenously administered, and these models were always accompanied by tubular damage. Small RNA-sequencing was performed to analyze time-dependent changes in the plasma miRNA profiles. The cluster analyses showed that there were distinct plasma miRNA profiles according to the types of injury, and the changes reflected the progress of renal damages. In the differential analysis, miR-3473 was specifically up-regulated in the glomerular injury models. miR-143-3p and miR-122-5p were commonly down-regulated in all models, and the changes were earlier than the traditional biomarkers, such as plasma CRE and BUN. These data indicated that changes in the specific miRNAs in plasma may enable the early and sensitive detection of tubular and glomerular injuries. The present study suggests the potential utility of plasma miRNAs in the early and type-specific detection of drug-induced AKI.

Efficacy of Co-administration of Liuwei Dihuang Pills and Ginkgo Biloba Tablets on Albuminuria in Type 2 Diabetes: A 24-Month, Multicenter, Double-Blind, Placebo-Controlled, Randomized Clinical Trial

Purpose: We investigated the effects of Traditional Chinese Medicine (TCM) on the occurrence and progression of albuminuria in patients with type 2 diabetes. Methods: In this randomized, double-blind, multicenter, controlled trial, we enrolled 600 type 2 diabetes without diabetic nephropathy (DN) or with early-stage DN. Patients were randomly assigned (1:1) to receive Liuwei Dihuang Pills (LWDH) (1.5 g daily) and Ginkgo biloba Tablets (24 mg daily) orally or matching placebos for 24 months. The primary endpoint was the change in urinary albumin/creatinine ratio (UACR) from baseline to 24 months. Results: There were 431 patients having UACR data at baseline and 24 months following-up in both groups. Changes of UACR from baseline to follow-up were not affected in both groups: -1.61(-10.24, 7.17) mg/g in the TCM group and -0.73(-7.47, 6.75) mg/g in the control group. For patients with UACR ≥30 mg/g at baseline, LWDH and Ginkgo biloba significantly reduced the UACR value at 24 months [46.21(34.96, 58.96) vs. 20.78(9.62, 38.85), P < 0.05]. Moreover, the change of UACR from baseline to follow-up in the TCM group was significant higher than that in the control group [-25.50(-42.30, -9.56] vs. -20.61(-36.79, 4.31), P < 0.05]. Conclusion: LWDH and Ginkgo biloba may attenuate deterioration of albuminuria in type 2 diabetes patients. These results suggest that TCM is a promising option of renoprotective agents for early stage of DN. Trial registration: The study was registered in the Chinese Clinical Trial Registry. (no. ChiCTR-TRC-07000037, chictr.org).

New Understanding on the Role of Proteinuria in Progression of Chronic Kidney Disease

Proteinuria is identified as an important marker and risk factor of progression in chronic kidney disease. However, the precise mechanism of action in the progress of chronic kidney disease is still unclear. Mesangial toxicity from specific filtered compounds such as albumin-bound fatty acids and transferrin/iron, tubular overload and hyperplasia, and induction of proinflammatory molecules such as MCP-1 and inflammatory cytokines are some of the proposed mechanisms. Reversing intraglomerular hypertension with protein restriction or antihypertensive therapy may be beneficial both by diminishing hemodynamic injury to the glomeruli and by reducing protein filtration. Therefore, understanding proteinuria and its role in renal tubular interstitial inflammation and fibrosis is of great significance for the study of renal protective therapy, such as antiproteinuric treatments, and delaying the progression of chronic renal disease.

Cell Apoptosis and Autophagy in Renal Fibrosis

Renal fibrosis is the final common pathway of all chronic kidney diseases progressing to end-stage renal diseases. Autophagy, a highly conserved lysosomal degradation pathway, plays important roles in maintaining cellular homeostasis in all major types of kidney cells including renal tubular cells as well as podocytes, mesangial cells and endothelial cells in glomeruli. Autophagy dysfunction is implicated in the pathogenesis of various renal pathologies. Here, we analyze the pathological role and regulation of autophagy in renal fibrosis and related kidney diseases in both glomeruli and tubulointerstitial compartments. Further research is expected to gain significant mechanistic insights and discover pathway-specific and kidney-selective therapies targeting autophagy to prevent renal fibrosis and related kidney diseases.

The role of properdin in complement-mediated renal diseases: a new player in complement-inhibiting therapy?

Properdin is known as the only positive regulator of the complement system. Properdin promotes the activity of this defense system by stabilizing its key enzymatic complexes: the complement alternative pathway (AP) convertases. Besides, some studies have indicated a role for properdin as an initiator of complement activity. Though the AP is a powerful activation route of the complement system, it is also involved in a wide variety of autoimmune and inflammatory diseases, many of which affect the kidneys. The role of properdin in regulating complement in health and disease has not received as much appraisal as the many negative AP regulators, such as factor H. Historically, properdin deficiency has been strongly associated with an increased risk for meningococcal disease. Yet only recently had studies begun to link properdin to other complement-related diseases, including renal diseases. In the light of the upcoming complement-inhibiting therapies, it is interesting whether properdin can be a therapeutic target to attenuate AP-mediated injury. A full understanding of the basic concepts of properdin biology is therefore needed. Here, we first provide an overview of the function of properdin in health and disease. Then, we explore its potential as a therapeutic target for the AP-associated renal diseases C3 glomerulopathy, atypical hemolytic uremic syndrome, and proteinuria-induced tubulointerstitial injury. Considering current knowledge, properdin-inhibiting therapy seems promising in certain cases. However, knowing the complexity of properdin's role in renal pathologies in vivo, further research is required to clarify the exact potential of properdin-targeted therapy in complement-mediated renal diseases.

Mathematical model of hemodynamic mechanisms and consequences of glomerular hypertension in diabetic mice

Many preclinically promising therapies for diabetic kidney disease fail to provide efficacy in humans, reflecting limited quantitative translational understanding between rodent models and human disease. To quantitatively bridge interspecies differences, we adapted a mathematical model of renal function from human to mice, and incorporated adaptive and pathological mechanisms of diabetes and nephrectomy to describe experimentally observed changes in glomerular filtration rate (GFR) and proteinuria in db/db and db/db UNX (uninephrectomy) mouse models. Changing a small number of parameters, the model reproduced interspecies differences in renal function. Accounting for glucose and Na⁺ reabsorption through sodium glucose cotransporter 2 (SGLT2), increasing blood glucose and Na⁺ intake from normal to db/db levels mathematically reproduced glomerular hyperfiltration observed experimentally in db/db mice. This resulted from increased proximal tubule sodium reabsorption, which elevated glomerular capillary hydrostatic pressure (P_gc) in order to restore sodium balance through increased GFR. Incorporating adaptive and injurious effects of elevated P_gc, we showed that preglomerular arteriole hypertrophy allowed more direct transmission of pressure to the glomerulus with a smaller mean arterial pressure rise; Glomerular hypertrophy allowed a higher GFR for a given P_gc; and P_gc-driven glomerulosclerosis and nephron loss reduced GFR over time, while further increasing P_gc and causing moderate proteinuria, in agreement with experimental data. UNX imposed on diabetes increased P_gc further, causing faster GFR decline and extensive proteinuria, also in agreement with experimental data. The model provides a mechanistic explanation for hyperfiltration and proteinuria progression that will facilitate translation of efficacy for novel therapies from mouse models to human.

Many drugs for diabetic kidney disease appear to work in rodents, but fail in humans, reflecting incomplete understanding of disease processes. A team led by Melissa Hallow at the University of Georgia has developed a mathematical model that explains how elevated blood glucose in diabetes causes kidney injury in mice. They first showed that normal human, rat, or mouse kidney physiology could be reproduced with the same model by changing a small number of parameters. They then showed that diabetes-induced increases in sodium reabsorption cause unintuitive changes in kidney function that increase pressure on glomerular capillaries, causing protein leakage and nephron loss. The model reproduced faster disease progression observed in diabetic mice who have had one kidney removed. This mathematical understanding of diabetic kidney injury may improve translation of novel therapies from mice to human.

Sex-dependent differences in the adverse renal changes induced by an early in life exposure to a high-fat diet

This study examines whether the intake of a high-fat diet very early in life leads to changes in arterial pressure and renal function and evaluates whether the mechanisms involved in these changes are sex-dependent. Experiments were performed in male and female Sprague-Dawley rats fed a normal or high-fat diet from weaning to 4 mo of age. This exposure to a high-fat diet lead to an angiotensin II-dependent elevation in arterial pressure and to significant increments in fat abdominal volume and plasma leptin that were similar in both sexes. In addition, the angiotensin II-induced increment in renal vascular resistance was greater ( P < 0.05) in male (106 ± 14%) and female (97 ± 15%) rats fed a high-fat diet than in rats fed a normal-fat diet (51 ± 8%). However, the high-fat intake during early life induced increments in albuminuria, interleukin-6, and infiltration of CD3 lymphocytes in the renal parenchyma that were greater ( P < 0.05) in male than in female rats. Other sex-dependent differences in response to high-fat intake were that adiponectin levels only decreased in females (21%, P < 0.05), and renal NF-κB expression only increased in males (31%, P < 0.05). In summary, the early exposure to a high-fat diet leads to angiotensin II-dependent arterial pressure elevations and to increments in abdominal fat and in the renal sensitivity to angiotensin II that are similar in both sexes. However, the mechanisms involved in the renal changes associated with early exposure to a high-fat diet are different in males and females.

Effectiveness of renoprotective approaches for persistent proteinuria in lupus nephritis: more than just immunosuppression

OBJECTIVE

The objective of this study is to evaluate the efficacy of a tightly controlled renoprotective protocol in systemic lupus erythematosus (SLE) patients with persistent proteinuria.

METHODS

Thirteen SLE patients with nephritis and persistent proteinuria (>1 g/24 hours) were included. The protocol consisted of regular clinical evaluations every two weeks to assess blood pressure (BP, target <130/80 mmHg), adherence to therapy, diet and smoking. No change in immunosuppressive drugs was allowed but reduction of glucocorticoid dose was permitted if indicated. Clinical, laboratory and treatment evaluations were performed at baseline and at the end of the study (after three months).

RESULTS

SLE patients had a mean age of 37.85 ± 7.68 years and disease duration of 9.85 ± 7.29 years. At baseline, patients had a mean duration of maintenance therapy of 10.38 ± 7.56 months, 12 with mycophenolate mofetil (92.3%) and one with azathioprine (7.7%). At least one dose optimization of antihypertensive regimen was required in all patients during the study. Seven patients (53.8%) had BP>130/80mmHg at baseline. At the end, 11 patients (84.6%) achieved stable BP target; 92.3% were using an angiotensin-converting enzyme inhibitor, 53.9% an angiotensin receptor blocker, and 46.2% were using combined therapy. All patients had a significant reduction in proteinuria levels (2.26 ± 1.09 vs 0.88 ± 0.54 g/24 hours, p < 0.001) and 61.5% achieved proteinuria <1 g/24 hours. A significant decrease in mean prednisone dose was observed (10.96 ± 6.73 vs 5.38 ± 3.36 mg/day, p = 0.013) as well as mean Systemic Lupus Erythematosus Disease Activity Index score (4.38 ± 0.72 vs 3.08 ± 1.86, p = 0.043). No significant changes were identified in serum creatinine, albumin, potassium, complement 3 and complement 4 levels ( p > 0.05).

CONCLUSION

This study provides evidence that a tightly controlled renoprotective protocol is effective in reducing persistent proteinuria in lupus nephritis. The concomitant reduction of prednisone without any change in immunosuppression reinforces the importance of strategies beyond the treatment of nephritis activity.

Preeclampsia: A close look at renal dysfunction

Preeclampsia (PE) is a unique pathophysiologic situation that physiologic interests of mother, fetus, and placenta diverge. PE is related to the increased circulating antiangiogenic factors originated from hypoxic placenta. It is simply defined by the new onset of hypertension (≥140/90 mmHg) and proteinuria (≥0.3 g/day) after 20 weeks of gestation. PE is associated with kidney dysfunction due to deficiency in podocyte specific vascular endothelial growth factor (VEGF). Hypoxic placenta in PE patients produces increased levels of fms-like tyrosine kinase 1(sFlt-1), a soluble receptor of VEGF. sFlt-1 abrogates binding of VEGF to its receptor on endothelial cells and podocytes, and ultimately damages the filtration barrier. Glomerular endotheliosis and thrombotic microangiopathy (TMA) are the main features of kidney involvement in PE and can induce clotting and vessel occlusion. This complex pathophysiology is ameliorated after delivery; however, permanent kidney damages may remain and is intensified thereafter. This review aims to highlight the biochemical, genetic, and immunological-involved factors in the initiation of PE and explores the relationship between the kidney and PE. This work mainly discusses the pathologic mechanisms of kidney involvement in PE through the lens of the imbalanced VEGF-VEGF receptor signaling pathway.

Correlation of Point Shear Wave Velocity and Kidney Function in Chronic Kidney Disease

OBJECTIVES

Point shear wave elastography is a quantitative ultrasound-based imaging method used in the assessment of renal disease. Among point shear wave elastographic options, 2 techniques have been studied considerably: Virtual Touch quantification (VTQ; Siemens AG, Erlangen, Germany) and ElastPQ (EPQ; Philips Healthcare, Bothell, WA). Both rely on the tissue response to an acoustic beam generated by the ultrasound transducer. The data on renal VTQ are more extensive, whereas EPQ has been used less thus far in the assessment of the kidneys. This study aimed to evaluate the performance of EPQ in the kidney and compare it with VTQ.

METHODS

We studied 124 participants using EPQ: 22 with no renal disease and 102 with chronic kidney disease (CKD). Ninety-one were studied with both the EPQ and VTQ methods. We obtained 5 valid measurements in each kidney, expressed in meters per second.

RESULTS

The mean kidney stiffness measurements ± SD obtained with EPQ in the healthy control group were as follows: right kidney, 1.23 ± 0.33 m/s; and left kidney, 1.26 ± 0.32 m/s (P = .6). In the patients with CKD (all stages), the mean kidney stiffness measurements obtained were significantly lower: right kidney, 1.09 ± 0.39 m/s; and left kidney, 1.04 ± 0.38 m/s (P = .4). We observed that, similar to VTQ, EPQ values decreased with CKD progression, based on analysis of variance results using different CKD stages. From a receiver operating characteristic curve analysis, the cutoff value for an estimated glomerular filtration rate of less than 45 mL/min was 1.24 m/s, and the value for an estimated glomerular filtration rate of less than 30 mL/min was 1.07 m/s.

CONCLUSIONS

When using EPQ, the kidney shear wave velocity is decreased in patients with CKD, an observation similar to that obtained by using the VTQ method.

The ratio of urinary sodium and potassium and chronic kidney disease progression: Results from the KoreaN Cohort Study for Outcomes in Patients with Chronic Kidney Disease (KNOW-CKD)

The Na/K ratio in urine stands for the dietary of sodium and potassium intake in patients with chronic kidney disease remains unclear for the renal progression. We aimed to determine the risk of progression of chronic kidney disease based on the Na/K ratio in a 24-hour urine collection.We determined the association between the progression of renal disease and 24-hour urinary sodium and potassium (Na/K) ratios in 2238 patients over a 5-year timespan using data obtained from the KoreaN cohort study for Outcomes in patients With Chronic Kidney Disease (KNOW-CKD). Renal events were defined as a 50% decrease in the glomerular filtration rate (GFR) below baseline, or the onset of end-stage renal disease (ESRD). Patients were divided into 4 groups based on the quartile range of the 24-hour urinary sodium and potassium ratio. We analyzed those variables in the 4 groups. Multiple logistic regression analyses were performed using the data of 1001 patients to identify the independent factors associated with renal events.Age and male sex accounted for the greatest number of patients in the group with the highest values (group 4) of the 24-hour urinary Na/K ratio (≥3.85). There was no difference in the prevalence of hypertension or diabetes mellitus, the ratio of use of antihypertensive drugs, blood pressures, or estimated GFRs. In the group with the highest urinary Na/K ratio, the 24-hour urinary Na concentration mean ± standard deviation was 188.7 ± 70.6 mmol and that of urinary K was 39.9 ± 16.1 mmol. The urinary protein excretion was highest in the group with the highest urinary Na/K ratio. In the logistic regression analysis, the effect on renal events increased with increasing urinary Na/K ratios. After adjusting for other factors, the risk of renal events was 2.48 (95% confidence interval (CI) 1.30-4.90) in group 3, and 3.75 (95% CI: 1.35-11.27) in group 4. In the Kaplan-Meier analysis, the higher the urinary Na/K ratio, the higher the rate of CKD progression.Based on our analyses, we concluded that the higher the urinary Na/K ratio, the greater the risk of CKD progression.

Changes in lectin-binding patterns in the kidneys of canines with immune-complex mediated glomerulonephritis

We surveyed the kidneys of dogs with immune-complex mediated glomerulonephritis (ICGN) by lectin histochemistry using seven lectins—namely WGA, RCA-I, ConA, PNA, SBA, DBA, and UEA-I. Their binding patterns were compared with those from normal dogs. RCA-I signals became weak in the brush borders of the proximal tubules, whereas DBA signals became positive in Bowman’s capsules. Also, varying intensity of the UEA-I signal was noted in the distal tubules, especially in the macula densa. The binding pattern profiles varied among the cases; this diversity in the lectin-binding patterns might be induced as a result of the diverse pathologies seen in canine ICGN.

NIX-mediated mitophagy protects against proteinuria-induced tubular cell apoptosis and renal injury

Proteinuria, the most common symptom of renal injury, is an independent factor for renal tubular injury. However, the underlying mechanism remains to be fully elucidated. Mitochondrion is an important target for proteinuria-induced renal tubular cell injury. Insufficient mitophagy exacerbates cell injury by initiating mitochondrial dysfunction-related cell apoptosis. In the experiment, the role of NIP3-like protein X (NIX)-mediated mitophagy was investigated in proteinuria-induced renal injury. In this study, we demonstrated that NIX expression was reduced in renal tubules and correlated with the decline of estimated glomerular filtration rate and increase of the proteinuria in patients. In proteinuric mice, NIX-mediated mitophagy was significantly suppressed. Meanwhile, the proteinuric mice exhibited renal dysfunction, increased mitochondrial fragmentation, and tubular cell apoptosis. Overexpression of NIX attenuated those disruptions in proteinuric mice. In cultured renal tubular epithelial cells, albumin induced a decrease in NIX-mediated mitophagy and an increase in cell apoptosis. Overexpression of NIX attenuated albumin-induced cell apoptosis, whereas NIX siRNA aggravated these perturbations. These results indicate that proteinuria suppresses NIX-mediated mitophagy in the renal tubular epithelial cell, which triggers the cell undergoing mitochondria-dependent cell apoptosis. Collectively, our finding suggests that restoration of NIX-mediated mitophagy might be a novel therapeutic target for alleviating proteinuria-induced kidney injury.

The angiotensin II/AT1 receptor pathway mediates malaria-induced acute kidney injury

Malaria-induced acute kidney injury (MAKI) is a life-threatening complication of severe malaria. Here, we investigated the potential role of the angiotensin II (Ang II)/AT1 receptor pathway in the development of MAKI. We used C57BL/6 mice infected by Plasmodium berghei ANKA (PbA-infected mice), a well-known murine model of severe malaria. The animals were treated with 20 mg/kg/day losartan, an antagonist of AT1 receptor, or captopril, an angiotensin-converting enzyme inhibitor. We observed an increase in the levels of plasma creatinine and blood urea nitrogen associated with a significant decrease in creatinine clearance, a marker of glomerular flow rate, and glomerular hypercellularity, indicating glomerular injury. PbA-infected mice also presented proteinuria and a high level of urinary γ-glutamyltransferase activity associated with an increase in collagen deposition and interstitial space, showing tubule-interstitial injury. PbA-infected mice were also found to have increased fractional excretion of sodium (FENa+) coupled with decreased cortical (Na++K+)ATPase activity. These injuries were associated with an increase in pro-inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-6, interleukin-17, and interferon gamma, in the renal cortex of PbA-infected mice. All modifications of these structural, biochemical, and functional parameters observed in PbA-infected mice were avoided with simultaneous treatment with losartan or captopril. Our data allow us to postulate that the Ang II/AT1 receptor pathway mediates an increase in renal pro-inflammatory cytokines, which in turn leads to the glomerular and tubular injuries observed in MAKI.

Serum level of the autophagy biomarker Beclin-1 in patients with diabetic kidney disease

Autophagy is a major cellular clearance mechanism that maintains cellular survival and homeostasis. Autophagy has a crucial role in the progression of diabetes and kidney diseases.

AIMS

To investigate serum concentrations of Beclin-1, a key regulator of autophagy, in patients with diabetic kidney disease (DKD).

METHODS

The study included 70 patients with type 2 diabetes and DKD (group 1; 35 patients with estimated glomerular filtration rate (eGFR) ≥ 30 ml/min/1.73 m² and group 2; 35 patients with eGFR < 30 ml/min/1.73 m²) and 20 age- and sex-matched healthy subjects (group 3). Laboratory work up included; glycated hemoglobin (HbA1c), serum creatinine, eGFR using modification of diet in renal disease (MDRD) formula, urine albumin to creatinine ratio (ACR), and serum Beclin-1 measurement.

RESULTS

Patients with DKD had significantly lower Beclin-1 levels (2.38 ± 1.46 ng/mL) compared to control group (6.03 ± 1.94 ng/mL; P < 0.001). Moreover, serum Beclin-1 significantly decreased in group 2 (1.43 ± 0.83 ng/mL) compared to group 1 (3.36 ± 1.30 ng/mL; P < 0.001). In univariate analysis, the concentration of Beclin-1 correlated well with eGFR (r = 0.64, P < 0.001), ACR (r = -0.63, P < 0.001), and duration of diabetes (r = -0.43, P < 0.001) but didn't correlate with HbA1c (r = -0.17, P = 0.15). However, ACR was the only significant predictor of Beclin-1 level on performing multiple regression analysis (β = -0.40, P = 0.01).

CONCLUSION

Serum level of Beclin-1 is reduced in patients with DKD. Furthermore, its level is related to the stage of DKD and correlates with the degree of albuminuria.

MiR-874 alleviates renal injury and inflammatory response in diabetic nephropathy through targeting toll-like receptor-4

Diabetic nephropathy (DN) is a kind of diabetic complication with capillary damage, and its pathogenesis remains obscure. Recently, microRNAs have been identified as diagnostic biomarkers in various diseases including DN. Toll-like receptor 4 (TLR4) contributes to inflammation, and it has been implicated in diabetes pathophysiology. This study was designed to investigate the role of miR-874 and TLR4 in a streptozotocin (STZ)-induced DN rat model and glucose-induced mouse podocyte model. In the current study, we reported that miR-874 was markedly downregulated in DN rats and glucose-induced mouse podocytes compared with the corresponding control groups with the activation of TLR4. In addition, we observed that overexpression of miR-874 was able to alleviate renal injury in DN rats. The cell counting kit (CCK-8) assay and 5-Ethynyl-2'-deoxyuridine (EdU) assay demonstrated that glucose simulation significantly inhibited podocyte proliferation and induced cell apoptosis, which can be reversed by miR-874 mimics significantly. Notably, miR-874 overexpression dramatically attenuated the inflammatory response, indicated by the decreased levels of interleukin-6, L-1β, and tumor necrosis factor α (TNF-α). Finally, the binding correlation between miR-874 and TLR4 was confirmed by carrying out dual-luciferase reporter assay in our study. It was found that overexpression of miR-874 depressed TLR4 levels in podocytes. These findings implied for the first time that the overexpression of miR-874 repressed glucose-triggered podocyte injury through targeting TLR4 and suggested that miR-874/TLR4 axis might represent a pathological mechanism of DN.

Cryptotanshinone Attenuates Oxidative Stress and Inflammation through the Regulation of Nrf-2 and NF-κB in Mice with Unilateral Ureteral Obstruction

Oxidative stress and inflammatory responses are closely implicated in the progression of renal interstitial fibrosis, thereby leading to chronic kidney disease. Cryptotanshinone (CTS) is a natural compound involved in antioxidant and anti-inflammatory activities. We evaluated the effects of CTS on inflammation and oxidative stress in obstructed kidneys. Mice received gastric gavage of CTS from 7 days before unilateral ureteral obstruction operation to 1 week after surgery. Administration of CTS at 50 and 100 mg/kg/day significantly decreased collagen production, as shown by Masson staining. Immunohistochemistry staining and RT-PCR confirmed that CTS reduced extracellular matrix proteins, such as fibronectin and collagen-1, in the obstructed kidneys in a dose-dependent manner. Furthermore, immunohistochemistry staining indicated that CTS inhibited infiltration of the macrophage (CD68-positive) and lymphocyte (CD3-positive) cells, which were associated with the suppression of the nuclear factor-κB signalling activation. CTS increased superoxide dismutase, catalase and glutathione while decreased malondialdehyde production. More importantly, CTS activated Nrf-2 and HO-1 in the obstructed kidneys for 7 days. CTS could protect renal interstitial fibrosis by ameliorating inflammation and oxidative stress, which might be through the regulation of NF-κB and Nrf-2/HO-1 signalling pathways.

Effects of the SGLT-2 inhibitor dapagliflozin on glomerular and tubular injury markers

The mechanisms by which SGLT-2 inhibitors lower albuminuria are incompletely understood. We assessed in a post-hoc analysis of a cross-over trial the effects of the SGLT2 inhibitor dapagliflozin on glomerular markers (IgG to IgG4 and IgG to albumin), tubular markers (urinary KIM-1, NGAL and LFABP) and inflammatory markers (urinary MCP-1 and IL-6) to provide more insight into kidney protective effects. Dapagliflozin decreased albuminuria by 43.9% (95% CI, 30.3%-54.8%) and eGFR by 5.1 (2.0-8.1) mL/min/1.73m² compared to placebo. Dapagliflozin did not change glomerular charge or size selectivity index compared to placebo. Dapagliflozin decreased urinary KIM-1 excretion by 22.6% (0.3%-39.8%; P = .05) and IL-6 excretion by 23.5% (1.4%-40.6%; P = .04) compared to placebo, whereas no changes in NGAL, LFABP and MCP-1 were observed. During dapagliflozin treatment, changes in albuminuria correlated with changes in eGFR (r = 0.36; P = .05) and KIM-1 (r = 0.39; P = .05). In conclusion, the albuminuria-lowering effect of 6 weeks of dapagliflozin therapy may be the result of decreased intraglomerular pressure or reduced tubular cell injury.

Associations of body condition score with health conditions related to overweight and obesity in cats

OBJECTIVES

To explore the associations of cat body condition score with various health conditions, such as diabetes mellitus, dermatological conditions and hypertension, that have been shown to relate to overweight and/or obesity in cats, dogs or humans.

MATERIALS AND METHODS

Electronic patient records between January 3, 2005 and June 21, 2015 were obtained from a cat-focused primary accession clinic in metropolitan Sydney where the body condition score of cats was routinely evaluated. Binomial logistic regression modelling was conducted to investigate the associations, after adjusting for age, sex and breed, between 21 health conditions and body condition score recorded on a 9-point scale.

RESULTS

Fourteen of the 21 health conditions examined showed significant associations with an increased body condition score, particularly those of 7 and above. These were dermatological conditions, atopic dermatitis, musculoskeletal conditions, arthritis, hypertension, respiratory conditions, asthma, oral conditions, diarrhoea, general and lower urinary tract conditions, ophthalmic conditions, diabetes mellitus and allergic conditions. Additionally, cats with body condition score of 8 or 9 had significantly higher odds for gastrointestinal conditions and upper urinary tract conditions when compared with cats with body condition score of 5.

CLINICAL SIGNIFICANCE

As far as we know, this is the first study reporting positive associations of high body condition score with atopic dermatitis, hypertension, asthma, diarrhoea, ophthalmic conditions and allergic conditions in cats. A large number of positive associations between health conditions and high body condition score indicates that excess fat mass should be given a greater emphasis in preventive health care for cats.

Simultaneous activation of innate and adaptive immunity participates in the development of renal injury in a model of heavy proteinuria

Protein overload of proximal tubular cells (PTCs) can promote interstitial injury by unclear mechanisms that may involve activation of innate immunity. We investigated whether prolonged exposure of tubular cells to high protein concentrations stimulates innate immunity, triggering progressive interstitial inflammation and renal injury, and whether specific inhibition of innate or adaptive immunity would provide renoprotection in an established model of massive proteinuria, adriamycin nephropathy (ADR). Adult male Munich-Wistar rats received a single dose of ADR (5 mg/kg, iv), being followed for 2, 4, or 20 weeks. Massive albuminuria was associated with early activation of both the NF-κB and NLRP3 innate immunity pathways, whose intensity correlated strongly with the density of lymphocyte infiltration. In addition, ADR rats exhibited clear signs of renal oxidative stress. Twenty weeks after ADR administration, marked interstitial fibrosis, glomerulosclerosis, and renal functional loss were observed. Administration of mycophenolate mofetil (MMF), 10 mg/kg/day, prevented activation of both innate and adaptive immunity, as well as renal oxidative stress and renal fibrosis. Moreover, MMF treatment was associated with shifting of M from the M1 to the M2 phenotype. In cultivated NRK52-E cells, excess albumin increased the protein content of Toll-like receptor (TLR) 4 (TLR4), NLRP3, MCP-1, IL6, IL-1β, Caspase-1, α-actin, and collagen-1. Silencing of TLR4 and/or NLRP3 mRNA abrogated this proinflammatory/profibrotic behavior. Simultaneous activation of innate and adaptive immunity may be key to the development of renal injury in heavy proteinuric disease. Inhibition of specific components of innate and/or adaptive immunity may be the basis for future strategies to prevent chronic kidney disease (CKD) in this setting.

O-GlcNAcylation reduces proximal tubule protein reabsorption and promotes proteinuria in spontaneously hypertensive rats

Hypertensive individuals are at greater risk for developing chronic kidney disease (CKD). Reducing proteinuria has been suggested as a possible therapeutic approach to treat CKD. However, the mechanisms underlying the development of proteinuria in hypertensive conditions are incompletely understood. Cardiac and vascular dysfunction is associated with changes in the O-GlcNAcylation pathway in hypertensive models. We hypothesized that O-GlcNAcylation is also involved in renal damage, especially development of proteinuria, associated with hypertension. Using the spontaneously hypertensive rat (SHR) model, we observed higher renal cortex O-GlcNAcylation, glutamine-fructose aminotransferase (GFAT), and O-GlcNAc transferase (OGT) protein expression, which positively correlated with proteinuria. Interestingly, this was observed in hypertensive, but not pre-hypertensive, rats. Pharmacological inhibition of GFAT decreased renal cortex O-GlcNAcylation, proteinuria, and albuminuria in SHR. Using a proximal tubule cell line, we observed that increased O-GlcNAcylation reduced megalin surface expression and albumin endocytosis in vitro, and the effects were correlated in vivo Moreover, megalin is O-GlcNAcylated both in vitro and in vivo In conclusion, our results demonstrate a new mechanism involved in hypertension-associated proteinuria.

Increased megalin expression in early type 2 diabetes: role of insulin-signaling pathways

The megalin/cubilin complex is responsible for the majority of serum protein reclamation in the proximal tubules. The current study examined if decreases in their renal expression, along with the albumin recycling protein neonatal Fc receptor (FcRn) could account for proteinuria/albuminuria in the Zucker diabetic fatty rat model of type 2 diabetes. Immunoblots of renal cortex samples obtained at worsening disease stages demonstrated no loss in megalin, cubilin, or FcRn, even when proteinuria was measured. Additionally, early diabetic rats exhibited significantly increased renal megalin expression when compared with controls (adjusted P < 0.01). Based on these results, the ability of insulin to increase megalin was examined in a clonal subpopulation of the opossum kidney proximal tubule cell line. Insulin treatments (24 h, 100 nM) under high glucose conditions significantly increased megalin protein ( P < 0.0001), mRNA ( P < 0.0001), and albumin endocytosis. The effect on megalin expression was prevented with inhibitors against key effectors of insulin intracellular signaling, phosphatidylinositide 3-kinase and Akt. Studies using rapamycin to inhibit the mechanistic target of rapamycin complex 1 (mTORC1) resulted in a loss of insulin-induced megalin expression. However, subsequent evaluation demonstrated these effects were independent of initial mTORC1 suppression. The presented results provide insight into the expression of megalin, cubilin, and FcRn in type 2 diabetes, which may be impacted by elevated insulin and glucose. Furthermore, proximal tubule endocytic activity in early diabetics may be enhanced, a process that could have a significant role in proteinuria-induced renal damage.

Nutrients, Nutraceuticals, and Xenobiotics Affecting Renal Health

Chronic kidney disease (CKD) affects 8–16% of the population worldwide. In developed countries, the most important risk factors for CKD are diabetes, hypertension, and obesity, calling into question the importance of educating and acting on lifestyles and nutrition. A balanced diet and supplementation can indeed support the maintenance of a general health status, including preservation of renal function, and can help to manage and curb the main risk factors for renal damage. While the concept of protein and salt restriction in nephrology is historically acknowledged, the role of some nutrients in renal health and the importance of nutrition as a preventative measure for renal care are less known. In this narrative review, we provide an overview of the demonstrated and potential actions of some selected nutrients, nutraceuticals, and xenobiotics on renal health and function. The direct and indirect effects of fiber, protein, fatty acids, curcumin, steviol glycosides, green tea, coffee, nitrates, nitrites, and alcohol on kidney health are reviewed here. In view of functional and personalized nutrition, understanding the renal and systemic effects of dietary components is essential since many chronic conditions, including CKD, are related to systemic dysfunctions such as chronic low-grade inflammation.

Lysyl oxidase-like 2 inhibition ameliorates glomerulosclerosis and albuminuria in diabetic nephropathy

Diabetic nephropathy is characterised by the excessive amount of extracellular matrix in glomeruli and tubulointerstitial space. Lysyl oxidase-like 2 (LOXL2) is elevated in renal fibrosis and known to play key roles in ECM stabilisation by facilitating collagen cross-links, epithelial to mesenchymal transition and myofibroblast activation. Thus, targeting LOXL2 may prove to be a useful strategy to prevent diabetic nephropathy. We explored the renoprotective effect of a selective small molecule LOXL2 inhibitor (PXS-S2B) in a streptozotocin-induced diabetes model. Diabetic mice were treated with PXS-S2B for 24 weeks and outcomes compared with untreated diabetic mice and with telmisartan treated animals as comparator of current standard of care. Diabetic mice had albuminuria, higher glomerulosclerosis scores, upregulation of fibrosis markers and increased renal cortical LOXL2 expression. Treatment with PXS-S2B reduced albuminuria and ameliorated glomerulosclerosis. This was associated with reduced expression of glomerular fibronectin and tubulointerstitial collagen I. The renoprotective effects of both PXS-S2B and telmisartan were more marked in the glomerular compartment than in the tubulointerstitial space. The study reveals that LOXL2 inhibition was beneficial in preserving glomerular structure and function. Thus, LOXL2 may be a potential therapeutic target in diabetic nephropathy.

High glucose reduces megalin-mediated albumin endocytosis in renal proximal tubule cells through protein kinase B O-GlcNAcylation

The role of albumin reabsorption in proximal tubule (PT) cells has emerged as an important factor in the genesis of albuminuria observed in the early stages of diabetes. Evidence has shown that a decrease in megalin expression could be the key mechanism in this process. In the present work, we investigated the molecular mechanism underlying the modulation of albumin endocytosis in LLC-PK1 cells, a model of PT cells. High glucose concentrations (HG) inhibited megalin expression and albumin endocytosis after 48 h of incubation. This inhibitory effect involves the entrance of glucose into PT cells through SGLT located at the luminal membrane. Once inside PT cells, glucose is diverted to the hexosamine biosynthetic pathway (HBP) increasing O-GlcNAcylation of several intracellular proteins, including PKB. This process promotes the inhibition of PKB activity measured by its phosphorylation at Thr-308 and Ser-473 and phosphorylation of specific substrates, glycogen synthase kinase 3β (GSK3β) and tuberous sclerosis complex 2. The decrease in PKB activity led to a decrease in megalin expression and, consequently, reducing albumin endocytosis in LLC-PK1 cells. HG did not change mammalian target of rapamycin (mTOR) C2 activity, responsible for phosphorylated PKB at Ser-473. In addition, HG activated the mTORC1/S6K pathway, but this effect was not correlated to the decrease in megalin expression or albumin endocytosis. Taken together, our data help to clarify the current understanding underlying the genesis of tubular albuminuria induced by hyperglycemia in the early stage of diabetes pathogenesis.

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.

Distribution of exogenous complement factor H in mice in vivo

Factor H is an important regulator of complement activation in plasma and on cell surfaces in both humans and mice. If FH function is compromised, inappropriate complement activation on self-surfaces can have disastrous effects as seen in the kidney diseases atypical haemolytic uremic syndrome (aHUS) and C3 glomerulopathy. As FH constructs have been proposed to be used in treatment for these diseases, we studied the distribution of exogenous FH fragments in mice. Full-length mFH, mFH1-5 and mFH18-20 fragments were radiolabelled, and their distribution was examined in WT, FH^-/- and FH^-/- C3^-/- mice in vivo. Whole body scintigraphy revealed accumulation of radioactivity in the abdominal part of the mice, but also to the thyroid gland and urinary bladder. At organ level in WT mice, some full-length FH accumulated in internal organs, but most of it remained in the circulation. Both of the mFH fragments accumulated in the kidneys and were excreted in urine. For mFH1-5, urinary secretion is the likely cause for the accumulation. Concentration of mFH18-20 to kidneys was slower, and at tissue level, mFH18-20 was localized at the proximal tubuli in WT and FH^-/- C3^-/- mice. No C3-independent binding to glomeruli was detected. In conclusion, these results show that glomerular glycosaminoglycans and sialic acids alone do not collect FH in kidneys. Deposition of C3 fragments is also needed, which implies that in aHUS, the problem is in simultaneous recognition of C3 fragments and glycosaminoglycans or sialic acids by FH, not just the inability of FH to recognize glomerular endothelium as such.

Effect of Pinocembrin Isolated from Mexican Brown Propolis on Diabetic Nephropathy

Propolis is a resinous beehive product that has been used worldwide in traditional medicine to prevent and treat colds, wounds, rheumatism, heart disease and diabetes. Diabetic nephropathy is the final stage of renal complications caused by diabetes and for its treatment there are few alternatives. The present study aimed to determine the chemical composition of three propolis samples collected in Chihuahua, Durango and Zacatecas and to evaluate the effect of pinocembrin in a model of diabetic nephropathy in vivo. Previous research demonstrated that propolis of Chihuahua possesses hypoglycemic and antioxidant activities. Two different schemes were assessed, preventive (before renal damage) and corrective (once renal damage is established). In the preventive scheme, pinocembrin treatment avoids death of the rats, improves lipid profile, glomerular filtration rate, urinary protein, avoid increases in urinary biomarkers, oxidative stress and glomerular basement membrane thickness. Whereas, in the corrective scheme, pinocembrin only improves lipid profile without showing improvement in any other parameters, even pinocembrin exacerbated the damage. In conclusion, pinocembrin ameliorates diabetic nephropathy when there is no kidney damage but when it is already present, pinocembrin accelerates kidney damage.

Urinary Iron Excretion is Associated with Urinary Full-Length Megalin and Renal Oxidative Stress in Chronic Kidney Disease

BACKGROUND/AIMS

Megalin mediates the uptake of glomerular-filtered iron in the proximal tubules. Urinary full length megalin (C-megalin) excretion has been found to be increased in association with megalin-mediated metabolic load to the endo-lysosomal system in proximal tubular epithelial cells (PTECs) of residual nephrons. In the present study, we investigated the association between urinary iron and C-megalin in chronic kidney disease (CKD) patients, and the possible harmful effect of iron in renal tubules.

METHODS

Urinary levels of iron and C-megalin were measured in 63 CKD patients using automatic absorption spectrometry and a recently-established sandwich ELISA, respectively.

RESULTS

Although both urinary C-megalin and urinary total protein levels were correlated with urinary iron (C-megalin: ρ = 0.574, p <0.001; total protein: ρ = 0.500, p <0.001, respectively), urinary C-megalin alone emerged as an independent factor positively associated with urinary iron (β = 0.520, p <0.001) (R2 = 0.75, p <0.001). Furthermore, urinary iron was significantly and positively associated with urinary 8-hydroxydeoxyguanosine, an oxidative stress marker, while no association with other markers of renal tubular injury, i.e., β2-microglobulin and N-acetyl-β-D-glucosaminidase, was noted.

CONCLUSIONS

Our findings suggest that renal iron handling may be associated with megalin-mediated endo-lysosomal metabolic load in PTECs of residual nephrons and oxidative stress in renal tubules.

Glomerular hyperpermeability after acute unilateral ureteral obstruction: effects of Tempol, NOS, RhoA, and Rac-1 inhibition

It is well known that proteinuria following urinary tract obstruction is mainly of a tubular nature. However, it is unknown whether there are also changes in glomerular permeability. In this study, we compared glomerular sieving coefficients (θ) of polydisperse fluorescein isothiocyanate (FITC)-Ficoll 70/400 following a 120- or 180-min unilateral ureteral obstruction (UUO) in anesthetized Sprague-Dawley rats. Samples were collected from the obstructed kidney at 5, 15, and 30 min postrelease and analyzed by means of high-pressure size-exclusion chromatography. After 120-min UUO, mean θ for Ficoll_70Å was increased ( P < 0.01) from 2.2 ± 0.5 × 10^-5 (baseline) to 10.6 ± 10 × 10^-5 15 min postrelease (highest value). After 180-min UUO, mean θ for Ficoll_70Å was further increased ( P < 0.001) from 1.4 ± 0.5 × 10^-5 (baseline) to 40 ± 10 × 10^-5 at 5 min postrelease (highest value). Administration of a reactive oxygen species (ROS) scavenger (Tempol; 1 mg·kg^-1·min^-1) partly abrogated the permeability effects following 120-min UUO but not after 180 min. Moreover, administration of the RhoA kinase inhibitor Y-27632, the nitric oxide synthase inhibitor N^G-nitro-l-arginine methyl ester, or Rac-1 inhibition did not ameliorate glomerular hyperpermeability following 180-min UUO. We show, for the first time, that acute UUO results in marked elevations in glomerular permeability. In addition, our data suggest a time-dependent pathophysiology of UUO-induced hyperpermeability, where reactive oxygen species generation may play an important role in the early stages.

Antihypertensive therapy in nondiabetic chronic kidney disease: a review and update

Hypertension is an important contributor to progression of nondiabetic chronic kidney disease (CKD). Compelling observational evidence indicates that the divergence of blood pressure (BP) away from an ideal range in either direction is associated with a progressive rise in the risk of mortality and cardiovascular and renal disease progression. To date, various clinical trials and meta-analyses examining strict versus less intensive BP control in nondiabetic CKD have not conclusively demonstrated a renal advantage of one BP-lowering approach over another, except in certain subgroups such as proteinuric patients where evidence is circumstantial. As recent data have come to light suggesting that intensive BP control yields superior survival and cardiovascular outcomes in patients at high risk for cardiovascular disease, interest in the prospect of whether such benefit extends to individuals with CKD has surged. This review is a comprehensive analysis of antihypertensive literature in nondiabetic renal disease, with a particular emphasis on BP target.

Autophagy in diabetic kidney disease: regulation, pathological role and therapeutic potential

Diabetic kidney disease, a leading cause of end-stage renal disease, has become a serious public health problem worldwide and lacks effective therapies. Autophagy is a highly conserved lysosomal degradation pathway that removes protein aggregates and damaged organelles to maintain cellular homeostasis. As important stress-responsive machinery, autophagy is involved in the pathogenesis of various diseases. Emerging evidence has suggested that dysregulated autophagy may contribute to both glomerular and tubulointerstitial pathologies in kidneys under diabetic conditions. This review summarizes the recent findings regarding the role of autophagy in the pathogenesis of diabetic kidney disease and highlights the regulation of autophagy by the nutrient-sensing pathways and intracellular stress signaling in this disease. The advances in our understanding of autophagy in diabetic kidney disease will facilitate the discovery of a new therapeutic target for the prevention and treatment of this life-threatening diabetes complication.

The effects of short sleep duration on proteinuria and chronic kidney disease: a systematic review and meta-analysis

Background

The risks of proteinuria and chronic kidney disease (CKD) in adults who regularly have short sleep duration (short sleepers) are controversial. The aim of this meta-analysis was to assess the effects of short sleep duration on proteinuria and CKD.

Methods

A literature search was conducted using MEDLINE, EMBASE and the Cochrane Database of Systematic Reviews from the inception of the databases through November 2015. Studies that reported relative risks, odd ratios or hazard ratios comparing the risks of proteinuria and CKD in short sleepers were included. Pooled risk ratios (RR) and 95% confidence intervals (CI) were computed utilizing a random-effect, generic inverse variance method.

Results

Six observational studies with 252 075 individuals and three observational studies with 37 197 individuals were included in the analyses to assess the risks of CKD and proteinuria in short sleepers, respectively. The pooled RR of CKD in short sleepers was 1.51 (95% CI, 0.99-2.55). When meta-analysis was restricted only to studies with adjusted analysis for confounders assessing the risk of CKD in short sleepers, the pooled RR of CKD was 1.54 (95% CI, 0.80-2.95). The pooled RR of proteinuria in short sleepers was 1.47 (95% CI, 1.26-1.72).

Conclusions

Despite the lack of significant association between short sleep duration and CKD, our meta-analysis suggests a potential association between short sleep duration and proteinuria, a surrogate marker for kidney disease progression. Future study is required to investigate if reversal of short sleep helps reduce proteinuria.

Gremlin Regulates Podocyte Apoptosis via Transforming Growth Factor-β (TGF-β) Pathway in Diabetic Nephropathy

BACKGROUND Gremlin has been reported to be up-regulated in glomerular mesangial cells in diabetic nephropathy (DN). However, the regulation of gremlin in podocytes is still rarely reported. This study aimed to investigate the underlying mechanisms by which gremlin mediates the pathogenesis of DN via transforming growth factor-β (TGF-β) signaling pathways. MATERIAL AND METHODS Lentiviral and RNAi transfection were performed to increase and decrease gremlin expression in high-glucose conditions. Expression at the mRNA and protein level was detected by RT-qPCR and Western blotting. RESULTS The expression of gremlin was significantly higher in high-glucose (HG, 30mM) than normal-glucose (NG, 5.5 mM) conditions. The gremlin overexpression significantly suppressed the expression of nephrin and synaptopodin. The phosphorylation of canonical TGF-b signaling pathway components, including Smad2/3 and MKK, was increased in the gremlin-overexpressing group. In addition, the expression levels of Bax and cleaved caspase-3 were also higher in the gremlin-overexpressing group. TGF-β pathway inhibitor (SB505124) significantly inhibited TGF-β pathway activity and enhanced the expression of nephrin and synaptopodin. CONCLUSIONS These results indicate that gremlin can aggravate podocyte lesions through the TGF-β signaling pathway, providing a novel therapeutic target for DN.

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

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