Prevention of granulocyte-mediated oxidant lung injury in rats by a hydroxyl radical scavenger, dimethylthiourea.

Toxic, partially reduced metabolites of oxygen (toxic oxygen radicals) are increasingly implicated in acute leukocyte-mediated tissue injury. To further probe the roles of oxygen radicals in acute lung edema, I studied the effects of a recently described and very potent oxygen radical scavenger, dimethylthiourea (DMTU) (Fox, R. B., R. N. Harada, R. M. Tate, and J. E. Repine, 1983, J. Appl. Physiol., 55:1456-1459) on polymorphonuclear leukocyte (PMN) oxidant function and on two types of lung injury mediated by oxygen radicals and PMN. DMTU (10 mM) blocked 79% of hydroxyl radical (OH) production by PMN in vitro without interfering with other PMN functions, such as O-2 production, myeloperoxidase activity, chemotaxis, degranulation, or aggregation. When isolated rat lung preparations were perfused with PMN activated to produce OH, lung weights were increased from 2.3 +/- 0.2 to 11.2 +/- 0.8 g. DMTU (10 mM) prevented 70% of these increases (lung weights, 5.0 +/- 1.1 g, P less than 0.005). Finally, when intact rats were exposed to 100% O2 for 66 h, lung weight:body weight ratios were increased from 5.78 +/- 0.33 to 8.87 +/- 0.16 g. DMTU (500 mg/kg) prevented 83% of this hyperoxia-induced lung edema in vivo (lung:body weight ratios, 6.05 +/- 0.21, P less than 0.001). Pharmacokinetic studies showed that DMTU diffused effectively into lung interstitial fluids and had a relatively long half-life (25-35 h) in the circulation. Because a variety of oxygen radicals, such as superoxide (O-2), hydrogen peroxide (H2O2), or OH are produced by PMN, there is usually some uncertainty about which one is responsible for injury. However, in these studies, DMTU did not scavenge O-2 and scavenged H2O2 only very slowly while scavenging OH very effectively. Therefore, DMTU may be useful in the investigation of the roles of oxygen radicals, especially OH, in acute granulocyte-mediated tissue injury.

Generation of hydroxyl radical by enzymes, chemicals, and human phagocytes in vitro. Detection with the anti-inflammatory agent, dimethyl sulfoxide.

Methane (CH(4)) production from the anti-inflammatory agent, dimethyl sulfoxide (DMSO), was used to measure .OH from chemical reactions or human phagocytes. Reactions producing .OH (xanthine/xanthine oxidase or Fe(++)/EDTA/H(2)O(2)) generated CH(4) from DMSO, whereas reactions yielding primarily O-(2) or H(2)O(2) failed to produce CH(4). Neutrophils (PMN), monocytes, and alveolar macrophages also produced CH(4) from DMSO. Mass spectroscopy using d(6)-DMSO showed formation of d(3)-CH(4) indicating that CH(4) was derived from DMSO. Methane generation by normal but not chronic granulomatous disease or heat-killed phagocytes increased after stimulation with opsonized zymosan particles or the chemical, phorbol myristate acetate. Methane production from DMSO increased as the number of stimulated PMN was increased and the kinetics of CH(4) production approximated other metabolic activities of stimulated PMN. Methane production from stimulated phagocytes and DMSO was markedly decreased by purportedly potent .OH scavengers (thiourea or tryptophane) and diminished to lesser degrees by weaker .OH scavengers (mannitol, ethanol, or sodium benzoate). Superoxide dismutase or catalase also decreased CH(4) production but urea, albumin, inactivated superoxide dismutase, or boiled catalase had no appreciable effect. The results suggest that the production of CH(4) from DMSO may reflect release of .OH from both chemical systems and phagocytic cells. Interaction of the nontoxic, highly permeable DMSO with .OH may explain the anti-inflammatory actions of DMSO and provide a useful measurement of .OH in vitro and in vivo.

Effects of oxygen toxicity on cuprolinic blue-stained proteoglycans in alveolar basement membranes.

Effects of oxygen toxicity on distribution and density of proteoglycans in basement membranes of newborn rat lungs were assessed by electron microscopic analysis of tissues processed with cuprolinic blue, a cationic label that characteristically labels these anionically charged macromolecules. Newborn rats placed in greater than 95% oxygen at birth were killed at weekly intervals for 4 wk, and lung tissues fixed in 2.5% glutaraldehyde with 0.2% cuprolinic blue were processed for electron microscopy. Alveolar basement membranes from oxygen-treated and control animals were compared for differences in thickness and proteoglycan concentration and distribution. Results showed progressive thickening of alveolar basement membranes with increased duration of oxygen exposure. The normal distribution of proteoglycans, which is predominantly in the lamina rara externa of alveolar basement membranes, was frequently lost in thickened membranes found in oxygen-treated animals. Density of proteoglycans in these membranes decreased to 56% of normal by 2 wk of age and remained low with continued oxygen administration. Proteoglycan concentration in basement membranes on the interstitial side of alveolar capillaries in both control and oxygen-treated animals was low compared with proteoglycan concentration in basement membranes that opposed the alveolar air space, and administration of oxygen diminished these differences. These results demonstrate a direct alteration of proteoglycan distribution and density in the developing lung as a result of oxygen toxicity. This could result in decreased cell adhesion, influence the cellular response to lung injury, and contribute to the increased permeability seen with this disorder.

Defective oxidative metabolic responses in vitro of alveolar macrophages in chronic granulomatous disease.

After stimulation with bacteria, alveolar macrophages (AM) from uninfected normal subjects or persons with pneumonia approximately doubled their rates of O2 consumption, superoxide anion generation, and glucose (1(-14)C) oxidation. In contrast, bacteria-stimulated AM from a patient with chronic granulomatous disease (CGD) failed to consume more O2, make superoxide anion, or oxidize glucose. In addition, AM from the patient with CGD did not respond to stimulation by a chemical agent, phorbol myristate acetate, which increased the metabolic activities of AM from control subjects. The appearance, esterase and Gomori acid phosphatase staining, phagocytic ability, unstimulated O2 consumption, and response to methylene blue of AM from the CGD patient were normal. The results extend the biochemical defect in patients with CGD beyond abnormalities in their circulating neutrophils and monocytes, to their tissue-associated lung macrophages. The results also indicate that AM from patients with CGD may have an additional abnormality in metabolism, which is a lack of enhanced mitochondrial respiration during phagocytosis. The studies also document the selective action of phorbol myristate acetate, which stimulated the metabolic activities of normal AM, but not of those from the patient with CGD.

Hydrogen peroxide kills Staphylococcus aureus by reacting with staphylococcal iron to form hydroxyl radical.

Two lines of investigation supported the premise that killing of Staphylococcus aureus, 502A, by hydrogen peroxide involves formation of the more toxic hydroxyl radical (.OH) through the iron-dependent Fenton reaction. First, growing S. aureus overnight in broth media with increasing concentrations of iron increased their content of iron and dramatically enhanced their subsequent susceptibility to killing by H2O2. Second, in direct relation to their effectiveness as .OH scavengers, thiourea, dimethyl thiourea, sodium benzoate, and dimethyl sulfoxide inhibited H2O2-mediated killing of S. aureus.

Dimethyl sulfoxide inhibits killing of Staphylococcus aureus by polymorphonuclear leukocytes.

Increasing concentrations of the highly permeable, hydroxyl radical scavenger dimethyl sulfoxide progressively decreased killing of Staphylococcus aureus 502A by human polymorphonuclear leukocytes; methane, a product of the reaction of the hydroxyl radical with dimethyl sulfoxide, was generated in the process.

Effects of dimethylthiourea on chronic hypoxia-induced pulmonary arterial remodelling and ventricular hypertrophy in rats.

Ischemia, followed by reperfusion and restoration of oxygen to tissues, generates hydrogen peroxide which in turn generates injurious free radicals, particularly hydroxyl. Chronic hypoxia may also result in liberation of free radicals. In rats, chronic hypoxia causes pulmonary hypertension, associated with structural remodelling of pulmonary arteries, polycythemia, and vasoconstriction. We studied in rats the effects of dimethylthiourea (DMTU), a hydroxyl and hydrogen peroxide scavenger, on acute hypoxic vasoconstriction, and on the arterial structure and development of polycythemia after chronic hypoxia (FIO2 0.10 for 10 days, daily DMTU). DMTU did not affect acute vasoconstriction nor polycythemia. It significantly reduced muscularization of alveolar wall and alveolar duct arteries, medial thickening of alveolar wall and preacinar arteries, and right ventricular hypertrophy, suggesting reduction of pulmonary hypertension. However, DMTU caused marked growth retardation in both control and hypoxic rats, an effect not previously described. In other rats a similar degree of growth retardation due to reduced food intake failed to prevent the effects of hypoxia, suggesting that DMTU's effect is not through this mechanism. The results of this study support but do not confirm the hypothesis that free radicals may have a role in the pathogenesis of the arterial structural changes in the microcirculation contributing to chronic hypoxic pulmonary hypertension. However, in view of DMTU's effects on growth, definitive testing of the hypothesis will not be possible until other, less toxic, chronic hydroxyl scavengers become available.

Prevention of thiourea-induced pulmonary edema by hydroxyl-radical scavengers.

Thiourea (TU), a very effective hydroxyl radical (.OH) scavenger, has little value as a probe of .OH in vivo because it causes fatal pulmonary edema. To test the hypothesis that TU-induced lung injury results from .OH-mediated oxidation of TU to toxic cyanamide, we pretreated rats with .OH scavengers, dimethylsulfoxide (DMSO), ethanol, and mannitol, prior to treatment with TU (3 mg/kg), preventing 91, 63, and 53%, respectively, of increases in lung weight to body weight ratios and 93, 67, and 46% of increases in lung lavage albumin concentrations. Furthermore, treatment of rats with cyanamide (CYN) (100 mg/kg) also caused increases in lung weight to body weight ratios (CYN: 7.39 +/- 0.57 X 10(-3) vs. controls: 5.46 +/- 0.26). N,N'-dimethylation of TU (DMTU) prevented TU toxicity, because treatment with DMTU did not significantly increase lung weight to body weight ratios (DMTU: 5.12 +/- 0.16 X 10(-3) vs. controls: 5.46 +/- 0.26) or lung lavage albumin (DMTU: 14 +/- 1 mg/100 ml vs. controls: 11 +/- 1). DMTU remained a very effective in vivo .OH scavenger, increasing survival of lethally irradiated mice treated with 600 mg/kg DMTU to 79% compared with 8% in untreated controls.

Pulmonary inflammation due to oxygen toxicity: involvement of chemotactic factors and polymorphonuclear leukocytes.

Although the pathogenesis of pulmonary oxygen toxicity is not fully understood, the fact that increased numbers of polymorphonuclear leukocytes (PMN) are found in the lung and that these increases coincide with the massive endothelial damage raises the possibility that PMN may contribute to lung injury caused by hyperoxia. In order to begin to elucidate a mechanism for this influx of PMN, we measured the chemoattractant activity for PMN of lung lavages of rats exposed to greater than 95% oxygen for various durations. We found that the chemoattractant activity of the lavages of the lungs of rats exposed to hyperoxia for 66 h was markedly increased (9.66 +/- 1.0 times greater) compared with activities in lavages of normoxic control rats. Furthermore, these increases in chemoattractant activity in lung lavages correlated well with increases in the number of PMN (7 times greater than that in normoxic control animals) in the alveolar lavages that occurred after the rats had been exposed to hyperoxia for 66 h. These increases were followed in a few hours by the death of most of the rats (71%). These findings suggested that a close temporal relationship exists between the generation of high concentrations of chemoattractants in lung lavages, PMN influx into lung lavages, and death of rats exposed to hyperoxia. The results supported the possibility that PMN may be involved in the pathogenesis of pulmonary oxygen toxicity.

Altered oxidative metabolic responses in vitro of alveolar macrophages from asymptomatic cigarette smokers.

Superoxide anion (O2) release by alveolar macrophages (AM) from young asymptomatic cigarette smokers was greater than that by AM from age-matched nonsmokers. Greater O2 release by AM from cigarette smokers was observed before and after stimulation by bacteria or phorbol myristate acetate (PMA). In contrast, oxygen uptake and glucose (1(-14)C) oxidation by unstimulated or stimulated AM from cigarette smokers was the same as that by AM from non-smokers. The selective increase of O2 release by AM from cigarette smokers was not due to a lack of O2 scavenging agent within the cells, since intracellular superoxide dismutase (SOD) was increased in AM from smokers. The potential importance of enhanced O2 release by AM from cigarette smokers was confirmed by demonstrating that lysis of fibroblasts induced by AM from smokers was completely prevented by addition of SOD and catalase.

Reduction of the edema of acute hyperoxic lung injury by granulocyte depletion.

Increased numbers of granulocytes are found in lungs acutely injured by hyperoxia, but their contribution to lung injury remains unknown. We found that circulating granulocytes markedly increased (P less than 0.01) in rabbits exposed to hyperoxia for 72 h and that the numbers of granulocytes in lung lavages also increased and were correlated (r = 0.72, P less than 0.01) with the degree of edematous lung injury. Furthermore, when rabbits were treated with nitrogen mustard (1.75 mg/kg) and developed sustained granulocytopenia, exposure to hyperoxia for 72 h resulted in fewer granulocytes in lung lavages and less edematous lung injury. In contrast, when rabbits were similarly treated with nitrogen mustard but did not maintain sustained granulocytopenia throughout the exposure to hyperoxia, increased numbers of granulocytes were found in lung lavages and the degree of edematous lung injury increased to levels not different from those observed in oxygen-exposed rabbits that had not been treated with nitrogen mustard. These findings suggest that granulocytes may contribute to production of edema in acute oxygen toxicity.

Effect of staphylococcal iron content on the killing of Staphylococcus aureus by polymorphonuclear leukocytes.

Preincubation of Staphylococcus aureus 502A in broth with increasing concentrations of ferrous sulfate progressively increased their iron content, markedly increased their susceptibility to killing by hydrogen peroxide, and did not alter their susceptibility to killing by polymorphonuclear leukocytes.

Angiotensin converting enzyme concentrations in the lung lavage of normal rabbits and rabbits treated with nitrogen mustard exposed to hyperoxia.

Increased concentrations of angiotensin converting enzyme (ACE) were found in lung lavages from rabbits exposed to hyperoxia for 72 h and the concentrations of ACE were correlated with ratios of extravascular lung water to body weight (r = 0.69, p less than 0.05) and albumin concentrations in lung lavages (r = 0.89, p less than 0.01). In parallel studies, rabbits treated with nitrogen mustard in which granulocytopenia was maintained throughout the 72-h hyperoxic exposure period had less evidence of edematous lung injury and lower concentrations of ACE in their lung lavages than similarly treated rabbits in which granulocytopenia was not maintained. The results suggested that granulocytes contribute to acute edematous lung injury from hyperoxia and that ACE concentrations in lung lavages reflect this process.