In vitro and in vivo protective effect of atriopeptin III on ischemic acute renal failure

Natriuretic peptides in acute kidney injury - A sojourn on parallel tracks?

OBJECTIVE

The focus of this review was to elicit the mechanistic logic of the experimental and clinical study designs of natriuretic peptides (NP) in acute kidney injury (AKI) and to understand their respective outcomes.

METHODS

Online search of PubMed and manual review of articles. Randomized trials, observational and physiologic studies of NPs and AKI were extracted. Rationale, design and study outcomes were analyzed.

RESULTS

In experimental models of AKI, infusion of NP prevented post-ischemic fall in renal blood flow (RBF) or improvement in RBF, GFR, diuresis and natriuresis and demonstrated anti-inflammatory properties. NPs were most effective in the early stages of AKI, also in established phase of AKI but their effectiveness were limited to the time of infusion. Hypotension was a major side-effect. Based on these observations, preliminary clinical studies were performed which demonstrated improved urine output, RBF and GFR and reduced need for dialysis. However, randomized, controlled trials failed to demonstrate improvement in dialysis-free survival in different cohorts and study designs. Although NPs reduced the incidence of AKI in the postoperative period in cardiac surgery, it was not associated with improved long-term survival. In contrast to randomized trials, meta-analysis reported favorable results.

CONCLUSIONS

Reasons for the divergence of experimental and clinical outcomes of NPs in AKI are discussed in this review article.

Expression patterns of natriuretic peptides in pre-hibernating and hibernating Anatolian ground squirrel (Spermophilus xanthoprymnus) kidney

Hibernation is characterized by marked suppression of renal function. Natriuretic peptides (NPs) are involved in the regulation of renal function. However, the role of NPs in the renal function during hibernation remains unclear. We aimed to investigate the distribution patterns of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in Anatolian ground squirrel (Spermophilus xanthoprymnus) kidneys during pre-hibernation and hibernation periods. Cortical proximal tubules showed weak ANP immunoreactivity, with moderate staining on the brush border during the pre-hibernation period. In the hibernation period, moderate ANP immunoreactivity was seen in cortical proximal tubules, with very weak reaction in hibernating cortical distal tubules, medullary proximal and collecting tubules. Cortical proximal and distal tubules of both periods had strong and weak BNP immunoreactivity, respectively. Medullary proximal, distal and Henle's loop segments showed very weak BNP immunoreactivity during pre-hibernation. Medullary distal, proximal and collecting tubules and Henle's loop segments had moderate staining during hibernation. In both periods, cortical proximal tubules displayed strong immunoreactivity to CNP. Distal tubules had moderate CNP staining during pre-hibernation, albeit weak staining during hibernation. Medullary proximal tubules exhibited moderate to strong immunoreactivity during pre-hibernation. Medullary distal and proximal tubules had weak and moderate CNP staining, respectively, during pre-hibernation. In both periods, Henle's loop segments displayed moderate CNP immunoreactivity. Glomeruli had similar weak ANP, BNP and CNP staining in both periods. These results suggest that heterothermic conditions differently affected the expression of NPs in the squirrel kidney. This different expression of NPs may contribute to the renal adaptation during hibernation.

The physiological and clinical importance of sodium potassium ATPase in cardiovascular diseases

The Na/K-ATPase has been extensively studied, but it is only recently that its role as a scaffolding and signaling protein has been identified. It has been identified that cardiotonic steroids (CTS) such as digitalis mediate signal transduction through the Na/K-ATPase in a process found to result in the generation of reactive oxygen species (ROS). As these ROS also appear capable of initiating this signal cascade, a feed forward amplification process has been postulated and subsequently implicated in some disease pathways including uremic cardiomyopathy.

C-type natriuretic peptide ameliorates ischemia/reperfusion-induced acute kidney injury by inhibiting apoptosis and oxidative stress in rats

AIMS

Although atrial natriuretic peptide has been shown to attenuate ischemia-reperfusion (IR)-induced kidney injury, the effect of natriuretic peptide receptor (NPR)-B activation on IR-induced acute kidney injury is not well documented. The purpose of the present study was to identify the effect of C-type natriuretic peptide (CNP), a selective activator of NPR-B, on the IR-induced acute kidney injury and its mechanisms involved.

MAIN METHODS

Unilaterally nephrectomized rats were insulted by IR in their remnant kidney, and they were randomly divided into three groups: sham, vehicle+IR, and CNP+IR groups. CNP (0.2μg/kg/min) was administered intravenously at the start of a 45-min renal ischemia for 2h. Rats were then killed 24h after I/R, and the blood and tissue samples were collected to assess renal function, histology, TUNEL assay, and Western blot analysis of kidney Bax and Bcl-2 expressions.

KEY FINDINGS

The levels of blood urea nitrogen and serum creatinine were significantly increased in rats after IR compared with vehicle-treated rats. IR elevated apoptosis, Bcl-2/Bax ratio, TUNEL positivity, oxidative stress parameters, malondialdehyde concentration, and superoxide dismutase activity. IR also induced epithelial desquamation of the proximal tubules and glomerular shrinkage. CNP significantly attenuated the IR-induced increase in BUN and serum creatinine. Furthermore, CNP restored the suppressed renal cyclic guanosine 3' 5'-monophosphate levels caused by IR insult.

SIGNIFICANCE

Study findings suggest that CNP could ameliorate IR-induced acute kidney injury through inhibition of apoptotic and oxidative stress pathways, possibly through NPR-B-cGMP signaling.

Pharmacological strategies to prevent contrast-induced acute kidney injury

Contrast-induced acute kidney injury (CI-AKI) is the most common iatrogenic cause of acute kidney injury after intravenous contrast media administration. In general, the incidence of CI-AKI is low in patients with normal renal function. However, the rate is remarkably elevated in patients with preexisting chronic kidney disease, diabetes mellitus, old age, high volume of contrast agent, congestive heart failure, hypotension, anemia, use of nephrotoxic drug, and volume depletion. Consequently, CI-AKI particularly in high risk patients contributes to extended hospitalizations and increases long-term morbidity and mortality. The pathogenesis of CI-AKI involves at least three mechanisms; contrast agents induce renal vasoconstriction, increase of oxygen free radicals through oxidative stress, and direct tubular toxicity. Several strategies to prevent CI-AKI have been evaluated in experimental studies and clinical trials. At present, intravascular volume expansion with either isotonic saline or sodium bicarbonate solutions has provided more consistent positive results and was recommended in the prevention of CI-AKI. However, the proportion of patients with risk still develops CI-AKI. This review critically evaluated the current evidence for pharmacological strategies to prevent CI-AKI in patients with a risk of developing CI-AKI.

The Trade-Off between Dietary Salt and Cardiovascular Disease; A Role for Na/K-ATPase Signaling?

It has been postulated for some time that endogenous digitalis-like substances, also called cardiotonic steroids (CTS), exist, and that these substances are involved in sodium handling. Within the past 20 years, these substances have been unequivocally identified and measurements of circulating and tissue concentrations have been made. More recently, it has been identified that CTS also mediate signal transduction through the Na/K-ATPase, and consequently been implicated in profibrotic pathways. This review will discuss the mechanism of CTS in renal sodium handling and a potential "trade-off" effect from their role in inducing tissue fibrosis.

The therapeutic potential of synthetic human atrial natriuretic peptide in nephrotic syndrome: a randomized controlled trial

BACKGROUND

In nephrotic syndrome, the combination of furosemide and albumin infusion is a standard regimen to treat systemic edema. The efficacy of synthetic human atrial natriuretic peptide (hANP) for nephrotic syndrome to ameliorate the systemic edema and retain renal functions has not been fully demonstrated.

TRIAL DESIGN

We conducted a prospective, randomized, controlled, open-label clinical trial. Patients were randomly assigned by a stratified biased coin design.

METHODS

A total of 12 patients with nephrotic syndrome between the ages of 20 to 79 years were enrolled and randomly assigned to either the conventional (CON) group treated with furosemide and albumin, and hANP group, in which carperitide was administered in addition to the conventional therapies. The primary end points were: (1) the differences in serum creatinine levels, and (2) the reduction of total dosage of furosemide and albumin by the treatments of hANP. Secondary end points were body weight, systolic blood pressure, heart rate, serum protein, albumin, and urinary protein excretion.

RESULTS

A total of 13 patients were enrolled, and one patient was excluded due to severe pneumonia. In both hANP (n = 7) and CON (n = 5) groups, body weight was reduced after 2-week treatments. Serum creatinine levels at follow-up significantly increased compared with baseline. The increase in serum creatinine levels (Δ serum creatinine) was smaller in the hANP group compared with the CON group (P = 0.31). The serum uric acid, serum urea nitrogen, and urinary protein excretion were reduced in the hANP group, and increased in the CON group, though these differences were not statistically significant. The usage of hANP significantly reduced the total dosage of furosemide (P < 0.05) during the treatment periods. No adverse effects were observed.

CONCLUSIONS

The concomitant use of synthetic hANP with conventional therapies is beneficial for reducing the dosage of loop diuretics, and the elevation of serum creatinine and uric acid may be avoided.

Cardiac biomarkers in the critically ill

Cardiac biomarkers have well-established roles in acute coronary syndrome and congestive heart failure. In many instances, the detection of cardiac biomarkers may aid in the diagnosis and risk assessment of critically ill patients. Despite increasing interest in the use of cardiac biomarkers in noncardiac critical illness, no clear consensus exists on how and in which settings markers should be measured. This article briefly describes what constitutes an ideal biomarker and focuses on those that have been most well studied in critical illness, specifically troponin, the natriuretic peptides, and heart-type fatty acid-binding protein.

How to reduce the incidence of contrast induced acute kidney injury after cardiac invasive procedures, a review and practical recommendations

BACKGROUND

Contrast induced acute kidney injury is an important complication after cardiac (invasive) procedures and is associated with substantial morbidity and mortality. The aim of the current article is to provide a comprehensive overview of the current knowledge regarding contrast induced acute kidney injury.

METHODS

Current literature was reviewed and relevant articles were selected. Articles were identified through MEDLINE and Pubmed selecting articles, limited between 1980 and 2010.

RESULTS

The pathophysiological process resulting in contrast induced acute kidney injury is not completely understood, nevertheless several mechanisms involved have been proposed. However, the risk factors for contrast induced acute kidney injury and its timing are well known, making it amenable for preventive strategies. In the past decade various preventive strategies have been investigated with different results.

CONCLUSIONS

Currently, only adequate hydration, with saline, is uniformly accepted as a beneficial prophylactic strategy. Furthermore promising results have also been reported for several other prophylactic strategies. These results, however, need to be confirmed in future trials.

Early intervention in acute kidney injury

The prevalence of acute kidney injury (AKI) in the US is increasing, which can be attributed in part to the aging population and the pandemic of obesity, diabetes and hypertension. Individuals over the age of 70 years constitute 7% of the US population, but account for 36-70% of AKI cases. Presently, major efforts are underway to enable the early detection of AKI by use of various innovative biomarkers, thereby facilitating early intervention. Now is the time, therefore, to consider potential interventions to attenuate or prevent AKI. Several randomized studies have failed to alter the course of AKI, but these studies have been complicated by extrarenal consequences, which could have obscured the potential intrarenal benefit of the agent. Thus, agents that have exclusive effects on renal hemodynamics and tubular function, or the intrarenal infusion of short-acting agents that do not have systemic effects, need to be considered in future studies for the prevention of AKI.

Effect of intravenous atrial natriuretic peptide on pulmonary dysfunction and renal function following burn shock

BACKGROUND

The typical response to burn stress causes burn shock, followed by a diuretic phase; however, fluid management remains crucial in this phase in the treatment of the elderly, patients with preexisting cardiac or renal diseases, and patients developing acute renal failure. We studied the effects of human atrial natriuretic peptide (hANP), which is a renal vasodilator, natriuretic, and inhibitor of renin secretion, on renal function in these patients with burn injuries.

METHODS

Thirty-three severely burned patients (44.8% +/- 20.6% total burn surface area) with prolonged cardiovascular overload and pulmonary edema after burn shock receiving a continuous infusion of hANP (0.025 microg/kg/min and 0.05 microg/kg/min, hANP group) were compared with control (no-hANP group, n = 25). Vital signs, urine output (UO) and blood gas analysis before and 72 hour after the start of hANP were recorded. Creatinine clearance, free water clearance, and fractional excretion of sodium were also calculated.

RESULTS

Sixteen (48%) patients were elderly, over 80 years old. Twenty (60%) had preexisting cardiovascular disease, renal insufficiency, or diabetes. hANP infusion increased UO in 25 (66%) cases and improved oxygenation in 31 (82%) cases. Treatment with hANP increased creatinine clearance, fractional excretion of sodium, and UO, except in four cases that had already progressed to complete renal failure before the infusion of hANP.

CONCLUSIONS

Intravenous hANP seems to be effective for postresuscitative pulmonary dysfunction and renal function after burn shock in the vulnerable elderly, or patients with preexisting disease, suggesting that it could be valuable in facilitating fluid management in the acute phase in severely burned patients.

Renal protective effects and the prevention of contrast-induced nephropathy by atrial natriuretic peptide

OBJECTIVES

This study was designed to examine the protective effects of atrial natriuretic peptide (ANP) on contrast-induced nephropathy (CIN) after coronary angiography.

BACKGROUND

Contrast-induced nephropathy is a common complication after angiography. Some studies have shown that ANP has renal protective effects, but the beneficial effects for CIN prevention remain to be clearly shown.

METHODS

In a prospective, controlled, randomized trial in 254 consecutive patients with serum creatinine concentrations of > or =1.3 mg/dl, patients received either ANP (0.042 microg/kg/min; ANP group, n = 126) or Ringer solution alone (control group, n = 128). Treatment of either type was initiated 4 to 6 h before angiography and continued for 48 h.

RESULTS

There were no significant differences in age, sex, diabetes mellitus, or baseline serum creatinine level between the 2 groups. The prevalence of CIN, defined as a 25% increase in creatinine or an increase in creatinine of > or =0.5 mg/dl from baseline within 48 h, was significantly lower in the ANP group than in the control group (3.2% vs. 11.7%, respectively; p = 0.015). Multivariate analysis revealed that the use of >155 ml of contrast medium (odds ratio: 6.89; p < 0.001) and ANP treatment (odds ratio: 0.24; p = 0.016) were significant predictors of developing CIN. The incidence of an increase in creatinine of > or =25% or of > or =0.5 mg/dl from baseline at 1 month was also significantly lower in the ANP group than in the control group (p = 0.006).

CONCLUSIONS

In addition to hydration, ANP administration is effective in the prevention of CIN in patients with chronic renal failure, and the effect was maintained for 1 month.

Endogenous cardiotonic steroids: physiology, pharmacology, and novel therapeutic targets

Endogenous cardiotonic steroids (CTS), also called digitalis-like factors, have been postulated to play important roles in health and disease for nearly half a century. Recent discoveries, which include the specific identification of endogenous cardenolide (endogenous ouabain) and bufadienolide (marinobufagenin) CTS in humans along with the delineation of an alternative mechanism by which CTS can signal through the Na(+)/K(+)-ATPase, have increased the interest in this field substantially. Although CTS were first considered important in the regulation of renal sodium transport and arterial pressure, more recent work implicates these hormones in the regulation of cell growth, differentiation, apoptosis, and fibrosis, the modulation of immunity and of carbohydrate metabolism, and the control of various central nervous functions and even behavior. This review focuses on the physiological interactions between CTS and other regulatory systems that may be important in the pathophysiology of essential hypertension, preeclampsia, end-stage renal disease, congestive heart failure, and diabetes mellitus. Based on our increasing understanding of the regulation of CTS as well as the molecular mechanisms of these hormone increases, we also discuss potential therapeutic strategies.

Oxytocin alleviates hepatic ischemia-reperfusion injury in rats

Various mechanisms have been proposed for the pathogenesis of postischemic hepatic injury, including the generation of reactive oxygen metabolites. Oxytocin (OT) possesses antisecretory, antiulcer effects, facilitates wound healing and has anti-inflammatory properties. Hepatic ischemia-reperfusion (I/R)-injury was induced by inflow occlusion to median and left liver lobes ( approximately 70%) for 30 min of ischemia followed by 1h reperfusion in female Sprague-Dawley rats under anesthesia. I/R group (n=8) was administered intraperitoneally either OT (500 microg/kg) or saline at 24 and 12 h before I/R and immediately before reperfusion. Sham-operated group that underwent laparotomy without hepatic ischemia served as the control. Rats were decapitated at the end of reperfusion period. Hepatic samples were obtained for the measurement of myeloperoxidase (MPO) activity, malondialdehyde (MDA), glutathione (GSH) and collagen levels and histopathological analysis. Tumor necrosis factor-alfa (TNF-alpha) and transaminases (SGOT, SGPT) were assayed in serum samples. I/R injury caused significant increases in hepatic microscopic damage scores, MPO activity, collagen levels, transaminase, serum TNF-alpha levels. Oxytocin treatment significantly reversed the I/R-induced elevations in serum transaminase and TNF-alpha levels and in hepatic MPO and collagen levels, and reduced the hepatic damage scores. OT treatment had tendency to abolish I/R-induced increase in MDA levels, while GSH levels were not altered. These results suggest that OT has a protective role in hepatic I/R injury and its protective effect in the liver appears to be dependent on its inhibitory effect on neutrophil infiltration.

Effects of human atrial natriuretic peptide on renal function in patients undergoing abdominal aortic aneurysm repair

OBJECTIVE

Ischemia-reperfusion injury is an important cause of renal dysfunction after abdominal aortic aneurysm repair. Human atrial natriuretic peptide (hANP) is a potent endogenous natriuretic, diuretic, and vasorelaxant peptide. The objective of the present study was to evaluate the effects of hANP on renal function in patients undergoing abdominal aortic aneurysm repair.

DESIGN

A prospective, randomized, placebo-controlled study

SETTING

Intensive care unit of a university hospital.

PATIENTS

Forty patients undergoing elective abdominal aortic aneurysm repair.

INTERVENTIONS

The patients were randomized to receive a continuous infusion of either hANP (0.01-0.05 microg/kg/min) (n = 20) or placebo (n = 20) immediately before aortic cross-clamping. The infusion of hANP or placebo continued for 48 hrs.

MEASUREMENTS AND MAIN RESULTS

Blood and urine samples were taken before surgery, at admission to the intensive care unit, and on days 1, 2, and 3 postoperatively, for measurement of serum concentrations of sodium, creatinine, and blood urea nitrogen and plasma concentrations of ANP and brain natriuretic peptide (BNP). Urine volume and urinary concentrations of N-acetyl-beta-D-glucosaminidase (NAG), sodium, and creatinine were also measured. The mean plasma concentration of ANP was significantly higher in the hANP group than in the placebo group. The mean plasma BNP concentration was significantly lower in the hANP group than in the placebo group. The mean serum concentrations of creatinine and blood urea nitrogen were significantly (p < .05) lower in the hANP group than in the placebo group. The mean urine volume and mean creatinine clearance were significantly (p < .05) higher in the hANP group than in the placebo group. The mean urinary NAG/creatinine ratio was significantly (p < .05) lower in the hANP group than in the placebo group.

CONCLUSIONS

The intraoperative and postoperative infusion of low-dose hANP preserved renal function in patients undergoing abdominal aortic aneurysm repair. Further studies are needed to assess the efficacy of prophylactic hANP infusion on perioperative renal outcome.

The effect of seventy-two-hour continuous infusion of long-acting natriuretic peptide on acute ischemic renal failure in the rat

OBJECTIVES

Atrial natriuretic peptide (ANP(1-28)) protects the kidneys against acute renal failure in animals; however, its use in humans has been disappointing. Long-acting natriuretic peptide (LANP(1-30)) has natriuretic and diuretic actions similar to ANP(1-28), but it has a longer half-life and a different receptor site. Therefore, this study's aim was to determine if LANP(1-30) has better renal protection than ANP(1-28), which may make it useful in the treatment of acute renal failure.

SUBJECTS/METHODS

Three groups of male Sprague-Dawley rats were used, each with a body weight between 250-300 gm. Group 1 (ischemia only, n = 6) had a right nephrectomy followed by 30 minutes of left renal pedicle clamping. Group 2 (LANP Peptide treated, n = 7) had renal ischemia similar to Group 1, followed by an intraperitoneal bolus of 10 microg of LANP(1-30) and the placement of mini-osmotic pumps delivering LANP(1-30) at a rate of 1 microg/hr for 72 hours. Group 3 (controls, n = 6) was used to measure the baseline creatinine level and had no renal ischemia or surgery.

RESULTS

Seventy-two hours post-renal ischemia, the weight loss in the ischemia group was similar to the peptide treated group (7.65 +/- 1.14% and 10.03 +/- 0.9% body weight loss, respectively, p = 0.126). The ischemia group had significantly higher creatinine levels compared to the controls (66.3 +/- 5.3 versus 30.1 +/- 0.9 micromol/L, p = 0.002). The peptide-treated group had higher creatinine (174.1 +/- 77.8 versus 66.3 +/- 5.3 micromol/L, p = 0.035) and LANP(1-30) levels (673.14 +/- 69.64 versus 45.83 +/- 8.45 pg/mL, p = 0.001) than the ischemia group.

CONCLUSION

Prolonged use of LANP(1-30) has no renal protective effect.

Transgenic overexpression of brain natriuretic peptide prevents the progression of diabetic nephropathy in mice

AIMS/HYPOTHESIS

Brain natriuretic peptide (BNP) is a potent vasorelaxing and natriuretic peptide that is secreted from the heart and has cardioprotective properties. We have previously generated hypotensive transgenic mice (BNP-Tg mice) that overproduce BNP in the liver, which is released into the circulation. Using this animal model, we successfully demonstrated the amelioration of renal injury after renal ablation and in proliferative glomerulonephritis. Glomerular hyperfiltration is an early haemodynamic derangement, representing one of the key mechanisms of the pathogenesis of diabetic nephropathy. Based on the suggested involvement of increased endogenous natriuretic peptides, the aim of this study was to investigate their role in the development and progression of diabetic nephropathy.

MATERIALS AND METHODS

We evaluated the progression of renal injury and fibrogenesis in BNP-Tg mice with diabetes induced by streptozotocin. We also investigated the effect of BNP on high glucose-induced signalling abnormalities in mesangial cells.

RESULTS

After induction of diabetes, control mice exhibited progressively increased urinary albumin excretion with impaired renal function, whereas these changes were significantly ameliorated in BNP-Tg mice. Notably, diabetic BNP-Tg mice revealed minimal mesangial fibrogenesis with virtually no glomerular hypertrophy. Glomerular upregulation of extracellular signal-regulated kinase, TGF-beta and extracellular matrix proteins was also significantly inhibited in diabetic BNP-Tg mice. In cultured mesangial cells, activation of the above cascade under high glucose was abrogated by the addition of BNP.

CONCLUSIONS/INTERPRETATION

Chronic excess of BNP prevents glomerular injury in the setting of diabetes, suggesting that renoprotective effects of natriuretic peptides may be therapeutically applicable in preventing the progression of diabetic nephropathy.

Perioperative acute renal failure

PURPOSE OF REVIEW

Recent biochemical evidence increasingly implicates inflammatory mechanisms as precipitants of acute renal failure. In this review, we detail some of these pathways together with potential new therapeutic targets.

RECENT FINDINGS

Neutrophil gelatinase-associated lipocalin appears to be a sensitive, specific and reliable biomarker of renal injury, which may be predictive of renal outcome in the perioperative setting. For estimation of glomerular filtration rate, cystatin C is superior to creatinine. No drug is definitively effective at preventing postoperative renal failure. Clinical trials of fenoldopam and atrial natriuretic peptide are, at best, equivocal. As with pharmacological preconditioning of the heart, volatile anaesthetic agents appear to offer a protective effect to the subsequently ischaemic kidney.

SUMMARY

Although a greatly improved understanding of the pathophysiology of acute renal failure has offered even more therapeutic targets, the maintenance of intravascular euvolaemia and perfusion pressure is most effective at preventing new postoperative acute renal failure. In the future, strategies targeting renal regeneration after injury will use bone marrow-derived stem cells and growth factors such as insulin-like growth factor-1.

Which of the cardiac natriuretic peptides is most effective for the treatment of congestive heart failure, renal failure and cancer?

Cardiac natriuretic peptides consist of a family of six peptide hormones that are synthesised by three separate genes and then stored as three separate prohormones (i.e. 126 amino acid atrial natriuretic peptide (ANP), 108 amino acid B-type natriuretic peptide (BNP) and 103 amino acid C-type natriuretic peptide (CNP) prohormones). The ANP prohormone contains four peptide hormones: long-acting natriuretic peptide (LANP), vessel dilator, kaliuretic peptide and ANP. 2. Currently, the only natriuretic peptide available commercially to treat congestive heart failure (CHF) is BNP (Nesiritide/Natrecor; SCIOS, Sunnyvale, CA, USA), which causes a small increase in the urine volume of 90 38 mL/h compared with 67 27 mL/h and no significant natriuresis, but has beneficial haemodynamic effects in acute CHF individuals. These haemodynamic effects probably contribute to the side-effects of BNP in patients with acute CHF with a 27% incidence of hypotension and possibly to 22% worsening of renal function, defined as an increase in serum creatinine of 0.5 mg/dL, associated with a worse prognosis. A review of clinical trials suggests a twofold increased risk of death at 30 days post-nesiritide treatment, a finding that needs further investigation. 3. The best of the natriuretic peptides for treating chronic CHF is the vessel dilator, which increases urinary flow up to 13-fold and sodium excretion up to fourfold, without the previously mentioned side-effects. The natriuretic and diuretic effects of vessel dilators last 6 h, which would allow them to be used on a four times per day basis in treating chronic CHF. 4. Atrial natriuretic peptide does not cause significant improvement in acute renal failure (ARF) in humans. The only natriuretic peptide that significantly improves ARF is the vessel dilator. Even when ARF has been established for 2 days before treatment in an ischaemic ARF animal model, vessel dilator decreases serum creatinine from 8.2 0.5 to 0.98 0.12 mg/dL in 6 days. At day 6 of ARF, mortality decreases to 14% (from 88%) without the vessel dilator. After 6 days of treatment with the vessel dilator, the proximal and distal tubules regenerate. 5. In cancer, vessel dilator, LANP, kaliuretic peptide and ANP at 1 mmol/L, decrease up to 97% of human breast, pancreatic and prostate adenocarcinoma cells, as well as small cell and squamous cell lung cancer cells within 24 h. In vivo, vessel dilator, LANP and kaliuretic peptide completely stop the growth of human pancreatic adenocarcinomas in athymic mice and decrease their tumour volume by 49, 28 and 11%, respectively in 1 week.

Natriuretic Peptides in Acute and Chronic Kidney Disease and during Renal Replacement Therapy

Plasma levels of natriuretic peptides are elevated in patients with chronic kidney disease owing to impairment of renal function, hypertension, hypervolemia, and/or concomitant heart disease. Proteinuria and/or immunosuppression also contribute to enhanced plasma levels and increased urinary excretion of natriuretic peptides. Atrial natriuretic peptide (ANP) and particularly brain natriuretic peptide (BNP) levels are linked independently to left ventricular mass and function and predict total and cardiovascular mortality. ANP and BNP decrease significantly during hemodialysis treatment but increase again during the interdialytic interval. Intraperitoneal administration of ANP decreases peritoneal fluid and glucose absorption, as well as lymphatic flow rate. Successful kidney transplant normalizes the plasma levels of natriuretic peptides in the majority of patients. In experimental animals but not in humans, ANP administration protects against ischemic acute renal failure. Since proANP31-67 peptide does not cause hypotension, this vessel dilator may protect the kidney during acute renal failure by intrarenal vasodilation and stimulation of endogenous prostaglandin E2 synthesis.

The role of atrial natriuretic peptide in the immune system

Atrial natriuretic peptide (ANP) is a hormone predominately produced by the heart atria which regulates the water and salt balance as well as blood pressure homeostasis. Being expressed in various parts of the immune system a link of the peptide to the immune system has been proposed. In fact, this review focus on effects of ANP in the immune system and reports about the role of the peptide in innate immune functions as well as in the adaptive immune response.

Differential effects of human atrial natriuretic peptide and furosemide on glomerular filtration rate and renal oxygen consumption in humans

OBJECTIVE

Imbalance in the renal medullary oxygen supply/demand relationship can cause hypoxic medullary damage and ischemic acute renal failure. Human atrial natriuretic peptide (h-ANP) increases glomerular filtration rate in clinical acute renal failure. This would increase renal oxygen consumption due to increased tubular load of sodium. Loop diuretics are commonly used in acute renal failure. Data on the effects of loop diuretics on glomerular filtration rate and renal oxygen consumption in humans are, however, controversial. We evaluated the effects of h-ANP and furosemide on renal oxygen consumption, glomerular filtration rate, and renal hemodynamics in humans.

DESIGN AND SETTING

Prospective two-agent interventional study in a university hospital cardiothoracic ICU.

PATIENTS

Nineteen uncomplicated, mechanically ventilated postcardiac surgery patients with normal renal function.

INTERVENTIONS

h-ANP (25 and 50 ng/kg per minute, n=10) or furosemide (0.5 mg/kg per hour, n=9).

MEASUREMENTS AND RESULTS

Renal plasma flow and glomerular filtration rate were measured using the infusion clearance technique for (51)Cr-labeled EDTA and paraaminohippurate, corrected for by renal extraction of PAH. h-ANP increased glomerular filtration rate, renal filtration fraction, fractional excretion of sodium, and urine flow. This was accompanied by an increase in tubular sodium reabsorption (9%) and renal oxygen consumption (26%). Furosemide infusion caused a 10- and 15-fold increase in urine flow and fractional excretion of sodium, respectively, accompanied by a decrease in tubular sodium reabsorption (-28%), renal oxygen consumption (-23%), glomerular filtration rate and filtration fraction (-12% and -7%, respectively).

CONCLUSIONS

The filtered load of sodium is an important determinant of renal oxygen consumption. h-ANP improves glomerular filtration rate but does not have energy-conserving tubular effects. In contrast, furosemide decreases tubular sodium reabsorption and renal oxygen consumption and thus has the potential to improve the oxygen supply/demand relationship in clinical ischemic acute renal failure.

Acute renal failure: definitions, diagnosis, pathogenesis, and therapy

Acute renal failure (ARF), characterized by sudden loss of the ability of the kidneys to excrete wastes, concentrate urine, conserve electrolytes, and maintain fluid balance, is a frequent clinical problem, particularly in the intensive care unit, where it is associated with a mortality of between 50% and 80%. In this review, the epidemiology and pathophysiology of ARF are discussed, including the vascular, tubular, and inflammatory perturbations. The clinical evaluation of ARF and implications for potential future therapies to decrease the high mortality are described.

Science review: natriuretic peptides in critical illness

The present review will cover the mechanisms of release and the potential pathophysiological role of different natriuretic peptides in critically ill patients. By focusing on the cardiovascular system, possible implications of natriuretic peptides for diagnosis and treatment will be presented. In critical illness such as sepsis, trauma or major surgery, systemic hypotension and an intrinsic myocardial dysfunction occur. Impairment of the cardiovascular system contributes to poor prognosis in severe human sepsis. Natriuretic peptides have emerged as valuable marker substances to detect left ventricular dysfunction in congestive heart failure of different origins. Increased plasma levels of circulating natriuretic peptides, atrial natriuretic peptide, N-terminal pro-atrial natriuretic peptide, brain natriuretic peptide and its N-terminal moiety N-terminal pro-brain natriuretic peptide have also been found in critically ill patients. All of these peptides have been reported to reflect left ventricular dysfunction in these patients. The increased wall stress of the cardiac atria and ventricles is followed by the release of these natriuretic peptides. Furthermore, the release of atrial natriuretic peptide and brain natriuretic peptide might be triggered by members of the IL-6-related family and endotoxin in the critically ill. Apart from the vasoactive actions of circulating natriuretic peptides and their broad effects on the renal system, anti-ischemic properties and immunological functions have been reported for atrial natriuretic peptide. The early onset and rapid reversibility of left ventricular impairment in patients with good prognosis associated with a remarkably augmented plasma concentration of circulating natriuretic peptides suggest a possible role of these hormones in the monitoring of therapy success and the estimation of prognosis in the critically ill.

Recombinant human atrial natriuretic peptide in ischemic acute renal failure: A randomized placebo-controlled trial*

OBJECTIVE

Acute renal failure is associated with significant morbidity and mortality rates. Need for dialysis is an independent risk factor for early mortality after complicated cardiac surgery. Human atrial natriuretic peptide (h-ANP) is a potent endogenous natriuretic and diuretic substance. Exogenous administration of h-ANP increases glomerular filtration rate and renal blood flow in clinical acute renal failure. We have studied the effects of h-ANP on renal outcome in ischemic acute renal failure.

DESIGN

A prospective, double-blind, randomized, placebo-controlled study.

SETTING

Cardiothoracic intensive care units of two tertiary care centers.

PATIENTS

Sixty-one patients with normal preoperative renal function suffering from postcardiac surgical heart failure requiring significant inotropic and vasoactive support.

INTERVENTIONS

The patients were randomized to receive a continuous infusion of either recombinant h-ANP (50 ng.kg(-1).min(-1)) or placebo when serum creatinine increased by >50% from baseline. The treatment with h-ANP/placebo continued until serum creatinine decreased below the trigger value for inclusion or the patients fulfilled predefined criteria for dialysis.

MEASUREMENTS AND MAIN RESULTS

The primary outcome variable was dialysis on or before day 21 after the start of treatment. Secondary renal outcome variables were dialysis-free survival at day 21 and creatinine clearance. Twenty-nine patients were assigned h-ANP and 30 placebo. Six (21%) patients in the h-ANP group compared with 14 (47%) in the placebo group needed dialysis before or at day 21 (hazard ratio, 0.28; 95% confidence interval, 0.10-0.73; p =.009). Eight (28%) patients in the h-ANP group compared with 17 (57%) in the placebo group suffered from the combined end point dialysis or death before or at day 21 (hazard ratio, 0.35; 95% confidence interval, 0.14-0.82; p =.017). h-ANP improved creatinine clearance in contrast to placebo (p =.040).

CONCLUSIONS

Infusion of h-ANP at a rate of 50 ng.kg(-1).min(-1) enhances renal excretory function, decreases the probability of dialysis, and improves dialysis-free survival in early, ischemic acute renal dysfunction after complicated cardiac surgery.

Atrial natriuretic peptide infusion improves ischemic renal failure after suprarenal abdominal aortic cross-clamping in dogs

OBJECTIVE

The suprarenal abdominal aortic cross-clamping during aortic aneurysm repair causes renal dysfunction after surgery. Atrial natriuretic peptide (ANP), a hormone synthesized by the cardiac atria, induces diuresis-natriuresis and increases glomerular filtration rate. Therefore, we tested the hypothesis that prophylactic ANP infusion could limit the development of acute renal failure after aortic cross-clamping.

DESIGN

Prospective, comparative, experimental study.

SETTING

Laboratory at a university hospital.

SUBJECTS

Twelve male beagle dogs (10-13 kg) with mechanical ventilation under pentobarbital anesthesia.

INTERVENTIONS

A catheter was inserted into the femoral vein, and lactated Ringer solution (10 mL/kg/hr) was administered throughout the study period. Two groups of animals were studied: the control group (n = 6), which received saline vehicle before and after suprarenal abdominal aortic cross-clamping for 1.5 hrs; and the ANP group (n = 6), which received ANP (1 microg/kg/min) for 5 hrs, starting from 10 mins before suprarenal abdominal aortic cross-clamping until the end of procedure.

MEASUREMENTS AND MAIN RESULTS

Changes in systemic and renal hemodynamics, blood gases, and renal function were measured at baseline and 1, 2, 3, 4, and 5 hrs after aortic cross-clamping. After aortic cross-clamping, urine volume, renal blood flow, and creatinine clearance significantly (p <.01) decreased, and serum creatinine concentrations significantly (p <.01) increased, but these effects were limited by continuous ANP infusion.

CONCLUSIONS

The present study shows that ANP infusion preserved renal function after suprarenal abdominal aortic cross-clamping in dogs. These results justify a trial of ANP infusion in humans during aortic aneurysm repair.

Natriuretic peptides and acute renal failure

Atrial natriuretic peptides (ANPs) are a family of peptide hormones, e.g., ANP, long-acting natriuretic peptide, vessel dilator, and kaliuretic peptide synthesized by the ANP gene. Brain natriuretic peptide (BNP) and C-type natriuretic peptide are also members of this family but are synthesized by separate genes. Within the kidney, the ANP prohormone's posttranslational processing is different from that of other tissues, resulting in an additional four amino acids added to the NH2 terminus of ANP (e.g., urodilatin). Each of these natriuretic and diuretic peptides increases within the circulation with acute renal failure (ARF). Renal transplantation but not hemodialysis returns their circulating concentrations to those of healthy individuals. BNP and adrenomedullin, a 52-amino acid natriuretic peptide, have beneficial effects on glomerular hypertrophy and glomerular injury but do not improve tubular injury (i.e., acute tubular necrosis). Vessel dilator ameliorates acute tubular necrosis with regeneration of the brush borders of proximal tubules. Vessel dilator decreases mortality in ARF from 88 to 14% at day 6 of ARF, even when given 2 days after renal failure has been established.

Using a dopamine type 1A receptor agonist in high-risk patients to ameliorate contrast-associated nephropathy

OBJECTIVE

The objective of our study was to evaluate the effects of fenoldopam mesylate, a dopamine type 1A receptor agonist and a potent renal vasodilator that markedly increases renal blood flow, on kidney function of patients who were receiving iodinated contrast material for an interventional procedure and thought to be at high risk of contrast-associated nephropathy.

MATERIALS AND METHODS

We retrospectively reviewed the records of all patients who received fenoldopam mesylate to determine the acute and, when possible, the longer term effects on kidney function.

RESULTS

Twenty-nine cases were reviewed. The average serum creatinine value before contrast administration was 2.55 mg/dL (range, 1.3-5.8 mg/dL) [corrected]. Twenty-four hours after contrast administration, serum creatinine was measured in 28 of the 29 patients. The serum creatinine values had decreased in 16 of the 28 patients by an average of 0.55 mg/dL [corrected]. In nine patients, the serum creatinine value had not changed. Two of the three increases in the serum creatinine value appear to have been caused primarily by problems that did not involve the contrast material.

CONCLUSION

The use of fenoldopam mesylate at appropriate doses offers patients at high risk for contrast-associated nephropathy a chance to avoid this complication. To learn the extent and true nature of the effect of fenoldopam mesylate in this patient population requires a rigorous scientific trial, which is currently underway.

Overexpression of brain natriuretic peptide in mice ameliorates immune-mediated renal injury

One of major causes of end-stage renal disease is glomerulonephritis, the treatment of which remains difficult clinically. It has already been shown that transgenic mice that overexpress brain natriuretic peptide (BNP), with a potent vasorelaxing and natriuretic property, have ameliorated glomerular injury after subtotal nephrectomy. However, the role of natriuretic peptides in immune-mediated renal injury still remains unknown. Therefore, the effects of chronic excess of BNP on anti-glomerular basement membrane nephritis induced in BNP-transgenic mice (BNP-Tg) were investigated and the mechanisms how natriuretic peptides act on mesangial cells in vitro were explored. After induction of nephritis, severe albuminuria (approximately 21-fold above baseline), tissue damage, including mesangial expansion and cell proliferation, and functional deterioration developed in nontransgenic littermates. In contrast, BNP-Tg exhibited much milder albuminuria (approximately fourfold above baseline), observed only at the initial phase, and with markedly ameliorated histologic and functional changes. Up-regulation of transforming growth factor-beta (TGF-beta) and monocyte chemoattractant protein-1 (MCP-1), as well as increased phosphorylation of extracellular signal-regulated kinase (ERK), were also significantly inhibited in the kidney of BNP-Tg. In cultured mesangial cells, natriuretic peptides counteracted the effects of angiotensin II with regard to ERK phosphorylation and fibrotic action. Because angiotensin II has been shown to play a pivotal role in the progression of nephritis through induction of TGF-beta and MCP-1 that may be ERK-dependent, the protective effects of BNP are likely to be exerted, at least partly, by antagonizing the renin-angiotensin system locally. The present study opens a possibility of a novel therapeutic potential of natriuretic peptides for treating immune-mediated renal injury.

Long-term infusion of atrial natriuretic peptide (ANP) improves renal blood flow and glomerular filtration rate in clinical acute renal failure

BACKGROUND

Short-term infusion of atrial natriuretic peptide (ANP) increases renal blood flow (RBF) and glomerular filtration rate (GFR) in patients with acute renal dysfunction. In the present study we evaluated the effects of long-term infusion (>48 h) of ANP on (RBF) and (GFR) in 11 postcardiac surgical patients requiring pharmacological circulatory support and with acute renal impairment.

METHODS

Urinary clearance of Cr-EDTA and PAH as well as central hemodynamic measurements were performed for 2-3 consecutive 30-min periods during ANP infusion (50 ng. kg-1. min-1), one hour after abrupt discontinuation of ANP and again immediately after reinstitution of ANP infusion.

RESULTS

During ANP infusion, urine flow (UF), GFR, RBF and renal vascular resistance (RVR) were 6.4+/-1.1 ml. min-1, 19.9+/-3.1 ml. min-1, 408+/-108 ml. min-1 and 0.286+/-0.054 mmHg. min. ml-1, respectively. UF, GFR and RBF decreased significantly by 28% (P<0.001), 32% (P<0.01) and 31% (P<0.05), respectively when ANP infusion was discontinued. RVR increased by 93% (P<0.05) while there was no change in filtration fraction. After reinstitution of ANP infusion, all measured renal variables returned to baseline. There was no significant correlation between the number of ANP treatment days and the percentage decrease in GFR (r=0.18) or RBF (r=0.22) during ANP withdrawal. Central hemodynamic variables were not affected by ANP withdrawal.

CONCLUSIONS

ANP infusion improves RBF and GFR in patients with acute renal impairment after cardiac surgery. This renal vasodilatory effect is maintained during a long-term infusion and seems to be hemodynamically safe.

Changes in intrarenal oxygenation as evaluated by BOLD MRI in a rat kidney model for radiocontrast nephropathy

The pathogenesis of radiocontrast nephropathy is poorly understood. In an animal model, inhibition of the synthesis of nitric oxide and prostaglandins appears to predispose rats to severe renal injury following the administration of radiocontrast. Here we have investigated whether administration of radiocontrast, as well as changes in renal medullary oxygenation following pharmacologic inhibition of nitric oxide and prostaglandin synthesis, might be evaluated by blood oxygenation level-dependent (BOLD) MRI. Nineteen anesthetized (Inactin 100 mg/kg) rats were studied. BOLD MRI measurements were performed following administration of L-NAME (N-nitro-L-arginine methyl ester, 10 mg/kg), Indomethacin (10 mg/kg), and a radiocontrast agent (sodium iothalamate 60%, 6 mL/kg). Marked sequential changes in medullary R(*)(2), presumably reflecting decline in medullary pO(2), were noted after each of the pharmacological interventions employed. These results, obtained by noninvasive MRI, are consistent with prior direct recordings of pO(2) and doppler flow in the rat renal medulla after administration of L-NAME, Indomethacin and iothalamate. Medullary oxygenation in rats was reduced by inhibition of the synthesis of prostaglandins and nitric oxide, as well as by intravenous injection of radiocontrast agents. BOLD MRI can noninvasively evaluate changes in medullary oxygenation in rats that appear to predispose acute renal failure. J. Magn. Reson. Imaging 2001;13:744-747.

New pharmacologic options for renal preservation

The understanding of the cause and pathophysiology of renal failure has guided the rational development of pharmacologic renoprotective strategies. Although traditionally anesthesiologists have focused on renal hemodynamic derangements, newer information suggests that cellular interactions amplify and perpetuate the insult. Consequently, the potential renoprotective armamentarium not only encompasses the more traditional vasoactive agents but also therapeutic approaches that may modify the cellular response to injury. Although few of these agents have reached the clinical arena, preliminary work suggests that this new approach to renal injury and protection may be promising.

Novel approaches to the treatment of acute renal failure

Acute renal failure (ARF) occurs frequently in hospitalised patients and is associated with significant morbidity and mortality. Many therapeutic strategies have been undertaken both to prevent acute renal injury and, once ARF occurs, to improve renal function and reduce mortality. Among the available pharmacological options, no specific therapy has been shown to alter the course of ARF. This article reviews the efficacy of several strategies in experimental renal disease and raises the possibility that similar interventions might be available to the clinician in the near future for the prevention and management of ARF. The prospect of these novel strategies together with the ever-increasing understanding of the complex pathophysiology of ARF, offers the promise of effective and more physiological therapeutic interventions in this new millennium.

Ameliorated glomerular injury in mice overexpressing brain natriuretic peptide with renal ablation

Brain natriuretic peptide (BNP) is a cardiac hormone produced by the ventricle, and its secretion is markedly increased in heart failure, hypertension, and renal failure. Transgenic mice that overexpress BNP in the liver (BNP-Tg) were recently generated, resulting in low BP. To elucidate the role of BNP in renal pathophysiology, the effect of chronic excess of BNP in transgenic mice on glomerular injury after subtotal nephrectomy induced by resection of the renal poles was examined. After nephrectomy, glomerular cross-sectional areas in control nontransgenic mice markedly increased as compared with those in sham-operated mice (+81 +/- 7%), whereas there was only a modest increase in BNP-Tg (+10 +/- 6%). Expansion of the mesangial area and increase in the intraglomerular cell number were also inhibited in BNP-Tg. Glomerular expressions of transforming growth factor-beta and fibronectin were increased with hypertrophy and were significantly suppressed in BNP-Tg. Furthermore, increases in the urinary albumin excretion and BP were significantly ameliorated in BNP-Tg. Chronic hydralazine treatment in nephrectomized nontransgenic mice failed to inhibit glomerular hypertrophy. These findings indicate that the chronic excess of BNP in mice ameliorates glomerular hypertrophy and mesangial expansion after renal ablation. The results also suggest that the observed effects of natriuretic peptides under reduced renal mass are not due merely to systemic BP reduction and may be therapeutically applicable in various renal diseases.

Amelioration with vessel dilator of acute tubular necrosis and renal failure established for 2 days

Seventeen Sprague-Dawley rats had ischemic nonoliguric acute renal failure (ARF) induced by vascular clamping resulting in their preischemic blood urea nitrogen (BUN) and creatinine levels of 16 +/- 1 and 0.56 +/- 0.05 mg/dl to increase to 162 +/- 4 and 8.17 +/- 0.5 mg/dl, P < 0.001, respectively, at day 4 of postischemia. Vessel dilator, a 37-amino-acid cardiac peptide hormone (0.3 microg x kg(-1) x min(-1) ip), decreased the BUN and creatinine levels to 53 +/- 17 mg/dl and 0.98 +/- 0.12 mg/dl (P < 0.001) in another seven animals where ARF had been established for 2 days. Water excretion doubled with ARF and was further augmented by vessel dilator. Transthoracic echocardiography revealed left ventricular dilation as a probable cause of the increase in vessel dilator in the circulation with ARF, and vessel dilator infusion reversed this dilation. At day 6 of ARF, mortality decreased to 14% with vessel dilator from 88% without vessel dilator. Acute tubular necrosis was <5% in the vessel dilator-treated rats compared with 25% to >75% in the placebo-treated ARF animals. We conclude that vessel dilator improves acute tubular necrosis and renal function in established ARF.

Evaluation of changes in intrarenal oxygenation in rats using multiple gradient-recalled echo (mGRE) sequence

Changes in intrarenal oxygenation in rats during pharmacological stimuli were evaluated with a multiple gradient-recalled echo (mGRE) sequence. With administration of the loop diuretic furosemide, oxygenation in the medulla improved; acetazolamide, a proximal tubular diuretic, produced no significant change. These results are consistent with our previous studies in humans and resemble earlier studies of medullary oxygenation using oxygen microelectrodes in anesthetized rats. The technique may be useful in the evaluation of therapeutic strategies in animal models of pathophysiological states such as acute renal failure.

Prevention of Kupffer cell-induced oxidant injury in rat liver by atrial natriuretic peptide

The generation of reactive oxygen species (ROS) by activated Kupffer cells contributes to liver injury following liver preservation, shock, or endotoxemia. Pharmacological interventions to protect liver cells against this inflammatory response of Kupffer cells have not yet been established. Atrial natriuretic peptide (ANP) protects the liver against ischemia-reperfusion injury, suggesting a possible modulation of Kupffer cell-mediated cytotoxicity. Therefore, we investigated the mechanism of cytoprotection by ANP during Kupffer cell activation in perfused rat livers of male Sprague-Dawley rats. Activation of Kupffer cells by zymosan (150 microgram/ml) resulted in considerable cell damage, as assessed by the sinusoidal release of lactate dehydrogenase and purine nucleoside phosphorylase. Cell damage was almost completely prevented by superoxide dismutase (50 U/ml) and catalase (150 U/ml), indicating ROS-related liver injury. ANP (200 nM) reduced Kupffer cell-induced injury via the guanylyl cyclase-coupled A receptor (GCA receptor) and cGMP: mRNA expression of the GCA receptor was found in hepatocytes, endothelial cells, and Kupffer cells, and the cGMP analog 8-bromo-cGMP (8-BrcGMP; 50 microM) was as potent as ANP in protecting from zymosan-induced cell damage. ANP and 8-BrcGMP significantly attenuated the prolonged increase of hepatic vascular resistance when Kupffer cell activation occurred. Furthermore, both compounds reduced oxidative cell damage following infusion of H2O2 (500 microM). In contrast, superoxide anion formation of isolated Kupffer cells was not affected by ANP and only moderately reduced by 8-BrcGMP. In conclusion, ANP protects the liver against Kupffer cell-related oxidant stress. This hormonal protection is mediated via the GCA receptor and cGMP, suggesting that the cGMP receptor plays a critical role in controlling oxidative cell damage. Thus ANP signaling should be considered as a new pharmacological target for protecting liver cells against the inflammatory response of activated Kupffer cells without eliminating the vital host defense function of these cells.

Therapeutic use of the natriuretic peptide ularitide in acute renal failure

BACKGROUND

Ularitide is a member of the natriuretic peptide family. This hormone exhibits an N-terminal extension by four amino acids compared with atrial natriuretic peptide. Ularitide was shown to exert strong diuretic and natriuretic effects when infused intravenously. Its main action sites are the glomerulum, inducing preglomerular vasodilation and postglomerular vasoconstriction and thereby elevating the glomerular filtration rate, and the tubular system inhibiting Na(+)-reabsorption. In initial uncontrolled clinical trials, this peptide was shown to have beneficial effects in patients suffering from oliguric acute renal failure.

METHODS

We conducted a double-blind, placebo-controlled, multicenter, dose-finding trial recruiting 176 patients randomized into 4 different Ularitide doses groups (U5, U20, U40, and U80 ng/kg/min) and a placebo group (U0). Ularitide/placebo infusion was performed for 5 days with half the originally infused dose on day 5. The primary objective of the study was to test various doses of Ularitide in patients suffering from oliguric acute renal failure to avoid mechanical renal replacement therapy during the first 12 hours.

FINDINGS

The results indicate that Ularitide does not reduce the incidence of mechanical renal replacement therapy compared with placebo-treated patients during the first 12 h of treatment (U0: 36 (20), U5: 35 (11), U20: 36 (9), U40: 28 (8), U80: 41 (12), (% (n) (p = 0.87)). Diuresis increased in the Ularitide-treated groups and the placebo group after onset of infusion and did not show any significant difference in the first 12 h collection period (U0: 576, U5: 514, U20: 500, U40: 360, U80: 158 ML/12h (Median), (p = 0.16)).

INTERPRETATION

In summary, the incidence of mechanical renal replacement therapy in critically ill patients suffering from oliguric acute renal failure could not be altered positively by Ularitide administration according to our protocol. Further prospective clinical trials are needed to answer the question whether a different patient collective or a prophylactic administration of Ularitide are more promising approaches in the clinical setting of oliguric acute renal failure.

The guanylate cyclase-coupled natriuretic peptide receptor: a new target for prevention of cold ischemia-reperfusion damage of the rat liver

The aim of our studies was to investigate hormonal prevention of hepatic preservation damage by the atrial natriuretic peptide (ANP) and the mechanisms involved. Isolated perfusion of rat livers was performed in a nonrecirculating fashion. Twenty minutes of preischemic perfusion was performed with or without different concentrations of ANP, followed by 24-hour storage in cold University of Wisconsin (UW) solution. Two hundred nanomoles of ANP prevented hepatocellular damage during a 2-hour reperfusion period as indicated by a marked attenuation of the sinusoidal efflux of lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP), and by reduced Trypan blue uptake. Furthermore, postischemic bile flow as an indicator of liver function was significantly improved by about 60% with 200 nmol/L ANP. No protection was conveyed by 20 nmol/L ANP nor by pretreatment with 200 nmol/L ANP for only 10 minutes. The effects of ANP seemed to be mediated by the guanylate cyclase-coupled A (GC-A) receptor and cyclic guanosine monophosphate (cGMP): whereas expression of both GC-A and GC-B receptors as well as of the GC-C receptor was found, cGMP did protect from ischemia-reperfusion damage, but selective ligands of the B and C receptor did not. To begin to determine the mechanisms of ANP-mediated protection, different parameters were investigated: ANP had no effect on portal pressure as an indicator of hepatic circulation, nor on intracellular energy depletion determined by adenosine nucleotide concentration. However, the marked augmentation of nuclear factor kappaB (NF-kappaB) binding activity during reperfusion was prevented in ANP-pretreated livers. In conclusion, pretreatment with ANP protects the rat liver from cold ischemia-reperfusion damage. This effect is mediated via the GC-A receptor and cGMP, and may be linked to an influence of ANP on NF-kappaB activation. Thus, ANP signaling via the GC-A receptor should be considered as a new pharmacological target to prevent preservation injury of the liver.

Anaritide in acute tubular necrosis. Auriculin Anaritide Acute Renal Failure Study Group

BACKGROUND

Atrial natriuretic peptide, a hormone synthesized by the cardiac atria, increases the glomerular filtration rate by dilating afferent arterioles while constricting efferent arterioles. It has been shown to improve glomerular filtration, urinary output, and renal histopathology in laboratory animals with acute renal dysfunction. Anaritide is a 25-amino-acid synthetic form of atrial natriuretic peptide.

METHODS

We conducted a multicenter, randomized, double-blind, placebo-controlled clinical trial of anaritide in 504 critically ill patients with acute tubular necrosis. The patients received a 24-hour intravenous infusion of either anaritide (0.2 microgram per kilogram of body weight per minute) or placebo. The primary end point was dialysis-free survival for 21 days after treatment. Other end points included the need for dialysis, changes in the serum creatinine concentration, and mortality.

RESULTS

The rate of dialysis-free survival was 47 percent in the placebo group and 43 percent in the anaritide group (P = 0.35). In the prospectively defined subgroup of 120 patients with oliguria (urinary output, < 400 ml per day), dialysis-free survival was 8 percent in the placebo group (5 of 60 patients) and 27 percent in the anaritide group (16 of 60 patients, P = 0.008). Anaritide-treated patients with oliguria who no longer had oliguria after treatment benefited the most. Conversely, among the 378 patients without oliguria, dialysis-free survival was 59 percent in the placebo group (116 of 195 patients) and 48 percent in the anaritide group (88 of 183 patients, P = 0.03).

CONCLUSIONS

The administration of anaritide did not improve the overall rate of dialysis-free survival in critically ill patients with acute tubular necrosis. However, anaritide may improve dialysis-free survival in patients with oliguria and may worsen it in patients without oliguria who have acute tubular necrosis.