Albumin stimulates interleukin-8 expression in proximal tubular epithelial cells in vitro and in vivo

Evaluating nephrotoxicity reduction in a novel polymyxin B formulation: insights from a 3D kidney-on-a-chip model

This study aimed to assess the nephrotoxicity associated with VRP-034 (novel formulation of polymyxin B [PMB]) compared to marketed PMB in a three-dimensional (3D) kidney-on-a-chip model. To model the human kidney proximal tubule for analysis, tubular structures were established using 23 triple-channel chips seeded with RPTEC/hTERT1 cells. These cells were exposed to VRP-034 or PMB at seven concentrations (1-200 µM) over 12, 24, and 48 h. A suite of novel kidney injury biomarkers, cell health, and inflammatory markers were quantitatively assessed in the effluent. Additionally, caspase and cytochrome C levels were measured, and cell viability was evaluated using calcein AM and ethidium homodimer-1 (EthD-1). Exposure to marketed PMB resulted in significantly elevated levels (P < 0.05) of four key biomarkers (KIM-1, cystatin C, clusterin, and OPN) compared to VRP-034, particularly at clinically relevant concentrations of ≥10 µM. At 25 µM, all biomarkers demonstrated a significant increase (P < 0.05) with marketed PMB exposure compared to VRP-034. Inflammatory markers (interleukin-6 and interleukin-8) increased significantly (P < 0.05) with marketed PMB at concentrations of ≥5 µM, relative to VRP-034. VRP-034 displayed superior cell health outcomes, exhibiting lower lactate dehydrogenase release, while ATP levels remained comparable. Morphological analysis revealed that marketed PMB induced more severe damage, disrupting tubular integrity. Both treatments activated cytochrome C, caspase-3, caspase-8, caspase-9, and caspase-12 in a concentration-dependent manner; however, caspase activation was significantly reduced (P < 0.05) with VRP-034. This study demonstrates that VRP-034 significantly reduces nephrotoxicity compared to marketed PMB within a 3D microphysiological system, suggesting its potential to enable the use of full therapeutic doses of PMB with an improved safety profile, addressing the need for less nephrotoxic polymyxin antibiotics.

Tubulointerstitial nephritis in children and adolescents

The tubulointerstitial compartment comprises most of the kidney parenchyma. Inflammation in this compartment (tubulointerstitial nephritis-TIN) can be acute and resolves if the offending factor is withdrawn or may enter a chronic process leading to irreversible kidney damage. Etiologic factors differ, including different exposures, infections, and autoimmune and genetic tendency, and the initial damage can be acute, recurrent, or permanent, determining whether the acute inflammatory process will lead to complete healing or to a chronic course of inflammation leading to fibrosis. Clinical and laboratory findings of TIN are often nonspecific, which may lead to delayed diagnosis and a poorer clinical outcome. We provide a general review of TIN, with special mention of the molecular pathophysiological mechanisms of the associated kidney damage.

Analysis of risk factors related to chronic non-healing wound infection and the construction of a clinical prediction model

This study is aimed to analyse the risk factors associated with chronic non-healing wound infections, establish a clinical prediction model, and validate its performance. Clinical data were retrospectively collected from 260 patients with chronic non-healing wounds treated in the plastic surgery ward of Shanxi Provincial People's Hospital between January 2022 and December 2023 who met the inclusion criteria. Risk factors were analysed, and a clinical prediction model was constructed using both single and multifactor logistic regression analyses to determine the factors associated with chronic non-healing wound infections. The model's discrimination and calibration were assessed via the concordance index (C-index), receiver operating characteristic (ROC) curve and calibration curve. Multivariate logistic regression analysis identified several independent risk factors for chronic non-healing wound infection: long-term smoking (odds ratio [OR]: 4.122, 95% CI: 3.412-5.312, p < 0.05), history of diabetes (OR: 3.213, 95% CI: 2.867-4.521, p < 0.05), elevated C-reactive protein (OR: 2.981, 95% CI: 2.312-3.579, p < 0.05), elevated procalcitonin (OR: 2.253, 95% CI: 1.893-3.412, p < 0.05) and reduced albumin (OR: 1.892, 95% CI: 1.322-3.112, p < 0.05). The clinical prediction model's C-index was 0.762, with the corrected C-index from internal validation using the bootstrap method being 0.747. The ROC curve indicated an area under the curve (AUC) of 0.762 (95% CI: 0.702-0.822). Both the AUC and C-indexes ranged between 0.7 and 0.9, suggesting moderate-to-good predictive accuracy. The calibration chart demonstrated a good fit between the model's calibration curve and the ideal curve. Long-term smoking, diabetes, elevated C-reactive protein, elevated procalcitonin and reduced albumin are confirmed as independent risk factors for bacterial infection in patients with chronic non-healing wounds. The clinical prediction model based on these factors shows robust performance and substantial predictive value.

Receptor-mediated endocytosis in kidney cells during physiological and pathological conditions

Mammalian cell membranes are very dynamic where they respond to several environmental stimuli by rearranging the membrane composition by basic biological processes, including endocytosis. In this context, receptor-mediated endocytosis, either clathrin-dependent or caveolae-dependent, is involved in different physiological and pathological conditions. In the last years, an important amount of evidence has been reported that kidney function involves the modulation of different types of endocytosis, including renal protein handling. In addition, the dysfunction of the endocytic machinery is involved with the development of proteinuria as well as glomerular and tubular injuries observed in kidney diseases associated with hypertension, diabetes, and others. In this present review, we will discuss the mechanisms underlying the receptor-mediated endocytosis in different glomerular cells and proximal tubule epithelial cells as well as their modulation by different factors during physiological and pathological conditions. These findings could help to expand the current understanding regarding renal protein handling as well as identify possible new therapeutic targets to halt the progression of kidney disease.

Combination therapy with DHA and BMSCs suppressed podocyte injury and attenuated renal fibrosis by modulating the TGF-β1/Smad pathway in MN mice

Artemisinin has immunomodulatory, anti-inflammatory, and antifibrotic effects. Some studies have demonstrated that artemisinins have a protective effect on the kidney. DHA is a derivative of artemisinin and has effects similar to those of artemisinin. Human bone marrow-derived mesenchymal stem cells (BMSCs) accelerate renal repair following acute injury. In the study, we investigated the effects of combination therapy with DHA and BMSCs on membranous nephropathy (MN) mice. The 24-h urinary protein, serum total cholesterol (TC) and triglyceride (TG) levels, and renal histopathology, were measured to evaluate kidney damage. Anti-PLA2R, IgG, and complement 3 (C3) were detected by ELISA. The expression levels of the podocyte injury-related proteins were analyzed by immunohistochemistry. The protein expression levels of α-SMA, ED-1, TGF-β1, p-Smad2, and p-Smad3 were detected by western blot to analyze renal fibrosis and its regulatory mechanism. Results showed that combination therapy with DHA and BMSCs significantly ameliorated kidney damage in MN model mice by decreasing the levels of 24 h urinary protein, TC and TG. This combination therapy also improved renal histology and reduced the expression of IgG and C3 in the glomerulus. In addition, this combination therapy decreased the expression of podocin and nephrin and relieved renal fibrosis by downregulating α-SMA and ED-1. Furthermore, this combination therapy suppressed TGF-β1 expression and Smad2/3 phosphorylation. This result (i.e., this combination therapy inhibited the TGF-β1/Smad pathway) was also supported in vitro. Taken together, combination therapy with DHA and BMSCs ameliorated podocyte injury and renal fibrosis in MN mice by downregulating the TGFβ1/Smad pathway.

Advances in understanding and treating diabetic kidney disease: focus on tubulointerstitial inflammation mechanisms

Diabetic kidney disease (DKD) is a serious complication of diabetes that can lead to end-stage kidney disease. Despite its significant impact, most research has concentrated on the glomerulus, with little attention paid to the tubulointerstitial region, which accounts for the majority of the kidney volume. DKD's tubulointerstitial lesions are characterized by inflammation, fibrosis, and loss of kidney function, and recent studies indicate that these lesions may occur earlier than glomerular lesions. Evidence has shown that inflammatory mechanisms in the tubulointerstitium play a critical role in the development and progression of these lesions. Apart from the renin-angiotensin-aldosterone blockade, Sodium-Glucose Linked Transporter-2(SGLT-2) inhibitors and new types of mineralocorticoid receptor antagonists have emerged as effective ways to treat DKD. Moreover, researchers have proposed potential targeted therapies, such as inhibiting pro-inflammatory cytokines and modulating T cells and macrophages, among others. These therapies have demonstrated promising results in preclinical studies and clinical trials, suggesting their potential to treat DKD-induced tubulointerstitial lesions effectively. Understanding the immune-inflammatory mechanisms underlying DKD-induced tubulointerstitial lesions and developing targeted therapies could significantly improve the treatment and management of DKD. This review summarizes the latest advances in this field, highlighting the importance of focusing on tubulointerstitial inflammation mechanisms to improve DKD outcomes.

Acute kidney injury in diabetes mellitus: Epidemiology, diagnostic, and therapeutic concepts

Acute kidney injury (AKI) and diabetes mellitus (DM) are public health problems that cause a high socioeconomic burden worldwide. In recent years, the landscape of AKI etiology has shifted: Emerging evidence has demonstrated that DM is an independent risk factor for the onset of AKI, while an alternative perspective considers AKI as a bona fide complication of DM. Therefore, it is necessary to systematically characterize the features of AKI in DM. In this review, we summarized the epidemiology of AKI in DM. While focusing on circulation- and tissue-specific microenvironment changes after DM, we described the active cellular and molecular mechanisms of increased kidney susceptibility to AKI under DM stress. We also reviewed the current diagnostic and therapeutic strategies for AKI in DM recommended in the clinic. Updated recognition of the epidemiology, pathophysiology, diagnosis, and medications of AKI in DM is believed to reveal a path to mitigate the frequency of AKI and DM comorbidity that will ultimately improve the quality of life in DM patients.

Identification of a novel immune landscape signature as effective diagnostic markers related to immune cell infiltration in diabetic nephropathy

Background

The study aimed to identify core biomarkers related to diagnosis and immune microenvironment regulation and explore the immune molecular mechanism of diabetic nephropathy (DN) through bioinformatics analysis.

Methods

GSE30529, GSE99325, and GSE104954 were merged with removing batch effects, and different expression genes (DEGs) were screened at a criterion |log2FC| >0.5 and adjusted P <0.05. KEGG, GO, and GSEA analyses were performed. Hub genes were screened by conducting PPI networks and calculating node genes using five algorithms with CytoHubba, followed by LASSO and ROC analysis to accurately identify diagnostic biomarkers. In addition, two different GEO datasets, GSE175759 and GSE47184, and an experiment cohort with 30 controls and 40 DN patients detected by IHC, were used to validate the biomarkers. Moreover, ssGSEA was performed to analyze the immune microenvironment in DN. Wilcoxon test and LASSO regression were used to determine the core immune signatures. The correlation between biomarkers and crucial immune signatures was calculated by Spearman analysis. Finally, cMap was used to explore potential drugs treating renal tubule injury in DN patients.

Results

A total of 509 DEGs, including 338 upregulated and 171 downregulated genes, were screened out. "chemokine signaling pathway" and "cell adhesion molecules" were enriched in both GSEA and KEGG analysis. CCR2, CX3CR1, and SELP, especially for the combination model of the three genes, were identified as core biomarkers with high diagnostic capabilities with striking AUC, sensitivity, and specificity in both merged and validated datasets and IHC validation. Immune infiltration analysis showed a notable infiltration advantage for APC co-stimulation, CD8+ T cells, checkpoint, cytolytic activity, macrophages, MHC class I, and parainflammation in the DN group. In addition, the correlation analysis showed that CCR2, CX3CR1, and SELP were strongly and positively correlated with checkpoint, cytolytic activity, macrophages, MHC class I, and parainflammation in the DN group. Finally, dilazep was screened out as an underlying compound for DN analyzed by CMap.

Conclusions

CCR2, CX3CR1, and SELP are underlying diagnostic biomarkers for DN, especially in their combination. APC co-stimulation, CD8+ T cells, checkpoint, cytolytic activity, macrophages, MHC class I, and parainflammation may participate in the occurrence and development of DN. At last, dilazep may be a promising drug for treating DN.

Is the proximal tubule the focus of tubulointerstitial fibrosis?

Tubulointerstitial fibrosis (TIF), a common end result of almost all progressive chronic kidney diseases (CKD), is also the best predictor of kidney survival. Almost all cells in the kidney are involved in the progression of TIF. Myofibroblasts, the primary producers of extracellular matrix, have previously received a great deal of attention; however, a large body of emerging evidence reveals that proximal tubule (PT) plays a central role in TIF progression. In response to injury, renal tubular epithelial cells (TECs) transform into inflammatory and fibroblastic cells, producing various bioactive molecules that drive interstitial inflammation and fibrosis. Here we reviewed the increasing evidence for the key role of the PT in promoting TIF in tubulointerstitial and glomerular injury and discussed the therapeutic targets and carrier systems involving the PT that holds particular promise for treating patients with fibrotic nephropathy.

Protective Effects of Xanthohumol against Diabetic Nephropathy in a Mouse Model

INTRODUCTION

Diabetic nephropathy (DN) is a long-term loss of renal function occurring in the diabetic patients, leading to 5 million deaths in 2015, and this number is dramatically growing annually. Due to unsatisfied outcome of current treatment, there is urgent need to develop more effective therapeutic drugs for DN.

METHODS

Approximately 150 kinds of natural small molecule drugs that have been used on the market or in the clinical trials in the presence of high glucose were tested individually on the same batch of human renal glomerular endothelial cells (GECs) and human kidney 2 (HK-2) cells with triplicated wells by using a robotic pipetting workstation to screen for the potential drug candidate. Cell viability and oxidative stress were examined in the GECs and HK-2 cells. DN mouse model was established and treated with 25 mg/kg xanthohumol.

RESULTS

By measuring cell viability, xanthohumol was selected as our predicted drug candidate for DN because it could mostly protect renal cells from high glucose with about 90% survived GECs and HK-2 cells, about 2.12- and 2.37-fold increase compared to glucose group which was with 42.78% and 37.69% survived GECs and HK-2 cells, respectively. Then, xanthohumol inhibited high glucose-induced oxidative stress through nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway in vitro. Moreover, xanthohumol (25 mg/kg) significantly decreased the levels of serum creatinine, blood urea nitrogen, urea protein, and kidney weight/body weight ratio in DN mice. In addition, the increase of reactive oxygen species production and the decrease of superoxide dismutase and catalase activities in DN mice were partially reversed by xanthohumol. mRNA levels of Nrf2, Hmox1, and Nqol genes were all decreased by xanthohumol DN mice.

CONCLUSION

Xanthohumol could ameliorate DN-related impairments via Nrf2 signaling pathway, which might serve as a promising drug candidate for treatment of DN.

Quantifying Podocyte Number in a Small Sample Size of Glomeruli with CUBIC to Evaluate Podocyte Depletion of db/db Mice

The loss of podocyte is crucial for diagnosis and prognosis of diabetic kidney disease, whereas commonly two-dimensional methods for quantifying podocyte number existed with issues of low fidelity and accuracy. In this study, clear, unobstructed brain imaging cocktails and computational analysis (CUBIC), one of three-dimensional optical clearing approaches, was used which combines tissue clearing, immunolabeling, and a light-sheet microscope to image and evaluate podocytes in C57BL/6 (C57) and db/db mice. We discovered that 77 podocytes per glomerulus were in C57 mice. On the subject of db/db mice, there were 74 podocytes by the age of 8 w, 72 podocytes by the age of 12 w, and 66 podocytes by the age of 16 w, compared with 76 podocytes in the control group, suggesting that there was a significant decrease in podocyte number in db/db mice with the age of 16 w, showing a trend which positively correlated to the deterioration of kidney function. Sample size estimation using the PASS software revealed that taking 5%, 7.5%, and 10% of the mean podocyte number per glomerulus as the statistical allowable error and 95% as total confidence interval, 33, 15, and 9 glomeruli were independently needed to be sampled in C57 mice to represent the overall glomeruli to calculate podocyte number. Furthermore, in the control group of db/db mice, 36, 18, and 11 glomeruli were needed, compared with 46, 24, and 14 glomeruli in db/db mice by the age of 8 w, 43, 21, and 12 glomeruli by the age of 12 w, and 52, 27, and 16 by the age of 16 w. These findings indicated that precise quantification of podocyte number could judge the progression of diabetic kidney disease. In addition, a small number of glomeruli could be actually representative of the whole sample size, which indicated apparent practicability of CUBIC for clinical use.

Antioxidation and Nrf2-mediated heme oxygenase-1 activation contribute to renal protective effects of hydralazine in diabetic nephropathy

Reactive oxygen species (ROS) and oxidative stress are associated with the progression of diabetic nephropathy (DN). Hydralazine is an antihypertensive agent and may act as a xanthine oxidase (XO) inhibitor to reduce uric acid levels in a mouse renal injury model. This study aimed to investigate the potential mechanisms of hydralazine in experimental DN. Streptozotocin-induced diabetic mice were fed a high-fat diet to generate DN. Human renal proximal tubular epithelial cells were used in vitro. Nitrendipine and allopurinol which can reduce blood pressure or XO activity levels, were used as two positive controls. Hydralazine downregulated NF-κB/p38 signaling pathways and reduced TNF-α/IL-6 expressions in high glucose-stimulated renal proximal tubular epithelial cells. Hydralazine reduced in vitro ROS production via XO inhibition and nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated heme oxygenase (HO)-1 activation. Furthermore, hydralazine reduced high glucose-induced apoptosis by downregulating PARP/caspase-3 signaling. Hydralazine and allopurinol but not nitrendipine reduced serum uric acid levels and systemic inflammation. Hydralazine and allopurinol treatment improved renal function with decreased urinary albumin-to-creatinine ratios, glomerular hypertrophy, glomerulosclerosis, and fibrosis in the kidney of DN mice. While both hydralazine and allopurinol downregulated XO and NADPH oxidase expression, only hydralazine upregulated Nrf2/HO-1 renal expression, suggesting the additional effects of hydralazine independent of XO/ NADPH oxidase inhibition. In conclusion, hydralazine protected renal proximal tubular epithelial cells against the insults of high glucose and prevented renal damage via XO/NADPH oxidase inhibition and Nrf-2/HO-1 activation, suggesting the comprehensive antioxidation and anti-inflammation mechanisms for the management of DN.

Effects of preoperative high-oral protein loading on short- and long-term renal outcomes following cardiac surgery: a cohort study

BACKGROUND

Post-cardiac surgery acute kidney injury (AKI) is associated with increased mortality. A high-protein meal enhances the renal blood flow and glomerular filtration rate (GFR) and might protect the kidneys from acute ischemic insults. Hence, we assessed the effect of a preoperative high-oral protein load on post-cardiac surgery renal function and used experimental models to elucidate mechanisms by which protein might stimulate kidney-protective effects.

METHODS

The prospective "Preoperative Renal Functional Reserve Predicts Risk of AKI after Cardiac Operation" study follow-up was extended to postoperative 12 months for 109 patients. A 1:2 ratio propensity score matching method was used to identify a control group (n = 214) to comparatively evaluate the effects of a preoperative protein load and standard care. The primary endpoints were AKI development and postoperative estimated GFR (eGFR) loss at 3 and 12 months. We also assessed the secretion of tissue inhibitor of metalloproteases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), biomarkers implicated in mediating kidney-protective mechanisms in human kidney tubular cells that we exposed to varying protein concentrations.

RESULTS

The AKI rate did not differ between the protein loading and control groups (13.6 vs. 12.3%; p = 0.5). However, the mean eGFR loss was lower in the former after 3 months (0.1 [95% CI - 1.4, - 1.7] vs. - 3.3 [95% CI - 4.4, - 2.2] ml/min/1.73 m²) and 12 months (- 2.7 [95% CI - 4.2, - 1.2] vs - 10.2 [95% CI - 11.3, - 9.1] ml/min/1.73 m²; p < 0.001 for both). On stratification based on AKI development, the eGFR loss after 12 months was also found to be lower in the former (- 8.0 [95% CI - 14.1, - 1.9] vs. - 18.6 [95% CI - 23.3, - 14.0] ml/min/1.73 m²; p = 0.008). A dose-response analysis of the protein treatment of the primary human proximal and distal tubule epithelial cells in culture showed significantly increased IGFBP7 and TIMP-2 expression.

CONCLUSIONS

A preoperative high-oral protein load did not reduce AKI development but was associated with greater renal function preservation in patients with and without AKI at 12 months post-cardiac surgery. The potential mechanisms of action by which protein loading may induce a kidney-protective response might include cell cycle inhibition of renal tubular epithelial cells. Clinical trial registration ClinicalTrials.gov: NCT03102541 (retrospectively registered on April 5, 2017) and ClinicalTrials.gov: NCT03092947 (retrospectively registered on March 28, 2017).

Pre-treatment serum albumin and mutational burden as biomarkers of response to immune checkpoint blockade

The effects of cytokine and protein stabilizing carriers, such as serum albumin, on tumor response to immune checkpoint blockade (ICB) is not well understood. By examining 1714 patients across 16 cancer types, we found that high pretreatment serum albumin level predicts favorable tumor radiographic response following ICB treatment in a dose-dependent fashion. Serum albumin is a candidate biomarker that can be combined with tumor mutational burden (TMB) for additional predictive capacity, and the tumor response rate to ICB was ~49% in the albumin-high/TMB-high group.

Which Is a Better Predictor of GFR Decline: 24-h Urine Protein or 24-h Protein-Creatinine Ratio? An Exploration of the MDRD Study Data

Background

Proteinuria is a known risk factor for progression of chronic kidney disease. Proteinuria magnitude can be estimated by measuring spot urine protein-to-creatinine ratio (least accurate), 24-h urine collection for protein (24 P), or 24-h protein-creatinine ratio (24 PCR). The MDRD study found that 24 P measured at baseline was the strongest single predictor of the rate of GFR decline during study follow-up. However, predictive powers of 24 P and 24 PCR have not been compared in the literature. The current study addresses this question using the MDRD cohort data.

Methods

The study is a retrospective analysis of prospectively collected data from the MDRD cohort using simple and multiple regression models. Slope of measured GFR (mGFR) over time was used as the response and models that included baseline 24 PCR or 24 P were compared for the entire sample and for subgroups formed by restricting the values of 24-h creatinine and 24 P.

Results

Log 24 P and Log 24 PCR correlated almost equally with mGFR slope. However, in simple linear regression models and multivariable linear regression models adjusting for age and sex, the model with 24 PCR had a higher R 2 than the corresponding one that had 24 P except for the subgroup 24 P < 1 g.

Conclusion

We observe that 24 PCR may be a better marker of proteinuria magnitude in predicting decline in kidney function compared to 24 P in particular for patients with 24 P ≥ 1. This finding needs validation in prospective clinical trials.

Cell stress response impairs de novo NAD+ biosynthesis in the kidney

The biosynthetic routes leading to de novo nicotinamide adenine dinucleotide (NAD⁺) production are involved in acute kidney injury (AKI), with a critical role for quinolinate phosphoribosyl transferase (QPRT), a bottleneck enzyme of de novo NAD⁺ biosynthesis. The molecular mechanisms determining reduced QPRT in AKI, and the role of impaired NAD⁺ biosynthesis in the progression to chronic kidney disease (CKD), are unknown. We demonstrate that a high urinary quinolinate-to-tryptophan ratio, an indirect indicator of impaired QPRT activity and reduced de novo NAD⁺ biosynthesis in the kidney, is a clinically applicable early marker of AKI after cardiac surgery and is predictive of progression to CKD in kidney transplant recipients. We also provide evidence that the endoplasmic reticulum (ER) stress response may impair de novo NAD⁺ biosynthesis by repressing QPRT transcription. In conclusion, NAD⁺ biosynthesis impairment is an early event in AKI embedded with the ER stress response, and persistent reduction of QPRT expression is associated with AKI to CKD progression. This finding may lead to identification of noninvasive metabolic biomarkers of kidney injury with prognostic and therapeutic implications.

Autophagy gene ATG7 regulates albumin transcytosis in renal tubule epithelial cells

Receptor-mediated albumin transport in proximal tubule epithelial cells (PTECs) is important to control proteinuria. Autophagy is an evolutionarily conserved degradation pathway, and its role in intracellular trafficking through interactions with the endocytic pathway has recently been highlighted. Here, we determined whether autophagy regulates albumin transcytosis in PTECs and suppresses albumin-induced cytotoxicity using human proximal tubule (HK-2) cells. The neonatal Fc receptor (FcRn), a receptor for albumin transcytosis, is partially colocalized with autophagosomes. Recycling of FcRn was attenuated, and FcRn accumulated in autophagy-related 7 (ATG7) knockdown HK-2 cells. Colocalization of FcRn with RAB7-positive late endosomes and RAB11-positive recycling endosomes was reduced in ATG7 knockdown cells, which decreased recycling of FcRn to the plasma membrane. In ATG7 or autophagy-related 5 (ATG5) knockdown cells and Atg5 or Atg7 knockout mouse embryonic fibroblasts, albumin transcytosis was significantly reduced and intracellular albumin accumulation was increased. Finally, the release of kidney injury molecule-1, a marker of tubule injury, from ATG7 or ATG5 knockdown cells was increased in response to excess albumin. In conclusion, suppression of autophagy in tubules impairs FcRn transport, thereby inhibiting albumin transcytosis. The resulting accumulation of albumin induces cytotoxicity in tubules.NEW & NOTEWORTHY Albumin transport in proximal tubule epithelial cells (PTECs) is important to control proteinuria. The neonatal Fc receptor (FcRn), a receptor for albumin transcytosis, is partially colocalized with autophagosomes. Recycling of FcRn to the plasma membrane was decreased in autophagy-related 7 (ATG7) knockdown cells. In addition, albumin transcytosis was decreased in ATG7 or autophagy-related 5 (ATG5) knockdown PTECs. Finally, release of kidney injury molecule-1 from ATG7 or ATG5 knockdown cells was increased in response to excess albumin.

miR-23a-3p regulates the inflammatory response and fibrosis in diabetic kidney disease by targeting early growth response 1

Diabetic kidney disease (DKD) has become the most common cause of chronic kidney disease. Proteinuria is generally considered one of the clinical indicators of renal damage, and it is also closely related to the progression of DKD. Accumulating evidence indicates that proteinuria induces an upregulation of the expression levels of inflammatory cytokines and fibrosis markers in renal tubular epithelial cells, but the mechanism remains unclear. Previously, we showed that early growth response 1 (Egr1) played a key role in renal tubular injury. However, the upstream mechanism of Egr1 in the development of DKD is poorly understood. In this study, we found that albumin stimulation significantly increased the expression levels of Egr1, interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and fibronectin (FN) in HK-2 cells but decreased miR-23a-3p levels. We then identified that miR-23a-3p targeted the 3′ untranslated region (UTR) of Egr1 and directly suppressed the expression of Egr1. Moreover, we found that overexpression and inhibition of miR-23a-3p in HK-2 cells attenuated and promoted the expression of IL-6, TNF-α, and FN, respectively. Additionally, Egr1 silencing reversed the inflammation and fibrosis caused by the miR-23a-3p inhibitor. Thus, we conclude that miR-23a-3p attenuates the development of DKD through Egr1, suggesting that targeting miR-23a-3p may be a novel therapeutic approach for DKD.

Albumin Might Attenuate Bacteria-Induced Damage on Kupffer Cells for Patients with Chronic Liver Disease

Chronic liver diseases (CLDs) are complex diseases that cause long-term inflammation and infection, which in turn accelerate their development. The usage of albumin in patients with CLDs has been debated for years. Human serum albumin (HSA) plays a key role in immunomodulation during the process of CLDs. The correlation between albumin and C-reactive protein (CRP) in CLD patients was analyzed by linear regression with the Pearson statistic. The damage of THP-1 and primary cells was evaluated by measuring the lactate dehydrogenase (LDH) in the supernatant. Immunofluorescence staining was performed to determine underlying pathways in Kupffer cells (KCs). Albumin negatively correlated with infection in patients with CLDs. In vitro experiments with THP-1 cells and KCs showed that albumin reduced LDH release after stimulation with bacterial products, while no differences in hepatic stellate cells (HSCs) and sinusoidal endothelial cells (SECs) were detected. Moreover, immunofluorescence staining revealed an increase of p-ERK and p-NF-kB p65 density after albumin treatment of KCs stimulated by bacterial products. In conclusion, albumin could assist CLD patients in alleviating inflammation caused by bacterial products and might be beneficial to patients with CLDs by securing KCs from bacteria-induced damage, providing a compelling rationale for albumin therapy in patients with CLDs.

Kidney involvement in multisystem inflammatory syndrome in children: a pediatric nephrologist's perspective

The initial report of the multisystem inflammatory syndrome in children (MIS-C) was from the UK in April 2020; since then, cases have been reported worldwide. Renal involvement has been seen commonly, ranging from 10% to 46%. Kidney involvement following severe acute respiratory syndrome coronavirus 2 infection in children with MIS-C is more common than initially thought and is associated with higher morbidity and mortality. There are several reports of a direct viral tropism of coronavirus disease 2019 and MIS-C-associated renal damage. This study’s objective was to systematically review the current understanding of kidney involvement in children suffering from MIS-C. Based on our systemic literature search, 19 studies have either partially or fully discussed kidney involvement in MIS-C patients. Furthermore, we discuss the multifactorial pathogenesis contributing to acute kidney injury (AKI) development in MIS-C. The current review gives a pediatric nephrologist’s perspective of the renal involvement in MIS-C, the incidence of AKI, the pathophysiology of AKI in MIS-C and the proposed therapeutic regimens available, including the need for kidney replacement therapy for a child with AKI associated with MIS-C. As the disease is rapidly evolving, more detailed clinical prospective studies are required to understand MIS-C and its role in AKI better.

Informatics Analysis of Health Indicators and Pathological Manifestations of Foot-Process in Patients with Primary IgA Nephropathy

Objective: This paper focuses on the foot-process in renal biopsies of patients with lgA, and examines their correlation with baseline clinical indicators and pathological manifestations in patients with lgA. Method: A retrospective data of patients who performed renal biopsy proven IgA nephropathy was selected. The patients who reached the agreed standard were grouped based on the degree of foot-process. There were three groups (ABC Groups) (Du, Y. and Huang, C, 2009. The value of proteinuria and foot process fusion in the onset of prognosis of acute kidney disease. Chinese Journal of Integrated Traditional and Western Medicine, 10(1), pp.44-45): group A for patients with no obvious foot-process lesion; group B for patients with segmental foot-process; group C for patients with massive foot-process. The three groups were reviewed in the aspects of baseline clinical indicators and Oxford classification, so as to discover foot-process’ effect on patients with IgA nephropathy. Results: A total of 129 patients with IgA nephropathy were included in the study. Concerning about the clinical baseline indicators related to the degree of foot-process, the 24-hour proteinuria level at admission was statistically significant and positively correlated (r = 0.324, P = 0.000). The comparison between groups showed there was statistically significant difference between group C and group A and group B (P = 0.001, P = 0.035). According to the Oxford Classification, only the differences of mesangial hypercellularity (M) and segmental sclerosis/adhesion (S) were statistically significant (r = 0.239, P = 0.006; r = 0.257, P = 0.003) and were positively correlated. In terms of mesangial hypercellularity (M), the differences between group A and B, group A and C were statistically significant (P = 0.01, P = 0.003). The comparison between group B and group C showed statistical difference (P = −0.031) in segmental sclerosis/adhesion (S). Among the 76 patients with S0 revealed by the Oxford classification, there were 55 patients of glomerulosclerosis, which was positively correlated with the degree of foot process (r = 0.211, P = 0.016). The comparison between group A and group C showed statistical difference (P = 0.014). Conclusion: The severity foot-process was positively correlated with the level of proteinuria. Foot-process is positively related with mesangial hypercellularity, segmental sclerosis and glomerulosclerosis. With more severe the foot-process, there will be more serious mesangial hypercellularity and irreversible glomerular injury. Foot-process is positively correlated with Lee’s Pathological Grading.

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.

The Use of Chinese Yang/Qi-Invigorating Tonic Botanical Drugs/Herbal Formulations in Ameliorating Chronic Kidney Disease by Enhancing Mitochondrial Function

Background: Chronic kidney disease (CKD) is a leading cause of morbidity and mortality. Mitochondrial dysfunction has been implicated as a key factor in the development of CKD. According to traditional Chinese medicine (TCM) theory, many Chinese Yang/Qi-invigorating botanical drugs/herbal formulations have been shown to produce promising outcomes in the clinical management of CKD. Experimental studies have indicated that the health-promoting action of Yang/Qi invigoration in TCM is related to the up-regulation of mitochondrial energy generation and antioxidant status. Objective: In this review, we aim to test whether Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations can provide medical benefits in CKD and its complications. And we also explore the possible involvement of mitochondrial-associated signaling pathway underlying the beneficial effects of Yang/Qi invigoration in TCM. Methods: A systematic search of "PubMed", "China National Knowledge Infrastructure (CNKI)" and "Google Scholar" was carried out to collect all the available articles in English or Chinese related to Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations and their effects on mitochondrial function and chronic kidney disease. Result and Discussion: The relationship between the progression of CKD and mitochondrial function is discussed. The effects of Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations and their active ingredients, including phytosterols/triterpenes, flavonoids, and dibenzocyclooctadiene lignans, on CKD and related alterations in mitochondrial signaling pathways are also presented in this review. In the future, exploration of the possible beneficial effects and clinical studies of more Yang- and Qi-invigorating botanical drugs/herbal formulations in the prevention and/or/treatment of CKD and the molecular mechanisms relating to the enhancement of mitochondrial functions warrants further investigation. Conclusion: Given the critical role of mitochondrial function in safeguarding renal functional integrity, the enhancement of mitochondrial energy metabolism and antioxidant status in kidney tissue is likely involved in renal protection. Future studies on the biochemical and chemical basis underlying the effects of Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations from a mitochondrial perspective will hopefully provide novel insights into the rational development of new drugs for the prevention and/or treatment of CKD.

Megalin-mediated albumin endocytosis in renal proximal tubules is involved in the antiproteinuric effect of angiotensin II type 1 receptor blocker in a subclinical acute kidney injury animal model

BACKGROUND

Tubule-interstitial injury (TII) is one of the mechanisms involved in the progression of renal diseases with progressive proteinuria. Angiotensin II (Ang II) type 1 receptor blockers (ARBs) have been successfully used to treat renal diseases. However, the mechanism correlating treatment with ARBs and proteinuria is not completely understood. The hypothesis that the anti-proteinuric effect of losartan is associated with the modulation of albumin endocytosis in PT epithelial cells (PTECs) was assessed.

METHODS

We used a subclinical acute kidney injury animal model (subAKI) and LLC-PK1 cells, a model of PTECs.

RESULTS

In subAKI, PT albumin overload induced TII development, measured by: (1) increase in urinary lactate dehydrogenase and γ-glutamyltranspeptidase activity; (2) proteinuria associated with impairment in megalin-mediated albumin reabsorption; (3) increase in luminal and interstitial space in tubular cortical segments. These effects were avoided by treating the animals with losartan, an ARB. Using LLC-PK1 cells, we observed that: (1) 20 mg/mL albumin increased the secretion of Ang II and decreased megalin-mediated albumin endocytosis; (2) the effects of Ang II and albumin were abolished by 10^-8 M losartan; (3) MEK/ERK pathway is the molecular mechanism underlying the Ang II-mediated inhibitory effect of albumin on PT albumin endocytosis.

CONCLUSION

Our results show that PT megalin-mediated albumin endocytosis is a possible target during the treatment of renal diseases patients with ARB.

GENERAL SIGNIFICANCE

The findings obtained in the present work represents a step forward to the current knowledge on about the role of ARBs in the treatment of renal disease.

Improving the Dysregulation of FoxO1 Activity Is a Potential Therapy for Alleviating Diabetic Kidney Disease

A substantial proportion of patients with diabetes will develop kidney disease. Diabetic kidney disease (DKD) is one of the most serious complications in diabetic patients and the leading cause of end-stage kidney disease worldwide. Although some mechanisms have been revealed to contribute to the understanding of the pathogenesis of DKD and some drugs currently in use have been shown to be beneficial, prevention and management of DKD remain tricky and challenging. FoxO1 transcriptional factor is a crucial regulator of cellular homeostasis and posttranslational modification is a major mechanism to alter FoxO1 activity. There is increasing evidence that FoxO1 is involved in the regulation of various cellular processes such as stress resistance, autophagy, cell cycle arrest, and apoptosis, thereby playing an important role in the pathogenesis of DKD. Improving the dysregulation of FoxO1 activity by natural compounds, synthetic drugs, or manipulation of gene expression may attenuate renal cell injury and kidney lesion in the cells cultured under a high-glucose environment and in diabetic animal models. The available data imply that FoxO1 may be a potential clinical target for the prevention and treatment of DKD.

The PAR-1 antagonist vorapaxar ameliorates kidney injury and tubulointerstitial fibrosis

Protease-activated receptor (PAR)-1 has emerged as a key profibrotic player in various organs including kidney. PAR-1 activation leads to deposition of extracellular matrix (ECM) proteins in the tubulointerstitium and induction of epithelial-mesenchymal transition (EMT) during renal fibrosis. We tested the anti-fibrotic potential of vorapaxar, a clinically approved PAR-1 antagonist for cardiovascular protection, in an experimental kidney fibrosis model of unilateral ureteral obstruction (UUO) and an AKI-to-chronic kidney disease (CKD) transition model of unilateral ischemia-reperfusion injury (UIRI), and dissected the underlying renoprotective mechanisms using rat tubular epithelial cells. PAR-1 is activated mostly in the renal tubules in both the UUO and UIRI models of renal fibrosis. Vorapaxar significantly reduced kidney injury and ameliorated morphologic changes in both models. Amelioration of kidney fibrosis was evident from down-regulation of fibronectin (Fn), collagen and α-smooth muscle actin (αSMA) in the injured kidney. Mechanistically, inhibition of PAR-1 inhibited MAPK ERK1/2 and transforming growth factor-β (TGF-β)-mediated Smad signaling, and suppressed oxidative stress, overexpression of pro-inflammatory cytokines and macrophage infiltration into the kidney. These beneficial effects were recapitulated in cultured tubular epithelial cells in which vorapaxar ameliorated thrombin- and hypoxia-induced TGF-β expression and ECM accumulation. In addition, vorapaxar mitigated capillary loss and the expression of adhesion molecules on the vascular endothelium during AKI-to-CKD transition. The PAR-1 antagonist vorapaxar protects against kidney fibrosis during UUO and UIRI. Its efficacy in human CKD in addition to CV protection warrants further investigation.

Cylindrospermopsin impairs tubular transport function in kidney cells LLC-PK1

Cylindrospermopsin (CYN) has been involved in cases of poisoning in humans following ingestion. Studies have demonstrated that the kidney is the most affected organ. CYN exposure leads to low-molecular-weight proteinuria and increased excretions of the tubular enzymes in mice, suggesting the damage caused by CYN is mainly tubular. However, the mechanism involved in CYN nephrotoxicity remains unknown. Thus, in order to evaluate the effects of CYN exposure (0.1, 0.5 and 1.0 μg/mL) on tubular renal cells LLC-PK1 distinct mechanisms were analyzed by assessing cell death using flow cytometry, albumin uptake by fluorescence analysis, Na⁺/K⁺-ATPase activity by a colorimetric method, RT-qPCR of genes related to tubular transport and function as well as internalization of CYN by ELISA. In this study, CYN was found to induce necrosis in all concentrations. CYN also decreased albumin uptake as well as downregulated megalin and dab2 expression, both proteins involved in albumin endocytosis process. Moreover, CYN appears to be internalized by renal tubular cells through a receptor-mediated endocytosis. Finally, the present study demonstrates that CYN is responsible for disrupting tubular cell transport and function in LLC-PK1 cells.

Molecular and functional profiling of apical versus basolateral small extracellular vesicles derived from primary human proximal tubular epithelial cells under inflammatory conditions

Proximal tubular epithelial cells (PTEC) are central players in inflammatory kidney diseases. However, the complex signalling mechanism/s via which polarized PTEC mediate disease progression are poorly understood. Small extracellular vesicles (sEV), including exosomes, are recognized as fundamental components of cellular communication and signalling courtesy of their molecular cargo (lipids, microRNA, proteins). In this study, we examined the molecular content and function of sEV secreted from the apical versus basolateral surfaces of polarized human primary PTEC under inflammatory diseased conditions. PTEC were cultured under normal and inflammatory conditions on Transwell inserts to enable separate collection and isolation of apical/basolateral sEV. Significantly increased numbers of apical and basolateral sEV were secreted under inflammatory conditions compared with equivalent normal conditions. Multi‐omics analysis revealed distinct molecular profiles (lipids, microRNA, proteins) between inflammatory and normal conditions for both apical and basolateral sEV. Biological pathway analyses of significantly differentially expressed molecules associated apical inflammatory sEV with processes of cell survival and immunological disease, while basolateral inflammatory sEV were linked to pathways of immune cell trafficking and cell‐to‐cell signalling. In line with this mechanistic concept, functional assays demonstrated significantly increased production of chemokines (monocyte chemoattractant protein‐1, interleukin‐8) and immuno‐regulatory cytokine interleukin‐10 by peripheral blood mononuclear cells activated with basolateral sEV derived from inflammatory PTEC. We propose that the distinct molecular composition of sEV released from the apical versus basolateral membranes of human inflammatory PTEC may reflect specialized functional roles, with basolateral‐derived sEV pivotal in modulating tubulointerstitial inflammatory responses observed in many immune‐mediated kidney diseases. These findings provide a rationale to further evaluate these sEV‐mediated inflammatory pathways as targets for biomarker and therapeutic development.

Mechanism and restoration strategy of lysosomal abnormalities induced by urinary protein overload in proximal tubule epithelial cells

BACKGROUND

Persistent elevated concentrations of urinary protein can destroy proximal tubule epithelial cells (PTECs) by inducing lysosomal abnormalities, thereby aggravating PTEC damage and renal fibrosis. However, the specific mechanisms of these serial biochemical events and methods for treating or preventing PTEC damage upon proteinuria need further investigation.

RESULTS

In this study, electron microscopy and dual-labeled immunofluorescence analysis for identifying lysosome type revealed inadequate primary lysosome biogenesis and secondary lysosome accumulation in the PTECs of patients with minimal change nephrotic syndrome or membranous nephropathy who suffered from proteinuria. In vitro studies on HK-2 cells indicated that this abnormality was associated with decreased expression of transcription factor EB (TFEB). In contrast, TFEB overexpressing HK-2 cells under urinary protein overload exhibited significantly reduced accumulation of secondary lysosomes and increased proportion and quantity of primary lysosomes as indicated by dual-labeled immunofluorescence. Further, these cells could upregulate lysosomal degradation functions, as determined using Cathepsin L activity assays and flow cytometry for dye quenched-albumin.

CONCLUSIONS

These results indicate that abnormal TFEB expression is a key mechanism of lysosomal dyshomeostasis caused by protein overload in PTECs. TFEB is thus a potential therapeutic target for the treatment of urinary protein-related kidney disease.

SARS-CoV-2 and Viral Sepsis: Immune Dysfunction and Implications in Kidney Failure

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of coronavirus disease 2019 (COVID-19), first emerged in Wuhan, China. The clinical manifestations of patients infected with COVID-19 include fever, cough, and dyspnea, up to acute respiratory distress syndrome (ARDS) and acute cardiac injury. Thus, a lot of severe patients had to be admitted to intensive care units (ICU). The pathogenic mechanisms of SARS-CoV-2 infection are mediated by the binding of SARS-CoV-2 spikes to the human angiotensin-converting enzyme 2 (ACE-2) receptor. The overexpression of human ACE-2 is associated with the disease severity in SARS-CoV-2 infection, demonstrating that viral entry into cells is a pivotal step. Although the lung is the organ that is most commonly affected by SARS-CoV-2 infection, acute kidney injury (AKI), heart dysfunction and abdominal pain are the most commonly reported co-morbidities of COVID-19. The occurrence of AKI in COVID-19 patients might be explained by several mechanisms that include viral cytopathic effects in renal cells and the host hyperinflammatory response. In addition, kidney dysfunction could exacerbate the inflammatory response started in the lungs and might cause further renal impairment and multi-organ failure. Mounting recent evidence supports the involvement of cardiovascular complications and endothelial dysfunction in COVID-19 syndrome, in addition to respiratory disease. To date, there is no vaccine, and no specific antiviral medicine has been shown to be effective in preventing or treating COVID-19. The removal of pro-inflammatory cytokines and the shutdown of the cytokine storm could ameliorate the clinical outcome in severe COVID-19 cases. Therefore, several interventions that inhibit viral replication and the systemic inflammatory response could modulate the severity of the renal dysfunction and increase the probability of a favorable outcome.

Effects of Albumin Infusion on Serum Levels of Albumin, Proinflammatory Cytokines (TNF-α, IL-1, and IL-6), CRP, and MMP-8; Tissue Expression of EGRF, ERK1, ERK2, TGF-β, Collagen, and MMP-8; and Wound Healing in Sprague Dawley Rats

In this study, we sought to determine the roles of albumin in wound healing, which is infused both pre- and postoperatively in malnourished patients presenting with hypoalbuminemia. For the purposes of the study, we used 25 male Sprague Dawley rats of predetermined weight and age, which were initially maintained in a standard environment and fed the same diet for 7 days prior to being segregated into one of the following five groups: A, control, normal protein feed (20% casein); B, hypoalbuminemia, 25% rat albumin infusion prior to surgery; C, hypoalbuminemia, normal protein feed (20% casein); D, hypoalbuminemia, 25% rat albumin infusion after surgery; and E, hypoalbuminemia, low-protein feed (casein 2%). The animals in all five groups were subjected to four deep incisions in their dorsal muscle fascia. On days 1, 3, 5, and 7 after surgery, ELISA was used to determine serum levels of TNF-α, IL-1, IL-6, CRP, and MMP-8, whereas immunohistochemistry was used to determine the tissue expression of EGFR, ERK1, ERK2, TGF-β, collagen, and MMP-8. Significant reductions in serum levels of TNF-α, IL-1, and CRP were detected in the groups receiving albumin infusion and the high-casein diet (P < 0.05). The administration of albumin and a high-casein diet also increased the tissue expression of EGFR, ERK1, ERK2, TGF-β, and collagen and decreased that of MMP-8 relative to the hypoalbuminemia control (P < 0.05). We propose that the administration of albumin promoted NF-κB signaling which, in turn, induced the transduction and transcription of factors involved in wound healing. Albumin infusion and dietary proteins play vital roles in accelerating the wound healing process, as they can contribute to correcting the hypoalbuminemic state. These findings provide insights that will contribute to our understanding of wound healing, particularly in malnourished patients.

IL-4 Receptor α Chain Protects the Kidney Against Tubule-Interstitial Injury Induced by Albumin Overload

Increasing evidence has highlighted the role of tubule-interstitial injury (TII) as a vital step in the pathogenesis of acute kidney injury (AKI). Incomplete repair of TII during AKI could lead to the development of chronic kidney disease. Changes in albumin endocytosis in proximal tubule epithelial cells (PTECs) is linked to the development of TII. In this context, interleukin (IL)-4 has been shown to be an important factor in modulating recovery of TII. We have studied the possible role of IL-4 in TII induced by albumin overload. A subclinical AKI model characterized by albumin overload in the proximal tubule was used, without changing glomerular function. Four groups were generated: (1) CONT, wild-type mice treated with saline; (2) BSA, wild-type mice treated with 10 g/kg/day bovine serum albumin (BSA); (3) KO, IL4Rα^–/– mice treated with saline; and (4) KO + BSA, IL4Rα^–/– mice treated with BSA. As reported previously, mice in the BSA group developed TII without changes in glomerular function. The following parameters were increased in the KO + BSA group compared with the BSA group: (1) tubular injury score; (2) urinary γ-glutamyltransferase; (3) CD4⁺ T cells, dendritic cells, macrophages, and neutrophils are associated with increases in renal IL-6, IL-17, and transforming growth factor β. A decrease in M2-subtype macrophages associated with a decrease in collagen deposition was observed. Using LLC-PK1 cells, a model of PTECs, we observed that (1) these cells express IL-4 receptor α chain associated with activation of the JAK3/STAT6 pathway; (2) IL-4 alone did not change albumin endocytosis but did reverse the inhibitory effect of higher albumin concentration. This effect was abolished by JAK3 inhibitor. A further increase in urinary protein and creatinine levels was observed in the KO + BSA group compared with the BSA group, but not compared with the CONT group. These observations indicate that IL-4 has a protective role in the development of TII induced by albumin overload that is correlated with modulation of the pro-inflammatory response. We propose that megalin-mediated albumin endocytosis in PTECs could work as a sensor, transducer, and target during the genesis of TII.

Innate immunity in diabetic kidney disease

Increasing evidence suggests that renal inflammation contributes to the pathogenesis and progression of diabetic kidney disease (DKD) and that anti-inflammatory therapies might have renoprotective effects in DKD. Immune cells and resident renal cells that activate innate immunity have critical roles in triggering and sustaining inflammation in this setting. Evidence from clinical and experimental studies suggests that several innate immune pathways have potential roles in the pathogenesis and progression of DKD. Toll-like receptors detect endogenous danger-associated molecular patterns generated during diabetes and induce a sterile tubulointerstitial inflammatory response via the NF-κB signalling pathway. The NLRP3 inflammasome links sensing of metabolic stress in the diabetic kidney to activation of pro-inflammatory cascades via the induction of IL-1β and IL-18. The kallikrein-kinin system promotes inflammatory processes via the generation of bradykinins and the activation of bradykinin receptors, and activation of protease-activated receptors on kidney cells by coagulation enzymes contributes to renal inflammation and fibrosis in DKD. In addition, hyperglycaemia leads to protein glycation and activation of the complement cascade via recognition of glycated proteins by mannan-binding lectin and/or dysfunction of glycated complement regulatory proteins. Data from preclinical studies suggest that targeting these innate immune pathways could lead to novel therapies for DKD.

Increased Proteinuria is Associated with Increased Aortic Arch Calcification, Cardio-Thoracic Ratio, Rapid Renal Progression and Increased Overall and Cardiovascular Mortality in Chronic Kidney Disease

Background: Patients with chronic kidney disease (CKD) are associated with high prevalence rates of proteinuria, vascular calcification and cardiomegaly. In this study, we investigated relationships among proteinuria, aortic arch calcification (AoAC) and cardio-thoracic ratio (CTR) in patients with CKD stage 3A-5. In addition, we investigated correlations among proteinuria and decline in renal function, overall and cardiovascular (CV) mortality. Methods: We enrolled 482 pre-dialysis patients with CKD stage 3A-5, and determined AoAC and CTR using chest radiography at enrollment. The patients were stratified into four groups according to quartiles of urine protein-to-creatinine ratio (U_PCR). Results: The patients in quartile 4 had a lower estimated glomerular filtration rate (eGFR) slope, and higher prevalence rates of rapid renal progression, progression to commencement of dialysis, overall and CV mortality. Multivariable analysis showed that a high U_PCR was associated with high AoAC (unstandardized coefficient β: 0.315; p = 0.002), high CTR (unstandardized coefficient β: 1.186; p = 0.028) and larger negative eGFR slope (unstandardized coefficient β: -2.398; p < 0.001). With regards to clinical outcomes, a high U_PCR was significantly correlated with progression to dialysis (log per 1 mg/g; hazard ratio [HR], 2.538; p = 0.003), increased overall mortality (log per 1 mg/g; HR, 2.292; p = 0.003) and increased CV mortality (log per 1 mg/g; HR, 3.195; p = 0.006). Conclusions: Assessing proteinuria may allow for the early identification of high-risk patients and initiate interventions to prevent vascular calcification, cardiomegaly, and poor clinical outcomes.

Urinary oxylipin signature as biomarkers to monitor the allograft function during the first six months post-renal transplantation

Oxylipins such as isoprostanes (IsoPs), prostaglandins (PGs) and thromboxanes (TXs) are lipid mediators derived from the oxidation of polyunsaturated fatty acids, which regulate the magnitude of oxidative stress and inflammation processes and play an important role in pathophysiological processes in the kidney. A total of 36 oxylipins were analyzed by UHPLC-QqQ-MS/MS in the urine of 41 renal recipients from cadaveric donors of the Nephrology Unit of the University Hospital Virgen de la Arrixaca during the first six months after renal transplantation, in order to investigate several candidate oxylipins as more accurate and predictive biomarkers in renal transplantation than classical biological variables. A decrease in nine PGs, mostly from the AA-D pathway (p < 0.05) and one IsoP: 15-keto-15-F_2t-IsoP (p < 0.001) was observed. Moreover, two PGs (2,3-dinor-11β-PGF_2α and 17-trans-PGF_3α) increased between five days and six months after renal transplantation (p < 0.05). In addition, when kidney function improved, a positive correlation between oxylipin levels and the excretion of urine proteins was observed. These results suggest that oxylipins could be useful markers for monitoring renal function in the post-renal transplantation period. These findings could be of utility not only for the development of strategies for long-term preservation of graft function, but also for innovative and alternative therapies -using oxylipins as predictive markers-to avoid organ rejection.

Electron Compensation Effect Suppressed Silver Ion Release and Contributed Safety of Au@Ag Core-Shell Nanoparticles

Silver nanoparticles (Ag NPs) have promising plasmonic properties, however, they are rarely used in biomedical applications because of their potent toxicity. Herein, an electron compensation effect from Au to Ag was applied to design safe Au@Ag core-shell NPs. The Ag shell thickness was precisely regulated to enable the most efficient electron enrichment in Ag shell of Au@Ag_2.4 NPs, preventing Ag oxidation and subsequent Ag⁺ ion release. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analysis revealed the electron transfer process from Au core to Ag shell, and inductively coupled plasma optical emission spectroscopy analysis confirmed the low Ag⁺ ion release from Au@Ag_2.4 NPs. Bare Au@Ag_2.4 NPs showed much lower toxicological responses than Ag NPs in BEAS-2B and Raw 264.7 cells and acute lung inflammation mouse models, and PEGylation of Au@Ag_2.4 NPs could further improve their safety to L02 and HEK293T cells as well as mice through intravenous injection. Further, diethylthiatri carbocyanine iodide attached pAu@Ag_2.4 NPs exhibited intense surface-enhanced Raman scattering signals and were used for Raman imaging of MCF7 cells and Raman biosensing in MCF7 tumor-bearing mice. This electron compensation effect opens up new opportunity for broadening biomedical application of Ag-based NPs.

Cold Storage Increases Albumin and Advanced Glycation-End Product-Albumin Levels in Kidney Transplants: A Possible Cause for Exacerbated Renal Damage

Prolonged cold storage (CS) of kidneys is associated with poor renal outcome after transplantation (Tx). We recently showed that in rats (Lewis), proteasome and renal function were severely compromised in kidney transplants subjected to CS (CS/Tx) as compared with those without CS exposure (autotransplanted [ATx]).

Effect of bardoxolone methyl on the urine albumin-to-creatinine ratio in patients with type 2 diabetes and stage 4 chronic kidney disease

Bardoxolone methyl attenuates inflammation by inducing nuclear factor erythroid-derived 2-related factor 2 and suppressing nuclear factor κB. The Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes (BEACON) trial was a phase 3 placebo-controlled, randomized, double-blind, parallel-group, international, multicenter trial in 2185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease. BEACON was terminated because of safety concerns, largely related to a significant increase in early heart failure events in patients randomized to bardoxolone methyl. Bardoxolone methyl resulted in increased estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio. Herein, we present post hoc analyses characterizing the relation between the urine albumin-to-creatinine ratio and eGFR. The urine albumin-to-creatinine ratio and eGFR were assessed every four weeks through Week 12, followed by assessments every eight weeks thereafter, and 4 weeks after the last dose of bardoxolone methyl was administered. The initial increases in urine albumin-to-creatinine ratio observed in patients randomized to bardoxolone methyl were attenuated after six months. Multivariable regression analysis identified baseline eGFR and eGFR over time as the dominant factors associated with change in the urine albumin-to-creatinine ratio. Relative to placebo, bardoxolone methyl resulted in a significant decrease in albuminuria when indexed to eGFR (least-squared means: -0.035 [95% confidence interval -0.031 to -0.039]). Thus, among patients with type 2 diabetes mellitus and stage 4 chronic kidney disease treated with bardoxolone methyl, changes in albuminuria are directly related to changes in eGFR, challenging the conventional construct that increases in albuminuria universally reflect kidney injury and denote harm.

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.

Vitamin D attenuates human gingival fibroblast inflammatory cytokine production following advanced glycation end product interaction with receptors for AGE

BACKGROUND AND OBJECTIVES

Vitamin D [1,25(OH)₂ D₃ or 1,25D3] is critical in musculoskeletal health, inflammation, immune response, and glucose metabolism. Patients with vitamin D deficiency may be at higher risk of diabetes and periodontitis. Diabetic patients exhibit exacerbated inflammation and more periodontal destruction. Advanced glycation end products (AGEs), formed during diabetic hyperglycemia, activate inflammatory pathways in periodontitis. Human gingival fibroblasts (HGFs) express receptors for AGEs (RAGEs) and can contribute to inflammation.

OBJECTIVES

Determine whether glycated human serum albumin (G-HSA) augments HGF IL-6 and IL-8 production, and whether treatment with 1,25D3 attenuates cytokine production following stimulation with G-HSA + IL-1β and/or IL-17.

MATERIAL AND METHODS

HGFs were incubated ±G-HSA or normal human serum albumin (HSA), ±IL-1β and/or IL-17, ±1,25D3. Cytokines were measured by ELISA. Neutralizing anti-RAGE was used to assess AGE-RAGE interaction. Endotoxin was measured using the ToxinSensor™ System. Data were expressed as mean ± standard deviation and analyzed using a one-way analysis of variance (ANOVA) and Scheffe's F procedure for post hoc comparisons.

RESULTS

G-HSA or IL-1β, but not HSA, significantly stimulated IL-6 and IL-8 production. G-HSA or HSA when combined with IL-1β or IL-1β + IL-17 synergistically stimulated IL-6 and IL-8. Neutralizing anti-RAGE inhibited IL-6 and IL-8 produced by cells stimulated with IL-1β + G-HSA but not (+HSA). Synergism caused by HSA did not appear to be mediated by endotoxin since its levels in G-HSA and HSA were not sufficient to stimulate fibroblasts. Vitamin D inhibited IL-6 and IL-8 production stimulated by G-HSA or HSA + IL-1β or IL-1β + IL-17.

CONCLUSIONS

Results suggest that the "perioprotective" effects of vitamin D are related to its ability to regulate inflammatory cytokine production by HGFs following AGE-RAGE interaction.

Role of (pro)renin receptor in albumin overload-induced nephropathy in rats

Proteinuria is not only a common feature of chronic kidney diseases (CKD) but also an independent risk factor promoting CKD progression to end-stage renal failure. However, the underlying molecular mechanisms for protein overload-induced renal injury remain elusive. The present study examined the role of (pro)renin receptor (PRR) in pathogenesis of albumin overload (AO)-induced nephropathy and activation of the intrarenal renin-angiotensin system (RAS) in rats. Wistar rats underwent unilateral nephrectomy and were treated for 7 wk with vehicle, bovine serum albumin (5 g·kg^-1·day^-1 via a single ip injection), alone or in conjunction with the PRR decoy inhibitor PRO20 (500 μg·kg^-1·day^-1 via 3 sc injections). The AO rat model exhibited severe proteinuria, tubular necrosis, and interstitial fibrosis, oxidative stress, and inflammation, accompanied by elevated urinary N-acetyl-β-d-glucosaminidase activity and urinary β₂-microglobulin secretion, all of which were significantly attenuated by PRO20. Urinary and renal levels of renin, angiotensinogen, and ANG II were elevated by AO and suppressed by PRO20, contrasting to largely unaltered plasma levels of the RAS parameters. The AO model also showed increased renal expression of full-length PRR and soluble PRR (sPRR) and urinary excretion of sPRR. Taken together, we conclude that PRR antagonism with PRO20 alleviates AO-induced nephropathy via inhibition of intrarenal RAS.

Activated renal tubular Wnt/β-catenin signaling triggers renal inflammation during overload proteinuria

Imbalance of Wnt/β-catenin signaling in renal cells is associated with renal dysfunction, yet the precise mechanism is poorly understood. Previously we observed activated Wnt/β-catenin signaling in renal tubules during proteinuric nephropathy with an unknown net effect. Therefore, to identify the definitive role of tubular Wnt/β-catenin, we generated a novel transgenic "Tubcat" mouse conditionally expressing stabilized β-catenin specifically in renal tubules following tamoxifen administration. Four weeks after tamoxifen injection, uninephrectomized Tubcat mice displayed proteinuria and elevated blood urea nitrogen levels compared to non-transgenic mice, implying a detrimental effect of the activated signaling. This was associated with infiltration of the tubulointerstitium predominantly by M1 macrophages and overexpression of the inflammatory chemocytokines CCL-2 and RANTES. Induction of overload proteinuria by intraperitoneal injection of low-endotoxin bovine serum albumin following uninephrectomy for four weeks aggravated proteinuria and increased blood urea nitrogen levels to a significantly greater extent in Tubcat mice. Renal dysfunction correlated with the degree of M1 macrophage infiltration in the tubulointerstitium and renal cortical up-regulation of CCL-2, IL-17A, IL-1β, CXCL1, and ICAM-1. There was overexpression of cortical TLR-4 and NLRP-3 in Tubcat mice, independent of bovine serum albumin injection. Finally, there was no fibrosis, activation of epithelial-mesenchymal transition or non-canonical Wnt pathways observed in the kidneys of Tubcat mice. Thus, conditional activation of renal tubular Wnt/β-catenin signaling in a novel transgenic mouse model demonstrates that this pathway enhances intrarenal inflammation via the TLR-4/NLRP-3 inflammasome axis in overload proteinuria.

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.

Cannabinoid-1 receptor deletion in podocytes mitigates both glomerular and tubular dysfunction in a mouse model of diabetic nephropathy

AIMS

To determine the specific role of podocyte-expressed cannabinoid-1 receptor (CB₁ R) in the development of diabetic nephropathy (DN), relative to CB₁ R in other renal cell types.

MATERIAL AND METHODS

We developed a mouse model with a podocyte-specific deletion of CB₁ R (pCB1Rko) and challenged this model with streptozotocin (STZ)-induced type-1 DN. We also assessed the podocyte response to high glucose in vitro and its effects on CB₁ R activation.

RESULTS

High glucose exposure for 48 hours led to an increase in CB₁ R gene expression (CNR1) and endocannabinoid production in cultured human podocytes. This was associated with podocyte injury, reflected by decreased podocin and nephrin expression. These changes could be prevented by Cnr1-silencing, thus identifying CB1R as a key player in podocyte injury. After 12 weeks of chronic hyperglycaemia, STZ-treated pCB1Rko mice showed elevated blood glucose similar to that of their wild-type littermates. However, they displayed less albuminuria and less podocyte loss than STZ-treated wild-type mice. Unexpectedly, pCB1Rko mice also have milder tubular dysfunction, fibrosis and reduction of cortical microcirculation compared to wild-type controls, which is mediated, in part, by podocyte-derived endocannabinoids acting via CB₁ R on proximal tubular cells.

CONCLUSIONS

Activation of CB₁ R in podocytes contributes to both glomerular and tubular dysfunction in type-1 DN, which highlights the therapeutic potential of peripheral CB₁ R blockade.

Acute Kidney Injury and Progression of Diabetic Kidney Disease

Diabetic kidney disease, commonly termed diabetic nephropathy (DN), is the most common cause of end-stage kidney disease (ESKD) worldwide. The characteristic histopathology of DN includes glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis, and tubulointerstitial fibrosis. Diabetes is associated with a number of metabolic derangements, such as reactive oxygen species overproduction, hypoxic state, mitochondrial dysfunction, and inflammation. In the past few decades, our knowledge of DN has advanced considerably although much needs to be learned. The traditional paradigm of glomerulus-centered pathophysiology has expanded to the tubule-interstitium, the immune response and inflammation. Biomarkers of proximal tubule injury have been shown to correlate with DN progression, independent of traditional glomerular injury biomarkers such as albuminuria. In this review, we summarize mechanisms of increased susceptibility to acute kidney injury in diabetes mellitus and the roles played by many kidney cell types to facilitate maladaptive responses leading to chronic and end-stage kidney disease.

Resonance Energy Transfer-Promoted Photothermal and Photodynamic Performance of Gold-Copper Sulfide Yolk-Shell Nanoparticles for Chemophototherapy of Cancer

Gold (Au) core@void@copper sulfide (CuS) shell (Au-CuS) yolk-shell nanoparticles (YSNPs) were prepared in the present study for potential chemo-, photothermal, and photodynamic combination therapy, so-called "chemophototherapy". The resonance energy transfer (RET) process was utilized in Au-CuS YSNPs to achieve both enhanced photothermal and photodynamic performance compared with those of CuS hollow nanoparticles (HNPs). A series of Au nanomaterials as cores that had different localized surface plasmon resonance (LSPR) absorption peaks at 520, 700, 808, 860, and 980 nm were embedded in CuS HNPs to screen the most effective Au-CuS YSNPs according to the RET process. Thermoresponsive polymer was fabricated on these YSNPs' surface to allow for controlled drug release. Au₈₀₈-CuS and Au₉₈₀-CuS YSNPs were found capable of inducing the largest temperature elevation and producing the most significant hydroxyl radicals under 808 and 980 nm laser irradiation, respectively, which could accordingly cause the most severe 4T1 cell injury through oxidative stress mechanism. Moreover, doxorubicin-loaded (Dox-loaded) P(NIPAM-co-AM)-coated Au₉₈₀-CuS (p-Au₉₈₀-CuS@Dox) YSNPs could more efficiently kill cells than unloaded particles upon 980 nm laser irradiation. After intravenous administration to 4T1 tumor-bearing mice, p-Au₉₈₀-CuS YSNPs could significantly accumulate in the tumor and effectively inhibit the tumor growth after 980 nm laser irradiation, and p-Au₉₈₀-CuS@Dox YSNPs could further potentiate the inhibition efficiency and exhibit excellent in vivo biocompatibility. Taken together, this study sheds light on the rational design of Au-CuS YSNPs to offer a promising candidate for chemophototherapy.

Recombinant human GLP-1(rhGLP-1) alleviating renal tubulointestitial injury in diabetic STZ-induced rats

GLP-1-based treatment improves glycemia through stimulation of insulin secretion and inhibition of glucagon secretion. Recently, more and more findings showed that GLP-1 could also protect kidney from diabetic nephropathy. Most of these studies focused on glomeruli, but the effect of GLP-1 on tubulointerstitial and tubule is not clear yet. In this study, we examined the renoprotective effect of recombinant human GLP-1 (rhGLP-1), and investigated the influence of GLP-1 on inflammation and tubulointerstitial injury using diabetic nephropathy rats model of STZ-induced. The results showed that rhGLP-1 reduced urinary albumin without influencing the body weight and food intake. rhGLP-1 could increased the serum C-peptide slightly but not lower fasting blood glucose significantly. In diabetic nephropathy rats, beside glomerular sclerosis, tubulointerstitial fibrosis was very serious. These lesions could be alleviated by rhGLP-1. rhGLP-1 decreased the expression of profibrotic factors collagen I, α-SMA, fibronectin, and inflammation factors MCP-1 and TNFα in tubular tissue and human proximal tubular cells (HK-2 cells). Furthermore, rhGLP-1 significantly inhibited the phosphorylation of NF-κB, MAPK in both diabetic tubular tissue and HK-2 cells. The inhibition of the expression of TNFα, MCP-1, collagen I and α-SMA in HK-2 cells by GLP-1 could be mimicked by blocking NF-κB or MAPK. These results indicate that rhGLP-1 exhibit renoprotective effect by alleviation of tubulointerstitial injury via inhibiting phosphorylation of MAPK and NF-κB. Therefore, rhGLP-1 may be a potential drug for treatment of diabetic nephropathy.