Proenkephalin Compared to Conventional Methods to Assess Kidney Function in Critically Ill Sepsis Patients

A comparison of the renal function biomarkers serum creatinine, pro-enkephalin and cystatin C to predict clearance of pemetrexed

INTRODUCTION

For drugs with a narrow therapeutic window, there is a delicate balance between efficacy and toxicity, thus it is pivotal to administer the right dose from the first administration onwards. Exposure of pemetrexed, a cytotoxic drug used in lung cancer treatment, is dictated by kidney function. To facilitate optimized dosing of pemetrexed, accurate prediction of drug clearance is pivotal. Therefore, the aim of this study was to investigate the performance of the kidney function biomarkers serum creatinine, cystatin C and pro-enkephalin in terms of predicting the elimination of pemetrexed.

METHODS

We performed a population pharmacokinetic analysis using a dataset from two clinical trials containing pharmacokinetic data of pemetrexed and measurements of all three biomarkers. A three-compartment model without covariates was fitted to the data and the obtained individual empirical Bayes estimates for pemetrexed clearance were considered the "true" values (Cltrue). Subsequently, the following algorithms were tested as covariates for pemetrexed clearance: the Chronic Kidney Disease Epidemiology Collaboration equation using creatinine (CKD-EPICR), cystatin C (CKD-EPICYS), a combination of both (CKD-EPICR-CYS), pro-enkephalin as an absolute value or in a combined algorithm with age and serum creatinine, and lastly, a combination of pro-enkephalin with cystatin C.

RESULTS

The dataset consisted of 66 subjects with paired observations for all three kidney function biomarkers. Inclusion of CKD-EPICR-CYS as a covariate on pemetrexed clearance resulted in the best model fit, with the largest decrease in objective function (p < 0.00001) and explaining 35% of the total inter-individual variability in clearance. The predictive performance of the model to containing CKD-EPICR-CYS to predict pemetrexed clearance was good with a normalized root mean squared error and mean prediction error of 19.9% and 1.2%, respectively.

CONCLUSIONS

In conclusion, this study showed that the combined CKD-EPICR-CYS performs best in terms predicting pharmacokinetics of pemetrexed. Despite the hypothesized disadvantages, creatinine remains to be a suitable and readily available marker to predict pemetrexed clearance in clinical practice.

Plasma proenkephalin and neutrophil gelatinase-associated lipocalin predict mortality in ICU patients with acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common complication in patients admitted to intensive care unit (ICU) and mortality rates for this condition are high. To reduce the high incidence of short-term mortality, reliable prognostic indicators are required to facilitate early diagnosis and treatment of AKI. We assessed the ability of plasma proenkephalin (p‑PENK) and plasma neutrophil gelatinase-associated lipocalin (p‑NGAL) to predict 28-day mortality in AKI patients in intensive care.

METHODS

This prospective study, carried out between January 2019 and December 2019, comprised 150 patients (100 male) diagnosed with AKI after excluding 20 patients discharged within 24 h and those with missing hospitalization data. Blood samples were collected to determine admission p-PENK and p-NGAL levels. The study outcome was 28‑day mortality.

RESULTS

The mean patient age was 68 years (female, 33%). The average P‑PENK and p‑NGAL levels were 0.24 ng/µL and 223.70 ng/mL, respectively. P‑PENK levels >0.36 ng/µL and p‑NGAL levels >230.30 ng/mL were used as critical values to reliably indicate 28‑day mortality for patients with AKI (adjusted hazard ratios 0.785 [95% confidence interval 0.706-0.865, P<0.001] and 0.700 [95% confidence interval 0.611-0.789, P<0.001], respectively). This association was significant for mortality in patients in intensive care with AKI. Baseline p-PENK (0.36 ng/µL) and p-NGAL (230.30 ng/mL) levels and their respective cut-off values showed clinical value in predicting 28-day mortality.

CONCLUSION

Serum PENK and NGAL levels, when used in conjunction, improved the accuracy of predicting 28-day mortality in patients with AKI while retaining sensitivity and specificity.

Questionable Validity of Creatinine-Based eGFR in Elderly Patients but Cystatin C Is Helpful in First-Line Diagnostics

BACKGROUND

The recommended chronic kidney disease (CKD) first-line diagnostic test is based on the creatinine-derived (estimated) glomerular filtration rate (eGFR). Cystatin C use may provide a better assessment.

METHODS

We compared creatinine- and cystatin C-derived eGFR determination as the first-line diagnostic test for 112 hospital patients aged > 60 years (median = 76 years). The patients were judged to not have CKD (no-CKD group) according to the first-line diagnostic recommendations (n = 61, eGFR (CKD Epidemiology Collaboration (CKD-EPI)) ≥ 60 mL/min/1.73 m2, total urine protein < 150 mg/g creatinine, urinary red/white blood cells not increased) or classified to be at risk for kidney insufficiency due to aortic valve dysfunction (at-risk group; n = 51). The accuracy of the eGFR values was evaluated retrospectively with the final case diagnoses.

RESULTS

The eGFR (Caucasian, Asian, pediatric, and adult formula (CAPA)) was found to be linearly correlated to the eGFR (CKD-EPI) (R2 = 0.5, slope = 0.69, p < 0.0001). In 93/112 (>80%) cases, the eGFR (CAPA) yielded lower values (on average ≈-20%). In 55/112 (49%) cases, the cystatin C-derived CKD stage was lower. CKD reclassification from no-CKD to a kidney-insufficient state (i.e., CKD1/2 to CKD3a/b or 4) or reclassification to a more severe kidney insufficiency (i.e., CKD3a → 3b/4 or 3b → 4) was found in 41/112 (37%) cases. A worse CKD classification (no-CKD → kidney-insufficient) based on the eGFR (CAPA) was plausible in 30% of cases in light of the final case diagnoses.

CONCLUSION

In elderly patients (>60 years), renal function appears to be systematically overestimated by the creatinine-based eGFR (CKD-EPI), indicating that, for this group, the cystatin C-based eGFR (CAPA) should be used as the first-line diagnostic test.

When to discontinue renal replacement therapy. what do we know?

PURPOSE OF REVIEW

Acute kidney injury is common in intensive care patients. Supportive care involves the use of renal replacement therapies as organ support. Initiation of renal replacement therapy has been the subject of much interest over the last few years with several randomised controlled studies examining the optimal time to commence treatment. In contrast to this, little evidence has been generated regarding cessation of therapy. Given that this treatment is complex, not without risk and expensive it seems timely that efforts should be expended at examining this vexing issue.

RECENT FINDINGS

Although several studies have been reported examining the successful discontinuation of renal replacement therapies all studies reported to-date are observational in nature. Conventional biochemical criteria have been used as well as physiological parameters including urine output. More recently, more novel biomarkers of renal function have been studied. Although to-date no optimal variable nor threshold for discontinuation can be established.

SUMMARY

Several variables have been described which may have a role in determining which patients may be successfully weaned from renal replacement therapy. However, few have been exposed to vigorous examination and evidence is sparse in support of any potential approach although urine output currently is the most often described. More recently novel biomarkers have also been examined but again are limited by study design and heterogeneity. Further research is clearly needed focussing on proposed variables preferably in multivariate models to improve predictive ability and successful cessation of therapy.

Assessing GFR With Proenkephalin

Introduction

In clinical practice, kidney (dys)function is monitored through creatinine-based estimations of glomerular filtration rate (eGFR: Modification of Diet in Renal Disease [MDRD], Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI]). Creatinine is recognized as a late and insensitive biomarker of glomerular filtration rate (GFR). The novel biomarker proenkephalin (PENK) may overcome these limitations, but no PENK-based equation for eGFR is currently available. Therefore, we developed and validated a PENK-based equation to assess GFR.

Methods

In this international multicenter study in 1354 stable and critically ill patients, GFR was measured (mGFR) through iohexol or iothalamate clearance. A generalized linear model with sigmoidal nonlinear transfer function was used for equation development in the block-randomized development set. Covariates were selected in a data-driven fashion. The novel equation was assessed for bias, precision (mean ± SD), and accuracy (eGFR percentage within ±30% of mGFR, P30) in the validation set and compared with MDRD and CKD-EPI.

Results

Median mGFR was 61 [44-81] ml/min per 1.73 m2. In order of importance, PENK, creatinine, and age were included, and sex or race did not improve performance. The PENK-based equation mean ± SD bias of the mGFR was 0.5 ± 15 ml/min per 1.73 m2, significantly less compared with MDRD (8 ± 17, P < 0.001) and 2009 CKD-EPI (5 ± 17, P < 0.001), not reaching statistical significance compared with 2021 CKD-EPI (1.3 ± 16, P = 0.06). The P30 accuracy of the PENK-based equation was 83%, significantly higher compared with MDRD (68%, P < 0.001) and 2009 CKD-EPI (76%, P < 0.001), similar to 2021 CKD-EPI (80%, P = 0.13).

Conclusion

Overall, the PENK-based equation to assess eGFR performed better than most creatinine-based equations without using sex or race.

Proenkephalin Levels and Its Determinants in Patients with End-Stage Kidney Disease Treated with Hemodialysis and Peritoneal Dialysis

Recently, proenkephalin A (PENK A) has been shown to reflect glomerular dysfunction and to predict new-onset acute kidney injury and heart failure. While previous studies have investigated PENK A as a biomarker in individuals with preserved renal function, PENK A concentration in patients with end-stage kidney disease (ESKD) was not investigated. Plasma PENK A concentration was assessed in 88 patients with ESKD treated with hemodialysis (HD) or peritoneal dialysis (PD), and its associations with kidney function and heart failure indicators were investigated. In HD patients, the difference in PENK A levels before and after hemodialysis, was measured and further assessed for an association with the type of HD membrane used. PENK A levels did not differ significantly between HD and PD patients. In HD patients, the median PENK A concentration was significantly higher before than after hemodialysis (1.368 vs. 2.061, p = 0.003). No correlation was found between PENK A level and urea (p = 0.192), eGFR (p = 0.922), dialysis vintage (p = 0.637), and residual urine output (p = 0.784). Heart failure (p = 0.961), EF (p = 0.361), and NT-proBNP (p = 0.949) were not associated with increased PENK A concentration. PENK A does not reflect renal function and cardiac status in patients with ESKD. Further research is required to establish the clinical utility of the new biomarker in patients with impaired kidney function.

Medication Management in the Critically Ill Patient with Acute Kidney Injury

ABSTRACT

AKI occurs frequently in critically ill patients. Patients with AKI, including those who require KRT, experience multiple pharmacokinetic and pharmacodynamic perturbations that dynamically influence medication effectiveness and safety. Patients with AKI may experience both subtherapeutic drug concentrations, which lead to ineffective therapy, and supratherapeutic drug concentrations, which increase the risk for toxicity. In critically ill patients with AKI not requiring KRT, conventional GFR estimation equations, especially those based on serum creatinine, have several limitations that can limit the accuracy when used for medication dosing. Alternative methods to estimate kidney function may be informative, including use of measured urinary creatinine clearance, kinetic eGFR, and equations that integrate novel kidney biomarkers. For critically ill patients with AKI requiring KRT, physicochemical properties of the drug, the KRT prescription and circuit configuration, and patient-specific factors each contribute to medication clearance. Evidence-based guidance for medication dosing during AKI requiring KRT is often limited. A working knowledge of the basic tenets of drug elimination during KRT can provide a framework for how to approach decision making when the literature is lacking. Iterative re-evaluation of a patient's progress toward therapeutic goals with a medication must occur over the arc of critical illness, including and especially in the setting of dynamic kidney function.

Evaluation of Proenkephalin A 119-159 for liberation from renal replacement therapy: an external, multicenter pilot study in critically ill patients with acute kidney injury

INTRODUCTION

Recent evidence suggests an association of plasma Proenkephalin A 119-159 (penKid) with early and successful liberation from continuous renal replacement therapy (CRRT) in critically ill patients with acute kidney injury. However, these exploratory results are derived from a monocentric trial and therefore require external validation in a multicenter cohort.

METHODS

Data and plasma samples from the "Effect of Regional Citrate Anticoagulation versus Systemic Heparin Anticoagulation During Continuous Kidney Replacement Therapy on Dialysis Filter Life Span and Mortality Among Critically Ill Patients With Acute Kidney Injury-A Randomized Clinical Trial" (RICH Trial) were used for this validation study. PenKid was measured in all plasma samples available at CRRT initiation and at day 3 of CRRT. Patients were categorized into low and high penKid groups with a cutoff at 100 pmol/l. Competing-risk time-to-event analyses were performed. Competing risk endpoints were successful and unsuccessful liberation from CRRT, the latter meaning death or initiation of a new RRT within one week of discontinuation of primary CRRT. Then penKid was compared to urinary output.

RESULTS

Low pre-CRRT penKid levels at CRRT initiation were not associated with early and successful liberation from CRRT compared to patients with high pre-CRRT penKid levels [subdistribution hazard ratio (sHR) 1.01, 95% CI 0.73-1.40, p = 0.945]. However, the landmark analysis on day 3 of ongoing CRRT demonstrated an association between low penKid levels and successful liberation from CRRT (sHR 2.35, 95% CI 1.45-3.81, p < 0.001) and an association between high penKid levels and unsuccessful liberation (sHR 0.46, 95% CI 0.26-0.80, p = 0.007). High daily urinary output (> 436 ml/d) was even stronger associated with successful liberation (sHR 2.91, 95% CI 1.80-4.73, p < 0.001) compared to penKid.

DISCUSSION

This study suggests that penKid may be a competent biomarker to monitor the recovery of kidney function during CRRT. This is in line with previous findings and investigated this concept in a multicenter cohort. Again, low penKid was associated with early and successful CRRT liberation, but was outperformed by high daily urinary output. The findings of this study now warrant further evaluation in prospective studies or a randomized controlled trial. Trial registration The RICH Trial was registered at clinicaltrials.gov: NCT02669589. Registered 01 February 2016.

Biomarkers as Prognostic Predictors and Therapeutic Guide in Critically Ill Patients: Clinical Evidence

A biomarker is a molecule that can be measured in a biological sample in an objective, systematic, and precise way, whose levels indicate whether a process is normal or pathological. Knowing the most important biomarkers and their characteristics is the key to precision medicine in intensive and perioperative care. Biomarkers can be used to diagnose, in assessment of disease severity, to stratify risk, to predict and guide clinical decisions, and to guide treatments and response to them. In this review, we will analyze what characteristics a biomarker should have and how to ensure its usefulness, and we will review the biomarkers that in our opinion can make their knowledge more useful to the reader in their clinical practice, with a future perspective. These biomarkers, in our opinion, are lactate, C-Reactive Protein, Troponins T and I, Brain Natriuretic Peptides, Procalcitonin, MR-ProAdrenomedullin and BioAdrenomedullin, Neutrophil/lymphocyte ratio and lymphopenia, Proenkephalin, NefroCheck, Neutrophil gelatinase-associated lipocalin (NGAL), Interleukin 6, Urokinase-type soluble plasminogen activator receptor (suPAR), Presepsin, Pancreatic Stone Protein (PSP), and Dipeptidyl peptidase 3 (DPP3). Finally, we propose an approach to the perioperative evaluation of high-risk patients and critically ill patients in the Intensive Care Unit (ICU) based on biomarkers.

Localization and characterization of proenkephalin-A as a potential biomarker for kidney disease in murine and human kidneys

INTRODUCTION

Exact measurement of renal function is essential for the treatment of patients. Elevated serum-creatinine levels, while established, are influenced by other parameters and show a significant time-lag. This drives the search for novel biomarkers of renal function and injury. Beside Lipocalin-2 and kidney-injury-molecule-1 (KIM-1), the endogenous opioid precursor proenkephalin-A (Penk) has recently emerged as a promising marker for renal function. But the cellular origin and regulation of Penk outside the brain has not yet been investigated in depth.

MATERIALS AND METHODS

This study characterizes the cellular origin of Penk expression with high-resolution in situ hybridization in two models of renal fibrosis in mice and human tissue.

RESULTS

Interstitial cells are the main expression site for renal Penk. This classifies Penk as biomarker for interstitial damage as opposed to tubular damage markers like Lipocalin-2 and KIM-1. Furthermore, our data indicate that renal Penk expression is not regulated by classical profibrotic pathways.

DISCUSSION

This study characterizes changing Penk expression in the kidneys. The similarity of Penk expression across species gives rise to further investigations into the function of Penk in healthy and injured kidneys.

CONCLUSION

Penk is a promising biomarker for interstitial renal damage that warrants further studies to utilize its predictive potential.Clinical significanceKnowledge of real-time renal function is essential for proper treatment of critically ill patients and in early diagnosis of acute kidney injury (AKI). Proenkephalin-A has been measured in a number of patient cohorts as a highly accurate and predictive biomarker of renal damage.The present study identifies Penk as a biomarker for interstitial damage in contrast to the tubular biomarkers such as Lipocalin-2 or KIM-1.Our data show that Penk is regulated independently of classical profibrotic or proinflammatory pathways, indicating it might be more robust against extra-renal influences.Data presented in this study provide fundamental information about cell type-specific localization and regulation of the potential new biomarker Penk across species as foundation for further research.

Definitions, phenotypes, and subphenotypes in acute kidney injury-Moving towards precision medicine

The current definition of acute kidney injury (AKI) is generic and, based only on markers of function, is unsuitable for guiding individualized treatment. AKI is a complex syndrome with multiple presentations and causes. Targeted AKI management will only be possible if different phenotypes and subphenotypes of AKI are recognised, based on causation and related pathophysiology. Molecular signatures to identify subphenotypes are being recognised, as specific biomarkers reveal activated pathways. Assessment of individual clinical risk needs wider dissemination to allow identification of patients at high risk of AKI. New and more timely markers for glomerular filtration rate (GFR) are available. However, AKI diagnosis and classification should not be limited to GFR, but include tubular function and damage. Combining damage and stress biomarkers with functional markers enhances risk prediction, and identifies a population enriched for clinical trials targeting AKI. We review novel developments and aim to encourage implementation of these new techniques into clinical practice as a strategy for individualizing AKI treatment akin to a precision medicine-based approach.

Proenkephalin A as a marker for glomerular filtration rate in critically ill children: validation against gold standard iohexol GFR measurements

OBJECTIVES

Accurate determination of glomerular filtration rate (GFR) is important. Several endogenous biomarkers exist for estimating GFR, yet, they have limited accuracy, especially in the paediatric population. Proenkephalin A 119-159 (PENK) is a novel and promising GFR marker, but its relation with age in children remains unknown. Also, the value of PENK has never been validated against measured GFR (mGFR) in children when compared to traditional GFR markers including serum creatinine (SCr), SCr-based estimated GFR (eGFR) and cystatin C (cysC).

METHODS

Critically ill children and term-born neonates were included in this single-centre, prospective study. Iohexol-based mGFR, SCr, and cysC were determined in each patient. eGFR was calculated using the bedside Schwartz equation, incorporating SCr and height. Spearman correlation coefficients were calculated to determine the correlation between mGFR and PENK, SCr, cysC and eGFR.

RESULTS

For 97 patients (56 children and 41 neonates), mGFR, SCr, cysC and PENK levels were available. PENK levels were higher in young children and decreased to adult PENK reference values around two years of age. PENK levels were highly correlated with mGFR (ρ=-0.88, p<0.001), and similar to mGFR-eGFR correlation (ρ=-0.87, p<0.001). For cysC and SCr the correlation with mGFR was lower (ρ=-0.77 and ρ=-0.46, respectively. Both p<0.001).

CONCLUSIONS

The correlation of PENK with mGFR was as good as SCr-based eGFR-mGFR correlation. To determine the added value of PENK in paediatric clinical care and prior to implementation, PENK reference values are needed and the development and validation of a paediatric PENK-based eGFR equation is necessary.

Utility of Measuring Circulating Bio-Adrenomedullin and Proenkephalin for 30-Day Mortality Risk Prediction in Patients with COVID-19 and Non-COVID-19 Interstitial Pneumonia in the Emergency Department

Background and Objectives: In order to accelerate the risk stratification of patients referred to the Emergency Department (ED) with interstitial pneumonia, it could be useful to provide new and effective laboratory tests for use. The aim of our study was to evaluate the prognostic role of two biomarkers, bio-adrenomedullin (Bio-ADM) and proenkephalin (penKid), in patients with interstitial pneumonia (IP) at ED admission. Materials and Methods: In 153 consecutive patients with IP, both from COVID-19 or non-COVID-19 etiology, we measured, in a prospective observational manner, penKid and Bio-ADM at ED admission and after 24 h. In order to evaluate patient outcomes, 30-day follow-ups were also performed. The endpoints were 24 h, 10-day, and 30-day mortality. Results: Both biomarkers were shown to be good predictors of adverse events at 30 days, with Bio-ADM outperforming penKid. Bio-ADM was linked with 24 h and 10-day patient mortality. Moreover, PenKid was related to parameters defining worsening kidney function. Conclusions: Both in patients with COVID-19 or non-COVID-19 interstitial pneumonia at ED admission, Bio-ADM and penKid were good predictors of patient mortality. To evaluate these two biomarkers could be considered to be useful during the first evaluation in the ED when integrated with clinical scores.

Reliability of glomerular filtration rate estimating formulas compared to iohexol plasma clearance in critically ill children

Accurate renal function assessment is crucial to guide intensive care decision-making and drug dosing. Estimates of glomerular filtration rate (eGFR) are routinely used in critically ill children; however, these formulas were never evaluated against measured GFR (mGFR) in this population. We aimed to assess the reliability of common eGFR formulas compared to iohexol plasma clearance (CL_iohexol) in a pediatric intensive care (PICU) population. Secondary outcomes were the prevalence of acute kidney injury (AKI) (by pRIFLE criteria) and augmented renal clearance (ARC) (defined as standard GFR for age + 2 standard deviations (SD)) within 48 h after admission based on mGFR and eGFR by the revised Schwartz formula and the difference between these two methods to diagnose AKI and ARC. In children, between 0 and 15 years of age, without chronic renal disease, GFR was measured by CL_iohexol and estimated using 26 formulas based on creatinine (Scr), cystatine C (CysC), and betatrace protein (BTP), early after PICU admission. eGFR and mGFR results were compared for the entire study population and in subgroups according to age, using Bland-Altman analysis with calculation of bias, precision, and accuracy expressed as percentage of eGFR results within 30% (P30) and 10% (P10) of mGFR. CL_iohexol was measured in 98 patients. Mean CL_iohexol (± SD) was 115 ± 54 ml/min/1.73m². Most eGFR formulas showed overestimation of mGFR with large bias and poor precision reflected by wide limits of agreement (LoA). Bias was larger with CysC- and BTP-based formulas compared to Scr-based formulas. In the entire study population, none of the eGFR formulas showed the minimal desired P30 > 75%. The widely used revised Schwartz formula overestimated mGFR with a high percentage bias of - 18 ± 51% (95% confidence interval (CI) - 29; - 9), poor precision with 95% LoA from - 120 to 84% and insufficient accuracy reflected by P30 of only 51% (95% CI 41; 61), and P10 of 21% (95% CI 13; 66) in the overall population. Although performance of Scr-based formulas was worst in children below 1 month of age, exclusion of neonates and younger children did not result in improved agreement and accuracy. Based on mGFR, prevalence of AKI and ARC within 48 h was 17% and 45% of patients, respectively. There was poor agreement between revised Schwartz formula and mGFR to diagnose AKI (kappa value of 0.342, p < 0.001; sensitivity of 30%, 95% CI 5; 20%) and ARC (kappa value of 0.342, p < 0.001; sensitivity of 70%, 95% CI 33; 58).

CONCLUSION

In this proof-of-concept study, eGFR formulas were found to be largely inaccurate in the PICU population. Clinicians should therefore use these formulas with caution to guide drug dosing and therapeutic interventions in critically ill children. More research in subgroup populations is warranted to conclude on generalizability of these study findings.

CLINICALTRIALS

gov NCT05179564, registered retrospectively on January 5, 2022.

WHAT IS KNOWN

• Both acute kidney injury and augmented renal clearance may be present in PICU patients and warrant adaptation of therapy, including drug dosing. • Biomarker-based eGFR formulas are widely used for GFR assessment in critically ill children, although endogenous filtration biomarkers have important limitations in PICU patients and eGFR formulas have never been validated against measured GFR in this population.

WHAT IS NEW

• eGFR formulas were found to be largely inaccurate in the PICU population when compared to measured GFR by iohexol clearance. Clinicians should therefore use these formulas with caution to guide drug dosing and therapeutic interventions in critically ill children. • Iohexol plasma clearance could be considered an alternative for accurate GFR assessment in PICU patients.

Proenkephalin A 119-159 predicts early and successful liberation from renal replacement therapy in critically ill patients with acute kidney injury: a post hoc analysis of the ELAIN trial

BACKGROUND

Renal replacement therapy (RRT) remains the key rescue therapy for critically ill patients with severe acute kidney injury (AKI). However, there are currently no tools available to predict successful liberation from RRT. Biomarkers may allow for risk stratification and individualization of treatment strategies. Proenkephalin A 119-159 (penKid) has been suggested as a promising marker of kidney function in the context of AKI, but has not yet been evaluated for RRT liberation in critically ill patients with AKI.

METHODS

This post hoc analysis included 210 patients from the randomized clinical ELAIN trial and penKid levels were measured in the blood of these patients. Competing risk time-to-event analyses were performed for pre-RRT penKid at initiation of RRT and in a landmark analysis at day 3 after initiation of RRT. Competing risk endpoints were successful liberation from RRT or death without prior liberation from RRT.

RESULTS

Low pre-RRT penKid levels (penKid ≤ 89 pmol/l) at RRT initiation were associated with early and successful liberation from RRT compared to patients with high pre-RRT penKid levels (subdistribution hazard ratio (sHR) 1.83, 95%CI 1.26-2.67, p = 0.002, estimated 28d-cumulative incidence function (28d-CIF) of successful liberation from RRT 61% vs. 45%, p = 0.022). This association persisted in the landmark analysis on day 3 of RRT (sHR 1.78, 95%CI 1.17-2.71, p = 0.007, 28d-CIF of successful liberation from RRT 67% vs. 47%, p = 0.018). For both time points, no difference in the competing event of death was detected.

CONCLUSIONS

In critically ill patients with RRT-dependent AKI, plasma penKid appears to be a useful biomarker for the prediction of shorter duration and successful liberation from RRT and may allow an individualized approach to guide strategies of RRT liberation in critically ill patients with RRT-dependent AKI.

TRIAL REGISTRATION

The ELAIN trial was prospectively registered at the German Clinical Trial Registry (Identifier: DRKS00004367) on 28th of May 2013.

Characterising acute kidney injury: The complementary roles of biomarkers of renal stress and renal function

PURPOSE

Although epidemiological studies have enhanced our understanding of acute kidney injury, defining the biologic processes corresponding to the clinical phenotype remains challenging. We have examined biomarkers associated with renal stress plus markers of glomerular function to assess whether this approach may aid prediction of AKI or other relevant endpoints.

MATERIALS & METHODS

Urinary [TIMP-2]·[IGFBP7], serum creatinine, plasma cystatin C and plasma proenkephalin 119-159 ² were analyzed in patients enrolled in the prospective, international, Sapphire study. Heterogenous critically ill patients (n = 723) were examined with a primary endpoint of development of KDIGO stage 2-3 within 12 h and a secondary endpoint of major adverse kidney events at 30 days (MAKE₃₀).

RESULTS

100 patients (14%) reached the primary endpoint. Markers of renal stress outperformed those associated with glomerular function. Combining [TIMP-2]•[IGFBP7] with serum creatinine, but not the other functional markers, significantly (p = 0.02) increased the area under the ROC curve (AUC) from 0.80 (0.76-0.84) to 0.85 (0.81-0.89). In patients who did not develop AKI, all markers of glomerular filtration, but not [TIMP-2]·[IGFBP7], were significantly elevated in patients with a history of CKD (p < 0.05).

CONCLUSIONS

The combination of cell-cycle arrest biomarkers, TIMP-2 and IGFBP7, with serum creatinine but not cystatin C or PENK improved risk stratification for the development of stage 2 or 3 AKI over [TIMP-2]·[IGFBP7] alone.

Advances in the study of subclinical AKI biomarkers

Acute kidney injury (AKI) is a prevalent and serious illness in all clinical departments, with a high morbidity and death rate, particularly in intensive care units, where prevention and treatment are crucial. As a result, active prevention, early detection, and timely intervention for acute kidney injury are critical. The current diagnostic criteria for acute kidney injury are an increase in serum creatinine concentration and/or a decrease in urine output, although creatinine and urine output merely reflect changes in kidney function, and AKI suggests injury or damage, but not necessarily dysfunction. The human kidney plays a crucial functional reserve role, and dysfunction is only visible when more than half of the renal mass is impaired. Tubular damage markers can be used to detect AKI before filtration function is lost, and new biomarkers have shown a new subset of AKI patients known as "subclinical AKI." Furthermore, creatinine and urine volume are only marginally effective for detecting subclinical AKI. As a result, the search for new biomarkers not only identifies deterioration of renal function but also allows for the early detection of structural kidney damage. Several biomarkers have been identified and validated. This study discusses some of the most promising novel biomarkers of AKI, including CysC, NGAL, KIM-1, lL-18, L-FABP, IGFBP7, TIMP-2, Clusterin, and Penkid. We examine their performance in the diagnosis of subclinical AKI, limitations, and future clinical practice directions.

Endogenous opiates and behavior: 2020

This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Optimized Dosing: The Next Step in Precision Medicine in Non-Small-Cell Lung Cancer

In oncology, and especially in the treatment of non-small-cell lung cancer (NSCLC), dose optimization is often a neglected part of precision medicine. Many drugs are still being administered in "one dose fits all" regimens or based on parameters that are often only minor determinants for systemic exposure. These dosing approaches often introduce additional pharmacokinetic variability and do not add to treatment outcomes. Fortunately, pharmacological knowledge is increasing, providing valuable information regarding the potential of, for example, therapeutic drug monitoring. This article focuses on the evidence for the most promising and easily implemented optimized dosing approaches for the small-molecule inhibitors, chemotherapeutic agents, and monoclonal antibodies as treatment options currently approved for NSCLC. Despite limitations such as investigations having been conducted in oncological diseases other than NSCLC or the retrospective origin of many analyses, an alternative dosing regimen could be beneficial for treatment outcomes, prescriber convenience, or financial burden on healthcare systems. This review of the literature provides recommendations on the implementation of dose optimization and advice regarding promising strategies that deserve further research in NSCLC.

Perioperative renal protection

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common but underestimated syndrome in the perioperative setting. AKI can be induced by different causes and is associated with increased morbidity and mortality. Unfortunately, no specific treatment options are available at the moment.

RECENT FINDINGS

AKI is now understood as being a continuum ranging from normal kidney function over AKI and acute kidney disease to ultimately chronic kidney disease. The KDIGO organization recommend in 2012 implementation of preventive bundles in patients at high risk for AKI. In the perioperative setting, relevant measures include hemodynamic optimization, with careful consideration of blood pressure targets, adequate fluid therapy to maintain organ perfusion and avoidance of hyperglycaemia. These measures are most effective if patients at risk are identified as soon as possible and measures are implemented accordingly. Although current point of care functional biomarkers can detect patients at risk earlier than the established damage biomarkers, some components of the preventive bundle are still under investigation.

SUMMARY

Good evidence exists for the use of biomarkers to identify individual patients at risk for AKI and for the implementation of haemodynamic optimization, abdication of nephrotoxins, adequate fluid administration using balanced crystalloid solutions and glycaemic control. The data for using colloids or the degree of nephrotoxicity of contrast media still remain inconclusive.

Pro-Enkephalin and its association with renal function in Middle Eastern immigrants and native Swedes

Iraqi-born immigrants residing in Sweden exhibit lower blood pressure as well as better renal function despite an overall worse metabolic risk profile in comparison with native Swedes. This may indicate the presence of cardiorenal protective mechanisms in the Middle Eastern population. Hence, the aim of this study was to investigate whether the association between renal function and Pro-Enkephalin (PENK), a biomarker predictive of both acute and chronic kidney dysfunction, differs across ethnicities. The MEDIM population-based study including a cohort of women and men, born in Iraq or Sweden, aged 30-75 years was conducted in Malmö, Sweden, from 2010 to 2012. The study included fasting blood samples, physical examinations and self-administrated questionnaires. Despite significantly better renal function assessed by creatinine-based eGFR in the Iraqi group, levels of PENK did not differ between the groups, (70.0 pmol/L, born in Iraq (n = 1263) vs 71.1, born in Sweden (n = 689), p = .4). However, the association between PENK and renal function was relatively weaker in the Iraqi born group, as supported by a significant interaction between PENK and country of birth (P_Interaction= Country of birth x PENK = 0,010). This observational study suggests that the association between renal function and PENK was weaker in Middle Eastern immigrants. This is of interest as PENK may exhibit a direct effect on renal function, however further research is needed including studies on causality.

Proenkephalin as a new biomarker for pediatric acute kidney injury - reference values and performance in children under one year of age

Objectives Acute kidney injury (AKI) is common in critically ill children, but current biomarkers are suboptimal. Proenkephalin A 119-159 (PENK) is a promising new biomarker for AKI in adults, but pediatric data is lacking. We determined PENK reference intervals for healthy children, crucial for clinical implementation, and explored concentrations in critically ill infants aged under 1 year. Methods Observational cohort study in healthy infants and critically ill children aged 0-1 years. Reference values were determined using generalized additive models. Plasma PENK concentrations between healthy children and critically ill children with and without AKI, were compared using linear mixed modelling. The performance of PENK as AKI biomarker was compared to cystatin C (CysC) and β-trace protein (BTP) using receiver-operating-characteristic (ROC) analysis. Results PENK concentrations in 100 healthy infants were stable during the first year of life (median 517.3 pmol/L). Median PENK concentrations in 91 critically ill children, were significantly higher in those with AKI (n=40) (KDIGO Stage 1 507.9 pmol/L, Stage 2 704.0 pmol/L, Stage 3 930.5 pmol/L) than non-AKI patients (n=51, 432.2 pmol/L) (p < 0.001). PENK appeared to relate better to AKI diagnosis than CysC and BTP (AUROC PENK 0.858, CysC 0.770 and BTP 0.711) in the first 24 h after recruitment. Conclusions PENK reference values are much higher in young infants than adults, but clearly discriminate between children with and without AKI, with comparable or better performance than CysC and BTP. Our results illustrate the importance of establishing age-normalized reference values and indicate PENK as a promising pediatric AKI biomarker.

Plasma proenkephalin A 119-159 on intensive care unit admission is a predictor of organ failure and 30-day mortality

BACKGROUND

Proenkephalin A 119-159 (penKid) has been suggested as a marker of renal failure and poor outcome. We aimed to investigate the association of penKid on ICU admission with organ dysfunction and mortality in a mixed ICU population. In this retrospective, observational study, admission penKid levels from prospectively collected blood samples of consecutive patients admitted to four Swedish ICUs were analysed. The association of penKid with day-two sequential organ failure assessment (SOFA) scores and 30-day mortality was investigated using (ordinal) logistic regression. The predictive power of penKid for 30-day mortality and dialysis was assessed using the area under the receiver operating characteristic curve (AUC).

RESULTS

Of 1978 included patients, 632 fulfilled the sepsis 3-criteria, 190 had a cardiac arrest, and 157 had experienced trauma. Admission penKid was positively associated with 30-day mortality with an odds ratio of 1.95 (95% confidence interval 1.75-2.18, p < 0.001), and predicted 30-day mortality in the entire ICU population with an AUC of 0.71 (95% confidence interval 0.68-0.73) as well as in the sepsis, cardiac arrest and trauma subgroups (AUCs of 0.61-0.84). Correction for admission plasma creatinine revealed that penKid correlated with neurological dysfunction.

CONCLUSION

Plasma penKid on ICU admission is associated with day-two organ dysfunction and predictive of 30-day mortality in a mixed ICU-population, as well as in sepsis, cardiac arrest and trauma subgroups. In addition to being a marker of renal dysfunction, plasma penKid is associated with neurologic dysfunction in the entire ICU population, and cardiovascular dysfunction in sepsis.

A Novel Standardized Method of Renal Biopsy in Mice

Introduction

In animal models, it can be difficult to confirm therapeutic effects due to technical inconsistencies and other reasons. Although renal biopsy is widely used in clinical diagnosis, it is rarely used in animal experimental models, especially in mice, because the problems of surgery-induced renal injury and bleeding have not been solved.

Methods

We developed an easy-to-use method of renal biopsy in mice and evaluated whether 3 consecutive renal biopsies can be performed in the same kidney in a standardized manner. This method was verified using 2 mouse models, a healthy mouse model and a unilateral ureteral obstruction (UUO) mouse model, and evaluated based on renal function and histological changes.

Results

There were no perioperative complications in any of the model mice. There was no significant difference in serum Cr, 24-h urine protein, or kidney/body weight ratio between the biopsy and control groups. Each biopsy sample contained sufficient renal tissue. The damage to the operated tissue was limited to the tissue near the biopsy site. Compared with renal tissues in the corresponding control group, the renal tissues obtained from the 3 biopsies (healthy model days 0, 4, and 7 and UUO model days 3, 7, and 10) and the remnant renal tissues after the biopsy showed no significant difference in the glomerular sclerosis index, degree of renal tubular damage, inflammatory response and renal fibrosis in these 2 models.

Conclusions

Our new standardized method of renal biopsy in mice is a safe and cost-saving approach that allows repeated renal biopsies and ensures minimal trauma and sufficient sample size to quality in experimental disease models.

Predictive value of plasma proenkephalin and neutrophil gelatinase-associated lipocalin in acute kidney injury and mortality in cardiogenic shock

BACKGROUND

Acute kidney injury (AKI) is a frequent form of organ injury in cardiogenic shock. However, data on AKI markers such as plasma proenkephalin (P-PENK) and neutrophil gelatinase-associated lipocalin (P-NGAL) in cardiogenic shock populations are lacking. The objective of this study was to assess the ability of P-PENK and P-NGAL to predict acute kidney injury and mortality in cardiogenic shock.

RESULTS

P-PENK and P-NGAL were measured at different time points between baseline and 48 h in 154 patients from the prospective CardShock study. The outcomes assessed were AKI defined by an increase in creatinine within 48 h and all-cause 90-day mortality. Mean age was 66 years and 26% were women. Baseline levels of P-PENK and P-NGAL (median [interquartile range]) were 99 (71-150) pmol/mL and 138 (84-214) ng/mL. P-PENK > 84.8 pmol/mL and P-NGAL > 104 ng/mL at baseline were identified as optimal cut-offs for AKI prediction and independently associated with AKI (adjusted HRs 2.2 [95% CI 1.1-4.4, p = 0.03] and 2.8 [95% CI 1.2-6.5, p = 0.01], respectively). P-PENK and P-NGAL levels at baseline were also associated with 90-day mortality. For patients with oliguria < 0.5 mL/kg/h for > 6 h before study enrollment, 90-day mortality differed significantly between patients with low and high P-PENK/P-NGAL at baseline (5% vs. 68%, p < 0.001). However, the biomarkers provided best discrimination for mortality when measured at 24 h. Identified cut-offs of P-PENK_24h > 105.7 pmol/L and P-NGAL_24h > 151 ng/mL had unadjusted hazard ratios of 5.6 (95% CI 3.1-10.7, p < 0.001) and 5.2 (95% CI 2.8-9.8, p < 0.001) for 90-day mortality. The association remained significant despite adjustments with AKI and two risk scores for mortality in cardiogenic shock.

CONCLUSIONS

High levels of P-PENK and P-NGAL at baseline were independently associated with AKI in cardiogenic shock patients. Furthermore, oliguria before study inclusion was associated with worse outcomes only if combined with high baseline levels of P-PENK or P-NGAL. High levels of both P-PENK and P-NGAL at 24 h were found to be strong and independent predictors of 90-day mortality.

TRIAL REGISTRATION

NCT01374867 at www.clinicaltrials.gov , registered 16 Jun 2011-retrospectively registered.

Biomarkers and predicting acute kidney injury

AIM

How can we convert biomarkers into reliable, validated laboratory tests? Glomerular filtration rate (GFR) estimators exist for more than a century. The first utilitarian biomarkers were endogenously produced urea and creatinine. Clinicians then developed simple tests to determine whether or not renal tubular function was maintained. Are there faster and better tests that reflect decreased renal function and increased acute kidney injury (AKI) risk?

METHODS

We inspect earlier, and recently propagated biomarkers. Cystatin C reflects GFR and is not confounded by muscle mass. Direct GFR and plasma volume can now be measured acutely within 3 hours. Better yet would be tests that give information before GFR decreases and prior to urea, creatinine, and cystatin C increases. Prospective tests identifying those persons likely to develop AKI would be helpful. Even more utilitarian would be a test that also suggests a therapeutic avenue.

RESULTS

A number of highly provocative biomarkers have recently been proposed. Moreover the application of big data from huge electronic medical records promise new directions in identifying and dealing with AKI.

CONCLUSIONS

Pipedreams are in the pipeline; the novel findings require immediate testing, verification, and perhaps application. Future research promises to make such dreams come true.

Proenkephalin Predicts Organ Failure, Renal Replacement Therapy, and Mortality in Patients With Sepsis

BACKGROUND

Kidney failure occurs frequently and is associated with high mortality during sepsis. Proenkephalin (PENK) is an emerging biomarker of kidney function. We explored whether PENK levels could predict severity, organ failure, and mortality in septic patients.

METHODS

We measured the PENK level in the plasma of 215 septic patients using the sphingotest penKid assay (Sphingotec GmbH, Hennigsdorf, Germany). This was analyzed in terms of sepsis severity, vasopressor use, 30-day mortality, sequential organ failure assessment (SOFA) renal subscore, the Chronic Kidney Disease Epidemiology Collaboration estimated glomerular filtration rate (CKD-EPI eGFR) categories, and renal replacement therapy (RRT) requirement.

RESULTS

The PENK levels were significantly higher in patients with septic shock, vasopressor use, and non-survivors than in patients with solitary sepsis, no vasopressor use, and survivors, respectively (P=0.02, P=0.007, P<0.001, respectively). The PENK levels were significantly associated with SOFA renal subscore and CKD-EPI eGFR categories (both P<0.001). The distribution of lower eGFR (<60 mL/min/1.73 m2), RRT requirement, SOFA renal subscore, and the number of organ failures differed significantly according to the PENK quartile (P for trend<0.001 or 0.017). The 30-day mortality rate also differed significantly according to the PENK quartile (P for trend<0.001).

CONCLUSIONS

PENK could be an objective and reliable marker to predict severity, organ failure, and 30-day mortality in septic patients.

Proenkephalin: A New Biomarker for Glomerular Filtration Rate and Acute Kidney Injury

Assessment of kidney function is primarily based on urine output and Creatinine (Cr)-based methods to estimate glomerular filtration rate (GFR). The latter is confounded as Cr is not exclusively filtered by the kidney and rises relatively late after the onset of acute kidney injury (AKI). This leads to delays in recognition of reduced kidney function and diagnosis of AKI, particularly in critically ill patients where kidney function can change rapidly. The gold standard methods of GFR determination, such as inulin or iohexol clearance, are labor intensive and unfeasible in acute clinical settings. Proenkephalin A 119-159 (PENK) has been intensively studied as a novel biomarker of kidney function. PENK belongs to the enkephalin peptide family and is freely filtrated in the glomerulus. Plasma PENK concentration appears to correlate strongly with GFR. Moreover, increased plasma PENK concentrations are found to be associated with long-term kidney outcomes and mortality. In this review, we summarize the role of PENK in assessment of kidney function and its capacity to predict various clinical outcomes.

Assessment of Kidney Function in Patients With Extreme Obesity: A Narrative Review

Objectives:

To discuss the evidence and caveats associated with estimated and measured creatinine clearance (eClCr and mClCr) and glomerular filtration rate (eGFR and mGFR) assessments of kidney function in patients with more extreme forms of obesity.

Data Sources:

PubMed (1976 to mid-May 2020) was used, with bibliographies of retrieved articles searched for additional articles.

Study Selection and Data Extraction:

Articles using gold standard mGFR to evaluate eClCr, mClCr, and eGFR assessments of kidney function in patients with more extreme forms of obesity were included.

Data Synthesis:

The overestimation of GFR by mClCr is well established, but mClCr is an alternative to mGFR assessments for determining medication dosing in patients with extremes of body size or muscle mass, or in patients receiving narrow therapeutic index medications when eGFR is likely to be inaccurate. The vast majority of studies comparing eGFR assessments with gold standard indicators of kidney function were attempts to validate eGFR equations for diagnosing and staging chronic kidney disease (CKD).

Relevance to Patient Care and Clinical Practice:

For dosing medications in patients with stable kidney function and extreme obesity, a deindexed 4-variable Modification of Diet in Renal Disease or CKD Epidemiology Collaboration equation is an alternative to Cockcroft-Gault. Consistent use of the same equation by provider and between providers within any given setting is of paramount importance.

Conclusions:

In patients with extreme obesity and stable kidney function, eClCr or eGFR using deindexed values provides estimates of function for dosing adjustments of medications with elimination by the kidneys, but more research is needed with respect to the best size descriptor to use with estimating equations.