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Carbon Monoxide Reversibly Alters Iron Homeostasis and Respiratory Epithelial Cell Function

¹ National Health and Environmental Effects Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, North Carolina; ² Center for Environmental Medicine, Asthma and Lung Biology, University of North Carolina, Chapel Hill, North Carolina; ³ Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio, Texas; and ⁴ Department of Medicine, Duke University Medical Center, Durham, North Carolina

Correspondence and requests for reprints should be addressed to Andrew J. Ghio, MD, Campus Box 7315, Human Studies Division, US EPA, 104 Mason Farm Road, Chapel Hill, NC 27599-7315. E-mail: ghio.andy{at}epa.gov

The dissociation of iron from heme is a major factor in iron metabolism and the cellular concentrations of the metal correlate with heme degradation. We tested the hypotheses that (1) exposure to a product of heme catabolism, carbon monoxide (CO), alters iron homeostasis in the lung and in cultured respiratory epithelial cells; (2) this response includes both decreased uptake and increased release of cell metal; and (3) the effects of CO on cell function track changes in metal homeostasis. In rats exposed to 50 ppm CO for 24 hours, non-heme iron concentrations decreased in the lung and increased in the liver. In respiratory epithelial cells cultured at air–liquid interface, CO exposure decreased cell non-heme iron and ferritin concentrations within 2 hours and the effect was fully reversible. CO significantly depressed iron uptake by epithelial cells, despite increased expression of divalent metal transporter-1, while iron release was elevated. The loss of non-heme iron after CO reduced cellular oxidative stress, blocked the release of the proinflammatory mediator (interleukin-8), and interfered with cell cycle protein expression. We conclude that CO reduces the iron content of the lung through both the metal uptake and release mechanisms. This loss of cellular iron after CO is in line with certain biological effects of the gas that have been implicated in the protection of cell viability.

Key Words: oxidants • oxidative stress • inflammation • cell proliferation • ferritin

CLINICAL RELEVANCE This research impacts clinical medicine by providing a mechanism of biological effect exerted by carbon monoxide.