Advanced oxidation protein products activate intrarenal renin-angiotensin system via a CD36-mediated, redox-dependent pathway

Accumulation of advanced oxidation protein products aggravates bone-fat imbalance during skeletal aging

Background

Skeletal aging is characterized by a decrease in bone mass and an increase in marrowfat content. Advanced oxidation protein products (AOPPs) accumulate easily with aging and disrupt redox homeostasis. We examined whether AOPPs accumulation contributes to the bone-fat imbalance during skeletal aging.

Methods

Both young and aged mice were employed to assess the changes of AOPPs levels and its contribution to bone-fat imbalance during skeletal aging. Primary bone marrow mesenchymal stromal cells (MSCs) were used to examine the potential role of AOPPs in age-related switch between osteogenic and adipogenic differentiation. Aged mice were also gavaged by non-selective antioxidant N-acetyl-L-cysteine (NAC), followed by close monitoring of the changes in AOPPs levels and bone-fat metabolism. Furthermore, young mice were chronically exposed to AOPPs and then evaluated for the changes of bone mass and marrow adiposity.

Results

The levels of AOPPs in serum and bone marrow were markedly higher in aged mice than that in young mice. Age-related accumulation of AOPPs was accompanied by reduced bone formation, increased marrow adiposity and deterioration of bone microstructure. Reduced AOPPs accumulation by antioxidant NAC leaded to improvement of the bone-fat imbalance in aged mice. Similarly, the bone-fat imbalance was induced by chronic AOPPs loading in young mice. Compared with MSCs from young mice, MSCs from aged mice tended to differentiate into adipocytes rather than osteoblasts and displayed cellular senescence. Exposure of primary MSCs to AOPPs resulted in the switch from osteogenic to adipogenic lineage and cellular senescence. AOPPs challenge also increased intracellular ROS generation by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondria. The antioxidant NAC, after scavenging ROS, ameliorated the AOPPs-induced lineage switch and senescence in MSCs by inhibiting the PI3K/AKT/mTOR pathway.

Conclusion

Our findings revealed the involvement of AOPPs in age-related switch between osteogenic and adipogenic differentiation, and illuminated a novel potential mechanism underlying bone-fat imbalance during skeletal aging.

The translational potential of this article

Reducing AOPPs accumulation and its cascading effects on MSCs might be an attractive strategy for delaying skeletal aging.

Downregulation of CD36 alleviates IgA nephropathy by promoting autophagy and inhibiting extracellular matrix accumulation in mesangial cells

BACKGROUND

Immunoglobulin A Nephropathy (IgAN) is a leading cause of end-stage renal disease (ESRD), but its pathogenesis remains unclear, and specific therapies are currently lacking. Consequently, identifying novel differentially expressed genes (DEGs) and therapeutic targets is of paramount importance to IgAN.

METHODS

The Gene Expression Omnibus (GEO) databases GSE37460 and GSE104948, containing data from renal tissue of patients with IgAN and normal controls, were screened for DEGs, followed by enrichment pathway analysis. The potential key gene for IgAN, CD36, was identified through the single-cell sequencing dataset GSE166793 and histopathological analysis of patients with IgAN. Clinical and pathological data from patients with IgAN were collected to analyze the correlation between CD36 expression and various indicators in renal tissue, thereby evaluating the influence of CD36 on IgAN progression. The accuracy of the risk score model was assessed using receiver operating characteristic (ROC) curve analysis. Finally, CD36 expression was knocked down to explore its regulatory role in polymeric IgA1 (pIgA1)-stimulated mouse mesangial cells (MCs).

RESULTS

CD36 was identified as a key DEG from two GEO databases and a single-cell sequencing dataset. Compared to peritumoral normal tissues, CD36 expression levels were significantly increased in the IgAN group. Statistically significant differences were observed between M0 and M1, E0 and E1, S0 and S1, C0 and C1-2 in the updated Oxford Classification. CD36 expression showed positive correlations with 24-hour proteinuria, serum creatinine, and levels of fibrosis-related and autophagy-related factors in renal tissue. Additionally, CD36 and fibrosis-related factors were significantly elevated in MCs following pIgA1 stimulation. CD36 knockdown resulted in decreased extracellular matrix (ECM) accumulation in pIgA1-stimulated MCs. RNA-seq analysis of MCs with CD36 knockdown revealed significant alterations in autophagy and CD36 silencing restored autophagy levels in MCs treated with the autophagy inhibitor 3MA.

CONCLUSION

Our study confirmed that CD36 expression increases with the clinical progression of IgAN and CD36 knockdown alleviates MCs injury by inhibiting ECM accumulation and restoring autophagy.

GWAS Meta-analysis of Kidney Function Traits in Japanese Populations

BACKGROUND

Genetic epidemiological evidence for the kidney function traits in East Asian populations, including Japanese, remain still relatively unclarified. Especially, the number of genome-wide association studies (GWASs) for kidney traits reported still remains limited, and the sample size of each independent study is relatively small. Given the genetic variability between ancestries/ethnicities, implementation of GWAS with sufficiently large sample sizes in specific population of Japanese is considered meaningful.

METHODS

We conducted the GWAS meta-analyses of kidney traits by leveraging the GWAS summary data of the representative large genome cohort studies with about 200,000 Japanese participants (n = 202,406 for estimated glomerular filtration rate [eGFR] and n = 200,845 for serum creatinine [SCr]).

RESULTS

In the present GWAS meta-analysis, we identified 110 loci with 169 variants significantly associated with eGFR (on chromosomes 1-13 and 15-22; P < 5 × 10-8), whereas we also identified 112 loci with 176 variants significantly associated with SCr (on chromosomes 1-22; P < 5 × 10-8), of which one locus (more than 1 Mb distant from known loci) with one variant (CD36 rs146148222 on chromosome 7) for SCr was considered as the truly novel finding.

CONCLUSION

The present GWAS meta-analysis of the largest genome cohort studies in Japanese subjects provided some original genomic loci associated with kidney function, which may contribute to the possible development of personalized prevention of kidney diseases based on genomic information in the near future.

Therapeutic approaches and novel antifibrotic agents in renal fibrosis: A comprehensive review

Renal fibrosis (RF) is one of the underlying pathological conditions leading to progressive loss of renal function and end-stage renal disease (ESRD). Over the years, various therapeutic approaches have been explored to combat RF and prevent ESRD. Despite significant advances in understanding the underlying molecular mechanism(s), effective therapeutic interventions for RF are limited. Current therapeutic strategies primarily target these underlying mechanisms to halt or reverse fibrotic progression. Inhibition of transforming growth factor-β (TGF-β) signaling, a pivotal mediator of RF has emerged as a central strategy to manage RF. Small molecules, peptides, and monoclonal antibodies that target TGF-β receptors or downstream effectors have demonstrated potential in preclinical models. Modulating the renin-angiotensin system and targeting the endothelin system also provide established approaches for controlling fibrosis-related hemodynamic changes. Complementary to pharmacological strategies, lifestyle modifications, and dietary interventions contribute to holistic management. This comprehensive review aims to summarize the underlying mechanisms of RF and provide an overview of the therapeutic strategies and novel antifibrotic agents that hold promise in its treatment.

Cardiovascular Consequences of Uremic Metabolites: an Overview of the Involved Signaling Pathways

The crosstalk of the heart with distant organs such as the lung, liver, gut, and kidney has been intensively approached lately. The kidney is involved in (1) the production of systemic relevant products, such as renin, as part of the most essential vasoregulatory system of the human body, and (2) in the clearance of metabolites with systemic and organ effects. Metabolic residue accumulation during kidney dysfunction is known to determine cardiovascular pathologies such as endothelial activation/dysfunction, atherosclerosis, cardiomyocyte apoptosis, cardiac fibrosis, and vascular and valvular calcification, leading to hypertension, arrhythmias, myocardial infarction, and cardiomyopathies. However, this review offers an overview of the uremic metabolites and details their signaling pathways involved in cardiorenal syndrome and the development of heart failure. A holistic view of the metabolites, but more importantly, an exhaustive crosstalk of their known signaling pathways, is important for depicting new therapeutic strategies in the cardiovascular field.

The CXCR4-AT1 axis plays a vital role in glomerular injury via mediating the crosstalk between podocyte and mesangial cell

Glomeruli stand at the center of nephrons to accomplish filtration and albumin interception. Podocytes and mesangial cells are the major constituents in the glomeruli. However, their interdependency in glomerular injury has rarely been reported. Herein, we investigated the role of C-X-C chemokine receptor type 4 (CXCR4) in mediating the crosstalk between podocytes and mesangial cells. We found CXCR4 and angiotensin II (AngII) increased primarily in injured podocytes. However, type-1 receptor of angiotensin II (AT1) and stromal cell-derived factor 1α (SDF-1α), a ligand of CXCR4, were evidently upregulated in mesangial cells following the progression of podocyte injury. Ectopic expression of CXCR4 in 5/6 nephrectomy mice increased the decline of renal function and glomerular injury, accelerated podocyte injury and mesangial cell activation, and initiated CXCR4-AT1 axis signals. Additionally, treatment with losartan, an AT1 blocker, interrupted the cycle of podocyte injury and mesangial matrix deposition triggered by CXCR4. Podocyte-specific ablation of CXCR4 gene blocked podocyte injury and mesangial cell activation. In vitro, CXCR4 overexpression induced oxidative stress and renin angiotensin system (RAS) activation in podocytes, and triggered the communication between podocytes and mesangial cells. In cultured mesangial cells, AngII treatment induced the expression of SDF-1α, which was secreted into the supernatant to further promote oxidative stress and cell injury in podocytes. Collectively, these results demonstrate that the CXCR4-AT1 axis plays a vital role in glomerular injury via mediating pathologic crosstalk between podocytes and mesangial cells. Our findings uncover a novel pathogenic mechanism by which the CXCR4-AT1 axis promotes glomerular injury.

Tiliroside Protects against Lipopolysaccharide-Induced Acute Kidney Injury via Intrarenal Renin-Angiotensin System in Mice

Tiliroside, a natural flavonoid, has various biological activities and improves several inflammatory diseases in rodents. However, the effect of Tiliroside on lipopolysaccharide (LPS)-induced acute kidney injury (AKI) and the underlying mechanisms are still unclear. This study aimed to evaluate the potential renoprotective effect of Tiliroside on LPS-induced AKI in mice. Male C57BL/6 mice were intraperitoneally injected with LPS (a single dose, 3 mg/kg) with or without Tiliroside (50 or 200 mg/kg/day for 8 days). Tiliroside administration protected against LPS-induced AKI, as reflected by ameliorated renal dysfunction and histological alterations. LPS-stimulated renal expression of inflammatory cytokines, fibrosis markers, and kidney injury markers in mice was significantly abolished by Tiliroside. This flavonoid also stimulated autophagy flux but inhibited oxidative stress and tubular cell apoptosis in kidneys from LPS-injected mice. Mechanistically, our study showed the regulation of Tiliroside on the intrarenal renin-angiotensin system in LPS-induced AKI mice. Tiliroside treatment suppressed intrarenal AGT, Renin, ACE, and Ang II, but upregulated intrarenal ACE2 and Ang1-7, without affecting plasma Ang II and Ang1-7 levels. Collectively, our data highlight the renoprotective action of Tiliroside on LPS-induced AKI by suppressing inflammation, oxidative stress, and tubular cell apoptosis and activating autophagy flux via the shift towards the intrarenal ACE2/Ang1-7 axis and away from the intrarenal ACE/Ang II axis.

Renal-Protective Roles of Lipoic Acid in Kidney Disease

The kidney is a crucial organ that eliminates metabolic waste and reabsorbs nutritious elements. It also participates in the regulation of blood pressure, maintenance of electrolyte balance and blood pH homeostasis, as well as erythropoiesis and vitamin D maturation. Due to such a heavy workload, the kidney is an energy-demanding organ and is constantly exposed to endogenous and exogenous insults, leading to the development of either acute kidney injury (AKI) or chronic kidney disease (CKD). Nevertheless, there are no therapeutic managements to treat AKI or CKD effectively. Therefore, novel therapeutic approaches for fighting kidney injury are urgently needed. This review article discusses the role of α-lipoic acid (ALA) in preventing and treating kidney diseases. We focus on various animal models of kidney injury by which the underlying renoprotective mechanisms of ALA have been unraveled. The animal models covered include diabetic nephropathy, sepsis-induced kidney injury, renal ischemic injury, unilateral ureteral obstruction, and kidney injuries induced by folic acid and metals such as cisplatin, cadmium, and iron. We highlight the common mechanisms of ALA's renal protective actions that include decreasing oxidative damage, increasing antioxidant capacities, counteracting inflammation, mitigating renal fibrosis, and attenuating nephron cell death. It is by these mechanisms that ALA achieves its biological function of alleviating kidney injury and improving kidney function. Nevertheless, we also point out that more comprehensive, preclinical, and clinical studies will be needed to make ALA a better therapeutic agent for targeting kidney disorders.

(Pro)Renin Receptor Decoy Peptide PRO20 Protects against Oxidative Renal Damage Induced by Advanced Oxidation Protein Products

Chronic kidney disease (CKD) is associated with advanced oxidation protein products (AOPPs). A recent study has shown that AOPP-induced renal tubular injury is mediated by the (pro)renin receptor (PRR). However, it is unclear whether the PRR decoy inhibitor PRO20 can protect against renal damage related to AOPPs in vivo. In this study, we examined the role of the PRR in rats with AOPP-induced renal oxidative damage. Male SD rats were subjected to unilateral nephrectomy, and after a four-day recuperation period, they were randomly divided into four groups (n = 6/group) for four weeks: control (CTR), unmodified rat serum albumin (RSA, 50 mg/kg/day via tail-vein injection), AOPPs-RSA (50 mg/kg/day via tail-vein injection), and AOPPs-RSA + PRO20 (50 mg/kg/day via tail-vein injection + 500 μg/kg/day via subcutaneous injection) groups. PRO20 was administered 3 days before AOPPs-RSA injection. Renal histopathology evaluation was performed by periodic acid–Schiff (PAS) staining, and biochemical parameters related to renal injury and oxidative stress biomarkers were evaluated. The expression of related indicators was quantified by RT-qPCR and immunoblotting analysis. In the results, rats in the AOPPs-RSA group exhibited higher levels of albuminuria, inflammatory cell infiltration, and tubular dilation, along with upregulation of oxidative stress, profibrotic and proinflammatory factors, and elevation of AOPP levels. Meanwhile, in the PRO20 group, these were significantly reduced. Moreover, the levels of almost all components of the renin-angiotensin system (RAS) and Nox4-dependent H2O2 production in urine and the kidneys were elevated by AOPPs-RSA, while they were suppressed by PRO20. Furthermore, AOPPs-RSA rats showed elevated kidney expression of the PRR and soluble PRR (sPRR) and increased renal excretion of sPRR. In summary, these findings suggest that PRR inhibition may serve as a protective mechanism against AOPP-induced nephropathy by inhibiting the intrarenal RAS and Nox4-derived H2O2 mechanisms.

Advanced oxidation protein products induce annulus fibrosus cell senescence through a NOX4-dependent, MAPK-mediated pathway and accelerate intervertebral disc degeneration

Background

Intervertebral disc degeneration (IVDD) is closely associated with senescence. Annulus fibrosus (AF) cell senescence is a crucial driver of AF tissue tearing and fissures, thereby exacerbating IVDD. Increased advanced oxidative protein products (AOPPs) were found in human degenerative discs and aged rat discs and may be involved in IVDD. This study aimed to explore the mechanism of AOPPs-induced senescence in AF cells.

Methods

The pathological effects of AOPPs in vivo were investigated using a rat lumbar disc persistent degeneration model and a rat caudal disc puncture model. Rat primary AF cells were selected as in vitro models, and AOPPs were used as direct stimulation to observe their pathological effects. Setanaxb (NOX1/4 inhibitor), apocynin (NADPH oxidase inhibitor) and adenovirus (ADV) packed NADPH oxidase 4 (NOX4) specific shRNAs were used for pathway inhibition, respectively. Finally, adeno-associated viruses (AAVs) packed with NOX4-specific blocking sequences were used to inhibit the in vivo pathway.

Results

AOPPs accumulated in the rat lumbar and caudal degenerative discs. Intra-discal loading of AOPPs up-regulated the expression of NOX4, p53, p21, p16, IL-1β, and TNF-α, ultimately accelerating IVDD. Exposure of AOPPs to AF primary cells up-regulated NOX4 expression, induced phosphorylation of mitogen-activated protein kinases (MAPK), triggered senescence and increased IL-1β and TNF-α. Apocynin, setanaxib, and ADV pre-cultured AF cells abrogated AOPPs-induced senescence. AAV-mediated inhibition of NOX4 expression in vivo reduced the expression of p53, p21, p16, IL-1β and TNF-α in vivo and delayed IVDD.

Conclusions

AOPPs induced AF cell senescence through a NOX4-dependent and MAPK-mediated pathway.

Expression of CCL2, FOS, and JUN May Help to Distinguish Patients With IgA Nephropathy From Healthy Controls

Background

IgA nephropathy (IgAN), the most common type of glomerulonephritis worldwide, can only be diagnosed mainly by renal biopsy owing to lack of effective biomarkers. It is urgent to explore and identify the potential diagnostic biomarkers through assessing the gene expression profiles of patients with IgAN.

Methods

Two datasets were obtained from the Gene Expression Omnibus (GEO) database, including GSE115857 (55 IgAN, 7 living healthy donors) and GSE35487 (25 IgAN, 6 living healthy donors), then underwent differentially expressed genes (DEGs) and function enrichment analyses utilizing R packages. The common gene list was screened out between DEGs and immune-associated genes by Venn diagram, then performed gene-gene interaction, protein-protein interaction (PPI) and function enrichment analyses. Top three immune-associated hub genes were selected by Maximal Clique Centrality (MCC) method, then the expression and diagnostic value of these hub genes were determined. Consensus clustering algorithm was applied to conduct the unsupervised cluster analysis of the immune-associated hub gene list in IgAN. Finally, the Nephroseq V5 tool was applied to identify the expression level of CCL2, FOS, JUN in kidney diseases, as well as the correlation between CCL2, FOS, JUN expression and renal function in the patients with IgAN.

Results

A total of 129 DEGs were obtained through comparing IgAN with healthy controls via the GSE115857 and GSE35487 datasets. Then, we screened out 24 immune-associated IgAN DEGs. CCL2, JUN, and FOS were identified as the top three hub genes, and they were all remarkably downregulated in IgAN. More importantly, CCL2, JUN, and FOS had a high accuracy [area under the curve (AUC) reached almost 1] in predicting IgAN, which could easily distinguish between IgAN patients and healthy individuals. Three distinct subgroups of IgAN were determined based on 24 immune-associated DEGs, with significant differences in the expression of CCL2, JUN, and FOS genes. Finally, CCL2, FOS, JUN were manifested a meaningful association with proteinuria, glomerular filtration rate (GFR), and serum creatinine level.

Conclusion

In summary, our study comprehensively uncovers that CCL2, JUN, and FOS may function as promising biomarkers for diagnosis of IgAN.

Advanced Oxidation Protein Product Promotes Oxidative Accentuation in Renal Epithelial Cells via the Soluble (Pro)renin Receptor-Mediated Intrarenal Renin-Angiotensin System and Nox4-H2O2 Signaling

Full-length (pro)renin receptor (fPRR), a research hotspot of the renin-angiotensin system (RAS), plays a serious role in kidney injury. However, the relationship between fPRR and advanced oxidation protein product (AOPP) remains largely unexplored. This study was aimed at exploring the effect of fPRR, especially its 28 kDa soluble form called soluble PRR (sPRR), in AOPP-induced oxidative stress in HK-2 cells, a renal proximal tubular epithelial cell line. Incubation of HK-2 cells with 100 μg/ml AOPP resulted in significant upregulation of fPRR expression and caused an approximately fourfold increase in medium sPRR secretion. However, unmodified albumin did not demonstrate the same effects under the same concentration. Treatment of HK-2 cells with the site-1 protease (S1P) inhibitor PF429242 (40 μM) or S1P siRNA significantly inhibited AOPP-induced sPRR generation. fPRR decoy inhibitor PRO20 and PF429242 treatment for 24 h remarkably attenuated the AOPP-induced upregulation of RAS components. Furthermore, PF429242 significantly reduced the AOPP-stimulated expression of NADPH oxidase 4 (Nox4) and H₂O₂ expression. The use of a small recombinant protein, named sPRR-His, reversed these alterations. In conclusion, these results provided the first demonstration of AOPP-promoted activation of sPRR. Increased renal proximal tubule Nox4-derived H₂O₂ contributed to the aggravation of oxidative stress. Targeting S1P-derived sPRR is a promising intervention strategy for chronic kidney disease.

Advanced oxidation protein products contribute to chronic kidney disease-induced muscle atrophy by inducing oxidative stress via CD36/NADPH oxidase pathway

BACKGROUND

Sarcopenia with chronic kidney disease (CKD) progression is associated with life prognosis. Oxidative stress has attracted interest as a trigger for causing CKD-related muscular atrophy. Advanced oxidation protein products (AOPPs), a uraemic toxin, are known to increase oxidative stress. However, the role of AOPPs on CKD-induced muscle atrophy remains unclear.

METHODS

In a retrospective case-control clinical study, we evaluated the relationship between serum AOPPs levels and muscle strength in haemodialysis patients with sarcopenia (n = 26, mean age ± SEM: 78.5 ± 1.4 years for male patients; n = 22, mean age ± SEM: 79.1 ± 1.5 for female patients), pre-sarcopenia (n = 12, mean age ± SEM: 73.8 ± 2.0 years for male patients; n = 4, mean age ± SEM: 74.3 ± 4.1 for female patients) or without sarcopenia (n = 12, mean age ± SEM: 71.3 ± 1.6 years for male patients; n = 7, mean age ± SEM: 77.7 ± 1.6 for female ). The molecular mechanism responsible for the AOPPs-induced muscle atrophy was investigated by using 5/6-nephrectomized CKD mice, AOPPs-overloaded mice, and C2C12 mouse myoblast cells.

RESULTS

The haemodialysis patients with sarcopenia showed higher serum AOPPs levels as compared with the patients without sarcopenia. The serum AOPPs levels showed a negative correlation with grip strength (P < 0.01 for male patients, P < 0.01 for female patients) and skeletal muscle index (P < 0.01 for male patients). Serum AOPPs levels showed a positive correlation with cysteinylated albumin (Cys-albumin), a marker of oxidative stress (r2  = 0.398, P < 0.01). In the gastrocnemius of CKD mice, muscle AOPPs levels were also increased, and it showed a positive correlation with atrogin-1 (r2  = 0.538, P < 0.01) and myostatin expression (r2  = 0.421, P < 0.05), but a negative correlation with PGC-1α expression (r2  = 0.405, P < 0.05). Using C2C12 cells, AOPPs increased atrogin-1 and myostatin expression through the production of reactive oxygen species via CD36/NADPH oxidase pathway, and decreased myotube formation. AOPPs also induced mitochondrial dysfunction. In the AOPPs-overloaded mice showed that decreasing running time and hanging time accompanied by increasing AOPPs levels and decreasing cross-sectional area in gastrocnemius.

CONCLUSIONS

Advanced oxidation protein products contribute to CKD-induced sarcopenia, suggesting that AOPPs or its downstream signalling pathway could be a therapeutic target for the treatment of CKD-induced sarcopenia. Serum AOPPs or Cys-albumin levels could be a new diagnostic marker for sarcopenia in CKD.

The Relationship between Advanced Oxidation Protein Products, Vascular Calcifications and Arterial Stiffness in Predialysis Chronic Kidney Disease Patients

Background and Objectives: Cardiovascular morbidity and mortality are increased in patients with chronic kidney disease (CKD). It is likely that the accumulation of uremic toxins resulting in increased oxidative stress (OS) is a major contributing factor, but no clear link has been identified. The purpose of this research is to establish if advanced oxidation protein product (AOPP) levels in the serum of predialysis patients are a contributing factor to vascular calcification and increased arterial stiffness. Materials and Methods: After obtaining the informed consent, 46 predialysis patients (CKD stages G3-G5) were included in the study. In order to identify vascular calcifications, hand and pelvic radiographs were performed. Valvular calcifications were identified using cardiac ultrasound. AOPP were measured using a commercially available ELISA kit. The relationships between serum AOPP values and biochemical parameters relevant in the evaluation of CKD patients were analyzed. In addition to identifying the differences in AOPP levels between patients with/without vascular or valvular calcifications, the research focused on describing the relationship between OS and arterial stiffness assessed by oscillometric pulse-wave velocity (PWV) measurement. Results: No significant relationship between serum AOPP and vascular or valvular calcifications was highlighted, but significant correlations of AOPP with C-reactive protein (p = 0.025), HDL-cholesterol levels (p = 0.04), HbA1c (p = 0.05) and PWV values (p = 0.02) were identified. Conclusions: The usefulness of (OS) measurement in clinical practice remains debatable; however, the relationship between AOPP and arterial stiffness could be valuable in improving cardiovascular risk assessment of patients with CKD.

The Study of Angptl4-Modulated Podocyte Injury in IgA Nephropathy

Background

Increasing evidence shows that Angptl4 affects proteinuria in podocytes injured kidney disease, however, whether there is a relationship between Angptl4 and IgA nephropathy (IgAN) has not been studied yet.

Methods

Plasma and urine samples were obtained from 71 patients with IgAN and 61 healthy controls. Glomeruli from six renal biopsy specimens (three IgAN patients and three healthy controls) were separated by RNA-Seq. Differentially expressed genes (DEGs) related to podocytes and Angptl4 between IgAN patients and healthy controls were performed using the Limma package. Gene set enrichment analysis was used to determine whether there was a statistically significant difference between the two groups. STRING was used to create a protein-protein interaction network of DEGs. Association analysis between Angptl4 levels and clinical features of IgAN was performed.

Results

Thirty-three podocyte-related and twenty-three Angpt4-related DEGs were found between IgAN patients and healthy controls. By overlapping the genes, FOS and G6PC were found to be upregulated in IgAN patients, while MMP9 was downregulated in IgAN patients. Plasma and urine Angptl4 levels were closely related to the degree of podocyte injury and urine protein, but not to the protein-creatine ratio.

Conclusion

Our findings show that Angptl4 levels in plasma and urine are related to podocyte damage and, therefore, may be a promising tool for assessing the severity of IgAN patients to identify and reverse the progression to ESRD.

Low Molecular Weight Fucoidan Can Inhibit the Fibrosis of Diabetic Kidneys by Regulating the Kidney Lipid Metabolism

In this study, a diabetic kidney disease model was established by placing the test rats on a high-sugar/high-fat diet combined with streptozotocin induction. Histopathological examination (H&E, Masson, and PASM stain) showed pathological changes in the diabetic rat kidneys, in addition to fibrotic symptoms and collagen deposition. Immunohistochemistry and western blot analyses indicated that the diabetic condition significantly increased the expressions of fibrotic markers including collagen, α-SMA, and fibronectin. The levels of cholesterol, triglyceride, and low-density lipoprotein were also increased in diabetic kidney disease (DKD) rat blood, while the level of high-density lipoprotein was decreased. The results of Oil red O staining experiments indicated that the kidneys of diabetic rats exhibited appreciable fat deposition, with high contents of triglyceride and cholesterol. To inhibit fibrosis and reduce fat deposition, low molecular weight fucoidan (LMWF) may be used. Based on PCR and western blot analyses, LMWF can regulate the expression levels of important lipid metabolism regulators, thereby impeding the development of kidney fibrosis. Through the vitro model, it also be indicated that LMWF could inhibit fibrosis process through regulating lipid metabolism which induced by palmitic acid.

The Multifunctionality of CD36 in Diabetes Mellitus and Its Complications-Update in Pathogenesis, Treatment and Monitoring

CD36 is a multiligand receptor contributing to glucose and lipid metabolism, immune response, inflammation, thrombosis, and fibrosis. A wide range of tissue expression includes cells sensitive to metabolic abnormalities associated with metabolic syndrome and diabetes mellitus (DM), such as monocytes and macrophages, epithelial cells, adipocytes, hepatocytes, skeletal and cardiac myocytes, pancreatic β-cells, kidney glomeruli and tubules cells, pericytes and pigment epithelium cells of the retina, and Schwann cells. These features make CD36 an important component of the pathogenesis of DM and its complications, but also a promising target in the treatment of these disorders. The detrimental effects of CD36 signaling are mediated by the uptake of fatty acids and modified lipoproteins, deposition of lipids and their lipotoxicity, alterations in insulin response and the utilization of energy substrates, oxidative stress, inflammation, apoptosis, and fibrosis leading to the progressive, often irreversible organ dysfunction. This review summarizes the extensive knowledge of the contribution of CD36 to DM and its complications, including nephropathy, retinopathy, peripheral neuropathy, and cardiomyopathy.

Advanced oxidation protein products change biological behaviors of rat endometrial epithelial cells by activating ERK/P38 signaling pathways

Advanced oxidation protein products (AOPPs) are a family of oxidized protein compounds and could induce oxidative stress and inflammatory lesion in various cells. The accumulation of AOPPs was associated with female reproductive diseases such as polycystic ovary syndrome (PCOS), leiomyoma and endometriosis. However, the relationship between AOPPs and endometrial cells is unclear. To explore the effects of accumulated AOPPs on endometrial cells, we treated normal rat endometrial epithelial cells (rEECs) and endometriosis model rats with AOPPs. Primary rEECs were collected from 8-week-old female Wistar rats. Increasing the amount of AOPPs in the media of rEECs enhanced rEEC proliferation and migration, and inhibited apoptosis. Moreover, AOPPs triggered the production of reactive oxygen species and nitrite along with activated ERK and P38 signal and this, in turn, led to an upregulation of proliferation and migration. With the treatment of antioxidants or the inhibitors of ERK and P38, the above effects of AOPPs on rEECs were attenuated. Additionally, in an endometriosis rat model, a similar phenomenon was observed in that the growth of endometriotic implants were promoted by AOPPs and EECs were significantly increased. This study indicated that the accumulation of AOPPs could promote rEEC proliferation and migration through ERK and P38 signal both in vivo and in vitroThis article has an associated First Person interview with the first author of the paper.

Lipotoxicity and Diabetic Nephropathy: Novel Mechanistic Insights and Therapeutic Opportunities

Lipotoxicity is characterized by the ectopic accumulation of lipids in organs different from adipose tissue. Lipotoxicity is mainly associated with dysfunctional signaling and insulin resistance response in non-adipose tissue such as myocardium, pancreas, skeletal muscle, liver, and kidney. Serum lipid abnormalities and renal ectopic lipid accumulation have been associated with the development of kidney diseases, in particular diabetic nephropathy. Chronic hyperinsulinemia, often seen in type 2 diabetes, plays a crucial role in blood and liver lipid metabolism abnormalities, thus resulting in increased non-esterified fatty acids (NEFA). Excessive lipid accumulation alters cellular homeostasis and activates lipogenic and glycogenic cell-signaling pathways. Recent evidences indicate that both quantity and quality of lipids are involved in renal damage associated to lipotoxicity by activating inflammation, oxidative stress, mitochondrial dysfunction, and cell-death. The pathological effects of lipotoxicity have been observed in renal cells, thus promoting podocyte injury, tubular damage, mesangial proliferation, endothelial activation, and formation of macrophage-derived foam cells. Therefore, this review examines the recent preclinical and clinical research about the potentially harmful effects of lipids in the kidney, metabolic markers associated with these mechanisms, major signaling pathways affected, the causes of excessive lipid accumulation, and the types of lipids involved, as well as offers a comprehensive update of therapeutic strategies targeting lipotoxicity.

Identification of key genes, pathways and potential therapeutic agents for IgA nephropathy using an integrated bioinformatics analysis

PURPOSE

This study aims to identify immunoglobulin-A-nephropathy-related genes based on microarray data and to investigate novel potential gene targets for immunoglobulin-A-nephropathy treatment.

METHODS

Immunoglobulin-A-nephropathy chip data was obtained from the Gene Expression Omnibus database, which included 10 immunoglobulin-A-nephropathy and 22 normal samples. We used the limma package of R software to screen differentially expressed genes in immunoglobulin-A-nephropathy and normal glomerular compartment tissues. Functional enrichment (including cellular components, molecular functions, biological processes) and signal pathways were performed for the differentially expressed genes. The online analysis database (STRING) was used to construct the protein-protein interaction networks of differentially expressed genes, and Cytoscape software was used to identify the hub genes of the signal pathway. In addition, we used the Connectivity Map database to predict possible drugs for the treatment of immunoglobulin-A-nephropathy.

RESULTS

A total of 348 differentially expressed genes were screened including 107 up-regulated and 241 down-regulated genes. Functional analysis showed that up-regulated differentially expressed genes were mainly concentrated on leukocyte migration, and the down-regulated differentially expressed genes were significantly enriched in alpha-amino acid metabolic process. A total of six hub genes were obtained: JUN, C3AR1, FN1, AGT, FOS, and SUCNR1. The small-molecule drugs thapsigargin, ciclopirox and ikarugamycin were predicted therapeutic targets against immunoglobulin-A-nephropathy.

CONCLUSION

Differentially expressed genes and hub genes can contribute to understanding the molecular mechanism of immunoglobulin-A-nephropathy and providing potential therapeutic targets and drugs for the diagnosis and treatment of immunoglobulin-A-nephropathy.

[Association of advanced oxidation protein products in seminal plasma with teratospermia and outcome parameters of in vitro fertilization]

OBJECTIVE

To study the association of the level of advanced oxidation protein products (AOPPs) in seminal plasma with teratospermia and the outcome parameters of in vitro fertilization (IVF).

METHODS

We conducted a cross-sectional study among 272 male patients receiving assisted reproduction treatment in the Center for Reproductive Medicine of our hospital between October, 2018 and March, 2019. The levels of seminal AOPPs and reactive oxygen species (ROS), demographic data, sperm parameters and IVF outcome parameters were analyzed for all the patients. According to the percentage of sperms with normal morphology, the patients were divided before IVF into teratozoospermia group and normal sperm morphology group, and those in teratozoospermia group were further divided into 3 subgroups with mild, moderate and severe teratozoospermia. The patients were also divided on the day oocyte retrieval into 2 groups with fertilizing rates lower (group Ⅰ) and higher (group Ⅱ) than the median rate.

RESULTS

We found a significant negative correlation of seminal AOPP level before treatment with the percentage of normal sperm morphology (P=0.003) and seminal ROS level (P=0.013). The seminal levels of AOPPs (P= 0.027) and ROS (P=0.036) were significantly elevated in patients with teratospermia, and seminal AOPP level was significantly higher in severe teratospermia group than in mild (P=0.019) and moderate (P=0.015) teratospermia groups. The seminal levels of AOPPs (P=0.003) and ROS (P=0.017) on the day of oocyte retrieval were negatively correlated with the fertilization rate in IVF cycles, and the levels of AOPPs (P=0.049) and ROS (P=0.036) were significantly higher in group Ⅰ than in group Ⅱ.

CONCLUSIONS

An elevated level of seminal AOPPs may indicate an increased risk of severe teratospermia and a lower fertilization rate in IVF.

Origin and pathophysiology of protein carbonylation, nitration and chlorination in age-related brain diseases and aging

Non-enzymatic protein modifications occur inevitably in all living systems. Products of such modifications accumulate during aging of cells and organisms and may contribute to their age-related functional deterioration. This review presents the formation of irreversible protein modifications such as carbonylation, nitration and chlorination, modifications by 4-hydroxynonenal, removal of modified proteins and accumulation of these protein modifications during aging of humans and model organisms, and their enhanced accumulation in age-related brain diseases.

Advanced oxidation protein products induce G1 phase arrest in intestinal epithelial cells via a RAGE/CD36-JNK-p27kip1 mediated pathway

Intestinal epithelial cell (IEC) cycle arrest has recently been found to be involved in the pathogenesis of Crohn's disease (CD). However, the mechanism underlying the regulation of this form of cell cycle arrest, remains unclear. Here, we investigated the roles that advanced oxidation protein products (AOPPs) may play in regulating IEC cycle arrest. Plasma AOPPs levels and IEC cycle distributions were evaluated in 12 patients with CD. Molecular changes in various cyclins, cyclin-dependent kinases (CDKs), and other regulatory molecules were examined in cultured immortalized rat intestinal epithelial (IEC-6) cells after treatment with AOPPs. The in vivo effects exerted by AOPPs were evaluated using a normal C57BL/6 mouse model with an acute AOPPs challenge. Interestingly, plasma AOPPs levels were elevated in active CD patients and correlated with IEC G1 phase arrest. In addition, IEC treatment with AOPPs markedly reduced the expression of cyclin E and CDK2, thus sensitizing epithelial cells to cell cycle arrest both in vitro and in vivo. Importantly, we found that AOPPs induced IEC G1 phase arrest by modulating two membrane receptors, RAGE and CD36. Furthermore, phosphorylation of c-jun N-terminal kinase (JNK) and the expression of p27kip1 in AOPPs-treated cells were subsequently increased and thus affected cell cycle progression. Our findings reveal that AOPPs influence IEC cycle progression by reducing cyclin E and CDK2 expression through RAGE/CD36-depedent JNK/p27kip1 signaling. Consequently, AOPPs may represent a potential therapeutic molecule. Targeting AOPPs may offer a novel approach to managing CD.

Advanced oxidation protein products play critical roles in liver diseases

There is a complex oxidant and antioxidant system that maintains the redox homoeostasis in the liver. While suffering from exogenous or endogenous risk factors, the balance between oxidants and antioxidants is disturbed and excessive reactive oxygen species are generated, resulting in oxidative stress. Oxidative stress is prevalent in various liver diseases and is thought to be involved in their pathophysiology. Advanced oxidation protein products are generated under conditions of oxidative damage and are newly described protein markers of oxidative stress. Previous studies have underscored the universal pathogenic roles of oxidation protein products in various diseases. However, investigations into how these products participate in the development of liver diseases have been superficial and insufficient. In this review, we highlight the current understanding of the roles of advanced oxidation protein products in liver disease pathogenesis and the underlying mechanisms. Moreover, we summarize the current studies on advanced oxidation protein products in infectious and noninfectious, acute and chronic liver diseases. Different strategies for targeting these advanced oxidation protein products and future perspectives, which may pave the way for developing new therapeutic strategies, will also be discussed here.

Advanced Oxidation Protein Products Aggravate Tubulointerstitial Fibrosis Through Protein Kinase C-Dependent Mitochondrial Injury in Early Diabetic Nephropathy

AIMS

Diabetic nephropathy (DN) is the most common microvascular complications and the principal cause of mortality and morbidity rates in patients with diabetes. The expression of advanced oxidation protein products (AOPPs) has been found in vacuolated renal tubules in DN and correlated with patients' decreased renal function. The accumulation of AOPPs is regarded as an initiating factor in podocyte injuries via the protein kinase C (PKC) signaling, which plays a critical role in triggering oxidative stress and mitochondrial injuries in diseases including DN. Whether AOPPs could induce mitochondrial injuries and fibrosis in renal tubules remains largely unknown. Herein, we tested the hypothesis that the accumulation of AOPPs in diabetes incurs mitochondrial dysfunction and oxidative stress, causing renal tubulointerstitial fibrosis (TIF) via PKC signaling pathway.

RESULTS

In vivo, intrarenal AOPPs accumulation correlated with oxidative stress, renal fibrosis, proteinuria, and declined renal function in DN patients and diabetic rats. AOPPs-induced mitochondrial injuries, apoptosis, and TIF were significantly mitigated by PKCη inhibition in diabetic rats. In vitro, high glucose (HG) stimulated AOPP expression and augmented PKC-mediated oxidative stress and fibrosis in HK-2 cells. Furthermore, we provide mechanistic evidence that inhibition of PKCη isoform alleviated mitochondrial injuries and function, attenuated apoptosis, and renal fibrosis in HG-cultured AOPPs-induced HK-2 cells. Innovation and Conclusion: We propose a novel mechanism that AOPPs-induced mitochondrial dysfunction and oxidative stress cause TIF in DN via activation of the PKCη isoform.

Lipid Metabolism Disorder and Renal Fibrosis

Since the lipid nephrotoxicity hypothesis was proposed in 1982, increasing evidence has supported the hypothesis that lipid abnormalities contributed to the progression of glomerulosclerosis. In this chapter, we will discuss the general promises of the original hypothesis, focusing especially on the role of lipids and metabolic inflammation accompanying CKD in renal fibrosis and potential new strategies of prevention.

Urinary angiotensinogen predicts progressive chronic kidney disease after an episode of experimental acute kidney injury

One of the major obstacles to prevent AKI-CKD transition is the lack of effective methods to follow and predict the ongoing kidney injury after an AKI episode. In the present study, we test the utility of urinary angiotensinogen (UAGT) for dynamically evaluating renal structural changes and predicting AKI-CKD progression by using both mild and severe bilateral renal ischemia/reperfusion injury mice. UAGT returns to pre-ischemic levels 14 days after mild AKI followed by kidney architecture restoration, whereas sustained increase in UAGT accompanies by ongoing renal fibrosis after severe AKI. UAGT at day 14-42 correlates with renal fibrosis 84 days after AKI. For predicting fibrosis at day 84, the area under receiver operating characteristics curve of UAGT at day 14 is 0.81. Persistent elevation in UAGT correlates with sustained activation of intrarenal renin-angiotensin system (RAS) during AKI-CKD transition. Abrogating RAS activation post AKI markedly reduced renal fibrosis, with early RAS intervention (from 14 days after IRI) more beneficial than late intervention (from 42 days after IRI) in alleviating fibrosis. Importantly, UAGT decreases after RAS intervention, and its level at day 14-28 correlates with the extent of renal fibrosis at day 42 post RAS blockade. A pilot study conducted in patients with acute tubular necrosis finds that compared with those recovered, patients with AKI-CKD progression exhibits elevated UAGT during the 3-month follow-up after biopsy. Our study suggests that UAGT enables the dynamical monitoring of renal structural recovery after an AKI episode and may serve as an early predictor for AKI-CKD progression and treatment response.

Melatonin ameliorates intrarenal renin-angiotensin system in a 5/6 nephrectomy rat model

BACKGROUND

Activation of the intrarenal renin-angiotensin system (RAS) plays a critical role in the pathophysiology of chronic kidney disease (CKD) and hypertension. It has been reported that reactive oxygen species (ROS) are important components of intrarenal RAS activation. Melatonin is recognized as a powerful antioxidant, and we recently reported that impaired nighttime melatonin secretion correlates negatively with urinary angiotensinogen excretion, the surrogate marker of intrarenal RAS activity in patients with CKD. However, whether melatonin supplementation ameliorates the augmentation of intrarenal RAS in CKD has remained unknown. We aimed to clarify whether exogenous melatonin ameliorates intrarenal RAS activation via the reduction of ROS production.

METHODS

5/6 Nephrectomized (Nx) rats were used as a chronic progressive CKD model and compared with sham-operated control rats. The Nx rats were divided into untreated Nx rats and melatonin-treated Nx rats. The levels of intrarenal RAS, ROS components, and renal injury were evaluated after 4 weeks of treatment.

RESULTS

Compared with the control rats, the untreated Nx rats exhibited significant increases in intrarenal angiotensinogen, angiotensin II (AngII) type 1 receptors, and AngII, accompanied by elevated blood pressure, higher oxidative stress (8-hydroxy-2'-deoxyguanosine), lower antioxidant (superoxide dismutase) activity, and increased markers of interstitial fibrosis (α-smooth muscle actin, Snail, and type I collagen) in the remnant kidneys. Treatment with melatonin significantly reversed these abnormalities.

CONCLUSION

Antioxidant treatment with melatonin was shown to ameliorate intrarenal RAS activation and renal injury in a 5/6 Nx rat model.

A new model of diabetic nephropathy in C57BL/6 mice challenged with advanced oxidation protein products

There remains a lack of robust mouse models with key features of advanced human diabetic nephropathy (DN). Few options of murine models of DN require mutations to be superimposed to obtain desired phenotypic characteristics. Most genetically modified mice are on the C57BL/6 background; however, they are notorious for resistance to develop DN. To overcome these conundrums, this study reports a novel DN model by challenging with advanced oxidation protein products (AOPPs) in streptozotocin-induced diabetic C57BL/6 mice. AOPPs-challenged diabetic C57BL/6 mice were more sensitive to develop progressive proteinuria, causing a 5.59-fold increase in urine albumin to creatinine ratio as compared to diabetic controls by 24 weeks. Typical lesions were present as demonstrated by significant diffuse mesangial expansion, diffuse podocyte foot process effacement, increased glomerular basement membrane thickness, focal arteriolar hyalinosis, mesangiolysis, and mild interstitial fibrosis. These changes were alleviated by losartan treatment. Collectively, these results suggest that AOPPs can accelerate the progression of DN in the resistant C57BL/6 mouse strain. Our studies offer a novel model for studying the pathogenesis of DN that resembles human diabetic kidney disease. It also makes it possible to interrogate the role of specific genetic modifications and to evaluate novel therapeutics to treat DN in preclinical setting.

Novel RAS Inhibitors Poricoic Acid ZG and Poricoic Acid ZH Attenuate Renal Fibrosis via a Wnt/β-Catenin Pathway and Targeted Phosphorylation of smad3 Signaling

Renal fibrosis is a common end point of the progression of chronic kidney disease (CKD). Suppressing the development and progression of renal fibrosis is essential in the treatment of kidney disease. Our previous study demonstrated that the ethyl acetate extract of the surface layer of Poria cocos exhibited beneficial antitubulointerstitial fibrosis. In this study, we isolated new diterpene (PZF) and triterpenes (PZG and PZH) and examined their antifibrotic effect. TGF-β1 upregulated the collagen I protein expression in HK-2 cells, and PZG and PZH treatment significantly inhibited the upregulated collagen I expression (TGF group 0.59 ± 0.08 vs TGF+PZG group 0.36 ± 0.08, P < 0.01; TGF+PZH group 0.39 ± 0.12, P < 0.01). Triterpenes, PZG and PZH, exhibited a stronger inhibitory effect on renal fibrosis and podocyte injury than PZF. PZG and PZH further showed a stronger inhibitory effect on the activation of the renin-angiotensin system (RAS) than PZF. Additionally, PZG and PZH markedly inhibited the activation of Wnt/β-catenin signaling, which played an important role in fibrogenesis. Interestingly, PZG and PZH suppressed the TGF-β/Smad pathway by selectively inhibiting the phosphorylation of Smad3 through blocking the interactions of SARA with TGFβI and Smad3. The analysis of the structure-activity relationship demonstrated that their antifibrotic effects were closely associated with the first six-membered ring structure and the number of carboxyl groups in this type of compounds. Additionally, fifteen known triterpenes were identified. These novel tetracyclic triterpenoid compounds provided the potential lead compounds for the research and development of antifibrosis drug, and they possessed the potential to be utilized as RAS inhibitors.

Advanced oxidation protein products induce chondrocyte death through a redox-dependent, poly (ADP-ribose) polymerase-1-mediated pathway

This study aimed to investigate the effect of AOPPs on apoptosis in human chondrocytes. Chondrocytes were treated with AOPPs. Cell death, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, reactive oxygen species (ROS) generation, and the expression of apoptotic proteins were detected in vitro. AOPPs levels were detected by colorimetric method. The results in vitro demonstrated that AOPPs induced cell death in human chondrocyte through a redox-dependent pathway, including RAGE-mediated, NADPH oxidase-dependent ROS generation, and poly (ADP-ribose) polymerase-1 (PARP-1) activation. Targeting AOPPs-induced cellular mechanisms might emerge as a promising therapeutic option for patients with RA.

Functional networks of aging markers in the glomeruli of IgA nephropathy: a new therapeutic opportunity

IgA nephropathy(IgAN) is the most common primary glomerular disease in China. Primary infections always occur before IgAN. However, the pathology of IgAN is still unclear. Previously we found that LL37, a protein secreted by senescent cells, was specific for the progression of IgAN, and also played a role in the neutrophil function. So we hypothesized that the infiltration of neutrophils, inflammation factors, and aging markers, which were modulated by functional networks, induced the immune response and renal injury. RNA-Sequencing (RNA-seq) can be used to study the whole transcriptome and detect splicing variants that are expressed in a specific cell type or tissue. We separate glomerulus from the renal biopsy tissues. After RNA extraction, the sequences were analyzed with Illumina HiSeq 2000/2500. 381 genes with differential expression between the IgAN patients and the healthy controls were identified. Only PLAU, JUN, and FOS were related to DNA damage, telomere dysfunction-induced aging markers, neutrophil function and IgA nephropathy. The networks showed the possibility of these genes being connected. We conclude that DNA damage and telomere dysfunction could play important roles in IgA nephropathy. In addition, neutrophils are also important factors in this disease. The networks of these markers showed the mechanism pathways that are involved in the duration of the occurrence and progression of IgA nephropathy and might be a new therapeutic opportunity for disease treatment.

Contrast-Enhanced Ultrasound for Assessing Renal Perfusion Impairment and Predicting Acute Kidney Injury to Chronic Kidney Disease Progression

AIMS

Acute kidney injury (AKI) is increasingly recognized as a major risk factor leading to progression to chronic kidney disease (CKD). However, the diagnostic tools for predicting AKI to CKD progression are particularly lacking. Here, we tested the utility of contrast-enhanced ultrasound (CEUS) for predicting progression to CKD after AKI by using both mild (20-min) and severe (45-min) bilateral renal ischemia-reperfusion injury mice.

RESULTS

Renal perfusion measured by CEUS reduced to 25% ± 7% and 14% ± 6% of the pre-ischemic levels in mild and severe AKI 1 h after ischemia (p < 0.05). Renal perfusion returned to pre-ischemic levels 1 day after mild AKI followed by restoration of kidney function. However, severe AKI caused persistent renal perfusion impairment (60% ± 9% of baseline levels) accompanied by progressive renal fibrosis and sustained decrease in renal function. Renal perfusion at days 1-21 significantly correlated with tubulointerstitial fibrosis 42 days after AKI. For predicting renal fibrosis at day 42, the area under the receiver operating characteristics curve of renal perfusion impairment at day 1 was 0.84. Similar changes in the renal image of CEUS were observed in patients with AKI-CKD progression.

INNOVATION

This study demonstrates that CEUS enables dynamic and noninvasive detection of renal perfusion impairment after ischemic AKI and the perfusion abnormalities shown by CEUS can early predict the progression to CKD after AKI.

CONCLUSIONS

These results indicate that CEUS enables the evaluation of renal perfusion impairment associated with CKD after ischemic AKI and may serve as a noninvasive technique for assessing AKI-CKD progression. Antioxid. Redox Signal. 27, 1397-1411.

Advanced oxidation protein products from the follicular microenvironment and their role in infertile women with endometriosis

Endometriosis (EM) is associated with oxidative stress. Advanced oxidation protein products (AOPPs) are novel markers of oxidative stress, which serve an important role as an inflammatory mediator in various chronic diseases. In order to examine the role of AOPPs in infertile women with EM, the present study analyzed the levels of AOPPs, estradiol (E₂) and progesterone (P₄) in the follicular fluid (FF) of 89 women with or without EM undergoing in vitro fertilization (IVF). The AOPP concentration in the FF of the EM group was significantly higher when compared with that of the control group (51.5±22.4 vs. 41.8±18.3 µmol/l; P<0.05). However, the FF P₄ levels and blastocyst rate were significantly lower in the EM group compared with the control group (P₄:1,249.6±465.4 vs. 1,752.7±565.4 ng/ml, P<0.05; blastocyst rate: 0.511±0.322 vs. 0.662±0.278; P<0.05). The AOPP concentration and P₄ level in the FF presented a significant negative correlation in the EM and control groups, as well as in the total cohort of patients (EM group: r=-0.406, P=0.006; control group: r=-0.315, P=0.035; total: r=-0.421, P<0.001). In addition, there was a significant negative correlation between the FF AOPP concentrations and blastocyst rate in the EM group and in the total cohort (EM group: r=-0.376, P=0.012; total: r=-0.367, P<0.001). In conclusion, these results suggested that AOPPs may be a potentially effective marker for predicting the oocyte quality and outcomes of IVF in infertile women with EM.

Reno-Cerebral Reflex Activates the Renin-Angiotensin System, Promoting Oxidative Stress and Renal Damage After Ischemia-Reperfusion Injury

AIMS

A kidney-brain interaction has been described in acute kidney injury, but the mechanisms are uncertain. Since we recently described a reno-cerebral reflex, we tested the hypothesis that renal ischemia-reperfusion injury (IRI) activates a sympathetic reflex that interlinks the renal and cerebral renin-angiotensin axis to promote oxidative stress and progression of the injury.

RESULTS

Bilateral ischemia-reperfusion activated the intrarenal and cerebral, but not the circulating, renin-angiotensin system (RAS), increased sympathetic activity in the kidney and the cerebral sympathetic regulatory regions, and induced brain inflammation and kidney injury. Selective renal afferent denervation with capsaicin or renal denervation significantly attenuated IRI-induced activation of central RAS and brain inflammation. Central blockade of RAS or oxidative stress by intracerebroventricular (ICV) losartan or tempol reduced the renal ischemic injury score by 65% or 58%, respectively, and selective renal afferent denervation or reduction of sympathetic tone by ICV clonidine decreased the score by 42% or 52%, respectively (all p < 0.05). Ischemia-reperfusion-induced renal damage and dysfunction persisted after controlling blood pressure with hydralazine.

INNOVATION

This study uncovered a novel reflex pathway between ischemic kidney and the brain that sustains renal oxidative stress and local RAS activation to promote ongoing renal damage.

CONCLUSIONS

These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral sympathetic reflex that is activated by ischemia-reperfusion, which contributes to ischemia-reperfusion-induced brain inflammation and worsening of the acute renal injury. Antioxid. Redox Signal. 27, 415-432.

Dioscin induces prostate cancer cell apoptosis through activation of estrogen receptor-β

Recent researches have shown that estrogen receptor-β (ERβ) activator may be a potent anticancer agent for prostate cancer (PCa), and our previous study also indicated that dioscin can upregulate the expression of ERβ in MC3T3-E1 cell. In the present work, the activity and mechanism of dioscin, a natural product, against PCa were investigated. The results showed that dioscin markedly inhibited cell viability, colony formation, motility and induced apoptosis in PC3 cells. Moreover, dioscin disrupted the formation of PC3 cell-derived mammospheres and reduced aldehyde dehydrogenase (ALDH) level and the CD133⁺/CD44⁺ cells, indicating that dioscin had a potent inhibitory activity on prostate cancer stem cells (PCSCs). In vivo results also showed that dioscin significantly suppressed the tumor growth of PC3 cell xenografts in nude mice. Furthermore, mechanism investigation showed that dioscin markedly upregulated ERβ expression level, subsequently increased prolyl hydroxylase 2 level, decreased the levels of hypoxia-inducible factor-1α, vascular endothelial growth factor A and BMI-1, and thus induced cell apoptosis by regulating the expression levels of caspase-3 and Bcl-2 family proteins. In addition, transfection experiment of ERβ-siRNA further indicated that diosicn showed excellent activity against PCa in vitro and in vivo by increasing ERβ expression level. The co-immunoprecipitation (Co-IP) results further suggested that dioscin promoted the interaction of c-ABL and ERβ, but did not change c-ABL expression. Moreover, the molecular docking assay showed that dioscin processed powerful affinity toward to ERβ mainly through the strong hydrogen bonding and hydrophobic effects, and the actions of dioscin on ERβ activation and tumor cells inhibition were significantly weakened in the mutational (Phe-336, Phe-468) PC3 cells. Collectively, these findings proved that dioscin exerted efficient anti-PCa activity via activation of ERβ, which should be developed as an efficient candidate in clinical for treating this cancer in the future.

Advanced oxidation protein products promote NADPH oxidase-dependent β-cell destruction and dysfunction through the Bcl-2/Bax apoptotic pathway

The accumulation of plasma advanced oxidation protein products (AOPPs) has been linked with diverse disorders, including diabetes, chronic kidney disease, obesity, and metabolic syndrome. The aim of the present study was to evaluate the pathophysiological relevance of AOPPs in β-cell destruction and dysfunction. Exposure of cultured rat β-cells (INS-1) to AOPPs induced an increase in Bax expression, caspase-3 activity, and apoptosis as well as a decrease in Bcl-2 expression in a dose- and time-dependent manner. AOPP challenge rapidly increased the production of intracellular superoxide by activation of NADPH oxidases, demonstrated by p47^phox translocation and interaction with p22^phox and gp91^phox, and this in turn led to apoptosis. AOPPs treatment resulted in β-cell apoptosis, AOPPs accumulation, and decreased insulin content in pancreas and plasma in unilateral nephrectomized rats. Chronic inhibition of NADPH oxidase by apocynin prevented β-cell apoptosis and ameliorated insulin deficiency in AOPP-challenged rats. This study demonstrates for the first time that accumulation of AOPPs promotes NADPH oxidase-dependent β-cell destruction and dysfunction by the Bcl-2/Bax-caspase apoptotic pathway. This finding may provide a mechanistic explanation for β-cell destruction and dysfunction in patients with diverse disorders.

Advanced Oxidation Protein Products Induce Epithelial-Mesenchymal Transition of Intestinal Epithelial Cells via a PKC δ-Mediated, Redox-Dependent Signaling Pathway

AIMS

Epithelial-mesenchymal transition (EMT) has been considered a fundamental mechanism in complications of Crohn's disease (CD), especially intestinal fibrosis. However, the mechanism underlying EMT regulation in intestinal fibrosis remains unclear. This study aimed to investigate the role of advanced oxidation protein products (AOPPs) in the occurrence of intestinal EMT.

RESULTS

AOPPs accumulated in CD tissues and were associated with EMT marker expression in fibrotic lesions from CD patients. Challenge with AOPPs induced intestinal epithelial cell (IEC) phenotype transdifferentiation, fibroblast-like phenotype acquisition, and production of extracellular matrix, both in vitro and in vivo. The effect of AOPPs was mainly mediated by a protein kinase C (PKC) δ-mediated redox-dependent pathway, including phosphorylation of PKC δ, recruitment of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, production of reactive oxygen species, and NF-κB p65 activation. Inhibition of AOPP-redox signaling activation effectively blocked AOPP-induced EMT in vitro. Studies performed in normal rats showed that chronic administration of AOPPs triggered the occurrence of EMT in rat intestinal epithelia, accompanied by disruption of intestinal integrity, and by promotion of collagen deposition. These effects could be reversed by inhibition of NADPH oxidase. Innovation and Conclusion: This is the first study to demonstrate that AOPPs triggered the occurrence of EMT in IECs in vitro and in vivo through PKC δ-mediated redox-dependent signaling. Our study identifies the role of AOPPs and, in turn, EMT in intestinal fibrosis and provides novel potential targets for the treatment of intestinal fibrotic diseases. Antioxid. Redox Signal. 27, 37-56.

Fenton Reaction-Generated Advanced Oxidation Protein Products Induces Inflammation in Human Embryonic Kidney Cells

Fenton reaction is a new mechanism able to generate advanced oxidation protein products (AOPPs) by exposing the human serum albumin to the Fenton system. Here, we characterized the effects of Fenton reaction-generated advanced oxidation protein products (AOPP-FR) on the gene transcription of the nuclear factor-κB (NF-κB), cyclooxygenase-2 (COX-2), and interleukin-6 (IL-6) in human embryonic kidney cells (HEK 293). To investigate the effects of AOPP-FR and AOPP-HOCl on transcription of inflammatory genes, the NF-κB, COX-2, and IL-6 luciferase promoter activities were analyzed. AOPP-FR and AOPP-HOCl were able to induce the activation of the gene transcription of NF-κB, COX-2, and IL-6 in HEK 293 cells. However, the effects of AOPP-FR were significantly higher than the effects of AOPP-HOCl in relation to COX-2 and IL-6. AOPP-FR induces the activation of the gene transcription of NF-κB, COX-2, and IL-6 and may represent a novel pathogenic mediator of inflammation in kidney.

Advanced Oxidation Protein Products-Modified Albumin Induces Differentiation of RAW264.7 Macrophages into Dendritic-Like Cells Which Is Modulated by Cell Surface Thiols

Local accumulation of Advanced Oxidation Protein Products (AOPP) induces pro-inflammatory and pro-fibrotic processes in kidneys and is an independent predictor of renal fibrosis and of rapid decline of eGFR in patients with chronic kidney disease (CKD). In addition to kidney damage, circulating AOPP may be regarded as mediators of systemic oxidative stress and, in this capacity, they might play a role in the progression of atherosclerotic damage of arterial walls. Atherosclerosis is a chronic inflammatory disease that involves activation of innate and adaptive immunity. Dendritic cells (DCs) are key cells in this process, due to their role in antigen presentation, inflammation resolution and T cell activation. AOPP consist in oxidative modifications of proteins (such as albumin and fibrinogen) that mainly occur through myeloperoxidase (MPO)-derived hypochlorite (HOCl). HOCl modified proteins have been found in atherosclerotic lesions. The oxidizing environment and the shifts in cellular redox equilibrium trigger inflammation, activate immune cells and induce immune responses. Thus, surface thiol groups contribute to the regulation of immune functions. The aims of this work are: (1) to evaluate whether AOPP-proteins induce activation and differentiation of mature macrophages into dendritic cells in vitro; and (2) to define the role of cell surface thiol groups and of free radicals in this process. AOPP-proteins were prepared by in vitro incubation of human serum albumin (HSA) with HOCl. Mouse macrophage-like RAW264.7 were treated with various concentrations of AOPP-HSA with or without the antioxidant N-acetyl cysteine (NAC). Following 48 h of HSA-AOPP treatment, RAW264.7 morphological changes were evaluated by microscopic observation, while markers of dendritic lineage and activation (CD40, CD86, and MHC class II) and allogeneic T cell proliferation were evaluated by flow cytometry. Cell surface thiols were measured by AlexaFluor-maleimide binding, and ROS production was assessed as DCF fluorescence by flow cytometry. HSA-AOPP induced the differentiation of RAW264.7 cells into a dendritic-like phenotype, as shown by morphological changes, by increased CD40, CD86 and MHC class II surface expression and by induction of T cell proliferation. The cell surface thiols dose dependently decreased following HSA-AOPP treatment, while ROS production increased. NAC pre-treatment enhanced the amount of cell surface thiols and prevented their reduction due to treatment with AOPP. Both ROS production and RAW264.7 differentiation into DC-like cells induced by HSA-AOPP were reduced by NAC. Our results highlight that oxidized plasma proteins modulate specific immune responses of macrophages through a process involving changes in the thiol redox equilibrium. We suggest that this mechanism may play a role in determining the rapid progression of the atherosclerotic process observed in CKD patients.

Wnt/β-catenin signaling and renin-angiotensin system in chronic kidney disease

PURPOSE OF REVIEW

Intrarenal activation of the renin-angiotensin system (RAS) plays an essential role in the pathogenesis of hypertension and chronic kidney diseases (CKD). However, how RAS genes are regulated in vivo was poorly understood until recently. This review focuses on recent findings of the transcriptional regulation of RAS components, as well as their implication in developing novel strategies to treat the patients with CKD.

RECENT FINDINGS

Bioinformatics analyses have uncovered the presence of putative binding sites for T-cell factor/β-catenin in the promoter region of all RAS genes. Both in-vitro and in-vivo studies confirm that Wnt/β-catenin is the master upstream regulator that controls the expression of all RAS components tested, such as angiotensinogen, renin, angiotensin converting enzyme and the angiotensin II type I receptor in the kidney. Targeted inhibition of Wnt/β-catenin, by either small molecule ICG-001 or endogenous Wnt antagonist Klotho, represses RAS activation and ameliorates proteinuria and kidney injury. Blockade of Wnt/β-catenin signaling also normalizes blood pressure in a mouse model of CKD.

SUMMARY

These recent studies identify Wnt/β-catenin as the master regulator that controls multiple RAS genes, and suggest that targeting this upstream signaling could be an effective strategy for the treatment of patients with hypertension and CKD.

Oxidized plasma albumin promotes platelet-endothelial crosstalk and endothelial tissue factor expression

Plasma advanced oxidation protein products (AOPPs), a class of pro-inflammatory pathogenic mediators, accumulate in subjects with chronic kidney disease. Whether AOPPs contribute to coagulation abnormalities, which are frequently seen in uremic patients, is unknown. Here we report that AOPPs activate platelets via a CD36-mediated signaling pathway. Activation of signaling pathways by AOPP-platelet interaction resulted in the expression of several platelet activation markers and rapidly induced the expression of CD40 ligand, triggering platelet adhesion to endothelial cells and promoting endothelial tissue factor expression. AOPPs and serum tissue factor levels were considerably increased in end stage renal disease patients on hemodialysis and a significant correlation of AOPPs and serum tissue factor was found. Interestingly, serum levels of AOPPs and tissue factor were substantially lower in stable kidney transplant patients when compared with hemodialysis patients. Given that CD36 is known to transduce the effects of oxidized lipids into platelet hyperactivity, our findings reveal previously unknown pro-thrombotic activities of oxidized plasma albumin via a CD36 dependent pathway.

Klotho Ameliorates Kidney Injury and Fibrosis and Normalizes Blood Pressure by Targeting the Renin-Angiotensin System

Loss of Klotho and activation of the renin-angiotensin system (RAS) are common pathological findings in chronic kidney diseases. However, whether these two events are intricately connected is poorly understood. We hypothesized that Klotho might protect kidneys by targeted inhibition of RAS activation in diseased kidneys. To test this hypothesis, mouse models of remnant kidney, as well as adriamycin nephropathy and unilateral ureteral obstruction, were utilized. At 6 weeks after 5/6 nephrectomy, kidney injury was evident, characterized by elevated albuminuria and serum creatinine levels, and excessive deposition of interstitial matrix proteins. These lesions were accompanied by loss of renal Klotho expression, up-regulation of RAS components, and development of hypertension. In vivo expression of exogenous Klotho through hydrodynamic-based gene delivery abolished the induction of multiple RAS proteins, including angiotensinogen, renin, angiotensin-converting enzyme, and angiotensin II type 1 receptor, and normalized blood pressure. Klotho also inhibited β-catenin activation and ameliorated renal fibrotic lesions. Similar results were obtained in mouse models of adriamycin and obstructive nephropathy. In cultured kidney tubular epithelial cells, Klotho dose-dependently blocked Wnt1-triggered RAS activation. Taken together, these results demonstrate that Klotho exerts its renal protection by targeted inhibition of RAS, a pathogenic pathway known to play a key role in the evolution and progression of hypertension and chronic kidney disorders.

Olmesartan protects endothelial cells against oxidative stress-mediated cellular injury

BACKGROUND

The primary cause of death of hemodialysis (HD) patients is cardiovascular disease, and increased oxidative stress has been proposed to be involved in the disease pathogenesis. In this study, we examined the effect of olmesartan on oxidative stress induced by angiotensin II, lipopolysaccharide, indoxyl sulfate, advanced oxidation protein products (AOPP) or hydrogen peroxide (H2O2), which are known to be present at higher concentrations in the blood of HD patients, using human umbilical vein endothelial cells (HUVECs).

METHODS

Oxidative stress was evaluated by measuring the mean fluorescence intensity of CM-H2DCFCA, an ROS-sensitive fluorescent dye, in HUVECs. HUVECs were incubated with each of the above compounds in the presence or absence of olmesartan. Moreover, these oxidant-stimulated cells were also treated with the reactive oxygen species (ROS) inhibitor N-acetyl-cysteine (NAC), NADPH oxidase inhibitor diphenylene iodonium (DPI) or PKC inhibitor calphostin C. In addition, we investigated the effects of olmesartan on cytotoxicity and vascular endothelial growth factor (VEGF) secretion, which is involved in vascular inflammation in HUVECs induced by AOPP or H2O2.

RESULTS

The treatment of these oxidant-stimulated cells with olmesartan resulted in a significant reduction in intracellular ROS production to an extent that was nearly equivalent to that of NAC, DPI or calphostin C. Furthermore, olmesartan reduced the cytotoxicity and VEGF secretion induced by AOPP or H2O2.

CONCLUSIONS

These results demonstrated that the antioxidant activity of olmesartan might contribute to both its vasculoprotective and anti-hypertensive effects.

Soluble CD36 in plasma and urine: a plausible prognostic marker for diabetic nephropathy

AIMS

This study was designed to analyze the level of soluble CD36 (sCD36) in both plasma and urine of type 2 diabetic patients with and without microalbuminuria/macroalbuminuria.

METHODS

Study subjects (n=20 each) comprised of those with normal glucose tolerance, type 2 diabetes (T2DM) with normoalbuminiria, T2DM with microalbuminuria and T2DM with macroalbuminuria. The biochemical parameters were analyzed using auto-analyzer, and the level of sCD36 was estimated using an in-house Sandwich ELISA.

RESULTS

The presence of sCD36 has been identified for the first time in the urine sample. Significant increase in the level of sCD36 was observed in both plasma and urine of diabetic patients with microalbuminuria (P<0.01) and macroalbuminuria (P<0.001). Positive correlation of sCD36 with the kidney markers such as urea, creatinine and eGFR confirmed the association of sCD36 with kidney damage in diabetic patients. Microalbuminuria, which is clinically used as a biomarker for nephropathy showed a strong positive correlation with urine sCD36 (r=0.642; P<0.001) and plasma sCD36 (r=0.498; P<0.001) in Pearson correlation analysis, which was further substantiated in stepwise multiple regression analysis.

CONCLUSIONS

Our study implies a plausible prognostic/adjuvant biomarker role of soluble CD36 for diabetic nephropathy.