The effect of some carbonyl compounds on rat liver glutathione levels

Glutathione-Depleting Nanomedicines for Synergistic Cancer Therapy

Cancer cells frequently exhibit resistance to various molecular and nanoscale drugs, which inevitably affects the drugs' therapeutic outcomes. Overexpression of glutathione (GSH) has been observed in many cancer cells, and solid evidence has corroborated the resulting tumor resistance to a variety of anticancer therapies, suggesting that this biochemical characteristic of cancer cells can be developed as a potential target for cancer treatments. The single treatment of GSH-depleting agents can potentiate the responses of the cancer cells to different cell death stimuli; therefore, as an adjunctive strategy, GSH depletion is usually combined with mainstream cancer therapies for enhancing the therapeutic outcomes. Propelled by the rapid development of nanotechnology, GSH-depleting agents can be readily constructed into anticancer nanomedicines, which have shown a steep rise over the past decade. Here, we review the common GSH-depleting nanomedicines which have been widely applied in synergistic cancer treatments in recent years. Some current challenges and future perspectives for GSH depletion-based cancer therapies are also presented. With the understanding of the structure-property relationship and action mechanisms of these biomaterials, we hope that the GSH-depleting nanotechnology will be further developed to realize more effective disease treatments and even achieve successful clinical translations.

Derived esterase activity in Drosophila sechellia contributes to evolved octanoic acid resistance

The dietary specialist fruit fly Drosophila sechellia has evolved resistance to the secondary defence compounds produced by the fruit of its host plant, Morinda citrifolia. The primary chemicals that contribute to lethality of M. citrifolia are the medium-chain fatty acids octanoic acid (OA) and hexanoic acid. At least five genomic regions contribute to this adaptation in D. sechellia and whereas the fine-mapped major effect locus for OA resistance on chromosome 3R has been thoroughly analysed, the remaining four genomic regions that contribute to toxin resistance remain uncharacterized. To begin to identify the genetic basis of toxin resistance in this species, we removed the function of well-known detoxification gene families to determine whether they contribute to toxin resistance. Previous work found that evolution of cytochrome P450 enzymatic activity or expression is not responsible for the OA resistance in D. sechellia. Here, we tested the role of the two other major detoxification gene families in resistance to Morinda fruit toxins - glutathione-S-transferases and esterases - through the use of the pesticide synergists diethyl maleate and tribufos that inhibit the function of these gene families. This work suggests that one or more esterase(s) contribute to evolved OA resistance in D. sechellia.

The effect of insecticide synergist treatment on genome-wide gene expression in a polyphagous pest

Synergists can counteract metabolic insecticide resistance by inhibiting detoxification enzymes or transporters. They are used in commercial formulations of insecticides, but are also frequently used in the elucidation of resistance mechanisms. However, the effect of synergists on genome-wide transcription in arthropods is poorly understood. In this study we used Illumina RNA-sequencing to investigate genome-wide transcriptional responses in an acaricide resistant strain of the spider mite Tetranychus urticae upon exposure to synergists such as S,S,S-tributyl phosphorotrithioate (DEF), diethyl maleate (DEM), piperonyl butoxide (PBO) and cyclosporin A (CsA). Exposure to PBO and DEF resulted in a broad transcriptional response and about one third of the differentially expressed genes (DEGs), including cytochrome P450 monooxygenases and UDP-glycosyltransferases, was shared between both treatments, suggesting common transcriptional regulation. Moreover, both DEF and PBO induced genes that are strongly implicated in acaricide resistance in the respective strain. In contrast, CsA treatment mainly resulted in downregulation of Major Facilitator Superfamily (MFS) genes, while DEGs of the DEM treatment were not significantly enriched for any GO-terms.

Action of bis(betachloroethyl)sulphide (BCES) on human epidermis reconstituted in culture: Morphological alterations and biochemical depletion of glutathione

Human keratinocyte cultures were treated with bis(betachloroethyl)sulphide (BCES), an alkylating and vesicant agent. At concentrations of 5 x 10(-4) to 5 x 10(-3)m, spontaneous detachment of the epithelium from the culture plate was observed, reproducing in vitro the cutaneous vesication observed in vivo. Progressive cellular alterations were shown with increasing concentrations of BCES (5 x 10(-5) to 5 x 10(-3)m). At low concentrations (5 x 10(-5)m), lesions of the nucleus, a significant target for BCES, were observed, along with lesions in the cytoplasmic organelles. An acute, dose-dependent depletion of cellular glutathione was observed, which occurred within 1 hr of treatment. Mechlorethamine, an analogue of BCES, induced at equivalent doses the same glutathione depletion and similar spontaneous detachment in vitro. We suggest that BCES, in addition to its genetic effects, acts by direct metabolic toxicity and induces glutathione depletion by direct conjugation. The lesions obtained in vitro reproduced those observed in vivo. Human keratinocyte cultures can be proposed as a good model for the study of the mechanisms of action of BCES.

Kinetics of ethylene and ethylene oxide in subcellular fractions of lungs and livers of male B6C3F1 mice and male fischer 344 rats and of human livers

Ethylene (ET) is metabolized in mammals to the carcinogenic ethylene oxide (EO). Although both gases are of high industrial relevance, only limited data exist on the toxicokinetics of ET in mice and of EO in humans. Metabolism of ET is related to cytochrome P450-dependent mono-oxygenase (CYP) and of EO to epoxide hydrolase (EH) and glutathione S-transferase (GST). Kinetics of ET metabolism to EO and of elimination of EO were investigated in headspace vessels containing incubations of subcellular fractions of mouse, rat, or human liver or of mouse or rat lung. CYP-associated metabolism of ET and GST-related metabolism of EO were found in microsomes and cytosol, respectively, of each species. EH-related metabolism of EO was not detectable in hepatic microsomes of rats and mice but obeyed saturation kinetics in hepatic microsomes of humans. In ET-exposed liver microsomes, metabolism of ET to EO followed Michaelis-Menten-like kinetics. Mean values of V(max) [nmol/(min·mg protein)] and of the apparent Michaelis constant (K(m) [mmol/l ET in microsomal suspension]) were 0.567 and 0.0093 (mouse), 0.401 and 0.031 (rat), and 0.219 and 0.013 (human). In lung microsomes, V(max) values were 0.073 (mouse) and 0.055 (rat). During ET exposure, the rate of EO production decreased rapidly. By modeling a suicide inhibition mechanism, rate constants for CYP-mediated catalysis and CYP inactivation were estimated. In liver cytosol, mean GST activities to EO expressed as V(max)/K(m) [μl/(min·mg protein)] were 27.90 (mouse), 5.30 (rat), and 1.14 (human). The parameters are most relevant for reducing uncertainties in the risk assessment of ET and EO.

The cytosolic ribonuclease inhibitor contributes to intracellular redox homeostasis

The hypothesis that the cytosolic RNase inhibitor (cRI) has a role in the protection of the cellular redox homeostasis was investigated testing the effects of oxidants and anti-oxidants on normal, primary endothelial HUVE cells, and malignant HeLa cells, before and after their engineering into cRI-deprived cells. We found that cRI plays an important, possibly a key, physiological role in the protection of cells from redox stress, as demonstrated by decreased GSH levels as well as increased oxidant-induced DNA damage in cRI deprived cells.

Methionine alters Na+,K+‐ATPase activity, lipid peroxidation and nonenzymatic antioxidant defenses in rat hippocampus

In the present study we investigated the effect of methionine exposure of hippocampus homogenates on Na+,K+-ATPase activity from synaptic plasma membrane of rats. Results showed that methionine significantly decreased this enzyme activity. We also evaluated the effect of incubating glutathione (GSH) and trolox (alpha-tocopherol) alone or combined with methionine on Na+,K+-ATPase activity. The tested antioxidants per se did not alter the enzymatic activity, but prevented the inhibitory action of methionine on Na+,K+-ATPase activity, indicating that Met inhibitory effect was probably mediated by free radical formation. Besides, we tested the in vitro effect of methionine on some parameters of oxidative stress, namely chemiluminescence, thiobarbituric acid reactive substances (TBARS), total radical-trapping antioxidant potential (TRAP), as well as on the antioxidant enzyme activities catalase, glutathione peroxidase and superoxide dismutase in rat hippocampus. We observed that methionine significantly increased chemiluminescence and TBARS, decreased TRAP, but did not change the activity of the antioxidant enzymes. These findings suggest that reduction of Na+,K+-ATPase activity and induction of oxidative stress may be involved in the brain damage observed in human hypermethioninemia.

Fragrance material review on cinnamaldehyde

A toxicologic and dermatologic review of cinnamaldehyde when used as a fragrance ingredient is presented.

Catalase Regulates Cell Growth in HL60 Human Promyelocytic Cells: Evidence for Growth Regulation by H2O2

Reactive oxygen species (ROS) including hydrogen peroxide (H(2)O(2)) are generated constitutively in mammalian cells. Because of its relatively long life and high permeability across membranes, H(2)O(2) is thought to be an important second messenger. Generation of H(2)O(2) is increased in response to external insults, including radiation. Catalase is located at the peroxisome and scavenges H(2)O(2). In this study, we investigated the role of catalase in cell growth using the H(2)O(2)-resistant variant HP100-1 of human promyelocytic HL60 cells. HP100-1 cells had an almost 10-fold higher activity of catalase than HL60 cells without differences in levels of glutathione peroxidase, manganese superoxide dismutase (MnSOD), and copper-zinc SOD (CuZnSOD). HP100-1 cells had higher proliferative activity than HL60 cells. Treatment with catalase or the introduction of catalase cDNA into HL60 cells stimulated cell growth. Exposure of HP100-1 cells to a catalase inhibitor resulted in suppression of cell growth with concomitant increased levels of intracellular H(2)O(2). Moreover, exogenously added H(2)O(2) or depletion of glutathione suppressed cell growth in HL60 cells. Extracellular signal regulated kinase 1/2 (ERK1/2) was constitutively phosphorylated in HP100-1 cells but not in HL60 cells. Inhibition of the ERK1/2 pathway suppressed the growth of HP100-1 cells, but inhibition of p38 mitogen-activated protein kinase (p38MAPK) did not affect growth. Moreover, inhibition of catalase blocked the phosphorylation of ERK1/2 but not of p38MAPK in HP100-1 cells. Thus our results suggest that catalase activates the growth of HL60 cells through dismutation of H(2)O(2), leading to activation of the ERK1/2 pathway; H(2)O(2) is an important regulator of growth in HL60 cells.

Modulating carbonyl cytotoxicity in intact rat hepatocytes by inhibiting carbonyl metabolizing enzymes. II. Aromatic aldehydes

The molecular cytotoxic mechanisms of dietary benzaldehydes towards hepatocytes and its modulation by metabolizing enzymes were compared. Salicylaldehyde was found to be the most cytotoxic followed by cinnamaldehyde and both rapidly depleted some glutathione before an inhibition of respiration occurred, which preceded cell lysis. Reactive oxygen species were formed, but lipid peroxidation was induced with cinnamaldehyde, but not salicylaldehyde. Glutathione depleted hepatocytes were more susceptible to cytotoxicity. Mitochondrial toxicity and cytotoxicity were prevented by glycolytic substrates (e.g. fructose), citric acid cycle substrates (e.g. glutamine) or cyclosporin, the mitochondrial permeability transition inhibitor. Inhibition of mitochondrial ALDH with chloral hydrate, crotonaldehyde or citral or decreasing mitochondrial NAD+ with rotenone increased cinnamaldehyde induced cytotoxicity with a much smaller effect on salicylaldehyde induced cytotoxicity. Cyanamide was the most effective ALDH inhibitor for increasing cinnamaldehyde induced cytotoxicity, presumably because cyanamide also inhibits microsomal ALDH. Although cinnamaldehyde was a better substrate than salicylaldehyde for ADH1, cytosolic NADH generators (e.g. xylitol) prevented salicylaldehyde and cinnamaldehyde cytotoxicity similarly. This could be explained as salicylaldehyde was not a substrate for the ALDHs and would then be more dependent on ADH for detoxification.

Effects of diethylmaleate on DNA damage and repair in the mouse brain

The enzyme 8-oxoguanine DNA glycosylase 1 participates in the repair of damaged DNA by excising the oxidized base 8-hydroxy-2'-deoxyguanosine. We have previously demonstrated that enzymatic activity of this enzyme is inversely related to the levels of the damaged base in specific brain regions. We now report that the activity of 8-oxoguanine DNA glycosylase 1 is increased in a region-specific manner following treatment with diethylmaleate, a compound that reduces glutathione levels in the cell. A single treatment with diethylmaleate elicited a significant increase ( approximately 2-fold) in the activity of 8-oxoguanine DNA glycosylase 1 in three brain regions with low basal levels of activity (cerebellum, cortex, and pons/medulla). There was no change in the activity of 8-oxoguanine DNA glycosylase 1 in those regions with high basal levels of activity (hippocampus, caudate/putamen, and midbrain). This is the first report to demonstrate that DNA repair capacity can be upregulated in the CNS, and the increased repair activity correlates with a reduction in the levels of DNA damage. The brain region-specific capacity to deal with increased oxidative damage to DNA may be responsible, in part, for the vulnerability of specific neuronal populations with aging, sources of oxidative stress, and neurodegenerative diseases.

Role of glutathione in metabolic degradation of dichloromethane in rats

Dichloromethane (DCM) elimination and carboxyhemoglobin (COHb) generation were examined in adult female SD rats pretreated with a glutathione (GSH) depletor(s). Rats were treated with either buthionine sulfoximine (BSO; 2 mmol/kg, i.p.), diethylmaleate (DEM; 3 mmol/kg, i.p.), phorone (PHO; 1 mmol/kg, i.p.) or BSO plus PHO (BSO; 2 mmol/kg +PHO; 0.5 mmol/kg, i.p.). The hepatic GSH concentration was significantly reduced by each treatment. Decrease in hepatic GSH was maintained at least for 10 h after BSO treatment but recovered rapidly in rats treated with DEM or PHO. The hepatic p-nitrophenol hydroxylase activity was not affected by the GSH depletors at the dose used in this study. Rats were treated with an i.p. injection of DCM (3 mmol/kg) and the concentrations of DCM and the COHb levels in blood were monitored. In rats pretreated with a GSH depletor, the peak COHb level was significantly greater than that of rats treated with DCM only. The peak COHb level attained in each group of rats appeared to be inversely related to the magnitude of reduction in hepatic GSH levels. The half-life of DCM in blood was also increased in rats pretreated with the GSH depletor(s). The results indicate that the GSH-dependent metabolic reaction has an important role in the overall elimination of DCM as well as in the metabolic generation of carbon monoxide (CO) from this solvent.

Glutathione synthesis during the rewarming of rat hepatocytes preserved in the University of Wisconsin solution

In this study, we used isolated rat hepatocytes to investigate the effect of nucleoside content of the preserved cells on the ability to synthesize glutathione (GSH) during the rewarming process. We cold-stored hepatocytes in University of Wisconsin (UW) solution (72 h, 0 degrees C, N(2)) without nucleosides and with the addition of 5 mM adenosine or 10 mM ATP. After 72 h of cold storage, we determined the GSH synthesis rate and the ATP content of the cells. We found a GSH synthesis rate similar to that of freshly isolated hepatocytes only in the group of cells cold-stored with 10 mM ATP. When we tested the cellular ATP concentrations, we found that controls and preserved cells with 10 mM ATP showed a similar value of ATP during the rewarming step. Our results suggested that the incorporation of ATP in the UW solution increased the ATP content and the rate of GSH synthesis of cold-stored hepatocytes during rewarming.

DNA-damaging potential and glutathione depletion of 2-cyclohexene-1-one in mammalian cells, compared to food relevant 2-alkenals

2-Cyclohexene-1-one (CHX) occurs as a natural ingredient in some tropical fruits and has been detected as a contaminant in certain artificially sweetened soft drinks. To elucidate its cytotoxic/genotoxic effectiveness, CHX was tested in mammalian cell lines (V79 and Caco-2) and in primary human colon cells in comparison to structurally related 2-alkenals. Inhibition of cell growth (IC(50)) and cytotoxicity (LC(50)) were determined by protein staining with sulforhodamin B (SRB) and by trypan blue exclusion, respectively. DNA damage--both strand breaks and oxidised purines--was quantified by comet assay. Depletion of glutathione was measured in a kinetic assay, based on 5-thio-2-nitrobenzoate (TNB) formation. For CHX, a moderate cytotoxicity was observed after 1h incubation in V79 cells (LC(50): 4.75mM). The 2-alkenals ((E)-2-octenal (OCTE), (2E,4Z)-2,4-hexadienal (HEXDI), (E)-2-nonenal (NONE), (2E,6Z)-2,6-nonadienal (NONDI)) exhibited a distinctly higher cytotoxicity, except for (E)-2-hexenal (HEX) (LC(50): 3.67mM) and cinnamaldehyde (CA) (LC(50): 4.45mM). If the incubation time was prolonged to 24h, an IC(50) of 15microM was obtained for CHX which is well within the range obtained for the 2-alkenals (4 and 17microM). Concentration-dependent DNA damage was observed after 1h incubation with CHX. The respective DC(50) values (concentration inducing DNA damage in 50% of cells) were 272microM (V79) and 455microM (Caco-2). All 2-alkenals were more active under these conditions, except for CA. In primary human colon cells, CHX (800microM, 30min) exhibited a weak, but still significant DNA-damaging potential. Glutathione levels in V79 cells were effectively depleted (down to approximately 20%) by CHX concentrations not yet inducing DNA damage (c < or = 50microM). Incubation with CHX or 2-alkenals (50 and 100microM, 1h), followed by H2O2 treatment (5min, 25microM) resulted in increased levels of oxidised purines in the modified comet assay. CHX and HEX, additionally tested in primary human colon cells, depleted glutathione and increased the sensitivity towards oxidative stress.

First-pass metabolism of 1,3-butadiene in once-through perfused livers of rats and mice

First-pass metabolism of 1,3-butadiene (BD) leading to 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB), 3-butene-1,2-diol (B-diol), 3,4-epoxy-1,2-butanediol (EBD) and crotonaldehyde (CA) was studied quantitatively in the once-through BD perfused liver of mouse and rat by means of an all-glass gas-tight perfusion system. Metabolites were analyzed using gas chromatography equipped with mass selective detection. The perfusate consisted of Krebs-Henseleit buffer (pH 7.4) containing bovine erythrocytes (40%v/v) and BD. The perfusion flow rates through the livers were 3-4 ml/min (mouse) and 17-20 ml/min (rat). The BD concentrations in the liver perfusates were 330 nmol/ml (mouse) and 240 nmol/ml (rat) being high enough to reach almost saturation of BD metabolism. The mean rates of BD transformation were about 0.014 and 0.055 mmol/h per liver of a mouse and a rat, respectively, being similar to the values expected from in-vivo measurements. There were marked species differences in the formation of BD metabolites. In the effluent of mouse livers, all three epoxides (EB: 9.4 nmol/ml; DEB: 0.06 nmol/ml; EBD: 0.07 nmol/ml) and B-diol (8.2 nmol/ml) were detected. In the perfusate leaving naïve rat livers, only EB and B-diol were found. In that of rat liver, EB concentration was 8.5 times smaller than in that of mouse liver, whereas B-diol concentrations were similar in the effluent liver perfusate of both species. CA was below the limit of its detection (60 nmol/l) in the liver perfusate of mice and of naïve rats. Of BD metabolized, the sum of the metabolites investigated in the effluent amounted to only 30% (mouse) and 20% (rat). In first experiments with rat liver, glutathione (GSH) was depleted by pretreating the animals with diethylmaleate. With the exception of EBD (not quantifiable due to an interfering peak), all other metabolites including CA were found in the effluent perfusate summing up to about 70 and 100% of BD metabolized, which indicates the quantitative importance of the GSH dependent metabolism. In summary, the results demonstrate the relevance of an intrahepatic first-pass metabolism for metabolic intermediates of BD, which undergo further transformation immediately after their production in the liver before leaving this organ. Hitherto, the occurrence of this first-pass metabolism was only hypothesized. The findings will help to explain the drastic species difference between mice and rats in the carcinogenic potency of BD.

Glutathione depletion in rat hepatocytes: a mixture toxicity study with alpha, beta-unsaturated esters

1. Glutathione (GSH) depletion is often reported as an early cytotoxic effect, caused by many reactive organic chemicals. In the present study, GSH depletion in primary rat hepatocytes was used as an in vitro effect-equivalent to measure the toxic potency of alpha,beta-unsaturated esters (acrylates and methacrylates). 2. When these compounds were administered as a mixture, GSH depletion was dose additive. The result of the mixture study shows that GSH depletion may be a useful effect-equivalent for the risk assessment of mixtures of alpha,beta-unsaturated esters. 3. To get more insight in the underlying mechanisms of GSH depletion, the metabolism of two esters was investigated in greater detail. One of them, allyl methacrylate, was metabolized to acrolein. This metabolic pathway can explain the high potency of allyl methacrylate to deplete GSH despite its low intrinsic chemical reactivity.

Cerebral antioxidant status and free radical generation following glutathione depletion and subsequent recovery

This study was aimed to evaluate the oxidative damage, production of reactive oxygen species and the status of antioxidative defenses following cerebral GSH depletion induced by two classical depletors, diethylmaleate (DEM, 3 mmol/kg, i.p.) and phorone (PHO, 4 mmol/kg, i.p.). The treatment decreased (40-43%) brain glutathione levels at 2 h, followed by a partial recovery at 24 h. Cerebral glutathione depletion by these agents increased the levels of superoxide anion and hydroxyl radical at both the time intervals; however, hydrogen peroxide was high at 24 h only. It also produced a dramatic increase in the protein carbonyls at 2 h but not at 24h, without any significant effect on lipid peroxidation and conjugated diene levels. These rats showed a significantly lowered superoxide dismutase activity both at 2 h and 24 h of exposure, as compared to controls. Glutathione depletion enhanced catalase activity markedly at 2 h, followed by some recovery at 24 h. While Se-independent glutathione peroxidase (GPx) and glutathione S-transferase activities were increased at both 2 and 24 h time intervals, Se-dependent GPx and glucose-6-phosphate dehydrogenase were induced at 2 h only. Glutathione depletion decreased ceruloplasmin and vitamin E levels significantly at 2 h. However, ascorbic acid remained unaffected. It may be concluded that an acute cerebral glutathione depletion generates higher levels of reactive oxygen species, which may be responsible for oxidative modification of proteins. Some of these changes appear to recover soon after an activation of a variety of cellular antioxidant defense mechanisms and glutathione restoration. It appears that central nervous system is highly vulnerable to oxidative damage following a moderate glutathione depletion that may result from certain diseases or xenobiotic exposures.

Effects of glutathione depletion on oxidant-induced endothelial cell injury

Ischemia-reperfusion produces edema in vivo by disrupting endothelial cell junctional integrity. A cultured rat pulmonary artery endothelial cell (RPAEC) model was used to analyze the effects of oxidants and ischemic plasma in vitro. RPAEC cultures were treated with ischemic human plasma from transverse rectus abdominis musculocutaneous (TRAM) flaps following mastectomy or with an equal quantity of nonischemic plasma taken peripherally. Endothelial cells treated with ischemic plasma rounded and formed gaps within 5 min, then ruffled and blebbed after 10 min. Cultures treated with human nonischemic plasma had no gross morphological changes. Additionally, cultures treated with human ischemic plasma demonstrated an increase in diffusion rate of 125I-albumin across monolayers while monolayers treated with human nonischemic plasma had no increase in diffusion rate. RPAEC monolayers were treated with malic acid diethyl ester (DEM) or L-buthionine-[S, R]-sulfoximine (BSO) to decrease cellular stores of glutathione before exposure to oxidant stress. Cultures depleted of cellular glutathione stores were significantly (P < 0.05) more susceptible to 50 microM H2O2 than controls, as determined by an increase in diffusion rate of 125I-albumin across monolayers. To determine if ischemic plasma effects were mediated by oxidants, cultures were depleted of glutathione by DEM or BSO pretreatment before exposure to plasma from the ischemic hind limbs of Sprague-Dawley rats. Glutathione-depleted RPAEC monolayers were significantly (P < 0.05) and substantially (2-3 X) more susceptible to the effects of ischemic plasma than were cultures with normal glutathione levels. Glutathione depletion had no effect on cultures treated with an equal amount of nonischemic plasma from sham-operated rats. These data strongly suggest that ischemic plasma in the absence of any cellular component are able to induce an oxidant injury in endothelial cells and thereby compromise junctional integrity.

Effect of glutathione deficiency on the adipocyte sn-glycerol-3-phosphate acyltransferase

The present study investigates the effects of various glutathione (GSH) depleting agents on sn-glycerol-3-phosphate acyltransferase (GPAT) activity, the first committed step in adipose triacylglycerol formation. GPAT activity was measured in the presence of [14C]glycerol-3-phosphate and palmitoyl-CoA, using different subcellular fractions. Glutathione deficiency in animals was induced in the presence of diethylmaleate (DEM) or buthionine sulfoximine. In this respect, DEM (1.75 mmoles/kg) was more effective and caused over 75% decrease in GPAT activity within 4 h of DEM administration. Further studies indicated that this decrease in GPAT activity was mainly related to the microsomal form of GPAT, without any significant effect on mitochondrial GPAT activity. Adipocytes incubated with 2.5 mm DEM for 1 h at 37 degrees C also showed a reduction in the adipocyte glutathione content, which was accompanied by decreases in GPAT activity. The effect of DEM on adipocyte GPAT activity was partially reversible in the presence of cell permeable glutathione ethyl ester. Preincubation of adipose tissue homogenates with 2.5 mM DEM at 30 degrees C for 45 min also showed a significant loss of the GPAT activity. The presence of 5 mM dithiothreitol in the preincubation mixture offered a significant protection of the GPAT activity against DEM. However, glutathione was ineffective in this respect as it interfered with the utilization of palmitoyl-CoA in the GPAT assay. Therefore, on the basis of these three different approaches, the present studies suggest that the thiol environment offered by glutathione (in vivo and in vitro studies) or dithiothreitol (in a cell-free system) is critical for the maintenance of GPAT activity.

Effects of glutathione depletors on post-ischemic reperfusion in rat brain

The present paper reports the effects of GSH depletion (diethylmaleate induced) on partial cerebral ischemia and reperfusion for 7 and 20 days. Our results confirm that there is a paradoxical protective effect of the GSH-depletor and suggest an improved neuronal trophism induced by diethylmaleate treatment.

Glutathione movements during cold preservation of rat hepatocytes

In this study we have examined the movements of glutathione (GSH) during cold preservation of rat hepatocytes in University of Wisconsin solution. During the preservation process at a low temperature (4 degrees C), with a high extracellular potassium concentration, an extracellular nondiffusible anion (lactobionate), and a Cl(-)-free medium, there is a depletion of metabolites and the development of a time-dependent injury. Also, there is a loss of GSH that is not compensated by transport or synthesis and is basically due to increased catabolic processes. This sensitizes the cells to different forms of oxidative injury, which can play a negative role during transplantation. The addition of GSH improves liver cell preservation but the mechanism is unclear. To elucidate this process we have isolated hepatocytes and preserved them under different conditions: with or without GSH: in the presence of DL-buthionine-[S,R]-sulfoximine, an inhibitor of glutathione synthetase, and acivicine to inhibit the ectoactivity of cellular gammaglutamyl transpeptidase; or by obtaining hepatocytes from rats depleted of GSH by an injection of diethyl maleate. Under all these conditions we evaluated the GSH content of the cells during cold storage. We also report the time course of accumulation of [glycine-2-3H]GSH. Our results show that during hypothermic storage in University of Wisconsin solution, hepatocytes are permeable to GSH, and the mechanism involved is a rapid nonsaturable process, with linear dependence of the extracellular GSH concentration. This finding may have valuable applications in the improvement of the delivery of compounds to cells.

Modulation of glutathione conjugation in vivo: how to decrease glutathione conjugation in vivo or in intact cellular systems in vitro

Glutathione conjugation is involved in detoxification and toxification of a variety of electrophilic substrates. Thus it plays a major role in protection against reactive intermediates. At the same time this conjugation may cause resistance of tumor cells against certain cytostatics. In this review the methods available to decrease glutathione conjugation in vivo are discussed. So far the only in vivo active inhibitors of glutathione S-transferases are ethacrynic acid and a number of glutathione-derived structures; the latter seem very promising for further development. For (chronic) glutathione-depletion, buthionine sulfoximine is most effective, and surprisingly safe in clinical studies. Diethylmaleate can be used for acute depletion. Inhibition of glutathione transferases offers advantages over glutathione depletion as a method of decreasing glutathione conjugation since inhibition may be accomplished without changing the activities of other glutathione-dependent reactions in the cell. However, clinically safe, in vivo effective and isoenzyme-selective glutathione S-transferase inhibitors have not yet been developed.

Biochemical studies on the toxicity of 1, 1'-dimethyl-4, 4'-bipyridylium dichloride in the rat

The effect of intraperitoneal administration of lethal dose (50 mg/kg) of paraquat on the microsomal cysteine levels in the plasma, liver and lung of adult male Wistar rats has been investigated using Rank Chromaspek amino acid analyzer. The microsomal alanine levels were also determined to help in assessing the extent of paraquat interference with cellular protein. DL-Buthionine-[S,R]-Sulfoximine (BSO) and Diethyl maleate (DEM) were used to potentiate the toxic effect of the bipyridyl. The microsomal cysteine levels were significantly (P < or = 0.05) depressed in the plasma, liver and lung of the paraquat-treated rats compared with the saline-injected group but the alanine levels were not similarly affected. Probably, paraquat poisoning interferes specifically with the cellular cysteine content in the rat. These findings could provide a valuable information on the biochemical mechanism of paraquat intoxication.

Effect of glutathione deficiency on the adipocyte Mg(2+)-dependent phosphatidate phosphohydrolase

Previous studies from this laboratory [Jamdar S. C. and Cao W. F. (1994) Biochem. J. 301, 793-799] show that the adipocyte Mg(2+)-dependent phosphatidate phosphohydrolase (MGPPH), a major regulatory enzyme in adipose triacylglycerol metabolism, requires an active thiol group for its activity and perturbation of this group results in the loss of enzyme activity. Since glutathione (GSH) is important in maintaining the intracellular thiol state, we have used GSH-deficient animals and adipocytes to test the possibility that intracellular GSH concentration is critical in controlling the MGPPH activity. The MGPPH was measured in the presence of aqueous dispersed phosphatidate, and the release of P1 was taken as a measure of enzyme activity. The GSH deficiency in animals and isolated adipocytes was produced in the presence of diethylmaleate (DEM) or buthionine sulfoximine (BSO). Intraperitoneal administration of BSO into animals (3 mmoles/kg) showed 10-25% reduction in the blood and adipose GSH and 25% decline in the adipose MGPPH activity. However, DEM (0.3 ml/kg) was more effective and caused over 70% reduction of the blood and adipose tissue GSH content and 75% decline in the adipose MGPPH activity within 4 hr of drug administration. After 24 hr, these values returned to normal. Adipocytes incubated with 2.5 mM DEM for 60 min at 37 degrees C also showed a significant reduction in the GSH content and the MGPPH activity present in the cytosol and membrane fractions. The loss of membrane MGPPH was associated with decreased rates of triacylglycerol formation from [14C]palmitate. Pre-incubation of adipocyte homogenates with 1 mM DEM also resulted in > 90% decline in the MGPPH activity, which was preventable in the presence of GSH and dithiothreitol. Therefore, these studies suggest that the sulfhydryl environment offered by glutathione is critical for the maintenance of adipocyte MGPPH activity.

A p53-independent pathway for activation of WAF1/CIP1 expression following oxidative stress

Incubating human cells in diethylmaleate (DEM) depletes the intracellular pool of reduced glutathione (GSH) and increases the concentration of oxidative free radicals. We found that DEM-induced oxidative stress reduced the ability of p53 to bind its consensus recognition sequence and to activate transcription of a p53-specific reporter gene. Nevertheless, DEM treatment induced expression of WAF1/CIP1 but not GADD45 mRNA. The fact that N-acetylcysteine, a precursor of GSH that blocks oxidative stress, prevented WAF1/CIP1 induction by DEM suggests that WAF1/CIP1 induction probably was a consequence of the ability of DEM to reduce intracellular GSH levels. DEM induced WAF1/CIP1 expression in Saos-2 and T98G cells, both of which lack functional p53 protein. DEM treatment did not produce an increase in membrane-associated protein kinase C, but ERK2, a mitogen-activated protein kinase, was phosphorylated in a manner consistent with ERK2 activation. DEM treatment also produced a dose-dependent delay in cell cycle progression, which at low concentrations (0.25 mM) consisted of a G2/M arrest and at higher concentrations (1 mM) also involved G1 and S phase delays. Our results indicate that oxidative stress induces WAF1/CIP1 expression and arrests cell cycle progression through a mechanism that is independent of p53. This mechanism may provide for cell cycle checkpoint control under conditions that inactivate p53.

Differentially expressed mRNAs as a consequence of oxidative stress in intact cells

Intracellular redox conditions influence the activity of several transcription factors leading to a modulation of the expression of the genes controlled by these factors. We examined the changes in cell transcription patterns after oxidative stress induced by diethylmaleate (DEM). Using the differential display technique we identified several differentially expressed sequence tags, four of which are identical or highly homologous to sequences contained in the human cDNAs encoding vimentin, c-fos, cytochrome oxidase IV and ribosomal protein L4; another one corresponds to a transcript of the mitochondrial genome of unknown function. The remaining five cDNAs are not recorded in any sequence data bank. One of these, named Rox3, lights up two mRNA species of approximately 3400 and 3600 bp, significantly increased after treatment with DEM or with other oxidizing agents. This increase appears precociously after exposure to DEM and it is completely prevented by pretreatment with N-acetylcysteine. The Rox3 fragment was used to screen a cDNA library; one fully sequenced clone showed 100% homology with the putative human guanine nucleotide regulatory protein nep1.

Influence of diethyl maleate and cysteine on tissue glutathione and growth in broiler chickens

The objectives of this study were to determine the effects of diethyl maleate (DEM) and l-cysteine (L-Cys) on tissue glutathione (GSH) and growth in male broiler chickens. In Experiment 1, broilers were treated with DEM (0, 1.5, 3, 6, or 12.0 mmol/kg BW, i.p.). After 1 h, maximum GSH depletions were to 9, 24, 20, 19, and 35% of control (0 mmol DEM/kg) for liver, lung, kidney, heart, and brain, respectively. In Experiment 2, time-course changes following 1.5 mmol DEM/kg (i.p.) were determined; time-controls received an equal amount of corn oil (CO, .25 mL/kg BW). Levels of GSH in all tissues were low at 1 and 2 h after DEM in comparison to time-control values. Tissue GSH concentrations returned to values that were not different from controls by 5 h in liver and kidney, by 12 h in heart, and by 24 h in brain and lung. In Experiment 3, the effects of feeding a control diet (0% L-Cys) or one supplemented with 1% L-Cys from 3 to 7 wk of age with weekly i.p. injections (at 3,4,5, and 6 wk of age) of DEM (1.5 mmol/kg BW) or CO (.25 mL/kg BW) on growth rate and tissue GSH were determined. There were no differences in BW among treatment groups between 3 and 6 wk of age. Although there were no differences in 7-wk BW between controls (0% L-Cys/CO) and birds treated with DEM fed either diet, the 1% L-Cys/CO group was heavier (P < .05) than either the 0% or 1% L-Cys/DEM groups, and heavier (P = .066) than controls at 7 wk of age. At 5 wk of age, 1% L-Cys raised GSH concentrations in liver, kidney, lung, and duodenum, but had no effect on heart GSH in birds treated with either CO or DEM. Control hepatic GSH concentrations were higher at 7 than at 5 wk of age. With the exception of duodenal GSH in CO birds, 1% L-Cys had no effect on tissue GSH concentrations in 7-wk-old birds. The results of this study provide an initial characterization of GSH metabolism in commercial male broilers and indicate that DEM produced dose- and time-dependent changes in GSH similar to reported changes in mammals. Results of this study also indicate that increased tissue GSH may be beneficial for growth.

DNA binding activity of the glucocorticoid receptor is sensitive to redox changes in intact cells

The effect of changes of redox conditions on glucocorticoid receptor (GR) activity in intact cells has been studied using two approaches. One was to evaluate the GR-DNA binding in extracts of COS2 cells transiently overexpressing GR and in which reactive oxygen intermediates (ROI) accumulate as a consequence of glutathione (GSH) depletion. GR-DNA binding was significantly decreased in COS2 cells treated with diethylmaleate (DEM), which causes GSH depletion by forming GSH-DEM complexes. A similar effect was observed for Sp1, another Zn-finger transcription factor, whereas no difference was observed for the C/EBP transcription factor, which is known to be unaffected by redox changes in vitro. N-Acetylcysteine (NAC), which counteracts the effects of DEM by increasing GSH biosynthesis, prevents the decrease of GR-DNA binding in cells treated with DEM. The GR-DNA binding efficiency was similarly decreased using extracts from H2O2-treated COS2 cells and from COS2 cells treated with buthionine sulphoximine, which causes GSH depletion via a mechanism different from that of DEM. The other approach was to evaluate the efficiency of a GR-regulated promoter under different redox conditions. In HeLa cells, transfected with a plasmid containing the CAT gene under the control of the glucocorticoid responsive element (GRE) within the mouse mammary tumor virus promoter, and treated with dexamethasone to activate GR, exposure to DEM significantly impaired the activation of CAT gene expression induced by dexamethasone. Also in this case NAC treatment inhibited the effects of DEM.

Role of renal gamma-glutamyltransferase activity in hepatic utilization of exogenous glutathione

The importance of renal gamma-glutamyltransferase activity in the hepatic utilization of exogenous glutathione (GSH) was evaluated by injecting GSH (1.67 mmol/kg body wt) i.v. into bilaterally nephrectomized and sham-operated Sprague-Dawley rats in which endogenous hepatic GSH had been decreased (0.20 +/- 0.01 mumol/g liver vs 5.87 +/- 0.26 mumol/g liver in normal controls, mean +/- SD) by diethylmaleate (0.5 ml/kg body wt, i.p.). Hepatic GSH concentration 60 min after GSH administration was lower in the nephrectomized than in the sham-operated rats (0.87 +/- 0.25 mumol/g liver vs 3.08 +/- 0.81 mumol/g liver, P < 0.001), while plasma GSH concentration was higher in the former (4.61 +/- 1.07 mM vs 0.11 +/- 0.06 mM, P < 0.001). In rats with intact kidneys which had been given a gamma-glutamyltransferase inhibitor (acivicin, 25 mumol/kg body wt i.v.) prior to GSH administration, the hepatic GSH concentrations (1.11 +/- 0.49 mumol/g liver) were comparable to those obtained in the nephrectomized rats. When N-acetylcysteine (1.67 mmol/kg body wt, i.v.) was administered instead of GSH, the hepatic GSH concentrations were similar in nephrectomized and sham-operated rats (1.54 +/- 0.23 mumol/g liver vs 2.22 +/- 0.58 mumol/g liver, NS). The gamma-glutamyltransferase activity was much higher in the kidney than in the liver (4460 +/- 830 IU/kg body wt vs 14 +/- 7 IU/kg body wt). These results indicate that the kidney plays an essential role in the hepatic utilization of exogenous GSH through its high gamma-glutamyltransferase activity.

Studies on trans-cinnamaldehyde. 1. The influence of dose size and sex on its disposition in the rat and mouse

The metabolism of trans-[3-14C]cinnamaldehyde was investigated in male and female Fischer 344 rats and CD1 mice at doses of 2 and 250 mg/kg body weight given by ip injection and in males at 250 mg/kg by oral gavage. Some 94% of the administered dose was recovered in the excreta in 72 hr in both species with most (75-81%) present in the 0-24-hr urine. Less than 2% of the administered dose was found in the carcasses at 72 hr after dosing. Urinary metabolites were identified by their chromatographic characteristics. In both species the major urinary metabolite was hippuric acid accompanied by 3-hydroxy-3-phenylpropionic acid, benzoic acid and benzoyl glucuronide. The glycine conjugate of cinnamic acid was formed to a considerable extent only in the mouse. The oxidative metabolism of cinnamaldehyde essentially follows that of cinnamic acid, by beta-oxidation analogous to that of fatty acids. Apart from the metabolites common to cinnamic acid and cinnamaldehyde, 7% of 0-24-hr urinary 14C was accounted for by two new metabolites in the rat and three in the mouse, which have been shown in other work to arise from a second pathway of cinnamaldehyde metabolism involving conjugation with glutathione. The excretion pattern and metabolic profile of cinnamaldehyde in rats and mice are not systematically affected by sex, dose size and route of administration. The data are discussed in terms of their relevance to the safety evaluation of trans-cinnamaldehyde, particularly the validity or otherwise of extrapolation of toxicity data from high to low dose.

Inhibition of the differentiation of human myeloid cell lines by redox changes induced through glutathione depletion

We have investigated the effect of redox changes in vivo on the differentiation of two human myeloid cell lines, HL-60 and KG-1. The glutathione-depleting agent diethyl maleate (DEM) prevented the development of differentiated features in response to phorbol esters, including adherence of the cells to plastic surfaces and repression of the myeloperoxidase and CD34 genes. Moreover, DEM abolished phorbol 12-myristate 13-acetate-induced activation of the transcription factors AP-1 and Egr-1, suggesting that inhibition of differentiation may be due, at least in part, to redox modifications of these proteins.

Role of detoxication pathways in acute toxicity levels of phosphorothionate insecticides in the rat

Phosphorothionate insecticides and their active oxon metabolites can be detoxified by a variety of hepatic mechanisms. Cytochrome P450-mediated dearylation activity was higher in males than in females. While dearylation was induced by phenobarbital in both sexes, it was induced by beta-naphthoflavone in females only. Detoxication of oxons in the presence of EDTA was inducible by phenobarbital, was higher in males than in females, and paralleled aliesterase activity. In vitro Ca(++)-dependent A-esterase-mediated hydrolysis of chlorpyrifos-oxon but not of paraoxon occurred at biologically relevant nM concentrations. This hydrolysis was also inducible by phenobarbital. Glutathione-mediated conjugation did not appear to be relevant to the disposition of the phosphorothionates studied here. Hepatic detoxication via dearylation, aliesterase phosphorylation and A-esterase-mediated hydrolysis (for some organophosphates) all appear to be relevant reactions in the attenuation of acute toxicity.

Free radical scavenger depletion in post-ischemic reperfusion brain damage

In the present study the influence of pretreatment with various GSH depletors such as buthionine sulfoximine (BSO) and diethylmaleate (DEM) was investigated in rats following cerebral post-ischemic reperfusion. Moreover, the effect of diethyldithiocarbamic acid (DDC), inhibitor of endogenous Cu,Zn-SOD, was evaluated. A significant depletion (40% of control value) of GSH levels was observed 24 h after DEM administration; after 48 h the value reached control levels. BSO showed maximal GSH depletion (59%) 24 h after administration and it was constant for almost 48 h. DDC administration caused a marked decrease (60%) of Cu,Zn-SOD activity 4 h after the injection and induced a marked decrease in percentage of survival with respect to control (untreated, ischemic) rats, when administered 4 h before ischemia. BSO and DEM prolonged the survival time of animals when administered 24 h before ischemia. This last paradoxical effect is unclear at present, but it might be due to an influence on glutamate cascade.

Synthesis rates of glutathione and activated sulphate (PAPS) and response to cysteine and acetaminophen administration in glutathione-depleted rat hepatocytes

The effects of cysteine and acetaminophen (AA) on the synthesis rates of glutathione (GSH), adenosine 3'-phosphate 5'-phosphosulphate (PAPS, activated sulphate) and the AA metabolites, AA-GSH and AA-sulphate were studied in rat hepatocytes depleted of GSH by diethyl maleate (DEM). The synthesis rates were determined simultaneously by a previously described radioactive tracer method. Preincubation of the hepatocytes with 0.7 mM DEM for 30 min depleted GSH by 59% (P < 0.05) and PAPS by 28% (P < 0.05). Incubation with a toxic AA concentration resulted in GSH synthesis at a rate of 95 nmol/(10(6) cells.min) which increased to 281 nmol/(10(6) cells.min) (P = 0.05) after addition of cysteine. However, increased GSH synthesis was not followed by increased AA-GSH synthesis [4.7 vs 4.8 nmol/(10(6) cells.hr)]. Also, PAPS synthesis increased after cysteine administration [10.2 to 19.1 nmol/(10(6) cells.min)] (P < 0.05) without any change in AA-sulphate synthesis 18.5 vs 18.3 nmol/(10(6) cells.hr)]. Thus, in contrast to hepatocytes with normal GSH concentration, cysteine stimulated both GSH and PAPS synthesis rates in GSH-depleted rat hepatocytes incubated with a toxic AA concentration without stimulation of AA-GSH or AA-sulphate synthesis rates, indicating that the hepatoprotective effect of cysteine on AA toxicity is primarily due to stimulation of a GSH-mediated reduction of the reactive AA metabolite N-acetyl-p-benzoquinoneimine back to AA.