Xanthine oxidase mediates elastase-induced injury to isolated lungs and endothelium

Cardiovascular effects of hyperoxia during and after cardiac surgery

During and after cardiac surgery with cardiopulmonary bypass, high concentrations of oxygen are routinely administered, with the intention of preventing cellular hypoxia. We systematically reviewed the literature addressing the effects of arterial hyperoxia. Extensive evidence from pre-clinical experiments and clinical studies in other patient groups suggests predominant harm, caused by oxidative stress, vasoconstriction, perfusion heterogeneity and myocardial injury. Whether these alterations are temporary and benign, or actually affect clinical outcome, remains to be demonstrated. In nine clinical cardiac surgical studies in low-risk patients, higher oxygen targets tended to compromise cardiovascular function, but did not affect clinical outcome. No data about potential beneficial effects of hyperoxia, such as reduction of gas micro-emboli or post-cardiac surgery infections, were reported. Current evidence is insufficient to specify optimal oxygen targets. Nevertheless, the safety of supraphysiological oxygen suppletion is unproven. Randomised studies with a variety of oxygen targets and inclusion of high-risk patients are needed to identify optimal oxygen targets during and after cardiac surgery.

Mechanism for the increased permeability in endothelial monolayers induced by elastase

The aim of this study was to investigate the mechanism for the increase in endothelial permeability induced by human neutrophil elastase (HNE). Pretreatment of bovine pulmonary artery endothelial cells (BPAEC) with HNE(0-30 μg/ml) for 1 h produced a concentration dependent increase in ¹²⁵I-albumin clearance. The effect was reversible and was not due to cytolysis. Pretreatment of BPAEC with sodium tungstate, which depletes xanthine oxidase, or with oxypurinol, did not prevent HNE induced increased permeability. Heparin, which neutralizes the cationic charge of HNE, also had no protective effect. Pretreatment with heat inactivated HNE, which still had positive charge sites, did not result in increased endothelial permeability. Also, ONO-5046, a novel specific inhibitor of HNE, did prevent increased permeability. These results suggest that elastase increases endothelial permeability mainly through its proteolytic effects.

Plasma neutrophil elastase correlates with pulmonary vascular permeability: a prospective observational study in patients with pneumonia

BACKGROUND AND OBJECTIVE

Little is known about plasma neutrophil elastase (PNE) levels in patients with community-acquired pneumonia (CAP) requiring treatment in the intensive care unit (ICU) or high care unit (HCU). In addition, the influence of PNE on pulmonary vascular permeability in a clinical setting has not been investigated. The aims of this study were (i) to investigate PNE levels in patients with CAP and (ii) to explore the relationship between PNE and pulmonary vascular permeability.

METHODS

Fourteen consecutive CAP patients who were admitted to the HCU (n = 8) or ICU (n = 6) were prospectively investigated over a 6-month period. A group of eight patients with hydrostatic pulmonary oedema without CAP served as a control group (CG). PNE levels were measured at regular intervals. The pulmonary vascular permeability index (PVPI) was monitored in all ICU and CG patients, using the PiCCO system.

RESULTS

PNE levels were higher in the CAP patients (132 (84-261) ng/mL) than in the CG patients (77 (64-107) ng/mL) (P = 0.04), and were highest in the ICU patients (186 (75-466) ng/mL). The PVPI was higher in the ICU patients (2.85 (1.90-4.00)) than in the CG patients (1.15 (0.75-2.35)) (P = 0.02). PNE levels correlated with PVPI in the ICU patients (r = 0.81, P < 0.001) but there was no correlation among the CG patients (r = 0.14, P = 0.73).

CONCLUSIONS

Patients with severe CAP had high levels of PNE, which was closely correlated with PVPI. PNE may be involved in the pathogenesis of severe pneumonia.

Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene

The xanthine oxidoreductase gene (XOR) encodes an important source of reactive oxygen species and uric acid, and its expression is associated with various human diseases including several forms of cancer. We previously reported that basal human XOR (hXOR) expression is restricted or repressed by E-box and TATA-like elements and a cluster of transcriptional proteins, including AREB6-like proteins and DNA-dependent protein kinase (DNA-PK). We now demonstrate that the cluster contains the tumor suppressors SAFB1, BRG1, and SAF-A. We further demonstrate that SAFB1 silencing increases hXOR expression and that SAFB1 directly binds to the E-box. Multiple studies in vitro and in vivo including pulldown, immunoprecipitation and chromatin immunoprecipitation analyses indicate that SAFB1, Ku86, and BRG1 associate with each other. The results suggest that the SAFB1 complex binds to the hXOR promoter in a chromatin environment and plays a critical role in restricting hXOR expression via its direct interaction with the E-box, DNA-PK, and tumor suppressors. Moreover, we demonstrate that the cytokine, oncostatin M (OSM), induces the phosphorylation of SAFB1 and that the OSM-induced hXOR mRNA expression is significantly inhibited by silencing the DNA-PK catalytic subunit or SAFB1 expression. The present studies for the first time demonstrate that hXOR is a tumor suppressor-targeted gene and that the phosphorylation of SAFB1 is regulated by OSM, providing a molecular basis for understanding the role of SAFB1-regulated hXOR transcription in cytokine stimulation and tumorigenesis.

Inhibitory effects of prior low-dose x-irradiation on ischemia-reperfusion injury in mouse paw

We have reported that low-dose, unlike high-dose, irradiation enhanced antioxidation function and reduced oxidative damage. On the other hand, ischemia-reperfusion injury is induced by reactive oxygen species. In this study, we examined the inhibitory effects of prior low-dose X-irradiation on ischemia-reperfusion injury in mouse paw. BALB/c mice were irradiated by sham or 0.5 Gy of X-ray. At 4 hrs after irradiation, the left hind leg was bound 10 times with a rubber ring for 0.5, 1, or 2 hrs and the paw thickness was measured. Results show that the paw swelling thickness by ischemia for 0.5 hr was lower than that for 2 hrs. At 1 hr after reperfusion from ischemia for 1 hr, superoxide dismutase activity in serum was increased in those mice which received 0.5 Gy irradiation and in the case of the ischemia for 0.5 or 1 hr, the paw swelling thicknesses were inhibited by 0.5 Gy irradiation. In addition, interstitial edema in those mice which received 0.5 Gy irradiation was less than that in the mice which underwent by sham irradiation. These findings suggest that the ischemia-reperfusion injury is inhibited by the enhancement of antioxidation function by 0.5 Gy irradiation.

Effect of Wen-Pi-Tang extract on lung damage by influenza virus infection

The effect of Wen-Pi-Tang extract on influenza virus infection in mice was investigated. The administration of Wen-Pi-Tang extract at a dose of 100mg/kg body wt. for 8 consecutive days to influenza virus-infected mice reversed the lack of body wt. gain and prevented the increase in lung weight caused by the infection in comparison with uninfected mice, while allopurinol, a xanthine oxidase (XOD) inhibitor, did not show these effects. The serum levels of uric acid and allantoin in influenza virus-infected mice were reduced by Wen-Pi-Tang extract administration. Moreover, Wen-Pi-Tang extract reduced the uric acid level more as the dose increased, although it exerted lower activity than allopurinol. The XOD activity of the lungs was elevated by influenza virus infection, but Wen-Pi-Tang extract administration inhibited this activity, indicating prevention of lung damage by oxygen free radicals generated by XOD. After the administration of Wen-Pi-Tang extract to influenza virus-infected mice, the lung superoxide dismutase activity was not significantly different from that of uninfected mice, whereas lung catalase activity was lower in the former than the latter, but slightly higher than that of influenza virus-infected mice, suggesting that Wen-Pi-Tang extract may prevent the generation of highly toxic hydroxyl radicals in the lung. In addition, the administration of both Wen-Pi-Tang extract and allopurinol reduced the degree of lung consolidation caused by influenza virus infection. In particular, Wen-Pi-Tang extract reduced the consolidation score in a dose-dependent manner and more markedly than allopurinol did. This study suggests that Wen-Pi-Tang extract could improve pathological conditions of the lungs induced by influenza virus infection.

Acute respiratory distress syndrome of the contralateral lung after reexpansion pulmonary edema of a collapsed lung

STUDY OBJECTIVE

To report that leukocyte-mediated acute injury may develop in a nonhypoxic lung after hypoxia-reoxygenation injury of the hypoxic lung and in other systemic organs in patients with reexpansion pulmonary edema.

DESIGN

Case report analysis with examination of the literature.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Three patients who developed leukocyte-mediated acute lung injury in the contralateral lung and systemic organ injury after ipsilateral reexpansion pulmonary edema of a collapsed lung.

MEASUREMENTS

To rule out the possibility that the acute lung injury in the contralateral lung was an extension of the hypoxia-reoxygenation injury, we analyzed changes in leukocyte and platelet count in the peripheral blood in relation to the development of pulmonary edema in each lung. Changes in liver enzymes were also analyzed to detect hepatic dysfunction as evidence of systemic organ injury.

MAIN RESULTS

Both leukocyte and platelet counts decreased when reexpansion pulmonary edema developed, and decreased further when acute lung injury developed in the contralateral lung (F = 8.42, p = 0.037 for leukocytes, and F = 17.66, p = 0.01 for platelets). Significant hepatic dysfunction developed, as evidenced by increases in both serum bilirubin (p = 0.001) and lactic dehydrogenase, indicating the presence of systemic organ injury.

CONCLUSIONS

The hypoxia-reoxygenation injury of one lung can induce acute lung injury in the other lung and systemic organ injury.

Characterization of Proteins Binding to E-box/Ku86 Sites and Function of Ku86 in Transcriptional Regulation of the Human Xanthine Oxidoreductase Gene

We reported previously that E-box and TATA-like elements repress human xanthine oxidoreductase gene (hXOR) expression. In the present investigation, we determined the means by which the E-box site functions in this basal repression. DNA affinity purification demonstrated that at least five proteins are involved in the nuclear protein complex binding to the E-box and adjacent Ku86-binding sites. Amino acid sequence analysis demonstrated that three proteins, DNA-PK catalytic subunit, Ku86, and Ku70 are components of DNA-dependent protein kinase (DNA-PK). By electrophoretic mobility shift assays, gel-shift, and site-directed mutagenesis, we confirmed Ku86 binding to the Ku86 site. Studies indicated that the other two proteins of the complex are AREB6-like proteins binding to the E-box. Pull-down and immunoprecipitation analyses demonstrated the binding of Ku86 to AREB6-like proteins. The functional loss of Ku86 increases hXOR promoter activity and transcript expression. Based on the findings, we propose that DNA-PK/AREB6-like proteins play a central role in repression of basal hXOR activity. AREB6-like proteins specifically bind to the E-box, whereas Ku86 binds an adjacent site and recruits DNA-PK catalytic subunit and Ku70 proteins. A working model is presented to account for the role of DNA-PK and AREB6-like proteins in regulating hXOR activity.

Mononuclear phagocyte xanthine oxidoreductase contributes to cytokine-induced acute lung injury

Acute lung injury (ALI) is characterized by increased alveolar cytokines, inflammatory cell infiltration, oxidative stress, and alveolar cell apoptosis. Previous work suggested that xanthine oxidoreductase (XOR) may contribute to oxidative stress in ALI as a product of the vascular endothelial cell. We present evidence that cytokine induced lung inflammation and injury involves activation of XOR in the newly recruited mononuclear phagocytes (MNP). We found that XOR was increased predominantly in the MNP that increase rapidly in the lungs of rats that develop ALI following intratracheal cytokine insufflation. XOR was recovered from the MNP largely converted to its oxygen radical generating, reversible O-form, and alveolar MNP exhibited increased oxidative stress as evidenced by increased nitrotyrosine staining. Cytokine insufflation also increased alveolar cell apoptosis. A functional role for XOR in cytokine-induced inflammation was demonstrated when feeding rats two different XOR inhibitors, tungsten and allopurinol, decreased MNP XOR induction, nitrotyrosine staining, inflammatory cell infiltration, and alveolar cell apoptosis. Transfer of control or allopurinol treated MNP into rat lungs confirmed a specific role for MNP XOR in promoting lung inflammation. These data indicate that XOR can contribute to lung inflammation by its expression and conversion in a highly mobile inflammatory cell population.

Non-invasive analysis of reactive oxygen species generated in NH4OH-induced gastric lesions of rats using a 300 MHz in vivo ESR technique

Free radicals are reportedly involved in mucosal injury, including NH4OH-induced gastric lesions, but the kind, location and origin of radical generation have yet to be clarified. We developed the non-invasive measurement of reactive oxygen species (ROS) in stomach, and applied to mucosal injury. NH4OH-induced gastric lesions were prepared in rats, which were then given a nitroxyl probe intragastrically or intravenously, and the spectra of the gastric region were obtained by in vivo 300 MHz electron spin resonance (ESR) spectroscopy. The spectral change of the nitroxyl probe administered intragastrically was significantly enhanced 30 min after NH4OH administration, but no change occurred when the probe was given by intravenous injection. The enhanced change was confirmed to be due to *OH generation, because it was completely suppressed by mannitol, catalase and desferrioxamine (DFO), and was not observed in neutropenic rats. NH4OH-induced neutrophil infiltration of the gastric mucosa was suppressed by intravenous injection of superoxide dismutase (SOD) or catalase, or by administration of allopurinol. The present study provided the direct evidence in NH4OH-treated living rats that *OH produced from O2*- derived from neutrophils caused gastric lesion formation, while O2*- or H2O2 derived from the xanthine oxidase system in endothelial cells was involved in neutrophil infiltration.

Leukotoxin-activated human pulmonary artery endothelial cell produces nitric oxide and superoxide anion

To provide evidence that pulmonary endothelial cells exposed to 9,10-epoxy-12-octadecenoate (Lx) produce nitric oxide (NO) and superoxide anion (O(2)(*-), we measured NO production, using a NO chemiluminescence analyzer, and nitric oxide synthase (NOS) activity, monitoring the conversion of L- [14C] arginine to L- [14C] citrulline, and O(2)(*-) by a fluorescence assay using a fluorescence spectrophotometer with hydroethidine (HE) in human pulmonary artery endothelial cells (HPAEC). NO production and eNOS were increased significantly when HPAEC were incubated with 10 microM Lx, and this effect was inhibited by L-NMMA or in the absence of extracellular Ca2+. Addition of 10 mM HE to the cell suspension spontaneously and continuously caused a subtle increase in fluorescence intensity, due to intracellular oxidation of HE to ethidium bromide (EB). Treatment of the cell suspension with Lx after the addition of HE exerted a dose-dependent increase in intracellular EB fluorescence. Pre-treatment with allopurinol, a xanthine oxidase inhibitor, decreased the intracellular EB fluorescence by 54% in HPAEC incubated with 100 microM Lx. These results show that Lx induces NO production via activation of eNOS and O(2)(*-) production in endothelial cells via activation of cellular xanthine oxidase. Thus, Lx is a bioactive lipid.

Neutrophil activation in preterm infants who have respiratory distress syndrome

OBJECTIVE

To study neutrophil activation in circulation as a sign of systemic inflammation in preterm infants with respiratory distress syndrome.

METHODS

The study comprised very low birth weight preterm infants who had respiratory distress syndrome and required intubation and mechanical ventilation (n = 51), 1-day-old preterm infants who had no need for mechanical ventilation (n = 12), term infants (n = 47), and adult volunteers (n = 25). Neutrophil surface expression of CD11b was quantified with flow cytometry.

RESULTS

In preterm infants with respiratory distress syndrome, neutrophil CD11b expression during the first day of life was higher than in cord blood (mean: 165 relative fluorescence units [RFU] [standard deviation [SD]: 53], n = 29 vs 83 RFU [SD: 21], n = 11; 95% confidence interval [CI] for difference: 59-106) or in preterm infants without mechanical ventilation (106 RFU [SD: 33], n = 12; 95% CI for difference: 17-90). CD11b expression decreased by age of 10 days. CD11b expression was lower in preterm cord than in term cord blood (95% CI for difference: 5-53). However, in preterm infants with respiratory distress syndrome aged 2 to 5 days, it was higher than in term infants of that age.

CONCLUSIONS

The observations demonstrate an early transient postnatal neutrophil activation indicative of systemic inflammation that may contribute to the tissue injury in preterm infants with respiratory distress syndrome.

Neutrophil elastase and acute lung injury: prospects for sivelestat and other neutrophil elastase inhibitors as therapeutics

OBJECTIVES

To review the evidence and rationale that suggest that neutrophil elastase (NE) may contribute to the development of acute lung injury (ALI) and the acute respiratory distress syndrome. To review selected preliminary data regarding the effectiveness of NE inhibition in animals, in in vitro models, and in patients with ALI.

DATA SOURCES

The published literature and observations provided by Ono Pharmaceutical and Eli Lilly investigators and their colleagues.

DATA SUMMARY

Taken en toto, the data suggest that NE could contribute to ALI and endothelial cell injury that is relevant to ALI. Moreover, the toxic effects of NE are greatly enhanced by increased oxidative stress, which commonly occurs in patients with ALI. In addition to neutrophils, xanthine oxidase, a constituent of endothelial cells, is a potential source of oxidative stress in ALI; xanthine oxidase-derived oxidants enhance NE toxicity in in vivo, isolated lung, and in vitro endothelial cell test systems. Not surprisingly, endogenous nonoxidatively sensitive NE inhibitors (e.g., eglin C) are more effective in combating the detrimental effects of NE than oxidatively sensitive NE inhibitors (e.g., alpha-1-proteinase inhibitor). In addition, a synthetic NE inhibitor, sivelestat (ONO-5046 and LY544349), is effective in reducing measures of inflammation and injury in multiple animal models of ALI. In a trial of ALI patients with systemic inflammatory response syndrome, conducted in Japan by Ono Pharmaceutical scientists, sivelestat treatment improved the investigator assessment of global improvement and the percentages of patients who were removed from ventilators and transferred out of the intensive care unit.

CONCLUSIONS

Further study of the role of NE inhibition as a treatment for ALI is warranted. Additional clinical and preclinical studies with sivelestat and various other NE inhibitors should not only clarify the clinical potential of this intervention strategy, but also better define the activities of NE in inflammatory disorders such as ALI and multiple organ failure.

Role of the mitochondrial permeability transition and cytochrome C release in hydrogen peroxide-induced apoptosis

We investigated the role of the mitochondrial inner membrane permeability transition and subsequent release of cytochrome c into the cytosol during oxidative stress-evoked apoptosis. Sublethal oxidative stress was applied by treating L929 cells with 0.5 mM H2O2 for 90 min. Then the cellular localization of cytochrome c was examined by immunofluorescent staining and Western blotting. H2O2 treatment caused the permeability transition and pore formation, resulting in membrane depolarization and translocation of cytochrome c from the mitochondria into the cytosol. Pretreatment with cyclosporin A and aristolochic acid (to inhibit pore formation) significantly attenuated a reduction of the mitochondrial membrane potential, as well as signs of apoptosis such as DNA fragmentation, increased plasma membrane permeability, and chromatin condensation. Therefore, exposure to H2O2 caused the opening of permeability transition pores in the inner mitochondrial membrane. An essential role of cytosolic cytochrome c in the execution of apoptosis was demonstrated by its direct microinjection into the cytosol, thus bypassing the need for cytochrome c release from the mitochondrial intermembrane space. Microinjection of cytochrome c caused caspase-dependent apoptosis.

Leukocyte filtration in cardiac surgery: a review

Leukocyte filtration has evolved as an important technique in cardiac surgery with cardiopulmonary bypass to prevent pathogenic effector functions mediated by activated leukocytes. The underlying mechanisms that result in an improvement of laboratory variables as well as clinical outcome are not resolved yet. Moreover, the optimum strategy for the use of current filtration technology has not been systematically evaluated. This paper, therefore, reviews how activated leukocytes may lead to tissue damage, summarizes the known effects of leukocyte filtration on clinical outcome and laboratory parameters, and deals with current experimental and clinical efforts to further limit the pathogenic effects of leukocytes in cardiac surgery.

Protective effect of lipophilic antioxidants on phorbol-induced acute lung injury in rats

OBJECTIVE

To determine whether the lipophilic antioxidant U-74389G can ameliorate the acute lung injury induced by phorbol myristate acetate (PMA) in our isolated lung model in rats, and to compare its activity with the intracellular enzymes superoxide dismutase (SOD) or catalase.

DESIGN

Randomized, controlled study.

SETTING

Animal-care facility procedure room.

SUBJECTS

Forty-two adult male Sprague-Dawley rats each weighing 250-350 g.

INTERVENTIONS

Typical acute lung injury was induced successfully by PMA during 60 mins of observation. PMA (2 microg/kg) elicited a significant increase in microvascular permeability (measured by using the capillary filtration coefficient Kfc), lung weight gain, the lung weight/body weight ratio, pulmonary arterial pressure, and the protein concentration of the bronchoalveolar lavage fluid.

MEASUREMENTS AND MAIN RESULTS

Pretreatment with 1 mg of U-74389G significantly attenuated the acute lung injury induced by PMA, all parameters having decreased significantly (p <.001). The protective effect of U-74389G was dose dependent, but SOD (6,000 U/kg) or catalase (50,000 U/kg) exhibited no protective effect.

CONCLUSIONS

U-74389G significantly ameliorates acute lung injury induced by PMA in rats.

Effects of lecithinized superoxide dismutase and a neutrophil elastase inhibitor (ONO-5046) on hyperoxic lung injury in rat

Reactive oxygen and neutrophil metabolites have been implicated in the development of hyperoxic lung injury. We determined the protective effects of either a superoxide dismutase or neutrophil elastase inhibitor and the combination of both agents on the development of hyperoxic lung injury in rats. Two drugs (lecithinized superoxide dismutase and ONO-5046) were used in the present study. Lecithinized superoxide dismutase, a lecithin derivative bound to recombinant CuZn superoxide dismutase, has a higher affinity for cells such as polymorphonuclear leukocytes and endothelial cells than recombinant human superoxide dismutase. N-[2-[4-2,2-dimethylpropionyloxy) phenylsulfonylamino] benzoyl]¿ aminoacetic acid (ONO-5046), a specific neutrophil elastase inhibitor, which was developed as a low-molecular weight inhibitor, showed protective effects against various lung injuries. Rats were exposed to over 90% oxygen for 72 h, and bronchoalveolar lavage was performed to evaluate the permeability and neutrophil accumulation in the lungs. Rats were treated with lecithinized superoxide dismutase (30,000 U/day, intravenously n=7) or ONO-5046 (10 mg/kg, intramuscularly twice a day, n=7) or a combination of both drugs (n=7). Albumin concentration and neutrophil counts in bronchoalveolar lavage fluid were compared between animals with and without drug treatment. Either lecithinized superoxide dismutase or ONO-5046 treatment significantly decreased albumin concentration and neutrophil counts in bronchoalveolar lavage fluid compared to those in the animals of the hyperoxia-alone group (n=9). However, albumin leakage and neutrophil accumulation in the rat lung treated with combined agents were identical to that of either the lecithinized superoxide dismutase or ONO-5046 treatment. These findings suggest that lecithinized superoxide dismutase and ONO-5046 are useful drugs to protect against hyperoxic lung injury in rats. However, there were no additive effects by the combination in preventing hyperoxic lung injury.

Repressed expression of the human xanthine oxidoreductase gene. E-box and TATA-like elements restrict ground state transcriptional activity

Studies were initiated to address the basis for the low xanthine oxidoreductase (XOR) activity in humans relative to nonprimate mammalian species. The expression of the XOR in humans is strikingly lower than in mice, and both transcription rates and core promoter activity of the gene are repressed. Analysis of human XOR promoter activity in hepatocytes and vascular endothelial cells showed that the region from -258 to -1 contains both repressor and activator binding regions regulating core promoter activity. The region between -138 and -1 is necessary and sufficient for initiating, and the region between -258 and -228 is critical for restricting core promoter activity. Within the latter region, site-directed mutations identified a consensus sequence "acacaggtgtgg" (-242 to -230) that contains an E-box that binds a repressor. In addition, the TATA-like element is also required to restrict promoter activity and TFIID binds to this site. The results demonstrate that both an E-box and TATA-like element are required to restrict gene activity. A model is proposed to account for human XOR regulation.

Can we learn from the pathogenetic strategies of group A hemolytic streptococci how tissues are injured and organs fail in post-infectious and inflammatory sequelae?

The purpose of this review-hypothesis is to discuss the literature which had proposed the concept that the mechanisms by which infectious and inflammatory processes induce cell and tissue injury, in vivo, might paradoxically involve a deleterious synergistic 'cross-talk', among microbial- and host-derived pro-inflammatory agonists. This argument is based on studies of the mechanisms of tissue damage caused by catalase-negative group A hemolytic streptococci and also on a large body of evidence describing synergistic interactions among a multiplicity of agonists leading to cell and tissue damage in inflammatory and infectious processes. A very rapid cell damage (necrosis), accompanied by the release of large amounts of arachidonic acid and metabolites, could be induced when subtoxic amounts of oxidants (superoxide, oxidants generated by xanthine-xanthine oxidase, HOCl, NO), synergized with subtoxic amounts of a large series of membrane-perforating agents (streptococcal and other bacterial-derived hemolysins, phospholipases A2 and C, lysophosphatides, cationic proteins, fatty acids, xenobiotics, the attack complex of complement and certain cytokines). Subtoxic amounts of proteinases (elastase, cathepsin G, plasmin, trypsin) very dramatically further enhanced cell damage induced by combinations between oxidants and the membrane perforators. Thus, irrespective of the source of agonists, whether derived from microorganisms or from the hosts, a triad comprised of an oxidant, a membrane perforator, and a proteinase constitutes a potent cytolytic cocktail the activity of which may be further enhanced by certain cytokines. The role played by non-biodegradable microbial cell wall components (lipopolysaccharide, lipoteichoic acid, peptidoglycan) released following polycation- and antibiotic-induced bacteriolysis in the activation of macrophages to release oxidants, cytolytic cytokines and NO is also discussed in relation to the pathophysiology of granulomatous inflammation and sepsis. The recent failures to prevent septic shock by the administration of only single antagonists is disconcerting. It suggests, however, that since tissue damage in post-infectious syndromes is caused by synergistic interactions among a multiplicity of agents, only cocktails of appropriate antagonists, if administered at the early phase of infection and to patients at high risk, might prevent the development of post-infectious syndromes.

Mechanisms of hyperoxia-induced reductions in retinal blood flow in newborn pig

Although reductions in retinal blood flow (RBF) in response to acute hyperoxia are well described, the mechanistic basis of this response has yet to be clarified. The present study was undertaken in order to determine the possible involvement of two arachidonic acid-derived vasoconstrictors, the cyclooxygenase metabolite thromboxane and the cytochrome P450 metabolite 20-HETE, as well as the involvement of the peptide endothelin and superoxide free radical. Fluorescein videoangiography was performed on the intact eyes of isoflurane-anesthetized newborn piglets. RBF responses to 20 min of hyperoxia were calculated from the angiograms off-line, using changes in mean arteriovenous transit times and arteriolar and venular diameters. The effect of hyperoxia (PaO2=351+/-9 mmHg; n=39) on RBF was examined in each animal under control conditions and again after intravitreal perivascular administration of drugs that block the synthesis or receptors of known vasoconstrictors. Estimated RBF decreased by a maximum of 42+/-3% in the 7 animal groups in response to 20 min of hyperoxia. The magnitude and time course of the change in RBF resulting from two successive hyperoxic challenges did not differ, and were unaffected by intravitreal administration of vehicle. The response to hyperoxia was attenuated 46+/-6 (n=6; P=0.001) after intravitreal CGS 22652 (2 nmol), a combined thromboxane synthesis inhibitor and receptor antagonist. DDMS (12.5 nmol), a competitive inhibitor of the P450 enzyme omega-hydroxylase that forms 20-HETE, blocked hyperoxic constriction by 23+/-7% (n=6; P=0.01). Intravitreal pretreatment with TBC 1241z (2 nmol), a receptor antagonist of the peptide endothelin, blocked the hyperoxic response by 26+/-5% (n=6; P=0.01). A combination of CGS 22652 (2 nmol), DDMS (12.5 nmol), and TBC 1241z (2 nmol), blocked the hyperoxic flow response by 51+/-3% (n=5; P=0.003). Administration of a combination of superoxide dismutase (10 U intravitreally, 10000 U kg-1 of the polyethylene glycol-conjugate intravenously) and catalase (10 U intravitreally, 10000 U kg-1 intravenously) was without effect on hyperoxia-induced reductions in RBF (n=5). The present results indicate that the arachidonic acid metabolites thromboxane and 20-HETE, and the peptide endothelin, participate in mediating the acute reduction in RBF in response to hyperoxia.

Neutrophil elastase promotes lung microvascular injury and proteolysis of endothelial cadherins

Intestinal ischemia-reperfusion (I-R) is associated with lung injury and the acute respiratory distress syndrome. The hypothesis of this study was that intestinal I-R activates circulating neutrophils to promote elastase-mediated lung injury. Isolated rat lungs were perfused with blood or plasma obtained after intestinal I-R, and lung neutrophil retention and injury and bronchoalveolar lavage (BAL) elastase were measured. Perfusion with I-R blood caused lung neutrophil accumulation and injury and increased BAL elastase. These effects were attenuated by the elastase inhibitor L-658758. Interference with neutrophil adherence before gut reperfusion blocked BAL elastase accumulation. The role of endothelial junction proteins (cadherins) in I-R-elicited lung damage was also evaluated. Activated human neutrophils proteolyzed cadherins in human umbilical vein endothelial cells. Furthermore, plasma of patients with acute respiratory distress syndrome contained soluble cadherin fragments. The results of this study suggest that the elastase released by systemically activated neutrophils contributes to lung neutrophil accumulation and pulmonary microvascular injury. Elastase-mediated proteolysis of endothelial cell cadherins may represent the mechanism through which lung microvascular integrity is disrupted after intestinal I-R.

Inflammatory responses to ischemia and reperfusion in skeletal muscle

Skeletal muscle ischemia and reperfusion is now recognized as one form of acute inflammation in which activated leukocytes play a key role. Although restoration of flow is essential in alleviating ischemic injury, reperfusion initiates a complex series of reactions which lead to neutrophil accumulation, microvascular barrier disruption, and edema formation. A large body of evidence exists which suggests that leukocyte adhesion to and emigration across postcapillary venules plays a crucial role in the genesis of reperfusion injury in skeletal muscle. Reactive oxygen species generated by xanthine oxidase and other enzymes promote the formation of proinflammatory stimuli, modify the expression of adhesion molecules on the surface of leukocytes and endothelial cells, and reduce the bioavailability of the potent antiadhesive agent nitric oxide. As a consequence of these events, leukocytes begin to form loose adhesive interactions with postcapillary venular endothelium (leukocyte rolling). If the proinflammatory stimulus is sufficient, leukocytes may become firmly adherent (stationary adhesion) to the venular endothelium. Those leukocytes which become firmly adherent may then diapedese into the perivascular space. The emigrated leukocytes induce parenchymal cell injury via a directed release of oxidants and hydrolytic enzymes. In addition, the emigrating leukocytes also exacerbate ischemic injury by disrupting the microvascular barrier during their egress across the vasculature. As a consequence of this increase in microvascular permeability, transcapillary fluid filtration is enhanced and edema results. The resultant increase in interstitial tissue pressure physically compresses the capillaries, thereby preventing microvascular perfusion and thus promoting the development of the no-reflow phenomenon. The purpose of this review is to summarize the available information regarding these mechanisms of skeletal muscle ischemia/reperfusion injury.

Early albumin leakage in pulmonary endothelial monolayers exposed to varying levels of hyperoxia

We assessed the effect of varying levels of hyperoxia on 14C-albumin flux across bovine pulmonary artery endothelial cell (BPAEC) monolayers. Endothelialized nitrocellulose filters were mounted in Ussing-type chambers which were filled with cell culture medium (M 199). Equimolar amounts of 14C-labeled and unlabeled albumin were added to the "hot" and "cold" chambers, respectively, and the monolayers were exposed to 3 hours of varying levels of oxygen (16%, 30%, 40%, 60%, and 95%). When compared to 16% O2, exposure to hyperoxic gas mixtures of 40% or greater progressively increased albumin permeability across endothelial monolayers within 3 hours to a value 2.5 times higher at 95% O2 compared to 16% O2 (p < 0.001). Hyperoxia-induced permeability increases were prevented by catalase, superoxide dismutase, desferrioxamine, and allopurinol. Our data indicate that hyperoxia induces endothelial permeability changes more rapidly than previously reported even at O2 concentrations as low as 40%.

Endothelial cell associated anti-elastolytic activity

Addition of cultured and then carefully-washed bovine pulmonary artery endothelial cells (EC) decreased (p < 0.05) human neutrophil elastase activity (HNE) in vitro. HNE activity was also decreased (p < 0.05) by addition of histone or protamine treated EC. However, addition of papain or trypsin treated EC decreased HNE activity less than addition of untreated cells suggesting that a protein rather than a difference in cell surface charge was responsible. Other observations suggest that EC anti-elastolytic activity was not due to binding of antiprotease from culture media but was dependent on EC protein synthesis. First, addition of EC grown previously in serum-free media decreased HNE activity the same (p < 0.05) as addition of EC cultured in media containing serum. Second, addition of EC treated beforehand with cycloheximide decreased HNE activity less than (p < 0.05) addition of untreated control EC. We conclude that EC most likely make and have anti-elastolytic activity on their surfaces and speculate that EC associated anti-elastolytic activity may modulate inflammatory, repair and other biologic processes involving neutrophil elastase.

The synergistic effect of elastase and hydrogen peroxide on vascular endothelial cell injury is due to the production of hydroxylradical in the endothelial cells

Protease inhibitors such as aprotinin and urinastatin inhibited vascular endothelial cell injury induced by PMA-stimulated leukocytes, although their inhibitors did not suppress the production of active oxygen species released from leukocytes. On the other hand, in the presence of pancreas elastase (10 micrograms/ml), hydrogen peroxide (50 microM) caused severe injury of endothelial cells isolated from the bovine carotid artery (% specific 51Cr release, % SR = 42.9 +/- 3.3%), although the % SR elicited by elastase or hydrogen peroxide alone, respectively, was below 1%. Elastase and hydrogen peroxide acted synergistically on the injury of endothelial cells from the bovine carotid artery similarly to that in the endothelial cells isolated from the bovine coronary artery and human umbilical vein. Furthermore, elastase derived from both pancreas and leukocyte induced this synergistic action on endothelial cell injury. To clarify the mechanism of vascular endothelial cell injury induced by the combination of elastase and hydrogen peroxide, we examined the effects of various radical scavengers and protease inhibitors. Deferoxamine mesylate completely inhibited the endothelial cell injury, while protease inhibitors such as antitrypsin and macroglobulin had a protective effect. Pretreatment of endothelial cells with deferoxamine mesylate also protected against this cytotoxicity. These findings suggested that the synergistic effect of elastase and hydrogen peroxide on the endothelial cell injury is due to the production of hydroxylradical in the endothelium and that this synergistic action might be partially involved in the endothelial cell injury induced by activated leukocytes.

Effect of hypoxia and reoxygenation on the formation and release of reactive oxygen species by porcine pulmonary artery endothelial cells

Endothelial cells are critical targets in both hypoxia- and reoxygenation-mediated lung injury. Reactive O2 species (ROS) have been implicated in the pathogenesis of hypoxic and reoxygenation lung injury, and xanthine dehydrogenase/oxidase (XDH/XO) is a major generator of the ROS. Porcine pulmonary artery endothelial cells (PAEC) have no detectable XDH/XO. This study was undertaken to examine 1) ROS production by hypoxic porcine PAEC and their mitochondria and 2) ROS production and injury in reoxygenated PAEC lacking XDH/XO activity. Intracellular H2O2 generation and extracellular H2O2 and O2 divided release were measured after exposure to normoxia (room air-5% CO2), hypoxia (0% O2-95% N-5% CO2), or hypoxia followed by normoxia or hyperoxia (95% O2-5% CO2). Exposure to hypoxia results in significant reductions in intracellular H2O2 formation and extracellular release of H2O2 and O2 by PAEC and mitochondria. The reductions occur with as little as a 2 h exposure and progress with continued exposure. During reoxygenation, cytotoxicity was not observed, and the production of ROS by PAEC and their mitochondria never exceeded levels observed in normoxic cells. The absence of XDH/XO may prevent porcine PAEC from developing injury and increased ROS production during reoxygenation.

Xanthine oxidase mediates paraquat-induced toxicity on cultured endothelial cell

The role of xanthine oxidase in paraquat toxicity was investigated using cultured bovine pulmonary artery endothelial cells. Exposure to paraquat 0.1 mM was done for 24 hr with or without tungsten pretreatment and in the presence or absence of xanthine oxidase inhibitors. Exposure to paraquat significantly increased O2- production and relative xanthine oxidase activity (xanthine oxidase activity divided by total xanthine dehydrogenase plus xanthine oxidase) while depressing cell growth. In contrast, tungsten and allopurinol inhibited the increase of xanthine oxidase activity and decreased O2- release. Cell injury was assessed by leakage of lactate dehydrogenase and by fluorescein diacetate staining; it was found that oxidase inhibitors (both allopurinol and tungsten) reduced paraquat cytotoxicity. Thus the toxicity of paraquat was at least partly due to intracellular O2- production mediated by xanthine oxidase and the subsequent formation of other free radicals.

Xanthine oxidase contributes to lung leak in rats subjected to skin burn

We found that rats subjected to thermal skin injury (skin burn) had increased serum xanthine oxidase (XO) activities, increased serum complement activation (decreased serum CH50 levels), increased erythrocyte (RBC) fragility, increased lung neutrophil accumulation, and increased lung leak compared to sham-treated rats. Treatment of rats with allopurinol (an XO inhibitor) not only decreased serum XO activity, but also decreased complement activation, RBC fragility, lung neutrophil accumulation, and lung leak abnormalities in rats subjected to skin burn. We conclude that XO may contribute to acute lung injury and a number of events associated with the development of acute lung leak following skin burn.

Vanadate, molybdate and tungstate for orthomolecular medicine

Recent studies indicate that oxyanions, such as vanadate (V) or vanadyl (IV), cause insulin-like effects on rats by stimulating the insulin receptor tyrosine kinase. Tungstate (VI) and molybdate (VI) show the same effects on rat adipocytes and hepatocytes. Results of uncontrolled trials on volunteers accumulated in Japan also suggest that tungstate effectively regulates diabetes mellitus without detectable side effects. Since these oxyanions naturally exist in organisms, oxyanion therapy, the oral administration of vanadate, vanadyl, molybdate, or tungstate, can be considered to be orthomolecular medicine. Therefore, these oxyanions may provide a viable alternative to chemotherapy. Many diseases in addition to diabetes mellitus might also be treated since the implication of these results is that tyrosine kinases are involved in a variety of diseases.

Effects of FK506, an immunosuppressive agent, on genesis of water-immersion stress-induced gastric lesions in rats

We examined the effects of FK506, an immunosuppressive agent, on the genesis of water immersion stress-induced gastric lesions in rats. Using high-performance liquid chromatography, four kinds of prostaglandins, ie, 6-keto-prostaglandin F1 alpha, prostaglandin F2 alpha, prostaglandin E2, and prostaglandin D2, were detected, and no leukotrienes were detected in gastric mucosa in rats without stress. After 6 hr of stress, gastric lesions developed with decreases in all prostaglandin contents, and the emergence of peptide leukotrienes was observed. Intramuscular administration of FK506 (0.1, 0.25, 0.5, 1.0, and 2.0 mg/kg) reduced lesion index dose-dependently. Administration of FK506 at doses over 0.25 mg/kg decreased all prostaglandin contents, but did not affect the increase in leukotriene contents. Pretreatment with famotidine or omeprazole reduced lesion index, and the protective effects were equivalent to those of 1.0 mg/kg of FK506, although FK506 did not affect gastric secretion during water-immersion stress. Water-immersion stress did not change the activities of xanthine oxidase in either stomach or serum. Polyoxyethylene-modified superoxide dismutase did not prevent gastric lesions. Water-immersion stress significantly increased myeloperoxidase activity in gastric mucosa, and FK506 reduced the increase in myeloperoxidase activity induced by stress. From our results, other factors besides gastric acid secretion and tissue eicosanoid contents, such as chemoattractant factor, might also be involved in the genesis of water-immersion stress-induced gastric lesions in rats.

Interaction of viable group A streptococci and hydrogen peroxide in killing of vascular endothelial cells

Previous studies have shown that the streptococcal hemolysin, streptolysin S, is capable of interacting with hydrogen peroxide (H2O2) to injure vascular endothelial cells (Free Radic. Biol. Med. 7:369-376; 1989). To extend these observations, intact group A streptococci (strain 203S) were examined for ability to injure endothelial cells alone and for ability to injure the same cells in the presence of sublethal concentrations of H2O2 (generated from glucose/glucose oxidase). While neither control bacteria nor bacteria that had been pretreated with poly-L-histidine to render them cationic were cytotoxic to endothelial cells by themselves under the conditions of the experiment, endothelial cells were injured by combinations of streptococcal cells and sublytic amounts of H2O2. Taken together, these data suggest that the sequelae which often occur following primary infection with group A streptococci may be the result of a combined assault of host inflammatory cells and the invading bacteria on the vascular lining cells of the host.

Enzyme-biomaterial interactions: effect of biosystems on degradation of polyurethanes

Enzyme-induced liberation of hard-segment-containing components from polyurethanes was evaluated using two 14C-labeled polyurethanes. A polyester urea-urethane and polyether urea-urethane were synthesized from toluene-2,4-diisocyanate (TDI)/polycaprolactone diol (PCL) or TDI/polyethylene glycol (PEO) with 14C-labeled ethylene diamine. Both materials were characterized using electron spectroscopy for chemical analysis (ESCA), differential scanning calorimetry (DSC), size exclusion chromatography, and material chemistry by Fourier transform infrared (FTIR) spectroscopy. Biodegradation assays were carried out using cholesterol esterase (CE), collagenase (CO), cathepsin B (CB), and xanthine oxidase (XO) at the pH optimum conditions for each enzyme at 37 degrees C. Biodegradation was analyzed by monitoring the release of radiolabel, by weight change, and by surface analysis using scanning electron microscopy. The polyester urea-urethane was shown to be susceptible to enzymatic degradation above the effect of the buffer control solution by the CE but not by the other enzyme systems as monitored by radiolabel released. In the initial period of incubation, the rate of degradation was increased for all systems, including buffer controls; however, the rates dropped off rapidly by day 28. The change in weight data for the polyester urea-urethane and polyether urea-urethane showed no enzyme-dependent biodegradation above the buffer controls. However, in sodium acetate buffer at pH = 5, the polymers showed a significant weight loss relative to other buffers. In conclusion, this study showed that the biological component responsible for the onset of the biodegradation process is more likely the result of a multitude of biologically mediated compounds acting synergistically, with the process being enhanced by physical parameters such as material dissolution. In addition characterization of surface and bulk chemistry as well as material structure evaluation have been shown to be essential to interpret degradation data.

Mesangial cell killing by leukocytes: Role of leukocyte oxidants and proteolytic enzymes

Mesangial cells from human and rat kidney were examined for sensitivity to killing by neutrophils. Cells from both species were sensitive to killing by phorbol myristate acetate-stimulated neutrophils. Catalase was highly protective while superoxide dismutase was less protective and a number of protease inhibitors were not protective. Strong protection was also observed with the iron chelators, deferoxamine and phenanthroline, and with the hydroxyl radical scavengers, dimethylthiourea and 5,5-dimethyl-1-pyrroline N-oxide. Pretreatment of the mesangial cells with deferoxamine followed by washing also provided protection. Mesangial cells were also killed by reagent hydrogen peroxide (H2O2) but were much less sensitive to injury by direct application of proteolytic enzymes. The ability of H2O2 to injure mesangial cells was prevented by pre-incubation of the H2O2 with human leukocyte myeloperoxidase. These data suggest that killing is due primarily to the generation of H2O2 by the stimulated neutrophils and its further reduction in an iron-catalyzed reaction. The hydroxyl radical may be the reduction product that actually mediates lethal injury but lack of scavenger specificity prevents definitively concluding this. Mesangial cell killing by activated neutrophils could be significantly inhibited by monoclonal antibodies to CD11/CD18 molecules, suggesting that close contact between the target and effector cells is required for cytotoxicity. Although qualitatively similar to endothelial cells, the mesangial cells appeared to be quantitatively more oxidant sensitive than previously examined human and rat endothelial cells. Taken together, these data show that mesangial cells from rat and human are sensitive to leukocyte-induced injury and that injury results via an oxidant pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

The contribution of vascular endothelial xanthine dehydrogenase/oxidase to oxygen-mediated cell injury

The conversion of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) and the reaction of XO-derived partially reduced oxygen species (PROS) have been suggested to be important in diverse mechanisms of tissue pathophysiology, including oxygen toxicity. Bovine aortic endothelial cells expressed variable amounts of XDH and XO activity in culture. Xanthine dehydrogenase plus xanthine oxidase specific activity increased in dividing cells, peaked after achieving confluency, and decreased in postconfluent cells. Exposure of BAEC to hyperoxia (95% O2; 5% CO2) for 0-48 h caused no change in cell protein or DNA when compared to normoxic controls. Cell XDH+XO activity decreased 98% after 48 h of 95% O2 exposure and decreased 68% after 48 h normoxia. During hyperoxia, the percentage of cell XDH+XO in the XO form increased to 100%, but was unchanged in air controls. Cell catalase activity was unaffected by hyperoxia and lactate dehydrogenase activity was minimally elevated. Hyperoxia resulted in enhanced cell detachment from monolayers, which increased 112% compared to controls. Release of DNA and preincorporated [8-14C]adenine was also used to assess hyperoxic cell injury and did not significantly change in exposed cells. Pretreatment of cells with allopurinol for 1 h inhibited XDH+XO activity 100%, which could be reversed after oxidation of cell lysates with potassium ferricyanide (K3Fe(CN)6). After 48 h of culture in air with allopurinol, cell XDH+XO activity was enhanced when assayed after reversal of inhibition with K3Fe(CN)6, and cell detachment was decreased. In contrast, allopurinol treatment of cells 1 h prior to and during 48 h of hyperoxic exposure did not reduce cell damage. After K3Fe(CN)6 oxidation, XDH+XO activity was undetectable in hyperoxic cell lysates. Thus, XO-derived PROS did not contribute to cell injury or inactivation of XDH+XO during hyperoxia. It is concluded that endogenous cell XO was not a significant source of reactive oxygen species during hyperoxia and contributes only minimally to net cell production of O2- and H2O2 during normoxia.

Pulmonary microvascular endothelial cells constitutively release xanthine oxidase

The generation of oxidants in reperfused ischemic tissues by xanthine oxidase (XO) may contribute to tissue damage. We exposed bovine pulmonary microvascular endothelial (BPMVE) cells to hypoxia and subsequent reoxygenation and examined alterations in intracellular and extracellular XO activities. BPMVE cells incubated 24 h under hypoxic conditions (less than 1% O2) showed a twofold increase in intracellular xanthine dehydrogenase activity and a smaller increase in intracellular XO activity compared to normoxic BPMVE. Both normoxic and hypoxic BPMVE cells constitutively released XO activity into their culture media. Incubation of hypoxic or normoxic BPMVE cells with oxygenated medium (95% O2) stimulated the release of XO activity into the extracellular medium within 5 min. The XO activity could not be detected in the oxygenated medium after 60 min incubation with 95% O2. These results indicate that endothelial cells in culture constitutively release XO and that oxygenation rapidly enhances XO release. The released XO activity may play an important role in generation of oxidants in the extracellular milieu during reperfusion.

Implication of oxygen radicals on airway hyperresponsiveness after ovalbumin challenge in guinea pigs

We elucidated the implication of oxygen radicals on airway hyperresponsiveness after ovalbumin (OA) challenge in guinea pigs. Ten days OA exposure increased airway responsiveness, i.e., a significant decrease in log [acetylcholine (Ach) PC200] (2.445 +/- 0.227) was observed compared with the control group (3.398 +/- 0.269). After OA exposure, the number of beta-adrenoceptors decreased by 38%, and adenylate cyclase activity decreased by 36% (isoproterenol stimulated) and 28% (basal). Significant increases in xanthine oxidase activities in lung tissue, bronchoalveolar lavage fluid (BALF), and serum were observed after the tenth OA exposure (49.1 +/- 11.7 mU/g tissue, 12.6 +/- 3.16 mU/ml, and 11.5 +/- 2.66 mU/ml, respectively) compared with those in the control group (7.35 +/- 6.48 mU/g tissue, 2.85 +/- 1.17 mU/ml, and 3.51 +/- 1.15 mU/ml, respectively). Administration of long-acting superoxide dismutase (SOD) (5,000 U/kg twice a day intraperitoneally) or gamma-glutamylcysteine ethyl ester (gamma-GCE) (10 mg/kg, twice a day, intraperitoneally), a prodrug of glutathione, maintained log [Ach PC200] (3.248 +/- 0.415 and 3.298 +/- 0.246, respectively) in spite of 10 days OA exposure. Decreases in the number of beta-adrenoceptors and adenylate cyclase activity were prevented by long-acting SOD or gamma-GCE. In contrast, long-acting SOD or gamma-GCE inhibited significantly, but not completely, the elevation of xanthine oxidase activities. These results support suggestions that oxygen radicals might be involved in the underlying mechanism of airway hyperresponsiveness after OA challenge in guinea pigs.

Mechanism of neutrophil-induced xanthine dehydrogenase to xanthine oxidase conversion in endothelial cells: evidence of a role for elastase

Activated neutrophils cause conversion of xanthine dehydrogenase to its oxidase form (xanthine oxidase) in endothelial cells, the mechanism of which may be related to the cytotoxic effect of activated neutrophils. The elastase inhibitors, elastatinal, alpha 1-antitrypsin, and MeO-Suc-(Ala)2-Pro-Val-CH2Cl, significantly inhibited xanthine dehydrogenase to oxidase conversion by phorbol myristate acetate-stimulated neutrophils without inhibition of neutrophil adherence to the endothelial cell monolayer. The role of elastase in this enzyme conversion process was confirmed by the ability of purified elastase to cause conversion of xanthine dehydrogenase to xanthine oxidase in intact endothelial cells (or cell extracts) without causing cytotoxicity. In contrast, cathepsin G failed to cause conversion. The kinetics of conversion induced by elastase was relatively rapid, being essentially completed by 30 min. Upon removal of elastase, the effect was slowly (greater than 12 h) reversible and could be inhibited by cycloheximide treatment. Exposure of endothelial cells to hypoxia failed to enhance the elastase-induced conversion. Treatment of endothelial cells with Ca2+ ionophores failed to cause conversion of xanthine dehydrogenase to oxidase, suggesting that intracellular Ca(2+)-activated proteases are not sufficient to induce this process. Neutrophil-induced xanthine dehydrogenase to oxidase conversion was inhibited by concomitant treatment with antibodies to CD11b. The results suggest that activated neutrophils induce conversion of xanthine dehydrogenase to oxidase by secretion of elastase in close proximity to the endothelial cells and that this intimate contact between the two cell types enables high local concentrations of elastase to be attained, which are sufficient to cause xanthine dehydrogenase to xanthine oxidase conversion.

Regulation of xanthine dehydrogenase and xanthine oxidase activity and gene expression in cultured rat pulmonary endothelial cells

The central importance of xanthine dehydrogenase (XDH) and xanthine oxidase (XO) in the pathobiochemistry of a number of clinical disorders underscores the need for a comprehensive understanding of the regulation of their expression. This study was undertaken to examine the effects of cytokines on XDH/XO activity and gene expression in pulmonary endothelial cells. The results indicate that IFN-gamma is a potent inducer of XDH/XO activity in rat lung endothelial cells derived from both the microvasculature (LMVC) and the pulmonary artery. In contrast, interferon-alpha/beta, tumor necrosis factor-alpha, interleukin-1 or -6, lipopolysaccharide and phorbol myristate acetate have no demonstrable effect. The increase in XDH/XO activity requires new protein synthesis. By Northern analysis, IFN-gamma markedly increases the level of the 5.0-kb XDH/XO mRNA in LMVC. The increase is due, in part, to increased transcription rate of the XDH/XO gene. Transcriptional activation does not require new protein synthesis. The physiologic relevance of these observations was evaluated by administering IFN-gamma to rats. Intraperitoneal administration leads to an increased XDH/XO activity and XDH/XO mRNA level in rat lungs. In sum, IFN-gamma is a potent and biologically relevant inducer of XDH/XO expression; the major site of upregulation occurs at the transcriptional level.

Xanthine oxidase/dehydrogenase activity in intact cultured cells (in situ analysis)

The measured ratio of xanthine oxidase activity to the total activity of xanthine oxidase and dehydrogenase showed higher values in intact cells than when similar cells were homogenized. The total activity was the same for both systems. The xanthine oxidase ratio was 90, 60, 50, 50, 60% in V79, RIF/Ha3, SCC7, KHT intact cells and freshly extracted murine peritoneal macrophages respectively while the corresponding ratios measured were 25, 40, 38, 35, 22% when the cells were lysed by homogenization. Superoxide radical O2-. production by addition of xanthine to intact or homogenized cells to activate intracellular xanthine oxidase was higher in intact than homogenized cells. Homogenization of cells and tissues in the presence of dithioerythritol (DTE) can evidently lead to a considerable under-estimation of the xanthine oxidase ratio. The effect of hypoxia on cells has also been examined.

Oxidant-antioxidant balance: some observations from studies of ischemia-reperfusion in isolated perfused rat hearts

Alteration in oxidant-antioxidant balance is a key feature of many common vascular diseases. Using an isolated perfused heart model, we found that (a) xanthine oxidase-derived oxygen radicals contributed to ischemia-reperfusion injury; (b) addition of antioxidants within or outside erythrocytes decreased injury following ischemia-reperfusion; (c) endotoxin pretreatment increased myocardial catalase activity and decreased injury following ischemia-reperfusion; (d) interleukin pretreatment increased myocardial glucose-6-phosphate activity and decreased ischemia-reperfusion injury, and (e) neutrophils mediated tolerance to a subsequent oxidative stress by causing a small oxidant stress that in turn increased antioxidant protection mechanisms.

Oxygen radicals and lung injury

This article describes the formation of oxygen radicals and their biological effects, especially in relation to lung injury. Various recent experimental data are reviewed. The relationships between hydrostatic effects and permeability effects in producing injury and edema are stressed. Means of prevention and problems related to extrapolation to clinical situations are focused.

Generation of superoxide anion by brain endothelial cell xanthine oxidase

Bovine brain endothelial cells (EC) that were isolated and propagated in pure culture had increased (greater than 20-fold) levels of xanthine oxidase and xanthine dehydrogenase activity compared to whole brain homogenate. Brain EC also released superoxide anion (O2-) into the extracellular medium. Treatment of EC with tungsten decreased (P less than 0.05) both XO activity and O2- release. XO appears to be highly concentrated in cerebral vascular endothelium and may be an important source of O2-.

The role of xanthine oxidase in paraquat intoxication

The role of xanthine oxidase in the mechanism of paraquat toxicity was assessed by in vitro and in vivo experiments. Paraquat stimulated the reduction of cytochrome c by xanthine-xanthine oxidase system in vitro. Paraquat, when added in vitro, stimulated hypoxanthine-dependent superoxide production in the cytosol of rat lung. Tungsten-feeding inhibits xanthine oxidase activity in a variety of tissues in experimental animals. Its therapeutic effect on paraquat intoxication was studied in this paper. In rats fed a tungsten-enriched diet for 5 weeks prior to intraperitoneal injection of 50 mg/kg paraquat dichloride, the mortality decreased significantly compared with rats fed a standard diet. Pretreatment with oxypurinol (1000 mg/kg, s.c.) also ameliorated the paraquat toxicity in rats. We conclude that xanthine oxidase plays an important role in paraquat toxicity and that xanthine oxidase inhibitors may become antidotes for paraquat intoxication.

Characterization of cultured alveolar epithelial cell xanthine dehydrogenase/oxidase

Conversion of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) and the toxic reactions of subsequent XO-derived superoxide, hydrogen peroxide and hydroxyl radical, have been suggested to be critical factors in several mechanisms of tissue pathophysiology. In the lung, intracellular XO-derived products may modulate type II pneumocyte surfactant turnover and barrier function, jeopardizing the pulmonary air-blood barrier. We characterized total cellular XDH/XO enzymatic activity in freshly isolated and cultured rat pulmonary type II epithelial cells. Type II cells were isolated and cultured on fibronectin-pretreated dishes, with a plating efficiency after 36 h in culture of 40% or 14% when quantified via cellular protein or DNA, respectively. Over the subsequent 96 h in culture, monolayer DNA was unchanged, whereas protein per cell increased continuously. Alterations in different cellular enzymatic activities were also detected in these cultured cells. In culture, total cellular XDH/XO and catalase activities decreased in a logarithmical fashion with respect to time, whether normalized for cellular protein or DNA. The rate of loss of these enzymes was greatest when normalized for cell protein, but was also significant when the activities were normalized for DNA. When compared to freshly isolated type II cells, catalase and total XDH/XO activities normalized for protein decreased 78% and 72%, respectively, during the first 36 h of culture. After 132 h in culture, XDH/XO and catalase activities normalized for protein decreased 93% and 84%, respectively, when compared to freshly isolated cell values. Total cellular XDH/XO activity in the oxidase form (% XO) was initially 31% in freshly isolated type II cells and increased to 67% during the 132 h culture period. In contrast to the loss of total cellular XDH/XO and catalase, no significant change in lactate dehydrogenase (LDH) activity occurred during culture of the type II cells. In type II cells the conversion of XDH to XO, the cytotoxic potential of XO, and the activity of the hydrogen peroxide scavenger, catalase, is expected to be strongly influenced by in vitro culture. Thus, strong consideration should be made before transposing information obtained from cultured type II cells to in vivo situations.

Dependence on O2- generation by xanthine oxidase of pathogenesis of influenza virus infection in mice

We evaluated various biochemical parameters in influenza virus-infected mice and focused on adenosine catabolism in the supernatant of bronchoalveolar lavage fluid (s-BALF), lung tissue, and serum (plasma). The activities of adenosine deaminase (ADA) and xanthine oxidase (XO), which generates O2-, were elevated in the s-BALF, lung tissue homogenate, and serum (plasma). The elevations were most remarkable in s-BALF and in lung tissue: We found a 170-fold increase in ADA activity and a 400-fold increase in XO activity as measured per volume of alveolar lavage fluid. The ratio of activity of XO to activity of xanthine dehydrogenase in s-BALF increased from 0.15 +/- 0.05 (control; no infection) to 1.06 +/- 0.13 on day 6 after viral infection. Increased levels of various adenosine catabolites (i.e., inosine, hypoxanthine, xanthine, and uric acid) in serum and s-BALF were confirmed. We also identified O2- generation from XO in s-BALF obtained on days 6 and 8 after infection, and the generation of O2- was enhanced remarkably in the presence of adenosine. Lastly, treatment with allopurinol (an inhibitor of XO) and with chemically modified superoxide dismutase (a scavenger of O2-) improved the survival rate of influenza virus-infected mice. These results indicate that generation of oxygen-free radicals by XO, coupled with catabolic supply of hypoxanthine from adenosine catabolism, is a pathogenic principle in influenza virus infection in mice and that a therapeutic approach by elimination of oxygen radicals thus seems possible.