Transition from placental to air breathing stimulates haem-oxygenase-1 expression without functional consequence for pulmonary vascular adaptation in pigs and mice

Serial Carboxyhemoglobin Levels and Its Relationship with Late Onset Sepsis in Preterm Infants: An Observational Cohort Study

Objective: This study aimed at assessing the serial carboxyhemoglobin (COHb) levels in preterm infants during the first week of life and their variation with late-onset sepsis (LOS). Study Design: Infants with <37 gestational weeks were categorized into two groups according to the presence of culture proven LOS. Serial COHb levels were obtained during the first week of life, at the onset of the LOS episode, and upon blood culture negativity with response to antibiotics. Result: Overall 207 infants were enrolled. A LOS episode resulted in a significant increase in COHb levels (p < 0.001), which decreased to normal levels when the blood cultures were sterile (p < 0.001). At a cut of level of 1.35% COHb had a sensitivity of 56% and a specificity of 90% to confirm LOS (p < 0.001). Conclusion: In this study, we demonstrated an increase in COHb levels at the onset of LOS and a decrease with response to antibiotherapy.

The role of gasotransmitters in neonatal physiology

The gasotransmitters, nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO), are endogenously-produced volatile molecules that perform signaling functions throughout the body. In biological tissues, these small, lipid-permeable molecules exist in free gaseous form for only seconds or less, and thus they are ideal for paracrine signaling that can be controlled rapidly by changes in their rates of production or consumption. In addition, tissue concentrations of the gasotransmitters are influenced by fluctuations in the level of O₂ and reactive oxygen species (ROS). The normal transition from fetus to newborn involves a several-fold increase in tissue O₂ tensions and ROS, and requires rapid morphological and functional adaptations to the extrauterine environment. This review summarizes the role of gasotransmitters as it pertains to newborn physiology. Particular focus is given to the vasculature, ventilatory, and gastrointestinal systems, each of which uniquely illustrate the function of gasotransmitters in the birth transition and newborn periods. Moreover, given the relative lack of studies on the role that gasotransmitters play in the newborn, particularly that of H₂S and CO, important gaps in knowledge are highlighted throughout the review.

Heme oxygenase in neonatal lung injury and repair

SIGNIFICANCE

Premature and sick neonates are often exposed to high concentrations of oxygen, which results in lung injury and long-term adverse consequences. Nevertheless, neonates are more tolerant to hyperoxia than are adults. This may be, in part, explained by the high lung content of heme oxygenase-1 (HO-1), the rate-limiting enzyme in the degradation of heme and an important stress protein. The abundance of HO-1 dictates its cytoprotective and deleterious effects. Interestingly, in response to hyperoxia, lung HO-1 mRNA is not further up-regulated in neonates, suggesting that lung HO-1 gene expression is tightly regulated so as to optimize cytoprotection when faced with an oxidative stress such as hyperoxia.

RECENT ADVANCES

In addition to the lack of induction of HO-1 mRNA, neonatal lung HO-1 protein is observed in the nucleus in neonatal mice exposed to hyperoxia but not in adults, which is further evidence for the developmental regulation of HO-1. Nuclear HO-1 had unique properties independent of its enzymatic activity. In addition, there has been increasing evidence that nuclear HO-1 contributes to cellular proliferation and malignant transformation in several human cancers.

CRITICAL ISSUES

Since HO-1 has dual effects in cytoprotection and cellular proliferation, the titration of HO-1 effects is critical to ensure beneficial actions against oxidative stress.

FUTURE DIRECTIONS

Much more has to be understood about the specific roles of HO-1 so as to manipulate its abundance and/or nuclear migration to maximize the therapeutic benefit of this pleiotropic protein in the neonatal lung.

Suppression of inflammatory cell trafficking and alveolar simplification by the heme oxygenase-1 product carbon monoxide

Bronchopulmonary dysplasia (BPD), a lung disease of prematurely born infants, is characterized in part by arrested development of pulmonary alveolae. We hypothesized that heme oxygenase (HO-1) and its byproduct carbon monoxide (CO), which are thought to be cytoprotective against redox stress, mitigate lung injury and alveolar simplification in hyperoxia-exposed neonatal mice, a model of BPD. Three-day-old C57BL/6J mice were exposed to air or hyperoxia (FiO2, 75%) in the presence or absence of inhaled CO (250 ppm for 1 h twice daily) for 21 days. Hyperoxic exposure increased mean linear intercept, a measure of alveolar simplification, whereas CO treatment attenuated hypoalveolarization, yielding a normal-appearing lung. Conversely, HO-1-null mice showed exaggerated hyperoxia-induced hypoalveolarization. CO also inhibited hyperoxia-induced pulmonary accumulation of F4/80+, CD11c+, and CD11b+ monocytes and Gr-1+ neutrophils. Furthermore, CO attenuated lung mRNA and protein expression of proinflammatory cytokines, including the monocyte chemoattractant CCL2 in vivo, and decreased hyperoxia-induced type I alveolar epithelial cell CCL2 production in vitro. Hyperoxia-exposed CCL2-null mice, like CO-treated mice, showed attenuated alveolar simplification and lung infiltration of CD11b+ monocytes, consistent with the notion that CO blocks lung epithelial cell cytokine production. We conclude that, in hyperoxia-exposed neonatal mice, inhalation of CO suppresses inflammation and alveolar simplification.

Vasculoprotective effects of heme oxygenase-1 in a murine model of hyperoxia-induced bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is characterized by simplified alveolarization and arrested vascular development of the lung with associated evidence of endothelial dysfunction, inflammation, increased oxidative damage, and iron deposition. Heme oxygenase-1 (HO-1) has been reported to be protective in the pathogenesis of diseases of inflammatory and oxidative etiology. Because HO-1 is involved in the response to oxidative stress produced by hyperoxia and is critical for cellular heme and iron homeostasis, it could play a protective role in BPD. Therefore, we investigated the effect of HO-1 in hyperoxia-induced lung injury using a neonatal transgenic mouse model with constitutive lung-specific HO-1 overexpression. Hyperoxia triggered an increase in pulmonary inflammation, arterial remodeling, and right ventricular hypertrophy that was attenuated by HO-1 overexpression. In addition, hyperoxia led to pulmonary edema, hemosiderosis, and a decrease in blood vessel number, all of which were markedly improved in HO-1 overexpressing mice. The protective vascular response may be mediated at least in part by carbon monoxide, due to its anti-inflammatory, antiproliferative, and antiapoptotic properties. HO-1 overexpression, however, did not prevent alveolar simplification nor altered the levels of ferritin and lactoferrin, proteins involved in iron binding and transport. Thus the protective mechanisms elicited by HO-1 overexpression primarily preserve vascular growth and barrier function through iron-independent, antioxidant, and anti-inflammatory pathways.

Cigarette smoke inhibits macrophage sensing of Gram-negative bacteria and lipopolysaccharide: relative roles of nicotine and oxidant stress

BACKGROUND AND PURPOSE

Smoking cigarettes is a major risk factor for the development of cardiovascular and respiratory disease. Moreover, smokers are more prone to infections. This has been associated with a suppression of the immune system by smoke. However, it is not clear how cigarette smoke affects the ability of immune cells to sense pathogens. Cigarette smoke contains a large number of molecules which may mediate responses on immune cells and of these, nicotine and oxidants have both been identified as inhibitory for the sensing of bacterial lipopolysaccharide (LPS). Nitric oxide synthase (NOS) and tumour necrosis factor (TNF)-alpha are both induced in macrophages on stimulation with Gram negative bacteria or LPS.

EXPERIMENTAL APPROACH

We used murine macrophages stimulated with whole heat-killed bacteria or LPS. We measured output of NO (as nitrite) and TNFalpha, NOS protein by Western blotting and cellular oxidant stress.

KEY RESULTS

Cigarette smoke extract suppressed the ability of murine macrophages to release NO, but not TNFalpha in response to whole bacteria. Cigarette smoke extract also inhibited nitric oxide synthase II protein expression in response to LPS. The effects of cigarette smoke extract on nitrite formation stimulated by LPS were unaffected by inhibition of nicotinic receptors with alpha-bungarotoxin (100 units ml(-1)). However, the effects of cigarette smoke extract on LPS-induced nitrite formation were mimicked by hydrogen peroxide and reversed by the anti-oxidants N-acetyl cysteine and glutathione.

CONCLUSIONS AND IMPLICATIONS

We suggest that cigarette smoke exerts its immunosuppressive effects through an oxidant-dependent and not a nicotine-dependent mechanism.

Hypoxia and heme oxygenases: oxygen sensing and regulation of expression

Heme is an essential molecule for life, as it is involved in sensing and using oxygen. Heme must be synthesized and degraded within an individual nucleated cell. Physiologic heme degradation is catalyzed by two functional isozymes of heme oxygenase, heme oxygenase-1 (HO-1) and HO-2, yielding carbon monoxide, iron, and biliverdin, an immediate precursor to bilirubin. HO-1 is an inducible enzyme, but the expression level of HO-2 is maintained in a narrow range. Characteristically, human HO-1 contains no Cys residue, whereas human HO-2 contains three Cys residues, each of which might be involved in heme binding. These features suggest separate physiologic roles of HO-1 and HO-2. Recent studies have shown that the expression levels of HO-1 and HO-2 are reduced under hypoxia, depending on the cell types. Moreover, we have proposed HO-2 as a potential O(2) sensor, because HO-2-deficient mice show hypoxemia and a blunted hypoxic ventilatory response with normal hypercapnic ventilatory response. HO-2-deficient mice also show hypertrophy of the pulmonary venous myocardium and enlargement of the carotid body. These morphometric changes are attributable to chronic hypoxemia. Here, we update the understanding of the regulation of HO-1 and HO-2 expression and summarize the regulatory role of HO-2 in the intercellular communication.

Heme oxygenase-1 expression in premature and mature neonates during the first week of life

Newborns are exposed to mechanical and oxidative stress during labor and to relative hyperoxia thereafter during the course of adaptation to the extrauterine conditions. Part of the adaptation mechanism is the rapid degradation of fetal hemoglobin and the oxidation of its heme moiety by heme oxygenases (HOs). Heme oxygenase-1 enzyme (HO-1) is the inducible isoform, which is induced by and protective against oxidative stress. We hypothesized that HO-1 may play a role in the physiological adaptation of newborns. We therefore measured the HO-1 mRNA expression with cRT-PCR during the first week after birth in healthy mature and premature newborns. We found that HO-1 was induced until day 2 or 3 after birth, but its level had dropped below the birth HO-1 mRNA level by the end of the first week. HO-1 levels and inducibility were similar in mature newborns and premature newborns. The fact that HO-1 was inducible even in gestation week 26 suggests that HO-1 plays an important role in the early adaptation processes.

Pulmonary endothelium dependent vasodilation emerges after birth in mice

At birth, with the first breath, pulmonary vessels undergo profound adaptive processes. A failure in the ability of pulmonary vessels to adapt at birth results in persistent pulmonary hypertension of the new born. The mechanisms regulating pulmonary adaptation at birth are still unclear. Progress in this area is slow, not least because genetically modified mice have not yet been used to address questions in this area of research, principally because pulmonary vessels in new born mice are very small making the study of dilator response in vitro difficult. In the current study we have used precision cut lung slices to characterise the functional vasomotor changes in lung vessels of new born mice (1-4 days old), 8-15 day old mice or adult mice. The internal luminal area of pulmonary artery and airways was measured digitally. Vasoconstriction and vasodilatation were expressed as the percentage change in internal luminal area compared with the control area. The thromboxane A(2) mimetic U-46619 (3x10(-7) M) caused a significant vasoconstriction in vessels of all groups. However, acetylcholine (3x10(-5) M) induced arterial dilation only in the 8-15 days, and adult groups. By contrast, sodium nitroprusside, which acts independently of the endothelium, was an effective vasodilator in lung vessels from neonates. These data are the first to characterise the development of endothelium dependent vasodilatation in lung after birth in mice. This approach can be used with genetically modified mice, which is important to further our understanding of the physiology in this area.