Detection of acetaminophen protein adducts in children with acute liver failure of indeterminate cause

Biomarkers for assessing pain and pain relief in the neonatal intensive care unit

Newborns admitted to the neonatal intensive care unit (NICU) regularly undergo painful procedures and may face various painful conditions such as postoperative pain. Optimal management of pain in these vulnerable preterm and term born neonates is crucial to ensure their comfort and prevent negative consequences of neonatal pain. This entails accurate and timely identification of pain, non-pharmacological pain treatment and if needed administration of analgesic therapy, evaluation of treatment effectiveness, and monitoring of adverse effects. Despite the widely recognized importance of pain management, pain assessment in neonates has thus far proven to be a challenge. As self-report, the gold standard for pain assessment, is not possible in neonates, other methods are needed. Several observational pain scales have been developed, but these often rely on snapshot and largely subjective observations and may fail to capture pain in certain conditions. Incorporation of biomarkers alongside observational pain scores holds promise in enhancing pain assessment and, by extension, optimizing pain treatment and neonatal outcomes. This review explores the possibilities of integrating biomarkers in pain assessment in the NICU.

Acetaminophen Hepatotoxicity: Paradigm for Understanding Mechanisms of Drug-Induced Liver Injury

Acetaminophen (APAP) overdose is the clinically most relevant drug hepatotoxicity in western countries, and, because of translational relevance of animal models, APAP is mechanistically the most studied drug. This review covers intracellular signaling events starting with drug metabolism and the central role of mitochondrial dysfunction involving oxidant stress and peroxynitrite. Mitochondria-derived endonucleases trigger nuclear DNA fragmentation, the point of no return for cell death. In addition, adaptive mechanisms that limit cell death are discussed including autophagy, mitochondrial morphology changes, and biogenesis. Extensive evidence supports oncotic necrosis as the mode of cell death; however, a partial overlap with signaling events of apoptosis, ferroptosis, and pyroptosis is the basis for controversial discussions. Furthermore, an update on sterile inflammation in injury and repair with activation of Kupffer cells, monocyte-derived macrophages, and neutrophils is provided. Understanding these mechanisms of cell death led to discovery of N-acetylcysteine and recently fomepizole as effective antidotes against APAP toxicity.

Acute Liver Failure Guidelines

Acute liver failure (ALF) is a rare, acute, potentially reversible condition resulting in severe liver impairment and rapid clinical deterioration in patients without preexisting liver disease. Due to the rarity of this condition, published studies are limited by the use of retrospective or prospective cohorts and lack of randomized controlled trials. Current guidelines represent the suggested approach to the identification, treatment, and management of ALF and represent the official practice recommendations of the American College of Gastroenterology. The scientific evidence was reviewed using the Grading of Recommendations, Assessment, Development and Evaluation process to develop recommendations. When no robust evidence was available, expert opinions were summarized using Key Concepts. Considering the variety of clinical presentations of ALF, individualization of care should be applied in specific clinical scenarios.

Metabolomic Evaluation of N-Acetyl-p-Benzoquinone Imine Protein Adduct Formation with Therapeutic Acetaminophen Administration: Sex-based Physiologic Differences

BACKGROUND

Acetaminophen (APAP)-associated transaminase elevation, induced by N-acetyl-p-benzoquinone imine (NAPQI) protein adduction, remains an area of research interest. Distinct from known genetic, physiologic, and dosage associations dictating severity of hepatic injury, no known factors predict an absence of protein adduct formation at therapeutic APAP dosing.

HYPOTHESIS

Sex-based physiology is predictive of APAP-induced protein adduct formation and differential metabolite expression at therapeutic doses.

METHODS

This retrospective study interrogated serum samples collected for a prior study investigating fluctuations of alanine aminotransferase (ALT) over time with 4G daily APAP dosing for ≥ 16 days in subjects from Denver, Colorado. Subjects were grouped by adduct formation (n = 184) vs no adducts (n = 20). Samples were run on ultra-high-performance liquid chromatography mass spectrometry from study days 0, 7, 16, and 31. Significant metabolite expressions were identified using t-tests with false discovery rate correction (FDR), partial least squares discriminant, and ANOVA simultaneous comparison analyses. Demographic and clinical data were explored using t-tests with FDR (age, weight, BMI, ALT) and Chi-square (sex, ethnicity, race) analyses.

RESULTS

In pre-treatment samples, relative quantitation caprylic acid was expressed ninefold higher and 6-carboxyhexanoate was expressed threefold lower in subjects who did not develop adducts. Lactate had greater expression in the no adducts group (p = 0.001). Using absolute quantitation, glutathione was expressed 2.6-fold greater among no adduct subjects. Odds of males developing NAPQI protein adducts at therapeutic APAP dosing were 5.91 times lower than females (95% CI = 2.3-14.9; p = 0.0001).

CONCLUSION

Multiple metabolites were differentially expressed based on adduct group and sex. Metabolites were identified unique to adduct development independent of sex. At therapeutic APAP dosing, males were less likely to develop APAP protein adducts. Further research into lipid biosynthesis and metabolism may provide further insight into physiology associated with adduct production.

Acute Liver Failure in Children

Acute liver failure (ALF) in children, irrespective of cause, is a rapidly evolving catastrophic clinical condition that results in high mortality and morbidity without prompt identification and intervention. Massive hepatocyte necrosis impairs the synthetic, excretory, and detoxification abilities of the liver, with resultant coagulopathy, jaundice, metabolic disturbance, and encephalopathy. Extrahepatic organ damage, multiorgan failure, and death result from circulating inflammatory mediators released by the hepatocytes undergoing necrosis. There are yet no treatment options available for reversing or halting hepatocellular necrosis, thus current therapy focuses on supporting failing organs and preventing life threatening complications pending either spontaneous liver recovery or transplantation. The aims of this review are to define pediatric acute liver failure (PALF), understand the pathophysiologic processes that lead to multiorgan failure, to describe the consequences of a failing liver on extrahepatic organs, to enumerate the critical care challenges encountered during PALF management, and to describe pharmacologic and extracorporeal options available to support a critically ill child with ALF in the intensive care unit.

Different approaches for patent ductus arteriosus in premature infants using acetaminophen

BACKGROUND

Acetaminophen use for pharmacological treatment of hemodynamically significant patent ductus arteriosus (hsPDA) in preterm infants is becoming more popular with emerging evidence that it is effective as well as safe alternative for other agents used to close hsPDA.

DATA SOURCES

We performed a narrative review of literature about pharmacological treatment of PDA using acetaminophen.

RESULTS

Acetaminophen was used as a prophylaxis, symptomatic, targeted, and a rescue approach.

CONCLUSIONS

It appears that acetaminophen could be used in different approaches to close the hsPDA. Long-term outcomes of acetaminophen exposure early in life still lack certainty.

Transcriptional Analysis of Liver Tissue Identifies Distinct Phenotypes of Indeterminate Pediatric Acute Liver Failure

Many patients with indeterminate pediatric acute liver failure (PALF) have evidence of T-cell driven immune injury; however, the precise inflammatory pathways are not well defined. We have characterized the hepatic cytokine and transcriptional signatures of patients with PALF. A retrospective review was performed on 22 children presenting with indeterminate (IND-PALF; n = 17) or other known diagnoses (DX-PALF; n = 6) with available archived liver tissue. Specimens were stained for clusters of differentiation 8 (CD8) T cells and scored as dense, moderate, or minimal. Measurement of immune analytes and RNA sequencing (RNA-seq) was performed on whole-liver tissue. Immune analyte data were analyzed by principal component analysis, and RNA-seq was analyzed by unsupervised hierarchical clustering, differential gene expression, and gene-set enrichment analysis. Most patients with IND-PALF (94%) had dense/moderate CD8 staining and were characterized by Th1 immune analytes including tumor necrosis factor α, interferon γ (IFN-γ), interleukin (IL) 1β, IL-12, C-X-C motif chemokine ligand (CXCL) 9, and CXCL12. Transcriptional analyses identified two transcriptional PALF phenotypes. Most patients in group 1 (91%) had IND-PALF and dense/moderate CD8 staining. This group was characterized by increased expression of genes and cell subset-specific signatures related to innate inflammation, T-cell activation, and antigen stimulation. Group 1 expressed significantly higher levels of gene signatures for regulatory T cells, macrophages, Th1 cells, T effector memory cells, cytotoxic T cells, and activated dendritic cells (adjusted P < 0.05). In contrast, patients in group 2 exhibited increased expression for genes involved in metabolic processes. Conclusion: Patients with IND-PALF have evidence of a Th1-mediated inflammatory response driven by IFN-γ. Transcriptional analyses suggest that a complex immune network may regulate an immune-driven PALF phenotype with less evidence of metabolic processes. These findings provide insight into mechanisms of hepatic injury in PALF, areas for future research, and potential therapeutic targets.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms. Damaged organelles, lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell. Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports. In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy. Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma. We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases. We analyzed autophagy not only in well studied diseases, like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis, biliary diseases, autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity. We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells, sinusoidal endothelial cells or hepatic stellate cells. Finally, we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Paracetamol overdose in the newborn and infant: a life-threatening event

PURPOSE

Paracetamol is the only drug recommended to treat fever in neonates. At recommended doses, paracetamol has not been associated with liver injury in neonates, while hepatotoxicity may occur after intake of a single high dose or multiple excessive doses. The aim of this narrative review is to critically analyze and summarize the available literature on newborns and infants exposed to supratherapeutic doses of paracetamol, with special focus on their clinical features, outcome, and management.

METHODS

The PubMed, SCOPUS, and Google Scholar search engines were used to collect data, without time limitation. The following keywords were used: paracetamol/acetaminophen, overdose, hepatotoxicity, N-acetylcysteine, newborn, infant.

RESULTS

The literature search identified a total of 27 case reports, a number of review articles, and few other relevant publications. Neonatal poisoning from paracetamol resulted from transplacental drug transfer after maternal overdose in some published cases, while it was the consequence of medication errors in other cases. Newborns and infants who have received a single overdose and have paracetamol concentrations below the Rumack-Matthew nomogram limits are at low risk of serious hepatic damage, while those who have recently ingested more than one supratherapeutic dose of paracetamol should be managed with caution. The treatment of choice for paracetamol poisoning is N-acetylcysteine, a specific antidote which reduces paracetamol hepatotoxic effects. N-Acetylcysteine should be given according to specific regimens through weight-based dosing tables.

CONCLUSIONS

Caution should be used when paracetamol is administered to the newborn. In the event of an overdose, careful patient monitoring and personalization of post-overdose procedures are recommended.

Differential Diagnosis of Acute Liver Failure in Children: A Systematic Review

PURPOSE

To develop a probability-based differential diagnosis for pediatric acute liver failure (PALF) based on age and socioeconomic status of the country of origin.

METHODS

Comprehensive literature search using PubMed, EMBASE, and SCOPUS databases was performed. Children 0-22 years of age who met PALF registry criteria were included. Articles included >10 children, and could not be a case report, review article, or editorial. No language filter was utilized, but an English abstract was required. Etiology of PALF, age of child, and country of origin was extracted from included articles.

RESULTS

32 full text articles were reviewed in detail; 2,982 children were included. The top diagnosis of PALF in developed countries was acetaminophen toxicity (9.24%; 95% CredI 7.99-10.6), whereas in developing countries it was Hepatitis A (28.9%; 95% CredI 26.3-31.7). In developed countries, the leading diagnosis of PALF in children aged <1 year was metabolic disorder (17.2%; 95% CredI 10.3-25.5), whereas in developing countries it was unspecified infection (39.3%; CredI 27.6-51.8). In developed countries, the leading diagnosis in children aged >1 year was Non-A-B-C Hepatitis (8.18%; CredI 5.28-11.7), whereas in developing countries it was Hepatitis A (32.4%; CredI 28.6-36.3).

CONCLUSION

The leading causes of PALF in children aged 0-22 years differ depending on the age and developmental status of their country of origin, suggesting that these factors must be considered in the evaluation of children with PALF.

Acetaminophen Toxicity: A History of Serendipity and Unintended Consequences

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Dried blood microsamples: Suitable as an alternative matrix for the quantification of paracetamol-protein adducts?

Paracetamol (acetaminophen, APAP) is the most frequently used analgesic drug worldwide. However, patients in several specific populations can have an increased exposure to toxic APAP metabolites. Therefore, APAP-protein adducts have been proposed as an alternative marker for the assessment of APAP intoxications and as an effective tool to study and steer APAP treatment in patients with an increased risk of APAP-induced liver damage. These adducts have been determined in plasma or serum as a matrix. Blood microsampling allows the determination of a variety of analytes, including protein adducts, in a drop of blood, facilitating convenient follow-up of patients in a home-sampling context, as well as repeated sampling of pediatric patients. We therefore evaluated the use of blood-based volumetric microsamples for the quantification of APAP-protein adducts. Quantitative methods for the determination of APAP-protein adducts in dried blood and dried plasma volumetric absorptive microsamples were developed and validated. Also a preliminary evaluation of pediatric patient dried blood microsamples was conducted. Method validation encompassed the evaluation of selectivity, carry over, calibration model, accuracy and precision, matrix effect, recovery and the effect of the hematocrit on the recovery, dilution integrity, and stability. All pre-set acceptance criteria were met, except for stability. Spiking of blank blood with APAP revealed a concentration-dependent ex vivo formation of APAP-protein adducts, resulting in a response for the measurand APAP-Cys, with an apparent role for the red blood cell fraction. Analysis of authentic samples, following intake of APAP at therapeutic dosing, revealed much higher APAP-Cys concentrations in dried blood vs. dried plasma samples, making interpretation of the results in the context of published intervals difficult. In addition, in contrast to what was observed during method validation, the data obtained for the patient samples showed a high and unacceptable variation. We conclude that, for a combination of reasons, dried blood is not a suitable matrix for the quantification of APAP-protein adducts via the measurement of the APAP-Cys digestion product. The collection of plasma or serum, either in the form of a liquid sample or a dried microsample for this purpose is advised.

Advances in biomarker development in acetaminophen toxicity

Acetaminophen liver injury is the most common cause of acute liver injury in the United States and several other countries. Diagnosis of acetaminophen-induced acute liver injury in the clinic is challenging due to the lack of validated and specific biomarkers. The following chapter provides an overview of recent advances evaluating candidate biomarkers in development for acetaminophen acute liver injury. Relationships of biomarkers to mechanisms of acetaminophen toxicity and their potential role in confirming the diagnosis and/or predicting evolving toxicity are addressed.

Corticosteroid Therapy for Indeterminate Pediatric Acute Liver Failure and Aplastic Anemia with Acute Hepatitis

OBJECTIVE

To examine the characteristics and outcomes of a multicenter patient cohort with indeterminate pediatric acute liver failure (IND-PALF) and with aplastic anemia with acute hepatitis treated with corticosteroids.

STUDY DESIGN

Retrospective study of patients age 1-17 years with IND-PALF and aplastic anemia with acute hepatitis who presented between 2009 and 2018 to 1 of 4 institutions and were treated with corticosteroids for presumed immune dysregulation.

RESULTS

Of 28 patients with IND-PALF (median of 4.0 years of age [range 1-16] and 71% male) 71% (n = 20) were treated with 0.5-4 mg/kg/day of intravenous methylprednisolone, and 8 patients received 10 mg/kg/day followed by a taper. By 21 days postcorticosteroid initiation, 14 patients (50%) underwent liver transplantation, 13 patients (46%) recovered with their native liver, and 1 patient (4%) died. Patients who recovered with their native liver received a median of 139 days (range 19-749) of corticosteroid therapy, with a median of 12 days (range 1-240) to international normalized ratio ≤1.2. Patients with aplastic anemia with acute hepatitis (n = 6; median of 9.5 years of age [range 1-12], 83% male), received 1-2 mg/kg/day of methylprednisolone for a median of 100 days (range 63-183), and all recovered with their native liver. One patient with IND-PALF and 2 patients with aplastic anemia with acute hepatitis developed a serious infection within 90 days postcorticosteroid initiation.

CONCLUSIONS

Many patients with IND-PALF or aplastic anemia with acute hepatitis that were treated with corticosteroids improved, but survival with native liver may not be different from historical reports. A randomized controlled trial exploring the benefits and risks of steroid therapy is needed before it is adopted broadly.

Animal models of drug-induced liver injury

Drug-induced liver injury (DILI) presents unique challenges for consumers, clinicians, and regulators. It is the most common cause of acute liver failure in the US. It is also one of the most common reasons for termination of new drugs during pre-clinical testing and withdrawal of new drugs post-marketing. DILI is generally divided into two forms: intrinsic and idiosyncratic. Many of the challenges with DILI are due in large part to poor understanding of the mechanisms of toxicity. Although useful models of intrinsic DILI are available, they are frequently misused. Modeling idiosyncratic DILI presents greater challenges, but promising new models have recently been developed. The purpose of this manuscript is to provide a critical review of the most popular animal models of DILI, and to discuss the future of DILI research.

Indeterminate pediatric acute liver failure is uniquely characterized by a CD103+ CD8+ T-cell infiltrate

The cause of pediatric acute liver failure (PALF) is unknown in up to 40% of cases. Evidence suggests that aberrant immune system activation may play a role. We hypothesized that indeterminate PALF cases would exhibit a unique pattern of hepatic inflammation. This was a retrospective and prospective study of PALF cases due to indeterminate (iPALF), autoimmune hepatitis, or known diagnosis (dPALF) etiology. Liver tissue sections were stained with immunohistochemical markers for cytotoxic T-cells (cluster of differentiation 8 [CD8]), perforin, and tissue resident memory T-cells (CD103) and scored as minimal, moderate, or dense. Lymphocytes were isolated from liver tissue for T-cell receptor beta sequencing and flow-cytometric studies. Thirty-three iPALF, 9 autoimmune hepatitis, and 14 dPALF cases were included. Dense hepatic infiltrates of CD8⁺ T-cells were found in 27 (82%) iPALF cases compared to 1 (7%) dPALF case (P < 0.0001). Perforin staining was dense or moderate in 19 (73%) of 26 iPALF cases compared to minimal in all 7 dPALF cases (P = 0.004); 16 (62%) of 26 iPALF cases had dense CD103 staining compared to none of the 6 dPALF cases (P = 0.001). T-cell receptor beta sequencing of iPALF cases demonstrated increased clonality compared to dPALF and control cases. Flow cytometry and immunohistochemistry revealed that iPALF intrahepatic leukocytes were predominantly tissue resident memory CD8⁺ T-cells.

CONCLUSION

Indeterminate PALF is characterized by a dense CD8⁺ T-cell hepatic infiltrate consistent with expansion of a tissue resident memory T-cell phenotype; CD8⁺ T-cells are a biomarker of immune dysregulation in iPALF and may be used to better identify and define this group. (Hepatology 2018).

Role and mechanisms of autophagy in acetaminophen-induced liver injury

Acetaminophen (APAP) overdose is the most frequent cause of acute liver failure in the USA and many other countries. Although the metabolism and pathogenesis of APAP has been extensively investigated for decades, the mechanisms by which APAP induces liver injury are incompletely known, which hampers the development of effective therapeutic approaches to tackle this important clinical problem. Autophagy is a highly conserved intracellular degradation pathway, which aims at recycling cellular components and damaged organelles in response to adverse environmental conditions and stresses as a survival mechanism. There is accumulating evidence indicating that autophagy is activated in response to APAP overdose in specific liver zone areas, and pharmacological activation of autophagy protects against APAP-induced liver injury. Increasing evidence also suggests that hepatic autophagy is impaired in nonalcoholic fatty livers (NAFLD), and NAFLD patients are more susceptible to APAP-induced liver injury. Here, we summarized the current progress on the role and mechanisms of autophagy in protecting against APAP-induced liver injury.

Serum paracetamol-protein adducts in ambulatory subjects: Relationship to recent reported paracetamol use

CONTEXT

Serum paracetamol-protein adducts (PPAs) are a novel potential biomarker of paracetamol exposure. The relationship between serum PPA concentrations and reported paracetamol use in ambulatory adults has not been previously described.

MATERIALS AND METHODS

This was a cross-sectional study of ambulatory adults. A detailed medication history was obtained from all subjects and subjects were stratified by reported paracetamol use in the 2 weeks prior to enrolment. Serum PPAs were measured in all subjects and correlated with reported dose, time of last ingestion and demographics.

RESULTS

We enrolled 230 in the paracetamol exposure arm and 74 in the no exposure arm. 98/230 (42.6%)of subjects who reported paracetamol exposure had PPA detected and 68/74 (91.9%) of subjects who denied paracetamol exposure had no PPA detected. PPA concentrations were positively correlated with total paracetamol dose and with more recent ingestion.

DISCUSSION

Detection of serum PPA generally reflects paracetamol exposure histories in ambulatory adults. Concentrations are well correlated with reported dose and time from last dose.

CONCLUSIONS

Serum PPA can be detected with reported therapeutic use of paracetamol but may not be detected in all patients who report taking paracetamol.

Race, Gender, and Genetic Polymorphism Contribute to Variability in Acetaminophen Pharmacokinetics, Metabolism, and Protein-Adduct Concentrations in Healthy African-American and European-American Volunteers

Over 30 years ago, black Africans from Kenya and Ghana were shown to metabolize acetaminophen faster by glucuronidation and slower by oxidation compared with white Scottish Europeans. The objectives of this study were to determine whether similar differences exist between African-Americans and European-Americans, and to identify genetic polymorphisms that could explain these potential differences. Acetaminophen plasma pharmacokinetics and partial urinary metabolite clearances via glucuronidation, sulfation, and oxidation were determined in healthy African-Americans (18 men, 23 women) and European-Americans (34 men, 20 women) following a 1-g oral dose. There were no differences in acetaminophen total plasma, glucuronidation, or sulfation clearance values between African-Americans and European-Americans. However, median oxidation clearance was 37% lower in African-Americans versus European-Americans (0.57 versus 0.90 ml/min per kilogram; P = 0.0001). Although acetaminophen total or metabolite clearance values were not different between genders, shorter plasma half-life values (by 11-14%; P < 0.01) were observed for acetaminophen, acetaminophen glucuronide, and acetaminophen sulfate in women versus men. The UGT2B15*2 polymorphism was associated with variant-allele-number proportional reductions in acetaminophen total clearance (by 15-27%; P < 0.001) and glucuronidation partial clearance (by 23-48%; P < 0.001). UGT2B15 *2/*2 genotype subjects also showed higher acetaminophen protein-adduct concentrations than *1/*2 (by 42%; P = 0.003) and *1/*1 (by 41%; P = 0.003) individuals. Finally, CYP2E1 *1D/*1D genotype African-Americans had lower oxidation clearance than *1C/*1D (by 42%; P = 0.041) and *1C/*1C (by 44%; P = 0.048) African-Americans. Consequently, African-Americans oxidize acetaminophen more slowly than European-Americans, which may be partially explained by the CYP2E1*1D polymorphism. UGT2B15*2 influences acetaminophen pharmacokinetics in both African-Americans and European-Americans.

EASL Clinical Practical Guidelines on the management of acute (fulminant) liver failure

The term acute liver failure (ALF) is frequently applied as a generic expression to describe patients presenting with or developing an acute episode of liver dysfunction. In the context of hepatological practice, however, ALF refers to a highly specific and rare syndrome, characterised by an acute abnormality of liver blood tests in an individual without underlying chronic liver disease. The disease process is associated with development of a coagulopathy of liver aetiology, and clinically apparent altered level of consciousness due to hepatic encephalopathy. Several important measures are immediately necessary when the patient presents for medical attention. These, as well as additional clinical procedures will be the subject of these clinical practice guidelines.

Role of N-acetylcysteine treatment in non-acetaminophen-induced acute liver failure: A prospective study

BACKGROUND/AIMS

Acute liver failure (ALF) is a rare but severe medical emergency. To date, there is no established treatment for non-acetaminophen-induced acute liver failure (NAI-ALF) other than liver transplantation, and little is known about the use of N-acetylcysteine (NAC) in NAI-ALF. A randomized case control study was conducted with the aim to determine the effect of NAC on the mortality of NAI-ALF patients, as well as to evaluate the safety and efficacy of NAC use.

PATIENTS AND METHODS

A total of 80 patients diagnosed with NAI-ALF were included in the study. Forty patients received NAC infusion for 72 h whereas the control group received placebo. The variables evaluated were demographic characteristics, signs and symptoms, biochemical parameters, and clinical course during hospitalization.

RESULTS

The two groups (NAC and control) were comparable for various baseline characteristics (such as etiology of ALF, INR, alanine aminotransferase, creatinine, albumin, and grade of encephalopathy), except for age. Although majority of patients had undetermined etiology (32.5% in NAC group and 42.5% in control group), the second main cause was acute hepatitis E and drug or toxin-induced ALF. The mortality decreased to 28% with the use of NAC versus 53% in the control group (P = 0.023). The use of NAC was associated with shorter length of hospital stay in survived patients (P = 0.002). Moreover, the survival of patients was improved by NAC (P = 0.025). Also, drug-induced ALF showed improved outcome compared to other etiologies.

CONCLUSION

The findings of the study recommend the use of NAC along with conventional treatments in patients with NAI-ALF in non-transplant centers while awaiting referrals and conclude the use of NAC as safe.

Serum Acetaminophen Protein Adduct Concentrations in Pediatric Emergency Department Patients

OBJECTIVES

Acetaminophen toxicity is a common cause of pediatric liver failure. The diagnosis may be limited by the short window of detection of acetaminophen in serum. Recently acetaminophen protein adducts (APAP-CYS) have been used as a biomarker with a longer duration of detection. The objective of this study was to describe the serum concentrations of APAP-CYS in pediatric patients with and without reported therapeutic acetaminophen exposure.

METHODS

A cross-sectional study of children age 1 to <12 years presenting to a pediatric emergency department. Subjects were stratified by recent acetaminophen use and had serum APAP-CYS measured using LC/MS.

RESULTS

One hundred patients were enrolled. All of the patients whose caregivers denied acetaminophen exposure had nondetectable APAP-CYS. Fifty-two percent of subjects who were reported to have taken acetaminophen in the preceding 2 weeks had detectable serum APAP-CYS. The APAP-CYS concentrations were positively correlated with higher overall dose and more recent ingestion.

CONCLUSIONS

APAP-CYS is detectable in the majority of children taking acetaminophen and not detected in the majority of children who are not exposed to acetaminophen.

Detection of Acetaminophen-Protein Adducts in Decedents with Suspected Opioid-Acetaminophen Combination Product Overdose

Acetaminophen overdose is a leading cause of drug-induced liver failure in the United States. Acetaminophen-protein adducts have been suggested as a biomarker of hepatotoxicity. The purpose of this study was to determine whether protein-derived acetaminophen-protein adducts are quantifiable in postmortem samples. Heart blood, femoral blood, and liver tissue were collected at autopsy from 22 decedents suspected of opioid-acetaminophen overdose. Samples were assayed for protein-derived acetaminophen-protein adducts, acetaminophen, and selected opioids found in combination products containing acetaminophen. Protein-derived APAP-CYS was detected in 17 of 22 decedents and was measurable in blood that was not degraded or hemolyzed. Heart blood concentrations ranged from 11 ng/mL (0.1 μM) to 7817 ng/mL (28.9 μM). Protein-derived acetaminophen-protein adducts were detectable in liver tissue for 20 of 22 decedents. Liver histology was also performed for all decedents, and no evidence of centrilobular hepatic necrosis was observed.

Removal of acetaminophen protein adducts by autophagy protects against acetaminophen-induced liver injury in mice

BACKGROUND & AIMS

Acetaminophen (APAP)-induced liver injury is the most frequent cause of acute liver failure in the US and many other countries. Metabolism of APAP results in formation of APAP protein adducts (APAP-AD) in hepatocytes and triggers mitochondrial dysfunction and necrosis. However, the mechanisms for how APAP-AD are removed from hepatocytes remain unknown.

METHODS

Mice or primary hepatocytes were treated with APAP. APAP-AD were determined by immunoblot, immunostaining and high pressure liquid chomatography with electrochemical detection analysis.

RESULTS

We found that APAP-AD were detected at 1h, peaked at approximately 2h, declined at 6h and almost full removed at 24h post treatment with APAP in mouse livers and in primary mouse hepatocytes. APAP-AD displayed a punctate pattern and were colocalized with GFP-LC3 positive autophagosomes and Lamp1 positive lysosomes in APAP-treated primary hepatocytes. Moreover, isolated autophagosomes and autolysosomes from APAP-treated mouse livers contained APAP-AD, suggesting autophagy may selectively remove APAP-AD. APAP-AD were detected in both detergent soluble and insoluble pools in APAP-treated mouse livers and hepatocytes. More importantly, pharmacological inhibition of autophagy by leupeptin or chloroquine increased whereas induction of autophagy by Torin 1 decreased serum APAP-AD levels in APAP-treated mice, which correlated with alanine aminotransferase levels and liver necrosis. Furthermore, SQSTM1/p62, an autophagy receptor protein, was recruited to APAP-AD. Adenovirus-mediated shRNA knockdown of SQSTM1/p62 led to increased APAP-AD and necrosis in primary hepatocytes.

CONCLUSIONS

Our data indicate that APAP-AD are removed though selective autophagy. Pharmacological induction of autophagy may be a novel promising approach for treating APAP-induced liver injury.

LAY SUMMARY

Acetaminophen overdose can form acetaminophen protein adducts and mitochondria damage in hepatocytes resulting in liver injury. Activation of autophagy-lysosomal degradation pathway can help to remove acetaminophen protein adducts. Pharmacological induction of autophagy may be a novel promising approach for treating APAP-induced liver injury.

Protein-Derived Acetaminophen-Cysteine Can Be Detected After Repeated Supratherapeutic Ingestion of Acetaminophen in the Absence of Hepatotoxicity

Generation of protein-derived acetaminophen-cysteine (APAP-CYS) is reported after ingestion of large and therapeutic dosages of acetaminophen in healthy and in liver-damaged patients. The incidence of protein-derived APAP-CYS adducts in repeated supratherapeutic dosages of APAP is not known.

METHODS

for 12 months, a standardized and comprehensive questionnaire was used to interview every consecutive patient at a pain management clinic. Patients found to ingest more than 4 g of APAP per day for a minimum of 14 consecutive days at the time of the encounter were invited to have blood drawn for hepatic transaminases and APAP-CYS adduct levels. Twelve subjects out of 990 interviewees met inclusion criteria. Ten of the 12 had measurable protein-derived APAP-CYS, none had evidence of liver injury. Patients that ingest repeated supratherapeutic amounts of APAP over several weeks may generate APAP-CYS protein adducts in the absence of hepatic injury.

Bortezomib alleviates drug-induced liver injury by regulating CYP2E1 gene transcription

Acute liver failure, i.e., the fatal deterioration of liver function, is the most common indication that emergency liver transplantation is necessary. Moreover, in the USA, drug-induced liver injury (DILI), including acetaminophen (APAP)-induced hepatotoxicity, is the main cause of acute liver failure. Matching a donor for liver transplantation is extremely difficult, and thus the development of a novel therapy for DILI is urgently needed. Following recent approval by the FDA of the proteasomal inhibitor bortezomib, its therapeutic effects on various human diseases, including solid and hematologic malignancies, have been validated. However, the specific action of proteasomal inhibition in cases of DILI had not been elucidated prior to this study. To examine the effects of proteasomal inhibition in DILI experimentally, male C56Bl/6 mice were injected with 1 mg bortezomib/kg before APAP treatment. Bortezomib not only alleviated APAP-induced hepatotoxicity in a time- and dose-dependent manner, it also alleviated CCl4- and thioacetamide-induced hepatotoxicity. We also noted that bortezomib significantly reduced cytochrome P450 2E1 (CYP2E1) expression and activity in the liver, which was accompanied by the induction of endoplasmic reticulum (ER) stress. In addition, bortezomib decreased hepatocyte nuclear factor‑1α-induced promoter activation of CYP2E1 in Hep3B cells. By contrast, another proteasome inhibitor, MG132, did not cause ER stress and did not markedly affect CYP2E1 enzyme activity. Liver injury induced by APAP was aggravated by MG132, possibly via elevation of connexin 32 expression. This study suggests that proteasome inhibition has different effects in cases of DILI depending on the specific inhibitor being used. Furthermore, results from the mouse model indicated that bortezomib, but not MG132, was effective in alleviating DILI. ER stress induced by proteasome inhibition has previously been shown to exert various effects on DILI patients, and thus each available proteasomal inhibitor should be evaluated individually in order to determine its potential for clinical application.

Paracetamol (acetaminophen) protein adduct concentrations during therapeutic dosing

BACKGROUND

Paracetamol protein adducts (PPA) are a biomarker of paracetamol exposure. PPA are quantified as paracetamol-cysteine (APAP-CYS), and concentrations above 1.1 μmol l(-1) have been suggested as a marker of paracetamol-induced hepatotoxicity. However, there is little information on the range of concentrations observed during prolonged therapeutic dosing.

AIM

The aim of the present study was to describe the concentration of PPA in the serum of subjects taking therapeutic doses of paracetamol for at least 16 days.

METHODS

Preplanned secondary aim of a prospective randomized controlled (placebo vs. 4g day(-1) paracetamol) trial. We measured subjects' serum PPA concentrations every 3 days for a minimum of 16 days. We also measured concentrations on study days 1-3 and 16-25 in subsets of patients. PPA were quantified as APAP-CYS after gel filtration and protein digestion using liquid chromatography/mass spectrometry.

RESULTS

Ninety per cent of subjects had detectable PPA after five doses. Median APAP-CYS concentrations in paracetamol-treated subjects increased to a plateau of 0.1 μmol l(-1) on day 7, where they remained. The highest concentration measured was 1.1 μmol l(-1) and two subjects never had detectable PPA levels. PPA were detected in the serum of 78% of subjects 9 days after their final dose.

CONCLUSIONS

PPA are detectable in the vast majority of subjects taking therapeutic doses of paracetamol. While most have concentrations well below the threshold associated with hepatotoxicity, concentrations may approach 1.1 μmol l(-1) in rare cases. Adducts are detectable after a few doses and can persist for over a week after dosing is stopped.

Clinical pharmacology of paracetamol in neonates: a review

Paracetamol is commonly used to control mild-to-moderate pain or to reduce opioid exposure as part of multimodal analgesia, and is the only compound recommended to treat fever in neonates. Paracetamol clearance is lower in neonates than in children and adults. After metabolic conversion, paracetamol is subsequently eliminated by the renal route. The main metabolic conversions are conjugation with glucuronic acid and with sulphate. In the urine of neonates sulphated paracetamol concentration is higher than the glucuronidated paracetamol level, suggesting that sulfation prevails over glucuronidation in neonates. A loading dose of 20 mg/kg followed by 10 mg/kg every 6 hours of intravenous paracetamol is suggested to achieve a compartment concentration of 11 mg/L in late preterm and term neonates. Aiming for the same target concentration, oral doses are similar with rectal administration of 25 to 30 mg/kg/d in preterm neonates of 30 weeks' gestation, 45 mg/kg/d in preterm infants of 34 weeks' gestation, and 60 mg/kg/d in term neonates are suggested. The above-mentioned paracetamol doses for these indications (pain, fever) are well tolerated in neonates, but do not result in a significant increase in liver enzymes, and do not affect blood pressure and have limited effects on heart rate. In contrast, the higher doses suggested in extreme preterm neonates to induce closure of the patent ductus arteriosus have not yet been sufficiently evaluated regarding efficacy or safety. Moreover, focussed pharmacovigilance to explore the potential causal association between paracetamol exposure during perinatal life and infancy and subsequent atopy is warranted.

Target biomarker profile for the clinical management of paracetamol overdose

Paracetamol (acetaminophen) overdose is one of the most common causes of acute liver injury in the Western world. To improve patient care and reduce pressure on already stretched health care providers new biomarkers are needed that identify or exclude liver injury soon after an overdose of paracetamol is ingested. This review highlights the current state of paracetamol poisoning management and how novel biomarkers could improve patient care and save healthcare providers money. Based on the widely used concept of defining a target product profile, a target biomarker profile is proposed that identifies desirable and acceptable key properties for a biomarker in development to enable the improved treatment of this patient population. The current biomarker candidates, with improved hepatic specificity and based on the fundamental mechanistic basis of paracetamol-induced liver injury, are reviewed and their performance compared with our target profile.

Acetaminophen Adducts Detected in Serum of Pediatric Patients With Acute Liver Failure

OBJECTIVES

Previous studies in patients with acute liver failure identified acetaminophen (APAP) protein adducts in the serum of 12% and 19% of children and adults, respectively, with acute liver failure of indeterminate etiology. This article details the testing of APAP adducts in a subset (n = 393) of patients with varied diagnoses in the Pediatric Acute Liver Failure Study Group (PALFSG).

METHODS

Serum samples were available from 393 participants included in the PALFSG registry. Adduct measurement was performed using validated methods. Participants were grouped by diagnostic category as known APAP overdose, known other diagnosis, and indeterminate etiology. Demographic and clinical characteristics and participant outcomes were compared by adduct status (positive or negative) within each group.

RESULTS

APAP adduct testing was positive in 86% of participants with known APAP overdose, 6% with other known diagnoses, and 11% with an indeterminate cause of liver failure. Adduct-positive participants were noted to have marked elevation of serum alanine aminotransferase and aspartate aminotransferase coupled with total serum bilirubin that was significantly lower than adduct-negative patients. In the indeterminate group, adduct-positive patients had different outcomes than adduct-negative patients (P = 0.03); spontaneous survival was 16 of 21 (76%) in adduct-positive patients versus 75 of 169 (44%) in adduct-negative patients. Prognosis did not vary by adduct status in patients with known diagnoses.

CONCLUSIONS

Furthermore, study is needed to understand the relation of APAP exposure, as determined by the presence of APAP adducts, to the clinical phenotype and outcomes of children with acute liver failure.

Acute liver failure in a term neonate after repeated paracetamol administration

Objective:

Severe hepatotoxicity caused by paracetamol is rare in neonates. We report a case of paracetamol-induced acute liver failure in a term neonate.

Case description:

A 26-day-old boy was admitted with intestinal bleeding, shock signs, slight liver enlargement, coagulopathy, metabolic acidosis (pH=7.21; bicarbonate: 7.1mEq/L), hypoglycemia (18mg/dL), increased serum aminotransferase activity (AST=4,039IU/L; ALT=1,087IU/L) and hyperbilirubinemia (total: 9.57mg/dL; direct: 6.18mg/dL) after receiving oral paracetamol (10mg/kg/dose every 4 hours) for three consecutive days (total dose around 180mg/kg; serum concentration 36-48 hours after the last dose of 77µg/ mL). Apart from supportive measures, the patient was successfully treated with intravenous N-acetylcysteine infusion during 11 consecutive days, and was discharged on day 34. The follow-up revealed full recovery of clinical and of laboratory findings of hepatic function.

Comments:

The paracetamol pharmacokinetics and pharmacodynamics in neonates and infants differ substantially from those in older children and adults. Despite the reduced rates of metabolism by the P-450 CYP2E1 enzyme system and the increased ability to synthesize glutathione - which provides greater resistance after overdoses -, it is possible to produce hepatotoxic metabolites (N-acetyl-p-benzoquinone) that cause hepatocellular damage, if glutathione sources are depleted. Paracetamol clearance is reduced and the half-life of elimination is prolonged. Therefore, a particular dosing regimen should be followed due to the toxicity risk of cumulative doses. This report highlights the risk for severe hepatotoxicity in neonates after paracetamol multiple doses for more than two to three days.

New problems arising from old drugs: second-generation effects of acetaminophen

Acetaminophen (APAP)/paracetamol is one of the most commonly used over-the-counter drugs taken worldwide for treatment of pain and fever. Although considered as safe when taken in recommended doses not higher than 4 g/day, APAP overdose is currently the most important cause of acute liver failure (ALF). ALF may require liver transplantation and can be fatal. The reasons for APAP-related ALF are mostly intentional (suicidal) or unintentional overdose. However, results from large scale epidemiological studies provide increasing evidence for second generation effects of APAP, even when taken in pharmacological doses. Most strikingly, APAP medication during pregnancy has been associated with health problems including neurodevelopmental and behavioral disorders such as attention deficit hyperactivity disorder and increase in the risk of wheezing and incidence of asthma among offspring. This article reviews the epidemiological findings and aims to shed light into the molecular and cellular mechanisms responsible for APAP-mediated prenatal risk for asthma.

Mechanistic biomarkers in acetaminophen-induced hepatotoxicity and acute liver failure: from preclinical models to patients

INTRODUCTION

Drug hepatotoxicity is a major clinical issue. Acetaminophen (APAP) overdose is especially common. Serum biomarkers used to follow patient progress reflect either liver injury or function, but focus on biomarkers that can provide insight into the basic mechanisms of hepatotoxicity is increasing and enabling us to translate mechanisms of toxicity from animal models into humans.

AREAS COVERED

We review recent advances in mechanistic serum biomarker research in drug hepatotoxicity. Specifically, biomarkers for reactive drug intermediates, mitochondrial dysfunction, nuclear DNA damage, mode of cell death and inflammation are discussed, as well as microRNAs. Emphasis is placed on APAP-induced liver injury.

EXPERT OPINION

Several serum biomarkers of reactive drug intermediates, mitochondrial damage, nuclear DNA damage, apoptosis and necrosis and inflammation have been described. These studies have provided evidence that mitochondrial damage is critical in APAP hepatotoxicity in humans, while apoptosis has only a minor role, and inflammation is important for recovery and regeneration after APAP overdose. Additionally, mechanistic serum biomarkers have been shown to predict outcome as well as, or better than, some clinical scores. In the future, such biomarkers will help determine the need for liver transplantation and, with improved understanding of the human pathophysiology, identify novel therapeutic targets.

Intravenous N-acetylcysteine in pediatric patients with nonacetaminophen acute liver failure: a placebo-controlled clinical trial

N-acetylcysteine (NAC) was found to improve transplantation-free survival in only those adults with nonacetaminophen (non-APAP) acute liver failure (ALF) and grade 1-2 hepatic encephalopathy (HE). Because non-APAP ALF differs significantly between children and adults, the Pediatric Acute Liver Failure (PALF) Study Group evaluated NAC in non-APAP PALF. Children from birth through age 17 years with non-APAP ALF enrolled in the PALF registry were eligible to enter an adaptively allocated, doubly masked, placebo-controlled trial using a continuous intravenous infusion of NAC (150 mg/kg/day in 5% dextrose in water [D5W]) or placebo (D5W) for up to 7 days. The primary outcome was 1-year survival. Secondary outcomes included liver transplantation-free survival, liver transplantation (LTx), length of intensive care unit (ICU) and hospital stays, organ system failure, and maximum HE score. A total of 184 participants were enrolled in the trial with 92 in each arm. The 1-year survival did not differ significantly (P = 0.19) between the NAC (73%) and placebo (82%) treatment groups. The 1-year LTx-free survival was significantly lower (P = 0.03) in those who received NAC (35%) than those who received placebo (53%), particularly, but not significantly so, among those less than 2 years old with HE grade 0-1 (NAC 25%; placebo 60%; P = 0.0493). There were no significant differences between treatment arms for hospital or ICU length of stay, organ systems failing, or highest recorded grade of HE.

CONCLUSION

NAC did not improve 1-year survival in non-APAP PALF. One-year LTx-free survival was significantly lower with NAC, particularly among those <2 years old. These results do not support broad use of NAC in non-APAP PALF and emphasizes the importance of conducting controlled pediatric drug trials, regardless of results in adults.

Chronic acetaminophen exposure in pediatric acute liver failure

BACKGROUND

Acetaminophen (N-acetyl-p-aminophenol [APAP]) is a widely used medication that can cause hepatotoxicity. We examined characteristics and outcomes of children with chronic exposure (CE) to APAP in the multinational Pediatric Acute Liver Failure (PALF) Study.

METHODS

A total of 895 children enrolled from 2002 to 2009 were grouped by APAP exposure history as: CE (received multiple doses \x{2265}2 days; n = 83), single dose exposure (SE; n = 85), and no exposure (NE; n = 498). CE was the reference group for pairwise comparisons. Median values are shown.

RESULTS

Patients with CE compared with those with SE were younger (3.5 vs 15.2 years, P < .0001), less likely to be female (46% vs 82%, P < .0001), and more likely to be Hispanic (25% vs 7%, P = .001), but they did not differ significantly from the NE group. At enrollment, total bilirubin was lower with CE than with NE (3.2 vs 13.1 mg/dL, P < .001). Alanine aminotransferase levels were higher with CE than with NE (2384 vs 855 IU/L, P < .0001), but lower than with SE (5140 IU/L, P < .0001). Survival without liver transplantation at 21 days was worse for CE than for SE (68% vs 92%, P = .0004) but better than for NE (49%, P = .008).

CONCLUSIONS

Children in the PALF study with CE had lower bilirubin and higher alanine aminotransferase than those with NE. Outcomes with CE were worse than with SE but better than with NE. Potential reasons for this outcomes advantage over non-APAP-exposed subjects should be explored.

The proper use of acetaminophen

Acetaminophen (N-acetyl-p-aminophenol, paracetamol [APAP])-induced acute liver failure is the most common cause of acute liver failure in adults. In children, APAP accounts for 25% of all cases of acute liver failure. The high mortality rate associated with this preventable condition makes it vital that paediatricians are aware of the potential adverse effects associated with this widely used drug. While APAP is generally considered to be safe when used as directed, its inclusion in multiple over-the-counter medications, as well as in prescription drugs, mandates that physicians promote and educate the general public about the proper use of acetaminophen in children.

Recent developments in acute liver failure

Acute liver failure is a remarkably rare syndrome, the result of rapid hepatocyte injury occurring over days or a few weeks, and encompassing multiple etiologies, but all with a remarkably similar clinical picture. The clinical features of coagulopathy and encephalopathy characterize this severe and often fatal condition. To date, transplantation has been the only reliable form of rescue for many patients. Recent developments have included a clearer understanding of the different contributing etiologies, how to build a diagnosis and prognosis based on initial laboratory findings, a more aggressive approach to intensive care management and more detailed understanding of the role of transplantation in this setting. This review will provide an overview of standard practices and new research initiatives and findings for this interesting but vexing orphan disease. Particular attention will be paid to practical matters for clinicians to consider in approaching the ALF patient. Few controlled clinical trials have been possible because of the condition's rarity. Critical care of these rare patients is key to their survival and decisions must be made decisively, sometimes with inadequate information. Experience is helpful but experienced clinician managers are even rarer than the disease: few hepatologists or intensivists have in-depth experience with ALF patients.

Acetaminophen-cysteine adducts during therapeutic dosing and following overdose

BACKGROUND

Acetaminophen-cysteine adducts (APAP-CYS) are a specific biomarker of acetaminophen exposure. APAP-CYS concentrations have been described in the setting of acute overdose, and a concentration >1.1 nmol/ml has been suggested as a marker of hepatic injury from acetaminophen overdose in patients with an ALT >1000 IU/L. However, the concentrations of APAP-CYS during therapeutic dosing, in cases of acetaminophen toxicity from repeated dosing and in cases of hepatic injury from non-acetaminophen hepatotoxins have not been well characterized. The objective of this study is to describe APAP-CYS concentrations in these clinical settings as well as to further characterize the concentrations observed following acetaminophen overdose.

METHODS

Samples were collected during three clinical trials in which subjects received 4 g/day of acetaminophen and during an observational study of acetaminophen overdose patients. Trial 1 consisted of non-drinkers who received APAP for 10 days, Trial 2 consisted of moderate drinkers dosed for 10 days and Trial 3 included subjects who chronically abuse alcohol dosed for 5 days. Patients in the observational study were categorized by type of acetaminophen exposure (single or repeated). Serum APAP-CYS was measured using high pressure liquid chromatography with electrochemical detection.

RESULTS

Trial 1 included 144 samples from 24 subjects; Trial 2 included 182 samples from 91 subjects and Trial 3 included 200 samples from 40 subjects. In addition, we collected samples from 19 subjects with acute acetaminophen ingestion, 7 subjects with repeated acetaminophen exposure and 4 subjects who ingested another hepatotoxin. The mean (SD) peak APAP-CYS concentrations for the Trials were: Trial 1- 0.4 (0.20) nmol/ml, Trial 2- 0.1 (0.09) nmol/ml and Trial 3- 0.3 (0.12) nmol/ml. APAP-CYS concentrations varied substantially among the patients with acetaminophen toxicity (0.10 to 27.3 nmol/ml). No subject had detectable APAP-CYS following exposure to a non-acetaminophen hepatotoxin.

CONCLUSIONS

Lower concentrations of APAP-CYS are detectable after exposure to therapeutic doses of acetaminophen and higher concentrations are detected after acute acetaminophen overdose and in patients with acetaminophen toxicity following repeated exposure.

Unrecognized acetaminophen toxicity as a cause of indeterminate acute liver failure

Despite extensive investigations, the cause of liver injury in 14% of patients with acute liver failure remains unknown (indeterminate). In a pilot study using a novel assay, highly specific acetaminophen-cysteine adducts were detected in 7 of 36 indeterminate patients (19%). To extend these observations, sera from 110 subjects enrolled in the Acute Liver Failure Study Group registry with indeterminate acute liver failure were analyzed with a similar but more efficient and sensitive adduct assay. As positive controls, another 199 patients with known or presumed acetaminophen-induced liver failure were assessed for the presence and quantity of adducts. Clinical, laboratory, and outcome data were compared for the two groups. On the basis of previous data for known therapeutic exposures and acetaminophen overdoses, an adduct concentration ≥1.0 nmol/mL of serum indicated a definite acetaminophen overdose. Among the 110 indeterminate cases, 18% had assay values ≥1.0 with a median level of 9.2 nmol/mL; 94.5% of the positive controls (known acetaminophen cases) had values ≥1.0 nmol/mL. Regardless of the initial diagnosis, subjects with elevated adduct levels demonstrated the clinical profile and hyperacute biochemical injury pattern associated with acetaminophen overdose: a predominance of female gender, very high aminotransferase levels, and low bilirubin levels.

CONCLUSION

These data confirm and extend previous observations regarding the high (18%) prevalence of unrecognized or uncertain acetaminophen toxicity among subjects with indeterminate acute liver failure. N-Acetylcysteine use was limited in this group, presumably because of the lack of a specific diagnosis of acetaminophen toxicity.

Therapeutic acetaminophen is not associated with liver injury in children: a systematic review

BACKGROUND

Concern exists about the potential for liver injury with therapeutic dosing of acetaminophen in children.

OBJECTIVE

We systematically reviewed the medical literature to determine the rate at which liver injury has been reported for children prescribed therapeutic doses of acetaminophen (≤75 mg/kg per day orally or intravenously or ≤100 mg/kg per day rectally).

METHODS

We searched Medline, Embase, and the Cochrane Central Register of Controlled Trials to locate all studies in which acetaminophen was administered to a defined pediatric population for ≥24 hours and for all case reports of liver injury after therapeutic acetaminophen dosing. Trained reviewers extracted data from each report. Major and minor hepatic adverse events (AEs) were defined prospectively. Causality was assessed by using the Naranjo algorithm.

RESULTS

A total of 62 studies that enrolled 32,414 children were included. No child (0% [95% confidence interval: 0.000-0.009]) was reported to have exhibited signs or symptoms of liver disease, to have received an antidote or transplantation, or to have died. Major or minor hepatic AEs were reported for 10 children (0.031% [95% confidence interval: 0.015-0.057]). The highest transaminase value reported was 600 IU/L. Naranjo scores (2-3) suggested "possible" causation. Twenty-two case reports were identified. In 9 cases, the Naranjo score suggested "probable" causation (5-6).

CONCLUSIONS

Hepatoxicity after therapeutic dosing of acetaminophen in children is rarely reported in defined-population studies. Case reports suggest that this phenomenon may occur, but few reports contain sufficient data to support a probable causal relationship.

Acute liver failure

Acute liver failure is a rare disorder with high mortality and resource cost. In the developing world, viral causes predominate, with hepatitis E infection recognised as a common cause in many countries. In the USA and much of western Europe, the incidence of virally induced disease has declined substantially in the past few years, with most cases now arising from drug-induced liver injury, often from paracetamol. However, a large proportion of cases are of unknown origin. Acute liver failure can be associated with rapidly progressive multiorgan failure and devastating complications; however, outcomes have been improved by use of emergency liver transplantation. An evidence base for practice is emerging for supportive care, and a better understanding of the pathophysiology of the disorder, especially in relation to hepatic encephalopathy, will probably soon lead to further improvements in survival rates.

Intravenous N-acetylcysteine improves transplant-free survival in early stage non-acetaminophen acute liver failure

BACKGROUND & AIMS

N-acetylcysteine (NAC), an antidote for acetaminophen poisoning, might benefit patients with non-acetaminophen-related acute liver failure.

METHODS

In a prospective, double-blind trial, acute liver failure patients without clinical or historical evidence of acetaminophen overdose were stratified by site and coma grade and assigned randomly to groups that were given NAC or placebo (dextrose) infusion for 72 hours. The primary outcome was overall survival at 3 weeks. Secondary outcomes included transplant-free survival and rate of transplantation.

RESULTS

A total of 173 patients received NAC (n = 81) or placebo (n = 92). Overall survival at 3 weeks was 70% for patients given NAC and 66% for patients given placebo (1-sided P = .283). Transplant-free survival was significantly better for NAC patients (40%) than for those given placebo (27%; 1-sided P = .043). The benefits of transplant-free survival were confined to the 114 patients with coma grades I-II who received NAC (52% compared with 30% for placebo; 1-sided P = .010); transplant-free survival for the 59 patients with coma grades III-IV was 9% in those given NAC and 22% in those given placebo (1-sided P = .912). The transplantation rate was lower in the NAC group but was not significantly different between groups (32% vs 45%; P = .093). Intravenous NAC generally was well tolerated; only nausea and vomiting occurred significantly more frequently in the NAC group (14% vs 4%; P = .031).

CONCLUSIONS

Intravenous NAC improves transplant-free survival in patients with early stage non-acetaminophen-related acute liver failure. Patients with advanced coma grades do not benefit from NAC and typically require emergency liver transplantation.

Pharmacokinetics of acetaminophen-protein adducts in adults with acetaminophen overdose and acute liver failure

Acetaminophen (APAP)-induced liver toxicity occurs with formation of APAP-protein adducts. These adducts are formed by hepatic metabolism of APAP to N-acetyl-p-benzoquinone imine, which covalently binds to hepatic proteins as 3-(cystein-S-yl)-APAP adducts. Adducts are released into blood during hepatocyte lysis. We previously showed that adducts could be quantified by high-performance liquid chromatography with electrochemical detection following proteolytic hydrolysis, and that the concentration of adducts in serum of overdose patients correlated with toxicity. The following study examined the pharmacokinetic profile and clinical associations of adducts in 53 adults with acute APAP overdose resulting in acute liver failure. A population pharmacokinetic analysis using nonlinear mixed effects (statistical regression type) models was conducted; individual empiric Bayesian estimates were determined for the elimination rate constant and elimination half-life. Correlations between clinical and laboratory data were examined relative to adduct concentrations using nonparametric statistical approaches. Peak concentrations of APAP-protein adducts correlated with peak aminotransferase concentrations (r = 0.779) in adults with APAP-related acute liver failure. Adducts did not correlate with bilirubin, creatinine, and APAP concentration at admission, international normalized ratio for prothrombin time, or reported APAP dose. After N-acetylcysteine therapy, adducts exhibited first-order disappearance. The mean elimination rate constant and elimination half-life were 0.42 +/- 0.09 days(-1) and 1.72 +/- 0.34 days, respectively, and estimates from the population model were in strong agreement with these data. Adducts were detected in some patient samples 12 days post-ingestion. The persistence and specificity of APAP-protein adducts as correlates of toxicity support their use as specific biomarkers of APAP toxicity in patients with acute liver injury.