Pulmonary surfactant preserves viability of alveolar type II cells exposed to polymyxin B in vitro.

BACKGROUND: Exogenous surfactant derived from animal lungs is applied for treatment of surfactant deficiency. By means of its rapid spreading properties, it could transport pharmaceutical agents to the terminal air spaces. The antimicrobial peptide Polymyxin B (PxB) is used as a topical antibiotic for inhalation therapy. Whereas it has been shown that PxB mixed with surfactant is not inhibiting surface activity while antimicrobiotic activity is preserved, little is known concerning the effects on synthesis of endogenous surfactant in alveolar type II cells (ATIIC). OBJECTIVE: To investigate ATIIC viability and surfactant-exocytosis depending on PxB and/or surfactant exposure. METHODS: ATIIC were isolated from rat lungs as previously described and were cultivated for 48 h. After incubation for a period of 1-5 h with either PxB (0.05 or 0.1 mg/ml), modified porcine surfactant (5 or 10 mg/ml) or mixtures of both, viability and exocytosis (spontanously and after stimulation) were determined by fluorescence staining of intracellular surfactant. RESULTS: PxB 0.1 mg/ml, but not porcine surfactant or porcine surfactant plus PxB reduces ATIIC-viability. Only PxB alone, but not in combination with porcine surfactant, rapidly reduces fluorescence in ATIIC at maximum within 3 h, indicating stimulation of exocytosis. Subsequent ionomycin-stimulation does not further increase exocytosis of PxB incubated ATIIC. In presence of surfactant, stimulating effects of PxB and ionomycin on exocytosis are reduced. CONCLUSION: PxB alone shows negative effects on ATIIC, which are counterbalanced in mixtures with surfactant. So far, our studies found no results discouraging the concept of a combined treatment with PxB and surfactant mixtures.

Continuous noninvasive monitoring of lung recruitment during high-frequency oscillatory ventilation by electrical impedance measurement: an animal study.

BACKGROUND: Ventilatory pressures should target the range between the upper and lower inflection point of the pressure volume curve in order to avoid atelecto- and volutrauma. During high-frequency oscillatory ventilation (HFOV), this range is difficult to determine. Quadrant impedance measurement (QIM) has recently been shown to allow accurate and precise measurement of lung volume changes during conventional mechanical ventilation. OBJECTIVES: To investigate if QIM can be used to determine a static pressure-residual impedance curve during a recruitment-derecruitment manoeuvre on HFOV and to monitor the time course of alveolar recruitment after changing mean airway pressure (MAP). METHODS: An incremental and decremental MAP trial (6 cm H2O to 27 cm H2O) was conducted in five surfactant-depleted newborn piglets during HFOV. Ventilatory, gas exchange and haemodynamic parameters were recorded. Continuous measurement of thoracic impedance change was performed. RESULTS: Mean residual impedance (RI) increased with each stepwise increase of MAP resulting in a total mean increase of +26.5% (±4.0) at the highest MAP (27 cm H2O) compared to baseline ventilation at 6 cm H2O. Upon decreasing MAP levels, RI fell more slowly compared to its ascent; 83.4% (±19.1) and 84.8% (±16.4) of impedance changes occurred in the first 5 min after an increase or decrease in airway pressure, respectively. CONCLUSIONS: QIM could be used for continuous monitoring of thoracic impedance and determination of the pressure-RI curve during HFOV. The method could prove to be a promising bedside method for the monitoring of lung recruitment during HFOV in the future.

Effect of exogenous surfactants on viability and DNA synthesis in A549, immortalized mouse type II and isolated rat alveolar type II cells.

BACKGROUND: In mechanically ventilated preterm infants with respiratory distress syndrome (RDS), exogenous surfactant application has been demonstrated both to decrease DNA-synthesis but also and paradoxically to increase epithelial cell proliferation. However, the effect of exogenous surfactant has not been studied directly on alveolar type II cells (ATII cells), a key cell type responsible for alveolar function and repair. OBJECTIVE: The aim of this study was to investigate the effects of two commercially available surfactant preparations on ATII cell viability and DNA synthesis. METHODS: Curosurf® and Alveofact® were applied to two ATII cell lines (human A549 and mouse iMATII cells) and to primary rat ATII cells for periods of up to 24 h. Cell viability was measured using the redox indicator resazurin and DNA synthesis was measured using BrdU incorporation. RESULTS: Curosurf® resulted in slightly decreased cell viability in all cell culture models. However, DNA synthesis was increased in A549 and rat ATII cells but decreased in iMATII cells. Alveofact® exhibited the opposite effects on A549 cells and had very mild effects on the other two cell models. CONCLUSION: This study showed that commercially available exogenous surfactants used to treat preterm infants with RDS can have profound effects on cell viability and DNA synthesis.

Nutrition of preterm infants in relation to bronchopulmonary dysplasia.

BACKGROUND: The pathogenesis of bronchopulmonary dysplasia (BPD) is multifactorial. In addition to prenatal inflammation, postnatal malnutrition also affects lung development. METHODS: A retrospective study was performed to analyse during the first two weeks of life the total, enteral and parenteral nutrition of premature infants (<31 weeks, birth weight ≤1500 g) born between 08/04 and 12/06. RESULTS: Ninety-five premature infants were analysed: 26 with BPD (27 ± 1 weeks) and 69 without BPD (28 ± 1 weeks). There was no statistical significant difference in the total intake of fluids, calories, glucose or protein and weight gain per day in both groups. The risk of developing BPD was slightly increased in infants with cumulative caloric intake below the minimal requirement of 1230 kcal/kg and a cumulative protein intake below 43.5 g/kg. Furthermore, the risk of developing BPD was significantly higher when infants had a cumulative fluid intake above the recommended 1840 ml/kg. In infants who developed BPD, the enteral nutrition was significantly lower than in non-BPD infants [456 ml/kg (IQR 744, 235) vs. 685 (IQR 987, 511)]. Infants who did not develop BPD reached 50% of total enteral feeding significantly faster [9.6 days vs. 11.5]. CONCLUSIONS: Preterm infants developing BPD received less enteral feeding, even though it was well compensated by the parenteral nutrient supply. Data suggest that a critical minimal amount of enteral feeding is required to prevent development of BPD; however, a large prospective clinical study is needed to prove this assumption.

Effects of perfluorocarbons on surfactant exocytosis and membrane properties in isolated alveolar type II cells.

BACKGROUND: Perfluorocarbons (PFC) are used to improve gas exchange in diseased lungs. PFC have been shown to affect various cell types. Thus, effects on alveolar type II (ATII) cells and surfactant metabolism can be expected, data, however, are controversial. OBJECTIVE: The study was performed to test two hypotheses: (I) the effects of PFC on surfactant exocytosis depend on their respective vapor pressures; (II) different pathways of surfactant exocytosis are affected differently by PFC. METHODS: Isolated ATII cells were exposed to two PFC with different vapor pressures and spontaneous surfactant exocytosis was measured. Furthermore, surfactant exocytosis was stimulated by either ATP, PMA or ionomycin. The effects of PFC on cell morphology, cellular viability, endocytosis, membrane permeability and fluidity were determined. RESULTS: The spontaneous exocytosis was reduced by PFC, however, the ATP and PMA stimulated exocytosis was slightly increased by PFC with high vapor pressure. In contrast, Ionomycin-induced exocytosis was decreased by PFC with low vapor pressure. Cellular uptake of FM 1-43 - a marker of membrane integrity - was increased. However, membrane fluidity, endocytosis and viability were not affected by PFC incubation. CONCLUSIONS: We conclude that PFC effects can be explained by modest, unspecific interactions with the plasma membrane rather than by specific interactions with intracellular targets.

Inflammatory cytokine mRNA in monocytes is modified by a recombinant (SP-C)-based surfactant and porcine surfactant.

Respiratory distress syndrome (RDS) is mainly caused by a deficiency of surfactant in structurally immature lungs. Therapy for RDS consists of mechanical ventilation and administration of exogenous surfactant. Animal-derived surfactant preparations that are used to treat newborn infants show inhibition of proinflammatory cytokines. There are no data available concerning the effects of the new generation of surfactants. In the present study, the effects of an animal-derived surfactant (Curosurf) and a synthetic surfactant (Venticute) on lipopolysaccharide (LPS)-induced inflammation were tested in human monocyte THP-1 cells. The effects were measured as changes in messenger RNA (mRNA) expression of the chemokine interleukin-8 (IL-8), proinflammatory TNF-alpha and the anti-inflammatory IL-10 cytokine. Both surfactant preparations inhibited the LPS-induced increase in TNF-alpha expression. A comparison of both preparations revealed a similar effect on IL-10 expression. However, IL-10 expression was higher after incubation with Venticute. Curosurf increased IL-8 expression at higher concentrations, but Venticute had no effect. The anti-inflammatory effect of an animal-derived surfactant and a new-generation synthetic surfactant preparation may influence postnatal pulmonary inflammation.

Tolerability of inhaled N-chlorotaurine in the pig model.

BACKGROUND: N-chlorotaurine, a long-lived oxidant produced by human leukocytes, can be applied in human medicine as an endogenous antiseptic. Its antimicrobial activity can be enhanced by ammonium chloride. This study was designed to evaluate the tolerability of inhaled N-chlorotaurine (NCT) in the pig model. METHODS: Anesthetized pigs inhaled test solutions of 1% (55 mM) NCT (n = 7), 5% NCT (n = 6), or 1% NCT plus 1% ammonium chloride (NH4Cl) (n = 6), and 0.9% saline solution as a control (n = 7), respectively. Applications with 5 ml each were performed hourly within four hours. Lung function, haemodynamics, and pharmacokinetics were monitored. Bronchial lavage samples for captive bubble surfactometry and lung samples for histology and electron microscopy were removed. RESULTS: Arterial pressure of oxygen (PaO2) decreased significantly over the observation period of 4 hours in all animals. Compared to saline, 1% NCT + 1% NH4Cl led to significantly lower PaO2 values at the endpoint after 4 hours (62 +/- 9.6 mmHg vs. 76 +/- 9.2 mmHg, p = 0.014) with a corresponding increase in alveolo-arterial difference of oxygen partial pressure (AaDO2) (p = 0.004). Interestingly, AaDO2 was lowest with 1% NCT, even lower than with saline (p = 0.016). The increase of pulmonary artery pressure (PAP) over the observation period was smallest with 1% NCT without difference to controls (p = 0.91), and higher with 5% NCT (p = 0.02), and NCT + NH4Cl (p = 0.05).Histological and ultrastructural investigations revealed no differences between the test and control groups. The surfactant function remained intact. There was no systemic resorption of NCT detectable, and its local inactivation took place within 30 min. The concentration of NCT tolerated by A549 lung epithelial cells in vitro was similar to that known from other body cells (0.25-0.5 mM). CONCLUSION: The endogenous antiseptic NCT was well tolerated at a concentration of 1% upon inhalation in the pig model. Addition of ammonium chloride in high concentration provokes a statistically significant impact on blood oxygenation.