Characterization of the hydroperoxide-reducing activity of human plasma

Does the Anionic Surfactant Isopropylamine Dodecylbenzene Sulfonate Induce Hepatic Oxidative Stress and Impairment in Carassius auratus gibelio?

Isopropylamine dodecylbenzene sulfonate (IDS) is a new kind of anionic surfactant (ANS). To preliminarily evaluate the aquatic toxicity of IDS, this study took gibel carp (Carassius auratus gibelio) as the research object. The well-acclimatized fish were divided into six groups and exposed to 0 mg/L, 0.5 mg/L, 1.0 mg/L, 2.0 mg/L, 4.0 mg/L, or 8.0 mg/L of IDS for 7, 14, 21 or 28 days. Our results showed that the superoxide dismutase (SOD) activity and malondialdehyde (MDA) content of the liver were unaffected by IDS exposure, while glutathione peroxidase (GSH-Px) activity was significantly inhibited. Hepatic tissue exhibited pathological damage, characterized by nuclear migration and dissolution and cell boundary blurring. The results suggest that IDS does not cause oxidative stress in the liver, but cause hepatic histopathological damage. GSH-Px can be considered as a biomarker of IDS exposure in gibel carp.

Assessment of histopathology of wounds based on protein distribution detected by wound blotting

Background:

Shortening the duration of healing based on an accurate assessment is important in pressure ulcer management. This study focused on the peroxidase and alkaline phosphatase activity detected by wound blotting, a non-invasive method of collecting wound exudate, to establish a non-invasive and point-of-care assessment method for analyzing the histopathology of wounds using an animal model.

Methods:

Wounds were created on the dorsal skin of rats. Peroxidase and alkaline phosphatase activities in the wound exudate were detected by wound blotting on post-wounding days 1, 4, 7, and 10. Wound tissue was collected on the same sampling days. Peroxidase and alkaline phosphatase activity within the tissue and myeloperoxidase were visualized. Two types of peroxidase activities were detected by wound blotting: ring and non-ring signals. The histopathological features were compared between wounds with ring and non-ring signals.

Results:

The wounds with ring signals showed a high level of peroxidase activity, and histological analysis demonstrated that the secreted or deviated peroxidase activity originated from myeloperoxidase, indicating a strong inflammation reaction within the tissue. The histopathology of wounds related to the alkaline phosphatase signals was not identified.

Conclusion:

The results suggested that ring signals indicated a strong inflammatory reaction and that they could be used to assess non-visible inflammation.

Ebselen does not improve oxidative stress and vascular function in patients with diabetes: a randomized, crossover trial

Oxidative stress is a key driver of vascular dysfunction in diabetes mellitus. Ebselen is a glutathione peroxidase mimetic. A single-site, randomized, double-masked, placebo-controlled, crossover trial was carried out in 26 patients with type 1 or type 2 diabetes to evaluate effects of high-dose ebselen (150 mg po twice daily) administration on oxidative stress and endothelium-dependent vasodilation. Treatment periods were in random order of 4 wk duration, with a 4-wk washout between treatments. Measures of oxidative stress included nitrotyrosine, plasma 8-isoprostanes, and the ratio of reduced to oxidized glutathione. Vascular ultrasound of the brachial artery and plethysmographic measurement of blood flow were used to assess flow-mediated and methacholine-induced endothelium-dependent vasodilation of conduit and resistance vessels, respectively. Ebselen administration did not affect parameters of oxidative stress or conduit artery or forearm arteriolar vascular function compared with placebo treatment. There was no difference in outcome by diabetes type. Ebselen, at the dose and duration evaluated, does not improve the oxidative stress profile, nor does it affect endothelium-dependent vasodilation in patients with diabetes mellitus.

Selenium prevents microparticle-induced endothelial inflammation in patients after cardiopulmonary resuscitation

Introduction

Microparticles are elevated in patients after successful cardiopulmonary resuscitation (CPR) and may play a role in the development of endothelial dysfunction seen in post-cardiac arrest syndrome (PCAS), a life threatening disease with high mortality. To identify mechanisms of endothelial activation and to develop novel approaches in the therapy of PCAS, the impact of selenium, a trace element with antioxidative properties, was characterized in endothelial dysfunction induced by microparticles of resuscitated patients. Additionally, course of plasma selenium levels was characterized in the first 72 hours post-CPR.

Methods

Endothelial cells were exposed to microparticles isolated of the peripheral blood of resuscitated patients, and leukocyte-endothelial interaction was measured by dynamic adhesion assay. Expression of adhesion molecules was assessed by immunoblotting and flow chamber. Blood samples were drawn 24, 48 and 72 hours after CPR for determination of plasma selenium levels in 77 resuscitated patients; these were compared to 50 healthy subjects and 50 patients with stable cardiac disease and correlated with severity of illness and outcome.

Results

Microparticles of resuscitated patients enhance monocyte-endothelial interaction by up-regulation of ICAM-1 and VCAM-1. Selenium administration diminished ICAM-1 and VCAM-1-mediated monocyte adhesion induced by microparticles of resuscitated patients, suggesting that selenium has anti-inflammatory effects after CPR. Lowered selenium plasma levels were observed in resuscitated patients compared to controls and selenium levels immediately and 24 hours after CPR, inversely correlated with clinical course and outcome after resuscitation.

Conclusions

Endothelial dysfunction is a pivotal feature of PCAS and is partly driven by microparticles of resuscitated patients. Administration of selenium exerted anti-inflammatory effects and prevented microparticle-mediated endothelial dysfunction. Decline of selenium was observed in plasma of patients after CPR and is a novel predictive marker of ICU mortality, suggesting selenium consumption promotes inflammation in PCAS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0774-3) contains supplementary material, which is available to authorized users.

Platelets oxidative stress in Indian patients with ischemic heart disease

BACKGROUND

Oxidative stress has been implicated in the development of atherosclerosis and vascular tissue injury. Both platelet activation and lipid peroxidation are known to play major role in ischemic heart disease. The purpose of this study was to investigate the status of platelets oxidative stress in Indian patients with ischemic heart disease.

METHODS

We measured platelets aggregation, malonyldialdehyde (MDA), plasma-ionized Ca2+, and antioxidant enzymes, i.e., glutathione peroxidase and superoxide dismutase in healthy volunteers and patients with myocardial infarction, unstable and stable angina 40 subjects each.

RESULTS

Platelets aggregation, MDA, and plasma-ionized Ca(2+) have increased significantly across the patients groups compared with controls, this increase was accompanied by an overall decrease in the antioxidant enzymes activity; except for the slight increases in the glutathione peroxidase levels among the myocardial infarction patients.

CONCLUSIONS

The current results suggest that platelet lipid peroxidation as marked by increased MDA level is augmented in ischemic heart diseases. The increased oxidative stress seen in these patients was accompanied by platelet activation and impaired antioxidant enzymes activity.

Role of promoter polymorphisms in the plasma glutathione peroxidase (GPx-3) gene as a risk factor for cerebral venous thrombosis

BACKGROUND AND PURPOSE

Plasma glutathione peroxidase (GPx-3) is a major antioxidant enzyme in plasma and the extracellular space that scavenges reactive oxygen species produced during normal metabolism or after oxidative insult. A deficiency of this enzyme increases extracellular oxidant stress, promotes platelet activation, and may promote oxidative posttranslational modification of fibrinogen. We recently identified a haplotype (H(2)) in the GPx-3 gene promoter that increases the risk of arterial ischemic stroke among children and young adults.

METHODS

The aim of this study is to identify possible relationships between promoter haplotypes in the GPx-3 gene and cerebral venous thrombosis (CVT). We studied the GPx-3 gene promoter from 23 patients with CVT and 123 young controls (18 to 45 years) by single-stranded conformational polymorphism and sequencing analysis.

RESULTS

Over half of CVT patients (52.1%) were heterozygous (H(1)H(2)) or homozygous (H(2)H(2)) carriers of the H(2) haplotype compared with 12.2% of controls, yielding a more than 10-fold independent increase in the risk of CVT (OR=10.7; 95% CI, 2.70 to 42.36; P<0.0001). Among women, the interaction of the H(2) haplotype with hormonal risk factors increased the OR of CVT to almost 70 (P<0.0001).

CONCLUSIONS

These findings show that a novel GPx-3 promoter haplotype is a strong, independent risk factor for CVT. As we have previously shown that this haplotype is associated with a reduction in transcriptional activity, which compromises antioxidant activity and antithrombotic benefits of the enzyme, these results suggest that a deficiency of GPx-3 leads to a cerebral venous thrombophilic state.

Tissue and species distribution of the glutathione pathway transcriptome

The goal of this study was to compare and contrast the basal gene expression levels of the various enzymes involved in glutathione metabolism among tissues and genders of the rat, mouse and canine. The approach taken was to use Affymetrix GeneChip microarray data for rat, mouse and canine tissues, comparing intensity levels for individual probes between tissues and genders. As was hypothesized, the relative expression in liver, lung, heart, kidney and testis varied from gene to gene, with differences of expression between tissues sometimes greater than a 1000-fold. The pattern of differential expression was usually similar between male and female animals, but varied greatly between the three species. Gstp1 appears to be expressed at high levels in male mouse liver, reasonable levels in canine liver, but very low levels in male rat liver. In all species examined, Gstp1 expression was below detectable levels in testis. Gsta3/Yc2 expression appeared high in rodent liver and female canine liver, but not male canine liver. Finally, Mgst1 and Gpx3 expression appeared to be lower in canine heart and testis than seen in rodents. Given the critical role of the glutathione pathway in the detoxification of many drugs and xenobiotics, the observed differences in basal tissue distribution among mouse, rat and canine has far-reaching implications in comparing responses of these species in safety testing.

Molecular characterization of phospholipid hydroperoxide glutathione peroxidases from Hydra vulgaris

Apparent full-length cDNA sequences coding respectively for mitochondrial (HvGPx41) and nuclear (HvGPx42) phospholipid hydroperoxide glutathione peroxidase were isolated from Hydra vulgaris. The cDNA sequences share total identity in their 3'-end and differ in their 5'-end. The protein-coding regions of the HvGPx41 and HvGPx42 cDNA encode polypeptides of 190 and 168 amino acids, including a TGA-encoded selenocysteine, respectively. Phylogenetic analysis showed that the HvGPx41 and HvGPx42 are clustered together along with other phospholipid hydroperoxide glutathione peroxidases (PHGPx) from several organisms. A tertiary structure model generated for the H. vulgaris PHGPx displayed the thioredoxin fold. Hydrae exposed to starvation, metal and oxidative stress responded by regulating their PHGPx mRNA transcription. These results indicated that the PHGPx gene is affected by the cellular stress response and (anti)oxidative processes triggered by stressor and contaminant exposure. Hence the expression of PHGPx mRNA in hydra may have potential use as molecular biomarkers for assessing stress, toxicity and pro-oxidant quality of chemicals and aquatic environmental quality.

The regulation and role of extracellular glutathione peroxidase

Reactive oxygen species and reactive nitrogen species are mediators of lung tissue damage. To minimize the effect of oxidative stress, the lung is well equipped with an integrated antioxidant system. In some circumstances, antioxidants increase in response to oxidants and reduce tissue injury. The lung is somewhat unique in that it has an extracellular surface, which is often directly exposed to oxidative stresses. In this context, the extracellular antioxidant system, comprised primarily of glutathione and glutathione peroxidase, is especially important in protecting against oxidant injury. Induction of extracellular glutathione peroxidase occurs in airway inflammation and undoubtedly plays an important defense against oxidative injury to the airway surface.

Depletion of phospholipid hydroperoxide glutathione peroxidase up-regulates arachidonate metabolism by 12S-lipoxygenase and cyclooxygenase 1 in human epidermoid carcinoma A431 cells

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), a selenium-dependent glutathione peroxidase, can interact with lipophilic substrates, including the phospholipid hydroperoxides, fatty-acid hydroperoxides, and cholesteryl ester hydroperoxides, and reduce them to hydroxide compounds. We studied the functional role of endogenous PHGPx in regulation of 12(S)-lipoxygenase and cyclooxygenase 1 activities in human epidermoid carcinoma A431 cells by using a cell system overexpressing anti-PHGPx mRNA. A retroviral expression vector designated as L1-3, wherein cDNA of PHGPx was reversely inserted into pFB-ERV in antisense orientation, was constructed. A number of stable transfectants of A431 cells with PHGPx depletion were generated from virions containing plasmid L1-3. In an intact cell assay system, the metabolism of arachidonic acid to prostaglandin E2 and 12(S)-hydroxyeicosatetraenoic acid was significantly enhanced in stable L1-3 transfectants compared with that in vector-control cells. Flow cytometric analysis revealed a significant elevated level of intracellular hydroperoxides in stable L1-3 transfectants. Treatment of stable L1-3 transfectants with 50 microM arsenite induced more significant formation of intracellular hydroperoxides than that of vector-control cells. Taken together, these results support the notion that the endogenous PHGPx plays a pivotal role in the regulation of 12(S)-lipoxygenase and cyclooxygenase 1 activities by reducing the level of intracellular lipid hydroperoxides in arachidonate metabolism in A431 cells.

Review of the current status of tooth whitening with the walking bleach technique

Internal bleaching procedures such as the walking bleach technique can be used for whitening of discoloured root-filled teeth. The walking bleach technique is performed by application of a paste consisting of sodium perborate-(tetrahydrate) and distilled water (3% H2O2), respectively, in the pulp chamber. Following a critical review of the scientific literature, heating of the mixture is contra-indicated as the risk of external cervical resorption and the formation of chemical radicals is increased by application of heat. An intracoronal dressing using 30% H2O2 should not be used in order to reduce the risk of inducing cervical resorption. This review provides advice based on the current literature and discusses how the walking bleach technique can lead to successful whitening of non-vital root-filled teeth without the risks of side-effects.

Involvement of reactive oxygen species in arsenite-induced downregulation of phospholipid hydroperoxide glutathione peroxidase in human epidermoid carcinoma A431 cells

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is unique in the substrate specificity among the glutathione peroxidase family because it can interact with lipophilic substrates, including the peroxidized phospholipids and cholesterol, and reduce these hydroperoxide to hydroxide compounds. However, what kinds of ligand can regulate the PHGPx expression is still unknown. In the present study, we found that sodium arsenite induced downregulation of mRNA, protein expression, and enzyme activity of PHGPx in time- and dose-dependent manners. At the same time, it upregulated mRNA and protein expression of p21(WAF1/CIP1). With the aid of agarose gel electrophoresis, and propidium iodide and annexin-V staining, we found that treatment of 30 microM sodium arsenite for 24 h induced apoptosis in human epidermoid carcinoma A431 cells and EA.hy926 cells. An increase of intracellular peroxide levels was measured by flow cytometry using 2',7'-dichlorofluorescin diacetate (DCFH-DA) after treatment of arsenite. Overexpression of PHGPx prevented arsenite-induced increase of intracellular peroxide levels, downregulation of PHGPx, upregulation of p21(WAF1/CIP1), and apoptosis in A431 cells. N-Acetyl-L-cysteine also significantly prevented arsenite-induced effects in A431 cells. Therefore, we concluded that reactive oxygen species were involved in arsenite-induced downregulation of PHGPx, upregulation of p21(WAF1/CIP1), and apoptosis in A431 cells.

Inhibition of arachidonate metabolism in human epidermoid carcinoma a431 cells overexpressing phospholipid hydroperoxide glutathione peroxidase

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), a selenium-dependent glutathione peroxidase, can interact with lipophilic substrates, including phospholipid hydroperoxides, fatty acid hydroperoxides and cholesterol hydroperoxides, and can reduce them to hydroxide compounds. It also seems to be a major regulator of lipid oxygenation in human epidermoid carcinoma A431 cells. In order to study the functional role of PHGPx in the regulation of 12-lipoxygenase and cyclooxygenase, cDNA of PHGPx was inserted into pcDNA3.1/His, and a plasmid designated as S4 with the His-tag sequence inserted between PHGPx and its 3'-untranslated region was constructed. A number of stable transfectants of A431 cells that could express the tag-PHGPx were generated using plasmid S4. Using an intact cell assay system, the metabolism of arachidonic acid to prostaglandin E(2) significantly decreased in stable transfectants of overexpressing PHGPx compared to that in a vector control cell line. If the intact cell assay was carried out in the presence of 13-hydroperoxyoctadecadienoic acid as a stimulator of lipid peroxidation, formation of 12-hydroxyeicosatetraenoic acid from arachidonic acid also significantly decreased in stable transfectants of overexpressing PHGPx compared to that in a vector control cell line, indicating that PHGPx could downregulate the 12-lipoxygenase activity in cells. These results support the hypothesis that PHGPx plays a pivotal role in the regulation of arachidonate metabolism in A431 cells.

Immunohistochemical detection of human gastrointestinal glutathione peroxidase in normal tissues and cultured cells with novel mouse monoclonal antibodies

This is the first report to describe the successful detection of human gastrointestinal glutathione peroxidase in normal tissues by Western blotting and immunohistochemical staining techniques. Four hybridoma clones producing monoclonal antibodies (MAbs) against the human gastrointestinal glutathione peroxidase were established from mice immunized with a gastrointestinal glutathione peroxidase-derived peptide. The MAbs did not crossreact with other members of the glutathione peroxidase family, be it cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, or extracellular glutathione peroxidase. Although the MAbs were found to react with a 24-kD protein in a Western blotting assay using gastric carcinoma cell extracts as antigen, they did not react with a B-lymphoblastoid cell extract. Immunohistochemical staining showed gastrointestinal glutathione peroxidase localized in the cytoplasm and in the nucleus of gastric carcinoma cells. Moreover, gastrointestinal glutathione peroxidase was detected in tissue extracts of human stomach, small intestine, large intestine, liver, and gallbladder by Western blotting, and its localization was immunohistochemically confirmed in the mucosal epithelia of the basal area of gastric pits and intestinal crypts.

Role of glutathione S-transferases in protection against lipid peroxidation. Overexpression of hGSTA2-2 in K562 cells protects against hydrogen peroxide-induced apoptosis and inhibits JNK and caspase 3 activation

The physiological significance of the selenium-independent glutathione peroxidase (GPx) activity of glutathione S-transferases (GSTs), associated with the major Alpha class isoenzymes hGSTA1-1 and hGSTA2-2, is not known. In the present studies we demonstrate that these isoenzymes show high GPx activity toward phospholipid hydroperoxides (PL-OOH) and they can catalyze GSH-dependent reduction of PL-OOH in situ in biological membranes. A major portion of GPx activity of human liver and testis toward phosphatidylcholine hydroperoxide (PC-OOH) is contributed by the Alpha class GSTs. Overexpression of hGSTA2-2 in K562 cells attenuates lipid peroxidation under normal conditions as well as during the oxidative stress and confers about 1.5-fold resistance to these cells from H(2)O(2) cytotoxicity. Treatment with 30 microm H(2)O(2) for 48 h or 40 microm PC-OOH for 8 h causes apoptosis in control cells, whereas hGSTA2-2-overexpressing cells are protected from apoptosis under these conditions. In control cells, H(2)O(2) treatment causes an early (within 2 h), robust, and persistent (at least 24 h) activation of JNK, whereas in hGSTA2-2-overexpressing cells, only a slight activation of JNK activity is observed at 6 h which declines to basal levels within 24 h. Caspase 3-mediated poly(ADP-ribose) polymerase cleavage is also inhibited in cells overexpressing hGSTA2-2. hGSTA2 transfection does not affect the function of antioxidant enzymes including GPx activity toward H(2)O(2) suggesting that the Alpha class GSTs play an important role in regulation of the intracellular concentrations of the lipid peroxidation products that may be involved in the signaling mechanisms of apoptosis.

Nitric oxide insufficiency, platelet activation, and arterial thrombosis

Nitric oxide (NO) was originally discovered as a vasodilator product of the endothelium. Over the last 15 years, this vascular mediator has been shown to have important antiplatelet actions as well. By activating guanylyl cyclase, inhibiting phosphoinositide 3-kinase, impairing capacitative calcium influx, and inhibiting cyclooxygenase-1, endothelial NO limits platelet activation, adhesion, and aggregation. Platelets are also an important source of NO, and this platelet-derived NO pool limits recruitment of platelets to the platelet-rich thrombus. A deficiency of bioactive NO is associated with arterial thrombosis in animal models, individuals with endothelial dysfunction, and patients with a deficiency of the extracellular antioxidant enzyme glutathione peroxidase-3. This enzyme catalyzes the reduction of hydrogen and lipid peroxides, which limits the availability of these reactive oxygen species to react with and inactivate NO. The complex biochemical reactions that underlie the function and inactivation of NO in the vasculature represent an important set of targets for therapeutic intervention for the prevention and treatment of arterial thrombotic disorders.

Selenium and glutathione levels, and glutathione peroxidase activities in blood components of uremic patients on hemodialysis supplemented with selenium and treated with erythropoietin

Patients with chronic renal failure (CRF) often have reduced concentrations of selenium (Se) and lowered activities of glutathione peroxidase (GSH-Px) in blood components. The kidney is a major source of plasma GSH-Px. We measured Se and glutathione levels in blood components and red cell and plasma GSH-Px activities in 58 uremic patients on regular (3 times a week) hemodialysis (HD). The dialyzed patients were divided in 4 subgroups and were supplemented for 3 months with: 1) placebo (bakers yeast), 2) erythropoietin (EPO; 3 times a week with 2,000 U after each HD session), 3) Se-rich yeast (300 microg 3 times a week after each HD), and 4) Se-rich yeast plus EPO in doses as above. The results were compared with those for 25 healthy subjects. The Se concentrations and GSH-Px activities in the blood components of dialyzed uremic patients were significantly lower compared with the control group. Treatment of the HD patients with placebo and EPO only did not change the parameters studied. The treatment with Se as well as with Se and EPO caused an increase in Se levels and red cell GSH-Px activity. Plasma GSH-Px activity, however, increased only slowly or did not change after treatment with Se and with Se plus EPO. In the group treated with Se plus EPO the element concentration in blood components was higher compared with the group supplemented with Se alone. The weak or absence of response in plasma GSH-Px activity to Se supply indicates that the impaired kidney of uremic HD patients has reduced possibilities to synthesize this enzyme.

Relationship between metabolic glycaemic control and platelet content of glutathione and its related enzymes, in insulin-dependent diabetes mellitus

The relationship between glycaemic metabolic control and intracellular concentration of reduced glutathione (GSH) and related enzymes GSH-peroxidase (GSH-Px), GSH-reductase (GSH-Red), GSH-transferase (GSH-Tr), glucose-6-P-dehydrogenase (G6PDH), and thioltransferase (TT) in patients with insulin-dependent diabetes mellitus (IDDM) is controversial. Choosing platelets as cell model (as commonly done in previous studies), the aim of this study was to relate the platelet content of GSH and related enzymes to glycaemic metabolic control, expressed as glycated haemoglobin (HbA1c), as well as to presence of retinopathy and nephropathy in 114 IDDM patients. As compared to controls, both GSH and GSH-Red (geometric means (95% CI)) were significantly increased in platelets of diabetic patients: 3.3 (0.7-9.6) vs. 2.4 (0.8-7.6) mmol 10(-9) platelets; P=0.01 for GSH, and 30.6 (14.7-61.6) vs. 22.2 (8.7-52.2) mU 10(-9) platelets, P=0.0002 for GSH-Red, and TT activity was marginally decreased in the IDDM group (P=0.06). While no clear relationship was present between GSH-related enzymes and HbA1c, a trend was present toward a non-linear relation between HbA1c and GSH, being significantly related by a parabolic curve (P=0.002). As compared to patients with normoalbuminuria (n=88), diabetic patients with increased urinary albumin excretion rate (n=26) had a significant decrease in platelet TT concentration (3.2 (0.9-6.7) vs. 5.1 (1.9-18.7) mU 10(-9) platelets; P=0.0002), whereas retinopathy was not associated to modifications in GSH or in the enzymatic pattern. In summary: (a) platelet GSH and GSH-Red are increased in IDDM, while other enzymes are unmodified; (b) GSH seems to be related to metabolic control according to non-linear parabolic curve; (c) presence of increased albuminuria is associated to a selective decrease in platelet TT content.

Regulation of cyclooxygenase and 12-lipoxygenase catalysis by phospholipid hydroperoxide glutathione peroxidase in A431 cells

Regulation of arachidonate metabolism in human epidermoid carcinoma A431 cells by phospholipid hydroperoxide glutathione peroxidase (PHGPx) and cytosolic glutathione peroxidase (GPx1) was studied. In order to study the effect of reduced glutathione (GSH) on the catalysis regulation of these oxygenation enzymes, diethyl maleate was used to deplete the intracellular GSH. In the presence of 13-hydroperoxyoctadecadienoic acid, the enzymatic catalysis of cyclooxygenase and 12-lipoxygenase was significantly increased in the GSH-depleted cells. In terms of the inhibitory effect on 12-lipoxygenase, PHGPx was more sensitive to GSH concentrations than GPx1. Inhibition of PHGPx activity by the treatment of cells with antisense oligonucleotide of PHGPx mRNA increased the enzymatic catalysis of both cyclooxygenase and 12-lipoxygenase. In conclusion, the results indicate that catalysis of cyclooxygenase and 12-lipoxygenase in A431 cells was regulated by redox-reaction, and PHGPx seems to play an important role in the controlling of these reactions.

Inhibitory effect of phospholipid hydroperoxide glutathione peroxidase on the activity of lipoxygenases and cyclooxygenases

The partially purified phospholipid hydroperoxide glutathione peroxidase (PHGPx) from A431 cells was used to systematically compare the inhibitory effect on the enzyme activity of various lipoxygenases and cyclooxygenases. Under the standard assay system, platelet 12-lipoxygenase, 15-lipoxygenase, and cyclooxygenase-2 were the most sensitive to the inhibition by PHGPx. 5-Lipoxygenase and cyclooxygenase-1 were less sensitive to the inhibition by PHGPx than platelet 12-lipoxygenase and cyclooxygenase-2, respectively, and the difference was approximately 10-fold. Reduction of 12(S)-hydroperoxyeicosatetraenoic acid to 12(S)-hydroxyeicosatetraenoic acid by PHGPx was observed in the presence of glutathione (GSH), and the inhibitory effect of PHGPx on 12-lipoxygenase-catalyzed arachidonate metabolism was reversed by the addition of exogenous lipid hydroperoxide. The results indicate that PHGPx directly reduced lipid hydroperoxides and then down-regulated the activity of arachidonate oxygenases. Moreover, a high-level expression of PHGPx mRNA and its 12-lipoxygenase-inhibitory activity was observed in cancer cells and endothelial cells, and these results suggest that PHGPx may play a significant role in the regulation of reactive oxygen species formation in these cells.

The CCAAT-box binding factor NF-Y is required for the expression of phospholipid hydroperoxide glutathione peroxidase in human epidermoid carcinoma A431 cells

Promoter activation in the expression of phospholipid hydroperoxide glutathione peroxidase (PHGPx) gene in human epidermoid carcinoma A431 cells was studied in the present investigation. Luciferase reporter assays with plasmids carrying a 400 bp of the promoter DNA were performed to analyze the regulatory element in the proximal promoter of human PHGPx gene. Transient transfection with a series of 5'-deletion and internal truncation mutants showed that the 5'-flanking region spanning from -212 to -121 bp was important for the basal expression of PHGPx gene in A431 cells. A region from -170 to -140 bp was protected in DNase I footprinting assays and bound the nuclear proteins in electrophoretic mobility shift assays. This region, denoted FP3, contains the consensus recognition sites for AP-2, CCAAT-box and CRE. The oligonucleotide competitor with the mutation at CCAAT-box could not eliminate the nuclear protein binding in gel-shift assay and the site-directed mutagenesis at the CCAAT-box decreased the luciferase activity of PHGPx promoter for approximate 50% in reporter gene assays. Competition experiments indicate that the binding of nuclear factor to the FP3 region was abolished by oligodeoxyribonucleotide corresponding to NF-Y/CP1 binding site to a greater extent than by those corresponding to sites for CTF/NFI and C/EBP. Taken together, the CCAAT-box in the promoter ranging from -156 to -151 bp, bound to NF-Y/CP1, was essential for the basal expression of human PHGPx gene in A431 cells.

The role of human glutathione S-transferases hGSTA1-1 and hGSTA2-2 in protection against oxidative stress

In order to elucidate the protective role of glutathione S-transferases (GSTs) against oxidative stress, we have investigated the kinetic properties of the human alpha-class GSTs, hGSTA1-1 and hGSTA2-2, toward physiologically relevant hydroperoxides and have studied the role of these enzymes in glutathione (GSH)-dependent reduction of these hydroperoxides in human liver. We have cloned hGSTA1-1 and hGSTA2-2 from a human lung cDNA library and expressed both in Escherichia coli. Both isozymes had remarkably high peroxidase activity toward fatty acid hydroperoxides, phospholipid hydroperoxides, and cumene hydroperoxide. In general, the activity of hGSTA2-2 was higher than that of hGSTA1-1 toward these substrates. For example, the catalytic efficiency (kcat/Km) of hGSTA1-1 for phosphatidylcholine (PC) hydroperoxide and phosphatidylethanolamine (PE) hydroperoxide was found to be 181.3 and 199.6 s-1 mM-1, respectively, while the catalytic efficiency of hGSTA2-2 for PC-hydroperoxide and PE-hydroperoxide was 317.5 and 353 s-1 mM-1, respectively. Immunotitration studies with human liver extracts showed that the antibodies against human alpha-class GSTs immunoprecipitated about 55 and 75% of glutathione peroxidase (GPx) activity of human liver toward PC-hydroperoxide and cumene hydroperoxide, respectively. GPx activity was not immunoprecipitated by the same antibodies from human erythrocyte hemolysates. These results show that the alpha-class GSTs contribute a major portion of GPx activity toward lipid hydroperoxides in human liver. Our results also suggest that GSTs may be involved in the reduction of 5-hydroperoxyeicosatetraenoic acid, an important intermediate in the 5-lipoxygenase pathway.

Human plasma glutathione peroxidase and symptom severity in schizophrenia

BACKGROUND

Previous studies have shown impaired antioxidant defense system in schizophrenia, including alterations in glutathione peroxidase (GSH-Px) activity in erythrocytes. There exists a related enzyme, human plasma GSH-Px (hpGSH-Px), that has not been previously examined in schizophrenia.

METHODS

An enzyme-linked immunoassay was used to determine hpGSH-Px levels in male schizophrenic patients (n = 39), using a within-subject, on-off haloperidol (HD) treatment design, compared with age- and gender-matched normal control subjects (n = 37).

RESULTS

hpGSH-Px was not significantly different between normal control subjects and patients, consistent with our previous findings in erythrocyte GSH-Px. There were no significant treatment effects. hpGSH-Px was significantly and positively correlated with psychosis rating scores in patients both on and off HD treatment.

CONCLUSIONS

Although not different from normal controls, hpGSH-Px levels in patients may reflect oxidative stress associated with greater psychosis severity. The present findings thus suggest that schizophrenic patients, without obvious increase of endogenous antioxidant enzymes (e.g., hpGSH-Px), may be at risk for oxidative damage.

Extracellular glutathione peroxidase from the blood-sucking bug, rhodnius prolixus

Glutathione peroxidase (GPX) activity was measured in several tissues of the blood-sucking bug, Rhodnius prolixus. In contrast to the pattern found in vertebrates, where GPX is predominantly intracellular, the highest levels of this enzyme in Rhodnius were found in the hemolymph. The hemolymph glutathione-dependent peroxidase accepted both H(2)O(2) and t-butyl hydroperoxide as substrates. This fact, together with the absolute glutathione dependence, inhibition by mercaptosuccinate, insensitivity to cyanide, and a molecular mass (100.7 kDa) similar to vertebrate GPXs, led us to attribute this peroxidatic activity to a Se-dependent enzyme. Hemolymph GPX specific activity increases during development and a twofold stimulation was observed after an oxidative challenge with hemin, suggesting that enzyme synthesis is under regulatory control. A role for extracellular GPX as an antioxidant protection against oxidative damage produced by heme derived from digestion of blood hemoglobin is discussed. Arch. Copyright 1999 Wiley-Liss, Inc.

Selenoproteins are expressed in fetal human osteoblast-like cells

Selenoproteins are involved in mechanisms of cell differentiation and defense. We investigated the expression of glutathione peroxidases, as well as other selenoproteins, in fetal human osteoblasts (hFOB-cells). Using 75-selenium metabolic labelling of viable hFOB-cells, we identified several selenoproteins in cell lysates of about 45-80 kDa and in the migration range of 14 kDa to 24 kDa. Cells expressed low mRNA levels of both cellular glutathione peroxidase and plasma glutathione peroxidase mRNA as analysed by Southern analysis of RT-PCR products. Basal cellular glutathione peroxidase enzyme activity in hFOB-cells (19.7 nmol NADPH oxidised per min and microg protein) was further increased 2.5-fold by the addition of 100 nM sodium selenite to the culture medium for 3 days. Furthermore, expression of selenoprotein P mRNA was demonstrated by RT-PCR. hFOB-cells did not show activities of the selenoproteins type I or type II 5'-deiodinase. In summary, we identified cellular glutathione peroxidase, plasma glutathione peroxidase and selenoprotein P among of a panel of several 75-selenium labelled proteins in human fetal osteoblasts. The expression of selenoproteins like glutathione peroxidases in hFOB-cells represents a new system of osteoblast antioxidative defense that may be relevant for the protection against hydrogen peroxide produced by osteoclasts during bone remodelling.

Identification of a lipoxygenase inhibitor in A431 cells as a phospholipid hydroperoxide glutathione peroxidase

An endogenous lipoxygenase inhibitor, purified from the cytosol of human epidermoid carcinoma A431 cells, was analyzed by N-terminal microsequencing and mass spectrometric analysis. The inhibitor was purified by SDS-PAGE, then subjected to in-gel CNBr cleavage and trypsin digestion. The N-terminal sequence data obtained from a 6-8 kDa band of in-gel CNBr cleavage and the three isolated peptides of in-gel trypsin digestion, and the C-terminal peptide sequence from matrix-assisted laser desorption ionization mass spectrometry matched the sequence of human phospholipid hydroperoxide glutathione peroxidase. The purified inhibitor exhibited peroxidase activity using phosphatidylcholine hydroperoxides as the substrate. We therefore concluded that the lipoxygenase inhibitor present in A431 cells was a phospholipid hydroperoxide glutathione peroxidase.

Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia

Glutathione peroxidase, a selenium-containing enzyme, is believed to protect cells from the toxicity of hydroperoxides. The physiological role of this enzyme has previously been implicated mainly using animals fed with a selenium-deficient diet. Although selenium deficiency also affects the activity of several other cellular selenium-containing enzymes, a dramatic decrease of glutathione peroxidase activity has been postulated to play a role in the pathogenesis of a number of diseases, particularly those whose progression is associated with an overproduction of reactive oxygen species, found in selenium-deficient animals. To further clarify the physiological relevance of this enzyme, a model of mice deficient in cellular glutathione peroxidase (GSHPx-1), the major isoform of glutathione peroxidase ubiquitously expressed in all types of cells, was generated by gene-targeting technology. Mice deficient in this enzyme were apparently healthy and fertile and showed no increased sensitivity to hyperoxia. Their tissues exhibited neither a retarded rate in consuming extracellular hydrogen peroxide nor an increased content of protein carbonyl groups and lipid peroxidation compared with those of wild-type mice. However, platelets from GSHPx-1-deficient mice incubated with arachidonic acid generated less 12-hydroxyeicosatetraenoic acid and more polar products relative to control platelets at a higher concentration of arachidonic acid, presumably reflecting a decreased ability to reduce the 12-hydroperoxyeicosatetraenoic acid intermediate. These results suggest that the contribution of GSHPx-1 to the cellular antioxidant mechanism under normal animal development and physiological conditions and to the pulmonary defense against hyperoxic insult is very limited. Nevertheless, the potential antioxidant role of this enzyme in protecting cells and animals against the pathogenic effect of reactive oxygen species in other disorders remains to be defined. The knockout mouse model described in this report will also provide a new tool for future study to distinguish the physiological role of this enzyme from other selenium-containing proteins in mammals under normal and disease states.

Expression of selenoproteins in various rat and human tissues and cell lines

Various rat and human tissues and cell lines naturally exposed to endogenous or exogenous oxidative stress were examined for their pattern of selenoprotein transcripts. Selenoprotein P mRNA was mainly expressed in rat kidney, testis, liver and lung. In testis, a high phospholipid hydroperoxide glutathione peroxidase (PHGPx) but only a weak cytosolic glutathione peroxidase (cGPx) signal was obtained. In kidney, spleen, heart, liver and lung cGPx mRNA levels were higher than those of PHGPx and for both only weak signals were obtained with brain mRNA. The Northern blot results concerning the tissue distribution of cGPx in the rat were fully supported by activity measurements. None of the human tissues revealed a PHGPx mRNA signal, whereas selenoprotein P transcripts were present in all human tissues with the highest abundance in heart, liver, and lung, tissues which also exhibited strong cGPx signals. The gastrointestinal glutathione peroxidase (GPx-GI) was only expressed in human liver and colon liver. Liver, the organ that showed the broadest repertoire of selenoproteins, has to cope with reactive oxygen intermediates produced during detoxification reactions. Human cell lines of the myeloic system that may be exposed to oxidative stress during inflammatory processes showed distinct cGPx signals: epithelial cells showed low cGPx signals. Similar cGPx mRNA levels were found in normal human thyroid tissue and thyroid carcinoma cells. Among the human cell lines selenoprotein P expression was detected in HepG2 and HTh74 thyroid cells. Our data confirm the necessity of getting specific information on distinct tissue- and cell-specific patterns of selenoprotein expression as endpoints of selenium supply and biological function of the selenoprotein family. Analysis of total selenium contents of tissues or body fluids only provides integrative information on the global selenium status of individuals.

The crystal structure of seleno-glutathione peroxidase from human plasma at 2.9 A resolution

Glutathione peroxidase belongs to the family of selenoproteins and plays an important role in the defense mechanisms of mammals, birds and fish against oxidative damage by catalyzing the reduction of a variety of hydroperoxides, using glutathione as the reducing substrate. However, the physiological role of human plasma glutathione peroxidase remains unclear due to the low levels of reduced glutathione in human plasma and the low reactivity of this enzyme. The crystal structure of human plasma glutathione peroxidase was determined by Patterson search methods using a polyalanine model modified from the known structure of bovine erythrocyte glutathione peroxidase. The structure was refined to a crystallographic R-factor of 0.228 (R(free) = 0.335) with I > 2sigma(I) reflections in the resolution range of 8 to 2.9 A. The asymmetric unit contains a dimer. Tetramers are built up from dimers by crystallographic symmetry. The subunit structure of the plasma enzyme shows the typical structure motif of the thioredoxin fold consisting of a central beta-sheet and several flanking alpha-helices. The active site selenocysteine residue is situated in the loop between beta1 and alpha1 and is located in a pocket on the protein surface. The overall structure of the human plasma enzyme is similar to that of the bovine erythrocyte enzyme. The main differences in their subunit structures are an extended N terminus and the possible existence of a disulfide bridge in the plasma enzyme. Compared to the bovine erythrocyte enzyme, a number of residues in the active site are mutated or deleted in the plasma enzyme, including all the residues that were previously suggested to be involved in glutathione binding. The observed structural differences between the two enzymes suggest differences in substrate binding and specificity.

Selenium status of preterm infants: the effect of postnatal age and method of feeding

Indicators of selenium (Se) status were measured in a longitudinal study of 63 preterm and 46 term infants. Se levels in both groups were similar in the first few days of life. Preterm infants fed parenteral nutrition (PN) for several weeks developed very low plasma Se levels (< 10 micrograms/l). In those receiving either breast milk or formula in conjunction with PN, plasma Se also declined over the first 6 weeks. In the breastfed term infants plasma levels increased by 50%, but there was no increase in the term formula-fed group. In healthy preterm infants who received mainly breast milk, plasma Se concentrations remained constant at newborn levels and were below those of breastfed term infants at 6 weeks. Erythrocyte GSHPx activity did not reflect plasma Se or Se intake. In conclusion, the type of feeding, and hence Se intake, influenced plasma Se concentration in preterm infants. Provision of enteral feeding in conjunction with PN was unable to prevent a decline in plasma Se and at 6 weeks levels were well below those of the reference breastfed term infants.

Selenium metabolism and bioavailability

Selenium (Se) is at once an essential and toxic nutrient that occurs in both inorganic and organic forms. The biological functions of Se are mediated through at least 13 selenoproteins that contain Se as selenocysteine (Se-cyst). The endogenous synthesis of this amino acid from inorganic Se (selenide Se-2) and serine is encoded by a stop codon UGA in mRNA and involves a unique tRNA. Selenium can also substitute for sulfur in methionine to form an analog, selenomethionine (Se-meth), which is the main form of Se found in food. Animals cannot synthesize Se-meth or distinguish it from methionine and as a result it is nonspecifically incorporated into a wide range of Se-containing proteins. The metabolic fate of Se varies according to the form ingested and the overall Se status of an individual. This paper reviews the bioavailability, including absorption, transport, metabolism, storage, and excretion, of the different forms of exogenous and endogenous Se.

Hydrogen peroxide: a review of its use in dentistry

Several dentifrices that contain hydrogen peroxide are currently being marketed. The increased use of bleaching agents containing (or generating) H2O2 prompted this review of the safety of H2O2 when used in oral hygiene. Daily exposure to the low levels of H2O2 present in dentifrices is much lower than that of bleaching agents that contain or produce high levels of H2O2 for an extended period of time. Hydrogen peroxide has been used in dentistry alone or in combination with salts for over 70 years. Studies in which 3% H2O2 or less were used daily for up to 6 years showed occasional transitory irritant effects only in a small number of subjects with preexisting ulceration, or when high levels of salt solutions were concurrently administered. In contrast, bleaching agents that employ or generate high levels of H2O2 or organic peroxides can produce localized oral toxicity following sustained exposure if mishandled. Potential health concerns related to prolonged hydrogen peroxide use have been raised, based on animal studies. From a single study using the hamster cheek pouch model, 30% H2O2 was referred to as a cocarcinogen in the oral mucosa. This (and later) studies have shown that at 3% or less, no cocarcinogenic activity or adverse effects were observed in the hamster cheek pouch following lengthy exposure to H2O2. In patients, prolonged use of hydrogen peroxide decreased plaque and gingivitis indices. However, therapeutic delivery of H2O2 to prevent periodontal disease required mechanical access to subgingival pockets. Furthermore, wound healing following gingival surgery was enhanced due to the antimicrobial effects of topically administered hydrogen peroxide. For most subjects, beneficial effects were seen with H2O2 levels above 1%.

Glutathione peroxidase potentiates the inhibition of platelet function by S-nitrosothiols

GSH peroxidase (Px) catalyzes the reduction of lipid hydroperoxides (LOOH), known metabolic products of platelets and vascular cells. Because interactions between these cells are modulated by nitric oxide (NO) and LOOH inactivate NO, we investigated the effect of GSH-Px on the inhibition of platelet function by the naturally occurring S-nitrosothiol, S-nitroso-glutathione (SNO-Glu). Concentrations of SNO-Glu that alone did not inhibit platelet function (subthreshold inhibitory concentrations) were added to platelet-rich plasma together with GSH-Px (0.2-20 U/ml); this led to a dose-dependent inhibition of platelet aggregation with an IC50 of 0.6 U/ml GSH-Px. In the presence of subthreshold inhibitory concentrations of SNO-Glu, the LOOH, 5-hydroperoxy-6,8,11,14-eicosatetraenoic acid, increased platelet aggregation, an effect reversed by GSH-Px. Glutathione and SNO-Glu were equally effective as cosubstrates for GSH-Px. Incubation of SNO-Glu with GSH-Px for 1 min led to a 48.5% decrease in the concentration of SNO-Glu. Incubation of SNO-Glu with serum albumin led to the formation of S-nitroso-albumin, an effect enhanced by GSH-Px. These observations suggest that GSH-Px has two functions: reduction of LOOH, thereby preventing inactivation of NO, and metabolism of SNO-Glu, thereby liberating NO and/or supporting further transnitrosation reactions.

Suppression of plasma glutathione peroxidase activity by ifosfamide

Plasma glutathione peroxidase (GPx) is synthesized predominantly in the kidneys. Plasma-GPx activities were measured in 12 patients with gynecological malignancies before and after chemotherapy. The patients were treated with cisplatin alone (P); with VP16 and cisplatin (EP); with cyclophosphamide, doxorubicin, and cisplatin (CAP); or with ifosfamide, doxorubicin, and cisplatin (IAP). The protein levels of the enzyme were semi-quantitatively determined by immuno-blot analysis. Plasma GPx activity was decreased by an average of 61% (p < 0.01) in patients treated with IAP, while no significant decreases were observed in patients treated with any drug combinations without ifosfamide. Immuno-blot analysis of plasma samples from a patient treated with IAP revealed no differences in the protein levels of plasma GPx either before or after IAP administration, although the plasma GPx activity decreased 83%, from 0.173 to 0.029 units/ml. The results indicate that the decrease in plasma GPx activity was not due to impaired production of the enzyme in the kidneys, and that ifosfamide is responsible for inhibition of the enzyme activity. Since GPx is an enzyme of major importance in detoxification of lipid peroxides in the brain, CNS toxicity induced by ifosfamide might be related to severe suppression of plasma GPx activity.

Effect of plasma on the degradation of hydroperoxides of unesterified linoleic acid and copper-peroxidized LDL

The determination of lipid hydroperoxides in plasma and lipoproteins recently reached a clinical relevance in disorders such as atherosclerosis, where oxidative reactions have been suggested to play a fundamental pathogenetic role. The peroxide content of lipoproteins is usually measured after ultracentrifugation and extraction. During this procedure, some peroxides might decompose causing a too low recovery. To screen this possibility, the disappearance, in the presence of human plasma, of hydroperoxides of linoleic acid and Cu-oxidized low density lipoprotein (LDL) have been investigated, using both a iodometric titration and an enzymatic assay. While only in the presence of GSH plasma decomposes linoleic acid hydroperoxides quite rapidly, peroxides in Cu-oxidized LDL were stable both in presence as well as in absence of GSH. This indicated that lipid hydroperoxides are stable in plasma and that peroxides of Cu-oxidized LDL are not substrate for the glutathione-dependent peroxidase activity in plasma. The relevant decrease of the iodometric titre of LDL peroxides observed in the presence of elevated amounts of plasma was shown to be artifactual, since some compounds extracted from plasma do react with iodine generated by peroxides. Whole plasma itself, indeed, has been shown to reduce back to I- appreciable amount of free iodine.

Effect of the K+/H+ ionophore nigericin on response of A549 cells to photodynamic therapy and tert-butylhydroperoxide

The K+/H+ ionophore nigericin dramatically increases killing of V79 cells and A549 cells by photodynamic therapy (PDT) sensitized by chloroaluminum phthalocyanine. Previous studies suggested that the interaction between PDT and nigericin is related to the ability of this ionophore to reduce intracellular pH (pHi). The present study was undertaken to test the possibility that nigericin, by lowering pHi, inhibits reductive detoxification of PDT-produced peroxides by enzymes of the glutathione (GSH) redox cycle and the pentose cycle. To test this possibility we examined the effects of nigericin on the toxicity and metabolism of a model peroxide, tert-butylhydroperoxide (tert-BOOH), in A549 cells, a cell line in which the GSH redox cycle is known to be the principal pathway for reduction and detoxification of tert-BOOH. We found that nigericin equilibrates pHi of A549 cells with extracellular pH (pHe) in a time-dependent manner. It increases the toxicity of tert-BOOH toward A549 cells, inhibits loss of tert-BOOH from the buffer overlying the cells, and reduces the rate of 14CO2 release from radiolabelled glucose, which is a measure of pentose cycle activity. These effects are significantly greater at pHe 6.40 than at 7.40. Monensin, a Na+/H+ ionophore which does not reduce pHi, does not enhance the toxicity of tert-BOOH and has only a minimal effect on tert-BOOH reduction. These data suggest that nigericin-induced inhibition of peroxide detoxification is at least a plausible mechanism by which the ionophore might interact with PDT.

Oxygen toxicity

OBJECTIVE

The objective of this article is to provide an overview of the biochemistry of oxygen metabolism, including the formation of free radicals and the role of endogenous antioxidants. Pathophysiologic correlates underlying the clinical manifestations of oxygen toxicity are reviewed and management strategies are outlined.

DATA SOURCES

References from basic science and clinical journals were selected from the authors' files and from a search of a computerized database of the biomedical literature.

STUDY SELECTION

Articles selected for review included both historical and current literature concerning the biochemistry and pathophysiology of oxygen toxicity in animals and humans.

DATA SYNTHESIS

The benefits of oxygen therapy have been known for many years; however, its potential toxicity has not been recognized until the last two decades. The lungs, the eyes, and, under certain conditions, the central nervous system are the organs most affected by prolonged exposure to hyperoxic environments. Free radical formation during cellular metabolism under hyperoxic conditions is recognized as the biochemical basis of oxygen injury to cells and organs. Endogenous antioxidants are a primary means of detoxifying reactive oxygen species and preventing hyperoxia-induced cellular damage. When this defense fails or is overwhelmed by the excessive production of hyperoxia-induced free-radical species, distinctive morphologic changes occur at the cellular level. The amount of hyperoxia required to cause cellular damage and the time course of these changes vary from species to species and from individual to individual within the same species. Age, nutritional status, presence of underlying diseases, and certain drugs may influence the development of oxygen toxicity.

CONCLUSIONS

There is currently no reliably effective drug for preventing or delaying the development of oxygen toxicity in humans. Use of the lowest effective oxygen concentration, the avoidance of certain drugs, and attention to nutritional and metabolic factors remain the best means currently available to avoid or minimize oxygen toxicity. Research is continuing into more effective ways to prevent, diagnose, and treat this disorder.

Molecular cloning of putative odorant-binding and odorant-metabolizing proteins

Olfactory reception occurs via the interaction of odorants with the chemosensory cilia of the olfactory receptor cells located in the nasal epithelium. The cDNA clones from mRNA specific to olfactory mucosa were studied. One of these clones, OBPII, encodes a secretory protein with significant homology to odorant-binding protein (OBP), a protein with broad odorant-binding ability, and is expressed in the lateral nasal gland, which is the site of expression of OBP. The OBPII sequence also shows significant homology to the VEG protein, which is thought to be involved in taste transduction. OBPII is a new member of the lipophilic molecule carrier protein family. The second cDNA clone encodes a novel homologue of glutathione peroxidase, an enzyme involved in cellular biotransformation pathways. Its expression appears to be localized to the Bowman's glands, the site of several previously identified olfactory-specific biotransformation enzymes.

Glutathione and glutathione-metabolizing enzymes in the erythrocytes of healthy children and in children with insulin-dependent diabetes mellitus, juvenile rheumatoid arthritis, coeliac disease and acute lymphoblastic leukaemia

Oxidative biotransformation of xenobiotics and endogenous substances involves glutathione in reduced form as an integral component through two mechanisms: glutathione peroxidase catalysing the reduction of hydrogen peroxide and organic hydroperoxides, and glutathione-S-transferases catalysing the conjugation of oxygenated derivatives with glutathione. We studied glutathione and glutathione-related enzyme activities in haemolysed venous blood samples from 49 healthy children and from 11 children with diabetes mellitus, 10 children with rheumatoid arthritis, seven children with active coeliac disease, and seven children with acute lymphoblastic leukaemia. Among the healthy children glutathione content and the activities of glutathione reductase, glutathione peroxidase, and glutathione-S-transferase were unrelated to sex; age-dependent differences were also minor. The patients with diabetes mellitus had decreased activity of glutathione reductase. The patients with acute lymphoblastic leukaemia had increased activity of both glutathione peroxidase and glutathione-S-transferase, possibly reflecting an adaptive response to free-radicals. The patients with active coeliac disease had control levels of all measured parameters of glutathione-related reactions indicating, since we earlier found decreased activities of glutathione peroxidase in intestinal mucosa of celiacs, that blood may not always reflect tissue-specific changes.

Effects of variation in glutathione peroxidase activity on DNA damage and cell survival in human cells exposed to hydrogen peroxide and t-butyl hydroperoxide

The selenium-dependent glutathione peroxidase activities of two human cell lines, the colon carcinoma HT29 and the mesothelioma P31, cultured in medium containing 2% serum, increased from 195 to 541 and from 94 to 361 units/mg of protein respectively after supplementation with 100 nM-selenite. The catalase activity remained unchanged by this treatment. The effects of the obtained variation in glutathione peroxidase activities were investigated by exposing cells to H2O2 and t-butyl hydroperoxide. Selenite supplementation resulted in a decrease in H2O2-induced DNA single-strand breaks in both HT29 and P31 cells. A small, but significant, decrease in the number of DNA single-strand breaks for low doses (10-50 microM) of t-butyl hydroperoxide was found only in P31 cells and not in HT29 cells. We could detect neither induction of double-strand breaks (detection limit approx. 1000 breaks per cell) nor DNA-protein cross-links after exposing the cells to the two peroxides. In spite of the apparent protective effect of increased glutathione peroxidase activity on DNA single-strand break formation, there were no differences between selenite-supplemented and non-supplemented cells in cell survival after exposure to peroxide.

Enzymic pathways involved in cell response to H2O2

An influence of possible interaction of glutathione peroxidase and cyclooxygenase on the clonogenic survival of epithelial cells exposed in vitro to H2O2 was investigated. Indomethacin served as the inhibitor of cyclooxygenase, and the use of alkaline (7.5) or acidic (6.5) pH combined with controlled supply of glucose modified glutathione peroxidase activity. Indomethacin affected survival of cells exposed to H2O2 in a biphasic manner, enhancing cytotoxicity at lower hydrogen peroxide concentrations, and diminishing it at higher concentrations. The turning point moved gradually to higher concentrations of H2O2 corresponding to the augmented decomposition of hydrogen peroxide caused by increased activity of glutathione peroxidase. The data revealed that both enzymic pathways interact in the presence of H2O2, resulting in the overall cell survival different from that obtained after inhibition of either.

Measurement of hydrogen peroxide in plasma and blood

Measurement of the oxygen metabolite hydrogen peroxide (H2O2) in biological fluids such as plasma could be of interest because it might indicate participation of toxic oxygen species in tissue injury. Recently several reports claimed to measure H2O2 using spectrophotometric and high pressure liquid chromatographic (HPLC) techniques that utilize oxidation of a substrate to a product by a peroxidase. In such a system it is crucial to perform two control experiments to verify whether the measured substance is H2O2. The specificity of the assay for H2O2 should be checked with catalase, and the degradation of H2O2 or inhibition of the assay system by the sample should be checked by determining the recovery of exogenously added H2O2. We performed both types of controls for HPLC and spectrophotometric determinations of H2O2 in plasma and blood. Our results indicate that contrary to previous reports in the literature the measured substance(s) in plasma or blood is not H2O2. Moreover, quantitative measurements of H2O2 in plasma or blood by HPLC was unreliable due to the irreversible binding of H2O2 to the column surface.

Hormonal contraceptive increases plasma lipid peroxides in female rats. Relationship to platelet aggregation and lipid biosynthesis

We investigated whether changes in plasma oxidative properties could occur after oral (hormonal) contraceptive (OC) administration in female rats and whether such changes could be responsible for the platelet increase in aggregation and lipid biosynthesis observed with that treatment. Platelets and plasma (platelet-poor) from control and OC (ethinyl estradiol + lynestrenol)-treated rats were prepared separately. Thrombin-induced aggregation of control platelets was markedly enhanced after incubation for 4 (p less than 0.025) to 60 (p less than 0.001) minutes in OC as compared with control plasma. Under the same conditions, platelet lipid biosynthesis was increased also (p less than 0.05 to p less than 0.01), but after 3 hours incubation. The enhanced response of platelets to aggregation induced by OC plasma could be inhibited by adding either glutathione (p less than 0.025), vitamin E (p less than 0.025), catalase (p less than 0.05), or peroxidase + glutathione (p less than 0.005) to plasma or 2,6,di-bis(ter-butyl)p-cresol (p less than 0.05) to platelets before incubation. The peroxidized free fatty acids isolated from OC plasma added to normal platelets induced a 150% (p less than 0.001) increase in the response to thrombin as compared with the fatty acids from control plasma. In addition, the level of malondialdehyde and conjugated dienes was significantly (p less than 0.02 to p less than 0.001) increased in OC compared with control plasma. We conclude that the enhanced formation in plasma of lipid hydroperoxides seems to be the initial event stimulating platelets after OC treatment, at least in rats.