tert-Butyl hydroperoxide-induced radical production in rat liver mitochondria

A versatile multiplexed assay to quantify intracellular ROS and cell viability in 3D on-a-chip models

Reactive oxygen species (ROS) have different properties and biological functions. They contribute to cell signaling and, in excessive amounts, to oxidative stress (OS). Although ROS is pivotal in a wide number of physiological systems and pathophysiological processes, direct quantification in vivo is quite challenging and mainly limited to in vitro studies. Even though advanced in vitro cell culture techniques, like on-a-chip culture, have overcome the lack of crucial in vivo-like physiological aspects in 2D culture, the majority of in vitro ROS quantification studies are generally performed in 2D. Here we report the development, application, and validation of a multiplexed assay to quantify ROS and cell viability in organ-on-a-chip models. The assay utilizes three dyes to stain live cells for ROS, dead cells, and DNA. Confocal images were analyzed to quantify ROS probes and determine the number of nuclei and dead cells. We found that, in contrast to what has been reported with 2D cell culture, on-a-chip models are more prone to scavenge ROS rather than accumulate them. The assay is sensitive enough to distinguish between different phenotypes of endothelial cells (ECs) based on the level of OS to detect higher level in tumor than normal cells. Our results indicate that the use of physiologically relevant models and this assay could help unravelling the mechanisms behind OS and ROS accumulation. A further step could be taken in data analysis by implementing AI in the pipeline to also analyze images for morphological changes to have an even broader view of OS mechanism.

S-1-propenylmercaptocysteine protects murine hepatocytes against oxidative stress via persulfidation of Keap1 and activation of Nrf2

The onion-derived metabolite, S-1-propenylmercaptocysteine (CySSPe), protects against oxidative stress and exhibits anti-inflammatory effects by modulating cellular redox homeostasis. We sought to establish whether CySSPe activates nuclear factor erythroid 2-related factor 2 (Nrf2) and whether activation of Nrf2 by CySSPe involves modification of the Kelch-like ECH-associated protein-1 (Keap1) to manifest these effects. We found that CySSPe stabilized Nrf2 protein and facilitated nuclear translocation to induce expression of antioxidant enzymes, including NQO1, HO-1, and GCL. Moreover, CySSPe attenuated tert-butyl hydroperoxide-induced cytotoxicity and dose-dependently inhibited reactive oxygen species production. Silencing experiments using Nrf2-siRNA confirmed that CySSPe conferred protection against oxidative stress by activating Nrf2. CySSPe enhanced cellular pool of reduced glutathione (GSH) and improved GSH:GSSG ratio. Pretreatment of cells with l-buthionine-S,R-sulfoximine (BSO) confirmed that CySSPe increases de novo synthesis of GSH by upregulating expression of the GSH-synthesizing enzyme GCL. Treatment of cells with CySSPe elevated hydrogen sulfide (H₂S) production. Inhibition of H₂S-synthesizing enzymes, cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthase (CBS), by pretreating cells with propargylglycine (PAG) and oxyaminoacetic acid (AOAA) revealed that H₂S production was partially dependent on a CSE/CBS-catalyzed β-elimination reaction with CySSPe that likely produced 1-propenyl persulfide (RSSH). Depleting cells of their GSH pool by exposure to BSO and diethylmaleate attenuated H₂S production, suggesting a GSH-dependent formation of H₂S, likely via the reduction of RSSH by GSH. Finally, treatment of cells with CySSPe persulfidated Keap1, which may be the mechanism involved for the stabilization of Nrf2 by CySSPe. Taken together, our results showed that attenuation of oxidative stress by CySSPe is associated with its ability to produce H₂S or RSSH, which persulfidates Keap1 and activates Nrf2 signaling. This study provides insights on the potential of CySSPe as an onion-derived dietary agent that modulates redox homeostasis and combats oxidative stress.

Effect of Antioxidant Water on the Bioactivities of Cells

It has been reported that water at the interface of a hydrophilic thin film forms an exclusion zone, which has a higher density than ordinary water. A similar phenomenon was observed for a hydrated hydrophilic ceramic powder, and water turns into a three-dimensional cell-like structure composed of high density water and low density water. This structured water appears to have a stimulative effect on plant growth. This report outlines our study of antioxidant properties of this structured water and its effect on cell bioactivities. Culturing media which were prepared utilizing this antioxidant structured water promoted the viability of RAW 264.7 macrophage cells by up to three times. The same tendency was observed for other cells including IEC-6, C2C12, and 3T3-L1. Also, the cytokine expression of the splenocytes taken from a mouse spleen increased in the same manner. The water also appears to suppress the viability of cancer cell, MCF-7. These results strongly suggest that the structured water helps the activities of normal cells while suppressing those of malignant cells.

Selenopheno quinolinones and coumarins promote cancer cell apoptosis by ROS depletion and caspase-7 activation

AIM

This study was designed to investigate the mechanism underlying cancer cell apoptosis caused by selenophenoquinolinones and coumarins.

MATERIALS AND METHODS

Twelve derivatives were studied according to their ability to suppress the proliferation of cancer cells in vitro (i.e., HepG2, MH-22A, MCF-7), induce cell apoptosis, modulate cellular antioxidant enzyme system activities (i.e., SOD, GPx, TrxR), influence the level of ROS, and modulate caspase activity.

RESULTS

A plausible mechanism of apoptosis is presented. The lack of change in the activity of caspase-8 demonstrates that these compounds affect the intrinsic rather than the extrinsic pathway; moreover, the absence of caspase-9 activation suggests that the studied compounds are involved in the intrinsic pathway of apoptosis in a non-canonical manner. Provisionally, the increase in Smac/Diablo released from the mitochondria removes the inhibitory effect and activates caspase-7, leading to apoptosis. Additionally, the activation of caspase-1 activates effector caspase-7, thereby increasing the amount of cytochrome c and Smac/Diablo released from the mitochondria and ultimately leading to apoptosis.

CONCLUSION

This present study provides scientific evidence that selenopheno quinolinones and coumarins promote cancer cell apoptosis by ROS depletion and caspase-7 activation in malignant cells.

Calcium-Induced Mitochondrial Permeability Transitions: Parameters of Ca2+ Ion Interactions with Mitochondria and Effects of Oxidative Agents

We evaluated the parameters of Ca²⁺-induced mitochondrial permeability transition (MPT) pore formations, Ca²⁺ binding constants, stoichiometry, energy of activation, and the effect of oxidative agents, tert-butyl hydroperoxide (tBHP), and hypochlorous acid (HOCl), on Ca²⁺ -mediated process in rat liver mitochondria. From the Hill plot of the dependence of MPT rate on Ca²⁺ concentration, we determined the order of interaction of Ca²⁺ ions with the mitochondrial sites, n = 3, and the apparent K_d = 60 ± 12 µM. We also found the apparent Michaelis-Menten constant, K_m, for Ca²⁺ interactions with mitochondria to be equal to 75 ± 20 µM, whereas that in the presence of 300 µM tBHP was 120 ± 20 µM. Using the Arrhenius plots of the temperature dependences of apparent mitochondrial swelling rate at various Ca²⁺ concentrations, we calculated the activation energy of the MPT process. ΔE_a was 130 ± 20 kJ/mol at temperatures below the break point of the Arrhenius plot (30-34 °C) and 50 ± 9 kJ/mol at higher temperatures. Ca²⁺ ions induced rapid mitochondrial NADH depletion and membrane depolarization. Prevention of the pore formation by cyclosporin A inhibited Ca²⁺-dependent mitochondrial depolarization and Mg²⁺ ions attenuated the potential dissipation. tBHP (10-150 µM) dose-dependently enhanced the rate of MPT opening, whereas the effect of HOCl on MPT depended on the ratio of HOCl/Ca²⁺. The apparent K_m of tBHP interaction with mitochondria in the swelling reaction was found to be K_m = 11 ± 3 µM. The present study provides evidence that three calcium ions interact with mitochondrial site with high affinity during MPT. Ca²⁺-induced MPT pore formations due to mitochondrial membrane protein denaturation resulted in membrane potential dissipation. Oxidants with different mechanisms, tBHP and HOCl, reduced mitochondrial membrane potential and oxidized mitochondrial NADH in EDTA-free medium and had an effect on Ca²⁺-induced MPT onset.

Effects of colored and noncolored phenolics of Echium plantagineum L. bee pollen in Caco-2 cells under oxidative stress induced by tert-butyl hydroperoxide

Bee pollen is used as a dietary supplement, being promoted as a health food. Echium plantagineum L. bee pollen fractions enriched in flavonols (fraction I) or anthocyanins (fraction II) and the whole extract were characterized by HPLC-DAD. Both in the whole extract and in fraction II seven flavonols and five anthocyanins were identified, while fraction I contained six flavonols (in higher levels than fraction II) and small amounts of petunidin-3-O-rutinoside. Antioxidant capacity was evaluated in Caco-2 cells under oxidative stress induced by tert-butyl hydroperoxide (t-BHP). Fraction I pre-exposure imparted a tendency to protect cells, while fraction II and the whole extract aggravated t-BHP toxicity at some concentrations. The protective effects seem to be correlated with the levels of total glutathione, while no correlation between cellular viability and reactive species was seen. The extracts displayed no significant effect on antioxidant enzymes activity. Overall, anthocyanins seem to abrogate the antioxidant potential of flavonoid-rich extracts.

Cuscuta chinensis seeds water extraction protecting murine osteoblastic MC3T3-E1 cells against tertiary butyl hydroperoxide induced injury

ETHNOPHARMACOLOGICAL RELEVANCE

Cuscuta chinensis (C. chinensis) is a well-known traditional Chinese herb that has been used to treat heart disease, diabetes, liver injury, cancer, and aging.

MATERIALS AND METHODS

Murine osteoblastic MC3T3-E1 cells were treated with various concentrations of C. chinensis water extraction at different time intervals. The antioxidant effect of C. chinensis on MC3T3-E1 cells was evaluated using MTT and TUNEL assays. The effect of C. chinensis on cell cycle was analyzed by flow cytometry with propidium iodide. Lipid peroxidation was measured by the HPLC method. The cellular redox status was determined from the reduced glutathione to oxidized glutathione ratio (GSH/GSSG) and the enzymes involved in glutathione metabolism, including glutathione reductase (GR), Glutathione S-transferase (GST), and Glucose-6-phosphate dehydrogenase (G6PD). The changes in relative mitochondrial transmembrane potential (ΔΨm) in the MC3T3-E1 cells were analyzed with rhodamine 123 staining. Western blot analysis was used to evaluate the levels of cytochrome c (cyto c), Bax, Bcl-2, caspase 3, Sirt3, and IDH2 expressions.

RESULTS

The C. chinensis water extraction protects tertiary butyl hydroperoxide (TBHP)-treated MC3T3-E1 cells from death in a dose-dependent manner. C. chinensis treatment significantly inhibited the reactive oxygen species (ROS) generation, malondialdehyde (MDA) production, and increased the activity of superoxide dismutase (SOD), GR, GST, and G6PD. The release of cyto c from mitochondria was reduced by C. chinensis, which increased the expression of antiapoptotic IDH2, Sirt3, and Bcl-2 and decreased the expression of Bax, cyto c, and caspase 3.

CONCLUSIONS

C. chinensis modulated the oxidative stress-induced apoptosis in MC3T3-E1 cells, probably due to its antioxidant activity and functioning via mitochondria-dependent pathways.

Oxidative damage of rat liver mitochondria during exposure to t-butyl hydroperoxide. Role of Ca²⁺ ions in oxidative processes

AIMS

The present study was designed for further evaluation of the biochemical mechanism of hepatic mitochondrial dysfunction under oxidative damages induced by organic hydroperoxide, tert-butyl hydroperoxide (tBHP), for estimation of the molecular targets impaired during oxidative stress, and for investigation of the role of Ca(2+) ions in mitochondrial oxidative reactions and of the protective effect of melatonin during mitochondrial peroxidative damage.

MAIN METHODS

Mitochondria were isolated by differential centrifugation from the rat liver. The effects of tBHP exposure, EDTA, Ca(2+) ions and melatonin on mitochondrial respiratory activity, mitochondrial enzyme activities and redox status were measured.

KEY FINDINGS

The present study provides evidence that tBHP (at low concentrations of 0.02-0.065mM, in EDTA-free medium) induced uncoupling of the oxidation and phosphorylation processes and decreased the efficiency of the phosphorylation reaction. This effect depended on the respiratory substrate used. The presence of EDTA prevented oxidative impairment of mitochondrial respiration, but Ca(2+) ions in the medium enhanced oxidant-induced mitochondrial damage considerably. In the presence of 0.5mM EDTA, tBHP (at high concentrations, 0.5-2mM) considerably oxidized mitochondrial reduced glutathione, enhanced accumulation of membrane lipid peroxidation products and mixed protein-glutathione disulfides and led to an inhibition of oxoglutarate dehydrogenase and succinate dehydrogenase.

SIGNIFICANCE

Direct oxidative modification of enzymatic complexes of the respiratory chain and mitochondrial matrix, mitochondrial reduced glutathione depletion, protein glutathionylation, membrane lipid peroxidation and Ca(2+) overload are the main events of mitochondrial peroxidative damages. Experiments in vitro demonstrated that melatonin inhibited the mitochondrial peroxidative damage, preventing redox-balance changes and succinate dehydrogenase inactivation.

LC-MS/MS Determination of Isoprostanes in Plasma Samples Collected from Mice Exposed to Doxorubicin or Tert-Butyl Hydroperoxide

Isoprostanes are stable products of arachidonic acid peroxidation and are regarded as the most reliable markers of oxidative stress in vivo. Here we describe the LC-MS/MS procedure enabling simultaneous determination of four regioisomers (8-iso prostaglandin F2α, 8-iso-15(R)-prostaglandin F2α, 11β-prostaglandin F2α, 15(R)-prostaglandin F2α) in plasma samples collected from mice. The four plasma isoprostanes are determined by LC-ESI-MS/MS with deuterated 8-iso-PGF2α-d4 as an internal standard (I.S.). For plasma samples spiked with the isoprostanes at a level of 200 pg/mL each, the method imprecision has been below 7.1% and mean inaccuracy equaled 8.7%. The applicability of the proposed approach has been verified by the assessment of changes in isoprostane levels in plasma samples derived from mice exposed to tert-butyl hydroperoxide (TBHP), a model inducer of oxidative stress, or to antitumor drug doxorubicin (DOX) known for potent stimulation of redox cycling. Compared to the control group of mice, both oxidative stress inducers tested increased the levels of three out of four isoprostanes in exposed animals; 11β-prostaglandin F2α being the exception. The greatest rise was observed in the case of 15(R)-prostaglandin F2α, by about 50% and 70% in plasma samples derived from mice exposed to DOX and TBHP, respectively.

Subacute oral and dermal toxicity of tert-butyl hydroperoxide in Fischer F344/N rats and B6C3F1 mice

Tert-butyl hydroperoxide (TBHP) is a catalyst frequently used in oxidation and sulfonation reactions in the plastics industry. Since the toxicological evaluation of TBHP remains unknown, the National Toxicology Program (NTP) designed studies to characterize and compare TBHP toxicity by the dermal and oral (gavage) routes in male and female Fischer 344 rats and B6C3F1 mice in 14-day exposures. Rats and mice were administered TBHP at 22, 44, 88, 176 or 352 mg/kg in 0.5% aqueous methylcellulose for the gavage studies. In the dermal studies, mice were administered the same doses as above, while rats were administered four doses (22, 44, 88, 176 mg/kg) in 50% aqueous acetone. Results from the gavage studies revealed treatment-related decreases in survival in male rats and body weights in both male and female rats in the 352 mg/kg group. Clinical signs included post-treatment lethargy, thinness, abnormal breathing, ruffled fur, and/or ataxia which occurred sporadically. The male mice showed a statistically significant decrease in body weight in the 44, 88, 176, and 352 mg/kg groups. The major target organs of toxicity were the forestomach in male and female rats and mice, and the esophagus in male and female rats and in male mice. In addition, there was an increase in the absolute and relative liver weight in female mice with hepatocellular hypertrophy in the top-dose group only. Results from spin trapping experiments revealed the presence of electron paramagnetic resonance signals from radical adducts in the blood and organic extracts of the liver and kidneys of rats treated by gavage with 176 mg/kg TBHP, suggesting the involvement of free- radical generation. The no observed adverse effect level (NOAEL) was considered to be 22 mg/kg in rats and male mice, and 44 mg/kg in female mice. In the dermal studies, there was no effect on survival, body weight, or organ weights in either rats or mice. TBHP administration at the site of application resulted in dermal irritation, hyperkeratosis, hyperplasia, and/or inflammation of the epidermis and inflammation of the dermis at 176 mg/kg and above in male and female rats. Dermal irritation at the site of application was noted in all the mice exposed to 352 mg/kg TBHP. Histopathological lesions in the epidermis and dermis were seen in the 88-352 mg/kg males and in the 176-352 mg/kg females. The NOAEL was found to be 88 mg/kg for male rats and female mice, and 44 mg/kg for female rats and male mice. In conclusion, these studies demonstrate that TBHP is metabolized to free radicals and is a contact irritant affecting skin by the dermal route of exposure, and forestomach and esophagus by oral administration. There was no evidence of systemic absorption by the dermal route of exposure based on lack of pathological findings (Supported by National Institute of Environmental Health Sciences Contract No. N01-ES-65406).

Radiation-induced signaling results in mitochondrial impairment in mouse heart at 4 weeks after exposure to X-rays

Backround

Radiation therapy treatment of breast cancer, Hodgkin's disease or childhood cancers expose the heart to high local radiation doses, causing an increased risk of cardiovascular disease in the survivors decades after the treatment. The mechanisms that underlie the radiation damage remain poorly understood so far. Previous data show that impairment of mitochondrial oxidative metabolism is directly linked to the development of cardiovascular disease.

Methodology/Principal findings

In this study, the radiation-induced in vivo effects on cardiac mitochondrial proteome and function were investigated. C57BL/6N mice were exposed to local irradiation of the heart with doses of 0.2 Gy or 2 Gy (X-ray, 200 kV) at the age of eight weeks, the control mice were sham-irradiated. After four weeks the cardiac mitochondria were isolated and tested for proteomic and functional alterations. Two complementary proteomics approaches using both peptide and protein quantification strategies showed radiation-induced deregulation of 25 proteins in total. Three main biological categories were affected: the oxidative phophorylation, the pyruvate metabolism, and the cytoskeletal structure. The mitochondria exposed to high-dose irradiation showed functional impairment reflected as partial deactivation of Complex I (32%) and Complex III (11%), decreased succinate-driven respiratory capacity (13%), increased level of reactive oxygen species and enhanced oxidation of mitochondrial proteins. The changes in the pyruvate metabolism and structural proteins were seen with both low and high radiation doses.

Conclusion/Significance

This is the first study showing the biological alterations in the murine heart mitochondria several weeks after the exposure to low- and high-dose of ionizing radiation. Our results show that doses, equivalent to a single dose in radiotherapy, cause long-lasting changes in mitochondrial oxidative metabolism and mitochondria-associated cytoskeleton. This prompts us to propose that these first pathological changes lead to an increased risk of cardiovascular disease after radiation exposure.

Identification of mitochondrial electron transport chain-mediated NADH radical formation by EPR spin-trapping techniques

The mitochondrial electron transport chain (ETC) is a major source of free radical production. However, due to the highly reactive nature of radical species and their short lifetimes, accurate detection and identification of these molecules in biological systems is challenging. The aim of this investigation was to determine the free radical species produced from the mitochondrial ETC by utilizing EPR spin-trapping techniques and the recently commercialized spin-trap, 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO). We demonstrate that this spin-trap has the preferential quality of having minimal mitochondrial toxicity at concentrations required for radical detection. In rat heart mitochondria and submitochondrial particles supplied with NADH, the major species detected under physiological pH was a carbon-centered radical adduct, indicated by markedly large hyperfine coupling constant with hydrogen (a(H) > 2.0 mT). In the presence of the ETC inhibitors, the carbon-centered radical formation was increased and exhibited NADH concentration dependency. The same carbon-centered radical could also be produced with the NAD biosynthesis precursor, nicotinamide mononucleotide, in the presence of a catalytic amount of NADH. The results support the conclusion that the observed species is a complex I derived NADH radical. The formation of the NADH radical could be blocked by hydroxyl radical scavengers but not SOD. In vitro experiments confirmed that an NADH-radical is readily formed by hydroxyl radical but not superoxide anion, further implicating hydroxyl radical as an upstream mediator of NADH radical production. These findings demonstrate the identification of a novel mitochondrial radical species with potential physiological significance and highlight the diverse mechanisms and sites of production within the ETC.

Protective role of a coumarin-derived schiff base scaffold against tertiary butyl hydroperoxide (TBHP)-induced oxidative impairment and cell death via MAPKs, NF-κB and mitochondria-dependent pathways

The present study investigated the antioxidant signalling mechanism of a coumarin-derived schiff base (CSB) scaffold against tert-butylhydroperoxide (TBHP) induced oxidative insult in murine hepatocytes. CSB possesses DPPH and other free radical scavenging activities. TBHP reduced cell viability and intracellular antioxidant status accompanied by an increase in intracellular ROS production in hepatocytes. TBHP also activated phospho-ERK1/2, phospho-p38 and NF-κB, altered the Bcl-2/Bad ratio, reduced mitochondrial membrane potential, released cytochrome C and activated caspase 3, suggesting that TBHP induced oxidative stress responsive cell death via apoptotic pathway. FACS analysis and DNA fragmentation studies also confirmed the apoptotic cell death in TBHP exposed hepatocytes. Treatment with CSB effectively reduced these adverse effects by preventing the oxidative insult, alteration in the redox-sensitive signalling cascades and mitochondrial events. Combining, results suggest that antioxidant property of CSB make the molecule to be a potential protective measure against oxidative insult, cytotoxicity and cell death.

The mechanism of vitexin-4''-O-glucoside protecting ECV-304 cells against tertbutyl hydroperoxide induced injury

The aim of this article is to investigate the mechanism of vitexin-4''-O-glucoside (VOG) protecting ECV-304 cells against tertbutyl hydroperoxide (TBHP)-induced injury. ECV-304 cell viability was measured by MTT assay. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) assay. Cellular morphological changes were observed using phase contrast microscopy. The change of relative mitochondrial transmembrane potential in the ECV-304 cells was analysed with rhodamine 123 staining. Lipid peroxidation was measured by the HPLC method. The results showed that 128 µmol L(-1) VOG could effectively protect ECV-304 cells against cytotoxicity induced by TBHP. VOG protected TBHP-treated ECV-304 cells from death, significantly decreased MDA production, and increased superoxide dismutase (SOD) activity and mitochondrial membrane potential (ΔΨ). Taken together, VOG protects against TBHP-induced ECV-304 cell injury partially through resuming mitochondrial function.

High susceptibility of activated lymphocytes to oxidative stress-induced cell death

The present study provides evidence that activated spleen lymphocytes from Walker 256 tumor bearing rats are more susceptible than controls to tert-butyl hydroperoxide (t-BOOH)-induced necrotic cell death in vitro. The iron chelator and antioxidant deferoxamine, the intracellular Ca2+ chelator BAPTA, the L-type Ca2+ channel antagonist nifedipine or the mitochondrial permeability transition inhibitor cyclosporin A, but not the calcineurin inhibitor FK-506, render control and activated lymphocytes equally resistant to the toxic effects of t-BOOH. Incubation of activated lymphocytes in the presence of t-BOOH resulted in a cyclosporin A-sensitive decrease in mitochondrial membrane potential. These results indicate that the higher cytosolic Ca2+ level in activated lymphocytes increases their susceptibility to oxidative stress-induced cell death in a mechanism involving the participation of mitochondrial permeability transition.

HPLC determination of malondialdehyde in ECV304 cell culture medium for measuring the antioxidant effect of vitexin-4''-O-glucoside

To investigate the antioxidant effect of vitexin-4''-O-glucoside, a flavone glycoside, isolated from the leaves of Crataegus pinnatifida Bge. var. major, we developed a simple and sensitive high-performance liquid chromatography (HPLC) method to determine levels of malondialdehyde (MDA) in ECV304 cell culture medium after induction by tert-butyl-hydroperoxide (TBHP). The preparation of analyzed samples involved a one-step derivatization with thiobarbituric acid (TBA). HPLC analysis was performed on a Synergi Hydro-RP, a polar end-capped C18 column (250 x 4.6 mm, 4 mum), using an acetonitrile-ammonium acetate aqueous solution (10 mM, pH 6.8) as the mobile phase under linear gradient conditions with UV detection at 532 nm. The calibration curve was linear over 0.0125-1.25 microM MDA (r = 0.9951). Relative standard deviations (RSDs) of intra-day and inter-day precision were less than 6.1% and 5.0%, respectively. The mean recovery was 96.9 +/- 1.6%. The lower limit of quantification (LLOQ) of MDA was 0.0125 microM. This chromatographic method was successfully applied to investigating the in vitro antioxidant effect of vitexin-4''-O-glucoside. Vitexin-4''-O-glucoside (120 M) protected ECV304 cells from peroxidation induced by TBHP.

Protective effect of magnolol on TBHP-induced injury in H460 cells partially via a p53 dependent mechanism

The aim is to investigate the effect of Magnolol preserved H460 cells from an oxidative agent tert-butylhydroperoxide (TBHP)-induced cell death. Magnolol augmented cell survival ratio after TBHP challenged. The protective action of this drug was more efficacious than that of N-acetylcysteine (NAC) which is a putative antioxidant. DNA damage, detected by the comet assay, was diminished after treatment of Magnolol. The cells viability decreased after treatment with 0.15 mM TBHP for 24 h, accompanied by inducing apoptotic death of the cells. Cytotoxicity and apoptosis induced by TBHP were significantly inhibited or attenuated after pretreatment with 20 microM Magnolol. Magnolol contributes to the cells survival through downregulated the p53 phosphorylation and PTEN expression, and upregulated Akt phosphorylation. Taken together, Magnolol was effective against DNA single strand breaks (SSB) formation, cytotoxicity and lipid peroxidation induced by TBHP, and its effects on p53 phosphorylation, PTEN and Akt phosphorylation were due to its antioxidative function, and partially via a p53 dependent mechanism in this protective effects.

Evaluation of the probe dihydrocalcein acetoxymethylester as an indicator of reactive oxygen species formation and comparison with oxidative DNA base modification determined by modified alkaline elution technique

Reactive oxygen species (ROS) play a predominant role in various diseases and the development of fast and easy methods for the quantification of intracellular ROS represents an important goal. Therefore, the aim of the present study was the evaluation of the fluorogenic probe dihydrocalcein acetoxymethylester (AM) for the detection of intracellular ROS. A flow cytometric method was developed using MCF-7 cells and the kinetics of ester hydrolysis and the cellular distribution and stability of calcein were characterized using calcein AM. Then, MCF-7 cells were challenged with model agents for the generation of singlet oxygen (illumination with visible light), peroxyl and hydroxyl radicals (tert-butylhydroperoxide, tBHP), superoxide anion radicals (potassium dioxide), and the intracellular formation of superoxide anion radicals by redox cycling (menadione) and the formation of calcein was compared with the induction of oxidative DNA base modifications assessed by modified alkaline elution technique. Every model agent significantly induced formamidopyrimidine-DNA glycosylase-sensitive sites (i.e. oxidative DNA base modifications) and most also induced DNA strand breaks. In contrast, exclusively tBHP and illumination with visible light induced the intracellular formation of calcein. In conclusion, though intracellular oxidation of dihydrocalcein represents a fast screening method, it detects a limited spectrum of ROS.

Lack of molecular relationships between lipid peroxidation and mitochondrial DNA single strand breaks in isolated rat hepatocytes and mitochondria

We investigated the molecular relationships between lipid peroxidation and mitochondrial DNA (mtDNA) single strand breaks (ssb) in isolated rat hepatocytes and mitochondria exposed to tert-butylhydroperoxide (TBH). Our results show that mtDNA ssb induced by TBH are independent of lipid peroxidation and dependent on the presence of iron and of hydroxyl free radicals. These data contribute to the definition of the mechanisms whereby mtDNA ssb are induced and provide possible molecular targets for the prevention of this kind of damage in vivo.

Separation and identification of DMPO adducts of oxygen-centered radicals formed from organic hydroperoxides by HPLC-ESR, ESI-MS and MS/MS

Many electron spin resonance (ESR) spectra of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) radical adducts from the reaction of organic hydroperoxides with heme proteins or Fe(2+) were assigned to the adducts of DMPO with peroxyl, alkoxyl, and alkyl radicals. In particular, the controversial assignment of DMPO/peroxyl radical adducts was based on the close similarity of their ESR spectra to that of the DMPO/superoxide radical adduct in conjunction with their insensitivity to superoxide dismutase, which distinguishes the peroxyl adducts from the DMPO/superoxide adduct. Although recent reports assigned the spectra suggested to be DMPO/peroxyl radical adducts to the DMPO/methoxyl adduct based on independent synthesis of the adduct and/or (17)O-labeling, (17)O-labeling is extremely expensive, and both of these assignments were still based on hyperfine coupling constants, which have not been confirmed by independent techniques. In this study, we have used online high performance liquid chromatography (HPLC or LC)/ESR, electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) to separate and directly characterize DMPO oxygen-centered radical adducts formed from the reaction of Fe(2+) with t-butyl or cumene hydroperoxide. In each reaction system, two DMPO oxygen-centered radical adducts were separated and detected by online LC/ESR. The first DMPO radical adduct from both systems showed identical chromatographic retention times (t(R) = 9.6 min) and hyperfine coupling constants (a(N) = 14.51 G, a(H)(beta) = 10.71 G, and a(H)(gamma) = 1.32 G). The ESI-MS and MS/MS spectra demonstrated that this radical was the DMPO/methoxyl radical adduct, not the peroxyl radical adduct as was thought at one time, although its ESR spectrum is nearly identical to that of the DMPO/superoxide radical adduct. Similarly, based on their MS/MS spectra, we verified that the second adducts (a(N) = 14.86 G and a(H)(beta) = 16.06 G in the reaction system containing t-butyl hydroperoxide and a(N) = 14.60 G and a(H)(beta) = 15.61 G in the reaction mixture containing cumene hydroperoxide), previously assigned as DMPO adducts of t-butyloxyl and cumyloxyl radical, were indeed from trapping t-butyloxyl and cumyloxyl radicals, respectively.

Rapid mtDNA deletion by oxidants in rat liver mitochondria after hemin exposure

The amounts of superoxide and hydrogen peroxide generated by mitochondria under physiological conditions can be enhanced by cellular stress. This study tested the hypothesis that the response to hemin-induced stress, which includes heme oxygenase-1 (HO-1) induction, predisposes to oxidative damage of mitochondrial DNA (mtDNA). Hepatic mitochondria from control, hemin-, and CO-exposed rats were incubated with tert-butyl hydroperoxide (tert-BH) or the NO donor 1,2,3,4-oxatriazolium, 5-amino-3- (3,4-dichlorophenyl)-chloride (GEA 3162). Mitochondrial total and oxidized glutathione (GSH and GSSG), total and free iron, and 8-oxo-7, 8-dihydro-2' deoxyguanosine (8-OHdG) were determined with and without oxidants. As expected, oxidation by tert-BH induced significant GSH depletion and increased amounts of free iron and 8-OhdG. Oxidant exposure rapidly produced a large mtDNA deletion involving the coding regions for cytochrome c oxidase (COX 1) and NADH dehydrogenase (ND1 and ND2). Hemin and CO greatly exacerbated susceptibility to the deletion of mtDNA by tert-BH, and this was attenuated by preincubation with GSH methyl ester. Analysis of mitochondria-associated proteins Bax and Bcl-xl in hemin- and CO-exposed rats showed significant responses, revealing interactions with apoptotic pathways. Thus, hemin-induced mitochondrial events sensitize a specific region of the mitochondrial genome to deletion, which is related to depletion of GSH and is not explained by effects of CO. This mtDNA damage is associated with altered expression of mitochondrial cell death proteins, thereby suggesting a novel mechanism for systemic or environmental pro-oxidants to influence apoptosis.

Cytochrome c catalyses the formation of pentyl radical and octanoic acid radical from linoleic acid hydroperoxide

A reaction of 13-hydroperoxide octadecadienoic acid (13-HPODE) with cytochrome c was analysed using ESR, HPLC-ESR and HPLC-ESR-MS by the combined use of the spin-trapping technique. The ESR, HPLC-ESR and HPLC-ESR-MS analyses showed that cytochrome c catalyses formation of pentyl and octanoic acid radicals from 13-HPODE. On the other hand, only the alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone/octanoic acid radical adduct was detected in the elution profile of HPLC-ESR for a mixture of 13-HPODE with haematin, indicating that haematin catalyses the formation of octanoic acid radical. In addition, the reaction of 13-HPODE with cytochrome c was inhibited by chlorogenic acid, caffeic acid and ferulic acid via two possible mechanisms, i.e. reducing cytochrome c (chlorogenic acid and caffeic acid) and scavenging the radical intermediates (chlorogenic acid, caffeic acid and ferulic acid).

Modulatory effect of cyclosporin A on tert-butyl hydroperoxide-induced oxidative damage in hepatocytes

In the present work, we followed an in vitro protective action of cyclosporin A (CsA) against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage in hepatocytes. Various parameters (cell viability, cytosolic calcium level, rhodamine 123 accumulation as indicator of mitochondrial membrane potential and alanine-aminotransferase leakage from cells) were measured as an index of cytotoxicity. Tert-butyl hydroperoxide (1 mM) significantly increased cytosolic Ca2+ and affected mitochondrial membrane potential. Pretreatment with cyclosporin A (0.5 microM) reduced t-BHP-induced cytosolic Ca2+ increase and ALT (alanine-aminotransferase) leakage, but had no protective effect on t-BHP-induced changes of mitochondrial membrane potential. Our data thus suggest that the mechanism of cytoprotection of CsA on the cytosolic Ca2+ changes and ALT leakage induced by t-BHP, does not directly correlate with protection of t-BHP-induced changes of mitochondrial membrane potential.

trans-resveratrol protects embryonic mesencephalic cells from tert-butyl hydroperoxide: electron paramagnetic resonance spin trapping evidence for a radical scavenging mechanism

In recent years, the antioxidant and other pharmacological properties of resveratrol, a natural product present in grapes and wine, have attracted considerable interest from the biomedical research community. In an examination of the potential neuroprotective properties of the compound, we have investigated the ability of resveratrol to protect rat embryonic mesencephalic tissue, rich in dopaminergic neurones, from the prooxidant tert-butyl hydroperoxide. Using the electron paramagnetic resonance (EPR) spin-trapping technique, the main radicals detected in cell suspensions were the tert-butoxyl radical and the methyl radical, indicating the one-electron reduction of the peroxide followed by a beta-scission reaction. The appearance of EPR signals from the trapped radicals preceded the onset of cytotoxicity, which was almost exclusively necrotic in nature. The inclusion of resveratrol in incubations resulted in the marked protection of cells from tert-butyl hydroperoxide. In parallel spin-trapping experiments, we were able to demonstrate the scavenging of radicals by resveratrol, which involved direct competition between resveratrol and the spin trap for reaction with the radicals. To our knowledge, this is the first example in which cytoprotection by resveratrol has been demonstrated by EPR spin-trapping competition kinetics to be due to its scavenging of the radicals responsible for the toxicity of a prooxidant.

Modifications in heme iron of free and vesicle bound cytochrome c by tert-butyl hydroperoxide: a magnetic circular dichroism and electron paramagnetic resonance investigation

To characterize changes to the heme and the influence of membrane lipids in the reaction of cytochrome c with peroxides, we studied the reaction of cytochrome c with tert-butyl hydroperoxide (tert-BuOOH) by magnetic circular dichroism (MCD) and direct electron paramagnetic resonance (EPR) in the presence and absence of different liposomes. Direct low-temperature (11 degrees K) EPR analysis of the cytochrome c heme iron on exposure to tert-BuOOH shows a gradual (180 s) conversion of the low-spin form to a high-spin Fe(III) species of rhombic symmetry (g = 4.3), with disappearance of a prior peroxyl radical signal (g(o) = 2.014). The conversion to high spin precedes Soret band bleaching, observable by UV/Vis spectroscopy and by magnetic circular dichroism (MCD) at room temperature, that indicates loss of iron coordination by the porphyrin ring. The presence of cardiolipin-containing liposomes delayed formation of the peroxyl radical and conversion to high-spin iron, while dicetylphosphate (DCP) liposomes accelerated these changes. Correspondingly, bleaching of cytochrome c by tert-BuOOH at room temperature was accelerated by several negatively charged liposome preparations, and inhibited by mitochondrial-mimetic phosphatidylcholinephosphatidylethanolaminecardiolipin (PCPECL) liposomes. Concomitant with bleaching, spin-trapping measurements with 5,5-dimethyl-1-pyroline-N-oxide showed that while the relative production of peroxyl, alkoxyl, and alkyl radicals was unaffected by DCP liposomes, PCPECL liposomes decreased the spin-trapped alkoxyl radical signal by 50%. The EPR results show that the primary initial change on exposure of cytochrome c to tert-BuOOH is a change to a high-spin Fe(III) species, and together with MCD measurements show that unsaturated cardiolipin-containing lipid membranes influence the interaction of tert-BuOOH with cytochrome c heme iron, to alter radical production and decrease damage to the cytochrome.

In the neuronal cell line SH-SY5Y, oxidative stress-induced free radical overproduction causes cell death without any participation of intracellular Ca(2+) increase

Adding the membrane-permeant oxidant tert-butylhydroperoxide (t-BOOH) to the incubation medium, in SH-SY5Y human neuroblastoma cells, induced a marked and progressive concentration-dependent (300, 500 and 1000 microM) increase of free radical production, as evaluated by the fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) and of the intracellular Ca(2+) ion concentrations [Ca(2+)](i). The removal of extracellular Ca(2+) ions did not prevent t-BOOH-induced [Ca(2+)](i) elevation, whereas the intracellular Ca(2+) ion chelator 1,2-bis(o-aminophenoxy) ethane-N,N, N',N'-tetraacetic acid (BAPTA) (10 microM) was shown to be effective. Both t-BOOH-induced free radical formation and the [Ca(2+)](i) increase were completely prevented by the peroxyl scavenger alpha-tocopherol (50 microM). t-BOOH induced a time-dependent SH-SY5Y cell injury, monitored by a 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay (approximately 25% at 1 h, 50% at 3 h, 80% at 5 h) and by fluorescein diacetate (FDA)-propidium iodide (PI) fluorescent staining. The entity of t-BOOH-induced cell damage was the same both in the absence and in the presence of the intracellular Ca(2+) ion chelator BAPTA. By contrast, the peroxyl scavenger alpha-tocopherol (50 microM) completely prevented cell injury due to oxidative stress. Finally, superoxide dismutase (SOD) (500 ng/ml) caused a 30% reduction of t-BOOH-induced 2', 7'-dichlorofluorescein (DCF) fluorescence, whereas it did not modify the extent of cell injury produced by the oxidant. Collectively, the results of the present study demonstrated that in SH-SY5Y human neuroblastoma cells, the rise of [Ca(2+)](i) which occurs during oxidative stress is not involved in cell injury. Therefore, oxidative stress-induced cell death may be exclusively attributed to free radical overproduction.

Antioxidant effect of dipyridamole and its derivative RA-25 in mitochondria: correlation of activity and location in the membrane

Dipyridamole (DIP), a coronary vasodilator, presents coactivator activity for a number of antitumor drugs as well as antioxidant activity in membrane systems. DIP and derivatives interact with membrane systems such as micelles, phospholipid monolayers and vesicles. The antioxidant effect of DIP and several derivatives upon iron-induced lipoperoxidation on mitochondria has been reported and a good correlation between the hydrophobicity and their protective effect was found (M.F. Nepomuceno et al., Free Radic. Biol. Med., 23 (1997) 1046-1054). In the present work an effort is made to better understand the role of DIP as inhibitor of Fe2+-induced lipid peroxidation in mitochondria. At low concentration, no significant effect on either state IV or state III respiration was found, discarding a possible direct interaction of DIP or RA-25 with the peripheral benzodiazepine receptor. The association constants for DIP and RA-25 in mitochondria were estimated, being 0.7 (mg/ml)-1 for DIP and 0.2 (mg/ml)-1 for RA-25. Oxygen consumption studies in the presence of FeSO4 showed that the antioxidant effect of DIP or RA-25 did not involved the initial step of Fe2+ oxidation. Our data strongly support the hypothesis that the antioxidant effect of both DIP and RA-25 is related to their partition in the lipid phase of the mitochondrial membrane and not to a specific interaction with membrane proteins. This protection may be due either to a direct inhibition of the propagation steps or a scavenger effect on the radicular species that would trigger the peroxidative process.

Mitochondrial damage induced by conditions of oxidative stress

Up to 2% of the oxygen consumed by the mitochondrial respiratory chain undergoes one electron reduction, typically by the semiquinone form of coenzyme Q, to generate the superoxide radical, and subsequently other reactive oxygen species such as hydrogen peroxide and the hydroxyl radical. Under conditions in which mitochondrial generation of reactive oxygen species is increased (such as in the presence of Ca2+ ions or when the mitochondrial antioxidant defense mechanisms are compromised), these reactive oxygen species may lead to irreversible damage of mitochondrial DNA, membrane lipids and proteins, resulting in mitochondrial dysfunction and ultimately cell death. The nature of this damage and the cellular conditions in which it occurs are discussed in this review article.

Recovery of cellular functions following oxidant injury

This study investigated the recovery of renal proximal tubule cellular (RPTC) functions following oxidant-induced sublethal injury. tert-Butylhydroperoxide (TBHP) treatment resulted in 24% cell death and loss 4 h following the exposure. The remaining sublethally injured RPTC proliferated, and monolayer DNA content returned to control values on day 4 following TBHP exposure. Basal oxygen consumption (Qo2) and ATP content in sublethally injured RPTC were decreased 64 and 63%, respectively, at 4 h and returned to control values on day 6. Net lactate consumption decreased 71% at 4 h and returned to control values on day 4. In contrast, net glutamine consumption increased 2.7-fold at 4 h and returned to control values on day 6. Ouabain-sensitive Qo2, Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) activity, and Na(+)-coupled glucose transport were inhibited 77, 88, and 83%, respectively, at 4 h and recovered to control values on day 6. These data show that 1) mitochondrial function, Na(+)-K(+)-ATPase activity, active Na+ transport, and Na(+)-coupled glucose transport are decreased in sublethally injured RPTC following oxidant exposure and are repaired over time; 2) monolayer regeneration precedes the recovery of mitochondrial and transport functions, and 3) sublethal injury and subsequent regeneration are associated with alterations in metabolic substrate utilization. These results suggest that oxidant-induced sublethal injury to RPTC may contribute to renal dysfunction and that RPTC can repair and regain cellular functions following oxidant injury.

Induction of free radicals in hepatocytes, mitochondria and microsomes of rats by ochratoxin A and its analogs

Oxidative damage may be one of the manifestations of cellular damage in the toxicity of ochratoxin A (OA). OA; its three natural analogs, OB, OC and O alpha; and three synthetic analogs, the ethyl amide of OA (OE-OA), O-methylated OA (OM-OA), and the lactone-opened OA (OP-OA) were used to study free radical generation in hepatocytes, mitochondria and microsomes from rats. Electron paramagnetic resonance spectroscopy (EPR) using alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN) as a spin trapping agent showed an enhanced free radical generation due to the addition of NADPH to the microsomes. An EPR signal was not observed in the mitochondria and hepatocyte samples when they were treated with a variety of agents. Addition of OM-OA together with NADPH and Fe3+ to the microsomes resulted in a strong EPR signal compared with the other analogs, whereas the signal could be quenched by the addition of catalase. OM-OA does not have a dissociable phenolate group and does not chelate Fe3+. The spin adduct hyperfine splitting constants indicated the presence of alpha-hydroxyethyl radicals resulting from generated hydroxyl radicals, which were trapped by 4-POBN. The results also suggested that the production of hydroxyl radicals by OA does not require a dissociable phenolate group or the prior formation of an OA-Fe complex.

Effect of butylhydroxytoluene and related compounds on permeability of the inner mitochondrial membrane

Mitochondrial inner membrane contains a latent pore (PTP) that when opened uncouples mitochondrial energy transduction and allows rapid equilibration of low-molecular-weight solutes between the matrix and exterior. Based on sensitivity of the PTP to well-known free radical scavenger butylhydroxytoluene (BHT), it has been proposed that increased steady-state level of oxygen radicals, and subsequent radical attack of proteins and lipids, is a central event in activation of this pore (Novgorodov et al., J. Bioenerg. Biomembr. 19, 191-202, 1987; Carbonera and Azzone, Biochim. Biophys. Acta 943, 245-255, 1988). Present studies revealed that DBT, a derivative of BHT devoid of radical scavenging activity, exerts an analogous effect on the permeability of the inner membrane. Inhibition of the Ca2+-induced PTP opening is essentially complete at dose range of 50-60 nmol/mg protein with IC50 values of about 32 and 23 nmol/mg protein for DBT and BHT, respectively. Electron microscopy and osmotic experiments utilizing polyethylene glycols with different Stokes radii showed that the apparent lack of inhibition seen at high concentrations of these compounds results from cyclosporin A- and Ca2+-insensitive pore formation in the inner membrane. Experiments employing antioxidants with similar structure but dissimilar hydrophobicity provided evidence for localization of the antioxidant binding sites within the hydrophobic zone of the inner membrane or in the matrix space. The data obtained do not refute the notion that oxygen radicals modulate the PTP, but rather indicate that BHT operates independently of its free radical scavenging activity. Overall, the sensitivity to BHT and other antioxidants is not always a reliable criterion for the involvement of free radical reactions in the processes under study.

Influence of the redox state of pyridine nucleotides on mitochondrial sulfhydryl groups and permeability transition

This work addresses a correlation between the redox state of pyridine nucleotides and that of sulfhydryl groups of the mitochondrial membranes. Several major observations emerge: (1) Conditions leading to an oxidation of the pyridine nucleotides such as incubation with tert-butyl hydroperoxide or acetoacetate determine a decrease of total mitochondrial sulfhydryl groups. Glutathione does not follow the same pattern since it decreases in the presence of tert-butyl hydroperoxide but not in the presence of acetoacetate. In addition, only in the presence of tert-butyl hydroperoxide is the decrease of sulfhydryl groups concomitant with a membrane protein polymerization, observed by polyacrylamide gel electrophoresis. (2) Under all conditions tested, the oxidation of sulfhydryl groups is further stimulated by the presence of calcium and phosphate ions. (3) Respiratory substrates, which prevent the swelling of mitochondria, also partially prevent the decrease of sulfhydryl groups.

Antioxidant reactions of vitamin E in the perfused rat liver: product distribution and effect of dietary vitamin E supplementation

We have investigated the relationship between vitamin E (alpha-tocopherol, TH) oxidation and antioxidant protection in a perfused rat liver model. Perfusion of a male Sprague-Dawley rat liver with 2 mM tert-butylhydroperoxide (t-BuOOH) for 10 min resulted in lipid peroxidation and metabolic changes reflecting oxidative stress. Mitochondria isolated from the liver exhibited increases in state 3 and state 4 respiration and a decline in the respiratory control ratio. In livers from rats given supplementary vitamin E in the diet, TH content was 7- to 10-fold higher than in controls and lipid peroxidation and metabolic changes induced by t-BuOOH were decreased. In mitochondria from these vitamin E-supplemented livers, the t-BuOOH-induced increase in state 4 respiration was reduced and the respiratory control ratio was maintained. In livers from unsupplemented rats, t-BuOOH induced oxidation of TH to alpha-tocopherolquinone, alpha-tocopherolhydroquinone, 2,3-epoxy-alpha-tocopherolquinone, and 5,6-epoxy-alpha-tocopherolquinone, as determined by gas chromatography-mass spectrometry analysis. Yields of these products were approximately doubled by treatment of samples with dilute acid, which indicated the presence of tocopherone and epoxytocopherone precursors. Oxidation of TH in vitamin E-supplemented livers yielded the same products and the relative extent of TH oxidation appeared similar to that in unsupplemented livers. In livers from both unsupplemented and vitamin E-supplemented animals, the distribution of oxidation products was similar in whole liver and isolated mitochondria. These data provide the first simultaneous documentation of TH antioxidant reactions and antioxidant effects in an intact organ system during oxidative stress.

Inhibitory effect of dipyridamole and its derivatives on lipid peroxidation in mitochondria

Dipyridamole (DIP), 2,6-bis(diethanolamino)-4,8-dipiperidino-[5,4-d] pyrimidine, is a coronary vasodilator widely used in clinics. It has also been reported to have coactivator activity for a number of antitumour drugs and antioxidant activity in membrane systems. In recent years we have been studying the spectroscopic properties of this drug and several of its derivatives as well as their interaction with charged micelles and phospholipid monolayers. A strong interaction of DIP and DIP derivatives with these model membrane systems and a dependence of the strength of the interaction upon the chemical structure of the DIP derivative was observed. Here, the antioxidant effect of DIP and the derivatives, RA14, RA47, and RA25, was compared. We observed that although it strongly inhibits the iron-induced lipoperoxidation on mitochondria (IC50 = 1 microM), it shows no protection against an organic oxidant, cumene hydroperoxide. The order of hydrophobicity of the DIP derivatives, DIP > RA14 > RA47 > RA25, correlates very well with both the values of the association constants of these derivatives to micelles, their localization in the micelles, and phospholipid films and their antioxidant effect on mitochondria. So, a very good correlation of the structure of the drug in regarded to the nature of its substituents with the biological activity is observed. Essentially the same result was observed either measuring the lipid peroxidation or the membrane fluidity by ESR, suggesting that the effect of DIP and DIP derivatives is probably associated to their binding to the lipid bilayer and not to interaction with membrane proteins.

Antioxidant N-acetyl-cysteine increasing cell adhesion capability could facilitate the biocompatibility processes

Cell adhesion plays an important role in several cell processes and functions, including differentiation, proliferation and death. An important role for cell attachment to medical devices in biocompatibility studies has also been hypothesized. In this paper we report that the use of the antioxidant drug N-acetyl-cysteine is capable of increasing the adhesion properties of epithelial cells in culture. This is associated with a modification of specific cytoskeletal element assembly, such as microfilament system molecules. In contrast, no quantitative alterations in the expression of certain surface receptors for extracellular matrix molecules, such as VLA2, VLA3 and VLA6, are found. These data seem to indicate that intracellular oxidative balance, in particular of thiol groups, could play a key role in the cell adhesion properties and that N-acetyl-cysteine treatment, acting as 'thiol supply', could be of importance in several circumstances, including biocompatibility of medical devices.

tBHP induced in vitro swelling of rat liver mitochondria

Tert-butyl hydroperoxide induced swelling of freshly isolated rat liver mitochondria was inhibited by butylated hydroxytoluene, butylated hydroxyanisole and alpha-tocopherol by acting at the initial phase. EDTA was more effective than EGTA in reducing the initial swelling and so were desferal and bipyrridyl. Spermine, an allosteric activator of calcium uptake, enhanced swelling whereas lanthanum and ruthenium red, the Ca2+ uniport blockers, reduced it. Inhibition of phospholipase A2 by dibucaine and Ca2+ activated proteases by antipain and leupeptin also reduced t-BHP induced swelling. The data indicate that peroxidative mitochondrial swelling involves an iron mediated initial rapid phase and a subsequent calcium dependent propagation phase.

Oxidative DNA damage by t-butyl hydroperoxide causes DNA single strand breaks which is not linked to cell lysis. A mechanistic study in freshly isolated rat hepatocytes

In rat hepatocytes, DNA damage by t-butyl hydroperoxide (tBOOH) was measured by using the fluorimetric analysis of alkaline DNA unwinding. The electrophoretic profile of genomic DNA suggests single rather than double DNA strand breaks formation. Oxidative DNA modifications, measured as increased 8-hydroxy-deoxyguanosine content, were not detected. Lysis of hepatocytes and DNA strand breaks induced by tBOOH did not correlate, indicating that both processes are not interconnected. Since o-phenanthroline prevents against tBOOH-mediated effects on both DNA and membrane integrity, we discussed about a putative role of iron.

Detection of free radicals by microdialysis/spin trapping EPR following focal cerebral ischemia-reperfusion and a cautionary note on the stability of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)

We have examined free radical production in a rat model of focal cerebral ischemia using microdialysis coupled with EPR analysis. A microdialysis probe was inserted 2 mm into the cerebral cortex, supplied by the right middle cerebral artery (MCA), and after a 2-hour washout period with artificial cerebral spinal fluid (ACSF), the perfusate solution was changed to ACSF containing the spin trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). No free radicals were detected by DMPO during the pre-ischemia period. Both common carotid arteries and the right MCA were then ligated for 90 minutes. Microdialysate collected every 15 min during the ischemic period demonstrated predominantly superoxide or peroxyl radical production. After release of the occlusive sutures, hydroxyl radical became apparent initially, then thiyl and carbon centered radicals appeared later in samples collected every 15 min for two hours following cortical reperfusion. Careful studies on the purification and stability of DMPO solution were performed to circumvent artifacts and spurious signals.

The antioxidant N-acetyl-cysteine protects cultured epithelial cells from menadione-induced cytopathology

The effects of the antioxidant N-acetyl-cysteine (NAC) were assessed after short term exposure of A431 epithelial cells. The drug was able to protect, at least partially, the cells from the oxidative stress induced by the quinone menadione. In particular, the oxidizing agent-induced cell rounding and detachment from the substrate were strongly impaired by pre-exposure to the compound. The mechanism of such an effect seems to be ascribable to a target effect of the drug on the adhesion properties of the cells. In fact, a modification of morphological features of NAC-exposed cells and of their ability to adhere to different coated substrates was found. These changes resulted in a significant improvement of the A431 tumor cell adhesion pattern which was associated with a noticeable rearrangement of some cytoskeletal components, mainly of the microfilament system. These data add new importance to the subcellular activity of NAC and seem to indicate that the redox status of the cells, i.e. the intracellular balance between proxidants and antioxidants, could also play a role in their adhesive properties.

Permeabilization of the inner mitochondrial membrane by Ca2+ ions is stimulated by t-butyl hydroperoxide and mediated by reactive oxygen species generated by mitochondria

The extent of swelling undergone by deenergized mitochondria incubated in KCl/sucrose medium in the presence of Ca2+ alone or Ca2+ and t-butyl hydroperoxide decreases by decreasing molecular oxygen concentration in the reaction medium; under anaerobiosis no swelling occurs. This swelling is also inhibited by the presence of exogenous catalase or by the Fe2+ chelator o-phenanthroline in a time-dependent manner. The production of protein thiol cross-linking that leads to the formation of protein aggregates induced by Ca2+ and t-butyl hydroperoxide does not occur when mitochondria are incubated in anaerobic medium or in the presence of o-phenanthroline. In addition, it is also shown that the yield of stable methyl radical adducts, obtained from rat liver mitochondria treated with t-butyl hydroperoxide and the spin trap DMPO, is reduced by addition of EGTA and increases by addition of Ca2+ ions. These data support the hypothesis that Ca2+ ions stimulate electron leakage from the respiratory chain, increasing the mitochondrial production of reactive oxygen species.

Mitochondrial metabolism of a hydroperoxide to free radicals in human endothelial cells: an electron spin resonance spin-trapping investigation

Oxidative damage to the vascular endothelium may be an important event in the promotion of atherosclerosis. Several lines of evidence suggest that lipid hydroperoxides may be responsible for the induction of such damage. Hydroperoxides cause loss of endothelial cell integrity, increase the permeability of the endothelium to macromolecules, and compromise its ability to control vascular tone via the secretion of vasoactive molecules in response to receptor stimulation. The molecular mechanisms responsible for these effects are, however, poorly understood. In this paper, we describe an e.s.r. spin-trapping investigation into the metabolism of the model hydroperoxide compound tert-butylhydroperoxide to reactive free radicals in intact human endothelial cells. The hydroperoxide is shown to undergo a single electron reduction to form free radicals. Experiments with metabolic poisons indicate that the mitochondrial electron-transport chain is the source of electrons for this reduction. The metal-ion-chelating agent desferrioxamine was found to prevent cell killing by tert-butylhydroperoxide, but did not affect free radical formation, suggesting that free metal ions may serve to promote free-radical chain reactions involved in cell killing following the initial conversion of the hydroperoxide to free radicals by mitochondria. These processes may well be responsible for many of the reported effects of hydroperoxides on endothelial cell integrity and function.

Different susceptibilities to cell death induced by t-butylhydroperoxide could depend upon cell histotype-associated growth features

The effects of the oxidizing agent t-butylhydroperoxide (t-BHP) were investigated on three human cell lines of different origin and growth features (A431 epithelial cells, ADF astrocytoma cells and U937 leukemic cells) using electron microscopy and electron paramagnetic resonance spectroscopy. The results indicate that important biophysical and ultrastructural modifications are induced in the plasma and mitochondrial membranes of these cells and that these changes can ultimately lead to cell death. In addition, the cell cytoskeleton also appears to be a target of hydroperoxide-mediated stress. In particular, all three cell types undergo cytoskeletal alterations leading to surface blebbing, a typical characteristic of cell damage. However, the timing and extent of this damage as well as that occurring at the mitochondrial and plasma membrane levels seems to be different: cells with weak (ADF) or absent (U937) cell-to-cell and cell-substrate contacts and a poorly developed cytoskeleton appear to be more susceptible than other cell types (e.g., A431) to t-BHP-mediated injury. These diverse cell susceptibilites to hydroperoxide-mediated oxidative stress could thus depend upon cell histotype-associated growth features.

Direct detection of radical generation in rat liver nuclei on treatment with tumour-promoting hydroperoxides and related compounds

EPR spin trapping has been employed to directly detect radical production in isolated rat liver nuclei on exposure to a variety of hydroperoxides and related compounds which are known, or suspect, tumour promoters. The hydroperoxides, in the absence of reducing equivalents, undergo oxidative cleavage, generating peroxyl radicals. In the presence of NADPH (and to a lesser extent NADH) reductive cleavage of the O-O bond generates alkoxyl radicals. These radicals undergo subsequent rearrangements and reactions (dependent on the structure of the alkoxyl radical), generating carbon-centred radicals. Acyl peroxides and peracids appear to undergo only reductive cleavage of the O-O bond. With peracids this cleavage can generate aryl carboxyl (RCO2.) or hydroxyl radicals (HO.); with acyl peroxides, aryl carboxyl radicals are formed and, in the case of t-butyl peroxybenzoate, alkoxyl radicals (RO.). The radicals detected with each peroxide are similar in type to those detected in the rat liver microsomal fraction, although the extent of radical production is lower. The subsequent reactions of the initially generated radicals are similar to those determined in homogeneous chemical systems, suggesting that they are in free solution. Experiments with NADPH/NADH, heat denaturation of the nuclei and various inhibitors suggest that radical generation is an enzymatic process catalysed by haemoproteins, in particular cytochrome P-450, and that NADPH/cytochrome P-450 reductase is involved in the reductive cleavage of the O-O bond. The generation of these radicals by the rat liver nuclear fraction is potentially highly damaging for the cell due to the proximity of the generating source to DNA. Several previous studies have shown that some of the radicals detected in this study, such as aryl carboxyl and aryl radicals, can damage DNA, via various reactions which result in the generation of strand breaks and adducts to DNA bases: these processes are suggested to play an important role in the tumour promoting activity of these hydroperoxides and related compounds.