Alterations in mitochondrial respiratory functions, redox metabolism and apoptosis by oxidant 4-hydroxynonenal and antioxidants curcumin and melatonin in PC12 cells

Cellular oxidative stress and alterations in redox metabolisms have been implicated in the etiology and pathology of many diseases including cancer. Antioxidant treatments have been proven beneficial in controlling these diseases. We have recently shown that 4-hydroxynonenal (4-HNE), a by-product of lipid peroxidation, induces oxidative stress in PC12 cells by compromising the mitochondrial redox metabolism. In this study, we have further investigated the deleterious effects of 4-HNE on mitochondrial respiratory functions and apoptosis using the same cell line. In addition, we have also compared the effects of two antioxidants, curcumin and melatonin, used as chemopreventive agents, on mitochondrial redox metabolism and respiratory functions in these cells. 4-HNE treatment has been shown to cause a reduction in glutathione (GSH) pool, an increase in reactive oxygen species (ROS), protein carbonylation and apoptosis. A marked inhibition in the activities of the mitochondrial respiratory enzymes, cytochrome c oxidase and aconitase was observed after 4-HNE treatment. Increased nuclear translocation of NF-kB/p65 protein was also observed after 4-HNE treatment. Curcumin and melatonin treatments, on the other hand, maintained the mitochondrial redox and respiratory functions without a marked effect on ROS production and cell viability. These results suggest that 4-HNE-induced cytotoxicity may be associated, at least in part, with the altered mitochondrial redox and respiratory functions. The alterations in mitochondrial energy metabolism and redox functions may therefore be critical in determining the difference between cell death and survival.     

Green tea polyphenol epigallocatechin-3-gallate differentially modulates oxidative stress in PC12 cell compartments

Tea polyphenols have been reported to be potent antioxidants and beneficial in oxidative stress related diseases. Prooxidant effects of tea polyphenols have also been reported in cell culture systems. In the present study, we have studied oxidative stress in the subcellular compartments of PC12 cells after treatment with different concentrations of the green tea polyphenol, epigallocatechin-3-gallate (EGCG). We have demonstrated that EGCG has differentially affected the production of reactive oxygen species (ROS), glutathione (GSH) metabolism and cytochrome P450 2E1 activity in the different subcellular compartments in PC12 cells. Our results have shown that although the cell survival was not inhibited by EGCG, there was, however, an increased DNA breakdown and activation of apoptotic markers, caspase 3 and poly- (ADP-ribose) polymerase (PARP) at higher concentrations of EGCG treatment. Our results suggest that the differential effects of EGCG might be related to the alterations in oxidative stress, GSH pools and CYP2E1 activity in different cellular compartments. These results may have implications in determining the chemopreventive therapeutic use of tea polyphenols in vivo.     

Nitric oxide donors prevent while the nitric oxide synthase inhibitor L-NAME increases arachidonic acid plus CYP2E1-dependent toxicity

Polyunsaturated fatty acids such as arachidonic acid (AA) play an important role in alcohol-induced liver injury. AA promotes toxicity in rat hepatocytes with high levels of cytochrome P4502E1 and in HepG2 E47 cells which express CYP2E1. Nitric oxide (NO) participates in the regulation of various cell activities as well as in cytotoxic events. NO may act as a protectant against cytotoxic stress or may enhance cytotoxicity when produced at elevated concentrations. The goal of the current study was to evaluate the effect of endogenously or exogenously produced NO on AA toxicity in liver cells with high expression of CYP2E1 and assess possible mechanisms for its actions. Pyrazole-induced rat hepatocytes or HepG2 cells expressing CYP2E1 were treated with AA in the presence or absence of an inhibitor of nitric oxide synthase L-N(G)-Nitroarginine Methylester (L-NAME) or the NO donors S-nitroso-N-acetylpenicillamine (SNAP), and (Z)-1-[-(2-aminoethyl)-N-(2-aminoethyl)]diazen-1-ium-1,2-diolate (DETA-NONO). AA decreased cell viability from 100% to 48+/-6% after treatment for 48 h. In the presence of L-NAME, viability was further lowered to 23+/-5%, while, SNAP or DETA-NONO increased viability to 66+/-8 or 71+/-6%. The L-NAME potentiated toxicity was primarily necrotic in nature. L-NAME did not affect CYP2E1 activity or CYP2E1 content. SNAP significantly lowered CYP2E1 activity but not protein. AA treatment increased lipid peroxidation and lowered GSH levels. L-NAME potentiated while SNAP prevented these changes. Thus, L-NAME increased, while NO donors decreased AA-induced oxidative stress. Antioxidants prevented the L-NAME potentiation of AA toxicity. Damage to mitochondria by AA was shown by a decline in the mitochondrial membrane potential (MMP). L-NAME potentiated this decline in MMP in association with its increase in AA-induced oxidative stress and toxicity. NO donors decreased this decline in MMP in association with their decrease in AA-induced oxidative stress and toxicity. These results indicate that NO can be hepatoprotective against CYP2E1-dependent toxicity, preventing AA-induced oxidative stress.     

Casiopeína IIgly-induced oxidative stress and mitochondrial dysfunction in human lung cancer A549 and H157 cells

Casiopeínas are a series of mixed chelate copper complexes that are being evaluated as anticancer agents. Their effects in the cell include oxidative damage and mitochondrial dysfunction, yet the molecular mechanisms leading to such effects remain unclear. We tested whether [Cu(4,7-dimethyl-phenanthroline)(glycinate)]NO₃ (Casiopeína IIgly or Cas IIgly) could alter cellular glutathione (GSH) levels by redox cycling with GSH to generate ROS and cellular oxidative stress. Cas IIgly induced a dramatic drop in intracellular levels of GSH in human lung cancer H157 and A549 cells, and is able to use GSH as source of electrons to catalyze the Fenton reaction. In both cell lines, the toxicity of Cas IIgly (2.5–5 μM) was potentiated by the GSH synthesis inhibitor l-buthionine sulfoximine (BSO) and diminished by the catalytic antioxidant manganese(III) meso-tetrakis(N,N′-diethylimidazolium-2-yl)porphyrin (MnTDE-1,3-IP⁵⁺), thus supporting an important role for oxidative stress. Cas IIgly also caused an over-production of reactive oxygen species (ROS) in the mitochondria and a depolarization of the mitochondrial membrane. Moreover, Cas IIgly produced mitochondrial DNA damage that resulted in an imbalance of the expression of the apoproteins of the mitochondrial respiratory chain, which also can contribute to increased ROS production. These results suggest that Cas IIgly initiates multiple possible sources of ROS over-production leading to mitochondrial dysfunction and cell death.     

In vitro protection of reactive oxygen species-induced degradation of lipids, proteins and 2-deoxyribose by tea catechins.

Both the anti- and pro-oxidant effects of tea catechins, have been implicated in the alterations of cellular functions which determine their chemoprotective and therapeutic potentials in toxicity and diseases. Here, we have studied the protective mechanism (s) of three main green tea catechins namely, epicatechin (EC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) on free radical induced oxidative degradation of membrane lipids and proteins under in vitro conditions using isolated cell free fractions from rat liver. In addition, we have also studied the effects of the tea catechins on 2-deoxyribose degradation in the presence of Fenton and Haber-Weiss oxidants. Glutathione S-transferase and cytochrome P450 2E1 activities and lipid peroxidation were found to be markedly inhibited by tea catechins. These catechins also inhibited the reactive oxygen species formation and oxidative carbonylation of subcellular proteins induced by a physiological oxidant, 4-hydroxynonenal. EGCG and the other catechins showed a time and concentration-dependent effects on the degradation of 2-deoxyribose in the presence of Fenton oxidants. Our results indicate that tea catechins prevent molecular degradation in oxidative stress conditions by directly altering the subcellular ROS production, glutathione metabolism and cytochrome P450 2E1 activity. These results may have implications in determining the chemotherapeutic use of tea catechins in oxidative stress related diseases.     

Arsenic induces apoptosis in mouse liver is mitochondria dependent and is abrogated by N-acetylcysteine

Arsenicosis, caused by arsenic contamination of drinking water supplies, is a major public health problem in India and Bangladesh. Chronic liver disease, often with portal hypertension occurs in chronic arsenicosis, contributes to the morbidity and mortality. The early cellular events that initiate liver cell injury due to arsenicosis have not been studied. Our aim was to identify the possible mechanisms related to arsenic-induced liver injury in mice. Liver injury was induced in mice by arsenic treatment. The liver was used for mitochondrial oxidative stress, mitochondrial permeability transition (MPT). Evidence of apoptosis was sought by TUNEL test, caspase assay and histology. Pretreatment with N-acetyl-L-cysteine (NAC) was done to modulate hepatic GSH level. Arsenic treatment in mice caused liver injury associated with increased oxidative stress in liver mitochondria and alteration of MPT. Altered MPT facilitated cytochrome c release in the cytosol, activation of caspase 9 and caspase 3 activities and apoptotic cell death. Pretreatment of NAC to arsenic-treated mice abrogated all these alteration suggesting a glutathione (GSH)-dependent mechanism. Oxidative stress in mitochondria and inappropriate MPT are important in the pathogenesis of arsenic induced apoptotic liver cell injury. The phenomenon is GSH dependent and supplementation of NAC might have beneficial effects.     

Modulation of GSH levels in ABCC1 expressing tumor cells triggers apoptosis through oxidative stress

The over-expression of ABCC1 transmembrane protein has been shown to cause multidrug resistance in tumor cell lines. ABCC1 is a member of the ABC transmembrane proteins that function as efflux pumps with diverse substrate specificity. Several endogenous cell metabolites, including the leukotriene C4 (LTC(4)) and glutathione (GSH) are substrates for ABCC1 protein. ABCC1 expression in certain tumor cells was demonstrated to confer hypersensitivity to glutathione modulating agents. In this report we have investigated the mechanism of collateral sensitivity seen in tumor cells over-expressing ABCC1 protein. The results of this study show that ABCC1 expression in tumor cells correlates with their hypersensitivity to various glutathione modulating agents, as demonstrated in H69AR-drug selected and HeLa/ABCC1-transfectant cells. This effect was triggered either through inhibition of GSH synthesis with BSO or by increasing ABCC1-mediated GSH transport with verapamil or apigenin. In addition, our results show that the hypersensitivity of ABCC1-expressing cells to BSO, verapamil or apigenin was preceded by an increase in reactive oxygen species (or ROS). A decrease in GSH level is also observed prior the increase in ROS. In addition, we show that hypersensitivity to the BSO, verapamil or apigenin leads to tumor cell death by apoptosis. Together, the results of this study demonstrate that ABCC1 potentiates oxidative stress in tumor cells through reductions in cellular GSH levels.     

Involvement of oxidative sress in the toxicity of 4-monochlorophenol in Hep G2 cells in culture

Chlorophenols, mainly used as biocides, are compounds with a wide spectrum of toxic effects, including teratogenic and carcinogenic actions. The aim of this study was to examine possible 4-monochlorophenol (4-MCP) toxicity related to metabolic pathways, which may implicate semiquinones and reactive oxygen species (ROS), in human Hep G2 cells. The effects of 4-MCP were performed through cytotoxicity assays (viability, ATP level), metabolic activities (4-MCP intracellular concentration, NADPH cytochrome P-450 reductase (Cyt P-450 red.) and glutathione-S-transferase activities, CYP 3A7 mRNA expression) and oxidative stress (superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activities, glutathione status, malondialdehyde concentration, CYP 2E1 mRNA expression). According to the literature, in this work Hep G2 cells were incubated in the continuous presence of 4-MCP at 350 microM over 24 or 48 h. Results showed statistically significant decreases in ATP levels (24 or 48 h, P < 0.05) versus controls. The 4-MCP intracellular concentrations increased as early as 8-24 h and then decreased (P < 0.01). Decreases in Cyt. P-450 red. (24 h, P < 0.05), catalase (24 h, P < 0.05; 48 h, P < 0.01), glutathione peroxidase activities (48 h, P < 0.05) and reduced glutathione concentrations (48 h, P < 0.05) were observed. In addition, exposure to 4-MCP increased mRNA expressions of CYP 3A7 (24 h, P < 0.05; 48 h, P < 0.01) and CYP 2E1 (24 h, P < 0.01) versus controls. Taken together, these results suggest that 4-MCP metabolites could induce oxidative stress conditions in Hep G2 cells.     

Role of reactive oxygen species, glutathione and NF-kappaB in apoptosis induced by 3,4-methylenedioxymethamphetamine ("Ecstasy") on hepatic stellate cells

"Ecstasy" (3,4-methylenedioxymethamphetamine, MDMA), is a derivative of amphetamine with hepatotoxic effects that has been shown to induce apoptosis of cultured liver cells. In the present work, we studied the role played by oxidative stress in the apoptotic response caused by MDMA on a cell line of hepatic stellate cells (HSC). MDMA-treatment provoked oxidative stress determined as reactive oxygen species (ROS) accumulation and decrease of intracellular reduced glutathione levels. Pre-treatment with the antioxidant pyrrolidine dithiocarbamate blocked ROS production but did not prevent MDMA-induced apoptosis of HSC. The pro-oxidant menadione induced in HSC ROS production and apoptosis that were prevented by pyrrolidine dithiocarbamate, showing HSC to be susceptible to oxidative stress-induced apoptosis. Addition of exogenous GSH or its precursor NAC potentiated the apoptotic action of MDMA but blocked apoptosis induced by menadione. Pre-treatment of HSC with the cytochrome P450 inhibitor quinine diminished the extent of apoptosis caused by MDMA, suggesting the involvement of a metabolic derivative of MDMA on its apoptotic effect. Nuclear factor NF-kappaB was activated by MDMA in a oxidative stress independent fashion and played a protective role in the apoptotic response, since inhibition of NF-kappaB by treatment with parthenolide or by viral infection with a dominant-negative form of NIK (Ad5dnNIK) resulted in an increase of MDMA-induced cell death. In summary, MDMA-induced apoptosis of HSC is accompanied, but not caused by oxidative stress; a metabolic derivative of the drug is responsible for the apoptotic effect of MDMA, which is partially blocked by NF-kappaB activation.     

Synergistic effects of hydrogen peroxide and ethanol on cell viability loss in PC12 cells by increase in mitochondrial permeability transition

The promoting effect of ethanol against the cytotoxicity of hydrogen peroxide (H2O2) in differentiated PC12 cells was assessed by measuring the effect on the mitochondrial membrane permeability. Treatment of PC12 cells with H2O2 resulted in the nuclear damage, decrease in the mitochondrial transmembrane potential, cytosolic accumulation of cytochrome c, activation of caspase-3, increase in the formation of reactive oxygen species (ROS) and depletion of GSH. In PC12 cells and dopaminergic neuroblastoma SH-SY5Y cells, the promoting effect of ethanol on the H2O2-induced cell death was increased with exposure time. Ethanol promoted the nuclear damage, change in the mitochondrial membrane permeability, ROS formation and decrease in GSH contents due to H2O2 in PC12 cells. Catalase, carboxy-PTIO, Mn-TBAP, N-acetylcysteine, cyclosporin A and trifluoperazine inhibited the H2O2 and ethanol-induced mitochondrial dysfunction and cell injury. The results show that the ethanol treatment promotes the cytotoxicity of H2O2 against PC12 cells. Ethanol may enhance the H2O2-induced viability loss in PC12 cells by promoting the mitochondrial membrane permeability change, release of cytochrome c and subsequent activation of caspase-3, which is associated with the increased formation of ROS and depletion of GSH. The findings suggest that ethanol as a promoting agent for the formation of mitochondrial permeability transition may enhance the neuronal cell injury caused by oxidants.     

The course of CCl4 induced hepatotoxicity is altered in mGSTA4-4 null (-/-) mice

Glutathione S-transferases (GSTs) play a key role in cellular detoxification of environmental toxicants through their conjugation to glutathione (GSH). Recent studies have shown that the alpha-class GSTs also provide protection against oxidative stress and lipid peroxidation (LPO). GSTA4-4 is a member of a sub group of the alpha-class GSTs. It has been shown to metabolize 4-hydroxynonenal (4-HNE) with high catalytic efficiency through its conjugation to glutathione (GSH) and has been suggested to be a major component of cellular defense against toxic electrophiles such as 4-HNE generated during LPO. Since the hepatotoxicity of carbon tetrachloride (CCl(4)) has been suggested to be due to the generation of free radicals leading to membrane LPO, the present studies were designed to compare hepatotoxicity of CCl(4) in GSTA4-4 null (-/-) and wild type (+/+) mice. The results show that administration of a single dose of CCl(4) (1 ml/kg i.p.) resulted in time dependent hepatotoxicity in both -/- and +/+ mice; the extent of cellular damage by serum enzymes suggests that progression was more rapid in -/- mice, although injury was similar by 24 h. Histopathologic examination showed similar degrees of centrilobular necrosis by 24 h but much greater surrounding degenerative change, including cellular swelling, disarray, and vacuolization, in the liver of -/- mice. As expected -/- mice did not show any expression of mGSTA4-4; after CCl(4) a compensatory increase in the activities of total GST activity was noted at 24 h. Major alterations in other antioxidant enzymes was not observed. 4-HNE levels in the liver of -/- mice were about four-fold higher than in +/+ mice, suggesting a positive correlation between 4-HNE levels and the altered course of CCl(4) hepatotoxicity. These studies suggest that GSTA4-4 is an important component during the early stages (1-6 h) of cellular defense against oxidative stress and LPO although, it is not effective in protecting against the ultimate degree of overall cell injury.     

ROS generated by CYP450, especially CYP2E1, mediate mitochondrial dysfunction induced by tetrandrine in rat hepatocytes

Aim:

Tetrandrine, an alkaloid with a remarkable pharmacological profile, induces oxidative stress and mitochondrial dysfunction in hepatocytes; however, mitochondria are not the direct target of tetrandrine, which prompts us to elucidate the role of oxidative stress in tetrandrine-induced mitochondrial dysfunction and the sources of oxidative stress.

Methods:

Rat primary hepatocytes were isolated by two-step collagenase perfusion. Mitochondrial function was evaluated by analyzing ATP content, mitochondrial membrane potential (MMP) and the mitochondrial permeability transition. The oxidative stress was evaluated by examining changes in the levels of reactive oxygen species (ROS) and glutathione (GSH).

Results:

ROS scavengers largely attenuated the cytotoxicity induced by tetrandrine in rat hepatocytes, indicating the important role of ROS in the hepatotoxicity of tetrandrine. Of the multiple ROS inhibitors that were tested, only inhibitors of CYP450 (SKF-525A and others) reduced the ROS levels and ameliorated the depletion of GSH. Mitochondrial function assays showed that the mitochondrial permeability transition (MPT) induced by tetrandrine was inhibited by SKF-525A and vitamin C (VC), both of which also rescued the depletion of ATP levels and the mitochondrial membrane potential. Upon inhibiting specific CYP450 isoforms, we observed that the inhibitors of CYP2D, CYP2C, and CYP2E1 attenuated the ATP depletion that occurred following tetrandrine exposure, whereas the inhibitors of CYP2D and CYP2E1 reduced the ROS induced by tetrandrine. Overexpression of CYP2E1 enhanced the tetrandrine-induced cytotoxicity.

Conclusion:

We demonstrated that CYP450 plays an important role in the mitochondrial dysfunction induced by the administration of tetrandrine. ROS generated by CYP450, especially CYP2E1, may contribute to the mitochondrial dysfunction induced by tetrandrine.     

Curcumin protects mitochondria from oxidative damage and attenuates apoptosis in cortical neurons

AIM: To investigate the effect of curcumin on tert-butyl hydroperoxide (t-BHP)-induced oxidative damage in rat cortical neurons and to explore the possible mechanism. METHODS: Primary cultured rat cortical neurons wereperformed in vitro and cell viability was measured by MTT assay. DNA fragmentation was used to evaluate cellapoptosis. Intracellular reactive oxygen species (ROS) and mitochondrial membrane potential (Aψm) was determined by flow cytometric assay. Cellular glutathione (GSH) content was measured by spectrophotometer.‘ Bcl-2family proteins, cytochrome c, cleaved caspase-3, and poly (ADP-ribose) polymerase (PARP) were detected byWestern blot. RESULTS: Exposure of tBHP 100 μmol/L to neurons for 60 rain resulted in △ψm loss and cyto-chrome c release from mitochondria and subsequent activation of caspase-3 and PARP cleavation, and cell apoptosis.After removal of tBHP and then further treatment with curcumin (2.5-20 μmol/L) for 18 h, curcumin abrogated △ψm loss and cytochrome c release, blocked activation of caspase 3, and altered the expression of Bcl-2 family.Further curcumin treatment also prevented cellular GSH and decreased intracellular ROS generation markedly.Curcumin eventually attenuated tBHP-induced apoptosis in cortical neurons. CONCLUSION: Curcumin mayattenuate oxidative damages in cortical neurons by reducing intracellular production of ROS and protecting mito-chondria from oxidative damage.     

Several glutathione S-transferase isozymes that protect against oxidative injury are expressed in human liver mitochondria

The mitochondrial environment is rich in reactive oxygen species (ROS) that may ultimately peroxidize membrane proteins and generate unsaturated aldehydes such as 4-hydroxy-2-nonenal (4HNE). We had previously demonstrated the presence of hGSTA4-4, an efficient catalyst of 4HNE detoxification, in human liver mitochondria to the exclusion of the cytosol. In the present study, GSH-affinity chromatography was used in conjunction with biochemical and proteomic analysis to determine the presence of additional cytosolic glutathione S-transferases (GSTs) in human hepatic mitochondria. HPLC-subunit analysis of GSH affinity-purified liver mitochondrial proteins indicated the presence of several potential mitochondrial GST isoforms. Electrospray ionization-mass spectrometry analysis of eluted mitochondrial GST subunits yielded molecular masses similar to those of hGSTP1, hGSTA1 and hGSTA2. Octagonal matrix-assisted laser desorption/ionization time of flight mass spectrometry and proteomics analysis using MS-FIT confirmed the presence of these three GST subunits in mitochondria, and HPLC analysis indicated that the relative contents of the mitochondrial GST subunits were hGSTA1>hGSTA2>hGSTP1. The mitochondrial localization of the alpha and pi class GST subunits was consistent with immunoblotting analysis of purified mitochondrial GST. Enzymatic studies using GSH-purified mitochondrial GST fractions demonstrated the presence of significant GST activity using the nonspecific GST substrate 1-chloro-2,4-dinitrobenzene (CDNB), as well as 4HNE, delta(5)-androstene-3,17-dione (ADI), and cumene hydroperoxide (CuOOH). Interestingly, the specific mitochondrial GST activities toward 4HNE, a highly toxic alpha,beta-unsaturated aldehyde produced during the breakdown of membrane lipids, exceeded that observed in liver cytosol. These observations are suggestive of a role of GST in protecting against mitochondrial injury during the secondary phase of oxidative stress, or modulation of 4HNE-mediated mitochondrial signaling pathways. However, other properties of mitochondrial GST, such as conjugation of environmental chemicals and binding of lipophilic non-substrate xenobiotics and endogenous compounds, remain to be investigated.     

Transfection of HepG2 cells with hGSTA4 provides protection against 4-hydroxynonenal-mediated oxidative injury

4-Hydroxynonenal (4-HNE) is a mutagenic ,β-unsaturated aldehyde produced during oxidative injury that is conjugated by several glutathione S-transferase (GST) isoforms. The alpha class human GSTA4-4 enzyme (hGSTA4-4) has a particularly high catalytic efficiency toward 4-HNE conjugation. However, hGST4-4 expression is low in most human cells and there are other aldehyde metabolizing enzymes that detoxify 4-HNE. In the current study, we determined the effect of over-expression of hGSTA4 mRNA on the sensitivity of HepG2 cells to 4-HNE injury. HepG2 cells transfected with an hGSTA4 vector construct exhibited high steady-state hGSTA4 mRNA, high GST–4-HNE catalytic activities, but lower basal glutathione (GSH) concentrations relative to insert-free vector (control) cells. Exposure to 4-HNE elicited an increase in GSH concentrations in the control and hGSTA4 cells, although the dose-response of GSH induction differed among the two cell types. Specifically, hGSTA4 cells had significantly higher GSH concentrations when exposed to 5–15 μM 4-HNE, but not at 20 μM 4-HNE, suggesting extensive GSH utilization at high concentrations of 4-HNE. The hGSTA4 cells exhibited a significant growth advantage relative to control cells in the absence of 4-HNE, and a trend towards increased growth at low dose exposures to 4-HNE. However, the hGSTA4 cells did not exhibit a growth advantage relative to control cells at higher 4-HNE exposures associated with increased GSH utilization. As expected, the hGSTA4 cells showed resistance to 4-HNE stimulated lipid peroxidation at all 4-HNE doses. In summary, our data indicates that over-expression of hGSTA4 at levels conferring high GST–4-HNE conjugating activity confers a partial growth advantage to HepG2 cells and protects against 4-HNE oxidative injury. However, the loss of proliferative capacity of hGSTA4 cells challenged with levels of 4-HNE associated with severe oxidative stress indicates a role of other aldehyde metabolizing enzymes, and/or GSH–electrophile transporter proteins, in providing full cellular protection against 4-HNE toxicity.     

Glycyrrhizic acid modulates t-BHP induced apoptosis in primary rat hepatocytes

Glycyrrhizic acid (GA) is the main bioactive ingredient of licorice (Glycyrrhiza glabra). The object of this study was to evaluate the protective effects of GA on tert-butyl hydroperoxide (t-BHP) induced oxidative injury leading to apoptosis in cultured primary rat hepatocytes. Throughout the study silymarin was used as positive control. Molecular mechanisms involved in apoptotic pathways induced in hepatocytes by t-BHP at 250 μM were explored in detail. DNA fragmentation, activation of caspases and cytochrome c release were demonstrated. In addition, changes in the mitochondrial membrane potential and ROS generation were detected confirming involvement of mitochondrial pathway. Pre-treatment with GA (4 μg) protected the hepatocytes against t-BHP induced oxidative injury and the results were comparable to the pre-treatment with positive control, i.e. silymarin. The protective potential against cell death was achieved mainly by preventing intracellular GSH depletion, decrease in ROS formation as well as inhibition of mitochondrial membrane depolarization. GA was found to modulate critical end points of oxidative stress induced apoptosis and could be beneficial against liver diseases where oxidative stress is known to play a crucial role.     

Influence of repeated preexposure to arsenic on acetaminophen-induced oxidative stress in liver of male rats

We evaluated whether repeated arsenic preexposure can increase acetaminophen-induced hepatic oxidative stress. Rats were exposed to arsenic (25 ppm; rat equivalent concentration of maximum groundwater contamination level) via drinking water for 28 days. Next day, they were given single oral administration of acetaminophen (420 or 1000 mg/kg b.w.). Hepatotoxicity was evaluated by assessing serum biomarkers, cytochrome-P450 (CYP) content, CYP3A4- and CYP2E1-dependent enzymes, lipid peroxidation and antioxidants. Arsenic or acetaminophen increased serum ALT and AST activities and depleted CYP. Arsenic decreased, but acetaminophen increased CYP-dependent enzyme activities. These agents independently increased lipid peroxidation and decreased antioxidants. Arsenic did not alter the effects of acetaminophen on serum biomarkers, caused further CYP depletion and decreased acetaminophen-mediated induction of drug-metabolizing enzymes. Arsenic enhanced the lower dose of acetaminophen-mediated lipid peroxidation and glutathione depletion with no further alterations in enzymatic antioxidants. However, arsenic attenuated the higher dose-mediated lipid peroxidation and glutathione depletion with improvement in glutathione peroxidase and glutathione reductase activities, further decrease in catalase and no alterations in superoxide dismutase and glutathione-S-transferase activities. Results show that arsenic preexposure increased the susceptibility of rats to hepatic oxidative stress induced by the lower dose of acetaminophen, but reduced the oxidative stress induced by the higher dose.     

Mitochondrial CYP2E1 is sufficient to mediate oxidative stress and cytotoxicity induced by ethanol and acetaminophen

Several cytochromes P450 (CYPs) are not only located in the endoplasmic reticulum but also within mitochondria. One such CYP is CYP2E1 which metabolizes numerous substrates and generates significant amount of reactive oxygen species. The presence of CYP2E1 in these organelles raises questions regarding its physiological role but also its possible deleterious effects in the context of drug-induced cytotoxicity. The aim of our study was to investigate the role of mitochondrial CYP2E1 in the toxicity of acetaminophen and ethanol. Hence the effects of these two compounds in cells expressing CYP2E1 in mitochondria only, or in both endoplasmic reticulum and mitochondria, were compared to those observed in mock-transfected cells. Our results indicated that when acetaminophen or ethanol were used as CYP2E1 substrates, the exclusive localization of CYP2E1 within mitochondria was sufficient to induce reactive oxygen species overproduction, depletion of reduced glutathione, increased expression of mitochondrial Hsp70, mitochondrial dysfunction and cytotoxicity. Importantly, these harmful events happened despite lower cellular level and activity of CYP2E1 when compared to cells expressing CYP2E1 in both endoplasmic reticulum and mitochondria, and this was particularly obvious with acetaminophen. Taken together, these data suggest that mitochondrial CYP2E1 could play a major role in drug-induced oxidative stress and cell demise.     

Taurine protects acetaminophen-induced oxidative damage in mice kidney through APAP urinary excretion and CYP2E1 inactivation

Acute exposure of acetaminophen (APAP), a widely used analgesic and antipyretic drug, causes severe renal damage and no specific agent has been reported so far that plays any beneficial role in this organ pathophysiology. In the present study, the protective role of taurine on APAP-induced nephrotoxicity was investigated in mice. In order to induce acute nephrotoxicity, APAP was administered at a single dose of 2 g/kg body weight orally to male adult albino mice of Swiss strain. APAP exposure for 24 h significantly increased plasma level of blood urea nitrogen (BUN), creatinine, uric acid, TNF-α, NO production, urinary γ-glutamyl transpeptidase (γ-GT) activity, total urinary protein and urinary glucose level accompanied by a decrease in Na⁺–K⁺–ATPase activity. Moreover, APAP administration significantly increased MDA, protein carbonylation, GSSG level, intracellular ROS production and cytochrome P450 enzyme (CYPP450) activity. The same exposure decreased GSH level, ferric reducing/antioxidant power (FRAP) as well as the activities of antioxidant enzymes indicating that APAP-induced renal damage was mediated through oxidative stress. Besides, APAP exposure significantly reduced mitochondrial membrane potential and induced up-regulation of CYP2E1 in renal tissues although JNK did not play any significant role in this APAP-induced renal pathophysiology. Caspase 9/3 immunoblot and DNA fragmentation analyses showed that APAP-induced renal cell damage was mostly necrotic in nature, although some apoptosis also occurred simultaneously. Taurine treatment both pre and post (150 mg/kg body weight for 3 days, orally) to APAP exposure, however, significantly reduced APAP-induced nephrotoxicity through its antioxidant properties, urinary excretion of APAP and suppression of CYP2E1. Results suggest that taurine might be a potential therapeutic candidate against APAP-induced acute nephrotoxicity.     

Cisplatin-induced hepatotoxicity is enhanced by elevated expression of cytochrome P450 2E1.

In this study, the possible potentiation of cisplatin-induced hepatotoxicity by cytochrome P450 2E1 (CYP2E1) was examined both in vitro and in vivo. Transfected HepG2 cells expressing CYP2E1 (E47 cells) and not expressing CYP2E1 (C34 cells) were used as an in vitro model, and mice drinking 2% acetone for 7 days to induce CYP2E1 were used as an in vivo model. Exposure of E47 cells to cisplatin caused a much greater loss of cell viability, more striking depletion of reduced glutathione (GSH), and higher reactive oxygen species (ROS) production as compared with C34 cells. The prooxidant L-buthionine-[R,S]-sulfoximine (BSO), which depletes GSH, enhanced cisplatin-induced loss of cell viability, whereas the antioxidant glutathione ethyl ester, or the iron chelator deferoxamine mesylate (DFO) protected against the cisplatin-induced loss of E47 cell viability. Diallyl sulfide (DAS), an inhibitor of CYP2E1, also protected against the cisplatin toxicity in the E47 cells. After being injected with cisplatin (ip, 45 mg/kg), mice drinking 2% acetone with increased CYP2E1 levels exhibited elevated levels of serum ALT and AST, liver caspase-3 activity and positive staining of TUNEL increased, and histopathology indicated the presence of necrotic foci in livers of acetone plus cisplatin-treated mice. Lipid peroxidation and protein oxidation as indicated by carbonyl formation, staining of 3-nitrotyrosine (3-NT) and iron were higher in the cisplatin plus acetone group, compared with cisplatin alone group. Both in vitro and in vivo results indicate that elevated CYP2E1 enhances cisplatin-induced hepatotoxicity, and the mechanism may involve increased production of ROS and oxidative stress.