Independent and combined effects of prolonged inhaled nitric oxide and oxygen on lung inflammation in newborn piglets.

Clinical use of nitric oxide (NO) is usually in conjunction with high oxygen concentrations, the effects of which may include lung neutrophil accumulation, apoptosis and upregulation of antioxidant enzyme activity. To define the effects of NO on neutrophils from young piglets and its relationship to lung neutrophil dynamics during hyperoxia we exposed thirty piglets to room air (RA), RA+NO (50 ppm NO), O2 (FiO2> or =0.96) or O2+NO for 5 days. Ten additional animals breathed RA+NO or O2+NO, then recovered in RA for 3 days before sacrifice. Neutrophil CD18 and intracellular oxidant production were measured by flow cytometry. Lung apoptosis were assessed by TUNEL assay. Lung myeloperoxidase, SOD and catalase were measured biochemically. When compared to RA group, there was significant reduction in neutrophil CD18 and intracellular oxidant production in the RA+NO group, but lung MPO was unchanged. The O2 and O2+NO groups did not differ in CD18 expression or in intracellular oxidant production, but had significant increase in lung myeloperoxidase compared to the RA group. Apoptosis increased significantly only in the O2+NO group. The O2 group showed significantly increased lung SOD and catalase activity compared to the RA group, whereas the RA+NO and O2+NO groups did not. We conclude that inhaled NO at 50 ppm decreases neutrophil CD18 expression as well as intracellular oxidant production. However, this effect does not impact lung neutrophil accumulation during concurrent hyperoxia. The combination of NO and O2 exposure produces an increase in lung apoptosis. Finally, NO may prevent upregulation of SOD and catalase activity during hyperoxia, potentially increasing injury.

Influence of inhaled nitric oxide and hyperoxia on Na,K-ATPase expression and lung edema in newborn piglets.

This study was undertaken to examine the combined effect of nitric oxide (NO) and hyperoxia on lung edema and Na,K-ATPase expression. Newborn piglets were exposed to room air (FiO2 = 0.21), room air plus 50 ppm NO, hyperoxia (FiO2 >/= 0.96) or to hyperoxia plus 50 ppm NO for 4-5 days. Animals exposed to NO in room air experienced only a slight decrease in Na,K-ATPase alpha subunit protein level. Hyperoxia, in the absence of NO, induced both the mRNA and the protein level of Na,K-ATP-ase alpha subunit and significantly increased wet lung weight, extravascular lung water, and alveolar permeability. NO in hyperoxia decreased the hyperoxic-mediated induction of Na,K-ATPase alpha subunit mRNA and protein while wet lung weight, extravascular lung water, and alveolar permeability remained elevated. These results suggest that 50 ppm of inhaled NO may not improve hyperoxic-induced lung injury and may interfere with the expression of Na,K-ATPase which constitutes a part of the cellular defense mechanism against oxygen toxicity.

Compressed air as a source of inhaled oxidants in intensive care units.

Exhaled gas from mechanically ventilated preterm infants was found to have similar oxidant concentrations, regardless of lung disease, leading to the hypothesis that wall outlet gases were an oxidant source. Oxidants in compressed room air and oxygen from wall outlets were assessed in three hospitals. Samples were collected by flowing wall outlet gas through a heated humidifier and an ice-packed condenser. Nitric oxide (NO) was measured in intensive care room air and in compressed air with and without a charcoal filter using a Sievers NOA280 nitric oxide analyzer (Boulder, CO). Oxidants were measured by spectrophotometry and expressed as nMol equivalents of H2O2/mL. The quantity of oxidant was also expressed as amount of Vitamin C (nMol/mL) added until the oxidant was nondetectable. This quantity of Vitamin C was also expressed in Trolox Equivalent Antioxidant Capacity (TEAC) units (mMol/L). Free and total chlorine were measured with a Chlorine Photometer. Oxidants were not found in compressed oxygen and were only found in compressed air when the compression method used tap water. At a compressed room air gas flow of 1.5 L/min, the total volume of condensate was 20.2 +/- 1 mL/hr. The oxidant concentration was 1.52 +/- 0.09 nMol/mL equivalents of H2O2/mL of sample and 30.8 +/- 1.2 nMol/hr; 17.9% of that found in tap water. Oxidant reduction required 2.05 +/-0.12 nMol/mL vitamin C, (1.78 +/- 0.1 x 10(-3) TEAC units). Free and total chlorine in tap water were 0.3 +/- 0.02 mg/mL and 2.9 +/- 0.002 mg/mL, respectively. Outlet gas contained 0.4 +/- 0.06 mg/mL and 0.07 + 0.01 mg/mL total and free chlorine, respectively; both 14% of tap water. When a charcoal filter was installed in the hospital with oxidants in compressed air, oxidants were completely removed. Nursery room air contained 12.4 +/- 0.5 ppb NO; compressed wall air without a charcoal filter, 8.1 +/- 0.1 ppb and compressed air with a charcoal filter 12.5 +/- 0.5 ppb. A charcoal filter does not remove NO. (Table 3) We recommend that all compressed air methods using tap water have charcoal filters at the compression site and the gases be assessed periodically for oxidants.

Eight-epi-PGF2alpha: a possible marker of lipid peroxidation in term infants with severe pulmonary disease.

A prostaglandin F2-like compound, 8-epi-PGF2alpha, formed from oxidation of arachidonate, has been proposed as an indicator of lipid peroxidation. We determined whether tracheal aspirate or urinary 8-epi-PGF2alpha levels would differ over time or between infants in a control group and infants with severe respiratory failure. We correlated tracheal aspirate 8-epi-PGF2alpha levels with the fraction of inspired oxygen and with mean airway pressures at 24 and 48 hours of life. Levels in tracheal aspirates were in the range of 0 to 36 pg/microg of fSC of IgA and were higher in infants with severe pulmonary disorders compared with those in infants in the control group (p < 0.02). Urinary concentrations did not discriminate between sick infants and infants in the control group.

Comparative age-related acute and chronic pulmonary oxygen tolerance in rats.

Young rats are thought to be more tolerant to hyperoxia. We propose that this may not be proven and depends on how tolerance is defined. We assessed oxygen tolerance in Sprague-Dawley rats from birth to maturity by comparing survival, lung water, antioxidant enzyme activity, lung morphometrics, heart weight, and arterial blood gases in newborn and 27-, 44-, 48-, and 96-day-old rats exposed to 100% O2 or room air for 22 days. Some 96-day-old rats (rest group) received only 50% O2 between 48 and 72 h. Mortality after 5 days of O2 was 0% in newborn and 27-day-old rats and 27% in 44-day-old rats but was > 80% in 48- and 96-day-old rats. Between 5 and 22 days, the death rate was 100% in newborns, 25% in 27-day-old rats, and 0% in 44- to 96-day-old rats. Death occurred when lung water was > 84% except in newborns, which tolerated high lung water for the first 7 days. In chronically exposed 44- and 96-day-old rats, lung water returned to normal. Enzyme activity increased with O2 at all ages but did not relate to survival. In 96-day-old rats, the initial increase was suppressed on day 3. All chronically O2-exposed rats had minimal nonvascular parenchymal changes but developed right ventricular hypertrophy and increased alveolar ductal artery muscularization and lost alveolar capillaries. The most mature rats were least affected. In O2, there was pulmonary insufficiency the first 3 days, followed by recovery, and later hypercarbia and decreased arterial PO2. We conclude that young rats, 0-44 days old, are more O2 tolerant for 5 days. More mature animals, surviving 5 days, are more tolerant to chronic exposure.

Chronic modifications of lung and heart development in glucocorticoid-treated newborn rats exposed to hyperoxia or room air.

We assessed the mechanics and morphology of the lung in 165 rats treated neonatally with either room air (RA), O2, RA + steroids, or O2 + steroids. Newborn Sprague-Dawley male rats were randomly assigned to these groups. O2-exposure (0.96-1.0 FiO2) lasted 5 days, and dexamethasone treatment consisted of eight daily S.C. injections of drug or buffer in successive doses of 0.5, 0.4, 0.3, 0.2, 0.1, 0.1, 0.1, and 0.1 mg/kg. At 58 days, right ventricular systolic pressure (RVP) was measured. At 60 days, all rats were sacrificed for obtaining lung weight and DNA, saline pressure-volume (P-V) curves, and morphometry. We weighted right ventricles (RV) and left ventricles + septa (LV). Hyperoxia alone did not, but steroid decreased survival rate to 79.4% (95.3% in RA rats, P < 0.02). Only 21 of 40 (52%) O2 + steroids rats survived, less than in both RA groups (P < 0.001). RV weight, RVP and muscularization of alveolar duct arteries were significantly increased in O2 vs. RA rats. In RA + steroids rats, weight of the LV was decreased but RV, RVP, and lung vasculature were not affected. These effects were additive in the O2 + steroid group. Wet lung weights and DNA were increased for RA + steroid rats over all others. O2 and steroids shifted the P-V curve to the left and O2 + steroids still further. Maximal lung volume increased significantly with RA + steroids and still further in O2 + steroids but not in O2 alone. O2 and steroids significantly increased the mean linear intercept and O2 + steroids even more so.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung antioxidant enzymes and cardiopulmonary responses in young rats exposed to hyperoxia and treated intratracheally with PEG catalase and superoxide dismutase.

The 27-day-old rat exposed to 100% oxygen (O2) for 8 days will have predictable lung vascular and parenchymal changes at 60 days of age. Using this model, the goals of this study are (1) to measure the lung antioxidant enzyme activities serially following intratracheal PEG antioxidant therapy during the 8-day O2 exposure; and (2) to assess chronic cardiopulmonary changes in the O2-exposed rats treated with PEG-CAT and/or PEG-CuZn SOD given intraperitoneally (IP) and/or intratracheally (IT). The study encompassed 202 male rats exposed to room air or oxygen. CuZn SOD doses were 300 U IT and 2000 U IP. The CAT dose was 500 or 4000 U IT and 10,000 U IP. At 60 days of age, the right ventricular systolic pressure (RVP), RV weight, % acinar wall arterial thickness, and parenchymal air space were significantly increased in O2-exposed rats compared to RA rats. The RVP, RV weight, and parenchymal changes were prevented by daily IT PEG-CAT 4000 U + CuZn SOD 300 U but the increased small artery muscularization was not. Three hours after the initial dose of IT PEG-CAT 4000 U, lung CAT activity was more than doubled and remained constant throughout the 8-day daily treatment course. This dose of CAT depressed the induction response to O2 of CuZn and MnSOD. It is concluded that daily intratracheal administration of PEG-CAT 4000 U + CuZn SOD 300 U can significantly ameliorate some of the chronic parenchymal and vascular lung O2 toxic changes. However, it appears that high-dose exogenous PEG-CAT suppresses the endogenous enzyme induction to hyperoxia of both CuZn and Mn-SOD.

Prevention of chronic pulmonary oxygen toxicity in young rats with liposome-encapsulated catalase administered intratracheally.

The lungs and hearts of young rats exposed to 100% oxygen (O2) for 8 days (27 to 35 days of age) were studied following recovery in room air at 60 days of age using morphometric, biochemical, and physiological techniques. In an attempt to prevent chronic oxygen toxicity 153 rats had transtracheal catheters surgically implanted and were treated during the O2 exposure with daily intratracheal injections of liposome-encapsulated superoxide dismutase (SOD) and/or catalase (CAT). Oxygen exposure in this model results in chronic cardiopulmonary alterations which include pulmonary hypertension, right ventricular hypertrophy, and a decrease in number of pulmonary arterioles 25 to 50 microns in diameter with increased muscularization of their walls. The volume densities of the parenchyma, parenchymal air space, and the alveolar space are increased, while that of the combined alveolar ductal and respiratory bronchiolar space is decreased. Daily intratracheal administration of liposome-encapsulated CAT (160 U) during the O2 exposure prevented these chronic changes. Liposome-encapsulated SOD (110 U) or SOD (50 U) + CAT (70 U) did not appear to have a preventive effect. During the first 3 to 5 days following oxygen exposure the lung tissue enzymes SOD, CAT, and glutathione peroxidase markedly increased. We conclude that in the young rat animal model liposome-encapsulated CAT (160 U) given intratracheally during the period of O2 exposure is safe and will prevent the chronic vascular and parenchymal damage due to oxygen toxicity.

Neonatal pulmonary oxygen toxicity in the rat and lung changes with aging.

The aims of this study were to determine if neonatal hyperoxia exposure causes permanent lung damage and to define the relationship between neonatal lung oxygen toxicity and aging. Sprague-Dawley newborn rats (n = 85) breathed 100% oxygen (O2) or room air (RA) during the first 8 days of life, and then RA. At 2 and 22 months of age we assessed right ventricular (RV) systolic pressure (RVSP), RV weight, saline and air pressure-volume curves, volume density of lung parenchyma and nonparenchyma, parenchymal air space (PAS), mean linear intercept (Lm), number of small arteries/mm2 and the extent of their medial muscularization. Aging in RA did not affect the RVSP, RV weight, the number of small arteries/mm2, or their muscularization. The maximal lung volume/g of dry lung and the elastic recoil pressure between 40 and 90% maximal lung volume decreased. The volume density of lung parenchyma increased but the fraction of the lung parenchyma that was PAS decreased and that of the alveolar septa and Lm increased. The O2-treated rats at 60 days of age had increased RVSP and RV weights with a decrease in the small arteries/mm2. The lung parenchymal volume density and PAS increased and the density of alveolar septa decreased. The Lm increased and the alveoli/mm2 and elastic recoil pressure decreased. The lung damage seen in the O2-treated rats at 60 days persisted and in addition underwent the changes seen in the aging controls. However, the extent of muscularization of the arteries decreased. We conclude that neonatal hyperoxia causes permanent functional and structural changes of the lung but these do not interact with aging; that is, the effects of O2 toxicity and aging are additive but not synergistic.