Resistance to renal damage by chronic nitric oxide synthase inhibition in the Wistar-Furth rat

Synergistic Interaction of Hypertension and Diabetes in Promoting Kidney Injury and the Role of Endoplasmic Reticulum Stress

Diabetes mellitus and hypertension are major risk factors for chronic kidney injury, together accounting for >70% of end-stage renal disease. In this study, we assessed interactions of hypertension and diabetes mellitus in causing kidney dysfunction and injury and the role of endoplasmic reticulum (ER) stress. Hypertension was induced by aorta constriction (AC) between the renal arteries in 6-month-old male Goto-Kakizaki (GK) type 2 diabetic and control Wistar rats. Fasting plasma glucose averaged 162±11 and 87±2 mg/dL in GK and Wistar rats, respectively. AC produced hypertension in the right kidney (above AC) and near normal blood pressure in the left kidney (below AC), with both kidneys exposed to the same levels of glucose, circulating hormones, and neural influences. After 8 weeks of AC, blood pressure above the AC (and in the right kidney) increased from 109±1 to 152±5 mm Hg in GK rats and from 106±4 to 141±5 mm Hg in Wistar rats. The diabetic-hypertensive right kidneys in GK-AC rats had much greater increases in albumin excretion and histological injury compared with left kidneys (diabetes mellitus only) of GK rats or right kidneys (hypertension only) of Wistar-AC rats. Marked increases in ER stress and oxidative stress indicators were observed in diabetic-hypertensive kidneys of GK-AC rats. Inhibition of ER stress with tauroursodeoxycholic acid for 6 weeks reduced blood pressure (135±4 versus 151±4 mm Hg), albumin excretion, ER and oxidative stress, and glomerular injury, while increasing glomerular filtration rate in hypertensive-diabetic kidneys. These results suggest that diabetes mellitus and hypertension interact synergistically to promote kidney dysfunction and injury via ER stress.

Glomerulosclerosis in the diet-induced obesity model correlates with sensitivity to nitric oxide inhibition but not glomerular hyperfiltration or hypertrophy

The diet-induced obesity (DIO) model is frequently used to examine the pathogenesis of obesity-related pathologies; however, only minimal glomerulosclerosis (GS) has been reported after 3 mo. We investigated if GS develops over longer periods of DIO and examined the potential role of hemodynamic mechanisms in its pathogenesis. Eight-week-old male obesity-prone (OP) and obesity-resistant (OR) rats (Charles River) were administered a moderately high-fat diet for 5 mo. Radiotelemetrically measured blood pressure, proteinuria, and GS were assessed. OP (n=10) rats developed modest hypertension (142±3 vs. 128±2 mmHg, P<0.05) and substantial levels of proteinuria (63±12 vs. 12±1 mg/day, P<0.05) and GS (7.7±1.4% vs. 0.4±0.2%) compared with OR rats (n=8). Potential hemodynamic mechanisms of renal injury were assessed in additional groups of OP and OR rats fed a moderately high-fat diet for 3 mo. Kidney weight (4.3±0.2 vs. 4.3±0.1 g), glomerular filtration rate (3.3±0.3 vs. 3.1±0.1 ml/min), and glomerular volume (1.9±0.1 vs. 2.0±0.1 μm3×10(-6)) were similar between OP (n=6) and OR (n=9) rats. Renal blood flow autoregulation was preserved in both OP (n=7) and OR (n=7) rats. In contrast, Nω-nitro-L-arginine methyl ester (L-NAME) administration in conscious, chronically instrumented OP (n=11) rats resulted in 15% and 39% increases in blood pressure and renal vascular resistance, respectively, and a 16% decrease in renal blood flow. Minimal effects of L-NAME were seen in OR (n=9) rats. In summary, DIO-associated GS is preceded by an increased hemodynamic sensitivity to L-NAME but not renal hypertrophy or hyperfiltration.

Strain of experimental animals and modulation of nitric oxide pathway: their influence on development of renal failure in an experimental model of hepatorenal syndrome

INTRODUCTION

Pathomechanism of HRS is still poorly understood. The aim of our study was: (1) to test whether different strains of rats could develop typical HRS, and (2) to estimate the influence of activation and inhibition of nitric oxide for development of renal failure in course of HRS.

MATERIAL AND METHODS

First, we used 16 of Wistar and 16 of Sprague-Dawley rats in galactosamine model of HRS. Next, we used 48 of SDR rats, which received saline, N-nitro-L-arginine or L-arginine before and after liver damage. Twenty four hours urine and blood samples were collected 48 h after saline or Ga1N injection. Biochemical parameters were determined in serum or urine and then creatinine clearance and osmolality clearance were calculated. Liver and kidney tissues were collected for histopathological examination.

RESULTS

Liver failure developed in all tested groups with significant increase of bilirubin (p < 0.001), ALT (p < 0.001) and ammonia (p < 0.001). Nevertheless we did not achieve any evidence of renal failure in Wistar, but we found typical renal failure in Sprague-Dawley group with significant decrease in creatinine clearance (p < 0.0012) and increase in concentration of creatinine and urea (p < 0.001) and (p < 0.001) respectively. Inhibition of NOS prevented development of renal failure with significant improvement of GFR both before (p < 0.0017) and after (p < 0.003) Ga1N injection. Injection of L-arginine after Ga1N injection did not caused significant improvement of GFR.

CONCLUSIONS

Our study showed, that genetic factors might be responsible for development of renal failure in course of HRS and nitric oxide play important role in acute model of this syndrome.

Large BP-dependent and -independent differences in susceptibility to nephropathy after nitric oxide inhibition in Sprague-Dawley rats from two major suppliers

The N(ω)-nitro-l-arginine methyl ester (l-NAME) model is widely employed to investigate the role of nitric oxide (NO) in renal injury. The present studies show that Sprague-Dawley rats from Harlan (H) and Charles River (CR) exhibit strikingly large differences in susceptibility to l-NAME nephropathy. After 4 wk of l-NAME (∼50 mg·kg(-1)·day(-1) in drinking water), H rats (n = 13) exhibited the expected hypertension [average radiotelemetric systolic blood pressure (BP), 180 ± 3 mmHg], proteinuria (136 ± 17 mg/24 h), and glomerular injury (GI) (12 ± 2%). By contrast, CR rats developed less hypertension (142 ± 4), but surprisingly no proteinuria or GI, indicating a lack of glomerular hypertension. Additional studies showed that conscious H, but not CR, rats exhibit dose-dependent renal vasoconstriction after l-NAME. To further investigate these susceptibility differences, l-NAME was given 2 wk after 3/4 normotensive nephrectomy (NX) and comparably impaired renal autoregulation in CR-NX and H-NX rats. CR-NX rats, nevertheless, still failed to develop proteinuria and GI despite moderate hypertension (144 ± 2 mmHg, n = 29). By contrast, despite an 80-90% l-NAME dose reduction and lesser BP increases (169 ± 4 mmHg), H-NX rats (n = 20) developed greater GI (26 ± 3%) compared with intact H rats. Linear regression analysis showed significant (P < 0.01) differences in the slope of the relationship between BP and GI between H-NX (slope 0.56 ± 0.14; r = 0.69; P < 0.008) and CR-NX (slope 0.09 ± 0.06; r = 0.29; P = 0.12) rats. These data indicate that blunted BP responses to l-NAME in the CR rats are associated with BP-independent resistance to nephropathy, possibly mediated by a resistance to the renal (efferent arteriolar) vasoconstrictive effects of NO inhibition.

Protective actions of nebivolol on chronic nitric oxide synthase inhibition-induced hypertension and chronic kidney disease in the rat: a comparison with angiotensin II receptor blockade

BACKGROUND

Nitric oxide (NO) deficiency contributes to chronic kidney disease (CKD) progression and hypertension. The β-blocker, nebivolol (N), also enhances NO production, and we studied whether N attenuates CKD and hypertension caused by chronic NO synthase inhibition (CNOSI).

METHODS

Male Sprague-Dawley rats on 6 weeks of CNOSI (L-NAME, 150 mg/L drinking water) received placebo (P), N (10 mg/kg/day), olmesartan (O, 2.5 mg/kg/day) or N + O. Blood pressure (BP) and urine protein and NOx (metabolites of NO) were monitored throughout. We measured glomerular sclerosis (GS), creatinine clearance (C(Cr)) and components of the NO and oxidant pathways in the renal cortex.

RESULTS

BP increased >50 mmHg in P by weeks 4-6, but no change occurred in N, O or N + O. P rats developed proteinuria and GS and C(Cr) was ∼30% of normal. In N, O and N + O, all values remained normal. In renal cortex of P, p22phox and nitrotyrosine abundance as well as H(2)O(2) levels were higher and extracellular superoxide dismutase (EC SOD) was lower versus normal kidneys. N, O and N + O normalized p22phox, H(2)O(2) and EC SOD and increased Mn SOD above normal. The cortical neuronal NO synthase (nNOS) β abundance increased in P and this was prevented by N, O and N + O.

CONCLUSION

We suggest that the major benefit from both N and O is reduction in oxidative stress in the renal cortex, which may potentiate residual local NO. There was no additive benefit of N + O since each drug effectively prevented injury, but a combination may be beneficial where protection is incomplete with each drug. The increased nNOSβ protein seen early in the course of the CKD may contribute to the evolving GS.

Chronic nitric oxide deficiency and progression of kidney disease after renal mass reduction in the C57Bl6 mouse

BACKGROUND/AIMS

the C57Bl6 mouse is resistant to chronic kidney disease (CKD) induced by reduction of renal mass (RRM). Nitric oxide (NO) deficiency exacerbates CKD progression so this study investigated whether combination of RRM and NO deficiency would render the C57Bl6 mouse vulnerable to CKD.

METHODS

we used wild-type (WT) mice with RRM, chronic NO synthase (NOS) inhibition and a combination. Also, endothelial NOS (eNOS) knockout (KO) C57Bl6 mice were studied with and without RRM. Primary endpoints were albuminuria and structural damage.

RESULTS

both nonselective (+L-NAME) and neuronal NOS 'selective' (+7NI) NOS inhibition greatly exacerbated the albuminuria and structural damage seen with RRM in the WT mice; NOS inhibition alone had little effect. The eNOS KO mice showed marked structural damage and significant albuminuria in the shams and RRM produced minimal exacerbation of structural damage although the albuminuria was massively amplified.

CONCLUSION

these studies demonstrate that the C57Bl6 mouse is rendered vulnerable to RRM-induced CKD when concomitant NO deficiency is produced. This observation supports previous work in CKD-resistant rats and suggests that NO deficiency is required for progression of CKD.

Transient nitric oxide reduction induces permanent cardiac systolic dysfunction and worsens kidney damage in rats with chronic kidney disease

Left ventricular systolic dysfunction (LVSD) in patients with chronic kidney disease (CKD) is associated with poorer prognosis. Because patients with CKD often exhibit progressively decreased nitric oxide (NO) availability and inhibition of NO production can reduce cardiac output, we hypothesized that loss of NO availability in CKD contributes to pathogenesis of LVSD. Subtotally nephrectomized (SNX) rats were treated with a low dose of the NO synthase inhibitor Nω-nitro-l-arginine (l-NNA; 20 mg/l water; SNX+l-NNA) and compared with relevant control groups. To study permanent changes separate from hemodynamic effects, l-NNA was stopped after week 8 and rats were followed up to week 15, until blood pressure was similar in SNX+l-NNA and SNX groups. To study effects of NO depletion alone, a control group with high-dose l-NNA (l-NNA-High: 100 mg/l) was included. Mild systolic dysfunction developed at week 13 after SNX. In SNX+l-NNA, systolic function decreased by almost 50% already from week 4 onward, together with markedly reduced whole body NO production and high mortality. In l-NNA-High, LVSD was not as severe as in SNX+l-NNA, and renal function was not affected. Both LVSD and NO depletion were reversible in l-NNA-High after l-NNA was stopped, but both were persistently low in SNX+l-NNA. Proteinuria increased compared with rats with SNX, and glomerulosclerosis and cardiac fibrosis were worsened. We conclude that SNX+l-NNA induced accelerated and permanent LVSD that was functionally and structurally different from CKD or NO depletion alone. Availability of NO appears to play a pivotal role in maintaining cardiac function in CKD.

Dietary doses of nitrite restore circulating nitric oxide level and improve renal injury inl-NAME-induced hypertensive rats

We have reported that pharmacological doses of oral nitrite increase circulating nitric oxide (NO) and exert hypotensive effects in Nω-nitro-l-arginine methyl ester (l-NAME)-induced hypertensive rats. In this study, we examined the effect of a chronic dietary dose of nitrite on the hypertension and renal damage induced by chronic l-NAME administration in rats. The animals were administered tap water containing l-NAME (1 g/l) or l-NAME + nitrite (low dose: 0.1 mg/l, medium dose: 1 mg/l, high dose: 10 mg/l) for 8 wk. We evaluated blood NO levels as hemoglobin-NO adducts (iron-nitrosyl-hemoglobin), using an electron paramagnetic resonance method. Chronic administration of l-NAME for 8 wk induced hypertension and renal injury and reduced the blood iron-nitrosyl-hemoglobin level (control 38.8 ± 8.9 vs. l-NAME 6.0 ± 3.1 arbitrary units). Coadministration of a low dose of nitrite with l-NAME did not change the reduced iron-nitrosyl-hemoglobin signal and did not improve the l-NAME-induced renal injury. The blood iron-nitrosyl-hemoglobin signals of the medium dose and high dose of nitrite were significantly higher than that of l-NAME alone. Chronic administration of a medium dose of nitrite attenuated l-NAME-induced renal histological changes and proteinuria. A high dose of nitrite also attenuated l-NAME-induced renal injury. These findings suggest that dietary doses of nitrite that protect the kidney are associated with significant increase in iron-nitrosyl-hemoglobin levels. We conclude that dietary nitrite-derived NO generation may serve as a backup system when the nitric oxide synthase/l-arginine-dependent NO generation system is compromised.

Nitric oxide deficiency in chronic kidney disease

The overall production of nitric oxide (NO) is decreased in chronic kidney disease (CKD) which contributes to cardiovascular events and further progression of kidney damage. There are many likely causes of NO deficiency in CKD and the areas surveyed in this review are: 1. Limitations on substrate (l-Arginine) availability, probably due to impaired renal l-Arginine biosynthesis, decreased transport of l-Arginine into endothelial cells and possible competition between NOS and competing metabolic pathways, such as arginase. 2. Increased circulating levels of endogenous NO synthase (NOS) inhibitors, in particular asymmetric dimethylarginine (ADMA). Increased methylation of proteins and their subsequent breakdown to release free ADMA may contribute but the major culprit is probably reduced ADMA catabolism by the enzymes dimethylarginine dimethylaminohydrolases. 3. Reduced renal cortex abundance of the neuronal NOS (nNOS)α protein correlates with injury while increasing nNOSβ abundance may provide a compensatory, protective response. Interventions that can restore NO production by targeting these various pathways are likely to reduce the cardiovascular complications of CKD as well as slowing the rate of progression.

DOCA/NaCl-induced chronic kidney disease: a comparison of renal nitric oxide production in resistant and susceptible rat strains

Recent studies show nitric oxide (NO) deficiency is both a cause and consequence of chronic kidney disease (CKD). Reduced renal neuronal NO synthase (nNOS) abundance and activity parallel development of CKD with different models in the Sprague-Dawley (SD) rats, whereas Wistar Furth (WF) rats are protected against CKD and show preserved renal NO production. In this study, we compared renal NO in response to DOCA/salt-induced injury between the WF and SD. Studies were conducted on sham WF (n = 6) and SD (n = 6) and uninephrectized (UNX)+75 mg DOCA+1% NaCl (WF n = 9; SD n = 10) rats followed for 5 wk. Kidneys were harvested for Western blot, NOS activity, and histology. Other measurements included creatinine clearance and 24-h total NO production and urinary protein excretion. Absolute values of kidney weight were lower in WF than SD rats that showed similar percent increases with UNX+DOCA/NaCl. Proteinuria and decreased creatinine clearance were present in the SD but not the WF rats following UNX+DOCA/NaCl. Glomerular injury was mild in the WF compared with SD rats that showed many globally damaged glomeruli. Although renal nNOS abundance was decreased in both strains (higher baseline in WF), soluble NOS activity was maintained in the WF but significantly reduced in the SD rats. Renal endothelial NOS abundance and membrane NOS activity were unaffected by treatment. In summary, WF rats showed resistance to UNX+DOCA/NaCl-induced CKD with maintained renal NO production despite mild reduction in nNOS abundance. Further studies are needed to evaluate how WF rats maintain renal NO production despite similar changes in abundance as the vulnerable SD strain.