Using hyperoxia as a model of oxidant-induced lung injury in the rat, we explored the regulation of heme oxygenase-1 (HO-1) expression in vivo and in vitro. We demonstrate marked increase of HO-1 messenger ribonucleic acid (mRNA) levels in rat lungs after hyperoxia. Increased HO-1 mRNA expression correlated with increased HO-1 protein and enzyme activity. Immunohistochemical studies of the rat lung after hyperoxia showed increased HO-1 expression in a variety of cell types, including the bronchoalveolar epithelium and interstitial and inflammatory cells. We then examined the regulation of HO-1 expression in vitro after hyperoxia and observed increased HO-1 gene expression in various cultured cells including epithelial cells, fibroblasts, macrophages, and smooth muscle cells. Increased HO-1 mRNA expression correlated with increased HO-1 protein in vitro, and resulted from increased gene transcription and not from increased mRNA stability. We show that transcriptional activation of the HO-1 gene by hyperoxi...

Regulation of Heme Oxygenase-1 Expression in Vivo and in Vitro in Hyperoxic Lung Injury

Hyperoxic lung injury is commonly encountered in patients who require treatment with high concentrations of inspired oxygen. To determine whether interleukin (IL)-6 is protective in oxygen toxicity, we compared the effects of 100% O 2 in transgenic mice that overexpress IL-6 in the lung and transgene ( 2 ) controls. IL-6 markedly enhanced survival, with 100% of transgene ( 2 ) animals dying within 72 to 96 h, 100% of transgene ( 1 ) animals living for more than 8 d and more than 90% of transgene ( 1 ) animals living longer than 12 d. This protection was associated with markedly diminished alveolar-capillary protein leak, endothelial and epithelial membrane injury, and lung lipid peroxidation. Hyperoxia also caused cell death with DNA fragmentation in the lungs of transgene ( 2 ) animals and IL-6 markedly diminished this cytopathic response. The protective effects of IL-6 were not associated with significant alterations in the activities of copper/ zinc superoxide dismutase (SOD) or manganese SOD. They were, however, associated with the enhanced accumulation of the cell-death inhibitor Bcl-2, but not the cell-death stimulator BAX, and with the heightened accumulation of the cell-death regulator tissue inhibitor of metalloproteinase-1 (TIMP-1). These studies demonstrate that IL-6 markedly diminishes hyperoxic lung injury and that this protection is associated with a marked diminution in hyperoxia-induced cell death and DNA fragmentation. They also demonstrate that this protection is not associated with significant alterations in SOD activity, but is associated with the induction of Bcl-2 and TIMP-1. Supplemental oxygen is commonly given to patients with cardiopulmonary disorders to enhance tissue oxygenation. Unfortunately, the prolonged administration of fractional inspired concentrations of oxygen greater than 50 to 60% leads to a variety of forms of tissue damage, including acute lung injury. The pathophysiology of this pulmonary toxicity has been characterized in animal models (1‐4). These studies demonstrated that toxic concentrations of O 2 generate oxygen-derived free radicals that damage lung epithelial and endothelial cells, leading to a protein-rich fluid that floods the alveolar space. Recent researchers have also demonstrated that this injury is associated with a cell-death response with features of both cell necrosis and apoptosis (4, 5). Interleukin (IL)-6 is a pleiotropic cytokine that is produced at sites of tissue inflammation. It is classified as an IL-6‐type cytokine with IL-11, leukemia inhibitory factor, cardiotrophin-1, oncostatin M, and ciliary neurotrophic factor on the basis of the overlapping effector profiles of these cytokines and their shared use of gp130 as the b -subunit in their multimeric receptor complexes (6). IL-6 induces fever, activates B and T lymphocytes, and stimulates hepatocytes to produce acute phase proteins. Recent studies have shown that IL-6 also has potent anti-inflammatory and protective properties. These include the ability to inhibit the production of tumor necrosis factor (TNF), IL-1, and macrophage inflammatory protein-2; decrease neutrophil sequestration; increase levels of IL-1 receptor antagonist and TNF soluble receptor; stimulate the production of metalloproteinase inhibitors; reduce intracellular superoxide production; reduce tissue matrix degradation; and inhibit cellular apoptosis (7‐ 14). Surprisingly, the ability of IL-6 to regulate hyperoxic lung injury has not been adequately investigated. We hypothesized that the anti-inflammatory and cytoproptective effects of IL-6 could ameliorate hyperoxic lung injury. To test this hypothesis we compared the injury induced by 100% O 2 in transgenic mice in which IL-6 was selectively overexpressed in the lung (CC10‐IL-6 mice) with appropriate transgene ( 2 ) littermate controls. These experiments demonstrated that CC10‐IL-6 transgene ( 1 ) mice have an impressive ability to tolerate 100% O 2 . This tolerance manifests as enhanced survival, decreased pulmonary edema and alveolar-capillary protein leakage, and decreased lung lipid peroxidation when compared with transgene ( 2 ) controls. Further, transgene ( 2 ) mice manifest an impressive cell-death response associated with DNA fragmentation which was inhibited in the IL-6 ( 1 ) animals. This protection was associated with the enhanced accumulation of the regulatory proteins Bcl-2 and tissue inhibitor of metalloproteinase-1 (TIMP-1).

https://www.atsjournals.org/doi/pdf/10.1165/ajrcmb.22.5.3808

Interleukin-6-induced protection in hyperoxic acute lung injury.

TNFα concentrations and mRNA expression are increased in preeclamptic placentas

Oxidative stress and degenerative temporomandibular joint disease: a proposed hypothesis.

Pathways of cell signaling in hyperoxia.

mRNA from lungs of mice exposed to high-dose oxygen (greater than 95%) for 3 days demonstrated increased expression of the genes for tumor necrosis factor (TNF), interleukin-1, and interleukin-6 compared with mRNA from lungs of mice exposed to room air. Daily treatment of mice exposed to high-dose oxygen with an antibody to TNF improved survival compared with mice receiving a similar dose of control immunoglobulin G. Pretreatment of mice with repetitive sublethal intraperitoneal doses of recombinant human TNF for 3 days or a single intravenous dose followed by exposure to high-dose oxygen afforded a significant survival advantage compared with high-dose oxygen-exposed mice pretreated with vehicle or interleukin-1. The repetitive intraperitoneal TNF pretreatment reduced the development of interstitial pneumonitis, pulmonary edema, and lung weight gain associated with oxygen toxicity and enhanced expression of the gene for the free radical protective enzyme manganous superoxide dismutase in lung tissue, a gene that is augmented as mice are exposed to high-dose oxygen. Furthermore a single intravenous dose of TNF 24 h after oxygen exposure was still protective. The results suggest that the toxicity of oxygen therapy can be partially ameliorated by either treatment with anti-TNF antibody or pretreatment and early treatment with TNF. These findings are consistent with the hypothesis that oxygen exposure induces TNF, which causes part of the toxicity of high-dose oxygen, and that pretreatment or early treatment with TNF induces the gene for an enzyme that recently has been shown to be very effective in protecting mice from the toxicity of oxygen.

D. Kauffman

Papers

Role of tumor necrosis factor in oxygen toxicity.