Plasma protein biomarkers enhance the clinical prediction of kidney injury recovery in patients undergoing liver transplantation

Long-Term Follow-Up of Kidney Function after Acute Liver Failure or Acute Liver Injury: A Cohort Study

Introduction

Acute liver failure (ALF) is a rare disease with high mortality. Acute kidney injury (AKI) following ALF is frequent. We assessed AKI impact on long-term kidney function among ALF survivors.

Methods

Observational cohort study including consecutive adult (age ≥16 years) patients with ALF or acute liver injury (ALI) admitted to a Portuguese tertiary center intensive care unit (ICU) between October 2013 and February 2020. KDIGO criteria were used to define AKI and chronic kidney disease (CKD). Primary outcome was the estimated glomerular filtration rate (eGFR), defined by the Chronic Kidney Disease Epidemiology Collaboration formula, at least 1 year after index ICU admission.

Results

Among 104 patients with ALF (n = 74) or ALI (n = 30), mean (SD) age was 43.7 (18.0) years, and 44 were male. Among all patients (n = 104), following adjustment for age and SOFA score, AKI during the first 7 ICU days (n AKI = 57 and n renal replacement therapy [RRT] = 32) was independently associated with all-cause mortality (adjusted HR [95% CI] 11.61 [1.49-90.34]; p = 0.019). Among hospital survivors with long-term kidney function available (n = 56), median (interquartile range) >1 year eGFR was 95.3 (75.0-107.7) mL/min/1.73 m2 (mean [SD] follow-up of 3.1 [1.6] years). Among these hospital survivors, following adjustment for baseline eGFR, AKI during the first 7 ICU days (n AKI = 19 and n RRT = 10) was not associated with >1 year eGFR (p = 0.15). At least 1 year after index ICU admission, 5 patients developed CKD, none RRT-dependent.

Conclusions

Among ALF or ALI survivors, AKI was not associated with significant long-term loss of kidney function.

Differential in Kidney Graft Years on the Basis of Solitary Kidney, Simultaneous Liver-Kidney, and Kidney-after-Liver Transplants

BACKGROUND

The number of simultaneous liver-kidney (SLK) transplants has significantly increased in the United States. There has also been an increase in kidney-after-liver transplants associated with 2017 policy revisions aimed to fairly allocate kidneys after livers. SLK and kidney-after-liver candidates are prioritized in allocation policy for kidney offers ahead of kidney-alone candidates.

METHODS

We compared kidney graft outcomes of kidney-alone transplant recipients with SLK and kidney-after-liver transplants using paired kidney models to mitigate differences among donor risk factors. We evaluated recipient characteristics between transplant types and calculated differential graft years using restricted mean survival estimates.

RESULTS

We evaluated 3053 paired donors to kidney-alone and SLK recipients and 516 paired donors to kidney-alone and kidney-after-liver recipients from August 2017 to August 2022. Kidney-alone recipients were younger, more likely on dialysis, and Black race. One-year and 3-year post-transplant kidney graft survival for kidney-alone recipients was 94% and 86% versus SLK recipients 89% and 80%, respectively, P < 0.001. One-year and 3-year kidney graft survival for kidney-alone recipients was 94% and 84% versus kidney-after-liver recipients 93% and 87%, respectively, P = 0.53. The additional kidney graft years for kidney-alone versus SLK transplants was 21 graft years/100 transplants (SEM=5.0) within 4 years post-transplantation, with no significant difference between kidney-after-liver and kidney-alone transplants.

CONCLUSIONS

Over a 5-year period in the United States, SLK transplantation was associated with significantly lower kidney graft survival compared with paired kidney-alone transplants. Most differences in graft survival between SLK and kidney-alone transplants occurred within the first year post-transplantation. By contrast, kidney-after-liver transplants had comparable graft survival with paired kidney-alone transplants.

A novel multiplex biomarker panel for profiling human acute and chronic kidney disease

Acute and chronic kidney disease continues to confer significant morbidity and mortality in the clinical setting. Despite high prevalence of these conditions, few validated biomarkers exist to predict kidney dysfunction. In this study, we utilized a novel kidney multiplex panel to measure 21 proteins in plasma and urine to characterize the spectrum of biomarker profiles in kidney disease. Blood and urine samples were obtained from age-/sex-matched healthy control subjects (HC), critically-ill COVID-19 patients with acute kidney injury (AKI), and patients with chronic or end-stage kidney disease (CKD/ESKD). Biomarkers were measured with a kidney multiplex panel, and results analyzed with conventional statistics and machine learning. Correlations were examined between biomarkers and patient clinical and laboratory variables. Median AKI subject age was 65.5 (IQR 58.5-73.0) and median CKD/ESKD age was 65.0 (IQR 50.0-71.5). Of the CKD/ESKD patients, 76.1% were on hemodialysis, 14.3% of patients had kidney transplant, and 9.5% had CKD without kidney replacement therapy. In plasma, 19 proteins were significantly different in titer between the HC versus AKI versus CKD/ESKD groups, while NAG and RBP4 were unchanged. TIMP-1 (PPV 1.0, NPV 1.0), best distinguished AKI from HC, and TFF3 (PPV 0.99, NPV 0.89) best distinguished CKD/ESKD from HC. In urine, 18 proteins were significantly different between groups except Calbindin, Osteopontin and TIMP-1. Osteoactivin (PPV 0.95, NPV 0.95) best distinguished AKI from HC, and β2-microglobulin (PPV 0.96, NPV 0.78) best distinguished CKD/ESKD from HC. A variety of correlations were noted between patient variables and either plasma or urine biomarkers. Using a novel kidney multiplex biomarker panel, together with conventional statistics and machine learning, we identified unique biomarker profiles in the plasma and urine of patients with AKI and CKD/ESKD. We demonstrated correlations between biomarker profiles and patient clinical variables. Our exploratory study provides biomarker data for future hypothesis driven research on kidney disease.

Renal damage in Hepatorenal Syndrome: A still unsolved issue

Acute kidney injury (AKI) is a common complication of cirrhosis, burdened by high morbidity and mortality rates and progression to chronic kidney disease. Hepatorenal syndrome (HRS) is a peculiar type of functional AKI observed in cirrhotic patients with ascites. HRS diagnosis is still clinical, once pre-renal azotemia and intrinsic kidney damage have been excluded by applying well-established and internationally adopted criteria. HRS is considered reversible because of the absence of intrinsic renal damage. However, HRS reversibility has been questioned, due to the lack of response to treatment with vasoconstrictors plus albumin in a relevant percentage of patients and to the persistence of renal dysfunction in HRS patients who underwent liver transplantation (LT). Indeed, LT is the only ultimate treatment, as it solves both liver failure and portal hypertension. Thus, the presence of renal damage in HRS can be hypothesized. In this scenario, neutrophil gelatinase-associated lipocalin (NGAL), one of the most promising biomarkers, may help in characterizing the type of renal injury, distinguishing between HRS and acute tubular necrosis. This review gathers the available evidence in favor and against the presence of structural lesions in HRS in terms of either renal histology and urinary biomarkers with a particular focus on NGAL. The ability to properly characterize which component of renal dysfunction prevails - functional rather than structural - entails a relevant clinical impact for the treatment of these patients, both in terms of medical therapy and liver vs. combined liver-kidney transplantation.

Novel Biomarkers of AKI in Cirrhosis

Acute kidney injury (AKI) is a frequent complication in patients with cirrhosis that is associated with poor outcomes and decreased survival. The definition of AKI in cirrhosis is currently based on changes of serum creatinine levels with respect to baseline values. Differential diagnosis of the causes of AKI is of major relevance, considering that some causes of AKI, such as hepatorenal syndrome, have specific treatment options and different prognosis. Prediction of kidney function recovery and patients' survival is also crucial in this patient population to guide clinical decisions. AKI biomarkers in cirrhosis have emerged as a promising tool for differential diagnosis and prognosis in this situation. There are consistent data showing that some urine biomarkers, particularly neutrophil gelatinase-associated lipocalin, may be useful in daily clinical practice for the differential diagnosis of the cause of AKI in cirrhosis. AKI biomarkers may constitute a useful tool for use in differential diagnosis, prognosis of renal function, and survival in patients with cirrhosis. This review focuses on the current state of knowledge and future perspective of novel biomarkers of AKI in cirrhosis.

Update on hepatorenal Syndrome: Definition, Pathogenesis, and management

Hepatorenal syndrome (HRS) is acute kidney injury (AKI) that occurs without evidence of structural abnormalities in the kidneys in patients with liver disease. It is thought to be due to splanchnic vasculature dilatation that is associated with intense increase of renal arteries' tone, leading to renal cortex ischemia and AKI. Nitric oxide, endotoxins, neurohormonal changes, bacterial infection, high serum bilirubin and bile acids are examples for factors contributing to HRS development. Nevertheless, other unknown factors may have role in HRS pathophysiology. Hence, further discussion and research are needed to clearly understand HRS. Plasma volume restoration and vasoconstrictors are the cornerstone of HRS treatment. Others such as octreotide, noradrenaline, infection control, systemic inflammatory response prevention, shunting, and renal replacement therapy are currently used to manage HRS. Liver or combined liver and kidney transplantation is currently the ultimate cure for HRS. This review was written to help in better understanding the pathogenesis, diagnosis, and treatment options for HRS.

[Kidney failure after liver transplantation]

One third of cirrhotic patients present impaired kidney function. It has multifactorial causes and has a harmful effect on patients' morbi-mortality before and after liver transplant. Kidney function does not improve in all patients after liver transplantation and liver-transplant recipients are at high risk of developing chronic kidney disease. Causes for renal dysfunction can be divided in three groups: preoperative, peroperative and postoperative factors. To date, there is no consensus for the modality of evaluation the risk for chronic kidney disease after liver transplantation, and for its prevention. In the present review, we describe the outcome of kidney function after liver transplantation, and the prognostic factors of chronic kidney disease to determine a risk stratification for each patient. Furthermore, we discuss therapeutic options to prevent kidney dysfunction in this setting, and highlight the indications of combined liver-kidney transplantation.

Role of Novel Kidney Biomarkers in Patients With Cirrhosis and After Liver Transplantation

Acute kidney injury (AKI) and chronic kidney disease (CKD) are important drivers of morbidity and mortality in patients with cirrhosis before and after liver transplantation (LT). In this review, we examine the role of novel kidney biomarkers for early recognition of kidney injury. Studies are limited by lack of reference standards, heterogeneous definitions of outcomes and biomarker cutoffs, and inconsistent diagnostic performance. Overall, a change in biomarker is more relevant than an absolute cutoff. Cystatin C and urinary neutrophil gelatinase-associated lipocalin (uNGAL) are the most studied candidate biomarkers and identify AKI or progression of AKI earlier than serum creatinine (sCr). Kidney injury molecule 1 and liver-type fatty acid-binding protein (L-FABP) also show potential. NGAL and interleukin 18 may play a role in differentiating acute tubular necrosis from other forms of AKI. Combining novel biomarkers with the Model for End-Stage Liver Disease score may assist prognosis. Persistent elevations in select markers (eg, NGAL) can portend irreversible injury. Several pretransplantation markers (including sCr) predict posttransplantation kidney dysfunction. Pretransplantation assessment of clinical factors (eg, age, diabetes) and novel markers (osteopontin and tissue inhibitor of metalloproteinases 1 [TIMP-1]) may predict renal kidney recovery after LT. Intraoperative changes in biomarkers predict early post-LT AKI. Prediction of CKD remains difficult, although a combination of biomarkers (eg, beta-2 microglobulin, CD40) is promising. Novel biomarkers have yet to replace sCr in guideline-based evaluation and management of kidney dysfunction in patients with cirrhosis. We propose a theoretical framework for practical incorporation of these biomarkers that considers patient characteristics (risk for irreversible injury), markers of functional and structural change, and assessment of the AKI-CKD continuum to identify patients at the highest risk for progressive kidney disease before and after LT.

Higher Mean Corpuscular Hemoglobin Concentration is Associated with Worse Prognosis of Hepatorenal Syndrome: A Multicenter Retrospective Study

BACKGROUND

Hepatorenal syndrome (HRS) is a severe complication of decompensated cirrhosis with high mortality. However, few prognostic factors have been identified and studies are urgently needed to facilitate precise treatment.

METHODS

Patients with decompensated cirrhosis and acute kidney injury were enrolled from four general hospitals between January 2010 and March 2020. Demographic and laboratory data were compared between surviving and non-surviving patients and also among different levels of HRS severity. COX regression analysis was performed to determine the effect of mean corpuscular hemoglobin concentration (MCHC) on survival of patients with HRS.

RESULTS

Out of a total of 1287 patients enrolled, 325 patients were analyzed. MCHC was significantly higher in non-survivors than in survivors, and in patients with more serious disease, defined as failure of organ systems. The hazard ratio (HR) of mortality was 1.17, 1.18 and 1.11, when adjusted by the crude model, model 1 and model 2, respectively. When MCHC was converted to a categorical variable based on the quartile of MCHC, the HR for the highest quartile of MCHC was 2.11 (95% CI: 1.45-3.06, P <0.05) compared to the lowest quartile of MCHC in the crude model, and when adjusted for age and sex (model 1), the HR was 2.20 (95% CI: 1.52-3.20, P <0.05). In model 2, which was adjusted for complex characteristics, the HR was 1.77 (95% CI: 1.17-2.68, P <0.05). The results of Kaplan-Meier curves were consistent with those from Cox regression analysis.

CONCLUSIONS

Higher MCHC was associated with worse prognosis in HRS.

Kidney Failure after Liver Transplantation

One-third of patients with cirrhosis present kidney failure (AKI and CKD). It has multifactorial causes and a harmful effect on morbidity and mortality before and after liver transplantation. Kidney function does not improve in all patients after liver transplantation, and liver transplant recipients are at a high risk of developing chronic kidney disease. The causes of renal dysfunction can be divided into three groups: pre-operative, perioperative and post-operative factors. To date, there is no consensus on the modality to evaluate the risk of chronic kidney disease after liver transplantation, or for its prevention. In this narrative review, we describe the outcome of kidney function after liver transplantation, and the prognostic factors of chronic kidney disease in order to establish a risk categorization for each patient. Furthermore, we discuss therapeutic options to prevent kidney dysfunction in this context, and highlight the indications of combined liver–kidney transplantation.

Current and Evolving Indications for Simultaneous Liver Kidney Transplantation

This review will discuss the etiologies of kidney disease in liver transplant candidates, provide a historical background of the prior evolution of simultaneous liver-kidney (SLK) transplant indications, discuss the current indications for SLK including Organ Procurement and Transplantation Network policies and Model for End Stage Liver Disease exception points, as well as provide an overview of the safety net kidney transplant policy. Finally, the authors explore unanswered questions and future research needed in SLK transplantation.

Monitoring Renal Function and Therapy of Hepatorenal Syndrome Patients with Cirrhosis

Acute kidney injury (AKI) is a frequent complication in patients with cirrhosis. Patients with cirrhosis can develop AKI due to different causes. Hepatorenal syndrome (HRS) is a unique cause of AKI occurring in patients with advanced cirrhosis and is associated with high short-term mortality. The differential diagnosis between different causes of AKI may be challenging. In this regard, new urine biomarkers may be helpful. Liver transplantation is the definitive treatment of patients with HRS-AKI. Vasoconstrictors and albumin represent the first-line pharmacologic treatment of HRS-AKI. This review summarizes current knowledge for the diagnosis and management of HRS in cirrhosis.

Discovery and Validation of a Biomarker Model (PRESERVE) Predictive of Renal Outcomes After Liver Transplantation

BACKGROUND AND AIMS

A high proportion of patients develop chronic kidney disease (CKD) after liver transplantation (LT). We aimed to develop clinical/protein models to predict future glomerular filtration rate (GFR) deterioration in this population.

APPROACH AND RESULTS

In independent multicenter discovery (CTOT14) and single-center validation (BUMC) cohorts, we analyzed kidney injury proteins in serum/plasma samples at month 3 after LT in recipients with preserved GFR who demonstrated subsequent GFR deterioration versus preservation by year 1 and year 5 in the BUMC cohort. In CTOT14, we also examined correlations between serial protein levels and GFR over the first year. A month 3 predictive model was constructed from clinical and protein level variables using the CTOT14 cohort (n = 60). Levels of β-2 microglobulin and CD40 antigen and presence of hepatitis C virus (HCV) infection predicted early (year 1) GFR deterioration (area under the curve [AUC], 0.814). We observed excellent validation of this model (AUC, 0.801) in the BUMC cohort (n = 50) who had both early and late (year 5) GFR deterioration. At an optimal threshold, the model had the following performance characteristics in CTOT14 and BUMC, respectively: accuracy (0.75, 0.8), sensitivity (0.71, 0.67), specificity (0.78, 0.88), positive predictive value (0.74, 0.75), and negative predictive value (0.76, 0.82). In the serial CTOT14 analysis, several proteins, including β-2 microglobulin and CD40, correlated with GFR changes over the first year.

CONCLUSIONS

We have validated a clinical/protein model (PRESERVE) that early after LT can predict future renal deterioration versus preservation with high accuracy. This model may help select recipients at higher risk for subsequent CKD for early, proactive renal sparing strategies.

External Validation of a Pretransplant Biomarker Model (REVERSE) Predictive of Renal Recovery After Liver Transplantation

In patients with end-stage liver disease, the ability to predict recovery of renal function following liver transplantation (LT) remains elusive. However, several important clinical decisions depend on whether renal dysfunction is recoverable after LT. We used a cohort of patients undergoing LT to independently validate a published pre-LT model predictive of post-transplant renal recovery (Renal Recovery Assessment at Liver Transplant [REVERSE]: high osteopontin [OPN] and tissue inhibitor of metalloproteinases-1 [TIMP-1] levels, age < 57, no diabetes). Serum samples pre-LT and 4-12 weeks post-LT (n = 117) were analyzed for kidney injury proteins from three groups of recipients: (1) estimated glomerular filtration rate (eGFR) < 30 mL/minute/1.73 m² prior to and after LT (irreversible acute kidney injury [AKI]), (2) eGFR < 30 mL/minute/1.73 m² prior to LT and >50 mL/minute/1.73 m² after LT (reversible AKI [rAKI]) (3) eGFR > 50 mL/minute/1.73 m² prior to and after LT (no AKI). In patients with elevated pre-LT serum levels of OPN and TIMP-1, recovery of renal function correlated with decreases in the level of both proteins. At 4 weeks post-LT (n = 77 subset), the largest decline in OPN and TIMP-1 was seen in the rAKI group. Validation of the REVERSE model in this independent data set had high area under the curve (0.78) in predicting full post-LT renal recovery (sensitivity 0.86, specificity 0.6, positive predictive value 0.81, negative predictive value 0.69). Our eGFR findings were confirmed using measured GFR. Conclusion: The REVERSE model, derived from an initial training set combining plasma biomarkers and clinical characteristics, demonstrated excellent external validation performance characteristics in an independent patient cohort using serum samples. Among patients with kidney injury pre-LT, the predictive ability of this model may prove beneficial in clinical decision-making both prior to and following transplantation.

Outcomes of Liver Transplantation in Patients on Renal Replacement Therapy: Considerations for Simultaneous Liver Kidney Transplantation Versus Safety Net

As the liver transplant (LT) waiting list continues to outpace organ availability, many patients require renal replacement therapy (RRT) before LT. It is unclear which patients will benefit from simultaneous liver kidney (SLK) transplant as opposed to awaiting a Safety Net kidney transplant (KT) post-LT.

Methods

In this study, a retrospective analysis of the United Network for Organ Sharing dataset was performed to identify risk factors associated with poor outcome for patients on RRT before LT who were listed for SLK and received either SLK vs LT alone (LTA).

Results

Between January 2003 and December 2016, 8971 adult LT recipients were on RRT at the time of LT. 5359 were listed for and received LTA (Group 1). Of 3612 patients listed for SLK, 3414 (38.1%) received SLK (Group 2) and 198 (2.2%) received LTA (Group 3). Overall, Group 3 had lower graft and patient survival post-LT when compared with Groups 1 and 2 (P < 0.001). Serum creatinine at 1 year post-LT and cumulative incidence for KT at 3 years post-LT were higher for Group 3 (P < 0.001). On multivariate analysis, pre-LT diabetes (P = 0.002), Model of End-Stage Liver Disease score (P = 0.01), and donor kidney donor profile index (P = 0.025) were significant in Group 2. Recipient age >60 (P < 0.001) and RRT pre-LT (>90 days; P = 0.001) were associated with lower patient survival in Group 3.

Conclusions

Among LT recipients on RRT before LT who were listed for SLK, RRT >90 days, and age >60 were associated with poor outcome following LTA. This suggests that programs should carefully weigh the decision to proceed with LTA vs waiting for SLK in this patient population. Future access to Safety Net KT will be an important consideration for these patients moving forward.

Hepatorenal Syndrome

Hepatorenal syndrome is a severe complication of end-stage cirrhosis characterized by increased splanchnic blood flow, hyperdynamic state, a state of decreased central volume, activation of vasoconstrictor systems, and extreme kidney vasoconstriction leading to decreased GFR. The contribution of systemic inflammation, a key feature of cirrhosis, in the development of hepatorenal syndrome has been highlighted in recent years. The mechanisms by which systemic inflammation precipitates kidney circulatory changes during hepatorenal syndrome need to be clarified. Early diagnosis is central in the management and recent changes in the definition of hepatorenal syndrome help identify patients at an earlier stage. Vasoconstrictive agents (terlipressin in particular) and albumin are the first-line treatment option. Several controlled studies proved that terlipressin is effective at reversing hepatorenal syndrome and may improve short-term survival. Not all patients are responders, and even in responders, early mortality rates are very high in the absence of liver transplantation. Liver transplantation is the only curative treatment of hepatorenal syndrome. In the long term, patients transplanted with hepatorenal syndrome tend to have lower GFR compared with patients without hepatorenal syndrome. Differentiating hepatorenal syndrome from acute tubular necrosis (ATN) is often a challenging yet important step because vasoconstrictors are not justified for the treatment of ATN. Hepatorenal syndrome and ATN may be considered as a continuum rather than distinct entities. Emerging biomarkers may help differentiate these two conditions and provide prognostic information on kidney recovery after liver transplantation, and potentially affect the decision for simultaneous liver-kidney transplantation.

Analysis of the differential urinary protein profile in IgA nephropathy patients of Uygur ethnicity

Background

IgA nephropathy (IgAN) is one of the most common forms of idiopathic glomerular diseases and might lead to end-stage kidney disease. Accurate and non-invasive biomarkers for early diagnosis are required for early intervention and consequent therapy for IgAN patients. Because variance in the disease incidence and predisposing genes of IgAN has been detected among different ethnicities, the ethnicity factor should be considered in IgAN biomarker discovery. The differences in the protein profiles and pathological mechanisms of IgAN in patients of Uygur ethnicity need to be clearly illustrated.

Methods

In this study, we used urinary proteomics to discover candidate biomarkers of IgAN in patients of Uygur ethnicity. The urinary proteins from Uygur normal control and Uygur IgAN patients were extracted and analyzed using 2D-LC-MS/MS and isobaric tags for relative and absolute quantitation (iTRAQ) analysis.

Results

A total of 277 proteins were found to be differentially represented in Uygur IgAN compared with the respective normal controls. The bioinformatics analysis revealed that the immune response, cell survival, and complement system were activated in Uygur IgAN. Many differentially expressed proteins were found to be related to nephropathy and kidney injuries. Four candidate biomarkers were validated by Western blot, and these results were consistent with the iTRAQ results. ICAM1, TIMP1, SERPINC1 and ADIPOQ were upregulated in Uygur IgAN. Bioinformatic analysis revealed that the increase of ICAM1 and TIMP1 might be caused by IgAN, but the increase of SERPINC1 and ADIPOQ might be caused by proteinuria. SERPINC1 and ICAM1 were identified as the candidate biomarkers with excellent area-under-the-curve (AUC) values (0.84) for distinguishing Uygur IgAN from normal controls.

Conclusions

Using urinary proteomic analysis, we identified several candidate biomarkers for IgAN in patients of Uygur ethnicity. These results will prove helpful for exploring the pathological mechanism of IgAN in patients of Uygur ethnicity and for developing better treatments for these patients.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-1139-3) contains supplementary material, which is available to authorized users.

VI consensus document by the Spanish Liver Transplantation Society

The goal of the Spanish Liver Transplantation Society (La Sociedad Española de Trasplante Hepático) is to promote and create consensus documents about current topics in liver transplantation with a multidisciplinary approach. To this end, on October 20, 2016, the 6th Consensus Document Meeting was held, with the participation of experts from the 24 authorized Spanish liver transplantation programs. This Edition discusses the following subjects, whose summary is offered below: 1) limits of simultaneous liver-kidney transplantation; 2) limits of elective liver re-transplantation; and 3) liver transplantation after resection and hepatocellular carcinoma with factors for a poor prognosis. The consensus conclusions for each of these topics is provided below.

Polyomavirus BK Nephropathy-Associated Transcriptomic Signatures: A Critical Reevaluation

Background

Recent work using DNA microarrays has suggested that genes related to DNA replication, RNA polymerase assembly, and pathogen recognition receptors can serve as surrogate tissue biomarkers for polyomavirus BK nephropathy (BKPyVN).

Methods

We have examined this premise by looking for differential regulation of these genes using a different technology platform (RNA-seq) and an independent set 25 biopsies covering a wide spectrum of diagnoses.

Results

RNA-seq could discriminate T cell–mediated rejection from other common lesions seen in formalin fixed biopsy material. However, overlapping RNA-seq signatures were found among all disease processes investigated. Specifically, genes previously reported as being specific for the diagnosis of BKPyVN were found to be significantly upregulated in T cell–mediated rejection, inflamed areas of fibrosis/tubular atrophy, as well as acute tubular injury.

Conclusions

In conclusion, the search for virus specific molecular signatures is confounded by substantial overlap in pathogenetic mechanisms between BKPyVN and nonviral forms of allograft injury. Clinical heterogeneity, overlapping exposures, and different morphologic patterns and stage of disease are a source of substantial variability in “Omics” experiments. These variables should be better controlled in future biomarker studies on BKPyVN, T cell–mediated rejection, and other forms of allograft injury, before widespread implementation of these tests in the transplant clinic.

New Developments in Hepatorenal Syndrome

Hepatorenal syndrome (HRS) continues to be one of the major complications of decompensated cirrhosis, leading to death in the absence of liver transplantation. Challenges in precisely evaluating renal function in the patient with cirrhosis remain because of the limitations of serum creatinine (Cr) alone in estimating glomerular filtration rate (GFR); current GFR estimating models appear to underestimate renal dysfunction. Newer models incorporating renal biomarkers, such as the Cr-Cystatin C GFR Equation for Cirrhosis appear to estimate measured GFR more accurately. A major change in the diagnostic criteria for HRS based on dynamic serial changes in serum Cr that regard HRS type 1 as a special form of acute kidney injury promises the possibility of earlier identification of renal dysfunction in patients with cirrhosis. The diagnostic criteria of HRS still include the exclusion of other causes of kidney injury. Renal biomarkers have been disappointing in assisting with the differentiation of HRS from prerenal azotemia and other kidney disorders. Serum metabolomic profiling may be a more powerful tool to assess renal dysfunction, although the practical clinical significance of this remains unclear. As a result of the difficulties of assessing renal function in cirrhosis and the varying HRS diagnostic criteria and the rigor with which they are applied, the precise incidence and prevalence of HRS is unknown, but it is likely that HRS occurs more commonly than expected. The pathophysiology of HRS is rooted firmly in the setting of progressive reduction in renal blood flow as a result of portal hypertension and splanchnic vasodilation. Progressive marked renal cortical ischemia in patients with cirrhosis parallels the evolution of diuretic-sensitive ascites to diuretic-refractory ascites and HRS, a recognized continuum of renal dysfunction in cirrhosis. Alterations in nitrous oxide production, both increased and decreased, may play a major role in the pathophysiology of this evolution. The inflammatory cascade, triggered by bacterial translocation and endotoxemia, increasingly recognized as important in the manifestation of acute-on-chronic liver failure, also may play a significant role in the pathophysiology of HRS. The mainstay of treatment remains vasopressor therapy with albumin in an attempt to reverse splanchnic vasodilation and improve renal blood flow. Several meta-analyses have confirmed the value of vasopressors, chiefly terlipressin and noradrenaline, in improving renal function and reversing HRS type 1. Other interventions such as renal replacement therapy, transjugular intrahepatic portosystemic shunt, and artificial liver support systems have a very limited role in improving outcomes in HRS. Liver transplantation remains the definitive treatment for HRS. The frequency of simultaneous liver-kidney transplantation has increased dramatically in the Model for End-stage Liver Disease era, with changes in organ allocation policies. This has resulted in a more urgent need to predict native kidney recovery from HRS after liver transplantation alone, to avoid unnecessary simultaneous liver-kidney transplantation.

Biomarkers of Renal Injury in Cirrhosis: Association with Acute Kidney Injury and Recovery after Liver Transplantation

BACKGROUND

To define urine or serum biomarkers in predicting renal function recovery after liver transplantation (LT).

METHODS

Adults listed for LT (February 2011-July 2014) and with modified diet for renal disease-6 (MDRD-6) <60 mL/min provided urine/blood samples at baseline and serially until LT for biomarkers in serum (pg/mL) and urine (pg/mg creatinine).

RESULTS

Of 271 LT listed patients (mean age 57 years, 63% males, median listing MELD 17.5), 1 year acute kidney injury (AKI) probability was 49%, with odds of 1.3-, 3.0-, 4.6-, and 8.5-fold times for listing MELD 16-20, 21-25, 26-30, and >30, compared to MELD <16. Thirty-seven people died over 1 year from the time of listing, with twofold increased odds with AKI. Among 67 patients with MDRD <60, only urinary epidermal growth factor was different comparing AKI (increase in serum creatinine ≥0.3 mg/dL from baseline within past 3 months) vs. no AKI (2,254 vs. 4,253, p = 0.003). Differences between acute tubular necrosis (ATN) and hepatorenal syndrome could not be ascertained for a small sample of 3 patients with ATN. Analyzing 15 of 43 receiving LT and MDRD-6 <30 prior to LT, biomarkers were not different comparing 5 patients recovering renal function (MDRD-6 >50 mL/min) at 6 months vs. 10 without recovery.

CONCLUSIONS

AKI is common among LT listed patients, with a negative impact on transplant-free survival. Serum and urine biomarkers are not associated with the recovery of renal function after LT. Multicenter studies are suggested to (a) develop strategies to reduce the development of AKI and (b) derive novel biomarkers for use in accurately predicting renal recovery after LT.

Renal recovery after acute kidney injury

Acute kidney injury (AKI) is a frequent complication of critical illness and carries a significant risk of short- and long-term mortality, chronic kidney disease (CKD) and cardiovascular events. The degree of renal recovery from AKI may substantially affect these long-term endpoints. Therefore maximising recovery of renal function should be the goal of any AKI prevention and treatment strategy. Defining renal recovery is far from straightforward due in part to the limitations of the tests available to assess renal function. Here, we discuss common pitfalls in the evaluation of renal recovery and provide suggestions for improved assessment in the future. We review the epidemiology of renal recovery and of the association between AKI and the development of CKD. Finally, we stress the importance of post-discharge follow-up of AKI patients and make suggestions for its incorporation into clinical practice. Summary key points are that risk factors for non-recovery of AKI are age, CKD, comorbidity, higher severity of AKI and acute disease scores. Second, AKI and CKD are mutually related and seem to have a common denominator. Third, despite its limitations full recovery of AKI may best be defined as the absence of AKI criteria, and partial recovery as a fall in AKI stage. Fourth, after an episode of AKI, serial follow-up measurements of serum creatinine and proteinuria are warranted to diagnose renal impairment and prevent further progression. Measures to promote recovery are similar to those preventing renal harm. Specific interventions promoting repair are still experimental.

Acute kidney injury after liver transplantation: Recent insights and future perspectives

Acute kidney injury (AKI) is a common postoperative complication after liver transplantation (LT). The occurrence of postoperative AKI after LT (Post-LT AKI) is associated with inferior patient and graft outcomes. Post-LT AKI is multifactorial in origin and has been related to the severity of liver disease, pre-LT renal dysfunction, graft quality, perioperative events and toxicity of immunosuppressive therapy. Furthermore it is thought that hepatic ischaemia reperfusion injury might be a driving force in the aetiology of post-LT AKI. Novel biomarkers for AKI are emerging and can be useful for early identification and characterization of AKI. There is a clear need for strategies aimed at preventing or treating post-LT AKI. Several pharmacological and non-pharmacological interventions have been studied, but so far failed to show any benefit in the prevention of post-LT AKI. Further studies are needed to develop and evaluate new interventions aimed at preventing post-LT AKI and improve patient outcomes.

Biomarkers in Transplantation--Proteomics and Metabolomics

Modern multianalyte "omics" technologies allow for the identification of molecular signatures that confer significantly more information than measurement of a single parameter as typically used in current medical diagnostics. Proteomics and metabolomics bioanalytical assays capture a large set of proteins and metabolites in body fluids, cells, or tissues and, complementing genomics, assess the phenome. Proteomics and metabolomics contribute to the development of novel predictive clinical biomarkers in transplantation in 2 ways: they can be used to generate a diagnostic fingerprint or they can be used to discover individual proteins and metabolites of diagnostic potential. Much fewer metabolomics than proteomics biomarker studies in transplant patients have been reported, and, in contrast to proteomics discovery studies, new lead metabolite markers have yet to emerge. Most clinical proteomics studies have been discovery studies. Several of these studies have assessed diagnostic sensitivity and specificity. Nevertheless, none of these newly discovered protein biomarkers have yet been implemented in clinical decision making in transplantation. The currently most advanced markers discovered in proteomics studies in transplant patients are the chemokines CXCL-9 and CXCL-10, which have successfully been validated in larger multicenter trials in kidney transplant patients. These chemokines can be measured using standard immunoassay platforms, which should facilitate clinical implementation. Based on the published evidence, it is reasonable to expect that these chemokine markers can help guiding and individualizing immunosuppressive regimens, may be able to predict acute and chronic T-cell-mediated and antibody-mediated rejection, and may be useful tools for risk stratification of kidney transplant patients.

A modular microfluidic bioreactor with improved throughput for evaluation of polarized renal epithelial cells

Most current microfluidic cell culture systems are integrated single use devices. This can limit throughput and experimental design options, particularly for epithelial cells, which require significant time in culture to obtain a fully differentiated phenotype. In addition, epithelial cells require a porous growth substrate in order to fully polarize their distinct apical and basolateral membranes. We have developed a modular microfluidic system using commercially available porous culture inserts to evaluate polarized epithelial cells under physiologically relevant fluid flow conditions. The cell-support for the bioreactor is a commercially available microporous membrane that is ready to use in a 6-well format, allowing for cells to be seeded in advance in replicates and evaluated for polarization and barrier function prior to experimentation. The reusable modular system can be easily assembled and disassembled using these mature cells, thus improving experimental throughput and minimizing fabrication requirements. The bioreactor consists of an apical microfluidic flow path and a static basolateral chamber that is easily accessible from the outside of the device. The basolateral chamber acts as a reservoir for transport across the cell layer. We evaluated the effect of initiation of apical shear flow on short-term intracellular signaling and mRNA expression using primary human renal epithelial cells (HRECs). Ten min and 5 h after initiation of apical fluid flow over a stable monolayer of HRECs, cells demonstrated increased phosphorylation of extracellular signal-related kinase and increased expression of interleukin 6 (IL-6) mRNA, respectively. This bioreactor design provides a modular platform with rapid experimental turn-around time to study various epithelial cell functions under physiologically meaningful flow conditions.

Kidney biomarkers in cirrhosis

Impaired renal function due to acute kidney injury (AKI) and/or chronic kidney diseases (CKD) is frequent in cirrhosis. Recurrent episodes of AKI may occur in end-stage cirrhosis. Differential diagnosis between functional (prerenal and hepatorenal syndrome) and acute tubular necrosis (ATN) is crucial. The concept that AKI and CKD represent a continuum rather than distinct entities, is now emerging. Not all patients with AKI have a potential for full recovery. Precise evaluation of kidney function and identification of kidney changes in patients with cirrhosis is central in predicting reversibility. This review examines current biomarkers for assessing renal function and identifying the cause and mechanisms of impaired renal function. When CKD is suspected, clearance of exogenous markers is the reference to assess glomerular filtration rate, as creatinine is inaccurate and cystatin C needs further evaluation. Recent biomarkers may help differentiate ATN from hepatorenal syndrome. Neutrophil gelatinase-associated lipocalin has been the most extensively studied biomarker yet, however, there are no clear-cut values that differentiate each of these conditions. Studies comparing ATN and hepatorenal syndrome in cirrhosis, do not include a gold standard. Combinations of innovative biomarkers are attractive to identify patients justifying simultaneous liver and kidney transplantation. Accurate biomarkers of underlying CKD are lacking and kidney biopsy is often contraindicated in this population. Urinary microRNAs are attractive although not definitely validated. Efforts should be made to develop biomarkers of kidney fibrosis, a common and irreversible feature of CKD, whatever the cause. Biomarkers of maladaptative repair leading to irreversible changes and CKD after AKI are also promising.

Protecting the Kidney in Liver Transplant Recipients: Practice-Based Recommendations From the American Society of Transplantation Liver and Intestine Community of Practice

Both acute and chronic kidney disease are common after liver transplantation and result in significant morbidity and mortality. The introduction of the Model for End-stage Liver Disease score has directly correlated with an increased prevalence of perioperative renal dysfunction and the number of simultaneous liver-kidney transplantations performed. Kidney dysfunction in this population is typically multifactorial and related to preexisting conditions, pretransplantation renal injury, perioperative events, and posttransplantation nephrotoxic immunosuppressive therapies. The management of kidney disease after liver transplantation is challenging, as by the time the serum creatinine level is significantly elevated, few interventions affect the course of progression. Also, immunological factors such as antibody-mediated kidney rejection have become of greater interest given the rising liver-kidney transplant population. Therefore, this review, assembled by experts in the field and endorsed by the American Society of Transplantation Liver and Intestine Community of Practice, provides a critical assessment of measures of renal function and interventions aimed at preserving renal function early and late after liver and simultaneous liver-kidney transplantation. Key points and practice-based recommendations for the prevention and management of kidney injury in this population are provided to offer guidance for clinicians and identify gaps in knowledge for future investigations.

Protecting the Kidney in Liver Transplant Candidates: Practice-Based Recommendations From the American Society of Transplantation Liver and Intestine Community of Practice

Acute kidney injury (AKI) and chronic kidney disease (CKD) are common in patients awaiting liver transplantation, and both have a marked impact on the perioperative and long-term morbidity and mortality of liver transplant recipients. Consequently, we reviewed the epidemiology of AKI and CKD in patients with end-stage liver disease, highlighted strategies to prevent and manage AKI, evaluated the changing liver transplant waiting list's impact on kidney function, delineated important considerations in simultaneous liver-kidney transplant selection, and projected possible future transplant policy changes and outcomes. This review was assembled by experts in the field and endorsed by the American Society of Transplantation Liver and Intestinal Community of Practice and Board of Directors and provides practice-based recommendations for preservation of kidney function in patients with end-stage liver disease.

Variation in serum biomarkers with sex and female hormonal status: implications for clinical tests

Few serum biomarker tests are implemented in clinical practice and recent reports raise concerns about poor reproducibility of biomarker studies. Here, we investigated the potential role of sex and female hormonal status in this widespread irreproducibility. We examined 171 serum proteins and small molecules measured in 1,676 participants from the Netherlands Study of Depression and Anxiety. Concentrations of 96 molecules varied with sex and 66 molecules varied between oral contraceptive pill users, postmenopausal females, and females in the follicular and luteal phases of the menstrual cycle (FDR-adjusted p-value <0.05). Simulations of biomarker studies yielded up to 40% false discoveries when patient and control groups were not matched for sex and up to 41% false discoveries when premenopausal females were not matched for oral contraceptive pill use. High accuracy (over 90%) classification tools were developed to label samples with sex and female hormonal status where this information was not collected.

Assessment of Urine Proteomics in Type 1 Primary Hyperoxaluria

BACKGROUND

Primary hyperoxaluria type 1 (PH1) and idiopathic hypercalciuria (IHC) are stone-forming diseases that may result in the formation of calcium (Ca) oxalate (Ox) stones, nephrocalcinosis, and progressive chronic kidney disease (CKD). Poorer clinical outcome in PH1 is segregated by the highest urine (Ur)-Ox (UrOx), while IHC outcomes are not predictable by UrCa. We hypothesized that differences would be found in selected Ur-protein (PRO) patterns in PH1 and IHC, compared to healthy intra-familial sibling controls (C) of PH1 patients. We also hypothesized that the PRO patterns associated with higher UrOx levels would reflect injury, inflammation, biomineralization, and abnormal tissue repair processes in PH1.

METHODS

Twenty four-hour Ur samples were obtained from 3 cohorts: PH1 (n = 47); IHC (n = 35) and C (n = 13) and were analyzed using targeted platform-based multi-analyte profile immunoassays and for UrOx and UrCa by biochemical measurements.

RESULTS

Known stone matrix constituents, osteopontin, calbindin, and vitronectin were lowest in PH1 (C > IHC > PH1; p < 0.05). Ur-interleukin-10; chromogranin A; epidermal growth factor (EGF); insulin-like growth factor-1 (IGF-1), and macrophage inflammatory PRO-1α (MIP-1α) were higher in PH1 > C (p = 0.03 to p < 0.05). Fetuin A; IGF-1, MIP-1α, and vascular cell adhesion molecule-1 were highest in PH1 > IHC (p < 0.001 to p = 0.005).

CONCLUSION

PH1 Ur-PROs reflected overt inflammation, chemotaxis, oxidative stress, growth factors (including EGF), and pro-angiogenic and calcification regulation/inhibition compared to the C and IHC cohorts. Many of the up- and downregulated PH1-PROs found in this study are also found in CKD, acute kidney injury, stone formers, and/or stone matrices. Further data analyses may provide evidence for PH1 unique PROs or demonstrate a poorer clinical outcome.

Keeping high model for end-stage liver disease score liver transplantation candidates alive

As the mean Model for End-Stage Liver Disease (MELD) score at time of liver transplantation continues to increase, it is crucial to implement preemptive strategies to reduce wait-list mortality. We review the most common complications that arise in patients with a high MELD score in an effort to highlight strategies that can maximize survival and successful transplantation.

Pathogenesis of Hepatorenal Syndrome: Implications for Therapy

Patients with cirrhosis are prone to develop acute kidney injury (AKI) due to a number of causes, including bacterial infections with or without septic shock, hypovolemia, administration of nephrotoxic drugs, and intrinsic kidney diseases, among others. Most importantly, patients with advanced cirrhosis develop a distinctive cause of AKI, characterized by rapidly progressive glomerular filtration rate loss associated with marked disturbances in circulatory function in the absence of obvious pathologic abnormalities in the kidneys, known as hepatorenal syndrome (HRS). Decreased kidney function results from intense renal vasoconstriction secondary to the complex circulatory changes of cirrhosis with splanchnic vasodilatation and effective hypovolemia. Beyond activation of vasoactive systems, factors including impaired renal blood flow autoregulation and systemic inflammation may play a role in the development of HRS. Most patients improve with albumin and vasopressors; however, the prognosis of HRS remains very poor. Novel biomarkers may be helpful in distinguishing HRS from other causes of AKI in patients with cirrhosis.

Chronic Kidney Disease and Related Long-Term Complications After Liver Transplantation

Liver transplantation is the standard of care for patients with decompensated cirrhosis. Liver transplantation recipients have excellent short-term and long-term outcomes including patient and graft survival. Since the adoption of model for end-stage liver disease (MELD)-based allocation policy, the incidence of post-transplant end stage renal disease has risen significantly. Occurrence of Stage 4 chronic kidney disease and end stage renal disease substantially increases the risk of post-transplant deaths. Because majority of late post-transplant mortality is due to nonhepatic post-transplant comorbidities, personalized care directed toward risk factor modification may further improve post-transplant survival.

Kidney Failure and Liver Allocation: Current Practices and Potential Improvements

In February 2002, the United Network for Organ Sharing implemented a system for prioritizing candidates for liver transplantation that was based on the risk of 90-day mortality as determined by the Model for End-Stage Liver Disease (MELD) score. As the MELD score is driven in part by serum creatinine as a marker of kidney function, the prevalence of kidney dysfunction and failure in patients with end-stage liver disease at the time of listing and at transplantation has steadily risen. In this review, we discuss current practices in liver transplantation in patients with kidney dysfunction focusing briefly on the decision to perform simultaneous liver-kidney transplantation. We then discuss pitfalls to the current practices of liver transplantation in patients with kidney dysfunction. We conclude by discussing potential improvements to current practices including the use of the MELD-Na score, alternatives to creatinine and creatinine-based equation for estimating kidney function, and the use of intraoperative kidney replacement therapy during liver transplantation.

Analysis of a urinary biomarker panel for clinical outcomes assessment in cirrhosis

BACKGROUND

Biomarkers are potentially useful in assessment of outcomes in patients with cirrhosis, but information is very limited. Given the large number of biomarkers, adequate choice of which biomarker(s) to investigate first is important.

AIM

Analysis of potential usefulness of a panel of urinary biomarkers in outcome assessment in cirrhosis.

PATIENTS AND METHODS

Fifty-five patients with acute decompensation of cirrhosis were studied: 39 had Acute Kidney Injury (AKI) (Prerenal 12, type-1 HRS (hepatorenal syndrome) 15 and Acute Tubular Necrosis (ATN) 12) and 16 acute decompensation without AKI. Thirty-four patients had Acute-on-chronic liver failure (ACLF). A panel of 12 urinary biomarkers was assessed, using a multiplex assay, for their relationship with ATN, ACLF and mortality.

RESULTS

Biomarker with best accuracy for ATN diagnosis was NGAL (neutrophil-gelatinase associated lipocalin): 36 [26-125], 104 [58-208] and 1807 [494-3,716] μg/g creatinine in Prerenal-AKI, type-1 HRS and ATN, respectively; p<0.0001 (AUROC 0.957). Other attractive biomarkers for ATN diagnosis were IL-18, albumin, trefoil-factor-3 (TFF-3) and glutathione-S-transferase-π (GST-π) Biomarkers with less accuracy for ATN AUCROC<0.8 were β2-microglobulin, calbindin, cystatin-C, clusterin and KIM-1 (kidney injury molecule-1). For ACLF, the biomarker with the best accuracy was NGAL (ACLF vs. No-ACLF: 165 [67-676] and 32 [19-40] μg/g creatinine; respectively; p<0.0001; AUROC 0.878). Interestingly, other biomarkers with high accuracy for ACLF were osteopontin, albumin, and TFF-3. Biomarkers with best accuracy for prognosis were those associated with ACLF.

CONCLUSIONS

A number of biomarkers appear promising for differential diagnosis between ATN and other types of AKI. The most interesting biomarkers for ACLF and prognosis are NGAL, osteopontin, albumin, and TFF-3. These results support the role of major inflammatory reaction in the pathogenesis of ACLF.