Oxidative damage of the pulmonary surfactant system

Molecular regulation of lung maturation in near-term fetal sheep by maternal daily vitamin C treatment in late gestation

BACKGROUND

In the fetus, the appropriate balance of prooxidants and antioxidants is essential to negate the detrimental effects of oxidative stress on lung maturation. Antioxidants improve respiratory function in postnatal life and adulthood. However, the outcomes and biological mechanisms of antioxidant action in the fetal lung are unknown.

METHODS

We investigated the effect of maternal daily vitamin C treatment (200 mg/kg, intravenously) for a month in late gestation (105-138 days gestation, term ~145 days) on molecular regulation of fetal lung maturation in sheep. Expression of genes and proteins regulating lung development was quantified in fetal lung tissue. The number of surfactant-producing cells was determined by immunohistochemistry.

RESULTS

Maternal vitamin C treatment increased fetal lung gene expression of the antioxidant enzyme SOD-1, hypoxia signaling genes (HIF-2α, HIF-3α, ADM, and EGLN-3), genes regulating sodium movement (SCNN1-A, SCNN1-B, ATP1-A1, and ATP1-B1), surfactant maturation (SFTP-B and ABCA3), and airway remodeling (ELN). There was no effect of maternal vitamin C treatment on the expression of protein markers evaluated or on the number of surfactant protein-producing cells in fetal lung tissue.

CONCLUSIONS

Maternal vitamin C treatment in the last third of pregnancy in sheep acts at the molecular level to increase the expression of genes that are important for fetal lung maturation in a healthy pregnancy.

IMPACT

Maternal daily vitamin C treatment for a month in late gestation in sheep increases the expression of gene-regulating pathways that are essential for normal fetal lung development. Following late gestation vitamin C exposure in a healthy pregnancy, an increase in lung gene but not protein expression may act as a mechanism to aid in the preparation for exposure to the air-breathing environment after birth. In the future, the availability/development of compounds with greater antioxidant properties than vitamin C or more specific targets at the site of oxidative stress in vivo may translate clinically to improve respiratory outcomes in complicated pregnancies at birth.

Intonation of Nrf2 and Hif1-α pathway by curcumin prophylaxis: A potential strategy to augment survival signaling under hypoxia

BACKGROUND

Pulmonary surfactant oxidation leads to alveolar collapse- a condition often noticed in high altitude pulmonary edema (HAPE). The present study was aimed to determine the effect of curcumin prophylaxis in augmenting the phase II antioxidant enzymes and surfactant proteins expression in enabling the pulmonary surfactant homeostasis under hypoxia.

METHODS

A549 cells were exposed to 3% hypoxia for different time durations (1 h, 3 h, 6 h, 12 h and 24 h). The Cells were pretreated (1 h) with 10 μM curcumin and exposed to hypoxia. The in-vivo results were extrapolated into in-vivo system using male Sprague Dawley rats, exposed to a stimulated altitude of 7620 m for 6 h. The rats were supplemented with curcumin (50 mg/kgBW) 1 h prior to hypoxia exposure.

RESULTS

Results showed that, the expression of surfactant proteins (SPs) A and B decreased from 3 h of hypoxic exposure, whereas expression of SP-C and SP-D proteins were increased within 1 h of hypoxic exposure over control cells. Hypoxic exposure resulted into significant increase in protein and lipid peroxidation (p < 0.001), reduced levels of antioxidants (GSH, GPx and SOD) (p < 0.001) along with significant down regulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and Heme oxygenase-1 (HO-1) in A549 cells over control. However, the curcumin supplementation both in-vitro and in-vivo resulted into increased expressions of HO-1 and Nrf2 significantly (p < 0.001), which enabled the cells in balanced expression of SPs with reduced levels of oxidants. Further curcumin significantly enhanced the levels of antioxidant enzymes in BALF along with stabilized expression of hypoxia inducible factor 1(HIF-1α) followed by reduced expression of vascular endothelial growth factor (VEGF) in lungs of rats. The immunohistochemistry observations provided substantial evidence of enhanced surfactant protein expressions in lungs of curcumin administered hypoxia exposed rats.

CONCLUSION

These results indicate that curcumin augment survival signaling by reinforcing the induction of phase II antioxidant enzymes thereby enabling the pulmonary surfactant homeostasis under hypoxia.

Chronic hypoxaemia as a molecular regulator of fetal lung development: implications for risk of respiratory complications at birth

Exposure to altered intrauterine conditions during pregnancy influences both fetal growth and organ development. Chronic fetal hypoxaemia is a common pregnancy complication associated with intrauterine growth restriction (IUGR) that may influence the risk of infants experiencing respiratory complications at birth. There are a variety of signalling pathways that contribute to normal fetal lung development at the molecular level. The specific molecular effects of chronic hypoxaemia associated with IUGR on lung development are likely to be dependent on the specific aetiology (maternal, placental and/or fetal factors) that can alter hormone concentrations, oxygen and nutrient transport to the fetus. This review discusses molecular pathways that may contribute to altered fetal lung maturation following exposure to chronic hypoxaemia. Importantly, these studies highlight that the heterogeneity in respiratory outcomes at birth in this obstetric subpopulation are likely determined by the timing, severity and duration of chronic hypoxaemia encountered by the fetus during pregnancy.

Modifications to surfactant protein B structure and lipid interactions under respiratory distress conditions: consequences of tryptophan oxidation

These studies detail the altered structure-function relationships caused by oxidation of surfactant protein B (SP-B), a mode of damage thought to be important in acute respiratory distress syndrome (ARDS), a common and frequently fatal condition. An 18-residue fragment comprising the N-terminal helix of SP-B was investigated in oxidized and unmodified forms by solution and solid-state nuclear magnetic resonance (NMR), circular dichroism (CD), and molecular dynamics (MD) simulation. Taken together, the results indicate that tryptophan oxidation causes substantial disruptions in helical structure and lipid interactions. The structural modifications induced by tryptophan oxidation were severe, with a reduction in helical extent from approximately three helical turns to, at most, one turn, and were observed in a variety of solvent environments, including sodium dodecyl sulfate (SDS) micelles, dodecyl phosphocholine (DPC) micelles, and a 40% hexafluoro-2-propanol (HFIP) aqueous solution. The unmodified peptide takes on an orientation within lipid bilayers that is tilted approximately 30° away from an in-plane position. Tryptophan oxidation causes significant modifications to the peptide-lipid interactions, and the peptide likely shifts to a more in-plane orientation within the lipids. Interestingly, the character of the disruptions to peptide-lipid interactions caused by tryptophan oxidation was highly dependent on the charge of the lipid headgroup.

Surfactant in the preterm infant: what's going on

Surfactant treatment has been demonstrated to decrease pneumothorax and mortality in preterm infants. Natural surfactants are better than synthetic surfactants. Early rescue treatment with surfactant is better than late treatment, whereas the role of surfactant prophylaxis is under re-evaluation due to the actual large diffusion of antenatal steroid and nasal continuous positive airway pressure treatment which have changed the clinical characteristics of preterm infants with respiratory distress syndrome. It is possible that in the next future anti-inflammatory and anti-oxidant properties of exogenous natural surfactants may be improved through their combination with adequate agents with the aim of counteracting the pathogenetic role of inflammatory and oxidative lung injury injuries in the development of brochopulmonary dysplasia.

Natural surfactant combined with beclomethasone decreases oxidative lung injury in the preterm lamb

We performed a randomized study in preterm lambs to assess the hypothesis that the treatment with natural surfactant combined with beclomethasone might decrease pulmonary oxidative stress in an animal model of respiratory distress syndrome (RDS). Animals received 200 mg/kg of porcine natural surfactant or 200 mg/kg of natural surfactant combined with 400 or 800 microg/kg of beclomethasone. Lung tissue oxidation was studied by measuring total hydroperoxide (TH), advanced oxidation protein products (AOPP), and non-protein bound iron (NPBI) in bronchial aspirate samples. In addition, lung mechanics was evaluated. TH was lower in the groups treated with surfactant plus 400 or 800 microg/kg of beclomethasone than in the surfactant group; AOPP was lower in the group treated with surfactant plus 800 microg/kg of beclomethasone than in the other groups; NPBI was similar in all groups. Surfactant treatment was followed by a sustained improvement of tidal volume (TV) and airway resistance, while dynamic compliance did not vary. However, the mean airway pressure needed to obtain similar values of TV was lower in the group treated with surfactant plus 800 microg/kg of beclomethasone than in other groups. We concluded that natural surfactant combined with beclomethasone at 800 microg/kg is effective in reducing the oxidative lung stress and improving the respiratory function in an animal model of RDS.

[Oxidative stress in the neonatal lung disease]

Oxidative stress is a risk factor for bronchopulmonary dysplasia in the preterm newborn. Antioxidant defense is impaired in the preterm newborn. Oxidative stress is also involved in cell growth and development. The relationship between oxidative stress and cell growth needs to be understood before antioxidant therapy can be routinely introduced. Several antioxidant therapies have been unsuccessfully tried until now. This review highlights the importance of oxygen free radicals in the pathogenesis of bronchopulmonary dysplasia.

Bronchopulmonary dysplasia-oxidative stress and antioxidants

There is increasing evidence that oxidative stress is implicated in the development of bronchopulmonary dysplasia. Several important factors contribute to augmented oxidative stress in the newborn and especially the preterm infant: first, because of its immaturity, the lung of preterm infants is frequently exposed to oxygen therapy and hyperoxia. Second, the antioxidant defense and its ability to be induced during an hyperoxic challenge are impaired. Third, the preterm infant has an increased susceptibility to infection and inflammation, which increases oxidative stress. Fourth, free iron, which catalyzes the production of toxic reactive oxygen species, can be detected in preterm infants. The molecular and cellular mechanisms for free radical-induced injury are now understood in more detail, and it is clear that oxidative stress plays an important role in triggering apoptosis, in serving as second messenger and in signal transduction. This new insight might lead to novel and efficient therapies. So far, there has been no significant breakthrough regarding antioxidant therapies. Care should, however, be exercised in supplementing the preterm infant with antioxidants since this may affect growth and development.