Endotoxin-induced Renal Failure Research Articles

LOW-DOSE DEXAMETHASONE-SUPPLEMENTED FLUID RESUSCITATION REVERSES ENDOTOXIN-INDUCED ACUTE RENAL FAILURE AND PREVENTS CORTICAL MICROVASCULAR HYPOXIA

There is growing evidence that impairment in intrarenal oxygenation and hypoxic injury might contribute to the pathogenesis of septic renal failure. An important molecule known to act on the renal microvascular tone and therefore consequently being involved in the regulation of intrarenal oxygen supply is NO. The main production of NO under septic conditions derives from iNOS, an enzyme that can be blocked by dexamethasone (DEX). In an animal model of endotoxin-induced renal failure, we tested the hypothesis that inhibition of iNOS by low-dose DEX would improve an impaired intrarenal oxygenation and kidney function. Twenty-two male Wistar rats received a 30-min intravenous infusion of LPS (2.5 mg/kg) and consecutively developed endotoxemic shock. Two hours later, in 12 animals, fluid resuscitation was initiated. Six rats did not receive resuscitation; four animals served as time control. In addition to the fluid, six animals received a bolus of low-dose DEX (0.1 mg/kg). In these animals, the renal iNOS mRNA expression was significantly suppressed 3 h later. Dexamethasone prevented the appearance of cortical microcirculatory hypoxic areas, improved renal oxygen delivery, and significantly restored oxygen consumption. Besides a significant increase in MAP and renal blood flow, DEX restored kidney function and tubular sodium reabsorption to baseline values. In conclusion, treatment with low-dose DEX in addition to fluid resuscitation reversed endotoxin-induced renal failure associated by an improvement in intrarenal microvascular oxygenation. Therefore, low-dose DEX might have potential application in the prevention of septic acute renal failure.

Endotoxemic renal failure in mice: Role of tumor necrosis factor independent of inducible nitric oxide synthase

Renal failure is a frequent complication of sepsis with a high mortality. Tumor necrosis factor (TNF) has been suggested to be a factor in the acute renal failure in sepsis or endotoxemia. Recent studies also suggest involvement of nitric oxide (NO), generated by inducible NO synthase (iNOS), in the pathogenesis of endotoxin-induced renal failure. The present study tested the hypothesis that the role of TNF in endotoxic renal failure is mediated by iNOS-derived NO. Renal function was evaluated in endotoxemic [Escherichia coli lipopolysaccharide (LPS), 5 mg/kg IP] wild-type and iNOS knockout mice. The effect of TNF neutralization on renal function during endotoxemia in mice was assessed by a TNF-soluble receptor (TNFsRp55). An injection of LPS to wild-type mice resulted in a 70% decrease in glomerular filtration rate (GFR) and in a 40% reduction in renal plasma flow (RPF) 16 hours after the injection. The results occurred independent of hypotension, morphological changes, apoptosis, and leukocyte accumulation. In mice pretreated with TNFsRp55, only a 30% decrease in GFR without a significant change in RPF in response to LPS, as compared with vehicle-treated mice, was observed. Also, the serum NO concentration was significantly lower in endotoxemic wild-type mice pretreated with TNFsRp55, as compared with untreated endotoxemic wild-type mice (260 +/- 52 vs. 673 +/- 112 micromol/L, P < 0.01). In LPS-injected iNOS knockout mice and wild-type mice treated with a selective iNOS inhibitor, 1400W, the development of renal failure was similar to that in wild-type mice. As in wild-type mice, TNFsRp55 significantly attenuated the decrease in GFR (a 33% decline, as compared with 75% without TNFsRp55) without a significant change in RPF in iNOS knockout mice given LPS. These results demonstrate a role of TNF in the early renal dysfunction (16 h) in a septic mouse model independent of iNOS, hypotension, apoptosis, leukocyte accumulation, and morphological alterations, thus suggesting renal hypoperfusion secondary to an imbalance between, as yet to be defined, renal vasoconstrictors and vasodilators.

Endotoxin-induced renal failure. II. A role for tubular hypoxic damage.

Endotoxin-induced hypotension and altered renal microcirculation could lead to tubular injury, particularly at the physiologically hypoxic outer medulla. We explored this hypothesis in isolated perfused kidneys and in vivo in rats subjected to endotoxemia. Rat kidneys were removed 15 min after endotoxin injection in vivo (from Escherichia coli 0127:B8, 1 mg/kg i.p.) and perfused with oxygenated medium supplemented with 20 amino acids and endotoxin. Glomerular filtration rate and filtration fraction markedly declined (0.4 +/- 0. 1 ml/min and 1.1 +/- 0.1, respectively) as compared with control kidneys (0.7 +/- 0.1 ml/min and 1.8 +/- 0.1, n = 8-12 per group; p < 0.05). Hypoxic injury to medullary thick ascending limbs in the innermost outer medulla increased (47 +/- 9% of tubules vs. 16 +/- 8% in controls, p < 0.05). When rats were preconditioned with an additional endotoxin injection 16 h earlier (a manipulation that markedly reduces cortical and medullary blood flow), glomerular filtration rate and filtration fraction further declined to 0.1 +/- 0.0 ml/min and 0.4 +/- 0.1, respectively (p < 0.01), and tubular sodium reabsorption fell to 81 +/- 12 vs 98 +/- 0% in controls (p < 0.05). Tubular damage, however, did not increase (20 +/- 7%), probably reflecting a decline in reabsorptive workload and oxygen requirement. In rats subjected to a single or two repeated daily doses of endotoxin (1 mg/kg i.p.) plasma creatinine comparably rose 41% on the average over 24 h, creatinine clearance fell by 27% (p < 0.0001), but tubular damage was absent. By contrast, in rats preconditioned with indomethacin and the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10 mg/kg), the addition of endotoxin markedly augmented outer medullary hypoxic tubular damage both in S(3) segments (27 +/- 10 vs 1 +/- 1%) and in medullary thick ascending limbs (38 +/- 11 vs. 10 +/- 5%, n = 7-8; p < 0.05). It is concluded that under special conditions, such as altered medullary oxygen balance or defective nitric oxide or prostaglandin synthesis, endotoxin may predispose to hypoxic outer medullary tubular damage.

Endotoxin-induced renal failure. I. A role for altered renal microcirculation.

The pathogenesis of sepsis-induced renal failure is multifactorial and only partially understood. In these studies we evaluated intrarenal microcirculatory changes during endotoxemia and the potential role of nitric oxide (NO) and endothelin in these changes. In anesthetized rats endotoxin infusion [lipopolysaccharide (LPS), Escherichia coli serotype 0127:B8; 10 mg/kg/h] resulted in hypotension and a transient enhancement of renal blood flow, with cortical vasodilation and a loss of outer medullary vasodilatory response to hypotension. The initial cortical vasodilation was abolished by the NO synthase inhibitor NG-nitro-L-arginine methyl ester, but not by indomethacin. Direct NO measurements disclosed a gradual rise in cortical NO, despite the waning vasodilatory effect, suggesting antagonizing vasoconstrictive stimuli. In rats pretreated by LPS (1 mg/kg i.p. 1 day earlier) the renal blood flow was reduced to 55% of that of controls. Moreover, the vasodilatory response to LPS infusion was converted into profound cortical and medullary vasoconstriction. In these preconditioned rats the endothelin receptor antagonist bosentan evoked a vasodilatory response and attenuated the vasoconstrictive reaction to LPS infusion. The infusion of another LPS (E. coli serotype 0111:B4) exerted predominant and protracted renal vasodilation without hypotension. In conclusion, different LPS exert diverse systemic and renal hemodynamic responses. The 0127:B8 serotype attenuates renal medullary vasodilation during hypotension, exerts transient cortical vasodilation, and following repeated exposure induces profound renal vasoconstriction. NO and endothelin participate in LPS-induced vascular responses that may predispose to hypoxic tubular damage.

Lack of Effect of ET Antibody or SB 209670 on Endotoxin-Induced Renal Failure

Elevated plasma levels of endothelin-1 (ET-1) in patients with septic shock have implicated ET-1 in the vascular hypoperfusion and organ dysfunction, including renal failure, that occur in this condition. Administration of endotoxin to rats induces renal dysfunction characterized by increased blood urea nitrogen (BUN) and plasma creatinine (Cr) levels. Here, we have found that neither SB 209670 (an ETA and ETB receptor antagonist) nor an affinity-purified ET antibody blocked the endotoxin-induced changes in renal function, suggesting that ET-1 is not involved in the pathophysiology of endotoxin-induced renal dysfunction.

Lack of Effect of ET Antibody or SB 209670 on Endotoxin-Induced Renal Failure

Summary: Elevated plasma levels of endothelin-1 (ET-1) in patients with septic shock have implicated ET-1 in the vascular hypoperfusion and organ dysfunction, including renal failure, that occur in this condition. Administration of endotoxin to rats induces renal dysfunction characterized by increased blood urea nitrogen (BUN) and plasma creatinine (Cr) levels. Here, we have found that neither SB 209670 (an ETA and ETB receptor antagonist) nor an affinity-purified ET antibody blocked the endotoxin-induced changes in renal function, suggesting that ET-1 is not involved in the pathophysiology of endotoxin-induced renal dysfunction.

Reactive oxygen metabolites in endotoxin-induced acute renal failure in rats

Based on recent reports that reactive oxygen metabolites may play a role in endotoxin-induced injury in other tissues, we postulated that reactive oxygen metabolites may be important mediators of endotoxin-induced acute renal failure. Superoxide dismutase, a scavenger of superoxide, or catalase, which destroys hydrogen peroxide, did not protect against endotoxin-induced renal failure. Similarly, neither the hydroxyl radical scavenger dimethylthiourea nor the iron chelator deferoxamine (which presumably would act by preventing the generation of hydroxyl radical via the iron-catalyzed Haber-Weiss reaction) prevented the endotoxin-induced fall in renal function. In separate experiments, we found no increase in renal cortical lipid peroxidation (a marker of reactive oxygen metabolite-mediated tissue injury) in endotoxin-treated rats, providing further evidence against a role for reactive oxygen metabolites in endotoxin-induced renal injury. Finally, using the aminotriazole-induced inhibition of catalase (a measure of in vivo changes in the hydrogen peroxide generation) we found no evidence of enhanced hydrogen peroxide generation in the renal cortex in endotoxin-treated rats. Taken together, the data from these three separate experimental approaches suggest that reactive oxygen metabolites are not important mediators of endotoxin-induced acute renal failure.