Protection against hyperoxia by serum from endotoxin treated rats: absence of superoxide dismutase induction

Endotoxin greatly reduces lung injury and pleural effusions in adult rats exposed to normobaric hyperoxia (greater than 98% oxygen for 60 hours). This study reports that serum from endotoxin treated donor rats protects serum recipients against hyperoxic lung injury without altering lung superoxide dismutase (SOD) activity. Rats pretreated with endotoxin alone were protected and exhibited an increase in lung SOD activity as previously reported by others. Protection by serum was not due to the transfer of residual endotoxin or SOD. These results show that protection from oxygen toxicity can occur in rats without an increase in lung SOD and suggest that a serum factor may be involved.     

Cytokines increase rat lung antioxidant enzymes during exposure to hyperoxia

Pretreatment with the combination of tumor necrosis factor/cachectin (TNF/C) and interleukin 1 (IL-1) increased glucose-6-phosphate dehydrogenase (G6PDH), glutathione reductase (GR), glutathione peroxidase (GPX), catalase (CAT), and superoxide dismutase (SOD) activities in lungs of rats continuously exposed to hyperoxia for 72 h, a time when all untreated rats had already died. Pretreatment with TNF/C and IL-1 also increased, albeit slightly, lung G6PDH and GR activities of rats exposed to hyperoxia for 4 or 16 h. By comparison, no differences occurred in lung antioxidant enzyme activities of TNF/C and IL-1- or saline-pretreated rats exposed to hyperoxia for 36 or 52 h; the latter is a time just before untreated rats began to succumb during exposure to hyperoxia. The results raise the possibility that TNF/C and IL-1 treatment can increase lung antioxidant enzyme activities and that increased lung antioxidant enzymes may contribute to the increased survival of TNF/C and IL-1-pretreated rats in hyperoxia for greater than 72 h.     

Effects of bacterial endotoxin on protecting copper-deficient rats from hyperoxia

The administration of very low doses of bacterial endotoxin protects rats during exposure to hyperoxia and is associated with the induction of lung antioxidant enzyme activities. Copper-deficient rats have increased susceptibility to O2 toxicity, which may be related to their decreased lung superoxide dismutase activity (SOD) or decreased plasma ceruloplasmin concentrations. To determine whether endotoxin can protect against hyperoxia in this susceptible model, we exposed copper-deficient and control rats to a fractional inspiratory concentration of O2 greater than 0.95 for 96 h after pretreatment with 500 micrograms/kg of bacterial endotoxin or phosphate-buffered saline (PBS). Mortality in the copper-deficient and control rats given PBS and exposed to O2 for 96 h was 100%. Copper-deficient rats died significantly earlier during the exposure than controls. No mortality occurred in either group treated with endotoxin and hyperoxia despite the decreased activity of copper-dependent enzymes in the copper-deficient rats. Copper-deficient rats treated with endotoxin and exposed to hyperoxia did increase lung Cu-Zn-SOD activity, but activity remained below levels found in air-exposed controls. Mn-SOD activity was found to be induced above air-exposed controls in the copper-deficient rats treated with endotoxin and exposed to hyperoxia. Hyperoxic exposure resulted in a marked increase in plasma ceruloplasmin concentrations in the control rats, but no increases in ceruloplasmin occurred in the copper-deficient animals. Endotoxin protects copper-deficient rats from hyperoxia despite their decreased lung Cu-Zn-SOD activity, and decreased plasma ceruloplasmin.     

Dexamethasone protects against high-dose endotoxin without loss of tolerance to oxygen

Endotoxin (500 micrograms/kg)-treated rats are very tolerant to hyperoxia (greater than 95% O2, 1 ATA). We have now attempted to determine if dexamethasone given to rats 1 h before a usually lethal dose of endotoxin would diminish endotoxin's lethality without substantially abrogating its capacity to confer tolerance to hyperoxia. Endotoxin (20 mg/kg) given alone killed 70-80% of air- or O2-breathing rats within 24 h; dexamethasone (0.6 mg) given 1 h before endotoxin decreased mortality at 24 h to 10-15%. About 90% of the rats that were alive 24 h after receiving dexamethasone plus endotoxin (20 mg/kg) survived 72 h of hyperoxia. Dexamethasone plus endotoxin (10 mg/kg) provided as much protection against pulmonary edema resulting from 72 h of hyperoxia as did 500 micrograms/kg endotoxin alone. Tolerance to hyperoxia produced by dexamethasone plus high-dose endotoxin was accompanied by a rise in the activity in the lung of antioxidant enzymes. We conclude that dexamethasone protects rats against the lethal effects of high doses of endotoxin without interfering with endotoxin's capacity to engender tolerance to hyperoxia.     

Effect of oxygen and endotoxin on lactate dehydrogenase release, 5-hydroxytryptamine uptake, and antioxidant enzyme activities in endothelial cells

We compared the effects of 95% O2 (hyperoxia) alone, endotoxin (20 ng/ml) alone, and 95% O2 plus endotoxin on the release of lactate dehydrogenase (LDH), uptake of 5-hydroxytryptamine (5-HT), and antioxidant enzyme activities in porcine pulmonary arterial and aortic endothelial cells in monolayer culture. Hyperoxia increased LDH release and decreased 5-HT in both endothelial cell types. Hyperoxia also caused a decrease in catalase (CAT) activity and an increase in total superoxide dismutase (SOD) and glutathione reductase (GSH-Red) activities in both cell types. Endotoxin alone had no effect on LDH release, 5-HT uptake, or antioxidant enzyme activities. However, endotoxin prevented the hyperoxic increase in LDH release and the hyperoxic decrease in 5-HT uptake. Endotoxin plus 95% O2 had no consistent effect on the antioxidant enzyme profile in pulmonary artery or aortic endothelial cells. These results indicate that (1) hyperoxia injures both pulmonary artery and aortic endothelial cells in culture and causes changes in the antioxidant enzyme profile that are similar in the two cell types; (2) hyperoxia-induced decreases in CAT activity and increases in SOD activity may be responsible for increased sensitivity of endothelial cells to O2 toxicity; and (3) endotoxin protects against hyperoxic injury to endothelial cells in vitro, but increases in antioxidant enzyme activities are not the mechanism for this protection.     

Polyethylene glycol-attached antioxidant enzymes decrease pulmonary oxygen toxicity in rats

When exposed continuously to hyperoxia (100% O2, 760 Torr barometric pressure), rats pretreated with polyethylene glycol (PEG)-attached superoxide dismutase and catalase (PEG-SOD + PEG-CAT) lived longer (79.1 + 7.6 h) than rats pretreated with saline (60.7 +/- 2.1 h) or PEG-inactivated-SOD + PEG-inactivated-CAT (62.3 +/- 1.6 h). Rats pretreated with PEG-SOD + PEG-CAT also had less hyperoxia-induced acute oxidative edematous lung injury, as assessed by increases in lung oxidized glutathione (GSSG) contents, pleural effusions, and lung lavage albumin concentrations than saline-pretreated rats. Rats pretreated with the long-lived conjugates PEG-inactivated-SOD + PEG-inactivated-CAT or PEG-albumin also had decreased acute oxidative edematous lung injury compared with rats pretreated with PEG, SOD + CAT + PEG, SOD + CAT, or saline. In vitro studies suggested that PEG itself may have contributed to protection by scavenging hydroxyl radical (.OH) but not superoxide (O2-.) or H2O2. Compared with more effective endogenous (via preexposure to hypoxia) or exogenous (via liposomes) means for increasing lung antioxidant enzymes, PEG enzymes are less protective against lung injury from continuous hyperoxia.     

Mitogenic effect of endotoxin on lung and tolerance of rats to hyperoxia

Treatment of rats with endotoxin, as late as 24 h after beginning exposure to greater than 95 O2 at 1 atm, increases survival at 72 h from 20-30% to greater than 95% (J. Clin. Invest. 65: 1104, 1980), whereas treatment with corticosteroids reduces survival (Toxicol. Appl. Pharmacol. 47: 367, 1979). Since endotoxin is mitogenic to some cells and glucocorticosteroids decrease DNA synthesis by lung cells, we asked 1) is endotoxin mitogenic to the lung, and, if so, 2) is the mitogenic effect required for endotoxin to produce tolerance to hyperoxia? We found endotoxin administered in vivo does have a mitogenic effect on the lung as indicated by an increased rate of DNA synthesis by lung slices; dexamethasone blocked this effect. However, although dexamethasone given alone markedly diminished survival in hyperoxia, dexamethasone did not impair the protection conferred to rats by endotoxin against the edemogenicity and lethality of hyperoxia. Furthermore, dexamethasone did not diminish the rise of antioxidant enzyme activity in the lungs of endotoxin-treated O2-exposed rats. We conclude endotoxin can produce tolerance to hyperoxia even when its mitogenic action on the lung is substantially diminished.     

Adenovirus-mediated transfer of the SOCS-1 gene to mouse lung confers protection against hyperoxic acute lung injury

Suppressor of cytokine signaling-1 (SOCS-1) is a member of the suppressor of cytokine signaling family of proteins and an inhibitor of interleukin-6 (IL-6) signaling. SOCS-1 has been shown to protect cells from cellular damage and apoptosis induced by tumor necrosis factor (TNF), lipopolysaccharide (LPS), and interferon gamma (IL-γ). However, it is not known whether increased SOCS-1 is protective during pulmonary oxidative stress. Therefore, we hypothesized that increased SOCS-1 in the lungs of mice would be protective in the setting of hyperoxic lung injury. We administered SOCS-1 adenovirus (Ad-SOCS-1) intratracheally into the lungs and exposed the mice to 100% O₂. Mice infected with GFP adenovirus (Ad-GFP) were used as controls. Mice treated with Ad-SOCS-1 had enhanced survival in 100% oxygen compared to Ad-GFP-administered mice. After 3 days of hyperoxia, Ad-GFP mice were ill and tachypnic and died after 4 days. In contrast, all Ad-SOCS-1-treated mice survived for at least 6 days in hyperoxia and 80% survived beyond 7 days. Ad-SOCS-1 transfection protected mouse lungs from injury as indicated by lower lung wet/dry weight, alveolar–capillary protein leakage, reduced infiltration of inflammatory cells, and lower content of thiobarbituric acid-reactive substances in lung homogenate. Our results also indicated that Ad-SOCS-1 significantly inhibits hyperoxia-induced ASK-1 (apoptosis signal-regulating kinase 1) expression. Taken together, these findings show that increased expression of adenovirus-mediated SOCS-1 in the lungs of mice significantly protects against hyperoxic lung injury.     

Protective effects of selenium against cadmium induced hematological disturbances,immunosuppressive, oxidative stress and hepatorenal damage in rats

Cadmium is a non-essential toxic metal used in industrial process, causes severe risk to human health. Selenium (Se) is an essential trace mineral of fundamental importance for human health. Selenium has antioxidant enzymes roles and is needed for the proper function of the immune system. In this study, the protective effects of selenium against cadmium intoxication in rats have been investigated by monitoring some selective cytokines (IL-1β, TNF α, IL-6, IL-10 and IFN-γ), antioxidant enzymes reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and lipid peroxidation malondialdehyde (MDA) as well as some selective biochemical markers of liver and kidney functions. Thirty-two rats were divided into four equal groups; the first group was used as a control. Groups 2–4 were treated with selenium (Se; 0.1 mg/kg BW), cadmium (Cd; 40 mg/L drinking water) and selenium plus cadmium, respectively. Rats were orally administered their relevant doses daily for 30 days. Blood samples were collected from heart puncture at the end of the experiment (30 days) for complete blood picture (CBC) and serum was separated to evaluate the different immunological parameters and biochemical parameters, as well as liver specimens for Cd and Se estimation. Rats in the Cd treated group have a significantly higher hepatic concentration of Cd than in other treated groups. Results revealed that cadmium significantly increased IL-1β, TNF α, IL-6 and IL-10, beside peripheral neutrophils count, while the IFN-γ and lymphocytes were decreased in rat sera. In addition, GSH level, CAT, SOD and GPx activities were significantly decreased while lipid peroxidation (MDA) was increased. Regarding, liver and renal markers, they were significantly increased in the activities of aminotransferases (AST, ALT), urea and creatinine, while total plasma proteins and albumin were significantly decreased. On the other hand, selenium treated group, showed significantly increased IFN-γ, GSH level, CAT, and GPx activities, as well as lymphocyte count while IL-10 was decreased. Selenium in combination with cadmium, significantly improved the elevation of serum IL-1β, IL-6, TNF α, IL-10 and malondialdehyde in addition to enhancing the antioxidant enzyme activities of GSH, CAT, GPx and SOD. Moreover, selenium has ameliorated the cadmium-induced liver and kidney damage by improving hepatic and renal markers. The results of this investigation demonstrated that selenium has the potential to countermeasure the immunosuppressive as well as hepatic and renal oxidative damage induced by cadmium in rats; selenium has shown promising effects against Cd toxicity.     

Different levels of hyperoxia reversibly induce catalase activity in amphibian tadpoles

Studies about the proposed antioxidant physiological role of the catalase (CAT) enzyme in relation to different environmental oxygen tensions are reported for the first time in amphibian larvae of Discoglossus pictus and Rana ridibunda perezi during their development. The CAT levels of whole tadpoles increased constantly in both species during the larval period, reaching a maximum during the metamorphic climax. All through development, CAT activity levels were always greater in D. pictus than in R. ridibunda perezi. This correlates well with the already reported higher SOD activity and hyperoxia resistance of the D. pictus species when compared to R. ridibunda perezi. Long-term acclimation to different levels of hyperoxia (40, 60, and 100% O2) showed dose-related increases in the CAT activity of D. pictus tadpoles. These increases did not take place when the animals were subjected to acute hyperoxia (24 h). The increase in CAT activity observed after 15 days of acclimation to acute hyperoxia (710 mm Hg: 100% O2) was reversed after 15 additional days of postacclimation to normal air (149 mm Hg O2). When recently metamorphosed frogs were acclimated to acute hyperoxia, significant increases in CAT activity were observed after 15 days, but not after 7 days. The results are interpreted as supporting a protective role for the CAT enzyme in amphibian larvae and froglets against oxygen toxicity.     

Protective Mechanism of Panax notoginseng Saponins on Rat Hemorrhagic Shock Model in Recovery Stage

To explore protective mechanism of Panax notoginseng saponins (PNS) on rat hemorrhagic shock model in recovery stage. 72 Wistar rats were selected and divided into control group, model group and PNS group with 24 rats in each group. 200 mg/kg PNS was injected intravenously at 60 min of hemorrhagic shock stage in PNS groups. Changes of endotoxin, MPO, IL-6, SOD, MDA and TNF α were observed at 30 and 120 min of recovery stage by ELISA; water content of lung and intestine was detected; HE staining was applied to observe morphological change of intestinal mucosa, kidney, liver and lung; western blot was used to detect intercellular adhesion molecule-1 (ICAM-1) level in lung tissue and intestine tissue. At 30 min and 120 min of recovery stage, MDA, MPO, endotoxin, TNF α and IL-6 levels significantly increased in model group compared with control group, however SOD level significantly decreased, the difference was statistically significant (P < 0.05); PNS dose-dependently decreased MDA, MPO, endotoxin, TNF α and IL-6 levels, and increased SOD level, which was statistically significant (P < 0.05); In results of water content detection, water content in lung tissue and intestine tissue was significantly higher than in control group, however, after being treated with PNS, the water content was significantly decreased; HE staining showed the morphologic change of lung tissue cells; Western blot showed that in lung tissue and intestine tissue, ICAM-1 level in model group was significantly higher than in control group, and it was lower in PNS group than in model group. PNS can increase SOD activity, decrease levels of MDA, endotoxin and MPO, decrease expression of TNF α and IL-6, and decrease water content in lung tissue and intestine tissue. Thus, PNS is protective to rat hemorrhagic shock model by anti oxidative stress and anti-inflammatory pathways, and ICAM-1 may play an important role in the mechanism.     

Endotoxin extends survival of adult mice in hyperoxia

Research on endotoxin protection from oxygen toxicity is presently limited to the rat model since only rats have been protected by endotoxin. This study reports that endotoxin also extends survival of adult male mice in hyperoxia (greater than 99% oxygen at 1 ATA). Initially, 4-month-old male mice were treated with Boivin-extracted E. coli endotoxin and placed in hyperoxia. Zymosan-primed mice receiving 2 or 10 micrograms endotoxin, and unprimed mice receiving 10-40 micrograms endotoxin, showed moderate protection against hyperoxia; 11/15 Boivin-treated mice survived 120 hours exposure to hyperoxia with time-of-death in hyperoxia = 126.7 +/- 4.4 hours (mean +/- SEM, n = 15). This contrasts with untreated male mice; 0/4 survived 120 hours exposure to hyperoxia with mean survival = 103.5 +/- 3.5 hours. Mice receiving 20 or 60 micrograms Westphal-extracted endotoxin were not protected nor were older female mice receiving 20 micrograms Boivin-extracted endotoxin. This study suggests that age, sex, the extraction method used to obtain endotoxin, and possibly the time of year when endotoxin is administered, are important variables in allowing endotoxin to extend survival of mice in hyperoxia.     

牙髓紫卟啉菌内毒素对炎症性细胞因子的介导作用

牙髓紫叶琳菌ＡＴＣＣ３５４０６是近年来新发现的重要致病性专性厌氧菌,采用改良酚－氯仿－石油醚法提取牙髓紫卟啉菌ＡＴＣＣ３５４０６内毒素脂多糖,通过Ｋｒａｍｅｒ测定法、软琼脂细胞培养法以及胸腺细胞增殖法测定脂多糖的细胞生物学活性。结果显示：纯化脂多糖可不同程度地诱导小鼠模型生成肿瘤坏死因子（ＴＮＦ）、集落刺激因子（ＣＳＦ）和白介素－１（ＩＬ－１）,并在一定范围内呈剂量依赖型,提示牙髓紫卟啉菌内毒素在动物模型和细胞模型中具有显著的细胞生物学和免疫学活性．     

Protection from hyperbaric oxidant stress by administration of buthionine sulfoximine.

To explore the role of glutathione in protecting rats from hyperbaric hyperoxia, we administered buthionine sulfoximine (BSO) to block gamma-glutamyl cysteine synthase activity and decrease tissue glutathione synthesis. We then exposed these animals and their vehicle-treated matched controls to 100% oxygen at 4 ATA or room air at 1 ATA. After BSO treatment, glutathione concentrations in air-exposed controls decreased 62% in lung, 76% in liver, 28% in brain, and 62% in plasma. Paradoxically, BSO-treated rats were protected from hyperbaric hyperoxia. The BSO-treated animals seized significantly later and had a markedly prolonged time of survival compared with the vehicle-treated controls. We conclude that BSO treatment protects rats from hyperbaric hyperoxia, despite its effects of lowering plasma and tissue glutathione concentrations. This protection may be related to a direct effect of the compound in decreasing free radical-mediated tissue injury, increasing tissue antioxidant defenses, or increasing seizure threshold.     

Modulation of oxidant lung injury by using liposome-entrapped superoxide dismutase and catalase

Increased cellular generation of partially reduced species of oxygen mediates the toxicity of hyperoxia to cultured endothelial cells and rats exposed to 95-100% oxygen. Liposomal entrapment and intracellular delivery of superoxide dismutase (SOD) to cultured porcine aortic endothelial cells increased the specific activity of cellular SOD up to 15-fold. The liposome-mediated augmentation of SOD activity persisted in cell monolayers and rendered these cells resistant to oxygen-induced injury in a cell SOD activity-dependent manner. Addition of free SOD to culture medium had no effect on cell SOD activity or resistance to oxygen toxicity. SOD and catalase-containing liposomes injected i.v. into rats increased lung-associated enzyme specific activities two- to fourfold. Liposome entrapment of both SOD and catalase significantly increased the circulating half-lives of these enzymes and was critical for prevention of in vivo oxygen toxicity. Free SOD and catalase injected i.v. in the absence or presence of control liposomes did not increase corresponding lung enzyme activities or survival time in 100% oxygen. These studies show that O2- and H2O2 are important mediators of oxygen toxicity and that intracellular delivery of oxygen protective enzymes can reduce tissue injury owing to overproduction of partially reduced oxygen species.     

Endotoxin tolerance in rats: expression of TNF-alpha, IL-6, IL-10, VCAM-1 AND HSP 70 in lung and liver during endotoxin shock.

Endotoxin can induce a state of tolerance against its own pathological effects, commonly referred to as endotoxin tolerance. This phenomenon has been found to be associated with reduced serum levels of cytokines such as TNF-alpha, IL-1, IL-6 and IL-10. In the present study the expression of TNF-alpha, IL-6, IL-10, the adhesion molecule VCAM-1 and the heat shock protein 70 was determined in vivo in lung and liver of LPS-tolerant and naive rats by means of semiquantitative RT-PCR after i.v. LPS injection. TNFalpha, IL-6, IL-10, HSP 70 and VCAM-1 were induced in lung and liver after LPS injection. In liver and lung of endotoxin-tolerant rats TNF-alpha and IL-6 were induced to a lower degree after LPS treatment when compared to non-tolerant controls. The LPS-induced IL-10 expression was also slightly attenuated in the lung of tolerant rats, but in the liver no differences between tolerant and non-tolerant animals were observed. HSP 70 and VCAM-1 were expressed after systemic LPS treatment in liver and lung. The degree of induction, however, was the same in tolerant and untreated controls. The presented data show that endotoxin tolerance is reflected by a reduced cytokine expression in lung and liver in vivo. On the other hand, levels of expression of the adhesion molecule VCAM-1 and the stress protein HSP 70 do not appear to be changed by endotoxin tolerance.     

Effects of various antioxidants on endotoxin-induced lung injury and gene expression: mRNA expressions of MnSOD, interleukin-1beta and iNOS

Antioxidants have been shown to be effective in attenuating acute lung injury. In this study, we determine the effects of various antioxidants by different mechanisms on the lipopolysaccharide (LPS)-induced changes. LPS was administered intravenously at a dose of 10 mg/kg to anesthetized rats. LPS induced a significant decrease in blood pressure (P < 0.01) and increased exhaled nitric oxide (NO) from 3.60+/-0.18 to 35.53+/-3.23 ppb (P < 0.01) during an observation period of 4 h. Plasma nitrate concentrations also increased from 0.61+/-0.06 to 1.54+/-0.22 micromol/l (P < 0.05). LPS-induced oxygen radical release from white blood cells isolated from rat peripheral blood also increased significantly (P < 0.001). After the experiment, the lung weight was obtained and lung tissues were taken for the determination of mRNA expression of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta) and manganese superoxide dismutase (MnSOD). Histological examination of the lungs was also performed. In the control group injected with saline solution, mRNA expressions of iNOS, IL-1beta, TNF-alpha and MnSOD were absent. Four hours after LPS administration, mRNA expressions of iNOS, IL-1beta, and MnSOD were significantly enhanced, but TNF-alpha was not discernibly expressed. LPS also caused a twofold increase in lung weight. Pathological examination revealed endothelial cell damage and interstitial edema. Various antioxidants were given 1 h after LPS administration. These agents include SOD, catalase (CAT), SOD + CAT or vitamin C (ascorbic acid). These antioxidants effectively reversed the systemic hypotension, reduced the quantity of exhaled NO and plasma nitrate concentration, and prevented acute lung injury. Administration of various antioxidants also significantly attenuated LPS-induced oxygen radical release by rat white blood cells. LPS induced mRNA expressions of MnSOD and iNOS were significantly depressed by these antioxidants. However, only SOD + CAT and vitamin C inhibited the mRNA expression of IL-1beta. These results suggest that oxygen radicals are responsible for LPS-induced lung injury. Antioxidants can attenuate the lung injury by inhibiting mRNA expressions of iNOS and IL-1beta.     

Resistance to hyperoxia with heme oxygenase-1 disruption: role of iron

In many models, a protective role for heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, has been demonstrated. Also, HO-1 null mice (KO) are more susceptible to inflammation and hypoxia and transplant rejection. Nonetheless, their response to hyperoxia (> 95% O(2)) has not yet been evaluated. Surprisingly, after acute hyperoxic exposure, KO had significantly decreased markers of lung oxidative injury and survived chronic hyperoxia as well as wild-type (WT) controls. Disrupted HO-1 expression was associated with decreased lung reactive iron and iron-associated proteins, decreased NADPH cytochrome cp450 reductase activity, and decreased lung peroxidase activity compared to WT. Injection of tin protoporphyrin, an inhibitor of HO, in the WT decreased acute hyperoxic lung injury, whereas transduction of human HO-1 in the KO reversed the relative protection of the KO to acute injury and worsened hyperoxic survival. This suggests that disruption of HO-1 protects against hyperoxia by diminishing the generation of toxic reactive intermediates in the lung via iron and H(2)O(2).     

N-acetylcysteine and glutathione as inhibitors of tumor necrosis factor production.

TNF is a major mediator in the pathogenesis of endotoxic shock, and its inhibition has a protective effect in various animal models of sepsis or endotoxin (lipopolysaccharide, LPS) toxicity. LPS treatment also induces an oxidative damage mediated by increased production of reactive oxygen intermediates. N-Acetylcysteine (NAC) is an antioxidant and a precursor of the synthesis of glutathione (GSH) and was reported to protect against LPS toxicity and LPS-induced pulmonary edema. In this study we investigated the effect of NAC on TNF production and LPS lethality in mice. The results indicated that oral administration of NAC protects against LPS toxicity and inhibits the increase in serum TNF levels in LPS-treated mice. The inhibition was not confined to the released form of TNF, since NAC also inhibited LPS-induced spleen-associated TNF. On the other hand, the inhibitor of GSH synthesis, DL-buthionine-(SR)-sulfoximine (BSO), had the opposite effect of potentiating LPS-induced TNF production, and this was associated with a decrease in liver GSH levels. Repletion of liver GSH with NAC reversed this effect. NAC was also active in inhibiting TNF production and hepatotoxicity in mice treated with LPS in association with a sensitizing dose of Actinomycin D. These data indicate that GSH can be an endogenous modulator of TNF production in vivo. On the other hand, NAC pretreatment did not inhibit other effects of LPS, particularly induction of serum IL-6, spleen IL-1 alpha, and corticosterone, in the same experimental model, suggesting that the observed effect could be specific for TNF.