Hemin, a heme oxygenase substrate analog, both inhibits and enhances neutrophil random migration and chemotaxis

Background: Carbon monoxide (CO), is an endogenously produced gas, generated by the rate-limiting enzyme heme oxygenase (HO), present in man throughout the respiratory tract. CO can elicit important physiological responses like bronchial relaxation and vasodilation. Both HO expression and CO levels in the airways increase in response to hypoxic challenge and to a wide variety of inflammatory stimuli, such as intermittent allergic rhinitis, asthma and upper respiratory tract infections. A role for CO in airway regulation and inflammation has therefore been suggested. However, information about CO-induced effects on cells involved in airway inflammation is scarce. The present study was designed to investigate if the HO substrate analog hemin could affect neutrophil random migration, and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induced chemotaxis. Methods: Hemin was added to and incubated with whole blood and the effects of the anticipated CO production were then evaluated on isolated neutrophils using a chemotaxis chamber. Results: A biphasic dose-response curve emerged for both the neutrophil spontaneous random migration and the fMLP-induced chemotaxis. Low concentrations of hemin (10(-11)m to 10(-9) m) enhanced the migratory response, whereas higher concentrations (10(-7) m and 10(-5) m) inhibited migration. The inhibition induced by hemin on fMLP-induced migration was abolished after pre-treatment with Rp-8Br-cyclicGMPS, an inhibitor of cyclicGMP. Conclusions: The present data indicate that endogenously produced CO can affect both spontaneous and stimulated neutrophil migration, partly via a cyclicGMP-related process, hence strengthening the idea of a role for CO in airway inflammation.