Increase in alveolar antioxidant levels in hyperoxic and anoxic ventilated rabbit lungs during ischemia

Using lung ultrasound to quantitatively evaluate pulmonary water content

BACKGROUND

Increases in extravascular lung water (EVLW) can lead to respiratory failure. This study aimed to investigate whether the B-line score (BLS) was correlated with the EVLW content determined by the lung wet/dry ratio in a rabbit model.

METHODS

A total of 45 New Zealand rabbits were randomly assigned to nine groups. Among the animals, models of various lung water content levels were induced by the infusion of different volumes of warm sterile normal saline (NS) via the endotracheal tube. The arterial blood gas, spontaneous respiratory rate, and PaO₂ /FiO₂ ratio were detected before and after infusion. In addition, the B-lines were determined before and immediately after infusion in each group. Finally, both lungs were resected to determine the wet/dry ratio. In addition, all lung specimens were analyzed histologically, and EVLW was quantified using the BLS based on the number and confluence of B-lines in the intercostal space.

RESULTS

The BLS increased with increasing infusion volume. The BLS was statistically correlated with the wet/dry ratio (r² = .946) and with the PaO₂ /FiO₂ ratio (r² = .916). Furthermore, a repeatability study was performed for the lung ultrasound (LUS) technology (Bland-Altman plots), and the results suggest that LUS had favorable intraobserver and interobserver reproducibility.

CONCLUSIONS

This study is the first to suggest that the BLS can serve as a sensitive, quantitative, noninvasive, and real-time indicator of EVLW in a rabbit model of lung water accumulation. Notably, the BLS displayed an obvious correlation with the experimental gravimetry results and could also be used to predict the pulmonary oxygenation status.

The relationship between plasma lipid peroxidation products and primary graft dysfunction after lung transplantation is modified by donor smoking and reperfusion hyperoxia

BACKGROUND

Donor smoking history and higher fraction of inspired oxygen (FIO2) at reperfusion are associated with primary graft dysfunction (PGD) after lung transplantation. We hypothesized that oxidative injury biomarkers would be elevated in PGD, with higher levels associated with donor exposure to cigarette smoke and recipient hyperoxia at reperfusion.

METHODS

We performed a nested case-control study of 72 lung transplant recipients from the Lung Transplant Outcomes Group cohort. Using mass spectroscopy, F2-isoprostanes and isofurans were measured in plasma collected after transplantation. Cases were defined in 2 ways: grade 3 PGD present at day 2 or day 3 after reperfusion (severe PGD) or any grade 3 PGD (any PGD).

RESULTS

There were 31 severe PGD cases with 41 controls and 35 any PGD cases with 37 controls. Plasma F2-isoprostane levels were higher in severe PGD cases compared with controls (28.6 pg/ml vs 19.8 pg/ml, p = 0.03). Plasma F2-isoprostane levels were higher in severe PGD cases compared with controls (29.6 pg/ml vs 19.0 pg/ml, p = 0.03) among patients reperfused with FIO2 >40%. Among recipients of lungs from donors with smoke exposure, plasma F2-isoprostane (38.2 pg/ml vs 22.5 pg/ml, p = 0.046) and isofuran (66.9 pg/ml vs 34.6 pg/ml, p = 0.046) levels were higher in severe PGD compared with control subjects.

CONCLUSIONS

Plasma levels of lipid peroxidation products are higher in patients with severe PGD, in recipients of lungs from donors with smoke exposure, and in recipients exposed to higher Fio2 at reperfusion. Oxidative injury is an important mechanism of PGD and may be magnified by donor exposure to cigarette smoke and hyperoxia at reperfusion.

Barrier enhancing signals in pulmonary edema

Increased endothelial permeability and reduction of alveolar liquid clearance capacity are two leading pathogenic mechanisms of pulmonary edema, which is a major complication of acute lung injury, severe pneumonia, and acute respiratory distress syndrome, the pathologies characterized by unacceptably high rates of morbidity and mortality. Besides the success in protective ventilation strategies, no efficient pharmacological approaches exist to treat this devastating condition. Understanding of fundamental mechanisms involved in regulation of endothelial permeability is essential for development of barrier protective therapeutic strategies. Ongoing studies characterized specific barrier protective mechanisms and identified intracellular targets directly involved in regulation of endothelial permeability. Growing evidence suggests that, although each protective agonist triggers a unique pattern of signaling pathways, selected common mechanisms contributing to endothelial barrier protection may be shared by different barrier protective agents. Therefore, understanding of basic barrier protective mechanisms in pulmonary endothelium is essential for selection of optimal treatment of pulmonary edema of different etiology. This article focuses on mechanisms of lung vascular permeability, reviews major intracellular signaling cascades involved in endothelial monolayer barrier preservation and summarizes a current knowledge regarding recently identified compounds which either reduce pulmonary endothelial barrier disruption and hyperpermeability, or reverse preexisting lung vascular barrier compromise induced by pathologic insults.

Hyperoxia during one lung ventilation: inflammatory and oxidative responses

BACKGROUND

It is common practice during one lung ventilation (OLV) to use 100% oxygen, although this may cause hyperoxia- and oxidative stress-related lung injury. We hypothesized that lower oxygen (FiO(2) ) during OLV will result in less inflammatory and oxidative lung injury and improved lung function.

METHODS

Twenty pigs (8.88 ± 0.84 kg; 38 ± 4.6 days) were assigned to either the hyperoxia group (n = 10; FiO(2)  = 100%) or the normoxia group (n = 10; FiO(2)  < 50%). Both groups were subjected to 3 hr of OLV. Blood samples were tested for pro-inflammatory cytokines and lung tissue was tested for these cytokines and oxidative biomarkers.

RESULTS

There were no differences between groups for partial pressure of CO(2) , tidal volume, end-tidal CO(2) , plasma cytokines, or respiratory compliance. Total respiratory resistance was greater in the hyperoxia group (P = 0.02). There were higher levels of TNF-α, IL-1β, and IL-6 in the lung homogenates of the hyperoxia group than in the normoxia group (P ≤ 0.01, 0.001, and 0.001, respectively). Myeloperoxidase and protein carbonyls (PC) were higher (P = 0.03 and P = 0.01, respectively) and superoxide dismutase (SOD) was lower in the lung homogenates of the hyperoxia group (P ≤ 0.001).

CONCLUSION

Higher myeloperoxidase, PC, and cytokine levels, and lower SOD availability indicate a greater degree of injury in the lungs of the hyperoxia animals, possibly from using 100% oxygen. In this translational study using a pig model, FiO(2)  ≤ 50% during OLV reduced hyperoxic injury and improved function in the lungs.

Hypoxemic resuscitation from hemorrhagic shock prevents lung injury and attenuates oxidative response and IL-8 overexpression

We investigated whether hypoxemic resuscitation from hemorrhagic shock prevents lung injury and explored the mechanisms involved. We subjected rabbits to hemorrhagic shock for 60 min by exsanguination to a mean arterial pressure of 40 mm Hg. By modifying the fraction of the inspired oxygen, we performed resuscitation under normoxemia (group NormoxRes, P(a)O(2)=95-105 mm Hg) or hypoxemia (group HypoxRes, P(a)O(2)=35-40 mm Hg). Animals not subjected to shock constituted the sham group (P(a)O(2)=95-105 mm Hg). We performed bronchoalveolar lavage (BAL) fluid, lung wet-to-dry weight ratio, and morphological studies. U937 monocyte-like cells were incubated with BAL fluid from each group. Cell peroxides, malondialdehyde, proteins, and cytokines in the BAL fluid were lower in sham than in shocked animals and in HypoxRes than in NormoxRes animals. The inverse was true for ascorbic acid and reduced glutathione. Lung edema, lung neutrophil infiltration, myeloperoxidase, and interleukin (IL)-8 gene expression were reduced in lungs of HypoxRes compared with NormoxRes animals. A colocalized higher expression of IL-8 and nitrotyrosine was found in lungs of NormoxRes animals compared to HypoxRes animals. The BAL fluid of NormoxRes animals compared with HypoxRes animals exerted a greater stimulation of U937 monocyte-like cells for proinflammatory cytokine release, particularly for IL-8. In the presence of p38-MAPK and Syk inhibitors and monosodium urate crystals, IL-8 release was reduced. We conclude that hypoxemic resuscitation from hemorrhagic shock ameliorates lung injury and reduces oxygen radical generation and lung IL-8 expression.

Abnormal platelet-derived growth factor signaling accounting for lung hypoplasia in experimental congenital diaphragmatic hernia

PURPOSE

The pathogenesis of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) is not fully understood. Platelet-derived growth factor A (PDGFA) and platelet-derived growth factor receptor α (PDGFRα) play a crucial role in lung development. It has been reported that PDGF induces H(2)O(2)-production and that oxidative stress may be an important mechanism for the impaired lung development in the nitrofen rat model. We hypothesized that pulmonary expression of PDGFA and PDGFRα is altered in the nitrofen induced CDH model.

MATERIALS AND METHODS

Pregnant rats received 100 mg nitrofen or vehicle on gestational day 9 (D9) and were sacrificed on D15, D18 or D21. RNA was extracted from fetal left lungs and mRNA levels of PDGFA and PDGFRα were determined using real-time polymerase chain reaction. Immunohistochemistry for protein expression of PDGFA and PDGFRα was performed. Pulmonary H(2)O(2) was measured colorimetrically.

RESULTS

mRNA levels of PDGFRα at D15 (4.50 ± 0.87) and PDGFA at D18 (2.90 ± 1.38) were increased in the nitrofen group (P < .05). Immunohistochemistry revealed increased pulmonary expression of PDGFRα and PDGFA. H(2)O(2) content was significantly higher in the nitrofen group.

CONCLUSIONS

Increased expression of PDGFA and PDGFRα suggests that pulmonary hypoplasia in the nitrofen CDH model may be owing to PDGF-induced oxidative stress during lung development.

Surfactant replacement and open lung concept--comparison of two treatment strategies in an experimental model of neonatal ARDS

Background

Several concepts of treatment in neonatal ARDS have been proposed in the last years. The present study compared the effects of open lung concept positive pressure ventilation (PPV_OLC) with a conventional ventilation strategy combined with administration of two different surfactant preparations on lung function and surfactant homoeostasis.

Methods

After repeated whole-lung saline lavage, 16 newborn piglets were assigned to either PPV_OLC (n = 5) or surfactant treatment under conventional PPV using a natural bovine (n = 5) or a monomeric protein B based surfactant (n = 6).

Results

Comprehensive monitoring showed each treatment strategy to improve gas exchange and lung function, although the effect on Pa_O2 and pulmonary compliance declined over the study period in the surfactant groups. The overall improvement of the ventilation efficiency index (VEI) was significantly greater in the PPV_OLC group. Phospholipid and protein analyses of the bronchoalveolar lavage fluid showed significant alterations to surfactant homoeostasis in the PPV_OLC group, whereas IL-10 and SP-C mRNA expression was tendentially increased in the surfactant groups.

Conclusion

The different treatment strategies applied could be shown to improve gas exchange and lung function in neonatal ARDS. To which extent differences in maintenance of lung function and surfactant homeostasis may lead to long-term consequences needs to be studied further.

Primary graft nonfunction and Kupffer cell activation after liver transplantation from non-heart-beating donors in pigs

More extensive use of non-heart-beating donors (NHBD) could reduce mortality on liver transplantation waiting lists, but this is associated with more primary nonfunction (PNF). We assessed which parameters are involved in the development of PNF in livers from NHBD in a previously validated pig liver transplantation model, in which livers were transplanted after exposure to incremental periods of warm ischemia. The risk of PNF was unacceptably high (>50%) when livers were exposed to >30 minutes' warm ischemia before a short cold ischemic period. This study examined how PNF is affected by Kupffer cell activation (beta-galactosidase), the generation of cytokines tumor necrosis factor alpha and interleukin 6, antioxidant mechanisms (ascorbic acid, alpha-tocopherol, reduced glutathione), circulating redox-active iron, and sinusoidal endothelial cell function (hyaluronic acid clearance). Kupffer cells were more activated in PNF recipients, as suggested by higher beta-galactosidase levels (15 minutes after reperfusion), and secondarily, by higher production of tumor necrosis factor alpha and interleukin 6 (180 minutes after reperfusion). In addition, alpha-tocopherol and reduced glutathione were lower, and ascorbic acid and redox-active iron higher in PNF recipients. Finally, PNF grafts displayed progressively decreasing hyaluronic acid clearance (suggesting sinusoidal endothelial cell dysfunction) and parenchymal edema. Consequently, a reduced-flow phenomenon was documented. In grafts from NHBD that are destined to fail, beta-galactosidase activity (a surrogate of Kupffer cell activation) is higher, proinflammatory cytokines are overproduced, some antioxidant mechanisms fail, and circulating redox-active iron is more rapidly released. A no-flow phenomenon is eventually observed in these failing grafts.

The effects of exogenous interleukin-4 on hypoxia-induced lung injury

The aim of this study was to determine the effects of recombinant human interleukin-4 (rhIL-4) on hypoxia-induced lung injury in immature rats. The study was performed on 1-day-old Sprague Dawley rat pups. Group 1 (n = 7) served as nonhypoxic controls. Group 2 (untreated, n = 7) rats were subjected to hypoxia-reoxygenation (H/O) and were then returned to their mothers. Group 3 (rhIL-4 treated, n = 7) rats were subjected to H/O, were returned to their mothers, and were treated with rhIL-4 (75 microg/kg subcutaneously) for the next 3 days. All animals were killed on day 4 and lung specimens were obtained to determine the tissue level of malondialdehyde (MDA) and histological changes. In the untreated group, MDA levels were significantly increased compared to control and rhIL-4 groups. In the rhIL-4 treated group, MDA levels were not significantly different compared to control group. The rhIL-4 treated group had a significantly lower score of pathological lesions and alveolar hemorrhage grade values than the untreated group. The untreated animals had areas marked intraalveolar hemorrhage, capillary congestion, interstitial edema, and hypercellularity of lung that were not seen in the rhIL-4 treated rats. In conclusion, this study found beneficial effects of rhIL-4 in an experimental model on the hypoxia-induced lung injury.