Prolonged survival after paraquat. Role of the lung antioxidant enzyme systems

Alterations in aortic antioxidant components in an experimental model of atherosclerosis: a time-course study

Antioxidant component alterations in the aorta during atherogenesis were examined in atherosclerosis-susceptible (SUS) Japanese quail fed a cholesterol-supplemented (0.5% w/w) diet. Birds fed a non-supplemented diet provided information on the effects of aging on endogenous antioxidants. One hundred adult SUS males were used. Birds were sacrificed after 0, 4, 8 and 12 weeks on the diets and were examined for plaque development and corresponding antioxidant component alterations in aorta and myocardium. With aging, superoxide dismutase (SOD) activity was increased in both tissues, whereas aortic glutathione peroxidase (GPx) activity and myocardial glutathione reductase (GRd) activity decreased. Myocardial ascorbate levels increased with aging, with a reciprocal decrease in myocardial tocopherol levels. Following 4 weeks of cholesterol supplementation, aortic GRd decreased, SOD activity increased, but activities of GPx and catalase were unchanged. This same qualitative pattern of antioxidant enzyme changes was also found in myocardium. Thus, although aortic antioxidant enzyme changes produced by cholesterol feeding and aging showed some similarities, the early phase of atherogenesis does not simply reflect accelerated aging. In the late stages of atherogenesis, SOD activity returned to baseline, but other antioxidant enzymes remained unaltered from levels characterizing the early phase of lesion development. There was no detectable functional coupling between changes in GPx and GRd, nor between SOD (which produces hydrogen peroxide) and GPx or catalase (which utilize hydrogen peroxide as substrate). Previously reported alterations in erythrocyte antioxidant enzyme components during atherogenesis in quail were not predictive of changes in the corresponding enzymes in the aorta and myocardium.

The effect of hyperbaric oxygenation on the viability of human fat injected into nude mice

Autologous free-fat injection for the correction of soft-tissue defects has become a common procedure in plastic surgery. The main shortcoming of this method for achieving permanent soft-tissue augmentation is the partial absorption of the injected fat, an occurrence that leads to the need for both overcorrection and repeated fat reinjection. Improving the oxygenation of the injected fat has been suggested as a means of helping to overcome the initial critical phase that occurs postinjection (when the fat cells are nourished by osmosis), increasing phagocyte activity, accelerating fibroblast activity and collagen formation, and enhancing angiogenesis. In addition, the hyperbaric oxygen-mediated decrement in endothelial leukocyte adhesion will decrease cytokine release, thereby reducing edema and inflammatory responses. The purpose of the present study was to examine the effect of hyperbaric oxygenation on improving the viability of injected fat. Adipose tissue obtained from human breasts by suction-assisted lipectomy was injected into the subcuticular nuchal region in nude mice. The mice were then exposed to daily hyperbaric oxygen treatments, breathing 100% oxygen at 2 atmospheres absolute (ATA) for 90 minutes. The duration of the administered hyperbaric oxygen therapy was 5, 10, or 15 days, according to the study group. Mice exposed to normobaric air alone served as the control group, and each group included 10 animals. The rats were killed 15 weeks after fat injection. The grafts were dissected out, weight and volume were measured, and histologic evaluation was performed. In all of the study groups, at least part of the injected fat survived, giving the desired clinical outcome. No significant differences could be found between the groups regarding fat weight and volume. Histopathologic examination of the dissected grafts demonstrated a significantly better integrity of the fat tissue in the group that received hyperbaric oxygen for 5 days (p = 0.047). This finding was manifested by the presence of well-organized, intact fat cells, along with a normal appearance of the fibrous septa and blood vessels. The worst results were found in animals treated by hyperbaric oxygenation for 15 consecutive days. An inverse correlation was found between an increased dose of the high-pressure oxygen and fat tissue integrity (r = -0.87, p = 0.076). The toxic effects of highly reactive oxygen species on fat cells might explain the failure of an excessively high dose of hyperbaric oxygen to provide any beneficial outcome. The clinical relevance of these results should be further investigated.

Regulation of antioxidant enzyme gene expression in response to oxidative stress and during differentiation of mouse skeletal muscle

Various properties of skeletal muscle, including high metabolic activity and high levels of heme-containing proteins, render it particularly susceptible to free radical injury. Indeed, cellular injury from reactive oxygen species (ROS) has been implicated in many muscle disorders. Thus muscle cell survival is critically dependent on the ability of the cell to respond to periods of oxidative stress. To investigate this important homeostatic response, we studied the effect of oxidative challenges on the expression of genes encoding the antioxidant enzymes Cu,Zn-superoxide dismutase (CuZnSOD), Mn-superoxide dismutase (MnSOD), glutathione peroxidase (GPx), and catalase (CAT) in myotube cultures. Using Northern blot analysis, we found that treatment with the pro-oxidant paraquat resulted in time- and dose-dependent increases of transcript levels that were greatest for GPx and CAT (approximately 4-5 fold). CuZnSOD and MnSOD transcripts were also increased, albeit more modestly (approximately 2-3 fold). Transcript levels were also induced by treatment of the cells with two other pro-oxidants, menadione and H2O2, and correlated with the level of oxidative injury to the cells, measured as protein carbonyl group formation. Activities of all of the enzymes increased in response to the oxidative challenges, although the magnitudes of the increases were less robust than the increases of the respective transcript levels. In studying the effect of cellular differentiation on antioxidant gene expression and susceptibility to oxidative stress, we found that pro-oxidant treatment resulted in greater oxidative injury to differentiated myotubes than to undifferentiated myoblasts. Furthermore, the increased susceptibility of myotubes correlated with decreased antioxidant defenses-as muscle cells differentiated, both transcript and activity levels of antioxidant enzymes decreased. These data suggest that muscle cells regulate antioxidant defenses in response to oxidative stress and cellular differentiation.

Effect of the MAO-B inhibitor, MDL72974, on superoxide dismutase activity and lipid peroxidation levels in the mouse brain

MDL72974 is a member of a series of MAO-B inhibitors to be used as potential therapeutic agents in the treatment of Parkinson's and Alzheimer's diseases. However, we have recently observed a reduction in the density of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra of mice treated with MDL72974. As oxidative stress is known to play a significant role in the nigrostriatal pathway, analysis of the relationship between TH+ cell losses induced by MDL72974 and by free radical production was investigated in the present study. Results demonstrate a significant increase in superoxide dismutase (SOD) activity, a key antioxidant, in the striatum and cerebellum of MDL72974-treated mice, presumably in response to free radical production. An increase in lipid peroxidation levels was also observed in the striatum of these animals in a manner which is consistent with oxidative stress-inducing agents. We therefore suggest that MDL72974 may be detrimental to dopaminergic neurons of the nigrostriatal pathway via free radical-mediated reactions.

The effect of L-deprenyl, D-deprenyl and MDL72974 on mitochondrial respiration: a possible mechanism leading to an adaptive increase in superoxide dismutase activity

L-Deprenyl is an irreversible monoamine oxidase-B inhibitor with a complex pharmacological profile. For instance, L-deprenyl administration to rat and mice increases cytosolic CuZn- and mitochondrial Mn-superoxide dismutase activities in the striatum. CuZn- and Mn-superoxide dismutase are enzymes involved in defense against superoxide (O2.) radicals. Hence, an increase in CuZn- and Mn-superoxide dismutase activities is suggestive of oxidative stress. The major intracellular site of O2. radicals formation is the mitochondrial respiratory chain. Several reports indicated that alterations in mitochondrial respiratory functions enhances O2. production. We observed that L-deprenyl induced a dose-dependent inhibition of oxygen (O2) consumption (state 3) during ATP synthesis in presence of complex I (pyruvate and malate) and complex II (succinate) substrates in fresh mitochondrial preparations. D-Deprenyl produced a similar inhibitory profile whereas MDL72974, a selective monoamine oxidase-B inhibitor, was less effective. Administration of D-deprenyl or MDL72974 to mice resulted in an increase in both striatal CuZn- and -Mn-superoxide dismutase activities. Accordingly, we propose that the impairment of mitochondrial respiratory functions which stimulates O2. formation could modulate CuZn- and Mn-superoxide dismutase activities, through a mechanism that appears to be independent of monoamine oxidase-B inhibition.

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

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

Oxygen free radicals and human disease

Oxygen free radicals are very reactive molecules which can react with every cellular component. They are normally produced in organisms being involved in various biologic reactions. However, too high levels of these partially-reduced O2 species can give rise to functional and morphologic disturbances in cells. There is evidence to implicate oxygen free radicals as important pathologic mediators in many human disease processes.

Overproduction of human Mn-superoxide dismutase modulates paraquat-mediated toxicity in mammalian cells

Manganese superoxide dismutase (MnSOD) is a nuclear encoded mitochondrial matrix enzyme that functions to scavenge superoxide radicals. The human MnSOD cDNA under the transcriptional control of a human beta-actin promoter was introduced into mouse C3H10T1/2 cells by cotransfection with a recombinant plasmid containing the NeoR selectable marker. C3H10T1/2 transformants (C3H-SOD) were obtained that expressed high levels of authentic enzymatically active human MnSOD. Overexpression of the MnSOD gene did not affect the protein levels of CuZnSOD, catalase (CAT), or glutathione peroxidase (GPX) in the transformants. Treatment of cells with paraquat was less toxic to the C3H-SOD cells than to the control cells. These results are consistent with the possibility that superoxide radicals are mediators of paraquat cytotoxicity.

Different effects of paraquat on microsomal lipid peroxidation in mouse brain, lung and liver

Paraquat stimulates NADPH-Fe(2+)-dependent microsomal lipid peroxidation in mouse brain and strongly inhibits it in the liver. In lung microsomes, the lipid peroxidation was stimulated by paraquat at 10(-4) M, but not at higher doses. An antioxidant action of paraquat seemed to account, at least in part, for the lack of stimulation in lung microsomes, but it was inappropriate to explain the result in hepatic microsomes. There was no apparent correlation between the effects of paraquat on the lipid peroxidation and on the activity of NADPH-cytochrome P-450 reductase, the enzyme which initiates redox cycling of paraquat, resulting in generation of active oxygen species. In fact, the effect of paraquat on the lipid peroxidation was independent of paraquat radical production, an intermediate in the cycle. However, the inhibitory potency of N-ethylmaleimide on NADPH-cytochrome P-450 reductase activity paralleled that on the lipid peroxidation stimulated by paraquat in brain and lung. These findings indicate that the effect of paraquat on microsomal lipid peroxidation differs among the organs and that other factors, besides NADPH-cytochrome P-450 reductase, might be involved in the stimulation of lipid peroxidation by paraquat.

An evaluation of the redox cycling potencies of paraquat and nitrofurantoin in microsomal and lung slice systems

The redox cycling abilities of the pulmonary toxins paraquat and nitrofurantoin have been compared with those of the potent redox cyclers, diquat and menadione in lung and liver microsomes by using the oxidation of NADPH and consumption of oxygen. The relative potencies of these compounds to undergo redox cycling were in the order: diquat approximately menadione much greater than paraquat congruent to nitrofurantoin. This was partly attributed to the much lower affinity (Km) of lung and liver microsomes for paraquat and nitrofurantoin than for diquat and menadione. The potential to redox cycle was assessed in an intact cellular system by determining the oxygen consumption of rat lung slices in the presence (10(-6), 10(-5) and 10(-4) M) or absence of each of the four substrates. At concentrations of paraquat (10(-5) M) known to be accumulated by lung slices, a small but significant stimulation of lung slice oxygen uptake was observed. Nitrofurantoin (10(-4)-10(-6) M) did not affect lung slice oxygen uptake in lung slices, an observation consistent with its being a poor redox cycling compound, which is not actively accumulated into lung cells. This data has important implications in assessing the risk of exposure to paraquat. Low levels of paraquat would not be expected to cause lung damage because insufficient compound is present in the lung to exert its toxicity by redox cycling (due to the high Km observed).

Antioxidant enzyme level response to prooxidant allelochemicals in larvae of the southern armyworm moth, Spodoptera eridania

Larvae of the southern armyworm, Spodoptera eridania, are highly polyphagous feeders which frequently encounter and feed upon plants containing high levels of prooxidant allelochemicals. While ingestion of moderate quantities of prooxidants can be tolerated by these larvae, ingestion of larger quantities can result in toxicity. Studies were conducted to assess the role of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) in the protection of S. eridania against redox active prooxidant plant allelochemicals. Dietary exposure of mid-fifth-instar larvae to either quercetin (a flavonoid) or xanthotoxin (a photoactive furanocoumarin), which generate superoxide radical, and singlet oxygen, respectively, resulted in an increase in SOD levels. CAT levels increased in all groups of S. eridania including control insects. This may have been due to the sudden exposure to food following an extended fast of 18 h (to insure that larvae would not reject the diet because of the prooxidants' bitter taste) with an eventual lowering of CAT values with time. GR activities did not significantly change except for a slight inhibition at the highest prooxidant concentrations used at 12-h post-ingestion. The data from these studies suggest that SOD responds to prooxidant challenges in these insects and together with CAT and GR contributes to the insect's defense against potentially toxic prooxidant compounds.

Oxygen radicals in lung pathology

Pulmonary tissue can be damaged in different ways, for instance by xenobiotics (paraquat, butylated hydroxytoluene, bleomycin), during inflammation, ischemia reperfusion, or exposure to mineral dust or to normobaric pure oxygen levels. Reactive oxygen species are partly responsible for the observed pulmonary tissue damage. Several mechanisms leading to toxicity are described in this review. The reactive oxygen species induce bronchoconstriction, elevate mucus secretion, and cause microvascular leakage, which leads to edema formation. Reactive oxygen species even induce an autonomic imbalance between muscarinic receptor-mediated contraction and the beta-adrenergic-mediated relaxation of the pulmonary smooth muscle. Vitamin E and selenium have a regulatory role in this balance between these two receptor responses. The autonomic imbalance might be involved in the development of bronchial hyperresponsiveness, occurring in lung inflammation. Finally, several antioxidants are discussed which may be beneficial as therapeutics in several lung diseases.

Pulmonary indoleamine 2,3-dioxygenase activity and its significance in the response of rats, mice, and rabbits to oxidative stress

The physiological significance of the enzyme indoleamine 2,3,-dioxygenase (IDO) (EC 1.13.11.17), which consumes superoxide anion (O2-), is not known. Since this enzyme is found in high concentrations in lung tissue, we examined the possibility that IDO may protect against chemically induced oxidative stress in the lung. The induction of IDO by bacterial lipopolysaccharide (LPS) was found to be 20-fold in the mouse and 4-fold in the rat, but did not confer protection against paraquat-induced pulmonary toxicity. Moreover, paraquat, when dosed to rats or mice, did not induce pulmonary IDO activity. An elevation in the intracellular O2- concentration was sought by incubating lung slices with 5 mM diethyldithiocarbamate (DDTC) (to inhibit SOD), paraquat (10(-4) M), or methylene blue (10(-4) M) or under an atmosphere of 100% oxygen. These attempts did not enhance the IDO activity in lung slices prepared from control or LPS-treated rats and mice. There was also no evidence that the uptake of an IDO substrate, tryptophan, was limiting for IDO activity in rat and mouse lung slices. We have concluded in the case of rats and mice that the pulmonary IDO activity, even following induction, is too low for O2- to be the rate-limiting factor. For this reason IDO cannot act as a protective enzyme by scavenging O2- in the lung of these species. However, in the rabbit, a species comparatively resistant to paraquat- and oxygen-induced lung damage, pulmonary IDO activity is 170 times that of rats or mice. IDO activity in rabbit lung slices was increased 4-fold by incubation with 5 mM DDTC and 10-fold by incubation with methylene blue (10(-4) M). However, paraquat (10(-4) M and oxygen (100% atmosphere) were able to enhance IDO activity (5-fold) only when SOD had previously been inhibited. We have concluded that in the rabbit lung IDO is able to scavenge O2- and therefore has the potential to act as a protective enzyme in this species.

Induction of antioxidant enzyme activities by a phenylurea derivative, EDU

Oxygen free radicals have the potential to mediate cell injury. Defenses against such radicals include the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX). The purposes of this study were (1) to develop an in vitro model using human cells in which to investigate a potential pharmacologic agent as an inducer of these antioxidant enzymes; (2) to investigate the phenylurea derivative N-[2-(2-oxo-1-imidazolindinyl)ethyl]-N-phenylurea (EDU) in this model with paraquat (PQ) serving as the positive control; and (3) to determine if induction of the antioxidant enzymes by EDU occurs in vivo. Human gingival fibroblasts (Gin-1) were used as the target cell in vitro; PQ and EDU, an inducer of SOD and CAT activities in plants, were evaluated as antioxidant enzyme inducers. Total SOD activity in Gin-1 cells increased 2-fold (p less than 0.05) in the presence of 1.0 mM PQ for 18-48 hr compared with untreated controls. Gin-1 cells incubated with 0.25-2.0 mM PQ for 24 hr had significantly increased total SOD (1.5 to 2.0-fold; p less than 0.05). CAT activity increased with 1.0 and 2.0 mM PQ (p less than 0.05). In the presence of PQ, GSH-PX activity decreased (p less than 0.05) in a concentration-dependent manner, indicating inactivation of this enzyme. No toxicity, indicated by lactate dehydrogenase released into the incubation medium, was noted at PQ concentrations below 5.0 mM. In the presence of 0.125-2.0 mM EDU, total SOD activity in Gin-1 cells significantly increased (1.5 to 2.0-fold; p less than 0.05). CAT activity significantly increased in a dose-dependent manner (p less than 0.05), while GSH-PX activity remained constant following exposure to 0.125-2.0 mM EDU. Intraperitoneal administration of EDU to rats twice a day for 2 days at 100 mg/kg induced SOD activity in heart, liver, and lung compared to controls (p less than 0.05). CAT activity increased in the liver 56% and in the lung 36% (p less than 0.05). GSH-PX activity remained constant. Our findings indicate that Gin-1 cells are a useful model in which to study inducers of antioxidant enzymes in vitro and that the phenylurea compound EDU induces SOD and CAT activities both in vitro and in vivo.

Free radicals and oxygen toxicity

Most organisms are constantly exposed to molecular oxygen, and this has become a requirement of life for many of them. Oxygen is not totally innocuous, however, and it has long been known to be toxic to many organisms, including humans. The deleterious effects of oxygen are thought to result from its metabolic reduction to highly reactive and toxic species, including superoxide anion radical and hydroxyl radical. Peroxidation of lipids is a major consequence of exposure to these species and the cell possesses various enzymes, including superoxide dismutase and catalase, as well as cellular antioxidants which are able to scavenge oxygen free radicals and repair peroxidized lipids. These aspects of oxygen toxicity are reviewed, as well as the involvement of oxygen free radicals in the toxicity of the herbicide paraquat.

Influence of lipid peroxidation on beta-adrenoceptors

The peroxidation of lipids in biological membranes is a destructive phenomenon that can be elicited in various ways. Surface receptor molecules that allow cells to respond to hormones are possibly inactivated during lipid peroxidation. Effects of lipid peroxidation on receptors have not been extensively examined thus far. This investigation shows that there is a decrease in beta-adrenoceptor density (measured as specific (-)-[125I]iodocyanopindolol binding) during lipid peroxidation, in both lungs and erythrocytes of the rat. To this end, lung membranes (containing both beta 1- and beta 2-adrenoceptors) and intact erythrocytes (containing a homogeneous beta 2-adrenoceptor population) were pretreated with cumene hydroperoxide (lung membranes with 0.1 mM and erythrocytes with 1 mM) and Fe2+ (1 X 10(-5) M) for 60 min which resulted in extensive lipid peroxidation measured as malondialdehyde formation. The ration beta 1-:beta 2-adrenoceptor density in lung membranes after treatment with cumene hydroperoxide did not change and remained at 30%:70%. A single injection (i.p.) with the herbicide paraquat (50 mg/kg, 24 h), which is known to cause lung damage via lipid peroxidation, resulted in similar alterations in receptor density to those caused by cumene hydroperoxide in the in vitro experiments.

Systematically applied chemicals that damage lung tissue

A large, and increasing number of drugs and chemicals have been found which are toxic to lung following systemic administration. These agents damage lung tissue specifically, or in addition to damage to other tissues. Mechanisms explaining the pulmonary damage produced by some lung toxins have been uncovered. These include concentration of the agent within lung, the absence of adequate pulmonary detoxication systems, and bioactivation to a toxic species within specific lung cells or at distant sites followed by transport to the lung. The basic biochemical lesions underlying lung damage, responses of individual lung cells and pulmonary repair processes to the toxic agent, and species and age differences in susceptibility to lung damage have not, however, been well defined for most lung toxins. This review describes the information available on pulmonary biochemical and pathological changes associated with some of these lung-toxic agents. In addition, mechanisms proposed to explain the lung damage are discussed. The agents covered include: paraquat, the thioureas, butylated hydroxytoluene, the trialkylphosphorothioates, various lung-toxic furans and antineoplastic agents, the pyrrolizidine alkaloids, metals and organometallic compounds, amphiphilic agents, hydrocarbons, oleic acid, 3-methylindole, and diabetogenic agents. Detailed reviews on the overall toxicity of many of these agents have been published elsewhere. This review concentrates on their pulmonary toxicity. Information is presented as an overview to illustrate both the extensive literature that is available and the important questions that remain to be answered about systemic chemicals that damage lung tissue.

Paraquat toxicity in vitro. I. Pulmonary alveolar macrophages

When the herbicide paraquat (1,1'-dimethyl-4,4'-bipyridylium) was administered to adult rat pulmonary alveolar macrophages (PAM) in primary culture, both a time-dependent and a dose-dependent cytotoxic response (cell death) was observed. An LD50 value of 1 mM was calculated when these cells were exposed to paraquat in vitro for 12 h in Ham's F12 culture medium at 30 degrees C. Cell death was accompanied by the formation of TBA-reactive substances (lipid peroxidation) and was potentiated by hyperoxia (95% O2). In a 95% O2-5% CO2 atmosphere, an LD50 value of 0.1 mM was calculated. In addition, the presence of superoxide dismutase in the culture medium (1700 units/ml) inhibited the cytotoxic response. Since [14C]paraquat was not absorbed into these cells, extracellular superoxide anion radical formation was investigated as the cause of the observed cell death. Paraquat (0.5 mM) was found to stimulate extracellular O-2 generation, from PAM, but only in nonactivated cells. A sevenfold enhancement over the resting rate of radical generation was observed in the presence of paraquat. No increase in the O-2 generation rate of activated macrophages was observed upon the addition of paraquat to the culture medium. These data indicate that paraquat is cytotoxic to the pulmonary alveolar macrophage and further suggest that this cytotoxicity is mediated, at least in part, by an excess, extracellular production of active oxygen species. Implications of these findings with respect to the currently accepted hypothesis of paraquat poisoning in vivo are discussed.

Hyperoxia exposure in mechanically ventilated primates with and without previous lung injury

The response of the injured lung to hyperoxia is uncertain. In the present study, we evaluated the effects of 100% oxygen exposure for 120-168 h in mechanically ventilated baboons with or without previous diffuse alveolar damage (DAD) induced by oleic acid. These two groups were compared with another group of six baboons previously studied in our laboratory in which DAD induced with oleic acid was followed by ventilation with 40% oxygen. Oleic acid infusion caused a prompt reduction in total lung capacity, static compliance, and diffusion capacity and an increase in lung tissue volume. The magnitude and course of oleic acid lung injury was similar for 4 days in animals breathing 100% or 40% O2. Animals breathing 100% O2 without previous lung injury developed significant decreases in total lung capacity, oxygenation, and diffusion capacity after 72 h of hyperoxia. By 120 h, lung function was similarly impaired in both 100% O2-breathing groups, and rapidly worsening pulmonary edema appeared radiographically between 5.5 and 7 days in all O2-exposed animals. Subsequent weaning was successful in only three animals after 100% O2 exposure. All but one animal in the 40% O2 group were easily weaned. Histologic changes between 6 and 14 days in 100% O2 animals showed a marked proliferative response, particularly of type 2 cells; no differences were found due to prior oleic acid injury. Resolution of this process occurred in a surviving animal, resulting in focal fibrotic residua at 6 weeks, similar to that observed in 40% O2 oleic acid-treated survivors. Previous lung injury due to oleic acid did not modify the response of the baboon lung to hyperoxia.

Effects of multiple doxorubicin doses on mouse cardiac and hepatic catalase

Catalase activity was followed up in the hearts and livers of CD 1 mice treated with Doxorubicin 4 mg/Kg, i.v., weekly for 9 weeks. In this murine model the antiblastic induces cardiac morphological lesions which are progressively severer with the increase of the administered cumulative dose. Heart catalase showed a consistent elevation which reached a maximum (+116.2%, P less than 0.05) after the 5th dose. In the case of hepatic catalase no significant variation was observed except a transitory elevation following the first administration. The specific increase of heart catalase activity following multiple Doxorubicin doses could be an indicator that an enhanced free radical generation acts "in vivo" along with the onset of the cardiac lesions due to antiblastic.

Biliary excretion of glutathione and glutathione disulfide in the rat. Regulation and response to oxidative stress

Regulation of the biliary excretion of reduced glutathione (GSH) and glutathione disulfide (GSSG) and responses to selected model toxins were examined in male Sprague-Dawley rats. In control and phenobarbital-pretreated rats in which the intrahepatic concentration of GSH was modulated by the administration of diethyl maleate or acetaminophen, the biliary concentration of GSH was consistently lower than, but directly proportional to, the intrahepatic concentration of GSH. Furthermore, increments in bile flow produced by the infusion of sulfobromophthalein (BSP)-glutathione were associated with proportional increases in the biliary excretion of GSH, suggesting that GSH passes into bile passively along a concentration gradient. In contrast, GSSG appears to be secreted into bile against a steep concentration gradient. An increased hepatic production and biliary excretion of GSSG resulted from the administration of t-butyl hydroperoxide. Measurement of biliary GSSG and BSP during a constant infusion of the GSH adduct of BSP indicated that GSSG shares a common excretory mechanism with GSH adducts. Diquat, nitrofurantoin, and paraquat also markedly stimulated the biliary excretion of GSSG. On a molar basis, these compounds generated much more GSSG than a direct substrate for glutathione peroxidase such as t-butyl hydroperoxide, indicating that the compounds undergo redox-cycling with concomitant production of hydrogen peroxide. Aminopyrine (0.8 mmol/kg) also significantly increased biliary GSSG. This increase, however, was associated with a proportional increase in bile flow and in the biliary excretion of GSH such that the GSSG/GSH ratio in bile did not change. Acetaminophen and chloroform, two compounds generating electrophilic metabolites that deplete intrahepatic GSH, led to a progressive decrease in the biliary excretion of GSH and GSSG. Furosemide and dimethylnitrosamine, the electrophilic metabolites of which do not deplete hepatic GSH, minimally altered biliary GSH and GSSG. Similarly, carbon tetrachloride and iproniazid, which yield organic radical metabolites that can peroxidize membrane lipids, did not increase the biliary excretion of GSSG. This finding indicates that membrane-bound lipid hydroperoxides may not be good substrates for glutathione peroxidases. The measurement of the biliary excretion of GSSG and of the GSSG/GSH ratio in bile is a sensitive index of oxidative stress in vivo and thus complements other in vivo parameters for the study of reactive intermediates of xenobiotics such as the determination of covalent binding, the formation of lipid hydroxy acids, and the depletion of intracellular GSH.

Superoxide, hydrogen peroxide, and oxygen toxicity in two free-living nematode species

Two species of free-living nematodes, Turbatrix aceti and Caenorhabditis elegans, exhibited a marked sensitivity to 3 atm of 100% O2. Environmental changes in pH and temperature, which altered nematode respiration, resulted in alterations in the survival of these organisms under high pO2. Levels of defensive enzymes such as superoxide dismutase, catalase, glutathione peroxidase, and dianisidine peroxidase were measured in the two species. No changes in the level of superoxide dismutase or catalase activity were induced by exposure of the nematodes to high pO2. Manipulation of these two enzymes was however achieved using the inhibitors 3-amino-1,2,4-triazole and diethyldithiocarbamate. 3-Amino-1,2,4-triazole (20 mM) eliminated greater than or equal to 80% of the catalase activity in vivo and diethyldithiocarbamate (5 mM) decreased the level of CuZn superoxide dismutase by greater than or equal to 70%. Both of these compounds increased the sensitivity of C. elegans to high pO2 toxicity. Compounds capable of intracellular redox-cycling with O2- -production, such as plumbagin, increased CN- -resistant respiration in the nematodes and imposed an O2-dependent toxicity. These experiments demonstrate the toxicity of intracellular O2- and H2O2 in nematodes and the importance of superoxide dismutase and catalase in providing a defense against these toxic molecules in vivo.

Some new data to the toxicological effects of paraquat and the therapy

1. Substances previously tested therapeutically were studied to obtain evidence on the pathomechanism in mice of paraquat, the active ingredient of Gramoxon, connected with the radicals formed from molecular oxygen, and also to extend the therapeutic possibilities. 2. The effects of these substances were assessed on the basis of the 72-hr survival rate and the percentage ratio of the wet lung weight to the overall body weight. 3. Other toxicological parameters too were followed. 4. Our present investigations indicate that, in agreement with our earlier results, besides reduced glutathione and ascorbic acid, vitamin E and C-ase are of the greatest importance from the aspect of the protection against paraquat toxicity. 5. In addition to those listed, other materials too, e.g. antifibrotic substances, naturally possess considerable detoxicating properties too.