Intracellular signaling mechanisms of acetaminophen-induced liver cell death

Nicorandil attenuates lithocholic acid-induced hepatotoxicity in mice through impeding oxidative stress, inflammation and apoptosis

This study was performed to explore the beneficial protective impact of nicorandil (Nico) against lithocholic acid (LCA)-induced hepatotoxicity.

MATERIALS AND METHODS

Mice received Nico (50 and 100 mg/kg. orally) for 7 days and LCA (125 mg/kg, i.p.) was injected for the last 4 days two times daily.

RESULTS

Nico improved both structural and functional abnormalities induced by LCA. Nico significantly decreased serum levels of transaminases, ALP, GGT and markedly elevated albumin levels. Additionally, Nico mitigated oxidative stress; it decreased contents of MDA and NO and increased GSH level and SOD activity. Moreover, Nico markedly decreased the elevated levels of TNF-α, JNK, Bax, Caspase-3 and iNOS, and increased the levels of eNOS in hepatic tissues. Furthermore, Nico substantially decreased the expression of NFκBp65 in hepatic tissues. Histopathological and transmission electron microscopy findings further supported these biomarkers.

CONCLUSION

Nico might be used as an adjuvant medication to prevent LCA-induced hepatotoxicity, pending further clinical research, through impeding oxidative stress, inflammation and apoptosis.

Drug-induced oxidative stress actively prevents caspase activation and hepatocyte apoptosis

Cell death is a fundamental process in health and disease. Emerging research shows the existence of numerous distinct cell death modalities with similar and intertwined signaling pathways, but resulting in different cellular outcomes, raising the need to understand the decision-making steps during cell death signaling. Paracetamol (Acetaminophen, APAP)-induced hepatocyte death includes several apoptotic processes but eventually is executed by oncotic necrosis without any caspase activation. Here, we studied this paradoxical form of cell death and revealed that APAP not only fails to activate caspases but also strongly impedes their activation upon classical apoptosis induction, thereby shifting apoptosis to necrosis. While APAP intoxication results in massive drop in mitochondrial respiration, low cellular ATP levels could be excluded as an underlying cause of missing apoptosome formation and caspase activation. In contrast, we identified oxidative stress as a key factor in APAP-induced caspase inhibition. Importantly, caspase inhibition and the associated switch from apoptotic to necrotic cell death was reversible through the administration of antioxidants. Thus, exemplified by APAP-induced cell death, our study stresses that cellular redox status is a critical component in the decision-making between apoptotic and necrotic cell death, as it directly affects caspase activity.

Role of Mitochondrial Iron Uptake in Acetaminophen Hepatotoxicity

Overdose of acetaminophen (APAP) produces fulminant hepatic necrosis. The underlying mechanism of APAP hepatotoxicity involves mitochondrial dysfunction, including mitochondrial oxidant stress and the onset of mitochondrial permeability transition (MPT). Reactive oxygen species (ROS) play an important role in APAP-induced hepatotoxicity, and iron is a critical catalyst for ROS formation. This review summarizes the role of mitochondrial ROS formation in APAP hepatotoxicity and further focuses on the role of iron. Normally, hepatocytes take up Fe3+-transferrin bound to transferrin receptors via endocytosis. Concentrated into lysosomes, the controlled release of iron is required for the mitochondrial biosynthesis of heme and non-heme iron-sulfur clusters. After APAP overdose, the toxic metabolite, NAPQI, damages lysosomes, causing excess iron release and the mitochondrial uptake of Fe2+ by the mitochondrial calcium uniporter (MCU). NAPQI also inhibits mitochondrial respiration to promote ROS formation, including H2O2, with which Fe2+ reacts to form highly reactive •OH through the Fenton reaction. •OH, in turn, causes lipid peroxidation, the formation of toxic aldehydes, induction of the MPT, and ultimately, cell death. Fe2+ also facilitates protein nitration. Targeting pathways of mitochondrial iron movement and consequent iron-dependent mitochondrial ROS formation is a promising strategy to intervene against APAP hepatotoxicity in a clinical setting.

Dose-dependent effects of acetaminophen and ibuprofen on mitochondrial respiration of human platelets

Acetaminophen and ibuprofen are widely used over-the-counter medications to reduce fever, pain, and inflammation. Although both drugs are safe in therapeutic concentrations, self-medication is practiced by millions of aged patients with comorbidities that decrease drug metabolism and/or excretion, thus raising the risk of overdosage. Mitochondrial dysfunction has emerged as an important pathomechanism underlying the organ toxicity of both drugs. Assessment of mitochondrial oxygen consumption in peripheral blood cells is a novel research field Cu several applications, including characterization of drug toxicity. The present study, conducted in human platelets isolated from blood donor-derived buffy coat, was aimed at assessing the acute, concentration-dependent effects of each drug on mitochondrial respiration. Using the high-resolution respirometry technique, a concentration-dependent decrease of oxygen consumption in both intact and permeabilized platelets was found for either drug, mainly by inhibiting complex I-supported active respiration. Moreover, ibuprofen significantly decreased the maximal capacity of the electron transport system already from the lowest concentration. In conclusion, platelets from healthy donors represents a population of cells easily available, which can be routinely used in studies assessing mitochondrial drug toxicity. Whether these results can be recapitulated in patients treated with these medications is worth further investigation as potential peripheral biomarker of drug overdose.

Deletion of hepatocyte cysteine dioxygenase type 1, a bile acid repressed gene, enhances glutathione synthesis and ameliorates acetaminophen hepatotoxicity

Liver is a major organ that metabolizes sulfur amino acids cysteine, which is the substrate for the synthesis of many essential cellular molecules including GSH, taurine, and coenzyme A. Bile acid-activated farnesoid x receptor (FXR) inhibits cysteine dioxygenase type 1 (CDO1), which mediates hepatic cysteine catabolism and taurine synthesis. To define the impact of bile acid inhibition of CDO1 on hepatic sulfur amino acid metabolism and antioxidant capacity, we developed hepatocyte-specific CDO1 knockout mice (Hep-CDO1 KO) and hepatocyte specific CDO1 transgenic mice (Hep-CDO1 Tg). Liver metabolomics revealed that genetic deletion of hepatic CDO1 reduced de novo taurine synthesis but had no impact on hepatic taurine abundance or bile acid conjugation. Consistent with reduced cysteine catabolism, Hep-CDO1 KO mice showed increased hepatic cysteine abundance but unaltered methionine cycle intermediates and coenzyme A synthesis. Upon acetaminophen overdose, Hep-CDO1 KO mice showed increased GSH synthesis capacity and alleviated liver injury. In contrast, hepatic CDO1 overexpression in Hep-CDO1 Tg mice stimulated hepatic cysteine to taurine conversion, resulting in reduced hepatic cysteine abundance. However, Hep-CDO1 Tg mice and WT showed similar susceptibility to acetaminophen-induced liver injury. Hep-CDO1 Tg mice showed similar hepatic taurine and coenzyme A compared to WT mice. In summary, these findings suggest that bile acid and FXR signaling inhibition of CDO1-mediated hepatic cysteine catabolism preferentially modulates hepatic GSH synthesis capacity and antioxidant defense, but has minimal effect on hepatic taurine and coenzyme A abundance. Repression of hepatic CDO1 may contribute to the hepatoprotective effects of FXR activation under certain pathologic conditions.

Phenelzine protects against acetaminophen induced apoptosis in HepG2 cells

Acetaminophen (APAP) overdosing is the most common cause of drug-induced liver failure. Despite extensive study, N-acetylcysteine is currently the only antidote utilized for treatment. The purpose of this study was to evaluate the effect and mechanisms of phenelzine, an FDA-approved antidepressant, on APAP-induced toxicity in HepG2 cells. The human liver hepatocellular cell line HepG2 was used to investigate APAP-induced cytotoxicity. The protective effects of phenelzine were determined by examining the cell viability, combination index calculation, Caspase 3/7 activation, Cytochrome c release, H2O2 levels, NO levels, GSH activity, PERK protein levels, and pathway enrichment analysis. Elevated H2O2 production and decreased glutathione (GSH) levels were indicators of APAP-induced oxidative stress. The combination index of 2.04 indicated that phenelzine had an antagonistic effect on APAP-induced toxicity. When compared to APAP alone, phenelzine treatment considerably reduced caspase 3/7 activation, cytochrome c release, and H2O2 generation. However, phenelzine had minimal effect on NO and GSH levels and did not alleviate ER stress. Pathway enrichment analysis revealed a potential connection between APAP toxicity and phenelzine metabolism. These findings suggested that phenelzine's protective effect against APAP-induced cytotoxicity could be attributed to the drug's capacity to reduce APAP-mediated apoptotic signaling.

Hepatocyte-specific deletion of small heterodimer partner protects mice against acetaminophen-induced hepatotoxicity via activation of Nrf2

Acetaminophen (APAP) overdose stands as the primary cause of acute liver failure in the United States. APAP hepatotoxicity involves hepatic glutathione (GSH) depletion and mitochondrial damage. To counteract the toxicity of APAP, the nuclear factor erythroid 2 like 2 (Nrf2) activates the expression of genes responsible for drug detoxification and GSH synthesis. In this study, we present evidence that the elimination of hepatocyte small heterodimer partner, a critical transcriptional repressor for liver metabolism, results in Nrf2 activation and protects mice from APAP-induced acute liver injury. Initial investigations conducted on wildtype (WT) mice revealed a swift downregulation of Shp mRNA within the first 24 h after APAP administration. Subsequent treatment of hepatocyte-specific Shp knockout (ShpHep-/-) mice with 300 mg/kg APAP for 2 h exhibited comparable bioactivation of APAP with that observed in the WT controls. However, a significant reduction in liver injury was observed in ShpHep-/- after APAP treatment for 6 and 24 h. The decreased liver injury correlated with a faster recovery of GSH, attributable to heightened expression of Nrf2 target genes involved in APAP detoxification and GSH synthesis. Moreover, in vitro studies revealed that SHP protein interacted with NRF2 protein, inhibiting the transcription of Nrf2 target genes. These findings hold relevance for humans, as overexpression of SHP hindered APAP-induced NRF2 activation in primary human hepatocytes. In conclusion, our studies have unveiled a novel regulatory axis involving SHP and NRF2 in APAP-induced acute liver injury, emphasizing SHP as a promising therapeutic target in APAP overdose-induced hepatotoxicity.

Inhibitor of nuclear factor kappa B kinase subunit epsilon regulates murine acetaminophen toxicity via RIPK1/JNK

Drug-induced liver injury (DILI) still poses a major clinical challenge and is a leading cause of acute liver failure. Inhibitor of nuclear factor kappa B kinase subunit epsilon (IKBKE) is essential for inflammation and metabolic disorders. However, it is unclear how IKBKE regulates cellular damage in acetaminophen (APAP)-induced acute liver injury. Here, we found that the deficiency of IKBKE markedly aggravated APAP-induced acute liver injury by targeting RIPK1. We showed that APAP-treated IKBKE-deficient mice exhibited severer liver injury, worse mitochondrial integrity, and enhanced glutathione depletion than wild-type mice. IKBKE deficiency may directly upregulate the expression of total RIPK1 and the cleaved RIPK1, resulting in sustained JNK activation and increased translocation of RIPK1/JNK to mitochondria. Moreover, deficiency of IKBKE enhanced the expression of pro-inflammatory factors and inflammatory cell infiltration in the liver, especially neutrophils and monocytes. Inhibition of RIPK1 activity by necrostatin-1 significantly reduced APAP-induced liver damage. Thus, we have revealed a negative regulatory function of IKBKE, which acts as an RIPK1/JNK regulator to mediate APAP-induced hepatotoxicity. Targeting IKBKE/RIPK1 may serve as a potential therapeutic strategy for acute or chronic liver injury.

Luteolin as a potential hepatoprotective drug: Molecular mechanisms and treatment strategies

Luteolin is a flavonoid widely present in various traditional Chinese medicines. In recent years, luteolin has received more attention due to its impressive liver protective effect, such as metabolic associated fatty liver disease, hepatic fibrosis and hepatoma. This article summarizes the pharmacological effects, pharmacokinetic characteristics, and toxicity of luteolin against liver diseases, and provides prospect. The results indicate that luteolin improves liver lesions through various mechanisms, including inhibiting inflammatory factors, reducing oxidative stress, regulating lipid balance, slowing down excessive aggregation of extracellular matrix, inducing apoptosis and autophagy of liver cancer cells. Pharmacokinetics research manifested that due to metabolic effects, the bioavailability of luteolin is relatively low. It is worth noting that appropriate modification, new delivery systems, and derivatives can enhance its bioavailability. Although many studies have shown that the toxicity of luteolin is minimal, strict toxicity experiments are still needed to evaluate its safety and promote its reasonable development. In addition, this study also discussed the clinical applications related to luteolin, indicating that it is a key component of commonly used liver protective drugs in clinical practice. In view of its excellent pharmacological effects, luteolin is expected to become a potential drug for the treatment of various liver diseases.

Cysteine conjugates of acetaminophen and p-aminophenol are potent inducers of cellular impairment in human proximal tubular kidney HK-2 cells

Acetaminophen (APAP) belong among the most used analgesics and antipyretics. It is structurally derived from p-aminophenol (PAP), a potent inducer of kidney toxicity. Both compounds can be metabolized to oxidation products and conjugated with glutathione. The glutathione-conjugates can be cleaved to provide cysteine conjugates considered as generally nontoxic. The aim of the present report was to synthesize and to purify both APAP- and PAP-cysteine conjugates and, as the first study at all, to evaluate their biological effects in human kidney HK-2 cells in comparison to parent compounds. HK-2 cells were treated with tested compounds (0-1000 µM) for up to 24 h. Cell viability, glutathione levels, ROS production and mitochondrial function were determined. After 24 h, we found that both APAP- and PAP-cysteine conjugates (1 mM) were capable to induce harmful cellular damage observed as a decrease of glutathione levels to 10% and 0%, respectively, compared to control cells. In addition, we detected the disappearance of mitochondrial membrane potential in these cells. In the case of PAP-cysteine, the extent of cellular impairment was comparable to that induced by PAP at similar doses. On the other hand, 1 mM APAP-cysteine induced even larger damage of HK-2 cells compared to 1 mM APAP after 6 or 24 h. We conclude that cysteine conjugates with aminophenol are potent inducers of oxidative stress causing significant injury in kidney cells. Thus, the harmful effects cysteine-aminophenolic conjugates ought to be considered in the description of APAP or PAP toxicity.

Role of HNF4alpha-cMyc interaction in liver regeneration and recovery after acetaminophen-induced acute liver injury

BACKGROUND AND AIMS

Overdose of acetaminophen (APAP) is the major cause of acute liver failure in the western world. We report a novel signaling interaction between hepatocyte nuclear factor 4 alpha (HNF4α) cMyc and nuclear factor erythroid 2-related factor 2 (Nrf2) during liver injury and regeneration after APAP overdose.

APPROACH AND RESULTS

APAP-induced liver injury and regeneration were studied in male C57BL/6J (WT) mice, hepatocyte-specific HNF4α knockout mice (HNF4α-KO), and HNF4α-cMyc double knockout mice (DKO). C57BL/6J mice treated with 300 mg/kg maintained nuclear HNF4α expression and exhibited liver regeneration, resulting in recovery. However, treatment with 600-mg/kg APAP, where liver regeneration was inhibited and recovery was delayed, showed a rapid decline in HNF4α expression. HNF4α-KO mice developed significantly higher liver injury due to delayed glutathione recovery after APAP overdose. HNF4α-KO mice also exhibited significant induction of cMyc, and the deletion of cMyc in HNF4α-KO mice (DKO mice) reduced the APAP-induced liver injury. The DKO mice had significantly faster glutathione replenishment due to rapid induction in Gclc and Gclm genes. Coimmunoprecipitation and ChIP analyses revealed that HNF4α interacts with Nrf2 and affects its DNA binding. Furthermore, DKO mice showed significantly faster initiation of cell proliferation resulting in rapid liver regeneration and recovery.

CONCLUSIONS

These data show that HNF4α interacts with Nrf2 and promotes glutathione replenishment aiding in recovery from APAP-induced liver injury, a process inhibited by cMyc. These studies indicate that maintaining the HNF4α function is critical for regeneration and recovery after APAP overdose.

Sesamin Protects against APAP-Induced Acute Liver Injury by Inhibiting Oxidative Stress and Inflammatory Response via Deactivation of HMGB1/TLR4/NFκB Signal in Mice

Acetaminophen (APAP) overdose would lead to liver toxicity and even acute liver failure in severe cases by triggering an inflammatory response and oxidative stress. Sesamin has been reported to possess anti-inflammatory and antioxidant actions in several animal disease models. In the present study, the effects and mechanisms of sesamin on APAP-induced acute liver injury (ALI) were explored. The results showed that pretreatment with sesamin significantly alleviated APAP-induced ALI, as indicated by decreased serum aminotransferase activities, hepatic pathological damages, and hepatic cellular apoptosis. But sesamin has no significant effects on the expression of cytochrome P450 2E1 (CYP2E1), APAP-cysteine adducts (APAP-CYS) production, and glutathione content in the liver of APAP-administered mice. Moreover, APAP-induced liver oxidative stress and inflammatory response also were remarkedly attenuated by sesamin, including reducing hepatic reactive oxygen species levels, promoting antioxidant generation, and inhibiting the expression of TNF-α and IL-1β, as well as decreasing inflammatory cell recruitment. Notably, sesamin inhibited serum high-mobility group box 1 (HMGB1) releases and blocked hepatic activation of Toll-like receptor 4 (TLR4)-interleukin 1 receptor-associated kinase 3-nuclear factor kappa B (NF-κB) signaling pathway in APAP-administered mice. These findings indicated that sesamin could mitigate APAP-induced ALI through suppression of oxidative stress and inflammatory response, which might be mediated by the deactivation of HMGB1/TLR4/NF-κB signaling in mice.

The Role of Endoplasmic Reticulum Stress Response in Liver Regeneration

Exposure to hepatotoxic chemicals is involved in liver disease-related morbidity and mortality worldwide. The liver responds to damage by triggering compensatory hepatic regeneration. Physical agent or chemical-induced liver damage disrupts hepatocyte proteostasis, including endoplasmic reticulum (ER) homeostasis. Post-liver injury ER experiences a homeostatic imbalance, followed by active ER stress response signaling. Activated ER stress response causes selective upregulation of stress response genes and downregulation of many hepatocyte genes. Acetaminophen overdose, carbon tetrachloride, acute and chronic alcohol exposure, and physical injury activate the ER stress response, but details about the cellular consequences of the ER stress response on liver regeneration remain unclear. The current data indicate that inhibiting the ER stress response after partial hepatectomy-induced liver damage promotes liver regeneration, whereas inhibiting the ER stress response after chemical-induced hepatotoxicity impairs liver regeneration. This review summarizes key findings and emphasizes the knowledge gaps in the role of ER stress in injury and regeneration.

Jasminum elongatum Ameliorates Acetaminophen Induced Hepatotoxicity by Modulating Dysregulated Antioxidant Enzyme System

Objectives

To evaluate the hepatoprotective activity of fractions of Jasminum elongatum methanolic extract against acetaminophen-induced hepatic damage.

Materials and Methods

Fractions obtained from methanolic extract of J. elongatum (petroleum ether, chloroform and hydroalcoholic) were investigated for hepatoprotective activity. Doses of 100 mg/kg and 200 mg/kg of different fractions were administered for 7 days, and acetaminophen toxicity was induced on the eighth day. After 24 hr of toxicity induction, biochemical markers and histological alterations were measured to determine the amount of hepatoprotection.

Results

The chloroform and hydroalcoholic fractions showed a significant decrease in biochemical parameters when compared to the toxic group, which was confirmed by histopathological changes and antioxidant parameters.

Conclusion

The results of this study revealed that the chloroform and hydroalcoholic fraction of J. elongatum have significant hepatoprotective activity against acetaminophen-induced toxicity.

Hepatoprotective effect of nicorandil against acetaminophen-induced oxidative stress and hepatotoxicity in mice via modulating NO synthesis

Acetaminophen (APAP) overdose can produce hepatotoxicity and consequently liver damage. This study investigated the hepatoprotective impacts of nicorandil on hepatic damage induced by APAP. Nicorandil was administered orally (100 mg/kg) for seven days before APAP challenge (500 mg/kg, ip). Pretreatment with nicorandil reduced serum levels of aminotransferases, bilirubin, GGT and LDH, and increased serum level of albumin. Moreover, nicorandil inhibited the increase in liver MDA levels and reversed the decline in GSH content and SOD activity. Besides, it notably alleviated APAP-induced necrosis observed in histopathological findings. Additionally, nicorandil alleviated APAP-induced NO overproduction and iNOS expression; however, the protein expression of eNOS was significantly increased. Moreover, nicorandil markedly reduced hepatic TNF-α and NF-κB levels, in addition to decreasing the protein expression of MPO in hepatic tissues. Furthermore, flow cytometry (annexin V-FITC/PI) displayed a significant decline in late apoptotic and necrotic cells, and an increase in viable cells in nicorandil group. Also, nicorandil caused a significant boost in hepatic antiapoptotic marker bcl-2 level. The presented data proposed that the protective effect of nicorandil might be attributed to its antioxidant, its impact on NO homeostasis, and its anti-inflammatory properties. Therefore, nicorandil may be a promising candidate for protection from liver injury induced by APAP.

Procyanidins Ameliorate Acetaminophen-induced Acute Liver Injury via Activating the Nrf-2/SOD-1 Signal Pathway

Background and Objectives

An overdose of acetaminophen (APAP) usually leads to acute liver injury, and oxidative stress is one of the fundamental mechanisms used to characterize it. Procyanidins (PCs) can reduce the oxidative stress in the liver of mice. This study aimed to investigate the potential protective role of PCs against APAP-induced acute liver injury.

Materials and Methods

Experiments were performed on male Kunming mice in six groups: phosphate-buffered saline, PCs, APAP, and PCs pretreated with 10, 50, and 100 mg/kg. The mice were peritoneally injected with PCs 30 min before the administration of APAP. First, survival rates of mice were scored every 12 hr for three days in succession. Furthermore, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (T-Bil), total cholesterol (TC), triglyceride (TG), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-1 (IL-6) were determined. Additionally, histological analysis and hepatic oxidative stress including the levels of superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione (GSH) were assessed. Finally, the protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and SOD-1 was detected by Western blotting.

Results

The data indicated that PCs improved survival rates of APAP-induced liver injury in mice models. Moreover, PCs could reduce the elevated serum levels of ALT, AST, T-Bil, TC, TG, TNF-α, IL-1β, and IL-6 due to APAP exposure with a dose-dependent manner. Besides, PCs pretreatment attenuated hepatic histopathological damage and oxidative stress which manifested the increases of SOD and GSH, whereas the decrease of MDA. Furthermore, PCs enhanced the protein expression of Nrf2 and SOD-1 in the PCs pretreatment groups compared with the APAP group.

Conclusion

PCs ameliorated APAP-induced acute liver injury, and Nrf2 signaling pathway modulating antioxidative stress might be involved in it.

Hepatorenal Protective Effects of Hydroalcoholic Extract of Solidago canadensis L. against Paracetamol-Induced Toxicity in Mice

Paracetamol (AKA acetaminophen) is a widely used drug and is used for mild to moderate pains, such as mild osteoarthritis, toothache, headache, and pain caused by minimally invasive surgeries. Despite being a harmless drug in lower doses, acetaminophen can be toxic to the liver and kidneys if overdosed and even results in death. In this study, the therapeutic effects of Solidago canadensis L. extract (SCE) were investigated. 48 adult male Swiss albino mice (20-30 grams) were randomly divided into six groups of 8. The control group was gavaged with normal saline every 12 hours for 6 days. The second group received paracetamol at a 500 mg/kg intraperitoneally (i.p) dose on the sixth day. The third, fourth, and fifth groups were gavaged doses of 125, 250, and 500 mg/kg of SCE every 12 hours for six days, respectively, and on the sixth day, we received paracetamol at a dose of 500 mg/kg i.p. The sixth group only received SCE every 12 hours at a dose of 1000 mg/kg via gavaging for six days. On the seventh day (24 hours after paracetamol injection), blood samples were collected to measure the serum level of creatinine, uric acid, blood urea nitrogen (BUN), total protein, albumin, alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and total and direct bilirubin, and liver and kidney tissues were also sampled for histopathological examination. It was observed that paracetamol caused a considerable increase in the ALT, AST, ALP, uric Acid, and BUN levels (P < 0.01), while those in SCE-treated groups were significantly lower. In addition, various lesions in the paracetamol group were observed, while in the SCE-receiving groups, receiving prophylactic SCE inhibited the high-intense lesions such as the infiltration of inflammatory cells, hyperemia, and vacuolar degeneration, which decreased significantly in the control group in comparison with that of the paracetamol group (P < 0.05). In conclusion, SCE can have substantial protective effects against paracetamol's hepatorenal toxicity.

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.

Intracellular Quantum Sensing of Free-Radical Generation Induced by Acetaminophen (APAP) in the Cytosol, in Mitochondria and the Nucleus of Macrophages

Acetaminophen overdoses cause cell injury in the liver. It is widely accepted that liver toxicity is initiated by the reactive N-acetyl-para-aminophenol (APAP) metabolite N-acetyl-p-benzoquinone imine (NAPQI), which first depletes glutathione and then irreversibly binds to mitochondrial proteins and nuclear DNA. As a consequence, mitochondrial respiration is inhibited, and DNA strands break. NAPQI also promotes the oxidative stress since glutathione is one of the main free-radical scavengers in the cell. However, so far it is unknown where exactly free radicals are generated. In this study, we used relaxometry, a novel technique that allows nanoscale magnetic resonance imaging detection of free radicals. The method is based on fluorescent nanodiamonds, which change their optical properties based on their magnetic surrounding. To achieve subcellular resolution, these nanodiamonds were targeted to cellular locations, that is, the cytoplasm, mitochondria, and the nucleus. Since relaxometry is sensitive to spin noise from radicals, we were able to measure the radical load in these different organelles. For the first time, we measured APAP-induced free-radical production in an organelle-specific manner, which helps predict and better understand cellular toxicity.

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.

Galium aparine L. protects against acetaminophen-induced hepatotoxicity in rats

The toxicity of acetaminophen (N-acetyl-para-aminophenol (APAP)) is the most frequent cause of drug-induced liver damage. Galium aparine L. (GA) is traditionally used to treat jaundice. We aimed to investigate the hepatoprotective potential of GA in the APAP-induced hepatic encephalopathy (HE) rat model. Qualitative phytochemical characterization of GA was performed by LC/Q-TOF/MS analysis. Wistar rats were pretreated with GA (250 and 500 mg/kg b.wt. per oral) for five days. On the 6th day, the rats were exposed to APAP (1500 mg/kg b.wt. oral gavage) and behavioral tests (open field and passive avoidance tests) were applied on the 7th and 8th days. The animals were killed, and biochemical and histopathological parameters were assessed in blood and hepatic specimens. GA pretreated rats exhibited a significant reduction in APAP-induced liver damage, evidenced by the reduction in liver necrosis and alanine aminotransferase (ALT), aspartate aminotransferase (AST), and bilirubin (BIL). GA demonstrated an anxiolytic effect, as seen in the acquisition trial and grooming behavior. The short-term memory performances of animals were not changed in all groups, suggesting that APAP intoxication did not affect hippocampal function. These results show that GA extract markedly exerts hepatoprotective activity, while its effect on hepatic encephalopathy was limited.

Possible Role of Extracellular Vesicles in Hepatotoxicity of Acetaminophen

We examined proteomic profiles of rat liver extracellular vesicles (EVs) shed following treatment with a sub-toxic dose (500 mg/kg) of the pain reliever drug, acetaminophen (APAP). EVs representing the entire complement of hepatic cells were isolated after perfusion of the intact liver and analyzed with LC-MS/MS. The investigation was focused on revealing the function and cellular origin of identified EVs proteins shed by different parenchymal and non-parenchymal liver cells and their possible role in an early response of this organ to a toxic environment. Comparison of EV proteomic profiles from control and APAP-treated animals revealed significant differences. Alpha-1-macroglobulin and members of the cytochrome P450 superfamily were highly abundant proteins in EVs shed by the normal liver. In contrast, proteins like aminopeptidase N, metalloreductase STEAP4, different surface antigens like CD14 and CD45, and most members of the annexin family were detected only in EVs that were shed by livers of APAP-treated animals. In EVs from treated livers, there was almost a complete disappearance of members of the cytochrome P450 superfamily and a major decrease in other enzymes involved in the detoxification of xenobiotics. Additionally, there were proteins that predominated in non-parenchymal liver cells and in the extracellular matrix, like fibronectin, receptor-type tyrosine-protein phosphatase C, and endothelial type gp91. These differences indicate that even treatment with a sub-toxic concentration of APAP initiates dramatic perturbation in the function of this vital organ.

Unraveling the effect of intra- and intercellular processes on acetaminophen-induced liver injury

In high dosages, acetaminophen (APAP) can cause severe liver damage, but susceptibility to liver failure varies across individuals and is influenced by factors such as health status. Because APAP-induced liver injury and recovery is regulated by an intricate system of intra- and extracellular molecular signaling, we here aim to quantify the importance of specific modules in determining the outcome after an APAP insult and of potential targets for therapies that mitigate adversity. For this purpose, we integrated hepatocellular acetaminophen metabolism, DNA damage response induction and cell fate into a multiscale mechanistic liver lobule model which involves various cell types, such as hepatocytes, residential Kupffer cells and macrophages. Our model simulations show that zonal differences in metabolism and detoxification efficiency are essential determinants of necrotic damage. Moreover, the extent of senescence, which is regulated by intracellular processes and triggered by extracellular signaling, influences the potential to recover. In silico therapies at early and late time points after APAP insult indicated that prevention of necrotic damage is most beneficial for recovery, whereas interference with regulation of senescence promotes regeneration in a less pronounced way.

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.

Arsenic compounds induce apoptosis by activating the MAPK and caspase pathways in FaDu oral squamous carcinoma cells

For a number of years, oral cancer has remained in the top ten most common types of cancer, with an incidence rate that is steadily increasing. In total, ~75% oral cancer cases are associated with lifestyle factors, including uncontrolled alcohol consumption, betel and tobacco chewing, and the excessive use of tobacco. Notably, betel chewing is highly associated with oral cancer in Southeast Asia. Arsenic is a key environmental toxicant; however, arsenic trioxide has been used as a medicine for the treatment of acute promyelocytic leukemia, highlighting its anticancer properties. The present study aimed to investigate the role of arsenic compounds in the treatment of cancer, using FaDu oral squamous carcinoma cells treated with sodium arsenite (NaAsO₂) and dimethyl arsenic acid (DMA). The results demonstrated that FaDu cells exhibited membrane blebbing phenomena and high levels of apoptosis following treatment with 10 µM NaAsO₂ and 1 mM DMA for 24 h. The results of cell viability assay demonstrated that the rate of FaDu cell survival was markedly reduced as the concentration of arsenic compounds increased from 10 to 100 µM NaAsO₂, and 1 to 100 mM DMA. Moreover, flow cytometry was carried out to further examine the effects of arsenic compounds on FaDu cell cycle regulation; the results revealed that treatment with NaAsO₂ and DMA led to a significant increase in the percentage of FaDu cells in the sub‑G1 and G2/M phases of the cell cycle. An Annexin V/PI double staining assay was subsequently performed to verify the levels of FaDu cell apoptosis following treatment with arsenic compounds. Furthermore, the results of the western blot analyses revealed that the expression levels of caspase‑8, ‑9 and ‑3, and poly ADP‑ribose polymerase, as well the levels of phosphorylated JNK and ERK1/2 were increased following treatment with NaAsO₂ and DMA in the FaDu cells. On the whole, the results of the present study revealed that treatment with NaAsO₂ and DMA promoted the apoptosis of FaDu oral cancer cells, by activating MAPK pathways, as well as the extrinsic and intrinsic apoptotic pathways.

Protective Effect of Eugenol against Acetaminophen-Induced Hepatotoxicity in Human Hepatocellular Carcinoma Cells via Antioxidant, Anti-Inflammatory, and Anti-Necrotic Potency

BACKGROUND: Overdoses acetaminophen (APAP) could cause acute liver failure, even though it used is for analgesics. APAP could cause hepatotoxicity due to multiple mediators of inflammation and oxidative stress. Eugenol has been reported to have anti-inflammatory and antioxidant activity but its hepatoprotective effect has not been widely reported. AIM: The purpose of this research is to know if eugenol could protect HepG2 cells from APAP. METHODS: HepG2 that induced by APAP as hepatotoxicity cells model was treated by using eugenol at 6.25 and 25 μg/mL. The protective effects of eugenol toward hepatotoxicity were evaluated by determine tumor necrosis factor-α (TNF-α) concentration, apoptotic activity, reactive oxygen species (ROS) level, also cytochrome (CYP)2E1 and GPX gene expression. RESULTS: Eugenol at 6.25 and 25 μg/mL concentration can reduce TNF-α concentration, the apoptotic, necrotic, dead cells, and ROS level. Besides it can increase the gene expression (GPX and CYP2E1). The best hepatoprotective effect was found when using the eugenol at 25 μg/mL. CONCLUSION: Therefore, eugenol can be used to protect HepG2 cells against APAP.

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.

The dual role of immune response in acetaminophen hepatotoxicity: Implication for immune pharmacological targets

Acetaminophen (APAP), one of the most widely used antipyretic and analgesic drugs, principally contributes to drug-induced liver injury when taken at a high dose. APAP-induced liver injury (AILI) results in extensive necrosis of hepatocytes along with the occurrence of multiple intracellular events such as metabolic activation, cell injury, and signaling pathway activation. However, the specific role of the immune response in AILI remains controversial for its complicated regulatory mechanisms. A variety of inflammasomes, immune cells, inflammatory mediators, and signaling transduction pathways are activated in AILI. These immune components play antagonistic roles in aggravating the liver injury or promoting regeneration. Recent experimental studies indicated that natural products showed remarkable therapeutic effects against APAP hepatotoxicity due to their favorable efficacy. Therefore, this study aimed to review the present understanding of the immune response in AILI and attempted to establish ties among a series of inflammatory cascade reactions. Also, the immune molecular mechanisms of natural products in the treatment of AILI were extensively reviewed, thus providing a fundamental basis for exploring the potential pharmacological targets associated with immune interventions.

Advanced preclinical models for evaluation of drug-induced liver injury - consensus statement by the European Drug-Induced Liver Injury Network [PRO-EURO-DILI-NET]

Drug-induced liver injury (DILI) is a major cause of acute liver failure (ALF) and one of the leading indications for liver transplantation in Western societies. Given the wide use of both prescribed and over the counter drugs, DILI has become a major health issue for which there is a pressing need to find novel and effective therapies. Although significant progress has been made in understanding the molecular mechanisms underlying DILI, our incomplete knowledge of its pathogenesis and inability to predict DILI is largely due to both discordance between human and animal DILI in preclinical drug development and a lack of models that faithfully recapitulate complex pathophysiological features of human DILI. This is exemplified by the hepatotoxicity of acetaminophen (APAP) overdose, a major cause of ALF because of its extensive worldwide use as an analgesic. Despite intensive efforts utilising current animal and in vitro models, the mechanisms involved in the hepatotoxicity of APAP are still not fully understood. In this expert Consensus Statement, which is endorsed by the European Drug-Induced Liver Injury Network, we aim to facilitate and outline clinically impactful discoveries by detailing the requirements for more realistic human-based systems to assess hepatotoxicity and guide future drug safety testing. We present novel insights and discuss major players in APAP pathophysiology, and describe emerging in vitro and in vivo pre-clinical models, as well as advanced imaging and in silico technologies, which may improve prediction of clinical outcomes of DILI.

A bioactive ligand-conjugated iridium(III) metal-based complex as a Keap1-Nrf2 protein-protein interaction inhibitor against acetaminophen-induced acute liver injury

Hepatotoxicity caused by an overdose of acetaminophen (APAP) is the leading reason for acute drug-related liver failure. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a protein that helps to regulate redox homeostasis and coordinate stress responses via binding to the Kelch-like ECH-associated protein 1 (Keap1). Targeting the Keap1-Nrf2 interaction has recently emerged as a potential strategy to alleviate liver injury caused by APAP. Here, we designed and synthesized a number of iridium (III) and rhodium (III) complexes bearing ligands with reported activity against oxidative stress, which is associated with Nrf2 transcriptional activation. The iridium (III) complex 1 bearing a bioactive ligand 2,9-dimethyl-1,10-phenanthroline and 4-chloro-2-phenylquinoline, a derivative of the bioactive ligand 2-phenylquinoline, was identified as a direct small-molecule inhibitor of the Keap1–Nrf2 protein-protein interaction. 1 could stabilize Keap1 protein, upregulate HO-1 and NQO1, and promote Nrf2 nuclear translocation in normal liver cells. Moreover, 1 reversed APAP-induced liver damage by disrupting Keap1–Nrf2 interaction and without inducing organ damage and immunotoxicity in mice. Our study demonstrates the identification of a selective and efficacious antagonist of Keap1–Nrf2 interaction possessed good cellular permeability in cellulo and ideal pharmacokinetic parameters in vivo, and, more importantly, validates the feasibility of conjugating metal complexes with bioactive ligands to generate metal-based drug leads as non-toxic Keap1–Nrf2 interaction inhibitors for treating APAP-induced acute liver injury.

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1 reversed APAP-induced liver damage by disrupting Keap1–Nrf2 interaction without inducing organ damage or immunotoxicity.

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Complex 1 possessed good cellular permeability in cellulo and ideal pharmacokinetic parameters in vivo.

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Conjugating metal complexes with bioactive ligands opens a novel avenue for the treatment of APAP-induced liver damage.

Liver regeneration and inflammation: from fundamental science to clinical applications

Liver regeneration is a complex process involving the crosstalk of multiple cell types, including hepatocytes, hepatic stellate cells, endothelial cells and inflammatory cells. The healthy liver is mitotically quiescent, but following toxic damage or resection the cells can rapidly enter the cell cycle to restore liver mass and function. During this process of regeneration, epithelial and non-parenchymal cells respond in a tightly coordinated fashion. Recent studies have described the interaction between inflammatory cells and a number of other cell types in the liver. In particular, macrophages can support biliary regeneration, contribute to fibrosis remodelling by repressing hepatic stellate cell activation and improve liver regeneration by scavenging dead or dying cells in situ. In this Review, we describe the mechanisms of tissue repair following damage, highlighting the close relationship between inflammation and liver regeneration, and discuss how recent findings can help design novel therapeutic approaches.

Plasmin-mediated cleavage of high-molecular-weight kininogen contributes to acetaminophen-induced acute liver failure

Acetaminophen (APAP)-induced liver injury is associated with activation of coagulation and fibrinolysis. In mice, both tissue factor-dependent thrombin generation and plasmin activity have been shown to promote liver injury after APAP overdose. However, the contribution of the contact and intrinsic coagulation pathways has not been investigated in this model. Mice deficient in individual factors of the contact (factor XII [FXII] and prekallikrein) or intrinsic coagulation (FXI) pathway were administered a hepatotoxic dose of 400 mg/kg of APAP. Neither FXII, FXI, nor prekallikrein deficiency mitigated coagulation activation or hepatocellular injury. Interestingly, despite the lack of significant changes to APAP-induced coagulation activation, markers of liver injury and inflammation were significantly reduced in APAP-challenged high-molecular-weight kininogen-deficient (HK-/-) mice. Protective effects of HK deficiency were not reproduced by inhibition of bradykinin-mediated signaling, whereas reconstitution of circulating levels of HK in HK-/- mice restored hepatotoxicity. Fibrinolysis activation was observed in mice after APAP administration. Western blotting, enzyme-linked immunosorbent assay, and mass spectrometry analysis showed that plasmin efficiently cleaves HK into multiple fragments in buffer or plasma. Importantly, plasminogen deficiency attenuated APAP-induced liver injury and prevented HK cleavage in the injured liver. Finally, enhanced plasmin generation and HK cleavage, in the absence of contact pathway activation, were observed in plasma of patients with acute liver failure due to APAP overdose. In summary, extrinsic but not intrinsic pathway activation drives the thromboinflammatory pathology associated with APAP-induced liver injury in mice. Furthermore, plasmin-mediated cleavage of HK contributes to hepatotoxicity in APAP-challenged mice independently of thrombin generation or bradykinin signaling.

Effect of Chronic Kidney Disease on Hepatic Clearance of Drugs in Rats

The pharmacokinetics of some hepatically cleared drugs have been reported to fluctuate in patients with renal impairment, but the definitive factors have not been clarified. We compared the pharmacokinetics of some drugs with different hepatic elimination processes in a chronic kidney disease (CKD) rat model, to optimize their administration during kidney injury. We chose indocyanine green (ICG), midazolam (MDZ), and acetaminophen (APAP) as reference drugs to determine changes in hepatic clearance pathways in presence of CKD. Drugs were intravenously administered via the jugular vein to the CKD model rats, previously established by adenine administration, and then, blood, bile, and urine samples were collected. The plasma concentration of ICG, which is eliminated into the bile without biotransformation, increased; and its total body clearance (CL_tot) significantly decreased in the CKD group compared to the control group. Moreover, the plasma concentrations of MDZ and APAP, metabolized in the liver by CYP3A and Ugt1a6 enzymes, respectively, were higher in the CKD group than in the control group. The biliary clearances of APAP and its derivative APAP-glucuronide increased in the CKD group, whereas their renal clearances were markedly decreased with respect to those in the control group. Altogether, plasma concentrations of some hepatically eliminated drugs increased in the CKD rat model, but depending on their pharmacokinetic characteristics. This study provides useful information for optimizing the administration of some hepatically cleared drugs in CKD patients.

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.

Effects of paracetamol on the polychaete Hediste diversicolor: occurrence of oxidative stress, cyclooxygenase inhibition and behavioural alterations

Pharmaceuticals are significant environmental stressors, since they are utilized around the world; they are usually released in to the aquatic system without adequate treatment and several non-target species can be harmed because of their intrinsic properties. Paracetamol is one of the most widely prescribed analgesics in human medical care. Consequently, this compound is systematically reported to occur in the wild, where it may exert toxic effects on non-target species, which are mostly uncharacterized so far. The objective of the present work was to assess the acute (control, 5, 25, 125, 625 and 3125 μg/L) and chronic (control, 5, 10, 20, 40 and 80 μg/L) effects of paracetamol on behavioural endpoints, as well as on selected oxidative stress biomarkers [superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GRed)] and the anti-inflammatory activity biomarker cyclooxygenase (COX), in the polychaete Hediste diversicolor (Annelida: Polychaeta). Exposure to paracetamol caused effects on behavioural traits, with increased burrowing time (96 h) and hypoactivity (28 days). In addition, exposure to paracetamol resulted also in significant increases of SOD activity, but only for intermediate levels of exposure, but for both acute and chronic exposures. Both forms of GPx had their activities significantly increased, especially after chronic exposure. Acutely exposed organisms had their GRed significantly decreased, while chronically exposed worms had their GRed activity augmented only for the lowest tested concentrations. Effects were also observed in terms of COX activity, showing that paracetamol absorption occurred and caused an inhibition of COX activity in both exposure regimes. It is possible to conclude that the exposure to concentrations of paracetamol close to the ones in the environment may be deleterious to marine ecosystems, endangering marine life by changing their overall redox balance, and the biochemical control of inflammatory intermediaries. Behaviour was also modified and the burrowing capacity was adversely affected. This set of effects clearly demonstrate that paracetamol exposure, under realistic conditions, it not exempt of adverse effects on marine invertebrates, such as polychaetes.

Individual Control and Quantification of 3D Spheroids in a High-Density Microfluidic Droplet Array

As three-dimensional cell culture formats gain in popularity, there emerges a need for tools that produce vast amounts of data on individual cells within the spheroids or organoids. Here, we present a microfluidic platform that provides access to such data by parallelizing the manipulation of individual spheroids within anchored droplets. Different conditions can be applied in a single device by triggering the merging of new droplets with the spheroid-containing drops. This allows cell-cell interactions to be initiated for building microtissues, studying stem cells’ self-organization, or observing antagonistic interactions. It also allows the spheroids’ physical or chemical environment to be modulated, as we show by applying a drug over a large range of concentrations in a single parallelized experiment. This convergence of microfluidics and image acquisition leads to a data-driven approach that allows the heterogeneity of 3D culture behavior to be addressed across the scales, bridging single-cell measurements with population measurements.

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Microfluidic droplet pairs sequentially trapped in capillary anchors before merging

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1 spheroid/droplet, with microenvironment modulations driven by droplet merging

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A wide range of drug concentrations tested on hepatic-like spheroids in a single chip

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Data-driven approach unravels 3D tissue-level dynamic drug response

Changes in the proteome of extracellular vesicles shed by rat liver after subtoxic exposure to acetaminophen

To identify changes in extracellular vesicles (EVs) secreted by the liver following drug-induced liver injury (DILI), rats were treated with a subtoxic dose (500 mg/kg) of the analgesic drug, acetaminophen (APAP). EVs were collected by liver perfusion of sham and APAP-treated rats. Changes in EVs morphology were examined by transmission electron microscopic analysis of negatively stained vesicles. Results from morphometric analysis of EVs revealed striking differences in their size and distribution. Proteome composition of EVs collected by liver perfusion was determined by mass spectrometry using methods of sample preparation that enabled better detection of both highly hydrophobic proteins and proteins with complex post-translational modifications. The collection of EVs after liver perfusion is an approach that enables the isolation of EVs shed not only by isolated hepatocytes, but also by the entire complement of hepatic cells. EVs derived after DILI had a lower content of alpha-1-macroglobulin, ferritin, and members of cytochrome 450 family. Fibronectin, aminopeptidase N, metalloreductase STEAP4, integrin beta, and members of the annexin family were detected only in APAP-treated samples of EVs. These results show that the present approach can provide valuable insights into the response of the liver following drug-induced liver injury.

Quercitrin Attenuates Acetaminophen-Induced Acute Liver Injury by Maintaining Mitochondrial Complex I Activity

The flavonoid quercitrin has a strong antioxidant property. It is also reported to have a protective effect on the liver. However, the mechanism by which it exerts a protective effect on the liver is not fully understood. The objective of this article is to confirm the protective effect of quercitrin extracted from Albiziae flos on acetaminophen (APAP)-induced liver injury and to explain its mechanism. In the in vivo study, quercitrin was administered orally to BALB/c mice at a dose of 50, 100, and 200 mg/kg for seven consecutive days. APAP (300 mg/kg) was injected intraperitoneally after a last dose of quercitrin was administered. Determination of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-Px), catalase (CAT), and malondialdehyde (MDA) levels showed that quercitrin effectively attenuated APAP-induced acute liver injury in mice. Results of the in vitro study showed that quercitrin reduced the levels of ROS, protected mitochondria from damage, and restored the activity of mitochondrial complex I in APAP-treated L-02 cells. The addition of rotenone which is an inhibitor of complex I blocked the protective effect of quercitrin. The expression of mitochondrial complex I was also maintained by quercitrin. Our results suggest that quercitrin can maintain the level of mitochondrial complex I in injured cells and restore its activity, which reduces the production of ROS, protects the mitochondria from oxidative stress, and has a protective effect on the liver.

Can granulocyte colony stimulating factor (G-CSF) ameliorate acetaminophen-induced hepatotoxicity?

Acetaminophen (APAP) is often used as an antipyretic and analgesic agent. Overdose hepatotoxicity, which often results in liver cell failure and liver transplantation, is a severe complication of APAP usage. To save the liver and save lives from acute liver damage caused by APAP, the search for new strategies for liver defense is important. Wistar rats have been used for the induction of APAP hepatotoxicity. Elevated levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) were evaluated for liver toxicity. In addition, the levels of hepatic tissue oxidative markers such as malondialdehyde (MDA), nitric oxide (NO) increased while glutathione (GSH) was depleted and catalase (CAT) activity was curtailed. The biochemical findings were consistent with the changes in histology that suggested liver damage and inflammation. Treated rats with N-acetylcysteine (N-AC) and granulocyte colony stimulating factor (G-CSF) showed a decrease in serum levels of ALT, AST and LDH, while the level of ALP in the G-CSF group was still high. After administration of APAP, treatment with N-AC or G-CSF substantially reduced the level of MDA and NO while maintaining the GSH content and CAT activity. Treatment with N-AC and G-CSF after administration of APAP has also attenuated inflammation and hepatocytes necrosis. The results of this study showed that G-CSF could be viewed as an alternative hepatoprotective agent against APAP-induced acute liver injury compared to N-AC.

The cross-talk of NLRP3 inflammasome activation and necroptotic hepatocyte death in acetaminophen-induced mice acute liver injury

Overdose acetaminophen (APAP) can result in severe liver injury, which is responsible for nearly half of drug-induced liver injury in western countries. Previous studies have found that there existed massive hepatocellular necrosis and severe inflammatory response in APAP-induced liver injury. However, the mechanistic linkage between necroptosis and NLRP3 inflammasome pathway in APAP-induced hepatotoxicity remains poorly understood. In order to investigate the relationship between inflammation and hepatocytes death in APAP hepatotoxicity, a time-course model for APAP hepatotoxicity in C57/BL6 mice was established by intraperitoneal (i.p) injection of 300 mg/kg APAP in this study. The activity of serum enzymes and pathological changes of APAP-treated mice were evaluated, and the critical molecules in necroptosis and NF-κB-NLRP3 inflammasome signaling pathway were determined by immunoblot and immunofluorescence analysis. The results demonstrated that APAP overdose resulted in a severe liver injury. Furthermore, the expression of critical molecules in NLRP3 inflammasome and necroptosis pathways peaked at 12-24 h, and then was decreased gradually, which is consistent with the pattern of pathological injury induced by APAP. Our further investigation found that the level of IL-1β in mouse liver was closely correlated with the level of phosphorylated MLKL following exposure to APAP. Furthermore, inhibition of necroptosis with necrostatin-1 significantly suppressed the activation of NLRP3 inflammasome signaling. Taken together, our results highlighted that the cross-talk between necroptosis and NLRP3 inflammasome played a critical role for promoting APAP-induced liver injury. Inhibition of the interaction of inflammation and necroptosis by pharmaceutical methods may represent a promising therapeutic strategy for APAP-induced liver injury.

Aedes aegypti mosquito saliva ameliorates acetaminophen-induced liver injury in mice

Acetaminophen (N-acetyl-p-aminophenol, APAP) overdose is the most common cause of drug-induced liver injury (DILI). Although the primary hepatic damage is induced by APAP-derived toxic intermediates resulting from cytochrome P450 metabolism, immune components also play an important role in DILI pathophysiology. Aedes aegypti saliva is a source of bioactive molecules with in vitro anti-inflammatory and immunomodulatory activities. However, evidences on the therapeutic use of Ae. aegypti salivary preparations in animal models of relevant clinical conditions are still scarce. Thus, the present study was designed to evaluate the protective role of Ae. aegypti saliva in a murine model of APAP-induced DILI. C57BL/6 mice were exposed to Ae. aegypti bites 2 hours after APAP overdose. Biochemical and immunological parameters were evaluated in blood and liver samples at different time points after APAP administration. Exposure to Ae. aegypti saliva attenuated liver damage, as demonstrated by reduced hepatic necrosis and serum levels of alanine aminotransferase in APAP-overdosed mice. The levels of hepatic CYP2E1, the major enzyme responsible for the bioactivation of APAP, were not changed in Ae. aegypti exposed animals, suggesting no effects in the generation of hepatotoxic metabolites. On the other hand, mice treated with Ae. aegypti saliva following APAP overdose presented lower serum concentration of TNF-α, IL-6, IL-1β and IL-10, as well as reduced frequency of inflammatory cell populations in the liver, such as NKT cells, macrophages and dendritic cells. These findings show that Ae. aegypti saliva has bioactive molecules with therapeutic properties and may represent a prospective source of new compounds in the management of DILI-associated inflammatory disorders and, perhaps, many other inflammatory/autoimmune diseases.

Dibenzazepine combats acute liver injury in rats via amendments of Notch signaling and activation of autophagy

Paracetamol is a commonly used over-the-counter analgesic and antipyretic drug. Nevertheless, an overdose of paracetamol leads to hepatic necrosis that can be lethal. This study aimed to assess the potential hepatoprotective effects of dibenzazepine, a Notch inhibitor, against acute liver injury in rats via interfering with oxidative stress, inflammation, apoptosis, autophagy, and Notch signaling. Silymarin (200 mg/kg, p.o.) or dibenzazepine (2 mg/kg, i.p.) were administered to rats for 5 days before a single hepatotoxic dose of paracetamol (800 mg/kg, i.p.). Pretreatment with silymarin and dibenzazepine significantly mitigated oxidative stress, inflammatory and apoptotic markers induced by paracetamol hepatotoxicity where dibenzazepine showed greater repression of inflammation. Furthermore, dibenzazepine was found to be significantly more efficacious than silymarin in inhibiting Notch signaling as represented by expression of Notch-1 and Hes-1. A significantly greater response was also demonstrated with dibenzazepine pretreatment with regard to the expression of autophagic proteins, Beclin-1 and LC-3. The aforementioned biochemical results were confirmed by histopathological examination. Autophagy and Notch signaling seem to play a significant role in protection provided by dibenzazepine for paracetamol-induced hepatotoxicity in rats, which could explain its superior results relative to silymarin. Graphical abstract.

Orostachys japonicus ameliorates acetaminophen-induced acute liver injury in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Orostachys japonicus A. Berger (O. japonicus), referred to as Wa-song in Korea is a traditional and herbal medicine. Even though it has been traditionally used to treat inflammation- and toxicity-related diseases, the effects of ethanol extract of O. japonicus (OJE) on acetaminophen (N-acetyl-p-aminophenol, APAP) overdose-induced hepatotoxicity have not been determined yet.

AIM OF THE STUDY

The present study was aimed to investigate the effects of OJE against APAP-induced acute liver injury (ALI) and explore the underlying mechanisms.

MATERIALS AND METHODS

Mice were treated orally with OJE (50, 100, or 200 mg/kg) for seven days before APAP (300 mg/kg) injection. After 12 h of APAP treatment, serum and liver tissues were collected. An in vitro system using primary hepatocytes was also applied in this study.

RESULTS

Pretreatment with OJE, especially at a dose of 200 mg/kg, reduced APAP overdose-induced ALI in mice, as evidenced by decreased serum alanine/aspartate aminotransferase levels, histopathological damage, and inflammation. Consistently, OJE pretreatment reduced the gene transcription of cytochrome P450 (CYP) 3A11 and CYP1A2 in livers of mice injected with or without APAP, at least in part, via inactivation of nuclear receptor pregnane X receptor (PXR). Furthermore, the role of PXR in mediating the OJE regulation of CYPs was confirmed in primary hepatocytes, which showed that OJE pretreatment inhibited PXR activity and APAP hepatotoxicity enhanced by pregnenolone 16α-carbonitrile, a mouse agonist of PXR. Besides, the antioxidative activity provided by OJE, involving increases in hepatic glutathione (GSH) content and decreases in malondialdehyde levels, has been shown to exert hepatoprotective effects in normal and injured livers. Moreover, APAP-activated c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) in mice liver were indirectly inhibited by pretreatment with OJE.

CONCLUSIONS

Taken together, our findings showed that OJE attenuated APAP-induced ALI by decreasing APAP-metabolizing enzymes via inactivation of PXR and the restoration of hepatic GSH content. Therefore, OJE could be a promising hepatoprotective agent.

Interaction of RIPK1 and A20 modulates MAPK signaling in murine acetaminophen toxicity

Acetaminophen (APAP)-induced liver necrosis is a form of regulated cell death (RCD) in which APAP activates the mitogen-activated protein kinases (MAPKs) and specifically the c-Jun-N-terminal kinase (JNK) pathway, leading to necrotic cell death. Previously, we have shown that receptor interacting protein kinase-1 (RIPK1) knockdown is also protective against APAP RCD upstream of JNK. However, whether the kinase or platform function of RIPK1 is involved in APAP RCD is not known. To answer this question, we used genetic mouse models of targeted hepatocyte RIPK1 knockout (RIPK1^HepCKO) or kinase dead knock-in (RIPK1^D138N) and adult hepatocyte specific knockout of the cytoprotective protein A20 (A20^HepCKO), known to interact with RIPK1, to study its potential involvement in MAPK signaling. We observed no difference in injury between WT and RIPK^1D138N mice post APAP. However, RIPK1^HepCKO was protective. We found that RIPK1^HepCKO mice had attenuated pJNK activation, while A20 was simultaneously upregulated. Conversely, A20^HepCKO markedly worsened liver injury from APAP. Mechanistically, we observed a significant upregulation of apoptosis signal-regulating kinase 1 (ASK1) and increased JNK activation in A20^HepCKO mice compared with littermate controls. We also demonstrated that A20 coimmunoprecipitated (co-IP) with both RIPK1 and ASK1, and that in the presence of RIPK1, there was less A20-ASK1 association than in its absence. We conclude that the kinase-independent platform function of RIPK1 is involved in APAP toxicity. Adult RIPK1^HepCKO mice are protected against APAP by upregulating A20 and attenuating JNK signaling through ASK1, conversely, A20^HepCKO worsens injury from APAP.

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.

Aspirin Eugenol Ester Protects Vascular Endothelium From Oxidative Injury by the Apoptosis Signal Regulating Kinase-1 Pathway

Aspirin eugenol ester (AEE) is a new potential pharmaceutical compound possessing anti-inflammatory, anti-cardiovascular disease, and antioxidative stress activity. The pharmacological activities of AEE are partly dependent on its regulation of cell apoptosis. However, it is still unclear how AEE inhibits cell apoptosis on the basis of its antioxidative stress effect. This study aimed to reveal the vascular antioxidative mechanism of AEE in response to H₂O₂-induced oxidative stress in HUVECs and paraquat-induced oxidative stress in rats. In the different intervention groups of HUVECs and rats, the expression of ASK1, ERK1/2, SAPK/JNK, and p38 and the phosphorylation levels of ERK1/2, SAPK/JNK, and p38 were measured. The effects of ASK1 and ERK1/2 on the anti-apoptotic activity of AEE in the oxidative stress model were probed using the corresponding inhibitors ASK1 and ERK1/2. The results showed that in the HUVECs, 200 μM H₂O₂ treatment significantly increased the phosphorylation of SAPK/JNK and the level of ASK1 but decreased the phosphorylation of ERK1/2, while in the HUVECs pretreated with AEE, the H₂O₂-induced changes were significantly ameliorated. The findings were observed in vitro and in vivo. Moreover, inhibition of ASK1 and ERK1/2 showed that ASK1 plays a vital role in the protective effect of AEE on H₂O₂-induced apoptosis. All findings suggested that AEE protects the vascular endothelium from oxidative injury by mediating the ASK1 pathway.

Biofabrication of Hepatic Constructs by 3D Bioprinting of a Cell-Laden Thermogel: An Effective Tool to Assess Drug-Induced Hepatotoxic Response

A thermoresponsive Pluronic/alginate semisynthetic hydrogel is used to bioprint 3D hepatic constructs, with the aim to investigate liver-specific metabolic activity of the 3D constructs compared to traditional 2D adherent cultures. The bioprinting method relies on a bioinert hydrogel and is characterized by high-shape fidelity, mild depositing conditions and easily controllable gelation mechanism. Furthermore, the dissolution of the sacrificial Pluronic templating agent significantly ameliorates the diffusive properties of the printed hydrogel. The present findings demonstrate high viability and liver-specific metabolic activity, as assessed by synthesis of urea, albumin, and expression levels of the detoxifying CYP1A2 enzyme of cells embedded in the 3D hydrogel system. A markedly increased sensitivity to a well-known hepatotoxic drug (acetaminophen) is observed for cells in 3D constructs compared to 2D cultures. Therefore, the 3D model developed herein may represent an in vitro alternative to animal models for investigating drug-induced hepatotoxicity.