Copyright ©ERS Journals Ltd 2003 Variable tissue expression of transferrin receptors: relevance to acute respiratory distress syndromeDepts of 1 Critical Care and 2 Histopathology, Royal Brompton Hospital, Imperial College Faculty of Medicine CORRESPONDENCE: G.J. Quinlan, Unit of Critical Care, Royal Brompton Hospital, Sydney St, London, SW3 6NP, UK. Fax: 44 2073518524. E-mail: g.quinlan@imperial.ac.uk Keywords: acute respiratory distress syndrome, iron regulation, oxidative stress, transferrin receptor
Received: August 15, 2002
This study was supported by a British Lung Foundation/BOC Group Programme Grant, the Dunhill Medical Trust and British Heart Foundation. ¶Joint first authors.
Acute respiratory distress syndrome (ARDS) is associated with altered plasma and lung iron chemistry. Iron can promote microbial virulence and catalyse pro-oxidant reactions, thereby contributing to the oxidative stress that characterises the syndrome.
Therefore, the expression of ferritin and transferrin receptors (TfR) were sought in the lungs and hearts of rodents treated with lipopolysaccharide (LPS), and measurements of TfR and ferritin protein expression were taken from lung biopsy specimens from patients with ARDS and appropriate controls.
TfR messenger ribonucleic acid (mRNA) was significantly upregulated in the lungs and significantly downregulated in the hearts of rats 4 h after LPS. Ferritin mRNA levels (light and heavy chains) remained unaltered. Protein TfR levels were significantly upregulated in lungs and downregulated in hearts 4 h post-LPS. Ferritin protein levels were significantly downregulated in lungs compared to baseline values but were unaltered in hearts. Nonhaem iron levels were increased in lungs and decreased in hearts, and iron-regulatory-protein activity increased in hearts but not lungs. TfR protein levels were significantly increased in lung biopsies from patients with ARDS compared to controls.
Transferrin receptors are upregulated in rodent lungs during inflammation but are downregulated in the heart. Transferrin receptor protein levels were significantly increased in the lungs in clinical acute respiratory distress syndrome. These findings have implications for the pathogenesis of acute respiratory distress syndrome, especially in relation to the role of iron as a mediator of oxidative stress.
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