Keiji Kono

Vitamin D Activates the Nrf2-Keap1 Antioxidant Pathway and Ameliorates Nephropathy in Diabetic Rats

BACKGROUND Diabetic nephropathy is a major risk of end-stage kidney disease. Many complex factors relate to the progression of diabetic nephropathy. Using nonobese type 2 diabetes model rats, we confirmed that oxidative stress was a crucial factor. Because recent studies suggest that vitamin D could suppress oxidative stress, we explored whether the active vitamin D analog, maxacalcitol, could also attenuate oxidative stress and prevent the progression of diabetic nephropathy. METHODS Diabetic rats aged 20 weeks were divided into 3 groups and treated with insulin, maxacalcitol, and vehicle. At age 30 weeks, blood and urine analyses, renal histology, immunohistochemistry, real-time polymerase chain reaction, and western blot were performed. RESULTS Although maxacalcitol reduced albuminuria and mesangial matrix expansion, no significant differences were observed in blood pressure and creatinine clearance among the 3 treatment groups. Systemic and intrarenal oxidative stress was reduced by maxacalcitol therapy. Expressions of nuclear factor-κB and nicotinamide adenine dinucleotide phosphate oxidase in the kidney also decreased in the insulin-treated and maxacalcitol-treated groups but increased in the vehicle-alone group. In addition, the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) decreased and Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1) increased in the vehicle-treated group; however, these expressions were restored in the maxacalcitol- and insulin-treated groups. CONCLUSIONS It is suggested that maxacalcitol attenuates the progression of diabetic nephropathy by suppression of oxidative stress and amelioration of the Nrf2-Keap1 pathway in nonobese type 2 diabetes without significant changes in blood pressure and glomerular filtration rate.

Oxidative and Nitrosative Stress and Progression of Diabetic Nephropathy in Type 2 Diabetes

Background: The role of nitric oxide (NO) is controversial in diabetes nephropathy progression and the mechanisms remain unknown, especially in non-obese type 2 diabetes. To examine mechanisms of nephropathy progression in non-obese type 2 diabetes, we used spontaneously diabetic Torii (SDT) rats, a newly established model of non-obese type 2 diabetes. Methods: Fourteen male Sprague-Dawley rats were used as a control (20 weeks, n = 6; 30 weeks, n = 8), and 20-week-old male SDT rats were divided into 2 groups: diabetic (DM, n = 8) and DM + insulin (n = 8) groups. Twenty- and 36-week-old rats were sacrificed, and blood, urine, and histomorphometric analyses, mRNA expression analysis of endothelial NO synthase (eNOS) and NADPH oxidase, and blood pressure measurement were performed. Results: At 36 weeks, NO metabolites, and 8-hydroxydeoxyguanosine (8-OHdG) were significantly higher in the diabetic group than in the other 2 groups. Further renal studies showed increased glomerular volume and mesangial area, and intensified eNOS, 8-OHdG, and nitrotyrosine immunostaining in the diabetic group. Oxidative and nitrosative stress were positively associated with increased glomerular volume and mesangial area, which were mostly recovered by insulin therapy. Conclusions: NO and oxidative stress increased in SDT rats, suggesting that these play key roles in nephropathy progression in non-obese type 2 diabetes.

Composition and plaque patterns of coronary culprit lesions and clinical characteristics of patients with chronic kidney disease

Coronary artery disease is a serious complication of chronic kidney disease (CKD); however, there is little information about coronary plaque morphology in these patients. Here we identified the characteristics of coronary culprit plaques and their clinical manifestations in 78 patients with CKD divided into four groups based on their estimated glomerular filtration rate. Patients were examined by Virtual Histology-Intravascular Ultrasound, a tomographic imaging method that can visualize atherosclerotic plaques in vivo using radiofrequency analysis of ultrasound backscatter signals. These ultrasound analyses showed an increase in the relative volumes of both dense calcium and necrotic core with decreasing renal function. The necrotic core/dense calcium ratio was significantly higher in patients with acute myocardial infarction compared to those with stable angina pectoris. Furthermore, the necrotic core/dense calcium ratio decreased in advanced CKD. Thus, the plaque composition of coronary culprit lesions changed from necrotic core-rich to extensively calcium-rich plaques as renal function decreased, suggesting that such coronary culprit composition was associated with stability, particularly in advanced CKD.

Effects of AST-120 on Left Ventricular Mass in Predialysis Patients

Background: Cardiovascular disease (CVD) is a leading cause of death in chronic kidney disease (CKD) patients. One of the proposed mechanisms assumes that accumulated uremic toxins play an important role in the progression of CVD in CKD. Recently, it has been reported that AST-120 may attenuate progression of CVD through absorption of uremic toxins. In this study, we examined the association between the use of AST-120 and cardiac abnormalities in CKD patients. Methods: This was a cross-sectional study of predialysis CKD patients hospitalized in our institution between April 2008 and October 2009. We divided 107 patients into two groups based on whether AST-120 had been administered for more than 6 months (AST-120 group: n = 43) or not (control group: n = 64). Echocardiography and laboratory tests were performed for all patients; we examined the relationship between clinical characteristics and cardiac abnormalities. Results: The number of patients with left ventricular (LV) concentric change was significantly smaller in the AST-120 group than in the control group. In multivariable analysis, the administration of AST-120, gender, and pulse pressure were significantly correlated with LV concentric change. Conclusions: Our findings suggest that AST-120 prevents the development of LV concentric change in predialysis CKD patients.

Prevalence and cardiovascular features of Japanese hemodialysis patients with Fabry disease.

Background: Fabry disease (FD) is a rare disease and one of the causes of progressive renal dysfunction. It results from an X-linked deficiency of α-galactosidase A activity. It has been reported that its prevalence is much higher in hemodialysis patients than in the general population. However, its prevalence in Japanese hemodialysis patients and cardiovascular manifestations remain unclear. Methods: We screened the α-galactosidase A activity of 1,024 Japanese hemodialysis patients using a dried blood spot test. Patients with a low α-galactosidase A activity were assessed clinically, and a genetic study of the α-galactosidase A gene was performed for these patients. Furthermore, patients with FD underwent detailed cardiovascular examination. Results: Forty-six patients had low α-galactosidase A activity, and 1 man and 2 women had α-galactosidase A mutations (0.29%). All of these patients had a previously identified mutation (E66Q). The result of detailed cardiovascular examination showed that 2 patients had significantly impaired coronary flow reserve, reduced myocardial contraction and relaxation tissue Doppler velocities, and left ventricular hypertrophy. Conclusions: Measurement of the α-galactosidase A activity and the results of a genetic analysis indicated that the prevalence of FD in our hemodialysis patients was 0.29% (0.16% in men and 0.5% in women). Furthermore, comprehensive examination detected cardiovascular abnormalities in Japanese hemodialysis patients with FD.

Coronary plaque morphology using virtual histology-intravascular ultrasound analysis in hemodialysis patients.

Most dialysis patients have coronary artery disease at the initiation of dialysis therapy and these patients also have marked vascular calcification. Virtual histology–intravascular ultrasound (VH–IVUS) provides coronary tissue maps that are color coded by four major plaque components and facilitate the characterization of coronary plaque composition in vivo. The aim of this study was to identify coronary plaque characteristics in dialysis patients using VH–IVUS. Twenty‐three patients with coronary artery disease were included in this study. Of these, 12 patients had normal renal function or mild renal insufficiency (control group) and 11 patients were receiving maintenance dialysis therapy (hemodialysis group). We performed coronary angiography and VH–IVUS analysis on culprit lesions of all patients in the study. The result of VH–IVUS analysis showed that the hemodialysis group had a greater plaque volume, lower percentage of fibrous plaque, and higher percentage of dense calcium plaque compared with the control group. In addition, the serum phosphate levels were significantly associated with the percentage of necrotic core and dense calcium plaque in all study patients. Our findings suggest that the amount of necrotic core and dense calcium plaques increase significantly in hemodialysis patients, and that disordered mineral metabolism may be associated with coronary plaque morphology.

Anti-Oxidative Effect of Vitamin D Analog on Incipient Vascular Lesion in Non-Obese Type 2 Diabetic Rats

Background/Aims: Vascular disease is one of the critical complications of diabetes. A growing body of evidence suggests that oxidative stress plays a key role for vascular disease progression. Recent studies have demonstrated a strong link between vitamin D and cardiovascular disease. Methods: We investigated the anti-oxidative effects of a vitamin D analog, 22-oxacalcitriol (maxacalcitol), on vascular lesions in type 2 diabetic rats. We used Spontaneously Diabetic Torii (SDT) rats, a model of non-obese type 2 diabetes. At 20 weeks of age, SDT rats were randomly divided into three groups: diabetes mellitus (DM, n = 10), DM + maxacalcitol (DM + D, n = 10), and DM + insulin (DM + I, n = 10). The rats were sacrificed at 30 weeks for the evaluation of blood and urine samples as well as histopathology and mRNA expression in the aorta. Results: Urinary 8-hydroxydeoxyguanosine (8-OHdG) excretion and the number of 8-OHdG-positive cells were significantly lower in the DM + I and DM + D groups than in the DM group. Real-time polymerase chain reaction analysis demonstrated that NADPH p22 phox and NADPH p47 phox mRNA levels were markedly decreased in the DM + I and DM + D groups compared with the DM group. Furthermore, the mRNA expression of MCP-1, ICAM-1 and VCAM-1 was significantly reduced in the DM + I and DM + D groups compared with the DM group. Conclusion: Our results suggest that the vasoprotective effects of vitamin D are mediated by reducing oxidative stress.

Carvedilol Ameliorates Low-Turnover Bone Disease in Non-Obese Type 2 Diabetes

Background: Diabetic bone disease is a major complication in diabetes mellitus and is characterized by low-turnover bone formation. Recent studies have demonstrated that oxidative stress could be associated with diabetic bone disease and that β-adrenergic antagonists could increase bone formation. Our study investigated the effect of carvedilol (β-blocker), possessing an antioxidant effect, on diabetic bone disease. Methods: We used the non-obese, type 2 diabetes model Spontaneously Diabetic Torii (SDT) rats in this study. Sprague-Dawley rats were used as controls (control, n = 6). SDT rats were divided into four groups: diabetic (DM, n = 8), DM+insulin (DM+I, n = 7), DM+carvedilol (DM+C, n = 8), and DM+N-acetylcysteine (DM+N, n = 10) at 20 weeks. The rats were sacrificed at 30 weeks, after which blood and urine samples, bone mineral density, histomorphometry, and oxidative stress were evaluated. Results: The number of 8-hydroxydeoxyguanosine-positive cells in bone tissue was significantly lower in the DM+C and DM+N groups than in the DM group. Mineral apposition rate and bone formation rate per bone surface in the DM+C and DM+N groups were significantly higher than those in the DM group, and these parameters were better in the DM+C group than in the DM+N group. Conclusion: Our data suggest that carvedilol has stronger effects on diabetic low-turnover bone disease beyond that which can be attributed to its antioxidative stress mechanism.

Renin-Angiotensin System Inhibitors Reduce Serum Asymmetric Dimethylarginine Levels and Oxidative Stress in Normotensive Patients with Chronic Kidney Disease

Background/Aims: The purpose of our study was to elucidate the relationship between asymmetric dimethylarginine (ADMA) and intrarenal lesions and to determine the effect of renin-angiotensin system inhibitors (RAS-Is) on serum ADMA levels, nitric oxide (NO) synthesis and oxidative stress in normotensive patients with chronic kidney disease (CKD). Methods: This study included 23 normotensive patients with chronic glomerulonephritis and normal or mildly impaired renal function who underwent renal biopsy. We evaluated the relationship between serum ADMA levels and intrarenal lesions, and examined renal function, urinary protein excretion, ADMA levels, NO synthesis, oxidative stress and blood pressure (BP) before and 3 months after starting the treatment with RAS-Is. Results: Serum ADMA levels were correlated only with arterial intimal fibroplastic thickness. Despite comparable renal function and BP, serum ADMA levels and excretion of urinary protein excretion significantly decreased, and urinary NO metabolite excretion significantly increased after starting the treatment with RAS-Is. Oxidative stress markers also tended to be reduced by the treatment. Conclusion: These findings suggest that RAS-Is improve the NO system and decrease oxidative stress in normotensive patients with CKD. In addition, ADMA may be associated with intrarenal lesions and can be a useful marker for the effects of treatment in the early stages of CKD.

Anti-oxidative effect of AST-120 on kidney injury after myocardial infarction.

Chronic kidney disease (CKD) is a crucial risk factor for cardiovascular disease (CVD), and combined CKD and CVD further increases morbidity and mortality. Here, we investigated effects of AST‐120 on oxidative stress and kidney injury using a model of myocardial infarction (MI) in rats.