Kento Kitada

Renal Sympathetic Denervation Suppresses De Novo Podocyte Injury and Albuminuria in Rats With Aortic Regurgitation

Background— The presence of chronic kidney disease is a significant independent risk factor for poor prognosis in patients with chronic heart failure. However, the mechanisms and mediators underlying this interaction are poorly understood. In this study, we tested our hypothesis that chronic cardiac volume overload leads to de novo renal dysfunction by coactivating the sympathetic nervous system and renin-angiotensin system in the kidney. We also examined the therapeutic potential of renal denervation and renin-angiotensin system inhibition to suppress renal injury in chronic heart failure. Methods and Results— Sprague-Dawley rats underwent aortic regurgitation and were treated for 6 months with vehicle, olmesartan (an angiotensin II receptor blocker), or hydralazine. At 6 months, albuminuria and glomerular podocyte injury were significantly increased in aortic regurgitation rats. These changes were associated with increased urinary angiotensinogen excretion, kidney angiotensin II and norepinephrine (NE) levels, and enhanced angiotensinogen and angiotensin type 1a receptor gene expression and oxidative stress in renal cortical tissues. Aortic regurgitation rats with renal denervation had decreased albuminuria and glomerular podocyte injury, which were associated with reduced kidney NE, angiotensinogen, angiotensin II, and oxidative stress. Renal denervation combined with olmesartan prevented podocyte injury and albuminuria induced by aortic regurgitation. Conclusions— In this chronic cardiac volume-overload animal model, activation of the sympathetic nervous system augments kidney renin-angiotensin system and oxidative stress, which act as crucial cardiorenal mediators. Renal denervation and olmesartan prevent the onset and progression of renal injury, providing new insight into the treatment of cardiorenal syndrome.

Apoptosis inhibitor of macrophage protein enhances intraluminal debris clearance and ameliorates acute kidney injury in mice

Acute kidney injury (AKI) is associated with prolonged hospitalization and high mortality, and it predisposes individuals to chronic kidney disease. To date, no effective AKI treatments have been established. Here we show that the apoptosis inhibitor of macrophage (AIM) protein on intraluminal debris interacts with kidney injury molecule (KIM)-1 and promotes recovery from AKI. During AKI, the concentration of AIM increases in the urine, and AIM accumulates on necrotic cell debris within the kidney proximal tubules. The AIM present in this cellular debris binds to KIM-1, which is expressed on injured tubular epithelial cells, and enhances the phagocytic removal of the debris by the epithelial cells, thus contributing to kidney tissue repair. When subjected to ischemia-reperfusion (IR)-induced AKI, AIM-deficient mice exhibited abrogated debris clearance and persistent renal inflammation, resulting in higher mortality than wild-type (WT) mice due to progressive renal dysfunction. Treatment of mice with IR-induced AKI using recombinant AIM resulted in the removal of the debris, thereby ameliorating renal pathology. We observed this effect in both AIM-deficient and WT mice, but not in KIM-1–deficient mice. Our findings provide a basis for the development of potentially novel therapies for AKI.

Chymase Plays an Important Role in Left Ventricular Remodeling Induced by Intermittent Hypoxia in Mice

Intermittent hypoxia caused by sleep apnea is associated with cardiovascular disease. Chymase has been reported to play an important role in the development of cardiovascular disease, but it is unclear whether chymase is involved in the pathogenesis of left ventricular remodeling induced by intermittent hypoxia. The aim of this study was to evaluate the effect of a novel chymase inhibitor (NK3201) on hypoxia-induced left ventricular remodeling in mice. Male C57BL/6J mice (9 weeks old) were exposed to intermittent hypoxia or normoxia and were treated with NK3201 (10 mg/kg per day) or the vehicle for 10 days. Left ventricular systolic pressure showed no significant differences among all of the experimental groups. Exposure to intermittent hypoxia increased left ventricular chymase activity and angiotensin II expression, which were both suppressed by treatment with NK3201. Intermittent hypoxia also increased the mean cardiomyocyte diameter, perivascular fibrosis, expression of inflammatory cytokines, oxidative stress, and NADPH-dependent superoxide production in the left ventricular myocardium. These changes were all suppressed by NK3201 treatment. Therefore, chymase might play an important role in intermittent hypoxia-induced left ventricular remodeling, which is independent of the systemic blood pressure.

Aldosterone/Mineralocorticoid Receptor Stimulation Induces Cellular Senescence in the Kidney

Recent studies demonstrated a possible role of aldosterone in mediating cell senescence. Thus, the aim of this study was to investigate whether aldosterone induces cell senescence in the kidney and whether aldosterone-induced renal senescence affects the development of renal injury. Aldosterone infusion (0.75 μg/h) into rats for 5 weeks caused hypertension and increased urinary excretion rates of proteins and N-acetyl-β-D-glucosaminidase. Aldosterone induced senescence-like changes in the kidney, exhibited by increased expression of the senescence-associated β-galactosidase, overexpression of p53 and cyclin-dependent kinase inhibitor (p21), and decreased expression of SIRT1. These changes were abolished by eplerenone (100 mg/kg/d), a mineralocorticoid receptor (MR) antagonist, but unaffected by hydralazine (80 mg/liter in drinking water). Furthermore, aldosterone induced similar changes in senescence-associated β-galactosidase, p21, and SIRT1 expression in cultured human proximal tubular cells, which were normalized by an antioxidant, N-acetyl L-cysteine, or gene silencing of MR. Aldosterone significantly delayed wound healing and reduced the number of proliferating human proximal tubular cells, while gene silencing of p21 diminished the effects, suggesting impaired recovery from tubular damage. These findings indicate that aldosterone induces renal senescence in proximal tubular cells via the MR and p21-dependent pathway, which may be involved in aldosterone-induced renal injury.

Hyperglycemia causes cellular senescence via a SGLT2- and p21-dependent pathway in proximal tubules in the early stage of diabetic nephropathy

AIMS Kidney cells in patients with diabetic nephropathy are reported to be senescent. However, the mechanisms that regulate cellular senescence in the diabetic kidney are still unknown. In the present study, we evaluated the contribution of high glucose to renal cell senescence in streptozotocin (STZ)-induced diabetic mice. METHODS Non-diabetic and streptozotocin (STZ, 10mgkg(-1)day(-1) for 7days, i.p.)-induced type 1 diabetic C57BL/6J mice and cultured human proximal tubular cells were used in this study. RESULTS Hyperglycemia dramatically increased the renal expression of p21 but not other CDK inhibitors such as p16 and p27 at 4weeks after STZ injection. These changes were accompanied by an increase in senescence-associated β-galactosidase staining in tubular epithelial cells. Administration of insulin at doses that maintained normoglycemia or mild hypoglycemia suppressed the changes induced by STZ. Insulin did not affect the senescent markers in non-diabetic mice. Exposure of cultured human proximal tubular cells to 25mmol/L, but not 8mmol/L, glucose medium increased the expression of senescence markers, which was suppressed by knock-down of p21 or sodium glucose cotransporter (SGLT) 2. CONCLUSIONS These results suggest that hyperglycemia causes tubular senescence via a SGLT2- and p21-dependent pathway in the type 1 diabetic kidney.

Inhibition of Endothelin ETB Receptor System Aggravates Neointimal Hyperplasia after Balloon Injury of Rat Carotid Artery

Endothelin-1 (ET)/ETA receptor system has been known to play an important role in the pathogenesis of neointimal hyperplasia after endothelial injury. However, the pathological role of endothelin ETB receptors on neointimal hyperplasia remains to be elucidated. In the present study, we investigated the pathological role of ETB receptors on neointimal hyperplasia in balloon-injured rat carotid arteries by pharmacological blockade with use of 2R-(4-propoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N-(2,6-diethylphenyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid (A-192621), a selective ETB receptor antagonist, 2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid (ABT-627), a selective ETA receptor antagonist, and (+)-(5S,6R,7R)-2-butyl-7-[2-((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3,4-methylenedioxyphenyl)cyclopenteno[1,2-b]pyridine-6-carboxylic acid (J-104132), an ETA/ETB dual receptor antagonist. Moreover, the spotting-lethal rats, which carry a naturally occurring deletion in the endothelin ETB receptor gene, were used to examine the effects of genetic deficiency for this receptor subtype. Two weeks after balloon injury, the ratio of the neointimal to the medial area (neointima/media ratio) was determined. Treatment with A-192621 (30 mg/kg/day) for 2 weeks after injury significantly increased the neointima/media ratio in the injured artery. In contrast, ABT-627 (10 mg/kg/day) and J-104132 (10 mg/kg/day) markedly decreased the neointima/media ratio to the same extent. Furthermore, the neointima/media ratio in the injured artery of the ETB-deficient rat was significantly increased compared with that of the wild-type rat, and this increase was abolished by treatment with J-104132. These findings suggest that the inhibition of the ETB receptor system leads to an aggravation of neointimal hyperplasia after balloon injury, and the augmentation of ETA-mediated actions are responsible for the neointimal hyperplasia aggravated by the pharmacological blockade of ETB receptor or by its genetic deficiency. The antagonism of the ETA receptor system is essential for preventing restenosis after angioplasty.

High salt intake reprioritizes osmolyte and energy metabolism for body fluid conservation

Natriuretic regulation of extracellular fluid volume homeostasis includes suppression of the renin-angiotensin-aldosterone system, pressure natriuresis, and reduced renal nerve activity, actions that concomitantly increase urinary Na+ excretion and lead to increased urine volume. The resulting natriuresis-driven diuretic water loss is assumed to control the extracellular volume. Here, we have demonstrated that urine concentration, and therefore regulation of water conservation, is an important control system for urine formation and extracellular volume homeostasis in mice and humans across various levels of salt intake. We observed that the renal concentration mechanism couples natriuresis with correspondent renal water reabsorption, limits natriuretic osmotic diuresis, and results in concurrent extracellular volume conservation and concentration of salt excreted into urine. This water-conserving mechanism of dietary salt excretion relies on urea transporter–driven urea recycling by the kidneys and on urea production by liver and skeletal muscle. The energy-intense nature of hepatic and extrahepatic urea osmolyte production for renal water conservation requires reprioritization of energy and substrate metabolism in liver and skeletal muscle, resulting in hepatic ketogenesis and glucocorticoid-driven muscle catabolism, which are prevented by increasing food intake. This natriuretic-ureotelic, water-conserving principle relies on metabolism-driven extracellular volume control and is regulated by concerted liver, muscle, and renal actions.

Increased salt consumption induces body water conservation and decreases fluid intake

BACKGROUND. The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions. METHODS. Over the course of 2 separate space flight simulation studies of 105 and 205 days’ duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance. RESULTS. A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion. CONCLUSION. Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion. FUNDING. Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

Inhibition of soluble epoxide hydrolase is renoprotective in 5/6 nephrectomized Ren-2 transgenic hypertensive rats

The aim of the present study was to test the hypothesis that increasing kidney tissue concentrations of epoxyeicosatrienoic acids (EETs) by preventing their degradation to the biologically inactive dihydroxyeicosatrienoic acids (DHETEs) using blockade of soluble epoxide hydrolase (sEH) would attenuate the progression of chronic kidney disease (CKD). Ren‐2 transgenic rats (TGR) after 5/6 renal mass reduction (5/6 NX) served as a model of CKD associated with angiotensin (Ang) II‐dependent hypertension. Soluble epoxide hydrolase was inhibited using cis‐4‐[4‐(3‐adamantan‐1‐yl‐ureido)cyclohexyloxy]benzoic acid (c‐AUCB; 3 mg/L drinking water) for 20 weeks after 5/6 NX. Sham‐operated normotensive transgene‐negative Hannover Sprague‐Dawley (HanSD) rats served as controls. When applied in TGR subjected to 5/6 NX, c‐AUCB treatment improved survival rate, prevented the increase in blood pressure, retarded the progression of cardiac hypertrophy, reduced proteinuria and the degree of glomerular and tubulointerstitial injury and reduced glomerular volume. All these organ‐protective actions were associated with normalization of the intrarenal EETs : DHETEs ratio, an index of the availability of biologically active EETs, to levels observed in sham‐operated HanSD rats. There were no significant concurrent changes of increased intrarenal AngII content. Together, these results show that 5/6 NX TGR exhibit a profound deficiency of intrarenal availability of active epoxygenase metabolites (EETs), which probably contributes to the progression of CKD in this model of AngII‐dependent hypertension, and that restoration of intrarenal availability of EETs using long‐term c‐AUCB treatment exhibits substantial renoprotective actions.

The cyclin-dependent kinase inhibitor p21 is essential for the beneficial effects of renal ischemic preconditioning on renal ischemia/reperfusion injury in mice.

The cyclin-dependent kinase inhibitor p21 plays important roles in chronic renal disorders; however, its roles in response to acute renal stress are unclear. Here we evaluated p21 in acute kidney injury and ischemic preconditioning using wild-type and p21 knockout mice that underwent renal ischemia followed by reperfusion. The decline in renal function and histological changes were worse in the knockout than in wild-type mice. Ischemia/reperfusion increased p21 expression in the kidney of wild-type mice compared with sham surgery, suggesting p21 may confer tolerance to ischemia/reperfusion injury. We next tested whether p21 is associated with the protective effect of ischemic preconditioning, an established method to reduce ischemia/reperfusion injury. Ischemic preconditioning attenuated ischemia/reperfusion injury in wild-type but not p21-knockout mice. This preconditioning decreased the number of proliferating tubular cells before but increased them at 24 h after ischemia/reperfusion in the kidneys of wild-type mice. In p21-knockout mice, ischemic preconditioning did not change the number of proliferating cells before but decreased them after ischemia/reperfusion. Ischemic preconditioning increased renal p21 expression and the number of cells in the G1 phase of the cell cycle before ischemia/reperfusion compared with sham surgery. Thus, renal p21 is essential for the beneficial effects of renal ischemic preconditioning. Transient cell cycle arrest induced by ischemic preconditioning by a p21-dependent pathway seems to be important for subsequent tubular cell proliferation after ischemia/reperfusion.