Ju-Young Moon

Attenuating effect of angiotensin-(1–7) on angiotensin II-mediated NAD(P)H oxidase activation in type 2 diabetic nephropathy of KK-Ay/Ta mice

ANG-(1-7) is associated with vasodilation and nitric oxide synthase stimulation. However, the role of ANG-(1-7) in type 2 diabetes mellitus is unknown. In this study, we examined the hypothesis that ANG-(1-7) attenuates ANG II-induced reactive oxygen species stress (ROS)-mediated injury in type 2 diabetic nephropathy of KK-A(y)/Ta mice. KK-A(y)/Ta mice were divided into four groups: 1) a control group; 2) ANG II infusion group; 3) ANG II+ANG-(1-7) coinfusion group; and 4) ANG II+ANG-(1-7)+d-Ala(7)-ANG-(1-7) (A779) coinfusion group. In addition, primary mesangial cells were cultured and then stimulated with 25 mM glucose with or without ANG II, ANG-(1-7), and A779. The ANG II+ANG-(1-7) coinfusion group showed a lower urinary albumin/creatinine ratio increase than the ANG II group. ANG-(1-7) attenuated ANG II-mediated NAD(P)H oxidase activation and ROS production in diabetic glomeruli and mesangial cells. ANG II-induced NF-κB and MAPK signaling activation was also attenuated by ANG-(1-7) in the mesangial cells. These findings were related to improved mesangial expansion and to fibronectin and transforming growth factor-β1 production in response to ANG II and suggest that ANG-(1-7) may attenuate ANG II-stimulated ROS-mediated injury in type 2 diabetic nephropathy. The ACE2-ANG-(1-7)-Mas receptor axis should be investigated as a novel target for treatment of type 2 diabetic nephropathy.

Angiotensin II-induced mitochondrial Nox4 is a major endogenous source of oxidative stress in kidney tubular cells.

Angiotensin II (Ang II)-induced activation of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase leads to increased production of reactive oxygen species (ROS), an important intracellular second messenger in renal disease. Recent findings suggest that Ang II induces mitochondrial depolarization and further amplifies mitochondrial generation of ROS. We examined the hypothesis that ROS injury mediated by Ang II-induced mitochondrial Nox4 plays a pivotal role in mitochondrial dysfunction in tubular cells and is related to cell survival. In addition, we assessed whether angiotensin (1-7) peptide (Ang-(1-7)) was able to counteract Ang II-induced ROS-mediated cellular injury. Cultured NRK-52E cells were stimulated with 10−6 M Ang II for 24 h with or without Ang-(1-7) or apocynin. Ang II simulated mitochondrial Nox4 and resulted in the abrupt production of mitochondrial superoxide (O2 −) and hydrogen peroxide (H2O2). Ang II also induced depolarization of the mitochondrial membrane potential, and cytosolic secretion of cytochrome C and apoptosis-inducing factor (AIF). Ang-(1-7) attenuated Ang II-induced mitochondrial Nox4 expression and apoptosis, and its effect was comparable to that of the NAD(P)H oxidase inhibitor. These findings suggest that Ang II-induced activation of mitochondrial Nox4 is an important endogenous source of ROS, and is related to cell survival. The ACE2-Ang-(1-7)-Mas receptor axis should be investigated further as a novel target of Ang II-mediated ROS injury.

Effects of Sildenafil on Oxidative and Inflammatory Injuries of the Kidney in Streptozotocin-Induced Diabetic Rats

Background: Oxidative stress and inflammation are implicated in the pathogenesis of diabetic nephropathy. Because sildenafil citrate (Viagra®) has variable cardiovascular benefits, including antioxidative and immunomodulating effects, we investigated its influence on oxidative stress and inflammation in diabetic rat kidney. Methods: Streptozotocin-induced diabetic rats received sildenafil (3 mg/kg/day in drinking water) or not (undosed water) for 8 weeks and were compared to age-matched nondiabetic animals. We evaluated 8-hydroxydeoxyguanosine (8-OHdG; for oxidative DNA damage), inducible nitric oxide synthase (iNOS) and nitrotyrosine (for excessive NO production and peroxynitrite formation), and representative chemoattractants [monocyte chemotactic protein-1, MCP-1; for inflammation and monocyte/macrophage infiltrations (ED-1)] in the kidney. Results: Sildenafil-treated rats had a lower kidney-to-body weight ratio than untreated diabetic rats. Urinary albumin excretion in diabetic rats decreased significantly after sildenafil treatment without changes in systolic blood pressure. Sildenafil-treated rats had significantly lower urinary and renal cortical 8-OHdG levels than the nonsildenafil group. Sildenafil administration significantly attenuated the increased renal nitrotyrosine protein expression, positive iNOS and ED-1 staining in glomeruli and tubulointerstitium, and nitrotyrosine staining in tubulointerstitium. Cortical MCP-1 RNA expression in the sildenafil group was significantly lower than in the nonsildenafil group. Conclusions: Sildenafil treatment may attenuate renal damage by ameliorating oxidative and inflammatory injuries in diabetic rats.

Repeated administration of bone marrow-derived mesenchymal stem cells improved the protective effects on a remnant kidney model.

Mesenchymal stem cell (MSC) has been implied to have the therapeutic potential on chronic kidney disease (CKD). However, the underlying mechanism is still unclear and administration frequency of MSCs could be an issue in a chronic disease model. We evaluated the effect of repeated administration of MSCs on a remnant kidney model. MSCs from 5-week male Sprague–Dawley rats were infused by tail vein into 7-week female 5/6 nephrectomized rats after tagging with a fluorescent probe, chloromethyl-1,1-dioctadecyl-3,3,3′,3′-tetramethyl- indocarbocyanine perchlorate (CM-Dil). Effect of weekly administration of MSCs was compared with the effect of once injection of MSCs and mesangial cells (MCs) at 1 and 5 weeks, respectively. Engraftment of MSCs into the kidney was evaluated by the presence of CM-Dil fluorescence or SRY gene expression. Weekly MSCs administration showed significant improvement in systolic blood pressure (SBP), urinary protein excretion amount, and serum creatinine level at 5 weeks, whereas once MSCs or MCs administration did not. Although once MSCs administration attenuated glomerulosclerosis and infiltration of ED-1 positive cells at 5 weeks as compared with MCs, weekly MSC administration led to a more significant improvement. Renal SRY gene expression and presence of CM-Dil-tagged cells could be confirmed at 1 week after injection of MSCs or weekly injected group, but not at 5 weeks after once injection. MSCs attenuated cortical expression of interleukin (IL)-6 and elevated the expression of IL-10, but these effects were only sustained in the weekly group. Thus, repeated administration of MSCs improves the protective effect on remnant kidney injury, but primarily via the paracrine effect rather than differentiation.

Hyperuricemia-induced NLRP3 activation of macrophages contributes to the progression of diabetic nephropathy

IL-1β-secreting nucleotide-binding oligomerization domain protein 3 (NLRP3) inflammasomes play a pivotal role in triggering innate immune responses in metabolic disease. We investigated the role of soluble uric acid in NLRP3 inflammasome activation in macrophages to demonstrate the effect of systemic hyperuricemia on progressive kidney damage in type 2 diabetes. THP-1 cells, human acute monocytic leukemia cells, were cultured to obtain macrophages, and HK-2 cells, human renal proximal tubule cells, were cultured and stimulated with uric acid. In vivo, we designed four rat groups as follows: 1) Long-Evans Tokushima Otsuka (LETO); 2) Otsuka Long-Evans Tokushima Fatty (OLETF); 3) OLETF+high-fructose diet (HFD) for 16 wk; and 4) OLETF+HFD+allopurinol (10 mg/dl administered in the drinking water). Soluble uric acid stimulated NLRP3 inflammasomes to produce IL-1β in macrophages. Uric acid-induced MitoSOX mediates NLRP3 activation and IL-1β secretion. IL-1β from macrophages activates NF-κB in cocultured proximal tubular cells. In vivo, intrarenal IL-1β expression and macrophage infiltration increased in HFD-fed OLETF rats. Lowering the serum uric acid level resulted in improving the albuminuria, tubular injury, macrophage infiltration, and renal IL-1β (60% of HFD-fed OLETF) independently of glycemic control. Direct activation of proximal tubular cells by uric acid resulted in (C-X-C motif) ligand 12 and high mobility group box-1 release and accelerated macrophage recruitment and the M1 phenotype. Taken together, these data support direct roles of hyperuricemia in activating NLRP3 inflammasomes in macrophages, promoting chemokine signaling in the proximal tubule and contributing to the progression of diabetic nephropathy through cross talk between macrophages and proximal tubular cells.

Aberrant Recruitment and Activation of T Cells in Diabetic Nephropathy

Background/Aims: Recent evidence has shown that an inflammatory process is involved in the development and progression of diabetic nephropathy. This study examined the impact of activated intrarenal lymphocytes in this inflammatory process. Methods: We studied T cell recruitment in mice with streptozotocin (STZ)-induced diabetes by flow cytometry and immunohistochemistry. The kidney biopsy specimens from patients with type 2 diabetes mellitus and diabetic nephropathy were evaluated by immunohistochemistry. Results: In flow cytometry, intrarenal CD3+ T cells were significantly increased in proteinuric mice at 20 weeks after STZ injection. However, the population of T cells and B cells in diabetic spleen was not different from that of control mice. Immunohistochemistry also showed a marked infiltration of interstitial CD4+, CD8+ T cells in diabetic kidney. Interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) mRNA expression was significantly increased in diabetic mouse kidney compared with controls. Interestingly, flow cytometry analysis of kidney-derived mononuclear cells from diabetic mice showed significantly increased production of IFN-γ and TNF-α by CD3+ T cells. Type 2 diabetic patients also showed a marked increase in CD4+, CD8+ and CD20+ cells in interstitium, and the number of CD4+ and CD20+ cells correlated with the amount of proteinuria. Conclusion: Our results clearly showed that aberrant intrarenal infiltration and the activation of T cells in interstitium are the underlying immunopathological mechanisms of diabetic kidney injury.

Association of Polymorphisms in Monocyte Chemoattractant Protein-1 Promoter with Diabetic Kidney Failure in Korean Patients with Type 2 Diabetes Mellitus

Monocyte chemoattractant protein-1 (MCP-1) is suggested to be involved in the progression of diabetic nephropathy. We investigated the association of the -2518 A/G polymorphism in the MCP-1 gene with progressive kidney failure in Korean patients with type 2 diabetes mellitus (DM). We investigated -2518 A/G polymorphism of the MCP-1 gene in type 2 DM patients with progressive kidney failure (n=112) compared with matched type 2 DM patients without nephropathy (diabetic control, n=112) and healthy controls (n=230). The overall genotypic distribution of -2518 A/G in the MCP-1 gene was not different in patients with type 2 DM compared to healthy controls. Although the genotype was not significantly different between the patients with kidney failure and the diabetic control (p=0.07), the A allele was more frequent in patients with kidney failure than in DM controls (42.0 vs. 32.1%, p=0.03). The carriage of A allele was significantly associated with kidney failure (68.8 vs. 54.5%, OR 1.84, 95% CI 1.07-3.18). In logistic regression analysis, carriage of A allele retained a significant association with diabetic kidney failure. Our result shows that the -2518 A allele of the MCP-1 gene is associated with kidney failure in Korean patients with type 2 DM.

Recent Update of Renin-angiotensin-aldosterone System in the Pathogenesis of Hypertension

The activation of renin-angiotensin-aldosterine system(RAAS) is one of the main pathogenesis of hypertension. All the components of RAAS are present in the kidneys at higher concentrations compared to plasma levels, and intrarenal formation of angiotensin II (Ang II) is independent of the systemic RAAS. There are some unique features in intrarenal RAAS compared to systemic RAAS. Unlike JG cells where Ang II inhibits renin release via the AngII type 1 (AT1) receptor by negative feedback, in the collecting duct Ang II stimulates renin expression via the AT1 receptor. Upregulated renin produced in the distal nephron may be able to support continued intrarenal Ang II formation leading to amplification or maintenance of the hypertensive state.The recently discovered angiotensin-converting enzyme-related carboxypeptidase 2 (ACE2)-Angiotensin-(1-7) Ang-(1-7)-Mas receptor axis has an opposing function to that of the ACE-Ang II-AT1 receptor axis.The ACE2 deficiency was associated with an increase in blood pressure, and ACE2 knockout mice have highlighted hypertensive response to Ang II infusion associated with exaggerated accumulation of Ang II in the kidney. Recently, several numbers of patients have been evaluated as the activators of ACE2-Ang-(1-7)-Mas receptor axis, which can be divided into two main classes: aimed to increase the activity of ACE2, and directed to stimulate the Ang-(1-7) receptor Mas. In order to investigate new targets for hypertension and kidney disease, further research on the function of the ACE-Ang-(1-7)-Mas receptor axis is required.

The Dose-Dependent Organ-Specific Effects of a Dipeptidyl Peptidase-4 Inhibitor on Cardiovascular Complications in a Model of Type 2 Diabetes

Objective Although dipeptidyl peptidase-4 (DPP-4) inhibitors have been suggested to have a non-glucoregulatory protective effect in various tissues, the effects of long-term inhibition of DPP-4 on the micro- and macro-vascular complications of type 2 diabetes remain uncertain. The aim of the present study was to investigate the organ-specific protective effects of DPP-4 inhibitor in rodent model of type 2 diabetes. Methods Eight-week-old diabetic and obese db/db mice and controls (db/m mice) received vehicle or one of two doses of gemigliptin (0.04 and 0.4%) daily for 12 weeks. Urine albumin excretion and echocardiography measured at 20 weeks of age. Heart and kidney tissue were subjected to molecular analysis and immunohistochemical evaluation. Results Gemigliptin effectively suppressed plasma DPP-4 activation in db/db mice in a dose-dependent manner. The HbA1c level was normalized in the 0.4% gemigliptin, but not in the 0.04% gemigliptin group. Gemigliptin showed a dose-dependent protective effect on podocytes, anti-apoptotic and anti-oxidant effects in the diabetic kidney. However, the dose-dependent effect of gemigliptin on diabetic cardiomyopathy was ambivalent. The lower dose significantly attenuated left ventricular (LV) dysfunction, apoptosis, and cardiac fibrosis, but the higher dose could not protect the LV dysfunction and cardiac fibrosis. Conclusion Gemigliptin exerted non-glucoregulatory protective effects on both diabetic nephropathy and cardiomyopathy. However, high-level inhibition of DPP-4 was associated with an organ-specific effect on cardiovascular complications in type 2 diabetes.

Reducing serum uric acid attenuates TGF-β1-induced profibrogenic progression in type 2 diabetic nephropathy.

Background: The pivotal role of transforming growth factor-β1 (TGF-β1)-induced tubulointerstitial fibrosis in the progression of chronic kidney disease is an active topic of research. Recent evidence indicates that hyperuricemia is associated with increased TGF-β1 and progressive tubulointerstitial injury. We examined the hypothesis that lowering serum uric acid attenuates TGF-β1-induced profibrogenic tubular change in type 2 diabetic nephropathy. Methods: KK-Ay/Ta mice, an animal model of type 2 diabetes, were provided access to either regular drinking water or drinking water containing 10 mg/dl of allopurinol. Normal rat kidney epithelial cells were cultured and stimulated with 5 mM uric acid with or without allopurinol. Results: Type 2 diabetic mice that received allopurinol exhibited smaller increases in urinary albumin:creatinine ratio than diabetic control mice, as well as attenuated TGF-β1 and Smad pathway-induced profibrogenic tubular changes in diabetic kidneys. Allopurinol attenuated TGF-β1-induced Smad pathway activation in tubular cells. These findings were related to increases in E-cadherin, and decreases in vimentin and α-smooth muscle actin. Uric acid-induced upregulation of TGF-β1 depends on mitogen-activated protein kinase signaling. Conclusions: This is the first study to demonstrate that reducing serum uric acid has preventive effects against to profibrogenic progression in type 2 diabetic kidney disease. These findings suggest that lowering serum uric acid may be an effective therapeutic intervention to prevent the progression of type 2 diabetic kidney disease.