Serum fibronectin is elevated during normobaric and hyperbaric oxygen exposure in rats

Multiple-organ effect of normobaric hyperoxia in neonatal rats

PURPOSE

Prolonged exposure to normobaric hyperoxia (NH) is associated with blood leukocyte activation and sequestration in the lung. Whether NH-induced leukocyte activation and sequestration can affect extrapulmonary organs or blood cellular profile has not been systematically investigated. We studied simultaneous changes in blood cellular profile and pulmonary, renal, and intestinal histology during NH and after return to air breathing ("weaning").

MATERIALS AND METHODS

One-day-old rats were exposed to 2 to 4 days of NH (FiO2 >0.98) or normoxia (FiO2 = 0.21), with or without weaning. Pups were then euthanized and 100 microL of blood was collected (cardiac puncture) for differential white blood cells analysis (n = 12 per group). The lungs, a piece of distal ileum, and the left kidney were removed for histologic evaluation.

RESULTS

Both NH and weaning generated significant increases in blood neutrophil count, whereas lymphocyte population was significantly increased only after weaning (P < .05; analysis of variance with Bonferroni correction for multiple comparisons). Normobaric hyperoxia created mild increases in the renal tubular necrosis, dilation, regeneration, and interstitial inflammation. A significant increase in the intestinal serosal and submucosal vasodialation and vascularization occurred 1 day after weaning from 4 days of NH (P < .001). These extrapulmonary events coincided with the development of histologic manifestations of pulmonary oxygen toxicity.

CONCLUSIONS

Development of pulmonary oxygen toxicity in neonatal rats is associated with significant changes in differential leukocyte counts and histologic alterations in the kidney and ileum. We speculate that activation of circulating leukocytes and/or direct effect of NH may affect certain peripheral organs independently from the NH-induced pulmonary pathology.

Circulating factors that modify lung cell DNA synthesis following exposure to inhaled oxidants. III. Effects of plasma on lung pneumocyte and fibroblast DNA synthesis following exposure of adult rats to 85% oxygen

Previous studies, in which adult rats were exposed to 1 ppm ozone for 2 weeks, demonstrated the appearance in plasma of separate factors that stimulated DNA synthesis by cultured pneumocytes and lung fibroblasts in a dose-dependent and cell-specific fashion. Both factors had isoelectric points of 6.45-6.75, but differed by molecular mass. The pneumocyte factor had an estimated weight of 38 +/- 3 kDa, while the fibroblast factor had an estimated molecular weight of 32 +/- 2 kDa. To determine whether the appearance of these factors in plasma is specific for ozone injury or whether they appear in response to other oxidant injuries, adult rats were exposed to 85% O2 or air for up to 2 weeks. Animals were sacrificed at 3, 5, 7, or 14 days after the onset of exposure. Plasma samples were subjected to sequential preparative electrofocusing and high-performance liquid chromatography (HPLC). Heat-inactivated plasma fractions, with an isoelectric point of 6.45-6.75, contained a factor of 32 +/- 2 kDa, which enhanced lung fibroblast DNA synthesis at a single time point on day 5 of 85% O2 exposure, and a factor of 38 +/- 3 kDa, which enhanced pneumocyte DNA synthesis on days 5, 7, and 14 of 85% O2 exposure. Of the known growth factors, those most likely to have these physical characteristics are platelet-derived growth factor (PDGF) and insulin-like growth factor-1. Additional groups of animals were exposed to air or 85% O2 for 5 days for plasma collection. Animals exposed to 85% O2 had a 60% increase of plasma immunoreactive PDGF and a 90% increase of plasma immunoreactive IGF-1, compared with values for control animals exposed to air.

Circulating factors that modify lung cell DNA synthesis following exposure to inhaled oxidants. II. Effect of serum and lavage on lung pneumocytes following exposure of adult rats to 1 ppm ozone

Adult rats were exposed to 1 ppm (1.96 mg/m3) ozone or air for 2 wk. Animals were sacrificed at 3, 5, 7, or 14 d after the onset of exposure, and samples of plasma and lung lavage were obtained. Heat-inactivated plasma and lavage from animals exposed to ozone for 5 or 7 d significantly increased DNA synthesis by lung pneumocytes compared with plasma or lavage from air-exposed animals. Fractionation of plasma and lavage samples indicated that the factor responsible had an isoelectric point of 6.45-6.75, and a molecular weight of 38 +/- 3 kDa. This factor has a dose-dependent effect on lung pneumocyte DNA synthesis in culture. It has no effect on cultured fibroblast DNA synthesis, and is distinct from a previously described factor in the plasma of these ozone-exposed animals that enhances fibroblast DNA synthesis. The factor is detectable within 5 d of exposure, and may hold some promise as a marker of early oxidant lung injury.

Retrosternal pain is an early indicator of oxygen toxicity

To determine the most sensitive early indicator of toxicity from exposure to O2, we measured respiratory clearance of 99mTc-diethylenetriamine pentaacetate (Tc-DTPA), pulmonary function, serum Factor VIII antigen, and plasma fibronectin values and monitored symptoms in six normal volunteers who breathed 21, 40, and 100% O2, administered in random order, for 17 h at least 1 wk apart. Twenty minutes after beginning O2, arterial PO2 differed among the three exposure groups. After exposure to the three concentrations of O2, there were no differences in Tc-DTPA clearance, vital capacity, FEV1/FVC, diffusing capacity, Factor VIII antigen, or fibronectin concentration. In contrast, all subjects complained of retrosternal pain during and after breathing 100% O2 (p less than 0.001). We conclude that with exposure to 100% O2, retrosternal pain, presumably from tracheal inflammation, occurs before detectable abnormalities of epithelial solute permeability (Tc-DTPA clearance), endothelial O2 injury (fibronectin concentration and Factor VIII), or pulmonary function. These findings indicate that symptoms are more sensitive than signs in detecting early O2 toxicity.

Modulation of endothelial fibronectin synthesis by polymorphonuclear granulocytes

The attachment of polymorphonuclear granulocytes (PMNs) to vascular endothelial cells occurs continually in normal tissues; however, knowledge of the factors that control leukocyte margination is incomplete. In the present study, we used cell cultures of pulmonary artery endothelium to study their interaction with PMNs. Endothelial cells were seeded in Costar 24-well plates following which PMNs were inoculated onto the endothelial monolayers and incubated for 2 to 20 hours. During this period, fibronectin synthesis by endothelial cells was estimated by ELISA. In wells to which PMNs had been added, supernatant fibronectin concentration was increased at all time points during the 20 hour incubation. At 20 hours, supernatants from wells to which PMNs had been added contained approximately 2 1/2 times the control level of fibronectin. Since the amount of fibronectin, as determined by ELISA, adsorbed onto the added PMNs was negligible, these data suggest that PMNs can modulate the synthesis of fibronectin by pulmonary artery cells. Pulse labeling experiments and measurements of endothelial intracellular fibronectin also suggest this possibility. The endothelial response does not appear to be owing to nonspecific physical interaction since similarly sized polystyrene beads did not cause any change in supernatant fibronectin levels while glutaraldehyde-fixed PMNs caused only a 20-25% increase in fibronectin levels.

Circulating factors that modify lung cell DNA synthesis following exposure to inhaled oxidants. I. Effect of serum and lavage on lung fibroblasts following exposure of adult rats to 1 ppm ozone

Adult rats were exposed to 1 ppm (1.96 mg/m3) ozone or air for 2 wk. Animals were sacrificed at 3, 5, 7, or 14 d after the onset of exposure, and samples of plasma and lung lavage were obtained. Heat-inactivated plasma, from animals exposed to ozone for 7 or 14 d, significantly increased DNA synthesis by lung fibroblasts compared with plasma from air-exposed animals. Fractionation of plasma and lavage samples indicated that the factor responsible had an isoelectric point of 6.45-6.75 and a molecular weight of 32 +/- 2 kDa. This factor has a dose-dependent effect on lung fibroblast DNA synthesis in culture, but no significant effect on cultured pneumocyte DNA synthesis. The factor is detectable within 72 h of exposure, and may hold some promise as a marker of early oxidant lung injury.

Intravascular release of intact cellular fibronectin during oxidant-induced injury of the in vitro perfused rabbit lung

Fibronectin (Fn) is produced by cells in blood vessels at inflammatory sites in vivo. Fn release into the circulation thus may be a marker for vascular injury. In support of this, we found that oxidant-induced vascular injury of isolated perfused rabbit lungs caused elevated circulating Fn levels. Western blot analysis indicated that Fn released from the injured blood vessels was intact, dimeric, and possessed electrophoretic mobility identical with Fn produced by fibroblasts. Unlike Fn isolated from rabbit plasma, Fn derived from lung perfusate or produced by fibroblasts reacted with antibodies raised to a synthetic peptide containing sequences from the extra type III Fn domain that is transcribed in fibroblasts but not hepatocytes. Vascular injury by protease was also associated with intravascular release of Fn, but with cleavage. Oxidant-induced vascular injury causes release of tissue-derived Fn, which can be distinguished from plasma Fn by its size and content of antigenic determinants of the extra type III domain.