Treatment of paracetamol (acetaminophen) poisoning with N-acetylcysteine

A non-inferiority randomised controlled trial of a Shorter Acetylcysteine Regimen for Paracetamol Overdose - the SARPO trial

BACKGROUND

Paracetamol is a common overdose worldwide. Early acetylcysteine treatment can prevent hepatotoxicity. Multiple intravenous acetylcysteine regimens exist; the commonest recommending 300mg/kg over 20h. We investigated the effectiveness and safety of a shorter regimen in paracetamol overdoses ≤30g.

METHODS

In a multicentre non-inferiority randomised controlled trial, 204 patients from three hospitals with acute paracetamol overdose ≤ 30g presenting within 8h, were randomised to standard 20h acetylcysteine (200mg/kg/4h, 100mg/kg/16h) regimen or short 12h acetylcysteine (200mg/kg/4h, 50mg/kg/8h) regimen. The primary outcome was the absolute difference between alanine transaminase (ALT) 24h post-ingestion and admission ALT (ΔALT24). Secondary outcomes included ALT>150U/L at 24h and double admission ALT, systemic hypersensitivity and gastrointestinal adverse effects.

RESULTS

The two groups were similar in age, gender, dose ingested, paracetamol concentration, baseline ALT, hospital, charcoal administration and time until acetylcysteine. The shorter regimen was non-inferior to the standard regimen. ΔALT24 for 107 patients given the shorter regimen was median -2U/L (Interquartile range [IQR]:-7 to 1U/L) compared to 97 given the standard regimen, median -1U/L (IQR:-5 to 1.5U/L); difference in medians of -1U/L; 95% confidence interval:-3 to 1U/L; less than the upper non-inferiority margin of 5). No patient receiving the shorter regimen had a 24h ALT double admission and >150U/L, compared to one receiving the standard regimen. No patient had an ALT>1000U/L. Systemic hypersensitivity reactions were similar between groups [9/107 (8%) for short versus 10/97 (10%) standard regimen]. Gastrointestinal adverse effects occurred in 78/107 patients (73%) receiving the short versus 63/97 (65%) receiving the standard regimen.

CONCLUSIONS

The shorter 12h acetylcysteine regimen had the same effectiveness and safety as the standard 20h regimen in acute paracetamol overdoses ≤30g, almost halving the length of treatment required.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry number ACTRN12616001617459.

HiSNAP trial-a multicentre, randomised, open-label, blinded end point, safety and efficacy trial of conventional (300 mg/kg) versus higher doses of acetylcysteine (450 mg/kg and 600 mg/kg) in patients with paracetamol overdose in the UK: study protocol

INTRODUCTION

In overdose, a larger proportion of paracetamol (acetaminophen) is converted in the liver to the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). Glutathione (GSH) is the endogenous antioxidant that protects cells from NAPQI-induced injury. In overdose, GSH stores may become depleted, leaving NAPQI free to produce liver damage. N-Acetylcysteine (NAC) helps prevent paracetamol toxicity by replenishing liver GSH. This protective effect of NAC produces specific metabolites in the circulation. Currently, regardless of the paracetamol dose ingested, patients in the UK receive a dose of NAC based only on their weight. Basic pharmacology, mathematical modelling and observational studies suggest that this dose may be insufficient in some patients (particularly those taking a large overdose).

METHODS AND ANALYSIS

A multicentre trial, taking place across several hospitals in Scotland, UK, within Emergency Departments and Acute Medical Units. Recruitment commenced on 19 February 2024 and is anticipated to run for approximately 2 years. This is a three-group dose-finding trial, in which participants are assigned in a 1:1:1 ratio to either Standard NAC (300 mg/kg) or higher doses of 450 mg/kg (Group 1) and 600 mg/kg (Group 2). The primary outcome is the proportion of paracetamol metabolites in the circulation that are directly produced by GSH/NAC detoxification of NAPQI. A higher proportion of these metabolites will indicate that the additional NAC is reducing the amount of toxic paracetamol metabolites in the body. The study will first test the primary outcome on the HiSNAP Group 2 against Standard NAC; only if that is significant will HiSNAP Group 1 be tested against Standard NAC.

ETHICS AND DISSEMINATION

The HiSNAP trial has been approved by the East Midlands (Derby) Research Ethics Committee (reference 23/EM/0129), NHS Lothian Research and Development Department, and the MHRA. Results will be disseminated by peer-reviewed publication, conferences and linked on isrctn.com.

TRIAL REGISTRATION NUMBER

ISRCTN17516192.

Comparison of two-bag and three-bag acetylcysteine regimens in the treatment of paracetamol poisoning: a systematic review and meta-analysis

INTRODUCTION

Worldwide, paracetamol poisoning is a common cause of acute liver failure and referral to transplant centers. Acetylcysteine has long been the mainstay of treatment, but recent literature suggests that a simplification of the "three-bag" method may decrease adverse effects. Our primary hypothesis is that a simplified dosing regimen (two-bag regimen) is non-inferior to the three-bag method in preventing liver injury. Our secondary hypothesis is that a simplified regimen will have lower rates of adverse effects.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we searched Medline/PubMed, Google, Google Scholar, Cochrane Library, Embase and Toxnet on May 23, 2022. The Medical Subject Headings terms were NAC, acetaminophen toxicity, acetyl-cysteine, N-acetylcysteine, paracetamol, APAP, 2-bag, and 3-bag. The Embase terms were acetylcysteine, NAC, 2-bag, two bag, 3-bag, three bag, simplified dosing, acetaminophen, Tylenol®, paracetamol, APAP, drug overdose, poisoning, and overdose. Studies included both non-United States Food and Drug Administration-approved and United States Food and Drug Administration-approved acetylcysteine regimens. Case reports, review articles, and animal studies were excluded. Two authors independently reviewed each study using Rayyan QCRI to determine if the studies met search criteria while blinded to the selections of each other. The two authors discussed until reaching a consensus. We used a primary outcome of non-inferiority of hepatotoxicity. We used secondary outcomes of non-allergic anaphylactoid reactions and adverse events. We conducted a fixed-effect meta-analysis using R package meta. To visually summarize the meta-analysis results, we also produced forest plots. We used Cochran's Q test and I2 statistical analysis to assess heterogeneity between the studies.

RESULTS

Our search resulted in 657 total citations, which were reduced to unique citations. Of the 643 studies, 46 met the criteria for full text review, and eight met the study criteria. Of the eight studies investigating a simplified acetylcysteine regimen, four studies utilized some form of a modified two-bag infusion regimen, varying in duration or dosing of infusions, and four studies shared the same "common" two-bag treatment, a regimen that delivers acetylcysteine 200 mg/kg over 4 h, followed by 100 mg/kg acetylcysteine over 16 h. The six studies comparing a two-bag dosing regimen to the three-bag technique were utilized for our random effect model meta-analysis. We found no significant heterogeneity amongst the six studies for either hepatotoxicity (Q(5) = 1.11; P = 0.95; I2 = 0%; 95% CI: 0%-74.6%) or non-allergic anaphylactoid reactions and adverse events (Q(5) = 10.15; P = 0.07; I2 = 50.7%; 95% CI: 0%-80.4%). Compared to the traditional three-bag dosing regimen, the two-bag method did not demonstrate a difference in relative risk for hepatotoxicity (OR: 0.88; 95% CI: 0.72-1.08; P = 0.23) but did demonstrate a significantly decreased likelihood of non-allergic anaphylactoid reactions and other adverse events (OR: 0.24; 95% CI: 0.17-0.35; P <0.0001).

DISCUSSION

The two-bag method is a safe and effective treatment for acute paracetamol poisoning. The two-bag regimen is correlated with a significant reduction in non-allergic anaphylactoid reactions, compared to the three-bag method, and is non-inferior with respect to hepatotoxicity. While we feel this information is practice changing for many, further research in the form of a randomized control trial would be beneficial to compare even more abbreviated methods such as a "single bag method."

CONCLUSION

Two-bag acetylcysteine dosing regimens appear to be non-inferior to the three-bag method with respect to hepatotoxicity, and result in fewer anaphylactoid, cutaneous, and gastrointestinal reactions.

Novel reduced heteropolyacid nanoparticles for effective treatment of drug-induced liver injury by manipulating reactive oxygen and nitrogen species and inflammatory signals

With the rapid advancements in biomedicine, the use of clinical drugs has surged sharply. However, potential hepatotoxicity limits drug exploitation and widespread usage, posing serious threats to patient health. Hepatotoxic drugs disrupt liver enzyme levels and cause refractory pathological damage, creating a challenge in the application of diverse first-line drugs. The activation and deterioration of reactive oxygen and nitrogen species (RONS) and inflammatory signals are key pathological mechanisms of drug-induced liver injury (DILI). Herein, a novel reduced heteropolyacid nanoparticle (RNP) has been developed, possessing high RONS-scavenging ability, strong anti-inflammatory activity, and excellent biosafety. These features enable it to swiftly restore the redox and immune balance of the liver. Intravenous administration of RNP effectively scavenged RONS storm, reversing liver oxidative stress and restoring normal mitochondrial membrane potential and function. Furthermore, by inhibiting c-Jun-N-terminal kinase phosphorylation, RNP facilitated the restoration of nuclear factor erythroid 2-related factor 2-mediated endogenous antioxidant signaling, ultimately rescuing the liver function and tissue morphology in acetaminophen-induced DILI mice. Crucially, the high biocompatible RNP exhibited superior efficacy in the DILI mouse model compared to the clinical antioxidant N-acetylcysteine. This targeted therapeutic approach, tailored to address the onset and progression of DILI, offers valuable new insights into controlling the condition and restoring liver structure and function.

Simultaneous Quantitation of Multiple Biological Thiols Using Reactive Ionization and Derivatization with Charged Mass Tags

The biologically important thiols (cysteine, homocysteine, N-acetyl cysteine, and glutathione) are key species in redox homeostasis, and there is a clinical need to measure them rapidly, accurately, and simultaneously at low levels in complex biofluids. The solution to the challenge presented here is based on a new derivatizing reagent that combines a thiol-selective unit to optimize the chemical transformation and a precharged pyridinium unit chosen to maximize sensitivity in mass spectrometry. Derivatization is performed simultaneously with ionization ("reactive ionization"), and mass spectrometry is used to record and characterize the thiol reaction products. The method is applicable over the concentration range from 1 μM to 10 mM and is demonstrated for 25 blood serum, 1 plasma, and 3 types of tissue samples. The experiment is characterized by limited sample preparation (<4 min) and short analysis time (<1 min). High precision and accuracy (both better than 8%) are validated using independent HPLC-MS analysis. Cystine-cysteine redox homeostasis can be monitored by introducing an additional reduction step, and the accuracy and precision of these results are also validated by HPLC-MS.

Clinically relevant therapeutic approaches against acetaminophen hepatotoxicity and acute liver failure

Liver injury and acute liver failure caused by an acetaminophen (APAP) overdose is a significant clinical problem in western countries. With the introduction of the mouse model of APAP hepatotoxicity in the 1970 s, fundamental mechanisms of cell death were discovered. This included the recognition that part of the APAP dose is metabolized by cytochrome P450 generating a reactive metabolite that is detoxified by glutathione. After the partial depletion of glutathione, the reactive metabolite will covalently bind to sulfhydryl groups of proteins, which is the initiating event of the toxicity. This insight led to the introduction of N-acetyl-L-cysteine, a glutathione precursor, as antidote against APAP overdose in the clinic. Despite substantial progress in our understanding of the pathomechanisms over the last decades viable new antidotes only emerged recently. This review will discuss the background, mechanisms of action, and the clinical prospects of the existing FDA-approved antidote N-acetylcysteine, of several new drug candidates under clinical development [4-methylpyrazole (fomepizole), calmangafodipir] and examples of additional therapeutic targets (Nrf2 activators) and regeneration promoting agents (thrombopoietin mimetics, adenosine A2B receptor agonists, Wharton's Jelly mesenchymal stem cells). Although there are clear limitations of certain therapeutic approaches, there is reason to be optimistic. The substantial progress in the understanding of the pathophysiology of APAP hepatotoxicity led to the consideration of several drugs for development as clinical antidotes against APAP overdose in recent years. Based on the currently available information, it is likely that this will result in additional drugs that could be used as adjunct treatment for N-acetylcysteine.

Investigating a Novel Two-Bag N-Acetylcysteine Regimen for Acetaminophen Toxicity

BACKGROUND

Acetaminophen toxicity remains one of the most common causes of liver failure and is treated with a course of n-acetylcysteine (NAC). This exceptionally effective medication is traditionally administered using a complicated three-bag protocol that is prone to administration errors.

OBJECTIVE

We aimed to assess whether switching to a novel two-bag protocol (150 mg/kg over 1 h followed by 150 mg/kg over 20 h) reduced administration errors while not increasing liver injury or anaphylactoid reactions.

METHODS

This was a retrospective chart review of hospital encounters for patients with acetaminophen toxicity, comparing outcomes before and after the change from a three-bag protocol to a two-bag protocol at two affiliated institutions. The primary outcome was incidence of medication errors with secondary outcomes including acute liver injury (ALI) and incidence of non-anaphylactoid allergic reactions (NAAR). The study was approved by the health system's Institutional Review Board.

RESULTS

483 encounters were included for analysis (239 in the three-bag and 244 in the two-bag groups). NAAR were identified in 11 patients with no difference seen between groups. Similarly, no differences were seen in ALI. Medication administration errors were observed significantly less often in the two-bag group (OR 0.24) after adjusting for confounders.

CONCLUSION

Transitioning to a novel two-bag NAC regimen decreased administration errors. This adds to the literature that two-bag NAC regimens are not only safe but also may have significant benefits over the traditional NAC protocol.

Central Mechanisms of Acetaminophen Hepatotoxicity: Mitochondrial Dysfunction by Protein Adducts and Oxidant Stress

Acetaminophen (APAP) is an analgesic and antipyretic drug used worldwide, which is safe at therapeutic doses. However, an overdose can induce liver injury and even liver failure. Mechanistic studies in mice beginning with the seminal papers published by B.B. Brodie's group in the 1970s have resulted in important insight into the pathophysiology. Although the metabolic activation of APAP with generation of a reactive metabolite, glutathione depletion, and protein adduct formation are critical initiating events, more recently, mitochondria have come into focus as an important target and decision point of cell death. This review provides a comprehensive overview of the induction of mitochondrial superoxide and peroxynitrite formation and its propagation through a mitogen-activated protein kinase cascade, the mitochondrial permeability transition pore opening caused by iron-catalyzed protein nitration, and the mitochondria-dependent nuclear DNA fragmentation. In addition, the role of adaptive mechanisms that can modulate the pathophysiology, including autophagy, mitophagy, nuclear erythroid 2 p45-related factor 2 activation, and mitochondrial biogenesis, are discussed. Importantly, it is outlined how the mechanisms elucidated in mice translate to human hepatocytes and APAP overdose patients, and how this mechanistic insight explains the mechanism of action of the clinically approved antidote N-acetylcysteine and led to the recent discovery of a novel compound, fomepizole, which is currently under clinical development. SIGNIFICANCE STATEMENT: Acetaminophen (APAP)-induced liver injury is the most frequent cause of acute liver failure in western countries. Extensive mechanistic research over the last several decades has revealed a central role of mitochondria in the pathophysiology of APAP hepatotoxicity. This review article provides a comprehensive discussion of a) mitochondrial protein adducts and oxidative/nitrosative stress, b) mitochondria-regulated nuclear DNA fragmentation, c) adaptive mechanisms to APAP-induced cellular stress, d) translation of cell death mechanisms to overdose patients, and e) mechanism-based antidotes against APAP-induced liver injury.

Anti-Inflammatory and Anti-Oxidant Properties of N-Acetylcysteine: A Fresh Perspective

N-acetyl-L-cysteine (NAC) was initially introduced as a treatment for mucus reduction and widely used for chronic respiratory conditions associated with mucus overproduction. However, the mechanism of action for NAC extends beyond its mucolytic activity and is complex and multifaceted. Contrary to other mucoactive drugs, NAC has been found to exhibit antioxidant, anti-infective, and anti-inflammatory activity in pre-clinical and clinical reports. These properties have sparked interest in its potential for treating chronic lung diseases, including chronic obstructive pulmonary disease (COPD), bronchiectasis (BE), cystic fibrosis (CF), and idiopathic pulmonary fibrosis (IPF), which are associated with oxidative stress, increased levels of glutathione and inflammation. NAC's anti-inflammatory activity is noteworthy, and it is not solely secondary to its antioxidant capabilities. In ex vivo models of COPD exacerbation, the anti-inflammatory effects have been observed even at very low doses, especially with prolonged treatment. The mechanism involves the inhibition of the activation of NF-kB and neurokinin A production, resulting in a reduction in interleukin-6 production, a cytokine abundantly present in the sputum and breath condensate of patients with COPD and correlates with the number of exacerbations. The unique combination of mucolytic, antioxidant, anti-infective, and anti-inflammatory properties positions NAC as a safe, cost-effective, and efficacious therapy for a plethora of respiratory conditions.

N-acetylcysteine ameliorates erectile dysfunction in rats with hyperlipidemia by inhibiting oxidative stress and corpus cavernosum smooth muscle cells phenotypic modulation

Hyperlipidemia is a major risk factor for erectile dysfunction (ED). Oxidative stress and phenotypic modulation of corpus cavernosum smooth muscle cells (CCSMCs) are the key pathological factors of ED. N-acetylcysteine (NAC) can inhibit oxidative stress; however, whether NAC can alleviate pathological variations in the corpus cavernosum and promote erectile function recovery in hyperlipidemic rats remains unclear. A hyperlipidemia model was established using 27 eight-week-old male Sprague-Dawley (SD) rats fed a high-fat and high-cholesterol diet (hyperlipidemic rats, HR). In addition, 9 male SD rats were fed a normal diet to serve as controls (NC). HR rats were divided into three groups: HR, HR+normal saline (NS), and HR+NAC (n = 9 for each group; NS or NAC intraperitoneal injections were administered daily for 16 weeks). Subsequently, the lipid profiles, erectile function, oxidative stress, phenotypic modulation markers of CCSMCs, and tissue histology were analyzed. The experimental results revealed that erectile function was significantly impaired in the HR and HR + NS groups, but enhanced in the HR + NAC group. Abnormal lipid levels, over-activated oxidative stress, and multi-organ lesions observed in the HR and HR + NS groups were improved in the HR + NAC group. Moreover, the HR group showed significant phenotypic modulation of CCSMCs, which was also inhibited by NAC treatment. This report focuses on the therapeutic effect of NAC in restoring erectile function using a hyperlipidemic rat model by preventing CCSMC phenotypic modulation and attenuating oxidative stress.

Fifty years of paracetamol (acetaminophen) poisoning: the development of risk assessment and treatment 1973-2023 with particular focus on contributions published from Edinburgh and Denver

INTRODUCTION

Fifty years ago, basic scientific studies and the availability of assay methods made the assessment of risk in paracetamol (acetaminophen) poisoning possible. The use of the antidote acetylcysteine linked to new methods of risk assessment transformed the treatment of this poisoning. This review will describe the way in which risk assessment and treatments have developed over the last 50 years and highlight the remaining areas of uncertainty.

METHODS

A search of PubMed and its subsidiary databases revealed 1,166 references published in the period 1963-2023 using the combined terms "paracetamol", "poisoning", and "acetylcysteine". Focused searches then identified 170 papers dealing with risk assessment of paracetamol poisoning, 141 with adverse reactions to acetylcysteine and 114 describing different acetylcysteine regimens. To manage the extensive literature, we focused mainly on contributions made by the authors during their time in Edinburgh and Denver.

DOSE AND CONCENTRATION RESPONSE

The key relationship between paracetamol dose and toxicity risk was established in 1971 and led to the development of the Rumack-Matthew nomogram from data collected in Edinburgh.

MECHANISMS OF TOXICITY

A series of papers on the mechanisms of toxicity were published in 1973, and these showed that paracetamol hepatotoxicity was caused by the formation of a toxic intermediate epoxide metabolite normally detoxified by glutathione but which, in excess, was bound covalently to hepatic enzymes and proteins. An understanding of the relationship between the rate of paracetamol metabolism, paracetamol concentration, and toxic hazard in humans soon followed.

ANTIDOTE DEVELOPMENT AND EFFICACY IN PATIENTS

These discoveries were followed by the testing of a range of sulfhydryl-donors in animals and "at risk" patients. Acetylcysteine was developed as the lead intravenous antidote in the United Kingdom. The license holder in the United States refused to make an intravenous formulation. Thus, oral acetylcysteine became the antidote trialed in the United States National Multicenter Study. Intravenous acetylcysteine regimens used initially in the United Kingdom and subsequently in the United States used loading doses of 150 mg/kg over 15 minutes or one hour, 50 mg/kg over four hours, and 100 mg/kg over 16 hours. These regimens were associated with adverse drug reactions (nausea, vomiting and anaphylactoid reactions) and hence, treatment interruption. Newer dosing regimens now give loading doses more slowly. One, the Scottish and Newcastle Anti-emetic Pretreatment protocol, using an acetylcysteine regimen of 100 mg/kg over two hours followed by 200 mg/kg over 10 hours, has been widely adopted in the United Kingdom. A cohort comparison study suggests this regimen has comparable efficacy to standard regimens and offers opportunities for selective higher acetylcysteine dosing.

RISK ASSESSMENT AT PRESENTATION

No dose-ranging studies with acetylcysteine were done, and no placebo-controlled studies were performed. Thus, there is uncertainty regarding the optimal dose of acetylcysteine, particularly in patients ingesting very large overdoses of paracetamol. The choice of intervention concentration on the Rumack-Matthew nomogram has important consequences for the proportion of patients treated. The United States National Multicenter Study used a "treatment" line starting at 150 mg/L (992 µmol/L) at 4 hours post overdose, extending to 24 hours with a half-life of 4 hours, now standard there, and subsequently adopted in Australia and New Zealand. In the United Kingdom, the treatment line was initially 200 mg/L (1,323 µmol/L) at 4 hours (the Rumack-Matthew "risk" line). In 2012, the United Kingdom Medicines and Healthcare products Regulatory Agency lowered the treatment line to 100 mg/L (662 µmol/L) at 4 hours for all patients, increasing the number of patients admitted and treated at a high cost. Risk assessment is a key issue for ongoing study, particularly following the development of potential new antidotes that may act in those at greatest risk. The development of biomarkers to assess risk is ongoing but has yet to reach clinical trials.

CONCLUSION

Even after 50 years, there are still areas of uncertainty. These include appropriate acetylcysteine doses in patients who ingest different paracetamol doses or multiple (staggered) ingestions, early identification of at-risk patients, and optimal treatment of late presenters.

Fomepizole Therapy for Acetaminophen-Induced Liver Failure in an Infant

Acetaminophen overdose is common in the pediatric population. N-acetylcysteine (NAC) is effective at preventing liver injury in most patients when started shortly after the overdose. Delays to therapy increase risk of hepatotoxicity and liver failure that may necessitate organ transplant. Animal studies have demonstrated fomepizole may provide added benefit in acetaminophen overdose because of its ability to block the metabolic pathway that produces the toxic acetaminophen metabolite and downstream inhibition of oxidative stress pathways that lead to cell death. Several adult case reports describe use of fomepizole in patients at higher risk for poor outcomes despite NAC. We describe a case of a 7-month-old female who presented in acute liver failure with persistently elevated acetaminophen concentration secondary to repeated supratherapeutic doses of acetaminophen to manage fever. Fomepizole and NAC antidotes were used in the management of the patient. She fully recovered despite demonstrating multiple markers of poor outcome on initial presentation. Although randomized trials are lacking, this case suggests that fomepizole may safely provide additional benefit in pediatric patients at risk for severe acetaminophen toxicity.

Late N-acetylcysteine for successful recovery of acetaminophen-related acute liver failure: A case report

Acetaminophen toxicity is one of the leading causes of liver failure. Although N-acetylcysteine (NAC) is generally successful in preventing acetaminophen hepatotoxicity when given in a timely manner, if not prescribed in the early golden time, the only practical way to save the patient might be liver transplantation. The case presented was a 20-year-old female with an acetaminophen overdose (30 g), for which more than 24 h had passed since the ingestion. Despite the critical clinical condition, loss of consciousness (Glasgow Coma Score of 4) of the patient, and passing the golden time of antidote administration, the decision was made by the healthcare team to administer NAC. After transferring the patient to the intensive care unit, the three-bag NAC regimen was initiated and appropriate monitoring was performed. After this, the regimen of 3 g q8h was continued for the patient. The patient's condition began to improve slowly on the second day and then she was extubated on the fourth day. Finally, she was discharged on the tenth day. Although the golden period of antidote administration had passed outwardly, there was no need for a liver transplant and the patient recovered successfully with late NAC administration. Hence, clinicians can benefit from the use of NAC even in the late phases of acetaminophen liver toxicity.

Protective Effect of Water-Soluble Acacetin Prodrug on APAP-Induced Acute Liver Injury Is Associated with Upregulation of PPARγ and Alleviation of ER Stress

A water-soluble acacetin prodrug has been synthesized and reported by our group previously. Acetaminophen (APAP) overdose is a leading cause of acute liver injury. We found that subcutaneous injection of acacetin prodrug (5, 10, 20 mg/kg) decreased serum ALT, AST, and ALP, corrected the abnormal MDA and GSH in liver, and improved intrahepatic hemorrhage and destruction of liver structures in APAP (300 mg/kg)-treated mice. Molecular mechanism analysis revealed that the expressions of endoplasmic reticulum (ER) stress markers ATF6, CHOP, and p-PERK, apoptosis-related protein BAX, and cleaved caspase 3 were decreased by acacetin in a dose-dependent manner in vivo and in vitro. Moreover, via the acacetin-upregulated peroxisome-proliferator-activated receptor gamma (PPARγ) of HepG2 cells and liver, the suppressive effect of acacetin on ER stress and apoptosis was abolished by PPARγ inhibitor (GW9662) or PPARγ-siRNA. Molecular docking revealed that acacetin can bind to three active pockets of PPARγ, mainly by hydrogen bond. Our results provide novel evidence that acacetin prodrug exhibits significant protective effect against APAP-induced liver injury by targeting PPARγ, thereby suppressing ER stress and hepatocyte apoptosis. Acacetin prodrug is likely a promising new drug candidate for treating patients with acute liver injury induced by APAP.

Development of Dipeptide N–acetyl–L–cysteine Loaded Nanostructured Carriers Based on Inorganic Layered Hydroxides

N–acetyl–L–cysteine (NAC), a derivative of the L–cysteine amino acid, presents antioxidant and mucolytic properties of pharmaceutical interest. This work reports the preparation of organic-inorganic nanophases aiming for the development of drug delivery systems based on NAC intercalation into layered double hydroxides (LDH) of zinc–aluminum (Zn2Al–NAC) and magnesium–aluminum (Mg2Al–NAC) compositions. A detailed characterization of the synthesized hybrid materials was performed, including X-ray diffraction (XRD) and pair distribution function (PDF) analysis, infrared and Raman spectroscopies, solid-state 13carbon and 27aluminum nuclear magnetic resonance (NMR), simultaneous thermogravimetric and differential scanning calorimetry coupled to mass spectrometry (TG/DSC–MS), scanning electron microscopy (SEM), and elemental chemical analysis to assess both chemical composition and structure of the samples. The experimental conditions allowed to isolate Zn2Al–NAC nanomaterial with good crystallinity and a loading capacity of 27.3 (m/m)%. On the other hand, NAC intercalation was not successful into Mg2Al–LDH, being oxidized instead. In vitro drug delivery kinetic studies were performed using cylindrical tablets of Zn2Al–NAC in a simulated physiological solution (extracellular matrix) to investigate the release profile. After 96 h, the tablet was analyzed by micro-Raman spectroscopy. NAC was replaced by anions such as hydrogen phosphate by a slow diffusion-controlled ion exchange process. Zn2Al–NAC fulfil basic requirements to be employed as a drug delivery system with a defined microscopic structure, appreciable loading capacity, and allowing a controlled release of NAC.

Large paracetamol overdose-Higher dose acetylcysteine is required

Paracetamol poisoning continues to be a worldwide problem and, despite the availability of an effective antidote, acetylcysteine (NAC), the optimal way to use this antidote, particularly following very large doses of paracetamol, has not been established. Recent case series have shown an increased toxicity from high doses of paracetamol, even in those receiving prompt NAC therapy, particularly in patients above the 300 mg/L nomogram treatment line. Clinical trial evidence supporting shorter NAC dosing now allows the possibility for intensifying treatment without the risk of very high rates of ADRs. New biomarkers also show the possibility of early identification of patients at risk of liver injury who might also benefit from increased intensity treatment. This article discusses these data and proposes a logical therapy for increasing NAC dosing which now requires clinical trial testing.

Comparison of Two-Bag Versus Three-Bag N-Acetylcysteine Regimens for Pediatric Acetaminophen Toxicity

BACKGROUND

Acetaminophen overdose is a leading cause of liver failure, and a leading cause of pediatric poisoning requiring hospital admission. The antidote, N-acetylcysteine (NAC), is traditionally administered as a three-bag intravenous infusion. Despite its efficacy, NAC is associated with high incidence of nonallergic anaphylactoid reactions (NAARs). Adult evidence demonstrates that alternative dosing regimens decrease NAARs and medication errors (MEs).

OBJECTIVES

To compare NAARs and MEs associated with two- versus three-bag NAC for acetaminophen overdose in a pediatric population.

METHODS

This is a retrospective observational cohort study comparing pediatric patients who received three- versus two-bag NAC for acetaminophen toxicity. The primary outcome was incidence of NAARs. Secondary outcomes were rates of MEs and relevant hospital outcomes (length of stay [LOS], intensive care unit (ICU) admission, liver transplant, death).

RESULTS

Two hundred forty-three patients met inclusion criteria (median age of 15 years): 150 (62%) three-bag NAC and 93 (38%) two-bag NAC. There was no difference in overall NAARs (p = 0.54). Fewer cutaneous NAARs were observed in the two-bag group, three-bag: 15 (10%), two-bag: 2 (2%), p = 0.02. MEs were significantly decreased with the two-bag regimen, three-bag: 59 (39%), two-bag: 21 (23%), p = 0.01. No statistical differences were observed in LOS, ICU admissions, transplant, or death.

CONCLUSION AND RELEVANCE

A significant decrease in cutaneous NAARs and MEs was observed in pediatric patients by combining the first two bags of the traditional three-bag NAC regimen. In pediatric populations, a two-bag NAC regimen for acetaminophen overdose may improve medication tolerance and safety.

Yinhuang oral liquid protects acetaminophen-induced acute liver injury by regulating the activation of autophagy and Nrf2 signaling

This study aimed to investigate the protective effect and potential mechanism of Yinhuang oral liquid (YOL) against acetaminophen (APAP) induced liver injury in mice. C57BL/6 mice were randomly divided into control group, model group (300 mg/kg APAP), NAC group and YOL group. Mice were treated intragastrical with YOL (8 g/kg) and N-Acetylcysteine (NAC, 300 mg/kg) 6 h before and 6 h after the APAP (300 mg/kg) intraperitoneal injection. 12 h after APAP exposure, blood and liver samples were collected for subsequent testing. The results showed that APAP decreased liver index, induced liver pathological injury with hepatocytes swelling, necrosis and apoptosis and inflammatory cell infiltration. APAP exposure significantly increased serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels to 35 and 6 multiples than their original levels. YOL alleviated liver pathological damage, decreased the serum levels of ALT and AST in APAP exposure mice, and it worked better than NAC. Moreover, APAP promoted oxidative stress by increasing lipid peroxidation (MDA) and decreasing anti-oxidant enzyme activities of SOD and GSH, inhibited the mRNA levels of Nrf2, HO-1, Gclc and Gclm, and decreased the protein levels of Nrf2, HO-1 and Keap1, compared to control group. Furthermore, APAP exposure significantly down-regulated the mRNA and protein levels of autophagy related genes (Beclin-1, LC3-II, LC3-I, Atg4B, Atg5, Atg16L1 and Atg7). However, the gene levels of mTOR and p-mTOR increased, and p-ULK1 protein level decreased in liver of APAP treated mice. Additionally, YOL alleviated the oxidative injury by up-regulating Nrf2 pathway. The gene and protein levels of autophagy-related genes Beclin-1, LC3-II, LC3-I, Atg4B, Atg5, Atg16L1 and Atg7 reached the basal levels after YOL treatment. In conclusion, YOL had a protective and therapeutic role in APAP-induced liver injury in mice by activating Nrf2 signaling pathway and autophagy.

Nicotinamide adenine dinucleotide attenuates acetaminophen-induced acute liver injury via activation of PARP1, Sirt1, and Nrf2 in mice

The aim of this study was to investigate the protective effect of nicotinamide adenine dinucleotide (NAD⁺) against acute liver injury (ALI) induced by acetaminophen (APAP) overdose in mice. First, serum transaminases were used to assess the protective effect of NAD⁺, and the data revealed that NAD⁺ mitigated the APAP-induced ALI in a dose-dependent manner. Then, we performed hematoxylin-eosin staining of liver tissues and found that NAD⁺ alleviated the abnormalities of histopathology. Meanwhile, increase in the malondialdehyde content and decrease in glutathione, superoxide dismutase (SOD), and glutathione peroxidase were identified in the APAP group, which were partially prevented by the NAD⁺ pretreatment. Moreover, compared with the mice treated with APAP only, the expression of poly ADP-ribose polymerase 1 (PARP1), Sirtuin1 (Sirt1), SOD2, nuclear factor erythroid 2-related factor 2 (Nrf2), and hemoxygenase-1 was upregulated, while Kelch-like ECH-associated protein 1 and histone H2AX phosphorylated on Ser-139 were downregulated by NAD⁺ in NAD⁺ + APAP group. Conversely, NAD⁺ could not correct the elevated expression of phospho-Jun N-terminal kinase and phospho-extracellular signal-regulated kinase induced by APAP. Taken together, these findings suggest that NAD⁺ confers an anti-ALI effect to enhance the expression of PARP1 and Sirt1, and to simultaneously stimulate the Nrf2 anti-oxidant signaling pathway.

Platanosides, a Potential Botanical Drug Combination, Decrease Liver Injury Caused by Acetaminophen Overdose in Mice

Oxidative stress plays an important role in acetaminophen (APAP)-induced hepatotoxicity. Platanosides (PTSs) isolated from the American sycamore tree (Platanus occidentalis) represent a potential new four-molecule botanical drug class of antibiotics active against drug-resistant infectious disease. Preliminary studies have suggested that PTSs are safe and well tolerated and have antioxidant properties. The potential utility of PTSs in decreasing APAP hepatotoxicity in mice in addition to an assessment of their potential with APAP for the control of infectious diseases along with pain and pyrexia associated with a bacterial infection was investigated. On PTS treatment in mice, serum alanine aminotransferase (ALT) release, hepatic centrilobular necrosis, and 4-hydroxynonenal (4-HNE) were markedly decreased. In addition, inducible nitric oxide synthase (iNOS) expression and c-Jun-N-terminal kinase (JNK) activation decreased when mice overdosed with APAP were treated with PTSs. Computational studies suggested that PTSs may act as JNK-1/2 and Keap1-Nrf2 inhibitors and that the isomeric mixture could provide greater efficacy than the individual molecules. Overall, PTSs represent promising botanical drugs for hepatoprotection and drug-resistant bacterial infections and are effective in protecting against APAP-related hepatotoxicity, which decreases liver necrosis and inflammation, iNOS expression, and oxidative and nitrative stresses, possibly by preventing persistent JNK activation.

N-Acetylcysteine protects against cobalt chloride-induced endothelial dysfunction by enhancing glucose-6-phosphate dehydrogenase activity

Hypoxia‐induced endothelial dysfunction is known to be involved in the pathogenesis of several vascular diseases. However, it remains unclear whether the pentose phosphate pathway (PPP) is involved in regulating the response of endothelial cells to hypoxia. Here, we established an in vitro model by treating EA.hy926 (a hybrid human umbilical vein cell line) with cobalt chloride (CoCl₂; a chemical mimic that stabilizes HIF‐1α, thereby leading to the development of hypoxia), and used this to investigate the involvement of PPP by examining expression of its key enzyme, glucose‐6‐phosphate dehydrogenase (G6PD). We report that CoCl₂ induces the accumulation of HIF‐1α, leading to endothelial cell dysfunction characterized by reduced cell viability, proliferation, tube formation, and activation of cytokine production, accompanied with a significant decrease in G6PD expression and activity. The addition of 6‐aminonicotinamide (6‐AN) to inhibit PPP directly causes endothelial dysfunction. Additionally, N‐Acetylcysteine (NAC), a precursor of glutathione, was further evaluated for its protective effects; NAC displayed a protective effect against CoCl₂‐induced cell damage by enhancing G6PD activity, and this was abrogated by 6‐AN. The effects of CoCl₂ and the involvement of G6PD in endothelial dysfunction have been confirmed in primary human aortic endothelial cells. In summary, G6PD was identified as a novel target of CoCl₂‐induced damage, which highlighted the involvement of PPP in regulating the response of endothelial cell CoCl₂. Treatment with NAC may be a potential strategy to treat hypoxia or ischemia, which are widely observed in vascular diseases.

Has the time come to stop routine N-acetylcysteine treatment in young children in Denmark? A review of 300 suspected paracetamol overdoses in children aged 0-6 years

AIM

To evaluate the prevalence of potentially hepatoxic paracetamol ingestion and associated N-acetylcysteine treatment in young children suspected of paracetamol poisoning.

METHODS

A retrospective cohort study of children aged 0-6 years suspected of paracetamol poisoning with a related plasma-paracetamol measurement in the Capital Region of Denmark in the period 2010-2017. Data from the clinical laboratory system were linked to data from electronic patient records via the unique identification number given to all Danish residents.

RESULTS

Of 297 children included, suspected single paracetamol overdoses were present in 281 (95%). Sixty-nine per cent were treated with N-acetylcysteine, and the mean treatment period was 20.3 h (SD 20.8). A maximum of 6 (2%) of the children suspected of single overdose had plasma-paracetamol concentrations that exceeded the recommended treatment thresholds. No cases of severe hepatotoxicity were registered. Adverse events to N-acetylcysteine-treatment were registered in 3 (2%) children including one anaphylactoid reaction (0.5%).

CONCLUSION

This study shows that initiating N-acetylcysteine as a 'one size fit all' treatment regimen in all children aged 0-6 years with a suspected single paracetamol overdose leads to substantial overtreatment. The data support that it is feasible to initiate N-acetylcysteine within 10 h based on an early plasma-paracetamol test.

Comparing N-acetylcysteine and 4-methylpyrazole as antidotes for acetaminophen overdose

Acetaminophen (APAP) overdose can cause hepatotoxicity and even liver failure. N-acetylcysteine (NAC) is still the only FDA-approved antidote against APAP overdose 40 years after its introduction. The standard oral or intravenous dosing regimen of NAC is highly effective for patients with moderate overdoses who present within 8 h of APAP ingestion. However, for late-presenting patients or after ingestion of very large overdoses, the efficacy of NAC is diminished. Thus, additional antidotes with an extended therapeutic window may be needed for these patients. Fomepizole (4-methylpyrazole), a clinically approved antidote against methanol and ethylene glycol poisoning, recently emerged as a promising candidate. In animal studies, fomepizole effectively prevented APAP-induced liver injury by inhibiting Cyp2E1 when treated early, and by inhibiting c-jun N-terminal kinase (JNK) and oxidant stress when treated after the metabolism phase. In addition, fomepizole treatment, unlike NAC, prevented APAP-induced kidney damage and promoted hepatic regeneration in mice. These mechanisms of protection (inhibition of Cyp2E1 and JNK) and an extended efficacy compared to NAC could be verified in primary human hepatocytes. Furthermore, the formation of oxidative metabolites was eliminated in healthy volunteers using the established treatment protocol for fomepizole in toxic alcohol and ethylene glycol poisoning. These mechanistic findings, together with the excellent safety profile after methanol and ethylene glycol poisoning and after an APAP overdose, suggest that fomepizole may be a promising antidote against APAP overdose that could be useful as adjunct treatment to NAC. Clinical trials to support this hypothesis are warranted.

Orally administered bismuth drug together with N-acetyl cysteine as a broad-spectrum anti-coronavirus cocktail therapy

A cocktail therapy comprising bismuth drugs and N-acetyl-l-cysteine is reported to suppress the replication of SARS-CoV-2 via the oral route. The broad-spectrum inhibitory activities of the combination upon key viral cysteine enzymes are verified.

Suppression of glomerular damage and apoptosis and biomarkers of acute kidney injury induced by acetaminophen toxicity using a combination of resveratrol and quercetin

Acute renal failure induced by a toxic dose of acetaminophen (also known as paracetamol, or APAP) is common in both humans and experimental animal models. Glomerular ultrastructural alterations induced by APAP overdose associated with the suppression of biomarkers of kidney injury have not been investigated before. Also, we investigated whether the combined polyphenolic antioxidants and anti-inflammatory compounds, resveratrol (RES) and quercetin (QUR) can protect against APAP-induced nephrotoxicity. Rats either received a single dose of APAP (2 g/kg) before being sacrificed after 24 hours or were pretreated for 7 days with combined doses of RES (30 mg/kg) and QUR (50 mg/kg) before being given a single dose of APAP and then sacrificed 24 hours post APAP ingestion. APAP significantly (p < 0.05) increased blood levels of urea, creatinine, malondialdehyde (MDA), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), which were effectively reduced by RES + QUR. In addition, APAP overdose induced the tissue expression of the apoptotic biomarker, p53, and caused profound kidney damage as demonstrated by substantial alterations to the glomerular basement membrane, podocytes, endothelial cells, widening of Bowman's space, and vacuolation of the cells lining the parietal layer, which were substantially protected by RES + QUR. Furthermore, a significant (p < 0.0001) positive correlation was observed between either glomerular basement membrane or podocyte foot processes and these parameters, urea, creatinine, MDA, and TNF-α. Thus, we conclude that APAP induces alterations to the glomerulus ultrastructure, which is protected by resveratrol plus quercetin, which also reduces blood levels of urea and creatinine, and biomarkers of oxidative stress and inflammation.

Site-specific protein modification by 3-n-butylphthalide in primary hepatocytes: Covalent protein adducts diminished by glutathione and N-acetylcysteine

AIMS

3-n-Butylphthalide (NBP) is widely used for the treatment of cerebral ischaemic stroke but can causeliver injury in clinical practice. This study aims to elucidate the underlying mechanisms and propose potential preventive strategies.

MAIN METHODS

NBP and its four major metabolites, 3-hydroxy-NBP (3-OH-NBP), 10-hydroxy-NBP, 10-keto-NBP and NBP-11-oic acid, were synthesized and evaluated in primary human or rat hepatocytes (PHHs, PRHs). NBP-related substances or amino acid adducts were identified and semi-quantitated by ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). The target proteins and binding sites were identified by shotgun proteomics based on peptide mass fingerprinting coupled with tandem mass spectrometry and verified by molecular docking.

KEY FINDINGS

The toxicity of NBP and its four major metabolites were compared in both PHHs and PRHs, and 3-OH-NBP was found to be the most toxic metabolite. 3-OH-NBP induced remarkable cell death and oxidative stresses in hepatocytes, which correlated well with the levels of glutathione and N-acetylcysteine adducts (3-GSH-NBP and 3-NAC-NBP) in cell supernatants. Additionally, 3-OH-NBP covalently conjugated with intracellular Cys, Lys and Ser, with preferable binding to Cys sites at Myh9 Cys1380, Prdx4 Cys53, Vdac2 Cys48 and Vdac3 Cys36. Furthermore, we found that CYP3A4 induction by rifampicin augmented NBP-induced cell toxicity and supplementing with GSH or NAC alleviated the oxidative stresses and reactive metabolites caused by 3-OH-NBP.

SIGNIFICANCE

Our work suggests that glutathione depletion, mitochondrial injury and covalent protein modification are the main causes of NBP-induced hepatotoxicity, which may be prevented by exogenous GSH or NAC supplementation and avoiding concomitant use of CYP3A4 inducers.

Comparing development of liver injury using the two versus three bag acetylcysteine regimen despite early treatment in paracetamol overdose

INTRODUCTION

Some studies have reported that early administration of acetylcysteine using a 3-bag regimen may not fully prevent development of liver injury in some patients. We compared the incidence of acute liver injury (ALI) in patients receiving acetylcysteine within eight hours of ingestion between the two-bag acetylcysteine regimen (200 mg/kg over four hours, 100 mg/kg over 16 h) and the three-bag regimen (150 mg/kg over 1 h, 50 mg/kg over 4 h, 100 mg/kg over 16 h).

METHOD

This was a retrospective cohort study of the two-bag and three-bag acetylcysteine regimens from Monash Health, Victoria, Australia (2009-2020), compared to the three-bag acetylcysteine regimen data from the Canadian Acetaminophen Overdose Study (CAOS) database (1980-2005). The inclusion criteria included patients with an acute single ingestion of paracetamol; normal aminotransferases on presentation and acetylcysteine administered within eight hours post-overdose. The primary outcome was development of ALI (defined as: peak aminotransferase >150 IU/L).

RESULTS

At Monash Health, 191 patients were treated with the two-bag acetylcysteine regimen, and 180 patients with the three-bag regimen. The CAOS cohort provided 515 patients treated with the three-bag regimen. ALI developed in 1.6% (3/191) of the two-bag Monash Health group, 2.2% (4/180) of the three-bag Monash Health group (difference -0.6%, p 0.7), and 2.9% (15/515) of the three-bag CAOS group (difference compared to two-bag -1.3%, p 0.4). Hepatotoxicity (ALT >1000) developed in 0.5% (1/191) of patients treated with the two-bag regimen, 1.7% (3/180) in the Monash Health three-bag regimen and 1% (5/515) of the three-bag CAOS group. There were no statistically significant differences between groups.

CONCLUSIONS

ALI and hepatotoxicity were observed in a small, comparable percentage of patients despite early acetylcysteine administration using the two-bag and three-bag regimens. Repeating blood tests at the end of acetylcysteine treatment will identify these patients and indicate those requiring continuation of acetylcysteine.

Mitochondrial Dysfunction and Oxidative Stress in Liver Transplantation and Underlying Diseases: New Insights and Therapeutics

Mitochondria are essential organelles for cellular energy and metabolism. Like with any organ, the liver highly depends on the function of these cellular powerhouses. Hepatotoxic insults often lead to an impairment of mitochondrial activity and an increase in oxidative stress, thereby compromising the metabolic and synthetic functions. Mitochondria play a critical role in ATP synthesis and the production or scavenging of free radicals. Mitochondria orchestrate many cellular signaling pathways involved in the regulation of cell death, metabolism, cell division, and progenitor cell differentiation. Mitochondrial dysfunction and oxidative stress are closely associated with ischemia-reperfusion injury during organ transplantation and with different liver diseases, including cholestasis, steatosis, viral hepatitis, and drug-induced liver injury. To develop novel mitochondria-targeting therapies or interventions, a better understanding of mitochondrial dysfunction and oxidative stress in hepatic pathogenesis is very much needed. Therapies targeting mitochondria impairment and oxidative imbalance in liver diseases have been extensively studied in preclinical and clinical research. In this review, we provide an overview of how oxidative stress and mitochondrial dysfunction affect liver diseases and liver transplantation. Furthermore, we summarize recent developments of antioxidant and mitochondria-targeted interventions.

The Potential Role of Efficacy and Safety Evaluation of N-Acetylcysteine Administration During Liver Procurement. The NAC-400 Single Center Randomized Controlled Trial

BACKGROUND

N-acetylcysteine infusions have been widely used to reduce ischemia/reperfusion damage to the liver; however, convincing evidence of their benefits is lacking.

OBJECTIVE

To perform the largest randomized controlled trial to compare the impact of N-acetylcysteine infusion during liver procurement on liver transplant outcomes.

METHODS

Single center, randomized trial with patients recruited from La Fe University Hospital, Spain, from February 2012 to January 2016. A total of 214 grafts were transplanted and randomized to the N-acetylcysteine group (n = 113) or to the standard protocol without N-acetylcysteine (n = 101). The primary endpoint was allograft dysfunction (Olthoff criteria). Secondary outcomes included metabolomic biomarkers of oxidative stress levels, interactions between cold ischemia time and alanine aminotransferase level and graft and patient survival (ID no. NCT01866644).

RESULTS

The incidence of primary dysfunction was 34% (31% in the N-acetylcysteine group and 37.4% in the control group [P = 0.38]). N-acetylcysteine administration reduced the alanine aminotransferase level when cold ischemia time was longer than 6 h (P = 0.0125). Oxidative metabolites (glutathione/oxidized glutathione and ophthalmic acid) were similar in both groups (P > 0.05). Graft and patient survival rates at 12 mo and 3 y were similar between groups (P = 0.54 and P = 0.69, respectively).

CONCLUSIONS

N-acetylcysteine administration during liver procurement does not improve early allograft dysfunction according to the Olthoff classification. However, when cold ischemia time is longer than 6 h, N-acetylcysteine improves postoperative ALT levels.

Paracetamol toxicity in mild overdose in combination with opioids: A retrospective observational study

AIMS

Toxicity in paracetamol overdose with opioid co-ingestion is poorly understood. We compared outcomes in both paracetamol-only and paracetamol-opioid overdoses to determine whether toxicity differed significantly between the groups, and to assess the utility of the ratio of measured plasma paracetamol concentration relative to the 4-hour nomogram-adjusted level (APAP_pl /APAP_t ).

METHODS

We conducted a retrospective observational study of all patients (n = 1159) presenting to 2 large UK hospitals between 2005 and 2013 with acute single-dose ingestion paracetamol overdose, with (n = 221) or without (n = 938) opioid co-ingestion. Adverse outcomes included biomarkers of hepatotoxicity and the need for extended treatment. Several outcomes were assessed in relation to the APAP_pl /APAP_t ratio.

RESULTS

Median ingested dose of paracetamol was low in both groups (10 g). Statistical comparison of the median APAP_pl /APAP_t ratios showed a significant difference (0.65 vs. 0.56 for the paracetamol-only and paracetamol-opioid groups respectively, P = .0329). Although there was a trend towards a lower risk of predefined toxic outcomes with opioid co-ingestion, statistical analysis did not show a significant difference, with outcomes for the paracetamol-only and paracetamol-opioid groups including the following: alanine transaminase >2× upper limit of normal, 7.7 vs. 5.7% (P = .6480); alanine transaminase >1000 IU/L, 2.4 vs. 0% (P = .2145); international normalised ratio > 1.3, 8.6 vs. 4.4% (P = .2774); and transfer to tertiary liver unit, 0.2 vs. 0% (P nonsignificant).

CONCLUSION

Our study does not support a change in current clinical practise beyond standard testing at 4 hours or longer post ingestion for mixed low dose paracetamol-opioid overdose.

Acetaminophen Poisoning

Acetaminophen is a common medication taken in deliberate self-poisoning and unintentional overdose. It is the commonest cause of severe acute liver injury in Western countries. The optimal management of most acetaminophen poisonings is usually straightforward. Patients who present early should be offered activated charcoal and those at risk of acute liver injury should receive acetylcysteine. This approach ensures survival in most. The acetaminophen nomogram is used to assess the need for treatment in acute immediate-release overdoses with a known time of ingestion. However, scenarios that require different management pathways include modified-release, large/massive, and repeated supratherapeutic ingestions.

Population Pharmacokinetic Analysis of N-Acetylcysteine in Pediatric Patients With Inherited Metabolic Disorders Undergoing Hematopoietic Stem Cell Transplant

N-acetylcysteine (NAC) has been used in patients with cerebral adrenoleukodystrophy as an antioxidant agent in association with hematopoietic stem cell transplant (HSCT). However, an understanding of the pharmacokinetic characteristics of intravenous NAC dosing in these patients is limited. If and how NAC pharmacokinetics change following the transplant is unknown. Toward that end, a total of 260 blood samples obtained from 18 pediatric patients with inherited metabolic disorders who underwent HSCT were included in a population pharmacokinetic analysis using nonlinear mixed-effects modeling. NAC clearance (CL) and volume of distribution (V) were explored on 3 occasions: -7, +7, and +21 days relative to transplant. Additionally, the effect of transplant procedure on NAC disposition was explored by accounting for between-occasion variability. The covariate OCC was modeled as a fixed-effect parameter on CL and/or V1. A 2-compartment model adequately described the pharmacokinetics of total NAC. Weight-based allometric scaling on pharmacokinetic parameters was assumed using standard coefficients. Estimates for CL, central (V1), and peripheral volume (V2), and intercompartment clearance were 14.7 L/h, 23.2 L, 17.1 L, 3.99 L/h, respectively, for a 70-kg person. The data only supported between-subject variability in CL (12%) and V1 (41%). Residual variability was estimated to be 16%. HSCT did not change CL and V1 significantly, and analysis across occasions did not reveal any trends. Pharmacokinetic parameter estimates were in general comparable to those reported previously in different populations. These results suggest that dosing of NAC does not need to be altered following HSCT.

Dietary thiols accelerate aging of C. elegans

Glutathione (GSH) is the most abundant cellular antioxidant. As reactive oxygen species (ROS) are widely believed to promote aging and age-related diseases, and antioxidants can neutralize ROS, it follows that GSH and its precursor, N-acetyl cysteine (NAC), are among the most popular dietary supplements. However, the long- term effects of GSH or NAC on healthy animals have not been thoroughly investigated. We employed C. elegans to demonstrate that chronic administration of GSH or NAC to young or aged animals perturbs global gene expression, inhibits skn-1-mediated transcription, and accelerates aging. In contrast, limiting the consumption of dietary thiols, including those naturally derived from the microbiota, extended lifespan. Pharmacological GSH restriction activates the unfolded protein response and increases proteotoxic stress resistance in worms and human cells. It is thus advantageous for healthy individuals to avoid excessive dietary antioxidants and, instead, rely on intrinsic GSH biosynthesis, which is fine-tuned to match the cellular redox status and to promote homeostatic ROS signaling.

The mechanism of action of N-acetylcysteine (NAC): The emerging role of H2S and sulfane sulfur species

Initially adopted as a mucolytic about 60 years ago, the cysteine prodrug N-acetylcysteine (NAC) is the standard of care to treat paracetamol intoxication, and is included on the World Health Organization's list of essential medicines. Additionally, NAC increasingly became the epitome of an "antioxidant". Arguably, it is the most widely used "antioxidant" in experimental cell and animal biology, as well as clinical studies. Most investigators use and test NAC with the idea that it prevents or attenuates oxidative stress. Conventionally, it is assumed that NAC acts as (i) a reductant of disulfide bonds, (ii) a scavenger of reactive oxygen species and/or (iii) a precursor for glutathione biosynthesis. While these mechanisms may apply under specific circumstances, they cannot be generalized to explain the effects of NAC in a majority of settings and situations. In most cases the mechanism of action has remained unclear and untested. In this review, we discuss the validity of conventional assumptions and the scope of a newly discovered mechanism of action, namely the conversion of NAC into hydrogen sulfide and sulfane sulfur species. The antioxidative and cytoprotective activities of per- and polysulfides may explain many of the effects that have previously been ascribed to NAC or NAC-derived glutathione.

Role of Noncoding RNAs in Acetaminophen-Induced Liver Injury

Genomic and transcriptomic analyses have well established that the major fraction of the mammalian genome is transcribed into different classes of RNAs ranging in size from a few nucleotides to hundreds of thousands of nucleotides, which do not encode any protein. Some of these noncoding RNAs (ncRNAs) are directly or indirectly linked to the regulation of expression or functions of 25,000 proteins coded by <2% of the human genome. Among these regulatory RNAs, microRNAs are small (2125 nucleotides) RNAs that are processed from precursor RNAs that have stemloop structure, whereas noncoding RNAs >200 nucleotides are termed long noncoding RNAs (lncRNAs). Circular RNAs (circRNAs) are newly identified lncRNA members that are generated by back-splicing of primary transcripts. The functions of ncRNAs in modulating liver toxicity of xenobiotics are emerging only recently. Acetaminophen (N-acetyl-para-aminophenol, paracetamol or APAP) is a safe analgesic and antipyretic drug at the therapeutic dose. However, it can cause severe liver toxicity that may lead to liver failure if overdosed or combined with alcohol, herbs, or other xenobiotics. This review discusses the role of ncRNAs in acetaminophen metabolism, toxicity, and liver regeneration after APAP-induced liver injury (AILI).

Novel Therapeutic Approaches Against Acetaminophen-induced Liver Injury and Acute Liver Failure

Liver injury and acute liver failure caused by acetaminophen (APAP, N-acetyl-p-aminophenol, paracetamol) overdose is a significant clinical problem in most western countries. The only clinically approved antidote is N-acetylcysteine (NAC), which promotes the recovery of hepatic GSH. If administered during the metabolism phase, GSH scavenges the reactive metabolite N-acetyl-p-benzoquinone imine. More recently, it was shown that NAC can also reconstitute mitochondrial GSH levels and scavenge reactive oxygen/peroxynitrite and can support mitochondrial bioenergetics. However, NAC has side effects and may not be efficacious after high overdoses. Repurposing of additional drugs based on their alternate mechanisms of action could be a promising approach. 4-Methylpyrazole (4MP) was shown to be highly effective against APAP toxicity by inhibiting cytochrome P450 enzymes in mice and humans. In addition, 4MP is a potent c-Jun N-terminal kinase inhibitor expanding its therapeutic window. Calmangafodipir (CMFP) is a SOD mimetic, which is well tolerated in patients and has the potential to be effective after severe overdoses. Other drugs approved for humans such as metformin and methylene blue were shown to be protective in mice at high doses or at human therapeutic doses, respectively. Additional protective strategies such as enhancing antioxidant activities, Nrf2-dependent gene induction and autophagy activation by herbal medicine components are being evaluated. However, at this point, their mechanistic insight is limited, and the doses used are high. More rigorous mechanistic studies are needed to advance these herbal compounds. Nevertheless, based on recent studies, 4-methylpyrazole and calmangafodipir have realistic prospects to become complimentary or even alternative antidotes to NAC for APAP overdose.

Glutamate homeostasis and dopamine signaling: Implications for psychostimulant addiction behavior

Cocaine, amphetamine, and methamphetamine abuse disorders are serious worldwide health problems. To date, there are no FDA-approved medications for the treatment of these disorders. Elucidation of the biochemical underpinnings contributing to psychostimulant addiction is critical for the development of effective therapies. Excitatory signaling and glutamate homeostasis are well known pathophysiological substrates underlying addiction-related behaviors spanning multiple types of psychostimulants. To alleviate relapse behavior to psychostimulants, considerable interest has focused on GLT-1, the major glutamate transporter in the brain. While many brain regions are implicated in addiction behavior, this review focuses on two regions well known for their role in mediating the effects of cocaine and amphetamines, namely the nucleus accumbens (NAc) and the ventral tegmental area (VTA). In addition, because many investigators have utilized Cre-driver lines to selectively control gene expression in defined cell populations relevant for psychostimulant addiction, we discuss potential off-target effects of Cre-recombinase that should be considered in the design and interpretation of such experiments.

Supplementation with γ-glutamylcysteine (γ-GC) lessens oxidative stress, brain inflammation and amyloid pathology and improves spatial memory in a murine model of AD

INTRODUCTION

The accumulation of oxidative stress, neuroinflammation and abnormal aggregation of amyloid β-peptide (Aβ) have been shown to induce synaptic dysfunction and memory deficits in Alzheimer's disease (AD). Cellular depletion of the major endogenous antioxidant Glutathione (GSH) has been linked to cognitive decline and the development of AD pathology. Supplementation with γ-glutamylcysteine (γ-GC), the immediate precursor and the limiting substrate for GSH biosynthesis, can transiently augment cellular GSH levels by bypassing the regulation of GSH homeostasis.

METHODS

In the present study, we investigated the effect of dietary supplementation of γ-GC on oxidative stress and Aβ pathology in the brains of APP/PS1 mice. The APP/PS1 mice were fed γ-GC from 3 months of age with biomarkers of apoptosis and cell death, oxidative stress, neuroinflammation and Aβ load being assessed at 6 months of age.

RESULTS

Our data showed that supplementation with γ-GC lowered the levels of brain lipid peroxidation, protein carbonyls and apoptosis, increased both total GSH and the glutathione/glutathione disulphide (GSH/GSSG) ratio and replenished ATP and the activities of the antioxidant enzymes (superoxide dismutase (SOD), catalase, glutamine synthetase and glutathione peroxidase (GPX)), the latter being a key regulator of ferroptosis. Brain Aβ load was lower and acetylcholinesterase (AChE) activity was markedly improved compared to APP/PS1 mice fed a standard chow diet. Alteration in brain cytokine levels and matrix metalloproteinase enzymes MMP-2 and MMP-9 suggested that γ-GC may lower inflammation and enhance Aβ plaque clearance in vivo. Spatial memory was also improved by γ-GC as determined using the Morris water maze.

CONCLUSION

Our data collectively suggested that supplementation with γ-GC may represent a novel strategy for the treatment and/or prevention of cognitive impairment and neurodegeneration.

Macrophage-Inducible C-Type Lectin Signaling Exacerbates Acetaminophen-Induced Liver Injury by Promoting Kupffer Cell Activation in Mice

Overdose of acetaminophen (APAP) has become one of the most frequent causes of acute liver failure. Macrophage-inducible C-type lectin (Mincle) acts as a key moderator in immune responses by recognizing spliceosome-associated protein 130 (SAP130), which is an endogenous ligand released by necrotic cells. This study aims to explore the function of Mincle in APAP-induced hepatotoxicity. Wild-type (WT) and Mincle knockout (KO) mice were used to induce acute liver injury by injection of APAP. The hepatic expressions of Mincle, SAP130, and Mincle signaling intermediate (Syk) were markedly upregulated after the APAP challenge. Mincle KO mice showed attenuated injury in the liver, as shown by reduced pathologic lesions, decreased alanine aminotransferase and aspartate aminotransferase levels, downregulated levels of inflammatory cytokines, and decreased neutrophil infiltration. Consistently, inhibition of Syk signaling by GS9973 alleviated APAP hepatotoxicity. Most importantly, Kupffer cells (KCs) were found as the major cellular source of Mincle. The depletion of KCs abolished the detrimental role of Mincle, and the adoptive transfer of WT KC to Mincle KO mice partially reversed the hyporesponsiveness to hepatotoxicity induced by APAP. Furthermore, the expression levels of interleukin (IL)-1β and neutrophil-attractant CXC chemokines were substantially lower in KCs isolated from APAP-treated Mincle KO mice compared with those from WT mice. Similar results were found in primary Mincle KO KCs treated with a ligand of Mincle (trehalose-6,6-dibehenate) or in conditioned media obtained from APAP-treated hepatocytes. Collectively, Mincle can regulate the inflammatory response of KCs, which is necessary for the complete progression of hepatotoxicity induced by APAP. SIGNIFICANCE STATEMENT: Acetaminophen (APAP) overdose is becoming a main cause of drug-induced acute liver damage in the developed world. This study showed that macrophage-inducible C-type lectin (Mincle) deletion or inhibition of Mincle downstream signaling attenuates APAP hepatotoxicity. Furthermore, Mincle as a modulator of Kupffer cell activation contributes to the full process of hepatotoxicity induced by APAP. This mechanism will offer valuable insights to overcome the limitation of APAP hepatotoxicity treatment.

Increased risk of acute liver failure by pain killer drugs in NAFLD: Focus on nuclear receptors and their coactivators

Non-alcoholic fatty liver disease (NAFLD) is a global condition characterized by an accumulation of lipids in the hepatocytes. NAFLD ranges from simple steatosis, a reversible and relatively benign condition, to fibrosis with non-alcoholic steatohepatitis (NASH), potentially leading to cirrhosis and hepatocarcinoma. NAFLD can increase the susceptibility to severe liver injury with eventual acute liver failure induced by specific hepatotoxic drugs, including acetaminophen (APAP), which is commonly used as analgesic and antipyretic. Although several animal models have been used to clarify the predisposing role of hepatic steatosis to APAP intoxication, the exact mechanism is still not clear. Here, we shed a light into the association between NAFLD and APAP toxicity by examining the peculiar role of nuclear receptor peroxisome proliferator-activated receptor α (PPARα) and coactivator peroxisome proliferator-activated receptor gamma coactivator 1-β (PGC-1β) in driving fatty acid metabolism, inflammation and mitochondria redox balance. The knowledge of the mechanism that exposes patients with NAFLD to higher risk of acute liver failure by pain killer drug is the first step to eventually claim for a reduction of the maximal diurnal dose of APAP for subjects with liver steatosis.

Locus-Level Changes in Macular Sensitivity in Patients with Retinitis Pigmentosa Treated with Oral N-acetylcysteine

PURPOSE

To identify characteristics of loci associated with locus-level sensitivity loss or improvement during treatment with N-acetylcysteine (NAC) in retinitis pigmentosa (RP).

DESIGN

Retrospective analysis of prospectively collected data in the FIGHT RP clinical trial.

METHODS

Patients (n = 30) were treated with 600, 1,200, or 1,800 mg of NAC twice daily for 3 months and then 3 times/day for 3 months. Microperimetry locus-level changes between baseline and month 6 were correlated with baseline characteristics of loci using regression models. The main outcome measurement was locus-level sensitivity change ≥6 dB.

RESULTS

Baseline mean sensitivity (3,468 loci; 51 evaluable eyes) was 7.7 dB and for foveal, parafoveal, and perifoveal loci were 20.2, 11.8, and 5.8 dB. During treatment, 287 loci (8.28%) increased ≥6 dB, and 119 of 1,613 loci with baseline sensitivity ≥6 dB decreased ≥6 dB (7.38%). A higher dose of NAC was associated with lower likelihood of sensitivity loss ≥6 dB (P = .033). Loci with low baseline sensitivity were more likely to decrease ≥6 dB (P = .034) but also more likely to increase ≥6 dB (P < .001). Foveal versus perifoveal loci (P < .001) and superior versus inferior loci (P = .005) were more likely to increase ≥6 dB.

CONCLUSIONS

Higher doses of NAC reduced risk of macular loci sensitivity loss in RP. Greater sensitivity depression reversibility in the fovea during treatment suggests that high foveal cone density protects cones from irreversible loss of function in RP making them more likely to show improved function during NAC treatment.

The Multifaceted Therapeutic Role of N-Acetylcysteine (NAC) in Disorders Characterized by Oxidative Stress

Oxidative stress, which results in the damage of diverse biological molecules, is a ubiquitous cellular process implicated in the etiology of many illnesses. The sulfhydryl-containing tripeptide glutathione (GSH), which is synthesized and maintained at high concentrations in all cells, is one of the mechanisms by which cells protect themselves from oxidative stress. N-acetylcysteine (NAC), a synthetic derivative of the endogenous amino acid L-cysteine and a precursor of GSH, has been used for several decades as a mucolytic and as an antidote to acetaminophen (paracetamol) poisoning. As a mucolytic, NAC breaks the disulfide bonds of heavily cross-linked mucins, thereby reducing mucus viscosity. In vitro, NAC has antifibrotic effects on lung fibroblasts. As an antidote to acetaminophen poisoning, NAC restores the hepatic GSH pool depleted in the drug detoxification process. More recently, improved knowledge of the mechanisms by which NAC acts has expanded its clinical applications. In particular, the discovery that NAC can modulate the homeostasis of glutamate has prompted studies of NAC in neuropsychiatric diseases characterized by impaired glutamate homeostasis. This narrative review provides an overview of the most relevant and recent evidence on the clinical application of NAC, with a focus on respiratory diseases, acetaminophen poisoning, disorders of the central nervous system (chronic neuropathic pain, depression, schizophrenia, bipolar disorder, and addiction), cardiovascular disease, contrast-induced nephropathy, and ophthalmology (retinitis pigmentosa).

[Acute liver failure-The importance of rapid diagnostics and early initiation of treatment]

Acute liver failure (ALF) is a rare disease with high mortality. It is defined as coagulopathy and encephalopathy in a person with a previously healthy liver. The etiology of ALF is a decisive prognostic factor and varies depending on the country of origin of the patient. Although in many countries the main triggers are hepatotropic viruses, in western industrial countries toxic medicinal causes and autoimmune phenomena predominate. The course of ALF runs through various phases. The complete picture of ALF can mostly no longer be casually treated but necessitates in particular timely contact with a transplantation center. If a causal treatment exists, the effectiveness is greatly dependent on the timing of initiation. In the best case scenario this can completely avoid liver damage. In the complete picture of ALF the main focus is on the intensive medical care of a threatening multiorgan failure. In this context new standards of treatment were established by studies on plasmapheresis.

Oral N-acetylcysteine improves cone function in retinitis pigmentosa patients in phase I trial

BACKGROUNDIn retinitis pigmentosa (RP), rod photoreceptors degenerate from 1 of many mutations, after which cones are compromised by oxidative stress. N-acetylcysteine (NAC) reduces oxidative damage and increases cone function/survival in RP models. We tested the safety, tolerability, and visual function effects of oral NAC in RP patients.METHODSSubjects (n = 10 per cohort) received 600 mg (cohort 1), 1200 mg (cohort 2), or 1800 mg (cohort 3) NAC bid for 12 weeks and then tid for 12 weeks. Best-corrected visual acuity (BCVA), macular sensitivity, ellipsoid zone (EZ) width, and aqueous NAC were measured. Linear mixed-effects models were used to estimate the rates of changes during the treatment period.RESULTSThere were 9 drug-related gastrointestinal adverse events that resolved spontaneously or with dose reduction (maximum tolerated dose 1800 mg bid). During the 24-week treatment period, mean BCVA significantly improved at 0.4 (95% CI: 0.2-0.6, P < 0.001), 0.5 (95% CI: 0.3-0.7, P < 0.001), and 0.2 (95% CI: 0.02-0.4, P = 0.03) letters/month in cohorts 1, 2, and 3, respectively. There was no significant improvement in mean sensitivity over time in cohorts 1 and 2, but there was in cohort 3 (0.15 dB/month, 95% CI: 0.04-0.26). There was no significant change in mean EZ width in any cohort.CONCLUSIONOral NAC is safe and well tolerated in patients with moderately advanced RP and may improve suboptimally functioning macular cones. A randomized, placebo-controlled trial is needed to determine if oral NAC can provide long-term stabilization and/or improvement in visual function in patients with RP.TRIAL REGISTRATIONNCT03063021.FUNDINGMr. and Mrs. Robert Wallace, Mr. and Mrs. Jonathan Wallace, Rami and Eitan Armon, Marc Sumerlin, Cassandra Hanley, and Nacuity Pharmaceuticals, Inc.

N-acetylcysteine reduces brain injury after delayed hypoxemia following traumatic brain injury

Preclinical investigations into neuroprotective agents for traumatic brain injury (TBI) have shown promise when administered before or very early after experimental TBI. However clinical trials of therapeutics demonstrating preclinical efficacy for TBI have failed to replicate these results in humans, a lost in translation phenomenon. N-acetylcysteine (NAC) is a potent anti-oxidant with demonstrated efficacy in pre-clinical TBI when administered early after primary injury. Utilizing our clinically relevant mouse model, we hypothesized that NAC administration in a clinically relevant timeframe could improve the brain's resilience to the secondary insult of hypoxemia. NAC or vehicle administered daily starting 2 h prior to hypoxemia (24 h after controlled cortical impact) for 3 doses in male mice reduced short-term axonal injury and hippocampal neuronal loss. Six month behavioral assessments including novel object recognition, socialization, Barnes maze, and fear conditioning did not reveal performance differences between sham controls and injured mice receiving NAC or saline vehicle. At 7 months after injury, NAC administered mice had reduced hippocampal neuronal loss but no reduction in lesion volume. In summary, our preclinical trial to test the neuroprotective efficacy of NAC against a secondary hypoxic insult after TBI demonstrated short and long-term neuropathological evidence of neuroprotection but a lack of detectable differences in long-term behavioral assessments between sham controls and injured mice limits conclusions on its impact on long-term neurobehavioral outcomes.

Treatment of dilated cardiomyopathy in a mouse model of Friedreich's ataxia using N-acetylcysteine and identification of alterations in microRNA expression that could be involved in its pathogenesis

Deficient expression of the mitochondrial protein, frataxin, leads to a deadly cardiomyopathy. Our laboratory reported the master regulator of oxidative stress, nuclear factor erythroid 2-related factor-2 (Nrf2), demonstrates marked down-regulation after frataxin deletion in the heart. This was due, in part, to a pronounced increase in Keap1. To assess if this can be therapeutically targeted, cells were incubated with N-acetylcysteine (NAC), or buthionine sulfoximine (BSO), which increases or decreases glutathione (GSH), respectively, or the NRF2-inducer, sulforaphane (SFN). While SFN significantly (p < 0.05) induced NRF2, KEAP1 and BACH1, NAC attenuated SFN-induced NRF2, KEAP1 and BACH1. The down-regulation of KEAP1 by NAC was of interest, as Keap1 is markedly increased in the MCK conditional frataxin knockout (MCK KO) mouse model and this could lead to the decreased Nrf2 levels. Considering this, MCK KO mice were treated with i.p. NAC (500- or 1500-mg/kg, 5 days/week for 5-weeks) and demonstrated slightly less (p > 0.05) body weight loss versus the vehicle-treated KO. However, NAC did not rescue the cardiomyopathy. To additionally examine the dys-regulation of Nrf2 upon frataxin deletion, studies assessed the role of microRNA (miRNA) in this process. In MCK KO mice, miR-144 was up-regulated, which down-regulates Nrf2. Furthermore, miRNA screening in MCK KO mice demonstrated 23 miRNAs from 756 screened were significantly (p < 0.05) altered in KOs versus WT littermates. Of these, miR-21*, miR-34c*, and miR-200c, demonstrated marked alterations, with functional clustering analysis showing they regulate genes linked to cardiac hypertrophy, cardiomyopathy, and oxidative stress, respectively.

Metabolic and mitochondrial treatments for severe paracetamol poisoning: a systematic review

BACKGROUND

Paracetamol (acetaminophen) remains a leading cause of poisoning in Europe, North America, and Australia. For over four decades, acetylcysteine has been the antidote of choice. However, despite the use of acetylcysteine, some patients who ingest very large doses of paracetamol or who reach hospital late in the course of their poisoning, develop acute liver failure. Some will develop metabolic acidosis indicating mitochondrial toxicity.

OBJECTIVE

We review the experimental and clinical data reported with the use of cimetidine, fomepizole, and calmangafodipir in the treatment of paracetamol toxicity to determine if these treatments alone or in combination with acetylcysteine might be of benefit.

METHODS

We searched Ovid Medline 1946-2020, Embase 1947-2020, Scopus 2004-2020, Cochrane Databases of Systematic Reviews (CDSR), Cochrane Central Register of Controlled Trials (CENTRAL), and clinicaltrials.gov 1997-2020 for records including the concepts of paracetamol poisoning and cimetidine, fomepizole, calmangafodipir, and acetylcysteine. We included basic science studies in animals and all available study types in humans. We reviewed the reference lists of included articles to search for references missed in the original search. We registered the protocol in PROSPERO.

RESULTS

We completed all search strategies on 20 August 2019, 27 January 2020, and 15 June 2020. These produced 6,826 citations. We identified and deleted 2,843 duplicate resulting in a total of 3,856 unique citations. After applying inclusion and exclusion criteria, 89 studies remained. The largest numbers of studies described the past use of cimetidine, and the more recent use of fomepizole.Cimetidine: There is good animal evidence that cimetidine blocks CYP 2E1 with the potential to inhibit the toxic metabolism of paracetamol. Early case reports were inconclusive regarding the benefit to humans in paracetamol poisoning. Two comparative trials found no benefit of cimetidine in paracetamol poisoning, but few patients had severe poisoning.Fomepizole: There is good animal evidence that fomepizole blocks CYP 2E1 with the potential to inhibit the toxic metabolism of paracetamol. There are no comparative trials of fomepizole for acute paracetamol poisoning. Case reports are inconclusive due to multiple other interventions including the use of acetylcysteine in all cases. The benefit of fomepizole as adjunct treatment has not been demonstrated.Calmangafodipir: Calmangafodipir, a drug mimicking superoxide dismutase, has emerged as a potential treatment for severe paracetamol toxicity because the formation of superoxide free radicals appears to explain part of the mitochondrial toxicity of extremely large paracetamol overdoses. Calmangafodipir has reached Phase I/II trial of safety in humans with acute paracetamol overdose. Planning for a Phase III study of efficacy is currently underway.

CONCLUSIONS

The vast majority of patients with acute paracetamol overdose enjoy excellent outcomes with acetylcysteine alone. Although cimetidine and fomepizole inhibit CYP 2E1 in animals, there is insufficient evidence to recommend their use either as a primary treatment or adjunct therapy in paracetamol poisoning. Calmangafodipir remains investigational.