Effects of nimesulide and its reduced metabolite on mitochondria

Antioxidant-Based Preventive Effect of Phytochemicals on Anticancer Drug-Induced Hepatotoxicity

Significance: Drug-induced liver injury (DILI) or hepatotoxicity has been a hot issue to overcome on the safety and physiological function of the liver, since it is known to have biochemical, cellular, immunological, and molecular alterations in the liver mainly induced by alcohol, chemicals, drugs, heavy metals, and genetic factors. Recently efficient therapeutic and preventive strategies by some phytochemicals are of interest, targeting oxidative stress-mediated hepatotoxicity alone or in combination with anticancer drugs. Recent Advances: To assess DILI, the variety of in vitro and in vivo animal models has been developed mainly by using carbon tetrachloride, d-galactosamine, acetaminophen, and lipopolysaccharide. Also, the mechanisms on hepatotoxicity by several drugs and herbs have been explored in detail. Recent studies reveal that antioxidants including vitamins and some phytochemicals were reported to prevent against DILI. Critical Issues: Antioxidant therapy with some phytochemicals is noteworthy, since oxidative stress is critically involved in DILI via production of chemically reactive oxygen species or metabolites, impairment of mitochondrial respiratory chain, and induction of redox cycling. Future Directions: For efficient antioxidant therapy, DILI susceptibility, Human Leukocyte Antigen genetic factors, biomarkers, and pathogenesis implicated in hepatotoxicity should be further explored in association with oxidative stress-mediated signaling, while more randomized preclinical and clinical trials are required with optimal safe doses of drugs and/or phytochemicals alone or in combination for efficient clinical practice along with the development of advanced DILI diagnostic tools.

Mitochondria Matter: Systemic Aspects of Nonalcoholic Fatty Liver Disease (NAFLD) and Diagnostic Assessment of Liver Function by Stable Isotope Dynamic Breath Tests

The liver plays a key role in systemic metabolic processes, which include detoxification, synthesis, storage, and export of carbohydrates, lipids, and proteins. The raising trends of obesity and metabolic disorders worldwide is often associated with the nonalcoholic fatty liver disease (NAFLD), which has become the most frequent type of chronic liver disorder with risk of progression to cirrhosis and hepatocellular carcinoma. Liver mitochondria play a key role in degrading the pathways of carbohydrates, proteins, lipids, and xenobiotics, and to provide energy for the body cells. The morphological and functional integrity of mitochondria guarantee the proper functioning of β-oxidation of free fatty acids and of the tricarboxylic acid cycle. Evaluation of the liver in clinical medicine needs to be accurate in NAFLD patients and includes history, physical exam, imaging, and laboratory assays. Evaluation of mitochondrial function in chronic liver disease and NAFLD is now possible by novel diagnostic tools. "Dynamic" liver function tests include the breath test (BT) based on the use of substrates marked with the non-radioactive, naturally occurring stable isotope 13C. Hepatocellular metabolization of the substrate will generate 13CO2, which is excreted in breath and measured by mass spectrometry or infrared spectroscopy. Breath levels of 13CO2 are biomarkers of specific metabolic processes occurring in the hepatocyte cytosol, microsomes, and mitochondria. 13C-BTs explore distinct chronic liver diseases including simple liver steatosis, non-alcoholic steatohepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug, and alcohol effects. In NAFLD, 13C-BT use substrates such as α-ketoisocaproic acid, methionine, and octanoic acid to assess mitochondrial oxidation capacity which can be impaired at an early stage of disease. 13C-BTs represent an indirect, cost-effective, and easy method to evaluate dynamic liver function. Further applications are expected in clinical medicine. In this review, we discuss the involvement of liver mitochondria in the progression of NAFLD, together with the role of 13C-BT in assessing mitochondrial function and its potential use in the prevention and management of NAFLD.

Exploring Liver Mitochondrial Function by (13)C-Stable Isotope Breath Tests: Implications in Clinical Biochemistry

The liver is at the crossroad of key metabolic processes, which include detoxification, glycolipidic storage and export, and protein synthesis. The gut-liver axis, moreover, provides hepatocytes with a series of bacterial products and metabolites, which contribute to maintain liver function in health and disease. Breath tests (BTs) are developed as diagnostic tools for indirect, rapid, noninvasive assessment of several metabolic processes in the liver. BTs monitor the appearance of CO₂ in breath as a marker of a specific substrate metabolized in the liver, typically within microsomes, cytosol, or mitochondria. The noninvasiveness of BTs originates from the use of the, nonradioactive, naturally occurring stable isotope ¹³C marking a specific substrate which is metabolized in the liver, leading to the appearance of ¹³CO₂ in expired air. Some substrates (ketoisocaproic acid, methionine, and octanoic acid) provide information about dynamic liver mitochondrial function in health and disease. In humans, the application of ¹³C-breath tests ranges from nonalcoholic and alcoholic liver diseases to liver cirrhosis, hepatocarcinoma, preoperative and postoperative assessment of liver function, and drug-induced liver damage. ¹³C-BTs are an indirect, cost-effective, and easy method to evaluate dynamic liver function and gastric kinetics in health and disease, with ongoing studies focusing on further applications in clinical medicine.

Diazinon impairs bioenergetics and induces membrane permeability transition on mitochondria isolated from rat liver

Diazinon (DZN) is a broad-spectrum insecticide extensively used to control pests in crops and animals. Several investigators demonstrated that DZN produced tissue toxicity especially to the liver. In addition, the mitochondrion was implicated in DZN-induced toxicity, but the precise role of this organelle remains to be determined. The aim of this study was thus to examine the effects of DZN (50 to 150 μM) on the bioenergetics and mitochondrial permeability transition (MPT) associated processes in isolated rat liver mitochondria. DZN inhibited state-3 respiration in mitochondria energized with glutamate plus malate, substrates of complex I, and succinate, substrate of complex II of the respiratory chain and decreased the mitochondrial membrane potential resulting in inhibition of ATP synthesis. MPT was estimated by the extent of mitochondrial swelling, in the presence of 10 µM Ca²⁺. DZN elicited MPT in a concentration-dependent manner, via a mechanism sensitive to cyclosporine A, EGTA, ruthenium red and N-ethylmaleimide, which was associated with mitochondrial Ca²⁺ efflux and cytochrome c release. DZN did not result in hydrogen peroxide accumulation or glutathione oxidation, but this insecticide oxidized endogenous NAD(P)H and protein thiol groups. Data suggest the involvement of mitochondria, via apoptosis, in the hepatic cytotoxicity attributed to DZN.

[Reye syndrome and sudden death symptoms after oral administration of nimesulide due to upper respiratory tract infection in a boy]

A boy aged 6 years and 3 months developed upper respiratory tract infection and pyrexia 2 months ago and was given oral administration of nimesulide by his parents according to directions. Half an hour later, the boy experienced convulsions and cardiopulmonary arrest, and emergency examination found hypoketotic hypoglycemia, metabolic acidosis, significant increases in serum aminotransferases and creatine kinase, and renal damage. Recovery of consciousness and vital signs was achieved after cardiopulmonary resuscitation, but severe mental and movement regression was observed. The boy had a significant reduction in free carnitine in blood and significant increases in medium- and long-chain fatty acyl carnitine, urinary glutaric acid, 3-hydroxy glutaric acid, isovalerylglycine, and ethylmalonic acid, suggesting the possibility of multiple acyl-CoA dehydrogenase deficiency. After the treatment with vitamin B2, L-carnitine, and bezafibrate, the boy gradually improved, and reexamination after 3 months showed normal biochemical parameters. The boy had compound heterozygous mutations in the ETFDH gene, i.e., a known mutation, c.341G>A (p.R114H), from his mother and a novel mutation, c.1484C>G (p.P495R), from his father. Finally, he was diagnosed with multiple acyl-CoA dehydrogenase deficiency. Reye syndrome and sudden death symptoms were caused by nimesulide-induced acute metabolic crisis. It is concluded that inherited metabolic diseases may be main causes of Reye syndrome and sudden death, and biochemical and genetic analyses are the key to identifying underlying diseases.

[Reye syndrome and sudden death symptoms after oral administration of nimesulide due to upper respiratory tract infection in a boy]

A boy aged 6 years and 3 months developed upper respiratory tract infection and pyrexia 2 months ago and was given oral administration of nimesulide by his parents according to directions. Half an hour later, the boy experienced convulsions and cardiopulmonary arrest, and emergency examination found hypoketotic hypoglycemia, metabolic acidosis, significant increases in serum aminotransferases and creatine kinase, and renal damage. Recovery of consciousness and vital signs was achieved after cardiopulmonary resuscitation, but severe mental and movement regression was observed. The boy had a significant reduction in free carnitine in blood and significant increases in medium- and long-chain fatty acyl carnitine, urinary glutaric acid, 3-hydroxy glutaric acid, isovalerylglycine, and ethylmalonic acid, suggesting the possibility of multiple acyl-CoA dehydrogenase deficiency. After the treatment with vitamin B2, L-carnitine, and bezafibrate, the boy gradually improved, and reexamination after 3 months showed normal biochemical parameters. The boy had compound heterozygous mutations in the ETFDH gene, i.e., a known mutation, c.341G>A (p.R114H), from his mother and a novel mutation, c.1484C>G (p.P495R), from his father. Finally, he was diagnosed with multiple acyl-CoA dehydrogenase deficiency. Reye syndrome and sudden death symptoms were caused by nimesulide-induced acute metabolic crisis. It is concluded that inherited metabolic diseases may be main causes of Reye syndrome and sudden death, and biochemical and genetic analyses are the key to identifying underlying diseases.

Exposure to decabromodiphenyl ether (BDE-209) produces mitochondrial dysfunction in rat liver and cell death

Polybrominated diphenyl ethers (PBDE) are ubiquitous environmental pollutants. Exposure to these chemicals has been associated with developmental neurotoxicity, endocrine dysfunctions, reproductive disorders, and hepatotoxicity. The widespread use of PBDE as flame retardants has culminated in daily exposure of humans and wildlife to these contaminants and resulted in their banned use. Thus assessment of the potential effects of each PBDE congener on living organisms has become cause for concern. The aim of this study was to (1) examine the effects of decabromodiphenyl ether (BDE)-209 on different functions of HepG2 cells and (2) investigate whether this congener is involved in mitochondrial toxicity. The use of multiple methods was employed to (i) study the influence of BDE-209 on mitochondrial permeability transition (MPT) process in mitochondria isolated from rat liver and (ii) determine the consequential cellular damage. Our results showed that BDE-209 induced matrix swelling related to MPT with 10 µM and ATP depletion with 0.1 µM. In addition, 0.5 μM BDE-209 reduced HepG2 cell viability, produced collapse of membrane potential, but increased levels of reactive oxygen species (ROS) after 48 h incubation. After 24 h with 5 μM treatment elevated levels of ROS, DNA fragmentation and cytochrome c release, accompanied by caspase 9 and caspase 3 activation was noted. Taken together, these results suggest that short-duration exposure (24 or 48 h) to 0.5 μM or 5 μM BDE-209 concentrations diminished HepG2 cell viability due to apoptosis associated with mitochondrial dysfunction.

Hyaluronic acid-nimesulide conjugates as anticancer drugs against CD44-overexpressing HT-29 colorectal cancer in vitro and in vivo

Carrier-mediated drug delivery systems are promising therapeutics for targeted delivery and improved efficacy and safety of potent cytotoxic drugs. Nimesulide is a multifactorial cyclooxygenase 2 nonsteroidal anti-inflammatory drug with analgesic, antipyretic and potent anticancer properties; however, the low solubility of nimesulide limits its applications. Drugs conjugated with hyaluronic acid (HA) are innovative carrier-mediated drug delivery systems characterized by CD44-mediated endocytosis of HA and intracellular drug release. In this study, hydrophobic nimesulide was conjugated to HA of two different molecular weights (360 kDa as HA with high molecular weight [HAH] and 43kDa as HA with low molecular weight [HAL]) to improve its tumor-targeting ability and hydrophilicity. Our results showed that hydrogenated nimesulide (N-[4-amino-2-phenoxyphenyl]methanesulfonamide) was successfully conjugated with both HA types by carbodiimide coupling and the degree of substitution of nimesulide was 1%, which was characterized by ¹H nuclear magnetic resonance 400 MHz and total correlation spectroscopy. Both Alexa Fluor^® 647 labeled HAH and HAL could selectively accumulate in CD44-overexpressing HT-29 colorectal tumor area in vivo, as observed by in vivo imaging system. In the in vitro cytotoxic test, HA-nimesulide conjugate displayed >46% cell killing ability at a nimesulide concentration of 400 µM in HT-29 cells, whereas exiguous cytotoxic effects were observed on HCT-15 cells, indicating that HA-nimesulide causes cell death in CD44-overexpressing HT-29 cells. Regarding in vivo antitumor study, both HAL-nimesulide and HAH-nimesulide caused rapid tumor shrinkage within 3 days and successfully inhibited tumor growth, which reached 82.3% and 76.4% at day 24 through apoptotic mechanism in HT-29 xenografted mice, without noticeable morphologic differences in the liver or kidney, respectively. These results indicated that HA-nimesulide with improved selectivity through HA/CD44 receptor interactions has the potential to enhance the therapeutic efficacy and safety of nimesulide for cancer treatment.

The Importance of Patient-Specific Factors for Hepatic Drug Response and Toxicity

Responses to drugs and pharmacological treatments differ considerably between individuals. Importantly, only 50%-75% of patients have been shown to react adequately to pharmacological interventions, whereas the others experience either a lack of efficacy or suffer from adverse events. The liver is of central importance in the metabolism of most drugs. Because of this exposed status, hepatotoxicity is amongst the most common adverse drug reactions and hepatic liabilities are the most prevalent reason for the termination of development programs of novel drug candidates. In recent years, more and more factors were unveiled that shape hepatic drug responses and thus underlie the observed inter-individual variability. In this review, we provide a comprehensive overview of different principle mechanisms of drug hepatotoxicity and illustrate how patient-specific factors, such as genetic, physiological and environmental factors, can shape drug responses. Furthermore, we highlight other parameters, such as concomitantly prescribed medications or liver diseases and how they modulate drug toxicity, pharmacokinetics and dynamics. Finally, we discuss recent progress in the field of in vitro toxicity models and evaluate their utility in reflecting patient-specific factors to study inter-individual differences in drug response and toxicity, as this understanding is necessary to pave the way for a patient-adjusted medicine.

Asiatic acid uncouples respiration in isolated mouse liver mitochondria and induces HepG2 cells death

Asiatic acid, one of the triterpenoid components isolated from Centella asiatica, has received increasing attention due to a wide variety of biological activities. To date, little is known about its mechanisms of action. Here we examined the cytotoxic effect of asiatic acid on HepG2 cells and elucidated some of the underlying mechanisms. Asiatic acid induced rapid cell death, as well as mitochondrial membrane potential (MMP) dissipation, ATP depletion and cytochrome c release from mitochondria to the cytosol in HepG2 cells. In mitochondria isolated from mouse liver, asiatic acid treatment significantly stimulated the succinate-supported state 4 respiration rate, dissipated the MMP, increased Ca(2+) release from Ca(2+)-loaded mitochondria, decreased ATP content and promoted cytochrome c release, indicating the uncoupling effect of asiatic acid. Hydrogen peroxide (H2O2) produced by succinate-supported mitochondrial respiration was also significantly inhibited by asiatic acid. In addition, asiatic acid inhibited Ca(2+)-induced mitochondrial swelling but did not induce mitochondrial swelling in hyposmotic potassium acetate medium which suggested that asiatic acid may not act as a protonophoric uncoupler. Inhibition of uncoupling proteins (UCPs) or blockade of adenine nucleotide transporter (ANT) attenuated the effect of asiatic acid on MMP dissipation, Ca(2+) release, mitochondrial respiration and HepG2 cell death. When combined inhibition of UCPs and ANT, asiatic acid-mediated uncoupling effect was noticeably alleviated. These results suggested that both UCPs and ANT partially contribute to the uncoupling properties of asiatic acid. In conclusion, asiatic acid is a novel mitochondrial uncoupler and this property is potentially involved in its toxicity on HepG2 cells.

Comparative effects of fipronil and its metabolites sulfone and desulfinyl on the isolated rat liver mitochondria

Fipronil is an insecticide extensively used to control pests in crops and animals. There are relates of poisoning due to exposure of fipronil in mammals and the liver has been suggested as potential target. In this study, we evaluated the effects of fipronil and its metabolites sulfone and desulfinyl on the bioenergetics, reactive oxygen species (ROS) production and calcium efflux from mitochondria isolated from rat liver. Fipronil (5-25 μM) inhibited state-3 respiration in mitochondria energized with glutamate plus malate, substrates of complex I of the respiratory chain and decreased the mitochondrial membrane potential resulting in inhibition of ATP synthesis. Fipronil also caused uncoupling in succinate-energized mitochondria and calcium efflux. The metabolites sulfone and desulfinyl also acted as mitochondrial inhibitors and uncouplers and caused calcium efflux, but with different potencies, being the sulfone the more potent one. These effects of fipronil and its metabolites on mitochondrial bioenergetics and calcium homeostasis may be related to toxic effects of the insecticide in the liver.

Exploring liver mitochondrial function by ¹³C-stable isotope breath tests: implications in clinical biochemistry

The liver plays a pivotal role in a myriad of metabolic processes, including detoxification, glycolipidic storage and export, and protein synthesis. Breath tests employing (13)C as stable isotope have been introduced to explore such energy-dependent pathways involving mitochondrial function in the liver. Specific substrates are ketoisocaproic acid, methionine, and octanoic acid. In humans, the application of (13)C-breath tests ranges from nonalcoholic and alcoholic liver diseases to liver cirrhosis, hepatocarcinoma, preoperative and postoperative assessment of liver function, and drug-induced liver damage. Studying liver mitochondrial function by (13)C-breath tests represents a complementary tool to monitor complex metabolic processes in health and disease.

Synthesis and biological evaluation of nimesulide based new class of triazole derivatives as potential PDE4B inhibitors against cancer cells

A new class of 1,2,3-triazol derivatives derived from nimesulide was designed as potential inhibitors of PDE4B. Synthesis of these compounds was carried out via a multi-step sequence consisting of copper-catalyzed azide-alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required azide was prepared via the reaction of aryl amine (obtained from nimesulide) with α-chloroacetyl chloride followed by displacing the α-chloro group by an azide. Some of the synthesized compounds showed encouraging PDE4B inhibitory properties in vitro that is >50% inhibition at 30 μM that were supported by the docking studies of these compounds at the active site of PDE4B enzyme (dock scores ~ -28.6 for a representative compound). Two of these PDE4 inhibitors showed promising cytotoxic properties against HCT-15 human colon cancer cells in vitro with IC50 ~ 21-22 μg/mL.

Utilization of causal reasoning of hepatic gene expression in rats to identify molecular pathways of idiosyncratic drug-induced liver injury

Drug-induced liver injury (DILI) represents a leading cause of acute liver failure. Although DILI can be discovered in preclinical animal toxicology studies and/or early clinical trials, some human DILI reactions, termed idiosyncratic DILI (IDILI), are less predictable, occur in a small number of individuals, and do not follow a clear dose-response relationship. The emergence of IDILI poses a critical health challenge for patients and a financial challenge for the pharmaceutical industry. Understanding the cellular and molecular mechanisms underlying IDILI is key to the development of models that can assess potential IDILI risk. This study used Reverse Causal Reasoning (RCR), a method to assess activation of molecular signaling pathways, on gene expression data from rats treated with IDILI or pharmacologic/chemical comparators (NON-DILI) at the maximum tolerated dose to identify mechanistic pathways underlying IDILI. Detailed molecular networks involved in mitochondrial injury, inflammation, and endoplasmic reticulum (ER) stress were found in response to IDILI drugs but not negative controls (NON-DILI). In vitro assays assessing mitochondrial or ER function confirmed the effect of IDILI compounds on these systems. Together our work suggests that using gene expression data can aid in understanding mechanisms underlying IDILI and can guide in vitro screening for IDILI. Specifically, RCR should be considered for compounds that do not show evidence of DILI in preclinical animal studies positive for mitochondrial dysfunction and ER stress assays, especially when the therapeutic index toward projected human maximum drug plasma concentration is low.

Interaction of nonsteroidal anti-inflammatory drugs with membranes: in vitro assessment and relevance for their biological actions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world due to their anti-inflammatory, analgesic and antipyretic properties. Nevertheless, the consumption of these drugs is still associated with the occurrence of a wide spectrum of adverse effects. Regarding the major role of membranes in cellular events, the hypothesis that the biological actions of NSAIDs may be related to their effect at the membrane level has triggered the in vitro assessment of NSAIDs-membrane interactions. The use of membrane mimetic models, cell cultures, a wide range of experimental techniques and molecular dynamics simulations has been providing significant information about drugs partition and location within membranes and also about their effect on diverse membrane properties. These studies have indeed been providing evidences that the effect of NSAIDs at membrane level may be an additional mechanism of action and toxicity of NSAIDs. In fact, the pharmacokinetic properties of NSAIDs are closely related to the ability of these drugs to interact and overcome biological membranes. Moreover, the therapeutic actions of NSAIDs may also result from the indirect inhibition of cyclooxygenase due to the disturbing effect of NSAIDs on membrane properties. Furthermore, increasing evidences suggest that the disordering effects of these drugs on membranes may be in the basis of the NSAIDs-induced toxicity in diverse organ systems. Overall, the study of NSAIDs-membrane interactions has proved to be not only important for the better understanding of their pharmacological actions, but also for the rational development of new approaches to overcome NSAIDs adverse effects.

Antioxidative burst and hepatoprotective effects of ethanol root extract of Hippocratea africana against paracetamol-induced liver injury

CONTEXT

Hippocratea africana (Willd.) Loes. ex Engl. (Celastraceae) root is used traditionally as an antipoison or antidote to treat liver diseases.

OBJECTIVE

To evaluate antioxidative burst and hepatoprotective potentials of H. africana against paracetamol-induced liver injury in rats.

MATERIALS AND METHOD

Antioxidative burst activity of the extract (1-100 µg/ml) in whole blood, neutrophils and macrophages was investigated using a luminol/lucigenin-based chemiluminescence assay. The hepatoprotective effect of the extract (200-600 mg/kg) was evaluated by the assay of liver function parameters, antioxidant enzymes and histopathological studies of the liver. GC-MS analyses of hexane and dichloromethane fractions were also carried out.

RESULTS AND DISCUSSION

The root extract/fractions exerted pronounced inhibition of oxidative burst activity in whole blood, neutrophils (intracellular and extracellular) and macrophages (3.04-99.70%). The administration of the root extract caused significant (p < 0.05-0.001) reduction of high levels of liver enzymes (AST, ALT and ALP), total cholesterol, direct and total bilirubin as well as elevation of serum levels of total protein, albumin and antioxidant enzymes (SOD, CAT, GPx and GSH). Histology of the liver sections of extract and silymarin-treated animals showed reductions in the pathological features compared to the paracetamol-treated animals. The chemical pathological changes were consistent with histopathological observations suggesting a marked hepatoprotective effect of the root extract of H. africana. The GC-MS analysis revealed some pharmacologically active compounds.

CONCLUSION

The results show that the root extract of H. africana has hepatoprotective potential probably due to its antioxidative burst activity.

Modeling xenobiotic susceptibility to hepatotoxicity using an in vitro oxidative stress inflammation model

Evidence suggests xenobiotic exposure during periods of inflammation can increase an individual's susceptibility to toxicity. The present study aimed to validate an in-vitro inflammatory model to identify compounds that increase hepatotoxicity during inflammation. Using freshly isolated hepatocytes exposed to a low nontoxic flow of H2O2 using glucose (G) and glucose oxidase (GO) and supplementing it with either peroxidase or Fe(II), the effects of inflammation on 2 classes of drugs known to cause hepatotoxicity were examined: nitroaromatics (nimesulide, nilutamide, flutamide) and aromatic amines (clozapine, thioridazine). Co-incubation with G/GO and the nitroaromatics increased toxicity that was further increased when peroxidase was present. While the aromatic amines did not increase cytotoxicity with G/GO alone, they demonstrated significant increases in cytotoxicity when incubated with peroxidase+G/GO. Liver injury is commonly observed with alcohol abusers; therefore, the effects of inflammation on ethanol, and its metabolite acetaldehyde, were observed. Both ethanol and acetaldehyde increased cytotoxicity, which was further increased when Fe(II) was present. These results implicate H2O2, a cellular mediator of inflammation, as a potential risk factor for hepatotoxicity. A H2O2-enhanced hepatocyte-system in the presence of peroxidase or Fe(II) may prove useful for a more robust screening of xenobiotics for assessing potential toxicity associated with inflammation.

Nimesulide Based Novel Glycolamide Esters: Their Design, Synthesis, and Pharmacological Evaluation

The nimesulide based novel glycolamide esters were designed and synthesized for the first timeviaa three-step method starting from nimesulide. Structures of the synthesized compounds were confirmed by spectroscopic analysis. All the synthesized compounds were examined for their cytotoxic effectsin vitro,some of which showed significant cytotoxic activities against HCT-15 human colon cancer cell line.

Protective role ofPhyllanthus niruri against nimesulide induced hepatic damage

Present study aimed to evaluate the protective role of the aqueous extract of Phyllanthus niruri (P. niruri) against nimesulide-induced hepatic disoder in mice by determining levels of glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) and alkaline phosphatase (ALP) in serum and also by measuring the hepatic content of the antioxidant enzymes, superoxide dismitase (SOD) and catalase (CAT); the free radical scavenger, reduced glutathione (GSH) and thiobarbituric acid reacting substances (TBARS). Aqueous extract of P. niruri was administered either orally or intraperitoneally in different doses and times as needed for the experiments. Intraperitoneal of the extract (100 mg/kg body weight for seven days) reduced nimesulide (750 mg/kg body weight for 3 days) induced increased levels of GOT (37.0±1.8 units/ml in control group vs. 91.8±2.0 units/ml in nimesulide treated group vs. 35.0±1.0 units/ml in extract treated group), GPT (30.0±2.1 units/ml in control group vs. 88.4±2.9 units/ml in nimesulide treated group vs. 34.1±1.8 units/ml in extract treated group), and ALP (7.86±0.47 KA units/ml in control group vs. 23.80±0.60 KA units/ml in nimesulide treated group vs. 7.30±0.40 KA units/ml, in extract treated group) to almost nomal. In addition, P. niruri restored the nimesulide induced alterations of hepatic SOD (550±20 units/mg total protein in control group vs. 310±13 units/mg total protein in nimesulide treated group vs. 515±10 units/mg total protein in extract treated group), CAT (99.5±2 units/mg total protein in control group vs. 25.0±1.5 units/mg total protein in nimesulide treated group vs. 81.0±0.8 units/mg total protein in extract treated group), GSH (90±3 nmoles/mg total protein in control group vs. 17±4.2 nmoles/mg total protein in nimesulide treated group vs. 81±1 nmoles/mg total protein in extract treated group) and TBARS (measured as MDA, 36.6±3.0 nmoles/g liver tissue in control group vs. 96.3±5.2 nmoles/g liver tissue in nimesulide treated group vs. 41.2±1.7 nmoles/g liver tissue in extract treated group) contents. Dose-dependent studies showed that the herb could protect liver even if the nimesulide-induced injury is severe. Intraperitoneal administration of the extract showed better protective effect than oral administration. Combining all, the data suggest that P. niruri possesses hepatoprotective activity against nimesulide-induced liver toxicity and probably acts via an antioxidant defense mechanism. To the best of our knowledge, this is the first report of the hepatoprotective action of P. niruri against nimesulide induced liver damage.

Mechanism for the uncoupling of oxidative phosphorylation by juliprosopine on rat brain mitochondria

Prosopis juliflora, popularly known as Algaroba, is a major problem because the lack of food during the driest times of the year and its high palatability and nutritional value make its fruits (pods) much appreciated by cattle, goats, sheep and other animals. However, the consumption of this plant for long periods can cause a disease called cara-torta (pie face), which is characterized by cranial nerve dysfunction, mainly due to the degeneration and disappearance of neurons in the trigeminal motor nucleus. Algaroba contains piperidine alkaloids that have been suggested as being responsible for its toxicity; one of these alkaloids is juliprosopine. This study was conducted to evaluate the mechanisms of action of juliprosopine in isolated rat brain mitochondria to evaluate the potential mechanisms that lead to neurotoxicity in animals intoxicated by algaroba. Juliprosopine stimulated state-4 respiration at concentrations of 10-25 μM, affected the membrane potential at all concentrations studied (5-25 μM) and affected ATP production only at higher concentrations (15 and 25 μM). Juliprosopine cannot be classified as a member of the protonophoric class of uncouplers, such as 2,4-dinitrophenol or CCCP (m-chlorophenylhydrazone), due to its inability to promote mitochondrial swelling in the hyposmotic medium of potassium acetate. In addition, carboxyatractyloside, Mg(2+), cyclosporine A and dithiothreitol did not protect the uncoupling induced by juliprosopine. Because juliprosopine increased the fluorescence responses of mitochondria labeled with 1-aniline-8-naphthalene sulfonate (ANS) and DPH (1,6-diphenyl-1,3,5-hexatriene), we suggested that its uncoupling action must be attributed to a modification of the arrangement of the inner mitochondrial membrane.

Role of mitochondria in nonalcoholic fatty liver disease--from origin to propagation

OBJECTIVES

Mitochondria play a major role in cell energy-generating processes and integrate several signalling pathways to control cellular life and death.

DESIGN AND METHODS

Several liver diseases are characterized by mitochondrial alterations which are directly or indirectly dependent on the activation of intracellular stress cascades or receptor-mediated pathways. This article examines the role of mitochondrial dysfunction in critical initiating or propagating events in fatty liver infiltration and nonalcoholic fatty liver disease (NAFLD). Genetic variants and the role of drug-induced toxicity have been considered.

RESULTS

Key alterations of mitochondrial physiology associated with hepatocyte fatty changes are described. The value of novel non-invasive diagnostic methods to detect mitochondrial metabolic alterations is also discussed.

CONCLUSIONS

Mitochondrial metabolic remodeling is a predominant factor in the appearance and perpetuation of hepatocyte fat accumulation. Non-invasive techniques to identify mitochondrial dysfunction and proper mitochondria protection are two necessary clinical steps for an efficient management of NAFLD.

Abamectin affects the bioenergetics of liver mitochondria: A potential mechanism of hepatotoxicity

Abamectin (ABA) is a macrocyclic lactone of the avermectin family used worldwide as an antiparasitic agent in farm animals and pets and as the active ingredient of insecticides and nematicides. In this study, the effects of abamectin on the bioenergetics of mitochondria isolated from rat liver were evaluated. Mitochondria are responsible for converting the energy released by electron transport and stored as the binding energy molecule ATP. Xenobiotics that interfere with its synthesis or utilization can be acutely or chronically toxic. Abamectin (5-25μM) caused concentration-dependent inhibition of the respiratory chain without affecting the membrane potential or the activity of enzymes NADH dehydrogenase or succinate dehydrogenase. This behavior is similar to oligomycin and carboxyatractyloside and suggests direct action on F(o)F(1)-ATPase and/or the adenine nucleotide translocator (ANT). ABA more pronouncedly inhibited ATPase phosphohydrolase activity in intact, uncoupled mitochondria than in freeze-thawed disrupted mitochondria. ADP-stimulated depolarization of the mitochondrial membrane potential was also inhibited by ABA. Our results indicate that ABA interacts more specifically with the ANT, resulting in functional inhibition of the translocator with consequent impairment of mitochondrial bioenergetics. This effect could be involved in the ABA toxicity to hepatocytes.

Gastric acid induces mitochondrial superoxide production and lipid peroxidation in gastric epithelial cells

BACKGROUND

Gastric hydrochloric acid (HCl) has been regarded as an inciting factor in gastric mucosal injuries and has been reported to induce lipid peroxidation in vitro. However, because HCl is not an oxidant per se, the exact mechanism by which the acid induces lipid peroxidation is unknown. We hypothesized that gastric acid may disrupt mitochondrial transmembrane potential and induce the production of superoxide in mitochondria, which subsequently may induce lipid peroxidation and apoptosis in gastric mucosal cells.

METHODS

Firstly we treated gastric epithelial RGM1 cells with solutions containing various concentrations of HCl (i.e., of varying pH), and examined cellular injury, lipid peroxidation, and apoptosis with specific fluorescent dyes. Secondly, we performed electron paramagnetic resonance (EPR) spectroscopy of isolated, acid-exposed mitochondria from the cells, using a spin-trapping reagent for superoxide, 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO). Finally, we established novel RGM1 cells that overexpressed manganese superoxide dismutase (MnSOD), which removes superoxide from mitochondria, and examined the effect of acid treatment on cellular membrane lipid peroxidation.

RESULTS

The results indicated that the exposure to acid indeed induced cellular injury, cellular lipid peroxidation, apoptosis, and the demonstration of the exact superoxide spectra on EPR spectroscopy in gastric epithelial cells, and that overexpression of MnSOD decreased superoxide production and prevented cellular lipid peroxidation.

CONCLUSION

These results suggested that gastric acid, like nonsteroidal anti-inflammatory drugs (NSAIDs), induces mitochondrial superoxide production, which induces gastric cellular injury by triggering cellular lipid peroxidation and apoptosis.

Protective effect of Woodfordia fruticosa flowers against acetaminophen-induced hepatic toxicity in rats

CONTEXT

The flowers of Woodfordia fruticosa Kurz. (Lythraceae) are commonly used for the treatment of several ailments which includes rheumatism, leucorrhea, menorrhagia, asthma, liver disorder, and inflammatory conditions.

OBJECTIVE

To evaluate the hepatoprotective property of Woodfordia fruticosa flowers against acetaminophen-induced hepatic injury in rats.

MATERIAL AND METHODS

Acetaminophen (3 g/kg bw)-induced hepatotoxicity study was carried out by observing the effect of methanol extract of Woodfordia fruticosa flowers (400 and 600 mg/kg, bw) on some serum marker enzymes, albumin, blood urea nitrogen levels as well as liver total protein, nonenzymetic glutathione reduced content, and enzymatic antioxidant glutathione peroxidase, with histopathological evidence.

RESULTS AND DISCUSSION

Pretreatment of rats with methanol extract of Woodfordia fruticosa flowers effectively prevented the acetaminophen-induced hepatic damage as indicated by the serum marker enzymes aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase and other biochemical parameters (albumin and blood urea nitrogen). Parallel to these changes, the methanol extract of Woodfordia fruticosa flowers also prevented acetaminophen-induced oxidative stress in the rat liver by inhibiting depletion of liver total protein and restoring the levels of nonenzymatic antioxidant glutathione reduced. The biochemical changes were consistent with histopathological observations suggesting marked hepatoprotective effect of the methanol extract of Woodfordia fruticosa flowers.

CONCLUSION

The results suggested that methanol extract of Woodfordia fruticosa flowers possesses protective effect against acetaminophen-induced hepatotoxicity.

The anti-cancer agent nemorosone is a new potent protonophoric mitochondrial uncoupler

Nemorosone, a natural-occurring polycyclic polyprenylated acylphloroglucinol, has received increasing attention due to its strong in vitro anti-cancer action. Here, we have demonstrated the toxic effect of nemorosone (1-25 μM) on HepG2 cells by means of the MTT assay, as well as early mitochondrial membrane potential dissipation and ATP depletion in this cancer cell line. In mitochondria isolated from rat liver, nemorosone (50-500 nM) displayed a protonophoric uncoupling activity, showing potency comparable to the classic protonophore, carbonyl cyanide m-chlorophenyl hydrazone (CCCP). Nemorosone enhanced the succinate-supported state 4 respiration rate, dissipated mitochondrial membrane potential, released Ca(2+) from Ca(2+)-loaded mitochondria, decreased Ca(2+) uptake and depleted ATP. The protonophoric property of nemorosone was attested by the induction of mitochondrial swelling in hyposmotic K(+)-acetate medium in the presence of valinomycin. In addition, uncoupling concentrations of nemorosone in the presence of Ca(2+) plus ruthenium red induced the mitochondrial permeability transition process. Therefore, nemorosone is a new potent protonophoric mitochondrial uncoupler and this property is potentially involved in its toxicity on cancer cells.

Nimesulide-induced electrophile stress activates Nrf2 in human hepatocytes and mice but is not sufficient to induce hepatotoxicity in Nrf2-deficient mice

Nimesulide is a widely prescribed nitroaromatic sulfoanilide-type nonsteroidal anti-inflammatory drug that, despite its favorable safety profile, has been associated with rare cases of idiosyncratic drug-induced liver injury (DILI). Because reactive metabolites have been implicated in DILI, we aimed at investigating whether hepatic bioactivation of nimesulide produces a protein-reactive intermediate in hepatocytes. Also, we explored whether nimesulide can activate the transcription factor Nrf2 that would protect from drug-induced hepatocyte injury. We found that [(14)C]-nimesulide covalently bound to human liver microsomes (<50 pmol/mg under standard conditions) or immortalized human hepatocytes in a sulfaphenazole-sensitive, rifampicin-inducible manner; yet the overall extent of binding was modest. Although exposure of hepatocytes to nimesulide was not associated with increased net levels of superoxide anion, nimesulide (100 microM, 24 h) caused nuclear translocation of Nrf2 in a sulfaphenazole-sensitive manner, indicating a role of electrophilic metabolites. However, knockdown of Nrf2 with siRNA did not make the cells more sensitive to nimesulide-induced cell injury. Similarly, exposure of wild-type C57BL/6x129 Sv mice to nimesulide (100 mg/kg/day, po, for 5 days) was associated with nuclear translocation of immunoreactive Nrf2 in a small number of hepatocytes and induced >2-fold the expression levels of the Nrf2-target gene Nqo1 in wild-type but not Nrf2-null mice. Nimesulide administered to Nrf2(-/-) knockout mice did not cause increases in serum ALT activity or any apparent histopathological signs of liver injury. In conclusion, these data indicate that nimesulide is bioactivated by CYP2C to a protein-reactive electrophilic intermediate that activates the Nrf2 pathway even at nontoxic exposure levels.

Comparative effects of lantadene A and its reduced metabolite on mitochondrial bioenergetics

Lantana (Lantana camara Linn.) is a noxious weed to which certain medicinal properties have been attributed, but its ingestion has been reported to be highly toxic to animals and humans, especially in the liver. The main hepatotoxin in lantana leaves is believed to be the pentacyclic triterpenoid lantadene A (LA), but the precise mechanism by which it induces hepatotoxicity has not yet been established. This work addressed the action of LA and its reduced derivative (RLA) on mitochondrial bioenergetics. At the concentration range tested (5-25 microM), RLA stimulated state-4 respiration, inhibited state-3 respiration, circumvented oligomycin-inhibited state-3 respiration, dissipated membrane potential and depleted ATP in a concentration-dependent manner. However, LA did not stimulate state-4 respiration, nor did it affect the other mitochondrial parameters to the extent of its reduced derivative. The lantadenes didn't inhibit the CCCP-uncoupled respiration but increased the ATPase activity of intact coupled mitochondria. The ATPase activity of intact uncoupled or disrupted mitochondria was not affected by the compounds. We propose, therefore, that RLA acts as a mitochondrial uncoupler of oxidative phosphorylation, a property that arises from the biotransformation (reduction) of LA, and LA acts in other mitochondrial membrane components rather than the ATP synthase affecting the mitochondrial bioenergetics. Such effects may account for the well-documented hepatoxicity of lantana.

Uncoupling of oxidative phosphorylation by curcumin: implication of its cellular mechanism of action

Curcumin is a phytochemical isolated from the rhizome of turmeric. Recent reports have shown curcumin to have antioxidant, anti-inflammatory and anti-tumor properties as well as affecting the 5'-AMP activated protein kinase (AMPK), mTOR and STAT-3 signaling pathways. We provide evidence that curcumin acts as an uncoupler. Well-established biochemical techniques were performed on isolated rat liver mitochondria in measuring oxygen consumption, F(0)F(1)-ATPase activity and ATP biosynthesis. Curcumin displays all the characteristics typical of classical uncouplers like fccP and 2,4-dinitrophenol. In addition, at concentrations higher than 50 microM, curcumin was found to inhibit mitochondrial respiration which is a characteristic feature of inhibitory uncouplers. As a protonophoric uncoupler and as an activator of F(0)F(1)-ATPase, curcumin causes a decrease in ATP biosynthesis in rat liver mitochondria. The resulting change in ATP:AMP could disrupt the phosphorylation status of the cell; this provides a possible mechanism for its activation of AMPK and its downstream mTOR and STAT-3 signaling.

4-hydroxy nimesulide effects on mitochondria and HepG2 cells. A comparison with nimesulide

We previously reported that the nonsteroidal anti-inflammatory drug, nimesulide (N-[4-nitro-2-phenoxyphenyl]-methanesulfonamide), is an uncoupler and oxidizes NAD(P)H in isolated rat liver mitochondria, triggering mitochondrial Ca2+ efflux or, if this effect is inhibited, eliciting mitochondrial permeability transition (Mingatto et al., Br. J. Pharmacol. 131:1154-1160, 2000). We presently demonstrated that nimesulide's hydroxylated metabolite (4-hydroxy nimesulide) lacks the uncoupling property of the parent drug, while keeping its ability to oxidize mitochondrial NADPH. In the presence of 10 microM Ca2+, low (5-50 microM) concentrations of 4-hydroxy nimesulide elicited mitochondrial permeability transition, as assessed by cyclosporin A-sensitive mitochondrial swelling, associated with mitochondrial Ca2+ efflux/membrane potential dissipation (Deltapsi), apparently occurring on account of the oxidation of mitochondrial protein thiols; no involvement of reactive oxygen species was observed. While nimesulide (0.5 or 1 mM, 30 h incubation) did not lead to significant HepG2 cell death, 4-hydroxy nimesulide caused a low extent (approximately 15%) of cell necrosis, partly prevented by cyclosporine A, suggesting the involvement of mitochondrial permeability transition. Both nimesulide and 4-hydroxy nimesulide caused NADPH oxidation and Deltapsi dissipation in HepG2 cells. Because such Deltapsi dissipation induced by the metabolite was almost completely inhibited by cyclosporine A, it probably results from the mitochondrial permeability transition. Therefore, mitochondrial permeability transition, in apparent association with NADPH oxidation, constitutes the most probable cause of HepG2 cell death elicited by 4-hydroxy nimesulide.

Unaltered hepatic oxidative phosphorylation and mitochondrial permeability transition in wistar rats treated with nimesulide: Relevance for nimesulide toxicity characterization

Nonsteroidal anti-inflammatory drugs have been associated with hepatotoxicity in susceptible patients. One such example is nimesulide, a preferential cyclooxygenase 2-inhibitor, widely used for the treatment of inflammation and pain. It was suggested that nimesulide could exert its hepatotoxicity by altering hepatic mitochondrial function, which was demonstrated in vitro. The objective of this study was to verify whether liver mitochondria isolated from rats treated with doses of nimesulide well above therapeutic levels possessed decreased calcium tolerance and oxidative phosphorylation, which indicates in vivo nimesulide mitochondrial toxicity. Male and female rats received nimesulide or its vehicle twice daily, for 5 days, and were killed on the seventh day for the isolation of liver mitochondria. Mitochondrial respiration, transmembrane electric potential, and calcium tolerance were characterized in all experimental groups. Nimesulide had no effect on liver mitochondrial function. Indexes of mitochondrial integrity, calcium loading capacity, and oxidative phosphorylation efficiency were unchanged between liver mitochondria from treated and control animals. In the animals tested, no evidence of degraded mitochondrial function due to nimesulide administration could be found. The results corroborate the notion that despite recognized in vitro mitochondrial toxicity, nimesulide does not cause detectable mitochondrial dysfunction in Wistar rats, even when administered in much higher concentrations than those known to have anti-inflammatory effects.

Mitochondrial abnormalities--a link to idiosyncratic drug hepatotoxicity?

Idiosyncratic drug-induced liver injury (DILI) is a major clinical problem and poses a considerable challenge for drug development as an increasing number of successfully launched drugs or new potential drugs have been implicated in causing DILI in susceptible patient subsets. Although the incidence for a particular drug is very low (yet grossly underestimated), the outcome of DILI can be serious. Unfortunately, prediction has remained poor (both for patients at risk and for new chemical entities). The underlying mechanisms and the determinants of susceptibility have largely remained ill-defined. The aim of this review is to provide both clinical and experimental evidence for a major role of mitochondria both as a target of drugs causing idiosyncratic DILI and as mediators of delayed liver injury. We develop a unifying hypothesis that involves underlying genetic or acquired mitochondrial abnormalities as a major determinant of susceptibility for a number of drugs that target mitochondria and cause DILI. The mitochondrial hypothesis, implying gradually accumulating and initially silent mitochondrial injury in heteroplasmic cells which reaches a critical threshold and abruptly triggers liver injury, is consistent with the findings that typically idiosyncratic DILI is delayed (by weeks or months), that increasing age and female gender are risk factors and that these drugs are targeted to the liver and clearly exhibit a mitochondrial hazard in vitro and in vivo. New animal models (e.g., the Sod2(+/-) mouse) provide supporting evidence for this concept. However, genetic analyses of DILI patient samples are needed to ultimately provide the proof-of-concept.

The Anti-Inflammatory Drug, Nimesulide (4-Nitro-2-phenoxymethane-sulfoanilide), Uncouples Mitochondria and Induces Mitochondrial Permeability Transition in Human Hepatoma Cells: Protection by Albumin

Like other nonsteroidal anti-inflammatory drugs, nimesulide (4-nitro-2-phenoxymethane-sulfoanilide) triggers hepatitis in a few recipients. Although nimesulide has been shown to uncouple mitochondrial respiration and cause hepatocyte necrosis in the absence of albumin, mechanisms for cell death are incompletely understood, and comparisons with human concentrations are difficult because 99% of nimesulide is albumin-bound. We studied the effects of nimesulide, with or without a physiological concentration of albumin, in isolated rat liver mitochondria or microsomes and in human hepatoma cells. Nimesulide did not undergo monoelectronic nitro reduction in microsomes. In mitochondria incubated without albumin, nimesulide (50 microM) decreased the mitochondrial membrane potential (DeltaPsim), increased basal respiration, and potentiated the mitochondrial permeability transition (MPT) triggered by calcium preloading. In HUH-7 cells incubated for 24 h without albumin, nimesulide (1 mM) decreased the DeltaPsim and cell NADPH and increased the glutathione disulfide/reduced glutathione ratio and cell peroxides; nimesulide triggered MPT, ATP depletion, high cell calcium, and caused mostly necrosis, with rare apoptotic cells. Coincubation with either cyclosporin A (an MPT inhibitor) or the combination of fructose-1,6-diphosphate (a glycolysis substrate) and oligomycin (an ATPase inhibitor) prevented the decrease in DeltaPsim, ATP depletion, and cell death. A physiological concentration of albumin abolished the effects of nimesulide on isolated mitochondria or HUH-7 cells. In conclusion, the weak acid, nimesulide, uncouples mitochondria and triggers MPT and ATP depletion in isolated mitochondria or hepatoma cells incubated without albumin. However, in the presence of albumin, only a fraction of the drug enters cells or organelles, and uncoupling and toxicity are not observed.

Nimesulide-induced hepatic mitochondrial injury in heterozygous Sod2(+/-) mice

Nimesulide, a preferential COX-2 inhibitor, has been associated with rare idiosyncratic hepatotoxicity. The underlying mechanisms of liver injury are unknown, but experimental evidence has identified oxidative stress as a potential hazard and mitochondria as a target. The aim of this study was to explore whether genetic mitochondrial abnormalities, resulting in impaired mitochondrial function and mildly increased oxidative stress, might sensitize mice to the hepatic adverse effects of nimesulide. We used heterozygous superoxide dismutase 2 (Sod2(+/-)) mice as a model, as these mice develop clinically silent mitochondrial stress but otherwise appear normal. Nimesulide was administered for 4 weeks (10 mg/kg, ip, bid), at a dose equivalent to human therapeutic dosage. We found that the drug potentiated hepatic mitochondrial oxidative injury (decreased aconitase activity, increased protein carbonyls) in Sod2(+/-), but not wild-type, mice. Furthermore, the nimesulide-treated mutant mice exhibited increased hepatic cytosolic levels of cytochrome c and caspase-3 activity, as well as increased numbers of apoptotic hepatocytes. Finally, nimesulide in vitro caused a concentration-dependent net increase in superoxide anion in mitochondria from Sod2(+/-), but not Sod2(+/+) mice. In conclusion, repeated administration of nimesulide can superimpose an oxidant stress, potentiate mitochondrial damage, and activate proapoptotic factors in mice with genetically compromised mitochondrial function.

Rebamipide significantly inhibits indomethacin-induced mitochondrial damage, lipid peroxidation, and apoptosis in gastric epithelial RGM-1 cells

Nonsteroidal antiinflammatory drugs (NSAIDs) cause complications such as gastrointestinal injury. NSAIDs were recently reported to cause mitochondrial injury: to dissipate the mitochondrial transmembrane potential (MTP), and to induce mitochondrial permeability transition pore (PTP), which liberates cytochrome c. This enzyme generates reactive oxygen species (ROS) thereby triggers caspase cascade and cellular lipid peroxidation, resulting in cellular apoptosis. However, the mechanism of this NSAID-induced MTP's role in cellular apoptosis remains unknown. Rebamipide, an antiulcer drug, is reported to scavenge ROS and to show the protective effects on indomethacin-induced tissue peroxidations. Since cytochrome c and its generation of ROS are involved in indomethacin-induced cellular apoptosis, rebamipide may attenuate mitochondrial damage. The aim of this study was to elucidate whether indomethacin induces both the MTP decrease and cellular apoptosis, and the effect of rebamipide on these phenomena. We examined the effect of rebamipide on 1) MTP change, 2) lipid peroxidation, 3) apoptosis, and 4) caspase activation using gastric mucosal epithelial cell-line treated with indomethacin. With a specially designed fluorescence analyzing microscope system, MTP change, cellular lipid peroxidation, and cellular apoptosis were investigated with the small star, filled following fluorescent dyes, MitoRed, DPPP, and Hoechst 33,258, respectively. Indomethacin treatment decreased MTP but increased both cellular lipid peroxidation and cellular apoptosis via caspase 3 and 9 activation. Rebamipide clearly inhibited these phenomena {in vitro}. We demonstrated that fluorescent dyes such as MitoRed, DPPP, and Hoechst 33,258 are useful indicators for detecting oxidative cellular injuries in living cells. Rebamipide exerts a protective effect on mitochondrial membrane stability in gastric epithelial cells.

Mitochondrial permeability transition as a source of superoxide anion induced by the nitroaromatic drug nimesulide in vitro

Nimesulide, a widely used nonsteroidal anti-inflammatory drug containing a nitroaromatic moiety, has been associated with rare but serious hepatic adverse effects. The mechanisms underlying this idiosyncratic hepatotoxicity are unknown; however, both mitochondrial injury and oxidative stress have been implicated in contributing to liver injury in susceptible patients. The aim of this study was, first, to explore whether membrane permeability transition (MPT) could contribute to nimesulide's mitochondrial toxicity and, second, whether metabolism-derived reactive oxygen species (ROS) were responsible for MPT. We found that isolated mouse liver mitochondria readily underwent Ca2+-dependent, cyclosporin A-sensitive MPT upon exposure to nimesulide (at >or=3 microM). Net increases in mitochondrial superoxide anion levels, determined with the fluorescent probe dihydroethidium, were induced by nimesulide only in the presence of Ca2+ and were cyclosporin A-sensitive, indicating that superoxide production was a consequence, rather than the cause, of MPT. In addition, nimesulide caused a rapid dissipation of the inner mitochondrial transmembrane potential (at >or=3 microM), followed by a concentration-dependent decrease in ATP biosynthesis. Because nimesulide, unlike the related nitroaromatic drug nilutamide, did not produce any detectable ROS during incubation with mouse hepatic microsomes, we conclude that mitochondrial uncoupling causes MPT and that ROS production is a secondary effect.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Naproxen affects Ca2+ fluxes in mitochondria, microsomes and plasma membrane vesicles

There is substantial evidence that nonsteroidal anti-inflammatory drugs (NSAIDs) affect cellular processes regulated by Ca(2+) ions, including the metabolic responses of the liver to Ca(2+)-dependent hormones. The aim of the present study was to determine whether the effects of naproxen are mediated by a direct action on cellular Ca(2+) fluxes. The effects of naproxen on 45Ca(2+) fluxes in mitochondria, microsomes and inside-out plasma membrane vesicles were examined. Naproxen strongly impaired the mitochondrial capacity to retain 45Ca(2+) and inhibited also ATP-dependent 45Ca(2+) uptake by microsomes. Naproxen did not modify 45Ca(2+) uptake by inside-out plasma membrane vesicles, but it inhibited the hexokinase/glucose-induced Ca(2+) efflux from preloaded vesicles. Additional assays performed in isolated mitochondria revealed that naproxen causes mitochondrial uncoupling and swelling in the presence of Ca(2+) ions. These effects were prevented by EGTA, ruthenium red and cyclosporin A, indicating that naproxen acts synergistically with Ca(2+) ions by promoting the mitochondrial permeability transition. The experimental results suggest that naproxen may impair the metabolic responses to Ca(2+)-dependent hormones acting by at least two mechanisms: (1) by interfering with the supply of external Ca(2+) through a direct action on the plasma membrane Ca(2+) influx, and (2) by affecting the refilling of the agonist-sensitive internal stores, including endoplasmic reticulum and mitochondria.

The critical role of mitochondrial energetic impairment in the toxicity of nimesulide to hepatocytes

We described the effects of nimesulide (N-[4-nitro-2-phenoxyphenyl]-methanesulfonamide) and its reduced metabolite in isolated rat hepatocytes. Nimesulide stimulated the succinate-supported state 4 respiration of mitochondria, indicating an uncoupling effect of the drug. Incubation of hepatocytes with nimesulide (0.1-1 mM) elicited a concentration- and time-dependent decrease in cell viability as assessed by lactate dehydrogenase leakage, a decrease of mitochondrial membrane potential as assessed by rhodamine 123 retention, and cell ATP depression. Nimesulide also decreased the levels of NAD(P)H and glutathione in hepatocytes, but the extent of the effects was less pronounced in relation to the energetic parameters; in addition, these effects did not imply the peroxidation of membrane lipids. The decrease in the viability of hepatocytes was prevented by fructose and, to a larger extent, by fructose plus oligomycin; it was stimulated by proadifen, a cytochrome P450 inhibitor. In contrast, the reduced metabolite of nimesulide did not present any of the effects observed for the parent drug. These results indicate that: 1) nimesulide causes injury to the isolated rat liver cells, 2) this effect is mainly mediated by impairment of ATP production by mitochondria due to uncoupling, and 3) on account of the activity of its nitro group, the parent drug by itself is the main factor responsible for its toxicity to the hepatocytes.

Biomimetic reduction of nimesulide with NaBH4 catalyzed by metalloporphyrins

The biomimetic reduction of anti-inflammatory drug, nimesulide (1) with sodium borohydride catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides [TAPFe(III)Cl] has been studied in organic solvents under anaerobic and aerobic conditions.

Mechanisms of NSAID-induced hepatotoxicity: focus on nimesulide

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been associated with idiosyncratic hepatotoxicity in susceptible patients. The molecular mechanisms underlying this toxicity have not yet been fully elucidated. However, experimental evidence suggests that they include increased concentration of the drugs in the hepatobiliary compartment, formation of reactive metabolites that covalently modify proteins and produce oxidative stress, and mitochondrial injury. Genetic and/or acquired patient factors can either augment the pathways leading to hepatic toxicity or impede the protective and detoxifying pathways. An example is nimesulide, a selective cyclo-oxygenase-2 inhibitor widely used for the treatment of inflammatory and pain conditions, which has been recently associated with rare but serious and unpredictable adverse reactions in the liver (increases in serum aminotransferase activities, hepatocellular necrosis, and/or intrahepatic cholestasis). Similar to other drugs causing idiosyncratic hepatotoxicity, both the molecule and the patient contribute to the hazard. Here, the weakly acidic sulfonanilide drug undergoes bioreductive metabolism of the nitroarene group to reactive intermediates that have been implicated in oxidative stress, covalent binding, and mitochondrial injury. It is only in a small number of susceptible patients, however, that genetic or nongenetic factors will cause this potential toxicity to become clinically manifest. In view of the very large recipient population, the incidence of nimesulide-induced liver injury has been low (approximately 0.1 per 100,000 patients treated). Although this estimation is based on spontaneous reporting data versus sales units and needs correction due to the classical bias of this system, the type and incidence of these rare but severe hepatic adverse reactions are comparable to that of other NSAIDs.

Role of mitochondrial permeability transition in diclofenac-induced hepatocyte injury in rats

Hepatotoxicity of diclofenac has been known in experimental animals and humans but its mechanism has not been fully understood. The present study examined the role of mitochondrial permeability transition (MPT) in the pathogenesis of diclofenac-induced hepatocyte injury by using isolated mitochondria and primary culture hepatocytes from rats. Incubation of energized mitochondria with succinate in the presence of Ca(2+) and diclofenac resulted in mitochondrial swelling, leakage of accumulated Ca(2+), membrane depolarization, and oxidation of nicotinamide adenine dinucleotide phosphate and protein thiol. All of these phenomena were suppressed by coincubation of the mitochondria with cyclosporin A, a typical inhibitor of MPT, showing that diclofenac opened the MPT pore. It was also suggested that reactive oxygen species probably generated during mitochondrial respiration and/or voltage-dependent mechanism was involved in MPT, which are proposed as mechanisms of MPT by uncouplers of mitochondrial oxidative phosphorylation. Culture of hepatocytes for 24 hours with diclofenac caused a decrease in cellular ATP, leakage of lactate dehydrogenase and membrane depolarization. The hepatocyte toxicity thus observed was attenuated by coincubation of the hepatocytes with cyclosporin A and verapamil, a Ca(2+) channel blocker. In conclusion, these results showed the important role of MPT in pathogenesis of hepatocyte injury induced by diclofenac and its possible contribution to human idiosyncratic hepatotoxicity.