Urine IL-18 is an early diagnostic marker for acute kidney injury and predicts mortality in the intensive care unit

Assessing the health of the nephron in acute kidney injury: biomarkers of kidney function and injury

PURPOSE OF REVIEW

Serum creatinine and urine output continue to be the mainstays of diagnosis of acute kidney injury, though both of these measures have significant limitations, especially in acutely hospitalized patients. Biomarkers in both blood and urine have been studied extensively in the research setting and are on the verge of clinical practice to improve diagnosis of AKI.

RECENT FINDINGS

Blood and urine biomarkers can be localized to specific areas or functions within the nephron. Biomarkers can help to characterize glomerular or tubular function; glomerular, tubular, or interstitial injury; inflammation; or repair. Further, biomarkers can improve diagnosis of AKI in various clinical settings including acute interstitial nephritis, acute tubular injury, and hepatorenal syndrome, and cardiorenal syndrome.

SUMMARY

Biomarkers are becoming more prevalent in both research and getting close to clinical use. Both blood and urine biomarkers can help to localize impairment in nephron health by either location or function within the nephron and among various causes of AKI.

Mechanism of Chronic Kidney Disease Progression and Novel Biomarkers: A Metabolomic Analysis of Experimental Glomerulonephritis

While a complex network of cellular and molecular events is known to be involved in the pathophysiological mechanism of chronic kidney disease (CKD), the divergence point between reversal and progression and the event that triggers CKD progression are still unknown. To understand the different mechanisms between reversible and irreversible kidney disease and to search for urinary biomarkers that can predict prognosis, a metabolomic analysis was applied to compare acute and chronic experimental glomerulonephritis (GN) models. Four metabolites, namely, epoxyoctadecenoic acid (EpOME), epoxyeicosatetraenoic acid (EpETE), α-linolenic acid (ALA), and hydroxyretinoic acid, were identified as predictive markers after comparing the chronic nephritis model with acute nephritis and control groups (false discovery rate adjusted p-value (q-value) < 0.05). Renal mRNA expression of cytochrome P450 and epoxide hydrolase was also identified as being involved in the production of epoxide metabolites from these polyunsaturated fatty acids (p < 0.05). These results suggested that the progression of chronic kidney disease is associated with abnormally activated epoxide hydrolase, leading to an increase in EpOME and EpETE as pro-inflammatory eicosanoids.

Diagnostics, Risk Factors, Treatment and Outcomes of Acute Kidney Injury in a New Paradigm

Acute kidney injury (AKI) is a common clinical condition among patients admitted in the hospitals. The condition is associated with both increased short-term and long-term mortality. With the development of a standardized definition for AKI and the acknowledgment of the impact of AKI on patient outcomes, there has been increased recognition of AKI. Two advances from past decades, the usage of computer decision support and the discovery of AKI biomarkers, have the ability to advance the diagnostic method to and further management of AKI. The increasingly widespread use of electronic health records across hospitals has substantially increased the amount of data available to investigators and has shown promise in advancing AKI research. In addition, progress in the finding and validation of different forms of biomarkers of AKI within diversified clinical environments and has provided information and insight on testing, etiology and further prognosis of AKI, leading to future of precision and personalized approach to AKI management. In this this article, we discussed the changing paradigms in AKI: from mechanisms to diagnostics, risk factors, and management of AKI.

Cytokine and Cancer Biomarkers Detection: The Dawn of Electrochemical Paper-Based Biosensor

Although the established ELISA-based sensing platforms have many benefits, the importance of cytokine and cancer biomarkers detection for point-of-care diagnostics has propelled the search for more specific, sensitive, simple, accessible, yet economical sensor. Paper-based biosensor holds promise for future in-situ applications and can provide rapid analysis and data without the need to conduct in a laboratory. Electrochemical detection plays a vital role in interpreting results obtained from qualitative assessment to quantitative determination. In this review, various factors affecting the design of an electrochemical paper-based biosensor are highlighted and discussed in depth. Different detection methods, along with the latest development in utilizing them in cytokine and cancer biomarkers detection, are reviewed. Lastly, the fabrication of portable electrochemical paper-based biosensor is ideal in deliberating positive societal implications in developing countries with limited resources and accessibility to healthcare services.

Biomarkers for Diagnosis and Prediction of Outcomes in Contrast-Induced Nephropathy

Background

Serum creatinine is suboptimal as a biomarker in the early diagnosis of contrast-induced nephropathy (CIN). In this study, we investigated a panel of novel biomarkers in the early diagnosis of CIN and in assessing patient outcomes.

Methods

This single-centre, nested, prospective case-controlled study included 30 patients with CIN and 60 matched controls. Serum and urine samples were collected before contrast administration and at 24 hours, 48 hours, and ≥5 days after contrast administration. Concentrations of NGAL, cystatin C, β₂M, IL18, IL10, KIM1, and TNFα were determined using Luminex and ELISA assays. Outcomes were biomarker diagnostic discrimination performance for CIN and mortality after generation of area under receiver operating characteristic curves (AUROCs).

Results

Median serum levels for 24 h cystatin C (p < 0.01) and 48 h β₂M levels (p < 0.001) and baseline urine NGAL (p=0.02) were higher in CIN patients compared to controls with AUROCs of 0.75, 0.78, and 0.74, respectively, for the early diagnosis of CIN. Serum β₂M levels were higher in CIN patients at all time points. Elevated baseline serum concentrations of IL18 (p < 0.001), β₂M (p=0.04), TNFα (p < 0.001), and baseline urine KIM (p=0.01) and 24 h urine NGAL (p=0.02) were significantly associated with mortality. Baseline serum concentrations of IL18, β₂M, and TNFα showed the best discrimination performance for mortality with AUROCs, all >0.80. Baseline NGAL was superior for excluding patients at risk for CIN, with positive and negative predictive ranges of 0.50–0.55 and 0.81–0.88, respectively. Cystatin C (p=0.003) and β₂M (p=0.03) at 24 h independently predicted CIN risk. β₂M predicted increased mortality of 40% at baseline and 50% at 24 hours.

Conclusion

Serum cystatin C at 24 h was the best biomarker for CIN diagnosis, while baseline levels of serum IL18, β₂M, and TNFα were best for predicting prognosis.

Management of Presumed Acute Kidney Injury during Hypertensive Therapy: Stay Calm and Carry on?

BACKGROUND

Recent studies have demonstrated that intensive blood pressure control is associated with improved cardiovascular outcomes. Acute kidney injury (AKI), however, was more common in the intensive treatment group prompting concern in the nephrology community.

SUMMARY

Clinical trials on hypertension control have traditionally defined AKI by changes in serum creatinine. However, serum creatinine has several inherent limitations as a marker of kidney injury, with various factors influencing its production, secretion, and elimination. Urinary biomarkers of kidney injury and repair have the potential to provide insight on the presence and phenotype of kidney injury. In both the Systolic Blood Pressure Intervention Trial and the Action to Control Cardiovascular Risk in Diabetes study, urinary biomarkers have suggested that the increased risk of AKI associated with intensive treatment was due to hemodynamic changes rather than structural kidney injury. As such, clinicians who encounter rises in serum creatinine during intensification of hypertension therapy should "stay calm and carry on." Alternative explanations for serum creatinine elevation should be considered and addressed if appropriate. When the rise in serum creatinine is limited, particularly if albuminuria is stable or improving, intensive blood pressure control should be continued for its potential long-term benefits. Key Messages: Increases in serum creatinine during intensification of blood pressure control may not necessarily reflect kidney injury. Clinicians should evaluate for other contributing factors before stopping therapy. Urinary biomarkers may address limitations of serum creatinine as a marker of kidney injury.

Biomarkers in Acute Kidney Injury

How to cite this article: Bhosale SJ, Kulkarni AP. Biomarkers in Acute Kidney Injury. Indian J Crit Care Med 2020;24(Suppl 3):S90-S93.

Development of a risk stratification-based model for prediction of acute kidney injury in critically ill patients

Acute kidney injury (AKI) is a complex syndrome with a variety of possible etiologies and symptoms. It is characterized by high mortality and poor recovery of renal function. The incidence and mortality rates of patients with AKI in intensive care units are extremely high. It is generally accepted that early identification and prompt treatment of AKI are essential to improve outcomes. This study aimed to develop a model based on risk stratification to identify and diagnose early stage AKI for improved prognosis in critically ill patients.This was a single-center, retrospective, observational study. Based on relevant literature, we selected 13 risk factors (age, sex, hypertension, diabetes, coronary heart disease, chronic kidney disease, total bilirubin, emergency surgery, mechanical ventilation, sepsis, heart failure, cancer, and hypoalbuminemia) for AKI assessment using the Kidney Disease Improving Global Outcomes (KDIGO) diagnostic criteria. Univariate and multivariate analyses were used to determine risk factors for eventual entry into the predictive model. The AKI predictive model was established using binary logistic regression, and the area under the receiver operating characteristic curve (AUROC or AUC) was used to evaluate the predictive ability of the model and to determine critical values.The AKI predictive model was established using binary logistic regression. The AUROC of the predictive model was 0.81, with a sensitivity of 69.8%, specificity of 83.4%, and positive likelihood ratio of 4.2.A predictive model for AKI in critically ill patients was established using 5 related risk factors: heart failure, chronic kidney disease, emergency surgery, sepsis, and total bilirubin; however, the predictive ability requires validation.

The SPRINT trial suggests that markers of tubule cell function in the urine associate with risk of subsequent acute kidney injury while injury markers elevate after the injury

Urine markers can quantify tubular function including reabsorption (α-1 microglobulin [α1m]) and β-2-microglobulin [β2m]) and protein synthesis (uromodulin). Individuals with tubular dysfunction may be less able to compensate to insults than those without, despite similar estimated glomerular filtration rate (eGFR) and albuminuria. Among Systolic Blood Pressure Intervention Trial (SPRINT) participants with an eGFR under 60 ml/min/1.73m2, we measured urine markers of tubular function and injury (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule-1 [KIM-1], interleukin-18 [IL-18], monocyte chemoattractant protein-1, and chitinase-3-like protein [YKL-40]) at baseline. Cox models evaluated associations with subsequent acute kidney injury (AKI) risk, adjusting for clinical risk factors, baseline eGFR and albuminuria, and the tubular function and injury markers. In a random subset, we remeasured biomarkers after four years, and compared changes in biomarkers in those with and without intervening AKI. Among 2351 participants, 184 experienced AKI during 3.8 years mean follow-up. Lower uromodulin (hazard ratio per two-fold higher (0.68, 95% confidence interval [0.56, 0.83]) and higher α1m (1.20; [1.01, 1.44]) were associated with subsequent AKI, independent of eGFR and albuminuria. None of the five injury markers were associated with eventual AKI. In the random subset of 947 patients with repeated measurements, the 59 patients with intervening AKI versus without had longitudinal increases in urine NGAL, IL-19, and YKL-40 and only 1 marker of tubule function (α1m). Thus, joint evaluation of tubule function and injury provided novel insights to factors predisposing to AKI, and responses to kidney injury.

Dexmedetomidine alleviates lipopolysaccharide-induced acute kidney injury by inhibiting the NLRP3 inflammasome activation via regulating the TLR4/NOX4/NF-κB pathway

Dexmedetomidine (DEX) prevents kidney damage caused by sepsis, but the mechanism of this effect remains unclear. In this study, the protective molecular mechanism of DEX in lipopolysaccharide (LPS)-induced acute kidney injury was investigated and its potential pharmacological targets from the perspective of inhibiting oxidative stress damage and the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome activation. Intraperitoneal injection of DEX (30 μg/kg) significantly improved LPS (10 mg/kg) induced renal pathological damage and renal dysfunction. DEX also ameliorated oxidative stress damage by reducing the contents of reactive oxygen species, malondialdehyde and hydrogen peroxide, and increasing the level of glutathione, as well as the activity of superoxide dismutase and catalase. In addition, DEX prevented nuclear factor-kappa B (NF-κB) activation and I-kappa B (IκB) phosphorylation, as well as the expressions of NLRP3 inflammasome-associated protein and downstream IL-18 and IL-1β. The messengerRNA (mRNA) and protein expressions of toll-like receptor 4 (TLR4), NADPH oxidase-4 (NOX4), NF-κB, and NLRP3 were also significantly reduced by DEX. Their expressions were further evaluated by immunohistochemistry, yielding results were consistent with the results of mRNA and protein detection. Interestingly, the protective effects of DEX were reversed by atipamezole-an alpha 2 adrenal receptor (α₂ AR) inhibitor, whereas idazoxan-an imidazoline receptor (IR) inhibitor failed to reverse this change. In conclusion, DEX attenuated LPS-induced AKI by inhibiting oxidative stress damage and NLRP3 inflammasome activation via regulating the TLR4/NOX4/NF-κB pathway, mainly acting on the α₂ AR rather than IR.

Are Urinary Biomarkers Better Than Acute Kidney Injury Duration for Predicting Readmission?

BACKGROUND

Acute kidney injury (AKI) is a common complication of cardiac surgery. Postprocedural AKI is a risk factor for 30-day readmission. We sought to examine the association of AKI and kidney injury biomarkers with readmission after cardiac surgery.

METHODS

Patients alive at discharge who underwent cardiac surgery from the Translational Research Investigating Biomarker Endpoints-AKI cohort were enrolled from six medical centers in the United States and Canada. AKI duration was defined as the total number of days AKI was present during index admission (no AKI, 1-2, 3-6, and 7+ days). Preoperative and postoperative urinary levels were collected for interleukin-18, neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, liver-fatty-acid-binding protein, cystatin C, microalbumin, creatinine, and albumin-to-creatinine ratio. Readmission and death events were identified through US (Medicare) and Canadian administrative databases at 30 days and 365 days after discharge.

RESULTS

Of 968 patients 15.9% were readmitted or died within 30 days of discharge and 35.9% were readmitted or died within 365 days. AKI duration of 3 to 6 days was significantly associated with 30-day readmission or death (adjusted odds ratio, 1.82%; 95% confidence interval, 1.08-3.05). Patients with AKI duration ≥ 7 days had increased odds of readmission or death at both 30 days (adjusted odds ratio, 2.49%; 95% confidence interval, 1.15-5.43) and 365 days (adjusted odds ratio, 3.67%; 95% confidence interval, 1.73-7.79). Urinary biomarkers had no association with readmission and death.

CONCLUSIONS

AKI duration ≥ 3 days, and not kidney biomarkers, was strongly associated with readmission or death. These clinical outcomes are potentially due to cardiovascular or hemodynamic causes rather than intrinsic injury to the kidney parenchyma.

Urinary and Serum Biomarkers for Prediction of Acute Kidney Injury in Patients Undergoing Liver Transplantation

Acute kidney injury (AKI) is a frequent and serious complication of orthotopic liver transplantation (OLT), with a significant impact on mortality, graft survival, and chronic kidney disease. Currently, the diagnosis of AKI is based on changes in serum creatinine, which is a late marker, usually rising when there is already significant damage to the renal parenchyma. During the last 2 decades, various biomarkers have been studied in many clinical situations, mostly after cardiac surgery, in drug-induced AKI, or in sepsis. The present article summarizes the data on those biomarkers that have been evaluated for the prediction of AKI in patients undergoing OLT.

Wogonin pre-treatment attenuates cisplatin-induced nephrotoxicity in rats: Impact on PPAR-γ, inflammation, apoptosis and Wnt/β-catenin pathway

Cisplatin, a platinum chemotherapeutic agent, is used in a diversity of malignancies; nevertheless, the excessive nephrotoxicity following cisplatin treatment is the dose-limiting devastating reaction. This study was designed to explore the possible nephroprotective impact of wogonin, a forceful anti-oxidant, anti-inflammatory, and anti-tumor agent, in a rat model of cisplatin-induced renal injury. The potential nephroprotective mechanisms were additionally investigated. Wogonin was given at a dose of 40 mg/kg. Acute nephrotoxicity was indicated by a significant rise in BUN, and serum creatinine levels in cisplatin-injected rats. Also, cisplatin enhanced the lipid peroxidation, diminished GSH, catalase, and PPAR-γ levels. Additionally, cisplatin-injected rats showed a significant rise in tissue levels of IL-1β, TNF-α, NF-kB, and caspase-3 enzymatic activity. Notably, the pre-treatment with wogonin ameliorated the nephrotoxicity indices, oxidative stress, inflammation, and apoptosis induced by cisplatin. Also, wogonin up-regulated PPAR-γ expression. The involvement of Wnt/β-catenin pathway was debatable; however, our findings showed that it was significantly induced by cisplatin. Wogonin pre-treatment markedly attenuated Wnt/β-catenin pathway. Collectively, these findings imply that wogonin is a promising nephroprotective agent that improves the therapeutic index of cisplatin via reducing oxidative stress, inflammation as well as inducing PPAR-γ. Also, Wnt/β-catenin pathway is partially involved in the pathogenesis of cisplatin nephrotoxicity.

The Overexpression of Sirtuin1 (SIRT1) Alleviated Lipopolysaccharide (LPS)-Induced Acute Kidney Injury (AKI) via Inhibiting the Activation of Nucleotide-Binding Oligomerization Domain-Like Receptors (NLR) Family Pyrin Domain Containing 3 (NLRP3) Inflammasome

Background

Sepsis-induced acute kidney injury (AKI) is threatening the patients with sepsis, and nucleotide-binding oligomerization domain-like receptors (NLR) family pyrin domain containing 3 (NLRP3) inflammasome is considered to play a critical role in this complication of sepsis and might be regulated by sirtuin1 (SIRT1). Thus, we explored the roles of NLRP3 and SIRT1 in the lipopolysaccharide (LPS)-induced AKI in the HK-2 cell line.

Material/Methods

Cell viability was assessed by Cell Counting Kit-8 (CCK-8). Apoptosis rate was measured by flow cytometry. Protein levels of interleukin (IL)-1β and IL-18 were tested by enzyme-linked immunosorbent assay (ELISA) and NLRP3, cleaved caspase-1, caspase-1 were tested by western blot. The mRNA levels of IL-1β, IL-18, and SIRT1 were quantified by qPCR.

Results

LPS could decrease cell viability and the expression of SIRT1 and elevate the expressions of IL-1β, IL-18, NLRP3, and cleaved caspase-1. However, the overexpression of SIRT1 could upregulate cell viability and expression of caspase-1 and downregulate apoptosis rate, expressions of NLRP3, IL-1β, IL-18, and cleaved caspase-1.

Conclusions

NLRP3 inflammasome could act as a critical regulator promoting the process of AKI induced by LPS, and the overexpression of SIRT1 might be able to suppress the activation of NLRP3 and therefore resist the kidney injury, showing promise to be used as a target in the treatment of sepsis-induced AKI.

Urinary Biomarkers of Tubular Damage Are Associated with Mortality but Not Cardiovascular Risk among Systolic Blood Pressure Intervention Trial Participants with Chronic Kidney Disease

BACKGROUND

Kidney tubulointerstitial fibrosis on biopsy is a strong predictor of chronic kidney disease (CKD) progression, and CKD is associated with elevated risk of cardiovascular disease (CVD). Tubular health is poorly quantified by traditional kidney function measures, including estimated glomerular filtration rate (eGFR) and albuminuria. We hypothesized that urinary biomarkers of tubular injury, inflammation, and repair would be associated with higher risk of CVD and mortality in persons with CKD.

METHODS

We measured urinary concentrations of interleukin-18 (IL-18), kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and chitinase-3-like protein-1 (YKL-40) at baseline among 2,377 participants of the Systolic Blood Pressure Intervention Trial who had an eGFR < 60 mL/min/1.73 m2. We used Cox proportional hazards models to evaluate biomarker associations with CVD events and all-cause mortality.

RESULTS

At baseline, the mean age of participants was 72 ± 9 years, and eGFR was 48 ± 11 mL/min/1.73 m2. Over a median follow-up of 3.8 years, 305 CVD events (3.6% per year) and 233 all-cause deaths (2.6% per year) occurred. After multivariable adjustment including eGFR, albuminuria, and urinary creatinine, none of the biomarkers showed statistically significant associations with CVD risk. Urinary IL-18 (hazard ratio [HR] per 2-fold higher value, 1.14; 95% CI 1.01-1.29) and YKL-40 (HR per 2-fold higher value, 1.08; 95% CI 1.02-1.14) concentrations were each incrementally associated with higher mortality risk. Associations were similar when stratified by randomized blood pressure arm.

CONCLUSIONS

Among hypertensive trial participants with CKD, higher urinary IL-18 and YKL-40 were associated with higher risk of mortality, but not CVD.

Kidney Injury Biomarkers in an Academic Hospital Setting: Where Are We Now?

Acute kidney injury (AKI) is a frequent complication in hospitalised patients and is diagnosed by urinary output and serum creatinine. Serum creatinine is an indirect marker for renal glomerular filtration, but lacks specificity for damage to kidney tissue and the relatively late response to injury precludes early recognition of AKI. Timely diagnosis of kidney injury using biomarkers that provide information about the aetiology of kidney injury is an unmet clinical need. To overcome the suboptimal performance of serum creatinine, injury biomarkers have been proposed that predict AKI in diverse clinical settings. The clinical performance of these markers is considered moderate due to the lack of specificity for kidney tissue or the underlying injury mechanisms, poor test specificity and confounding by interventions or comorbidities. Hence, it is not unequivocally beneficial to implement current kidney injury biomarkers in the clinical laboratory for diagnostic purposes. In this article we review biomarkers that might fulfil AKI-related unmet clinical needs in the academic hospital setting.

Inflammatory milieu in contrast-induced nephropathy: a prospective single-center study

Background

Acute kidney injury (AKI) caused by contrast exposure is a common problem, which may cause a significant increase in patients in-hospital stay and therefore the cost of treatment. This study was conducted to evaluate the role of inflammation, inflammatory markers in predicting contrast induced nephropathy (CIN). This is a prospective study that was carried out in a major tertiary referral hospital in Jordan.

Methods

Clinical data, blood and urine samples were collected from all patients admitted to the cardiology unit. All patients who agreed to participate in the study had creatinine level analysis 48-72 hours after the procedure. The CIN was defined as an increase in serum creatinine by 25% or 44 μmol/L from the baseline within 48-72 hours after the contrast administration. Patients with stage 4, 5 renal failure, patients on dialysis, and patients with recent intravenous contrast use, active infection or cancer were excluded from the study.

Results

Of the total 202 patients, 30 (14.8%) developed CIN. The incidence rate was 21.1% among females and 12.4% among males. In the multivariate analysis, beside eGFR, diuretics, and alkaline phosphatase, IL-33 was significantly associated with CIN, while the other cytokines did not to show this an association.

Conclusion

Serum level of IL-33 was a significant predictor for development of CIN. Good clinical judgment and high serum levels of IL-33 may stratify patients into low and high risk for CIN.

Biomarkers in acute kidney injury (AKI)

Acute kidney injury is common in critically ill patients and portends a significant impact on mortality, progressive chronic kidney disease, and cardiovascular disease and mortality. Though most physicians alter therapy depending on changes in serum creatinine, this often represents delayed intervention. Various AKI biomarkers have been discovered and validated to improve timely detection, differentiation and stratification into risk groups for progressive renal decline, need for renal replacement therapy or death. This chapter will review AKI biomarkers validated over the past decade. We also describe the clinical performance of the biomarkers. We suggest that using AKI biomarkers to complement serum creatinine (or cystatin C) and urine output will better integrate patient care through earlier recognition and clinical outcome prediction after AKI.

Circulating Cytokine/Chemokine Concentrations Respond to Ionizing Radiation Doses but not Radiation Dose Rates: Granulocyte-Colony Stimulating Factor and Interleukin-18

Exposure to ionizing radiation is a crucial life-threatening factor in nuclear and radiological incidents. It is known that ionizing radiation affects cytokine/chemokine concentrations in the blood of B6D2F1 mice. It is not clear whether radiation dose rates would vary the physiological response. Therefore, in this study we utilized data from two experiments using B6D2F1 female mice exposed to six different dose rates ranging from low to high rates. In one experiment, mice received a total dose of 8 Gy (LD_0/30) of ⁶⁰Co gamma radiation at four dose rates: 0.04, 0.15, 0.30 and 0.47 Gy/min. Blood samples from mice were collected at 24 and 48 h postirradiation for cytokine/chemokine measurements, including interleukin (IL)-1β, IL-6, IL-10, keratinocyte cytokine (KC), IL-12p70, IL-15, IL-17A, IL-18, granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage (GM)-CSF, macrophage (M)-CSF, monokine induced by gamma interferon (MIG), tumor necrosis factor (TNF)-α, fibroblast growth factor (FGF)-basic, vascular endothelial growth factor (VEGF) and platelet-derived growth factor basic (PDGF-bb). At 24 h after ionizing irradiation at dose rate of 0.04 Gy/min, significant increases were observed only in G-CSF and M-CSF ( P < 0.05). At 0.15 Gy/min, IL-10, IL-17A, G-CSF and GM-CSF concentrations were increased. At 0.3 Gy/min, IL-15, IL-18, G-CSF, GM-CSF, M-CSF, MCP-1, MIP-2, MIG, FGF-basic, VEGF and PDGF-bb were significantly elevated ( P < 0.05). At 0.47 Gy/min, IL-6, KC, IL-10, MCP-1, G-CSF, GM-CSF and M-CSF were significantly increased. At 48 h postirradiation, all cytokines/chemokines except MCP-1 returned to or were below their baselines, suggesting these increases are transient at LD_0/30 irradiation. Of note, there is a limitation on day 2 because cytokines/chemokines are either at or below their baselines. Other parameters such as fms-like tyrosine kinase receptor-3 ligand (Flt-3 ligand) concentrations and lymphocyte counts, which have proven to be unaffected by radiation dose rates, can be used instead for assessing the radiation dose. However, in a separate radiation dose and time-course experiment, increases in IL-18 and G-CSF depended on the radiation doses but showed no significant differences between 0.58 and 1.94 Gy/min ( P > 0.05) at 3 and 6 Gy but not 12 Gy. G-CSF continued to increase up to day 7, whereas IL-18 increased on day 4 and remained above baseline level on day 7. Therefore, time after irradiation at different doses should be taken into consideration. To our knowledge, these results are the first to suggest that ionizing radiation, even at a very low-dose-rate (0.04 Gy/min), induces circulating G-CSF increases but not others for selected time points; radiation-induced increases in IL-18 at radiation dose rates between 0.15 and 1.94 Gy/min are also not in a radiation dose-rate-dependent manner. C-CSF, lymphocyte counts and circulating Flt-3 ligand should be explored further as possible biomarkers of radiation exposure at early time points. IL-18 is also worthy of further study as a potential biomarker at later time points.

Identification of Urinary Activin A as a Novel Biomarker Reflecting the Severity of Acute Kidney Injury

Acute kidney injury (AKI) is a common but complex condition that is associated with increased morbidity and mortality. In the present study, we examined whether urinary activin A, a member of the TGF-beta superfamily, is present in mice with ischemia-reperfusion injury and in humans with AKI, as well as its potential as a biomarker for AKI. Expression of activin A was markedly increased in ischemic mouse kidneys. In situ hybridization demonstrated that activin mRNA was expressed in tubular cells of ischemic kidneys but not of normal kidneys. Immunoreactive activin A, which was absent in normal kidneys, was detected in the cytoplasm of proximal tubular cells in ischemic kidneys. Activin A was undetectable in the urine of normal mice. In contrast, activin A was significantly increased in the urine of ischemic mice at 3 h after reperfusion. Urinary activin A levels increased according to the period of ischemia. In humans, urinary activin A was almost undetectable in healthy volunteers and in patients with pre-renal AKI, but was significantly increased in patients with renal AKI. There was no significant correlation between urinary activin A and serum activin A. Collectively, urinary activin A might be a useful biomarker reflecting the severity of AKI.

Physiological and molecular effects of interleukin-18 administration on the mouse kidney

BACKGROUND

The cytokine interleukin-18 was originally identified as an interferon-γ-inducing proinflammatory factor; however, there is increasing evidence to suggest that it has non-immunological effects on physiological functions. We previously investigated the potential pathophysiological relationship between interleukin-18 and dyslipidemia, non-alcoholic fatty liver disease, and non-alcoholic steatohepatitis, and suggested interleukin-18 as a possible novel treatment for not only these diseases but also for cancer immunotherapy. Before clinical application, the effects of interleukin-18 on the kidney need to be determined. In the current study, we examined the kidney of interleukin-18 knockout (Il18^-/-) mice and the effects of interleukin-18 on the kidney following intravenous administration of recombinant interleukin-18.

METHODS

Il18^-/- male mice were generated on the C57Bl/6 background and littermate C57Bl/6 Il18^+/+ male mice were used as controls. To assess kidney damage, serum creatinine and blood urea nitrogen levels were measured and histopathological analysis was performed. For molecular analysis, microarray and quantitative reverse transcription PCR was performed using mice 6 and 12 weeks old. To evaluate the short- and long-term effects of interleukin-18 on the kidney, recombinant interleukin-18 was administered for 2 and 12 weeks, respectively.

RESULTS

Compared with Il18^+/+ mice, Il18^-/- mice developed kidney failure in their youth-6 weeks of age, but the condition was observed to improve as the mice aged, even though dyslipidemia, arteriosclerosis, and higher insulin resistance occurred. Analyses of potential molecular mechanisms involved in the onset of early kidney failure in Il18^-/- mice identified a number of associated genes, such as Itgam, Nov, and Ppard. Intravenous administration of recombinant interleukin-18 over both the short and long term showed no effects on the kidney despite significant improvement in metabolic diseases.

CONCLUSIONS

Short- and long-term administration of interleukin-18 appeared to have no adverse effects on the kidney in these mice, suggesting that administration may be a safe and novel treatment for metabolic diseases and cancer.

Biomarkers of AKI Progression after Pediatric Cardiac Surgery

Background As children progress to higher stages of AKI, the risk for adverse outcomes dramatically increases. No reliable methods exist to predict AKI progression in hospitalized children. To determine if biomarkers of inflammation and kidney injury can predict AKI progression, we conducted a three-center prospective cohort study of children undergoing cardiopulmonary bypass.Methods On the first day of serum creatinine-defined AKI, we measured urine biomarkers (neutrophil gelatinase-associated lipocalin [NGAL], IL-18, kidney injury molecule 1, liver fatty acid binding protein [L-FABP], albumin, and cystatin C) and plasma biomarkers (IFN, IL-1, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, TNF-α, NGAL, and cystatin C). We defined AKI progression as a worsening of AKI stage or persisting stage 3 AKI (≥2 consecutive days).Results In all, 176 of 408 (43%) children developed postoperative AKI. Among the children with AKI, we diagnosed stages 1, 2, and 3 AKI in 145 (82.5%), 25 (14%), and six (3.5%) children, respectively, on the first day of AKI; 28 (7%) children had AKI progression. On the first day of AKI, nine of 17 biomarkers were significantly higher in patients with than without AKI progression. Urine L-FABP (among injury biomarkers) and plasma IL-8 (among inflammatory biomarkers) had the highest discrimination for AKI progression: optimism-corrected area under the curve, 0.70; 95% confidence interval, 0.58 to 0.81 and optimism-corrected area under the curve, 0.80; 95% confidence interval, 0.69 to 0.91, respectively.Conclusions If validated in additional cohorts, plasma IL-8 could be used to improve clinical care and guide enrollment in therapeutic trials of AKI.

Fluid and Volume Monitoring

Background

Fluid resuscitation is not only used to prevent acute kidney injury (AKI) but fluid management is also a cornerstone of treatment for patients with established AKI and renal failure. Ultrafiltration removes volume initially from the intravascular compartment inducing a relative degree of hypovolemia. Normal reflex mechanisms attempt to sustain blood pressure constant despite marked changes in blood volume and cardiac output. Thus, compensated shock with a normal blood pressure is a major cause of AKI or exacerbations of AKI during ultrafiltration.

Methods

We undertook a systematic review of the literature using MEDLINE, Google Scholar and PubMed searches. We determined a list of key questions and convened a 2-day consensus conference to develop summary statements via a series of alternating breakout and plenary sessions. In these sessions, we identified supporting evidence and generated clinical practice recommendations and/or directions for future research.

Results

We defined three aspects of fluid monitoring: i) normal and pathophysiological cardiovascular mechanisms; ii) measures of volume responsiveness and impending cardiovascular collapse during volume removal, and; iii) measured indices of each using non-invasive and minimally invasive continuous and intermittent monitoring techniques. The evidence documents that AKI can occur in the setting of normotensive hypovolemia and that under-resuscitation represents a major cause of both AKI and mortality ion critically ill patients. Traditional measures of intravascular volume and ventricular filling do not predict volume responsiveness whereas dynamic functional hemodynamic markers, such as pulse pressure or stroke volume variation during positive pressure breathing or mean flow changes with passive leg raising are highly predictive of volume responsiveness. Numerous commercially-available devices exist that can acquire these signals.

Conclusions

Prospective clinical trials using functional hemodynamic markers in the diagnosis and management of AKI and volume status during ultrafiltration need to be performed. More traditional measure of preload be abandoned as marked of volume responsiveness though still useful to assess overall volume status.

Overview of the IL-1 family in innate inflammation and acquired immunity

The interleukin-1 (IL-1) family of cytokines and receptors is unique in immunology because the IL-1 family and Toll-like receptor (TLR) families share similar functions. More than any other cytokine family, the IL-1 family is primarily associated with innate immunity. More than 95% of living organisms use innate immune mechanisms for survival whereas less than 5% depend on T- and B-cell functions. Innate immunity is manifested by inflammation, which can function as a mechanism of host defense but when uncontrolled is detrimental to survival. Each member of the IL-1 receptor and TLR family contains the cytoplasmic Toll-IL-1-Receptor (TIR) domain. The 50 amino acid TIR domains are highly homologous with the Toll protein in Drosophila. The TIR domain is nearly the same and present in each TLR and each IL-1 receptor family. Whereas IL-1 family cytokine members trigger innate inflammation via IL-1 family of receptors, TLRs trigger inflammation via bacteria, microbial products, viruses, nucleic acids, and damage-associated molecular patterns (DAMPs). In fact, IL-1 family member IL-1a and IL-33 also function as DAMPs. Although the inflammatory properties of the IL-1 family dominate in innate immunity, IL-1 family member can play a role in acquired immunity. This overview is a condensed update of the IL-1 family of cytokines and receptors.

Lipopolysaccharide-Induced Acute Kidney Injury Is Dependent on an IL-18 Receptor Signaling Pathway

The proinflammatory cytokine interleukin (IL)-18 is an important mediator of the organ failure induced by endotoxemia. IL-18 (known as an interferon-gamma (IFN-γ) inducing factor), and other inflammatory cytokines have important roles in lipopolysaccharide (LPS)-induced acute kidney injury (AKI). We investigated the effect of inflammatory cytokines and Toll-like receptor 4 (TLR4) expression, an event that is accompanied by an influx of monocytes, including CD4⁺ T cells and antigen-presenting cells (APCs) in IL-18Rα knockout (KO) mice and wild-type (WT) mice after LPS injection. In the acute advanced phase, the IL-18Rα KO mice showed a higher survival rate and a suppressed increase of blood urea nitrogen, increased levels of proinflammatory cytokines such as IFN-γ and IL-18, the infiltration of CD4⁺ T cells and the expression of kidney injury molecule-1 as an AKI marker. In that phase, the renal mRNA expression of the M1 macrophage phenotype and C-C chemokine receptor type 7 as the maturation marker of dendritic cells (DCs) was also significantly decreased in the IL-18Rα KO mice, although there were small numbers of F4/80⁺ cells and DCs in the kidney. Conversely, there were no significant differences in the expressions of mRNA and protein TLR4 after LPS injection between the WT and IL-18Rα KO groups. Our results demonstrated that the IL-18Rα-mediated signaling pathway plays critical roles in CD4⁺ T cells and APCs and responded more quickly to IFN-γ and IL-18 than TLR4 stimulation in the pathogenesis of LPS-induced AKI.

The assessment of acute kidney injury in critically ill patients

Acute kidney injury (AKI) is common in critically ill patients and is associated with high morbidity and mortality. The availability of several biomarkers of kidney injury offers new tools for its early recognition and management. The early identification of high-risk patients provides an opportunity to develop strategies for the prevention, early diagnosis and treatment of AKI. Despite progress in critical care medicine over the past decade, the treatment strategies for AKI in critically ill patients, such as when to start renal replacement therapy, remain controversial. A recently proposed risk prediction score for AKI, based on routinely available clinical variables, presents a new means of identifying patients at high risk of AKI.

Resveratrol-loaded nanoparticles conjugated with kidney injury molecule-1 as a drug delivery system for potential use in chronic kidney disease

AIM

We used resveratrol (Res)-loaded nanoparticles (Res NPs) as a novel method for improving the pharmacokinetic properties of Res and analyzed the effect of Res NPs in chronic kidney disease (CKD).

MATERIALS & METHODS

We coupled anti-kidney injury molecule-1 antibodies to Res NPs and analyzed safety and efficacy.

RESULTS

Res NPs had low toxicity and induced autophagy. Res NPs inhibited the NLRP3 inflammasome and IL-1β secretion. Higher NLRP3 expression levels were observed in peripheral blood monocytic cells of CKD patients than healthy individuals. Treatment with kidney injury molecule-1-Res NPs significantly reduced creatinine and protected against tubulointerstitial injury in a murine model of CKD.

CONCLUSION

Res NPs through NLRP3 inflammasome attenuation and autophagy induction may be as a strategy to prevent CKD.

Kidney Injury and Repair Biomarkers in Marathon Runners

BACKGROUND

Investigation into strenuous activity and kidney function has gained interest given increasing marathon participation.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

Runners participating in the 2015 Hartford Marathon.

PREDICTOR

Completing a marathon.

OUTCOMES

Acute kidney injury (AKI) as defined by AKI Network (AKIN) criteria. Stage 1 AKI was defined as 1.5- to 2-fold or 0.3-mg/dL increase in serum creatinine level within 48 hours of day 0 and stage 2 was defined as a more than 2- to 3-fold increase in creatinine level. Microscopy score was defined by the number of granular casts and renal tubular epithelial cells.

MEASUREMENTS

Samples were collected 24 hours premarathon (day 0), immediately postmarathon (day 1), and 24 hours postmarathon (day 2). Measurements of serum creatinine, creatine kinase, and urine albumin were completed, as well as urine microscopy analysis. 6 injury urine biomarkers (IL-6, IL-8, IL-18, kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, and tumor necrosis factor α) and 2 repair urine biomarkers (YKL-40 and monocyte chemoattractant protein 1) were measured.

RESULTS

22 marathon runners were included. Mean age was 44 years and 41% were men. 82% of runners developed an increase in creatinine level equivalent to AKIN-defined AKI stages 1 and 2. 73% had microscopy diagnoses of tubular injury. Serum creatinine, urine albumin, and injury and repair biomarker levels peaked on day 1 and were significantly elevated compared to day 0 and day 2. Serum creatine kinase levels continued to significantly increase from day 0 to day 2.

LIMITATIONS

Small sample size and limited clinical data available at all time points.

CONCLUSIONS

Marathon runners developed AKI and urine sediment diagnostic of tubular injury. An increase in injury and repair biomarker levels suggests structural damage to renal tubules occurring after marathon. The results of our study should be validated in larger cohorts with longer follow-up of kidney function.

Biomarkers of acute kidney injury: the pathway from discovery to clinical adoption

Acute kidney injury (AKI) is a common complication of critical illnesses and has a significant impact on outcomes, including mortality and morbidities. Unfortunately, apart from prophylactic measures, no effective treatment for this syndrome is known. Therefore, early recognition of AKI not only can provide better opportunities for preventive interventions, but also opens many gates for research and development of effective therapeutic options. Over the last few years, several new AKI biomarkers have been discovered and validated to improve early detection, differential diagnosis, and differentiation of patients into risk groups for progressive renal failure, need for renal replacement therapy (RRT), or death. These novel AKI biomarkers complement serum creatinine (SCr) and urine output, which are the standard diagnostic tools for AKI detection. In this article, we review the available literature on characteristics of promising AKI biomarkers that are currently the focus of preclinical and clinical investigations. These biomarkers include neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), liver-type fatty acid-binding protein, interleukin 18 (lL-18), insulin-like growth factor-binding protein 7, tissue inhibitor of metalloproteinase 2 (TIMP-2), calprotectin, urine angiotensinogen (AGT), and urine microRNA. We then describe the clinical performance of these biomarkers for diagnosis and prognostication. We also appraise each AKI biomarker's advantages and limitations as a tool for early AKI recognition and prediction of clinical outcomes after AKI. Finally, we review the current and future states of implementation of biomarkers in the clinical practice.

Urinary Glycosaminoglycans Predict Outcomes in Septic Shock and Acute Respiratory Distress Syndrome

RATIONALE

Degradation of the endothelial glycocalyx, a glycosaminoglycan (GAG)-rich layer lining the vascular lumen, is associated with the onset of kidney injury in animal models of critical illness. It is unclear if similar pathogenic degradation occurs in critically ill patients.

OBJECTIVES

To determine if urinary indices of GAG fragmentation are associated with outcomes in patients with critical illnesses such as septic shock or acute respiratory distress syndrome (ARDS).

METHODS

We prospectively collected urine from 30 patients within 24 hours of admission to the Denver Health Medical Intensive Care Unit (ICU) for septic shock. As a nonseptic ICU control, we collected urine from 25 surgical ICU patients admitted for trauma. As a medical ICU validation cohort, we obtained serially collected urine samples from 70 patients with ARDS. We performed mass spectrometry on urine samples to determine GAG (heparan sulfate, chondroitin sulfate, and hyaluronic acid) concentrations as well as patterns of heparan sulfate/chondroitin sulfate disaccharide sulfation. We compared these indices to measurements obtained using dimethylmethylene blue, an inexpensive, colorimetric urinary assay of sulfated GAGs.

MEASUREMENTS AND MAIN RESULTS

In septic shock, indices of GAG fragmentation correlated with both the development of renal dysfunction over the 72 hours after urine collection and with hospital mortality. This association remained after controlling for severity of illness and was similarly observed using the inexpensive dimethylmethylene blue assay. These predictive findings were corroborated using urine samples previously collected at three consecutive time points from patients with ARDS.

CONCLUSIONS

Early indices of urinary GAG fragmentation predict acute kidney injury and in-hospital mortality in patients with septic shock or ARDS. Clinical trial registered with www.clinicaltrials.gov (NCT01900275).

Urine Interleukin-18 (IL-18) as a Biomarker of Total-Body Irradiation: A Preliminary Study in Nonhuman Primates

We have reported that circulating IL-18 can be used as a radiation biomarker in mice, minipigs and nonhuman primates (NHPs, Macaca mulatta). Here, we report the levels of IL-18 in individual NHP's urine before and at 6 h-7 days after 5.0, 6.5 and 8.5 Gy ⁶⁰Co total-body irradiation (TBI) using enzyme linked immunosorbent assay (ELISA). Six animals (3.5-5.5 kg, 3-4 years old) per radiation dose were investigated. Correlation values between urine IL-18 and blood cell counts and serum chemistry parameters including lactate dehydrogenase (LDH), lipase, and serum total protein (TP), as well as between urine IL-18 and 60-day survival, were analyzed. Our data, to the best of our knowledge, for the first time, demonstrate that concentrations of urine IL-18 from irradiated NHPs were increased in a radiation dose-dependent manner compared to pre-TBI levels in samples from these animal (N = 18, 11.02 ± 1.3 pg/ml). A 5.0 Gy low dose of radiation (∼LD_10/60) did not increase urine IL-18 levels. In contrast, high-dose TBI significantly increased urine IL-18 at day 1 to day 5 in a bell-shaped time course, reaching a peak of 5- to 10-fold of control levels on day 3 after 6.5 Gy (∼LD_50/60) and 8.5 Gy (∼LD_90/60), respectively. Statistical analysis using receiver operator characteristic (ROC) and MultiROC analysis indicated that white blood cell and platelet counts, serum LDH, lipase and TP, when combined with urine IL-18, provide discriminatory predictors of total-body radiation injury with a very high ROC area of 0.98. Urine IL-18 measurement, as an early prognostic indicator of survival, may facilitate rapid detection of lethal doses of radiation, based on the currently available data set.

Predicting acute kidney injury: current status and future challenges

Acute kidney injury (AKI) is characterized by an acute decline in renal function and is associated to increased mortality rate, hospitalization time, and total health-related costs. The severity of this ‘fearsome’ clinical complication might depend on, or even be worsened by, the late detection of AKI, when the diagnosis is based on the elevation of serum creatinine (SCr). For these reasons, in recent years a great number of new tools, biomarkers and predictive models have been proposed to clinicians in order to improve diagnosis and prevent the development of AKI. The purpose of this narrative paper is to review the current state of the art in prediction and early detection of AKI and outline future challenges.

Predominant Tubular Interleukin-18 Expression in Polyomavirus-Associated Nephropathy

Polyomavirus-associated nephropathy (PVAN) occurs in a significant percentage of renal transplant recipients, with BK virus reactivation as the main causative agent. PVAN leads to tubular damage and may result in allograft loss. In this study, we analyzed the antiviral immune response in PVAN. Transcription of the proinflammatory cytokine interleukin-18 (IL-18) was significantly higher in PVAN biopsies compared with T cell-mediated rejection (TCMR) (1.42 ± 0.20 and 0.69 ± 0.10, respectively; *P = 0.0021). Tubular expression of IL-18 was significantly increased in PVAN compared with TCMR (2.00 ± 0.24 and 1.333 ± 0.13, respectively; *P = 0.028). In contrast, in TCMR, IL-18 was expressed predominantly by CD163-positive macrophages. These data suggest that the antiviral immune response in PVAN is partly coordinated by the tubular epithelium, whereas in TCMR, this may be controlled by inflammatory cells.

Urinary Tissue Inhibitor of Metalloproteinase-2 and Insulin-Like Growth Factor-Binding Protein 7 for Risk Stratification of Acute Kidney Injury in Patients With Sepsis

Supplemental Digital Content is available in the text.

Objectives:

To examine the performance of the urinary biomarker panel tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 in patients with sepsis at ICU admission. To investigate the effect of nonrenal organ dysfunction on tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 in this population.

Method:

In this ancillary analysis, we included patients with sepsis who were enrolled in either of two trials including 39 ICUs across Europe and North America. The primary endpoint was moderate-severe acute kidney injury (equivalent to Kidney Disease Improving Global Outcome stage 2–3) within 12 hours of enrollment. We assessed biomarker performance by calculating the area under the receiver operating characteristic curve, sensitivity, specificity, and negative and positive predictive values at three cutoffs: 0.3, 1.0, and 2.0 (ng/mL)²/1,000. We also calculated nonrenal Sequential Organ Failure Assessment scores for each patient on enrollment and compared tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 results in patients with and without acute kidney injury and across nonrenal Sequential Organ Failure Assessment scores. Finally, we constructed a clinical model for acute kidney injury in this population and compared the performance of the model with and without tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7.

Results:

We included 232 patients in the analysis and 40 (17%) developed acute kidney injury. We observed significantly higher urine tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 in patients with acute kidney injury than without acute kidney injury in both patients with low and high nonrenal Sequential Organ Failure Assessment scores (p < 0.001). The area under the receiver operating characteristic curve (95% CI) of tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 was 0.84 (0.73–0.92) and 0.85 (0.76–0.94), in low and high nonrenal Sequential Organ Failure Assessment score subgroups. Performance of the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 test was not modified by nonrenal Sequential Organ Failure Assessment (p = 0.70). In multivariate analysis, the addition of tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 significantly improved the performance of a clinical model for predicting acute kidney injury (p = 0.015).

Conclusion:

Urinary tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 accurately predicts acute kidney injury in septic patients with or without other organ failures.

The ischemic/nephrotoxic acute kidney injury and the use of renal biomarkers in clinical practice

The term Acute Renal Failure (ARF) has been replaced by the term Acute Kidney Injury (AKI). AKI indicates an abrupt (within 24-48h) decrease in Glomerular Filtraton Rate, due to renal damage, that causes fluid and metabolic waste retention and alteration of electrolyte and acid-base balance. The renal biomarkers of AKI are substances or processes that are indicators of normal or impaired function of the kidney. The most used renal biomarker is still serum creatinine that is inadequate for several reasons, one of which is its inability to differentiate between hemodynamic changes of renal function ("prerenal azotemia") from intrinsic renal failure or obstructive nephropathy. Cystatin C is no better in this respect. After the description of the pathophysiology of "prerenal azotemia" and of Acute Kidney Injury (AKI) due to ischemia or nephrotoxicity, the renal biomarkers are listed and described: urinary NAG, urinary and serum KIM-1, serum and urinary NGAL, urinary IL-18, urinary L-FABP, serum Midkine, urinary IGFBP7 and TIMP2, urinary α-GST and π-GST, urinary ɣGT and AP, urinary β₂M, urinary RBP, serum and urinary miRNA. All have been shown to appear much earlier than the rise of serum Creatinine. Some of them have been demonstrated to predict the clinical outcomes of AKI, such as the need for initiation of dialysis and mortality.

Evaluation of clinically available renal biomarkers in critically ill adults: a prospective multicenter observational study

BACKGROUND

Although serum cystatin C (sCysC), urinary N-acetyl-β-D-glucosaminidase (uNAG), and urinary albumin/creatinine ratio (uACR) are clinically available, their optimal combination for acute kidney injury (AKI) detection and prognosis prediction remains unclear. We aimed to assess the discriminative abilities of these biomarkers and their possible combinations for AKI detection and intensive care unit (ICU) mortality prediction in critically ill adults.

METHODS

A multicenter, prospective observational study was conducted in mixed medical-surgical ICUs at three tertiary care hospitals. One thousand eighty-four adult critically ill patients admitted to the ICUs were studied. We assessed the use of individual biomarkers (sCysC, uNAG, and uACR) measured at ICU admission and their combinations with regard to AKI detection and prognosis prediction.

RESULTS

AUC-ROCs for sCysC, uNAG, and uACR were calculated for total AKI (0.738, 0.650, and 0.683, respectively), severe AKI (0.839, 0.706, and 0.771, respectively), and ICU mortality (0.727, 0.793, and 0.777, respectively). The panel of sCysC plus uNAG detected total and severe AKI with significantly higher accuracy than either individual biomarkers or the other two panels (uNAG plus uACR or sCysC plus uACR). For detecting total AKI, severe AKI, and ICU mortality at ICU admission, this panel yielded AUC-ROCs of 0.756, 0.863, and 0.811, respectively; positive predictive values of 0.71, 0.31, and 0.17, respectively; and negative predictive values of 0.81, 0.97, and 0.98, respectively. Moreover, this panel significantly contributed to the accuracy of the clinical models for AKI detection and ICU mortality prediction, as measured by the AUC-ROC, continuous net reclassification index, and incremental discrimination improvement index. The comparable performance of this panel was further confirmed with bootstrap internal validation.

CONCLUSIONS

The combination of a functional marker (sCysC) and a tubular damage marker (uNAG) revealed significantly superior discriminative performance for AKI detection and yielded additional prognostic information on ICU mortality.

Predictive ability of urinary biomarkers for outcome in children with acute kidney injury

BACKGROUND

Urinary neutrophil gelatinase-associated lipocalin (NGAL), N-acetyl-beta-D-glucosaminidase (NAG), and interleukin 18 (IL-18) were found to be useful for early detection of acute kidney injury (AKI). The objective of this study was to determine the predictive ability of biomarkers for mortality and variation in levels in relation to different stages of AKI, need for dialysis, etiologies, and with duration of hospital stay.

METHODS

Urinary NGAL, NAG, and IL-18 levels were measured in 50 children with AKI and 30 age- and gender-matched healthy controls. AKI was classified as per pediatric Risk, Injury, Failure, Loss, and End-stage (RIFLE) criteria.

RESULTS

Median NGAL, NAG, and IL-18 values were significantly increased in AKI patients compared with controls (p < 0.001), with significant increase among risk, injury, and failure stages. Nonsurvivors had significantly higher median levels of NGAL (p = 0.008) and NAG (p = 0.018) than survivors. NGAL had highest area under the curve (AUC) at 0.750 [confidence interval (CI) 0.580-0.920], followed by NAG at 0.724 (CI 0.541-0.907), with sensitivity and specificity of 75 % each; and IL-18 (AUC 0.688, CI 0.511-0.864), with sensitivity 62.5 % and specificity 70.8 %, for predicting mortality. Values were significantly higher in patients who required peritoneal dialysis (PD) than in those in whom it was not indicated. Levels were comparable among different etiologies. Only NGAL level was found to be a significant risk factor associated with longer duration of hospital stay.

CONCLUSIONS

Urinary NGAL and NAG had modest predictive ability for mortality. Children requiring dialysis had significantly raised levels, and the NGAL level had significant association with duration of hospital stay.

Administration of HES in elderly patients undergoing hip arthroplasty under spinal anesthesia is not associated with an increase in renal injury

Background

Hydroxyethyl starch (HES) is applied to achieve volume expansion during surgery; however, nephrotoxicity may be induced in patients with sepsis. Simultaneously, neutrophil gelatinase-associated lipocalin (NGAL) and IL-18 have been illustrated as pivotal indicators to diagnose the acute kidney injury (AKI) early. This multi-center, randomized, double-blinded, placebo-controlled study aimed to investigate whether 6% HES 130/0.4 administration caused postoperative AKI, which can be revealed by urinary and plasma NGAL and IL-18 estimations in elderly patients with normal renal function undergoing hip arthroplasty under spinal anesthesia.

Methods

120 ASA I–III, patients aged >65 y undergoing hip arthroplasty under spinal anesthesia randomly received 6% HES 130/0.4 or sodium lactate Ringer’s solution 7.5 mL/kg during the first hour of surgery. 118 patients completed the study. Blood pressure, NGAL concentrations, IL18, β₂ micro-albumin and albumin in urine and creatinine, NGAL and IL-18 in plasma were repeatedly measured before, during, and after surgery.

Results

The groups were balanced in mean arterial pressure, urine and plasma NGAL, plasma IL-18 and creatinine, urine β₂ microalbumin and albumin (P > 0.05). Urine IL-18 was dramatically elevated in both groups after surgery (P < 0.05), but did not vary significantly between the groups (P > 0.05).

Conclusion

Elderly patients undergoing surgery under spinal anesthesia are a high-risk population in AKI. These patients with normal renal function receiving a spinal anesthesia for a short duration surgery would not develop AKI when 500 mL (small volume) HES is infused.

Trial registration

Identifier: NCT02361736. Registration date was 2 February 2015.

Perspective on Clinical Application of Biomarkers in AKI

Several biomarkers of renal injury have been identified but the utility of these biomarkers is largely confined to research studies, whereas widespread clinical applicability is limited. This is partly because the use of serum creatinine as the comparator has several limitations and restricts the full interpretation of biomarker performance. To highlight the potential for clinical application of biomarkers, the most pertinent biomarker data are summarized here, using clinically relevant scenarios in which biomarkers could assist with diagnostic and management dilemmas. The paradigms proposed in this review aim to enhance the clinical diagnosis, management, and prognosis of AKI through the combined use of available clinical markers and novel inflammatory, injury, and repair biomarkers.

Correlation of Impedance Threshold Device use during cardiopulmonary resuscitation with post-cardiac arrest Acute Kidney Injury

PURPOSE

To assess whether use of Impedance Threshold Device (ITD) during cardiopulmonary resuscitation (CPR) reduces the degree of post-cardiac arrest Acute Kidney Injury (AKI), as a result of improved hemodynamics, in a porcine model of ventricular fibrillation (VF) cardiac arrest.

METHODS

After 8 min of untreated cardiac arrest, the animals were resuscitated either with active compression-decompression (ACD) CPR plus a sham ITD (control group, n=8) or with ACD-CPR plus an active ITD (ITD group, n=8). Adrenaline was administered every 4 min and electrical defibrillation was attempted every 2 min until return of spontaneous circulation (ROSC) or asystole. After ROSC the animals were monitored for 6 h under general anesthesia and then returned to their cages for a 48 h observation, before euthanasia. Two novel biomarkers, Neutrophil Gelatinase-Associated Lipocalin (NGAL) in plasma and Interleukin-18 (IL-18) in urine, were measured at 2 h, 4 h, 6 h, 24 h and 48 h post-ROSC, in order to assess the degree of AKI.

RESULTS

ROSC was observed in 7 (87.5%) animals treated with the sham valve and 8 (100%) animals treated with the active valve (P=NS). However, more than twice as many animals survived at 48 h in the ITD group (n=8, 100%) compared to the control group (n=3, 37.5%). Urine IL-18 and plasma NGAL levels were augmented post-ROSC in both groups, but they were significantly higher in the control group compared with the ITD group, at all measured time points.

CONCLUSION

Use of ITD during ACD-CPR improved hemodynamic parameters, increased 48 h survival and decreased the degree of post-cardiac arrest AKI in the resuscitated animals.

Urinary Biomarkers IGFBP7 and TIMP-2 for the Diagnostic Assessment of Transient and Persistent Acute Kidney Injury in Critically Ill Patients

OBJECTIVE

The capability of urinary TIMP-2 (tissue inhibitor of metalloproteinase) and IGFBP7 (insulin-like growth factor binding protein)-NephroCheck Test (NC) = ([TIMP-2] x [IGFBP7]) / 1000)-to predict renal recovery from acute kidney injury (AKI) has been poorly studied. The aim of this study was to assess the performance of measurements of ([TIMP-2] x [IGFBP7]) / 1000) over 24 hours to differentiate transient from persistent AKI.

METHODS

Of 460 consecutive adult patients admitted to the ICU, 101 were prospectively studied: 56 men, 62 (52-71) years old. A fresh urine sample was collected at H0, H4, H12 and H24 to determine ([TIMP-2] x [IGFBP7]) / 1000) levels. Areas under the curves of Delta NC H4-Ho and H12-H4 and serum creatinine (sCr) for detection of AKI recovery were compared.

RESULTS

Forty-one (40.6%) patient were diagnosed with AKI: 27 transient and 14 persistent AKI. At admission (H0), AKI patients had a significantly higher NC score than patients without AKI (0.43 [0.07-2.06] vs 0.15 [0.07-0.35], p = 0.027). In AKI groups, transient AKI have a higher NC, at H0 and H4, than persistent AKI (0.87 [0.09-2.82] vs 0.13 [0.05-0.66] p = 0.035 and 0.13 [0.07-0.61] vs 0.05 [0.02-0.13] p = 0.013). Thereafter, NC level decreased in both AKI groups with a Delta NC score H4-H0 and H12-H4 significantly more important in transient AKI. Roc curves showed however that delta NC scores did not discriminate between transient and persistent AKI.

CONCLUSION

In our population, absolute urinary levels of NC score were higher at early hours after ICU admission (H0 and H4) in transient AKI as compared to persistent AKI patients. NC variations (Delta NC scores) over the first 12 hours may indicate the AKI's evolving nature with a more significant decrease in case of transient AKI but were not able to differentiate transient from persistent AKI.

Biomarkers for the Early Detection and Prognosis of Acute Kidney Injury

AKI is an increasingly common disorder that is strongly linked to short- and long-term morbidity and mortality. Despite a growing heterogeneity in its causes, providing a timely and certain diagnosis of AKI remains challenging. In this review, we summarize the evolution of AKI biomarker studies over the past few years, focusing on two major areas of investigation: the early detection and prognosis of AKI. We highlight some of the lessons learned in conducting AKI biomarker studies, including ongoing attempts to address the limitations of creatinine as a reference standard and the recent shift toward evaluating the prognostic potential of these markers. Lastly, we suggest current gaps in knowledge and barriers that may be hindering their incorporation into care and a full ascertainment of their value.

Leptospira seropositivity as a risk factor for Mesoamerican Nephropathy

BACKGROUND

Leptospirosis is postulated as a possible cause of Mesoamerican Nephropathy (MeN) in Central American workers.

OBJECTIVES

Investigate job-specific Leptospira seroprevalence and its association with kidney disease biomarkers.

METHODS

In 282 sugarcane workers, 47 sugarcane applicants and 160 workers in other industries, we measured anti-leptospiral antibodies, serum creatinine, and urinary injury biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), and N-acetyl-D-glucosaminidase (NAG).

RESULTS

Leptospira seroprevalence differed among job categories and was highest among sugarcane cutters (59%). Seropositive sugarcane workers had higher NGAL concentrations (relative mean: 1.28; 95% CI: 0.94-1.75) compared to those who were seronegative, with similar findings among field and non-field workers.

CONCLUSIONS

Leptospira seroprevalence varied by job category. There was some indication that seropositivity was associated with elevated biomarker levels, but results were inconsistent. Additional studies may help establish whether Leptospira infection plays any role in MeN among Central American workers.

Suppression of NLRP3 Inflammasome Activation Ameliorates Chronic Kidney Disease-Induced Cardiac Fibrosis and Diastolic Dysfunction

Cardiac fibrosis is a common finding in patients with chronic kidney disease. Here, we investigate the cardio-renal effects of theracurmin, a novel formulation of the polyphenolic compound curcumin, in a rat model of chronic kidney disease. Briefly, Sprague-Dawley rats were randomized to undergo sham or subtotal nephrectomy (SNx) surgery. At 3 weeks post surgery, SNx animals were further randomized to received theracurmin via once daily oral gavage or vehicle for 5 consecutive weeks. At 8 weeks post surgery, cardiac function was assessed via echocardiography and pressure volume loop analysis, followed by LV and renal tissue collection for analysis. SNx animals developed key hallmarks of renal injury including hypertension, proteinuria, elevated blood urea nitrogen, and glomerulosclerosis. Renal injury in SNx animals was also associated with significant diastolic dysfunction, macrophage infiltration, and cardiac NLRP3 inflammasome activation. Treatment of SNx animals with theracurmin improved structural and functional manifestations of cardiac injury associated with renal failure and also attenuated cardiac NLRP3 inflammasome activation and mature IL-1β release. Taken together, our findings suggest a significant role for the NLRP3 inflammasome in renal injury-induced cardiac dysfunction and presents inflammasome attenuation as a unique strategy to prevent adverse cardiac remodeling in the setting of chronic kidney disease.