Iron and oxidized beta-casein in the lavages of hyperoxic Fischer-344 rats

We reported previously that Fischer-344 (F344) rats were more susceptible to hyperoxic lung injury than were Sprague Dawley (SD) rats. In the present study we exposed adult male F344 and SD rats to >95% oxygen for up to 48 h, and measured lung wet-to-dry weight ratios and lavage protein concentrations as indices of lung injury. In addition, we measured nonheme iron contents in the lung subcellular fractions and in bronchoalveolar lavages (BAL), and we derivatized samples from the subcellular compartments and lavages with 2,4-dinitrophenylhydrazine (DNPH), separated the proteins electrophoretically, and detected DNPH-derivatized proteins by western blotting. After 48 h of hyperoxia, BAL protein and nonheme iron concentrations were higher in F344 rats than in SD rats (2.17+/-0.77 versus 0.17+/-0.17 mg/ml, and 1.61+/-0.45 versus 0.45+/-0.18 nmol/ml, respectively, both P<0.05). In addition, two DNPH-reactive proteins of about 40 and 120 kDa were identified in the lavage fluids of hyperoxic F-344 rats that were not observed similarly in hyperoxic SD rats or in air-breathing rats of either strain. N-terminal amino acid sequences of the two DNPH-reactive proteins 100% identical over 16 residues to rat beta-casein, which is a potent neutrophil chemotaxin, and has been reported to be a product of cytotoxic T-lymphocytes. There were no significant alterations in iron contents in lung subcellular fractions in either strain of rat as a consequence of hyperoxia-exposure, nor were there any significant alterations in DNPH-reactive carbonyls, as determined by western blotting. These data suggest that increased iron concentrations in the airspaces reflect altered iron homeostasis, which may contribute to the greater susceptibility of F344 rats than SD rats to hyperoxic lung injury. The identification of oxidized beta-casein in the BAL of the hyperoxic F344 rats suggests a role for cytotoxic T-lymphocytes in hyperoxic lung inflammation and injury, although the nature of this possible involvement is not known at this time.

Exogenous surfactant enhances the delivery of recombinant adenoviral vectors to the lung

Somatic gene therapy for pulmonary diseases must be accomplished in vivo, requiring the spread of a gene transfer vector across a vast expanse of respiratory epithelium. Surfactant, a naturally occurring protein and lipid mixture used to treat the respiratory distress syndrome of prematurity, disperses rapidly and evenly throughout the lung. We employed exogenous bovine surfactant (Survanta beractant) as a carrier vehicle for pulmonary delivery of a recombinant adenovirus expressing beta-galactosidase (beta-Gal). Rats treated with an adenovirus-beractant mixture demonstrated more uniform lobar distribution of transgene expression than rats treated with the same amount of virus in saline. Tissue homogenates were examined for quantitative beta-Gal expression by reaction with o-nitrophenol beta-n-galactopyranoside (ONPG). The degree of beta-Gal activity was affected by both the volume and type of carrier used to deliver the virus. At low volumes (0.5 ml, 1.3 ml/kg), beractant-treated animals demonstrated significantly greater pulmonary beta-Gal activity than saline-treated animals (p < 0.002) and untreated controls. At high volume (1.2 ml, 4 ml/kg), average beta-Gal activity was similar between groups treated with beractant or saline, but was more variable within the saline treated group. Higher volumes of delivery medium were associated with increased levels of beta-Gal expression regardless of the carrier used. Survanta was well tolerated by the animals and did not affect the duration of transgene expression. Exogenous beractant provides a useful medium for delivering recombinant adenoviruses to the lung when diffuse distribution of transgene expression is desired.

Induction and decline of hepatic cytochromes P4501A1 and 1A2 in rats exposed to hyperoxia are not paralleled by changes in glutathione S-transferase-alpha

We investigated the effects of hyperoxia on the activities of hepatic ethoxyresorufin O-deethylase (EROD) (CYP1A1), methoxyresorufin O-demethylase (MROD) (CYP1A2), and glutathione transferase-alpha (GST-alpha), and the status of protein thiols (PSH) in male Sprague-Dawley rats. Twenty-four h of hyperoxia more than doubled EROD and MROD activities, which were increased 7.6- and 3.3-fold, respectively, after 48 h of hyperoxia. The increases in EROD and MROD activities were paralleled by enhanced CYP1A1/1A2 apoproteins contents, as detected by Western analysis. At 60 h of hyperoxia, by which time hyperoxic Sprague-Dawley rats display marked respiratory distress, pulmonary edema, and other markers of pulmonary dysfunction, the activities and levels of hepatic CYP1A1 and 1A2 had declined dramatically and returned to levels observed in air-breathing control animals. Hepatic activities of GST-alpha, as well as PSH status, were not altered significantly in the hyperoxic animals at any time point. The marked induction and subsequent decline of hepatic CYP1A1/1A2 activities in rats exposed to hyperoxia suggest that these enzymes may contribute to the mechanisms of injury and/or to adaptive responses to hyperoxic exposures in vivo.

Hyperoxic increases in lung ICAM-1 mRNA are independent of TNF-alpha and IL-1 beta mRNA

Hyperoxia-exposure results in neutrophil accumulation and edema in the exposed lung. Intercellular adhesion molecule-1 (ICAM-1), a ligand for neutrophil beta 2 integrins, is upregulated in hyperoxia-exposed lungs and enhances neutrophil-mediated injury. Because tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) are potent inducers of ICAM-1, we investigated whether TNF-alpha and IL-1 beta mRNA increase prior to the increase in ICAM-1 mRNA in hyperoxia-exposed mouse lungs. We exposed mice to > 95% oxygen for up to 96 h, isolated lung RNA, and assessed ICAM-1, TNF-alpha, and IL-1 beta mRNA by Northern blotting. We found that neither, TNF-alpha nor IL-1 beta mRNA was detectable prior to 96 h, while ICAM-1 mRNA increased by 48 h. To further assess TNF-alpha and IL-1 beta mRNA, we employed quantitative reverse-transcriptase polymerase chain reaction (RTPCR) using a mimic DNA (mimic) species as an internal control for PCR. Mimic DNA was identical to reverse-transcribed cDNA (wild type), except for 147 bp of irrelevant DNA ligated into the original cDNA. For each lung RNA sample we reverse transcribed total lung RNA and coamplified the resulting wild-type cDNA with serial dilutions of mimic DNA in a PCR containing [32P] dCTP. After PCR, we electrophoresed the samples and determined the concentration of TNF-alpha and IL-1 beta wild-type cDNAs by the ratios of wild type to mimic counts. We found no increase in TNF-alpha or IL-1 beta mRNA through 72 h of hyperoxia exposure, while there was an approximately 10-fold increase in TNF-alpha mRNA and a 35-fold increase in IL-1 beta mRNA within 2 h in the lungs of animals exposed to endotoxin. In conclusion, our data suggest that TNF-alpha and IL-1 beta are not responsible for the upregulation of ICAM-1 in hyperoxia-exposed mouse lungs.

Oxidation of bovine beta-casein by hypochlorite

We recently observed two 2,4-dinitrophenylhydrazine (DNPH)-reactive proteins of 40 and 120 kDa in the bronchoalveolar lavage fluids of rats exposed to >95% O(2) for 48 h. The N-terminal sequences of these proteins were both identical over 16 amino acids with rat beta-casein, which, in addition to its more common association with milk, is produced by cytotoxic T-lymphocytes, and has been found to have proinflammatory properties. Because of the inflammatory response that accompanies hyperoxic lung injury, we investigated the oxidation of bovine beta-casein by HOCl. Following exposure to HOCl at 4 degrees C for 15 min, derivatization with DNPH, washing, and digestion with trypsin, the resultant peptides were separated by reverse-phase HPLC. One peptide isolated from a peak absorbing at 365 nm was identified as AVP(Y*)PQR, corresponding to amino acids 177-183 of bovine beta-casein. Analysis of the peptide by both electrospray and matrix assisted laser desorption ionization (MALDI) mass spectrometry identified a molecular ion MH+ of 1008.5 Da, which represents an increase of 178 Da from the calculated monoisotopic MH+ of the unmodified peptide of 830.45 Da. Daughter ion spectra of the doubly charged parent ion of the peptide further support the oxidation of the tyrosine to the quinone methide, with subsequent conversion to the corresponding hydrazone with DNPH. A second pair of products were identified as arising from oxidation of Y(193) within the tryptic peptide constituted by amino acids 184-202, and the corresponding chymotryptic cleavage side product, 191-202. Exposure of beta-casein to increasing amounts of HOCl revealed that M and Y residues were the most susceptible, although bovine beta-casein contains no C, and a single W, which would not be detected by our methods. The approach described in the present report can be used to evaluate the contributions of distinct mechanisms of oxidation in other experimental or pathological models.

Increased soluble E-Selectin is associated with lung inflammation, and lung injury in hyperoxia-exposed rats

The pulmonary damage caused by prolonged exposure to high oxygen concentrations is accompanied by lung inflammation, which may contribute to the expression of hyperoxic lung injury. In turn, adhesion molecules are crucial for initiating inflammatory responses. The goal of the present study was to investigate the association of contents of soluble adhesion molecules in plasma or alveolar fluids of hyperoxic rats with lung expression of adhesion molecules, lung inflammation and lung injury. We exposed adult Sprague-Dawley rats to > 95% oxygen for up to 60 h and measured the contents of intercellular adhesion molecule-I (ICAM-I) and E-Selectin in plasma and lung tissue expression of the same molecules, and we assessed lung myeloperoxidase (MPO) activties and lung water contents as indices of lung inflammation and injury, respectively. We also assessed ICAM-I content in lavage samples, because ICAM-I may be shed from the alveolar epithelium. Lung water was elevated at 60 h of hyperoxia-exposure, and this effect was preceded by increases in lung MPO activities. Lung ICAM-I expression was more than doubled at 48 h, although soluble ICAM-I contents were not elevated in plasma or lavage. Soluble E-Selectin was increased by more than 50% at 24 h of hyperoxia-exposure, while lung expressions of E-Selectin were not increased until 48 h. The sequence of the events observed in the present studies suggests that E-Selectin contributes to lung inflammation in hyperoxia and the acceleration of lung injury immediately following the inflammatory response suggests a pivotal role for inflammation in this injury.

In vivo expression of intercellular adhesion molecule 1 in type II pneumocytes during hyperoxia

Cell-to-cell communication is often disrupted when tissue damage occurs, triggering new signals to cope with the injury. The expression of intercellular adhesion molecule (ICAM-1), a protein involved in the migration, binding, and activation of leukocytes, is markedly increased in mouse lungs damaged by acute hyperoxic exposure. Type I alveolar epithelial cells are sensitive to hyperoxic lung injury, and must be removed from the air spaces following their destruction. In contrast, type II pneumocytes are relatively resistant to hyperoxia and may have a role in the removal process. Two reports demonstrate increased ICAM-1 in alveoli after hyperoxia (Welty et al., 1993, AJRCMB 9:393-400; and Kang et al., 1993, AJRCMB 9:350-355), but the cellular site(s) of ICAM-1 synthesis were not determined. We hypothesized that during in vivo exposure to 100% oxygen (O2), type II pneumocytes synthesize and secrete ICAM-1, an important step in attracting inflammatory cells to the site of injury. Adult mice were exposed to 100% O2 for up to 72 h. To determine whether type II cells express ICAM-1, tissue sections were studied by electron microscopy single-label in situ hybridization or light microscopy dual-label in situ hybridization, using radiolabeled and nonradiolabeled probes. In the lungs of unexposed animals, ICAM-1 mRNA was detected in many cells-including type I pneumocytes-but not in type II cells. After hyperoxia, ICAM-1 transcripts were detected in bona fide, surfactant protein C mRNA-containing, type II alveolar epithelial cells. This observation suggests that type II cells play an important and previously unrecognized role in pulmonary inflammation from O2 toxicity and emphasizes the importance of type II pneumocytes in alveolar repair after injury.

P-selectin is upregulated early in the course of hyperoxic lung injury in mice

While treatment with supplemental oxygen is often essential in patients with lung disease, prolonged therapy may cause lung injury by itself. Although the mechanisms responsible for initiating hyperoxic lung damage almost certainly involve primary oxidative transformations, the possible contributions of inflammation to the tissue injury have been attracting increasing research activity. Increases in intercellular adhesion molecule-1 (ICAM-1) coincide with the inflammation, but in other models of inflammation transient adhesion mediated by members of the Selectin gene family was found to be essential before ICAM-1/beta 2 interactions could occur. We, therefore, wondered whether a similar sequence of initial transient adhesion followed by subsequent responses would be observed in hyperoxic lung inflammation. We, therefore, determined the effects of hyperoxia exposure on lung mRNA for P- and E-Selectin in mouse lungs. We found that there was no detectable mRNA for E-Selectin through 72 h of hyperoxia exposure by Northern blotting, but that mRNA for P-Selectin was detectable as early as 48 h after initiation of hyperoxia. To determine the location of P-Selectin upregulation we examined hyperoxia-exposed mouse lungs by in situ hybridization and found that the upregulation of P-Selectin at 48 h was localized to large muscularized vessels, at 72 h expression was detected in some medium size muscularized vessels, and at 96 h abundant expression was observed also on nonmuscularized small vessels. In conclusion, increases in mRNA for P-Selectin early in the course of hyperoxia exposure suggest that P-Selectin expression in hyperoxic lungs increases in parallel with upregulation of ICAM-1, leading to the accumulation of neutrophils in hyperoxic lungs, and that interventions targeting these two adhesion molecules may lead to a diminution in hyperoxic lung inflammation and lung injury.

Antenatal steroids are associated with less need for blood pressure support in extremely premature infants

OBJECTIVE

To determine if antenatal steroids decrease the amount of blood pressure support required by extremely premature infants between 23 and 27 weeks' gestation.

DESIGN

Retrospective cohort study.

SETTING

Texas Children's Hospital neonatal intensive care unit from January 1986 to December 1991.

PARTICIPANTS

Two hundred forty premature infants between 23 and 27 weeks' gestation who survived at least 48 hours.

MAIN OUTCOME MEASURES

The amount of blood pressure support received in the form of dopamine and colloid. Secondary analysis investigated differences in mortality, respiratory support requirements, the incidence of intraventricular hemorrhage, necrotizing enterocolitis, infection, retinopathy of prematurity requiring surgery, and the length of hospitalization.

RESULTS

During the first 48 hours of life, premature newborns exposed to antenatal corticosteroids were less likely to receive dopamine for blood pressure support (47% vs 67%), and if they did, the amount of dopamine expressed as a dopamine score was less than that received by those infants not exposed to antenatal corticosteroids (281 +/- 240 vs 407 +/- 281). Those exposed to antenatal corticosteroids also had a lower mortality rate (8% vs 24%) and lower respiratory support requirements. The incidence of grade 3 or 4 intraventricular hemorrhage was 8% in infants exposed to antenatal corticosteroids and 17% in infants not exposed. No difference was found in the incidence of necrotizing enterocolitis, infection, or retinopathy of prematurity requiring surgery, or length of hospitalization.

CONCLUSION

Receipt of antenatal corticosteroids is associated with less need for blood pressure support during the first 48 hours after birth in premature infants between 23 and 27 weeks' gestation.

Pre mortem analysis of lung injury and lung function in oxygen toxic rabbits

OBJECTIVES

To determine whether respiratory system mechanics measurements could detect lung injury in oxygen toxic rabbits before clinical deterioration. To determine whether respiratory system mechanics measurements, using a power analysis, have the statistical power to detect significant reductions in hyperoxic lung injury due to an intervention when compared with traditional post mortem measurements of lung injury, extravascular lung water, and bronchoalveolar lavage protein concentration.

DESIGN

Prospective, controlled study.

SETTING

Institutional animal laboratories.

SUBJECTS

Adult New Zealand white rabbits.

INTERVENTIONS

Spontaneously breathing adult New Zealand white rabbits were exposed continuously to either > 95% oxygen or room air.

MEASUREMENTS AND MAIN RESULTS

We measured arterial pH, blood gas tensions, and respiratory system mechanics in rabbits twice, both before exposure to > 95% oxygen, and after the rabbits developed symptoms of mild lung dysfunction. After the second set of respiratory system mechanics measurements, we measured extravascular lung water and bronchoalveolar lavage protein concentration in the hyperoxia-exposed rabbits and compared the values with those values obtained in animals that breathed room air only. Our hyperoxia-exposed rabbits developed symptoms of mild respiratory impairment at 69 +/- 2 hrs. In these hyperoxia-exposed rabbits, measurements of static compliance, quasi-static compliance and resistance all changed significantly (p < .05) when compared with baseline measurements. Functional residual capacity and arterial blood gas values did not change significantly. Furthermore, assuming that an intervention reduced hyperoxic lung injury by a given amount, we performed a power analysis and found that the measurement of static compliance had at least equivalent power to detect a reduction in lung injury from an intervention when compared with measurement of extravascular lung water and bronchoalveolar lavage protein concentration.

CONCLUSIONS

Measurements of respiratory system mechanics can detect lung injury in hyperoxic rabbits before the onset of severe clinical deterioration or death. Furthermore, measurement of static compliance of the respiratory system is likely to be a powerful tool to detect a reduction in lung injury produced by an intervention.

Endotoxin induces glutathione reductase activity in lungs of mice

Glutathione reductase catalyzes the NADPH-dependent conversion of glutathione disulfide to glutathione and helps protect the lung from injury by reactive oxygen. In animals allowed to breathe nearly 100% oxygen, the activities of other antioxidants in the lung can be induced by treatment with endotoxin, and this induction is associated with increased tolerance to hyperoxia. The purpose of this study was to see whether glutathione reductase activity in the lungs of mice increased with endotoxin treatment alone. We studied 60 FVB mice (20 males and 40 females). Half received endotoxin (500 micrograms/kg) intraperitoneally at time 0 and 24 h, and the controls received an equal volume of saline. At 48 h we killed the mice and removed their lungs. Treatment of mice with endotoxin increased glutathione reductase activity in the lung 55% (0.035 +/- 0.005 to 0.054 +/- 0.010 mumol NADPH reduced/min/mg protein; mean +/- SD; endotoxin different from control, p < 0.001). The increase in activity was the same for male and female mice. We measured the specific protein for glutathione reductase by Western analysis and mRNA for glutathione reductase using a slot-blot analysis and found that both increased roughly 2-fold with endotoxin treatment. This suggests that endotoxin treatment resulted in either increased rate of transcription of glutathione reductase mRNA or increased mRNA stability. We conclude that endotoxin treatment increases glutathione reductase activity in the lung and that this increase in activity may play a role in subsequent protection from hyperoxia.

Increases in lung tissue expression of intercellular adhesion molecule-1 are associated with hyperoxic lung injury and inflammation in mice

Lung injury caused by breathing enriched oxygen continues to be a major problem in clinical medicine. Experimentally, hyperoxic lung injury is characterized by pulmonary edema and associated neutrophil accumulation. Although extensively investigated, the mechanisms for neutrophil accumulation and the role of this accumulation in hyperoxic lung injury remain controversial. Intercellular adhesion molecule-1 (ICAM-1) is an adhesion molecule that when increased on endothelium by inflammatory cytokines leads to increased adhesion of neutrophils to the inflamed endothelium and transendothelial migration. The purpose of this study was to examine the role of inflammation in hyperoxia-induced lung injury by investigating ICAM-1 expression in the lungs of mice exposed to > 95% oxygen continuously. Lung tissue from mice exposed to > 95% oxygen was analyzed for ICAM-1 mRNA by slot blot analysis and for ICAM-1 protein expression. We also examined lungs from mice exposed to hyperoxia for up to 96 h by light microscopy to correlate pulmonary inflammation with ICAM-1 expression. We found that mRNA for ICAM-1 increased 56% over baseline after 48 h of exposure to hyperoxia, that ICAM-1 protein increased by more than 5-fold over baseline after 96 h of exposure to hyperoxia, and that lung inflammation and injury were not evident until 96 h of exposure. Our data demonstrate that exposure to hyperoxia causes an increase in ICAM-1 gene transcription and/or mRNA stability in mouse lungs, and that this increase is followed by an increase in ICAM-1 protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperoxic lung injury in Fischer-344 and Sprague-Dawley rats in vivo

Supplemental oxygen remains an important therapy for pulmonary insufficiency, despite the potential adverse effects of hyperoxic exposures. Recently, He et al. reported that hyperoxic ventilation more readily damaged isolated perfused lungs from Fischer-344 rats than from Sprague-Dawley rats (Am. J. Physiol. 259:L451), which correlates with the previously reported strain differences in hepatic responses to diquat-induced oxidant stress in vivo (J. Pharmacol. Exp. Ther. 235:172). We therefore examined the differences in hyperoxic lung injury in Fischer-344 and Sprague-Dawley rats in vivo. Adult male rats were exposed to > 95% O2 and were sacrificed after 24, 48, or 60 h. Control animals were maintained in room air. Dramatically greater increases in pleural effusions and bronchoalveolar lavage protein concentrations in response to hyperoxia were observed in the Fischer-344 rats than in the Sprague-Dawley rats (p < .05 at both 48 and 60 h for both measurements). Additionally, the glutathione concentrations in alveolar lining fluid decreased from 800 microM to 115 microM in Fischer-344 rats after 60 h of > 95% O2, but did not change in Sprague-Dawley rats. We conclude that the greater susceptibility of Fischer-344 than of Sprague-Dawley rats to hyperoxic lung injury in vitro reported previously also is observed in vivo and that this strain difference offers unique opportunities to study mechanisms of hyperoxic lung injury.

Investigation of possible mechanisms of hepatic swelling and necrosis caused by acetaminophen in mice

Vascular congestion and liver swelling have long been recognized as features of the hepatotoxic effects of acetaminophen (AAP) in mice and rats and have been proposed as contributing factors to the eventual extent of necrosis produced. Neutrophil accumulation in the hepatic microcirculation has been proposed as being responsible for the blockage of hepatic blood flow and thereby the expansion of the region of damage. We therefore determined in mice the effects of hepatotoxic doses of AAP on the messenger RNA for intercellular adhesion molecule-1 (ICAM-1), which is a critical determinant of neutrophil adhesion, activation and ultimately of neutrophil-mediated tissue injury. Hepatotoxic doses of AAP did not upregulate ICAM-1 messenger RNA. However, doses of bacterial lipopolysaccharide (LPS) did cause a rapid and dramatic increase in ICAM-1 message, which was accompanied by a much greater hepatic accumulation of neutrophils, but which led to only scattered single cell necrosis. In addition, we investigated the effects of pentoxifylline (PTX) on AAP-induced vascular congestion and on hepatic necrosis as evaluated histologically and by measurement of plasma transaminase activities. Although PTX has been shown to increase blood cell deformability and improve vascular perfusion in a number of animal models of restricted blood flow, and is used in humans for the treatment of intermittent claudication, we found no decrease in AAP-induced hepatic swelling or in AAP-induced necrosis in response to PTX. With some dosing regimens, PTX-treated animals proved to be slightly more susceptible to AAP, which may be related to the reported potentiation of the cytotoxicities of a number of alkylating anti-cancer drugs by PTX and other methylxanthines. We conclude from these studies that upregulation of ICAM-1 and subsequent adhesion and vascular plugging by neutrophils are not significant determinants of AAP-induced liver swelling and necrosis and that whatever hemorheological advantages PTX might offer in AAP-induced hepatic damage appear to be overshadowed by effects that potentiate the toxic responses.

The effect of blood flow and left atrial pressure on the DLCO in lambs and sheep

Previous studies suggest that pulmonary capillary distensibility and recruitment may differ in lambs and sheep. To study the effect of pulmonary blood flow (PBF) and vascular pressure on capillary hemodynamics in lambs and sheep we measured the diffusing capacity for carbon monoxide (DLCO) as an index of pulmonary capillary blood volume during a baseline period, after increasing PBF, and during left atrial hypertension. In the lamb, DLCO did not change significantly either with a 65% increase in PBF or with an increase in left atrial pressure (Pla) of 1.33 kPa at constant PBF. In the sheep on the other hand, doubling PBF led to a 28% increase in DLCO (P less than 0.02), and an increase in Pla of 1.87 kPa at constant PBF led to a 19% increase in DLCO (P less than 0.01). These results suggest that the neonatal lamb has a nearly fully recruited and relatively non-compliant pulmonary capillary bed at rest, unlike the adult sheep which can respond to hemodynamic changes with distension and recruitment of the pulmonary capillary bed.