Alterations in pulmonary surfactant composition and activity after experimental lung transplantation

Vascular distension and continued ventilation are protective in lung ischemia/reperfusion

Biophysical factors have been implicated in the development of pulmonary ischemia-reperfusion injury. In isolated rabbit lungs, the impact of vascular and alveolar distension, with and without alveolar oxygen supply, was investigated. With interruption of both perfusion (zero intravascular pressure) and ventilation, reperfusion after 120 min of warm ischemia resulted in transient pulmonary hypertension, with largely unchanged microvascular pressures, followed by a dramatic leakage response with approximately 10-fold increased capillary filtration coefficients (Kfc) and severe edema. Maintenance of vascular distension during ischemia (intravascular pressure of approximately 2 to 3 mm Hg) reduced the hypertension and fully suppressed the leakage. Employing ischemic periods of 180 and 240 min, ventilation of the lungs with 21 or 100% oxygen > ventilation with nitrogen during perfusion stop, but not static anoxic inflation, further enhanced the protective effect of vascular distension. At optimal biophysical support (vascular distension and ongoing normoxic ventilation), even 240 min of warm ischemia was tolerated with only moderate Kfc increase. We conclude that biophysical factors exert marked influence on pulmonary ischemia-reperfusion injury. Maintenance of vascular distension possesses strong protective potency, further enhanced by continued ventilation and alveolar oxygen supply during ischemia. These results may have important implications for organ preservation in lung transplantation.

Increase of C-reactive protein and decrease of surfactant protein A in surfactant after lung transplantation

In this study, we asked whether the serum acute-phase protein C-reactive protein (CRP) increased in large surfactant aggregates after lung transplantation and analyzed the changes in composition and interfacial adsorption activity of those aggregates. Single left lung transplantation was performed in weight-matched pairs of dogs. A double-lung block from the donor animal was flushed with either modified Euro-Collins solution (EC) (n = 6) or University of Wisconsin solution (UW) (n = 6) at 4 degrees C followed by immersion in cold EC or UW for 22 h. The left donor lung was transplanted. The recipient dog was then reperfused for 4.5 h. Irrespective of the preservation fluid, gas exchanged was impaired in the transplanted lung after 4.5 h of reperfusion. Large surfactant aggregates obtained from this lung showed reduced ability to rapidly adsorb to an air-liquid interface. Phospholipid (PL) content and PL composition of surfactant from lung transplants was similar to that of the control lungs. However, the content of surfactant protein A decreased after reperfusion. In addition, Western blot analyses showed that levels of CRP increased in surfactant from transplanted but not from donor lungs. The addition of human CRP to control surfactant (CRP:PL weight ratio, 0.01:1) caused a decrease of surfactant adsorption. We conclude that the impairment of adsorption facilities of surfactant from transplanted lungs may be correlated with decreased levels of surfactant protein A and increased levels of CRP. The presence of elevated levels of CRP in bronchoalveolar lavage could be a very sensitive marker of lung injury.

Influence of oxygen in inflation gas during lung ischemia on ischemia-reperfusion injury

OBJECTIVES

Previous studies have reported that hyperinflation during lung ischemia improves pulmonary function after reperfusion. However, it has not been clarified whether hyperinflation itself or oxygen in inflation gas causes good pulmonary function. The aim of this study is to evaluate the effect of oxygen in pulmonary inflation gas during lung ischemia on ischemia-reperfusion injury.

METHODS

Twenty-one mongrel dogs were randomly divided into three groups: the lung during a 90-minute period of warm ischemia was inflated to 30 cm H2O with 100% oxygen in group A and 100% nitrogen in group B; it was not inflated in group C. Pulmonary function and hemodynamics were measured before ischemia and 1, 2, and 3 hours after reperfusion. Total protein and phosphorus of phospholipid in bronchoalveolar lavage fluid were measured 210 minutes after reperfusion. Adenine nucleotide levels in lung tissue were estimated 210 minutes after reperfusion.

RESULTS

No significant differences in pulmonary function and hemodynamics were noted between group A and group B, but these two groups had significantly better pulmonary function and hemodynamics than group C. No significant differences were detected in the concentrations of total protein and phosphorus of phospholipids in bronchoalveolar lavage fluid and in adenine nucleotide levels of lung tissue after reperfusion among the three groups.

CONCLUSIONS

The results indicate that pulmonary inflation during warm ischemia improves pulmonary function and hemodynamics after reperfusion in this model. The effect is caused by inflation itself and is not due to oxygen as a metabolic substrate during warm ischemia.

Effects of early surfactant treatment persisting for one week after lung transplantation in rats

We investigated whether pulmonary surfactant in rat lung transplants recovered during the first week post-transplantation, along with symptoms of the reimplantation response, and whether this recovery was affected by early surfactant treatment. The severity of pulmonary injury was varied by transplanting left lungs with 6-h and 20-h ischemia (n = 12 and 19, respectively). Half of the transplants were treated by instillation of surfactant before reperfusion. Lungs from sham operated, and normal rats (n = 4 and 5, respectively) served as controls. The pulmonary injury severely impaired lung transplant function; 10 of the worst affected animals died. After 1 wk, symptoms of reimplantation response and properties of pulmonary surfactant were assessed. If untreated, the reimplantation response had almost resolved in the 6-h but not in the 20-h ischemia group; pulmonary surfactant, however, continued to be deficient in both ischemia groups (low amounts of surfactant phospholipids and surfactant protein A [SP-A]). Surfactant treatment improved the recovery from injury in the 20-h ischemia group resulting in normal lung function and amounts of surfactant phospholipids. Amounts of SP-A were not improved by surfactant treatment. In conclusion, early surfactant treatment enhances recovery from transplantation injury and is persistently beneficial for pulmonary surfactant in lung transplants.

Alterations of the endogenous surfactant system in septic adult rats

Sepsis is the most common factor leading to the acute respiratory distress syndrome (ARDS) and is associated with the highest mortality rate. It has been suggested that the pulmonary surfactant system is altered and contributes to the lung dysfunction associated with ARDS. The objective of this study was to characterize the lung injury, specifically the endogenous surfactant system in septic adult rats. Sepsis was induced in male Sprague-Dawley rats by cecal ligation and perforation and resulted in significant increases in heart rates, respiratory rates, and lactate levels along with positive blood cultures in septic animals compared with a sham control group. Two distinct septic groups were developed, a septic group and a sepsis with lung injury (septic+LI) group. The septic group had no significant differences in oxygenation compared with the sham group, whereas the septic+LI group had significantly lower PaO2 and higher A-a gradient values compared to both the sham and septic groups. The total surfactant pool size was significantly lower in the septic+LI group compared with the sham group. The small surfactant aggregate to large surfactant aggregate ratio was significantly lower in the septic group and was further reduced in the septic+LI group. There were also significantly higher levels of surfactant protein A (SP-A) in both septic and septic+LI groups compared to the sham group. These results demonstrated that the endogenous surfactant system was altered in systemic sepsis without lung dysfunction and is further altered when a lung injury is present.

Exogenous surfactant treatment before and after sixteen hours of ischemia in experimental lung transplantation

OBJECTIVE

A syngeneic, acute, double lung transplant model in the rat was used to determine the impact of exogenous surfactant treatment on graft function after prolonged cold storage.

METHODS

The donor grafts were flush perfused, preserved for 16 hours, and then reperfused for 120 minutes. Untreated lungs served as controls (group I). In group II the recipient received a 200 mg/kg dose of surfactant (CuroSurf) before reperfusion. In groups III and IV, surfactant was administered before perfusion and harvesting (III, 20 mg/kg; IV, 200 mg/kg). Serial measurements of graft pulmonary vascular resistance, alveolar-arterial oxygen difference, and compliance were obtained. Final graft assessment included weight gain and histologic study.

RESULTS

Repeated-measures analysis of variance showed significant improvement of graft performance in respect to compliance, alveolar-arterial oxygen difference, and pulmonary vascular resistance in donor surfactant treatment group IV (200 mg/kg) in comparison with recipient treatment (group II) and untreated controls (group I). Reducing the donor surfactant supplementation from 200 mg/kg to 20 mg/kg (group III) improved oxygenation and lung compliance as compared with untreated controls. Grafts in groups I and II had significantly more weight gain after 2 hours of reperfusion. Recipient treatment resulted in significantly more pulmonary hemorrhage in histologic sections.

CONCLUSION

Donor treatment with exogenous surfactant is advantageous for preservation of graft function after extended ischemia. Positive effects may be seen with as little as 20 mg/kg of exogenous surfactant given before donor organ perfusion.

Low-dose sodium nitroprusside reduces pulmonary reperfusion injury

BACKGROUND

Reperfusion injury is a significant cause of early allograft dysfunction after lung transplantation. We hypothesized that direct pulmonary arterial infusion of an intravascular nitric oxide donor, sodium nitroprusside (SNP), would ameliorate pulmonary reperfusion injury more effectively than inhaled nitric oxide without causing profound systemic hypotension.

METHODS

Using an isolated, ventilated, whole-blood-perfused rabbit lung model, we studied the effects of both inhaled and intravascular nitric oxide during lung reperfusion. Group I (control) lungs (New Zealand White rabbits, 3 to 3.5 kg) were harvested en bloc, flushed with Euro-Collins solution, and then stored inflated for 18 hours at 4 degrees C. Lungs were then reperfused with whole blood and ventilated with 60% oxygen for 30 minutes. Groups II, III, and IV received pulmonary arterial infusions of SNP at 0.2, 1.0, and 5.0 micrograms.kg-1.min-1, respectively, whereas group V was ventilated with 60% oxygen and nitric oxide at 80 ppm during reperfusion.

RESULTS

Pulmonary arterial infusions of SNP even at 0.2 microgram.kg-1.min-1 (group II) showed significant improvements in pulmonary artery pressure (31.35 +/- 0.8 versus 40.37 +/- 3.3 mm Hg; p < 0.05) and pulmonary vascular resistance (38,946 +/- 1,269 versus 52,727 +/- 3,421 dynes.s/cm-5; p < 0.05) when compared with control (group I) lungs after 30 minutes of reperfusion. Infusions of SNP at 1.0 microgram.kg-1.min-1 (group III) showed additional significant improvements in dynamic airway compliance (1.98 +/- 0.10 versus 1.46 +/- 0.02 mL/mm Hg; p < 0.05), venous-arterial oxygenation gradient (116.00 +/- 24.4 versus 34.43 +/- 2.5 mm Hg; p < 0.05), and wet-to-dry ratio (6.9 +/- 0.9 versus 9.1 +/- 2.2; p < 0.05) when compared with control (group I) lungs. Lungs that received inhaled nitric oxide at 80 ppm (group V) were significantly more compliant (1.82 +/- 0.13 versus 1.46 +/- 0.02 mL/mm Hg; p < 0.05) than control (group I) lungs.

CONCLUSIONS

Pulmonary arterial infusion of low-dose SNP during lung reperfusion significantly improves pulmonary hemodynamics, oxygenation, compliance, and edema formation. These effects were achieved at doses of SNP that did not cause profound systemic hypotension. Direct intravascular infusion of SNP via pulmonary arterial catheters could potentially abate reperfusion injury immediately after allograft implantation.

Mitigation of injury in canine lung grafts by exogenous surfactant therapy

BACKGROUND

Exogenous surfactant therapy of lung donors improves the preservation of normal canine grafts. The current study was designed to determine whether exogenous surfactant can mitigate the damage in lung grafts induced by mechanical ventilation before procurement.

METHODS AND RESULTS

Five donor dogs were subjected to 8 hours of mechanical ventilation (tidal volume 45 ml/kg). This produced a significant decrease in oxygen tension (p = 0.007) and significant increases in bronchoscopic lavage fluid neutrophil count (p = 0.05), protein concentration (p = 0.002), and the ratio of poorly functioning small surfactant aggregates to superiorly functioning large aggregates (p = 0.02). Five other animals given instilled bovine lipid extract surfactant and undergoing mechanical ventilation in the same manner demonstrated no significant change in oxygen tension values, lavage fluid protein concentration, or the ratio of small to large aggregates. All 10 lung grafts were then stored for 17 hours at 4 degrees C. Left lungs were transplanted and reperfused for 6 hours. After 6 hours of reperfusion the ratio of oxygen tension to inspired oxygen fraction was 307 +/- 63 mm Hg in lung grafts administered surfactant versus 73 +/- 14 mm Hg in untreated grafts (p = 0.007). Furthermore, peak inspired pressure was significantly (p < 0.05) lower in treated animals from 90 to 360 minutes of reperfusion. Analysis of lavage fluid of transplanted grafts after reperfusion revealed small to large aggregate ratios of 0.17 +/- 0.04 and 0.77 +/- 0.17 in treated versus untreated grafts, respectively (p = 0.009).

CONCLUSIONS

Instillation of surfactant before mechanical ventilation reduced protein leak, maintained a low surfactant small to large aggregate ratio, and prevented a decrease of oxygen tension in donor animals. After transplantation, surfactant-treated grafts had superior oxygen tension values and a higher proportion of superiorly functioning surfactant aggregate forms in the air space than untreated grafts. Exogenous surfactant therapy can protect lung grafts from ventilation-induced injury and may offer a promising means to expand the donor pool.

Surfactant: current and potential therapeutic application in infants and adults

Exogenous surfactant administration is currently being evaluated for the Acute Respiratory Distress Syndrome (ARDS). Although surfactant supplementation is now a routine therapy for babies born with neonatal RDS, this treatment modality for adults does not appear to result in a predictable improvement in lung function as is noted in neonates. This article will review the basic abnormalities of the surfactant system in patients with ARDS and contrast them with the primary surfactant deficient state of nRDS. Various factors that have been shown to influence an individual's response to exogenous surfactant will the be outlined. Finally, potential treatment approaches for patients with ARDS utilizing exogenous surfactant will be proposed.

Donor pretreatment with intravenous prostacyclin versus inhaled nitric oxide in experimental lung transplantation

The pulmonary vasodilatory effects of prostacyclin (PGI2) were compared with inhaled nitric oxide (NO) for donor treatment in an acute double lung transplantation model in the rat. The PGI2 group (n=10) received 35 microg/kg PGI2 both intravenously and into the flush solution. The NO group (n=10) was ventilated before and during perfusion with nitric oxide for an expiratory NO concentration of 20 ppm. Both groups were compared with untreated controls (n=10). Following cold ischemia of 16 hr the donor lungs were implanted in syngeneic recipients via specially designed stents to the left pulmonary artery and vein. Separate graft ventilation permitted determination of compliance and resistance. During 120 min of reperfusion serial measurements of graft pulmonary vascular resistance (PVR) and alveolar arterial oxygen difference (AAD02) were obtained. Final graft assessment included weight gain and histological analysis. Data are listed as mean+/-SE. The type of donor pretreatment had a definite and negative impact on survival (NO: 106+/-6, controls: 116+/-4, PGI2: 120+/-0 min; P<0.02) and overall graft function. During reperfusion the compliance was significantly reduced in NO (23+/-4) in comparison with controls (34+/-3) and PGI2 (50+/-4 ml/cmH2O; P<0.01). The PVR was 785+/-238 in NO, 240+/-60 in controls and 181+/-71 mmHg/ml/min in PGI2 (P<0.02). The AaD02 was compromised in NO (486+/-44) compared with controls (396+/-53) and PGI2 (108+/-34 mmHg; P<0.02). The weight increase at the end of reperfusion amounted to 101+/-17% in NO, 98+/-13% in controls, and 69+/-7% in PGI2 (P<0.05). Histological analysis showed significantly more interstitial edema in the NO group. In conclusion, PGI2 administration significantly improves global lung function while the inhalation of nitric oxide before and during donor perfusion has a detrimental effect on the quality of graft preservation.

Intratracheal surfactant administration preserves airway compliance during lung reperfusion

BACKGROUND

Decreased airway compliance after lung transplantation has been observed with severe ischemia-reperfusion injury. Further, it has been shown that the surfactant system is impaired after lung preservation and reperfusion. We hypothesized that surfactant replacement after allograft storage could preserve airway compliance during reperfusion.

METHODS

Rabbit lungs were harvested after flush with 50 mL/kg of cold saline solution. Immediate control lungs were studied with an isolated ventilation/perfusion apparatus using venous rabbit blood recirculated at 40 mL/min, room-air ventilation at 20 breaths/min, and constant airway pressure (n = 8). Twenty-four-hour control lungs were preserved at 4 degrees C for 24 hours and then similarly studied (n = 7). Surfactant lungs underwent similar harvest and preservation for 24 hours, but received 1.5 mL/kg of intratracheal surfactant 5 minutes before reperfusion (n = 10). Airway pressure and flow were recorded continuously during 30 minutes of reperfusion. Tidal volume and airway compliance were calculated at 30 minutes.

RESULTS

Tidal volume was 33.67 +/- 0.57, 15.75 +/- 5.72, and 29.83 +/- 1.07 mL in the immediate control, 24-hour control, and surfactant groups, respectively (p = 0.004, surfactant versus 24-hour control). Airway compliance was 1.94 +/- 0.27, 0.70 +/- 0.09, and 1.46 +/- 0.10 mL/mm Hg in the immediate control, 24-hour control, and surfactant groups, respectively (p = 0.002, surfactant versus 24-hour control).

CONCLUSIONS

We conclude that surfactant administration before reperfusion after 24 hours of cold storage preserves tidal volume and airway compliance in the isolated ventilated/perfused rabbit model of lung reperfusion injury.

Lung preservation: the importance of endothelial and alveolar type II cell integrity

The practice of lung transplantation is constrained by a shortage of suitable donor organs. Furthermore, even "optimal" donor lung grafts are at risk of significant dysfunction perioperatively. Significant insights into the cellular and molecular mechanisms of pulmonary ischemia-reperfusion injury have occurred since the publication of previous reviews on lung preservation 3 to 4 years ago. Recent evidence indicates that the endothelium plays an essential role in regulating the dynamic interaction between pulmonary vasodilatation and vasoconstriction and is a major target during lung injury. In addition, the composition, function, and metabolism of pulmonary surfactant produced by alveolar type II cells are increasingly being recognized as important factors in pulmonary ischemia-reperfusion injury. We hypothesize that reperfusion after a period of pulmonary ischemia results in significant endothelial and alveolar type II cell dysfunction and that an important strategy in lung preservation is to preserve the integrity of these cells in the face of this injury. Given the persistent shortage of lungs available for transplantation, laboratory studies need to focus also on the "rescue" of compromised donor lungs that would have been previously regarded as unsuitable. Importantly, innovative work from the laboratory needs to be translated into clinical practice via prospective, randomized trials to ensure that the prevalence of postoperative lung graft dysfunction is reduced and the shortage of lung grafts for transplantation is alleviated.

Surfactant-associated protein A is important for maintaining surfactant large-aggregate forms during surface-area cycling

Alveolar surfactant can be separated into two major subfractions, the large surfactant aggregates (LAs) and the small surfactant aggregates (SAs). The surface-active LAs are the metabolic precursors of the inactive SAs. This conversion of LAs into SAs can be studied in vitro using a technique called surface-area cycling. We have utilized this technique to examine the effect of trypsin on aggregate conversion. Our results show that trypsin increases the conversion of LAs into SAs in a concentration- and time-dependent manner. Immunoblot analysis revealed that surfactant-associated Protein A (SP-A) was the main target of trypsin. To examine further the role of SP-A in aggregate conversion, we tested the effect of Ca2+ and mannan on this process. The absence of Ca2+ (l mM EDTA) and the presence of mannan both increased the formation of SAs. Electron microscopy revealed that highly organized multilamellar and tubular myelin structures were present in samples that converted slowly to SAs. We concluded that SP-A is important for maintaining LA forms during surface-area cycling by stabilizing tubular myelin and multilamellar structures.

Morphometric characterisation of the fine structure of human type II pneumocytes

BACKGROUND

Pulmonary type II pneumocytes have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and morphometry in numerous mammals. Until now, the fine structure of the human type II pneumocyte has not been studied by means of morphometry.

METHODS

Eleven human donor lungs, which could not be made available for a suitable recipient, were preserved with Euro Collins solution (ECS) according to clinical organ preservation techniques. The lungs were fixed via the airways. Systematic random samples were analyzed by SEM, TEM, and classical stereological methods.

RESULTS

Type II pneumocytes showed normal fine structural characteristics. Morphometry revealed that although inter-individual variation due to some oedematous swelling was present, the cells were in a normal size range as indicated by an estimated mean volume of 763 +/- 64 microns 3. The volume densities were: nucleus 21.9 +/- 2.2%, mitochondria 5.8 +/- 0.9%, lamellar bodies 9.8 +/- 3.6%, and remaining cytoplasmic components 62.4 +/- 2.9% of the cell volume. Since the inter-individual variations in the volume densities referred to the cell may, to variable degrees, reflect the variation in the reference space, the volume densities referred to the constant test point system and the respective volume-to-surface ratios were used for inter-individual comparisons. These parameters indicate that lamellar bodies were independent of cellular swelling, while mitochondria < nucleus < remaining cytoplasmic components increased in size with increasing cell size.

CONCLUSIONS

Two to 7.5 hours of cold ischemia following ECS preservation do not deteriorate the fine structure of type II pneumocytes of human donor lungs. For reliable assessment of fine structural variations, morphometric parameters are required that are independent of variations in cell size.

Surface-area cycling of different surfactant preparations: SP-A and SP-B are essential for large-aggregate integrity

Surface-area cycling is an in vitro procedure for the conversion of large into small surfactant aggregates. In this procedure a tube containing a surfactant suspension is rotated end-over-end at 37 degrees C so that the surface area of the suspension changes twice each cycle. We have utilized this method to study the mechanisms involved in aggregate conversion. Several different surfactant preparations were analysed: (1) bovine natural surfactant, a sucrose-gradient-purified material containing surfactant phospholipid and surfactant-associated proteins (SP-) SP-A, SP-B and SP-C; (2) bovine lipid-extract surfactant, which contains the surfactant phospholipids and SP-B and SP-C; (3) mixtures of dipalmitoyl phosphatidylcholine and phosphatidylglycerol (7:3, w/w) reconstituted with one or more surfactant proteins. Aggregate conversion was measured by phosphorus analysis of a 40,000 g supernatant (small aggregate) and pellet (large aggregates) before and after surface-area cycling. Surface-area cycling of lipid extract surfactant or lipids plus SP-B or SP-C resulted in rapid aggregate conversion. Lipids alone were not converted. Only a small percentage of purified natural surfactant was converted into small aggregates. Addition of SP-A to lipid extract surfactant could inhibit aggregate conversion of this material, but this was only observed when an additional 1% (w/w) of SP-B was added to the lipid extract. It is concluded that SP-A is important for large-aggregate integrity. It appears that SP-A acts in conjunction with SP-B. The presence of SP-B and/or SP-C is required for aggregate conversion; it is proposed that this reflects the necessity for lipid adsorption in aggregate conversion.