Mechanisms of acetaminophen-induced hepatotoxicity: role of oxidative stress and mitochondrial permeability transition in freshly isolated mouse hepatocytes

The Role of Mechanistic Biomarkers in Understanding Acetaminophen Hepatotoxicity in Humans

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

Inhibition of ALK3-mediated signalling pathway protects against acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury is one of the most prevalent causes of acute liver failure (ALF). We assessed the role of the bone morphogenetic protein (BMP) type I receptors ALK2 and ALK3 in APAP-induced hepatotoxicity. The molecular mechanisms that regulate the balance between cell death and survival and the response to oxidative stress induced by APAP was assessed in cultured human hepatocyte-derived (Huh7) cells treated with pharmacological inhibitors of ALK receptors and with modulated expression of ALK2 or ALK3 by lentiviral infection, and in a mouse model of APAP-induced hepatotoxicity. Inhibition of ALK3 signalling with the pharmacological inhibitor DMH2, or by silencing of ALK3, showed a decreased cell death both by necrosis and apoptosis after APAP treatment. Also, upon APAP challenge, ROS generation was ameliorated and, thus, ROS-mediated JNK and P38 MAPK phosphorylation was reduced in ALK3-inhibited cells compared to control cells. These results were also observed in an experimental model of APAP-induced ALF in which post-treatment with DMH2 after APAP administration significantly reduced liver tissue damage, apoptosis and oxidative stress. This study shows the protective effect of ALK3 receptor inhibition against APAP-induced hepatotoxicity. Furthermore, findings obtained from the animal model suggest that BMP signalling might be a new pharmacological target for the treatment of ALF.

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

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

Extraction, structure and antioxidant activity of the polysaccharides from morels (Morchella spp.): A review

Morels (Morchella spp.), which are cultivated only in a few regions of the world, are edible mushrooms known for their various properties including antioxidation, immune regulation, antiinflammation, and antitumor effects. Polysaccharides from Morchella are principally responsible for its antioxidant activity. This paper reviews the extraction, purification, structural analysis and antioxidant activity of Morchella polysaccharides (MPs), providing updated research progress. Meanwhile, the structural-property relationships of MPs were further discussed. In addition, based on in vitro and in vivo studies, the major factors responsible for the antioxidant activity of MPs were summarized including scavenging free radicals, reduction capacity, inhibitory lipid peroxidation activity, regulating the signal transduction pathway, reducing the production of ROS and NO, etc. Finally, we hope that our research can provide a reference for further research and development of MPs.

Ameliorative effects of umbelliferone against acetaminophen-induced hepatic oxidative stress and inflammation in mice

Background and purpose

Acetaminophen (APAP) is a commonly used antipyretic and pain reliever that its overdose causes acute liver toxicity. Umbelliferone (UMB) has many pharmacological effects. In this study, the hepatoprotective effect of UMB on acute hepatotoxicity induced by APAP was investigated.

Experimental approach

Forty-nine male mice were separated into seven groups. The control received vehicle (i.p.), UMB group received UMB (120 mg/kg, i.p.), APAP group was treated with a single dose of APAP (350 mg/kg, i.p.), and pretreated groups received N-acetylcysteine (NAC, 200 mg/kg, i.p.) or different doses of UMB (30, 60, and 120 mg/kg, i.p.), respectively before APAP. Twenty-four hours after APAP injection, mice were sacrificed and blood and liver samples were collected. Then, serum and tissue samples were investigated for biochemical and histological studies.

Findings/Results

A single dose of APAP caused elevation in the serum liver enzymes, including alanine aminotransferase, aspartate transaminase, and alkaline phosphatase. The amounts of thiobarbituric acid reactive substances, tumor necrosis factor-alpha, and nitric oxide increased in the mice's liver tissue. Moreover, the amount of total thiol and the activity of antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) significantly diminished in the APAP group. Histological results confirmed the hepatotoxicity induced by APAP. However, UMB (more effective at 60 and 120 mg/kg) lessened APAP-induced hepatic injuries, which is comparable with NAC effects.

Conclusion and implications

The findings of this study provided evidence that UMB ameliorates liver injury induced by APAP through its antioxidant and anti-inflammatory effects.

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

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

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

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

Investigation of the metabolomic crosstalk between liver sinusoidal endothelial cells and hepatocytes exposed to paracetamol using organ-on-chip technology

Organ-on-chip technology is a promising in vitro approach recapitulating human physiology for the study of responses to drug exposure. Organ-on-chip cell cultures have paved new grounds for testing and understanding metabolic dose-responses when evaluating pharmaceutical and environmental toxicity. Here, we present a metabolomic investigation of a coculture of liver sinusoidal endothelial cells (LSECs, SK-HEP-1) with hepatocytes (HepG2/C3a) using advanced organ-on-chip technology. To reproduce the physiology of the sinusoidal barrier, LSECs were separated from hepatocytes by a membrane (culture insert integrated organ-on-chip platform). The tissues were exposed to acetaminophen (APAP), an analgesic drug widely used as a xenobiotic model in liver and HepG2/C3a studies. The differences between the SK-HEP-1, HepG2/C3a monocultures and SK-HEP-1/HepG2/C3a cocultures, treated or not with APAP, were identified from metabolomic profiles using supervised multivariate analysis. The pathway enrichment coupled with metabolite analysis of the corresponding metabolic fingerprints contributed to extracting the specificity of each type of culture and condition. In addition, we analysed the responses to APAP treatment by mapping the signatures with significant modulation of the biological processes of the SK-HEP-1 APAP, HepG2/C3a APAP and SK-HEP-1/HepG2/C3a APAP conditions. Furthermore, our model shows how the presence of the LSECs barrier and APAP first pass can modify the metabolism of HepG2/C3a. Altogether, this study demonstrates the potential of a "metabolomic-on-chip" strategy for pharmaco-metabolomic applications predicting individual response to drugs.

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.

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

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

Synthesis, Molecular Docking, and Preclinical Evaluation of a New Succinimide Derivative for Cardioprotective, Hepatoprotective and Lipid-Lowering Effects

Cardiac and hepatotoxicities are major concerns in the development of new drugs. Better alternatives to other treatments are being sought to protect these vital organs from the toxicities of these pharmaceuticals. In this regard, a preclinical study is designed to investigate the histopathological effects of a new succinimide derivative (Comp-1) on myocardial and liver tissues, and the biochemical effects on selected cardiac biomarkers, hepatic enzymes, and lipid profiles. For this, an initially lethal/toxic dose was determined, followed by a grouping of selected albino rats into five groups (each group had n = 6). The control group received daily oral saline for 8 days. The 5-FU (5-Fluorouracil) group received oral saline daily for 8 days, added with the administration of a single dose of 5-FU (150 mg/kg I.P.) on day 5 of the study. The atenolol group received oral atenolol (20 mg/kg) for 8 days and 5-FU (150 mg/kg I.P.) on day 5 of the protocol. Similarly, two groups of rats treated with test compound (Comp-1) were administered with 5 mg/kg I.P. and 10 mg/kg I.P. for 8 days, followed by 5-FU (150 mg/kg I.P.) on day 5. Toxicity induced by 5-FU was manifested by increases in the serum creatinine kinase myocardial band (CK-MB), troponin I (cTnI) and lactate dehydrogenase (LDH), lipid profile, and selected liver enzymes, including ALP (alkaline phosphatase), ALT (alanine transaminase), AST (aspartate aminotransferase), BT (bilirubin total), and BD (direct bilirubin). These biomarkers were highly significantly decreased after the administration of the mentioned doses of the test compound (5 mg/kg and 10 mg/kg). Similarly, histological examination revealed cardiac and hepatic tissue toxicity by 5-FU. However, those toxic effects were also significantly recovered/improved after the administration of Comp-1 at the said doses. This derivative showed dose-dependent effects and was most effective at a dose of 10 mg/kg body weight. Binding energy data computed via docking simulations revealed that our compound interacts toward the human beta2-adrenergic G protein-coupled receptor (S = −7.89 kcal/mol) with a slight stronger affinity than the calcium channel T-type (S = −7.07 kcal/mol). In conclusion, the histological and biochemical results showed that the test compound (Comp-1) had prominent cardioprotective, hepatoprotective, and lipolytic effects against 5-FU-induced toxicity in the subjected animal model.

Mitochondrial ATP synthase c-subunit leak channel triggers cell death upon loss of its F1 subcomplex

Mitochondrial ATP synthase is vital not only for cellular energy production but also for energy dissipation and cell death. ATP synthase c-ring was suggested to house the leak channel of mitochondrial permeability transition (mPT), which activates during excitotoxic ischemic insult. In this present study, we purified human c-ring from both eukaryotic and prokaryotic hosts to biophysically characterize its channel activity. We show that purified c-ring forms a large multi-conductance, voltage-gated ion channel that is inhibited by the addition of ATP synthase F₁ subcomplex. In contrast, dissociation of F₁ from F_O occurs during excitotoxic neuronal death suggesting that the F₁ constitutes the gate of the channel. mPT is known to dissipate the osmotic gradient across the inner membrane during cell death. We show that ATP synthase c-subunit knock down (KD) prevents the osmotic change in response to high calcium and eliminates large conductance, Ca²⁺ and CsA sensitive channel activity of mPT. These findings elucidate the gating mechanism of the ATP synthase c-subunit leak channel (ACLC) and suggest how ACLC opening is regulated by cell stress in a CypD-dependent manner.

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.

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

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

Syringa microphylla Diels: A comprehensive review of its phytochemical, pharmacological, pharmacokinetic, and toxicological characteristics and an investigation into its potential health benefits

BACKGROUND

Syringa microphylla Diels is a plant in the family Syringa Linn. For hundreds of years, its flowers and leaves have been used as a folk medicine for the treatment of cough, inflammation, colds, sore throat, acute hepatitis, chronic hepatitis, early liver cirrhosis, fatty liver, and oesophageal cancer.

PURPOSE

For the first time, we have comprehensively reviewed information on Syringa microphylla Diels that is not included in the Pharmacopoeia, clarified the pharmacological mechanisms of Syringa microphylla Diels and its active ingredients from a molecular biology perspective, compiled in vivo and in vitro animal experimental data and clinical data, and summarized the toxicology and pharmacokinetics of Syringa microphylla Diels. The progress in toxicology research is expected to provide a theoretical basis for the development of new drugs from Syringa microphylla Diels, a natural source of compounds that are potentially beneficial to human health.

METHODS

The PubMed, Google Scholar, China National Knowledge Infrastructure, Web of Science, SciFinder Scholar and Thomson Reuters databases were utilized to conduct a comprehensive search of published literature as of July 2021 to find original literature related to Syringa microphylla Diels and its active ingredients.

RESULTS

To date, 72 compounds have been isolated and identified from Syringa microphylla Diels, and oleuropein, verbascoside, isoacteoside, echinacoside, forsythoside B, and eleutheroside B are the main active components. These compounds have antioxidant, antibacterial, anti-inflammatory, and neuroprotective effects, and their safety and effectiveness have been demonstrated in long-term traditional applications. Molecular pharmacology experiments have indicated that the active ingredients of Syringa microphylla Diels exert their pharmacological effects in various ways, primarily by reducing oxidative stress damage via Nrf2/ARE pathway regulation, regulating inflammatory factors and inducing apoptosis through the MAPK and NF-κB pathways.

CONCLUSION

This comprehensive review of Syringa microphylla Diels provides new insights into the correlations among molecular mechanisms, the importance of toxicology and pharmacokinetics, and potential ways to address the limitations of current research. As Syringa microphylla Diels is a natural low-toxicity botanical medicine, it is worthy of development and utilization and is an excellent choice for treating various diseases.

Bcl-xL Is Required by Primary Hippocampal Neurons during Development to Support Local Energy Metabolism at Neurites

B-cell lymphoma-extra large (Bcl-xL) is a mitochondrial protein known to inhibit mitochondria-dependent intrinsic apoptotic pathways. An increasing number of studies have demonstrated that Bcl-xL is critical in regulating neuronal energy metabolism and has a protective role in pathologies associated with an energy deficit. However, it is less known how Bcl-xL regulates physiological processes of the brain. In this study, we hypothesize that Bcl-xL is required for neurite branching and maturation during neuronal development by improving local energy metabolism. We found that the absence of Bcl-xL in rat primary hippocampal neurons resulted in mitochondrial dysfunction. Specifically, the ATP/ADP ratio was significantly decreased in the neurites of Bcl-xL depleted neurons. We further found that neurons transduced with Bcl-xL shRNA or neurons treated with ABT-263, a pharmacological inhibitor of Bcl-xL, showed impaired mitochondrial motility. Neurons lacking Bcl-xL had significantly decreased anterograde and retrograde movement of mitochondria and an increased stationary mitochondrial population when Bcl-xL was depleted by either means. These mitochondrial defects, including loss of ATP, impaired normal neurite development. Neurons lacking Bcl-xL showed significantly decreased neurite arborization, growth and complexity. Bcl-xL depleted neurons also showed impaired synapse formation. These neurons showed increased intracellular calcium concentration and were more susceptible to excitotoxic challenge. Bcl-xL may support positioning of mitochondria at metabolically demanding regions of neurites like branching points. Our findings suggest a role for Bcl-xL in physiological regulation of neuronal growth and development.

Kushenol C Prevents Tert-Butyl Hydroperoxide and Acetaminophen-Induced Liver Injury

Sophora flavescens, also known as Kushen, has traditionally been used as a herbal medicine. In the present study we evaluated the ameliorative effects of kushenol C (KC) from S. flavescens against tBHP (tert-Butyl hydroperoxide)-induced oxidative stress in hepatocellular carcinoma (HEPG2) cells and acetaminophen (APAP)-induced hepatotoxicity in mice. KC pretreatment protected the HEPG2 cells against oxidative stress by reducing cell death, apoptosis and reactive oxygen species (ROS) generation. KC pretreatment also upregulated pro-caspase 3 and GSH (glutathione) as well as expression of 8-Oxoguanine DNA Glycosylase (OGG1) in the HEPG2 cells. The mechanism of action was partly related by KC's activation of Akt (Protein kinase B (PKB)) and Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) in the HepG2 cells. In in vivo investigations, coadministration of mice with KC and APAP significantly attenuated APAP-induced hepatotoxicity and liver damage, as the serum enzymatic activity of aspartate aminotransferase and alanine aminotransferase, as well as liver lipid peroxidation and cleaved caspase 3 expression, were reduced in APAP-treated mice. Coadministration with KC also up-regulated antioxidant enzyme expression and prevented the production of proinflammatory mediators in APAP-treated mice. Taken together, these results showed that KC treatment has potential as a therapeutic agent against liver injury through the suppression of oxidative stress.

Circadian clock disruption attenuated growth hormone(GH)-mediated signalling

The circadian molecular clock is an internal time-keeping system, which regulates various physiological processes through the generation of approximately 24-hour circadian rhythms. BMAL1 (brain and muscle arnt-like 1) is a core component of the circadian clock. Previous studies have shown that the circadian clock correlates with rhythmic secretion of endocrine hormone (such as growth hormone, GH). Currently, the effect of circadian clock on the GH-mediated biological activities is not fully understood. In this work, we used BMAL1 gene knockout mice (BMAL^-/- mice) model to explore the effect of circadian clock dysfunction on GH's activities, and the results from in vivo and in vitro experiments showed that GH-induced signaling is down-regulated. In vivo, GH/GHR-mediated tyrosine phosphorylation of signaling molecules (such as the Janus kinase-signal transducer and activator of transcription, JAK-STAT) in BMAL^-/- mice was significantly lower compared to control mice. In vitro, GH/GHR-mediated signaling in the hepatocytes from BMAL^-/- mice is decreased compared to hepatocytes from control mice. Furthermore, we explore the mechanism by which GH/GHR-mediated signalling is down-regulated in BMAL^-/- mice, and results indicated that the expression levels of negative regulators of cytokine signaling (such as the suppressor of cytokine signaling (SOCS) and protein phosphatase) were increased, which may be one of the factors that cause the GH signaling downregulation. In summary, our results show that the circadian clock affects the biological activities of GH. This finding lays the foundation for future investigations into the relationship between the circadian clock and biological activities of GH.

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.

Therapeutic Potential of Umbilical Cord Stem Cells for Liver Regeneration

The liver is a vital organ for life and the only internal organ that is capable of natural regeneration. Although the liver has high regeneration capacity, excessive hepatocyte death can lead to liver failure. Various factors can lead to liver damage including drug abuse, some natural products, alcohol, hepatitis, and autoimmunity. Some models for studying liver injury are APAP-based model, Fas ligand (FasL), D-galactosamine/endotoxin (Gal/ET), Concanavalin A, and carbon tetrachloride-based models. The regeneration of the liver can be carried out using umbilical cord blood stem cells which have various advantages over other stem cell types used in liver transplantation. UCB-derived stem cells lack tumorigenicity, have karyotype stability and high immunomodulatory, low risk of graft versus host disease (GVHD), low risk of transmitting somatic mutations or viral infections, and low immunogenicity. They are readily available and their collection is safe and painless. This review focuses on recent development and modern trends in the use of umbilical cord stem cells for the regeneration of liver fibrosis.

Inhibitory mechanisms and fate of the analgesic drug acetaminophen in nitrifying activated sludge

This work investigated the inhibitory effects and fate of acetaminophen (N-acetyl-p-aminophenol, APAP) on activated sludge (AS) under nitrifying and aerobic conditions. APAP disrupted the two-step biological nitrification process in a dose-dependent manner. 100 mg/L APAP inhibited ammonia oxidation (the first step of nitrification) accompanied by a significant reduction (> 80 %) of Nitrosomonas oligotropha in relative abundance. 50 mg/L of APAP had no significant effects on ammonia oxidation but interrupted nitrite oxidation (the second step of nitrification) with more than 90 % reduction of Candidatus Nitrospira defluvii. APAP was removed in nitrifying activated sludge via largely the biotransformation route. Both nitrifiers and heterotrophic microorganisms contributed to overall APAP removal. An AS bioreactor was acclimated to 100 mg/L APAP as the sole source of carbon, nitrogen, and energy to enrich the microbial community with APAP-metabolizing heterotrophs. During acclimation, dynamic changes in community phenotypes occurred with significant reduction in species richness and diversity. Community acclimation significantly increased APAP biotransformation rates. 16S rRNA gene-based community profiling showed selective enrichment for Pseudomonas and Sphingomonas, both with demonstrated APAP metabolic capacity.

The development and hepatotoxicity of acetaminophen: reviewing over a century of progress

Acetaminophen (APAP) was first synthesized in the 1800s, and came on the market approximately 65 years ago. Since then, it has become one of the most used drugs in the world. However, it is also a major cause of acute liver failure. Early investigations of the mechanisms of toxicity revealed that cytochrome P450 enzymes catalyze formation of a reactive metabolite in the liver that depletes glutathione and covalently binds to proteins. That work led to the introduction of N-acetylcysteine (NAC) as an antidote for APAP overdose. Subsequent studies identified the reactive metabolite N-acetyl-p-benzoquinone imine, specific P450 enzymes involved, the mechanism of P450-mediated oxidation, and major adducted proteins. Significant gaps remain in our understanding of the mechanisms downstream of metabolism, but several events appear critical. These events include development of an initial oxidative stress, reactive nitrogen formation, altered calcium flux, JNK activation and mitochondrial translocation, inhibition of mitochondrial respiration, the mitochondrial permeability transition, and nuclear DNA fragmentation. Additional research is necessary to complete our knowledge of the toxicity, such as the source of the initial oxidative stress, and to greatly improve our understanding of liver regeneration after APAP overdose. A better understanding of these mechanisms may lead to additional treatment options. Even though NAC is an excellent antidote, its effectiveness is limited to the first 16 hours following overdose.

Pre-treatment twice with liposomal clodronate protects against acetaminophen hepatotoxicity through a pre-conditioning effect

BACKGROUND AND AIM

Acetaminophen (APAP) overdose is a major cause of acute liver injury, but the role of macrophages in propagation of the hepatotoxicity is controversial. Early research revealed that macrophage inhibitors protect against APAP injury. However, later work demonstrated that macrophage ablation by acute pre-treatment with liposomal clodronate (LC) exacerbates the toxicity. To our surprise, during other studies, we observed that pre-treatment twice with LC seemed to protect against APAP hepatotoxicity, in contrast to acute pre-treatment. The aim of this study was to confirm that observation and to explore the mechanisms.

METHODS

We treated mice with empty liposomes (LE) or LC twice per week for 1 week before APAP overdose and collected blood and liver tissue at 0, 2, and 6 h post-APAP. We then measured liver injury (serum ALT activity, histology), APAP bioactivation (total glutathione, APAP-protein adducts), oxidative stress (oxidized glutathione [GSSG]), glutamate cysteine-ligase subunit c (Gclc) mRNA, and nuclear factor erythroid 2-related factor (Nrf2) immunofluorescence. We also confirmed ablation of macrophages by F4/80 immunohistochemistry.

RESULTS

Pre-treatment twice with LC dramatically reduced F4/80 staining, protected against liver injury, and reduced oxidative stress at 6 h post-APAP, without affecting APAP bioactivation. Importantly, Gclc mRNA was higher in the LC group at 0 h and total glutathione was higher at 2 h, indicating accelerated glutathione re-synthesis after APAP overdose due to greater basal glutamate-cysteine ligase. Oxidative stress was lower in the LC groups at both time points. Finally, total Nrf2 immunofluorescence was higher in the LC group.

CONCLUSIONS

We conclude that multiple pre-treatments with LC protect against APAP by accelerating glutathione re-synthesis through glutamate-cysteine ligase. Investigators using two or possibly more LC pre-treatments to deplete macrophages, including peritoneal macrophages, should be aware of this possible confounder.

Hepatoprotective Activity of Leptadenia hastata (Asclepiadaceae) on Acetaminophen-Induced Toxicity in Mice: In Vivo Study and Characterization of Bioactive Compounds through Molecular Docking Approaches

MATERIALS AND METHODS

Various aqueous extracts were prepared from this plant and preadministered per os to albino mice 3 h before APAP administration, once daily for one week. Animals from the normal group were given only distilled water while those from negative control received only APAP 250 mg/kg. After treatment, mice were sacrificed, the liver was collected for histopathology analysis, and different biochemical markers (alanine aminotransferase (ALT), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), malondialdehyde (MDA), and tumor necrosis factor-alpha (TNFα)) were measured. The content of the active extract was analyzed by HPLC/UV. Molecular docking was conducted using iGEMDOCK software, and the drug-likeness and pharmacokinetic profiles were evaluated using Swiss ADME.

RESULTS

APAP administration significantly increased (p < 0.001) ALT in liver homogenates when compared to normal controls whereas the stem decoction at 250 mg/kg significantly (p < 0.001) reduced this activity to a normal value comparable to silymarin 50 mg/kg which is better than leaf and root extracts. Moreover, the stem decoction also significantly reduced the MDA levels (p < 0.05) and increased those of GSH, SOD, and CAT (p < 0.001) at doses of 250 and 500 mg/kg compared to the negative control. A significant (p < 0.001) decrease of TNFα levels and leukocyte infiltration was observed following treatment with this extract. The HPLC/UV analysis of the decoction revealed the presence of dihydroxycoumarin, quinine, and scopoletin with the following retention times: 2.6, 5.1, and 7.01 min, respectively. In silico studies showed that quinine and dihydroxycoumarin had great potentials to be orally administered drugs and possessed strong binding affinities with TNFα, TNF receptor, cyclooxygenase-2, iNOS, cytochrome P450 2E1, and GSH reductase.

CONCLUSION

Based on these results, L. hastata could be considered a source of promising hepatoprotective compounds with antioxidant and anti-inflammatory properties.

Liver-specific Bid silencing inhibits APAP-induced cell death in mice

Acetaminophen (APAP)-induced acute liver failure (ALF) is a life-threatening disease with only a few treatment options available. Though extensive research has been conducted for more than 40 years, the underlying pathomechanisms are not completely understood. Here, we studied as to whether APAP-induced ALF can be prevented in mice by silencing the BH3-interacting domain death agonist (Bid) as a potential key player in APAP pathology. For silencing Bid expression in mice, siRNA^Bid was formulated with the liver-specific siRNA delivery system DBTC and administered 48 h prior to APAP exposure. Mice which were pre-treated with HEPES (vehicle^HEPES) and siRNA^Luci served as siRNA controls. Hepatic pathology was assessed by in vivo fluorescence microscopy, molecular biology, histology and laboratory analysis 6 h after APAP or PBS exposure. Application of siRNA^Bid caused a significant decrease of mRNA and protein expression of Bid in APAP-exposed mice. Off-targets, such as cytochrome P450 2E1 and glutathione, which are known to be consumed under APAP intoxication, were comparably reduced in all APAP-exposed mice, underlining the specificity of Bid silencing. In APAP-exposed mice non-sterile inflammation with leukocyte infiltration and perfusion failure remained almost unaffected by Bid silencing. However, the Bid silencing reduced hepatocellular damage, evident by a remarkable decrease of DNA fragmented cells in APAP-exposed mice. In these mice, the expression of the pro-apoptotic protein Bax, which recently gained importance in the cell death pathway of regulated necrosis, was also significantly reduced, in line with a decrease in both, necrotic liver tissue and plasma transaminase activities. In addition, plasma levels of HMGB1, a marker of sterile inflammation, were significantly diminished. In conclusion, the liver-specific silencing of Bid expression did not protect APAP-exposed mice from microcirculatory dysfunction, but markedly protected the liver from necrotic cell death and in consequence from sterile inflammation. The study contributes to the understanding of the molecular mechanism of the APAP-induced pathogenic pathway by strengthening the importance of Bid and Bid silencing associated effects.

Visualization and isolation of zone-specific murine hepatocytes that maintain distinct cytochrome P450 oxidase expression in primary culture

Parenchymal hepatocytes are responsible for most of the metabolic functions of the liver, but exhibit distinct functional properties depending on their localization within the hepatic lobule. Cytochrome P450 oxidases represent a family of drug-metabolizing enzymes, which are expressed predominantly in hepatocytes localized in the centrilobular area (zone 3). The present study describes a unique transgenic mouse strain that distinguishes zone 3 hepatocytes from periportal zone 1 hepatocytes by the intensity of EGFP fluorescence. Both zone 1 and zone 3 hepatocytes isolated from these mice showed the same zone-specific gene expression patterns as in liver tissue in vivo. Experiments using primary cultures of hepatocytes indicated that a combination of low oxygen concentration and activation of Wnt/β-catenin signaling maintained the expression of zone 3-specific P450 drug-metabolizing enzymes, which was characterized by their susceptibility to acetaminophen-induced mitochondrial dysfunction. These zone-specific hepatocytes provide a useful system in the research area of liver pathophysiology and drug development.

Controlled Functional Zonation of Hepatocytes In Vitro by Engineering of Wnt Signaling

Key liver functions, including protein synthesis, carbohydrate metabolism, and detoxification, are performed by specific populations of hepatocytes that are defined by their relative positions within the liver lobules. On a molecular level, the functional heterogeneity with periportal and pericentral phenotypes, so-called metabolic liver zonation, is mainly established by a gradient of canonical Wnt signaling activity. Since the relevant physiological cues are missing in in vitro liver models, they fail to reflect the functional heterogeneity and thus lack many liver functions. We synthetically re-engineered Wnt signaling in murine and human hepatocytes using a doxycycline-dependent cassette for externally controlled digital expression of stabilized β-catenin. Thereby, we achieved adjustable mosaic-like activation of Wnt signaling in in vitro-cultured hepatocytes that was resistant to negative-feedback loops. This allowed the establishment of long-term-stable periportal-like and pericentral-like phenotypes that mimic the heterogeneity observed in vivo. The in vitro-zonated hepatocytes show differential expression of drug-metabolizing enzymes and associated differential toxicity and higher levels of autophagy. Furthermore, recombinant adeno-associated virus and hepatitis C virus preferentially transduce the pericentral-like zonation phenotype, suggesting a bias of these viruses that has been unappreciated to date. These tightly controlled in vivo-like systems will be important for studies evaluating aspects of liver zonation and for the assessment of drug toxicity for mouse and man.

Mechanism of protection of rat hepatocytes from acetaminophen-induced cellular damage by ethanol extract of Aerva lanata

The aim of this study is to evaluate the protective effect of ethanol extract of Aerva lanata (EEAL) in preventing acetaminophen induced liver toxicity. EEAL was prepared and its hepatoprotective effect was studied in both isolated primary hepatocytes in vitro and in Sprague Dawley rats in vivo. For in vivo studies, the animals were grouped as Group I – Control; Group II – ACN (2 g/kg b.w.); Group III – EEAL (50 mg/kg b.w.) + ACN (2 g/kg b.w.), Group IV – EEAL (100 mg/kg b.w.) + ACN (2 g/kg b.w.). Extracellular activities of the enzymes liver aminotransferease (GOT, GPT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in isolated hepatocytes and rat plasma were studied colorimetrically. Expression of GST, Nrf2, COX 1 & COX2 genes in rat liver were evaluated by RT-PCR. The results showed that ACN induced down-regulation of Nrf2 and upregulation of GST gene expression, which were modulated by EEAL treatment. GOT, GPT, ALP and LDH levels were found to be lowered in both hepatocyte culture media and plasma following EEAL treatment. In addition, the medium GOT and GPT levels were diminished following EEAL treatment only. Moreover, only ALP and LDH in serum appeared to be at normal level following EEAL treatment, whereas GOT and GPT showed levels lower than control. ACN treatment increased the expression of pro-inflammatory COX 1 and COX 2 genes and the levels of these genes were reduced by EEAL treatment. EEAL pre-treated rats exposed to ACN were found to retain normal hepatic structure compared to ACN alone treated rats. From these results it can be concluded that ethanol extract of A. lanata possesses both anti-inflammatory and hepatoprotective activity.

Mitochondrial depolarization and repolarization in the early stages of acetaminophen hepatotoxicity in mice

Mitochondrial injury and depolarization are primary events in acetaminophen hepatotoxicity. Previous studies have shown that restoration of mitochondrial function in surviving hepatocytes, which is critical to recovery, is at least partially accomplished via biogenesis of new mitochondria. However, other studies indicate that mitochondria also have the potential to spontaneously repolarize. Although repolarization was previously observed only at a sub-hepatotoxic dose of acetaminophen, we postulated that mitochondrial repolarization in hepatocytes outside the centrilobular regions of necrosis might contribute to recovery of mitochondrial function following acetaminophen-induced injury. Our studies utilized longitudinal intravital microscopy of millimeter-scale regions of the mouse liver to characterize the spatio-temporal relationship between mitochondrial polarization and necrosis early in acetaminophen-induced liver injury. Treatment of male C57BL/6J mice with a single intraperitoneal 250 mg/kg dose of acetaminophen resulted in hepatotoxicity that was apparent histologically within 2 h of treatment, leading to 20 and 60-fold increases in serum aspartate aminotransferase and alanine aminotransferase, respectively, within 6 h. Intravital microscopy of the livers of mice injected with rhodamine123, TexasRed-dextran, propidium iodide and Hoechst 33342 detected centrilobular foci of necrosis within extended regions of mitochondrial depolarization within 2 h of acetaminophen treatment. Although regions of necrosis were more apparent 6 h after acetaminophen treatment, the vast majority of hepatocytes with depolarized mitochondria did not progress to necrosis, but rather recovered mitochondrial polarization within 6 h. Recovery of mitochondrial function following acetaminophen hepatotoxicity thus involves not only biogenesis of new mitochondria, but also repolarization of existing mitochondria. These studies also revealed a spatial distribution of necrosis and mitochondrial depolarization whose single-cell granularity is inconsistent with the hypothesis that communication between neighboring cells plays an important role in the propagation of necrosis during the early stages of APAP hepatotoxicity. Small islands of healthy, intact cells were frequently found surrounded by necrotic cells, and small islands of necrotic cells were frequently found surrounded by healthy, intact cells. Time-series studies demonstrated that these "islands", consisting in some cases of single cells, are persistent; over a period of hours, injury does not spread from individual necrotic cells to their neighbors.

The Bile Acid Receptor GPBAR1 Modulates CCL2/CCR2 Signaling at the Liver Sinusoidal/Macrophage Interface and Reverses Acetaminophen-Induced Liver Toxicity

Drug-induced liver injury caused by acetaminophen (acetyl-para-aminophenol [APAP]) is the main cause of acute liver failure and liver transplantation in several Western countries. Whereas direct toxicity exerted by APAP metabolites is a key determinant for early hepatocytes injury, the recruitment of cells of innate immunity exerts a mechanistic role in disease progression, determining the clinical outcomes. GPBAR1 is a G protein-coupled receptor for secondary bile acids placed at the interface between liver sinusoidal cells and innate immunity. In this report, using genetic and pharmacological approaches, we demonstrate that whereas Gpbar1 gene deletion worsens the severity of liver injury, its pharmacological activation by 6β-ethyl-3a,7b-dihydroxy-5b-cholan-24-ol rescues mice from liver injury caused by APAP. This protective effect was supported by a robust attenuation of liver recruitment of monocyte-derived macrophages and their repolarization toward an anti-inflammatory phenotype. Macrophage depletion by gadolinium chloride pretreatment abrogated disease development, whereas their reconstitution by spleen-derived macrophage transplantation restored the sensitivity to APAP in a GPBAR1-dependent manner. RNA sequencing analyses demonstrated that GPBAR1 agonism modulated the expression of multiple pathways, including the chemokine CCL2 and its receptor, CCR2. Treating wild-type mice with an anti-CCL2 mAb attenuated the severity of liver injury. We demonstrated that negative regulation of CCL2 production by GPBAR1 agonism was promoter dependent and involved FOXO1. In conclusion, we have shown that GPBAR1 is an upstream modulator of CCL2/CCR2 axis at the sinusoidal cell/macrophage interface, providing a novel target in the treatment of liver damage caused by APAP.

Suppression of iron mobilization from lysosomes to mitochondria attenuates liver injury after acetaminophen overdose in vivo in mice: Protection by minocycline

Acetaminophen (APAP) overdose causes hepatotoxicity involving mitochondrial dysfunction. Previous studies showed that translocation of Fe²⁺ from lysosomes into mitochondria by the mitochondrial Ca²⁺ uniporter (MCU) promotes the mitochondrial permeability transition (MPT) after APAP. Here, our Aim was to assess protection by iron chelation and MCU inhibition against APAP hepatotoxicity in mice. C57BL/6 mice and hepatocytes were administered toxic doses of APAP with and without starch-desferal (an iron chelator), minocycline (MCU inhibitor), or N-acetylcysteine (NAC). In mice, starch-desferal and minocycline pretreatment decreased ALT and liver necrosis after APAP by >60%. At 24 h after APAP, loss of fluorescence of mitochondrial rhodamine 123 occurred in pericentral hepatocytes often accompanied by propidium iodide labeling, indicating mitochondrial depolarization and cell death. Starch-desferal and minocycline pretreatment decreased mitochondrial depolarization and cell death by more than half. In cultured hepatocytes, cell killing at 10 h after APAP decreased from 83% to 49%, 35% and 27%, respectively, by 1 h posttreatment with minocycline, NAC, and minocycline plus NAC. With 4 h posttreatment in vivo, minocycline and minocycline plus NAC decreased ALT and necrosis by ~20% and ~50%, respectively, but NAC alone was not effective. In conclusion, minocycline and starch-desferal decrease mitochondrial dysfunction and severe liver injury after APAP overdose, suggesting that the MPT is likely triggered by iron uptake into mitochondria through MCU. In vivo, minocycline and minocycline plus NAC posttreatment after APAP protect at later time points than NAC alone, indicating that minocycline has a longer window of efficacy than NAC.

Advanced Research on the Antioxidant Activity and Mechanism of Polyphenols from Hippophae Species-A Review

Oxidation is a normal consequence of metabolism in biological organisms. The result is the formation of detrimental reactive oxygen species (ROS) and reactive nitrogen species (RNS). A large number of studies have shown that polyphenolic compounds have good antioxidant properties. Hippophae species plants have high polyphenolic content and are widely used in food, medicinal, or the cosmetic field. The main polyphenols in Hippophae species are flavonoids, phenolic acids and tannins, which have multiple effects. However, there is a limited number of studies on polyphenols in Hippophae species plants. This review systematically summarizes the polyphenols compounds and antioxidant activity of Hippophae species plants, and it is noteworthy that the main mechanisms of the polyphenols of Hippophae with antioxidant activity have been summarized as follows: regulating enzyme activity, affect the antioxidant reaction of cells, and others. This review provides useful information for the further study and application of Hippophae species polyphenols and their antioxidant activity.

Lophenol and lathosterol from resin of Commiphora kua possess hepatoprotective effects in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Drug induced liver damage remains a prevalent concern in healthcare and may reduce the effectiveness of therapy by compromising therapeutic regimens. Many Commiphora species are known for their medicinal properties, and some of them are used traditionally for hepatoprotective effect. In the course of our drugs discovery from natural sources, phytosterols (lophenol (Lop) and lathosterol (Lat)), isolated from Commiphora kua were studied to evaluate their hepatoprotective effects in acetaminophen (APAP) induced hepatotoxicity in mice.

AIMS AND OBJECTIVE

To evaluate the hepatoprotective effects of phytosterols isolated from C. kua using in vivo experimental model.

MATERIALS AND METHODS

Mice of either sex were divided into 7 groups: Vehicle, silymarin (SLY), acetaminophen (APAP), Lop 25, Lop 50, Lat 25, Lat 50 (n = 5). Vehicle group received only vehicle (0.1% DMSO solution) for 7 days, APAP group received single dose of acetaminophen on day 7 and SLY group received silymarin for 7 days. Lop 25 and Lop 50 received low and high doses of Lop (25 μg/kg BW and 50 μg/kg BW), respectively, for 7 days, while Lat 25 and Lat 50 received low and high doses of Lat (25 μg/kg BW and 50 μg/kg BW) for 7 days. On day 7, all animals except Vehicle group kept fasted for 18 h and received APAP i. p. 400 mg/kg BW. After 20 h of APAP administration, the animals anesthetized with light chloroform and scarified by cervical decapitation. The blood serum and liver tissue samples were collected for biochemical and histopathological analysis. Liver function tests (LFTs) including lactate deydrogenase (LDH), alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST) and direct bilirubin) were used as biochemical parameters. While catalase (CAT), superoxide dismutase (SOD) and reduced glutathione (GSH) were taken as anti-oxidant enzymes.

RESULTS

Significant increase in levels of ALT, AST, ALP, LDH and direct bilirubin, and significant decrease in concentration of anti-oxidant enzymes (SOD, CAT and GSH) was observed in APAP-treated group. Similarly, histological slides showed obvious signs of damage to liver cells, reflecting acetaminophen induced hepatotoxicity. Treatment of test animals with phytosterols resulted in significant recovery of LFTs profile and concentration of anti-oxidant enzymes. Similarly, significant improvement of liver tissues was noted in histological analysis.

CONCLUSIONS

Both phytosterols possessed hepatoprotective potential and should be further evaluated for acute toxicity studies and pharmacokinetics/pharmacodynamics profile.

Alpha-Tocotrienol Prevents Oxidative Stress-Mediated Post-Translational Cleavage of Bcl-xL in Primary Hippocampal Neurons

B-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic member of the Bcl2 family of proteins, which supports neurite outgrowth and neurotransmission by improving mitochondrial function. During excitotoxic stimulation, however, Bcl-xL undergoes post-translational cleavage to ∆N-Bcl-xL, and accumulation of ∆N-Bcl-xL causes mitochondrial dysfunction and neuronal death. In this study, we hypothesized that the generation of reactive oxygen species (ROS) during excitotoxicity leads to formation of ∆N-Bcl-xL. We further proposed that the application of an antioxidant with neuroprotective properties such as α-tocotrienol (TCT) will prevent ∆N-Bcl-xL-induced mitochondrial dysfunction via its antioxidant properties. Primary hippocampal neurons were treated with α-TCT, glutamate, or a combination of both. Glutamate challenge significantly increased cytosolic and mitochondrial ROS and ∆N-Bcl-xL levels. ∆N-Bcl-xL accumulation was accompanied by intracellular ATP depletion, loss of mitochondrial membrane potential, and cell death. α-TCT prevented loss of mitochondrial membrane potential in hippocampal neurons overexpressing ∆N-Bcl-xL, suggesting that ∆N-Bcl-xL caused the loss of mitochondrial function under excitotoxic conditions. Our data suggest that production of ROS is an important cause of ∆N-Bcl-xL formation and that preventing ROS production may be an effective strategy to prevent ∆N-Bcl-xL-mediated mitochondrial dysfunction and thus promote neuronal survival.

Rifampicin activates AMPK and alleviates oxidative stress in the liver as mediated with Nrf2 signaling

Although rifampicin could have a hepatic toxic effect, it has also been shown that this chemical acts as a cellular protectant against oxidative stress. Therefore, we wondered whether rifampicin has a beneficial effect such as an anti-oxidant in the liver, because the efficacy of some drugs sometimes relates with their toxicity as well as protective effects. The present study aimed to investigate the antioxidant effect of rifampicin against arachidonic acid (AA) plus iron (AA + iron) cotreatment and against acetaminophen (APAP, 500 mg/kg)-induced oxidative stress, in vitro and in vivo, respectively. In vivo, oral administration of rifampicin (100 or 200 mg/kg) attenuated elevation of serum alanine aminotransferase (ALT) and aspartate transaminase (AST), serum liver injury markers, against APAP treatment and, histologically, ameliorated tissue damage. Under in vitro examination, MTT assays were used to assess the cell death inhibitory effect of rifampicin against AA + iron-induced oxidative stress. In addition, DCFH-DA and Rh 123 staining showed that rifampicin treatment reduced reactive oxygen species (ROS) production and mitochondrial membrane damage, which had been induced by AA + iron treatment. Further, we explored whether rifampicin treatment enhanced phosphorylation of AMP-activated protein kinase (AMPK) by activation of liver kinase B1 (LKB1), the upstream kinase of AMPKα. Activated AMPKα induced activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), which are proteins functioning in redox balance. Moreover, we confirmed a reversed cell protective effect of rifampicin under compound C (an AMPK inhibitor) treatment. Overall, our data demonstrate that rifampicin effectively protects the liver against cellular oxidative stress through AMPKα and Nrf2 pathway.

Auriculatone Sulfate Effectively Protects Mice Against Acetaminophen-Induced Liver Injury

Acetaminophen (APAP) overdose is very common worldwide and has been widely recognized as the leading cause of drug-induced liver injury in the Western world. In our previous investigation, auriculatone, a natural product firstly obtained from Aster auriculatus, has demonstrated a potent protective effect against APAP-induced hepatotoxicity in HL-7702 cells. However, the poor water solubility and low bioavailability restrict its application. Auriculatone sulfate (AS) is a sulfated derivative of auriculatone with highly improved water-solubility. Hepatoprotective effects against APAP-induced liver injury (AILI) showed that intragastric pretreatment with AS at 50 mg/kg almost completely prevented mice against APAP-induced increases of serum alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase and ATPase. Histological results showed that AS could protect the liver tissue damage. In addition, AS pretreatment not only significantly retained hepatic malondialdehyde and the activities of glutathione, superoxide dismutase, and glutathione peroxidase at normal levels, but also markedly suppressed the increase of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 levels in mouse liver caused by overdose APAP. Immunohistochemical analysis showed that AS obviously attenuated the expression of CD45 and HNE in liver tissue. Further mechanisms of action investigation showed that inhibition of cytochrome P450 3A11 (CYP 3A11) and CYP2E1 enzymatic activities (but not that of CYP1A2) was responsible for APAP bioactivation. In conclusion, AS showed a hepatoprotective effect against AILI through alleviating oxidative stress and inflammation and inhibiting CYP-mediated APAP bioactivation. It may be an effective hepatoprotective agent for AILI and other forms of human liver disease.

Mechanisms of soft and hard electrophile toxicities

Electron-deficient chemicals (electrophiles) react with compounds that have one or more unshared valence electron pairs (nucleophiles). The resulting covalent reactions between electrophiles and nucleophiles (e.g., Michael addition, SN2 reactions) are important, not only to Organic Chemistry, but also to the fields of Molecular Biology and Toxicology. Specifically, covalent bond formation is the operational basis of many critically important cellular processes; e.g., enzyme function, neurotransmitter release, and membrane-vesicle fusion. Given this context it is understandable that these reactions are also relevant to Toxicology, since a significant number of xenobiotic chemicals are toxic electrophiles that can react with endogenous nucleophilic residues. Therefore, the purpose of this Review is to discuss electrophile-nucleophile chemistry as it pertains to cell injury and resulting organ toxicity. Our discussion will involve an introduction to the Hard and Soft, Acids and Bases (HSAB) theory of Pearson. The HSAB concept provides a framework for calculation of quantum chemical parameters that classify the electrophile and nucleophile covalent components according to their respective electronic nature (softness/hardness) and reactivity (electrophilicity/nucleophilicity). The calculated quantum indices in conjunction with corroborative in vivo, in chemico (cell free) and in vitro research can offer an illuminating approach to mechanistic discovery. Accordingly, we will provide examples that demonstrate how this approach has been used to discern mechanisms and sites of electrophile action.

Mechanisms and biomarkers of liver regeneration after drug-induced liver injury

Liver, the major metabolic organ in the body, is known for its remarkable capacity to regenerate. Whereas partial hepatectomy (PHx) is a popular model for the study of liver regeneration, the liver also regenerates after acute injury, but less is known about the mechanisms that drive it. Recent studies have shown that liver regeneration is critical for survival in acute liver failure (ALF), which is usually due to drug-induced liver injury (DILI). It is sometimes assumed that the signaling pathways involved are similar to those that regulate regeneration after PHx, but there are likely to be critical differences. A better understanding of regeneration mechanisms after DILI and hepatotoxicity in general could lead to development of new therapies for ALF patients and new biomarkers to predict patient outcome. Here, we summarize what is known about the mechanisms of liver regeneration and repair after hepatotoxicity. We also review the literature in the emerging field of liver regeneration biomarkers.

Shikonin Attenuates Acetaminophen-Induced Hepatotoxicity by Upregulation of Nrf2 through Akt/GSK3β Signaling

Acetaminophen (APAP) overdose-induced acute liver damage is mostly due to overwhelmingly increased oxidative stress. Nuclear factor-erythroid 2-related factor2 (Nrf2) plays an important role in alleviating APAP hepatic toxicity. Shikonin (SHK) enhances Nrf2 in multiple lines of normal cells. Nevertheless, whether SHK protects against APAP-induced liver toxicity remains undefined. This study found SHK defended APAP-induced liver toxicity, as well as reversed the levels of serum alanine/aspartate aminotransferases (ALT/AST), liver myeloperoxidase (MPO) activity, and reactive oxygen species (ROS), while it enhanced the liver glutathione (GSH) level in APAP-treated mice. SHK rescued the cell viability and GSH depletion, but neutralized oxidative stress in APAP-treated human normal liver L-02 cells. Mechanically, SHK increased Nrf2 expression in the exposure of APAP at the protein level but not at the mRNA level. Inhibition of Nrf2 blocked the SHK effect in APAP-treated hepatocytes. Furthermore, SHK improved Nrf2 stability through stimulating PI3K/Akt pathway, thus inhibiting GSK-3β. In vivo studies confirmed the close correlation of liver protection of SHK against APAP and Akt/GSK-3β/Nrf2 pathway. In conclusion, this study reveals that SHK prevents APAP hepatotoxicity by upregulation of Nrf2 via PI3K/Akt/GSK-3β pathway. Therefore, SHK may be a promising candidate against APAP-induced liver injury.

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.

Targeted cellular delivery of robust enzyme nanoparticles for the treatment of drug-induced hepatotoxicity and liver injury

Direct delivery of proteins into cells has been considered an effective approach for treating the protein-related diseases. However, clinical use of proteins has still been limited due to their instability in the blood and poor membrane permeability. To achieve an efficient cellular delivery of the protein to target cells via a systemic administration, a multifunctional carrier system having desirable stability both in the blood stream and the cells, specific cell-targeting property and endosomal escape functions may be required. In this study, we prepared a catalytic nanoparticle containing an active enzyme by cross-tethering multiple superoxide dismutase (SOD) molecules with catechol-derivatized hyaluronic acid (HA). The permeable shell of hydrophilic HA chains effectively protects the enzyme from degradation in the blood after intravenous administration and provides an additional function for targeting hepatocytes expressing HA receptor (CD44). The structure and catalytic activity of the enzyme molecules in the nanoparticle were not significantly compromised in the nanoparticle. In addition, ultra-small calcium phosphate nanoparticles (USCaP, 2-5 nm) were crystalized and decorated on the surface of the nanoparticle for the efficient endosomal escape after cellular uptake. The SOD-containing nanoparticle fortified with USCaP was used for the treatment of acetaminophen (APAP)-induced fulminant hepatotoxicity and liver injury. The nanoparticle achieved the efficient hepatic cellular delivery of SOD via a systemic administration and resulted in efficient removal of reactive oxygen species (ROS) in the liver and remarkable improvement of APAP-induced hepatotoxicity and liver injury in animals. STATEMENT OF SIGNIFICANCE: Despite the enormous therapeutic potential, the intracellular delivery of proteins has been limited due to their poor membrane permeability and stability. In this study, we demonstrated an active enzyme-containing nanoparticle functionalized by hyaluronic acid and ultra-small size calcium phosphate nanoparticles (2-5 nm) for targeted cellular delivery of superoxide dismutase (SOD). The nanoparticle was designed to integrate all the essential functions, including serum stability, target specificity, and endosomal escape capability, for a systemic delivery of a therapeutic protein to the cells of the liver tissue. The intravenous administration of the nanoparticle efficiently removes reactive oxygen species (ROS) in the liver and remarkably improves the drug-induced hepatotoxicity and the progress of fulminant liver injury in an acetaminophen-overdose animal model.

Hepatoprotective Effect of Polysaccharides Isolated from Dendrobium officinale against Acetaminophen-Induced Liver Injury in Mice via Regulation of the Nrf2-Keap1 Signaling Pathway

The effect of polysaccharides isolated from Dendrobium officinale (DOP) on acetaminophen- (APAP-) induced hepatotoxicity and the underlying mechanisms involved are investigated. Male Institute of Cancer Research (ICR) mice were randomly assigned to six groups: (1) control, (2) vehicle (APAP, 230 mg/kg), (3) N-acetylcysteine (100 mg/kg), (4) 50 mg/kg DOP, (5) 100 mg/kg DOP, and (6) 200 mg/kg DOP. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the serum and glutathione (GSH), malondialdehyde (MDA), catalase (CAT), total antioxidant capacity (T-AOC), myeloperoxidase (MPO), and reactive oxygen species (ROS) levels in the liver were determined after the death of the mice. The histological examination of the liver was also performed. The effect of DOP on the Kelch-like ECH-associated protein 1- (Keap1-) nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway was evaluated using Western blot analysis and real-time polymerase chain reaction (PCR). The results showed that DOP treatment significantly alleviated the hepatic injury. The decrease in ALT and AST levels in the serum and ROS, MDA, and MPO contents in the liver, as well as the increases in GSH, CAT, and T-AOC in the liver, were observed after DOP treatment. DOP treatment significantly induced the dissociation of Nrf2 from the Nrf2-Keap1 complex and promoted the Nrf2 nuclear translocation. Subsequently, DOP-mediated Nrf2 activation triggered the transcription and expressions of the glutamate-cysteine ligase catalytic (GCLC) subunit, glutamate-cysteine ligase regulatory subunit (GCLM), heme oxygenase-1 (HO-1), and NAD(P)H dehydrogenase quinone 1 (NQO1) in APAP-treated mice. The present study revealed that DOP treatment exerted potentially hepatoprotective effects against APAP-induced liver injury. Further investigation about mechanisms indicated that DOP exerted the hepatoprotective effect by suppressing the oxidative stress and activating the Nrf2-Keap1 signaling pathway.

Mitochondrial-Lysosomal Axis in Acetaminophen Hepatotoxicity

Acetaminophen (APAP) toxicity is the most common cause of acute liver failure and a major indication for liver transplantion in the United States and Europe. Although significant progress has been made in understanding the molecular mechanisms underlying APAP hepatotoxicity, there is still an urgent need to find novel and effective therapies against APAP-induced acute liver failure. Hepatic APAP metabolism results in the production of the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI), which under physiological conditions is cleared by its conjugation with glutathione (GSH) to prevent its targeting to mitochondria. APAP overdose or GSH limitation leads to mitochondrial NAPQI-protein adducts formation, resulting in oxidative stress, mitochondrial dysfunction, and necrotic cell death. As mitochondria are a major target of APAP hepatotoxicity, mitochondrial quality control and clearance of dysfunctional mitochondria through mitophagy, emerges as an important strategy to limit oxidative stress and the engagement of molecular events leading to cell death. Recent evidence has indicated a lysosomal-mitochondrial cross-talk that regulates APAP hepatotoxicity. Moreover, as lysosomal function is essential for mitophagy, impairment in the fusion of lysosomes with autophagosomes-containing mitochondria may compromise the clearance of dysfunctional mitochondria, resulting in exacerbated APAP hepatotoxicity. This review centers on the role of mitochondria in APAP hepatotoxicity and how the mitochondrial/lysosomal axis can influence APAP-induced liver failure.