The effects of hyperoxia, mechanical ventilation, and dexamethasone on pulmonary antioxidant enzyme activity in the newborn piglet

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Glucocorticosteroids as antioxidants in treatment of asthma and COPD. New application for an old medication?

Inhaled corticosteroids (ICS) are the standard of care in asthma and are widely used in the treatment of patients with COPD. The influence of steroids on inflammatory processes has long been established since glucocorticoids and their receptor belong to the regulatory network involved in inhibition of several inflammatory pathways. Inflammatory processes are usually accompanied by an increased oxidative burden followed by a depletion of antioxidants. Therefore, the effects of steroids on antioxidant status have been investigated revealing possible positive effects on the reduced antioxidant enzyme activity. Nevertheless, the mechanisms of this modulation have not been fully elucidated yet. It is possible that antioxidant enzyme activity is regulated at the level of transcription. Additionally, because of the fact that antioxidant enzymes are trace element dependent, steroids may affect their activity through influence on trace element accumulation. This review summarizes the effects of steroids on the antioxidant enzymes activity in vitro and in vivo in relation to asthma and COPD.

Heme oxygenase-1 and carbon monoxide in pulmonary medicine

Heme oxygenase-1 (HO-1), an inducible stress protein, confers cytoprotection against oxidative stress in vitro and in vivo. In addition to its physiological role in heme degradation, HO-1 may influence a number of cellular processes, including growth, inflammation, and apoptosis. By virtue of anti-inflammatory effects, HO-1 limits tissue damage in response to proinflammatory stimuli and prevents allograft rejection after transplantation. The transcriptional upregulation of HO-1 responds to many agents, such as hypoxia, bacterial lipopolysaccharide, and reactive oxygen/nitrogen species. HO-1 and its constitutively expressed isozyme, heme oxygenase-2, catalyze the rate-limiting step in the conversion of heme to its metabolites, bilirubin IXalpha, ferrous iron, and carbon monoxide (CO). The mechanisms by which HO-1 provides protection most likely involve its enzymatic reaction products. Remarkably, administration of CO at low concentrations can substitute for HO-1 with respect to anti-inflammatory and anti-apoptotic effects, suggesting a role for CO as a key mediator of HO-1 function. Chronic, low-level, exogenous exposure to CO from cigarette smoking contributes to the importance of CO in pulmonary medicine. The implications of the HO-1/CO system in pulmonary diseases will be discussed in this review, with an emphasis on inflammatory states.

Pulmonary antioxidant enzyme activity during early development: Effect of ventilation

OBJECTIVE: To examine the effect of tidal liquid ventilation (TLV) and conventional gas ventilation (GV) on the pulmonary antioxidant enzyme (AOE) activity in two groups of preterm lambs at 110 and 120 days of gestation and to compare these results to age-matched fetal controls. DESIGN: Experimental, prospective, randomized, controlled study. SETTING: School of medicine, department of physiology. SUBJECTS: Thirty-two premature lambs at 110 days (n = 16) and 120 days (n = 16) gestation. INTERVENTIONS: Six lambs at 110 and 120 days were ventilated with TLV for 4 hrs. Three lambs at 110 days were ventilated with GV for 3 hrs, and six lambs at 120 days were ventilated with GV for 4 hrs. Four lambs, each at 110 and 120 days, were used as age-matched fetal controls. Measurements: Sequential measurements of arterial blood chemistries were performed in all groups. Biochemical assays included catalase activity, superoxide dismutase activity, and glutathione peroxidase activity. Histologic examinations of lung sections from TLV and GV lungs were performed. Main Result: Despite vast differences in physiologic outcome, there were fewer differences in AOE activity as a function of ventilation (fetal control, GV, and TLV lambs) and/or gestational age. There were no significant differences in superoxide dismutase and glutathione peroxidase activity as a function of age or ventilation. Catalase activity was significantly higher (p <.05) in fetal 120-day control lambs (24.8 +/- 1.9 units/mg protein) relative to the 110-day control lambs (14.3 +/- 1.7 units/mg protein). Catalase activity significantly (p <.05) decreased in both GV and TLV 120 day lambs compared with fetal controls; yet, in the 110-day gestational lambs, there were no significant differences in enzyme level as a function of ventilation. Thus, an age-specific response to ventilation was evident for catalase activity. CONCLUSION: The present data demonstrate several developmental differences in AOE activity. The lack of ventilation effect in AOE activity, in view of the big difference in physiologic and inflammatory outcomes, suggests that mechanisms associated with free radicals do not underlie the response to different modes of ventilation.

Modification of biophysical properties of lung epithelial Na(+) channels by dexamethasone

There is considerable interest in identifying the basic mechanisms by which dexamethasone alters ion transport across the adult alveolar epithelium. Herein, we incubated synchronized A549 cells, a human alveolar epithelial cell line, with dexamethasone (1 microM) for 24-48 h. When normalized to HPRT (a housekeeping gene), A549 beta- and gamma-subunit mRNA levels for the human amiloride-sensitive epithelial sodium channel (hENaC), assessed by RT-PCR, increased by 1.6- and 17-fold respectively, compared with control values (P < 0.05). These changes were abolished by actinomycin D, indicating transcriptional regulation. Western blotting studies revealed that dexamethasone also increased expression of beta- and gamma-hENaC protein levels. In contrast, alpha-hENaC mRNA increased by onefold (P > 0.05) and alpha-hENaC protein level was unchanged. Incubation of A549 cells with dexamethasone increased their whole cell amiloride-sensitive sodium currents twofold and decreased the K(0.5) for amiloride from 833 +/- 69 to 22 +/- 5.4 nM (mean +/- SE; P < 0.01). Single channel recordings in the cell-attached mode showed that dexamethasone treatment increased single channel open time and open probability threefold and decreased channel conductance from 8.63 +/- 0.036 to 4. 4 +/- 0.027 pS (mean +/- SE; P < 0.01). We concluded that dexamethasone modulates the amiloride-sensitive Na(+) channels by differentially regulating the expression of beta- and gamma-subunits at the mRNA and protein levels in the human A549 cell line, with little effect on alpha-hENaC subunit.

Superoxide dismutase, catalase and glutathione peroxidase activities in the lymphoid organs and skeletal muscles of rats treated with dexamethasone

The effect of dexamethasone (a synthetic glucocorticoid) on the activity of antioxidant enzymes (superoxide dismutase (SOD), catalase and glutathione peroxidase) of the lymphoid organs (mesenteric lymph nodes (MLN), spleen and thymus) was investigated. For comparison with non-immune tissues, skeletal muscles (soleus and gastrocnemius (GC) were also studied. As an indication of the occurrence of lipid peroxidation, the content of thiobarbituric acid reactant substances (TBARs) was also determined. Dexamethasone treatment decreased the TBARs content of the lymphoid organs and raised it in the GC and soleus muscles. The activity of Cu/Zn-SOD was reduced in all tissues. However, the activity of Mn-SOD was decreased in the MLN and soleus muscle only. The activity of catalase was reduced in the MLN and thymus and raised in the spleen and GC and soleus muscles. The imposed treatment raised the activity of GPX in the MLN, thymus and spleen and reduced it in GC and soleus muscles. These data led us to postulate that the mechanism for the therapeutic effect of glucocorticoids as antiinflammatory and immunosuppressive agents might include modification of antioxidant enzyme activities.