Cholemic nephropathy - Historical notes and novel perspectives

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

Acute hyperbilirubinemia determines an early subclinical renal damage: Evaluation of tubular biomarkers in cholemic nephropathy

BACKGROUND AND AIMS

Cholemic nephropathy is a cause of acute kidney injury occurring in patients with jaundice. The aim of this study was to evaluate early renal function impairment in patients with mild acute hyperbilirubinemia in the absence of alterations of the common parameters used in clinical practice (serum creatinine or urea) and with normal renal morphology. We studied urinary biomarkers of tubular damage urinary neutrophil gelatinase-associated lipocalin (u-NGAL), urinary beta-2-microglobulin (u-B2M), urinary osteopontin (u-OPN), urinary trefoil factor 3 (u-TFF3) and urinary Cystatin C (u-Cys).

METHODS

This is a case-control study investigating the following urinary biomarkers of tubular damage: u-NGAL, u-B2M, u-OPN, u-TFF3 and u-Cys, in patients with mild acute hyperbilirubinemia. Seventy-four patients were included in this study: 36 patients with jaundice and 38 patients without jaundice.

RESULTS

Subjects with jaundice (total bilirubin 12.4 ± 7.3 mg/dL) showed higher u-NGAL, u-B2M, u-OPN, u-TFF3 and u-Cys compared with controls. After logistic regression analyses, including the following independent variables: age, estimated Glomerular Filtration Rate (eGFR), haemoglobin, diabetes, hypertension and jaundice, we observed a higher risk of elevated u-NGAL values (OR = 3.8, 95% CI 1.07-13.5, p = .03) and u-B2M (OR = 9.4, 95% CI 2.3-38.9, p = .0018) in jaundiced subjects. Moreover, urinary biomarkers had a direct correlation with serum cholestasis indexes.

CONCLUSIONS

This study demonstrated increased urinary biomarkers of tubular damage (u-NGAL, u-B2M, u-OPN, u-TFF3, and u-Cys) in patients with mild hyperbilirubinemia in comparison with a control group. These findings suggest early renal tubular damage in the absence of alterations of the normal parameters used in clinical practice (eGFR, serum urea and renal morphology).

Cholemic Nephropathy: Role in Acute Kidney Injury in Cholestasis and Cirrhosis

The concept of structural kidney damage and renal dysfunction as a result of jaundice attracted attention in the medical community in the early and mid-20th century. The postulated doctrine of the time was that the excretion of elevated concentrations of bile results in bile-stained casts occupying collecting and distal convoluted tubules, degeneration of tubular epithelium, and decreased renal function. Compared to the hepatorenal syndrome, the poster child of hepatology and nephrology collaboration, the notion of structural kidney damage and renal dysfunction as a result of cholemia lost its traction and has almost disappeared from modern textbooks. Today, cholemic nephropathy is experiencing a renaissance, with multiple case reports and case series of jaundiced patients with kidney dysfunction and evidence of bile acid casts upon histologic examination. Published cases include acute hepatitis, chronic liver injury, cirrhosis, and obstructive etiologies. Diagnosis of cholemic nephropathy is based on histological examination, typically showing intraluminal bile casts predominantly located in the distal tubules. In common bile duct-ligated mice, the histomorphological and functional alterations of cholemic nephropathy mimic those seen in humans. Some argue against the concept of cholemic nephropathy and postulate that bile casts are a secondary phenomenon. What we need are carefully designed trials to establish diagnostic criteria and subsequently translate this knowledge into evidence-based therapies.

Inhibition of the renal apical sodium dependent bile acid transporter prevents cholemic nephropathy in mice with obstructive cholestasis

BACKGROUND & AIMS

Cholemic nephropathy (CN) is a severe complication of cholestatic liver diseases for which there is no specific treatment. We revisited its pathophysiology with the aim of identifying novel therapeutic strategies.

METHODS

Cholestasis was induced by bile duct ligation (BDL) in mice. Bile flux in kidneys and livers was visualized by intravital imaging, supported by MALDI mass spectrometry imaging and liquid chromatography-tandem mass spectrometry. The effect of AS0369, a systemically bioavailable apical sodium-dependent bile acid transporter (ASBT) inhibitor, was evaluated by intravital imaging, RNA-sequencing, histological, blood, and urine analyses. Translational relevance was assessed in kidney biopsies from patients with CN, mice with a humanized bile acid (BA) spectrum, and via analysis of serum BAs and KIM-1 (kidney injury molecule 1) in patients with liver disease and hyperbilirubinemia.

RESULTS

Proximal tubular epithelial cells (TECs) reabsorbed and enriched BAs, leading to oxidative stress and death of proximal TECs, casts in distal tubules and collecting ducts, peritubular capillary leakiness, and glomerular cysts. Renal ASBT inhibition by AS0369 blocked BA uptake into TECs and prevented kidney injury up to 6 weeks after BDL. Similar results were obtained in mice with humanized BA composition. In patients with advanced liver disease, serum BAs were the main determinant of KIM-1 levels. ASBT expression in TECs was preserved in biopsies from patients with CN, further highlighting the translational potential of targeting ASBT to treat CN.

CONCLUSIONS

BA enrichment in proximal TECs followed by oxidative stress and cell death is a key early event in CN. Inhibiting renal ASBT and consequently BA enrichment in TECs prevents CN and systemically decreases BA concentrations.

IMPACT AND IMPLICATIONS

Cholemic nephropathy (CN) is a severe complication of cholestasis and an unmet clinical need. We demonstrate that CN is triggered by the renal accumulation of bile acids (BAs) that are considerably increased in the systemic blood. Specifically, the proximal tubular epithelial cells of the kidney take up BAs via the apical sodium-dependent bile acid transporter (ASBT). We developed a therapeutic compound that blocks ASBT in the kidneys, prevents BA overload in tubular epithelial cells, and almost completely abolished all disease hallmarks in a CN mouse model. Renal ASBT inhibition represents a potential therapeutic strategy for patients with CN.

Male lake char release taurocholic acid as part of a mating pheromone

The evolutionary origins of sexual preferences for chemical signals remain poorly understood, due, in part, to scant information on the molecules involved. In the current study, we identified a male pheromone in lake char (Salvelinus namaycush) to evaluate the hypothesis that it exploits a non-sexual preference for juvenile odour. In anadromous char species, the odour of stream-resident juveniles guides migratory adults into spawning streams. Lake char are also attracted to juvenile odour but have lost the anadromous phenotype and spawn on nearshore reefs, where juvenile odour does not persist long enough to act as a cue for spawning site selection by adults. Previous behavioural data raised the possibility that males release a pheromone that includes components of juvenile odour. Using metabolomics, we found that the most abundant molecule released by males was also released by juveniles but not females. Tandem mass spectrometry and nuclear magnetic resonance were used to identify the molecule as taurocholic acid (TCA), which was previously implicated as a component of juvenile odour. Additional chemical analyses revealed that males release TCA at high rates via their urine during the spawning season. Finally, picomolar concentrations of TCA attracted pre-spawning and spawning females but not males. Taken together, our results indicate that male lake char release TCA as a mating pheromone and support the hypothesis that the pheromone is a partial match of juvenile odour.

Austrian consensus on the diagnosis and management of portal hypertension in advanced chronic liver disease (Billroth IV)

The Billroth IV consensus was developed during a consensus meeting of the Austrian Society of Gastroenterology and Hepatology (ÖGGH) and the Austrian Society of Interventional Radiology (ÖGIR) held on the 26th of November 2022 in Vienna.Based on international recommendations and considering recent landmark studies, the Billroth IV consensus provides guidance regarding the diagnosis and management of portal hypertension in advanced chronic liver disease.

Extracorporeal liver support techniques: a comparison

ExtraCorporeal Liver Support (ECLS) systems were developed with the aim of supporting the liver in its detoxification function by clearing the blood from hepatic toxic molecules. We conducted a retrospective comparative analysis on patients presenting with liver failure who were treated with different extracorporeal techniques in our intensive care unit to evaluate and compare their detoxification abilities. To verify the effectiveness of the techniques, mass balance (MB) and adsorption per hour were calculated for total bilirubin (TB), direct bilirubin (DB), and bile acids (BA) from the concentrations measured. MB represents the total amount (mg or mcMol) of a molecule removed from a solution and is the only representative parameter to verify the purification effectiveness of one system as it is not affected by the continuous production of the molecules, released in the circulation from the tissues, as it is the case for the reduction rate (RR). The total adsorption per hour is calculated by the ratio between MB and the time duration and shows the adsorption ability in an hour. Our comparative study shows the superior adsorption capability of CytoSorb system regarding TB, DB, and BA, evaluated through the MB and adsorption per hour, in comparison with CPFA, MARS, Prometheus, and PAP. In conclusion, as extracorporeal purification in liver failure could be considered useful for therapeutic purposes, Cytosorb, being more performing than other systems considered, could represent the device of first choice.

Bile Cast Nephropathy Due to Hepatitis A-induced Hyperbilirubinemia: A Case Report and Literature Review

Bile cast nephropathy (BCN) or cholemic nephrosis (CN) is a form of acute renal dysfunction that occurs in the setting of hepatic dysfunction and hyperbilirubinemia. We present a case of a 58-year-old woman with a four-day history of intractable nausea, vomiting, and yellowish discoloration of her skin and eyes. Laboratory workup was notable for elevated total bilirubin (mainly direct), liver enzymes, creatinine, and blood urea nitrogen (BUN). The ultrasonography (US) of the abdomen showed hepatic steatosis. The hepatitis panel was remarkable for hepatitis A IgM. She was initially treated with supportive therapy. However, her bilirubin levels reached over 20 mg/dl, creatine was >8 mg/dl, and her estimated glomerular filtration rate (eGFR) was <10. Kidney biopsy showed pigmented casts consistent with BCN. She was started on hemodialysis with significant improvement in her symptoms and liver enzymes. This case underscores the importance of a broad differential diagnosis in cases with hyperbilirubinemia and acute kidney injury. BCN requires renal biopsy for a definitive diagnosis, and these patients usually require hemodialysis.

Extracorporeal organ support and the kidney

The concept of extracorporeal organ support (ECOS) encompasses kidney, respiratory, cardiac and hepatic support. In an era of increasing incidence and survival of patients with single or multiple organ failure, knowledge on both multiorgan crosstalk and the physiopathological consequences of extracorporeal organ support have become increasingly important. Immerse within the cross-talk of multiple organ failure (MOF), Acute kidney injury (AKI) may be a part of the clinical presentation in patients undergoing ECOS, either as a concurrent clinical issue since the very start of ECOS or as a de novo event at any point in the clinical course. At any point during the clinical course of a patient with single or multiple organ failure undergoing ECOS, renal function may improve or deteriorate, as a result of the interaction of multiple factors, including multiorgan crosstalk and physiological consequences of ECOS. Common physiopathological ways in which ECOS may influence renal function includes: 1) multiorgan crosstalk (preexisting or de-novo 2)Hemodynamic changes and 3) ECOS-associated coagulation abnormalities and 3) Also, cytokine profile switch, neurohumoral changes and toxins clearance may contribute to the expected physiological changes related to ECOS. The main objective of this review is to summarize the described mechanisms influencing the renal function during the course of ECOS, including renal replacement therapy, extracorporeal membrane oxygenation/carbon dioxide removal and albumin dialysis.

Bile Cast Nephropathy: A Comprehensive Review

Bile cast nephropathy (BCN) or cholemic nephropathy (CN) is an acute renal dysfunction, including acute kidney injury (AKI) in the setting of liver injury. It is a common phenomenon in patients with liver disease and is associated with significant morbidity and mortality. CN is characterized by hemodynamic changes in the liver, kidney, systemic circulation, intratubular cast formation, and tubular epithelial cell injury. CN has been overlooked as a differential diagnosis in chronic liver disease patients due to more importance to hepatic injury. However, frequent and considerable reporting of case reports recently has further investigated this topic in the last two decades. This review determines the evidence behind the potential role of bile acids and bilirubin in acute renal dysfunction in liver injury, summarizing the implied pathophysiology risk factors, and incorporating the therapeutic mechanisms and outcomes.

Predictors of mortality at 28-days in infection associated acute kidney injury in cirrhosis

BACKGROUND

Acute kidney injury (AKI) in cirrhosis is important complication with poor outcomes. And infections are common cause for acute decompensation. Infections in cirrhosis lead to acute deterioration of hemodynamics leading to precipitation of AKI.

AIM

To study predictors of mortality in patients with infection-associated AKI in cirrhosis.

METHODS

This was a prospective, observational study conducted at tertiary care centre from January 2018 till April 2019. Total 119 participants with cirrhosis of liver presenting with AKI were included into the study. AKI was defined as per international club of Ascites-AKI criteria 2015. Patients were grouped into infection AKI and non-infection AKI. Non-infection AKI included patients with diuretic induced AKI and pre-renal AKI. Logistic regression analysis was used to determine predictors of mortality at 28-d.

RESULTS

Out of 119 patients, alcohol (n = 104) was most common etiology of cirrhosis. The infection AKI included 67 (56%) patients and non-infection AKI (n = 52) included pre-renal AKI in 36 (30%) and diuretic-induced AKI in 16 (14%) patients. Infection AKI had significantly higher bilirubin, higher international normalized ratio (INR), low serum sodium, higher total leukocyte count (TLC) and higher prevalence of hepatic encephalopathy (HE) as compared to non-infection AKI. Infection AKI had higher progression of AKI (19/67 vs 2/52; P = 0.01) and 28-d mortality (38/67 vs 4/5; P ≤ 0.01) as compared to non-infection AKI. At 28-d, non-survivors (n = 42) had significantly higher bilirubin, higher INR, low serum sodium, higher TLC and higher prevalence of HE as compared to survivors (n = 77). On subgroup analysis of Infection AKI group, on multivariate analysis, serum bilirubin as well as presence of HE were independent predictors of 28-d mortality. There was no significant difference of mortality at 90-d between two groups.

CONCLUSION

Infection AKI in cirrhosis has a dismal prognosis with higher 28-d mortality as compared to non-infection AKI. Serum bilirubin and presence of HE predict 28-d mortality in infection AKI.

Cholemic Nephropathy as Cause of Acute and Chronic Kidney Disease. Update on an Under-Diagnosed Disease

Cholemic nephropathy (CN) is a recognized cause of acute kidney injury (AKI) in patients with severe hyperbilirubinemia (sHyb) and jaundice. Pathophysiological mechanisms of CN are not completely understood, but it seems caused both by direct toxicity of cholephiles and bile casts formation in nephrons enhanced by prolonged exposure to sHyb, particularly in the presence of promoting factors, as highlighted by a literature reviewed and by personal experience. The aim of our update is to retrace CN in its pathophysiology, risk factors, diagnosis and treatment, underlining the role of sHyb, promoting factors, and CN-AKI diagnostic criteria in the different clinical settings associated with this often-concealed disease. Our purpose is to focus on clinical manifestation of CN, exploring the possible transition to CKD. Cholemic nephropathy is an overlooked clinical entity that enters differential diagnosis with other causes of AKI. Early diagnosis and treatment are essential because renal injury could be fully reversible as rapidly as bilirubin levels are reduced. In conclusion, our proposal is to introduce an alert for considering CN in diagnostic and prognostic scores that include bilirubin and/or creatinine with acute renal involvement, with the aim of early diagnosis and treatment of sHyb to reduce the burden on renal outcome.

The multivariable prognostic models for severe complications after heart valve surgery

Background

To provide multivariable prognostic models for severe complications prediction after heart valve surgery, including low cardiac output syndrome (LCOS), acute kidney injury requiring hemodialysis (AKI-rH) and multiple organ dysfunction syndrome (MODS).

Methods

We developed multivariate logistic regression models to predict severe complications after heart valve surgery using 930 patients collected retrospectively from the first affiliated hospital of Sun Yat-Sen University from January 2014 to December 2015. The validation was conducted using a retrospective dataset of 713 patients from the same hospital from January 2016 to March 2017. We considered two kinds of prognostic models: the PRF models which were built by using the preoperative risk factors only, and the PIRF models which were built by using both of the preoperative and intraoperative risk factors. The least absolute shrinkage selector operator was used for developing the models. We assessed and compared the discriminative abilities for both of the PRF and PIRF models via the receiver operating characteristic (ROC) curve.

Results

Compared with the PRF models, the PIRF modes selected additional intraoperative factors, such as auxiliary cardiopulmonary bypass time and combined tricuspid valve replacement. Area under the ROC curves (AUCs) of PRF models for predicting LCOS, AKI-rH and MODS are 0.565 (0.466, 0.664), 0.688 (0.62, 0.757) and 0.657 (0.563, 0.751), respectively. As a comparison, the AUCs of the PIRF models for predicting LOCS, AKI-rH and MODS are 0.821 (0.747, 0.896), 0.78 (0.717, 0.843) and 0.774 (0.7, 0.847), respectively.

Conclusions

Adding the intraoperative factors can increase the predictive power of the prognostic models for severe complications prediction after heart valve surgery.

The inhibition of NFкB signaling and inflammatory response as a strategy for blunting bile acid-induced hepatic and renal toxicity

The cholestatic liver injury could occur in response to a variety of diseases or xenobiotics. Although cholestasis primarily affects liver function, it has been well-known that other organs such as the kidney could be influenced in cholestatic patients. Severe cholestasis could lead to tissue fibrosis and organ failure. Unfortunately, there is no specific therapeutic option against cholestasis-induced organ injury. Hence, finding the mechanism of organ injury during cholestasis could lead to therapeutic options against this complication. The accumulation of potentially cytotoxic compounds such as hydrophobic bile acids is the most suspected mechanism involved in the pathogenesis of cholestasis-induced organ injury. A plethora of evidence indicates a role for the inflammatory response in the pathogenesis of several human diseases. Here, the role of nuclear factor-kB (NFkB)-mediated inflammatory response is investigated in an animal model of cholestasis. Bile duct ligated (BDL) animals were treated with sulfasalazine (SSLZ, 10 and 100 mg/kg, i.p) as a potent inhibitor of NFkB signaling. The NFkB proteins family activity in the liver and kidney, serum and tissue levels of pro-inflammatory cytokines, tissue biomarkers of oxidative stress, serum markers of organ injury, and the liver and kidney histopathological alterations and fibrotic changes. The oxidative stress-mediated inflammatory-related indices were monitored in the kidney and liver at scheduled time intervals (3, 7, and 14 days after BDL operation). Significant increase in serum and urine markers of organ injury, besides changes in biomarkers of oxidative stress and tissue histopathology, were evident in the liver and kidney of BDL animals. The activity of NFkB proteins (p65, p50, p52, c-Rel, and RelB) was significantly increased in the liver and kidney of cholestatic animals. Serum and tissue levels of pro-inflammatory cytokines (IL-1β, IL-2, IL-6, IL-7, IL-12, IL-17, IL-18, IL-23, TNF-α, and INF-γ) were also higher than sham-operated animals. Moreover, TGF- β, α-SMA, and tissue fibrosis (Trichrome stain) were evident in cholestatic animals' liver and kidneys. It was found that SSLZ (10 and 100 mg/kg/day, i.p) alleviated cholestasis-induced hepatic and renal injury. The effect of SSLZ on NFkB signaling and suppression of pro-inflammatory cytokines could play a significant role in its protective role in cholestasis. Based on these data, NFkB signaling could receive special attention to develop therapeutic options to blunt cholestasis-induced organ injury.

Bidirectional Role of NLRP3 During Acute and Chronic Cholestatic Liver Injury

BACKGROUND AND AIMS

Cholestatic liver injury leads to cell death and subsequent inflammation and fibrosis. As shown for primary biliary cholangitis (PBC), the mechanisms and circuits between different cell death pathways leading to disease progression are incompletely defined. Common bile duct ligation (BDL) is a well-established murine model to mimic cholestatic liver injury. Here, we hypothesized that pyroptotic cell death by the Nucleotide-Binding Domain, Leucine-Rich-Containing Family, Pyrin Domain-Containing-3 (Nlrp3) inflammasome plays an essential role during human and murine cholestasis.

APPROACH AND RESULTS

NLRP3 activation was analyzed in humans with cholestatic liver injury. Wild-type (WT) and Nlrp3^-/- mice were subjected to BDL for 2 or 28 days. Chronic cholestasis in humans and mice is associated with NLRP3 activation and correlates with disease activity. Acute BDL in Nlrp3-deficient mice triggered increased inflammation as well as liver injury, associated with stronger apoptotic and necroptotic cell death. In contrast, NLRP3 deletion led to decreased liver injury and inflammation in chronic cholestasis. Moreover, bridging fibrosis was observed in WT, but not in NLRP3 knockout, mice 28 days after BDL. In contrast, lack of NLRP3 expression attenuated kidney injury and fibrosis after acute and chronic BDL. Importantly, administration of MCC950, an NLRP3 small molecule inhibitor, reduced BDL-induced disease progression in WT mice.

CONCLUSIONS

NLRP3 activation correlates with disease activity in patients with PBC. NLRP3 has a differential role during acute and chronic cholestatic liver injury in contrast to kidney injury. Disease progression during chronic cholestasis can be targeted through small molecules and thus suggests a potential clinical benefit for humans, attenuating liver and kidney injury.

Hepatorenal syndrome: a historical appraisal of its origins and conceptual evolution

The hepatorenal syndrome (HRS), a progressive but potentially reversible deterioration of kidney function, constitutes a serious complication of hepatic decompensation. Coexistence of liver/kidney damage, mentioned in the dropsy literature, was highlighted by Richard Bright in 1827 and confirmed in 1840 by his contemporary nephrology pioneer Pierre Rayer. Cholemic nephrosis was described in 1861 by Friedrich Frerichs, and the renal tubular lesions of HRS by Austin Flint in 1863. The term "acute hepato-nephritis" was introduced in 1916 by Paul Merklen, and its chronic form was designated HRS by Marcel Dérot in 1930s. HRS then was applied to renal failure in biliary tract surgery and to cases of coexistent renal and hepatic failure of diverse etiology. The pathogenesis of HRS was elucidated during the 1950 studies of renal physiology. Notably, studies of salt retention in edema and its relation to regulating the circulating plasma volume by John Peters and subsequently Otto Gauer defined the concept of "effective blood volume" and the consequent elucidation of ascites formation in liver failure. Parallel studies of intrarenal hemodynamics demonstrated severe renal vasoconstriction and preferential cortical ischemia to account for the functional renal dysfunction of HRS. Dialysis and liver or combined liver-kidney transplantation transformed the fatal HRS of old into a treatable disorder by the 1970s. Elucidation of the pathogenetic mechanisms of renal injury and refinements in definition, classification, and diagnosis of HRS since then have allowed for earlier therapeutic intervention with combined i.v. albumin and vasoconstrictor therapy, enabling the continued improvement of patient outcomes.

Silymarin mitigates bile duct obstruction-induced cholemic nephropathy

Bile duct obstruction or cholestasis can occur by several diseases or xenobiotics. Cholestasis and the accumulation of the bile constituents in the liver primarily damage this organ. On the other hand, extrahepatic organs are also affected by cholestasis. The kidney is the most affected tissue during cholestatic liver injury. Cholestasis-associated renal injury is known as cholemic nephropathy (CN). Several lines of evidence specify the involvement of oxidative stress and mitochondrial impairment in the pathogenesis of CN. The current study aimed to assess the role of silymarin as a potent antioxidant on CN-induced oxidative stress and mitochondrial dysfunction in the kidney. Bile duct ligated (BDL) rats were treated with silymarin (10 and 100 mg/kg, oral) for seven consecutive days. A significant increase in reactive oxygen species (ROS), lipid peroxidation, protein carbonylation, and oxidized glutathione (GSSG) levels were evident in the kidney of BDL animals. Moreover, reduced glutathione (GSH) content and total antioxidant capacity were significantly decreased in the kidney of cholestatic rats. Mitochondrial depolarization, decreased mitochondrial dehydrogenases activity, mitochondrial permeabilization, and depleted ATP stores were detected in the kidney mitochondria isolated from BDL animals. Kidney histopathological alterations, as well as serum and urine levels of renal injury biomarkers, were also significantly different in the BDL group. It was found that silymarin treatment significantly ameliorated CN-induced renal injury. The antioxidant effects of silymarin and its positive impact on mitochondrial indices seem to play a significant role in its renoprotective effects during cholestasis.

Apoptosis-inducing factor plays a role in the pathogenesis of hepatic and renal injury during cholestasis

Cholestasis is a clinical complication with different etiologies. The liver is the primary organ influenced in cholestasis. Renal injury is also a severe clinical complication in cholestatic/cirrhotic patients. Several studies mentioned the importance of oxidative stress and mitochondrial impairment as two mechanistically interrelated events in cholestasis-induced organ injury. Apoptosis-inducing factor (AIF) is a flavoprotein located in the inner mitochondrial membrane. This molecule is involved in a distinct pathway of cell death. The current study aimed to evaluate the role of AIF in the pathophysiology of cholestasis-associated hepatic and renal injury. Bile duct ligation (BDL) was used as an animal model of cholestasis. Serum, urine, and tissue samples were collected at scheduled time intervals (3, 7, 14, and 28 days after BDL surgery). Tissues' AIF mRNA levels, as well as serum, urine, and tissue activity of AIF, were measured. Moreover, markers of DNA fragmentation and apoptosis were assessed in the liver and kidney of cholestatic animals. A significant increase in liver and kidney AIF mRNA levels, in addition to increased AIF activity in the liver, kidney, serum, and urine, was detected in BDL rats. DNA fragmentation and apoptosis were raised in the liver and kidney of cholestatic animals, especially at the early stage of the disease. The apoptotic mode of cell death in the liver and kidney was connected to a higher AIF level. These data mention the importance of AIF in the pathogenesis of cholestasis-induced organ injury, especially at the early stage of this disease. Mitochondrial release of apoptosis-inducing factor (AIF) seems to play a pathogenic role in cholestasis-associated hepatic and renal injury. AIF release is directly connected to oxidative stress and mitochondrial impairment in cholestatic animals.

The pathogenesis of renal injury in obstructive jaundice: A review of underlying mechanisms, inducible agents and therapeutic strategies

Kidney injury is one of the main complications of obstructive jaundice (OJ) and its pathogenesis has not been clarified. As an independent risk factor for OJ associated with significant morbidity and mortality, it can be mainly divided into two types of morphological injury and functional injury. We called these dysfunctions caused by OJ-induced kidney injury as OJKI. However, the etiology of OJKI is still not fully clear, and research studies on how OJKI becomes a facilitated factor of OJ are limited. This article reviews the underlying pathological mechanism from five aspects, including metabolisms of bile acids, hemodynamic disturbances, oxidative stress, inflammation and the organic transporter system. Some nephrotoxic drugs and measures that can enhance or reduce the renal function with potential intervention in perioperative periods to alleviate the incidence of OJKI were also described. Furthermore, a more in-depth study on the pathogenesis of OJKI from multiple aspects for exploring more targeted treatment measures were further put forward, which may provide new methods for the prevention and treatment of clinical OJKI and improve the prognosis.

Poly (ADP-Ribose) polymerase-1 (PARP-1) overactivity plays a pathogenic role in bile acids-induced nephrotoxicity in cholestatic rats

Cholestatic liver disease is a clinical complication with a wide range of etiologies. The liver is the primary organ influenced by cholestasis. Other organs, rather than the liver (e.g., kidneys), could also be affected by cholestatic liver disease. Cholestasis-induced renal injury is known as cholemic nephropathy (CN). Although the structural and functional alterations of the kidney in cholestasis have been well described, the cellular and molecular mechanisms of CN are not well understood. Some studies mentioned the role of oxidative stress and mitochondrial impairment in CN. Several cellular targets, including proteins, lipids, and DNA, could be affected by oxidative stress. Poly (ADP-Ribose) polymerase-1 (PARP-1) is an enzyme that its physiological activity plays a fundamental role in DNA repair. However, PARP-1 overexpression is associated with enhanced oxidative stress and cell death. The current study was designed to evaluate the role of PARP-1 activity in the pathogenesis of CN. Bile duct ligated (BDL) rats were treated with nicotinamide (NA) as a PARP-1 inhibitor. Kidney, urine, and plasma samples were collected at scheduled time intervals (3, 7, 14, and 28 days after BDL surgery). Serum and urine biomarkers of kidney injury, markers of oxidative stress and DNA damage, PARP-1 expression and activity in the kidney tissue, inflammatory response, renal fibrosis markers, and kidney histopathological alterations were assessed. Significant changes in the serum and urine biomarkers of kidney injury were evident in the BDL rats. Markers of oxidative stress were increased, and tissue ATP levels and antioxidant capacity were decreased in the kidney of cholestatic animals. A significant increase in PARP-1 expression and activity was evident in BDL rats (3, 7, 14, and 28 days after BDL). Moreover, inflammatory response (IL-1β and TNF-α expression; and myeloperoxidase activity), renal tissue histopathological alterations, and kidney fibrosis (α-SMA and TGF-β expression, as well as collagen deposition) were detected in cholestatic animals. It was found that the PARP-1 inhibitor, NA (50 and 100 mg/kg, i.p), significantly mitigated cholestasis-induced renal injury. The positive effects of NA were more significant at a lower dose and the early stage of CN. These data indicate a pathogenic role for PARP-1 overexpression in CN.

Suppression of cirrhosis-related renal injury by N-acetyl cysteine

Cirrhosis-induced renal injury or cholemic nephropathy (CN) is a serious clinical complication with poor prognosis. CN could finally lead to renal failure and the need for organ transplantation. Unfortunately, there is no specific pharmacological intervention against CN to date. On the other hand, various studies mentioned the role of oxidative stress and mitochondrial impairment in the pathogenesis of CN. The current study aimed to evaluate the potential protective effects of NAC as a thiol-reducing agent and antioxidant in CN. Bile duct ligation (BDL) was used as a reliable animal model of cholestasis. BDL animals received NAC (0.25% and 1% w: v) in drinking water for 28 consecutive days. Finally, urine, blood, and kidney samples were collected and analyzed. Significant elevation in serum biomarkers of renal injury, along with urine markers of kidney damage, was evident in the BDL group. Moreover, markers of oxidative stress, including reactive oxygen species (ROS) formation, lipid peroxidation, protein carbonylation, and increased oxidized glutathione (GSSG) were evident detected in the kidney of cholestatic rats. Renal tissue antioxidant capacity and reduced glutathione (GSH) were also significantly depleted in the BDL group. Significant mitochondrial depolarization, depleted ATP content, and mitochondrial permeabilization was also detected in mitochondria isolated from the kidney of cholestatic animals. Renal histopathological alterations consisted of significant tissue fibrosis, interstitial inflammation, and tubular atrophy. It was found that NAC (0.25 and 1% in drinking water for 28 consecutive days) blunted histopathological changes, decreased markers of oxidative stress, and improved mitochondrial indices in the kidney of cirrhotic rats. Moreover, serum and urine biomarkers of renal injury were also mitigated in upon NAC treatment. These data indicate a potential renoprotective role for NAC in cholestasis. The effects of NAC on cellular redox state and mitochondrial function seem to play a fundamental role in its renoprotective effects during CN.

Liver Graft Failure and Bile Cast Nephropathy

The consequences of graft failure after liver transplantation (LT) range far beyond the liver. The kidneys are often affected, where persistent and progressive cholestasis can result in acute kidney injury (AKI) leading to the development of bile cast nephropathy (BCN). BCN is an often unrecognized condition that is characterized by proximal tubulopathy and the formation of bile casts in the distal tubules, which is almost diagnosed exclusively on a kidney biopsy or autopsy. This condition is potentially reversible, provided the bilirubin levels can be reduced early. LT may represent a treatment option in the case of irreversible liver (or liver graft) failure, which is beneficial for both the liver and the kidney. This paper reports a case of BCN in a patient with idiopathic graft failure after LT. Despite his chronic kidney disease, liver re-transplantation led to the successful improvement of his AKI.

Role of inflammation and inflammasome activation in human bile cast nephropathy

Bile cast nephropathy (BCN) is an underdiagnosed cause of acute kidney injury (AKI). The precise pathogenesis of bilirubin tubular toxicity remains unknown. The aim of this study is to explore the cellular and molecular pathophysiology of human BCN. Paraffin-embedded sections of renal biopsy tissue from a BCN patient were stained by immunohistochemistry (IHC) for oxidative stress (4-hydroxynonenal), immune cell subpopulations, including dendritic cells (CD1c), macrophages (CD68) and T cells (CD3), and inflammasome activation by staining for active-caspase-1 and the inflammasome adaptor protein, ASC (apoptosis-associated speck-like protein containing a caspase activation and recruitment domain). Quantitative analyses of IHC staining were compared to healthy renal cortical tissue. We identified yellow to brown granular casts within the BCN case, consistent with the presence of bile pigment. The presence of bile pigment was associated with strong tubular 4-hydroxynonenal staining intensity, a marker of oxidative stress. Diffuse tubulointerstitial inflammatory cell infiltrate was detected, with elevated CD1c, CD68 and CD3 staining. Foci of inflammasome activity were co-localized with this intense immune cell infiltration, with increased active-caspase-1 and ASC staining. Our findings are the first to suggest that bile casts may lead to oxidative stress and trigger the inflammasome signalling cascade, leading to interstitial inflammation and driving AKI pathobiology. SUMMARY AT A GLANCE The report suggests that bile casts may lead to oxidative stress and trigger the inflammasome signalling cascade, leading to interstitial inflammation and driving bile cast nephropathy pathobiology.

Reappraising the spectrum of AKI and hepatorenal syndrome in patients with cirrhosis

The occurrence of acute kidney injury (AKI) in patients with end-stage liver disease constitutes one of the most challenging clinical scenarios in in-hospital and critical care medicine. Hepatorenal syndrome type 1 (HRS-1), which is a specific type of AKI that occurs in the context of advanced cirrhosis and portal hypertension, is associated with particularly high mortality. The pathogenesis of HRS-1 is largely viewed as a functional derangement that ultimately affects renal vasculature tone. However, new insights suggest that non-haemodynamic tubulo-toxic factors, such as endotoxins and bile acids, might mediate parenchymal renal injury in patients with cirrhosis, suggesting that concurrent mechanisms, including those traditionally associated with HRS-1 and non-traditional factors, might contribute to the development of AKI in patients with cirrhosis. Moreover, histological evidence of morphological abnormalities in the kidneys of patients with cirrhosis and renal dysfunction has prompted the functional nature of HRS-1 to be re-examined. From a clinical perspective, a diagnosis of HRS-1 guides utilization of vasoconstrictive therapy and decisions regarding renal replacement therapy. Patients with cirrhosis are at risk of AKI owing to a wide range of factors. However, the tools currently available to ascertain the diagnosis of HRS-1 and guide therapy are suboptimal. Short of liver transplantation, goal-directed haemodynamically targeted pharmacotherapy remains the cornerstone of treatment for this condition; improved understanding of the underlying pathogenic mechanisms might lead to better clinical outcomes. Here, we examine our current understanding of the pathophysiology of HRS-1 and existing challenges in its diagnosis and treatment.

Bile acid signaling in renal water regulation

Emerging evidence has shown that bile acids play important roles in renal physiology and diseases by activating two major receptors, the nuclear farnesoid X receptor (FXR) and the membrane G protein-coupled bile acid receptor-1 (Gpbar1; also known as TGR5). Both FXR and TGR5 have been identified in human and rodent kidneys, where they are deeply involved in renal water handling. In mice, FXR- or TGR5-related gene deficiency has been associated with reduced aquaporin-2 expression accompanied with impaired urinary concentration ability. In this mini-review, we briefly discuss the current understanding of FXR/TGR5 signaling in the kidneys, with a special focus on the regulation of aquaporin-2 expression by bile acids in the collecting ducts and its potential significance in disease conditions.

Cholemic Nephropathy Causes Acute Kidney Injury and Is Accompanied by Loss of Aquaporin 2 in Collecting Ducts

Impairment of renal function often occurs in patients with liver disease. Hepatorenal syndrome is a significant cause of acute kidney injury (AKI) in patients with cirrhosis (HRS-AKI, type 1). Causes of non-HRS-AKI include cholemic nephropathy (CN), a disease that is characterized by intratubular bile casts and tubular injury. As data on patients with CN are obtained primarily from case reports or autopsy studies, we aimed to investigate the frequency and clinical course of CN. We identified 149 patients who underwent kidney biopsy between 2000 and 2016 at the Department of Gastroenterology, Hepatology and Endocrinology at Hannover Medical School. Of these, 79 had a history of liver disease and deterioration of renal function. When applying recent European Association for the Study of the Liver criteria, 45 of 79 patients (57%) presented with AKI, whereas 34 patients (43%) had chronic kidney disease (CKD). Renal biopsy revealed the diagnosis of CN in 8 of 45 patients with AKI (17.8%), whereas none of the patients with CKD was diagnosed with CN. Univariate analysis identified serum bilirubin, alkaline phosphatase, and urinary bilirubin and urobilinogen as predictive factors for the diagnosis of CN. Histological analysis of AKI patients with normal bilirubin, elevated bilirubin, and the diagnosis of CN revealed loss of aquaporin 2 (AQP2) expression in collecting ducts in patients with elevated bilirubin and CN. Biopsy-related complications requiring medical intervention occurred in 4 of 79 patients (5.1%). Conclusion: CN is a common finding in patients with liver disease, AKI, and highly elevated bilirubin. Loss of AQP2 in AKI patients with elevated bilirubin and CN might be the result of toxic effects of cholestasis and in part be responsible for the impairment of renal function.

Cholangitis Lenta Causing Bile Cast Nephropathy: A Unique Model of Hepatorenal Failure in Sepsis

INTRODUCTION

Inadequate perfusion and abnormal cellular metabolism are among the mechanisms of organ dysfunction in sepsis. Concomitant hepatorenal failure during the late phase of sepsis is poorly understood.

CASE REPORT

The autopsy of a child who developed sepsis-induced hepatorenal failure revealed bile cast nephropathy, hepatic centrilobular necrosis and cholangitis lenta, a type of sepsis-induced cholestasis, with no biliary obstruction, fibrosis or cirrhosis. The liver and renal function declined at the same rate as procalcitonin increased.

DISCUSSION

Failure of resolution and persistent inflammation in sepsis can result in ductular injury and stagnation of bile with subsequent cholemia. The kidney failure was associated with the formation of intratubular bile casts.

CONCLUSION

This case illustrates how severe cholestasis in combination with bile cast nephropathy may be potential and unrecognized contributors to hepatorenal failure in sepsis. Whether bile toxicity causes renal failure in the context of cholangitis lenta should be further studied.

Bile Cast Nephropathy: A Pathologic Finding with Manifold Causes Displayed in an Adult with Alcoholic Steatohepatitis and in a Child with Wilson's Disease

Bile cast nephropathy (BCN) is seen in patients who have acute kidney injury and severe hyperbilirubinemia due to a wide range of hepatobiliary system diseases. Findings seen by renal biopsy include acute tubular injury with necrotic and sloughed epithelial cells, yellow-green pigment within tubular epithelial cells, and pigmented granular casts. Hall's special stain for bile turns these casts green. In recent years, BCN has been described in a small number of case reports and clinical studies primarily in the setting of severe liver dysfunction. We present 2 diverse cases of BCN. The first involves an adult with hepatorenal syndrome secondary to alcoholic steatohepatitis and early cirrhosis. Second, we describe the first reported case of BCN in a child with fulminant hepatic failure due to Wilson's disease. Our cases expand the spectrum of causative diseases, and they provide further evidence that BCN is a distinct pathologic entity which may be found in both adult and pediatric patients with a variety of severe liver diseases.

Bile cast nephropathy in a patient with cholangiocarcinoma - a case report

Bile cast nephropathy is characterized by the presence of bile casts associated with renal failure and/or proximal tubulopathy in cases of severe hyperbilirubinemia. The clinician should carefully examine the urine samples for characteristic bile‐stained granular casts in suspected case.