The role of glutathione and glutathione S-transferases in fatty acid ozonide detoxification

Reductive Cleavage of Organic Peroxides by Iron Salts and Thiols

Despite the low bond strength of the oxygen-oxygen bond, organic peroxides are often surprisingly resistant to cleavage by nucleophiles and reductants. As a result, achieving decomposition under mild conditions can be challenging. Herein, we explore the reactivity of a selection of peroxides toward thiolates, phenyl selenide, Fe(II) salts, and iron thiolates. Peroxides activated by conjugation, strain, or stereoelectronics are rapidly cleaved at room temperature by thiolate anions, phenylselenide, or Fe(II) salts. Under the same conditions, unhindered dialkyl peroxides are only marginally reactive; hindered peroxides, including triacetone triperoxide and diacetone diperoxide (DADP), are inert. In contrast, all but the most hindered of peroxides are rapidly (<1 min at concentrations down to ∼40 mM) cleaved by mixtures of thiols and iron salts. Our observations suggest the possible intermediacy of strongly reducing complexes that are readily regenerated in the presence of stoichiometric thiolate or hydride. In the case of DADP, an easily prepared explosive of significant societal concern, catalytic amounts of iron and thiol are capable of promoting rapid and complete disproportionation. The availability of inexpensive and readily available catalysts for the mild reductive degradation of all but the most hindered of peroxides could have significant applications for controlled remediation of explosives or unwanted radical initiators.

To What Extent Does Ozone Therapy Need a Real Biochemical Control System? Assessment and Importance of Oxidative Stress

Ozone therapy is not officially allowed in many countries, but private medical services are using this therapy worldwide. However, appropriate control systems to assess the benefits and risks of systemic ozone therapy are not always used and in such cases the treatment is based on anecdotal reports. Oxidative stress phenomenon is becoming a highlighted biological process for ozone therapy because it is deeply involved in its mechanism of action. On the contrary, ozone therapy is an efficient regulator of the oxidative stress processes. In terms of therapeutic effects, it is convenient to know the metabolic status of the organism to face new oxidative challenges before and during ozone therapy applications. Oxidative stress is also important because it is involved as a cause or effect of many diseases. Since the 1990s, there has been the necessity of developing reliable systems for measuring oxidative stress in humans. In this sense, we have proposed a system for oxidative stress diagnosis that can serve as a control system for systemic ozone therapy applications. The system is based on the blood measurement of eight biomarkers (GSH, GPx, GST, SOD, CAT, DC, SRATB, and HPT) and the interpretation of these values by a computer-developed algorithm yielding four new indices (total antioxidant activity, total prooxidant activity, redox index and grade of oxidative stress). The system shows the patient's redox status and estimation of the oxidative stress level, with this information being relevant regarding implications on dosage and therapeutic effectiveness of ozone therapy.

Antioxidant and inflammatory responses of healthy horses and horses affected by recurrent airway obstruction to inhaled ozone

REASONS FOR PERFORMING STUDY

Inhaled ozone can induce oxidative injury and airway inflammation. Horses affected by recurrent airway obstruction (RAO) have a decreased pulmonary antioxidant capacity, which may render them more susceptible to oxidative challenge. It is currently unknown whether RAO-affected horses are more susceptible to oxidative stress than those unaffected by RAO.

OBJECTIVES

To determine whether ozone exposure induces greater oxidative stress and airway inflammation in RAO-affected horses in remission than in healthy horses.

METHODS

Seven healthy control horses and 7 RAO-affected horses were exposed to 0.8 ppm ozone for 2 h at rest.

RESULTS

At baseline, bronchoalveolar lavage fluid (BALF) ascorbic acid concentrations were lower in RAO-affected horses than healthy controls. Ozone appeared to preferentially oxidise glutathione rather than ascorbic acid 6 h after exposure. Individual healthy and RAO-affected horses demonstrated oxidation of BALF glutathione after ozone exposure. Overall, RAO-affected horses did not demonstrate increased oxidative stress following ozone exposure, compared with healthy horses. Ozone did not induce significant airway inflammation in either group.

CONCLUSIONS

RAO-affected horses in remission are not more sensitive to ozone despite a decreased pulmonary antioxidant capacity. Sensitivity to ozone appears to be independent of initial pulmonary antioxidant status.

POTENTIAL RELEVANCE

Horses with high susceptibility to oxidative stress may benefit from antioxidant supplementation.

Generation of oxidative stress in human cutaneous models following in vitro ozone exposure

Ozone, one of the main components of photochemical smog, represents an important source of environmental oxidative stress. The skin, being the outermost barrier of the body, is directly exposed to environmental oxidant toxicants. Skin sebum and cellular plasma membrane lipids contain polyunsaturated fatty acids which are primary targets for ozone and free radical attack induced lipid peroxides. These ozonation processes in skin can also generate aldehydes, hydroxyhydroperoxides and specific Criegee's ozonides. In order to evaluate in vitro human skin susceptibility to ozone, we have exposed cultured immortalized human keratinocytes (DK7-NR) and the reconstructed human epidermis Episkin to 10 ppm of ozone in a specific incubator. We measured the formation of protein carbonyls by an ELISA method and monitored the oxidative stress using the fluorogenic probe 2',7'-dichlorofluorescin-diacetate (DCFH-DA). Results showed a time-dependent increase of fluorescence levels (linked to oxidative stress) in both models exposed to ozone. Using this protocol, we investigated the protective potential of different products including vitamin C, a thiol derivative and a plant extract. All products dramatically reduced oxidative responses during ozone exposure. Decreases observed in fluorescence levels were between 60 and 90% as compared to non-protected controls. These results demonstrate: (a) cutaneous in vitro models are remarkably susceptible to oxidative stress generated by an environmental air pollutant as ozone, and (b) raw antioxidants, thiols and vitamin C were efficient products to prevent ozone induced cellular oxidative damage.

Microsomal glutathione transferase: lipid-derived substrates and lipid dependence

Rat liver microsomal glutathione transferase was found to display glutathione peroxidase activity toward a variety of oxidized lipids. 1-Linoleoyl-2-palmitoyl phosphatidylcholine hydroperoxide, 2-linoleoyl-1-palmitoyl phosphatidylcholine hydroperoxide, 2-linoleoyl-1-palmitoyl phosphatidylethanolamine hydroperoxide, and cholesteryl linoleate hydroperoxide all served as substrates (0.02, 0.04, 0.02, and 0.02 mumol/min mg, respectively). The phospholipid hydroperoxide glutathione peroxidase activity of the enzyme was found not to require detergent and increased when liposomes containing peroxidized phospholipid were fused with liposomes containing microsomal glutathione transferase. Methyl linoleate ozonide serves as a very efficient substrate for the microsomal glutathione transferase. The unactivated and N-ethylmaleimide-activated enzyme displayed specific activities of 0.74 and 5.9 mumol/min mg, respectively. Upon examination of a series of 4-hydroxyalk-2-enals it was found that the catalytic efficiency of the enzyme increases from the 4-hydroxyhept-2-enal up to the 4-hydroxytetradec-2-enal. The specific activities with the various 4-hydroxyalk-2-enals tested varied between 0.28 and 0.95 mumol/min mg. The phospholipid dependence of the microsomal glutathione transferase was examined in proteoliposomes formed by cholate dialysis. Phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, and rat liver microsomal phospholipids could all be used successfully to reconstitute the enzyme. In conclusion, microsomal glutathione transferase can detoxify a number of lipid peroxidation products as well as a fatty acid ozonide. The results imply a protective role for the enzyme under conditions of oxidative stress.

Ozone-induced lung toxicity: mediated by ozonides?

In an in vitro study a comparison was made between the cytotoxicities of a model ozonide, methyl linoleate-9,10-ozonide (MLO), and a model peroxidative agent, cumene hydroperoxide (CumOOH), by measuring the effects of both compounds on the phagocytosing capacity of rat alveolar macrophages. Toxicity as well as detoxication characteristics of the ozonide were found to be similar to those of ozone: (1) vitamin E protected the alveolar macrophages in vitro against the ozonide, (2) glutathione (GSH) depletion enhanced the sensitivity of the cells towards the ozonide and (3) the ozonide did not enhance lipid peroxidation. This also suggests that GSH depletion, followed by lipid peroxidation, does not underlie the MLO toxicity. This was supported by the differences in protection provided by vitamin C, vitamin E and GSH. Supplementation of the macrophages with vitamin C resulted in a decrease in their sensitivity towards MLO and an increase in their sensitivity towards CumOOH. Following GSH depletion the sensitivity of the cells towards CumOOH had increased more than that towards MLO. Exposure to CumOOH led to a more extensive vitamin E depletion. The results of an in vivo study on the toxicity of MLO (in the rat) largely confirmed the findings of the in vitro study: partial contributions of vitamin E and the glutathione system to the protection against MLO.

Effects of air pollutants on the growth and antioxidative system of Norway spruce exposed in open-top chambers

Grafted Norway spruce trees were subjected to exposure beginning in April 1988, to one of four different air treatments in open-top chambers: Charcoal filtered air (CF), non-filtered air (NF), non-filtered air with the addition of O(3) during summer (NFO), and SO(2) plus NO(2) during winter (NFOSN). CF trees were considered as the reference group. No effects on growth parameters were observed. Samples of the two youngest needle year classes were taken late in November 1989 for enzyme determinations. The activity of ascorbic acid peroxidase (A-POD) increased the same level in all treatments, and activities of catalase and dehydroascorbic acid reductase (DHA-R) increased only in NF and NFO treatments. A higher level of activity in the NFOSN treatment was observed only for glucose-6-phosphate-dehydrogenase (Glc-6-P-DH) and non-specific peroxidase (POD). Isoelectric focusing of POD showed a changed pattern in the NFOSN treatment. Neither activity nor isoelectric focusing of superoxidase dismutase (SOD) was changed in any of the treatments.

Molecular orbital study on the glutathione-dependent detoxication of ozonides

The present paper describes a theoretical study on the mechanism underlying the reaction of cellular glutathione (GSH) with polyunsaturated fatty acid ozonides. The reaction can be catalyzed by glutathione S-transferases and leads to detoxication of the ozonides. Semi-empirical molecular orbital computer calculations suggest that the reaction of glutathione with ozonides involves a nucleophilic attack at one of the carbon atoms of the ozonide ring, instead of at one of the peroxidic oxygen atoms of the ozonide ring. This implies a mechanism different from that of the glutathione S-transferase-mediated reaction with hydroperoxides, previously proposed for the glutathione-dependent detoxication of fatty acid ozonides.

Separation and spectral data of the six isomeric ozonides from methyl oleate

The structures of the products obtained on ozonation of methyl oleate have been re-examined. The assignments for the six isomeric ozonides of methyl oleate have been made by 1H and 13C nuclear magnetic resonance (NMR), which were consistent with the retention times observed in high-performance liquid chromatography; the assignments were confirmed by mass and infrared spectroscopy. Two triplets for the ozonide ring protons of the cis and trans isomers in the normal (MOO1) and the two cross ozonides (MOO1 and MOO3) can be resolved by 400 MHz NMR. For MOO1 and MOO3, where the two ring carbons are equivalent, two peaks for the ring carbons of each cross ozonides are resolved in the 13C NMR spectra, one for the cis and one for the trans isomer. For MOO2, four peaks for the ring carbons are resolved in the 13C NMR spectra, two for the cis and two for the trans isomer.

Comparative study on the toxicity of methyl linoleate-9,10-ozonide and cumene hydroperoxide to alveolar macrophages

In the present study the in vitro toxicities of methyl linoleate-9,10-ozonide (MLO) and cumene hydroperoxide (CumOOH), a model peroxidative agent, are compared. This was carried out using the inhibition of alveolar macrophage phagocytosis as an assessment of in vitro toxicity. Both agents, MLO and CumOOH caused a dose-dependent decrease in the phagocytosing activity of alveolar macrophages isolated from rat lungs. MLO was found to be three times more toxic than CumOOH. Supplementation of macrophages with vitamin C resulted in a decrease of their sensitivity towards MLO and an increase of their sensitivity towards CumOOH, suggesting that different mechanisms underlie the toxic effects of the compounds concerned. This was supported by the data on GSH and vitamin E depletion. In both cases, depletion of the antioxidant was more extensive on exposure to CumOOH. In addition, following GSH depletion, the sensitivity of the macrophages towards CumOOH was more increased than towards MLO. Further, MLO was not able to enhance the peroxide formation from methyl linoleate (ML), whereas CumOOH initiated the peroxide formation of ML. The results of ESR spin trap experiments further supported that MLO-induced toxicity is independent of lipid peroxidation. From all this it is concluded that both mechanisms known to be of importance for peroxide-induced cell toxicity, i.e., depletion of cellular GSH levels and/or lipid peroxidation are not the main processes causing MLO toxicity in vitro.

Ozone inactivates HIV at noncytotoxic concentrations

The inactivation of human immunodeficiency virus (HIV) and cytotoxic properties of ozone-treated serum and serum-supplemented media were examined. The titer of HIV suspensions in human serum was reduced in a dose-dependent manner when treated with total reacted ozone concentrations at a range of 0.5 to 3.5 micrograms/ml-1. Complete inactivation of HIV suspensions was achieved by 4.0 micrograms/ml-1 of ozone in the presence or absence of H-9 cells. In contrast, cellular metabolism, as measured by MTT dye cleavage, and DNA replication, as measured by BUdR incorporation, were enhanced in H-9 cells grown in media treated with quantities of ozone that completely inactivate HIV. The permissively HIV-infected cell line HXB/H-9 was cultured in ozone-treated media for six days with culture supernatants being sampled and assayed on alternate days for HIV p24 core protein. HIV p24 was reduced in all treated cultures compared to control cultures, with an average reduction of 46% [p24].

Effects of in vitro ozone exposure on peroxidative damage, membrane leakage, and taurine content of rat alveolar macrophages

Rat alveolar macrophages (AM) were isolated by pulmonary lavage, allowed to adhere to a tissue culture flask, and then exposed to 0.45 +/- 0.05 ppm ozone. After exposures ranging from 0 to 60 min, the medium was decanted and cells were harvested. Cells were assayed for oxidant damage and media analyzed for leakage of intracellular components. Increasing length of exposure to ozone resulted in a decreased number of adherent AM and decreased cell viability. Resting and zymosan-stimulated chemiluminescence increased immediately after ozone exposure and reached a maximum at 15-30 min, then declined to initial levels after 60 min of ozone exposure. Lipid peroxidation and leakage of protein and K+ ions increased with increasing length of exposure to ozone, while leakage of reduced and oxidized glutathione increased through 30 min, then declined (reduced) or leveled off (oxidized). Activity of the Na+/K+ ATPase decreased with time while intracellular taurine concentration exhibited an initial rise, peaked at 30 min, and then returned to the untreated level. Leakage of taurine into the medium increased with time of exposure, suggesting that exposure of AM to ozone results in a shift from bound to free intracellular taurine. These data indicate that in vitro exposure of AM to ozone results in a time-dependent alteration of cell function, membrane integrity, and viability.

Methyl linoleate ozonide as a substrate for rat glutathione S-transferases: reaction pathway and isoenzyme selectivity

The 9,10-mono-ozonide of methyl linoleate was shown to be a substrate for rat hepatic cytosolic, rat lung cytosolic and rat hepatic microsomal glutathione S-transferases (GST). The activities of lung cytosol and liver microsomes with methyl linoleate ozonide (MLO) were found to be high relative to the activity demonstrated by liver cytosol, as compared with their respective activities towards 1-chloro-2,4-dinitrobenzene (CDNB). Only a slight catalytic activity towards the ozonide was noticed for rat lung microsomes. Isoenzyme 2-2 exhibited the highest specific activity (208 nmol/min/mg) when isoenzymes 1-1, 1-2, 2-2, 3-3, 3-4, 4-4 and 7-7 were compared. This isoenzyme accounts for approx. 25% of cytosolic GST protein in rat lung, while in rat liver it represents approx. 9%. This may partly explain the high activity towards the ozonide noticed for rat lung cytosol. No stable conjugates were formed as products of the reaction of MLO with glutathione; although two glutathione-conjugates were noticed on TLC, they were only formed as intermediate compounds. Coupling of an aldehyde dehydrogenase assay or a glutathione reductase assay to the GST-catalyzed conjugation, demonstrated that oxidized glutathione and aldehydes are formed as the major products in the reaction. To further confirm the formation of aldehydes, the products of the GST-catalyzed reaction were incubated with 2,4-dinitrophenylhydrazine, which resulted in hydrazone formation. In conclusion, the activity of the GST towards the ozonide of methyl linoleate is similar to their peroxidase activity with lipid hydroperoxides as substrates.

Methyl linoleate ozonide: a substrate for rat glutathione S-transferases

Glutathione S-transferases (GST) were shown to be capable of reducing the toxicity of the ozonide of methyl linoleate (MLO) by catalyzing its reaction with reduced glutathione (GSH). MLO was a substrate for both cytosolic and microsomal GST. Isoenzyme 2-2 demonstrated the highest specific activity. Oxidised glutathione and aldehydes were identified as products of the reaction, with unstable glutathione-conjugates being formed as intermediates only. It was concluded that the GST-activity toward MLO may be similar to the GST-peroxidase activity with lipid hydroperoxides as substrates.