Effects of water-soluble antioxidant from spinach, NAO, on doxorubicin-induced heart injury

Doxorubicin (DOX) produces clinically restorative responses in numerous human cancers, but its cardiotoxicity has limited its usefulness. Because reactive oxygen species may affect DOX-induced antitumor activity and cardiotoxicity, we evaluated the prophylactic effect of spinach natural antioxidant (NAO) on DOX-induced cardiotoxicity and oxidative stress in female Balb/c mice using histological, electron microscopical and biochemical parameters. Mice were treated with NAO for 7 days prior to and/or for 6 days after DOX administration. Pretreatment with NAO (cumulative dose: 130 mg/kg) did not hinder the effectiveness of DOX. Light and electron microscopy of DOX-treated heart revealed myocardial degeneration. When administered combined before and after DOX, NAO conferred the most significant cardiac protection. The effects of NAO on the lipid peroxidation product, malondialdehyde, and on H2O2/ hydroperoxides were examined on day 6 following DOX administration; levels of both were elevated in DOX-treated mice, compared to control. Pretreatment with NAO prevented these changes. Pretreatment with NAO before DOX administration decreased catalase and increased superoxide dismutase activities compared to the DOX group. Our results suggest usage of NAO in combination with DOX as a prophylactic strategy to protect heart muscle from DOX-induced cellular damage.

Oxidative DNA damage and cardiovascular disease

Reactive oxygen species can directly cause covalent modifications to DNA. Alternatively, they can initiate the formation of lipid hydroperoxides, which undergo homolytic decomposition to the alpha,beta-unsaturated aldehyde genotoxins, 4-oxo-2-nonenal, 4,5-epoxy-2(E)-decenal, and 4-hydroxy-2-nonenal through two quite separate pathways. One pathway involves a complex rearrangement of the alkoxy radical derived from the lipid hydroperoxide. The other pathway involves the intermediate formation of 4-hydroperoxy-2-nonenal. Lipid hydroperoxides can also be derived from the action of lipoxygenases and cyclooxygenases on polyunsaturated fatty acids. 4,5-Epoxy-2(E)-decenal forms etheno-2'-deoxyadenosine adduct with DNA, a mutagenic lesion observed in human tissue DNA samples. Several new ethano- and etheno-DNA adducts have been identified from the reaction of 4-oxo-2-nonenal with DNA. Malondialdehyde, another genotoxic bifunctional electrophile, forms a propano adduct with 2'-deoxyguanosine (M1G-dR) rather than an etheno adduct. Very little is known about the consequences of lipid hydroperoxide-mediated DNA damage in cardiovascular diseases. This should prove to be an important area for future research.

Oxidant injury, nitric oxide and pulmonary vascular function: implications for the exercising horse

The athletic ability of the horse is facilitated by vital physiological adaptations to high-intensity exercise, including a thin (but strong) pulmonary blood-gas barrier, a large pulmonary functional reserve capacity and a consequent maximum oxygen uptake (VO2max) far higher than in other species. A high pulmonary artery pressure also serves to enhance pulmonary function, although stress failure of lung capillaries at high pulmonary transmural pressures, and the contribution of other factors which act in the exercising horse to increase pulmonary vascular tone, may lead to pathological or pathophysiological sequelae, such as exercise-induced pulmonary haemorrhage (EIPH). Reactive oxygen species (ROS) are an important component of the mammalian inflammatory response. They are released during tissue injury and form a necessary component of cellular defences against pathogens and disease processes. The effects of ROS are normally limited or neutralized by a multifactorial system of antioxidant defences, although excessive production and/or deficient antioxidant defences may expose healthy tissue to oxidant damage. In the lung, ROS can damage pulmonary structures both directly and by initiating the release of other inflammatory mediators, including proteases and eicosanoids. Vascular endothelial cells are particularly susceptible to ROS-induced oxidant injury in the lung, and both the destruction of the pulmonary blood-gas barrier and the action of vasoactive substances will increase pulmonary vascular resistance. Moreover, ROS can degrade endothelium-derived nitric oxide (NO), a major pulmonary vasodilator, thereby, with exercise, synergistically increasing the likelihood of stress failure of pulmonary capillaries, a contributing factor to EIPH. This review considers the implications for the exercising horse of oxidant injury, pulmonary vascular function and NO and the contribution of these factors to the pathogenesis of equine respiratory diseases.

An introduction to oxygen free radicals

Oxygen free radicals are byproducts from the fundamental metabolic activities within the body. Normally, radicals are neutralized by enzymatic activity or natural antioxidants. Thus the generation of free radicals poses no problem so long as the balance between oxygen radical production and eradication remains in balance. There are multiple medical conditions, such as myocardial infarction, carcinogenesis, and neurologic trauma, to name a few, that may be aggravated by the presence of oxygen free radicals. This article will present an overview of oxygen free radicals: their normal formation and control and how they might further injure tissue in particular diseases. The implications for health care professionals are highlighted.

Antioxidants in pediatric gastrointestinal disease

Oxidant stress seems to be involved in the pathogenesis of several important gastroenterologic disorders in infants and children. The question can still be asked, in most circumstances, whether the oxidant stress precedes, and therefore is involved in, tissue or cellular injury or is a result of injury and not of clinical importance. The data favor the former situation in several inflammatory conditions of the bowel and in a variety of liver diseases. Experimental and clinical testing of this possible basic mechanism of tissue injury over the next few years will shed light on the role of antioxidants in treating gastrointestinal disorders.

The direct reduction of cytochrome c by some anthraquinone antitumor compounds

The ability of various anthraquinone antitumor agents to undergo oxidative metabolism with concomitant cytochrome c reduction has been examined. The reduction of cytochrome c by the compounds had enzymatic character and occurred without the formation of oxygen radicals. We have found that the presence of at least two phenolic groups in ring A of the compounds studied was indispensable for their oxidative metabolism. It is suggested that these groups are essential for the binding to cytochrome c. Furthermore, it has been shown that the existence of hydroxy groups in side chains of these compounds augments their interaction with this hemoprotein. On the basis of the results obtained for a series of analogs of mitoxantrone, we can conclude that the structural factor directly responsible for cytochrome c reduction is the primary or secondary amino group of the side chains.

Metal-induced hepatotoxicity

Figure 3 summarizes several proposed mechanisms of iron- or copper-induced hepatotoxicity. It has long been suspected that free radicals may play a role in iron- and copper-induced cell toxicity because of the powerful prooxidant action of iron and copper salts in vitro. In the presence of available cellular reductants, iron or copper in low molecular weight forms may play a catalytic role in the initiation of free radical reactions. The resulting oxyradicals have the potential to damage cellular lipids, nucleic acids, proteins, and carbohydrates, resulting in wide-ranging impairment in cellular function and integrity. However, cells are endowed with cytoprotective mechanisms (antioxidants, scavenging enzymes, repair processes) that act to counteract the effects of free radical production. Thus, the net effect of metal-induced free radicals on cellular function will depend on the balance between radical production and the cytoprotective systems As a result, there may be a rate of free radical production that must be exceeded before cellular injury occurs. Evidence has now accumulated that iron or copper overload in experimental animals can result in oxidative damage to lipids in vivo, once the concentration of the metal exceeds a threshold level. In the liver, this lipid peroxidation is associated with impairment of membrane-dependent functions of mitochondria (oxidative metabolism) and lysosomes (membrane integrity, fluidity, pH). Although these findings do not prove causality, it seems likely that lipid peroxidation is involved, since similar functional defects are produced by metal-induced lipid peroxidation in these organelles in vitro. Both iron and copper overload impair hepatic mitochondrial respiration, primarily through a decrease in cytochrome c oxidase activity. In iron overload, hepatocellular calcium homeostasis may be impaired through damage to mitochondrial and microsomal calcium sequestration. DNA has also been reported to be a target of metal-induced damage in the liver; this may have consequences as regards malignant transformation. The levels of some antioxidants in the liver are decreased in rats with iron or copper overload, which is also suggestive of ongoing oxidative stress. Reduced cellular ATP levels, lysosomal fragility, impaired cellular calcium homeostasis, and damage to DNA may all contribute to hepatocellular injury in iron and copper overload. There are few data addressing the key issue of whether free radical production is increased in patients with iron or copper overload. Patients with hereditary hemochromatosis have elevated plasma levels of TBA-reactants and increased hepatic levels of MDA-protein and HNE-protein adducts, indicative of lipid peroxidation. Mitochondria isolated from the livers of Wilson disease patients have evidence of lipid peroxidation, and some patients with Wilson disease have decreased hepatic and plasma levels of vitamin E. Additional investigation will be required to fully assess oxidant stress and its potential pathophysiologic role in patients with iron or copper overload.

New approaches to biochemical radioprotection: antioxidants and DNA repair enhancement

Chemical repair may be provided by radioprotective compounds present during exposure to ionizing radiation. Considering DNA as the most sensitive target it is feasible to biochemically improve protection by enhancing DNA repair mechanisms. Protection of DNA by reducing the amount of damage (by radical scavenging and chemical repair) followed by enhanced repair of DNA will provide much improved protection and recovery. Furthermore, in cases of prolonged exposure, such as is possible in prolonged space missions, or of unexpected variations in the intensity of radiation, as is possible when encountering solar flares, it is important to provide long-acting protection, and this may be provided by antioxidants and well functioning DNA repair systems. It has also become important to provide protection from the potentially damaging action of long-lived clastogenic factors which have been found in plasma of exposed persons from Hiroshima & Nagasaki, radiation accidents, radiotherapy patients and recently in "liquidators"--persons involved in salvage operations at the Chernobyl reactor. The clastogenic factor, which causes chromatid breaks in non-exposed plasma, might account for late effects and is posing a potential carcinogenic hazard. The enzyme superoxide dismutase (SOD) has been shown to eliminate the breakage factor from cultured plasma of exposed persons. Several compounds have been shown to enhance DNA repair: WR-2721, nicotinamide, glutathione monoester (Riklis et al., unpublished) and others. The right combination of such compounds may prove effective in providing protection from a wide range of radiation exposures over a long period of time.

Susceptibility of cloned K+ channels to reactive oxygen species

Free radical-induced oxidant stress has been implicated in a number of physiological and pathophysiological states including ischemia and reperfusion-induced dysrhythmia in the heart, apoptosis of T lymphocytes, phagocytosis, and neurodegeneration. We have studied the effects of oxidant stress on the native K+ channel from T lymphocytes and on K+ channels cloned from cardiac, brain, and T-lymphocyte cells and expressed in Xenopus oocytes. The activity of three Shaker K+ channels (Kv1.3, Kv1.4, and Kv1.5), one Shaw channel (Kv3.4), and one inward rectifier K+ channel (IRK3) was drastically inhibited by photoactivation of rose bengal, a classical generator of reactive oxygen species. Other channel types (such as Shaker K+ channel Kv1.2, Shab channels Kv2.1 and Kv2.2, Shal channel Kv4.1, inward rectifiers IRK1 and ROMK1, and hIsK) were completely resistant to this treatment. On the other hand tert-butyl hydroperoxide, another generator of reactive oxygen species, removed the fast inactivation processes of Kv1.4 and Kv3.4 but did not alter other channels. Xanthine/xanthine oxidase system had no effect on all channels studied. Thus, we show that different types of K+ channels are differently modified by reactive oxygen species, an observation that might be of importance in disease states.

The skin, free radicals, and oxidative stress

Oxidative stress involves the adverse effects of oxygen and other free radicals on living tissue. An overview of the various types of free radicals generated in the body, the basic chemistry of free radicals, and how they arise is presented. The importance of understanding the action of free radicals on specific target tissues in the skin and how this affects the physiology of the skin in relation to treatment is covered.

Lipid peroxidation and antioxidants as biomarkers of tissue damage

Disturbance of the balance between the production of reactive oxygen species such as superoxide; hydrogen peroxide; hypochlorous acid; hydroxyl, alkoxyl, and peroxyl radicals; and antioxidant defenses against them produces oxidative stress, which amplifies tissue damage by releasing prooxidative forms of reactive iron that are able to drive Fenton chemistry and lipid peroxidation and by eroding away protective sacrificial antioxidants. The body has a hierarchy of defense strategies to deal with oxidative stress within different cellular compartments, and superimposed on these are gene-regulated defenses involving the heat-shock and oxidant stress proteins.

Deleterious effects of xanthine oxidase on rat liver endothelial cells after ischemia/reperfusion

Previous studies have demonstrated that reactive oxygen species are involved in ischemic injury. The present work was undertaken to determine in vivo the role of xanthine oxidase in the oxygen free radical production during rat liver ischemia and to examine the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) during the same period. Our results indicate a 4-fold increase in xanthine oxidase activity between 2 and 3 hours of normothermic ischemia, in parallel with a decrease in cell viability. Moderate hypothermia delays both events. Under the same conditions, the activity of oxygen radical scavenging enzymes remains unchanged. Moreover, we have compared in vitro the susceptibility of isolated liver cells to an oxidative stress induced by O2.-, H2O2 and .OH. Our results reveal that endothelial cells are much more susceptible to reactive oxygen species than hepatocytes, probably because they lack H2O2-detoxifying enzymes. These findings suggest that xanthine oxidase might play a major role in the ischemic injury mainly at the level of the sinusoidal space where most endothelial cells are located.

Freshly fractured quartz inhalation leads to enhanced lung injury and inflammation. Potential role of free radicals

Silicosis is a devastating pulmonary disease that continues to occur in industrial workplaces. Its pathogenesis is under critical evaluation, and this report provides new concepts on the possible early events that occur in lungs resulting from the inhalation of freshly fractured versus aged quartz in the development of two diverse disease entities. In this study, we evaluated the biochemical and pathologic changes in the lavagate and lungs of rats exposed to freshly fractured quartz (generated by jet milling), aged quartz (milled then aged for 2 mo prior to use), or clean air 5 h a day for 10 d over a 2-wk period. The concentration of crystalline quartz in the chambers averaged 20 mg/m3. Particle concentrations and particle size were similar for the freshly milled and aged quartz exposures. However, free radical concentrations associated with the freshly milled quartz samples were significantly higher than those for aged quartz. After a 2-wk exposure, animals were killed and studied by bronchoalveolar lavage and pulmonary histopathology. Inhalation of aged quartz increased the number of bronchoalveolar lavage cells, demonstrated histopathologic evidence of increased pulmonary infiltrates, showed enhanced concentrations of biochemical markers of lung injury, increased lipid peroxidation, and the ability of pulmonary phagocytes to produce more oxygen radicals. In general, all these pulmonary responses were significantly more pronounced after inhalation of freshly fractured quartz compared with aged quartz. In contrast, antioxidant enzymes showed decreased concentrations in the freshly fractured quartz-exposed group compared with the aged quartz-exposed animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Scavenging of reactive oxygen species by letosteine, a molecule with two blocked-SH groups. Comparison with free-SH drugs

Acute production of reactive oxygen species by polymorphonuclear neutrophils during the respiratory burst may induce tissue injuries. In this in vitro study, it was demonstrated that letosteine, a mucolytic agent containing two blocked thiol groups, had antioxidant activity, but only when it was first submitted to alkaline hydrolysis. In a cell-free system, hydrogen peroxide, hypochlorous acid and hydroxyl radical concentrations were reduced by half by letosteine concentrations of 200, 15 and 350 mumol/l, respectively. The mechanism of letosteine action may be related to the -SH group liberated in vitro by hydrolysis, which seemed to react by scavenging the reactive oxygen species in the same way as acetylcysteine and MESNA, free-thiol drugs known for their antioxidant properties. So, letosteine, a compound with blocked -SH groups which in vivo can metabolically become free, may have a therapeutic application in preventing oxidative tissue injury damage induced by the respiratory burst.

The oxidative stress response

Oxidative stress resulting from toxic effects of reactive oxygen species (ROS) plays an important role in the pathogenesis of a variety of diseases and important biological processes. Toxic effects of these ROS, including the superoxide and hydroxyl radicals, and hydrogen peroxide can cause cellular damage by oxidizing nucleic acids, proteins, and membrane lipids. While the chemical reactions involved in the generation and detoxification of ROS have been studied in great detail, little is known about the cellular and molecular responses to oxidative stress in mammalian cells. This article discusses some of the major aspects of these molecular responses, including alterations in the gene expression of antioxidant enzymes, stress-response genes, and cytokines. The regulatory mechanisms that control this genetic response are highly complex, involving activation of transcription factors and signal transduction pathways. Further characterization of the mechanisms that regulate these molecular responses is essential for understanding the physiologic function of the responses and for the development of new therapeutic modalities to defend and/or adapt to oxidant injury.

Role of oxygen-derived metabolites in the rat gastric mucosal injury induced by nitric oxide donors

Local intra-arterial infusion of high doses of the nitric oxide (NO) donor, nitroprusside (10-40 micrograms kg-1 min-1 for 15 min) induced dose-dependent haemorrhagic injury to the rat gastric mucosa and reduced systemic arterial blood pressure, whereas intragastric nitroprusside (10-50 mg ml-1), which caused similar falls in blood pressure, failed to induce such injury. The mucosal damage induced by nitroprusside was reduced by local concurrent infusion of superoxide dismutase (500-4000 i.u. kg-1). Local superoxide dismutase also abolished the mucosal injury induced by local infusion of the NO donor, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1) indicating specific actions. Intravenous infusion of the iron chelator and peroxyl scavenger, desferrioxamine (0.25-1 mg kg-1 min-1) or the hydroxyl radical scavenger, dimethylthiourea (20 mg kg-1 min-1) also reduced the mucosal damage induced by the local administration of the NO donors, but not that induced by endothelin-1. These findings implicate the involvement of superoxide and possibly other oxygen-derived free radicals in the injurious actions of high levels of nitric oxide generated from NO donors, and may reflect a role of the cytotoxic peroxynitrite moiety.

Suppressive effects of tranilast on pulmonary fibrosis and activation of alveolar macrophages in mice treated with bleomycin: role of alveolar macrophages in the fibrosis

We have reported that tranilast, an anti-allergic drug that inhibits chemical mediator release from mast cells, suppresses bleomycin (BLM)-induced pulmonary fibrosis in mice through mechanisms other than inhibiting chemical mediator release from mast cells. The purpose of this paper is to examine the effect of tranilast on alveolar macrophage (AM) activation and on the development of fibrosis in ICR mice instilled with BLM intratracheally. Twenty eight days after the BLM instillation (0.01 mg/mouse), AM often migrated into alveolar spaces surrounding the fibrotic areas. Flow cytometry analysis for the size and density of AM (MAC-1 positive cells) suggested that AM were activated not only in the earlier acute inflammatory phase, but also in the later chronic phase. The p.o. administration of tranilast suppressed an increase of AM activity to produce reactive oxygen species in BLM-instilled mice, and it inhibited the subsequent development of pulmonary fibrosis. In vitro treatment with tranilast suppressed the reactive oxygen species production from murine peritoneal macrophages. However, several different anti-oxidants failed to inhibit the development of fibrosis. These results suggest that the activation of AM plays an important role in the development of fibrosis, and it is likely that tranilast suppresses fibrosis by inhibiting AM activation but not by scavenging reactive oxygen species.

Combination therapy with probucol prevents adriamycin-induced cardiomyopathy

Adriamycin (doxorubicin) is a broad spectrum anti-tumor antibiotic used to treat cancer patients. However, the potential usefulness of this drug is currently limited by the development of a dose-dependent cardiomyopathic process terminating in severe heart failure. Although several mechanisms have been suggested to explain the pathogenesis of adriamycin-induced cardiomyopathy, free-radical induced oxidative stress appears to play an important role. A concise description of adriamycin-induced cardiomyopathy is provided. Various combination therapies which have been attempted in the past to modulate the adriamycin-induced cardiomyopathy are also discussed. Recently, it has been discovered that probucol, a lipid lowering agent and potent antioxidant, provides complete protection against adriamycin-induced cardiomyopathy in rats without interfering with the anti-tumor properties of this antibiotic. Clinical trials employing adriamycin therapy in combination with probucol are needed to determine the applied value of these laboratory findings.

Scavenging of reactive oxygen species as the mechanism of drug action

Reactive oxygen species (ROS) are generated when oxygen is supplied in excess and/or its reduction is insufficient. The best explored ROS are superoxide anions, hydroxyl radicals and hydrogen peroxide. The first two are free radicals. ROS are harmful for the living cells and are implicated in a variety of pathological processes and diseases. Drugs used in the treatment of these states are either stimulators of endogenous defense mechanisms against ROS or inhibitors of ROS formation. Six groups of anti-ROS substances have been described in this paper. 1) Antioxidant substances used in substitutive therapy such as enzymes (e.g. superoxide dismutase), substances containing thiol groups and vitamins (A, E, P, C). 2) Chelating agents (e.g. desferoxamine), which lower the level of prooxidative transition metal ions. 3) Inhibitors of superoxide ions generation by stimulated cells or xanthine oxidase. Such mechanism of action was described for xanthine oxidase inhibitor-allopurinol. 4) Superoxide scavengers. Many known drugs were investigated for this activity, but the best documentation was presented for flavonoids. 5) Substances which eliminate hydrogen peroxide, mainly glutathione and its precursors. 6) Scavengers of hydroxyl radicals. Studies of the above activity were conducted mainly using an unspecific method--estimation of malondialdehyde generated during the action of hydroxyl radicals on lipids or on desoxyribose. Inhibition of malondialdehyde formation was described for many drugs of plant and synthetic origin.

ESR evidence for the generation of reactive oxygen species from the copper-mediated oxidation of the benzene metabolite, hydroquinone: role in DNA damage

In previous studies, we observed that Cu(II) strongly induces the oxidation of hydroquinone (HQ), producing benzoquinone and H2O2 through a Cu(II)/Cu(I) redox cycle mechanism. The oxidation of HQ by Cu(II) also results in plasmid DNA cleavage. In this study, using ESR spectroscopy we have investigated whether this chemical-metal redox system can generate reactive oxygen species which induce DNA damage. In order to set the stage for the ESR experiments and the inhibitors to be used in these experiments, some preliminary O2 consumption and plasmid DNA cleavage experiments were performed. Mixing 100 microM HQ with 10 microM Cu(II) in phosphate-buffered saline (PBS) resulted in a marked consumption of O2 and the concomitant generation of H2O2, and extensive DNA degradation in chi X-174 RF I DNA. The presence of superoxide dismutase (SOD) or mannitol did not affect either the O2 consumption, H2O2 generation or DNA damage. In contrast, the Cu(I) chelators, bathocuproinedisulfonic acid (BCS) and glutathione (GSH), extensively inhibited the HQ/Cu(II)-mediated O2 consumption and DNA damage. The presence of catalase also prevented the DNA damage. Although the HQ/Cu(II)-mediated O2 consumption increased in the presence of azide, azide markedly inhibited the HQ/Cu(II)-induced DNA degradation, resulting in primarily open circles. Using ESR spectroscopy, it was observed that Cu(II) strongly mediated the formation of semiquinone anion radicals from HQ in PBS, which could be blocked by BCS. alpha-(4-Pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN)-spin trapping experiments showed that the interaction of HQ with Cu(II) produced 4-POBN-CH3 and 4-POBN-CH(OH)CH3 adducts in the presence of dimethyl sulfoxide (DMSO) and ethanol, respectively, suggesting that hydroxyl radical or an equivalent reactive intermediate is generated from the HQ/Cu(II) system. The presence of catalase, BCS or GSH but not SOD completely prevented the formation of 4-POBN-CH3 adduct from the HQ/Cu(II) plus 4-POBN/DMSO system. This indicates that both H2O2 and Cu(I) are critical for the formation of reactive oxygen from the HQ/Cu(II) system. Anaerobic conditions induced an approximately 85% decrease in the formation of 4-POBN-CH3 adduct. Reactive oxygen scavenger experiments showed that the formation of the 4-POBN-CH3 adduct was significantly inhibited by azide but not by mannitol. Overall, the above results indicate that through a copper-redox cycling mechanism the copper-mediated oxidation of HQ generates reactive oxygen species which may participate in DNA damage.

Oxidative stress from environmental pollutants

Recently progress has been made on O2 toxicity and pathology related to numerous environmental contaminants in insects. The pro-oxidants studied included: dioxin, paraquat, and an assorted array of quinones, 8-methoxypsorlen, arsenic, and mercury. The responses to these oxidants are diverse, but they arise from the reactive oxygen species. These pro-oxidants in insects cause lipid peroxidation, protein and enzyme oxidation, and GSH depletion. Potentially, they may also cause DNA oxidation, and form DNA adducts. Oxidative challenge is alleviated by antioxidant compounds, but more importantly by the induction of antioxidant enzymes, which are crucial for the termination of O2 radical cascade and lipid peroxidation chain reaction. Insects exhibit a wasting syndrome under sub-acute stress. In acute toxicity vital physiological processes impaired are hemolymph melanization and diuresis. Thus, insects resemble vertebrates in both the response to oxidative stress and its pathological consequences. These results raise the prospect that insects may serve as non-mammalian model species for monitoring the oxidative-stress component of environmental toxicity.

A method of human semen centrifugation to minimize the iatrogenic sperm injuries caused by reactive oxygen species

Current techniques of sperm preparation for in vitro fertilization or intrauterine insemination require centrifugation of human semen to separate spermatozoa from the seminal plasma. Centrifugation increases reactive oxygen species (ROS) formation in semen. Moreover, high levels of ROS are associated with sperm membrane injury through spontaneous lipid peroxidation, which may alter sperm function. We investigated the relationship between centrifugation variables (time and g-force) and ROS production to establish an optimal centrifugation protocol for sperm preparation techniques. Semen from 38 men (24 patients and 14 normal volunteers) was evaluated for the formation of ROS before centrifugation and after centrifugation at 200 g for 2 or 10 min and after 500 g for 2 or 10 min. The absence of white blood cells in semen which can also produce ROS was determined with the myeloperoxidase technique (Endtz test). All specimens were negative (< 1 x 10(6)/ml) by the Endtz test. The formation of ROS was measured by chemiluminescence. ROS formation was regarded as high (positive) when the chemiluminescence response was at least 10 x 10(4) counted photons/min (cpm). The sperm concentration in each sample was adjusted to 15-20 x 10(6) cells/ml before analysis. Eight specimens (7 patients and 1 donor) exhibited high levels of ROS before centrifugation. All 8 showed further, significant increases in ROS formation regardless of g-force or time. The increase in ROS was significantly less when semen was centrifuged for 2 as compared to 10 min (p < 0.001). Six specimens previously ROS-negative became ROS-positive after centrifugation for 10 min at 200 and 500g. We conclude that the time of centrifugation is more important than g-force for inducing ROS formation in semen. Based on these results, we recommend a shorter centrifugation period in the preparation of sperm for assisted reproductive techniques.

Effect of N-acetylcysteïne on Photofrin-induced skin photosensitivity in patients

BACKGROUND AND OBJECTIVE

One of the major side effects of photodynamic therapy (PDT) employing Photofrin as the sensitizer is enhanced photosensitivity of the skin. The basic mechanism in PDT damage is believed to be the formation of singlet oxygen and radical species. N-acetylcysteïne (NAC) increases glutathione levels and is known to prevent pathology elicited by radicals and reactive species.

STUDY DESIGN/MATERIALS AND METHODS

NAC was tested in a randomized, open label study for its protective effect on skin photosensitivity. Twenty-seven patients treated with PDT for central obstructive lung cancer or esophageal cancer received either "early" or "delayed" NAC, starting 5 or 10 days after Photofrin, in a dose of 3 x 600 mg per day for 5 days. Light, obtained from a halogen lamp (fluence rate 200 mW.cm-2) was used to illuminate skin patches of 2.5 cm2 on the back (10, 25, and 50 J.cm-2). Skin response was measured by using a visual scoring system and by measuring the redness using a reflectance meter.

RESULTS

Skin responses varied from no changes at 10 J.cm-2 to redness with edema at energies of 50 J.cm-2. In the absence of edema, measurements with the reflectance meter appeared to be more sensitive than visual scoring.

CONCLUSION

In a limited number of patients, there was a trend for decreased sensitivity after NAC, but statistical analysis failed to show any significant protective effect of this short course of NAC.

Free radicals, antioxidants and preventive geriatrics

Despite a realisation that antioxidants will not delay ageing in healthy older people, there is increasing scientific interest in the role of free radical oxidants in a number of diseases associated with older age. For most of these diseases there is suggestive theoretical and laboratory evidence but not confirmatory clinical evidence. Free radical damage seems likely to be significant in the pathophysiology of atherosclerosis, ischaemia-reperfusion injury, Parkinson's disease, cataract, some cancers and rheumatoid arthritis. Evidence to suggest a protective effect from antioxidant vitamins exists for ischaemic heart disease, cataract and some cancers. Attempts to influence the outcome of other diseases such as ischaemia-reperfusion injury, Parkinson's disease and rheumatoid arthritis have so far failed to achieve positive results. Research interest in the field is increasing although hampered by methodological difficulties and the limited financial return for drug companies. In the meantime there seems no reason to discourage older people who wish to ingest extra vitamin E and vitamin C. A diet with adequate vegetables and fruits should provide sufficient beta carotene.

Could oxidative stress initiate programmed cell death in HIV infection? A role for plant derived metabolites having synergistic antioxidant activity

Evidence supports the premise that a pro-oxidant condition exists in HIV-seropositive patients, a result of an overabundance in production of reactive oxygen forms combined with a multilevel deficiency in nutritional and metabolic sources of antioxidants. Apoptosis (a programmed cell death) is recognized as a possible pathway of immune cell loss in patients with HIV infection and AIDS. The cascade of events that results from 'oxidative stress' (OS) is markedly similar to that which can initiate apoptosis and includes oxidation of cellular membranes, alteration of metabolic pathways, disruption of electron transport systems, depletion of cellular ATP production, loss of Ca2+ homeostasis, endonuclease activation and DNA/chromatin fragmentation. Downstream events secondary to these effects may also play a role in activation of latent virus and subsequent viral replication. Primary and secondary metabolites found in plants act as synergistic antioxidants, and can protect plants from oxidation-induced cell death. Experiments have shown that some of these same metabolites can inhibit cell killing by HIV. Can these compounds be useful in inhibiting viral activation and the death of immune cells in HIV/AIDS through their synergistic antioxidant properties? A brief review of the evidence for OS in HIV is presented and the potential basis for OS playing a role in the initiation of cell death and viral replication is explored. The functional antioxidant activities of plant metabolites are illustrated and the use of these synergistic antioxidants from plants are proposed as a mechanism by which viral replication and cell killing in HIV infection can be inhibited.

Some biochemical and pharmacological aspects of free radical-mediated tissue damage

Living in aerobic conditions carries a risk of oxidative stress, in connection with free radical deleterious action on tissues and cells. Free radical mechanisms have been implicated in the pathogenesis of many diseases, as well as in host defense against various invading microorganisms. A substantial body of evidence has been reported on free radical involvement in inflammation, ischaemia/reperfusion injury, atherosclerosis and many other pathologies. The aim of this paper is to review selected literature and opinions concerning free radical-induced damage to tissues and to present xenobiotic contribution to oxidative stress.

Increase in filtration coefficient from actions of melittin on neutrophils in isolated rabbit lungs

Activation of neutrophils may contribute to lung injury in the adult respiratory distress syndrome. We added rabbit neutrophils to the pulmonary circulation of salt-perfused and ventilated isolated rabbit lungs. These neutrophils were activated by adding synthetically pure melittin to the perfusate. This led to lung injury as measured by filtration coefficient under no-flow conditions. We also activated neutrophils in vitro before addition to the pulmonary circulation. These preactivated neutrophils also produced lung injury, indicating a primary action of melittin on neutrophils rather than on lung. The injury was prevented by aristolochic acid, which is an inhibitor of phospholipase A2 (PLA2), and independently by catalase, which is scavenger of hydrogen peroxide (H2O2). Aristolochic acid also appeared to act primarily on neutrophils since addition to neutrophils in vitro prevented injury from in vitro activation by melittin. Aristolochic acid did not appear to act as a free radical scavenger since it did not prevent injury from neutrophils activated by phorbol myristate acetate (PMA). PMA is a direct activator of protein kinase C in neutrophils and leads to formation of H2O2 with consequent lung injury. We conclude that activation of neutrophils by melittin leads to oxidant lung injury possibly from activation of PLA2. Since PLA2 does not directly produce a second messenger, such as diacylglycerol or inositol triphosphate, it is likely that other actions of PLA2 produce an intermediary mediator. We previously showed that an inhibitor of eicosanoid synthesis prevents lung injury from exogenous PLA2. This suggests that the formation of leukotriene B4 (LTB4), a 5-lipoxygenase product of arachidonic acid, may contribute to the oxidant lung injury from melittin.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial reperfusion injury: role of oxygen radicals and potential therapy with antioxidants

Experimental studies have demonstrated that reperfusion is associated with a host of distinctive pathophysiologic derangements, the most important of which are reperfusion arrhythmias, transient mechanical dysfunction or "myocardial stunning," and cell death. Reperfusion arrhythmias and myocardial stunning occur in experimental animals after transient ischemia followed by reperfusion, and there is considerable evidence that these derangements also develop in humans, although the existence of malignant reperfusion arrhythmias in humans remains uncertain. Reperfusion arrhythmias and myocardial stunning can be considered manifestations of sublethal, reversible cellular injury. The pathogenesis of reperfusion arrhythmias and stunning has not been conclusively established; however, there is considerable evidence that generation of oxygen radicals and perturbations of calcium homeostasis play an important role. Antioxidants and calcium antagonists have been shown to mitigate these manifestations of reperfusion injury. In contrast, the likelihood of lethal reperfusion-induced injury remains highly controversial. Although many studies have reported reduction of infarct size with antioxidants, numerous others have failed to reproduce these results. Consequently, intense controversy persists regarding whether oxygen radicals contribute to extending cell death following reperfusion and whether reperfusion itself causes cell death. Neither the resolution of this controversy nor the availability of clinical therapies to reduce reperfusion-induced cell death is likely in the near future.

Endogenous vasoactive substances and oxygen-derived free radicals in pulpal haemodynamics

An adequate blood supply to the dental pulp is essential to the health of the tooth. A recent concept is that repeated stimulation of sensitive teeth may induce pulpal changes; this could occur through induction of neurogenic inflammation and alteration of pulpal blood flow. One possibility is that production of oxygen-derived free radicals at sites of inflammation contributes to alterations in local blood flow. The first target of free radicals, generated in several pathological processes, is the vascular system (essentially the endothelium). Although the exact mechanism by which free radicals induce changes in vascular conductance is still uncertain, they may act directly on vascular smooth muscle or modify vascular tone by interacting with the production and/or biological activity of endogenous vasoactive mediators. Recent data indicate that the oxygen-derived, free radical-generating system can decrease pulpal blood flow in the dog via endothelial dysfunction when applied locally in deep dentinal cavities. In addition to the part played by oxygen-derived free radicals, the measurement of pulpal blood flow and the effects of endogenous vasoactive substances on flow are discussed.

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Oxidant-induced alterations of lung surfactant system

Lung surfactant is subject to oxidant injury from inhaled pollutants and free radicals generated by activated leukocytes in various disease states. Both lipid and protein components of surfactant can be altered by oxygen radicals. Changes were investigated in the lung surfactant system using a rat model with ozone injury to simulate adult respiratory distress syndrome, in which surfactant activity is thought to be inadequate. A significant decrease in dynamic lung compliance was correlated with the accumulation of protein in the alveolar lavage fluid. The amount of dipalmitoylphosphatidylcholine, the most abundant phospholipid in surfactant, increased two-fold indicating that the acute changes in lung function were related to the inactivation of surfactant by edema fluid and not to a quantitative lack of surfactant phospholipids. The amount of surfactant stored in lamellar bodies of the alveolar type II cells also increased and was abnormal in composition. The amount of cholesterol and albumin increased following ozone stress, suggesting that an altered uptake and incorporation of alveolar components into the lamellar bodies may be an important process in oxidant-induced lung injury. In contrast, lysozyme, an abundant protein in the alveolar fluid and lamellar bodies, rapidly decreased in concentration in the intracellular surfactant. Using an in vitro system we found that lysozyme is very sensitive to ozone injury and may function as a "sacrificial" antioxidant in the alveolar lining fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

[Free radicals]

Free radicals are continuously threatening living organs. Firstly generated by endogenic pathway during normal and vital metabolic reactions, they can be also produced by environmental factors: atmospheric pollution, radiations... An energetic source ensures the initiation of free radicals reaction. Its expanding is strengthened by oxygen (bi-radical form) and transition metals (chiefly iron). Eyes are very sensitive organs to the deleterious action from the oxygen active species. Protection systems against free radicals action are necessary in living cells. A part the pathologic or ageing conditions, oxygen toxicity doesn't; in fact, neutralised by protection systems coming from enzymes (endogenic way) and food contribution: vitamins, carotenoids, flavonoids... (exogenic way).

Carvedilol, a new antihypertensive agent, prevents lipid peroxidation and oxidative injury to endothelial cells

The protective effects of carvedilol, a new beta-adrenergic receptor blocker and vasodilating antihypertensive agent, against oxygen free radical-mediated injury were studied in cultured bovine endothelial cells and compared with five other beta-blockers. Carvedilol dose-dependently inhibited oxygen radical-induced lipid peroxidation (50% inhibition at 2.6 mumol/L) and glutathione depletion (50% inhibition at 1.8 mumol/L) in the cells. Under the same conditions, other beta-blockers--propranolol, labetalol, pindolol, atenolol, and celiprolol--had only mild or no effect. Moreover, carvedilol protected against oxygen radical--mediated cell damage, as assessed by cellular lactate dehydrogenase release, with a 50% inhibition at 4.1 mumol/L and increased the cell survival in a dose-dependent manner, whereas other beta-blockers had mild or no effects. Pretreatment of the cells with carvedilol for 7 days significantly enhanced the protective effects of carvedilol. Using 2-methyl-2-nitrosopropane as a trapping agent, the spin adduct in cell lipids was monitored by electron paramagnetic resonance. Carvedilol dose-dependently decreased the intensity of the free radical signals, indicating its free radical-scavenging ability. The prevention of oxidative injury to endothelial cells might potentially contribute to the clinical beneficial effects of carvedilol as an antihypertensive agent.

Rat pleural mesothelial cells show damage after exposure to external but not internal cigarette smoke

The combination of cigarette smoke and high-level occupational asbestos exposure produces a synergistic increase in the incidence of lung cancer; however, smoking does not affect the incidence of mesothelioma. Here we present the results of tests of two theories that have been proposed to explain this phenomenon; namely, that pleural mesothelial cells are resistant to cigarette smoke-induced damage and that the pleural connective tissue acts as a barrier that prevents smoke from reaching the mesothelial cells. To test these hypotheses, excised whole rat lung preparations were exposed to either internal (intratracheal) or external (pleural surface) smoke. For comparison, additional excised lung preparations were exposed to solutions of hydrogen peroxide either externally or intratracheally. Mesothelial cells exposed to external smoke showed widespread, dose-dependent uptake of Trypan blue. Mesothelial cells did not take up Trypan blue after exposure to internal smoke. Bronchial epithelial cells exposed to internal smoke did show uptake, but to a lesser degree than externally exposed mesothelial cells. Examination by scanning and transmission electron microscopy showed that internal smoke did not affect mesothelial cell ultrastructure, whereas external smoke produced obvious mesothelial cell damage and mesothelial cell detachment. Catalase and deferoxamine, scavengers of active oxygen species, provided protection against smoke-induced mesothelial cell injury, but inactivated catalase did not. External hydrogen peroxide produced a very similar, dose-dependent pattern of Trypan blue uptake and ultrastructural changes. Intratracheal hydrogen peroxide also damaged mesothelial cells, but the extent of damage was always less than with comparable concentrations of external hydrogen peroxide.(ABSTRACT TRUNCATED AT 250 WORDS)