Tert-Butyl Hydroperoxide Stimulated Apoptosis Independent of Prostaglandin E2 and IL-6 in the HTR-8/SVneo Human Placental Cell Line.

Significant gaps exist in our knowledge of how cellular redox status, sometimes referred to as oxidative stress, impacts placental trophoblasts. The present study used tert-butyl hydroperoxide (TBHP) as a known generator of reactive oxygen species (ROS) in the extravillous trophoblast cell line HTR-8/SVneo to examine the role of cellular redox disruption of prostaglandin E2 (PGE2) and the cytokine IL-6 in cell death. Cells were exposed to 0, 12.5, 25, or 50 µM TBHP for 4, 8, and 24 h to ascertain effects on cell viability, caspase 3/7 activity, PGE2 release, PTGS2 mRNA expression, and IL-6 release. Experiments with inhibitors included the cyclooxygenase inhibitor indomethacin, mitogen-activated protein kinase inhibitors (PD169316, U0126, or SP600125), or treatments to counter expected consequences of TBHP-stimulated generation of ROS (deferoxamine [DFO], butylated hydroxyanisole [BHA], and N,N'-diphenyl-1,4-phenylenediamine [DPPD]) using 24-h exposure to 50 µM TBHP. Cell viability, measured by ATP content, decreased 24% relative to controls with a 24-h exposure to 50 µM TBHP, but not at lower TBHP concentrations nor at earlier time points. Exposure to 50 µM TBHP increased caspase 3/7 activity, an indicator of apoptosis, after 8 and 24 h. Antioxidant treatment markedly reduced TBHP-stimulated caspase 3/7 activity, PGE2 release, and IL-6 release. TBHP-stimulated IL-6 release was blocked by PD169316 but unaltered by indomethacin. These data suggest that TBHP-stimulated IL-6 release and caspase 3/7 activation were independent of PGE2 yet were interrupted by treatments with known antioxidant properties, providing new insight into relationships between PGE2, IL-6, and apoptosis under conditions of chemically induced cellular oxidation.

Generic synthesis of small-sized hollow mesoporous organosilica nanoparticles for oxygen-independent X-ray-activated synergistic therapy.

The success of radiotherapy relies on tumor-specific delivery of radiosensitizers to attenuate hypoxia resistance. Here we report an ammonia-assisted hot water etching strategy for the generic synthesis of a library of small-sized (sub-50 nm) hollow mesoporous organosilica nanoparticles (HMONs) with mono, double, triple, and even quadruple framework hybridization of diverse organic moieties by changing only the introduced bissilylated organosilica precursors. The biodegradable thioether-hybridized HMONs are chosen for efficient co-delivery of tert-butyl hydroperoxide (TBHP) and iron pentacarbonyl (Fe(CO)5). Distinct from conventional RT, radiodynamic therapy (RDT) is developed by taking advantage of X-ray-activated peroxy bond cleavage within TBHP to generate •OH, which can further attack Fe(CO)5 to release CO molecules for gas therapy. Detailed in vitro and in vivo studies reveal the X-ray-activated cascaded release of •OH and CO molecules from TBHP/Fe(CO)5 co-loaded PEGylated HMONs without reliance on oxygen, which brings about remarkable destructive effects against both normoxic and hypoxic cancers.

Cell-cell contacts protect against t-BuOOH-induced cellular damage and ferroptosis in vitro.

Ferroptosis is a recently discovered pathway of regulated necrosis dependent on iron and lipid peroxidation. It has gained broad attention since it is a promising approach to overcome resistance to apoptosis in cancer chemotherapy. We have recently identified tertiary-butyl hydroperoxide (t-BuOOH) as a novel inducer of ferroptosis. t-BuOOH is a widely used compound to induce oxidative stress in vitro. t-BuOOH induces lipid peroxidation and consequently ferroptosis in murine and human cell lines. t-BuOOH additionally results in a loss of mitochondrial membrane potential, formation of DNA double-strand breaks, and replication block. Here, we specifically address the question whether cell-cell contacts regulate t-BuOOH-induced ferroptosis and cellular damage. To this end, murine NIH3T3 or human HaCaT cells were seeded to confluence, but below their saturation density to allow the establishment of cell-cell contacts without inducing quiescence. Cells were then treated with t-BuOOH (50 or 200 µM, respectively). We revealed that cell-cell contacts reduce basal and t-BuOOH-triggered lipid peroxidation and consequently block ferroptosis. Similar results were obtained with the specific ferroptosis inducer erastin. Cell-cell contacts further protect against t-BuOOH-induced loss of mitochondrial membrane potential, and formation of DNA double-strand breaks. Interestingly, cell-cell contacts failed to prevent t-BuOOH-mediated replication block or formation of the oxidative base lesion 8-oxo-dG. Since evidence of protection against cell death was both (i) observed after treatment with hydrogen peroxide, methyl methanesulfonate or UV-C, and (ii) seen in several cell lines, we conclude that protection by cell-cell contacts is a widespread phenomenon. The impact of cell-cell contacts on toxicity might have important implications in cancer chemotherapy.

Attenuation of Oxidative Stress in HEK 293 Cells by the TCM Constituents Schisanhenol, Baicalein, Resveratrol or Crocetin and Two Defined Mixtures.

PURPOSE: Our working hypothesis is that single bioactive phytochemicals with antioxidant properties that are important constituents of Traditional Chinese Medicine (TCM) and their defined mixtures have potential as chemoprotective agents for chronic conditions characterized by oxidative and nitrosative stress, including Alzheimer's. Here we evaluate the ability of baicalein, crocetin, trans-resveratrol or schisanhenol and two defined mixtures of these TCM phytochemicals to attenuate the toxicity resulting from exposure to cell permeant t-butyl hydroperoxide (tBPH) in wild-type and bioengineered (to express choline acetyltransferase) HEK 293 cells. METHODS: Endpoints of tBHP-initiated oxidative and nitrosative stress in both types of HEK 293 cells and its attenuation by TCM constituents and mixtures included cytotoxicity (LDH release); depletion of intracellular glutathione (GSH); formation of S-glutathionylated proteins; oxidative changes to the disulfide proteome; and real-time changes in intracellular redox status. RESULTS: At low µM concentrations, each of the TCM constituents and mixtures effectively attenuated intracellular toxicity due to exposure of HEK 293 cells to 50 or 250 µM tBHP for 30 min to 3 h. Confocal microscopy of HEK 293 cells transfected with mutated green fluorescent protein (roGFP2) showed effective attenuation of tBHP oxidation by baicalein in real time. Three redox-regulated proteins prominent in the disulfide proteome of HEK 293 cells were identified by MALDI-TOF mass spectrometry. CONCLUSIONS: We conclude that single TCM chemicals and their simple mixtures have potential for use in adjunct chemoprotective therapy. Advantages of mixtures compared to single TCM constituents include the ability to combine compounds with varying molecular mechanisms of cytoprotection for enhanced biological activity; and to combine chemicals with complementary pharmacokinetic properties to increase half-life and prolong activity in vivo. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Critical role of peroxiredoxin 6 in the repair of peroxidized cell membranes following oxidative stress.

Phospholipids are a major structural component of all cell membranes; their peroxidation represents a severe threat to cellular integrity and their repair is important to prevent cell death. Peroxiredoxin 6 (Prdx6), a protein with both GSH peroxidase and phospholipase A(2) (PLA(2)) activity, plays a critical role in antioxidant defense of the lung and other organs. We investigated the role of Prdx6 in the repair of peroxidized cell membranes in pulmonary microvascular endothelial cells (PMVEC) and isolated mouse lungs treated with tert-butyl hydroperoxide and lungs from mice exposed to hyperoxia (100% O(2)). Lipid peroxidation was evaluated by measurement of thiobarbituric acid reactive substances, oxidation of diphenyl-1-pyrenylphosphine, or ferrous xylenol orange assay. The exposure dose was varied to give a similar degree of lipid peroxidation at the end of exposure in the different models. Values for lipid peroxidation returned to control levels within 2 h after oxidant removal in wild-type PMVEC and perfused lungs but were unchanged in Pxdx6 null preparations. An intermediate degree of repair was observed with PMVEC and lungs that expressed only C47S or D140A mutant Prdx6; the former mutant does not have peroxidase activity, while the latter loses its PLA(2) activity. Prdx6 null mice showed markedly delayed recovery from lipid peroxidation during 20 h observation following exposure to hyperoxia. Thus, Prdx6 plays a critical role in the repair of peroxidized phospholipids in cell membranes and the recovery of lung cells from peroxidative stress; the peroxidase and PLA(2) activity each contribute to the recovery process.

Exploring the effects of tert-butylhydroperoxide induced liver injury using proteomic approach.

Tert-butyl hydroperoxide (t-BHP), an organic lipid hydroperoxide analog, has been demonstrated to exert pro-oxidant effects to evaluate mechanisms involving oxidative stress in hepatocyte cells and rat liver. Herein, we present an investigation of the event of molecular mechanism of t-BHP related acute liver injury. A proteomic approach was used to identify proteins which are differentially expressed in liver cells following t-BHP treatment and the mechanism of its action in apoptotic and endoplasmic reticulum stress pathways. Our results demonstrate that the t-BHP treatment of liver cells increased cell cytoxicity and apoptosis. t-BHP dose-dependent induction of cell apoptosis and stained liver sections relieved the acute rat liver injury were accompanied by sustained phosphorylation of JNK1/2 and p65. In addition, there were 13 differentially displayed proteins between the t-BHP-induced and untreated were assayed and validated in vivo. Furthermore, we demonstrated that t-BHP induced human Chang liver cell viability and apoptosis properties by up-regulating the levels of ETFA (electron transfer flavoprotein subunit alpha). This study demonstrated that there was an increase in the cellular levels of ETFA in the t-BHP induction in viability and apoptosis via the activation of JNK1/2 and NFκB signaling modules. NAC administration and shRNA ETFA conferred resistance to t-BHP-increased ETFA and CHOP expression via IRE1-alpha/TRAF2 complex formation, activation of JNK1/2 and p50. We concluded that the mechanism of t-BHP-induced an apoptosis cascade and endoplasmic reticulum stress in hepatocyte cells by up-regulation of ETFA, providing a new mechanism for liver injury.

The gap junction inhibitor 2-aminoethoxy-diphenyl-borate protects against acetaminophen hepatotoxicity by inhibiting cytochrome P450 enzymes and c-jun N-terminal kinase activation.

Acetaminophen (APAP) hepatotoxicity is the leading cause of acute liver failure in the US. Although many aspects of the mechanism are known, recent publications suggest that gap junctions composed of connexin32 function as critical intercellular communication channels which transfer cytotoxic mediators into neighboring hepatocytes and aggravate liver injury. However, these studies did not consider off-target effects of reagents used in these experiments, especially the gap junction inhibitor 2-aminoethoxy-diphenyl-borate (2-APB). In order to assess the mechanisms of protection of 2-APB in vivo, male C56Bl/6 mice were treated with 400 mg/kg APAP to cause extensive liver injury. This injury was prevented when animals were co-treated with 20 mg/kg 2-APB and was attenuated when 2-APB was administered 1.5 h after APAP. However, the protection was completely lost when 2-APB was given 4-6 h after APAP. Measurement of protein adducts and c-jun-N-terminal kinase (JNK) activation indicated that 2-APB reduced both protein binding and JNK activation, which correlated with hepatoprotection. Although some of the protection was due to the solvent dimethyl sulfoxide (DMSO), in vitro experiments clearly demonstrated that 2-APB directly inhibits cytochrome P450 activities. In addition, JNK activation induced by phorone and tert-butylhydroperoxide in vivo was inhibited by 2-APB. The effects against APAP toxicity in vivo were reproduced in primary cultured hepatocytes without use of DMSO and in the absence of functional gap junctions. We conclude that the protective effect of 2-APB was caused by inhibition of metabolic activation of APAP and inhibition of the JNK signaling pathway and not by blocking connexin32-based gap junctions.

Differential oxidative stress induction and lethality of rat embryos after maternal exposure to t-butyl hydroperoxide during postimplantation period.

In mammals, reactive oxygen species (ROS) are essential factors for cell proliferation, differentiation, and growth, notably during gestation, but are also potentially damaging agents. The present study describes the extent and pattern of oxidative stress (OS) induction in maternal milieu, placenta, and embryos of rats after in vivo exposure to sublethal doses of a well-known model prooxidant, such as t-butyl hydroperoxide (tbHP). tbHP administered (intraperitoneally) to pregnant rats on specific gestation days (GDs) (either GD(5-7) or GD(8-10)) at dosages of [one tenth the median lethal dose (LD(50)) and one fifth LD(50)/day) caused significant OS, as evident by enhancement of malondialdehyde (MDA) and ROS levels, depleted reduced glutathione levels and elevated protein carbonyl content in maternal liver and kidney. Further, tbHP treatment also caused significant oxidative impairments in placenta, whereas the weights were marginally increased. Further, tbHP treatment induced a higher incidence of embryonic lethality (4- to 6-fold higher than controls) and induced marked OS among GD(13) embryos, as evidenced by elevated MDA, ROS generation, altered redox status, and enzymatic antioxidant defenses, suggesting the vulnerability of embryos. Interestingly, incidence of embryonic mortality and degree of oxidative dysfunctions caused by tbHP treatment during GD(5-7) was relatively higher, compared with GD(8-10), suggesting differential susceptibility of embryos during the early postimplantation period. Based on these findings, it is hypothesized that critical windows during early gestation may account for the differential susceptibility of developing embryos to pro-oxidants and necessitate a better understanding of this embryonic response to pro-oxidant exposures.

Intra-arterial tert-Butyl-hydroperoxide infusion induces an exacerbated sensory response in the rat hind limb and is associated with an impaired tissue oxygen uptake.

The objective of this study was to investigate oxidative stress and oxygen extraction mechanisms in an animal model of continuous intra-arterial infusion of a free radical donor and in an in vitro model using isolated mitochondria. tert-Butyl-hydroperoxide (tert-BuOOH, 25 mM) was infused for 24 h in the left hind limb of rats to induce soft tissue damage (n = 8). After 7 days, we assessed local sensory response, tissue oxygen consumption, oxygen radicals, and antioxidant levels. In vitro mitochondrial function was measured after stimulation of isolated mitochondria of skeletal muscle cells with increasing doses of tert-BuOOH. tert-BuOOH infusion resulted in an increased skin temperature (p = 0.04), impaired function, and a significantly increased pain sensation (p = 0.03). Venous oxygen saturation levels (p = 0.01) and the antioxidant ceruloplasmin (p = 0.04) were increased. tert-BuOOH inhibited mitochondrial function in vitro. Induction of free radical formation in the rat hind limb results in an exacerbated sensory response and is associated with impaired oxygen extraction, which likely results from mitochondrial dysfunction caused by free radicals.

Thermal sensitization using induced oxidative stress decreases tumor growth in an in vivo model of hyperthermic intraperitoneal perfusion.

BACKGROUND: The purpose of this study was to extend our in vitro observations that induced oxidative stress under hyperthermic conditions decreases tumor cell growth into a preclinical murine model of hyperthermic perfusion. METHODS: A nude mouse model of colon cancer carcinomatosis with HT-29-Luc-D6 colon cancer cells was established, and tumor growth was measured by serial bioluminescent imaging. RESULTS: By means of a survival model of hyperthermic perfusion, we demonstrated that perfusion with normothermic saline decreased tumor growth compared with no perfusion controls, and tumor growth was further decreased with hyperthermic perfusion alone. The induction of oxidative stress with hydrogen peroxide in the perfusate at concentrations as high as 600 microM was well tolerated in this model of hyperthermic perfusion. Importantly, induced oxidative stress using hydrogen peroxide under hyperthermic conditions significantly decreased in vivo tumor cell growth compared with all other controls. CONCLUSIONS: On the basis of our observations, thermal sensitization through modulation of cellular oxidative stress may represent a novel approach to increase the efficacy of hyperthermia as an anticancer modality.

Stimulation of apical and basolateral VEGF-A and VEGF-C secretion by oxidative stress in polarized retinal pigment epithelial cells.

PURPOSE: To investigate whether oxidative stress modulates vascular endothelial growth factor (VEGF)-A and VEGF-C expression and polarized secretion in a human retinal pigment epithelium cell line (ARPE-19). METHODS: Long-term culture of ARPE-19 cells in Dulbecco's modified Eagle medium (DMEM)/F12 containing 1% fetal bovine serum (FBS) on transwell filters (12 mm or 6 mm, pore size 0.4 microm) was performed to produce polarized retinal pigment epithelium (RPE) monolayers. The integrity of polarized monolayer was established by measurement of transepithelial resistance (TER) and presence of tight junctions assessed by zonula occludens (ZO-1) and occludin expression and apical Na/K ATPase localization. Paracellular permeability was studied using radiolabeled mannitol. Confluent cells were treated with tertiary butyl hydrogen peroxide (tBH) for varying durations (0-5 h) and doses (50-200 microM). VEGF-A and -C expression was evaluated by western blot and quantitative RT-PCR, while secretion to the apical and basolateral surfaces was quantitated by ELISA. RESULTS: Polarity of ARPE-19 cells was verified by the localization of tight junction proteins, ZO-1 and its binding partner occludin by confocal microscopy as well as by localization of Na,K-ATPase at the apical surface. The TER in confluent ARPE-19 cells averaged 48.7+/-2.1 Omega. cm(2) and tBH treatment (0-5 h) did not alter TER significantly (46.9+/-1.9 Omega. cm(2); p>0.05 versus controls) or ZO-1 expression. Whole cell mRNA in nonpolarized ARPE-19 increased with tBH at 5 h both for VEGF-A and VEGF-C and the increase was significant (p<0.05 vs controls). A similar, maximal increase at 5 h tBH treatment was also observed for VEGF-A and VEGF-C cellular protein levels. The secretion of VEGF-A and VEGF-C in nonpolarized ARPE showed an increase with tBH exposure. The levels of secretion of VEGF-A and -C were significantly higher in polarized monolayers and were stimulated significantly with tBH at both apical and basolateral domains. The secretion of VEGF-A increased with 150 microM of tBH treatment as a function of time (1-5 h) with maximal increases at 5 h from 410 to 2080 pg/10(6) cells on the apical and 290 to 1680 pg/10(6) cells on basolateral domains. The pattern of VEGF-C secretion was similar. VEGF-A secretion was dose-dependent for the tBH range of 50-200 microM and apical secretion tended to be higher than basolateral secretion. CONCLUSIONS: Our data show that oxidative stress to RPE from tBH upregulates secretion of both VEGF-A and C. The secretion to the apical side was higher than that of basolateral side for VEGF-A and C. Given the role of VEGF in choroidal neovascularization, these data may be of value in understanding pathogenic mechanisms and designing antiangiogenic therapies.

Hypericum androsaemum infusion increases tert-butyl hydroperoxide-induced mice hepatotoxicity in vivo.

Increasing evidence regarding free radical generating agents indicates that the sustained production of high levels of reactive oxygen species (ROS) can cause hepatotoxicity. Being a short chain analog of lipid peroxide, tert-butyl hydroperoxide (t-BHP) is metabolized into free radical intermediates by cytochrome P450 in hepatocytes, which initiate lipid peroxidation, glutathione depletion and cell damage. The aim of the present study was to evaluate the putative protective effect of Hypericum androsaemum lyophilised infusion against t-BHP-induced mice hepatotoxicity in vivo, which has already been shown to be antioxidant in vitro. However, the results showed that the oral pretreatment with Hypericum androsaemum infusion (4, 20 and 100 mg/kg) for 4 days before a single intraperitoneal dose of t-BHP (1.8 mmol/kg) potentiated the t-BHP-induced hepatotoxicity. In fact, it was observed a potentiation in the depletion of total glutathione and reduced glutathione (GSH) contents and increase in oxidised glutathione (GSSG) level. Also the histopathological evaluation of the mice livers revealed that the infusion raised the incidence of liver lesions induced by t-BHP. These data do not corroborate any effect of Hypericum androsaemum infusion as hepatoprotector, but rather as a potentiator of hepatotoxicity in the present experimental conditions.

Evaluation of toxic/protective effects of the essential oil of Salvia officinalis on freshly isolated rat hepatocytes.

For this study the essential oil (EO) of sage (Salvia officinalis L.) was isolated from air-dried vegetative aerial parts of the plants by hydrodistillation and analysed by GC and GC-MS. A total yield of 12.07 mg of EO per g of plant dry mass was obtained and more than 50 compounds identified. The major compounds were cis-thujone (17.4%), alpha-humulene (13.3%), 1,8-cineole (12.7%), E-caryophyllene (8.5%) and borneol (8.3%). The EO fraction of sage tea was also isolated by partition with pentane and the respective components identified. The toxic and antioxidant protective effects of S. officinalis EO were evaluated on freshly isolated rat hepatocytes. Cell viability (LDH leakage), lipid peroxidation and glutathione status were measured in experiments undertaken with cells (suspensions of 1 x 10(6) cells per millilitre) exposed to EO alone (toxicity of the EO;t-BHP as positive control); and with cells exposed to EO and an oxidative compound (t-BHP) together (in EO protection evaluation; quercetin as positive control) for 30 min. The results show that the EO is not toxic when present at concentrations below 200 nl/ml; it was only at 2000 nl EO/ml that a significant LDH leakage and GSH decrease were observed indicating cell damage. In the range of concentrations tested, the EO did not show protective effects against t-BHP-induced toxicity.

Schisandrin B protects against tert-butylhydroperoxide induced cerebral toxicity by enhancing glutathione antioxidant status in mouse brain.

Schisandrin B (Sch B), a dibenzocyclooctadiene derivative isolated from Fructus Schisandrae, has been shown to produce antioxidant effect on rodent liver and heart. A mouse model of tert-butylhydroperoxide (t-BHP) induced cerebral toxicity was adopted for examining the antioxidant potential of Sch B in the brain. Intracerebroventricular injection of t-BHP caused a time-dependent increase in mortality rate in mice. The t-BHP toxicity was associated with an increase in the extent of cerebral lipid peroxidation and an impairment in cerebral glutathione antioxidant status, as evidenced by the abrupt decrease in reduced glutathione (GSH) level and the inhibition of Se-glutathione peroxidase activity at 5 min following t-BHP challenge. Sch B pretreatment (1 or 2 mmol/kg/day x 3) produced a dose-dependent protection against t-BHP induced mortality. The protection was associated with a decrease in the extent of lipid peroxidation and an enhancement in glutathione antioxidant status in brain tissue detectable at 5 min post t-BHP challenge, with the assessed biochemical parameters being returned to normal values at 60 min in Sch B pretreated mice at a dose of 2 mmol/kg. The ensemble of results suggests the antioxidant potential of Sch B pretreatment in protecting against cerebral oxidative stress.

T-butyl hydrogen peroxide increases the activities of the Maxi-K channels of rat brain.

In this study, we investigated the effects of tertiary-butyl hydrogen peroxide (tBHP) on the large-conductance Ca2+-activated K+ (Maxi-K) channel of rat brain using lipid bilayer. When tBHP was applied to the cytosolic side, the open probability (Po) of both fast- and slow-gating Maxi-K channels increased within 1 min in dose-dependent manner. tBHP effects did not reverse immediately, suggesting tBHP induces some chemical modification on the channel protein. From kinetic analysis of single channel data, the increase in the Po appears to be mainly due to shortening of closed dwell time in both types of the Maxi-K channels. 50 microM diamide, a sulfhydryl-specific oxidant, irreversibly decreased the Po. However, further addition of 7.3 mM tBHP still increased the Po, suggesting that tBHP does not share the target for oxidation with diamide.