doi:10.1369/jhc.6A7007.2006
Volume 54 (11): 1239-1246, 2006 Copyright ©The Histochemical Society, Inc. Prolonged Exposure to Hyperoxia Increases Perivascular Mast Cells in Rat Lungs
Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan (TGB), and Department of Biomedical Sciences, School of Medicine, University of Chieti, Chieti, Italy (CDG) Correspondence to: Thomas G. Brock, 6301C MSRB III, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109-0642. E-mail: brocko{at}umich.edu
Prolonged hyperoxia, as may be used to treat patients with severe hypoxemia, can lead to lung injury, respiratory failure, and death. Resident mast cells play important roles in regulating the lung response to changing environmental conditions, as evidenced by their roles in asthma and airway hyperresponsiveness. In this study we evaluated the effect of prolonged hyperoxia on the number and distribution of mast cells in the rat lung. In rats maintained in normoxia, mast cells were distributed primarily in the loose connective tissue surrounding large bronchioles and vessels of the lung. In rats exposed to normobaric hyperoxia for 72 hr, mast cell number in lung sections increased significantly, and mast cells were found preferentially accumulated around vessels throughout the lung. Notably, mast cells around smaller vessels were abundant in hyperoxic lungs but rare in normoxic lungs. Also, mast cells were increased in the pleura of lungs exposed to hyperoxia. These changes in mast cell number and distribution in response to hyperoxia were evident in aged (22-month-old) rats as well as young (3-month-old) rats. As mast cell-derived mediators have many effects, e.g., on vascular leak and vascular tone, positioning of increased mast cell numbers throughout the lung vasculature may be an important contributor to changes in lung function subsequent to persistent hyperoxia. (J Histochem Cytochem 54:12391246, 2006)
Key Words: hyperoxia mast cells lung rat young aged 5-lipoxygenase
PATIENTS ARE TREATED with high-inspired levels of oxygen, or hyperoxia, for a variety of conditions and for varying lengths of times. In addition to the positive effects derived from the treatment, significant deleterious effects can also occur. For example, prolonged hyperoxia may contribute to bronchopulmonary dysplasia in neonates (Coalson et al. 1982
One consequence of prolonged exposure to hyperoxic conditions involves lung remodeling. For example, chronic hyperoxic exposure leads to thickening of the airway epithelial and smooth muscle layers (Hershenson et al. 1992
Mast cells are resident immune cells that typically can be found in the larger airways of the lung, predominantly in the lamina propria of the bronchi and the supporting tissue of the bronchioles. Upon activation, mast cells release a variety of mediators including leukotrienes, prostaglandins, histamine, serine proteases, and cytokines. Mast cells are known to contribute to airway hyperreactivity (Page et al. 2001
Animals and Treatments Following previously published protocols (Di Giulio et al. 1998
Toluidine Blue Staining and Immunohistochemistry
Quantitative and Statistical Analysis
The presence of mast cells in lung tissues was first evaluated using toluidine blue staining, as has been used to quantify mast cell numbers in lungs (Vignola et al. 1998
Edema, or vascular leak, is an important symptom associated with exposure to hyperoxia, and cysteinyl leukotrienes are mediators produced by mast cells that can cause edema. The enzyme 5-lipoxygenase (5-LO) initiates the synthesis of cysteinyl leukotrienes from arachidonic acid, and the subcellular localization of 5-LO can regulate leukotriene synthesis (Luo et al. 2003 In addition to the larger vessels, smaller vessels measuring <100 µm in diameter were also scattered across lung sections. In lung sections from young rats maintained under normoxic conditions, zero to two mast cells could be found associated with these smaller vessels (Figures 2A 2C). Positive staining of mast cells along the pleura (Figure 2A) as well as along larger vessels (Figure 1) demonstrated that the staining was effective in these sections. In contrast to the pattern observed in normoxic lungs, multiple mast cells were commonly observed around the smaller vessels of lung sections from young animals exposed to hyperoxia (Figures 2D2F). Quantitatively, sections from normoxic rats had 0.195 (SE = 0.100) mast cells per vessel, whereas sections from hyperoxic animals averaged 2.88 (SE = 0.532) mast cells per vessel, which was statistically different (p=0.0077). This indicated that these immunomodulatory leukocytes were increased along the more narrow vessels, as well as the larger vessels, following hyperoxia.
Mast cells were also evident within the pleura of all lung sections. Mast cells were evident in the pleura of lung sections from young normoxic rats (Figure 3A ), with fewer lining the pleura of oblique fissures between adjacent lobes (Figure 3B). The number of mast cells in peripheral pleura of hyperoxic lungs from young rats was increased (Figure 3C). Pleura surfaces of oblique fissures between adjacent lung lobes showed abundant mast cells by staining with either toluidine blue (Figure 3D) or 5-LO (Figure 3E). Surprisingly, many mast cells in the pleura had nuclear 5-LO (Figure 3E, inset), whereas mast cells at vessels had cytoplasmic 5-LO (e.g., Figure 1K). Thus, exposure to hyperoxia led to an increase in mast cell number along the lung pleura as well as around vessels, although redistribution of 5-LO to the cytoplasm, evident near vessels, was not found at the pleura.
It was not clear whether older rats would be more or less affected by exposure to hyperoxia. Examination of lung sections from 22-month-old rats exposed to hyperoxia indicated abundant mast cells around large vessels (Figures 4A and 4B) and smaller vessels (Figures 4C and 4D). As in young animals, many mast cells had cytoplasmic 5-LO, as indicated by the lighter, non-staining cell center (Figure 4D, inset). The number and distribution of mast cells in hyperoxic lungs from older animals were virtually indistinguishable from those of younger animals. Abundant mast cells were also present in the pleura of lungs from old, hyperoxic animals (Figure 4E). Lung sections from 22-month-old rats maintained in room air, like those from young rats, had few masts cells, with their distribution mostly restricted to the largest vessels and bronchioles (not shown). These results indicate that mast cells increase in number, particularly around vessels, in response to hyperoxia in aged animals as well as in young animals.
Increased inspired oxygen fractions may be used to treat premature infants and patients with acute lung injury or severe hypoxemia. Physiologic manifestations of oxygen toxicity include decreases in vital capacity, diffusing capacity, and lung compliance, with pathologic changes resembling those of the adult respiratory distress syndrome (Jackson 1985
The mechanism behind the increase in toluidine-positive cells is unclear. It seems likely that mast cells generated from precursors in the bone marrow during persistent hyperoxia migrated through the vasculature and into the lung, where they matured. However, it is also possible that hyperoxia triggered the differentiation of immature, toluidine-negative mast cells already present in the lung. Finally, it has been reported that hyperoxia induces mast cell hyperplasia (Subramaniam et al. 2003
The most remarkable aspect of this study is the increase in mast cell number, specifically in the loose connective tissue around large and small vessels. In most cases, mast cells were accumulated just outside the muscle layer. In addition to increasing mast cell number, hyperoxia induces an increase in smooth muscle in the lung, particularly in the airways (Hershenson et al. 1992
In addition to tryptase, mast cells secrete a broad range of other mediators. Notably, mast cells release histamine, cysteinyl leukotrienes, and prostaglandin D2 (PGD2). Both histamine and cysteinyl leukotrienes increase vascular permeability resulting in edema, an effect associated with chronic hyperoxia. Histamine and cysteinyl leukotrienes promote smooth muscle constriction, whereas PGD2 relaxes vascular smooth muscle. We also find that the enzyme 5-LO, which initiates leukotriene synthesis, is present in the mast cells, but that its subcellular localization changes, being nuclear in normoxic conditions and cytoplasmic in hyperoxic conditions. As cytoplasmic localization of 5-LO can allow greater cysteinyl leukotriene synthesis than nuclear localization (Brock et al. 1999
The presence of mast cells at the pleura of the lung has been previously reported (Li et al. 1994
The presence of mast cells does not necessarily indicate their impact on lung function: they typically need to be activated to release mediators and granule contents. Furthermore, the magnitude of their response to activation can be modified by priming agents (Boyce 2003
In this study we used a relatively high level of oxygen for 3 days and observed profound effects on mast cell number and distribution. Levels of hyperoxia, as well as duration of exposure, are important variables that may affect these outcomes. For example, exposure of rats to moderate hypoxia (FiO2, 50%) for 15 days increased airway reactivity and tracheal smooth muscle surface area in neonatal rats but not in adult rats (Denis et al. 2001 In summary, prolonged hyperoxia may contribute to bronchopulmonary dysplasia in neonates as well as to decreased pulmonary compliance, edema, remodeling, and inflammation in adults. Hyperplasia of mast cells and their migration to vessels throughout the pulmonary vasculature, as well as the pleura, in response to chronic hyperoxia positions these important immunoregulatory cells in key positions. Once accumulated at these sites, mast cells may become activated to secrete mediators that will have profound effects on pulmonary function. Future studies will examine the effects of varying levels and durations of increased oxygen exposure on mast cell accumulation, as well as the effects of bacterial infection on mast cell activation and change in lung function.
This study was supported by Grant AI-43574 from the National Institutes of Health, Bethesda, MD.
Received for publication May 3, 2006; accepted July 12, 2006
Abonia JP, Hallgren J, Jones T, Shi T, Xu Y, Koni P, Flavell RA, et al. (2006) Alpha-4 integrins and VCAM-1, but not MAdCAM-1, are essential for recruitment of mast cell progenitors to the inflamed lung. Blood 108:15881594. Published online May 2, 2006 (DOI: 10.1182/blood-2005-12-012781) Ainsworth DM, Keith IM, Lobas JG, Farrell PM, Eicker SW (1986) Oxygen toxicity in the infant rhesus monkey lung. Light microscopic and ultrastructural studies. Histol Histopathol 1:7587[Medline] Arkovitz MS, Garcia VF, Szabo C, McConnell K, Bove K, Wispe JR (1997) Decreased pulmonary compliance is an early indicator of pulmonary oxygen injury. J Surg Res 67:193198[CrossRef][Medline] Boyce JA (2003) Mast cells: beyond IgE. J Allergy Clin Immunol 111:2432[CrossRef][Medline] Brock TG, Anderson JA, Fries FP, Peters-Golden M, Sporn PHS (1999) Decreased leukotriene C4 synthesis accompanies nuclear import of 5-lipoxygenase in human blood eosinophils. J Immunol 162:16691676 Brock TG, Maydanski E, McNish RW, Peters-Golden M (2001) Co-localization of leukotriene A4 hydrolase with 5-lipoxygenase in nuclei of alveolar macrophages and rat basophilic leukemia cells but not neutrophils. J Biol Chem 276:3507135077 Brown JK, Tyler CL, Jones CA, Ruoss SJ, Hartmann T, Caughey GH (1995) Tryptase, the dominant secretory granular protein in human mast cells, is a potent mitogen for cultured dog tracheal smooth muscle cells. Am J Respir Cell Mol Biol 13:227236[Abstract] Burghardt JS, Boros V, Biggs DF, Olson DM (1996) Lipid mediators in oxygen-induced airway remodeling and hyperresponsiveness in newborn rats. Am J Respir Crit Care Med 154:837842[Abstract] Caughey GH (1997) Of mites and men: trypsin-like proteases in the lungs. Am J Respir Cell Mol Biol 16:621628[Abstract] Coalson JJ, Kuehl TJ, Escobedo MB, Hilliard JL, Smith FKM, Null DMJ, Walsh W, et al. (1982) A baboon model of bronchopulmonary dysplasia. II. Pathologic features. Exp Mol Pathol 37:335350[CrossRef][Medline] Denis D, Fayon MJ, Berger P, Molimard M, De Lara MT, Roux E, Marthan R (2001) Prolonged moderate hyperoxia induces hyperresponsiveness and airway inflammation in newborn rats. Pediatr Res 50:515519[Medline] Di Giulio C, Di Muzio M, Sabatino G, Spoletini L, Amicarelli F, Di Ilio C, Modesti A (1998) Effect of chronic hyperoxia on young and old rat carotid body ultrastructure. Exp Gerontol 33:319329[CrossRef][Medline] Freeman B, Crapo J (1981) Hyperoxia increases oxygen radical production in rat lungs and lung mitochondria. J Biol Chem 256:1098610992 Gore RG, Jones R (1989) Pulmonary vascular reactivity in hyperoxic pulmonary hypertension in the rat. J Appl Physiol 65:26172623 Hershenson MB, Abe MK, Kelleher MD, Naureckas ET, Garland A, Zimmermann A, Rubinstein VJ, et al. (1994) Recovery of airway structure and function after hyperoxic exposure in immature rats. Am J Respir Crit Care Med 149:16631669[Abstract] Hershenson MB, Aghili S, Punjabi N, Hernandez C, Ray DW, Garland A, Glagov S, et al. (1992) Hyperoxia-induced airway hyperresponsiveness and remodeling in immature rats. Am J Physiol 262:L263269 Hu LM, Jones R (1989) Injury and remodeling of pulmonary veins by high oxygen. A morphometric study. Am J Pathol 134:253262[Abstract] Jackson RM (1985) Pulmonary oxygen toxicity. Chest 88:900905 Jones R, Zapol WM, Reid L (1984) Pulmonary artery remodeling and pulmonary hypertension after exposure to hyperoxia for 7 days. A morphometric and hemodynamic study. Am J Pathol 117:273285[Abstract] Kasacka I, Humenczyk-Zybala M, Niczyporuk M, Mycko G (2003) The evaluation of quantity and distribution of murine pulmonary mast cells in experimental hemorrhagic shock. Folia Histochem Cytobiol 41:8386[Medline] Li XY, Lamb D, Donaldson K (1994) Mesothelial cell injury caused by pleural leukocytes from rats treated with intratracheal instillation of crocidolite asbestos or Corynebacterium parvum. Environ Res 64:181191[Medline] Luo M, Jones SM, Peters-Golden M, Brock TG (2003) Nuclear localization of 5-lipoxygenase as a determinant of leukotriene B4 synthetic capacity. Proc Natl Acad Sci USA 100:1216512170 Maezawa Y, Nakajima H, Kumano K, Kubo S, Karasuyama H, Iwamoto I (2003) Role of IgE in Th2 cell-mediated allergic airway inflammation. Int Arch Allergy Immunol 131:26 Minoo P, Segura L, Coalson JJ, King RJ, DeLemos RA (1991) Alterations in surfactant protein gene expression associated with premature birth and exposure to hyperoxia. Am J Physiol 261:L386392 Page S, Ammit AJ, Black JL, Armour CL (2001) Human mast cell and airway smooth muscle cell interactions: implications for asthma. Am J Physiol Lung Cell Mol Physiol 281:L13131323 Shaffer SG, O'Neill D, Bradt SK, Thibeault DW (1987) Chronic vascular pulmonary dysplasia associated with neonatal hyperoxia exposure in the rat. Pediatr Res 21:1420[Medline] Shenberger JS, Shew RL, Johnson DE (1997) Hyperoxia-induced airway remodeling and pulmonary neuroendocrine cell hyperplasia in the weanling rat. Pediatr Res 42:539544[Medline] Subramaniam M, Sugiyama K, Coy DH, Kong Y, Miller YE, Weller PF, Wada K, et al. (2003) Bombesin-like peptides and mast cell responses: relevance to bronchopulmonary dysplasia? Am J Respir Crit Care Med 168:601611 Szarek JL, Ramsay HL, Andringa A, Miller ML (1995) Time course of airway hyperresponsiveness and remodeling induced by hyperoxia in rats. Am J Physiol 269:L227233 Varadaradjalou S, Feger F, Thieblemont N, Hamouda NB, Pleau JM, Dy M, Arock M (2003) Toll-like receptor 2 (TLR2) and TLR4 differentially activate human mast cells. Eur J Immunol 33:899906[CrossRef][Medline] Vignola AM, Chanez P, Campbell AM, Souques F, Lebel B, Enander I, Bousquet J (1998) Airway inflammation in mild intermittent and in persistent asthma. Am J Respir Crit Care Med 157:403409 White MV (1990) The role of histamine in allergic diseases. J Allergy Clin Immunol 86:599605[CrossRef][Medline]
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