The renin-angiotensin system in glomerular podocytes: Mediator of glomerulosclerosis and link to hypertensive nephropathy

Mechanisms of inflammation modulation by different immune cells in hypertensive nephropathy

Hypertensive nephropathy (HTN) is the second leading cause of end-stage renal disease (ESRD) and a chronic inflammatory disease. Persistent hypertension leads to lesions of intrarenal arterioles and arterioles, luminal stenosis, secondary ischemic renal parenchymal damage, and glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Studying the pathogenesis of hypertensive nephropathy is a prerequisite for diagnosis and treatment. The main cause of HTN is poor long-term blood pressure control, but kidney damage is often accompanied by the occurrence of immune inflammation. Some studies have found that the activation of innate immunity, inflammation and acquired immunity is closely related to the pathogenesis of HTN, which can cause damage and dysfunction of target organs. There are more articles on the mechanism of diabetic nephropathy, while there are fewer studies related to immunity in hypertensive nephropathy. This article reviews the mechanisms by which several different immune cells and inflammatory cytokines regulate blood pressure and renal damage in HTN. It mainly focuses on immune cells, cytokines, and chemokines and inhibitors. However, further comprehensive and large-scale studies are needed to determine the role of these markers and provide effective protocols for clinical intervention and treatment.

Inflammation in kidney repair: Mechanism and therapeutic potential

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

Histopathological nephrotoxic features of high oral doses of ubiquinone in rats

Co-enzyme Q10 (Co-Q10) plays a key role in the cellular respiration for the production of ATP. The toxicity of quinones to the kidney appears to depend on variety of factors, including genetic polymorphisms and the individual’s comorbidites. The aim of the present study was to assess histologically the nephrotoxic effects of 6 weeks daily oral intake of Co-Q10 in experimental animals.

Twenty-five Wistar rats weighing between 220-270 g were randomly divided into two groups: experimental “treated” and control “untreated” groups (n=15, n=10, respectively). The animals of the experimental group received 300 mg/kg daily dose of gelatinous capsules of Co-Q10 by oral gavage for six weeks. At the end of the study, all animals were sacrificed under general anesthesia and samples of the kidneys were excised for microscopic histopathological assessment of renal tissue using stain. The experimental group showed a range of mild to severe dilatation of Bowman’s space, with a mean corpuscular diameter of 294±38 µm that was significantly higher (p <0.05) than that of the untreated control group 208±31 µm. Shrinkage to complete destruction of the glomeruli was observed in the experimental group only. The long-term use of high doses of Co-Q10 had revealed a selective nephrotoxicity towards podocytes. This might be a risk factor leading to renal proximal tubular necrosis in rats and the subsequent renal function deterioration.

Diabetic Nephropathy: Challenges in Pathogenesis, Diagnosis, and Treatment

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide. Chronic hyperglycemia and high blood pressure are the main risk factors for the development of DN. In general, screening for microalbuminuria should be performed annually, starting 5 years after diagnosis in type 1 diabetes and at diagnosis and annually thereafter in type 2 diabetes. Standard therapy is blood glucose and blood pressure control using the renin-angiotensin system blockade, targeting A1c < 7%, and <130/80 mmHg. Regression of albuminuria remains an important therapeutic goal. However, there are problems in diagnosis and treatment of nonproteinuric DN (NP-DN), which does not follow the classic pattern of DN. In fact, the prevalence of DN continues to increase, and additional therapy is needed to prevent or ameliorate the condition. In addition to conventional therapies, vitamin D receptor activators, incretin-related drugs, and therapies that target inflammation may also be promising for the prevention of DN progression. This review focuses on the role of inflammation and oxidative stress in the pathogenesis of DN, approaches to diagnosis in classic and NP-DN, and current and emerging therapeutic interventions.

Exacerbation of Hyperparathyroidism, Secondary to a Reduction in Kidney Function, in Individuals With Vitamin D Deficiency

Aims/Introduction: Chronic kidney disease (CKD)-mineral and bone disorders (CKD-MBD) are an adverse outcome derived from decreases in kidney function, where abnormality of serum concentrations of calcium (Ca), phosphorus, parathyroid hormone (PTH), and vitamin D can be seen simultaneously. To identify individuals at risk for CKD-MBD or secondary hyperparathyroidism, the relationships between estimated glomerular filtration rate (eGFR) and serum PTH concentration were evaluated, allowing for confounding factors, in particular vitamin D status, in a general Japanese population.

Materials and Methods: Nine-hundred-and-thirty participants in the population-based Iwaki study conducted in 2016 who were not on drugs affecting mineral metabolism nor hemodialysis, were included in the study (326 men and 604 women; age: 55.4 ± 15.9 years).

Results: Regression analysis showed a significant correlation between eGFR and serum intact PTH concentration, after adjustment for possible confounding factors (β = −0.122, p < 0.001). The smoothed spline curve applied for the correlation analysis revealed a biphasic correlation, with a division at an eGFR of ~60 mL/min/1.73 m², below which the correlation coefficient was higher (β = −0.405, p < 0.001). Stratification on the basis of vitamin D status showed that the correlation was present only in participants with vitamin D deficiency (25-dihydroxyvitamin D3: <15 pg/mL) (β = −0.154, p < 0.001).

Conclusions: These results indicate that a reduction in eGFR is a significant risk factor for an increase in serum PTH concentration when it is <60 mL/min/1.73 m² and vitamin D is deficient, in the general Japanese population.

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.

Lower serum calcium levels are a risk factor for a decrease in eGFR in a general non-chronic kidney disease population

Association between serum calcium (Ca) levels and kidney dysfunction progression in a non-chronic kidney disease (CKD) population has not been well elucidated, especially in consideration for classical metabolic risk conditions such as hypertension, dyslipidemia, and diabetes, and those related to Ca metabolism. Among participants of the population-based Iwaki study of Japanese people, those with an estimated glomerular filtration rate (eGFR) ≧60 ml/min/1.73 m² and age ≧40 years, and who attended the study consecutively in 2014 and 2015 were enrolled (gender (M/F): 218/380; age: 58.9 ± 10.2). Regression analysis showed a significant correlation between serum Ca levels and a change in eGFR in the 1-year period (∆eGFR) after adjustment with multiple factors including those related to Ca metabolism (β = 0.184, p < 0.001). When subjects were stratified into tertiles based on their serum Ca levels (higher >9.6 mg/dL, middle 9.4–9.6 mg/dL, lower <9.4 mg/dL), lower serum Ca levels were a significant risk for a rapid decliner of eGFR designated as the lower one third of ∆eGFR (<−4.40 ml/min/1.73 m²) (odds ratio 2.41, 95% confidence interval 1.47–3.94). Lower serum Ca levels are a significant risk for rapid decrease in eGFR, independent of previously reported metabolic risk factors in this general population with non-CKD, or eGFR ≧60 ml/min/1.73 m².

Activation of mineralocorticoid receptor by ecdysone, an adaptogenic and anabolic ecdysteroid, promotes glomerular injury and proteinuria involving overactive GSK3β pathway signaling

Ecdysone is an arthropod molting hormone and has been marketed as a non-androgenic natural anabolic and adaptogen. However, the safety profile of ecdysone is largely undetermined. After ecdysone treatment for 2 weeks, mice developed albuminuria with histologic signs of glomerular injury, including hypertrophy, mesangial expansion, mild glomerulosclerosis and podocyte injury. A direct glomerulopathic activity of ecdysone seems to contribute, since addition of ecdysone to cultured glomerular cells induced cytopathic changes, including apoptosis, activation of mesangial cells, podocyte shape changes and a decreased expression of podocyte markers. To explore the molecular target responsible for the pathogenic actions, we employed an in silico modeling system of compound-protein interaction and identified mineralocorticoid receptor (MR) as one of the top-ranking proteins with putative interactions with ecdysone. The molecular structure of ecdysone was highly homologous to mineralocorticoids, like aldosterone. Moreover, ecdysone was capable of both inducing and activating MR, as evidenced by MR nuclear accumulation in glomerular cells both in vitro and in vivo following ecdysone treatment. Mechanistically, glycogen synthase kinase (GSK) 3β, which has been recently implicated in pathogenesis of glomerular injury and proteinuria, was hyperactivated in glomeruli in ecdysone-treated mice, concomitant with diverse glomerulopathic changes. In contrast, spironolactone, a selective blockade of MR, largely abolished the cytopathic effect of ecdysone in vitro and attenuated albuminuria and glomerular lesions in ecdysone treated mice, associated with a mitigated GSK3β overactivity in glomeruli. Altogether, ecdysone seems able to activate MR and thereby promote glomerular injury and proteinuria involving overactive GSK3β pathway signaling.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

RAGE-aptamer attenuates deoxycorticosterone acetate/salt-induced renal injury in mice

The mineralocorticoid receptor (MR) and its downstream signaling play an important role in hypertensive renal injury. The interaction of advanced glycation end products (AGE) with their receptor (RAGE) is involved in the progression of renal disease. However, the pathological crosstalk between AGE–RAGE axis and MR system in kidney derangement remains unclear. We screened DNA-aptamer directed against RAGE (RAGE-apt) in vitro and examined its effects on renal injury in uninephrectomized deoxycorticosterone acetate (DOCA)/salt-induced hypertensive mice. RAGE, GTP-bound Rac-1 (Rac1), and MR were co-localized in the podocytes of DOCA mice. The deletion of RAGE gene significantly inhibited mesangial matrix expansion and tubulointerstitial fibrosis in DOCA mice, which was associated with the reduction of glomerular oxidative stress, MR, Rac1, and urinary albumin excretion (UAE) levels. RAGE-apt attenuated the increase in carboxymethyllysine (CML), RAGE, nitrotyrosine, Rac1, and MR levels in the kidneys and reduced UAE in DOCA mice. Aldosterone (Aldo) increased nitrotyrosine, CML, and RAGE gene expression in murine podocytes, whereas CML stimulated MR and Rac1 levels, which were blocked by RAGE-apt. The present study indicates the crosstalk between the AGE–RAGE axis and Aldo–MR system, suggesting that RAGE-apt may be a novel therapeutic tool for the treatment of MR-associated renal diseases.

Angiotensin II induces cholesterol accumulation and injury in podocytes

Angiotensin II (Ang II) is a risk factor for the initiation and progression of chronic kidney disease (CKD), as elevated Ang II levels can lead to podocyte injury. However, there have been no studies on the role of Ang II in lipid metabolism or on podocyte injury caused by lipid dysfunction. Our study showed that Ang II induced lipid droplet (LD) accumulation and expression of the LD marker adipose differentiation-related protein (ADRP) in podocytes, and the extent of lipid deposition could be alleviated by losartan. Our study also demonstrated that Ang II increased the content of cholesterol in podocytes, which is an LD component, and this change was accompanied by decreased expression of the cholesterol efflux-related molecule ATP-binding cassette transporter-1 (ABCA1) and increased expression of the cholesterol uptake-related molecule LDL receptor (LDLR) and the cholesterol synthesis-related molecules sterol regulatory element-binding protein (SREBP1 and SREBP2) and 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR). Pretreating podocytes with methyl-β-cyclodextrin (CD), which induces cholesterol efflux, decreased Ang II-mediated cholesterol accumulation and Ang II-induced podocyte apoptosis and maintained the podocyte cytoskeleton and spreading. These results suggested that Ang II induced podocyte cholesterol accumulation by regulating the expression of cholesterol metabolism-related molecules and that the subsequent cholesterol metabolism dysfunction resulted in podocyte injury.

Identification of potential candidate genes for hypertensive nephropathy based on gene expression profile

Background

This study was aimed to explore the molecular mechanisms of hypertensive nephropathy (HTN).

Methods

Gene expression profile of GSE37460, which based on 27 healthy living donor samples (HTN group) and 15 hypertensive nephropathy samples (control group), were downloaded from Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) between two groups were identified. STRING database was used to reveal protein-protein interaction (PPI) network of DEGs, followed by the functional enrichment analysis of the PPI network. Additionally, miRNA-DEG regulatory network was constructed to reveal the validated miRNAs targeting the DEGs.

Results

In total, 51 up-regulated genes and 140 down-regulated genes were obtained. In the PPI network, cytochrome P450 3A4 (CYP3A4) and angiotensin II receptor type 1 (AGTR1) had a higher degree, and CYP3A4 interacted with CYP4A11. The DEGs in the network were significantly enriched in drug metabolism, focal adhesion and arachidonic acid metabolism. Furthermore, in the miRNA-DEG regulatory network, hsa-miR-335-5p and hsa-miR-26b-5p were the two most outstanding miRNAs. AGTR1, CYP3A4 and CYP4A11 were predicted to be regulated by hsa-miR-26b-5p.

Conclusion

The DEGs, such as AGTR1, CYP3A4 and CYP4A11 may play critical roles in the development of HTN likely via the regulation by hsa-miR-26b-5p and taking part in some pathways.

The Association of Vitamin D With Estimated Glomerular Filtration Rate and Albuminuria: 5th Korean National Health and Nutritional Examination Survey 2011-2012

OBJECTIVES

The kidney plays a key role in the metabolism of vitamin D. However, the relationship between GFR and 25(OH)D is not well understood. Moreover, few studies have investigated the effect of albuminuria, a known mediator of kidney function, on vitamin D levels. Our aim was to investigate the associations among estimated GFR (eGFR), albumin-creatinine ratio (ACR), and 25(OH)D.

METHODS

We investigated the relationship of 25-hydroxyvitamin D (25[OH]D) with eGFR and albuminuria in 11,336 adults who participated in the 5th Korea National Health and Nutrition Examination Survey (KNHANES) 2011-2012. The eGFR, ACR, and serum 25(OH)D were measured in participants who met the detailed inclusion criteria.

RESULTS

We found that after adjusting for covariates and log-ACR values, the mean (95% CI) eGFR decreased significantly with increasing 25(OH)D levels (Q1: 93.4 [92.7-94.0]; Q2: 91.9 [91.2-92.5]; Q3: 90.9 [90.3-91.6]; and Q4: 90.2 [89.5-90.8] mL/min/1.73m²; P < .001). However, the mean 25(OH)D value was highest at eGFR 61-90 mL/min per 1.73 m² and decreased significantly with decreasing eGFR levels (>90: 17.3 [17.1-17.5]; 61-90: 17.6 [17.4-17.8]; 46-60: 17.1 [16.2-18.0]; 31-45: 16.2 [14.2-18.2]; ≤30: 13.8 [17.0-10.7] ng/mL; P = .008). After adjusting for covariates and log-eGFR, the mean ACR decreased significantly with increasing 25(OH)D quartiles (Q1: 22.0 [18.1-25.9]; Q2: 20.4 [16.6-24.2]; Q3: 16.3 [12.5-20.0]; Q4: 15.0 [11.2-18.8] μg/mg; P = .043).

CONCLUSIONS

The mean eGFR values were negatively associated with 25(OH)D levels independently of ACR. However, the mean 25(OH)D values were decreased significantly with decreasing eGFR levels in moderate and severe chronic kidney disease stages. Also, the mean ACR values were negatively associated with 25(OH)D levels independently of eGFR in an Korean adult population.

Angiotensin II induces reorganization of the actin cytoskeleton and myosin light-chain phosphorylation in podocytes through rho/ROCK-signaling pathway

AIMS

In the present study, we have evaluated the effect of angiotensin II (Ang II) on actin cytoskeleton reorganization and myosin light-chain (MLC) phosphorylation in podocytes to demonstrate whether the Rho/Rho-associated coiled kinase (ROCK) pathway is involved podocyte injury.

METHODS

Eighteen male Sprague-Dawley rats were divided into three groups and treated with Ang II, saline or telmisartan. Morphological changes were studied at 28 days after treatment. Immunohistochemistry and Western blotting were used to determine the renal expression of p-MLC and ROCK2. Cultured podocytes were treated with Ang II (10(-7 )M) with or without Rho-kinase inhibitor (Y27632, 10(-6 )M) for variable time periods. F-actin was visualized with fluorescein isothiocyanate (FITC)-conjugated phalloidin or tetraethyl rhodamine isothiocyanate (TRITC)-conjugated phalloidin. p-MLC expression was evaluated by immunofluorescence and Western blot. The activation of Rho/ROCK was evaluated by Western blot.

RESULTS

The expression of p-MLC in glomeruli increased significantly in rats treated with Ang II when compared to the control rats as shown by Western blot (p < 0.05). In cultured podocytes, Rho A and ROCK2 increased after incubation with Ang II. Ang II increased the expression of ROCK2, which was accompanied with altered morphology, redistribution of actin and increased phosphorylation of MLC. The distribution of actin changed to a large extent, although overall quantitative differences were not observed. Addition of Y-27632 to podocytes treated with Ang II could ameliorate F-actin cytoskeleton remodeling and the increment in p-MLC expression.

CONCLUSION

Ang II-induced podocyte cytoskeleton protein expression changing through the RhoA/ROCK2 p-MLC/F-actin pathway.

Causes and pathogenesis of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) describes both a common lesion in progressive kidney disease, and a disease characterized by marked proteinuria and podocyte injury. The initial injuries vary widely. Monogenetic forms of FSGS are largely due to alterations in structural genes of the podocyte, many of which result in early onset of disease. Genetic risk alleles in apolipoprotein L1 are especially prevalent in African Americans, and are linked not only to adult-onset FSGS but also to progression of some other kidney diseases. The recurrence of FSGS in some transplant recipients whose end-stage renal disease was caused by FSGS points to circulating factors in disease pathogenesis, which remain incompletely understood. In addition, infection, drug use, and secondary maladaptive responses after loss of nephrons from any cause may also cause FSGS. Varying phenotypes of the sclerosis are also manifest, with varying prognosis. The so-called tip lesion has the best prognosis, whereas the collapsing type of FSGS has the worst prognosis. New insights into glomerular cell injury response and repair may pave the way for possible therapeutic strategies.

A possible mechanism for the progression of chronic renal disease and congestive heart failure

Chronic neurologic diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as various forms of chronic renal disease and systolic congestive heart failure, are among the most common progressive degenerative disorders encountered in medicine. Each disease follows a nearly relentless course, albeit at varying rates, driven by progressive cell dysfunction and drop-out. The neurologic diseases are characterized by the progressive spread of disease-causing proteins (prion-like proteins) from cell to cell. Recent evidence indicates that cell autonomous renin angiotensin systems operate in heart and kidney, and it is known that functional intracrine proteins can also spread between cells. This then suggests that certain progressive degenerative cardiovascular disorders such as forms of chronic renal insufficiency and systolic congestive heart failure result from dysfunctional renin angiotensin system intracrine action spreading in kidney or myocardium.

Roles of Na⁺/H⁺ exchanger type 1 and intracellular pH in angiotensin II-induced reactive oxygen species generation and podocyte apoptosis

A growing body of evidence suggests that podocyte apoptosis is a major cause of decreased podocyte number, which leads to albuminuria and glomerular injury. The aim of this study was to clarify the molecular mechanisms of angiotensin II (Ang II)-induced apoptosis in cultured mouse podocytes. We examined the effects of Ang II (100 nmol/L) on apoptosis, superoxide anions, and cytosol pH in podocytes. For intracellular pH measurements, image analysis was conducted using confocal laser microscopy after incubation with carboxy-seminaphthorhodafluor-1. Superoxide anions and intracellular pH were elevated with Ang II treatment. Apoptotic cell numbers, as measured by TUNEL staining and caspase 3 activity, were also augmented in the Ang II-treated group. Pre-treatment with olmesartan (100 nmol/L, an Ang II type 1-receptor blocker), apocynin (50 μmol/L, NADPH oxidase inhibitor), or 5-N,N hexamethylene amiloride [30 μmol/L, Na⁺/H⁺ exchanger type 1 (NHE-1) inhibitor] abolished Ang II-induced podocyte apoptosis, whereas NHE-1 mRNA and protein expression was not affected by Ang II treatment. Moreover, Ang II increased NHE-1 phosphorylation. These results suggest that superoxide production, NHE-1 activation, and intracellular alkalization were early features prior to apoptosis in Ang II-treated mouse podocytes, and may offer new insights into the mechanisms responsible for Ang II-induced podocyte injury.

Calmodulin-dependent protein kinase II/cAMP response element-binding protein/Wnt/β-catenin signaling cascade regulates angiotensin II-induced podocyte injury and albuminuria

Angiotensin II (Ang II) plays a pivotal role in promoting podocyte dysfunction and albuminuria, however, the underlying mechanisms have not been fully delineated. In this study, we found that Ang II induced Wnt1 expression and β-catenin nuclear translocation in cultured mouse podocytes. Blocking Wnt signaling with Dickkopf-1 (Dkk1) or β-catenin siRNA attenuated Ang II-induced podocyte injury. Ang II could also induce the phosphorylation of calmodulin-dependent protein kinase (CaMK) II and cAMP response element-binding protein (CREB) in cultured podocytes. Blockade of this pathway with CK59 or CREB siRNA could significantly inhibit Ang II-induced Wnt/β-catenin signaling and podocyte injury. In in vivo studies, administration of Ang II promoted Wnt/β-catenin signaling, aggregated podocyte damage, and albuminuria in mice. CK59 could remarkably ameliorate Ang II-induced podocyte injury and albuminuria. Furthermore, ectopic expression of exogenous Dkk1 also attenuated Ang II-induced podocytopathy in mice. Taken together, this study demonstrates that the CaMK II/CREB/Wnt/β-catenin signaling cascade plays an important role in regulating Ang II-induced podocytopathy. Targeting this signaling pathway may offer renal protection against the development of proteinuric kidney diseases.

A review on the role of quinones in renal disorders

Quinones are electron and proton carriers that play a primary role in the aerobic metabolism of virtually every cell in nature. Most physiological quinones are benzoquinones. They undergo highly regulated redox reactions in the mitochondria, Golgi apparatus, plasma membrane and endoplasmic reticulum. Important consequences of these electron transfer reactions are the production of and protection against reactive oxygen species (ROS). Quinones have been extensively studied for both their cytotoxic as well as cellular protective properties and they have been particularly useful in rational drug design. The role of quinones in medicine is explored in this literature review with a particular focus on renal diseases. Due to their high basal metabolism and detoxification role, the kidneys are particularly sensitive to oxidative stress. Regardless of the underlying etiology, ROS plays an important role in both acute kidney injury (AKI) and chronic kidney diseases (CKD). Depending on the oxidative state of the kidney, quinones can be nephrotoxoic or nephro-protective. Many factors play a role in the interaction between quinones and the kidney and the consequences of this are just beginning to be explored.

A case of secondary focal segmental glomerulosclerosis associated with malignant hypertension

Focal segmental glomerulosclerosis (FSGS) is associated with various clinicopathological conditions, including hypertension. We report here a case of secondary FSGS associated with malignant hypertension. A 33-year-old man with a 1-month history of visual impairment and headache visited the Department of Ophthalmology at our hospital and was found to have hypertensive retinopathy and severe hypertension (230/160 mmHg). He was referred to our department based on suspected renal dysfunction. His blood pressure on admission was 250/130 mmHg. Physical examination and laboratory tests revealed hypertensive cardiac dysfunction, focal brain edema, renal dysfunction (serum creatinine, Cr 7.07 mg/dl, blood urea nitrogen, BUN 49.9 mg/dl), massive proteinuria (10.7 g/day), and thrombotic microangiopathy. Funduscopy showed exudate, hemorrhage, and papilledema. The cause of secondary hypertension could not be identified. He was treated for primary malignant hypertension, but required hemodialysis 3 days after admission due to anuria. Treatment with antihypertensive agents resulted in the gradual recovery of renal function, although heavy proteinuria continued with nephrotic syndrome. Renal biopsy performed 1 month after admission showed features of malignant nephrosclerosis with secondary FSGS. Hemodialysis was discontinued following further improvement in renal function and the most recent laboratory tests showed proteinuria 1.8 g/day and persistent renal dysfunction (BUN 36.5 mg/dl, Cr 3.14 mg/dl). Malignant hypertension may cause various injuries, including glomerular endothelial and epithelial cell injuries in glomerular hypertension and hyperfiltration, increase of the renin-angiotensin-aldosterone system, and endothelial-epithelial interaction, resulting in the development of secondary FSGS and heavy proteinuria.

Oxidative damages in tubular epithelial cells in IgA nephropathy: role of crosstalk between angiotensin II and aldosterone

Background

Inhibition of the renin-angiotensin-aldosterone system (RAAS) slows down the progression of chronic renal diseases (CKD) including IgA nephropathy (IgAN). Herein, we studied the pathogenetic roles of aldosterone (Aldo) in IgAN.

Methods

Human mesangial cells (HMC) was activated with polymeric IgA (pIgA) from IgAN patients and the effects on the expression of RAAS components and TGF-β synthesis examined. To study the roles of RAAS in the glomerulotubular communication, proximal tubular epithelial cells (PTEC) was cultured with conditioned medium from pIgA-activated HMC with eplerenone or PD123319, the associated apoptotic event was measured by the generation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and reactive oxygen species (ROS).

Results

Polymeric IgA up-regulated the Aldo synthesis and aldosterone synthase expression by HMC. The release of TGF-β by HMC was up-regulated synergistically by AngII and Aldo and this was inhibited by incubation of HMC with losartan plus eplerenone. Cultured PTEC express the mineralocorticoid receptor, but not synthesizing aldosterone. Apoptosis, demonstrated by cleaved PARP expression and caspase 3 activity, was induced in PTEC activated by conditioned medium prepared from HMC cultured with pIgA from IgAN patients. This apoptotic event was associated with increased generation of NADPH oxidase and ROS. Pre-incubation of PTEC with PD123319 and eplerenone achieved complete inhibition of PTEC apoptosis.

Conclusions

Our data suggest that AngII and Aldo, released by pIgA activated HMC, served as mediators for inducing apoptosis of PTEC in glomerulo-tubular communications. Crosstalk between AngII and Aldo could participate in determining the tubular pathology of IgAN.

Podocyte COX-2 exacerbates diabetic nephropathy by increasing podocyte (pro)renin receptor expression

Diabetic nephropathy (DN) increases podocyte cyclooxygenase-2 (COX-2) expression, and COX-2 inhibition reduces proteinuria and glomerular injury in animal models of diabetes. To investigate the role of podocyte COX-2 in development of diabetic nephropathy, we employed a streptozotocin model of diabetic mellitus in wild-type and transgenic mice expressing COX-2 selectively in podocytes. Progressive albuminuria developed only in diabetic COX-2 transgenic mice despite hyperglycemia, BP, and GFR being similar to those in wild-type mice. Transgenic mice also manifested significant foot-process effacement, moderate mesangial expansion, and segmental thickening of the glomerular basement membrane. In cultured podocytes overexpressing COX-2, high glucose induced cell injury and increased both expression of the pro(renin) receptor and activation of the renin-angiotensin system. Downregulation of the (pro)renin receptor attenuated the injury induced by high glucose. In vivo, podocyte pro(renin) receptor expression increased in diabetic COX-2-transgenic mice, and treatment with a COX-2 inhibitor abrogated the upregulation of (pro)renin receptor and reduced albuminuria, foot-process effacement, and mesangial matrix expansion. In summary, these results demonstrate that increased expression of podocyte COX-2 predisposes to diabetic glomerular injury and that the (pro)renin receptor may be one mediator for this increased susceptibility to injury.

Serum 25-hydroxyvitamin D and change in estimated glomerular filtration rate

BACKGROUND AND OBJECTIVES

Mounting evidence suggests that 1,25-dihydroxyvitamin D prevents the progression of chronic kidney disease (CKD). It is not clear whether "nutritional" forms of vitamin D affect GFR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We tested whether serum 25-hydroxyvitamin D concentration (25(OH)D), a measure of total vitamin D intake from cutaneous synthesis and dietary consumption, is associated with loss of estimated GFR among 1705 older adults with predominantly normal baseline kidney function participating in the Cardiovascular Health Study. Baseline 25(OH)D was measured by HPLC-tandem mass spectrometry. GFR was estimated at baseline and 4 years later using the CKD-EPI formula, with rapid GFR loss defined as 12 ml/min per 1.73 m(2) or more over 4 years.

RESULTS

Rapid GFR loss was observed for 207 participants (12%). Each 10 ng/ml lower 25(OH)D was associated with a 25% greater risk of rapid GFR loss (95% confidence interval [CI] 5%, 49%, P = 0.01), adjusting for potential confounding characteristics. Compared with 25(OH)D ≥30 ng/ml, 25(OH)D concentrations 15 to 29 ng/ml and <15 ng/ml were associated with 29% (95% CI -13%, 91%) and 68% (95% CI 1%, 177%) greater adjusted risks of rapid GFR loss, respectively. Magnitudes of association were largest among participants with diabetes.

RESULTS

were similar evaluating a composite outcome of rapid GFR loss, end stage renal disease, and death. Conclusions Insufficient 25(OH)D may be a modifiable risk factor for early GFR loss. We recommend clinical trials to determine whether vitamin D supplementation prevents the development and progression of CKD.

Clinicopathological characteristics of obesity-associated focal segmental glomerulosclerosis

Obesity-related glomerulopathy (ORG) is a secondary form of focal segmental glomerulosclerosis (FSGS) occurring in obese patients with a body-mass index higher than 30 kg/m(2). It is typically manifested by nephrotic-range proteinuria without full nephrotic syndrome, and progressive renal insufficiency. Characteristic morphologic features include the consistent presence of glomerulomegaly, predominance of perihilar variant of FSGS, and the relatively mild fusion of visceral epithelial cell foot processes. The concept of podocyte depletion as a driver of the glomerular scarring in obesity-associated FSGS is well documented. The underlying mechanisms are likely to be related in part to the oxidative stress and the impairment of the integrity of the slit diaphragm and cell adhesion resulting mainly from angiotensin II and transforming growth factor-β. These proapoptotic cytokines are upregulated in obesity in response to insulin resistance, compensatory hyperinsulinemia and glomerular hyperfiltration-hypertension mediated mechanical stress. This review is designed to discuss the clinicopathologic features of obesity-associated FSGS, with a focus on the podocyte injury, which is involved in the onset and progression of the glomerulosclerotic process. Ultrastructural glomerular lesions are documented.

Podocyte dysfunction in aging--related glomerulosclerosis

We review podocyte molecular structure and function, consider the underlying mechanisms related to podocyte dysfunction and propose that podocyte dysfunction be considered in the evaluation and management of age-associated glomerulosclerosis. With aging, progressive sympathetic activation, increased intrarenal renin-angiotensin system (RAS) activity, endothelin system and oxidative stress and reduced nitric oxide (NO)-availability can damage podocytes. Apoptosis and proliferation are the principal podocyte changes following injury with the latter leading to sclerosis and loss of nephrons. Podocyte loss can be evaluated by either determining their average number in biopsed glomeruli or by estimating podocyte number or their associated molecules in urine sediment. Podocyturia may be considered a marker of active glomerular disease. Preliminary data suggest that antiadrenergic drugs, angiotensin converting enzyme (ACE) inhibitors, RAS blocking drugs, endothelin system inhibitors and reduced oxidative stress can protect podocytes. Thus podocytes appear to play an important role in the pathogenesis, evaluation and therapy of age related glomerulosclerosis.

Glucose, insulin, and incident hypertension in the multi-ethnic study of atherosclerosis

Diabetes mellitus and hypertension commonly coexist, but the nature of this link is not well understood. The authors tested whether diabetes and higher concentrations of fasting serum glucose and insulin are associated with increased risk of developing incident hypertension in the community-based Multi-Ethnic Study of Atherosclerosis. At baseline, 3,513 participants were free of hypertension, defined as systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihypertensive medications to treat high blood pressure. Of these, 965 participants (27%) developed incident hypertension over 4.7 years' median follow-up between 2002 and 2007. Compared with participants with normal baseline fasting glucose, those with impaired fasting glucose and diabetes had adjusted relative risks of hypertension of 1.16 (95% confidence interval (CI): 0.96, 1.40) and 1.41 (95% CI: 1.17, 1.71), respectively (P = 0.0015). The adjusted relative risk of incident hypertension was 1.08 (95% CI: 1.04, 1.13) for each mmol/L higher glucose (P < 0.0001) and 1.15 (95% CI: 1.05, 1.25) for each doubling of insulin (P = 0.0016). Further adjustment for serum cystatin C, urinary albumin/creatinine ratio, and arterial elasticity measured by tonometry substantially reduced the magnitudes of these associations. In conclusion, diabetes and higher concentrations of glucose and insulin may contribute to the development of hypertension, in part through kidney disease and arterial stiffness.

Activation of NFAT signaling in podocytes causes glomerulosclerosis

Mutant forms of TRPC6 can activate NFAT-dependent transcription in vitro via calcium influx and activation of calcineurin. The same TRPC6 mutants can cause FSGS, but whether this involves an NFAT-dependent mechanism is unknown. Here, we generated mice that allow conditional induction of NFATc1. Mice with NFAT activation in nascent podocytes in utero developed proteinuria and glomerulosclerosis postnatally, resembling FSGS. NFAT activation in adult mice also caused progressive proteinuria and FSGS. Ultrastructural studies revealed podocyte foot process effacement and deposition of extracellular matrix. NFAT activation did not initially affect expression of podocin, synaptopodin, and nephrin but reduced their expression as glomerular injury progressed. In contrast, we observed upregulation of Wnt6 and Fzd9 in the mutant glomeruli before the onset of significant proteinuria, suggesting a potential role for Wnt signaling in the pathogenesis of NFAT-induced podocyte injury and FSGS. These results provide in vivo evidence for the involvement of NFAT signaling in podocytes, proteinuria, and glomerulosclerosis. Furthermore, this study suggests that NFAT activation may be a key intermediate step in the pathogenesis of mutant TRPC6-mediated FSGS and that suppression of NFAT activity may contribute to the antiproteinuric effects of calcineurin inhibitors.

The glomerulus--a view from the outside--the podocyte

In the past decade, podocyte research has been greatly aided by the development of powerful new molecular, cellular and animal tools, leading to elucidation of an increasing number of proteins involved in podocyte function and identification of mutated genes in hereditary glomerulopathies. Accumulating evidence indicates that podocyte disorders may not only underlie these hereditary glomerulopathies but also play crucial role in a broad spectrum of acquired glomerular diseases. Genetic susceptibility, environmental influence and systemic responses are all involved in the mediation of the pathogenesis of podocytopathies. Injured podocytes may predisopose to further injury of other podocytes and other adjacent/distant renal cells in a vicious cycle, leading to inexorable progression of glomerular injury. The classic view is that podocytes have a limited ability to proliferate in the normal mature kidney. However, recent research in rodents has provided suggestive evidence for podocyte regeneration resulting from differentiation of progenitor cells within Bowman's capsule.

Elevations in serum creatinine with RAAS blockade: why isn't it a sign of kidney injury?

PURPOSE OF REVIEW

The aim of this article is to review the pertinent physiology and pathophysiology of the renin-angiotensin-aldosterone system (RAAS), summarize the proven beneficial cardiovascular and renal effects of RAAS blockade, examine clinical situations in which RAAS blockade may induce reductions in glomerular filtration rate, and explore why increases in serum creatinine in the setting of angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) therapy do not necessarily signify the presence of clinically relevant kidney failure.

RECENT FINDINGS

RAAS inhibition appears to reduce the likelihood of atrial fibrillation. RAAS inhibition leads to improved insulin sensitivity and glycemic control, but does not appear to prevent diabetes. The beneficial effects of ACEi/ARB therapy extend to those with significant renal disease. Combination ACEi/ARB is safe, and reduces proteinuria more than either agent alone in patients with macroalbuminuric nephropathy. Acute deteriorations in renal function that result from RAAS inhibition are usually reversible.

SUMMARY

RAAS blockade exerts potent hemodynamic, antihypertensive, and antiinflammatory effects, and slows progression of kidney disease beyond that due to lowering of blood pressure. The benefit extends to those with advanced disease. In spite of established benefit, ACEi and ARB therapy remains underutilized, in part due to concerns about acute deteriorations in renal function that result from interruption of the RAAS.

Angiotensin-(1-7) prevents activation of NADPH oxidase and renal vascular dysfunction in diabetic hypertensive rats

BACKGROUND/AIM

We examined the influence of chronic treatment with angiotensin-(1-7) [Ang-(1-7)] on renox (renal NADPH oxidase, NOX-4) and the development of renal dysfunction in streptozotocin-treated spontaneously hypertensive rats (diabetic SHR).

METHODS

Mean arterial pressure, urinary protein and vascular responsiveness of the isolated renal artery to vasoactive agonists were studied in vehicle- or Ang-(1-7)-treated SHR and diabetic SHR.

RESULTS

Ang-(1-7) decreased the elevated levels of renal NADPH oxidase (NOX) activity and attenuated the activation of NOX-4 gene expression in the diabetic SHR kidney. Ang-(1-7) treatment increased sodium excretion but did not affect mean arterial pressure in diabetic SHR. There was a significant increase in urinary protein (266 +/- 22 mg/24 h) in the diabetic compared to control SHR (112 +/- 13 mg/24 h) and treatment of diabetic SHR with Ang-(1-7) reduced the degree of proteinuria (185 +/- 23 mg/24 h, p < 0.05). Ang-(1-7) treatment also attenuated the diabetes-induced increase in renal vascular responsiveness to endothelin-1, norepinephrine, and angiotensin II in SHR, but significantly increased the vasodilation of the renal artery of SHR and diabetic SHR to the vasodilator agonists.

CONCLUSION

These results suggest that treatment with Ang-(1-7) constitutes a potential therapeutic strategy to alleviate NOX-mediated oxidative stress and to reduce renal dysfunction in diabetic hypertensive rats.

25-Hydroxyvitamin D levels and albuminuria in the Third National Health and Nutrition Examination Survey (NHANES III)

BACKGROUND

Albuminuria is a risk factor for chronic kidney disease progression, end-stage renal disease, cardiovascular events, and mortality. Animal studies suggested that vitamin D insufficiency may contribute to the pathogenesis of albuminuria.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

15,068 adults participating in the Third National Health and Nutrition Examination Survey.

PREDICTOR

Serum 25-hydroxyvitamin D concentration, examined in quartiles.

OUTCOMES & MEASUREMENTS

Albuminuria, defined using established sex-specific cutoff values for urine albumin-creatinine ratio (25 to 2,999 mg/g for women, 17 to 2,999 mg/g for men).

RESULTS

A stepwise increase in the prevalence of albuminuria was observed with decreasing quartiles of vitamin D concentration: 8.9%, 11.5%, 13.7%, and 15.8% (P < 0.001). Adjusting for age, sex, race/ethnicity, region and season of measurement, smoking status, body mass index, and estimated glomerular filtration rate, relative risks for albuminuria by decreasing quartile of vitamin D concentration were 1.00 (reference group), 1.14 (95% confidence interval, 0.95 to 1.37), 1.22 (95% confidence interval, 1.03 to 1.45), and 1.37 (95% confidence interval, 1.10 to 1.71; P = 0.006). Additionally adjusting for blood pressure and diabetes mellitus, these risks were somewhat attenuated and retained statistical significance.

LIMITATIONS

The cross-sectional design of this study does not allow demonstration of temporal or causal relationships between vitamin D and albuminuria.

CONCLUSIONS

Additional studies are needed to clarify the relationship of vitamin D with albuminuria and determine whether vitamin D therapy prevents or improves markers of kidney and cardiovascular disease.