Mitochondrial permeability transition in acetaminophen-induced necrosis and apoptosis of cultured mouse hepatocytes

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.

Sappanone A enhances hepatocyte proliferation in lipopolysaccharide-induced acute liver injury in mice by promoting injured hepatocyte apoptosis and regulating macrophage polarization

OBJECTIVES

Lipopolysaccharide (LPS), also known as endotoxin, is the main toxic component of the cell wall of gram negative bacteria, which is released after bacterial death and widely exists in the living environment. Human exposure to endotoxin may cause sepsis. The occurrence of septic liver injury is a prominent factor contributing to mortality in patients with sepsis. The purpose of this study is to explore the role of Sappanone A (SA), a homoisoflavonoid isolated from the heartwood of Caesalpinia sappan Linn., in LPS-induced acute liver injury (ALI).

METHODS

An LPS-induced ALI mouse model was used to evaluate the effects of SA on septic ALI, and murine cells were treated with LPS to explore the mechanisms underlying SA-provided effects.

RESULTS

Treating SA substantially improved LPS-induced ALI. We also performed in silico prediction and RNA-seq analysis to elucidate SA's potential mechanisms of action. The terms generated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment of predicted target proteins of SA include inflammation, oxidative stress, and apoptosis; protein-protein interaction network (PPI) analysis indicated that fas binding protein 1 (Fbf1) has the strongest correlation with SA. Consistently, RNA-seq analysis displayed that SA administration regulates cell apoptosis and inflammatory responses, which was further confirmed by checking related markers in livers of mice and murine cells challenged with LPS. Of note, SA significantly decreased the expression of Fbf1 in mouse livers, and promoted apoptosis of injured hepatocytes and hepatocyte proliferation, which were substantially abolished by Fbf1 knockdown in AML12 cells. Besides, SA could increase M2 phenotype polarization but inhibit M1 macrophage polarization in LPS-induced ALI in mice.

CONCLUSION

SA enhances hepatocyte proliferation and liver repair in LPS-induced ALI in mcie by promoting injured hepatocyte apoptosis through Fbf1 inhibition and regulating macrophage polarization.

Changes in chemical components and hepatoprotective effect of red Panax notoginseng processed by aspartic acid impregnation treatment

BACKGROUND

Red Panax notoginseng (RPN) is one of the major processed products of P. notoginseng (PN), with more effective biological activities. However, the traditional processing method of RPN has some disadvantages, such as low conversion rate of ginsenosides and long processing time.

RESULTS

In this work, we developed a green, safe, and efficient approach for RPN processing by aspartic acid impregnation pretreatment. Our results showed that the optimized temperature, steaming time, and concentration of aspartic acid were 120 °C, 1 h, and 3% respectively. The original ginsenosides in PN treated by aspartic acid (Asp-PN) were completely converted to rare saponins at 120 °C within just 1 h. The concentration of the rare ginsenosides in Asp-PN was two times higher than that in untreated RPN. In addition, we examined the protective effect of RPN and Asp-PN on acetaminophen-induced liver injury in a mouse model. The results showed that Asp-PN has significantly more potent hepatoprotective action than the RPN. The hepatoprotection of Asp-PN in acetaminophen-induced hepatotoxicity may be due to its anti-oxidative stress, anti-apoptotic, and anti-inflammatory activities.

CONCLUSION

These results indicated that aspartic acid impregnation pretreatment may provide an effective method to shorten the steaming time, improve the conversion rate of ginsenosides, and enhance hepatoprotective activity of RPN. © 2024 Society of Chemical Industry.

Effect of ferroptosis inhibitors in a murine model of acetaminophen-induced liver injury

Liver injury caused by acetaminophen (APAP) overdose is the leading cause of acute liver failure in western countries. The mode of APAP-induced cell death has been controversially discussed with ferroptosis emerging as a more recent hypothesis. Ferroptosis is characterized by ferrous iron-catalyzed lipid peroxidation (LPO) causing cell death, which can be prevented by the lipophilic antioxidants ferrostatin-1 and UAMC-3203. To assess the efficacy of these ferroptosis inhibitors, we used two murine models of APAP hepatotoxicity, APAP overdose alone or in combination with FeSO4 in fasted male C57BL/6J mice. APAP triggered severe liver injury in the absence of LPO measured as hepatic malondialdehyde (MDA) levels. In contrast, ferrous iron co-treatment aggravated APAP-induced liver injury and caused extensive LPO. Standard doses of ferrostatin-1 did not affect MDA levels or the injury in both models. In contrast, UAMC-3203 partially protected in both models and reduced LPO in the presence of ferrous iron. However, UAMC-3203 attenuated the translocation of phospho-JNK through downregulation of the mitochondrial anchor protein Sab resulting in reduced mitochondrial dysfunction and liver injury. Thus, APAP toxicity does not involve ferroptosis under normal conditions. The lack of effects of ferroptosis inhibitors in the pathophysiology indicates that ferroptosis signaling pathways are not relevant therapeutic targets.

The Role of Mechanistic Biomarkers in Understanding Acetaminophen Hepatotoxicity in Humans

Our understanding of the fundamental molecular mechanisms of acetaminophen (APAP) hepatotoxicity began in 1973 to 1974, when investigators at the US National Institutes of Health published seminal studies demonstrating conversion of APAP to a reactive metabolite that depletes glutathione and binds to proteins in the liver in mice after overdose. Since then, additional groundbreaking experiments have demonstrated critical roles for mitochondrial damage, oxidative stress, nuclear DNA fragmentation, and necrotic cell death as well. Over the years, some investigators have also attempted to translate these mechanisms to humans using human specimens from APAP overdose patients. This review presents those studies and summarizes what we have learned about APAP hepatotoxicity in humans so far. Overall, the mechanisms of APAP hepatotoxicity in humans strongly resemble those discovered in experimental mouse and cultured hepatocyte models, and emerging biomarkers also suggest similarities in liver repair. The data not only validate the first mechanistic studies of APAP-induced liver injury performed 50 years ago but also demonstrate the human relevance of numerous studies conducted since then. SIGNIFICANCE STATEMENT: Human studies using novel translational, mechanistic biomarkers have confirmed that the fundamental mechanisms of acetaminophen (APAP) hepatotoxicity discovered in rodent models since 1973 are the same in humans. Importantly, these findings have guided the development and understanding of treatments such as N-acetyl-l-cysteine and 4-methylpyrazole over the years. Additional research may improve not only our understanding of APAP overdose pathophysiology in humans but also our ability to predict and treat serious liver injury in patients.

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.

Effects of Moringa oleifera Leaf Extract on Liver Histopathology: A Systematic Review

Introduction

Moringa leaves (Moringa oleifera), which are members of the Moringaceae family, are one of the herbal plants that are widely known in Indonesia. Phytochemical contents of moringa leaf, such as flavonoid, quercetin, and phenolic acid, are believed to have an effect on improvement of NAFLD. Therefore, moringa leaf is considered as one the herbal plants that can be used as supplementation in the form of adjuvant therapy to NAFLD. The study objective of our research is to review the effect of giving moringa leaf to the liver, especially the histopathologic features. This study will be conducted on literature review research design, more specifically in the form of a systematic review. Research Method. Five major electronic web databases, including PubMed, Cochrane Library, Google Scholar, Scopus, and ScienceDirect, were used in identifying literature from 2014 to 2023.

Results

From a comprehensive analysis of 13 relevant literature sources, we elucidate the impact of Moringa oleifera leaf extract on liver histopathology, glucose, and lipid metabolism. Furthermore, we provide insights into its safety profile concerning human health.

Conclusion

The phytochemical content of Moringa oleifera leaf extract had shown a significant benefit in plant medicinal sector. From the research that had been done, Moringa oleifera leaf extract contributes to give significant improvement on liver histopathological features, glucose, and lipid metabolism on animal sample model.

Acetaminophen overdose causes a breach of the blood-bile barrier in mice but not in rats

Acetaminophen (APAP) is known to cause a breach of the blood-bile barrier in mice that, via a mechanism called futile bile acid (BA) cycling, increases BA concentrations in hepatocytes above cytotoxic thresholds. Here, we compared this mechanism in mice and rats, because both species differ massively in their susceptibility to APAP and compared the results to available human data. Dose and time-dependent APAP experiments were performed in male C57BL6/N mice and Wistar rats. The time course of BA concentrations in liver tissue and in blood was analyzed by MALDI-MSI and LC-MS/MS. APAP and its derivatives were measured in the blood by LC-MS. APAP-induced liver damage was analyzed by histopathology, immunohistochemistry, and by clinical chemistry. In mice, a transient increase of BA in blood and in peri-central hepatocytes preceded hepatocyte death. The BA increase coincided with oxidative stress in liver tissue and a compromised morphology of bile canaliculi and immunohistochemically visualized tight junction proteins. Rats showed a reduced metabolic activation of APAP compared to mice. However, even at very high doses that caused cell death of hepatocytes, no increase of BA concentrations was observed neither in liver tissue nor in the blood. Correspondingly, no oxidative stress was detectable, and the morphology of bile canaliculi and tight junction proteins remained unaltered. In conclusion, different mechanisms cause cell death in rats and mice, whereby oxidative stress and a breach of the blood-bile barrier are seen only in mice. Since transient cholestasis also occurs in human patients with APAP overdose, mice are a clinically relevant species to study APAP hepatotoxicity but not rats.

Natural Products That Protect Against Acetaminophen Hepatotoxicity: A Call for Increased Rigor in Preclinical Studies of Dietary Supplements

Acetaminophen (APAP) overdose is one of the most common causes of acute liver injury. The current standard-of-care treatment for APAP hepatotoxicity, N-acetyl-l-cysteine, is highly effective when administered early after overdose, but loses efficacy in later-presenting patients. As a result, there is interest in the identification of new treatments for APAP overdose patients. Natural products are a promising source of new treatments because many are purported to have hepatoprotective effects. In fact, a great deal of research has been done to identify natural products that can protect against APAP-induced liver injury. However, serious concerns have been raised about the rigor and human relevance of these studies. Here, we systematically reviewed the APAP-natural product literature from 2013 to 2023 to determine the veracity of these concerns and the scope of the potential problem. The results substantiate the concerns that have been previously raised and point to concrete steps that can be taken to improve APAP-natural product research.

Gasdermin-E-Dependent Non-Canonical Pyroptosis Promotes Drug-Induced Liver Failure by Promoting CPS1 deISGylation and Degradation

Drug-induced liver injury (DILI) is a significant global health issue that poses high mortality and morbidity risks. One commonly observed cause of DILI is acetaminophen (APAP) overdose. GSDME is an effector protein that induces non-canonical pyroptosis. In this study, the activation of GSDME, but not GSDMD, in the liver tissue of mice and patients with APAP-DILI is reported. Knockout of GSDME, rather than GSDMD, in mice protected them from APAP-DILI. Mice with hepatocyte-specific rescue of GSDME reproduced APAP-induced liver injury. Furthermore, alterations in the immune cell pools observed in APAP-induced DILI, such as the replacement of TIM4+ resident Kupffer cells (KCs) by monocyte-derived KCs, Ly6C+ monocyte infiltration, MerTk+ macrophages depletion, and neutrophil increase, reappeared in mice with hepatocyte-specific rescue of GSDME. Mechanistically, APAP exposure led to a substantial loss of interferon-stimulated gene 15 (ISG15), resulting in deISGylation of carbamoyl phosphate synthetase-1 (CPS1), promoted its degradation via K48-linked ubiquitination, causing ammonia clearance dysfunction. GSDME deletion prevented these effects. Delayed administration of dimethyl-fumarate inhibited GSDME cleavage and alleviated ammonia accumulation, mitigating liver injury. This findings demonstrated a previously uncharacterized role of GSDME in APAP-DILI by promoting pyroptosis and CPS1 deISGylation, suggesting that inhibiting GSDME can be a promising therapeutic option for APAP-DILI.

Hepatocyte miR-21-5p-deficiency alleviates APAP-induced liver injury by inducing PPARγ and autophagy

Acetaminophen (APAP)-induced liver injury is one of the most frequent causes of acute liver failure worldwide. Significant increases in the levels of miRNA-21 in both liver tissues and plasma have been observed in APAP-overdosed animals and humans. However, the mechanistic effect of miRNA-21 on acute liver injury remains unknown. In this study, we generated a new hepatocyte-specific miRNA-21 knockout (miR-21-HKO) mouse line. miR-21-HKO and the background-matched sibling wild-type (WT) mice were treated with a toxic dose of APAP. Compared with WT mice, miR-21 HKO mice showed an increased survival, a reduction of necrotic hepatocytes, and an increased expression of light chain 3 beta, which suggested an autophagy activation. The expression of PPARγ was highly induced in the livers of miR-21-HKO mice after a 2-h APAP treatment, which preceded the activation of LC3B at the 12 h APAP treatment. miR-21 negatively regulated PPARγ protein expression by targeting its 3'-UTR. When PPARγ function was blocked by a potent antagonist GW9662 in miR-21-HKO mice, the autophage activation was significantly diminished, suggesting an indispensable role of PPARγ signaling pathway in miR-21-mediated hepatotoxicity. Taken together, hepatocyte-specific depletion of miRNA-21 alleviated APAP-induced hepatotoxicity by activating PPARγ and autophagy, demonstrating a crucial new regulatory role of miR-21 in APAP-mediated liver injury.

Synergistic suppression of ovarian cancer by combining NRF2 and GPX4 inhibitors: in vitro and in vivo evidence

Ovarian cancer is a significant challenge in women's health due to the lack of effective screening and diagnostic methods, often leading to late detection and the highest mortality rate among all gynecologic tumors worldwide. Recent research has shown that ovarian cancer has an "iron addiction" phenotype which makes it vulnerable to ferroptosis inducers. We tested the combination of NRF2-targeted inhibitors with GPX4-targeted inhibitors in ovarian cancer through in vitro and in vivo experiment. The data showed that combination treatment effectively suppressed adherent cell growth, inhibited suspended cell spheroid formation, and restrained the ability of spheroid formation in 3D-culture. Mechanistically, the combination induced accumulation of ROS, 4-HNE, as well as activation of caspase-3 which indicates that this combination simultaneously increases cell ferroptosis and apoptosis. Notably, inhibition of GPX4 or NRF2 can suppress ovarian cancer spreading and growth in the peritoneal cavity of mice, while the combination of NRF2 inhibitor ML385 with GPX4 inhibitors showed a significant synergistic effect compared to individual drug treatment in a syngeneic mouse ovarian cancer model. Overall, these findings suggest that combining NRF2 inhibitors with GPX4 inhibitors results in a synergy suppression of ovarian cancer in vitro and in vivo, and maybe a promising therapeutic strategy for the treatment of ovarian cancer.

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.

Biomarker discovery in acetaminophen hepatotoxicity: leveraging single-cell transcriptomics and mechanistic insight

INTRODUCTION

Acetaminophen (APAP) overdose is the leading cause of drug-induced liver injury and can cause a rapid progression to acute liver failure (ALF). Therefore, the identification of prognostic biomarkers to determine which patients will require a liver transplant is critical for APAP-induced ALF.

AREAS COVERED

We begin by relating the mechanistic investigations in mouse models of APAP hepatotoxicity to the human APAP overdose pathophysiology. We draw insights from the established sequence of molecular events in mice to understand the progression of events in the APAP overdose patient. Through this mechanistic understanding, several new biomarkers, such as CXCL14, have recently been evaluated. We also explore how single-cell RNA sequencing, spatial transcriptomics, and other omics approaches have been leveraged for identifying novel biomarkers and how these approaches will continue to push the field of biomarker discovery forward.

EXPERT OPINION

Recent investigations have elucidated several new biomarkers or combination of markers such as CXCL14, a regenerative miRNA signature, a cell death miRNA signature, hepcidin, LDH, CPS1, and FABP1. While these biomarkers are promising, they all require further validation. Larger cohort studies analyzing these new biomarkers in the same patient samples, while adding these candidate biomarkers to prognostic models will further support their clinical utility.

The Evolution of Circulating Biomarkers for Use in Acetaminophen/Paracetamol-Induced Liver Injury in Humans: A Scoping Review

Acetaminophen (APAP) is a widely used drug, but overdose can cause severe acute liver injury. The first reports of APAP hepatotoxicity in humans were published in 1966, shortly after the development of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) as the first biomarkers of liver injury as opposed to liver function. Thus, the field of liver injury biomarkers has evolved alongside the growth in APAP hepatotoxicity incidence. Numerous biomarkers have been proposed for use in the management of APAP overdose patients in the intervening years. Here, we comprehensively review the development of these markers from the 1960s to the present day and briefly discuss possible future directions.

Nrf2 as a therapeutic target in acetaminophen hepatotoxicity: A case study with sulforaphane

Acetaminophen (APAP) overdose can cause severe liver injury and acute liver failure. The only clinically approved antidote, N-acetylcysteine (NAC), is highly effective but has a narrow therapeutic window. In the last 2 decades, activation of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates acute phase proteins and antioxidant defense genes, has emerged as a putative new therapeutic target against APAP hepatotoxicity. However, virtually all studies that propose Nrf2 activation as mechanism of protection used prolonged pretreatment, which is not a clinically feasible approach to treat a drug overdose. Therefore, the objective of this study was to assess if therapeutic activation of Nrf2 is a viable approach to treat liver injury after APAP overdose. We used the water-soluble Nrf2 activator sulforaphane (SFN; 5 mg/kg) in a murine model of APAP hepatotoxicity (300 mg/kg). Our results indicate that short-term treatment (≤3 h) with SFN alone did not activate Nrf2 or its target genes. However, posttreatment with SFN after APAP partially protected at 6 h likely due to more rapid activation of the Nrf2-target gene heme oxygenase-1. A direct comparison of SFN with NAC given at 1 h after APAP showed a superior protection with NAC, which was maintained at 24 h unlike with SFN. Thus, Nrf2 activators have inherent problems like the need to create a cellular stress to activate Nrf2 and delayed adaptive responses which may hamper sustained protection against APAP hepatotoxicity. Thus, compared to the more direct acting antidote NAC, Nrf2 activators are less suitable for this indication.

Lack of mitochondrial Cyp2E1 drives acetaminophen-induced ER stress-mediated apoptosis in mouse and human kidneys: Inhibition by 4-methylpyrazole but not N-acetylcysteine

Acetaminophen (APAP) overdose causes liver injury and acute liver failure, as well as acute kidney injury, which is not prevented by the clinical antidote N-acetyl-L-cysteine (NAC). The absence of therapeutics targeting APAP-induced nephrotoxicity is due to gaps in understanding the mechanisms of renal injury. APAP metabolism through Cyp2E1 drives cell death in both the liver and kidney. We demonstrate that Cyp2E1 is localized to the proximal tubular cells in mouse and human kidneys. Virtually all the Cyp2E1 in kidney cells is in the endoplasmic reticulum (ER), not in mitochondria. By contrast, hepatic Cyp2E1 is in both the ER and mitochondria of hepatocytes. Consistent with this subcellular localization, a dose of 600 mg/kg APAP in fasted C57BL/6J mice induced the formation of APAP protein adducts predominantly in mitochondria of hepatocytes, but the ER of the proximal tubular cells of the kidney. We found that reactive metabolite formation triggered ER stress-mediated activation of caspase-12 and apoptotic cell death in the kidney. While co-treatment with 4-methylpyrazole (4MP; fomepizole) or the caspase inhibitor Ac-DEVD-CHO prevented APAP-induced cleavage of procaspase-12 and apoptosis in the kidney, treatment with NAC had no effect. These mechanisms are clinically relevant because 4MP but not NAC also significantly attenuated APAP-induced apoptotic cell death in primary human kidney cells. We conclude that reactive metabolite formation by Cyp2E1 in the ER results in sustained ER stress that causes activation of procaspase-12, triggering apoptosis of proximal tubular cells, and that 4MP but not NAC may be an effective antidote against APAP-induced kidney injury.

The mitochondrial calcium uniporter mediates mitochondrial Fe2+ uptake and hepatotoxicity after acetaminophen

Acetaminophen (APAP) overdose disrupts hepatocellular lysosomes, which release ferrous iron (Fe2+) that translocates into mitochondria putatively via the mitochondrial calcium uniporter (MCU) to induce oxidative/nitrative stress, the mitochondrial permeability transition (MPT), and hepatotoxicity. To investigate how MCU deficiency affects mitochondrial Fe2+ uptake and hepatotoxicity after APAP overdose, global MCU knockout (KO), hepatocyte specific (hs) MCU KO, and wildtype (WT) mice were treated with an overdose of APAP both in vivo and in vitro. Compared to strain-specific WT mice, serum ALT decreased by 88 and 56%, respectively, in global and hsMCU KO mice at 24 h after APAP (300 mg/kg). Hepatic necrosis also decreased by 84 and 56%. By contrast, when MCU was knocked out in Kupffer cells, ALT release and necrosis were unchanged after overdose APAP. Intravital multiphoton microscopy confirmed loss of viability and mitochondrial depolarization in pericentral hepatocytes of WT mice, which was decreased in MCU KO mice. CYP2E1 expression, hepatic APAP-protein adduct formation, and JNK activation revealed that APAP metabolism was equivalent between WT and MCU KO mice. In cultured hepatocytes after APAP, loss of cell viability decreased in hsMCU KO compared to WT hepatocytes. Using fructose plus glycine to prevent cell killing, mitochondrial Fe2+ increased progressively after APAP, as revealed with mitoferrofluor (MFF), a mitochondrial Fe2+ indicator. By contrast in hsMCU KO hepatocytes, mitochondrial Fe2+ uptake after APAP was suppressed. Rhod-2 measurements showed that Ca2+ did not increase in mitochondria after APAP in either WT or KO hepatocytes. In conclusion, MCU mediates uptake of Fe2+ into mitochondria after APAP and plays a central role in mitochondrial depolarization and cell death during APAP-induced hepatotoxicity.

Hepatic pyruvate and alanine metabolism are critical and complementary for maintenance of antioxidant capacity and resistance to oxidative insult

OBJECTIVE

Mitochondrial pyruvate is a critical intermediary metabolite in gluconeogenesis, lipogenesis, and NADH production. As a result, the mitochondrial pyruvate carrier (MPC) complex has emerged as a promising therapeutic target in metabolic diseases. Clinical trials are currently underway. However, recent in vitro data indicate that MPC inhibition diverts glutamine/glutamate away from glutathione synthesis and toward glutaminolysis to compensate for loss of pyruvate oxidation, possibly sensitizing cells to oxidative insult. Here, we explored this in vivo using the clinically relevant acetaminophen (APAP) overdose model of acute liver injury, which is driven by oxidative stress.

METHODS

We used pharmacological and genetic approaches to inhibit MPC2 and alanine aminotransferase 2 (ALT2), individually and concomitantly, in mice and cell culture models and determined the effects on APAP hepatotoxicity.

RESULTS

We found that MPC inhibition sensitizes the liver to APAP-induced injury in vivo only with concomitant loss of alanine aminotransferase 2 (ALT2). Pharmacological and genetic manipulation of neither MPC2 nor ALT2 alone affected APAP toxicity, but liver-specific double knockout (DKO) significantly worsened APAP-induced liver damage. Further investigation indicated that DKO impaired glutathione synthesis and increased urea cycle flux, consistent with increased glutaminolysis, and these results were reproducible in vitro. Finally, induction of ALT2 and post-treatment with dichloroacetate both reduced APAP-induced liver injury, suggesting new therapeutic avenues.

CONCLUSIONS

Increased susceptibility to APAP toxicity requires loss of both the MPC and ALT2 in vivo, indicating that MPC inhibition alone is insufficient to disrupt redox balance. Furthermore, the results from ALT2 induction and dichloroacetate in the APAP model suggest new metabolic approaches to the treatment of liver damage.

The mitochondrial fusion protein OPA1 is dispensable in the liver and its absence induces mitohormesis to protect liver from drug-induced injury

Mitochondria are critical for metabolic homeostasis of the liver, and their dysfunction is a major cause of liver diseases. Optic atrophy 1 (OPA1) is a mitochondrial fusion protein with a role in cristae shaping. Disruption of OPA1 causes mitochondrial dysfunction. However, the role of OPA1 in liver function is poorly understood. In this study, we delete OPA1 in the fully developed liver of male mice. Unexpectedly, OPA1 liver knockout (LKO) mice are healthy with unaffected mitochondrial respiration, despite disrupted cristae morphology. OPA1 LKO induces a stress response that establishes a new homeostatic state for sustained liver function. Our data show that OPA1 is required for proper complex V assembly and that OPA1 LKO protects the liver from drug toxicity. Mechanistically, OPA1 LKO decreases toxic drug metabolism and confers resistance to the mitochondrial permeability transition. This study demonstrates that OPA1 is dispensable in the liver, and that the mitohormesis induced by OPA1 LKO prevents liver injury and contributes to liver resiliency.

G-Quadruplex-Filtered Selective Ion-to-Ion Current Amplification for Non-Invasive Ion Monitoring in Real Time

Living cells efflux intracellular ions for maintaining cellular life, so intravital measurements of specific ion signals are of significant importance for studying cellular functions and pharmacokinetics. In this work, de novo synthesis of artificial K+ -selective membrane and its integration with polyelectrolyte hydrogel-based open-junction ionic diode (OJID) is demonstrated, achieving a real-time K+ -selective ion-to-ion current amplification in complex bioenvironments. By mimicking biological K+ channels and nerve impulse transmitters, in-line K+ -binding G-quartets are introduced across freestanding lipid bilayers by G-specific hexylation of monolithic G-quadruplex, and the pre-filtered K+ flow is directly converted to amplified ionic currents by the OJID with a fast response time at 100 ms intervals. By the synergistic combination of charge repulsion, sieving, and ion recognition, the synthetic membrane allows K+ transport exclusively without water leakage; it is 250× and 17× more permeable toward K+ than monovalent anion, Cl- , and polyatomic cation, N-methyl-d-glucamine+ , respectively. The molecular recognition-mediated ion channeling provides a 500% larger signal for K+ as compared to Li+ (0.6× smaller than K+ ) despite the same valence. Using the miniaturized device, non-invasive, direct, and real-time K+ efflux monitoring from living cell spheroids is achieved with minimal crosstalk, specifically in identifying osmotic shock-induced necrosis and drug-antidote dynamics.

Xanthohumol protect against acetaminophen-induced hepatotoxicity via Nrf2 activation through the AMPK/Akt/GSK3β pathway

OBJECTIVE

Acetaminophen (APAP) is one of the world's popular and safe painkillers, and overdose can cause severe liver damage and even acute liver failure. The effect and mechanism of the xanthohumol on acetaminophen-induced hepatotoxicity remains unclear.

METHODS

The hepatoprotective effects of xanthohumol were studied using APAP-induced HepG2 cells and acute liver injury of mouse, seperately.

RESULTS

In vitro, xanthohumol inhibited H2O2- and acetaminophen-induced cytotoxicity and oxidative stress. Xanthohumol up-regulated the expression of Nrf2. Further mechanistic studies showed that xanthohumol triggered Nrf2 activation via the AMPK/Akt/GSK3β pathway to exert a cytoprotective effect. In vivo, xanthohumol significantly ameliorated acetaminophen-induced mortality, the elevation of ALT and AST, GSH depletion, MDA formation and histopathological changes. Xanthohumol effectively suppressed the phosphorylation and mitochondrial translocation of JNK, mitochondrial translocation of Bax, the activation o cytochrome c, AIF secretion and Caspase-3. In vivo, xanthohumol increased Nrf2 nuclear transcription and AMPK, Akt and GSK3β phosphorylation in vivo. In addition, whether xanthohumol protected against acetaminophen-induced liver injury in Nrf2 knockout mice has not been illustated.

CONCLUSION

Thus, xanthohumol exerted a hepatoprotective effect by inhibiting oxidative stress and mitochondrial dysfunction through the AMPK/Akt/GSK3β/Nrf2 antioxidant pathway.

Geometric Isomer of Guanabenz Confers Hepatoprotection to a Murine Model of Acetaminophen Toxicity

Overdose of acetaminophen, a widely used antipyretic and analgesic drug, is one of the leading causes of drug-induced acute liver injury in the United States and worldwide. Phase-I metabolism of acetaminophen generates the toxic N-acetyl-p-benzoquinone imine (NAPQI) intermediate. Reactions of NAPQI with a wide range of biomolecules cause increased oxidative stress, endoplasmic reticulum (ER) stress, inflammation, and mitochondrial dysfunction, some of the cellular events contributing toward liver toxicity. Previously, we evaluated the potential of an FDA-approved, ER stress-modulating antihypertensive drug, Wytensin (trans-guanabenz, E-GA), as an antidote for acetaminophen hepatotoxicity. E-GA prevented elevation of the liver enzyme alanine aminotransferase (ALT), even when administered up to 6 h after acetaminophen overdose, and exhibited synergistic analgesic interactions. However, the commercially available guanabenz exists solely as a trans-isomer and suffers from sedative side effects resulting from the inhibition of central α2A-adrenergic receptors in locus coeruleus. Here, we studied the utility of the relatively unexplored cis-isomer of guanabenz as a treatment option for acetaminophen-induced liver toxicity. cis(Z)-Guanabenz acetate (Z-GA) lacks interaction with α2A-adrenoreceptors and is thus devoid of sedative, blood-pressure-lowering side effects of E-GA. Treatment of mice with Z-GA (10 mg/kg) before acetaminophen overdose and up to 6 h post APAP administration prevented liver injury and suppressed the elevation of serum ALT levels. Mechanistically, hepatoprotective effects of both isomers are similar and partly attributed to attenuation of the ER stress and oxidative stress in the liver. The results of this study suggest that Z-GA may be a safer, effective antidote for the clinical management of acute liver injury resulting from acetaminophen overdose. It also raises a tantalizing possibility of a prophylactic combination of the geometric isomer of the approved drug guanabenz with acetaminophen in a clinical setting.

The Wnt/β-catenin signaling pathway plays a role in drug-induced liver injury by regulating cytochrome P450 2E1 expression

Drug-induced liver injury (DILI) is a major cause of acute liver failure and drug withdrawal. Cytochrome P450 (CYP) 2E1 is involved in the metabolism of several drugs, and can induce liver injury through the production of toxic metabolites and the generation of reactive oxygen species. This study aimed to elucidate the role of Wnt/β-catenin signaling in CYP2E1 regulation for drug-induced hepatotoxicity. To achieve this, mice were administered cisplatin or acetaminophen (APAP) 1 h after treatment with the CYP2E1 inhibitor dimethyl sulfoxide (DMSO), and histopathological and serum biochemical analyses were performed. APAP treatment induced hepatotoxicity, as evidenced by an increase in liver weight and serum ALT levels. Moreover, histological analysis indicated severe injury, including apoptosis, in the liver tissue of APAP-treated mice, which was confirmed by TUNEL assay. Additionally, APAP treatment suppressed the antioxidant capacity of the mice and increased the expression of the DNA damage markers γ-H2AX and p53. However, these effects of APAP on hepatotoxicity were significantly attenuated by DMSO treatment. Furthermore, the activation of Wnt/β-catenin signaling using the Wnt agonist CHIR99021 (CHIR) increased CYP2E1 expression in rat liver epithelial cells (WB-F344), whereas treatment with the Wnt/β-catenin antagonist IWP-2 inhibited nuclear β-catenin and CYP2E1 expression. Interestingly, APAP-induced cytotoxicity in WB-F344 cells was exacerbated by CHIR treatment and suppressed by IWP-2 treatment. Overall, these results showed that the Wnt/β-catenin signaling is involved in DILI through the upregulation of CYP2E1 expression by directly binding the transcription factor β-cat/TCF to the Cyp2e1 promoter, thus exacerbating DILI.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00180-6.

Mitochondria in Acetaminophen-Induced Liver Injury and Recovery: A Concise Review

Mitochondria are critical organelles responsible for the maintenance of cellular energy homeostasis. Thus, their dysfunction can have severe consequences in cells responsible for energy-intensive metabolic function, such as hepatocytes. Extensive research over the last decades have identified compromised mitochondrial function as a central feature in the pathophysiology of liver injury induced by an acetaminophen (APAP) overdose, the most common cause of acute liver failure in the United States. While hepatocyte mitochondrial oxidative and nitrosative stress coupled with induction of the mitochondrial permeability transition are well recognized after an APAP overdose, recent studies have revealed additional details about the organelle's role in APAP pathophysiology. This concise review highlights these new advances, which establish the central role of the mitochondria in APAP pathophysiology, and places them in the context of earlier information in the literature. Adaptive alterations in mitochondrial morphology as well as the role of cellular iron in mitochondrial dysfunction and the organelle's importance in liver recovery after APAP-induced injury will be discussed.

Peli3 ablation ameliorates acetaminophen-induced liver injury through inhibition of GSK3β phosphorylation and mitochondrial translocation

The signaling pathways governing acetaminophen (APAP)-induced liver injury have been extensively studied. However, little is known about the ubiquitin-modifying enzymes needed for the regulation of APAP-induced liver injury. Here, we examined whether the Pellino3 protein, which has E3 ligase activity, is needed for APAP-induced liver injury and subsequently explored its molecular mechanism. Whole-body Peli3-/- knockout (KO) and adenovirus-mediated Peli3 knockdown (KD) mice showed reduced levels of centrilobular cell death, infiltration of immune cells, and biomarkers of liver injury, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), upon APAP treatment compared to wild-type (WT) mice. Peli3 deficiency in primary hepatocytes decreased mitochondrial and lysosomal damage and reduced the mitochondrial reactive oxygen species (ROS) levels. In addition, the levels of phosphorylation at serine 9 in the cytoplasm and mitochondrial translocation of GSK3β were decreased in primary hepatocytes obtained from Peli3-/- KO mice, and these reductions were accompanied by decreases in JNK phosphorylation and mitochondrial translocation. Pellino3 bound more strongly to GSK3β compared with JNK1 and JNK2 and induced the lysine 63 (K63)-mediated polyubiquitination of GSK3β. In rescue experiments, the ectopic expression of wild-type Pellino3 in Peli3-/- KO hepatocytes restored the mitochondrial translocation of GSK3β, but this restoration was not obtained with expression of a catalytically inactive mutant of Pellino3. These findings are the first to suggest a mechanistic link between Pellino3 and APAP-induced liver injury through the modulation of GSK3β polyubiquitination.

Mitochondrial Toxic Effects of Antiepileptic Drug Valproic Acid on Mouse Kidney Stem Cells

Valproic acid (VPA) is a histone deacetylase inhibitor that is used mainly as an antiepileptic and anticonvulsant drug. The side effects of VPA usually appears as hepatic injury and various metabolic disorders. On the other hand, it is rarely reported to cause kidney injury. Despite the many studies on the influence of VPA exposure on the kidneys, the specific mechanism remains unclear. This study examined the changes after VPA treatment to the mouse kidney stem cells (mKSCs). VPA triggers an increase in mitochondrial ROS, but there was no change in either mitochondrial membrane potential or the mitochondrial DNA copy number in mKSCs. The VPA treatment increased the mitochondrial complex III but decreased complex V significantly compared to the DMSO treatment as a control. The inflammatory marker (IL-6) and the expression of the apoptosis markers (Caspase 3) and were increased by VPA. In particular, the expression of the podocyte injury markers (CD2AP) was increased significantly. In conclusion, VPA exposure has adverse effects on mouse kidney stem cells.

Meat tenderization using acetaminophen (paracetamol/APAP): A review on deductive biochemical mechanisms, toxicological implications and strategies for mitigation

Meats consist of edible portions originating from domestic and wild animals. Meat's palatability and sensory accessibility largely depend on its tenderness to consumers. Although many factors influence meat tenderness, the cooking method cannot be neglected. Different chemical, mechanical, and natural means of meat tenderization have been considered healthy and safe for consumers. However, many households, food vendors, and bars in developing countries engage in the unhealthy use of acetaminophen (paracetamol/APAP) in meat tenderization due to the cost reduction it offers in the overall cooking process. Acetaminophen (paracetamol/APAP) is one of the most popular, relatively cheap, and ubiquitous over-the-counter drugs that induce serious toxicity challenges when misused. It is important to note that acetaminophen during cooking is hydrolyses into a toxic compound known as 4-aminophenol, which damages the liver and kidney and results in organ failure. Despite the reports on the increase in the use of acetaminophen for meat tenderizing in many web reports, there have not been any serious scientific publications on this subject. This study adopted classical/traditional methodology to review relevant literature retrieved from Scopus, PubMed, and ScienceDirect using relevant key terms (Acetaminophen, Toxicity, Meat tenderization, APAP, paracetamol, mechanisms) and Boolean operators (AND and OR). This paper provides in-depth information on the hazard and health implications of consuming acetaminophen tenderized meat via genetic and metabolic pathways deductions. Understanding these unsafe practices will promote awareness and mitigation strategies.

The Role and Mechanism of Action of Mitophagy in Various Liver Diseases

Significance: Liver disease is one of the biggest threats to public health, affecting as much as 5.5 million people worldwide. Mitochondrial dysfunction is associated with various acute and chronic liver diseases. Mitophagy, a selective form of autophagy for damaged/excessive mitochondria, plays a key role either in the pathogenesis or in maintaining hepatic homeostasis in response to various liver diseases. Recent Advances: Significant progress has been achieved to ascertain the causes of liver disease. The conserved pathways for mitochondrial degradation via mitophagy, the deregulation of mitophagy in liver diseases, and pharmacological or genetic maneuvers that alter the mitophagic flux for liver disease treatment have been widely studied but yet to be comprehensively reviewed. Critical Issues: Liver disease is considered a leading cause of mortality globally, causing the heavy burden of disability and the increased health care utilization that needs to be settled urgently. Mitophagy plays an important role in protecting liver from tissue damage to maintain hepatic homeostasis or in pathogenesis of liver disease. Elaborating mitophagy implicated in the pathogenesis of liver disease, as well as potential therapeutic regimens by targeting mitophagy is of great significance for the understanding and treatment of liver disease. Future Directions: This review comprehensively describes the distinct mitophagy signaling pathways and their interplay with various liver diseases. Given that mitophagy affects a wide array of physiological processes, a deeper understanding of how to modulate mitophagy could provide innovative avenues for precise therapy. Future studies based on pharmacologically or genetically targeting mitophagy-relevant factors will uncover the links between intact mitophagic responses and hepatic homeostasis in physiological and pathological settings. This will allow us to overcome obstacles of applying mitophagy as the therapeutic target in the clinic. Antioxid. Redox Signal. 38, 529-549.

Role of Pyroptosis in Acetaminophen-Induced Hepatotoxicity

Acetaminophen (APAP) is a widely used pain reliever that can cause liver injury or liver failure in response to an overdose. Understanding the mechanisms of APAP-induced cell death is critical for identifying new therapeutic targets. In this respect it was hypothesized that hepatocytes die by oncotic necrosis, apoptosis, necroptosis, ferroptosis and more recently pyroptosis. The latter cell death is characterized by caspase-dependent gasdermin cleavage into a C-terminal and an N-terminal fragment, which forms pores in the plasma membrane. The gasdermin pores can release potassium, interleukin-1β (IL-1β), IL-18, and other small molecules in a sublytic phase, which can be the main function of the pores in certain cell types such as inflammatory cells. Alternatively, the process can progress to full lysis of the cell (pyroptosis) with extensive cell contents release. This review discusses the experimental evidence for the involvement of pyroptosis in APAP hepatotoxicity as well as the arguments against pyroptosis as a relevant mechanism of APAP-induced cell death in hepatocytes. Based on the critical evaluation of the currently available literature and understanding of the pathophysiology, it can be concluded that pyroptotic cell death is unlikely to be a relevant contributor to APAP-induced liver injury.

Human Wharton's Jelly-derived mesenchymal stem cells prevent acetaminophen-induced liver injury in a mouse model unlike human dermal fibroblasts

The persistence of hepatotoxicity induced by N-acetyl-para-aminophenol (Acetaminophen or Paracetamol, abbreviated as APAP) as the most common cause of acute liver failure in the United States, despite the availability of N-acetylcysteine, illustrates the clinical relevance of additional therapeutic approaches. While human mesenchymal stem cells (MSCs) have shown protection in mouse models of liver injury, the MSCs used are generally not cleared for human use and it is unclear whether these effects are due to xenotransplantation. Here we evaluated GMP manufactured clinical grade human Wharton's Jelly mesenchymal stem cells (WJMSCs), which are currently being investigated in human clinical trials, in a mouse model of APAP hepatotoxicity in comparison to human dermal fibroblasts (HDFs) to address these issues. C57BL6J mice were treated with a moderate APAP overdose (300 mg/kg) and WJMSCs were administered 90 min later. Liver injury was evaluated at 6 and 24 h after APAP. WJMSCs treatment reduced APAP-induced liver injury at both time points unlike HDFs, which showed no protection. APAP-induced JNK activation as well as AIF and Smac release from mitochondria were prevented by WJMSCs treatment without influencing APAP bioactivation. Mechanistically, WJMSCs treatment upregulated expression of Gclc and Gclm to enhance recovery of liver GSH levels to attenuate mitochondrial dysfunction and accelerated recovery of pericentral hepatocytes to re-establish liver zonation and promote liver homeostasis. Notably, preventing GSH resynthesis with buthionine sulfoximine prevented the protective effects of WJMSCs. These data indicate that these GMP-manufactured WJMCs could be a clinically relevant therapeutic approach in the management of APAP hepatotoxicity in humans.

Inhibition of mitochondrial function: An alternative explanation for the antipyretic and hypothermic actions of acetaminophen

AIMS

Acetaminophen is the medication of choice when treating fever because of its limited anti-inflammatory effects. However at overdose it can cause mitochondrial dysfunction and damage, often associated with metabolism to N-acetyl-p-benzoquinone imine (NAPQI). What has never been investigated is whether the inhibition of mitochondrial function, particularly fatty acid uptake and oxidation could be the key to its antipyretic and hypothermic properties.

METHODS

Mitochondrial function and fatty acid oxidation (FAO) was determined by measuring oxygen consumption rate (OCR) in isolated mitochondria and in 3T3-L1 adipocytes using the XFp Analyser. Basal fatty acids and adrenergic stimulated OCR of mitochondria and 3T3-L1 adipocytes were assessed with acetaminophen and compared to NAPQI, etomoxir, and various mitochondrial stress compounds.

KEY FINDINGS

Using the XFp Analyser, acetaminophen (10 mM) decreased FAO by 31 % and 29 % in basal and palmitate stimulated adipocytes. NAPQI (50 μM) caused a 63 % decrease in both basal and palmitate stimulated FAO. Acetaminophen (10 mM) caused a 34 % reduction in basal and adrenergic stimulated OCR. In addition acetaminophen also inhibited complex I and II activity at 5 mM. NAPQI was far more potent at reducing mitochondrial respiratory capacity, maximum respiratory rates and ATP production than acetaminophen.

SIGNIFICANCE

These studies demonstrate the direct inhibition of mitochondrial function by acetaminophen at concentrations which have been shown to reduce fever and hypothermia in mammals. Understanding how antipyretics directly affect mitochondrial function and heat generation could lead to the development of new antipyretics which are not compromised by the anti-inflammatory and toxicity of the current medications.

SIRT4 Expression Ameliorates the Detrimental Effect of Heat Stress via AMPK/mTOR Signaling Pathway in BMECs

Sirtuin 4 (SIRT4), a member of the SIRT family, has been reported to be a key factor involved in antioxidant defense in mitochondria. This study aimed to explore the potential molecular mechanism via which SIRT4 regulates heat stress-induced oxidative stress and lactoprotein synthesis in bovine mammary epithelial cells (BMECs). Our results showed that SIRT4 was significantly decreased in heat stressed mammary tissue. Depletion of SIRT4 in BMECs induced the generation of ROS, which, as exhibited by the decreased activity of antioxidant enzymes, changed mitochondrial morphology through mediating protein and mRNA levels related to mitochondrial fission and fusion. Moreover, we found that depletion of SIRT4 or stress conditions inhibited the expression of milk proteins, as well as lipid and glucose synthesis-related genes, and activated the AMPK/mTOR signaling pathway. Increased SIRT4 expression was found to have the opposite effect. However, blocking the AMPK/mTOR signaling pathway could inhibit the regulatory function of SIRT4 in milk synthesis-related gene expression. In summary, our results suggest that SIRT4 may play critical roles in maintaining mammary gland function by regulating the AMPK/mTOR signaling pathway in dairy cows, indicating that SIRT4 may be a potential molecular target for curing heat stress-induced BMEC injury and low milk production in dairy cows.

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.

Adrenergic blocker terazosin potentially suppresses acetaminophen induced-acute liver injury in animal models via CYP2E1 gene

Drug induced liver injury (DILI) is a global issue and acetaminophen (APAP) is considered as the main cause of this. Due to increasing incidents of DILI, current study attempted to investigate an alternative but better role of terazosin (alpha-adrenergic blocker) in APAP-induced acute liver injury in an animal model using New Zealand rabbits. APAP (1 g/kg of body weight) was given to New Zealand rabbits either with or without terazosin (0.5 mg/kg) and serum was collected after 4 h. Serum alanine transaminase (ALT), alkaline phosphatase (ALP) and ferritin level were determined to analyze the liver functioning of treated rabbits. Furthermore, total cholesterol (TC), total lipids (TL), high-density lipoproteins (HDL), low-density lipoprotein (LDL) and triglycerides (TG) levels were estimated to find any change in lipid profile of the treated animals. Moreover, the urea and creatinine levels assayed the actual renal functionality. To identify any modification in gene expression, qPCR of cytochrome P2E1 (CYP2E1) was performed. Terazosin in combination with APAP enhanced liver functioning by reducing the levels of liver injury markers viz. ALP and ALT, while lipid profile was also lowered by down regulation of TC, TL, LDL and TG with enhanced HDL levels. It caused significant down regulation of expression level of CYP2E1. It is concluded that terazosin has better effects induced on the recovery of normal liver functioning, by improving the liver profile, lipid profile and renal functioning both at tissue and molecular levels.

The role of Iron in lipid peroxidation and protein nitration during acetaminophen-induced liver injury in mice

Acetaminophen (APAP) hepatotoxicity, a leading cause of acute liver failure in western countries, is characterized by mitochondrial superoxide and peroxynitrite formation. However, the role of iron, especially as facilitator of lipid peroxidation (LPO), has been controversial. Our aim was to determine the mechanism by which iron promotes cell death in this context. Fasted male C57BL/6J mice were treated with the iron chelator deferoxamine, minocycline (inhibitor of the mitochondrial calcium uniporter) or vehicle 1 h before 300 mg/kg APAP. Deferoxamine and minocycline significantly attenuated APAP-induced elevations in serum alanine amino transferase levels and hepatic necrosis at 6 h. This protection correlated with reduced 3-nitro-tyrosine protein adducts; LPO (malondialdehyde, 4-hydroxynonenal) was not detected. Activation of c-jun N-terminal kinase (JNK) was not affected but mitochondrial release of intermembrane proteins was reduced suggesting that the effect of iron was at the level of mitochondria. Co-treatment of APAP with FeSO4 exacerbated liver injury and protein nitration and triggered significant LPO; all effects were reversed by deferoxamine. Thus, after APAP overdose, iron imported into mitochondria facilitates protein nitration by peroxynitrite triggering mitochondrial dysfunction and cell death. Under these conditions, endogenous defense mechanisms largely prevent LPO. However, after iron overload, protein nitration and LPO contribute to APAP hepatotoxicity.

Activation of the adenosine A2B receptor even beyond the therapeutic window of N-acetylcysteine accelerates liver recovery after an acetaminophen overdose

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in the USA. The short therapeutic window of the current antidote, N-acetylcysteine (NAC) highlights the need for novel late acting therapeutics. The neuronal guidance cue netrin-1 provides delayed protection against APAP hepatotoxicity through the adenosine A2B receptor (A2BAR). The clinical relevance of this mechanism was investigated here by administration of the A2BAR agonist BAY 60-6583, after an APAP overdose (300 or 600 mg/kg) in fasted male and female C57BL/6J mice with assessment of liver injury 6 or 24 h after APAP in comparison to NAC. BAY 60-6583 treatment 1.5 h after APAP overdose (600 mg/kg) protected against liver injury at 6 h by preserving mitochondrial function despite JNK activation and its mitochondrial translocation. Gender independent protection was sustained when BAY 60-6583 was given 6 h after APAP overdose (300 mg/kg), when NAC administration did not show benefit. This protection was accompanied by enhanced infiltration of macrophages with the reparative anti-inflammatory phenotype by 24 h, accompanied by a decrease in neutrophil infiltration. Thus, our data emphasize the remarkable therapeutic utility of using an A2BAR agonist, which provides delayed protection long after the standard of care NAC ceased to be effective.

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.

Role of caspase-8 and/or -9 as biomarkers that can distinguish the potential to cause toxic- and immune related-adverse event, for the progress of acetaminophen-induced liver injury

AIMS

Acetaminophen (APAP) overdose can cause acute liver failure. Although it is well known that APAP-induced liver injury (AILI) is caused by toxic mechanism, recently it is also reported to be immune related. However, the detail of the mechanism has been unclear. Therefore, elucidation of the pathophysiology is required.

MAIN METHODS

In AILI model rats (800 mg/kg), the levels of AST, ALT and Caspase (C)-3/-8/-9 levels were measured. In in vitro study using human hepatocyte cells (FLC-4) and THP-1 cells, APAP (1.0 mM) were added to FLC-4 and the cell viability, C-9, cytochrome c, mitochondria membrane potential, and glutathione levels of FLC-4 and inflammasome activation of THP-1 were evaluated.

KEY FINDINGS

In AILI model rats, the levels of AST and ALT were increased only at 12-24 h. C-3/-9 levels rose at 6-9 h, whereas C-8 level rose hours later, moreover, 24 h after; C-3/-8/-9 levels re-rose. In FLC-4 cells, cytochrome c was released from the mitochondria which is promoted by oxidative stress due to drug metabolism and C-9 was activated. Thus, AILI was caused mitochondrial damage by NAPQI as early reaction (first stage). In the next stage, inflammasomes of human antigen presenting cells, which released inflammatory cytokines were activated by damage-associated molecular patterns (DAMPs) released from damaged hepatocyte by APAP.

SIGNIFICANCE

It is confirmed that AILI includes immune related mechanism. Thereby, in case of N-acetylcysteine refractory, additional administration of steroid hormones should be effective and recommended as a novel strategy for AILI with immune related adverse event (irAE).

Kupffer cells regulate liver recovery through induction of chemokine receptor CXCR2 on hepatocytes after acetaminophen overdose in mice

Acetaminophen (APAP) is a widely used analgesic, but also a main cause of acute liver injury in the United States and many western countries. APAP hepatotoxicity is associated with a sterile inflammatory response as shown by the infiltration of neutrophils and monocytes. While the contribution of the immune cells to promote liver repair have been demonstrated, the direct interactions between macrophages or neutrophils with hepatocytes to help facilitate hepatocyte proliferation and tissue repair remain unclear. The purpose of this study was to investigate the relationship between resident macrophages (Kupffer cells) and hepatocytes with a focus on the chemokine receptor CXCR2. C57BL/6J mice were subjected to an APAP overdose (300 mg/kg) and the role of CXCR2 on hepatocytes was investigated using a selective antagonist, SB225002. In addition, clodronate liposomes were used to deplete Kupffer cells to assess changes in CXCR2 expression. Our data showed that CXCR2 was mainly expressed on hepatocytes and it was induced specifically in hepatocytes around the necrotic area 24 h after APAP treatment. Targeting this receptor using an inhibitor caused a delayed liver recovery. Depletion of Kupffer cells significantly prevented CXCR2 induction on hepatocytes. In vitro and in vivo experiments also demonstrated that Kupffer cells regulate CXCR2 expression and pro-regenerative gene expression in surviving hepatocytes through production of IL-10. Thus, Kupffer cells support the transition of hepatocytes around the area of necrosis to a proliferative state through CXCR2 expression.

Kaempferol suppresses acetaminophen-induced liver damage by upregulation/activation of SIRT1

CONTEXT

Kaempferol, a flavonoid glycoside, has many hepatoprotective effects in several animals due to its antioxidant potential.

OBJECTIVE

This study evaluated the hepatoprotective effect of kaempferol against acetaminophen (APAP)-induced liver damage and examined whether the protection involved modulation of silent information regulator 1 (SIRT1) signalling.

MATERIALS AND METHODS

Adult male Wistar rats were classified into four groups (n = 8) and treated as follows: control + normal saline (vehicle), control + kaempferol (250 mg/kg), APAP (800 mg/kg, a single dose) and APAP + kaempferol. Kaempferol was administered for the first seven days followed by administration of APAP. The study was ended 24 h after APAP administration.

RESULTS

At the histological level, kaempferol reduced liver damage in APAP-treated rats. It also reduced the hepatic levels of TNF-α (66.3%), IL-6 (38.6%) and protein levels of caspase-3 (88.2%), and attenuated the increase in circulatory serum levels of ALT (47.6%), AST (55.8%) and γ-GT (35.2%) in APAP-treated rats. In both the controls and APAP-treated rats, kaempferol significantly increased the hepatic levels of glutathione (GSH) and superoxide dismutase, suppressed MDA and reactive oxygen species (ROS) levels, increased protein levels of Bcl-2 and downregulated protein levels of Bax and cleaved Bax. Concomitantly, it reduced the expression of CYP2E1, and the activity and protein levels of SIRT1. Consequently, it decreased the acetylation of all SIRT1 targets including PARP1, p53, NF-κB, FOXO-1 and p53 that mediate antioxidant, anti-inflammatory and anti-apoptotic effects.

DISCUSSION AND CONCLUSIONS

This study encourages the use of kaempferol in further clinical trials to treat APAP-induced hepatotoxicity.

Exogenous phosphatidic acid reduces acetaminophen-induced liver injury in mice by activating hepatic interleukin-6 signaling through inter-organ crosstalk

We previously demonstrated that endogenous phosphatidic acid (PA) promotes liver regeneration after acetaminophen (APAP) hepatotoxicity. Here, we hypothesized that exogenous PA is also beneficial. To test that, we treated mice with a toxic APAP dose at 0 h, followed by PA or vehicle (Veh) post-treatment. We then collected blood and liver at 6, 24, and 52 h. Post-treatment with PA 2 h after APAP protected against liver injury at 6 h, and the combination of PA and N-acetyl-l-cysteine (NAC) reduced injury more than NAC alone. Interestingly, PA did not affect canonical mechanisms of APAP toxicity. Instead, transcriptomics revealed that PA activated interleukin-6 (IL-6) signaling in the liver. Consistent with that, serum IL-6 and hepatic signal transducer and activator of transcription 3 (Stat3) phosphorylation increased in PA-treated mice. Furthermore, PA failed to protect against APAP in IL-6-deficient animals. Interestingly, IL-6 expression increased 18-fold in adipose tissue after PA, indicating that adipose is a source of PA-induced circulating IL-6. Surprisingly, however, exogenous PA did not alter regeneration, despite the importance of endogenous PA in liver repair, possibly due to its short half-life. These data demonstrate that exogenous PA is also beneficial in APAP toxicity and reinforce the protective effects of IL-6 in this model.

Recommendations for the use of the acetaminophen hepatotoxicity model for mechanistic studies and how to avoid common pitfalls

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug, which is safe at therapeutic doses but can cause severe liver injury and even liver failure after overdoses. The mouse model of APAP hepatotoxicity recapitulates closely the human pathophysiology. As a result, this clinically relevant model is frequently used to study mechanisms of drug-induced liver injury and even more so to test potential therapeutic interventions. However, the complexity of the model requires a thorough understanding of the pathophysiology to obtain valid results and mechanistic information that is translatable to the clinic. However, many studies using this model are flawed, which jeopardizes the scientific and clinical relevance. The purpose of this review is to provide a framework of the model where mechanistically sound and clinically relevant data can be obtained. The discussion provides insight into the injury mechanisms and how to study it including the critical roles of drug metabolism, mitochondrial dysfunction, necrotic cell death, autophagy and the sterile inflammatory response. In addition, the most frequently made mistakes when using this model are discussed. Thus, considering these recommendations when studying APAP hepatotoxicity will facilitate the discovery of more clinically relevant interventions.

Halogen-Induced Chemical Injury to the Mammalian Cardiopulmonary Systems

The halogens chlorine (Cl₂) and bromine (Br₂) are highly reactive oxidizing elements with widespread industrial applications and a history of development and use as chemical weapons. When inhaled, depending on the dose and duration of exposure, they cause acute and chronic injury to both the lungs and systemic organs that may result in the development of chronic changes (such as fibrosis) and death from cardiopulmonary failure. A number of conditions, such as viral infections, coexposure to other toxic gases, and pregnancy increase susceptibility to halogens significantly. Herein we review their danger to public health, their mechanisms of action, and the development of pharmacological agents that when administered post-exposure decrease morbidity and mortality.

Hepatoprotective effect of kaempferol glycosides isolated from Cedrela odorata L. leaves in albino mice: involvement of Raf/MAPK pathway

Background and purpose:

Paracetamol is the most implicated xenobiotic in inducing hepatotoxicity. Our study aimed to determine the impact of some kaempferol glycosides isolated from the leaves of Cedrela odorata L. on paracetamol hepatotoxicity.

Experimental approach:

The methanolic extract of dried leaves of C. odorata L. was subjected to the combination of spectroscopic methods (¹H and ¹³CNMR). Six kaempferol glycosides were isolated: kaempferol-3-O-β-D-glycopyranoside (astragalin), kaempferol-3-O-β-L-rhamnopyranoside, kaempferol-3-O-β-D-rutinoside, kaempferide-3-O-β-D-rutinoside, kaempferide-3-O-β-Drutinosyl-7-O-β-D-rhamnopyranoside, and kaempferol-3-O-β-D- rutinosyl-7-O-a-D-arabinopyranoside. Fifty-four female Swiss Albino mice were divided randomly into 9 groups including (1) control negative (1 mL/kg saline; IP), (2) control positive (paracetamol 300 mg/kg; IP), (3) silymarin 50 mg/kg (IP). Animals of groups 4-9 were injected with 6 different samples of isolated compounds at 100 mg/kg (IP). One h later, groups 3-9 were injected with paracetamol (300 mg/kg IP). Two h later, tissue samples were taken from all animals to assess nitrotyrosine, c-Jun N-terminal protein kinase (c-JNK), Raf -1kinase, and oxidative stress biomarkers viz. reduced glutathione (GSH) and malondialdehyde (MDA).

Findings/Results:

Isolated glycosides had a prominent anti-apoptotic effect via inhibition of c-JNK and Raf-1 kinase. They also exerted a powerful antioxidant effect by modulating the oxidative stress induced by paracetamol via increasing GSH, reducing MDA and nitrotyrosine concentrations compared to positive control. The glycoside (1) showed a better effect than silymarin (standard) in ameliorating the formation of nitrotyrosine, Raf-1 kinase, c-JNK, and GSH.

Conclusion and implication:

Kaempferol glycosides isolated for the first time from C. odorata L. leaves exerted antioxidant and antiapoptotic effects via amelioration of oxidative stress and inhibition of Raf/MAPK pathway.

Titanium Dioxide Induces Apoptosis under UVA Irradiation via the Generation of Lysosomal Membrane Permeabilization-Dependent Reactive Oxygen Species in HaCat Cells

Titanium dioxide nanoparticles (TiO₂ NPs) have wide commercial applications, owing to their small size; however, the biosafety of TiO₂ NPs should be evaluated further. In this study, we aimed to investigate the cytotoxicity of TiO₂ NPs in the presence and absence of ultraviolet A (UVA) irradiation in human keratinocyte HaCaT cells. TiO₂ NPs did not significantly affect cell viability in the absence of UVA irradiation. Nonetheless, UVA-irradiated TiO₂ NPs induced caspase-dependent apoptosis of HaCaT cells. Exposure of HaCaT cells to TiO₂ NPs and UVA resulted in reactive oxygen species (ROS) generation and lysosomal membrane permeabilization (LMP); both effects were not observed in the absence of UVA irradiation. An analysis of the relationship between LMP and ROS, using CA-074 as a cathepsin inhibitor or NAC as an antioxidant, showed that LMP stimulates ROS generation under these conditions. These results imply that LMP-dependent oxidative stress plays a critical role in the UVA phototoxicity of TiO₂ NPs in HaCaT cells.

Critical Roles of Calpastatin in Ischemia/Reperfusion Injury in Aged Livers

Ischemia/reperfusion (I/R) injury unavoidably occurs during hepatic resection and transplantation. Aged livers poorly tolerate I/R during surgical treatment. Although livers have a powerful endogenous inhibitor of calpains, calpastatin (CAST), I/R activates calpains, leading to impaired autophagy, mitochondrial dysfunction, and hepatocyte death. It is unknown how I/R in aged livers affects CAST. Human and mouse liver biopsies at different ages were collected during in vivo I/R. Hepatocytes were isolated from 3-month- (young) and 26-month-old (aged) mice, and challenged with short in vitro simulated I/R. Cell death, protein expression, autophagy, and mitochondrial permeability transition (MPT) between the two age groups were compared. Adenoviral vector was used to overexpress CAST. Significant cell death was observed only in reperfused aged hepatocytes. Before the commencement of ischemia, CAST expression in aged human and mouse livers and mouse hepatocytes was markedly greater than that in young counterparts. However, reperfusion substantially decreased CAST in aged human and mouse livers. In hepatocytes, reperfusion rapidly depleted aged cells of CAST, cleaved autophagy-related protein 5 (ATG5), and induced defective autophagy and MPT onset, all of which were blocked by CAST overexpression. Furthermore, mitochondrial morphology was shifted toward an elongated shape with CAST overexpression. In conclusion, CAST in aged livers is intrinsically short-lived and lost after short I/R. CAST depletion contributes to age-dependent liver injury after I/R.

Late Protective Effect of Netrin-1 in the Murine Acetaminophen Hepatotoxicity Model

Acetaminophen (APAP) overdose-induced acute liver failure is an important clinical problem in the United States and the current antidote N-acetylcysteine, has a short early therapeutic window. Since most patients present late to the clinic, there is need for novel late-acting therapeutic options. Though the neuronal guidance cue netrin-1, has been shown to promote hepatic repair and regeneration during liver ischemia/reperfusion injury, its effect in APAP-induced hepatotoxicity is unknown. In the quest for a late-acting therapeutic intervention in APAP-induced liver injury, we examined the role of netrin-1 in a mouse model of APAP overdose. Male C57BL/6J mice were cotreated with exogenous netrin-1 or vehicle control, along with 300 mg/kg APAP and euthanized at 6, 12, and 24 h. Significant elevations in alanine aminotransferase indicative of liver injury were seen in control mice at 6 h and this was not affected by netrin-1 administration. Also, netrin-1 treatment did not influence mitochondrial translocation of phospho-JNK, or peroxynitrite formation indicating that there was no interference with APAP-induced injury processes. Interestingly however, netrin-1 administration attenuated liver injury at 24 h, as seen by alanine aminotransferase levels and histology, at which time significant elevations in the netrin-1 receptor, adenosine A2B receptor (A2BAR) as well as macrophage infiltration was evident. Removal of resident macrophages with clodronate liposomes or treatment with the A2BAR antagonist PSB1115 blocked the protective effects of netrin-1. Thus, our data indicate a previously unrecognized role for netrin-1 in attenuation of APAP hepatotoxicity by enhancing recovery and regeneration, which is mediated through the A2BAR and involves resident liver macrophages.

Ferroptosis and Acetaminophen Hepatotoxicity: Are We Going Down Another Rabbit Hole?

Acetaminophen (APAP) hepatotoxicity is the most frequent cause of acute liver failure in the US. The mechanisms of APAP-induced liver injury have been under extensive investigations for decades, and many key events of this necrotic cell death are known today. Initially, two opposing hypotheses for cell death were proposed: reactive metabolite and protein adduct formation versus reactive oxygen and lipid peroxidation (LPO). In the end, both mechanisms were reconciled, and it is now generally accepted that the toxicity starts with formation of reactive metabolites that, after glutathione depletion, bind to cellular proteins, especially on mitochondria. This results in a mitochondrial oxidant stress, which requires amplification through a mitogen-activated protein kinase cascade, leading ultimately to enough reactive oxygen and peroxynitrite formation to trigger the mitochondrial membrane permeability transition and cell death. However, the earlier rejected LPO hypothesis seems to make a comeback recently under a different name: ferroptosis. Therefore, the objective of this review was to critically evaluate the available information about intracellular signaling mechanisms of APAP-induced cell death and those of ferroptosis. Under pathophysiologically relevant conditions, there is no evidence for quantitatively enough LPO to cause cell death, and thus APAP hepatotoxicity is not caused by ferroptosis. However, the role of mitochondria-localized minor LPO remains to be further investigated.

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.