Acute renal failure in endotoxemia is caused by TNF acting directly on TNF receptor-1 in kidney

Polymorphism of host response genes: Implications in the pathogenesis and treatment of acute renal failure

Acute inflammatory disorders are the result of an interaction between genetic and environmental factors, and are often characterized by an imbalance between pro- and anti-inflammatory host immune responses. Over the past decade, polymorphisms of host response genes have been explored as genetic risk and prognostic markers in the course and severity of acute inflammatory disorders. Increasing evidence supports an important role for inflammatory mechanisms in the pathogenesis of acute renal failure (ARF) following both ischemic and nephrotoxic injury. The use of genetic epidemiology may become a useful tool to identify patients with an altered susceptibility to developing hospital-acquired ARF, and stratify those who may benefit from preventive therapies that modulate host immune responses in a favorable way. This review summarizes the existing experimental and clinical studies supporting the role of inflammation in ARF and critically appraises studies that have examined polymorphism of immune response genes as potential determinants of susceptibility to and severity of acute inflammatory disorders. Conclusions are drawn on the application of genetic epidemiology to the field of ARF and the rationale for further research on the role of genetic markers in ARF.

Excretion of vitamin A in urine of women during normal pregnancy and pregnancy complications

BACKGROUND/AIMS

The renal function, including the excretion of low-molecular-weight proteins, changes during pregnancy and may cause a urinary excretion of retinol-binding protein (RBP). Whether it is accompanied by a substantial loss of vitamin A (retinol) has not been established yet. We therefore determined the excretion of retinol and RBP in urine of pregnant women.

METHODS

The study involved analyses of urine samples from 40 healthy pregnant women and 29 women with pregnancy complications during the third trimester. Analyses of plasma and urine of 7 healthy women and 5 women with pregnancy complications were also carried out 6 weeks antepartum, at time of delivery and 1 week postpartum.

RESULTS

Urinary retinol was higher in women who suffered from pregnancy disorders with an influence on maternal metabolism (p < 0.01). RBP was excreted at substantial concentrations in the urine of all 69 women, but there were no differences between the groups. Women with a concomitant excretion of retinol had higher levels of urinary RBP than those without a retinol excretion (p < 0.05). Differences in plasma retinol and RBP were not significant.

CONCLUSION

The excretion of urinary retinol may increase significantly during pregnancy complications, which needs further clarification to which extent this condition may negatively affect the vitamin A status in such women.

N-acetylcysteine reduces contrast-associated nephropathy but not clinical events during long-term follow-up

BACKGROUND

Contrast-associated nephropathy (CAN) is associated with increased morbidity and mortality following percutaneous coronary intervention (PCI). N-acetylcysteine (NAC) has been shown to reduce the risk of nephropathy; however, the impact of NAC on long-term clinical outcomes has not been assessed.

METHODS

This randomized, double-blind, placebo-controlled trial enrolled 180 patients with moderate renal dysfunction undergoing PCI or coronary angiography with a high likelihood of ad hoc PCI; 171 patients completed the clinical follow-up. Patients received oral NAC (2000 mg/dose, n = 95) or placebo (n = 85) twice a day for 3 doses if randomized the night prior to the procedure, and 2 doses if randomized the day of the procedure. The primary end point was the incidence of a > or =25% increase in serum creatinine level 48 to 72 hours after PCI. Secondary end points were the inhospital incidence of death, nonfatal myocardial infarction, or urgent dialysis, and the 9-month incidence of death, nonfatal myocardial infarction, need for dialysis, or repeat hospitalization for cardiac reasons.

RESULTS

CAN occurred in 9.6% of patients assigned to NAC and 22.2% of patients assigned to placebo (P =.04); 1 patient receiving NAC required urgent dialysis. The inhospital composite end point occurred in 7 (7.4%) NAC-treated and 3 (3.5%) placebo-treated patients, P = NS. At 9 months, the composite end point occurred in 23 (24.2%) NAC-treated patients and 18 (21.2%) placebo-treated, P = NS.

CONCLUSION

Although high-dose NAC prevented periprocedural CAN, this benefit did not translate into a decrease in adverse outcomes over 9 months. Further studies to determine the clinical utility of this drug are required.

Inflammatory cytokines in acute renal failure

A growing body of evidence indicates that inflammatory mechanisms contribute to toxin-induced acute renal failure as well as ischemia/reperfusion injury. A role for tumor necrosis factor-alpha (TNF-alpha) in mediating the inflammatory injury in cisplatin-induced acute renal failure has recently been established. Cisplatin induces the expression of TNF-alpha and TNF receptor subtype 2 (TNFR2) within the kidney. Genetic deletion of either TNF-alpha or TNFR2 substantially reduces cisplatin-induced renal failure and also necrosis and apoptosis within the kidney. Studies will be required to determine if pharmacologic inhibition of TNF-alpha might reduce cisplatin-induced renal failure in humans.

Pattern of acute renal failure in a tertiary hospital in the United Arab Emirates

Acute renal failure (ARF) is a challenging problem in nephrology. To evaluate the pattern, management and outcome of ARF in our tertiary hospital, we analyzed the data of all 81 patients admitted with or developing ARF in hospital between January 2002 and June 2003. The 45 men and 36 women of mean age 56.2 +/- 21 (range 13 to 91) years were managed either on the ward (n = 48; 59%) and or in the ICU (n = 33; 41%) 10% were direct admissions to the nephrology service with ARF, and 90% developed ARF in hospital. Thirty percent were referred by oncology services and 15% by general medicine. Sepsis was the cause of ARF in 36 (44%) patients, followed by drug nephrotoxicity in 11 (14%), and obstructive uropathy in 9 (11%). Comorbid conditions were hypertension in 28 (35%); diabetes in 27 (33%); chronic renal failure, 19 (23%); ischemic heart disease 19 (23%); and liver disease 12 (15%). The most common predisposing factor was hypotension in 42 (52%), dehydration in 32 (40%), and drug nephrotoxicity in 20 (25%). Sixty patients (74%) were managed conservatively, and 21 (26%) required renal replacement therapy. The length of hospital stay was 29.5 +/- 38.4 (range 2 to 279) days. Patient survival for those managed on the ward was 71% compared to 33% for ICU patients (P <.00001). Renal survival was 83% for ward patients, compared to 48% for those in the ICU (P <.001). This study showed that majority of ARF developed in-hospital with oncology patients constituting the greatest proportion. Sepsis was the leading cause of ARF and hypotension, the main predisposing factor. Patients treated in the ICU showed a worse prognosis for both patient and renal survival.

Ethyl pyruvate decreases sepsis-induced acute renal failure and multiple organ damage in aged mice

BACKGROUND

Sepsis is a common cause of acute renal failure (ARF). The incidence of sepsis increases dramatically after 50 years of age; however, most ARF studies are performed in young mice.

METHODS

We performed two common sepsis models, lipopolysaccharide (LPS) administration and cecal ligation puncture (CLP) in aged mice. We developed a fully treated CLP model in aged mice by treating mice with fluid resuscitation and antibiotics.

RESULTS

LPS induced renal injury in aged but not young mice. However, volume resuscitation starting within 6 hours decreased renal injury. We then used this fluid resuscitation scheme, along with antibiotics, to develop a fully treated CLP model in aged mice. Mice subjected to CLP developed functional and histologic ARF and multiple organ damage. Treatment with ethyl pyruvate, even when started 12 hours after surgery, decreased serum creatinine, tubular damage, and multiple organ injury at 24 hours. Ethyl pyruvate decreased plasma tumor necrosis factor-alpha (TNF-alpha), and kidney mRNA for TNF alpha, tissue factor, and plasminogen activator inhibitor-1 (PAI-1), and increased mRNA for urokinase-like plasminogen activator.

CONCLUSION

CLP in aged mice causes functional and histologic changes consistent with human ARF. A single dose of ethyl pyruvate inhibits renal and multiple organ damage, and is still effective when given 12 hours after surgery.

Role of Toll-like receptor 4 in endotoxin-induced acute renal failure

Toll-like receptor 4 (TLR4) is present on monocytes and other cell types, and mediates inflammatory events such as the release of TNF after exposure to LPS. C3H/HeJ mice are resistant to LPS-induced mortality, due to a naturally occurring mutation in TLR4. We therefore hypothesized that LPS-induced acute renal failure (ARF) requires systemic TNF release triggered by LPS acting on extrarenal TLR4. We injected C3H/HeJ mice and C3H/HeOuJ controls with 0.25 mg of LPS, and sacrificed them 6 h later for analysis of blood urea nitrogen (BUN) and kidney tissue (n = 8 per group). In contrast to C3H/HeOuJ controls, C3H/HeJ mice were completely resistant to LPS-induced ARF (6-h BUN of 32.3 +/- 1.1 vs 61.7 +/- 5.6 mg/dl). C3H/HeJ mice released no TNF into the circulation at 2 h (0.00 vs 1.24 +/- 0.16 ng/ml), had less renal neutrophil infiltration (6.4 +/- 1.0 vs 11.4 +/- 1.3 neutrophils per high power field), and less renal apoptosis, as assessed by DNA laddering. Transplant studies showed that C3H/HeJ recipients of wild-type kidneys (n = 9) were protected from LPS-induced ARF, while wild-type recipients of C3H/HeJ kidneys (n = 11) developed severe LPS-induced ARF (24-h BUN 44.0 +/- 4.1 vs 112.1 +/- 20.0 mg/dl). These experiments support our hypothesis that LPS acts on extrarenal TLR4, thereby leading to systemic TNF release and subsequent ARF. Renal neutrophil infiltration and renal cell apoptosis are potential mechanisms by which endotoxemia leads to functional ARF.

Pharmacologic treatment of acute renal failure in sepsis

The pathophysiology of acute renal failure in sepsis is complex and includes intrarenal vasoconstriction, infiltration of inflammatory cells in the renal parenchyma, intraglomerular thrombosis, and obstruction of tubuli with necrotic cells and debris. Attempts to interfere pharmacologically with these dysfunctional pathways, including inhibition of inflammatory mediators, improvement of renal hemodynamics by amplifying vasodilator mechanisms and blocking vasoconstrictor mechanisms, and administration of growth factors to accelerate renal recovery, have yielded disappointing results in clinical trials. Interruption of leukocyte recruitment is a potential promising approach in the treatment of septic acute renal failure, but no data in humans are presently available. Activated protein C and steroid replacement therapy have been shown to reduce mortality in patients with sepsis and are now accepted adjunctive treatment options for sepsis in general.

Leukocyte recruitment and acute renal failure

Despite advances in medical technology, acute renal failure (ARF) still represents a major challenge in clinical medicine, as morbidity and mortality have remained unchanged over the past two decades. The pathophysiology of ARF is highly complex and only poorly understood; new insights into the pathophysiology of ARF are therefore of utmost importance to develop better understanding and therapies. Acute tubular necrosis (ATN) is the predominant cause of ARF and often arises as a consequence of septic, toxic, or ischemic insults. The recruitment of leukocytes into the kidney has recently emerged as a key event in the development of experimental ischemic and septic ARF. A few descriptive clinical studies support this idea. However, the clinical relevance of various animal models remains unclear, as does the importance of different leukocyte subsets, and even methodological aspects as how to quantify renal leukocyte recruitment. This review summarizes and critically evaluates experimental findings that provide insight into the role of leukocytes and their recruitment during ARF. We aim to provide a valid description of ARF, illustrate animal models of ARF, review qualitative and quantitative methods to assess renal leukocyte recruitment, and discuss the components of the leukocyte recruitment cascade and their role in ARF.

The pathogenesis of septic acute renal failure

PURPOSE OF REVIEW

Acute renal failure is a serious condition that affects as many as 20% of ICU patients. The most common causes of acute renal failure in the ICU patient are severe sepsis and septic shock. The mortality of acute renal failure in septic critically ill patients remains high despite our increasing ability to support vital organs. This is partly the result of our poor understanding of the pathogenesis of sepsis-induced renal dysfunction. Accordingly, a review of our current understanding of the pathogenesis of septic acute renal failure is timely and relevant.

RECENT FINDINGS

Throughout the past half century, acute renal failure of acute illness has essentially been considered a hemodynamic disease caused by kidney ischemia, a view derived by findings in animal models. Unfortunately most such models are greatly deficient in that they do not reproduce the high cardiac output, low systemic vascular resistance state typically seen during human sepsis. Furthermore, most models inducing so-called acute tubular necrosis are based on ischemia-reperfusion (renal artery clamping), an event with little relevance to human sepsis. Recent research highlights a new possible and emerging concept for the pathogenesis of septic acute renal failure: acute apoptosis. This concepts fits well with the typical paucity of histologic changes seen in so-called acute tubular necrosis and with growing evidence of a role for apoptosis in organ injury during sepsis and inflammation in general. Furthermore, the authors present evidence that some potential treatments recently shown to affect the mortality of critically ill patients, (activated protein C, intensive insulin treatment, and low-volume mechanical ventilation) might have antiapoptotic activity.

SUMMARY

This review suggests that, on the evidence available, septic acute renal failure is more likely to be an immune or toxic state rather than simply a hemodynamic condition. The authors speculate that future insights into its pathogenesis might lead to a paradigm shift away from the concept of acute tubular necrosis, which has never been convincingly shown in sepsis, to that of acute tubular apoptosis.

Lipopolysaccharide stimulates mitochondrial biogenesis via activation of nuclear respiratory factor-1

Exposure to bacterial lipopolysaccharide (LPS) in vivo damages mitochondrial DNA (mtDNA) and interferes with mitochondrial transcription and oxidative phosphorylation (OXPHOS). Because this damage accompanies oxidative stress and is reversible, we postulated that LPS stimulates mtDNA replication and mitochondrial biogenesis via expression of factors responsive to reactive oxygen species, i.e. nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor-A. In testing this hypothesis in rat liver, we found that LPS induces NRF-1 protein expression and activity accompanied by mRNA expression for mitochondrial transcription factor-A, mtDNA polymerase gamma, NRF-2, and single-stranded DNA-binding protein. These events restored the loss in mtDNA copy number and OXPHOS gene expression caused by LPS and increased hepatocyte mitotic index, nuclear cyclin D1 translocation, and phosphorylation of pro-survival kinase, Akt. Thus, NRF-1 was implicated in oxidant-mediated mitochondrial biogenesis to provide OXPHOS for proliferation. This implication was tested in novel mtDNA-deficient cells generated from rat hepatoma cells that overexpress NRF-1. Depletion of mtDNA (rhoo clones) diminished oxidant production and caused loss of NRF-1 expression and growth delay. NRF-1 expression and growth were restored by exogenous oxidant exposure indicating that oxidative stress stimulates biogenesis in part via NRF-1 activation and corresponding to recovery events after LPS-induced liver damage.

TNFR2-mediated apoptosis and necrosis in cisplatin-induced acute renal failure

Cisplatin produces acute renal failure in humans and mice. Previous studies have shown that cisplatin upregulates the expression of TNF-alpha in mouse kidney and that inhibition of either the release or action of TNF-alpha protects the kidney from cisplatin-induced nephrotoxicity. In this study, we examined the effect of cisplatin on the expression of TNF receptors TNFR1 and TNFR2 in the kidney and the role of each receptor in mediating cisplatin nephrotoxicity. Injection of cisplatin into C57BL/6 mice led to an upregulation of TNFR1 and TNFR2 mRNA levels in the kidney. The upregulation of TNFR2 but not TNFR1 was blunted in TNF-alpha-deficient mice, indicating ligand-dependent upregulation of TNFR2. To study the roles of each receptor, we administered cisplatin to TNFR1- or TNFR2-deficient mice. TNFR2-deficient mice developed less severe renal dysfunction and showed reduced necrosis and apoptosis and leukocyte infiltration into the kidney compared with either TNFR1-deficient or wild-type mice. Moreover, renal TNF-alpha expression, ICAM-1 expression, and serum TNF-alpha levels were lower in TNFR2-deficient mice compared with wild-type or TNFR1-deficient mice treated with cisplatin. These results indicate that TNFR2 participates in cisplatin-induced renal injury in mice and may play an important role in TNF-alpha-mediated inflammation in the kidney in response to cisplatin.

TNF-alpha elimination with high cut-off haemofilters: a feasible clinical modality for septic patients?

BACKGROUND

Renal replacement therapies with high cut-off haemofilters are new approaches in the adjuvant therapy of sepsis. We analysed the cytokine elimination capacity of a newly developed polyflux high cut-off haemofilter. Different renal replacement therapies are compared and tested for their clinical feasibility.

METHODS

Blood from healthy volunteers (n=15) was incubated for 4 h with 1 mg of endotoxin and then circulated through a closed extracorporeal circuit. A newly developed polyflux haemofilter (P2SX) was used. Haemofiltration, haemodialysis and albumin dialysis were tested. IL-1ra (17 kDa), interleukin-6 (IL-6) (28 kDa), tumour necrosis factor alpha (TNF-alpha) (51 kDa), albumin (64 kDa), creatinkinase (CK) (80 kDa) and IgG (140 kDa) were measured in blood and filtrates prior to the initiation and after 5 min, 1, 2 and 4 h.

RESULTS

Haemofiltration was superior to haemodialysis in the clearance capacity of all substances when applied in the 1 l/h ultrafiltration mode. Increasing the ultrafiltration rate/dialysate flow from 1 to 3 l/h led to a significant increase in cytokine clearances (P<0.001). At 3 l/h the differences between haemofiltration and haemodialysis vanished and both techniques achieved comparable cytokine clearances. Median clearance values ranged between 25 and 54 ml/min for interleukin-1 receptor antagonist (IL-1ra), 23 and 42 ml/min for IL-6 and 15 and 28 ml/min for TNF-alpha. Albumin loss was highest in the haemofiltration group with albumin clearances ranging between 7 and 13 ml/min. Using diffusion instead of convection significantly reduced the loss of albumin (P<0.01 for 1 l/h, P<0.05 for 3 l/h). Albumin dialysis was able to completely inhibit albumin loss but cytokine clearance capacity was limited.

CONCLUSIONS

High cut-off haemofilters achieve high clearances for inflammatory IL-6 and TNF-alpha. Due to the high protein loss in haemofiltration, dialysis in combination with balanced protein substitution seems to be a suitable approach for clinical trials.

Epr analysis reveals three tissues responding to endotoxin by increased formation of reactive oxygen and nitrogen species

The excessive formation of reactive oxygen and nitrogen species (RONS) in tissue has been implicated in the development of various diseases. In this study we adopted ex vivo low temperature EPR spectroscopy combined with spin trapping technique to measure local RONS levels in frozen tissue samples. CP-H (1-hydroxy-3-carboxy-pyrrolidine), a new nontoxic spin probe, was used to analyze RONS in vivo. In addition, nitrosyl complexes of hemoglobin were determined to trace nitric oxide released into blood. By this technique we found that RONS formation in tissue of control animals increased in the following order: liver < heart < brain < cerebellum < lung < muscle < blood < ileum < kidney < duodenum < jejunum. We also found that endotoxin challenge, which represents the most common model of septic shock, increased the formation of RONS in rat liver, heart, lung, and blood, but decreased RONS formation in jejunum. We did not find changes in RONS levels in other parts of gut, brain, skeletal muscles, and kidney. Scavenging of RONS by CP-H was accompanied by an increase in blood pressure, indicating that LPS-induced vasodilatation may be due to RONS, but not due to nitric oxide. Experiments with tissue homogenates incubated in vitro with CP-H showed that ONOO(-) and O(2)(*)(-), as well as other not identified RONS, are detectable by CP-H in tissue. In summary, low-temperature EPR combined with CP-H infusion allowed detection of local RONS formation in tissues. Increased formation of RONS in response to endotoxin challenge is organ specific.

Elevated serum levels of the type I and type II receptors for tumor necrosis factor-alpha as predictive factors for ARF in patients with septic shock

BACKGROUND

Acute renal failure (ARF), a common and serious complication in patients with septic shock, has high mortality. Recent data suggest that proinflammatory cytokines may contribute to sepsis-associated ARF.

METHODS

To examine the role of proinflammatory cytokines, we evaluated 537 patients enrolled in the placebo arm of the Norasept II study, of whom 112 patients (20%) developed ARF.

RESULTS

By univariate analysis, the following factors were significantly associated with the development of ARF: male sex, younger age, increased heart rate, higher Acute Physiology and Chronic Health Evaluation II score, oliguria, increased blood urea nitrogen level, increased serum creatinine (Scr) level, decreased arterial pH, and increased serum potassium level. Although there were no statistically significant differences in serum levels of tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 between patients with and without ARF, elevated serum levels of the two soluble TNF-alpha receptors (S-TNF-RI and S-TNF-RII) were strongly associated with the development of ARF (S-TNF-RI, 25 +/- 16 versus 18 +/- 13 ng/mL; P = 0.00006; S-TNF-RII, 25 +/- 21 versus 18 +/- 17 ng/mL; P = 0.0007). Using forward stepwise regression analysis, elevated S-TNF-R level remained an independent predictor for ARF, even when we limited our analysis to patients with Scr levels of 1.4 mg/dL or less (< or =124 micromol/L) at study entry, suggesting that decreased renal clearance of S-TNF-R alone cannot account for this association. Elevated S-TNF-R level also was an independent predictor of mortality among patients developing ARF.

CONCLUSION

S-TNF-R level is an independent predictor for the development of ARF and mortality. We speculate that elevated S-TNF-R levels may reflect a more intense inflammatory response.

Calcium-sensing receptor-mediated TNF production in medullary thick ascending limb cells

Medullary thick ascending limb (mTAL) cells in primary culture express the Ca(2+)-sensing receptor (CaR), a G protein-coupled receptor that senses changes in extracellular Ca(2+) (Ca(o)(2+)) concentration, resulting in increases of intracellular Ca(2+) concentration and PKC activity. Exposure of mTAL cells to either Ca(o)(2+) or the CaR-selective agonist poly-L-arginine increased TNF-alpha synthesis. Moreover, the response to Ca(o)(2+) was enhanced in mTAL cells transfected with a CaR overexpression vector. Transfection of mTAL cells with a TNF promoter construct revealed an increase in reporter gene activity after exposure of the cells to Ca(o)(2+), suggesting that intracellular signaling pathways initiated by means of activation of a CaR contribute to TNF synthesis by a mechanism that involves transcription of the TNF gene. Neutralization of TNF activity with an anti-TNF antibody attenuated Ca(2+)-mediated increases in cyclooxygenase-2 (COX-2) protein expression and PGE(2) synthesis, suggesting that TNF exerts an autocrine effect in the mTAL, which contributes to COX-2-mediated PGE(2) production. Preincubation with the PKC inhibitor bisindolylmaleimide I inhibited Ca(2+)-mediated TNF production. Significant inhibition of COX-2 protein expression and PGE(2) synthesis also was observed when cells were challenged with Ca(o)(2+) in the presence of bisindolylmaleimide I. The data suggest that increases in TNF production subsequent to activation of the CaR may be the basis of an important renal mechanism that regulates salt and water excretion.