Hypoxia and Carbon Monoxide in the Vasculature

Department of Medicine, Division of Newborn Medicine, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Antioxidants and Redox Signaling (Impact Factor: 7.41). 05/2002; 4(2):291-9. DOI: 10.1089/152308602753666343
Source: PubMed


Hypoxia is sensed by all mammalian cells and elicits a variety of adaptive and pathophysiological responses at the molecular and cellular level. For the pulmonary vasculature, hypoxia causes increased vasoconstriction and vessel-wall remodeling. These responses are mediated by complex intracellular cascades leading to altered gene expression and cell-cell interaction. Hypoxia transiently increases the transcriptional rate of the heme oxygenase-1 (HO-1) gene, resulting in increased production of carbon monoxide (CO) and bilirubin. CO has vasodilatory and antiinflammatory properties in the vasculature, whereas bilirubin is an antioxidant. Both enzymatic products could thus modulate the hypoxic cellular response. Accumulating data suggest that CO inhibits the hypoxic induction of genes encoding vasoconstrictors and smooth muscle cell mitogens in the early hypoxic phase. During chronic hypoxia, low CO levels tilt the balance toward increased production of growth factors and vasoconstrictors that promote vessel-wall remodeling. Mice null in the HO-1 gene manifest decreased tolerance to hypoxia with right ventricular dilatation and infarction, whereas targeted lung overexpression of HO-1 prevents hypoxia-induced inflammatory responses and protects against the development of pulmonary hypertension. Such observations point to CO as a critical modulator of the body's adaptive responses to hypoxia.

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    • "Carbon monoxide reduces the pulmonary vascular resistance by (a) producing pulmonary vasodilatation from activation of soluble guanylate cyclase (sGC) and potassium channels (Ndisang and Wang, 2003; Williams et al., 2004; Wilkinson and Kemp, 2011) and (b) decreasing the cardiovascular remodeling and smooth muscle cell proliferation in the pulmonary vasculature induced by hypoxia (Kourembanas, 2002; Vitali et al., 2005; Kourembanas, 2011). Modifying the remodeling seems to be the more effective mechanism for carbon monoxide, rather than enhancing the vasodilatation. "
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    ABSTRACT: Pulmonary arterial hypertension is one of the most serious pathologies that can affect the 140 million people living at altitudes over 2500m. The primary emphasis of this review is pulmonary artery hypertension in mammals (sheep and llamas) at high altitude, with specific focus on the heme oxygenase and carbon monoxide (HO-CO) system. We highlight the fact that the neonatal llama has neither pulmonary artery hypertension nor pulmonary vascular remodeling in the Andean altiplano. These neonates have an enhanced HO-CO system function, increasing the HO-1 protein expression and CO production by the pulmonary vessels, when compared to llamas raised at low altitude, or neonatal sheep raised at high altitude. The neonatal sheep has high altitude pulmonary artery hypertension in spite of enhancement of the NO system, with high eNOS protein expression and NO production by the lung. The gasotransmitters NO and CO are important in the regulation of the pulmonary vascular function at high altitudes in both high altitude acclimatized species, such as the sheep, and high altitude adapted species, such as the llama.
    Respiratory Physiology & Neurobiology 05/2012; 184(2). DOI:10.1016/j.resp.2012.05.003 · 1.97 Impact Factor
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    • "The impairment of NO-dependent dilatation has also been closely related to pulmonary hypertension in the postnatal period (1, 44). In addition, the endogenous gas carbon monoxide (CO) is a dilator in the pulmonary vascular bed, and it protects against pulmonary vascular remodeling (31, 37, 48). In newborn llamas, augmented pulmonary CO, rather than pulmonary NO, helps to prevent pulmonary hypertension in the newborn period at high altitude (25). "
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    ABSTRACT: We determined whether postnatal pulmonary hypertension induced by 70% of pregnancy at high altitude (HA) persists once the offspring return to sea level and investigated pulmonary vascular mechanisms operating under these circumstances. Pregnant ewes were divided into two groups: conception, pregnancy, and delivery at low altitude (580 m, LLL) and conception at low altitude, pregnancy at HA (3,600 m) from 30% of gestation until delivery, and return to lowland (LHL). Pulmonary arterial pressure (PAP) was measured in vivo. Vascular reactivity and morphometry were assessed in small pulmonary arteries (SPA). Protein expression of vascular mediators was determined. LHL lambs had higher basal PAP and a greater increment in PAP after N(G)-nitro-L-arginine methyl ester (20.9 ± 1.1 vs. 13.7 ± 0.5 mmHg; 39.9 ± 5.0 vs. 18.3 ± 1.3 mmHg, respectively). SPA from LHL had a greater maximal contraction to K(+) (1.34 ± 0.05 vs. 1.16 ± 0.05 N/m), higher sensitivity to endothelin-1 and nitroprusside, and persistence of dilatation following blockade of soluble guanylate cyclase. The heart ratio of the right ventricle-to-left ventricle plus septum was higher in the LHL relative to LLL. The muscle area of SPA (29.3 ± 2.9 vs. 21.1 ± 1.7%) and the protein expression of endothelial nitric oxide synthase (1.7 ± 0.1 vs. 1.1 ± 0.2), phosphodiesterase (1.4 ± 0.1 vs. 0.7 ± 0.1), and Ca(2+)-activated K(+) channel (0.76 ± 0.16 vs. 0.30 ± 0.01) were greater in LHL compared with LLL lambs. In contrast, LHL had decreased heme oxygenase-1 expression (0.82 ± 0.26 vs. 2.22 ± 0.44) and carbon monoxide production (all P < 0.05). Postnatal pulmonary hypertension induced by 70% of pregnancy at HA promotes cardiopulmonary remodeling that persists at sea level.
    AJP Regulatory Integrative and Comparative Physiology 09/2010; 299(6):R1676-84. DOI:10.1152/ajpregu.00123.2010 · 3.11 Impact Factor
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    • "Moreover, studies have demonstrated that CO derived from heme oxygenase expression may mediate decreased pulmonary artery vascular resistance and inhibit hypoxic vasoconstriction (18–20). CO also exerts potent antiinflammatory effects, inhibits platelet aggregation, and can be pro- or antiapoptotic depending on the cell type (16, 21). There is no information whether CO might act therapeutically to treat and modulate established PAH. "
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    ABSTRACT: Pulmonary arterial hypertension (PAH) is an incurable disease characterized by a progressive increase in pulmonary vascular resistance leading to right heart failure. Carbon monoxide (CO) has emerged as a potently protective, homeostatic molecule that prevents the development of vascular disorders when administered prophylactically. The data presented in this paper demonstrate that CO can also act as a therapeutic (i.e., where exposure to CO is initiated after pathology is established). In three rodent models of PAH, a 1 hour/day exposure to CO reverses established PAH and right ventricular hypertrophy, restoring right ventricular and pulmonary arterial pressures, as well as the pulmonary vascular architecture, to near normal. The ability of CO to reverse PAH requires functional endothelial nitric oxide synthase (eNOS/NOS3) and NO generation, as indicated by the inability of CO to reverse chronic hypoxia-induced PAH in eNOS-deficient (nos3-/-) mice versus wild-type mice. The restorative function of CO was associated with a simultaneous increase in apoptosis and decrease in cellular proliferation of vascular smooth muscle cells, which was regulated in part by the endothelial cells in the hypertrophied vessels. In conclusion, these data demonstrate that CO reverses established PAH dependent on NO generation supporting the use of CO clinically to treat pulmonary hypertension.
    Journal of Experimental Medicine 10/2006; 203(9):2109-19. DOI:10.1084/jem.20052267 · 12.52 Impact Factor
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