Safety and effectiveness of acetadote for acetaminophen toxicity

Deciphering Acetaminophen-Induced Hepatotoxicity: The Crucial Role of Transcription Factors like Nuclear Factor Erythroid 2-Related Factor 2 as Genetic Determinants of Susceptibility to Drug-Induced Liver Injury

Acetaminophen (APAP) is the most commonly used over-the-counter medication throughout the world. At therapeutic doses, APAP has potent analgesic and antipyretic effects. The efficacy and safety of APAP are influenced by multifactorial processes dependent upon dosing, namely frequency and total dose. APAP poisoning by repeated ingestion of supratherapeutic doses, depletes glutathione stores in the liver and other organs capable of metabolic bioactivation, leading to hepatocellular death due to exhausted antioxidant defenses. Numerous genes, encompassing transcription factors and signaling pathways, have been identified as playing pivotal roles in APAP toxicity, with the liver being the primary organ studied due to its central role in APAP metabolism and injury. Nuclear factor erythroid 2-related factor 2 (NRF2) and its array of downstream responsive genes are crucial in counteracting APAP toxicity. NRF2, along with its negative regulator Kelch-like ECH-associated protein 1, plays a vital role in regulating intracellular redox homeostasis. This regulation is significant in modulating the oxidative stress, inflammation, and hepatocellular death induced by APAP. In this review, we provide an updated overview of the mechanisms through which NRF2 activation and signaling critically influence the threshold for developing APAP toxicity. We also describe how genetically modified rodent models for NRF2 and related genes have been pivotal in underscoring the significance of this antioxidant response pathway. While NRF2 is a primary focus, the article comprehensively explores other genetic factors involved in phase I and phase II metabolism of APAP, inflammation, oxidative stress, and related pathways that contribute to APAP toxicity, thereby providing a holistic understanding of the genetic landscape influencing susceptibility to this condition. SIGNIFICANCE STATEMENT: This review summarizes the genetic elements and signaling pathways underlying APAP-induced liver toxicity, focusing on the crucial protective role of the transcription factor NRF2. This review also delves into the genetic intricacies influencing APAP safety and potential liver harm. It also emphasizes the need for deeper insight into the molecular mechanisms of hepatotoxicity, especially the interplay of NRF2 with other pathways.

Febuxostat ameliorates APAP-induced acute liver injury by activating Keap1/Nrf2 and inhibiting TLR4/NF-κB p65 pathways

Excessive acetaminophen (APAP) application is a major cause of drug-induced liver injury (DILI). Febuxostat (Feb), a drug for reducing uric acid (UA) levels, was demonstrated to relieve hepatic inflammation and reverse organ functions. However, the effect of Feb on APAP-induced DILI and its mechanisms have not been fully explored. In this study, Feb (10 mg/kg) was given to mice by gavage 1 h after APAP (300 mg/kg, i.g.) induction. Serum and liver samples were collected 12 or 3 h after APAP challenge. Feb treatment was found to remarkably improve APAP-induced DILI, as evidenced by reduced serum ALT, AST and UA levels, pathomorphology, inflammatory, and oxidative responses. Consistently, treatment with Feb also reduced the cell injury induced by APAP in LO2 cells. Mechanistically, Feb induced GPX4 expression, activated the Keap1/Nrf2 pathway, and inhibited the TLR4/NF-κB p65 pathway. Feb also inhibited glutathione (GSH) depletion and Jun N-terminal kinase (JNK) activation in the early injury phase. Notably, pretreatment with Feb for 3 days also revealed preventive effects against APAP-induced DILI in mice. Overall, our data revealed a potential health impact of Feb on APAP-mediated DILI in vivo and in vitro, suggesting that Feb might be a potential candidate for treating DILI.

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

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

Kahweol Protects against Acetaminophen-Induced Hepatotoxicity in Mice through Inhibiting Oxidative Stress, Hepatocyte Death, and Inflammation

Acetaminophen (APAP) can cause acute liver failure, but treatment options are still limited. Kahweol is the main diterpene compound of coffee and possesses antioxidant and anti-inflammatory properties. Emerging evidence suggests that this natural diterpene exerts favorable effects on several inflammatory diseases. However, the action of kahweol on APAP toxicity has not been addressed. The purpose of this study was to explore whether kahweol has a protective activity against APAP-induced hepatotoxicity and to investigate the mechanism. Administration of kahweol reduced serum levels of liver injury indicators and ameliorated histological abnormalities in APAP-treated mice. Kahweol inhibited lipid peroxidation and nucleic acid oxidation with restoration of glutathione content and stimulation of nuclear factor erythroid-2-related factor 2-dependent cellular defense system. Hepatocyte death was also decreased by kahweol, which was associated with inhibition of endoplasmic reticulum (ER) stress. Moreover, kahweol reduced hepatic levels of inflammatory mediators, inhibited nuclear factor-κB activation, and attenuated infiltration of neutrophils and macrophages. These findings suggest that kahweol has a protective activity against APAP-induced liver injury and this effect is related to the suppression of oxidative stress, hepatocyte death, ER stress, and inflammation.

Enhancement of TEX264-Mediated ER-Phagy Contributes to the Therapeutic Effect of Glycycoumarin against APA Hepatotoxicity in Mice

Acetaminophen (APA)-induced hepatotoxicity is coupled with the activation of autophagy. We sought to determine whether selective autophagy of the endoplasmic reticulum (ER), termed ER-phagy, is involved in APA hepatotoxicity and to explore its potential as a therapeutic target for APA-induced liver injury (AILI). APA (300 or 600 mg/kg) was administered to male C57BL/6N mice, with and without rapamycin, glycycoumarin (GCM) and N-acetylcysteine (NAC). The results demonstrated that ER-phagy accompanied with ER stress was activated after APA overdose. The dynamic changes of LC3 and TEX264 revealed that ER-phagy was induced as early as 6 h and peaked at 24 h following the APA injection. A delayed treatment with GCM, but not rapamycin, considerably attenuated a liver injury and, consequently, reduced its mortality. This is probably due to the inhibition of ER stress and the acceleration of liver regeneration via enhanced ER-phagy. Unlike the impaired hepatocyte proliferation and more severe liver injury in mice that received prolonged treatment with NAC, liver recovery is facilitated by repeated treatment with GCM. These findings suggest that TEX264-mediated ER-phagy is a compensatory mechanism against ER stress provoked by an APA overdose. A delayed and prolonged treatment with GCM enhances ER-phagy, thus serving as a potential therapeutic approach for patients presenting at the late stage of AILI.

UPLC-PDA-ESI/MS metabolic profiling of dill shoots bioactive fraction; evidence of its antioxidant and hepatoprotective effects in vitro and in vivo

Hydroxyl radical (^• OH) scavenging capacity of aqueous dill (Anethum graveolens L.) shoot (ADSh) extract was assessed using electron paramagnetic resonance (EPR) spectroscopy. ADSh extract (at concentrations of 0.5 and 10 mg/ml) exerted high (OH) radical scavenging power. ADSh extract was further fractionated on Diaion HP-20 column to yield five fractions. EPR spin-trapping assay revealed fraction 4 (eluted with 75% aq. MeOH) to possess (^• OH) radical scavenging capacity over a concentration range (0.01-10 mg/ml), whereas fraction 2 (eluted with 25% aq. MeOH) appeared to be pro-oxidant at concentration 0.01 mg/ml. UPLC-PDA-ESI-MS metabolite profiling of ADSh extract revealed 87 metabolites, of which 64 compounds were identified in fraction 4, the most active fraction. Furthermore, ADSh extract demonstrated a hepatoprotective effect against acetaminophen (APAP)-induced hepatotoxicity in rats. Pretreatment of rats with ADSh extract (200 mg/kg b.wt) markedly attenuated the increased in the serum hepatic enzyme levels. It also increased free glutathione level and total antioxidant capacity in the serum of treated rats. [Correction added on May 3, 2021, after first online publication: "rates" has been changed to "rats" in the previous sentence.] Additionally, levels of (TNF-α and IL-1β) were back to almost normal levels compared to the control group. The above findings suggest that ADSh extract has a protective effect against APAP-induced liver damage.

Protective Effect of Dihydrokaempferol on Acetaminophen-Induced Liver Injury by Activating the SIRT1 Pathway

Acetaminophen (APAP) overdose is the leading cause of acute liver failure (ALF) in the Western world, with limited treatment opportunities. 3,5,7,4[Formula: see text]-Tetrahydroxyflavanone (Dihydrokaempferol, DHK, Aromadendrin) is a flavonoid isolated from Chinese herbs and displays high anti-oxidant and anti-inflammatory capacities. In this study, we investigated the protective effect by DHK against APAP-induced liver injury in vitro and in vivo and the potential mechanism of action. Cell viability assays were used to determine the effects of DHK against APAP-induced liver injury. The levels of reactive oxygen species (ROS), serum alanine/aspartate aminotransferases (ALT/AST), liver myeloperoxidase (MPO), and malondialdehyde (MDA) were measured and analyzed to evaluate the effects of DHK on APAP-induced liver injury. Western blotting, immunofluorescence staining, RT-PCR, and Transmission Electron Microscope were carried out to detect the signaling pathways affected by DHK. Here, we found that DHK owned a protective effect on APAP-induced liver injury with a dose-dependent manner. Meanwhile, Western blotting showed that DHK promoted SIRT1 expression and autophagy, activated the NRF2 pathway, and inhibited the translocation of nuclear p65 (NF-[Formula: see text]B) in the presence of APAP. Furthermore, SIRT1 inhibitor EX-527 aggravated APAP-induced hepatotoxicity when treating with DHK. Molecular docking results suggested potential interaction between DHK and SIRT1. Taken together, our study demonstrates that DHK protects against APAP-induced liver injury by activating the SIRT1 pathway, thereby promoting autophagy, reducing oxidative stress injury, and inhibiting inflammatory responses.

Apigenin Attenuates Acetaminophen-Induced Hepatotoxicity by Activating AMP-Activated Protein Kinase/Carnitine Palmitoyltransferase I Pathway

Overuse of acetaminophen (APAP) is a major cause of drug-induced liver failure at the clinics. Apigenin (API) is a natural flavonoid derived from Matricaria chamomilla. The aim of the present study was to investigate the amelioration function of API in APAP-induced hepatotoxicity both in vitro and in vivo and investigate its potential mechanisms. Analysis results of the activities of serum alanine and aspartate aminotransferases (ALT and AST), malondialdehyde, myeloperoxidase (MPO), and reactive oxygen species (ROS) demonstrated therapeutic effects of API. MTT assay results revealed that API attenuated APAP and its metabolic product, N-acetyl-p-benzoquinone imine (NAPQI) induced cytotoxicity in a dose-dependent manner in human liver cells, L-02 cells. Subsequently, metabolomic results of cells and serum analyses demonstrated an aberrant level of carnitine palmitoyltransferase I (CPT1A). We established that API stimulated CPT1A activity in mice liver tissues and L-02 cells. Molecular docking analyses revealed potential interaction of API with CPT1A. Further investigation of the role of CPT1A in L0-2 cells revealed that API reversed cytotoxicity via the AMP-activated protein kinase (AMPK)/GSK-3β signaling pathway and compound C, which is a selective AMPK inhibitor, inhibited activation of CPT1A induced by API. API was bound to the catalytic region of AMPK as indicated by molecular docking results. In addition, compound C suppressed nuclear translocation of nuclear factor erythroid 2–related factor 2 (NRF2) that is enhanced by API and inhibited the antioxidative function of API. In summary, the study demonstrates that API attenuates APAP-induced hepatotoxicity by activating the AMPK/GSK-3β signaling pathway, which subsequently promotes CPT1A activity and activates the NRF2 antioxidant pathway.

NIR-II FL/PA dual-modal imaging long-term tracking of human umbilical cord-derived mesenchymal stem cells labeled with melanin nanoparticles and visible HUMSC-based liver regeneration for acute liver failure

Acetaminophen (APAP) has been widely used for relieving pain and fever, whilst overdose would lead to the occurrence of acute liver failure (ALF). Currently, few effective treatments are available for ALF in clinic, especially for severe, advanced- or end-stage patients who need liver transplantation. Human umbilical cord-derived mesenchymal stem cells (hUMSCs), as one of the mesenchymal stem cells, not only contribute to relieving hepatotoxicity and promoting hepatocyte regeneration due to their self-renewing, multi-differentiation potential, anti-inflammatory, immunomodulatory and paracrine properties, but possess lower immunomodulatory effects, faster self-renewal properties and noncontroversial ethical concerns, which may play a better role in the treatment of ALF. In this work, hUMSCs were rapidly labeled with near-infrared II fluorescent dye-modified melanin nanoparticles (MNP-PEG-H2), which could realize long-term tracking of hUMSCs by NIR-II fluorescent (FL)/photoacoustic (PA) dual-modal imaging and could visualize hUMSC-based liver regeneration in ALF. The nanoparticles exhibited good dispersibility and biocompatibility, high labeling efficiency for hUMSCs and excellent NIR-II FL/PA imaging performance. Moreover, the MNP-PEG-H2 labeled hUMSCs could be continuously traced in vivo for up to 21 days. After intravenous delivery, the NIR-II FL and PA images revealed that labeled hUMSCs were able to engraft in the injured liver and repair damaged tissue in ALF mice. Therefore, the hUMSCs labeled with endogenous melanin nanoparticles solve the key tracing problem of MSC-based regenerative medicine and realize the visualization of the treatment process, which may provide an efficient, safe and potential choice for ALF.

Anti-inflammatory and antioxidant effects of Apium graveolens L. extracts mitigate against fatal acetaminophen-induced acute liver toxicity

In the present work, antioxidant activity, total phenolics (TP), and total flavonoids (TF) contents of aqueous and methanol extracts of celery were determined, in addition to untargeted metabolites profiling its methanol celery root extract (MCRE) via UPLC-MS. Although MCRE exhibited the lowest TPC and TFC levels, it presented the most potential hydroxyl radical quenching effect using electron paramagnetic resonance spin trapping technique. Treatment of Acetaminophen-induced hepatotoxicity (AAH) rats with MCRE lowered serum levels of AST, ALT, ALP, TNF-α, and IL-1β significantly. Additionally, MCRE significantly increased total antioxidant capacity (TAC) and glutathione (GSH) levels relative to AAH rats. Strikingly, Kaplan-Meier survival analysis of all groups revealed a 100% prevention of acetaminophen-induced mortality of rats by MCRE pretreatment (100 mg/kg/day). MCRE prevented AAH-associated severe weight loss and elicited normal behavior in the rescued rats. Our results suggest that pretreatment with MCRE can mitigate against overdosed acetaminophen-induced acute liver failure and warrant further investigations on the potential of postinjury intervention. PRACTICAL APPLICATIONS: Acetaminophen-induced hepatotoxicity (AAH) accounts for alerting numbers of overdose-related acute liver failure and liver transplant cases with increased morbidity and mortality rates. Currently proposed mechanisms implicate mitochondria-mediated oxidative stress and inflammation in the pathogenesis of AAH, which underline current interventions employing antioxidants to combat liver damage by over-dosed acetaminophen. The present work uncovers potent protective effects of some celery extracts (and their fractions) against acetaminophen-induced oxidative stress and inflammation. Treatment of rats with fatal liver injury with methanol extract of celery root significantly reduced secretion of liver enzymes and markedly decreased inflammatory as well as oxidative stress markers in these animals. This, in turn, rescued challenged rats exposed to fatal doses of acetaminophen completely, which establishes methanol extracts of celery roots as effective therapeutic intervention against AAH. The antioxidant capacity of the extracts was determined using EPR technique, and the secondary metabolites related to antioxidant activity were characterized via UPLC-MS.

Oroxyloside ameliorates acetaminophen-induced hepatotoxicity by inhibiting JNK related apoptosis and necroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Oroxyloside is a natural flavonoid isolated from Scutellaria baicalensis Georgi (Lamiaceae) which is a Chinese herb widely used for liver diseases. However, its mechanisms on protecting against drug induced liver injury has not been investigated yet.

AIM OF THE STUDY

To investigate the protecting effects and the primary mechanisms of oroxyloside on acetaminophen (APAP)-induced liver injury.

MATERIALS AND METHODS

After a 12 h fasting period with free access to water, C57BL/6 mice were injected with APAP (300 mg/kg) intragastrically (i.g.) and 1 h later with oroxyloside (100 mg/kg, i.g.). When mice sacrificed, blood samples were collected from fundus venous plexus and liver tissues were collected. In addition, cells were incubated with 10 mM APAP alone and 10 mM APAP combined with 100 μM oroxyloside for 24 h. ELISA, TUNEL assay, qRT-PCR et al. were used to assess the effect of oroxyloside on ameliorating APAP-induced hepatotoxicity in vitro and in vivo. Western bolt and immunohistochemistry were used in the signaling pathway analysis.

RESULTS

Oroxyloside administration significantly decreased the accumulations of CYP2E1, CYP1A2, IL-6, IL-1β, ALT and AST induced by APAP in vivo. In addition, oroxyloside inhibited the APAP-induced JNK related apoptosis by enhancing the antioxidant defenses, reversing ER-stress and keeping the mito-balance of liver cells in vivo and in vitro. Furthermore, oroxyloside protected the liver cells from necroptosis by affecting JNK pathway.

CONCLUSION

Oroxyloside acted as a protective agent against APAP-induced liver injury through inhibiting JNK-related apoptosis and necroptosis.

Improving retinal mitochondrial function as a treatment for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly. Currently, there are no treatments for dry AMD, which is characterized by the death of retinal pigment epithelium (RPE) and photoreceptors. Reports from human donors with AMD suggest that RPE mitochondrial defects are a key event in AMD pathology. Thus, the most effective strategy for treating dry AMD is to identify compounds that enhance mitochondrial function and subsequently, preserve the RPE. In this study, primary cultures of RPE from human donors with (n = 20) or without (n = 8) AMD were used to evaluate compounds that are designed to protect mitochondria from oxidative damage (N-acetyl-l-cysteine; NAC), remove damaged mitochondria (Rapamycin), increase mitochondrial biogenesis (Pyrroloquinoline quinone; PQQ), and improve oxidative phosphorylation (Nicotinamide mononucleotide, NMN). Mitochondrial function measured after drug treatments showed an AMD-dependent response; only RPE from donors with AMD showed improvements. All four drugs caused a significant increase in maximal respiration (p < 0.05) compared to untreated controls. Treatment with Rapamycin, PQQ, or NMN significantly increased ATP production (p < 0.05). Only Rapamycin increased basal respiration (p < 0.05). Notably, robust responses were observed in only about 50% of AMD donors, with attenuated responses observed in the remaining AMD donors. Further, within the responders, individual donors exhibited a distinct reaction to each drug. Our results suggest drugs targeting pathways involved in maintaining healthy mitochondria can improve mitochondrial function in a select population of RPE from AMD donors. The unique response of individual donors to specific drugs supports the need for personalized medicine when treating AMD.

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Human primary RPE cultures were used to test the efficacy of drugs on mitochondrial function.

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Drugs targeting mitochondrial homeostasis pathways improved mitochondrial function in AMD RPE.

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The donor-specific response to drugs suggests personalized medicine is needed to treat AMD.

N-Acetyl-L-cysteine Protects Human Retinal Pigment Epithelial Cells from Oxidative Damage: Implications for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) involves the loss of retinal pigment epithelium (RPE) and photoreceptors and is one of the leading causes of blindness in the elderly. Oxidative damage to proteins, lipids, and DNA has been associated with RPE dysfunction and AMD. In this study, we evaluated oxidative stress in AMD and the efficacy of antioxidant, N-acetyl-L-cysteine (NAC), in protecting RPE from oxidative damage. To test this idea, primary cultures of RPE from human donors with AMD (n = 32) or without AMD (No AMD, n = 21) were examined for expression of NADPH oxidase (NOX) genes, a source of reactive oxygen species (ROS). Additionally, the cells were pretreated with NAC for 2 hours and then treated with either hydrogen peroxide (H₂O₂) or tert-butyl hydroperoxide (t-BHP) to induce cellular oxidation. Twenty-four hours after treatment, ROS production, cell survival, the content of glutathione (GSH) and adenosine triphosphate (ATP), and cellular bioenergetics were measured. We found increased expression of p22phox, a NOX regulator, in AMD cells compared to No AMD cells (p = 0.02). In both AMD and No AMD cells, NAC pretreatment reduced t-BHP-induced ROS production and protected from H₂O₂-induced cell death and ATP depletion. In the absence of oxidation, NAC treatment improved mitochondrial function in both groups (p < 0.01). Conversely, the protective response exhibited by NAC was disease-dependent for some parameters. In the absence of oxidation, NAC significantly reduced ROS production (p < 0.001) and increased GSH content (p = 0.02) only in RPE from AMD donors. Additionally, NAC-mediated protection from H₂O₂-induced GSH depletion (p = 0.04) and mitochondrial dysfunction (p < 0.05) was more pronounced in AMD cells compared with No AMD cells. These results demonstrate the therapeutic benefit of NAC by mitigating oxidative damage in RPE. Additionally, the favorable outcomes observed for AMD RPE support NAC's relevance and the potential therapeutic value in treating AMD.

Fucoidan Alleviates Acetaminophen-Induced Hepatotoxicity via Oxidative Stress Inhibition and Nrf2 Translocation

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug that leads to severe hepatotoxicity at excessive doses. Fucoidan, a sulfated polysaccharide derived from brown seaweeds, possesses a wide range of pharmacological properties. However, the impacts of fucoidan on APAP-induced liver injury have not been sufficiently addressed. In the present study, male Institute of Cancer Research (ICR) mice aged 6 weeks were subjected to a single APAP (500 mg/kg) intraperitoneal injection after 7 days of fucoidan (100 or 200 mg/kg/day) or bicyclol intragastric administration. The mice continued to be administered fucoidan or bicyclol once per day, and were sacrificed at an indicated time. The indexes evaluated included liver pathological changes, levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum, levels of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT) in the liver, and related proteins levels (CYP2E1, pJNK and Bax). Furthermore, human hepatocyte HL-7702 cell line was used to elucidate the potential molecular mechanism of fucoidan. The mitochondrial membrane potential (MMP) and nuclear factor-erythroid 2-related factor (Nrf2) translocation in HL-7702 cells were determined. The results showed that fucoidan pretreatment reduced the levels of ALT, AST, ROS, and MDA, while it enhanced the levels of GSH, SOD, and CAT activities. Additionally, oxidative stress-induced phosphorylated c-Jun N-terminal protein kinase (JNK) and decreased MMP were attenuated by fucoidan. Although the nuclear Nrf2 was induced after APAP incubation, fucoidan further enhanced Nrf2 in cell nuclei and total expression of Nrf2. These results indicated that fucoidan ameliorated APAP hepatotoxicity, and the mechanism might be related to Nrf2-mediated oxidative stress.

Mechanisms of acetaminophen-induced liver injury and its implications for therapeutic interventions

Acetaminophen (APAP) overdose is the leading cause of drug-induced acute liver failure in many developed countries. Mitochondrial oxidative stress is considered to be the predominant cellular event in APAP-induced liver injury. Accordingly, N-acetyl cysteine, a known scavenger of reactive oxygen species (ROS), is recommended as an effective clinical antidote against APAP-induced acute liver injury (AILI) when it is given at an early phase; however, the narrow therapeutic window limits its use. Hence, the development of novel therapeutic approaches that can offer broadly protective effects against AILI is clearly needed. To this end, it is necessary to better understand the mechanisms of APAP hepatotoxicity. Up to now, in addition to mitochondrial oxidative stress, many other cellular processes, including phase I/phase II metabolism, endoplasmic reticulum stress, autophagy, sterile inflammation, microcirculatory dysfunction, and liver regeneration, have been identified to be involved in the pathogenesis of AILI, providing new targets for developing more effective therapeutic interventions against APAP-induced liver injury. In this review, we summarize intracellular and extracellular events involved in APAP hepatotoxicity, along with emphatic discussions on the possible therapeutic approaches targeting these different cellular events.

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.

Evaluation of an Alternative Intravenous N-Acetylcysteine Regimen in Pediatric Patients

OBJECTIVE

Conventionally, intravenous N-acetylcysteine (IV-NAC) administration is a 3-bag regimen administered over the course of 21 hours, which increases the risk of reconstitution and administration errors. To minimize errors, an alternative IV-NAC regimen consists of a loading dose (150 mg/kg) followed by a maintenance infusion (15 mg/kg/hr) until termination criteria are met. The aim was to determine the clinical outcomes of an alternative IV-NAC regimen in pediatric patients.

METHODS

A retrospective review of pharmacy dispensing records and diagnostic codes at a pediatric hospital identified patients who received alternative IV-NAC dosing from March 1, 2008, to September 10, 2012, for acetaminophen overdoses. Exclusion criteria included chronic liver disease, initiation of oral or other IV-NAC regimens, and initiation of standard IV-NAC infusion prior to facility transfer. Clinical and laboratory data were abstracted from the electronic medical record. Descriptive statistics were utilized. Clinical outcomes and adverse drug reaction incidences were compared between the alternative and Food and Drug Administration (FDA)-approved IV-NAC regimens.

RESULTS

Fifty-nine patients (mean age 13.4 ± 4.3 years; range: 2 months-18 years) with acetaminophen overdoses were identified. Upon IV-NAC discontinuation, 45 patients had normal alanine transaminase (ALT) concentrations, while 14 patients' ALT concentrations remained elevated (median 140 units/L) but were trending downward. Two patients (3.4%) developed hepatotoxicity (aspartate transaminase/ALT > 1000 units/L). No patients developed hepatic failure, were listed for a liver transplant, were intubated, underwent hemodialysis, or died. Two patients (3.4%) developed anaphylactoid reactions. No known medication or administration errors occurred. Clinical outcome incidences of the studied endpoints with the alternative IV-NAC regimen are at the lower end of published incidence ranges compared to the FDA IV-NAC regimen for acetaminophen overdoses.

CONCLUSIONS

This alternative IV-NAC regimen appears to be effective and well tolerated among pediatric patients when compared to the FDA-approved regimen. It may also result in fewer reconstitution and administration errors, leading to improved patient safety.

Hepato-protective effects of six schisandra lignans on acetaminophen-induced liver injury are partially associated with the inhibition of CYP-mediated bioactivation

Acetaminophen (APAP) overdose is the most frequent cause of drug-induced acute liver failure. Schisandra fructus is widely-used traditional Chinese medicine which possesses hepato-protective potential. Schisandrin A (SinA), Schisandrin B (SinB), Schisandrin C (SinC), Schisandrol A (SolA), Schisandrol B (SolB), and Schisantherin A (SthA) are the major bioactive lignans. Most recently, we found SolB exerts significant hepato-protection against APAP-induced liver injury. In this study, the protective effects of the other five schisandra lignans against APAP-induced acute hepatotoxicity in mice were investigated and compared with that of SolB. The results of morphological and biochemical assessment clearly demonstrated significant protective effects of SinA, SinB, SinC, SolA, SolB, and SthA against APAP-induced liver injury. Among these schisandra lignans, SinC and SolB exerted the strongest hepato-protective effects against APAP-induced hepatotoxicity. Six lignans pretreatment before APAP dosing could prevent the depletions of total liver glutathione (GSH) and mitochondrial GSH caused by APAP. Additionally, the lignans treatment inhibited the enzymatic activities of three CYP450 isoforms (CYP2E1, CYP1A2, and CYP3A11) related to APAP bioactivation, and further decreased the formation of APAP toxic intermediate N-acetyl-p-benzoquinone imine (NAPQI) in mouse microsomal incubation system. This study demonstrated that SinA, SinB, SinC, SolA, SolB and SthA exhibited significant protective actions toward APAP-induced liver injury, which was partially associated with the inhibition of CYP-mediated APAP bioactivation.

N-acetylcysteine overdose after acetaminophen poisoning

N-acetylcysteine (NAC) is used widely and effectively in oral and intravenous forms as a specific antidote for acetaminophen poisoning. Here we report a rare case of iatrogenic NAC overdose following an error in preparation of the solution, and describe its clinical symptoms. Laboratory results and are presented and examined. A 23-year-old alert female patient weighing 65 kg presented to the emergency ward with weakness, lethargy, extreme fatigue, nausea, and dizziness. She had normal arterial blood gas and vital signs. An excessive dosage of NAC over a short period of time can lead to hemolysis, thrombocytopenia, and acute renal failure in patients with normal glucose-6-phosphate dehydrogenase, and finally to death. Considering the similarity between some of the clinical symptoms of acetaminophen overdose and NAC overdose, it is vitally important for the administration phases and checking of the patient’s symptoms to be carried out attentively and cautiously.

I-FABP as biomarker for the early diagnosis of acute mesenteric ischemia and resultant lung injury

Acute mesenteric ischemia (AMI) is a life-threatening condition that can result in multiple organ injury and death. A timely diagnosis and treatment would have a significant impact on the morbidity and mortality in high-risk patient population. The purpose of this study was to investigate if intestinal fatty acid binding protein (I-FABP) and α-defensins can be used as biomarkers for early AMI and resultant lung injury. C57BL/6 mice were subjected to intestinal ischemia by occlusion of the superior mesenteric artery. A time course of intestinal ischemia from 0.5 to 3 h was performed and followed by reperfusion for 2 h. Additional mice were treated with N-acetyl-cysteine (NAC) at 300 mg/kg given intraperitoneally prior to reperfusion. AMI resulted in severe intestinal injury characterized by neutrophil infiltrate, myeloperoxidase (MPO) levels, cytokine/chemokine levels, and tissue histopathology. Pathologic signs of ischemia were evident at 1 h, and by 3 h of ischemia, the full thickness of the intestine mucosa had areas of coagulative necrosis. It was noted that the levels of α-defensins in intestinal tissue peaked at 1 h and I-FABP in plasma peaked at 3 h after AMI. Intestinal ischemia also resulted in lung injury in a time-dependent manner. Pretreatment with NAC decreased the levels of intestinal α-defensins and plasma I-FABP, as well as lung MPO and cytokines. In summary, the concentrations of intestinal α-defensins and plasma I-FABP predicted intestinal ischemia prior to pathological evidence of ischemia and I-FABP directly correlated with resultant lung injury. The antioxidant NAC reduced intestinal and lung injury induced by AMI, suggesting a role for oxidants in the mechanism for distant organ injury. I-FABP and α-defensins are promising biomarkers, and may guide the treatment with antioxidant in early intestinal and distal organ injury.

Therapeutic efficacy of Wuzhi tablet (Schisandra sphenanthera Extract) on acetaminophen-induced hepatotoxicity through a mechanism distinct from N-acetylcysteine

Acetaminophen (APAP) hepatotoxicity is the most common cause of drug-induced liver injury and N-acetylcysteine (NAC) is the primary antidote of APAP poisoning. Wuzhi tablet (WZ), the active constituents well identified and quantified, is a preparation of an ethanol extract of Schisandra sphenanthera and exerts a protective effect toward APAP-induced hepatotoxicity in mice. However, the clinical use of WZ to rescue APAP-induced acute liver injury and the mechanisms involved in the therapeutic effect of WZ remain unclear. Therefore, the effect of WZ on APAP hepatotoxicity was compared with NAC in mice, and molecular pathways contributing to its therapeutic action were investigated. Administration of WZ 4 hours after APAP treatment significantly attenuated APAP hepatotoxicity and exerted much better therapeutic effect than NAC, as revealed by morphologic, histologic, and biochemical assessments. Both WZ and NAC prevented APAP-induced c-Jun N-terminal protein kinase activation and mitochondrial glutathione depletion in livers. The protein expression of nuclear factor erythroid 2-related factor 2 target genes including Gclc, Gclm, Ho-1, and Nqo1 was increased by WZ administration. Furthermore, p53 and p21 levels were upregulated upon APAP exposure, which were completely reversed by postdosing of WZ 4 hours after APAP treatment over 48 hours. In comparison with NAC, WZ significantly increased the expression of cyclin D1, cyclin D-dependent kinase 4, proliferating cell nuclear antigen, and augmenter of liver regeneration in APAP-injured livers. This study demonstrated that WZ possessed a therapeutic efficacy against APAP-induced liver injury by inhibiting oxidative stress and stimulating a regenerative response after liver injury. Thus WZ may represent a new therapy for APAP-induced acute liver injury.

Green tea extract can potentiate acetaminophen-induced hepatotoxicity in mice

Green tea extract (GTE) has been advocated as a hepatoprotective compound and a possible therapeutic agent for acetaminophen (APAP) overdose. This study was conducted to determine if GTE can provide protection against APAP-induced hepatotoxicity. Three different exposure scenarios were tested. The first involved administering APAP (150 mg/kg, orally) to mice followed 6h later by GTE (500 or 1000 mg/kg). The other two involved administering GTE prior to the APAP dose. GTE (500 or 1000 mg/kg, orally) was administered 3h prior to APAP (200 mg/kg, orally) or for three consecutive days (once-daily) followed by APAP (300 mg/kg) on the fourth day. Indices of hepatotoxicity were assessed 24h after the APAP dose. GTE potentiated APAP-induced hepatotoxicity when administered after the APAP dose. GTE caused significant glutathione depletion and this effect likely contributed to the observed potentiation. In contrast, GTE provided protection against APAP-induced hepatotoxicity when administered prior to the APAP dose. GTE dramatically decreased APAP covalent binding to protein indicating that less reactive metabolite was available to cause hepatocellular injury. These results highlight the potential for drug-dietary supplement interactions and the importance of testing multiple exposure scenarios to adequately model different types of potential interactions.