Renal and pressor effects of aminoguanidine in cirrhotic rats with ascites

Can Chronic Nitric Oxide Inhibition Improve Liver and Renal Dysfunction in Bile Duct Ligated Rats?

The aims of the present work were to study the effects of chronic NO inhibition on liver cirrhosis and to analyze its relationship with liver and kidney damage markers. Two inhibitors of NO synthesis (inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), and nonselective NOS inhibitor, L-nitroarginine methyl ester (L-NAME)) were administered for 6 weeks to bile duct ligated (BDL) rats 3 days after surgery. The present study showed that BDL was associated with liver injury and renal impairment. BDL increased liver NO content and myeloperoxidase (MPO) activity. This was corroborated by increased oxidative stress, TNF-α, TGF-1β, and MMP-13 genes overexpression. Although both drugs reduced NO synthesis and TNF-α gene overexpression, only AG improved renal dysfunction and liver damage and reduced liver oxidative stress. However, L-NAME exacerbated liver and renal dysfunction. Both drugs failed to modulate TGF-1β and MMP-13 genes overexpression. In conclusion, inhibition of NO production by constitutive nitric oxide synthase (cNOS) plays a crucial role in liver injury and renal dysfunction while inhibition of iNOS by AG has beneficial effect. TNF-α is not the main cytokine responsible for liver injury in BDL model. Nitric oxide inhibition did not stop the progression of cholestatic liver damage.

Renal effects of NO-inhibition in patients with cirrhosis vs. healthy controls: a randomized placebo-controlled crossover study

BACKGROUND

Nitric oxide (NO) is an important regulator of renal hemodynamics and sodium excretion. Systemic and splanchnic NO-synthesis is increased in liver cirrhosis contributing to the characteristic hyperdynamic circulation. The significance of renal NO in human cirrhosis is not clear.

AIMS

In order to clarify the role of NO in the regulation of renal hemodynamics and sodium excretion in human cirrhosis, we studied the effects of N(G)-monomethyl-L-arginine (L-NMMA) - a nonselective NO-inhibitor - on blood pressure (MAP), heart rate (HR), GFR, RPF, UNa × V, FENa, FELi and plasma levels of renin, angII, aldo, ANP, BNP and cGMP in 13 patients with cirrhosis (Child gr.A: 8; Child gr.B+C: 5) and 13 healthy controls.

METHODS

The study was randomized and placebo-controlled. Renal hemodynamics were assessed by measuring renal clearance of (51) Cr-EDTA and (125) I-Hippuran for GFR and RPF, respectively.

RESULTS

L-NMMA induced a similar, significant increase in MAP in both groups and a more pronounced relative decrease in HR in the CIR group (P = 0.0209, anova). L-NMMA did not change GFR in any group, but RPF decreased significantly in both groups, but most pronouncedly in CIR (P = 0.0478, anova). FENa decreased significantly in both groups after l-NMMA, but the response was again most pronounced in the CIR group (P = 0.0270, anova). All parameters remained stable after placebo. No significant differences were observed between the effects of L-NMMA in Child gr.A vs. Child gr. B+C patients.

CONCLUSION

The data supports the hypothesis that renal NO is enhanced in human cirrhosis.

Effects of chronic L-NAME on nitrotyrosine expression and renal vascular reactivity in rats with chronic bile-duct ligation

In liver cirrhosis, elevated levels of NO and ROS (reactive oxygen species) might greatly favour the generation of peroxynitrite. Peroxynitrite is a highly reactive oxidant and it can potentially alter the vascular reactivity and the function of different organs. In the present study, we evaluated whether peroxynitrite levels are related to the progression of renal vascular and excretory dysfunction during experimental cirrhosis induced by chronic BDL (bile-duct ligation) in rats. Experiments were performed at 7, 15 and 21 days after BDL in rats and in rats 21 days post-BDL chronically treated with L-NAME (NG-nitro-L-arginine methyl ester). Sodium balance, BP (blood pressure), basal RPP (renal perfusion pressure) and the renal vascular response to PHE (phenylephrine) and ACh (acetylcholine) in isolated perfused kidneys were measured. NO levels were calculated as 24-h urinary excretion of nitrites, ROS as TBARS (thiobarbituric acid-reacting substances), and peroxynitrite formation as the renal expression of nitrotyrosine. BDL rats had progressive sodium retention, and decreased BP, RPP and renal vascular responses to PHE and ACh in the time following BDL. They also had increasing levels of NO and ROS, and renal nitrotyrosine accumulation, especially in the medulla. All of these changes were either prevented or significantly decreased by chronic L-NAME administration. In conclusion, these results suggest that the increasing levels of peroxynitrite might contribute to the altered renal vascular response and sodium retention in the development of the experimental biliary cirrhosis. Moreover, the beneficial effects of decreasing NO synthesis are, at least in part, mediated by anti-peroxinitrite-related effects.

Vitamin E supplementation reverses renal altered vascular reactivity in chronic bile duct-ligated rats

An altered vascular reactivity is an important manifestation of the hemodynamic and renal dysfunction during liver cirrhosis. Oxidative stress-derived substances and nitric oxide (NO) have been shown to be involved in those alterations. In fact, both can affect vascular contractile function, directly or by influencing intracellular signaling pathways. Nevertheless, it is unknown whether oxidative stress contributes to the impaired systemic and renal vascular reactivity observed in cirrhosis. To test this, we evaluated the effect of vitamin E supplementation (5,000 IU/kg diet) on the vasoconstrictor and vasodilator responses of isolated perfused kidneys and aortic rings of rats with cirrhosis induced by bile duct ligation (BDL), and on the expression of renal and aortic phospho-extracellular regulated kinase 1/2 (p-ERK1/2). BDL induced a blunted renal vascular response to phenylephrine and ACh, while BDL aortic rings responded less to phenylephrine but normally to ACh. Cirrhotic rats had higher levels of oxidative stress-derived substances [measured as thiobarbituric acid-reactive substances (TBARS)] and NO (measured as urinary nitrite excretion) than controls. Vitamin E supplementation normalized the renal hyporesponse to phenylephrine and ACh in BDL, although failed to modify it in aortic rings. Furthermore, vitamin E decreased levels of TBARS, increased levels of NO, and normalized the increased kidney expression of p-ERK1/2 of the BDL rats. In conclusion, BDL rats showed a blunted vascular reactivity to phenylephrine and ACh, more pronounced in the kidney and reversed by vitamin E pretreatment, suggesting a role for oxidative stress in those abnormalities.

Effects of chronic inhibition of inducible nitric oxide synthase in hyperthyroid rats

We hypothesized that nitric oxide generated by inducible nitric oxide synthase (iNOS) may contribute to the homeostatic role of this agent in hyperthyroidism and may, therefore, participate in long-term control of blood pressure (BP). The effects of chronic iNOS inhibition by oral aminoguanidine (AG) administration on BP and morphological and renal variables in hyperthyroid rats were analyzed. The following four groups (n = 8 each) of male Wistar rats were used: control group and groups treated with AG (50 mg.kg(-1).day(-1), via drinking water), thyroxine (T4, 50 microg.rat(-1).day(-1)), or AG + T4. All treatments were maintained for 3 wk. Tail systolic BP and heart rate (HR) were recorded weekly. Finally, we measured BP (mmHg) and HR in conscious rats and morphological, plasma, and renal variables. T(4) administration produced a small BP (125 +/- 2, P < 0.05) increase vs. control (115 +/- 2) rats. AG administration to normal rats did not modify BP (109 +/- 3) or any other hemodynamic variable. However, coadministration of T4 and AG produced a marked increase in BP (140 +/- 3, P < 0.01 vs. T4). Pulse pressure and HR were increased in both T4- and T4 + AG -treated groups without differences between them. Plasma NOx (micromol/l) were increased in the T4 group (10.02 +/- 0.15, P < 0.05 vs. controls 6.1 +/- 0.10), and AG reduced this variable in T4-treated rats (6.81 +/- 0.14, P < 0.05 vs. T4) but not in normal rats (5.78 +/- 0.20). Renal and ventricular hypertrophy and proteinuria of hyperthyroid rats were unaffected by AG treatment. In conclusion, the results of the present paper indicate that iNOS activity may counterbalance the prohypertensive effects of T4.

Nitric oxide synthases inhibition results in renal failure improvement in cirrhotic rats

Nitric oxide (NO) has been implicated in cirrhosis and might be implicated in renal failure end-stage cirrhosis.

AIM

Our aim was to evaluate NO role in renal failure induced during decompensated cirrhosis, using the following inhibitors: aminoguanidine (AG), a specific inducible nitric oxide synthase (iNOS) inhibitor and NG-nitro-l-arginine methyl ester (L-NAME), a nonselective blocker of NOS isoforms.

METHODS

Endothelial (eNOS) and iNOS gene expression was analyzed by reverse transcriptase-polymerase chain reaction. Cirrhotic rats received a single intragastric dose of CCl(4) to induce acute liver damage (ALD).

RESULTS

After ALD, aspartate aminotransferase highest levels were observed in rats treated with AG and ALT in rats treated with L-NAME. Inhibitors decreased creatinine serum levels to normal values and serum sodium levels re-established after the third day of ALD. L-NAME diminished (P<0.05) eNOS RNA renal expression. Renal iNOS with no inhibitor was overexpressed but was down-regulated by AG treatment. Liver eNOS RNA expression had a decreased expression before ALD in cirrhotic rats, but L-NAME treatment down-regulated eNOS after ALD. AG induced an important iNOS liver decrease.

CONCLUSION

Both inhibitors improved renal function, although AG displayed a better effect and did not aggravate liver function. We concluded that NOS isoforms are implicated in the renal pathophysiologic events induced by ALD.

Endothelial Nitric Oxide Contributes to the Renal Protective Effects of Ischemic Preconditioning

We determined whether endothelial nitric oxide synthase (eNOS) plays an important role in the renal protective effect of ischemic preconditioning (IP) against the ischemia/reperfusion-induced acute renal failure (ARF) by using eNOS-deficient (eNOS(-/-)) and wild-type (eNOS(+/+)) mice. Ischemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. IP, which consists of three cycles of 2-min ischemia followed by 5-min reperfusion, was performed prior to 45-min ischemia. In eNOS(+/+) mice, IP treatment markedly attenuated the ischemia/reperfusion-induced renal dysfunction and significantly improved histological renal damage such as tubular necrosis, proteinaceous casts in tubuli, and medullary congestion. Constitutive nitric oxide synthase activity in the kidney without IP was markedly decreased 6 h after reperfusion, but this decreased response was not observed in eNOS(+/+) mice with IP treatment. The improvement of renal dysfunction in eNOS(+/+) mice with IP treatment was abolished by pretreatment with N(G)-nitro-l-arginine, a nonselective NOS inhibitor, whereas aminoguanidine, an inducible NOS inhibitor, had no effect. Finally, no protective effects of IP on ischemia/reperfusion-induced renal dysfunction and histological damage were observed in eNOS(-/-) mice. These findings strongly support the view that eNOS-mediated NO production plays a pivotal role in the protective effect of IP on ischemia/reperfusion-induced ARF.

Role of nitric oxide in the renal protective effects of ischemic preconditioning

Possible involvement of nitric oxide (NO) in the protective effect of ischemic preconditioning against the ischemia/reperfusion-induced acute renal failure was investigated. Ischemic preconditioning, which consists of three cycles of 2-minute ischemia followed by 5-minute reperfusion, was performed prior to 45-minute ischemia. Ischemic preconditioning significantly improved the renal dysfunction induced by 45-minute ischemia followed by 24-hour reperfusion. Histopathological examination of the kidney of ischemia/reperfusion rats revealed severe renal damage, and suppression of the damage was seen with the ischemic preconditioning treatment. NO metabolites (NOx) production in the kidney after 45-minute ischemia and reperfusion was markedly increased in ischemia/reperfusion rats with ischemic preconditioning, compared with animals not subjected to ischemic preconditioning, and these increases correlated with changes in endothelial NO synthase (eNOS) protein expression in renal tissues. The improvement of renal dysfunction in ischemic preconditioning rats was abolished by the pretreatment with NG-nitro-L-arginine, a nonselective NOS inhibitor, but not with aminoguanidine, an inducible NOS inhibitor. In addition, increment of endothelin-1 (ET-1) content in the kidney after the reperfusion was markedly suppressed by ischemic preconditioning treatment. These findings suggest that the protective effect of ischemic preconditioning on ischemia/reperfusion -induced acute renal failure is closely related to the renal nitric oxide production following the increase in eNOS expression after the reperfusion and that the suppressive effect of ischemic preconditioning on the ischemia/reperfusion -induced renal ET-1 overproduction may be partly involved in the ameliorating effect of ischemic preconditioning.

Vitamin E prevents renal dysfunction induced by experimental chronic bile duct ligation

BACKGROUND

The mechanisms by which prolonged cholestasis alters renal hemodynamics and excretory function are unknown but may be related to increased oxidative stress, with subsequent formation of lipid peroxidation-derived products (e.g., F2-isoprostanes) and endothelin (ET). We investigated whether antioxidant therapy prevents chronic bile duct ligation (CBDL)-induced alterations in systemic and renal hemodynamics, and reduces F2-isoprostane and ET levels.

METHODS

Sprague-Dawley rats were placed on either a normal or a high vitamin E diet for 7 days and then underwent either CBDL or sham surgery. They were then maintained on their respective diets for 21 more days, at which time the physiologic studies were performed.

RESULTS

Thirty-three percent of the CBDL rats died by day 21. The remaining rats had a lower mean arterial pressure (MAP), renal blood flow (RBF), glomerular filtration rate (GFR), and sodium and water excretion than control rats. CBDL rats had higher portal pressure, renal venous pressure, and renal vascular resistance (RVR). These changes were associated with increased levels of systemic and renal venous F2-isoprostanes and ET. Vitamin E normalized MAP, RBF, GFR, RVR, and sodium and water excretion, and improved the 21-day survival without altering portal or renal venous pressures. Surprisingly, vitamin E did not alter the systemic levels of F2-isoprostanes but markedly reduced their levels in the renal venous circulation.

CONCLUSION

Vitamin E improves MAP and renal function in CBDL rats, and selectively decreases renal levels of oxidative stress and ET, suggesting that local redox balance is implicated in CBDL-induced renal dysfunction.

Beneficial effect of nitric oxide synthase inhibitor on hepatotoxicity induced by allyl alcohol

The effect of aminoguanidine (a selective inhibitor of inducible nitric oxide synthase) on allyl alcohol-induced liver injury was assessed by the measurement of serum ALT and AST activities and histopathological examination. When aminoguanidine (50-300 mg/kg, i.p.) was administered to mice 30 min before a toxic dose of allyl alcohol (75 microL/kg, i.p.), significant changes related to liver injury were observed. In the presence of aminoguanidine the level of ALT and AST enzymes were significantly decreased. All symptoms of liver necrosis produced by allyl alcohol toxicity almost completely disappeared when animals were pretreated with aminoguanidine at 300 mg/kg. Depletion of hepatic glutathione as a consequence of allyl alcohol metabolism was minimal in mice pretreated with aminoguanidine at 300 mg/kg. It was found that the inhibition of toxicity was not due to alteration in allyl alcohol metabolism since aminoguanidine did not effect alcohol dehydrogenase activity both in vivo and in vitro.