Natriuretic peptides and acute renal failure

Hormonal Regulation of Renal Fibrosis

Fibrosis is a severe complication of many acute and chronic kidney pathologies. According to current concepts, an imbalance in the synthesis and degradation of the extracellular matrix by fibroblasts is considered the key cause of the induction and progression of fibrosis. Nevertheless, inflammation associated with the damage of tissue cells is among the factors promoting this pathological process. Most of the mechanisms accompanying fibrosis development are controlled by various hormones, which makes humoral regulation an attractive target for therapeutic intervention. In this vein, it is particularly interesting that the kidney is the source of many hormones, while other hormones regulate renal functions. The normal kidney physiology and pathogenesis of many kidney diseases are sex-dependent and thus modulated by sex hormones. Therefore, when choosing therapy, it is necessary to focus on the sex-associated characteristics of kidney functioning. In this review, we considered renal fibrosis from the point of view of vasoactive and reproductive hormone imbalance. The hormonal therapy possibilities for the treatment or prevention of kidney fibrosis are also discussed.

New drugs for acute kidney injury

PURPOSE OF REVIEW

To describe recent advances in the development of therapeutic agents for acute kidney injury (AKI).

RECENT FINDINGS

Traditional care for AKI is mostly supportive. At present, no specific therapy has been developed to prevent or treat AKI. However, based on a better understanding of the pathophysiology of AKI, various potential compounds have been recently identified and tested. A variety of pathways has been targeted, including oxidative and mitochondrial stress, cellular metabolism and repair, inflammation, apoptosis and hemodynamics. Many of these potential agents are currently ongoing early-phase clinical trials, and the purpose of this review is to provide a summary of those with the most potential.

SUMMARY

Despite the lack of therapies specifically approved for AKI, many interesting potential agents are entering clinical trials, with the potential to transform the care of patients with AKI.

NT-pro-BNP as marker for cardiac strain that may be caused by high-output arteriovenous shunting in a haemodialysis patient. A case report

BACKGROUND

An arteriovenous fistula (AVF) is the first choice when considering access for haemodialysis (HD). When a forearm AVF fails an upper arm AVF is a frequent subsequent dialysis access option. The latter may cause cardiac strain. NT-pro-B-type natriuretic peptide (NT-NT-proBNP) is a marker used to estimate volume overload and cardiac strain. This case report shows the benefit of using longitudinal individual follow-up of pre-dialysis NT-proBNP in clinical practice to detect changes in cardiac condition that may be due to high-output AVF.

CASE PRESENTATION

An 18 years old patient performed HD via an upper arm AVF before he was admitted to our unit. NT-proBNP was above the upper detection level of 70,000 ng/L. Echocardiography revealed a left-ventricular cardiac insufficiency. Interdialytic weight gain (IDWG) was above 5%. He was instructed to lower fluid intake and IDWG towards 2%. Four months later NT-proBNP surpassed 70,000 ng/L again. Flow in the brachial artery was at 3034 ml/min. Reconstructive surgery of the AVF did not reduce flow and NT-proBNP in the long run. Clinically, he worsened to NYHA class III-IV. It was decided to close the upper arm AVF and to replace it with a lower arm AVF leading to a reduced artery flow of 1344 mL/min. The clinical condition successively recovered and NT-proBNP decreased to 7000 ng/L.

CONCLUSIONS

Pre-dialysis NT-proBNP should be considered as a suitable routine marker for cardiac strain such as caused by high-output AVF besides variables such as IDWG. Brachial artery flow besides AVF flow measurement is helpful.

Neprilysin, the kidney brush border neutral proteinase: a possible potential target for ischemic renal injury

Neprilysin (NEP) is an endogenously induced peptidase for modulating production and degradation of various peptides in humans. It is most abundantly present in kidney and regulates the intrinsic renal homeostatic mechanism. Recently, drugs inhibiting NEP have been approved for the use in heart failure. In the context of increased prevalence of ischemia associated renal failure, NEP could be an attractive target for treating kidney failure. In the kidney, targeting NEP may possess potential benefits as well as adverse consequences. The unfavorable outcomes of NEP are mainly attributed to the degradation of the natriuretic peptides (NPs). NPs are involved in the inhibition of the renin-angiotensin-aldosterone system (RAAS) and activation of the sympathetic system contributing to the tubular and glomerular injury. In contrary, NEP exerts the beneficial effect by converting angiotensin-1 (Ang I) to angiotensin-(1-7) (Ang-(1-7)), thus activating MAS-related G-protein coupled receptor. MAS receptor antagonizes angiotensin type I receptor (AT-1R), reduces reactive oxygen species (ROS) and inflammation, thus ameliorating renal injury. However, the association of NEP with complex cascades of renal ischemia remains vague. Therefore, there is a need to evaluate the putative mechanism of NEP and its overlap with other signaling cascades in conditions of renal ischemia.

Salt Inducible Kinase Signaling Networks: Implications for Acute Kidney Injury and Therapeutic Potential

A number of signal transduction pathways are activated during Acute Kidney Injury (AKI). Of particular interest is the Salt Inducible Kinase (SIK) signaling network, and its effects on the Renal Proximal Tubule (RPT), one of the primary targets of injury in AKI. The SIK1 network is activated in the RPT following an increase in intracellular Na⁺ (Na⁺_in), resulting in an increase in Na,K-ATPase activity, in addition to the phosphorylation of Class IIa Histone Deacetylases (HDACs). In addition, activated SIKs repress transcriptional regulation mediated by the interaction between cAMP Regulatory Element Binding Protein (CREB) and CREB Regulated Transcriptional Coactivators (CRTCs). Through their transcriptional effects, members of the SIK family regulate a number of metabolic processes, including such cellular processes regulated during AKI as fatty acid metabolism and mitochondrial biogenesis. SIKs are involved in regulating a number of other cellular events which occur during AKI, including apoptosis, the Epithelial to Mesenchymal Transition (EMT), and cell division. Recently, the different SIK kinase isoforms have emerged as promising drug targets, more than 20 new SIK2 inhibitors and activators having been identified by MALDI-TOF screening assays. Their implementation in the future should prove to be important in such renal disease states as AKI.

The Kidney as an Endocrine Organ

The column in this issue is supplied by Vinay Acharya, D.O., and Juan Jose Olivero, M.D. Dr. Acharya is a nephrology fellow at Houston Methodist Hospital. He earned his Doctor of Osteopathic Medicine degree at Arizona College of Osteopathic Medicine and completed an internal medicine residency at Houston Methodist Hospital. Dr. Olivero is a nephrologist at Houston Methodist Hospital and a member of the hospital's Nephrology Training Program. He obtained his medical degree from the University of San Carlos School of Medicine in Guatemala and completed his residency and nephrology fellowship at Baylor College of Medicine in Houston, Texas.

Low-dose atrial natriuretic peptide for prevention or treatment of acute kidney injury: a systematic review and meta-analysis

Background

Theoretically, atrial natriuretic peptide (ANP), especially low-dose ANP, is beneficial in acute kidney injury (AKI). In this study, we examined whether low-dose ANP is effective in preventing or treating AKI by conducting an updated systematic review for randomized controlled trials (RCTs).

Method

We searched the Excerpta Medica database (EMBASE), PubMed, and Cochrane CENTRAL databases for RCTs that compare the effects of low-dose ANP (≤ 50 ng/kg/min) with a placebo or conventional therapy in at-risk patients or patients with AKI. The primary outcome was the incidence of new AKI (in prevention RCTs), while the secondary outcomes were in-hospital mortality rate, renal replacement therapy (RRT) requirement, length of hospital and intensive care unit (ICU) stay, incidence of hypotension, and peak serum creatinine levels. The risk-of-bias was evaluated using the Cochrane Collaboration risk-of-bias tool. Trial sequential analysis (TSA) was used for each outcome of interest.

Results

A total of 18 RCTs (16 prevention and two treatment trials) fulfilled our inclusion criteria. In prevention RCTs, the incidence of new AKI was significantly low in the low-dose ANP group (relative risk [RR] = 0.51; 95% confidence interval [CI] = 0.36–0.72; P = 0.0001) compared to the control group. In addition, the low-dose ANP group showed a significantly reduced RRT requirement in both prevention (RR = 0.17; 95% CI = 0.04–0.64; P = 0.009) and treatment (RR = 0.43; 95% CI = 0.20–0.93; P = 0.03) RCTs. Among secondary outcomes, in some cases, low-dose ANP was associated with a reduction in ICU and in-hospital stay. The risk-of-bias assessment and TSA results indicated that the sample sizes and qualities of the RCTs were insufficient to conclude the efficacy of low-dose ANP.

Conclusion

Low-dose ANP might be effective in preventing or treating AKI. However, the evidence accumulated so far is not strong enough to demonstrate ANP’s beneficial effects. The next step is to elucidate the effects of low-dose ANP by conducting multicenter, high-quality, large-sample RCTs.

Trial registration

PROSPERO registry CRD42017068568. Registered 20 June 2017.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2330-z) contains supplementary material, which is available to authorized users.

Guanylyl Cyclase A in Both Renal Proximal Tubular and Vascular Endothelial Cells Protects the Kidney against Acute Injury in Rodent Experimental Endotoxemia Models

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Natriuretic peptides are used, based on empirical observations, in intensive care units as antioliguric treatments. We hypothesized that natriuretic peptides prevent lipopolysaccharide-induced oliguria by activating guanylyl cyclase A, a receptor for natriuretic peptides, in proximal tubules and endothelial cells.

METHODS

Normal Sprague-Dawley rats and mice lacking guanylyl cyclase A in either endothelial cells or proximal tubular cells were challenged with lipopolysaccharide and assessed for oliguria and intratubular flow rate by intravital imaging with multiphoton microscopy.

RESULTS

Recombinant atrial natriuretic peptide efficiently improved urine volume without changing blood pressure after lipopolysaccharide challenge in rats (urine volume at 4 h, lipopolysaccharide: 0.6 ± 0.3 ml · kg · h; lipopolysaccharide + fluid resuscitation: 4.6 ± 2.0 ml · kg · h; lipopolysaccharide + fluid resuscitation + atrial natriuretic peptide: 9.0 ± 4.8 ml · kg · h; mean ± SD; n = 5 per group). Lipopolysaccharide decreased glomerular filtration rate and slowed intraproximal tubular flow rate, as measured by in vivo imaging. Fluid resuscitation restored glomerular filtration rate but not tubular flow rate. Adding atrial natriuretic peptide to fluid resuscitation improved both glomerular filtration rate and tubular flow rate. Mice lacking guanylyl cyclase A in either proximal tubules or endothelium demonstrated less improvement of tubular flow rate when treated with atrial natriuretic peptide, compared with control mice. Deletion of endothelial, but not proximal tubular, guanylyl cyclase A augmented the reduction of glomerular filtration rate by lipopolysaccharide.

CONCLUSIONS

Both endogenous and exogenous natriuretic peptides prevent lipopolysaccharide-induced oliguria by activating guanylyl cyclase A in proximal tubules and endothelial cells.

Natriuretic Peptides in Cardiac Anesthesia and Intensive Care

Natriuretic peptides, predominantly B-type, are widely used in cardiology as prognostic and diagnostic biomarkers or, much less often, as a substantive treatment tool. They are hormones that are produced mainly in the myocardium in response to overload and ischemia, and their level quite accurately reflects the degree of myocardial dysfunction. Although their use in cardiac anesthesia and intensive care setting seems to be very beneficial for assessing the risk of acute disturbance of myocardial function or its laboratory monitoring, the actual significance of natriuretic peptides in this area is not yet recognized. This is due to the lack of clear diagnostic and prognostic values for these biomarkers supported by high-quality researches. On the basis of the available data, main advantages, existing difficulties, and most effective ways of using natriuretic peptides for determining the risk of heart surgery and assessing the severity of sepsis, pneumonia, and other critical conditions have been discussed in this review. In addition, the expediency of using natriuretic peptides as target parameters for goal-oriented therapy and as a substantive tool for treatment is considered.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

Acute kidney injury induces high-sensitivity troponin measurement changes after cardiac surgery

BACKGROUND

The value of cardiac troponin as a risk assessment tool for cardiac disease in the setting of end-stage renal diseases (ESRD) is not equivalent to its value in those with normal renal function. This consideration had not been studied in settings of acute kidney injury (AKI). We aim to explore the diagnostic value of high sensitive troponin T (hsTnT) in the settings of cardiac surgery-induced AKI.

METHODS

Single center observational retrospective study. Based on the AKI Network, patients divided into 2 groups, group I without AKI (259 patients) and group II with AKI (100 patients) where serial testing of hsTnT and creatine kinase (CK)-MB were followed in both groups. Patients with (ESRD) were excluded.

RESULTS

The mean age in our study was 55.1 ± 10.2 years. High association of AKI (27.8%) was found in our patients. Both groups were matched regarding the age, gender, body mass index, the association of diabetes or hypertension, and Euro score. AKI group had significantly higher mortality 5% vs group I 1.1% (p = 0.03). The hsTnt showed a significant sustained rise in the AKI group as compared to the non-AKI group, however CK-MB changes were significant initially but not sustained. The AKI group was more associated with heart failure 17.9% vs 4.9% (p = 0.001); and post-operative atrial fibrillation, 12.4% vs 2.9% (p = 0.005). Lengths of ventilation, stays in ICU and in hospital were significantly higher in the AKI group.

CONCLUSIONS

Unlike the CK-MB profile, the hsTnT showed significant changes between both groups all over the course denoting possible delayed clearance in patients with AKI.

Genetic Analysis of the Atrial Natriuretic Peptide Gene Polymorphisms among Essential Hypertensive Patients in Malaysia

Background. Atrial natriuretic peptide (ANP) considerably influences blood pressure regulation through water and sodium homoeostasis. Several of the studies have utilized anonymous genetic polymorphic markers and made inconsequent claims about the ANP relevant disorders. Thus, we screened Insertion/Deletion (ID) and G191A polymorphisms of ANP to discover sequence variations with potential functional significance and to specify the linkage disequilibrium pattern between polymorphisms. The relationships of detected polymorphisms with EH with or without Type 2 Diabetes Mellitus (T2DM) status were tested subsequently. Method. ANP gene polymorphisms (I/D and A191G) were specified utilizing mutagenically separated Polymerase Chain Reaction (PCR) in 320 subjects including 163 EH case subjects and 157 controls. Result. This case-control study discovered a significant association between I/D polymorphisms of ANP gene in EH patient without T2DM. However, the study determined no association between G191A polymorphisms of ANP in EH with or without T2DM. In addition, sociodemographic factors in the case and healthy subjects exhibited strong differences (P < 0.05). Conclusion. As a risk factor, ANP gene polymorphisms may affect hypertension. Despite the small sample size in this study, it is the first research assessing the ANP gene polymorphisms in both EH and T2DM patients among Malaysian population.

NT-proBNP and troponin T levels differ after haemodialysis with a low versus high flux membrane

BACKGROUND

Brain natriuretic peptide (BNP), N-terminal-proBNP (NT-proBNP), and high sensitive cardiac troponin T (TnT) are markers that are elevated in chronic kidney disease and correlate with increased risk of mortality. Data are conflicting on the effect of biomarker levels by hemodialysis (HD).Our aim was to clarify to what extent HD with low-flux (LF) versus high-flux (HF) membranes affects the plasma levels of BNP, NT-proBNP, and TnT.

METHODS AND MATERIALS

31 HD patients were included in a crossover design, randomized to start dialysis with a LF-HD or HF-HD dialyzer. Each patient was his/her own control. The dialyses included in the study were the first treatments of two consecutive weeks with each mode of dialysis. Patients normally on hemodiafiltration (HDF) also performed a HDF the third week. Values after HD were corrected for extent of ultrafiltration.

RESULTS

During LF-HD the biomarkers NT-proBNP and TnT increased (15 versus 6%, P ≤ .001) while there was a slight decrease in BNP (P<.05). During HF-HD the NT-proBNP, BNP and TnT levels decreased (P ≤ .01 for all). During HDF all three markers decreased (P<.01 for all). The rise in TnT during LF-HD correlated with dialysis vintage (months on HD, r = .407, P = .026), Kt/V-urea (r = .383, P = .037), HD time in hours/treatment (r = .447, P = .013) and inversely with residual urinary output (r = -.495, P = .005). The baseline levels of BNP and NT-proBNP correlated with blood pressure.

CONCLUSIONS

Cardiac biomarkers increase slightly during LF-HD. A HF-HD eliminates the biomarkers and can mask increases caused by, e.g., myocardial infarction.

Cautious application of pleural N-terminal pro-B-type natriuretic peptide in diagnosis of congestive heart failure pleural effusions among critically ill patients

Background and Objective

Several studies on diagnostic accuracy of pleural N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) for effusions from congestive heart failure (CHF) conclude that pleural NT-pro-BNP is a useful biomarker with high diagnostic accuracy for distinguishing CHF effusions. However, its applicability in critical care settings remains uncertain and requires further investigations.

Methods

NT-proBNP was measured in pleural fluid samples of a prospective cohort of intensive care unit patients with pleural effusions. Receiver operating characteristic curve analysis was performed to determine diagnostic accuracy of pleural NT-proBNP for prediction of CHF effusions.

Results

One hundred forty-seven critically ill patients were evaluated, 38 (26%) with CHF effusions and 109 (74%) with non-CHF effusions of various causes. Pleural NT-proBNP levels were significantly elevated in patients with CHF effusions. Pleural NT-pro-BNP demonstrated the area under the curve of 0.87 for diagnosing effusions due to CHF. With a cutoff of 2200 pg/mL, pleural NT-proBNP displayed high sensitivity (89%) but moderate specificity (73%). Notably, 29 (27%) of 109 patients with non-CHF effusions had pleural NT-proBNP levels >2200 pg/mL and these patients were more likely to experience septic shock (18/29 vs. 10/80, P<0.001) or acute kidney injury (19/29 vs. 9/80, P<0.001).

Conclusions

Among critically ill patients, pleural NT-proBNP measurements remain a useful diagnostic aid in evaluation of pleural effusions. However, patients with non-CHF effusions may exhibit high pleural NT-proBNP concentrations if they suffer from septic shock or acute kidney injury. Accordingly, it is suggested that clinical context should be taken into account when interpreting pleural NT-proBNP values in critical care settings.

Patients with cardiorenal syndrome revealed increased neurohormonal activity, tubular and myocardial damage compared to heart failure patients with preserved renal function

BACKGROUND

Cardiorenal syndrome (CRS) is associated with increased cardiovascular morbidity and mortality; still, its biomarker pattern has been poorly evaluated so far. The aim of this study was to measure the inflammatory activation, neurohormonal status and kidney and myocardial damage in patients with CRS compared to patients with heart failure (HF) without renal impairment (RI).

METHODS

We analyzed 246 patients on the basis of renal function (group 1: 120 HF patients without RI; group 2: 126 CRS patients). In each group, interleukin-6, tumor necrosis factor-α, B-type natriuretic peptide (BNP), neutrophil gelatinase-associated lipocalin (NGAL), troponin T (TnT), osteoprotegerin and blood urea nitrogen (BUN) were measured. The diagnostic power of all laboratory parameters to detect CRS was evaluated by the receiver operating characteristic (ROC) curve and logistic regression analysis.

RESULTS

A significant increase in BNP [626.4 pg/ml, confidence interval (CI) 518-749 vs. 487.8 pg/ml, CI 411-578; p < 0.05], NGAL (156 ng/ml, CI 129-186 vs. 89.1 ng/ml, CI 72-109; p < 0.0001), BUN (108.9 mg/dl, CI 98-120 vs. 51 mg/dl, CI 46-55; p < 0,0001) and TnT (0.62 ng/ml, CI 0.51-0.75 vs. 0.21 ng/ml, CI 0.15-0.28; p < 0.001) was seen in CRS patients compared to HF patients without RI. ROC curve analysis showed that only NGAL, BUN, BUN/creatinine ratio and TnT can discriminate patients with CRS from patients without RI.

CONCLUSIONS

In CRS patients, renal tubular damage and neurohormonal and cardiac injury activation are increased compared to patients without RI. The current biomarker pattern could be used for an early diagnosis of RI in acute and chronic HF.

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.

Serum levels of N-terminal proB-type natriuretic peptide in mechanically ventilated critically ill patients--relation to tidal volume size and development of acute respiratory distress syndrome

Background

Serum levels of N–terminal proB–type natriuretic peptide (NT–proBNP) are elevated in patients acute respiratory distress syndrome (ARDS). Recent studies showed a lower incidence of acute cor pulmonale in ARDS patients ventilated with lower tidal volumes. Consequently, serum levels of NT–proBNP may be lower in these patients.

We investigated the relation between serum levels of NT–proBNP and tidal volumes in critically ill patients without ARDS at the onset of mechanical ventilation.

Methods

Secondary analysis of a randomized controlled trial of lower versus conventional tidal volumes in patients without ARDS. NT–pro BNP were measured in stored serum samples. Serial serum levels of NT–pro BNP were analyzed controlling for acute kidney injury, cumulative fluid balance and presence of brain injury. The primary outcome was the effect of tidal volume size on serum levels of NT–proBNP. Secondary outcome was the association with development of ARDS.

Results

Samples from 150 patients were analyzed. No relation was found between serum levels of NT–pro BNP and tidal volume size. However, NT-proBNP levels were increasing in patients who developed ARDS. In addition, higher levels were observed in patients with acute kidney injury, and in patients with a more positive cumulative fluid balance.

Conclusion

Serum levels of NT–proBNP are independent of tidal volume size, but are increasing in patients who develop ARDS.

Natriuretic peptides in the management of solid organ transplantation associated acute kidney injury: a systematic review and meta-analysis

Randomized controlled trials involving natriuretic peptide administration in solid organ transplantation setting have shown inconsistent effects for renal endpoints. We conducted a systematic review and meta-analysis of these trials to ascertain the role of natriuretic peptides in the management of solid organ transplantation associated acute kidney injury (AKI). MEDLINE, EMBASE, and Google scholar were searched independently by two authors for randomized trials evaluating renal effects of natriuretic peptides in solid organ transplantation settings. Two reviewers independently assessed the studies for eligibility and extracted the relevant data. The pooled estimate showed that natriuretic peptide administration is associated with a reduction in AKI requiring dialysis (odds ratio = 0.50 [0.26–0.97]), a statistically nonsignificant trend toward improvement in posttransplant creatinine clearance (weighted mean difference = 5.5 mL/min, [−1.3 to 12.2 mL/min]), and reduction in renal replacement requirement duration (weighted mean difference −44.0 hours, [−60.5 to −27.5 hours]). There were no mortality events and no adverse events related to natriuretic peptides. In conclusion, administration of natriuretic peptides in solid organ transplantation may be associated with significant improvements in renal outcomes. These observations need to be confirmed in an adequately powered, prospective multicenter study.

Equal performance of novel N-terminal proBNP (Cardiac proBNP®) and established BNP (Triage BNP®) point-of-care tests

Background: Recently, a novel point-of-care test (POCT) for N-terminal proBNP (NTproBNP) has been introduced (Cardiac proBNP®, Roche). Aim: The aim was to compare the novel POCT for NTproBNP with the established POCT for BNP. Methods: NTproBNP and BNP were assessed in 222 individuals with chronic heart failure (n = 151) or controls (n = 71) with both POCTs. Results: NTproBNP and BNP were closely correlated upon regression analysis (r = 0.93; p < 0.01). NTproBNP and BNP were both correlated with ejection fraction and New York Heart Association stage. Receiver operating characteristic analysis yielded satisfying and equivalent predictive values for the detection of left ventricular dysfunction (ejection fraction <40%; NTproBNP: area under the curve 0.97; BNP: area under the curve 0.96; p > 0.05) and presence of New York Heart Association stage >2 (area under the curve 0.92 vs 0.91 for NT-proBNP and BNP, respectively; p > 0.05). Conclusion: The NTproBNP POCT allows biochemical detection of heart failure with satisfactory predictive values, is equivalent to the BNP POCT and will improve near-patient testing.

Peri-operative renal protection: The strategies revisited

Postoperative acute renal failure (ARF) is a serious complication which can result in a prolonged hospital stay and a high mortality and morbidity. Underlying renal disease, cardiac diseases, nephrotoxin exposure and renal hypoperfusion are the possible predisposing risk factors which can create a high probability for the development of ARF. The incidence of ARF is highest after major vascular, cardiac and high-risk thoraco-abdominal surgery. Among the various renal protection strategies, adequate peri-operative volume expansion and avoidance of hypovolemia is the most accepted and practiced strategy. Numerous bio-markers of renal injury are used to estimate the presence and extent of renal insult and various new are currently under trial. Traditional pharmacological interventions like dopamine, diuretics and calcium antagonists are not currently the first line of reno-protective agents. The new non-pharmacological and pharmacological methods may improve outcome in renal transplantation, contrast-induced nephropathy and in various other settings of ARF. The current review is an attempt to refresh the knowledge and put forth the various renal protection strategies during the peri-operative period.

The role of B-type and other natriuretic peptides in health and disease

Natriuretic peptide (NP) physiology is a complex field. NPs also are known to be highly phylogenetically preserved. NPs can be thought of as counterregulatory hormones antagonizing the effects of the renin-angiotensin-aldosterone and sympathetic systems. These peptides are primarily responsible for maintaining salt and water homeostasis, but they also have vasodilatory properties. It was originally thought that B-type NP (BNP) and N-terminal-pro-BNP are secreted in a 1:1 ratio. However, recent data has shed further light into this area. Commercial assays for NPs will need to keep up with these changes. Currently, BNP levels within Kaiser Permanente are obtained by multiple providers in a variety of clinical scenarios in order to help them manage their patients. Therefore, a basic understanding of the physiology of NPs and the methodology of assays are needed to appropriately interpret an NP test result within the corresponding clinical scenario.

[Physiology and clinical role of natriuretic peptides]

In the last three decades many members of the natriuretic peptide family was isolated. The function and physiological role of these peptides are pleiotropic. All natriuretic peptides are synthesized from polypeptide precursors. Together with the sympathetic nervous system and other hormones they play key roles, like an endogenous system in the regulation of the body fluid homeostasis and blood pressure. Changes in this balance lead to dysfunction in the endothel and left ventricle, which can cause severe complications. In many cardiovascular diseases natriuretic peptides serve not only as marker for diagnosis and prognosis but they have therapeutic importance. In the last years the potential use of the elevated BNP levels for diagnosis of pre-eclampsia was examined. In our review we discuss the current understanding of molecular biology, biochemistry and clinical relevance of natriuretic peptides.

Mechanism of 1-deamino-arginine vasotocin induced natriuresis in rats

1-Deamino-arginine vasotocin (1dAVT) induced diuresis and a considerable increase in urinary sodium excretion in female Wistar rats. Sodium fractional excretion rose up to 19.3 ± 1.1%. An increase in urine flow rate after 1dAVT (0.5 nmol/kg body-weight [bw]) injection was accompanied by a significant rise of the solute-free water reabsorption. The 1dAVT-induced natriuresis was as high as natriuresis produced by injection of a maximal dose of furosemide (10mg/kg bw). V(1)-receptor antagonists (ОРС-21268, [β-mercapto-β,β-cyclopentamethylenepropionyl(1),O-Me-Tyr(2),Arg(8)]-vasopressin) blocked the increase in urinary sodium excretion after the 1dAVT injection. The 1dAVT-induced natriuresis was strongly correlated with an increase in the urinary cGMP and prostaglandin E(2) excretion. The natriuretic effect of 1dAVT did not depend on the formation of nitric oxide (NO) or atrial natriuretic peptide of which concentration in the rat blood serum remained stable. The above results indicate that the 1dAVT has unique effects on rat kidney compared to all other known diuretics - it induces extremely high natriuresis and stimulates solute-free water reabsorption. Mechanism of the natriuretic effect of 1dAVT includes decrease in tubular sodium reabsorption due to activation of V(1)-like receptors and formation of cGMP and PGЕ(2).

Vessel dilator and C-type natriuretic peptide enhance the proliferation of human osteoblasts

C-natriuretic peptide (CNP) has been shown to regulate proliferation of mouse and rat osteoblasts. Genetic deletion of CNP results in dwarfism. Overexposure of CNP has been associated with arachnodactyly of hands and feet with a very long hallux bilaterally in a 14-y-old girl. CNP effects on bone growth involve inhibition of MEK 1 and ERK 1/2 kinases mediated via the intracellular messenger cGMP. Vessel dilator is another natriuretic peptide synthesized by the atrial natriuretic peptide gene whose biologic half-life is 12 times longer than CNP. Vessel dilator's biologic effects on proliferating cells are mediated via inhibiting MEK 1/2 and ERK 1/2 kinases via cGMP. Vessel dilator has never been studied on osteoblasts. CNP at 10 (nanomolar) nM (p = 0.02) and vessel dilator at 10 nM, 1 nM, 100 (picomolar) pM, and 10 pM (p ≤ 0.01) in dose-response studies enhanced human osteoblasts' proliferation. This first study of human osteoblasts would suggest that vessel dilator with a much longer biologic half-life and with osteoblast-stimulatory effects at lower concentrations than CNP may have therapeutic potential in human achondroplasia, short stature, and osteoporosis. Vessel dilator stimulates osteoblast proliferation whereas most current therapies of osteoporosis target osteoclasts.

N-terminal pro-brain natriuretic peptide from fresh urine for the biochemical detection of heart failure and left ventricular dysfunction

AIMS

Plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) is a strong biochemical marker of heart failure and left ventricular dysfunction (LVD). Due to renal arterio-venous clearance of NT-proBNP and the correlation of plasma concentrations with renal function, we hypothesized that NT-proBNP may have potential as a urinary marker. The objective of this study was to assess urinary concentrations of NT-proBNP and to identify the predictive value of urinary NT-proBNP for detecting LVD and heart failure.

METHODS AND RESULTS

N-terminal pro-brain natriuretic peptide (Elecsys proBNP((R)), Roche) was assessed simultaneously in fresh spot urine and plasma from 191 individuals. In patients with heart failure (n = 149), urinary and plasma NT-proBNP concentrations were positively correlated (r = 0.79, P < 0.001), but urinary NT-proBNP was significantly lower than plasma NT-proBNP (42 +/- 25 vs. 1389 +/- 325 pg/mL, P < 0.001). Upon receiver operating curve analysis, urinary NT-proBNP detected LV dysfunction (ejection fraction <40%) with a sensitivity of 91% and a specificity of 98% at a cutpoint of 22 pg/mL [area under the curves (AUC) 0.98]. At the same cutpoint, symptomatic heart failure (NYHA-class > 2) was detected with a sensitivity of 97% and specificity of 98% (AUC 0.99) and clinical signs of fluid retention were detected with a sensitivity and specificity of 98% each (AUC 0.99).

CONCLUSION

N-terminal pro-brain natriuretic peptide concentrations were markedly lower in the urine than in the plasma. However, urinary NT-proBNP levels increased stepwise with the severity of heart failure and LVD, and therefore yielded satisfactory predictive values for the detection of significant LVD and symptomatic heart failure. Measurement of urinary NT-proBNP is a novel, promising, and simple method for the biochemical detection of heart failure.

Atrial natriuretic peptide for preventing and treating acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is common in hospitalised patients and is associated with significant morbidity and mortality. Despite recent advances, outcomes have not substantially changed in the last four decades. Atrial natriuretic peptide (ANP) has shown promise in animal studies, however randomised controlled trials (RCTs) have shown inconsistent clinical benefits.

OBJECTIVES

To assess the benefits and harms of ANP for preventing and treating AKI.

SEARCH STRATEGY

We searched CENTRAL, MEDLINE and EMBASE and reference lists of retrieved articles.

SELECTION CRITERIA

RCTs that investigated all forms of ANP versus any other treatment in adult hospitalised patients with or "at risk" of AKI.

DATA COLLECTION AND ANALYSIS

Results were expressed as risk ratios (RR) with 95% confidence intervals (CI) or mean difference (MD). Outcomes were analysed separately for low and high dose ANP for preventing or treating AKI.

MAIN RESULTS

Nineteen studies (11 prevention, 8 treatment; 1,861 participants) were included. There was no difference in mortality between ANP and control in either the low or high dose prevention studies. Low (but not high) dose ANP was associated with a reduced need for RRT in the prevention studies (RR 0.32, 95% CI 0.14 to 0.71). Length of hospital and ICU stay were significantly shorter in the low dose ANP group. For established AKI, there was no difference in mortality with either low or high dose ANP. Low (but not high) dose ANP was associated with a reduction in the need for RRT (RR 0.54, 95% CI 0.30 to 0.98). High dose ANP was associated with more adverse events (hypotension, arrhythmias). After major surgery there was a significant reduction in RRT requirement with ANP in the prevention studies (RR 0.56, 95% CI 0.32 to 0.99), but not in the treatment studies. There was no difference in mortality between ANP and control in either the prevention or treatment studies. There was a reduced need for RRT with low dose ANP in patients undergoing cardiovascular surgery (RR 0.35, 95% CI 0.18 to 0.70). ANP was not associated with outcome improvement in either radiocontrast nephropathy or oliguric AKI.

AUTHORS' CONCLUSIONS

ANP may be associated with improved outcomes when used in low doses for preventing AKI and in managing postsurgery AKI and should be further explored in these two settings. There were no significant adverse events in the prevention studies, however in the high dose ANP treatment studies there were significant increases hypotension and arrhythmias.

Atrial natriuretic peptide for management of acute kidney injury: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

Randomized controlled trials (RCTs) with atrial natriuretic peptide (ANP) have shown inconsistent effects for renal end-points. The authors aimed to systematically review these trials to ascertain the benefit of ANP in prevention and treatment of acute kidney injury (AKI).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The authors searched MEDLINE, EMBASE, and Cochrane Renal Health Library that investigated ANP in adult patients considered with or at risk for AKI. Outcomes were analyzed separately for prevention and treatment of AKI.

RESULTS

Nineteen RCTs (11 prevention, 8 treatment) involving 1861 participants were included. Pooled analysis of prevention trials showed a trend toward reduction in renal replacement therapy in the ANP group (OR = 0.45, 95% CI, 0.21 to 0.99) and good safety profile, but no improvement in mortality. For the treatment of established AKI, ANP, particularly in high doses, was associated with a trend toward increased mortality and more adverse events. Subgroup analysis of AKI after a major surgery (14 RCTs, 817 participants) showed a significant reduction in renal replacement therapy requirement in the ANP group (OR = 0.49, 95% CI, 0.27 to 0.88). Included RCTs were mostly low- or moderate-quality, underpowered studies.

CONCLUSIONS

There are an insufficient number of high-quality studies to make any definite statement about the role of ANP in AKI. Analysis of the existing literature suggests ANP might be associated with beneficial clinical effects when administered in patients undergoing major surgery such as cardiovascular surgery. Its use, in low doses, should be explored further in this setting.

Pro-A-type natriuretic peptide and pro-adrenomedullin predict progression of chronic kidney disease: the MMKD Study

A-type natriuretic peptide (ANP) and adrenomedullin (ADM) are potent hypotensive, diuretic, and natriuretic peptides involved in maintaining cardiovascular and renal homeostasis. We conducted a prospective 7-year study of 177 nondiabetic patients with primary chronic kidney disease to see if ANP and ADM plasma concentrations predict the progression of their disease, using novel sandwich immunoassays covering the midregional epitopes of the stable prohormones (MRproANP and MR-proADM). Progression of chronic kidney disease was defined as doubling of baseline serum creatinine and/or terminal renal failure, which occurred in 65 patients. Analysis of the receiver operating characteristic curve for the prediction of renal endpoints showed similar areas under the curve for the glomerular filtration rate (GFR) (0.838), MR-proANP (0.810), and MRproADM (0.876), respectively, as did the Kaplan-Meier curve analyses of the patients stratified according to the median of the respective markers. In separate multiple Cox-proportional hazard regression analyses, increased plasma concentrations of both peptides were each strongly predictive of the progression of chronic kidney disease after adjustments for age, gender, GFR, proteinuria and amino-terminal pro-B-type natriuretic peptide. Our study suggests that MR-proANP and MR-proADM are useful new markers of progression of primary nondiabetic chronic kidney disease.

Urodilatin: a better natriuretic peptide?

The kidney natriuretic peptide urodilatin (ie, ularitide) decreases pulmonary capillary wedge pressure (PCWP) but does not cause diuresis in persons with congestive heart failure (CHF). Thirty-three percent of patients with CHF treated with 30 ng/kg/min ularitide develop hypotension with systolic blood pressures below 90 mmHg. Nesiritide and atrial natriuretic peptide lower PCWP and cause hypotension. They do not produce diuresis or natriuresis in patients with CHF. The best natriuretic peptide for treating CHF is the cardiac hormone vessel dilator which decreases PCWP and decreases systemic and pulmonary vascular resistance while simultaneously increasing cardiac output and cardiac index. What makes the vessel dilator markedly better than atrial natriuretic peptide, nesiritide, and ularitide for treatment of CHF is that it enhances sodium excretion fivefold and causes a fivefold enhanced diuresis in patients with CHF with its biologic effects lasting over 6 hours compared with less than 30 minutes for the above peptides.

Expression, purification and characterization of human urodilatin in E. coli

Urodilatin is a 32-amino acid peptide hormone synthesized in kidney to regulate natriuresis and diuresis. It has been shown clinically useful for the treatment of acute decompensated heart failure. A synthetic deoxyoligonucleotide encoding urodilatin was cloned into a pET32a vector immediately after the thioredoxin encoding sequence with a hexa-hisditine tag and an enterokinase recognition site incorporated in between. The fusion protein was overexpressed in Escherichia coli, which constituted 28% of the total cell proteins. More than 85% of Trx-urodilatin was soluble and purified nearly homogenous by Ni-Sepharose affinity chromatography. Urodilatin was then released from the fusion protein by the enterokinase treatment and separated from the fusion partner by the subtractive chromatography using Ni-Sepharose once again. The urodilatin sample was further purified with reverse phase HPLC. Via a biological activity assayed in vitro, it was found that urodilatin had a potent vasodilatory effect on rabbit aortic strips with an EC50 of (2.02+/-0.36)x10(-6)mg/ml, which was similar to that of the synthetic urodilatin standard. The method described here promises to produce about 4.5mg fully active recombinant urodilatin with homogeneity over 97% from one liter shaking flask culture of E. coli.

Urinary B-Type Natriuretic Peptide Levels in the Diagnosis and Prognosis of Heart Failure

BACKGROUND

Plasma B-type natriuretic peptide (BNP) is a useful biomarker for diagnosis and prognosis of heart failure (HF); however, urine BNP has never been calculated. We sought to compare urinary and plasma BNP levels and to investigate the potential diagnostic and prognostic value of this peptide in HF.

METHODS AND RESULTS

Urine and plasma BNP levels were measured in 92 HF patients and 30 control subjects. Urinary BNP levels were higher in HF patients than in control subjects (P < .0001), correlating with plasma BNP levels (r = 0.64, P < .0001). Urine BNP was a good tool for the diagnosis of HF, the area under the curve (AUC) being 0.91 +/- 0.06 (P < .0001). Urinary BNP levels had prognostic power for cardiac events (cardiac admissions + mortality) with an odds ratio of 6.6 (P < .05). To determine the prognostic power of urinary BNP in detecting 12-month cardiac mortality, we obtained an AUC of 0.76 +/- 0.6 (P = .014).

CONCLUSIONS

The data suggest that urine BNP is a new candidate marker for diagnosis and prognosis of HF mortality and cardiac events. This raises the possibility of using this relatively simple noninvasive test in primary care settings or in specific conditions where the collection of blood samples could be difficult.