Upregulation of mitochondrial Nox4 mediates TGF-β-induced apoptosis in cultured mouse podocytes

The role of mitochondrial dysfunction in kidney injury and disease

Mitochondria are the main sites of aerobic respiration in the cell and mainly provide energy for the organism, and play key roles in adenosine triphosphate (ATP) synthesis, metabolic regulation, and cell differentiation and death. Mitochondrial dysfunction has been identified as a contributing factor to a variety of diseases. The kidney is rich in mitochondria to meet energy needs, and stable mitochondrial structure and function are essential for normal kidney function. Recently, many studies have shown a link between mitochondrial dysfunction and kidney disease, maintaining mitochondrial homeostasis has become an important target for kidney therapy. In this review, we integrate the role of mitochondrial dysfunction in different kidney diseases, and specifically elaborate the mechanism of mitochondrial reactive oxygen species (mtROS), autophagy and ferroptosis involved in the occurrence and development of kidney diseases, providing insights for improved treatment of kidney diseases.

Amifostine ameliorates bleomycin-induced murine pulmonary fibrosis via NAD+/SIRT1/AMPK pathway-mediated effects on mitochondrial function and cellular metabolism

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a devastating chronic lung disease characterized by irreversible scarring of the lung parenchyma. Despite various interventions aimed at mitigating several different molecular aspects of the disease, only two drugs with limited clinical efficacy have so far been approved for IPF therapy.

OBJECTIVE

We investigated the therapeutic efficacy of amifostine, a detoxifying drug clinically used for radiation-caused cytotoxicity, in bleomycin-induced murine pulmonary fibrosis.

METHODS

C57BL6/J mice were intratracheally instilled with 3 U/kg of bleomycin. Three doses of amifostine (WR-2721, 200 mg/kg) were administered intraperitoneally on days 1, 3, and 5 after the bleomycin challenge. Bronchoalveolar lavage fluid (BALF) was collected on day 7 and day 21 for the assessment of lung inflammation, metabolites, and fibrotic injury. Human fibroblasts were treated in vitro with transforming growth factor beta 1 (TGF-β1), followed by amifostine (WR-1065, 1-4 µg/mL) treatment. The effects of TGF-β1 and amifostine on the mitochondrial production of reactive oxygen species (ROS) were assessed by live cell imaging of MitoSOX. Cellular metabolism was assessed by the extracellular acidification rate (ECAR), the oxygen consumption rate (OCR), and the concentrations of various energy-related metabolites as measured by mass spectrum (MS). Western blot analysis was performed to investigate the effect of amifostine on sirtuin 1 (SIRT1) and adenosine monophosphate activated kinase (AMPK).

RESULTS

Three doses of amifostine significantly attenuated lung inflammation and pulmonary fibrosis. Pretreatment and post-treatment of human fibroblast cells with amifostine blocked TGF-β1-induced mitochondrial ROS production and mitochondrial dysfunction in human fibroblast cells. Further, treatment of fibroblasts with TGF-β1 shifted energy metabolism away from mitochondrial oxidative phosphorylation (OXPHOS) and towards glycolysis, as observed by an altered metabolite profile including a decreased ratio of NAD + /NADH and increased lactate concentration. Treatment with amifostine significantly restored energy metabolism and activated SIRT1, which in turn activated AMPK. The activation of AMPK was required to mediate the effects of amifostine on mitochondrial homeostasis and pulmonary fibrosis. This study provides evidence that repurposing of the clinically used drug amifostine may have therapeutic applications for IPF treatment.

CONCLUSION

Amifostine inhibits bleomycin-induced pulmonary fibrosis by restoring mitochondrial function and cellular metabolism.

Folic acid antioxidant supplementation to binge drinking adolescent rats improves hydric-saline balance and blood pressure, but fails to increase renal NO availability and glomerular filtration rate

Binge drinking (BD) is an especially pro-oxidant pattern of alcohol consumption, particularly widespread in the adolescent population. In the kidneys, it affects the glomerular filtration rate (GFR), leading to high blood pressure. BD exposure also disrupts folic acid (FA) homeostasis and its antioxidant properties. The aim of this study is to test a FA supplementation as an effective therapy against the oxidative, nitrosative, and apoptotic damage as well as the renal function alteration occurred after BD in adolescence. Four groups of adolescent rats were used: control, BD (exposed to intraperitoneal alcohol), control FA-supplemented group and BD FA-supplemented group. Dietary FA content in control groups was 2 ppm, and 8 ppm in supplemented groups. BD provoked an oxidative imbalance in the kidneys by dysregulating antioxidant enzymes and increasing the enzyme NADPH oxidase 4 (NOX4), which led to an increase in caspase-9. BD also altered the renal nitrosative status affecting the expression of the three nitric oxide (NO) synthase (NOS) isoforms, leading to a decrease in NO levels. Functionally, BD produced a hydric-electrolytic imbalance, a low GFR and an increase in blood pressure. FA supplementation to BD adolescent rats improved the oxidative, nitrosative, and apoptotic balance, recovering the hydric-electrolytic equilibrium and blood pressure. However, neither NO levels nor GFR were recovered, showing in this study for the first time that NO availability in the kidneys plays a crucial role in GFR regulation that the antioxidant effects of FA cannot repair.

MAGI2 ameliorates podocyte apoptosis of diabetic kidney disease through communication with TGF-β-Smad3/nephrin pathway

Podocytes, the key component of the glomerular filtration barrier (GFB), are gradually lost during the progression of diabetic kidney disease (DKD), severely compromising kidney functionality. The molecular mechanisms regulating the survival of podocytes in DKD are incompletely understood. Here, we show that membrane-associated guanylate kinase inverted 2 (MAGI2) is specifically expressed in renal podocytes, and promotes podocyte survival in DKD. We found that MAGI2 expression was downregulated in podocytes cultured with high-glucose in vitro, and in kidneys of db/db mice as well as DKD patients. Conversely, we found enforced expression of MAGI2 via AAV transduction protected podocytes from apoptosis, with concomitant improvement of renal functions. Mechanistically, we found that MAGI2 deficiency induced by high glucose levels activates TGF-β signaling to decrease the expression of anti-apoptotic proteins. These results indicate that MAGI2 protects podocytes from cell death, and can be harnessed therapeutically to improve renal function in diabetic kidney disease.

Comprehensive analysis of the relationship between xanthine oxidoreductase activity and chronic kidney disease

Chronic kidney disease (CKD) is a common disease that seriously endangers human health. However, the potential relationship between xanthine oxidoreductase (XOR) activity and CKD remains unclear. In this study, we used clinical data, CKD datasets from the Gene Expression Omnibus database, and untargeted metabolomics to explain the relationship between XOR activity and CKD. First, XOR activity showed high correlation with the biomarkers of CKD, such as serum creatinine, blood urea nitrogen, uric acid, and estimated glomerular filtration rate. Then, we used least absolute shrinkage and selection operator logical regression algorithm and random forest algorithm to screen CKD molecular markers from differentially expressed genes, and the results of qRT-PCR of XDH, KOX-1, and ROMO1 were in accordance with the results of bioinformatics analyses. In addition, untargeted metabolomics analysis revealed that the purine metabolism pathway was significantly enriched in CKD patients in the simulated models of kidney fibrosis.

Biofactors regulating mitochondrial function and dynamics in podocytes and podocytopathies

Podocytes are terminally differentiated kidney cells acting as the main gatekeepers of the glomerular filtration barrier; hence, inhibiting proteinuria. Podocytopathies are classified as kidney diseases caused by podocyte damage. Different genetic and environmental risk factors can cause podocyte damage and death. Recent evidence shows that mitochondrial dysfunction also contributes to podocyte damage. Understanding alterations in mitochondrial metabolism and function in podocytopathies and whether altered mitochondrial homeostasis/dynamics is a cause or effect of podocyte damage are issues that need in-depth studies. This review highlights the roles of mitochondria and their bioenergetics in podocytes. Then, factors/signalings that regulate mitochondria in podocytes are discussed. After that, the role of mitochondrial dysfunction is reviewed in podocyte injury and the development of different podocytopathies. Finally, the mitochondrial therapeutic targets are considered.

COL4A3 Mutation Induced Podocyte Apoptosis by Dysregulation of NADPH Oxidase 4 and MMP-2

Introduction

Podocyte apoptosis is a common mechanism driving progression in Alport syndrome (AS). This study aimed to investigate the mechanism of podocyte apoptosis caused by COL4A3 mutations.

Methods

We recruited patients with autosomal dominant AS (ADAS). Patients with minimal change disease (MCD) were recruited as controls. Microarray analysis was carried out on isolated glomeruli from the patients and validated. Then, corresponding mutant human podocytes (p.C1616Y) and 129 mice (p.C1615Y, the murine homolog to the human p.C1616Y) were constructed. The highest differentially expressed genes (DEGs) from microarray analysis were validated in transgenic mice and podocytes before and after administration of MMP-2 inhibitor (SB-3CT) and NOX4 inhibitor (GKT137831). We further validated NOX4/MMP-2/apoptosis pathway by real-time polymerase chain reaction (PCR), immunohistochemistry, and western blot in renal tissues from the ADAS patients.

Results

Using microarray analysis, we observed that DEGs, including NOX4/H2O2, MMP-2, and podocyte apoptosis-related genes were significantly upregulated. These genes were validated by real-time PCR, histologic analysis, and western blot in corresponding mutant human podocyte (p.C1616Y) and/or mice models (p.C1615Y). Moreover, we found podocyte apoptosis was abrogated and MMP-2 expression was down-regulated both in vivo and in vitro by NOX4 inhibition, urinary albumin-to-creatinine ratio, 24-hour proteinuria; and renal pathologic lesion was attenuated by NOX4 inhibition in vivo. Furthermore, podocyte apoptosis was attenuated whereas NOX4 expression remained the same by inhibition of MMP-2 both in vivo and in vitro.

Conclusion

These results indicated that NOX4 might induce podocyte apoptosis through the regulation of MMP-2 in patients with COL4A3 mutations. Our findings provided new insights into the mechanism of ADAS.

Sodium butyrate enhances titanium nail osseointegration in ovariectomized rats by inhibiting the PKCα/NOX4/ROS/NF-κB pathways

BACKGROUND

Elevated levels of oxidative stress as a consequence of estrogen deficiency serve as a key driver of the onset of osteoporosis (OP). In addition to increasing the risk of bone fractures, OP can reduce the bone volume proximal to titanium nails implanted to treat these osteoporotic fractures, thereby contributing to titanium nail loosening. Sodium butyrate (NaB) is a short-chain fatty acid produced by members of the gut microbiota that exhibits robust antioxidant and anti-inflammatory properties.

METHODS

OP fracture model rats parameters including bone mineral density (BMD), new bone formation, and the number of bonelets around the implanted nail were analyzed via micro-CT scans, H&E staining, and Masson's staining. The protective effects of NaB on such osseointegration and the underlying mechanisms were further studied in vitro using MC3T3-E1 cells treated with carbonyl cyanide m-chlorophenylhydrazone (CCCP) to induce oxidative stress. Techniques including Western immunoblotting, electron microscopy, flow cytometry, alkaline phosphatase (ALP) staining, and osteoblast mineralization assays were employed to probe behaviors such as reactive oxygen species production, mineralization activity, ALP activity, protein expression, and the ability of cells to attach to and survive on titanium plates.

RESULTS

NaB treatment was found to enhance ALP activity, mineralization capacity, and Coll-I, BMP2, and OCN expression levels in CCCP-treated MC3T3-E1 cells, while also suppressing PKC and NF-κB expression and enhancing Nrf2 and HO-1 expression in these cells. NaB further suppressed intracellular ROS production and malondialdehyde levels within the cytosol while enhancing superoxide dismutase activity and lowering the apoptotic death rate. In line with these results, in vivo work revealed an increase in BMD in NaB-treated rats that was associated with enhanced bone formation surrounding titanium nails.

CONCLUSION

These findings indicate that NaB may represent a valuable compound that can be postoperatively administered to aid in treating OP fractures through the enhancement of titanium nail osseointegration.

Perfluorooctane sulfonate-induced apoptosis in kidney cells by triggering the NOX4/ROS/JNK axis and antagonism of cannabidiol

Perfluorooctane sulfonate (PFOS) is one of the persistent organic pollutants (POPs), which can cause severe nephrotoxicity in mammals. Cannabinol (CBD), a nonpsychoactive cannabinoid obtained from the cannabis plant, has attracted attention in recent years for its excellent antioxidant properties. NADPH oxidase 4 (NOX4) has an important effect in supporting normal renal physiological function. The potential mechanisms of PFOS nephrotoxicity and whether CBD can prevent renal damage caused by PFOS remain unclear. This work aimed to study the mechanisms of PFOS-induced kidney damage and the protective role of CBD against PFOS-induced kidney damage. We demonstrated that PFOS led to renal insufficiency and structural damage in mice, induced overexpression of NOX4 and the onset of oxidative stress, and activated apoptosis of the mitochondrial pathway via the JNK signaling pathway. However, treatment with CBD reversed these changes. For further investigation of the potential mechanism of PFOS-induced renal cell apoptosis, the expression of NOX4 was inhibited in vitro experiments using Apocynin, an effective NOX4 inhibitor. The outcomes showed that PFOS-induced ROS production and JNK signaling pathway activation and apoptosis in human embryonic kidney (HEK293) cells were significantly reduced after inhibition of NOX4. This suggests that PFOS-induced NOX4 overexpression serves as an upstream event for JNK pathway activation. In conclusion, the findings suggest that PFOS induces apoptosis in renal cells via the NOX4/ROS/JNK pathway. Meanwhile, CBD alleviated PFOS-induced renal apoptosis through the inhibition of NOX4/ROS/JNK axis activation.

Nox4 as a novel therapeutic target for diabetic vascular complications

Diabetic vascular complications can affect both microvascular and macrovascular. Diabetic microvascular complications, such as diabetic nephropathy, diabetic retinopathy, diabetic neuropathy, and diabetic cardiomyopathy, are believed to be caused by oxidative stress. The Nox family of NADPH oxidases is a significant source of reactive oxygen species and plays a crucial role in regulating redox signaling, particularly in response to high glucose and diabetes mellitus. This review aims to provide an overview of the current knowledge about the role of Nox4 and its regulatory mechanisms in diabetic microangiopathies. Especially, the latest novel advances in the upregulation of Nox4 that aggravate various cell types within diabetic kidney disease will be highlighted. Interestingly, this review also presents the mechanisms by which Nox4 regulates diabetic microangiopathy from novel perspectives such as epigenetics. Besides, we emphasize Nox4 as a therapeutic target for treating microvascular complications of diabetes and summarize drugs, inhibitors, and dietary components targeting Nox4 as important therapeutic measures in preventing and treating diabetic microangiopathy. Additionally, this review also sums up the evidence related to Nox4 and diabetic macroangiopathy.

Non-Haemodynamic Mechanisms Underlying Hypertension-Associated Damage in Target Kidney Components

Arterial hypertension (AH) is a global challenge that greatly impacts cardiovascular morbidity and mortality worldwide. AH is a major risk factor for the development and progression of kidney disease. Several antihypertensive treatment options are already available to counteract the progression of kidney disease. Despite the implementation of the clinical use of renin-angiotensin aldosterone system (RAAS) inhibitors, gliflozins, endothelin receptor antagonists, and their combination, the kidney damage associated with AH is far from being resolved. Fortunately, recent studies on the molecular mechanisms of AH-induced kidney damage have identified novel potential therapeutic targets. Several pathophysiologic pathways have been shown to play a key role in AH-induced kidney damage, including inappropriate tissue activation of the RAAS and immunity system, leading to oxidative stress and inflammation. Moreover, the intracellular effects of increased uric acid and cell phenotype transition showed their link with changes in kidney structure in the early phase of AH. Emerging therapies targeting novel disease mechanisms could provide powerful approaches for hypertensive nephropathy management in the future. In this review, we would like to focus on the interactions of pathways linking the molecular consequences of AH to kidney damage, suggesting how old and new therapies could aim to protect the kidney.

Myostatin silencing inhibits podocyte apoptosis in membranous nephropathy through Smad3/PKA/NOX4 signaling pathway

This article focuses on deciphering the effect of myostatin (MSTN) on podocyte apoptosis in membranous nephropathy (MN) and fathoming out its underlying mechanism. Rats received the intravenous injection of cationized-bovine serum albumin to induce MN in vivo, while angiotensin II (Ang II) was exposed to AB8/13 cells to induce MN model in vitro. The mRNA expression of MSTN was detected by qRT-PCR. The effects of MSTN silencing on MN model rats and cells were assessed by cell counting kit-8 assay, flow cytometry, hematoxylin and eosin staining, and TUNEL assay. The expressions of proteins related to apoptosis and Smad3/protein kinase A (PKA)/NADPH oxidase 4 (NOX4) signaling pathway were examined by western blot. As a result, MSTN was highly expressed in MN cell and rat models. Besides, knockdown of MSTN elevated the MN cell viability and dwindled apoptosis rate, as well as attenuated kidney injury in MN rats. Meanwhile, MSTN silencing lessened the expressions of phosphorylated (p)-Smad3 and Nox4, while boosting the p-PKA expression in MN rats and cells. Additionally, Smad3 overexpression reversed the above effects of MSTN silencing on Ang II-induced podocytes. In conclusion, MSTN knockdown restrains the podocyte apoptosis through regulating Smad3/PKA/NOX4 signaling pathway.

The association between renal accumulation of pancreatic amyloid-forming amylin and renal hypoxia

Chronic kidney disease (CKD) is increasing worldwide and is associated with diabetic states (obesity, prediabetes and type-2 diabetes mellitus). The kidney is intrinsically susceptible to low oxygen (hypoxia) and renal hypoxia plays a vital role in the progression of CKD. Recent studies suggest an association between CKD and renal deposition of amyloid-forming amylin secreted from the pancreas. Renal accumulation of amyloid-forming amylin is associated with hypertension, mitochondrial dysfunction, increased production of reactive oxygen species (ROS) and activation of hypoxia signaling in the kidney. In this review we will discuss potential associations between renal amylin amyloid accumulation, hypertension, and mechanism of hypoxia-induced kidney dysfunction, including activation of hypoxia-inducible factors (HIFs) and mitochondrial dysfunction.

Signaling Pathways of Podocyte Injury in Diabetic Kidney Disease and the Effect of Sodium-Glucose Cotransporter 2 Inhibitors

Diabetic kidney disease (DKD) is one of the most important comorbidities for patients with diabetes, and its incidence has exceeded one tenth, with an increasing trend. Studies have shown that diabetes is associated with a decrease in the number of podocytes. Diabetes can induce apoptosis of podocytes through several apoptotic pathways or induce autophagy of podocytes through related pathways. At the same time, hyperglycemia can also directly lead to apoptosis of podocytes, and the related inflammatory reactions are all harmful to podocytes. Podocyte damage is often accompanied by the production of proteinuria and the progression of DKD. As a new therapeutic agent for diabetes, sodium-glucose cotransporter 2 inhibitors (SGLT2i) have been demonstrated to be effective in the treatment of diabetes and the improvement of terminal outcomes in many rodent experiments and clinical studies. At the same time, SGLT2i can also play a protective role in diabetes-induced podocyte injury by improving the expression of nephrotic protein defects and inhibiting podocyte cytoskeletal remodeling. Some studies have also shown that SGLT2i can play a role in inhibiting the apoptosis and autophagy of cells. However, there is no relevant study that clearly indicates whether SGLT2i can also play a role in the above pathways in podocytes. This review mainly summarizes the damage to podocyte structure and function in DKD patients and related signaling pathways, as well as the possible protective mechanism of SGLT2i on podocyte function.

Complanatoside A targeting NOX4 blocks renal fibrosis in diabetic mice by suppressing NLRP3 inflammasome activation and autophagy

BACKGROUND

Diabetic nephropathy (DN) is an important cause of end-stage renal disease. Complanatoside A (CA), an active component from Semen Astragali Complanati, has been reported to be a potential candidate for the treatment of kidney diseases. However, the underlying mechanisms and protective effects of CA in DN remain unclear.

PURPOSE

In this paper, the effects and the mechanism of CA against ameliorating DN were investigated in vivo and in vitro.

STUDY DESIGN

Here, a high-fat diet/streptozotocin-induced diabetic model and TGF-β1-induced HK-2 cells were used to explore the protective effects and mechanisms of CA on DN in vivo and in vitro.

METHODS

Major biochemical indexes, Histopathological morphology, and Immunohistochemistry have explored the therapeutic effect of CA on DN. Subsequently, TGF-β1-induced HK-2 cells were utilized to investigate the anti-renal fibrosis effect of CA. Finally, the mechanism of CA against renal fibrosis was studied via western blotting, immunofluorescence, transfection, and molecular docking.

RESULTS

The results showed that CA attenuated glomerular hypertrophy, collagen matrix deposition, and tubular interstitial fibrosis in diabetic mice. Moreover, the activation of TGF-β1-inducible epithelial-mesenchymal transition (EMT) was hindered by CA treatment in HK-2 cells. Mechanistically, the data suggested that upregulated NOX4 during diabetes and TGF-β1 in HK-2 cells was prominently diminished after CA treatment. Furthermore, CA exposure inhibited NLRP3 inflammasome activation and downstream inflammation gene expression such as IL-18 and IL-1β in vivo and vitro. These findings indicated that CA obstructed the EMT to protect renal tubular epithelial cells against fibrosis via blocking NLRP3 activation, which was associated with inhibiting NOX4. Besides, the markedly raised autophagy levels in the diabetic model characterized by increasing LC3II/LC3I and Beclin1 were reversed after CA treatment, which is also a pivotal mechanism against renal fibrosis. More importantly, specific NOX4 overexpressed in HK-2 cells abolished that CA exposure blocked TGF-β1-induced-EMT, ROS generation, NLRP3, and autophagy activation. Meanwhile, the inhibition of cell migration, ROS generation, autophagy, and renal inflammation after CA treatment was more pronounced in NOX4-deficient HK-2 cells.

CONCLUSION

Our findings provided evidence that CA might be a potential therapeutic agent for DN by ameliorating NLRP3 inflammasome and autophagy activation via targeting NOX4 inhibition.

SB431542 alleviates lupus nephritis by regulating B cells and inhibiting the TLR9/TGFβ1/PDGFB signaling

Lupus nephritis (LN) is the most common cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Currently, immunosuppressive treatments for LN are suboptimal and can induce significant side effects. SB431542 is a selective and potent inhibitor of the TGFβ/Activin/NODAL pathway. Here, we study the effects of SB431542 treatment on LN and discuss the potential mechanisms. SB431542 ameliorated clinical outcomes with a consequent histological improvement in NZB/W mice. A comparative transcriptional profiling analysis revealed 586 differentially expressed genes (247 downregulated genes) in the SB431542 group compared to the control group. We found that the downregulated genes were mainly enriched in the biological processes of B cell activation, B cell proliferation, B cell differentiation, and B cell receptor signaling. Kyoto encyclopedia of genes and genomes pathway analysis revealed that the hematopoietic cell linage pathway was significantly downregulated in the SB431542 group. In addition, we observed that SB431542 reduced the splenic or renal levels of CD20 and the serum levels of anti-dsDNA antibody (IgG) in NZB/W mice. Furthermore, qRT-PCR and immunohistochemistry confirmed that SB431542 inhibits the production of TLR9, TGFβ1, and PDGFB. Thus, due to its immunomodulatory activities, SB431542 could be considered for clinical therapy development for LN.

Renin‑angiotensin system inhibitors may have an advantage over calcium channel blockers in reducing proteinuria in gastric cancer patients receiving ramucirumab

This study aimed to investigate whether renin-angiotensin system inhibitors (RAS-I) have an advantage over calcium channel blockers (CCB) for suppression of proteinuria in hypertensive patients with gastric cancer receiving ramucirumab (RAM) treatment. Adult Japanese patients with gastric cancer who were outpatients at Asahikawa Medical University Hospital, National Hospital Organization Hokkaido Cancer Center, and Iwate Medical University Hospital between July 1, 2015, and March 31, 2021, were included in this study. Of these patients, those who had received first-time RAM treatment, and those treated with antihypertensive agents including RAS-I or a CCB at initial RAM administration were included. A total of 36 patients were analyzed in this study. Of these patients, 17 patients were classified into the RAS-I group and the remaining 19 into the CCB group. After 12 weeks of RAM administration, the prevalence of proteinuria in the RAS-I group was significantly lower than that in the CCB group. Additionally, Kaplan-Meier analysis showed that the cumulative occurrence of proteinuria in the RAS-I group over 12 weeks following RAM administration was significantly lower than that in the CCB group. Furthermore, simulation of the time course of RAM blood concentrations based on the O'Brien model showed that there may not be differences in the RAM blood concentration profiles over 12 weeks between the two groups. RAS-I may have an advantage over CCB for suppressing proteinuria in hypertensive patients with gastric cancer treated with blood pressure antihypertensive agents. Our results provide useful information to healthcare professionals involved in the administration of RAM treatment.

Signaling pathways of chronic kidney diseases, implications for therapeutics

Chronic kidney disease (CKD) is a chronic renal dysfunction syndrome that is characterized by nephron loss, inflammation, myofibroblasts activation, and extracellular matrix (ECM) deposition. Lipotoxicity and oxidative stress are the driving force for the loss of nephron including tubules, glomerulus, and endothelium. NLRP3 inflammasome signaling, MAPK signaling, PI3K/Akt signaling, and RAAS signaling involves in lipotoxicity. The upregulated Nox expression and the decreased Nrf2 expression result in oxidative stress directly. The injured renal resident cells release proinflammatory cytokines and chemokines to recruit immune cells such as macrophages from bone marrow. NF-κB signaling, NLRP3 inflammasome signaling, JAK-STAT signaling, Toll-like receptor signaling, and cGAS-STING signaling are major signaling pathways that mediate inflammation in inflammatory cells including immune cells and injured renal resident cells. The inflammatory cells produce and secret a great number of profibrotic cytokines such as TGF-β1, Wnt ligands, and angiotensin II. TGF-β signaling, Wnt signaling, RAAS signaling, and Notch signaling evoke the activation of myofibroblasts and promote the generation of ECM. The potential therapies targeted to these signaling pathways are also introduced here. In this review, we update the key signaling pathways of lipotoxicity, oxidative stress, inflammation, and myofibroblasts activation in kidneys with chronic injury, and the targeted drugs based on the latest studies. Unifying these pathways and the targeted therapies will be instrumental to advance further basic and clinical investigation in CKD.

Mechanisms of podocyte injury and implications for diabetic nephropathy

Albuminuria is the hallmark of both primary and secondary proteinuric glomerulopathies, including focal segmental glomerulosclerosis (FSGS), obesity-related nephropathy, and diabetic nephropathy (DN). Moreover, albuminuria is an important feature of all chronic kidney diseases (CKDs). Podocytes play a key role in maintaining the permselectivity of the glomerular filtration barrier (GFB) and injury of the podocyte, leading to foot process (FP) effacement and podocyte loss, the unifying underlying mechanism of proteinuric glomerulopathies. The metabolic insult of hyperglycemia is of paramount importance in the pathogenesis of DN, while insults leading to podocyte damage are poorly defined in other proteinuric glomerulopathies. However, shared mechanisms of podocyte damage have been identified. Herein, we will review the role of haemodynamic and oxidative stress, inflammation, lipotoxicity, endocannabinoid (EC) hypertone, and both mitochondrial and autophagic dysfunction in the pathogenesis of the podocyte damage, focussing particularly on their role in the pathogenesis of DN. Gaining a better insight into the mechanisms of podocyte injury may provide novel targets for treatment. Moreover, novel strategies for boosting podocyte repair may open the way to podocyte regenerative medicine.

Mitochondrial Oxidative Stress and Cell Death in Podocytopathies

Podocytopathies are kidney diseases that are driven by podocyte injury with proteinuria and proteinuria-related symptoms as the main clinical presentations. Albeit podocytopathies are the major contributors to end-stage kidney disease, the underlying molecular mechanisms of podocyte injury remain to be elucidated. Mitochondrial oxidative stress is associated with kidney diseases, and increasing evidence suggests that oxidative stress plays a vital role in the pathogenesis of podocytopathies. Accumulating evidence has placed mitochondrial oxidative stress in the focus of cell death research. Excessive generated reactive oxygen species over antioxidant defense under pathological conditions lead to oxidative damage to cellular components and regulate cell death in the podocyte. Conversely, exogenous antioxidants can protect podocyte from cell death. This review provides an overview of the role of mitochondrial oxidative stress in podocytopathies and discusses its role in the cell death of the podocyte, aiming to identify the novel targets to improve the treatment of patients with podocytopathies.

Association between Maternal Periodontitis and Development of Systematic Diseases in Offspring

Periodontal disease (PD) is one of the most common oral conditions affecting both youths and adults. There are some research works suggesting a high incidence of PD in pregnant women. As an inflammatory disease of bacterial origin, PD may result in the activation of the pathways affecting the course and the pregnancy outcome. The authors, based on the literature review, try to answer the PICO question: Does maternal periodontitis (exposure) influence the incidence of complications rates in pregnancy and the development of systemic diseases in childhood and adult offspring (outcome) in the humans of any race (population) compared to the offspring of mothers with healthy periodontium (comparison)? The authors try to describe the molecular pathways and mechanisms of these interdependencies. There is some evidence that maternal periodontitis may affect the pregnancy course and outcome, resulting in preeclampsia, preterm delivery, vulvovaginitis and low birth weight. It can be suggested that maternal periodontitis may affect offspring epigenome and result in some health consequences in their adult life.

Novel ferroptosis-related gene signature as a potential prognostic tool for gastric cancer

Objectives

Gastric cancer (GC) is a major global health concern and is difficult to diagnose in the early stage. Ferroptosis is an iron-dependent, novel form of non-apoptotic cell death. In recent years, inducing the upregulation of ferroptosis-related genes has become a promising therapeutic alternative for cancers, especially those resistant to traditional treatments. However, the relationship between ferroptosis-related genes and GC remains to be further elucidated.

Methods

In the present study, mRNA expression profiles and corresponding clinical data of patients with GC were retrieved from The Cancer Genome Atlas and used as test data. A multigene signature was constructed using the least absolute shrinkage and selection operator Cox regression model. Data of patients with GC from ‘GSE84426’ in the Gene Expression Omnibus database were used as Training data for validation.

Results

More than half ferroptosis-related genes were differentially expressed in GC tissues and adjacent normal tissue samples (58.43%) in the test data. Univariate Cox regression analysis showed that 16 differentially expressed genes were related to the prognosis of GC (all p < 0.05). Expression profiles of the 16 DGEs were analysed using LASSO Cox regression, and a prognostic model was established by selecting the 10 best genes for λ. These 10 genes were used to construct a 10-gene signature and stratify patients into two risk groups. Based on the median risk score in the test data, patients with GC were divided into high- and low-risk groups ( p < 0.001). Risk score was an independent predictor for overall survival in multivariate Cox regression analyses ( p < 0.001 and <0.01 in the test and training data, respectively; hazard ratio >1). Receiver operating characteristic curve analysis confirmed the predictive capacity of the 10-gene signature. Functional analysis revealed that tumour-infiltrating lymphocytes, antigen-presenting cell co-stimulation, and cytokine-cytokine receptors were enriched; however, the immune status differed between the two risk groups.

Conclusion

The novel ferroptosis-related gene signature can be used for GC prognosis. In addition, ferroptosis may provide a novel alternative for the diagnosis and treatment of GC.

Therapeutic potential of resveratrol in diabetic nephropathy according to molecular signaling

BACKGROUND

Diabetic nephropathy (DN) as a severe complication of diabetes mellitus (DM), is a crucial menace for human health and survival and remarkably elevates the healthcare systems' costs. Therefore, it is worth noting to identify novel preventive and therapeutic strategies to alleviate the disease conditions. Resveratrol, as a well-defined anti-diabetic/ antioxidant agent has capabilities to counteract diabetic complications. It has been predicted that resveratrol will be a fantastic natural polyphenol for diabetes therapy in the next few years.

OBJECTIVE

Accordingly, the current review aims to depict the role of resveratrol in the regulation of different signaling pathways that are involved in the reactive oxygen species (ROS) production, inflammatory processes, autophagy, and mitochondrial dysfunction, as critical contributors to DN pathophysiology.

RESULTS

The pathogenesis of DN can be multifactorial; hyperglycemia is one of the prominent risk factors of DN development that is closely related to oxidative stress. Resveratrol, as a well-defined polyphenol, has various biological and medicinal properties, including anti-diabetic, anti-inflammatory, and anti-oxidative effects.

CONCLUSION

Resveratrol prevents kidney damages that are caused by oxidative stress, enhances antioxidant capacity, and attenuates the inflammatory and fibrotic responses. For this reason, resveratrol is considered an interesting target in DN research due to its therapeutic possibilities during diabetic disorders and renal protection.

Contribution of Oxidative Stress to HIF-1-Mediated Profibrotic Changes during the Kidney Damage

Hypoxia and oxidative stress are the common causes of various types of kidney injury. During recent years, the studies on hypoxia inducible factor- (HIF-) 1 attract more and more attention, which can not only mediate hypoxia adaptation but also contribute to profibrotic changes. Through analyzing related literatures, we found that oxidative stress can regulate the expression and activity of HIF-1α through some signaling molecules, such as prolyl hydroxylase domain-containing protein (PHD), PI-3K, and microRNA. And oxidative stress can take part in inflammation, epithelial-mesenchymal transition, and extracellular matrix deposition mediated by HIF-1 via interacting with classical NF-κB and TGF-β signaling pathways. Therefore, based on previous literatures, this review summarizes the contribution of oxidative stress to HIF-1-mediated profibrotic changes during the kidney damage, in order to further understand the role of oxidative stress in renal fibrosis.

Scutellarin-induced A549 cell apoptosis depends on activation of the transforming growth factor-β1/smad2/ROS/caspase-3 pathway

Scutellarin plays an anti-tumor role in A549 lung cancer cells, but the underlying mechanism is unclear. In this study, scutellarin was used to treat A549 cells for 12, 24, and 48 h, followed by the addition of Tempo, a selective scavenger of mitochondrial reactive oxygen species (ROS) and SB431542, a transforming growth factor (TGF)-β1 receptor inhibitor. A dihydroethidium fluorescence probe was used to measure the intracellular ROS level, Cell Counting Kit-8 (CCK-8) was used to detect cell viability, and flow cytometry was performed to examine apoptosis. Western blots were used to detect the total protein level of TGF-β1, p-smad2, and cleaved caspase-3 in A549 cells. The results showed that scutellarin significantly inhibited cell viability and increased apoptosis. Scutellarin also promoted intracellular ROS production, TGF-β1/smad2 signaling pathway activation, and cleaved caspase-3 expression, which was partly reversed by Tempo. Moreover, scutellarin-induced intracellular ROS production and cleaved caspase-3 expression were inhibited by blocking the TGF-β1/smad2 pathway with SB431542. In conclusion, scutellarin promoted apoptosis and intracellular ROS accumulation, which could be abrogated by Tempo and SB431542 treatment in A549 cells. Our study indicated that scutellarin induced A549 cell apoptosis via the TGF-β1/smad2/ROS/caspase-3 pathway.

Transforming Growth Factor-β and Oxidative Stress in Cancer: A Crosstalk in Driving Tumor Transformation

Simple Summary

Metabolic changes in tumor microenvironment play a critical role in cancer, related to the accumulated alterations in signaling pathways that control cellular metabolism. Cancer metabolic deregulation is related to specific events such as the control of oxidative stress, and in particular the redox imbalance with aberrant oxidant production and/or a deregulation of the efficacy of the antioxidant systems. In cancer cells, different cytokines are involved in the development and/or progression of cancer; among these cytokines, the transforming growth factor β (TGF-β) is central to tumorigenesis and cancer progression. In tumor cells, it has been demonstrated that there is a close correlation between oxidative stress and TGF-β; this crosstalk strongly contributes to tumorigenesis, both in tumor development and in mediating its invasiveness. This review is addressed to better understanding this crosstalk between TGF-β and oxidative stress in cancer cell metabolism, in an attempt to improve the pharmacological and therapeutic approach against cancer.

Abstract

Cancer metabolism involves different changes at a cellular level, and altered metabolic pathways have been demonstrated to be heavily involved in tumorigenesis and invasiveness. A crucial role for oxidative stress in cancer initiation and progression has been demonstrated; redox imbalance, due to aberrant reactive oxygen species (ROS) production or deregulated efficacy of antioxidant systems (superoxide dismutase, catalase, GSH), contributes to tumor initiation and progression of several types of cancer. ROS may modulate cancer cell metabolism by acting as secondary messengers in the signaling pathways (NF-kB, HIF-1α) involved in cellular proliferation and metastasis. It is known that ROS mediate many of the effects of transforming growth factor β (TGF-β), a key cytokine central in tumorigenesis and cancer progression, which in turn can modulate ROS production and the related antioxidant system activity. Thus, ROS synergize with TGF-β in cancer cell metabolism by increasing the redox imbalance in cancer cells and by inducing the epithelial mesenchymal transition (EMT), a crucial event associated with tumor invasiveness and metastases. Taken as a whole, this review is addressed to better understanding this crosstalk between TGF-β and oxidative stress in cancer cell metabolism, in the attempt to improve the pharmacological and therapeutic approach against cancer.

The effects of carvacrol on oxidative stress, inflammation, and liver function indicators in a systemic inflammation model induced by lipopolysaccharide in rats

The effect of carvacrol (CAR) on oxidative stress, inflammation, and liver dysfunction induced by lipopolysaccharide (LPS) was explored. The rats (n=40) were daily injected (2 weeks) by saline as control, LPS (1 mg/kg, i.p.), and 25, 50 or 100 mg/kg CAR (i.p.) before LPS. LPS increased aspartate transaminase (AST: 162±13 U/L), alanine aminotransferase (ALT: 74.6±2.15 U/L), alkaline phosphatase (ALK-P: 811±51 U/L), interlukine-1β (IL-1β: 1254±51 pg/g tissue), malondialdehyde (MDA: 32±1.09 nM/g tissue), and nitric oxide (NO: 224±13.5 nM/g tissue) (P<0.01-P<0.001) while, decreased total protein(4.08±0.38 g/dl), albumin(2.79±0.16 g/dl), thiol (5.16±0.19 μM/g tissue), superoxide dismutase (SOD: 10.57±0.13 U/g tissue), and catalase (CAT: 0.78±0.02 U/g tissue) compared to control (P<0.001). CAR reversed the effects of LPS (P<0.05-P<0.001). In the rats treated by 100 mg/kg CAR, the indicators were as follows: AST: 118±10.1 U/L, ALT: 42.5±4.13 U/L, ALK-P: 597±39.91 U/L, IL-1β: 494±15 pg/g tissue, and NO: 141±5.35 nM/g tissue. Both 50 and 100 mg/kg CAR corrected oxidative stress indicators and in the group treated by 100 mg/kg CAR, they were: MDA: 23.4±0.91 nM/g tissue, thiol: 7.98±0.18 μM/g tissue, SOD: 21±0.8 U/g tissue, and CAT: 1.12±0.02 U/g tissue(P<0.05-P<0.001). In conclusion, CAR improved liver function, accompanied with antioxidant and antiinflammatory effects.

High glucose induces Nox4 expression and podocyte apoptosis through the Smad3/ezrin/PKA pathway

Podocytes are the major target in proteinuric kidney diseases such as diabetic nephropathy. The underlying molecular mechanisms by which high glucose (HG) results in podocyte damage remain unclear. This study investigated the regulatory role of Smad3, ezrin, and protein kinase A (PKA) in NADPH oxidase (Nox4) expression, reactive oxidative species (ROS) production, and apoptosis in HG-treated podocytes. A human podocyte cell line was cultured and differentiated, then treated with 30 mM HG. Apoptosis and intracellular ROS levels were assessed using TUNEL and DCF assays, respectively. Expressions of Nox4, phospho-Smad3^Ser423/425, phospho-PKA^Thr197, and phospho-ezrin^Thr567 were evaluated using western blotting. ELISA was used to quantify intracellular cAMP concentration and PKA activity. Knockdown assay was used to inhibit the expressions of Smad3, Nox4, and ezrin by lentiviral shRNA. In HG-treated podocytes, the level of phospho-Smad3^Ser423/425 and phospho-ezrin^Thr567 was increased significantly, which was accompanied by the reduction of cAMP and phospho-PKA^Thr197. HG-induced apoptosis was significantly prevented by the Smad3-inhibitor SIS3 or shRNA-Smad3. In podocytes expressing shRNA-ezrin or shRNA-Nox4, apoptosis was remarkably mitigated following HG treatment. HG-induced upregulation of phospho-ezrin^Thr567 and downregulation of phospho-PKA^Thr197 was significantly prevented by SIS3, shRNA-ezrin or shRNA-Smad3. Forskolin, a PKA activator, significantly inhibited HG-mediated upregulation of Nox4 expression, ROS generation, and apoptosis. Additionally, an increase in the ROS level was prohibited in HG-treated podocytes with the knockdown of Nox4, Smad3, or ezrin. Taken together, our findings provided evidence that Smad3-mediated ezrin activation upregulates Nox4 expression and ROS production, by suppressing PKA activity, which may at least in part contribute to HG-induced podocyte apoptosis.

Summary: The actin-membrane linker protein ezrin-related signaling plays a critical role in podocyte apoptosis through regulation of Nox4 expression and ROS production.

Apigenin ameliorates doxorubicin-induced renal injury via inhibition of oxidative stress and inflammation

BACKGROUND AND OBJECTIVE

Doxorubicin (DOX) is an anthracycline antitumor antibiotic widely utilized in treating various tumors. Nevertheless, the toxicity of DOX toward normal cells limits its applicability, with nephrotoxicity considered a major dose-limiting adverse effect. Apigenin (APG), a flavonoid widely distributed in natural plants, has been reported to have antioxidant, anti-inflammatory, and mild tumor-suppressive properties. In this study, we investigated the role of APG in DOX-induced nephrotoxicity and chemotherapeutic efficacy.

METHODS

Male BALB/c mice were administered DOX (11.5 mg/kg) via the tail vein to establish the DOX nephropathy model. After treatment with or without APG (125, 250, and 500 mg/kg) for two weeks, urine, serum, and tissue samples were collected to evaluate proteinuria, serum albumin, serum creatinine (Scr), blood urea nitrogen (BUN), superoxide dismutase (SOD) activity, malondialdehyde (MDA), glutathione (GSH), and pathological changes. Rat renal tubular epithelial cells (NRK52E), murine podocyte cells (MPC5), and murine breast cancer cells (4T1) were utilized to verify the effect of APG on DOX-induced cell injury. An MTT assay was employed to analyze cell viability. Apoptosis was evaluated using a colorimetric TUNEL staining and cleaved caspase-3 protein analysis by western blotting. A reactive oxygen species (ROS)/superoxide (O2-) fluorescence probe was employed to determine oxidative injury. Western blotting was used to analyze nephrin, α-smooth muscle actin (α-SMA), collagen I (Col1), fibronectin (FN), and SOD2 expression. The mRNA levels of tumor necrosis factor-α (TNF-α), interleukin-18 (IL-18), IL-6, NACHT, LRR, PYD domain-containing protein 3 (NLRP3), caspase-1, and IL-1β were tested by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

APG ameliorated DOX-elicited renal injuries in both the glomeruli and tubules. The DOX + APG groups had much lower tissue MDA, IL-6, TNF-α, NLRP3, caspase-1, and IL-1β levels and generation of intracellular ROS, but significantly higher SOD activity and GSH levels compared to those of the DOX group. Additionally, APG attenuated DOX-induced morphological changes, loss of cellular viability, and apoptosis in NRK-52E and MPC-5 cells, but not in 4T1 cells.

CONCLUSION

APG has a protective role against DOX-induced nephrotoxicity, without weakening DOX cytotoxicity in malignant tumors. Thus, APG may serve as a potential protective agent against renal injury and inflammatory diseases and may be a promising candidate to attenuate renal toxicity in cancer patients treated with DOX.

Inhibition of NLRP3 inflammasome ameliorates podocyte damage by suppressing lipid accumulation in diabetic nephropathy

BACKGROUND

Nucleotide leukin-rich polypeptide 3 (NLRP3) inflammasome is documented as a potent target for treating metabolic diseases and inflammatory disorders. Our recent work demonstrated that inhibition of NLRP3 inflammasome activation inhibits renal inflammation and fibrosis in diabetic nephropathy. This study was to investigate the effect of NLRP3 inflammasome on podocyte injury and the underlying mechanism in diabetic nephropathy.

METHODS

In vivo, db/db mice were treated with MCC950, a NLRP3 inflammasome specific inhibitor. NLRP3 knockout (NKO) mice were induced to diabetes by intraperitoneal injections of streptozotocin (STZ). We assessed renal function, albuminuria, podocyte injury and glomerular lipid accumulation in diabetic mice. In vitro, apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation and reactive oxygen species (ROS) generation were evaluated in podocytes interfered with NLRP3 siRNA or MCC950 under high glucose (HG) conditions. In addition, the effect and mechanism of IL-1β on lipid accumulation was explored in podocytes exposed to normal glucose (NG) or HG.

RESULTS

MCC950 treatment improved renal function, attenuated albuminuria, mesangial expansion, podocyte loss, as well as glomerular lipid accumulation in db/db mice. The diabetes-induced podocyte loss and glomerular lipid accumulation were reversed in NLRP3 knockout mice. The increased expression of sterol regulatory element-binding protein1 (SREBP1) and SREBP2, and decreased expression of ATP-binding cassette A1 (ABCA1) in podocytes were reversed by MCC950 treatment or NLRP3 knockout in diabetic mice. In vitro, NLRP3 siRNA or MCC950 treatment markedly inhibited HG-induced apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation, and mitochondrial ROS production in cultured podocytes. In addition, BAY11-7082 or tempol treatment inhibited HG-induced lipid accumulation in podocytes. Moreover, exposure of IL-1β to podocytes induced lipid accumulation, NF-κB p65 activation and mitochondrial ROS generation.

CONCLUSION

Inhibition of NLRP3 inflammasome protects against podocyte damage through suppression of lipid accumulation in diabetic nephropathy. IL-1β/ROS/NF-κB p65 mediates diabetes-associated lipid accumulation in podocytes. The suppression of NLRP3 inflammasome activation may be an effective therapeutic approach to diabetic nephropathy.

[Involvement of Notch1 and ALK4/5 Signaling Pathways in Renal Tubular Cell Death: Their Application to Clarification of Cadmium Toxicity]

Renal tubular cell death is caused by various extracellular stresses including toxic amounts of cadmium, an occupational and environmental pollutant metal, and is responsible for renal dysfunction. While cadmium exposure disrupts many intracellular signaling pathways, the molecular mechanism underlying cadmium-induced renal tubular cell death has not yet been fully elucidated. We have recently identified two important intracellular signaling pathways that promote cadmium-induced renal tubular cell death: the Notch1 signaling and activin receptor-like kinase (ALK) 4/5 signaling (also known as the activin-transforming growth factor β receptor pathways). In this review paper, we introduce our previous experimental findings, focusing on Notch1 and ALK4/5 signaling pathways, which may uncover the molecular mechanisms involved in cadmium-induced renal tubular cell death.

Intracellular Sources of ROS/H2O2 in Health and Neurodegeneration: Spotlight on Endoplasmic Reticulum

Reactive oxygen species (ROS) are produced continuously throughout the cell as products of various redox reactions. Yet these products function as important signal messengers, acting through oxidation of specific target factors. Whilst excess ROS production has the potential to induce oxidative stress, physiological roles of ROS are supported by a spatiotemporal equilibrium between ROS producers and scavengers such as antioxidative enzymes. In the endoplasmic reticulum (ER), hydrogen peroxide (H2O2), a non-radical ROS, is produced through the process of oxidative folding. Utilisation and dysregulation of H2O2, in particular that generated in the ER, affects not only cellular homeostasis but also the longevity of organisms. ROS dysregulation has been implicated in various pathologies including dementia and other neurodegenerative diseases, sanctioning a field of research that strives to better understand cell-intrinsic ROS production. Here we review the organelle-specific ROS-generating and consuming pathways, providing evidence that the ER is a major contributing source of potentially pathologic ROS.

Huidouba Improved Podocyte Injury by Down-Regulating Nox4 Expression in Rats With Diabetic Nephropathy

Diabetic nephropathy (DN), as the most common microvascular complication of diabetes mellitus (DM), has become one of the leading causes of end-stage renal disease (ESRD). Numerous studies have indicated that podocyte loss plays an important role in the development of DN and can even cause proteinuria in the early stage of DN. In the study, we found that Huidouba (HDB) significantly decreased the level of fasting blood glucose (FBG), the ratio of microalbumin to urine creatine (mAlb/Ucr), serum creatine (Scr), serum urea nitrogen (BUN), and malondialdehyde (MDA) in the kidney and downregulated the expression of Nox4 predominantly located in glomerular tissue while upregulating nephrin and WT1 expression in DN rats. In addition, HDB could also reduce podocyte damage and glomerular basement membrane (GBM) pathologic changes, as shown by transmission electron microscopy (TEM). In vitro study showed that HDB could inhibit high glucose (HG)-induced Reactive Oxygen Species (ROS) production and protect against podocyte apoptosis by downregulated Nox4 expression in podocytes. These results may provide a scientific basis for developing HDB as a potential folk medicine for the treatment of DN.

Salvianolate ameliorates oxidative stress and podocyte injury through modulation of NOX4 activity in db/db mice

Podocyte injury is associated with albuminuria and the progression of diabetic nephropathy (DN). NADPH oxidase 4 (NOX4) is the main source of reactive oxygen species (ROS) in the kidney and NOX4 is up-regulated in podocytes in response to high glucose. In the present study, the effects of Salvianolate on DN and its underlying mechanisms were investigated in diabetic db/db mice and human podocytes. We confirmed that the Salvianolate administration exhibited similar beneficial effects as the NOX1/NOX4 inhibitor GKT137831 treated diabetic mice, as reflected by attenuated albuminuria, reduced podocyte loss and mesangial matrix accumulation. We further observed that Salvianolate attenuated the increase of Nox4 protein, NOX4-based NADPH oxidase activity and restored podocyte loss in the diabetic kidney. In human podocytes, NOX4 was predominantly localized to mitochondria and Sal B treatment blocked HG-induced mitochondrial NOX4 derived superoxide generation and thereby ameliorating podocyte apoptosis, which can be abrogated by AMPK knockdown. Therefore, our results suggest that Sal B possesses the reno-protective capabilities in part through AMPK-mediated control of NOX4 expression. Taken together, our results identify that Salvianolate could prevent glucose-induced oxidative podocyte injury through modulation of NOX4 activity in DN and have a novel therapeutic potential for DN.

Morroniside Inhibits H2O2-Induced Podocyte Apoptosis by Down-Regulating NOX4 Expression Controlled by Autophagy In Vitro

Podocyte apoptosis is the common pathological basis for the progression of various kidney diseases. The overexpression of NOX4, a key enzyme involved in oxidative stress, has been proved to participate in the occurrence of podocyte apoptosis. Autophagy is a kind of adaptive response of cells under stress. However, as a “double-edged sword”, the effect of autophagy on apoptosis in different cells and conditions is complex and variable, which has not been fully explained yet. Morroniside, extracted from the traditional medicinal plant Cornus officinalis, has remarkable antioxidant and anti-apoptosis effects, and has been proven to inhibit the overexpression of NOX4 in kidney tissue. Therefore, H₂O₂ was used in this study to explore the effects of autophagy on podocyte NOX4 overexpression and apoptosis induced by oxidative stress, as well as the protection mechanism of morroniside in podocytes. The results showed that the autophagy activator rapamycin, as well as the autophagy inhibitor chloroquine, could induce podocyte apoptosis cultured in normal condition, and chloroquine could also significantly increase the NOX4 expression. The NOX4 expression and apoptosis rate of podocytes increased after H₂O₂ treatment, the expression of LC3-II decreased, and the expressions of p62, mTOR, and p-mTOR increased. The intervention of morroniside and rapamycin improved autophagy activity and inhibited NOX4 overexpression and apoptosis induced by H₂O₂. And chloroquine reversed the inhibitory effect of morroniside on NOX4 overexpression and podocyte apoptosis. Taken together, our results suggest that the expression level of NOX4 in podocytes is regulated by autophagy activity. Morroniside can reduce oxidative stress induced podocyte apoptosis by restoring the damaged autophagy flux and inhibit the overexpression of NOX4.

FOXO3a accumulation and activation accelerate oxidative stress-induced podocyte injury

Podocyte injury is the primary cause of glomerular injury in diabetic nephropathy (DN). Advanced oxidation protein products (AOPPs), the triggers and markers of oxidative stress in DN, have been linked to podocyte damage. However, the underlying mechanism is not yet clear. Here, we investigated the potential role of FOXO3a, a key transcription factor in the response to stress, in mediating AOPPs-induced podocyte injury. We found that FOXO3a expression was increased in the glomeruli of kidney biopsies from patients with DN and it was positively correlated with proteinuria. The serum from patients with DN significantly increased FOXO3a and its downstream genes FasL and Bim, thereby inducing the high level of cleaved caspase3 and the loss of nephrin and podocin expressions in podocytes. Blockade of AOPPs signaling by a neutralizing antibody against the receptor of advanced glycation end products (αRAGE) abolished the effect of DN serum on podocytes, confirming the pathogenic role of AOPPs in DN serum. Downregulation of FOXO3a decreased AOPPs-induced podocyte apoptosis and restored the levels of podocyte markers nephrin and podocin, and upregulation of FOXO3a exacerbated these changes in podocytes after AOPPs treatment. Furthermore, FOXO3a specifically activated proapoptotic genes in podocytes only in the presence of AOPPs. Mechanistically, AOPPs increased the FOXO3a protein levels by inhibiting their autophagic degradation in a ROS/mTOR-dependent manner. Moreover AOPPs activated the accumulated FOXO3a by maintaining FOXO3a in the nucleus, and this process was dependent on ROS-mediated AKT signaling deactivation. These studies suggest that FOXO3a plays a critical role in mediating AOPPs-induced podocyte injury and reveal a new mechanistic linkage of oxidative stress, FOXO3a activation and podocyte injury in DN.

Activation of ERK1/2-mTORC1-NOX4 mediates TGF-β1-induced epithelial-mesenchymal transition and fibrosis in retinal pigment epithelial cells

Transforming growth factor-β (TGF-β) plays a crucial role in the development of epithelial to mesenchymal transition (EMT) and fibrosis, particularly in an ocular disorder such as proliferative vitreoretinopathy (PVR). However, the key molecular mechanism underlying its pathogenesis remains unknown. In the present study, using cultured ARPE-19 cells, we determined that TGF-β initiates a signaling pathway through extracellular signal-regulated kinase (ERK)-mammalian target of rapamycin complex 1 (mTORC1) that stimulates trans-differentiation and fibrosis of retinal pigment epithelium. Blocking this pathway by a TGF-βRI, ERK or mTORC1 inhibitor protected cells from EMT and fibrotic protein expression. TGF-β1 treatment increased reactive oxygen species (ROS) via NOX4 upregulation, which acts downstream of ERK and mTORC1, as the ROS scavenger N-acetylcysteine and a pan-NADPH oxidase (NOX) inhibitor DPI dissipated excess ROS generation. TGF-β1-induced oxidative stress resulted in EMT and fibrotic changes, as NAC and DPI prevented α-SMA, Col4α3 expression and cell migration. All these inhibitors blocked the downstream pathway activation in addition to clearly preventing the activation of its upstream molecules, indicating the presence of a feedback loop system that may boost the upstream events. Furthermore, the FDA-approved drug trametinib (10 nM) blunted TGF-β1-induced mTORC1 activation and downstream pathogenic alterations through ERK1/2 inhibition, which opens a therapeutic avenue for the treatment of PVR in the future.

RIPK3: A New Player in Renal Fibrosis

Chronic kidney disease (CKD) is the end result of a plethora of renal insults, including repeated episodes of acute or toxic kidney injury, glomerular, or diabetic kidney disease. It affects a large number of the population worldwide, resulting in significant personal morbidity and mortality and economic cost to the community. Hence it is appropriate to focus on treatment strategies that interrupt the development of kidney fibrosis, the end result of all forms of CKD, in addition to upstream factors that may be specific to certain diseases. However, the current clinical approach to prevent or manage renal fibrosis remains unsatisfactory. The rising importance of receptor-interacting serine/threonine-protein kinase (RIPK) 3 in the inflammatory response and TGF-β1 signaling is increasingly recognized. We discuss here the biological functions of RIPK3 and its role in the development of renal fibrosis.

High salt-induced weakness of anti-oxidative function of natriuretic peptide receptor-C and podocyte damage in the kidneys of Dahl rats

BACKGROUND

Atrial natriuretic peptide (ANP) and its natriuretic peptide receptors A (NPR-A) and C (NPR-C) are involved in the regulation of physiological and pathophysiological process of blood pressure. The present study aimed to determine the role of NPR-C in the development of salt-sensitive hypertension.

METHODS

The Dahl salt-sensitive (DS) and salt-resistant (DR) rats were used in this study. Animals were matched according to their age and weight, and then placed on either a high-salt (HS, 8%) or a normal-salt (NS, 0.4%) diet for 6 weeks randomly using random number table. The systolic blood pressure (SBP), plasmatic sodium concentration (PLNa), urinary sodium excretion (UVNa), and serum creatinine concentration (Scr) were measured. The concentration of ANP in blood and tissues (heart and kidney) was detected by enzyme-linked immunosorbent assay. The expression of ANP, NPR-A, and NPR-C in kidney was evaluated with western blot analysis. Regarding renal redox state, the concentration changes in malondialdehyde (MDA), lipofuscin, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox), and nitric oxide synthase (NOS) in kidney were detected by a spectrophotometric method. The kidney damage was evaluated using pathological techniques and the succinodehydrogenase (SDHase) examination. Furthermore, after an intra-peritoneal injection of C-atrial natriuretic peptide (ANP)4-23 (C-ANP4-23), an NPR-C receptor agonist, the SBP, biochemical values in blood and urine, and renal redox state were evaluated. The paired Student's t test and analysis of variance followed by the Bonferroni test were performed for statistical analyses of the comparisons between two groups and multiple groups, respectively.

RESULTS

The baseline SBP in all groups was within the normal range. At the end of the 6-week experiment, HS diet significantly increased the SBP in DS rats from 116.63 ± 2.90 mmHg to 162.25 ± 2.15 mmHg (t = -10.213, P < 0.001). The changes of SBP were not significant in DS rats on an NS diet and DR rats on an NS diet or on an HS diet (all P > 0.05). The significant increase of PLNa, UVNa, and Scr related to an HS diet was found in both DS and DR rats (all P < 0.05). However, significant changes in the concentration (t = -21.915, P < 0.001) and expression of renal ANP (t = -3.566, P = 0.016) and the expression of renal NPR-C (t = 5.864, P = 0.002) were only observed in DS hypertensive rats. The significantly higher desmin immunochemical staining score (t = -5.715, P = 0.005) and mitochondrial injury score (t = -6.325, P = 0.003) accompanied by the lower SDHase concentration (t = 3.972, P = 0.017) revealed mitochondrial pathologic abnormalities in podocytes in DS rats with an HS diet. The distinct increases of MDA (t = -4.685, P = 0.009), lipofuscin (t = -8.195, P = 0.001), and Nox (t = -12.733, P < 0.001) but not NOS (t = -0.328, P = 0.764) in kidneys were also found in DS hypertensive rats. C-ANP4-23 treatment significantly decreased the SBP induced by HS in DS rats (P < 0.05), which was still higher than NS groups with the vehicle or C-ANP4-23 treatment (P < 0.05). Moreover, the HS-induced increase of MDA, lipofuscin, Nox concentrations, and Nox4 expression in DS rats was significantly attenuated by C-ANP4-23 treatment as compared with those with HS diet and vehicle injection (all P < 0.05).

CONCLUSIONS

The results indicated that the renal NPR-C might be involved in the salt-sensitive hypertension through the damage of mitochondria in podocytes and the reduction of the anti-oxidative function. Hence, C-ANP4-23 might serve as a therapeutic agent in treating salt-sensitive hypertension.

Sphingosine Kinase 1/S1P Signaling Contributes to Pulmonary Fibrosis by Activating Hippo/YAP Pathway and Mitochondrial Reactive Oxygen Species in Lung Fibroblasts

The sphingosine kinase 1 (SPHK1)/sphingosine–1–phosphate (S1P) signaling axis is emerging as a key player in the development of idiopathic pulmonary fibrosis (IPF) and bleomycin (BLM)-induced lung fibrosis in mice. Recent evidence implicates the involvement of the Hippo/Yes-associated protein (YAP) 1 pathway in lung diseases, including IPF, but its plausible link to the SPHK1/S1P signaling pathway is unclear. Herein, we demonstrate the increased co-localization of YAP1 with the fibroblast marker FSP1 in the lung fibroblasts of BLM-challenged mice, and the genetic deletion of Sphk1 in mouse lung fibroblasts (MLFs) reduced YAP1 localization in fibrotic foci. The PF543 inhibition of SPHK1 activity in mice attenuated YAP1 co-localization with FSP1 in lung fibroblasts. In vitro, TGF-β stimulated YAP1 translocation to the nucleus in primary MLFs, and the deletion of Sphk1 or inhibition with PF543 attenuated TGF-β-mediated YAP1 nuclear localization. Moreover, the PF543 inhibition of SPHK1, or the verteporfin inhibition of YAP1, decreased the TGF-β- or BLM-induced mitochondrial reactive oxygen species (mtROS) in human lung fibroblasts (HLFs) and the expression of fibronectin (FN) and alpha-smooth muscle actin (α-SMA). Furthermore, scavenging mtROS with MitoTEMPO attenuated the TGF-β-induced expression of FN and α-SMA. The addition of the S1P antibody to HLFs reduced TGF-β- or S1P-mediated YAP1 activation, mtROS, and the expression of FN and α-SMA. These results suggest a role for SPHK1/S1P signaling in TGF-β-induced YAP1 activation and mtROS generation, resulting in fibroblast activation, a critical driver of pulmonary fibrosis.

Angiotensin II promotes podocyte injury by activating Arf6-Erk1/2-Nox4 signaling pathway

Angiotensin II (Ang II) is a key contributor to glomerular disease by predominantly resulting in podocyte injury, whereas the underlying molecular mechanisms has not been fully understood. This study aimed to investigate if and how ADP-ribosylation factor 6 (Arf6), a small GTP-binding protein, involves Ang II-induced cellular injury in cultured human podocytes. Cellular injury was evaluated with caspase 3 activity, reactive oxygen species (ROS) level and TUNEL assay. Arf6 activity was measured using an Arf6-GTP Pull-Down Assay. Ang II significantly enhanced Arf6 expressions accompanied by increase of Arf6-GTP. The TUNEL-positive cells as well as activated caspase 3, NADPH oxidase 4 protein (Nox4) and ROS levels were dramatically increased in Ang II-treated podocytes, which was prevented by secinH3, an Arf6 activity inhibitor. Induction of ROS by Ang II was inhibited in podocytes with Nox4 knockdown. Ang II-induced elevation of Nox4 and ROS was prevented by Arf6 knockdown. Phpspho-Erk1/2^{Thr202/Tyr204} levels were upregulated remarkably following Ang II treatment, and Erk inhibitor LY3214996 significantly downregulated Nox4 expression. In addition, Ang II decreased CD2AP expression. Overexpression of CD2AP prevented Ang II-induced upregulation of Arf6-GTP. Our data demonstrated that Ang II promotes ROS production and podocytes injury through activation of Arf6-Erk1/2-Nox4 signaling. We also provided evidence that Ang II activates Arf6 by degradation of CD2AP.

Research Progress on the Pathological Mechanisms of Podocytes in Diabetic Nephropathy

Diabetic nephropathy (DN) is not only an important microvascular complication of diabetes but also the main cause of end-stage renal disease. Studies have shown that the occurrence and development of DN are closely related to morphological and functional changes in podocytes. A series of morphological changes after podocyte injury in DN mainly include podocyte hypertrophy, podocyte epithelial-mesenchymal transdifferentiation, podocyte detachment, and podocyte apoptosis; functional changes mainly involve podocyte autophagy. More and more studies have shown that multiple signaling pathways play important roles in the progression of podocyte injury in DN. Here, we review research progress on the pathological mechanism of morphological and functional changes in podocytes associated with DN, to provide a new target for delaying the occurrence and development of this disorder.

Blockade of ALK4/5 signaling suppresses cadmium- and erastin-induced cell death in renal proximal tubular epithelial cells via distinct signaling mechanisms

Various types of cell death, including apoptosis, necrosis, necroptosis, and ferroptosis, are induced in renal tubular epithelial cells following exposure to environmental stresses and toxicants such as osmotic stress, ischemia/reperfusion injury, cisplatin, and cadmium. This is known to cause renal dysfunction, but the cellular events preceding stress-induced cell death in renal tubules are not fully elucidated. The activin receptor-like kinase (ALK) 4/5, also known as activin-transforming growth factor (TGF) β receptor, is involved in stress-induced renal injury. We, therefore, studied the role of ALK4/5 signaling in HK-2 human proximal tubular epithelial cell death induced by cisplatin, cadmium, hyperosmotic stress inducer, sorbitol, and the ferroptosis activator, erastin. We found that ALK4/5 signaling is involved in cadmium- and erastin-induced cell death, but not sorbitol- or cisplatin-induced apoptotic cell death. Cadmium exposure elevated the level of phosphorylated Smad3, and treatment with the ALK4/5 kinase inhibitors, SB431542 or SB505124, suppressed cadmium-induced HK-2 cell death. Cadmium-induced cell death was attenuated by siRNA-mediated ALK4 or Smad3 silencing, or by treatment with SIS3, a selective inhibitor of TGFβ1-dependent Smad3 phosphorylation. Furthermore, ALK4/5 signaling activated Akt signaling to promote cadmium-induced HK-2 cell death. In contrast, siRNA-mediated Inhibin-bA silencing or treatment with TGFβ1 or activin A had little effect on cadmium-induced HK-2 cell death. On the other hand, treatment with SB431542 or SB505124 attenuated erastin-induced ferroptosis by hyperactivating Nrf2 signaling in HK-2 cells. These results suggest that blockade of ALK4/5 signaling protects against cadmium- and erastin-induced HK-2 cell death via Akt and Nrf2 signaling pathways, respectively.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

A causal link between oxidative stress and inflammation in cardiovascular and renal complications of diabetes

Chronic renal and vascular oxidative stress in association with an enhanced inflammatory burden are determinant processes in the development and progression of diabetic complications including cardiovascular disease (CVD), atherosclerosis and diabetic kidney disease (DKD). Persistent hyperglycaemia in diabetes mellitus increases the production of reactive oxygen species (ROS) and activates mediators of inflammation as well as suppresses antioxidant defence mechanisms ultimately contributing to oxidative stress which leads to vascular and renal injury in diabetes. Furthermore, there is increasing evidence that ROS, inflammation and fibrosis promote each other and are part of a vicious connection leading to development and progression of CVD and kidney disease in diabetes.

Nox4 in renal diseases: An update

Reactive oxygen species derived from NADPH oxidase contribute to a wide variety of renal diseases. Nox4, the major NADPH isoform in kidney, produces mainly H₂O₂ that regulates physiological functions. Nox4 contributes to redox processes involved in diabetic nephropathy, acute kidney injury, obstructive nephropathy, hypertensive nephropathy, renal cell carcinoma and other renal diseases by activating multiple signaling pathways. Although Nox4 is found in a variety of cell types, including epithelial cells, podocytes, mesangial cells, endothelial cells and fibroblasts, its role is not clear and even controversial. In some conditions, Nox4 protects cells by promoting cell survival in response to harmful stimuli. In other scenarios it induces cell apoptosis, inflammation or fibrogenesis. This functional variability may be attributed to distinct cell types, subcellular localization, molecular concentrations, disease type or stage, and other factors yet unexplored. In this setting, we reviewed the function and mechanism of Nox4 in renal diseases, highlighted the contradictions in Nox4 literature, and discussed promising therapeutic strategies targeting Nox4 in the treatment of certain types of renal diseases.

AT2 R deficiency mediated podocyte loss via activation of ectopic hedgehog interacting protein (Hhip) gene expression

Angiotensin II type 2 receptor (AT₂ R) deficiency in AT₂ R knockout (KO) mice has been linked to congenital abnormalities of the kidney and urinary tract; however, the mechanisms by which this occurs are poorly understood. In this study, we examined whether AT₂ R deficiency impaired glomerulogenesis and mediated podocyte loss/dysfunction in vivo and in vitro. Nephrin-cyan fluorescent protein (CFP)-transgenic (Tg) and Nephrin/AT₂ RKO mice were used to assess glomerulogenesis, while wild-type and AT₂ RKO mice were used to evaluate maturation of podocyte morphology/function. Immortalized mouse podocytes (mPODs) were employed for in vitro studies. AT₂ R deficiency resulted in diminished glomerulogenesis in E15 embryos, but had no impact on actual nephron number in neonates. Pups lacking AT₂ R displayed features of renal dysplasia with lower glomerular tuft volume and podocyte numbers. In vivo and in vitro studies demonstrated that loss of AT₂ R was associated with elevated NADPH oxidase 4 levels, which in turn stimulated ectopic hedgehog interacting protein (Hhip) gene expression in podocytes. Consequently, ectopic Hhip expression activation either triggers caspase-3 and p53-related apoptotic processes resulting in podocyte loss, or activates TGFβ1-Smad2/3 cascades and α-SMA expression to transform differentiated podocytes to undifferentiated podocyte-derived fibrotic cells. We analyzed HHIP expression in the kidney disease database (Nephroseq) and then validated this using HHIP immunohistochemistry staining of human kidney biopsies (controls versus focal segmental glomerulosclerosis). In conclusion, loss of AT₂ R is associated with podocyte loss/dysfunction and is mediated, at least in part, via augmented ectopic Hhip expression in podocytes. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Wnt signaling and podocyte dysfunction in diabetic nephropathy

Nephropathy is a major microvascular complication of diabetes mellitus and often leads to terminal renal failure in addition to contributing significantly to cardiovascular morbidity and mortality. Despites continuous advances, the pathogenesis of diabetic nephropathy remains poorly understood. Recent studies have underscored the significance of structural and functional changes in podocytes in the development and progression of diabetic nephropathy. The role of podocytes in health and diabetic nephropathy and abnormalities including podocyte hypertrophy, effacement, and apoptosis, and a detailed discussion on the role played by the Wnt-β-catenin signaling pathway in podocyte injury and dysfunction are the focus of this review. In addition, the role played by Wnt signaling in mediating the effects of known therapeutic strategies for diabetic nephropathy is also discussed.

NADPH oxidase inhibitor, diphenyleneiodonium prevents necroptosis in HK-2 cells

The aim of the present study was to investigate the protective effect of the NADPH oxidase inhibitor, diphenyleneiodonium (DPI) against necroptosis in renal tubular epithelial cells. A necroptosis model of HK-2 cells was established using tumor necrosis factor-α, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone and antimycin A (collectively termed TZA), as in our previous research. The necroptosis inhibitor, necrostatin-1 (Nec-1) or the NADPH oxidase inhibitor, DPI were administered to the necroptosis model. Production of reactive oxygen species (ROS) was detected by dichlorodihydrofluorescein diacetate in the different groups, and the manner of cell death was identified by flow cytometry. Western blot analysis was used to determine the levels of phosphorylation of receptor-interacting protein kinase 3 (RIP-3) and mixed lineage kinase domain-like (MLKL), which are essential to necroptosis. The results revealed that TZA increased the percentages of propidium iodide-positive HK-2 cells from 1.22±0.69 to 8.98±0.73% (P<0.001), and augmented the phosphorylation of RIP-3 and MLKL. ROS levels were increased in the TZA group compared with the control group (27.74±1.60×10⁴ vs. 18.51±1.10×10⁴, respectively; P<0.001), and could be inhibited by Nec-1 (TZA + Nec-1 group, 22.90±2.22×10⁴ vs. TZA group, 27.74±1.60×10⁴; P=0.01). DPI decreased ROS production (TZA + DPI group, 22.13±1.86×10⁴ vs. TZA group, 27.74±1.60×10⁴; P<0.001) and also reduced the proportions of necrosis in the necroptosis model (TZA + DPI group, 4.40±1.51% vs. TZA group, 8.98±0.73%; P<0.001). Phosphorylated RIP-3 and MLKL were also decreased by DPI treatment. The results indicate that ROS production increases in HK-2 cells undergoing necroptosis, and that the NADPH oxidase inhibitor, DPI may protect HK-2 cells from necroptosis via inhibition of ROS production.