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.

Hemin, a heme oxygenase substrate analog, inhibits the cell surface expression of CD11b and CD66b on human neutrophils.

BACKGROUND: Neutrophils are signaled to sites of infection and inflammation by different chemotactic stimuli. In order to reach the airways they have to adhere to, and then migrate through, the endothelium of pulmonary vessels. Carbon monoxide (CO) is a gaseous mediator, endogenously produced in the human airways. Increased CO production has been demonstrated during airway inflammation and CO as well as hemin, a substrate for CO producing enzymes, has been shown to affect neutrophil migration. Our objective was to investigate if the neutrophil cell surface expression of CD11b, CD66b and CD63 was changed during intermittent allergic rhinitis and to establish whether CO could affect the expression of these markers of cellular activation. METHODS: Blood from 10 healthy volunteers was drawn and incubated with different concentrations of hemin. Blood from 12 other healthy volunteers and from 12 patients with intermittent allergic rhinitis was also drawn during grass pollen season. Neutrophils were then isolated from all these three sets, and their expression of CD antigens measured using flow cytometry. RESULTS: Patients with symptomatic intermittent allergic rhinitis exhibited lower levels of CD11b and CD66b on the neutrophil cell surface. Incubation with hemin decreased the expression of CD11b and CD66b. CD63 was generally weakly expressed and not significantly affected by hemin incubation. CONCLUSION: Our results demonstrate that expressions of neutrophil cell surface glycoproteins are changed during the season in patents with intermittent allergic rhinitis and that hemin, a substrate for CO production, may act as an inhibitor of neutrophil activation. This indicates a possible role for CO in the immune defense system.

Increased carbon monoxide levels in the nasal airways of subjects with a history of seasonal allergic rhinitis and in patients with upper respiratory tract infection.

BACKGROUND: Carbon monoxide (CO) has emerged as an endogenously produced gaseous mediator known to be involved in bronchial smooth muscle regulation. Increased amounts of CO have been found in exhaled air during asthma and lower airway inflammation. Recently CO has been shown to be produced in the nasal airways, but there are no reports of altered CO levels in nasal airways during inflammation. OBJECTIVE: This study was designed to investigate if CO levels increase in the human nasal airways during inflammatory conditions, such as allergy and upper airway respiratory tract infection (URTI). METHODS: CO was sampled separately from the upper and lower airways of 13 healthy control subjects, six patients with a history of allergic rhinitis and six patients with URTI. RESULTS: Nasal CO levels were increased in subjects with allergic rhinitis, compared to healthy controls (2.07 +/- 0.15 ppm, n = 6 and 1.62 +/- 0.08 ppm, n = 13, respectively, P < 0.01). CO levels were also increased in patients with URTI, compared to the same controls (1.92 +/- 0.09 ppm, n = 6, P < 0.05). Normal levels of CO were found in air from the lower airways among subjects with allergic rhinitis, whereas corresponding levels in the URTI patients were increased. CONCLUSION: The present data demonstrates that upper airway CO levels increase in parallel with different inflammatory stimuli, such as allergy and infection, suggesting a role for CO as marker or mediator of nasal inflammation.

Pituitary adenylate cyclase-activating peptide 38 a potent endogenously produced dilator of human airways.

Pituitary adenylate cyclase-activating peptide (PACAP) 38 displays several biological activities relevant to obstructive airway disease. In this study, the occurrence of PACAP 38 in human small bronchi and corresponding pulmonary arteries was analysed immunocytochemically. The dilatory effects of this peptide on the same structures were also studied in vitro. A moderate number of PACAP-like immunoreactive nerve fibres was seen in association with bronchial and vascular smooth muscle and around seromucous glands. PACAP 38 caused a concentration-dependent relaxation of precontracted bronchial and pulmonary arterial segments. The maximal relaxation was more pronounced in the airways than in the arteries, whereas the potency in both was identical. PACAP 38 caused relaxation of all segments tested (nine patients), whereas vasoactive intestinal polypeptide (VIP) failed to cause relaxation of bronchial segments from six of nine patients. Both PACAP and VIP dilated all pulmonary arterial segments tested. In conclusion, pituitary adenylate cyclase-activating peptide 38 is a potent dilator of human bronchi and is present in the human lung. Pituitary adenylate cyclase-activating peptide 38 may, therefore, play a role in the endogenous regulation of airway tone. The inhibitory effects of pituitary adenylate cyclase-activating peptide 38 are more consistent than those of the related neuropeptide vasoactive intestinal polypeptide, perhaps reflecting a difference in susceptibility to degrading enzymes.

Carbon monoxide is endogenously produced in the human nose and paranasal sinuses.

BACKGROUND: Carbon monoxide (CO) has recently emerged as an endogenously produced gaseous mediator that, like nitric oxide (NO), appears to be involved in both upper and lower airway inflammation. In healthy subjects a large part of the exhaled NO seems to originate from the nasal airways, and the paranasal sinuses have been described as a dominating site for NO production. OBJECTIVE: The current study was designed to investigate whether CO could also be produced in the nose and paranasal sinuses. METHODS: The occurrence in the nasal mucosa of the enzyme heme oxygenase, the rate limiting step for CO production, was analyzed with use of immunocytochemistry. CO in exhaled and sampled air was measured with an infrared analyzer. Forty-two healthy subjects and two patients with a tracheostoma volunteered for the study. RESULTS: Heme oxygenase-like immunoreactivity was seen in the respiratory epithelium, in connection with seromucous glands and in the vascular smooth muscle of the nose. When CO was continuously sampled from one nostril during normal breathing through the mouth, stable levels of CO could be measured within 40 seconds in all subjects tested (n = 33). Repeated measurements indicated only minor variations in the values obtained. Sampling through a drainage tube inserted into the maxillary sinus revealed CO levels comparable to the levels obtained by sampling through the nose (n = 6). Breathing through the nose increased the CO levels obtained in the exhaled air (n = 33, P <. 001). CONCLUSION: These results imply that the nose and paranasal sinuses contribute to the CO production of the human airways.