Glutathione reductase is inhibited by acetaminophen-glutathione conjugate in vitro

Unveiling the molecular basis of paracetamol-induced hepatotoxicity: Interaction of N-acetyl-p-benzoquinone imine with mitochondrial succinate dehydrogenase

Background and aim

N-acetyl-p-benzoquinoneimine (NAPQI), a toxic byproduct of paracetamol (Acetaminophen, APAP), can accumulate and cause liver damage by depleting glutathione and forming protein adducts in the mitochondria. These adducts disrupt the respiratory chain, increasing superoxide production and reducing ATP. The goal of this study was to provide computational proof that succinate dehydrogenase (SDH), a subunit of complex II in the mitochondrial respiratory chain, is a favorable binding partner for NAPQI in this regard.

Method

Molecular docking, molecular dynamics simulation, protein-protein interaction networks (PPI), and KEGG metabolic pathway analysis were employed to identify binding characteristics, interaction partners, and their associations with metabolic pathways. A lipid membrane was added to the experimental apparatus to mimic the natural cellular environment of SDH. This modification made it possible to develop a context for investigating the role and interactions of SDH within a cellular ecosystem that was more realistic and biologically relevant.

Result

The molecular binding affinity score for APAP and NAPQI with SDH was predicted -6.5 and -6.7 kcal/mol, respectively. Furthermore, RMSD, RMSF, and Rog from the molecular dynamics simulations study revealed that NAPQI has slightly higher stability and compactness compared to APAP at 100 ns timeframe with mitochondrial SDH.

Conclusion

This study serves to predict the mechanistic process of paracetamol toxicity by using different computational approaches. In addition, this study will provide information about the drug target against APAP hepatotoxicity.

Anticancer Activity of Ω-6 Fatty Acids through Increased 4-HNE in Breast Cancer Cells

Simple Summary

Epidemiological evidence suggests that breast cancer risk is lowered by Ω-3 and increased by Ω-6 polyunsaturated fatty acids (PUFAs). Paradoxically, the Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE) inhibits cancer cell growth. This duality prompted us to study whether arachidonic acid (AA) would enhance doxorubicin (dox) cytotoxicity towards breast cancer cells. We found that supplementing AA or inhibiting 4-HNE metabolism potentiated doxorubicin (dox) toxicity toward Her2-dependent breast cancer but spared myocardial cells. Our results suggest that Ω-6 PUFAs could improve outcomes of dox chemotherapy in Her2-overexpressing breast cancer.

Abstract

Her2-amplified breast cancers resistant to available Her2-targeted therapeutics continue to be a challenge in breast cancer therapy. Dox is the mainstay of chemotherapy of all types of breast cancer, but its usefulness is limited by cumulative cardiotoxicity. Because oxidative stress caused by dox generates the pro-apoptotic Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE), we surmised that Ω-6 PUFAs would increase the effectiveness of dox chemotherapy. Since the mercapturic acid pathway enzyme RALBP1 (also known as RLIP76 or Rlip) that limits cellular accumulation of 4-HNE also mediates dox resistance, the combination of Ω-6 PUFAs and Rlip depletion could synergistically improve the efficacy of dox. Thus, we studied the effects of the Ω-6 PUFA arachidonic acid (AA) and Rlip knockdown on the antineoplastic activity of dox towards Her2-amplified breast cancer cell lines SK-BR-3, which is sensitive to Her2 inhibitors, and AU565, which is resistant. AA increased lipid peroxidation, 4-HNE generation, apoptosis, cellular dox concentration and dox cytotoxicity in both cell lines while sparing cultured immortalized cardiomyocyte cells. The known functions of Rlip including clathrin-dependent endocytosis and dox efflux were inhibited by AA. Our results support a model in which 4-HNE generated by AA overwhelms the capacity of Rlip to defend against apoptosis caused by dox or 4-HNE. We propose that Ω-6 PUFA supplementation could improve the efficacy of dox or Rlip inhibitors for treating Her2-amplified breast cancer.

Home pharmacological therapy in early COVID-19 to prevent hospitalization and reduce mortality: Time for a suitable proposal

The COVID‐19 pandemic is a highly dramatic concern for mankind. In Italy, the pandemic exerted its major impact throughout the period of February to June 2020. To date, the awkward amount of more than 134,000 deaths has been reported. Yet, post‐mortem autopsy was performed on a very modest number of patients who died from COVID‐19 infection, leading to a first confirmation of an immune‐thrombosis of the lungs as the major COVID‐19 pathogenesis, likewise for SARS. Since then (June–August 2020), no targeted early therapy considering this pathogenetic issue was approached. The patients treated with early anti‐inflammatory, anti‐platelet, anticoagulant and antibiotic therapy confirmed that COVID‐19 was an endothelial inflammation with immuno‐thrombosis. Patients not treated or scarcely treated with the most proper and appropriate therapy and in the earliest, increased the hospitalization rate in the intensive care units and also mortality, due to immune‐thrombosis from the pulmonary capillary district and alveoli. The disease causes widespread endothelial inflammation, which can induce damage to various organs and systems. Therapy must be targeted in this consideration, and in this review, we demonstrate how early anti‐inflammatory therapy may treat endothelia inflammation and immune‐thrombosis caused by COVID‐19, by using drugs we are going to recommend in this paper.

Prenatal exposure to acetaminophen increases the risk of atopic dermatitis in children: A nationwide nested case-control study in Taiwan

BACKGROUND

Acetaminophen (APAP) has been associated with the development of atopic diseases. However, little is known about the relationship between prenatal APAP exposure and atopic dermatitis (AD) in offspring.

OBJECTIVE

To investigate the association between prenatal APAP exposure and AD risk in offspring.

METHODS

In this study, 2029 study pairs (AD-affected children and their mothers) and 5,058 control pairs were identified between 1998 and 2008 from the Taiwan Longitudinal Health Insurance Database. Maternal APAP exposure during pregnancy was assessed.

RESULTS

After adjustment for potential confounders, there was a significant association between risk of offspring AD and exposure to acetaminophen in the first trimester (OR 1.16; 95% CI 1.05-1.28), the second trimester (OR 1.14; 95% CI 1.03-1.27), both first and second trimesters (OR 1.30; 95% CI 1.13-1.51), both first and third trimester (OR 1.20; 95% CI 1.04-1.39), any trimester (OR 1.12; 95% CI 1.00-1.26), and all three trimesters (OR 1.32; 95% CI 1.08-1.62) in a dose-response manner.

CONCLUSIONS

Prenatal exposure to acetaminophen was associated with an increased incidence of offspring AD.

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

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

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

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

Oxidative Stress in the Tumor Microenvironment and Its Relevance to Cancer Immunotherapy

Simple Summary

Cancer cells are consistently under oxidative stress, as reflected by elevated basal level of reactive oxygen species (ROS), due to increased metabolism driven by aberrant cell growth. This feature has been exploited to develop therapeutic strategies that control tumor growth by modulating the oxidative stress in tumor cells. This review provides an overview of recent advances in cancer therapies targeting tumor oxidative stress, and highlights the emerging evidence implicating the effectiveness of cancer immunotherapies in intensifying tumor oxidative stress. The promises and challenges of combining ROS-inducing agents with cancer immunotherapy are also discussed.

Abstract

It has been well-established that cancer cells are under constant oxidative stress, as reflected by elevated basal level of reactive oxygen species (ROS), due to increased metabolism driven by aberrant cell growth. Cancer cells can adapt to maintain redox homeostasis through a variety of mechanisms. The prevalent perception about ROS is that they are one of the key drivers promoting tumor initiation, progression, metastasis, and drug resistance. Based on this notion, numerous antioxidants that aim to mitigate tumor oxidative stress have been tested for cancer prevention or treatment, although the effectiveness of this strategy has yet to be established. In recent years, it has been increasingly appreciated that ROS have a complex, multifaceted role in the tumor microenvironment (TME), and that tumor redox can be targeted to amplify oxidative stress inside the tumor to cause tumor destruction. Accumulating evidence indicates that cancer immunotherapies can alter tumor redox to intensify tumor oxidative stress, resulting in ROS-dependent tumor rejection. Herein we review the recent progresses regarding the impact of ROS on cancer cells and various immune cells in the TME, and discuss the emerging ROS-modulating strategies that can be used in combination with cancer immunotherapies to achieve enhanced antitumor effects.

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.

Rlip Depletion Suppresses Growth of Breast Cancer

RLIP76 (RAL-binding protein-1, Rlip) is a stress-protective mercapturic-acid-pathway transporter protein that also plays a key role in regulating clathrin-dependent endocytosis as a Ral effector. Targeted inhibition or depletion of Rlip causes regression of xenografts of many cancers and is capable of abrogating tumor formation in p53-null mice. This is associated with the reversion of the abnormal methylomic profile of p53-null mice to wild-type. In a query of The Cancer Genome Atlas (TCGA) databases, we found that Rlip expression was associated with poor survival and with significant differences in the frequencies of PIK3CA mutation, MYC amplification, and CDKN2A/B deletion, which were the most commonly mutated, amplified, and deleted genes, respectively, among TCGA breast cancer patients. We conducted the present study to further examine the effects of Rlip inhibition and to evaluate the in vitro and in vivo efficacy in breast cancer. Using immunogold electron microscopy, we found that plasma-membrane Rlip was accessible to cell-surface antibodies in the MCF7 (ER+) breast cancer cell line. Rlip depletion resulted in decreased survival of MCF7 and MDA-MB-231 cells and increased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positivity and DNA laddering, indicating apoptotic cell death. Additionally, in vitro knockdown of Rlip inhibited EGF endocytosis and WNT/MAPK signaling. Xenograft studies in nude mice showed regression of breast cancer via antisense-mediated depletion of Rlip mRNA as well as by anti-Rlip antibody. Finally, knockdown of Rlip by antisense locked nucleic acid oligonucleotides increased markers for apoptotic signaling and decreased markers for proliferation, angiogenesis, and cell cycling in MCF7 and MDA-MB-231luc xenografts. Our findings validate Rlip as an attractive target in breast cancer.

Sirtuin 1 Modulation in Rat Model of Acetaminophen-Induced Hepatotoxicity

Sirtuin 1 (SIRT1) is involved in important biological processes such as energy metabolism and regulatory functions of the cell cycle, apoptosis, and inflammation. Our previous studies have shown hepatoprotective effect of polyphenolic compound resveratrol, which is also an activator of SIRT1. Therefore, the aim of our present study was to clarify the role of SIRT1 in process of hepatoprotection in animal model of drug-induced liver damage. Male Wistar rats were used for both in vivo and in vitro studies. Hepatotoxicity was induced by single dose of acetaminophen (APAP). Some rats and hepatocytes were treated by resveratrol or synthetic selective activator of sirtuin 1 (CAY10591). The degree of hepatotoxicity, the activity and expression of the SIRT1 were determined by biochemical, histological and molecular-biological assessments of gained samples (plasma, liver tissue, culture media and hepatocytes). Resveratrol and CAY attenuated APAP-induced hepatotoxicity in vivo and in vitro. Moreover, both drugs enhanced APAP-reduced SIRT1 activity. Our results show that modulation of the SIRT1 activity plays a role in hepatoprotection. Synthetic activators of SIRT1 would help in understanding the role of SIRT1 and are therefore a major boost towards the search for specific treatment of liver disease.

Hitting the Bull's-Eye in Metastatic Cancers-NSAIDs Elevate ROS in Mitochondria, Inducing Malignant Cell Death

Tumor metastases that impede the function of vital organs are a major cause of cancer related mortality. Mitochondrial oxidative stress induced by hypoxia, low nutrient levels, or other stresses, such as genotoxic events, act as key drivers of the malignant changes in primary tumors to enhance their progression to metastasis. Emerging evidence now indicates that mitochondrial modifications and mutations resulting from oxidative stress, and leading to OxPhos stimulation and/or enhanced reactive oxygen species (ROS) production, are essential for promoting and sustaining the highly metastatic phenotype. Moreover, the modified mitochondria in emerging or existing metastatic cancer cells, by their irreversible differences, provide opportunities for selectively targeting their mitochondrial functions with a one-two punch. The first blow would block their anti-oxidative defense, followed by the knockout blow—promoting production of excess ROS, capitulating the terminal stage—activation of the mitochondrial permeability transition pore (mPTP), specifically killing metastatic cancer cells or their precursors. This review links a wide area of research relevant to cellular mechanisms that affect mitochondria activity as a major source of ROS production driving the pro-oxidative state in metastatic cancer cells. Each of the important aspects affecting mitochondrial function are discussed including: hypoxia, HIFs and PGC1 induced metabolic changes, increased ROS production to induce a more pro-oxidative state with reduced antioxidant defenses. It then focuses on how the mitochondria, as a major source of ROS in metastatic cancer cells driving the pro-oxidative state of malignancy enables targeting drugs affecting many of these altered processes and why the NSAIDs are an excellent example of mitochondria-targeted agents that provide a one-two knockout activating the mPTP and their efficacy as selective anticancer metastasis drugs.

Protective effect of artichoke leaf extract against paracetamol-induced hepatotoxicity in rats

CONTEXT

Paracetamol overdose is a predominant cause of hepatotoxicity in both humans and experimental animals.

OBJECTIVE

In this study, we investigated the protective effect of aqueous artichoke leaf extract (ALE) against paracetamol-induced liver injury in rats using N-acetylcysteine (NAC) as a reference drug.

MATERIALS AND METHODS

Rats were divided into five groups: negative control, paracetamol (2 g/kg, single oral dose), ALE (1.5 g/kg, orally for 14 d), ALE + paracetamol, and NAC (100 mg/kg) + paracetamol. Indices of liver damage (serum alanine aminotransferase and aspartate aminotransferase) were measured. Liver homogenates were analyzed for oxidative stress biomarkers (MDA, malondialdehyde; SOD activity, superoxide dismutase activity; NO, nitric oxide; GSH content, reduced glutathione), glutathione cycling (GR, glutathione reductase), and utilization (GST, glutathione-S-transferase). Apoptosis was assessed using the comet assay.

RESULTS

Paracetamol caused marked liver damage as noted by significant increased activities of serum aminotransferases (p < 0.05) as well as a significant increase in hepatic MDA and NO levels (p < 0.001) compared with the negative control group. GSH content, GR, GST, and SOD activities were decreased significantly (p < 0.001). Comet assay parameters (tail length, percentage of tailed cells, percentage of migrated DNA, and tail moment) were increased (p < 0.05), indicating apoptosis. Histopathological examination showed necrotic areas. Pre-treatment with ALE replenished hepatic GSH, reversed oxidative stress parameters, DNA damage, and necrosis induced by paracetamol.

DISCUSSION AND CONCLUSION

These results suggest that ALE may protect from paracetamol-induced liver toxicity via its antioxidant and anti-apoptotic properties.

Automated evaluation of the inhibition of glutathione reductase activity: application to the prediction of ionic liquids' toxicity

An automated bioassay based on glutathione reductase was developed and applied to the evaluation of the toxicity of ionic liquids.

Insights in the mechanism underlying the protective effect of α-lipoic acid against acetaminophen-hepatotoxicity

Acetaminophen (APAP) is one of the most widely used analgesic antipyretic drugs and is a major cause of acute liver failure at overdose. The aim of this study is to investigate the possible protective effect of α-lipoic acid (α-LA, 20 or 100 mg/kg administered simultaneously or after 1.5 h) against APAP-induced hepatotoxicity in rats. Administration of APAP (1.5 g/kg i.p.) resulted in elevation of serum ALT and hepatic malondialdehyde (MDA) content, as well as decrease in hepatic glutathione (GSH) content. In addition, elevation in hepatic hemeoxygenase-1 (HO-1) and NADPH oxidase expression was observed accompanied with a significant reduction in glutathione synthase and cystathionine-beta-synthase (CβS) expression. Furthermore, nuclear factor kappa-B (NF-κB) activity was enhanced in APAP-treated rats. Administration of the standard APAP antidote; N-acetylcysteine (NAC, 1200 mg/kg) or α-LA (20 mg/kg), simultaneously or 1.5 h after APAP, ameliorated APAP-induced alterations in liver function, oxidant and inflammatory markers. Importantly, simultaneous administration of NAC or α-LA (20 mg/kg) was more protective than their later administration. However, the beneficial effect of α-LA was lost at higher dose level (100 mg/kg). Taken together, the beneficial effects of α-lipoic acid (20 mg/kg) were comparable to those of NAC which provides a new possible treatment for APAP-induced hepatotoxicity in patients who cannot tolerate NAC. However, careful dose selection is warranted since the beneficial effects of α-LA were lost at higher doses.

Protective effect of Baccharis trimera extract on acute hepatic injury in a model of inflammation induced by acetaminophen

BACKGROUND

Acetaminophen (APAP) is a commonly used analgesic and antipyretic. When administered in high doses, APAP is a clinical problem in the US and Europe, often resulting in severe liver injury and potentially acute liver failure. Studies have demonstrated that antioxidants and anti-inflammatory agents effectively protect against the acute hepatotoxicity induced by APAP overdose.

METHODS

The present study attempted to investigate the protective effect of B. trimera against APAP-induced hepatic damage in rats. The liver-function markers ALT and AST, biomarkers of oxidative stress, antioxidant parameters, and histopathological changes were examined.

RESULTS

The pretreatment with B. trimera attenuated serum activities of ALT and AST that were enhanced by administration of APAP. Furthermore, pretreatment with the extract decreases the activity of the enzyme SOD and increases the activity of catalase and the concentration of total glutathione. Histopathological analysis confirmed the alleviation of liver damage and reduced lesions caused by APAP.

CONCLUSIONS

The hepatoprotective action of B. trimera extract may rely on its effect on reducing the oxidative stress caused by APAP-induced hepatic damage in a rat model. General Significance. These results make the extract of B. trimera a potential candidate drug capable of protecting the liver against damage caused by APAP overdose.

Presence of UV filters in surface water and the effects of phenylbenzimidazole sulfonic acid on rainbow trout (Oncorhynchus mykiss) following a chronic toxicity test

UV filters belong to a group of compounds that are used by humans and are present in municipal waste-waters, effluents from sewage treatment plants and surface waters. Current information regarding UV filters and their effects on fish is limited. In this study, the occurrence of three commonly used UV filters - 2-phenylbenzimidazole-5-sulfonic acid (PBSA), 2-hydroxy-4-methoxybenzophenone (benzophenone-3, BP-3) and 5-benzoyl-4-hydroxy-2-methoxy-benzenesulfonic acid (benzophenone-4, BP-4) - in South Bohemia (Czech Republic) surface waters is presented. PBSA concentrations (up to 13μgL(-1)) were significantly greater than BP-3 or BP-4 concentrations (up to 620 and 390ngL(-1), respectively). On the basis of these results, PBSA was selected for use in a toxicity test utilizing the common model organism rainbow trout (Oncorhynchus mykiss). Fish were exposed to three concentrations of PBSA (1, 10 and 1000µgL(-1)) for 21 and 42 days. The PBSA concentrations in the fish plasma, liver and kidneys were elevated after 21 and 42 days of exposure. PBSA increased activity of certain P450 cytochromes. Exposure to PBSA also changed various biochemical parameters and enzyme activities in the fish plasma. However, no pathological changes were obvious in the liver or gonads.

Comparison of inhibitory effects between acetaminophen-glutathione conjugate and reduced glutathione in human glutathione reductase

Acetaminophen overdose is the most frequent cause of acute liver injury. The main mechanism of acetaminophen toxicity has been attributed to oxidation of acetaminophen. The oxidation product is very reactive and reacts with glutathione generating acetaminophen-glutathione conjugate (APAP-SG). Although this conjugate has been recognized to be generally nontoxic, we have found recently that APAP-SG could produce a toxic effect. Therefore, the aim of our study was to estimate the toxicity of purified APAP-SG by characterizing the inhibitory effect in human glutathione reductase (GR) and comparing that to the inhibitory effect of the natural inhibitor reduced glutathione. We used two types of human GR: recombinant and freshly purified from red blood cells. Our results show that GR was significantly inhibited in the presence of both APAP-SG and reduced glutathione. For example, the enzyme activity of recombinant and purified GR was reduced in the presence of 4 mm APAP-SG (with 0.5 mm glutathione disulfide) by 28% and 22%, respectively. The type of enzyme inhibition was observed to be competitive in the cases of both APAP-SG and glutathione. As glutathione inhibits GR activity in cells under physiological conditions, the rate of enzyme inhibition ought to be weaker in the case of glutathione depletion that is typical of acetaminophen overdose. Notably, however, enzyme activity likely remains inhibited due to the presence of APAP-SG, which might enhance the pro-oxidative status in the cell. We conclude that our finding could reflect some other pathological mechanism that may contribute to the toxicity of acetaminophen.

Steatotic rat hepatocytes in primary culture are more susceptible to the acute toxic effect of acetaminophen

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in humans. Non-alcoholic fatty liver disease is the most frequent chronic liver disease in developed countries. The aim of our work was to compare the effect of APAP on intact rat hepatocytes and hepatocytes isolated from steatotic liver in primary cultures. Male Wistar rats were fed with standard diet (10 % energy from fat) and high-fat diet (71 % energy from fat) for 6 weeks and then hepatocytes were isolated. After cell attachment, APAP (1; 2.5; 3.75 and 5 mM) was added to culture media (William's E medium) and hepatocytes were cultured for up to 24 hours. APAP caused more severe dose-dependent damage of steatotic hepatocytes as documented by increased release of lactate dehydrogenase (LDH) and LDH leakage, decreased activity of cellular dehydrogenases (WST-1 test) and reduced albumin production. Intact steatotic hepatocytes contained lower amount of reduced glutathione (GSH). Treatment with APAP (1 and 2.5 mmol/l) caused more pronounced decrease in GSH in steatotic hepatocytes. ROS (reactive oxygen species) formation after 24-hour incubation was significantly higher in fatty hepatocytes using APAP at concentration of 3.75 and 5 mmol/l. Interleukin 6 (IL-6) production was elevated in 2.5 mM APAP-treated nonsteatotic and steatotic hepatocyte cultures at 8 hours, compared to appropriate controls. In conclusions, our results indicate that steatotic hepatocytes exert higher sensitivity to the toxic action of APAP. This sensitivity may be caused by lower content of GSH in intact steatotic hepatocytes and by more pronounced APAP-induced decrease in intracellular concentration of GSH.

Purified acetaminophen-glutathione conjugate is able to induce oxidative stress in rat liver mitochondria

Acetaminophen overdose is the most often cause of acute liver injury. The toxic mechanism is linked to formation of an active metabolite that reacts with glutathione generating acetaminophen-glutathione conjugate (APAP-SG). This compound has been recognized to be non-toxic generally. Our preliminary results showed, however, that APAP-SG could possess a toxic effect too. Therefore, the aim of our study was to prepare, purify and to test possible toxicity of APAP-SG. We prepared APAP-SG using organic synthesis. The conjugate was purified by preparative HPLC and its structure was confirmed using mass spectrometry. Final purity of APAP-SG was >98 %. We estimated a toxic effect of APAP-SG in isolated rat liver mitochondria using a fluorescent ROS probe. We assessed ROS production in presence of complex I or complex II substrates. The increase of ROS-dependent fluorescence in presence of glutamate/malate was 104 ± 13 % and 130 ± 10 % in 1 mM and 5 mM APAP-SG, respectively, in comparison with controls. ROS production related to presence of complex II substrate was enhanced 4-times in APAP-SG (5 mM) treated mitochondria (compared to controls). We conclude, we proved our hypothesis that APAP-SG conjugate is able to induce a mitochondrial impairment leading to enhanced ROS production.

Hepatoprotective effects of mushrooms

The particular characteristics of growth and development of mushrooms in nature result in the accumulation of a variety of secondary metabolites such as phenolic compounds, terpenes and steroids and essential cell wall components such as polysaccharides, β-glucans and proteins, several of them with biological activities. The present article outlines and discusses the available information about the protective effects of mushroom extracts against liver damage induced by exogenous compounds. Among mushrooms, Ganoderma lucidum is indubitably the most widely studied species. In this review, however, emphasis was given to studies using other mushrooms, especially those presenting efforts of attributing hepatoprotective activities to specific chemical components usually present in the mushroom extracts.

Assessment of reduced glutathione: comparison of an optimized fluorometric assay with enzymatic recycling method

Glutathione is an important tripeptide involved in a variety of cellular processes. Thus, precise knowledge of its levels is essential. Glutathione exists in two free forms-reduced and oxidized-and a number of methods exist to measure its levels. The aim of our work was to optimize a spectrofluorometric assay for reduced glutathione based on the reaction between glutathione and o-phthalaldehyde. We found that a change of excitation wavelength to 340 nm and modification of pH to 6.0 enhance sensitivity and specificity of the method (intraassay coefficient of variation CV < 3%, interassay CV = 5.1%, recovery = 98-102%, linearity = 0-1000 μM GSH, calibration R2 = 1.00). We also anticipated possible effect of various amino acids on the fluorescence signal, but no interference was found. We compared the optimized fluorometric method with a popular enzymatic recycling glutathione assay and found very strong correlation of results (r = 0.99, n = 45). We introduce here an optimized fluorometric method possessing sufficient sensitivity and specificity that is comparable to the enzymatic glutathione assay. Because the fluorometric assay procedure is faster and lower in cost, it could be ideal for routine analysis of reduced glutathione levels in a large number of samples.

Comparison of the protective actions of N-acetylcysteine, hypotaurine and taurine against acetaminophen-induced hepatotoxicity in the rat

When used in overdoses, acetaminophen (APAP) is a common cause of morbidity and mortality in humans. At present, N-acetylcysteine (NAC) is the antidote of choice for acetaminophen overdoses. Prompt administration of NAC can prevent the deleterious actions of APAP in the liver. In view of the similarities in antioxidant effects demonstrated by NAC, hypotaurine (HYTAU) and taurine (TAU) in this and other our laboratories, the present study was undertaken to compare these compounds for the ability to attenuate plasma and liver biochemical changes associated with a toxic dose of APAP. For this purpose, fasted male Sprague-Dawley rats, 225-250 g in weight, were intraperitoneally treated with APAP (800 mg/kg), NAC, HYTAU or TAU (2.4 mM/kg) followed 30 min later by APAP, or 50% PEG 400 (the vehicle for APAP). At 6 hr after APAP administration, all animals were sacrificed by decapitation and their blood and livers collected. The plasma fractions were analyzed for indices of liver damage (alanine transaminase, aspartate transaminase, lactate dehydrogenase), levels of malondialdehyde (MDA), reduced (GSH) and oxidized (GSSG) glutathione, and activities of glutathione reductase (GR), glutathione S-transferase (GST) and gamma-glutamylcisteinyl synthetase (GCS). Suitable liver homogenates were analyzed for the same biochemical parameters as the plasma but indices of liver damage. By itself, APAP increased MDA formation and had a significant lowering influence on the levels of GSH and GSSG, the GSH/GSSH ratio, and the activities of GR, GST and GCS both in the plasma and liver. In addition, APAP promoted the leakage of transaminases and lactate dehydrogenase from the liver into the plasma. Without exceptions, a pretreatment with a sulfur-containing compound led to a significant attenuation of the liver injury and the biochemical changes induced by APAP. Within a narrow range of potency differences, HYTAU appeared to be the most protective and TAU the least. The present results suggest that, irrespective of the differences in structural features and in vitro antioxidant properties that may exist among NAC, TAU and HYTAU, these compounds demonstrate equivalent patterns of protection and, to a certain extent, equipotent protective actions against the toxic actions of APAP in the liver when tested in equimolar doses and under the same conditions in an animal model.

Similarities in features of autism and asthma and a possible link to acetaminophen use

Autism and autism spectrum disorders are enigmatic conditions that have their origins in the interaction of genes and environmental factors. In this hypothesis, genes statistically associated with autism are emphasized to be important in inflammation and in innate immune pathways, including pathways for susceptibility to asthma. The role of acetaminophen (paracetamol) in an increased risk for asthma is described and a possible similar link to an increased risk for autism is suggested.