Cytochrome P450-derived versus mitochondrial oxidant stress in acetaminophen hepatotoxicity

Acute Acetaminophen Hepatotoxicity And Platelet Dysfunction

INTRODUCTION

Acetaminophen (APAP) overdose remains a common cause of liver injury, primarily due to its toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). This study sought to investigate APAP-induced platelet aggregation in vitro, and the implication of CYP2E1 in the metabolism of APAP and hepatic cell toxicity.

METHODS

Co-cultures of platelets and hepatic cells that do not (HepG2) and do express CYP2E1 (HepG2E47) were exposed to APAP (0-20 mM), NAPQI (0-250 µM), APAP in the absence/presence of inhibitors of glutathione (50 μM buthionine sulphoximine (BSO)), or APAP in the absence/presence of inhibitors CYP2E1 (chlormethiazole (CMZ, 100 µM), or 4-methylpyrazole (4-MP, 5 mM)). Platelet aggregation, cell viability and reactive oxygen species (ROS) were analyzed. Changes in platelet aggregation was determined in platelets directly exposed to APAP/NAPQI.

RESULTS

Exposure to APAP decreased platelet aggregation under co-culture conditions but not in platelet-only cultures. Conversely, NAPQI exposure decreased platelet aggregation in both co-culture and platelet-only conditions. Both APAP and NAPQI reduced cell viability in HepG2 and HepG2E47 cells, with BSO enhancing APAP toxicity, while 4-MP mitigated it. Acetaminophen exposure led to ROS production in HepG2E47 cells, with no effect of CMZ and 4-MP.

CONCLUSIONS

Acetaminophen exposure impacts platelet aggregation in co-cultures of platelets and HepG2/HepG2E47 cells with increased ROS production in HepG2E47 cells and 4-MP preventing APAP-induced cytotoxicity in HepG2E47 cells. While APAP had no direct effect on platelets, NAPQI exposure acted to decrease platelet aggregation. These findings enhance our understanding of the mechanisms of APAP-induced hepatotoxicity and the potential role of APAP-induced hepatocellular toxicity in platelet aggregation.

PPARβ/δ agonist GW0742 mitigates acute liver damage induced by acetaminophen overdose in mice

Liver damage caused by acetaminophen (APAP) overdose remains a worldwide medical problem. New therapeutic medicines for APAP poisoning are needed as the efficacy of the only antidote, N-acetyl-cysteine (NAC), significantly decreases if administered after 8 h of APAP intake and massive APAP overdose remains to induce hepatotoxicity despite the timely administration of NAC. Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) possesses versatile roles including regulation of lipid homeostasis and anti-inflammation in the liver. This study aimed to investigate the effects of GW0742, one specific PPARβ/δ agonist, on APAP-caused liver damage in mice. We found that GW0742 (40 mg/kg, i.p.) pretreatment completely blocked the increase of serum aminotransferase activities, hepatocyte necrosis, oxidative stress, and liver inflammation in mice exposed to 300 mg/kg APAP (i.p.). Mechanistically, GW0742 pretreatment significantly suppressed the M1 polarization of liver Kupffer cells and activation of NLRP3 inflammasome. Interestingly, GW0742 remained effective when administered 6 h after APAP exposure, although its efficacy was less pronounced than that administered 6 h before the APAP challenge. Notably, GW0742 exhibited a more profound effect than NAC evidenced by the lower serum alanine transaminase (ALT) level and the improved histopathological manifestation. Furthermore, exposure to APAP for 6 h had resulted in dramatic liver inflammation, while pretreatment with GW0742 prior to APAP exposure did not influence the increase in serum aminotransferase activity and oxidative stress at 2 h after APAP exposure. These results highlight that PPARβ/δ may be a promising therapeutic target for treating APAP-caused acute liver damage probably acting on liver macrophages.

Causal, predictive or observational? Different understandings of key event relationships for adverse outcome pathways and their implications on practice

The Adverse Outcome Pathways (AOPs) framework is pivotal in toxicology, but the, terminology describing Key Event Relationships (KERs) varies within AOP guidelines.This study examined the usage of causal, observational and predictive terms in AOP, documentation and their adaptation in AOP development. A literature search and text, analysis of key AOP guidance documents revealed nuanced usage of these terms, with KERs often described as both causal and predictive. The adaptation of, terminology varies across AOP development stages. Evaluation of KER causality often, relies targeted blocking experiments and weight-of-evidence assessments in the, putative and qualitative stages. Our findings highlight a potential mismatch between,terminology in guidelines and methodologies in practice, particularly in inferring,causality from predictive models. We argue for careful consideration of terms like, causal and essential to facilitate interdisciplinary communication. Furthermore, integrating known causality into quantitative AOP models remains a challenge.

AIM2 regulates autophagy to mitigate oxidative stress in aged mice with acute liver injury

The cytoplasmic pattern recognition receptor, absent in melanoma 2 (AIM2), detects cytosolic DNA, activating the inflammasome and resulting in pro-inflammatory cytokine production and pyroptotic cell death. Recent research has illuminated AIM2's contributions to PANoptosis and host defense. However, the role of AIM2 in acetaminophen (APAP)-induced hepatoxicity remains enigmatic. In this study, we unveil AIM2's novel function as a negative regulator in the pathogenesis of APAP-induced liver damage in aged mice, independently of inflammasome activation. AIM2-deficient aged mice exhibited heightened lipid accumulation and hepatic triglycerides in comparison to their wild-type counterparts. Strikingly, AIM2 knockout mice subjected to APAP overdose demonstrated intensified liver injury, compromised mitochondrial stability, exacerbated glutathione depletion, diminished autophagy, and elevated levels of phosphorylated c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, our investigation revealed AIM2's mitochondrial localization; its overexpression in mouse hepatocytes amplified autophagy while dampening JNK phosphorylation. Notably, induction of autophagy through rapamycin administration mitigated serum alanine aminotransferase levels and reduced the necrotic liver area in AIM2-deficient aged mice following APAP overdose. Mechanistically, AIM2 deficiency exacerbated APAP-induced acute liver damage and inflammation in aged mice by intensifying oxidative stress and augmenting the phosphorylation of JNK and ERK. Given its regulatory role in autophagy and lipid peroxidation, AIM2 emerges as a promising therapeutic target for age-related acute liver damage treatment.

Fructose as a novel nutraceutical for acetaminophen (APAP)-induced hepatotoxicity

Acetaminophen (APAP) is the most widely used analgesic in the world. APAP overdose can cause severe hepatotoxicity and therefore is the most common cause of drug-induced liver injury. The only approved treatment for APAP overdose is N-acetyl-cysteine (NAC) supplementation. However, the narrow efficacy window of the drug severely limits its clinical use, prompting the search for other therapeutic options to counteract APAP toxicity. Recent research has pointed to fructose as a novel nutraceutical for APAP-induced liver injury. This review summarizes the current understanding of the molecular mechanisms underlying APAP-induced liver injury, introduces how fructose supplementation could prevent and treat APAP liver toxicity with a focus on the ChREBPα-FGF21 pathway, and proposes possible future directions of study.

Potential Curative Effects of Aqueous Extracts of Cissus quadrangularis (Vitaceae) and Jatropha gossypiifolia (Euphorbiaceae) on Acetaminophen-Induced Liver Injury in Mice

Background

Acetaminophen-induced liver injury remains a significant public health problem because available treatments are limited due to their adverse effects. Medicinal plants, which are an important source of bioactive molecules, could be an alternative treatment for liver disease.

Objective

This study was designed to investigate the curative effect of aqueous extracts of Cissus quadrangularis (Vitaceae) and Jatropha gossypiifolia (Euphorbiaceae) on acetaminophen-induced liver injury in mice.

Methods

Mice were divided into groups and treated with distilled water, silymarin (50 mg/kg), a reference hepatoprotective agent, and aqueous extracts of C quadrangularis and J gossypiifolia (50 and 100 mg/kg, PO, respectively). These substances were given as a single daily dose 4 hours after acetaminophen administration (300 mg/kg, PO) for 2 days. Mice were humanely put to death 24 hours after the last dose and serum alanine aminotransferase and aspartate aminotransferase activities, total bilirubin and protein levels, reduced glutathione, superoxide dismutase, malondialdehyde, catalase, and nitrite tissue levels were assessed. Histology of the livers of the mice was performed by hematoxylin and eosin staining.

Results

Acetaminophen administration induced a significant (P < 0.05) mean (SEM) body weight loss (-14.45% [5.92%]), a significant elevation of alanine aminotransferase activity (15.08%), total protein and bilirubin levels (25.80%), and a significant (P < 0.05) increase in liver superoxide dismutase (67.71%), catalase (63.00%), glutathione (40.29%), malondialdehyde (30.67%), and nitrite levels compared with the control group. In curative treatment, C quadrangularis and J gossypiifolia (50 and 100 mg/kg) significantly (P < 0.05) reduced mean (SEM) body weight loss (16.67% [7.16%] and 1.25% [0.51%], respectively), serum alanine aminotransferase activity (17.62% and 11.14%, respectively), bilirubin level (29.62% and 49.14%, respectively) compared with acetaminophen group, and J gossypiifolia normalized serum total protein level. Both extracts significantly (P < 0.05) reduced the levels of glutathione and malondialdehyde and normalized that of nitrite, superoxide dismutase, and catalase compared with the acetaminophen group. Hepatocyte necrosis and inflammatory cell infiltration were remarkably reduced by the plant extracts.

Conclusions

The results obtained are evidence in favor of the development of a formulation based on the extracts of these plants against liver diseases.

Role of NADPH Oxidase-Derived ROS-Mediated IL-6/STAT3 and MAPK/NF-κB Signaling Pathways in Protective Effect of Corilagin against Acetaminophen-Induced Liver Injury in Mice

Acetaminophen (APAP) overdose causes acute liver injury via oxidative stress, uncontrolled inflammatory response, and subsequent hepatocyte death. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is a potent source of cellular reactive oxygen species (ROS) and may contribute to oxidative stress in many inflammatory processes. Corilagin, a component of Phyllanthus urinaria, possesses antioxidant, anti-inflammatory, and hepatoprotective effects. We evaluated the mechanisms underlying the protective effect of corilagin against acetaminophen-induced liver injury. Mice were intraperitoneally administrated 300 mg/kg APAP or equal volume of saline (control), with or without various concentrations of corilagin (0, 1, 5, or 10 mg/kg) administered after 30 min. All animals were sacrificed 16 h after APAP administration, and serum and liver tissue assays including histology, immunohistochemistry, and Western blot assay were performed. Corilagin post-treatment significantly attenuated APAP-induced liver injury (p < 0.005), inflammatory cell infiltration, hepatic proinflammatory cytokine levels, and hepatic oxidative stress. Furthermore, corilagin attenuated the protein levels of NOX1, NOX2, signal transducer and activator of transcription 3 (STAT3), and nuclear factor kappa B (NF-κB) in APAP-induced liver injury. These results indicated that the antioxidant, anti-inflammatory, and protective effects of corilagin in APAP-induced liver injury might involve the regulation of interleukin (IL)-6/STAT3 and mitogen-activated protein kinase (MAPK)/NF-κB signaling pathways through NOX-derived ROS.

Acetaminophen induced hepatotoxicity: An overview of the promising protective effects of natural products and herbal formulations

BACKGROUND

The liver plays an important role in regulating the metabolic processes and is the most frequently targeted organ by toxic chemicals. Acetaminophen (APAP) is a well-known anti-allergic, anti-pyretic, non-steroidal anti-inflammatory drug (NSAID), which upon overdose leads to hepatotoxicity, the major adverse event of this over-the-counter drug.

PURPOSE

APAP overdose induced acute liver injury is the second most common cause that often requires liver transplantation worldwide, for which N-acetyl cysteine is the only synthetic drug clinically approved as an antidote. So, it was felt that there is a need for the novel therapeutic approach for the treatment of liver diseases with less adverse effects. This review provides detailed analysis of the different plant extracts; phytochemicals and herbal formulations for the amelioration of APAP-induced liver injury.

METHOD

The data was collected using different online resources including PubMed, ScienceDirect, Google Scholar, Springer, and Web of Science using keywords given below.

RESULTS

Over the past decades various reports have revealed that plant-based approaches may be a better treatment choice for the APAP-induced hepatotoxicity in pre-clinical experimental conditions. Moreover, herbal compounds provide several advantages over the synthetic drugs with fewer side effects, easy availability and less cost for the treatment of life-threatening diseases.

CONCLUSION

The current review summarizes the hepatoprotective effects and therapeutic mechanisms of various plant extracts, active phytoconstituents and herbal formulations with potential application against APAP induced hepatotoxicity as the numbers of hepatoprotective natural products are more without clinical relativity. Further, pre-clinical pharmacological research will contribute to the designing of natural products as medicines with encouraging prospects for clinical application.

A review: Systematic research approach on toxicity model of liver and kidney in laboratory animals

Therapeutic experiments are commonly performed on laboratory animals to investigate the possible mechanism(s) of action of toxic agents as well as drugs or substances under consideration. The use of toxins in laboratory animal models, including rats, is intended to cause toxicity. This study aimed to investigate different models of hepatotoxicity and nephrotoxicity in laboratory animals to help researchers advance their research goals. The current narrative review used databases such as Medline, Web of Science, Scopus, and Embase and appropriate keywords until June 2021. Nephrotoxicity and hepatotoxicity models derived from some toxic agents such as cisplatin, acetaminophen, doxorubicin, some anticancer drugs, and other materials through various signaling pathways are investigated. To understand the models of renal or hepatotoxicity in laboratory animals, we have provided a list of toxic agents and their toxicity procedures in this review.

Customizable Microfluidic Origami Liver-on-a-Chip (oLOC)

The design and manufacture of an origami-based liver-on-a-chip device are presented, together with demonstrations of the chip's effectiveness at recapitulating some of the liver's key in vivo architecture, physical microenvironment, and functions. Laser-cut layers of polyimide tape are folded together with polycarbonate nanoporous membranes to create a stack of three adjacent flow chambers separated by the membranes. Endothelial cells are seeded in the upper and lower flow chambers to simulate sinusoids, and hepatocytes are seeded in the middle flow chamber. Nutrients and metabolites flow through the simulated sinusoids and diffuse between the vascular pathways and the hepatocyte layers, mimicking physiological microcirculation. Studies of cell viability, metabolic functions, and hepatotoxicity of pharmaceutical compounds show that the endothelialized liver-on-a-chip model is conducive to maintaining hepatocyte functions and evaluation of the hepatotoxicity of drugs. Our unique origami approach speeds chip development and optimization, effectively simplifying the laboratory-scale fabrication of on-chip models of human tissues without necessarily reducing their structural and functional sophistication.

Diacerein counteracts acetaminophen-induced hepatotoxicity in mice via targeting NLRP3/caspase-1/IL-1β and IL-4/MCP-1 signaling pathways

The current study aims at repurposing the anti-arthritic drug diacerein (DCN) for the treatment of acetaminophen hepatotoxicity and investigating the potential underlying mechanisms. Mice were randomly divided into six groups receiving either no treatment (control group), 20 mg/kg DCN i.p, 400 mg/kg acetaminophen i.p, DCN 4 h before acetaminophen, DCN 2 h after acetaminophen, or 400 mg/kg N-acetylcysteine (NAC) i.p, 2 h after acetaminophen. Biomarkers of liver dysfunction, oxidative stress, and apoptosis were assessed. Hepatic necroinflammatory changes were evaluated along with hepatic expression of NF-κB and caspase-1. The levels of NLRP3, IL-1β, IL-4, MCP-1, and TNF-α in the liver, as well as CYP2E1 mRNA expression, were measured. Diacerein significantly reduced biomarkers of liver dysfunction, oxidative stress, hepatocyte necrosis, and infiltration of neutrophils and macrophages whether administered 4 h before or 2 h after acetaminophen. Further, the effects were comparable to those of NAC. Diacerein also counteracted acetaminophen-induced hepatocellular apoptosis by increasing Bcl-2 and decreasing Bax and caspase-3 expression levels. Moreover, DCN normalized hepatic TNF-α and significantly decreased NF-κB p65 expression. Accordingly, DCN can prevent or reverse acetaminophen hepatotoxicity in mice, suggesting potential utility as a repurposed drug for clinical treatment.

Myrrhanone B and Myrrhanol B from resin of Commipohora mukul exhibit hepatoprotective effects in-vivo

Despite a large number of liver disorders, clinically useful drugs are scarce. Moreover, the available therapies are facing the challenges of efficacy and safety. Commipohora mukul has been used in folk medicine globally for millennia for the treatment of several ailments. The current study was designed to evaluate the possible hepatoprotective activity of Myrrhanone B (MN) and Myrrhanol B (ML) isolated from C. mukul using an animal model. The animals (Swiss albino mice) were segregated into seven groups, each comprising six mice. The first group was treated with normal saline at a dose of 1 ML/kg daily intraperitoneally (i.p.) for one week. The second group was treated with acetaminophen (APAP) (250 mg/kg, i.p.), it was taken as a negative control. Group 3 was used as a positive control (treated with Silymarin (100 mg/kg, i.p.)). While groups 4-7 were used as experimental groups (termed as groups II to IV), which were treated with ML and MN at a dose of 0.6 mg/kg, and 1.2 mg/kg (i.p.) for one week. Subsequently, blood serum and liver tissue samples were collected for biochemical and histopathological analysis. Both compounds significantly improved the levels of liver biomarkers including aspartate transaminase (AST), alkaline phosphatase (ALP), bilirubin, lactate dehydrogenase (LDH), and alanine transaminase (ALT) as compared to the normal saline-treated group in APAP-induced hepatotoxic mice. Moreover, both compounds significantly modulated the expression of oxidative biomarkers including superoxide dismutase (SOD), reduced glutathione (GSH), and catalase (CAT) at the same doses. Additionally, ML and MN showed a remarkable improvement in histological changes with only mild inflammation, mild hemorrhage, no necrosis, and no pyknosis as compared to the control groups. In conclusion, MN and ML exhibited significant hepatoprotective effects in the animal model used in this study.

Emodin Attenuates Acetaminophen-Induced Hepatotoxicity via the cGAS-STING Pathway

Emodin is a natural bioactive compound from traditional Chinese herbs that exerts anti-inflammatory, antioxidant, anticancer, hepatoprotective, and neuroprotective effects. However, the protective effects of emodin in acetaminophen (APAP)-induced hepatotoxicity are not clear. The present study examined the effects of emodin on APAP-induced hepatotoxicity and investigated the potential molecular mechanisms. C57BL/6 mice were pretreated with emodin (15 and 30 mg/kg) for 5 consecutive days and then given APAP (300 mg/kg) to establish an APAP-induced liver injury model. Mice were sacrificed to detect the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and albumin (ALB) and the liver tissue levels of glutathione (GSH), malondialdehyde (MDA), and superoxide dismutase (SOD). Histological assessment, Western blotting, and ELISA were performed. Emodin pretreatment significantly reduced the levels of ALT, AST, and ALP; increased the levels of ALB; alleviated hepatocellular damage and apoptosis; attenuated the exhaustion of GSH and SOD and the accumulation of MDA; and increased the expression of antioxidative enzymes, including nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1), and NAD(P)H quinone dehydrogenase 1 (NQO1). Emodin also inhibited the expression of NLRP3 and reduced the levels of pro-inflammatory factors, including interleukin-1 beta (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α). Emodin inhibited interferon (IFN)-α, cyclic GMP-AMP synthase (cGAS), and its downstream signaling effector stimulator of interferon genes (STING) expression to protect the liver against APAP-induced inflammatory responses and apoptosis. These results suggest that emodin protected hepatocytes from APAP-induced liver injury via the upregulation of the Nrf2-mediated antioxidative stress pathway, the inhibition of the NLRP3 inflammasome, and the downregulation of the cGAS-STING signaling pathway.

Kaempferol from Penthorum chinense Pursh suppresses HMGB1/TLR4/NF-κB signaling and NLRP3 inflammasome activation in acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) is one of the safest and most effective over-the-counter (OTC) analgesics and antipyretics, but excessive doses of APAP will induce hepatotoxicity with high morbidity and mortality worldwide. Kaempferol (KA), a flavonoid compound derived from the medicinal and edible plant of Penthorum chinense Pursh, has been reported to exert a profound anti-inflammatory and antioxidant activity. In this study, we explored the protective effect and novel mechanism of KA against APAP-induced hepatotoxicity. The results revealed that KA pretreatment significantly reduced the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), relieved hepatocellular damage and apoptosis, attenuated the exhaustion of glutathione (GSH) and accumulation of malondialdehyde (MDA), increased the expression of antioxidative enzymes (e.g., heme oxygenase 1 (HO-1) and NADPH quinone oxidoreductase 1 (NQO1)), and thus restrained APAP-induced oxidative damage in the liver. KA suppressed the expression of NLRP3 and reduced the levels of pro-inflammatory factors, including interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6). Moreover, KA remarkably inhibited high-mobility group box 1 (HMGB1) and toll-like receptor 4 (TLR4) expression as well as nuclear factor kappa-B (NF-κB) activation for liver protection against APAP-induced inflammatory responses and apoptosis. Taken together, our findings suggested that KA could effectively protect hepatocytes from APAP hepatotoxicity through the up-regulation of HO-1 and NQO1 expression, the down-regulation of NLRP3 expression, and the inhibition of the HMGB1/TLR4/NF-κB signaling pathway.

Metabolomics analysis reveals the protective effect of quercetin-3-O-galactoside (Hyperoside) on liver injury in mice induced by acetaminophen

We investigated the protective effect of Hyperoside (HPS) on liver injury induced by acetaminophen (APAP) in C57 mice. HPS was administered orally for 7 days and APAP was administered orally on the 7th day. Serum and liver samples were then collected for biochemical analyses, histopathology assessments, and metabolomics studies. Metabolites were assessed using a UHPLC-MS system. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used to process the data. Pathway analyses were performed using Metaboanalyst 4.0. Western blot and qRT-PCR were used to determine the protein and mRNA levels, respectively. HPS interacted with active sites in CYP2E1 and caused protein degradation. In conclusion, our results suggested that HPS prevented the oxidative stress-induced liver injury caused by APAP. PRACTICAL APPLICATIONS: Hyperoside was shown to have potential protective and therapeutic effects against liver diseases. Male C57 mice were used to perform pharmacodynamic, pharmacology, and metabolomics evaluations. At a dose of 60 mg/kg, HPS prevented oxidative stress-induced liver injury caused by APAP by regulating the glutathione-related metabolites and enzymes through the inhibition of CYP2E1.

The c-Met inhibitor capmatinib alleviates acetaminophen-induced hepatotoxicity

Acetaminophen (APAP)-induced hepatotoxicity comes among the most frequent humans' toxicities caused by drugs. So far, therapeutic interventions for such type of drug-induced toxicity are still limited. In the current study, we examined the influence of capmatinib (Cap), a novel c-Met inhibitor, on APAP-induced hepatotoxicity in mice when administered 2 h prior, 2 h post and 4 h post APAP-challenge. The results revealed that Cap administration significantly attenuated APAP-induced liver injury when administered only 2 h prior and post APAP-administration. Cap hepatoprotective effect was mediated by lowering the excessive formation of lipid peroxidation and nitrosative stress products caused by APAP. Besides, Cap attenuated APAP-induced overproduction and release of proinflammatory mediators like TNF-α, IL-1β, IL-17A, IL-6, and MCP-1. Cap treatment also led to avoidance of APAP-subsequent repair by abating APAP-induced elevation of hepatic IL-22 and PCNA expressions. In conclusion, c-Met receptor inhibition may be a potential strategy for alleviating APAP-hepatotoxicity, especially when administered in the early phase of intoxication.

Comparative Study of Protective Effect of Cimetidine and Verapamil on Paracetamol-Induced Hepatotoxicity in Mice

Paracetamol, chemically known as acetaminophen, if taken in higher doses has hepatotoxic potential. Cimetidine by inhibiting the cytochromal enzymes and reducing the production of the toxic metabolite can reduce the hepatotoxic potential while Verapamil can act as a hepatoprotective by maintaining calcium homeostasis. The present study was conducted to study the hepatoprotective activity of Cimetidine and Verapamil against the toxicity induced by paracetamol. In addition to the group receiving only distilled water or 300 mg/kg paracetamol additional groups were added treated with 150 mg/kg Cimetidine and Verapamil alone or both. The Liver function tests and histopathology revealed hepatotoxicity in the group receiving paracetamol (PCM) while normal parameters were observed in the groups receiving Cimetidine and Verapamil. Our results strongly suggested that Cimetidine and Verapamil possess hepatoprotective potential against paracetamol induced hepatotoxicity.

Acetaminophen-induced liver injury is mediated by the ion channel TRPV4

Overdosing of the analgesic acetaminophen (APAP) is one of the most common causes for acute liver failure in modern countries. Although the exact molecular mechanisms mediating hepatocellular necrosis are still elusive, it is preceded by oxidative stress triggered by excessive levels of the metabolite N-acetyl-para-benzoquinone imine (NAPQI). Here, we describe the role of the redox-sensitive transient receptor potential (TRP) ion channel TRP vanilloid 4 (TRPV4) for APAP-induced hepatoxicity. Both pharmacological inhibition and genetic deletion of TRPV4 ameliorate APAP-induced necrosis in mouse and human hepatocytes in vitro. Liver injury caused by a systemic overdose of APAP is reduced in TRPV4-deficient mice and in wild-type mice treated with a TRPV4 inhibitor. The reduction of hepatotoxicity accomplished by systemic TRPV4 inhibition is comparable to the protective effects of the antioxidant N-acetyl-cysteine. Although TRPV4 does not modulate intrahepatic levels of glutathione, both its inhibition and genetic deletion attenuate APAP-induced oxidative and nitrosative stress as well as mitochondrial membrane depolarization. NAPQI evokes a calcium influx by activating heterologously expressed TRPV4 channels and endogenous TRPV4 channels in hepatoma cells but not in primary mouse hepatocytes. Taken together, our data suggest that TRPV4 mediates APAP-induced hepatotoxicity and thus may be a suitable target for treatment of this critical side effect.-Echtermeyer, F., Eberhardt, M., Risser, L., Herzog, C., Gueler, F., Khalil, M., Engel, M., Vondran, F., Leffler, A. Acetaminophen-induced liver injury is mediated by the ion channel TRPV4.

Recombinant human soluble thrombomodulin ameliorates acetaminophen-induced liver toxicity in mice

Recombinant human soluble thrombomodulin alpha (rhTM) has been developed as an anticoagulant with anti-inflammatory activity. Notably, acetaminophen (APAP) -induced liver disease (AILI) is caused by direct metabolite-induced hepatotoxicity as well as hepatic hyper-coagulation. To evaluate the utility of anticoagulant for the treatment of AILI, rhTM was administered in a mouse AILI model and liver damage was analyzed. AILI was induced in 8-week-old mice by intraperitoneal injection of APAP. rhTM (20 mg/kg) or placebo was injected at the same time as APAP administration. Serum alanine aminotransferase, fibrin degradation products and high-mobility group box 1 levels were significantly decreased in the rhTM-treated group compared with the control group. Furthermore, rhTM reduced the necrotic area and fibrin deposition in liver sections. rhTM suppressed the mRNA expression of heme oxygenase-1, plasminogen activator inhibitor type-1, tissue factors, and inflammatory cytokines compared with the control group. rhTM did not change the hepatic GSH content at 2 h after APAP injection, but restored them at 4 h after the insult. rhTM ameliorated liver damage in mice with AILI, probably via the improvement in liver perfusion induced by it's anticoagulant acitivity, which can lead to the suppression of secondary liver damage.

Cryopreserved Human Intestinal Mucosal Epithelium: A Novel In Vitro Experimental System for the Evaluation of Enteric Drug Metabolism, Cytochrome P450 Induction, and Enterotoxicity

We report here a novel in vitro enteric experimental system, cryopreserved human intestinal mucosa (CHIM), for the evaluation of enteric drug metabolism, drug-drug interaction, drug toxicity, and pharmacology. CHIM was isolated from the small intestines of four human donors. The small intestines were first dissected into the duodenum, jejunum, and ileum, followed by collagenase digestion of the intestinal lumen. The isolated mucosa was gently homogenized to yield multiple cellular fragments, which were then cryopreserved in a programmable liquid cell freezer and stored in liquid nitrogen. After thawing and recovery, CHIM retained robust cytochrome P450 (P450) and non-P450 drug-metabolizing enzyme activities and demonstrated dose-dependent induction of transcription of CYP24A1 (approximately 300-fold) and CYP3A4 (approximately 3-fold) by vitamin D3 as well as induction of CYP3A4 (approximately 3-fold) by rifampin after 24 hours of treatment. Dose-dependent decreases in cell viability quantified by cellular ATP content were observed for naproxen and acetaminophen, with higher enterotoxicity observed for naproxen, consistent with that observed in humans in vivo. These results suggest that CHIM may be a useful in vitro experimental model for the evaluation of enteric drug properties, including drug metabolism, drug-drug interactions, and drug toxicity.

Connexin hemichannel inhibition reduces acetaminophen-induced liver injury in mice

Historically, connexin hemichannels have been considered as structural precursors of gap junctions. However, accumulating evidence points to independent roles for connexin hemichannels in cellular signaling by connecting the intracellular compartment with the extracellular environment. Unlike gap junctions, connexin hemichannels seem to be mainly activated in pathological processes. The present study was set up to test the potential involvement of hemichannels composed of connexin32 and connexin43 in acute hepatotoxicity induced by acetaminophen. Prior to this, in vitro testing was performed to confirm the specificity and efficacy of TAT-Gap24 and TAT-Gap19 in blocking connexin32 and connexin43 hemichannels, respectively. Subsequently, mice were overdosed with acetaminophen followed by treatment with TAT-Gap24 or TAT-Gap19 or a combination of both after 1.5h. Sampling was performed 3, 6, 24 and 48h following acetaminophen administration. Evaluation of the effects of connexin hemichannel inhibition was based on a series of clinically relevant read-outs, measurement of inflammatory cytokines and oxidative stress. Subsequent treatment of acetaminophen-overdosed mice with TAT-Gap19 only marginally affected liver injury. In contrast, a significant reduction in serum alanine aminotransferase activity was found upon administration of TAT-Gap24 to intoxicated animals. Furthermore, co-treatment of acetaminophen-overdosed mice with both peptides revealed an additive effect as even lower serum alanine aminotransferase activity was observed. Blocking of connexin32 or connexin43 hemichannels individually was found to decrease serum quantities of pro-inflammatory cytokines, while no effects were observed on the occurrence of hepatic oxidative stress. This study shows for the first time a role for connexin hemichannels in acetaminophen-induced acute liver failure.

Oxidative stress during acetaminophen hepatotoxicity: Sources, pathophysiological role and therapeutic potential

Acetaminophen (APAP) hepatotoxicity is characterized by an extensive oxidative stress. However, its source, pathophysiological role and possible therapeutic potential if targeted, have been controversially described. Earlier studies argued for cytochrome P450-generated reactive oxygen species (ROS) during APAP metabolism, which resulted in massive lipid peroxidation and subsequent liver injury. However, subsequent studies convincingly challenged this assumption and the current paradigm suggests that mitochondria are the main source of ROS, which impair mitochondrial function and are responsible for cell signaling resulting in cell death. Although immune cells can be a source of ROS in other models, no reliable evidence exists to support a role for immune cell-derived ROS in APAP hepatotoxicity. Recent studies suggest that mitochondrial targeted antioxidants can be viable therapeutic agents against hepatotoxicity induced by APAP overdose, and re-purposing existing drugs to target oxidative stress and other concurrent signaling events can be a promising strategy to increase its potential application in patients with APAP overdose.

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Oxidative stress plays a critical role in acetaminophen hepatotoxicity.

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Mitochondria are the main source of ROS and RNS that are responsible for the toxicity.

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Cytochrome P450 and inflammatory cells are probably not relevant sources of ROS for the toxicity.

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Mitochondrial oxidative stress is a promising therapeutic target against APAP overdose.

Acetaminophen-Induced Hepatotoxicity: a Comprehensive Update

Hepatic injury and subsequent hepatic failure due to both intentional and non-intentional overdose of acetaminophen (APAP) has affected patients for decades, and involves the cornerstone metabolic pathways which take place in the microsomes within hepatocytes. APAP hepatotoxicity remains a global issue; in the United States, in particular, it accounts for more than 50% of overdose-related acute liver failure and approximately 20% of the liver transplant cases. The pathophysiology, disease course and management of acute liver failure secondary to APAP toxicity remain to be precisely elucidated, and adverse patient outcomes with increased morbidity and mortality continue to occur. Although APAP hepatotoxicity follows a predictable timeline of hepatic failure, its clinical presentation might vary. N-acetylcysteine (NAC) therapy is considered as the mainstay therapy, but liver transplantation might represent a life-saving procedure for selected patients. Future research focus in this field may benefit from shifting towards obtaining antidotal knowledge at the molecular level, with focus on the underlying molecular signaling pathways.

Scanning and transmission electron microscopy of the cells forming the hepatic sinusoidal wall of rat in acetaminophen and Escherichia coli endotoxin-induced hepatotoxicity

Drugs and xenobiotics as well as bacterial endotoxins may reach the liver either systematically or after intestinal absorption. Therefore, cells lining the sinusoidal wall form the last barrier before blood constituents get in contact with the parenchymal cells. In this work, the ultrastructure of the cells forming the sinusoidal wall was studied after acetaminophen and Escherichia coli endotoxin treatments. Rats received acetaminophen at a dose of 1000 mg/kg body weight by intraperitoneal injection once in acute and four times with a 1-week interval in chronic treatments, and E. coli endotoxin at a dose of 5 mg/kg of body weight by intraperitoneal injection once in acute and four times with a 1-week interval in chronic treatments. Tissue samples were collected for scanning and transmission electron microscopy. Swelling of sinusoidal endothelial cells was noticed in both acute intoxicated groups with narrowing of the fenestrae, whereas large gaps were formed in chronic toxicity. Activation of Kupffer cells was a prominent common feature between the four toxicity groups. Interestingly, hepatic stellate cell activation was evident in both chronic acetaminophen and chronic endotoxin groups. Large amounts of collagen fibers were seen surrounding the hepatic stellate cells and in Disse space.