Mechanism of increased angiotensin II levels in glomerular mesangial cells cultured in high glucose

Potential therapeutic value of melatonin in diabetic nephropathy: improvement beyond anti-oxidative stress

Diabetic nephropathy (DN) is a common complication of diabetes, and it is also the main cause of chronic renal failure. Physiological/pathological changes mediated by high glucose are the main factors causing injury of DN, including the enhancement of polyol pathway, the accumulation of advanced glycation products (AGEs), and the activation of protein kinase C (PKC) and transforming growth factor-β (TGF-β) signals. In addition, the abnormal activation of renin-angiotensin system (RAS) and oxidative stress are also involved. Melatonin is a physiological hormone mainly secreted by the pineal gland which has been proved to be related to diabetes. Studies have shown that exogenous melatonin intervention can reduce blood glucose and alleviate high glucose mediated pathological damage. At the same time, melatonin also has a strong antioxidant effect, and can inhibit the activation of RAS. Therefore, it is of great significance to explore the therapeutic effect and value of melatonin on DN.

[Classical nephroprotection: Renin angiotensin aldosterone system inhibitors]

The role of the renin angiotensin aldosterone system (RAAS) in the pathophysiology of hypertension, cardiovascular disease and kidney disease has been known for years. RAAS inhibitors have been the mainstay of chronic kidney disease (CKD) treatment. Studies have shown that therapy with angiotensin-converting enzyme inhibitors (ACE inhibitors) or angiotensinII receptor blockers (ARBs) reduce the excretion of albuminuria and slow the progression of kidney disease in patients with and without diabetes. In clinical practice, RAAS inhibitors are recommended as the antihypertensive of choice in patients with CKD and albuminuria with or without diabetes. In addition, they have demonstrated cardiovascular benefits beyond blood pressure control. The use of RAAS inhibitors in non-proteinuric nephropathy and advanced CKD is not without controversy. Double blockade of the RAAS is contraindicated. On the other hand, it is essential to know how to titrate doses and avoid side effects, mainly hyperkalaemia.

The Mechanism of Hyperglycemia-Induced Renal Cell Injury in Diabetic Nephropathy Disease: An Update

Diabetic Nephropathy (DN) is a serious complication of type I and II diabetes. It develops from the initial microproteinuria to end-stage renal failure. The main initiator for DN is chronic hyperglycemia. Hyperglycemia (HG) can stimulate the resident and non-resident renal cells to produce humoral mediators and cytokines that can lead to functional and phenotypic changes in renal cells and tissues, interference with cell growth, interacting proteins, advanced glycation end products (AGEs), etc., ultimately resulting in glomerular and tubular damage and the onset of kidney disease. Therefore, poor blood glucose control is a particularly important risk factor for the development of DN. In this paper, the types and mechanisms of DN cell damage are classified and summarized by reviewing the related literature concerning the effect of hyperglycemia on the development of DN. At the cellular level, we summarize the mechanisms and effects of renal damage by hyperglycemia. This is expected to provide therapeutic ideas and inspiration for further studies on the treatment of patients with DN.

Urinary Angiotensinogen in Patients With Type 1 Diabetes With Microalbuminuria: Gender Differences and Effect of Intensive Insulin Therapy

Introduction

Angiotensinogen (AOG) is the precursor of peptides of the renin angiotensin system (RAS). Because insulin up-regulates transcriptional factors that normally repress kidney AOG synthesis, we evaluated urinary AOG (uAOG) in patients with type 1 diabetes (T1D) and microalbuminuria who are receiving either intensive or conventional insulin therapy.

Methods

Urine samples from participants of the Diabetes Control and Complications Trial (DCCT) were used for the following: (i) uAOG/creatinine measurements in 103 patients with microalbuminuria and 103 patients with normoalbuminuria, matched for age, gender, disease duration, and allocation to insulin therapy; and (ii) uAOG/creatinine measurements from patients with microalbuminuria allocated to intensive insulin therapy (n = 58) or conventional insulin therapy (n = 41) after 3 years on each modality.

Results

uAOG was higher in patients who started with microalbuminuria than in those with normoalbuminuria (6.65 vs. 4.0 ng/mg creatinine, P < 0.01). uAOG was higher in females than in males with microalbuminuria (11.7 vs. 5.4 ng/mg creatinine, P = 0.015). uAOG was lower in patients with microalbuminuria allocated to intensive insulin therapy than in conventional insulin therapy (3.98 vs. 7.42 ng/mg creatinine, P < 0.01). These differences in uAOG were observed though albumin excretion rate (AER) was not significantly different.

Conclusion

In patients with T1D and microalbuminuria, uAOG is increased and varies with gender and the type of insulin therapy independently of AER. This suggests that AOG production is increased in females and it is decreased by intensive insulin therapy. The reduction in uAOG with intensive insulin therapy, by kidney RAS downregulation, may contribute to the known renoprotective action associated with intensive insulin and improved glycemic control.

The role of protein kinase C in diabetic microvascular complications

Protein kinase C (PKC) is a family of serine/threonine protein kinases, the activation of which plays an important role in the development of diabetic microvascular complications. The activation of PKC under high-glucose conditions stimulates redox reactions and leads to an accumulation of redox stress. As a result, various types of cells in the microvasculature are influenced, leading to changes in blood flow, microvascular permeability, extracellular matrix accumulation, basement thickening and angiogenesis. Structural and functional disorders further exacerbate diabetic microvascular complications. Here, we review the roles of PKC in the development of diabetic microvascular complications, presenting evidence from experiments and clinical trials.

N-type calcium channel and renal injury

Accumulating evidences indicated that voltage-gated calcium channels (VDCC), including L-, T-, N-, and P/Q-type, are present in kidney and contribute to renal injury during various chronic diseases trough different mechanisms. As a voltage-gated calcium channel, N-type calcium channel was firstly been founded predominately distributed on nerve endings which control neurotransmitter releases. Since sympathetic nerve is distributed along renal afferent and efferent arterioles, N-type calcium channel blockade on sympathetic nerve terminals would bring renal dynamic improvement by dilating both arterioles and reducing glomerular pressure. In addition, large body of scientific research indicated that neurotransmitters, such as norepinephrine, releases by activating N-type calcium channel can trigger inflammatory and fibrotic signaling pathways in kidney. Interestingly, we recently demonstrated that N-type calcium channel is also expressed on podocytes and may directly contribute to podocyte injury in denervated animal models. In this paper, we will summarize our current knowledge regarding renal N-type calcium channels, and discuss how they might contribute to the river that terminates in renal injury.

Management of hypertension and renin-angiotensin-aldosterone system blockade in adults with diabetic kidney disease: Association of British Clinical Diabetologists and the Renal Association UK guideline update 2021

People with type 1 and type 2 diabetes are at risk of developing progressive chronic kidney disease (CKD) and end-stage kidney failure. Hypertension is a major, reversible risk factor in people with diabetes for development of albuminuria, impaired kidney function, end-stage kidney disease and cardiovascular disease. Blood pressure control has been shown to be beneficial in people with diabetes in slowing progression of kidney disease and reducing cardiovascular events. However, randomised controlled trial evidence differs in type 1 and type 2 diabetes and different stages of CKD in terms of target blood pressure. Activation of the renin-angiotensin-aldosterone system (RAAS) is an important mechanism for the development and progression of CKD and cardiovascular disease. Randomised trials demonstrate that RAAS blockade is effective in preventing/ slowing progression of CKD and reducing cardiovascular events in people with type 1 and type 2 diabetes, albeit differently according to the stage of CKD. Emerging therapy with sodium glucose cotransporter-2 (SGLT-2) inhibitors, non-steroidal selective mineralocorticoid antagonists and endothelin-A receptor antagonists have been shown in randomised trials to lower blood pressure and further reduce the risk of progression of CKD and cardiovascular disease in people with type 2 diabetes. This guideline reviews the current evidence and makes recommendations about blood pressure control and the use of RAAS-blocking agents in different stages of CKD in people with both type 1 and type 2 diabetes.

Retinal Protein O-GlcNAcylation and the Ocular Renin-angiotensin System: Signaling Cross-roads in Diabetic Retinopathy

It is well established that diabetes and its associated hyperglycemia negatively impact retinal function, yet we know little about the role played by augmented flux through the Hexosamine Biosynthetic Pathway (HBP). This offshoot of the glycolytic pathway produces UDP-Nacetyl- glucosamine, which serves as the substrate for post-translational O-linked modification of proteins in a process referred to as O-GlcNAcylation. HBP flux and subsequent protein O-GlcNAcylation serve as nutrient sensors, enabling cells to integrate metabolic information to appropriately modulate fundamental cellular processes including gene expression. Here we summarize the impact of diabetes on retinal physiology, highlighting recent studies that explore the role of O-GlcNAcylation- induced variation in mRNA translation in retinal dysfunction and the pathogenesis of Diabetic Retinopathy (DR). Augmented O-GlcNAcylation results in wide variation in the selection of mRNAs for translation, in part, due to O-GlcNAcylation of the translational repressor 4E-BP1. Recent studies demonstrate that 4E-BP1 plays a critical role in regulating O-GlcNAcylation-induced changes in the translation of the mRNAs encoding Vascular Endothelial Growth Factor (VEGF), a number of important mitochondrial proteins, and CD40, a key costimulatory molecule involved in diabetes-induced retinal inflammation. Remarkably, 4E-BP1/2 ablation delays the onset of diabetes- induced visual dysfunction in mice. Thus, pharmacological interventions to prevent the impact of O-GlcNAcylation on 4E-BP1 may represent promising therapeutics to address the development and progression of DR. In this regard, we discuss the potential interplay between retinal O-GlcNAcylation and the ocular renin-angiotensin system as a potential therapeutic target of future interventions.

Baseline Urinary Angiotensinogen Excretion Predicts Deterioration of the Kidney Function in Patients with Chronic Kidney Disease

Objective The intrarenal renin-angiotensin system (RAS) is activated in patients with chronic kidney disease (CKD), and urinary angiotensinogen (AGT) levels, a surrogate marker of the intrarenal RAS activation, are associated with blood pressure (BP) and urinary albumin excretion. In addition, it has been shown that changes in urinary AGT levels correlate with annual changes in the estimated glomerular filtration rate (eGFR) in patients with type 2 diabetes and that elevated levels of urinary AGT in type 2 diabetic patients with albuminuria are a high-risk factor for worsening renal and cardiovascular complications. However, whether or not baseline urinary AGT levels predict deterioration of the kidney function in all patients with CKD is unclear. Methods We recruited 62 patients with CKD whose eGFR was >15 mL/min/1.73 m². We performed 24-hour ambulatory BP monitoring at 30-min intervals and daily urinary collection to examine the urinary AGT levels and albumin excretion and measured the levels of plasma angiotensin II (Ang II), a surrogate marker of circulating RAS. In addition, annual changes in the eGFR were followed up for 3.4±1.5 years. Results Annual changes in the eGFR were significantly and negatively associated with urinary AGT levels (r=-0.31, p=0.015) as well as the age, systolic BP, and urinary albumin levels. In contrast, annual changes in the eGFR were not correlated with plasma Ang II levels. Furthermore, when dividing patients into quartiles according to urinary AGT levels, patients with the highest urinary AGT levels showed a progressive decline in the eGFR. Conclusion These results suggest that elevated baseline urinary AGT levels can predict renal dysfunction in patients with CKD.

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.

Renin-Angiotensin System overactivation in polycystic ovary syndrome, a risk for SARS-CoV-2 infection?

Background

The SARS-CoV-2 coronavirus gains entry to target cells via the angiotensin-converting enzyme 2 (ACE2) receptor present on cells in blood vessels, lungs, heart, intestines, and kidneys. Renin-Angiotensin System (RAS) overactivity has also been described in metabolic syndrome, type 2 diabetes (T2D) and obesity, conditions shared by women with polycystic ovary syndrome (PCOS) We hypothesized that RAS overactivity may be present in PCOS.

Methods

We determined plasma levels of RAS-related proteins in a cohort of age matched control women (n = 97) and women with PCOS (n = 146). Plasma levels of RAS-related proteins (ACE2, Renin and Angiotensinogen (AGT)) were determined by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement.

Results

PCOS women had a higher BMI (p < 0.001), systolic (p < 0.0001) and diastolic (p < 0.05) blood pressure, waist circumference (p < 0.0001), testosterone (p < 0.0001), free androgen index (p < 0.0001) and CRP (p < 0.0001). Renin was elevated in PCOS (p < 0.05) and angiotensinogen was lower in PCOS (p < 0.05), indicating overactivity of the RAS system in PCOS. ACE2 levels were lower in PCOS (p < 0.05), suggesting that PCOS women are at risk for development of hypertension.

Conclusion

RAS proteins levels differed between PCOS and control women, suggesting that the insulin resistance inherent in PCOS may predispose these women to more severe COVID-19 infection.

TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Background

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-β1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-β1 in a number of different cell types; although this has not been demonstrated in HPMC.

Objective

To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-β1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-β1 and proliferation of HPMC.

Methods

Expression of mRNA for the AII-forming pathway and TGF-β1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-β1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-β1 and the proliferation of HPMC incubated at high glucose for 48 hours.

Results

AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-β1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of AII and TGF-β1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-β1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs.

Conclusion

The present study provides evidence that ( 1 ) HPMC express mRNA for the AII-forming pathway; ( 2 ) ACEI and ARB inhibit the TGF-β1 production induced by high glucose; ( 3 ) the AII-forming pathway is one mechanism by which high glucose causes production of TGF-β1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.

Angiotensin II Mediates High Glucose-Induced TGF-β1 and Fibronectin Upregulation in HPMC through Reactive Oxygen Species

Objective

To demonstrate the presence of an independent renin–angiotensin system (RAS) in the peritoneum and to determine the role of locally produced angiotensin (Ang) II in high glucose-induced upregulation of transforming growth factor (TGF)-β1 and fibronectin by human peritoneal mesothelial cells (HPMC).

Methods

In cultured HPMC, the expression of mRNAs for angiotensinogen, angiotensin-converting enzyme (ACE), Ang II type 1 receptor (AT1), and TGF-β1 was evaluated by real-time polymerase chain reaction; ACE, AT1, and fibronectin proteins by Western blot analysis; and Ang I, Ang II, and TGF-β1 proteins by ELISA. Dichlorofluorescein (DCF)-sensitive cellular reactive oxygen species (ROS) were measured by fluorometry.

Results

HPMC constitutively expressed all the components of RAS, and 50 mmol/L D-glucose (high glucose) significantly increased angiotensinogen, ACE, and AT1 mRNAs and ACE, AT1, and Ang II proteins. Ang II increased TGF-β1 and fibronectin protein expression and DCF-sensitive cellular ROS. Losartan prevented Ang II-induced increase in cellular ROS. Both losartan and captopril inhibited high glucose-induced upregulation of TGF-β1 and fibronectin expression in HPMC in a dose-dependent manner. Antioxidant catalase and NADPH oxidase inhibitor diphenyleneiodinium effectively inhibited Ang II-induced TGF-β1 and fibronectin protein expression.

Conclusions

The present data demonstrate that HPMC constitutively express RAS, that Ang II produced by HPMC mediates high glucose-induced upregulation of TGF-β1 and fibronectin expression, and that Ang II-induced TGF-β1 and fibronectin expression in HPMC is mediated by NADPH oxidase-dependent ROS. These data suggest that locally produced Ang II and ROS in the peritoneum may be potential therapeutic targets in peritoneal fibrosis during long-term peritoneal dialysis.

Keap1/Nrf2/ARE signaling unfolds therapeutic targets for redox imbalanced-mediated diseases and diabetic nephropathy

Hyperglycemia/oxidative stress has been implicated in the initiation and progression of diabetic complications while the components of Keap1/Nrf2/ARE signaling are being exploited as therapeutic targets for the treatment/management of these pathologies. Antioxidant agents like drugs, nutraceuticals and pure compounds that target the proteins of this pathway and their downstream genes hold the therapeutic strength to put the progression of this disease at bay. Here, we elucidate how the modulation of Keap1/Nrf2/ARE had been exploited for the treatment/management of end-stage diabetic kidney complication (diabetic nephropathy) by looking into (1) Nrf2 nuclear translocation and phosphorylation by some protein kinases at specific amino acid sequences and (2) Keap1 downregulation/Keap1-Nrf2 protein-protein inhibition (PPI) as potential therapeutic mechanisms exploited by Nrf2 activators for the modulation of diabetic nephropathy biomarkers (Collagen IV, Laminin, TGF-β1 and Fibronectin) that ultimately lead to the amelioration of this disease progression. Furthermore, we brought to limelight the relationship between diabetic nephropathy and Keap1/Nrf2/ARE and finally elucidate how the modulation of this signaling pathway could be further explored to create novel therapeutic milestones.

Blockade of myeloid differentiation 2 attenuates diabetic nephropathy by reducing activation of the renin-angiotensin system in mouse kidneys

BACKGROUND AND PURPOSE

Both innate immunity and the renin-angiotensin system (RAS) play important roles in the pathogenesis of diabetic nephropathy (DN). Myeloid differentiation factor 2 (MD2) is a co-receptor of toll-like receptor 4 (TLR4) in innate immunity. While TLR4 is involved in the development of DN, the role of MD2 in DN has not been characterized. It also remains unclear whether the MD2/TLR4 signalling pathway is associated with RAS activation in diabetes.

EXPERIMENTAL APPROACH

MD2 was blocked using siRNA or the low MW inhibitor, L6H9, in renal proximal tubular cells (NRK-52E cells) exposed to high concentrations of glucose (HG). In vivo, C57BL/6 and MD2-/- mice were injected with streptozotocin to induce Type 1 diabetes and nephropathy.

KEY RESULTS

Inhibition of MD2 by genetic knockdown or the inhibitor L6H9 suppressed HG-induced expression of ACE and angiotensin receptors and production of angiotensin II in NRK-52E cells, along with decreased fibrosis markers (TGF-β and collagen IV). Inhibition of the MD2/TLR4-MAPKs pathway did not affect HG-induced renin overproduction. In vivo, using the streptozotocin-induced diabetic mice, MD2 was overexpressed in diabetic kidney. MD2 gene knockout or L6H9 attenuated renal fibrosis and dysfunction by suppressing local RAS activation and inflammation.

CONCLUSIONS AND IMPLICATIONS

Hyperglycaemia activated the MD2/TLR4-MAPKs signalling cascade to induce renal RAS activation, leading to renal fibrosis and dysfunction. Pharmacological inhibition of MD2 may be considered as a therapeutic approach to mitigate DN and the low MW inhibitor L6H9 could be a candidate for such therapy.

Sex and salt intake dependent renin-angiotensin plasticity in the liver of the rat

OBJECTIVE

Epidemiological studies confirm that hypertensive patients respond differently to renin-angiotensin system (RAS) inhibition depending on their gender. The aim of present work is to focus on sex-dependent differences in RAS regulation under conditions of increased salt intake.

METHOD

To investigate RAS, we measured the expression of angiotensinogen (Agt) mRNA, angiotensin receptor type 1 (AT1) mRNA and mitochondria assembly receptor (MasR) in the liver of rats under control conditions and after feeding with a salt diet (2% NaCl). In parallel, vascular endothelial growth factor A (VEGF-A) mRNA was analyzed.

RESULTS

Regression analysis revealed sex-dependent differences in the correlation between mRNA expression of AT1 and that of Agt, MasR and VEGF-A in both groups. There was a significant negative correlation between AT1 and Agt mRNA expression in the male control group, but this correlation disappeared in males exposed to a salt diet. In females, AT1 and Agt expression correlated only in the group exposed to the salt diet. In control males, there was a borderline trend to correlation between AT1 and MasR mRNA expression. The correlation between AT1 and VEGF-A mRNA expression was significant only in the control females, however, after exposure to a salt diet, this correlation diminished.

CONCLUSIONS

We hypothesize that RAS components expression is compensated differently in males and females. The observed loss of compensatory relationships in RAS between AT1 and Agt and AT1 and MasR in male rats under a salt diet can contribute to the differences observed in human with hypertension associated with an unhealthy diet.

Angiotensin II-Induced Oxidative Stress in Human Endothelial Cells: Modification of Cellular Molecules through Lipid Peroxidation

Angiotensin (Ang) II is a major bioactive peptide of the renin/angiotensin system and is involved in various cardiovascular functions and diseases. Ang II type 1 (AT₁) receptor mediates most of the physiological effects of Ang II. Previous studies have revealed that the lipid peroxidation products 4-oxo-2(E)-nonenal (ONE) and 4-hydroxy-2(E)-nonenal (HNE) readily modify the N-terminus and Asp¹, Arg², and His⁶ residues of Ang II, and these modifications alter the biological activities of Ang II. Ang II is known to stimulate the formation of reactive oxygen species (ROS) that mediate cardiovascular remodeling. Another major consequence of ROS-derived damage is lipid peroxidation, which generates genotoxic aldehydes such as ONE and HNE. This study demonstrated that Ang II induced lipid peroxidation-derived modifications of cellular molecules in EA.hy926 cells, a human vascular endothelial cell line. Ang P (ONE- and ROS-derived N-terminal pyruvamide Ang II) and [His⁶(HNE)]-Ang II were detected in the medium of EA.hy926 cells incubated with Ang II, and their concentrations increased dose-dependently upon the addition of ascorbic acid (AscA) and CuSO₄. Cells were then subjected to metabolic labeling using SILFAC (stable isotope labeling by fatty acids in cell culture) with [¹³C₁₈]-linoleic acid. Analysis of cellular phospholipids indicated over 90% labeling. [¹³C₉]-Thiadiazabicyclo-ONE-glutathione adduct as well as Ang P and [His⁶([¹³C₉]-HNE)]-Ang II was detected in the labeled cells upon treatment with Ang II and their concentrations increased in an Ang II dose-dependent manner. Incubation of the labeled cells with losartan, an AT₁ receptor blocker, inhibited the formation of modified Ang IIs in a dose-dependent manner. These results indicate that Ang II induces lipid peroxidation and modification of various cellular molecules and these reactions are mediated by the activation of AT₁ receptor. Therefore, lipid peroxidation could be one mechanism by which Ang II contributes to cardiovascular dysfunction.

Influence of high glucose on mesangial cell-derived exosome composition, secretion and cell communication

Mesangial cells stimulated with high glucose (HG) exhibit increased intracellular angiotensin II (AngII) synthesis that is correlated with the upregulation of AngII target genes, such as profibrotic cytokines. The intracrine effects of AngII can be mediated by several molecules transferred to other cells via exosomes (Exos), which play a key role in cellular communication under many physiological and pathological conditions. The aim of this study was to investigate the effects of exosomes derived from HG-stimulated human mesangial cells (HG-HMCs) on normal unstimulated HMCs. Exosomes from HMCs (C-Exos) and HG-HMCs (HG-Exos) were obtained from cell culture supernatants. HMCs were incubated with C-Exos or HG-Exos. HG stimulus induced a change in the amount but not the size of Exos. Both C-Exos and HG-Exos contained angiotensinogen and renin, but no angiotensin converting enzyme was detected. Compared with HMCs treated with C-Exos, HMCs treated with HG-Exos presented higher levels of fibronectin, angiotensinogen, renin, AT₁ and AT₂ receptors, indicating that HG-Exos modified the function of normal HMCs. These results suggest that the intercellular communication through Exos may have pathophysiological implications in the diabetic kidney.

High glucose level and angiotensin II type 1 receptor stimulation synergistically amplify oxidative stress in renal mesangial cells

Oxidative stress in renal mesangial cell causes diabetic glomerular changes. High glucose levels and angiotensin II (Ang II) are known to stimulate superoxide production in renal mesangial cells. However, it has been unclear whether Ang II stimulation and pre-conditioning with high glucose affects the same pathway of superoxide production in renal mesangial cells or not. In this study, we examined the levels of oxidative stress under Ang II stimulation in renal mesangial cells preincubated for six hours at various glucose levels. Intracellular levels of reactive oxidative species (ROS) were measured using dihydroethidium or 5′,6′-chloromethyl- 2′,7′ dichlorodihydro-fluorescein diacetate, which facilitates the detection of intracellular ROS under real-time fluorescent microscope. Ang II-induced elevated intracellular ROS levels were detected only when the cells were pre-incubated with high levels of glucose (13.5 mM, 27.8 mM), but was not detected under normal glucose condition (5.5 mM). Production of Ang II-induced intracellular ROS was higher under pre-treatment with 27.8 mM glucose compared to pretreatment with 13.5 mM glucose level. This ROS production in mesangial cells was induced within several minutes of the initiation of Ang II stimulation under high glucose levels. The production of intracellular ROS was significantly reduced in the presence of angiotensin II type1-receptor (AT1R) antagonist, whereas it was augmented in the presence of angiotensin II type2-receptor antagonist. In conclusion, Ang II-induced oxidative stress was augmented by high glucose levels and ROS levels were further alleviated in the presence of AT1R antagonists.

Intracrine action of angiotensin II in mesangial cells: subcellular distribution of angiotensin II receptor subtypes AT1 and AT2

Biological effects of angiotensin II (AngII) such as regulation of AngII target genes may be triggered by interaction of AngII with intracellular AngII receptor types 1 and 2 (AT₁ and AT₂), defined as intracrine response. The aim of this study was to examine the presence of AT₁ and AT₂ receptors in nuclear membrane of human mesangial cells (HMCs) and evaluate the possible biological effects mediated by intracellular AT₁ through an intracrine mechanism. Subcellular distribution of AT₁ and AT₂ was evaluated by immunofluorescence and by western blot in isolated nuclear extract. Endogenous intracellular synthesis of AngII was stimulated by high glucose (HG). Effects of HG were analyzed in the presence of candesartan, which prevents AngII internalization. Both receptors were found in nuclear membrane. Fluorescein isothiocyanate (FITC)-labeled AngII added to isolated nuclei produced a fluorescence that was reduced in the presence of losartan or PD-123319 and quenched in the presence of both inhibitors simultaneously. HG induced overexpression of fibronectin and increased cell proliferation in the presence of candesartan, indicating an intracrine action of AngII induced by HG. Results showed the presence of nuclear receptors in HMCs that can be activated by AngII through an intracrine response independent of cytoplasmic membrane AngII receptors.

The Renin-Angiotensin-Aldosterone System as a Therapeutic Target in Late Injury Caused by Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a well-known phenomenon that involves different pathophysiological processes. Connection in diverse systems of survival brings about cellular dysfunction or even apoptosis. One of the survival systems of the cells, to the assault caused by ischemia, is the activation of the renin-angiotensin-aldosterone system (also known as an axis), which is focused on activating diverse signaling pathways to favor adaptation to the decrease in metabolic supports caused by the hypoxia. In trying to adapt to the I/R event, great changes occur that unchain cellular dysfunction with the capacity to lead to cell death, which translates into a poor prognosis due to the progression of dysfunction of the cellular activity. The search for the understanding of the diverse therapeutic alternatives in molecular coupling could favor the prognosis and evolution of patients who are subject to the I/R process.

The locally activated renin-angiotensin system is involved in albumin permeability in glomerular endothelial cells under high glucose conditions

Background

Although the diabetic milieu per se , hemodynamic changes, oxidative stress and local growth factors such as angiotensin II (AII) are considered to be mediators in the pathogenesis of diabetic nephropathy, the underlying pathways mediating the changes in glomerular endothelial cells (GECs) are not well understood. Therefore, we investigated changes in the renin-angiotensin system (RAS) components in high glucose (HG)-stimulated GECs and the role of the local RAS in morphological and functional changes in GECs under diabetic conditions.

Methods

We stimulated GECs with 5.6 mM glucose or 30 mM glucose with or without an angiotensin II type I receptor blocker (ARB) in vitro and also performed experiments with Sprague-Dawley rats injected with diluent ( n = 16) or streptozotocin [ n = 16, diabetes (DM)]. Eight rats from each group were treated with ARB for 3 months in vivo . Real-time polymerase chain reaction, western blot analysis, enzyme-linked immunosorbent assay and immunofluorescent staining using cultured GECs were performed. The permeability of GECs to macromolecules was assessed by measuring the passage of fluorescein isothiocyanate-labeled bovine serum albumin. Morphological changes were also evaluated by scanning and transmission electron microscopy.

Results

There were significant increases in angiotensinogen expression in HG-stimulated GECs along with significant increases in AI and AII levels. Moreover, the expression of heparan sulfate glycosaminoglycans (HS-GAG) assessed by immunofluorescent staining was significantly lower and the permeability to albumin was significantly higher in GECs exposed to HG medium, and ARB treatment significantly abrogated these changes. Upon electron microscopy examination, the mean size of the GEC fenestrae was significantly greater in HG-stimulated GECs and DM rats, and these increases were significantly ameliorated by ARB.

Conclusions

The local RAS within GECs was activated under HG conditions, and this activation may be associated with both an alteration in GEC fenestration and a decrease in HS-GAG, resulting in the development of albuminuria in diabetic nephropathy.

The roles of sodium-glucose cotransporter 2 inhibitors in preventing kidney injury in diabetes

Diabetic nephropathy (DN) is the leading cause of end stage renal disease (ESRD) worldwide. The early effective treatment of high plasma glucose could delay or prevent the onset of DN. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are new target treatments for ameliorating high plasma glucose and help to maintain glucose homeostasis in diabetic patients. Reduced renal glucose reabsorption by SGLT2 inhibition seems to have high potential to improve glycemic control in diabetes mellitus (DM) not only through glucose lowering but also through glucose-independent effects such as blood pressure-lowering and direct renal effects in diabetes. Of note, the important events in the pathogenesis of glucose-induced renal injury and DN including oxidative stress, inflammation, fibrosis and apoptosis conditions have shown to be ameliorate after the treatment with SGLT2 inhibitors. Interestingly, SGLT2 inhibitors have been reported to reduce albuminuria in DM via an activation of renal tubuloglomerular feedback by increased macula densa sodium and chloride delivery, leading to afferent vasoconstriction and attenuated diabetes-induced renal hyperfiltration. These effects also help to conserve glomerular integrity. Thus, the treatment of diabetes mellitus using SGLT2 inhibitors could be one of the effective approach for the management of diabetic-associated kidney disease like DN. This review summarizes the up to date information and discusses the bidirectional relationship between the SGLT2 inhibitor treatments and the renal functions that are available from both basic research and clinical reports. The details of renal outcomes of SGLT2 inhibitors in DN are also provide in this review.

Feasibility of fluorescence energy transfer system for imaging the renoprotective effects of aliskiren in diabetic mice

Introduction:

We investigated the feasibility of using a fluorescence resonance energy transfer system to image enzymatic activity in order to evaluate the effects of aliskiren (a direct renin inhibitor) on diabetic nephropathy.

Materials and methods:

First, we induced diabetes in C57BL/6J mice using streptozotocin, then treated them with either aliskiren (25 mg/kg/day) or the angiotensin type 1 receptor blocker valsartan (15 mg/kg/day) for four weeks. Finally, we utilized renin fluorescence resonance energy transfer substrate to assess renin activity.

Results:

Renin activity was much higher in the kidneys of diabetic mice compared to those of the non-diabetic control mice. While aliskiren inhibited this activity, valsartan did not. We noted that production of reactive oxygen species intensified and the bioavailability of nitric oxide diminished in the glomeruli of diabetic mice. Aliskiren and valsartan significantly ameliorated these effects. They suppressed glomerular production of reactive oxygen species and urinary albumin excretion. In fact, urinary albumin excretion in diabetic mice treated with aliskiren or valsartan was lower than that in untreated diabetic mice. Furthermore, aliskiren and valsartan significantly reduced glomerular permeability by maintaining the glomerular endothelial surface layer.

Conclusion:

Fluorescence resonance energy transfer could provide a new tool for evaluating tissue and plasma enzymatic activity.

New molecular insights in diabetic nephropathy

Diabetes mellitus represents one of the major causes of functional kidney impairment. The review highlights the most significant steps made over the last decades in understanding the molecular basis of diabetic nephropathy (DN), which may provide reliable biomarkers for early diagnosis and prognosis, along with new molecular targets for personalized medicine. There is an increased interest in developing new therapeutic strategies to slow DN progression for improving patients' quality of life and reducing all-cause morbidity and disease-associated mortality. It is highly important to have a science-based medical attitude when facing diabetic patients with associated comorbidities and risk of rapid evolution toward end-stage renal disease. The data discussed herein were mainly from MEDLINE and PubMed articles published in English from 1990 to 2015 and from up-to-date. The search term was "diabetic nephropathy and oxidative stress".

Assessment of urinary angiotensinogen as a marker of podocyte injury in proteinuric nephropathies

Urinary protein (UP) is widely used as a clinical marker for podocyte injury; however, not all proteinuric nephropathies fit this model. We previously described the elevation of urinary angiotensinogen (AGT) accompanied by AGT expression by injured podocytes in a nitric oxide inhibition rat model (Eriguchi M, Tsuruya K, Haruyama N, Yamada S, Tanaka S, Suehiro T, Noguchi H, Masutani K, Torisu K, Kitazono T. Kidney Int 87: 116-127, 2015). In this report, we performed the human and animal studies to examine the significance and origin of urinary AGT. In the human study, focal segmental glomerulosclerosis (FSGS) patients presented with higher levels of urinary AGT, corrected by UP, than minimal-change disease (MCD) patients. Furthermore, AGT was evident in podocin-negative glomerular segmental lesions. We also tested two different nephrotic models induced by puromycin aminonucleoside in Wistar rats. The urinary AGT/UP ratio and AGT protein and mRNA expression in sieved glomeruli from FSGS rats were significantly higher than in MCD rats. The presence of AGT at injured podocytes in FSGS rats was detected by immunohistochemistry and immunoelectron microscopy. Finally, we observed the renal tissue and urinary metabolism of exogenous injected human recombinant AGT (which is not cleaved by rodent renin) in FSGS and control rats. Significant amounts of human AGT were detected in the urine of FSGS rats, but not of control rats. Immunostaining for rat and human AGT identified that only rat AGT was detected in injured podocytes, and filtered human AGT was seen in superficial proximal tubules, but not in injured podocytes, suggesting AGT generation by injured podocytes. In conclusion, the urinary AGT/UP ratio represents a novel specific marker of podocyte injury.

Significant association between glycemic status and increased estimated postglomerular resistance in nondiabetic subjects - study of inulin and para-aminohippuric acid clearance in humans

We investigated whether glomerular hemodynamic parameters in nondiabetic subjects, including healthy subjects, are associated with glycemic status indices, by simultaneous measurement of inulin (C_in) and para-aminohippuric acid (C_PHA) clearance. Twenty-six subjects (age 49.5 ± 13.3 years; 13 men and 13 women; 14 healthy subjects and 12 subjects with mild proteinuria) were enrolled. C_in and C_PAH were measured simultaneously. All 26 subjects were nondiabetics. Estimated preglomerular resistance, estimated postglomerular resistance, and estimated glomerular hydrostatic pressure (P_glo) were calculated according to Gomez’ formula. P_glo correlated significantly and positively with hemoglobin A1c (HbA1c) in both healthy subjects (r = 0.532, P = 0.0498) and subjects with mild proteinuria (r = 0.681, P = 0.015). While there was no significant correlation between estimated preglomerular resistance and HbA1c, estimated postglomerular resistance correlated significantly and positively with HbA1c both in healthy subjects (r = 0.643, P = 0.013) and subjects with mild proteinuria (r = 0.589, P = 0.044). Glomerular filtration fraction, estimated P_glo and estimated postglomerular resistance in total subjects were associated significantly with HbA1c after adjustment for age, gender, and body mass index. These results demonstrate that, even in nondiabetic subjects, glycemic status is associated with estimated postglomerular resistance, but not estimated preglomerular resistance. It is suggested that increased estimated postglomerular resistance associated with higher HbA1c levels, even within the normal range, causes increased estimated P_glo, leading to increased FF. Thus, hemodynamic abnormalities associated with higher HbA1c levels may be related to glomerular hypertension, even in nondiabetic subjects.

Cross-talk between angiotensin-II and toll-like receptor 4 triggers a synergetic inflammatory response in rat mesangial cells under high glucose conditions

Toll-like Receptor 4 (TLR4) may play an important role in the pathogenesis of diabetic nephropathy (DN). In this study, We observed the TLR4 signal and the release of inflammation factors after angiotensin II (Ang II) stimulation in rat mesangial cells (MCs) under high glucose conditions, this revealed the innate immune mechanism of injury by Ang II in DN. Our data showed that TLR4 and MyD88 were up-regulated significantly in high glucose and AngII-induced MCs; meanwhile, NF-κB as well as MCP-1, IL-6 were also highly expressed. In cells that were transfected with TLR4 SiRNA，the parameters were greatly inhibited; similar effects were detected in cells that were treated with Irbesartan. We concluded that Ang II synergized with high glucose in the release of pro-inflammatory factors mainly through the upregulation of TLR4 signaling in MCs, Cross-talk between Ang II and TLR4 contributed to the MC inflammatory injury under high glucose conditions.

Diabetic Nephropathy Induced by Increased Ace Gene Dosage Is Associated with High Renal Levels of Angiotensin (1-7) and Bradykinin

Population studies have shown an association between diabetic nephropathy (DN) and insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene (ACE in humans, Ace in mice). The aim was to evaluate the modulation of Ace copies number and diabetes mellitus (DM) on renal RAS and correlate it with indicators of kidney function. Increased number of copies of the Ace gene, associated with DM, induces renal dysfunction. The susceptibility to the development of DN in 3 copies of animals is associated with an imbalance in activity of RAS enzymes leading to increased synthesis of Ang II and Ang-(1-7). Increased concentration of renal Ang-(1-7) appears to potentiate the deleterious effects triggered by Ang II on kidney structure and function. Results also show increased bradykinin concentration in 3 copies diabetic group. Taken together, results indicate that the deleterious effects described in 3 copies diabetic group are, at least in part, due to a combination of factors not usually described in the literature. Thus, the data presented here show up innovative and contribute to understanding the complex mechanisms involved in the development of DN, in order to optimize the treatment of patients with this complication.

Poor glycemic control and decreased renal function are associated with increased intrarenal RAS activity in Type 2 diabetes mellitus

AIMS

The renin-angiotensin system (RAS) plays an important role in the pathogenesis of diabetic nephropathy. The aim of the present study was to investigate intrarenal RAS activity in patients with type 2 diabetes (T2DM).

METHODS

We measured urinary angiotensinogen, a reliable biomarker of intrarenal RAS activity, in 14 controls without T2DM, 25 T2DM patients without nephropathy, 11 chronic kidney disease (CKD) patients without T2DM and 46 CKD patients with T2DM. Associations between urinary angiotensinogen and clinical parameters were examined.

RESULTS

Compared with the controls, urinary [angiotensinogen:creatinine] were significantly higher in T2DM patients without nephropathy (4.70 ± 2.22 vs. 8.31 ± 5.27 μg/g, p=0.037). Age, hemoglobin A1c (HbA1c) and fasting plasma glucose correlated significantly and positively with the log{urinary [angiotensinogen:creatinine]} (r=0.632, p=0.007; r=0.405, p=0.027; r=0.583, p=0.003, respectively) in T2DM patients without nephropathy. In contrast, the urinary [angiotensinogen:creatinine] were not significantly different between CKD patients with and without T2DM (22.7 ± 27.8 vs. 33.5 ± 40.8 μg/g, p=0.740); although they were significantly higher when compared with non-CKD patients. In the CKD patients with T2DM systolic blood pressure, serum creatinine, estimated glomerular filtration rate and urinary [albumin:creatinine] correlated significantly with the log{urinary [angiotensinogen:creatinine]} (r=0.412, p=0.004; r=0.308, p=0.037; r=-0.382, p=0.001; r=0.648, p<0.001, p<0.001, respectively).

CONCLUSIONS

Our findings indicate that poor glycemic control is significantly associated with intrarenal RAS activity in T2DM patients without nephropathy, and that decreased renal function is significantly associated with intrarenal RAS activity in CKD patients with T2DM.

Significant association of poor glycemic control with increased resistance in efferent arterioles--study of inulin and para-aminohippuric acid clearance in humans

AIMS

To examine whether glomerular hemodynamic parameters in humans are associated with glycemic control indices, by simultaneously measuring clearance of inulin (Cin) and para-aminohippuric acid (CPHA).

METHODS

Thirty-one subjects (age 55.4±14.7 years; 15 men and 16 women; 21 diabetics and 10 non-diabetics) were enrolled. Cin and CPAH were measured simultaneously. Afferent arteriolar resistance (Ra), efferent arteriolar resistance (Re), glomerular hydrostatic pressure (Pglo) and glomerular filtration fraction (FF) were calculated according to Gomez' formula.

RESULTS

FF correlated significantly and positively with fasting plasma glucose (FPG), hemoglobin A1c (HbA1c) and glycated albumin (GA) (r=0.396, p=0.0303; r=0.587, p=0.0007; r=0.525, p=0.0070, respectively). Pglo correlated significantly and positively with FPG, HbA1c and GA (r=0.572, p=0.0008; r=0.535, p=0.0019; r=0.540, p=0.0053, respectively). Although there was no significant correlation between Ra and glycemic control indices, Re correlated significantly and positively with HbA1c and GA (r=0.499, p=0.0043; r=0.592, p=0.0018, respectively). FF, Pglo and Re were associated significantly with HbA1c and GA after adjustment for age.

CONCLUSIONS

These results demonstrate, in humans, that poor glycemic control is associated with increased Re, but not Ra. It is suggested that increased Re causes increased Pglo, leading to increased FF. Thus, hemodynamic abnormalities with poor glycemic control may be related to glomerular hypertension in humans.

ROCK/NF-κB axis-dependent augmentation of angiotensinogen by angiotensin II in primary-cultured preglomerular vascular smooth muscle cells

In angiotensin II (ANG II)-dependent hypertension, the augmented intrarenal ANG II constricts the renal microvasculature and stimulates Rho kinase (ROCK), which modulates vascular contractile responses. Rho may also stimulate angiotensinogen (AGT) expression in preglomerular vascular smooth muscle cells (VSMCs), but this has not been established. Therefore, the aims of this study were to determine the direct interactions between Rho and ANG II in regulating AGT and other renin-angiotensin system (RAS) components and to elucidate the roles of the ROCK/NF-κB axis in the ANG II-induced AGT augmentation in primary cultures of preglomerular VSMCs. We first demonstrated that these preglomerular VSMCs express renin, AGT, angiotensin-converting enzyme, and ANG II type 1 (AT1) receptors. Furthermore, incubation with ANG II (100 pmol/l for 24 h) increased AGT mRNA (1.42 ± 0.03, ratio to control) and protein (1.68 ± 0.05, ratio to control) expression levels, intracellular ANG II levels, and NF-κB activity. In contrast, the ANG II treatment did not alter AT1a and AT1b mRNA levels in the cells. Treatment with H-1152 (ROCK inhibitor, 10 nmol/l) and ROCK1 small interfering (si) RNA suppressed the ANG II-induced AGT augmentation and the upregulation and translocalization of p65 into nuclei. Functional studies showed that ROCK exerted a greater influence on afferent arteriole responses to ANG II in rats subjected to chronic ANG II infusions. These results indicate that ROCK is involved in NF-κB activation and the ROCK/NF-κB axis contributes to ANG II-induced AGT upregulation, leading to intracellular ANG II augmentation.

Tissue Renin-Angiotensin systems: a unifying hypothesis of metabolic disease

The actions of angiotensin peptides are diverse and locally acting tissue renin-angiotensin systems (RAS) are present in almost all tissues of the body. An activated RAS strongly correlates to metabolic disease (e.g., diabetes) and its complications and blockers of RAS have been demonstrated to prevent diabetes in humans. Hyperglycemia, obesity, hypertension, and cortisol are well-known risk factors of metabolic disease and all stimulate tissue RAS whereas glucagon-like peptide-1, vitamin D, and aerobic exercise are inhibitors of tissue RAS and to some extent can prevent metabolic disease. Furthermore, an activated tissue RAS deteriorates the same risk factors creating a system with several positive feedback pathways. The primary effector hormone of the RAS, angiotensin II, stimulates reactive oxygen species, induces tissue damage, and can be associated to most diabetic complications. Based on these observations, we hypothesize that an activated tissue RAS is the principle cause of metabolic syndrome and type 2 diabetes, and additionally is mediating the majority of the metabolic complications. The involvement of positive feedback pathways may create a self-reinforcing state and explain why metabolic disease initiate and progress. The hypothesis plausibly unifies the major predictors of metabolic disease and places tissue RAS regulation in the center of metabolic control.

Attenuated mesangial cell proliferation related to store-operated Ca2+ entry in aged rat: the role of STIM 1 and Orai 1

Store-operated Ca(2+) entry (SOCE) is a common and ubiquitous mechanism regulating Ca(2+) influx into cells and participates in numerous biological processes including cell proliferation. Glomerular mesangial cells (GMCs) play a role in the regulation of the glomerular filtration rate. From a clinical point of view, many physiological functions alter with age. In the present study, we used angiotensin II, glucagon, and the sarco/endoplasmic reticulum membrane Ca(2+) pump inhibitor thapsigargin to deplete the internal Ca(2+) stores for the activation of SOCE. We found that SOCE was significantly attenuated in GMCs from aged (22-month-old) rats. The expression of SOCE-related components, stromal interaction molecule 1 (STIM 1) and Orai 1, in freshly isolated glomeruli notably decreased, and STIM 1 and Orai 1 puncta formation significantly reduced in primary-cultured GMCs in aged rats. Moreover, specific knockdown of STIM 1 and Orai 1 by small interfering RNA markedly suppressed SOCE and cell proliferation of GMCs isolated from young (3-month-old) rats. We conclude that the attenuation of GMCs proliferation can be attributed to the decreased SOCE partially caused by reduced expression of STIM 1 and Orai 1.

Oxidative stress/angiotensinogen/renin-angiotensin system axis in patients with diabetic nephropathy

Although recent studies have proven that renin-angiotensin system (RAS) blockades retard the progression of diabetic nephropathy, the detailed mechanisms of their reno-protective effects on the development of diabetic nephropathy remain uncertain. In rodent models, it has been reported that reactive oxygen species (ROS) are important for intrarenal angiotensinogen (AGT) augmentation in the progression of diabetic nephropathy. However, no direct evidence is available to demonstrate that AGT expression is enhanced in the kidneys of patients with diabetes. To examine whether the expression levels of ROS- and RAS-related factors in kidneys are increased with the progression of diabetic nephropathy, biopsied samples from 8 controls and 27 patients with type 2 diabetes were used. After the biopsy, these patients were diagnosed with minor glomerular abnormality or diabetes mellitus by clinical and pathological findings. The intensities of AGT, angiotensin II (Ang II), 4-hydroxy-2-nonenal (4-HNE), and heme oxygenase-1 (HO-1) were examined by fluorescence in situ hybridization and/or immunohistochemistry. Expression levels were greater in patients with diabetes than in control subjects. Moreover, the augmented intrarenal AGT mRNA expression paralleled renal dysfunction in patients with diabetes. These data suggest the importance of the activated oxidative stress/AGT/RAS axis in the pathogenesis of diabetic nephropathy.

The renal endothelium in diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetes mellitus is characterized by generalized endothelial dysfunction. However, recent data also emphasizes the role of local renal endothelium dysfunction in the pathogenesis of diabetic nephropathy. Hyperglycemia triggers a complex network of signal-transduction molecules, transcription factors, and mediators that culminate in endothelial dysfunction. In the glomerulus, vascular endothelial growth factor-A (VEGF)-induced neoangiogenesis may contribute to the initial hyperfiltration and microalbuminuria due to increased filtration area and immaturity of the neovessels, respectively. However, subsequent decrease in podocytes number decreases VEGF production resulting in capillary rarefaction and decreased glomerular filtration rate (GFR). Decreased nitric oxide availability also plays a significant role in the development of advanced lesions of diabetic nephropathy through disruption of glomerular autoregulation, uncontrolled VEGF action, release of prothrombotic substances by endothelial cells and angiotensin-II-independent aldosterone production. In addition, disturbances in endothelial glycocalyx contribute to decreased permselectivity and microalbuminuria; whereas there are recent evidences that reduced glomerular fenestral endothelium leads to decreased GFR levels. Endothelial repair mechanisms are also impaired in diabetes, since circulating endothelial progenitor cells number is decreased in diabetic patients with microalbuminuria. Finally, in the context of elevated profibrotic cytokine transforming growth factor-β levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

Adenosine A(2B) receptor-mediated VEGF induction promotes diabetic glomerulopathy

Diabetic nephropathy ranks as the most devastating kidney disease worldwide. It characterizes in the early onset by glomerular hypertrophy, hyperfiltration and mesangial expansion. Experimental models show that overproduction of vascular endothelial growth factor (VEGF) is a pathogenic condition for podocytopathy; however the mechanisms that regulate this growth factor induction are not clearly identified. We determined that the adenosine A(2B) receptor (A(2B)AR) mediates VEGF overproduction in ex vivo glomeruli exposed to high glucose concentration, requiring PKCα and Erk1/2 activation. The glomerular content of A(2B)AR was concomitantly increased with VEGF at early stages of renal disease in streptozotocin-induced diabetic rats. Further, in vivo administration of an antagonist of A(2B)AR in diabetic rats blocked the glomerular overexpression of VEGF, mesangial cells activation and proteinuria. In addition, we also determined that the accumulation of extracellular adenosine occurs in glomeruli of diabetic rats. Correspondingly, raised urinary adenosine levels were found in diabetic rats. In conclusion, we evidenced that adenosine signaling at the onset of diabetic kidney disease is a pathogenic event that promotes VEGF induction.

Aliskiren prevents the toxic effects of peritoneal dialysis fluids during chronic dialysis in rats

The benefits of long-term peritoneal dialysis (PD) in patients with end-stage renal failure are short-lived due to structural and functional changes in the peritoneal membrane. In this report, we provide evidence for the in vitro and in vivo participation of the renin-angiotensin-aldosterone system (RAAS) in the signaling pathway leading to peritoneal fibrosis during PD. Exposure to high-glucose PD fluids (PDFs) increases damage and fibrosis markers in both isolated rat peritoneal mesothelial cells and in the peritoneum of rats after chronic dialysis. In both cases, the addition of the RAAS inhibitor aliskiren markedly improved damage and fibrosis markers, and prevented functional modifications in the peritoneal transport, as measured by the peritoneal equilibrium test. These data suggest that inhibition of the RAAS may be a novel way to improve the efficacy of PD by preventing inflammation and fibrosis following peritoneal exposure to high-glucose PDFs.

Involvement of glomerular renin-angiotensin system (RAS) activation in the development and progression of glomerular injury

Recently, there has been a paradigm shift away from an emphasis on the role of the endocrine (circulating) renin-angiotensin system (RAS) in the regulation of the sodium and extracellular fluid balance, blood pressure, and the pathophysiology of hypertensive organ damage toward a focus on the role of tissue RAS found in many organs, including kidney. A tissue RAS implies that RAS components necessary for the production of angiotensin II (Ang II) reside within the tissue and its production is regulated within the tissue, independent of the circulating RAS. Locally produced Ang II plays a role in many physiological and pathophysiological processes such as hypertension, inflammation, oxidative stress, and tissue fibrosis. Both glomerular and tubular compartments of the kidney have the characteristics of a tissue RAS. The purpose of this article is to review the recent advances in tissue RAS research with a particular focus on the role of the glomerular RAS in the progression of renal disease.

Enzymatic processing of angiotensin peptides by human glomerular endothelial cells

The intraglomerular renin-angiotensin system (RAS) is linked to the pathogenesis of progressive glomerular diseases. Glomerular podocytes and mesangial cells play distinct roles in the metabolism of angiotensin (ANG) peptides. However, our understanding of the RAS enzymatic capacity of glomerular endothelial cells (GEnCs) remains incomplete. We explored the mechanisms of endogenous cleavage of ANG substrates in cultured human GEnCs (hGEnCs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and isotope-labeled peptide quantification. Overall, hGEnCs metabolized ANG II at a significantly slower rate compared with podocytes, whereas the ANG I processing rate was comparable between glomerular cell types. ANG II was the most abundant fragment of ANG I, with lesser amount of ANG-(1-7) detected. Formation of ANG II from ANG I was largely abolished by an ANG-converting enzyme (ACE) inhibitor, whereas ANG-(1-7) formation was decreased by a prolylendopeptidase (PEP) inhibitor, but not by a neprilysin inhibitor. Cleavage of ANG II resulted in partial conversion to ANG-(1-7), a process that was attenuated by an ACE2 inhibitor, as well as by an inhibitor of PEP and prolylcarboxypeptidase. Further fragmentation of ANG-(1-7) to ANG-(1-5) was mediated by ACE. In addition, evidence of aminopeptidase N activity (APN) was demonstrated by detecting amelioration of conversion of ANG III to ANG IV by an APN inhibitor. While we failed to find expression or activity of aminopeptidase A, a modest activity attributable to aspartyl aminopeptidase was detected. Messenger RNA and gene expression of the implicated enzymes were confirmed. These results indicate that hGEnCs possess prominent ACE activity, but modest ANG II-metabolizing activity compared with that of podocytes. PEP, ACE2, prolylcarboxypeptidase, APN, and aspartyl aminopeptidase are also enzymes contained in hGEnCs that participate in membrane-bound ANG peptide cleavage. Injury to specific cell types within the glomeruli may alter the intrarenal RAS balance.

Exogenous hydrogen sulfide (H2S) reduces blood pressure and prevents the progression of diabetic nephropathy in spontaneously hypertensive rats

The coexistence of hypertension and diabetes results in the rapid development of nephropathy. Hydrogen sulfide (H2S) is claimed to control the vascular and renal functions. This study tested the hypothesis that exogenous H2S lowers the blood pressure and decreases the progression of nephropathy in spontaneously hypertensive rats (SHR) that were diabetic. Eighteen SHR were divided into three groups: SHR, SHR diabetic, and SHR diabetic treated with a group of Wistar-Kyoto rats serving as normotensive nondiabetic control. Diabetes was induced with streptozotocin (STZ) in two groups and one diabetic group received sodium hydrosulfide (NaHS), a H2S donor for 5 weeks. Blood pressure was measured in conscious and anesthetized states and renal cortical blood perfusion in acute studies. Plasma and urinary H2S levels, creatinine concentrations, and electrolytes were measured on three different occasions throughout the 35-day period. Diabetic SHR had higher blood pressure, lower plasma and urinary H2S levels, and renal dysfunction as evidenced by increased plasma creatinine, creatinine clearance, and decreased urinary sodium-to-potassium ratio and renal cortical blood perfusion. NaHS reduced blood pressure, increased H2S levels in plasma and urinary excretion, and reversed the STZ-induced renal dysfunction. The findings of this study suggest that the administration of exogenous H2S lowers the blood pressure and confers protection against the progression of STZ-induced nephropathy in SHR.

Evidence for a functional intracellular angiotensin system in the proximal tubule of the kidney

ANG II is the most potent and important member of the classical renin-angiotensin system (RAS). ANG II, once considered to be an endocrine hormone, is now increasingly recognized to also play novel and important paracrine (cell-to-cell) and intracrine (intracellular) roles in cardiovascular and renal physiology and blood pressure regulation. Although an intracrine role of ANG II remains an issue of continuous debates and requires further confirmation, a great deal of research has recently been devoted to uncover the novel actions and elucidate underlying signaling mechanisms of the so-called intracellular ANG II in cardiovascular, neural, and renal systems. The purpose of this article is to provide a comprehensive review of the intracellular actions of ANG II, either administered directly into the cells or expressed as an intracellularly functional fusion protein, and its effects throughout a variety of target tissues susceptible to the impacts of an overactive ANG II, with a particular focus on the proximal tubules of the kidney. While continuously reaffirming the roles of extracellular or circulating ANG II in the proximal tubules, our review will focus on recent evidence obtained for the novel biological roles of intracellular ANG II in cultured proximal tubule cells in vitro and the potential physiological roles of intracellular ANG II in the regulation of proximal tubular reabsorption and blood pressure in rats and mice. It is our hope that the new knowledge on the roles of intracellular ANG II in proximal tubules will serve as a catalyst to stimulate further studies and debates in the field and to help us better understand how extracellular and intracellular ANG II acts independently or interacts with each other, to regulate proximal tubular transport and blood pressure in both physiological and diseased states.

(Pro)renin receptor: another member of the system controlled by angiotensin II?

The prorenin receptor [(P)RR] is upregulated in the diabetic kidney and has been implicated in the high glucose (HG)-induced overproduction of profibrotic molecules by mesangial cells (MCs), which is mediated by ERK1/2 phosphorylation. The regulation of (P)RR gene transcription and the mechanisms by which HG increases (P)RR gene expression are not fully understood. Because intracellular levels of angiotensin II (AngII) are increased in MCs stimulated with HG, we used this in vitro system to evaluate the possible role of AngII in (P)RR gene expression and function by comparing the effects of AT1 receptor blockers (losartan or candesartan) and (P)RR mRNA silencing (siRNA) in human MCs (HMCs) stimulated with HG. HG induced an increase in (P)RR and fibronectin expression and in ERK1/2 phosphorylation. These effects were completely reversed by (P)RR siRNA and losartan but not by candesartan (an angiotensin receptor blocker that, in contrast to losartan, blocks AT1 receptor internalization). These results suggest that (P)RR gene activity may be controlled by intracellular AngII and that HG-induced ERK1/2 phosphorylation and fibronectin overproduction are primarily induced by (P)RR activation. This relationship between AngII and (P)RR may constitute an additional pathway of MC dysfunction in response to HG stimulation.