Kinetic Changes of Plasma Renin Concentrations Predict Acute Kidney Injury in Cardiac Surgery Patients

Kinetics of Renin Concentrations in Infants Undergoing Congenital Cardiac Surgery

BACKGROUND

Elevated renin has been shown to predict poor response to standard vasoactive therapies and is associated with poor outcomes in adults. Similarly, elevated renin was associated with mortality in children with septic shock. Renin concentration profiles after pediatric cardiac surgery are unknown. The purpose of this study was to characterize renin kinetics after pediatric cardiac surgery.

METHODS

Single-center retrospective study of infants who underwent cardiac surgery with cardiopulmonary bypass (CPB) utilizing serum samples obtained in the perioperative period to measure plasma renin concentrations (pg/mL). Time points included pre-bypass and 1, 4, and 24 h after initiation of CPB.

RESULTS

Fifty patients (65% male) with a median age 5 months (interquartile range (IQR) 3.5, 6.5) were included. Renin concentrations peaked 4 h after CPB. There was a significant difference in preoperative and 4 h post-CPB renin concentration (4 h post-CPB vs preoperative: mean difference 100.6, 95% confidence interval (CI) 48.9-152.4, P < .001). Median renin concentration at 24 h after CPB was lower than the preoperative baseline.

CONCLUSIONS

We describe renin kinetics in infants after CPB. Future studies based on these data can now be performed to evaluate the associations of elevated renin concentrations with adverse outcomes.

A Pilot Study of Renin-Guided Angiotensin-II Infusion to Reduce Kidney Stress After Cardiac Surgery

BACKGROUND

Vasoplegia is common after cardiac surgery, is associated with hyperreninemia, and can lead to acute kidney stress. We aimed to conduct a pilot study to test the hypothesis that, in vasoplegic cardiac surgery patients, angiotensin-II (AT-II) may not increase kidney stress (measured by [TIMP-2]*[IGFBP7]).

METHODS

We randomly assigned patients with vasoplegia (cardiac index [CI] > 2.1l/min, postoperative hypotension requiring vasopressors) and Δ-renin (4-hour postoperative-preoperative value) ≥3.7 µU/mL, to AT-II or placebo targeting a mean arterial pressure ≥65 mm Hg for 12 hours. The primary end point was the incidence of kidney stress defined as the difference between baseline and 12 hours [TIMP-2]*[IGFBP7] levels. Secondary end points included serious adverse events (SAEs).

RESULTS

We randomized 64 patients. With 1 being excluded, 31 patients received AT-II, and 32 received placebo. No significant difference was observed between AT-II and placebo groups for kidney stress (Δ-[TIMP-2]*[IGFBP7] 0.06 [ng/mL] 2 /1000 [Q1-Q3, -0.24 to 0.28] vs -0.08 [ng/mL] 2 /1000 [Q1-Q3, -0.35 to 0.14]; P = .19; Hodges-Lehmann estimation of the location shift of 0.12 [ng/mL] 2 /1000 [95% confidence interval, CI, -0.1 to 0.36]). AT-II patients received less fluid during treatment than placebo patients (2946 vs 3341 mL, P = .03), and required lower doses of norepinephrine equivalent (0.19 mg vs 4.18mg, P < .001). SAEs were reported in 38.7% of patients in the AT-II group and in 46.9% of patients in the placebo group.

CONCLUSIONS

The infusion of AT-II for 12 hours appears feasible and did not lead to an increase in kidney stress in a high-risk cohort of cardiac surgery patients. These findings support the cautious continued investigation of AT-II as a vasopressor in hyperreninemic cardiac surgery patients.

Impaired angiotensin II signaling in septic shock

Recent years have seen a resurgence of interest for the renin-angiotensin-aldosterone system in critically ill patients. Emerging data suggest that this vital homeostatic system, which plays a crucial role in maintaining systemic and renal hemodynamics during stressful conditions, is altered in septic shock, ultimately leading to impaired angiotensin II-angiotensin II type 1 receptor signaling. Indeed, available evidence from both experimental models and human studies indicates that alterations in the renin-angiotensin-aldosterone system during septic shock can occur at three distinct levels: 1. Impaired generation of angiotensin II, possibly attributable to defects in angiotensin-converting enzyme activity; 2. Enhanced degradation of angiotensin II by peptidases; and/or 3. Unavailability of angiotensin II type 1 receptor due to internalization or reduced synthesis. These alterations can occur either independently or in combination, ultimately leading to an uncoupling between the renin-angiotensin-aldosterone system input and downstream angiotensin II type 1 receptor signaling. It remains unclear whether exogenous angiotensin II infusion can adequately address all these mechanisms, and additional interventions may be required. These observations open a new avenue of research and offer the potential for novel therapeutic strategies to improve patient prognosis. In the near future, a deeper understanding of renin-angiotensin-aldosterone system alterations in septic shock should help to decipher patients' phenotypes and to implement targeted interventions.

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

Renin in critically ill patients

The renin-angiotensin system (RAS) constitutes one of the principal mechanisms to maintain hemodynamic and fluid homeostasis. However, most research until now on RAS primarily focuses on its relationship with hypertension and its role in critically ill hypotensive populations is not well understood. With the approval of angiotensin II (Ang II) in the United States and Europe, following a phase 3 randomized controlled trial showing efficacy in catecholamine-resistant vasodilatory shock, there is growing interest in RAS in critically ill patients. Among the fundamental components of RAS, renin acts as the initial stimulus for the entire system. In the context of hypotension, its release increases in response to low blood pressure sensed by renal baroreceptors and attenuated negative Ang II feedback loop. Thus, elevated renin could reflect disease severity and predict poor outcomes. Studies investigating this hypothesis have validated the prognostic accuracy of renin in various critically ill populations, with several reports indicating its superiority to lactate for mortality prediction. Accordingly, renin reduction has been used to assess the effectiveness of Ang II administration. Furthermore, renin holds potential to identify patients who might benefit from Ang II treatment, potentially paving the way for personalized vasopressor management. Despite these promising data, most available evidence is derived from retrospective analysis and necessitates prospective confirmation. The absence of a rapid, point-of-care and reliable renin assay presents another hurdle to its integration into routine clinical practice. This narrative review aims to describe the current understanding and future directions of renin as a biomarker during resuscitation of critically ill patients.

Renin as a Prognostic Marker in Intensive Care and Perioperative Settings: A Scoping Review

Serum renin increases in response to sympathetic nerve activation and hypotension. Recent studies have reported the association of serum renin levels with adverse clinical outcomes in acute care settings. This scoping review aimed to systematically review the available literature on renin as a prognostic marker in intensive care and perioperative patients. We searched for studies published since inception until March 31, 2023, which assessed the association between serum renin levels and clinical outcomes or the effect of synthetic angiotensin II administration on serum renin levels in critically ill and perioperative patients in PubMed, Embase, and the Cochrane Library. The primary outcome was mortality at the longest follow-up; the secondary outcomes were adverse renal outcomes (ie, acute kidney injury, the need for renal replacement therapy, and major adverse kidney events), hemodynamic instability, outcomes to angiotensin II administration, and prognostic performance for mortality when compared with lactate. Among the 2081 studies identified, we included 16 studies with 1573 patients (7 studies on shock, 5 on nonspecific critical illness, 2 on cardiac surgery, 1 on noncardiac surgery, and 1 on coronavirus disease 2019). A significant association between serum renin levels and poor outcomes was identified in 14 studies, with 10 studies demonstrating an association with mortality. One post hoc analysis found that angiotensin II administration reduced mortality in patients with markedly elevated renin values. Two studies showed that renin was superior to lactate as a prognostic marker of mortality. Our scoping review showed that elevated serum renin levels may be associated with clinically relevant outcomes among various perioperative and intensive care populations. Increased serum renin levels may identify patients in which synthetic angiotensin II administration improves clinical outcomes and may outperform serum lactate in predicting mortality.

The scientific rationale and study protocol for the DPP3, Angiotensin II, and Renin Kinetics in Sepsis (DARK-Sepsis) randomized controlled trial: serum biomarkers to predict response to angiotensin II versus standard-of-care vasopressor therapy in the treatment of septic shock

BACKGROUND

Data to support the use of specific vasopressors in septic shock are limited. Since angiotensin II (AT2) was approved by the Food and Drug Administration in 2017, multiple mechanistically distinct vasopressors are available to treat septic shock, but minimal data exist regarding which patients are most likely to benefit from each agent. Renin and dipeptidyl peptidase 3 (DPP3) are components of the renin-angiotensin-aldosterone system which have been shown to outperform lactate in predicting sepsis prognosis, and preliminary data suggest they could prove useful as biomarkers to guide AT2 use in septic shock.

METHODS

The DARK-Sepsis trial is an investigator-initiated industry-funded, open-label, single-center randomized controlled trial of the use of AT2 versus standard of care (SOC) vasopressor therapy in patients admitted to the intensive care unit (ICU) with vasodilatory shock requiring norepinephrine ≥ 0.1 mcg/kg/min. In both groups, a series of renin and DPP3 levels will be obtained over the first 24 h of treatment with AT2 or SOC. The primary study outcome will be the ability of these biomarkers to predict response to vasopressor therapy, as measured by change in total norepinephrine equivalent dose of vasopressors at 3 h post-drug initiation or the equivalent timepoint in the SOC arm. To determine if the ability to predict vasopressor response is specific to AT2 therapy, the primary analysis will be the ability of baseline renin and DPP3 levels to predict vasopressor response adjusted for treatment arm (AT2 versus control) and Sequential Organ Failure Assessment (SOFA) scores. Secondary outcomes will include rates of acute kidney injury, need for mechanical ventilation and kidney replacement therapy, lengths of stay in the ICU and hospital, ICU and hospital mortality, and rates of prespecified adverse events.

DISCUSSION

With an armamentarium of mechanistically distinct vasopressor agents now available, sub-phenotyping patients using biomarkers has the potential to improve septic shock outcomes by enabling treatment of the correct patient with the correct vasopressor at the correct time. However, this approach requires validation in a large definitive multicenter trial. The data generated through the DARK-Sepsis study will prove crucial to the optimal design and patient enrichment of such a pivotal trial.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05824767. Registered on April 24, 2023.

Urinary Chloride Excretion Postcardiopulmonary Bypass in Pediatric Patients-A Pilot Study

The aim of this study was to describe renal chloride metabolism following cardiopulmonary bypass (CPB) surgery in pediatric patients. A prospective observational trial in a tertiary pediatric intensive care unit (PICU) with 20 recruited patients younger than 2 years following CPB surgery was conducted. Urinary electrolytes, plasma urea, electrolytes, creatinine, and arterial blood gases were collected preoperatively, on admission to PICU and at standardized intervals thereafter. The urinary and plasma strong ion differences (SID) were calculated from these results at each time point. Fluid input and output and electrolyte and drug administration were also recorded. Median chloride administration was 67.7 mmol/kg over the first 24 hours. Urinary chloride (mmol/L; median interquartile range [IQR]) was 30 (19, 52) prior to surgery, 15 (15, 65) on admission, and remained below baseline until 24 hours. Plasma chloride (mmol/L; median [IQR]) was 105 (98, 107) prior to surgery and 101 (101, 106) on admission to PICU. It then increased from baseline, but remained within normal limits, for the remainder of the study. The urinary SID increased from 49.8 (19.1, 87.2) preoperatively to a maximum of 122.7 (92.5, 151.8) at 6 hours, and remained elevated until 48 hours. Plasma and urinary chloride concentrations were not associated with the development of acute kidney injury. Urinary chloride excretion is impaired after CPB. The urinary SID increase associated with the decrease in chloride excretion suggests impaired production and/or excretion of ammonium by the nephron following CPB, with gradual recovery postoperatively.

Angiotensin ii therapy in refractory septic shock: which patient can benefit most? A narrative review

Patients with septic shock who experience refractory hypotension despite adequate fluid resuscitation and high-dose noradrenaline have high mortality rates. To improve outcomes, evidence-based guidelines recommend starting a second vasopressor, such as vasopressin, if noradrenaline doses exceed 0.5 µg/kg/min. Recently, promising results have been observed in treating refractory hypotension with angiotensin II, which has been shown to increase mean arterial pressure and has been associated with improved outcomes. This narrative review aims to provide an overview of the pathophysiology of the renin-angiotensin system and the role of endogenous angiotensin II in vasodilatory shock with a focus on how angiotensin II treatment impacts clinical outcomes and on identifying the population that may benefit most from its use.

Higher perfusion pressure and pump flow during cardiopulmonary bypass are beneficial for kidney function-a single-centre prospective study

Background: Kidneys play an essential role in the circulatory system, regulating blood pressure and intravascular volume. They are also set on maintaining an adequate filtration pressure in the glomerulus. During the CPB, a decrease in systemic blood pressure and hemoglobin concentration may lead to renal ischemia and subsequent acute kidney injury. Methods: One hundred nine adult patients were prospectively enrolled in this study. The intervention in this study was increasing the flow of the CPB pump to reach the target MAP of > 90 mmHg during the procedure. The control group had a standard pump flow of 2.4 L/min/m2. Results: Standard pump flow of 2.4 L/min/m2 resulted in mean MAP < 90 mmHg during the CPB in most patients in the control group. Maintaining a higher MAP during CPB in this study population did not affect CSA-AKI incidence. However, it increased the intraoperative and postoperative diuresis and decreased renin release associated with CPB. Higher MAP during the CPB did not increase the incidence of cerebrovascular complications after the operation; patients in the highest MAP group had the lowest incidence of postoperative delirium, but the result did not obtain statistical significance. Conclusion: Maintaining MAP > 90 mmHg during the CPB positively impacts intraoperative and postoperative kidney function. It significantly reduces renal hypoperfusion during the procedure compared to MAP < 70 mmHg. MAP > 90 mmHg is safe for the central nervous system, and preliminary results suggest that it may have a beneficial impact on the incidence of postoperative delirium.

Acute kidney injury after cardiac surgery

PURPOSE OF REVIEW

Patients undergoing cardiac surgery are at high risk to develop cardiac surgery-associated acute kidney injury (CS-AKI) postoperatively. CS-AKI is associated with an increased risk for persistent renal dysfunction, morbidity and mortality. This review summarizes the epidemiology and pathophysiology of CS-AKI, as well as current treatment and prevention strategies.

RECENT FINDINGS

As AKI is a syndrome with complex pathophysiology, no causative treatment strategies exist. Recent advances in the field of AKI biomarkers offer new perspectives on the issue and the implementation of biomarker-guided preventive strategies may reduce rates of CS-AKI. Finally, nephroprotective treatments and angiotensin II as a novel vasopressor may offer new opportunities for high-risk patients undergoing cardiac surgery.

SUMMARY

Based on the described novel approaches for early detection, prevention and management of CS-AKI, a precision-medicine approach should be implemented in order to prevent the development of AKI in patients undergoing cardiac surgery.

Personalized acute kidney injury treatment

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a complex syndrome that might be induced by different causes and is associated with an increased morbidity and mortality. Therefore, it is a very heterogeneous syndrome and establishing a "one size fits all" treatment approach might not work. This review aims to examine the potential of personalized treatment strategies for AKI.

RECENT FINDINGS

The traditional diagnosis of AKI is based on changes of serum creatinine and urine output, but these two functional biomarkers have several limitations. Recent research identified different AKI phenotypes based on clinical features, biomarkers, and pathophysiological pathways. Biomarkers, such as Cystatin C, NGAL, TIMP2∗IGFBP7, CCL14, and DKK-3, have shown promise in predicting AKI development, renal recovery, and prognosis. Biomarker-guided interventions, such as the implementation of the KDIGO bundle, have demonstrated an improvement in renal outcomes in specific patient groups.

SUMMARY

A personalized approach to AKI treatment as well as research is becoming increasingly important as it allows the identification of distinct AKI phenotypes and the potential for targeted interventions. By utilizing biomarkers and clinical features, physicians might be able to stratify patients into subphenotypes, enabling more individualized treatment strategies. This review highlights the potential of personalized AKI treatment, emphasizing the need for further research and large-scale clinical trials to validate the efficacy of these approaches.

The alternative renin-angiotensin system in critically ill patients: pathophysiology and therapeutic implications

The renin-angiotensin system (RAS) plays a crucial role in regulating blood pressure and the cardio-renal system. The classical RAS, mainly mediated by angiotensin I, angiotensin-converting enzyme, and angiotensin II, has been reported to be altered in critically ill patients, such as those in vasodilatory shock. However, recent research has highlighted the role of some components of the counterregulatory axis of the classical RAS, termed the alternative RAS, such as angiotensin-converting Enzyme 2 (ACE2) and angiotensin-(1-7), or peptidases which can modulate the RAS like dipeptidyl-peptidase 3, in many critical situations. In cases of shock, dipeptidyl-peptidase 3, an enzyme involved in the degradation of angiotensin and opioid peptides, has been associated with acute kidney injury and mortality and preclinical studies have tested its neutralization. Angiotensin-(1-7) has been shown to prevent septic shock development and improve outcomes in experimental models of sepsis. In the context of experimental acute lung injury, ACE2 activity has demonstrated a protective role, and its inactivation has been associated with worsened lung function, leading to the use of active recombinant human ACE2, in preclinical and human studies. Angiotensin-(1-7) has been tested in experimental models of acute lung injury and in a recent randomized controlled trial for patients with COVID-19 related hypoxemia. Overall, the alternative RAS appears to have a role in the pathogenesis of disease in critically ill patients, and modulation of the alternative RAS may improve outcomes. Here, we review the available evidence regarding the methods of analysis of the RAS, pathophysiological disturbances of this system, and discuss how therapeutic manipulation may improve outcomes in the critically ill.

Pharmacokinetic and pharmacodynamic considerations for antifungal therapy optimisation in the treatment of intra-abdominal candidiasis

Intra-abdominal candidiasis (IAC) is one of the most common of invasive candidiasis observed in critically ill patients. It is associated with high mortality, with up to 50% of deaths attributable to delays in source control and/or the introduction of antifungal therapy. Currently, there is no comprehensive guidance on optimising antifungal dosing in the treatment of IAC among the critically ill. However, this form of abdominal sepsis presents specific pharmacokinetic (PK) alterations and pharmacodynamic (PD) challenges that risk suboptimal antifungal exposure at the site of infection in critically ill patients. This review aims to describe the peculiarities of IAC from both PK and PD perspectives, advocating an individualized approach to antifungal dosing. Additionally, all current PK/PD studies relating to IAC are reviewed in terms of strength and limitations, so that core elements for the basis of future research can be provided.

Angiotensin II in liver transplantation (AngLT-1): protocol of a randomised, double-blind, placebo-controlled trial

INTRODUCTION

Catecholamine vasopressors such as norepinephrine are the standard drugs used to maintain mean arterial pressure during liver transplantation. At high doses, catecholamines may impair organ perfusion. Angiotensin II is a peptide vasoconstrictor that may improve renal perfusion pressure and glomerular filtration rate, a haemodynamic profile that could reduce acute kidney injury. Angiotensin II is approved for vasodilatory shock but has not been rigorously evaluated for treatment of hypotension during liver transplantation. The objective is to assess the efficacy of angiotensin II as a second-line vasopressor infusion during liver transplantation. This trial will establish the efficacy of angiotensin II in decreasing the dose of norepinephrine to maintain adequate blood pressure. Completion of this study will allow design of a follow-up, multicentre trial powered to detect a reduction of organ injury in liver transplantation.

METHODS AND ANALYSIS

This is a double-blind, randomised clinical trial. Eligible subjects are adults with a Model for End-Stage Liver Disease Sodium Score ≥25 undergoing deceased donor liver transplantation. Subjects are randomised 1:1 to receive angiotensin II or saline placebo as the second-line vasopressor infusion. The study drug infusion is initiated on reaching a norepinephrine dose of 0.05 µg kg-1 min-1 and titrated per protocol. The primary outcome is the dose of norepinephrine required to maintain a mean arterial pressure ≥65 mm Hg. Secondary outcomes include vasopressin or epinephrine requirement and duration of hypotension. Safety outcomes include incidence of thromboembolism within 48 hours of the end of surgery and severe hypertension. An intention-to-treat analysis will be performed for all randomised subjects receiving the study drug. The total dose of norepinephrine will be compared between the two arms by a one-tailed Mann-Whitney U test.

ETHICS AND DISSEMINATION

The trial protocol was approved by the local Institutional Review Board (#20-30948). Results will be posted on ClinicalTrials.gov and published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ClinicalTrials.govNCT04901169.

Alterations to Kidney Physiology during Cardiopulmonary Bypass-A Narrative Review of the Literature and Practical Remarks

INTRODUCTION

According to different authors, cardiac surgery-associated acute kidney injury (CSA-AKI) incidence can be as high as 20-50%. This complication increases postoperative morbidity and mortality and impairs long-term kidney function in some patients. This review aims to summarize current knowledge regarding alterations to renal physiology during cardiopulmonary bypass (CPB) and to discuss possible nephroprotective strategies for cardiac surgeries. Relevant sections: Systemic and renal circulation, Vasoactive drugs, Fluid balance and Osmotic regulation and Inflammatory response.

CONCLUSIONS

Considering the available scientific evidence, it is concluded that adequate kidney perfusion and fluid balance are the most critical factors determining postoperative kidney function. By adequate perfusion, one should understand perfusion with proper oxygen delivery and sufficient perfusion pressure. Maintaining the fluid balance is imperative for a normal kidney filtration process, which is essential for preserving the intra- and postoperative kidney function.

FUTURE DIRECTIONS

The review of the available literature regarding kidney function during cardiac surgery revealed a need for a more holistic approach to this subject.

Renin-angiotensin-aldosterone system dynamics after targeted blood pressure control using angiotensin II or norepinephrine in cardiac surgery: mechanistic randomised controlled trial

BACKGROUND

The role of the renin-angiotensin-aldosterone axis in vasoplegia after cardiac surgery remains unclear. We tested the hypothesis that, compared with norepinephrine, infusion of angiotensin II titrated to achieve similar mean arterial pressure (MAP) would suppress plasma renin concentration (PRC) while maintaining aldosterone levels.

METHODS

In a double-blind, randomised controlled trial, subjects received either an infusion of angiotensin II or norepinephrine to maintain MAP 70-80 mm Hg from induction of anaesthesia. We compared PRC, aldosterone, dipeptidyl peptidase-3, and angiotensin-converting enzyme 2 activity between treatment groups, before surgery, on ICU admission, and 24 h after surgery.

RESULTS

In 60 patients (11.7% female; mean age 68 yr [11 yr]), norepinephrine increased median PRC at ICU admission (median difference [MD] 46 [inter-quartile range, IQR, 3-88] μU ml-1; P<0.001) but angiotensin II did not (MD -3 [IQR -62 to 35] μU ml-1; P=0.36). Aldosterone levels increased with both. The aldosterone:PRC ratio did not change with norepinephrine (MD -0.01 [IQR -0.14 to 0.03] μU ml-1 per ng dl-1, P=0.76) but increased with angiotensin II (MD 0.05 [IQR 0.004-0.26] μU ml-1 per ng dl-1, P<0.001). The upper quartile of PRC before surgery was associated with higher vasopressor requirements when norepinephrine was used to maintain MAP, but not angiotensin II. Dipeptidyl peptidase-3 levels and angiotensin-converting enzyme 2 activities were similar at all time points.

CONCLUSIONS

Angiotensin II suppressed renin release while maintaining aldosterone levels compared with norepinephrine. Higher plasma renin concentration before surgery was associated with greater vasopressor requirement for norepinephrine, but not angiotensin II.

CLINICAL TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry-ACTRN12621000195853 23/02/2021.

Renin as a Biomarker of Acute Kidney Injury and Mortality in Children With Severe Malaria or Sickle Cell Disease

BACKGROUND

Globally, a very high percentage of acute kidney injury (AKI) occurs in low- and middle-income countries (LMICs) where late recognition contributes to increased mortality. There are challenges with using existing biomarkers of AKI in LMICs. Emerging evidence suggests renin may serve as a biomarker of kidney injury that can overcome limitations in creatinine-based diagnostics.

METHODS

Two study populations in Uganda were assessed. Cohort #1 was a two-site, prospective cohort study enrolling 600 children with severe malaria (SM). Cohort #2 was a prospective cohort study enrolling 185 children with sickle cell disease (SCD) hospitalized with a vaso-occlusive crisis. Plasma or serum renin concentrations were measured in both cohorts of children at the time of hospital admission using Luminex® (Luminex Corporation, Austin, Texas, United States) or enzyme-linked immunosorbent assay (ELISA), respectively. We assessed the ability of renin to discriminate between children with or without AKI and between children who survived and children who died using receiver operating characteristic curves.

RESULTS

In both cohorts, renin concentrations were strongly associated with AKI and mortality. Renin was able to discriminate between children with or without AKI with an area under the curve (AUC) of 0.70 (95%CI, 0.65-0.74) in children with SM and 0.72 (95%CI, 0.6co3-0.81) in children with SCD. Renin was able to discriminate between children who survived and children who died with an AUC of 0.73 (95%CI, 0.63-0.83) in children with SM and 0.94 (95%CI, 0.89-0.99) in children with SCD. In Cohort #2, we compared renin against urine neutrophil gelatinase-associated lipocalin (NGAL) as the leading biomarker of AKI, and it had comparable performance in discriminating AKI and predicting mortality.

CONCLUSIONS

In two independent populations of children at risk of AKI with key differences in the etiology of kidney injury, renin was strongly associated with AKI and mortality and had moderate to good diagnostic performance to predict mortality.

Initiating angiotensin II at lower vasopressor doses in vasodilatory shock: an exploratory post-hoc analysis of the ATHOS-3 clinical trial

BACKGROUND

High dose vasopressors portend poor outcome in vasodilatory shock. We aimed to evaluate the impact of baseline vasopressor dose on outcomes in patients treated with angiotensin II (AT II).

METHODS

Exploratory post-hoc analysis of the Angiotensin II for the Treatment of High-Output Shock (ATHOS-3) trial data. The ATHOS-3 trial randomized 321 patients with vasodilatory shock, who remained hypotensive (mean arterial pressure of 55-70 mmHg) despite receiving standard of care vasopressor support at a norepinephrine-equivalent dose (NED) > 0.2 µg/kg/min, to receive AT II or placebo, both in addition to standard of care vasopressors. Patients were grouped into low (≤ 0.25 µg/kg/min; n = 104) or high (> 0.25 µg/kg/min; n = 217) NED at the time of study drug initiation. The primary outcome was the difference in 28-day survival between the AT II and placebo subgroups in those with a baseline NED ≤ 0.25 µg/kg/min at the time of study drug initiation.

RESULTS

Of 321 patients, the median baseline NED in the low-NED subgroup was similar in the AT II (n = 56) and placebo (n = 48) groups (median of each arm 0.21 µg/kg/min, p = 0.45). In the high-NED subgroup, the median baseline NEDs were also similar (0.47 µg/kg/min AT II group, n = 107 vs. 0.45 µg/kg/min placebo group, n = 110, p = 0.75). After adjusting for severity of illness, those randomized to AT II in the low-NED subgroup were half as likely to die at 28-days compared to placebo (HR 0.509; 95% CI 0.274-0.945, p = 0.03). No differences in 28-day survival between AT II and placebo groups were found in the high-NED subgroup (HR 0.933; 95% CI 0.644-1.350, p = 0.71). Serious adverse events were less frequent in the low-NED AT II subgroup compared to the placebo low-NED subgroup, though differences were not statistically significant, and were comparable in the high-NED subgroups.

CONCLUSIONS

This exploratory post-hoc analysis of phase 3 clinical trial data suggests a potential benefit of AT II introduction at lower doses of other vasopressor agents. These data may inform design of a prospective trial.

TRIAL REGISTRATION

The ATHOS-3 trial was registered in the clinicaltrials.gov repository (no. NCT02338843). Registered 14 January 2015.

Downregulation of G protein-coupled receptor kinase 4 protects against kidney ischemia-reperfusion injury

Ischemia/reperfusion injury of the kidney is associated with high morbidity and mortality, and treatment of this injury remains a challenge. G protein-coupled receptor kinase 4 (GRK4) plays a vital role in essential hypertension and myocardial infarction, but its function in kidney ischemia/reperfusion injury remains undetermined. Among the GRK subtypes (GRK2-6) expressed in kidneys, the increase in GRK4 expression was much more apparent than that of the other four GRKs 24 hours after injury and was found to accumulate in the nuclei of injured mouse and human renal tubule cells. Gain- and loss-of-function experiments revealed that GRK4 overexpression exacerbated acute kidney ischemia/reperfusion injury, whereas kidney tubule-specific knockout of GRK4 decreased injury-induced kidney dysfunction. Necroptosis was the major type of tubule cell death mediated by GRK4, because GRK4 significantly increased receptor interacting kinase (RIPK)1 expression and phosphorylation, subsequently leading to RIPK3 and mixed lineage kinase domain-like protein (MLKL) phosphorylation after kidney ischemia/reperfusion injury, but was reversed by necrostatin-1 pretreatment (an RIPK1 inhibitor). Using co-immunoprecipitation, mass spectrometry, and siRNA screening studies, we identified signal transducer and activator of transcription (STAT)1 as a GRK4 binding protein, which co-localized with GRK4 in the nuclei of renal tubule cells. Additionally, GRK4 phosphorylated STAT1 at serine 727, whose inactive mutation effectively reversed GRK4-mediated RIPK1 activation and tubule cell death. Kidney-targeted GRK4 silencing with nanoparticle delivery considerably ameliorated kidney ischemia/reperfusion injury. Thus, our findings reveal that GRK4 triggers necroptosis and aggravates kidney ischemia/reperfusion injury, and its downregulation may provide a promising therapeutic strategy for kidney protection.

Plasma Renin Activity Increases With Cardiopulmonary Bypass and is Associated With Vasoplegia After Cardiac Surgery

OBJECTIVES

To describe the trend in plasma renin activity over time in patients undergoing cardiac surgery on cardiopulmonary bypass, and to investigate if increased plasma renin activity is associated with postcardiopulmonary bypass vasoplegia.

DESIGN

A prospective cohort study.

SETTING

Patients were enrolled from June 2020 to May 2021 at a tertiary cardiac surgical institution.

PATIENTS

A cohort of 100 adult patients undergoing cardiac surgery on cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma renin activity was measured at 5 time points: baseline, postoperatively, and at midnight on postoperative days 1, 2, and 3. Plasma renin activity and delta plasma renin activity were correlated with the incidence of vasoplegia and clinical outcomes. The median plasma renin activity increased approximately 3 times from baseline immediately after cardiac surgery, remained elevated on postoperative days 0, 1, and 2, and began to downtrend on postoperative day 3. Plasma renin activity was approximately 3 times higher at all measured time points in patients who developed vasoplegia versus those who did not.

CONCLUSIONS

In patients undergoing cardiac surgery on cardiopulmonary bypass, plasma renin activity increased postoperatively and remained elevated through postoperative day 2. Additionally, patients with vasoplegic syndrome after cardiac surgery on cardiopulmonary bypass had more robust elevations in plasma renin activity than nonvasoplegic patients. These findings support the need for randomized controlled trials to determine if patients undergoing cardiac surgery with high plasma renin activity may benefit from targeted treatment with therapies such as synthetic angiotensin II.

A double-blind randomised feasibility trial of angiotensin-2 in cardiac surgery. Anaesthesia 2022;77:999-1009. [PMID: 35915923 PMCID: PMC9543254 DOI: 10.1111/anae.15802]

Acute kidney injury is common after cardiac surgery. Vasoplegic hypotension may contribute to kidney injury, and different vasopressors may have variable effects on kidney function. We conducted a double-blind, randomised feasibility trial comparing peri-operative angiotensin-2 with noradrenaline. We randomly allocated 60 patients at two centres to a blinded equipotent angiotensin-2 or noradrenaline infusion intra-operatively and for up to 48 h postoperatively, titrated to mean arterial pressure of 70-80 mmHg. Primary feasibility outcomes included consent rate, protocol adherence, infusion duration, mean arterial pressure maintenance in the target range and major adverse outcomes. Secondary outcomes included kidney injury rate. The consent rate was 47%. Protocol adherence was 100% in the angiotensin-2 group and 94% in the noradrenaline group. Study drug duration was median (IQR [range]) 217 (160-270 [30-315]) vs. 185 (135-301 [0-480]) min (p = 0.78) min intra-operatively, and 5 (0-16 [0-48]) vs. 14.5 (4.8-29 [0-48]) hours (p = 0.075) postoperatively for angiotensin-2 and noradrenaline, respectively. The mean arterial pressure target was achieved postoperatively in 25 of 28 (89%) of the angiotensin-2 group and 27 of 32 (84%) of the noradrenaline group. One participant had a stroke, one required extracorporeal support and three required renal replacement therapy, all in the noradrenaline group (p = 0.99, p = 0.99 and p = 0.1). Acute kidney injury occurred in 7 of 28 in the angiotensin-2 group vs. 12 of 32 patients in the noradrenaline group (p = 0.31). This pilot study suggests that a trial comparing angiotensin-2 with noradrenaline is feasible. Its findings justify further investigations of angiotensin-2 in cardiac surgery.

Alveolar, Endothelial, and Organ Injury Marker Dynamics in Severe COVID-19

Rationale: Alveolar and endothelial injury may be differentially associated with coronavirus disease (COVID-19) severity over time. Objectives: To describe alveolar and endothelial injury dynamics and associations with COVID-19 severity, cardiorenovascular injury, and outcomes. Methods: This single-center observational study enrolled patients with COVID-19 requiring respiratory support at emergency department presentation. More than 40 markers of alveolar (including receptor for advanced glycation endproducts [RAGE]), endothelial (including angiopoietin-2), and cardiorenovascular injury (including renin, kidney injury molecule-1, and troponin-I) were serially compared between invasively and spontaneously ventilated patients using mixed-effects repeated-measures models. Ventilatory ratios were calculated for intubated patients. Associations of biomarkers with modified World Health Organization scale at Day 28 were determined with multivariable proportional-odds regression. Measurements and Main Results: Of 225 patients, 74 (33%) received invasive ventilation at Day 0. RAGE was 1.80-fold higher in invasive ventilation patients at Day 0 (95% confidence interval [CI], 1.50-2.17) versus spontaneous ventilation, but decreased over time in all patients. Changes in alveolar markers did not correlate with changes in endothelial, cardiac, or renal injury markers. In contrast, endothelial markers were similar to lower at Day 0 for invasive ventilation versus spontaneous ventilation, but then increased over time only among intubated patients. In intubated patients, angiopoietin-2 was similar (fold difference, 1.02; 95% CI, 0.89-1.17) to nonintubated patients at Day 0 but 1.80-fold higher (95% CI, 1.56-2.06) at Day 3; cardiorenovascular injury markers showed similar patterns. Endothelial markers were not consistently associated with ventilatory ratios. Endothelial markers were more often significantly associated with 28-day outcomes than alveolar markers. Conclusions: Alveolar injury markers increase early. Endothelial injury markers increase later and are associated with cardiorenovascular injury and 28-day outcome. Alveolar and endothelial injury likely contribute at different times to disease progression in severe COVID-19.

The Association Between Angiotensin II and Renin Kinetics in Patients After Cardiac Surgery

BACKGROUND

Hyperreninemia after cardiac surgery is associated with cardiovascular instability. Angiotensin II (AT-II) could potentially attenuate hyperreninemia while maintaining target blood pressure. This study assesses the association between AT-II usage and renin levels in cardiac surgery patients with postoperative hyperreninemia and vasoplegia.

METHODS

Between September 2020 and March 2021, we retrospectively identified 40 cardiac surgery patients with high Δ-renin levels (4 hours after cardiopulmonary bypass [CPB] minus preoperative levels) (defined as higher than 3.7 µU/mL) and vasopressor use who received a vasopressor therapy with either AT-II or continued norepinephrine alone. The primary outcome was the renin plasma level at 12 hours after surgery, adjusted by the renin plasma level at 4 hours after surgery.

RESULTS

Overall, the median renin plasma concentration increased from a baseline with median of 44.3 µU/mL (Q1-Q3, 14.6-155.5) to 188.6 µU/mL (Q1-Q3, 29.8-379.0) 4 hours after CPB. High Δ-renin (difference between postoperation and preoperation) patients (higher than 3.7 µU/mL) were then treated with norepinephrine alone (median dose of 3.25 mg [Q1-Q3, 1.00-4.75]) or with additional AT-II (norepinephrine dose: 1.33 mg [Q1-Q3, 0.78-2.04]; AT-II dose: 0.34 mg [Q1-Q3, 0.29-0.78]). At 12 hours after surgery, AT-II patients had lower renin levels than standard of care patients (71.7 µU/mL [Q1-Q3, 21.9-211.4] vs 130.6 µU/mL [Q1-Q3, 62.9-317.0]; P = .034 adjusting for the renin plasma level at 4 hours after surgery).

CONCLUSIONS

In cardiac surgery patients with hypotonia and postoperative high Δ-renin levels, AT-II was associated with reduced renin plasma levels for at 12 hours and significantly decreased norepinephrine use, while norepinephrine alone was associated with increased renin levels. Further studies of AT-II in cardiac surgery appear justified.

Plasma Metabolites-Based Prediction in Cardiac Surgery-Associated Acute Kidney Injury

Background

Cardiac surgery–associated acute kidney injury (CSA‐AKI) is a common postoperative complication following cardiac surgery. Currently, there are no reliable methods for the early prediction of CSA‐AKI in hospitalized patients. This study developed and evaluated the diagnostic use of metabolomics‐based biomarkers in patients with CSA‐AKI.

Methods and Results

A total of 214 individuals (122 patients with acute kidney injury [AKI], 92 patients without AKI as controls) were enrolled in this study. Plasma samples were analyzed by liquid chromatography tandem mass spectrometry using untargeted and targeted metabolomic approaches. Time‐dependent effects of selected metabolites were investigated in an AKI swine model. Multiple machine learning algorithms were used to identify plasma metabolites positively associated with CSA‐AKI. Metabolomic analyses from plasma samples taken within 24 hours following cardiac surgery were useful for distinguishing patients with AKI from controls without AKI. Gluconic acid, fumaric acid, and pseudouridine were significantly upregulated in patients with AKI. A random forest model constructed with selected clinical parameters and metabolites exhibited excellent discriminative ability (area under curve, 0.939; 95% CI, 0.879–0.998). In the AKI swine model, plasma levels of the 3 discriminating metabolites increased in a time‐dependent manner (R², 0.480–0.945). Use of this AKI predictive model was then confirmed in the validation cohort (area under curve, 0.972; 95% CI, 0.947–0.996). The predictive model remained robust when tested in a subset of patients with early‐stage AKI in the validation cohort (area under curve, 0.943; 95% CI, 0.883–1.000).

Conclusions

High‐resolution metabolomics is sufficiently powerful for developing novel biomarkers. Plasma levels of 3 metabolites were useful for the early identification of CSA‐AKI.

Diagnosis of Cardiac Surgery-Associated Acute Kidney Injury

Acute kidney injury after cardiac surgery is characterized by specific patterns of damage and recovery that are important to consider for management and outcome. The Kidney Disease: Improving Global Outcomes (KDIGO) classification covers only part of the conceptual framework and is thus insufficient for a comprehensive diagnosis. This review highlights the strengths and limitations of the recent criteria and provides an overview of biomarkers of cardiac surgery-associated acute kidney injury (CSA-AKI). The evolving understanding of CSA-AKI as a time-sensitive condition has increased the demand to enhance the diagnostic criteria and translate biomarkers into clinical practice.

Serum renin and major adverse kidney events in critically ill patients: a multicenter prospective study

BACKGROUND

Preliminary studies have suggested that the renin-angiotensin system is activated in critical illness and associated with mortality and kidney outcomes. We sought to assess in a larger, multicenter study the relationship between serum renin and Major Adverse Kidney Events (MAKE) in intensive care unit (ICU) patients.

METHODS

Prospective, multicenter study at two institutions of patients with and without acute kidney injury (AKI). Blood samples were collected for renin measurement a median of 2 days into the index ICU admission and 5-7 days later. The primary outcome was MAKE at hospital discharge, a composite of mortality, kidney replacement therapy, or reduced estimated glomerular filtration rate to ≤ 75% of baseline.

RESULTS

Patients in the highest renin tertile were more severely ill overall, including more AKI, vasopressor-dependence, and severity of illness. MAKE were significantly greater in the highest renin tertile compared to the first and second tertiles. In multivariable logistic regression, this initial measurement of renin remained significantly associated with both MAKE as well as the individual component of mortality. The association of renin with MAKE in survivors was not statistically significant. Renin measurements at the second time point were also higher in patients with MAKE. The trajectory of the renin measurements between time 1 and 2 was distinct when comparing death versus survival, but not when comparing MAKE versus those without.

CONCLUSIONS

In a broad cohort of critically ill patients, serum renin measured early in the ICU admission is associated with MAKE at discharge, particularly mortality.

Acute Kidney Injury following Cardiopulmonary Bypass: A Challenging Picture

Recent studies have recognized several risk factors for cardiopulmonary bypass- (CPB-) associated acute kidney injury (AKI). However, the lack of early biomarkers for AKI prevents practitioners from intervening in a timely manner. We reviewed the literature with the aim of improving our understanding of the risk factors for CPB-associated AKI, which may increase our ability to prevent or improve this condition. Some novel early biomarkers for AKI have been introduced. In particular, a combinational use of these biomarkers would be helpful to improve clinical outcomes. Furthermore, we discuss several interventions that are aimed at managing CPB-associated AKI, may increase the effect of renal replacement therapy (RRT), and may contribute to preventing CPB-associated AKI. Collectively, the conclusions of this paper are limited by the availability of clinical trial evidence and conflicting definitions of AKI. A guideline is urgently needed for CPB-associated AKI.