A Mutation in γ-Adducin Impairs Autoregulation of Renal Blood Flow and Promotes the Development of Kidney Disease.

BACKGROUND: The genes and mechanisms involved in the association between diabetes or hypertension and CKD risk are unclear. Previous studies have implicated a role for γ-adducin (ADD3), a cytoskeletal protein encoded by Add3. METHODS: We investigated renal vascular function in vitro and in vivo and the susceptibility to CKD in rats with wild-type or mutated Add3 and in genetically modified rats with overexpression or knockout of ADD3. We also studied glomeruli and primary renal vascular smooth muscle cells isolated from these rats. RESULTS: This study identified a K572Q mutation in ADD3 in fawn-hooded hypertensive (FHH) rats-a mutation previously reported in Milan normotensive (MNS) rats that also develop kidney disease. Using molecular dynamic simulations, we found that this mutation destabilizes a critical ADD3-ACTIN binding site. A reduction of ADD3 expression in membrane fractions prepared from the kidney and renal vascular smooth muscle cells of FHH rats was associated with the disruption of the F-actin cytoskeleton. Compared with renal vascular smooth muscle cells from Add3 transgenic rats, those from FHH rats had elevated membrane expression of BKα and BK channel current. FHH and Add3 knockout rats exhibited impairments in the myogenic response of afferent arterioles and in renal blood flow autoregulation, which were rescued in Add3 transgenic rats. We confirmed these findings in a genetic complementation study that involved crossing FHH and MNS rats that share the ADD3 mutation. Add3 transgenic rats showed attenuation of proteinuria, glomerular injury, and kidney fibrosis with aging and mineralocorticoid-induced hypertension. CONCLUSIONS: This is the first report that a mutation in ADD3 that alters ACTIN binding causes renal vascular dysfunction and promotes the susceptibility to kidney disease.

Hydrochlorothiazide ameliorates polyuria caused by tolvaptan treatment of polycystic kidney disease in PCK rats.

BACKGROUND: Tolvaptan is an effective treatment for polycystic kidney disease (PKD), but also causes unfortunate polyuria. Hydrochlorothiazide (HCTZ) has been shown to reduce urine volume in nephrogenic diabetes insipidus, raising the possibility that HCTZ could also be effective in reducing tolvaptan-induced polyuria. In this study, we examined the combined administration of HCTZ and tolvaptan. METHODS: Male PCK rats were divided into four groups of normal chow (Cont), normal chow plus tolvaptan, gavage HCTZ treatment, and tolvaptan + HCTZ. Biochemical examinations of the plasma and urine were performed as well as histological and molecular (mRNA and protein expression) analyses. RESULTS: Groups treated with tolvaptan had significantly higher 24 h urine excretion, which was significantly reduced in the tolvaptan + HCTZ group after 2 weeks. Cyst size, pERK protein expression, and Cyclin D1 mRNA expression were all significantly reduced in both the tolvaptan and tolvaptan + HCTZ groups, indicating that HCTZ did not affect the beneficial functions of tolvaptan. Notably, aquaporin 2 redistribution from the apical to intracellular domains was observed in tolvaptan-treated rats and was partially reversed in the tolvaptan + HCTZ group. The renal glomerular filtration rate was reduced in the tolvaptan + HCTZ group. Significantly lowered mRNA expression of neuronal nitric oxide synthase, prostaglandin E synthase 2 and renin were also found in the medulla, but not in the cortex. CONCLUSION: HCTZ reduces tolvaptan-induced polyuria without altering its beneficial effects on PKD. This novel therapeutic combination could potentially lead to better PKD treatments and improved quality of life for the affected patients.

Enhanced renal ischemia-reperfusion injury in aging and diabetes.

The incidence and severity of acute kidney injury is increased in patients with diabetes and with aging. However, the mechanisms involved have not been clearly established. The present study examined the effects of aging and diabetes on the severity of renal ischemia-reperfusion (IR) injury in Sprague-Dawley (SD) and type 2 diabetic (T2DN) rats. T2DN rats develop diabetes at 3 mo of age and progressive proteinuria and diabetic nephropathy as they age from 6 to 18 mo. Plasma creatinine levels after bilateral IR were significantly higher (3.4 ± 0.1 mg/dl) in 18-mo-old elderly T2DN rats than in middle-aged (12 mo) T2DN rats with less severe diabetic nephropathy or young (3 mo) and elderly (18 mo) control SD rats (1.5 ± 0.2, 1.8 ± 0.1, and 1.7 ± 0.1 mg/dl, respectively). Elderly T2DN rats exhibited a greater fall in medullary blood flow 2 h following renal IR and a more severe and prolonged decline in glomerular filtration rate than middle-aged T2DN and young or elderly SD rats. The basal expression of the adhesion molecules ICAM-1 and E-selectin and the number of infiltrating immune cells was higher in the kidney of elderly T2DN than age-matched SD rats or young and middle-aged T2DN rats before renal IR. These results indicate that elderly T2DN rats with diabetic nephropathy are more susceptible to renal IR injury than diabetic animals with mild injury or age-matched control animals. This is associated with increased expression of ICAM-1, E-selectin and immune cell infiltration, renal medullary vasocongestion, and more prolonged renal medullary ischemia.

Angiotensin II upregulates CYP4A isoform expression in the rat kidney through angiotensin II type 1 receptor.

Angiotensin II (AngII) stimulates the renal production and release of 20-hydroxyeicosatetraenoic acids (20-HETE), which is a major metabolite of arachidonic acid catalyzed by CYP4A isoforms. However, the effects of AngII on CYP4A isoform expression in the kidney and its mechanism remains unclear. To clarify the regulation of CYP4A isoform expression by AngII, we examined the chronic effects of AngII and AngII type 1 receptor (AT1-R) blockade on CYP4A isoform expression. Sprague-Dawley rats were infused with vehicle or AngII for 1 week, and the AngII-infused rats were also treated with or without the AT1-R blocker, candesartan. AngII increased CYP4A isoform protein expression in the renal cortex (CO) and outer medulla (OM) in a dose-dependent manner, and candesartan inhibited the AngII-increased CYP4A expression in a dose-dependent manner. AngII increased the CYP4A isoform mRNA expression in the CO and OM, and candesartan inhibited AngII-increased CYP4A isoform mRNA expression. These results indicated that AngII chronically increased the CYP4A isoform expression in the rat kidney. The AngII-induced CYP4A isoform expression was mediated by AT1-R.

Effectiveness of a New Lead-Shielding Device and Additional Filter for Reducing Staff and Patient Radiation Exposure During Videofluoroscopic Swallowing Study Using a Human Phantom.

Interventional radiology procedures often involve lengthy exposure to fluoroscopy-derived radiation. We therefore devised a videofluoroscopic swallowing study (VFSS) procedure using a human phantom that proved to protect the patient and physician by reducing the radiation dose. We evaluated a new lead-shielding device and separately attached additional filters (1.0-, 2.0-, and 3.0-mm Al filters and a 0.5-mm Cu filter) during VFSS to reduce the patient's entrance skin dose (ESD). A monitor attached to the human phantom's neck measured the ESD. We also developed another lead shield (VFSS Shielding Box, 1.0-mm Pb equivalent) and tested its efficacy using the human phantom and an ionization chamber radiation survey meter with and without protection from scattered radiation at the physician's position on the phantom. We then measured the scattered radiation (at 90 and 150 cm above the floor) after combining the filters with the VFSS Shielding Box. With the additional filters, the ESD was reduced by 15.4-55.1%. With the VFSS Shielding Box alone, the scattered radiation was reduced by about 10% compared with the dose without additional shielding. With the VFSS Shielding Box and filters combined, the scattered radiation dose was reduced by a maximum of about 44% at the physician's position. Thus, the additional lead-shielding device effectively provided protection from scattered radiation during fluoroscopy. These results indicate that the combined VFSS Shielding Box and filters can effectively reduce the physician's and patient's radiation doses.

Better Healing of the Exit Site with Negative-Pressure Wound Therapy.

Exit-site infection poses a risk for peritonitis and can shorten peritoneal dialysis (PD) vintage. A loose fit of the skin around the catheter at the exit site can push bacteria surrounding the catheter into the subcutaneous tunnel. Negative-pressure wound therapy (NPWT) has been used to hasten healing of the wound after an operation or to treat pressure ulcers. We hypothesized that NPWT could speed the healing of the exit site and tighten the fit of the skin around the catheter. Using a V.A.C. Therapy system [vacuum-assisted closure (KCI, San Antonio, TX, U.S.A.)], NPWT was therefore applied in 9 patients for 1 - 2 weeks after the PD catheter insertion operation. Results in those patients were compared with results in patients who did not receive NPWT.The healed exit site was classified as either tightly fitted (when the skin was tightly connected around the PD catheter) or loosely fitted (when the skin was not tightly connected around the catheter). The relevant data were retrieved from the medical record and analyzed retrospectively.Patients who received NPWT had a tight exit site after 1 - 2 weeks. Those who did not receive NPWT did not have a tight exit site after 1 - 2 weeks. No bleeding was observed in patients receiving NPWT. Bleeding from the exit site after the catheter insertion operation was observed in 3 patients not receiving NPWT.Because we use a fine trocar to make the subcutaneous catheter tunnel, bleeding from the vasculature can often be observed. That bleeding could be minimized with the application of NPWT. Negative pressure could also hasten wound healing and result in a tight fit of the skin around the catheter within in 1 - 2 weeks compared with the 1 month typically required with the use of conventional film dressings.Negative-pressure wound therapy is beneficial for creating a tight fit of the skin to the catheter within 1 - 2 weeks and might reduce the number of exit-site and tunnel infections, which could result in a reduction in the peritonitis rate.

Effect of clofibrate on fatty acid metabolism in the kidney of puromycin-induced nephrotic rats.

BACKGROUND: Proteinuria plays an essential role in the progression of tubulointerstitial damage, which causes end-stage renal disease. An increased load of fatty acids bound to albumin reabsorbed into proximal tubular epithelial cells (PTECs) contributes to tubulointerstitial damage. Fibrates, agonists of peroxisome proliferator-activated receptor α (PPARα), have renoprotective effects against proteinuria whereas the effects of these compounds on fatty acid metabolism in the kidney are still unknown. Therefore, the present study examined whether the renoprotective effects of clofibrate were associated with improvement of fatty acid metabolism in puromycin aminonucleoside (PAN)-induced nephrotic rats. METHODS: Rats were allocated to the control, PAN or clofibrate-treated PAN group. Biochemical parameters, renal injury and changes in fatty acid metabolism were studied on day14. RESULTS: PAN increased proteinuria, lipid accumulation in PTECs, excretions of N-acetyl-ß-D-glucosaminidase (NAG) and 8-hydroxydeoxyguanosine (8OHdG) and the area of caspase 3-positive tubular cells. It decreased renal expressions of medium-chain acyl-CoA dehydrogenase (MCAD), cytochrome P450 (CYP)4A, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and estrogen-related receptor α (ERRα) without change of the expression of PPARα. Clofibrate reduced proteinuria, lipid accumulation, NAG excretion and the area of caspase 3-positive tubular cells. However, albumin excretion was not reduced and 8OHdG excretion was increased. Clofibrate minimized changes in MCAD, CYP4A, PGC-1α and ERRα expressions with increased PPARα, very long-chain acyl-CoA dehydrogenase (VLCAD) and long-chain acyl-CoA dehydrogenase (LCAD) expressions. CONCLUSION: Clofibrate is protective against renal lipotoxicity in PAN nephrosis. This study indicates that clofibrate has renoprotective effects through maintaining fatty acid metabolism in the kidney of PAN-induced nephrotic rats.

Deficiency in the Formation of 20-Hydroxyeicosatetraenoic Acid Enhances Renal Ischemia-Reperfusion Injury.

Ischemia-reperfusion (IR) injury is the most common cause of AKI. The susceptibility to develop AKI varies widely among patients. However, little is known about the genes involved. 20-Hydroxyeicosatetraenoic acid (20-HETE) has an important role in the regulation of renal tubular and vascular function and has been implicated in IR injury. In this study, we examined whether a deficiency in the renal formation of 20-HETE enhances the susceptibility of Dahl salt-sensitive (SS) rats to ischemic AKI. Transfer of chromosome 5 containing the CYP4A genes responsible for the formation of 20-HETE from the Brown Norway (BN) rat onto the SS genetic background increased renal 20-HETE levels after ischemia and reduced plasma creatinine levels (±SEM) 24 hours after IR from 3.7±0.1 to 2.0±0.2 mg/dl in an SS.5(BN)-consomic strain. Transfer of this chromosome also prevented the secondary decline in medullary blood flow and ischemia that develops 2 hours after IR in the susceptible SS strain. Blockade of the synthesis of 20-HETE with HET0016 reversed the renoprotective effects in SS.5(BN) rats. Similar results were observed in an SS.5(Lew)-congenic strain, in which a smaller region of chromosome 5 containing the CYP4A genes from a Lewis rat was introgressed onto the SS genetic background. These results indicate that 20-HETE has a protective role in renal IR injury by maintaining medullary blood flow and that a genetic deficiency in the formation of 20-HETE increases the susceptibility of SS rats to ischemic AKI.

Cytochrome P450 eicosanoids in hypertension and renal disease.

PURPOSE OF REVIEW: Cytochrome (CYP) P450 metabolites of arachidonic acid, 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) contribute to the regulation of renal tubular and vascular function. This review highlights the results of the recent genetic studies in humans and rodent models, indicating that these eicosanoids participate in the control of blood pressure (BP), chronic kidney disease (CKD), renal ischemia-reperfusion injury (IRI) and polycystic kidney disease (PKD). RECENT FINDINGS: Endogenous 20-HETE has been reported to play an essential role in the myogenic and tubuloglomerular feedback responses in the afferent arteriole, and a deficiency of 20-HETE contributes to the development of hypertension and renal injury in Dahl S rats. Mutations in CYP4A11 and CYP4F2 have been linked to elevated BP in humans. EETs have been shown to regulate epithelial sodium channel in the collecting duct, lower BP and have renoprotective properties. 20-HETE also opposes the development of CKD and IRI, and may play a role in PKD. SUMMARY: These studies indicate that CYP P450 metabolites of arachidonic acid play an important role in the control of BP, CKD, AKI and PKD. Drugs targeting these pathways could be useful in the treatment of IRI and CKD.

Effects of exercise training on nitric oxide synthase in the kidney of spontaneously hypertensive rats.

Exercise training is known to have antihypertensive effects in humans and animals with hypertension, as well as to exhibit renal protective effects in animal models of hypertension and chronic renal failure. However, the mechanisms regulating these effects of exercise training remain unclear. The present study examined the effects of exercise training on nitric oxide synthase (NOS) in the kidneys of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Male SHR and WKY rats were randomly divided into a sedentary group and a treadmill exercise group for 8 weeks. Systolic blood pressure (SBP) was measured every 2 weeks by the tail-cuff method and urine and blood samples were collected after the exercise protocol. Nitric oxide synthase activity and protein expression and endothelial (e) NOS phosphorylation in the kidney were examined. Exercise training significantly lowered SBP, decreased urinary albumin excretion, thiobarbituric acid-reactive substances levels and renal NADPH oxidase activity, and increased creatinine clearance in SHR. Exercise training significantly increased plasma and urinary nitrate/nitrite, NOS activity and eNOS and neuronal NOS expression, but decreased eNOS phosphorylation at Ser(1177) and Thr(495) in kidneys of SHR and WKY rats. Renal NOS may be involved in the antihypertensive and renal protective effects of exercise training in SHR.

Exercise training upregulates nitric oxide synthases in the kidney of rats with chronic heart failure.

There is an interaction between heart and kidney diseases, which is a condition termed cardiorenal syndrome. Exercise training has cardioprotective effects, involving upregulation of endothelial (e) nitric oxide synthase (NOS) in the cardiovascular system. However, the effects of exercise training on NOS in the kidney with heart disease are unknown. The aim of the present study was to investigate whether exercise training upregulates NOS in the kidney, left ventricle and aorta of rats with chronic heart failure (CHF). Male Sprague-Dawley rats underwent left coronary artery ligation (LCAL) to induce CHF and were randomly assigned to sedentary or treadmill exercise groups 4 weeks after LCAL. Three days after exercising for 4 weeks, urine samples were collected for 24 h and blood samples were collected following decapitation. Nitric oxide synthase activity and protein expression were examined. Significant interactions between CHF and exercise training were observed on parameters of cardiac and renal function. Exercise training improved cardiac function, decreased plasma B-type natriuretic peptide levels, decreased urinary albumin excretion and increased creatinine clearance in CHF rats. Nitric oxide synthase activity, eNOS expression and neuronal (n) NOS expression were significantly decreased in the left ventricle and kidney of CHF rats. Exercise training significantly increased NOS activity and eNOS and nNOS expression. Upregulation of NOS in the kidney and left ventricle may contribute, in part, to the renal and cardiac protective effects of exercise training in cardiorenal syndrome in CHF rats.

Disorder of fatty acid metabolism in the kidney of PAN-induced nephrotic rats.

Proteinuria is considered to play an essential role in the progression of tubulointerstitial damage, which causes end-stage renal disease. Fatty acid-binding albumins are filtered through glomeruli and reabsorbed into proximal tubular epithelial cells (PTECs). However, the role of fatty acid metabolism associated with albuminuria in the development of tubulointerstitial damage remains unclear. Thus, the present study was designed to determine the changes of fatty acid metabolism in the nephrotic kidney. To induce nephrotic syndrome, Sprague-Dawley rats (SDRs) and Nagase analbuminemic rats (NARs) with inherited hypoalbuminemia were treated with a single injection of puromycin aminonucleoside (PAN). In SDRs, PAN treatment induced massive proteinuria and albuminuria and caused tubular damage, apoptosis, and lipid accumulation in PTECs. Among the enzymes of fatty acid metabolism, expressions of medium-chain acyl-CoA dehydrogenase (MCAD) and cytochrome P-450 (CYP)4A significantly decreased in PTECs of PAN-treated SDRs. Expressions of peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC)-1α and estrogen-related receptor (ERR)α also significantly decreased, without changes in the expression of PPAR-α. In NARs, PAN treatment induced proteinuria but not albuminuria and did not cause tubular damage, apoptosis, or lipid accumulation. Expressions of MCAD, PGC-1α, or ERRα did not change in the kidney cortex of PAN-treated NARs, but the expression of CYP4A significantly decreased. These results indicate that massive albuminuria causes tubular damage and lipid accumulation with the reduction of MCAD, CYP4A, PGC-1α, and ERRα in PTECs.

Exercise training delays renal disorders with decreasing oxidative stress and increasing production of 20-hydroxyeicosatetraenoic acid in Dahl salt-sensitive rats.

OBJECTIVE: Exercise training has antihypertensive and renoprotective effects in humans and rats. However, the effects of exercise training on renal disorders that occur with salt-sensitive hypertension remains unclear. The study aim was to investigate the effects and mechanisms of exercise training on renal function in a rat model of salt-sensitive hypertension. METHODS: Six-week-old male Dahl salt-sensitive rats were divided into normal-salt (0.6% NaCl) diet, high-salt (8% NaCl) diet, and high-salt diet with exercise training groups. The high-salt diet with exercise training group underwent daily treadmill running for 8 weeks. RESULTS: The high-salt diet induced severe hypertension and renal dysfunction. Exercise training significantly improved high-salt diet-induced urinary protein, albumin, and L-type fatty acid-binding protein excretion, and glomerulosclerosis but not renal interstitial fibrosis without changing blood pressure. Exercise training significantly attenuated high-salt diet-induced oxidative stress in the kidneys and decreased high-salt diet-stimulated xanthine oxidoreductase activity but not nicotinamide adenine dinucleotide phosphate oxidase activity. The high-salt diet did not change urinary excretion of 20-hydroxyeicosatetraenoic acid and decreased cytochrome P450 4A protein expression in the kidneys. Exercise training increased urinary 20-hydoroxyeicosatetraenoic acid excretion and renal cytochrome P450 4A protein expression. CONCLUSION: Exercise training improved renal disorders without lowering blood pressure in Dahl salt-sensitive rats. Exercise training also decreased oxidative stress and increased 20-hydroxyeicosatetraenoic acid production in the kidneys. These results suggest that improvements in oxidative stress and 20-hydroxyeicosatetraenoic acid production may be potential mechanisms by which exercise training improved renal disorders in Dahl salt-sensitive rats.

Acidic organelles mediate TGF-ß1-induced cellular fibrosis via (pro)renin receptor and vacuolar ATPase trafficking in human peritoneal mesothelial cells.

TGF-ß1, which can cause renal tubular injury through a vacuolar-type H+-ATPase (V-ATPase)-mediated pathway, is induced by the glucose degradation product methylglyoxal to yield peritoneal injury and fibrosis. The present study investigated the roles of V-ATPase and its accessory protein, the (pro)renin receptor, in peritoneal fibrosis during peritoneal dialysis. Rats daily administered 20 mM methylglyoxal intraperitoneally developed significant peritoneal fibrosis after 7 days with increased expression of TGF-ß and V-ATPase, which was reduced by the inhibition of V-ATPase with co-administration of 100 mM bafilomycin A1. The (pro)renin receptor and V-ATPase were expressed in acidic organelles and cell membranes of human peritoneal mesothelial cells. TGF-ß1 upregulated the expression of collagens, α-SMA, and EDA-fibronectin, together with ERK1/2 phosphorylation, which was reduced by inhibition of V-ATPase, (pro)renin receptor, or the MAPK pathway. Fibronectin and the soluble (pro)renin receptor were excreted from cells by acidic organelle trafficking in response to TGF-ß1; this excretion was also suppressed by inhibition of V-ATPase. Soluble (pro)renin receptor concentrations in effluents of patients undergoing peritoneal dialysis were associated with the dialysate-to-plasma ratio of creatinine. Together, these results demonstrate a novel fibrosis mechanism through the (pro)renin receptor and V-ATPase in the acidic organelles of peritoneal mesothelial cells.

Molecular mechanisms and cell signaling of 20-hydroxyeicosatetraenoic acid in vascular pathophysiology.

Cytochrome P450s enzymes catalyze the metabolism of arachidonic acid to epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid and hydroxyeicosatetraeonic acid (HETEs). 20-HETE is a vasoconstrictor that depolarizes vascular smooth muscle cells by blocking K+ channels. EETs serve as endothelial derived hyperpolarizing factors. Inhibition of the formation of 20-HETE impairs the myogenic response and autoregulation of renal and cerebral blood flow. Changes in the formation of EETs and 20-HETE have been reported in hypertension and drugs that target these pathways alter blood pressure in animal models. Sequence variants in CYP4A11 and CYP4F2 that produce 20-HETE, UDP-glucuronosyl transferase involved in the biotransformation of 20-HETE and soluble epoxide hydrolase that inactivates EETs are associated with hypertension in human studies. 20-HETE contributes to the regulation of vascular hypertrophy, restenosis, angiogenesis and inflammation. It also promotes endothelial dysfunction and contributes to cerebral vasospasm and ischemia-reperfusion injury in the brain, kidney and heart. This review will focus on the role of 20-HETE in vascular dysfunction, inflammation, ischemic and hemorrhagic stroke and cardiac and renal ischemia reperfusion injury.

Chronic Running Exercise Alleviates Early Progression of Nephropathy with Upregulation of Nitric Oxide Synthases and Suppression of Glycation in Zucker Diabetic Rats.

Exercise training is known to exert multiple beneficial effects including renal protection in type 2 diabetes mellitus and obesity. However, the mechanisms regulating these actions remain unclear. The present study evaluated the effects of chronic running exercise on the early stage of diabetic nephropathy, focusing on nitric oxide synthase (NOS), oxidative stress and glycation in the kidneys of Zucker diabetic fatty (ZDF) rats. Male ZDF rats (6 weeks old) underwent forced treadmill exercise for 8 weeks (Ex-ZDF). Sedentary ZDF (Sed-ZDF) and Zucker lean (Sed-ZL) rats served as controls. Exercise attenuated hyperglycemia (plasma glucose; 242 ± 43 mg/dL in Sed-ZDF and 115 ± 5 mg/dL in Ex-ZDF) with increased insulin secretion (plasma insulin; 2.3 ± 0.7 and 5.3 ± 0.9 ng/mL), reduced albumin excretion (urine albumin; 492 ± 70 and 176 ± 11 mg/g creatinine) and normalized creatinine clearance (9.7 ± 1.4 and 4.5 ± 0.8 mL/min per body weight) in ZDF rats. Endothelial (e) and neuronal (n) NOS expression in kidneys of Sed-ZDF rats were lower compared with Sed-ZL rats (p<0.01), while both eNOS and nNOS expression were upregulated by exercise (p<0.01). Furthermore, exercise decreased NADPH oxidase activity, p47phox expression (p<0.01) and α-oxoaldehydes (the precursors for advanced glycation end products) (p<0.01) in the kidneys of ZDF rats. Additionally, morphometric evidence indicated renal damage was reduced in response to exercise. These data suggest that upregulation of NOS expression, suppression of NADPH oxidase and α-oxoaldehydes in the kidneys may, at least in part, contribute to the renal protective effects of exercise in the early progression of diabetic nephropathy in ZDF rats. Moreover, this study supports the theory that chronic aerobic exercise could be recommended as an effective non-pharmacological therapy for renoprotection in the early stages of type 2 diabetes mellitus and obesity.

Expression of (pro)renin receptor and its upregulation by high salt intake in the rat nephron.

A functional receptor for renin and prorenin ((P)RR) was identified as a new component of the renin-angiotensin system. The precise localization of (P)RR in the kidney has not been clarified. The present study was designed to determine the localization of (P)RR in the rat nephron and to investigate the regulation of renal (P)RR expression by high salt (HS) intake. (P)RR mRNA levels in the kidney sections and isolated nephron segments were examined using reverse transcription and polymerase chain reaction (RT-PCR), and (P)RR protein levels were examined by immunoblot and immunohistochemical analyses. Renal (P)RR mRNA and protein levels in rats fed a HS diet for 4 weeks were also compared with those fed a normal salt diet. (P)RR mRNA was expressed in various nephron segments of the cortex and medulla; glomeruli (Glm), proximal tubules (PT), thick ascending limbs (TAL) and collecting ducts (CD). (P)RR protein was highly expressed in the PT, medullary TAL (MTAL) and inner medullary CD (IMCD), and lowly in the preglomerular arterioles (Art) and Glm. HS intake increased (P)RR protein levels in the Glm, PT and tubules of medullary rays. These results indicated that (P)RR is expressed throughout various nephron segments and Art, and that (P)RR protein is expressed predominantly in the PT, MTAL and IMCD. HS intake appears to upregulate the (P)RR expression in the Glm, PT and tubules of medullary rays, suggesting that (P)RR may be involved in the regulation of renal function and HS-induced disorders.

Endogenous hydrogen peroxide up-regulates the expression of nitric oxide synthase in the kidney of SHR.

BACKGROUND AND METHOD: Both nitric oxide synthase (NOS) expression and oxidative stress are elevated in the tissues of spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto rats (WKY). The purpose of the present study was to determine the relationship between the endothelial and neuronal NOS (eNOS and nNOS) expression and oxidative stress in the kidney of SHR and WKY. RESULTS: Plasma and urinary hydrogen peroxide (H2O2) and nitrate/nitrite (NOx), the renal NADPH oxidase activity and eNOS and nNOS expressions were all higher in SHR than in WKY. Although the treatment with either the NADPH oxidase inhibitor, apocynin or the superoxide dismutase mimetic, tempol for 8 weeks decreased the systolic blood pressure (SBP) and inhibited the renal NADPH oxidase activity in SHR, apocynin decreased but tempol increased the plasma and urinary H2O2 and NOx and the eNOS and nNOS expressions in the renal cortex and medulla of SHR. In contrast to SHR, neither apocynin nor tempol affected these parameters in WKY. H2O2 administered intravenously for 1 week in WKY increased plasma and urinary H2O2 and NOx and the eNOS and nNOS expressions in the renal cortex and medulla in a dose-dependent manner without changing the renal NADPH oxidase activity. CONCLUSION: These results indicate that oxidative stress up-regulates the NOS expression in the kidney of SHR compared with WKY; and that endogenous H2O2 is a mediator of the up-regulation of the NOS expression in the kidney of SHR.

Atorvastatin upregulates nitric oxide synthases with Rho-kinase inhibition and Akt activation in the kidney of spontaneously hypertensive rats.

OBJECTIVE: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, statins reduce blood pressure and have beneficial effects in cardiovascular and kidney diseases. The present study examined the effect of chronic treatment with atorvastatin (ATV) on the expression of nitric oxide synthase (NOS) and the activity of Rho-kinase and Akt in the kidney of spontaneously hypertensive rats (SHRs). METHODS: SHRs were treated with ATV for 8 weeks and the SBP was measured. The expressions of endothelial, neuronal and inducible NOS (eNOS, nNOS and iNOS, respectively) proteins in the kidney were examined by immunoblot analysis. The activity of eNOS, Rho-kinase and Akt in the kidney was examined by assessing the phosphorylation of eNOS, ezrin/radixin/moesin (ERM) and Akt, respectively. RESULTS: ATV reduced the SBP without changing the plasma cholesterol levels. ATV increased eNOS expression in the cortex and medulla and nNOS expression in the medulla, whereas it did not affect iNOS expression. Although it upregulated eNOS expression in the kidney, ATV decreased the levels of phosphorylated eNOS in the cortex and did not affect the ratio of phosphorylated eNOS to total eNOS in the medulla. ATV also inhibited Rho-kinase activity and enhanced Akt activity in the kidney of SHRs. CONCLUSION: ATV upregulates eNOS and nNOS expressions with Rho-kinase inhibition and Akt activation in the kidney of SHRs. The renal nitric oxide system, Rho-kinase and Akt may contribute to the antihypertensive and renoprotective effects of statins.