The aim of this study was to investigate whether the heme oxygenase (HO) pathway could modulate proliferation of airway smooth muscle (ASM) and the mechanism(s) involved in this phenomenon. In cultured human ASM cells, 10% fetal calf serum or 50 ng/ml platelet-derived growth factor AB induced cell proliferation, extracellular and intracellular reactive oxygen species (ROS) production and ERK1/2 phosphorylation. Pharmacological HO-1 induction (by 10 microm hemin or by 20 microm cobalt-protoporphyrin) and HO inhibition (by 25 microm tin-protoporphyrin or by an antisense oligonucleotide), respectively, reduced and enhanced significantly both cell proliferation and ROS production. Neither the carbon monoxide scavenger myoglobin (5-20 microm) nor the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one could reverse ASM proliferation induced by tin-protoporphyrin, making a role of the CO-cGMP pathway in HO-modulated proliferation unlikely. By contrast, bilirubin (1 microm) and the antioxidant N-acetyl-cysteine (1 mm) significantly reduced mitogen-induced cell proliferation, ROS production, and ERK1/2 phosphorylation. Furthermore, both bilirubin and N-acetyl-cysteine and the ERK1/2 inhibitor PD98059 significantly reversed the effects of HO inhibition on ASM proliferation. These results could be relevant to ASM alterations observed in asthma because activation of the HO pathway prevented the increase in bronchial smooth muscle area induced by repeated ovalbumin challenge in immunized guinea pigs, whereas inhibition of HO had the opposite effect. In conclusion, this study provides evidence for an antiproliferative effect of the HO pathway in ASM in vitro and in vivo through a bilirubin-mediated redox modulation of phosphorylation of ERK1/2.

Heme oxygenase (HO), the heme-degrading enzyme, has shown anti-inflammatory effects in several models of pulmonary diseases. HO is induced in airways during asthma; however, its functional role is unclear. Therefore, we evaluated the role of HO on airway inflammation [evaluated by bronchoalveolar lavage (BAL) cellularity and BAL levels of eotaxin, PGE(2), and proteins], mucus secretion (evaluated by analysis of MUC5AC gene expression and periodic acid-Schiff staining), oxidative stress (evaluated by quantification of 4-hydroxynonenal adducts and carbonylated protein levels in lung homogenates), and airway responsiveness to histamine in ovalbumin (OVA)-sensitized and multiple aerosol OVA or saline-challenged guinea pigs (6 challenges, once daily, OVA group and control group, respectively). Airway inflammation, mucus secretion, oxidative stress, and responsiveness were significantly increased in the OVA group compared with the control group. HO upregulation by repeated administrations of hemin (50 mg/kg i.p.) significantly decreased airway responsiveness in control animals and airway inflammation, mucus secretion, oxidative stress, and responsiveness in OVA animals. These effects were reversed by the concomitant administration of the HO inhibitor tin protoporphyrin-IX (50 micromol/kg i.p.). Repeated administrations of tin protoporphyrin-IX alone significantly increased airway responsiveness in control animals but did not modify airway inflammation, mucus secretion, oxidative stress, and responsiveness in OVA animals. These results suggest that upregulation of the HO pathway has a significant protective effect against airway inflammation, mucus hypersecretion, oxidative stress, and hyperresponsiveness in a model of allergic asthma in guinea pigs.

Reactive oxygen species are strongly implicated in diaphragmatic dysfunction during sepsis. We investigated whether the heme oxygenase (HO) pathway, which is a powerful protective cellular system, protects the diaphragm against oxidative stress and contractile failure during sepsis. A basal expression of both the inducible and constitutive HO protein isoforms (HO-1 and HO-2, respectively) was found in the diaphragm. Enhanced HO-1 expression in diaphragmatic myocytes was observed 24 h after Escherichia coli endotoxin (lipopolysaccharide, LPS) inoculation and remained elevated for at least 96 h. Enhanced HO-1 expression was also observed in the rectus abdominis and soleus muscles and in the left ventricular myocardium of endotoxemic animals. Diaphragmatic HO-2 expression was not modified by endotoxin. Diaphragmatic HO activity exhibited a biphasic time course characterized by a transient decrease during the first 12 h followed by a significant increase at 24 h, corresponding to HO-1 induction. Diaphragmatic force was significantly reduced 24 h after LPS, concomitantly with muscular oxidative stress. Administation of an inhibitor of heme oxygenase activity, zinc protoporphyrin IX (ZnPP-IX), further impaired muscular oxidative stress and contractile failure. By contrast, increased levels of HO-1 expression obtained by pretreatment of rats with hemin, a powerful inducer of HO-1, completely prevented LPS-mediated diaphragmatic oxidative stress and contractile failure. This protective effect was reversed by ZnPP-IX. These results show an important protective role for the HO pathway against sepsis-induced diaphragmatic dysfunction, which could be related to its antioxidant properties.

Background and Purpose-It is not well established what are the features, if any, that distinguish symptomatic from asymptomatic carotid atherosclerotic plaques. Inducible heme oxygenase-1 (HO-1) is a component of cellular defense mechanisms against oxidative stress. We aimed to assess the presence of Helicobacter pylori (H pylori) and the expression of HO-1 in carotid atherosclerotic plaques of patients with and without prior neurologic symptoms attributable to the operated artery. Methods-We examined 25 symptomatic and 23 asymptomatic carotid atherosclerotic plaques removed during endarterectomy and 7 normal carotid arteries obtained at autopsy. We investigated the presence of H pylori DNA in the vessel wall and performed immunohistochemical detection of HO-1. Results-H pylori DNA was present in 28 plaques and HO-1 was expressed in 30 plaques. HO-1 was found in 27 H pylori-positive specimens but in only 3 H pylori-negative specimens (PϽ0.001). All 7 normal carotid arteries were negative for both H pylori and HO-1. Although 82% of asymptomatic specimens were positive for H pylori and 87% for HO-1, only 36% of symptomatic specimens were positive for both H pylori and HO-1 (PϽ0.01). Conclusions-This study suggests a strong association between H pylori infection and expression of HO-1 in carotid atherosclerotic plaques. There was a substantial prevalence of these features in specimens obtained from asymptomatic subjects. (Stroke. 2005;36:000-000.)